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Title: Radiative interactions with micromachined surfaces: Spectral polarized emittance

Abstract

The spectral, angular, polarized emittance (SAPE) is a simple means for observing the allowed electromagnetic energy states associated with periodic structures whose dimensions are comparable to the wavelength of the observed light. Other methods for measuring absorption are far more time consuming when a broad survey is of interest. An extensive body of SAPE data was obtained on 350-- 400{degrees}C intrinsic silicon lamellar gratings. Current approximations to the vector wave equation such as guided wave, modal and Bloch wave methods provided insight into our experiments. A qualitative picture of the stationary electromagnetic states (SES) of lamellar gratings has been developed which agrees with experiment for a number of polarizations, and angular orientations of the emission k vector relative to the gratings. However, one type of emission does not fit any simple model we have examined and raises intriguing questions about emission from grating structures. A new, higher angular resolution emissometer (0.8{degrees} instead of 5{degrees}) has been completed. This system significantly increases the wavelength range from the current 3--14 {mu}m range to 2-25{mu}m, a doubling of the spectral regime. The system is currently in a shakedown'' mode. Preliminary data indicates that the new emissometer meets the design goals. 24 refs., 10more » figs.« less

Authors:
Publication Date:
Research Org.:
Pennsylvania Univ., Philadelphia, PA (United States). Dept. of Electrical Engineering
Sponsoring Org.:
USDOE; USDOE, Washington, DC (United States)
OSTI Identifier:
6257052
Report Number(s):
DOE/ER/13964-3; CONF-9105275-1
ON: DE92001742
DOE Contract Number:
FG02-88ER13964
Resource Type:
Conference
Resource Relation:
Conference: Micro-macro studies of multiphase media, Argonne, IL (United States), 9-11 May 1991
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 36 MATERIALS SCIENCE; SILICON; EMISSIVITY; ANALYTICAL SOLUTION; DIFFRACTION GRATINGS; ELECTROMAGNETIC RADIATION; ELLIPSOMETERS; HIGH TEMPERATURE; MEASURING METHODS; POLARIZATION; PROGRESS REPORT; SURFACES; THERMAL RADIATION; DOCUMENT TYPES; ELEMENTS; GRATINGS; MEASURING INSTRUMENTS; OPTICAL PROPERTIES; PHYSICAL PROPERTIES; POLARIMETERS; RADIATIONS; SEMIMETALS; SURFACE PROPERTIES; 664200* - Spectra of Atoms & Molecules & their Interactions with Photons- (1992-); 360606 - Other Materials- Physical Properties- (1992-)

Citation Formats

Zemel, J.N. Radiative interactions with micromachined surfaces: Spectral polarized emittance. United States: N. p., 1991. Web.
Zemel, J.N. Radiative interactions with micromachined surfaces: Spectral polarized emittance. United States.
Zemel, J.N. 1991. "Radiative interactions with micromachined surfaces: Spectral polarized emittance". United States. doi:. https://www.osti.gov/servlets/purl/6257052.
@article{osti_6257052,
title = {Radiative interactions with micromachined surfaces: Spectral polarized emittance},
author = {Zemel, J.N.},
abstractNote = {The spectral, angular, polarized emittance (SAPE) is a simple means for observing the allowed electromagnetic energy states associated with periodic structures whose dimensions are comparable to the wavelength of the observed light. Other methods for measuring absorption are far more time consuming when a broad survey is of interest. An extensive body of SAPE data was obtained on 350-- 400{degrees}C intrinsic silicon lamellar gratings. Current approximations to the vector wave equation such as guided wave, modal and Bloch wave methods provided insight into our experiments. A qualitative picture of the stationary electromagnetic states (SES) of lamellar gratings has been developed which agrees with experiment for a number of polarizations, and angular orientations of the emission k vector relative to the gratings. However, one type of emission does not fit any simple model we have examined and raises intriguing questions about emission from grating structures. A new, higher angular resolution emissometer (0.8{degrees} instead of 5{degrees}) has been completed. This system significantly increases the wavelength range from the current 3--14 {mu}m range to 2-25{mu}m, a doubling of the spectral regime. The system is currently in a shakedown'' mode. Preliminary data indicates that the new emissometer meets the design goals. 24 refs., 10 figs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1991,
month = 1
}

Conference:
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  • This report covers work aimed at obtaining additional information on the electromagnetic emissions from heated, microstructured surface. Earlier work had established that thermal emission was a useful means for obtaining broad band information on the electromagnetic properties of these surfaces. Among the earlier results obtained was a demonstration that there was an increased amount of coherent radiation emitted from these structures. Also found was that the nature of the emission was dependent on the carrier concentration of the emitting material as well as the details of the geometry of surface structures. Described in this report is the normal polarized emissivitymore » of undoped silicon gratings of different dimensions measured with a new emissometer. Deep grating fabrication, formation of a titanium silicide layer, and wafer cutting is described.« less
  • Experimental results of thermal emittance from lamellar gratings in intrinsic silicon are presented along with a theoretical discussion. For azimuthal angular directions in shallow gratings, enhanced thermal emission plateaus and maxima are observed. In the case of [ital p]-polarized emission in the [Phi] = 90[degree] azimuth (parallel to the grating vector), the plateau arises when two diffractive orders can be supported; it lies between the Rayleigh polar angles corresponding to the forbidden zone. The experimentally observed angular dependence of the [ital s]-polarized emission for the [Phi] = 90[degree] azimuth has been compared with a coupled-wave calculation, and a respectable agreementmore » has been obtained. For the experimentally observed s-polarized emission in the [Phi] = 0[degree] azimuth (perpendicular to the grating vector), there is an onset of enhanced emission at the polar angles that follows a simple empirical relation unrelated to any known diffraction law. By contrast, the [ital p]-polarized emission in the [Phi] = 0[degree] azimuth shows relatively little structure. These data illustrate the value of thermal emission for surveying multivariate absorption processes involving microstructures.« less
  • Experimental results of thermal emittance from deep gratings are presented along with a theoretical discussion. We have found that for a certain grating geometry thermal emission peaks coincide with the cutoff frequencies of slab waveguides. The coincidence was found with {ital s}- but not {ital p}-polarized emission. This suggests that coupling between grating fins for {ital s}-polarized emission is small. It was also found that emission peaks do not correlate directly with the well-known grating equation for these deep gratings.
  • Coatings or surface modifications are needed to improve the surface emissivity of materials under consideration for TPV radiator applications to a value of 0.8 or higher. Vacuum plasma spray coatings (ZrO{sub 2} + 18% TiO{sub 2} + 10% Y{sub 2}O{sub 3}, ZrC, Fe{sub 2}TiO{sub 5}, ZrTiO{sub 4}, ZrO{sub 2} + 8% Y{sub 2}O{sub 3} + 2% HfO{sub 2}, and Al{sub 2}O{sub 3} + TiO{sub 2}) and a chemical vapor deposited coating of rhenium whiskers were used to increase the surface emissivity of refractory metal and nickel-base materials. Emittance measurements following 4000 hours of vacuum annealing at 1100 C show thatmore » only the ZrO{sub 2} + 18% TiO{sub 2} + 10% Y{sub 2}O{sub 3}, ZrC, and Al{sub 2}O{sub 3} + TiO{sub 2} coatings have the desired thermal stability, and maintain emissivity values higher than 0.8. These coatings are graybody emitters, and provide a high emissivity value in the wavelength range that is relevant to the TPV cells. The highest emissivity values were observed for the Al{sub 2}O{sub 3} + TiO{sub 2} coatings, with post-anneal values higher than graphite.« less
  • No abstract prepared.