| 1. |
- Aad, G., et al.
(författare)
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- 2013
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Ingår i: The European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6052. ; 73:3
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Alami, Jones, et al.
(författare)
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High-power impulse magnetron sputtering of Ti-Si-C thin films from a Ti3SiC2 compound target
- 2006
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Ingår i: Thin Solid Films. - : Institutionen för fysik, kemi och biologi. - 0040-6090 .- 1879-2731. ; 515:4, s. 1731-1736
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Tidskriftsartikel (refereegranskat)abstract
- We have deposited Ti-Si-C thin films using high-power impulse magnetron sputtering (HIPIMS) from a Ti3SiC2 compound target. The as-deposited films were composite materials with TiC as the main crystalline constituent. X-ray diffraction and photoelectron spectroscopy indicated that they also contained amorphous SiC, and for films deposited on inclined substrates, crystalline Ti5Si3Cx. The film morphology was dense and flat, while films deposited with dc magnetron sputtering under comparable conditions were rough and porous. Due to the high degree of ionization of the sputtered species obtained in HIPIMS, it is possible to control the film composition, in particular the C content, by tuning the substrate inclination angle, the Ar process pressure, and the bias voltage.
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| 3. |
- Alami, Jones, et al.
(författare)
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Ion-assisted Physical Vapor Deposition for enhanced film properties on non-flat surfaces
- 2005
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 23:2, s. 278-280
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Tidskriftsartikel (refereegranskat)abstract
- We have synthesized Ta thin films on Si substrates placed along a wall of a 2-cm-deep and 1-cm-wide trench, using both a mostly neutral Ta flux by conventional dc magnetron sputtering (dcMS) and a mostly ionized Ta flux by high-power pulsed magnetron sputtering (HPPMS). Structure of the grown films was evaluated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The Ta thin film grown by HPPMS has a smooth surface and a dense crystalline structure with grains oriented perpendicular to the substrate surface, whereas the film grown by dcMS exhibits a rough surface, pores between the grains, and an inclined columnar structure. The improved homogeneity achieved by HPPMS is a direct consequence of the high ion fraction of sputtered species.
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| 4. |
- Alami, Jones, et al.
(författare)
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Phase tailoring of Ta thin films by highly ionized pulsed magnetron sputtering
- 2007
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 515:7-8, s. 3434-3438
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Tidskriftsartikel (refereegranskat)abstract
- Ta thin films were grown on Si substrates at different inclination angles with respect to the sputter source using high power impulse magnetron sputtering (HIPIMS), an ionized physical vapor deposition technique. The ionization allowed for better control of the energy and directionality of the sputtered species, and consequently for improved properties of the deposited films. Depositions were made on Si substrates with the native oxide intact. The structure of the as deposited films was investigated using X-ray diffraction, while a four-point probe setup was used to measure the resistivity. A substrate bias process-window for growth of bcc-Ta was observed. However, the process-window position changed with changing inclination angles of the substrate. The formation of this low-resistivity bcc-phase could be understood in light of the high ion flux from the HIPIMS discharge.
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| 5. |
- Alami, Jones, 1971-
(författare)
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Plasma characterisation in high power pulsed magnetron sputtering
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, plasma parameters including plasma and floating potentials, electron energy distribution function (EEDF) plasma density and electron temperature are studied in a high power pulsed magnetron (HPPM) discharge at different Argon (Ar) gas pressures and different magnetron powers. It is reported that the EEDF during and shortly after the pulse can be represented by a bi-Maxwellian distribution indicating two energy groups of electrons.Furthermore, we report on the variation of the plasma parameters and electron energy distribution function with gas pressure in the pressure range 0.5-20 mtorr. At a high pressure (> 10 mTorr) two density peaks are present, the second of which occurs hundreds of microseconds after the pulse is switched off. It shows that the second peaks occurrence depends on the target material used as well as the chamber pressure and the magnetron power. It is found that the electron density is very high (up to 1019 m-3, during the whole of the measured 2000 µs, indicating the importance of the second density peak in maintaining the high plasma density.Measurements on the electron temperature show that this does not exceed 3 eV while the pulse is on, and that it is no more than 0.5 after the pulse is off. A movie is constructed using Langmuir probe measurements data, showing the temporal evolution of the plasma at 20 mTorr argon pressure and 11 J pulse energy. Analysis shows the existence of a magnetic trap underneath the center of the target. Furthermore, the electron flux in the substrate vicinity 10 - 12 cm from the target is found to be homogeneous. Ti thin films are grown along the sidewalls of a hole, 1 cm2 in area and 2 cm in depth, using both de magnetron and HPPM sputtering. Secondary electron microscopy shows that the film grown by de magnetron sputtering shows clear columnar growth, while a dense and flat film was produced using the HPPM sputtering technique.
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| 6. |
- Alami, Jones, 1971-
(författare)
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Plasma Characterization & Thin Film Growth and Analysis in Highly Ionized Magnetron Sputtering
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis addresses two research areas related to film growth in a highly ionized magnetron sputtering system: plasma characterization, and thin film growth and analysis. The deposition technique used is called high power pulsed magnetron sputtering (HPPMS). Characteristic for this technique are high energy pulses (a few Joules) of length 50-100 µs that are applied to the target (cathode) with a duty time of less than 1 % of the total pulse time. This results in a high electron density in the discharge (>1x1019 m-3) and leads to an increase of the ionization fraction of the sputtered material reaching up to 70 % for Cu.In this work the spatial and temporal evolution of the plasma parameters, including the electron energy distribution function (EEDF), the electron density and the electron temperature are determined using electrostatic Langmuir probes. Electron temperature measurements reveal a low effective temperature of 2-3 eV. The degree of ionization in the HPPMS discharge is explained in light of the self-sputtering yield of the target material. A simple model is therefore provided in order to compare the sputtering yield in HPPMS and that in dc magnetron sputtering (dcMS) for the same average power.Thin Ta films are grown using HPPMS and dcMS and their properties are studied. It is shown that enhanced microstructure and morphology of the deposited films is achieved by HPPMS. The Ta films are also deposited at a number of substrate inclination angles ranging from 0o (i.e., facing the target surface) up to 180 o (i.e., facing away from the target). Deposition rate measurements performed at all inclination angles for both techniques, reveal that growth made using HPPMS resulted in an improved film thickness at higher inclination. Furthermore, the high ionization of the Ta atoms in HPPMS discharge is found to allow for phase tailoring of the deposited films at all inclination angles by applying a bias voltage to the substrate. Finally, highly ionized magnetron sputtering of a compound MAX-phase material (Ti3SiC2) is performed, demonstrating that the HPPMS discharge could also be used to tailor the composition of the growing Ti-Si-C films.
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| 7. |
- Alami, Jones, et al.
(författare)
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Plasma dynamics in a highly ionized pulsed magnetron discharge
- 2005
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 14:3, s. 525-531
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Tidskriftsartikel (refereegranskat)abstract
- We report on electrostatic probe measurements of a high-power pulsed magnetron discharge. Space- and time-dependent characteristics of the plasma parameters are obtained as functions of the process parameters. By applying high-power pulses (peak power of ~0.5 MW), with a pulse-on time of ~100 µs and a repetition frequency of 20 ms, peak electron densities of the order of ~1019 m− 3, i.e. three orders of magnitude higher than for a conventional dc magnetron discharge, are achieved soon after the pulse is switched on. At high sputtering gas pressures (>5 mTorr), a second peak occurs in the electron density curve, hundreds of microseconds after the pulse is switched off. This second peak is mainly due to an ion acoustic wave in the plasma, reflecting off the chamber walls. This is concluded from the time delay between the two peaks in the electron and ion saturation currents, which is shown to be dependent on the chamber dimensions and the sputtering gas composition. Finally, the electron temperature is determined, initially very high but decreasing rapidly as the pulse is turned off. The reduction seen in the electron temperature, close to the etched area of the cathode, is due to cooling by the sputtered metal atoms.
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| 8. |
- Böhlmark, Johan, et al.
(författare)
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Ionization of sputtered metals in high power pulsed magnetron sputtering
- 2005
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 23:1, s. 18-22
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Tidskriftsartikel (refereegranskat)abstract
- The ion to neutral ratio of the sputtered material have been studied for high power pulsed magnetron sputtering and compared with a continuous direct current (dc) discharge using the same experimental setup except for the power source. Optical emission spectroscopy (OES) was used to study the optical emission from the plasma through a side window. The emission was shown to be dominated by emission from metal ions. The distribution of metal ionized states clearly differed from the distribution of excited states, and we suggest the presence of a hot dense plasma surrounded by a cooler plasma. Sputtered material was ionized close to the target and transported into a cooler plasma region where the emission was also recorded. Assuming a Maxwell–Boltzmann distribution of excited states the emission from the plasma was quantified. This showed that the ionic contribution to the recorded spectrum was over 90% for high pulse powers. Even at relatively low applied pulse powers, the recorded spectra were dominated by emission from ions. OES analysis of the discharge in a continuous dc magnetron discharge was also made, which demonstrated much lower ionization.
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| 9. |
- Böhlmark, Johan, et al.
(författare)
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Measurement of the magnetic field change in a pulsed high current magnetron discharge
- 2004
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Ingår i: Plasma Sources Science and Technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 13:4, s. 654-661
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a study of how the magnetic field of a circular planar magnetron is affected when it is exposed to a pulsed high current discharge. Spatially resolved magnetic field measurements are presented and the magnetic disturbance is quantified for different process parameters. The magnetic field is severely deformed by the discharge and we record changes of several millitesla, depending on the spatial location of the measurement. The shape of the deformation reveals the presence of azimuthally drifting electrons close to the target surface. Time resolved measurements show a transition between two types of magnetic perturbations. There is an early stage that is in phase with the axial discharge current and a late stage that is not in phase with the discharge current. The later part of the magnetic field deformation is seen as a travelling magnetic wave. We explain the magnetic perturbations by a combination of E × B drifting electrons and currents driven by plasma pressure gradients and the shape of the magnetic field. A plasma pressure wave is also recorded by a single tip Langmuir probe and the velocity (~103 m s−1) of the expanding plasma agrees well with the observed velocity of the magnetic wave. We note that the axial (discharge) current density is much too high compared to the azimuthal current density to be explained by classical collision terms, and an anomalous charge transport mechanism is required.
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| 10. |
- Böhlmark, Johan, et al.
(författare)
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Spatial electron density distribution in a high-power pulsed magnetron discharge
- 2005
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 33:2, s. 346-347
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Tidskriftsartikel (refereegranskat)abstract
- The spatial electron density distribution was measured as function of time in a high-power pulsed magnetron discharge. A Langmuir probe was positioned in various positions below the target and the electron density was mapped out. We recorded peak electron densities exceeding 1019 m-3 in a close vicinity of the target. The dynamics of the discharge showed a dense plasma expanding from the "race-track" axially into the vacuum chamber. We also record electrons trapped in a magnetic bottle where the magnetron magnetic field is zero, formed due to the unbalanced magnetron.
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| 11. |
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| 12. |
- Doubaji, Siham, et al.
(författare)
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On the P2-NaxCo1−y(Mn2/3Ni1/3)yO2 Cathode Materials for Sodium-Ion Batteries : Synthesis, Electrochemical Performance, and Redox Processes Occurring during the Electrochemical Cycling
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:1, s. 488-501
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Tidskriftsartikel (refereegranskat)abstract
- P2-type NaMO2sodiated layered oxides withmixed transition metals are receiving considerable attention foruse as cathodes in sodium-ion batteries. A study on solidsolution (1−y)P2-NaxCoO2−(y)P2-NaxMn2/3Ni1/3O2(y=0,1/3, 1/2, 2/3, 1) reveals that changing the composition of thetransition metals affects the resulting structure and the stabilityof pure P2 phases at various temperatures of calcination. For 0≤y≤1.0, the P2-NaxCo(1−y)Mn2y/3Niy/3O2solid-solutioncompounds deliver good electrochemical performance whencycled between 2.0 and 4.2 V versus Na+/Na with improved capacity stability in long-term cycling, especially for electrodematerials with lower Co content (y= 1/2 and 2/3), despite lower discharge capacities being observed. The (1/2)P2-NaxCoO2−(1/2)P2-NaxMn2/3Ni1/3O2composition delivers a discharge capacity of 101.04 mAh g−1with a capacity loss of only 3% after 100cycles and a Coulombic efficiency exceeding 99.2%. Cycling this material to a higher cutoffvoltage of 4.5 V versus Na+/Naincreases the specific discharge capacity to≈140 mAh g−1due to the appearance of a well-defined high-voltage plateau, but afteronly 20 cycles, capacity retention declines to 88% and Coulombic efficiency drops to around 97%. In situ X-ray absorption near-edge structure measurements conducted on composition NaxCo1/2Mn1/3Ni1/6O2(y= 1/2) in the two potential windows studiedhelp elucidate the operating potential of each transition metal redox couple. It also reveals that at the high-voltage plateau, all ofthe transition metals are stable, raising the suspicion of possible contribution of oxygen ions in the high-voltage plateau.
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| 13. |
- Elofsson, Viktor
(författare)
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Thin Film Growth using Pulsed and Highly Ionized Vapor Fluxes
- 2014
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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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| 14. |
- Gudmundsson, Jon Tomas, 1965-, et al.
(författare)
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Evolution of the electron energy distribution and plasma parameters in a pulsed magnetron discharge
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:22, s. 3427-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the creation of high-density plasma in a pulsed magnetron discharge. A 2.4 MW pulse, 100 µs wide, with a repetition frequency of 50 Hz is applied to a planar magnetron discharge to study the temporal behavior of the plasma parameters: the electron energy distribution function, the electron density, and the average electron energy. The electron density in the vicinity of the substrate, 20 cm below the cathode target, peaks at 8×1017 m–3, 127 µs after initiating the pulse. Towards the end of the pulse two energy groups of electrons are present with a corresponding peak in average electron energy. With the disapperance of the high-energy electron group, the electron density peaks, and the electron energy distribution appears to be Maxwellian like. Following the electron density peak, the plasma becomes more Druyvesteyn like with a higher average electron energy.
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| 15. |
- Gudmundsson, Jon Tomas, 1965-, et al.
(författare)
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Spatial and temporal behavior of the plasma parameters in a pulsed magnetron discharge
- 2002
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Ingår i: Surface and Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 161:2-3, s. 249-256
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the evolution of the electron, energy distribution and the plasma parameters in a high-density plasma in a pulsed magnetron discharge. The high-density plasma is created by applying a high power pulse (1–2.4 MW) with pulse length 100 μs and repetition frequency of 50 Hz to a planar magnetron discharge. The spatial and temporal behavior of the plasma parameters are investigated using a Langmuir probe; the electron energy distribution function, the electron density and the average electron energy. The electron energy distribution function during and shortly after the pulse can be represented by a bi-Maxwellian distribution indicating two energy groups of electrons. Furthermore, we report on the variation of the plasma parameters and electron energy distribution function with gas pressure in the pressure range 0.5–20 mtorr. We report electron density as high as 4×1018 m−3 at 10 mtorr and 9 cm below the target in a pulsed discharge with average power 300 W. We estimate the traveling speed of the electron density peak along the axis of the discharge. The traveling speed decreases with increased gas pressure from 4×105 cm/s at 0.5 mtorr to 0.87×105 cm s−1 at 10 mtorr. The effective electron temperature peaks at the same time independent of position in the discharge, which indicates a burst of high energy electrons at the end of the pulse.
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| 16. |
- Gylfason, Kristinn B., 1978-, et al.
(författare)
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Ion-acoustic solitary waves in a high power pulsed magnetron sputtering discharge
- 2005
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 38:18, s. 3417-3421
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Tidskriftsartikel (refereegranskat)abstract
- We report on the creation and propagation of ion-acoustic solitary waves in a high power pulsed magnetron sputtering discharge. A dense localized plasma is created by applying high energy pulses (4-12 J) of length; approximate to 70 mu s, at a repetition frequency of 50 pulses per second, to a planar magnetron sputtering source. The temporal behaviour of the electron density, measured by a Langmuir probe, shows solitary waves travelling away from the magnetron target. The velocity of the waves depends on the gas pressure but is roughly independent of the pulse energy.
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| 17. |
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| 18. |
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| 19. |
- Jin, P., et al.
(författare)
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Low temperature deposition of a-Al2O3 thin films by sputtering using a Cr2O3 template
- 2002
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 20:6, s. 2134-2136
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Tidskriftsartikel (refereegranskat)abstract
- A description about low temperature deposition of a-Al2O3 thin films by sputtering was presented. Cr2O3 thin layer was used as a template. Nanoindentation was used to study the mechanical properties of the deposited films. Calculations were made to obtain the hardness and Young's modulus of the films.
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| 20. |
- Ni, Wei-Xin, et al.
(författare)
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X-ray reciprocal space mapping studies of strain relaxation in thin SiGe layers (=100 nm) using a low temperature growth step
- 2001
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 227-228, s. 756-760
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Relaxation of thin SiGe layers (~90 nm) grown by molecular beam epitaxy using a low temperature growth step (120-200°C) has been investigated using two-dimensional reciprocal space mapping of X-ray diffraction. The samples studied have been divided in two groups, depending on the substrate cooling process during the growth of the low temperature layer. It has been found that a higher degree of relaxation was easily achieved for the sample group without growth interruption. A process window for full relaxation of the Si0.74Ge0.26 layer has been observed in the range of 140-150°C. © 2001 Elsevier Science B.V.
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| 21. |
- Shu, Rui, 1990-
(författare)
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Nonstoichiometric Multicomponent Nitride Thin Films
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High entropy ceramics have rapidly developed as a class of materials based on high entropy alloys; the latter being materials that contain five or more elements in near-equal proportions. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical, electrical and chemical properties. In this thesis, high entropy ceramic films, (TiNbZrTa)Nx were deposited using reactive magnetron sputtering with segmented targets. The stoichiometry x was tuned with two deposition parameters, i.e., substrate temperature and nitrogen flow ratio fN, their effect on microstructure and mechanical, electric, and electrochemical properties were investigated.Understoichiometric MeNx (Me = TiNbZrTa, 0.25 ≤ x ≤ 0.59) films were synthesized at a constant fN when substrate temperature was varied from room temperature (RT) to 700 °C. For low-temperature deposition, the coatings exhibited fcc solid-solution polycrystalline structures. A NaCl-type structure with (001) preferred orientation was observed in MeN0.46 coating deposited at 400 ºC, while an hcp structure was found for the coatings deposited above 500 ºC. The maximum hardness value of 26 GPa as well as the highest and values (0.12 and 0.34 GPa) were obtained for the MeN0.46 coating. These films exhibited low RT electrical resistivities. In 0.1 M H2SO4 aqueous solution, the most corrosion resistant film was MeN0.46 featured dense structure and low roughness.The MeNx films (x=0, 0.57 < x ≤ 0.83) were deposited with different fN. The maximum hardness was achieved at 22.1 GPa for MeN0.83 film. Their resistivities increased from 95 to 424 μΩcm with increasing nitrogen content. The corrosion resistance is related to the amount of nitrogen in the films. The corrosion current density was around 10-8 A/cm2, while the films with lower nitrogen contents (x < 0.60) exhibited a nearly stable current plateau up to 4.0 V, similar to the metallic films, while the films with a higher nitrogen content only featured a plateau up to 2.0 V, above which a higher nitrogen content resulted in higher currents. The reason was that the oxidation of these films at potentials above about 2.0 V vs. Ag/AgCl resulted in the formation of porous oxide layers as significant fraction of the generated N2 was lost to the electrolyte.Hence, these observed effects of deposition temperature and nitrogen content on the overall properties of nonstoichiometric MeNx films provide insights regarding protective multicomponent nitride films, e.g. as corrosion resistant coatings on metallic bipolar plates in fuel cells or batteries.
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