Nanowires are very tiny structures that can be used for a variety of different applications. They can be used in Photovoltaic devices, Chem-FET device conduction, and Optical properties. This article will cover some of these areas.
Optical properties
Silicon nanowires (SiNWs) are a promising candidate for future nano-photonic and nano-electronic technologies. Their low dielectric constant, high thermal conductivity, and high refractive index make them suitable for use in photovoltaic and thermoelectric applications. In the last two decades, silicon nanowires have found application in photonics and sensorics.
However, despite their potential, there is very little data on their optical properties. Optical microscopy measurements are necessary to explore the scattering and absorption of these materials. Here we investigate the optical properties of SiNWs using near-field optical microscopy. We find that these semiconductor nanowires have a strong resonant field enhancement. Moreover, we found that the PL spectral emission is anisotropic. The PL out-coupled at the wire ends, indicating that waveguided PL emits along the nanowires.
In addition to the wavelength dependent properties of SiNWs, we found that their spectra are strongly dependent on polarization of the incident light. These results suggest that the PL emission is reabsorbed at the tip. Moreover, we also observed that PFO:F8BT nanowires act as nanoscale optical waveguides.
Furthermore, we show that metallic nanoparticles incorporated into the nanowires enhance their optical properties. This is achieved through the formation of in situ nucleation of the nanoparticles in the silicon nanowire. Another interesting strategy for enhancing the properties of semiconductor nanowires is to modify their crystal structure by doping. Interestingly, a change in the doping concentration can significantly alter the crystal structure of InP nanowires grown on (111)B InP by MOVPE.
We investigated the optical properties of InP nanowires by applying an inverse parabolic potential on an infinite cylindrical square well. We show that the inverse parabolic potential leads to a redistribution of the anomalous region of change in the refractive index. It increases the strength of the material and also redshifts the peaks of the absorption coefficient.
Thermal conductivity
Nanowires are an attractive candidate for thermal-electric conversion applications due to their very small thermal conductivity. The results of these experiments demonstrate that the mean free path of phonons in a nanowire is in good agreement with experimental data from nanowires with diameters down to 22 nm.
In addition to phonon-boundary scattering, nanowires have roughness that limits the formation of idealized confined dispersion relations. These properties result in higher electrical resistivity and reduced specific heat. Thus, the effective thermal conductivity of nanowires is dependent on the orientation of the crystal.
The thermal conductivity of nanowires with large roughness is significantly lower than theoretical predictions based on mean-free-paths of phonons. On the other hand, the thermal conductivity of nanowires with relatively low roughness is close to the theoretical prediction. It is not surprising that this trend has been documented in literature.
An integrated method of nanowire preparation and measurement can efficiently control the growth conditions, crystallization process, and size of the nanowire. These methods also provide the opportunity to study the intrinsic properties of the nanowires.
Thermal conductivity measurements were performed on single crystalline Si nanowires. The results show that the thermal conductivity of the smallest nanowire investigated is 56 W/mK. However, it is two orders of magnitude lower than the bulk value. Interestingly, the thermal conductivity of the smallest nanowire decreased with increasing width.
Chem-FET device conduction
Silicon nanowires can be chemically doped to form p-n junctions and FETs. These devices modulate conductance by changing the electrostatic potential between the drain and the source terminals. Several chemistries are used to do so. This article provides an overview of these techniques.
A silicon nanowire can be used as a single-channel biosensor, or a multi-channel multiplex detector. The size of the nanowire makes the device useful for detecting a particular molecule. For example, a single nanowire can be used to detect a hydrogen ion.
One possible route to do this is to immobilize an enzyme on the nanoparticle. Another option is to use liquid metal nanoclusters. Liquid metals can be deposited on the substrate or dissolved in a buffer solution. They can be self-assembled into a thin film.
In contrast to the many methods used to produce a nanowire, catalyst free methods can provide an advantage. This method also minimizes technological steps.
It can be used to make nanowires of various materials. The most effective catalysts are liquid metal nanoclusters. These can be purchased in colloidal form. Dewetting the nanoclusters onto the substrate enables self-assembly.
Nanowires exhibit unique electrical properties due to their size. In particular, a nanowire’s conductivity decreases in stepwise fashion as its diameter decreases. This phenomenon is commonly called the ‘edge effect’. There are two types of edge effects: direct and indirect. In the latter, atoms on the surface of the nanowire aren’t fully bonded.
This can affect the tunneling current and the overall device response. By using a source and drain that are positioned close to each other, the contact can result in a short response time. However, the contact can increase the sensitivity of the device.
Photovoltaic device based on a coaxial nanowire
A coaxial nanowire can be used for a variety of solar energy conversion applications. Its unique three-dimensional morphology provides a unique charge-carrier transfer pathway. These nanoscale elements are promising for powering a range of nanosystems. However, they suffer from upscaling issues. Therefore, development of highly efficient characterization techniques is needed to facilitate the production of high quality p-n junctions.
Solar cell devices based on nanowires are a good way to overcome the low efficiency of conventional photovoltaic devices. Nanowires offer fast charge-transfer routes, mitigating interfacial recombination losses. The key to the efficacy of a photovoltaic cell is the separation of light absorption and charge-carrier transport.
Nanowire solar cells are capable of competing with crystalline silicon solar cells. The use of nanowires in solar cell research has gained widespread interest. They can be processed in a similar manner as thin-film solar cells, allowing them to compete with crystalline silicon solar cells in terms of photovoltaic performance.
A coaxial nanowire-based solar cell can provide an alternative for traditional silicon PV cells, which have an absorption coefficient of only 0.3%. In addition, the nanowires can be made to support a single wire or several nanowires. This allows for a radial p-n junction, which is an approachable method of forming a p-n junction.
The use of coaxial core/shell nanowires is important because of their unique properties. They can support a single nanowire, or they can be used to form a conformal p-n junction.
Studies have focused on optimizing the conversion rate of the solar cell, which enables it to generate more electricity from solar radiation than it absorbs. Photovoltaic cells can be used to convert a range of renewable energy sources, including wind, hydro, and hydrogen.
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