Using nanowires for sensing applications is something that is getting more and more popular. This is because of the fact that these materials are quite thin, and have quite a large surface area. This makes them very good for sensing applications because you can put a lot of electronics in a small space.
Carbon nanotubes
Several groups are trying to commercialize highly conducting electrical wires assembled from single carbon nanotubes. But there are many constraints to consider. The electrical conductivity of macroscopic nanotube wires is lowered by impurities. Also, undesired current saturation under voltage is a major challenge.
A possible approach to the problem is to connect two metallic nanotubes, representing a nanoscale heterojunction. This would form part of a nanotube-based electronic circuit. It would also be an effective conductivity enhancer in composite materials.
The electronic properties of nanotube junctions have been studied theoretically and experimentally. It is known that the band gap of a nanotube can vary from zero to two eV. It has also been shown that a non-substituted dopant will donate electrons to the p-electron system of the nanotube. This is different from doping in bulk semiconductors, which results in n-type conduction.
Spectroscopic methods can characterize large amounts of carbon nanotubes. This is useful to identify defects and determine the structural structure of the produced nanotubes. Spectroscopy can also identify the amount of non-tubular carbon content in the nanotubes. Spectroscopy may also be used to characterize the optical properties of the nanotube.
Si and Ge
Several researchers have studied the thermal conductivity of Si and Ge nanowires. The results of their work are important for improving the thermoelectric properties of Si/Ge-based SNWs.
The thermal conductivity of pure Si and Ge nanowires is enhanced by surface scattering. This is due to the phonon-Umklapp scattering phenomenon. The magnitude of this effect is correlated to the width of the “dip” in the thermal conductivity curve. This is a result of the Ge adatoms’ mean diffusion length being a few times longer than the Si adatoms’ mean diffusion length.
Despite their differences, Si and Ge nanowires grow in a similar fashion. Growth is limited by thermodynamic and kinetics constraints. The growth rate of Ge NWs is much higher than that of Si NWs. Moreover, the growth of Ge NWs can be greatly increased by applying biotemplates.
During growth, electrical dopants are usually introduced into Ge nanowires. The process is carried out by CVD precursors. These dopants can be either n-type or p-type. The growth process is usually confined to a narrow fluence range. The incubation fluence for Ge is less than 0.25 x 1018 cm-2.
Silica
Using a variety of approaches, researchers have successfully synthesized novel silica nanostructures. They have been used in many applications such as sensors for bioimaging and redox applications. The structure and properties of these structures have been determined by electron diffraction and energy dispersive x-ray spectroscopy (EDS).
The synthesis of these nanostructures was achieved using a Vapor-Liquid-Solid (VLS) growth process. The process synthesizes nanostructures by combining the self-assembly of droplet confined colloidal self-assembly with a catalytic reaction.
The first successful fabrication of these nanostructures was achieved using graphite paper. They were then grown on Pt coated Si substrates using a dynamic vacuum. This technique was subsequently used to synthesize silica nanowires on photoresist-derived 3D carbon microelectrode arrays during carbonization. The technique also facilitated the integration of these nanostructures into sensing structures. The integrated structures significantly improve electrochemical performance. They have also been used to develop simple nanomanufacturing techniques.
Electronic
During the past decade, intense research on electronic nanowires has been conducted. This is due to their unique morphology and chemical properties. These nanostructures can also be used to develop new classes of electronic chips and fiber optics.
The electronic properties of semiconductors become tunable at the nanoscale. These nanostructures can also exhibit superior chemical properties. Some of these devices include chemical Nano sensors and logic nano-instruments. The electronic properties of these devices can be analyzed and optimized using a semiconductor parameter analyzer. This is done by integrating a theoretical model to predict the effect of size on the band gap and dielectric constant. The electronic properties of the device can be characterized through its resistivity, mobility, and response time.
The electronic properties of these devices can be modified by the application of catalytic metal nanoparticles. These nanoparticles can also improve the selectivity of the nanowires. The electronic properties of the device are also correlated with the density of the nanowires.
Electronic nanowires can be used as energy harvester devices with the right parameters. They can be fabricated using a simple and inexpensive method. These nanowires have also been used in array morphology.
Sensing applications
Various sensing applications have been shown for silicon nanowires. The devices are known to exhibit high thermal to electrical conversion efficiency and good thermoelectric properties. The devices are also tunable through doping level. They can be used in various applications, including gas sensing.
In 2001, the first demonstration of a hydrogen ion concentration sensor was made using a basic p-type Si nanowire device. A positive gate voltage leads to depletion of the carriers while a negative gate voltage accumulates them. The device is also able to detect the concentration of NO2 down to 20 ppb.
The sensitivity of the device is attributed to the presence of a surface receptor group. The receptor groups undergo protonation/deprotonation over different pH ranges, which changes the surface charge of the nanowire. This change is reflected by the back-gate voltage DVbg.
The ability to detect a change in fluorescence intensity is another feature of the SiNW device. This is a feature that is advantageous for the device’s application in the field of biology. This type of detection is important for a number of biological and health related applications, including the discovery of new drugs molecules.
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