Thin zirconium nitride films prepared by plasma-enhanced CVD

Thin films of zirconium nitride have been deposited at temperatures as low as 573 K by PECVD using tetrakis(diethylamido)zirconium, Zr[N(C₂H₅)₂]₄ as precursor. The influence of the various experimental parameters on film properties and deposition rates has been studied. Under most experimental conditions hard coatings of good adherence and low carbon contamination resulted.     

The microwave response of MgB2 /Al2O3 superconducting thin films

Microwave characteristics of MgB2/Al2O3 superconducting thin films were investigated by coplanar resonator technique. The thin films studied have different grain sizes resulting from different growth techniques. The experimental results can be described very well by a grain-size model which combines coplanar resonator theory and Josephson junction network model. It was found that the penetration depth and surface resistance of thin films with smaller grain sizes are larger than those of thin films with larger grain sizes.     

Profile of the refractive index distribution over the depth of (HfO2)x(Al2O3)1 ? x films

Capabilities of the method of laser null ellipsometry for the study of optical parameters of thin films of multicomponent alloys are demonstrated. Films of alloys (HfO₂) _x (Al₂O₃)_{1 − x} on single-crystal silicon are obtained by the chemical vapor deposition with the use of the following volatile compounds: hafnium dipivaloylmethanate (IV) and aluminum acetylacetonate (III). The selection of initial sets for their optical parameters is justified. The selected model is shown to correspond to experimental data. In films deposited from the mixture of precursors, the refractive index increases from a substrate to a film surface. Due to the separation of sources, films described by a single-layer model were deposited. This fact is indicative of the homogeneous distribution of components over the film thickness.     

GaAs(100)衬底上C60单晶膜的取向生长

利用双温区真空蒸发沉积技术成功地在GaAs（100）衬底上实现了完全（111）取向的C₆₀单晶膜的生长．用扫描电子显微镜和Ｘ射线衍射技术对C₆₀单晶膜的形貌和结构进行了分析．结果表明：能实现C₆₀取向生长的衬底温度范围很窄，温度过高或过低都易造成晶粒的取向无序．对实验结果做出了合理的解释，并讨论了C₆₀单晶膜的生长机制 关键词：     

Gamma irradiation effects on structural and optical properties of amorphous and crystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films

The structural and optical properties of RF sputtered Nb₂O₅ thin films are studied before and after gamma irradiation. The films are subjected to structural and surface morphological analyses by using X-ray (XRD) and field emission scanning electron microscope techniques. In the wavelength range of 300–2000 nm, the optical parameters for amorphous and crystalline Nb₂O₅ thin films are estimated at differently exposed γ-irradiation doses (0, 50, 100 and 200 kGy). The optical constants, such as optical energy band gap, absorption coefficient, refractive index and oscillators parameters of amorphous and crystalline Nb₂O₅ thin films are calculated. The optical band gaps of γ-irradiated amorphous and crystalline Nb₂O₅ thin films are determined. In the non-absorbing region, the real part of the refractive index of amorphous and crystalline Nb₂O₅ thin films slightly increases with the increase in the exposed γ-irradiation dose.     

Relative performances of effective medium formulations in interpreting specific composite thin films optical properties

Several powerful effective medium formulations/approximation (EMA) and associated theories with different origins and concepts have been discussed and utilized here in order to model the experimental refractive index evolutions of ZrO₂-SiO₂ and Gd₂O₃-SiO₂ composite films with respect to their compositional mixings. Amongst these formulations, the Böttcher's generalized theory has been noticed to have more versatility and can simulate varieties of experimental observations incorporating a form factor parameter to account for the grain structure and morphology to a great extent. The refractive index modeling results of most of the available theories were compared with respect to their functional evolutions and limitations. It was noticed that at higher silica fractions (>20%) in our composite films, the effective experimental refractive index parameters have remained close to the most modeling results and Böttcher's expression has shown to fit the observable parameters very accurately. However, under low silica compositions (<20%) the refractive index values of the composite films depicted different functional evolutions. Such deviations have been attributed to the various morphological, grain structure and band gap supremacies observed in these specific composite films which are not accounted by the effective medium formulations and approximations. These observations are well supported by the atomic force microscopy results.     

Deposition of copper oxide (Cu2O,CuO) thin films at high temperatures by plasma-enhanced CVD

Copper-oxide films are deposited by plasma-enhanced CVD using copper acetylacetonate as a precursor. The influence of various experimental parameters on deposition rate, film composition and resistivity have been studied. The substrate temperature and the bias are the parameters which affect these properties the most. An increase of the substrate temperature changes the phases of the deposit from Cu₂O-CuO over Cu₂O to Cu. At temperatures 500° C the deposition rates are high but the films consist mainly of metallic Cu. A negative bias enhances the deposition rate only slightly but has a strong effect on the film composition and can completely balance the oxygen deficiency. At a bias of –120 V the films consist of pure CuO even at temperatures 500° C.     

Chemical bath-deposited ZnS thin films: Preparation and characterization

Chemical bath deposition of ZnS thin films from NH₃/SC(NH₂)₂/ZnSO₄ solutions has been studied. The effect of various process parameters on the growth and the film quality are presented. The influence on the growth rate of solution composition and the structural, optical properties of the ZnS thin films deposited by this method have been studied. The XRF analysis confirmed that volume of oxygen of the as-deposited film is very high. The XRD analysis of as-deposited films shows that the films are cubic ZnS structure. The XRD analysis of annealed films shows the annealed films are cubic ZnS and ZnO mixture structure. Those results confirmed that the as-deposited films have amorphous Zn(OH)₂. SEM studies of the ZnS thin films grown on various growth phases show that ZnS film formed in the none-film phase is discontinuous. ZnS film formed in quasi-linear phase shows a compact and a granular structure with the grain size about 100 nm. There are adsorbed particles on films formed in the saturation phase. Transmission measurement shows that an optical transmittance is about 90% when the wavelength over 500 nm. The band gap (E_g) value of the deposited film is about 3.51 eV.     

Influence of front contact work function on silicon heterojunction solar cell performance

In this study, we present numerical and experimental analyses of the effect of the work function of the transparent conducting oxide (TCO) on the performance of silicon heterojunction solar cells. The simulation results showed that the solar cell performance such as V_oc and FF were strongly affected by the work function of TCO films due to band bending. The experimental analysis was carried out by preparing Zn–In–Sn–O films with varying work function by varying the composition. The compositional dependence of the work function, optical and electronic properties of Zn–In–Sn–O films was examined, and the performance of the silicon heterojunction solar cells with corresponding TCO films was analyzed. The electrical properties and work function in Zn–In–Sn–O films were significantly influenced by Zn content, and Zn–In–Sn–O film with 12.7 at.% Zn content, which had the highest work function and lowest resistivity among the studied films, resulted in the highest conversion efficiency of solar cell due to increased V_oc and FF. It was shown that the behavior of performance parameters in silicone heterojunction solar cells closely correlated with the work function and electrical properties of TCO films.     

Spatial distribution of structural disorder in Co2FeSi films studied by anisotropic magnetoresistance

We studied the spatial distribution of the partially disordered B2 phase in Co₂FeSi films by anisotropic magnetoresistance measurements. The analysis of our experimental results allows not only for the discrimination between different models for the spatial distribution of structural disorder, but also enables us to estimate the volume fraction occupied by the partially disordered B2 phase within the Co₂FeSi films grown on GaAs. In particular, our findings are in accordance with a laterally inhomogeneous distribution of the structural disorder in the topmost part of Co₂FeSi films.     

An analysis of absorption-desorption of volatile organic compounds by molecularly imprinted polymer films

A theoretical analysis of the experimental data on absorption (desorption) of volatile organic compounds by (from) molecularly imprinted polymer films was performed. The theoretical time dependences of the amount of absorbed analyte in a film were calculated using a system of equations with four kinetic parameters (Γ, K, K _sur , and C _eq ), which were determined by theoretically approximating the experimental data. The special features of the absorption-desorption process in a polymer film were suggested to be described using a parameter called the specificity coefficient. Specificity coefficients were determined for all the polymers and analytes studied. The specificity coefficients obtained from the chromatographing data were compared with the imprinting factors of chromatograms calculated from the experimental retention time values. An empirical linear dependence of specificity coefficients on imprinting factor values was obtained.     

Growth and characterization of CuxS (x=1.0, 1.76, and 2.0) thin films grown by solution growth technique (SGT)

Thin films of Cu_xS (x=1.0, 1.76, and 2.0) were grown by solution growth technique (SGT). The deposition parameters such as pH of solution, deposition time, and deposition temperature were optimized. The deposited films were annealed in Ar atmosphere at 250 °C. The changes in structural and optical transport phenomenon of annealed films have been studied. The surface morphology and composition of films were studied by SEM micrographs and EDAX analysis, respectively, and the surface roughness was calculated by atomic force microscopy (AFM). The XRD study showed the polycrystalline nature of annealed film. The lattice parameters of different phases of the material were calculated from the XRD pattern. The absorption coefficient varies in the range of 1×10⁵-6×10⁵ cm⁻¹. The optical bandgaps of CuS, Cu_1.76S, and Cu₂S are 1.72, 2.11, and 2.48 eV, respectively.     

Relaxation oscillations in circuits containing sandwich switches based on vanadium dioxide

Electrical switching with an S-shaped I–V characteristic is studied in metal/oxide/metal structures based on vanadium oxide thin films fabricated by electrochemical oxidation. This switching effect is associated with the metal–insulator phase transition in VO₂, and the channels consisting of vanadium dioxide are formed in the initial anodic films during the process of electroforming. An expression for the relaxation oscillation frequency, as a function of the external circuit RC factor and I–V curve parameters, is obtained. It is shown that the experimental data on the frequency–capacitance dependence match well this theoretical relation. Applied aspects of the obtained results, particularly concerning oscillatory neural networks and frequency-output sensors, are discussed.     

Growth of stoichiometric and textured LiNbO3 films on Si by pulsed laser deposition

Laser ablation of single-crystal LiNbO₃ in a gas environment is used to grow films on (100) Si substrates heated to 650 °C. The film composition and crystallinity are studied as a function of the nature (reactive, O₂, or inert, Ar) and pressure of the gas environment applied during deposition and cooling-down processes, the laser energy density and the target–substrate distance. Experimental results show that a gas pressure close to 1 mbar is required to produce stoichiometric films in either O₂ or Ar. The modification of the laser energy density and the target–substrate distance allows us to improve the crystallinity of the films that become textured along the (006) direction. The influence of the experimental parameters on the film properties is discussed in the frame of the formation of a blast wave, that leads to the focusing of the expanding Li species and thus, to the increase of the Li content in the films. Received: 8 February 2001 / Accepted: 9 February 2001 / Published online: 3 May 2001     

Investigation of gas sensor based on In2O3:Ga2O3 film

We have fabricated a LPG and butane sensor whose sensitive element is a nanosize In₂O₃:Ga₂O₃ (96:4 weight %) film covered with a thin palladium catalytic layer. Technology of deposition of these films on a glassceramic substrate by the method of rf magnetron sputtering was elaborated. The surfaces of fabricated films were studied with use of a scanning electron microscope and the thickness of films was measured. The sensitivity of sensors based on the glassceramic/In₂O₃:Ga₂O₃ (96:4 weight %)/Pd structure depending on the thickness and sizes of film grains was studied. We revealed technological regimes of sputtering providing fabrication of films with the best parameters.     

A study of structural, compositional and optical properties of spray-deposited non-stoichiometric (Zn,Fe)S thin films

Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl₂, FeCl₂ and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N₂ as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase.     

The refractive index of homogeneous SiO<Subscript>2</Subscript> thin films

The effect of the through-thickness inhomogeneity of SiO₂ films on their refractive index is studied. The SiO₂ films, deposited by tetraethoxysilane pyrolysis on plane-parallel oriented crystalline quartz substrates and on silicon plates, were etched layer-by-layer in Pliskin’s solution. The refractive index and the geometric thickness of films were calculated from the measured ellipsometric angles after each etching. The determination errors of the refractive indices as functions of the film thickness, which result from the measurement errors of the polarization angles and substrate parameters, are numerically analyzed. For SiO₂ films thicker than 20nm, no effect of inhomogeneity is found. The refractive indices of thinner films were observed to depend on the thickness. The reasons for such dependences are discussed.     

Discharge characteristics of polymer blend (PVP/PVA) electrolyte films doped with potassium bromide

Solid polymer blend electrolyte films based on PVP/PVA complexed with KBr were prepared by the solution cast technique. Various experimental techniques such as electrical conductivity and transport number measurement were used to characterize the polymer electrolyte films. Electrochemical cells with the polymer electrolytes (PVP + PVA + KBr) were fabricated in the configuration K / (PVP + PVA + KBr) / (I₂ + C + electrode). The discharge characteristics of the cells were studied under a constant load of 100 KΩ. The open-circuit voltage, short-circuit current, and discharge time for the plateau region are measured. Several other cell parameters were evaluated and are reported.     

Magnetic and structural properties of FeX/Tb15 Å multilayers

Magnetic domains in Fe/Tb sputter-deposited multilayer films are studied magneto-optically using a Kerr microscope. These observations together with other experimental measurements (vibrating sample- and torque magnetometry) showed the important role of the iron-layer thickness d_Fe on the magnetic properties of the films. At certain combinations of the layer thicknesses both perpendicular and in-plane anisotropies are present in the film. The structural investigations indicate that a gradual increase of the iron-layer thickness d_Fe leads to a phase transition of iron from amorphous to crystalline at certain thicknesses of the iron layer, which is also reflected in the magnetic behavior of the films. The differences between the magnetic properties of the investigated multilayered Fe/Tb films and those of amorphous FeTb films are discussed as well.     

激光等离子体淀积硅膜

本工作研究了低温、低压下硅薄膜的激光淀积过程,获得均匀性好,平方厘米量级的多晶和非晶态薄膜。仔细测量了淀积过程的最佳条件,在380℃基片温度做得多晶膜。利用有共振吸收的光学击穿以及气体被击穿后产生爆炸波导致高能Si原子产生的模型,讨论了激光等离子体CVD动力学过程。发现TEACO₂激光击穿SiH₄,以及诱发的爆炸波对硅膜生长有重要作用。理论算得的硅膜生长面积和晶态结构与实验定性符合。 关键词：