Metal nanoparticles (NPs) can increase the absorption of light within semiconductors and hence improve the efficiency of solar cells. We experimentally investigate the effect that gold and silver NPs have on the reflectance of silicon wafers. The NPs are fabricated using the low cost, large area technique of thermal dewetting. We show that a dielectric spacer layer between the NPs and the semiconductor is required to achieve a net reduction of reflection. Furthermore, the optimum thickness of the spacer layer is found to be independent of NP size and metal type.
A customized planetary rotation stage has been fitted to a commercial ion beam sputter coater to enable the deposition of
high uniformity, multilayer optical coatings on large substrates without the use of masks.
Uniformity in this system achieved by sequentially depositing each layer in two fixed locations in the sputtered particle
plume where the geometry of the natural thickness distributions on a rotating substrate in these locations are of
complementary shape and add to produce an overall uniform layer. The modified planetary stage allows substrate
rotation about its own axis at any fixed position of the substrate centre about the axis of the planetary system. The
suitable locations in the plume of each material that allow maximum uniformity are found by trial and error refinement
of locations obtained by modelling of the plume distribution and expected thickness distributions. Ellipsometric
monitoring of the thickness of the layer in each fixed position is used to determine the precise ratio of thicknesses in each
location needed to obtain the correct total layer thickness simultaneously with high uniformity.
The system has thus far enabled single wavelength antireflection coatings of less than 0.001% reflectance to be
fabricated over 270 mm diameter substrates. This requires the film thickness uniformity on all layers to be less than ± 0.2%. In addition, 4-layer, dual wavelength antireflection coatings have been fabricated with less than 0.01% reflectance
on both wavelengths over similar substrate dimensions.
NASA's Space Interferometer Mission (SIM) PlanetQuest requires, among other things, very precise retroreflectors. The CSIRO Australian Centre for Precision Optics (ACPO) has developed Double Corner Cubes (DCCs) to meet the requirements. The DCC consists of an assembly of three 30o wedged prisms optically contacted to a 132 mm diameter flat base plate. The material for all components was Zerodur. The specifications for the DCC were extremely challenging and posed considerable difficulties in the fabrication, coating, assembly, alignment and metrology. Some of the key specifications included: flatness of all reflecting surfaces to be ~ 10 nm peak to valley (P-V); dihedral angle errors < 0.5 arc seconds; collocation of the vertices of the two corner cubes within a circle of 5 um radius; all reflecting surfaces to be gold coated for a final microroughness < 0.5 nm rms; the clear or working aperture extended to within 0.2 mm of all physical edges; and the assembly had to withstand large vibrational forces. CSIRO delivered to JPL a DCC that was used as the primary unit in the so-called Kite testbed to satisfactorily meet the demonstration requirements of the SIM Milestone 8. This paper will discuss some of the procedures used to realize the DCCs and will show examples of results achieved.
The Space Interferometry Mission (SIM) PlanetQuest is managed by the Jet Propulsion Laboratory for the National Aeronautics and Space Administration. SIM requires, among other things, high precision double cube-corner retroreflectors. A test device has recently been fabricated for this project with demanding specifications on the optical surfaces and gold reflective coatings. Several gold deposition techniques were examined to meet the stringent specifications on uniformity, optical properties, micro-roughness and surface quality. We report on a comparative study of optical performance of gold films deposited by resistive and e-beam pvaporation, including measurements of the scattering from the coated surfaces. The effects of oxygen bombardment and titanium under-layer on optical properties and adhesion were evaluated. The influence of surface preparation on the optical properties was examined also.
Narrow bandpass Fabry-Perot etalons are widely used in solar astronomy for spectroscopic imaging. Solid electro-optically tunable filters made of thin, single-crystal lithium niobate are presented in this article. The pass-band is typically ~0.02nm at 550nm. We describe customized corrective and high-reflectivity optical coatings designed and manufactured to tailor the filter for the specific application. Spectral reflectance is calculated to satisfy wavelength requirements and to achieve optimal optical performance. The measured optical thickness of the lithium niobate wafer is an important factor in determining the optimal design of the etalon mirrors. Out-of-band rejection and bandwidth requirements are also taken into account, as well as the influence of the spectral properties of a high-order filter which blocks adjacent etalon orders. Design customization is particularly important in the case of tandem and double-pass etalons.
The issue of low emittance in angular selective window systems is discussed in the context of the overall aims of controlling glare and lowering solar gains while maintaining a clear view. Low e adds considerably to the overall performance of the window. The spectral dependence of both angular selectivity and overall transmittance in single layer anisotropic metal-insulator films needed to be improved. While these have excellent visible properties, they have high infrared transmittance and hence the window has high emittance. Results on coatings and systems set up to give the glazing a low e are examined. It is found that the visible performance is not impaired but the solar and thermal performance are improved substantially. Two methods of achieving a low emittance are discussed.
Theories developed to understand angular selective films, recent new deposition procedures , the structural information on the resulting films, and new advances in effective medium theories have together provided the insights into controlling the spectral optical response of cermets to a degree not previously realized. The key is understanding the resonance characteristics of cermets. Several factors play a role, but three have a prime influence. They are the spatial distribution of the metal particles (even more important than total content), the dielectric constant of the host material and the metal itself.
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