10:00 AM - 10:15 AM
▲ [6a-A410-4] Tip-enhanced Raman scattering microscope using quartz-tuning-fork AFM probe
Keywords:Enhanced Raman, Scanning Probe Microscopy, Carbon Materials
Tip-enhanced Raman scattering (TERS) microscopy is one of the powerful scanning probe microscopy, which enables Raman analysis at the nanoscale. Typically, the distance between the metal tip and samples are controlled by contact-mode atomic force microscopy (AFM). However, the contact-mode AFM can limit the range of applications. It is difficult to measure samples which are soft or unfixed on a glass substrate. Moreover, a laser beam to detect a cantilever deflection can interfere with Raman measurements in visible wavelengths. We believe that the introduction of advanced AFMs can expand the applications and contribute to commercialization.
Here, we present a TERS microscope using a quartz-tuning-fork (QTF) AFM probe. The QTF is known as one of the probes for frequency-modulation AFM. The QTF has a quite high spring constant (> 103 N/m), which realizes an extremely small oscillation amplitude below 1 nm in dynamic-mode operation. The dynamic-mode operation with small amplitude can enables us to measure soft or unfixed samples by the sufficient Raman enhancement. Moreover, the piezoelectric QTF is a non-optical detection scheme, and does not affect Raman measurements.
We have developed a QTF- TERS probe on which a metal coated cantilever is mounted as a tip. First, we report simultaneous measurements of TERS spectrums and forces between the tip and samples. Single-walled carbon nanotubes (CNTs) are employed as the sample, and excited by a laser of wavelength λ=488 nm. TERS spectrums and the tip-sample force as a resonance frequency shift Δf of the QTF were measured simultaneously, changing the tip-sample distance z. As z approached to 0, the G band intensity I exponentially increased at z where the Δf switched from a negative to a positive value. This means that the effective Raman enhancement is expected in the repulsive tip-sample force region. Although our CNTs are not fixed on the substrate, we have also succeeded to observe TERS images with a spatial resolution of approximately 16 nm.
Our TERS microscope is now extended for experiments using deep-ultraviolet (DUV) light. We expect that a DUV-TERS microscope is useful for studying bio-molecules or wide-gap semiconductors at the nanoscale, because a resonant Raman scattering is expected due to the absorption in the DUV region. As a preliminary result, we have succeeded to observe DUV-TERS spectrums on a monolayer graphene by using an aluminum tip excited by a laser of wavelength λ=266 nm. The details are shown in the presentation.
Here, we present a TERS microscope using a quartz-tuning-fork (QTF) AFM probe. The QTF is known as one of the probes for frequency-modulation AFM. The QTF has a quite high spring constant (> 103 N/m), which realizes an extremely small oscillation amplitude below 1 nm in dynamic-mode operation. The dynamic-mode operation with small amplitude can enables us to measure soft or unfixed samples by the sufficient Raman enhancement. Moreover, the piezoelectric QTF is a non-optical detection scheme, and does not affect Raman measurements.
We have developed a QTF- TERS probe on which a metal coated cantilever is mounted as a tip. First, we report simultaneous measurements of TERS spectrums and forces between the tip and samples. Single-walled carbon nanotubes (CNTs) are employed as the sample, and excited by a laser of wavelength λ=488 nm. TERS spectrums and the tip-sample force as a resonance frequency shift Δf of the QTF were measured simultaneously, changing the tip-sample distance z. As z approached to 0, the G band intensity I exponentially increased at z where the Δf switched from a negative to a positive value. This means that the effective Raman enhancement is expected in the repulsive tip-sample force region. Although our CNTs are not fixed on the substrate, we have also succeeded to observe TERS images with a spatial resolution of approximately 16 nm.
Our TERS microscope is now extended for experiments using deep-ultraviolet (DUV) light. We expect that a DUV-TERS microscope is useful for studying bio-molecules or wide-gap semiconductors at the nanoscale, because a resonant Raman scattering is expected due to the absorption in the DUV region. As a preliminary result, we have succeeded to observe DUV-TERS spectrums on a monolayer graphene by using an aluminum tip excited by a laser of wavelength λ=266 nm. The details are shown in the presentation.