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43409-G10
Effect of Chemical Functionalization on the Raman and Optical Spectra of Carbon Nanotubes
In the second year of the program, our research has been focused on predicting the structures, vibrational modes, and optical characteristics of covalently functionalized carbon nanotubes and nanocomposite materials. Major research activities during this period included (i) the development of computational infrastructure and software tools for studying the properties of functionalized carbon nanotubes, (ii) a theoretical study of cross-linking and self-assembly of thiolated carbon nanotubes, (iii) a study of covalent sidewall functionalization of defective carbon nanotubes with carboxyl groups, and (iv) an investigation of the electronic and optical properties of metal-nanotube heterostructures.
One of the challenging problems in the design of nanocomposite materials is the creation of a sufficiently strong interface connecting carbon nanotubes to each other and the surrounding polymer network. In a recent study, the formation of covalent links between nanotubes was detected after S-thiolation of acid-treated multi-walled carbon nanotubes with phosphorus pentasulfide. To verify the validity of the proposed reaction scheme, we applied the first-principles electronic structure methods to examine the mechanism of cross-linking between thiolated carbon nanotubes. Our calculations indicated an important role of surface defects when forming chemical bonds that connect thiolated nanotubes to each other. The results of this study were presented at the March 2007 Meeting of the American Physical Society in Denver, Colorado. A paper based on this study was published in the Journal of Applied Physics in July 2007.
The assembly of chemical species on the surface of nanotubes opens the way for the use of nanotubes as building blocks for nanoscale electronic devices and as reinforcing agents in polymer and epoxy composite materials. To study the mechanism of covalent sidewall functionalization of carbon nanotubes, we calculated the bonding energies and dissociation energy barriers for a carboxyl group attached to a single-walled nanotube. The formation of the covalent bond between the carboxyl group and the nanotube surface was investigated in three specific cases: (a) a nanotube sidewall containing no defects, (b) sidewall containing a Stone-Wales defect, and (c) sidewall containing a vacancy. The results of this study will be submitted for publication to the Journal of Physical Chemistry B. These results will also be presented at the Four Corners Section meeting of the American Physical Society in Flagstaff, Arizona in October 2007 and at the March Meeting of the American Physical Society in New Orleans, Louisiana, in March 2008.
Metal-nanotube heterostructures exhibit a variety of unique properties. The interest in these structures has recently been stimulated by their potential application in catalysis, fuel cell technology, and hydrogen storage. However, theoretical modeling of metal-carbon structures presents significant challenges to computational methods employed in computational chemistry. To address these challenges, we conducted a detailed theoretical study of potassium atom adsorption on the surface of graphene and carbon nanotubes. Our study demonstrated an important role of long-range ionic forces in the interaction between potassium and the carbon surface. These findings were presented at the March 2007 Meeting of the American Physical Society in Denver, Colorado. A paper based on the results of this study was submitted for publication to Physical Review B and is currently under editorial review.
Education activities related to the proposed research program included (i) the introduction of a new ABET-accredited Engineering Physics program at New Mexico State University, (ii) the development of ABET-compliant undergraduate courses, course curricula, syllabi, and instructor's notebooks, and (iii) academic advising, training, and support of graduate students.
Over the last year, the PI has made a number of contributions to the development of the Engineering Physics program at NMSU. The program has now been officially accredited by the Accreditation Board for Engineering and Technology (ABET). As a part of the ABET accreditation effort, the PI has developed lesson plans and curricula for two ABET-compliant undergraduate courses: Engineering Physics 461 and 462 ("Intermediate Electricity and Magnetism I and II"). The courses promoted the use of computers in the classroom by offering class projects and homework assignments which required students to utilize simulation tools to solve problems. These projects taught students to work in the environment of common scientific and engineering program packages, such as "Matlab" and "Mathematica".
During the second year of the project, two graduate students were involved in research related to this proposal. The contributions of these students provided a basis for three peer-reviewed scientific publications. Scientific research carried out under this proposal is expected to form the foundation of Ph.D. dissertations for these students.
