| 1. |
- Jablonka, Lukas, et al.
(författare)
-
Improving the morphological stability of nickel germanide by tantalum and tungsten additions
- 2018
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 112:10
-
Tidskriftsartikel (refereegranskat)abstract
- To enhance the morphological stability of NiGe, a material of interest as a source drain-contact in Ge-based field effect transistors, Ta or W, is added as either an interlayer or a capping layer. The efficacy of this Ta or W addition is evaluated with pure NiGe as a reference. While interlayers increase the NiGe formation temperature, capping layers do not retard the NiGe formation. Regardless of the initial position of Ta or W, the morphological stability of NiGe against agglomeration can be improved by up to 100 degrees C. The improved thermal stability can be ascribed to an inhibited surface diffusion, owing to Ta or W being located on top of NiGe after annealing, as confirmed by means of transmission electron microscopy, Rutherford backscattering spectrometry, and atom probe tomography. The latter also shows a 0.3 at. % solubility of Ta in NiGe at 450 degrees C, while no such incorporation of W is detectable.
|
|
| 2. |
- Kubart, Tomas, 1977-, et al.
(författare)
-
High rate reactive magnetron sputter deposition of titanium oxide
- 2008
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:22, s. 221501-
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic experimental study of reactive sputtering from substoichiometric targets of TiOx with x ranging from 0 to 1.75 is reported. Experimental results are compared with results from modeling. The developed model describes the observed behavior and explains the origins of the unexpectedly high deposition rate. The behavior is shown to originate from the presence of titanium suboxides at the target surface caused by preferential sputtering of the oxide. The model can be used for optimization of the target composition with respect to the deposition rate and film composition in a stable hysteresis-free reactive sputtering process.
|
|
| 3. |
- Kubart, Tomas, 1977-, et al.
(författare)
-
Influence of the target composition on reactively sputtered titanium oxide films
- 2009
-
Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 83:10, s. 1295-1298
-
Tidskriftsartikel (refereegranskat)abstract
- Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiOx targets with different oxygen contents. The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films.
|
|
| 4. |
- Kubart, Tomas, 1977-, et al.
(författare)
-
Modelling of sputtering yield amplification effect in reactive deposition of oxides
- 2010
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 204:23, s. 3882-3886
-
Tidskriftsartikel (refereegranskat)abstract
- Many reactive sputter deposition applications require high deposition rates. The primary limiting parameters in magnetron sputtering are the target power dissipation and sputtering yields of the target elements. In reactive deposition of oxides, the deposition rate is of particular interest due to the low sputtering yield of most commonly used oxides. Traditional high rate techniques rely on a feedback control of the oxygen partial pressure to prevent formation of oxide on the target and hence enable operation in the transition area. An alternative approach, based on target doping, is presented in this paper.By doping the sputtering target with heavy elements, it is possible to substantially enhance the sputtering yield and hence the deposition rate. Simulations of the partial sputtering yield values for aluminium from doped targets sputtered in reactive atmosphere have been carried out. The Monte Carlo based TRIDYN computer code has been used for simulations. The program has been used to find out optimum alloying conditions to obtain maximum partial sputtering yield for deposition of Al2O3. Our simulations indicate that the sputtering yield amplification in reactive sputtering may lead to much higher relative deposition rate increase than in a nonreactive case. The highest relative increase may be achieved in the transition region but substantial increase is predicted also in the oxide mode.
|
|
| 5. |
- Kubart, Tomas, 1977-, et al.
(författare)
-
On the description of metal ion return in reactive high power impulse magnetron sputtering
- 2021
-
Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 418
-
Tidskriftsartikel (refereegranskat)abstract
- Back-attraction of ionized metal is an important process in reactive high power impulse magnetron sputtering (R-HiPIMS). Here, we discuss the implementation of the metal return in balance type models for reactive magnetron sputtering. We show that the existing description of surface processes needs to be modified to satisfy mass conservation. A new steady-state time-averaged model is presented and used to evaluate the effect of the metal return in R-HiPIMS. The results show that the metal return leads to an increased oxide fraction in the deposited coating in R-HiPIMS. This effect can explain the high rate deposition of stoichiometric compounds deposited in the metal mode of operation that has been observed experimentally.
|
|
| 6. |
- Kubart, Tomas, 1977-, et al.
(författare)
-
Reactive high power impulse magnetron sputtering
- 2019
-
Ingår i: High Power Impulse Magnetron Sputtering: Fundamentals, Technologies, Challenges and Applications. - : Elsevier. - 9780128124543 - 9780128124550 ; , s. 223-263
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Reactive magnetron sputtering is essential in many industrial processes where it is applied to deposit compound films or coatings. Reactive sputtering is attractive because a range of compounds can be prepared from a low-cost metal target by addition of an appropriate reactive gas to the noble working gas. To understand the reactive HiPIMS process, we here start with an overview of reactive sputtering and an introduction to process hysteresis in dcMS, which is followed by an overview of fundamental surface and plasma processes focusing on the behavior specific for reactive sputtering. In the second half of the chapter, HiPIMS-specific aspects of reactive sputtering are reviewed. This includes hysteresis in reactive HiPIMS operation, which is the subject of much debate, as some report reduction or elimination of the hysteresis effect, while others claim that a feedback control is essential. To provide a deeper insight into the process physics, a combination of experimental and computational model results are presented and discussed throughout the text.
|
|
| 7. |
- Prusakova, Lucie, et al.
(författare)
-
Room Temperature Reactive Deposition of InGaZnO and ZnSnO Amorphous Oxide Semiconductors for Flexible Electronics
- 2020
-
Ingår i: Coatings. - : MDPI. - 2079-6412. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Amorphous oxide semiconductors (AOSs) are interesting materials which combine optical transparency with high electron mobility. AOSs can be prepared at low temperatures by high throughput deposition techniques such as magnetron sputtering and are thus suitable for flexible transparent electronics such as flexible displays, thin-film transistors, and sensors. In magnetron sputtering the energy input into the growing film can be controlled by the plasma conditions instead of the substrate temperature. Here, we report on magnetron sputtering of InGaZnO (IGZO) and ZnSnO (ZTO) with a focus on the effect of deposition conditions on the film properties. IGZO films were deposited by radio-frequency (RF) sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to microstructure, electron mobility, and resistivity. The best as-deposited IGZO films exhibited a resistivity of about 2 x 10(-2) Ohm center dot cm and an electron mobility of 18 cm(2)center dot V-1 center dot s(-1). The lateral distribution of the electrical properties in such films is mainly related to the activity and amount of oxygen reaching the substrate surface as well as its spatial distribution. The lateral uniformity is strongly influenced by the composition and energy of the material flux towards the substrate.
|
|
| 8. |
- Aiempanakit, Montri, 1977-, et al.
(författare)
-
Ag2Cu2O3 thin films deposited by reactive high power impulse magnetron sputtering
- 2013
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ag2Cu2O3 thin films were prepared by reactive high power impulse magnetron sputtering (HiPIMS) from an alloy silver-copper (Ag0.5Cu0.5) target on silicon and glass substrates. The effects of the oxygen gas flow and the peak power on the structural properties of the films were investigated. Structural characterization by grazing incidence X-ray diffraction measurements show that the structure of Ag2Cu2O3 is related to the oxygen flow and the peak power. Films grown with high peak power required higher oxygen flow rate in order to get stoichiometric Ag2Cu2O3 thin films. It was further found that using HiPIMS, polycrystalline Ag2Cu2O3 films can be grown at room temperature without substrate heating or post-deposition annealing, while films deposited by DCMS exhibit poor crystallinity under the same process conditions.
|
|
| 9. |
- Aiempanakit, Montri, 1977-
(författare)
-
Reactive High Power Impulse Magnetron Sputtering of Metal Oxides
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis deals with reactive magnetron sputtering processes of metal oxides with a prime focus on high power impulse magnetron sputtering (HiPIMS). The aim of the research is to contribute towards understanding of the fundamental mechanisms governing a reactive HiPIMS process and to investigate their implications on the film growth.The stabilization of the HiPIMS process at the transition zone between the metal and compound modes of Al-O and Ce-O was investigated for realizing the film deposition with improved properties and higher depositionrate and the results are compared with direct current magnetron sputtering (DCMS) processes. The investigations were made for different sputtering conditions obtained by varying pulse frequency, peak power and pumping speed. For the experimental conditions employed, it was found that reactive HiPIMS can eliminate/suppress the hysteresis effect for a range of frequency, leading to a stable deposition process with a high deposition rate. The hysteresis was found to be eliminated for Al-O while for Ce-O, it was not eliminated but suppressed as compared to the DCMS. The behavior of elimination/suppression of the hysteresis may be influenced by high erosion rate during the pulse, limited target oxidation between the pulses and gas rarefaction effects in front of the target. Similar investigations were made for Ti-O employing a larger target and the hysteresis was found to be suppressed as compared to the respective DCMS, but not eliminated. It was shown that the effect of gas rarefaction is a powerful mechanism for preventing oxide formation upon the target surface. The impact of this effect depends on the off-time between the pulses. Longer off-times reduce the influence of gas rarefaction.To gain a better understanding of the discharge current-voltage behavior in a reactive HiPIMS process of metal oxides, the ion compositions and ion energy distributions were measured for Al-O and Ti-O using time averaged and time-resolved mass spectrometry. It was shown that the different discharge current behavior between non-reactive and reactive modes couldn’t be explained solely by the change in the secondary electron emission yield from the sputtering target. The high fluxes of O1+ ions contribute substantially to the discharge current giving rise to an increase in the discharge current in the oxide mode as compared to the metal mode. The results also show that the source of oxygen in the discharge is both, the target surface (via sputtering) as well as the gas phase.The investigations on the properties of HiPIMS grown films were made by synthesizing metal oxide thin films using Al-O, Ti-O and Ag-Cu-O. It was shown that Al2O3 films grown under optimum condition using reactive HiPIMS exhibit superior properties as compared to DCMS. The HiPIMS grown films exhibit higher refractive index as well as the deposition rate of the film growth was higher under the same operating conditions. The effect of HiPIMS peak power on TiO2 film properties was investigated and the results are compared with the DCMS. The properties of TiO2 films such as refractive index, film density and phase structure were experimentally determined. The ion composition during film growth was investigated and an explanation on the correlation of the film properties and ion energy was made. 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. These phases can be obtained at room temperature without external substrate heating or post-deposition annealing which is in contrast to the reactive DCMS where both, anatase and rutile phases of TiO2 are obtained at either elevated growth temperatures or by employing post deposition annealing. The effect of HiPIMS peak power on the crystal structure of the grown films was also investigated for ternary compound, Ag-Cu-O, for which films were synthesized using reactive HiPIMS as well as reactive DCMS. It was found that the stoichiometric Ag2Cu2O3 can be synthesized by all examined pulsing peak powers. The oxygen gas flow rate required to form stoichiometric films is proportional to the pulsing peak power in HiPIMS. DCMS required low oxygen gas flow to synthesis the stoichiometric films. The HiPIMS grown films exhibit more pronounced crystalline structure as compared to the films grown using DCMS. This is likely an effect of highly ionized depositing flux which facilitates an intense ion bombardment during the film growth using HiPIMS. Our results indicate that Ag2Cu2O3film formation is very sensitive to the ion bombardment on the substrate as well as to the backattraction of metal and oxygen ions to the target.
|
|
| 10. |
- Aiempanakit, Montri, 1977-, et al.
(författare)
-
Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:13, s. 133302-
-
Tidskriftsartikel (refereegranskat)abstract
- The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.
|
|
| 11. |
- Aijaz, Asim, et al.
(författare)
-
Ion induced stress relaxation in dense sputter-deposited DLC thin films
- 2017
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 111:5
-
Tidskriftsartikel (refereegranskat)abstract
- Deposition of high-density and low-stress hydrogen-free diamond like carbon (DLC) thin films is demonstrated using a pulsed ionized sputtering process. This process is based on high power impulse magnetron sputtering, and high C ionization is achieved using Ne as the sputtering gas. The intrinsic compressive stress and its evolution with respect to ion energy and ion flux are explained in terms of the compressive stress based subplantation model for DLC growth by Davis. The highest mass density was similar to 2.7 g/cm(3), and the compressive stresses did not exceed similar to 2.5 GPa. The resulting film stresses are substantially lower than those achieved for the films exhibiting similar mass densities grown by filtered cathodic vacuum arc and pulsed laser deposition methods. This unique combination of high mass density and low compressive stress is attributed to the ion induced stress relaxation during the pulse-off time which corresponds to the post thermal spike relaxation timescales. We therefore propose that the temporal ion flux variations determine the magnitude of the compressive stress observed in our films. Published by AIP Publishing.
|
|
| 12. |
- Aijaz, Asim, et al.
(författare)
-
Mechanical Properties of Hydrogen Free Diamond-Like Carbon Thin Films Deposited by High Power Impulse Magnetron Sputtering with Ne
- 2018
-
Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 8:11
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-free diamond-like carbon (DLC) thin films are attractive for a wide range of industrial applications. One of the challenges related to the use of hard DLC lies in the high intrinsic compressive stresses that limit the film adhesion. Here, we report on the mechanical and tribological properties of DLC films deposited by High Power Impulse Magnetron Sputtering (HiPIMS) with Ne as the process gas. In contrast to standard magnetron sputtering as well as standard Ar-based HiPIMS process, the Ne-HiPIMS lead to dense DLC films with increased mass density (up to 2.65 g/cm(3)) and a hardness of 23 GPa when deposited on steel with a Cr + CrN adhesion interlayer. Tribological testing by the pin-on-disk method revealed a friction coefficient of 0.22 against steel and a wear rate of 2 x 10(-17) m(3)/Nm. The wear rate is about an order of magnitude lower than that of the films deposited using Ar. The differences in the film properties are attributed to an enhanced C ionization in the Ne-HiPIMS discharge.
|
|
| 13. |
- Cheng, Fangwen, et al.
(författare)
-
Embedding biocatalysts in a redox polymer enhances the performance of dye-sensitized photocathodes in bias-free photoelectrochemical water splitting
- 2024
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- Dye-sensitized photoelectrodes consisting of photosensitizers and molecular catalysts with tunable structures and adjustable energy levels are attractive for low-cost and eco-friendly solar-assisted synthesis of energy rich products. Despite these advantages, dye-sensitized NiO photocathodes suffer from severe electron-hole recombination and facile molecule detachment, limiting photocurrent and stability in photoelectrochemical water-splitting devices. In this work, we develop an efficient and robust biohybrid dye-sensitized NiO photocathode, in which the intermolecular charge transfer is enhanced by a redox polymer. Owing to efficient assisted electron transfer from the dye to the catalyst, the biohybrid NiO photocathode showed a satisfactory photocurrent of 141±17 μA·cm−2 at neutral pH at 0 V versus reversible hydrogen electrode and a stable continuous output within 5 h. This photocathode is capable of driving overall water splitting in combination with a bismuth vanadate photoanode, showing distinguished solar-to-hydrogen efficiency among all reported water-splitting devices based on dye-sensitized photocathodes. These findings demonstrate the opportunity of building green biohybrid systems for artificial synthesis of solar fuels.
|
|
| 14. |
- Cheng, Haoliang, et al.
(författare)
-
Atomic Layer Deposition of SnO2 as an Electron Transport Material for Solid-State P-type Dye-Sensitized Solar Cells
- 2022
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:10, s. 12022-12028
-
Tidskriftsartikel (refereegranskat)abstract
- Tin oxide (SnO2) as an electron transport material was prepared by atomic layer deposition in dye-sensitized NiO films to fabricate solid-state p-type dye-sensitized solar cells using two organic dyes PB6 and TIP as photosensitizers. Due to the excellent electron mobility and satisfactory penetration of SnO2 material into the NiO film, a record photocurrent density over 1 mA cm–2 was achieved with a power conversion efficiency of 0.14%. The effect of an inserted Al2O3 layer between the dye-sensitized NiO and SnO2 layer on photovoltaic performance of the devices was also investigated. The results suggest that the charge recombination between NiO and SnO2 can be significantly suppressed, showing prolonged charge lifetime and enhanced photovoltage.
|
|
| 15. |
- Comparotto, Corrado, et al.
(författare)
-
Chalcogenide Perovskite BaZrS3 : Thin Film Growth by Sputtering and Rapid Thermal Processing
- 2020
-
Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:3, s. 2762-2770
-
Tidskriftsartikel (refereegranskat)abstract
- Tandem solar cells based on hybrid organic-inorganic metal halide perovskites have reached efficiencies up to 28%, but major concerns for long-term stability and the presence of Pb have raised interest in searching for fully earth-abundant, intrinsic chemically stable, and nontoxic alternatives. With a direct band gap around 1.8 eV and stability in air up to at least 500 degrees C, BaZrS3 is a promising candidate. This work presents the first approach of synthesizing a thin film of such compound by sputtering at ambient temperature with a subsequent rapid thermal process. Despite the short fabrication time, the width of the XRD diffraction peaks and the energy and distribution of the photoluminescence response show comparable crystalline quality to that from bulk synthesis methods. Good crystallization required around 900 degrees C. Such a high temperature could be incompatible with fabrication of tandem solar cells.
|
|
| 16. |
- Comparotto, Corrado, et al.
(författare)
-
Synthesis of BaZrS3 Perovskite Thin Films at a Moderate Temperature on Conductive Substrates
- 2022
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:5, s. 6335-6343
-
Tidskriftsartikel (refereegranskat)abstract
- Chalcogenide perovskites are being considered for various energy conversion applications, not least photovoltaics. BaZrS3 stands out for its highly stable, earth-abundant, and nontoxic nature. It exhibits a very strong light-matter interaction and an ideal band gap for a top subcell in a two-junction photovoltaic device. So far, thin-film synthesis-necessary for proper optoelectronic characterization as well as device integration-remains underdeveloped. Sputtering has been considered, among others, but the need for an annealing step of at least 900 degrees C has been a cause for concern: such a high temperature could lead to damaging the bottom layers of prospective tandem devices. Still, a solid-state fabrication route has already demonstrated that BaZrS3 can form at much lower temperatures if excess S is present. In this work, sputtered Ba-Zr precursors capped by SnS are sulfurized at under 600 degrees C for 20 min. Although some Sn is still present at the surface after sulfurization, the resulting crystalline quality is comparable to samples synthesized at much higher temperatures. The results are rationalized, and the effect of key process variables is examined. This study represents the first successful synthesis of BaZrS3 perovskite that is compatible with conductive substrates-an important step forward for device integration.
|
|
| 17. |
- Elo, Robin, 1988-, et al.
(författare)
-
Tailoring residual stresses in CrNx films on alumina and silicon deposited by high-power impulse magnetron sputtering
- 2020
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 397
-
Tidskriftsartikel (refereegranskat)abstract
- Chromium nitride films, deposited using reactive magnetron sputtering, were optimised for wear resistance. The performance was measured by scratch resistance and optimised by tailoring the residual stresses. The depositions were carried out with either direct current magnetron sputtering (DCMS) or high-power impulse magnetron sputtering (HiPIMS), and with varying substrate bias and nitrogen gas flow. With DCMS, all films remained under tensile stresses and exhibited poor performance in scratch testing. Although the tensile stresses could be reduced by increasing the nitrogen flow, compressive stresses could only be induced when employing HiPIMS. Substrate bias had a strong effect in HiPIMS in contrast to the DCMS. The effect of the substrate bias in HiPIMS can be explained by the high ionisation of the flux of film forming species. In all cases, increased nitrogen flow favoured formation of CrN over Cr2N. All films showed signs of limited adhesion, which was improved using a titanium interlayer. Cracking across the scratch could be completely avoided for films with lower tensile or compressive stresses, the latter also exhibiting the highest critical load. The results show that it is possible to increase the scratch resistance by tailoring the residual stresses, for which HiPIMS proved a very useful tool.
|
|
| 18. |
- Englund, Sven, et al.
(författare)
-
Antimony-Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin-Film Solar Cells
- 2019
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 216:22
-
Tidskriftsartikel (refereegranskat)abstract
- Antimony-doped tin oxide (Sn2O3:Sb, ATO) is investigated as a transparent back contact for Cu2ZnSnS4 (CZTS) thin-film solar cells. The stability of the ATO under different anneal conditions and the effect from ATO on CZTS absorber growth are studied. It is found that ATO directly exposed to sulfurizing anneal atmosphere reacts with S, but when covered by CZTS, it does not deteriorate when annealed at T < 550 degrees C. The electrical properties of ATO are even found to improve when CZTS is annealed at T = 534 degrees C. At T = 580 degrees C, it is found that ATO reacts with S and degrades. Analysis shows repeatedly that ATO affects the absorber growth as large amounts of Sn-S secondary compounds are found on the absorber surfaces. Time-resolved anneal series show that these compounds form early during anneal and evaporate with time to leave pinholes behind. Device performance can be improved by addition of Na prior to annealing. The best CZTS device on ATO back contact herein has an efficiency of 2.6%. As compared with a reference on a Mo back contact, a similar open-circuit voltage and short-circuit current density are achieved, but a lower fill factor is measured.
|
|
| 19. |
- Fernandes, Daniel Filipe Félix, et al.
(författare)
-
Photocatalytic activity of TiO2 deposited by reactive HiPIMS with long target-to-substrate distance
- 2023
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 467
-
Tidskriftsartikel (refereegranskat)abstract
- Reactive High Power Impulse Magnetron Sputtering (HiPIMS) of TiO2 thin films was carried out to investigate the influence of ion parameters and the deposition temperature on the film crystallinity and photocatalytic performance. In order to limit unintentional substrate heating, a deposition setup with long target-to-substrate distance was used. Different HiPIMS pulse configurations, deposition temperatures and substrate bias were evaluated. TiO2 films prepared by pulsed dc magnetron sputtering were used as reference. Films deposited at room temperature were all found to be X-ray amorphous, and a minimum temperature of 200 degrees C was needed for film crystallization irrespective of the mode of operation. This is attributed to the relatively long target-to -substrate distance of 180 mm used in this work. The growth of a specific polymorph was shown to be depen-dent on the operation mode, where a high oxygen partial pressure was ideal for anatase formation. The pho-todegradation rates were, as expected, found to be highest for crystalline samples, where single-and mixed-phase films yielded similar rates. Furthermore, the photodegradation rates of HiPIMS films deposited without substrate heating could be enhanced up to 3 times as compared to the corresponding pulsed dc reference film. The ion assistance in HiPIMS is also beneficial at moderate temperatures, here 200 degrees C, where an improved crystallinity as compared to pdcMS, was observed.
|
|
| 20. |
- Ferreira, Fabio, et al.
(författare)
-
Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering
- 2018
-
Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 336, s. 92-98
-
Tidskriftsartikel (refereegranskat)abstract
- Recent developments in the automotive industry to improve engine efficiency and minimize pollutant emissions are driving the need for higher operating temperatures and loading densities in internal combustion engines. Future engines for internal combustion engines will require coatings with increased temperature stability (up to 500 degrees C) and wear resistance as compared to present day solutions. Hard tetrahedral DLC coatings (ta-C coatings) very low coefficient of friction and performed very well under mixed and boundary lubrication, and, thus, they are very attractive for automotive industry. In this work, DLC coatings were deposited by deep oscillations magnetron sputtering (DOMS), a variant of high power magnetron sputtering (HiPIMS). The main objective is to increase the sp(3) content in the films, as compared to d.c. magnetron sputtering (DCMS), and thus extend their operating range to higher temperatures. Increasing the bias voltage results in denser and smoother films with increasing hardness, as measured by nano-indentation, and increasing mass density, as measured by x-ray reflectivity. Accordingly, the UV Raman spectroscopy analysis of the films shows that the sp(3)/sp(2) ratio in the films increases with increasing substrate biasing. However, the sp(3) bonds convert back to sp(2) upon annealing. Never the less, a significantly higher amount of sp(3) bonds is formed in the DLC films deposited by DOMS, as compared to the DCMS ones, showing that DOMS is a promising path for the development of hard DLC films.
|
|
| 21. |
- Honnali, Sanath Kumar, 1996-
(författare)
-
Energy-efficient physical vapor deposition of transition metal nitride thin films
- 2024
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on providing insights into energy-efficient ways of growing protective thin films using physical vapor deposition (PVD) by magnetron sputtering, specifically high-power impulse magnetron sputtering (HiPIMS). This technique involves ionizing the material to be deposited to a high degree. The properties of the film for applications such as protective coatings could thus be controlled by modulating the energy and guiding the ions using electric and magnetic fields, respectively. The multiprincipal element TiZrNbTa nitride system is of interest for its corrosion-resistant coating applications. This material system consists of refractory metals that exhibit different ionic charge states with significant mass contrast. Thus, when sputtered with HiPIMS, the properties of the films strongly depend on the mass and energy of the bombarding metal ions. The transport of these ions to the substrate is influenced by the magnetic field distribution in the chamber. To demonstrate the influence of the magnetron arrangement, the deposition is performed without external heating. Two magnetron arrangements were chosen: a tilted closed-field design with four magnetrons and a single magnetron. The films exhibited different properties depending on the magnetron design used. The single magnetron design induces changes in the preferred orientation of the films from 111 to 200 along with film composition and density. A reduction in residual stress was observed with only a ~6 % degradation in the hardness compared to the closed-field design. I also demonstrate epitaxial growth of TiZrNbTaNx films without external heating. The films were grown with a single magnetron design on single crystal sapphire substrate. Applying a pulsed substrate bias with a long pulse width instead of a constant bias, resulted in low argon (~1 at. %) and oxygen (0.5 at. %) content in the films. In addition, the films exhibited a higher optical absorbance in the near-infrared region than the high-temperature grown films. The total energy consumption for film deposition was reduced by approximately 50 % compared to dc magnetron sputtering (DCMS) at 400°C growth temperature. This reduction is without considering the substrate heating and stabilization phase, which is shorter compared to the industry standard where the entire chamber is heated up to ~500-600°C. These findings are beneficial in designing film growth conditions for energy-efficient processes without compromising film quality. This could also address the challenges of growing high-quality films on temperature-sensitive substrates.
|
|
| 22. |
- Jablonka, Lukas, et al.
(författare)
-
Formation of nickel germanides from Ni layers with thickness below 10 nm
- 2017
-
Ingår i: Journal of Vacuum Science & Technology B. - : A V S AMER INST PHYSICS. - 1071-1023 .- 1520-8567. ; 35:2
-
Tidskriftsartikel (refereegranskat)abstract
- The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3 to NiGe was found to be nucleationcontrolled for Ni thicknesses < 5 nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness.
|
|
| 23. |
- Jablonka, Lukas, et al.
(författare)
-
Highly conductive ultrathin Co films by high-power impulse magnetron sputtering
- 2018
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:4
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 mu Omega cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 mu Omega cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.
|
|
| 24. |
- Jablonka, Lukas, Dipl.-NanoSc., et al.
(författare)
-
Metal Filling by High Power Impulse Magnetron Sputtering
- 2019
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 52:36
-
Tidskriftsartikel (refereegranskat)abstract
- High power impulse magnetron sputtering (HiPIMS) is an emerging thin film deposition technology that provides a highly ionized flux of sputtered species. This makes HiPIMS attractive for metal filling of nanosized holes for highly scaled semiconductor devices. In this work, HiPIMS filling with Cu and Co is investigated. We show that the quality of the hole filling is determined mainly by the fraction of ions in the deposited flux and their energy. The discharge waveforms alone are insufficient to determine the ionization of the metal flux. The experimental results are in a good agreement with Monte-Carlo simulations using the measured flux characteristics. Based on the simulations, strategies to improve the filling are discussed.
|
|
| 25. |
- Jacobo-Martin, Alejandra, et al.
(författare)
-
Resilient moth-eye nanoimprinted antireflective and self-cleaning TiO2 sputter-coated PMMA films
- 2022
-
Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 585
-
Tidskriftsartikel (refereegranskat)abstract
- Moth-eye nanostructures are amongst the most remarkable surfaces in nature because of their multi-functionality including antireflection, self-cleaning and bactericidal ability. Moth-eye surfaces consist of subwavelength arrays of tapered nanostructures, which are challenging to reproduce artificially. Nanoimprint lithography is probably one of the most suited technologies for this purpose. However, the poor mechanical resilience and durability of the polymeric nanocones when exposed to the environment, hinders their use in actual applications. To overcome these limitations, this work demonstrates the use of a thin oxide coating over the polymer moth-eye features imprinted on poly methyl methacrylate (PMMA) films. Particularly TiO2 conformal thin film coatings are deposited by unipolar pulsed dc magnetron sputtering over the antireflective nanopatterns acting as encapsulant. The coating, while preserving the antireflective properties, protects the nanostructures against mechanical scratching and improves substantially their thermal stability to over 250 ?. Furthermore, the TiO2 layer provides additional photoinduced self-cleaning functionality and at the same time it protects the matrix from UV photodegradation. The robust and durable antireflective surfaces developed here may find application on solar cells covers, flat panel displays or on optical components.
|
|
| 26. |
|
|
| 27. |
- Keller, Jan, et al.
(författare)
-
Bifacial Cu(In,Ga)Se2 solar cells using hydrogen‐doped In2O3 films as a transparent back contact
- 2018
-
Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:10, s. 846-858
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen‐doped In2O3 (IOH) films are used as a transparent back contact in bifacial Cu(In,Ga)Se2 (CIGS) solar cells. The effect of the IOH thickness and the impact of the sodium incorporation technique on the photovoltaic parameters are studied, and clear correlations are observed. It is shown that a loss in short circuit current density (JSC) is the major limitation at back side illumination. The introduction of a thin Al2O3 layer on top of the IOH significantly increases the collection efficiency (ϕ(x)) for electrons generated close to the back contact. In this way, the JSC loss can be mitigated to only ~ 25% as compared with front side illumination. The Al2O3 film potentially reduces the interface defect density or, alternatively, creates a field effect passivation. In addition, it prevents the excessive formation of Ga2O3 at the CIGS/IOH interface, which is found otherwise when a NaF layer is added before absorber deposition. Consequently, detrimental redistributions in Ga and In close to the back contact can be avoided. Finally, a bifacial CIGS solar cell with an efficiency (η) of η = 11.0% at front and η = 6.0% at back side illumination could be processed. The large potential for further improvements is discussed.
|
|
| 28. |
- Keller, Jan, et al.
(författare)
-
Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells
- 2018
-
Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:1, s. 13-23
-
Tidskriftsartikel (refereegranskat)abstract
- This contribution studies the impact of the KF-induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)-In-Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well-designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF-PDT) was applied.
|
|
| 29. |
- Keller, Jan, et al.
(författare)
-
Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells
- 2018
-
Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:3, s. 159-170
-
Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the potential of hydrogen‐doped In2O3 (IOH) as a transparent back contact material in (Agy,Cu1‐y)(In1‐x,Gax)Se2 solar cells. It is found that the presence of Na promotes the creation of Ga2O3 at the back contact during (Agy,Cu1‐y)(In1‐x,Gax)Se2 growth. An excessive Ga2O3 formation results in a Ga depletion, which extends deep into the absorber layer. Consequently, the beneficial back surface field is removed and a detrimental reversed electrical field establishes. However, for more moderate Ga2O3 amounts (obtained with reduced Na supply), the back surface field can be preserved. Characterization of corresponding solar cells suggests the presence of an ohmic back contact, even at absorber deposition temperatures of 550°C. The best solar cell with an IOH back contact shows a fill factor of 74% and an efficiency (η) of 16.1% (without antireflection coating). The results indicate that Ga2O3 does not necessarily act as a transport barrier in the investigated system. Observed losses in open circuit voltage (VOC) as compared to reference samples with a Mo back contact are ascribed to a lower Na concentration in the absorber layer.
|
|
| 30. |
- Keller, Jan, et al.
(författare)
-
Wide-Gap Chalcopyrite Solar Cells with Indium Oxide-Based Transparent Back Contacts
- 2022
-
Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:8
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, the performance of wide-gap Cu(In,Ga)Se-2 (CIGS) and (Ag,Cu)(In,Ga)Se-2 (ACIGS) solar cells with In2O3:Sn (ITO) and In2O3:H (IOH) as transparent back contact (TBC) materials is evaluated. Since both TBCs restrict sodium in-diffusion from the glass substrate, fine-tuning of a NaF precursor layer is crucial. It is found that the optimum Na supply is lower for ACIGS than for CIGS samples. An excessive sodium amount deteriorates the solar cell performance, presumably by facilitating GaOx growth at the TBC/absorber interface. The efficiency (eta) further depends on the absorber stoichiometry, with highest fill factors (and eta) reached for close-stoichiometric compositions. An ACIGS solar cell with eta = 12% at a bandgap of 1.44 eV is processed, using IOH as a TBC. The best CIGS device reaches eta = 11.2% on ITO. Due to its very high infrared transparency, IOH is judged superior to ITO for implementation in a top cell of a tandem device. However, while ITO layers maintain their conductivity, IOH films show an increased sheet resistance after absorber deposition. Chemical investigations indicate that incorporation of Se during the initial stage of absorber processing may be responsible for the deteriorated conductivity of the IOH back contact in the final device.
|
|
| 31. |
- Kubart, Tomas, 1977-, et al.
(författare)
-
High power impulse magnetron sputtering of diamond-like carbon coatings
- 2020
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 38:4
-
Tidskriftsartikel (refereegranskat)abstract
- High power impulse magnetron sputtering (HiPIMS) of diamond-like carbon coatings is reviewed. Three variations of HiPIMS were used to deposit diamond-like carbon coatings: use of neon as compared to argon for sputtering, very high discharge peak current density in an Ar atmosphere, and the use of bursts of short sputtering pulses. All three variations were able to provide sufficient ion-to-neutral ratios to effectively control the coating quality using substrate bias. The resulting coatings are typically smooth, amorphous, hard (up to 25 GPa), and dense but have low stress (below 2.5 GPa). The coatings exhibit an increased stability at higher temperature (up to 500 °C) compared to the coatings prepared using standard magnetron sputtering. The resulting coatings also exhibited low wear rates in ambient ball-on-disc tests (2.1 × 10−8 mm3 N−1 m−1). These improvements are explained in terms of the rate of sputtered carbon atom ionization in the plasma and material transport to the substrate. However, the chemical bonding in the films is not yet well understood as relatively low sp3 bond content has been observed.
|
|
| 32. |
- Oliveira, Joao, et al.
(författare)
-
Correlation between Substrate Ion Fluxes and the Properties of Diamond-Like Carbon Films Deposited by Deep Oscillation Magnetron Sputtering in Ar and Ar plus Ne Plasmas
- 2020
-
Ingår i: Coatings. - : MDPI. - 2079-6412. ; 10:10
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, the use of Ne as a processing gas has been shown to increase the ionization degree of carbon in High Power Impulse Magnetron Sputtering (HiPIMS) plasmas. In this work, time-resolved measurements of the substrate's current density were carried out in order to study the time evolution of the ionic species arriving at the growing film. The addition of Ne to the plasma resulted in a steep increase of the sp(3)/sp(2) ratio in the films once the Ne contents in the processing atmosphere exceeded 26%. Increasing the Ne content is shown to increase both the total number of C ions generated in the plasmas and the ratio of C/gaseous ions. The time-resolved substrate ion current density was used to evaluate the possibility of substrate biasing synchronizing with the discharge pulses in the HiPIMS process. It is shown that in pure Ar plasmas, substrate biasing should be confined to the time interval between 25 and 40 mu s after the pulse starts, in order to maximize the C+/Ar+ ratio bombarding the substrate and minimize the formation of film stresses. However, Ne addition to the processing gas shortens the traveling time of the carbon species towards the substrate, reducing the separation between the gaseous and carbon ion arrival times.
|
|
| 33. |
- Platzer Björkman, Charlotte, 1976-, et al.
(författare)
-
Back and front contacts in kesterite solar cells : state-of-the-art and open questions
- 2019
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7655. ; 1:4
-
Tidskriftsartikel (refereegranskat)abstract
- We review the present state-of-the-art within back and front contacts in kesterite thin film solar cells, as well as the current challenges. At the back contact, molybdenum (Mo) is generally used, and thick Mo(S, Se)2 films of up to several hundred nanometers are seen in record devices, in particular for selenium-rich kesterite. The electrical properties of Mo(S, Se)2 can vary strongly depending on orientation and indiffusion of elements from the device stack, and there are indications that the back contact properties are less ideal in the sulfide as compared to the selenide case. However, the electronic interface structure of this contact is generally not well-studied and thus poorly understood, and more measurements are needed for a conclusive statement. Transparent back contacts is a relatively new topic attracting attention as crucial component in bifacial and multijunction solar cells. Front illuminated efficiencies of up to 6% have so far been achieved by adding interlayers that are not always fully transparent. For the front contact, a favorable energy level alignment at the kesterite/CdS interface can be confirmed for kesterite absorbers with an intermediate [S]/([S]+[Se]) composition. This agrees with the fact that kesterite absorbers of this composition reach highest efficiencies when CdS buffer layers are employed, while alternative buffer materials with larger band gap, such as Cd1−x Zn x S or Zn1−x Sn x O y , result in higher efficiencies than devices with CdS buffers when sulfur-rich kesterite absorbers are used. Etching of the kesterite absorber surface, and annealing in air or inert atmosphere before or after buffer layer deposition, has shown strong impact on device performance. Heterojunction annealing to promote interdiffusion was used for the highest performing sulfide kesterite device and air-annealing was reported important for selenium-rich record solar cells.
|
|
| 34. |
- Ravensburg, Anna Lena
(författare)
-
Growth of high quality Fe thin films : A study of the effect of mismatch strain on the physical properties of Fe
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work in this licentiate is devoted to investigating the epitaxial growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The aim is to qualitatively and quantitatively determine the crystal quality of the grown Fe layers depending on their thickness, substrate material, and selected deposition parameters. The effect of the crystal quality on the magnetic and electronic transport properties is discussed. The structural characterization of the epitaxial Fe thin films is carried out by x-ray reflectometry and diffraction as well as transmission electron microscopy. X-ray scattering measurements and analysis with related models allow for a quantitative determination of layering, crystal quality, and strain profiles in the growing Fe. Magnetic properties are determined using a combination of longitudinal magneto-optical Kerr effect measurements, Kerr microscopy, and scanning electron microscopy with polarization analyser. Electronic transport properties are characterized by four-point probe measurements of the thin films. The epitaxial growth of Fe is found to be highly substrate dependent: Fe layers grown on MgAl2O4 have a significantly higher crystal quality, as compared to Fe grown on MgO. The difference in crystal quality is attributed to different strain states in Fe, which is supported by theoretical calculations of the critical thickness on both substrates. Moreover, an anomalous elastic response in Fe at the thin film limit is found. The magnetic properties of Fe are weakly reflecting the differences in crystal quality of the Fe layers. However, the difference in crystal quality affects the electronic transport properties. The results of this study on epitaxial Fe layers can provide insights into strain and defect engineering in Fe thin films, which can additionally serve as model systems for finite size effects.
|
|
| 35. |
- Tian, Lei, et al.
(författare)
-
Mechanistic Insights into Solid-State p-Type Dye-Sensitized Solar Cells
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 123:43, s. 26151-26160
-
Tidskriftsartikel (refereegranskat)abstract
- The study of p-type dye sensitized solar cells (p-DSCs) is appealing but challenging. Although the devices have been studied for 20 years, the light conversion efficiency lags far behind those of n-DSCs. Very recently, on the basis of a core-shell structure, a novel solid-state p-DSC (p-ssDSCs) has been fabricated, which showed great enhancement in open-circuit voltage and dye regeneration rate. To further improve the performance of such devices, charge diffusion, recombination process, and the main limiting factors have to be understood. In the present paper, core-shell p-ssDSCs with ZnO as an electron conductor were fabricated by atomic layer deposition. The charge transport time was determined to be ca. 0.1 ms, which is about 2 orders of magnitude faster than those of typical liquid devices with I-/I-3(-) as a redox mediator. As a consequence, the devices exhibit the highest reported charge diffusion coefficient (D-d)' among p-DSCs. It is ascribed to an electron-limiting diffusion process by the ambipolar diffusion model, suggesting a different charge-transport-determining mechanism in contrast to liquid p-DSCs. The charge recombination rate is 1-2 orders of magnitude slower than its charge transport time, mandating that the estimated charge collection efficiency is near unity. Detailed analysis of the incident photon-to-electron conversion efficiency suggests that the energy conversion efficiency in these p-ssDSCs is currently limited by a large fraction of dyes that is not fully electrically connected in the device.
|
|
| 36. |
- Tian, Lei, et al.
(författare)
-
Solid state p-type dye sensitized NiO-dye-TiO2 core-shell solar cells
- 2018
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 54:30, s. 3739-3742
-
Tidskriftsartikel (refereegranskat)abstract
- Solid state p-type dye sensitized NiO-dye-TiO2 core-shell solar cells with an organic dye PB6 were successfully fabricated for the first time. With Al2O3 as an inner barrier layer, the recombination process between injected holes in NiO and injected electrons in TiO2 was significantly suppressed and the charge transport time was also improved.
|
|
| 37. |
- Tian, Lei, et al.
(författare)
-
Ultrafast dye regeneration in a core-shell NiO-dye-TiO2 mesoporous film
- 2018
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : The Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:1, s. 36-40
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, a core-shell NiO-dye-TiO2 mesoporous film was fabricated for the first time, utilizing atomic layer deposition technique and a newly designed triphenylamine dye. The structure of the film was confirmed by SEM, TEM, and EDX. Excitation of the dye led to efficient and fast charge separation, by hole injection into NiO, followed by an unprecedentedly fast dye regeneration (t1/2 [less-than-or-equal] 500 fs) by electron transfer to TiO2. The resulting charge separated state showed a pronounced transient absorption spectrum caused by the Stark effect, and no significant decay was found within 1.9 ns. This indicates that charge recombination between NiO and TiO2 is much slower than that between the NiO and the reduced dye in the absence of the TiO2 layer (t1/2 [approximate] 100 ps).
|
|
| 38. |
- Vethaak, T. D., et al.
(författare)
-
Influence of substrate-induced thermal stress on the superconducting properties of V3Si thin films
- 2021
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 129:10
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of superconducting V3Si were prepared by means of RF sputtering from a compound V3Si target at room temperature onto sapphire and oxide-coated silicon wafers, followed by rapid thermal processing under secondary vacuum. The superconducting properties of the films thus produced are found to improve with annealing temperature, which is ascribed to a reduction in defects in the polycrystalline layer. Critical temperatures (Tc) up to 15.3 K were demonstrated after thermal processing, compared to less than 1 K after deposition. The Tc was always found to be lower on the silicon wafers, by on average 1:9+ 0:3 K for the annealed samples. This difference, as well as a broadening of the superconducting transitions, is nearly independent of the annealing conditions. In situ XRD measurements reveal that the silicide layer becomes strained upon heating due to a mismatch between the thermal expansion of the substrate and that of V3Si. Taking into account the volume reduction due to crystallization, this mismatch is initially larger on sapphire, though stress relaxation allows the silicide layer to be in a relatively unstrained state after cooling. On oxidized silicon, however, no clear evidence of relaxation upon cooling is observed, and V3Si ends up with an out-of-plane strain of 0.3% at room temperature. This strain increases as the sample is cooled down to cryogenic temperatures, though the deformation of the polycrystalline layer is expected to be highly inhomogeneous. Taking into account also the reported occurrence of a Martensitic transition just above the critical temperature, this extrapolated strain distribution is found to closely match an existing model of the strain dependence of A-15 superconducting compounds.
|
|
| 39. |
- Vethaak, T. D., et al.
(författare)
-
Superconducting V3Si for quantum circuit applications
- 2021
-
Ingår i: Microelectronic Engineering. - : Elsevier. - 0167-9317 .- 1873-5568. ; 244
-
Tidskriftsartikel (refereegranskat)abstract
- V3Si thin films are known to be superconducting with transition temperatures up to 15 K, depending on the annealing temperature and the properties of the substrate underneath. Here we investigate the film structural properties with the prospect of further integration in silicon technology for quantum circuits. Two challenges have been identified: (i) the large difference in thermal expansion coefficient between V3Si and the Si substrate leads to large thermal strains after thermal processing, and (ii) the undesired silicide phase VSi2 forms when V3Si is deposited on silicon. The first of these is studied by depositing layers of 200 nm V3Si on wafers of sapphire and oxidized silicon, neither of which react with the silicide. These samples are then heated and cooled between room temperature and 860 degrees C, during which in-situ XRD measurements are performed. Analysis reveals a highly nonlinear stress development during heating with contributions from crystallization and subsequent grain growth, as well as the thermal expansion mismatch between silicide and substrate, while the film behaves thermoelastically during cooling. The second challenge is explored by depositing films of 20, 50, 100 and 200 nm of V3Si on bulk silicon. For each thickness, six samples are prepared, which are then annealed at temperatures between 500 and 750 degrees C, followed by measurements of their resistivity, residual resistance ratio and superconducting critical temperature. A process window is identified for silicide thicknesses of at least 100 nm, within which a trade-off needs to be made between the quality of the V3Si film and its consumption by the formation of VSi2.
|
|
| 40. |
- Vitelaru, Catalin, et al.
(författare)
-
A Strategy for Alleviating Micro Arcing during HiPIMS Deposition of DLC Coatings
- 2020
-
Ingår i: Materials. - : MDPI. - 1996-1944. ; 13:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we investigate the use of high power impulse magnetron sputtering (HiPIMS) for the deposition of micrometer thick diamond like carbon (DLC) coatings on Si and steel substrates. The adhesion on both types of substrates is ensured with a simple Ti interlayer, while the energy of impinging ions is adjusted by using RF (Radio Frequency) biasing on the substrate at -100 V DC self-bias. Addition of acetylene to the working Ar+Ne atmosphere is investigated as an alternative to Ar sputtering, to improve process stability and coatings quality. Peak current is maintained constant, providing reliable comparison between different deposition conditions used in this study. The main advantages of adding acetylene to the Ar+Ne gas mixture are an increase of deposition rate by a factor of 2, when comparing to the Ar+Ne process. Moreover, a decrease of the number of surface defects, from similar to 40% surface defects coverage to similar to 1% is obtained, due to reduced arcing. The mechanical and tribological properties of the deposited DLC films remain comparable for all investigated gas compositions. Nanoindentation hardness of all coatings is in the range of 25 to 30 GPa, friction coefficient is between 0.05 and 0.1 and wear rate is in the range of 0.47 to 0.77 x 10(-6) mm(3) N(-1)m(-1).
|
|
| 41. |
- Vitelaru, Catalin, et al.
(författare)
-
Discharge runaway in high power impulse magnetron sputtering of carbon : the effect of gas pressure, composition and target peak voltage
- 2018
-
Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 51:16
-
Tidskriftsartikel (refereegranskat)abstract
- Pressure and target voltage driven discharge runaway from low to high discharge current density regimes in high power impulse magnetron sputtering of carbon is investigated. The main purpose is to provide a meaningful insight of the discharge dynamics, with the ultimate goal to establish a correlation between discharge properties and process parameters to control the film growth. This is achieved by examining a wide range of pressures (2-20 mTorr) and target voltages (700-850 V) and measuring ion saturation current density at the substrate position. We show that the minimum plasma impedance is an important parameter identifying the discharge transition as well as establishing a stable operating condition. Using the formalism of generalized recycling model, we introduce a new parameter, 'recycling ratio', to quantify the process gas recycling for specific process conditions. The model takes into account the ion flux to the target, the amount of gas available, and the amount of gas required for sustaining the discharge. We show that this parameter describes the relation between the gas recycling and the discharge current density. As a test case, we discuss the pressure and voltage driven transitions by changing the gas composition when adding Ne into the discharge. We propose that standard Ar HiPIMS discharges operated with significant gas recycling do not require Ne to increase the carbon ionization.
|
|
