<title>Near-field light microscopy with SEM light generation</title>

Abstract

ABSTRACT A new near field light microscope with SEM light generation (NFLEM) has been developed on the basis ofmodified SEM (Hitachi ILU-12A). The scanning electron beam of the SEM passed trough thin luminescent film coating a sample generates a small light spot. The light transmitted trough the sample is registered by PMT. The wavelength of the light can be easy modified (from infrared to X-ray) by changing the luminescentfilm. The images of test objects (latex O.1im, thin metal films) are obtained by the microscope.Keywords: probe microscopy, near field optical microscopy, scanning electron microscopy, biology. hi a near field scanning optical microscope (NSOM)' working in illumination mode object is scanned by a small light source. The NSOM resolution is determined, mainly, by size ofthe scanning lightsource. Many different methods are used to fabricate the small light source. Most commonly, a lightpassed through small aperture is used as a light source. There are many different methods of the aperturefabrication, such as capfflary pulling2, etching a various optical fibers'4, forming a small hole in metal5.As a small size scanning light sources are also used: a tip of atomic force microscopy6, small latexparticle7, and small drop ofluminescent substance in micropipette illuminated by laser lights. However, allthe methods do not allow to obtain a light source smaller than 100-300 A.Inour lab have been proposed anew method ofgeneration of small light spot. A scanning electron beam of conventional scanning electronmicroscope (SEM) passed through thin luminescent film generates the light spot of very small size. Themain advantages of this method are the veiy small size of electron beam spot of modem SEM (a fewAngctroms), and high energy of electrons that allows generating a light of wide spectral range (up to X-rays). Now we describe the SEM modifications and preliminary experimental results obtained by themethod.BACKGROUNDS AND MATERIALSIf a sample of SEM is covered by thin luminescent film, an incident electron beam will generate aluminescent light. The wavelength of light is determined by the luminiferous substance and energy ofincident electron beam. The spot size of luminescent light is defmed by electron spot size, luminescentfilm thickness and electron scattering power ofthe film. The light passed through the sample is registeredby photodetector that allow imaging the sample in near-field optical microscopy manner. To perform theexperiment, electron microscope 'Hitachi HU-12A' with scanning attachment 'HSE-2' (electron beamsize is about 30 A) has been used in our lab. The microscope has been modified to increase its sensitivity.A metal mirror and photodiode were mounted under a SEM sample holder in the near proximity to thespecimen. The mirror reflects the light passed through the sample in the photodiode. Electrical signalfrom photodiode is amplified by additional preamplifier, processed and visualized by SEM electronequipment.