The pH and current density dependence of DC electrodeposited CoCu thin films

CoCu thin films were fabricated on a nanocrystalline substrate by DC electrodeposition. It is found that the composition, structure and magnetic properties of the thin films exhibit a strong dependence on the current density and pH values of the bath electrolyte. The effect of annealing as well as the structure–property relation was investigated.     

Planar Hall effect in electrodeposited CoCu/Cu multilayer

Electrodeposited CoCu/Cu multilayers were investigated by measuring both anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) simultaneously. Studies have been carried out on a [Co(3 nm)/Cu(4 nm)]₅₀ multilayer sample, where a maximum of ?8.8 % GMR was observed at room temperature. A direct comparison of AMR and PHE output has been made both as a function of field and its relative orientation with respect to the current. Marked changes in PHE loops were observed at different angles (between magnetic field and applied current) whereas no noticeable changes could be found for AMR results. Such PHE outputs are the manifestations of complex spin reorganization due to strong antiferromagnetic-coupling between adjacent magnetic layers. In case of angular dependence output, when the applied field is less than the coercive field, the PHE output shows a deviation from the Sin2θ dependence that can be correlated to the domain wall propagation.     

Evaluation of carbon films electrodeposited on different substrates from different organic solvents

Diamond-like-carbon (DLC) films have been deposited on Si, aluminum and indium tin oxide-coated glass from several organic solvents with pulse-modulated power. The films are characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS spectra show that the main composition of the films is carbon and Raman spectra show that the films are typical DLC films and a high potential is preferable in the formation of sp ³-structure carbon. Comparing the results from different solvents and different substrates we deduce that the methyl group of the solvents has a critical function in forming the DLC films. However, the formation process and the characters of the films, such as appearance, resistivity and thickness, are mainly determined by the substrate. We may call this deposition a substrate-controlled reaction. Received: 31 May 2000 / Accepted: 9 January 2001 / Published online: 3 April 2001     

Ferromagnetic resonance studies in granular CoCu codeposited films

Experimental ferromagnetic resonance (FMR) data are presented for CoCu granular films obtained by electron beam codeposition. Co_xCu_100−x films were prepared for x=10 and 30 and were subsequently submitted to a thermal treatment. For the 10% Co samples one found three main resonance modes, one of them constituting of non-interacting Co particles. External field angular variation and temperature-dependent FMR experiments were proceeded and straight calculations of the involved resonance intensities as well. A strict correlation of the presented FMR data with the previous X-Ray diffraction, magnetization, and particle size investigations was possible. The link between structural changes and magnetic properties of the samples could be verified. For the 30% Co samples a broad resonance line for the in-plane configuration was found, which is characteristic for polycrystalline systems. In the perpendicular configuration a spin wave spectra were present on all samples and one could identify some of the modes as surface modes. These samples with 30% Co become more heterogeneous with increasing thermal treatment.     

Contribution of electrolyte pH and deposition potentials to the magnetic anisotropy of electrodeposited nickel films

The influence of electrolyte pH and cathode potential on the magnetic properties of single layer Nickel films electrodeposited on polycrystalline titanium substrates was studied. The films were deposited at the electrolyte pH=3.5±0.1, 2.5±0.1 and 2.1±0.1 by varying the deposition potentials (?1.2, ?1.5 and ?1.8 V vs saturated calomel electrode, SCE) applied in continuous waveform. The structural analysis by X-ray diffraction revealed that the films have face-centred cubic structure. Results of the magnetic measurements obtained by vibrating sample magnetometer (VSM) indicated that the magnetic properties were affected by the electrolyte pH and the cathode potentials in terms of magnetic anisotropy. At the highest pH the films deposited at the lowest potential had in-plane magnetic anisotropy. As the electrolyte pH decreased from the high (pH=3.5±0.1) to low (pH=2.5±0.1), which is aided by increasing the potentials, resulted in an almost magnetic isotropy in the films. However, isotropic magnetic behaviour was observed for the film deposited at the low pH combined with the high potential (?1.8 V vs SCE). Magnetic thickness profile of the samples obtained by VSM revealed that the isotropic films have a smoother magnetic variation across the film from one edge than the anisotropic ones. This is also verified with a microscopic observation by an optical microscope and the surface of the isotropic films is observed to be smoother than that of the anisotropic ones. Furthermore, all films were found to have planar magnetic anisotropy irrespective of the pH’s and the potentials.     

Controlled Cu content of electrodeposited CoCu nanowires through pulse features and investigations of microstructures and magnetic properties

CoCu alloy nanowire arrays embedded in anodic alumina template were fabricated by ac pulse electrodeposition. Different off-times between pulses in an electrolyte with constant concentration of Co⁺² and Cu⁺² and acidity of 4 were employed. The effect of deposition parameters on the alloy contents, microstructures and magnetic properties of Co_xCu_1−x nanowires were studied. It is shown that Co content decreased by increasing the off-time between pulses in a wide range (x = 0.53-0.07). These results are in consistence with saturation magnetization, which was reduced with increase in the off-time between pulses. It was also found that by optimizing the off-times, it is possible to fabricate CoCu nanowires with mixed phase of hcp Co, fcc Cu and fcc CoCu crystal phase.     

Low-temperature oxidation of CoCu films with long-term irradiation by oxygen ion beams

The surface and surface layers of Co_xCu_100?x inhomogeneous thin films irradiated by an oxygen ion beam for a long time (to 100 min) are studied. The films are obtained by electrolytic deposition. With X-ray photoelectron spectroscopy and conversion electron Mössbauer spectroscopy, it is shown that the irradiation leads to the formation of an oxidized surface layer. The continuity and thickness of the layer depend on the roughness of the initial film. For a cobalt content of 8≤x≤20 at. %, the oxide layer is continuous and nonuniform in thickness, the mean thickness being estimated at several tens of nanometers. The interface between the layer and the underlying film is sharp. The films irradiated are smoother than the asdeposited ones. The formation of the oxide layer is treated in terms of a qualitative model.     

Anomalous scaling for thick electrodeposited films

Anomalous surface roughness scaling, where both the local and the large-scale roughness show a power-law dependence on the film thickness, has been widely observed. Here we show that the value of the local roughness exponent in the early stages of Cu electrodeposition depends on the deposition potential. However, initial anomalous scaling can lead to two qualitatively different types of behavior for large film thickness (t>/ or =4 microm). For Cu films electrodeposited with forced convection at high potential and current density, the anomalous scaling is transient: the local roughness saturates for the thickest films studied. When Cu films are electrodeposited at similar potential and current density but with reduced convection, no saturation of the local roughness is observed. Instead the film forms overhangs such that the surface height becomes a multivalued function of the lateral position.     

Giant magnetoresistance of electrodeposited Cu-Co-Ni alloy films

Electrodeposition of CuCoNi alloys was performed in an acid-citrate medium. Nickel density parameter was varied in order to analyse its influence on the magnetoresistance. The structure and giant magneto-resistance (GMR) effect of CuCoNi alloys have been investigated. The maximum value for GMR ratio, at room temperature is 1% at a field of 12 kOe, and at 20 K is 2.1% at a field of 8.5 kOe for 3.1 Ni. The MR ratio of Cu_100-y-x Co_yNi_x alloys first increases and then decreases monotonically with increasing Ni content. The GMR and its dependence on magnetic field and temperature were discussed.      

Morphology and photoluminescence study of electrodeposited ZnO films

ZnO films on ITO substrates and Au coated ITO substrates were fabricated by using electrodeposition technique. We carried out the experiments by adjusting the concentration of solution, potential, substrate, and temperature. The effect of temperature on the growth of the film has been examined. SEM images have shown that there are several kinds of grown competitions for the deposition of ZnO films, but three kinds of them are dominant. One is the discrete hexagonal column structure, the other is the pentagonal structure, and the third one is of well-oriented hexagonal columns with well-aligned structure. The explanation on the grown competition is discussed. ZnO hexagonal column structures with well-aligned and well-perpendicular to the surface were successfully obtained on Au/ITO substrate in aqueous solvent of electrolyte. Clearly the main columns in the film were obtained by increasing the temperature. Its photoluminescence (PL) study at low temperature exhibited the optical properties as wurtzite ZnO and indicated the existence of macrocrystalline ZnO. A better quality of ZnO columnar structures after annealing was demonstrated from PL analysis and discussion on the existence of 370 nm, 384 nm and 639 nm in the emission bands before and after annealing.     

Thin films of ZnTe electrodeposited on stainless steel

The electrodeposition of zinc telluride (ZnTe) thin films on stainless steel foil substrates from an aqueous solution containing ZnSO₄ (150 mM) and TeO₂ (0.5 mM) is performed. For the deposition of stoichiometric films at a bath temperature 80 °C and pH=3.5, the suitable deposition potential is found to be in the range -740 mV to -800 mV against a Ag/AgCl reference electrode. The films structure, surface morphology, chemical composition, optical absorption coefficient, bandgap energy and electrical resistivity are measured and the results are discussed. Films are composed of small crystallites, and their surface texture, which depends on the film stoichiometry, varies with the deposition potential. Films have a resistivity greater than 10⁹ cm and a bandgap energy that is measured in the range 2.1 to 2.3 eV. Films annealed in nitrogen for 15 min and at 350 °C show p-type conductivity. PACS 81.15.Pq; 78.66.Hf; 68.55.Jk; 73.61.Ga     

Preparation and characterization of electrodeposited SnS thin films

Tin sulfide (SnS) thin films have been deposited by electrodeposition using potentiostaic method on indium doped tin oxide (ITO) coated glass substrates from aqueous solution containing SnCl₂·2H₂O and Na₂S₂O₃ at various potentials. Good quality thin films were obtained at a cathodic potential −1000 mV versus saturated calomel electrode (SCE). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR). X-ray diffraction analysis shows that the crystal structure of SnS thin films is orthorhombic with preferential orientation along 〈0 2 1〉 plane. Microstructural parameters such as crystallite size, micro strain, and dislocation density are calculated and found to depend upon cathodic potentials. SEM studies reveal that the SnS films exhibited uniformly distributed grains over the entire surface of the substrate. The optical transmittance studies showed that the direct band gap of SnS is 1.1 eV. FTIR was used to further characterize the SnS films obtained at various potentials.     

Substrate dependent properties of electrodeposited EuTe thin films

In electrodeposition, substrate besides providing mechanical support to the electrodeposit, affects significantly the structural and morphological properties of a film. Electrodeposition and characterization of EuTe thin films onto different substrates such as stainless steel (SS), titanium (Ti), copper (Cu), fluorine-doped tin oxide (F:SnO₂) covered glasses have been described. The deposition potentials have been estimated from the polarization curves. The reaction mechanism is proposed for the formation of EuTe electrodeposits. Preparative parameters such as deposition potential, current density, and deposition time are studied. The films have been characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive analysis by X-rays (EDAX) techniques. The electrodeposited EuTe films are polycrystalline on all the substrates with same cubic crystal structure. The SEM studies reveal that the surface morphology is different for the substrates studied. However, no cracks have been observed in the SEM micrographs. The AFM images show large spherical grains supporting the polycrystalline nature of the samples. The EDAX analysis shows that the EuTe films are nearly stoichiometric, slightly rich in tellurium.     

Influence of different deposition potentials on morphology and structure of CdSe films

Cadmium selenide (CdSe) thin films have been electrodeposited on the titanium or ITO substrate in an electrolyte containing CdSO₄ and H₂SeO₃ at pH = 2.50 and temperature 298 K. Influence of different deposition potentials on the surface morphology and crystal structure of CdSe films has been discussed. Compared with other deposition potentials (−0.65, −0.71 and −0.72 V versus SCE), the nearly stoichiometric CdSe nanocrystalline films with smaller grain sizes of 80 nm were obtained from 0.25 M CdSO₄ + 0.25 mM H₂SeO₃ + 0.25 M Na₂SO₄ solution at deposition potential of −0.70 V versus SCE. X-ray diffraction, atomic force microscope and scanning electron microscope were used to measure structure and morphology of CdSe films. The results indicated that the electrodeposited films were the smooth, compact and uniform at deposition potentials of −0.70 V versus SCE.     

Conduction studies on electrodeposited indium selenide thin films

Indium Selenide thin films were electrodeposited on Indium Tin Oxide (ITO) coated glass substrates from a mixture of Indium trichloride (InCl₃) and selenium dioxide (SeO₂) in aqueous solution by the potentiostatic electrodeposition technique. The InSe films showed that Mott’s variable-range hopping conductivity (VRH) is dominant under low field (∼2×10⁵ Vcm⁻¹) condition. At high field the Current-Voltage studies (in the temperature range 300 – 380 K) revealed that the conductivity of Indium selenide thin films is of Poole-Frenkel type. The plot drawn between Ln (I/V) and tV showed a straight line and also the experimental data and the theoretical data closely matches. Hence Poole-Frenkel mechanism is confirmed and discussed in detail. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Characteristics of electrodeposited bismuth telluride thin films with different crystal growth by adjusting electrolyte temperature and concentration

Bismuth telluride (Bi₂Te₃) thin films were prepared with various electrolyte temperatures (10°C–70 °C) and concentrations [Bi(NO₃)₃ and TeO₂: 1.25–5.0 mM] in this study. The surface morphologies differed significantly between the experiments in which these two electrodeposition conditions were separately adjusted even though the applied current density was in the same range in both cases. At higher electrolyte temperatures, a dendrite crystal structure appeared on the film surface. However, the surface morphology did not change significantly as the electrolyte concentration increased. The dendrite crystal structure formation in the former case may have been caused by the diffusion lengths of the ions increasing with increasing electrolyte temperature. In such a state, the reactive points primarily occur at the tops of spiked areas, leading to dendrite crystal structure formation. In addition, the in-plane thermoelectric properties of Bi₂Te₃ thin films were measured at approximately 300 K. The power factor decreased drastically as the electrolyte temperature increased because of the decrease in electrical conductivity due to the dendrite crystal structure. However, the power factor did not strongly depend on the electrolyte concentration. The highest power factor [1.08 μW/(cm·K²)] was obtained at 3.75 mM. Therefore, to produce electrodeposited Bi₂Te₃ films with improved thermoelectric performances and relatively high deposition rates, the electrolyte temperature should be relatively low (30 °C) and the electrolyte concentration should be set at 3.75 mM.     

热处理对TbDyFe薄膜性能的影响

采用磁控溅射方法利用镶嵌靶材制备非晶TbDyFe薄膜,然后分别在150,300,450,550℃下退火,研究了热处理对TbDyFe薄膜性能的影响.结果显示,550℃温度下退火的样品出现RFe2相.随着退火温度的升高,晶粒逐渐长大,空洞网络变短而宽.薄膜的磁特性显示,其矫顽力及矩磁比均在出现RFe2相的550℃退火的样品中达到最大值.随着退火温度的增加,薄膜的易磁化轴从垂直膜面方向向平行膜面方向转动.     

ps-laser scribing of CIGS films at different wavelengths

Continuous growth of the thin-film electronics market stimulates the development of versatile technologies for large-scale patterning of thin-film materials on rigid and flexible substrates, and laser technologies are a promising method to accomplish the scribing processes. Lasers with picosecond pulse duration were applied in scribing of complex multilayered CuIn _x Ga_(1−x)Se₂ (CIGS) solar cells deposited on a polyimide substrate. The ablative properties of the films were examined as a function of the wavelength of laser radiation, pulse energy, and the irradiation dose. The selective removal of ITO and CIGS layers was achieved with 355 nm irradiation without any significant damage to the underlying layers in the ITO/CIGS/Mo/PI solar cell system. The 355 nm wavelength was also found to be favorable for scribing of absorber layer in a ZnO/CIGS/Mo/PI solar cell system. 266 nm radiation significantly modified the film structure due to high absorption. Extensive melt formation in the CIGS layer was found when 532 nm radiation was applied, though the trenches were smooth and crack-free.     

The wavelength of the magnetization ripple of electrodeposited Ni-Fe films

Thin films of Ni-Fe were electrodeposited onto Cu-substrates, subsequently stripped from their substrates and examined by Lorentz microscopy. The long range wavelengthλ _LR of the magnetization ripple, the anisotropy fieldH _K, the distance between crossties in cross-tie walls, and average crystallite size were determined for several films. Within a certain range of anisotropy fields the relationshipλ _LR=2.99H+ _K ^?1/2 +0.2 micron was experimentally found for as-stripped films. Each film was also given a series of annealing treatments. A large decrease of anisotropy field, and an increase of ripple wavelength occurred after the first few anneals. On increased annealing no significant change in ripple wavelength could be measured although the anisotropy field continued to decrease. This result might suggest that only a part ofH _K is effective in determining the wavelength.