Mapping VIS-terahertz (≤17 THz) surface plasmons sustained on native and chemically functionalized percolated gold thin films using EELS

Abstract

Heterogeneous assemblies of molecules (Rhodamine B) adsorbed onto a nano-corrugated metallic surface (a percolated Au network) are investigated using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS). Our first measurements target the native metallic substrate, which consists of a commercial Au thin film atop an ultrathin carbon membrane. The Au film displays a percolated morphology with nanostructures of estimated thickness ≤10 nm approximately. We observe a rich plasmonic response from the metallic substrate; one which varies nanometrically and spans the VIS-terahertz region. Multiple localized plasmons are detected at individual nanometric integrated areas, while an analysis of their spatial distribution reveals that for each integrated energy range (50 meV integration window) resonances are simultaneously supported at different locations within the film. We record subsequent EEL spectrum images of the hybrid molecular–metallic construct after deposition of Rhodamine B molecules onto the substrate, where plasmons, molecular vibrations and electronic excitations might all be simultaneously detected. A comparison of average signals for both systems is performed and spectral variations within the three spectral regions where molecular signatures may be observed are discussed. Our measurements and their analysis, if applied to the same location before and after molecular deposition, may be used to rationalize optical microscopic and spectroscopic measurements that take advantage of the interplay between molecules and plasmons.

Bond Dissociation and Reactivity of HF and H2O in a Nano Test Tube

“…In addition to e-beam damage to the host C 60 molecules allowing the endohedral F to move more freely, the low inelastic scattering cross-section of F at its K ionization edge makes the spectroscopic identification of single F atoms challenging: Figure nevertheless presents strong evidence of the presence of single F atoms in two intact C 60 molecules, whereas no F signal is detected within polymerized molecules (see Methods for experimental details). Vibrational electron energy loss spectroscopy performed on the molecules in individual nanotubes did not show a sufficiently strong signal from the endohedral molecules due to the large amount of carbon around them (relative to the small molecule concentration) and to the possible screening effects of the host nanotube; however, the EELS of a nanosheet of HF@C 60 approximately five monolayers thick and suspended over a hole (Figure d) in an aloof beam configuration to protect the molecules from the impact of the e-beam itself ,− revealed strong vibrational features in the region between 0.1 and 1.7 eV ( i.e. , ∼800 and 13 700 cm –1 ).…”

“…Vibrational electron energy loss spectroscopy (EELS) performed on the molecules in individual nanotubes did not show sufficiently strong signal from the endohedral molecules due to the large amount of carbon around them (relative to the small molecule concentration) and to possible screening effects of the host nanotube; however EELS of a nano-sheet of HF@C60 approximately five monolayers thick and suspended over a hole (Fig. 3d) in an aloof beam configuration to protect the molecules from the impact of the e-beam itself, 31,[33][34][35] revealed strong vibrational features in the region between 0.1-1.7 eV (~800-13700 cm -1 ). The observed vibrational bands before and after intentional e-beam irradiation are compared in Fig.…”

From SERS to TERS and Beyond: Molecules as Probes of Nanoscopic Optical Fields

“…This nanorod work thus adds a new dimension to local optical field mapping via TERS: not only can the vector components and spatial profiles of local optical fields be imaged, but also spatially varying local optical resonances are direct observables. This recent realization may hold the key to understanding the TERS maps of corrugated surfaces and nanostructures, where local resonances have been found to span the deep-UV through mid-IR spectral region . Note that all the aforementioned AFM-based TERS measurements were recorded using corrugated/sputtered probes with an intermittent contact mode feedback, whereby the tip is in contact when the spectra are measured and in semicontact as the sample is scanned relative to the probe.…”

“…This recent realization may hold the key to understanding the TERS maps of corrugated surfaces and nanostructures, where local resonances have been found to span the deep-UV through mid-IR spectral region. 55 Note that all the aforementioned AFM-based TERS measurements were recorded using corrugated/sputtered probes with an intermittent contact mode feedback, whereby the tip is in contact when the spectra are measured and in semicontact as the sample is scanned relative to the probe. As noted above, the proximity of the tip to the surface appears to modulate the accessed plasmon and the electric field environment.…”