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Gauge invariant theory for super high resolution Raman images
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 19, article id 194106Article in journal (Refereed) Published
Abstract [en]

The use of a highly localized plasmonic field has enabled us to achieve sub-nanometer resolution of Raman images for single molecules. The inhomogeneous spatial distribution of plasmonic field has become an important factor that controls the interaction between the light and the molecule. We present here a gauge invariant interaction Hamiltonian (GIIH) to take into account the nonuniformity of the electromagnetic field distribution in the non-relativistic regime. The theory has been implemented for both resonant and nonresonant Raman processes within the sum-over-state framework. It removes the gauge origin dependence in the phenomenologically modified interaction Hamiltonian (PMIH) employed in previous studies. Our calculations show that, in most resonant cases, the Raman images from GIIH are similar to those from PMIH when the origin is set to the nuclear charge center of the molecule. In the case of nonresonant Raman images, distinct differences can be found from two different approaches, while GIIH calculations provide more details and phase information of the images. Furthermore, the results from GIIH calculations are more stable with respect to the computational parameters. Our results not only help to correctly simulate the resonant and nonresonant Raman images of single molecules but also lay the foundation for developing gauge invariant theory for other linear and nonlinear optical processes under the excitation of non-uniform electromagnetic field. Published by AIP Publishing.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017. Vol. 146, no 19, article id 194106
National Category
Physical Sciences Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-208805DOI: 10.1063/1.4983391ISI: 000401776300006PubMedID: 28527435Scopus ID: 2-s2.0-85029898916OAI: oai:DiVA.org:kth-208805DiVA, id: diva2:1108943
Funder
Swedish Research Council
Note

QC 20170613

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2019-11-07Bibliographically approved
In thesis
1. High Resolution Tip-Enhanced Raman Images of Single Molecules from First Principles Simulations
Open this publication in new window or tab >>High Resolution Tip-Enhanced Raman Images of Single Molecules from First Principles Simulations
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the precise control of spatially confined plasmon (SCP), tip-enhanced Raman spectroscopy (TERS) has achieved sub-nanometer resolution, leading to the chemical and physical characterization of the single molecule by optical Raman images. In the high resolution TERS measurements, the SCP spatial distribution generates the position-dependent Raman images. The position dependence challenges the conventional response theory, because the assumption of interactions between the molecule and the uniform electromagnetic field does not hold anymore. Moreover, as an emerging technology, potential applications of high resolution TERS are required to be fully explored. In this thesis, the developed theory for modeling high resolution Raman images is presented. By taking a series of typical molecular systems as examples, we theoretically predict some fine applications of single-molecule TERS.

The first part of the thesis introduces the development of Raman spectroscopy and images. To achieve the final target of single molecule characterization, high spatial resolution single-molecule TERS is established and improved. As a nondestructive measuring tool, Raman imaging technology offers the means to study single molecules with unprecedented spatial resolution.

The high resolution Raman images theory with detailed derivations is given in the second part of the thesis. The key factor is to take the inhomogeneous spatial distribution of SCP field into account, when we construct the interaction Hamiltonian between the localized light field and the molecule. This makes the numerical simulations of Raman images feasible.

Other parts of the thesis give some theoretical predictions for potential applications of the emerging Raman imaging technology. Specifically, resonance Raman images can visualize the geometric changes of a single molecule switch and the intramolecular structure in real space. Since the localized plasmonic field can affect the electron transition, the excited quantum states can thus be effectively manipulated. This breaks down the intrinsic spatial selection rule imposed in conventional spectra. In addition, an effective linear response algorithm is used to simulate nonresonance Raman images. The unique superiority of spatial vibration resolution from non-resonance cases provides rich information about the single molecule. By constructing images from different vibrational modes, the spatial chemical distribution within a single molecule can be visualized. All these findings will facilitate fine applications of the emerging TERS technology in the coming years.

Place, publisher, year, edition, pages
Kungliga Tekniska högskolan, 2019. p. 69
Series
TRITA-CBH-FOU ; 67
Keywords
First Principles, Tip-Enhanced Raman Images, light-matter interactions at the nanoscale
National Category
Natural Sciences
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-263652 (URN)978-91-7873-373-6 (ISBN)
Public defence
2019-12-06, FP 41, Roslagstullsbacken 33, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 2019-11-14

Available from: 2019-11-14 Created: 2019-11-07 Last updated: 2019-11-14Bibliographically approved

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