INVESTIGATION OF THE ELECTRIC-FIELD DISTRIBUTION AT THE SUBWAVELENGTHAPERTURE OF A NEAR-FIELD SCANNING OPTICAL MICROSCOPE

The reflectivity of a 9 nm AlAs layer embedded in a GaAs matrix was me asured using a near-field scanning optical microscope. Results for fre shly cleaved surfaced are understood considering the electrostatic nat ure of the electric field in the near field of a subwavelength apertur e. The optical contrast arises from the different index of refraction of AlAs and GaAs, with topography associated effects playing no role. While keeping the wavelength of the incident radiation and the apertur e dimensions fixed, /E/ was mapped on planes perpendicular to the tip axis, as a function of the height of the tip above the sample. The res ults were compared with a finite element calculation for the scattered light. In the analysis, we model the sample with a position dependent dielectric constant. Good agreement between the model and the experim ental data was found. (C) 1997 American Institute of Physics.