Fabrication of vertically aligned single-crystalline lanthanum hexaboride nanowire arrays and investigation of their field emission

Abstract

High-quality, uniform, one-dimensional (1D) lanthanum hexaboride (LaB6) nanostructures with different morphologies (for example, sparse or dense nanoneedles, or nanorods and nanowire arrays) were fabricated through an effective, easily controlled, one-step, catalyst-free chemical vapor deposition process. The morphologies, structures and temperature-dependent field emission (FE) properties were systematically investigated. FE measurements at room temperature (RT) showed that LaB6 nanowire arrays possess the best FE characteristics among all 1D LaB6 nanostructures, with a low turn-on electric field (Eto, 1.82 V μm−1), a low threshold electric field (Ethr, 2.48 V μm−1), a high current (5.66 mA cm−2 at 2.92 V μm−1) and good stability (at a testing time of 1000 min, fluctuations were <6.0%). Temperature-dependent FE showed that the turn-on and threshold electric fields decreased from 1.82 to 1.06 and 2.48 to 1.62 V μm−1, respectively, whereas the emission current density increased significantly from 0.20 to 9.05 mA cm−2 at 2.20 V μm−1 when the temperature was increased from RT to 723 K. The emission current density and the dependence of the effective work function on temperature were also investigated. We attribute the significant reduction of the turn-on and threshold fields and the remarkable increase of emission current to a decrease in the effective work function with temperature. Nanostructured materials that can act as electron emitters are extremely valuable for electronic applications such as flat panel displays and other devices. However, problems associated with the efficiency and physical stability of candidate systems based on carbon nanotubes or oxide nanowires have hindered their practical development. An international team of researchers from China and Japan led by Tianyou Zhai has now developed a vapor deposition technique to controllably grow well-aligned arrays of lanthanum hexaboride (LaB6) nanowires as possible improved field emission devices. The LaB6 nanowires are mechanically strong with a low energy threshold for the emission of electrons, as well as good long-term field-emission stability. The nanowires display electron emission approximately ten times higher than that of competing systems and operate very efficiently at room temperature. Arrays made from these nanowires are promising for applications requiring electron emission on small scales such as electron microscopes and x-ray laser systems as well as flat panel displays. We have developed a simple, effective, one-step, catalyst-free chemical vapor deposition method for the synthesis of high-quality LaB6 nanostructure nanowire arrays. Field-emission (FE) measurements at room temperature (RT) show that LaB6 nanowire arrays possess the best FE characteristics among all one-dimensional LaB6 nanostructures, exhibiting with a low turn-on electric field, a low threshold electric field, a high current and a good stability. Temperature-dependent FE on the nanowire arrays shows that the turn-on and threshold electric fields decreased rapidly whereas the emission current density increases significantly in the ambient temperature from RT to 723 K.