Catálogo de publicaciones - revistas

<jats:p>Using first-principle calculations, we investigate the mechanical, structural, and electronic properties and formation energy of 25 kinds of <jats:italic>III</jats:italic>–<jats:italic>V</jats:italic> binary monolayers in detail. A relative radius of the binary compound according to the atomic number in the periodic table is defined, and based on the definition, the 25 kinds of <jats:italic>III</jats:italic>–<jats:italic>V</jats:italic> binary compounds are exactly located at a symmetric position in a symmetric matrix. The mechanical properties and band gaps are found to be very dependent on relative radius, while the effective mass of holes and electrons are found to be less dependent. A linear function between Young’s modulus and formation energy is fitted with a linear relation in this paper. The change regularity of physical properties of B–<jats:italic>V</jats:italic> (<jats:italic>V</jats:italic> = P, As, Sb, Bi) and <jats:italic>III</jats:italic>–N (<jats:inline-formula> <jats:tex-math><?CDATA ${III}=\mathrm{Al}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">III</mml:mi> <mml:mo>=</mml:mo> <mml:mi>Al</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_086105_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, Ga, In, Tl) are found to be very different from those of other <jats:italic>III</jats:italic>–<jats:italic>V</jats:italic> binary compounds.</jats:p>

<jats:p>CdTe is one of the leading materials for low cost, high efficiency thin-film solar cells with a nearly ideal band gap of 1.48 eV. However, its solar to electricity power conversion efficiency (PCE) is hindered by the relatively low open circuit voltage (<jats:italic>V</jats:italic> <jats:sub>OC</jats:sub>) due to intrinsic defect related issues. Here, we propose that alloying CdTe with CdSe could possibly improve the solar cell performance by reducing the “ideal” band gap of CdTe to gain more short-circuit current from long-wavelength absorption without sacrificing much <jats:italic>V</jats:italic> <jats:sub>OC</jats:sub>. Using the hybrid functional calculation, we find that the minimum band gap of the CdTe<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>Se<jats:sub> <jats:italic>x</jats:italic> </jats:sub> alloy can be reduced from 1.48 eV at <jats:italic>x</jats:italic> = 0 to 1.39 eV at <jats:inline-formula> <jats:tex-math><?CDATA $x=0.32$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>x</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.32</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_086106_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, and most of the change come from the lowering of the conduction band minimum. We also show that the formation of the alloy can improve the p-type doping of Cu<jats:sub>Cd</jats:sub> impurity based on the reduced effective formation energy and nearly constant effective transition energy level, thus possibly enhance <jats:italic>V</jats:italic> <jats:sub>OC</jats:sub>, thus PCE.</jats:p>

<jats:p>Surface charges can modify the elastic modulus of nanostructure, leading to the change of the phonon and thermal properties in semiconductor nanostructure. In this work, the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated. In the framework of continuum mechanics, the modified elastic modulus can be derived for the nanofilm with surface charges. The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation, phonon group velocity, density of states of phonons in nanofilm with the surface charges. The phonon thermal conductivity of nanofilm can be obtained by considering surface charges. The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm. Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons. The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm. Based on these theoretical results, one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.</jats:p>

<jats:p>A measurement scheme for detecting the <jats:italic>α</jats:italic> relaxation time (<jats:italic>τ</jats:italic>) of glass-forming liquid is proposed, which is based on the measured ionic conductivity of the liquid doped with probing ions by low- and middle-frequency dielectric spectroscopy and according to the Nernst–Einstein, Stokes–Einstein, and Maxwell equations. The obtained <jats:italic>τ</jats:italic> values of glycerol and propylene carbonate by the scheme are consistent with those obtained by traditional dielectric spectroscopy, which confirms its reliability and accuracy. Moreover, the <jats:italic>τ</jats:italic> of 1,2-propanediol in a larger temperature range is compared with existing data.</jats:p>

<jats:p>In this study, we present an organic field-effect transistor floating-gate memory using polysilicon (poly-Si) as a charge trapping layer. The memory device is fabricated on a N<jats:sup>+</jats:sup>–Si/SiO<jats:sub>2</jats:sub> substrate. Poly-Si, polymethylmethacrylate, and pentacene are used as a floating-gate layer, tunneling layer, and active layer, respectively. The device shows bidirectional storage characteristics under the action of programming/erasing (P/E) operation due to the supplied electrons and holes in the channel and the bidirectional charge trapping characteristic of the poly-Si floating-gate. The carrier mobility and switching current ratio (<jats:italic>I</jats:italic> <jats:sub>on</jats:sub>/<jats:italic>I</jats:italic> <jats:sub>off</jats:sub> ratio) of the device with a tunneling layer thickness of 85 nm are <jats:inline-formula> <jats:tex-math><?CDATA $0.01\,{\mathrm{cm}}^{2}\cdot {{\rm{V}}}^{-1}\cdot {{\rm{s}}}^{-1}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.01</mml:mn> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>·</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">V</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mo>·</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_086801_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and 10<jats:sup>2</jats:sup>, respectively. A large memory window of 9.28 V can be obtained under a P/E voltage of ±60 V.</jats:p>

<jats:p>A strict universal method of calculating the electronic structure of condensed matter from the Hartree–Fock equation is proposed. It is based on a partial differential equation (PDE) strictly equivalent to the Hartree–Fock equation, which is an integral–differential equation of fermion single-body wavefunctions. Although the maximum order of the differential operator in the Hartree–Fock equation is 2, the mathematical property of its integral kernel function can warrant the equation to be strictly equivalent to a 4th-order nonlinear partial differential equation of fermion single-body wavefunctions. This allows the electronic structure calculation to eliminate empirical and random choices of the starting trial wavefunction (which is inevitable for achieving rapid convergence with respect to iterative times, in the iterative method of studying integral–differential equations), and strictly relates the electronic structure to the space boundary conditions of the single-body wavefunction.</jats:p>

<jats:p>Topological materials have novel properties both in their bulk and boundaries, thereby attracting a wide interest in the theoretical and experimental communities. The recent development of the topological quantum chemistry and symmetry-based indicator theory in this field has significantly simplified the procedure for determining the topological properties of nonmagnetic crystalline materials. Accordingly, a large number of new topological materials have been found by scanning large crystal databases. This study provides details on the algorithm used in the Catalogue of Topological Electronic Materials. Moreover, based on the algorithm, we develop an automatic package named SymTopo, which calculates the symmetry representations of any given nonmagnetic crystalline material and predicts its topological properties. This package may facilitate the discovery of more topological materials in the future.</jats:p>

<jats:p>The exciton dynamics in a WS<jats:sub>2</jats:sub> monolayer with strain are studied by transient absorption measurements. We measure the differential transmission signal from monolayer WS<jats:sub>2</jats:sub> as a function of the probe wavelength at different levels of strain applied to the sample. The differential transmission spectrum has a positive maximum value at about 614 nm and shows no significant strain dependence. By time-resolving the differential transmission signal, we find that the strain has a minimal effect on the exciton formation process. However, the exciton lifetime is significantly reduced by strain. These results provide useful information for applications of WS<jats:sub>2</jats:sub> in flexible electronic and optoelectronic devices where strain is inevitable.</jats:p>

<jats:p>With the increasing interest in Cu<jats:sub>2</jats:sub>O-based devices for photovoltaic applications, the energy band alignment at the Cu<jats:sub>2</jats:sub>O/ZnO heterojunction has received more and more attention. In this work, a high-quality Cu<jats:sub>2</jats:sub>O/ZnO heterojunction is fabricated on a <jats:italic>c</jats:italic>-Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> substrate by laser-molecular beam epitaxy, and the energy band alignment is determined by x-ray photoelectron spectroscopy. The valence band of ZnO is found to be 1.97 eV below that of Cu<jats:sub>2</jats:sub>O. A type-II band alignment exists at the Cu<jats:sub>2</jats:sub>O/ZnO heterojunction with a resulting conduction band offset of 0.77 eV, which is especially favorable for enhancing the efficiency of Cu<jats:sub>2</jats:sub>O/ZnO solar cells.</jats:p>