Dielectric and conduction mechanism studies of PVA-orthophosphoric acid polymer electrolyte

Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The conductivity is observed to increase from 10⁻⁹ to 10⁻⁴ S cm⁻¹ as a result of orthophosphoric acid (H₃PO₄) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt% H₃PO₄. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H₃PO₄ is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity σ _ac = Aω ^s was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph of s vs T from which the conduction mechanism for sample PVA-17 wt% H₃PO₄ was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the sample PVA-33 wt% H₃PO₄ by way of the correlated barrier height (CBH) model.     

Fluid simulation of the pulsed bias effect on inductively coupled nitrogen discharges for low-voltage plasma immersion ion implantation

Planar radio frequency inductively coupled plasmas(ICP) are employed for low-voltage ion implantation processes,with capacitive pulse biasing of the substrate for modulation of the ion energy. In this work, a two-dimensional(2D) selfconsistent fluid model has been employed to investigate the influence of the pulsed bias power on the nitrogen plasmas for various bias voltages and pulse frequencies. The results indicate that the plasma density as well as the inductive power density increase significantly when the bias voltage varies from 0 V to-4000 V, due to the heating of the capacitive field caused by the bias power. The N+fraction increases rapidly to a maximum at the beginning of the power-on time, and then it decreases and reaches the steady state at the end of the glow period. Moreover, it increases with the bias voltage during the power-on time, whereas the N_2~+ fraction exhibits a reverse behavior. When the pulse frequency increases to 25 kHz and40 kHz, the plasma steady state cannot be obtained, and a rapid decrease of the ion density at the substrate surface at the beginning of the glow period is observed.     

Carbon-nanodot-coverage-dependent photocatalytic performance of carbon nanodot/TiO_2 nanocomposites under visible light

Carbon nanodots(CDs) with visible absorption band and TiO_2 are integrated to enhance the photosensitivity of TiO_2.The CD/TiO_2 nanocomposites show obvious CD-coverage-dependent photocatalytic performance. The CD/TiO_2 nanocomposites with moderate CD coverge exhibit the highest photocatalytic activity after being irradiated with visible light, which is more excellent than that of TiO_2. Too little CD coverage could result in poor visible light absorption, which limits the photocatalytic performance of CD/TiO_2 nanocomposites. While, too much CD coverage weakens the photocatalytic activity of CD/TiO_2 nanocomposites by restraining the extraction of conduction band electrons within TiO_2 to generate active oxygen radicals and the electron transfer(ET) process from CDs to TiO_2. These results indicate that rational regulation of CD coverage and the realization of efficient ET process are important means to optimize the photocatalytic performance of CD/TiO_2 nanocomposites.     

Degradation behavior of electrical properties of GaInAs (1.0 eV) and GaInAs (0.7 eV) sub-cells of IMM4J solar cells under1-MeV electron irradiation

In this work the degradation effects of the Ga_(0.7)In_(0.3)As(1.0 eV) and Ga_(0.42)In_(0.58)As(0.7 eV) sub-cells for IMM4J solar cells are investigated after 1-MeV electron irradiation by using spectral response and photoluminescence(PL) signal amplitude analysis, as well as electrical property measurements. The results show that, compared with the electrical properties of traditional single junction(SJ) GaAs(1.41 eV) solar cell, the electrical properties(such as Isc, Voc, and Pmax)of the newly sub-cells degrade similarly as a function of log ?, where ? represents the electron fluence. It is found that the degradation of Voc is much more than that of Isc in the irradiated Ga_(0.42)In_(0.58)As(0.7 eV) cells due to the additional intrinsic layer, leading to more serious damage to the space charge region. However, of the three types of SJ cells with the gap widths of 0.7, 1.0, and 1.4 eV, the electric properties of the Ga_(0.7)In_(0.3)As(1.0 eV) cell decrease largest under each irradiation fluence. Analysis on the spectral response indicates that the Jsc of the Ga_(0.7)In_(0.3)As(1.0 eV) cell also shows the most severe damage. The PL amplitude measurements qualitatively confirm that the degradation of the effective minority carrier life-time(τeff) in the SJ Ga_(0.7)In_(0.3)As cells is more drastic than that of SJ GaAs cells during the irradiation. Thus,the output current of Ga_(0.7)In_(0.3)As sub-cell should be controlled in the irradiated IMM4J cells.     

Mechanical,elastic, anisotropy,and electronic properties of monoclinic phase of m-Si_xGe_(3-x)N_4

The structural,mechanical,elastic anisotropic,and electronic properties of the monoclinic phase of m-Si_3N_4,mSi_2GeN_4,m-SiGe_2N_4,and m-Ge_3N_4are systematically investigated in this work.The calculated results of lattice parameters,elastic constants and elastic moduli of m-Si_3N_4and m-Ge_3N_4are in good agreement with previous theoretical results.Using the Voigt–Reuss–Hill method,elastic properties such as bulk modulus B and shear modulus G are investigated.The calculated ratio of B/G and Poisson’s ratio v show that only m-SiGe_2N_4should belong to a ductile material in nature.In addition,m-SiGe_2N_4possesses the largest anisotropic shear modulus,Young’s modulus,Poisson’s ratio,and percentage of elastic anisotropies for bulk modulus ABand shear modulus AG,and universal anisotropic index AUamong m-Si_xGe_(3-x)N_4(x=0,1,2,3.)The results of electronic band gap reveal that m-Si_3N_4,m-Si_2GeN_4,m-SiGe_2N_4,and m-Ge_3N_4 are all direct and wide band gap semiconducting materials.     

大尺度有效引力的E(2)规范理论模型

微波背景辐射的低l极矩的各向异性可能不能用微波背景辐射静止系boost到本动参考系来解释,我们推断boost对称性在宇宙学尺度上缺失,又由于单纯结合广义相对论和物质结构的标准模型不能解释星系以上尺度的引力现象,需要引入暗物质和暗能量.而迄今为止所有寻找暗物质粒子的实验给出的都是否定结果,暗能量的本质更是一个谜.因此,我们假设洛伦兹对称性是从星系以上尺度开始部分破缺,以非常狭义相对论对称群E(2)为例,用E(2)规范理论来构造大尺度有效引力理论,并分析了此规范理论的自洽性.从这些讨论中发现,当物质源即使为普通标量物质时,contortion也一般非零,非零contortion的存在会贡献一个等效能量动量张量的分布,它可能对暗物质效应给出至少部分的贡献.我们从对称性出发修改引力,有别于其他的修改引力理论.     

六角星形MoSe_2双层纳米片的制备及其光致发光性能

采用化学气相沉积法,以三氧化钼作为钼源,硒粉作为硒源,在H_2/Ar气氛下生长出硒化钼纳米片.扫描电镜、X射线衍射表征结果表明,MoSe_2产物呈六角星状,横向尺寸约10μm,具有很好的晶体质量和结构.拉曼光谱表征其结构,确定其为双层纳米片.研究表明,高温反应时间对双层纳米片的生长具有重要的影响.通过对双层纳米片的生长机理的探究,推测其经历了3个生长过程:在高温下,Mo源和Se源被气化成气态分子并发生硒化反应形成晶核;晶核呈三角形外延生长;当反应时间持续增加,在空间位阻效应的影响下,晶体以中心原子岛为核,外延耦合生长出第二层三角形,最终形成六角星状双层纳米片.光致发光光谱结果表明,六角星状MoSe_2双层纳米片在1.53 eV处具有直接带隙和1.78 eV处具有间接带隙,其较宽范围的激发光谱响应预测其在光电探测器件领域具有潜在的应用前景.     

吸附氢分子的振动态及熵的计算

用第一性原理方法研究了H_2在(MgO)_9及(AlN)_(12)团簇上的吸附态、振动模式及熵.分析表明,吸附体系的振动中有六个简正模式可归为氢分子的振动;由于氢分子质量很小,零点能修正对吸附能有重要影响.利用振动配分函数计算了吸附氢分子的熵,表明吸附态H_2的熵主要决定于较低的同相振动的频率,并不完全与吸附强度相关;在标准大气压下70—350 K的温度范围内,吸附H_2的熵与气态H_2的熵之间存在很好的线性关系,吸附后H_2的熵减小约10.2R.     

2D/3D CFETR真空室电磁计算

基于ANSYS对CFETR真空室简化模型进行了2D/3D电磁分析,得到了真空室磁场强度以及电磁力的分布。分析结果显示2D/3D真空室的磁场强度及电磁力分布基本一致,这表明了可以使用2D模型替代3D模型对未来真空室简化模型进行电磁分析。     

An Improved Upper Bound on the Linear 2-arboricity of 1-planar Graphs

The linear 2-arboricity la_2(G) of a graph G is the least integer k such that G can be partitioned into k edge-disjoint forests,whose component trees are paths of length at most 2.In this paper,we prove that if G is a 1-planar graph with maximum degree Δ,then la_2(G)≤[(Δ+1)/2]+7.This improves a known result of Liu et al.(2019) that every 1-planar graph G has la_2(G)≤[(Δ+1)/2]+14.We also observe that there exists a 7-regular 1-planar graph G such that la_2(G)=6=[(Δ+1)/2]+2,which implies that our solution is within 6 from optimal.