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Abstract: We demonstrate, for the first time, that a thin, strong, ductile, and adhesive coating renders bulk metallic glasses (BMGs) bendable. The bending ductility of 3mm thick BMGs, Zr50Cu30Al10Ni10 in this case, can be dramatically enhanced from ∼0% to ∼13.7% by the deposition of a thin bilayer film on the tensile side of the BMG sample. The bilayer, consisting of a 25nm thick Ti adhesive layer with a 200nm thick metallic glass (MG) overlayer, exhibits the required synergistic combination of good adhesion, high strength, and ductility compared with other single-layer films examined (Ti, TiN, and MG). Cross-sectional scanning and transmission electron microscopy, together with finite element modeling, reveal that the bilayer coating absorbs deformation while allowing more homogeneous formation of a high density of smaller shear bands at the bilayer/BMG interface. The bilayer coating, in turn, covers surface weak points and minimizes the formation of localized shear bands which lead to catastrophic failure under bending. As a result, the average shear-band spacing in bilayer-coated BMGs is small, 54μm, and approximately equal to that found in bendable, 450μm thick, MG ribbons. Thus, coated BMGs can accommodate large strains and overcome the MG size effect, without sacrificing their extraordinary mechanical properties. Our results for both coated and uncoated BMGs, as well as previously reported results for uncoated metallic glasses, with thicknesses ranging from ribbons to thin plates to bulk, are well described by a simple power law relationship between plastic strain to failure and shear band spacing. This scaling law may be useful in guiding future experiments toward producing more flexible BMGs. [Copyright &y& Elsevier]

Modeling of Si1−xGex(0 1 1) gas-source epitaxy from hydride precursors requires knowledge of reactive sticking probabilities and hydrogen desorption kinetics. We use D2 temperature programmed desorption (TPD), reflection high energy electron diffraction (RHEED), Auger electron spectroscopy (AES), and kinetic modeling to determine hydrogen desorption kinetics from, and Ge2H6 reactive sticking probabilities at, Si and Ge sites on Ge-adsorbed Si(0 1 1) samples with Ge surface coverages θGe between 0 and 1 ML. Following Ge adsorption, the samples were exposed to atomic D until saturation coverage at 250 °C. TPD spectra consist of five second-order peaks due to D2 desorption from, in order of decreasing temperature, Si rest-atom and adatom monodeuterides, Si dideuteride, and Ge rest-atom and adatom monodeuteride phases. The maximum temperatures of all five peaks shift to lower values with increasing θGe. We attribute this, as in the case of Ge-adsorbed Si(0 0 1), to a decrease in Si–D and Ge–D binding energies due to long-range electronic interactions. Ge/Si(0 1 1) surface reconstructions, determined by RHEED, are “16×2” with θGe<0.4 ML and “2×8” at higher coverages. Quantitative θGe values were obtained by fitting the D2 TPD spectra and validated using in situ AES. Based upon θGe vs Ge2H6 exposure data and modeling of the adsorption kinetics, we obtain zero-coverage Ge2H6 reactive sticking probabilities of 1.9×10−2 and 4.8×10−3 at Si and Ge sites, respectively. [Copyright &y& Elsevier]

Examines the preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputtering. Function of TiN films deposition of reactive magnetron sputtering; Importance of the presence of large intrinsic film stresses in determining TiN preferred orientation; Variety of kinetic effects associated with growth process.

Examines the antimony incorporation probability in homoepitaxial Si(001) films grown by ultrahigh vacuum ion-beam sputter deposition. Measurement of surface roughness and epitaxial thickness; Relationship between surface roughness rate and growth temperature; Role of interlayer transport for determining surface roughening.

Energy and time-dependent mass spectrometry is used to determine the relative number density of singly- and multiply-charged metal-ion fluxes incident at the substrate during high-power pulsed magnetron sputtering (HIPIMS) as a function of the average noble–gas ionization potential. Ti is selected as the sputtering target since the microstructure, phase composition, properties, and stress-state of Ti-based ceramic thin films grown by HIPIMS are known to be strongly dependent on the charge state of Ti n+ ( n = 1, 2, …) ions incident at the film growth surface. We find that the flux of Ti n+ with n > 2 is insignificant; thus, we measure the Ti 2+ /Ti + integrated flux ratio J T i 2 + / J T i + at the substrate position as a function of the choice of noble gas–Ne, Ar, Kr, Xe, as well as Ne/Ar, Kr/Ar, and Xe/Ar mixtures -- supporting the plasma. We demonstrate that by changing noble–gas mixtures, J T i 2 + varies by more than two orders of magnitude with only a small change in J T i + . This allows the ratio J T i 2 + / J T i + to be continuously tuned from less than 0.01 with Xe, which has a low first-ionization potential IP 1 , to 0.62 with Ne which has a high IP 1 . The value for Xe, I P X e 1 = 12 . 16 eV , is larger than the first ionization potential of Ti, I P T i 1 = 6 . 85 eV , but less than the second Ti ionization potential, I P T i 2 = 13 . 62 eV . For Ne, however, I P N e 1 = 21 . 63 eV is greater than both I P T i 1 and I P T i 2 . Therefore, the high-energy tail of the plasma-electron energy distribution can be systematically adjusted, allowing J T i 2 + / J T i + to be controllably varied over a very wide range. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial CoSi2 layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi2(001) follows the Volmer–Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi2/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)CoSi2 ||(001)Si and [100]CoSi2 ||[100]Si. Platelet-shaped CoSi2 islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)CoSi2 ||{111}Si) and their narrow 〈110〉 directions by {511}CoSi2 ||{111}Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}CoSi2 ||(001)Si, and {1¯1¯1}, with {1¯1¯1}CoSi2 ||{11¯1}Si, respectively. The early stages of film growth (t Co ≤13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2×1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t Co ≥13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi2(001) layer, with a twin density of 2.8×1010 cm−2, is obtained at t Co =50 Å. [Copyright &y& Elsevier]

We recently showed that sputter-deposited Zr 1-x Ta x B y thin films have hexagonal AlB 2 -type columnar nanostructure in which column boundaries are B-rich for x < 0.2, while Ta-rich for x ≥ 0.2. As-deposited layers with x ≥ 0.2 exhibit higher hardness and, simultaneously, enhanced toughness. Here, we study the mechanical properties of ZrB 2.4 , Zr 0.8 Ta 0.2 B 1.8 , and Zr 0.7 Ta 0.3 B 1.5 films annealed in Ar atmosphere as a function of annealing temperature T a up to 1200 °C. In-situ and ex-situ nanoindentation analyses reveal that all films undergo age hardening up to T a = 800 °C, with the highest hardness achieved for Zr 0.8 Ta 0.2 B 1.8 (45.5±1.0 GPa). The age hardening, which occurs without any phase separation or decomposition, can be explained by point-defect recovery that enhances chemical bond density. Although hardness decreases at T a > 800 °C due mainly to recrystallization, column coarsening, and planar defect annihilation, all layers show hardness values above 34 GPa over the entire T a range. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Refractory transition-metal diborides (TMB 2) are candidates for extreme environments due to melting points above 3000 °C, excellent hardness, good chemical stability, and thermal and electrical conductivity. However, they typically suffer from rapid high-temperature oxidation. Here, we study the effect of Al addition on the oxidation properties of sputter-deposited TiB 2 -rich Ti 1-x Al x B y thin films and demonstrate that alloying the films with Al significantly increases the oxidation resistance with a slight decrease in hardness. TiB 2.4 layers are deposited by dc magnetron sputtering (DCMS) from a TiB 2 target, while Ti 1-x Al x B y alloy films are grown by hybrid high-power impulse and dc magnetron co-sputtering (Al-HiPIMS/TiB 2 -DCMS). All as-deposited films exhibit columnar structure. The column boundaries of TiB 2.4 are B-rich, while Ti 0.68 Al 0.32 B 1.35 alloys have Ti-rich columns surrounded by a Ti 1-x Al x B y tissue phase which is predominantly Al rich. Air-annealing TiB 2.4 at temperatures above 500 °C leads to the formation of oxide scales that do not contain B and mostly consist of a rutile-TiO 2 (s) phase. The resulting oxidation products are highly porous due to the evaporation of B 2 O 3 (g) phase as well as the coarsening of TiO 2 crystallites. This poor oxidation resistance is significantly improved by alloying with Al. While air-annealing at 800 °C for 0.5 h results in the formation of an ~1900-nm oxide scale on TiB 2.4 , the thickness of the scale formed on the Ti 0.68 Al 0.32 B 1.35 alloys is ~470 nm. The enhanced oxidation resistance is attributed to the formation of a dense, protective Al-containing oxide scale that considerably decreases the oxygen diffusion rate by suppressing the oxide-crystallites coarsening. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate the deposition of fully dense, stoichiometric TiN films on amorphous SiO2 by reactive high power impulse magnetron sputtering (HiPIMS) in the absence of both substrate heating and applied bias. Contrary to the highly underdense layers obtained by reactive dc magnetron sputtering (dcMS) under similar conditions, the film nanostructure exhibits neither intra- nor intergrain porosity, exhibiting a strong 111 preferred orientation with flat surfaces. Competitive grain growth occurs only during the early stages of deposition (<100nm). The strong differences in the kinetically-limited nanostructural evolution for HiPIMS vs. dcMS are explained by high real-time deposition rates with long relaxation times, high ionization probabilities for Ti, and broad ion energy distributions. [Copyright &y& Elsevier]

High hardness and toughness are generally considered mutually exclusive properties for single-crystal ceramics. Combining experiments and ab initio molecular dynamics (AIMD) atomistic simulations at room temperature, we demonstrate that both the hardness and toughness of single-crystal NaCl-structure VN x /MgO(001) thin films are simultaneously enhanced through the incorporation of anion vacancies. Nanoindentation results show that VN 0.8 , here considered as representative understoichiometric VN x system, is ≈20% harder, as well as more resistant to fracture than stoichiometric VN samples. AIMD modeling of VN and VN 0.8 supercells subjected to [001] and [110] elongation reveal that the tensile strengths of the two materials are similar. Nevertheless, while the stoichiometric VN phase cleaves in a brittle manner at tensile yield points, the understoichiometric compound activates transformation-toughening mechanisms that dissipate accumulated stresses. AIMD simulations also show that VN 0.8 exhibits an initially greater resistance to both { 110 } 〈 1 1 ¯ 0 〉 and { 111 } 〈 1 1 ¯ 0 〉 shear deformation than VN. However, for progressively increasing shear strains, the VN 0.8 mechanical behavior gradually evolves from harder to more ductile than VN. The transition is mediated by anion vacancies, which facilitate { 110 } 〈 1 1 ¯ 0 〉 and { 111 } 〈 1 1 ¯ 0 〉 lattice slip by reducing activation shear stresses by as much as 35%. Electronic-structure analyses show that the two-regime hard/tough mechanical response of VN 0.8 primarily stems from its intrinsic ability to transfer d electrons between 2nd-neighbor and 4th-neighbor (i.e., across vacancy sites) V–V metallic states. Our work offers a route for electronic-structure design of hard materials in which a plastic mechanical response is triggered with loading. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Stoichiometric HfN layers, with N/Hf=1.0±0.03, were grown on MgO(001) substrates at 650 °C by ultrahigh-vacuum magnetically unbalanced magnetron sputter deposition in mixed N2/Ar discharges at 20 mTorr (2.67 Pa). High-resolution x-ray diffraction ω-2θ and azimuthal [lowercase_phi_synonym] scans combined with cross-sectional transmission electron microscopy establish that HfN grows epitaxially with a cube-on-cube orientational relationship to the substrate: (001)HfN∥(001)MgO and [100]HfN∥[100]MgO. The layers are fully relaxed at the growth temperature and have a room-temperature bulk lattice constant of 0.4524 nm. Electronic transport measurements show that HfN is metallic with a room-temperature resistivity of 14.2 μΩ cm, an n-type carrier concentration of 4.8×1021 cm-3, and an electron mobility of 86 cm2 V-1 s-1. The resistivity ρ remains constant at 3.5 μΩ cm, limited by defect scattering, between 10 and 50 K, while at higher temperatures ρ increases linearly and is limited primarily by phonon scattering. HfN(001) is also superconducting with a critical temperature of 9.18 K. The hardness and elastic modulus of HfN(001) were determined from nanoindentation measurements to be 25.2±0.7 and 450±9 GPa, respectively. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have grown single-crystal NaCl-structure δ-TiN[sub x] layers with x ranging from 0.67 to 1.00 on MgO(001) at 700 °C by ultra-high-vacuum reactive magnetron sputtering of Ti in mixed Ar/N[sub 2] discharges in order to investigate microstructural evolution and the physical properties of TiN[sub x] as a function of the N vacancy concentration. High-resolution x-ray diffraction and transmission electron microscopy results show that all layers grow with a cube-on-cube epitaxial relationship to the substrate, (001)[sub TiN]∥(001)[sub MgO] and [100][sub TiN]∥[100][sub MgO]. The relaxed lattice parameter a[sub o](x) decreases linearly from 4.240 Å with x=1.00 to 4.226 Å with x=0.67. Stoichiometric TiN(001) layers are fully relaxed at the growth temperature while layers with 0.67<=x<=0.92 are fully coherent with their substrates. Surface morphologies vary dramatically with x. TiN[sub x](001) layers with x=0.67–0.82 have very flat surfaces arising from large cation surface diffusion lengths approaching values corresponding to step flow. However, the surfaces of the TiN[sub 0.92](001) and TiN[sub 1.00](001) layers, which were grown at higher N[sub 2] partial pressures, consist of a periodic two-domain ripple structure along the <110> directions due to kinetic roughening associated with lower cation surface mobilities resulting from higher steady state N coverages. TiN[sub 1.0](001) layers grown in pure N[sub 2] exhibit growth mounds that are predominantly square with edges aligned along the <110> directions. The room-temperature resistivity, 13 μΩ cm with x=1.00, increases from 52 μΩ cm for TiN[sub x](001) layers with x=0.92 to 192 μΩ cm with x=0.67, due primarily to increased carrier scattering from N vacancies. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the room temperature utraviolet/ozone-induced oxidation of epitaxial silicon[sub 1-x]germanium[sub x](111) alloy. Use of x-ray photoelectron spectroscopy; Components of the two-phased oxide formed; Segregation of germanium layer at alloy/oxide interface; Dependence of oxidation rate on germanium content.

Focuses on the use of the Raman scattering in the study of the fully strained single-crystal Ge1-xSn alloys (x...0.22), which were deposited on Ge(001)2...1 by low-temperature molecular beam epitaxy. Characterization of results; Information on the samples obtained; Reference to the equilibrium solid solubility of Sn in Ge.

Provides information on an experiment investigating the ion-irradiation-induced strain relaxation in a metastable Si0.7Ge0.3 film grown on Si(001). Methodology used to conduct the experiment; Information on the in situ x-ray measurements done during ion irradiation; Analysis of symmetric diffuse scattering; Findings of the experiment.

Surface morphological and compositional evolution during the initial stages of Si growth on Ge(001)2×1 by cyclic gas-source molecular beam epitaxy from Si2H6 has been investigated using in situ reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy, electron-energy-loss spectroscopy, and scanning tunneling microscopy, combined with post-deposition high-resolution cross-sectional transmission electron microscopy. The layers were deposited using repetitive cycles consisting of saturation Si2H6 dosing at room temperature, followed by annealing for 1 min at 550 °C. Film growth was observed to proceed via a mixed Stranski–Krastanov mode. Single-step-height two-dimensional growth was obtained for nominal Si deposition thicknesses tSi up to [bar_over_tilde:_approx._equal_to]1.5 monolayers (ML). However, the upper layer remained essentially pure Ge which segregated to the surface through site exchange with deposited Si as H was desorbed. At higher tSi, the Ge coverage decreased slowly, the surface roughened, and two-dimensional multilayer island growth was observed for tSi up to [bar_over_tilde:_approx._equal_to]7.5 ML, where bulk reflections in RHEED patterns provided evidence for the evolution of three-dimensional island formula. [ABSTRACT FROM AUTHOR]

Transition-metal (TM) carbides are an important class of hard, protective coating materials; however, their brittleness often limits potential applications. We use density functional theory to investigate the possibility of improving ductility by forming pseudobinary cubic M 1 M 2 C alloys, for which M 1 = Ti or V and M 2 = W or Mo. The alloying elements are chosen based on previous results showing improved ductility of the corresponding pseudobinary nitride alloys with respect to their parent compounds. While commonly-used empirical criteria do not indicate enhanced ductility in the carbide alloys, calculated stress/strain curves along known slip systems, supported by electronic structure analyses, indicate ductile behavior for VMoC. As VMoC layers are sheared along the 1 1 ¯ 0 direction on {111} planes, the stress initially increases linearly up to a yield point where the accumulated stress is partially dissipated. With further increase in strain, the stress increases again until fracture occurs. A similar mechanical behavior is observed for the corresponding TM nitride VMoN, known to be a ductile ceramic material [1]. Thus, our results show that VMoC is a TM carbide alloy which may be both hard and ductile, i.e. tough. [ABSTRACT FROM AUTHOR]

High-power impulse magnetron sputtering (HiPIMS) of materials systems with metal/gas-atom mass ratios m Me / m g near, or less than, unity presents a challenge for precise timing of synchronous substrate-bias pulses to select metal-ion irradiation of the film and, thus, reduce stress while increasing layer density during low-temperature growth. The problem stems from high gas-ion fluxes F g + ( t ) at the substrate, which overlap with metal-ion fluxes F Me + ( t ). We use energy- and time-dependent mass spectrometry to analyze F Me + ( t ) and F g + ( t ) for Group IVb transition-metal targets in Ar and show that the time-and energy-integrated metal/gas ion ratio N Me + / N Ar + at the substrate can be controlled over a wide range by adjusting the HiPIMS pulse length τ ON , while maintaining the peak target current density J T,peak constant. The effect is a consequence of severe gas rarefaction which scales with J T ( t ). For Ti-HiPIMS, terminating the discharge at the maximum J T ( t ), corresponding to τ ON = 30 μs, there is an essentially complete loss of Ar + ion intensity, yielding N Ti + / N Ar + ~ 60. With increasing τ ON , J T ( t ) decreases and N Ti + / N Ar + gradually decays, due to Ar refill, to ~ 1 with τ ON = 120 μs. Time-resolved ion-energy distribution functions confirm that the degree of rarefaction depends on τ ON : for shorter pulses, τ ON < 60 μs, the original sputtered-atom Sigmund-Thompson energy distributions are preserved long after the HiPIMS pulse, which is in distinct contrast to longer pulses, τ ON ≥ 60 μs, for which the energy distributions collapse into narrow thermalized peaks. Thus, optimizing the HiPIMS pulse width minimizes the gas-ion flux to the substrate independent of m Me / m g . [ABSTRACT FROM AUTHOR]

V 0.5 Mo 0.5 N x /MgO(001) alloys with the B1-NaCl structure are grown by ultra-high-vacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N 2 atmospheres at temperatures T s between 100 and 900 °C. Alloy films grown at T s ≤ 500 °C are polycrystalline with a strong 002 preferred orientation; layers grown at T s ≥ 700 °C are epitaxial single-crystals. The N/Metal composition ratio x ranges from 1.02 ± 0.05 with T s = 100–500 °C to 0.94 ± 0.05 at 700 °C to 0.64 ± 0.05 at T s = 900 °C. N loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter a o from 4.212 Å with x = 1.02 to 4.175 Å at x = 0.94 to 4.120 Å with x = 0.64. V 0.5 Mo 0.5 N x nanoindentation hardnesses H and elastic moduli E increase with increasing T s from 17 ± 3 and 323 ± 30 GPa at 100 °C to 26 ± 1 and 370 ± 10 GPa at 900 °C. Both polycrystalline and single-crystal V 0.5 Mo 0.5 N x films exhibit higher toughnesses than that of the parent binary compound VN. V 0.5 Mo 0.5 N x films deposited at higher T s also exhibit enhanced wear resistance. Valence-band x-ray photoelectron spectroscopy analyses reveal an increased volume density of shear-sensitive d-t 2g – d-t 2g metallic states for V 0.5 Mo 0.5 N x compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., with increasing N-vacancy concentration. [ABSTRACT FROM AUTHOR]

We report the first results on nanostructured N-doped bcc -Cr films exhibiting the unique combination of ceramic hardness with metallic toughness and electrical conductivity at unexpectedly low N concentrations, ~ 5 at.%. The Cr:N films are deposited at 200 °C in N 2 /Ar mixtures by high-power pulsed magnetron sputtering using tunable time-domain control of Cr + and Cr 2+ ion fluxes incident at the film growth surface. Subplanted N atoms impede annealing of metal-ion induced point defects and hinder bcc -Cr grain growth, resulting in a material with a nearly isotropic nanostructure and atomically smooth surface, rather than typical Cr:N solid solutions consisting of faceted microcolumns. [ABSTRACT FROM AUTHOR]

We use molecular dynamics (MD) based on the modified embedded atom method (MEAM) to determine diffusion coefficients and migration pathways for Ti and N adatoms (Ti ad and N ad ) on TiN(111). The reliability of the classical model-potential is verified by comparison with density functional theory (DFT) results at 0 K. MD simulations carried out at temperatures between 600 and 1800 K show that both Ti ad and N ad favor fcc surface sites and migrate among them by passing through metastable hcp positions. We find that N ad species are considerably more mobile than Ti ad on TiN(111); contrary to our previous results on TiN(001). In addition, we show that lattice vibrations at finite temperatures strongly modify the potential energy landscape and result in smaller adatom migration energies, E a = 1.03 for Ti ad and 0.61 eV for N ad , compared to 0 K values E a0K = 1.55 (Ti ad ) and 0.79 eV (N ad ). We also demonstrate that the inclusion of dipole corrections, neglected in previous DFT calculations, is necessary in order to obtain the correct formation energies for polar surfaces such as TiN(111). [ABSTRACT FROM AUTHOR]

We carry out density functional theory calculations to compare the energetics of layer glide, as well as stress vs. strain curves, for cubic Ti 0.5 W 0.5 N pseudobinary alloys and reference B1-structure TiN. Irrespective of the degree of ordering on the metal sublattice, the hardness and stiffness of Ti 0.5 W 0.5 N, as estimated by stress–strain results and resistance to layer glide, are comparable to that of the parent binary TiN, while ductility is considerably enhanced. After an initial elastic response to an applied load, the pseudobinary alloy deforms plastically, thus releasing accumulated mechanical stress. In contrast, stress continues to increase linearly with strain in TiN. Layer glide in Ti 0.5 W 0.5 N is promoted by a high valence-electron concentration which enables the formation of strong metallic bonds within the slip direction upon deformation. [111]-oriented Ti 0.5 W 0.5 N layers characterized by high local metal-sublattice ordering exhibit low resistance to slip along <110> directions due to energetically favored formation of (111) hexagonal stacking faults. This is consistent with the positive formation energy of <111>-ordered Ti 0.5 W 0.5 N with respect to mixing of cubic-B1 TiN and hexagonal WC-structure WN. In the cubic pseudobinary alloy, slip occurs parallel, as well as orthogonal, to the resolved applied stress at the interface between layers with the lowest friction. We suggest that analogous structural metastability (mixing cubic and hexagonal TM nitride binary phases) and electronic (high valence electron concentration) effects are responsible for the enhanced toughness recently demonstrated experimentally for cubic single-crystal pseudobinary V 0.5 W 0.5 N and V 0.5 Mo 0.5 N epitaxial layers. [ABSTRACT FROM AUTHOR]

Ti 1− x Si x N (0 ≤ x ≤ 0.26) thin films are grown in mixed Ar/N 2 discharges using hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS). In the first set of experiments, the Si target is powered in HIPIMS mode and the Ti target in DCMS; the positions of the targets are then switched for the second set. In both cases, the Si concentration in co-sputtered films, deposited at T s = 500 °C, is controlled by adjusting the average DCMS target power. A pulsed substrate bias of − 60 V is applied in synchronous with the HIPIMS pulse. Depending on the type of pulsed metal-ion irradiation incident at the growing film, Ti + /Ti 2+ vs. Si + /Si 2+ , completely different nanostructures are obtained. Ti + /Ti 2+ irradiation during Ti-HIPIMS/Si-DCMS deposition leads to a phase-segregated nanocolumnar structure with TiN-rich grains encapsulated in a SiN z tissue phase, while Si + /Si 2+ ion irradiation in the Si-HIPIMS/Ti-DCMS mode results in the formation of Ti 1− x Si x N solid solutions with x ≤ 0.24. Film properties, including hardness, modulus of elasticity, and residual stress exhibit a dramatic dependence on the choice of target powered by HIPIMS. Ti-HIPIMS/Si-DCMS TiSiN nanocomposite films are superhard over a composition range of 0.04 ≤ x ≤ 0.26, which is significantly wider than previously reported. The hardness H of films with 0.13 ≤ x ≤ 0.26 is ~ 42 GPa; however, the compressive stress is also high, ranging from − 6.7 to − 8.5 GPa. Si-HIPIMS/Ti-DCMS films are softer at H ~ 14 GPa with 0.03 ≤ x ≤ 0.24, and essentially stress-free ( σ ~ 0.5 GPa). Mass spectroscopy analyses at the substrate position reveal that the doubly-to-singly ionized metal-ion flux ratio during HIPIMS pulses is 0.05 for Si and 0.29 for Ti due to the difference between the second ionization potentials of Si and Ti vs . the first ionization potential of the sputtering gas. The average momentum transfer to the film growth surface per deposited atom per pulse 〈 p d 〉 is ~ 20 × higher during Ti-HIPIMS/Si-DCMS, which results in significantly higher adatom mean-free paths (mfps) leading, in turn, to a phase-segregated nanocolumnar structure. In contrast, relatively low 〈 p d 〉 values during Si-HIPIMS/Ti-DCMS provide near-surface mixing with lower adatom mfps to form Ti 1− x Si x N solid solutions over a very wide composition range with x up to 0.24. Relaxed lattice constants decrease linearly, in agreement with ab-initio calculations for random Ti 1− x Si x N alloys, with increasing x . [ABSTRACT FROM AUTHOR]

It has been shown both experimentally and by density functional theory calculations that the primary diffusing species during the epitaxial growth of TiN/TiN(001) are Ti and N adatoms together with TiN x complexes (x = 1, 2, 3), in which the dominant N-containing admolecule species depends upon the incident N/Ti flux ratio. Here, we employ classical molecular dynamics (CMD) simulations to probe the dynamics of TiN x (x = 1–3) admolecules on 8 × 8 atom square, single-atom-high TiN islands on TiN(001), as well as pathways for descent over island edges. The simulations are carried out at 1000 K, a reasonable epitaxial growth temperature. We find that despite their lower mobility on infinite TiN(001) terraces, both TiN and TiN 2 admolecules funnel toward descending steps and are incorporated into island edges more rapidly than Ti adatoms. On islands, TiN diffuses primarily via concerted translations, but rotation is the preferred diffusion mechanism on infinite terraces. TiN 2 migration is initiated primarily by rotation about one of the N admolecule atoms anchored at an epitaxial site. TiN admolecules descend from islands by direct hopping over edges and by edge exchange reactions, while TiN 2 trimers descend exclusively by hopping. In contrast, TiN 3 admolecules are essentially stationary and serve as initiators for local island growth. Ti adatoms are the fastest diffusing species on infinite TiN(001) terraces, but on small TiN/TiN(001) islands, TiN dimers provide more efficient mass transport. The overall results reveal the effect of the N/Ti precursor flux ratio on TiN(001) surface morphological evolution and growth modes. [ABSTRACT FROM AUTHOR]

The physical properties of hard and superhard nanocomposite thin films are strongly dependent on their nanostructure. Here, we present the results of an investigation of nanostructural evolution and the resulting mechanical properties of (Zr 1− x Si x )N y films, with 0 ⩽ x ⩽ 1 and 1 ⩽ y ⩽ 1.27, grown on MgO(0 0 1) and Al 2 O 3 (0 0 0 1) substrates at temperatures T s = 500–900 °C by reactive magnetron sputter deposition from Zr and Si targets. X-ray diffraction and transmission electron microscopy (TEM) results show that there is a T s /composition window in which stoichiometric Zr–Si–N and amorphous a-Si 3 N 4 phases mutually segregate and self-organize into encapsulated 3–5 nm wide ZrN-rich (Zr 1− x Si x )N columns which extend along the growth direction with a strong (0 0 2) texture. Lattice-resolved scanning TEM and energy-dispersive X-ray spectroscopy reveal that the (Zr 1− x Si x )N y nanocolumns are separated by a bilayer tissue phase consisting of a thin crystalline SiN y -rich (Zr 1− x Si x )N y layer with an a-Si 3 N 4 overlayer. Incorporation of metastable SiN into NaCl-structure ZrN leads to an enhanced nanoindentation hardness H which is a function of T s and film composition. For nanocomposites with composition (Zr 0.8 Si 0.2 )N 1.14 (10 at.% Si) H, increases from 26 GPa at 500 °C to 37 GPa at 900 °C. For comparison, the hardness of epitaxial ZrN/MgO(0 0 1) layers grown at T s = 800 °C is 24 GPa. [ABSTRACT FROM AUTHOR]

Substituting Al for Ti in TiN(001), TiN(011), and N- and Ti-terminated TiN(111) surfaces has significant effects on adatom surface energetics which vary strongly with the adatom species and surface orientation. Here, we investigate Ti, Al, and N adatom surface dynamics using density functional methods. We calculate adatom binding and diffusion energies with both a nudged elastic band and grid-probing techniques. The adatom diffusivities are analyzed within a transition-state theory approximation. We determine the stable and metastable Ti, Al, and N binding sites on all three surfaces as well as the lowest energy migration paths. In general, adatom mobilities are fastest on TiN(001), slower on TiN(111), and slowest on TiN(011). The introduction of Al has two major effects on the surface diffusivity of Ti and Al adatoms. First, Ti adatom diffusivity on TiN(001) is significantly reduced near substituted Al surface atoms; we observe a 200% increase in Ti adatom diffusion barriers out of fourfold hollow sites adjacent to Al surface atoms, while Al adatom diffusivity between bulk sites is largely unaffected. Secondly, on TiN(111), the effect is opposite; Al adatoms are slowed near the substituted Al surface atom, while Ti adatom diffusivity is largely unaffected. In addition, we note the importance of magnetic spin polarization on Ti adatom binding energies and diffusion path. These results are of relevance for the atomistic understanding of Ti 1 − x Al x N alloy and Ti 1 − x Al x N/TiN multilayer thin-film growth processes. [ABSTRACT FROM AUTHOR]

We review results on the growth of metastable Ti 1− x Al x N alloy films by hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) using the time domain to apply substrate bias either in synchronous with the entire HIPIMS pulse or just the metal-rich portion of the pulse in mixed Ar/N 2 discharges. Depending upon which elemental target, Ti or Al, is powered by HIPIMS, distinctly different film-growth kinetic pathways are observed due to charge and mass differences in the metal-ion fluxes incident at the growth surface. Al + ion irradiation during Al–HIPIMS/Ti–DCMS at 500 °C, with a negative substrate bias V s = 60 V synchronized to the HIPIMS pulse (thus suppressing Ar + ion irradiation due to DCMS), leads to single-phase NaCl-structure Ti 1− x Al x N films ( x ≤ 0.60) with high hardness (> 30 GPa with x > 0.55) and low stress (0.2–0.8 GPa compressive). Ar + ion bombardment can be further suppressed in favor of predominantly Al + ion irradiation by synchronizing the substrate bias to only the metal-ion-rich portion of the Al–HIPIMS pulse. In distinct contrast, Ti–HIPIMS/Al–DCMS Ti 1 − x Al x N layers grown with Ti + /Ti 2 + metal ion irradiation and the same HIPIMS-synchronized V s value, are two-phase mixtures, NaCl-structure Ti 1− x Al x N plus wurtzite AlN, exhibiting low hardness (≃ 18 GPa) with high compressive stresses, up to − 3.5 GPa. In both cases, film properties are controlled by the average metal-ion momentum per deposited atom < p d > transferred to the film surface. During Ti–HIPIMS, the growing film is subjected to an intense flux of doubly-ionized Ti 2+ , while Al 2+ irradiation is insignificant during Al–HIPIMS. This asymmetry is decisive since the critical < p d > limit for precipitation of w -AlN, 135 [eV-amu] 1/2 , is easily exceeded during Ti–HIPIMS, even with no intentional bias. The high Ti 2 + ion flux is primarily due to the second ionization potential (IP 2 ) of Ti being lower than the first IP (IP 1 ) of Ar. New results involving the HIPIMS growth of metastable Ti 1− x Al x N alloy films from segmented TiAl targets are consistent with the above conclusions. [ABSTRACT FROM AUTHOR]

Thin films consisting of TiN nanocrystallites encapsulated in a fully percolated SiN y tissue phase are archetypes for hard and superhard nanocomposites. Here, we investigate metastable SiN y solid solubility in TiN and probe the effects of surface segregation during the growth of TiSiN films onto substrates that are either flat TiN(001)/MgO(001) epitaxial buffer layers or TiN(001) facets of length 1–5 nm terminating epitaxial TiN(111) nanocolumns, separated by voids, deposited on epitaxial TiN(111)/MgO(111) buffer layers. Using reactive magnetron sputter deposition, the TiSiN layers were grown at 550 °C and the TiN buffer layers at 900 °C. On TiN(001), the films are NaCl-structure single-phase metastable Ti 1 − x Si x N(001) with N/(Ti + Si) = 1 and 0 ≤ x ≤ 0.19. These alloys remain single-crystalline to critical thicknesses h c ranging from 100 ± 30 nm with x = 0.13 to 40 ± 10 nm with x = 0.19. At thicknesses h > h c , the epitaxial growth front breaks down locally to form V-shaped polycrystalline columns with an underdense feather-like nanostructure. In contrast, the voided epitaxial TiN(111) columnar surfaces, as well as the TiN(001) facets, act as sinks for SiN y . For Ti 1 − x Si x N layers with global average composition values 〈x〉 = 0.16, the local x value in the middle of Ti 1 − x Si x N columns increases from 0.08 for columns with radius r ⋍ 2 nm to x = 0.14 with r ⋍ 4 nm. The average out-of-plane lattice parameter of epitaxial nanocolumns encapsulated in SiN y decreases monotonically with increasing Si fraction 〈x〉, indicating the formation of metastable (Ti,Si)N solid solutions under growth conditions similar to those of superhard nanocomposites for which the faceted surfaces of nanograins also provide sinks for SiN y . [ABSTRACT FROM AUTHOR]

Abstract: Ab initio and classical molecular dynamics (AIMD and CMD) simulations reveal that Ti adatoms on TiN(001) surfaces migrate between neighboring fourfold hollow sites primarily along in-plane <100> channels. <100> and <110> single jumps, as well as <100> double jump rates, obtained directly from MD runs as a function of temperature, are used to determine diffusion activation energies Ea, and attempt frequencies A, for the three preferred Ti adatom migration pathways on TiN(001). From transition rates Aexp[−Ea /(kBT)], we determine adatom surface distribution probabilities as a function of time, which are used to calculate adatom diffusion coefficients Ds(T). AIMD and CMD predictions are consistent and complementary. Using CMD, we investigate the effect on the adatom jump rate of varying the phonon wavelength degrees of freedom by progressively increasing the supercell size. We find that long-wavelength phonons significantly contribute to increasing adatom mobilities at temperatures ≤600K, but not at higher temperatures. Finally, by directly tracking the Ti adatom mean-square displacement during CMD runs, we find that Ti adatom jumps are highly correlated on TiN(001), an effect that yields lower Ds values (Ds corr) than those estimated from uncorrelated transition probabilities. The temperature-dependent diffusion coefficient is Ds corr (T)=(4.5×10−4 cm2 s−1) exp[−0.55eV/(kBT)]. [Copyright &y& Elsevier]

Ab initio molecular dynamics simulations based on density functional theory show that N adatoms are chemisorbed in threefold sites close to a N surface atom and between the two diagonally opposed neighboring Ti surface atoms on TiN(001). The most probable N adatom reaction pathway, even in the presence of nearby N adatoms, is for the N adatom and N surface atom pair to first undergo several exchange reactions and then desorb as a N2 molecule, resulting in a surface anion vacancy, with an activation barrier E des of 1.37eV and an attempt frequency A des =3.4×1013 s−1. E des is essentially equal to the N adatom surface diffusion barrier, Es =1.39eV, while As is only three to four times larger than A des, indicating that isolated N adatoms migrate for only short distances prior to N2 desorption. The probability of N2 desorption via recombination of N adatoms on TiN(001) is much lower due to repulsive adatom/adatom interactions at separations less than ~3Å which rapidly increase to ~2eV at a separation of 1.5Å. We obtain good qualitative and quantitative agreement with the above results using the modified embedded atom method potential to perform classical molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

Abstract: We use classical molecular dynamics and the modified embedded atom method to determine residence times and descent pathways of Ti and N adatoms on square, single-atom-high, TiN islands on TiN(001). Simulations are carried out at 1000K, which is within the optimal range for TiN(001) epitaxial growth. Results show that the frequency of descent events, and overall adatom residence times, depend strongly on both the TiN(001) diffusion barrier for each species as well as the adatom island-edge location immediately prior to descent. Ti adatoms, with a low diffusion barrier, rapidly move toward the island periphery, via funneling, where they diffuse along upper island edges. The primary descent mechanism for Ti adatoms is via push-out/exchange with Ti island-edge atoms, a process in which the adatom replaces an island edge atom by moving down while pushing the edge atom out onto the terrace to occupy an epitaxial position along the island edge. Double push-out events are also observed for Ti adatoms descending at N corner positions. N adatoms, with a considerably higher diffusion barrier on TiN(001), require much longer times to reach island edges and, consequently, have significantly longer residence times. N adatoms are found to descend onto the terrace by direct hopping over island edges and corner atoms, as well as by concerted push-out/exchange with N atoms adjacent to Ti corners. For both adspecies, we also observe several complex adatom/island interactions, before and after descent onto the terrace, including two instances of Ti island-atom ascent onto the island surface. [Copyright &y& Elsevier]

Abstract: A hybrid deposition process consisting of reactive high-power pulsed and dc magnetron cosputtering (HIPIMS and DCMS) from Ti and Al targets is used to grow Ti1−x Al x N alloys, with x ~0.6, on Si(001) at 500°C. Two series of films are deposited in which the energy and momentum of metal ions incident at the growing film are individually varied. In both sets of experiments, a negative bias Vs ranging from 20 to 280V is applied to the substrate in synchronous, as determined by in-situ mass spectrometry, with the metal-ion-rich part of the HIPIMS pulse. Ion momentum is varied by switching the HIPIMS and dc power supplies to change the mass m and average charge of the primary metal ion. Al-HIPIMS/Ti-DCMS layers grown under Al+ (mAl =26.98amu) bombardment with 20≤ Vs ≤160V are single-phase NaCl-structure alloys, while films deposited with Vs >160V are two-phase, cubic plus wurtzite. The corresponding critical average metal-ion momentum transfer per deposited atom for phase separation is 〈p d ⁎〉≥135 [eV-amu]1/2. In distinct contrast, layers deposited in the Ti-HIPIMS/Al-DCMS configuration with Ti+/Ti2+ (mTi =47.88amu) ion irradiation are two-phase even with the lowest bias, Vs =20V, for which 〈p d ⁎〉>135 [eV-amu]1/2. Precipitation of wurtzite-structure AlN is primarily determined by the average metal-ion momentum transfer to the growing film, rather than by the deposited metal-ion energy. Ti-HIPIMS/Al-DCMS layers grown with Vs =20V are two-phase with compressive stress σ =−2GPa which increases to −6.2GPa at Vs =120V; hardness H values range from 17.5 to 27GPa and are directly correlated with σ. However, for Al-HIPIMS/Ti-DCMS, the relatively low mass and single charge of the Al+ ion permits tuning properties of metastable cubic Ti0.38Al0.62 N by adjusting Vs to vary, for example, the hardness from 12 to 31GPa while maintaining σ ~0. [Copyright &y& Elsevier]

Abstract: Metastable Ti1-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 experiments. In both cases, the AlN concentration in the co-sputtered films, deposited at T s =500°C with R =1.5–5.3Å/s, is controlled by adjusting the average DCMS target power. Resulting films are analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, elastic recoil detection analysis, and nanoindentation. Mass spectroscopy is used to determine ion energy distribution functions at the substrate. The distinctly different flux distributions obtained from targets driven in HIPIMS vs. DCMS modes allow the effects of Al n+ and Ti n+ (n =1, 2) ion irradiation on film growth kinetics, and resulting properties, to be investigated separately. Bombardment with Al n+ ions (primarily Al+ in the Al-HIPIMS/Ti-DCMS configuration) during film growth leads to NaCl-structure Ti1-x Al x N (0.53≤ x ≤0.60) films which exhibit high hardness (>30GPa) with low stress (0.2–0.7GPa tensile). In contrast, films with corresponding AlN concentrations grown under Ti n+ metal ion irradiation (with a significant Ti2+ component) in the Ti-HIPIMS/Al-DCMS mode have much lower hardness, 18–19GPa, and high compressive stress ranging up to 2.7GPa. The surprisingly large variation in mechanical properties results from the fact that the kinetic AlN solubility limit x max in Ti1-x Al x N depends strongly on, in addition to T s and R, the target power configuration during growth and hence the composition of the ion flux. AlN with x max ~64mol% can be accommodated in the NaCl structure under Al n+ ion flux, compared with ~40mol% for growth with Ti n+ flux. The strong asymmetry in film growth reaction paths is due primarily to the fact 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, −60V, applied synchronously with HIPIMS pulses, during growth. [Copyright &y& Elsevier]

Abstract: We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN-content Ti1−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 n+) of the growing film results in alloys 0.55 ≤ x ≤ 0.60 which exhibit hardness H ∼ 30 GPa and low stress σ = 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 Ti2+ 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 Ti0.41Al0.59N increases from 30 to 33 GPa following a 900 °C anneal. [Copyright &y& Elsevier]

Abstract: The AlN incorporation probability in single crystal Hf1− x Al x N(001) layers is controllably adjusted between ∼0% and 100% by varying the ion energy (E i) incident at the growing film over a narrow range, 10–40eV. The layers are grown on MgO(001) at 450°C using ultrahigh vacuum magnetically unbalanced reactive magnetron sputtering from a Hf0.7Al0.3 alloy target in a 5%-N2/Ar atmosphere at a total pressure of 20mTorr (2.67Pa). The ion to metal flux ratio incident at the growing film is constant at 8. Epitaxial film compositions vary from x =0.30 with E i =10eV, to 0.27 with E i =20eV, 0.17 with E i =30eV, and ⩽0.002 with E i ⩾40eV. Thus, the AlN incorporation probability decreases by greater than two orders of magnitude. This extraordinary range in real-time manipulation of film chemistry during deposition is due to the efficient resputtering of deposited Al atoms (27 amu) by Ar+ ions (40 amu) neutralized and backscattered from heavy Hf atoms (178.5 amu) in the film. This provides a new reaction pathway to synthesize, at high deposition rates, compositionally complex heterostructures, multilayers, and superlattices with abrupt interfaces from a single alloy target by controllably switching E i. For multilayer and superlattice structures, the choice of E i value determines the layer composition and the switching periods control the individual layer thickness. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial TiN layers, 0.3μm thick, are grown on MgO(001) in the absence of applied substrate heating using very high flux, low-energy (below the lattice atom displacement threshold), ion irradiation during reactive magnetron sputter deposition in pure N2 discharges. High-resolution x-ray diffraction, reciprocal lattice maps, and transmission electron microscopy analyses reveal that the TiN(001) films grow with an (001)TiN||(001)MgO and [100]TiN||[100]MgO orientation relationship to the substrate. The layers are fully coherent with no detectable misfit dislocations. For comparison, TiN/MgO(001) films grown at temperatures of 700–850°C under similar conditions, but with no intentional ion irradiation, are fully relaxed with a high misfit dislocation density. Thus, the present results reveal that intense low-energy ion irradiation during film growth facilitates high adatom mobilities giving rise to low-temperature epitaxy, while the low growth temperature quenches strain-induced relaxation and suppresses misfit dislocation formation. [Copyright &y& Elsevier]

Abstract: Epitaxial metastable Hf1− x Al x N alloys with 0≤ x ≤0.50 were grown on MgO(001) substrates at 600 °C by ultrahigh vacuum reactive magnetron sputtering from Hf and Al targets in 90% Ar+10% N2 discharges at 7 mTorr. X-Ray diffraction and cross-sectional transmission electron microscopy show that Hf1− x Al x N alloys are single crystals with the B1–NaCl structure. Rutherford backscattering spectroscopy investigations reveal that all films are slightly overstochiometric with N/(Hf+Al)=1.05±0.05. The relaxed lattice parameter decreased linearly from 0.4519 nm with x =0 to 0.4438 nm with x =0.50, compared to 0.4320 nm expected from the linear Vegard''s rule. We find a metastable single phase field that is remarkably broad given the large lattice mismatch (≃9%) between the two alloy components. Alloying HfN with AlN leads to an increase in hardness (≃30% to 32.4±0.7 GPa), as well as nanostructured compositional modulations due to the onset of spinodal decomposition. [Copyright &y& Elsevier]

Abstract: Embedded-atom molecular dynamics simulations were used to investigate the effects of low-energy (5–50 eV) normally-incident self-ion irradiation of two-dimensional compact Pt3, Pt7, Pt19, and Pt37 clusters on Pt(111). We follow atomistic pathways leading to bombardment-induced intra- and interlayer mass transport. The results can be described in terms of three impact energy regimes. With E ≤20 eV, we observe an increase in 2D island dimensions and negligible residual point defect formation. As the impact energy is raised above 20 eV, we observe an increase in irradiation-induced lateral mass transport, a decrease in island size, and the activation of interlayer processes. For E ≥35 eV, this trend continues, but point defects, in the form of surface vacancies, are also formed. The results illustrate the richness of the dynamical interaction mechanisms occurring among incident energetic species, target clusters, and substrate atoms, leading to island preservation, reconfiguration, disruption and/or residual point defects formation. We discuss the significance of these results in terms of thin film growth. [Copyright &y& Elsevier]

Abstract: We present a method for the determination of orientation-dependent mobilities Γ eff(φ) based upon analyses of the detachment-limited coarsening/decay kinetics of equilibrium-shaped two-dimensional islands. An exact analytical expression relating the orientation-dependence of Γ eff(φ) to that of the anisotropic step energies β(φ) is derived. This provides relative values of Γ eff(φ) to within an orientation-independent scale factor that is proportional to the decay rate of the island area. Using in situ high temperature (T =1550–1700 K) low-energy electron microscopy measurements of two-dimensional TiN island coarsening/decay kinetics on TiN(111) terraces for which β(φ) values are known [Phys. Rev. B 67 (2003) 35409], we demonstrate the applicability of our analytic formulation for the determination of absolute Γ eff(φ) values. [Copyright &y& Elsevier]

Abstract: Studies of surface dynamics, including the kinetics of two-dimensional (2D) island coarsening/decay, shape fluctuations, and shape evolution, enable determination of the rate-limiting mechanisms, corresponding surface mass transport parameters, and step energies. Most models describing these phenomena assume isotropic (circular) or near-isotropic island shapes and, hence, isotropic step energies. However, even simple elemental metal surfaces are anisotropic and more complex compound surfaces such as the low-index planes of TiN, GaAs, GaN, ZnO, Al2O3, ZrO2, are highly anisotropic. Here, we describe recent progress toward developing generalized theoretical and experimental approaches, applicable for analyses of 2D island coarsening/decay kinetics, coalescence kinetics, and determination of orientation-dependent step energies and step stiffnesses, on both isotropic and highly anisotropic surfaces. [Copyright &y& Elsevier]

Abstract: The effect of crystal orientation and microstructure on the mechanical properties of TaNx was investigated. TaNx films were grown on a SiO2 substrate by ultrahigh vacuum unbalanced magnetron sputter deposition in mixed Ar/N2 discharges at 20 mTorr (2.67 Pa) and at 350 °C. Unlike the Ti–N system, in which TiN is the terminal phase, a large number of N-rich phases in the Ta–N system could lead to layers which had self-organized nanosized lamella structure of coherent cubic and hexagonal phases, with a correct choice of nitrogen fraction in the sputtering mixture and ion irradiation energy during growth. The preferred orientations and the microstructure of TaNx layers were controlled by varying incident ion energy Ei (=30–50 eV) and nitrogen fractions fN2 (=0.1–0.15). TaNx layers were grown on (0002)-Ti underlayer as a crystallographic template in order to relieve the stress on the films. The structure of the TaNx film transformed from B1-NaCl δ–TaNx to lamellar structured B1-NaCl δ-TaNx+ hexagonal ɛ-TaNx or B1-NaCl δ-TaNx+hexagonal γ-TaNx with increasing ion energy at the same nitrogen fraction fN2. The hardness of the films also increased by the structural change. At the nitrogen fraction of 0.1–0.125, the structure of the TaNx films was changed from δ-TaNx+ɛ-TaNx to δ-TaNx+γ-TaNx with increasing ion energy. However, at the nitrogen fraction of 0.15, the film structure did not change from δ-TaNx+ɛ-TaNx over the whole range of the applied ion energy. The hardness increased significantly from 21.1 to 45.5 GPa with increasing ion energy. [Copyright &y& Elsevier]

Laser texturing enables the observation of island decays on the ‘1×1’ high temperature surface of Si(110) by low energy electron microscopy. At temperatures above the phase transition (T=790–980°C), the decay of the island areas exhibits a nonlinear dependence on time indicative of surface diffusion limited mass transport. The aspect ratios of the islands during the decay show a weak temperature dependence despite the fact that surface is anisotropic. We have obtained the activation energy of mass transport, the kink energy, step energy, and step stiffness for Si(110). [Copyright &y& Elsevier]

In situ low-energy electron microscopy was used to study interlayer mass transport kinetics during annealing of three-dimensional (3D) TiN(1 1 1) mounds, consisting of stacked 2D islands, at temperatures T between 1550 and 1700 K. At each T, the islands decay at a constant rate, irrespective of their initial position in the mounds, indicating that mass is not conserved locally. From temperature-dependent island decay rates, we obtain an activation energy of 2.8 ± 0.3 eV. This is consistent with the detachment-limited decay of 2D TiN islands on atomically flat TiN(1 1 1) terraces [Phys. Rev. Lett. 89 (2002) 176102], but significantly smaller than the value, 4.5 ± 0.2 eV, obtained for bulk-diffusion-limited spiral step growth [Nature 429 (2004) 49]. We model the process based upon step flow, while accounting for step–step interactions, step permeability, and bulk mass transport. The results show that TiN(1 1 1) steps are highly permeable and exhibit strong repulsive temperature-dependent step–step interactions that vary between 0.03 and 0.76 eV · Å. The rate-limiting process controlling TiN(1 1 1) mound decay is surface, rather than bulk, diffusion in the detachment-limited regime. [Copyright &y& Elsevier]

We employ in situ high-temperature (1030–1250 K) scanning tunneling microscopy to measure adatom island coarsening/decay kinetics and temporal fluctuations around the equilibrium shapes of two-dimensional TiN vacancy islands on atomically-smooth (0 0 1) and (1 1 1) TiN terraces. Using inverse Legendre transformations of the equilibrium island shapes, we obtain relative step energies as a function of step orientation within an orientation-independent scale factor λ, the equilibrium chemical potential of the island per unit TiN molecular area. We then use either quantitative island coarsening measurements [in the case of TiN(0 0 1)] or an exact approach for the analysis of shape fluctuations, applicable to highly anisotropic TiN(1 1 1) islands, to determine λ and, hence, absolute orientation-dependent step energies and step stiffnesses. [Copyright &y& Elsevier]

In situ high-temperature (1023–1223 K) scanning tunneling microscopy was used to study the coarsening/decay kinetics of two-dimensional (2D) TiN adatom islands on TiN(0 0 1) terraces and in single-atom-deep vacancy pits. Island coarsening/decay behavior was found to be non-linear with time and to depend on the local environment (i.e., on adatom concentration gradients on the terrace), the signature of surface-diffusion-limited kinetics. Two simple island geometries––a single 2D adatom island on an atomically smooth terrace and a single 2D adatom island within a vacancy island––were used to extract adatom surface transport parameters. We model diffusion-limited island decay kinetics for these configurations based upon steady-state diffusion equations solved by adaptive finite-element methods with a form of the Gibbs–Thomson equation describing anisotropic islands serving as the boundary condition. Calculated decay rates were compared with the experimental results to obtain an activation energy Ea for adatom formation and diffusion on TiN(0 0 1). Ea was found to be 2.6±0.6 and 3.1±0.5 eV for adatom islands in vacancy pits and on terraces, respectively. The difference in the two Ea values corresponds to the step edge Ehrlich barrier, which for TiN(0 0 1) is less than the experimental uncertainties in the measurements. [Copyright &y& Elsevier]

We describe an analytical form of the Wulff plot construction procedure and derive a general expression for the surface energy from the three-dimensional equilibrium crystal shape in generalized orthogonal curvilinear coordinates. Particular expressions in Cartesian, spherical polar, and circular cylindrical coordinates are also presented. Corresponding results for a two-dimensional (2D) island on a flat terrace provide relative orientation-dependent step energies within a scale factor λ, the equilibrium chemical potential of the island per unit area. In order to determine λ and, hence obtain absolute step energies, we have developed an exact theoretical approach, applicable to both isotropic and anisotropic 2D island shapes, relating the temporal change in island free energy to thermal fluctuations about the equilibrium shape. [Copyright &y& Elsevier]

We have used in situ D2 temperature-programmed desorption (TPD) to probe C incorporation and surface segregation kinetics, as well as hydrogen desorption pathways, during Si1−yCy(0 0 1) gas-source molecular beam epitaxy from Si2H6/CH3SiH3 mixtures at temperatures Ts between 500 and 650 °C. Parallel D2 TPD results from C-adsorbed Si(0 0 1) wafers exposed to varying CH3SiH3 doses serve as reference data. Si1−yCy(0 0 1) layer spectra consist of three peaks: first-order β1 at 515 °C and second-order β2 at 405 °C, due to D2 desorption from Si monodeuteride and dideuteride phases, as well as a new second-order C-induced γ1 peak at 480 °C. C-adsorbed Si(0 0 1) samples with very high CH3SiH3 exposures yielded a higher-temperature TPD feature, corresponding to D2 desorption from surface C atoms, which was never observed in Si1−yCy(0 0 1) layer spectra. The Si1−yCy(0 0 1) γ1 peak arises due to desorption from Si monodeuteride species with C backbonds. γ1 occurs at a lower temperature than β1 reflecting the lower D–Si* bond strength, where Si* represents surface Si atoms bonded to second-layer C atoms, as a result of charge transfer from dangling bonds. The total integrated monohydride (β1+γ1) intensity, and hence the dangling bond density, remains constant with y indicating that C does not deactivate surface dangling bonds as it segregates to the second-layer during Si1−yCy(0 0 1) growth. Si* coverages increase with y at constant Ts and with Ts at constant y. The positive Ts-dependence shows that C segregation is kinetically limited at Ts&les;650 °C. D2 desorption activation energies from β1, γ1 and β2 sites are 2.52, 2.22 and 1.88 eV. [Copyright &y& Elsevier]

In situ high-temperature (1030–1223 K) scanning tunneling microscopy was used to determine the equilibrium shapes of two-dimensional TiN vacancy islands on atomically smooth terraces of epitaxial TiN(0 0 1) layers. Inverse Legendre transformations of the equilibrium island shapes yield relative step energies as a function of step orientation within an orientation-independent scale factor λ, the equilibrium chemical potential of the island per unit TiN molecular area. We then use quantitative TiN(0 0 1) adatom island coarsening measurements to determine λ and, hence, absolute orientation-dependent step energies β and step stiffnesses β˜. For 〈1 1 0〉 and 〈1 0 0〉 steps on TiN(0 0 1), we obtain: β1 1 0=0.21±0.05 eV/A˚, β1 0 0=0.25±0.05 eV/A˚, β˜1 1 0=0.9±0.2 eV/A˚, and β˜1 0 0=0.07±0.02 eV/A˚. From the β˜ values, we calculate kink formation energies &epsiv;1 1 0=0.40±0.2 eV and &epsiv;1 0 0=0.11±0.1 eV based on the unrestricted terrace-step-kink model. [Copyright &y& Elsevier]

Refractory transition-metal (TM) diborides have high melting points, excellent hardness, and good chemical stability. However, these properties are not sufficient for applications involving extreme environments that require high mechanical strength as well as oxidation and corrosion resistance. Here, we study the effect of Cr addition on the properties of ZrB 2 -rich Zr 1-x Cr x B y thin films grown by hybrid high-power impulse and dc magnetron co-sputtering (Cr-HiPIMS/ZrB 2 -DCMS) with a 100-V Cr-metal-ion synchronized bias. Cr metal fraction, x = Cr/(Zr + Cr), is increased from 0.23 to 0.44 by decreasing the power P ZrB 2 applied to the DCMS ZrB 2 target from 4000 to 2000 W, while the average power, pulse width, and frequency applied to the HiPIMS Cr target are maintained constant. In addition, y decreases from 2.18 to 1.11 as a function of P ZrB 2 , as a result of supplying Cr to the growing film and preferential B resputtering caused by the pulsed Cr-ion flux. ZrB 2.18 , Zr 0·77 Cr 0·23 B 1.52 , Zr 0·71 Cr 0·29 B 1.42 , and Zr 0·68 Cr 0·32 B 1.38 films have hexagonal AlB 2 crystal structure with a columnar nanostructure, while Zr 0·64 Cr 0·36 B 1.30 and Zr 0·56 Cr 0·44 B 1.11 are amorphous. All films show hardness above 30 GPa. Zr 0.56 Cr 0.44 B 1.11 alloys exhibit much better toughness, wear, oxidation, and corrosion resistance than ZrB 2.18. This combination of properties makes Zr 0·56 Cr 0·44 B 1.11 ideal candidates for numerous strategic applications. • ZrB 2 -rich Zr 1-x Cr x B y films are grown by hybrid high-power impulse and dc magnetron (Cr-HiPIMS/ZrB 2 -DCMS) co-sputtering. • Films with x ≤ 0.32 have hexagonal structure with a columnar nanostructure, while alloys with x ≤ 0.44 are amorphous. • All films show nanoindentation hardness above 30 GPa. • Toughness increases as a function of Cr concentration. • Zr 0·56 Cr 0·44 B 1.11 exhibit much better wear, oxidation, and corrosion resistance than reference ZrB 2.18. [ABSTRACT FROM AUTHOR]

The atomic structure and local composition of high quality epitaxial substoichiometric titanium diboride (TiB 1.9) thin film, deposited by unbalanced magnetron sputtering, were studied using analytical high-resolution scanning transmission electron microscopy, density functional theory, and image simulations. The unpaired Ti is pinpointed to inclusion of Ti-based stacking faults within a few atomic layers, which terminates the { 1 1 ¯ 00 } prismatic planes of the crystal structure and attributed to the absence of B between Ti planes that locally relaxes the structure. This mechanism allows the line compound to accommodate off-stoichiometry and remain a line compound between defects. The planar defects are embedded in otherwise stoichiometric TiB 2 and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond lengths along and across the faults is observed. Image, graphical abstract [ABSTRACT FROM AUTHOR]