Synthesis of well-crystalline GaS nanobelts and their unique field emission behavior

Well-crystalline ultrathin GaS nanobelts have been successfully synthesized on silicon substrates by a simple thermal evaporation process. The GaS nanobelts were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), and energy dispersive X-ray analysis (EDAX). The XRD pattern indicates formation of well-crystalline hexagonal phase GaS nanostructures. The SEM image shows uniformly distributed GaS nanostructures covering the entire substrate surface. The TEM results reveal that the GaS nanostructures are "nanobelts" of widths 20 to 50 nm and lengths up to several microns, and some of them are L-shaped. The growth mechanism and formation of GaS straight and L-shaped nanobelts has been explained. The field emission studies revealed that the threshold field required to draw an emission current of similar to 1 nA is to be 2.9 V/mu m, and a current density of similar to 5.7 mu A/cm(2) can be drawn at an applied field of 6.0 V/mu m. The Fowler-Nordheim plot, derived from the observed current density-applied field characteristics depicts nonlinear behavior over the entire range of applied field. The field enhancement factor is estimated to be similar to 2.0 x 10(4). The emission current stability investigated over a duration of more than 2 h at the preset value similar to 4.0 mu A shows initial increment followed by stabilization to a higher value similar to 6.0 mu A. The average emission current at the stabilized value is seen to be fairly constant with current fluctuations within +/- 10%. The results suggest the use of GaS nanobelts as a promising electron source for applications in field emission based devices.