Nano

Movement and shape changes are fundamental aspects of all living organisms. This biological motility results from the biological nanomotors, in particular protein nanomotors. Cells contain a variety of protein nanomotors that rotate (e.g., F₀F₁-ATP synthase or bacterial flagellar motors) or move in a linear fashion (e.g., the kinesin, myosin and dynein motors). F₀F₁-ATP synthase is one of the ideal nanomotors or energy providing systems for micro/nanomachines because of its small size, smart and perfect structure, and ultra-high energy transfer efficiency. Therefore, in this paper, we have reviewed the structure, mechanism, and potential applications of the F₀F₁-ATP synthase nanomotor. In all organisms, the F₀F₁-ATP synthase consists of two distinct nanomotors, F₀ and F₁. The F₀ moiety is embedded in the membrane and is a detergent soluble unit while the F₁ moiety protrudes from the membrane and is a water soluble unit. F₀F₁-ATP synthase operates as two stepper motor/generators coupled by a common shaft and an electrochemical-to-mechanical-to-chemical energy transducer with an astounding 360° rotary motion of subunits. F₀F₁-ATP synthase nanomotor may enable the creation of a new class of sensors, mechanical force transducers, actuators, and nanomechanical devices. Thus, the F₀F₁-ATP synthase nanomotor field has expanded into a wide variety of science.

Biopolymers, such as deoxyribonucleic acid-hexadecyltrimethyl ammonium chloride (DNA-CTMA) and bovine serum albumin-polyvinyl alcohol (BSA-PVA), were studied using a novel capacitive test structure. A variety of external electrical stimuli were applied, including a low frequency alternating current signal and a rf/microwave frequency signal combined with a DC bias. The dynamic responses of the DNA-based biopolymer to the external stimuli are presented in this paper. The electrical transport measurements support the space-charge-limited conduction and the low frequency capacitance–voltage (CV) measurements showed large depletion layer capacitance at the Au–biopolymer interface, at 20 Hz, and the capacitance approaching bulk values at 1 MHz. Electric force microscopy (EFM) was utilized for visualization of charge dynamics and to examine the effect of DC bias combined with an AC signal. Ionic charges in the DNA-CTMA system seem to be responsible for the dynamic response to the various external electrical stimuli.

SWCNTs are important materials in manufacturing advanced devices like field effect transistor and field emitters. Fe₂O₃/MgO catalyst was developed to grow SWCNTs and was used in chemical vapor deposition (CVD) of methane. The catalyst was prepared by mixing iron powder (Fe₂O₃) with MgO at the prescribed stoichiometry ratio. The findings show that SWCNTs in bundle form were grown over the catalyst. Most of the observed bundles are broad with each bundle constitutes more than 20 individual SWCNTs. Raman analysis indicates that these nanotubes possessed highly graphitized structure. Comparing with other catalyst preparation methods, this approach creates better efficiency in the synthesis and reproducibility of SWCNTs in the methane CVD.

A simple approach by direct synthesis of few-layer graphene sheets and transferring them onto flexible substrate is demonstrated. The hydrogen effect on the D band intensity of Raman spectra for few-layer graphene sheets synthesized by chemical vapor deposition (CVD) on Ni-evaporated silicon substrate is investigated by optimizing the mixing ratio of C₂H₄/H₂. While the Ni etchant is used to melt away the squeezed Ni layers between graphene sheet and silicon substrate, the graphene sheet is transferred onto polyethylene terephthalate film by a fishing method. It is found that the condition of graphene transfer strongly relies on the cooling rate of the film during CVD synthesis. The sheet resistance of the film decreases as the film thickness increases. A sheet resistance of 233 Ω/sq is obtained at a transmittance of 62%.

The growth mechanism of WS₂ nanotubes in the large-scale fluidized-bed reactor is studied in greater detail. This study and careful parameterization of the conditions within the reactor lead to the synthesis of large amounts (50–100 g/batch) of pure nanotubes, which appear as a fluffy powder, and (400–500 g/batch) of nanotubes/nanoplatelets mixture (50:50), where nanotubes usually coming in bundles. The two products are obtained simultaneously in the same reaction but are collected in different zones of the reactor, in a reproducible fashion. The characterization of the nanotubes, which grow catalyst-free, by a number of analytical techniques is reported. The majority of the nanotubes range from 10 to 50 micron in length and 20–180 nm in diameter. The nanotubes reveal highly crystalline order, suggesting very good mechanical behavior with numerous applications.

A facile method was developed for in situ formation of Co nanoclusters in sol–gel silica thin films spin-coated on Si wafers. The size and density of Co nanoclusters can be controlled by spin-coating speeds, annealing methods, reduction temperatures under H₂, and metal precursor concentrations in tetraethylorthosilicate solutions. The optimized preparation condition, spin-coating speed of 9000 rpm, annealing at 500°C in air followed by reduction at 800°C in H₂, resulted in silica films as thin as 60 nm and Co nanoclusters with a mean diameter of 1.5 nm. Morphological and chemical characteristics of thin films and nanoclusters were studied by atomic force microscopy and X-ray photoelectron spectroscopy, respectively. Subsequently, these Co nanoclusters were successfully used to grow SWCNTs by CO decomposition. Film containing Co monometallic clusters produced SWCNTs of 1.3 nm in diameter, whereas film having Co/Mo bimetallic clusters produced SWCNTs of 0.9 nm. This sol–gel approach allowed not only easy catalyst patterning on a thin film but also a fine-tuning of SWCNT properties, e.g., diameter.

This paper presents a numerical model of silicon nanoparticle formation process during silane (SiH₄) pyrolysis. Aerosol dynamics model, which includes particle growth by surface reaction, coagulation, and transport, was coupled with a chemical kinetics model using CHEMKIN 4.1.1 with particle tracking module (PTM). The general dynamic equation (GDE) was solved by using the method of moment (MOM). The effect of reactor temperature, pressure, total flow rate, and initial silane concentration was successfully investigated under conditions typically used for atmospheric-pressure silane pyrolysis system and we compared the calculated results on particle formation with published experimental data. The simulation results show that particle formation is very sensitive to temperature and initial silane concentration. We observed that numerical simulation results showed a good agreement with experimental data for parameters such as particle concentration, diameter, growth rate, and total volume concentration.