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High Resolution Tip-Enhanced Raman Images of Single Molecules from First Principles Simulations
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. (Research group of Prof. Yi Luo)ORCID iD: 0000-0003-3383-8080
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 [en]
First Principles, Tip-Enhanced Raman Images, light-matter interactions at the nanoscale
National Category
Natural Sciences
Research subject
Theoretical Chemistry and Biology
Identifiers
URN: urn:nbn:se:kth:diva-263652ISBN: 978-91-7873-373-6 (print)OAI: oai:DiVA.org:kth-263652DiVA, id: diva2:1368635
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
List of papers
1. Gauge invariant theory for super high resolution Raman images
Open this publication in new window or tab >>Gauge invariant theory for super high resolution Raman images
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
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-208805 (URN)10.1063/1.4983391 (DOI)000401776300006 ()28527435 (PubMedID)2-s2.0-85029898916 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20170613

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2019-11-07Bibliographically approved
2. Molecular tumbling on Au(111) surface: a new pathway for reversible isomerization of a single azobenzene molecule
Open this publication in new window or tab >>Molecular tumbling on Au(111) surface: a new pathway for reversible isomerization of a single azobenzene molecule
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The switchable trans-cis isomerization of azobenzene (AB) and its derivatives on metallic surfaces has offered rich possibilities to functionalize molecular devices. However, the lack of good understanding on isomerization pathway has severely limited our ability for rational design. One of long debated issues is the cis configuration of parental AB on Au(111) surface, for which the experimentally inferred structure differs from the theoretically predicted global minimum. Here, we theoretically predict a new in-situ metastable configuration for cis-AB on Au(111) that can reproduce the observations reported in the scanning tunneling microscopy experiments. The calculated potential energy surface indicates that the stability of the newly discovered cis-AB isomer is kinetically much superior than that of the cis global minimum, which well explains the bistability of AB on Au(111) surface. Accordingly, we reveal a fascinating tumbling pathway that overcomes two energy barriers stimulated by tunneling electrons for the trans-cis AB isomerization on Au(111), suggesting a new type of molecular motor based on the AB systems.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-263650 (URN)
Note

QC 20191112

Available from: 2019-11-07 Created: 2019-11-07 Last updated: 2019-11-12Bibliographically approved
3. Theoretical modeling of tip-enhanced resonance Raman images of switchable azobenzene molecules on Au(111)
Open this publication in new window or tab >>Theoretical modeling of tip-enhanced resonance Raman images of switchable azobenzene molecules on Au(111)
Show others...
2018 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 25, p. 11850-11860Article in journal (Refereed) Published
Abstract [en]

With a highly localized plasmonic field, tip-enhanced Raman spectroscopy (TERS) images have reached atomic-scale resolution, providing an optical means to explore the structure of a single molecule. We have applied the recently developed theoretical method to simulate the TERS images of trans and cis azobenzene as well as its derivatives on Au(111). Our theoretical results reveal that when the first excited state is resonantly excited, TERS images from a highly confined plasmonic field can effectively distinguish the isomer configurations of the adsorbates. The decay of the plasmonic field along the surface normal can be further used to distinguish different nonplanar cis configurations. Moreover, subtle characteristics of different molecular configurations can also be identified from the TERS images of other resonant excited states with a super-high confined plasmonic field. These findings serve as good references for future TERS experiments on molecular isomers.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-232390 (URN)10.1039/c8nr01988f (DOI)000437761500015 ()29897090 (PubMedID)2-s2.0-85049505191 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20180727

Available from: 2018-07-27 Created: 2018-07-27 Last updated: 2019-11-07Bibliographically approved
4. Lighting up long-range charge-transfer states by a localized plasmonic field
Open this publication in new window or tab >>Lighting up long-range charge-transfer states by a localized plasmonic field
2017 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 46, p. 18189-18193Article in journal (Refereed) Published
Abstract [en]

The long-range charge-transfer states in a donor-acceptor system exhibit well separated electron-hole pairs, but are often difficult to achieve by optical means owing to a very small overlap between the wave functions of the donor and acceptor. We have found that the introduction of a spatially confined plasmon can enhance the transition probability to the long-range charge-transfer states as it can effectively break the intrinsic symmetry selection rule imposed on the system. Meanwhile, the intensity borrowed from local excitations could also be selectively promoted, allowing the manipulation of the excited quantum states. In addition, our calculations reveal that the donor and acceptor moieties can be unambiguously visualized in real space by tip-enhanced resonance Raman images. These findings can benefit light-harvesting and also be readily extended to diverse optical processes.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Theoretical Chemistry Biological Sciences
Identifiers
urn:nbn:se:kth:diva-220454 (URN)10.1039/c7nr06322a (DOI)000416824100006 ()2-s2.0-85036465256 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20180103

Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2019-11-07Bibliographically approved
5. Monitoring Hydrogen/Deuterium Tautomerization in Transient Isomers of Single Porphine by Highly Localized Plasmonic Field
Open this publication in new window or tab >>Monitoring Hydrogen/Deuterium Tautomerization in Transient Isomers of Single Porphine by Highly Localized Plasmonic Field
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 17, p. 11081-11093Article in journal (Refereed) Published
Abstract [en]

Inner proton transfer between two trans isomers (tautomerization) in porphyrins plays a crucial role in many biological systems as well as molecular nanotechnology. Although the stepwise mechanism of tautomerization is well accepted, the involved intermediate cis-isomer has not been directly detected owing to its short lifetime and the extremely low intensities of corresponding hydrogen vibrations. Here, taking a single porphine as the prototype, we theoretically demonstrate that Raman intensities of the hydrogen vibrations become accessible under the highly localized plasmonic field because of the symmetry breaking effect. In addition, with the ultrafast incident excitations, we find that Raman signals of cis-porphine could be distinguished from the stable trans isomer, suggesting a general protocol for the direct characterization of transient isomers. Moreover, calculated results reveal that the position of inner hydrogen/deuterium can be unambiguously visualized from Raman images of the corresponding stretching modes, providing a unique optical means for the chemical monitoring of tautomerization in porphine and its derivatives.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-252384 (URN)10.1021/acs.jpcc.9b00398 (DOI)000466988600040 ()2-s2.0-85065302261 (Scopus ID)
Note

QC 20190618

Available from: 2019-06-18 Created: 2019-06-18 Last updated: 2019-11-07Bibliographically approved

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