A novel approach to thermal Analysis of Thin films

A novel instrument is described called the Thin film Analyser (TFA) which quantitatively measures changes in mechanical and rheological properties of drying films in-situ on a test panel. It is based around a simple force-sensing device, capable of carrying various probes, which can be positioned in anX-Y plane over the panel. Temperature control is achieved by means of a heating block under the sample. By imposing a thermal gradient along the block, measurements can be obtained at a series of temperatures in a single experiment. Several applications of the TFA to the drying of curable and latex-based coatings are discussed, as well as some more specialized uses. The TFA concept represents a novel approach to the thermal analysis of thin films.The authors gratefully acknowledge the design, engineering and software development work of the Instrument Group at ICI Paints, in particular John Hayton, Neil Burrows, Tony Evans and Ian Francis, who have now built three versions of the TFA.     

Morphological and chemical study of the initial growth of CdS thin films deposited using an ammonia-free chemical process

We study the initial growth stages of CdS thin films deposited by an ammonia-free chemical bath deposition process. This ammonia-free process is more environmentally benign because it reduces potential ammonia release to the environment due to its high volatility. Instead of ammonia, sodium citrate was used as the complexing agent. We used atomic force microscopy (AFM), Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS) to investigate the morphological and chemical modifications at the substrate surface during the first initial stages of the CdS deposition process. Additionally, X-ray diffraction (XRD) and optical transmission spectroscopy measurements were carried out to compliment the study. XPS results show that the first nucleation centers are composed by Cd(OH)₂ which agglomerate in patterns of bands, as demonstrated by AFM results. It is also observed that the conversion to CdS (by anionic exchange) of the first nucleus begins before the substrate surface is completely covered by a homogenous film.     

MEASUREMENTS OF Fe AND Cu K-Shell IONIZATION CROSS SECTIONS BY SLOW ELECTRON IMPACT

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Experimental investigation of the aquatic propulsion caused by localised flexural wave propagation in immersed wedges and plates

This paper describes the results of the experimental verification of the idea of wave-like aquatic propulsion of autonomous and man-inhabited vessels first published about 10 years ago by one of the present authors (V.V.K.). The idea is based on employing the unique type of localised flexural elastic waves propagating along edges of wedge-like structures immersed in water (wedge elastic waves). Such wedge-like structures supporting localised elastic waves can be attached like fish fins to a body of a small ship or a submarine and used for their propulsion. The proposed principle of employing localised flexural waves as a source of aquatic propulsion has been biologically inspired by the specific swimming mode used in nature by stingrays. To verify the idea experimentally, the first working prototype of a small catamaran using the above-mentioned wave-like propulsion via the attached rubber keel has been build and tested in Loughborough University. The tests have been carried out in two phases, in a water tank and then in open water. The test results have shown that the catamaran was propelled very efficiently and could achieve the speed of 36 cm/s, i.e., about one vehicle length per second, thus demonstrating that the idea of wave-like propulsion of small man-inhabited craft is viable. The reported proof of the viability of this idea may open new opportunities for marine craft propulsion, which can have far reaching implications.     

Growth of oxide thin films for optical gas sensor applications

Tungsten trioxide and titanium dioxide thin films were synthesised by pulsed laser deposition. We used for irradiations of oxide targets an UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser source, at 2 J/cm² incident fluence value. The experiments were performed in low oxygen pressure. The (0 0 1) SiO₂ substrates were heated during the thin film deposition process at temperature values within the 300-500 °C range. The structure and crystalline status of the obtained oxide thin films were investigated by high resolution transmission electron microscopy. Our analyses show that the films are composed by nanoparticles with average diameters from a few to a few tens of nm. Moreover, the films deposited at substrate temperatures higher than 300 °C are crystalline. The tungsten trioxide films consist of a mixture of triclinic and monoclinic phases, while the titanium dioxide films structure corresponds to the tetragonal anatase phase. The oxide films average transmittance in the visible-infrared spectral range is higher than 80%, which makes them suitable for sensor applications.     

Influence of temperature-pressure treatment on heavily hydrogenated silicon surface

Microstructure and related properties of hydrogenated silicon samples, Si:H, treated at high-temperature (HT) up to 1270 K under hydrostatic argon pressure (HP) up to 1.1 GPa are investigated. To prepare Si:H, Czochralski grown 0 0 1 oriented single crystalline Si wafer with 50 nm thick surface SiO₂ layer was heavily implanted with hydrogen using the immersion plasma source of hydrogen ions with energy 24 keV.The surface of HT-HP treated Si:H was characterised by scanning electron microscopy. Reflectivity pattern measurements in the wavelength range of 350-2000 nm have been performed to analyse their surface and bulk properties. The volume averaging method for a model of layer-like structure has been used to simulate the HT-HP treated Si:H. The analysis of Si:H samples suggests the multi-layer structure composed of Si, Si:H, SiO, SiO₂, and of porous Si layers in the sub-surface region. The porous Si:H samples model is in good consistency with experimental data from reflectance measurements.     

A procedure for measuring the flexibility of single wood-pulp fibres

A way of determining the flexibility of wood-pulp fibres is developed, which involves i) a precise measurement of the topology of single-fibres by using a confocal laser scanning microscope and ii) the measurement of the elastic modulus of the fibres by using a single-fibre fatigue cell. Reported in this paper are the initial results of tests carried out on black spruce fibres, which have been subjected to three different levels of mechanical refining energy, namely ∼1100, 2300, and 3500 kWh/t. It is found that the fibre flexibility rises significantly between the first and second energy levels, but it does not change to the same degree between the second and third ones. The described procedure of measuring the flexibility of fibres may be used to establish the appropriate refiner energy necessary for the production of a specific grade of paper. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 115–128, January–February, 2006.     

Structural and electrical characterization of SxSe100−x thin films

Thin films of samples of the glassy S_xSe_100−x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system S_xSe_100−x were discussed. The characteristic temperatures (T_g, T_c and T_m) were evaluated. Dark electrical resistivities, ρ, of S_xSe_100−x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations.     

Matrix assisted pulsed laser evaporation processing of triacetate-pullulan polysaccharide thin films for drug delivery systems

We report the first successful deposition of triacetate-pullulan polysaccharide thin films by matrix assisted pulsed laser evaporation. We used a KrF* excimer laser source (λ = 248 nm, τ ≈ 20 ns) operated at a repetition rate of 10 Hz. We demonstrated by FTIR that our thin films are composed of triacetate-pullulan maintaining its chemical structure and functionality. The dependence on incident laser fluence of the induced surface morphology is analysed.     

半线性方程组边界层解的存在性

本文利用隐函数定理讨论了含小参数的半线性椭圆方程组边界层解的存在性．