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Applied Nanoscience (v.2, #1)

Effect of PVD process parameters on the quality and reliability of thin (10–30 nm) Al₂O₃ dielectrics by Shibesh Dutta; Sivaramakrishnan Ramesh; Balakrishnan Shankar; Sundar Gopalan (pp. 1-6).

Over the last decade, dielectric scaling in non-volatile memories (NVM) and CMOS logic applications has reached a point where better innovations will be required to meet the reliability and performance requirements of future products. For both these applications, high k materials are being explored as possible candidates to replace the traditional SiO₂ and oxide/nitride/oxide-based films used today. While there are several attractive candidates to replace these materials, HfO₂ and Al₂O₃ are considered as the most promising ones. Although there has been a lot of work on CVD-based Al₂O₃, there has not been much reported for PVD-based Al₂O₃ for NVM applications, especially in the thickness regime of 10–30 nm. This paper discusses the effects of process parameters such a plasma power and annealing conditions on the quality of Al₂O₃ dielectrics. It was observed that a post deposition anneal in O₂ ambient at 700°C for 15 s is essential to obtain a fully oxidized film with high density. While higher power (1,500 W) results in thicker films with better k values, they also lead to more substrate damage and poorer reliability. Annealing done at temperatures greater than 700°C for 60 s or more results in failure of the film possibly due to diffusion of silicon into Al₂O₃ and its subsequent reaction.

Keywords: High k ; Non-volatile memories; PVD

Fabrication and electrical characterization of highly ordered copper nanowires by Gurmeet Singh Lotey; Sanjeev Kumar; N. K. Verma (pp. 7-13).

The template-assisted electrodeposition technique has been employed to synthesize highly ordered: uniformly dense, well-aligned, parallel and homogeneous copper nanowires. Their morphological studies have been carried out using the scanning electron microscopy and transmission electron microscopy. The X-ray diffraction study exhibits cubic structure of the nanowires and their preferred orientation along the direction [111]. Their elemental composition has been done by energy dispersive X-ray analysis. The photoluminiscence spectra of copper nanowires show two excitation peaks at 209 and 268 nm; both these absorption pathways yield fluorescence at 296 nm. Their UV–Vis absorption spectra have been found to give a prominent peak at 570 nm. The current–voltage characteristics of the nanowires reveal their non-linear behavior. The impedance spectroscopy has also been carried out and it shows an increase in their impedance at higher frequencies.

Keywords: Electrodeposition; Nanowires; Nonlinear behavior; Impedance

Effect of manganese doping on the photoluminescence characteristics of chemically synthesized zinc sulfide nanoparticles by A. K. Kole; P. Kumbhakar (pp. 15-23).

The studies on luminescent II-VI semiconducting nanomaterials have attracted widespread attention recently, due to their potential applications in optoelectronic and biophotonic devices. Amongst other II-VI semiconductor nanoparticles (NPs), Mn²⁺-doped ZnS NPs having large exciton binding energy and wide direct band gap at room temperature have drawn considerable attention for exploring its interesting optical properties. However, in this report, water-soluble Mn²⁺-doped ZnS (ZnS:Mn) NPs with Mn²⁺ concentration varying between 1.5 and 5% (wt%) have been synthesized by chemical co-precipitation method at room temperature. X-ray diffraction (XRD) studies and the analysis of the selected area electron diffraction (SAED) pattern, obtained from transmission electron microscopy (TEM), confirmed the formation of zinc blende structure in all the synthesized samples. The particle sizes of the samples, as obtained from the optical absorption studies, varies between 2.2 and 2.7 nm with the increase of Mn²⁺ concentration between 1.5 and 5%. The room temperature photoluminescence (PL) emission measurements revealed the presence of yellow-orange emission band in all the Mn²⁺-doped samples which is attributed to Mn incorporation in ZnS. The Gaussian fittings of the measured PL spectra of all the samples show the presence of four PL peaks. Amongst the four PL peaks three peaks appeared at 445, 476, and 520 nm in all the samples but the fourth yellow-orange emission peak suffered a red shift from 593 to 600 nm with increasing Mn²⁺ concentration from 1.5 to 5%. In this report no quenching of yellow-orange emission peak is observed up to 5% Mn²⁺ doping concentration in ZnS. The synthesized water-soluble ZnS:Mn NPs can be further functionalized for using them as biolabels.

Keywords: II-VI semiconductor; Nanostructures; Optical properties; Photoluminescence

The photoelectronic behaviors of MoO₃-loaded ZrO₂/carbon cluster nanocomposite materials by H. Matsui; A. Ishiko; S. Karuppuchamy; M. A. Hassan; M. Yoshihara (pp. 25-30).

A novel nano-sized ZrO₂/carbon cluster composite materials (I_c’s) were successfully obtained by the calcination of ZrCl₄/starch complexes I’s under an argon atmosphere. Pt- and/or MoO₃-loaded ZrO₂/carbon clusters composite materials were also prepared by doping Pt and/or MoO₃ particles on the surface of I_c’s. The surface characterization of the composite materials was carried out using transmission electron microscopy (TEM). The TEM observation of the materials showed the presence of particles with the diameters of a few nanometers, possibly Pt particles, and of 50–100 nm, possibly MoO₃ particles, in the matrix. Pt- and/or MoO₃-loaded ZrO₂/carbon cluster composite materials show the efficient photocatalytic activity under visible light irradiation.

Keywords: Composites; Nano materials; Nanostructure; Sensitization

A multiferroic behavior of TbMnO₃ nanorods prepared by microwave-assisted chemical route by S. A. Acharya; S. M. Khule (pp. 31-34).

TbMnO₃ rods-like morphology were prepared by the microwave-assisted chemical route. The samples were synthesized at different microwave heating conditions. We synthesized nanorods of size 100 nm in diameter and length in several micrometers. SEM and TEM confirmed the morphology and size of the samples. Orthorhombic phase was indexed from XRD data. The temperature profile of the magnetization (M) at H = 50 Oe indicates well defined feature around 8 K for almost all samples. Temperature dependence of dielectric constant demonstrates an upward rise in dielectric constant start near 50 K and continues up to 23 K and lowering near 10 K. Magnetization and dielectric constant (ε) was observed to be strongly influenced by microwave power level used for synthesis of the samples.

Keywords: Multiferroic; TbMnO₃ nanorods; Microwave assisted chemical route; Microwave synthesis

Gold on oxide-doped alumina supports as catalysts for CO oxidation by Sónia A. C. Carabineiro; Pedro B. Tavares; José L. Figueiredo (pp. 35-46).

The effect of doping a commercial alumina support with metal oxides of Ce, Co, Cu, Fe, La, Mg, Mn, Ni and Zn was investigated. Doped δ-Al₂O₃ samples were obtained by simple physical mixture (PM) of the alumina with the desired commercial oxide and by traditional impregnation of alumina with precursor salts of the same metals followed by calcination (IC). The metal load (7% wt.) was the same in both cases. Gold (1% wt.) was loaded using a liquid phase reductive deposition method. The obtained materials were characterized by adsorption of N₂ at −196°C, temperature programmed reduction, X-ray diffraction, energy-dispersive X-ray spectrometry and transmission electron microscopy. Both samples prepared by PM and IC showed a mixture of the δ-alumina phase with the respective metal oxide, but the BET surface areas of the IC samples were, in general, higher than those of the PM materials. The particle size of the oxide phases were larger for the PM samples than for the IC materials. Nevertheless, catalytic experiments for CO oxidation showed that PM samples were much more active than IC. That could be explained by the size of gold nanoparticles, well known to be related with catalytic activity, that was lower in samples prepared by PM (7–16 nm) than by IC (11–17 nm). Gold was found to be in the metallic state. The most active samples were aluminas containing Zn and Fe prepared by PM that had the smallest gold nanoparticles sizes (7–13 and 8–12 nm, respectively) and had room temperature activities for CO conversion of 0.62 and 1.34 mol _COh⁻¹g _Au ⁻¹ , respectively, which are larger than those found in the literature for doped γ-alumina samples.

Keywords: Dopped aluminas; Metal oxides; Carbon monoxide; Oxidation; Catalysis; Gold nanoparticles

[O] [H] functionalization on carbon nanotube using (O₂–H₂) gas mixture DC glow discharge by Tamil Many K. Thandavan; Chiow San Wong; Siti Meriam Abdul Gani; Roslan Md Nor (pp. 47-53).

The [O] [H] functionalization of carbon nanotube (CNT) was studied using oxygen–hydrogen (O₂–H₂) gas mixture direct current (DC) glow discharge plasma technique for cathode/CNT-anode separation of 0.10 ± 0.01 cm. O₂ and H₂ were fixed at flowrate of 10.0 ml/min in order to obtain gas mixture ratio of 1:1. During the (O₂–H₂) gas mixture DC glow discharge, current–voltage (I–V) characteristic of gaseous species studied for various settings of gas pressures 1, 2, 3 and 4 mbar. The voltage at gap between cathode/CNT and anode, a breakdown voltage, was identified as “functionalization voltage” (V _func). V _func was noticed responsible for functionalization of functional groups on sidewall of CNT. The V _func were recorded as 796, 707, 594, and 663 V for gas pressures of 1, 2, 3 and 4 mbar, respectively. The co-relation between V _func and gas pressure was identified as linear relationship. But a voltage obtained due to the CNT/Cathode fall shows exponential relationship with the gas pressures. The possibility of [O] [H] functionalization was proved using Fourier transmission infra-red (FTIR) spectroscopy. Hydroxyl (–OH), carboxyl (–COOH), and carbonyl (–C=O) functional groups were identical as identified in the FTIR spectra. The field emission scanning electron microscope images show significant changes in the morphology of CNT which proves that the DC gas discharge plasma is a possible technique for [O] [H] functionalization on the sidewall of CNT.

Keywords: Functionalization; Hydroxyl; Carbon nanotube; DC glow discharge

Wet-electrospun CuNP/carbon nanofibril composites: potential application for micro surface-mounted components by Ashraf A. Ali; Awad Kh. Al-Asmari (pp. 55-61).

Wet electrospinning of polyacrylonitrile (PAN) and dimethylformamide (DMF) with copper nanoparticles (CuNP) at different concentrations from 0.2 to 1 wt% have been studied under certain spinning conditions. A specific coagulating water bath has been used to collect different fibroses and fibril diameters, the effect of spinning height on the produced nanofiber and CuNP/PAN nanofibril composites have been studied from 1 to 7 cm heights. A minimum average diameter of 64 nm has been reported at 7-cm spinning height. Two heat treatment steps have been used to enhance the electrical properties of CuNP/PAN nanofibril composites. SEM has been used to study the morphological characteristics of the electrospun nanofibroses membranes. Preliminary electrical measurements using 4-point probing system showed a noticeable improvement in the electrical conductivity of the produced nanofibril composite membranes. Also, electrical property of a single CuNP/carbon nanofibril composite has been theoretically calculated based on Lichtenecker formula. The produced membranes have been used to build a micro surface-mounted components (MSMC) such as Micro Field Effect Transistor (MFET). A high transconductance has been reported for such a device which will open the door for many promising applications especially in Electronics and Biomedicine .

Keywords: Wet Electrospinning; CuNP; Carbon; Nanofibril composites; Electrical Properties

Synthesis of ZnO submicron spheres by a two-stage solution method by Xinghua Zhan; Fei Chen; Zoran Salcic; Chee Cheong Wong; Wei Gao (pp. 63-70).

This paper presents a two-stage method to synthesize the mono-dispersed ZnO spheres. The size and uniformity of ZnO spheres can be controlled in the sub-micrometer range. This makes the method applicable to the fabrication of photonic crystal structures. The effects of different reaction parameters such as reaction temperatures, reaction times, and water concentrations on the formation of ZnO spheres were investigated. On the basis of the experimental results, we discuss and propose a possible mechanism to elucidate the formation of ZnO submicron spheres. Furthermore, the room temperature photoluminescence (PL) measurements of the products were carried out to investigate their optical properties. The PL results showed that the ZnO submicron spheres exhibited a strong ultraviolet emission and a broadband green emission in the visible region.

Keywords: ZnO spheres; Photonic crystal structure; Reaction parameters; Photoluminescence

Influence of mechanical stress in semiconductor heterostructure on density of p–n-junctions by E. L. Pankratov (pp. 71-89).

It has been recently shown that inhomogeneity of semiconductor heterostructure and optimization of annealing time leads to decrease depth of p–n-junctions and to increased homogeneity of dopant distribution in doped area. It has been also recently shown that mechanical stress in two-layer heterostructure (substrate and epitaxial layer) changes dopant distribution in heterostructure in directions, which are perpendicular to interface between layers of heterostructure, in comparison with unstressed sample. In this paper we consider an alternative approach to increase density of p–n-junctions in the same heterostructure by using overlayer. The overlayer leads to additional mechanical stress. The stress gives us possibility to increase density of p–n-junctions in the heterostructure.

Keywords: Diffusion-junction rectifier; Increasing of density of rectifiers; Mechanical stress

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Applied Nanoscience (v.2, #1)

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Applied Nanoscience (v.2, #1)