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Cu2ZnSnS4 is a promising low-cost, nontoxic, earth-abundant absorber material for thin-film solar cell applications. In this study, combinatorial coevaporation was used to synthesize individual thin-film samples spanning a wide range of compositions at low (325 °C) and high (475 °C) temperatures. Film composition, grain morphology, crystalline-phase and photo-excitation information have been characterized by x-ray fluorescence, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and photoluminescence imaging and mapping. Highly textured columnar grain morphology is observed for film compositions along the ZnS-Cu2ZnSnS4-Cu2SnS3 tie line in the quasi-ternary Cu2S-ZnS-SnS2 phase system, and this effect is attributed to structural similarity between the Cu2ZnSnS4, Cu2 SnS3, and ZnS crystalline phases. At 475 °C growth temperature, Sn-S phases cannot condense because of their high vapor pressures. As a result, regions that received excess Sn flux during growth produced compositions falling along the ZnS-Cu2ZnSnS4-Cu2SnS3 tie line. Room-temperature photoluminescence imaging reveals a strong correlation for these samples between film composition and photoluminescence intensity, where film regions with Cu/Sn ratios greater than ~2 show strong photoluminescence intensity, in comparison with much weaker photoluminescence in regions that received excess Sn flux during growth or subsequent processing. The observed photoluminescence quenching in regions that received excess Sn flux is attributed to the effects of Sn-related native point defects in Cu2ZnSnS4 on non-radiative recombination processes. Implications for processing and performance of Cu2ZnSnS4 solar cells are discussed. [ABSTRACT FROM AUTHOR]

In this work, the optical nonlinear absorption characteristics of the crystalline Ge2Sb2Te5 thin films were investigated by performing z-scan measurements with nanosecond laser pulse. The experimental results showed that the nonlinear saturable absorption coefficient was as large as -10-2 m/W for the excitation intensity lower than 0.17 GW/m2. The nonlinear saturable absorption changed to the nonlinear reverse-saturable absorption with a coefficient of about + 10-2 at the excitation intensity of above 0.17 GW/m2. To explore the internal mechanisms, the first-principle theory was employed to calculate the electronic structure, and a five-level structure suitable for explanation of nonlinear absorption reversal was suggested. The theoretical calculation and analysis indicated that for the excitation intensity smaller than 0.17 GW/m2, the contribution to the nonlinear saturable absorption is mainly from band-filling effect; for the excitation intensity larger than 0.17 GW/m2, the nonlinear reverse saturable absorption results from the thermal-induced nonlinearity, which is further confirmed by picosecond laser pulse z-scan measurement and the variable-temperature spectroscopy ellipsometric analysis. [ABSTRACT FROM AUTHOR]

The oxygen content and the local oxygen arrangement of laser processed YBa2Cu3O7-δ (YBCO) thin films grown on LaAlO3 substrates have been probed by micro-Raman spectroscopy On these films, channels for easy vortex motion have been laser written (LW) into the bridge constrictions by heat-induced, partial depletion of oxygen from the laser-illuminated areas of these films. Raman microscopy has been used to investigate and characterize the oxygen content and structure of the laser written channels. Direct evidence for local micro-structural changes in the film during the LW process is presented and the heat affected zone, surrounding the channel borders, has been mapped. [ABSTRACT FROM AUTHOR]

The optical constants n and k of holmium (Ho) films were obtained in the 3-1340-eV range from transmittance measurements performed at room temperature. Thin films of Ho with various thicknesses were deposited by evaporation in ultra high vacuum conditions and their transmittance was measured in situ. Ho films were deposited onto thin C-film substrates supported on high transmittance grids. Transmittance measurements were used to obtain the extinction coefficient k of Ho films. The refractive index n of Ho was calculated with Kramers-Krönig analysis; in order to do this, k data were extrapolated both on the high and on the low energy parts of the spectrum by using experimental and calculated k values available in the literature. Ho, similar to other lanthanides, has a low-absorption band below the O2,3 edge onset; the lowest absorption was measured at ∼22 eV. Therefore, Ho is a promising material for filters and multilayer coatings in the energy range below the O2,3 edge in which most materials have a large absorption. Good consistency of the data resulted from the application of f and inertial sum rules. [ABSTRACT FROM AUTHOR]

We investigate the film-growth process of the inhomogeneous sputtered TiO2 thin films by the in situ real-time spectroscopic ellipsometer. The growth process of the film is analyzed by both the uniform and the island film growth models. Based on the analyses from the Ψ-Δ trajectories, the initial thin-film growth corresponds to the island film growth model for a single-layer film. As the film grows, the microstructural phase changes cause the transition from the single-to the double-layer physical model, because of the development of the inhomogeneity in the TiO2 thin film. The dynamic fits with the double-layer physical model and the Cody–Lorentz optical model indicate three different stages of the film growth: the nucleation stage, the coalescence stage, and the continuous-layer stage. Although our presented model works well for most of the experimental data, the determination of the refractive index at the ultrathin thickness may be problematic. [ABSTRACT FROM AUTHOR]

Epitaxial thin films of LaMnO3 were grown by pulsed laser deposition in identical deposition conditions but in situ annealed in different oxygen environments. All the films showed an insulator to metal transition. It also showed a magnetic order that correlates well with an insulator to metal behavior. The transition temperature critically depends on annealing oxygen pressure and increases with increasing oxygen content. It is observed that instead of strain, oxygen content plays a major role in deciding the transport properties. X-ray diffraction and Raman spectroscopy measurements revealed that the increasing oxygen content results in a decrease in unit cell volume along with a reduction in Jahn–Teller distortion. It is shown that the intensities of the two Jahn–Teller activated modes in Raman spectra are highly sensitive to the oxygen stoichiometry of the films and that the intensity ratio can be effectively used to characterize oxygen content in these films. [ABSTRACT FROM AUTHOR]

Copper selenide, CuxSe(x∼2), was examined as a hole-injection layer for low-temperature organic devices. Crystalline CuxSe films grown at room temperature with atomically flat surfaces exhibited metallic conduction with a high electrical conductivity of 4.5×103 S/cm, a hole concentration of 1.4×1022 cm-3, and a mobility of 2.0 cm2/(V s). Analysis of the free carrier absorption using the Drude model estimated the effective mass of a hole as 1.0me. Photoemission spectroscopy measurements of the interfaces between CuxSe and organic hole transport layers, N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine (NPB) and copper phthalocyanine (CuPc), verified that the hole-injection barriers of these interfaces (0.4 eV for NPB and 0.3 eV for CuPc) are smaller than that of a conventional indium tin oxide (ITO) hole-injection electrode/NPB interface (0.6 eV) but are comparable to that of an ITO electrode/CuPc interface (0.3 eV). Hole-only devices using the CuxSe layer as a hole-injection anode exhibited very low threshold voltages (0.4–0.5 V) and nearly Ohmic characteristics. The NPB layer on the CuxSe layer was found to be highly doped at 1017–1019 cm-3, probably due to copper diffusion, while the CuPc layer is nearly intrinsic with a doping concentration lower than 1015 cm-3. These results indicated that a CuxSe film combined with CuPc is a promising candidate for a low-voltage hole-injection anode or a buffer layer in low-temperature devices such as organic light-emitting diodes and thin film transistors. [ABSTRACT FROM AUTHOR]

The topography evolution using the high energy heavy ion irradiation revealed the fact that ion bombardment produces self-affine nanostructures, creating peculiar surface morphologies and regular structures on the surface of the ZnO thin film at certain fluences. The self-affine nanopatterns produced on the surface of ZnO thin film under swift heavy ion irradiation are different types of nanostructures such as nanodimensional grains aligned like a linear array. Scanning probe microscopy is used for investigating the ZnO surfaces and UV-visible spectroscopy for studying the effect of surface modification on optical properties. The two-dimensional power spectral density of the irradiated ZnO thin films have been evaluated for each image to extract the value of growth factor (β) and roughness exponent (α). The exponent n increases from 2.2 to 4.0 up to a critical value of fluence and beyond which it decreases. These values suggest that ion assisted/induced diffusion process plays a crucial role in the evolution of self-affine nanostructures on ZnO surface. [ABSTRACT FROM AUTHOR]

The arsenic redistribution after NiSi formation has been measured by secondary ion mass spectrometry (SIMS). The NiSi film has been obtained by solid state reaction of a Ni thin film with a silicon substrate doped with As. An increase in the As SIMS signal at the NiSi/Si interface was observed for some experimental conditions. By varying the SIMS experimental parameters (incidence angle and the impact energy), the As signal at NiSi/Si interface was found to change. The SIMS experimental parameters have been optimized and were found to be an impact energy of 1 keV and an incidence angle superior to 50°. This allows us to minimize differences in sputtering rate and ion yield between NiSi and Si and to obtain a good depth resolution and dynamic range. Under these conditions the bump in the As signal does not appear: this illustrates the difficulty to measure concentration at interface by SIMS. [ABSTRACT FROM AUTHOR]

The optical constants of Pr films were obtained in the 4–1600 eV range from transmittance measurements performed at room temperature. Thin films of polycrystalline Pr were deposited by evaporation in ultrahigh vacuum conditions and their transmittance was measured in situ. Pr films were deposited onto grids coated with a thin, C support film. Transmittance measurements were used to obtain the optical extinction coefficient k of Pr films in the 4–1600 investigated photon energy range. The refractive index n of Pr was calculated using the Kramers–Krönig analysis. Data were extrapolated both on the high and low-energy sides by using experimental and calculated extinction coefficient data available from the literature. Pr, similar to other lanthanides, has a low-absorption band right below the O2,3 edge onset; the lowest absorption was measured at about 17 eV. Therefore, Pr is a promising material for filters and multilayer coatings in the energy range below O2,3 edge in which most materials have a strong absorption. A good consistency of the data were obtained through f and inertial sum rules. [ABSTRACT FROM AUTHOR]

The optical properties of nitrogen-doped SnO2 films with different N2/(N2+O2) gas ratios grown by reactive sputtering were studied by spectroscopy ellipsometry. The optical dielectric functions of the films were simulated by the Tauc-Lorentz model. It was found that the refractive index and extinction coefficient of nitrogen-doped SnO2 films increase and the band gap has a redshift with the increase of the N2 ratios. The general influences of the electronegativity and bond ionicity on the band gap, the refractive index in the spectral region below the fundamental absorption edge of nitrogen-doped SnO2, and other doped semiconductors are demonstrated. [ABSTRACT FROM AUTHOR]

In the present work, we investigate in detail the effect of both the deposition temperature and the cooling rate on the growth of calcium barium niobate (CBN) thin films on a magnesium oxide (MgO) single crystal substrate. As revealed by x-ray diffraction measurements, epitaxy occurs for films deposited at 800 °C with a slow in situ cooling rate. We have also investigated the chemical composition of the films by way of a Rutherford backscattering spectroscopy technique and of an elastic recoil detection analysis, which reveal a good stoichiometry for our samples. In addition, optical analysis (UV-visible spectroscopy and spectroscopic ellipsometry) is performed on both polycrystalline and epitaxial films. A high transmittance (>85%) and a refractive index close to that observed for bulk crystal are obtained for epitaxial CBN films deposited at a low oxygen pressure. X-ray reflectivity measurements have enabled us to correlate the density of the films with their refractive indices. [ABSTRACT FROM AUTHOR]

Thin films of nickel phthalocyanine (NiPc) are deposited on an as-received and on a mildly sputtered PEDOT:PSS film, spin coated on fluorine tin oxide coated glass. The electronic properties of the PEDOT:PSS surface, both as loaded and upon thermal treatment and sputtering, as well as of the interfaces between NiPc and PEDOT:PSS are studied by x-ray and UV photoelectron spectroscopies in order to investigate both the electronic and the chemical properties of the materials. Surface analysis of the PEDOT:PSS films showed that upon sputtering the insulating PSS film is removed leading to lower work function, as well as to an increase of the density of occupied states close to the Fermi level. The investigation of the interfaces between NiPc and PEDOT:PSS revealed charge transfer and a pinning of the Fermi level across the interface. The hole injection barrier was found significantly lower compared with that for the NiPc/Au interface, indicating that the presence of the PEDOT:PSS layer facilitates the carrier injection between the electrode and the organic semiconductor. [ABSTRACT FROM AUTHOR]

In order to investigate the mechanism behind bistable resistance switching in NiO thin films, we have done detailed x-ray photon spectroscopy (XPS) and x-ray diffraction Analysis (XRD) on NiO and Ti doped NiO samples fabricated under various conditions. We discovered that a high initial resistivity was required for samples to undergo bistable resistance switching, and the presence of metallic Ni content in these samples was determined by XPS. XRD data also showed that NiO grown with a relative (200) orientation was preferred over those grown with relative (111) orientation. [ABSTRACT FROM AUTHOR]

BiFeO3 thin films were processed on La0.8Sr0.2MnO3 (LSMO) buffered silicon substrate via chemical solution deposition. Short-wave ultraviolet assisted pyrolysis was conducted in oxygen atmosphere in order to improve microstructure. A fine, homogeneous, and phase-pure grain structure with smooth topography was obtained. X-ray photoelectron spectroscopy analysis indicates diffusion of lanthanum and manganese from LSMO into the BiFeO3 film leading to a diffuse interface. Nevertheless, improved polarization and leakage resistance properties were obtained. For the first time polarization switching was obtained in sol-gel BiFeO3 films using capacitance-voltage (C-V) curves. This has been imputed to homogeneous local electrical properties of the film, corroborated by surface scanning potential microscopy investigations. The leakage current mechanisms were investigated as function of temperature, and could be interpreted in terms of the Frenkel-Poole mechanism with a trap depth of 1.6 eV. Finally, the magnetic properties of the LSMO/BiFeO3 heterostructure are presented in comparison to those of BiFeO3 on platinized silicon. An exchange coupling between BiFeO3 and LSMO layers is suggested. [ABSTRACT FROM AUTHOR]

Photoinduced transient conductivity of pentacene thin films prepared by thermal vapor deposition is investigated using time-resolved microwave conductivity (TRMC) measurements, giving intrinsic charge carrier mobility in highly ordered structures without any electrode attached. The real and imaginary conductivity values are analyzed and compared with those predicted by molecular orbital calculations. The effects of substrate surface treatment by hexamethyldisilazane are discussed on the basis of kinetic traces of conductivity and morphology. A mobility of >0.7 cm2/V s was obtained from the TRMC measurements and analysis of transient absorption spectra. The measurement of field-effect-transistor mobility in single-crystal domains requires not only complicated fabrication techniques but also many assumptions on the carrier channels, density, injection, etc. The combination of TRMC and transient optical spectroscopy provides an approach for addressing this issue. The present technique is applicable to a wide variety of organic semiconducting materials. Moreover, it is the only technique revealing the intrinsic potentials of mobility in materials that is supported by complete experimental and quantitative procedures not based on any assumptions. [ABSTRACT FROM AUTHOR]

The textural dependence of the thermally sprayed Er-doped ZnO films on Er concentration is reported here. The [002] preferred growth orientation of hexagonal phase is obtained at the lower concentrations, while the [100] and [101] directions additionally raised from nearly 5 at. % Er content onwards. The cathodoluminescent characteristics of the samples in the near ultraviolet (UV) and visible region depict a complete extinction of the visible emitted bands (λ=445, 526, and 665 nm) at 1 at. % Er content. Their deactivation below this concentration is explained by a compensation of oxygen defects in the material due to the oxygen-rich medium of the deposition bath. Their reactivation beyond this particular concentration is ascribed to the increase of the Er+3 ion shells whose internal radiative transitions lead to a recovering of these visible emitted bands. The radiative mechanism of the transitions from the (4F9/2) excited states to the (4I15/2) ground state, responsible for the λ=665 nm emission, is predominant in that case. The respective normalized intensity of the violet (λ=445 nm) and green (λ=526 nm) emitted bands exhibits a maximal value for 3 at. % Er content, reaching a stabilized regime from about 5 at. % Er. [ABSTRACT FROM AUTHOR]

The secondary electron emission yield of fullerene, graphite, and diamondlike carbon after low-energy N2+ ion bombardment was studied for antimultipactor applications. Nitrogen incorporation into the carbon thin films decreases their secondary emission yield, contrary to the hydrogen or oxygen effect. Carbon nitride surface textured to a nanometric scale had the property of hindering secondary electron emission. Valence bands obtained from photoemission spectroscopy using synchrotron radiation were correlated with secondary electron emission measurements. Multipactor threshold power for carbon nitride was 7.5 kW. [ABSTRACT FROM AUTHOR]

The electronic structure of the hexagonal β-Nb2N, hexagonal δ′-NbN, and cubic δ-NbN thin films have been investigated by x-ray photoemission spectroscopy. Calculated density of states for these phases are also presented and used in the interpretation of the experimental valence band spectra. The experimental energy distribution curves are consistent with the calculated densities of states. Comparing hexagonal to cubic phases, both β-Nb2N and δ′-NbN are more covalent than the cubic phase NbN. Prominent covalent bonding in hexagonal β-Nb2N and δ′-NbN nitrides can be related with the higher hardness values as compared to that of the cubic phase. This study discloses relevant observations important for both the technological applications and fundamental properties. [ABSTRACT FROM AUTHOR]

Zn1-xCdxO(1120) films have been grown on (0112) sapphire (r-plane) substrates by metal-organic vapor phase epitaxy. A 800-nm-thick ZnO buffer, deposited prior to the alloy growth, helps to prevent the formation of pure CdO. A maximum uniform Cd incorporation of 8.5 at. % has been determined by Rutherford backscattering spectrometry. Higher Cd contents lead to the coexistence of Zn1-xCdxO alloys of different compositions within the same film. The near band-edge photoluminescence emission shifts gradually to lower energies as Cd is incorporated and reaches 2.93 eV for the highest Cd concentration (8.5 at. %). The lattice deformation, due to Cd incorporation, has been described using a new reference frame in which the lattice distortions are directly related to the a-plane surface structure. Cd introduction does not affect the c lattice parameter but expands the lattice along the two perpendicular directions, [1120] and [1100], resulting in a quadratic volume increase. [ABSTRACT FROM AUTHOR]

We present a simple method to determine the linear electro-optic coefficient of thin films with spectroscopic ellipsometry. This technique allows noncontact and nondestructive measurement of the as-grown state of films without the need to fabricate a waveguide. The principle behind this is that the electro-optic effect is regarded as perturbation to the optical parameters. Comparing differences in tan Ψ spectra in terms of applied voltage and wavelength yields a change in the effective wavelength of light propagating through a dielectric medium, which is equivalent to electro-optic-induced phase shift. We demonstrate the feasibility of this procedure to determine the Pockels coefficient (r33) of a preferentially c-axis-oriented LiNbO3 film on a Si(100) substrate. Dispersion of effective r33 values at wavelengths between 0.3 and 0.8 μm was obtained. [ABSTRACT FROM AUTHOR]

We measure pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(ZrxTi1-x)O3 (x=0.2,0.56,0.82) (PZT), Pb0.98Nb0.04(Zr0.2Ti0.8)0.96O3, Pb0.91La0.09(Zr0.65Ti0.35)0.98O3, and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method. Using a parametric optical constant model, we estimate the dielectric functions (ε) of the perovskite oxide thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical-point model, we determine the parameters of the critical points. In the second derivative spectra, the lowest band-gap energy peak near 4 eV is fitted as a double peak for annealed PZTs due to the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest band-gap peak is fitted as a single peak. We also examine the effect of dopants La and Nb, which substitute at Pb and Zr (Ti) sites, respectively. We found three band gaps Ea (∼3.9 eV), Eb (∼4.5 eV), and Ec (∼6.5 eV) in the order of increasing energy. The Ea and Eb band-gap energies were not sensitive to Zr composition. We discuss the change of critical-point parameters for PZTs in comparison to the band-structure calculations based on local-density approximation. The near constancy of the lowest band-gap energy independent of Zr composition is consistent with the band-structure calculations. [ABSTRACT FROM AUTHOR]

Transparent p-type copper aluminum oxide (Cu–Al–O) semiconducting thin films, with Cu/Al atomic ratios ranging from 1.0 to 4.3, were deposited by plasma-enhanced metal-organic chemical-vapor deposition. The films were grown on z-cut single-crystal quartz substrates, at a substrate temperature of 450 °C. Crystalline CuAlO2 was found dominant in the films, including small amounts of CuAl2O4, Al2O3, and amorphous Cu2O. The effect of varying Cu/Al ratio on the structural, electrical, and optical properties of the films were studied by x-ray diffraction, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, and Seebeck technique, and discussed. We were able to optimize the Cu/Al ratio for the p-type conductivity and transmittance in copper aluminum oxide thin films, and the best conductive film, with a room-temperature conductivity of 0.289 S cm-1 and a transparency of 80%, was found to have a Cu/Al ratio of 1.4±0.3. In addition, the mechanism of the p-type conduction of copper aluminum oxide was discussed. [ABSTRACT FROM AUTHOR]

Thermal helium desorption spectrometry (THDS) has been used for the investigation of defects and thermal stability of thin Cu films (5–200 Å) deposited on a polycrystalline Mo substrate in ultrahigh vacuum. These films are metastable at room temperature. On heating, the films transform into islands, giving rise to a relatively broad peak in the helium desorption spectra. The temperature of this island formation is dependent on film thickness, being 417 K for 10 Å and 1100 K for a 200 Å film. The activation energy for island formation was found to be 0.3±0.1 eV for 75 Å film. Grain boundaries have a strong effect on island formation. The defect concentration in the as-deposited films is ∼5×10-4, for films thicker than 50 Å and more for thinner films. Helium release from monovacancies was identified in the case of a 200 Å film. Helium release was also seen during sublimation of the Cu film (∼1350 K). Overlayer experiments were used to identify helium trapped close to the film surface. An increase of the substrate temperature during deposition resulted in a film that had already formed islands. Argon-ion assistance (250 eV) during film deposition with an ion/atom ratio of ∼0.1 resulted in a significant enhancement of helium trapping in the films. The argon concentration in the films was found to be 10-3. The temperature of island formation was increased due to argon-ion assistance. The helium and argon desorption spectra are found to be similar, which is due to most of the helium becoming trapped in the defects created by the argon beam. The role of the Mo surface in affecting the defects at the film-substrate interface is investigated. The effect of variation of helium fluence and helium implantation energy is also considered. The present THDS results of Cu/poly-Mo are compared to those of Cu/Mo(100) and Cu/Mo(100) reported earlier. [ABSTRACT FROM AUTHOR]

n doping of the molecular organic semiconductor perylene-3,4,9,10-tetracarboxylic–dianhydride (PTCDA) is often achieved by use of alkali metals as dopants. This doping process is commonly performed in two steps. In the first the dopant is evaporated onto the surface of the PTCDA film. As it has been believed that the dopant shows an inhomogeneous diffusion profile through the layer with most of the dopant accumulated in the first few layers, a subsequent annealing step has been performed in order to reach a homogeneous distribution of the dopant in the whole layer. In this paper experimental results concerning chemical composition ((angle resolved) X-ray photoemission spectroscopy, secondary-ion-mass spectrometry, Fourier transform infrared spectroscopy), electronic structure (ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy), as well as electrical properties (conductivity, Seebeck coefficient) are shown before and after doping and before and after annealing. These results suggest that the deposited dopant is redistributed and partially removed during the annealing step. A model for the dopant distribution is suggested. [ABSTRACT FROM AUTHOR]

GaN films have been deposited by reactive sputtering in nitrogen gas at pressures from 0.08 to 2.70 Pa with and without the addition of hydrogen gas. X-ray diffraction (XRD), Fourier transform infrared (FTIR), optical absorption, and photoluminescence (PL) spectroscopy have been used to characterize the sputter-deposited GaN films. The XRD pattern reveals that the GaN films deposited in nitrogen gas at pressures lower than 0.53 Pa are polycrystals with the (0001) texture (α-GaN), while those deposited at or above 1.07 Pa display mixed crystalline orientations or an amorphous-like nature. The GaN:H films deposited in nitrogen/hydrogen mixed gas, on the other hand, show an amorphous or amorphous-like nature. The FTIR spectra indicate that the GaN:H films show peaks arising from hydrogen-related bonds at ∼1000 and ∼3200 cm-1, in addition to the GaN absorption band at ∼555 cm-1. The optical absorption spectra at 300 K indicate the fundamental absorption edges at ∼3.38 and ∼3.7 eV for the highly oriented α-GaN and amorphous GaN:H films, respectively. PL emission has been observed from sputter-deposited α-GaN films at temperatures below 100 K. The GaN:H films also show strong band-edge and donor-acceptor pair emissions. The PL emission in the GaN:H film may arise from crystalline GaN particles embedded in the amorphous GaN matrix. [ABSTRACT FROM AUTHOR]

Plasma deposited nitrogen-rich silicon nitride thin films were prepared at temperatures between 80 and 300 °C. The infrared transmission (400–4000 cm-1) was measured, and selected absorption bands were quantified through a multiple Lorentzian oscillator parametric analysis. It is observed that the concentration of silicon-centered tetrahedra bonded together through nitrogen atoms increases monotonically with increasing deposition temperature. A qualitative model is presented to highlight the impact of the active adsorption site density on the degree of stepped (ordered) nucleation at the vapor-film interface. The importance of this growth profile, in particular for micro-systems-technology, is discussed in conjunction with measurements of the biaxial modulus and residual stress of the thin films. A mechanism for residual stress controllability is also presented. The atomic concentrations of silicon, nitrogen, and hydrogen in the thin films were calculated using infrared calibration factors derived from the deposition temperature dependent condensation processes. The results for silicon nitride thin films deposited at 300 °C were observed to be similar in composition to silicon diimide. Additional observations of the infrared transmission characteristics are reported, which include the identification of silazane bridge characteristics for the absorption feature around 610 cm-1, which is typically associated with Si–H (bending) absorption. [ABSTRACT FROM AUTHOR]

We report Raman measurements on thin films of strongly disordered GaN and GaN:O prepared by ion-assisted deposition. The incident photon energies used in the experiments ranged from 1.95 to 3.8 eV, spanning the interband edge. Under subgap excitation the signal resembles the crystalline GaN vibrational density-of-modes, with significant broadening as expected for disordered material. There is a strong resonant behavior at the interband edge of the same mode for which a strong resonance is found in crystalline GaN, with a width suggesting that the entire vibrational branch contributes to the signal. Even nanocrystalline material is found to display Raman spectra characteristic of very short-range (<1 n) translational symmetry, in agreement with x-ray diffraction evidence for the random stacking nature of the 3 nm diameter crystallites. The presence of oxygen at even 25 at.% has only a subtle effect on Raman spectra at the network vibrational frequencies below 800 cm-1, but its presence is signaled by the appearance of an oxygen mode at 1000 cm-1. An N2 line at 2360 cm-1 correlates with a nitrogen excess introduced during growth. [ABSTRACT FROM AUTHOR]

Carbon–nickel nanocomposite thin films were prepared by ion beam cosputtering a graphite target having a nickel chip attached to its surface. The amount of Ni incorporated in the films was controlled by the size of the Ni chip (from 5 to 22 wt %), and measured by in situ x-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy images indicated that the films have a granular structure with nanosize Ni particles embedded in an amorphous carbon matrix. The Ni particles have an average radius of ∼2 nm, with a rather narrow size distribution. Magnetization measurements revealed that films are superparamagnetic and present blocking temperatures TB<13 K. The combined results of XPS and magnetic measurements indicate that Ni particles are free from oxide layers. In addition, the estimated value of their anisotropy constant was found to be higher than the expected value for bulk Ni. The origin of this discrepancy is associated with both shape and interaction anisotropies. [ABSTRACT FROM AUTHOR]

The influence of postannealing in different gaseous environments on the optical properties of indiu-tin-oxide (ITO) thin films deposited on glass substrates using e-beam evaporation has been systematically investigated. It is found that the annealing conditions affect the optical and electrical properties of the films. Atomic force microscopy, x-ray diffraction, and x-ray photoemission spectroscopy (XPS) were employed to obtain information on the chemical state and crystallization of the films. These data suggest that the chemical states and surface morphology of the ITO film are strongly influenced by the gaseous environment during the annealing process. The XPS data indicate that the observed variations in the optical transmittance can be explained by oxygen incorporation into the film, decomposition of the indium oxide phases, as well as the removal of metallic In. [ABSTRACT FROM AUTHOR]

The present paper deals with substrate heterostructure effects on the microstructure and dielectric properties of Sm, Er, and La doped lead titanate (PT) thin films. The substrate heterostructures chosen include Si/(La0.8Sr0.2)MnO3 (LSMO), Y-stabilized zirconia (YSZ)/LSMO and Si/Pt. Both LSMO and PT thin films were processed via chemical solution deposition. The results are compared to those of Sm and Er doped lead-zirconate-titanate (PZT). It is shown that the dielectric properties, and particularly the ferroelectric-to-paraelectric transition temperature of PT, are strongly affected by the substrate heterostructure. In comparison to PT on platinized Si, the transition temperature is shifted by more than 100°C towards lower values in the case of Er and Sm doped PT on LSMO, while those of La doped PT and PZT are not affected at all. X-ray photoelectron spectroscopy investigations show a substantial interdiffusion between LSMO and PT. Particularly the diffusion of La towards the ferroelectric film and that of Pb towards LSMO are made responsible for the change in the dielectric properties. In the case of PZT we stipulate the formation of a stable pyrochlore diffusion barrier layer. [ABSTRACT FROM AUTHOR]

The phase transition behavior of BaNbxTi1-xO3 (BNTO) (0.0<=x<=0.50) thin films grown on MgO substrates by laser molecular beam epitaxy was systematically investigated by using x-ray diffraction (XRD) and micro-Raman spectroscopy. The asymmetric rocking XRD scan measurements show that with an increase of Nb-doped content, the lattice parameters c and a increase while c/a ratio decreases, indicating a decrease of tetragonality of the BNTO films. The intensity of Raman signal decreases and the width of the bands broaden with increase of Nb-doped content. The results of XRD and Raman spectra indicate that at room temperature BNTO thin films with Nb<=10 at. % have tetragonal structure, however, for Nb>=20 at. %, BNTO thin films exhibit typical disordering cubic structure. [ABSTRACT FROM AUTHOR]

The electronic properties of C[sub 60] thin films have been studied using surface photovoltage (SPV) spectroscopy at 120–300 K. Temperature variations of the SPV spectra are correlated with temperature-dependent x-ray diffraction patterns of the same samples, which indicate the first-order phase transition at T[sub c]=250 K. Absolute values of both the band-to-band and band (or band tail) -to-band tail SPV signals are shown to exhibit a clear minimum at T[sub c]=250 K in contrast with the well-known increasing background of the SPV intensity with decreasing temperature. The energy positions of the thresholds of the band-to-band and band (or band tail) -to-band tail regions in the SPV spectra also exhibit nonmonotonic behavior with a mirror symmetry and distinct extrema near T[sub c]. On the basis of the presented results, we discuss possible reasons behind the effect of rotational and orientational states of C[sub 60] molecules on the electronic structure of the C[sub 60] fullerite and charge carrier transport in C[sub 60] thin films. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electronic structure of strontium bismuth tantalate (SBT) thin films has been studied by x-ray photoelectron spectroscopy and ultraviolet-ray photoyield spectroscopy (UV-PYS). The SBT films were prepared by metalorganic decomposition (MOD) method using a chemical solution of Sr:Bi:Ta=0.8:2.3:2. The XPS spectra imply that pyrochlore-dominant MOD-SBT films include bismuth oxides other than oxidized bismuth [(Bi[sub 2]O[sub 2])[sup 2+]] layers after high-pressure-O[sub 2] annealing. The UV-PYS spectra exhibited that high-pressure-O[sub 2]-annealed SBT thin films with dominant pyrochlore structures have electron excitation energy of about 6.0 eV, which is excitation from the Fermi level to the vacuum level, while the as-crystallized SBT thin films with dominant perovskite structures exhibit about 5.5 eV. These results indicate that the high-pressure-O[sub 2] annealing oxidizes Bi atoms more in the pyrochlore-dominant SBT thin films than in the perovskite-dominant ones. The high-pressure-O[sub 2] annealing tends to suppress current through the pyrochlore-dominant MOD-SBT thin films, which is considered to be partly because bismuth oxides other than (Bi[sub 2]O[sub 2])[sup 2+] layers have been produced at the surface by the high-pressure-O[sub 2] annealing. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report an investigation of the influence of the crystal structure of Co thin films on the X-ray magnetic linear dichroism (XMLD) spectrum. We compare XMLD spectra measured in reflection at the 3p-edges for two distinct orientations of the magnetization in the crystalline Co film with ab initio calculated spectra. The latter was computed for the face-centered cubic as well as the hexagonal-close packed crystal structures of Co. We find that the XMLD signal is strongly dependent on the magnetization direction with respect to the crystal axes as well as strongly influenced by the crystal structure. [ABSTRACT FROM AUTHOR]

R-Fe-O (R=rare earth) compounds have recently attracted high interest as potential new multiferroic materials. Here, we report a method based on the solid-state reaction between Er2O3 and Fe layers, respectively grown by atomic layer deposition and chemical vapor deposition, to synthesize Er-Fe-O thin films. The reaction is induced by thermal annealing and evolution of the formed phases is followed by in situ grazing incidence X-ray diffraction. Dominant ErFeO3 and ErFe2O4 phases develop following subsequent thermal annealing processes at 850 °C in air and N2. Structural, chemical, and morphological characterization of the layers are conducted through X-ray diffraction and reflectivity, time-of-flight secondary ion-mass spectrometry, and atomic force microscopy. Magnetic properties are evaluated by magnetic force microscopy, conversion electron Mössbauer spectroscopy, and vibrating sample magnetometer, being consistent with the presence of the phases identified by X-ray diffraction. Our results constitute a first step toward the use of cost-effective chemical methods for the synthesis of this class of multiferroic thin films. [ABSTRACT FROM AUTHOR]

Epitaxial CaMnO3 thin films on (001) LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and SrTiO3 were synthesized in a range of strain states from coherently strained on LaAlO3 (1.6% strain) to fully relaxed on SrTiO3. We observed a magnetic ordering transition in CaMnO3 thin films suppressed from the Néel temperature of bulk CaMnO3 with the suppression increasing with increasing strain in the thin film. In contrast to bulk studies, our CaMnO3 films do not exhibit any sign of weak ferromagnetism according to field-dependent magnetization and x-ray magnetic circular dichroism measurements. Therefore, to within experimental resolution, all of our CaMnO3 films are antiferromagnetic with negligible oxygen off-stoichiometry. [ABSTRACT FROM AUTHOR]