A fast and stable Poisson-Schrödinger solver for the analysis of carbon nanotube transistors

When the coupled Schrödinger-Poisson system is solved iteratively with appropriate numerical damping, convergence problems are likely to occur. We show that these problems are due to inappropriate energy discretization for evaluating the carrier concentration. By using an adaptive method the self-consistent loop becomes stable, and most of the simulations converge in a few iterations. We applied this approach to investigate the behavior of carbon nanotube field effect transistors.     

Influence of different fluoride containing electrolytes on the formation of self-organized titania nanotubes by Ti anodization

The formation of self-organized porous titania nanotubes is achieved by electrochemical anodization under specific experimental conditions. In present work, the formation of porous titania nanotubes on titanium substrates is investigated in several SO₄²⁻/F⁻ based electrolytes. The presence of some non-porous layers covering the porous layers and accompanying the pore growth is observed. We discuss in details the influence of different electrolyte composition on the structure of self-organized porous layers, investigate the conditions for ideal pore growth. SEM investigations and XRD, AES and EDX surface analyses are carried out to characterize the self-organized porous layers. The results show that using SO₄²⁻/F⁻ electrolytes with different cations can drastically influence the final morphology of the self-organized porous nanotubes. We furthermore show that the nanotubes consist of TiO₂ and that they remain unchanged when annealed.     

用掺杂法改进碳纳米管气敏传感器的机理

碳纳米管气敏传感器在敏感性、选择性、操纵性等性能上，远胜于传统的金属氧化物膜传感器。但由于受本征碳纳米管(纯净碳纳米管)吸附能力的限制，碳纳米管气敏传感器能检测的气体种类很少。斯坦福大学的Shu Peng等人的实验发现，掺杂了B、N原子的碳纳米管第一次成功地检测出了CO和H2O分子。在详细阐述碳纳米管传感器工作机理的基础上，用半导体杂质理论和离子对吸附模型对这一最新实验结果作出理论解释。这种掺杂方法，很有可能从根本上解决碳纳米管气敏传感器检测范围小的问题。     

Self-organized porous TiO2 and ZrO2 produced by anodization

The present work investigates the electrochemical formation of self-organized high aspect ratio TiO₂ and ZrO₂ nanotube layers. The formation and growth of a self-organized porous layer can be achieved directly by anodization without any templates in fluoride containing electrolytes. The morphology of the porous layers is affected by the electrochemical conditions such as the electrolyte composition, the pH and the exact polarization treatment (such as the potential sweep rate from the open-circuit potential to the anodizing potential). For Ti, nanotube layers are formed with diameters varying from approx. 20 nm to 100 nm and lengths from approx. 0.25 μm to 2.5 μm depending on the electrolytes and pH. On the other hand, for Zr, tubes of 50 nm in diameter and up to approx. 17 μm in length can be grown—a key parameter in this case is the potential sweep rate. The large difference between Ti and Zr in the achievable thickness of nanotube layers indicates a difference in the growth mechanism which may be based on the different chemical dissolution rates of electrochemically formed oxides.     

碳、硅及氮化硼纳米管轴向拉伸的分子动力学研究

基于Tersoff势的分子动力学方法模拟(5,5)型单壁碳、硅及氮化硼纳米管的轴向拉伸过程.根据模拟结果,讨论三种纳米管拉伸时的构形、能量、载荷、径向收缩率等的变化及其差异.研究结果表明,(1)小应变时,系统能量随变形增大而增大,各纳米管截面构形基本保持圆形不变.(2)碳、硅及氮化硼纳米管的断裂应变值分别为42.8%、33.4% 和49.1%.(3)碳纳米管的能量吸收能力最好,承载最大,径向收缩率最小.     

Polypyrrole nanotube arrays on carbonized cotton textile for aqueous sodium battery

Polypyrrole (PPy) nanotubes on carbonized cotton textile have been prepared using ammonium vanadate nanowires as sacrificial templates, and characterized by scanning electron microscope, X-ray diffraction, fourier transform infrared spectrum and transmission electron microscope. The process contains cotton textile carbonation in Ar gas, growing ammonium vanadate nanowires on the carbon textile, electrodeposition PPy layer on the nanowire, and dissolving the ammonium vanadate nanowire core to obtain PPy nanotube. The results show that pyrrole is uniformly polymerized around the ammonium vanadate nanowires and the PPy nanotubes are firmly adhere to the carbon textile. The electrochemical properties of the PPy nanotubes for aqueous sodium-ion battery are investigated with cyclic voltammetry, galvanostatic charge-discharge test, and rate performance. The results exhibit a good electrochemical performance, which delivers a high discharge capacity of 108.8 mAh g⁻¹ over 100 cycles.     

Development of high oxidation resistant coating of nanostructured MgO on carbon nanotubes via simple precipitation technique in Mg/CO gas system

The synthesis of oxide-coated carbon nanotubes (CNTs) by a simple precipitation reaction in Mg/CO gaseous system was studied. The results showed that nanostructured MgO could be uniformly coated on the surface of CNTs via inhomogeneous Mg_(g) and CO_(g) precipitation reaction. Furthermore, we have developed a mixing procedure based on simultaneous agitation and ultra-sonication in order to break CNT bundles and prepare highly dispersed starting materials. By applying such mixing procedure, dispersed and distinct nano-oxide coated CNTs were synthesized which can be efficiently utilized in different composite matrices. Oxidation resistance of samples was investigated by DSC/TG thermal analysis. The results showed that oxide-coated CNTs present superior resistance against oxidation even at rather elevated temperature of 1000 °C and total weight loss of coated CNTs was measured to be less than 1 wt% during heat treatment at such temperature. Finally, coating adhesion was evaluated employing ultrasonic waves (as mechanical force) and subsequent weight loss measurement at temperature of 1000 °C.     

Young’s modulus of crystalline C60 nanotubes studied by in situ transmission electron microscopy

Bending tests of crystalline nanotubes composed of fullerene C₆₀ molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C₆₀ nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C₆₀ nanowhiskers. The result concerning the increase in the Young’s modulus of the C₆₀ nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C₆₀ nanowhiskers.     

Enhanced photoelectrochemical current response of titania nanotube array

Self-organized and highly-ordered TiO₂ nanotube array with disjunctive wall-hole structure has been synthesized from titanium foil by potentiostatic–galvanostatic anodization process. The morphology and microstructure of the TiO₂ layer depend greatly on the electrolyzing parameters and electrolyte components. TiO₂ formation mechanism by anodization oxidation is discussed. The crystallized TiO₂/Ti nanotube electrode exhibited a significant enhancement of photoelectrochemical current response in comparison with micrometer-sized TiO₂/Ti multiporous electrode. Such kind of TiO₂ nanotube will have many potential applications in various areas as an outstanding photoelectrochemical material.