Photocatalytic nitrogen reduction to ammonia: Insights into the role of defect engineering in photocatalysts

Engineering of defects in semiconductors provides an effective protocol for improving photocatalytic N2 conversion efficiency. This review focuses on the state-of-the-art progress in defect engineering of photocatalysts for the N2 reduction toward ammonia. The basic principles and mechanisms of thermal catalyzed and photon-induced N2 reduction are first concisely recapped, including relevant properties of the N2 molecule, reaction pathways, and NH3 quantification methods. Subsequently, defect classification, synthesis strategies, and identification techniques are compendiously summarized. Advances of in situ characterization techniques for monitoring defect state during the N2 reduction process are also described. Especially, various surface defect strategies and their critical roles in improving the N2 photoreduction performance are highlighted, including surface vacancies (i.e., anionic vacancies and cationic vacancies), heteroatom doping (i.e., metal element doping and nonmetal element doping), and atomically defined surface sites. Finally, future opportunities and challenges as well as perspectives on further development of defect-engineered photocatalysts for the nitrogen reduction to ammonia are presented. It is expected that this review can provide a profound guidance for more specialized design of defect-engineered catalysts with high activity and stability for nitrogen photochemical fixation.

Influence of penetrating radiations on electrical low frequency noise of semiconductors

The influence of penetrating radiations on the electrical low-frequency noise of semiconductors is studied. Expression is calculated that determines the number of structural defects in semiconductors arising from exposure to penetrating radia-tion. General form expression is calculated for the spectrum of electrical low-frequency noise in semiconductors when exposed to penetrating radiation. Quanti-tative relationship was established between the spectrum of electrical low-frequency noise and the development of disturbances in the structure of semicon-ductors caused by penetrating radiations. The results obtained can be used to de-termine the spectra of electrical noise in semiconductors of various types and in numerous semiconductor devices. The results of the article have practical applica-tions. Calculated expressions allow to make estimates of the intensity of electrical low-frequency noise, from which conclusions can be drawn about possibility of functioning and reliability of semiconductor devices. Established relationship be-tween electrical noise and radiation defects can be used to estimate, based on spec-tral characteristics of the noise, the defectiveness of structure of semiconductors subjected to radiation damage.

Realizing quinary charge states of solitary defects in two-dimensional intermetallic semiconductor

Creating and manipulating multiple charge states of solitary defects in semiconductors is of essential importance for solitary defect electronics, but is fundamentally limited by Coulomb's law. Achieving this objective is challenging, due to the conflicting requirements of the localization necessary for the sizable band gap and delocalization necessary for a low charging energy. Here, using scanning tunneling microscopy/spectroscopy experiments and first-principles calculations, we realized exotic quinary charge states of solitary defects in two-dimensional intermetallic semiconductor Sn2Bi. We also observed an ultralow defect charging energy that increases sublinearly with charge number rather than displaying the usual quadratic behavior. Our work suggests a promising route for constructing multiple defect-charge states by designing intermetallic semiconductors, and opens new opportunities for developing quantum devices with charge-based quantum states.