Characterization and electrochemical deposition of natural melanin thin films

Melanin is an important class of biological pigments because of its distinct chemical and physical properties. The electrochemical deposition of natural melanin thin films was studied using two different techniques; constant potential and cyclic voltammetry along with a deposition time of five hours. The thin films deposited electrochemically on a fluorine-doped tin oxide conductive glass substrate using the constant potential method, exhibited faster growth rate and better adhesion to the fluorine-doped tin oxide working electrodes than those deposited using the cyclic voltammetry method. The thin films deposited on the fluorine-doped tin oxide conductor glass using the constant potential method were also more homogeneous than those deposited via the cyclic voltammetry technique. The increase of film thickness is related to the increase of electrochemical deposition time. Interestingly, the electrochemical deposition using the constant potential method had the advantage of consuming less electric charge. The physical and chemical structures of the melanin thin films were characterized using ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The ultraviolet–visible absorption spectra showed the correlation between the variation of deposition rates of melanin and the type of electrochemical technique employed as well as the thickness of the film. The average thickness of the film is 500 nm which absorb 40% of light in both type of films. The atomic force microscopy images illustrated the homogeneous deposition of the melanin molecules on the fluorine-doped tin oxide conductive glass substrate, indicating that the thickness of the thin films can be controlled. We estimated an average grain size of 14.093 Å. The ease of preparing such thin films of organic materials can open new avenues towards the use of soft conductors, in contrast to the complex preparation of industrial semiconductors.     

Optimization of electrochemical aspects for epitaxial depositing nanoscale ZnSe thin films

Studies of the electrochemical optimization of ZnSe thin film deposition on polycrystalline Au substrates using electrochemical atomic layer epitaxy are reported. Electrochemical aspects were characterized by means of cyclic voltammetry, differential pulse voltammetry, and coulometry. To study the growth mechanism of the underpotential deposition in the formation of ZnSe, the effects of Zn and Se deposition potentials and a Se-stripping potential were adjusted to optimize the deposition program. The deposit, grown using the optimized program, was proved to be a single-phase ZnSe compound with a strong (220)-preferred orientation by X-ray diffraction analysis, and scanning electronic microscopy observation shows the deposit consisted of nanoscale particles with an average size about 100 nm. The right 1:1 stoichiometric ratio of Zn to Se according to the coulometry suggests that ZnSe is formed.     

Alkaline earth fluoride and Eu3+ doped thin films obtained by electrochemical processing

Journal of Solid State Electrochemistry - In this study, alkaline earth fluorides (MF2) and MF2:Eu3+ doped (M = Mg, Ca, Sr) thin films were obtained by electrochemical processing. In...     

Photoconductivity and photo-detecting properties of vacuum deposited ZnSe thin films

The paper reports the detailed analysis of photoconductivity and photo-detecting properties of vacuum deposited zinc selenide (ZnSe) thin films. The vacuum deposited ZnSe films were found to have high absorption coefficient and showed peak photo-response at 460 nm. The photocurrent and photo-response time of the films were measured as a function of substrate temperature and annealing conditions. Considerable increase in photocurrent and much faster photo-response was observed in films deposited at high substrate temperatures. Annealing at moderate temperatures also improved the photoconductivity and response time of the films.     

Characterization of zinc-modified lithium tantalate thin films fabricated by chemical solution deposition method

Zinc-substituted lithium tantalate thin films were fabricated for improving the electrical resistivity by compensating the valence of lattice defects in LiTaO₃ crystal. The films with the chemical composition of (Li_1.00-x Zn _x )TaO₃ were fabricated on (111)Pt/TiO₂/SiO₂/(100)Si substrate by a chemical solution deposition technique using metal-organic precursors. Dense films consisting of a ilumenite-type crystalline phase were deposited by spin coating on the substrates, followed by heat-treatment at 650°C for 5 min in air. The leakage current density of the LiTaO₃ film was reduced from approximately 10⁻⁴ to 10⁻⁶ A/cm² by substituting Zn²⁺ ions for Li⁺ ions in the LiTaO₃ films. Polarization–electric field hysteresis loop was improved significantly by partial substitution of Zn²⁺ for Li⁺ ions, which is based on the enhancement of electrical resistivity.     

Evolution of water vapor from indium-tin-oxide thin films fabricated by various deposition processes

Tin-doped In₂O₃ (indium-tin-oxide) transparent conducting films are widely used as electrodes of liquid crystal displays and low-E windows. In the present study, a systematic TDS study was undertaken for ITO films fabricated by various deposition processes; such as PVD, dip coating and spray deposition. Water vapor was the main gas evolved from the films; gas evolution from the silicon substrate was negligible. The evolution proceeded via two steps at approximately 373 and 473-623 K. The amount of the evolved water was in the order: (dip-coated film)>(PVD films)> (spray-deposited film). This order was identical to that of the film's resistivities. This revised version was published online in August 2006 with corrections to the Cover Date.     

Substrate assisted electrochemical deposition of patterned cobalt thin films

The patterned Co layers deposited on the scratched Cu surfaces were investigated with the use of the scanning electron microscopy. Patterned cobalt thin films were electrochemically deposited from the cobalt sulfate bath at room temperature. Pattering of cobalt was carried out by simple means of substrate scratching. Gentle scratching induces a direct pattering of cobalt from vertical to horizontal. The prepared pattered films were characterized for their structural, surface morphological and compositional properties by means of X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. X-ray diffraction studies reveal that the films are of cobalt. From the SEM images fabrication of patterns of cobalt is apparent. This work demonstrates a novel approach for obtaining patterned cobalt for many technological applications.     

Structural and ferromagnetic properties of epitaxial SrRuO3 thin films obtained by polymer-assisted deposition

Epitaxial ferromagnetic SrRuO3 thin films with a room-temperature resistivity of 300 microOmega.cm have been successfully grown on LaAlO3(001) substrates at a processing temperature in the range of 550-750 degrees C by a polymer-assisted deposition technique. X-ray diffraction analysis shows good epitaxial quality of SrRuO3 thin films, giving values of the full width at half-maximum (FWHM) of 0.42 degrees from the rocking curve for the (002) reflection and 1.1 degrees from the in-plane phi scan for the (204) reflection. Both the resistivity and the magnetization versus temperature measurements show that the SrRuO3 films are ferromagnetic with a transition temperature of 160 K. The spontaneous magnetization near the ferromagnetic transition follows the scaling law, and the low-temperature magnetization follows the Bloch law.     

Electron field emission of iron and cobalt‐doped DLC films fabricated by electrochemical deposition

Using a simple electrochemical depositing process, iron and cobalt‐doped diamond‐like carbon (DLC) films were deposited on Si (100) substrates. The results showed that metallic elements were inhomogeneously doped into highly cross‐linking amorphous carbon matrix, forming the typical nanocrystalline/amorphous nanocomposite structure, and simultaneously the microsturcture of amorphous carbon was changed by the doping of metals. Field emission performance showed that the incorporation of iron and cobalt effectively decreases the threshold field from 13.5 V/µm to 8.0 V/µm and 6.5 V/µm, respectively, and a highest current density of the Co‐DLC film was about 1.2 mA/cm² at the electric field of 23.5 V/µm. Copyright © 2012 John Wiley & Sons, Ltd.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO_2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on ITO coated glass by pulsed laser ablation of metallic Ti target in O_3/O_2 ambient gases. The intercalation of Li ions in the anatase TiO_2 film electrode is examined by cyclic vohammetry. The electrochromic behaviour of TiO_2 electrode is investigated by in-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These resuits suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on IT0 coated glass by pulsed laser ablation of metallic Ti target in 0₃/0₂ ambient gases. The intercalation of Li ions in the anatase TiO₂ film electrode is examined by cyclic voltammetry. The electrochromic behaviour of TiO₂ electrode is investigated byin-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These results suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property. Project supported by the National Natural Science Foundation of China (Grant No. 29783001) and State Key Laboratory for Physical Chemistry of Solid Surface of Xiamen University (1997).     

Spectroscopic and electrochemical properties of thin solid films of yttrium bisphthalocyanine

Langmuir—Blodgett (LB) and evaporated thin solid films of the yytrium bisphthalocyanine complex (YPc₂) have been prepared on various substrates. Cyclic voltammograms of films are discussed and the electrochromic effect on LB films is reported. A detailed spectroscopic characterization of the YPc₂ material is given using resonance Raman scattering (RRS), surface-enhanced resonance Raman scattering (SERRS), transmission and reflection absorption FT-IR spectroscopy and UV—vis spectra. The spectroscopic characterization of the chemical and electrochemical oxidations products of YPc₂ films and solutions was carried out by in situ UV—vis spectroscopy. Potential applications are discussed.     

Ellipsometric investigations of Fe3+-doped polyvinyl alcohol films

In this work, we study the inclusion mechanism of Fe³⁺ ions in a polyvinyl alcohol (PVA) matrix. Thin films of pure and FeCl₃-doped PVA on silicon substrates, prepared by the spin-coating method, are investigated using spectroscopic ellipsometry (SE) and Fourier transform infrared (FT-IR) spectroscopy. SE measurements of PVA and Fe³⁺-doped thin films are carried out at an incidence angle of 75° over the wavelength range of 0.24–1.1 μm. An optical model is used to obtain the refractive index (n) and the extinction coefficient (k). The gap energy E _g is afterwards evaluated. The Fe³⁺ doping is found to affect strongly the optical parameters of the polymer films. In fact, an increase in the refractive index with doping is observed, resulting from the intermolecular hydrogen bonding between Fe³⁺ ions with the adjacent OH group of PVA. The increase of the thin films' absorption with doping is estimated by the k spectral profile analysis. The gap energy is then calculated and shows an important decrease with the Fe³⁺ filling, more pronounced for low doped samples. Such a behavior is confirmed by FT-IR analysis.     

Electrophoretic deposition and characterization of self-doped SrTiO3 thin films

Herein, titanium (Ti³⁺) self-doped strontium titanate (SrTiO₃), so-called blue SrTiO₃, with a bandgap of 2.6 eV and favorable photocatalytic characteristics was fabricated through a facile and effective method. For electrochemical investigations, the electrophoretic deposition was applied to produce SrTiO₃ thin films on (fluorine-doped tin oxide) FTO conductive substrates. The electrophoretic voltage of 20 V and a process duration of 10 min were optimized to reach transparent and uniform coatings on FTO. The blue SrTiO₃ reveals lower resistance (charge transfer resistance of 6.38 Ω cm^-2) and higher electron mobility (current density value of 0.25 mA cm^-2) compared to a pure SrTiO₃ electrode. These findings may provide new insights for developing high-performance visible light photocatalysts.     

AFM phase imaging of thin films of electronically conducting polymer polybithiophene prepared by electrochemical potentiodynamic deposition

Nanoscale properties of thin films of conducting polymer polybithiophene (PBT) deposited under potentiostatic and potentiodynamic conditions were compared using ex-situ atomic force microscopy (AFM) and its extension called phase imaging (PI-AFM). While the morphologies of the films prepared using the two techniques were quite similar, the phase contrast measurements revealed a profound difference in the mechanisms of potentiostatic and potentiodynamic electropolymerization, as well as in the nanoscale crystallinity and grain structure of the resulting polymer films. The overall crystallinity and degree of order were always higher for films deposited at constant potential. The differences were especially pronounced at the early deposition stages (film thicknesses of ca. 10 nm).     

Growth and Spectral Properties of Yb^3＋-doped Ba3Gd（BO3）3 Crystal

Crystal of Yb3+-doped Ba3Gd(BO3)3 has been grown by the Czochralski method. The spectroscopic characterizations have been investigated at room temperature. The Yb3+:Ba3Gd(BO3)3 crystal exhibits broad absorption at 976nm with FWHM of 7nm and large overall spitting of 2F7/2 manifold (823cm-1). The absorption and emission cross sections are 5.09×10-21cm2 at 976nm and 0.97×10-21cm2 at 1040nm,respectively. The fluorescence lifetime is 2.84 ms.     

SrCO3:Tb3+ hollow microspheres fabricated via solvothermal process and their optical properties

Well-dispersed SrCO₃:Tb³⁺ hollow microspheres have been synthesized in the water-ethanol-ethylene glycol solvent system using oleic acid (OA) as an additive without further annealing treatment. X-ray diffraction (XRD), fourier transform-infrared spectroscopy (FT–IR), and field emission scanning electron microscopy (FE-SEM), as well as photoluminescence spectroscopy (PL) were used to characterize the resulting samples. The dosage of OA and the reaction time play key roles in the formation of the final samples. The possible formation mechanism for SrCO₃:Tb³⁺ hollow microsphere is proposed. The SrCO₃:Tb³⁺ phosphors show strong photoluminescence with green emission ⁵D₄–⁷F₅ (544 nm) as the most prominent group under ultraviolet excitation, which have potential applications in field emission displays. The present synthesis process may be extended to fabricate other inorganic materials with special morphologies and functions.     

Fluorescence properties of Nd3+-doped tellurite glasses

The compositional and concentration dependence of luminescence of the (4)F(3/2)-->(4)I(J) (J=13/2, 11/2 and 9/2) transitions in four Nd(3+)-doped tellurite based glasses has been studied. The free-ion energy levels obtained for 60TeO(2)+39ZnO(2)+1.0Nd(2)O(3) (TZN10) glass have been analysed using the free-ion Hamiltonian model and compared with similar results obtained for Nd(3+):glass systems. The absorption spectrum of TZN10 glass has been analysed using the Judd-Ofelt theory. Relatively longer decay rates have been obtained for Nd(3+)-doped phosphotellurite glasses. The emission characteristics of the (4)F(3/2)-->(4)I(11/2) transition, of the Nd(3+):TZN10 glass, are found to be comparable to those obtained for Nd(3+):phosphate laser glasses. The non-exponential shape of the emission decay curves for the (4)F(3/2)-->(4)I(11/2) transition is attributed to the presence of energy transfer processes between the Nd(3+) ions.     

Influence of varying molar concentration on the properties of electrochemically-deposited zirconium-doped ZnSe thin films

The effects of molar concentration on ZnSe and Zr-doped ZnSe thin films were studied after successful synthesis by electrochemical technique. 0.1 M zinc tetraoxosulphate (VI) heptahydrate (ZnSO₄·7H₂O) and 0.1 M selenium powder respectively served as the cationic and anionic precursors while 0.1 mol% of zirconium oxidchlorid (ZrOCl₂·8H₂O) was used as the dopant. The morphology, structure, elemental, light response, and electrical features of the samples were studied. The films exhibited uniform distribution of spherical balls with crystalline peaks at (220), (221), (300), and (310) planes. The elemental composition of the film confirmed the deposition of as-synthesized elements. Improved optical characteristics and reduced band gap energies of the films from 2.4 eV to 2.0 eV were gotten upon the addition of zirconium. Electrical results showed increased material conductivity at increasing dopant percentages. The synthesized materials are potentially applied in optoelectronics and photovoltaics.