%0 Journal Article
%A Kerfoot, James
%A Legge, Elizabeth J.
%A Collins, Amy
%A Chauhan, Jasbinder
%A Rossnagel, Kai
%A Beton, Peter H.
%A Mellor, Christopher J.
%A Pollard, Andrew J.
%A Rance, Graham A.
%A George, Michael W.
%T Benchmarking TERS and TEPL probes: towards a reference sample for quantification of near-field enhancement factors in gap and non-gap modes
%J The analyst
%V 150
%N 14
%@ 0003-2654
%C Cambridge
%I Soc.
%M PUBDB-2025-02495
%P 3077 - 3088
%D 2025
%Z 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.
%X 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<sub>2</sub>) 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<sup>1</sup><sub>2g</sub> + A<sub>1g</sub> and 2LA(M) peaks in the Raman spectra of WSe<sub>2</sub>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.
%F PUB:(DE-HGF)16
%9 Journal Article
%$ pmid:40525753
%R 10.1039/D5AN00456J
%U https://bib-pubdb1.desy.de/record/634412