Growth of GeO2 Nanowires by Thermal Annealing
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0940-P13-04
Growth of GeO2 Nanowires by Thermal Annealing C.-I Wu, and T. P. Hogan Department of Electrical and Computer Engineering, Michigan State University, 2120 Engineering Building, East Lansing, MI, 48824
ABSTRACT Germanium dioxide nanowires have gained considerable interest lately [1,2], partly, due to the 2.44 eV bandgap, and high index of refraction, n = 1.63 [3], of the bulk material. In this paper we report a simple fabrication technique for making large quantities of GeO2 wires with diameters ranging from 40 nm to >500 nm on different substrates. The nanowires were grown on silicon, tungsten, quartz, and nickel substrates at locations where a 10 nm of Au was deposited. The nanowires showed strong preferential growth at gold catalyst locations on the silicon substrate. Presented here are the growth conditions, and images of the resulting wires that were fabricated. The products are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as X-Ray diffraction (XRD). The observations show the products on Si substrates are crystalline GeO2 nanowires. INTRODUCTION Binary semiconducting oxides are attracting significant attention as candidates for sensing elements because the electrical conductivity of these materials depends sensitively on the nature and concentration of the adsorbed species on their surfaces. Intensive investigation of binary semiconducting nanostructures has helped to further understand the dimensionally confined transport phenomena in functional oxides and to build functional devices based on individual nanowires. Much of the work on germanium dioxide has focused on optical applications due to the high index of refraction, and low optical loss of this material. More recently, GeO2 nanowires have been prepared by physical evaporation [4], thermal treatment [5], carbon nanotube confined reaction of Ge [6], laser ablation [7], heating in an oxygen environment [8], thermal oxidation [9], and carbothermal reduction reaction [10]. The work presented here uses a straightforward method to synthesis GeO2 nanowires through a simple thermal annealing of a piece of germanium in reduced atmospheres on different substrates. EXPERIMENT The various substrates were coated with 10 nm of gold, and placed on a quartz boat near a piece of germanium. The silicon substrates were cleaned with acetone and methanol; however the native oxides were not removed before depositing the gold film. The boat was then placed in the center of a quartz tube (outer diameter = 90 mm) that was heated by a horizontal tube furnace and evacuated to 30 mTorr. An argon flow of 200 sccm passed through the quartz tube and was maintained throughout the reaction time. The argon flow increased the pressure inside the tube from 30 mTorr to 150 mTorr. The system was heated to 850 °C and maintained for 40 minutes
with the rotary pump turned off. During this time, the system pressure increased from 150 mTorr to 10 Torr while the argon gas continued to flow. An air valve was then opened to allow
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