Yuriko Tanaka

Apertureless near-field optical microscopy with differential and close-proximity detection

A new method of apertureless near-field optical microscopy that combines laterally differential detection with close-proximity detection has been developed. The laterally differential detection allows the light scattered from the probe apex to be distinguished from the background light. The close-proximity detection is done using a microfabricated photosensitive cantilever; it is thought to be a form of heterodyne detection, which provides a high signal level. This method makes it possible to detect the light scattered from the probe apex, which depends on the coupling between the probe apex dipole and the sample feature dipole.

Imaging of optical and topographical distributions by simultaneous near field scanning optical/atomic force microscopy with a microfabricated photocantilever

Simultaneous near field scanning optical and atomic force microscopy with a microfabricated photocantilever reveal both optical and topographical distributions. The cantilever tip changes the evanescent field into scattering light, and this scattering light is detected with a photodiode fabricated in the tip of the cantilever. The cantilever deflection signal leads to atomic force images. The resolution for imaging the evanescent field variation was 20 nm (λ/30). The near field optical and atomic force images indicate that the same point of the cantilever tip generates both optical and atomic force signals. This method is a new approach to optical and topographical microscopy with nanometer resolution.

MICROFABRICATION OF MICROTIP ON PHOTOCANTILEVER FOR NEAR-FIELD SCANNING MICROSCOPY AND INVESTIGATION OF EFFECT OF MICROTIP SHAPE ON SPATIAL RESOLUTION

We experimentally investigated the dependence of spatial resolution on the shape of a microtip on our photocantilever, in order to improve the spatial resolution of near-field scanning optical microscopy. Two different cone angles of silicon-dioxide microtips were microfabricated by a new fabrication process. The experimental results, which indicate there is a relationship between the spatial resolution and cone angle of the microtip, were interpreted by calculations based on a simple theoretical model.

Detection of an infrared near‐field optical signal by attaching an infrared‐excitable phosphor to the end of a photocantilever

To improve the signal‐to‐noise ratio of near‐field scanning optical microscopy, we propose attaching an infrared‐excitable phosphor (IEP) to a photocantilever. One source of noise is the light scattered from locations on the sample surface other than that of the probe tip. By detecting only the light scattered from the tip, we can obtain a near‐field optical signal without noise. We attached an IEP particle to a photocantilever to convert infrared light to visible light and we used 1550‐nm infrared illumination, so the light scattered from the sample was only infrared. The silicon photodiode of the photocantilever is 106 times less sensitive to infrared light than to visible light. As a result, only the converted visible light from the IEP particle, i.e. the signal containing the near‐field optical information from the tip, was detected. We verified that the photocantilever detected the signal in the evanescent light produced by infrared illumination and that the detected signal was the light converted by the IEP. The experimental results show the feasibility of detecting infrared light and not the background light through the use of the IEP.