Robert L. Whetten
Professor of Physics and Chemistry

Ph.D. Cornell University, 1984
Phone: (404)894-6814
Room: 136-Chemistry

Research

Dr. Robert L. Whetten heads the Nanocrystal Research Group.

Research into the properties of nanometer-scale single crystallites has recently matured into a field that is both fundamental and wide-ranging, although a major source of motivation arises from certain natural phenomena and from technological questions concerning ultimate limits on the miniaturization of solid-state device elements. As the smallest recognizable solid-state structures, nanocrystals typically measure from 1 up to 10 nm in diameter, or 3 to 30 lattice planes in each dimension, and are composed of from 102 up to 104 or 105 atomic or compound units. The latter numbers represent the limit of atom-counting (circa one part in 105 is the current world's record), and this laboratory accordingly is centered around specially designed mass spectrometers.

A central area of investigation concerns the equilibrium structures of small crystallites and their thermodynamic stability; the specification of structure encompasses lattice type, crystallite morphology (shape), and the surface structure (including reconstructed or passivated forms). High-resolution microscopy, performed at the best-resolution (atomic plane) limits in the newly established Georgia Tech Center for High-Resolution Electron Microscopy and elsewhere, is an essential resource for this laboratory. Recent experimental findings and theoretical modelling have made clear that high-symmetry, defect-free polyhedral structures can have unusual structural and thermochemical stability, and these have become the focus for intense exploration.

The electronic, optical and magnetic properties of nanocrystals are modified from those of extended solids by the quantum size effects, which arise from the discreteness of the energy level structure and finiteness of the number of electrons or excitations within a band. These are also under investigation in the laboratory by spectroscopic methods, both for isolated particles and for those in arrays of weakly coupled equivalent crystallites. These arrays constitute a novel material form with high potential for unusual and useful properties.

A third area of research is concerned with the elementary steps in the processing of nanometer-scale crystallites. Processing incorporates the sequence: crystallite growth, annealing of defective structures, etching, passivation, and separation of completely passivated crystallites according to size. A major effort of the laboratory over the past decade has been the development of universal instruments for carrying out and measuring these steps. The solid-state systems investigated are chosen largely for their tractability, both experimental and for modelling; these have included ionic solids (such as NaF), binary semiconductors (PbS), noble metals (Au), magnetic metal oxides, and ordered carbon structures.

Theoretical modelling, or simulations, are critical in establishing ideas and models for the structural, processing, and other properties of nanocrystals; supercomputer-based simulations are carried out in association with the Georgia Tech Center for Computational Materials Science.

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Publications

Refereed publications:

1. "Nanocrystal gold molecules," R. L. Whetten, J. T. Khoury, M. M. Alvarez, S. Murthy, I. Vezmar, Z. L. Wang, P. W. Stephens, C. L. Cleveland, W. D. Luedtke, U. Landman, Adv. Mater. 8, 428-433 + issue cover (1996).
2. "Highly oriented molecular Ag nanocrystal arrays," S. A. Harfenist, Z. L. Wang, M. M. Alvarez, I. Vezmar, R. L. Whetten, J. Phys. Chem. 100,13904-10 (1996).
3. "Reversible manipulations of room-temperature mechanical and quantum transport properties in nanowire junctions," U. Landman, W. D. Luedtke, B. E. Salisbury, R. L. Whetten, Phys. Rev. Lett. 77, 1362-5 (1996).
4. "Cluster beams from passivated nanocrystals," I. Vezmar, M. M. Alvarez, J. T. Khoury, B. E. Salisbury, R. L. Whetten, Z. Phys. D40, 147-51 (1997).
5. "Structural evolution of larger gold clusters," C. L. Cleveland, U. Landman, M. N. Shafigullin, P. W. Stephens, R. L. Whetten, Z. Phys. D40, 503-8 (1997).
6. "Critical sizes in the growth of Au clusters," M. M. Alvarez, J. T. Khoury, T. G. Schaaff, M. N. Shafigullin, I. Vezmar, R. L. Whetten, Chem. Phys. Lett. 266, 91-8 (1997).
7. "Optical absorption spectra of nanocrystal gold molecules," M. M. Alvarez, J. T. Khoury, T. G. Schaaff, M. N. Shafigullin, I. Vezmar, R. L. Whetten, J. Phys. Chem. 101, 3706-12 (1997).
8. "Electron dynamics of passivated gold nanocrystals probed by subpicosecond transientabsorption spectroscopy," S. L. Logunov, T. S. Ahmadi, J. T. Khoury, R. L. Whetten, M. A. El-Sayed, J. Phys. Chem. 101, 3713-19 (1997).
9. "Liquid-phase synthesis of thiol-derivatized silver nanocrystals," S. Murthy, T. P. Bigioni, Z. L. Wang, J. T. Khoury, R. L. Whetten, Mater. Lett. 30, 321-5 (1997).
10. "Three-dimensional hexagonal close-packed superlattice of passivated silver nanocrystals," S. A. Harfenist, Z. L. Wang, R. L. Whetten, I. Vezmar, M. M. Alvarez, Adv. Mater. 9, 817-22 (1997).
11. "Thin films of thio-derivatized gold nanocrystals," S. Murthy, Z. L. Wang, R. L. Whetten, Phil. Mag. Lett. 75, 321-7 (1997).
12. "Structural evolution of smaller gold nanocrystals: the truncated-decahedral motif," C. L. Cleveland, U. Landman, T. G. Schaaff, M. N. Shafigullin, P. W. Stephens, R. L. Whetten, Phys. Rev. Lett. 79, 1873-6 (1997).
13. "Isolation of smaller nanocrystal gold molecules: robust quantum effects in optical spectra," T. G. Schaaff, M. N. Shafigullin, J. T. Khoury, I. Vezmar, R. L. Whetten, W. G. Cullen, P. N. First, C. Guti?rrez-Wing, J. Ascensio, M. J. Jose-Yacam?n, J. Phys. Chem. 101(40),7885-91 (1997), and issue cover illustration.
14. "The ensemble coulomb staircase in solution electrochemistry of 28-kDa Au:SR clusters," R. S. Ingram, M. J. Hostetler, R. W. Murray, T. G. Schaaff, J. T. Khoury, R. L. Whetten, T. P. Bigioni, D. K. Guthrie, P. N. First, J. Am. Chem. Soc. 119, 9279-80 (1997).
15. "On-line sampling and intact mass-analysis of nanometer-size aerosols via time-of-flight high-mass spectrometry," M. M. Alvarez, I. Vezmar, R. L. Whetten, J. Aerosol Sci. 29, 115-127 (1998

In edited volumes:

1. "Nanocrystal gold molecules," R. L. Whetten, J. T. Khoury, M. M. Alvarez, S. Murthy, I. Vezmar, Z. L. Wang, C. L. Cleveland, W. D. Luedtke, U. Landman, in Chemical Physics of Fullerenes, 5 & 10 Years Later, ed. W. Andreoni (Kluwer, Dordrecht, 1997) pp. 475-90.
2. "Stability and reversibility of conductance steps in metallic nanowires under ordinary ambience," B. E. Salisbury, R. L. Whetten, in Nanowires, edited by P. A. Serena and N. Garc?a (Kluwer, Dordrecht, 1997) pp. 219-26.

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Group Sites

• Nanostructure Research

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