Synthesis of PbTe Nanoboxes Using a Solvothermal Technique

Abstract

tions and confined by {010} facets. It has been observed that the WO 3±d nanowires are always accompanied by ordered planar defects distributed in the planes parallel to the growth direction. Combining experimental and simulated HRTEM images, we find that the planar defects are due to the accumulation of oxygen vacancies in {010} planes. The presence of ordered in-plane oxygen vacancies in the {100} planes are suggested as the driving mechanism for the formation of 3D networks. The presence of planar oxygen vacancies in (100) and (010) planes, for example, results in the growth of a nanowire along the [001] direction. 3D interpenetrative growth along the six equivalent directions of á100ñ produces the 3D network. The field-emission properties of the nanonetworks have been measured and these networks may be useful as 3D field emitters. The newly grown 3D nanowire networks could be the foundation for investigating novel applications of tungsten oxide in electrochromics, optochromics, gaschromics, and field emission. ExperimentalThe tungsten oxide nanowire networks were synthesized by thermal evaporation of W powders (1 g), which were sprinkled on a W boat (120 mm 20 mm 0.3 mm) placed in a vacuum chamber, where the temperature, pressure, and evaporation time were controlled. The vacuum chamber was first evacuated down to about~5 Pa. Then, high-purity argon gas (99.99 %) was introduced into the chamber. The tungsten boat was heated to~1400±1450 C at a heating rate of 45 C min ±1 and held at that temperature for 10 min, which is very important for the formation of a network structure. The chamber pressure was kept at 70 Pa (1 Pa = 1 N m ±2 ) with Ar flux at 200 standard cubic centimeters per minute (sccm). During evaporation, the tungsten oxide nanowire networks were grown on the substrates mounted above the boat, where the deposition temperature is~950±1005 C.The as-synthesized products were characterized by high-resolution field-emission scanning electron microscopy (FESEM: LEO 1530 FEG at 10 kV) and transmission electron microscopy (TEM: JEOL 4000EX). The field-emission studies were carried out in a chamber having a vacuum of~1.0 10 ±7 torr at room temperature. The sample area is about 4.07 mm 2 , and it was first adhered to the surface of an oxygen-free high-conductivity copper disc using silver paint. A manipulator (Huntington PM-600-T) was used to control the separation (d) between the anode and the cathode. A vacuum gap (0.20 mm) was used when measuring the field-emission properties of the tungsten oxide nanowire networks. A charge-coupled device (CCD) was used to record the spatial distribution of the emission sites. Recently, research has shown that lead chalcogenides with narrow bandgaps and face-centered-cubic structure are very promising materials for TE applications.[1±4] It has been re-COMMUNICATIONS

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