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Electric-Field Controlled Magnetism
Published in Evgeny Y. Tsymbal, Igor Žutić, Spintronics Handbook: Spin Transport and Magnetism, Second Edition, 2019
Fumihiro Matsukura, Hideo Ohno
In this subsection, we introduce the electric field modulation of TC of ferromagnetic semiconductors, mainly focusing on the experimental results obtained for III–V compounds. Typical ferromagnetic III–V semiconductors contain a relatively large amount of holes, ranging from 1019 to 1021 cm−3. Hence, the electric field screening length is the order of a nanometer, and thus most of experiments were done on thin films with several nanometers to observe sizable electric field effects.
III-Nitride Materials and Characterization
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Bo Shen, Ning Tang, XinQiang Wang, ZhiZhong Chen, FuJun Xu, XueLin Yang, TongJun Yu, JieJun Wu, ZhiXin Qin, WeiYing Wang, YuXia Feng, WeiKun Ge
Other effects arising from the QCSE are the occurrence of a Stokes shift and a decrease of the exciton binding energy, respectively. Berkowicz et al. [27], as shown in Figure 1.8, and Lefebvre et al. [30] have unambiguously shown that for a given indium concentration, emissions from InGaN/GaN QWs exhibit a Stokes shift increasing with well thickness. The reason for such an effect has to be found in the progressive decrease in the oscillator strength of the fundamental transition energy with increasing thickness/height due to the reduced overlap of electron and hole envelope wave functions in the triangular part of the confining potentials. A decrease of the exciton binding energy with increasing well width is a further signature of the QCSE. Above a certain width, the impact of the built-in electric field dominates over quantum confinement effects, which leads to a progressive separation of bound electron-hole pairs by the electric field screening the Coulomb interaction.
Principles and Basic Modes of Atomic Force Microscopy
Published in Cai Shen, Atomic Force Microscopy for Energy Research, 2022
Anyang Cui, Menghan Deng, Yan Ye, Xiang Wang, Zhigao Hu
Recently, we have attempted to employ piezoresponse force microscopy (PFM) in the conductive liquid to obtain high-resolution PFM phase and amplitude images. Nanoscale ferroelectric domain boundaries and domain pattern in air and the deionized (DI) water have been achieved on a lead (Pb)-based relaxor ferroelectric single crystal, as shown in Figure 1.20b–c. Imaging in a liquid environment can reduce the long-range electrostatic contributions, van der Waals forces, and has precise control tip-sample interaction.101–103 Knittel et al. have combined QNM and SECM modes (QNM-AFM-SECM), enabling to provide quantitative nanomechanical information along with electrochemical properties in electrolytes at the same time. QNM-AFM-SECM simultaneously obtained topographic data, Young’s modulus, and the current image of the fabricated soft gold microelectrode on the PDMS substrate, as shown in Figure 1.20d–f.104 Domanski et al. applied Kelvin probe force microscopy (KPFM) in electrically insulating nonpolar solvents to investigate the work function of a gold surface upon chemisorption of hexadecanethiol. The work function of SiOx/Au patterned substrates varied from each other as different adsorption processes were employed, as shown in Figure 1.20g–j.105 However, when a charged surface and tip is exposed to a polar liquid, due to the ionization or ion adsorption, electric double layer (EDL) would form near the solid-liquid interface. A model referred to the Gouy-Chapman-Stern (GCS) model has been proposed to describe the behavior of EDL. When two surfaces are close to each other, the EDL force caused by the EDLs interaction would lead to a reduced resolution for electrical imaging by SPM.85,106 Therefore, owing to the effect of EDL, an electric field screening effect has been proposed in the tip-sample junction, leading to a reduction of AFM resolution in conductive liquids.
Improving experimental procedures for assessing electrical properties of advanced liquid crystal materials
Published in Liquid Crystals, 2023
O. V. Kovalchuk, Anatoliy Glushchenko, Yuriy Garbovskiy
If nanomaterials are used to modify the properties of liquid crystals, a multi-electrode twin-cell can be considered for electrical and electro-optical measurements (Figures 5 and 6). Such cells driven by a DC electric field allow for a direct visualisation of the electric field screening effect. In addition, they simplify the correct comparison of the properties of plain and doped with nanoparticles liquid crystals, thus eliminating ambiguous conclusions and leading to a better understanding of the effects of nanomaterials on the properties of liquid crystals.