Synthesis of Polymer-like Hydrogenated Amorphous Carbon by fs-pulsed Laser Induced Plasma Processing of Solid Hexane

Abstract

A new technique, that involves the plasma processing of frozen hydrocarbons by a pulsed laser generated graphitic plasma, is presented. Polymer-like hydrogenated amorphous carbon (a-C:H) thin films were created by allowing the plasma generated during the fs-pulsed laser ablation of a highly oriented pyrolytic graphite target in high vacuum, to impact on solid layers of n-hexane (CH3(CH2)4CH3) at 77 K. This technique results in the formation of thin films whose morphology and properties are shown to depend on the plasma processing time tp. Polymer-like a-C:H with residual hexane incorporated into the carbon matrix and exhibiting a unique dendritic surface morphology was formed after short processing times. Following longer processing times, these dendritic structures are destroyed resulting in thin films having similar spectral properties to those of conventional a-C:H. The composition of the plasma was studied using time of flight mass spectrometer (TOF-MS) and the surface morphology of the synthesized thin films was examined by atomic force microscopy (AFM). A variety of analytic techniques including photoluminescence (PS), UV–Vis absorption, surface enhanced Raman (SERS), and Fourier transform infrared (FTIR) spectroscopy have been used to characterize the structure and composition of these materials.