High‐Responsivity Photodetection by a Self‐Catalyzed Phase‐Pure p‐GaAs Nanowire

Defects are detrimental for optoelectronics devices, such as stacking faults can form carrier‐transportation barriers, and foreign impurities (Au) with deep‐energy levels can form carrier traps and nonradiative recombination centers. Here, self‐catalyzed p‐type GaAs nanowires (NWs) with a pure zinc blende (ZB) structure are first developed, and then a photodetector made from these NWs is fabricated. Due to the absence of stacking faults and suppression of large amount of defects with deep energy levels, the photodetector exhibits room‐temperature high photoresponsivity of 1.45 × 10⁵ A W^?1 and excellent specific detectivity (D*) up to 1.48 × 10¹⁴ Jones for a low‐intensity light signal of wavelength 632.8 nm, which outperforms previously reported NW‐based photodetectors. These results demonstrate these self‐catalyzed pure‐ZB GaAs NWs to be promising candidates for optoelectronics applications.     

Tuning the Electrical Properties of Si Nanowire Field‐Effect Transistors by Molecular Engineering

Exposed facets of n‐type silicon nanowires (Si NWs) fabricated by a top‐down approach are successfully terminated with different organic functionalities, including 1,3‐dioxan‐2‐ethyl, butyl, allyl, and propyl‐alcohol, using a two‐step chlorination/alkylation method. X‐ray photoemission spectroscopy and spectroscopic ellipsometry establish the bonding and the coverage of these molecular layers. Field‐effect transistors fabricated from these Si NWs displayed characteristics that depended critically on the type of molecular termination. Without molecules the source–drain conduction is unable to be turned off by negative gate voltages as large as ?20 V. Upon adsorption of organic molecules there is an observed increase in the “on” current at large positive gate voltages and also a reduction, by several orders of magnitude, of the “off” current at large negative gate voltages. The zero‐gate voltage transconductance of molecule‐terminated Si NW correlates with the type of organic molecule. Adsorption of butyl and 1,3‐dioxan‐2‐ethyl molecules improves the channel conductance over that of the original SiO₂? Si NW, while adsorption of molecules with propyl‐alcohol leads to a reduction. It is shown that a simple assumption based on the possible creation of surface states alongside the attachment of molecules may lead to a qualitative explanation of these electrical characteristics. The possibility and potential implications of modifying semiconductor devices by tuning the distribution of surface states via the functionality of attached molecules are discussed.     

Surface Coating Constraint Induced Anisotropic Swelling of Silicon in Si–Void@SiO x Nanowire Anode for Lithium‐Ion Batteries

Here a simple and an environmentally friendly approach is developed for the fabrication of Si–void@SiO_x nanowires of a high‐capacity Li‐ion anode material. The outer surface of the robust SiO_x backbone and the inside void structure in Si–void@SiO_x nanowires appropriately suppress the volume expansion and lead to anisotropic swelling morphologies of Si nanowires during lithiation/delithiation, which is first demonstrated by the in situ lithiation process. Remarkably, the Si–void@SiO_x nanowire electrode exhibits excellent overall lithium‐storage performance, including high specific capacity, high rate property, and excellent cycling stability. A reversible capacity of 1981 mAh g^?1 is obtained in the fourth cycle, and the capacity is maintained at 2197 mAh g^?1 after 200 cycles at a current density of 0.5 C. The outstanding overall properties of the Si–void@SiO_x nanowire composite make it a promising anode material of lithium‐ion batteries for the power‐intensive energy storage applications.     

Surface Energy Engineering in the Solvothermal Deoxidation of Graphene Oxide

A route to achieving high yields of monodisperse, deeply deoxidized graphene oxide (GO) in solution is presented. It overcomes many of the problems of dispersibility and inefficient reduction of GO in solvothermal deoxidation that are usually observed, despite the previous use of strong reducing agents (e.g. Fe²⁺, S or hydrazine). It is shown that the incomplete deoxidation is most likely due to agglomeration/self‐assembly of partially reduced GO, which also creates poor dispersibility. GO deoxidation is found to be highly sensitive to the solvent surface energy and, through experiments and empirical calculations, tuning the solvent surface energy to around 85.6 mJ/m² (at 100 °C) leads to fully deoxidized GO. These calculations also allow appropriate solvent surface energies to be calculated for other temperatures for deep deoxidation of GO. This approach makes solvothermal deoxidation of GO a potential route to large scale, economic production of highly disperse monolayered graphene.     

Coexistence of Vapor–Liquid–Solid and Vapor–Solid–Solid Growth Modes in Pd‐Assisted InAs Nanowires

During the growth of InAs nanowires from Pd catalyst particles on InAs(111)A substrates, two distinct classes of nanowires are observed with smooth or zigzagged sidewalls. It is shown that this is related to a bimodal distribution of the wire‐tip diameter: above a critical diameter wires grow with smooth sidewalls, and below with zigzagged morphology. Transmission electron microscopy analysis shows that the catalyst particles at the tip of zigzagged wires are smooth and have a higher aspect ratio than those at the tip of smooth wires. Zigzagged wires grow from liquid particles in the vapor–liquid–solid (VLS) mode whereas the smooth ones grow from solid particles in the vapor–solid–solid (VSS) mode.     

Simultaneous Enhancement of Charge Separation and Hole Transportation in a TiO2–SrTiO3 Core–Shell Nanowire Photoelectrochemical System

Efficient charge separation and transportation are key factors that determine the photoelectrochemical (PEC) water‐splitting efficiency. Here, a simultaneous enhancement of charge separation and hole transportation on the basis of ferroelectric polarization in TiO₂–SrTiO₃ core–shell nanowires (NWs) is reported. The SrTiO₃ shell with controllable thicknesses generates a considerable spontaneous polarization, which effectively tunes the electrical band bending of TiO₂. Combined with its intrinsically high charge mobility, the ferroelectric SrTiO₃ thin shell significantly improves the charge‐separation efficiency (η_separation) with minimized influence on the hole‐migration property of TiO₂ photoelectrodes, leading to a drastically increased photocurrent density ( J _ph). Specifically, the 10 nm‐thick SrTiO₃ shell yields the highest J _ph and η_separation of 1.43 mA cm^?2 and 87.7% at 1.23 V versus reversible hydrogen electrode, respectively, corresponding to 83% and 79% improvements compared with those of pristine TiO₂ NWs. The PEC performance can be further manipulated by thermal treatment, and the control of SrTiO₃ film thicknesses and electric poling directions. This work suggests a material with combined ferroelectric and semiconducting features could be a promising solution for advancing PEC systems by concurrently promoting the charge‐separation and hole‐transportation properties.     

Tunable Polarity Behavior and Self‐Driven Photoswitching in p‐WSe2/n‐WS2 Heterojunctions

Van der Waals (vdW) p–n heterojunctions consisting of various 2D layer compounds are fascinating new artificial materials that can possess novel physics and functionalities enabling the next‐generation of electronics and optoelectronics devices. Here, it is reported that the WSe₂/WS₂ p–n heterojunctions perform novel electrical transport properties such as distinct rectifying, ambipolar, and hysteresis characteristics. Intriguingly, the novel tunable polarity transition along a route of n‐“anti‐bipolar”–p‐ambipolar is observed in the WSe₂/WS₂ heterojunctions owing to the successive work of conducting channels of junctions, p‐WSe₂ and n‐WS₂ on the electrical transport of the whole systems. The type‐II band alignment obtained from first principle calculations and built‐in potential in this vdW heterojunction can also facilitate the efficient electron–hole separation, thus enabling the significant photovoltaic effect and a much enhanced self‐driven photoswitching response in this system.     

Surface Energy and Surface Stability of Ag Nanocrystals at Elevated Temperatures and Their Dominance in Sublimation‐Induced Shape Evolution

The surface energy and surface stability of Ag nanocrystals (NCs) are under debate because the measurable values of the surface energy are very inconsistent, and the indices of the observed thermally stable surfaces are apparently in conflict. To clarify this issue, a transmission electron microscope is used to investigate these problems in situ with elaborately designed carbon‐shell‐capsulated Ag NCs. It is demonstrated that the {111} surfaces are still thermally stable at elevated temperatures, and the victory of the formation of {110} surfaces over {111} surfaces on the Ag NCs during sublimation is due to the special crystal geometry. It is found that the Ag NCs behave as quasiliquids during sublimation, and the cubic NCs represent a featured shape evolution, which is codetermined by both the wetting equilibrium at the Ag–C interface and the relaxation of the system surface energy. Small Ag NCs (≈10 nm) no longer maintain the wetting equilibrium observed in larger Ag NCs, and the crystal orientations of ultrafine Ag NCs (≈6 nm) can rotate to achieve further shape relaxation. Using sublimation kinetics, the mean surface energy of Ag NCs at 1073 K is calculated to be 1.1–1.3 J m^?2.     

Surface Crystallization of Liquid Au–Si and Its Impact on Catalysis

In situ transmission electron microscopy reveals that an atomically thin crystalline phase at the surface of liquid Au–Si is stable over an unexpectedly wide range of conditions. By measuring the surface structure as a function of liquid temperature and composition, a simple thermodynamic model is developed to explain the stability of the ordered phase. The presence of surface ordering plays a key role in the pathway by which the Au–Si eutectic solidifies and also dramatically affects the catalytic properties of the liquid, explaining the anomalously slow growth kinetics of Si nanowires at low temperature. A strategy to control the presence of the surface phase is discussed, using it as a tool in designing strategies for nanostructure growth.     

Imparting Designer Biorecognition Functionality to Metal–Organic Frameworks by a DNA‐Mediated Surface Engineering Strategy

Surface functionality is an essential component for processing and application of metal–organic frameworks (MOFs). A simple and cost‐effective strategy for DNA‐mediated surface engineering of zirconium‐based nanoscale MOFs (NMOFs) is presented, capable of endowing them with specific molecular recognition properties and thus expanding their potential for applications in nanotechnology and biotechnology. It is shown that efficient immobilization of functional DNA on NMOFs can be achieved via surface coordination chemistry. With this strategy, it is demonstrated that such porphyrin‐based NMOFs can be modified with a DNA aptamer for targeting specific cancer cells. Furthermore, the DNA–NMOFs can facilitate the delivery of therapeutic DNA (e.g., CpG) into cells for efficient recognition of endosomal Toll‐like receptor 9 and subsequent enhanced immunostimulatory activity in vitro and in vivo. No apparent toxicity is observed with systemic delivery of the DNA–NMOFs in vivo. Overall, these results suggest that the strategy allows for surface functionalization of MOFs with different functional DNAs, extending the use of these materials to diverse applications in biosensor, bioimaging, and nanomedicine.     

Two-dimensional phase separation and surface-reconstruction driven atomic ordering in mixed III–V layers

In mixed III–V layers atomic species having different covalent tetrahedral radii are not distributed at random on their respective sublattices. Two types of deviation from randomness are observed: (i) phase separation, and (ii) atomic ordering. Phase separation is two-dimensional in nature, occurs on the surface while the layer is growing and is driven by surface thermodynamics. In contrast, atomic ordering is induced by subsurface stresses associated with (2×4) and (2×3) reconstructions of group V terminated (001) surfaces. These stresses bias the occupation of sites by atomic species differing in their tetrahedral radii and this feature leads to the evolution of double and triple period superlattices on ( 11)_B, (1 1)_B, and (111)_A, (11 )_A planes respectively.     

一种新型电磁能量选择表面结构设计与仿真分析

电磁干扰是通信系统在可靠性及设备安全性中必须考虑的因素,近些年迅速发展的高功率电磁脉冲对雷达天线等通信设备造成严重的威胁.提出一种新型电磁能量选择表面(ESS),该表面在十字形ESS的基础上增加了4个金属枝节,通过单元间加载PIN二极管获得自适应特性.在枝节处加载二极管可以在金属网格结构中引入栅格结构,有效增加屏蔽带宽,而且在透波模式下,枝节形成的二维狭缝阵列结构会在高频产生透射共振,使得表面在高频有一个频带使工作信号通过.仿真结果表明,提出的ESS在高功率电磁脉冲作用下会处于防护模式,其-20 dB带宽可达3.4 GHz;正常工作信号作用下ESS处于透波模式,此时表面为频率选择表面(FSS),其在低频和高频各有一个工作频带,低频部分带宽为0 GHz~1.3 GHz,高频谐振频率为5.36 GHz,带宽可达150 MHz.     

Engineering the Cell–Semiconductor Interface: A Materials Modification Approach using II‐VI and III‐V Semiconductor Materials

Developing functional biomedical devices based on semiconductor materials requires an understanding of interactions taking place at the material‐biosystem interface. Cell behavior is dependent on the local physicochemical environment. While standard routes of material preparation involve chemical functionalization of the active surface, this review emphasizes both biocompatibility of unmodified surfaces as well as use of topographic features in manipulating cell‐material interactions. Initially, the review discusses experiments involving unmodified II–VI and III–V semiconductors – a starting point for assessing cytotoxicity and biocompatibility – followed by specific surface modification, including the generation of submicron roughness or the potential effect of quantum dot structures. Finally, the discussion turns to more recent work in coupling topography and specific chemistry, enhancing the tunability of the cell‐semiconductor interface. With this broadened materials approach, researchers' ability to tune the interactions between semiconductors and biological environments continues to improve, reaching new heights in device function.     

Surface Modified MXene‐Based Nanocomposites for Electrochemical Energy Conversion and Storage

In recent years, the rapidly growing attention on MXenes makes the material a rising star in the 2D materials family. Although most researchers' interests are still focused on the properties of bare MXenes, little attention has been paid to the surface chemistry of MXenes and MXene‐based nanocomposites. To this end, this Review offers a comprehensive discussion on surface modified MXene‐based nanocomposites for energy conversion and storage (ECS) applications. Based on the structure and reaction mechanism, the related synthesis methods toward MXenes are briefly summarized. After the discussion of existing surface modification techniques, the surface modified MXene‐based nanocomposites and their inherent chemical principles are presented. Finally, the application of these surface modified nanocomposites for supercapacitors (SCs), lithium/sodium–ion batteries (LIBs/SIBs), and electrocatalytic water splitting is discussed. The challenges and prospects of MXene‐based nanocomposites for future ECS applications are also presented.