Spectroscopic ellipsometric properties and resistance switching behavior in Si_x（ZrO_2）_（100-x） films

We prepare Si x (ZrO 2 ) 100 x composite films using the co-sputtering method. The chemical structures of the films which are prepared under different conditions are analyzed with X-ray photoemission spectroscopy. Thermal treatment influences on optical property and resistance switching characteristics of these composite films are investigated by spectroscopic ellipsometry and semiconductor parameter ana- lyzer, respectively. With the proper Si-doped Si x (ZrO 2 ) 100 x interlayer, the Al/ Si x (ZrO 2) 100 x /Al device cell samples present very reliable and reproducible switching behaviors. It provides a feasible solution for easy multilevel storage and better fault tolerance in nonvolatile memory application.     

On RF magnetron-sputtering preparation of Ag–Sb–S thin films

One important application area of chalcogenide materials is rewritable optical data storage. This technology is based on a reversible phase transition between the crystalline and the amorphous state and vice versa. Currently dominant materials for rewritable optical recording are Ge–Sb–Te and Ag–In–Sb–Te alloys. Material research still continues due to the need for increasing storage capacity and data rates. Polycrystalline bulks of AgSbS₂ were prepared by melt-quench technique. Composition and homogeneity of these bulks were checked by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), crystallinity was studied by X-ray diffraction (XRD). Targets for RF magnetron sputtering were prepared from pulverized bulks by hot-pressing technique. Targets were characterized the same way as bulks. Thin Ag–Sb–S films were prepared by RF magnetron sputtering as potential candidates for rewritable optical data storage films. Composition and homogeneity of prepared thin films were characterized by SEM-EDX, Rutherford Back Scattering (RBS) and Elastic Recoil Detection Analysis (ERDA); character (amorphous/crystalline) was traced by XRD. Optical properties (spectral dependence of refractive index) were evaluated on the basis of UV–Vis–NIR spectroscopy and variable angle spectral ellipsometry (VASE). Crystallization abilities were studied by the measurement of thermal dependence of the prepared thin films optical transmission.     

Unusual temperature dependences of the photoconductivity and recombination luminescence of amorphous molecular semiconductors doped with ionic dyes

A nonexponential increase in photoconductivity with increasing temperature is discovered for poly(N-epoxypropylcarbazole) (PEPK) films doped with polymethine dyes. It is postulated that traps for nonequilibrium charge carriers form in these films during irradiation and are destroyed as the temperature is raised. Such traps are manifested by broadening of the high-temperature shoulder on the thermally stimulated luminescence (TSL) curves following the preliminary irradiation of PEPK films doped with polymethine and xanthene ionic dyes in the visible or UV range at 250–320 K and by the appearance of a new narrow TSL maximum near the preliminary irradiation temperature. These TSL features disappear after prolonged storage of the films in the dark or heating to higher temperatures. Fiz. Tverd. Tela (St. Petersburg) 41, 203–209 (February 1999)     

Variations in the structural, optical and electrochemical properties of CeO2-TiO2 films as a function of TiO2 content

Alcohol based sols of cerium chloride (CeCl₃·7H₂O) and titanium propoxide (Ti(OPr)₄) in ethanol mixed in different mole ratios have yielded mixed oxide films on densification at 500 °C. The reversibility of the intercalation/deintercalation reactions has shown electrochemical stability of the films. Addition of TiO₂ in an equivalent mole ratio manifests in producing highly transparent films with appreciable ion storage capacity. The electrochemical studies have revealed the significant role of TiO₂ in controlling the ion storage capacity of the films, as it tends to induce the disorder. In addition, the films prepared from an aged sol are observed to exhibit a much higher ion storage capacity than the films deposited using the as-prepared sol. The X-ray photoelectron spectroscopic studies have provided information on the variation of Ce⁴⁺/Ce³⁺ ratio as a function of increased TiO₂ content in the films. This study has led to a better understanding of the increased ion storage capacity with the increased TiO₂ proportion. The transmission electron microscopic study has demonstrated the presence of CeO₂ nanograins even in films, which are amorphous to X-rays. Elucidation of the structural, optical and electrochemical features of the films has yielded information on aspects relevant to their usage in transmissive electrochromic devices. The films have been found to exhibit properties that can find application as counter electrode in electrochromic smart windows in which they are able to retain their transparency under charge insertion, high enough for practical uses. Also, the fastest coloration-bleaching kinetics for the primary electrochromic electrode (WO₃) working in combination with Ce/Ti (1:1) electrode stimulates the use of latter in electrochromic windows (ECWs).     

Ultrafast pulsed laser deposition as a method for the synthesis of innovative magnetic films

Exchange-coupled monocomponent magnetic films constituted of disk-shaped Ni and Fe nanoparticles were produced by ultrafast pulsed laser deposition, in vacuum. These films show a peculiar cauliflower-like structure, made of granular agglomerates of nanoparticles sticking to one another with a significant shape and orientation anisotropy. Both as-deposited Ni and Fe films present hysteresis loops with a high in-plane remanence ratio (0.61 and 0.81 at 250 K, respectively), relatively low values of the saturation and coercive fields and a steep slope near coercivity. At temperature of 10 K and 250 K, the magnetization curves confirm the strong influence of the production technique on the topologic structure of these films, and consequently on their magnetic properties. In perspective, the striking and intriguing properties of these nanogranular films appear very promising for potential application as permanent magnets and in data storage technology.     

Neodymium doped, sol-gel processed polymer electrolytes

Polymer films prepared by the sol-gel method and containing neodymium trifluoromethanesulphonate (triflate) have been characterized by thermal, X-ray diffraction and conductivity measurements. The films were produced in a laboratory atmosphere and subsequently subjected to an appropriate drying pre-treatment before storage and study within an argon-filled drybox. The results of these experiments confirm that the amorphous hybrid host matrix has characteristics which are significantly better than poly(ethylene oxide)-based materials. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998     

Amorphous and crystalline IrO2 thin films as potential stimulation electrode coatings

Amorphous and crystalline iridium oxide thin films with potential use as coating materials for stimulation electrodes were studied. Characterization of these films by cyclic voltammetry and impedance spectroscopy has revealed a considerable decrease in impedance and an increase in charge capacity of iridium oxide thin films after an electrochemical activation process in 0.9% NaCl solution. The surface morphology of these films was studied by scanning electron microscopy. The two types of IrO₂ films were also compared under conditions relevant to applications as stimulation electrodes. The results indicate that amorphous IrO₂ films have significantly higher charge storage capacity and lower impedance than crystalline IrO₂ films. This makes the amorphous films a preferable coating material for stimulation applications.     

Hydrogenation properties of catalyzed and non-catalyzed magnesium films

The hydrogenation properties of 400 Å thick magnesium films, grown under ultra-high vacuum conditions, have been studied under conditions relevant for hydrogen storage, i.e., elevated temperatures and pressures. The hydrogen uptake of films modified by deposition of platinum on the magnesium surface was also investigated. A realistic hydrogen storage system is modeled by studying the combined effect on hydrogen sorption by a platinum catalyst and magnesium oxide, the latter a common impurity in magnesium-based hydrogen storage systems. Magnesium and platinum are found to inter-diffuse readily at room temperature. However, a partially oxidized magnesium layer stabilizes platinum on the surface, while still being permeable to hydrogen.     

基于Rotaxane类分子的稳定、重复、可反复擦写的纳米信息存储

Rotaxane类分子在溶液中可以发生可逆的分子构型改变,并随之引起分子电导特性的转变,在纳米电子器件和分子存储器件中具有潜在的应用前景.但是还不能确定这类分子在固体薄膜中是否具有类似于在溶液中的结构与电导转变,需要对Rotaxane类分子固态薄膜进行深入的结构和特性研究.文章作者在一类Rotaxane分子H1和H2的固态薄膜上获得了纳米尺度的电导转变和稳定、重复的、近于单分子尺度的纳米级存储;同时,成功地在H2分子薄膜上实现了信息记录点的可反复擦写.另外,在单个分子和亚分子的水平上直接观察到了Rotaxane分子在外电场诱导下分子结构的可逆变化以及随之发生的相应电导特性的可逆转变, 证实了Rotaxane分子在固态薄膜中的可逆结构和电导转变.     

Effects of rough interface on impedance of solid LiPON in MIM cells

The influences of the rough interface on the impedance of solid lithium phosphorus oxynitride (LiPON) in its metal/insulator/metal (MIM) cells over a wide frequency are studied. Using magnetron sputtering method, Al/LiPON/Al cells with different rough interfaces are fabricated. With increasing the Al films electrode roughness, the deposited LiPON films on these electrodes are correspondingly roughened, which result the interface in MIM cell roughened. Rough LiPON films make their ionic resistance decreasing and the real contact area and the bulk capacitance of MIM cells increasing. These lead to the ionic conductivity of LiPON films improved from 1.09 to 2.70 μS/cm. Meanwhile, the bulk capacitance and the electrolyte resistance in MIM cells could be separated by changing the interface roughness. Rough interfaces in MIM cells contribute to the differences in the morphology of LiPON thin films, which result in the decrease of the activation energy of ionic conductivity E _g from 0.45 to 0.38 eV. Without changing LiPON components ratio and sputtering conditions for the thin films deposition, or using any heat treatment, we demonstrate an effective way to improve the ionic conductivity by increasing the roughness of the contact electrode in MIM cells, corresponding roughening the LiPON films and decreasing its ionic impedance.     

Electrochromic phenomena in transition metal oxide thin films prepared by thermal evaporation

We present an experimental study on the electrochromic properties of MoO₃, WO₃ and mixed WO₃-MoO₃ thin films prepared by thermal evaporation. We have constructed symmetric and quasi-symmetric electrochromic cells incorporating the evaporated oxide films as electrochromic layers. Li⁺ doped V₂O₅ films served as ion storage layers. The symmetric cells were found to exhibit significantly improved optical properties compared to the quasi-symmetric ones, with very low luminous transmittance values in the colored state, which makes them suitable for large-area window applications. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Optical Storage in Side-Chain Liquid Crystalline Polyesters

Long-term, high resolution holographic storage has been achieved in side-chain liquid crystalline polyesters with high diffraction efficiency. The information can be completely erased by heating the film to about 80°C. The modular architecture of the polyesters permits a varition in the length of the main- and side-chains and the substituents of the azo chromophore. Each of these has a profound influence on the storage properties of the polyesters. In this article, we examine the influence of the length of the side-chains, the probe-beam-polarization dependence of the observed signal on the interface and the crystalline vs. amorphous nature of the films for optical storage.     

Nonlinear two-photon absorption properties induced by femtosecond laser with the films of two novel anthracene derivatives

Two novel anthracene derivatives containing 4-vinylpyridine (FPEA) and 2-vinylpyridine (TPEA) poly(methyl methacrylate) films are prepared on quartz glass substrates. Their nonlinear absorption properties are investigated by using a 120-fs, 800-nm Ti:sapphire femtosecond pulsed laser operating at a 1-kHz repetition rate. The unique nonlinear absorption properties of these new compounds are observed by utilizing a Z-scan system. These two-photon absorption (TPA) properties are proven by the two-photon fluorescence excited at 800 nm. The FPEA and TPEA films have nonlinear TPA coefficients of 0.164 and 0.148 cm/GW and the TPA cross sections of 3.345 × 10-48 and 3.081 × 10-48 cm4 ·s/photon, respectively. The influence of the chemical structures on the nonlinear TPA properties of the compounds is also discussed. The highly nonlinear TPA activities of the films implied that the new anthracene derivatives are suitable materials with promising applications in super-high-density three-dimensional data storage and nano- or microstructure fabrication.     

Angular Multiplexing Storage in Azo-polymer Liquid Crystal Films Using Shearing Interferometer of Double-frequency Grating

In this paper, the shearing interferometer of a double-frequency grating (DFG) and a small compact Nd∶YVO4 double frequency laser at 532 nm are used to study the multiple storage in azo-polymer liquid crystal (PLC) films. In a principle experiment, the angle-encoded multiple gratings are recorded and the experimental results give triplex gratings at the same region in azo-PLC films, the angle between two adjacent grating vectors being 45°. Compared to the two-beam interferometer and four-wave mixing method, this method has simple configuration, high fringe contrast and quake-proof. A compatible angular multiplexing storage system in azo-PLC films is proposed.     

Charge storage characteristics of hydrogenated nanocrystalline silicon film prepared by rapid thermal annealing

The early stages of hydrogenated nanocrystalline silicon (nc-Si:H) films deposited by plasma-enhanced chemical vapour deposition were characterized by atomic force microscopy. To increase the density of nanocrystals in the nc-Si:H films, the films were annealed by rapid thermal annealing (RTA) at different temperatures and then analysed by Raman spectroscopy. It was found that the recrystallization process of the film was optimal at around 1000℃. The effects of different RTA conditions on charge storage were characterized by capacitance--voltage measurement. Experimental results show that nc-Si:H films obtained by RTA have good charge storage characteristics for nonvolatile memory.     

Indium tin oxide thin films by bias magnetron rf sputtering for heterojunction solar cells application

In this investigation ITO thin films were prepared by bias magnetron rf sputtering technique at substrate temperature of 180 °C and low substrate-target distance for future a-Si:H/c-Si heterojunction (HJ) solar cells application. Microstructure, surface morphology, electrical and optical properties of these films were characterized and analyzed. The effects of ion bombardments on growing ITO films are well discussed. XRD analysis revealed a change in preferential orientation of polycrystalline structure from (2 2 2) to (4 0 0) plane with the increase of negative bias voltage. Textured surface were observed on AFM graphs of samples prepared at high negative bias. Hall measurements showed that the carrier density and Hall mobility of these ITO films are sensitive to the bias voltage applied. We attributed these effects to the sensitivity of energy of Ar⁺ ions bombarding on growing films to the applied bias voltage in our experiments. At last the figure of merit was calculated to evaluate the quality of ITO thin films, the results of which show that sample prepared at bias voltage of −75 V is good to be used in HJ cells application.     

Growth and decomposition of lithium and lithium hydride on nickel

In this paper we have investigated the deposition, structure and decomposition of lithium and lithium-hydride films on a nickel substrate. Using surface sensitive techniques it was possible to quantify the deposited Li amount, and to optimize the deposition procedure for synthesizing lithium-hydride films.By only making thin films of LiH it is possible to study the stability of these hydride layers and compare it directly with the stability of pure Li without having any transport phenomena or adsorbed oxygen to obscure the results. The desorption of metallic lithium takes place at a lower temperature than the decomposition of the lithium-hydride, confirming the high stability and sintering problems of lithium-hydride making the storage potential a challenge.     

Comparison of CdS films deposited by different techniques: Effects on CdTe solar cell

Polycrystalline cadmium sulfide (CdS) thin-films were deposited on glass substrate by chemical bath deposition (CBD) and vacuum evaporation (VE) techniques. VE-CdS films consisted primarily of hexagonal phase, whereas CBD CdS films containing primarily the cubic form. VE-grown films were shown to have better crystallinity than CBD-grown films. The grain size of the CBD films is smaller than the ones of VE films. VE-CdS films exhibited relatively high transmittance in the above-gap region and band gap compared with CBD films. However, CdTe solar cells with these low quality CBD-CdS layers yield higher and more stable characteristics. Current-voltage-temperature measurements showed that the current transport for both cells was controlled by both tunneling and interface recombination but the cells with CBD-CdS displayed less tunneling.     

Optimizing Film Design and Application for the Recordable Compact Disk Developed by Two Cyanine Dye Samples

Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ａｃｙａｎｉｎｅｄｙｅｗａｓｓｔｕｄｉｅｄａｎｄｕｓｅｄａｓｌａｓｅｒｄｙｅａｎｄｐｈｏｔｏｓｅｎｓｉｔｉｚｅｒｌｏｎｇａｇｏ．Ｉｎｔｈｅｃｕｒｒｅｎｔｙｅａｒｓ,ｃｙａｎｉｎｅｄｙｅｐｒｅｐａｒａｔｉｏｎｓａｒｅｓｔｕｄｉｅｄｄｅｅｐｌｙａｎｄｗｉｄｅｌｙｕｓｅｄａｓｏｐｔｉｃａｌｓｔｏｒａｇｅｍｅｄｉａ［１］．Ｃｙａｎｉｎｅｄｙｅｈａｓａｇｏｏｄｓｏｌｕｂｉｌｉｔｙｉｎｓｏｍｅｏｒｇａｎｉｃｓｏｌｖｅｎｔｓ,ｔｈｅｒｅｆｏｒｅ,ｐｒｅｐａｒａｔｉｏｎｏｆｃｙａｎｉ…     

Optimizing Film Design and Application for the Recordable Compact Disk Developed by Two Cyanine Dye Samples

The optical constants of two cyanine dye films we prepared have been measured by a RAP-1 typed spectroscopic ellipsometer. On the basis of making a simplified model for the wafers of a recordable compact disk (CD-R), the optimizing designs for them developed by the cyanine dye films are given. In addition, the dynamic storage performances of two sample disks have been tested by our dynamic storage testing system. Measurement results of the sample disks are obtained to test our film designs.