Enhanced field emission from hydrogenated TiO₂nanotube arrays

Abstract

The field emission (FE) properties of TiO(2) nanotube arrays (TNAs) synthesized by anodization are dramatically improved after hydrogenation at various temperatures in a range of 400-550 °C. Compared with pristine TNAs, the turn-on fields of hydrogenated TNAs (H:TNAs) are significantly decreased from 18.23 to 1.75 V μm(-1), and closely related to hydrogenation temperature. Importantly, the optimized sample of H:TNAs prepared at 550 °C shows excellent FE performances involving both a low turn-on field of 1.75 V μm(-1), a high current density of 4.0 mA cm(-2) at 4.50V μm(-1), and a remarkable FE stability over 480 min. The substantially enhanced FE properties can be attributed to the combination of a typical tubular morphology, a reduced work function and the improved conductivity of H:TNAs.

Mesoporous TiO2 nanoparticles terminated with carbonate-like groups: Amorphous/crystalline structure and visible-light photocatalytic activity

“…More interestingly, an obvious luminescent background occurred in the curve of TiO 2 -250, which was distinct from that of TiO 2 -120 and TiO 2 -400. These results maybe indicated the presence of the surface amorphous structure or defects on the anatase TiO 2 -250 [15,[26][27][28].…”

Surface reconstruction, oxygen vacancy distribution and photocatalytic activity of hydrogenated titanium oxide thin film

“…Moreover, the peak intensities of hydrogenated TiO 2 thin films are reduced with respect to the sample annealed in air. The annealing in a reducing environment appears to have created defects in the TiO 2 lattices [20,27]. The shift of a main anatase peak (1 0 1) to higher angles for samples annealed in hydrogen increases with the annealing temperature ( Fig.…”

“…Furthermore, the use of Raman spectroscopy to probe the defect states in modified TiO 2 is questionable since the inconsistency of available data in the literature raises doubt about reliability of this technique. In general, hydrogenation of TiO 2 leads to positive shift of Raman peaks [20,23,27], but there are several reports where Raman peaks remain almost the same [18,24,28] or even shift to negative side [29]. Therefore, this issue needs to be clarified.…”

Modifying oxide nanomaterials’ properties by hydrogenation

“…[25,49,61] Meanwhile, there are a few reports mentioning possible decrease in the photocatalytic activities, if the hydrogenated TiO 2 nanomaterials are not properly prepared. [37,38] So far, hydrogenation has been conducted on TiO 2 nanoparticles, [4,21,31] nanorods, [48] nanotubes, [45] nanowires, [46] nanosheets, [35,36] with anatase or rutile phase, [4,29,33] under high-pressure, [4,21] ambient pressure, [29,30,39] or low-pressure [43] pure hydrogen environment, or hydrogen-argon, [44][45][46][47][48] hydrogen-nitrogen [52][53][54] gas flow, in the temperature range from room temperature [21] to 700°C, [27] with a hydrogenation time from a few minutes [27] to 20 days. [21] With no doubt, we can image that the so-formed TiO 2 nanomaterials will display variations in their characteristics and performances.…”

“…[30] The oxygen vacancies introduced to the hydrogenated TiO 2 nanotubes lift the Fermi level, improve the electrical conductivity, and reduce the work function to decrease the field-penetration barrier at the surface resulting in easy electron emission in under electrical bias. [45] As the crystalline/disordered core/shell nanostructure is formed for hydrogenated TiO 2 nanoparticles, there is apparent electronic structural mismatch between the crystalline phase and the disordered phase. [4,77,78] The interface in between is expected to have structural and chemical defects with dangling bonds and charge imbalance.…”