Current Nanoscience - Volume 11, Issue 5, 2015

This review is a summary of applications of photoluminescence and galvanoluminescence techniques used to determine important characteristics of the porous anodic aluminum oxide films. Both photoluminescence and galvanoluminescence of porous anodic oxide films formed on highly reflective aluminum surfaces in either organic or inorganic electrolytes feature clearly pronounced interference maxima that can be used as a tool for determining oxide film thickness and inherent optical parameters. Following this finding, two methods (based on a particular observation angle) for determining such properties are developed and presented. Developed methods can be used for either galvanoluminescence or photoluminescence measurements, however only galvanoluminescence technique can be used to estimate the thickness of porous oxide films on aluminum during the anodization.

Anodizing of aluminum and its alloys is widely investigated and used for corrosion protection, electronic devices, and micro-/nanostructure fabrication. Anodizing of aluminum in acidic solutions causes formation of porous aluminum oxide films, which consists of numerous hexagonal cells perpendicular to the aluminum substrate, and each cell has nanoscale pores at its center. Recently, highly ordered porous aluminum oxide has been widely investigated for various novel nanoapplications. In this review article, we introduce the fundamentals of anodic oxide films including barrier and porous oxides. Then, we summarize the electrolyte species used so far for porous oxide fabrication and describe the self-ordering conditions during anodizing in these electrolyte solutions. Fabrication of highly ordered porous oxides through the vertical section can be achieved by a two-step anodizing and nanoimprint technique. Various nanoapplications based on the ordered porous oxide are also introduced.

In the last decade, the number of possible biological and biomedical applications suggested in the literature for anodic porous alumina has increased significantly. Here we shortly review the existing literature and show the most recent and successful directions taken by research in this area. In particular, the use of anodic porous alumina as a substrate for bioassays or biosensing in living cells, mostly based on surface-enhanced Raman scattering, seems to be promising.

A review of quantitative arrangement analysis methods of nanoporous anodic aluminum oxide has been done. Numerous researches trigger the need of reliable quantitative arrangement analysis of the nanopores. The reviewed methods are based on the quantitative image analysis and include: regularity ratio derived from fast Fourier transform, angle distribution function, pair distribution function, circularity, local order parameter and defect maps. Each of the method brings unique information about the ordering. In this review the fundamentals of all the applied quantitative arrangement analysis methods are discussed. Also applications of the methods in the research are described. The described arrangement analysis methods are complementary to each other.

Anodically synthesized TiO2 nanotube arrays (TNTAs) constitute an exciting ordered large bandgap semiconductor nanoarchitecture for use as scaffolds and active layers for solutionprocessable devices including but not limited to, optoelectronic sensors, photovoltaics, photodetectors, photocatalysts and photoelectrochemical cells. Charge transport, trapping and recombination are key attributes of the material architecture that significantly influence the properties and performance of the resulting optoelectronic devices, thus motivating this review article. Since nanocrystalline mesoporous TiO2 films (np-TiO2) are actively researched for the same applications, in many cases, TNTAs and np-TiO2 are direct competitors and it is therefore meaningful to compare the optoelectronic properties of the two architectures head-to-head. In addition, there exists a whole host of TNTA-specific applications such as bottom-up fabricated photonic crystals, bulk heterojunction organic solar cells and metallodielectric metamaterials that leverage the ordered channel architecture. Recent studies have established the order of magnitude superior recombination lifetimes in sensitized TNTAs as compared to sensitized np-TiO2 as well as the salutary effect of lower structural disorder in TNTAs resulting in trap-free electron diffusion coefficients approaching those of single crystals and two orders of magnitude larger than np-TiO2. Photoconductivity measurements using bandgap illumination in both single nanotubes and nanotube ensembles have resulted in similar values of the mobility-lifetime product (10-5-10-4 cm2V-1), which are four to six orders of magnitude higher than in nanoparticle electrodes. At the same time, TiO2 nanotubes have a larger trap density and a greater average trap-depth than nanoparticulate Ti2 films, pointing to the importance of synthesis modification to improve material quality and post-synthesis techniques for trap passivation.

The application of gold and carbon labels for the detection of antigen molecules using the atomic force microscopy (AFM) method is described in the current study. Direct AFM visualisation made it possible to observe the “antigen–antibody–gold+protein A” and “antigen–antibody– carbon+protein G” complexes. In addition, it was also possible to estimate the morphology and describe the distribution on a surface that used plastic microwell plates as a substrate. The sensitivity of the method for each conjugate was evaluated and compared to an enzyme-linked immunosorbent assay. The results obtained point to a high sensitivity of the approach, especially when using carbon tags. In addition, certain advantages of carbon tags are indicated, when compared with gold tags, because of their simple detection and unambiguous identification on the collected images.

We report the influence of deposition pressure on the morphology and structural properties of the nanocrystalline silicon (nc-Si) particles embedded in amorphous silicon oxide (a-SiOx) using hot wire chemical vapor deposition (HW-CVD). Catalyst material Tantalum (Ta) was employed for the decomposition of source gases in the reaction chamber. X-Ray diffraction (XRD) and Raman spectroscopy techniques were used to understand the thin film phase transition. Different bonds in the films, for example Si-H, were identified using Fourier transform infrared spectroscopy (FTIR) and the role of hydrogen species in inducing crystallization has been discussed. Particular pressure limit has been found to be adequate for the growth of silicon related crystalline particles. The samples deposited at substrate temperature of 200 °C, has shown photoluminescence spectra from blue to red zone, and the parts of the visible spectra has been found to be in correlation with the size of nc-Si and/or defects present in the thin film. This low temperature deposited Si based thin films using HW-CVD could be useful for a visible light emitting device production.

Sn-doped nano-Bi2WO6 photocatalyst has been synthesized by a hydrothermal route at 180 °C for 12 h. The as-prepared samples were characterized in details by SEM, EDS, XRD and UVvis DRS technologies. The photocatalytic activities of obtained products were determined by photodegradation of Rhodamine B (RhB) under simulated solar light. Experimental results indicated that the tin doping evidently improved the photocatalytic activity of Bi2WO6. The possible reasons for higher photocatalytic efficiency of Sn-doped nano-Bi2WO6 than that of pure Bi2WO6 are mainly ascribed to the addition of Sn ions which could suppress recombination between photogenerated electrons and holes.

A novel metal-semiconductor sample of CdS-coated Ag nanowires (NWs) has been synthesized by a simple and convenient hydrothermal method. The thickness of the CdS coating layer can be controlled by changing the concentration of the precursor solution. The as-prepared samples were thoroughly characterized using Scanning electron microscopy (SEM), the High-resolution TEM (HRTEM), X-ray diffraction (XRD) and UV-vis spectrophotometer. The photocatalytic activity of the as-prepared samples was investigated. The result shows that CdS layer has been successfully coated on the Ag NWs surface. It was found that CdS layer increases with increasing molar concentration of Cd2+. The absorption band of CdS-coated Ag NWs is distinctly broadened and red shifted to Ag NWs. It was also observed that the CdS-coated Ag NWs show better photocatalytic activities than the uncoated Ag NWs in the decomposition of an organic dye - Rhodamine B in aqueous solution under light irradiation.

Microbial synthesis of nanoparticles has a potential to develop simple, cost-effective and eco-friendly methods for production of technologically important materials. Silver nanoparticles are playing an important role in biomedical and various applications. In this study, we present a biological method for synthesis of silver nanoparticles (AgNPs) using cell-free supernatant. 40 actinomycete isolates were screened for their ability to synthesize silver nanoparticles. Among them, isolate SSHH-1, was selected and identified as Streptomyces viridodiastaticus SSHH-1 on the basis of morphological, cultural and physiological properties, together with 16S rRNA sequence. Sequencing product was deposited in the GenBank database under accession number KJ676475. Response surface methodology (RSM) was employed for optimization of different nutritional and physical parameters for the production of AgNPs by Streptomyces viridodiastaticus in submerged fermentation. Initial screening of production parameters was performed using a Plackett- Burman design and the variables with statistically significance effects on AgNPs production were identified. Among the 14 variables tested, inoculum age, medium volume, and peptone concentration were identified as the most significant factors for AgNPs production (confidence level above 99%). These variables were selected for further optimization studies using a Box-Behnken design. The statistical optimization by RSM resulted in a 4.43- fold increase in the production of AgNPs by Streptomyces viridodiastaticus. The synthesized AgNPs were characterized using UV-visible spectroscopy (UV-vis), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and Energy Dispersive X-ray (EDX) spectroscopy. TEM study indicated spherical silver nanoparticles in the size range of 15-45 nm. The biosynthesized AgNPs significantly inhibited the growth of Gram -positive (Staphylococcus aureus), Gram -negative bacteria (E. coli) and yeast (Candida albicans).

A novel sorbent, water treatment residual nanopaticles (nWTR), was synthesized using high energy ball milling. The nWTR was characterized by transmission electron microscopy (TEM) and scanning electron microscope (SEM) with energy dispersive X-ray (EDX). Phosphate adsorption data on nWTR were best described by the following isotherm models in the order: Langmuir > Temkin > Kiselev. Phosphate adsorption by nWTR was markedly enhanced as compared to bulk WTR (mWTR) due to the larger surface area of nWTR (129 m2g-1). The calculated maximum adsorption capacity of nWTR (50.0 mgg-1) was 30 times higher than that of mWTR (1.66 mgg-1). The highest adsorption capacity of nWTR was achieved at pH 3 and dramatically decreases with pH increases from 3 to 11. Moreover, arsenates and citrates could strongly inhibit P adsorption onto nWTR samples. The kinetic experiments revealed that approximately 95% of P was removed within 100 min and Elovich model was the most suitable model to describe P chemisorption by nWTR. Fourier transmission infrared (FTIR), SEM–EDX spectra and P fractionation results indicated that the surface hydroxyl groups played a crucial role in phosphate retention onto nWTR. The present study highlights the potential of using nWTR as economic and effective sorbent for phosphate removal from natural water and municipal wastewater.

Nano-antennas fabricated by Carbon nanotube arrays are investigated in this paper. By exposing a nano-antenna to electromagnetic wave, we evaluate the effects of nanotubes displacement, resonant frequency, and induced electrical field on the nano-antenna performance. The effects of the number of array elements, as well as statistical distribution of the elements length are presented. Furthermore, the effect of intertube distance on the induced electrostatic field is simulated. The results of this research can be effectively used in designing and fabricating Carbon nano-antennas for the innovative applications.

Memristor, as the fourth fundamental circuit element, has recently attracted considerable attention due to its widespread applications from programmable logic to neural networks. Today, the most representative memristor consists of a thin film of titanium oxide sandwiched by two electrodes. However, such a memristor gives rise to a relatively low switching speed, discouraging it from receiving more research enthusiasm. To overcome the disadvantages of the already established memristors (e.g. low switching speed and poor endurance) and thus to optimize the memristor performance, we proposed a novel memristor concept using chalcogenide alloy that has been widely used for nonvolatile memory storage. According to the developed electro-thermal model, the designed memristor using chalcogenide alloy clearly shows a variation of resistance along with the history of current as well as a fast switching speed and ultra-low energy consumption.