Electron microscopy of phase and structural transformations in soft magnetic nanocrystalline Fe-Zr-N films

The effect of deposition conditions (film thickness) on the structure of soft magnetic Fe_80–78Zr₁₀N_10–12 films formed by reactive magnetron deposition on a heat-resistant glass substrate has been investigated by analytical transmission electron microscopy, high-resolution electron microscopy, and diffraction analysis. The processes of evolution of the phase and structural state of films and the film-substrate interface upon annealing in the temperature range of 200–650°C have been analyzed taking into account the thermodynamic, kinetic, and structural factors and the specific features of the nanocrystalline state.     

Improvement of photoconductivity in Silicon Tin (SiSn) thin films

Hydrogenated-amorphous silicon tin alloy (a-SiSn (C:H)) films have been prepared by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique. We present investigations of the absorption and photoconductivity characteristics of a-SiSn(C:H) thin films as a function of the tin concentration, which could be a pivotal feature for the bottom solar cell development. We demonstrate that the photoconductivity is significantly improved by the film growth under enhanced hydrogen dilution. The results suggest that the hydrogen dilution plays an important role in development of high quality a-SiSn(C:H) photosensitive thin films.     

Angular correlation studies of thin metal films

Angular correlation of positron annihilation radiation is widely used in solid state physics studies (Goldanskii; Hautojärvi), in the defectoscopy of monocrystals in particular (Nielsen et al.). The interest to surface studies gave rise recently to very sophysticated and expensive method of positron beams (Goldanskii et al.). The recent study and recently published papers (Aravin et al.; Valiev et al.) demonstrate, however, that valuable information on surface properties can be obtained using the traditional angular correlation (AC) technique.     

Optical studies of aromatic polyazomethine thin films

Optical transmission and fundamental reflectivity spectra of aromatic polyazomethine thin films, obtained by vacuum evaporation via the polycondensation process have been investigated in the wide spectral range 0.49–6.2 eV. As initial monomers, terephaldehyde (TPA) and one of four different amines, i.e. paraphenylene-diamine (PPDA), 7,2-diamino-fluorene, 1,1′-biphenyl-3,3′,4,4′-tetramine and 3-amino-4-(1-naphthyldiazenyl)phenylamine (fat brown RR) have been used, respectively. Amorphous character of these films was confirmed by the results of X-ray diffraction and AFM investigations. Absorption coefficient of the films has been obtained and the edge of absorption seems to be similar to the absorption edge typical for amorphous semiconductors, what allowed to obtain the Urbach energy and E_T parameter. The energy gaps of the films, following the Tauc relation, are found to change from 2.05 to 2.4 eV, depending on the length of conjugated part of the polymer chain. Absorption bands above the absorption edge, observed for different polyazomethine films are connected with their chemical structure and possible electronic transitions.     

Electron microscopy studies of epitaxial MgB2 superconducting thin films grown by in situ reactive evaporation

The morphology and chemistry of epitaxial MgB₂ thin films grown using reactive Mg evaporation on different substrates have been characterized by transmission electron microscopy methods. For polycrystalline alumina and sapphire substrates with different surface planes, an MgO transition layer was found at the interface region. No such layer was present for films grown on MgO and 4-H SiC substrates, and none of the MgB₂ films had any detectable oxygen incorporation nor MgO inclusions. High-resolution electron microscopy revealed that the growth orientation of the MgB₂ thin films was closely related to the substrate orientation and the nature of the intermediary layer. Electrical measurements showed that very low resistivities (several μΩ cm at 300 K) and high superconducting transition temperatures (38 to 40 K) could be achieved. The correlation of electrical properties with film microstructure is briefly discussed.     

Crystallization kinetics and phase transformations of zinc- and cadmium diphosphide films

The kinetics of isothermal crystallization of amorphous ZnP₂ films in the temperature range from 730 to 810 K and amorphous CdP₂ films between 630–770 K has been investigated. The kinetic curves of isothermal transformation of amorphous films into crystalline ones have been obtained. For ZnP₂ the transformation occurs as follows: amorphous films → α-ZnP₂ (tetragonal modification) → β-ZnP₂ (monoclinic modification). For CdP₂ – amorphous films → γ-CdP₂ (cubic modification) → β-CdP₂ (tetragonal modification). From the experimentally determined kinetic curves the stability diagrams for ZnP₂ and CdP₂ films have been plotted. The most stable modification in the investigated temperature range are β-ZnP₂ and β-CdP₂ other ones are metastable. The values of effective energy of activation of transformation have been determined.     

Electron microscope observations of phase separation near spinodal boundary in a sodium borosilicate glass

Time evolution of volume fraction of the minor phase is studied in an alumina-doped sodium borosilicate glass inside the immiscible region. It is shown that such a study permits a distinction between the two mechanisms of phase separation; namely spinodal decomposition and nucleation and growth. For spinodal decomposition, the volume fraction decreases initially, whereas for nucleation and growth, it increases with heat-treatment time.     

Microstructure optical and electrical studies of cadmium selenide thin films

Nucleation and growth of cadmium selenide thin films are of considerable interest because of their direct effect on the optical and electrical properties of this material. Vacuum-deposited layers on amorphous and crystalline substrates showed a polycrystalline structure. The layers were deposited at a pressure of 10⁻⁴ Pa, with two deposition rates of 12 nm/s and 15 nm/s. The electrical resistivity and the optical absorption were studied for a group of layers on quartz substrate. As well the morphology and the microstructure were investigated by X-ray and electron microscopy. Few activation energies were estimated from the optical absorbance and thermo-resistance.     

Physicochemical investigation into the specific features of the phase transformations in electrodeposited nanocrystalline oxotungstate films

The structure of oxotungstate films (as-deposited and subjected to heat treatment at temperatures of up to 600°C) prepared through electrodeposition on platinum and gold polycrystalline substrates is investigated using different physicochemical methods. It is shown that the oxotungstate films consist of X-ray amorphous hydrated mixtures of isopoly compounds, predominantly in the form of paratungstates with [H₂W₁₂O₄₂]¹⁰⁻ anions. The structural transformation with an increase in the temperature in air is accompanied by the loss of water, the transformation of paratungstate anions into more oxidized forms, their destruction, and the crystallization of nonstoichiometric hydroxylated oxide phases.

     

Crystallinity of the mixed phase silicon thin films by Raman spectroscopy

Raman spectra of the mixed phase silicon films were studied for a sample with transition from amorphous to fully microcrystalline structure using four excitation wavelengths (325, 514.5, 632.8 and 785 nm). Factor analysis showed the presence of two and only two spectrally independent components in the spectra within the range from 250 to 750 cm^?1 for all four excitation wavelengths. The 785 nm excitation was found optimal for crystallinity evaluation and by comparison with surface crystallinity obtained by atomic force microscopy, we have estimated the ratio of integrated Raman cross-sections of microcrystalline and amorphous silicon at this wavelength as y = 0.88 ± 0.05.     

Electron spin resonance study of hydrogenated microcrystalline silicon–germanium alloy thin films

Paramagnetic defects of undoped hydrogenated microcrystalline silicon–germanium alloys (μc-Si_1?xGe_x:H) grown by low temperature (200 °C) plasma-enhanced chemical vapor desposition (PECVD) have been measured by electron spin resonance (ESR) and compared with those of hydrogenated amorphous silicon–germanium (a-Si_1?xGe_x:H). The spin density of μc-Si_1?xGe_x:H increases with Ge content and shows a broad maximum of ～10¹⁷ cm^?3 at x ～ 0.5, which reasonably accounts for the decreased photoconductivity. While the Ge dangling bond defects prevail in a-Si_1?xGe_x:H for Ge-rich compositions, we detected no ESR signal in μc-Si_1?xGe_x:H for x > 0.75 where an electrical change occurs from weak n- to strong p-type conduction. These results indicate that dangling bonds are charged in large densities due to the presence of the acceptor-like states in undoped μc-Si_1?xGe_x:H.     

Optical and electrical studies on spray deposited ZnO thin films

ZnO thin films were prepared by spray pyrolytic decomposition of zinc acetate onto a glass substrate. These films were analyzed for the optical and electrical properties. Optical studies show that in these films the electronic transition is of the direct transition type. The optical energy gap for the films of different thicknesses is estimated to be in the range 2.98 – 3.09 eV. Electrical studies indicate that the films exhibit thermally activated electronic conduction and the activation energies are found to be dependent on the film thickness. The complex impedance measurements were carried out over a wide range of frequencies at room temperature (300 K). All the impedance spectra contain only a single arc, but the arc has a non‐zero intersection with the real axis in the high frequency region. Also, the arc has its centre lying below with the real axis which indicates the multirelaxation behavior of the films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Corrosion dynamics of electric conductivity of metal films in ice under its structural and phase transformations

The corrosion-induced decrease in the electric conductivity of metal films in ice under its thermally induced structural relaxation and at the water crystallization front have been investigated. Mathematical models of corrosion enhancement are proposed that are based on the suggestion about overcoming the reaction barrier as a result of the release of recombination energy of orientational defects during structural and phase transformations of ice.     

Investigation of the thermal diffusion during the formation of a quasicrystalline phase in thin Al-Pd-Re films

The layer mixing during the formation of the Al₇₀Pd₂₀Re₁₀ icosahedral quasicrystalline phase in thin (55 nm) Al-Pd-Re layered film systems subjected to vacuum annealing has been studied. It is shown that a combined layer of Pd and Al atoms (with the Al₃Pd₂ phase dominating) is formed in the first stage (at 350°C), while the rhenium layer remains invariable. In the second annealing stage (at 450°C), the β′-AlPd phase is formed and the Re layer is diffused. In the third stage (700°C), Pd and Re atoms are uniformly distributed throughout the film with the formation of a quasicrystalline phase.     

Electron microscope study of cellular precipitation in ferritic iron-zinc alloys

Cellular precipitation in Fe/Zn system was studied by electron microscope methods. Experimental results, obtained by Speich, Predel and Frebel and the present authors were used to test equation (3) of Cahn's theory. The value of the specific surface energy σ of the Γ-ferrite interface was determined to be about 2960 erg. cm⁻².     

Morphology and crystal phase evolution of doctor-blade coated CuInSe2 thin films

CuInSe₂ (CIS) chalcopyrite thin films were prepared using a low-cost, non-vacuum doctor-blade coating and the thermal annealing method. An acetone-based precursor solution containing copper chloride, indium chloride, selenium chloride, and an organic binder was deposited onto a Mo-sputtered soda lime glass substrate using a doctor-blade coating method. After coating, the precursor films were annealed in a quartz tube furnace under low vacuum without the use of a Se atmosphere or reduction conditions. Evolution of the morphology, crystal structure, and thermal decomposition behavior of the films was analyzed by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis, and the film formation mechanism was suggested. The as-deposited precursor film gradually decomposed with increase in temperature and formed Cu_2−xSe and In₂Se₃ nuclei on the surface of the film. Incorporation of Cu_2−xSe with In₂Se₃ yielded a chalcopyrite CIS phase, which crystallized on annealing above 400 °C. The obtained CIS film showed low-resistive ohmic behavior with a Mo electrode and a high absorption efficiency for visible–infrared (IR) light, making it suitable for use in photovoltaic applications.     

Structure of anthracene thin films

Structure of anthracene thin films as dependent on the temperature of the substrate, thickness and condensation rate is studied. It was found that at temperatures t_s ≦ 55°C condensation is governed by a vapour crystal mechanism while at temperatures t_s > 55°C it follows as vapour fluid one. Depending on the condensation rate the crystals take pyramidal forms, those of dendrites and spherolites. At temperatures t_s < 55°C the films are mainly oriented with its plane (001) parallel to the substrate.     

Filamentary breakdown in thin anodic films

Experimental data are reported illustrating that the breakdown strength of metal/anodic-oxide/metal structures appear to have an upper bound at values close to the so-called formation field. It is suggested that this effect is real and is due to field enhancement at the cathode in the MIM structure resulting from ionic transport in the oxide. This, in turn, causes increased injection current as the electric field in the oxide reaches a critical value.