NERSC Initiative for Scientific Exploration (NISE) 2009 Awards

Theory and Applications of Diamondoid-Nanoparticle Enhanced Organometallic Surfaces

Thomas Devereaux, SLAC National Accelerator Laboratory

Sponsoring NERSC Project: Simulation of Photon Spectroscopies for Correlated Electron Systems (m772), Principal Investigator: Thomas Devereaux, Stanford Linear Accelerator Center

We propose to utilize the massively parallel computing resources at NERSC to assist with the numerical aspects of our currently funded DOE SISGR (Contract: DE-AC02-76SF00515 ) project for theory and applications of diamondoid-nanoparticle enhanced organometallic surfaces.

Diamondoids are nanoscale organic molecules that can be superimposed on the diamond lattice. The smallest diamondoid is adamantane (C10H16, Fig. 1), followed by diamantane (C14H20, Fig. 2), triamantane (C18H24, Fig. 3), tetramantane (C22H28, Fig. 4), and so on. The higher diamondoids such as tetramantane only recently have been isolated from petroleum [1] and have yet to be the subject of systematic theoretical and computational studies. This family of novel carbon nanomaterials is an ideal platform for approaching the DOE grand challenges [2] of energy flow at the nanoscale and synthesis of atomically perfect new forms of matter with applications in solar energy utilizations [3], solid-state lighting [4], and catalysis [5].

Our theoretical and numerical efforts are directed by our close collaboration with ongoing state-of-the-art experiments at Stanford University. Our experimental colleagues utilize a combination of techniques (photoemission, XAFS, and STM) to develop a unique and highly detailed picture of functional diamondoid- and diamondoid-fullerene hybrid-coated metallic surfaces.

We are interested in performing first-principles density functional theory (DFT) based calculations to understand the electronic and vibrational structure of diamondoid-coated metal surfaces and how these properties change, for example, with molecular orientation relative to the surface. In addition to pure diamondoids, we will study hybridizations of diamondoid molecules with fullerene (C60) molecules in contact with metal surfaces. Using DFT calculations we will be able to predict how to utilize hybrids and diamondoid structures as molecular tools for regulating electron flow through surfaces. Furthermore, the functionalization of higher diamondoids and the ability to attach diamondoids to metal surfaces is a newly developed chemical technique [6,7] and has allowed the development of never-before-seen surfaces. In particular, metal surfaces coated with tetramantane-thiol have excellent electron emission properties with potential applications in fields such as electron microscopy and solar power.[8]

Our proposed DFT-calculations are well suited for NERSC because the large size of the higher diamondoids and hybrids, and their proximity to a (two-dimensionally) periodic metallic supercell surface, will require massively parallel computing methods. Our proposed calculations include structural relaxation/optimization of the nuclear coordinates of diamondoid-thiol molecules above metallic surfaces which will predict the arrangement and orientation of the molecules relative to the surface for comparison with recent experiments [9]. Additionally, these calculations will allow us to compute the phonon/vibrational spectrum of the surface which can be measured using tunneling microscopy. Finally, a knowledge of the electronic and vibronic states of these unique surfaces will allow us to study the possibility of using diamondoid-thiol-metallic surfaces as organometallic superconductors [10,11].

[1] J. E Dahl et al. Science, 299, 96 (2003).
[2] Grand Science Challenges Report, "Directing Matter and Energy: Five Challenges for Science and the Imagination", http://www.sc.doe.gov/bes/reports/list.html
[3] DOE Basic Research Needs for Solar Energy Utilization http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf
[4] DOE Basic Research Needs for Solid State Lighting http://www.sc.doe.gov/bes/reports/files/SSL_rpt.pdf
[5] DOE Basic Research Needs: Catalysis for Energy http://www.sc.doe.gov/bes/reports/files/CAT_rpt.pdf
[6] B A. Tkachenko et al., Org. Lett. 8, 1767 (2006).
[7] P. R. Schreiner et al., J. Org. Chem., 71, 6709 (2006).
[8] W. L. Yang et al., Science 316, 1460 (2007).
[9] T. M. Willey et al., J. Am. Chem. Soc., 32, 130 (2008).
[10] W. A. Little, Phys. Rev., 134, A1416 (1964).
[11] Y. Ohta et al., Physica C, 460, 121 (2007).