Professor of Physics,
Senior Research Investigator, MURR
UMC
| Office: | 312 Physics Building |
| Phone: | 573-882-7345 |
| E-mail: | taubh@missouri.edu |
| Webpage: | http://web.missouri.edu/TaubLab/ |
| Biographical Information: | Ph.D., Cornell University, 1971 |
Research Interests
Structure, Phase Transitions, and Dynamics of Adsorbed Films
Several different scattering techniques (elastic and inelastic neutron scattering, x-ray diffraction, and low-energy electron diffraction) are being employed to study the physical properties of films as thin as a single molecular layer. Interest in these quasi two-dimensional (2D) films is based on the premise that phenomena such as crystal growth, structural phase transitions, and changes of state (e.g., melting) will be easier to understand in lower dimensional systems. In some cases, a theory may be easier to formulate conceptually in 2D as in elucidating steps in the melting process. In other cases, it may be easier to implement a model mathematically in 2D rather than 3D.
Experimental investigation of these thin films requires some method of holding the sample. In our experiments, the molecules are physically adsorbed on a solid surface. That is, molecules are bound to a substrate by weak van der Waals forces rather than by chemical bonds (chemisorption). These "physisorbed" monolayers can be composed of molecules of various sizes ranging from rare gas atoms and diatomic molecules (e.g., N2) to long-chain hydrocarbons. The condensed phases of these films are in many respects the 2D analogues of the simplest bulk solids, fluids, and gases.X-ray specular reflectivity profiles from xenon films adsorbed on a silver substrate.
Our most recent experiments have involved studies of the layer-by-layer structure and growth of physisorbed films. Neutron diffraction experiments with a variety of hydrocarbon films adsorbed on a polycrystalline graphite substrate are being conducted at MURR,. These utilize a diffractometer equipped with a specially designed multidetector-data acquisition system. Synchrotron x- ray sources are sufficiently intense to allow structural studies of films adsorbed on single-crystal substrates. For this purpose, we have developed a unique ultra-high vacuum chamber for use at the National Synchrotron Source at Brookhaven national Laboratory. We are currently investigating the multilayer structure and growth of both rare gas and hydrocarbon films on a Ag(111) substrate.
“The Mechanism of Melting in Submonolayer Films of Nitrogen Molecules Adsorbed on the Basal Planes of Graphite,” F. Y. Hansen, L. W. Bruch, and H. Taub, Phys. Rev. B 52, 8515-8527 (1995).
“Solvent Effects on the Monolayer Structure of Long n-Alkane Molecules Adsorbed on Graphite,” K. W. Herwig, B. Matthies, and H. Taub, Phys. Rev. Lett. 75, 3154-3157 (1995).
“Neutron Diffraction Investigation of the S2 Monolayer Phase of Ethane Physisorbed on Graphite,” J. C. Newton and H. Taub, Surf. Sci. 364, 273-278 (1996).
“Molecular Dynamics Simulations of the Dynamical Excitations in Commensurate Submonolayer Films of Nitrogen Molecules on Graphite,” F. Y. Hansen, L. W. Bruch, and H. Taub, Phys. Rev. B 54, 14077-14081 (1996).
“Quasielastic Neutron Scattering and Molecular Dynamics Simulation Studies of the Melting Transition in Butane and Hexane Monolayers Adsorbed on Graphite,” K. W. Herwig, Z. Wu, P. Dai, H. Taub, and F. Y. Hansen, J. Chem. Phys. 107, 5186-5196 (1997).
“Quasiepitaxial Growth of n-Alkane Films on a Solid Substrate,” Z. Wu, S. N. Ehrlich, B. Matthies, K. W. Herwig, P. Dai, U. G. Volkmann, and H. Taub; in Proceedings of the 7th National Conference on Experimental and Applied Physics, Santiago, Chile, Jan. 5-9, 1998, pp. 1-13 (invited).
“Neutron Diffraction Studies of the Structure, Growth, and Melting of Intermediate-length n-Alkane Films Adsorbed on Graphite,” H. Taub, F. Y. Hansen, K. W. Herwig, and B. Matthies, Proceedings of the First International Workshop on Nucleation and Non-linear Problems in First-order Phase Transitions, St. Petersburg, Russia, 29 June to 3 July 1998; Inorganic Materials 35, 847-851 (1999).
“The Mechanism of Melting in Monolayer Films of Short- and Intermediate-length n-Alkanes Adsorbed on Graphite,” F. Y. Hansen and H. Taub, Proceedings of the First International Workshop on Nucleation and Non-linear Problems in First-order Phase Transitions, St. Petersburg, Russia, 29 June to 3 July 1998; Inorganic Materials 35, 586-593 (1999).
“Synchrotron X-ray Diffraction Study of the Structure and Growth of Xe Films Adsorbed on the Ag(111) Surface,” Pengcheng Dai, Z. Wu, T. Angot, S.-K. Wang, H. Taub, and S. N. Ehrlich, Phys. Rev. B 59, 15464-15479 (1999)
“Intramolecular and Lattice Melting in n-Alkane Monolayers: An Analog of Melting in Lipid Bilayers,” F. Y. Hansen, K. W. Herwig, B. Matthies, and H. Taub, Phys. Rev. Lett. 83, 2362-2365 (1999).
“Diffusive Motion in Model Soft Matter Systems: Quasielastic Neutron Scattering Study of Short- and Intermediate-Length Alkane Layers,” D. Fuhrmann, L. Criswell, H. Mo, H. Taub, K. W. Herwig, U. G. Volkmann, and F. Y. Hansen, Proceedings of the Second European Conference on Neutron Scattering, Budapest, Hungary, 1-4 September 1999; Physica B 276-278, 345-346 (2000).
“Dynamics of Intermediate-Length Alkane Films Adsorbed on Graphite,” K. W. Herwig, D. Fuhrmann, L. Criswell, H. Taub, F. Y. Hansen, R. Dimeo, D. A. Neumann, Proceedings of the International Workshop on Dynamics in Confinement, Institut Laue-Langevin, Grenoble, France, 26 - 29 January, 2000; J. Phys. IV France 10, 157-160 (2000).
“Growth of n-Alkane Films on a Single-Crystal Substrate,” Z. Wu, S. N. Ehrlich, B. Matthies, K. W. Herwig, Pengcheng Dai, U. G. Volkmann, F. Y. Hansen, and H. Taub, Chem. Phys. Lett. 348, 168-174 (2001).
“Effects of Chain Branching on the Monolayer Structure of Alkanes at Interfaces: A Neutron and Helium Atom Scattering Study,” D. Fuhrmann, A. P. Graham, L. Criswell, H. Mo, B. Matthies, K. W. Herwig, and H. Taub, Proceedings of the 19th European Conference on Surface Science, Madrid, Spain, September 5 - 8, 2000; Surf. Sci. 482-485, 77-82 (2001).
“High-Resolution Ellipsometric Study of an n-Alkane Film, Dotriacontane, Adsorbed on a SiO2 Surface,” U. G. Volkmann, M. Pino, L. A. Altamirano, H. Taub, and F. Y. Hansen, J. Chem. Phys. 116, 2107-2115 (2002).
“A Novel Growth Mode of Alkane Films on a SiO2 Surface,” H. Mo, H. Taub, U. G. Volkmann, M. Pino, S. N. Ehrlich, F. Y. Hansen, E. Lu, and P. Miceli, submitted to Chem. Phys. Lett.
Book
Phase Transitions in Surface Films 2, Vol. 267 of NATO Advanced Study Institute, Series B: Physics, edited by H. Taub, G. Torzo, H. J. Lauter, and S. F. Fain, Jr. (Plenum, New York, 1991).