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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Linear and nonlinear optical probe of the ferroelectric-like phase transition in a polar metal, LiOsO 3

LiOsO 3 is one of the first materials identified in the current literature as a “polar metal,” a class of materials that are simultaneously noncentrosymmetric and metallic. In this work, the linear and nonlinear optical susceptibility of LiOsO 3 is studied by means of ellipsometry and optical second harmonic generation (SHG). Robust optical birefringence is observed using spectroscopic ellipsometry. The nonlinear optical susceptibility extracted from SHG polarimetry reveals that the tensor components are of the same magnitude as in the isostructural insulator LiNbO 3 , except the component along the polar axis d 33 is suppressed by an order of magnitude. Temperature-dependent SHG measurements in combination with Raman spectroscopy indicate a continuous order-disorder type polar phase transition at 140 K. Linear and nonlinear optical microscopy measurements reveal 109°/71° ferroelastic domain walls, like in other trigonal ferroelectrics. No 180° polar domain walls are observed to emerge across the phase transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Band-to-band transitions and critical points in the near-infrared to vacuum ultraviolet dielectric functions of single crystal urania and thoria

Band-to-band transition energy parameters for single-crystal actinide samples of uranium oxide and thorium oxide were determined and compared using spectroscopic ellipsometry and critical-point dielectric function analyses. Spectroscopic ellipsometry measurements from the near-infrared to the vacuum ultraviolet spectral region were used to determine the dielectric functions of uranium oxide and thorium oxide. Furthermore, the critical-point structure is similar between UO 2 and ThO 2 but strongly blue shifted for ThO 2 . We find bandgap energies of 2.1 eV and 5.4 eV for UO2 and ThO2, respectively.

42 ENGINEERING↗
DOE OSTI2020

Infrared-active phonon modes in single-crystal thorium dioxide and uranium dioxide

The infrared-active phonon modes, in single-crystal samples of thorium dioxide (ThO 2 ) and uranium dioxide (UO 2 ), were investigated using spectroscopic ellipsometry and compared with density functional theory. Both ThO 2 and UO 2 are found to have one infrared-active phonon mode pair [consisting of one transverse optic (TO) and one associated longitudinal optic (LO) mode], which is responsible for the dominant features in the ellipsometric data. Furthermore, at room temperature, our results for the mode pair’s resonant frequencies and broadening parameters are comparable with previous reflectance spectroscopy characterizations and density functional theory predictions. For ThO 2 , our ellipsometry and density function theory results both show that the LO mode broadening parameter is larger than the TO mode broadening. This signifies mode anharmonicity, which can be attributed to the intrinsic phonon–phonon interaction. In addition to the main mode pair, a broad low-amplitude impurity-like vibrational mode pair is detected within the reststrahlen band for both ThO 2 and UO 2 . Elevated temperature measurements were performed for ThO 2 in order to study the mechanisms by which the phonon parameters evolve with increased heat. The observed change in the TO resonant frequency is in excellent agreement with previous density functional calculations, which only consider volume expansion of the crystal lattice. This suggests that the temperature-dependent change in the TO frequency is primarily due to volume expansion. The change in the main mode pair’s broadening parameters is nearly linear within the temperature range of this study, which indicates the intrinsic anharmonic scattering (via cubic anharmonicities) as the main decay mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The 2022 magneto-optics roadmap

Abstract Magneto-optical (MO) effects, viz. magnetically induced changes in light intensity or polarization upon reflection from or transmission through a magnetic sample, were discovered over a century and a half ago. Initially they played a crucially relevant role in unveiling the fundamentals of electromagnetism and quantum mechanics. A more broad-based relevance and wide-spread use of MO methods, however, remained quite limited until the 1960s due to a lack of suitable, reliable and easy-to-operate light sources. The advent of Laser technology and the availability of other novel light sources led to an enormous expansion of MO measurement techniques and applications that continues to this day (see section 1). The here-assembled roadmap article is intended to provide a meaningful survey over many of the most relevant recent developments, advances, and emerging research directions in a rather condensed form, so that readers can easily access a significant overview about this very dynamic research field. While light source technology and other experimental developments were crucial in the establishment of today’s magneto-optics, progress also relies on an ever-increasing theoretical understanding of MO effects from a quantum mechanical perspective (see section 2), as well as using electromagnetic theory and modelling approaches (see section 3) to enable quantitatively reliable predictions for ever more complex materials, metamaterials, and device geometries. The latest advances in established MO methodologies and especially the utilization of the MO Kerr effect (MOKE) are presented in sections 4 (MOKE spectroscopy), 5 (higher order MOKE effects), 6 (MOKE microscopy), 8 (high sensitivity MOKE), 9 (generalized MO ellipsometry), and 20 (Cotton–Mouton effect in two-dimensional materials). In addition, MO effects are now being investigated and utilized in spectral ranges, to which they originally seemed completely foreign, as those of synchrotron radiation x-rays (see section 14 on three-dimensional magnetic characterization and section 16 on light beams carrying orbital angular momentum) and, very recently, the terahertz (THz) regime (see section 18 on THz MOKE and section 19 on THz ellipsometry for electron paramagnetic resonance detection). Magneto-optics also demonstrates its strength in a unique way when combined with femtosecond laser pulses (see section 10 on ultrafast MOKE and section 15 on magneto-optics using x-ray free electron lasers), facilitating the very active field of time-resolved MO spectroscopy that enables investigations of phenomena like spin relaxation of non-equilibrium photoexcited carriers, transient modifications of ferromagnetic order, and photo-induced dynamic phase transitions, to name a few. Recent progress in nanoscience and nanotechnology, which is intimately linked to the achieved impressive ability to reliably fabricate materials and functional structures at the nanoscale, now enables the exploitation of strongly enhanced MO effects induced by light–matter interaction at the nanoscale (see section 12 on magnetoplasmonics and section 13 on MO metasurfaces). MO effects are also at the very heart of powerful magnetic characterization techniques like Brillouin light scattering and time-resolved pump-probe measurements for the study of spin waves (see section 7), their interactions with acoustic waves (see section 11), and ultra-sensitive magnetic field sensing applications based on nitrogen-vacancy centres in diamond (see section 17). Despite our best attempt to represent the field of magneto-optics accurately and do justice to all its novel developments and its diversity, the research area is so extensive and active that there remains great latitude in deciding what to include in an article of this sort, which in turn means that some areas might not be adequately represented here. However, we feel that the 20 sections that form this 2022 magneto-optics roadmap article, each written by experts in the field and addressing a specific subject on only two pages, provide an accurate snapshot of where this research field stands today. Correspondingly, it should act as a valuable reference point and guideline for emerging research directions in modern magneto-optics, as well as illustrate the directions this research field might take in the foreseeable future.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Hole-induced electronic and optical transitions in L a 1 - x S r x Fe O 3 epitaxial thin films

We have investigated the electronic and optical properties of epitaxial La 1-x Sr x FeO 3 for 0 ≤ x ≤ 1 prepared by molecular-beam epitaxy. Core-level and valence-band x-ray photoemission features monotonically shift to lower binding energy with increasing x, indicating downward movement of the Fermi level toward the valence-band maximum. Combining valence-band photoemission and O K -edge x-ray absorption data, we map the evolution of the occupied and unoccupied bands and observe a narrowing of the gap, along with a transfer of state density from just below to just above the Fermi level as a result of hole doping. In-plane transport measurements confirm that the material becomes a p -type semiconductor at lower doping levels and exhibits a conversion from semiconducting to metallic behavior at x = 1. As a result, low-energy optical transitions revealed by spectroscopic ellipsometry are explained based on insight from theoretical densities of states and first-principles calculations of optical absorption spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Impact of hydrofluorocarbon molecular structure parameters on plasma etching of ultra-low-K dielectric

The authors report a systematic study aimed at evaluating the impact of molecular structure parameters of hydrofluorocarbon (HFC) precursors on plasma deposition of fluorocarbon (FC) films and etching performance of a representative ultra-low-k material, along with amorphous carbon. The precursor gases studied included fluorocarbon and hydrofluorocarbon gases whose molecular weights and chemical structures were systematically varied. Gases with three different degrees of unsaturation (DU) were examined. Trifluoromethane (CHF{sub 3}) is the only fully saturated gas that was tested. The gases with a DU value of one are 3,3,3-trifluoropropene (C{sub 3}H{sub 3}F{sub 3}), hexafluoropropene (C{sub 3}F{sub 6}), 1,1,3,3,3-pentafluoro-1-propene (C{sub 3}HF{sub 5}), (E)-1,2,3,3,3-pentafluoropropene (C{sub 3}HF{sub 5} isomer), heptafluoropropyl trifluorovinyl ether (C{sub 5}F{sub 10}O), octafluorocyclobutane (C{sub 4}F{sub 8}), and octafluoro-2-butene (C{sub 4}F{sub 8} isomer). The gases with a DU value of two includes hexafluoro-1,3-butadiene (C{sub 4}F{sub 6}), hexafluoro-2-butyne (C{sub 4}F{sub 6} isomer), octafluorocyclopentene (C{sub 5}F{sub 8}), and decafluorocyclohexene (C{sub 6}F{sub 10}). The work was performed in a dual frequency capacitively coupled plasma reactor. Real-time characterization of deposition and etching was performed using in situ ellipsometry, and optical emission spectroscopy was used for characterization of CF{sub 2} radicals in the gas phase. The chemical composition of the deposited FC films was examined by x-ray photoelectron spectroscopy. The authors found that the CF{sub 2} fraction, defined as the number of CF{sub 2} groups in a precursor molecule divided by the total number of carbon atoms in the molecule, determines the CF{sub 2} optical emission intensity of the plasma. CF{sub 2} optical emission, however, is not the dominant factor that determines HFC film deposition rates. Rather, HFC film deposition rates are determined by the number of weak bonds in the precursor molecule, which include a ring structure, C=C, C≡C, and C–H bonds. These bonds are broken preferentially in the plasma, and/or at the surface and fragments arriving at the substrate surface presumably provide dangling bonds that efficiently bond to the substrate or other fragments. Upon application of a radio-frequency bias to the substrate, substrate etching is induced. Highly polymerizing gases show decreased substrate etching rates as compared to HFC gases characterized by a lower HFC film deposition rate. This can be explained by a competition between deposition and etching reactions, and an increased energy and etchant dissipation in relatively thicker steady state FC films that form on the substrate surface. Deposited HFC films exhibit typically a high CF{sub 2} density at the film surface, which correlates with both the CF{sub 2} fractions in the precursor molecular structure and the deposition rate. The FC films deposited using hydrogen-containing precursors show higher degrees of crosslinking and lower F/C ratios than precursors without hydrogen, and exhibit a lower etch rate of substrate material. A small gap structure that blocks direct ion bombardment was used to simulate the sidewall plasma environment of a feature and was employed for in situ ellipsometry measurements. It is shown that highly polymerizing precursors with a DU of two enable protection of low-k sidewalls during plasma exposure from oxygen-related damage by protective film deposition. Dielectric film modifications are seen for precursors with a lower DU.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Challenges in atomic layer etching of gallium nitride using surface oxidation and ligand-exchange

Two atomic layer etching (ALE) methods were studied for crystalline GaN, based on oxidation, fluorination, and ligand exchange. Etching was performed on unintentionally doped GaN grown by hydride vapor phase epitaxy. For the first step, the GaN surfaces were oxidized using either water vapor or remote O 2 -plasma exposure to produce a thin oxide layer. Removal of the surface oxide was addressed using alternating exposures of hydrogen fluoride (HF) and trimethylgallium (TMG) via fluorination and ligand exchange, respectively. Several HF and TMG super cycles were implemented to remove the surface oxide. Each ALE process was monitored in situ using multiwavelength ellipsometry. X-ray photoelectron spectroscopy was employed for the characterization of surface composition and impurity states. Additionally, the thermal and plasma-enhanced ALE methods were performed on patterned wafers and transmission electron microscopy (TEM) was used to measure the surface change. The x-ray photoelectron spectroscopy measurements indicated that F and O impurities remained on etched surfaces for both ALE processes. Ellipsometry indicated a slight reduction in thickness. TEM indicated a removal rate that was less than predicted. In conclusion, we suggest that the etch rates were reduced due to the ordered structure of the oxide formed on crystalline GaN surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Optical functions of uniaxial rutile and anatase (TiO 2 ) revisited

In this study, the optical functions of uniaxial rutile and anatase (TiO2) were determined from 200 to 850 nm (6.2 to 1.46 eV) using several of four optical techniques: (1) standard spectroscopic two-modulator generalized ellipsometry (2-MGE), (2) near-normal-incidence two-modulator generalized ellipsometry microscopy (2-MGEM), (3) Mueller matrix transmission of rutile, and (4) polarized transmission of rutile. The 2-MGE measurements yielded highly accurate values of the dielectric functions and error estimates from 1.46 to 6.2 eV, whereas the polarization-dependent transmission yielded more accurate values of the absorption coefficient below the band edge of rutile. The 2-MGEM also measured the diattenuation, which is related to the birefringence, and other parameters but at near-normal incidence at a single wavelength (577 nm).

36 MATERIALS SCIENCE↗
DOE OSTI2026

Optical functions of crystalline and amorphous TeO2

The optical functions of crystalline paratellurite (α-TeO2) and amorphous TeO2 were determined using several optical techniques: (1) standard spectroscopic two-modulator generalized ellipsometry (2-MGE) of paratellurite (200–850 nm, 6.2–1.46 eV), (2) near-normal-incidence two-modulator generalized ellipsometry microscopy (2-MGEM) of paratellurite (577 nm, 2.15 eV), (3) Mueller matrix transmission of paratellurite (320–798 nm, 3.87–1.55 eV), and (4) polarized transmission of paratellurite (323.6–334.3 nm, 3.83–3.71 eV). The 2-MGE measurements yielded highly accurate values of the dielectric functions and error estimates from 1.46 to 6.2 eV for both paratellurite and amorphous TeO2, whereas the polarization-dependent transmission yielded more accurate values of the absorption coefficient below the band edge of paratellurite. The 2-MGEM measured the diattenuation of paratellurite, which is related to the birefringence. Mueller matrix transmission measurements of paratellurite of a (001) cut crystal as a function of angle of incidence were used to determine both the birefringence and the rotary power as a function of photon energy.

Jellison Jr, Gerald [ORNL]↗
DOE OSTI2018

Short-Range Order in Amorphous and Crystalline Ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2}

The microstructures of amorphous and polycrystalline ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO{sub 2} and ZrO{sub 2}. After rapid thermal annealing, the mixed Hf{sub 0.5}Zr{sub 0.5}O{sub 2} oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO{sub 2} and ZrO{sub 2}. The presence of the HfO{sub 2} and ZrO{sub 2} phases in the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films is also detected by ellipsometry.

36 MATERIALS SCIENCE↗
DOE OSTI2015

ZFSP Proposal: Understanding the Physics and Chemistry of Iron Alloys relevant to the Conditions of Planetary Cores

Recent research results by the deep-Earth geoscience and astronomy communities have revealed a wealth of interesting and outstanding fundamental science questions about the interiors of terrestrial planets and exoplanets including the origin of the magnetic field in the iron core and its impact on the evolution of life, the alloying of light elements on physics and chemistry of the planet’s dynamic processes, and the discovery of super-rotation and heterogeneous behavior of the inner core. Resolving these questions requires a first-hand experimental database at relevant pressure-temperature (P-T) conditions, but is technically challenging using static diamond anvil cell (DAC) and dynamic shock wave efforts alone, due to their limited P-T conditions and analytical capabilities. However, the recent advent of new capabilities of Sandia’s Z-Machine, coupled with our recent developments in in-situ ellipsometry at the UT Austin and Sandia National Laboratory and first-principles calculations and geodynamic modelling capabilities at UC Berkeley, motivates the joint collaborative effort presented here. In this collaborative research, we will use the capabilities of Sandia’s Z-Machine to investigate the elastic, thermal transport and melting properties of material relevant to both Earth and exoplanets at their relative P-T conditions. Our long-term research goal is to better understand the physics and dynamics of planetary interiors through interdisciplinary collaborations between physicists, mineral physicists, theorists, geodynamicists, and astrophysicists. The conditions in the Earth and super-Earth can range up to ~300-500 GPa and ~5000-8000 K. We will couple these experiments with a unique set of diagnostics, to include a new ellipsometry capability, in order to sensitively measure conductivity of these materials, and phase changes, including melting. Specifically, the newly demonstrated capability of Z to shock materials to a given P-T along the Hugoniot, and then to apply a pressure ramp taking the material along an isentrope, provides a unique opportunity to obtain P-T conditions not accessible by traditional DAC technology, or through shocks simply along the Hugoniot. Our physics team will perform experiments and analyze results to determine the physics underlying iron alloys as high-energy planetary impactors, classic transition metal alloys, and iron-bearing periclase relevant to the interiors of rocky planets, including exoplanets. The experimental results so analyzed will provide data that our collaborative team of mineral physicists, geodynamics, seismologists, and astrophysicists will apply toward obtaining a fundamental understanding of the physical and chemical states of the terrestrial planets and exoplanets, including their chemical compositions, thermal transport behavior, origin of magnetic fields, and dynamic evolution of the planet.

58 GEOSCIENCES↗
DOE OSTI2022

Structural, Optical and Mechanical Properties of Nanocrystalline Molybdenum Thin Films Deposited under Variable Substrate Temperature

Molybdenum (Mo), which is one among the refractory metals, is a promising material with a wide variety of technological applications in microelectronics, optoelectronics, and energy conversion and storage. However, understanding the structure–property correlation and optimization at the nanoscale dimension is quite important to meet the requirements of the emerging nanoelectronics and nanophotonics. In this context, we focused our efforts to derive a comprehensive understanding of the nanoscale structure, phase, and electronic properties of nanocrystalline Mo films with variable microstructure and grain size. Molybdenum films were deposited under varying temperature (25–500 °C), which resulted in Mo films with variable grain size of 9–22 nm. The grazing incidence X-ray diffraction analyses indicate the (110) preferred growth behavior the Mo films, though there is a marked decrease in hardness and elastic modulus values. In particular, there is a sizable difference in maximum and minimum elastic modulus values; the elastic modulus decreased from ~460 to 260–280 GPa with increasing substrate temperature from 25–500 °C. The plasticity index and wear resistance index values show a dramatic change with substrate temperature and grain size. Additionally, the optical properties of the nanocrystalline Mo films evaluated by spectroscopic ellipsometry indicate a marked dependence on the growth temperature and grain size. This dependence on grain size variation was particularly notable for the refractive index where Mo films with lower grain size fell in a range between ~2.75–3.75 across the measured wavelength as opposed to the range of 1.5–2.5 for samples deposited at temperatures of 400–500 °C, where the grain size is relatively higher. The conductive atomic force microscopy (AFM) studies indicate a direct correlation with grain size variation and grain versus grain boundary conduction; the trend noted was improved electrical conductivity of the Mo films in correlation with increasing grain size. The combined ellipsometry and conductive AFM studies allowed us to optimize the structure–property correlation in nanocrystalline Mo films for application in electronics and optoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Deriving the Infrared Complex Refractive Indices of Organic Powders for Optical Modeling: Comparison of Methods

Identification of solids via infrared reflection spectroscopy requires a spectral library of all solids likely to be encountered. A confounding factor in populating such a spectral library is that the reflectance spectra of solids vary with their form, including particle size, film thickness, and substrate. To reduce the efforts of experimentally constructing such a library, an alternate strategy is to use the wavelength-dependent optical constants, n and k, of a solid to calculate a series of reflectance spectra corresponding to each scenario or morphology. Because most n/k measurements are best performed on mm-sized crystals, however, the challenge of determining the optical constants increases when a solid is only readily available as a powder, as is often the case. Some organic solids, such as caffeine, are both unavailable in large crystals and difficult to press into pellets. In this study, the infrared optical constants, or complex refractive indices, of caffeine were determined using three different methods: single-angle reflectance, infrared spectroscopic ellipsometry, and quantitative absorbance measurements of KBr pellets. The n and k values derived through each method were used to model the hyperspectral imaging reflectance spectrum of a caffeine film on a steel planchet. Over 1,110 – 870 cm-1, the single-angle reflectance-derived n and k had the best correlation with the experimental spectrum. These results suggest different organic solids may require different methods to determine the most accurate infrared complex refractive indices for synthetic spectral libraries.

FTIR, hyperspectral imaging, infrared, infrared (I↗
DOE OSTI2024

Method to derive the infrared complex refractive indices n(λ) and k(λ) for organic solids from KBr pellet absorption measurements

Obtaining the complex refractive index vectors $n($$\tilde{v})$ and $k($$\tilde{v})$ allows calculation of the (infrared) reflectance spectrum that is obtained from a solid in any of its many morphological forms. Here, we report an adaptation to the KBr pellet technique using two gravimetric dilutions to derive quantitative $n($$\tilde{v})$/$k($$\tilde{v})$ for dozens of powders with greater repeatability. The optical constants of bisphenol A and sucrose are compared to those derived by other methods, particularly for powdered materials. The variability of the $k$ values for bisphenol A was examined by 10 individual measurements, showing an average coefficient of variation for $k$ peak heights of 5.6%. Though no established standards exist, the pellet-derived $k$ peak values of bisphenol A differ by 11% and 31% from their single-angle- and ellipsometry-derived values, respectively. These values provide an initial estimate of the precision and accuracy of complex refractive indices that can be derived using this method. Limitations and advantages of the method are discussed, the salient advantage being a more rapid method to derive $n$/$k$ for those species that do not readily form crystals or specular pellets.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Sharp and Tunable Crystal/Fano-Type Resonances Enabled by Out-of-Plane Dipolar Coupling in Plasmonic Nanopatch Arrays

Tuning resonance lineshapes of plasmonic structures is essential to create customized media with compelling optical properties for optimized light–matter interactions. The diversity of available metals and the variety of design architectures provide a rich portfolio for statically controlling the resonance lineshape. However, dynamic tuning of resonance attributes (e.g., the resonance wavelength and linewidth) are yet to be more expanded, especially when a narrow resonance linewidth is on demand. Here, using a plasmonic nanopatch array, sharp plasmonic crystal (PC) resonances are demonstrated across a wide spectral range of 230 nm, with full-width at half-maximum of only ≈6 nm. The combination of angle-resolved ellipsometry and full-wave simulations shows that diffractive coupling of out-of-plane electric dipoles is the principal contributor in the formation of such sharp PC resonances. In addition, the designed nanopatch PC supports a plasmonic Fabry–Pérot-like resonance that can be interfered with the PC resonance to generate complex Fano-type lineshapes. Finally, the coexistence of tunable resonance features renders the designed structures as a rich platform for applications seeking enhanced light–matter interactions and optical signal processing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Investigation of polymer–solvent interactions in poly(styrene sulfonate) thin films

The swelling behavior of acid form poly(styrene sulfonate) (PSS-H) thin films were investigated using in situ spectroscopic ellipsometry (SE) to probe the polymer–solvent interactions of ion-containing polymers under interfacial confinement. The interaction parameter (χ), related to the polymer and solvent solubility parameters in the Flory–Huggins theory, describes the polymer-solvent compatibility. In situ SE was used to measure the degree of polymer swelling in various solvent vapor environments, to determine χ for the solvent-PSS-H system. The calculated solubility parameter of 40–44 MPa 1/2 for PSS-H was determined through measured χ values in water, methanol, and formamide environments at a solvent vapor activity of 0.95. Flory–Huggins theory was applied to describe the thickness-dependent swelling of PSS-H and to quantify the water-PSS-H interactions. Confinement had a significant influence on polymer swelling at low water vapor activities expressed as an increased χ between the water and polymer with decreasing film thickness. Finally, as the volume fraction of water approached ~0.3, the measured χ value was ~0.65, indicating the water interacted with the polymer in a similar manner, regardless of thicknesses.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

Al is a commonly used material for rear side metallization in commercial silicon (Si) wafer solar cells. In this study, through-the-silicon spectroscopic ellipsometry is used in a test sample to measure Al+Si interface optical properties like those in Si wafer solar cells. Two different spectroscopic ellipsometers are used for measurement of Al+Si interface optical properties over the 1128-2500 nm wavelength range. For validation, the measured interface optical properties are used in a ray tracing simulation over the 300-2500 nm wavelength range for an encapsulated Si solar cell having random pyramidal texture. The ray tracing model matches well with the measured total reflectance at normal incidence of a commercially available Si module. The Al+Si optical properties presented here enable quantitative assessment of major irradiance/current flux losses arising from reflection and parasitic absorption in encapsulated Si solar cells.

14 SOLAR ENERGY↗