Carnegie Mellon University

The Hall Effects Edwin Hall Never Imagined

Xiaofeng Jin
Thursday, September 14, 2017 - 4:30pm

The anomalous Hall Effect (AHE) is one of the oldest and most prominent transport phenomena in magnetic materials. However, the microscopic mechanism of the AHE has remained unresolved for more than a century because its rich phenomenology defies standard classification, prompting conflicting claims of the dominant processes. We differentiate these processes through temperature--‐dependent measurements on epitaxial Fe, Ni, Co, and NixCu1--‐x  Films of varying thickness [1],  [2]. The results allow an unambiguous identification of both intrinsic and extrinsic mechanisms of the anomalous...

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Department of Chemical Engineering, Carnegie Mellon University
Ph.D., Chemistry, University of California, Berkeley, 1985

Professor Gellman's group uses experimental methods to study processes occurring on surfaces such as the bonding of molecules to metal surfaces, surface structure, reaction kinetics, catalysis, friction, and lubrication.  The use of surface science methods to create and study well-defined surfaces allows Professor Gellman's group to investigate surface chemistry relevant to these processes at the most fundamental level.

Professor Gellman’s group has pioneered the study of enantioselective surface chemistry on naturally chiral metal surfaces.  These surfaces are high Miller index planes that lack mirror symmetry and therefore exist as two enantiomorphs.  Recent work using D- and L-tartaric acid adsorbed on several Cu(hkl)R&S surfaces has demonstrated that one can achieve enormously high enantiospecific reaction rates via autocatalytic surface explosion mechanisms. Other work has used 13C isotopically labelled L-aspartic acid to monitor directly the enantioselective separation of DL-aspartic acid on Cu(3,1,17)R&S surfaces.  This work generates insight into some of the fundamental phenomena that lead to enantioselective adsorption and catalysis on chiral surfaces.

Recent work in Professor Gellman’s laboratory has focussed effort on the development of instrumentation and methods for high throughput study of surface phenomena.  Study of the surface science of multicomponent materials such as alloys is complicated by the fact that one needs to prepare, characterize and study many samples of varying composition.  Gellman’s group has worked to overcome this bottleneck by developing tools for the preparation of Composition Spread Alloy Films.  These are alloy films that have composition gradients parallel to their surfaces such that a 1x1 cm2 sample contains all possible compositions of a ternary alloy, AxByC1-x-y with x = 0 -> 1, y = 0 -> 1-x.  Spatially resolved materials and surface characterization methods (SEM, EDX, EBSD, XPS, UPS, LEIS, etc.) can then be used to map and study composition dependent phenomena such as surface segregation, catalysis, dewetting, and oxidation across the entire alloy composition space.

Another body of recent work exploits the use of spherically curved single crystal surfaces to conduct high throughput studies of structure sensitive surface chemistry that span surface orientations continuously.  This circumvents the need for study of many single crystals exposing surfaces of a single crystallographic orientation.  Surface Structure Spread Single Crystals expose a distribution of different surface orientations spanning a continuous region of the stereographic projection of all possible surface orientations.  Spatially resolved surface analysis methods such as STM, XPS and UPS can be used to study problems in surface structure, surface physics and structure sensitive surface chemistry

Selected Publications: 
  • "The Adsorption of Chiral Alcohols on "Chiral" Metal Surfaces," C.F. McFadden, P.S. Cremer, A.J. Gellman,  Langmuir, 12(10), 2483 (1996) 
  • “Polymers at Interfaces: Using Atom Transfer Radical Polymerization in the Controlled Growth of Homopolymers and Block Copolymers from Silicon Surfaces in the Absence of Untethered Sacrificial Initiator,' K. Matyjaszewski, P.J. Miller, N. Shukla, B. Immaraporn, A.J. Gellman, B.B. Luokala, T.M. Siclovan, G. Kickelbick, T. Vallant, H. Hoffmann, T. Pakula,  Macromolecules 32 (26), 8716 (1999) 
  • “Kinetics and Energetics of Oligomer Desorption from Surfaces,” K.R. Paserba, A.J. GellmanPhys. Rev. Lett.86(19), 4338 (2001) 
  • “Effects of Conformational Isomerism on the Desorption Kinetics of n-Alkanes from Graphite,” K.R. Paserba, A.J. Gellman, J. Chem. Phys. 115(14), 6737 (2001) 
  • “Enantioselective Separation on a Naturally Chiral Surface,”J. Horvath, P. Kamakoti, A. Koritnik, D.S. Sholl, A.J. GellmanJ. Amer. Chem. Soc. 126(45), 14988 (2004)
  • “The Real Structure of Naturally Chiral Cu{643},”A.E. Baber, A.J. Gellman, D.S. Sholl, E.C.H. Sykes, J. Phys. Chem. C  112(30), 11086 (2008)
Recent Publications: 
  1. “Enantiomeric Separations of Chiral Pharmaceuticals using Chirally Modified Tetrahexahedral Au Nanoparticles,” N. Shukla, D. Yang, A.J. GellmanSurface Science, 648, 29, (2016)
  2. “Xe Adsorption Site Distributions on Pt(111), Pt(221) and Pt(531),” A.J. Gellman, L.D. Baker, B.S. Holsclaw, Surface Science 646, 83 (2016)
  3. “Thermal interface conductance across metal alloy-dielectric interfaces,” J.P. Freedman, X. Yu, R.F. Davis, A.J. Gellman, J.A. Malen, Physical Review - B 93, 035309 (2016),
  4. “An Atomic-scale Picture of the Composition, Decay and Oxidation of 2D Radioactive Films,” A. Pronschinske, P. Pedevilla, B. Coughlin, C.J. Murphy, F.R. Lucci, M.A. Payne, A.J. Gellman, A. Michaelides, E.C.H. Sykes, ACS Nano 10, 2152 (2016)  
  5. “Editorial: Special issue dedicated to Gabor Somorjai’s 80th birthday,” A.J. Gellman, R.M. Rioux, P.C. Stair,  Surface Science 648, 1, (2016)