Quasi-one dimensional metal oxide semiconductors: Preparation, characterization and application as chemical sensors

The continuous evolution of nanotechnology in these years led to the production of quasi-one dimensional (Q1D) structures in a variety of morphologies such as nanowires, core-shell nanowires, nanotubes, nanobelts, hierarchical structures, nanorods, nanorings. In particular, metal oxides (MOX) are attracting an increasing interest for both fundamental and applied science. MOX Q1D are crystalline structures with well-defined chemical composition, surface terminations, free from dislocation and other extended defects. In addition, nanowires may exhibit physical properties which are significantly different from their coarse-grained polycrystalline counterpart because of their nanosized dimensions. Surface effects dominate due to the increase of their specific surface, which leads to the enhancement of the surface related properties, such as catalytic activity or surface adsorption: key properties for superior chemical sensors production.High degree of crystallinity and atomic sharp terminations make nanowires very promising for the development of a new generation of gas sensors reducing instabilities, typical in polycrystalline systems, associated with grain coalescence and drift in electrical properties. These sensitive nanocrystals may be used as resistors, and in FET based or optical based gas sensors.This article presents an up-to-date review of Q1D metal oxide materials research for gas sensors application, due to the great research effort in the field it could not cover all the interesting works reported, the ones that, according to the authors, are going to contribute to this field’s further development were selected and described.     

Titanate nanotubes: preparation, characterization, and application in the detection of dopamine

Titanate nanotubes were successfully synthesized via a hydrothermal process with the assistance of surfactant. These nanotubes with average length of several hundred nanometers and diameter of 10 nm were employed to modify glass carbon electrode and measure dopamine via electrochemistry method. The experiments showed ideal reversibility in cyclic voltammetry, which might be due to the decrease of the overvoltage of the electrode and increase of electron transference. The results illustrated the potential application in the detection of dopamine.     

X-Band microwave characterization of carbon-based nanocomposite material,absorption capability comparison and RAS design simulation

This paper presents a microwave characterization of several carbon-based composite materials interesting the future aircraft/aerospace systems. They consist in epoxy resin reinforced with five different carbon species: micro-sized granular graphite, fullerenes, carbon nanofibers, single- and multi-walled carbon nanotubes. Main goal of this work is to show how carbon inclusions size and geometry are able to significantly modify the electromagnetic properties at microwave frequencies. Microwave characterization is performed in terms of microwave permittivity and intrinsic wave impedance evaluation; all the computations are based on microwave scattering parameters measured in the X-band (8.2/12.4 GHz) by waveguide method. A theoretical analysis of the microwave absorbing capability is then performed assuming that a multilayer of nanocomposite material was backed on a conductor plate (such a structure is typically called Radar Absorbing Material). The results obtained for the reflection coefficient indicate that nanoparticles give better absorption properties to the matrix than micro-sized ones: nanocomposite materials could thus be used successfully as microwave absorbers, not only for their absorption performances but also for their light weight.     

Inter-sheet-effect-inspired graphene sensors: design, fabrication and characterization

With their sub-nanometer inter-sheet spacing, few-layer graphenes (FLGs) are alignment-free building blocks for nanosensors based on the inter-sheet effects. In this paper, we have tackled the challenges towards batch fabrication of inter-sheet graphene sensors through controlled layer engineering, edge tailoring and selective electrode fabrication on different atomic layers. An oxygen plasma etching (OPE) technique is developed to remove graphene layer by layer, enabling the batch fabrication of FLGs in a controllable fashion because of the faster speed and readiness of patterning of this process as compared to the conventional mechanical exfoliation. Vapor sensing experiments have shown that 'inter-sheet' sensors possess a higher sensitivity than conventional 'intra-sheet' ones. Vapor sensitivity is improved more than two times in normalized resistance changes by taking the 'inter-sheet' design upon exposure to 0.5% ethanol-nitrogen mixture and 500 Pa water vapor environments, respectively. These remarkable improvements can mainly be attributed to the inter-sheet effects such as electron tunneling, chemical doping, physical insertion and enhanced edge effects. Such effects may result from molecule adsorption/desorption, force/displacement, pressure, surface tension or thermal energy, and can potentially remarkably enrich the applicable transduction mechanisms.     

Gold/silicon nanocomposites: synthesis,characterization, and application in detection of dopamine

Silicon nanowires (SiNWs) with the length of several hundreds of micrometers and an average diameter of 15 nm were successfully synthesized via a thermal-evaporation oxide-assisted process. Then, a convenient method was applied to metallize the SiNWs just by dipping them into an aqueous deposition solution. During the metallization process, which is a redox reaction, gold nanoparticles (NPs) were prepared on SiNWs surface to confine the particle size and prevent agglomeration during the preparation and utilization of gold NPs. The synthesized SiNWs decorated with gold NPs were utilized to modify the glassy carbon electrode. Electrochemical measurements displayed that the modified electrode showed high sensitivity for dopamine (DA) detection.     

Rod-shaped polyaniline-barium ferrite nanocomposite: preparation, characterization and properties

Rod-shaped polyaniline (PANI)-barium ferrite nanocomposite was synthesized by in situ polymerization of aniline in the presence of BaFe(12)O(19) nanoparticles with diameters of 60-80?nm. The structure, morphology and properties of the nanocomposite were measured using powder x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry. Different ferrite/PANI ratios were selected in order to study magnetic and conductive properties. The results indicated that there were some interactions between PANI chains and ferrite particles. The saturation magnetization and the coercivity varied with the ferrite content. The conductivity at room temperature decreased from 43.35 to 6.9 × 10(-2)?S?cm(-1) when the ferrite content changed from 0 to 50?wt%. The composite has excellent electromagnetic parameters which indicates potential application in high performance adsorbing materials in broadband and high frequency ranges. The polymerization mechanism and interactions in the nanocomposites were also studied.     

Potential of interferometric cantilever detection and its application for SFM/AFM in liquids

We have developed an optical cantilever deflection detector with a spot size <3?μm and fm?Hz(-1/2) sensitivity over a>10?MHz bandwidth. In this work, we demonstrate its potential for detecting small-amplitude oscillations of various flexural and torsional oscillation modes of cantilevers. The high deflection sensitivity of the interferometer is particularly useful for detecting cantilever oscillations in aqueous solutions, enabling us to reach the thermal noise limit in scanning or atomic force microscopy experiments with stiff cantilevers. This has resulted in atomic-resolution images of solid-liquid interfaces and submolecular-resolution images of native membranes.     

Biopolymer-based trimetallic nanocomposite synthesis,characterization and its application in the catalytic degradation of 4-nitrophenol

Journal of Materials Science: Materials in Electronics - Gum kondagogu (GK), a natural biopolymer was successfully employed in the synthesis of trimetallic (AgAuPd) nanocomposites and characterized...     

Influence of aging temperature,time, and environment on thermo-oxidative behavior of PMR-15: nanomechanical characterization

A series of PMR-15 resin specimens were isothermally aged at 288, 316, and 343 °C over a range of time. For PMR-15 aged at 288 °C, the samples were also subjected to different aging environments including: ambient air, dry air, inert (argon), and pressurized air (0.414 MPa). Nanoindentation was performed to characterize localized mechanical properties as well as the development and growth of the oxidative layer. The measured increase in stiffness in the specimen surface oxidation layer is a manifestation of the chemical changes in the polymer occurring during oxidation. The average elastic modulus in the oxidized region is relatively insensitive to variations in aging temperature, time, and the environments. The thickness of the oxidative layer is observed to increase in the early stages of oxidation and the oxidation process eventually approaches an auto-retardation state. Aging under elevated pressure increases the thickness growth rate of the oxidation layer, while there is no significant difference in growth rate for specimens aged in dry air versus those aged in ambient air. It is shown that the measured average thickness of the oxidation layer and the transition region determined by the nanoindenter is in good agreement with optical microscopy measurements for all conditions considered.     

Silver/Polyethylene oxide nanocomposite: UV-fabrication, characterization, and antibacterial activity

In this article, silver-polyethylene oxide (Ag/PEO) biocompatible nanocomposite (BCNC) were successfully green synthesized by mixture containing low MW PEO, silver nitrate and by UV-irradiation at room temperature. The initially broad and asymmetric surface plasmon resonance (SPR) band was narrowed and blue-shifted as the exposure time to UV light was increased. Samples illuminated up to 3 h have an average particle size near 12.0 nm; a decrease to 10.0 nm was observed for longer exposure times up to 24 h. The asymmetric SPR band was due to particle aggregation; higher irradiation times led to a uniform particle distribution within the polymer matrix. The synthesized colloids and thin films have potent antibacterial activity toward gram-negative bacterium Escherichia coil (E. coli), and this activity is completely strong. The concentration of silver leading to a complete inhibition of bacteria growth was revealed as low as at 0.50 microg x ml(-1) and found much lower compared to other reports. Thus Ag/PEO BCNC could be suitable to antimicrobial applications and medical devices.     

Synthesis, characterization and application of an inorgano organic material:p-chlorophenol anchored onto zirconium tungstate

Tetravalent metal acid (TMA) salt zirconium tungstate (ZW) has been synthesized, followed by its derivatization usingpara-chlorophenol (pCP). The resulting compound is abbreviated as ZWpCP. ZWpCP has been characterized for elemental analysis, spectral analysis (FTIR), X-ray analysis and thermal analysis (TGA). Its chemical stability has been assessed in various mineral acids, bases and organic solvents. Ion exchange capacity (IEC) has been determined and distribution behaviour towards several metal ions in different electrolyte solutions with varying concentrations has been studied and a few binary separations achieved.     

Fabrication, characterization, and application of boron-doped diamond microelectrodes for in vivo dopamine detection

Highly boron-doped diamond (BDD) was deposited on chemically etched micrometer-sized tungsten wires using microwave plasma assisted chemical vapor deposition (MPCVD), and these were used to fabricate BDD microelectrodes. BDD microelectrodes with very small diameter (about 5 microm) and 250 microm in length could be made successfully. In addition to the unique properties of BDD electrodes, such as a very low background current, high stability, and selective oxidation of dopamine (DA) in the presence of ascorbic acid (AA), other superior properties of the microelectrodes, including a constant current response, an increase in the mass transport, and the ability for use in high resistance media were also shown. An application study was conducted for in vivo detection of DA in mouse brain, where the BDD microelectrode was inserted into the corpus striatum of the mouse brain. A clear signal current response following medial forebrain bundle (MFB) stimulation could be obtained with high sensitivity. Excellent stability was achieved, indicating that the BDD microelectrodes are very promising for future in vivo electroanalysis.     

Scalable vertical diaphragm pressure sensors: device and process Design, Design for packaging

We present a design, process How, and packaging scheme for a novel three-dimensional capacitive microelectromechanical systems pressure sensor [1], [10]. These sensors present a paradigm shift in pressure sensor technology. They contain an array of vertical diaphragms perpendicular to the wafer plane where each pair of diaphragms requires orders of magnitude lower footprint than traditional in-plane sensors. The sensor can be arrayed or scaled up for increased sensitivity and can be absolute, gauge or differential. Fabrication requires 2-4 masks, depending on process How and has been greatly simplified, without reduction in performance, for high yield and low cost. Multiple geometries have been modeled with sensitivities reaching several fF/kPa and temperature coefficient of sensitivity better than conventional devices. Pressure and electrical ports are individually interchangeable between front and back sides. This allows for a simple design that has only Si facing the sensing environment and the electrical connections on the backside, thus enabling simple packaging for both pressure and electrical ports.     

Bi-functional NiO-ZnO nanocomposite: Synthesis,characterization, antibacterial and photo assisted degradation study

NiO–ZnO mixed metal oxide nanocomposite was synthesized via chemical homogeneous precipitation method. The synthesized nanocomposite was also characterized by XRD, FESEM with EDS, FTIR, and UV. XRD exhibit an average crystallite size of 29 nm. The elemental composition obtained from EDS shows a nearly equal concentration of Ni and Zn with an atomic ratio of Ni/Zn = 0.96. The particles of nanocomposite are highly stable throughout a wide range of pH. The DLS exhibit an average hydrodynamic particle size ~49 nm. The high pore diameter and pore volume of nanocomposite obtained from BET exhibited a high photocatalytic activity for the removal of methylene blue (MB) dye under UV light irradiation. The kinetics of photocatalytic reduction of MB followed the Langmuir isotherm model, suggesting homogeneous surface adsorption of MB on the surface of the nanocomposite. NiO-ZnO nanocomposite was also found to be an effective antibacterial agent against Gram positive bacteria (Staphylococcus aureus) and Gram negative bacteria (Escherichia coli). Colony forming unit plate counting method showed that 95% and 85% of S. aureus and E. coli respectively were killed by the nanocomposite. Also, this suggested that nanocomposite was more effective towards S. aureus than E. coli. Release of intracellular components was evident from FESEM image of nanocomposite-bacteria cell, cell integrity study, and cell permeability study. This included the release of electrolytes, nucleic acid, and proteins, ultimately leading to cell lysis.     

"超材料(metamaterials)":设计思想、材料体系与应用

"超材料(metamaterial)"指的是一些具有天然材料所不具备的超常物理性质的人工复合结构或复合材料.从本质上讲,metamaterial更是一种新颖的材料设计思想,这一思想是通过在材料的关键物理尺度上的结构有序设计来突破某些表观自然规律的限制.从而获得超常的材料功能.迄今发展出的"超材料"包括"左手材料"、光子晶体、"超磁性材料"等.本文就这一领域近年来的发展动向及其在信息技术上的潜在应用做简单的介绍.     

AlGaN/GaN HEMTS: material, processing, and characterization

The growth of AlGaN/GaN high electron mobility transistor (HEMT) structures on sapphire by metal organic vapor phase epitaxy (MOVPE) is described, with special emphasis on procedures to reduce dislocation density. All the processing steps involved in the fabrication of nitride-based HEMTs have been optimized, including dry etching by ion beam milling, evaporation of Pt/Ti/Au gate contacts, and SiN _x surface passivation. Devices with several gate lengths and different geometries have been fabricated by standard photo- and e-beam lithography. d.c. drain current and transconductance increase when gate length is reduced, up to 950 mA mm^–1 and 230 mS mm^–1, respectively, at V _GS=0 V, in HEMTs with a gate length L _G=0.2 m. A maximum output power higher than 5 W mm^–1 is estimated. Finally, small-signal measurements yield f _T=12 GHz and f _max=25 GHz for HEMTs with L _G=0.5 m, which increase up to 20 and 35 GHz for L _G=0.2 m, respectively. Limitation of high-frequency performance by parasitics is discussed.     

Monodisperse hematite porous nanospheres: synthesis, characterization, and applications for gas sensors

Monodisperse α-Fe(2)O(3) porous nanospheres with uniform shape and size have been synthesized via a facile template-free route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Raman spectroscopy were employed to characterize the product, showing the high quality of the as-prepared α-Fe(2)O(3) porous nanospheres. Furthermore, the α-Fe(2)O(3) porous nanospheres can selectively detect ethanol, formaldehyde and acetic acid, with a rapid response and high sensitivity, from a series of flammable and toxic/corrosive gases, indicating their potential applications for high sensitivity gas sensors.     

Fabrication and characterization of functionally graded vermiculite nanocomposite material: the role of curing on glass transition and thermal stability

Journal of Materials Science: Materials in Electronics - Herein, vermiculite clay is used as a reinforcement for epoxy resin, which is pretreated with HCl and functionalized with an organosilane....     

Fiber-based multispeckle detection for time-resolved diffusing-wave spectroscopy: characterization and application to blood flow detection in deep tissue

We present a technique for the measurement of temporal field autocorrelation functions of multiply scattered light with subsecond acquisition time. The setup is based on the parallel detection and autocorrelation of intensity fluctuations from statistically equivalent but independent speckles using a fiber bundle, an array of avalanche photodiodes, and a multichannel autocorrelator with variable integration times between 6.5 and 104 ms. Averaging the autocorrelation functions from the different speckles reduces the integration time in diffusing-wave spectroscopy experiments drastically, thus allowing us to resolve nonstationary scatterer dynamics with single-trial measurements. We present applications of the technique to the measurement of arterial and venous blood flow in deep tissue. We find strong deviations both of the shape and characteristic decay time of autocorrelation functions recorded at different phases of the pulsation cycle from time-averaged autocorrelation functions.