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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]

We use in situ low-energy electron microscopy to investigate the near-equilibrium dynamics of TiN(111) steps, pinned by surface-terminated dislocations, as a function of N2 pressure pN2 and time during annealing of TiN(111) layers at temperatures T between 1600 and 1735 K. At each T, we observe the nucleation and growth of spiral steps rotating around dislocation cores. The spirals undergo a shape-preserving motion with a constant angular velocity ω as they grow inward, normal to the surface, forming vacancy pits. We find that ω for successive spirals emanating from the same source decreases slowly with time at all pN2 values between vacuum and 5×10-7 Torr. From the ω(T) data, we obtain an activation energy of 4.6±0.2 eV, irrespective of pN2, for the growth of spiral steps. [ABSTRACT FROM AUTHOR]

While many transition metal (TM) nitrides—including TiN, ZrN, and TaN—have been widely studied and are currently used as hard wear-resistant coatings, diffusion barriers, and optical coatings, little is known about a related TM nitride, HfN. Here, we report the results of a systematic investigation of the growth and physical properties of HfNx layers, with 0.80<=x<=1.50, deposited on MgO(001) by ultrahigh vacuum reactive magnetron sputtering at 650 °C in mixed N2/Ar discharges. HfNx layers with 0.80<=x<=1.20 crystallize in the B1–NaCl structure with a cube-on-cube epitaxial relationship to the MgO(001) substrate, while films with 1.24<=x<=1.50 contain a N-rich second phase. The relaxed bulk lattice parameter of HfNx(001) decreases only slightly with increasing N/Hf ratio, ranging from 0.4543 nm with x=0.80 to 0.4517 nm with x=1.20. The room-temperature resistivity ρ of stoichiometric HfN(001) is 14.2 μΩ cm and ρ(x) increases with both increasing and decreasing x to 140 μΩ cm with x=0.80 and 26.4 μΩ cm with x=1.20. The hardness H and elastic modulus E of HfN(001) are 25.2 and 450 GPa, respectively. H(x) initially increases for both over- and understoichiometric layers due to defect-induced hardening, while E(x) remains essentially constant. Single-phase HfNx(001) is metallic with a positive temperature coefficient of resistivity (TCR) between 50 and 300 K and a temperature-independent carrier density. It is also superconducting with the highest critical temperature, 9.18 K, obtained for layers with x=1.00. In the two phase regime, ρ ranges from 59.8 μΩ cm with x=1.24 to 2710 μΩ cm with x=1.50. TCR becomes positive with x>=1.38, no superconducting transition is observed, and both H and E decrease. [ABSTRACT FROM AUTHOR]

Fully strained single-crystal metastable Ge1-xSnx layers were grown on Ge(001) in order to probe the role of Sn dopant and alloy concentrations (CSn=1×1018 cm-3 to 6.1 at. %) on surface roughening pathways leading to epitaxial breakdown during low-temperature (155 °C) molecular-beam epitaxy of compressively strained films. The addition of Sn was found to mediate Ge(001) surface morphological evolution through two competing pathways. At very low Sn concentrations (x<=0.02), the dominant effect is a Sn-induced enhancement in both the Ge surface diffusivity and the probability of interlayer mass transport. This, in turn, results in more efficient filling of interisland trenches, and thus delays epitaxial breakdown. In fact, breakdown is not observed at all for Sn concentrations in the doping regime, 1×1018<=CSn<4.4×1020 cm-3 (2.3×10-5<=x<0.010)! At higher concentrations, there is a change in Ge1-xSnx(001) growth kinetics due to a rapid increase in the amount of compressive strain. This leads to a gradual reduction in the film thickness h1(x) corresponding to the onset of breakdown as strain-induced roughening overcomes the surface smoothening effects, and results in an increase in the overall roughening rate. We show that by varying the Sn concentration through the dopant to dilute alloy concentration range during low-temperature Ge(001) growth, we can controllably manipulate the surface roughening pathway, and hence the epitaxial thickness, over a very wide range. [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]

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]

Density functional methods were used to calculate binding and diffusion energies of adatoms, molecules, and small clusters on TiN(001) and TiN(111) surfaces in order to isolate the key atomistic processes which determine texture evolution during growth of polycrystalline TiN layers. The surface energy for nonpolar TiN(001), 81 meV/Å2, was found to be lower than that of both N- and Ti-terminated TiN(111) polar surfaces, 85 and 346 meV/Å2. While N[sub 2] molecules are only weakly physisorbed, Ti adatoms form strong bonds with both TiN(001), 3.30 eV, and TiN(111), 10.09 eV. Ti adatom diffusion is fast on (001), but slow on (111) surfaces, with calculated energy barriers of 0.35 and 1.74 eV, respectively. The overall results show that growth of 111-oriented grains is favored under conditions typical for reactive sputter deposition. However, the presence of excess atomic N (due, for example, to collisionally induced dissociation of energetic N[sub 2][sup +] ions) leads to a reduced Ti diffusion length, an enhanced surface island nucleation rate, and a lower chemical potential on the (001) surface. The combination of these effects results in preferential growth of 001 grains. Thus our results provide an atomistic explanation for the previously reported transition from 111 to 001 texture observed for sputter deposition of TiN in Ar/N[sub 2] mixtures with increasing N[sub 2] partial pressure P[sub N[sub 2]] and at constant P[sub N[sub 2]] with increasing N[sub 2][sup +]/Ti flux ratios incident at the growing film. © 2003 American Institute of Physics. [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]

In situ surface probes and postdeposition analyses were used to follow surface reaction paths and growth kinetics of Si[sub 1-y]C[sub y] alloys grown on Si(001) by gas-source molecular-beam epitaxy from Si[sub 2]H[sub 6]/CH[sub 3]SiH[sub 3] mixtures as a function of C concentration y (0-2.6 at %) and temperature T[sub s] (500-600°C). High-resolution x-ray diffraction reciprocal lattice maps show that all layers are in tension and fully coherent with their substrates. Film growth rates R decrease with both y and T[sub s], and the rate of decrease in R as a function of y increases rapidly with T[sub s]. In situ isotopically tagged D[sub 2] temperature-programmed desorption (TPD) measurements reveal that C segregation during steady-state Si[sub 1-y]C[sub y](001) growth results in charge transfer from Si surface dangling bonds to second-layer C atoms, which have a higher electronegativity than Si. From the TPD results, we obtain the coverage θ[sub Si[sup *]](y,T[sub s]) of Si[sup *] surface sites with C backbonds as well as H[sub 2] desorption energies E[sub d] from both Si and Si[sup *] surface sites. θ[sub Si[sup *]], increases with increasing y and T[sub s] in the kinetically limited segregation regime while E[sub d] decreases from 2.52 eV for H[sub 2] desorption from Si surface sites with Si back bonds to 2.22 eV from Si[sup *] surface sites. This leads to an increase in the H[sub 2] desorption rate, and hence should yield higher film deposition rates, with increasing y and/or T[sub s] during Si[sub 1-y]C[sub y](001) growth. The effect, however, is more than offset by the decrease in Si[sub 2]H[sub 6] reactive sticking probabilities at Si[sup *] surface sites. Film growth rates R(T[sub s],J[sub Si[sub 2]H[sub 6]],J[sub CH[sub 3]SiH[sub 3]]) calculated using a simple transition-state kinetic model, together with measured kinetic parameters, were found to be in excellent agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Compressively strained Si[sub 0.7]Ge[sub 0.3] layers were grown on Si(001) by gas-source molecular beam epitaxy from Ge[sub 2]H[sub 6]/Si[sub 2]H[sub 6] mixtures at 450°C. The combination of the relatively low growth temperature and high steady-state hydrogen surface coverage, θ[sub H]=0.52 monolayer, completely suppresses strain-induced roughening and provides extremely flat surfaces with root mean square widths w < 1.5 Å for fully coherent layers. These samples were used as the starting point to probe mechanisms that control misfit-dislocation-induced surface roughening (i.e., crosshatch) along 90°-rotated 〈110〉 directions. For film thicknesses t just larger than the critical value for misfit dislocation formation, t[sub c] ... 1000 Å, surface roughness is dominated by single- and multiple-atomic-height steps generated by the motion of threading dislocations associated with interfacial misfits. The surface steps are preferential H desorption sites and the increase in total step length results in a decrease in θ[sub H] on terraces as well as at step edges. The latter effect allows a higher adatom crossing probability at ascending steps, leading to the formation of periodic ridges in response to local strain fields associated with misfit dislocation clusters; w increases from 3.1 Å at t = 1350 Å (corresponding to strain relaxation R of 1%) to 27 Å at t = 4400 Å (R = 78%). Simultaneously, the decrease in θ[sub H] on terraces strongly affects film growth kinetics as the deposition rates increase from 10 Å min[sup -1] with t

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]

We use a combination of in situ and postdeposition experimental probes together with ab initio calculations of strain coefficients and formation energies associated with specific C configurations in the Si lattice to determine C incorporation pathways and lattice site distributions in fully coherent Si[sub 1-y]C[sub y] alloy layers grown by molecular-beam epitaxy on Si(001) as a function of deposition temperature T[sub s] (380 °C–680 °C) and C fraction y (0–0.026). Lattice strain and Raman spectroscopy measurements demonstrate that all C, irrespective of y, is incorporated into substitutional lattice sites in Si[sub 1-y]C[sub y](001) layers grown at T[sub s]≤480 °C. Increasing T[sub s]>=580 °C leads to strong C surface segregation, as shown by in situ angle-resolved x-ray photoelectron spectroscopy, yielding additional pathways for C incorporation. Photoluminescence measurements indicate that an increasing fraction of the incorporated C in the higher-temperature layers resides in dicarbon complexes. Reflection high-energy electron diffraction and cross sectional transmission electron microscopy reveal surface roughening at T[sub s]>=580 °C with the formation of bulk planar structures, interconnected by {113} segments, that are periodic along [001] with a periodicity which decreases with increasing T[sub s]. We interpret the planar structures as layers of C-rich Si[sub 1-y]C[sub y] which form in the presence of excess surface C resulting from segregation. Our ab initio density functional calculations show that substitutional C arranged in an ordered Si[sub 4]C phase is 0.34 eV per C atom more stable than isolated substitutional C atoms. © 2002 American Institute of Physics. [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]

Fully-coherent Si[sub 0.7]Ge[sub 0.3] layers were deposited on Si(001) by gas-source molecular beam epitaxy (GS-MBE) from Ge[sub 2]H[sub 6]/Si[sub 2]H[sub 6] mixtures in order to probe the effect of steady-state hydrogen coverages θ[sub H] on surface morphological evolution during the growth of compressively strained films. The layers are grown as a function of thickness t at temperatures, T[sub s]=450–550 °C, for which strain-induced roughening is observed during solid-source MBE (SS-MBE) and deposition from hyperthermal beams. With GS-MBE, we obtain three-dimensional (3D) strain-induced growth mounds in samples deposited at T[sub s]=550 °C for which θ[sub H] is small, 0.11 monolayer (ML). However, mound formation is dramatically suppressed at 500 °C (θ[sub H]=0.26 ML) and completely eliminated at 450 °C (θ[sub H]=0.52 ML). We attribute these large differences in surface morphological evolution primarily to θ[sub H](T[sub s])-induced effects on film growth rates R, adatom diffusion rates D[sub s], and ascending step-crossing probabilities. GS-MBE Si[sub 0.7]Ge[sub 0.3](001) growth at 450 °C remains two dimensional, with a surface width <0.15 nm, at all film thicknesses t=11–80 nm, since both R and the rate of mass transport across ascending steps are low. Raising T[sub s] to 500 °C increases R faster than D[sub s] leading to shorter mean surface diffusion lengths and the formation of extremely shallow, rounded growth mounds for which remains essentially constant at =0.2 nm while the in-plane coherence length increases from =70 nm at t=14 nm to 162 nm with t=75 nm. The low ascending step crossing probability at 500 °C results in mounds that spread laterally, rather than vertically, due to preferential attachment at the mound edges. At T[sub s]=550 °C, the ascending step crossing probability increases due to both higher thermal activation and lower hydrogen coverages. ... [ABSTRACT FROM AUTHOR]

Epitaxial metastable Ge[sub 1-y]C[sub y] alloy layers with y≤0.045 were grown on Ge(001) by solid-source molecular-beam epitaxy (MBE) at temperatures T[sub s]=200–400 °C. Using calculated strain coefficients and measured layer strains obtained from high-resolution reciprocal lattice maps (HR-RLMs), we determine C lattice site distributions as a function of T[sub s] and total C concentration y. HR-RLMs show that all as-deposited alloys are fully coherent with their substrates. Ge[sub 1-y]C[sub y](001) layers grown at T[sub s]≤350 °C are in a state of in-plane tension and contain C in substitutional sites, giving rise to tensile strain, as well as in nanocluster sites which induce negligible lattice strain. T[sub s]=400 °C layers are strain neutral with negligible substitutional C incorporation. Increasing y and/or T[sub s] leads to a decrease in substitutional C concentration, consistent with Raman spectroscopy results, with a corresponding increase in the C fraction incorporated in nanocluster sites. The latter suggests that nanocluster formation is kinetically limited during film deposition by the C–C adatom encounter probability at the growth surface. Overall, the results show that it is not possible by MBE to obtain fully substitutional C incorporation in Ge[sub 1-y]C[sub y](001) alloys, irrespective of y and T[sub s]. This is consistent with ab initio density functional calculations results showing that C incorporation in nanoclusters sites is energetically favored over incorporation in substitutional Ge lattice sites. Annealing the Ge[sub 1-y]C[sub y](001) layers at T[sub a]=550 °C leads to a significant decrease in the substitutional C fraction and, hence, lower tensile strain. Layers annealed at 650 °C are strain free as all substitutional C has migrated to lower-energy nanocluster sites. © 2002 American Institute of Physics. [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]

Si[sub 1-x]Ge[sub x](001) layers doped with B concentrations C[sub B] between 2x10[sup 16] and 2x10[sup 21] cm[sup -3] were grown on Si(001)2x1 at T[sub s]=500-700 °C by gas-source molecular-beam epitaxy (GS-MBE) from Si[sub 2]H[sub 6], Ge[sub 2]H[sub 6], and B[sub 2]H[sub 6]. Secondary-ion mass spectrometry measurements of modulation-doped structures demonstrate that B doping has no effect on the Ge incorporation probability. Steady-state B and Ge surface coverages (θ[sub B] and θ[sub Ge]) were determined as a function of C[sub B] using in situ isotopically tagged temperature-programmed desorption. Results for Si[sub 0.82]Ge[sub 0.18] layers grown at T[sub s]=500 °C show that θ[sub Ge] remains constant at 0.63 ML while the bulk B concentration increases linearly up to 4.6x10[sup 20] cm[sup -3], corresponding to saturation coverage at θ[sub B,sat]=0.5 ML, with the incident precursor flux ratio ξ=J[sub B[sub 2]H[sub 6]]/(J[sub Si[sub 2]H[sub 6]]+J[sub Ge[sub 2]H[sub 6]]). B is incorporated into substitutional electrically active sites over this entire concentration range. At higher B concentrations, C[sub B] increases faster than ξ and there is a large decrease in the activated fraction of incorporated B. The B segregation enthalpy during Si[sub 0.82]Ge[sub 0.18](001) growth is -0.42 eV, compared to -0.53 and -0.64 eV during Si(001):B and Ge(001):B GS-MBE, respectively. Measured segregation ratios r[sub B]=θ[sub B]/x[sub B], where x[sub B] is the bulk B fraction, range from 15 to 500 with a temperature dependence which is consistent with equilibrium segregation. Film deposition rates R[sub SiGe](C[sub B]) decrease by up to a factor of 2 with increasing C[sub B]>=5x10[sup 19] cm[sup -3], due primarily to a B-segregation-induced decrease in the dangling bond density. The above results were used to develop a robust model for predicting the steady-state H coverage θ[sub H], θ[sub B], θ[sub Ge], and R... [ABSTRACT FROM AUTHOR]

Single crystalline Sc[sub 1-x]Ti[sub x]N layers, with compositions spanning the entire range (0≤x≤1), were grown on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition at 750 °C. Optical transmission and reflectivity spectra are well described by a Drude-Lorentz model. The optical carrier density N[sup *] increases linearly from 1.0x10[sup 21] for ScN to 4.6x10[sup 22] cm[sup -3] for TiN while the room-temperature electrical resistivity ρ[sub 300K] varies by more than 2 orders of magnitude, from 2x10[sup -3] Ω cm for ScN to 13 μΩ cm for TiN. ρ[sub 300K] agrees well with optically determined resistivity values for alloys with compositions up to x=0.66, corresponding to the onset of electron filling in the second and third conduction bands. We calculated ScN and TiN band structures by ab initio density functional methods and used the results to simulate the field responses of free carriers in the Sc[sub 1-x]Ti[sub x]N layers. From this, we determined, in combination with the measured temperature dependence of the resistivity, the low-temperature carrier relaxation time τ(x). The composition dependence of τ is dominated by alloy scattering and agrees well with our measured optical results. Hall experiments were used to obtain the effective carrier density N[sub eff](x) which increases linearly with x up to x=0.4. N[sub eff](x) is relatively flat for alloy compositions between x=0.4 and 0.7, due to anisotropies in the conduction band, and exhibits a steep increase at x>0.7 as higher lying conduction bands begin to be occupied. Our simulated Sc[sub 1-x]Ti[sub x]N electronic transport properties are in good agreement with experiment. Interband optical absorption results can also be understood based upon the calculated band structures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The 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). Co was deposited by ultrahigh-vacuum magnetron sputtering and CoSi2 formed at 600 degree Celsius.

Single-crystal NaCl-structure delta-TiNx layers with x raging from 0.67 to 1.00 are grown at 700 degree C by ultra-high-vacuum magnetron sputtering of Ti in mixed Ar/N2 discharges to investigate microstructural evolution and the physical properties of TiNx as a function of the N vacancy concentration. Findings show that room-temperature resistivity, 13 Mu Omega cm with x=1.00, increases from 53 Mu Omega cm for TiNx(001) layers with x=0.92 to 192 Mu Omega cm with x=0.67, due primarily to increased carrier scattering from N vacancies.

Studies tungsten (W) deposition and titanium fluoride formation during WF... reduction by titanium using backscattering spectroscopy, scanning and high-resolution transmission electron microscopy and other methods. Experimental procedure; Results and discussion; Conclusions.

Refractory transition-metal diborides exhibit inherent hardness. However, this is not always sufficient to prevent failure in applications involving high mechanical and thermal stress, since hardness is typically accompanied by brittleness leading to crack formation and propagation. Toughness, the combination of hardness and ductility, is required to avoid brittle fracture. Here, the authors demonstrate a strategy for simultaneously enhancing both hardness and ductility of ZrB2-rich thin films grown in pure Ar on Al2O3(0001) and Si(001) substrates at 475 °C. ZrB2.4 layers are deposited by dc magnetron sputtering (DCMS) from a ZrB2 target, while Zr1−xTaxBy alloy films are grown, thus varying the B/metal ratio as a function of x, by adding pulsed high-power impulse magnetron sputtering (HiPIMS) from a Ta target to deposit Zr1−xTaxBy alloy films using hybrid Ta-HiPIMS/ZrB2-DCMS sputtering with a substrate bias synchronized to the metal-rich portion of each HiPIMS pulse. The average power P Ta (and pulse frequency) applied to the HiPIMS Ta target is varied from 0 to 1800 W (0 to 300 Hz) in increments of 600 W (100 Hz). The resulting boron-to-metal ratio, y = B/(Zr+Ta), in as-deposited Zr1−xTaxBy films decreases from 2.4 to 1.5 as P Ta is increased from 0 to 1800 W, while x increases from 0 to 0.3. A combination of x-ray diffraction (XRD), glancing-angle XRD, transmission electron microscopy (TEM), analytical Z-contrast scanning TEM, electron energy-loss spectroscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and atom-probe tomography reveals that all films have the hexagonal AlB2 crystal structure with a columnar nanostructure, in which the column boundaries of layers with 0 ≤ x < 0.2 are B-rich, whereas those with x ≥ 0.2 are Ta-rich. The nanostructural transition, combined with changes in average column widths, results in an ∼20% increase in hardness, from 35 to 42 GPa, with a simultaneous increase of ∼30% in nanoindentation toughness, from 4.0 to 5.2 MPa√m. [ABSTRACT FROM AUTHOR]

Context. An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs). Aims. The project examines the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks to investigate any possible connection between these disks and the radio continuum. Methods. We observed a sample of 18 LLAGNs in the 4.8 GHz (6 cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3–6.5 ms resolution. The sources were selected to show both an edge-on accretion disk revealed by 22 GHz H2O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33 GHz radio continuum observations made with the Very Large Array. Results. Five out of 18 galaxies observed were detected at 8σ or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273, and UGC 3193). While these five sources are known to have maser disks, four of them exhibit a maser disk with known orientation. For all four of these sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32° of the maser disk's normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5 GHz VLBA radio continuum and the [OIII] luminosity and also with the H2O maser disk's inner radius. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the mechanisms for the low-temperature growth of crytalline germanium and silicon films from germanium hydroxide and silicon hydrogen[sub4]. Model for the epitaxial growth of germanium from germanium hydrogen[sub4]; Discussion of the hydroxide desorption process; Conclusions.