Controllable growth of NbTe4 micro/nanostructures on Nb substrates and their field-emission performance

Single-crystalline NbTe4 microcone, microplate, and nanorod arrays were grown on Nb substrates by a surface-assisted chemical-vapor-transport under different conditions. The microcones are composed of small and large cones with a bending top. The small cones have a top diameter of about 0.2 mm, a bottom diameter of about 1.2 mm, and a length up to approx. 7.7 mm. The large cones originate from self-assembled small cones. The microplates mostly stand on Nb foils, with a diameter of about 2-3 mm and a thickness from 50 to 250 nm. The nanorods have a rectangle section of 250 x 150 to 250 x 250 nm(2) or a triangle section with a side of about 250 nm, and a length up to 4.5 mu m, partly standing on the substrates. Their growth mechanisms are briefly discussed. Field-emission experiments showed that the three micro/nanostructures have a notable emission current, and their turn-on fields (defined as the electric field required to produce a current density of 10 mA cm(-2)) are 4.7, 2.0, and 1.9 V mu m(-1), respectively, suggesting their potential application in electron emission devices.