Nano

This paper provides a comprehensive review on the methodological development and technical applications of in situ microscopy, including transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), developed in the last decade for investigating the structure-mechanical-property relationship of a single one-dimensional nanomaterial, such as nanotube, nanowire and nanobelt. The paper covers both the fundamental methods and detailed applications, including AFM-based static elastic and plastic measurements of a carbon nanotube, external field-induced resonance dynamic measurement of elastic modulus of a nanotube/nanowire, nano-indentation, and in situ plastic deformation process of a nanowire. Details are presented on the elastic property measurements and direct imaging of plastic to superplastic behavior of semiconductor nanowires at atomic resolution, providing quantitative information on the mechanical behavior of nanomaterials. The studies on the Si and SiC nanowires clearly demonstrated their distinct, "unexpected" and superior plastic mechanical properties. Finally, a perspective is given on the future of nanomechanics.

An applied force may cause the conformation and thus, the activity of a biological molecule to change. Here we consider a system in which an oscillating or fluctuating electric field is used to actuate membrane protein activities. Most proteins have electric dipoles and net charges in the structure and their conformations are susceptible to the electric and magnetic perturbation. The shape of a cell may also amplify an electric field across its plasma membrane. Therefore, a membrane integral protein such as an ion channel, an ion pump, or a molecular motor, is especially amenable to electric perturbation. The theory of electroconformational coupling addresses the functional implication of this field effect. When an alternating electric field or a fluctuating electric field is employed to actuate a two-state protein oscillator, the dynamics of the conformational change of the protein can be synchronized with the applied field. Through this two-state protein oscillator, we construct a four-state catalytic wheel by coupling an energy transducer mechanism to the two-state protein oscillator. Analysis shows that the catalytic wheel can extract energy from a disordered external energy source, be it electrical, mechanical, or chemical, and convert this stochastic energy source to a usable energy format. The catalytic wheel is tested with the experimental data on the electric field-stimulated cation pumping of Na, K-ATPase. A dipole ratchet model based on the electroconformational coupling concept will also be discussed and compared with the ATP-dependent rotation of a rotary motor F₁-ATPase. Since the working principle of this model is simpler than that of F₁-ATPase, it provides an easier way to realize a nanoscale rotary motor than artificially reconstructing a F₁-ATPase.

A phenol biosensor based on the skillful immobilization of tyrosinase on zinc oxide (ZnO) nanorods was proposed. The ZnO nanorods fabricated by a simple vapor-phase transport method possess a high aspect ratio, good electron communication, chemical purity, smooth and positive charged surface and are ready for immobilization of biochemicals with low isoelectric point (IEP). Electrochemical measurement and Scanning Electron Microscopic (SEM) analysis showed that the enzyme of tyrosinase with IEP 4.5 can be adsorbed on the surface of ZnO nanorods and kept its bioactivity of the oxidation of phenol to a large extent. This led us to develop phenol biosensor with good stability and reproducibility. The proposed method creates a new way to develop biosensors using nanostructured materials with high IEP.

We report here the current–voltage (i–V) characteristics of several (n⁺⁺-Si/MNOPE/C₆₀/Pt-tip) or (n⁺⁺-Si/MNOPE/SWCNT/Pt-tip) junctions, where MNOPE = 2'-mononitro-4, 4'-bis(phenylethynyl)-1-phenylenediazonium and SWCNT = single wall carbon nanotube. A layer of C₆₀ or SWCNT-derivatized MNOPE has strong effect on the i–V behavior of the junctions, including rectification, negative differential resistance (NDR) and switching behaviors. The i–V curve of a grafted molecular monolayer (GMM) of MNOPE atop n⁺⁺-Si shows NDR behavior, whereas those of C₆₀- and SWCNT-derivatized GMMs of MNOPE on n⁺⁺-Si show strong rectifying behavior with opposite rectification polarities. With C₆₀, larger currents were found with negative tip bias, while with SWCNT, the forward top bias was positive. Because C₆₀ tends to be a good electron acceptor and SWCNTs tend to be good electron donors, they show different i–V behavior, as observed. Some of the (n⁺⁺-Si/MNOPE/SWCNT/Pt-tip) junctions also show reversible bistable switching behavior.

Single-wall carbon nanotubes (SWNTs) can be well-dispersed in water by wrapping with short segments of natural DNA from salmon sperm. We report here the isolated DNA-wrapped SWNT hybrids. Measurements were carried out using UV-vis-NIR, near-infrared photoluminescence (PL) spectrum and atomic force microscopy (AFM). A possible charge transport between SWNTs and salmon-DNA is discussed in terms of observed spectral shifts in the photoluminescence spectra.

Diffusion in liquid SiO₂ nanoparticle with the diameter of 4 nm has been studied in a spherical model containing 2214 atoms via Molecular Dynamics simulation (MD). Diffusion constant of atomic species has been calculated over temperatures ranged from 2100 K to 7000 K and compared with those observed for the bulk. We found that temperature dependence of diffusion constant of atomic species in nanoparticle shows an Arrhenius law at temperatures above 2100 K and at T > 4200 K, it deviates from an Arrhenius law. However, unlike those observed in the bulk at T > 4200 K, it does not show a power law, D ~ (T - T_c)^γ. Moreover, at relatively low temperatures, diffusion constant in nanoparticle is higher than that in the bulk indicating the surface dynamics effects.