Kerfoot, J; Legge, E J; Collins, A; Chauhan, J; Rossnagel, K; Beton, P H; Mellor, C J; Pollard, A J; Rance, G A; George, M W (2025) Benchmarking TERS and TEPL probes: towards a reference sample for quantification of near-field enhancement factors in gap and non-gap modes. The Analyst, 150 (14). pp. 3077-3088. ISSN 0003-2654

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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 E12g + A 1g and 2LA(M) peaks in the Raman spectra of WSe 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.

Item Type:	Article
Keywords:	Tip-enhanced Raman spectroscopy, Tip-enhanced photoluminescence, atomic force microscopy, tungsten diselenide, nanomaterial
Subjects:	Nanoscience > Nano-Materials
Divisions:	Chemical & Biological Sciences
Identification number/DOI:	10.1039/D5AN00456J
Last Modified:	03 Jul 2026 13:29
URI:	https://eprintspublications.npl.co.uk/id/eprint/10476