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Magneto-optical garnets are attractive because of their high Faraday rotation and low optical loss in the near infrared. Therefore their use is generally in nonreciprocal devices, i.e., as optical isolators in optical communication. In this paper we present data concerning the deposition of Bi3Fe5O12 (BIG) thin films on (100) and (111) Gd3Ga5O12 substrates using pulsed-laser deposition. Laser-induced processes on the surface of the oxide target used for ablation were analyzed and numerous films were deposited. We found the BIG film quality to be strongly affected by oxygen pressure, laser energy density, and the Bi/Fe film ratio, whereas temperature had a minor influence. We also investigated the BIG-film deposition using a target pressed from metallic Bi and Fe powders and found information on the growth behavior of BIG. We report on details of the film deposition and film properties determined by environmental scanning electron microscopy, energy dispersive x-ray analysis, Rutherford backscattering spectroscopy, and x-ray diffraction. In addition, we determined the Faraday rotation of the films. [ABSTRACT FROM AUTHOR]

The Heusler alloy Co2MnSi with theoretically predicted 100% spin polarization has been successfully implemented in Co2MnSi/AlOx/Co7Fe3 magnetic tunnel junctions recently. Here we investigated 100 nm thick Co2MnSi films grown on a vanadium buffer and capped by a thin alumina film. This stack is similar to the lower electrode including the tunneling barrier of magnetic tunnel junctions. By soft x-ray absorption spectroscopy and magnetic circular dichroism in fluorescence and total electron yield detection we determined differences between the chemical and magnetic properties of the Co2MnSi thin films and the Co2MnSi/AlOx interface. Whereas MnO was formed directly at the interface during plasma oxidation of the Al layer, the interfacial Co was not oxidized and its x-ray absorption line shape at the L2,3 edge was similar to the line shape of bulk Co2MnSi. The atomically ordered bulk Co2MnSi showed characteristic differences in the x-ray absorption spectra in comparison with the disordered samples: in the ordered state of the bulk both, Co and Mn, showed additional shoulders about 4 eV above the L2,3 resonances, a large circular dichroism, and a pronounced x-ray absorption near edge fine structure. The same was found for interfacial Co, whereas for interfacial Mn these features were masked by the characteristic absorption multiplet structure of MnO right at the interface which also resulted in a strong reduction of the interfacial Mn moment in annealed samples. [ABSTRACT FROM AUTHOR]

The third-order nonlinear optical susceptibility of indium tin oxide (ITO) thin films on glass substrates, χ(3)ITO, was determined in the near-IR spectral region using degenerate four wave mixing (DFWM) spectroscopy with 100 fs laser pulses. A DFWM method for measuring thin films on thick substrates was refined for the characterization of films less than 100 nm thick and applied to ∼25 nm thick ITO films. It was found that χ(3)ITO is purely electronic at 900–1300 nm (11 000–7700 cm-1) and has a value of (2.16±0.18)×10-18 m2 V-2. The χ(3)ITO value reaches (3.36±0.28)×10-18 m2 V-2 at 1500 nm (6700 cm-1) due to two-photon absorption by free carriers (electrons). Ultrafast electron relaxation was also observed. The ∼100 fs lifetime of this process could reflect electron scattering in the conduction band. [ABSTRACT FROM AUTHOR]

In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy (UPS), respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1 eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface. [ABSTRACT FROM AUTHOR]

We have used photoreflectance (PR) and high-resolution x-ray diffraction (HRXRD) measurements to assess the composition of InxGa1-xAs1-yNy thin films (x∼20%, y∼3%) grown by molecular beam epitaxy on GaAs substrates with different surface orientations. The aim of our work is to investigate the effect of substrate orientation on the incorporation of N and In into the films. Whereas in principle the composition of the InxGa1-xAs1-yNy films cannot be characterized by HRXRD alone because lattice spacings depend on both x and y, we show that a combined analysis of the PR and HRXRD data allows us to determine the sample composition. Our data analysis suggests that the incorporation of N in (In, Ga)(As, N) exhibits some dependence on substrate orientation, although not as strong as previously observed in Ga(As, N). We determine shear deformation potentials for our samples that are sizably different than those obtained by linearly interpolating from the values of the pure binary compounds, which has already been observed in Ga(As, N) and contradicts the currently accepted idea that only the conduction band of dilute nitrides is perturbed by N. [ABSTRACT FROM AUTHOR]

Chemically cleaned GaP(001) surfaces in 25% NH4OH solution have been studied using spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and wettability measurement techniques. The SE data clearly indicate that the solution causes removal of the native oxide film immediately upon immersing the sample. The SE data also indicate that when the native oxide film is completely etch removed, the resulting surface is still roughened. The estimated roughness thickness is ∼1.2 nm, in excellent agreement with the AFM rms value (∼1.2 nm). The XPS spectra confirm the removal of the native oxide from the GaP surface. The XPS data also suggest a thin oxide overlayer, ∼0.3 nm thick, on the etch-cleaned GaP surface. The wettability measurements indicate that the as-degreased surface is hydrophobic, while the NH4OH-cleaned surface is hydrophilic. This result is in direct contrast to those obtained from acid cleaned surfaces, which are usually hydrophobic. The origin of hydrophilicity may be singular and associated hydroxyl groups bonded on the GaP surface. [ABSTRACT FROM AUTHOR]

The dielectric constant and ac conductivity of CaCu3Ti4O12 thin films deposited on platinized silicon substrate using pulsed laser deposition technique have been measured in the metal-insulator- metal configuration over wide temperature (80–500 K) and frequency (100 Hz–1 MHZ) ranges. The crystallographic structure and the phase purity of the deposited films were investigated using x-ray diffraction and micro-Raman spectroscopy. The dielectric dispersion data have been fitted to Debye-type relaxation with a distribution of relaxation times and an asymmetric distribution of relaxation was observed which increases with increase in ωτ. [ABSTRACT FROM AUTHOR]

Silicone-like SiOxCyHz polymeric thin films with different C/O atomic ratios have been studied by x-ray absorption spectroscopy and resonant Auger electron spectroscopy. The energy of the onset of the Si K absorption edge varies with the film composition from the value observed in SiC (i.e.,∼1840 eV) to that in SiO2 (i.e.,∼1844 eV). In the samples with a low C/O atomic ratio (i.e.,∼1),the main band of the Si K spectra depicts two well defined peaks that can be associated with the Si-C and Si-O bonds present in the samples. Their relative intensity can be used to assess the concentration of these two bond types. Resonant Si KLL Auger spectra of the polymeric thin film have been measured using photon energies across the Si K absorption edge. A first Auger peak appearing at a high kinetic energy was recorded for photon energies around the onset of the absorption edge and the first peak/shoulder of the Si K spectrum associated with the Si-C bonds. This resonant Si KLL Auger signal depicts the typical behavior of a resonant Auger process, i.e., its intensity increases when increasing the photon energy, passes through a maximum and then decreases to disappear. In parallel with the evolution of this resonant spectrum, a “normal” Si KLL Auger spectrum with a lower kinetic energy appeared for photon energies around the middle of the absorption curve. This spectrum is the only one prevailing at photon energies well above the absorption edge. An outstanding behavior of the Si KLL resonant Auger peaks in the polymers with a high C/O atomic ratio (i.e., >=4) is that they present a negative dispersion with photon energy, i.e., their kinetic energy decreases as the photon energy increases. This behavior is opposite to that generally found for resonant Auger peaks in most systems and particularly for SiO2. Although the origin of such behavior is still unclear, the study of the Si K absorption edge and the corresponding Si KLL resonant Auger spectra results helpful for the structural and electronic characterization of SiOxCyHz polymers. [ABSTRACT FROM AUTHOR]

Computer simulations of thin-film p-CdTe/n-CdS solar cells using the SCAPS software program are examined to offer explanations for a number of experimentally observed admittance spectroscopy results. We show that for a high concentration of deep level defects, the magnitude of the admittance spectroscopy signal which is an indicator of defect concentration is also affected by the cell thickness. For CdTe cells thinner than 3 μm, the signal for defects within 0.25 eV of the band edge can be weak and may not be detected at all. We also show that Fermi level pinning resulting from high concentrations of deep level defects can distort the measured activation energy and apparent capture cross section. Finally, we show that decreasing capacitance values with increasing temperature can be caused by the interaction between the CdTe cell back contact Schottky barrier, a defect concentration gradient adjacent to the back contact, and a small shallow acceptor concentration relative to the defect concentration. [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 growth of ultrathin TiN films by plasma-assisted atomic layer deposition (PA-ALD) was studied by in situ spectroscopic ellipsometry (SE). In between the growth cycles consisting of TiCl4 precursor dosing and H2–N2 plasma exposure, ellipsometry data were acquired in the photon energy range of 0.75–5.0 eV. The dielectric function of the TiN films was modeled by a Drude-Lorentz oscillator parametrization, and the film thickness and the TiN material properties, such as conduction electron density, electron mean free path, electrical resistivity, and mass density, were determined. Ex situ analysis was used to validate the results obtained by in situ SE. From the in situ spectroscopic ellipsometry data several aspects related to thin film growth by ALD were addressed. A decrease in film resistivity with deposition temperature between 100 and 400 °C was attributed to the increase in electron mean free path due to a lower level of impurities incorporated into the films at higher temperatures. A change in resistivity and electron mean free path was observed as a function of film thickness (2–65 nm) and was related to an increase in electron-sidewall scattering for decreasing film thickness. The TiN film nucleation was studied on thermal oxide covered c-Si substrates. A difference in nucleation delay was observed on these substrates and was related to the varying surface hydroxyl density. For PA-ALD on H-terminated c-Si substrates, the formation of an interfacial SiNx film was observed, which facilitated the TiN film nucleation. [ABSTRACT FROM AUTHOR]

We report on the lattice location of ion-implanted Ca and Sr in thin films of single-crystalline wurtzite GaN. Using the emission channeling technique the angular distributions of β- particles emitted by the radioactive isotopes 45Ca (t1/2=163.8 d) and 89Sr (t1/2=50.53 d) were monitored with a position-sensitive detector following 60 keV room-temperature implantation. Our experiments give direct evidence that ∼90% of Ca and >60% of Sr atoms were occupying substitutional Ga sites with root mean square displacements of the order of 0.15–0.30 Å, i.e., larger than the expected thermal vibration amplitude of 0.074 Å. Annealing the Ca implanted samples at 1100–1350 °C in high-pressure N2 atmosphere resulted in a better incorporation into the substitutional Ga site. The Sr implanted sample showed a small decrease in rms displacements for vacuum annealing up to 900 °C, while the substitutional fraction remained nearly constant. The annealing behavior of the rms displacements can explain why annealing temperatures above 1100 °C are needed to achieve electrical and optical activations, despite the fact that the majority of the acceptors are already located on Ga sites immediately after ion implantation. [ABSTRACT FROM AUTHOR]

Lanthanum oxide thin films were deposited at deposition temperatures ranging from 170 to 370 °C using alternate injection of tris(isopropyl-cyclopentadienyl)lanthanum and various reactants (H2O, O2, and NH3). It was possible to deposit films containing a carbon impurity concentration <1 at. %. The residual carbon could be further reduced by postdeposition annealing. X-ray photoelectron spectroscopy (XPS) showed that after rapid thermal annealing (RTA) at 870 °C the films transformed to silicate which increased the band gap of the films (7.0±0.15 eV). With changing the RTA ambient from O2 to N2, a binding energy shift of the substrate’s Si peaks by 0.9 eV was observed in the XPS spectra relative to the signals from the oxide layer. The shift was attributed to the electric field in the oxide film caused by the fixed charge distribution. A flat band voltage shift indicating the change of the fixed charge was also observed according to the RTA ambient. From Pt/La-oxide/p-Si(100) structures, the dielectric constant and the interface trap density were estimated to be ∼16 and ∼4×1011 eV-1 cm-2, respectively. An equivalent oxide thickness of 0.9 nm was obtained after RTA. [ABSTRACT FROM AUTHOR]

We present a study on n doping of C60 thin films by acridine orange base [3,6-bis(dimethylamino)acridine(AOB)] combining conductivity, field effect, and Seebeck measurements. An increase of more than six orders of magnitude in conductivity is observed for a doping ratio of 6 mol %, accompanied by a decrease in the activation energy from 0.64 to 0.15 eV compared to the undoped C60. We observe a clear doping effect immediately after sample preparation, but also a further activation by annealing or illumination. The field effect and Seebeck measurements confirm n-type conduction of C60 thin films and show that deep donor states are formed in AOB-doped C60 thin films. A field effect mobility of 0.2 cm2/V s is achieved for a doping level of 1.8 mol %. Near Infrared (NIR) and Fourier transform infrared (FTIR) spectra demonstrate electron transfer from the dopant to the matrix: For C60 doped with AOB, C60- is present in NIR absorption and FTIR spectra. On the other hand, a peak corresponding to acridine orange [3,6-bis(dimethylamino)acridinium chloride (AOBH+)] is also observed in the FTIR spectrum of C60:AOB, where AOBH+ corresponds to AOB with one additional proton attached. Electrochemical data of AOB and AOBH+ in acetontrile suggest that the AOB radical cation is not stable, but is rapidly transformed into a compound with similar properties to AOBH+. Conductivities of C60 thin films doped with bis(ethylenedithio)-tetrathiafulvalene were also investigated to confirm that the doping effect of AOB in C60 does not result from a simple electron transfer from AOB to C60. [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]

Positron annihilation lifetime spectroscopy (PALS) was used to study the nanoporous structure of spin-on and chemical vapor deposited low dielectric constant (low-k) films. Orthopositronium (o-Ps) lifetimes provided information on pore size, open and closed porosities, and depth profile of pore sizes in low-k films. In combination with three-photon (3γ) yield obtained from positron annihilation spectroscopy, the formation, diffusion, and annihilation of o-Ps are correlated with the chemical composition of matrix. The weak interaction between o-Ps and matrix with the network structure composed of Si, C, O, and H atoms allows us to extract nanoporous information from o-Ps lifetime and 3γ yield. The effects of pore generator (porogen) chemistry, thin film capping, plasma treatment, and positron radiation on nanoporous structure in several low-k films were demonstrated, which provided the information on process compatibility of low-k films. Unsolved issues related with Ps probing nano-structure of porous low-k films are summarized. [ABSTRACT FROM AUTHOR]

Praseodymium (Pr) silicate dielectric layers were prepared by oxidation and subsequent N2 annealing of thin Pr metal layers on SiO2/Si(100) substrates. Transmission electron microscopy studies reveal that the resulting dielectric has a bilayer structure. Nondestructive depth profiling by using synchrotron radiation x-ray photoelectron spectroscopy shows that, starting from the substrate, the dielectric stack is composed of a SiO2-rich and a SiO2-poor Pr silicate phase. Valence and conduction band offsets of about 2.9 and 1.6 eV, respectively, between the dielectric and the Si(100) substrate bands were deduced. Pr silicate films with an equivalent oxide thickness of 1.8 nm show approximately three orders of magnitude lower leakage currents than silicon oxynitride references. Capacitance versus voltage measurements of the Pr silicate/Si(100) system report a flat band voltage shift of 0.22 V, an effective dielectric constant of about 11 and a reasonably good interface quality with an interface state density on the order of 1011 cm-2. Experimental results are supplemented by ab initio considerations which review the most probable mechanisms of fixed charge formation in the Pr silicate layers. [ABSTRACT FROM AUTHOR]

We grow Zn1-xMnxO/Al2O3 (0<=x<=0.08) thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5 eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B 56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gap energy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3 eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3 eV Mn-related peak intensity is attributed to increasing N2 flow rate and Mn–N hybridization. [ABSTRACT FROM AUTHOR]

We propose a method for restoring the symmetry in the threshold voltage (Vth) in complementary metal-oxide-semiconductor field-effect transistors (FETs) with a Hf-based high-k dielectric. This technique is based on the Al composition adjustment in the HfAlOx(N) dielectric film to achieve the symmetric Vth. The asymmetry of |Vth| in n and p metal-oxide-semiconductor FET (MOSFETs) due to the Fermi-level pinning at the interface between the poly-Si gate electrode and Hf-based high-k dielectric is considered to be induced independently by two kinds of interfacial dipoles. The adjustment of the Al content in HfAlOx(N) enables us to balance these dipoles. Vth values of n- and p-MOSFETs are shifted in the positive direction as the Al content in HfAlOx(N) increases. Symmetrical Vth values can be obtained for poly-Si and single fully silicided nickel gate electrodes when the Al contents are about 25 and 7 at. % in HfAlOx(N), respectively. [ABSTRACT FROM AUTHOR]

The FeTaN thin films were deposited on the flexible plastic substrates by rf magnetron sputtering. Good soft magnetic properties with coercivity <10 Oe have been obtained in the films with thickness <250 nm. Relatively high values of the complex permeability and ferromagnetic resonance frequency were obtained and they can be adjusted by changing the film thickness. However, compared to the films on the rigid substrate, a decrease of the permeability level and a shift of the resonance peak in the permeability spectra have been noticed for the films on the flexible substrate. The electric properties, including sheet resistance, resistivity, and magnetoresistance for the films with various thicknesses, have also been investigated. [ABSTRACT FROM AUTHOR]

Undoped and Ga-doped (3 wt %) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200 °C under an oxygen flow rate from 0 to 50 SCCM. In this paper, we report on the defect and band edge related signals in the optical absorption spectra for ZnO thin film by using a piezoelectric photothermal (PPT) spectroscopy, which is effective in observing a nonradiative transition process. The PPT peak around 2.5 eV was observed only for the undoped ZnO samples grown under a low oxygen flow rate. This signal is considered to be related to the oxygen vacancies, because it disappears with the increase of the oxygen flow rates. No corresponding peak was found for the Ga-doped samples. This result indicates that Ga doping inhibits the generation of the oxygen vacancies, and it agrees with that from the first-principle electronic band structure calculations. We have also carried out the theoretical calculation for the optical absorption edge of degenerated ZnO as a function of the carrier concentration. Burstein-Moss effect and band-gap-narrowing effect in ZnO should be considered in the case of high carrier concentration. Comparing the experimental results with the theoretical predictions, we found out that the proposed PPT edge energy coincides well with the Fermi level EF. [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]

Silicidation in Ni/Si thin-film junction has been investigated using depth-resolved positron annihilation spectroscopy (PAS) and Rutherford backscattering spectrometry (RBS). Identification of various silicide phases from an analysis of the positron annihilation parameters is consistent with the RBS results. Absence of vacancy defects in the silicide region is clearly brought out by PAS. [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 have studied V2AlC (space group P63/mmc, prototype Cr2AlC) by ab initio calculations. The density of states (DOS) of V2AlC for antiferromagnetic, ferromagnetic, and paramagnetic configurations have been discussed. According to the analysis of DOS and cohesive energy, no significant stability differences between spin-polarized and non-spin-polarized configurations were found. Based on the partial DOS analysis, V2AlC can be classified as a strongly coupled nanolaminate according to our previous work [Z. Sun, D. Music, R. Ahuja, S. Li, and J. M. Schneider, Phys. Rev. B 70, 092102 (2004)]. Furthermore, this phase has been synthesized in the form of thin films by magnetron sputtering. The equilibrium volume, determined by x-ray diffraction, is in good agreement with the theoretical data, implying that ab initio calculations provide an accurate description of V2AlC. [ABSTRACT FROM AUTHOR]

Twin-free epitaxial cubic (111) praseodymium sesquioxide films were prepared on Si(111) by hexagonal-to-cubic phase transition. Synchrotron radiation grazing incidence x-ray diffraction and transmission electron microscopy were applied to characterize the phase transition and the film structure. As-deposited films grow single crystalline in the (0001)-oriented hexagonal high-temperature phase of praseodymium sesquioxide. In situ x-ray diffraction studies deduce an activation energy of 2.2 eV for the hexagonal-to-cubic phase transition. Transmission electron microscopy shows that the phase transition is accompanied by an interface reaction at the oxide/Si(111) boundary. The resulting cubic (111) low-temperature praseodymium sesquioxide film is single crystalline and exclusively shows B-type stacking. The 180° rotation of the cubic oxide lattice with respect to the Si substrate results from a stacking fault at the substrate/oxide boundary. [ABSTRACT FROM AUTHOR]

Ba0.5Sr0.5TiO3 (BST) thin films are among the best-known ferroelectric and dielectric materials. Ce-doped BST films have been fabricated by pulsed laser deposition in order to enhance their dielectric properties. X-ray diffraction, atomic force microscopy, and Raman spectroscopy have been used to study variations of crystal structure, surface morphologies, and phase stability of Ce-doped BST films, respectively. A strong influence of Ce doping on the properties of the BST films has been observed. First, a small amount of Ce dopant makes easy epitaxial growth of a BST film with a smooth surface on a MgO substrate. Second, residual stress in a BST film on a MgO substrate can be reduced by Ce doping, as demonstrated by the blueshift of phonon peaks in Raman spectroscopy. [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]

Two calibration methods, besides the conventional defocus method, have been presented to determine the in-depth probe response function (i.e., the function characterizing the spectral intensity distribution within the probe volume along the sample in-depth direction) in photostimulated spectroscopy. One method is based on “perturbing” the detected spectral probe of a selected band by varying the aperture of a confocal pinhole placed in the light path to the spectrometer; the other method is based on perturbing the spectral position of a selected band using an applied (equibiaxial) linear stress field, superimposed on the sample by means of a biaxial bending jig. Using the R1 band of a sapphire film, the validity of these two methods for determining the in-depth probe response function, and their reciprocal consistency are demonstrated. The calibration methods, which allow one to maintain unchanged the position of the focal plane within the sample, appear to work well for determining the in-depth probe response function of films, coatings, or highly transparent thin plates, where the laser probe size is close to the sample thickness, and thus, the defocus method is hardly applicable. [ABSTRACT FROM AUTHOR]

The modulated optical reflectance (MOR) measurement technique was applied to colossal magnetoresistive materials, in particular, La2/3Sr1/3MnO3 (LSMO) thin films. The contactless measurement scheme is prospective for many applications spanning from materials’ characterization to devices such as reading heads for magnetically recorded media. A contrasted room-temperature surface scan of a 100-μm-wide and 400-μm-long bridge patterned into LSMO film provided preliminary information about the film homogeneity. Then the temperature was varied between 240 and 400 K, i.e., through the ferromagnetic to paramagnetic transition. A clear relation between the MOR signal measured as a function of the temperature and the relative derivative of the resistivity up to the Curie temperature was observed. This relationship is fundamental for the MOR technique and its mechanism was explored in the particular case of LSMO. Analysis in the framework of the Drude model showed that, within certain conditions, the measured MOR signal changes are correlated to the changes in the charge-carrier concentration. [ABSTRACT FROM AUTHOR]

Room-temperature pseudodielectric function spectra 〈ε(ω)〉=〈ε1(ω)〉+i〈ε2(ω)〉 of AlxGa1-xSb (0.00<=x<=0.39) alloys were measured from 1.5 to 6.0 eV by spectroscopic ellipsometry. Effects of surface overlayers on the measured spectra have been minimized as far as possible by performing in situ chemical etching on samples immediately before the measurements rather than correcting the measured data mathematically for the presence of overlayers. Analysis of second energy derivatives numerically calculated from the measured data yielded the critical-point energies of the E1, E1+Δ1, E0′, E2, and E1′ interband transitions. Dependence of the critical-point energies on composition x is obtained. [ABSTRACT FROM AUTHOR]

Positronium time-of-flight spectroscopy with improved stability and signal-to-noise ratio, achieved by a developed off-line digital data analysis, was applied to the characterization of three types of nanoclustering silica porous films with different relative dielectric constants and refractive indices. The emission of triplet ortho-positronium (o-Ps) from the film surface was examined as a function of incident positron energy (Ein). It was found that the o-Ps emission peak energies from two highly porous films with similar total porosities decrease similarly to each other with increasing Ein up to 1.50 keV. On the other hand, o-Ps emission intensities from the two films differed considerably in the range between 0.5 keV

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]

Physical properties of ferromagnetic p-type Ga1-xMnxAs1-yNy epitaxial films (x=0.045 and y=0–0.032) grown by molecular-beam epitaxy are described. It is found that the incorporation of nitrogen gradually suppresses the metallic behavior of p-(Ga,Mn)As, especially at low temperatures. The Curie temperature TC decreases accordingly with increasing y value. The reduction in TC is discussed in terms of the suppression of hole-mediated long-range spin-exchange interaction due to the enhancement of carrier localization. Perpendicular magnetic anisotropy appears at the region around y=0.02, reflecting the reduced lattice constant due to substitutionally incorporated nitrogen. No significant change was found in the magnetic circular dichroism spectra in the photon energy region around the band gap of (Ga,Mn)As. Our experimental results show that the theoretical prediction based on the double exchange interaction [V. A. Dinh et al., Jpn. J. Appl. Phys., Part 2 42, L888 (2003)] is hardly materialized in this system. [ABSTRACT FROM AUTHOR]

Thin films of laser molecular-beam epitaxy grown n-type Ga-doped ZnO were investigated with respect to their optical properties. Intense room-temperature photoluminescence (PL) in the near-band edge (NBE) region was observed. Moreover, its broadening of PL band was significantly larger than predicted by theoretical results modeled in terms of potential fluctuations caused by the random distribution of donor impurities. In addition, the line shape was rather asymmetrical. To explain these features of the NBE bands, a vibronic model was developed accounting for contributions from a series of phonon replicas. [ABSTRACT FROM AUTHOR]

A test method to evaluate the complex permittivity of materials with thin configuration (thickness of 50–300 μm) is presented. We evaluate the complex permittivity of materials with various mechanical and electrical characteristics (films, powders, and liquids) at frequencies from 100 MHz to 20 GHz and at temperatures from 293 to 353 K using an experimental method presented in this paper. We have developed a fixture having a circular parallel-plate capacitor which is suitable for the measurement of materials with thin configuration. Our method is based on theoretical consideration of wave propagation in the capacitor, which is associated with multiple reflections along the diameter of the sample. The consideration of time delay in the sample section makes it possible to evaluate the permittivity of high dielectric constant materials in the frequency range up to 20 GHz. In addition, some examples for the measurements show that the resolution with tan δ is as low as 0.001. Our method is powerful to understand the relation between dielectric properties and the microscopic dynamics of dielectric materials, because of the broadband measurement, and finally can be applied for various areas both in fundamental researches and practical applications. [ABSTRACT FROM AUTHOR]

Organic phototransistors (OPTs) were fabricated from pentacene and copper phthalocyanine (CuPC) based on the geometry of organic field-effect transistors (OFETs); and the effect of the wavelength of the incident light source on their performance was examined. High performance OFETs with pentacene and CuPC were fabricated and the characteristics of the OPTs were examined under UV and visible-light irradiations with top illumination. The CuPC and pentacene OPTs show a high responsivities of 0.5–2 and 10–50 A/W and maximum IPh/IDark of 3000 and 1.3×105, respectively, under 365 nm UV light. However, under visible light, at a wavelength of 650 nm, the pentacene OPTs had 100 times less responsivity, 0.15–0.45 A/W, and a IPh/IDark of 1000, even though an absorption coefficient three times larger was observed at this wavelength than at 365 nm. A strong correlation was found between the performance of the OPTs and the incident photon to current conversion efficiency spectra of an organic semiconductor. The strong dependence on the wavelength of incident light of the performance of the prepared OPTs can be explained by an internal filter effect in which light with a large absorption coefficient is filtered at the top surface and through the bulk of the film when light is directed onto the opposite side of the OFET gate electrode. Thus, light cannot efficiently contribute to the generation of charge carriers in the channel regions that were formed in the first two molecular layers adjacent to the dielectric interface. Consequently, the most efficient OPTs were produced when the following conditions of incident light were satisfied: The photon energies (or frequencies) should be (i) larger than the band gap and (ii) have a relatively small absorption coefficient, since the light can penetrate down to the channel layer more efficiently when it is near the dielectric interface without any loss in absorption through the film. [ABSTRACT FROM AUTHOR]

We report investigations of ZnO plasma at various ambient pressures of oxygen produced by third harmonic 355 nm of neodymium: yttrium aluminum garnet laser for depositing quality nanocrystalline ZnO thin films. Time- and space-resolved optical emission spectroscopy is used to correlate the plasma properties with that of the deposited thin films. The temporally resolved images of the plumes are correlated with the time-resolved emission spectrum of plasma species in the plume. The deposited films of ZnO at 100 mTorr of ambient oxygen exhibited third-harmonic generation. MgxZn(1-x)O alloy thin films of different molar percentage of MgO were deposited on glass substrates with the aim of achieving variable band gap using pulsed laser deposition in 100-mTorr oxygen ambient at substrate temperatures ranging from 200 to 500 °C. The films with x=0.1 and 0.3 exhibit single hexagonal phase with (002) as the preferred orientation, however, with x=0.5, a transition to mixed phase with hexagonal phase of (100) and cubic phase of (200) orientation is observed. The absorption edge is blueshifted with and increase of x and deposition temperature. The band gap of the deposited films increases with molar percentage and deposition temperature. The deposited films exhibited high degree of transparency (>85%) over visible range. [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]

Lanthanum-modified lead zirconate titanate Pb0.97La0.03(Zr0.52Ti0.48)O3 doped with x at. % WO3 (x=0, 0.2, 0.5, 1, and 2) (PLWZT) ferroelectric thin films have been deposited on Pt/Ti/SiO2/Si substrates using a sol-gel spin-coating process. We have demonstrated that WO3 dopant plays a significant role on the structure and electrical properties of the PLWZT films. The x-ray-diffraction analysis shows that the PLWZT films undergo a dramatic tetragonal-to-cubic crystalline phase transformation with small amount of WO3 additives. Surface morphology (atomic force microscopy) analysis shows that the average grain size decreases with the increase of WO3 doping amount in the PLWZT films. The highest average grain size of 91 nm has been observed for PLWZT (WO3:0.2 at. %). It is also observed from x-ray photoelectron spectroscopy study that W varies its chemical state with the varying concentration of WO3 in the films. Moreover, the polycrystalline PLWZT thin films with a small amount of WO3 doping (0.2 at. %) show a reduced electrical conductivity, improved dielectric constant ([variant_greek_epsilon]) (1675 at 1 kHz) and decreased dielectric loss (D) (0.03 at 1 kHz), and improved remnant polarization (Pr) value of 30 μC/cm2 along with significantly improved fatigue resistance (∼5% attenuated after 108 switching cycles) compared with the other PLWZT films. A defect chemistry mechanism indicating the reduction of oxygen vacancies by the substitution of W for Ti at different doping concentrations has been proposed to well explain the observed experimental results. [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]

A series of systematic investigations has been conducted to examine the doping effects of dimethyl-tin-dichloride (DMTC) on the structural, electrical, and optical properties of CdS films used for photovoltaic applications. After the DMTC doping, Sn and Cl concentrations in CdS are found to increase to 6×1017 and 4.5×1018 atoms/cm3, respectively; the CdS grain size also tends to increase. A slight increase in the electrical conductivity is discussed in conjunction with the increase in the grain size and the Cl donor concentration. In addition, the optical-absorption spectra reveal almost no change in the band gap of CdS due to the doping, while the spectra indicate a deterioration of the crystallinity of the heavily doped CdS. The influence of the DMTC doping into the CdS films on the formation of the CdS/CdTe heterostructure is also discussed. With an increase in the grain size of the CdS underlayer due to the DMTC doping, the degree of the (111) preferential orientation of CdTe increases, which generally corresponds to an improvement in the photovoltaic performance. On the other hand, a fairly small reduction is observed in the sulfur fraction in the CdTe1-xSx mixed-crystal interlayer, which indicates no marked deterioration at the CdS/CdTe interface. The DMTC doping is also effective in reducing the optical reflectance in almost the entire active spectral region of the CdS/CdTe solar cell. [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]

The changes in the free-carrier concentration in polycrystalline ZnO films during exposure to H2 and O2 plasmas were studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. The carrier concentration and mobility were extracted from the free-carrier absorption in the infrared using a model for the dielectric function. The electron density in polycrystalline zinc oxide films may be significantly increased by >1019 cm-3 by brief exposures to hydrogen plasma at room temperature and decreased by exposure to O2 plasmas. Room-temperature oxygen plasma removes a fraction of the H at donor sites but both elevated temperatures (∼225 °C) and O2 plasma were required to remove the rest. We demonstrate that combinations of O2 and H2 plasma treatments can be used to manipulate the carrier density in ZnO films. However, we also show the existence of significant drifts (∼15%) in the carrier concentrations over very long time scales (hours). Possible sites for H incorporation in polycrystalline films and reasons for the observed carrier-concentration changes are proposed. [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]

We report postgrowth micro-Raman stress imaging of cracks in (111) homoepitaxial diamond films. Undoped and phosphorous-doped diamond thin films grown by microwave plasma-enhanced chemical-vapor deposition on Ib (111)-oriented diamond substrates have been studied by confocal micro-Raman spectroscopy. For comparison purposes, a film grown on a (100) Ib substrate was also examined. Thanks to the confocal optics, the Raman signal arising from the epilayer could be discriminated from that arising from the substrate. As was already reported, the (111) films exhibited substantial tensile stress, indicated by a downshift in the Raman peak and by spontaneous cracking in films grown thicker than 5 μm. The sixfold symmetry of the cracks supported that the films were homoepitaxial. A high compressive stress was also detected at the substrate near surface, and a partial stress relaxation was observed to occur in the vicinity of the cracks. Possible origins of the high tensile stress observed in the (111) homoepitaxial diamond films are discussed. [ABSTRACT FROM AUTHOR]