Piezo-photovoltaic Effect in Monolayer 2H-MoS2.

Noncentrosymmetric bulk materials effectively convert light energy into electricity by making use of the bulk photovoltaic effect (BPVE). However, whether such an effect persists when reducing the thickness of materials down to atomic-scale remains to be revealed. Here, we show the piezo-photovoltaic effect in atomically thin two-dimensional materials, where the strain-induced polarization can generate photovoltaic outputs in the noncentrosymmetric mono- and few-layer 2H-MoS2 crystals. The photocurrent is enhanced by orders of magnitude when the MoS2 crystals experience an in-plane strain of about 0.2%, with photopower-dependent responsivity up to 0.1 A/W that rivals other state-of-the-art BPVE materials. In addition, studies on the spatial distributions of photocurrents on MoS2 with a controlled number of layers also allow us to disentangle various factors that couple the piezoelectricity and photovoltaics. Therefore, our results also provide insights into the mechanisms of the piezo-photovoltaic effect in two-dimensional materials with thicknesses at the atomic-scale limit.

Angstrom-Scale Electrochemistry at Electrodes with Dimensions Commensurable and Smaller than Individual Reacting Species.

In nature and technologies, many chemical reactions occur at interfaces with dimensions approaching that of a single reacting species in nano- and angstrom-scale. Mechanisms governing reactions at this ultimately small spatial regime remain poorly explored because of challenges to controllably fabricate required devices and assess their performance in experiment. Here we report how efficiency of electrochemical reactions evolves for electrodes that range from just one atom in thickness to sizes comparable with and exceeding hydration diameters of reactant species. The electrodes are made by encapsulating graphene and its multilayers within insulating crystals so that only graphene edges remain exposed and partake in reactions. We find that limiting current densities characterizing electrochemical reactions exhibit a pronounced size effect if reactant's hydration diameter becomes commensurable with electrodes' thickness. An unexpected blockade effect is further revealed from electrodes smaller than reactants, where incoming reactants are blocked by those adsorbed temporarily at the atomically narrow interfaces. The demonstrated angstrom-scale electrochemistry offers a venue for studies of interfacial behaviors at the true molecular scale.

Seamlessly Splicing Metallic Sn x Mo1- x S2 at MoS2 Edge for Enhanced Photoelectrocatalytic Performance in Microreactor.

Accurate design of the 2D metal-semiconductor (M-S) heterostructure via the covalent combination of appropriate metallic and semiconducting materials is urgently needed for fabricating high-performance nanodevices and enhancing catalytic performance. Hence, the lateral epitaxial growth of M-S Sn x Mo1- x S2/MoS2 heterostructure is precisely prepared with in situ growth of metallic Sn x Mo1- x S2 by doping Sn atoms at semiconductor MoS2 edge via one-step chemical vapor deposition. The atomically sharp interface of this heterostructure exhibits clearly distinguished performance based on a series of characterizations. The oxygen evolution photoelectrocatalytic performance of the epitaxial M-S heterostructure is 2.5 times higher than that of pure MoS2 in microreactor, attributed to the efficient electron-hole separation and rapid charge transfer. This growth method provides a general strategy for fabricating seamless M-S lateral heterostructures by controllable doping heteroatoms. The M-S heterostructures show increased carrier migration rate and eliminated Fermi level pinning effect, contributing to their potential in devices and catalytic system.