Paper PS+AS+NS+SS-ThM3
Single Step Plasma Synthesis of Core-shell Group IV Nanoparticles

Thursday, October 31, 2013, 8:40 am, Room 102 B

There has been an increased interest in group IV nanoparticles (NPs) for a variety of applications including photovoltaics, lithium ion batteries, and bio-imaging. The properties of these quantum-confined NPs are governed by their size as well as the surface passivating layer. Si NPs, 3-7 nm in size, were synthesized in a tubular, capacitively-coupled, radio-frequency SiH₄/Ar plasma at pressures ranging from 5-8 Torr. The H-terminated surface of the as-synthesized Si NPs is highly reactive, and requires surface passivation to prevent oxidation. We have developed a single-step synthesis and in-flight surface passivation technique wherein we use a dual-plasma setup, which consists of a second capacitively-coupled C₂H₂ plasma, downstream from the SiH₄/Ar synthesis plasma. The Si NPs can be coated with amorphous carbon (a-C) to obtain core-shell nanostructures, with a thin SiC interface between Si and a-C. These core-shell NPs are transported by flow into a surface analysis chamber, which is equipped with in situ attenuated total reflection Fourier transform infrared and photoluminescence spectroscopy setups to determine the surface composition and the optical band gap of the NPs, respectively. The NPs are also extensively characterized using ex situ x-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM). The thickness of the coating, determined from TEM, is ~2-4 nm. We have also studied the effect of varying the C₂H₂ plasma parameters on the structure and composition of the a-C coating and the SiC interface. This plasma synthesis and passivation technique has been extended to other group IV NPs such as Ge and Sn, which are less likely to have a carbide interface.