Lao.5Sro.5MnO3薄膜的输运特性和光诱导效应

用磁控溅射方法制备了La0.5Sro 5MnO3薄膜,研究了薄膜的输运特性和光诱导效应.La0.5Sr0 5MnO3薄膜具有温度相变特征:低温为铁磁金属相,高温则为顺磁非导体相,相变温度420 K.为铁磁金属相时,光诱导效应导致薄膜的电阻增大,在360 K电阻变化相对值的最大值约为9.62%.根据双交换作用模型,激光导致顺磁非导体相小极化子的浓度增加,使电阻减小.     

2.24 Structural and electrical properties of discontinuous gold films on glass

In the present work thin gold films are investigated in the thickness interval 10–160 Å. The films are deposited in UHV on to glass substrates at room temperature and with an electric field in the substrate plane. In the thickness interval 10–45 Å the film is discontinuous and the size distribution of the islands as determined from electron micrographs is described with a log-normal distribution function. The onset of the in situ electrical conduction at the average thickness 45 Å makes it possible to measure the film resistance as a function of the film thickness during the condensation. At the thickness 53 Å stable metallic continuous paths are formed and the film achieves metallic properties. The fraction of the surface covered with material and the island density are measured 20 h after the deposition. Both these entities change rapidly at the stage when the film grows to be metallic continuous.     

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.     

Measurement and the effect of different solvents on thin polymer film surface resistance

A method of measuring the surface resistance of thin polymer films has been developed. The method uses a concentric cylindrical electrode arrangement for the measurements and has been studied analytically and experimentally. The effect of different solvents on the thin polymer film surface resistance is examined as well using the method.     

The effect of linear thermal expansion on the temperature coefficient of resistance of double-layer thin metallic films

A general theoretical expression for the temperature coefficient of resistance of double-layer thin metallic films, based on the well known Fuchs-Sondheimer model, is derived. This expression includes the linear thermal expansion coefficients and Poisson's ratios of the double layers and the substrate, also the film dimensions and temperature coefficient of resistance of the double-layer thin film, with and without the thermal expansion of both the film layers and the substrate. Numerical calculations are carried out for gold-silver double-layer films deposited on a glass substrate, where variations in the temperature coefficient of resistance depending on thermal expansion are studied as a function of reduced film thickness. The computed numerical results, using the derived new expression for the temperature coefficient of resistance of the double-layer thin metallic films, show that the thermal expansion decreases the value of the temperature coefficient of resistance.     

Measurement and the effect of different solvents on thin polymericfilm surface resistance

A method of measuring the thin polymeric film surface resistance has been developed. The method uses an arrangement of concentric cylindrical electrodes for the measurements and has been studied analytically and experimentally. The effect of different solvents on the thin polymeric film surface resistance as well as the use of the method are examined. The mathematical modeling of the cylindrical electrode measuring system fitted the experimental results     

Numerical simulation of periodic cracking mechanism in microscopic surface films during roll bonding processes

The microscopic surface films existing on the top of metallic layers play an important role in the process of joining by plastic deformation. The bond formation during cold welding processes is basically associated with the fracturing of surface films to produce intimate metallic contacts. The present paper aims at providing a numerical model to describe the cracking pattern of brittle surface films bonded to the ductile substrates. A microscale finite element model is developed which takes into account the fracturing mechanisms of thin surface films in roll bonding processes. The presented model is calibrated by using the existing experimental data for an aluminum alloy covered by a thin layer of oxide film. The model is also validated against a well‐known analytical model for periodic cracking. The distribution of stresses within the fractured surface film demonstrates that the generated cracks in the surface film have essentially a periodic pattern. Moreover, it is shown that the crack spacing is highly dependent on the properties of the surface film. Finally, the obtained results for the roll bonding show that a crack density saturation takes place at the entry of the roll bite where a small surface expansion is applied to the rolled samples.     

Structural and electrochemical behaviour of sol-gel zirconia films on 316L stainless-steel in simulated body fluid environment

Sol-gel thin film offers a number of advantages that makes it an attractive method for obtaining ceramic coatings on metallic implants. In this study, the feasibility of using a polymeric sol-gel zirconia film on 316L SS substrate was evaluated using potentiodynamic polarization measurements to measure the corrosion resistance in simulated body fluid environment. Fairly uniform, dense and crack-free films were produced by dip-coating the 316L stainless-steel substrate in a precursor solution containing sonocatalysed zirconium propoxide and yttrium acetate, followed by firing at 600 °C in vacuum. The resultant films were characterized by thermal studies (TGA-DTA), XRD, FT-IR and polarization studies.     

Stress behavior of FCC metallic thin films during thermal evaporation

The development of stress in metallic thin films, monitored by in-situ curvature measurements during deposition, is analyzed. Three distinct stress regions including initial compressive, broad tensile, and incremental compressive stress were reported in terms of the film thickness (deposition time) by F. Spaepen. An experimental set-up was assembled for the in-situ curvature measurements utilizing vacuum thermal evaporation and multi-beam laser reflection points arrayed in x- and y-axis. The change in the spacing of laser reflected points was converted to the curvature of specimen, in turn, to instantaneous stress levels in the growing films using Stoney's formula. To investigate the effect on the distinct stress regions, the flux of the depositing metallic atoms was used as an experimental variable in this study. For the lowest flux cases for Cu and Ag, an additional second compressive stress stages after tensile maximum stress was observed in this study. Initial compressive part and tensile maximum stress regions appeared in shorter period of time for the thin films deposited at higher flux of atoms. Thus the flux of depositing atoms may affect the mechanisms of each stage. The initial compressive stress is conjectured to stem from the state of thin film surfaces; dynamic and relaxed surface. A broad tensile region is reported from the fact that the reduction of excess volume associated with grain boundaries and/or the coalescence of grains for high mobility materials. The incremental compressive stress region may be related to surface state and atomic mobilities.     

Incoherent radiative processing of titanium silicides

Titanium silicide thin films were formed after short-time processing of thin films of metallic titanium over single-crystal silicon and polycrystalline silicon. Radiation from high intensity lamps provided a directional driving force for the reaction, which was carried out both in the presence of oxygen in the reactor and under vacuum. The effect of oxygen on the reaction was monitored using sheet resistance, X-ray diffraction and Auger electron spectroscopy (AES) measurements. The film quality was found to be strongly influenced by an oxygen partial pressure in the reactor. The effect of the processing time was also assessed and the optimum time and power input interval were determined. High quality, low resistivity films with TiSi₂ as the major phase were obtained after 10 s under a roughing vacuum. AES studies indicated that most of the oxygen and other contaminants remained in a narrow surface layer after processing.     

ZnO transparent thin films for gas sensor applications

Zinc oxide (ZnO) transparent thin films were deposited onto silicon and Corning glass substrates by dc magnetron sputtering using metallic and ceramic targets. Surface investigations carried out by Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) have shown a strong influence of deposition technique parameters on film surface topography. Film roughness (RMS), grain shape and dimensions are correlated with the deposition technique parameters as well as with the target material. XRD measurements have proven that the dc sputtered films are polycrystalline with the (002) as preferential crystallographic orientation. AFM analysis of thin films sputtered from a ceramic target has shown a completely different surface behavior compared with that of the films grown from a metallic target. This work demonstrates that the target material and the growth conditions determine the film surface characteristics. The gas sensing characteristics of these films are strongly influenced by surface morphology. Thus correlating the optical and electrical film properties with surface parameters (i.e. RMS and Grain Radius) can lead to an enhancement of the material's potential for gas sensing applications.     

Optical, electrical and thermoelectric power studies of Al-Sb thin film bilayer structure

The III-V semiconductors are of great importance due to their applications in various electro-optic devices. The Al-Sb thin film was deposited on glass substrate by thermal evaporation method at a pressure of 10^-5 torr. The samples were annealed for 3 h at different constant temperatures in a vacuum chamber at a pressure of 10^-5 torr. The electrical resistance vs temperature studies show phase transformation from metallic to semiconducting. The observed positive thermoelectric power indicates that Al-Sb thin films arep-type in nature. The Rutherford back scattering analysis and optical band gap measurements also indicate that the inter-diffusion concentration varies with temperature.     

Electrical and structural properties of NiCr thin film resistors reactively sputtered in O2

NiCr thin film resistors have been reactively sputtered using a d.c. diode system in which the anode is formed by a carousel. The substrates are mounted on this carousel and can be rotated through the discharge. For films deposited onto a stationary carousel (the substrates permanently fixed in the discharge), film resistivities range from 150 to 300 μΩ as the oxygen partial pressure is increased from the base pressure to 3 × 10^-5 torr. The TCR values range from 150 to 300 ppm/°C. For carousel rotation at 20 rev/min the corresponding resistivities may be increased by a factor as large as 20 without greatly affecting the TCR. Microprobe analysis indicates that the Ni/Cr concentration ratio is independent of the deposition conditions, but that for a given oxygen partial pressure the film density is less for films deposited onto a rotating carousel than for films deposited onto a stationary carousel. Transmission electron microscopy indicates that the crystallographic structure consists of a metallic phase and an oxide phase which do not change with carousel rotation, but that films deposited onto a stationary carousel have an island structure while those deposited onto a rotating carousel have a worm-like structure. The structural features of films deposited onto a rotating carousel may be due to oblique incidence effects. Measurements of film resistance at low temperatures indicate that conduction in the film may be considered to consist of a metallic conduction mechanism of positive TCR acting in conjunction with an oxide conduction mechanism of negative TCR, with the relative contribution of each mechanism being a function of the physical microstructure of the films. Heat treatment of films deposited onto a rotating carousel produces an increase in resistance which is attributed to oxidation of the film surface, while heat treatment of films deposited onto a stationary carousel produces a resistance decrease which is attributed to thermal annealing effects dominating surface oxidation effects.     

Probing molecular junctions using surface plasmon resonance spectroscopy

The optical absorption spectra of nanometer-thick organic films and molecular monolayers sandwiched between two metal contacts have been measured successfully using surface plasmon resonance spectroscopy (SPRS). The electric field within metal-insulator (organic)-metal (MIM) cross-bar junctions created by surface plasmon-polaritons excited on the metal surface allows sensitive measurement of molecular optical properties. Specifically, this spectroscopic technique extracts the real and imaginary indices of the organic layer for each wavelength of interest. The SPRS sensitivity was calculated for several device architectures, metals, and layer thicknesses to optimize the organic film absorptivity measurements. Distinct optical absorption features were clearly observed for R6G layers as thin as a single molecular monolayer between two metal electrodes. This method also enables dynamic measurement of molecular conformation inside metallic junctions, as shown by following the optical switching of a thin spiropyran/polymer film upon exposure to UV light. Finally, optical and electrical measurements can be made simultaneously to study the effect of electrical bias and current on molecular conformation, which may have significant impact in areas such as molecular and organic electronics.     

Influence of MgO nano-crystals on the thermodynamics, hydrogen uptake and kinetics in Mg films

Hydrogen uptake in thin sputtered magnesium films covered with a Palladium layer was studied by resistance measurements. During growth, oxygen was introduced into the chamber in small amounts and the effect on the resistance, measured in situ, while growing, was monitored. This resulted in the formation of a mixture of MgO nanocrystals and layers in the Mg films. The measurements were made in situ in the sputtering chamber where the samples were grown. The aim of the study was to study the effect of oxygen contamination on hydrogen uptake in Mg films, as well as studying the uptake kinetics. Previous work on clean Mg films has shown that hydride formation at the surface reduces greatly the rate of hydrogen uptake further inside the film. These measurements show that the presence of oxygen contamination initially increases the rate of uptake greatly but decreases it when the Mg film is contaminated further with more oxygen.     

高温ITO薄膜应变计制备及压阻性能EI北大核心CSCD

高温薄膜应变计被广泛应用于极端条件热端构件的应变测量。ITO薄膜应变计通常能够应用于1000℃以上的应变测量,为了研究ITO薄膜的显微结构、XPS光谱、阻温特性及压阻响应,采用磁控溅射在陶瓷基底上制备了ITO薄膜应变计,并在高温纯N2中热处理ITO薄膜。结果表明,其电阻温度系数稳定在-750×10-6℃-1,在1200℃下测试其应变特性,测得电阻漂移率为0.0018 h-1,应变因子为16。ITO薄膜在高温下具有稳定的电阻温度系数和低漂移率,为高温端部件应变的测量提供了可能。     

Thin film metallic glasses: Unique properties and potential applications

A new group of thin film metallic glasses (TFMGs) have been reported to exhibit properties different from conventional crystalline metal films, though their bulk forms are already well-known for high strength and toughness, large elastic limits, and excellent corrosion and wear resistance because of their amorphous structure. In recent decades, bulk metallic glasses have gained a great deal of interest due to substantial improvements in specimen sizes. In contrast, much less attention has been devoted to TFMGs, despite the fact that they have many properties and characteristics, which are not readily achievable with other types of metallic or oxide films. Nevertheless, TFMGs have been progressively used for engineering applications and, thus, deserve to be recognized in the field of thin film coatings. This article will thus discuss both properties and applications of TFMGs including a review of solid-state amorphization upon annealing, the glass-forming ability improvement due to thin film deposition, and mechanical properties, including residual stress, hardness and microcompression, adhesion, and wear resistance. Potential applications and simulations will also be discussed.     

Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y₂O₃ content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.     

The adhesion of copper films deposited onto aluminum nitride

Good adhesion between copper film and AlN substrate is obtained when the surface of AlN is laser-irradiated prior to copper film deposition and post deposition annealing is conducted. Surface chemistry of AlN substrates before and after laser irradiation and the interfacial reactions of copper film/AlN couples were studied with Auger Electron Spectroscopy (AES) to understand the adhesion mechanisms. The surface of as-received AlN substrates was covered with a thin sheath of Al₂O₃. Laser irradiation removed the surface Al₂O₃ layers, smoothened the surface, and decomposed AlN leaving metallic aluminum on the surface. The interfacial reactions in the copper film/AlN couple are affected by the amounts of oxygen and metallic aluminum available at the interface. The adhesion mechanism is the formation of a Cu-O-Al compound at the interface of copper film/AlN couple. Since copper does not react with AlN, laser induced decomposition of AlN seems to be the driving force for the formation of the compound. This revised version was published online in September 2006 with corrections to the Cover Date.     

Effect of substrate and metal layer deformation on recording characteristics of recordable discs with metallic thin film

Compact disc-recordable (CD-R) and digital versatile disc-recordable (DVD-R) discs were fabricated with a polycarbonate substrate, metallic thin film, organic buffer layer, reflective layer, and protective layer. Recording characteristics of a CD-R disc at various recording speeds, from 1x to 8x, were evaluated, and the deformation shapes of each layer after recording were investigated and compared with the DVD-R disc. The relationship between deformation and recording characteristics was studied and interpreted by numerical calculation. The modulated amplitude of recorded signals is increased as the recording speed increases, owing to the increase in decomposition of the buffer layer, which resulted from the localization of heat on the metallic thin film. On the basis of these results, a DVD-R disc with metallic thin film is expected to have better recording characteristics at a higher recording speed.