Thermal annealing effect on the structure, bandgap, and optical constants of Er-Mn oxide thin films

Thin films of erbium-manganese oxide were grown on glass and p-type Si substrates. The films were thermally pre-annealed at different temperatures ranging from 400 to 1000 °C to produce different crystalline structures and agitate a solid-state reaction. The structural characterisation of the films was carried out by X-ray diffraction (XRD) and energy dispersion X-ray fluorescence (XRF). The XRD investigation shows that the films annealed at 400 °C were amorphous and nanocrystals of ErMnO₃ appear under pre-annealing at about 800 °C or more. Mn oxide and Er oxide prevent each other from crystallising alone. The optical properties of the films pre-annealed at different temperatures were studied in the fundamental absorption region of the spectrum in wavelength range 230-800 nm. The spectral complex refractive index, complex optical dielectric constant, and optical bandgap were determined. A modified single-oscillator Forouhi-Bloomer (FB) technique, Wemple-Didomenico (WD) equation, Urbach's relation, Tauc et al. relation, and pointwise unconditioned minimisation approach (PUMA) were used in the analysing of the obtained spectral data.     

Dynamics in liquids studied by inelastic X-ray scattering

Inelastic X-ray scattering with an energy resolution of the order of milli-electron volts is a relatively new tool to investigate collective excitations in condensed matter. A high energy resolution can be achieved by extreme backreflection (Bragg angle close to 90°) from perfect crystals. This technique is used with the spectrometer INELAX for inelastic scattering experiments at DESY, Hamburg. Energy transfers from a few milli-electron volts up to 5 eV at any wavevector between 0.3 and 14 Å^–1 are accessible. One of the successful applications of this method is the investigation of the dynamical structure factor of liquids. Results on liquid lithium are presented and compared with neutron data and molecular dynamics.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Electronic structure characterization of ultra low-k carbon doped oxide using soft X-ray emission spectroscopy

In this study we report the electronic structure of ultra low-k dielectric constant carbon doped oxide (CDO) films, which have a k value of 2.4, using synchrotron radiation-excited resonant soft X-ray emission (SXE) spectroscopy. Conventional X-ray photoemission spectroscopy was used to determine that the chemical composition of the material was Si-31%, C-15% and O-54%. The C and O partial density of states for the valence bands has been measured by SXE. Radiation induced changes in the chemical bonding in the material have been identified and these can be minimised by continuously translating the sample during measurement. The spectral changes induced by the radiation damage are consistent with the breaking of Si–CH₃ bonds in the material and the formation of graphitic C = C double bonds. Investigation of the origin of a low energy subband in the C K spectrum reveal that it can be attributed to O K emission excited by second order rather than the hybridization of C 2p states in the CDO layer.     

Correlated structural and electrical properties of thin manganese oxide films

In the present work, different crystalline Mn-oxide thin films (MnO, α-Mn₂O₃, and γ-Mn₂O₃) were prepared on glass and Si(P) substrates by evaporation of MnO₂ powder followed by annealing in air and in vacuum at different temperatures. The oxide films were characterised by methods of energy-dispersion X-ray fluorescence method (EDXRF), X-ray diffraction (XRD), and ultraviolet-visible (UV-VIS) optical spectroscopy. The samples for electrical study were constructed in the form of metal-oxide-Si (MOS) structures and characterised by measurements of their capacitance and ac-conductance as a function of gate-voltage. The frequency dependence of ac-electrical properties of Mn-oxide films and their variation with the annealing temperatures or crystal-structural content were studied. The measured values of the relative permittivity for Mn oxides of different crystal structures were tabulated. It was found that the obtained MnO oxide because of the annealing in vacuum at about 500 °C has the highest relative permittivity, about 10, which suggests it to be a candidate for high-k insulator on Si applications. It was found that the data of the ac-measurements follow the correlated barrier-hopping (CBH) model and the model's parameters were determined.     

Distribution in orientation axis of thin film grown by pulsed laser deposition

Orientations of LaNiO₃ (LNO) and Pb(Zr_0.52Ti_0.48)TiO₃ (PZT) films deposited by laser ablation were evaluated using X-ray diffraction. (001)-oriented PZT and LNO films were achieved under optimized deposition conditions. Pole-figure measurements of both LNO and PZT films showed that (001) out-of-plan orientation was affected by plume direction. It was found that the (001) axes of both LNO and PZT films at locations away from the plume center were significantly tilted. The incline angle of tilt increases with the distance away from the center of the plume. The films grown in columnar structures and the column axis coincided with the crystalline orientation. Polarization of the PZT film was slightly affected by the difference in orientation tilt angles of the film investigated.     

New possibilities in nanoscale surface structure diagnostics using X-ray standing waves under conditions of continuous resonant X-ray Raman scattering

The main principles, new possibilities, and instrumental implementations of a structure-sensitive spectroscopy of the surface of condensed media probed by X-ray standing waves (XSWs) are considered in the case of electron emission under the action of continuous resonant X-ray Raman scattering. It is shown that prospects for the development and use of the new possibilities offered by the XSW method for surface investigations are related to the creation of a set of specific experimental equipment and special sources of synchrotron radiation.     

Critical current in YBCO thin film bridge studied using magneto-optic technique

The magnetic flux distribution from a transport superconducting current flowing through an YBa₂Cu₃O₇ (YBCO) thin film bridge is observed using a ferrimagnetic garnet indicator with in-plane magnetic anisotropy. After switching off the current from the maximum value that provides the electrically detected critical regime, the expected remanent flux was not observed. The only place where the irreversible magnetization takes place is a linear defect that crosses the bridge and thus reduces the electrically measured critical current compared with the value that could be reached without macroscopic defects. The observed reversibility of the main part of the sample is explained on the basis of theoretical calculations of the current-induced flux penetration: Perceptible penetration and trapping of the flux might be observed only upon the application of a current higher than approximately half the maximum critical current that could be reached in such a thin film without macroscopic inhomogeneities.     

Oxidation study of polycrystalline InN film using in situ X-ray scattering and X-ray photoemission spectroscopy

Oxidation process of polycrystalline InN films were investigated using in situ X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). The films were grown by dc sputter on sapphire (0001) substrates and were oxidized in air at elevated temperatures. The XRD data showed that the structure of the films changed to the bixbyite In₂O₃ (a = 10.11 Å) above 450 °C. Chemical configurations of the sample surfaces were investigated using high-resolution XPS. For the non-intentionally oxidized InN film, XPS analysis on the In 3d peak and the N 1s main peak at 396.4 eV suggests that indium and nitrogen are bound dominantly in the form of InN. An additional peak observed at 397.4 eV in the N 1s photoelectrons and the O 1s peaks indicate that the InN film surface is partly oxidized to have InO_xN_y configuration. After oxidation of the InN film at elevated temperature, the O 1s spectrum is dominated by In₂O₃ peak, which indicates that the structure is stable chemically with In₂O₃ configuration at least within the XPS probing depth of a few nm.     

Anharmonicity and electron-phonon coupling in cuprate superconductors studied by inelastic neutron scattering

An overview is given on anharmonic lattice vibrations originating from structural instabilities. The transverse vibrations of the chain oxygens in YBa₂Cu₃O₇ are found to be only moderately anharmonic. Measurements of the phonon linewidths in the Cu-O bond stretching vibrations strongly support recent calculations of the electron-phonon coupling. Results are presented on superconductivity-induced frequency shifts at short wavelengths.     

Anisotropic electronic structure in single crystalline orthorhombic TbMnO3 thin films

We have deposited the c-axis-oriented orthorhombic TbMnO₃ (o-TMO) films with well-aligned in-plane orientations on NdGaO₃ (001) substrates by using pulsed laser deposition. The distinctive orientation alignments between the film and substrate allow the study of the X-ray absorption spectroscopy (XAS) with the electric field along three major crystallographic directions, respectively. Polarization-dependent XAS spectra show significant anisotropy in the electronic structure of o-TMO. The correlation between the electronic structure, the bonding anisotropy, and the magnetoelectric effect in the multiferroic materials is revealed.     

Study of thin film multilayers using X-ray reflectivity and scanning probe microscopy

We have presented new schemes to analyse grazing incidence specular X-ray reflectivity data to obtain structural and chemical information of thin films. Analysis of specular reflectivity data gives information along the depth of the film, whereas, analysis of non-specular data reveals the structural information across the film surface and interfaces. The schemes proposed are based on the Born approximation and the distorted wave born approximation (DWBA). Surface structural parameters such as, height–height correlation and roughness exponent of the film obtained from the analysis of X-ray reflectivity was compared with results obtained from atomic force microscopy     

NiOx电致变色薄膜结构与性能的X射线研究

电致变色是指材料的光学性能(光的透射、反射和吸收)通过外加电场或电流的作用,在包括可见光波长的某一波长范围内发生可逆变化的现象。氧化镍薄膜是目前发现的性能最好的电致变色材料之一,采用反应性磁控射频溅射法,利用金属镍作为靶材,在氮与氧混合气体中,通过直流磁控反应溅射法制备氧化镍薄膜,用X射线衍射技术分析其结构,用循环伏安法对NiOx薄膜的电致变色过程进行分析。     

Surface and in depth chemistry of polycrystalline WO/sub 3/ thin films studied by X-ray and soft X-ray photoemission spectroscopies

The chemical composition of surface and underneath layers of WO/sub 3/ thin films, deposited by thermal evaporation and annealed in air at different temperatures, has been studied by means of soft X-ray and X-ray photoemission spectroscopies. Both the W 4f and valence band spectra have been analyzed. The analysis has been performed on samples as inserted and after an annealing process in an ultra high vacuum. The results have shown that the surface always presents a nonstoichiometric WO/sub 3/ compound, whose spectral components do not depend on the sample preparation. Instead, the study of the underneath layers has shown that the WO/sub 3/ films annealed in air at 500/spl deg/C are highly stoichiometric and stable, while the samples heated in air at 300/spl deg/C are much more sensitive to the vacuum thermal treatment showing the presence of reduced WO/sub x/ phases, whose intensity and chemical states change after the in vacuum annealing procedure.     

Effect of titanium oxide-polystyrene nanocomposite dielectrics on morphology and thin film transistor performance for organic and polymeric semiconductors

Previous studies have shown that organic thin film transistors with pentacene deposited on gate dielectrics composed of a blend of high K titanium oxide-polystyrene core-shell nanocomposite (TiO₂-PS) with polystyrene (PS) perform with an order of magnitude increase in saturation mobility for TiO₂-PS (K = 8) as compared to PS devices (K = 2.5). The current study finds that this performance enhancement can be translated to alternative small single crystal organics such as α-sexithiophene (α-6T) (enhancement factor for field effect mobility ranging from 30-100× higher on TiO₂-PS/PS blended dielectrics as compared to homogenous PS dielectrics). Interestingly however, in the case of semicrystalline polymers such as (poly-3-hexylthiophene) P3HT, this dramatic enhancement is not observed, possibly due to the difference in processing conditions used to fabricate these devices (film transfer as opposed to thermal evaporation). The morphology for α-sexithiophene (α-6T) grown by thermal evaporation on TiO₂-PS/PS blended dielectrics parallels that observed in pentacene devices. Smaller grain size is observed for films grown on dielectrics with higher TiO₂-PS content. In the case of poly(3-hexylthiophene) (P3HT) devices, constructed via film transfer, morphological differences exist for the P3HT on different substrates, as discerned by atomic force microscopy studies. However, these devices only exhibit a modest (2×) increase in mobility with increasing TiO₂-PS content in the films. After annealing of the transferred P3HT thin film transistor (TFT) devices, no appreciable enhancement in mobility is observed across the different blended dielectrics. Overall the results support the hypothesis that nucleation rate is responsible for changes in film morphology and device performance in thermally evaporated small molecule crystalline organic semiconductor TFTs. The increased nucleation rate produces organic polycrystalline films with small grain size which are better connected and exhibit lower barriers for charge transport and as such higher field effect mobilities are measured in these devices.     

Implications of stimulated resonant X-ray scattering for spectroscopy,imaging, and diffraction in the regime from soft to hard X-rays

The ultrahigh peak brilliance available at X-ray free-electron lasers opens the possibility to transfer nonlinear spectroscopic techniques from the optical and infrared into the X-ray regime. Here, we present a conceptual treatment of nonlinear X-ray processes with an emphasis on stimulated resonant X-ray scattering as well as a quantitative estimate for the scaling of stimulated X-ray scattering cross sections. These considerations provide the order of magnitude for the required X-ray intensities to experimentally observe stimulated resonant X-ray scattering for photon energies ranging from the extreme ultraviolet to the soft and hard X-ray regimes. At the same time, the regime where stimulated processes can safely be ignored is identified. With this basis, we discuss prospects and implications for spectroscopy, scattering, and imaging experiments at X-ray free-electron lasers.     

Study of annealing-induced changes in CdS thin films using X-ray diffraction and Raman spectroscopy

We have investigated as grown and annealed (300 °C, 400 °C and 500 °C) thin films of CdS grown on GaAs (001) by chemical bath deposition. X-ray diffraction (XRD) shows that the as grown CdS film is polycrystalline and predominantly cubic. A residual compressive stress of the order of 1.45% in the as grown film relaxes on annealing the film at 300 °C. Furthermore, CdS film undergoes a structural phase transition from the metastable cubic phase to the stable hexagonal phase, when, annealed at 500 °C. This is accompanied by significant improvement in crystalline quality of the film. Line shape analysis of the asymmetry of the longitudinal optical phonon shows a disorder-activated mode, which correlates well with the crystalline quality estimated from XRD and photoluminescence measurements. The additional features observed in the Raman spectra ∼ 254 cm^− 1 and 309 cm^− 1 are investigated using temperature dependent Raman spectroscopy and identified as superposition of transverse optical: E₁ (TO) and E₂ phonons at q = 0 and combination mode (two zone-edge E₂ phonons) respectively.     

X-ray diffraction and Raman scattering in SbSI nanocrystals

Lattice structure and rod-like shaped SbSI nanocrystals obtained by ball milling with rod thickness down to 70 nm, as estimated from X-ray diffraction (XRD) and electron microscopy, is similar to that of the bulk crystals. The dependence of the grain size on the milling duration is discussed in view of the chain-like crystalline structure of SbSI. Possible factors, responsible for the observed Raman line broadening, are discussed, scattering by surface phonons being considered the predominant one.     

Shelf-life time test of p- and n-channel organic thin film transistors using copper phthalocyanines

P- and n-type channel thin film transistors (OTFTs) were fabricated by using hexadecahydrogen copper phthalocyanine (H₁₆CuPc) and hexadecafluoro copper phthalocyanine (F₁₆CuPc) molecules, respectively. Top-contact and bottom-contact source-drain configurations were used for both semiconductors. Furthermore, the temperature and film thickness dependences on the mobility values were measured in the saturation regime of source-drain current. Unipolar mobilities in such single-layer OTFTs were correlated to thin film morphology by X-ray diffraction analysis and atomic force microscopy measurements. Shelf-life time tests of p-type and n-type OTFTs are detailed as OTFT configuration and substrate temperature dependence over a time period of 100 days.     

Nanoscale structure and atomic disorder in the iron-based chalcogenides

The multiband iron-based superconductors have layered structure with a phase diagram characterized by a complex interplay of charge, spin and lattice excitations, with nanoscale atomic structure playing a key role in their fundamental electronic properties. In this paper, we briefly review nanoscale structure and atomic disorder in iron-based chalcogenide superconductors. We focus on the Fe(Se,S)_1−xTe_x (11-type) and K_0.8Fe_1.6Se₂ (122-type) systems, discussing their local structure obtained by extended x-ray absorption fine structure. Local structure studies on the Fe(Se,S)_1−xTe_x system reveal clear nanoscale phase separation characterized by coexisting components of different atomic configurations, similar to the case of random alloys. In fact, the Fe–Se/S and Fe–Te distances in the ternary Fe(Se,S)_1−xTe_x are found to be closer to the respective distances in the binary FeSe/FeS and FeTe systems, showing significant divergence of the local structure from the average one. The observed features are characteristic of ternary random alloys, indicating breaking of the local symmetry in these materials. On the other hand, K_0.8Fe_1.6Se₂ is known for phase separation in an iron-vacancy ordered phase and an in-plane compressed lattice phase. The local structure of these 122-type chalcogenides shows that this system is characterized by a large local disorder. Indeed, the experiments suggest a nanoscale glassy phase in K_0.8Fe_1.6Se₂, with the superconductivity being similar to the granular materials. While the 11-type structure has no spacer layer, the 122-type structure contains intercalated atoms unlike the 1111-type REFeAsO (RE = rare earth) oxypnictides, having well-defined REO spacer layers. It is clear that the interlayer atomic correlations in these iron-based superconducting structures play an important role in structural stability as well as superconductivity and magnetism.     

Investigation of a metal-ionic conductor interface in thin film samples using X-ray photoelectron spectroscopy and electrical measurements

The surface of an evaporated thin film of the ionic conductor β-PbF₂ was analysed using X-ray photoelectron spectroscopy (XPS). The results were compared with those obtained from nuclear and secondary ion mass spectrometry measurements. An analysis of the Au-β-PbF₂ interface shows the presence of a thin layer of partly oxidized metallic lead. Part of this interfacial lead diffused across the gold film towards the external surface where it became bound to oxygen. An electrical analysis of the interface was performed by studying the capacitance as a function of the surface potential. The differences between experimental and calculated values are discussed in the light of the XPS measurements.