Computer based research

 

Surface Enhanced Raman Spectroscopy: Chemical Enhancement

Nano-scale semiconductors: organic-inorganic interface

Shape memory materials: Heusler alloys

2016

Two spectra of the same molecule look quite different: (left) Raman; (right) Surface Enhanced Raman Spectroscopy.

Origin of the difference is called “Chemical enhancement”. Some vibrations of the molecule perturb electronic structure of the molecule-metal chemical interface. This interfacial coupling changes significantly Raman signature of the metal adsorbed molecule.

Video demonstrates difference between two vibrational modes of benzene thiol molecule: (left) vibration causes disturbance of electron density inside the metal, strongly enhancing Raman cross section for this particular vibration; (right) example of a vibration that has no effect on the chemical binding between the molecule and the metal.

Why is this effect important?


This coupling is a unique tool that allows us to probe chemical coupling at the interface on the atomic scale, using Raman scattering.  

PbS

Quantum confinement

Role of ligands

Electronic structure

Heusler cubic structure

Modulated structure

e/a=7.25

e/a=7.5

e/a=7.625

e/a=7.75

Phonon instabilities that develop as a function of electron concentration, e/a - an opportunity for controlled design of functional Heusler alloys.

  1. •    A. T. Zayak, H. Choo, Y. S. Hu, D. J. Gargas, S .Cabrini, J. Bokor, P. J. Schuck, and J. B. Neaton, "Harnessing Chemical Raman Enhancement for Understanding Organic Adsorbate Binding on Metal Surfaces", J. Phys. Chem. Lett, 3, 1357-1362 (2012). [Link],

[SlideShare presentation featuring this paper, duration 8 min.]


  1. •    A. T. Zayak , Y. S. Hu, H. Choo, J. Bokor, S. Cabrini, P. J. Schuck, J. B. Neaton, "Chemical Raman Enhancement of Organic Adsorbates on Metal Surfaces", Phys. Rev. Lett. 106, 083003 (2011.) [Link]

Relevant publications

  1. •    A.T. Zayak, W. A. Adeagbo, P. Entel, and K. M. Rabe, “e/a dependence of the lattice instability of cubic Heusler alloys”, Appl. Phys. Lett. 88, 111903 (2006) [Link]


  1. •   A. Zayak, P. Entel, K. M. Rabe, W. A. Adeagbo, M. Acet, “Anomalous vibrational effects in non-magnetic and magnetic Heusler alloys”, Phys. Rev. B 72, 054113 (2005) [Link]

Relevant publications

Relevant publications

  1. •    K. H. Khoo, A. T. Zayak, H. Kwak, and J. R. Chelikowsky, "First-principles study of confinement effects on the Raman spectra of Si nanocrystals", Phys. Rev. Lett. 105, 115504 (2010). [Link]


  1. •    T.-L. Chan, A. T. Zayak, G. M. Dalpian, and J. R. Chelikowsky, "Role of Confinement on Diffusion Barriers in Semiconductor Nanocrystals", Phys. Rev. Lett. 102, 025901 (2009). [Link]

Magnetic oxides

  1. •     A. T. Zayak, X. Huang, J. B. Neaton, and Karin M. Rabe, “Crystal structure, electronic and magnetic properties of SrRuO3 under epitaxial strain”, Phys. Rev. B 74, 094104 (2006) [Link]


  1. •    A. T. Zayak, X. Huang, J. B. Neaton, and Karin M. Rabe, “Manipulating magnetic properties of SrRuO3 and CaRuO3 by epitaxial and uniaxial strains”, Phys. Rev. B 77, 214410 (2008) [Link]

Relevant publications

Semiconductor surfaces studied with Raman scattering

Raman scattering on surfaces is a very different process as compared to the conventional Raman. We are trying to show that Raman is capable of revealing chemical information right from the interface between organic adsorbates and the semiconductor surfaces. Not surprising, in our work we found that different crystallographic facets of semiconductor PbSe yield significantly different Raman signatures.

In the future this approach will be capable of measuring the local electronic properties of molecule-semiconductor interface.

  1. •    A. K. Kuhlman and A. T. Zayak, “Revealing Interaction of Organic Adsorbates with Semiconductor Surfaces Using Chemically Enhanced Raman”, J. Phys. Chem. Lett., 5 (6) 964-968 (2014) [Link]

Relevant publication

Tuning semiconductor surfaces with electric field: and Raman scattering

It is known that interfacial interactions between organic adsorbates and the surface can be tuned by applying external electric fields. But how can we “see” the changes? Among other possibilities, we show that surface enhances Raman scattering is a fantastic tool for observing the changes in the interfacial chemistry. But, we still have to learn a lot about the interfacial Raman signal in order to be able to use it as an analytical technique.

Relevant publication

  1. •   F. W. Hilty, A. K. Kuhlman, F. Pauly, and A. T, Zayak, “Raman Scattering from a Molecule-Semiconductor Interface Tuned by an Electric Field: Density Functional Theory Approach”, J. Phys. Chem. C, 119, 23113-23118 (2015) [Link]

By tuning the molecule-surface energy levels, we change Raman intensity. The way how it changes is indicative of the charge transfer mechanisms happening across the interface.