Pulsed laser deposition of glass-like cluster assembled carbon films

Carbon films have been synthesized at room temperature in helium atmosphere, at high pressure, on (1 0 0) Si substrates by pulsed KrF excimer laser ablation of highly oriented pyrolitic graphite. By changing laser power density (from 8.5 to 19 MW mm−2) and gas pressure (from 0.6 Pa to 2 kPa), nanometer sized clusterassembledfilms were obtained. Film morphology, as studied by scanning electron microscopy, changes with increasing helium pressure, from dense columns, to node-like morphology, then to an open dendritic structure. Carbon coordination was studied by visible Raman spectroscopy in all films. They are structurally disordered, sp2 coordinated and belong to the family of glass-likecarbons. The deduced film coherence length agrees with the average size of carbon aggregates that build up the films, as measured by transmission electron microscopy in representative samples. The average number of carbon atoms per cluster, that depends on helium (high) pressure, was obtained by a simple model

Properties of nanocomposite film combining hard TiN matrix with embedded fullerene-like WS2 nanoclusters

We have developed hard self-lubricant coatings combining a hard matrix (TiN) and a self-lubricant phase in the form of inorganic-like WS2 fullerene. The nanoparticles were injected from the preparation chamber directly to the sample surface during reactive sputtering from a Ti target in Ar/N2 atmosphere. The injection of the particles led to the local oxidation of the matrix due to the flow of residual oxygen from the preparation chamber; therefore, the final composite was TiN/Ti–O–WS2. The observation of the composite film by scanning and transmission electron microscopies showed the incorporation of the WS2 nanoparticles; however, their bonding with the matrix was weak. The analysis of the wear tracks did not show any presence of WS2 in the contact

Realization of Vertical and Zigzag Single Crystalline Silicon Nanowire Architectures

Silicon nanowire (SiNW) ensembles, with vertical and zigzag architectures have been realized using wet chemical etching of bulk silicon wafers (p-Si(l 11) and p-Si(100)) with it mask of silver nanoparticles that are deposited by wet electroless deposition. The etching of SiNWs is based oil Subsequent treatments in chemical Solutions Such is 0.02 M aqueous Solutions of silver nitrate (AgNO(3)) followed by 5 M hydrofluoric acid and 30% hydrogen peroxide (H(2)O(2)). The etching of the Si wafers is mediated by the reduction of silver oil the Silicon Surface and in parallel by the oxidation of Si thereby forming SiO(2) which is dissolved ill the HF Surroundings. The morphology of the starting silver (Ag) layer/Ag nanoparticles that form during processing oil the Si wafer surfaces strongly influences the morphology of the SiNW ensembles and homogeneity of the etch profile. Our observations Suggest that the Ag layer/Ag nanoparticles not only catalyze the wet chemical etching of silicon but also strongly catalyze the decomposition of H(2)O(2) so that the temperature of the etching Solution substantially increases (strong exothermic reaction) and thus the etching velocity of bulk material. The morphology and microstructure of single crystalline SiNWs with respect to their crystallographic orientation was investigated by scanning (SEM) and transmission electron (TEM) microscopies and by electron backscatter diffraction (EBSD) in ill SEM. Straight SiNWs Lis well as zigzag SiNWs can be realized depending oil processing peculiarities. The optical characteristics such as absorption, transmission, and reflectance of the different silicon 1D architectures were investigated in an integrating sphere. Strong absorption and less reflection of visible and near-infrared light by the SiNW ensembles Suggest that Such material call he applied in the fields of opto-electronics, photonics and photovoltaics

Photoluminescence of samples produced by electroless wet chemical etching: Between silicon nanowires and porous structures

Samples containing silicon nanowires (Si-NWs) and highly porous structures (P-Si) were prepared by electroless wet chemical etching (EWCE) of crystalline silicon wafers using various etching parameters. Photoluminescence (PL) measurements were performed with excitation at 488 nm and a photon energy flux of 337mWcm (2). According to the diameters of the Si-NWs (> 10 nm), from quantum confinement (QC) theory no shift in PL peak energy compared to the bandgap of crystalline silicon is expected. However, PL measurements show peak emission energies ranging between 1.4 and 1.6 eV. After further treatment of the samples with HF, substantial PL emission was still detectable with the measured PL peak pinned at 1.4 eV irrespective of etching time. We explain the observations by the hypothesis that the persistent part of PL emission is generated by nanocrystals located at the rough sidewalls of the Si-NWs or residing within the porous sample structure. The part of the PL, which was present before HF treatment, but vanished after the treatment, is attributed to the presence of silicon suboxide surrounding the Si-NWs or covering other Si surfaces. This hypothesis is explored by means of three sample series, prepared with different preparation parameters. In the first series the time used during the initial metallization step in order to prepare an Ag nanoparticle layer on the top surface was varied, in the second series the etching time was the changed parameter and in the third series the HF to H(2)O(2) concentration ratio was varied. [GRAPHICS] Strong visible orange colored PL of a sample produced by EWCE starting from a heavily doped wafer (n-type c-Si (111), As as dopant) and excited at 337 nm ( the sample was mounted on a glass substrate. Blue luminescence is due to the substrate). (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Knowledge selection for planning in complex domains

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