L. L. Li

A Self‐Charging Power Unit by Integration of a Textile Triboelectric Nanogenerator and a Flexible Lithium‐Ion Battery for Wearable Electronics

A novel integrated power unit realizes both energy harvesting and energy storage by a textile triboelectric nanogenerator (TENG)-cloth and a flexible lithium-ion battery (LIB) belt, respectively. The mechanical energy of daily human motion is converted into electricity by the TENG-cloth, sustaining the energy of the LIB belt to power wearable smart electronics.

Wearable Self‐Charging Power Textile Based on Flexible Yarn Supercapacitors and Fabric Nanogenerators

A novel and scalable self-charging power textile is realized by combining yarn supercapacitors and fabric triboelectric nanogenerators as energy-harvesting devices.

Freestanding Flag-Type Triboelectric Nanogenerator for Harvesting High-Altitude Wind Energy from Arbitrary Directions

Wind energy at a high altitude is far more stable and stronger than that near the ground, but it is out of reach of the wind turbine. Herein, we develop an innovative freestanding woven triboelectric nanogenerator flag (WTENG-flag) that can harvest high-altitude wind energy from arbitrary directions. The wind-driven fluttering of the woven unit leads to the current generation by a coupled effect of contact electrification and electrostatic induction. Systematic study is conducted to optimize the structure/material parameters of the WTENG-flag to improve the power output. This 2D WTENG-flag can also be stacked in parallel connections in many layers for a linearly increased output. Finally, a self-powered high-altitude platform with temperature/humidity sensing/telecommunicating capability is demonstrated with the WTENG-flag as a power source. Due to the light weight, low cost, and easy scale-up, this WTENG-flag has great potential for applications in weather/environmental sensing/monitoring systems.

Piezotronic Effect in Polarity-Controlled GaN Nanowires.

Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.

Piezo-Phototronic Effect Controlled Dual-Channel Visible light Communication (PVLC) Using InGaN/GaN Multiquantum Well Nanopillars

Visible light communication (VLC) simultaneously provides illumination and communication via light emitting diodes (LEDs). Keeping a low bit error rate is essential to communication quality, and holding a stable brightness level is pivotal for illumination function. For the first time, a piezo-phototronic effect controlled visible light communication (PVLC) system based on InGaN/GaN multiquantum wells nanopillars is demonstrated, in which the information is coded by mechanical straining. This approach of force coding is also instrumental to avoid LED blinks, which has less impact on illumination and is much safer to eyes than electrical on/off VLC. The two-channel transmission mode of the system here shows great superiority in error self-validation and error self-elimination in comparison to VLC. This two-channel PVLC system provides a suitable way to carry out noncontact, reliable communication under complex circumstances.

Enhanced thermoelectric performance of nanostructured topological insulator Bi2Se3

To enhance thermoelectric performance by utilizing topological properties of topological insulators has attracted increasing attention. Here, we show that as grain size decreases from microns to ∼80 nm in thickness, the electron mobility μ increases steeply from 12–15 cm2 V−1 s−1 to ∼600 cm2 V−1 s−1, owing to the contribution of increased topologically protected conducting surfaces. Simultaneously, its lattice thermal conductivity is lowered by ∼30%–50% due to enhanced phonon scattering from the increased grain boundaries. As a result, thermoelectric figure of merit, ZT, of all the fine-grained samples is improved. Specifically, a maximum value of ZT = ∼0.63 is achieved for Bi2Se3 at T = ∼570 K.

Band hybridization and spin-splitting in InAs/AlSb/GaSb type II and broken-gap quantum wells

We present a detailed theoretical study on the features of band hybridization and zero-field spin-splitting in InAs/AlSb/GaSb quantum wells (QWs). An eight-band k⋅p approach is developed to calculate the electronic subband structure in such structures. In the absence of the AlSb layer, the hybridized energy gaps can be observed at the anticrossing points between the lowest electron subband and the highest heavy-hole subband in the InAs and GaSb layers respectively. In such a case, the position and magnitude of the gaps are spin-dependent. When a thin AlSb layer is inserted between the InAs and GaSb layers, we find that the lowest electron subband in the InAs layer is only hybridized with the highest light-hole subband which is also hybridized with the highest heavy-hole subband in the GaSb layer. The hybridized energy gaps and spin-splitting in the InAs/AlSb/GaSb QWs are reduced significantly. These results can be used to understand why electrons and holes can be well separated and why relatively high mob...

Electric- and magnetic-field dependence of the electronic and optical properties of phosphorene quantum dots

Recently, black phosphorus quantum dots were fabricated experimentally. Motivated by these experiments, we theoretically investigate the electronic and optical properties of rectangular phosphorene quantum dots (RPQDs) in the presence of an in-plane electric field and a perpendicular magnetic field. The energy spectra and wave functions of RPQDs are obtained numerically using the tight-binding approach. We find edge states within the band gap of the RPQD which are well separated from the bulk states. In an undoped RPQD and for in-plane polarized light, due to the presence of well-defined edge states, we find three types of optical transitions which are between the bulk states, between the edge and bulk states, and between the edge states. The electric and magnetic fields influence the bulk-to-bulk, edge-to-bulk, and edge-to-edge transitions differently due to the different responses of bulk and edge states to these fields.

Midinfrared absorption by InAs/GaSb type-II superlattices

We present a systematic theoretical study on optical properties of short-period InAs/GaSb type-II superlattices (SLs) which can serve for midinfrared (MIR) detection. Using the standard Kronig–Penney model we calculate the miniband structure of such SLs. The obtained band-gap energies are in line with those realized experimentally. On the basis of the energy-balance equation derived from the Boltzmann equation we develop a simple approach to calculate the optical absorption coefficient for the corresponding SL systems. Our results agree with recent experimental findings. Moreover, the dependence of MIR absorption in InAs/GaSb type-II SLs on temperature and well width are examined. This study is pertinent to the application of InAs/GaSb type-II SLs as MIR photodetectors working in the ambient condition.

Electronic properties of bilayer phosphorene quantum dots in the presence of perpendicular electric and magnetic fields

Using the tight-binding approach, we investigate the electronic properties of bilayer phosphorene (BLP) quantum dots (QDs) in the presence of perpendicular electric and magnetic fields. Since BLP consists of two coupled phosphorene layers, it is of interest to examine the layer-dependent electronic properties of BLP QDs, such as the electronic distributions over the two layers and the so-produced layer-polarization features, and to see how these properties are affected by the magnetic field and the bias potential. We find that in the absence of a bias potential only edge states are layer-polarized while the bulk states are not, and the layer-polarization degree (LPD) of the unbiased edge states increases with increasing magnetic field. However, in the presence of a bias potential both the edge and bulk states are layer-polarized, and the LPD of the bulk (edge) states depends strongly (weakly) on the interplay of the bias potential and the interlayer coupling. At high magnetic fields, applying a bias potential renders the bulk electrons in a BLP QD to be mainly distributed over the top or bottom layer, resulting in layer-polarized bulk Landau levels (LLs). In the presence of a large bias potential that can drive a semiconductor-to-semimetal transition in BLP, these bulk LLs exhibit different magnetic-field dependences, i.e., the zeroth LLs exhibit a linear-like dependence on the magnetic field while the other LLs exhibit a square-root-like dependence.