Structural,electronic,and optical properties of hexagonal and triangular SiC NWs with different diameters

Silicon carbide(SiC) is a wideband gap semiconductor with great application prospects,and the SiC nanomaterials have attracted more and more attention because of their unique photoelectric properties.According to the first-principles calculations,we investigate the effects of diameter on the electronic and optical properties of triangular SiC NWs(T-NWs)and hexagonal SiC NWs(H-NWs).The results show that the structure of H-NWs is more stable than T-NWs,and the conduction band bottom of H-NWs is more and more deviated from the valence band top,while the conduction band bottom of T-NWs is closer to the valence band top.What is more,H-NWs and T-NWs have anisotropic optical properties.The result may be helpful in developing the photoelectric materials.     

Structure of Lennard–Jones nanowires encapsulated by carbon nanotubes

Molecular dynamics simulations have been performed to investigate the structures of Lennard–Jones(LJ) nanowires(NWs) encapsulated in carbon nanotubes(CNTs). We find that the structures of NWs in a small CNT only adopt multi-shell motifs, while the structures of NWs in a larger CNT tend to adopt various motifs. Among these structures, three of them have not been reported previously. The phase boundaries among these structures are obtained regarding filling fractions, as well as the interaction between NWs and CNTs.     

ZnSe、ZnS量子点的可控合成与表征

采用改进后的合成方法,以Se和ZnO粉末为原料,在十六胺(HDA)、月桂酸(LA)和三辛基膦(TOP)有机溶剂体系中合成了胶体ZnSe和ZnS量子点。主要研究了溶剂配比、反应温度及生长时间对ZnSe量子点粒径和光学性质的影响。结果表明:制得的ZnSe和ZnS量子点均是纤锌矿型结构,且具有较好的尺寸均匀性、分散性及荧光特性。粒子直径可控制在4.5~8 nm范围内。采用参数n(ZnO) : n(HDA) : n(LA)=1 : 2.1 : 5.2,c(TOPSe)=1 mol/L,在280 ℃成核,240 ℃生长条件下合成的ZnSe量子点具有最佳的尺寸范围,并且随着生长时间的延长,粒径变大,荧光发射峰明显红移。     

Effects of oxygen-containing defect complex on the electronic structures and transport properties of single-walled carbon nanotubes

The electronic structures and transport properties of (10,0)$(10,0)$ single-walled carbon nanotube ((10,0)$(10,0)$ (SWNT)) with oxygen-containing defect complex are investigated using density functional theory in combination with nonequilibrium Green?s function method. The complex delocalizes the local states of (10,0)$(10,0)$ SWNT induced by mono- and di-vacancy but strengthens the localization of the states induced by the Stone–Wales defect. As a result, the complex partially restores the transport properties of (10,0)$(10,0)$ SWNT with vacancies, but reduces the transmission of (10,0)$(10,0)$ SWNT with Stone–Wales defect. However, the oxygen-containing defect complex only slightly influences the transmission gap and threshold voltage of the system.     

Nanohole 3D-size tailoring through polystyrene bead combustion during thin film deposition

A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H₂O and CO₂ generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4-24 nm and diameter of 10-36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO₂ or Al₂O₃. These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters.     

Polymer assisted assembling of the semiconductor particles: Structural and electrical studies

CdS and Si semiconductor nanopraticles were embedded in a polymer matrix and characterized using various techniques. The surface properties and size distribution of the nanoparticles were monitored by POM and SEM and found to be uniform but around the crystalline frameworks of the polymer. XRD and FTIR analysis have been used to ensure the composite nature and particle size of the semiconductor loaded films. The electrical conductivity of these films were evaluated and found to increase with semiconductor dispersion and attains a percolation threshold at optimum composition. This composition and the distribution of the clusters is shown to vary with the type of the semiconductor, i.e., CdS or Si.     

单壁碳纳米管的快速、高效提纯方法研究

本文采用改进的流化床装置对碳纳米管进行空气氧化处理、浓盐酸浸泡处理、空气氧化、浓盐酸浸泡组合处理, 利用扫描电镜和拉曼光谱方法检测了四种处理方法对碳纳米管提纯的效果, 结果发现, 在873 K经空气氧化30分钟, 再用浓盐酸浸泡10分钟, 这种组合处理方法下, 得到的单壁碳管纯度最高, 产率最大。     

Morphology of single-wall carbon nanotube aggregates generated by electrospray of aqueous suspensions

Airborne single-wall carbon nanotubes (SWCNTs) have a high tendency to agglomerate due to strong interparticle attractive forces. The SWCNT agglomerates generally have complex morphologies with an intricate network of bundles of nanotubes and nanoropes, which limits their usefulness in many applications. It is thus desirable to produce SWCNT aerosol particles that have well-defined, unagglomerated fibrous morphologies. We present a method to generate unagglomerated, fibrous particles of SWCNT aerosols using capillary electrospray of aqueous suspensions. The effects of the operating parameters of capillary electrospray such as strength of buffer solution, capillary diameter, flow rate, and colloidal particle concentration on the size distributions of SWCNT aerosols were investigated. Results showed that electrospray from a suspension of higher nanotube concentration produced a bimodal distribution of SWCNT aerosols. Monodisperse SWCNT aerosols below 100 nm were mostly non-agglomerated single fibers, while polydisperse aerosols larger than 100 nm had two distinct morphologies: a ribbon shape and the long, straight fiber. Possible mechanisms are suggested to explain the formation of the different shapes, which could be used to produce SWCNT aerosols with different morphologies.     

基于层层自组装碳纳米管的应变检测仪

通过对微小应变检测意义的分析,提出了本检测仪在实际应用方面的价值和前景。基于对碳纳米管导电机理的分析、制备薄膜电阻,利用其电阻随形变变化较为灵敏的特性,将电阻的变化转换为电压值的变化,经过数据采集、放大和数字处理设计了应变传感器。     

Stabilization of atmospheric carbon dioxide via zero emissions-An alternative way to a stable global environment. Part 1: Examination of the traditional stabilization concept

The concept of "stabilization" of atmospheric CO2 concentration is re-examined in connection with climate-change mitigation strategies. A new "zero-emissions stabilization (Z-stabilization)" is proposed, where CO2 emissions are reduced to zero at some time and thereafter the concentration is decreased by natural removal processes, eventually reaching an equilibrated stable state. Simplified climate experiments show that, under Z-stabilization, considerably larger emissions are permissible in the near future compared with traditional stabilization, with the same constraint on temperature rise. Over longer time scales, the concentration and temperature decrease close to their equilibrium values, much lower than those under traditional stabilization. The smaller temperature rise at final state is essential to avoid longer-term risk of sea level rise, a significant concern under traditional stabilization. Because of these advantages a Z-stabilization pathway can be a candidate of practical mitigation strategies as treated in Part 2.(Contributed by Taroh MATSUNO, M.J.A.).