It is demonstrated that hydroxyapatite, a type of calcium phosphate commonly found in bone tissue, retains surprisingly large stored charge when synthesized electrochemically from aqueous solution. Thin films of hydroxyapatite formed on titanium and stainless steel electrodes were found to display giant polarization with quasi-permanent stored charge in excess of 70 000 microcoulombs per square centimeter. The polarization of the hydroxyapatite film develops during synthesis as a result of field-induced changes in concentration of ionic reactants in the electrical double layer near the electrode surface. This novel mechanism of polarization during synthesis provides much larger stored charge than what is possible by postsynthesis poling of ferroelectric or electret materials. The polarized hydroxyapatite films on titanium are shown through in vitro experiments to hold promise in stimulating bone growth and may enable new applications in ion exchange separations, drug delivery, or energy storage.

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Vanadium carbide films as wear-resistant coatings produced by salt bath immersion at high temperatures have found wide technological a plication in manufacturing industries. In order to reduce the substrate temperature, t 1 e deposition of VC-films by plasma-assisted chemical vapour deposition using a metal-organic compound as precursor was investigated.Bis(cyc1opentadien 1)-vanadium, a purple solid compound showing a sufficient sublimation rate at re r atively low evaporator temperatures, was used together with hydrogen and argon to deposite VC-films in a d.c. glow discharge. As one of the most important parameters the substrate temperature was varied from 200 "C to 400 "C. The compound decomposed into films and gaseous b products like C5H6 and other hydrocarbons wh~ch could be detected by quagkpole mass spectrometer. The deposition efficiency of the coatings was almost inde endent of the substrate temperature. It was established by means of EDX and XRD t R at cubic vanadium carbide coabngs were obtained. The morphology of these la ers was examined b scanning electron microscopy. In the entire temperature range ~7 ense, pol crystalline ? ayers were created, whose hardness measured between 2200-3300 HV. d t h the increase of the substrate temperature the adhesive strength of the coatings increased, too.