Spectral and Spatial Coherent Emission of Thermal Radiation from Metal- Semiconductor Nanostructures

摘要

The spectral and spatial radiative properties of coherent thermal emission in the mid-infrared and far-infrared through the use of micro- structured and nano-structured metal-semiconductor materials were demonstrated experimentally. Using an implementation of the Rigorous Coupled Wave Analysis (RCWA) numerical technique and Computer Simulation Technology (CST) electromagnetic modeling software, two structures were designed to selectively emit at mid- and far-IR wavelengths: a one-dimensional (1-D) truncated multilayer resonator and a three-dimensional (3-D) hybrid photonic crystal- multilayer (PC-multilayer) structure. A High Impulse Power Magnetron Sputtering (HIPIMS) deposition technique was used to fabricate two silver-germanium-silver (Ag-Ge-Ag) resonating structures with layer thicknesses of 6-240-160 nm for one sample and 6-700-200 nm for the other. The design thicknesses of each sample were verified through both reflectance and standard spectral ellipsometric measurements at wavelengths from 2-15 micrometers. Reflectance measurements demonstrated spectrally selective absorption at the designed IR wavelengths whose general behavior was largely unaffected by a wide range of incident angles. Ellipsometric measurements showed significant disagreement between HIPIMS-deposited material properties and bulk values found in literature. Radiance measurements taken at various high temperatures showed that spectral emittance was directly derived and compared to the emittance inferred from reflectance measurements. Inferring emittance can help to approximate the expected emission from a structure, but it is not an exact method of determining the actual emittance of a thermal source. Using CST, the PC- multilayer structure was modeled to examine its spatial coherence. Initial fabrication results of the PC-multilayer involving both HIPIMS deposition of a Ge-Ag-Ge-Ag (4-12-270-200 nm) multilayer and focused ion beam milling of a square hole array also are presented.