Method for producing graphite and alumina thin films

A simple comprehensible method for producing graphite and alumina films has been suggested. The optical properties of a graphite suspension in toluene and a suspension of natural clay with a high content of alumina particles in water have been studied. It has been found that the optical density of the suspensions varies from layer to layer, and the lowest optical density has been observed in upper layers. Graphite and aluminum films have been prepared by taking samples from different depths. The microstructure of the films has been examined. It has turned out that alumina particles coalesce into regularly shaped objects in the form of snowflakes. In addition, alumina films obtained from samples taken from different depths of the suspension have different thicknesses. In thin and thick films, the particle size is 0.29 and 2.81 μm or more, respectively.     

RF溅射的SiO_2和SiO_2/Al/SiO_2薄膜的喇曼散射光谱研究

用射频溅射(RF Sputtering)法制成了SiO_2和SiO_2/Al/SiO_2薄膜。应用喇曼光谱研究了薄膜结构。结果表明:RF溅射制成的SiO_2薄膜是含有大量环结构缺陷的玻璃态;SiO_2/Al/SiO_2层状薄膜的喇曼光谱中观察到Al_2O_3的特征峰,证实了Al/SiO_2薄膜界面确有氧化还原反应发生;从喇曼光谱中Al_2O_3的特性峰的位置和相对强度可推断出,SiO_2/Al/SiO_2薄膜界面处的Al_2O_3是非晶γ-Al_2O_3。     

Properties of ITO films prepared by rf magnetron sputtering

Recently, a detailed study of the properties of ITO thin films deposited under various preparation conditions using the rf magnetron sputtering technique (from ITO target in pure Ar gas) has been undertaken in our laboratory. The effect of substrate temperature has been studied in a previous paper. Here the results of a study of the structural, electrical and optical properties of the ITO films with different thickness are presented. The figure of merit for the films, which is a measure of the quality of the films as transparent conductive layers for photovoltaic applications, has been evaluated.     

Pyroelectric and piezoelectric responses of thin AlN films epitaxy-grown on a SiC/Si substrate

This paper presents the results of pyroelectric and piezoelectric studies of AlN films formed by chloride–hydride epitaxy (CHE) and molecular beam epitaxy (MBE) on epitaxial SiC nanolayers grown on Si by the atom substitution method. The surface topography and piezoelectric and pyroelecrtric responses of AlN films have been analyzed. The results of the study have shown that the vertical component of the piezoresponse in CHE-grown AlN films is more homogeneous over the film area than that in MBE-grown AlN films. However, the signal from the MBE-synthesized AlN films proved to be stronger. The inversion of the polar axis (polarization vector) on passage from MBE-grown AlN films to CHE-grown AlN films has been found experimentally. It has been shown that the polar axis in MBE-grown films is directed from the free surface of the film toward the Si substrate while, in CHE-grown films, the polarization vector is directed toward the free surface.     

多层溅射制备Wsix/Si薄膜的电阻率特性研究

利用多层溅射技术制备了ＷＳｉ_x／Ｓｉ薄膜，然后测量其平面电阻的退火行为，发现平面电阻在６００－７００℃之间退火后有陡降，这对应于非晶ＷＳｉ_x薄膜中Ｗ₅Ｓｉ₃四角相的形成。ｘ射线衍射和慢正电子湮没测量也证实了这一点。认为薄膜电阻率的突变反映了导电机制的变化，它和薄膜结构的变化有很好的对应关系。 关键词：     

Photoluminescence studies on nanostructured cadmium sulfide thin films prepared by chemical bath deposition method and annealed at different temperatures

Nanostructured cadmium sulfide (CdS) thin films have been prepared by chemical bath deposition (CBD) method and after post deposition annealing of the thin films at different temperatures, photoluminescence (PL) property has been studied. The effects of various photoexcitation wavelengths on the PL behaviour of different annealed films of CdS were studied by recording the PL spectra. The intensity of PL, the profile of the PL spectra and the effects of photoexcitation wavelength depend drastically on the temperature of the post deposition annealing of the thin films. The XRD patterns of the films show the presence of both the hexagonal and cubic phases (mixed phases). The emission peak arises from the surface defects of the CdS nanocrystalline thin films. Significant modification in the surface morphology of the CdS films upon annealing has been observed from the FESEM images. The morphology of the thin films is expected to influence the PL behaviour of the CdS thin films. The quantum size effect and size dependant PL have been observed.     

Sputter deposition and characterization of Ni-Mn-O and Ni-Co-Mn-O spinels on polymide and glass substrates

RF magnetron sputtering has been used to deposit films using sintered targets of Ni-Mn-O and Ni-Co-Mn-O. By varying the oxygen/argon gas ratio, films with electrical properties similar to the sintered target material have been obtained. An important advance has been the sputter deposition of these films on polyimide coated substrates. The resistivity-temperature behavior in these films is similar to that of the sintered oxides, and both show deviations from the predictions of the small polaron model of hopping conductivity.     

Structure of Ultrathin Polycrystalline Iron Films Grown on SiO<Subscript>2</Subscript>/Si(001)

The structure of polycrystalline Fe films grown on an oxidized Si(001) surface at room temperature has been studied by the technique of high-energy electron diffraction. It has been found that the grain orientation in the films depends of the amount of deposited iron. In Fe films less than 5 nm thick, grains have been found to be randomly oriented. Fe films more than 5 nm in thickness exhibit the (111) texture with an axis coinciding with the surface normal. The angular dispersion of the [111] direction in the Fe lattice from the surface normal is ±25°. It has been found that as the Fe films become thicker, the (111) texture changes to the (110) texture.     

On the porosity of coldly condensed sers active Ag films: II. Comparison of adsorption and Raman scattering of pyridine

The adsorption of pyridine on coldly deposited Ag films annealed at temperatures ranging from 58 to 330 K, the porous surface topography of which has been investigated in part I of this work, has been studied by means of UPS, work function change and thermal desorption measurements. Pyridine induced work function changes have been employed to follow the surface diffusion of pyridine molecles into the pores of these Ag films. The surface diffusion is very slow below 60 K, but readily takes place at 130 K with an estimated activation energy of surface migration of E_m ≈ 4 kcal/mol. Preadsorption of Xe into the pores of the films causes inhibition of pyridine diffusion into the pores. The onset of pyridine desorption from porous films is detected at ≈ 200 K while from flat films the desorption begins already at 150 K. The careful analysis of our data on the structure of the coldly deposited Ag films and the adsorption behavior of pyridine on these films as well as a survey of published SERS data lead us to conclude that the SERS active sites of coldly deposited Ag films are within the pores. This conclusion is in agreement with recent theoretical calculations.     

Formation of ZnO and Zn1−xCdxO films on CdTe/CdZnTe single crystals

In this work we report on the properties of ZnO and Zn_1−xCd_xO films formed on top of CdTe and CdZnTe single crystals. The films have been obtained by thermal evaporation of Zn metal films and further oxidation in atmospheric conditions. The structural and compositional characteristics of the films have been analysed by means of scanning electron microscopy and energy-dispersive X-ray analysis. The chemical composition of the films as a function of growth parameters has been obtained. It has been possible to demonstrate by Raman spectroscopy the formation of both ZnO and Zn_1−xCd_xO films. The possible inter-diffusion effects between the films and the substrate, derived from the oxidation process, have been discussed. It has been possible to check by means of photoluminescence, the optical quality of the ZnO and Zn_1−xCd_xO films, also regarding to the presence of local changes. Differences between the optical spectra obtained from various ZnO films grown on top of CdTe and CdZnTe substrates enabled the determination of compositional differences introduced by the substrate when the deposition parameters are modified.     

Photocatalytic and optical properties of titanium dioxide thin films prepared by metalorganic chemical vapor deposition

Titanium dioxide thin films have been deposited by metalorganic chemical vapor deposition (MOCVD) over sodalime glass substrates at substrate temperatures ranging from 250 °C to 450 °C. The effect of deposition temperature on the structure and microstructure of the obtained films has been studied by x-rays diffraction (XRD) and scanning electron microscopy (SEM), respectively. Diffraction patterns show the existence of a pure anatase phase beside a texture change with the increase of deposition temperature. Micrographs show grain fragmentation with the increase in deposition temperature. UV–Vis. spectra have been recorded by spectrophotometery. The optical energy gap has been calculated for the deposited films from the spectrophotometrical data. Photocatalytic experiments have been carried out. The photocatalytic activity has been found to decrease with the increase in deposition temperature.     

Microstructure and electrical properties of SnS thin films

Thin SnS films are of interest for optoelectronics. The influence of the preparation modes on the microstructure and electrical properties of thin SnS films obtained by the hot-wall method on substrates made of pure glass and glass with a molybdenum sublayer has been investigated. It has been established that the formation of SnS films with two texture types (111) and (010) is possible on the substrates made of pure glass, depending on the mode. The resistivity and the temperature coefficient of thermoelectric power of the SnS films on glass vary in the range from 12 to 817 Ω cm and from 37 to 597 μV/K, respectively, depending on the preparation modes. The activation energy is 0.11–0.12 eV.     

Specific features of the formation of arrays of silver clusters from a thin film on a SiO2 surface

The decomposition of thin silver films into clusters on a SiO₂ surface during thermal heating in vacuum has been studied. The experimental histograms of distribution of clusters formed from films of different thicknesses over their diameters have been constructed. It has been found that the decomposition of the films with thickness to 10 nm leads to the formation of monoclusters having one predominant diameter in the range from 15 to 20 nm. After a longer term annealing, the array of clusters almost does not change with time, and the predominant diameter is retained. From films with thicknesses ranging from 10 to 130 nm, an array of clusters with two predominant diameters containing monoclusters (40–80 nm) and globular clusters (400 nm) is formed. It is noted that, with increasing annealing time, the array is enlarged due to the coalescence process and is gradually evaporated; in this case, the predominant cluster diameters remain the same.     

Comparison of magnetoreflection from CoFe-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> multilayer and granular films in the infrared spectral region

The paper reports on a study of light reflection and of the magnetorefractive effect in CoFe-Al₂O₃ multilayer and granular films in the IR region at λ = 2.5–25 μm. These films exhibit a noticeable tunneling magnetoresistance of 5–8%. It has been found that the spectra of the magnetorefractive effect have features at λ ≈ 6.7 and ≈8.1 μm originating from phonon mode excitation in the dielectric matrix. It has been established that the magnitude of the magnetorefractive effect exceeds 2.5% for multilayer films, a value substantially larger than that for granular ones. Magnetoreflection has been analyzed for two film systems with roughly equal tunneling magnetoresistance. It has been shown that magnetoreflection for granular films can be described in a first approximation by the modified Hagen-Rubens relation, while the enhanced effect exhibited by multilayer films requires inclusion of interference of the magnetooptical response.     

X射线吸收谱测算锂氮共掺杂氧化锌薄膜局域电子结构

为了实现对Li—N共掺杂p型ZnO薄膜的形成机制以及其稳定p型导电原因的揭示,利用X射线光电子谱及基于同步辐射光源的X射线吸收精细结构谱测试对薄膜的局域电子结构进行了测算分析.获得了Li—N成键及Li—N复合型受主形成的信号,利用光致发光测量计算其受主能级为122 mV.证实了薄膜中Li—N复合型受主的形成,而Li—N...     

Effect of intrinsic stress on the optical properties of nanostructured ZnO thin films grown by rf magnetron sputtering

In this paper we report the effect of deposition temperature on the structural and optical properties of ZnO thin films prepared by rf magnetron sputtering. The films grown at lower deposition temperatures were in a state of large compressive stress, whereas the films grown at higher temperature (450 °C) were almost stress free. In the absorption spectra, the ZnO excitonic and the Zn surface plasmon resonance (SPR) peaks have been observed. A redshift in the optical band gap of ZnO films has also been observed with the increase in the deposition temperature. The shift in the band gap calculated from the size effect did not match with the observed shift values and the observed shift has been attributed to the compressive stress present in the films.     

Atomic force microscopy of the supramolecular organization and strength properties of ultrathin polysiloxane block copolymer films

Ultrathin films of polysiloxane block copolymers and their composites with modifying additives of the C₆₀ fullerene have been studied using atomic force microscopy. It has been revealed that, independently of the concentration of the additives, the surface relief of the films has an ordered structure with a period of approximately 35 nm, which is associated with the presence of a spatial network of rigid block domains of ladder phenylsilasesquioxane in the block copolymer. The mechanical properties of the films have been determined from indentation tests of their surface layers. Reliable quantitative measurements have been performed with specially fabricated spherical indenters of the calibrated submicron radius of curvature. The obtained values of the strength parameters correlate with the data derived from standard physical and mechanical tests of thick films. It has been found that the addition of the C₆₀ fullerene at a level of 0.01% significantly improves the elasticity of the surface layers of the block copolymer.     

Electronic properties of thin films of laser-ablated Al2O3

Laser ablation coupled to mass quadrupole spectrometry (LAMQS) has been used to prepare thin films of aluminum oxide deposited on Si substrates starting from commercial Al₂O₃ polycrystalline targets. X-ray photoemission (XPS) and reflection electron energy loss spectroscopy (REELS) have allowed the investigation of the electronic properties of the produced films. In particular, it was found that the Al/O atomic ratio assumes a value very near to 0.7 (stoichiometric ratio) only for films deposited normally with respect to the target surface, while films grown at larger deposition angles are more rich in oxygen content.The composition, the mass density, the optical energy gap, the complex dielectric function and refraction index of the films have been calculated and compared with the results obtained from our starting target material and with the literature. The morphology of the deposited samples has been analyzed by the AFM technique.     

Influence of hydrogenation on electrical conductivity of vanadium dioxide thin films

The influence of hydrogenation on electrical conductivity of vanadium dioxide thin films has been investigated. It has been shown using measurements of the electrical conductivity that the hydrogenation of vanadium dioxide thin films leads to a decrease in the temperature of the phase transition from the tetragonal phase (with “metallic” conductivity) to the semiconducting monoclinic phase. It has been found that, upon doping of vanadium dioxide with hydrogen, the electrical conductivity of the monoclinic phase can increase by several orders of magnitude. Nonetheless, the temperature dependence of the electrical conductivity of hydrogenated films exhibits a typical semiconducting behavior in the temperature range where the monoclinic phase is stable.     

Effect of Mg/Co on the properties of CdS thin films deposited by spray pyrolysis technique

Mg, Co doped and (Mg, Co) co-doped CdS thin films were prepared using chemical spray pyrolysis method. It is observed from the X-ray diffraction study that the deposited film exhibit cubic phase of CdS with preferred orientation along the (111) plane and incorporation of Mg and Co has been confirmed form energy dispersive analysis and XPS analysis as well. The doped and codoped CdS thin films exhibit 1LO and 2LO vibrations as confirmed by Raman spectrum. The core level XPS spectra ensures the incorporation of doping elements precisely. The morphological variations due to the incorporation of Co and Mg in CdS thin films have been observed by FE-SEM. The particle sizes and crystalline nature have been revealed from HRTEM images and corresponding SAED patterns. The co-doped CdS thin films show a significant shift blue in absorption spectrum. Improved magnetic properties have been observed for the co-doped CdS thin films.