Prof. Xie's Group
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Semiconductor Materials Research Lab
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Figure 1. a, Schematic illustration of the hybrid system for single molecular SERS. b, x-z view of electric field distribution around the Au nanostructures by FDTD simulation. Incident light wavelength 633nm. Scale 200nm. c, x-y view of electric field distribution at z=100nm. Scale 200nm

References:

  1. Wang, P.; Zhang, W.; Liang, O.; Pantoja, M.; Katzer, J.; Schroeder, T.; Xie, Y. H. Giant Optical Response from Graphene-Plasmonic System. ACS Nano, 6, 6244 (2012);
  2. Bonaccorso, F.; Sun, Z.; Hasan, T.; Ferrari, A. C. Graphene Photonics and Optoelectronics. Nature Photonics. 2010, 4, 611–622.
  3. Echtermeyer, T. J.; Britnell, L.; Jasnos, P. K.; Lombardo, A.; Gorbachev, R. V.; Grigorenko, A. N.; Geim, A. K.; Ferrari, A. C.; Novoselov, K. S. Strong Plasmonic Enhancement of Photovoltage in Graphene. Nature Communications. 2011, 2, 458.
  4. Pieczonka, N. P. W. & Aroca, R. F. Single molecule analysis by surfaced-enhanced Raman scattering. Chem.Soc.Rev. 2008, 37, 946–954.
  5. Wang, Y.; Li, Z. H.; Wang, J.; Li, J. H.; Lin, Y. H. Graphene and graphene oxide: bio-functionalization and applications in biotechnology. Trends in Biotechnology. 2011, 29, 205-212.

Semiconductor Materials Research Laboratory, Department of Materials Science and Engineering, University of California, Los Angeles

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Graphene-Plasmonic Hybrid System

 

The Xie group has been studying a graphene-plasmonic nano-structure hybrid platform for Surface Enhanced Raman Scattering (SERS). We have demonstrated label-free single molecule detection with detailed vibrational information using this platform. The overarching objective is to deepen the understanding of the fundamental mechanism of SERS for the purpose of exploring the extraction of molecular information beyond those from conventional SERS experiments. We have demonstrated and are continuing to further our understanding of the prominent role of bio-compatible graphene in the field of biophysics and SERS.

Our approach of fabricating the plasmonic surfaces is via nano-casting. The technique leverages heavily the very mature and the extremely versatile Si integrated circuit technology. Our goal is to establish a nano-fabrication platform for each of the major fields of application including in vitro, in vivo, and others. The guiding design principles include directional drying of aqueous solution droplets on engineered, superhydrophobic surfaces, the selective placement of SERS hot spots, etc.. 

Advanced plasmonics and van der Waals materials

Graphene serves as a platform to study the dynamic processes involved in the plasmonic hybrid system. The nanoscale optics and photophysics beyond simply scaling down the electromagnetic field volume are of great interest. One of our topics is to study the tunable coupling of electromagnetic energy between plasmonic metal nanostructures and the single layer semimetal – graphene. We are actively pushing the frontier to other van der Waals materials.

Graphene-based system for biosensing and biomedical applications

We also studied the potential of the unique graphene - Au nanopyramid hybrid structure for bio-applications. The SERS efficiency was demonstrated by comparing average Raman intensities of biomolecules. With Au nano-pyramid structure only, they achieved single molecule detection with R6G concentration down to 10-14 M. Raman microscopy indicated that a remarkable Raman enhancement of at least 1010 can be achieved. The Raman enhancement is expected to be 100-1000 fold larger at hotspots with highly localized electromagnetic field. Graphene is a multi-functional monolayer coating with superior bio-compatibility. It will improve the properties of SERS active substrate but minimizes the detrimental effects to the plasmonic behavior. When CVD graphene is superimposed on the Au nano-pyramid substrate, the molecular Raman intensities are even more enhanced. These observations indicate that graphene may facilitate the chemical enhancement for bio-molecules via molecule – graphene interaction. Work is in progress to verify the dominant mechanism responsible for the observed enhancement in Raman.

Participants of the project will gain hands-on experience in nano-fabrication, the fabrication of van der Waals materials, and in addition acquiring knowledge about the exciting field of biomedical sensing.

 

 

 

 

 

 

 

 

 

 

 

Figure 2.SERS of graphene on Au tips.

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Figure 3. Graphene 1-D folds serve as new origin of D band.