An ArF excimer laser deposition technique is used to fabricate hydroxyapatite [Ca10(PO4)6(OH)2]-(HAp) thin films on surface-modified polytetrafluoroethylene (PTFE) substrates. The surface of PTFE is modified by a sodium-naphthalene complex in a glycol ether solvent. X-ray diffraction (XRD) studies indicate that as-deposited films prepared at substrate temperatures below the glass transition temperature of PTFE (327°C) are in an amorphous state. The crystallization of as-deposited films needed annealing for 10 h at 310°C.
The structure, surface morphology and bond strength of HAp films were evaluated using XRD, the atomic force microscopy (AFM) and the Instron testing machine. The tensile bond strength of HAp films on surface-modified PTFE was 6.0 MPa, which is one order of magnitude larger than that of films on non-surface-modified PTFE, demonstrating its potential for practical applications.
We developed a low-temperature growth technique for polycrystalline silicon (poly-Si). When Si is deposited on glass substrates at 450 °C, it crystallizes as thickness increases, but 10-nm-thick layers of Si are mainly amorphous. Use of a ZnS buffer layer with 〈111〉 preferred orientation facilities crystallization of Si during the initial growth stages. The preferred orientation of poly-Si on glass substrates is 〈110〉, while that of poly-Si on the ZnS buffer layer is 〈111〉. This is probably due to local epitaxial growth on polycrystalline ZnS grains with 〈111〉 preferred orientation. Raman spectroscopy showed that the ZnS buffer layer significantly improved the crystallinity of 25-nm-thick Si layers.
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