| 1. |
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| 2. |
- Abadias, Gregory, et al.
(författare)
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Preface
- 2020
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 404
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
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| 3. |
- Aiempanakit, Montri, et al.
(författare)
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Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides
- 2011
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:22, s. 7779-7784
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Tidskriftsartikel (refereegranskat)abstract
- In the further development of reactive sputter deposition, strategies which allow for stabilization of the transition zone between the metallic and compound modes, elimination of the process hysteresis, and increase of the deposition rate, are of particular interest. In this study, the hysteresis behavior and the characteristics of the transition zone during reactive high power impulse magnetron sputtering (HiPIMS) of Al and Ce targets in an Ar-O(2) atmosphere as a function of the pulsing frequency and the pumping speed are investigated. Comparison with reactive direct current magnetron sputtering (DCMS) reveals that HiPIMS allows for elimination/suppression of the hysteresis and a smoother transition from the metallic to the compound sputtering mode. For the experimental conditions employed in the present study, optimum behavior with respect to the hysteresis width is obtained at frequency values between 2 and 4 kHz, while HiPIMS processes with values below or above this range resemble the DCMS behavior. Al-O films are deposited using both HiPIMS and DCMS. Analysis of the film properties shows that elimination/suppression of the hysteresis in HiPIMS facilitates the growth of stoichiometric and transparent Al(2)O(3) at relatively high deposition rates over a wider range of experimental conditions as compared to DCMS.
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| 4. |
- Aijaz, Asim, et al.
(författare)
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A strategy for increased carbon ionization in magnetron sputtering discharges
- 2012
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Ingår i: Diamond and related materials. - : Elsevier BV. - 0925-9635 .- 1879-0062. ; 23, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- A strategy that facilitates a substantial increase of carbon ionization in magnetron sputtering discharges is presented in this work. The strategy is based on increasing the electron temperature in a high power impulse magnetron sputtering discharge by using Ne as the sputtering gas. This allows for the generation of an energetic C+ ion population and a substantial increase in the C+ ion flux as compared to a conventional Ar-HiPIMS process. A direct consequence of the ionization enhancement is demonstrated by an increase in the mass density of the grown films up to 2.8 g/cm(3); the density values achieved are substantially higher than those obtained from conventional magnetron sputtering methods.
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| 5. |
- Aijaz, Asim, et al.
(författare)
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Exploring the potential of high power impulse magnetron sputtering for the synthesis of scratch resistant, antireflective coatings
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Broad band anti-reflective multilayer coatings require the use of a low-index material as a top layer. Normally SiO2 is used which exhibits sufficiently low refractive index (~1.5 at 550 nm) yet its low hardness (~10 GPa) hinders its application in abrasive environments. A strategy to circumnavigate these limitations is the synthesis of multicomponent materials that combine good mechanical and optical performance. In this work we synthesize Al-Si-O thin films seeking to combine the low refractive index of SiO2 and the relatively high hardness of Al2O3. The potential of reactive high power impulse magnetron sputtering (HiPIMS) for synthesizing Al-Si-O suitable for top-layers in anti-reflective coating stacks is explored by depositing films in an Ar+O2 ambient under varied target compositions (Al0.5Si0.5 and Al0.1Si0.9). The behavior of discharge current in metal and oxide mode is correlated with the plasma composition, plasma energetics as well as target surface composition in order to obtain information about the chemical nature and the energy of the film forming species. Plasma composition and plasma energetics are investigated by measuring electron density, electron temperature as well as energy distributions and as fluxes of Ar+, Al+, Si+ and O+ ions. Monte-Carlo based computer simulations are employed to assess the ion-target surface interactions to gain insight into the discharge characteristics as well as film growth. The properties of the grown films (chemical composition, mechanical and optical properties) are investigated and an understanding of the reactive HiPIMS-based growth of anti-reflective Al-Si-O thin films is established. For reference, the plasma and film properties of Al-O are also studied.
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| 6. |
- Aijaz, Asim
(författare)
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HiPIMS-based Novel Deposition Processes for Thin Films
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this research, high power impulse magnetron sputtering (HiPIMS) based new deposition processes are introduced to address; the issue of low degree of ionization of C in magnetron sputtering discharges, and the difficulty encountered in thin film deposition on complex-shaped surfaces. The issue of low degree of C ionization is addressed by introducing a new strategy which is based on promoting the electron impact ionization ofC by increasing the electron temperature in the plasma discharge using Ne, instead of conventionally used Ar. The Ne-based HiPIMS process provides highly ionized C fluxes which are essential for the synthesis of high-density and sp3 rich amorphous carbon (a-C) thin films such as diamond-like carbon (DLC) and tetrahedral a-C (ta-C). The feasibility of coating complex-shaped surfaces is demonstrated by using the dual-magnetron approach in an open-field (magnetic field of the magnetrons) configuration and performing sideways deposition of Ti films. The HiPIMS-based open-field configuration process enhances the sideways transport of the sputtered flux — an effect which is observed in the case of HiPIMS.The characterization of the Ne-HiPIMS discharge using a Langmuir probe and mass spectrometry shows that it provides an increase in the electron temperature resulting in an order of magnitude decrease in the mean ionization length of the sputtered C as compared to the conventional Ar-HiPIMS discharge. The C1+ ion energy distribution functions exhibit the presence of an energetic C1+ ion population and a substantial increase in the total C1+ ion flux. The higher C1+ ion flux facilitates the growth of sp3 rich carbon films with mass densities, measured by x-ray reflectometry, reaching as high as approx. 2.8 gcm-3.The dual-magnetron open-field configuration process is operated in DCMS as well as in HiPIMS modes. The plasma characterization, performed by Langmuir probe measurements and optical emission spectroscopy, shows that the plasma density in the Ti-HiPIMS discharge is higher than that of the Ti-DCMS discharge. This results in the higher ionized fraction of the sputtered Ti in the case of HiPIMS. The film uniformity and the deposition rate of the film growth, obtained by employing scanning electron microscopy, demonstrate that the sideways deposition approach can be used for depositing thin films on complex-shaped surfaces.
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| 7. |
- Aijaz, Asim, et al.
(författare)
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Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films
- 2014
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Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 44, s. 117-122
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Tidskriftsartikel (refereegranskat)abstract
- In the present study we contribute to the understanding that is required for designing sputtering-based routes for high rate synthesis of hard and dense amorphous carbon (a-C) films. We compile and implement a strategy for synthesis of a-C thin films that entails coupling a hydrocarbon gas (acetylene) with high density discharges generated by the superposition of high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species leads to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to HiPIMS Ar discharge (Aijaz et al. Diamond and Related Materials 23 (2012) 1). This is achieved without significant incorporation of H (< 10 %) and with relatively high hardness (> 25 GPa) and mass density (~2.32 g/cm3). Using our experimental data together with Monte-Carlo computer simulations and data from the literature we suggest that: (i) dissociative reactions triggered by the interactions of energetic discharge electrons with hydrocarbon gas molecules is an important additional (to the sputtering cathode) source of film forming species and (ii) film microstructure and film hydrogen content are primarily controlled by interactions of energetic plasma species with surface and sub-surface layers of the growing film.
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| 8. |
- Aijaz, Asim, et al.
(författare)
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Synthesis of amorphous carbon thin films using acetylene-based high power impulse magnetron sputtering discharges
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Amorphous carbon (a-C) thin films are synthesized using high power impulse magnetron sputtering (HiPIMS) based Ne-Ar/C2H2 discharges. Plasma properties and film growth are investigated under different gas phase composition and operating pressures. Film mass densities, H content, hardness and compressive stresses are measured. Mass densities in the order of 2.2 g/cm3, hardness close to 25 GPa and H content as low as 11% are obtained. The film properties manifest a dependence on energy and flux of the depositing species and energetic ion bombardment driven structural changes in the films are found to govern the resulting film properties.
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| 9. |
- Aijaz, Asim, 1980-
(författare)
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Synthesis of Carbon-based and Metal-Oxide Thin Films using High Power Impulse Magnetron Sputtering
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis deals with synthesis of carbon-based as well as metal-oxide thin films using highly ionized plasmas. The principal deposition method employed was high power impulse magnetron sputtering (HiPIMS). The investigations on plasma chemistry, plasma energetics, plasma-film interactions and its correlation to film growth and resulting film properties were made. The thesis is divided into two parts: (i) HiPIMS-based deposition of carbon-based thin films and (ii) HiPIMS-based deposition of metal-oxide thin films.In the first part of the thesis, HiPIMS based strategies are presented that were developed to address the fundamental issues of low degree of carbon ionization and low deposition rates of carbon film growth in magnetron sputtering. In the first study, a new strategy was introduced for increasing the degree of ionization of sputtered carbon via increasing the electron temperature in the discharge by using a higher ionization potential buffer gas (Ne) in place of commonly used Ar. A direct consequence of enhanced electron temperatures was observed in the form of measured large fluxes of ionized carbon at the substrate position. Consequently, high mass densities of the resulting amorphous carbon (a-C) thin films reaching 2.8 g/cm3 were obtained.In another study, feasibility of HiPIMS-based high density discharges for high-rate synthesis of dense and hard a-C thin films was explored. A strategy was compiled and implemented that entailed coupling a hydrocarbon precursor gas (C2H2) with high density discharges generated by the superposition of HiPIMS and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species lead to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to that obtained using HiPIMS Ar discharge in the first study. The increased deposition rate was achieved without significant incorporation of H (<10 %) and with relatively high hardness (>25 GPa) and mass density (~2.32 g/cm3). The knowledge gained in this work was utilized in a subsequent work where the feasibility of adding high ionization potential buffer gas (Ne) to increase the electron temperature in an Ar/C2H2 HiPIMS discharge was explored. It was found that the increased electron temperature lead to enhanced dissociation of hydrocarbon precursor and an increased H incorporation into the growing film. The resulting a-C thin films exhibited high hardness (~ 25 GPa), mass densities in the order of 2.2 g/cm3 and H content as low as about 11%. The striking feature of the resulting films was low stress levels where the films exhibited compressive stresses in the order of 100 MPa.In the second part of the thesis, investigations on reactive HiPIMS discharge characteristics were made for technologically relevant metal-oxide systems. In the first study, the discharge characteristics of Ti-O and Al-O were investigated by studying the discharge current characteristics and measuring the ion flux composition. Both, Ti-O and Al-O discharges were dominated by large fluxes of ionized metallic as well as sputtering and reactive gases species. The generation of large ionized fluxes influenced the discharge characteristics consequently surpassing the changes in the secondary electron emission yields which, in the case of DCMS discharges entail contrasting behavior of the discharge voltage for the two material systems. The study also suggested that the source of oxygen ions in the case of reactive HiPIMS is both, the target surface (via sputtering) as well as gas phase.In a subsequent study, the knowledge gained from the studies on metal-oxide HiPIMS discharges was utilized for investigating the behavior of reactive HiPIMS discharges related to ternary compound thin film growth. In this work Al-Si-O system, which is a promising candidate for anti-reflective and solar thermal applications, was employed to carry out the investigations under varied target compositions (Al, Al0.5Si0.5, and Al0.1Si0.9). It was found that the discharge current behavior of metal and oxide modes of Al-Si-O HiPIMS discharges were similar to those of Al-O and were independent of the target composition. The influence of energy and composition of the ionized depositing fluxes on the film growth was also investigated. It was shown that stoichiometric Al-Si-O thin films exhibiting a refractive index below 1.6 (which is desired for anti-reflective applications) can be grown. Furthermore, the refractive index and chemical composition of the resulting films were found to be unchanged with respect to the energy of the depositing species.The effect of ionized deposition fluxes that are generated in metal-oxide HiPIMS discharges was also investigated for the phase composition and optical properties of TiO2 thin films. It was found that energetic and ionized sputtered flux in reactive HiPIMS can be used to tailor the phase formation of the TiO2 films with high peak powers facilitating the rutile phase while the anatase phase can be obtained using low peak powers. It was also demonstrated that using HiPIMS, these phases can be obtained at room temperature without external substrate heating or post-deposition annealing. The results on plasma and film properties were also compared with DCMS.
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| 10. |
- Aijaz, Asim, et al.
(författare)
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Synthesis of hydrogenated diamondlike carbon thin films using neon-acetylene based high power impulse magnetron sputtering discharges
- 2016
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 34:6
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenated diamondlike carbon (DLC:H) thin films exhibit many interesting properties that can be tailored by controlling the composition and energy of the vapor fluxes used for their synthesis. This control can be facilitated by high electron density and/or high electron temperature plasmas that allow one to effectively tune the gas and surface chemistry during film growth, as well as the degree of ionization of the film forming species. The authors have recently demonstrated by adding Ne in an Ar-C high power impulse magnetron sputtering (HiPIMS) discharge that electron temperatures can be effectively increased to substantially ionize C species [Aijaz et al., Diamond Relat. Mater. 23, 1 (2012)]. The authors also developed an Ar-C2H2 HiPIMS process in which the high electron densities provided by the HiPIMS operation mode enhance gas phase dissociation reactions enabling control of the plasma and growth chemistry [Aijaz et al., Diamond Relat. Mater. 44, 117 (2014)]. Seeking to further enhance electron temperature and thereby promote electron impact induced interactions, control plasma chemical reaction pathways, and tune the resulting film properties, in this work, the authors synthesize DLC: H thin films by admixing Ne in a HiPIMS based Ar/C2H2 discharge. The authors investigate the plasma properties and discharge characteristics by measuring electron energy distributions as well as by studying discharge current characteristics showing an electron temperature enhancement in C2H2 based discharges and the role of ionic contribution to the film growth. These discharge conditions allow for the growth of thick (>1 mu m) DLC: H thin films exhibiting low compressive stresses (similar to 0.5 GPa), high hardness (similar to 25 GPa), low H content (similar to 11%), and density in the order of 2.2 g/cm(3). The authors also show that film densification and change of mechanical properties are related to H removal by ion bombardment rather than subplantation.
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| 11. |
- Alami, J., et al.
(författare)
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High power pulsed magnetron sputtering : Fundamentals and applications
- 2009
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 483:1-2, s. 530-534
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Tidskriftsartikel (refereegranskat)abstract
- Direct current magnetron sputtering (dcMS) is a widely used technique for deposition of a large number of compound and metallic coatings with specified mechanical, electrical and optical properties. Although dcMS is a successful coating technique, it suffers from fundamental problems, such as low target utilization and target poisoning during reactive sputtering, which results in process instabilities and poor deposition rates. In order to alleviate some of these problems, alternative techniques, such as radio frequency magnetron sputtering, additional ionization by rf coils or microwaves, or increased magnetic confinement by a multipolar magnetic setup are used. High power unipolar pulsing of the target voltage is another approach that has been used of late, in order to increase the ionization fraction in the discharge. in this deposition technique, known as high power pulsed magnetron sputtering (HPPMS), the power supply operates at low (or zero) power level and pulses to a high voltage for a short time each cycle. Thus, high electron densities are generated leading to increased ionization of the sputtered material. With peak power densities typically of several kW cm(-2), ionization fractions of the sputtered material ranging from 4.5% for C to 70% for Cu are achieved. HPPMS has been used to grow metallic and compound coatings. In the present work, a summary over some of the important results related to this technique are presented. The mechanisms taking place in the discharge and at the coating surface during deposition are discussed and the benefits of using HPPMS are reviewed: tailoring of coating properties, control of the coating bombardment during deposition, enhancement of the coating mechanical properties and morphology. Finally, TiAlN coatings are deposited using an industrial coater, and the coatings properties are studied.
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| 12. |
- Alami, J., et al.
(författare)
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On the deposition rate in a high power pulsed magnetron sputtering discharge
- 2006
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 89:15, s. 154104-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the high pulse current and the duty cycle on the deposition rate in high power pulsed magnetron sputtering (HPPMS) is investigated. Using a Cr target and the same average target current, deposition rates are compared to dc magnetron sputtering (dcMS) rates. It is found that for a peak target current density I-Tpd of up to 570 mA cm(-2), HPPMS and dcMS deposition rates are equal. For I-Tpd greater than 570 mA cm(-2), optical emission spectroscopy shows a pronounced increase of the Cr+/Cr-0 signal ratio. In addition, a loss of deposition rate, which is attributed to self-sputtering, is observed.
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| 13. |
- Alami, J., et al.
(författare)
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On the phase formation of titanium oxide films grown by reactive high power pulsed magnetron sputtering
- 2009
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Ingår i: Journal of Physics D. - : Institute of Physics. - 0022-3727 .- 1361-6463. ; 42:11, s. 115204-
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Tidskriftsartikel (refereegranskat)abstract
- High power pulsed magnetron sputtering is used for the growth of titanium dioxide (TiO(2)) films at different working pressures and orientations of the substrate with respect to the target surface. In the case of substrates oriented parallel to the target surface, the increase in the working pressure from 0.5 to 3 Pa results in the growth of crystalline TiO(2) films with phase compositions ranging from rutile to anatase/rutile mixtures. When depositions are performed on substrates placed perpendicularly to the target surface, rutile films that consist of TiO(2) nanocrystals embedded in an amorphous matrix are obtained at 0.5 Pa. Increase in the working pressure leads to the deposition of amorphous films. These findings are discussed in the light of the energetic bombardment provided to the growing film at the various deposition conditions.
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| 14. |
- Alami, J., et al.
(författare)
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On the relationship between the peak target current and the morphology of chromium nitride thin films deposited by reactive high power pulsed magnetron sputtering
- 2009
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Ingår i: Journal of Physics D. - : Institute of Physics. - 0022-3727 .- 1361-6463. ; 42:1, s. 015304-
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Tidskriftsartikel (refereegranskat)abstract
- High power pulsed magnetron sputtering (HPPMS) is used to deposit CrN films without external heating at different peak target currents, while the average current is kept constant. Films are also grown by dc magnetron sputtering (dcMS), for reference. The plasma properties, the deposition rate and the morphology of the films are investigated. The plasma analysis reveals that HPPMS provides higher fluxes of ionized species (both gas and sputtered) to the growing film, as compared with dcMS. In addition, the ionic bombardment during HPPMS increases, when the peak target current is increased. The HPPMS films exhibit changes of the density and the surface roughness as the peak target current increased, while the deposition rate decreases drastically. Furthermore, it is found that different thin-film morphologies are obtained starting from a porous columnar morphology for the dcMS films, which turns to a dense columnar one at low peak target currents and ends up to a featureless morphology at high peak target currents for the films grown by HPPMS. A new structure zone model specific for high ionization sputtering is, therefore, outlined.
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| 15. |
- Almyras, Georgios, 1983-, et al.
(författare)
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Semi-Empirical Force-Field Model For The Ti1-XAlXN (0 ≤ x ≤ 1) System
- 2019
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a modified embedded atom method (MEAM) semi-empirical force-field model for the Ti1-xAlxN (0 x 1) alloy system. The MEAM parameters, determined via an adaptive simulated-annealing (ASA) minimization scheme, optimize the models predictions with respect to 0 K equilibrium volumes, elastic constants, cohesive energies, enthalpies of mixing, and point-defect formation energies, for a set of approximate to 40 elemental, binary, and ternary Ti-Al-N structures and configurations. Subsequently, the reliability of the model is thoroughly verified against known finite-temperature thermodynamic and kinetic properties of key binary Ti-N and Al-N phases, as well as properties of Ti1-xAlxN (0 amp;lt; x amp;lt; 1) alloys. The successful outcome of the validation underscores the transferability of our model, opening the way for large-scale molecular dynamics simulations of, e.g., phase evolution, interfacial processes, and mechanical response in Ti-Al-N-based alloys, superlattices, and nanostructures.
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| 16. |
- Chason, E., et al.
(författare)
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A kinetic model for stress generation in thin films grown from energetic vapor fluxes
- 2016
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 119:14
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a kinetic model for residual stress generation in thin films grown from energetic vapor fluxes, encountered, e.g., during sputter deposition. The new analytical model considers sub-surface point defects created by atomic peening, along with processes treated in already existing stress models for non-energetic deposition, i.e., thermally activated diffusion processes at the surface and the grain boundary. According to the new model, ballistically induced subsurface defects can get incorporated as excess atoms at the grain boundary, remain trapped in the bulk, or annihilate at the free surface, resulting in a complex dependence of the steady-state stress on the grain size, the growth rate, as well as the energetics of the incoming particle flux. We compare calculations from the model with in situ stress measurements performed on a series of Mo films sputter-deposited at different conditions and having different grain sizes. The model is able to reproduce the observed increase of compressive stress with increasing growth rate, behavior that is the opposite of what is typically seen under non-energetic growth conditions. On a grander scale, this study is a step towards obtaining a comprehensive understanding of stress generation and evolution in vapor deposited polycrystalline thin films. Published by AIP Publishing.
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| 17. |
- Colin, Jonathan, et al.
(författare)
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In Situ and Real-Time Nanoscale Monitoring of Ultra-Thin Metal Film Growth Using Optical and Electrical Diagnostic Tools
- 2020
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 10:11
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Forskningsöversikt (refereegranskat)abstract
- Continued downscaling of functional layers for key enabling devices has prompted the development of characterization tools to probe and dynamically control thin film formation stages and ensure the desired film morphology and functionalities in terms of, e.g., layer surface smoothness or electrical properties. In this work, we review the combined use of in situ and real-time optical (wafer curvature, spectroscopic ellipsometry) and electrical probes for gaining insights into the early growth stages of magnetron-sputter-deposited films. Data are reported for a large variety of metals characterized by different atomic mobilities and interface reactivities. For fcc noble-metal films (Ag, Cu, Pd) exhibiting a pronounced three-dimensional growth on weakly-interacting substrates (SiO2, amorphous carbon (a-C)), wafer curvature, spectroscopic ellipsometry, and resistivity techniques are shown to be complementary in studying the morphological evolution of discontinuous layers, and determining the percolation threshold and the onset of continuous film formation. The influence of growth kinetics (in terms of intrinsic atomic mobility, substrate temperature, deposition rate, deposition flux temporal profile) and the effect of deposited energy (through changes in working pressure or bias voltage) on the various morphological transition thicknesses is critically examined. For bcc transition metals, like Fe and Mo deposited on a-Si, in situ and real-time growth monitoring data exhibit transient features at a critical layer thickness of similar to 2 nm, which is a fingerprint of an interface-mediated crystalline-to-amorphous phase transition, while such behavior is not observed for Ta films that crystallize into their metastable tetragonal beta-Ta allotropic phase. The potential of optical and electrical diagnostic tools is also explored to reveal complex interfacial reactions and their effect on growth of Pd films on a-Si or a-Ge interlayers. For all case studies presented in the article, in situ data are complemented with and benchmarked against ex situ structural and morphological analyses.
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| 18. |
- Elofsson, Viktor, et al.
(författare)
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Atomic arrangement in immiscible Ag-Cu alloys synthesized far-from-equilibrium
- 2016
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 110, s. 114-121
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Tidskriftsartikel (refereegranskat)abstract
- Physical attributes of multicomponent materials of a given chemical composition are determined by atomic arrangement at property-relevant length scales. A potential route to access a vast array of atomic configurations for material property tuning is by synthesis of multicomponent thin films using vapor fluxes with their deposition pattern modulated in the sub-monolayer regime. However, the applicability of this route for creating new functional materials is impeded by the fact that a fundamental understanding of the combined effect of sub-monolayer flux modulation, kinetics and thermodynamics on atomic arrangement is not available in the literature. Here we present a research strategy and verify its viability for addressing the aforementioned gap in knowledge. This strategy encompasses thin film synthesis using a route that generates multi-atomic fluxes with sub-monolayer resolution and precision over a wide range of experimental conditions, deterministic growth simulations and nanoscale micro structural probes. Investigations are focused on structure formation within the archetype immiscible Ag-Cu binary system, revealing that atomic arrangement at different length scales is governed by the arrival pattern of the film forming species, in conjunction with diffusion of near-surface Ag atoms to encapsulate 3D Cu islands growing on 2D Ag layers. The knowledge generated and the methodology presented herein provides the scientific foundation for tailoring atomic arrangement and physical properties in a wide range of miscible and immiscible multinary systems. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 19. |
- Elofsson, Viktor, et al.
(författare)
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Double in-plane alignment in biaxially textured thin films
- 2014
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 105:23, s. 233113-
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Tidskriftsartikel (refereegranskat)abstract
- The scientific interest and technological relevance of biaxially textured polycrystalline thin films stem from their microstructure that resembles that of single crystals. To explain the origin and predict the type of biaxial texture in off-normally deposited films, Mahieu et al. have developed an analytical model [S. Mahieu et al., Thin Solid Films 515, 1229 (2006)]. For certain materials, this model predicts the occurrence of a double in-plane alignment, however, experimentally only a single in-plane alignment has been observed and the reason for this discrepancy is still unknown. The model calculates the resulting in-plane alignment by considering the growth of faceted grains with an out-of-plane orientation that corresponds to the predominant film out-of-plane texture. This approach overlooks the fact that in vapor condensation experiments where growth kinetics is limited and only surface diffusion is active, out-of-plane orientation selection is random during grain nucleation and happens only upon grain impingement. Here, we compile and implement an experiment that is consistent with the key assumptions set forth by the in-plane orientation selection model by Mahieu et al.; a Cr film is grown off-normally on a fiber textured Ti epilayer to pre-determine the out-of-plane orientation and only allow for competitive growth with respect to the in-plane alignment. Our results show unambiguously a biaxially textured Cr (110) film that possesses a double in-plane alignment, in agreement with predictions of the in-plane selection model. Thus, a long standing discrepancy in the literature is resolved, paving the way towards more accurate theoretical descriptions and hence knowledge-based control of microstructure evolution in biaxially textured thin films.
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| 20. |
- Elofsson, Viktor, 1987-
(författare)
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Nanoscale structure forming processes : Metal thin films grown far-from-equilibrium
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin film growth from the vapor phase has for a long time intrigued researchers endeavouring to unravel and understand atomistic surface processes that govern film formation. Their motivation has not been purely scientific, but also driven by numerous applications where this understanding is paramount to knowledge-based design of novel film materials with tailored properties.Within the above framework, this thesis investigates growth of metal films on weakly bonding substrates, a combination of great relevance for applications concerning e.g., catalysis, graphene metallization and architectural glazing. When metal vapor condenses on weakly bonding substrates three dimensional islands nucleate, grow and coalesce prior to forming a continuous film. The combined effect of these initial growth stages on film formation and morphology evolution is studied using pulsed vapor fluxes for the model system Ag/SiO2. It is shown that the competition between island growth and coalescence completion determines structure evolution. The effect of the initial growth stages on film formation is also examined for the tilted columnar microstructure obtained when vapor arrives at an angle that deviates from the substrate surface normal. This is done using two metals with distinctly different nucleation behaviour, and the findings suggest that the column tilt angle is set by nucleation conditions in conjunction with shadowing of the vapor flux by adjacent islands. Vapor arriving at an angle can in addition result in films that exhibit preferred crystallographic orientations, both out-of-plane and in-plane. Their emergence is commonly described by an evolutionary growth model, which for some materials predict a double in-plane alignment that has not been observed experimentally. Here, an experiment is designed to replicate the model’s growth conditions, confirming the existence of double in-plane alignment.New and added film functionalities can further be unlocked by alloying. Properties are then largely set by chemistry and atomic arrangement, where the latter can be affected by thermodynamics, kinetics and vapor flux modulation. Their combined effect on atomic arrangement is here unravelled by presenting a research methodology that encompasses high resolution vapor flux modulation, nanoscale structure v vi probes and growth simulations. The methodology is deployed to study the immiscible Ag-Cu and miscible Ag-Au model systems, for which it is shown that capping of Cu by Ag atoms via near surface diffusion processes and rough morphology of the Ag-Au growth front are the decisive structure forming processes in each respective system.The results generated in this thesis are of relevance for tuning structure of metal films grown on weakly bonding substrates. They also indicate that improved growth models are required to accurately describe structure evolution and emergence of a preferred in-plane orientation in films where vapor arrives at an angle that deviates from the substrate surface normal. In addition, this thesis presents a methodology that can be used to identify and understand structure forming processes in multicomponent films, which may enable tailoring of atomic arrangement and related properties in technologically relevant material systems.
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| 21. |
- Elofsson, Viktor, et al.
(författare)
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Structure formation in Ag-X (X = Au, Cu) alloys synthesized far-from-equilibrium
- 2018
-
Ingår i: Journal of Applied Physics. - New York : A I P Publishing LLC. - 0021-8979 .- 1089-7550. ; 123:16
-
Tidskriftsartikel (refereegranskat)abstract
- We employ sub-monolayer, pulsed Ag and Au vapor fluxes, along with deterministic growth simulations, and nanoscale probes to study structure formation in miscible Ag-Au films synthesized under far-from-equilibrium conditions. Our results show that nanoscale atomic arrangement is primarily determined by roughness build up at the film growth front, whereby larger roughness leads to increased intermixing between Ag and Au. These findings suggest a different structure formation pathway as compared to the immiscible Ag-Cu system for which the present study, in combination with previously published data, reveals that no significant roughness is developed, and the local atomic structure is predominantly determined by the tendency of Ag and Cu to phase-separate.
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| 22. |
- Elofsson, Viktor
(författare)
-
Thin Film Growth using Pulsed and Highly Ionized Vapor Fluxes
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microstructure and morphology of thin films are decisive for many of their resulting properties. To be able to tailor these properties, and thus the film functionality, a fundamental understanding of thin film growth needs to be acquired. Film growth is commonly performed using continuous vapor fluxes with low energy, but additional handles to control growth can be obtained by instead using pulsed and energetic ion fluxes. In this licentiate thesis the physical processes that determine microstructure and morphology of thin films grown using pulsed and highly ionized vapor fluxes are investigated.The underlying physics that determines the initial film growth stages (i.e., island nucleation, island growth and island coalescence) and how they can be manipulated individually when using pulsed vapor fluxes have previously been investigated. Their combined effect on film growth is, however, paramount to tailor film properties. In the thesis, a route to generate pulsed vapor fluxes using the vapor-based technique high power impulse magnetron sputtering (HiPIMS) is established. These fluxes are then used to grow Ag films on SiO2 substrates. For fluxes with constant energy and deposition rate per pulse it is demonstrated that the growth evolution is solely determined by the characteristics of the vapor flux, as set by the pulsing frequency, and the average time required for coalescence to be completed.Highly ionized vapor fluxes have previously been used to manipulate film growth when deposition is performed both normal and off-normal to the substrate. For the latter case, the physical mechanisms that determine film microstructure and morphology are, however, not fully understood. Here it is shown that the tilted columnar microstructure obtained during off-normal film growth is positioned closer to the substrate normal as the ionization degree of the flux increases, but only if certain nucleation characteristics are present.
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| 23. |
- Elofsson, Viktor, et al.
(författare)
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Tilt of the columnar microstructure in off-normally deposited thin films using highly ionized vapor fluxes
- 2013
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:17, s. 7 pages-
-
Tidskriftsartikel (refereegranskat)abstract
- The tilt of the columnar microstructure has been studied for Cu and Cr thin films grown off-normally using highly ionized vapor fluxes, generated by the deposition technique high power impulse magnetron sputtering. It is found that the relatively large column tilt (with respect to the substrate normal) observed for Cu films decreases as the ionization degree of the deposition flux increases. On the contrary, Cr columns are found to grow relatively close to the substrate normal and the column tilt is independent from the ionization degree of the vapor flux when films are deposited at room temperature. The Cr column tilt is only found to be influenced by the ionized fluxes when films are grown at elevated temperatures, suggesting that film morphology during the film nucleation stage is also important in affecting column tilt. A phenomenological model that accounts for the effect of atomic shadowing at different nucleation conditions is suggested to explain the results.
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| 24. |
- Elofsson, Viktor, et al.
(författare)
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Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 116:4, s. 044302-
-
Tidskriftsartikel (refereegranskat)abstract
- The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapour phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here we address this question using growth of Ag on SiO2 from pulsed vapour fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapour flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapour flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed, leading to a coalescence-free growth regime.
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| 25. |
- Gervilla Palomar, Victor, et al.
(författare)
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Dynamics of 3D-island growth on weakly-interacting substrates
- 2019
-
Ingår i: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 488, s. 383-390
-
Tidskriftsartikel (refereegranskat)abstract
- The growth dynamics of faceted three-dimensional (3D) Ag islands on weakly-interacting substrates are investigated-using kinetic Monte Carlo (kMC) simulations and analytical modelling-with the objective of determining the critical top-layer radius R-c required to nucleate a new island layer as a function of temperature T, at a constant deposition rate. kMC shows that R-c decreases from 17.3 to 6.0 angstrom as T is increased at 25 K intervals, from 300 to 500 K. That is, a higher T promotes top-layer nucleation resulting in an increase in island height-to-radius aspect ratios. This explains experimental observations for film growth on weakly-interacting substrates, which are not consistent with classical homoepitaxial growth theory. In the latter case, higher temperatures yield lower top-layer nucleation rates and lead to a decrease in island aspect ratios. The kMC simulation results are corroborated by an analytical mean field model, in which R-c is estimated by calculating the steady-state adatom density on the island side facets and top layer as a function of T. The overall findings of this study constitute a first step toward developing rigorous theoretical models, which can be used to guide synthesis of metal nanostructures, and layers with controlled shape and morphology, on technologically important substrates, including two-dimensional crystals, for nanoelectronic and catalytic applications.
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| 26. |
- Gervilla Palomar, Víctor, 1992-
(författare)
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Metal film growth on weakly-interacting substrates : Stochastic simulations and analytical modelling
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films are nanoscale layers of material, with exotic properties useful in diverse areas, ranging from biomedicine to nanoelectronics and surface protection. Film properties are not only determined by their chemical composition, but also by their microstructure and roughness, features that depend crucially on the growth process due to the inherent out-of equilibrium nature of the film deposition techniques. This fact suggest that it is possible to control film growth, and in turn film properties, in a knowledge-based manner by tuning the deposition conditions. This requires a good understanding of the elementary film-forming processes, and the way by which they are affected by atomic-scale kinetics. The kinetic Monte Carlo (kMC) method is a simulation tool that can model film evolution over extended time scales, of the order of microseconds, and beyond, and thus constitutes a powerful complement to experimental research aiming to obtain an universal understanding of thin film formation and morphological evolution.In this work, kMC simulations, coupled with analytical modelling, are used to investigate the early stages of formation of metal films and nanostructures supported on weakly-interacting substrates. This starts with the formation and growth of faceted 3D islands, that relies first on facile adatom ascent at single-layer island steps and subsequently on facile adatom upward diffusion from the base to the top of the island across its facets. Interlayer mass transport is limited by the rate at which adatoms cross from the sidewall facets to the island top, a process that determines the final height of the islands and leads non-trivial growth dynamics, as increasing temperatures favour 3D growth as a result of the upward transport. These findings explain the high roughness observed experimentally in metallic films grown on weakly-interacting substrates at high temperatures.The second part of the study focus on the next logical step of film formation, when 3D islands come into contact and fuse into a single one, or coalesce. The research reveals that the faceted island structure governs the macroscopic process of coalescence as well as its dynamics, and that morphological changes depend on 2D nucleation on the II facets. In addition, deposition during coalescence is found to accelerate the process and modify its dynamics, by contributing to the nucleation of new facets.This study provides useful knowledge concerning metal growth on weakly-interacting substrates, and, in particular, identifies the key atomistic processes controlling the early stages of formation of thin films, which can be used to tailor deposition conditions in order to achieve films with unique properties and applications.
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| 27. |
- Gervilla Palomar, Víctor, 1992-
(författare)
-
Metal film growth on weakly-interacting substrates : Multiscale modeling
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films are nanoscale layers of material used to functionalize surfaces or to serve as building blocks in more complex devices. In recent years, thin metal films have become vital for modern devices within, e.g., biosensing, catalysis, and nanoelectronics, whereby synthesis of metal layers with specific morphological features on two-dimensional (2D) crystals and oxides is required. However, this entails a great scientific challenge: in most of the afore-mentioned film/substrate combinations substrate and metal atoms interact weakly, causing the latter to self-assemble without control into three-dimensional (3D) clusters.Nowadays, a significant fraction of thin films is synthesized via condensation from the vapor phase, a far-from-equilibrium process in which film morphology is governed by the kinetic rates of atomic-scale structure-forming processes. It is, therefore, evident that knowledge-based synthesis of metal layers in high-performance devices necessitates a comprehensive understanding of the dynamic competition among these processes at the nano- and mesoscale. Such understanding is today incomplete, since experimental materials science tools are often not capable of providing nanometer and sub-nanometer insights at time scales that are relevant for thin-film synthesis. Computational approaches offer the possibility to fill the afore-mentioned gap in knowledge by allowing to explore atomistic behaviors with picosecond resolution. Hence, in the present thesis, a combination of modern computer simulation techniques is used to investigate thin metal film growth on weakly-interacting substrates from a purely atomistic point of view and to elucidate the ways by which atomic diffusion mechanisms give rise to the final film morphologies.In the first part of the thesis, an in-house kinetic Monte Carlo (KMC) simulation code and analytical modelling are used to investigate the early growth stages of Ag films supported on a generic weakly-interacting substrate. The results show that the weak interaction strength between film atoms and substrates leads to the formation of strongly-faceted 3D Ag islands, whose vertical growth is mediated by the temperature-dependent upward adatom diffusion across the facets. Eventually, the 3D islands impinge on each other and coalesce via surface migration of facet layers. Migration can be promoted by an increase of the deposition flux, but it can also be hindered by material agglomeration if the flux exceeds a critical threshold. These findings provide the foundation for explaining several effects observed during thin film growth on weakly-interacting substrates, including the increase of film roughness with temperature, the transition from 3D to 2D film morphology upon suppression of coalescence, and the origin of changes in thin film roughness and grain boundary number densities when varying the magnitude of vapor flux arrival rate.In the second part, ab initio and classical Molecular Dynamics simulations are used to investigate the diffusion dynamics of several transition metal adatoms (Ag, Au, Cu, Pd, Pt and Ru) and multi-atomic clusters (Ag, Au, Cu and Pd) on single layer graphene at room temperature (300K). The simulated diffusion trajectories reveal that diffusing adspecies experiencing a deep (hundreds of meV) potential energy landscape (PEL) on the substrate surface follow random walks; whilst those with a weak interaction with the substrate (PEL depth of a few meV) follow a superdiffusive motion pattern known as Lévy walk. This type of anomalous movement— also observed in other phenomena in physical, biological, and social systems—manifests itself as a continuous atomic motion with occasional flights over distances covering multiple adsorption sites. The fact that adspecies follow a distinctly different type of motion than what is observed in classical homoepitaxial growth theory implies that energy barriers readily available from static (0K) calculations may not be able to provide a physical accurate description of surface diffusion of metal adspecies on 2D crystals. As such, anomalous diffusion is a potentially important aspect to be considered when modelling growth of metal films and nanostructures on 2D materials.The results and insights generated in the present thesis provide key knowledge for controlled synthesis of films and nanostructures with tailored properties. This, in turn, is relevant for developing high-performance energy-saving windows, improving the turnover frequency of catalytic reactions, and integrating 2D materials into novel nanoelectronic devices. Moreover, the techniques developed and employed herein contribute toward bringing modern computational tools closer to the field of thin film growth.
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| 28. |
- Gervilla, Víctor, 1992-, et al.
(författare)
-
Anomalous versus Normal Room-Temperature Diffusion of Metal Adatoms on Graphene
- 2020
-
Ingår i: The Journal of Physical Chemistry Letters. - Washington, DC, United States : American Chemical Society. - 1948-7185. ; 11:21, s. 8930-8936
-
Tidskriftsartikel (refereegranskat)abstract
- Fabrication of high-performance heterostructure devices requires fundamental understanding of the diffusion dynamics of metal species on 2D materials. Here, we investigate the room-temperature diffusion of Ag, Au, Cu, Pd, Pt, and Ru adatoms on graphene using ab initio and classical molecular dynamics simulations. We find that Ag, Au, Cu, and Pd follow Lévy walks, in which adatoms move continuously within ∼1–4 nm2 domains during ∼0.04 ns timeframes, and they occasionally perform ∼2–4 nm flights across multiple surface adsorption sites. This anomalous diffusion pattern is associated with a flat (<50 meV) potential energy landscape (PEL), which renders surface vibrations important for adatom migration. The latter is not the case for Pt and Ru, which encounter a significantly rougher PEL (>100 meV) and, hence, migrate via conventional random walks. Thus, adatom anomalous diffusion is a potentially important aspect for modeling growth of metal films and nanostructures on 2D materials.
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| 29. |
- Gervilla, Víctor, 1992-, et al.
(författare)
-
Coalescence dynamics of 3D islands on weakly-interacting substrates
- 2020
-
Ingår i: Scientific Reports. - : Taylor & Francis. - 2045-2322. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- We use kinetic Monte Carlo simulations and analytical modelling to study coalescence of three-dimensional (3D) nanoscale faceted silver island pairs on weakly-interacting fcc(111) substrates, with and without concurrent supply of mobile adatoms from the vapor phase. Our simulations show that for vapor flux arrival rates F < 1 monolayer/second (ML/s) coalescence manifests itself by one of the islands absorbing the other via sidewall facet migration. This process is mediated by nucleation and growth of two-dimensional (2D) layers on the island facets, while the supply of mobile atoms increases the nucleation probability and shortens the time required for coalescence completion. When F is increased above 1 ML/s, coalescence is predominantly governed by deposition from the vapor phase and the island pair reaches a compact shape via agglomeration. The crucial role of facets for the coalescence dynamics is further supported by a mean-field thermodynamic description of the nucleation energetics and kinetics. Our findings explain experimental results which show that two-dimensional film growth morphology on weakly-interacting substrates is promoted when the rate of island coalescence is suppressed. The present study also highlights that deviations of experimentally reported film morphological evolutions in weakly-interacting film/substrate systems from predictions based on the sintering and particle growth theories may be understood in light of the effect of deposition flux atoms on the energetics and kinetics of facet-layer nucleation during coalescence.
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| 30. |
- Ghaemi, M., et al.
(författare)
-
Growth of Nb films on Cu for superconducting radio frequency cavities by direct current and high power impulse magnetron sputtering: A molecular dynamics and experimental study
- 2024
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 476
-
Tidskriftsartikel (refereegranskat)abstract
- The use of superconducting radio frequency (rf) cavities in particle accelerators necessitates that copper (Cu) surfaces are coated by thin niobium (Nb) films, predominantly synthesized by magnetron sputtering. A key feature of the rf cavities is that they exhibit a complex three-dimensional geometry, such that during Nb film growth vapor is not deposited on a flat substrate. The latter, combined with the line-of-sight nature of the deposition flux in conventional magnetron sputtering methods (including direct current magnetron sputtering; DCMS) yields films with porous columnar morphologies on surfaces of the cavities that do not face the magnetron source. High-power impulse magnetron sputtering (HiPIMS) is a variant of sputtering that generates highly-ionized fluxes. Using electrical fields, such fluxes can be deflected to trajectories that are closer to the substrate normal and, thereby, dense and uniform layers can be deposited on all surfaces of the rf cavities. In the present work, we use classical molecular dynamics simulations to model Nb film growth on Cu substrates at conditions consistent with those prevailing during DCMS and HiPIMS. Our computational results are in qualitative agreement with experimental data (also generated in the present study), with respect to film morphology. Based on this agreement and by studying the evolution of the simulated systems, we suggest that the morphology of HiPIMS-grown films (as compared to their DCMS counterparts) is the result of the combined effects of deflection of ionized sputtered particles to trajectories parallel to the substrate normal, bombardment-induced interruption of crystal growth, and ballistic atomic rearrangement along with dynamic thermal annealing caused by energetic film-forming species. Moreover, the predictions of our model with respect to dynamic processes at the film-substrate interface and their effect on local epitaxial growth are discussed.
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| 31. |
- Jamnig, Andreas, et al.
(författare)
-
3D-to-2D Morphology Manipulation of Sputter-Deposited Nanoscale Silver Films on Weakly Interacting Substrates via Selective Nitrogen Deployment for Multifunctional Metal Contacts
- 2020
-
Ingår i: ACS APPLIED NANO MATERIALS. - : AMER CHEMICAL SOC. - 2574-0970. ; 3:5, s. 4728-4738
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to reverse the inherent tendency of noble metals to grow in an uncontrolled three-dimensional (3D) fashion on weakly interacting substrates, including two-dimensional (2D) materials and oxides, is essential for the fabrication of high-quality multifunctional metal contacts in key enabling devices. In this study, we show that this can be effectively achieved by deploying nitrogen (N-2) gas with high temporal precision during magnetron sputtering of nanoscale silver (Ag) islands and layers on silicon dioxide (SiO2) substrates. We employ real-time in situ film growth monitoring using spectroscopic ellipsometry, along with optical modeling in the framework of the finite-difference time-domain method, and establish that localized surface plasmon resonance (LSPR) from nanoscale Ag islands can be used to gauge the evolution of surface morphology of discontinuous layers up to a SiO2 substrate area coverage of similar to 70%. Such analysis, in combination with data on the evolution of room-temperature resistivity of electrically conductive layers, reveals that presence of N-2 in the sputtering gas atmosphere throughout all film-formation stages: (i) promotes 2D growth and smooth film surfaces and (ii) leads to an increase of the continuous-layer electrical resistivity by similar to 30% compared to Ag films grown in a pure argon (Ar) ambient atmosphere. Detailed ex situ nanoscale structural analyses suggest that N-2 favors 2D morphology by suppressing island coalescence rates during initial growth stages, while it causes interruption of local epitaxial growth on Ag crystals. Using these insights, we deposit Ag layers by deploying N-2 selectively, either during the early precoalescence growth stages or after coalescence completion. We show that early N-2 deployment leads to 2D morphology without affecting the Ag-layer resistivity, while postcoalescence introduction of N-2 in the gas atmosphere further promotes formation of three-dimensional (3D) nanostructures and roughness at the film growth front. In a broader context this study generates knowledge that is relevant for the development of (i) single-step growth manipulation strategies based on selective deployment of surfactant species and (ii) real-time methodologies for tracking film and nanostructure morphological evolution using LSPR.
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| 32. |
- Jamnig, Andreas, 1991-, et al.
(författare)
-
Atomic-scale diffusion rates during growth of thin metal films on weakly-interacting substrates
- 2019
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- We use a combined experimental and theoretical approach to study the rates of surface diffusion processes that govern early stages of thin Ag and Cu film morphological evolution on weakly-interacting amorphous carbon substrates. Films are deposited by magnetron sputtering, at temperatures T-S between 298 and 413 K, and vapor arrival rates F in the range 0.08 to 5.38 monolayers/s. By employing in situ and real-time sheet-resistance and wafer-curvature measurements, we determine the nominal film thickness Theta at percolation (Theta(perc)) and continuous film formation (Theta(cont)) transition. Subsequently, we use the scaling behavior of Theta(perc) and Theta(cont) as a function of F and T-s, to estimate, experimentally, the temperature-dependent diffusivity on the substrate surface, from which we calculate Ag and Cu surface migration energy barriers E-D(exp) and attempt frequencies nu(exp)(0). By critically comparing E-D(exp) and nu(exp)(0) with literature data, as well as with results from our ab initio molecular dynamics simulations for single Ag and Cu adatom diffusion on graphite surfaces, we suggest that: (i) E-D(exp) and nu(exp)(0) correspond to diffusion of multiatomic clusters, rather than to diffusion of monomers; and (ii) the mean size of mobile clusters during Ag growth is larger compared to that of Cu. The overall results of this work pave the way for studying growth dynamics in a wide range of technologically-relevant weakly-interacting film/substrate systems-including metals on 2D materials and oxides-which are building blocks in next-generation nanoelectronic, optoelectronic, and catalytic devices.
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| 33. |
- Jamnig, Andreas, et al.
(författare)
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Manipulation of thin metal film morphology on weakly interacting substrates via selective deployment of alloying species
- 2022
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 40:3
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a versatile concept for manipulating morphology of thin (& LE;25 nm) noble-metal films on weakly interacting substrates using growth of Ag on SiO2 as a model system. The concept entails deployment of minority metallic (Cu, Au, Al, Ti, Cr, and Mo) alloying species at the Ag-layer growth front. Data from in situ and real-time monitoring of the deposition process show that all alloying agents-when deployed together with Ag vapor throughout the entire film deposition-favor two-dimensional (2D) growth morphology as compared to pure Ag film growth. This is manifested by an increase in the substrate area coverage for a given amount of deposited material in discontinuous layers and a decrease of the thickness at which a continuous layer is formed, though at the expense of a larger electrical resistivity. Based on ex situ microstructural analyses, we conclude that 2D morphological evolution under the presence of alloying species is predominantly caused by a decrease of the rate of island coalescence completion during the initial film-formation stages. Guided by this realization, alloying species are released with high temporal precision to selectively target growth stages before and after coalescence completion. Pre-coalescence deployment of all alloying agents yields a more pronounced 2D growth morphology, which for the case of Cu, Al, and Au is achieved without compromising the Ag-layer electrical conductivity. A more complex behavior is observed when alloying atoms are deposited during the post-coalescence growth stages: Cu, Au, Al, and Cr favor 2D morphology, while Ti and Mo yield a more pronounced three-dimensional morphological evolution. The overall results presented herein show that targeted deployment of alloying agents constitutes a generic platform for designing bespoken heterostructures between metal layers and technologically relevant weakly interacting substrates.& nbsp;Published under an exclusive license by the AVS.
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| 34. |
- Jamnig, Andreas, 1991-, et al.
(författare)
-
On the effect of copper as wetting agent during growth of thin silver films on silicon dioxide substrates
- 2021
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 538
-
Tidskriftsartikel (refereegranskat)abstract
- We study the effect of Cu incorporation on the morphological evolution and the optoelectronic properties of thin Ag films deposited by magnetron sputtering on weakly-interacting SiO2 substrates. In situ and real time spectroscopic ellipsometry data show that by adding up to 4at.% Cu throughout the entire film deposition process, wetting of the substrate by the metal layer is promoted, as evidenced by a decrease of the thickness at which the film becomes continuous from 19.5nm (pure Ag) to 15nm (Ag96Cu4). The in situ data are consistent with ex situ x-ray reflectometry analyses which show that Cu-containing films exhibit a root mean square roughness of 1.3nm compared to the value 1.8nm for pure Ag films, i.e., Cu leads to smoother film surfaces. These morphological changes are coupled with an increase in continuous-layer electrical resistivity from 1.0×10-5Ωcm (Ag) to 1.25×10-5Ωcm (Ag96Cu4). Scanning electron microscopic studies of discontinuous layers reveal that the presence of Cu at the film growth front promotes smooth surfaces (as compared to pure Ag films) by hindering the rate of island coalescence. To further understand the effect of Cu on film growth and electrical properties, in a second set of experiments, we deploy Cu with high temporal precision to target specific film-formation stages. The results show that longer presence of Cu in the vapor flux and the film growth front promote flat morphology. However, both a flat surface and a continuous-layer electrical resistivity that is equal to that of pure Ag films can only be achieved when Cu is deployed during the first 2.4nm of film deposition, during which morphological evolution is, primarily, governed by island coalescence. Our overall results highlight potential pathways for fabricating high-quality multifunctional metal contacts in a wide range of optoelectronic devices based on weakly-interacting oxides and van der Waals materials.
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| 35. |
- Jamnig, Andreas, et al.
(författare)
-
The effect of kinetics on intrinsic stress generation and evolution in sputter-deposited films at conditions of high atomic mobility
- 2020
-
Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 127:4
-
Tidskriftsartikel (refereegranskat)abstract
- Vapor-based metal film growth at conditions that promote high atomic mobility is typically accompanied by compressive stress formation after completion of island coalescence, while an apparent stress relaxation is observed upon deposition interruption. Despite numerous experimental studies confirming these trends, the way by which growth kinetics affect postcoalescence stress magnitude and evolution is not well understood, in particular, for sputter-deposited films. In this work, we study in situ and in real-time stress evolution during sputter-deposition of Ag and Cu films on amorphous carbon. In order to probe different conditions with respect to growth kinetics, we vary the deposition rate F from 0:015 to 1:27 nm/s, and the substrate temperature T-S from 298 to 413 K. We find a general trend toward smaller compressive stress magnitudes with increasing T-S for both film/substrate systems. The stress-dependence on F is more complex: (i) for Ag, smaller compressive stress is observed when increasing F; (ii) while for Cu, a nonmonotonic evolution with F is seen, with a compressive stress maximum for F = 0.102 nm/s. Studies of postdeposition stress evolution show the occurrence of a tensile rise that becomes less pronounced with increasing T-S and decreasing F, whereas a faster tensile rise is seen by increasing F and T-S. We critically discuss these results in view of ex situ obtained film morphology which show that deposition-parameter-induced changes in film grain size and surface roughness are intimately linked with the stress evolution. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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| 36. |
- Jamnig, Andreas, 1991-
(författare)
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Thin metal films on weakly-interacting substrates : Nanoscale growth dynamics, stress generation, and morphology manipulation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vapor-based growth of thin metal films with controlled morphology on weakly-interacting substrates (WIS), including oxides and van der Waals materials, is essential for the fabrication of multifunctional metal contacts in a wide array of optoelectronic devices. Achieving this entails a great challenge, since weak film/substrate interactions yield a pronounced and uncontrolled 3D morphology. Moreover, the far-from-equilibrium nature of vapor-based film growth often leads to generation of mechanical stress, which may further compromise device reliability and functionality. The objectives of this thesis are related to metal film growth on WIS and seek to: (i) contribute to the understanding of atomic-scale processes that control film morphological evolution; (ii) elucidate the dynamic competition between nanoscale processes that govern film stress generation and evolution; and (iii) develop methodologies for manipulating and controlling nanoscale film morphology between 2D and 3D. Investigations focus on magnetron sputter-deposited Ag and Cu films on SiO2 and amorphous carbon (a-C) substrates. Research is conducted by strategically combining of in situ and real-time film growth monitoring, ex situ chemical and (micro)-structural analysis, optical modelling, and deterministic growth simulations.In the first part, the scaling behavior of characteristic morphological transition thicknesses (i.e., percolation and continuous film formation thickness) during growth of Ag and Cu films on a-C are established as function of deposition rate and temperature. These data are interpreted using a theoretical framework based on the droplet growth theory and the kinetic freezing model for island coalescence, from which the diffusion rates of film forming species during Ag and Cu growth are estimated. By combining experimental data with ab initio molecular dynamics simulations, diffusion of multiatomic clusters, rather than monomers, is identified as the rate-limiting structure-forming process.In the second part, the effect of minority metallic or gaseous species (Cu, N2, O2) on Ag film morphological evolution on SiO2 is studied. By employing in situ spectroscopic ellipsometry, it is found that addition of minority species at the film growth front promotes 2D morphology, but also yields an increased continuous-layer resistivity. Ex situ analyses show that 2D morphology is favored because minority species hinder the rate of coalescence completion. Hence, a novel growth manipulation strategy is compiled in which minority species are deployed with high temporal precision to selectively target specific film growth stages and achieve 2D morphology, while retaining opto-electronic properties of pure Ag films.In the third part, the evolution of stress during Ag and Cu film growth on a-C and its dependence on growth kinetics (as determined by deposition rate, substrate temperature) is systematically investigated. A general trend toward smaller compressive stress magnitudes with increasing temperature/deposition rate is found, related to increasing grain size/decreasing adatom diffusion length. Exception to this trend is found for Cu films, in which oxygen incorporation from the residual growth atmosphere at low deposition rates inhibits adatom diffusivity and decreases the magnitude of compressive stress. The effect of N2 on stress type and magnitude in Ag films is also studied. While Ag grown in N2-free atmosphere exhibits a typical compressive-tensile-compressive stress evolution as function of thickness, addition of a few percent of N2 yields to a stress turnaround from compressive to tensile stress after film continuity which is attributed to giant grain growth and film roughening.The overall results of the thesis provide the foundation to: (i) determine diffusion rates over a wide range of WIS film/substrates systems; (ii) design non-invasive strategies for multifunctional contacts in optoelectronic devices; (iii) complete important missing pieces in the fundamental understanding of stress, which can be used to expand theoretical descriptions for predicting and tuning stress magnitude.
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| 37. |
- Jiang, Kaiyun, et al.
(författare)
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Ab initio study of effects of substitutional additives on the phase stability of gamma-alumina
- 2010
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Ingår i: Journal of Physics. - : Institute of Physics. - 0953-8984 .- 1361-648X. ; 22:50, s. 505502-
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Tidskriftsartikel (refereegranskat)abstract
- Using ab initio calculations, we have evaluated two structural descriptions of gamma-Al(2)O(3), spinel and tetragonal hausmannite, and explored the relative stability of gamma-Al(2)O(3) with respect to alpha-Al(2)O(3) with 2.5 at.% of Si, Cr, Ti, Sc, and Y additives to identify alloying element induced electronic structure changes that impede the gamma to alpha transition. The total energy calculations indicate that Si stabilizes gamma-Al(2)O(3), while Cr stabilizes alpha-Al(2)O(3). As Si is added, a bond length increase in alpha-Al(2)O(3) is observed, while strong and short Si-O bonds are formed in gamma-Al(2)O(3), consequently stabilizing this phase. On the other hand, Cr additions induce a smaller bond length increase in alpha-Al(2)O(3) than in gamma-Al(2)O(3), therefore stabilizing the a-phase. The bulk moduli of gamma-Al(2)O(3) with these additives show no significant changes. The phase stability and elastic property data discussed here underline the application potential of Si alloyed gamma-Al(2)O(3) for applications at elevated temperatures. Furthermore it is evident that the tetragonal hausmannite structure is a suitable description for gamma-Al(2)O(3).
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| 38. |
- Jiang, Kaiyun, et al.
(författare)
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Low temperature synthesis of alpha-Al(2)O(3) films by high-power plasma-assisted chemical vapour deposition
- 2010
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Ingår i: Journal of Physics D. - : Institute of Physics. - 0022-3727 .- 1361-6463. ; 43:32, s. 325202-
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we deposit Al(2)O(3) films using plasma-assisted chemical vapour deposition (PACVD) in an Ar-H(2)-O(2)-AlCl(3) atmosphere. A novel generator delivering approximately 4 times larger power densities than those conventionally employed in PACVD enabling efficient AlCl(3) dissociation in the gas phase as well as a more intense energetic bombardment of the growing film is utilized. We demonstrate that these deposition conditions allow for the growth of dense alpha-Al(2)O(3) films with negligible Cl incorporation and elastic properties similar to those of the bulk alpha-Al(2)O(3) at a temperature of 560 +/- 10 degrees C.
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| 39. |
- Jiang, Kaiyun, et al.
(författare)
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On the high temperature stability of gamma-Al2O3/Ti0.33Al0.67N coated WC-Co cutting inserts
- 2012
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Ingår i: International Journal of Materials Research - Zeitschrift für Metallkunde. - : Carl Hanser Verlag GmbH. - 1862-5282 .- 2195-8556. ; 103:12, s. 1509-1516
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Tidskriftsartikel (refereegranskat)abstract
- The high temperature stability of gamma-Al2O3 films deposited using filtered cathodic arc and plasma assisted chemical vapor deposition on Ti0.33Al0.67N coated WC-Co cutting inserts is investigated. X-ray diffractometry reveals that filtered cathodic arc deposited films transform partially into the thermodynamically stable alpha-Al2O3 phase at a temperature of 1000 degrees C. The gamma to alpha-Al2O3 transformation for plasma assisted chemical vapor deposition grown films is observed at 900 degrees C. These results are in qualitative agreement with differential scanning calorimetry measurements. Transmission electron microscopy on filtered cathodic arc and plasma assisted chemical vapor deposition films annealed at 900 degrees C reveals the existence of hexagonal AlN in the Ti0.33Al0.67N interlayer, as well as Al depletion at the Al2O3/Ti0.33Al0.67N interface. After annealing the plasma assisted chemical vapor deposition sample at 900 degrees C, alpha-Al2O3 grains with a size of 100 nm are observed inside the gamma-Al2O3 matrix, while for filtered cathodic arc samples only the gamma-phase is identified. Transmission electron microscopy analysis on both filtered cathodic arc and plasma assisted chemical vapor deposition samples annealed at 1000 degrees C shows that the original Al2O3/Ti0.33Al0.67N/WC-Co layer architecture is no longer intact. The formation of TiO2 is detected along the growth direction of the Al2O3 films. The present study suggests that not only the morphology and the impurities incorporated into gamma-Al2O3 but also stability of the Ti0.33Al0.67N interlayer determine the high temperature stability of gamma-Al2O3/Ti0.33Al0.67N coated hard-metal.
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| 40. |
- Logothetidis, S, et al.
(författare)
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Investigation of bilayer period and individual layer thickness of CrN/TiN superlattices by ellipsometry and X-ray techniques
- 2006
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 200:22-23, s. 6176-6180
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Tidskriftsartikel (refereegranskat)abstract
- CrN/TiN superlattice (SL) coatings were prepared employing reactive magnetron sputtering in unbalanced configuration. The coatings were deposited in a mixed Ar/N-2 atmosphere rotating the substrate holder, located at the centre of the deposition chamber. Through the rotation, the substrate was sequentially exposed in two diametrically located Cr and Ti targets (purity 99.95%) leading to the deposition of the CrN and TiN single layers, respectively. The deposition was carried out at various values of substrate bias voltage and substrate rotation speed. The microstructure of the SL coatings was investigated in terms of the thickness of the individual CrN and TiN single layers and the bilayer period A, namely the sum of the thickness of two sequentially CrN and TiN layers. A values were calculated employing X-ray diffraction (XRD) at both low and high diffraction angles. Moreover, the high-angle XRD patterns enabled the determination of the single CrN and TiN layer thickness. In addition, the thickness of the single layers was determined from Spectroscopic Ellipsometry using the Bruggeman effective medium approximation. The results reveal good agreement between the various techniques.
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| 41. |
- Logothetidis, S, et al.
(författare)
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The effect of crystal structure and morphology on the optical properties of chromium nitride thin films
- 2004
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 180, s. 637-641
-
Tidskriftsartikel (refereegranskat)abstract
- We study the microstructure of various CrxNy (1 less than x less than 2, y similar to 1) coatings grown by unbalanced reactive magnetron sputtering (UBRMS), using X-ray diffraction (XRD) and reflectivity (XRR). The coatings consist of various Cr-N phases, depending on the growth conditions. XRD has shown that a Cr adhesion layer below CrxNy eliminates the stress and promotes the growth of bigger grains. XRR determined the film density, which can be used also for the phase identification. We found that the UBRMS can produce single-phase CrN and Cr2N coatings with density equivalent to the corresponding single-crystals. The optical properties of the coatings were studied by spectroscopic ellipsometry (SE). The variations of optical properties of CrxNy coatings have been evaluated from SE data using the combined Drude-Lorentz model, which describes the optical response of the conduction and valence electrons, respectively, and provides the conduction electron density and the energy positions of the interband transitions. Finally, the optical properties were used to quantify the volume fractions of each phase using effective medium theories.
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| 42. |
- Lü, Bo, et al.
(författare)
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Coalescence-controlled and coalescence-free growth regimes during deposition of pulsed metal vapor fluxes on insulating surfaces
- 2015
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 117:13
-
Tidskriftsartikel (refereegranskat)abstract
- The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the processes of island nucleation, growth, and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. These regimes can be accessed by tuning deposition conditions; however, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we derived the quantitative criterion to stop coalescence during continuous metal vapor flux deposition on insulating surfaceswhich typically yields 3-dimensional growthby describing analytically the competition between island growth by atomic incorporation and the coalescence rate of islands [Lu et al., Appl. Phys. Lett. 105, 163107 (2014)]. Here, we develop the analytical framework for entering a coalescence-free growth regime for metal vapor deposition on insulating substrates using pulsed vapor fluxes, showing that there exist three distinct criteria for suppressing coalescence that correspond to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using atomistic nucleation theory for pulsed vapor deposition to control morphology of thin films beyond the point of island density saturation. (C) 2015 AIP Publishing LLC.
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| 43. |
- Lü, Bo, et al.
(författare)
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Dynamic competition between island growth and coalescence in metal-on-insulator deposition
- 2014
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 105:16, s. 163107-1-163107-5
-
Tidskriftsartikel (refereegranskat)abstract
- The morphology of thin metal films and nanostructures synthesized from the vapor phase on insulating substrates is strongly influenced by the coalescence of islands. Here, we derive analytically the quantitative criterion for coalescence suppression by combining atomistic nucleation theory and a classical model of coalescence. Growth simulations show that using this criterion, a coalescence-free growth regime can be reached in which morphological evolution is solely determined by island nucleation, growth, and impingement. Experimental validation for the ability to control the rate of coalescence using this criterion and navigate between different growth regimes is provided by in situ monitoring of Ag deposition on SiO2. Our findings pave the way for creating thin films and nanostructures that exhibit a wide range of morphologies and physical attributes in a knowledge-based manner.
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| 44. |
- Lü, Bo
(författare)
-
Dynamics of the Early Stages in Metal-on-Insulator Thin Film Deposition
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films consist of nanoscale layers of material that are used in many technological applications to either functionalize a surface or serve as parts in miniaturized devices. The properties of a film are closely related to its microstructure, which in turn can be tuned during film preparation. Thin film growth involves a multitude of atomic-scale processes that cannot always be easily studied experimentally. Therefore, different types of computer simulations have been developed in order to test theoretical models of thin film growth in a highly controlled way. To be able to compare simulation and experimental results, the simulations must be able to model events on experimental time-scales, i.e. several seconds or minutes. This is achievable with the kinetic Monte Carlo method.In this work, kinetic Monte Carlo simulations are used to model the initial growth stages of metal films on insulating, amorphous substrates. This includes the processes of island nucleation, three-dimensional island growth and island coalescence. Both continuous and pulsed vapor fluxes are investigated as deposition sources, and relations between deposition parameters and film morphology are formulated. Specifically, the film thickness at what is known as the “elongation transition” is studied as a function of the temporal profile of the vapor flux, adatom diffusivity and the coalescence rate. Since the elongation transition occurs due to hindrance of coalescence completion, two separate scaling behaviors of the elongation transition film thickness are found: one where coalescence occurs frequently and one where coalescence occurs infrequently. In the latter case, known nucleation behaviors can be used favorably to control the morphology of thin films, as these behaviors are not erased by island coalescence. Experimental results of Ag growth on amorphous SiO2 that confirm the existence of these two “growth regimes” are also presented for both pulsed and continuous deposition by magnetron sputtering. Knowledge of how to avoid coalescence for different deposition conditions allows nucleation for metal-on-insulator material systems to be studied and relevant physical quantities to be determined in a way not previously possible. This work also aids understanding of the growth evolution of polycrystalline films, which in conjunction with advanced deposition techniques allows thin films to be tailored to specific applications.
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| 45. |
- Lü, Bo, et al.
(författare)
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Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:6
-
Tidskriftsartikel (refereegranskat)abstract
- Vapor condensation on weakly interacting substrates leads to the formation of three-dimensional (3D) nanoscale islands (i.e., nanostructures). While it is widely accepted that this process is driven by minimization of the total film/substrate surface and interface energy, current film-growth theory cannot fully explain the atomic-scale mechanisms and pathways by which 3D island formation and morphological evolution occurs. Here, we use kinetic Monte Carlo simulations to describe the dynamic evolution of single-island shapes during deposition of Ag on weakly interacting substrates. The results show that 3D island shapes evolve in a self-similar manner, exhibiting a constant height-to-radius aspect ratio, which is a function of the growth temperature. Furthermore, our results reveal the following chain of atomic-scale events that lead to compact 3D island shapes: 3D nuclei are first formed due to facile adatom ascent at single-layer island steps, followed by the development of sidewall facets bounding the islands, which in turn facilitates upward diffusion from the base to the top of the islands. The limiting atomic process which determines the island height, for a given number of deposited atoms, is the temperature-dependent rate at which adatoms cross from sidewall facets to the island top. The overall findings of this study provide insights into the directed growth of metal nanostructures with controlled shapes on weakly interacting substrates, including two-dimensional crystals, for use in catalytic and nanoelectronic applications.
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| 46. |
- Lü, Bo, et al.
(författare)
-
Growth regimes during metal-on-insulator deposition using pulsed vapor fluxes
- 2014
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the initial surface processes of nucleation, island growth and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. While these regimes can be accessed by tuning deposition conditions, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used in a straightforward manner to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we proposed a mechanism and derived the quantitative criterion to stop coalescence during continuous vapor flux deposition, based on a competition between island growth by atomic incorporation and the coalescence rate of islands [Lü et al., Appl. Phys. Lett. 105, 163107 (2014)]. In the present study, we develop the analytical framework for entering a coalescence-free growth regime for thin film deposition using pulse vapor fluxes, showing that there exist three distinct criteria corresponding to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using classical nucleation theory for pulsed vapor deposition to design materials which have an inherent tendency to coalesce.
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| 47. |
- Lü, Bo, 1986-
(författare)
-
Nano- and mesoscale morphology evolution of metal films on weakly-interacting surfaces
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films are structures consisting of one or several nanoscale atomic layers of material that are used to either functionalize a surface or constitute components in more complex devices. Many properties of a film are closely related to its microstructure, which allows films to be tailored to meet specific technological requirements. Atom-by-atom film growth from the vapor phase involves a multitude of atomic processes that may not be easily studied experimentally in real-time because they occur in small length- (≤ Å) and timescales (≤ ns). Therefore, different types of computer simulation methods have been developed in order to test theoretical models of thin film growth and unravel what experiments cannot show. In order to compare simulated and experimental results, the simulations must be able to model events on experimental time-scales, i.e. on the order of microseconds to seconds. This is achievable with the kinetic Monte Carlo (kMC) method.In this work, the initial growth stages of metal deposition on weakly-interacting substrates is studied using both kMC simulations as well as experiments whereby growth was monitored using in situ probes. Such film/substrate material combinations are widely encountered in technological applications including low-emissivity window coatings to parts of microelectronics components. In the first part of this work, a kMC algorithm was developed to model the growth processes of island nucleation, growth and coalescence when these are functions of deposition parameters such as the vapor deposition rate and substrate temperature. The dynamic interplay between these growth processes was studied in terms of the scaling behavior of the film thickness at the elongation transition, for both continuous and pulsed deposition fluxes, and revealed in both cases two distinct growth regimes in which coalescence is either active or frozen out during deposition. These growth regimes were subsequently confirmed in growth experiments of Ag on SiO2, again for both pulsed and continuous deposition, by measuring the percolation thickness as well as the continuous film formation thickness. However, quantitative agreement with regards to scaling exponents in the two growth regimes was not found between simulations and experiments, and this prompted the development of a method to determine the elongation transition thickness experimentally. Using this method, the elongation transition of Ag on SiO2 was measured, with scaling exponents found in much better agreement with the simulation results. Further, these measurement data also allowed the calculation of surface properties such as the terrace diffusion barrier of Ag on SiO2 and the average island coalescence rate.In the second part of this thesis, pioneering work is done to develop a fully atomistic, on-lattice model which describes the growth of Ag on weakly-interacting substrates. Simulations performed using this model revealed several key atomic-scale processes occurring at the film/substrate interface and on islands which govern island shape evolution, thereby contributing to a better understanding of how 3D island growth occurs at the atomic scale for a wide class of materials. The latter provides insights into the directed growth of metal nanostructures with controlled shapes on weakly-interacting substrates, including twodimensional crystals for use in catalytic and nano-electronic applications.
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| 48. |
- Lü, Bo, 1986-, et al.
(författare)
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Scaling of elongation transition thickness during thin-film growth on weakly interacting substrates
- 2017
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 111:8
-
Tidskriftsartikel (refereegranskat)abstract
- The elongation transition thickness (hElong) is a central concept in the theoretical description of thin-film growth dynamics on weakly interacting substrates via scaling relations of hElong with respect to rates of key atomistic film-forming processes. To date, these scaling laws have only been confirmed quantitatively by simulations, while experimental proof has been left ambiguous as it has not been possible to measure hElong. Here, we present a method for determining experimentally hElong for Ag films growing on amorphous SiO2: an archetypical weakly interacting film/substrate system. Our results confirm the theoretically predicted hElong scaling behavior, which then allow us to calculate the rates of adatom diffusion and island coalescence completion, in good agreement with the literature. The methodology presented herein casts the foundation for studying growth dynamics and cataloging atomistic-process rates for a wide range of weakly interacting film/substrate systems. This may provide insights into directed growth of metal films with a well-controlled morphology and interfacial structure on 2D crystals-including graphene and MoS2-for catalytic and nanoelectronic applications. Published by AIP Publishing.
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| 49. |
- Lundin, Daniel, et al.
(författare)
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An introduction to thin film processing using high-power impulse magnetron sputtering
- 2012
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Ingår i: Journal of Materials Research. - : Cambridge University Press (CUP) / Materials Research Society. - 0884-2914 .- 2044-5326. ; 27:5, s. 780-792
-
Forskningsöversikt (refereegranskat)abstract
- High-power impulse magnetron sputtering (HiPIMS) is a promising sputtering-based ionized physical vapor deposition technique and is already making its way to industrial applications. The major difference between HiPIMS and conventional magnetron sputtering processes is the mode of operation. In HiPIMS the power is applied to the magnetron (target) in unipolar pulses at a low duty factor (andlt;10%) and low frequency (andlt;10 kHz) leading to peak target power densities of the order of several kilowatts per square centimeter while keeping the average target power density low enough to avoid magnetron overheating and target melting. These conditions result in the generation of a highly dense plasma discharge, where a large fraction of the sputtered material is ionized and thereby providing new and added means for the synthesis of tailor-made thin films. In this review, the features distinguishing HiPIMS from other deposition methods will be addressed in detail along with how they influence the deposition conditions, such as the plasma parameters and the sputtered material, as well as the resulting thin film properties, such as microstructure, phase formation, and chemical composition. General trends will be established in conjunction to industrially relevant material systems to present this emerging technology to the interested reader.
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| 50. |
- Magnfält, Daniel, et al.
(författare)
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Atom insertion into grain boundaries and stress generation in physically vapor deposited films
- 2013
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:5
-
Tidskriftsartikel (refereegranskat)abstract
- We present evidence for compressive stress generation via atom insertion into grain boundaries in polycrystalline Mo thin films deposited using energetic vapor fluxes (<∼120 eV). Intrinsic stress magnitudes between −3 and +0.2 GPa are obtained with a nearly constant stress-free lattice parameter marginally larger (0.12%) than that of bulk Mo. This, together with a correlation between large compressive film stresses and high film densities, implies that the compressive stress is not caused by defect creation in the grains but by grain boundary densification. Two mechanisms for diffusion of atoms into grain boundaries and grain boundary densification are suggested.
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