Takayuki Umakoshi

Nanolight sources, which are based on resonant excitation of plasmons near a sharp metallic nanostructure, have attracted tremendous interest in the vast research fields of optical nanoimaging. However, being a resonant phenomenon, this ideally works only for one wavelength that resonates with the plasmons. Multiple wavelengths of light in a broad range confined to one spot within a nanometric volume would be an interesting form of light, useful in numerous applications. Plasmon nanofocusing can

Tip-enhanced Raman spectroscopy (TERS) offers one of the best techniques for optical analysis and imaging of samples at nanoscale. The most important point in TERS experiments is to obtain a high signal enhancement through a metallic nanotip. Compared with fully metallized tips, the tips that have only one metallic nanoparticle at the apex show better enhancement. Here, we demonstrate a new and simple way to fabricate metallic nanoparticles selectively at the tip apex through photoreduction. By

Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for analyzing chemical compositions at the nanoscale owing to near-field light localized at a metallic tip. In TERS, atomic force microscopy (AFM) is commonly used for tip position control. AFM is often controlled under the contact mode for TERS, whereas the tapping mode, which is another major operation mode, has not often been employed despite several advantages, such as low sample damage. One of the reasons is the low TERS signal inten

Plasmonics, particularly the one based on plasmon resonances in optical antennas for the excitation of localized and enhanced light fields, have enabled numerous nanophotonics applications over the past few decades. One of the most common applications is to generate a nanoscale light source through plasmon resonance. An alternative phenomenon that has recently gained increasing attention for creating nanoscale light sources is plasmon nanofocusing, in which an enhanced nanoscale light field is g

The high thermal conductivity of single-walled carbon nanotubes (SWCNTs) has gained much attention for their applications in potential thermal devices. Here, we investigate anharmonic effects, originated from phonon interactions, of SWCNT bundles by temperature dependent Raman imaging using our home-built mini cryostat system. The cryostat system is small enough to be mounted on a piezo scanner that suppresses thermal drift, enabling Raman imaging at different temperatures. We obtained Raman spe

High-speed atomic force microscopy (HS-AFM) is an indispensable technique in the field of biology owing to its imaging capability with high spatiotemporal resolution. Furthermore, recent developments established tip-scan stand-alone HS-AFM combined with an optical microscope, drastically improving its versatility. It has considerable potential to contribute to not only biology but also various research fields. A great candidate is a photoactive material, such as an azo-polymer, which is importan

An organic semiconductor film made of diphenyl derivative dinaphtho[2,3-<i>b</i>:2',3'-<i>f</i>]thieno[3,2-<i>b</i>]thiophene (DPh-DNTT) has high carrier mobility. However, this mobility may be greatly affected by the crystal orientation of the DPh-DNTT's first layer. Polarization Raman microscopy is widely used to quantitatively analyze the molecular orientation, and thus holds great potential as a powerful tool to investigate the crystal orientation of monolayer DPh-DNTT with high spatial reso

Near-field scanning optical microscopy (NSOM) is a super-resolution optical microscopy based on nanometrically small near-field light at a metallic tip. It can be combined with various types of optical measurement techniques, including Raman spectroscopy, infrared absorption spectroscopy, and photoluminescence measurements, which provides unique analytical capabilities to a variety of scientific fields. In particular, to understand nanoscale details of advance materials and physical phenomena, N

Visible light can interact efficiently with the vibronic and electronic systems of a sample and fetch rich information about the intrinsic features, such as the chemical, physical and biological properties of the sample. Optical techniques have therefore been convenient tools for a long time to analyze and image various materials. However, the spatial resolution in optical microscopy is restricted by the diffraction limit of light, making it impossible to study samples much smaller than the wave

Abstract Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for analyzing chemical compositions at the nanoscale owing to near-field light localized at a metallic tip. In TERS, atomic force microscopy (AFM) is commonly used for tip position control. AFM is often controlled under the contact mode for TERS, whereas the tapping mode, which is another major operation mode, has rarely been employed despite several advantages, such as low sample damage. One of the reasons is the low TERS signal

COA-Cl is a newly synthesized adenosine analogue that exhibits various physiological activities. Its angiogenic, neurotropic, and neuroprotective potencies make it promising for the development of medicines. In this study, we show Raman spectroscopic study of COA-Cl to elucidate molecular vibrations and related chemical properties. Density functional theory calculations were combined with the Raman spectroscopic data to understand the details of each vibrational mode. Comparative analysis with a

Tip-enhanced Raman spectroscopy (TERS) offers one of the best techniques for analysis and imaging of molecule structures at nanoscale spatial resolution. An important issue in TERS is to improve the detection sensitivity of inherently weak Raman scattering so as to observe varieties of materials. For enhancement of the Raman signal, fully metallized tips are utilized in TERS, which enhance signals through plasmon oscillation at the tip apex. However, length of metal along the tip axis is on the