固态镓的电子结构

本文采用第一性原理分子动力学方法,在让原子得到充分弛豫后,计算了固体镓的电子结构。结果与实验相符合。通过计算总能随体积的变化,讨论了零温下固体镓的相稳定性。结果表明在α-Ga中,最近邻原子之间存在共价性从而导致电阻各向异性,而镓的其它相均为良好的金属。 关键词：     

GeS2-Ga2S3-KCl系统玻璃的拉曼光谱研究

对GeS2-Ga2S3-KCl准三元系统玻璃3个系列样品的室温拉曼谱进行了系统的探测和分析。根据准二元系统GeS2-KCl和Ga2S-KCl的熔融淬冷产物的观察和拉曼谱的分析，得出了在GeS2-Ga2S3-KCl系统玻璃中仅Ga2S和KCl发生了化学反应并产生了新结构单元GaS3/2Cl的结论。根据系列Ⅰ和Ⅲ拉曼谱的演变证实了引入的K^ 离子是以氯原子为最近邻配位且仅形成单壳层结构。根据K^ 离子对结构单元GaS3/2Cl和亚结构单元Ga2S4Cl2影响的分析，成功地解释了GeS2-Ga2S3-KCl准三元系统玻璃中的拉曼谱演变。     

碳纳米管中α-Ga和β-Ga纳米线相对稳定性的理论研究

采用密度泛函理论研究了碳纳米管中填充的金属镓纳米线的稳定性.结果表明,无论是在碳纳米管内的受限空间,还是在自由空间,较大尺寸的β-Ga纳米线都要比α-Ga纳米线稳定.通过对镓纳米线的平均能量和镓纳米线与碳纳米管间的结合能的分析,揭示了实验中观测到碳纳米管中金属镓会存在β-Ga相而无α-Ga相的物理原因. 关键词： 碳纳米管 纳米线 密度泛函理论     

Diffusion of an Extra Ga Atom in GaAs(001)(2*4) Rich-As Surface

采用键序势计算了单个镓原子在GaAs(001) fi2(2￡4)富砷表面的迁移的势能面,发现了一些低能量的吸附位,这些吸附位与实验观测的结果一致. 同时也发现了多个可能的迁移路径,并根据迁移路径上的相对能量指出单个镓原子更优先在表面上平行于砷二聚体的两条路径上迁移. 这一结果可由吸附的镓原子所导致的应变予以理解. 此外,有限温度下单个镓原子迁移的动力学模拟结果支持了所计算的势能面.     

Zn掺杂β-Ga2O3薄膜的制备和特性研究（英文）

β-Ga2O3是一种宽带隙半导体材料,能带宽度Eg≈5.0eV,在光学和光电子学领域有广泛的应用.用射频磁控溅射方法在Si衬底和远紫外光学石英玻璃衬底制备了本征β-Ga2O3薄膜及Zn掺杂β-Ga2O3薄膜,用紫外-可见分光光度计、X射线衍射仪、荧光分光光度计对本征β-Ga2O3薄膜及Zn掺杂β-Ga2O3薄膜的光学透过、光学吸收、结构和光致发光进行了测量,研究了Zn掺杂和热退火对薄膜结构和光学性质的影响.退火后的β-Ga2O3薄膜为多晶结构,与本征β-Ga2O3薄膜相比,Zn掺杂β-Ga2O3薄膜的β-Ga2O3(111)衍射峰强度变小,结晶性变差,衍射峰位从35.69°减小至35.66°.退火后的Zn掺杂β-Ga2O3薄膜的光学带隙变窄,光学透过降低,光学吸收增强,出现了近边吸收,薄膜的紫外、蓝光及绿光发射增强.表明退火后Zn掺杂β-Ga2O3薄膜中的Zn原子被激活充当受主.     

Ti_2B_n(n=1—10)团簇的结构与稳定性:基于从头算的研究

采用密度泛函理论中的B3LYP方法,结合从头算的CCSD(T)方法对Ti2B n(n=1—10)团簇的稳定性和电子性质进行了研究.发现两个Ti原子的掺杂导致B n团簇结构发生了根本性变化.随着n的增大,Ti2B n团簇结构生长非常规律.所有的最稳定结构都可看成双锥结构,并且两个Ti原子处在双锥结构的锥顶.根据二阶差分能量分析,得出Ti2B n(n=1—10)团簇的幻数是6,7和8.进一步分析了团簇的Ti原子解离能、B原子解离能以及团簇的电子亲和势和电离势.这些能量分析表明Ti2B6团簇既有良好的热力学稳定性,又有良好的动力学稳定性.应用前线轨道理论,对Ti原子与B6之间的成键进行了分析,了解其稳定性的根源.     

原子（分子）集团及其应用

原子(分予)集团可用符号（An)表示，其中A是形成集团的原子(或分子)，n为组成集团的原子或分子数。现有不少方怯可以形成原子(分子)集团，且原子或分子数是可变的，因而集团的大小可以从二聚体直到由上百万原子组成的微粒。研究表明，随着n的增加集团的物理和化学性质在不断变化。     

Bn (n=2-8)团簇结构和稳定性的密度泛函理论研究

本文采用密度泛函理论（DFT）中的B3LYP方法,在6－31G*水平上对Bn（n＝2－8）团簇的各种可能的几何构型和电子结构进行了优化和振动频率计算,得到了多个平衡构型。结果表明,Bn微团簇的稳定结构大部分为平面结构,只有极少数立体结构属于基态稳定结构。平面结构又分为链状和环状结构两种,链状结构的所有原子均处于同一平面,而且处于链状结构两端的键长稍短,原子向内部收缩。环状稳定结构都是一个n元环中心有一个配位的硼原子。通过对基态结构的平均原子结合能和能量二次差分的计算,得到n为奇数时团簇较为稳定。     

镓原子的Stark能级结构

里德堡原子的Stark效应在偶极偶极相互作用、量子信息和量子调控等方面具有潜在的应用前景. 本文首先根据零场时镓原子的能级数据, 通过非线性拟合方法获得了镓原子各态的量子亏损, 仔细分析了量子亏损随主量子数的变化特征; 然后利用Numerov算法计算了镓原子的径向波函数; 最后采用矩阵对角化方法, 数值计算了镓原子高里德堡态在场强范围F=0-3000 V·cm^{- 1}时n=7和n=18附近的Stark能级结构. 结果显示在主量子数n=7多重态以上的能级结构中, (n+1)P态的能级接近并大于nD态的能级, 在n=7多重态以下的能级结构中, (n+1)P态的能级接近并小于nD态的能级. 这一现象不同于通常的碱金属原子的Stark结构, 论文对该现象及其他Stark能级结构特征进行了详细分析, 为相关研究工作提供了重要参考价值.     

Bn (n=2-8)团簇结构和稳定性的密度泛函理论研究

本文采用密度泛函理论(DFT)中的B3LYP方法,在6-31G*水平上对Bn(n=2-8)团簇的各种可能的几何构型和电子结构进行了优化和振动频率计算,得到了多个平衡构型。结果表明,Bn微团簇的稳定结构大部分为平面结构,只有极少数立体结构属于基态稳定结构。平面结构又分为链状和环状结构两种,链状结构的所有原子均处于同一平面,而且处于链状结构两端的键长稍短,原子向内部收缩。环状稳定结构都是一个n元环中心有一个配位的硼原子,通过对基态结构的平均原子结合能和能量二次差分的计算,得到n为奇数时团簇较为稳定。     

"Magic melters" have geometrical origin

Recent experimental reports bring out extreme size sensitivity in the heat capacities of gallium and aluminum clusters. In the present work we report results of our extensive ab initio molecular dynamical simulations on Ga30 and Ga31, the pair which has shown rather dramatic size sensitivity. We trace the origin of this size sensitive heat capacities to the relative order in their respective ground state geometries. Such an effect of nature of the ground state on the characteristics of heat capacity is also seen in case of small gallium and sodium clusters, indicating that the observed size sensitivity is a generic feature of small clusters.     

Why do gallium clusters have a higher melting point than the bulk?

Density functional molecular dynamical simulations have been performed on Ga17 and Ga13 clusters to understand the recently observed higher-than-bulk melting temperatures in small gallium clusters [Phys. Rev. Lett. 91, 215508 (2003)]]. The specific-heat curve, calculated with the multiple-histogram technique, shows the melting temperature to be well above the bulk melting point of 303 K, viz., around 650 and 1400 K for Ga17 and Ga13, respectively. The higher-than-bulk melting temperatures are attributed mainly to the covalent bonding in these clusters, in contrast with the covalent-metallic bonding in the bulk.     

Hot and solid gallium clusters: too small to melt

A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for Ga(+)(n) (n=17 39, and 40) over a 90-720 K temperature range. For Ga+39 and Ga+40 a broad maximum in the heat capacity-a signature of a melting transition for a small cluster-occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for Ga+17.     

Spin-polarised DFT study of cobalt-doped gallium clusters

The structural, electronic and magnetic properties of small gallium clusters doped with Cobalt have been studied using spin-polarised density functional theory. The binding energy per atom, second-order differences of total energies and fragmentation energies of equilibrium geometries of the host Ga_n+1 and doped Ga_nCo (n = 1–12) clusters are computed. Doped clusters are found to be more stable than pure Ga clusters; Ga₃Co, Ga₅Co and Ga₈Co clusters are exceptionally stable. Doping with Co changes the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) gap, and also affects the magnetic moments of clusters.     

Structural analysis of xCsCl(1−x)Ga2S3 glasses by means of DFT calculations and Raman spectroscopy

The alkali metal halide doping of gallium‐sulfide glasses yields improvements in the optical, thermal and glass forming properties. To understand these improvements, the short‐range order of xCsCl(1 − x)Ga₂S₃ glasses was probed by Raman spectroscopy. Raman spectra have been interpreted using density functional theory (DFT) harmonic frequency calculations on specific clusters of GaS₄H₄ and/or GaS₃H₃Cl tetrahedral subunits. The assignment of the observed vibrational bands confirms the main structural conclusions obtained with X‐ray and neutron diffraction experiments and gives some new insights into the gallium‐network present in the xCsCl(1 − x)Ga₂S₃ glasses. At the lowest concentration, the observed spectrum may be interpreted with small clusters such as dimers and trimers connected by corner‐sharing (CS) GaS₄H₄ tetrahedral subunits. The vibrational fingerprints of tri‐clusters with three‐fold coordinated sulfur atoms have also been identified; however, no Raman signature of chlorine‐doped subunits has been found to be caused by their insufficient intensity. For higher CsCl concentrations, distinct spectral features corresponding to chlorine‐doped clusters appear and are increasing in intensity with x. In other words, undoped and Cl‐doped tetrahedra coexist in the xCsCl(1 − x)Ga₂S₃ glasses. The added chlorine atoms induce a fragmentation of the glass network and replace the sulfur atoms in the CS tetrahedral environment. The comparison of the observed spectra with theoretical predictions and diffraction data favoured one‐fold coordinated chlorine atoms in the glass network. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of silicon negative ion implantation in semi-insulating gallium arsenide

ABSTRACT

In the present work, effects of silicon negative ion implantation into semi-insulating gallium arsenide (GaAs) samples with fluences varying between 1?×?10¹⁵ and 4?×?10¹⁷?ions?cm^?2 at 100?keV have been described. Atomic force microscopic images obtained from samples implanted with fluence up to 1?×?10¹⁷?ion?cm^?2 showed the formation of GaAs clusters on the surface of the sample. The shape, size and density of these clusters were found to depend on ion fluence. Whereas sample implanted at higher fluence of 4?×?10¹⁷?ions?cm^?2 showed bump of arbitrary shapes due to cumulative effect of multiple silicon ion impact with GaAs on the same place. GXRD study revealed formation of silicon crystallites in the gallium arsenide sample after implantation. The silicon crystallite size estimated from the full width at half maxima of silicon (111) XRD peak using Debye-Scherrer formula was found to vary between 1.72 and 1.87?nm with respect to ion fluence. Hall measurement revealed the formation of n-type layer in gallium arsenide samples. The current–voltage measurement of the sample implanted with different fluences exhibited the diode like behavior.     

Electronic properties of cesium ultrathin coatings on the Ga-rich GaAs(100) surface

The cesium submonolayer coatings on the Ga-rich GaAs(100) surface at different coverages have been investigated by threshold photoemission spectroscopy. The electronic spectra of surface states and the ion-ization energies are analyzed. At a cesium coverage of about one-half the monolayer, the spectrum exhibits two narrow adsorption-induced bands below the Fermi level. This indicates that cesium atoms interacting with gallium dimers occupy two nonequivalent positions. It is found that the gallium broken bonds are saturated at the cesium coverage of ～0.7 monolayer, and the adsorption bonding is predominantly covalent in character. At the coverages close to the monolayer, broad bands with energies of 1.9, 2.05, and 2.4 eV have been observed for the first time. These bands can be associated with the excitation of cesium islands, cesium clusters, and surface cesium plasmon, respectively. The results obtained suggest two adsorption stages characterized by the formation of strong and weak bonds.     

Pade spectroscopy of structural correlation functions: Application to liquid gallium

We propose the new method of fluid structure investigation based on numerical analytic continuation of structural correlation functions with Pade approximants. The method particularly allows extracting hidden structural features of disordered condensed matter systems from experimental diffraction data. The method has been applied to investigate the local order of liquid gallium, which has a non-trivial structure in both the liquid and solid states. Processing the correlation functions obtained from molecular dynamic simulations, we show the method proposed reveals non-trivial structural features of liquid gallium such as the spectrum of length-scales and the existence of different types of local clusters in the liquid.     

Theoretical study on the composition dependence of Ga8−nAsn (n=0-8) clusters

Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the dependence of GaAs clusters with eight atoms on composition. It is found that the ground state structures for Ga-rich and As-rich clusters are cube structures. As the ratio between gallium atoms and arsenic atoms is close to one, structural distortion become increasingly severe, or even the clusters adopt other geometrical configurations as their ground state structures. The energy gap E_g between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO), and the vertical electron affinity show a certain degree of even/odd alternation with cluster composition. Among nine Ga_8−nAs_n (n=0-8) clusters, only a few of clusters have different energy orders between the ionic and neutral isomers with large binding energy. Some ionic structures would change into other configurations due to severe structural distortion.     

Liquid-metal field electron source based on porous GaP

We have reported on a new method for obtaining a liquid-metal field emitter. The treatment of a porous crystal of GaP binary semiconducting compound with high-voltage pulses in a vacuum has made it possible to obtain stable structures on its surface in the form of discrete gallium clusters. These structures exhibit high emission properties, including stable currents at a level of a few microamperes, as well as the high uniformity of the distribution of emission nanocenters over the surface.