Flexoelectronics of centrosymmetric semiconductors

Piezophototronic Effect in Nanosensors

“…Recently, Wang and co‐workers reported the flexoelectronic effect in bulk centrosymmetric semiconductors such as Si, TiO 2 , and Nb–SrTiO 3 to achieve to obtain nanosensors with high strain sensitivity (>2650). [ 105 ] The principle of flexoelectronic effect is similar to the piezophototronic effect, which uses the polarization potential near the metal–semiconductor interface as the gate voltage to effectively control the Schottky barrier at the interface, thus controlling the carrier transport characteristics at the interface. Different from piezophototronic effect, the flexure polarization caused by local nonuniform strain not only exists on the surface of the material but also distributes inside the materials over a range of lengths or volumes.…”

Nanoscale Ferroelectric Characterization with Heterodyne Megasonic Piezoresponse Force Microscopy

“…Since the sample and tip modifications are almost inevitable during the contactmode PFM scanning, by far researchers can only have very limited solutions to reduce such effects, such as decreasing the setpoint of force feedback, using softer cantilever and mapping with a point-by-point manner (23,30,31). In addition to the modifications, the tip-sample contact force usually causes a significant stress field in the sample, which can potentially induce a remarkable flexoelectric polarization (32)(33)(34) and affect the ferroelectric polarization switching (35,36). Furthermore, as there is a contact area formed at the tip-sample junction which contains a large number of interactional atoms, the contact-mode operation fundamentally limits the spatial resolution of PFM to the best of sub-10 nanometers (7,15,37), and a higher spatial resolution, such as the molecular or atomic resolution, can hardly be achieved in conventional PFM.…”

Controllable, Self‐Powered, and High‐Performance Short‐Wavelength Infrared Photodetector Driven by Coupled Flexoelectricity and Strain Effect

“…The point-induced spatially distributed qualitative strain in silicon along xz-plane (z-axis is the applied force direction) is shown in Figure 1a, which was calculated using Hertzian contact theory with an approximation of a hemispherical shape tip. [1,6] The detail of the strain and its gradient calculation has been provided in the Section S1 and Figure S1 (Supporting Information). Interestingly, applied localized force with a pointed tip (diameter ≈120 µm) induces long-range (≈960 µm) distributed (over volume) inhomogeneous strain.…”

“…[1,5] Importantly, strain gradient is the key to the flexoelectric effect; however, applied strain, in principle, will also modulate the electronic structure, which in turn could introduce conceptually innovative and till "forbidden" functionalities. [1,4,6] For instance, applied strain-induced broken crystal symmetry modify the effective masses of charge carriers, which leads to generating a pronounced shift in the effective bandgap of semiconductors, like silicon, TiO 2 , and others. [7][8][9] In fact, theoretically, it has been predicted that the fundamental bandgap of the silicon could be shrunk considerably (up to 1800 nm, e.g., short-wavelength infrared) with strain engineering.…”