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<jats:p>GaAs multiple concentric nano-ring structures (CNRs) are prepared with multistep crystallization procedures by droplets epitaxy on GaAs (001) to explore the influence of different initial crystallization temperatures on CNRs morphology. Atomic force microscope (AFM) images show that GaAs nanostructures are more likely to form elliptical rings due to diffusion anisotropy. Meanwhile, with the increase of initial crystallization temperature, the inner ring height and density of CNRs are increased, and outer rings are harder to form. In addition, the mechanism of formation of CNRs is discussed by classical nucleation theory and diffusion theory. The method can be used to calculate the diffusion activation energy of gallium atoms (0.7±0.1 eV) on the GaAs (001) surface conveniently.</jats:p>

<jats:p>A coarse-grained molecular dynamics simulation model was developed in this study to investigate the friction process occurring between Fe and polytetrafluoroethylene (PTFE). We investigated the effect of an external load on the friction coefficient of Fe–PTFE using the molecular dynamics simulations and experimental methods. The simulation results show that the friction coefficient decreases with the external load increasing, which is in a good agreement with the experimental results. The high external load could result in a larger contact area between the Fe and PTFE layers, severer springback as a consequence of the deformed PTFE molecules, and faster motion of the PTFE molecules, thereby affecting the friction force and normal force during friction and consequently varying the friction coefficient.</jats:p>

<jats:p>Structural, elastic, electronic and optical properties of the Pt<jats:sub>3</jats:sub>Zr intermetallic compound are investigated using first principles calculations based on the density functional theory (DFT) within the generalized gradient approximation (GGA) and the local density approximation (LDA). The Pt<jats:sub>3</jats:sub>Zr compound is predicted to be of cubic L1<jats:sub>2</jats:sub> and hexagonal D0<jats:sub>24</jats:sub> structures. The calculated equilibrium ground-state properties (lattice parameters <jats:italic>a</jats:italic> and <jats:italic>c</jats:italic>, bulk modulus <jats:italic>B</jats:italic> and its pressure derivative <jats:italic>B</jats:italic>′, formation enthalpy Δ<jats:italic>H</jats:italic>) of the Pt<jats:sub>3</jats:sub>Zr compound, for both cubic and hexagonal phases, show good agreement with the experimental results and other theoretical data. Elastic constants (<jats:italic>C</jats:italic> <jats:sub>11</jats:sub>, <jats:italic>C</jats:italic> <jats:sub>12</jats:sub>, <jats:italic>C</jats:italic> <jats:sub>13</jats:sub>, <jats:italic>C</jats:italic> <jats:sub>33</jats:sub>, <jats:italic>C</jats:italic> <jats:sub>44</jats:sub>, and <jats:italic>C</jats:italic> <jats:sub>55</jats:sub>) are calculated. The predicted elastic properties such as Young’s modulus <jats:italic>E</jats:italic> and shear modulus <jats:italic>G</jats:italic> <jats:sub>H</jats:sub>, Poisson ratio <jats:italic>ν</jats:italic>, anisotropic ratio <jats:italic>A</jats:italic>, Kleinman parameter <jats:italic>ξ</jats:italic>, Cauchy pressure (<jats:italic>C</jats:italic> <jats:sub>12</jats:sub>−<jats:italic>C</jats:italic> <jats:sub>44</jats:sub>), ratios <jats:italic>B</jats:italic>/<jats:italic>C</jats:italic> <jats:sub>44</jats:sub> and <jats:italic>B</jats:italic>/<jats:italic>G</jats:italic>, and Vickers hardness <jats:italic>H</jats:italic> <jats:sub>v</jats:sub> indicate the stiffness, hardness and ductility of the compound. Thermal characteristic parameters such as Debye temperature <jats:italic>θ</jats:italic> <jats:sub>D</jats:sub> and melting temperature <jats:italic>T</jats:italic> <jats:sub>m</jats:sub> are computed. Electronic properties such as density of states (DOS) and electronic specific heat <jats:italic>γ</jats:italic> are also reported. The calculated results reveal that the Fermi level is on the psedogap for the D024 structure and on the antibonding side for the L12 structure. The optical property functions (real part <jats:italic>ε</jats:italic> <jats:sub>1</jats:sub>(<jats:italic>ω</jats:italic>) and imaginary part <jats:italic>ε</jats:italic> <jats:sub>2</jats:sub>(<jats:italic>ω</jats:italic>) of dielectric function), optical conductivity <jats:italic>σ</jats:italic>(<jats:italic>ω</jats:italic>), refraction index <jats:italic>n</jats:italic>(<jats:italic>ω</jats:italic>), reflectivity <jats:italic>R</jats:italic>(<jats:italic>ω</jats:italic>), absorption <jats:italic>α</jats:italic>(<jats:italic>ω</jats:italic>) and extinction coefficients <jats:italic>k</jats:italic>(<jats:italic>ω</jats:italic>) and loss function <jats:italic>L</jats:italic>(<jats:italic>ω</jats:italic>)) are also investigated for the first time for Pt<jats:sub>3</jats:sub>Zr in a large gamme of energy from 0 to 70 eV.</jats:p>

<jats:p>An analytical drain current model on the basis of the surface potential is proposed for indium–gallium zinc oxide (InGaZnO) thin-film transistors (TFTs) with an independent dual-gate (IDG) structure. For a unified expression of carriers’ distribution for the sub-threshold region and the conduction region, the concept of equivalent flat-band voltage and the Lambert <jats:italic>W</jats:italic> function are introduced to solve the Poisson equation, and to derive the potential distribution of the active layer. In addition, the regional integration approach is used to develop a compact analytical current–voltage model. Although only two fitting parameters are required, a good agreement is obtained between the calculated results by the proposed model and the simulation results by TCAD. The proposed current–voltage model is then implemented by using Verilog-A for SPICE simulations of a dual-gate InGaZnO TFT integrated inverter circuit.</jats:p>

<jats:p>The effects of uniaxial tensile strain on the structural and electronic properties of positively charged oxygen vacancy defects in amorphous silica (a-SiO<jats:sub>2</jats:sub>) are systematically investigated using <jats:italic>ab-initio</jats:italic> calculation based on density functional theory. Four types of positively charged oxygen vacancy defects, namely the dimer, unpuckered, and puckered four-fold (4 ×), and puckered five-fold (5 ×) configurations have been investigated. It is shown by the calculations that applying uniaxial tensile strain can lead to irreversible transitions of defect structures, which can be identified from the fluctuations of the curves of relative total energy versus strain. Driven by strain, a positively charged dimer configuration may relax into a puckered 5× configuration, and an unpuckered configuration may relax into either a puckered 4× configuration or a forward-oriented configuration. Accordingly, the Fermi contacts of the defects remarkably increase and the defect levels shift under strain. The Fermi contacts of the puckered configurations also increase under strain to the values close to that of <jats:inline-formula> <jats:tex-math><?CDATA ${E}_{\alpha }^{\prime}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>α</mml:mi> <mml:mo>′</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_4_047103_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> center in a-SiO<jats:sub>2</jats:sub>. In addition, it is shown by the calculations that the relaxation channels of the puckered configurations after electron recombination are sensitive to strain, that is, those configurations are more likely to relax into a two-fold coordinated Si structure or to hold a puckered structure under strain, both of which may raise up the thermodynamic charge-state transition levels of the defects into Si band gap. As strain induces more puckered configurations with the transition levels in Si band gap, it may facilitate directly the development of oxide charge accumulation and indirectly that of interface charge accumulation by promoting proton generation under ionization radiation. This work sheds a light on understanding the strain effect on ionization damage at an atomic scale.</jats:p>

<jats:p>The etch-stop structure including the <jats:italic>in-situ</jats:italic> SiN and AlGaN/GaN barrier is proposed for high frequency applications. The etch-stop process is realized by placing an <jats:italic>in-situ</jats:italic> SiN layer on the top of the thin AlGaN barrier. F-based etching can be self-terminated after removing SiN, leaving the AlGaN barrier in the gate region. With this <jats:italic>in-situ</jats:italic> SiN and thin barrier etch-stop structure, the short channel effect can be suppressed, meanwhile achieving highly precisely controlled and low damage etching process. The device shows a maximum drain current of 1022 mA/mm, a peak transconductance of 459 mS/mm, and a maximum oscillation frequency (<jats:italic>f</jats:italic> <jats:sub>max</jats:sub>) of 248 GHz.</jats:p>

<jats:p>Floquet engineering appears as a new protocol for designing topological states of matter, and features anomalous edge modes pinned at quasi-energy <jats:italic>π</jats:italic>/<jats:italic>T</jats:italic> with vanished topological index. We propose how to predict the anomalous edge modes via the bulk Hamiltonian in frequency space, and use Zak phase to quantitatively index the topological properties. The above methods are clarified by the example of time periodic Kitaev chain with chemical potential of harmonic driving and pulse driving, and topological phase transitions are manifested at different driving frequencies.</jats:p>

<jats:p>Hydrodynamic calculations of the chaotic behaviors in n<jats:sup>+</jats:sup>nn<jats:sup>+</jats:sup> In<jats:sub>0.53</jats:sub>Ga<jats:sub>0.47</jats:sub>As devices biased in terahertz (THz) electric field have been carried out. Their different transport characteristics have been carefully investigated by tuning the n-region parameters and the applied ac radiation. The oscillatory mode is found to transit between synchronization and chaos, as verified by the first return map. The transitions result from the mixture of the dc induced oscillation and the one driven by the ac radiation. Our findings will give further and thorough understanding of electron transport in In<jats:sub>0.53</jats:sub>Ga<jats:sub>0.47</jats:sub>As terahertz oscillator, which is a promising solid-state THz source.</jats:p>

<jats:p>The effect of AlGaN interlayer in quantum barrier on the electroluminescence characteristics of GaN-based green light emitting diodes (LEDs) grown on silicon substrate was investigated. The results show that AlGaN interlayer is beneficial to improve the luminous efficiency of LED devices and restrain the phase separation of InGaN. The former is ascribed to the inserted AlGaN layers can play a key role in determining the carrier distribution and screening dislocations in the active region, and the latter is attributed to the increased compressive stress in the quantum well. However, when the electrical stress aging tests were performed at a current density of 100 A/cm<jats:sup>2</jats:sup>, LED devices with AlGaN interlayers are more likely to induce the generation/proliferation of defects in the active region under the effect of electrical stress, resulting in the reduced light output power at low current density.</jats:p>

<jats:p>We investigate the instability of threshold voltage in D-mode MIS-HEMT with <jats:italic>in-situ</jats:italic> SiN as gate dielectric under different negative gate stresses. The complex non-monotonic evolution of threshold voltage under the negative stress and during the recovery process is induced by the combination effect of two mechanisms. The effect of trapping behavior of interface state at SiN/AlGaN interface and the effect of zener traps in AlGaN barrier layer on the threshold voltage instability are opposite to each other. The threshold voltage shifts negatively under the negative stress due to the detrapping of the electrons at SiN/AlGaN interface, and shifts positively due to zener trapping in AlGaN barrier layer. As the stress is removed, the threshold voltage shifts positively for the retrapping of interface states and negatively for the thermal detrapping in AlGaN. However, it is the trapping behavior in the AlGaN rather than the interface state that results in the change of transconductance in the D-mode MIS-HEMT.</jats:p>