空位和Si掺杂对In在石墨烯上吸附的影响

利用第一性原理方法计算了空位和Si(硅)替位掺杂对In(钢)原子在石墨烯上吸附的影响.结果表明:在低覆盖度下,空位比Si替位掺杂更能增强In在石墨烯上的吸附,主要原因在于空位引入更多的悬挂键,加强了In和石墨烯之间相互作用.而对于较高覆盖度,Si替位掺杂却比空位对In吸附在石墨烯上的影响更强.无论是较高覆盖度还是低覆盖度,空位和Si替位掺杂均增强了In在石墨烯上的吸附.     

4d过渡金属掺杂石墨烯对HCN吸附行为的第一性原理研究

采用第一性原理的密度泛函理论方法研究了掺杂Y、Zr、Nb、Mo、Tc和Ru的石墨烯体系对氰化氢(HCN)的吸附作用。首先考察了HCN分子中H、C或N原子分别靠近吸附点的三种吸附构型。然后比较了吸附HCN前后掺杂石墨烯的能带变化。研究结果表明,掺杂Mo和Ru的石墨烯吸附HCN后的带隙大小变化大于20%,并表现为半导体行为,说明吸附后掺杂石墨烯的电导性能受影响较大。此外,进一步研究了掺杂Mo和Ru的石墨烯吸附HCN的过程,讨论了吸附能、带隙、晶格常数、HCN电荷和键长的变化,并分析了掺杂Mo和Ru的石墨烯的振动特性。研究表明,掺杂Mo和Ru的石墨烯对HCN的吸附非常敏感,这可能是开发HCN传感器的有用材料。     

不同浓度硼掺杂石墨烯吸附多层金原子的第一性原理研究

石墨烯与金属间过高的接触电阻严重影响了其在微纳电子领域的应用,B掺杂可以有效降低石墨烯的接触电阻。利用第一性原理研究了不同浓度B掺杂对石墨烯吸附多层Au原子的影响。首先计算了不同浓度B掺杂石墨烯的结合能,验证了掺杂石墨烯的稳定性;然后对掺杂石墨烯进行了结构优化并在其表面置入多层Au原子,计算了吸附模型的吸附能、赝能隙、局部态密度、电荷密度分布和电荷转移量。B掺杂浓度分别为1.39%,4.17%,6.94%,9.72%,12.50%和15.28%。结果表明:随着B掺杂浓度的提高,石墨烯吸附多层Au原子体系的赝能隙变宽,吸附能增加,结构稳定性得到提升;B原子与Au原子间杂化作用明显,具有较高的电荷密度和电荷转移量,可有效地降低石墨烯与多层Au原子间的接触电阻;但掺杂浓度为15.28%时,由于浓度过高吸附模型中石墨烯几何结构变形过大。     

In-As共掺杂GaSb的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势法,计算未掺杂,In、As单掺及In-As共掺GaSb的晶格参数、能带结构、态密度和吸收光谱。结果表明:掺杂后GaSb晶格发生畸变,As单掺GaSb的晶格常数增大,带隙减小,导致吸收光谱蓝移;而In单掺和In-As共掺GaSb晶格常数变大,且禁带宽度均减小,致使吸收光谱红移,这也是实验上造成掺杂GaSb热光伏电池吸收光谱扩展的原因。     

Li在石墨烯表面吸附与迁移的第一性原理研究

本工作研究了Li在石墨烯表面的吸附和迁移行为。基于密度泛函理论(DFT)的第一性原理方法,计算了Li在本征石墨烯表面的吸附特性和迁移行为以及石墨烯吸附Li前后的能带结构、态密度、电荷转移、差分电荷密度。Li在4×4石墨烯表面的扩散能垒为0.336 eV,其在C6环芯位的吸附能为1.569 eV,电荷转移量为0.870 7e,Li原子的2p轨道和C原子的2p轨道出现杂化。Li主要通过跨越C-C键桥位而在相邻C_6环芯位间实现平行于石墨烯表面的连续扩散,Li原子在石墨烯表面的最稳定吸附位为C_6环芯位,吸附Li后的石墨烯+Li体系显示出金属性,且Li与石墨烯间同时存在离子键和共价键。     

纳米掺杂SnO2的研究及其第一性原理的计算

利用Castap软件计算了Co以不同比例掺杂SnO2的电子结构，分析了掺杂及掺杂比例对改善SnO2导电性的作用，建立了纯SnO2计算模型。计算结果表明：纯SnO2是一种包含离子键的共价键直接禁带半导体；通过掺杂能够在一定程度上改变成键性质，使其具有金属键性质，从而提高SnO2导电性。其中，掺杂比率为5％的价带到中间能级宽度最小，掺杂原子与其邻近原子的电荷重叠区更明显，系统电子共有化程度最高，费米能级处对电子态密度的贡献也最大，因此掺杂比率为5％的导电性最好。     

掺杂对锯齿形(Zigzag)石墨烯纳米带输运性质的影响

基于第一性原理计算,研究了掺杂对锯齿形石墨烯纳米带电子输运性质的影响。研究发现,掺杂原子种类、掺杂位置的不同将对电子输运产生极大的影响。当中间散射区域的中心C原子被B杂质原子代替时,在电子输运谱的费米能级以下会出现一个零透射的波谷,而另一侧则不变;当带中心杂质为N原子时情况正好相反。零透射波谷的出现意味着有带隙产生,即发生了从金属到半导体的转变。当杂质原子从中心位置移到带边缘时,波谷将移到费米能级的另一侧,从而引起从受主到施主特征的转变,这是杂质原子的束缚态与边缘态相互作用的结果。     

Li吸附对石墨烯、BC_3、C_3N电学性质影响的第一性原理研究

基于密度泛函理论(DFT)的第一性原理方法,对Li在未掺杂和B(N)掺杂浓度为25%(原子分数)的石墨烯表面最稳定位置的吸附进行了结构优化,计算了本征石墨烯及B(N)掺杂石墨烯吸附Li前后的能带结构、态密度、电荷转移、差分电荷密度和结合能。计算结果表明,B掺杂浓度为25%(原子分数)时可显著提高石墨烯的Li吸附能,N掺杂浓度为25%(原子分数)时减弱了石墨烯的Li吸附能。吸附Li后的石墨烯、BC3和C3N体系均显示出金属性。     

石墨烯吸附甲醛的第一性原理研究

采用第一性原理研究了甲醛分子吸附于本征石墨烯、缺陷石墨烯和掺杂石墨烯的体系.通过计算石墨烯掺杂前后对甲醛气体的吸附能、电荷转移及能带和态密度,发现掺杂Pt后甲醛分子吸附能和电荷转移显著增大,这是由于Pt的掺杂在本征石墨烯能带中引入了杂质能级,增强了石墨烯和甲醛分子间的相互作用,可以提高石墨烯对甲醛气体的气敏响应速度和吸附能力.     

贵金属Pd离子掺杂纳米ZnSnO3的氢敏性能及掺杂机理

为了提高ZnSnO3的氢敏性能,以共沉淀法制备ZnSnO3并对其进行了贵金属Pd2＋掺杂.采用X射线衍射仪（X-ray diffraction,XRD）及透射电镜（transmission electron microscopy,TEM）对制备的气敏材料进行结构及形貌表征,并使用静态配气法测试了掺杂前后ZnSnO3的氢敏性能.结果表明：掺杂Pd2＋可显著提高ZnSnO3的氢敏性能.在工作温度为240℃、浓度为300×10-6的条件下,Pd2＋掺杂纳米ZnSnO3对氢气的灵敏度为12,是未掺杂时的3倍.基于第一性原理探讨气敏机理,计算结果表明：Pd2＋掺杂改变了ZnSnO3能带间的电子运动状态,使ZnSnO3费米能级由0.725 eV移动到1.035 eV,在费米能级附近产生新的电子峰,使其电导性能在气敏反应过程中改变更为明显.Pd2＋掺杂还使ZnSnO3表面吸附氧的能力显著增加,对提高氢敏性能起到了关键作用.     

DFT方法研究一氧化氮在铬掺杂石墨烯上的吸附行为

石墨烯具有较高的比表面积,其电导率会因吸附微量气体分子而发生显著变化,有望用作超高灵敏度的气体传感器。本研究基于密度泛函理论(DFT)的计算方法,探讨了NO在石墨烯和Cr掺杂石墨烯上的吸附行为,通过对比吸附前后的各自体系的电子结构变化,发现Cr掺杂石墨烯有助于增强对NO气体分子的吸附能力,吸附能增大到–1.58 eV,基底转移到吸附物的电荷数增大了一个数量级,达到0.143 e,显著提升了气体探测灵敏度。本研究为工业、环境和军事监测领域中开发新型NO气体传感器提供了新的设计思路。     

Study of Vacancies and Pd Atom Decoration on the Electronic Properties of Bilayer Graphene

We have investigated the scenario of graphene when irradiated with high energetic protons and subsequently decorated with Pd atoms on one of the layers. Theoretical analyses were performed on graphene 2L (two layers) with vacancies (carbon 3 and 13) (sample A), graphene 2L with vacancies and the two carbon atoms intercalated in between the two carbon layers (sample B), graphene 2L with the vacancies intercalated and subsequently with two Pd atoms on one of the layers, the top layer (called surface) (sample C), and, last but not least, graphene 2L with vacancies intercalated and decorated with six Pd atoms on the surface (sample D). For the four cases enunciated, energy bands were performed which provided information about the semi-metallic behavior, showing more semi-metallic character for the first case, while less metallic behavior occurs for the second and third one. Moreover, sample D showed a mini gap (between the conduction and valence bands) of the order of 0.02 eV and manifest semiconductor behavior. Total and projected density of states were performed in order to provide information about the contributions from each selected atom to the total DOS in the vicinity of the Fermi level in order to analyze the effect on the electronic behavior. Pd d orbitals contribute with ∼6% to the total DOS, while graphene (carbon atoms) p orbitals contribute with ∼5%. Furthermore, a strong hybridization is manifest between these two multiple degenerate orbitals.     

掺杂和修饰的石墨烯对半胱氨酸吸附性能的密度泛函理论研究

使用密度泛函理论计算了掺杂或修饰Al或Mn原子的石墨烯对半胱氨酸的吸附性能。计算结果表明,掺杂或修饰Al或Mn原子后,Graphene与半胱氨酸之间结合稳定,具有较大的结合能。其中掺杂或修饰Mn原子的体系的吸附能整体高于掺杂或修饰Al原子的体系。石墨烯上修饰或掺杂Al或Mn原子,增加了石墨烯基底与半胱氨酸之间的电荷转移,特别是修饰方式显著改变了费米能级附近的性质,同时改变了Graphene的电导性质。Al或Mn原子修饰或者掺杂的Graphene除了增加对半胱氨酸吸附能力外,也是一种潜在的检测半胱氨酸的传感器材料,进而在生物领域得到更广泛的应用,比如用来检测富含半胱氨酸的金属硫蛋白。     

温度对堆叠双层石墨烯层间耦合的影响

将不同层数堆叠和化学气相沉积法（CVD）生长的石墨烯在室温下进行拉曼光谱表征分析其层间耦合状态,并分析了不同温度下堆叠和CVD生长的双层石墨烯温度对其层间耦合的影响。研究结果表明:室温下CVD生长双层石墨烯和堆叠双层石墨烯的层间耦合状态截然不同;在25～250 ℃范围内,层间没有耦合作用或存在弱耦合作用的堆叠双层石墨烯的G峰峰位温度系数小于存在电子耦合的CVD生长双层石墨烯;超过250 ℃后,堆叠双层石墨烯G峰峰位温度系数变为正值,层与层之间可能产生了耦合,性质发生改变;在25～400 ℃ 范围内两种材料的2D峰半峰宽和G峰/2D峰强度比变化趋势几乎相同,但堆叠双层石墨烯波动大,对温度更敏感。     

氧化石墨烯基复合材料对重金属吸附性能研究

近年来,重金属水污染问题突出,给环境和人类健康带来了严重的危害.常规的处理方法可以达到比较好的处理效果,但也会带来一些二次污染等其他问题.因此本文基于氧化石墨烯吸附剂,对其进行改良制得氧化石墨烯-MoS2气凝胶(简称为GMAs),并进行了表征分析和对重金属离子吸附试验,所制得的GMAs对汞离子、铅离子等污染物表现出较高的吸附能力.用MoS2修饰过的氧化石墨烯材料吸附重金属离子的吸附量比未修饰的石墨烯高出5倍;氧化石墨烯-MoS2对汞离子的吸附量达到1245mg/g.另外发现氧化石墨烯-MoS2对有机溶剂和有机染料也具有良好的吸附效果.     

Impact of Interfacial Electron Transfer on Electrochemical CO2 Reduction on Graphitic Carbon Nitride/Doped Graphene

Effective electrocatalysts are required for the CO₂ reduction reaction (CRR), while the factors that can impact their catalytic activity are yet to be discovered. In this article, graphitic carbon nitride (g‐C₃N₄) is used to investigate the feasibility of regulating its CRR catalytic performance by interfacial electron transfer. A series of g‐C₃N₄/graphene with and without heteroatom doping (C₃N₄/XG, XG = BG, NG, OG, PG, G) is comprehensively evaluated for CRR through computational methods. Variable adsorption energetics and electronic structures are observed among different doping cases, demonstrating that a higher catalytic activity originates from more interfacial electron transfer. An activity trend is obtained to show the best catalytic performance of CRR to methane on C₃N₄/XG with an overpotential of 0.45 V (i.e., ?0.28 V vs reverse hydrogen electrode [RHE]). Such a low overpotential has never been achieved on any previously reported metallic CRR electrocatalysts, therefore indicating the availability of C₃N₄/XG for CO₂ reduction and the applicability of electron transfer modulation to improve CRR catalytic performance.     

NO reduction by propene or CO over alkali-promoted Pd/YSZ catalysts

The catalytic activity and selectivity of Pd dispersed on 8mol% yttria stabilized zirconia (YSZ) support for the reduction of NO by propene or CO is strongly promoted by alkalis in a wide temperature range 200-500 degrees C. Rate increases by up to one order of magnitude are achievable, accompanied with significant improvement in N(2)-selectivity for the alkali promoted catalysts. The promoting effect of alkalis on both the activity and selectivity can be understood in terms of the effect of alkali promoter on the relative adsorption strengths of reactant species. These achievements could be very useful for the formulation of modern lower cost automotive catalytic converters, capable of controlling automotive emissions more efficiently.     

Selective Chemical Modification of Graphene Surfaces: Distinction Between Single‐ and Bilayer Graphene

Graphene modifications with oxygen or hydrogen are well known in contrast to carbon attachment to the graphene lattice. The chemical modification of graphene sheets with aromatic diazonium ions (carbon attachment) is analyzed by confocal Raman spectroscopy. The temporal and spatial evolution of surface‐adsorbed species allows accurate tracking of the chemical reaction and identification of intermediates. The controlled transformation of sp² to sp³ carbon proceeds in two separate steps. The presented derivatization is faster for single‐layer graphene and allows controlled transformation of adsorbed diazonium reagents into covalently bound surface derivatives with enhanced reactivity at the edge of single‐layer graphene. On bilayer graphene the derivatization proceeds to an adsorbed intermediate, which reacts slower to a covalently attached species on the carbon surface.     

Critical Annealing Temperature for Stacking Orientation of Bilayer Graphene

It is rarely reported that stacking orientations of bilayer graphene (BLG) can be manipulated by the annealing process. Most investigators have painstakingly fabricated this BLG by chemical vapor deposition growth or mechanical means. Here, it is discovered that, at ≈600 °C, called the critical annealing temperature (CAT), most stacking orientations collapse into strongly coupled or AB‐stacked states. This phenomenon is governed (i) macroscopically by the stress generation and release in top graphene domains, evolving from mild ripples to sharp billows in certain local areas, and (ii) microscopically by the principle of minimal potential obeyed by carbon atoms that have acquired sufficient thermal energy at CAT. Conspicuously, evolutions of stacking orientations in Raman mappings under various annealing temperatures are observed. Furthermore, MoS₂ synthesized on BLG is used to directly observe crystal orientations of top and bottom graphene layers. The finding of CAT provides a guide for the fabrication of strongly coupled or AB‐stacked BLG, and can be applied to aligning other 2D heterostructures.