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Nat Commun ; 10(1): 5544, 2019 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-31804496


Defects can induce drastic changes of the electronic properties of two-dimensional transition metal dichalcogenides and influence their applications. It is still a great challenge to characterize small defects and correlate their structures with properties. Here, we show that tip-enhanced Raman spectroscopy (TERS) can obtain distinctly different Raman features of edge defects in atomically thin MoS2, which allows us to probe their unique electronic properties and identify defect types (e.g., armchair and zigzag edges) in ambient. We observed an edge-induced Raman peak (396 cm-1) activated by the double resonance Raman scattering (DRRS) process and revealed electron-phonon interaction in edges. We further visualize the edge-induced band bending region by using this DRRS peak and electronic transition region using the electron density-sensitive Raman peak at 406 cm-1. The power of TERS demonstrated in MoS2 can also be extended to other 2D materials, which may guide the defect engineering for desired properties.

J Am Chem Soc ; 140(42): 13680-13686, 2018 10 24.
Artigo em Inglês | MEDLINE | ID: mdl-30280886


Precise measurement of the temperature right at the surface of thermoplasmonic nanostructures is a grand challenge but extremely important for the photochemical reaction and photothermal therapy. We present here a method capable of measuring the surface temperature of plasmonic nanostructures with surface-enhanced Raman spectroscopy, which is not achievable by existing methods. We observe a sensitive shift of stretching vibration of a phenyl isocyanide molecule with temperature (0.232 cm-1/°C) as a result of the temperature-dependent molecular orientation change. We develop this phenomenon into a method capable of measuring the surface temperature of Au nanoparticles (NPs) during plasmonic excitation, which is validated by monitoring the laser-induced desorption process of the adsorbed CO on Au NP surface. We further extend the method into a more demanding single living cell thermometry that requires a high spatial resolution, which allows us to successfully monitor the extracellular temperature distribution of a single living cell experiencing cold resistance and the intracellular temperature change during the calcium ion transport process.

Nanoscale ; 10(9): 4398-4405, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29451566


Tip-enhanced Raman spectroscopy (TERS), known as nanospectroscopy, has received increasing interest as it can provide nanometer spatial resolution and chemical fingerprint information of samples simultaneously. Since Ag tips are well accepted to show a higher TERS enhancement than that of gold tips, there is an urgent quest for Ag TERS tips with a high enhancement, long lifetime, and high reproducibility, especially for atomic force microscopy (AFM)-based TERS. Herein, we developed an electrodeposition method to fabricate Ag-coated AFM TERS tips in a highly controllable and reproducible way. We investigated the influence of the electrodeposition potential and time on the morphology and radius of the tip. The radii of Ag-coated AFM tips can be rationally controlled at a few to hundreds nanometers, which allows us to systematically study the dependence of the TERS enhancement on the tip radius. The Ag-coated AFM tips show the highest TERS enhancement under 632.8 nm laser excitation and a broad localized surface plasmon resonance (LSPR) response when coupled to a Au substrate. The tips exhibit a lifetime of 13 days, which is particularly important for applications that need a long measuring time.

Nat Commun ; 8: 14891, 2017 03 28.
Artigo em Inglês | MEDLINE | ID: mdl-28348368


Surface-enhanced Raman scattering (SERS) spectroscopy has attracted tremendous interests as a highly sensitive label-free tool. The local field produced by the excitation of localized surface plasmon resonances (LSPRs) dominates the overall enhancement of SERS. Such an electromagnetic enhancement is unfortunately accompanied by a strong modification in the relative intensity of the original Raman spectra, which highly distorts spectral features providing chemical information. Here we propose a robust method to retrieve the fingerprint of intrinsic chemical information from the SERS spectra. The method is established based on the finding that the SERS background originates from the LSPR-modulated photoluminescence, which contains the local field information shared also by SERS. We validate this concept of retrieval of intrinsic fingerprint information in well controlled single metallic nanoantennas of varying aspect ratios. We further demonstrate its unambiguity and generality in more complicated systems of tip-enhanced Raman spectroscopy (TERS) and SERS of silver nanoaggregates.

Anal Chem ; 87(2): 1058-65, 2015 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-25494875


Noble metal nanoparticles have unique localized surface plasmon resonance (LSPR), leading to their strong absorption and scattering in the visible light range. Up to date, the common practice in the selection of nanoparticles for a specific application is still based on the measured extinction spectra. This practice may be erroneous, because the extinction spectra contain both absorption and scattering contribution that may play different roles in different applications. It would be highly desirable to develop an efficient way to obtain the absorption and scattering spectra simultaneously. Herein, we develop a method to use the experimentally measured extinction and scattering signals to extract the absorption and scattering spectra that is in excellent agreement with that simulated by discrete dipole approximation (DDA). The heating curve measurement on the three types of gold nanorods, with almost the same extinction spectra but different absorption and scattering contribution, convincingly reveals an excellent correlation between the heating effect and the absorption strength rather than the extinction strength. The result demonstrates the importance to obtain the scattering and absorption spectra to predict the potential application for different types of nanoparticles, which in turn will screen efficiently nanoparticles for a specific application.