四元硫化物Cu2Zn(Ti,Zr, Hf)S4:一类新颖光伏材料

采用第一性原理电子结构方法研究了四价过渡金属Ti, Zr和Hf替代Cu₂ZnSnS₄(CZTS)中Sn原子以及Se替代S原子所得到的四元硫族化合物的电子结构、光学性质和晶体结构的稳定性. 实验上用Se替代CZTS中部分S得到的Cu₂ZnSnS_4-xSe_x(CZTSSe)作为光吸收材料, 可以进一步提高光伏效率. 我们计算表明用Se替代S后, CZTSe的价带顶明显下移, 并接近Cu(In, Ga) Se₂ (CIGS)价带顶位置. 与CZTSe的电子结构特征一样, Cu₂Zn(Ti, Zr, Hf)S₄四元硫化物的价带顶与母体材料CZTS相比也向低能移动, 并接近CIGS价带顶位置. 由于高光伏效率要求窗口材料ZnO、缓冲层材料和光吸收材料的价带顶和带隙满足一定的渐进的变化关系, 因此可以预见用Cu₂Zn(Ti, Zr, Hf)S₄作光吸收材料可以有效地提高甚至接近CIGS的光伏效率. 通过计算弹性常数和声子谱, 以及有限温度下第一性原理分子动力学模拟, 发现Cu₂Zn(Ti, Zr, Hf)S₄的结构稳定性与CZTS相近. 进一步计算Cu₂Zn(Ti, Zr, Hf)S₄与不同缓冲层间和窗口材料与缓冲层间的反射系数, 并讨论了ZnSe, In₂S₃, ZnS作为缓冲层材料和TiO₂作为窗口材料对光伏效率可能的影响.     

Multifaceted asymmetric radiation from the edge along improved confinement mode in LHCD plasmas with graphite limiters on HT-7 tokamak

Multifaceted asymmetric radiation from the edge (MARFE) phenomena during lower hybrid current drive (LHCD) Experiments on the HT-7 superconducting tokamak are summarized in this paper. The best correlation has been found between the total input (ohmic + LHCD) power and the product of the edge line average density and Z _eff. Studies show that the critical density of MARFE onset is observed in the region of Z _eff ^1/2f_GW = 0.6-0.9, where , (here is the maximum line average electron density and n_GW is the Greenwald density). These MARFEs generally appear to have the same characteristics as high f_GW MARFEs and are positionally stable throughout the LHCD pulse. Improved confinement mode induced by a MARFE is observed, and it is maintained for about 65 ms. MARFE cools the plasma edge, and the electron density profile is observed to become more narrow and peaked.     

退火对Hf_(1-x)Y_(x)O_(2 )体系的结构与磁性的影响

利用溶胶凝胶法制备不同掺杂浓度的Hf_(1-x)Y_(x)O_(2 )(α=0,0.07,0.3,0.5)系列样品,探究了不同退火时间对样品的结构、形貌、磁学性质的影响.X射线衍射分析表明,随着掺杂浓度的提高,样品从单斜相逐渐转变为立方相.掺杂浓度为=0.07的样品为单斜和立方的混合相,且随着退火时间的延长,单斜相的比例逐渐增加.扫描电子显微镜结果表明,样品为几十微米大小的不规则颗粒,不同退火时间对样品形貌无显著影响.磁性测量结果表明,掺杂样品在室温下具有铁磁特性,而且可以利用掺杂浓度和退火时长进行调控.我们认为Hf_(1-x)Y_(x)O_(2 )体系的室温铁磁性可能与Y掺杂导致的样品内氧空位及缺陷有关.     

The electrical, optical and magnetic properties of Si-doped ZnO films

In this paper, the influences of Si-doping on electrical, optical and magnetic properties of ZnO films have been systematically investigated. It is found that the resistivity of the films decreases from 3.0 × 10³ to 6.2 × 10^-2 Ωcm with Si-doping due to the increase of carrier concentration. The bandgap of ZnO films increases from 3.28 to 3.52 eV with increasing of Si concentration, which is found to be due to the collective effects of bandgap narrowing and Burstein-Moss effect induced by high carrier concentration. With increase of Si concentration, the near band edge (NBE) emission decreases due to the deterioration of crystal quality, while the yellow emission enhances due to the increase of extrinsic impurity or defects. The additional Si-doping has a profound influence on the enhancement of magnetic property and the maximum magnetic moment of 2.6 μ_B/Si is obtained. The ferromagnetic ordering is seen to be correlated with carrier concentration and structural defects.     

Anyonic order parameters for discrete gauge theories on the lattice

We present a new family of gauge invariant non-local order parameters for (non-abelian) discrete gauge theories on a Euclidean lattice, which are in one-to-one correspondence with the excitation spectrum that follows from the representation theory of the quantum double D(H) of the finite group H. These combine magnetic flux-sector labeled by a conjugacy class with an electric representation of the centralizer subgroup that commutes with the flux. In particular, cases like the trivial class for magnetic flux, or the trivial irrep for electric charge, these order parameters reduce to the familiar Wilson and the ’t Hooft operators, respectively. It is pointed out that these novel operators are crucial for probing the phase structure of a class of discrete lattice models we define, using Monte Carlo simulations.     

Effect of deposition parameters on structural, optical and electrical properties of nanocrystalline ZnSe thin films

This paper presents the chemical bath deposition of zinc selenide (n-ZnSe) nanocrystalline thin films on non-conducting glass substrates, in an aqueous alkaline medium using sodium selenosulphate as Se²⁻ ion source. The X-ray diffraction studies show that the deposited ZnSe material is nanocrystalline with a mixture of hexagonal and cubic phase. The direct optical band gap ‘E_g’ for the as-deposited n-ZnSe films is found to be 3.5 eV. TEM studies show that the ZnSe nanocrystals (NCs) are spherical in shape. Formation of ZnSe has been confirmed with the help of infrared (IR) spectroscopy by observing bands corresponding to the multiphonon absorption. We demonstrate the effect of the deposition temperature and reactant concentration on the structural, optical and electrical properties of ZnSe films.     

Gd2Hf2O7∶Ce纳米粒子表观活化能对发光性能影响

采用正、反向共沉淀法制备了掺杂Ce的Gd2Hf2O7纳米粒子,用XRD、SEM、TG-DTA和荧光分度计等测试手段分析了物相形貌及发光性能;在不同升温速率条件下由热力学计算了样品的表观活化能.结果表明:两种滴定法得到的前躯体分别经煅烧物相变化同为3个阶段,由Doyel-Ozawa法和Kissinger法计算取两者的平均值得到各阶段的表观活化能分别是48.18 kJ· mol-1、80.35 kJ·mol-1、285.7 kJ·mol-1和39.18 kJ· mol-1、64.3 kJ·mol-1、277.82 kJ·mol-1,晶粒生长活化能是29.61 kJ·mol-1和22.61 kJ·mol-1.后者样品分别在567 nm波长下的激发光谱和450 nm波长处发射光谱的相对发光强度优于前者,可见纳米粒子的活化能越小对发光离子的能级跃迁起到促进作用.     

Thermal unparticles: a new form of energy density in the universe

An unparticle with scaling dimension has peculiar thermal properties due to its unique phase space structure. We find that the equation of state parameter , the ratio of pressure to energy density, is given by providing a new form of energy in our universe. In an expanding universe, the unparticle energy density evolves dramatically differently from that for photons. For , even if at a high decoupling temperature T _D is very small, it is possible to have a large relic density at present photon temperature T _γ ⁰, large enough to play the role of dark matter. We calculate T _D and using photon–unparticle interactions for illustration.     

Surface energy evaluation of unhydrogenated DLC thin film deposited by thermionic vacuum arc (TVA) method

The aim of this paper is concerned with the surface energy evaluation by contact angle measurements of DLC films deposited by thermionic vacuum arc (TVA) on different substrates: glass plate, zinc foil, stainless steel and alumina foil. TVA is an original method based on a combination of the evaporation by electron bombardment and anodic arc. The evaluation of the surface free energy has been carried out by surface energy evaluation system (SEE System). The influence of the experimental conditions is also investigated.     

Photorefractive features of non‐stoichiometry codoped Hf:Fe:LiNbO3 single crystals

Hf(2mol%):Fe(0.05wt%):LiNbO₃ crystals with various [Li]/[Nb] ratios of 0.94, 1.05, 1.2 and 1.38 have been grown. The photorefractive resistant ability increases with the accretion of [Li]/[Nb] ratio. When the ratio of [Li]/[Nb] is 1.20 or 1.38, the OH^‐ absorption band shifts to about 3477cm^‐1. The mechanisms of the photorefractive resistant ability increase and the absorption band shift have been discussed. The exponential gain coefficient (Γ) of the crystals was measured with two‐beam coupling method and the effective charge carrier concentration (N_eff) was calculated. The results show that Γ and N_eff increase with the accretion of [Li]/[Nb] ratio. The temperature effect of codoped Hf:Fe:LiNbO₃ crystals was also studied, it was found that the exponential gain coefficient increase dramatically at about 55°C, 70°C and 110°C, this is due to the inner electric field which is resulted from structure phase change. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)