Growth of Amorphous SiO 2 Nanowires on Si using a Pd/Au Thin Film as a Catalyst Jose Luis Elechiguerra * , Alejandra Camacho-Bragado ** , Jorge Manriquez *** , J.P Zhou ** and Miguel Jose-Yacaman *,** * Department of Chemical Engineering, The University of Texas at Austin, 1 University Station C0400, Austin, Texas 78712, USA ** Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA *** Centro de Sistemas Integrados de Manufactura, Tecnológico de Monterrey, Monterrey, N.L. 64849, México Exciting discoveries of essentially new structures at the nanometric level [1, 2] and the potential of novel applications [3, 4] are the driving force for numerous studies reporting on distinct methods to produce arrays of them. The finding of significant luminescent behavior in porous silicon and later in nanocrystals of silicon[5], for instance, opened the possibility for developing Si-based nanostructures for optoelectronic devices such as displays, lasers, and sensors[6]. Numerous studies on the synthesis and characterization of silicon[7,8] and silica nanowires[6, 9] with photoluminiscent (PL) properties have been reported. However, there is still an on-going effort in developing new nanostructures as well as in understanding the various mechanisms responsible for their growth process. This paper reports on the synthesis and characterization of amorphous SiO 2 nanowires thermally grown by the VLS mechanism. The experimental setup used for this study is very simple. It is composed of a controlled temperature tube-furnace and a quartz tube. Commercial (100) Si- wafers are placed in the quartz tube and are used as substrates for the growth of nanowires. A 1:1 Pd/Au film approximately 15 nm thick is deposited onto the Si substrates using a simple sputtering chamber. The substrate was placed at the center of a quartz tube which was then slowly heated up to 1100 °C. Once thermally stabilized, a continuous nitrogen flow of 50 sccm was allowed to run through the tube for 40 minutes at that temperature. The tube was then cooled down to room temperature in about 3 hours. The nanowires grown on the surface of the substrates were characterized with a LEO-1530 Field Emission Scanning Electron Microscope (FESEM) equipped with an Energy Dispersive Spectrometer (EDS) unit, a JEOL 2010-F Transmission Electron Microscope (TEM) equipped with an EDS unit, and a Scintag theta-theta-theta X-Ray Diffractometer (XRD). The nanowires grown in this study were found to be primarily composed of amorphous silica (Figure 1). The observations that Pd 2 Si and Au-rich particles remained at the tip of the nanowires (Figure 2), suggest that the growth process was controlled by the VLS mechanism.The observation of small crystalline silicon areas at the center of the body ( Figure 3) and near the gold- rich tip of non-stoichiometric SiOx nanowires suggests that initially thin silicon nanowires start to grow from the substrate and rapidly oxidize from the outside until all the body is fully oxidized into SiO 2 . Since no vacuum was made before running the inert gas through the processing tube, some amount of oxygen must remain during the process which is the likely source for the oxidation of the wires. The observation of nanowires composed of a crystalline Si core and a shell of SiOx, processed at an argon pressure of 500 torr, has been previously reported[7]. It is interesting to note that in the experiments carried in this study, the only silicon vapor source available was the substrate itself. Similar self-provided processes for growing amorphous silica nanowires have been previously reported[9]. A significant characteristic of the amorphous nanowires reported here is that they can be grown up to several microns without tangling much with adjacent wires. Microsc Microanal 10(Suppl 2), 2004 Copyright 2004 Microscopy Society of America DOI: 10.1017/S1431927604886185 388