This award supports research and education in theoretical physics in an area related to nucleation and growth of single-walled carbon nanotubes (SWCNT) catalyzed by transition metal particles. The study is motivated by the unusual materials properties of these systems, particularly their remarkable electrical, mechanical, thermal and optical properties. SWCNTs are the best conductors of electricity and heat and have exceptional photophysical and chemical properties. The research intends to provide some of the essential understanding of the processes that occur in creating these materials so that the potential applications of SWCNTs may be realized. The area of particular emphasis includes the nucleation and growth of these materials but in the process researcher will identify processing avenues that make it possible to control the chirality and diameter of a SWCNT, two important parameters that determine whether a SWCNT is semiconducting or metallic.
Researchers will use theoretical and computer simulation techniques to better understand the growth process of SWCNT and how to achieve the desired uniformities of coherent and defect-free SWCNTs with controlled diameter, chirality, length and wall structure. This research will focus mainly on analyzing and describing catalyzed CVD technique, which is the most promising of the three major techniques for mass production of SWCNTs. Computer simulations will provide insight into the growth processes which are difficult to monitor experimentally because they occur at temperatures much higher than room temperature, in the range of approximately 400 ? 1000 Kn where the high temperature results in a high pressure, adding to the difficulty of monitoring the atomic level dynamics involved during the experiment despite advanced nanoscale measuring techniques. Computational studies are therefore necessary in order to examine the stages of the growth and pave the way for a more controlled growth of SWCNTs
In order to understand the factors and parameters determining the chirality and diameter of the SWCNTs, rigorous quantum mechanical simulations must be done. We intend to perform all?electron density functional theory (DFT) simulations at the generalized gradient approximation level (GGA). These calculations will serve as benchmarks for ab initio molecular dynamics (MD) calculations which can handle larger systems than the all electron DFT simulations as well as finite temperature calculations. In the final stage of these simulations tight binding molecular dynamics calculations will be performed for larger systems and larger time scales than ab initio MD.
The proposed work has both educational and applied impact beyond the basic research. Scientifically, this award will impact related research and applied work to develop carbon based technology at Florida A & M University (FAMU). The computational work will complement the experimental work in the growth of SWCNTS at FAMU Center for Nanoscience and Nanotechnology. The proposed work also will complement the development of the FAMU High Performance Computing Center where a computer cluster is being acquired for high performance computing and the simulations. The educational consequence of this includes the development of computational nanoscience coursework. Participation of minorities in science is supported through this effort. FAMU, one of the leading HBCUs, has one of the four Ph. Ds in physics and this grant will support the training of minority students. The research that has a strong education component involving the training of graduate students and a continuation of the PI's long history of recruiting undergraduates in cutting edge research projects with publishable outcomes.
NON-TECHNICAL SUMMARY: This award supports research and education in theoretical physics in an area related to nucleation and growth of single-walled carbon nanotubes (SWCNT). These ultra small tubes are seen as one of the key elements of future nanodevices. The study is motivated by the unusual materials properties of these systems, particularly their remarkable electrical, mechanical, thermal and optical properties. SWCNTs are the best conductors of electricity and heat and have exceptional optical and chemical properties. The research intends to provide some of the essential understanding of the processes that occur in creating these materials so that the potential applications of SWCNTs may be realized. The area of particular emphasis includes the nucleation and growth of these materials but in the process researchers will identify processing avenues that make it possible to control the structure of a SWCNT and the parameters that determine how a SWCNT is conducts electric current.
Researchers will use theoretical and computer simulation techniques to better understand the growth process of SWCNT and how to achieve the desired uniformities and defect-free SWCNTs with controlled diameter, length and wall structure. This research will focus mainly on analyzing and describing the most promising techniques for mass production of SWCNTs. Computer simulations will provide insight into the growth processes which are difficult to monitor experimentally because they occur at temperatures much higher than room temperature, and at high pressure, adding to the difficulty of monitoring the experiments despite advanced nanoscale measuring techniques. Computational studies are therefore necessary in order to examine the stages of the growth and pave the way for a more controlled growth of SWCNTs.
The proposed work has both educational and applied impact beyond the basic research. Scientifically, this award will impact related research and applied work to develop carbon based technology at Florida A & M University (FAMU). The computational work will complement the experimental work in the growth of SWCNTS at FAMU Center for Nanoscience and Nanotechnology. The proposed work also will complement the development of the FAMU High Performance Computing Center where a computer cluster is being acquired for high performance computing and the simulations. The educational consequence of this includes the development of computational nanoscience coursework. Participation of minorities in science is supported through this effort. FAMU, one of the leading HBCUs, has one of the four Ph. Ds in physics and this grant will support the training of minority students. The research that has a strong education component involving the training of graduate students and a continuation of the PI's long history of recruiting undergraduates in cutting edge research projects with publishable outcomes.
Chirality of single-walled carbon nanotubes (SWCNTs) determines whether they are metallic or semiconductors. Despite substantial progress in the synthesis of SWCNTs over nearly two decades, controlled growth of SWCNTs with specific chirality as desired has not been realized to date. The synthesis yields a mixture of chitalities, with semiconducting and metallic SWCNTs bundled together. Postmortem separation techniques are used to separate the metallic SWNTs from semiconducting ones, which could degrade the quality of the SWCNTs. Therefore, controlling the growth from the outset would be preferred instead of resorting to postmortem techniques. The nucleation and growth is a complex process involving a number of parameters. Experimentally it is not possible to diagnose the atomistic processes involved in a controlled way. Computer experiments come in handy in this regard. Thus quite a number of computational studies have been performed to shed light into the atomistic dynamics and compliment the experiments. The control of chirality, however, has been rarely addressed. The major goal of the project is to find a way in which chirally controlled growth of single walled carbon nanotubes (SWCNT) can be achieved. This problem is the holy grail of the SWCNT research in general. We proposed that one possible mechanism towards this goal is to grow SWCNTs on symmetric nanocatalysts at low temperatures, i.e. the nanocatalyst is a solid. We conjectured that the chirality is set during nucleation early in the growth process and is controlled by the symmetry of the surface of the nanocatalyst, in contrast to the hypothesis that the chirality is set at the end or towards the end of the growth process after undergoing a series of transformations during the course of growth. In our model the nancatalysts are very small, less than one nanometer in diameter, and that the adsorptions of the carbon species take place on multiple symmetric sites at the same time in contrast to single site adsorption used commonly in simulations. We have shown the realization of these ideas using the icosahedral symmetry of the small nanocatalyst to grow a chirally specific SWCNT. Our model is very distinct from existing ones. Subnanometer SWCNTs have been experimentally realized. These experiments, however, must be performed on symmetric nanocatalysts according to our model insteadof just any nanocatalyst. Chirally cintrolled growth of SWCNTs will have a huge impact on the electronics industry, therefore, on society at large.
