Electrodeposited films

This investigation covers: a) control of characteristics of electrodeposited vs. vacuum deposited Permalloy films; b) the preparation of substrates for electrodeposition; c) aging kinetics of electrodeposited NiFeSxfilms from 60° to 90°C; and d) comparison of aging of NiFeSxfilms with electrodeposited films containing other impurities, e.g., NiFeP, and with films made by other techniques, e.g., vacuum deposition. The concluding discussion is principally concerned with aging effects.     

Electrodeposited single-crystal cobalt films

Electrodeposition of single-crystal thin films of cobalt from a high concentration metal ion bath is described. The crystal structures observed by RHEED are related to the current densities and pH of the plating bath and the deposit thickness. Emphasis is on the parameter values within which single-crystal h.c.p. cobalt may be obtained with the c-axis perpendicular to the film plane.     

Electrodeposited carbon nanotube thin films

A successful attempt to grow carbon nanotubes (CNTs) by electrodeposition technique for the first time is reported here. Carbon nanotubes were grown on Si (001) substrate using acetonitrile (1% v/v) and water as electrolyte at an applied d.c. potential ∼20 V. The films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman, optical absorbance, Fourier Transform Infra Red spectroscopy (FTIR) and Electron Spin Resonance (ESR) measurements. The effect of magnetic field on the growth of nanotubes was studied critically. It was found that the presence of magnetic field during electro-deposition played a crucial role on the growth of carbon nanotubes and hence the electronic properties. Photoluminescence (PL) studies indicated band edge luminescence ∼0.72-0.83 eV. Field emission studies indicated lower turn-on voltage and higher current density for films deposited with magnetic field.     

Effect of supporting electrolyte on the polymerization of electrochemically deposited poly(o-anisidine) films

Poly(o-anisidine) films deposited galvanostatically exhibit the formation of different oxidation states of the polymer with varying pH of the solution. The influence of supporting electrolyte on the extent of formation of the conducting phase at pH 2.1 has been investigated with the help of optical, thermal and potential cycling techniques. The optical spectra of the films reveal the proportionate increase in the fraction of the conducting emeraldine salt phase with the amount of supporting electrolyte (NaCl) added to the solution. Similarly, clarity in the decomposition steps of the thermal patterns and redox peaks in the cyclic voltammograms are found to increase as a function of NaCl concentration. This revised version was published online in November 2006 with corrections to the Cover Date.     

Electrodeposited ZnO films with high UV emission properties

We report here our results in the preparation of ZnO films with high UV band to band characteristic luminescence emission by potentiostatic electrodeposition. Zinc nitrate aqueous baths with different concentration and additives were employed for the preparation of the films on platinum substrates. We focused our research in determining how the electrodeposition bath composition, i.e. zinc nitrate concentration and addition of KCl or polyvinyl pyrolidone and applied overpotential influence the morphological and optical properties of the oxide films. Scanning electron microscopy was employed for characterizing the films in terms of morphology. Optical reflection, photoluminescence spectroscopy and cathodoluminescence were used for determining the optical characteristics of the samples. The morphology of the deposit varies from hexagonal prisms to platelets as a function of the deposition rate. This experimental parameter also influences the luminescence properties. We found that at low deposition rates high UV luminescent material is obtained.     

Electrodeposited multilayer films with giant magnetoresistance (GMR): Progress and problems

The giant magnetoresistance (GMR) effect was discovered in 1988 in nanoscale metallic ferromagnetic/non-magnetic (FM/NM) multilayers. By now, devices based on this phenomenon have been widely commercialized which use multilayered structures manufactured via physical deposition (PD) methods, mainly sputtering. It was shown in the early 1990s that electrodeposition (ED) is also capable of producing multilayered magnetic nanostructures exhibiting a significant GMR effect. These layered structures include multilayer films similar to those prepared by PD methods on macroscopic substrates and multilayered nanowires deposited into nanosized template pores, the latter ones being unique to the ED technique. Whereas ED multilayered nanowires can exhibit a GMR effect comparable to the values obtained on PD multilayer films, the GMR values achieved on ED multilayer films still remain inferior to them and, quite often, require high magnetic fields for saturation. Therefore, in spite of the relative simplicity and cost-effectiveness of the ED method, the GMR characteristics of ED multilayer films are still not competitive with the corresponding parameters of their PD counterparts. The main purpose of the present review is to give a summary of the progress achieved over the last one and a half decades on ED multilayer films with GMR effect and to critically evaluate the GMR results reported for various element combinations accessible to the ED technique for the preparation of FM/NM multilayer films (ED multilayered nanowires will be treated very briefly only). In order to promote an understanding of the inferior behavior of ED multilayer films, a detailed discussion of the magnetoresistance effects occurring in bulk homogeneous ferromagnets as well as in magnetic nanostructures (FM/NM multilayers and granular alloys) will be provided. Particular attention will be paid to the case of non-ideal magnetic nanostructures which contain both FM and superparamagnetic (SPM) regions. This is an essential ingredient in explaining the high saturation field of GMR commonly observed in ED multilayer films. In addition to the GMR magnitude, this is another characteristic decisively influencing the magnetic field sensitivity, a key feature concerning applications in sensor devices. The controversial results reported for the spacer layer thickness dependence of GMR in ED multilayer films will also be discussed. It is pointed out that the still inferior GMR characteristics of ED multilayer films can be to a large extent ascribed to microstructural features leading to the appearance of SPM regions, pinholes in the spacer layers and probably not sufficiently perfect interfaces between the FM and NM layers. The origin of the latter deficiency is not yet well understood although it is clearly one of the main causes of a weak interlayer coupling (if there is any coupling at all) and, thus, a small degree of antiparallel alignment leading to a reduced GMR effect. Works will also be described in which attempts were made to produce ED multilayer films with view on possible applications in GMR sensor devices. Finally, problems will be identified which should still be solved in order to make the properties of ED multilayer films attractive for GMR applications.     

Modification of sputter deposited solid-state electrolyte thin films

All solid-state thin film batteries (TFBs) consisting of amorphous lithium phosphorus oxynitride (LiPON) solid electrolyte, crystalline LiMn₂O₄ cathode and crystalline SnO₂ anode have been fabricated and characterized. All of the thin films are prepared by RF magnetron sputtering. By fabricating under different pressures and applying low temperature post-annealing (200 °C), the performances of the LiPON electrolytes and SnO₂/LiPON/LiMn₂O₄ TFBs are improved. Suitable working pressures results in pinhole-free amorphous LiPON films with smooth surface and dense micro-structure. The TFBs post-annealed at 200 °C show smooth interface contacts between electrode and electrolyte thin films. The low pressure deposited and post-annealed TFBs exhibits lower impedance and higher cycling stability. Initial open-circuit voltage of 3.8 V and initial capacity of 12 μAh/cm² are obtained.     

Electrodeposited copper oxide films: Effect of bath pH on grain orientation and orientation-dependent interfacial behavior

Copper (I) oxide (Cu₂O) films were cathodically electrodeposited on Sn-doped indium oxide substrates. The influence of electrodeposition bath pH on grain orientation and crystallite shape was carefully re-examined using X-ray diffraction and scanning electron microscopy. In addition to the (100) and (111) preferred orientations identified in two previous sets of studies, as the bath pH was varied in the present study from ∼ 7.5 to ∼ 12, a third preferred orientation, (110), was identified in a narrow pH range, ∼ 9.4 to ∼ 9.9. A remarkable shift in the flat-band potential (spanning ∼ 500 mV) was measured in a non-aqueous electrolyte medium for the various Cu₂O samples obtained from baths of varying pH.     

Electrodeposited nanoporous versus nanoparticulate ZnO films of similar roughness for dye-sensitized solar cell applications

We present a comparative study of two different ZnO porous film morphologies for dye-sensitized solar cell (DSSC) fabrications. Nanoparticulate ZnO was prepared by the doctor-blade technique starting from a paste containing ZnO nanoparticles. Nanoporous ZnO films were grown by a soft template-assisted electrochemical growth technique. The film thicknesses were adjusted at similar roughness of about 300 in order to permit a worthy comparison. The effects on the cell performances of sensitization by dyes belonging to three different families, namely, xanthene (eosin Y) and indoline (D102, D131, D149 and D205) organic dyes as well as a ruthenium polypyridine complex (N719), have been investigated. The mesoporous electrodeposited matrix exhibits significant morphological changes upon the photoanode preparation, especially upon the dye sensitization, that yield to a dramatic change of the inner layer morphology and increase in the layer internal specific surface area. In the case of indoline dyes, better efficiencies were found with the electrodeposited ZnO porous matrixes compared to the nanoparticulate ones, in spite of significantly shorter electron lifetimes measured by impedance spectroscopy. The observation is interpreted in terms of much shorter transfer time in the oxide in the case of the electrodeposited ZnO films. Among the tested dyes, the D149 and D205 indoline organic dyes with a strong acceptor group were found the most efficient with the best cell over 4.6% of overall conversion efficiency.     

Neutral reagents in solutions with low content of supporting electrolyte: how to determine the steady-state conditions

Cyclic voltammograms obtained at ultramicroelectrodes in the electrochemical systems where an uncharged reactant is significantly more concentrated than the supporting electrolyte show an unusual feature. The forward and the backward waves cross over, forming a hysteresis loop. The width of the hysteresis increases with the relative concentration of the reactant, with the electrode size, and with the scan rate. We show that the reason for this hysteresis is the slow transport of supporting electrolyte ions that are necessary to compensate the charge of the reaction product. As a result, the steady-state concentration profile of counterions is reached significantly slower than the steady-state concentration gradient of the reactant, and the counterion transport determines how rapidly the steady state for the whole system is approached. The scan rate yielding near-steady-state voltammograms can differ by more than 1 order of magnitude for systems with high and low concentrations of supporting electrolyte. Experimental evidence for this, supported by digital simulation results, is presented. The appropriate criterion for assessing the steady state in such systems is thus the identity of the forward and backward scans, without hysteresis. If this condition is not fulfilled, the formal potentials and the related parameters determined from the obtained voltammograms may be erroneous.     

Dielectric properties of sol-gel derived high-k titanium silicate thin films

High-k dielectric titanium silicate (Ti_xSi_1 − xO₂) thin films have been deposited by means of an optimized sol-gel process. At the optimal firing temperature of 600 °C, the Ti_0.5Si_0.5O₂ films are shown to exhibit not only a dielectric constant (k) as high as ∼ 23 but more importantly the lowest leakage current and dielectric losses. Fourier transform infrared spectroscopy shows an absorbance peak at 930 cm^− 1, which is a clear signature of the formation of Ti-O-Si bondings in all the silicate films. The developed sol-gel process offers the required latitude to grow Ti_xSi_1 − xO₂ with any composition (x) in the whole 0 ≤ x ≤ 1 range. Thus, the k value of the Ti_xSi_1 − xO₂ films can be tuned at any value between that of SiO₂ (3.8) to that of TiO₂ (k ∼ 60) by simply controlling the TiO₂ content of the films. The composition dependence of the dielectric constant of the Ti_xSi_1 − xO₂ films is analyzed in the light of existing models for dielectric composites.     

热镀锌钢表面硅烷/硅酸盐复合膜的耐蚀性能研究

为了改善硅烷膜的耐蚀性,将硅烷化热镀锌钢板用硅酸钠溶液封闭后处理,获得了硅烷/硅酸盐复合膜.采用中性盐雾试验(NSS)、湿热试验、盐水全浸试验和电化学交流阻抗谱(EIS)评价了膜层的耐蚀性能.结果表明,与单一硅烷膜相比,复合膜的耐蚀性能明显提高,超过了常规铬酸盐钝化膜.尤其是在5%NaCl溶液中,复合膜的低频阻抗数值随浸泡时间的增加先增大后减小,表明其具有一定的"自修复"能力.     

Sol–gel deposition and characterization of Mn-doped silicate phosphor films

Mn²⁺-doped Zn₂SiO₄ and Mg₂Gd₈(SiO₄)₆O₂ phosphor films were deposited on silicon and quartz glass substrates by sol–gel process (dip-coating). The variations of sol viscosity with time and film thickness with the number of layers were investigated in Zn₂SiO₄: Mn system. The results of XRD and IR showed that the Zn₂SiO₄: Mn films remained amorphous below 700°C and crystallized completely around 1000°C. From AFM studies, it was observed that the grains with 0.5–0.8 μm size packed closely in Zn₂SiO₄: Mn films, which were uniform and crack free. The luminescence properties of Zn₂SiO₄: Mn films were characterized by absorption, excitation and emission spectra as well as luminescence decay. These properties were discussed in detail by a comparison with those of Mn²⁺ (and Pb²⁺)-doped Mg₂Gd₈(SiO₄)₆O₂ phosphor films.     

Chemical vapor deposition of electrolyte thin films based on yttria-stabilized zirconia

Gas-tight electrolyte films are obtained by chemical vapor deposition for solid oxide fuel cells from yttria-stabilized zirconia (YSZ) with a thickness of 4–15 μm on supporting porous ceramic anodes (YSZ/NiO). Volatile metal complexes with dipivaloylmethane Zr(dpm)₄ and Y(dpm)₃ are used as precursors. On the basis of an analysis of thermal properties of the starting compounds, parameter ranges in deposition processes are determined. Dependences of the structure, composition, and electrical characteristics on deposition conditions are found for YSZ electrolyte films. Electrochemical solid oxide fuel cells that operate at low temperatures with an open circuit voltage of 0.98–1.08 V and specific power up to 440 mW/cm² at 1073 K and 1200 mW/cm² at 1173 K are constructed.     

锂磷氧氮电解质薄膜制备与性能研究

首次采用355nm脉冲激光沉积(PLD)法在N2压强26.6Pa、激光能量密度15J/cm2、靶-基片距离5cm、基片温度为室温条件下制备了室温离子电导率为1.6×10-6S/cm、厚度均匀、无针孔、无裂缝的非晶态LiPON电解质薄膜。考察了反应气氛压强、激光能量密度对LiPON薄膜电化学性能的影响,并利用台阶仪、XPS、EDX、SEM等分析方法对薄膜进行表征。