Electronic and chemical structure of the H2O/GaN(0001) interface under ambient conditions

We employed ambient pressure X-ray photoelectron spectroscopy to investigate the electronic and chemical properties of the H(2)O/GaN(0001) interface under elevated pressures and/or temperatures. A pristine GaN(0001) surface exhibited upward band bending, which was partially flattened when exposed to H(2)O at room temperature. However, the GaN surface work function was slightly reduced due to the adsorption of molecular H(2)O and its dissociation products. At elevated temperatures, a negative charge generated on the surface by a vigorous H(2)O/GaN interfacial chemistry induced an increase in both the surface work function and upward band bending. We tracked the dissociative adsorption of H(2)O onto the GaN(0001) surface by recording the core-level photoemission spectra and obtained the electronic and chemical properties at the H(2)O/GaN interface under operando conditions. Our results suggest a strong correlation between the electronic and chemical properties of the material surface, and we expect that their evolutions lead to significantly different properties at the electrolyte/electrode interface in a photoelectrochemical solar cell

An on-chip electrical transport spectroscopy approach for in situ monitoring electrochemical interfaces

In situ monitoring electrochemical interfaces is crucial for fundamental understanding and continued optimization of electrocatalysts. Conventional spectroscopic techniques are generally difficult to implement for in situ electrochemical studies. Here we report an on-chip electrical transport spectroscopy approach for directly probing the electrochemical surfaces of metallic nanocatalysts in action. With a four-electrode device configuration, we demonstrate that the electrical properties of ultrafine platinum nanowires are highly sensitive and selective to the electrochemical surface states, enabling a nanoelectronic signalling pathway that reveals electrochemical interface information during in-device cyclic voltammetry. Our results not only show a high degree of consistency with generally accepted conclusions in platinum electrochemistry but also offer important insights on various practically important electrochemical reactions. This study defines a nanoelectronic strategy for in situ electrochemical surface studies with high surface sensitivity and surface specificity

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential

Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals

The large mobilities and carrier lifetimes of hybrid perovskite single crystals and the high atomic numbers of Pb, I and Br make them ideal for X-ray and gamma-ray detection. Here, we report a sensitive X-ray detector made of methylammonium lead bromide perovskite single crystals. A record-high mobility-lifetime product of 1.2 x 10(-2) cm(2) V-1 and an extremely small surface charge recombination velocity of 64 cm s(-1) are realized by reducing the bulk defects and passivating surface traps. Single-crystal devices with a thickness of 2-3 mm show 16.4% detection efficiency at near zero bias under irradiation with continuum X-ray energy up to 50 keV. The lowest detectable X-ray dose rate is 0.5 mu Gy(air) s(-1) with a sensitivity of 80 mu C Gy(air)(-1) cm(-2), which is four times higher than the sensitivity achieved with alpha-Se X-ray detectors. This allows the radiation dose applied to a human body to be reduced for many medical and security check applications