Udo C. Pernisz

Indium-tin-oxide-coated glass as dichroic mirror for far-infrared electromagnetic radiation

We propose to utilize glass plates coated with indium tin oxide (ITO) as far-infrared dichroic mirrors, e.g., in optoelectronic terahertz spectroscopy for purposes such as electro-optic detection of terahertz radiation or in time-resolved experiments with pump pulses in the visible or near-infrared spectral range and probe pulses at terahertz frequencies. Measurements of the complex reflection and transmission coefficients in the spectral range from 0.1 to 2.8 THz indicate that commercially available ITO glass is suitable for this purpose.

Synthesis and characterization of nanoscale zinc oxide particles: I. laser vaporization / condensation technique

Abstract A method which combines laser vaporization of metal targets with controlled condensation in a diffusion cloud chamber is used to synthesize nanoscale metal oxide and metal carbide particles (10 – 20 nm). In this work we present the results for the synthesis and characterization of ZnO as an example of metal oxide nanoparticles. In part II (this issue), we present the results for silicon carbide nanoparticles synthesized using the same method described here.

Diffusion of Water Molecules in Amorphous Silica

The diffusive penetration of atmospheric water vapor into amorphous silica (a-SiO2) degrades the performance of electronic devices. In this letter, we calculate the range of activation energies for water diffusion in a-SiO2 such that the diffusion time through, for example, a 0.5-m protective layer is on the order of the decadal time scale, as required in typical applications. We find that for all practical purposes, silica composed of n -member rings is impenetrable to water vapor for n ≤ 5 . Thus, we conclude that the distribution of n-member rings in a-SiO2 and, specifically, the n >; 5 fraction is the critical parameter for predicting device performance.

Thermophotovoltaic energy conversion: Technology and market potential

This report contains material displayed on poster panels during the Conference. The purpose of the contribution was to present a summary of the business overview of thermophotovoltaic generation of electricity and its market potential. The market analysis has shown that the TPV market, while currently still in an early nucleation phase, is evolving into a range of small niche markets out of which larger‐size opportunities can emerge. Early commercial applications on yachts and recreational vehicles which require a quiet and emission‐free compact electrical generator fit the current TPV technology and economics. Follow‐on residential applications are attractive since they can combine generation of electricity with space and hot water heating in a co‐generation system. Development of future markets in transportation, both private and communal or industrial, will be driven by legislation requiring emission‐free vehicles, and by a reduction in TPV systems cost. As a result of ‘‘moving down the learning curve,...

Silicone polymers for optical films and devices

Silicones are among the most suitable materials for optical telecommunication devices due to their tolerance to high optical flux and their thermo-mechanical and environmental stability; they also have excellent processability. This work focuses on utilizing silicon-based branched resins and linear polymers for optical waveguides and switches where both refractive index and thermo-optic coefficient need to be controlled to the requirements of specific applications. Materials were synthesized with high optical transmission bands between 1.3 and 1.6 μm by varying the amount of aliphatic and aromatic C-H in the material. At the same time, the ratio of methyl to phenyl groups also controls the refractive index in the range of nD = 1.4 ... 1.6 precisely enough that both core and cladding components (Δn < 0.5%) can be obtained. Films of 5 to 20 μm thickness prepared on silicon substrates by spin-coating from solution were evaluated by measuring refractive index, thermo-optic coefficient, optical loss, and film uniformity both before and after exposure to high temperature and humidity. These films can be patterned through a number of techniques to form the required features. The resinous materials show very low birefringence and excellent resistance to heat and moisture.

Silicon carbide emitter and burner elements for a TPV converter

SiC bulk material is manufactured in the desired shape from an organopolysiloxane‐based pre‐ceramic polymer by pyrolysis. For an evaluation prototype, an emitter was made in form of a 7’’ tube with 1.5’’ diameter for operation at 1400 °C–1700 °C in conjunction with a GaSb photovoltaic cell (Eg=0.67 eV). The spectral dependence of the emittance of the SiC material in this temperature range was determined between 1.2 μm and 3.2 μm. Additionally, the surface morphology for a high density and a porous low density silicon carbide specimen are compared using SEM micrography. The range of material properties obtainable with this manufacturing process, and the high emissivity of the SiC, suggest that this material may be suitable for the emitter and burner elements in a thermophotovoltaic converter.

Molecular modeling of water diffusion in amorphous SiC

The diffusion of water in amorphous SiC (a-SiC) was investigated by molecular modeling methods based on density functional theory. It was assumed that the structure of a-SiC at the molecular level can be described by a model that takes into account a distribution of cage structures which consist of SiC units forming n-member rings from a suitable precursor in a chemical vapor deposition process. Electronic structure calculations are then performed to determine the energy barrier that the water molecule encounters when it penetrates through SiC rings of various sizes. It has been found that along its diffusion path through the SiC network the water molecule neither breaks up nor attaches itself to the SiC network and the energy barrier for diffusion depends mainly on the local SiC ring topology.

SiC IR emitter design for thermophotovoltaic generators

An improved ceramic spine disc burner/emitter for use in a thermophotovoltaic (TPV) generator is described. A columnar infrared (IR) emitter consisting of a stack of silicon carbide (SiC) spine discs provides for both high conductance for the combustion gases and efficient heat transfer from the hot combustion gases to the emitter. Herein, we describe the design, fabrication, and testing of this SiC burner as well as the characterization of the IR spectrum it emits. We note that when the SiC column is surrounded with fused silica heat shields, these heat shields suppress the emitted power beyond 4 microns. Thus, a TPV generator using GaSb photovoltaic cells covered by simple dielectric filters can convert over 30% of the emitted IR radiation to DC electric power.

Preparation of solar-grade amorphous silicon from fluorinated silanes☆

Abstract Fluorinated silane derivatives were synthesized and used as precursors for preparing amorphous silicon (a-Si) thin films in a glow discharge deposition reactor. In addition to intrinsic material, doped a-Si films were generated by gas phase admixture of diborane and phosphine to the precursor. Measurements of photoconductivity and the temperature dependence of dark conductivity were performed to characterize the films. Photoresponse, optical absorption and electron microscopy data were also obtained. Representative samples of a-Si:H:F prepared by glow discharge from difluorosilane show high photoconductivity in the range of 10 −4 S cm −1 (under simulated sunlight), whereas the dark conductivity (at room temperature) is typically 10 −8 S cm −1 . The mobility-lifetime product, derived from the photoresponse at 640 nm, reaches typical values of 2 × 10 −6 cm 2 V −1 .