Optical Properties of Metallic Surfaces, Small Particles and Composite Coatings for Solar Energy Conversion Applications. Final Technical Report, April 1, 1977-August 31, 1979

摘要

The properties of heterogeneous materials appear to be central to solar energy research. Furthermore, it is becoming clear that materials with heterogeneity of widely varying sorts may be technologically useful, from amorphous films to composites of microcrystallites. A combined theoretical-experimental program to understand the optical properties of heterogeneous materials is described. The primary experimental quantity measured has been the optical response from the visible to the far infrared. The production, structure and optical properties of composite metal-insulator cermet films have been investigated. Using effective medium theories the optical properties were calculated and compared to experimental measurements. Studies of the design of spectrally selective solar energy absorbers using cermet films were made both experimentally and with computer simulations. Composite films were produced by controlled coevaporation of the metal and an insulator. The materials used include Ni, V, Fe, and Pt metals with dielectrics Al sub 2 O sub 3 , SiO sub 2 , MgO and ZrO sub 2 . Some preliminary results on amorphous aluminium are described. Crystalline aluminum has the disadvantage that its reflectance in the visible is smaller than those of some good free electron metals such as silver, which is unsuitable as a front surface reflector because of rapid corrosion. Interband transitions depress the reflectivity of aluminum in the solar spectrum.If these interband transitions could be eliminated and the free electron reflectance of aluminum obtained, a superior reflective coating would result. Experimental results suggest that amorphous aluminum films can be made by impurity stabilization. (ERA citation 05:015433)