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The quest for lowering energy consumption during thin film growth by magnetron sputtering techniques becomes of particular importance in view of sustainable development goals. As large fraction of the process energy is consumed in substrate heating for the purpose of providing high adatom mobility necessary to grow dense films, the most straightforward strategy toward more environment-friendly processing is to find alternatives to thermally activated surface diffusion. One possibility is offered by high mass metal ion irradiation of the growing film surface, which has been recently shown to be very effective in densification of transition metal nitride layers grown with no external heating, such that Zone 2 microstructures of the structure-zone model are obtained in the substrate temperature Ts range otherwise typical for Zone 1 growth. The large mass difference between the incident ion and the atoms constituting the film results in effective creation of low energy recoils, which leads to film densification at low Ts. Due to their high mass, metal ions become incorporated at lattice sites beyond the near-surface region of intense recoil generation leading to further densification, while preventing the buildup of residual stress. The practical implementation of this technique discussed in this Perspective employs heavy metal targets operating in the high-power impulse magnetron sputtering (HiPIMS) mode to provide periodic metal-ion fluxes that are accelerated in the electric field of the substrate to irradiate layers deposited from direct current magnetron sputtering (DCMS) sources. A key feature of this hybrid HiPIMS/DCMS configuration is the substrate bias that is synchronized with heavy metal ion fluxes for selective control of their energy and momentum. As a consequence, the major fraction of process energy is used at sputtering sources and for film densification, rather than for heating of the entire vacuum vessel. Model material systems include TiN and metastable NaCl-structure Ti1−yAlyN films, which are well-known for challenges in stoichiometry and phase stability control, respectively, and are of high relevance for industrial applications. This Perspective provides a comprehensive overview of the novel film growth method. After presenting basic concepts, time-resolved measurements of ion fluxes at the substrate plane, essential for selective control of metal ion energy and momentum, are discussed. The role of metal ion mass, energy, momentum, and concentration is described in more detail. As some applications require substrate rotation for conformal coating, a section is devoted to the related complexity in the implementation of metal-ion-synchronized growth under industrial conditions. [ABSTRACT FROM AUTHOR]

Hard Ti1-xAlxN thin films are of importance for metal-cutting applications. The hardness, thermal stability, and oxidation resistance of these coatings can be further enhanced by alloying with TaN. We use a hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) technique to grow dense and hard Ti0.41Al0.51Ta0.08N alloys without external heating (Ts<150 °C). Separate Ti and Al targets operating in the DCMS mode maintain a deposition rate of ~50 nm/min, while irradiation of the growing film by heavy Ta+/Ta2+ ions from the HIPIMS-powered Ta target, using dc bias synchronized to the metal-ion-rich part of each HIPIMS pulse, provides effective near-surface atomic mixing resulting in densification. The substrate is maintained at floating potential between the short bias pulses to minimize Ar+ bombardment, which typically leads to high compressive stress. Transmission and scanning electron microscopy analyses reveal dramatic differences in the microstructure of the co-sputtered HIPIMS/DCMS films (Ta-HIPIMS) compared to films with the same composition grown at floating potential with all targets in the DCMS mode (Ta-DCMS). The Ta-DCMS alloy films are only ~70% dense due to both inter- and intra-columnar porosity. In contrast, the Ta-HIPIMS layers exhibit no inter-columnar porosity and are essentially fully dense. The mechanical properties of Ta-HIPIMS films are significantly improved with hardness and elastic modulus values of 28.0 and 328 GPa compared to 15.3 and 289GPa for reference Ta-DCMS films. [ABSTRACT FROM AUTHOR]

For the investigation of 2D layered materials such as graphene, transition-metal dichalcogenides, boron nitride, and their heterostructures, dedicated substrates are required to enable unambiguous identification through optical microscopy. A systematic study is conducted, focusing on various 2D layered materials and substrates. The simulated colors are displayed and compared with microscopy images. Additionally, the issue of defining an appropriate index for measuring the degree of visibility is discussed. For a wide range of substrate stacks, layer thicknesses for optimum visibility are given along with the resulting sRGB colors. Further simulations of customized stacks can be conducted using our simulation tool, which is available for download and contains a database featuring a wide range of materials. [ABSTRACT FROM AUTHOR]

Elastic constants are determined for single-crystal stoichiometric NaCl-structure VN(001), VN(011), and VN(111) epitaxial layers grown by magnetically unbalanced reactive magnetron sputter deposition on 001-, 011-, and 111-oriented MgO substrates at 430 °C. The relaxed lattice parameter ao=0.4134±0.0004 nm, obtained from high-resolution reciprocal space maps, and the mass density ρ=6.1 g/cm³, determined from the combination of Rutherford backscattering spectroscopy and film thickness measurements, of the VN layers are both in good agreement with reported values for bulk crystals. Sub-picosecond ultrasonic optical pump/probe techniques are used to generate and detect VN longitudinal sound waves with measured velocities v001=9.8±0.3, v011±9.1±0.3, and v111=9.1±0.3 km/s. The VN c11 elastic constant is determined from the sound wave velocity measurements as 585±30 GPa; the c44 elastic constant, 12663 GPa, is obtained from surface acoustic wave measurements. From the combination of c11, c44, vhkl, and ρ we obtain the VN c12 elastic constant 178±33 GPa, the VN elastic anisotropy A=0.62, the isotropic Poisson ratio v=0.29, and the anisotropic Poisson ratios v001=0.23, v011=0.30, and v111=0.29. [ABSTRACT FROM AUTHOR]

Transport electron/phonon coupling parameters and Eliashberg spectral functions αtr2F(hω) are determined for group-IV transition-metal (TM) nitrides TiN, ZrN, and HfN, and the rare-earth (RE) nitride CeN using an inversion procedure based upon temperature-dependent (4 < T < 300 K) resistivity measurements of high-crystalline-quality stoichiometric epitaxial films grown on MgO(001) by magnetically-unbalanced reactive magnetron sputtering. Transport electron/phonon coupling parameters λtr vary from 1.11 for ZrN to 0.82 for HfN, 0.73 for TiN, and 0.44 for CeN. The small variation in λtr among the TM nitrides and the weak coupling in CeN are consistent with measured superconducting transition temperatures 10.4 (ZrN), 9.18 (HfN), 5.35 (TiN), and <4 K for CeN. The Eliashberg spectral function describes the strength and energy spectrum of electron/phonon coupling in conventional superconductors. Spectral peaks in α2F(hω), corresponding to regions in energy-space for which electrons couple to acoustic hωac and optical hωop phonon modes, are centered at hωac = 33 and hωop = 57 meV for TiN, 25 and 60 meV for ZrN, 18 and 64 meV for HfN, and 21 and 39 meV for CeN. The acoustic modes soften with increasing cation mass; optical mode energies remain approximately constant for the TM nitrides, but are significantly lower for the RE nitride due to a lower interatomic force constant. Optical/acoustic peak-intensity ratios are 1.15 ± 0.1 for all four nitrides, indicating similar electron/phonon coupling strengths αtr(hω) for both modes. [ABSTRACT FROM AUTHOR]

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]

The predeposition of P, with coverages θP ranging from 0 to 1 ML, on Si(001) significantly increases both the areal density and spatial self-organization of Ge islands grown by gas-source molecular beam epitaxy from hydride precursors. The Ge island density ρGe initially increases with θP, reaching a maximum of 1.4 × 1010 cm-2 at θP = 0.7 ML, a factor of four times higher than on bare Si(001) under the same deposition conditions, before decreasing at higher P coverages. The increase in ρGe(θP) is due to a corresponding decrease in Ge adatom mean free paths resulting from passivation of surface dangling bonds by adsorbed pentavalent P atoms which, in addition, leads to surface roughening and, therefore, higher Ge coverages at constant Ge2H6 dose. As θP (and hence, ρGe) increases, so does the degree of Ge island ordering along <100> directions due to the anisotropic strain field surrounding individual islands. Similar results are obtained for Ge island growth on P-doped Si(001) layers where strong P surface segregation provides partial monolayer coverage prior to Ge deposition. [ABSTRACT FROM AUTHOR]

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]

The effects of P doping on growth kinetics and surface morphological evolution during Si(001):P gas-source molecular beam epitaxy from Si2H6 and PH3 at temperatures Ts=500–900 °C have been investigated. With increasing PH3/Si2H6 flux ratio JP/Si at constant Ts, we observe a decrease in the film growth rate R and an increase in the incorporated P concentration CP, both of which tend toward saturation at high flux ratios, which is accompanied by increased surface roughening and pit formation. At constant JP/Si, R increases with increasing Ts, while CP initially increases, reaches a maximum at Ts=700 °C, and then decreases at higher growth temperatures. We use in situ isotopically tagged D2 temperature programed desorption (TPD) to follow changes in film surface composition and dangling bond density θdb as a function of JP/Si and Ts. Measurements are carried out on both as-deposited Si(001):P layers and P-adsorbed Si(001) surfaces revealing β1 and β2 peaks due to D2 desorption from Si monohydride and dihydride species, respectively, as well as the formation of a third peak β3 corresponding to D2 desorption from mixed Si[Single_Bond]P dimers. Dissociative PH3 adsorption on Si(001) results in a decrease in θdb and an initial increase in P surface coverage θP with increasing Ts. Saturation θP values reach a maximum of ∼1 ML at Ts=550 °C, and decrease with Ts>600 °C due to the onset of P2 desorption. Comparison of θP(Ts) results obtained during film growth with postdeposition CP(Ts) results reveals the presence of strong P surface segregation. From measurements of θP versus CP in Si(001):P layers grown as a function of Ts, we obtain a P segregation enthalpy ΔHs=-0.86 eV. By using the combined set of results, we develop a predictive model for CP versus Ts and, JP/Si incorporating the dependence of the PH3 reactive sticking probability SPH3 on θP, which provides an excellent fit to the experimental data. [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]

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]

Nanocrystalline films with high hardness have attracted increasing interest for wear resistant applications. Specifically, nanocrystalline Ti–B–N layers have been demonstrated to exhibit enhanced hardness and thermal stability. Here, we show that Ti–B–N films grown at 300 °C and consisting of a high volume fraction, ∼50%, of a fully percolated disordered phase encapsulating 2–3 nm wide TiN and TiB2 grains, have a hardness of 37 GPa and an elastic modulus of 332 GPa which increase with annealing to 43 and 362 GPa, respectively, at Ta=800 °C. The structural rearrangement which occurs during annealing results in the formation of compact interface boundaries which lead, in turn, to the observed hardness increase. Annealing at Ta>900 °C decreases the hardness, although the elastic modulus continues to increase, due to the combination of grain growth and B loss via the formation of volatile boron oxides and hydroxides. These conclusions, obtained based upon a combination of x-ray diffraction, nanoindentation, electron probe microanalysis, and transmission electron microscopy, are corroborated by calorimetric investigations. The overall results provide insight toward developing “design rules” for high-temperature superhard nanoscale based coatings. [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]

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]

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]

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]

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]

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]

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]

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]

Presents a study which reported results on the growth by reactive magnetron sputter deposition of nitride crystals. Characteristics of transition-metal nitrides; Methodology; Results and discussion; Conclusions.

Presents a study which demonstrated the growth of low-temperature fully dense polycrystalline titanium nitride (TiN) layers. Application of TiN diffusion barriers; Preparation of TiN thin films; Results of the study.

Provides information on a study which investigated the effects of low-energy N2... ion irradiation on microstructural and texture evolution, as well as the mechanical properties, of polycrystalline and epitaxial ScN layers grown on MgO(001). Experimental procedure; Results and discussion; Conclusions.

Investigates interfacial reaction paths and kinetics during annealing of Al/W and Al/TixW1-x bilayers sputter deposited in both Ar and Xe. Observed increases in WAl4 nucleation and growth rates; Ar and Xe discharges; Incorporation of Ti concentration; Interfacial blocking layer.

Reports that polycrystalline bcc W layers were grown on amorphous-SiO2/Si(001) substrates by ultrahigh vacuum magnetron sputter deposition. As-deposited Al/W bilayers; Annealed Al/W bilayers; Interfacial reaction pathway during the annealing of polycrystalline Al/W bilayers; Role of W surface orientation and grain boundaries on Al/W bilayer interaction kinetics.

Deals with a study that examined the reaction paths and kinetics of aluminide formation in aluminum/epitaxial-W(001) model diffusion barrier systems. Importance of understanding the microchemical and microstructural interfacial reaction paths affecting the integrity of layers used in applications; Changes in bilayer sheet resistance; Determination of reaction kinetics and activation energies.

Investigates the effects of incident ion/metal flux ratio J[subi]/J[subMe] and ion energy E[subi] on the microstructure, texture and phase composition of polycrystalline metastable Ti[0.5]Al[0.5]N films produced by reactive magnetron sputtering. Description of the polycrystalline metastable Ti[0.5]Al[0.5]N films; Analysis of the microstructures of as-deposited alloys using a combination of x-ray diffractometry and transmission electron microscopy.

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.

Presents a study on morphology and microstructure of tensile-strained thin epitaxial films by in situ scanning tunnelling microscopy. Methodology used to grow Si0.6Ge0.4 alloy films; Details on the strain relaxation plotted as a function of film thickness; Examination of the cross-sectional TEM micrograph.

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.

Presents information on a study which analyzed the effects of the incident ion/metal flux ratio on the microstructure, texture and stoichiometry of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputtering. Experimental procedure; Probe measurements; Results of TiN stoichiometry.

The authors report the growth and mechanical properties of epitaxial B1 NaCl-structure V1-xWxN/MgO(001) thin films with 0≤x≤0.60. The Gibbs free energy of mixing, calculated using density functional theory (DFT), reveals that cubic V1-xWxN solid solutions with 0≤x ≲ 0.7 are stable against spinodal decomposition and separation into the equilibrium cubic-VN and hexagonal-WN binary phases. The authors show experimentally that alloying VN with WN leads to a monotonic increase in relaxed lattice parameters, enhanced nanoindentation hardnesses, and reduced elastic moduli. Calculated V1-xWxN lattice parameters and elastic moduli (obtained from calculated C11, C12, and C44 elastic constants) are in good agreement with experimental results. The observed increase in alloy hardness, with a corresponding decrease in the elastic modulus at higher x values, combined with DFT-calculated decreases in shear to bulk moduli ratios, and increased Cauchy pressures (C12-C44) with increasing x reveal a trend toward increased toughness. [ABSTRACT FROM AUTHOR]

Single-crystal ZrN films, 830 nm thick, are grown on MgO(001) at 450 °C by magnetically unbalanced reactive magnetron sputtering. The combination of high-resolution x-ray diffraction reciprocal lattice maps, high-resolution cross-sectional transmission electron microscopy, and selected-area electron diffraction shows that ZrN grows epitaxially on MgO(001) with a cube-on-cube orientational relationship, (001)ZrN|(001)MgO and [100]ZrN|[100]MgO. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm, in good agreement with reported results for bulk ZrN crystals. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based on temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity ρ300K of 12.0 μΩ-cm, a temperature coefficient of resistivity between 100 and 300 K of 5.6 × 10-8 Ω-cm K-1, a residual resistivity ρo below 30 K of 0.78 μΩ-cm (corresponding to a residual resistivity ratio ρ300Κ/ρ15K = 15), and the layers exhibit a superconducting transition temperature of 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, ξ| = 18 nm and ξ⊥ = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7 ± 1.7 and 450 ± 25 GPa. [ABSTRACT FROM AUTHOR]