Tip-Enhanced Raman Scattering Imaging of Two-Dimensional Tungsten Disulfide with Optimized Tip Fabrication Process

We successfully achieve the tip-enhanced nano Raman scattering images of a tungsten disulfide monolayer with optimizing a fabrication method of gold nanotip by controlling the concentration of etchant in an electrochemical etching process. By applying a square-wave voltage supplied from an arbitrary waveform generator to a gold wire, which is immersed in a hydrochloric acid solution diluted with ethanol at various ratios, we find that both the conical angle and radius of curvature of the tip apex can be varied by changing the ratio of hydrochloric acid and ethanol. We also suggest a model to explain the origin of these variations in the tip shape. From the systematic study, we find an optimal condition for achieving the yield of ~60% with the radius of ~34 nm and the cone angle of ~35°. Using representative tips fabricated under the optimal etching condition, we demonstrate the tip-enhanced Raman scattering experiment of tungsten disulfide monolayer grown by a chemical vapor deposition method with a spatial resolution of ~40 nm and a Raman enhancement factor of ~4,760

Antenna-Enhanced Photocurrent Microscopy on Single-Walled Carbon Nanotubes at 30 nm Resolution

We present the first photocurrent measurements along single carbon nanotube (CNT) devices with 30 nm resolution. Our technique is based on tip-enhanced near-field optical microscopy, exploiting the plasmonically enhanced absorption controlled by an optical nanoantenna. This allows for imaging of the zero-bias photocurrent caused by charge separation in local built-in electric fields at the contacts and close to charged particles that cannot be resolved using confocal microscopy. Simultaneously recorded Raman scattering images reveal the structural properties and the defect densities of the CNTs. Antenna-enhanced scanning photocurrent microscopy extends the available set of scanning-probe techniques by combining high-resolution photovoltaic and optical probing and could become a valuable tool for the characterization of nanoelectronic devices

Launching Propagating Surface Plasmon Polaritons by a Single Carbon Nanotube Dipolar Emitter

International audienceWe report on the excitation of propagating surface plasmon polaritons in thin metal films by a single emitter. Upon excitation in the visible regime, individual semiconducting single-walled carbon nanotubes are shown to act as directional near-infrared point dipole sources launching propagating surface plasmons mainly along the direction of the nanotube axis. Plasmon excitation and propagation is monitored in Fourier and real space by leakage radiation microscopy and is modeled by rigorous theoretical calculations. Coupling to plasmons almost completely reshapes the emission of nanotubes both spatially and with respect to polarization as compared to photoluminescence on a dielectric substrate