溶胶-凝胶法制备PbS量子点玻璃的研究

采用溶胶-凝胶法合成了半导体PbS量子点掺杂的Na₂O-B₂O₃-SiO₂玻璃,研究了不同热处理工艺对玻璃结构的影响,利用多种表征手段研究了量子点掺杂玻璃中的微晶结构及其光学性能.孔径分析结果表明随着热处理温度的升高玻璃内部孔径不断减小,最终孔结构几乎完全消失;红外光谱分析表明玻璃网络结构在较低温度下己经形成,随温度的升高不断密实化; X射线光电子能谱证明了玻璃中存在PbS,高分辨透射电镜表征了玻璃基质中掺杂的微晶结构是PbS,统计计算表明,玻璃中微晶的平均粒径尺寸为3.5nm;吸收光谱分析发现,微晶掺杂玻璃的吸收边界较PbS的块体材料发生了明显的蓝移,产生了量子尺寸效应;通过Z扫描技术测得其非线性折射率γ为-2.03×10^-14cm²/GW. 关键词： PbS量子点 半导体 非线性光学效应 溶胶-凝胶法     

掺杂六角形石墨烯电子输运特性的研究

锯齿型和扶手椅型六角形石墨烯分别跨接在两Au电极上, 构成分子纳器件, 同时考虑对六角形石墨烯分别进行B, N和BN局部规则掺杂. 利用第一性原理方法, 系统地研究了这些器件的电子输运特性. 计算结果表明: B及BN掺杂到扶手椅型六角形石墨烯, 对其电流有较好的调控效应, 同时发现本征及掺杂后的锯齿型六角形石墨烯均表现为半导体性质, 且N及BN掺杂时, 表现出明显的负微分电阻现象, 特别是N掺杂的情况, 能呈现显著的负微分电阻效应, 这也许对于发展分子开关有重要应用. 通过其透射特性及掺杂诱发的六角形石墨烯电子结构的变化, 对这些结果的内在原因进行了说明.     

GaxN2:Zn3-x薄膜的分子束外延生长及其光学和电子输运性能表征

本文采用分子束外延技术,通过对金属分子束的精确控制,在MgO(002)基底上成功生长了Ga_xN₂∶Zn_3-x合金薄膜.高分辨率单晶X光衍射仪表征结果表明Ga_xN₂∶Zn_3-x合金薄膜仍是以(400)Zn₃N₂为主导的复合晶体结构,对衍射数据的分析得到该薄膜晶粒尺寸小.用扫描电子显微镜和能谱射线分析仪对其表面和成分做了深入的分析和讨论,在固定的金属流量比的生长环境下,不同厚度的样品在成膜后x均为0.65,化学通式Zn_2.35Ga_0.65N₂.该结果表明Ga元素属于重度掺杂,同时也体现了分子束外延技术在共掺杂技术中的优越性.本文也测量并讨论了Zn_2.35Ga_0.65N₂薄膜的光学性能,实验得到的1.85 eV的光学带隙与理论推算基本吻合,说明Ga的掺入有Ga-N结构...     

气体吸附对V掺杂石墨烯电子结构与光学性质的影响

基于密度泛函理论(DFT)的广义梯度近似(GGA)，采用第一性原理方法研究了气体分子吸附对V掺杂石墨烯的吸附能、电子结构与光学性质的影响．能带结构计算表明:吸附NO₂分子的V掺杂石墨烯的带隙显著增加，从0 e V变为0.368 e V，由金属性转变为半导体特性，而吸附CO与NH₃分子的V掺杂石墨烯的带隙则变化很小．三种吸附构型(NO₂,CO,NH₃)的吸附能分别为-8.499 e V、-2.05 e V和-2.01e V，说明V掺杂石墨烯对NO₂气体分子吸附最强．进而计算了本征、V掺杂石墨烯及其吸附NO₂分子的光学性质，结果表明:随着V掺杂与吸附NO₂气体，石墨烯介电吸收峰值有所增大，介电峰位向低能量区域移动;本征石墨烯仅吸收紫外光，V掺杂石墨烯吸附NO₂分子可以明显拓宽光吸收的光谱范围;掺杂与吸附使得石墨烯光电导率显著增强，能在红外与可见光区产生光电流．上述结果表明V掺杂石墨烯吸附NO₂后...     

SnO2量子点/石墨烯复合结构的合成及其光催化性能研究

本文以SnCl₄·5H₂O和氧化石墨烯为先驱物, 乙醇水溶液为溶剂, 采用一种简单的水热法一步合成了具有可见光催化活性的SnO₂量子点(约3–5 nm)与石墨烯复合结构, 利用透射电子显微镜(TEM), 高分辨透射电子显微镜(HRTEM), X射线衍射仪(XRD), 傅里叶变换红外光谱(FT-IR)等技术对其结构进行了表征, 利用紫外可见吸收光谱(UV-vis)分析了其光学性能, 罗丹明-B染料为目标降解物研究了SnO₂量子点/石墨烯复合结构可见光催化性能. 结果表明: 与纯SnO₂、纯石墨烯相比, 复合结构显示出了很高的可见光催化活性. 通过对其结构进行分析, 我们提出了SnO₂量子点/石墨烯复合结构的形成机制及其可见光催化活性机理.     

类富勒烯团簇发光性能的理论研究

热激活延迟荧光(TADF)作为一种特殊的分子荧光机制,对于提高发光效率有着重要意义.以C₆₀和C₇₀为代表的碳富勒烯具有高对称结构和离域π电子,被广泛证明具有显著的TADF效应;相比之下,其他类富勒烯团簇的光物理性质尚不清楚.本文利用含时密度泛函理论探索了一系列类富勒烯团簇的激发态性质,包括实验合成的具有不同尺寸的氮化硼笼型团簇B₁₂N₁₂, B₂₄N₂₄和B₃₆N₃₆,以及与B₁₂N₁₂结构相同、元素组成不同的B₁₂P₁₂, Al₁₂N₁₂和Ga₁₂N₁₂.计算结果表明,这些类富勒烯化合物团簇具有2.83—6.54 eV的能隙,主要吸收紫外光,荧光发射波长在可见光区间,包括红光、橙光、蓝光和紫光.它们的第一激发单重态和三重态的能量差较小(...     

CVD合成的掺杂BNx-石墨烯纳米复合材料:结构和发光性能

用B₄C为硼源,利用CVD系统在N₂-H₂等离子体中合成了掺杂BN_x纳米棒,接着在掺杂BN_x纳米棒表面用CH₄生长了石墨烯纳米片,制备出掺杂BN_x-石墨烯三维纳米复合材料。一系列表征结果说明合成的纳米复合材料由C和O共掺杂的BN_x纳米棒和石墨烯纳米片组成,其形成与碳氢基团的转换和掺杂BN_x纳米棒的形变在石墨烯纳米片中产生的应力有关。室温发光性能表明石墨烯纳米片对掺杂BN_x纳米棒的紫外光和绿光有明显的猝灭作用,起源于掺杂BN_x-石墨烯界面上的电荷转移和电子散射。     

基于石墨相氮化碳量子点直接荧光猝灭法检测碘离子的研究

石墨相氮化碳(g-C₃N₄)荧光纳米材料具有原料便宜、制备容易、荧光量子产率高、光学稳定性好、毒性低等优点,并且避免有机荧光染料复杂的合成步骤或者金属半导体量子点对环境潜在的危害,这些优点使得g-C₃N₄纳米材料成为新兴的荧光探针用于检测金属离子。最近,已有文献报道重金属汞离子能够高灵敏高选择性地猝灭g-C₃N₄量子点的荧光,加入碘离子能够提取被键合的汞离子形成碘化汞(HgI₂)进而恢复g-C₃N₄量子点的荧光,从而建立一种高灵敏检测碘离子的荧光传感器。然而,该方法依然需要重金属汞离子的参与,限制了该方法的推广应用。通过硝酸氧化块体g-C₃N₄并结合水热法处理制备了一种水溶性好、荧光强度高的g-C₃N₄量子点。该量子点的荧光发射波长位于368 nm,且其荧光发射波长不随激发波长的改变而改变,表明该量子点的尺寸比较均一。笔者发现碘离子在220 nm处有一个较强的吸收峰,与该量子点的激发光谱(中心波长245 nm)具有较大的重叠,从而产生内滤效应引起该量子点的荧光发生猝灭。利用这一性质,构建了一种选择性检测碘离子的新型荧光传感器。在最优检测条件下,g-C₃N₄量子点的荧光猝灭强度(ΔF)与碘离子浓度(X,μmol·L-1)在10～400 μmol·L-1之间具有良好的线性关系,线性方程为ΔF=0.325 79X+6.039 05(R2=0.999 5),检出限为5.0 μmol·L-1。通过“混合即检测”并且不需要借助与重金属离子的配位作用就能够检测碘离子,因此该方法具有快速、环保以及操作简便等优点。     

基于共掺杂调控C32多极矩的二阶非线性光学响应

基于密度泛函(DFT)理论,采用CAM-B3LYP方法,以C₃₂分子为多极矩构建骨架,设计了两类替位式共掺杂的富勒烯衍生物C₂₈B₂N₂和C₂₈B₂P₂,共16种同分异构体,并对它们的电子性质、线性极化率α和一阶超极化率β进行研究。结果表明,掺杂后分子的HOMO-LUMO能隙变小,C₂₈B₂P₂的α和β值均大于C28B2N2系列。其中偶极分子具有大的β值,八极分子则有较小的β值,筛选出具有优异的二阶非线性光学(NLO)响应特性的结构。含时密度泛函理论(TD-DFT)的结果表明,与C₃₂相比,掺杂后所有结构的吸收光谱的响应范围变宽,最大吸收强度减弱,且最大吸收波长的位置发生红移或蓝移。基于完全态求和(SOS)方法,分别用二能级或三能级公式解释了两类共掺杂结构中β值最大的来源,并且证明了与之有关的电子激发类型为π→π*激发。     

硼掺杂增强g-C3N4基单原子催化剂性能的第一性原理研究

单原子催化剂(SACs)以其最大的金属原子利用率和较高的催化活性而备受关注.本文提出了在Mn负载g-C₃N₄单层(Mn/g-C₃N₄)中进行B掺杂的方案来提升单原子催化剂的光催化活性,并利用第一性原理对Mn/B-g-C₃N₄单原子催化剂的晶体结构,电子结构,带边位置和光学性质进行计算.计算结果表明B掺杂具有较强的结构稳定性,带隙变小,同时带隙中出现杂质能级,导致吸收边向可见光区发生红移,提高了g-C₃N₄在太阳光下光吸收能力和光催化活性,研究结果为制备高效的g-C₃N₄基光催化SACs提供了理论指导.     

第一性原理研究O和S掺杂的石墨相氮化碳(g-C_3N_4)_6量子点电子结构和光吸收性质

利用密度泛函和含时密度泛函理论研究了氧(O)和硫(S)原子掺杂的石墨相氮化碳(g-C_3N_4)_6量子点的几何、电子结构和紫外-可见光吸收性质.结果表明:掺杂后(g-C_3N_4)_6量子点杂质原子周围的C-N键长发生了一定的改变,最高电子占据分子轨道-最低电子未占据分子轨道(HOMO-LUMO)能隙显著减小.形成能的计算表明O原子取代掺杂的(g-C_3N_4)_6量子点体系更稳定,且O原子更易取代N3位点,而S原子更易取代N8位点.模拟的紫外-可见电子吸收光谱表明,O和S原子的掺杂改善了(g-C_3N_4)_6量子点的光吸收,使其吸收范围覆盖了整个可见光区域,甚至扩展到了红外区.而且适当的杂质浓度使(g-C_3N_4)_6量子点光吸收在强度和范围上都得到明显改善.通过O和S掺杂的比较,发现二者在可见光区对(g-C_3N_4)_6量子点的光吸收有相似的影响,然而在长波长区域二者的影响有明显差异.总体而言,O掺杂要优于S掺杂对(g-C_3N_4)_6量子点光吸收的影响.     

Optical properties of geometrically optimized graphene quantum dots

We derive effective tight-binding model for geometrically optimized graphene quantum dots and based on it we investigate corresponding changes in their optical properties in comparison to ideal structures. We consider hexagonal and triangular dots with zigzag and armchair edges. Using density functional theory methods we show that displacement of lattice sites leads to changes in atomic distances and in consequence modifies their energy spectrum. We derive appropriate model within tight-binding method with edge-modified hopping integrals. Using group theoretical analysis, we determine allowed optical transitions and investigate oscillatory strength between bulk–bulk, bulk–edge and edge–edge transitions. We compare optical joint density of states for ideal and geometry optimized structures. We also investigate an enhanced effect of sites displacement which can be designed in artificial graphene-like nanostructures. A shift of absorption peaks is found for small structures, vanishing with increasing system size.     

基于石墨烯-钙钛矿量子点场效应晶体管的光电探测器

以等离子增强化学气相沉积法制备的石墨烯作为导电沟道材料,将其与无机CsPbI_3钙钛矿量子点结合,设计并制备了石墨烯-钙钛矿量子点场效应晶体管光电探测器.研究和分析了石墨烯作为场效应晶体管的电学特性及其与钙钛矿量子点结合作为光电探测器的光电特性.结果表明,石墨烯在场效应晶体管中表现出良好的电学性质,其与钙钛矿量子点的结合对波长为400 nm的光辐射具有明显的光响应,在光强为12μW时器件光生电流最大为64μA,响应率达6.4 A·W~(-1),对应的光电导增益和探测率分别为3.7×10~4,6×10~7Jones(1 Jones=1 cm·Hz~(1/2)·W~(-1)).     

Transport in graphene nanostructures

Graphene nanostructures are promising candidates for future nanoelectronics and solid-state quantum information technology. In this review we provide an overview of a number of electron transport experiments on etched graphene nanostructures. We briefly revisit the electronic properties and the transport characteristics of bulk, i.e., two-dimensional graphene. The fabrication techniques for making graphene nanostructures such as nanoribbons, single electron transistors and quantum dots, mainly based on a dry etching ??paper-cutting?? technique are discussed in detail. The limitations of the current fabrication technology are discussed when we outline the quantum transport properties of the nanostructured devices. In particular we focus here on transport through graphene nanoribbons and constrictions, single electron transistors as well as on graphene quantum dots including double quantum dots. These quasi-one-dimensional (nanoribbons) and quasi-zero-dimensional (quantum dots) graphene nanostructures show a clear route of how to overcome the gapless nature of graphene allowing the confinement of individual carriers and their control by lateral graphene gates and charge detectors. In particular, we emphasize that graphene quantum dots and double quantum dots are very promising systems for spin-based solid state quantum computation, since they are believed to have exceptionally long spin coherence times due to weak spin-orbit coupling and weak hyperfine interaction in graphene.     

Linear and nonlinear optical response of g-C_3N_4-based quantum dots

Graphite carbon nitride(g-C_3N_4) attracts wide-ranging research interest due to its extraordinary physicochemical properties and promising applications ranging from heterogeneous catalysis to fuel cells. In this work, we design different g-C_3N_4-based quantum dots(g CNQDs), carry out a systematic study of optical properties, and elucidate the shape selectivity, composite nanostructure, and outfield effect. In particular, composites of g CNQDs and metal nanochains present excellent optical response, making it applicable to bioimaging, nano-plasma devices, and metalloenzyme in infrared light related fields. Besides, QDs which original bridging nitrogen atoms are replaced by amino(–NH_2), hydroxyl(–OH),and methyl(–CH_3) functional groups respectively, have excellent spectral selectivity in the deep ultraviolet region. More interestingly, in the study of the laser interaction with materials, the g CNQDs exhibit extremely high stability and light corrosion resistance. Phase transition from insulation to metal is observed under the critical condition of about 5 e V intensity or 337 nm wavelength. All provided theoretical support for designs and applications in g-C_3N_4 quantum devices.     

First-principles investigation of the valley and electrical properties of carbon-doped α-graphyne-like BN sheet

Based on ab initio density functional theory calculations, we demonstrate that two carbon-doped boron nitride analog of α-graphyne structures, B_3C_2N_3 and BC_6 N monolayers, are two-dimensional direct wide band gap semiconductors, and there are two inequivalent valleys in the vicinities of the vertices of their hexagonal Brillouin zones. Besides, B_3C_2N_3 and BC_6 N monolayers exhibit relatively high carrier mobilities, and their direct band gap feature is robust against the biaxial strain. More importantly, the energetically most favorable B_3C_2N_3 and BC_6 N bilayers also have direct wide band gaps, and valley polarization could be achieved by optical helicity. Finally, we show that BC_6 N monolayer might have high efficiency in photo-splitting reactions of water, and a vertical van der Waals heterostructure with a type-II energy band alignment could be designed using B_3C_2N_3 and BC_6 N monolayers. All the above-mentioned characteristics make B_3C_2N_3 and BC_6 N monolayers, bilayers, and their heterostructures recommendable candidates for applications in valleytronic devices,metal-free photocatalysts, and photovoltaic cells.     

Third-order nonlinear optical properties of graphene composites: A review

Graphene has excellent thirdorder nonlinear optical (NLO) properties due to its unique electronic band structure and wideband gap tunability. This paper focuses on the research progress of graphene and its composite materials in nonlinear optics in recent years. In this review, recent results on graphene (or graphene oxide)-metal nanoparticles (G-MNPs), graphene-metal-oxide nanoparticles (G-MONPs), graphene-metal sulfide nanoparticles (G-MSNPs), and graphene-organic molecular composites (G-OM) have been discussed. In addition, the enhancement mechanism of nonlinear absorption (NLA) and optical limiting (OL) have also been covered.     

Theoretical calculation of excitonic binding energies and optical absorption spectra for Armchair graphene nanoribbons

In this paper the excitons of armchair graphene nanoribbons with layers of different width and thickness have been investigated. In this investigation, the band structure and energy gap of armchair graphene nanoribbons have been calculated using a tight-binding model including edge deformation effects (all edge atoms have been passivated with hydrogen atoms). Also, by calculating the conductance in armchair graphene nanoribbons (A-GNRs) optical absorption of armchair graphene nanoribbon in the single-electron approximation has been obtained. Finally, the binding energy of excitons in armchair graphene nanoribbons has been calculated using the Wannier model, Hartree-Fock approximation and the Bethe-Salpeter equation.     

The refractive nonlinearities of InAs/GaAs quantum dots above-bandgap energy

The third-order optical nonlinear refractive properties of InAs/GaAs quantum dots grown by molecular beam epitaxy have been measured using the reflection Z-scan technique at above-bandgap energy. The nonlinear refractive index and nonlinear absorption index of the InAs/GaAs quantum dots were determined for wavelengths from 740 to 777 nm. The measured results are compared with the nonlinear refractive response of several typical III-V group semiconductor materials. The corresponding mechanisms responsible for the large nonlinear response are discussed.