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Group-IV HfNx transition-metal nitride layers, with 0.85≤x≤1.50, are grown on MgO(001) and analyzed by Raman spectroscopy. Samples with 0.85≤x≤1.20 are single-phase epitaxial NaCl-structure HfNx(001), while layers with higher N concentrations are two-phase mixtures containing N-rich inclusions. All samples exhibit both first- and second-order Raman scattering. The presence of first-order scattering indicates that Oh symmetry, a characteristic of the NaCl crystal structure, is broken even in stoichiometric HfN. As x decreases in understoichiometric HfNx samples, corresponding to a decrease in the number of valence electrons per unit cell from nine (x=1) to eight (x=0.75), the positions of the acoustic lines shift to higher frequencies. This provides an indirect probe of phonon anomalies in acoustic mode dispersion curves and signifies an increase in N vacancy concentration. The persistence of strong first-order acoustic scattering from overstoichiometric (x>1) samples indicates that adding more N does not substantially reduce the average defect density around Hf sites. The absence of a frequency shift in the acoustic modes of overstoichiometric HfNx, with 1.17≤x≤1.27, also shows that the local order around Hf sites does not change significantly, while the observed shift of the first-order optical modes to higher frequency with increasing x is characteristic of increasing lattice disorder adjacent to N sites. The Raman results, together with the nature of the variation in the HfNx lattice parameter, the electron carrier concentration, and the superconducting transition temperature as a function of x, can be explained by the presence of N vacancies for x<1, both N and Hf vacancies in stoichiometric HfN(001), and the combination of N vacancies and NHf antisite defects for x>1. [ABSTRACT FROM AUTHOR]

An excellent adhesion of hard coatings to steel substrates is paramount in practically all application areas. Conventional methods utilize Ar glow etching or cathodic arc discharge pretreatments that have the disadvantage of producing weak interfaces or adding droplets, respectively. One tool for interface engineering is high power impulse magnetron sputtering (HIPIMS). HIPIMS is based on conventional sputtering with extremely high peak power densities reaching 3 kW cm-2 at current densities of >2 A cm-2. HIPIMS of Cr and Nb was used to prepare interfaces on 304 stainless steel and M2 high speed steel (HSS). During the pretreatment, the substrates were biased to Ubias=-600 V and Ubias=-1000 V in the environment of a HIPIMS of Cr and Nb plasma. The bombarding flux density reached peak values of 300 mA cm-2 and consisted of highly ionized metal plasma containing a high proportion of Cr1+ and Nb1+. Pretreatments were also carried out with Ar glow discharge and filtered cathodic arc as comparison. The adhesion was evaluated for coatings consisting of a 0.3 μm thick CrN base layer and a 4 μm thick nanolayer stack of CrN/NbN with a period of 3.4 nm, hardness of HK0.025=3100, and residual stress of -1.8 GPa. For HIPIMS of Cr pretreatment, the adhesion values on M2 HSS reached scratch test critical load values of LC=70 N, thus comparing well to LC=51 N for interfaces pretreated by arc discharge plasmas and to LC=25 N for Ar etching. Cross sectional transmission electron microscopy studies revealed a clean interface and large areas of epitaxial growth in the case of HIPIMS pretreatment. The HIPIMS pretreatment promoted strong registry between the orientation of the coating and polycrystalline substrate grains due to the incorporation of metal ions and the preservation of crystallinity of the substrate. Evidence and conditions for the formation of cube-on-cube epitaxy and axiotaxy on steel and γ-TiAl substrates are presented. [ABSTRACT FROM AUTHOR]

CoSi2 layers, <40 nm thick, were grown on Si(001) by reactive deposition epitaxy (RDE) in which Co was deposited at 700 °C by magnetically unbalanced ultrahigh vacuum magnetron sputtering. X-ray diffraction pole figures and transmission electron microscopy (TEM) reveal that the layers, which exhibit a cube-on-cube epitaxial relationship with the substrate, (001)CoSi2∥(001)Si and [100]CoSi2∥[100]Si, contain fourfold symmetric {111} twinned domains oriented such that {221}CoSi2∥(001)Si and <110>CoSi2∥[110]Si. We demonstrate that high-flux low-energy (EAr+=9.6 eV) Ar+ ion irradiation during deposition dramatically increases the area fraction fu of untwinned regions from 0.17 in films grown under standard magnetically balanced conditions in which the ratio JAr+/JCo of the incident Ar+ to Co fluxes is 1.4 to 0.72 with JAr+/JCo=13.3. TEM analyses show that the early stages of RDE CoSi2(001) film growth proceed via the Volmer-Weber mode with independent nucleation of both untwinned and twinned islands. Increasing JAr+/JCo results in larger values of both the number density and area of untwinned with respect to twinned islands. The intense Ar+ ion bombardment creates additional low-energy adsorption sites that favor the nucleation of untwinned islands while collisionally enhancing Co surface mobilities which, in turn, increases the probability of itinerant Co adatoms reaching these sites. [ABSTRACT FROM AUTHOR]

Stoichiometric single-crystal HfN layers grown on MgO(001) are analyzed by Raman spectroscopy. Second-order Raman scattering predominates, but first-order modes in the acoustic and optical ranges are also visible. The latter indicates that the Oh symmetry of NaCl-structure HfN is broken. The large mass difference between Hf and N leads to a correspondingly large separation, 250 cm-1, between the first-order acoustic and optical bands. Within this gap, four Raman lines are clearly observed. The first three are the second-order transverse acoustic mode (240 cm-1), the sum of the first-order transverse and longitudinal acoustic modes (280 cm-1), and the second-order longitudinal acoustic mode (325 cm-1). The fourth line at 380 cm-1 is identified as the difference between the first-order optical and acoustic modes. The observed first-order Raman scattering, as well as the width of the gap between the first-order acoustic and optical modes, is in good agreement with previously calculated HfN phonon density of states. [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]

While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO(001) and measured their physical properties. The films were grown at 700°C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N[SUB2] discharges maintained at 4 mTorr)(0.53 Pa). X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001)[SUBCeN]‖(001)[SUBMgO] with [100][SUBCeN]‖[100][SUBMgO], while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ce=0.99Plusmn;0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8±0.2×10[SUP22]cm[SUP-3] with a room temperature mobility of 0.31 cm[SUP2]V[SUP-1]s[SUP-1]. At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 μΩ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 μΩ cm. The hardness and elastic modulus of CeN(001) were determined from nanoindentation measurements to be 15.0±0.9 and 330±16 GPa. [ABSTRACT FROM AUTHOR]

We investigate the effect of N vacancies on the mechanical properties of epitaxial δ-Tin[SUBx](001)layers with x=0.67- 1.0. The relaxed lattice parameter increases linearly with x in good agreement with ab initio density functional calculations, indicating that deviations from stoichiometry are entirely due to anion vacancies. Hardness values increase continuously, while the elastic modulus decreases with increasing N-vacancy concentration. We attribute the observed vacancy hardening to a reduced dislocation mobility arising from an increase in the rate-limiting activation energy for cation migration. [ABSTRACT FROM AUTHOR]

Epitaxial metastable Ge[sub 1-y]C[sub y] alloy layers with y≤0.035 were grown on Ge(001) from hyperthermal Ge and C atomic beams at deposition temperatures T[sub s] of 250 and 300 °C. The use of hyperthermal beams allows us to controllably vary the concentration of C incorporated as Ge–C split interstitials. Ge[sub 1-y]C[sub y] layers grown with incident Ge-atom energy distributions corresponding to ≤0.14 lattice displacement per incident atom (dpa) are in a state of in-plane tension and contain significant concentrations of C atoms incorporated in substitutional sites. Increasing the dpa to 0.24 yields layers in compression with C incorporated primarily as Ge–C split interstitials. Ab initio density functional calculations of the formation energies and strain coefficients associated with C atomic arrangements in Ge show that configurations containing multiple C atoms, referred to collectively as C nanoclusters, are energetically more favorable than substitutional C and Ge–C split interstitials and yield a nearly zero average strain. In contrast, substitutional C and Ge–C split interstitials produce large tensile and compressive strains, respectively. Using the calculated strain coefficients, measured layer strains obtained from high-resolution reciprocal lattice maps, and substitutional C concentrations determined by Raman spectroscopy, we obtain the fraction of C atoms incorporated in substitutional, Ge–C split interstitial, and nanocluster sites as a function of the total C concentration y and T[sub s]. We find that at low y and T[sub s] values, all C atoms are incorporated in single-C configurations: substitutional C and Ge–C split interstitials. Their relative concentrations are controlled by the dpa through the production of near-surface Ge self-interstitials which are trapped by substitutional C atoms to form Ge–C split interstitials. Increasing y and T[sub s], irrespective of the dpa, leads to... [ABSTRACT FROM AUTHOR]

Single-crystal TiN(111) layers, 45 nm thick, were grown on MgO(111) by ultrahigh vacuum reactive magnetron sputter deposition in pure N[sub 2] discharges at T[sub s]=700 °C. Epitaxial Al(111) overlayers, 160 nm thick, were then deposited at T[sub s]=100 °C in Ar without breaking vacuum. Interfacial reactions and changes in bilayer microstructure due to annealing at 620 and 650 °C were investigated using x-ray diffraction and transmission electron microscopy (TEM). The interfacial regions of samples annealed at 620 °C consist of continuous =7-nm-thick epitaxial wurtzite-structure AlN(0001) layers containing a high density of stacking faults, with =22 nm thick tetragonal Al[sub 3]Ti(112) overlayers. Surprisingly, samples annealed at the higher temperature are more stable against Al[sub 3]Ti formation. TEM analyses of bilayers annealed at 650 °C (10 °C below the Al melting point!) reveal only the self-limited growth of an =3-nm-thick interfacial layer of perfect smooth epitaxial wurtzite-structure AlN(0001) which serves as an extremely effective deterrent for preventing further interlayer reactions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Provides information on a study that discussed the defect structure and phase transitions in epitaxial metastable cubic Ti[sub0.5]Al[sub0.5]N alloys grown on MgO(001) by ultra-high-vacuum magnetron sputter deposition. Occurrence of surface-initiated spinodal decomposition; Type of thin films used to increase the lifetimes of mechanical components; Areas where titanium nitride can be applied.

Examines the effect of self-ion energy E[subi] on the surface morphology and the orientation distribution of crystallites. Factors associated with thin film deposition methods; Description of an experiment which analyzes metal film growth on an amorphous substrate; Procedure for the measurement of the statistical properties of the surface roughness; Significant aspects of heteroepitaxial film growth.

V0.6W0.4N alloys are grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering from V and W targets in 10 mTorr pure-N2 atmospheres at temperatures Ts ranging from 600 to 900 °C. Based on x-ray diffraction and transmission electron microscopy results, all films have the B1-NaCl crystal structure and grow with a cube-on-cube epitaxial relationship to the substrate, (001)VWN|(001)MgO and [100]VWN|[100]MgO. Rutherford backscattering spectrometry analyses show that the N content in V0.6W0.4Nx alloys decreases with increasing Ts from overstoichiometric with x = 1.13 at 600 °C, to approximately stoichiometric with x = 1.08 at 700 °C, to understoichiometric at 800 °C (x = 0.80) and 900 °C (x = 0.75). High-resolution scanning transmission electron microscopy, Z-contrast, and selected-area electron diffraction investigations of V0.6W0.4N(001) alloys grown at 600 and 700 °C reveal the onset of W ordering on adjacent 111 planes of the metal sublattice; no ordering is observed for understoichiometric films grown at higher temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Ultrahigh-vacuum dual-target reactive magnetron sputtering, in a mixed Ar/N2 discharge was used to deposit epitaxial single-crystal MAX phase Ti2AlN(0001) thin films, without seed layers, onto Al2O3(0001) substrates kept at 1050°C. By varying the N2 partial pressure a narrow process window was identified for the growth of single-crystal Ti2AlN. The film microstructure was characterized by a combination of X-ray diffraction, spherical aberration (C s) corrected transmission electron microscopy (TEM), high-resolution image simulation and high-resolution scanning TEM. Nitrogen-depleted deposition conditions resulted in the concurrent formation of N-free Ti–Al intermetallics at the film/substrate interface and a steady-state growth of Ti2AlN together with N-free intermetallic phases. At higher N2 partial pressures the growth assumes a columnar epitaxial nature. 1Å resolution of the lattice enabling location of all elements in the Ti2AlN unit cell is demonstrated. [Copyright &y& Elsevier]

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]

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]

We perform large-scale molecular dynamics simulations of TiN deposition at 1200 K on TiN substrates consisting of under-stoichiometric (N/Ti = 0.86) misoriented grains. The energy of incoming Ti atoms is 2 eV and that of incoming N atoms is 10 eV. The simulations show that misoriented grains are reoriented during the early stages of growth, after which the film grows 001 epitaxially and is nearly stoichiometric. The grain reorientation coincides with an increase in film N/Ti ratio. As the grains reorient, additional nitrogen can no longer be accommodated, and the film composition becomes stoichiometric as the overlayer grows epitaxially. • Classical MD is used to model TiN deposition on misoriented grains. • Misoriented grains are reoriented in the early stages of deposition. • The grain reorientation coincides with an increase in the film N/Ti ratio. • The resulting film is epitaxial and stoichiometric. [ABSTRACT FROM AUTHOR]