Effect of negative substrate bias on HWCVD deposited nanocrystalline silicon (nc-Si) films

The influence of the negative substrate bias on the interfacial and microstructural characteristics of nanocrystalline silicon (nc-Si) thin films was deposited by hot wire chemical vapor deposition (HWCVD). Structural characterization of nc-Si films was performed by small angle X-ray diffraction (SAXRD), Raman spectroscopy, X-ray reflectivity (XRR) and field emission scanning electron microscopy (FESEM). Crystalline fraction and crystallite size increases from 61.31 to 74.13% and 13.3 to 21.6 nm, respectively, with an increasing negative bias from 0 to ?200 V. Furthermore, the deposition rate of nc-Si films increases from 25 to 68 nm/min by increase of negative substrate bias from 0 to ?200 V.     

Effect of Annealing on the Electrical Properties of CuxS Thin Films

Copper sulphide CuS was deposited on three substrates; glass, Indium Tin Oxide (ITO) and Ti by using spray pyrolysis deposition (SPD). After depositing CuS thin films on the substrates at 200 °C, they were annealed at 50, 100, 150, and 200 °C for 1 hour. Structural measurements revealed covellite CuS and chalcocite Cu₂S phases for thin films before and after annealing at 200 °C with changes in intensities, and only covellite CuS phase for thin films after annealing at 50, 100, and 150 °C. Morphological characteristics show hexagonal-cubic crystals for the CuS thin film deposited on glass substrate and plates structures for films deposited on ITO and Ti substrates before annealing, these crystals became bigger in size and there were be oxidation and some agglomerations in some regions with formation of plates for CuS on glass substrate after annealing at 200 °C. For Hall Effect measurements, thin films sheet resistivity and mobility increased after annealing while the carrier concentration decreased. Generally, the thin film deposited on ITO substrate had the lowest resistivity and the highest carrier concentration before and after annealing. The thin film deposited on Ti substrate had the highest mobility before and after annealing, which makes it the best thin film for device performance. The objective of this research is to show the improvement of thin films electrical properties especially the mobility after annealing those thin films.     

A study on solution deposited CuSCN thin films: Structural,electrochemical, optical properties

A cost-effective successive ionic layer adsorption and reaction (SILAR) method was used to deposit copper (I) thiocyanate (CuSCN) thin films on glass and steel substrates for this study. The deposited thin films were characterized for their structural, morphological, optical and electrochemical properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and VersaSTAT potentiostat. A direct band gap of 3.88 eV and 3.6 eV with film thickness of 0.7 μm and 0.9 μm was obtained at 20 and 30 deposition cycles respectively. The band gap, microstrain, dislocation density and crystal size were observed to be thickness dependent. The specific capacitance of the CuSCN thin film electrode at 20 mV/s was 760 F g⁻¹ for deposition 20 cycles and 729 F g⁻¹ for deposition 30 cycles.     

Electrochemical fabrication of novel fluorescent polymeric film: Poly(pyrrole–pyrene)

We describe herein the electrochemical characterization and polymerization of 4-pyren-1-yl-butyric acid 11-pyrrol-1-yl-decyl ester (pyrrole–pyrene) in CH₃CN. The electrochemical oxidation of the pyrrole group at 0.77 V vs Ag/Ag + 10 mM in CH₃CN led to the first example of a fluorescent polypyrrole film. The mechanism of deposition on platinum electrode was studied by voltammetry and chronoamperometry. The optical properties of the polymeric films electrogenerated on ITO electrodes were examined by UV–visible spectroscopy and fluorescence microscopy indicating an increase in fluorescence properties by increased polymer thickness. The electrochemical oxidation of pyrenyl group linked to the polypyrrole backbone was carried out at 1.2 V. This additional polymerization was demonstrated by UV–visible spectroscopy and induced the loss of the fluorescence properties of the resulting polymeric film.     

Direct electrochemistry of hemoglobin and glucose oxidase in electrodeposited sol–gel silica thin films on glassy carbon

This work points out that electrogeneration of silica gel (SG) films on glassy carbon electrodes (GCEs) can be applied to immobilize biomolecules – hemoglobin (Hb) or glucose oxidase (GOD) or both of them in mixture – without preventing their activity. These proteins were physically entrapped in the sol–gel material in the course of the electro-assisted deposition process applied to form the thin films onto the electrode surface. SG films were prepared from a precursor solution by applying a suitable cathodic potential likely to induce a local pH increase at the electrode/solution interface, accelerating thereby polycondensation of the silica precursors with concomitant film formation. Successful immobilization of proteins was checked by various physico-chemical techniques. Both Hb and GOD were found to undergo direct electron transfer, as demonstrated by cyclic voltammetry. GCE–SG–Hb gave rise to well-defined peaks at potentials E_c = −0.29 V and E_a = −0.17 V in acetate buffer, corresponding to the Fe^III/Fe^II redox system of heme group of the protein, while GCE–SG–GOD was characterized by the typical signals of FAD group at E_c = −0.41 V and E_a = −0.33 V in phosphate buffer. These two redox processes were also evidenced on a single voltammogram when both Hb and GOD were present together in the same SG film. Hb entrapped in the silica thin film displayed an electrocatalytic behavior towards O₂ and H₂O₂ in solution, respectively in the mM and μM concentration ranges. Immobilized GOD kept its biocatalytic properties towards glucose. Combined use of these two proteins in mixture has proven to be promising for detection of glucose in solution via the electrochemical monitoring of oxygen consumption (decrease of the oxygen electrocatalytic signal).     

Titanium vanadium nitride electrode for micro-supercapacitors

Here we report on the synthesis of binary transition metal nitride electrodes based on titanium vanadium nitride (TiVN) thin films. These films were deposited by a method compatible with micro-electronic processes which consists of DC co-sputtering of vanadium (V) and titanium (Ti) targets. TiVN films with different Ti/V ratio were deposited. A dependence of the capacitance and the cycling stability with the Ti/V atomic ratio in the films was established. While V rich sample exhibits a Faradic behavior that limits its cycling ability despite a high areal and volumetric capacity, the addition of Ti in the film drastically improves the cycling ability with virtually no fade in capacitance after 10,000 cycles. Furthermore, a 1.1 Ti/V ratio leads to an areal capacitance up to 15 mF·cm^− 2 in 1 M KOH electrolyte solution. Such electrodes shed light on the use of binary transition metal nitrides as candidate electrodes for micro-supercapacitor.     

XPS/EXAFS study of cycleability improved LiMn2O4 thin film cathodes prepared by solution deposition

The influence of Sn substitution in LiMn₂O₄ thin films as a cathode has been studied via solution deposition to improve the electrochemical performance of thin film lithium batteries. LiSn_0.025Mn_1.95O₄ thin films showed the most promising performance, i.e. a high capacity retention of 77% at 10 C after the 500th cycle, due to the increased average Mn valence state. The thin films of LiSn_x/2Mn_2?xO₄ (x ? 0.10) showed significant precipitation of SnO₂ and SnO after the cycling evaluation.     

Direct electrodeposition of PbTe thin films on n-type silicon

High quality lead telluride thin films were directly deposited onto n-type silicon (1 0 0) substrates by electrodeposition at room temperature. The deposition mechanism was studied using cyclic voltammetry. The films were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, and Fourier transform infrared spectroscopy. The results indicated that the deposited PbTe films exhibited a polycrystalline rock salt structure and good optical properties with a direct band gap of 0.31 eV.     

Effect of swift heavy ion irradiation on the physical properties of CuIn(S0.4Se0.6)2 alloy thin films prepared by solution growth technique

Alloy thin films of CuIn(S_0.4Se_0.6)₂ material were deposited using the solution growth technique. The various deposition parameters such as pH of solution, time, concentration of ions and temperature have been optimized for the device grade thin films. The as-deposited films were annealed in a rapid thermal annealing (RTA) system at 450 °C in air for 5 min and subjected to high-energy Ag ion irradiations. Ag ion irradiation has been performed with an energy of 100 MeV at a fluency of 5×10¹² ions/cm² on the thin film. The changes in optical and electrical properties that occurred before and after post-deposition treatments in CuIn(S_0.4Se_0.6)₂ thin films were studied using X-ray diffraction (XRD) and AFM; increase in crystallinity was observed after annealing and irradiation. In addition, structural damages were observed in irradiated thin films. After annealing and irradiation, the surface roughness was seen to be increased. Decrease in resistivity was observed, which is consistent with the optical energy band gap. The results are explained by considering the high energy deposited due to the electronic energy loss upon irradiation, which modified the properties of the material.     

Effect of Deposition Temperature on Structural and Optical Properties of Chemically Sprayed ZnS Thin Films

Zinc sulfide (ZnS) thin films have been successfully deposited via spray pyrolysis using an aqueous solution of thiourea and zinc acetate onto glass substrate. The effect of varying substrate temperature (150, 200,250 and 300 °C) on structure and optical properties is presented. The films have been characterized by X- ray diffraction (XRD), UV-Vis-NIR spectrometry, photoluminescence (PL) spectroscopy and field emission scanning electron microscopy (FESEM). All the deposited ZnS films exhibit a cubic structure, while crystallinity and morphology are found to depend on spray temperature. PL analysis indicates the presence of violet and green emissions arising from Zn and S vacancies. The value of bandgap of ZnS films is found to decrease slightly with increasing substrate temperature; varying in the range 3.52–3.25 eV, most probably associated with the formation of Zn(S,O) solid solution.     

Electropolymerizing polyaniline on undoped 100 nm diamond powder and its electrochemical characteristics

Conductive polyaniline (PANI) was electropolymerized on undoped 100 nm diamond powders in sulphuric acid solution containing aniline to improve the conductivity and the electrochemistry of the nano- or submicro-scaled diamond particles. Cyclic voltammetry (CV) experiment was carried out at an upper potential of 1.1 V in initial sweeps and a potential range of ?0.2–0.9 V for the growth of PANI on a diamond powder electrode. Field emission-scanning electron microscope (FESEM) result reveals that the diamond particles were well coated by PANI films with globular or fibroid surface morphology. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were employed to investigate the electrochemical properties of the PANI/diamond composite electrode. It presents lower resistance and better capacitance than the pristine diamond powder.     

Experimental indications for the existence of different states of palladium(0) at the surface of carbon paste electrodes

The deposition and dissolution of palladium(0) at non-modified carbon paste electrode (CPE) is studied in aqueous chloride solution. During the dissolution one or two Pd oxidation peaks are observed at + 0.1 V and about + 0.45 V vs. SCE, indicating the existence of different states of Pd⁰ at the CPE. In accordance with the experimental results it is assumed that a palladium monolayer is formed when low amounts of Pd are deposited and that multilayers are formed in the case of larger amounts of deposited palladium. The formation of a metal monolayers at CPE is described for the first time.     

Structural and electrical characterization of boron-containing diamond-like carbon films deposited by femtosecond pulsed laser ablation

The present study investigates the influence of the incorporation of boron in Diamond-Like Carbon (DLC) films deposited by femtosecond laser ablation, on the structure and electrical properties of the coatings within the temperature range 70–300 K. Doping with boron has been performed by ablating alternatively graphite and boron targets. The film structure and composition have been highlighted by coupling Atomic Force Microscopy (AFM), Scanning Electron Microscopy equipped with a field emission gun (SEM-FEG) and High Resolution Transmission Electron Microscopy (HRTEM). Boron dilution ranges between 2 and 8% and appears as nanometer size clusters embedded in the DLC matrix. Typical resistivity values are 100 W cm for pure a-C films, down to few W cm for a-C:B films at room temperature. The resistance decreases exponentially when the temperature increases in the range 70–300 K. The results are discussed considering the classical model of hopping conduction in thin films. Some coatings show temperature coefficients of resistance (TCR) as high as 3.85%. TCRs decrease when the doping increases. Such high values of TCR may have interests in the use of these films as thermometer elements in micro and nanodevices.     

Optical,structural and electrochromic studies of molybdenum oxide thin films with nanorod structure

The MoO₃ thin films were prepared via sol–gel dip coating method on glass and FTO glass substrate. The optical and other properties of multilayered MoO₃ films with 2–10 layers were investigated. The MoO₃ films were studied using UV–Visible transmission, XRD, SEM, FTIR and Cyclic Voltammetry (CV) measurements. The band gap value for MoO₃ films was evaluated and in the range of 3.2 eV–3.72 eV. The XRD spectrum reveals that the crystallinity increases along the (020) and (040) planes with the increase in thickness. The SEM images showed the formation of nanorods upto six layers. The FTIR spectrum confirms the formation of MoO₃. The 6 layered films show the maximum anodic (spike)/cathodic (peak) diffusion coefficient of 18.84/1.701 × 10^?11 cm²/s. The same film exhibits the change in optical transmission of 49% with the bleached/coloured state transmission of 62/13%.     

Visible light active hydrogen modified (HM)-n-TiO2 thin films for photoelectrochemical splitting of water

Visible light active hydrogen modified n-type titanium oxide (HM-n-TiO₂) thin films were synthesized by thermal oxidation of Ti metal sheet (Alfa Co. 0.25 mm thick) in an electric oven followed by incorporation of hydrogen electrochemically under cathodic polarization at ?1.6 V vs Pt. The photoresponse of the HM-n-TiO₂ was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen in terms of photocurrent density, J_p. The optimized electric oven-made n-TiO₂ and HM-n-TiO₂ photoelectrodes showed photocurrent densities of 0.2 mA cm^?2 and 1.60 mA cm^?2, respectively, at a measured potential of ?0.4 V vs Pt at illumination intensity of 100 mW cm^?2 from a 150 W xenon lamp. This indicated an eightfold increase in photocurrent density for HM-n-TiO₂ compared to oven-made n-TiO₂ at the same measured electrode potential. The band-gap energy of HM-n-TiO₂ was found to be 2.7 eV compared to 2.82 eV for electric oven-made n-TiO₂ and a mid-gap band at 1.67 eV above the valence band was also observed. The HM-n-TiO₂ thin film photoelectrodes were characterized using photocurrent density under monochromatic light illumination and UV–Vis spectral measurements.     

Preparation and optical absorption of electrodeposited or sputtered,dense or porous nanocrystalline CuInS2 thin films

Copper indium disulphide thin films were obtained by one-step deposition with two different techniques. Films are synthesised by electrodeposition using a single electrolytic bath and by r.f. sputtering using a single target. Deposition rates were about 75 nm/min and 2.5–6.5 nm/min, respectively. Electrodeposited films have rough and porous surfaces, with no preferential orientation. Smooth or particle-covered surfaces were observed for sputtered films with a highly (112)-oriented chalcopyrite structure. Absorption coefficients calculated from transmittance spectra have high values in visible range. Electrodeposited samples present higher absorption coefficients on a larger wavelength range. A relationship between morphology and optical properties was found; absorption coefficients increase with porosity and roughness of the films. Band gap values of about 1.3 eV for electrodeposited and 1.5 eV for sputtered thin films were calculated.     

Electrodeposition of hyaluronic acid and hyaluronic acid–bovine serum albumin films from aqueous solutions

Hyaluronic acid (HYH) films were prepared from aqueous sodium hyaluronate (HYNa) solutions by anodic electrodeposition. The film thickness was varied in the range of 0–20 μm by the variation of the deposition time and HYNa concentration. The deposition rate was low at HYNa concentration below 1 g L⁻¹ and increased significantly in the range of 3–5 g L⁻¹. The addition of bovine serum albumin (BSA) to the HYNa solutions resulted in increased deposition yield, which was attributed to the formation of composite HYH–BSA films. The thickness of the HYH–BSA films deposited by anodic electrodeposition was varied in the range of 0–80 μm. The HYH and composite HYH–BSA films were studied by scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and circular dichroism spectroscopy. The deposition mechanism and kinetics of deposition are discussed.     

Characterization of thin InP anodic oxide layers: Correlation of morphological investigations with chemical and electrical properties

Depending on the applied electrochemical parameters, various oxide films can be grown onto InP in aqueous media. In this work, two oxide layers have been grown in borate buffer solution at pH = 9 by applying a low (0.2 mA cm⁻²) or a high (30 mA cm⁻²) current density, but a similar coulometric charge. Capacitance–voltage measurements performed before and after the anodic processes have been made to investigate the electrical properties of new interfaces, while X-ray photoelectron spectroscopy (XPS) analysis and atomic force microscopy (AFM) observations were used to access to the chemical and topographic aspects of the two oxidized surfaces. It is demonstrated that AFM observations coupled with electrochemical and XPS measurements is a good probe for the study of thin oxide on InP. A correlation between the anodization parameters and the resulting electrical and morphological aspects of the anodic layers is clearly evidenced.     

Spontaneous deposition of Sn on Au(1 1 1). An in situ STM study

The tin adlayer formed by spontaneous deposition on Au(1 1 1) was characterized by cyclic voltammetry and in situ scanning tunneling microscopy (STM) in sulphuric acid solution. Cyclic voltammetry measurements showed oxidation peaks in the potential range −0.60 ⩽ E/V vs SSE ⩽ 0, which can be ascribed to the dissolution of the Sn adsorbed layer. STM images of the Au(1 1 1)/Sn modified surface showed that tin nucleated both on step edges and on the flat terraces forming two-dimensional islands. The anodic polarization of this modified surface produced the gradual dissolution of the Sn adlayer which was evidenced by the formation of some holes and the reduction of the initial terraces to many small islands. STM images with atomic resolution obtained on these islands displayed an hexagonal expanded atomic structure. After the anodic stripping of this Sn adsorbed layer the images exhibited the typical Au(1 1 1) terraces with a (1 × 1) atomic structure. However, at more anodic potentials another dissolution process was observed producing noticeable changes on the surface morphology which could be ascribed to the dissolution of a Au–Sn surface alloy.     

The influence of Se doping upon the phase change characteristics of GeSb2Te4

Se substituted GeSb₂Te₄ films have been investigated for property contrast using electrical four-point-probe measurements, in-situ X-ray diffraction (XRD), a static tester probing the optical changes and atomic force microscopy (AFM). The temperature dependent sheet resistance measurements show two transitions at 125 and 262 °C. The first transition at 125 °C is accompanied by a large resistance change of three orders of magnitude. The resistance change for the second step is less pronounced. In-situ X-ray scattering experiments evidence that the first steep change in resistance is due to an amorphous → NaCl type structural transformation. The second change is caused by the transition from the cubic structure to the stable rhombohedral phase. Power–time effect (PTE) diagrams recorded to monitor the optical contrast of the films upon laser irradiation exhibit a fast recrystallization time of about 100 ns. The change of film roughness and topography between the amorphous and crystalline phase has been determined by AFM.