Ambient Tip-Enhanced Photoluminescence with 5 nm Spatial Resolution

Abstract

We achieve record spatial resolution in ambient tip-enhanced photoluminescence (TEPL) from CdSe/ZnS semiconductor quantum dots (QDs). Our approach only takes advantage of surface roughness at the apex of a sputtered plasmonic gold probe. When irradiated with visible light (633 and 532 nm lasers), nanocorrugated regions of the apex of an Au tip support 5 nm spatial resolution in TEPL imaging of QD aggregates on silicon. The reproducibility of our observations is illustrated using different plasmonic probes and samples. The origin of the observed near-field contrast, underlying the demonstrated high spatial resolution in TEPL, is discussed in the context of field enhancement at the metal tip-fluorophore interface.

Imaging Charged Exciton Localization in van der Waals WSe2/MoSe2 Heterobilayers

“…Figure c shows PL spectra from the HBL region (see also below) as a function of the tip–sample distance, with the force (represented by AFM cantilever deflection)–distance curve shown in Figure S1 in the Supporting Information. The tip-enhanced effect is evident when the tip–sample distance is less than ∼5 nm, which is consistent with the inferred spatial resolution that was recently reported using the same setup …”

“…The tip-enhanced effect is evident when the tip−sample distance is less than ∼5 nm, which is consistent with the inferred spatial resolution that was recently reported using the same setup. 25 Both WSe 2 and MoSe 2 layers show characteristic chargeneutral band-edge exciton emission in their far-field micro-PL (μ-PL) spectra (Figure S2 in the Supporting Information), which is consistent with the monolayer (ML) configuration. That said, we find that the emission from WSe 2 MLs is usually stronger than that from MoSe 2 MLs, as observed in CVDgrown layers.…”

“…Measurements were performed using a previously described setup and measurement protocol. 25 For the purpose of this work, spectra were recorded following 633 nm laser irradiation using a laser fluence of 2.5 × 10 4 W/cm 2 with an integration time of 0.25 s/pixel and an NF shift (amplitude) of 20 (Figures 3, S1, and S3) and a laser fluence of 1.5 × 10 4 W/cm 2 with an integration time of 0.5 s/pixel and an NF shift of 20 (Figures 2 and S2). An oscillation amplitude of 20−40 nm was used in the AFM scans.…”

“…The tips that were used were purchased (silicon ATEC-NC) and coated with 100 nm of Au using physical vapor deposition. Since the spectral data for the nano-PL when the tip is in contact with the sample also includes a response from the larger-area far-field illumination, the far-field PL spectra were subtracted (within the AIST-NT software) from the near-field PL spectra at equivalent pixels, leaving a pure near-field PL signal, as noted in the text . The spectra were otherwise smoothed using 10-point (across a wavelength range of ±0.25 nm) adjacent averaging.…”

“…The as-received samples were annealed in Ar at 100 °C for 1 h to improve interlayer coupling. Nano-PL imaging was carried out using a previously described AFM optical setup. , Details of the measurements reported herein can be found in Methods. Figure c shows PL spectra from the HBL region (see also below) as a function of the tip–sample distance, with the force (represented by AFM cantilever deflection)–distance curve shown in Figure S1 in the Supporting Information.…”