Exploring efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts is of great importance for various electrochemical energy storage and conversion technologies. Ni-based electrocatalysts have been actively pursued because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Ni-based electrocatalysts has been intrinsically limited due to their low electrical conductivity and poor active site exposure yield. Herein, we report metallic Ni3N nanosheets as an efficient OER electrocatalyst for the first time. The first-principles calculations and electrical transport property measurements unravel that the Ni3N is intrinsically metallic, and the carrier concentration can be remarkably improved with dimensional confinement. The EXAFS spectra provide solid evidence that the Ni3N nanosheets have disordered structure resultant of dimensional reduction, which then could provide more active sites for OER. Benefiting from enhanced electrical conductivity with metallic behavior and atomically disordered structure, the Ni3N nanosheets realize intrinsically improved OER activity compared with bulk Ni3N and NiO nanosheets. Our finding suggests that metallic nitride nanosheets could serve as a new group of OER electrocatalysts with excellent property.

Complex three-dimensional (3D) structures in biology (e.g., cytoskeletal webs, neural circuits, and vasculature networks) form naturally to provide essential functions in even the most basic forms of life. Compelling opportunities exist for analogous 3D architectures in human-made devices, but design options are constrained by existing capabilities in materials growth and assembly. We report routes to previously inaccessible classes of 3D constructs in advanced materials, including device-grade silicon. The schemes involve geometric transformation of 2D micro/nanostructures into extended 3D layouts by compressive buckling. Demonstrations include experimental and theoretical studies of more than 40 representative geometries, from single and multiple helices, toroids, and conical spirals to structures that resemble spherical baskets, cuboid cages, starbursts, flowers, scaffolds, fences, and frameworks, each with single- and/or multiple-level configurations.

We have developed methods for creating microscale inorganic light-emitting diodes (LEDs) and for assembling and interconnecting them into unusual display and lighting systems. The LEDs use specialized epitaxial semiconductor layers that allow delineation and release of large collections of ultrathin devices. Diverse shapes are possible, with dimensions from micrometers to millimeters, in either flat or "wavy" configurations. Printing-based assembly methods can deposit these devices on substrates of glass, plastic, or rubber, in arbitrary spatial layouts and over areas that can be much larger than those of the growth wafer. The thin geometries of these LEDs enable them to be interconnected by conventional planar processing techniques. Displays, lighting elements, and related systems formed in this manner can offer interesting mechanical and optical properties.

Despite the fact that H-terminated, HF-etched Si crystals are the starting point for construction of most contemporary electronic devices, 1 little is known about the chemical reactions of H-terminated Si surfaces under ambient temperature and pressure. 2,3 Functionalization of Si without partial oxidation and/or formation of electrical defects is potentially important in fabricating improved electronic devices 4,5 as well as in measurement of charge transfer rate constants at semiconductor/ liquid contacts. 6 One recently described approach involves the reaction of HF-etched Si(111) with olefins and organic diacyl peroxides, in which formation of a self-assembled (near)monolayer of Si-alkyls was hypothesized. 2 We report here an alternative strategy to functionalize HF-etched Si surfaces involving halogenation and subsequent reaction with alkyl Grignard or alkyl lithium reagents. We report vibrational spectroscopic and temperature programmed desorption data which confirm that the alkyl groups are bonded covalently to the Si surface, and we demonstrate that such overlayer formation can impede the undesirable oxidation of Si in a variety of environments while providing surfaces of high electrical quality.The H-terminated Si surface 7 was first exposed to PCl 5 for 20-60 min at 80-100 °C, in chlorobenzene with benzoyl peroxide as the radical initiator. 8,9 Upon chlorination, the XP survey spectra (Figure 1) showed peaks at 270.2 ( 0.4 binding electron volts, BeV, (Cl 2s) and 199.3 ( 0.4 BeV (Cl 2p), indicating that this procedure yielded Cl on the surface. The high-resolution XP spectrum of the Si 2p peak of this surface displayed, in addition to the substrate Si signal, an additional peak located at 0.98 ( 0.12 BeV higher in binding energy (Figure 2) whose position and intensity was consistent with the formation of a surface Si-Cl bond. 10 Auger electron spectra (AES) also confirmed the presence of Cl on the silicon surface. High resolution electron energy loss spectra (HREELS) of this surface exhibited a characteristic peak at 560 cm -1 that was not present on the H-terminated Si surface, confirming the formation of covalent Si-Cl bonds at the surface. 11 Temperature programmed desorption spectra of the chlorinated surface showed dominant signals at 64 (SiCl), 71 (Cl 2 ), and 135 (SiCl 3 ) amu, peaking at 670 and 850 K, which is characteristic of chlorinated silicon surfaces. 10,12 The 560 cm -1 peak in the HREELS and the Cl peak in the AES disappeared following thermal desorption.Exposure of the chlorinated Si surface to alkyl-Li (RLi: R

Compound semiconductors like gallium arsenide (GaAs) provide advantages over silicon for many applications, owing to their direct bandgaps and high electron mobilities. Examples range from efficient photovoltaic devices to radio-frequency electronics and most forms of optoelectronics. However, growing large, high quality wafers of these materials, and intimately integrating them on silicon or amorphous substrates (such as glass or plastic) is expensive, which restricts their use. Here we describe materials and fabrication concepts that address many of these challenges, through the use of films of GaAs or AlGaAs grown in thick, multilayer epitaxial assemblies, then separated from each other and distributed on foreign substrates by printing. This method yields large quantities of high quality semiconductor material capable of device integration in large area formats, in a manner that also allows the wafer to be reused for additional growths. We demonstrate some capabilities of this approach with three different applications: GaAs-based metal semiconductor field effect transistors and logic gates on plates of glass, near-infrared imaging devices on wafers of silicon, and photovoltaic modules on sheets of plastic. These results illustrate the implementation of compound semiconductors such as GaAs in applications whose cost structures, formats, area coverages or modes of use are incompatible with conventional growth or integration strategies.