砷的化学形态分析方法的研究

本论文由三部分组成。第一部分是天然水中痕量砷（III）和无机砷总量的测定。我们提出了用硼氢化钾片作还原剂，在柠檬酸铵介质中选择还原砷（III），在洒石酸介质中还原无机砷总量，还原生成的砷化氢与同时生成的氢气一起通过吸收液显色，再用分光光度计分别测定砷（III）和无机砷总量的分析方法，并且对几种天然水样进行了分析和标准加入加收试验。本方法具有较好的精密度和较高的灵敏度，砷（III）的检出限为0.16ppb，无机砷总量的检出限为0.36ppb，而且分析速度快，操作简便，易于推广。第二部分是无机砷和有机胂的分离与测定。我们选用砷（III）和砷（v-bar）代表无机砷，二甲基胂酸和苯基胂酸代表有机胂，利用氢氧化铁对无机砷和有机胂的共沉淀能力的差异分离无机砷和有机胂，再用高氯酸—硝酸消化有机胂，以分光光度法分别测定。通过对水、土壤，特别是药物样品的分析，并把分析结果与高氯酸—硝酸消化测定的总砷量进行比较表明，本方法确实具有很好的实用价值。该方法的建立对于一些含砷量高的药物建立除砷方法和砷对人体毒害机理的进一步研究具有重要的意义。第三部分是对氢氧化铁吸附砷机理的探讨。文中讨论了氢氧化铁吸附砷的机制，认为溶液中砷离子是与不同水解度的铁的羟基化合物形成了离子缔合物而被氢氧化铁共沉淀的。同时观察到，随着砷的形态不同，氢氧化铁对它们的吸附能力也不相同。通过比较几种氢氧化物对不同形态砷吸附能力的差异和氢氧根离子对吸附能力的影响等试验，初步证明，三价铁离子水解过程中的某些产物以及不同形态砷离子的空间构型的氢氧化铁吸附不同形态砷的能力解产生很大的影响。文中还通过实验，确定了氢氧化铁吸附砷（III）和砷（v-bar）的等温吸附经验公式中的常数，并对砷（III）和砷（v-bar）在氢氧化铁上的吸附速率作了比较和讨论。

稀磁半导体的研究进展

本文主要介绍了III-V族稀磁半导体(Ga,Mn)As的研究进展,包括(Ga,Mn)As的生长制备、基本磁性质、磁输运特征、磁光性质、磁性起源、相关的异质结构和自旋注入等,同时还简单介绍了其它稀磁半导体如IV族、III-VI族和IV-VI族等稀磁半导体的研究进展,在文章的最后描述了理想的稀磁半导体应该具备的特征以及对未来的展望。

（111）A InP衬底上MOCVD外延InGaAsP的表面形貌和光学特性

为了研究(111)衬底的特性以及实现等边三角形微腔激光器，利用金属有机化学气相淀积(MOCVD)研究了(111)A InP衬底上InGaAsP外延层的表面形貌和光学特性。考虑到(111)A InP衬底的悬挂键密度比较低，在生长过程中有意提高了V／III比。通过扫描电子显微镜(SEM)和光荧光(PL)谱分别研究了外延层的表面形貌和光学特性。实验发现，表面形貌和光学特性随V／III比和温度的变化非常大。最佳V／IlI比和温度分别为400和625℃。

同步辐射光电子能谱研究室温下Na对InP（100）表面氮化反应的影响

利用同步辐射光电子能谱研究了室温下Na吸附下于P型InP(100)表面对其氮化反应的影响,通过P2p、In 4d芯能级谱的变化,对Na/InP(100)表面的氮化反应的研究表明,碱金属Na的吸附对InP(100)无明显的催化氮化作用,即使采用N_2/Na/N_2/Na/N_2/Na/InP(100)的类多层结构,在室温下也只有极少量的氮化物形成,而无明显的催化氮化反应发生.碱金属吸附层对III-V族半导体氮化反应的催化机制不同于碱金属对于元素半导体的催化反应机制,碱金属对元素半导体的催化氮化反应,吸附的碱金属与元素半导体衬底之间无需界面反应发生,而碱金属吸附层和III-V族半导体衬底之间发生界面反应而形成的表面缺陷在III-V族半导体的催化氮化反应过程中具有重要的作用.

Effects of polarization field on formation of two-dimensional electron gas in (0001) and (11(2)over-bar0) plane AlGaN/GaN heterostructures

Photoluminescence (PL) and temperature-dependent Hall effect measurements were carried out in (0001) and (11 (2) over bar0) AlGaN/GaN heterostructures grown on sapphire substrates by metalorganic chemical vapor deposition. There are strong spontaneous and piezoelectric electric fields (SPF) along the growth orientation of the (0001) AlGaN/GaN heterostructures. At the same time there are no corresponding SPF along that of the (1120) AlGaN/GaN. A strong PL peak related to the recombination between two-dimensional electron gas (2DEG) and photoexcited holes was observed at 3.258 eV at room temperature in (0001) AlGaN/GaN heterointerfaces while no corresponding PL peak was observed in (11 (2) over bar0). The existence of a 2DEG was observed in (0001) AlGaN/GaN multi-layers with a mobility saturated at 6000 cm(2)/V s below 80 K, whereas a much lower mobility was measured in (11 (2) over bar0). These results indicated that the SPF was the main element to cause the high mobility and high sheet-electron-density 2DEG in AlGaN/GaN heterostructures. (C) 2004 Elsevier B.V. All rights reserved.

Orientation relationship between hexagonal inclusions and cubic GaN grown on GaAs(001) substrates

Cubic GaN/GaAs(0 0 1) epilayers and hexagonal inclusions are characterized by X-ray diffraction (XRD), Photoluminescence (PL), Raman spectroscopy, and transmission electron microscopy (TEM). The X-ray {0 0 0 2} and (1 0 (1) over bar 0) pole figures show that the orientation relationships between cubic GaN and hexagonal inclusions are (1 1 1)//(0 0 0 1), <1 1 2 >//<1 0 (1) over bar 0 >. The distribution of hexagonal inclusions mainly results from the interfacial bonding disorder in the grain boundaries parallel to hexagonal <0 0 0 1 > directions and the lattice mismatch in <0 0 0 1 > directions on {1 0 (1) over bar 0} planes. In order to reduce the energy increase in cubic epilayers, hexagonal lamellas with smaller sizes in <0 0 0 1 > directions often nucleate inside the buffer layer or near the interface between the buffer layer and the epitaxial layer, and penetrate through the whole epitaxial layer with this orientation relationship. (C) 2001 Elsevier Science B.V. All rights reserved.

Self-assembled quantum dots, wires and quantum-dot lasers

Molecular beam epitaxy-grown self-assembled In(Ga)As/GaAs and InAs/InAlAs/InP quantum dots (QDs) and quantum wires (QWRs) have been studied. By adjusting growth conditions, surprising alignment. preferential elongation, and pronounced sequential coalescence of dots and wires under specific condition are realized. The lateral ordering of QDs and the vertical anti-correlation of QWRs are theoretically discussed. Room-temperature (RT) continuous-wave (CW) lasing at the wavelength of 960 nm with output power of 3.6 W from both uncoated facets is achieved fi-om vertical coupled InAs/GaAs QDs ensemble. The RT threshold current density is 218 A/cm(2). A RT CW output power of 0.6 W/facet ensures at least 3570 h lasing (only drops 0.83 dB). (C) 2001 Elsevier Science B.V, All rights reserved.

The influence of growth temperature and input V/III ratio on the initial nucleation and material properties of InN on GaN by MOCVD

The effects of growth temperature and V/III ratio on the InN initial nucleation of islands on the GaN (0 0 0 1) surface were investigated. It is found that InN nuclei density increases with decreasing growth temperature between 375 and 525 degrees C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters of less than 100 nm, whereas at elevated temperatures the InN islands can grow larger and well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. At a given growth temperature of 500 degrees C, a controllable density and size of separated InN islands can be achieved by adjusting the V/III ratio. The larger islands lead to fewer defects when they are coalesced. Comparatively, the electrical properties of the films grown under higher V/III ratio are improved.

Effects of V/III ratio on InGaAs and InP grown at low temperature by LP-MOCVD

Effects of V/III ratio on heavily Si doped InGaAs and InP were studied using low pressure metalorganic chemical vapor deposition (LP-MOCVD) at a growth temperature of 550degreesC. In InGaAs, as the V/III ratio decreases from 256 to 64, the carrier concentration increases from 3.0 x 10(18) to 5.8 x 10(18) cm(-3), and the lattice mismatch of InGaAs to InP was observed to vary from -5.70 x10(-4) to 1.49 x 10(-3). In InP, when the V/III ratio decreases from 230 to 92, the same trend as that in Si doped InGaAs was observed that the carrier concentration increases from 9.2 x 10(18) to 1.3 x 10(19) cm(-3). The change of AsH3 was found to have stronger effect on Si incorporation in InGaAs at lower growth temperature than at higher growth temperature. (C) 2003 Elsevier B.V. All rights reserved.

Chemical trends of defect formation in Si quantum dots: The case of group-III and group-V dopants

Using first-principles methods, we have systematically calculated the defect formation energies and transition energy levels of group-III and group-V impurities doped in H passivated Si quantum dots (QDs) as functions of the QD size. The general chemical trends found in the QDs are similar to that found in bulk Si. We show that defect formation energy and transition energy level increase when the size of the QD decreases; thus, doping in small Si QDs becomes more difficult. B-Si has the lowest acceptor transition energy level, and it is more stable near the surface than at the center of the H passivated Si QD. On the other hand, P-Si has the smallest donor ionization energy, and it prefers to stay at the interior of the H passivated Si QD. We explained the general chemical trends and the dependence on the QD size in terms of the atomic chemical potentials and quantum confinement effects.

The influence of V/III ratio in the initial growth stage on the properties of GaN epilayer deposited on low temperature AlN buffer layer

The V/III ratio in the initial growth stage of metalorganic chemical vapor deposition has an important influence on the quality of a GaN epilayer grown on a low-temperature AIN buffer layer and c-plane sapphire substrate. A weaker yellow luminescence, a narrower half-width of the X-ray diffraction peak, and a higher electron mobility result when a lower V/III ratio is taken. The intensity of in situ optical reflectivity measurements indicates that the film surface is rougher at the beginning of GaN growth, and a longer time is needed for the islands to coalesce and for a quasi-two dimensional mode growth to start. A comparison of front- and back-illuminated photoluminescence spectra confirms that many threading dislocations are bent during the initial stage, leading to a better structural quality of the GaN layer. (C) 2007 Elsevier B.V. All rights reserved.

Hydrothermal synthesis and structure of a bi-capped Keggin polyoxoanion, [(As2AsMo8V4O40)-As-III-Mo-V-O-IV](5-)

The title compound, [NH3CH2CH2CH2NH2][NH3CH2CH2CH2NH3](2)[As-2(III) As-v Mo-8 V-4(IV) O-40] (.) 5H(2)O, was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Crystal data: monoclinic, C2/c, a = 45.375(9) Angstrom, b = 11.774(2) Angstrom, c = 23.438(5) Angstrom, beta = 96.62(3)degrees. X-ray crystallographic study showed that the crystal structure was constructed by bi-capped alpha -Keggin fragments [(As2AsMo8V4O40)-As-III-Mo-v-O-IV](5-) polyoxoanion. (C) 2001 Elsevier Science B.V. All rights reserved.