| 1. |
- Pliatsikas, Nikolaos, et al.
(författare)
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Manipulation of thin silver film growth on weakly interacting silicon dioxide substrates using oxygen as a surfactant
- 2020
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 38:4
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Tidskriftsartikel (refereegranskat)abstract
- The authors study the morphological evolution of magnetron-sputtered thin silver (Ag) films that are deposited on weakly interacting silicon dioxide (SiO2) substrates in an oxygen-containing (O-2) gas atmosphere. In situ and real-time monitoring of electrically conductive layers, along with ex situ microstructural analyses, shows that the presence of O-2, throughout all film-formation stages, leads to a more pronounced two-dimensional (2D) morphology, smoother film surfaces, and larger continuous-layer electrical resistivities, as compared to Ag films grown in pure argon (Ar) ambient. In addition, the authors data demonstrate that 2D morphology can be promoted, without compromising the Ag-layer electrical conductivity, if O-2 is deployed with high temporal precision to target film formation stages before the formation of a percolated layer. Detailed real-space imaging of discontinuous films, augmented by in situ growth monitoring data, suggests that O-2 favors 2D morphology by affecting the kinetics of initial film-formation stages and most notably by decreasing the rate of island coalescence completion. Furthermore, compositional and bonding analyses show that O-2 does not change the chemical nature of the Ag layers and no atomic oxygen is detected in the films, i.e., O-2 acts as a surfactant. The overall results of this study are relevant for developing noninvasive surfactant-based strategies for manipulating noble-metal-layer growth on technologically relevant weakly interacting substrates, including graphene and other 2D crystals.
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| 2. |
- 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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| 3. |
- Grossmann, Birgit, et al.
(författare)
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Tailoring age hardening of Ti1-xAlxN by Ta alloying
- 2017
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 35:060604
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure, mechanical properties, and thermal stability of arc evaporated Ti1-x-yAlxTayN hard coatings were systematically investigated by varying the Ta content in the range of 01-xAlxN solid solution, spinodal decomposition and wurtzite phase formation are shifted to higher temperatures. Consequently,the temperature range where Ta-alloyed coatings maintain their hardness is extended up to 1000°C.
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| 4. |
- Jamnig, Andreas, et al.
(författare)
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3D-to-2D Morphology Manipulation of Sputter-Deposited Nanoscale Silver Films on Weakly Interacting Substrates via Selective Nitrogen Deployment for Multifunctional Metal Contacts
- 2020
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Ingår i: ACS APPLIED NANO MATERIALS. - : AMER CHEMICAL SOC. - 2574-0970. ; 3:5, s. 4728-4738
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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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| 5. |
- Jamnig, Andreas, 1991-, et al.
(författare)
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Atomic-scale diffusion rates during growth of thin metal films on weakly-interacting substrates
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
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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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| 6. |
- 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
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 40:3
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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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| 7. |
- Jamnig, Andreas, 1991-, et al.
(författare)
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On the effect of copper as wetting agent during growth of thin silver films on silicon dioxide substrates
- 2021
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 538
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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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| 8. |
- Jamnig, Andreas, et al.
(författare)
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The effect of kinetics on intrinsic stress generation and evolution in sputter-deposited films at conditions of high atomic mobility
- 2020
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 127:4
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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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| 9. |
- 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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| 10. |
- Shtepliuk, Ivan, et al.
(författare)
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Interplay between thin silver films and epitaxial graphene
- 2020
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 381
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Tidskriftsartikel (refereegranskat)abstract
- Thin Ag films, with nominal thickness in the range 2 to 30 nm, are deposited using direct current magnetron sputtering and film morphology is studied by means of plan-view scanning electron microscopy. We find that for 2 mn nominal thickness the film surface consists of isolated circular nanoscale islands, which become interconnected as further material is deposited, leading to a continuous film at a nominal thickness of 30 nm. Our experimental findings are discussed in the context of the density functional theory results, which show that van der Waals forces dominate the interaction between Ag and epitaxial graphene. We also performed micro-Raman analysis and we find that the G and 2D modes of epitaxial graphene exhibit a red-shift upon Ag-layer deposition; which is interpreted as a result of charge transfer at the Ag/graphene interface. Moreover, we observed a pronounced enhancement of the G peak amplitude and area irrespective of the film nominal thickness and morphology, which we attribute to a combination of the charge transfer and plasmonic resonance effects. Our observations provide a critical information on the interaction between Ag and epitaxial graphene, which can be useful to design electronic and sensing devices based on Ag-epitaxial graphene hybrids.
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| 11. |
- Shtepliuk, Ivan, et al.
(författare)
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Probing the uniformity of silver-doped epitaxial graphene by micro-Raman mapping
- 2020
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER. - 0921-4526 .- 1873-2135. ; 580
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Tidskriftsartikel (refereegranskat)abstract
- We present a Raman spectroscopy study on epitaxial graphene decorated with thin Ag films (2-15 nm), which are deposited using magnetron sputtering. We find that the presence of Ag on the graphene surface induces doping, the uniformity and efficiency of which is determined by Ag nominal thickness. Deposition of Ag films with thicknesses up to 5 nm favors the effective electron transfer from Ag to epitaxial graphene. A significant redshift and broadening of the 2D peak are observed with increasing the Ag-layer thickness above 5 nm, which is indicative of large strain and doping fluctuations. We also observe a non-trivial linear growth of 2D/G peak intensity ratio with increasing D/G ratio for all Ag-decorated samples, which is explained by increase of peak amplitude due to surface enhanced Raman scattering and charged impurity-induced screening caused by the presence of Ag on the graphene surface.
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