ABSTRACT Arc plasma from Ti3SiC2 compound cathodes used in a filtered dc arc system has been char... more ABSTRACT Arc plasma from Ti3SiC2 compound cathodes used in a filtered dc arc system has been characterized with respect to plasma chemistry and charge-state resolved ion energies. In vacuum, the plasma composition is dominated by Ti ions, with concentrations of 84.3, 9.3, and 6.4 at% for Ti, Si, and C ions, respectively. The reduced amount of Si and most notably C compared with the cathode composition is confirmed by analysis of film composition in corresponding growth experiments. The deposition of light-element deficient films is thus related to plasma generation or filter transport. The ion energy distributions in vacuum range up to 140, 90, and 70 eV for Ti, Si, and C, respectively. Corresponding average ion energies of 48, 36, and 27 eV are reduced upon introduction of gas, down to around 5 eV at 0.6 Pa Ar or 0.3 Pa N2 for all species. In vacuum, the charge state distributions of Si and C are shifted to higher values compared with corresponding elemental cathodes, likely caused by changed effective electron temperature of the plasma stemming from compound cathode material and/or by electron impact ionization in the filter. The average ion charge states are reduced upon addition of Ar, ranging between 1.97 and 1.48 for Ti, 1.91 and 1.46 for Si, and 1.25 and 1.02 for C. Similar effects are observed upon introduction of N2, though with more efficient charge state reduction with pressure. It is conceivable that the pressure-induced changes in ion energy and charge state are crucial for the film synthesis from a microstructure evolution point of view, as they affect the ion-surface interactions through supply of energy, especially when substrate biasing is employed during arc deposition from a compound cathode.
Metastable Ti 1-x Al x N (0.4 ≤ x ≤ 0.76) films are grown using a hybrid approach in which high-p... more Metastable Ti 1-x Al x N (0.4 ≤ x ≤ 0.76) films are grown using a hybrid approach in which high-power pulsed magnetron sputtering (HIPIMS) is combined with dc magnetron sputtering (DCMS). Elemental Al and Ti metal targets are co-sputtered with one operated in HIPIMS mode and the other target in DCMS; the positions of the targets are then switched for the next set of that the doubly-ionized metal ion flux is approximately two orders of magnitude higher from the Ti target, than from Al, powered with HIPIMS. This asymmetry becomes decisive upon application of a moderate substrate bias voltage, -60 V, applied synchronously with HIPIMS pulses, during growth.
Carbon and carbon nitride films, grown in argon or nitrogen discharges by reactive dc magnetron s... more Carbon and carbon nitride films, grown in argon or nitrogen discharges by reactive dc magnetron sputtering of a graphite target, were characterized by in situ scanning tunneling microscopy. When the growth temperature increased from ambient to 800 °C, we observed a topographic evolution of the carbon films from an amorphous to a graphitelike structure, and further to a distorted-graphitic phase with curved and intersecting basal planes, and finally to a surface containing nanotubes and nanodomes. When nitrogen was incorporated into the films, distortion of the graphitic basal planes occurred at a lower temperature compared to the pure carbon case. At temperatures of ϳ200 °C and above, regions of a nongraphitic phase, containing a high degree of carbon sp 3 bonds were observed. Spatially resolved tunneling spectroscopic measurements indicated that the band gaps were 0, ϳ0-0.6 eV, and ϳ0.4-2.0 eV for graphitelike structures, the distorted-graphitic phase, and the nongraphitic phase, respectively. Together with ex situ x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy measurements, the results suggest that the incorporation of nitrogen promotes bending of the graphitic basal planes and thereby facilitates the formation of three-dimensional covalently bonded networks with a high degree of sp 3 -coordinated carbon atoms.
We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN... more We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN-content Ti 1-x Al x N alloys (x ≤ 0.64) which simultaneously possess high hardness and low residual stress. The films are grown using a hybrid approach combining high-power pulsed magnetron (HPPMS/HIPIMS) and dc magnetron sputtering of opposing metal targets. With HIPIMS applied to the Al target, Al n+ ion irradiation (dominated by Al + ) of the growing film results in alloys 0.55 ≤ x ≤ 0.60 which exhibit hardness H 30 GPa and low stress = 0.2-0.7 GPa, tensile. In sharp contrast, films with corresponding AlN concentrations grown with HIPIMS applied to the Ti target, giving rise to Ti n+ ion irradiation (with a significant Ti 2+ component), are two-phase --cubic (Ti,Al)N and hexagonal AlN --with low hardness, H = 18-19 GPa, and high compressive stress ranging up to 2.7 GPa. Annealing alloys grown with HIPIMS applied to the Al target results in age hardening due to spinodal decomposition; the hardness of Ti 0.41 Al 0.59 N increases from 30 to 33 GPa following a 900 °C anneal.
The chemical desorption of carbon and nitrogen-containing species from the growth surface was inv... more The chemical desorption of carbon and nitrogen-containing species from the growth surface was investigated for the deposition of fullerene-like carbon nitride (FL CN x ) thin solid films by reactive magnetron sputtering of a carbon target in a N 2 -containing atmosphere. The desorption of mainly C 2 N 2 was suppressed by decreasing the substrate temperature for various N 2 fractions in the discharge stepwise from 873 K down to cryogenic temperatures of 153 K. This approach enabled us to quantify the film-forming flux by determining the carbon and nitrogen incorporation rates by elastic recoil detection. The incorporation of both, carbon and nitrogen, was found to increase substantially at lower substrate temperatures, whereas this effect is most pronounced for the higher N 2 fractions. In turn, a modified Arrhenius-type rate equation was applied to extrapolate the total flux of the elements as well as their respective activation energies of desorption for the series at higher N 2 fractions. The reasonable fit indicates that the desorption process is mainly determined by the surface diffusion rate of adsorbed C x N y species as well as their structure and total number. The extrapolated fluxes of carbon and nitrogen atoms arriving as preformed species at the growth surface scaled strongly with the availability of N 2 in the discharge, while the obtained activation energies of 0.05-0.17 eV point towards a saturation of the process at elevated temperatures. Furthermore, the constant C/N ratio found in the film-forming flux leads to the notion that most of the nitrogen incorporated originates from preformed species instead of N atoms or ions. The FL structure evolution has to be seen as a sensitive interplay between the type and magnitude of preformed C x N y species in the deposition flux and the selectiveness of the preferential etching by means of the chemical desorption.
High Velocity Oxy-Fuel has been utilized to spray coatings from Ti 2 AlC (MAXTHAL 211 ® ) powders... more High Velocity Oxy-Fuel has been utilized to spray coatings from Ti 2 AlC (MAXTHAL 211 ® ) powders. X-ray diffraction showed that the coatings consist predominantly of Ti 2 AlC with inclusions of the phases Ti 3 AlC 2 , TiC, and Al-Ti alloys. The fraction of Ti 2 AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H 2 and O 2 . A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti 2 AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3-5 GPa for the coatings sprayed with a powder size of 38 μm.
Microstructure and macroscopic properties of droplet free CrN films deposited by the recently dev... more Microstructure and macroscopic properties of droplet free CrN films deposited by the recently developed high power pulsed magnetron sputtering (HIPIMS) technique are presented. Magnetron glow discharges with peak power densities reaching 3000 W cm−2 were used to sputter Cr targets in both inert and reactive gas atmospheres. The flux arriving at the substrates consisted of neutrals and ions (approx. 70/30) of the sputtered metal and working gas atoms (Ar) with significantly elevated degree of ionization compared to conventional magnetron sputtering. The high-speed steel and stainless steel substrates were metal ion etched using a bias voltage of −1200 V prior to the deposition of CrN films. The film-to-substrate interfaces, observed by scanning transmission electron microscope cross-sections, were clean and contained no phases besides the film and substrate ones or recrystallized regions. CrN films were grown by reactive HIPIMS at floating potential reaching −160 V. Initial nucleation grains were large compared to conventional magnetron sputtered films, indicating a high adatom mobility in the present case. The films exhibited polycrystalline columnar growth morphology with evidence of renucleation. No intercolumnar voids were observed and the corrosion behavior of the film was superior to arc deposited CrNx. A high density of lattice defects was observed throughout the films due to the high floating potential. A residual compressive stress of 3 GPa and a hardness value of HK0.025=2600 were measured. A low friction coefficient of 0.4 and low wear rates against Al2O3 in these films are explained by the absence of droplets and voids known to contribute to extensive debris generation.
Ab initio calculations show that the energy cost for incorporating lattice defects such as pentag... more Ab initio calculations show that the energy cost for incorporating lattice defects such as pentagons and heptagons is significantly reduced for BCN compared to BN, thus promoting bending of basal planes in these compounds. Boron-carbon-nitride (B C N) thin films with a fullerene-like (FL) microstructure were then deposited by dual cathode magnetron sputtering from C and B 4 C targets. Up to 1 m thick films were grown at a total gas pressure of 3 mTorr (0.4 Pa) in varying Ar/N 2 ratios, and substrate temperatures between 225 and 350 • C. Compositional and microstructural studies were performed using RBS, SEM and HREM, respectively. Depending on the deposition condition, ternary B x C y N z films with fullerene-like microstructure could be prepared in agreement with the calculations within the composition range 0 ≤ x ≤ 53, 15 ≤ y ≤ 62, and 24 ≤ z ≤ 50 at.%. Fullerene-like structures also tend to form at lower temperatures in the case of BCN compared to CN. Nanoindentation measurements show that all B x C y N z films exhibited a highly elastic response independent of elemental composition. In addition, the calculations suggest a driving force for C and BN phase separation.
Carbon nitride is an emerging material for wear-resistant coatings. The fullerene-like CNx compou... more Carbon nitride is an emerging material for wear-resistant coatings. The fullerene-like CNx compounds generally exhibit extreme elasticity in combination with a low work of indentation hardness. Yet CNx shows a low-to-moderate resistance to penetration, depending on deposition conditions. Since the deformation energy is predominantly stored elastically, the material possesses an extremely resilient character. This new class of materials consists of sp2-coordinated basal planes that are buckled from the incorporation of pentagons and cross-linked at sp3-hybridized C sites, both of which are caused by structural incorporation of nitrogen. Carbon nitride thus deforms elastically due to bending of the structural units. The orientation, radius of curvature of the basal planes, and the degree of cross-linking between them defines the structure and properties of the material. Due to the unique deformation behavior, the hardness requires special care to assess, but can be very high for films...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1992
Transmission electron microscopy, x-ray diffraction, and Rutherford backscattering have been used... more Transmission electron microscopy, x-ray diffraction, and Rutherford backscattering have been used to investigate the effects of ion irradiation during growth on the deposition rate, composition, and microstructure of single-phase polycrystalline NaCl-structure TiNx films deposited by reactive magnetron sputtering with a negative substrate bias voltage Vs. The layers were deposited on thermally oxidized Si(001) substrates in mixed Ar+4% N2 discharges at a total pressure of 4.2 mTorr. Varying Vs between 0 and 1800 V resulted in incident ion-to-Ti atom flux ratios of 0.3 to 0.6 at the film growth surface and increases in the substrate temperature Ts (initially Ts=300 °C) of 40 to 200 °C. The Ti resputtering yield increased from ≤0.02 (Vs≤100 V) to 0.30 (Vs=1800 V) Ti atoms per incident ion (primarily Ar+), while the N/Ti ratio in as-deposited films increased from 1.03 for Vs=0 V to 1.12 for 100 V≤Vs≤400 V and then decreased to ≂0.95 as Vs was raised to 1800 V. Trapped Ar concentrations...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2012
Metastable NaCl-structure Ti1 − xAlxN is employed as a model system to probe the effects of metal... more Metastable NaCl-structure Ti1 − xAlxN is employed as a model system to probe the effects of metal versus rare-gas ion irradiation during film growth using reactive high-power pulsed magnetron sputtering (HIPIMS) of Al and dc magnetron sputtering of Ti. The alloy film composition is chosen to be x = 0.61, near the kinetic solubility limit at the growth temperature of 500 °C. Three sets of experiments are carried out: a −60 V substrate bias is applied either continuously, in synchronous with the full HIPIMS pulse, or in synchronous only with the metal-rich-plasma portion of the HIPIMS pulse. Alloy films grown under continuous dc bias exhibit a thickness-invariant small-grain, two-phase nanostructure (wurtzite AlN and cubic Ti1−xAlxN) with random orientation, due primarily to intense Ar+ irradiation leading to Ar incorporation (0.2 at. %), high compressive stress (−4.6 GPa), and material loss by resputtering. Synchronizing the bias with the full HIPIMS pulse results in films that exhi...
The microstructure formation and phase transformations in Ti2AlC-rich coatings deposited by High ... more The microstructure formation and phase transformations in Ti2AlC-rich coatings deposited by High Velocity Oxy-fuel spraying of Maxthal 211® powders is presented. High resolution electron microscopy analysis, using both scanning and transmission electron microscopy with energy dispersive spectrometry and energy filtering, combined with X-ray diffraction reveals that the coatings consist of Ti2AlC grains surrounded by regions of very small TiC grains embedded in Ti x Al y . The composition of the Ti x Al y depends on its surrounding and varies with size and distribution of the adjacent TiC grains. Impact of spray parameters on coating microstructure is also discussed. Two spray parameters were varied; powder size distribution and flame power. They were found to greatly affect the coating microstructure. Increasing powder size and decreasing flame power increase the amount of Ti2AlC, but produces thinner coatings with lower cohesion. Larger powder size will also decrease oxygen incorporation.
The incorporation behavior of Er into Si and Si Ge using ErF and Er O as dopant sources during mo... more The incorporation behavior of Er into Si and Si Ge using ErF and Er O as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. O took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4;10 cm\ using Er O and a high F background pressure. Using ErF compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF molecules, but also from CF V (x"1-4) and F background species, which are present due to a reaction between the ErF source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1;10 cm\ and without observable defects using ErF as source material. For the case of Er-doping of Si Ge using ErF , we observed contrast along lines in the growth direction at an Er concentration of 1;10 cm\, which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro-and photoluminescence.
Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetr... more Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a graphite target in Ar and Ar/N2 ambient. Ion energy distribution functions (IEDFs) were recorded in time-averaged and time-resolved mode for Ar+, C+, N2+, N+, and CxNy+ ions. An increase of N2 in the sputter gas (keeping the deposition pressure, pulse width, pulse frequency, and pulse energy constant) results for the HiPIMS discharge in a significant increase in C+, N+, and CN+ ion energies. Ar+, N2+, and C2N+ ion energies, in turn, did not considerably vary with the changes in working gas composition. The HiPIMS process showed higher ion energies and fluxes, particularly for C+ ions, compared to DCMS. The time evolution of the plasma species was analyzed for HiPIMS and revealed the sequential arrival of working gas ions, ions ejected from the target, and later during the pulse-on time molecular ions, in particula...
The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si... more The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si1−xGex layers were grown by molecular-beam epitaxy (MBE) and the silicides formed by different postdeposition reaction paths, were investigated using a combination of high-resolution cross-sectional transmission electron microscopy, high-resolution x-ray diffraction, and secondary-ion-mass spectrometry. In two of the three sample configurations investigated, Co was deposited either (S1) directly on a strained Si1−xGex layer or (S2) on a sacrificial MBE Si overlayer on Si0.9Ge0.1. In the third sample configuration (S3) Si1−xGex was grown on a Si(001) substrate containing a buried ion-implanted CoSi2 layer. Only in sample configuration S2 was it possible to obtain a fully strained nearly defect-free CoSi2/Si0.9Ge0.1 structure. A high density of threading dislocations, corresponding to ≊60% relaxation at the Si0.9Ge0.1/Si interface, was observed in S1 while S3, in addition to the dislocatio...
Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015 cm... more Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015 cm−2, were investigated by multicrystal x-ray diffraction, reciprocal space mapping (RSM), high-resolution transmission electron microscopy, and secondary-ion-mass spectrometry (SIMS). For Sn doses up to 3.30×1015 cm−2, annealing at 600 °C for 30 min under dry N2 atmosphere resulted in recrystallization by solid-phase epitaxy (SPE) to a layer thickness of more than 50 nm. These SPE-grown layers were shown to be free of extended defects and Sn redistribution was negligible. As measured by x-ray diffraction, the Sn-induced strain in Si increased with the implant dose. From RSM measurements, this strain was shown to be tetragonal with negligible in-plane relaxation. Mosaicity and defect-related effects were shown to be negligible. Instead, limited thickness effects and strain variation due to the implantation profile appeared to be the major sources of the observed broadening in the diffracti...
Embedded-atom molecular dynamics simulations are used to investigate the effects of low-energy se... more Embedded-atom molecular dynamics simulations are used to investigate the effects of low-energy self-ion irradiation of Pt adatoms on Pt(111). Here, we concentrate on self-bombardment dynamics, i.e., isolating and monitoring the atomic processes, induced by normally incident Pt atoms with energies E ranging from 5 to 50 eV, that can affect intra- and interlayer mass transport.. We find that adatom scattering, surface channeling, and dimer formation occur at all energies. Atomic intermixing events involving incident and terrace atoms are observed at energies ⩾15eV, while the collateral formation of residual surface vacancies is observed only with E>40eV. The overall effect of low-energy self-ion irradiation is to enhance lateral adatom and terrace atom migration.
We describe the temporal development of the plasma composition of pulsed aluminum plasma streams ... more We describe the temporal development of the plasma composition of pulsed aluminum plasma streams at various oxygen pressures. The plasma was formed with a vacuum arc plasma source and the time resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. The temporal development of the plasma composition as well as the Al average ion charge state was found to be a strong function of the oxygen pressure. Oxygen and hydrogen concentrations of up to 0.36 and 0.32, respectively, were found in the first 50 mus of the pulse at oxygen pressures of >=5×10-5 Torr. The average charge state of aluminum ions was found to vary from +1.2 to +2.5 depending on the oxygen pressure and the time elapsed after ignition of the arc. These results are of fundamental importance for the understanding of the evolution of the composition (through the plasma composition) and microstructure (through the Al ion flux energy) of alumina thin films produced by pulsed, reactive aluminum plasmas.
ABSTRACT Arc plasma from Ti3SiC2 compound cathodes used in a filtered dc arc system has been char... more ABSTRACT Arc plasma from Ti3SiC2 compound cathodes used in a filtered dc arc system has been characterized with respect to plasma chemistry and charge-state resolved ion energies. In vacuum, the plasma composition is dominated by Ti ions, with concentrations of 84.3, 9.3, and 6.4 at% for Ti, Si, and C ions, respectively. The reduced amount of Si and most notably C compared with the cathode composition is confirmed by analysis of film composition in corresponding growth experiments. The deposition of light-element deficient films is thus related to plasma generation or filter transport. The ion energy distributions in vacuum range up to 140, 90, and 70 eV for Ti, Si, and C, respectively. Corresponding average ion energies of 48, 36, and 27 eV are reduced upon introduction of gas, down to around 5 eV at 0.6 Pa Ar or 0.3 Pa N2 for all species. In vacuum, the charge state distributions of Si and C are shifted to higher values compared with corresponding elemental cathodes, likely caused by changed effective electron temperature of the plasma stemming from compound cathode material and/or by electron impact ionization in the filter. The average ion charge states are reduced upon addition of Ar, ranging between 1.97 and 1.48 for Ti, 1.91 and 1.46 for Si, and 1.25 and 1.02 for C. Similar effects are observed upon introduction of N2, though with more efficient charge state reduction with pressure. It is conceivable that the pressure-induced changes in ion energy and charge state are crucial for the film synthesis from a microstructure evolution point of view, as they affect the ion-surface interactions through supply of energy, especially when substrate biasing is employed during arc deposition from a compound cathode.
Metastable Ti 1-x Al x N (0.4 ≤ x ≤ 0.76) films are grown using a hybrid approach in which high-p... more Metastable Ti 1-x Al x N (0.4 ≤ x ≤ 0.76) films are grown using a hybrid approach in which high-power pulsed magnetron sputtering (HIPIMS) is combined with dc magnetron sputtering (DCMS). Elemental Al and Ti metal targets are co-sputtered with one operated in HIPIMS mode and the other target in DCMS; the positions of the targets are then switched for the next set of that the doubly-ionized metal ion flux is approximately two orders of magnitude higher from the Ti target, than from Al, powered with HIPIMS. This asymmetry becomes decisive upon application of a moderate substrate bias voltage, -60 V, applied synchronously with HIPIMS pulses, during growth.
Carbon and carbon nitride films, grown in argon or nitrogen discharges by reactive dc magnetron s... more Carbon and carbon nitride films, grown in argon or nitrogen discharges by reactive dc magnetron sputtering of a graphite target, were characterized by in situ scanning tunneling microscopy. When the growth temperature increased from ambient to 800 °C, we observed a topographic evolution of the carbon films from an amorphous to a graphitelike structure, and further to a distorted-graphitic phase with curved and intersecting basal planes, and finally to a surface containing nanotubes and nanodomes. When nitrogen was incorporated into the films, distortion of the graphitic basal planes occurred at a lower temperature compared to the pure carbon case. At temperatures of ϳ200 °C and above, regions of a nongraphitic phase, containing a high degree of carbon sp 3 bonds were observed. Spatially resolved tunneling spectroscopic measurements indicated that the band gaps were 0, ϳ0-0.6 eV, and ϳ0.4-2.0 eV for graphitelike structures, the distorted-graphitic phase, and the nongraphitic phase, respectively. Together with ex situ x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy measurements, the results suggest that the incorporation of nitrogen promotes bending of the graphitic basal planes and thereby facilitates the formation of three-dimensional covalently bonded networks with a high degree of sp 3 -coordinated carbon atoms.
We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN... more We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN-content Ti 1-x Al x N alloys (x ≤ 0.64) which simultaneously possess high hardness and low residual stress. The films are grown using a hybrid approach combining high-power pulsed magnetron (HPPMS/HIPIMS) and dc magnetron sputtering of opposing metal targets. With HIPIMS applied to the Al target, Al n+ ion irradiation (dominated by Al + ) of the growing film results in alloys 0.55 ≤ x ≤ 0.60 which exhibit hardness H 30 GPa and low stress = 0.2-0.7 GPa, tensile. In sharp contrast, films with corresponding AlN concentrations grown with HIPIMS applied to the Ti target, giving rise to Ti n+ ion irradiation (with a significant Ti 2+ component), are two-phase --cubic (Ti,Al)N and hexagonal AlN --with low hardness, H = 18-19 GPa, and high compressive stress ranging up to 2.7 GPa. Annealing alloys grown with HIPIMS applied to the Al target results in age hardening due to spinodal decomposition; the hardness of Ti 0.41 Al 0.59 N increases from 30 to 33 GPa following a 900 °C anneal.
The chemical desorption of carbon and nitrogen-containing species from the growth surface was inv... more The chemical desorption of carbon and nitrogen-containing species from the growth surface was investigated for the deposition of fullerene-like carbon nitride (FL CN x ) thin solid films by reactive magnetron sputtering of a carbon target in a N 2 -containing atmosphere. The desorption of mainly C 2 N 2 was suppressed by decreasing the substrate temperature for various N 2 fractions in the discharge stepwise from 873 K down to cryogenic temperatures of 153 K. This approach enabled us to quantify the film-forming flux by determining the carbon and nitrogen incorporation rates by elastic recoil detection. The incorporation of both, carbon and nitrogen, was found to increase substantially at lower substrate temperatures, whereas this effect is most pronounced for the higher N 2 fractions. In turn, a modified Arrhenius-type rate equation was applied to extrapolate the total flux of the elements as well as their respective activation energies of desorption for the series at higher N 2 fractions. The reasonable fit indicates that the desorption process is mainly determined by the surface diffusion rate of adsorbed C x N y species as well as their structure and total number. The extrapolated fluxes of carbon and nitrogen atoms arriving as preformed species at the growth surface scaled strongly with the availability of N 2 in the discharge, while the obtained activation energies of 0.05-0.17 eV point towards a saturation of the process at elevated temperatures. Furthermore, the constant C/N ratio found in the film-forming flux leads to the notion that most of the nitrogen incorporated originates from preformed species instead of N atoms or ions. The FL structure evolution has to be seen as a sensitive interplay between the type and magnitude of preformed C x N y species in the deposition flux and the selectiveness of the preferential etching by means of the chemical desorption.
High Velocity Oxy-Fuel has been utilized to spray coatings from Ti 2 AlC (MAXTHAL 211 ® ) powders... more High Velocity Oxy-Fuel has been utilized to spray coatings from Ti 2 AlC (MAXTHAL 211 ® ) powders. X-ray diffraction showed that the coatings consist predominantly of Ti 2 AlC with inclusions of the phases Ti 3 AlC 2 , TiC, and Al-Ti alloys. The fraction of Ti 2 AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H 2 and O 2 . A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti 2 AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3-5 GPa for the coatings sprayed with a powder size of 38 μm.
Microstructure and macroscopic properties of droplet free CrN films deposited by the recently dev... more Microstructure and macroscopic properties of droplet free CrN films deposited by the recently developed high power pulsed magnetron sputtering (HIPIMS) technique are presented. Magnetron glow discharges with peak power densities reaching 3000 W cm−2 were used to sputter Cr targets in both inert and reactive gas atmospheres. The flux arriving at the substrates consisted of neutrals and ions (approx. 70/30) of the sputtered metal and working gas atoms (Ar) with significantly elevated degree of ionization compared to conventional magnetron sputtering. The high-speed steel and stainless steel substrates were metal ion etched using a bias voltage of −1200 V prior to the deposition of CrN films. The film-to-substrate interfaces, observed by scanning transmission electron microscope cross-sections, were clean and contained no phases besides the film and substrate ones or recrystallized regions. CrN films were grown by reactive HIPIMS at floating potential reaching −160 V. Initial nucleation grains were large compared to conventional magnetron sputtered films, indicating a high adatom mobility in the present case. The films exhibited polycrystalline columnar growth morphology with evidence of renucleation. No intercolumnar voids were observed and the corrosion behavior of the film was superior to arc deposited CrNx. A high density of lattice defects was observed throughout the films due to the high floating potential. A residual compressive stress of 3 GPa and a hardness value of HK0.025=2600 were measured. A low friction coefficient of 0.4 and low wear rates against Al2O3 in these films are explained by the absence of droplets and voids known to contribute to extensive debris generation.
Ab initio calculations show that the energy cost for incorporating lattice defects such as pentag... more Ab initio calculations show that the energy cost for incorporating lattice defects such as pentagons and heptagons is significantly reduced for BCN compared to BN, thus promoting bending of basal planes in these compounds. Boron-carbon-nitride (B C N) thin films with a fullerene-like (FL) microstructure were then deposited by dual cathode magnetron sputtering from C and B 4 C targets. Up to 1 m thick films were grown at a total gas pressure of 3 mTorr (0.4 Pa) in varying Ar/N 2 ratios, and substrate temperatures between 225 and 350 • C. Compositional and microstructural studies were performed using RBS, SEM and HREM, respectively. Depending on the deposition condition, ternary B x C y N z films with fullerene-like microstructure could be prepared in agreement with the calculations within the composition range 0 ≤ x ≤ 53, 15 ≤ y ≤ 62, and 24 ≤ z ≤ 50 at.%. Fullerene-like structures also tend to form at lower temperatures in the case of BCN compared to CN. Nanoindentation measurements show that all B x C y N z films exhibited a highly elastic response independent of elemental composition. In addition, the calculations suggest a driving force for C and BN phase separation.
Carbon nitride is an emerging material for wear-resistant coatings. The fullerene-like CNx compou... more Carbon nitride is an emerging material for wear-resistant coatings. The fullerene-like CNx compounds generally exhibit extreme elasticity in combination with a low work of indentation hardness. Yet CNx shows a low-to-moderate resistance to penetration, depending on deposition conditions. Since the deformation energy is predominantly stored elastically, the material possesses an extremely resilient character. This new class of materials consists of sp2-coordinated basal planes that are buckled from the incorporation of pentagons and cross-linked at sp3-hybridized C sites, both of which are caused by structural incorporation of nitrogen. Carbon nitride thus deforms elastically due to bending of the structural units. The orientation, radius of curvature of the basal planes, and the degree of cross-linking between them defines the structure and properties of the material. Due to the unique deformation behavior, the hardness requires special care to assess, but can be very high for films...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1992
Transmission electron microscopy, x-ray diffraction, and Rutherford backscattering have been used... more Transmission electron microscopy, x-ray diffraction, and Rutherford backscattering have been used to investigate the effects of ion irradiation during growth on the deposition rate, composition, and microstructure of single-phase polycrystalline NaCl-structure TiNx films deposited by reactive magnetron sputtering with a negative substrate bias voltage Vs. The layers were deposited on thermally oxidized Si(001) substrates in mixed Ar+4% N2 discharges at a total pressure of 4.2 mTorr. Varying Vs between 0 and 1800 V resulted in incident ion-to-Ti atom flux ratios of 0.3 to 0.6 at the film growth surface and increases in the substrate temperature Ts (initially Ts=300 °C) of 40 to 200 °C. The Ti resputtering yield increased from ≤0.02 (Vs≤100 V) to 0.30 (Vs=1800 V) Ti atoms per incident ion (primarily Ar+), while the N/Ti ratio in as-deposited films increased from 1.03 for Vs=0 V to 1.12 for 100 V≤Vs≤400 V and then decreased to ≂0.95 as Vs was raised to 1800 V. Trapped Ar concentrations...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2012
Metastable NaCl-structure Ti1 − xAlxN is employed as a model system to probe the effects of metal... more Metastable NaCl-structure Ti1 − xAlxN is employed as a model system to probe the effects of metal versus rare-gas ion irradiation during film growth using reactive high-power pulsed magnetron sputtering (HIPIMS) of Al and dc magnetron sputtering of Ti. The alloy film composition is chosen to be x = 0.61, near the kinetic solubility limit at the growth temperature of 500 °C. Three sets of experiments are carried out: a −60 V substrate bias is applied either continuously, in synchronous with the full HIPIMS pulse, or in synchronous only with the metal-rich-plasma portion of the HIPIMS pulse. Alloy films grown under continuous dc bias exhibit a thickness-invariant small-grain, two-phase nanostructure (wurtzite AlN and cubic Ti1−xAlxN) with random orientation, due primarily to intense Ar+ irradiation leading to Ar incorporation (0.2 at. %), high compressive stress (−4.6 GPa), and material loss by resputtering. Synchronizing the bias with the full HIPIMS pulse results in films that exhi...
The microstructure formation and phase transformations in Ti2AlC-rich coatings deposited by High ... more The microstructure formation and phase transformations in Ti2AlC-rich coatings deposited by High Velocity Oxy-fuel spraying of Maxthal 211® powders is presented. High resolution electron microscopy analysis, using both scanning and transmission electron microscopy with energy dispersive spectrometry and energy filtering, combined with X-ray diffraction reveals that the coatings consist of Ti2AlC grains surrounded by regions of very small TiC grains embedded in Ti x Al y . The composition of the Ti x Al y depends on its surrounding and varies with size and distribution of the adjacent TiC grains. Impact of spray parameters on coating microstructure is also discussed. Two spray parameters were varied; powder size distribution and flame power. They were found to greatly affect the coating microstructure. Increasing powder size and decreasing flame power increase the amount of Ti2AlC, but produces thinner coatings with lower cohesion. Larger powder size will also decrease oxygen incorporation.
The incorporation behavior of Er into Si and Si Ge using ErF and Er O as dopant sources during mo... more The incorporation behavior of Er into Si and Si Ge using ErF and Er O as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. O took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4;10 cm\ using Er O and a high F background pressure. Using ErF compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF molecules, but also from CF V (x"1-4) and F background species, which are present due to a reaction between the ErF source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1;10 cm\ and without observable defects using ErF as source material. For the case of Er-doping of Si Ge using ErF , we observed contrast along lines in the growth direction at an Er concentration of 1;10 cm\, which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro-and photoluminescence.
Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetr... more Ion mass spectrometry was used to investigate discharges formed during high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a graphite target in Ar and Ar/N2 ambient. Ion energy distribution functions (IEDFs) were recorded in time-averaged and time-resolved mode for Ar+, C+, N2+, N+, and CxNy+ ions. An increase of N2 in the sputter gas (keeping the deposition pressure, pulse width, pulse frequency, and pulse energy constant) results for the HiPIMS discharge in a significant increase in C+, N+, and CN+ ion energies. Ar+, N2+, and C2N+ ion energies, in turn, did not considerably vary with the changes in working gas composition. The HiPIMS process showed higher ion energies and fluxes, particularly for C+ ions, compared to DCMS. The time evolution of the plasma species was analyzed for HiPIMS and revealed the sequential arrival of working gas ions, ions ejected from the target, and later during the pulse-on time molecular ions, in particula...
The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si... more The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si1−xGex layers were grown by molecular-beam epitaxy (MBE) and the silicides formed by different postdeposition reaction paths, were investigated using a combination of high-resolution cross-sectional transmission electron microscopy, high-resolution x-ray diffraction, and secondary-ion-mass spectrometry. In two of the three sample configurations investigated, Co was deposited either (S1) directly on a strained Si1−xGex layer or (S2) on a sacrificial MBE Si overlayer on Si0.9Ge0.1. In the third sample configuration (S3) Si1−xGex was grown on a Si(001) substrate containing a buried ion-implanted CoSi2 layer. Only in sample configuration S2 was it possible to obtain a fully strained nearly defect-free CoSi2/Si0.9Ge0.1 structure. A high density of threading dislocations, corresponding to ≊60% relaxation at the Si0.9Ge0.1/Si interface, was observed in S1 while S3, in addition to the dislocatio...
Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015 cm... more Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015 cm−2, were investigated by multicrystal x-ray diffraction, reciprocal space mapping (RSM), high-resolution transmission electron microscopy, and secondary-ion-mass spectrometry (SIMS). For Sn doses up to 3.30×1015 cm−2, annealing at 600 °C for 30 min under dry N2 atmosphere resulted in recrystallization by solid-phase epitaxy (SPE) to a layer thickness of more than 50 nm. These SPE-grown layers were shown to be free of extended defects and Sn redistribution was negligible. As measured by x-ray diffraction, the Sn-induced strain in Si increased with the implant dose. From RSM measurements, this strain was shown to be tetragonal with negligible in-plane relaxation. Mosaicity and defect-related effects were shown to be negligible. Instead, limited thickness effects and strain variation due to the implantation profile appeared to be the major sources of the observed broadening in the diffracti...
Embedded-atom molecular dynamics simulations are used to investigate the effects of low-energy se... more Embedded-atom molecular dynamics simulations are used to investigate the effects of low-energy self-ion irradiation of Pt adatoms on Pt(111). Here, we concentrate on self-bombardment dynamics, i.e., isolating and monitoring the atomic processes, induced by normally incident Pt atoms with energies E ranging from 5 to 50 eV, that can affect intra- and interlayer mass transport.. We find that adatom scattering, surface channeling, and dimer formation occur at all energies. Atomic intermixing events involving incident and terrace atoms are observed at energies ⩾15eV, while the collateral formation of residual surface vacancies is observed only with E>40eV. The overall effect of low-energy self-ion irradiation is to enhance lateral adatom and terrace atom migration.
We describe the temporal development of the plasma composition of pulsed aluminum plasma streams ... more We describe the temporal development of the plasma composition of pulsed aluminum plasma streams at various oxygen pressures. The plasma was formed with a vacuum arc plasma source and the time resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. The temporal development of the plasma composition as well as the Al average ion charge state was found to be a strong function of the oxygen pressure. Oxygen and hydrogen concentrations of up to 0.36 and 0.32, respectively, were found in the first 50 mus of the pulse at oxygen pressures of >=5×10-5 Torr. The average charge state of aluminum ions was found to vary from +1.2 to +2.5 depending on the oxygen pressure and the time elapsed after ignition of the arc. These results are of fundamental importance for the understanding of the evolution of the composition (through the plasma composition) and microstructure (through the Al ion flux energy) of alumina thin films produced by pulsed, reactive aluminum plasmas.
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Papers by Lars Hultman