Electrodeposition is a widely used materials-deposition technology with a number of unique features, in particular, the efficient use of starting materials, conformal, and directed coating. The properties of the solvent medium for electrodeposition are critical to the technique's applicability. Supercritical fluids are unique solvents which give a wide range of advantages for chemistry in general, and materials processing in particular. However, a widely applicable approach to electrodeposition from supercritical fluids has not yet been developed. We present here a method that allows electrodeposition of a range of metals from supercritical carbon dioxide, using acetonitrile as a co-solvent and supercritical difluoromethane. This method is based on a careful selection of reagent and supporting electrolyte. There are no obvious barriers preventing this method being applied to deposit a range of materials from many different supercritical fluids. We present the deposition of 3-nm diameter nanowires in mesoporous silica templates using this methodology.electrochemistry ͉ nanomaterials
The electrochemistry of [Cu(hfac)(2)], where hfac is hexafluoroacetylacetonate, and [Cu(MeCN)(4)](+) were investigated in liquid acetonitrile (MeCN), supercritical CO(2)/MeCN and supercritical trifluoromethane (CHF(3)) at 310-311 K and 17-20 MPa using either [NBu(n)(4)][BF(4)] or [NBu(n)(4)][B{3,5-(CF(3))(2)C(6)H(3)}(4)] as the supporting electrolyte. In liquid acetonitrile it is possible to deposit metallic Cu from both ([Cu(MeCN)(4)][BF(4)]) and [Cu(hfac)(2)] but voltammetry for the [Cu(hfac)(2)] system is more complex and there is evidence of stripping of the Cu by reaction with Cu(ii). Voltammetry of the two copper complexes in scCO(2)/MeCN showed typical plating and stripping features but with slightly increased diffusion limited currents for copper reduction due to the decreased viscosity of the supercritical solvent. In scCO(2)/MeCN the Cu(i) complex, tetrakis(acetonitrile)copper(i) tetrafluoroborate ([Cu(MeCN)(4)][BF(4)]), was found to produce better quality copper deposits than the Cu(ii) complex ([Cu(hfac)(2)]). The Cu(i) complex has the advantages that it is stable and does not undergo comproportionation with copper(0) and that its ligands are totally compatible with the scCO(2)/MeCN solvent system. The solubility of ([Cu(MeCN)(4)][BF(4)]) is limited in scCO(2)/MeCN but can be significantly improved by changing the anion for tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([B{3,5-(CF(3))(2)C(6)H(3)}(4)](-)). It was possible to deposit smooth copper films of high purity and low resistivity (down to 4.0 × 10(-6)Omega cm) from the Cu(i) complex. Copper was also deposited from supercritical CHF(3) using [Cu(hfac)(2)] as a precursor. Although the plating and stripping features in the voltammetry are complicated by the lack of cosolvent and electroreduction of the solvent or free ligands, it was possible to produce copper films with resistivities as low as 5.8 × 10(-6)Omega cm.
We studied the structural and electrical properties of TiO 2 thin films grown by thermal oxidation of e-beam evaporated Ti layers on Si substrates. Time of flight secondary ion mass spectroscopy (TOF-SIMS) was used to analyse the interfacial and chemical composition of the TiO 2 thin films. Metal oxide semiconductor (MOS) capacitors with Pt or Al as the top electrode were fabricated to analyse electrical properties of the TiO 2 thin films. We show that the reactivity of the Al top contact affects electrical properties of the oxide layers. The current transport mechanism in the TiO 2 thin films is shown to be Poole-Frenkel (P-F) emission at room temperature. At 84 K, FowlerNordheim (F-N) tunnelling and trap-assisted tunnelling are observed. By comparing the electrical characteristics of thermally grown TiO 2 thin films with the properties of those grown by other techniques reported in the literature, we suggest that, irrespective of the deposition technique, annealing of as-deposited TiO 2 in O 2 is a similar process to thermal oxidation of Ti thin films.
Optical absorption spectra of nanoclusters of lead iodide, synthesized by the colloidal technique, have been investigated. It is shown that the absorption peaks are due to different orders of interband transitions of a nominally single size of particles rather than the first-order transitions of a number of discrete sizes of particles, as reported earlier. The model used to explain the spectra of lead iodide has also been used to account for the optical absorption peaks of colloidal mercuric iodide and bismuth tri-iodide. ͓S0163-1829͑98͒01443-X͔
In this study, we report on the electrical characteristics of all-vacuum-processed pentacene thin film transistors, with stable and reproducible performance, using high throughput roll-toroll processing. The method allows a polymerised tripropyleneglycol diacrylate (TPGDA) insulator layer of thickness up to 1µm to be obtained in a single pass by ultrahigh flash evaporation of monomer onto a web travelling at 10 m min -1 and subsequent irradiation with an argon plasma emitted from a dc sputter cathode. From plots of I D 1/2 vs V G we deduce that the resulting OTFTs exhibited a field effect mobility of 0.12 cm 2 V -1 s -1 , a threshold voltage of -21 V, a turn-on voltage of -2V, and an on/off current ratio of 1x10 5 . In an initial attempt to understand degradation effects and thus optimise device performance, we investigated the effect of ambient air on the I-V characteristics of our OTFTs by cycling the device-testing environment from ambient-air to vacuum and back to ambient-air. The moisture absorbed by the device during such cycling has a reversible effect on the performance of the OTFTs showing a shift in the turn-on voltage and deterioration in the on-off ratio. However, the effect was eliminated using a simple conventional encapsulation method. Our vacuum-based process thus demonstrates excellent potential for providing an alternative route to low-cost, large area organic electronics manufacturing.
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