International Journal of Nanoscience

The formation and electrical properties of high surface area NiO/Al₂O₃ nanocomposite materials with composition ranging from 5 to 30% w/w have been studied. The temperature dependence of the DC electrical resistivity was monitored in the temperature range 350–600 K. The results revealed correlation between electrical resistivity and textural properties. The conductivity results were discussed in terms of variable-range-hopping mechanism.

Flash memory structure in which a silicon quantum dot embedded in the gate dielectric region between the channel and the control gate is considered. A self-consistent simulation for such memory devices is performed and aims to understand the relationship between the device structure and the meaningful quantities, as required for an efficient device operation. In this study, both the traditional SiO₂ and HfO₂ high-k dielectrics are being explored, and their results are compared and contrasted. In particular, the superiority of HfO₂ over the SiO₂ is demonstrated through various interlocking investigations on the relationships between the tunneling current, dielectric thickness, barrier height, programming and retention times.

A new method called Step Current Electrodeposition (SCE) is proposed for the nanocrystalline deposition of high uniformity large coating thickness of Ni₈₀Fe₂₀/Cu composite wires. The hysteresis loops of the composite wires, developed by SCE and conventional plating, were measured using an inductance method and a magneto-impedance (MI) experimental setup, and the magnetic properties of the composite wires in terms of the hysteresis loops and the magneto-impedance effect were measured. The results showed that the experimental results obtained, which was in the trend of increasing GMI with increasing coating thickness till an optimum, agree well with the simulated results as found in the literature.¹

The unique and novel physicochemical features of the nanosized magnetic particles, which are attained due to their size and shape morphology, have aggregated an interest in the fields of nanoscience and nanotechnology. In this work, magnetic particles coated with double-layer surfactants were prepared and characterized. The magnetic particles (Fe₃O₄) were synthesized by chemical precipitation of Fe²⁺ and Fe³⁺ salts (1:2 ratio) with ammonium hydroxide (NH₄OH) under inert atmosphere at 80°C followed by resuspension of the nanoparticles in water using thiodiglycolic acid. This procedure produced Fe₃O₄ nanoparticles stabilized against agglomeration. The primary surfactant coated particles were further treated with 4-vinylaniline at 25°C for about thirty minutes. As –SH group in thiodiglycolic acid has greater affinity formagnetic surface, it is easily attached to the iron particles through bonding. Subsequently, the –NH₂ functional group of 4-vinylaniline reacts with the acid group –COOH of the thiodiglycolic acid. The size and the distribution of these magnetic particles, their morphologies and magnetic properties were measured by Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM), respectively. TEM results show the formation of single domain nanoparticles of mean diameter of about 10 nm. The strength of the NH–CO bond was measured by FTIR (Bio-Rad), the vibration observed at a wavelength of 1613–1745 cm^-1. Thermo gravimetric analysis (TGA) reveals the existence of two distinct layers of surfactants on the particle surface. These surface-modified nanomagnetic particles can further be coated with thermo-sensitive polymeric materials which may be used in separation and purification of bio-molecules.

The mechanical properties of nanocrystalline (Nc) Ni (electrodeposited, sintered, rolled) and microcrystalline (Mc) Ni were investigated by nanoindentation technique. Force-displacement curves generated during loading and unloading of the nanoindenter tip (Berkovich diamond tip) were used to determine the hardness and elastic properties of the Nc-nickel. The influence of loading rate on the hardness of electrodeposited Nc-Ni and microcrystalline (Mc) Ni were studied in the present work. The electrodeposited Nc-nickel exhibits higher hardness and elastic modulus when compared to sintered Nc-nickel. The higher modulus of elasticity is observed for the rolled Nc-nickel due to the increased defect density and less porosity in the samples. The higher modulus of elasticity is observed for Mc-nickel when compared to that of Nc-nickel (electrodeposited) with varying load rate. The strain rate sensitivity of Nc-nickel is due to the grain boundary affected zone.

Photoluminescence (PL) measurements performed in a series of InAs self-assembled quantum dot (QD) structures grown by molecular beam epitaxy (MBE) on GaAs (100) substrates using a two-stage "nucleation-augmented" growth method show that an InAs QD "nucleation" layer grown at a fast growth rate, followed by a slowly grown InAs "augmented" layer, dramatically increases the dot density and improves the PL intensity. Besides red-shift in peak wavelength, the PL intensity was found to increase as the growth rate of the InAs augmented layer was reduced. The increased PL intensity was due to a higher dot density arising from the nucleation layer and an improved optical quality caused by the growth interruption in the augmented layer.

Nanocrystalline diamond films were deposited on high speed steel substrates by microwave plasma chemical vapor deposition. The best hardness improvement was about 130% of the substrate hardness, using -150 V substrate bias deposition conditions. Raman peaks of nanocrystalline diamond at 1190 cm^-1 and of graphite nanoclusters at 1522 cm^-1 wereobserved in this sample. Scanning electron microscope images show crystallite grains of different sizes between 25–250 nm.

Current cell tags using dyes lose their luminescence quickly and are not suitable for optical barcoding. Semiconductor quantum dots (QDs), on the other hand, can be engineered to emit different wavelengths, thus permitting tagging of various cells at the same time. Core/shell luminescent quantum dots, cadmium selenide (CdSe) and zinc sulphide (ZnS), were synthesized and incorporated into polystyrene (PS) particles grafted with carboxyl groups using microemulsion polymerization method. Highly luminescent monodispersed PS particles with diameters from 30 nm to 50 nm were chosen for subsequent surface modification. Two series of surface modifications were carried out with PS particles. One was modified with poly(L-Lysine) (PLL), polyethylenimine (PEI), Poly(Ethylene Glycol) (PEG) and folic acid (FA) side chains in sequence through chemical bonding. Another was conjugated with PEG and FA in sequence. The folic acid side chains can enter target cells via folate receptors and assisted in the uptake of the luminescent particles into the cells. This property allows them to be used as fluorescent labels for marking their ingress into cells and also for a cornucopia of biomedical applications.

Nanosized powders used for the preparation of bulk Na_1.5Co₂O₄ and Ag-doped Na_1.5Co₂O₄ nanosized crystalline grains were synthesized by the polymerized complex (PC) method. X-ray diffraction analysis revealed that the nondoped and Ag-doped PC products were composed of Co₃O₄ and Na₂CO₃ phases. After a subsequent calcination at 800°C, the nondoped PC product was converted to powder of single phase γ-Na_xCo₂O₄, whereas the Ag-doped PC products remained as mixed phases of Co₃O₄ and Na₂CO₃ and Ag₂O with a small trace of γ-Na_xCo₂O₄. SEM and TEM investigations showed that all the calcined products were powders of about 200–500 nm particle size.

Vertically oriented multiple-walled carbon nanotubes (MWCNTs) aligned on a silicon substrate were covalently bonded with horseradish peroxidase (HRP) and used as biosensors or electrodes. The modified platform was investigated with Scanning Electron Microscopy (SEM), UV-Vis spectrophotometer and Cyclic Voltammetry (CV). The enzyme catalyzed reaction and the subsequent reduction of the enzymatic products by the platform were carefully investigated. The assay was done by measuring the absorbance of the dye formed from the reaction product of the substrates (phenol) and 4-aminoantipyrine. From the linear response, phenol can be quantitized in the range from 47 ppm to 750 ppm with a detection limit of 19 ppm (based on S/N = 3). The resulting modified aligned MWCNTs still exhibited enzymatic activities after storage of 13 days. The activity of the attached HRP was also demonstrated electrochemically.

Self-assembled InAs elongated nanostructures were fabricated by continuous processing steps, starting from self-assembling of quantum dots, thin capping over the quantum dots to induce an anisotropic strain field, and to anneal the quantum dots in the molecular-beam-epitaxy machine. In-situ RHEED observations at each processing step were studied and confirmed by ex-situ AFM images of the surface morphology. The elongated nanostructures were demonstrated tobe templates for chains of uniform quantum dots.

In this paper, high-surface-area porous carbons with crumpled nanowalls were synthesized by carbonization of sucrose in the presence of zeolite template. The pore structures of the carbon materials were characterized using physical adsorption of nitrogen. Their surface chemistry was analyzed using X-ray photoelectron spectrometer (XPS). The microscopic structure features of the samples were imaged by field-emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM). The nanostructure of synthesized porous carbon with a combination of micro-, meso- and macropores has been obtained.