In the pursuit of ultrasmall electronic components, monolayer electronic devices have recently been fabricated using transition-metal dichalcogenides. Monolayers of these materials are semiconducting, but nanowires with stoichiometry MX (M = Mo or W, X = S or Se) have been predicted to be metallic. Such nanowires have been chemically synthesized. However, the controlled connection of individual nanowires to monolayers, an important step in creating a two-dimensional integrated circuit, has so far remained elusive. In this work, by steering a focused electron beam, we directly fabricate MX nanowires that are less than a nanometre in width and Y junctions that connect designated points within a transition-metal dichalcogenide monolayer. In situ electrical measurements demonstrate that these nanowires are metallic, so they may serve as interconnects in future flexible nanocircuits fabricated entirely from the same monolayer. Sequential atom-resolved Z-contrast images reveal that the nanowires rotate and flex continuously under momentum transfer from the electron beam, while maintaining their structural integrity. They therefore exhibit self-adaptive connections to the monolayer from which they are sculpted. We find that the nanowires remain conductive while undergoing severe mechanical deformations, thus showing promise for mechanically robust flexible electronics. Density functional theory calculations further confirm the metallicity of the nanowires and account for their beam-induced mechanical behaviour. These results show that direct patterning of one-dimensional conducting nanowires in two-dimensional semiconducting materials with nanometre precision is possible using electron-beam-based techniques.

Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of HB, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB) with an average yield of 42.3% at room temperature. The sheets feature an sp-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray atomic pair distribution functions, electron diffraction, transmission electron microscopy, photo absorption, core-level binding energy data, infrared absorption, electron energy loss spectroscopy, and density functional theory calculations. The established cation-exchange method for metal diboride opens new avenues for the mass production of several types of boron-based 2D materials by countercation selection and functionalization.

Hydrogen boride nanosheets (HB sheets) are facilely synthesized via ion-exchange treatment on magnesium diboride (MgB2) in an acetonitrile solution. Optical absorption and fluorescence spectra of HB sheets indicate that their bandgap energy is 2.8 eV. According to first-principles calculations, optical absorption seen at 2.8 eV is assigned to the electron transition between the σ-bonding states of B and H orbitals. In addition, density functional theory (DFT) calculations suggest the other allowed transition from the σ-bonding state of B and H orbitals to the antibonding state with the gap of 3.8 eV. Significant gaseous H2 release is found to occur only under photoirradiation, which causes the electron transition from the σ-bonding state to the antibonding state even under mild ambient conditions. The amount of H2 released from the irradiated HB sheets is estimated to be 8 wt%, indicating that the sheets have a high H2-storage capacity compared with previously reported metal H2-storage materials.

Two-dimensional transition-metal dichalcogenide (TMDC) monolayers, most of which are semiconducting with direct bandgaps, are promising candidates for flexible nanoelectronics [1]. TMDCbased atomically-thin devices have inspired research on assembling them into circuits [2, 3]. As the TMDC-based devices scale down to tens of nanometers, flexible conducting wires with efficient and robust junctions are essential for connecting multiple components in a nano-circuit for flexible electronics applications.Notably, one-dimensional ultrathin transition-metal chalcogenide nanowires have been predicted to be metallic. These nanowires could potentially serve as a better conducting interconnect for future TMDCbased flexible nanoelectronics since no extra elements are introduced, therefore, simplifying the fabrication process and providing reliable interconnections. Although such metallic nanowires have been synthesized individually, controllable connections of nanowires to the monolayers, an important step towards assembling them into devices, have so far remained elusive.Here, we report direct electron-beam fabrication of such ultrathin nanowires, including their ramified junctions, connecting designated points within a semiconducting TMDC monolayer (Fig. 1). The controllable fabrication is performed in a scanning transmission electron microscope with 5 th order aberration corrector which simultaneously records the movements of the atoms during the fabrication. The sequential images reveal that the formation of the nanowires is a self-regulating and self-healing process that is insensitive to precise beam parameters. In-situ electrical measurements further reveal the nanowires are intrinsically metallic. The nanowires remain conducting and maintain structural integrity as they undergo continuous electron-beam-induced rotations and flexing, indicating their self-adaptive connections to the monolayers. The observed mechanical behavior is explained by density-functionaltheory calculations, which further predict that the metal-semiconductor contacts could be Ohmic to p-

First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated SiO2 (0001) surface and a fully hydroxylated SiO2 (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated SiO2 surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and SiO2 (0001) surfaces. We also find that the graphene adsorbed on SiO2 is a semiconductor irrespective of the adsorption arrangement due to the variation of on-site energy induced by the SiO2 substrate.