Journal Article

PUBDB-2025-02495

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Benchmarking TERS and TEPL probes: towards a reference sample for quantification of near-field enhancement factors in gap and non-gap modes

Kerfoot, J. (Corresponding author) ; Legge, E. J. ; Collins, A. ; Chauhan, J. ; Rossnagel, K.DESY* ; Beton, P. H. ; Mellor, C. J. ; Pollard, A. J. ; Rance, G. A. (Corresponding author) ; George, M. W. (Corresponding author)

2025
Soc. Cambridge

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Please use a persistent id in citations: doi:10.1039/D5AN00456J  doi:10.3204/PUBDB-2025-02495

Abstract: Benchmarking the near-field signal enhancement attained using plasmonic metal-coated atomic force microscopy (AFM) probes for tip-enhanced Raman spectroscopy (TERS) and tip-enhanced photoluminescence (TEPL) measurements is challenging given the absence of a suitable reference sample that is simple to prepare, easy to use and compatible with different instrument configurations. To this end, in this study, we have fabricated a flake of monolayer tungsten diselenide (1L-WSe$_2$) stamped across the interface of gold and silver thin films on silicon dioxide and glass. We have demonstrated these samples to be effective for the facile determination of near-field Raman and photoluminescence contrast factors in both gap and non-gap mode, respectively. We show that the near-degenerate E$^1$$_{2g}$ + A$_{1g}$ and 2LA(M) peaks in the Raman spectra of WSe$_2$2 enable quantification of Raman contrast factors, with a ∼1.6-fold increase in TERS signal enhancement in gap mode, relative to non-gap mode, observed for a typical probe. Similar differences in the photoluminescence contrast factors were observed comparing in-contact and out-of-contact signal intensity ratios from gap and non-gap mode TEPL measurements. Moreover, in developing a reference methodology we found that the line shape of the TEPL profile was dependent upon the magnitude of the signal enhancement, with a disproportionate increase in the longer wavelength shoulder of the emission observed in gap mode. As this contribution to the asymmetric line shape is tentatively assigned to a dark exciton, which possesses an out-of-plane transition dipole moment, our TEPL measurements indicate that the directionality of the near-field enhancement provides a further handle enabling quantification of probe performance. Using samples prepared on glass, and comparing results obtained from two different instruments, each with a different excitation laser wavelength and optical access, we demonstrate the universal applicability of our reference material for sensitivity benchmarking of metallised AFM probes in both gap and non-gap mode, suitable for both reflection and transmission geometries, and across the range of laser wavelengths typically used for TERS and TEPL.

Note: JK, GAR and MWG acknowledge funding from the Engineeringand Physical Science Research Council (EPSRC) (Project: EP/V053884/1) and support from the Nanoscale and MicroscaleResearch Centre (nmRC). EJL and AJP would like to acknowl-edge the National Measurement System (NMS) of theDepartment for Science, Innovation and Technology (DSIT),UK ( projects #128826) for funding. The authors thankDongkuk Kim and Sebastian Wood at the National PhysicalLaboratory, U.K., for discussion associated with themanuscript.

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Contributing Institute(s):

1. FS-SXQM (FS-SXQM)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2025

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Database coverage:
; ; Clarivate Analytics Master Journal List ; Current Contents - Life Sciences ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; National-Konsortium ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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