Hydroxyapatite layers deposited from aqueous solutions on hydrophilic silicon substrate

Devices of micro-electro-mechanical systems or biochips for diagnosis to be implanted into human body require a biocompatible and protective coating to avoid inflammatory effects. We have developed a method to deposit a bioactive hydroxyapatite (HA) layer onto pretreated hydrophilic Si(1 1 1) from supersaturated solutions containing Ca2+ and PO43− ions with an initial pH value of 7.40±0.05 at 298 K. The deposition starts with an initial uniform deposit at a low rate approximately 25 nm/h. Growth then takes place predominantly along the direction normal to the substrate through in-plane nucleation of multiple embryos at a high rate approximately 325 nm/h. The deposition rate increases with increasing time duration, attaining a maximum at a thickness approximately 8 μm, and then decreases. X-ray photoelectron spectroscopy (XPS) indicates typical chemical states of HA phase. X-ray diffraction pattern of a 4-day deposit shows the direct formation of crystalline HA corroborating with the XPS results. XPS results indicate the possible incorporation of carbonate.