Structure and morphology of pulsed laser depos ited boron carbide films: Influence of deposition geometry

Abstract

Pulsed laser deposition (PLD) of a sintered boron carbide (B4C) target has been used for depositing crystalline thin films on room-temperature substrates of (100) oriented silicon surfaces. Deposition was accomplished by positioning the substrates parallel (on-axis geometry) to a rotating target or perpendicular (off-axis configuration) and tilted relative to the target. The morphology and structure of the B4C films were revealed by scanning electron microscopy and atomic force microscopy, while the crystalline structure and composition were elucidated by x-ray diffraction and Raman spectroscopy. The deposited film structures were found to be geometry dependent, consisting of crystalline B4C particles in an on-axis configuration and tilted nanocolumns (14°–59°), with respect to the surface normal in off-axis and tilted configurations. The tilt angles could be manipulated by changing the substrate to target angle (20°–90°) and consequently the vapor incident angle. The experimental column tilt angle could be described by the general relationship derived by Lichter and Chen [Phys. Rev. Lett. 56, 1396 (1986)]. The ability of PLD to produce crystalline dense films or columnar films of boron carbide with a desired tilt angle might provide a unique advantage in design of three dimensional structures.