By breaking intrinsic Si (100) and (111) wafers to expose sharp {111} and {112} facets, electrical conductivity measurements on single and different silicon crystal faces were performed through contacts with two tungsten probes. While Si {100} and {110} faces are barely conductive at low applied voltages, as expected, the Si {112} surface is highly conductive and Si {111} surface also shows good conductivity. Asymmetrical I-V curves have been recorded for the {111}/{112}, {111}/{110}, and {112}/{110} facet combinations because of different degrees of conduction band bending at these crystal surfaces presenting different barrier heights to current flow. In particular, the {111}/{110} and {112}/{110} facet combinations give I-V curves resembling those of p-n junctions, suggesting a novel field effect transistor design is possible capitalizing on the pronounced facet-dependent electrical conductivity properties of silicon.

Localized surface plasmon resonances (LSPR) in near-infrared (NIR) region have been extensively studied for copper chalcogenide nanostructures, not only for the absorption enhancement but also tunable LSPR characteristics with their free carrier concentrations or defects. In the present work, one-step cation exchange method has been used to synthesize Cu2−xS nanowires with x varied between 0 and 1, including Cu2S, Cu7S4 and CuS and so forth. The plasmonic band of Cu2−xS nanowires shifts to a shorter wavelength with the increase in x, as observed in vis-NIR spectra, which is attributed to the increase in density of copper vacancies. The Cu2−xS nanowires have been used as catalysts towards the photocatalytic generation of H2 from ammonia borane (AB). Among samples with different Cu-S compositions, Cu7S4 samples exhibited the highest activity in terms of H2 evolution rate (25.54 mmol/g h). Moreover, a marked enhancement of the H2 evolution rate (157.04 mmol/g h) could be achieved after decorating the Cu2−xS nanowires with Pd nanoparticles to form the hybrid structures. The results of the present investigation may lead to an effective strategy for the design and development of LSPR materials for photocatalytic applications.

MoS2 atomic layers have recently attracted much interest because of their two-dimensional structure as well as tunable optical, electrical, and mechanical properties for next-generation electronic and electro-optical devices. Here we have achieved facile fabrication of MoS2 thin films on CdS nanowires by cation exchange in solution at room temperature and importantly observed their extraordinary magnetic properties. We establish the atomic structure of the MoS2/CdS heterostructure by taking atomic images of the MoS2/CdS interface as well as performing first-principles density functional geometry optimizations and scanning transmission electron microscopy annular dark field image simulations. Furthermore, our first-principles density functional calculations for the MoS2/CdS heterostructure reveal that the magnetism in the MoS2/CdS heterostructure stems from the ferromagnetic MoS2 monolayer next to the MoS2/CdS interface. The ferromagnetism is attributed to the partial occupation of the Mo dx2-y2 /dxy conduction band in the interfacial MoS2 monolayer caused by the mixed covalent-ionic bonding among the MoS2 and CdS monolayers near the MoS2/CdS interface. These findings of the ferromagnetic MoS2 monolayer with large spin polarization at the MoS2/semiconductor interface suggest a new route for fabrication of the transition metal dichalcogenide-based magnetic semiconductor multilayers for applications in spintronic devices.

Large PbS protruded cubes, edge- A nd corner-truncated cubes and octahedra, and perfect octahedra with sizes over 200 nm have been synthesized in aqueous solution. By using two surface oxide-free tungsten probes to contact a clean particle, these PbS nanocrystals displayed facet-dependent electrical conductivity behaviors. Both {110} and {100} faces are highly conductive at applied voltages beyond 4 V, but the {111} faces can remain nonconductive even at 5 V. An asymmetric I-V curve was recorded when electrical contacts were made simultaneously on the {110} and {111} facets of a truncated cube. A modified band diagram of PbS is constructed to account for the observed facet-dependent effect. Density of states plots for varying numbers of PbS surface planes show larger areas of conduction band electron occupancy for the (110) and (100) planes than that for the (111) planes at a layer thickness of 3.0-3.4 nm. The work represents that, for the first time, the facet-dependent electrical properties of an n-type semiconductor nanocrystal are directly probed. Facet-dependent electrical conductivity should be a general semiconductor property and can be exploited to fabricate single-nanocrystal operating electronic components.