We have excited surface plasmons in a YBCO thin film at different temperatures using attenuated total reflection of light. The 300 nm thick c-axis film was fabricated using pulsed laser deposition onto an MgO (100) substrate with 248 nm KrF excimer radiation. Critical temperature of the film was 89.6 K and its roughness, as shown by atomic force microscopy, 20 nm rms, without droplets over areas of 10 micrometer by 10 micrometer. The sample was mounted in Otto geometry on a cooled stage which allowed the temperature to be varied between 300 K and 70 K. An infrared HeNe laser at 3392 nm was used to excite the surface plasmons. The dielectric function of the film was determined between room temperature and 80 K. The imaginary part of the dielectric function decreased substantially with reduction in temperature. Results obtained were: (epsilon) <SUB>r</SUB> equals -24.1 plus 0.0013T and (epsilon) <SUB>i</SUB> equals 7.7 plus 0.067T where T is the temperature in Kelvin. The ratio (epsilon) <SUB>i</SUB><SUP>300</SUP>/(epsilon) <SUB>i</SUB><SUP>80</SUP> at 2.13 is less than the resistance ratio R<SUP>300</SUP>/R<SUP>80</SUP> at 2.81. An explanation is offered in terms of two temperature independent mechanisms operative at optical frequencies: enhanced Rayleigh scattering of surface plasmons at grain boundaries and intraband/interband transitions. The real part of the dielectric function, (epsilon) <SUB>r</SUB>, was found to be only slightly temperature dependent. It was, however, highly sample dependent when comparison was made with the results of other films, a feature attributed to surface and grain boundary contamination.
Visible light is emitted from roughened metal-oxide-metal tunnel junctions subjected to a small (2 - 4 V) dc bias. The color of the emitted light is voltage tunable but device quantum efficiency is generally very low (10<SUP>-5</SUP> - 10<SUP>-7</SUP>). The optical emission is due to the roughness induced scattering of electronically excited surface plasmon polaritons. The characteristics of the surface roughness are clearly important in determining the overall device efficiency and spectral output. With a view to better understanding and improving the efficiency we have examined the surface topography of variously roughened devices and relate this to the optical output. For example, we have roughened devices by means of holographic crossed diffraction grating substrates which possess surface topography of greater rms roughness height and larger transverse correlation length than that of devices roughened by a pre-deposited CaF<SUB>2</SUB> layer. Devices roughened by means of a particulate aluminum substrate are also discussed.