Some of the projects that are currently in progress at the Nevada Nanotechnology Center are listed below. Click on the name of a project for a short description.
The objective of this project is to develop a single chip nanostructure based uncooled multi-spectral detector with detection capabilities in the Visible-Infrared spectral ranges. Multispectral detectors with narrow spectral sensitivities in the UV-Visible-Infrared ranges are of strong interest for space based reconnaissance and a broad range of military and civilian applications ranging from treaty monitoring to mapping of chemical spills, waste heat pollution in lakes and rivers, vegetation health, and volcanic activity. Multispectral detectors require spectral sensitivities ranging from blue to long-wave length infrared with the ability to correct for atmospheric effects. For such systems, it is necessary to have detectors with very narrow and contiguous spectral bands. We are currently developing a single low mass/power/cost detection system that can simultaneously measure multiple spectral bands with high selectivity. The nanostructure based detectors are expected to provide the following advantages: improved signal-to-noise ratio , potential temperature operation, significantly reduced dark current, elimination of the need for external gratings or the requirement for angular incidence, tunable peak responsivity and improved redundancy.
The objective of this project is to develop viable fabrication techniques for the implementation of solid matrices of carbon and boron nitride nanomaterials for optimal hydrogen storage for fuel cell applications. Implementation of nanomaterial matrices are being carried out using two different approaches: (i) chemical and electrochemical approach, and (ii) vacuum synthesis approach. While the former is a low cost technique, the latter will provide purer and higher quality samples. In the chemical/electrochemical approach, electrophoretic and electrochemical techniques are being pursued. In the vacuum synthesis approach, the nanoparticle matrices are being fabricated in an integrated manner leading to superior material quality, increased purity and improved nanomaterial structure. At the heart of this approach is the use of a solid state Nanomatrix system which allows the deposition of nanomaterials of dimensions <0.4 nm to ~100s of nm of any metal, semiconductor or insulator with 2% size resolution. The system also consists of a hot filament source as well as a PECVD system for the deposition of high quality carbon nanotubes. The Nanomatrix system allows the fabrication of nanomaterial matrices of high quality with fully controlled structures, including complex layers of metals, nanomaterials, and insulators.
The objective of this project is to develop quantum dot LEDs (QDLED) that will have improved energy conversion efficiency, reduced heat load, increased brightness, smaller dimension and lower cost. Unlike traditional LEDs, where the color of the emitted light is determined by the LED material, the color of QDLED emission is determined by the size of the quantum dot. Thus, multiple color light output can be realized from a single LED by incorporating quantum dots of the same material with different dimensions. Displays based on QDLED will have significantly improved characteristics, including higher resolution (smaller pixel size), higher efficiency, reduced heat load, longer lifetime (higher stability), increased brightness and lower cost. In addition, such displays will have the ability for dual use as a photovoltaic panel with the potential for being self powered. While the basic principle of QDLED has been demonstrated, it is far from a practical viable device. A major drawback in the approaches that have been pursued is the use of colloidal quantum dots synthesized separately and then being incorporated in the LED structure. Such colloidal quantum dots require surface passivation based on organic molecules which make charge injection into the quantum dots very difficult. In addition, such colloidal quantum dots tend to conglomerate at densities required for practical device implementations. In this project, we are developing an all solid-state technology for the fabrication of QDLED in an integrated manner. A major benefit of such an approach is the improved surface properties of the quantum dots that will allow efficient charge injection. In addition, an all solid state technique is more amenable for manufacturing compared to hybrid techniques thus leading to more viable commercialization.
The past decade has seen extensive research on giant magnetoresistance (GMR) devices with the objective to increase magnetic sensitivity thus leading to higher storage capacity. We are currently developing a novel GMR technology based on Nickel antidots of nanoscale dimensions fabricated using electrochemical techniques. A large magnetoresistance is expected in these devices due to large electron current path modulations caused by a small change in magnetic field. A schematic of a typical device is shown in Fig. 1. These devices are expected to lead to a novel, highly sensitive and very economical GMR technology for magnetic sensing applications.
Fig. 1: Typical antidot device structure
The sol-gel process is a simple and cost-effective process, which is based on the phase transformation of a sol (a solution containing particles in suspension) obtained from metallic alkoxides or organometallic precursors. This sol is polymerized at low temperature to form a wet gel, which is then densified through a thermal annealing to give an inorganic product like a glass, polycrystals or a dry gel. The advantages of the sol-gel methods are its versatility and the possibility to obtain high purity materials (shaped as monolithic blocks, powders, thin layers, nanostructured materials etc.), the composition of which is perfectly controlled.
The current activity involves the syntheses of some oxide nano-wires as well as II-VI semiconductor nano-particles and nano-wires/rods via sol-gel route for diverse device applications. The process involves the growth of nano-particles and nano-rods within some polymer and porous matrices. Also the major activities are related to the characterization of these nanostructured films by Photoluminescence, Raman effect etc. for practical applications.
A widely acknowledged goal of nanotechnology is to build intricate, useful nanoscale structures. Complex nano-products require some way to deliver large quantities of information to the nanoscale and proper fabrication process is the most important part to produce complex nanostructures having tailored properties.
In our current research activities, we pay our attention to the fabrication of some Group-IV as well as II-VI semiconductors in nanostructured form. With a nonocluster deposition system, quantum particles having uniform size-distribution (controlled by quadrupole mass filter) are deposited on various substrates. These nanoparticles can also be embedded within or coated with metallic, semiconducting or insulating layers by e-beam evaporation or dc pulsed sputtering techniques, installed in the same nanocluster-deposition system, without breaking the vacuum. Thus multilayer nanoscale structures can be created which have diverse applications in the field of nano-scale detectors, nano-optics, nano-sensors, field-emitters etc.
Characterizations of these nanostructures include FESEM, TEM, XRD, PL, Raman study etc.
Fig. 1: Si Nanoparticle on SiO2 substrate
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