Synergy of Photoinduced Force Microscopy and Tip-Enhanced Raman Spectroscopy—A Correlative Study on MoS₂

Abstract

In this contribution, we combine for the first time tip-enhanced Raman spectroscopy (TERS) and photoinduced force microscopy (PiFM) synergistically and examine this instrumental approach on the 2D material molybdenum disulfide (MoS2). In a first step the PiFM technique was applied to map the electrical field distribution of the incident light field with nanometer resolution according to the plasmon resonance of the TERS tip. This experiment provides a fast and nondestructive characterization of the TERS tips focus interaction and is in good agreement with theoretical models. Subsequently, combined TERS and PiFM experiments on a MoS2 monolayer finally demonstrate a correlation of maximum TERS signal enhancement and the corresponding PiFM image with respect to the depth and lateral position of the focal laser spot. Hence, the results indicate a significantly improved route toward the alignment efficiency of TERS experiments and establish MoS2 as an outstandingly suitable TERS test sample.

Thermomechanical Nanostraining of Two-Dimensional Materials

“…The AFM-TERS combines Raman spectroscopy with scanning probe microscopy . Upon illumination, the electric field strength at the tip apex (Supporting Information Section 12) strongly increases thanks to localized surface plasmon resonance. , Therefore, the Raman signal of the probed material is enhanced in the vicinity of the tip. Figure c shows an AFM topography of the nanopatterned 1L MoS 2 , acquired prior to the AFM-TERS study.…”

Enhancement of Raman Scattering and Exciton/Trion Photoluminescence of Monolayer and Few-Layer MoS2 by Ag Nanoprisms and Nanoparticles: Shape and Size Effects

“…23 Monolayer (ML) MoS 2 has a direct band gap of ∼1.85 eV, while bulk MoS 2 has an indirect band gap of 1.29 eV. 24 In ML MoS 2 , two absorption peaks can be observed at ∼1.86 eV (∼670 nm) and ∼1.98 eV (∼627 nm), known as A and B excitons, that arise from direct excitonic transitions at the K point of the Brillouin zone. 25 The binding energy of excitons is above 200 meV, 26 due to the strong Coulomb interaction between the electron and the hole (quantum confinement effect).…”

“…84 Ag Nanoprism Synthesis and Calculation. Ag NTs were synthesized according to a previous report: 85 24.75 mL of solutions containing 0.1 mM AgNO 3 and 1 mM trisodium citrate was stirred vigorously at room temperature. Then, 250 μL of mixed aqueous solution (8 mM NaBH 4 and 0.125 M NaOH) was injected via dropwise addition into the solution.…”

Photothermal Plasmonic Actuation of Micromechanical Cantilever Beams

“…However, the mechanical response of coated mechanical resonators, such as cantilever beams, when driven by optical excitation at various wavelengths across the visible spectral domain remains unexplored. This is critical for experiments conducted with tunable light sources, as needed for instance in microscopic photovoltage spectroscopy [42,43], Kelvin probe force microscopy under illumination [44,45], photo-piezoresponse and photoelectric force microcopy [46][47][48], or photoinduced force microscopy and spectroscopy [49][50][51][52].…”

“…Photoinduced force microscopy recently opened exciting opportunities for studying nanometer scale optical properties and light-matter interactions with unprecedent spatial resolution [49][50][51][52][53]. The central idea in this technique is the generation of optical forces between the apex of an atomic force microscope tip and a sample surface upon absorption of light by the latter [54][55][56].…”