Synthesis of GdB6 nanostructures using nanosecond (Nd: YAG) laser: field emission investigation
We herein report field emission characteristics of GdB6 nanostructures grown directly on a pellet via laser processing (laser fluence ~ 6 J/cm2). The laser processed GdB6 pellet was characterized by X-ray diffraction, which revealed no change in phase upon laser processing. The values of the turn-on field required to draw emission current density of 1 μA/cm2 is found to be ~ 2.95 V/μm, for the laser processed GdB6 emitter. Furthermore, the Fowler-Nordheim (F-N) plot exhibits nonlinear behavior over the entire range of applied field and the field enhancement factor (β) calculated from slope of the F-N plot (low field region) was found to be ~ 543. The emission current stability over a period of 3h was observed to be fairly good. The observed results demonstrate that laser processing can be efficiently used to make GdB6 nanostructure emitter having potential for practical applications.
Single-crystalline GdB6 nanowire field emitters.
Having the lowest work function in the rare-earth hexaboride family, GdB6 nanowires of rectangular cross-section with about 50 nm in lateral dimension and several microns in length have been successfully produced using a CVD method. The nanowires are grown in the 001 lattice direction, and both the tip-top and the side surfaces are terminated with the {100} lattice planes. A GdB6 single nanowire field emitter has also been built with an emission current of more than 150 nA at an applied field of less than 3.2 V/mum. The work function of the nanowire emitter was estimated to be about 1.5 eV.
X-ray photoelectron spectroscopy investigation of the initial oxygen adsorption sites on the LaB 6 (100) surface
Abstract X-ray photoelectron spectroscopy was used to investigate the initial stages of oxygen adsorption on the (100) surface of a single crystal of lanthanum hexaboride. Numerous previous studies had not resolved the issue of whether oxygen adsorbs at lanthanum sites, boron sites, or both. We find that oxygen adsorption markedly alters the La 3d lineshapes, whereas the B 1s peak is unaffected. On the clean surface the La 3d3/2 peak is split into two components at binding energies of 854.7 and 851.8 eV, a splitting that is typical of rare-earth metals and their compounds. The two components are associated with two different final states. In one final state the 3d core hole is poorly screened (854.7 eV) and in the other it is well-screened (851.8 eV). The relative intensity of the two components is known to be very sensitive to the chemical environment of the rare earth atom and a 10 L O2 exposure at room temperature produces a large increase in the relative intensity of the well-screened component. Annealing the surface to 600°C and then to 700°C produces sharp c(2×2) and p(2×1) LEED patterns respectively. The La 3d peaks associated with the two LEED patterns are similar to those observed after the initial 300 K 10 L O2 exposure, indicating oxygen bonding to La in both overlayer structures. Thus while the XPS data clearly reveal oxygen adsorption at La sites, there is no indication of adsorption at boron sites for low O2 exposures. More extensive oxidation at higher temperatures shows formation of both boron and lanthanum oxides.