Generation of electric current is observed when GaAs nanowires with wurtzite crystal structure are bent by the probe of an atomic force microscope. The current originates from a piezo active phase in the nanowires due to the piezoelectric effect. Increasing of the piezo-potential in bent nanowires enhances tunneling through the probe-nanowire Schottky barrier due to the thermionic field emission. Laser illumination amplifies short-circuit current pulses by two orders of magnitude from 9 pA to 1 nA due to the piezo-phototronic effect. Utilization of such piezo-phototronic effect in GaAs nanowires is a solution to accelerate the efficiency of hybrid energy sources "piezoelectric nanogenerator À solar cell" comprised of III-V nanowires.

Strain engineering is a powerful tool for tuning physical properties of 2D materials, including monolayer transition metal dichalcogenides (TMD) -direct bandgap semiconductors with strong excitonic response. Here, we demonstrate an approach for local characterization of strain-induced modification of excitonic photoluminescence in TMD-based materials. We reversibly stress a monolayer of MoSe 2 with an AFM tip and perform spatio-spectral mapping of the excitonic photoluminescence in the vicinity of the indentation point. To fully reproduce the experimental data, we introduce the linear dependence of the exciton energy and corresponding photoluminescence intensity on the induced strain. Careful account for the optical resolution allows extracting these quantities with good agreement with the previous measurements, which involved macroscopic sample deformation. Our approach is a powerful tool for the study of local optomechanical properties of 2D direct bandgap semiconductors with strong excitonic response.

Flexible optoelectronic structures are required in a wide range of applications. Large scale modified silicone-embedded n-GaP nanowire arrays of a record 6 µm thin membranes were studied. A homogeneous silicone encapsulation was enabled by G-coating using a heavy-load centrifuge. The synthesized graft-copolymers of polydimethylsiloxane (PDMS) and polystyrene demonstrated two times lower adhesion to Si compared to standard PDMS, allowing 3 square inch area high quality silicone/nanowire membrane mechanical release, preserving the growth Si substrate for a further re-use after chemical cleaning. The 90% transparent single-walled carbon nanotubes electrical contacts to the embedded n-GaP nanowires demonstrated mechanical and electrical stability. The presented methods can be used for the fabrication of large scale flexible inorganic optoelectronic devices.

Harvesting hybrid mechanical and solar ambient energy with one small device remains a challenge. Here, we report on producing electric current using a Schottky type metal-oxide-semiconductor structure formed by an n-InP layer covered with native oxide and an atomic force microscope (AFM) probe with a conductive coating. The tip’s sliding reciprocating motion during AFM scanning in contact mode produces a direct current signal in the probe-sample circuit. Two electric power generation mechanisms exist. A strong current was detected under sample illumination because of a photovoltaic effect with efficiency of 7% at the Si/InP heterojunction. Having the sample set in complete darkness, we observed current pulses of the opposite polarity, which suggests the existence of another mechanism not connected to photogeneration. This dark current originates from the tunneling of triboelectrically induced charge redistribution on the metal/oxide interface. The current polarity corresponds to electronic quantum mechanical tunneling through the oxide layer from the metal tip into InP. The current density exceeded 15 kA/m2. This is 2 and more than 4 orders greater than that in silicon- and polymer-based triboelectric nanogenerators, respectively. The open-circuit voltage value was 15 mV, and output electric power reached 110 W/m2. Understanding of triboelectric phenomena in photovoltaic semiconductor materials will allow creation of a new type of high-current hybrid energy devices that combine triboelectric nanogenerators and solar cells.