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

Pulsed laser deposition (PLD) of a sintered boron carbide (B4 C) 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 B4 C 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 B4 C 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.