Showing papers in "The Open Nanoscience Journal in 2007"

Size Dependence of Structures and Properties of Magnetic Materials

Abstract: Due to the involvement of high portion of atomic coordination imperfection in surfaces and interfaces, the properties of magnetic nanocrystals dramatically differ from that of the corresponding bulk counterparts, which have led to a surge in both experimental and theoretical investigations in the past decades. This review summarizes the studies for these size-dependent magnetic properties, and additional thermal or phase stabilities, and mechanical properties. To inter- pret the above phenomena, a thermodynamic model for the size dependence and interface dependences of these properties is described, which is based on Lindemann s criterion for melting, Mott s expression for the vibrational melting entropy, and Shi s model for the size-dependent melting temperature. The model without any adjustable parameter is confirmed by a large number of experimental results, and helps us to understand the structures and properties of the magnetic nanocrys- tals. Moreover, other theoretical works on the above properties are also mentioned and commented.

Preparation and Characterization of Different Shapes of Silver Nanostructures in Aqueous Solution

Abstract: We have developed a new and simple one-pot synthetic approach for the preparation of single-crystalline rose-, spike-, and snowflake-shaped silver nanostructures (NSs) in aqueous solution. We obtained these variously shaped Ag NSs by carefully controlling the nature and concentration of the stabilizers, which included sodium acetate, sodium citrate, and poly(ethylene glycol). To the best of our knowledge, this paper is the first to describe the preparation of roseshaped Ag NSs, also called Ag nanoflowers (NFs), through such a simple synthetic route. The thus-prepared Ag NFs exhibited a specific surface area of 15.6 m g, a contact angle of 97.6 ± 2.2°, high conductivity (1.97 10 S/cm), and efficient optothermal conversion efficiency (the temperature rose 23.03 ± 0.21 °C after laser irradiation at 808 nm for 3 min). The snowflake-shaped Ag NSs allowed the enhancement of Raman scattering (SERS) signals of rhodamine 6G by a factor of 2.4 10, leading to a detection limit of 10 nM.

Oscillatory Gas Flow in a Circular Nanotube

Abstract: Gas flow through nanoscale conduits shows distinctly different physics compared to flow at the macroscale. One of the first manifestations of this is the appearance of wall slip. Here we consider the oscillatory flow of an incom- pressible Newtonian gas through a circular nanotube, with first order wall slip due to rarefaction. It was found that the ma- jor effect of wall slip at lower oscillation frequencies is to alter the instantaneous velocity profiles from Poiseuille-like to more plug-like, with an overall enhancement to the fluid velocity magnitude. However, at higher frequencies the en- hancement to velocity magnitude due to wall slip is greatly diminished, and rarefaction introduces a region of backflow near the centerline of the nanotube. These flow characteristics may have important implications for the design of various practical applications of unsteady gas flow through nanoscale conduits, from fuel cell membranes to gas-powered nanomachines constructed from carbon nanotubes.

Nanotechnology and Nucleic Acids

Abstract: The peculiarities of two approaches in the nanodesign based on the double-stranded nucleic acid molecules are considered. Main attention is devoted to the formation and properties of nanoconstructions based on the double-stranded DNA molecules and the complexes with chitosan, fixed in the spatial structure of particles of their cholesteric liquidcrystalline dispersions, and cross-linked by artificial nanobridges consisting of alternating copper ions and daunomycin molecules. In contrast to initial DNA liquid-crystalline particles, the structure of resulting nanoconstruction is not “liquidcrystalline” any more; rather it is rigid, crystal-like, three-dimensional structure. The formed nanoconstructions possess the unique spatial and optical properties; this opens a gate for their application in biotechnology and medicine.

Mechanical Characterization of Micro/Nano Structures

Abstract: This paper reviews some of the important characterization techniques used to evaluate the mechanical proper- ties of the micro or nanostructures and components. Three techniques based on AFM, nanoindentation and electric field induced resonance excitation methods were discussed in detail. In the following section mechanical characteristics of typical semiconducting or metallic materials with an emphasis on their micro/nano components are discussed. The influ- ence of cross-section dimensions on the quasi-static strength of single and poly crystalline silicon micro specimens in bending and tension is examined. The differences in mechanical properties, testing methods and specimen dimensions were analyzed based on the recently reported data. A simple empirical correlation is presented with interpretation of the experimental data.

Review on Optimization Methods of Carbon Nanotube Field-Effect Transistors

Abstract: Carbon nanotube field-effect transistors (CNTFETs) have been considered as a replacement for, or complement to, future semiconductor devices due to high mobility, low defect structure, and intrinsic nanometer scale of carbon nano- tubes (CNTs). The great superiority in performance for CNTFETs vis-a-vis state-of-the-art silicon devices has attracted an intense research effort to explore their application viability. Since the first CNTFET was fabricated, CNTFETs have expe- rienced great advances at the device structure as well as device performance. Various methods had been attempted to op- timize the devices. These methods can mainly be divided into four aspects: (1) Decrease the contact resistance between CNTs and metal electrodes; (2) Increase the tuning efficiency of gate voltage to CNT channels; (3) Shorten the CNT channel length; (4) Adopt the optimized device structure. This review will briefly summarize these methods and describe the device performances achieved with these methods. Representative researches and updated progress on the optimiza- tion methods of CNTFETs will be introduced. From the review, the advances in CNTFETs can be also learned in the rough.