“Capture-activation-recapture” mechanism-guided design of double-atom catalysts for electrocatalytic nitrogen reduction

Compared with the traditional industrial nitrogen fixation, electrocatalytic methods, especially those utilizing double-atom catalysts containing nonmetals, can give good consideration to the economy and environmental protection. However, the existing “acceptance-donation” mechanism is only applicable to bimetallic catalysts and nonmetallic double-atom catalysts containing boron atoms. Herein, a novel “capture-activation-recapture” mechanism for metal-nonmetal double-atom catalyst is proposed to solve the problem by adjusting the coordination environments of nonmetallic atoms and utilizing the activation effect of metal atoms on nitrogen. Based on this mechanism, the nitrogen reduction reaction (NRR) activity of 48 structures is calculated by density functional theory calculation, and four candidates are selected as outstanding electrocatalytic nitrogen reduction catalysts: Si-Fe@NG (U_(L) = –0.14 V), Si-Co@NG (U_(L)= –0.15 V), Si-Mo@BP1 (U_(L) = 0 V), and Si-Re@BP1 (U_(L) = –0.02 V). The analyses of electronic properties further confirm “capture-activation-recapture” mechanism and suggest that the difference in valence electron distribution between metal and Si atoms triggers the activation of N≡N bonds. In addition, a machine learning approach is utilized to generate an expression and an intrinsic descriptor that considers the coordination environment to predict the limiting potential. This study offers profound insight into the synergistic mechanism of TM and Si for NRR and guidance in the design of novel double-atom nitrogen fixation catalysts.

A memristive-photoconductive transduction methodology for accurately nondestructive memory readout

Crossbar resistive memory architectures enable high-capacity storage and neuromorphic computing,accurate retrieval of the stored information is a prerequisite during read operation.However,conventional electrical readout normally suffer from complicated process,inaccurate and destructive reading due to crosstalk effect from sneak path current.Here we report a memristive-photoconductive transduction(MPT)methodology for precise and nondestructive readout in a memristive crossbar array.The individual devices present dynamic filament form/fuse for resistance modulation under electric stimulation,which leads to photogenerated carrier transport for tunable photoconductive response under subsequently light pulse stimuli.This coherent signal transduction can be used to directly detect the memorized on/off states stored in each cell,and a prototype 4*4 crossbar memories has been constructed and validated for the fidelity of crosstalk-free readout in recall process.

Wide-range-adjusted threshold voltages for E-mode AlGaN/GaN HEMT with a p-SnO cap gate

p-GaN cap layer has been recognized as a commercial technology to manufacture enhanced-mode(E-mode)AlGaN/GaN high electron mobility transistor(HEMT);however,the difficult activation of Mg doping and etching damage of p-GaN limit the further improvement of device performance.Thus,the more cost-effective cap layer has attracted wide attention in GaN-based HEMT.In this paper,p-type tin monoxide(p-SnO)was firstly investigated as a gate cap to realize E-mode AlGaN/GaN HEMT by both Silvaco simulation and experiment.Simulation results show that by simply adjusting the thickness(50 to 200 nm)or the doping concentration(3×10^(17)to 3×10^(18)cm^(-3))of p-SnO,the threshold voltage(V_(th))of HEMT can be continuously adjusted in the range from zero to 10 V.Simultaneously,the device demonstrated a drain current density above 120 mA mm^(-1),a gate breakdown voltage(V_(BG))of 7.5 V and a device breakdown voltage(V_(B))of 2470 V.What is more,the etching-free AlGaN/GaN HEMT with sputtered p-SnO gate cap were fabricated,and achieved a positive V_(th) of 1 V,V_(BG) of 4.2 V and V_(B) of 420 V,which confirms the application potential of the p-SnO film as a gate cap layer for E-mode GaN-based HEMT.This work is instructive to the design and manufacture of p-oxide gate cap E-mode AlGaN/GaN HEMT with low cost.