单原子层应变超晶格(Si)_1/(Si_(1-x)Ge_x)_1(100)的电子结构

在计入应力的紧束缚框架之下计算了单原子层应变超晶格(Si)_1/(Si_1-xGo_x)_1的电子结构.对应于不同应变条件,得出能隙随组分的变化,并结合能带边不连续的变动加以考察.超晶格取Si(或Ge)晶格常数后能隙随组分的非单调变化源自合金受相同应力后能隙的类似特点.超晶格能带及态密度均呈现类Si的闪锌矿结构对称性.在虚晶近似得出的能隙和电子状态密度的基础上,利用相干势近似作了进一步的修正.     

超晶格(Al_xGa_(1-x)As)_m/(GaAs)_m(110)的电子能带结构

采用紧束缚的重整化方法计算了超晶格(Al_xGa_1 xAs)_m/(GaAs)_m(110)的电子能带结构(1≤m≤10)。讨论了电子能带结构随超晶格层厚m及合金组分x的变化情况。计算结果表明,对于不同的合金组分x,超晶格可以处在三个不同区域:A区,直接能隙结构,Ⅰ-型超晶格;B区,间接能隙结构,Ⅰ-型超晶格;C区,间接能隙结构,Ⅱ—型超晶格。     

GaInPAs/InP晶格匹配超晶格材料电子态研究

本文研究了GaInPAs/InP晶格匹配超晶格材料<110>方向的电子结构,对薄层超晶格和与之具有相同化学组份的混晶的色散关系作了比较。研究了带边状态密度在超晶格每一层的分布情况,计算了GaInPAs/InP晶格匹配超晶格的能隙随厚度、组份的变化趋势。研究结果表明:薄层超晶格与具有相同化学组份的混晶的电子结构基本相同,能隙边状态密度偏重于分布在超晶格的GaInPAs原子层内。     

掺氮锯齿型单壁碳纳米管的电子结构

基于密度泛函理论(DFT)框架下的第一性原理平面波超软赝势方法,采用CASTEP软件包,在分析掺氮碳纳米管最可能存在方式并进行结构优化的基础上,对不同掺氮浓度的单壁碳纳米管的电子结构进行了计算,分析了掺杂碳纳米管的能带结构和态密度,结果表明随着掺杂浓度的增加能带间隙呈现减小的趋势.     

掺氮锯齿型单壁碳纳米管的电子结构

基于密度泛函理论(DFT)框架下的第一性原理平面波超软赝势方法,采用CASTEP软件包,在分析掺氮碳纳米管最可能存在方式并进行结构优化的基础上,对不同掺氮浓度的单壁碳纳米管的电子结构进行了计算,分析了掺杂碳纳米管的能带结构和态密度,结果表明随着掺杂浓度的增加能带间隙呈现减小的趋势.     

二维光子晶体1.55μm带隙中心的优化设计

利用平面波展开法对正方晶格二维光子晶体带隙随结构参数的变化进行了研究,计算结果表明,能带频率随着归一化半径r/a的增大有减小的趋势,带隙宽度是先增大后减小.带隙宽度随介电常数比ε的变大而增加,能带频率有减小的趋势.当格子常数a=0.594μm,r/a=0.16,ε=13时得到能带中心波长为1.55μm,最大能带归一化频率宽度为0.15.     

碳纳米管的电子能带结构和态密度研究

为了研究单壁碳纳米管的电子能带特性及其态密度,本文采用紧束缚法和态密度函数,对无限长碳纳米管进行了理论计算和模拟。结果表明:碳纳米管的电子能带结构与其几何结构密切相关,一般认为扶手型管呈现出金属性;而锯齿管则不同,当n=3k(k为整数)时,其能级存在一个较小的禁带宽度,具有半金属性质;而其它锯齿型管均存在较大的禁带宽度,且禁带宽度随管径的增大而减小,具有半导体性质,这为碳纳米管的电子结构的研究提供了必要且有价值的理论依据。     

(Al_xGa_(1-x)As)_m/(GaAs)_m(001)超晶格的能带结构与合金组分x间的关系

采用紧束缚的重整化方法研究了(Al_xGa_(1-x)As)_m/(GaAs)_m(001)超晶格的电子能带结构与合金组分x及层厚间的变化关系。给出了临界组分x_o与层厚m间的变化关系图。并以二次函数形式给出了直接能隙和间接能隙与合金组分x间的变化关系。最后,也用Kronig—Penney模型对超晶格的电子能带结构进行了计算,并与紧束缚的计算结果进行了比较。     

紧束缚法计算GaAs-GaP超晶格的能带结构及电子的有关性质

本文使用紧束缚法研究了GaAs-GaP超晶格的能带结构和电子的有关性质.久期方程的矩阵元中包括了一直到次近邻的原子轨道间的相互作用积分.本文计算了超晶格(GaAs)1-(GaP)_1布里渊区中三条主要对称线上的能带;计算了超晶格(GaAs)m-(GaP)n在Γ点、X点和M点的能带值,这里m+n≤10;讨论了m=n时禁带宽度随周期长度的变化、周期长度不变时组分变化对禁带宽度的影响以及在几个典型的单电子状态中电子处于各个原子上的几率.     

硼，氮共掺碳纳米管的第一性原理研究

小管径单壁碳纳米管因为曲率效应和局部效应的影响,有着不同的电学性能。传统的密度泛函计算并不能完全处理这些影响因素,但是杂化泛函计算却可以。我们通过HSE杂化泛函计算研究了（2,3）碳纳米管共掺杂不同浓度的氮,硼原子,发现了能隙和一些其他性质均随着掺杂成分的改变而发生振荡变化。我们的研究阐明了对小管径纳米管性质的认识。这对设计新型纳米电子设备有潜在作用。     

Influence of tension-twisting deformations and defects on optical and electrical properties of B, N doped carbon nanotube superlattices

As the era of nanoelectronics is dawning, CNT (carbon nanotube), a one-dimensional nano material with outstanding properties and performances, has aroused wide attention. In order to study its optical and electrical properties, this paper has researched the influence of tension-twisting deformation, defects, and mixed type on the electronic structure and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N by using the first-principle method. Our findings show that if tension-twisting deformation is conducted, then the geometric structure, bond length, binding energy, band gap and optical properties of B, N doped carbon nanotube superlattices with defects and mixed type will be influenced. As the degree of exerted tension-twisting deformation increases, B, N doped carbon nanotube superlattices become less stable, and B, N doped carbon nanotube superlattices with defects are more stable than that with exerted tension-twisting deformations. Proper tension-twisting deformation can adjust the energy gap of the system; defects can only reduce the energy gap, enhancing the system metallicity; while the mixed type of 5% tension, twisting angle of 15° and atomic defects will significantly increase the energy gap of the system. From the perspective of optical properties, doped carbon nanotubes may transform the system from metallicity into semi-conductivity.     

A new approach to regulate the photoelectric properties of two-dimensional SiC materials:first-principles calculation on B-N co-doping

This paper describes a new approach to regulate the photoelectric properties of two-dimensional SiC materials. The first-principles pseudo-potential plane wave method is used to calculate the geometric structure, electronic structure and optical properties of two-dimensional (2D) SiC co-doped by the adjacent elements of C-Si (such as B and N). The results show that:after B-N co-doping, the supercell lattices of 2D SiC are observed obviously deformation near the doped atoms. Meanwhile, the band structures of 2D SiC co-doped by B-N become rich. As the impurity level enters the forbidden band, the band gap decreases, and the distribution of density of states near the Fermi level changes accordingly. The calculation of optical properties shows that the ability to absorb electromagnetic waves of 2D SiC has been enhanced obviously in the low energy range after B-N co-doping. The reason is originated from the transition of the 2p state of B and N. At the same time, the static dielectric constant increases and the peak of reflectivity decreases. The above results indicate that the optoelectronic properties of 2D SiC can be modulated by co-doping B-N.     

Wide Range Control of Microstructure and Mechanical Properties of Carbon Nanotube Forests: A Comparison Between Fixed and Floating Catalyst CVD Techniques

Vertically aligned carbon nanotube (CNT) forests may be used as miniature springs, compliant thermal interfaces, and shock absorbers, and for these and other applications it is vital to understand how to engineer their mechanical properties. Herein is investigated how the diameter and packing density within CNT forests govern their deformation behavior, structural stiffness, and elastic energy absorption properties. The mechanical behavior of low‐density CNT forests grown by fixed catalyst CVD methods and high‐density CNT forests grown by a floating catalyst CVD method are studied by in situ SEM compression testing and tribometer measurements of force‐displacement relationships. Low‐density and small‐diameter CNT columns (fixed catalyst) exhibit large plastic deformation and can be pre‐deformed to act as springs within a specified elastic range, whereas high‐density and large‐diameter CNT columns (floating catalyst) exhibit significant elastic recovery after deformation. In this work the energy absorption capacity of CNT forests is tuned over three orders of magnitude and it is shown that CNT forest density can be tuned over a range of conventional foam materials, but corresponding stiffness is ～10× higher. It is proposed that the elastic behavior of CNT forests is analogous to open‐cell foams and a simple model is presented. It is also shown that this model can be useful as a first‐order design tool to establish design guidelines for the mechanical properties of CNT forests and selection of the appropriate synthesis method.     

First-principles study of p-type ZnO by S-Na co-doping

Using the first-principles method based on the density functional theory, the formation energy, electronic structures of S-Na co-doping in ZnO were calculated. The calculated results show that Na_Zn-S_O have smaller formation energy than Na_in-S_O in energy ranges from -3.10 to 0 eV of μ_O, indicating that it opens up a new opportunity for growth the p-type ZnO. The band structure shows that the Na_Zn system is a p-type direct-band-gap semiconductor material and the calculated band gap (0.84 eV) is larger than pure ZnO (0.74 eV). The Na_Zn-S_O system is also a p-type semiconductor material with a direct band gap (0.80 eV). The influence of S-Na co-doping in ZnO on p-type conductivity is also discussed. The effective masses of Na_Zn-S_O are larger than effective masses of Na_Zn and the Na_Zn-S_O have more hole carriers than Na_Zn, meaning the hole in the Na_Zn-S_O system may have a better carrier transfer character. So we inferred that Na_Zn-S_O should be a candidate of p-type conduction.     

Super‐Aligned Carbon Nanotube Films as Current Collectors for Lightweight and Flexible Lithium Ion Batteries

Carbon nanotube (CNT) current collectors with excellent flexibility, extremely low density (0.04 mg cm^?2), and tunable thickness are fabricated by cross‐stacking continuous CNT films drawn from super‐aligned CNT arrays. Compared with metal current collectors, better wetting, stronger adhesion, greater mechanical durability, and lower contact resistance are demonstrated at the electrode/CNT interface. Electrodes with CNT current collectors show improvements in cycling stability, rate capability, and gravimetric energy density over those with metal current collectors. These results suggest that CNT films can function as a promising type of current collector for lightweight and flexible lithium ion batteries with high energy density.     

碳纳米管介电电泳组装及过程控制研究进展

碳纳米管具有独特的结构和卓越的电学、热学、力学等性能,有望在微纳电子、微纳机电系统、传感器、新能源、光学等诸多领域获得具有深远影响的应用。碳纳米管的组装是其获得广泛应用的重要前提,基于介电电泳的组装和过程控制技术近年来得到了迅速发展。这些技术包括回路中串联自限制性电阻,间隙电信号实时监测和反馈控制,三维结构的组装和包覆,引入不同形状浮动电极等。对碳纳米管介电电泳组装及各种新技术做了系统介绍,并对各种方法的优缺点进行了对比与总结,为探索稳定、高效的碳纳米管自动组装方法提供帮助。     

A Hybrid Supercapacitor Fabricated with a Carbon Nanotube Cathode and a TiO2–B Nanowire Anode

Recently, a new hybrid supercapacitor, integrating both the advantages of supercapacitors and lithium‐ion batteries, was proposed and rapidly turned into state‐of‐the‐art energy‐storage devices with a high energy density, fast power capability, and a long cycle life. In this paper, a new hybrid supercapacitor is fabricated by making use of the benefits of 1D nanomaterials consisting of a carbon nanotube (CNT) cathode and a TiO₂–B nanowire (TNW) anode, and the preliminary results for such an energy‐storage device operating over a wide voltage range (0–2.8 V) are presented. The CNT–TNW supercapacitor is compared to a CNT–CNT supercapacitor, and discussed with regards to available energy densities, power capabilities, voltage profiles, and cycle life. On the basis of the total weight of both active materials, the CNT–TNW supercapacitor delivers an energy density of 12.5 W h kg^–1 at a rate of 10 C, double the value of the CNT–CNT supercapacitor, while maintaining desirable cycling stability. The combination of a CNT cathode and a TNW anode in a non‐aqueous electrolyte is proven to be suitable for high‐performance hybrid supercapacitor applications; this can reasonably be assigned to the interesting synergistic effects of the two nanomaterials. It is hoped that the results presented in this study might renew interest in the design of nanomaterials that are applicable not only to hybrid supercapacitors, but also to energy conversion and storage applications of the future.     

Inductance of mixed carbon nanotube bundles

The carbon nanotube (CNT) bundle is a promising candidate for next-generation interconnect/via applications. A realistic CNT bundle is a mixture of single-wall and multi-wall CNTs and its performance analysis needs to consider both kinds of CNTs. The inductances of the mixed CNT bundles are estimated, which are in agreement with the recent experimental results. Impacts of different parameters such as tube density, tube distribution, metallic tube ratio and bundle dimensions are discussed, providing an important guideline to design and fabricate a CNT bundle with a desirable inductance performance.     

Efficiency Enhancement of Single‐Walled Carbon Nanotube‐Silicon Heterojunction Solar Cells Using Microwave‐Exfoliated Few‐Layer Black Phosphorus

Carbon nanotube‐silicon (CNT‐Si)‐based heterojunction solar cells (HJSCs) are a promising photovoltaic (PV) system. Herein, few‐layer black phosphorus (FL‐BP) sheets are produced in N‐methyl‐2‐pyrrolidone (NMP) using microwave‐assisted liquid‐phase exfoliation and introduced into the CNTs‐Si‐based HJSCs for the first time. The NMP‐based FL‐BP sheets remain stable after mixing with aqueous CNT dispersion for device fabrication. Due to their unique 2D structure and p‐type dominated conduction, the FL‐BP/NMP incorporated CNT‐Si devices show an impressive improvement in the power conversion efficiency from 7.52% (control CNT‐Si cell) to 9.37%. Our density‐functional theory calculation reveals that lowest unoccupied molecular orbital (LUMO) of FL‐BP is higher in energy than that of single‐walled CNT. Therefore, we observed a reduction in the orbitals localized on FL‐BP upon highest occupied molecular orbital to LUMO transition, which corresponds to an improved charge transport. This study opens a new avenue in utilizing 2D phosphorene nanosheets for next‐generation PVs.