Microscope uses deep ultraviolet spectroscopy and near-field optics for high lateral resolution

The development of advanced nanometer-scale spectroscopy technologies that use shorter detection and excitation wavelengths has promise in semiconductor material characterization, as well as in gas sensing, molecular analysis and label-free live-cell imaging. But shorter wavelength light, such as deep ultraviolet light, cannot be used to conduct scanning microscopy over long periods of time due to the deterioration of optics, and they have low throughput and low pointing stability.

Ishii et al. conquered these problems using a design that combines deep ultraviolet spectroscopy with near-field optical microscope technology, with two negative feedback optical control systems adjusting for power and pointing stability. The device uses an optical fiber probe that is resistant to solarization, has a double-tapered structure and requires no metallic coating.

The device uses a 210 nm continuous-wave titanium-sapphire laser as the excitation source. The researchers tested the device by probing the ultra-wide bandgap semiconductor material aluminum gallium nitride while controlling the distance between the probe and the material to prevent a shallow depth of focus. They show effective individual visualizations of localization centers, with a lateral resolution higher than 150 nm.

The authors believe this work can be applied to deep-ultraviolet nanospectroscopic characterizations under cryogenic temperatures and magnetic fields, which may have potential biological and chemical applications. Their work also provides a way to apply the multi-mode methods currently available using the visible spectrum to expand to include deep ultraviolet wavelengths.

Source: “Pushing the limits of deep-ultraviolet scanning near-field optical microscopy,” by Ryota Ishii, Mitsuru Funato, and Yoichi Kawakami, APL Photonics (2019). The article can be accessed at https://doi.org/10.1063/1.5097865 .