Ce-N共掺锐钛矿TiO2(001)取向电子结构和光学性质

采用第一性原理研究了Ce和N共掺杂锐钛矿TiO_2的稳定性、电子结构和光学性质。结果表明在锐钛矿TiO_2中Ce倾向于间隙掺杂,而N更倾向于O替位掺杂;Ce单掺杂和Ce-N共掺杂都能使TiO_2带隙宽度减小,同时N原子还能在价带顶引入浅受主能级,有利于可见光的吸收和阻止光生载流子-空穴复合;Ce单掺杂和Ce-N共掺杂锐钛矿TiO_2(001)取向都满足光催化制氢条件,因此都具有良好的光催化特性。综合分析带边位置和吸收光谱发现Ce-N共掺杂能有效提高锐钛矿TiO_2(001)取向的光催化制氢能力。     

Cu掺杂GaN/ZnO异质结的光学性质

ZnO/GaN异质结由于错配度小,化学稳定性好, 具有优良的光学、压电和热电效应等 优点,是下一代电子器件的理想材料。但是ZnO/GaN异质结的带隙宽度较宽制约了ZnO/GaN的 应用。为了减小ZnO/GaN异质结的带隙宽度,提高对可见光的吸收,采用第一性原理研究了C u掺杂对ZnO/GaN异质结稳定性、带隙和光学性质的影响。研究结果表明:Cu掺杂ZnO/GaN异 质结的结合能是负值,因此结构稳定,但是Cu位于界面处的结合能要比基体内的小,因此更 容易在界面处形成。Cu置换Ga能够明显的减小带隙的宽度,且在带隙中引入了Cu-3d杂质态 ,有利于可见光的吸收,但是置换Zn后不是很明显。Cu掺杂ZnO/GaN后引起吸收系数产生红 移,且Cu置换Ga后吸收系数在3.2 eV附近处产生明显的吸收峰55377 cm－1。Cu掺杂也使得复 介电常数虚部以及折射率虚部产生红移,说明掺杂有利于可见光的吸收。虽然Cu置换Ga后反 射率有了较大的提升,但是总体仍然维持在较低的水平,因此反射率较低。     

Ag掺杂ZnO/GaN异质结可见光吸收特性的第一性原理

ZnO/GaN异质结带隙宽度较宽,制约了对可见光的吸收。为研究Ag对ZnO/GaN异质结可见光吸收的影响,在(1-100)非极性面上构建GaN/ZnO异质结,并用Ag分别取代不同位置的Zn和Ga原子,采用第一性原理计算Ag掺杂对ZnO/GaN异质结稳定性、电子结构、光学性质和带边位置的影响。研究结果表明：Ag掺杂ZnO/GaN异质结形成能为负值,结构稳定;Ag置换Zn和Ga使带隙宽度由2.93 eV分别减小至2.7 eV和2.3 eV,吸收系数和光电导产生红移,有利于可见光的吸收,Ag掺杂ZnO/GaN异质结具有良好的光催化活性。     

氮气流量对磁控溅射C掺杂TiO2薄膜光学性能的影响

采用磁控溅射法制备了C掺杂TiO₂薄膜,并研究了氮气引入溅射过程对薄膜光学性能的影响。利用X射线衍射仪、拉曼光谱仪、X射线光电子能谱仪、分光光度计和原子力显微镜分析了不同氮气流量下薄膜的微结构、元素价态、透光性能和表面形貌。结果表明,沉积的薄膜主要是非晶结构,拉曼光谱中存在少量锐钛矿相,且随着氮气流量增大,锐钛矿特征峰强度减弱,意味着晶粒出现细化。当氮气流量增大为4cm³/min时,C掺杂TiO₂薄膜内氮元素含量为3.54%,其光学带隙从3.29eV变化至3.55eV,可见光区的光学透过率明显提高。可见改变氮气流量可实现对C掺杂TiO₂薄膜光学带隙和光吸收率的有效调控。     

Al掺杂半导体Mg2Si薄膜的制备及光学带隙研究

用磁控溅射方法在Si衬底上制备了Al掺杂Mg2Si薄膜,通过X射线衍射仪(XRD)、扫描电镜(SEM)、原子力显微镜(AFM)和分光光度计研究了掺杂含量对Mg2Si薄膜组分、表面形貌、粗糙度及光学带隙值的影响,XRD结果表明随着Al掺杂量的增加, Mg2Si衍射峰先增强后减弱. SEM及AFM的结果表明随掺杂量的增加,结晶度先增加后降低,晶粒尺寸减小,粗糙度先增加后降低.得到掺杂后薄膜间接跃迁带隙范围为0.423～0.495 eV,直接跃迁带隙范围为0.72～0.748 eV,掺杂前薄膜间接跃迁带隙和直接跃迁带隙分别为0.53 eV、0.833 eV.     

Al掺杂硅烯材料吸附气体分子的第一性原理研究

通过Al原子吸附和取代的方法对硅烯材料进行掺杂,基于第一性原理计算方法研究了Al掺杂硅烯材料的吸附特性,分析H₂、SO₂和NH₃气体分子在其表面的吸附过程。研究发现,Al吸附硅烯体系由于强的物理吸附对H₂敏感,吸附能为-0.51 eV;SO₂和NH₃以成键的方式吸附在两种掺杂材料上,其中Al取代硅烯体系吸附SO₂后打开了0.3 eV的带隙,吸附能为-1.19 eV;Al吸附硅烯体系吸附SO₂后带隙缩小,吸附NH₃后带隙增大,吸附能分别为-1.01和-0.96 eV。结果表明,Al原子的吸附和取代提高了硅烯材料的吸附性能,为研究Al掺杂硅烯材料的储氢和气敏性能提供理论参考。     

稀土Dy掺杂对ZnO,CdO和SnO2薄膜性能的影响

用热蒸发法和热处理制备稀土Dy掺杂金属氧化物CdO,ZnO和SnO2薄膜,研究不同Dy掺杂浓度及热处理对3种薄膜性能的影响。XRD和SEM测试结果显示:适当的Dy掺杂和热处理可改善薄膜的结构特性,使薄膜表面的致密性变好。CdO,ZnO和SnO2薄膜的最佳掺Dy原子数分数为5%,5%和3%。掺Dy后Cd O,ZnO和SnO2薄膜的导电类型均为n型,电阻值降低约一个数量级。Dy掺杂使得薄膜的致密性增加而导致光透过率降低。制备的薄膜都是直接带隙半导体,相应的光学带隙:Cd O约2.232 eV,CdO∶Dy(Dy原子数分数5%)的略增为2.241 e V,ZnO薄膜约为3.31 eV;ZnO∶Dy(Dy原子数分数5%)约3.25 eV,SnO2薄膜约3.07 eV,SnO2∶Dy(Dy原子数分数3%)约3.03 eV。     

N 和 Fe 共掺杂对TiO2电子结构和光学性质影响的第一性原理研究

本文采用基于密度泛函理论的第一性原理研究了N 和 Fe共掺杂锐钛矿相TiO2的电子结构和光学特性。计算结果表明,不同位置N 和 Fe共掺杂影响共掺TiO2的稳定性。通过态密度讨论了掺杂TiO2带隙变窄的机理。 不同位置N 和 Fe共掺杂影响了可见光吸收。N 和 Fe共掺杂的协同效应导致了可见光吸收的增强。因此,N 和 Fe共掺杂也许增强TiO2在可见光区的光催化能力。     

氮δ掺杂Cu_2O薄膜的生长及物性研究

采用等离子体增强原子层沉积(PEALD)技术,以NH3为掺杂源,制备了氮δ掺杂Cu_2O薄膜,研究了N掺杂对Cu_2O薄膜表面形貌、光学及电学性质的影响。研究结果表明,N掺杂引起了晶格畸变,Cu_2O薄膜的表面粗糙度增大;掺杂后Cu_2O薄膜的带隙宽度从2.70eV增加到3.20eV,吸收边变得陡峭;掺杂后载流子浓度为6.32×1019 cm~(-3),相比于未掺杂样品(5.77×1018 cm~(-3))的提升了一个数量级。     

外压调制对Cr-Se共掺杂单层MoS2光电特性的影响

采用基于第一性原理的贋势平面波方法,对比研究了Cr-Se共掺杂单层MoS2未施应变和(0001)面施加应变的光电特性。计算结果表明:未施加应变体系属直接带隙半导体,张应变下体系的带隙值随应变增加而减小,压应变下带隙值随应变增加先增加后减小,在应变为-6%时转化为Γ-M间接带隙半导体,带隙值达到极大值1.595eV;介电函数和折射率随张应变的增加而增加,随压应变增加先减小后增大,在压应变为-6%时达到极小值3.627和1.905;光电导率和能量损失函数随张应变增加而减小,随压应变增加先增加后减小,应变分别为-5%和-2%时达到极大值2.588和9.428。可见,应变能更精细地调制Cr-Se共掺杂单层MoS2的光电特性。     

GEMNET: a generalized, shuffle-exchange-based, regular, scalable,modular, multihop, WDM lightwave network

GEMNET is a generalization of shuffle-exchange networks and it can represent a family of network structures (including ShuffleNet and de Bruijn graph) for an arbitrary number of nodes. GEMNET employs a regular interconnection graph with highly desirable properties such as small nodal degree, simple routing, small diameter, and growth capability (viz. scalability). GEMNET can serve as a logical (virtual), packet-switched, multihop topology which can be employed for constructing the next generation of lightwave networks using wavelength-division multiplexing (WDM). Various properties of GEMNET are studied     

Thermodynamics of copper matte converting: Part III. Steady-state volatilization of Au,Ag, Pb,Zn, Ni,Se, Te,Bi, Sb,and As from slag,matte, and metallic copper

A comprehensive compilation of various thermodynamic data required for a complete analysis of copper matte converting reactions is presented. The data comprise estimated free energies of formation for such gases as SeO, SeS, TeO, TeS, BiO, BiS, SbO, SbS, AsO, and AsS, as well as activity coefficients in dilute copper alloys and vapor pressures of various elements and compounds. The volatilization of minor elements in steady-state reactors comprising gas and several condensed phases is mathematically formulated, and a parameter which governs the volatilization in such reactors is defined and named volatilization constant. The vapor pressures of various volatile species are calculated thermodynamically for the Noranda Process reactor by assuming equilibrium conditions. The volatilization constants of various minor elements are expressed explicitly as functions of oxygen and sulfur activities. Formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT     

Bits, symbols, bauds, and bandwidth

The use of clear, concise, and unambiguous language in telecommunications engineering is vital to communicate a desired meaning and understanding. Terminology should be based on rigorous engineering principles and traceable to well known and dependable sources. This article deals with four everyday terms commonly encountered in the popular semi-technical press as well as in serious engineering periodicals. The misuse of these and other terms can lead to low-balled cost proposals, court litigation, and patent infringement cases. Imagine how an engineering student can be confused when she/he typically encounters bandwidth measured in bits per second     

Novel planar, square-shaped, dielectric-waveguide, single-, and dual-mode filters

This paper presents a novel concept of a square-shaped dielectric-waveguide resonator, which can easily realize a dielectric-waveguide cross-coupled filter or a dielectric-waveguide dual-mode filter, using the conventional printed circuit board (PCB) process. This planar dielectric-waveguide resonator has a higher Q value than a microstrip resonator. The physical mechanisms of both single- and dual-mode filters are elucidated. Some new coupling structures are developed for undergoing the PCB process. Filter design procedures are detailed. Design curves for the coupling coefficients of internal- and external-coupling structures are determined by full-wave finite-element-method electromagnetic calculations. Measurement results are highly consistent with theory for all trial filters. This study offers an effective means of producing low-cost high-performance planar circuit filters.     

PBX技术.市态.营销.选购

本文介绍了ＰＢＸ交换机的技术及市场需求态势。并提出ＰＢＸ产品的营销要素及其用户在选购时应遵循的原则。     

Dilemmas,uncertainty, risks,and board performance

This paper traces the origins of the words risk, uncertainty, governance and development and argues that a deeper understanding of each allows more effective decision taking in the boardroom. It argues that the role of the board of directors is to balance and rebalance continuously their irresolvable dilemma — ‘how do we drive our enterprise forward while keeping it under prudent control?’ It argues that it is the board’s role to focus on uncertainty, rather than risk, and this requires a different set of intellectual skills from board members to be able to cope with monitoring a range of diverse scenarios. This is crucial for a board to develop stronger ways of both leading their organisation and of ensuring the connectedness of the learning within and between the board and the operational unit’s risk taking. It advocates that to achieve this a board must develop new ways of learning — especially of thinking strategically and becoming more sensitised to the dynamics of their changing external environments. This will take them well beyond the comforts of their specialist managerial disciplines and into the true world of directing. The paper demonstrates the importance of continuous learning in reducing organisational uncertainty and risk. It uses the ‘Learning Board’ process and model as the central processor of both strategic and operational learning to create an annual rhythm for the board’s year.