Defects in ⅢNitrides Epilayers

【中文摘要】 采用光荧光和阴极荧光方法 ,对 Ga N外延层中的黄色和蓝色发光进行测量分析 ;同时 ,采用原子力显微镜、扫描电镜及其能谱测量外延层中的缺陷。结果表明 ,黄色和蓝色发光与残留杂质有关。采用第一原理计算结果显示 ,残留 C、O杂质、本征缺陷等是黄色和蓝色的可能物理起源。采用原子力显微镜、扫描电镜、透射电镜及其能谱对 Ga N/Al Ga N异质结中的纳米管进行观测 ,了解了纳米管的形貌。结果表明 ,构成纳米管的小面可能是外延过程中表面吸附引起的 ;计算结果显示 ,纳米管形貌变化与 Ga N/Al Ga N界面处晶格失配应力有关。采用透射电镜观察外延层中沉积物及其周围位错的结构表明 ,沉积物附近应力的存在是位错产生的主要原因 【英文摘要】 Blue and yellow luminescence bands in undoped GaN epilayers were investigated and related to main residual C and O impurities by photoluminescence, which are suggested to be attributable to the electron transitions from O N states to V Ga states and between the inner levels of the C N O N complex, respectively, according to ab initio local density functional calculations. Larger nanopipes in undoped GaN/AlGaN hetero epilayers were imaged as dodecagonal pyramidal indentations, using atomic fo...国家重点基础研究发展规划项目 (批准号 :001CB610505 );国家自然科学基金 (批准号 :69976023、90206030、10134030 );福建省自然 科学基金 (批准号 :A0020001);教育部部分资助项

Medium Optimization for Antitumor Agent Mycoepoxydiene by Marine Lignicolous Fungi Diaporthe sp.

从海洋木栖真菌HLY-2分离得到的真菌环氧二烯(Mycoepoxydiene)是新发现的高抗肿瘤活性化合物。通过正交设计,改良普通半海水PD培养基的配方,比较固体和液体两种发酵方法,得到了使该化合物产量大幅提高的最佳培养条件:在固体发酵条件下土豆250g/L,海水300mL/L,葡萄糖30g/L,乳糖50g/L,磷酸二氢钾0·65mmol/L,硫酸铵1g/L,产量高达543mg/L,比普通的PD培养基提高了43倍,也比液体发酵的最高产量提高了近15倍。同时还对固体发酵和液体发酵造成的产量差异进行了分析。并检验了发酵产物的抗肿瘤活性。Mycoepoxydiene is a novel antitumor agent extracted from marine lignicolous fungi HLY-2, which is Diaporthe phaseolorum by molecule identification. The medium optimization for mycoepoxydiene by orthogonal design and the comparison of submerged fermentation and solid state fermentation were studied. The rusult is that the maximal yield of the compound is 543mg/L, which is 43 times compared to the customary half-seawater PD medium and 15 times to the best submerged condition. This optimum culture medium included potato 250g/L, seawater 300mL/L, glucose 30g/L, lactose 50g/L, KH_ 2 PO_ 4 0.65mmol/L and (NH_ 4 )_ 2 SO_ 4 1g/L in the solid state condition. Differentiation analysis between submerged and solid state fermentation, and antitumor activity of these ferment products were also studied. The antitumor activity of products of the optimum medium approached the pure compound.国家自然科学基金资助项目(No.2003AA624010);; 福建省科技项目基金(No.2004N003);; 福建省自然科学基金(No.C0210001

Study on Electronic Structure of ZnS:Mn 2+

用自旋极化的LSD LMTO(Local Spin DensityLinearMuffin Tin OrbitalMethod)方法 ,对ZnS掺入Mn发光中心的电子结构进行了大型超原胞模拟计算。在自洽收敛的条件下 ,先对纯ZnS调节计算参数 (原子球、空球占空比 ) ,使计算的带隙Eg=3.2 3eV ;然后用原子球替代方式自洽计算杂质密度在Eg 中的相对位置 ,模拟计算了在六角结构ZnS中掺入不同浓度的Mn杂质后有关的杂质能级在Eg 中的相对位置。计算结果表明 :( 1 )单个缺陷的杂质能级性质与配位场理论结果相符合 ,直接用杂质态密度来表示 ;( 2 )掺入杂质的浓度对杂质能级位置的影响不大 ,这与实验结果相一致。The electronic structures of Mn 2+ luminescence centers in Mn-doped ZnS are studied by using first-principles linear muffin-tin-orbital method combining atomic sphere approximation.The calculated results for ZnS:Mn 2+ show that the property of impurity energy level for single bug satisfies the theory of crystal potential field,and the influence of impurity energy level caused by concentration of impurity is not evident,which is consistents with the experiment results.20 0 2年福建省教育厅科技项目 (JA0 2 2 6 2 );; 龙岩师范高等专科学校自然科学研究项目 (ZR3

Statistical Supercell Method for Calculating Electronic Structure of Che Mixed Crystals

【中文摘要】 提出了计算赝二元系(A_(1-x)C混晶材料任意组分电子结构的超原胞统计法,接替代格点数n选择超元胞,计算B原子数n_从零到n的所有超原胞电子结构为“样本”,结合以混晶键合性质决定的统计分布确定系统的电子结构,以(Ba_(1-x)K_)BiO_3为例,计算了x=0.2至x=0.5电子结构随组分的变化,结果表明,x>0.5的超元胞是不稳定的,费米面处总态密度TDOS(EF)随x变大而增加,与实验结果一致。 【英文摘要】 A new approach for calculating the electronic structrues of the binary alloys AnB1-n and pseudobinary alloys (AnB3-2 ).C in an any composition was prasenfod. In this method, the size of the supercell l is determined by the substituted lattice number n the electronic structure of zll sd-percells with its B atomic number from zero to n are calculated, then, the eletronic structure of miked system is determined by the statistical distribution which is rciated by the bonding properties of the mixed crystal. As ..

SELF-CONSISTENT BAND STRUCTURE, ELECTRONIC PRESSURE AND SUPERCONDUCTIVITY IN HCP-WC AND MON

【中文摘要】 本文基于局域密度泛函理论(LDF)和LMTO-ASA方法,计算了稳定的六角结构碳化钨和碳化钼的自洽能带结构,总态密度和分波态密度。在从头计算所得的理论参数基础上,研究了电子的总压力和分波压力,电子-离子相互作用常数η,电声子耦合常数λ和超导转变温度T_c。理论结果用实验的光发射谱和基态性质以及超导数据进行了验证。 【英文摘要】 The self-consistent band structure, total and partial density of states for the stable compounds hcp-WC and MoC are calculated by the LMTO-ASA method based on Kohn-Sham's LDF theory. On the basis of theoretical parameters obtained from our ab initio calculations, the total and partial electronic pressure, the electron-ion interaction constant η, electron- ph-onon coupling constant A and superconducting transion temperature Tc are studied. The theoretical results have been verified by both the experimental p...中国科学院科学基

LDF-LMTO Electronic Structure of YBa_2 Cu_3 O_7 System

【中文摘要】 本文用密度泛函理论和线性丸盒轨道方法计算了YBa_2Cu_3O_1系统的电子能带结构.结果表明有两个强2D特征的能带和一个1D特征的能带与Fermi面相交.它们分别对应于原胞中的两个准2D Cu-O平面和一个含有Cu-O线链的基平面上Cu 3d和O 2p态之间的相互作用.各原子分波态密度的分析表明,对电导和超导起决定作用的Cu-O平面和Cu-O线链中,2D Cu-O面对态密度的贡献是基本的. 【英文摘要】 The electronic band structure of the high Tc superconductor YBa2Cu3O7 system, has been calculated by using LDF-LMTO method. The results show that there are three bands of the 36 Cu(3d)-O(2p)bands complex crossing the Ferml energy. Among them are two 2D bands consisting of the states from Cu(2), O(2) and O(3), and one 1D band originating from Cu(1), O(4) and O(1) The calculated results of the partial density of states for all atoms indicate that the 2D Cu(2)-O(2)-O(3) Planes and 1D Cu(1)-O(4)-O(1) chain play...国家自然科学基

Ab initio calculation of the electronic structure of carbon and oxygen impurities in GaN

【中文摘要】 用局域密度泛函线性丸盒轨道大型超原胞方法 (32个原子 ) ,对纯纤锌矿结构的GaN用调节计算参数 (如原子球与“空球”的占空比 )在自洽条件下使Eg 的计算值 (3 2 3eV)接近实验值 (3 5eV) .然后以原子替代方式自洽计算杂质能级在Eg 中的相对位置 .模拟计算了六角结构GaN中自然缺陷以及与C和O有关的杂质能级位置 ,包括其复合物 .计算结果表明 ,单个缺陷如镓空位VGa、氮空位VN 、氧代替氮ON、炭代替氮CN、炭代替镓CGa等与已有的计算结果基本一致 .计算结果表明杂质复合物会导致单个杂质能级位置的相对变化 .计算了CN ON,CGa CN,CN OV 和CGa VGa,其中CN ON 分别具有深受主与浅施主的特征 ,是导致GaN黄光的一种可能的结构 . 【英文摘要】 Firstly we use the ab initio calculation with local density function-linear muffin tin orbital methods combined with a supercell(32atoms) to examine pure wurtzite GaN, and obtain the calculated E g value (3.23eV) for pure GaN close to that of experimental value by modifying the calculated parameter (for example, the proportion of atomic sphere and empty sphere). Then we examine the inpurity energy level by substituting the impurities for gallium or nitrogen or vacancy. We calculate the energy level of t...国家自然科学基金 (批准号 :69976023)资助的课

A SUPERCELL LDA-LMTO-ASA CALCULATION OF COMPOSI-TION DEPENDENCE OF HOPFIELD CONSTANT AND T_c IN Ba_(1-x)K_xBiO_3

【中文摘要】 用局域密度泛函线性丸盒轨道原子球近似(LDF-LMTO-ASA)超元胞法计算(Ba_(1-x)Kx)BiO_3特定组分x的电子结构,其中x=0.0,0.5,1.0三种组分由扩大1倍的元胞计算;x=0.25和0.75两种组分由扩大4倍的元胞计算,所得能带参数总态密度TDOS(E_F)、分波态密度PDOS(E_F)以及自洽晶体势V~ι(r),结合由实验测定的≈210K,按McMillan强耦合公式以及Gaspari-Gyorffy近似,分别计算各原子的Hopfield常数η_t,电声子耦合常数λ以及超导转变温度Tc随组分x的变化。计算结果λ≈1而Tc最大约10K,且随x变化缓慢。与实验结果对比似乎暗示,在(Ba_(1-x)K_x)BiO_3中除电声子机制外,随组分变化的复杂结构相变亦将起重要的作用。 【英文摘要】 The electronic structure of (Bal-xKr)BiO3 has been calculated by using a supercell LDA-LMTO-ASA method at some compositions. The calculation was performed by doubling unit-cell for x=0.25, 0.5 and 1.0 and by quadruple unit-cell for x = 0.25 and 0.75. The band parameters, total density of states TDOS (EF), partial DOS PDOS (EF) and self-consistent potential Vt(r), obtained from LMTO calculation were combined with the experimental Debye temperature D From this, the Hopfield constant ηt, electron-phonon coupli..

Self-consistent Band Structures and Superconductivity in B_1-WC and MoC

【中文摘要】 用Kohn—Sham局域密度泛函理论(LDF),原子球近似(ASA)和线性化丸盒轨道方法(LMTO)计算了具有以B_1结构的WC和MoC的自洽能带,总态密度(TDOS),分波态密度(PDOS)和不可约布里渊区的费米面。利用所得的参数(自洽晶体势,费米面处的总态密度与分波态密度),按McMillan强耦合超导理论及Gaspari—Gyorffy刚性离子近似,计算了WC和MoC的电子—离子相互作用常数η,电子质量增强因子λ和超导转变温度Tc。计算结果与实验值大致相符。 【英文摘要】 In this paper, the self-consistent band strncture, total and partial density of states and Fermi surface sections on symmetric planes of the IBZ for B1-WC and MoC are calculated by the LMTO-ASA method based on Kohn-Sham's LDF theory.On the basis of our band structure calculations (self-consistent potential and DOS at Fermi energy), the electron-ion interation constant η, electron-phonon coupling constant λ, and superconducting transition temperature To for these carbides are studied by using the McMillan's ...中国科学院科学基

A SUPERCELL CALCULATION OF ELECTRONIC STRUCTURE IN SUPERCONDUCTOR Ba_(1-x)K_xBiO_3 (x=0.25, 0.5 and 0.75)

【中文摘要】 用线性丸盒轨道原子球近似(LMTO-ASA)超元胞法计算(Ba_(1-x)Kx)BiO_3立方超导相x=0.25与x=0.5的电子结构,作为对照同时计算立方结构x=0.75的电子结构。计算结果表明,用超元胞法可以得到比“刚带近似”较精确的电子结构参数。给出Fermi面上的能带参数随组分的变化趋势。讨论了不等价的氧原子与周围金属原子价轨道的杂化特征。 【英文摘要】 Electronic structure for ordered Bal-xK3BiO3 alloys has been calculated with a supercell LMTO method. The results indicate that the band parameters obtained from this approach are more accurate than that from rigid-band approximation. The composition dependence of the band parameters at Fermi surface is given. The hybrid feature of the valence orbitals between the inequivalent oxygen and metal atoms is discussed