The 2D InSe/WS_2 Heterostructure with Enhanced Optoelectronic Performance in the Visible Region

Two-dimensional(2D)InSe and WS_2 exhibit promising characteristics for optoelectronic applications.However,they both have poor absorption of visible light due to wide bandgaps:2D InSe has high electron mobility but low hole mobility,while 2D WS_2 is on the contrary.We propose a 2D heterostructure composed of their monolayers as a solution to both problems.Our first-principles calculations show that the heterostructure has a type-Ⅱband alignment as expected.Consequently,the bandgap of the heterostructure is reduced to 2.19 eV,which is much smaller than those of the monolayers.The reduction in bandgap leads to a considerable enhancement of the visible-light absorption,such as about fivefold(threefold)increase in comparison to monolayer InSe(WS_2)at the wavelength of 490 nm.Meanwhile,the type-Ⅱ band alignment also facilitates the spatial separation of photogenerated electron-hole pairs;i.e.,electrons(holes)reside preferably in the InSe(WS_2)layer.As a result,the two layers complement each other in carrier mobilities of the heterostructure:the photogenerated electrons and holes inherit the large mobilities from the InSe and WS_2 monolayers,respectively.     

First-Principles Study on Native Defect Complexes in InN

We present first-principles calculations of the formation energy of different native defects and their complexes in wurtzite InN using density-functional theory and the pseudopotential plane-wave method. Our calculations are aimed in the three cases： N/In = 1, N/In 〉 1 （N-rich）, and N/In 〈 1 （In-rich）. Our results indicate that the antisite defect has the lowest formation energy under N/In = 1. The formation energy of nitrogen interstitial （nitrogen vacancy） defect is significantly low under the N-rich （In-rich） condition. Thus the antisite defect is an important defect if N/In = 1, and the nitrogen interstitial （nitrogen vacancy） defect is a vital defect under the N-rich （In-rich） condition. The atomic site relaxation around the nitrogen interstitial and vacancy is investigated. Our calculations show that the nitrogen vacancy cannot be observed although it is one of the most important defects in InN. Our results are confirmed by experiments.     

OPTICAL-PHONON MODES AND ELECTRON-OPTICAL-PHONON INTERACTION IN A COUPLED QUANTUM WELL

By applying the dielectric continuum model, optical-phonon modes of the lattice vibration and a complete interaction Frohlich-like Harniltonian between an electron and the optical phonons including the interface phonons, the confined LO phonons and the half-space LO phonons are derived for a general coupled quantum well (GCQW) structure of polar crystals. The dispersion curves of the interface modes and the electron-interface-phonon coupling function as functions of coordinate z and wavenumber k are given and discussed for a GCQW. We find that there are eight (not ten) frequency solutions for the interface optical-phonon modes in GCQW and that, in the long-wavelength limit, the longitudinal and transverse modes in the two side materials 1 and 5 are forbidden and two new frequency solutions ω± are obtained instead. Moreover, we also find that the electron-interface-phonon coupling functions are complicated functions of k and that the phonons with long wavelengths are important and the higher-frequency modes are more important than the lower-frequency modes for the electron-phonon interaction.     

功能高分子微球研究分散聚合法合成μ级聚苯乙烯微球

微米级聚苯乙烯微球广泛用于临床分析、生物医学、胶体研究等领城,亦可作为电子显微镜、光散射、沉降法等测定微小物体绝对长度的基准物、色谱柱填料等。用分散聚合法可以制得微米级单分散聚苯乙烯微球。本文通过对分散聚合条件和配方的研究,以水和醇为分散介质,分子量4000的聚乙二醇为稳定剂,过氧化苯甲酰为引发剂,合成了粒径为3至4μm的单分散聚苯乙烯微球。在分散聚合体系中,随着有机溶剂、单体、引发剂等用量的增加,胶乳粒径增大,粒径分布变宽。随着稳定剂、表面张力调节剂等用量的增加,胶乳粒径减小,粒径分布变窄。有机溶剂种类改变以及聚合反应温度变化,胶乳粒径也发生变化。     

磷系阻燃剂插层镁铝型水滑石复合物的制备及其在热塑性聚氨酯中的阻燃应用

采用直接的无溶剂制备方法,将3种磷系阻燃剂9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)、聚磷酸铵(APP)和三聚氰胺聚磷酸盐(MPP)分别插层到镁铝型水滑石(MAH)片层中,制备了3种含磷阻燃剂的MAH复合物(DOPO-MAH、APP-MAH和MPP-MAH),并采用模压成型法制备了MAH复合物与热塑性聚氨酯(TPU)的复合材料。采用X射线衍射、扫描电子显微镜和热重分析分别对复合物进行了表征,并且通过锥形量热仪对复合材料进行了表征。结果表明,MAH中MPP的分散性较差,DOPO和APP的分散性较好,并且磷元素分布均匀。MAH的初始层间距为4.11 nm,APP和MPP均在0.5 h时就已完成插层,最终层间距分别缩小到3.93和4.04 nm。DOPO则在0.5 h后完成,但插层后的层间距更小,为3.86 nm。与物理混合物所制得的复合材料相比,(DOPO-MAH-6h)/TPU和(APP-MAH-6h)/TPU的热释放速率峰值分别从669.3 kW/m²降至573.9 kW/m²,从657.7 kW/m²     

Ground state of excitons in quantum-dot quantum-well nanoparticles： stochastic variational method

Within the framework of effective mass approximation, the ground state of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles is solved by using the stochastic variational method, in which the finite band offset and the heavy (light) hole exciton states are considered. The calculated 1s_e－1s_h transition energies for the chosen CdS/HgS/CdS QDQW samples are in good agreement with the experimental measurements. Moreover, some previous theoretical results are improved.     

Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

The electronic structure and magnetic properties of the transition-metal(TM) atoms(Sc–Zn, Pt and Au) doped zigzag GaN single-walled nanotubes(NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Codoped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it.     

Enlargement of Photonic Band Gaps and Physical Picture of Photonic Band Structures

Light propagation in a one-dimensional photonic crystal （PC）, consisting of alternative slabs with refractive indices （layer thicknesses） nl （a） and n2 （b）, is investigated. An important optimal parameter matching condition, n1a ≈ n2b, is obtained for the largest photonic band gap （PBG）. Moreover, we find that the exact analytical solutions for the electric/magnetic field eigenmodes at the band edges are standing waves with odd or even symmetry about the centre of each layer. The electric/magnetic field eigenfunctions at the top and bottom of the nth band have n and n - 1 nodes in one period of PC, respectively. The PBG arises from the symmetric differences of the field eigenfunctions at the band edges.