Surface enhanced Raman scattering (SERS) signal fluctuate due to position between near field and adsorbed molecules. According to past works, the frequency of the bright period follows a power law. The purpose of this study is to analyze the blinking behavior of SERS spectra by Density-Based Spatial Clustering Analysis with Noise (DBSCAN) with temporal resolution higher than a conventional spectroscopic method. As a result, it was confirmed that the SERS blinking actually follows the power law even under adverse conditions such as extremely low sample concentration and a very short exposure time of 10 ms.
Wide-band gap semiconductor nanoparticles has been the focus of interest recently, due to their validity for energy creations, decomposition of harmful substances, boosting useful chemical reactions etc. In this work, we will evaluate optical characteristics of a single semiconductor nanoparticle via broadband-UV Rayleigh scattering spectroscopy and photoluminescence (PL) spectroscopy. Rayleigh scattering spectroscopy reveal the bandgap energies while PL spectroscopy provide the information on exciton generation efficiencies as well as existence of surface defects.
In our microscopy setup, a broadband white light source (LDLS) was collimated and obliquely illuminated on the sample to realize dark-field illumination to distinguish the position of individual particles in the microscopic image. Scattering from a single nanocrystal was collected by an reflection-type objective lens (NA0.5) and introduced to a spectrometer and detected by an EMCCD camera. The spectrometer was designed specifically for UV-DUV broadband spectroscopy and imaging. For photoluminescence (PL) measurements, we introduce 320 nm (CW) laser for excitation. The sample is enclosed in a temperature-controlled cell ranging from room temperature to 77K.
We especially focus on titanium dioxide (TiO2), a typical photocatalyst, and tangusten trioxide (WO3) which is one of the candidate for decomposition of water into oxygen and hydrogen by a visible or longer wavelength light. The band structure of nano-particles is changed when the size is smaller than several tens of nanometers, due to crystallinity and quantum size effects. PL of single zinc oxide (ZnO) nanoparticles were also measured together with the temperature effects. The spectra obtained from a single nanoparticle is different from aggregates both for exciton PL and defects PL.
We investigated two-dimensional lipid bilayers by spectroscopic imaging with surface enhanced Raman spectroscopy (SERS). A DSPC lipid bilayer incubated on a glass substrate was coated with a thin layer of silver. Due to the strong electromagnetic enhancement of the silver film and the affinity to lipid molecules, the Raman spectrum of a single bilayer was obtained in a 1 s exposure time with 0.1 mW of incident laser power. In the C-H vibrational region of the spectra, which is sensitive to bilayer configurations, a randomly stacked area was dominated by the CH3 asymmetric-stretch mode, whereas flat areas including double bilayers showed typical SERS spectra. The spectral features of the randomly stacked area are explained by the existence of many free lipid molecules, which is supported by DFT calculations of paired DSPC molecules. Our method can be applied to reveal the local crystallinity of single lipid bilayers, which is difficult to assess by conventional Raman imaging.
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