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Single-crystal metastable Bl-NaCl-structure delta-TaN(sub x) layers with x ranging from 0.94 to 1.37 were grown on MgO(001) at T(sub s)=600degreeC by UHV magnetically unbalanced reactive magnetron sputter deposition. All layers exhibited an epitaxial cube-on-cube relationship with the substrate: (001)(sub TaN)//(001)(sub MgO) and [100](sub TaN)//[100](sub MgO)

Epitaxial NaCl-structure δ-TiNx(001) layers, with x ranging across the single-phase compound field from 0.67 to 1.00, are grown on MgO(001) and analyzed by Raman spectroscopy. All samples, including stoichiometric TiN(001), exhibit first-order Raman peaks, which are forbidden by the Oh symmetry of NaCl-structure compounds. Thus, even stoichiometric TiN contains point defects, primarily N and Ti vacancies, consistent with previous electronic transport measurements. However, the presence of a well-resolved second-order longitudinal acoustic line at 615 cm-1 shows that the defect concentration is relatively low. The positions of the first-order acoustic lines are in good agreement with values obtained from calculated phonon density of states. As the N/Ti ratio x in TiNx and, hence, the number n of valence electrons per formula unit (n = 9 for stoichiometric TiN) decreases, the first-order acoustic lines shift to higher frequencies, due to the corresponding decrease in phonon anomalies associated with the acoustic branch. This is in agreement with the observed increase in the intensities of the first-order acoustic phonon peak with decreasing x, characteristic of a higher average N vacancy concentration adjacent to Ti atoms. However, the presence of antisite defects is also required to explain the frequency shift of the optical modes in under-stoichiometric TiNx. [ABSTRACT FROM AUTHOR]

Single-crystal group-V δ-TaNx transition-metal (TM) nitride layers, with x ranging from 0.94 to 1.37, are grown on MgO(001) and analyzed by Raman spectroscopy. In perfect NaCl-structure crystals, the first-order Raman modes are not allowed by the Oh crystal symmetry. Since first-order acoustic and optical bands are observed for all δ-TaNx samples, this indicates the presence of point defects, even for stoichiometric TaN. The large mass difference between Ta and N leads to a correspondingly large separation between the first-order acoustic and optical bands centered at 150 and 550 cm-1, respectively. A Raman peak at 440 cm-1, overlapping the first-order optical band, is identified as the difference between the first-order optical and acoustic modes. Contrary to the case for most TM nitrides, there is no peak visible in the second-order high-frequency range (700–1500 cm-1). In addition, the first-order transverse (120 cm-1) and longitudinal acoustic peaks (175 cm-1) do not exhibit the frequency shift with N/Ta ratio x (i.e., with the valence electron density) that has been reported for group-IV TM nitrides. This is consistent with the resistivity of TaNx remaining essentially constant, as well as with the very weak dependence of the lattice parameter as a function of the N/Ta ratio, and suggests that the wide single-phase region in this system is due to the presence of isoelectronic antisite substitutions rather than, as has been proposed previously, cation and anion vacancies. [ABSTRACT FROM AUTHOR]

CaF2-structure CoSi2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi2 layers obtained by conventional solid phase growth (SPG). In both sets of experiments, Co was deposited by ultrahigh-vacuum magnetron sputtering and CoSi2 formed at 600 °C. However, in the case of RDE, CoSi2 formation occurred during Co deposition while for SPG, Co was deposited at 25 °C and silicidation took place during subsequent annealing. X-ray diffraction pole figures and transmission electron microscopy results demonstrate that RDE CoSi2 layers are epitaxial with a cube-on-cube relationship, (001)CoSi2∥(001)Si and [100]CoSi2∥[100]Si. In contrast, SPG films are polycrystalline with an average grain size of ≃1000 Å and a mixed 111/002/022/112 orientation. We attribute the striking difference to rapid Co diffusion into the Si(001) substrate during RDE for which the high Co/Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. In contrast, sequential nucleation and transformation among increasingly Si-rich phases—from orthorhombic Co2Si to cubic CoSi to CoSi2—during SPG results in polycrystalline layers with a complex texture. [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]

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]

We have investigated the effects of low-energy ion irradiation on texture evolution during growth of B1-NaCl-structure polycrystalline δ-TaN layers on SiO[SUB2] by ultra-high-vacuum reactive magnetron sputter deposition at 350 °C in mixed Ar + 15%N[SUB2] discharges. In parallel sets of experiments, the ion-to-metal flux ratio J[SUBi]/J[SUBTa] was varied from 1.3 to 10.7 while maintaining the incident ion energy E[SUBi] constant at 20 eV, and E[SUBi] was varied from 8.5 to 30 eV with J[SUBi]/J[SUBTa]= 10.7. All TaN layers, irrespective of J[SUBi]/J[SUBTa] or E[SUBi], were overstoichiometric with N/Ta= 1.13±0.03. Layers grown with E[SUBi] = 30 eV are multiphase consisting of hexagonal ε-TaN and δ-TaN, while those grown with E[SUBi] &les;20 eV are single-phase δ-TaN. With E[SUBi] = 8.5 eV, the δ-TaN layers have a mixed 111/002/022/113 texture, even for film thicknesses t up to 500 nm. In contrast, δ-TaN layers deposited with E[SUBi] =20 eV initially exhibit competitive texture evolution until a single texture dominates at t &gsim;200 nm. The preferred orientation of 500-nm-thick E[SUBi]=20 eV layers can be selectively and continuously varied from predominantly 111 to nearly complete 002 by increasing J[SUBi]/J[SUBTa] from 1.3 to &ges; 7.4. The change in texture is primarily due to an increased steady-state atomic N coverage, resulting from collisionally induced dissociative chemisorption of incident energetic N[SUP+,SUB2] ions, with increasing J[SUBi]/J[SUBTa]. 111-oriented δ-TaN layers are underdense with both inter- and intracolumnar porosity and a tensile stress of ≃ 1.4 GPa, while 002-oriented layers are fully dense and have small compressive stresses, &lsim; 0.7 GPa. [ABSTRACT FROM AUTHOR]

B1–NaCl-structure CrN(001) layers were grown on MgO(001) at 600 °C by ultrahigh vacuum reactive magnetron sputter deposition in pure N[sub 2] discharges. X-ray diffraction analyses establish the epitaxial relationship as cube-on-cube, (001)[sub CrN]||(001)[sub MgO] with [100][sub CrN]||[100][sub MgO], while temperature-dependent measurements show that the previously reported phase transition to the orthorhombic P[sub nma] structure is, due to epitaxial constraints, absent in our layers. The resistivity increases with decreasing temperature, from 0.028 Ω cm at 400 K to 271 Ω cm at 20 K, indicating semiconducting behavior with hopping conduction. Optical absorption is low (α<2×10[sup 4] cm[sup -1]) for photon energies below 0.7 eV and increases steeply at higher energies. In situ ultraviolet photoelectron spectra indicate that the density of states vanishes at the Fermi level. The overall results provide evidence for CrN exhibiting a Mott–Hubbard type band gap. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

CrN layers, 0.5 μm thick, were grown on MgO(001) at T[sub s]=570–775 °C by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition in pure N[sub 2] discharges at 20 mTorr. Layers grown at T[sub s]≤700 °C are stoichiometric single crystals exhibiting cube-on-cube epitaxy: (001)[sub CrN]||(001)[sub MgO] with [100][sub CrN]||[100][sub MgO]. At higher temperatures, N[sub 2] desorption during deposition results in understoichiometric polycrystalline films with N fractions decreasing to 0.35, 0.28, and 0.07 with T[sub s]=730, 760, and 775 °C, respectively. The surface morphologies of epitaxial CrN(001) layers were found to depend strongly on the incident ion-to-metal flux ratio J[sub N[sub 2][sup +]]/J[sub Cr] which was varied between 1.7 and 14 with the ion energy maintained constant at 12 eV. The surfaces of layers grown with J[sub N[sub 2][sup +]]/J[sub Cr]=1.7 consist of self-organized square-shaped mounds, due to kinetic roughening, with edges aligned along orthogonal <100> directions. The mounds have an average peak-to-valley height =5.1 nm and an in-plane correlation length of =0.21 μm. The combination of atomic shadowing by the mounds with low adatom mobility results in the formation of nanopipes extending along the growth direction. Increasing J[sub N[sub 2][sup +]]/J[sub Cr] to 14 leads, due to increased adatom mobilities, to much smoother surfaces with =2.5 nm and =0.52 μm. Correspondingly, the nanopipe density decreases from 870 to 270 μm[sup -2] to <20 μm[sup -2] as J[sub N[sub 2][sup +]]/J[sub Cr] is increased from 1.7 to 6 to 10. The hardness of dense CrN(001) is 28.5±1 GPa, but decreases to 22.5±1 GPa for layers containing significant nanopipe densities. The CrN(001) elastic modulus, 405±15 GPa, room-temperature resistivity, 7.7×10[sup -2] Ω cm, and relaxed lattice constant, 0.4162±0.0008 nm, are independent of J[sub N[sub 2][sup +]]/J[sub Cr].... [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]

Presents a study that examined the structural and optical properties of zinc telluride (ZnTe)/gallium arsenide (GaAs) heterostructures grown by temperature-gradient vapor deposition. Methodology; Analysis of the lattice mismatched between the ZnTe epitaxial layer and the GaAs substrate; Examination of the reflectivity and photoreflectance measurements of the heterostructure.

While metastable B1-NaCl-structure δ-TaN[sub x] is presently used in a variety of hard coating, wear-resistant, and diffusion barrier applications, it is a complex material exhibiting a wide single-phase field, x=0.94–1.37, and little is known about its fundamental properties. Here, we report physical properties of epitaxial δ-TaN[sub x] layers grown as a function of x on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition. The room-temperature resistivity (ρ=225 μΩ cm), hardness (H=30.9 GPa), and elastic modulus (E=455 GPa) of δ-TaN[sub x](001) are independent of x over the range 0.94–1.22. However, changes in the electronic structure associated with increasing x>1.22 lead to an increase in ρ with a decrease in H and E. All δ-TaN[sub x](001) layers exhibit negative temperature coefficients of resistivity between 20 and 400 K due to weak carrier localization. δ-TaN[sub x] is superconducting with the highest critical temperature, 8.45 K, obtained for layers with the lowest N/Ta ratio, x=0.94. Based upon the above results, combined with the fact that the relaxed lattice constant a[sub 0] shows only a very weak dependence on x, we propose that the wide phase field in δ-TaN[sub x] is due primarily to antisite substitutions of Ta on N (and N on Ta) sites, rather than to cation and anion vacancies. To first order, antisite substitutions in TaN[sub x] are isoelectronic and hence have little effect on charge carrier density. At sufficiently high N/Ta ratios, however, simple electron-counting arguments are no longer valid since large deviations from stoichiometry alter the character of the band structure itself. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]