The interaction of cells and bacteria with surfaces structured at the nanometre scale.

Inorganic graphene analogues (IGAs) are a conceptually new class of materials with attractive applications in next-generation flexible and transparent nanodevices. However, their species are only limited to layered compounds, and the difficulty in extension to non-layered compounds hampers their widespread applicability. Here we report the fabrication of large-area freestanding single layers of non-layered ZnSe with four-atomic thickness, using a strategy involving a lamellar hybrid intermediate. Their surface distortion, revealed by means of synchrotron radiation X-ray absorption fine structure spectroscopy, is shown to give rise to a unique electronic structure and an excellent structural stability, thus determining an enhanced solar water splitting efficiency and photostability. The ZnSe single layers exhibit a photocurrent density of 2.14 mA cm(-2) at 0.72 V versus Ag/AgCl under 300 W Xe lamp irradiation, 195 times higher than that of bulk counterpart. This work opens the door for extending atomically thick IGAs to non-layered compounds and holds promise for a wealth of innovative applications.

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Fabrication of flexible and freestanding zinc chalcogenide single layers

Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made nanowires are over 30 µm long and 10–20 nm in diameter. The nanowires have a layered structure with a d-spacing of 1.07 nm. The nanowires can be fabricated into free-standing and flexible sheets by suction filtration. The electrical conductivity of the SVO nanowires is 0.5 S/cm, compared to 0.08 S/cm for the V2O5 nanowires. The Li ion diffusion coefficient in the SVO nanowires was 7 times higher than that in the V2O5 nanowires. An electrochromic device was fabricated from the SVO nanowires that displayed a color-switching time of 0.2 s from the bleached state (green) to the colored state (red-brown) and 60% transmittance contrast.

Fabrication of silver vanadium oxide and V2O5 nanowires for electrochromics.

The impact-induced deposition of Al13 clusters with icosahedral structure on Ni(0 0 1) surface was studied by molecular dynamics (MD) simulation using Finnis–Sinclair potentials. The incident kinetic energy (Ein) ranged from 0.01 to 30 eV per atom. The structural and dynamical properties of Al clusters on Ni surfaces were found to be strongly dependent on the impact energy. At much lower energy, the Al cluster deposited on the surface as a bulk molecule. However, the original icosahedral structure was transformed to the fcc-like one due to the interaction and the structure mismatch between the Al cluster and Ni surface. With increasing the impinging energy, the cluster was deformed severely when it contacted the substrate, and then broken up due to dense collision cascade. The cluster atoms spread on the surface at last. When the impact energy was higher than 11 eV, the defects, such as Al substitutions and Ni ejections, were observed. The simulation indicated that there exists an optimum energy range, which is suitable for Al epitaxial growth in layer by layer. In addition, at higher impinging energy, the atomic exchange between Al and Ni atoms will be favourable to surface alloying.

Nuclear instruments and methods in physics research section B : beam interactions with materials and atoms

Synthesis of antimicrobial monophase silver-doped hydroxyapatite nanopowders for bone tissue engineering

Bacterial adhesion studies on titanium, titanium nitride and modified hydroxyapatite thin films

ZnSe thin films were prepared by the vacuum evaporation technique. The influence of substrate temperature on compositional, structural, optical and electrical properties of polycrystalline ZnSe films was investigated using Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), Scanning electron microscopy (SEM), optical transmission and DC conduction studies. The composition analysis shows the nearly stoichiometric nature of the deposited film. The X-ray diffractograms reveals the cubic structure of the film oriented along the (1 1 1) direction. The structural parameters such as particle size [28.41–50.24 nm], strain [1.381–0.785×10−3 lin−2 m−4] and dislocation density [1.285–0.412×1015 lin m−2] were evaluated. Optical transmittance measurements indicate the existence of direct allowed optical transition with a corresponding energy gap in the range of 2.72–2.60 eV. In the DC conduction studies the conduction mechanism is found to be exponential trap distribution and the results are discussed.

Structure, optical and electrical properties of ZnSe thin films

Characterization of vacuum-evaporated ZnSe thin films

ZnSe thin films were deposited onto glass substrates under a vacuum of 3×10 −5  Torr by using vacuum evaporation technique. Rutherford backscattering spectrometry technique is used to measure the composition and thickness of the deposited films. The composition of the deposited films is found to be nearly stoichiometric. The X-ray diffractogram reveals a preferential orientation along (1 1 1) direction, and the structural parameters such as crystallite size, dislocation density, strain and lattice parameters are calculated, and also the effect of film thickness and substrate temperature of the deposited films was also discussed. It is observed that the crystallite size increases from 20.11 to 55.56 nm with the increase in film thickness. The X-ray diffraction (XRD) studies show that the structure of the deposited films is cubic. The crystalline nature of the deposited films is also confirmed by Raman scattering measurements. In the optical studies, optical band-gap values decrease with the increase in film thickness and substrate temperatures. In the DC conduction studies, the conduction mechanism is found to be exponential trap distribution and the results are discussed.

We report the structural, Raman and optical properties of Cd0.6Zn0.4Te polycrystalline thin films deposited onto well cleaned corning glass substrates by vacuum evaporation. X-ray diffraction pattern showed that the incorporation of zinc favours the growth of films preferentially oriented parallel to the (1 1 1) planes of cubic CdTe. The optical response of vacuum evaporated Cd0.6Zn0.4Te films in the 1.5–5.5 eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The measured dielectric-function spectra reveal distinct structures at energies of the E1 (3.53 eV), E1+Δ1 (3.9 eV) and E2 (5 eV) critical points corresponding to the interband transitions. In order to check the film local atomic order, the samples were studied by Raman spectroscopy. The transverse and longitudinal optic modes regularly found in CdTe and ZnTe were also observed in Cd0.6Zn0.4Te thin films. From the optical transmittance and absorption coefficient, the band gaps of the films are found to be direct allowed.

S. Venkatachalam

Papers

Bacterial adhesion studies on titanium, titanium nitride and modified hydroxyapatite thin films

Structure, optical and electrical properties of ZnSe thin films

Characterization of vacuum-evaporated ZnSe thin films

Characterization of vacuum-evaporated ZnSe thin films

Microstructure, Raman and optical studies on Cd0.6Zn0.4Te thin films