Energy band and acceptor binding energy of GaN and AlxGa1-xN

The hole effective-mass Hamiltonian for the semiconductors of wurtzite structure is established, and the effective-mass parameters of GaN and AlxGa1-xN are given. Besides the asymmetry in the z and x, y directions, the linear term of the momentum operator in the Hamiltonian is essential in determining the valence band structure, which is different from that of the zinc-blende structure. The binding energies of acceptor states are calculated by solving strictly the effective-mass equations. The binding energies of donor and acceptor for wurtzite GaN are 20 and 131, 97 meV, respectively, which are inconsistent with the recent experimental results. It is proposed that there are two kinds of acceptors in wurtzite GaN. One kind is the general acceptor such as C, substituting N, which satisfies the effective-mass theory, and the other includes Mg, Zn, Cd etc., the binding energy of which deviates from that given by the effective-mass theory. Experimentally, wurtzite GaN was grown by the MBE method, and the PL spectra were measured. Three main peaks are assigned to the DA transitions from the two kinds of acceptor. Some of the transitions were identified as coming from the cubic phase of GaN, which appears randomly within the predominantly hexagonal material. The binding energy of acceptor in ALN is about 239, 158 meV, that in AlxGa1-xN alloys (x approximate to 0.2) is 147, 111 meV, close to that in GaN. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Energy bands and acceptor binding energies of GaN

The energy bands of zinc-blende and wurtzite GaN are calculated with the empirical pseudopotential method, and the pseudopotential parameters for Ga and N atoms are-given. The calculated energy bands are in agreement with those obtained by the ab initio method. The effective-mass theory for the semiconductors of wurtzite structure is established, and the effective-mass parameters of GaN for both structures are given The binding energies of acceptor states are calculated by solving strictly the effective-mass equations. The binding energies of donor and acceptor are 24 and 142 meV for the zinc-blende structure, 20 and 131, and 97 meV for the wurtzite structure, respectively, which are consistent with recent experimental results. It is proposed that there are two kinds of acceptor in wurtzite GaN. One kind is the general acceptor such as C, which substitutes N, which satisfies the effective-mass theory. The other kind of acceptor includes Mg, Zn, Cd, etc., the binding energy of these accepters is deviated from that given by the effective mass theory. In this report, wurtzite GaN is grown by the molecular-beam epitaxy method, and the photoluminescence spectra were measured. Three main peaks are assigned to the donor-acceptor transitions from two kinds of accepters. Some of the transitions were identified as coming from the cubic phase of GaN, which appears randomly within the predominantly hexagonal material. [S0163-1829(99)15915-0].

镁-锌-稀土系合金的组织和性能研究

　　制备了Mg-4.5wt%Zn-1～5wt%RE系合金（RE元素包括轻稀土：La、Ce、Nd、Sm；重稀土：Gd和Y），研究了铸态和热处理态合金的组织和性能。（1）适量的稀土元素均可细化合金晶粒，其中轻稀土元素的细化效果好于重稀土元素；（2）含轻稀土元素合金中的析出相主要为(Mg,Zn)17RE2和Mg4Zn7，而含重稀土元素的合金中的析出相主要为MgZnxREy(Mg3Zn6RE, Mg3RE2Zn3)和Mg4Zn7；（3）加入稀土元素后，合金的强度提高；稀土含量相同时，含轻稀土元素的强化效果较好。Mg-4.5Zn-1Ce合金具有最高的强度。T5处理态合金的抗拉强度、屈服强度和伸长率分别为236 MPa、111 MPa和15.8%，T6处理态合金分别为233 MPa、131 MPa和8.9%。强度提高的主要原因是合金中生成了大量的纳米级Mg4Zn7强化相，以及晶界沉淀相的连续性降低；（4）含重稀土元素合金的时效硬化效果高于含轻稀土元素的合金，经T6处理后，含重稀土元素合金的断裂强度和屈服强度均提高，而含轻稀土元素合金只有屈服强度提高。 　　研究了挤压变形Mg-4.5Zn-1Ce合金的组织和性能。473 K时效后峰值态合金具有较高抗拉强度和屈服强度，其值分别为291 MPa和239 MPa，比铸态分别提提高了55 MPa和128 MPa。高强度产生的原因是合金中生成了大量棒状和点状混合结构的纳米级Mg4Zn7强化相和晶粒的细化。 　　应用Edge-to-edge匹配模型成功预测了MgZn2/α-Mg体系中的位相关系，扩大了该模型的应用范围。并对模型进行了改进，主要体现在：1)确定匹配方向的平面上所有原子的中心位置需在平面上；2）匹配方向之间可任意配对。应用优化后的模型预测了Mg17Al12/α-Mg体系中的位相关系，预测结果与实验结果的吻合率为4/6，好于原模型预测的吻合率4/8。另外，使用优化后的模型，成功的预测出了理想的Burgers位相关系，从而证实了该位相关系是确实存在的，而不是near Burgers位相关系测定的误差。使用优化后的模型还成功的解释了该合金体系中稀土元素的晶粒细化机制和沉淀强化机制。

硼磷酸盐及相关基质中稀土离子的UV－VUV光谱和XAFS

采用高温固相反应合成了稀土离子激活的碱土硼磷酸盐MBPO_5:RE（M=Ca, Sr, Ba；RE＝Sm, Eu, Tb, Dy), Ba_3BPO_7:RE和Ba_3BP_O_(12):RE、稀土硼磷酸盐Ln_7BP_2P_(17):RE (Ln=La, Gd)、碱土（稀土）磷酸盐M_3(PO_4)_2:RE (M=Sr, Ba),ABLa(PP_4)_2:Ce,Tb (A=K, Na;B＝Mg, Zn）、碱土（稀土）硼酸盐SrB_4O_7:RE（Re＝Sm, Eu），BaB_8O_(13):Eu，SrB_6O_(10):Sm, M_3Gd_2(BO_3）_4:RE (M＝Ca, Sr)，B_3O6:Eu(RE=La, Gd)和稀土硼钨酸盐Cd_3BWO_9:Eu。通过XRD、IR光谱和Raman光谱等表征了其结构。测定了上述19个基质的数十个发光体的UV佩VUV光谱和RE-L_3（RE=Sm,Eu, Gd)边的XANES和EXAFS。碱土硼磷酸盐Ba_3BPO_7和Ba_3BP_3O_(12)、稀土硼磷酸盐Ln_7BP_2O_(17) (Ln=La, Gd)和稀土钨硼酸盐Gd3Bwo9等6个基质中稀土离子的UV-VUV光谱和除个别基质（REB_3O_6等）外的VUV光谱均属首次报道。发现土稀土离子激活的这些发光体在VUV范围有丰富的基质吸收带。认为基质中阴离子的结构和基质的晶体结构可能是影响基质的吸收带位置的重要因素。通过XANEs和UV-VUV光谱的联系，结合经验公式首次确证了一些复合氧化物基质中一些RE~(3＋)在vuv范围的f-d跃迁位置。根据VUV光谱测定结果推测了一些基质中RE~(3+)的CTB位置。首次应用RE-L_3边的XANES和UV-VUV光谱两种方法分析比较了RE~(3＋)(RE=Eu, Sm)离子在空气条件下在碱土硼磷酸盐、硼酸盐和磷酸盐基质中的还原。首次应用高分辨发射光谱和RE-L_3边的EXAFS研究了在一些基质中发光中心的配位数、键长和格位对称性等结构因素。

稀土离子在硼铝酸盐及相关基质中的VUV-Vis范围发光性质

PDP(等离子平板显示器)是一种最有前途的大屏幕壁挂式彩电,而它需要VUV激发下的高效荧光粉,同时由于VUV荧光粉也是无汞荧光灯的需求,所以研究VUV激发的稀土激活的荧光粉是实际应用的需要.对于光谱分析该工作采用了理论计算与光谱数据分析相结合的方法,对所测光谱各个谱峰进行了详细的指认.得到了以下的结论和成果:1.得到了大量的含氧酸盐中稀土离子的VUV光谱数据.2.首次系统地应用两种方法预测了三价稀土离子的f-d跃迁位置,并首次系统地通过计算预测了三价稀土离子在含氧酸盐中的电荷迁移带的位置.3.首次实验观察到Ce<'3+>的电荷迁移带,观察到了Tb<'3+>的电荷迁移带.4.在所有含Dy<'3+>的样品中都观察到Dy<'3+>的f-d跃迁.5.LaPO<,4>和ABLa(PO<,4>)<,2>(A=K,Na;B=Mg,Zn)基质中,观察到了Ce<'3+>的5个f-d跃迁,指认了Tb<'3+>的5个f-d跃迁,指认了掺杂Ce、Tb的VUV光谱中的所有谱峰.6.对所研究基质中的稀土离子的f-d跃迁和电荷迁移带进行了系统地预测和指认.7.通过总结不同稀土离子在相同基质中的VUV光谱,并参考文献的相关报导,总结了所研究基质的基质吸收位置.8.通过Eu<'3+>的灾光探针作用和ce<'3+>的发射光谱等,确证三价稀土离子在La<,2>CaB<,10>O<,19>基质中同时取代了八配位的Ca<'2+>和十配位的La<'3+>,占据了两种格位.9.合成了一种新型绿色长余辉材料,具有亮度高,余辉时间长,可用日光激发等优点.10.合成了一种UV激发下性能优异的掺Eu<'3+>的红色荧光粉,亮度可以跟商业红粉Y<,2>O<,3>:Eu相比拟,而基质材料与Y<,2>O<,3>相比降低了成本.

Correlation of electrical and optical properties in dually Cd+ and N+ ion-implanted GaAs

Cd in GaAs is an acceptor atom and has the largest atomic diameter among the four commonly-used group-II shallow acceptor impurities (Be, Mg, Zn and Cd). The activation energy of Cd (34.7 meV) is also the largest one in the above four impurities, When Cd is doped by ion implantation, the effects of lattice distortion are expected to be apparently different from those samples ion-implanted by acceptor impurities with smaller atomic diameter. In order to compensate the lattice expansion and simultaneously to adjust the crystal stoichiometry, dual incorporation of Cd and nitrogen (N) was carried out into GaAs, Ion implantation of Cd was made at room temperature, using three energies (400 keV, 210 keV, 110 keV) to establish a flat distribution, The spatial profile of N atoms was adjusted so as to match that of Cd ones, The concentration of Cd and N atoms, [Cd] and [N] varied between 1 x 10(16) cm(-3) and 1 x 10(20) cm(-3). Two type of samples, i.e., solely Cd+ ion-implanted and dually (Cd+ + N+) ion-implanted with [Cd] = [N] were prepared, For characterization, Hall effects and photoluminescence (PL) measurements were performed at room temperature and 2 K, respectively. Hall effects measurements revealed that for dually ion-implanted samples, the highest activation efficiency was similar to 40% for [Cd] (= [N])= 1 x 10(18) cm(-3). PL measurements indicated that [g-g] and [g-g](i) (i = 2, 3, alpha, beta,...), the emissions due to the multiple energy levels of acceptor-acceptor pairs are significantly suppressed by the incorporation of N atoms, For [Cd] = [N] greater than or equal to 1 x 10(19) cm(-3), a moderately deep emission denoted by (Cd, N) is formed at around 1.45-1.41 eV. PL measurements using a Ge detector indicated that (Cd, N) is increasingly red-shifted in energy and its intensity is enhanced with increasing [Cd] = [N], (Cd, N) becomes a dominant emission for [Cd] = [N] = 1 x 10(20) cm(-3). The steep reduction of net hole carrier concentration observed for [Cd]/[N] less than or equal to 1 was ascribed to the formation of (Cd, N) which is presumed to be a novel radiative complex center between acceptor and isoelectronic atoms in GaAs.

Energy band and acceptor binding energy of GaN and AlxGa1-xN

The hole effective-mass Hamiltonian for the semiconductors of wurtzite structure is established, and the effective-mass parameters of GaN and AlxGa1-xN are given. Besides the asymmetry in the z and x, y directions, the linear term of the momentum operator in the Hamiltonian is essential in determining the valence band structure, which is different from that of the zinc-blende structure. The binding energies of acceptor states are calculated by solving strictly the effective-mass equations. The binding energies of donor and acceptor for wurtzite GaN are 20 and 131, 97 meV, respectively, which are inconsistent with the recent experimental results. It is proposed that there are two kinds of acceptors in wurtzite GaN. One kind is the general acceptor such as C, substituting N, which satisfies the effective-mass theory, and the other includes Mg, Zn, Cd etc., the binding energy of which deviates from that given by the effective-mass theory. Experimentally, wurtzite GaN was grown by the MBE method, and the PL spectra were measured. Three main peaks are assigned to the DA transitions from the two kinds of acceptor. Some of the transitions were identified as coming from the cubic phase of GaN, which appears randomly within the predominantly hexagonal material. The binding energy of acceptor in ALN is about 239, 158 meV, that in AlxGa1-xN alloys (x approximate to 0.2) is 147, 111 meV, close to that in GaN. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

川西地区几种优势苔藓植株元素含量及其时空差异性

揭示苔藓植株元素含量及其时空差异性是深入开展利用苔藓植物指示环境和筛选理想监测藓种的科学基础。采用微波消解（ICP-AES）方法对九寨沟自然遗产地原始林景点停车场周围三个采样带：I为停车场植被小岛（PS），向外约120 m半径为II带（D120），再向外距离约1,000 m为III带（D1000）和3个方向上的大羽藓和毛尖青藓2种苔藓中13种元素（A1, S, Ca, P, Cu, Fe, K, Mg, Mn, Pb, Ni,Zn和Cd）含量进行了测定和比较，并对采自边坡方向（PS-3）上2005和2007年的4种苔藓植物（南木藓、大羽藓、平藓和厚角絹藓）也进行了13种元素含量的测定和比较。同时对九寨沟自然遗产地、黄龙自然遗产地、夹金山和梦笔山的冷杉原始林4个地区的3种苔藓中（大羽藓、锦丝藓和塔藓）的A1、Ca、Cu、Fe、K、Mg、P、Zn、C和N 10种元素含量进行测定和比较。 对大羽藓和毛尖青藓2种苔藓植物内13种元素的测定发现：1）同种苔藓对不同元素的富集能力不同。A1、Ca、K、Mg和P的元素含量在苔藓中的富集较其他元素的要高。2）不同种苔藓植物对同种元素的富集能力不同，毛尖青藓较大羽藓能够监测出更多的元素；对于被检测出的元素，毛尖青藓监测出的累积量大于大羽藓，其中累积量最大的元素是Ca为10 874.286 μg.g-1.year-1，最小的是Cu元素为5.438 μg.g-1.year-1。对05年和07年的平藓、大羽藓、南木藓和厚角絹藓元素含量的测定表明：元素在两年中的积累量是不同的。综合分析表明，苔藓生物监测方法可有效监测景点停车场机动车尾气中排放出的典型元素（如Cu、Pb、Ni、Zn、Cd等）含量，而毛尖青藓较大羽藓能更可靠的监测九寨沟自然遗产地单景点汽车尾气金属元素种类及其排放量。 对4个地区3种苔藓10种元素监测发现：1）Ca、Mg、Zn、K和Cu元素在黄龙地区的含量高于在其它地区的含量；P元素在梦笔山地区的含量为最高；Fe和Al元素在夹金山地区的含量高于在其它地区的含量。2）C元素在其它因素一致的情况下，进行不同年龄间的元素含量比较，结果显示元素含量在各年龄间并不存在明显的差异性；N元素含量与年龄的差异出现在黄龙林下及林窗的塔藓、九寨沟林下的锦丝藓及塔藓和梦笔山的塔藓中，而在锦丝藓中未出现元素含量与年龄的差异性；塔藓能检测出更多的元素种类其含量与年龄间存在显著差异，锦丝藓检测到的元素种类次之；除锦丝藓（锦丝藓在林窗中几乎检测不到元素含量与年龄间的差异性）外，其他两种藓在林窗中能检测出的元素种类大于在林下的检测种类。3）元素含量与生境间存在差异性的元素分别有：黄龙大羽藓中的Ca、P和Mg元素；九寨锦丝藓中的Zn元素；夹金山塔藓中的Al、Fe和Zn元素；梦笔山大羽藓中的Al、Fe和Mg元素及锦丝藓中的Ca元素。4）区域、年龄和生境因素对苔藓植株元素含量均达到了显著水平，但两两之间及三者之间的交互作用由于元素种类的不同存在差异。综合分析表明，苔藓植物中的元素含量受年龄、区域的影响较生境的更大。 The revelation of mosses elements content and its spatiotemporal differences is the scientific foundation of moss monitoring. To determine the feasibility of moss monitoring metal depositions derived from travel bus emiss ions in scenic spot, we collected one year-growth samples of two mosses Brachythecim piligerum and Thuidium cymbifolium with different distance (island center, 120m，1000m ) and different direction (north, south and east) far from parking site island from Yuanshilin Spot at Jiuzhaigou World Nature Heritage in the Western Sichuan of China and determined thirteen element （A1, S, Ca, P, Cu, Fe, K, Mg, Mn, Pb, Ni, Zn, Cd）contents by ICP-AES analysis method. And picked 4 kinds of mosses (Macrothamnium macrocarpu m（Reinw. etHornsch.）Fleisch.，Thuidium cymbifolium，Entodon concinnus (De Not.) Par., Neckera pennata) from the direction PS-3 in 2005 and 2007, determined 13 element contents. Collected 3 kinds of moss (Thuidium cymbifo lium, Actinothuidium Hookeri (Mitt.) and Hyolcomium splendens (Hedw.) from Jiuzhaigou natural heritage, Huanglong natural heritage, Mt. Jiajin and Mt. Mengbi in primeval forest with two habitat (undergrowth and forest gap), determined element contents of A1, Ca, Cu, Fe, K, Mg, P, Zn, C and N. We found that, 1) The elements content are difference in same type of moss. Content of A1, Ca, K, Mg and P are higher than others. 2) While the contents of A1, S, Ca, P, Cu, Fe, K and Zn had significant correlation with the different distances from parking site, the nearer the distance was, the more accumulation was; 2) Comparing to Thuidium cymbifolium, Brachythecium piligerum can test more elements which contents show the significant correlation with distances. And Brachythecium piligerum can have greater element accumulation than Thuidium cymbifolium. The element contents in two years (2005 and 2007) are different. The present study found that moss can reliably bio-indicate metal deposition from traffic emissions in one scenic spot and Brachythecium piligerum is a good moss for bio-indicating element content from traffic emissions at Jiuzhaigou World natural Heritage. Determined the 10 element contents in 4 areas through 3 kinds of moss we found that, 1) Ca, Mg, Zn, K and Cu element content is higher in the Huanglong area than in other areas, The P element content in Mt. Jiajin is higher than other areas, Fe and Al element content is higher in the Mt. Jiajin than in other areas. 2) The content of C had no significant correlation with age. As for N, this significant correlation found in Hyolcomium splendens (Hedw.) with 2 habitat in Huanglong, Actinothuidium Hookeri (Mitt.) and Hyolcomium splendens (Hedw.) with undergrowth in Jiuzhai, Hyolcomium splendens (Hedw.) in Mt. Mengbi. The types of elements which content showt he significant correlation are most in Hyolcomium splendens (Hedw.) and least in Thuidium cymbifolium. Except Actinothuidium Hookeri (Mitt.), the types of elements that content had significant correlation with age in forest gap are more than in undergrowth. 3) The elements which content had significant correlation with habitat are P, Ca and Mg in Thuidium cymbifolium in Huanglong, Zn in Actinothuidium Hookeri (Mitt.) in Jiuzhai, Al, Fe and Zn in Hyolcomium splendens (Hedw.) in Mt. Jiajin, in Mt. Mengbi Al, Fe and Mg in Thuidium cymbifolium and Ca in Actinothuidium Hookeri (Mitt.). 4）The region, the age and the habitat factor has coeffect element content. The correlationship between element contents and the age, the region is closer than habitat.

炮制前后朝鲜淫羊藿化学成分的变化规律研究

采用电喷雾质谱技术、等离子体发射光谱技术以及紫外分光光度法分别对炮制前后朝鲜淫羊藿的化学成分进行了详细研究 ;结果表明 ,炮制后淫羊藿中与肾功能有密切关系的Ca、Mn、Fe、Mg、Zn等微量元素的含量明显增加 ,但黄酮类化合物的含量无明显变化 ,为进一步阐明淫羊藿炮制入药的科学内涵提供了实验依据。

生物样品与多变量分析——冠心病患者血液中金属元素的测定

运用等离子体发射光谱法测定了冠心病患者和对照组(即健康人)血液中Sr、Cu、Mg、Zn 4种元素的含量,并且运用主成份分析、聚类分析和逐步判别分析的多变量分析方法,对测试数据进进了综合评估,识别率达92.7％。结果预示出通过血液中微量金属元素的测定,有可能作为冠心病诊断的一种辅助手段。

藏药材白花龙胆花中微量元素的分析

对藏药材白花龙胆花中17种微量元素(Cu、Zn、Fe、Mn、Co、Ni、Se、Cr、Mg、Ca、K、Na、P、As、Hg、Pb、Cd)的含量作了测定。结果表明,白花龙胆花中含有较高的人体必需微量元素和常量元素,其中常量元素K、Ca、Na、Mg和微量元素Zn、Fe、Mn的含量均较高。

利用激光诱导击穿光谱对铝合金成分进行多元素同时定量分析

利用激光诱导击穿光谱定量分析了铝合金中多种元素的成分。采用Nd∶YAG脉冲激光器,在空气环境下烧蚀铝合金固体样品获得等离子体。利用多通道光栅光谱仪和CCD检测器对200～980nm波长范围的光谱进行同时检测。研究了检测时延、激光脉冲能量、元素深度分布对光谱强度的影响,考虑这些因素之后对实验参数进行了优化。在优化的实验参数下对国家标准铝合金样品中的八种元素Si,Fe,Cu,Mn,Mg,Zn,Sn及Ni进行了定标,并利用定标曲线对一种铝合金样品进行了定量分析。实验结果表明,测量结果的相对标准偏差(RSD)最大为5.89%,相对误差在-20.99%～15%范围内,说明对铝合金样品成分进行定量分析,激光诱导击穿光谱是一种有效的光谱分析工具,但是分析结果的准确度仍需要提高。

Caracterização fisiológica e nutritiva da clorose férrica em citrinos

Tese dout., Ciências Agrárias, Produção Vegetal, Unidade de Ciências e Tecnologias Agrárias, Universidade do Algarve, 2000

Caracterização fisiológica e nutritiva da clorose férrica em citrinos: avaliação dos mecanismos de resistência aos efeitos do HCO3

Tese de dout., Ciências Agrárias, Unidade de Ciências e Tecnologias Agrárias (Produção Vegetal), Univ. do Algarve, 2000

Elastic Constants And Structural Parameters Of Selected Polycrystalline Ceramics By Ultrasonic Technique

The present work is an attempt to probe the elastic properties in some dielectric ceramics, by using ultrasonic pulse echo overlap technique. The base Ba6-xSm8+2xTi18O54 and Ca5Nb2TiO12 are very important dielectrics ceramics used for microwave communication as well as for substrate materials. Ultrasonic is one of the most widely used and powerful techniques to measure elastic properties of solids. The ultrasonic technique is nondestructive in nature and the measurements are relatively straightforward to perform. One unique advantantage of the ultrasonic technique is that both static and dynamic properties can be measured simultaneously. The velocity and attenuation coefficients of the ultrasonic waves propagating through a medium are related to the microscopic structure of the material and they provide valuable information about the structural changes in the system. Among the various ultrasonic techniques, the pulse echo overlap method is the most accurate and precise one. In the present case the decreased elastic properties of Cas-XMg,Nb2TiO12 and Cas-,ZnNb2TiO12 ceramics can be attributed to their mixture phases beyond x = 1. Moreover, the abrupt change in elastic properties observed for x >1 can also be correlated to the structural transformation of the materials from their phase pure form to mixture phases for higher extent of substitution of the concerned material . Ca4(ANb2Ti)012 (A = Mg, Zn) is the strongest compound with the maximum values for elastic properties . This could be due to the possible substitution of Mg/Zn ions with lesser radius [25] than Ca2+ in perovskite B-site of Ca(Cali4Nb2i4Tili4) O3 material to contribute more ordering and symmetry to the system [20]. All other compositions (x > 1) contain mixed-phases and for such mixed-phase samples, the mechanical properties are difficult to explain.