Nanophysics - University of Houston
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Since the discovery of conducting polymers by Heeger et al, intensive research has been carried out over the last 25 years in order to find organic based molecular systems which would be suitable for electronic, photonic and all optical applications. Organic molecules possess desirable optical properties, while their responsiveness is such that the absorption and emission of such molecules can be tailored to specific needs. Fullerenes (C60) were discovered in 1985 by Curl, Kroto, and Smalley, while the discovery of carbon nanotubes (the next stage in Fullerene science) waited for the work of Sumio lijima (NEC, Japan) in 1991 and subsequent work of Ajayan (RPI, USA).

Since their discovery, much research has been devoted to learning more about the physical and chemical properties of carbon nanotube materials, as well as potential applications for these materials. In particular, since the initial discovery of multi-walled nanotubes (MWNTs) and revelation of helicity in single-walled nanotubes (SWNTs), we have been amazed that such a seemingly simple construction should have so many varied properties. Carbon nanotubes in particular possess unblemished conjugation with semiconducting or metallic properties, are stable in air, and do not require chemical doping to retain high conductivities which minimizes the degradation effects that can occur due to chemical treatment. These molecules have also been the subject of thousands of scientific review and publications, but their insolubility has in the past proven problematic. However, as with the field of superconductivity a number of years ago, nanotubes are at a threshold of being either very interesting but exotic materials or an actual material technology that is disruptive in nature beyond the scientific interest. Currently, nanotubes on their own have fallen short of the promise they clearly possess. However, since Curran et al first developed the polymer-nanotube composite, these nanomaterials have been extensively blended with a wide variety of polymers to produce nanocomposites with phenomenal mechanical, thermal, and electrical properties.

The current power conversion efficiencies for the blended nanocomposites (5.4%), while significantly higher than devices produced a decade ago (<1%), they are still far away from being economically practicable. In order to develop much higher power conversion efficiency certain facets of the nanomaterial composition has to be taken account of. Current blended materials only use a small component of the suns emission spectrum (mainly the visible), which means that substantial losses are already present within the device before any cell fabrication is carried out. Organic materials, while possessing certain semiconductor properties, also suffer from low charge carrier mobility. Consequently, when the exciton is generated (the electron-hole pair), the extent by which that exciton can travel has been calculate to be between 10 nm to 50 nm. In order to minimize the number of charge carriers lost to recombination, the organic semiconductor must remain relatively thin. The center will address the crucial problems of morphological control, spectral matching and consequently efficiency in thin film organic based photovoltaics. These devices will be formed from a number of nanocomposite components fabricated between n-type nanostructures (including quantum dots, quantum wells, organic dyes, up-converters and Fullerenes) and organic conjugated p-type polymers. While as a material type polymer based solar cells continue to show great promise, their development in terms of practical applications are hampered by certain characteristics specific for carbon based electronics. The breakdown of the program will focus on these major limiting factors by developing morphological control at the interface between the blended nanomaterials, understanding the role of percolation when combining distinctly different nanomaterial types, managing the spectral response for eventual linear tandem cell arrangements and new PV architectures for light and exciton management.

It is now widely accepted that electronic charge transport and thermal management in nanoscale electronics has become increasingly important as the size of transistors and telecom interconnects has been miniaturized. The reduction in transistor size with consequential miniaturization in semiconductor chips, whether for use in computers or telecom, increases processing speed and power generated but decreases the heat transfer surface area. This leads to very high heat fluxes localized to a small area which in turn increases the potential of thermal damage. In order to maintain transistors within their optimum operating conditions greater heat transfer is necessary. Heat fluxes of 50–100 W cm-2 will not be uncommon in the future, while pulsed transient heat loads can be expected to be generated up to 400 W cm-2. Significantly, current heat transfer methods are reaching their thermal limit and more sophisticated thermal management devices are a need that can be met by the development of nanoscale piezoelectric and pyroelectric coatings. The focus of this component of the Centers program is to deliver nanocomposites for Thermal, electronic, Piezo and Pyroelectric NEMS transducers and non-linear optical responsive nanocomposites. Plastics such as the conjugated polymer polyacetylene polypyrrole and polyaniline and non-conjugated polymers such as composites formed from non conjugated polymers and carbon black have been used in recent years in the electronics industry for either through hole bore plating or as antistatic coatings. Rather than trying to replace well known and well used inorganic electronics, organic materials are now studied for their additive properties within the telecom and electronic industries. The success of the program will be based on delivering stable and sustainable nanomaterials formed from nanotubes and polymers which can be seamlessly incorporated with current production methods and devices in the electronics, telecom and aerospace industries. To this end, it is crucial to develop nanocomposites through controlled fabrication in terms of self-assembly. The self-assembly process can be controlled by using Spectroscopic, microscopic and Proximal Probe analysis of the material fabrication process. The use of resonance Raman spectroscopy as well as Near Field Optical Microscopy and Spectroscopy will ensure tight morphological control and a deeper understanding of the self-assembly methods.