Highly transparent and conducting fluorine-doped ZnO thin films prepared by pulsed laser deposition

Highly transparent and conducting fluorine-doped ZnO (FZO) thin films were deposited on glass substrates by pulsed laser deposition. Structural, electrical, and optical properties of the films were investigated as a function of oxygen pressure ranging from 0.01 to 0.5 Pa. All the films had a highly preferential c-axis orientation. The films obtained were dense and very smooth with a typical columnar structure. A minimum resistivity of 4.83×10⁻⁴ Ω cm, with a carrier concentration of 5.43×10²⁰ cm⁻³ and a Hall mobility of 23.8 cm² V⁻¹ s⁻¹, was obtained for FZO film prepared at the optimal oxygen pressure of 0.1 Pa. The average optical transmittance in the entire visible wavelength region was higher than 90%.     

Pd/Mg/Pd thin films prepared by pulsed laser deposition under different helium pressures: Structure and electrochemical hydriding properties

Three-layered Pd/Mg/Pd thin films were prepared by pulsed laser deposition in the presence of helium gas. For Pd layer deposition, the He pressure was fixed at 200 mTorr whereas different pressures of He were used for Mg layer deposition (50, 200 and 600 mTorr). The degree of crystallinity and of (001) texture in the Mg layer increase with increasing He pressure. In addition, the increase in He pressure upon Mg deposition greatly accentuates the roughness of the Mg layer, which induces an extension of the outer Pd/Mg interface region. In contrast, the inner Pd/Mg interface is sharp for all the Pd/Mg/Pd films. The electrochemical hydrogen sorption properties of the Pd/Mg/Pd films are improved by increasing the He pressure for Mg layer deposition. However, the maximum H-solubility in the Mg layer remains low (H/Mg ∼0.26) and is not significantly increased by the presence of the inner Pd layer, indicating that Mg hydride phase is confined in the outer Pd/Mg interface region.     

Highly transparent and conductive Zn0.85Mg0.15O:Al thin films prepared by pulsed laser deposition

Zn_1−xMg_xO:Al thin films have been prepared on glass substrates by pulsed laser deposition (PLD). The effect of substrate temperature has been investigated from room temperature to 500 °C by analyzing the structural, optical and electrical properties. The best sample deposited at 250 °C shows the lowest room-temperature resistivity of 5.16×10⁻⁴ Ω cm, and optical transmittance higher than 80% in the visible region. It is observed that the optical band gap decreases from 3.92 to 3.68 eV when the substrate temperature increases from 100 to 500 °C. The probable mechanism is discussed.     

Preparation and electrochemical properties of Li4Ti5O12 thin film electrodes by pulsed laser deposition

Spinel Li₄Ti₅O₁₂ thin film anode material for lithium-ion batteries is prepared by pulsed laser deposition. Thin film anodes are deposited at ambient temperature, then annealed at three different temperatures under an argon gas flow and the influence of annealing temperatures on their electrochemical performances is studied. The microstructure and morphology of the films are characterized by XRD, SEM and AFM. Electrochemical properties of the films are evaluated by using galvanostatic discharge/charge tests, cyclic voltammetry and a.c. impedance spectroscopy. The results reveal that all annealed films crystallize and exhibit good cycle performance. The optimum annealing temperature is about 700 °C. The steady-state discharge capacity of the films is about 157 mAh g⁻¹ at a medium discharge/charge current density of 10 μA cm⁻². At a considerably higher discharge/charge current density of 60 μA cm⁻² (about 3.45 C) the discharge capacity of the films remains steady at a relative high value (146 mAh g⁻¹). The cycleability of the films is excellent. This implies that such films are suitable for electrodes to be used at high discharge/charge current density.     

Porous TiO2 thin films synthesized by a spray pyrolysis deposition (SPD) technique and their application to dye-sensitized solar cells

Titanium dioxide (TiO₂) thin films were synthesized on glass substrates from titanium(IV)oxy acetylacetonate 2-butanol solution by a spray pyrolysis deposition (SPD) technique. The films consisted of TiO₂ leaflets and showed the oriented growth along the (2 0 0) direction. The surface area of the film was successfully increased by adding a small amount of aluminum(III) acetylacetonate (AA) in the source solution. This is because AA sublimates easily during the film formation to leave many pores within the film. A dye-sensitized solar cell was constructed with the TiO₂ film which was deposited on the fluorine-doped tin(IV) oxide layer by the SPD technique. The conversion efficiency of the cell was effectively enhanced as high as 3.2% at AA content of 0.6 at% in the source solution, attributing to the fact that the amount of a dye anchored on the surface of TiO₂ layer was the highest at this AA content. Although the conversion efficiency is relatively low, this finding leads to the possibility of an industrial production of a dye-sensitized solar cell in the near future.     

The structural ordering of thin silicon films at the amorphous to nano-crystalline phase transition by GISAXS and Raman spectroscopy

Thin silicon films were deposited by the plasma-enhanced chemical vapour deposition method using microwave (MW) and standard radio frequency (RF) gas discharge in silane gas diluted by hydrogen in the range that produces a mixture of amorphous and crystalline phases. The samples were analysed by Raman spectroscopy and grazing incidence small-angle X-ray scattering (GISAXS), while the threshold for the transition between the amorphous and crystalline phase was checked by the change in electrical conductivity. The crystalline fraction, estimated by Raman spectroscopy, varied between 0% and 70% while the individual crystal sizes were between 3 and 9 nm. However, the size distribution was broad suggesting also the existence of smaller and larger crystals.The “particles” observed by GISAXS, most probably voids, were in the range between 2 and 12 nm. The voids in samples deposited by MW plasma were larger when closer to the surface. Their shape indicated the formation of a columnar structure perpendicular to the surface, more pronounced at higher temperature. The samples deposited by RF plasma and low power had spherically symmetric “particles” with uniform size across the depth of the samples. An increase of the RF power resulted in the formation of a columnar structure parallel to the surface. The observed differences are discussed in relation to the difference in growing kinetics of the used deposition methods.