Charge Polarization Effects and Hole Spectra Characteristics in Alxgai-xNGan Superlattices

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聚苯胺的制备

随着社会科技的发展，绿色能源成为人类可持续发展的重要条件，而风能、太阳能等非可持性能源的开发和利用面临着间歇性和不稳定性的问题，这就催生了大量的储能装置，其中比较引人注目的包括太阳能电池、锂子电池和超级电容器等。

超级电容器作为一种新型化学储能装置，具有高功率密度、快速充放电、较长循环寿命、较宽工作温度等优秀的性质，目前在储能市场上占有很重要的地位，同时它也广泛应用于军事国防、交通运输等领域。

目前，随着环境保护观念的日益增强，可持续性能源和新型能源的需求不断增加，低排放和零排放的交通工具的应用成为一种大势，电动汽车己成为各国研究的一个焦点。

超级电容器可以取代电动汽车中所使用的电池，超级电容器在混合能源技术汽车领域中所起的作用是十分重要的，据英国《新科学家》杂志报道，由纳米花和纳米草组成的纳米级牧场可以将越来越多的能量贮存在超级电容器中。

随着能源价格的不断上涨，以及欧洲汽车制造商承诺在1995年到2008年之间将汽车CO2的排放量减少25%，这些都促进了混合能源技术的发展，宝马、奔驰和通用汽车公司已经结成了一个全球联盟，共同研发混合能源技术。

2002年1月，我国首台电动汽车样车试制成功，这标志着我国在电动汽车领域处于领先地位。

而今各种能源对环境产生的负面影响很大，因此对绿色电动车辆的推广提出了迫切的要求，一项被称为Loading-leveling(负载平衡)的新技术应运而生，即采用超大容量电容器与传统电源构成的混合系统“Battery-capacitor hybrid”(Capacitor-battery bank) [1]。

目前对超级电容器的研究多集中于开发性能优异的电极材料，通过掺杂与改性，二氧化锰复合导电聚合物以提高二氧化锰的容量[1、2、3]。

生瑜(是这个人吗？)等[4]通过原位聚合法制备了聚苯胺/纳米二氧化锰复合材料，对产物特性进行细致分析。

因导电高分子具有可逆氧化还原性能，通过导电高分子改性，这对于提高二氧化锰的性能和利用率是很有意义的。

《2024年应变GaN-AlGaN量子阱中受屏蔽激子的压力效应》范文

《应变GaN-AlGaN量子阱中受屏蔽激子的压力效应》篇一应变GaN-AlGaN量子阱中受屏蔽激子的压力效应一、引言随着材料科学的不断进步，我们对半导体的研究和应用已日益广泛。

氮化镓（GaN）及其合金铝镓氮（AlGaN）由于具有优越的电子性能和光电性能，已被广泛运用于制作半导体器件和光电器件。

在GaN/AlGaN量子阱中，激子行为的研究对于理解其光学和电子性质至关重要。

本文将探讨在应变GaN/AlGaN量子阱中，受屏蔽激子在压力作用下的变化及其效应。

二、GaN/AlGaN量子阱的基本性质GaN和AlGaN材料由于其禁带宽度大、热导率高、击穿电场强等优点，在制作高性能电子和光电器件中有着广泛的应用。

在这些材料构成的量子阱结构中，电子和空穴被限制在二维平面内运动，形成了所谓的“量子阱”。

在无外界干扰的情况下，量子阱内的电子和空穴会形成激子。

三、激子的屏蔽效应在GaN/AlGaN量子阱中，激子受到周围介质的屏蔽效应。

这种屏蔽效应会影响激子的能级结构、跃迁几率等性质。

屏蔽效应在某种程度上取决于介质的介电常数，因此研究屏蔽效应有助于我们更好地理解激子在量子阱中的行为。

四、压力对激子的影响当外部压力作用于GaN/AlGaN量子阱时，量子阱的结构会发生应变，从而影响其中的激子。

压力会改变介质的介电常数，进而影响激子的屏蔽效应。

此外，压力还会改变量子阱的能带结构，影响电子和空穴的能量状态，从而影响激子的产生和复合过程。

五、应变对激子性质的影响在GaN/AlGaN量子阱中，由于晶格失配等原因，往往会产生应变。

这种应变会改变量子阱的能级结构，进而影响激子的性质。

在压力作用下，这种应变会进一步加剧，使得激子的性质发生更大的变化。

例如，压力可能导致激子能级发生移动，改变激子的跃迁能量；同时，压力还可能影响激子的寿命和复合速率等。

六、实验与讨论为了研究应变GaN/AlGaN量子阱中受屏蔽激子的压力效应，我们进行了系列实验。

非极性和半极性GaN的生长及特性研究

非极性和半极性GaN的生长及特性研究非极性和半极性GaN的生长及特性研究提要：氮化镓（GaN）是一种重要的宽能隙半导体材料，在光电子器件、高功率电子器件等领域有着广泛的应用前景。

本文主要研究了非极性和半极性GaN材料的生长方法及其特性，并对比了两种不同取向的GaN材料的优缺点。

1. 引言氮化镓是一种III-IV族氮化物半导体材料，具有较大的能隙，可用于制备高效的紫外光发射二极管和激光二极管。

GaN材料有三种主要取向，包括c-面极性、非极性和半极性，其中以c-面极性最为常见。

但是，非极性和半极性GaN也具有一些独特的性质和应用优势。

2. 非极性GaN的生长方法非极性GaN可以通过金属有机化学气相沉积（MOCVD）、分子束外延（MBE）等方法生长。

其中，MOCVD是最常用的方法之一。

通过调控生长参数，如温度、气流比等，可以控制非极性GaN的取向。

此外，还可以使用衬底工程技术，如衬底选择、衬底预处理等，来改善非极性GaN的生长质量。

3. 非极性GaN的特性研究非极性GaN的主要特性包括光电性能、电学性能和热学性能。

研究表明，非极性GaN具有较小的激子束缚能和较低的载流子损失，可用于制备高效的光电子器件。

此外，非极性GaN还具有较高的载流子迁移率和较好的热稳定性，可用于制备高功率电子器件。

4. 半极性GaN的生长方法半极性GaN的生长方法与非极性GaN类似，也可以使用MOCVD 和MBE等方法。

通过调控生长参数和衬底工程技术，可以获得较高质量的半极性GaN薄膜。

5. 半极性GaN的特性研究半极性GaN的特性研究主要集中在光学特性和电学特性。

研究表明，半极性GaN具有较大的外延晶格失配度和较强的光吸收能力，可用于制备紫外激光器。

此外，半极性GaN还具有较高的载流子迁移率和较快的载流子复合速率，可用于制备高速电子器件。

6. 对比和展望虽然非极性和半极性GaN具有各自的优势和应用前景，但也存在一些挑战和问题，如生长过程中的晶格失配等。

氮化镓衬底

氮化镓这是一种具有较大禁带宽度的半导体,属于所谓宽禁带半导体之列。

它是微波功率晶体管的优良材料，也是蓝色光发光器件中的一种具有重要应用价值的半导体。

简介GaN材料的研究与应用是目前全球半导体研究的前沿和热点，是研制微电子器件、光电子器件的新型半导体材料，并与SIC、金刚石等半导体材料一起，被誉为是继第一代Ge、Si半导体材料、第二代GaAs、InP化合物半导体材料之后的第三代半导体材料。

它具有宽的直接带隙、强的原子键、高的热导率、化学稳定性好（几乎不被任何酸腐蚀）等性质和强的抗辐照能力，在光电子、高温大功率器件和高频微波器件应用方面有着广阔的前景。

化学式GaNGaN材料的特性总述GaN是极稳定的化合物，又是坚硬的高熔点材料，熔点约为1700℃，GaN具有高的电离度，在Ⅲ—Ⅴ族化合物中是最高的（0.5或0.43）。

在大气压力下，GaN晶体一般是六方纤锌矿结构。

它在一个元胞中有4个原子，原子体积大约为GaAs的一半。

因为其硬度高，又是一种良好的涂层保护材料。

化学特性在室温下，GaN不溶于水、酸和碱，而在热的碱溶液中以非常缓慢的速度溶解。

NaOH、H2SO4和H3PO4能较快地腐蚀质量差的GaN，可用于这些质量不高的GaN 晶体的缺陷检测。

GaN在HCL或H2气下，在高温下呈现不稳定特性，而在N2气下最为稳定。

结构特性表1列出了纤锌矿GaN和闪锌矿GaN的特性比较。

电学特性GaN的电学特性是影响器件的主要因素。

未有意掺杂的GaN在各种情况下都呈n型,最好的样品的电子浓度约为4×1016/cm3。

一般情况下所制备的P型样品，都是高补偿的。

很多研究小组都从事过这方面的研究工作，其中中村报道了GaN最高迁移率数据在室温和液氮温度下分别为μn=600cm2/v·s和μn= 1500cm2/v·s，相应的载流子浓度为n=4×1016/cm3和n=8×1015/cm3。

N_和As_掺杂二维GeC_光电性质的第一性原理研究　

第53卷第3期2024年3月人㊀工㊀晶㊀体㊀学㊀报JOURNAL OF SYNTHETIC CRYSTALS Vol.53㊀No.3March,2024N 和As 掺杂二维GeC 光电性质的第一性原理研究李㊀萍1,秦彦军1,庞国旺1,唐玉柱2,张㊀遥2,王㊀鹏2,刘晨曦3(1.新疆理工学院理学院,阿克苏㊀843100;2.新疆理工学院机电工程学院,阿克苏㊀843100;3.西安工业大学光电工程学院,陕西省薄膜技术与光学检测重点实验室,西安㊀710021)摘要:本文基于密度泛函理论第一性原理,系统研究了单层GeC,N 掺杂㊁As 掺杂及N-As 共掺杂GeC 体系的稳定性㊁电子结构及光学性质等㊂结果表明,单层GeC 是一种禁带宽度为2.10eV 的直接带隙半导体㊂与单层GeC 相比,掺杂后体系的禁带宽度和功函数均减小,表明体系的电子跃迁所需的能量相对较少㊂并且,掺杂后体系的光吸收系数均有所提高,同时吸收带边也发生了红移,有效拓宽了体系对光的响应范围,提高了体系对光子的吸收能力㊂此外,As 掺杂GeC 体系不仅在费米能级附近出现了杂质能级,而且在低能区的吸收系数㊁静介电函数及消光系数等光学性质最优㊂本研究可为GeC 光电相关实验制备提供理论基础㊂关键词:GeC;掺杂;第一性原理;电子结构;光学性质中图分类号:O643.36;O644.1㊀㊀文献标志码:A ㊀㊀文章编号:1000-985X (2024)03-0519-07First-Principles Study on the Photoelectric Properties of N and As Doped Two-Dimensional GeCLI Ping 1,QIN Yanjun 1,PANG Guowang 1,TANG Yuzhu 2,ZHANG Yao 2,WANG Peng 2,LIU Chenxi 3(1.College of Science,Xinjiang Institute of Technology,Aksu 843100,China;2.School of Electrical and Mechanical Engineering,Xinjiang Institute of Technology,Aksu 843100,China;3.Shaanxi Province Key Laboratory of Thin Films Technology and Optical Test,School of Opto-electronical Engineering,Xi an Technological University,Xi an 710021,China)Abstract :Based on the first-principles calculations of density functional theory,the stability,electronic structure,and optical properties of single layer GeC,N-doped,As doped,and N-As doped GeC systems were systematically studied.The results show that the single layer GeC is a direct bandgap semiconductor with the bandgap of pared with the single layer GeC,the bandgap and work function of the doped system decrease,indicating that the required energy for electronic transition is relatively small in our doped system.Moreover,the light absorption coefficient of the doped system improves,and the absorption band edge has also undergone a red shift,effectively expanding the response range of the system to light andimproving the absorption ability of the system to photons.In addition,the As doped GeC system not only exhibits impurity levels near the Fermi level,but also shows the optimal optical properties such as absorption coefficient,static dielectric function,and extinction coefficient in the low energy region.The above research can provide a theoretical basis for the preparation of relevant GeC photoelectric experiments.Key words :GeC;doping;first-principle;electronic structure;optical property ㊀㊀收稿日期:2023-10-08㊀㊀基金项目:新疆维吾尔自治区自然科学基金(2021D01B46,2021D01B47);新疆维吾尔自治区重点研发计划项目(2020B02011)㊀㊀作者简介:李㊀萍(1990 ),女,甘肃省人,讲师㊂E-mail:1659681147@ ㊀㊀通信作者:刘晨曦,博士㊂E-mail:liuchenxi4674@ 0㊀引㊀㊀言2004年,Novoselov 等成功地剥离了石墨烯,并在其中检测到优异的光电性能[1]㊂自此,诸如二维的碳化物㊁氮化物及过渡金属硫化物等类石墨相材料因具有独特的物理特性而被研究者们广泛探索[2-3]㊂据文献520㊀研究论文人工晶体学报㊀㊀㊀㊀㊀㊀第53卷[4-5]报道,六方碳化锗(GeC)是二维材料的典型代表,具有稳定的结构和可调的带隙,可利用化学气相沉积和射频磁控溅射等多种实验方法制备㊂单层GeC具有比石墨烯更高的泊松比和更低的硬度,与此同时,GeC 原子间电负性的不同会导致电子转移并产生Lewis酸碱位点,被认为是析氢㊁CO2还原及光降解有机物等方面潜在的催化剂[6-7]㊂因此,本文选择单层GeC作为研究对象,以期制备出性能优异的光催化材料㊂然而,单层GeC的带隙略宽(约为3.25eV),在光催化水分解领域的应用有一定的局限性,但可通过元素掺杂㊁空位缺陷㊁外加应变和构建异质结等方式来改性单层GeC[8-9]㊂其中,元素掺杂是调控体系电子结构和光学性质的有效方式之一,在理论或实验上都处于相当成熟的阶段㊂例如:刘晨曦等[10]通过S和V掺杂石墨相氮化碳,发现掺杂后体系的吸收带边红移,其吸收系数均有所提高,有利于光催化性能的提高;Fan等[8]系统地研究了3d㊁4d和5d过渡金属元素掺杂单层GeC的电子结构,发现掺杂后单层GeC的能带结构发生了不同程度的改变,具有丰富的半金属㊁金属和半导体性质;Arellano等[11]采用密度泛函理论报道了Cu㊁Ag和Au 掺杂单层GeC,可提高体系的储氢能力,极大地拓展了绿色能源的开发应用㊂总之,掺杂是调节光学带隙及拓宽光响应范围的有效手段,为实现更高的太阳能利用率和光催化活性的新型GeC基光催化剂提供理论支撑㊂考虑到体系的晶格畸变和稳定性,本工作选择与C(Ge)邻近的N(As)元素进行掺杂,构建了单层GeC㊁N(As)掺杂,以及N-As共掺杂单层GeC体系㊂采用第一性原理方法对四种体系的稳定性㊁电子结构及光学性质等进行了计算分析㊂结果表明,N和As掺杂单层GeC在光催化中发生跃迁所需的能量更低,并具有更高的吸收率㊂1㊀计算方法与模型构建本工作是基于密度泛函理论第一性原理的方法进行的,应用Material Studio软件包计算了单层GeC及其掺杂体系的电子结构和光学性质[12]㊂使用广义梯度近似(generalized gradient approximation,GGA)下的Perdew-Burke-Ernzerhof(PBE)作为电子交换关联泛函[13]㊂根据Monkhorst-Pack方案选择了4ˑ4ˑ1为K 点,经收敛性测试后将截断能设置为550eV[14]㊂迭代过程中的能量和单原子受力分别收敛到10-5eV/atom 和0.05eV/Å㊂公差偏移量和内应力分别小于0.002Å和0.1GPa㊂为了避免周期性相互作用,在Z轴上增加了一个20Å的真空层㊂本工作的研究对象是六方相GeC,其单层中Ge原子以共价键形式与相邻的3个C原子相连,晶格参数为a=b=3.25Å,α=β=90ʎ,γ=120ʎ[4]㊂根据文献[8]调研与收敛性测试,本文选取了4ˑ4ˑ1的超胞进行元素掺杂,掺杂位置如图1所示㊂各原子的价电子组态分别为C(2s22p2)㊁Ge(4s24p2)㊁N(2s22p3)及As(4s24p3)㊂图1㊀晶体结构俯视图Fig.1㊀Top view of crystal structure2㊀结果与讨论2.1㊀结构优化本工作对N和As掺杂单层GeC体系进行了几何优化,优化后的晶格参数㊁形成能及键长等如表1所示㊂由表1可知,单层GeC优化后的晶格常数为a=b=3.25Å,而C Ge键长为1.87Å,这与Khossossi 等[15]的研究一致,说明本工作参数设置合理㊂与未掺杂体系相比,掺杂后体系最大键长均增大,最小键长均减小,这说明掺杂体系发生了晶格畸变,可能会破坏体系的对称性,使晶胞内的正负电荷中心不再重合,有利于载流子数量的增加[16]㊂同时,本文计算了掺杂前后体系的缺陷形成能(E form)来判断杂质原子掺入体系的㊀第3期李㊀萍等:N和As掺杂二维GeC光电性质的第一性原理研究521㊀相对难易程度,计算公式为[17]E form=E defect-E perfect+ðμi-ðμj(1)式中:E defect是掺杂后GeC的总能量,E perfect为未掺杂GeC的总能量,μi和μj表示掺杂原子和被替换原子的化学势㊂与未掺杂体系相比,掺杂后体系的形成能均较小,其中N-As掺杂GeC体系的形成能最低㊂此外,计算声子谱是研究动态稳定性的可靠方法㊂由图2可知,该体系的声子结构没有出现虚频,证实了其固有的动态稳定性㊂从形成能和声子谱的计算结果来看,该结构具有良好的稳定性,N和As掺杂GeC较易形成稳定的掺杂体系㊂表1㊀GeC体系掺杂前后的晶格参数㊁键长及形成能Table1㊀Lattice parameters,bond length and formation energy of GeC systems before and after dopingSystem a=b/Åd(C Ge min)/Åd(C Ge max)/ÅE form/eVGeC 3.25 1.870 1.871N-GeC 3.26 1.863 1.890 1.572As-GeC 3.24 1.864 1.873 1.236N-As-GeC 3.23 1.848 1.8840.431图2㊀N和As掺杂GeC的声子谱Fig.2㊀Phonon spectra of N and As doped GeC2.2㊀电子结构为了探究GeC掺杂前后体系电子结构的变化情况,本工作构建了N和As掺杂GeC的能带结构和态密度,设置能量零点为费米能级,如图3所示㊂由图3(a1)可知,单层GeC的带隙为2.10eV,属于直接跃迁,这与Xu等[18]的结果相近,说明本工作的合理性㊂但结果低于实验值[19],这可能是因为密度泛函理论在计算过程中没有考虑到交换-关联势的不连续性,但本工作研究的是体系的相对变化趋势,并不影响计算结果的准确性[10]㊂从态密度可以看出,单层GeC的价带和导带主要由C和Ge的2p轨道贡献,如图3(a2)所示㊂由于Ge(1.8)和C(2.5)原子电负性的差异,电子会从Ge原子转移到C原子,因此C周围富电子,Ge周围富空穴㊂与未掺杂体系相比,N和As掺杂后体系的带隙宽度均有所减小,有利于电子由价带跃迁至导带㊂众所周知,小带隙半导体可以增强光的吸收且益于光催化材料的制备㊂此外,N掺杂GeC体系的费米能级穿过导带,呈现出n型半导体特征,主要由N的2s和2p态贡献(见图3(b2)),可作为n型半导体材料[20]㊂而As掺杂GeC体系在费米能级附近出现了杂质能级,为电子的跃迁提供了桥梁,使电子的跃迁更加容易[21]㊂由图3(c2)可知,As掺杂GeC体系的费米能级附近出现了一个峰,主要由As的2s和2p态贡献及C 的2p态贡献㊂N和As掺杂GeC体系的带隙减小为1.72eV,在价带顶附近有浅能级出现,浅能级中的载流子易被电离成自由载流子,能有效提高载流子的迁移能力㊂综上所述,与未掺杂体系相比,N和As掺杂能够有效减小GeC体系的带隙宽度,提高电子的迁移能力㊂为了进一步理解电子的迁移情况,本工作计算了N和As掺杂单层GeC体系的功函数㊂功函数(Φ)表示电子由半导体内部移动至表面所需的能量,如公式(2)[22]:Φ=E vac-E f(2)522㊀研究论文人工晶体学报㊀㊀㊀㊀㊀㊀第53卷图3㊀单层GeC(a1)㊁N-GeC(b1)㊁As-GeC(c1)㊁N-As-GeC(d1)的能带结构图;单层GeC(a2)㊁N-GeC(b2)㊁As-GeC(c2)㊁N-As-GeC(d2)的态密度图Fig.3㊀Band structure diagrams of single layer GeC(a1),N-GeC(b1),As-GeC(c1),N-As-GeC(d1);density of states diagrams of single layer GeC(a2),N-GeC(b2),As-GeC(c2),N-As-GeC(d2)㊀第3期李㊀萍等:N和As掺杂二维GeC光电性质的第一性原理研究523㊀式中:E vac是真空能级,E f是费米能级㊂由图4可知,单层GeC㊁N掺杂GeC㊁As掺杂GeC及N-As共掺杂GeC 体系的功函数分别为4.567㊁3.578㊁3.859和4.301eV㊂另外,单层GeC的功函数最大,大的功函数说明表面对电子的束缚能力较强㊂与未掺杂体系相比,所有掺杂体系的功函数均有不同程度的减小,说明N和As 掺杂能够有效提高电子的跃迁能力㊂综上所述,N和As掺杂能有效减小体系的功函数,提高体系电子跃迁的能力㊂图4㊀功函数图Fig.4㊀Work function diagrams2.3㊀光学性质为探究N和As掺杂GeC体系的光学性质,本工作计算了单层GeC㊁N掺杂GeC㊁As掺杂GeC及N-As掺杂GeC体系的光吸收,如图5(a)所示㊂与未掺杂体系相比,N和As掺杂后体系的吸收系数在低能区均有所提高,可推测N和As掺杂能够有效提高体系的光吸收能力㊂此外,掺杂体系的吸收带边均向低能方向移动,也就是发生了红移,有效地拓宽了体系对光的响应范围㊂图5(b)是N和As掺杂GeC体系的复介电函数实部图㊂在无入射光时,介电函数实部曲线与纵轴的交点是静介电常数㊂静介电常数越大表示体系的极化能力越强,对光的利用率越高[23]㊂与未掺杂体系相比,掺杂后体系的静介电常数均有不同程度的增大,其中As掺杂GeC的静介电常数最大,说明As掺杂GeC体系的极化能力最强,对光的利用率最高㊂图5(c)是N和As掺杂GeC体系的介电函数虚部图㊂由文献[24]可知,介电函数虚部可表征体系对光子的吸收能力㊂可发现掺杂体系的介电函数虚部均比未掺杂体系高,且As掺杂GeC体系形成了一个新峰,说明As掺杂GeC体系对光子的吸收能力最强㊂上述分析与介电函数的实部相对应㊂图5(d)是N和As掺杂GeC体系的折射率(n)随能量变化的趋势图㊂由图5(d)可知单层GeC的静态折射率为1.63,而N掺杂GeC㊁As掺杂GeC及N-As掺杂GeC的静态折射率分别为1.73㊁1.82和1.67,说明掺杂体系的折射率均有不同程度的提高㊂图5(e)是N和As掺杂GeC体系的消光系数(k)曲线,用公式k=αλ4πn计算,其中α为吸收系数,λ为对应的波长,n为对应波长的折射率㊂也就是说消光系数是随波长变化的常量,可知掺杂体系的消光系数曲线在低能区高于未掺杂体系,其中As掺杂GeC体系在低能区的消光系数最大并且出现了一个新峰,与上述其他光学性质的分析结果一致㊂综上所述,N和As掺杂能够有效拓宽体系对光的响应范围,提高体系对光子的吸收能力㊂524㊀研究论文人工晶体学报㊀㊀㊀㊀㊀㊀第53卷图5㊀GeC体系掺杂前后的光学性质图㊂(a)吸收光谱;(b)介电函数实部;(c)介电函数虚部;(d)折射率;(e)消光系数Fig.5㊀Optical property diagrams of GeC system before and after doping.(a)Absorption spectra;(b)real part of dielectric function;(c)imaginary part of dielectric function;(d)refractive index;(e)extinction coefficient3㊀结㊀㊀论本文利用第一性原理,对掺杂前后GeC体系的超胞进行了优化并计算了相应的电子结构与光学性质,并得出以下结论:1)由稳定性计算可知,N和As掺杂GeC体系的形成能均较低,其中N-As掺杂GeC体系的形成能最低且声子谱未出现虚频,说明N和As共掺杂GeC不会影响体系的稳定性㊂2)由电子结构可知,单层GeC的带隙为2.10eV,导带和价带主要由C和Ge的2p轨道贡献㊂与单层GeC 相比,N掺杂GeC体系的费米能级穿过导带,可作为n型半导体材料;As掺杂GeC体系在费米能级附近出现杂质能级,为电子的跃迁提供了桥梁;N-As掺杂GeC体系的带隙最小,说明电子由价带顶跃迁至导带底最易跃迁㊂3)由光学性质可知,掺杂后体系的吸收带边均发生了红移,可推测N和As掺杂可能会提高GeC对光的响应能力,并且掺杂后体系的吸收系数㊁静介电常数㊁折射率及消光系数在低能区均有不同程度的提高㊂此外,As的掺杂对GeC光学性质的增强更为显著㊂上述结论为N和As掺杂GeC在光电领域的研究和应用提供了一定的理论参考㊂参考文献[1]㊀NOVOSELOV K S,GEIM A K,MOROZOV S V,et al.Electric field effect in atomically thin carbon films[J].Science,2004,306(5696):666-669.[2]㊀LIU C X,DAI Z H,HOU J E,et al.First-principles study for the electric field influence on electronic and optical properties of AlN/g-C3N4heterostructure[J].Journal of Applied Physics,2023,133(16):164902.[3]㊀TIEN T M,CHUNG Y J,HUANG C T,et al.Fabrication of WS2/WSe2Z-scheme 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Elsevier期刊被SCI收录最新一期题录信息

Elsevier期刊被SCI收录最新一期题录信息本内容包括：主题、各主题有代表性刊名、该刊最新一期目录信息（包括卷期、论文题名、页码及作者等）Automation & Control Systems（自动化及控制系统）SYSTEMS & CONTROL LETTERSVolume 59, Issue 5, Pages 265-322 (May 2010)1.Editorial BoardPage IFC2.Gain-scheduled open-loop system design for LPV systems using polynomially parameter-dependent Lyapunov functionsPages 265-276Masayuki Sato3.Delay-adaptive feedback for linear feedforward systemsPages 277-283Nikolaos Bekiaris-Liberis, Miroslav Krstic4.Implicit Euler numerical scheme and chattering-free implementation of sliding mode systemsPages 284-293Vincent Acary, Bernard Brogliato5.Decentralized dynamic nonlinear controllers to minimize transmit power in cellular networks, Part IPages 294-298Vishwesh V. Kulkarni, Mayuresh V. Kothare, Michael G. Safonov6. 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Hernández Creus7.Improvements in the extraction of cell electric properties from their electrorotation spectrumPages 25-30Damien Voyer, Marie Frénéa-Robin, Franois Buret, Laurent Nicolas8.Electrochemical DNA biosensor for the detection of specific gene related to Trichoderma harzianum speciesPages 31-36Shafiquzzaman Siddiquee, Nor Azah Yusof, Abu Bakar Salleh, Fatimah Abu Bakar, Lee Yook Heng9.Development of electrochemical DNA biosensor based on gold nanoparticle modified electrode by electroless depositionPages 37-42Shufeng Liu, Jing Liu, Li Wang, Feng Zhao10.Herbicides affect fluorescence and electron transfer activity of spinach chloroplasts, thylakoid membranes and isolated Photosystem IIPages 43-49Andrea Ventrella, Lucia Catucci, Angela Agostiano11.Nanostructured polypyrrole-coated anode for sun-powered microbial fuel cells Pages 50-56Yongjin Zou, John Pisciotta, Ilia V. Baskakov12.Anodic oxidation of 3,4-dihydroxyphenylacetic acid on carbon electrodes in acetic acid solutionsPages 57-65Slawomir Michalkiewicz, Agata Skorupa13.A voltammetric Rhodotorula mucilaginosa modified microbial biosensor for Cu(II) determinationPages 66-70Meral Yüce, Hasan Nazır, Gönül Dönmez14.Explore various co-substrates for simultaneous electricity generation and Congo red degradation in air-cathode single-chamber microbial fuel cellPages 71-76Yunqing Cao, Yongyou Hu, Jian Sun, Bin Hou15.Electrochemical oxidation of amphetamine-like drugs and application to electroanalysis of ecstasy in human serumPages 77-83E.M.P.J. Garrido, J.M.P.J. Garrido, N. Milhazes,F. Borges, A.M. Oliveira-Brett16.A l-cysteine sensor based on Pt nanoparticles/poly(o-aminophenol) film on glassy carbon electrodePages 84-89Li-Ping Liu, Zhao-Jing Yin, Zhou-Sheng Yang17.The effects of the electro-photodynamic in vitro treatment on human lung adenocarcinoma cellsPages 90-94Jolanta Saczko, Mariola Nowak, Nina Skolucka, Julita Kulbacka, Malgorzata Kotulska 18.Gadolinium blocks membrane permeabilization induced by nanosecond electric pulses and reduces cell deathPages 95-100Franck M. André, Mikhail A. Rassokhin, Angela M. Bowman, Andrei G. 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Rodaitė-Riševičienė24.Carbon nanotube-enhanced cell electropermeabilisationPages 136-141Vittoria Raffa, Gianni Ciofani, Orazio Vittorio, Virginia Pensabene, Alfred Cuschieri25.Dependence of catalytic activity and long-term stability of enzyme hydrogel films on curing timePages 142-146Joshua Lehr, Bryce E. Williamson, Frédéric Barrière, Alison J. Downard26.Enzymatic flow injection method for rapid determination of choline in urine with electrochemiluminescence detectionPages 147-151Jiye Jin, Masahiro Muroga, Fumiki Takahashi, Toshio NakamuraChemistry Applied（化学应用）CARBOHYDRATE POLYMERSVolume 81, Issue 4, Pages 751-970 (23 July 2010)1.Editorial BoardPage CO22.Adsorption separation of Ni(II) ions by dialdehyde o-phenylenediamine starch from aqueous solutionPages 751-757Ping Zhao, Jian Jiang, Feng-wei Zhang, Wen-feng Zhao, Jun-tao Liu, Rong Li3.Rheological and morphological characterization of the culture broth during exopolysaccharide production by Enterobacter sp.Pages 758-764Vítor D. 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Samad11.Banana fibers and microfibrils as lignocellulosic reinforcements in polymer compositesPages 811-819Maha M. Ibrahim, Alain Dufresne, Waleed K. El-Zawawy, Foster A. Agblevor12.Variability of biomass chemical composition and rapid analysis using FT-NIR techniquesPages 820-829Lu Liu, X. Philip Ye, Alvin R. Womac, Shahab Sokhansanj13.TEMPO oxidation of gelatinized potato starch results in acid resistant blocks of glucuronic acid moietiesPages 830-838Ruud ter Haar, Johan W. Timmermans, Ted M. Slaghek, Francisca E.M. Van Dongen, HenkA. Schols, Harry Gruppen14.Development of films based on quinoa (Chenopodium quinoa, Willdenow) starch Pages 839-848Patricia C. Araujo-Farro, G. Podadera, Paulo J.A. Sobral, Florencia C. Menegalli 15.Polysaccharide determination in protein/polysaccharide mixtures for phase-diagram constructionPages 849-854Jacob K. 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Part III: Structures and properties of the Naegeli dextrinsPages 885-891Hongxin Jiang, Sathaporn Srichuwong, Mark Campbell, Jay-lin Jane21.Multistage deacetylation of chitin: Kinetics studyPages 892-896N. Yaghobi, F. Hormozi22.Sulfated modification, characterization and structure–antioxidantrelationships of Artemisia sphaerocephala polysaccharidesPages 897-905Junlong Wang, Hongyun Guo, Ji Zhang, Xiaofang Wang, Baotang Zhao, Jian Yao, Yunpu Wang23.Magnetic chitosan/iron (II, III) oxide nanoparticles prepared by spray-drying Pages 906-910Hsin-Yi Huang, Yeong-Tarng Shieh, Chao-Ming Shih, Yawo-Kuo Twu24.Effect of adding a small amount of high molecular weight polyacrylamide on properties of oxidized cassava starchPages 911-918Yan Liu, Xu-chao Lv, Xiao Hu, Zhi-hua Shan, Pu-xin Zhu25.Preparation of nanofibrillar carbon from chitin nanofibersPages 919-924M. Nogi, F. Kurosaki, H. Yano, M. Takano26.Preparation and characterization of cellulose acetate–Fe2O3 composite nanofibrous materialsPages 925-930Costas Tsioptsias, Kyriaki G. Sakellariou, Ioannis Tsivintzelis, Lambrini Papadopoulou, Costas Panayiotou27.Synthesis, characteristic and antibacterial activity of N,N,N-trimethyl chitosan and its carboxymethyl derivativesPages 931-936Tao Xu, Meihua Xin, Mingchun Li, Huili Huang, Shengquan Zhou28.Fast compositional analysis of ramie using near-infrared spectroscopyPages 937-941Wei Jiang, Guangting Han, Yuanming Zhang, Mengmeng Wang29.Structure characterization of polysaccharide isolated from the fruiting bodies of Tricholoma matsutakePages 942-947Xiang Ding, Su Feng, Mei Cao, Mao-tao Li, Jie Tang, Chun-xiao Guo, Jie Zhang, Qun Sun, Zhi-rong Yang, Jian Zhao30.New insights into viscosity abnormality of sodium alginate aqueous solution Pages 948-952Dan Zhong, Xin Huang, Hu Yang, Rongshi Cheng31.Structural characterization and anti-inflammatory activity of two water-soluble polysaccharides from Bellamya purificataPages 953-960Hong Zhang, Lin Ye, Kuiwu WangComputer Science, Artificial Intelligence（计算机科学，人工智能）ARTIFICIAL INTELLIGENCEVolume 174, Issue 11, Pages 639-766 (July 2010)1.Editorial BoardPage IFC2.Partial observability and learnabilityPages 639-669Loizos Michael3.Monte Carlo tree search in KriegspielPages 670-684Paolo Ciancarini, Gian Piero Favini4.Learning conditional preference networksPages 685-703Frédéric Koriche, Bruno Zanuttini5.Planning to see: A hierarchical approach to planning visual actions on a robot using POMDPsPages 704-725Mohan Sridharan, Jeremy Wyatt, Richard Dearden6.Analysis of a probabilistic model of redundancy in unsupervised information extractionPages 726-748Doug Downey, Oren Etzioni, Stephen Soderland7. Designing competitions between teams of individualsPages 749-766Pingzhong Tang, Yoav Shoham, Fangzhen LinEnergy & Fuels（能源和燃料）APPLIED ENERGYVolume 87, Issue 8, Pages 2427-2768 (August 2010)1.IFCPage IFC2. Energy balance analysis of wind-based pumped hydro storage systems in remote island electrical networksPages 2427-2437J.K. Kaldellis, M. Kapsali, K.A. 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González9.Efficiency improvement of the DSSCs by building the carbon black as bridge in photoelectrodePages 2500-2505Chen-Ching Ting, Wei-Shi Chao10.Integer programming with random-boundary intervals for planning municipal power systemsPages 2506-2516M.F. Cao, G.H. Huang, Q.G. Lin11. Modeling the relationship between the oil price and global food prices Pages 2517-2525Sheng-Tung Chen, Hsiao-I Kuo, Chi-Chung Chen12.Marginal production in the Gulf of Mexico – II. Model resultsPages 2526-2534Mark J. Kaiser, Yunke Yu13.Marginal production in the Gulf of Mexico – I. Historical statistics & model frameworkPages 2535-2550Mark J. Kaiser14.Assessment of forest biomass for use as energy. GIS-based analysis of geographical availability and locations of wood-fired power plants in PortugalPages 2551-2560H. Viana, Warren B. Cohen, D. Lopes, J. Aranha15.Alkaline catalyzed biodiesel production from moringa oleifera oil with optimized production parametersPages 2561-2565G. Kafuku, M. Mbarawae of two-component Weibull mixtures in the analysis of wind speed in the Eastern MediterraneanPages 2566-2573S.A. Akdağ, H.S. Bagiorgas, G. Mihalakakou17.Evaluation of wind energy investment interest and electricity generation cost analysis for TurkeyPages 2574-2580Seyit Ahmet Akdağ, Önder Güler18.The role of demand-side management in the grid integration of wind power Pages 2581-2588Pedro S. Moura, Aníbal T. de Almeida19.Synthesis of biodiesel from waste vegetable oil with large amounts of free fatty acids using a carbon-based solid acid catalystPages 2589-2596Qing Shu, Jixian Gao, Zeeshan Nawaz, Yuhui Liao, Dezheng Wang, Jinfu Wang20.A study on the overall efficiency of direct methanol fuel cell by methanol crossover currentPages 2597-2604Sang Hern Seo, Chang Sik Lee21.Study of heat transfer between an over-bed oil burner flame and a fluidized bed during start-up: Determination of the flame to bed convection coefficientPages 2605-2614Vijay Jain, Dominic Groulx, Prabir Basu22.Predictive tools for the estimation of downcomer velocity and vapor capacity factor in fractionatorsPages 2615-2620Alireza Bahadori, Hari B. Vuthaluru23. Monitoring strategies for a combined cycle electric power generatorPages 2621-2627Joshua Finn, John Wagner, Hany Bassily24. Combustion and heat transfer at meso-scale with thermal recuperationPages 2628-2639V. Vijayan, A.K. 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Separation characteristics of clathrate hydrates from a cooling plate forefficient cold energy storagePages 2682-2689Tadafumi Daitoku, Yoshio Utaka32. A flexible numerical model to study an active magnetic refrigerator for near room temperature applicationsPages 2690-2698Ciro Aprea, Angelo Maiorino33. Feasibility study of an ice slurry-cooling coil for HVAC and R systems in a tropical buildingPages 2699-2711Y.H. Yau, S.K. Lee34. Optimum sizing of wind-battery systems incorporating resource uncertainty Pages 2712-2727Anindita Roy, Shireesh B. Kedare, Santanu Bandyopadhyay35. Peak current mode control of three-phase boost rectifiers in discontinuous conduction mode for small wind power generatorsPages 2728-2736O. Carranza, G. Garcerá, E. Figueres, L.G. González36. Experimental flow field characteristics of OFA for large-angle counter flow of fuel-rich jet combustion technologyPages 2737-2745Weidong Fan, Zhengchun Lin, Youyi Li, Mingchuan ZhangEngineering, Electrical & Electronic（电机及电子工程）MICROELECTRONIC ENGINEERINGVolume 87, Issue 9, Pages 1655-1808 (November 2010)1. Inside Front Cover - Editorial BoardPage IFC2 PrefacePage 1655Joel Barnett3.In0.53Ga0.47As(1 0 0) native oxide removal by liquid and gas phase HF/H2O chemistriesPages 1656-1660F.L. Lie, W. Rachmady, A.J. Muscat4.A study of the interaction of gallium arsenide with wet chemical formulations using thermodynamic calculations and spectroscopic ellipsometryPages 1661-1664J. Price, J. Barnett, S. Raghavan, M. Keswani, R. Govindarajan5.The removal of nanoparticles from sub-micron trenches using megasonicsPages 1665-1668Pegah Karimi, Taehoon Kim, Juan Aceros, Jingoo Park, Ahmed A. Busnaina6.In-line control of Si loss after post ion implantation stripPages 1669-1673D. Shamiryan, D. Radisic, W. Boullart7.Removal of post-etch 193 nm photoresist in porous low-k dielectric patterning using UV irradiation and ozonated waterPages 1674-1679E. Kesters, Q.T. Le, M. Lux, L. Prager, G. Vereecke8.Repair of plasma-damaged p-SiOCH dielectric films in supercritical CO2Pages 1680-1684Jae Mok Jung, Hong Seok Kwon, Won-Ki Lee, Byung-Chun Choi, Hyun Gyu Kim, Kwon Taek Lim9.Development of compatible wet-clean stripper for integration of CoWP metal cap in Cu/low-k interconnectsPages 1685-1688Aiping Wu, Eugene Baryschpolec, Madhukar Rao, Matthias Schaller, Christin Bartsch, Susanne Leppack, Andreas Ott10.Dissolution and electrochemical impedance spectroscopy studies of thin copper oxide films on copper in semi-aqueous fluoride solutionsPages 1689-1695N. Venkataraman, S. Raghavan11.The sacrificial oxide etching of poly-Si cantilevers having high aspect ratios using supercritical CO2Pages 1696-1700Ha Soo Hwang, Jae Hyun Bae, Jae Mok Jung, Kwon Taek Lim12.Monitoring wafer cleanliness and metal contamination via VPD ICP-MS: Case studies for next generation requirementsPages 1701-1705Meredith Beebe, Scott Anderson13.Fabrication of a two-step Ni stamp for blind via hole application on PWB Pages 1707-1710In-Soo Park, Jin-Soo Kim, Seong-Hun Na, Seung-Kyu Lim, Young-Soo Oh, Su-Jeong Suh 14.Arrays of metallic nanocones fabricated by UV-nanoimprint lithographyPages 1711-1715Juha M. Kontio, Janne Simonen, Juha Tommila, Markus Pessa15.Synthesis, characterization of CeO2@SiO2 nanoparticles and their oxide CMP behaviorPages 1716-1720Xiaobing Zhao, Renwei Long, Yang Chen, Zhigang Chen16.Development of a triangular-plate MEMS tunable capacitor with linear capacitance–voltage responsePages 1721-1727M. Shavezipur, S.M. Hashemi, P. Nieva, A. Khajepour17.The correlation of the electrical properties with electron irradiation and constant voltage stress for MIS devices based on high-k double layer (HfTiSiO:N and HfTiO:N) dielectricsPages 1728-1734V. Mikhelashvili, P. Thangadurai, W.D. Kaplan, G. Eisenstein18. Intra-level voltage ramping-up to dielectric breakdown failure on Cu/porous low-k interconnections in 45 nm ULSI generationPages 1735-1740C.H. Huang, N.F. Wang, Y.Z. Tsai, C.I. Hung, M.P. Houng19. Anodic bonding of glass–ceramics to stainless steel coated with intermediate SiO2 layerPages 1741-1746Dehua Xiong, Jinshu Cheng, Hong Li, Wei Deng, Kai Ye20.Preparation of silica/ceria nano composite abrasive and its CMP behavior on hard disk substratePages 1747-1750Hong Lei, Fengling Chu, Baoqi Xiao, Xifu Tu, Hua Xu, Haineng Qiu21.Investigation on the controllable growth of monodisperse silica colloid abrasives for the chemical mechanical polishing applicationPages 1751-1755XiaoKai Hu, Zhitang Song, Haibo Wang, Weili Liu, Zefang Zhang22.Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol–gel method and reaction-anneal treatmentPages 1756-1759You-Pin Gong, Ai-Dong Li, Chao Zhao, Yi-Dong Xia, Di Wu23.Frequency properties of on-die power distribution network in VLSI circuits Pages 1760-1763Pavel Livshits, Yefim Fefer, Anton Rozen, Yoram Shapira24.Analytical modelling for the current–voltage characteristics of undoped or lightly-doped symmetric double-gate MOSFETsPages 1764-1768A. Tsormpatzoglou, D.H. Tassis, C.A. Dimitriadis, G. Ghibaudo, G. Pananakakis, N. Collaert25.Anti-buckling S-shaped vertical microprobes with branch springsPages 1769-1776Jung Yup Kim, Hak Joo Lee, Young-Ho Cho26.Characterization of UV photodetectors with MgxZn1−xO thin filmsPages 1777-1780Tung-Te Chu, Huilin Jiang, Liang-Wen Ji, Te-Hua Fang, Wei-Shun Shi, Tian-Long Chang, Teen-Hang Meen, Jingchang Zhong27.Barrier height temperature coefficient in ideal Ti/n-GaAs Schottky contacts Pages 1781-1784T. Göksu, N. Yıldırım, H. Korkut, A.F. Özdemir, A. Turut, A. Kökçe28.Optical coherence tomography for non-destructive investigation of silicon integrated-circuitsPages 1785-1791K.A. Serrels, M.K. Renner, D.T. Reid29.Materials selection procedure for RF-MEMSPages 1792-1795G. Guisbiers, E. Herth, B. Legrand, N. Rolland, T. Lasri, L. 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氮化镓xps峰偏移

氮化镓xps峰偏移全文共四篇示例，供读者参考第一篇示例：氮化镓（GaN）是一种关键的半导体材料，具有广泛的应用范围，包括LED、激光二极管、功率电子器件等。

在研究和开发氮化镓材料时，一项非常重要的技术是X射线光电子能谱（XPS）分析。

通过XPS 分析，可以研究材料表面的化学成分及其电子结构，以便深入了解材料的性能和特性。

在进行氮化镓XPS分析时，研究者常常会关注氮化镓的XPS峰偏移情况。

XPS峰偏移是指在XPS谱图中各峰的位置相对于标准物质的特定位置的偏移量，这通常反映了材料的化学状态和晶格结构等信息。

对氮化镓的XPS峰偏移进行准确的分析和理解，可以帮助研究者更好地认识氮化镓材料的性质和特性。

氮化镓的XPS峰偏移主要受到以下几个方面的影响：1. 化学成分：氮化镓的XPS峰偏移与其化学成分密切相关。

氮化镓材料通常包含氮、镓等元素，不同的化学组分会导致XPS峰的位置发生变化。

氮的化学状态和镓原子与氮原子的相互作用会影响XPS峰的位置。

2. 晶格结构：氮化镓的晶格结构也会对XPS峰偏移产生影响。

晶格结构的改变会导致化学键的变化，从而影响XPS峰的位置。

研究者可以通过对氮化镓材料的晶格结构进行分析，来解释XPS峰偏移的原因。

3. 表面状态：氮化镓材料的表面状态也会对XPS峰偏移产生影响。

表面的缺陷、氧化物等都可能影响XPS峰的位置。

研究者需要充分了解氮化镓材料的表面状态，以确保XPS分析结果的准确性。

氮化镓的XPS峰偏移是一个重要的研究课题，可以帮助研究者深入了解氮化镓材料的性质和特性。

通过对氮化镓的XPS峰偏移进行系统研究，可以为氮化镓材料的应用和性能优化提供重要的参考。

希望未来能有更多关于氮化镓XPS峰偏移的研究成果出现，为氮化镓材料的发展和应用开拓新的可能性。

第二篇示例：氮化镓（GaN）是一种重要的半导体材料，具有广泛的应用，特别是在光电子学和电子器件领域。

X射线光电子能谱（XPS）是一种非常有用的表征材料表面元素化学状态和电子结构的技术。

德国应用化学--石墨烯综述

DOI:10.1002/anie.200901678Graphene:The New Two-Dimensional NanomaterialC.N.R.Rao,*A.K.Sood,K.S.Subrahmanyam,and indarajAngewandteChemieKeywords:carbon ·graphene ·graphene oxide ·monolayers ·nanostructures77522009Wiley-VCH Verlag GmbH &Co.KGaA,WeinheimAngew.Chem.Int.Ed.2009,48,7752–77771.IntroductionGraphene,the parent of all graphitic forms (Figure 1),has become one of the most exciting topics of research in the last three to four years.[1]This two-dimensional material consti-tutes a new nanocarbon comprising layers of carbon atoms arranged in six-membered rings.It is distinctly different from carbon nanotubes (CNTs)and fullerenes,and exhibits unique properties which have fascinated the scientific community.Typically important properties of graphene are a quantum Hall effect at room temperature,[2–4]an ambipolar electric field effect along with ballistic conduction of charge carriers,[5]tunable band gap,[6]and high elasticity.[7]Although graphene is expected to be perfectly flat,ripples occur because of thermal fluctuations.[1]Ideally graphene is a single-layer material,but graphene samples with two or more layers are being investigated with equal interest.Three different types of graphenes can be defined:single-layer graphene (SG),bilayer graphene (BG),and few-layer graphene (FG,number of layers 10).Although single-layer graphene and bilayer graphene were first obtained by micro-mechanical cleavage,[5]several strategies have since been developed for the synthesis of graphenes.[8]Graphene has been characterized by a variety of micro-scopic and other physical techniques including atomic force microscopy (AFM),transmission electron microscopy (TEM),scanning tunneling microscopy (STM),X-ray dif-fraction (XRD),and Raman spectroscopy.[1]It is interesting that single-layer graphene placed on a silicon wafer with a 300nm thick layer of SiO 2,becomes visible in an optical microscope (Figure 2a and b).[8–10]While AFM directly gives the number of layers (Figure 2c),[8]STM (Figure 2d)[11]and TEM (Figure 2e)[12]images are useful in determining the morphology and structure of graphene.Raman spectroscopy has emerged to be an important tool for the characterization of graphene samples.[13–16]Herein,we shall discuss various aspects of graphene,including synthesis,structure,properties,functionalization,and polymer composites.Although we have covered most of the important facets of graphene published up to May 2009,we have given somewhat greater importance to the chemical aspects and cited a large number of references from the rapidly increasing literature.We do hope that the[*]Prof.Dr.C.N.R.Rao,K.S.Subrahmanyam,indarajInternational Centre for Materials Science,New Chemistry Unit and CSIR Centre of Excellence in Chemistry,Jawaharlal Nehru Centre for Advanced Scientific ResearchJakkur P.O.,Bangalore 560064(India)Fax:(+91)80-2208-2760E-mail:cnrrao@jncasr.ac.in Prof.Dr.A.K.SoodDepartment of Physics,Indian Institute of Science Bangalore 560012(India)E very few years,a new material with unique properties emerges andfascinates the scientific community,typical recent examples being high-temperature superconductors and carbon nanotubes.Graphene is the latest sensation with unusual properties,such as half-integer quantum Hall effect and ballistic electron transport.This two-dimen-sional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer,but there is considerable interest in investigating two-layer and few-layer graphenes as well.Synthesis and characterization of graphenes pose challenges,but there has been considerable progress in the last year or so.Herein,wepresent the status of graphene research which includes aspects related to synthesis,characterization,structure,and properties.From the Contents1.Introduction 77532.Synthesis77543.Electronic Structure 77604.Phonons and Raman Spectroscopy 77625.Effects of Doping 77646.Functionalization and Solubilization 77677.Decoration with Metal and Metal Oxide Nanoparticles 77698.Properties77709.Polymer Composites 777310.Outlook7773Figure 1.Graphene:the parent of all graphitic forms.(From Ref.[1a].)7753Angew.Chem.Int.Ed.2009,48,7752–77772009Wiley-VCH Verlag GmbH &Co.KGaA,Weinheimreferences are sufficiently representative and will help the reader to obtain more detailed information.2.Synthesis2.1.Single-Layer GrapheneSingle-layer graphene has been generally prepared by micromechanical cleavage in which highly oriented pyrolitic graphite(HOPG)is pealed using scotch-tape and deposited on to a silicon substrate.Besides mechanical cleavage of graphite,the other important methods employed to produce graphene samples are epitaxial growth on an insulator surface (such as SiC),chemical vapor deposition(CVD)on the surfaces of single crystals of metals(e.g.,Ni),arc discharge of graphite under suitable conditions,use of intercalated graph-ite as the starting material,preparation of appropriate colloidal suspensions in selected solvents,and reduction of graphene oxide sheets.[8]By employing mechanical exfoliation of graphite,mono-layers and bilayers of graphene with minimum lateral dimensions of2–10nm can be deposited onto the Si(100)-2 1:H surface.[17]Room-temperature ultrahigh vacuum scan-ning tunneling spectroscopy has been used to characterize the nanometer-sized single-layer graphene to reveal a size-dependent energy gap ranging from0.1to1eV.By correlat-ing resolved tunneling spectroscope and atomically resolved images,the dependence of the electronic structure of single-layer graphene on lateral size,edge structure,and crystallo-graphic orientation has been examined.Single-and few-layer graphenes taken from freshly cleaved HOPG surfaces by the scotch-tape technique can be readily transferred on to a given substrate using electrostatic deposition.[18]While mechanical cleavage of graphene layers from a graphite crystal has afforded the study of the properties of single-layer graphene or bilayer graphene,the method is not suitable for large scale synthesis of single-layer graphene or of few-layer graphene(FG).Among the methods and proce-dures for large-scale synthesis two categories should be distinguished:a)those which start with graphite or a com-parable starting material not containing any oxygenfunction-C.N.R.Rao obtained his PhD degree fromPurdue University(1958)and DSc degreefrom the University of Mysore(1961).He isthe National Research Professor and LinusPauling Research Professor at the JawaharlalNehru Centre for Advanced ScientificResearch and Honorary Professor at theIndian Institute of Science(both at Banga-lore).His research interests are mainlyinthe chemistry of materials.He is the recipi-ent of the Einstein Gold Medal of theUNESCO,the Hughes Medal of the RoyalSociety,and the Somiya Award of theInternational Union of Materials Research Societies(IUMRS).In2005,hereceived the Dan David Prize for materials research and the first IndiaScience Prize.A.K.Sood is a Professor of Physics at theIndian Institute of Science,Bangalore.He isa member of the science academies of Indiaand has received various medals and hon-ours in physics including the BhatnagarPrize and the TWAS Prize.His main inter-ests are soft condensed matter,nanomateri-als,and light scattering.K.S.Subrahmanyam received his MSc(Chemistry)degree from University ofHyderabad in2006.He is a student of PhDprogramme in the Jawaharlal Nehru Centrefor Advanced Scientific Research,Bangaloreand received his MS(Engg.)degree in2008.He is working on synthesis and character-ization of graphenes.indaraj obtained his PhD degreefrom University of Mysore and is a SeniorScientific Officer at the Indian Institute ofScience,and Honorary Faculty Fellow at theJawaharlal Nehru Centre for Advanced Sci-entific Research.He works on different typesof nanomaterials.He has authored morethan100research papers and co-authored abook on nanotubes and nanowires.Figure2.Microscopy images of graphene crystallites on300nm SiO2imaged with a)white and b)green light.Figure(b)shows step-likechanges in the contrast for single-,bi-,and trilayer graphenes.c)AFMimage of single-layer graphene.The folded edge exhibits a relativeheight of approximately4 indicating that it is single-layer.d)High-resolution STM image.e)TEM images of folded edges of single-andbilayer graphenes.(From Refs.[9,11,12b].) 2009Wiley-VCH Verlag GmbH&Co.KGaA,Weinheim Angew.Chem.Int.Ed.2009,48,7752–7777alities and b)those which involve the exfoliation of graphite oxide (GO)followed by reduction.The latter methods yield sheets of reduced graphite oxide,some of which could be single-layer materials.Reduced graphite oxide layers are to be considered as chemically modified graphenes since they generally contain some oxygen functions,such as OH or COOH groups.Under category (a),some of the methods are growth on SiC surfaces,hydrogen arc discharge,conversion of nanodiamond,CVD on metal surfaces,and dispersion of graphite in solvents.Large-area single-layer graphene has been prepared by thermal decomposition of the (0001)face of a 6H-SiC wafer under ultrahigh vacuum (UHV)conditions.[19]Single-layer graphene has been grown on top of a 6H-SiC (0001)substrate by an ex situ method,which gives larger mono-layer graph-enes in comparison with an in situ method (Figure 3).[20a]Thus,ex situ graphitization of Si-terminated SiC (0001)in an argon atmosphere of 1bar yields monolayer films with large domain sizes.[20b]Temperature-dependent structural changes of graphene layers on the 6H-SiC(0001)surface studied by photoelectron spectroscopy,low-energy electron diffraction,and extended X-ray absorption spectroscopy (EXAFS)indicate that a bilayer-like graphene sheet is formed after annealing at 11508C.The tilting angle of the graphene sheet is estimated to be 14Æ28.As the number of the graphene layers increases,the angle gradually decreases to 7Æ28at 14008C.[20c]Graphene suspensions can be readily produced by dis-persing graphite in surfactant–water solutions.[21a]Individual sheets on HOPG have been manipulated by scanning probe microscope (SPM)tips,but it is more reliable to first pattern the HOPG surface to create an array of small graphite islands by reactive ion etching with an oxygen plasma.[21b]Exfoliation of lithium-intercalated multiwalled carbon nanotubes yields single-layer graphene flakes.[22a]Gram quantities of single-layer graphene have been prepared by employing a solvothermal procedure and sub-sequent by sonication.[23]In this process,thesolvothermalFigure 3.a)Low-energy electron microscope (LEEM)image of a single-domain single-layer graphene grown ex situ on the (0001)surface of SiC;the field of view is 20m m wide and the electron energy isE vac +4.4eV.b)LEEM image showing the existence of two domains of monolayer graphene.c)Photoelectron intensity map versus binding energy and parallel momentum showing the electronic structure close to the Dirac point at the K point of the Brillouin zone.(From Ref.[20a].)Figure 4.a,b)High-resolution TEM images of a)solution-cast monolayer and b)solution-cast bilayer graphenes (scale bar 500nm).c)Electron diffraction pattern of the monolayer in (a).d,e)Electron diffraction patterns taken from the positions of the d)black and e)white spots,respectively,of the sheet in (b).The graphene is one-layer thick in (d)and a bilayer in (e).f–h)Diffracted intensity taken along the 1À210to À2110axis for the patterns in (c–e).i)Histogram of the ratios of the intensity of the {1100}and {2110}diffraction peaks.A ratio >1is a signature of graphene.(From Ref.[24].)7755Angew.Chem.Int.Ed.2009,48,7752–77772009Wiley-VCH Verlag GmbH &Co.KGaA,Weinheimproduct of sodium and ethanol is subjected to low-temper-ature flash pyrolysis yielding a fused array of graphene sheets,which are dispersed by mild sonication.Single-layer graphene can be produced in good yields by solution-phase exfoliation of graphite in an organic solvent,such as N -methylpyrroli-done (NMP)(Figure 4).[24]This process works because the energy required to exfoliate graphene is balanced by the solvent–graphene interaction.Exfoliation of alkali-metal intercalated graphite in NMP yields a stable solution of negatively charged graphene sheets which can be deposited on substrates.[25]Two-dimensional linear graphene ribbons can be prepared chemically by the oxidative cyclodehydroge-nation of polyphenylene precursors.[26]Highly conducting graphene sheets produced by the exfoliation–reintercalation–expansion of graphite are readily suspended in organic solvents.[27]The sheets in organic solvents can be made into large,transparent,conducting films by Langmuir–Blodgett assembly in a layer-by-layer manner.The initial step is exfoliation of the commercial expandable graphite (160–50N,Grafguard)by brief (60s)heating to 10008C in forming gas (i.e.hydrogen and nitrogen),followed by reintercalation by oleum (fuming sulfuric acid with 20%free SO 3),and insertion of tetrabutylammonium hydroxide (TBA,40%solution in water)into the oleum-intercalated graphite in DMF.TBA-inserted oleum-interca-lated graphite is sonicated in a DMF solution of 1,2-distearoyl-sn -glycero-3-phosphoethanolamine-N -[methoxy-(polyethyleneglycol)-5000](DSPE-mPEG)for 60min to obtain a homogeneous suspension.This method gives large amounts of graphene sheets which can be transferred to other solvents including water and organic solvents (Figure 5).The average size of the single-layer graphene sheet was 250nm and the average topographic height was approximately 1nm.Graphitic oxide,obtained by the oxidation of graphite,contains a considerable amount of surface oxygen in the form of OH and COOH groups.Mechanical or thermal exfoliation graphitic oxide gives single-layer graphene oxide (SGO).Single-layer graphene oxide on reduction by hydro-gen,hydrazine or other reducing agents gives single-layer graphene.Single-layer graphene has been prepared on a large scale by a solution-based approach,involving the dispersion of graphitic oxide in pure hydrazine.Hydrazine-basedcolloids are deposited on different substrates to obtain chemically modified graphene sheets with large areas (20 40m m;Figure 6).[29a]Schniepp et al.[29b]have shown that exfoliation of graphitic oxide yields single-layer graphene oxide through the expansion of CO 2evolved in the space between the sheets during rapid heating (Figure 7).A detailed analysis of the thermal-expansion mechanism of graphitic oxide to produce single-layer graphene sheets has been described.[29c]Chemically modified graphenes have been produced in different ways.These include hydrazinereduc-Figure 5.a)Schematic representation of the exfoliated graphite reinter-calated with sulphuric acid molecules (spheres)between the layers.b)Schematic of tetrabutyl ammoniumhydroxide (TBA;dark blue spheres)in the intercalated graphite.c)Schematic of single-layer graphene coated with DSPE–mPEG molecules also shown is a photo-graph of the solution of single-layer graphene.d)AFM image of asingle-layer graphene with a topographic height of approximately 1nm (scale bar:300nm.e)Low-magnification TEM image of a single-layer graphene that is several hundred nanometres in size (scale bar:100nm).f)Electron diffraction pattern of a single-layer graphene as in (e).(From Ref.[27].)Figure 6.Photographs of chemically converted graphene suspensions.a)graphite oxide paper in a glass vial and b)the graphite oxide dispersion after addition of hydrazine.Below the vials,three-dimensional computer-generated molecular models of graphene oxide (C gray,O red,H white)and the reduced graphene are shown.Removal of -OH and -COOH groups by reduction gives the planar structure.c)SEM and d)AFM images of a chemically converted graphene sheet on Si/SiO 2substrate.(From Ref.[29a].)2009Wiley-VCH Verlag GmbH &Co.KGaA,Weinheim Angew.Chem.Int.Ed.2009,48,7752–7777tion of the colloidal suspension of single-layer graphene oxide in DMF/water [28a]or in water.[28b]Electrostatic stabilization enables stable aqueous dispersions of the single-layer graph-ene sheets.2.2.Graphenes with One to Three LayersThe dispersion behavior of graphene oxide in different organic solvents,such as DMF,NMP ,ethylene glycol and tetrahydrofuran (THF)has been studied.[30]As-prepared graphite oxide formed by the Hummers method undergoes full exfoliation into single-layer graphene oxide under sonication forming stable dispersions in the above solvents.The sample prepared from the dispersion in DMF yields sheets of uniform thickness (1.0–1.4nm).Single-layer and bi-layer graphene sheets are obtained by using a substrate-free,atmospheric-pressure microwave plasma reactor,wherein liquid ethanol droplets are passed through an argon plasma (Figure 8).[31]High-quality graphene sheets of 1–3layers have been synthesized on stainless steel substrates at 5008C bymicrowave plasma chemical vapor deposition (CVD)in an atmosphere of 10%methane and 90%hydrogen at a pressure of 30torr and a flow rate of 200sccm (standard cubic centimeter per minute).[32]Arc-discharge of graphite in hydrogen appears to yield primarily two-and three-layer graphenes (see next section).2.3.Few-Layer GraphenesStarting with graphite and by employing chemical exfo-liation,high-quality graphene with a predetermined number of layers can be obtained.[33]With artificial graphite,flake graphite powder,Kish graphite,and natural flake graphite as starting materials,nearly 80%of the final product has been found to be single-layer,single-and double-layer,double-and triple-layer,and few-layer (4–10layers)graphene respec-tively.A mixture of few-layer (4–10layers)graphene and thick graphene (>10layers)is obtained when HOPG is used (Figure 9).Large-scale transfer of mono and few-layer graphenes from SiO 2/Si,to any type of substratematerialFigure 7.a)Tapping-mode AFM image (8m m 8m m)showing an individual thermally exfoliated graphite oxide flakes.b)Pseudo-3D representa-tion of a 600nm 600nm AFM scan of an individual graphene sheet showing the wrinkled,rough surface.c)Contact-mode AFM scan of adifferent flake,providing an accurate thickness of the sheet.Inset:atomic-scale image of the HOPG lattice.d)Cross-section of an unwrinkled area in (b)(position indicated by black dashed line in (b)).e)Histogram showing the narrow distribution of sheet heights.f)Cross-section through the sheet in (c)showing a height minimum of 1.1nm.(From Ref.[29b].)7757Angew.Chem.Int.Ed.2009,48,7752–77772009Wiley-VCH Verlag GmbH &Co.KGaA,Weinheimhas been carried out.During the transferring process no morphological changes or corrugations are induced (Figure 10).[34]Well-ordered graphite films with a thickness of a few graphene layers have been grown on nickel substrates by CVD from a mixture of hydrogen and methane activated by a direct current (DC)discharge.[35]These films contain atomically smooth micron-size regions separated from each other by ridges.The film thickness is (1.5Æ0.5)nm.An arc-discharge method involving evaporation of graph-ite electrodes in a hydrogen atmosphere has been reported forpreparing graphene flakes.[36a]The presence of H 2during the arc-discharge process terminates the dangling carbon bonds with hydrogen and prevents the formation of closed struc-tures,[37–38]such as rolling of sheets into nanotubes and graphitic polyhedral particles.This method is useful to prepare boron-and nitrogen-doped graphene.To prepare pure graphene (HG),direct current arc evaporation of graphite was carried out in a water-cooled stainless steel chamber filled with a mixture of hydrogen and helium in different proportions,without using a catalyst.The propor-tions of H 2and He used in our experiments are,H 2(70torr)/He (500torr),H 2(100torr)/He (500torr),H 2(200torr)/He (500torr),and H 2(400torr)/He (300torr).In a typical experiment,the discharge current was in the 100–150A range,with a maximum open circuit voltage of 60V .[39]The arc was maintained by continuously translating the cathode to keep a constant distance of 2mm from the anode.The arc discharge deposit formed on the inner walls of the reaction chamber was examined to characterize the graphene (Figure 11).The deposit mainly contained graphenes with 2–4layers and the areas were in the 10–40 103nm 2range.Hydrogen arc discharge of graphitic oxide has also been employed to produce graphene sheets.[36b]Using microwave plasma-enhanced CVD,under a flow of a methane/hydrogen mixture,micrometer-wide flakes con-sisting of few-layer graphene sheets (four to six atomic layers)have been prepared on quartz and silicon by the controlled recombination of carbon radicals in the microwave plasma.[40]Continuous large-area films of single-to few-layer graphene have been grown on polycrystalline Ni films by ambient-pressure CVD using methane/hydrogen feed gas andtrans-Figure 9.Tapping-mode AFM images and the height profiles of graphenes derived from a),d)kish graphite,b),e)flake graphitepowder,and c),f)artifical graphite.The thickness of the graphenes are 1.9–2.3nm,1.3–2.1nm,and 1.1–1.3nm respectively.(From Ref.[33].)Figure 8.Synthesis of graphene sheets:a)Schematic representation of the atmospheric-pressure microwave plasma reactor.b)Photograph of graphene sheets dispersed in methanol.c)TEM image of graphene sheets suspended on a carbon TEM grid.Homogeneous and feature-less regions (indicated by arrows)indicate areas of single-layer graphene;Scale bar:100nm.(From Ref.[31].)Figure 10.a)Schematic representation of the transferring process.Graphene sheets are deposited on SiO 2/Si substrates via HOPGmicrocleaving and then transferred to a nonspecific substrate.b,c)Op-tical images of macroscopic regions having graphite and graphene flakes on b)the original substrate and c)the SiO 2/Si substrates.Arrows point to PMMA residues.(From Ref.[34].)2009Wiley-VCH Verlag GmbH &Co.KGaA,WeinheimAngew.Chem.Int.Ed.2009,48,7752–7777ferred on to substrates assisted by poly(methyl methacrylate)wet etching (Figure 12).[41]Highly crystalline graphene rib-bons (<20–30m m in length)with widths of 20–300nm and a small thickness (2–40layers)have been synthesized by aerosol pyrolysis using a mixture of ferrocene,thiophene,and ethanol.[42]A microwave plasma enhanced CVD strategy,also called a substrate-lift-up approach,has been used for the efficient synthesis of multilayer graphene nanoflake films on Si substrates without the use of metal catalysts.[43]Single-and few-layer graphene films exhibiting electrical characteristics somewhat similar to bilayer graphene have been deposited onto Si/SiO 2substrates starting from graphitic oxide.[44]Stable dispersions of graphitic oxide in a mixture of water and a non-aqueous solvent such as DMF,methanol,or acetone,are spray deposited on a pre-heated substrate,subsequent chemical reduction yields non-agglomerated graphene sheets.Stable aqueous dispersions of single to few-layer graphene sheets have been prepared using a water soluble pyrene derivative (1-pyrenebutyrate)as the stabilizer and hydrazine monohydrate as the reducing agent.[45]Since the pyrene moiety has strong affinity (because of p -stacking)with the basal plane of graphite,the flexible graphene sheets become non-covalently functionalized.Few-layer graphene nanosheets can also be produced by a soft chemistry route involving graphite oxidation,ultrasonic exfoliation,and chemical reduction by refluxing with hydroquinone.[46]Chemical vapor deposition using camphor (camphor graphene;CG),conversion of nanodiamond (nanodiamond graphene;DG)and thermal exfoliation of graphitic oxide (exfolitated graphitic oxide graphene;EG)produce few-layer graphenes in large quantities.[47]In the first method,camphor is pyrolysed over nickel nanoparticles at 7708C in the presence of argon.[48]The method to prepare DG involves annealing nanodiamond at 16508C or higher in a helium atmosphere.[49]It is generally found that the surface areas vary as EG >DG >HG.The number of layers is smallest (2–4)in rge and flat graphene flakes having single to few layers have been produced from HOPG by an initial epoxy bonding process followed by reverse exfoliation.[50]Kim et al [51a]have carried out large-scale growth of graphene films by CVD on thin nickel layers (<300nm)deposited on SiO 2/Si substra-tes.[51a]These workers also describe two methods of patterning the films and transferring them on to substrates (Figure 13).The reaction of CH 4/H 2/Ar is carried out at 10008C.13C labeled graphene has been prepared by CVD of 13CH 4over nickel foil.[51b]Layer-by-layer growth of graphene on Ru-(0001)has been accomplished by temperature annealing of the metal containing interstitial carbon atoms [51c,d]Films of giant graphene molecules such as C 42H 18and C 96H 30have been processed through soft-landing mass spectroscopy.[51e]Preparation and characterization of graphene oxide paper,a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets has been reported (Figure 14).[52]In this proce-dure,graphite oxide synthesized by the Hummers method was dispersed in water as individual graphene oxide sheets and the graphene oxide paper was made by filtration of the resulting colloid through an Anodisc membrane filter (47mm diame-ter,0.2m m pore size;Whatman),followed by air drying and peeling from the filter.While the exact procedures for large-scale synthesis of graphenes,specially single-layer graphene and few-layer graphene (with a relatively small number of layers, 6)have not been established,the most popular method appears to be one based on graphite oxide.Graphite oxide itself is prepared by treating graphite with a mixture of concentrated nitric acid,concentrated sulfuric acid,and potassium chlorate at room temperature for five days.[53]Exfoliation is carried out by giving a sudden thermal shock to graphitic oxide in a long quartz tube at 10508C under an argon atmosphere.[23]A stable suspension can be prepared by heating an exfoliated graphite oxide suspension under strongly alkaline conditions at moderate temperatures (50–908C).[54]Chemical reduction of exfoliated graphite oxide by reducing agents,such ashydra-Figure 11.a,b)High resolution TEM images of graphene (HG)pre-pared by the arc-discharge method (inset in (b)shows clearly a bi-layer graphene).c)AFM images and height profiles (1–2layers).(From Ref.[36a].)Figure 12.a)Optical image of a prepatterned nickel film on SiO 2/Si.CVD graphene is grown on the surface of the nickel pattern.b)Optical image of the grown graphene transferred from the nickel surface in panel (a)to another SiO 2/Si substrate.(From Ref.[41].)7759Angew.Chem.Int.Ed.2009,48,7752–77772009Wiley-VCH Verlag GmbH &Co.KGaA,Weinheimzine and dimethylhydrazine appears to be the promising strategy for the large-scale production of graphene.[55–56]Refluxing graphene oxide in hydrazine or even better,treating graphene oxide with hydrazine in a microwave oven,ensures reduction and produces aggregates of one-to-few (2–3)layer graphenes.Sonication and dispersion in a solvent,such as NMP ,favors the formation of a single-layer material.Reduction of graphene oxide with hydrazine is effectively carried out by first coating it with a surfactant,such as sodium dodecylbenzene sulfonate.[55–57]Reaction of the reduced species (coated with the surfactant)with an aryl diazonium salt gives the surfactant-wrapped chemically modified graphene which is readily dispersed in DMF or NMP .Reduced graphene oxide sheets dispersed in organic solvents can also be generated by taking graphite oxide up in an organic phase through the use of an amphiphile,and subsequent reduction with NaBH 4.[57]3.Electronic StructureThe graphene honeycomb lattice is composed of twoequivalent carbon sublattices A and B,shown in Figure 15a.Figure 15b shows the first Brillouin zone of graphene,with the high-symmetry points M,K,K ’,and G marked.Note that K and K ’are the two inequivalent points in the Brillouin zone.The s,p x and p y orbitals of carbon atoms form s bonds with the neighboring carbon atoms.The p electrons in the p z orbital,one from each carbon,form the bonding p and anti-bonding p *bands of graphene.The dispersion relation of these p electrons is described by the tight-binding model incorporating only the first nearest neighbor interactions [Eq.(1)][58–59]Figure 14.a–d)Digital camera images of graphene oxide paper:a)approximately 1m m thick;b)folded approximately 5m m thick semi-transparent film;c)folded approximately 25m m thick strip;d)strip after fracture from tensile loading.e–g)Low-,middle-,and high-resolution SEM side-view images of an approximately 10m m thick sample.(From Ref.[52].)Figure 13.Transfer processes for large-scale graphene films.a)Gra-phene film (centimetre-scale)grown on a Ni (300nm)/SiO2(300nm)/Si substrate,b)after etching the nickel layers in 1m FeCl 3aqueous solution.c)Graphene films having different shapes can be synthesized on top of patterned nickel layers.d,e)The dry-transfer method using a polydimethylsiloxane (PDMS)stamp is useful in transferring the patterned graphene films.d)the graphene film on the PDMS sub-strate,e)the underlying nickel layer is etched away using FeCl 3solution.f)Transparent and flexible graphene films on the PDMS substrates.g,h)The PDMS stamp makes conformal contact with a SiO 2substrate.Peeling back the stamp (g)leaves the film on a SiO 2substrate (h).(From Ref.[51a].)Figure 15.a)Graphene lattice.~a 1and ~a 2are the unit vectors.b)Recip-rocal lattice of graphene.The shaded hexagon is the first Brillouin zone.~b 1and ~b 2are reciprocal lattice vectors.2009Wiley-VCH Verlag GmbH &Co.KGaA,WeinheimAngew.Chem.Int.Ed.2009,48,7752–7777。

F离子注入AlGaN-GaN增强型HEMT机理和可靠性研究

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高分子论文参考文献

Published:May 12,2011COMMUNICATION /JACSInterface-Directed Assembly of One-Dimensional Ordered Architecture from Quantum Dots Guest and Polymer HostShengyang Yang,Cai-Feng Wang,and Su Chen*State Key Laboratory of Materials-Oriented Chemical Engineering,and College of Chemistry and Chemical Engineering,Nanjing University of Technology,Nanjing 210009,P.R.ChinabSupporting Information ABSTRACT:Assembly of inorganic semiconductor nano-crystals into polymer host is of great scienti ﬁc and techno-logical interest for bottom-up fabrication of functional devices.Herein,an interface-directed synthetic pathway to polymer-encapsulated CdTe quantum dots (QDs)has been developed.The resulting nanohybrids have a highly uniform ﬁbrous architecture with tunable diameters (ranging from several tens of nanometers to microscale)and enhanced optical performance.This interfacial assembly strategy o ﬀers a versatile route to incorporate QDs into a polymer host,forming uniform one-dimensional nanomaterials po-tentially useful in optoelectronic applications.Similar to the way that atoms bond to form molecules and complexes,inorganic nanoparticles (NPs)can be combined to form larger ensembles with multidimensional ordered hier-archical architecture,evoking new collective functions.To this end,the development of the controlled self-assembly method for well-de ﬁned structures of these ensembles is signi ﬁcant for creating new and high-performance tunable materials and hence has aroused appealing scienti ﬁc and industrial interest.1Particu-larly,much e ﬀort has been devoted to the construction of one-dimensional (1D)structures of NPs,owing in part to their application as pivotal building blocks in fabricating a new generation of optoelectronic devices.2In this context,directed host Àguest assembly of NPs into polymer matrices is an e ﬀective “bottom-up ”route to form 1D ordered functional materials with advantageous optical,electrical,magnetic,and mechanical properties.3Some typical routes have been developed for the generation of these 1D hybrids so far,involving template-assisted,4seeding,5and electro-static approaches.6However,the challenge still remains to precisely manipulate assembly of aqueous NPs and water-insoluble polymers into uniform 1D nanocomposites with a high aspect ratio because of phase separation and aggregation.7Moreover,facile synthetic strate-gies are highly needed to fabricate homogeneous 1D composites in which each component still preserves favorable properties to produce optimal and ideal multifunctional materials.A liquid Àliquid interface o ﬀers an ideal platform to e ﬃciently organize NPs into ordered nanostructures driven by a minimiza-tion of interfacial energy.8While much of this research has been directed toward NP hybrids with diverse morphologies based on small organic ligand-directed assembly,9some success has also been achieved in polymer-based NPs nanocomposites.10Russelland co-workers developed ultrathin membranes and capsules of quantum dots (QDs)stabilized by cross-linked polymers at the toluene/water interface.10a,11Brinker ’s group reported the fab-rication of free-standing,patternable NP/polymer monolayer arrays via interfacial NP assembly in a polymeric photoresist.12Herein,a simple host Àguest assembly route is developed to facilely create homogeneous 1D CdTe/polymer hybrids without any indication of phase separation at the aqueous/organic inter-face for the ﬁrst time.The CdTe nanocrystal is a semiconductor that has been used extensively for making thin ﬁlm for solar cells.13Some elegant studies have been made in synthesizing pure inorganic 1D CdTe nanowires via assembly from corre-sponding individual CdTe nanocrystals.14In this work,CdTe QDs are covalently grafted with poly(N -vinylcarbazole-co -glycidylmethacrylate)(PVK-co -PGMA)to form uniform ﬁbrous ﬂuorescent composites at the water/chloroform interface via the reaction between epoxy groups of PVK-co -PGMA and carboxyl groups on the surface of CdTe QDs (Scheme 1).15These 1D composite ﬁbers can be allowed to grow further in the radial direction by “side-to-side ”assembly.Additionally,this type of interfacial QD Àpolymer assembly can observably improve the ﬂuorescence lifetime of semiconductor QDs incorporated in theScheme 1.Schematic Representation of the Synthesis of PVK-co -PGMA/CdTe QDs Composite Nano ﬁbersReceived:February 8,2011polymeric matrix.It can be expected that this example of both linear axial organization and radial assembly methodology can be applied to fabricate spatial multiscale organic Àinorganic com-posites with desired properties of NPs and polymers.Figure 1a shows a typical scanning electron microscope (SEM)image of PVK-co -PGMA/CdTe QDs composite nano ﬁ-bers obtained at the water/chloroform interface after dialysis.The as-prepared ﬁbers have uniform diameters of about 250nm and typical lengths in the range of several tens to several hundreds of micrometers (Figures 1a and S4Supporting In-formation [SI]).Interestingly,PVK-co -PGMA/CdTe composite ﬁbers can randomly assemble into nestlike ring-shaped patterns (Figures 1b and S5[SI]).Given the interaction among epoxy groups,the formation of nestlike microstructures could be attributed to incidental “head-to-tail ”assembly of composite ﬁbers.Moreover,in order to establish the relationship between the role of epoxy groups and the formation of composite nano ﬁbers,control experiments were performed,in which pure PGMA or PVK was used to couple CdTe QDs.The PGMA/CdTe composites could be obtained with ﬁbrous patterns (Figure S6[SI]),but no ﬁbrous composites were achieved at the biphase interface with the use of PVK under the same conditions.The microstructures and ﬂuorescence properties of PVK-co -PGMA/CdTe composite ﬁbers were further character-ized using laser confocal ﬂuorescence microscopy (LCFM).Confocal ﬂuorescence micrographs of composite ﬁbers show that the di ﬀerently sized QDs have no obvious in ﬂuence on the morphology of composites (Figure 1c Àe).Clearly,uniform and strong ﬂuorescence emission is seen throughout all the samples,and the size-dependent ﬂuorescence trait of CdTe QDs in PVK-co -PGMA matrix remains well.In order to verify the existence and distribution of CdTe QDs in the ﬁbers,transmission electron microscopy (TEM)was employed to examine the assembled structures.Figure 2a shows a TEM image of PVK-co -PGMA/CdTe QDs composite nano ﬁ-bers,indicating each composite ﬁber shown in Figure 1a was assembled from tens of ﬁne nano ﬁbers.An individual ﬁne nano ﬁber with the diameter of about 30nm is displayed in Figure 2b,from which we can see that CdTe QDs have been well anchored into the ﬁber with polymeric protection layer,revealing this graft-form process at the interface e ﬀectively avoidednon-uniform aggregation in view of well-dispersed CdTe QDs within the composite ﬁber,consistent with the LCFM observa-tion.Unlike previous works where the nanoparticles were ad-sorbed onto the polymer ﬁbers,16CdTe QDs were expelled from the surface of ﬁbers (∼2.5nm)in our system (Figure 2c),albeit the high percentage of QDs in the polymer host (23wt %)was achieved (Figure S7[SI]).This peculiarity undoubtedly confers CdTe QDs with improved stability.The clear di ﬀuse rings in the selected area electron di ﬀraction (SAED)pattern further indicate excellent monodispersion and ﬁnely preserved crystalline struc-ture of QDs in the nano ﬁbers (Figure 2d).The SAED data correspond to the cubic zinc blende structure of CdTe QDs.A possible mechanism for the assembly of 1D nanostructure was proposed,as illustrated in Figure S8[SI].The hydrophilic epoxy groups of the PVK-co -PGMA chain in the oil phase orient toward the biphase interface and then react with carboxyl groups on the surface of CdTe QDs in the aqueous phase to a ﬀord premier PVK-co -PGMA/CdTe QDs composites.Such nanocomposites will reverse repeatedly,resulting from iterative reaccumulation of epoxy groups at the interface and the reaction between the active pieces (i.e.,epoxy or carboxyl groups)in the composites with intact CdTe QDs or PVK-co -PGMA,forming well-de ﬁned nano-ﬁbers.The control experiments showing that the diameter of composite ﬁbers increases with the increase in the concentration of PVK-co -PGMA are in agreement with the proposed mechan-ism (Figure S9[SI]).In addition,it is expected that the pure polymeric layer on the surface of the ﬁbers (red rectangular zone in Figure 2c)will allow further assembly of ﬁne ﬁbers into thick ﬁbers,and these ﬁbers also could randomly evolve into rings,forming nestlike microstructures when the “head ”and “tail ”of ﬁbers accidentally meet (Figure 1b).To further examine the assembly behavior of composite ﬁbers,the sample of PVK-co -PGMA/CdTe QDs composite nano ﬁbers were kept at the water/chloroform interface for an additional month in a close spawn bottle at room temperature (Figure S10[SI]).With longer time for assembly,thicker composite ﬁbers with tens of micrometers in diameter were obtained (Figure 3a).These micro-ﬁbers have a propensityto form twisted morphology (Figure 3a,b),Figure 1.(a,b)SEM images of PVK-co -PGMA/CdTe QDs composite nano ﬁbers.(c Àe)Fluorescence confocal microscopy images of PVK-co -PGMA/CdTe QDs composite nano ﬁbers in the presence of di ﬀerently sized QDs:(c)2.5nm,(d)3.3nm,and (e)3.6nm.The excitation wavelengths are 488(c),514(d),and 543nm (e),respectively.Figure 2.(a,b)TEM images of PVK-co -PGMA/CdTe QDs composite nano ﬁbers,revealing composite nano ﬁber assemblies.(c)HRTEM image and (d)SAED pattern of corresponding PVK-co -PGMA/CdTe QDs composite nano ﬁbers.while their re ﬁned nanostructures still reveal relatively parallel character and con ﬁrm the micro ﬁbers are assembled from countless corresponding nano ﬁbers (Figure 3c).The corresponding LCFM image of an individual micro ﬁber is shown in Figure 3d (λex =488nm),indicating strong and homogeneous green ﬂuorescence.Another indication is the ﬂuorescent performance of PVK-co -PGMA/CdTe QDs composite micro ﬁbers (Figure 4a).The ﬂuorescent spectrum of composite ﬁbers takes on emission of both PVK-co -PGMA and CdTe QDs,which suggests that this interfacial assembly route is e ﬀective in integrating the properties of organic polymer and inorganic nanoparticles.It is worth noting that there is a blue-shift (from 550to 525nm)and broadening of the emission peak for CdTe QDs upon their incorporation into polymeric hosts,which might be ascribed to the smaller QD size and less homogeneous QD size distribution resulting from the photooxidation of QD surfaces.17Since the emission spectra of PVK-co -PGMA spectrally overlap with the CdTe QD absorption (Figure S11[SI]),energy transfer from the copolymer to the CdTe QDs should exist.18However,the photoluminescence of PVK-co -PGMA does not vanish greatly in the tested sample in comparison with that of polymer alone,revealing inferior energy transfer between the polymer host and the QDs.Although e ﬃcient energy transfer could lead to hybrid materials that bring together the properties of all ingredients,18it is a great hurdle to combine and keep the intrinsic features of all constituents.19In addition,by changing the polymeric compo-nent and tailoring the element and size of QDs,it should be possible to expect the integration of organic and inorganic materials with optimum coupling in this route for optoelectronic applications.Finally,to assess the stability of CdTe QDs in the composite micro ﬁbers,time-resolved photoluminescence was performed using time-correlated single-photon counting (TCSPC)parative TCSPC studies for hybrid PVK-co -PGMA/CdTe QDs ﬁbers and isolated CdTe QDs in the solid state are presented in Figure 4b.We can see that the presence of PVK-co -PGMA remarkably prolongs the ﬂuorescence lifetime (τ)of CdTe QDs.Decay traces for the samples were well ﬁttedwith biexponential function Y (t )based on nonlinear least-squares,using the following expression.20Y ðt Þ¼R 1exp ðÀt =τ1ÞþR 2exp ðÀt =τ2Þð1Þwhere R 1,R 2are fractional contributions of time-resolved decaylifetimes τ1,τ2and the average lifetime τhcould be concluded from the eq 2:τ¼R 1τ21þR 2τ22R 1τ1þR 2τ2ð2ÞFor PVK-co -PGMA/CdTe QDs system,τh is 10.03ns,which is approximately 2.7times that of isolated CdTe QDs (3.73ns).Photooxidation of CdTe QDs during the assembly process can increase the surface states of QDs,causing a delayed emission upon the carrier recombination.21Also,the polymer host in this system could prevent the aggregation of QDs,avoid self-quench-ing,and delay the ﬂuorescence decay process.22The increased ﬂuorescence lifetime could be also ascribed to energy transfer from PVK-co -PGMA to CdTe QDs.18c The result suggests that this host Àguest assembly at the interface could ﬁnd signi ﬁcant use in the fabrication of QDs/polymer hybrid optoelectronic devices.In summary,we have described the ﬁrst example of liquid/liquid interfacial assembly of 1D ordered architecture with the incorporation of the QDs guest into the polymer host.The resulting nanohybrids show a highly uniform ﬁbrous architecture with tunable diameter ranging from nanoscale to microscale.The procedure not only realizes the coexistence of favorable properties of both components but also enables the ﬂuorescence lifetime of QDs to be enhanced.This interesting development might ﬁnd potential application for optoelectronic and sensor devices due to high uniformity of the 1D structure.Further e ﬀorts paid on optimal regulation of QDs and polymer composition into 1D hybrid nanostructure could hold promise for the integration of desirable properties of organic and inorganic compositions for versatile dimension-dependent applications.In addition,this facile approach can be easily applied to various semiconductor QDs and even metal NPs to develop highly functional 1D nanocomposites.’ASSOCIATED CONTENTbSupporting Information.Experimental details,FT-IR,GPC,UV Àvis,PL,SEM,TGA analysis,and complete ref 9c.This material is available free ofcharge via the Internet at .Figure 3.(a,b)SEM and (c)FESEM images of PVK-co -PGMA/CdTe QDs composite micro ﬁbers.(d)Fluorescence confocal microscopy images of PVK-co -PGMA/CdTe QDs composite micro ﬁbers inthe presence of green-emitting QDs (2.5nm).Figure 4.(a)Fluorescence spectra of PVK-co -PGMA,CdTe QD aqueous solution,and PVK-co -PGMA/CdTe QDs composite micro-ﬁbers.(b)Time-resolved ﬂuorescence decay curves of CdTe QDs (2.5nm diameter)powders (black curve)and the corresponding PVK-co -PGMA/CdTe QDs composite micro ﬁbers (green curve)mea-sured at an emission peak maxima of 550nm.The samples were excited at 410nm.Biexponential decay function was used for satisfactory ﬁtting in two cases (χ2<1.1).’AUTHOR INFORMATIONCorresponding Authorchensu@’ACKNOWLEDGMENTThis work was supported by the National Natural Science Foundation of China(21076103and21006046),National Natural Science Foundation of China-NSAF(10976012),the Natural Science Foundations for 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ai: nu up : / / www . ±cup . LIIBBUB . J.U/ puu_onUnited Nations Educational Scientific and Cultural OrganizationandInternational Atomic Energy Agency

THE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS

CHARGE POLARIZATION EFFECTS AND HOLE SPECTRACHARACTERISTICS IN AlxGai-xN/GaN SUPERLATTICES

Fatna AssaouiDepartment of Physics University Mohammed V, Scientific Faculty,Av. Ibn Battouta, B.P. 1014 Rabat, MoroccoandThe Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

andPedro Pereyra1Depto. de Ciencias Bdsicas, UAM-Azcapotzalco,Av. S. Pablo 180, C.P. 02200, Mexico D.F., MexicoandThe Abdus Salam International Centre for Theoretical Physics, Trieste, Italy.

AbstractWe study the effects of charge polarization on the extended physical properties of superlat-tices, such as transmission coefficients and valence band structure. We consider both linear andparabolic modulation of the band edge. Based on the theory of finite periodic systems (TFPS),analytic expressions and high precision calculations of the relevant physical quantities for n-cellsystems are obtained. New and also well-known features of these systems are identified. Besidesthe well-known energy bandstructure, we also have the field bandstructure, with interesting char-acteristics. Wider field gaps at stronger internal electric fields and higher density of field bandsfor larger layer widths are some of these characteristics. Well denned level density asymmetriesidentify the minibands induced by charge polarization or the so-called Quantum Confining StarkEffect. We present the n-cell transmission amplitudes, transmission coefficients and minibandstructures for different values of the relevant parameters.

MIRAMARE - TRIESTEOctober 2001

1 Regular Associate of the Abdus Salam ICTP.I. INTRODUCTIONThe spontaneous dielectric polarization and the piezoelectric response observed in Mg doped(AlxGa\-xN/GaN)n and {InxGa\-xN/ GaN)n superlattices, and heterostructures, lead to theexistence of localized 2D electron and hole gases on the opposite interfaces of the quantumwells1. Therefore, to the conduction- and valence-band bending. This effect denoted as thequantum confined Stark effect (QCSE) has important consequences on the extended superlatticeproperties like the miniband structure, intraband eigenfunctions and eigenvalues, and the intra-and inter-band transitions1 14. The understanding and description of this effect is importantfor the overwhelming number of applications, both in optoelectronic and electronic, based onthe nitrides' properties and their emission spectra.To study the effects of charge polarization on the transmission properties and band struc-ture, we shall consider two types of potential profiles: one with linear and the other withparabolic modulation of the band-edge. Solving the single-cell problem, and using the rigorousand compact formulas of the theory of finite periodic systems (TFPS)15, we can obtain analyticexpressions and perform high precision calculations of scattering amplitudes and the resonantband structure. We will present the n-cell transmission amplitudes, transmission coefficientsand miniband structures from different points of view: As a function of the energy and alsoas a function of the internal electric field strength. We analyze the effect of the layer width,especially on the reduction of the recombination energy. We will also show that, in the linearcase and for a fixed Fermi energy, a very appealing field bandstructure is obtained when theinternal electric field is varied. Our purpose is to offer a theoretical description of the way inwhich the extended properties depend on the internal electric field and on the layer widths.For these systems, three characteristic energy regions can be distinguished. In each regionthe consequences on the extended physical properties are clearly recognized. In the lowestenergy region (E < aF in the linear case and E < E\ in the parabolic case, see figure 1), thepotential barrier effectively increases and pushes up the allowed states and reduce their density.Depending on the specific physical parameters, some extremely thin and stable minibands (withband-widths of the order of 10~^'eV) are found. In the highest energy region the potential barriereffectively diminishes, and as a consequence more and wider minibands appear.We shall present here the principal theoretical expressions that will then be applied to ourspecific and particular cases. In Section II we obtain some general results for the transmissionamplitudes for the linear and parablic potential modulations. In section III we present the trans-mission coefficients and the minibands as a function of the electric field and other superlatticeparameters and conclude with a discussion on the results.