Effect of pulse reversal on the properties of pulse plated CdSe x Te1−x thin films

CdSe _x Te_1–x thin films with 0 < x < 1 were deposited on titanium and conducting glass substrates by pulse electrodeposition using microprocessor control. Formation of the solid solution takes place for values of x(0 < x < 1). The films were characterized by X-ray diffraction. While the as-deposited films are cubic in nature, those annealed at 475 °C in air indicate hexagonal structure and the lattice parameters increase with increasing value of x. From the optical absorption measurements the band gap of the material was calculated. The value of the band gap varies from 1.42 to 1.70 eV as x varies from 0 to 1. The photoelectrochemical (PEC) characteristics were obtained for all compositions of CdSe _x Te_1–x (x = 0–1). The output parameters for CdSe_0.66Te_0.34 with 9% duty cycle at an intensity of 80 mW cm^–2 using 1 M polysulphide as the redox electrolyte, are V _OC of 398 mV, J _SC of 5.59 mA cm^–2, ff of 0.45, of 4.73%, R _s of 13 , R _sh of 1.50 k. The output parameters were found to increase with 60 ms pulse reversal. After photoetching for 40 s, a V _OC of 481 mV, J _SC of 16.00 mA cm^–2, ff of 0.57, of 5.46%, R _s of 6 , R _sh of 2.16 k were obtained.     

Preparation and thermoelectric properties of Bi2SexTe3−x bulk materials

Bi₂Te₃ and Bi₂Se₃ nanoplates were synthesized by a microwave-assisted wet chemical method, and Bi₂Se_xTe_3−x (x=1, 2, 3) bulk nanocomposites were then prepared by hot pressing the Bi₂Te₃ and Bi₂Se₃ nanoplates at 80 MPa and 723 K in vacuum. The phase composition and microstructures of the bulk samples were characterized by powder X-ray diffraction and field-emission scanning electron microscopy, respectively. The electrical conductivity of the Bi₂Se_xTe_3−x bulk nanocomposites increases with increasing Se content, and the Seebeck coefficient value is negative, showing n-type conduction. The absolute Seebeck coefficient value decreases with increasing Se content. A highest power factor, 24.5 µWcm⁻¹ K⁻², is achieved from the sample of x=1 at 369 K among the studied samples.     

Microwave dielectric properties of the (BaxSr1−x)TiO3 thin films on alumina substrate

Barium strontium titanate, (Ba_xSr_1?x)TiO₃ (BST) thin films have been prepared on alumina substrate by sol–gel technique. The X-ray patterns analysis indicated that the thin films are perovskite and polycrystalline structure. The interdigital electrode with 140 nm thickness Au/Ti was fabricated on the film with the finger length of 80 μm, width of 10 μm and gaps of 5 μm. The temperature dependence of dielectric constant of the BST thin films in the range from ?50 °C to 50 °C was measured at 1 MHz. The dielectric properties of the BST thin films were measured by HP 8510C vector network analyzer from 50 MHz to 20 GHz.     

Effect of plating parameters on the properties of pulse electrodeposited Ni–TiN thin films

The influence of pulse plating parameters on the microstructure, microhardness, and properties of the Ni–TiN thin films was investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM), X–ray diffraction (XRD), scanning electron microscopy (SEM), and corrosion and wear tests. The results indicated the Ni–TiN thin films prepared via electrodeposition at 4 A/dm² current density to show an optimum microhardness and TiN content values of 984.7 HV and 8.69 wt%, respectively. The average grain sizes of Ni and TiN in the films obtained at 200 Hz were 127.8 and 48.5 nm, respectively. Numerous large pores can be noticed in the films prepared at pulse frequencies of 200 Hz and 500 Hz, whereas only a few small pits are visible on the surface of the Ni–TiN thin films deposited at 800 Hz. The films prepared at 20% duty cycle experienced the least weight loss.     

Direct multipulse laser processing of titanium oxide–graphene oxide nanocomposite thin films

Nanocomposite thin films consisting of titanium oxide (TiO₂) nanoparticles (NPs) and graphene oxide (GO) platelets were deposited by a spin-coating technique. The obtained films were submitted to direct laser irradiation using a frequency quadrupled Nd:YAG (λ=266 nm, τ_FWHM≅3 ns, ν=10 Hz) laser source. The effect of the laser processing conditions, as laser fluence value and number of subsequent laser pulses incident onto the same target location, on the surface morphology, crystalline structure, and chemical composition of the TiO₂/GO nanocomposite thin films was systematically investigated. The laser fluence values were maintained below the vaporization threshold of the irradiated composite material. With the increase of the laser fluence and number of incident laser pulses melting and coalescence of the TiO₂ NPs into inter-connected aggregates as well as rippling of the GO platelets take place. The gradual reduction of GO platelets and the onset of anatase to rutile phase transition were observed at high laser fluence values.     

Supermolecular structure of films based on poly-β-hydroxybutyrate

Conclusions -- Using methods of x-ray diffraction at low or wide angles, it has been shown that films based on polyhydroxybutyrate have a structure corresponding to the structure of a polymer based on 3HB in pure form or with only a slight content of 4HB units.-- Films formed by the dry method from a solution of polyhydroxybutyrate in methylene chloride have a heterogeneous supermolecular structure and less perfected crystallites than films prepared from a solution in chloroform.Khimvolokno LenNII. VNIIPV, Mytishchi. Translated from Khimicheskie Volokna, No. 5, pp. 18–19, September–October, 1992.     

Fischer-Tropsch synthesis in the presence∣ of cobalt-containing composite materials based on carbon

The Fischer-Tropsch synthesis in the presence of composite materials prepared by the IR pyrolysis of polyacrylonitrile (PAN) with cobalt salts immobilized on it was studied. The catalysts were small granules containing PAN carbonization products and to 80% cobalt metal particles of size 10–17 nm. The synthesis was performed in flow reactors with a fixed bed and a catalyst bed suspended in a liquid at 2–3 MPa and 200–310°C. It was established that the activity of the catalyst depends on the nature of the cobalt salt used, the temperature of IR pyrolysis, and the synthesis conditions. The catalyst prepared with the use of cobalt carbonate exhibited the greatest activity. The yield of liquid hydrocarbons on it reached ～70 g/m³ at ～60% selectivity. It was found that the test composite materials were characterized by an extremely high productivity of 2–5 kg (kg Co)^?1 h^?1.     

Influence of deposition parameters on the dielectric properties of rf magnetron sputtered Ba(ZrxTi1−x)O3 thin films

Ba(Zr_xTi_1−x)O₃ (BZ_xT_1−x in short) thin films have been deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering and their dielectric properties have been characterized as a function of sputtering parameters. The BZ_xT_1−x thin films are amorphous when sputtered at rf power (R_p)=100 W and substrate temperature (S_T)=300 °C. The crystalline phase of the BZ_xT_1−x thin films appears when the substrate temperature increases from 300 to 400 and 500 °C, respectively, and the films have a high degree of (100) preferred orientation. The dielectric constant decreases with increasing measurement temperature, irrespective of the rf power and Zr content of the BZ_xT_1−x thin films. The BZ_0.3T_0.7 thin films have a low dielectric loss tangent irrespective of the sputtering parameters. The dielectric constant of the BZ_0.3T_0.7 thin film increases with increasing Zr·(Zr+Ti)⁻¹ ratio and deposition temperature but decreases with increasing working pressure. Besides, the dielectric constant suddenly increases from 244.0 to 284.1 when the rf power increases from 100 to 130 W, then it decreases from 284.1 to 270.0 when the rf power increases from 130 to 160 W. The dielectric constant also suddenly increases from 164.1 to 281.5 when the sputtering gas contains O₂ from 0 to 10%, but its variation is insignificant when the sputtering gas contains O₂ from 10 to 20%.     

A study on the crystallization behavior of poly(β-hydroxybutyrate) thin films on Si wafers

The exact molecular chain orientation of poly(β-hydroxybutyrate) (PHB) in ultrathin films was successfully probed using surface-sensitive, grazing incidence X-ray diffraction techniques. The crystal orientation of spin-coated PHB films was very sensitive to free surface and thermal annealing. In pristine films, the free surface easily exerted its influence on PHB crystallization and caused lamellar orientation with the b-axis perpendicular to the film surface. The effect of the buried interface increased with temperature. With the increase in thermal annealing temperature, the lamellar orientation changed from the b-axis being perpendicular to the film surface to the c-axis becoming perpendicular to the film surface. As film thickness increased, the temperature, at which the lamellae with the b-axes oriented normal to the film surface disappeared, increased. The thickness and temperature dependence of the crystallization behavior of PHB in an ultrathin film could be attributed to the competition between the effects of the free surface and the buried interface.     

Synthesis and characterization of nanoparticle thin films of a-(PbSe)100?xCdx lead chalcogenides

We report the synthesis of amorphous (PbSe)_100−xCd_x (x = 5, 10, 15, and 20) nanoparticle thin films using thermal evaporation method under argon gas atmosphere. Thin films with a thickness of 20 nm have been deposited on glass substrates at room temperature under a continuous flow (50 sccm) of argon. X-ray diffraction patterns suggest the amorphous nature of these thin films. From the field emission scanning electron microscopy images, it is observed that these thin films contain quite spherical nanoparticles with an average diameter of approximately 20 nm. Raman spectra of these a-(PbSe)_100−xCd_x nanoparticles show a wavelength shift in the peak position as compared with earlier reported values on PbSe. This shift in peak position may be due to the addition of Cd in PbSe. The optical properties of these nanoparticles include the studies on photoluminescence and optical constants. On the basis of optical absorption measurements, a direct optical bandgap is observed, and the value of the bandgap decreases with the increase in metal (Cd) contents in PbSe. Both extinction coefficient (k) and refractive index (n) show an increasing trend with the increase in Cd concentration. On the basis of temperature dependence of direct current conductivity, the activation energy and pre-exponential factor of these thin films have been estimated. These calculated values of activation energy and pre-exponential factor suggest that the conduction is due to thermally assisted tunneling of the carriers.     

Electrochemical deposition of Co–Sb thin films on nanostructured gold

The electrochemical behavior of the Co–Sb system on Au substrate during cyclic voltammetry and potentiostatic deposition was investigated. Electrochemical behavior of Co and Sb was studied and compared to the Co–Sb system. At a negative potential (−0.9 V vs. Ag/AgCl) the electrochemical behavior of this binary system was similar to that of individual Co and Sb combined. For more negative vertex potentials (e.g., −1.2 V vs. Ag/AgCl), results from cyclic voltammetry have shown the presence of a new compound different from Co and Sb which could only be detected at slow sweep rate. The deposition performed at constant potentials between −1.0 and −1.2 V have resulted in films that were made of CoSb₃ and Sb as indicated by XRD. Surface film studied by SEM and EDS has shown morphological and compositional non-uniformities caused by hydrogen evolution.     

The effects of solvents on the formation of sol–gel-derived Bi12SiO20 thin films

The sol–gel method was used to synthesize Bi₁₂SiO₂₀ thin films. Two synthesis routes with two different solvents, i.e., 2-ethoxyethanol and acetic acid, were used and compared. Thin films were deposited onto Pt/TiO₂/SiO₂/Si substrates by spin-coating at 3000 rpm and annealed at 700 °C for 1 h. A different coordination of the bismuth ion was observed in the sols prepared with acetic acid (AcOH), and as a result, stable sols were formed with a shorter gelation time t_G = 84 h (c = 0.76 M), when compared with the sols prepared from 2-ethoxyethanol (EtoEtOH) t_G = 580 h (c = 0.76 M). The microstructures of the Bi₁₂SiO₂₀ thin films prepared from sols using EtoEtOH were homogeneous and dense. On the other hand, a porous microstructure was observed for the Bi₁₂SiO₂₀ thin films deposited from the sol in which AcOH was used as the solvent.     

Investigation of the formation of fractal structures in SiO2 · SnO x · CuO y thin films prepared by the sol-gel method

The processes of fractal structure formation have been considered in SiO₂ · SnO _x · CuO _y nanofilms prepared by the sol-gel method from a tetraethoxysilane alchohol solution modified by metal salts. The atomic force microscopy images of these films have been obtained. The surface morphology has been analyzed using the Takens embedding method and Grassberger-Procaccia algorithm. The correlation and fractal dimensions of the film samples and the coefficient of surface area increase have been calculated. The effects of the annealing temperature and concentration of the doping component on the formation of fractal structures in the materials under study have been estimated.     

Dependencies of microstructure and stress on the thickness of GdBa2Cu3O7 ? δ thin films fabricated by RF sputtering

GdBa₂Cu₃O_{7 − δ} (GdBCO) films with different thicknesses from 200 to 2,100 nm are deposited on CeO₂/yttria-stabilized zirconia (YSZ)/CeO₂-buffered Ni-W substrates by radio-frequency magnetron sputtering. Both the X-ray diffraction and scanning electron microscopy analyses reveal that the a-axis grains appear at the upper layers of the films when the thickness reaches to 1,030 nm. The X-ray photoelectron spectroscopy measurement implies that the oxygen content is insufficient in upper layers beyond 1,030 nm for a thicker film. The Williamson-Hall method is used to observe the variation of film stress with increasing thickness of our films. It is found that the highest residual stresses exist in the thinnest film, while the lowest residual stresses exist in the 1,030-nm-thick film. With further increasing film thickness, the film residual stresses increase again. However, the critical current (I_c) of the GdBCO film first shows a nearly linear increase and then shows a more slowly enhancing to a final stagnation as film thickness increases from 200 to 1,030 nm and then to 2,100 nm. It is concluded that the roughness and stress are not the main reasons which cause the slow or no increase in I_c. Also, the thickness dependency of GdBa₂Cu₃O_{7 − δ} films on the I_c is attributed to three main factors: a-axis grains, gaps between a-axis grains, and oxygen deficiency for the upper layers of a thick film.     

Influence of precursor solution volume on the properties of spray deposited α-MoO3 thin films

α-MoO₃ thin films were deposited onto a glass substrate with 0.01 M ammonium heptamolybdate tetrahydrate as a precursor salt and deionized water as solvent using spray pyrolysis technique. The influence of precursor solution volume on the structural, morphological, optical and electrical properties were analysed and reported.     

Influence of annealing temperature on the structural and anti-corrosion characteristics of sol–gel derived,spin-coated thin films

Recently, an aqueous particulate sol–gel process using metallic chloride precursors was introduced to synthesize zirconium titanate. In this paper, the effect of annealing temperature on the structural and corrosion protection characteristics of spin-coated thin films obtained from this sol–gel system was investigated. Based on scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic reflectometry studies, it was found that the flatness and thickness of the thin films were decreased by increasing the annealing temperature. Also, the corrosion protection of stainless steel AISI 316L provided by the prepared coatings, as analyzed by electrochemical potentiodynamic polarization experiments in a simulated body fluid, was improved in this order: 500 °C-annealed sample<900 °C-annealed sample<700 °C-annealed sample, attributed to a compromise between the defect density and the adhesion of the films to the substrate.     

The effect of ceramic nanoparticles on tribological properties of alumina sol–gel thin coatings

Thin alumina coatings containing zirconia or alumina nanoparticles having diameter of ～20–30 nm were deposited by the sol–gel dip-coating process on silicon wafers. The mass content of nanoparticles in the alumina coating was fixed at 15% in relation to the theoretical mass of alumina matrix resulted from the amount of the applied precursor. Atomic force microscopy (AFM) was used to image the surface topography of as-made coatings and find out the wear level after frictional tests. Tribological tests were performed with the use of a microtribometer operating in the load range of 30–100 mN. It was found that the presence of α-alumina (corundum) or zirconia nanoparticles enhances the tribological performance of alumina layers annealed at 100 °C by decreasing the average wear rate by 20% and 63% for zirconia and corundum nanoparticles, respectively. No wear was observed for samples containing both types of nanoparticles annealed at 500 °C.     

Purification of titania nanoparticle thin films: Triviality or a challenge?

Although purification of titania nanoparticles is a very common process in laboratory practice the specific purification protocol is often chosen without scientific justification. In the present work the efficiency of three different and in laboratory practice widely used treatments is compared for removing organic contaminants from the surface of titania nanoparticles. The most effective purification treatment was annealing of nanoparticles below 400 °C: annealing at higher temperatures causes besides purification the growth of nanoparticles.     

Search of high-capacity cathode materials based on lithium–iron silicate compounds

The crystal structures of 197 lithium–silicate compounds have been analyzed using the method of crystal chemistry analysis (TOPOS software package). The compounds whose structures are characterized with a combination of high values of such parameters as the channel radius, stability, gravimetric capacity, and capacity per volume unit have been revealed: LiFeSiO₄ (R3?), Li₄Fe₂Si₃O₁₀ (C2/c), Li₂FeSiO₄ (Pc2₁ n), and Li₂FeSiO₄ (C222₁). It has been demonstrated that lithium–iron silicates of the monoclinic syngony have high values of the capacity per volume unit, as compared to those of the rhombic syngony. The structural stability of the Li₂FeSiO₄ (Pc2₁ n) framework has been corroborated using the method of computer simulation within the scopes of the electron density functional theory. The obtained information could facilitate creation of novel cathode materials of high capacity and specific accumulated energy.