Laurence D. Marks

Department of Materials Science and Engineering
Northwestern University
Evanston IL 60208, USA
Phone: (847) 491 3996
Fax: (847) 491 7820

Research Interests

Research interests cover a wide range of topic some of which are relatively basic such as Direct Methods, Surface Structures, Quantum Electron Crystallography and Surface Charge Density while others such as Self-Lubricating Cutting Tools, Environmental Catalysis, Tribology and the Nanoscale structure of Cement have a stronger eye on applications; see the research page for more details. Much of the fundamental work involves combining cutting-edge variants of electron microscopy in a unique combination of an electron microscope and surface science system so we can combine more standard surface science probes, such as XPS or Auger, and chambers where samples are grown, all within one unique UHV system. Current projects include:

Oxide Surfaces

At the current moment it is very hard to predict the structure of oxide surfaces; this is an important problem because these are very important in a large number of different areas ranging from catalysis through new types of oxide devices and corrosion. We are exploiting both our direct methods approach as well as careful electron microscopy to understand the atomic scale structures.

Erdman, N., K.R. Poeppelmeier, M. Asta, O. Warschkow, D.E. Ellis, and L.D. Marks, The structure and chemistry of the TiO2-rich surface of SrTiO3(001). Nature, 2002. 419(6902): p. 55-58.

Erdman, N. and L.D. Marks, SrTiO3(001) surface structures under oxidizing conditions. Surface Science, 2003. 526(1-2): p. 107-114.

Erdman, N., O. Warschkow, M. Asta, K.R. Poeppelmeier, D.E. Ellis, and L.D. Marks, Surface structures of SrTiO3 (001): A TiO2-rich reconstruction with a c(4 x 2) unit cell. Journal of the American Chemical Society, 2003. 125(33): p. 10050-10056.

Chiaramonti, A.N., J.D. Pless, L. Liu, J.P. Smit, C.H. Lanier, K.R. Poeppelmeier, P.C. Stair, and L.D. Marks, Optical floating zone growth of single crystal alpha-Fe2O3 from a CaFe4O7-based solvent. Crystal Growth & Design, 2004. 4(4): p. 749-753.

Warschkow, O., M. Asta, N. Erdman, K.R. Poeppelmeier, D.E. Ellis, and L.D. Marks, TiO2-rich reconstructions of SrTiO3(001): a theoretical study of structural patterns. Surface Science, 2004. 573(3): p. 446-456.

Chiaramonti, A.N. and L.D. Marks, Atomic resolution transmission electron microscopy of surfaces. Journal of Materials Research, 2005. 20(7): p. 1619-1627.

Chiaramonti, A.N., P.C. Stair, and L.D. Marks, Impurity stabilized near-surface phase on ion bombarded alpha-Fe2O3(0001). Surface Science, 2005. 586(1-3): p. 38-44.

Direct Methods for Surfaces

Direct Methods were originally developed as techniques aimed at solving the phase problem encountered in bulk X-ray diffraction. We have recently shown that they can be used for surfaces, with both x-ray and electron diffraction data. This has made it possible to solve structures which were much more complicated than anything possible before, opening up many possibilities in terms of surface structure, phase diagrams etc. We have also shown that they can also be used for bulk materials, to determine structures previously only possible using neutron diffraction.

Erdman, N., K.R. Poeppelmeier, M. Asta, O. Warschkow, D.E. Ellis, and L.D. Marks, The structure and chemistry of the TiO2-rich surface of SrTiO3(001). Nature, 2002. 419(6902): p. 55-58.

Subramanian, A. and L.D. Marks, Surface crystallography via electron microscopy. Ultramicroscopy, 2004. 98(2-4): p. 151-157.

Hard Coatings

Hard coatings have numberous technological applications, ranging from coatings for cutting tools through protective layers for hard disc drives. We can use our unique instrumentation of SPEAR and the UHV-HREM to perform in-situ growth experiments with two chambers called SINBAD and MIBE. More recently this work has evolved to growing self-lubricating cutting tool coatings.

Widjaja, E.J. and L.D. Marks, In situ studies of magnetron sputtered Al-Cu-Fe-Cr quasicrystalline thin films. Thin Solid Films, 2002. 420: p. 295-299.

Widjaja, E.J. and L.D. Marks, Epitaxial decagonal thin films on crystalline substrates. Philosophical Magazine Letters, 2003. 83(1): p. 47-55.

Widjaja, E.J. and L.D. Marks, Coincidence of reciprocal lattice planes model for quasicrystal-crystal epitaxy. Physical Review B, 2003. 68(13): p. 134211.

Widjaja, E.J. and L.D. Marks, Microstructural evolution in Al-Cu-Fe quasicrystalline thin films. Thin Solid Films, 2003. 441(1-2): p. 63-71.

Charge Density Measurements

One of the most fundamental properties of a material is the atomic-scale electron density; if we knew this we would really not need to know where the atoms are. We have been very recently doing precise electron diffraction and x-ray diffraction from surfaces to get the first experimental measurements of charge redistribution at a surface. We are also working on methods of directly imaging the charge density inside a bulk material.

Subramanian, A., L.D. Marks, O. Warschkow, and D.E. Ellis, Direct observation of charge transfer at a MgO(111) surface. Physical Review Letters, 2004. 92(2).

Ciston, J., L.D. Marks, R. Feidenhans'l, O. Bunk, G. Falkenberg, and E.M. Lauridsen, Experimental surface charge density of the Si (100)-2x1H surface. Physical Review B, 2006. 74(8).

Deng, B. and L.D. Marks, Theoretical structure factors for selected oxides and their effects in high-resolution electron-microscope (HREM) images. Acta Crystallographica Section A, 2006. 62: p. 208-216.

Deng, B. and L.D. Marks, Charge Defects Glow in the Dark. Ultramicroscopy, 2006. In Press.

Nanotribology

The nanoscale processes that occur in tribology (friction) are very poorly understood, particularly the role of dislocations. We are exploring this both theoretically in terms of dislocation drag models, as well as experimentally using a unique holder where we can simultaneously move a tip across a surface and image it inside a transmission electron microscope.

Merkle, A. and L.D. Marks, A dislocation drag model for friction. Tribology Letters, 2006. Submitted.

Precession Electron Diffraction

This is a new approach to performing electron diffraction, which looks very promising in terms of solving some of the classical problems in interpretation which have caused problems for many years. We have a partial patent on the method, and are actively pursuing understanding the fundamentals.

Own, C.S., A.K. Subramanian, and L.D. Marks, Quantitative analyses of precession diffraction data for a large cell oxide. Microscopy and Microanalysis, 2004. 10(1): p. 96-104.

Own, C.S., L.D. Marks, and W. Sinkler, Electron precession: A guide for implementation. Review of Scientific Instruments, 2005. 76(3).

Own, C.S., L.D. Marks, and W. Sinkler, Precession electron diffraction 1: multislice simulation. Acta Crystallographica Section A, 2006. 62: p. 434-443.

Cement Nanostructures

Cement is one of the most common building materials, and has been used at least as far back as Roman times. However, we still do not really understand its nanoscale structure and properties. We have developed some unique techniques for probing the mechanical properties of cement and similar materials at the nanoscale.