Single-walled carbon nanotube networks for ethanol vapor sensing applications

Networks of pristine high quality single walled carbon nanotubes (SWNTs), the SWNTs after Ar-plasma treatment (from 2 to 12 min) and carbon nanobuds (CNBs) have been tested for ethanol vapor sensing. It was found that the pristine high quality SWNTs do not exhibit any ethanol sensitivity, while the introduction of defects in the tubes results in the appearance of the ethanol sensitivity. The CNB network showed ethanol sensitivity without plasma treatment. Both CNB and low defect (after 3 min treatment) SWNT networks exhibit significant drift in the resistance baseline, while heavily plasma-treated (9 min) SWNTs exhibited high ethanol vapor sensitivity without the baseline change. The mechanisms of the ethanol sensitivity and stability after the plasma irradiation are attributed to the formation of sensitive dangling bonds in the SWNTs and formation of defect channels facilitating access of the ethanol vapor to all parts of the bundled nanotubes.      

Activated carbon–carbon nanotube composite porous film for supercapacitor applications

Activated carbon/carbon nanotube composite electrodes have been assembled and tested in organic electrolyte (NEt₄BF₄ 1.5 M in acetonitrile). The performances of such cells have been compared with pure activated carbon-based electrodes. CNTs content of 15 wt.% seems to be a good compromise between power and energy, with a cell series resistance of 0.6 Ω cm² and an active material capacitance as high as 88 F g⁻¹.     

Hybrid carbon nanotube and dye-doped liquid crystal material for holographic imaging

Without the application of AC or DC electric fields, we recorded permanent holographic images in a hybrid material based on the nematic liquid crystal E7, doped with 0.6% Methyl Red (MR) and 0.002% single-wall carbon nanotubes (CNTs). The images were recorded using a 488-nm laser and reconstructed using 488, 532 and 633-nm probe beams. Multi-order diffraction patterns were observed, during image storage and reconstruction, for thin films having thicknesses of 15 μm. The quality and diffraction efficiency were higher for the hybrid cells than for cells doped only with MR. Average first-order diffraction efficiencies of 7.1 and 3.7% were found for the hybrid and MR-only doped cells, respectively. The primary objective of this study was to utilize the molecular properties of MR and CNTs to produce a hybrid material with improved holographic properties. Dynamics of image formation and a proposed CNT-enhancement mechanism are presented. The holograms are robust and have remained stable for over 2 years.     

Acceptable composition-ratio variations of a mixed crystal for nonlinear laser device applications

A theory is developed to predict some crucial parameters that optimize the performance of mixed nonlinear crystals in nonlinear devices. These include acceptable variations of the composition ratio of the parent crystals and the optimal as well as acceptable interaction lengths for any interaction. The theory is successfully applied to make necessary predictions for the newly developed LiIn(Se(x)S(1-x))2 crystal for second-harmonic and optical parametric generation.     

Lanthanum oxide nanostructured films synthesized using hot dense and extremely non-equilibrium plasma for nanoelectronic device applications

Lanthanum oxide (La₂O₃) nanostructured films are synthesized on a p-type silicon wafer by ablation of La₂O₃ pellet due to interaction with hot dense argon plasmas in a modified dense plasma focus (DPF) device. The nanostructured films are investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) spectra. SEM study shows the formation of nano-films having nano-size structures with the average nanostructures size ~25, ~53, and ~45 nm for one, two, and three DPF shots, respectively. The nanostructures sizes and morphology of nano-films are consistent between the AFM and SEM analyses. XRD spectra confirms nano-sized La₂O₃ with an average grain size ~34, ~51, and ~42 nm for one, two, and three DPF shots, respectively. The electrical properties such as current–voltage and capacitance–voltage (C–V) characteristics of the Al–La₂O₃–Si metal–oxide–semiconductor (MOS) capacitor structure are measured. The current conduction mechanism of the MOS capacitors is also demonstrated. The C–V characteristics are further used to obtain the electrical parameters such as the dielectric constant, oxide thickness, flat-band capacitance, and flat-band voltage of the MOS capacitors. These measurements demonstrate significantly lower leakage currents without any commonly used annealing or doping, thereby revealing a significant improvement of the MOS nanoelectronic device performance due to the incorporation of the DPF-produced La₂O₃ nano-films.     

Growth and characterization of 2-aminopyridinium malonate single crystal for photonic device applications

An organic conjugated chromophore 2-aminopyridinium malonate (2APM) single crystal was synthesized and grown-up by means of slow solvent evaporation method. The unit cell parameters were assessed from single-crystal X-ray diffraction analysis. The various characteristic fundamental vibration frequencies were identified by FTIR spectroscopic studies. Optical parameters like nature of transmittance, lower cut-off wavelength, and band gap (E_g) were found using UV–Vis–NIR spectrum. The mechanical property like microhardness of the 2APM sample was studied using a Vickers microhardness tester. The thermal stability nature of the grown crystal was determined using differential scanning calorimeter examination. The dielectric behavior of the 2APM crystal was studied at various frequencies and temperature. A Z-scan technique was used to investigate the third-order NLO response in 2APM.

     

Modification of nanostructured materials for biomedical applications

Adaptation (or incorporation) of nanostructured materials into biomedical devices and systems has been of great interest in recent years. Through the modification of existing nanostructured materials one can control and tailor the properties of such materials in a predictable manner, and impart them with biological properties and functionalities to better suit their integration with biomedical systems. These modified nanostructured materials can bring new and unique capabilities to a variety of biomedical applications ranging from implant engineering and modulated drug delivery, to clinical biosensors and diagnostics. This review describes recent advances of nanostructured materials for biomedical applications. The methods and technologies used to modify nanostructured materials are summarized briefly, while several current interests in biomedical applications for modified and functionalized nanostructured materials are emphasized.     

Random networks and aligned arrays of single-walled carbon nanotubes for electronic device applications

Singled-walled carbon nanotubes (SWNTs), in the form of ultrathin films of random networks, aligned arrays, or anything in between, provide an unusual type of electronic material that can be integrated into circuits in a conventional, scalable fashion. The electrical, mechanical, and optical properties of such films can, in certain cases, approach the remarkable characteristics of the individual SWNTs, thereby making them attractive for applications in electronics, sensors, and other systems. This review discusses the synthesis and assembly of SWNTs into thin film architectures of various types and provides examples of their use in digital electronic circuits with levels of integration approaching 100 transistors and in analog radio frequency (RF) systems with operating frequencies up to several gigahertz, including transistor radios in which SWNT transistors provide all of the active functionality. The results represent important steps in the development of an SWNT-based electronics technology that could find utility in areas such as flexible electronics, RF analog devices and others that might complement the capabilities of established systems. This article is published with open access at Springerlink.com     

Thermal diffusion in nanostructured porous InP

Nanostructured porous InP samples were prepared by electrochemical anodic dissolution of InP for various current densities and etching periods. The samples were characterized by SEM and photoluminescence (PL) where a blue shift was observed in PL. Thermal properties studied by photoacoustic (PA) spectroscopy revealed one order decrease in thermal conductivity of porous InP compared to the bulk. Further it is shown that the thermal conductivity of porous InP decreases with decrease in size of the particles.     

Photoinduced phenomena in nanostructured porous silicon

In this work we study the evolution of porous silicon photoluminescence under illumination. Samples were obtained by electrochemical etching of crystalline silicon wafers of different types. For the p-type samples the evolution of the spectra is explained in terms of photoinduced oxidation of nanostructures, which in turns leads to a discrete change in the photoluminescence spectra, as we reported in previous works. For the n-type material, a progressive decrease of the luminescence intensity is observed, which is attributed to the photoinduced generation of dangling bond related defect states at the surface layer surrounding the nanostructures. This model explains qualitatively well the kinetics of the evolution of the measured photoluminescence. Preliminary results of electronic paramagnetic resonance spectroscopy agree with this model.     

Processing and characterization of nanostructured Cu-carbon nanotube composites

Carbon nanotube (CNT) reinforced nanostructured Cu matrix composite with a grain size less than 25 nm has been successfully fabricated via a combination of ball milling and high-pressure torsion. CNTs were found to be homogeneously dispersed into the metal matrix, leading to grain refinement with a narrow grain size distribution and significant increase in hardness.     

Electromechanical carbon nanotube switches for high-frequency applications

We describe the fabrication and characterization of a nanoelectromechanical (NEM) switch based on carbon nanotubes. Our NEM structure consists of single-walled nanotubes (SWNTs) suspended over shallow trenches in a SiO(2) layer, with a Nb pull electrode beneath. The nanotube growth is done on-chip using a patterned Fe catalyst and a methane chemical vapor deposition (CVD) process at 850 degrees C. Electrical measurements of these devices show well-defined ON and OFF states as a dc bias up to a few volts is applied between the CNT and the Nb pull electrode. The CNT switches were measured to have speeds that are 3 orders of magnitude higher than MEMS-based electrostatically driven switches, with switching times down to a few nanoseconds, while at the same time requiring pull voltages less than 5 V.     

Biofunctionalization of surfaces of nanostructured porous silicon

For the biomedical applications of porous silicon (PS), biomolecules have to be first immobilized on its surface through functional groups deposited on it. In this work, PS was biofunctionalized through the deposition on its surface of functional groups by thermally activated chemical vapour deposition of 3-aminopropyltriethoxysilane (APTS) used as precursor. The presence of amine radicals was checked by XPS and their functionality was assessed by confocal microscopy. Polyclonal mouse immunoglobulines were used to confirm the immobilization of biomolecules and also in order to check if they keep their native character, once attached to the surface. Finally, the reflectance of PS substrates in the different stages of this development was measured to assess their possible use in biosensing applications.     

Diode properties of nanotube networks

Single-walled carbon nanotubes (SWCNT) were prepared using iron catalysts deposited by indirect evaporation on silicon substrate covered with 500 nm-thick thermal oxide. Diode SWCNT devices have been fabricated using Au and Al, as the asymmetric metal contacts, and a random network of metallic and semiconducting nanotubes as the device channel. No effort was made to align the SWCNTs or to eliminate metallic nanotubes in our devices. Asymmetric voltage-current behavior was seen. Current rectification was observed in the source-drain bias range of − 3 V to + 3 V. Rectification was somewhat surprising since, although metallic tubes are in the minority (∼ 1/3), they could potentially act as shunts and mask the electric properties of the semiconducting majority. No correlation between electrode spacing and current rectification was observed. The lowest leakage current measured was 1% of the maximum current carrying capacity. Maximum forward-biased current capacities range between 8 μA and 841 μA.     

Multi-walled carbon nanotube arrays for gas sensing applications

Vertically aligned multi-walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysis in anodized aluminum oxide (AAO) templates without the use of a catalyst were integrated into a resistive sensor design. Steady state sensitivities as high as 5% and 10% for 100?ppm of NH(3) and NO(2), respectively, at a flow rate of 750?sccm were observed. A thin layer of amorphous carbon (5-50?nm), formed on both sides of the template during xylene pyrolysis, was part of the sensor design. The thickness of the conducting amorphous carbon layers was found to play a crucial role in determining the sensitivity of the resistive sensor. A study was undertaken to elucidate (i) the dependence of sensitivity on the thickness of amorphous carbon layers, (ii) the effect of UV light on gas desorption characteristics and (iii) the dependence of room temperature sensitivity on different NH(3) flow rates. Variations in sensor resistance with exposure to oxidizing and reducing gases are explained on the basis of charge transfer between the analytes and the CNTs which were modeled as p-type semiconductors.     

Linear and nonlinear optical properties of ZnGeP2 crystal for infrared laser device applications: revisited

Measurement of refractive indices in the spectral bands 9-11 microm and 1.32 microm from a cw CO2 laser and a Q-switched Nd:YAG laser, respectively, is reported in a ZnGeP2 crystal. A new set of Sellmeier dispersion relations has been derived from the measured refractive indices data in this crystal. Second-harmonic generation (SHG) of CO2 laser radiation in this crystal is also reported. It is also seen that the previously reported phase-matching data for others experiments in SHG and optical parametric devices is explained satisfactorily with this new set of Sellmeier dispersion relation.     

Durable transparent carbon nanotube films for flexible device components

This paper describes a durable carbon nanotube (CNT) film for flexible devices and its mechanical properties. Films as thin as 10 nm thick have properties approaching those of existing electrodes based on indium tin oxide (ITO) but with significantly improved mechanical properties. In uniaxial tension, strains as high as 25% are required for permanent damage and at lower strains resistance changes are slight and consistent with elastic deformation of the individual CNTs. A simple model confirms that changes in electrical resistance are described by a Poisson's ratio of 0.22. These films are also durable to cyclic loading, and even at peak strains of 10% no significant damage occurs after 250 cycles. The scratch resistance is also high as measured by nanoscratch, and for a 50 μm tip a load of 140 mN is required to cause initial failure. This is more than 5 times higher than is required to cause cracking in ITO. The robustness of the transparent conductive coating leads to significant improvement in device performance. In touch screen devices fabricated using CNT no failure occurs after a million actuations while for devices based on ITO electrodes 400,000 cycles are needed to cause failure.These durable electrodes hold the key to developing robust, large-area, lightweight, optoelectronic devices such as lighting, displays, electronic-paper, and printable solar cells. Such devices could hold the key to producing inexpensive green energy, providing reliable solid-state lighting, and significantly reducing our dependence on paper.     

Carbon nanotube superconducting quantum interference device

A superconducting quantum interference device (SQUID) with single-walled carbon nanotube (CNT) Josephson junctions is presented. Quantum confinement in each junction induces a discrete quantum dot (QD) energy level structure, which can be controlled with two lateral electrostatic gates. In addition, a backgate electrode can vary the transparency of the QD barriers, thus permitting change in the hybridization of the QD states with the superconducting contacts. The gates are also used to directly tune the quantum phase interference of the Cooper pairs circulating in the SQUID ring. Optimal modulation of the switching current with magnetic flux is achieved when both QD junctions are in the 'on' or 'off' state. In particular, the SQUID design establishes that these CNT Josephson junctions can be used as gate-controlled pi-junctions; that is, the sign of the current-phase relation across the CNT junctions can be tuned with a gate voltage. The CNT-SQUIDs are sensitive local magnetometers, which are very promising for the study of magnetization reversal of an individual magnetic particle or molecule placed on one of the two CNT Josephson junctions.     

Semiconducting glass design for device applications

A method is presented by which stable amorphous semiconductors can be chosen for switching device applications. This method is based on the empirical relationship observed between the glass transition temperature, the band gap and the mean coordination number of covalent amorphous semiconductors. In particular, it is shown that tetrahedrally coordinated glasses with band gaps in the range 0.6–1.2 eV are excellent candidates for high reliability materials. One such material, a-CdAs₂, was studied in some detail and was found to be very stable and very easy to fabricate in thin film form. Both negative resistance and threshold switching devices were successfully fabricated with this material, and preliminary results from accelerated life testing are promising.