旋涂水溶液前驱体制备氧化锌薄膜及其性质

通过旋涂法, 采用Zn(OAc)2·2H2O和聚环氧乙烷(PEO)的水溶液为前驱体在不同的热处理温度下制备了ZnO薄膜. PEO的加入增加了溶液的成膜性, 其较低的热分解温度有利于制得纯净的ZnO薄膜. 文中考察了在不同热处理温度下制备的ZnO薄膜的形貌、结晶性、带隙(Eg)以及电导性. 原子力显微镜(AFM)测试表明在热处理温度为400、450和500 ℃制备的ZnO薄膜的粗糙度均方根值分别为3.3、2.7和3.6 nm. 采用透射电子显微镜(TEM)测试发现ZnO薄膜中含有大量纳晶粒子. 通过测试ZnO薄膜的UV-Vis吸收光谱, 根据薄膜位于373 nm处的吸收带边计算得到ZnO的带隙为3.3 eV. 通过对薄膜的电流-电压(I-V)曲线的测试计算得到在热处理温度为400、450和500 ℃制备的ZnO薄膜的电阻率分别为3.3×109、2.7×109和6.6×109 Ω·cm. 450 ℃时制备的ZnO薄膜的电阻率最小, 主要是由于较高的热处理温度有利于提高薄膜的纯度、密度和吸附氧. 而纯度较高、密度较大的薄膜电阻率比较小; 吸附氧含量增加, 晶界势垒增大, 电阻率增大. 因此在纯度和吸附氧的双重作用下450 ℃时制备的ZnO薄膜的电阻率最小, 而500 ℃时制备的ZnO薄膜的电阻率最大.     

(111)应变对正交相Ca_2P_(0.25)Si_(0.75)能带结构及光学性质影响的理论研究

采用第一性原理平面波贋势方法对(111)应变下正交相Ca2P0.25Si0.75的能带结构及光学性质进行模拟计算.计算结果表明:(111)面在晶格发生100%~104%张应变时,带隙随着应变增加而增大;在晶格发生104%~112%压应变时,带隙随着张应变的增加而减小;88%~100%压应变时,带隙随着压应变的增加而减小;当压应变达到88%后转变为导体.当施加应变后光学性质发生显著的变化,随着压应变的增加静态介电常数、折射率逐渐减小,张应变则反之.施加压应变反射向高能方向偏移,施加张应变反射向低能方向偏移.施压应变吸收谱增大,施加张应变吸收谱变小.综上所述,应变可以改变Ca2P0.25Si0.75的电子结构和光学常数,是调节Ca2P0.25Si0.75光电传输性能的有效手段.     

ZnO自组装薄膜的可控生长及其光催化性能

通过改变工艺参数, 制得了粒径可控的ZnO自组装薄膜. 该薄膜在可见光区域出现了光子带隙. 以染料甲基橙的光催化降解为模型评价了ZnO自组装薄膜的光催化活性. 利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征了ZnO的晶体结构和微观形貌. 实验结果表明, ZnO自组装薄膜在太阳光照射下表现出良好的光催化性能, 其光催化活性随着ZnO颗粒粒径的减小而提高. ZnO自组装薄膜光催化降解甲基橙的反应符合一级反应动力学规律.     

纳米结构ZnO在TiO_2薄膜上的电化学沉积及其表征

在三电极体系中,以硝酸锌水溶液作为电解液,采用阴极还原电沉积法成功实现了一维纳米结构ZnO阵列在TiO2纳米粒子/ITO导电玻璃薄膜基底上的沉积,并通过XRD、SEM、EDS和PL光谱等方法对样品进行了表征.重点研究了薄膜基底、电解液浓度、沉积时间、六次亚甲基四胺(HMT)的引入对ZnO沉积及其发光性质的影响.结果显示:与ITO玻璃基底相比,ZnO更易于在TiO2纳米粒子薄膜上实现电化学沉积.ZnO属于六方晶系的铅锌矿结构,并且沿着c-轴方向表现出明显的择优化生长,以形成垂直于基底的ZnO纳米棒阵列.延长沉积时间、增加电解液浓度和引入一定量的HMT等均对ZnO的生长有促进作用,进而使其纳米棒的结晶度和取向程度提高,进而解释了所得的薄膜分别约在375和520nm处表现出ZnO的强而窄的带边紫外光发射峰和弱而宽的表面态绿光发射带.     

聚合结晶化胶体阵列结构的压敏光响应性质

制备了由单分散聚苯乙烯微球构成的结晶化胶体阵列结构, 并制备了结晶化胶体阵列聚丙烯酰胺水凝胶薄膜. 通过微区反射光谱研究了其光子带隙位置随外加压力的变化规律. 实验结果表明, 该薄膜在垂直表面方向存在光子带隙, 并在一定载荷范围内带隙波长随外加压力呈可逆线性变化.     

介孔TiO2-ZnO复合薄膜的制备与表征

以三嵌段聚合物P123为模板剂, 以钛酸异丙酯和二水乙酸锌为无机前驱体, 利用溶胶-凝胶法和旋涂法成功地制备了不同ZnO含量的介孔TiO2-ZnO复合薄膜. 在ZnO前驱体摩尔分数为0~50％范围内获得薄膜质量较高的介孔TiO2-ZnO复合薄膜. 用小角XRD、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、能谱仪(EDS)、紫外-可见吸收光谱(UV-Vis)及X射线光电子能谱(XPS)对所得的复合薄膜进行了表征和分析. EDS和XPS等研究证明介孔薄膜为TiO2和ZnO的复合体系, 且ZnO前驱体含量的增加仍能保持TiO2-ZnO复合薄膜的均匀性. UV-Vis研究结果表明, 介孔复合薄膜的光学带隙宽度为3.45-3.58 eV, 随着ZnO含量的增加, 复合薄膜的紫外吸收蓝移.     

单轴应变对石墨烯掺杂硼、氮、铝、硅、磷的影响与调控

掺杂石墨烯因对石墨烯的性质有良好的修饰作用而备受关注. 掺杂石墨烯的实验合成一直都是研究热点, 但有一个普遍的难题, 就是掺杂困难, 掺杂浓度不高. 针对这一难题, 我们提出了通过对石墨烯施加单轴应变来降低掺杂过程反应形成能, 从而实现石墨烯的有效可控掺杂的可能性. 我们的第一性原理计算结果表明, 在施加应变时, 拉伸应变有利于硼掺杂, 而压缩应变使氮掺杂更容易, 对于铝、硅、磷, 不管是拉伸还是压缩均可以使掺杂更容易. 此外, 我们还进一步揭示了单轴应变对掺杂石墨烯的电子结构及磁性质的影响规律.     

高能Zn离子注入CaF2基质形成ZnO纳米粒子的机制、构型及电子结构

将高能Zn2+注入到CaF2介电基质中,在CaF2的表面下注入Zn2+浓度呈近似高斯分布,通过氧气氛后经热退火形成ZnO量子点.采用MaterialsStudio和Gaussian98W程序,结合实验结果计算分析了CaF2基质中ZnO纳米粒子的电子结构和光学性质.选取由4个ZnO原胞组成的超晶胞模型计算了ZnO纳米粒子的吸收光谱,理论结果与实验结果相符.对ZnO纳米粒子电子结构的研究结果表明,ZnO纳米粒子与CaF2基质的相互作用主要是ZnO表面的O与基质中Ca之间的作用,这种作用使ZnO纳米晶体的Fermi能级变窄,带隙相应减小;ZnO纳米粒子表面构型的变化对其本征吸收光谱没有影响,理论计算结果与实验值一致.     

TixV1-xO2薄膜的光学及相变特性

采用射频磁控溅射方法,在c-Al2O3(0001)基底上制备了不同钒钛比例的TixV1-xO2(0≤x≤1)薄膜,利用X射线衍射(XRD)、拉曼(Raman)光谱、紫外-可见-近红外(UV-Vis-NIR)光谱对薄膜结构及光学性能进行测试分析,计算薄膜的太阳能智能调节率和光学带隙.实验结果及分析表明:随着Ti含量的增加,薄膜的红外调节特性和热滞特性逐渐减弱直至消失;薄膜样品的光学带隙随着Ti含量的增加而变宽,光响应范围发生蓝移;其光学带隙随着V含量的增加而变窄,光响应范围发生红移.     

溶胶-凝胶法制备的MgxZn1-xO纳米薄膜结构和光学性质

用溶胶-凝胶法制备了不同组分的Mg_xZn_1-xO薄膜.X射线衍射结果表明,薄膜为具有六角纤锌矿结构的纳米薄膜,晶粒尺寸3～5nm,随着Mg进入ZnO晶格,其晶格常数变小.紫外-可见吸收光谱表明,随着Mg含量的增加带隙变宽,自由激子吸收峰明显蓝移.室温光致发光光谱由很强的且与氧空位相关的深能级缺陷发光和较弱的紫外激子发光组成,激子发光强度和缺陷发光强度比随x的增大而减小,表明Mg原子进入ZnO晶格会引起深能级缺陷的增加.Mg_0.03Zn_0.97O薄膜经700℃热氧化后,紫外与可见发光强度比达到30.     

Strain-dependent electronic and magnetic properties of MoS(2) monolayer, bilayer, nanoribbons and nanotubes

We investigate the strain-dependent electronic and magnetic properties of two-dimensional (2D) monolayer and bilayer MoS(2), as well as 1D MoS(2) nanoribbons and nanotubes using first-principles calculations. For 2D monolayer MoS(2) subjected to isotropic or uniaxial tensile strain, the direct band gap of MoS(2) changes to an indirect gap that decreases monotonically with increasing strain; while under the compressive strain, the original direct band gap is enlarged first, followed by gap reduction when the strain is beyond -2%. The effect of isotropic strain is even stronger than that of uniaxial strain. For bilayer MoS(2) subjected to isotropic tensile strain, its indirect gap reduces monotonically to zero at strain about 6%; while under the isotropic compressive strain, its indirect gap increases first and then reduces and turns into direct gap when the strain is beyond -4%. For strained 1D metallic zigzag MoS(2) nanoribbons, the net magnetic moment increases slightly with axial strain from about -5% to 5%, but drops to zero when the compressive strain is beyond -5% or increases with a power law beyond 5%. For 1D armchair MoS(2) nanotubes, tensile or compressive axial strain reduces or enlarges the band gap linearly, and the gap can be fully closed for nanotubes with relatively small diameter or under large tensile strain. For zigzag MoS(2) nanotubes, the strain effect becomes nonlinear and the tensile strain can reduce the band gap, whereas compressive strain can initially enlarge the band gap and then decrease it. The strain induced change in projected orbitals energy of Mo and the coupling between the Mo atom d orbital and the S atom p orbital are analyzed to explain the strong strain effect on the band gap and magnetic properties.     

A Semiempirical Study of Carbon Nanotubes with Finite Tubular Length and Various Tubular Diameters

A semiempirical PM3 quantum computational method has been used to generate the electronic and optimized geometrical structure of SWNT of zigzag and armchair types. We shed light on the electronic structures of SWNT with various diameters and lengths of the tube. Particularly, the calculated HOMO, LUMO and band‐gap of SWNT are not monotonic but exhibit a well‐defined oscillation, which depends on the tubular diameter and the tubular length. Calculated HOMO, LUMO and band‐gap of the zigzag SWNTs have oscillated with tubular diameter as they contain an odd or even number of benzenoids in the circular plane of the carbon nanotube. The zigzag SWNTs with an odd number of benzenoids have a higher band‐gap than those of SWNTs with an even number of benzenoids in the circular plane of the carbon nanotube. Calculated results also reveal that the tubular length in the zigzag SWNTs influences the band‐gaps very little. For the armchair SWNT, calculated HOMO, LUMO and band‐gap contained the oscillate depending on the number of carbon sections in the tubular length axis. Their repeat sections are 3n‐1, 3n and 3n+1. The armchair SWNT with 3n+1 sections has a high band‐gap while the SWNTs with 3n‐1 sections have a low band‐gap. The tubular diameters of armchair SWNT influence the HOMO, LUMO and band gap very little.     

Electronic and magnetic properties of armchair and zigzag graphene nanoribbons

The electronic properties, band gap, and ionization potential of zigzag and armchair graphene nanoribbons are calculated as a function of the number of carbon atoms in the ribbon employing density functional theory at the B3LYP6-31G* level. In armchair ribbons, the ionization potential and band gap show a gradual decrease with length. For zigzag ribbons, the dependence of the band gap and ionization potential on ribbon length is different depending on whether the ribbon has an unpaired electron or not. It is also found that boron and nitrogen zigzag and armchair doped graphene nanoribbons have a triplet ground state and could be ferromagnetic.     

Strain-tunable electronic properties and optical properties of Hf2CO2 MXene

Two-dimensional materials have been extensively applied because of their unusual electronic, mechanical, and optical properties. In this paper, the electronic structure and optical properties of Hf₂CO₂ MXene under biaxial and uniaxial strains are investigated by the Heys-Scuseria-Ernzerhof (HSE06) method. Monolayer Hf₂CO₂ can sustain stress up to 6.453 N/M for biaxial strain and 3.072 N/M for uniaxial strain. Monolayer Hf₂CO₂ undergoes the transition from semiconductor to metal under −12% strain whether it is under biaxial or uniaxial strain. With the increasing biaxial compressive strain, the blue shift of Hf-d, O-p, and C-p orbitals in valence band maximum results in the metallization of monolayer Hf₂CO₂, while the red shift of Hf-d and O-p orbitals in conduction band minimum results in the metallization of monolayer Hf₂CO₂ with increasing uniaxial compressive strain. The analysis of optical properties indicates that uniaxial strain weakens the reflectivity and refractive index of monolayer Hf₂CO₂ in the visible-light range. In addition, the effective mass and the charge distribution under biaxial and uniaxial strains are also explored.     

Electronic structure of GaN nanotubes

Nanotube properties are strongly dependent on their structures. In this study, gallium nitride nanotubes (GaNNTs) are analyzed in armchair and zigzag conformations. The wurtzite GaN (0001) surface is used to model the nanotubes. Geometry optimization is performed at the PM7 semiempirical level, and subsequent single-point energy calculations are carried out via Hartree–Fock and B3LYP methods, using the 6-311G basis set. Semiempirical and ab initio methods are used to obtain strain energy, charge distribution, dipole moment, |HOMO-LUMO| gap energy, density of states and orbital contribution. The gap energy of the armchair structure is 3.82 eV, whereas that of the zigzag structure is 3.92 eV, in agreement with experimental data.     

Tuning the Properties of Tetracene-Based Nanoribbons by Fluorination and N-Doping

The structural stabilities and electronic properties are studied for the recently synthesized one-dimensional (1-D) tetracene-based nanoribbons with four-membered rings by using first-principles calculation. All three configurations (named as straight, zigzag, and armchair) are stable and exhibit an indirect band gap of 1.46, 0.73, and 0.32 eV, respectively. The band gaps can be effectively tuned by substituting hydrogen with fluorine atoms and by doping with nitrogen atoms. Substituting hydrogen with fluorine atoms leads to gradual decrease of the electronic band gaps of all configurations. Nitrogen doping changes the band gap from indirect to direct, displaying flexibility of tuning the band structure.     

Theory of nitrogen doping of carbon nanoribbons: edge effects

Nitrogen doping of a carbon nanoribbon is profoundly affected by its one-dimensional character, symmetry, and interaction with edge states. Using state-of-the-art ab initio calculations, including hybrid exact-exchange density functional theory, we find that, for N-doped zigzag ribbons, the electronic properties are strongly dependent upon sublattice effects due to the non-equivalence of the two sublattices. For armchair ribbons, N-doping effects are different depending upon the ribbon family: for families 2 and 0, the N-induced levels are in the conduction band, while for family 1 the N levels are in the gap. In zigzag nanoribbons, nitrogen close to the edge is a deep center, while in armchair nanoribbons its behavior is close to an effective-mass-like donor with the ionization energy dependent on the value of the band gap. In chiral nanoribbons, we find strong dependence of the impurity level and formation energy upon the edge position of the dopant, while such site-specificity is not manifested in the magnitude of the magnetization.     

First-Principles Study on Electronic and Optical Properties of Graphene-Like Boron Phosphide Sheets

Two-dimensional semiconducting materials with moderate band gap and high carrier mobil-ity have a wide range of applications for electronics and optoelectronics in nanoscale. On the basis of first-principles calculations, we perform a comprehensive study on the electronics and optical properties of graphene-like boron phosphide (BP) sheets. The global structure search and first-principles based molecular dynamic simulation indicate that two-dimensional BP sheet has a graphene-like global minimum structure with high stability. BP monolayer is semiconductor with a direct band gap of 1.37 eV, which reduces with the number of layers. Moreover, the band gaps of BP sheets are insensitive to the applied uniaxial strain.= The calculated mobility of electrons in BP monolayer is as high as 10⁶ cm²/(V·s). Lastly, the MoS₂/BP van der Waals heterobilayers are investigated for photovoltaic applications, and their power conversion efficiencies are estimated to be in the range of 17.7%－19.7%. This study implies the potential applications of graphene-like BP sheets for electronic and optoelectronic devices in nanoscale.     

Theoretical study on the electronic structure nature of single and double walled carbon nanotubes and its role on the electron transport

Density functional theory and molecular dynamics (MD) calculations were used to evaluate electronic structure properties in a series of nanotubes with smallest possible diameters (both types: armchair and zigzag), and the corresponding chiral nanotubes (8,m) for 0 ≤ m ≤ 8. The calculations were performed considering a length of 16.5 Å. We evaluated a set of 26 combinations of dual nanotubes (armchair/armchair, zigzag/zigzag, armchair/zigzag, and zigzag/armchair), where the first label corresponds to the outer tube. We extended our study with nine additional systems of double-walled carbon nanotubes (DWCNT) with semiconductor nature. In this regard, we gave insight into the semiconductive or metallic nature inherited to the dual tubes. DWCNT systems were possible to construct by maintaining a radial distance of 3.392 Å for the armchair/armchair arrangement and 3.526 Å for the zigzag/zigzag type. It was considered as a reference, the interplanar distance of graphite (3.350 Å). Electronic transport calculations were also performed on selected DWCNT systems in order to understand the role played by the different symmetries under study. It was evidenced that the electronic structure nature of the systems rules the ability to transport electrons through the DWCNT interface.     

A computational study of aluminum phosphide nanotubes

Electronic structures of two representative zigzag and armchair models of aluminum phosphide nanotube (AlPNT) were investigated by density functional theory calculations. The structures were optimized and the bond lengths, tip diameters, band gaps, and dipole moments were calculated. Moreover, the quadrupole coupling constants (C_Q) were calculated for the Al‐27 atoms of the optimized structures. The same values of Al? P bond lengths were calculated for both models. The larger value of band gap of armchair model than the zigzag model indicated the stronger dielectric property for the former model. The values of C_Q(²⁷Al) were the largest for the Al atoms placed at the tips of both zigzag and armchair AlPNT than other Al atoms, which could reveal dominant role of the Al atoms placed at the tips of nanotube in determining the electronic properties of the AlPNT. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011