Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Ellipsometry”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Synthesis, microstructure, and electronic band structure properties of nanocrystalline neodymium-doped bismuth titanate ferroelectric films fabricated by the sol–gel method

Graphical abstract: X-ray diffraction indicates that the films are polycrystalline with the pure perovskite phase. Ten Raman active modes and one silicon substrate mode can be observed. The A{sub 1} {sub g}[Bi] at about 59 cm{sup −1} is unchanged whereas the B{sub 1} {sub g} and A{sub 1} {sub g}[Ti] phonon modes shift towards higher frequencies. Photoluminescence shows that the intensities of the two peaks increase with Nd concentration except the Bi{sub 3}NdTi{sub 3}O{sub 12} film, due to the smallest grain size and oxygen vacancy defects. Good optical functions of the BNT films are achieved due to the SE suggesting potential applications in ferroelectric-based optoelectronic devices. - Abstract: Bi{sub 4−x}Nd{sub x}Ti{sub 3}O{sub 12} (BNT) films with different Nd contents (from 0 to 1 with 0.25 intervals) are prepared by the sol–gel process. The Nd substitution effects on the preferred orientation, surface morphology, phonon modes, emission bands, andelectronic band structures of the BNT films are investigated by microscopy, Raman scattering, photoluminescence, and spectroscopic ellipsometry (SE) at room temperature. X-ray diffraction indicates that the films are polycrystalline with the pure perovskite phase. Ten Raman active modes and one silicon substrate mode can be observed. The A{sub 1} {sub g}[Bi] at about 59 cm{sup −1} is unchanged whereas the B{sub 1} {sub g} and A{sub 1} {sub g}[Ti] phonon modes shift towards higher frequencies. Photoluminescence shows that the intensities of the two peaks increase with Nd concentration except the Bi{sub 3}NdTi{sub 3}O{sub 12} film, due to the smallest grain size and oxygen vacancy defects. Good optical functions of the BNT films are achieved due to the SE suggesting potential applications in ferroelectric-based optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Influence of annealing temperature on structural and optical properties of Lu{sub 2}O{sub 3}:Eu{sup 3+}, Tb{sup 3+} transparent films

Highlights: • Lu{sub 2}O{sub 3}:Eu{sup 3+}, Tb{sup 3+} films were synthesized by sol–gel and by dip-coating technique. • Effects of annealing treatment on structural and optical properties were studied. • Optogeometrical characteristics of synthesized films were analyzed. • X-ray diffraction results showed that Lu{sub 2}O{sub 3}:Eu{sup 3+}, Tb{sup 3+} crystallizes at 700 °C. • High reddish emission on transparent films with at least 1 μm thick was observed. - Abstract: High-optical quality Lu{sub 2}O{sub 3}:Eu{sup 3+} 5 mol%, X Tb{sup 3+} (X = 0–0.04 mol%) thin films were prepared by the sol–gel process and dip-coating technique. The procedure was as follows: lutetium, europium and terbium nitrates were used as precursors, and ethanol as a solvent. Etylenglycol (EG) was added as a sol stabilizer, and the pH was adjusted by acetic acid. After 10 dipping-cycles, followed by an annealing process (600–900 °C) for 1 h, transparent, smooth and crack-free films (ra = 8–9 nm) were formed. The X-ray diffraction (XRD) results showed crystallized films into the cubic structure at 800 °C. The ellipsometry results showed that the thickness of the films varied from 1 to 1.4 μm at 1000 and 600 °C, respectively. Finally, the films presented a typical Eu{sup 3+} red emission at 611 nm ({sup 5}D{sub 0} → {sup 7}F{sub 2}); furthermore, the effect of the Tb{sup 3+} content showed that the highest emission intensity corresponded to the lower Tb{sup 3+} content.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Deposition temperature dependent optical and electrical properties of ALD HfO{sub 2} gate dielectrics pretreated with tetrakisethylmethylamino hafnium

Highlights: • ALD-derived HfO{sub 2} gate dielectrics have been deposited on Si substrates. • The leakage current mechanism for different deposition temperature was discussed. • Different emission at different field region has been determined precisely. - Abstract: The effect of deposition temperature on the growth rate, band gap energy and electrical properties of HfO{sub 2} thin film deposited by atomic layer deposition (ALD) has been investigated. By means of characterization of spectroscopy ellipsometry and ultraviolet–visible spectroscopy, the growth rate and optical constant of ALD-derived HfO{sub 2} gate dielectrics are determined precisely. The deposition temperature dependent electrical properties of HfO{sub 2} films were determined by capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements. The leakage current mechanism for different deposition temperature has been discussed systematically. As a result, the optimized deposition temperature has been obtained to achieve HfO{sub 2} thin film with high quality.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical, morphological and durability studies of quaternary chalcogenide Ge-Sb(As)-(S,Te) films

Highlights: • Films of two glassy chalcogenide systems of Ge{sub x}-Sb/As{sub 40-x}-S{sub 50}-Te{sub 10} were studied. • Optical constants as function of films composition are obtained in 0.25–30 μm range. • The transparent zone of the films is in the (0.6–2.5) μm spectral range. • The vibrational modes were determined from IR-SE, FTIR and Raman. • The stability of the films after QT was proved by AFM, SEM and SE analyses. - Abstract: Thin films from two glassy systems of Ge{sub x}Sb{sub 40-x}S{sub 50}Te{sub 10} and Ge{sub x}As{sub 40-x}S{sub 50}Te{sub 10}, with compositions x = 10, 20 and 27 at. %, were deposited on optical glass substrates by vacuum thermal evaporation of powdered parent chalcogenide glasses. The complex refractive index and dielectric constants of the films are determined by ellipsometry in a wide spectral range of 0.25–30 μm. In the transparent spectral region of 0.6–2.5 μm the refractive index values are within 2.9–2.3 and 3.3–2.4 for the As-contained and Sb-contained films, respectively. From the IR and Raman data analysis the basic chemical and oxygen-related impurity bonds are identified. The films durability properties were established by applying the US Military Standard quality tests. The quality-test-induced-changes in surface morphology were evaluated. The films are relatively stable after quality test treatments, which cause a small degree of densification and surface roughening for Sb-containing films and surface flattening for As-containing ones.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Special pure germanium-rich Ga-Ge-As-Se glasses for active mid-IR fiber optics

Highlights: • Special pure Ga{sub x}Ge{sub 25}As{sub 15}Se{sub 60-x} (x = 0; 1; 2; 3; 4; 5) glasses were prepared and investigated. • The glasses have high glass transition temperature (>320 °C) and low tendency to crystallization. • The microstructure, the transmission region and the linear refractive index of glasses were studied. • Dispersion optical parameters of glasses were calculated using the Wemple-DiDomenico model. • For the first time, a single-index Ga{sub 3}Ge{sub 25}As{sub 15}Se{sub 57} glass fiber was fabricated and investigated. - Abstract: Special pure Ga{sub x}Ge{sub 25}As{sub 15}Se{sub 60-x} (x = 0; 1; 2; 3; 4; 5) glasses were prepared using various methods for purification of the glass-forming melt. The glasses are characterized by high transparency in the spectral range 0.8–15 μm, low impurity content, high glass transition temperature (>320 °C), and low tendency to crystallization. The microstructure, the transmission range edges, the optical band-gap energy, and the linear refractive index of the glasses are studied. The refractive index of Ga{sub x}Ge{sub 25}As{sub 15}Se{sub 60-x} (x = 0÷5) glasses measured by ellipsometry increases with the substitution of selenium by gallium. It is for the first time that a single-index Ga{sub 3}Ge{sub 25}As{sub 15}Se{sub 57} glass fiber was fabricated, its minimum optical loss was about 0.6 dB/m at a wavelength of 6.7 μm. High-purity germanium-rich Ga-Ge-As-Se glasses were shown to be a promising material for active mid-IR fiber optics.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

Ammonium nitrate (AN) is a high interest material because of its wide usage in propellants and explosives but can be difficult to handle from a formulation standpoint. It is soluble in many common solvents and has complex phase behavior. Here, we formulate phase stabilized AN (PSAN) films in a polymer matrix and characterize thermal and phase behavior using neutron reflectometry and ellipsometry. Our PSAN films are generally stable up to 160 °C, though we observe small material loss between 60 and 100 °C, which we attribute to solvent interactions with the PSAN. Crystallization of AN from supersaturated polymer is most common at thicker regions of the film, suggesting a critical nucleation thickness for the AN which can be avoided by making very thin films.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2024

Temperature-dependent optical constants of vanadium dioxide thin films deposited on polar dielectrics

Coating polar dielectrics with thin film vanadium dioxide (VO 2 ) enables one to exploit the temperature-dependent phase transition within VO 2 to actively tune and modulate surface phonon polaritons at mid-infrared. However, controlling the behavior of such systems requires intimate knowledge of the temperature-dependent optical constants of VO 2 , which depend greatly on the growth conditions and substrate material. Here, in this work, we accurately determine the complex optical constants of VO 2 on polar dielectrics across the insulator-to-metal phase transition (IMT) using only normal incident reflectance spectra by analyzing the reflectance with Kramers–Kronig relations and thin film Fresnel equations. This non-ellipsometry technique offers an advantage in determining the refractive index using a standard infrared spectrometer.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Optical Properties of Bacteriorhodopsin–Gold Bionano Interfaces

Monolayers of different mutants of bacteriorhodopsin (bR) with purple membranes are deposited on gold (Au) substrates. Optical measurements and density functional theory-based electronic structure calculations are reported for the first time for the bR chromophore, which is the retinal protonated Schiff base. The dielectric function of the chromophore is extracted using spectroscopic ellipsometry. Designed mutants of bR are used to investigate the bonding with the gold substrate and bR–Au bonding changes can be tracked using the optical properties of the retinal fragment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Optical and Electronic Losses Arising from Physically Mixed Interfacial Layers in Perovskite Solar Cells

Perovskite solar cell device performance is affected by optical and electronic losses. To minimize these losses in solar cells, it is important to identify their sources. Here, we report the optical and electronic losses arising from physically mixed interfacial layers between the adjacent component materials in highly efficient two terminal (2T) all-perovskite tandem, single junction wide-bandgap, and single junction narrow-bandgap perovskite-based solar cells. Physically mixed interfacial layers as the sources of optical and electronic losses are identified from spectroscopic ellipsometry measurements and data analysis followed by comparisons of simulated and measured external quantum efficiency spectra. Parasitic absorbance in the physically mixed regions between silver metal electrical contacts and electron transport layers (ETLs) near the back contact and a physical mixture of commercial indium tin oxide and hole transport layers (HTL) near the front electrical contact lead to substantial optical loss. Here, a lower-density void + perovskite nucleation layer formed during perovskite deposition at the interface between the perovskite absorber layer and the HTL causes electronic losses due to incomplete collection of photogenerated carriers likely originating from poor coverage and passivation of the initially nucleating grains.

14 SOLAR ENERGY↗
DOE OSTI2016

Monitoring Volumetric Changes in Silicon Thin-Film Anodes through In Situ Optical Diffraction Microscopy

A high-resolution in situ spectroelectrochemical optical diffraction experiment has been created to understand the volume expansion/contraction process of amorphous silicon (a-Si) thin-film anodes. Electrodes consisting of 1D transmissive gratings of silicon have been produced through photolithographic methods. After glovebox assembly in a home-built Teflon cell, monitoring of the diffraction efficiency of these gratings during the lithiation/delithiation process is performed using an optical microscope equipped with a Bertrand lens. When the diffraction efficiency along with optical constants obtained from in situ spectroscopic ellipsometry is utilized, volume changes of the active materials can be deduced. Unlike transmission electron microscopy and atomic force microscopy characterization methods of observing silicon’s volume expansion, this experiment allows for real-time monitoring of the volume change at charge/discharge cycles greater than just the first few along with an experimental environment that directly mimics that of a real battery. This technique reflects promising results that provide needed insight into understanding the lithium alloying reaction and subsequent induced capacity fade during the cycling of alloying anodes in lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2019

Plasma-Enhanced Atomic Layer Deposition of TiAlN: Compositional and Optoelectronic Tunability

Titanium nitride (TiN) is a unique refractory plasmonic material, the nanocomposites and alloys of which provide further opportunities to tailor its optical and photonic properties. We prepare TiAlN films of continuously variable compositions through the systematic variation of TiN versus AlN cycle ratio in plasma-enhanced atomic layer deposition (PEALD) and investigate the resulting thin-film composition, crystallinity, and optical properties. The resulting properties of TiAIN films are not simple linear combinations of the TiN and AlN films, which exhibit distinct metallic and dielectric properties, but instead are dramatically influenced by the local chemical environment of neighboring constituents. In situ spectroscopic ellipsometry further enables measurement of the varying optical properties of TiAlN films, which evolve over 10 s of nm of film thickness. The tunable optoelectronic properties of TiAlN films enable durable coatings of variable electrical resistance as well as high-temperature diffusion barriers and optical coatings with application to selective solar absorbers and emitters.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Methods for Determining the Infrared Complex Refractive Indices n (λ) and k (λ) from Organic Solid Powders: Comparison of a Sucrose Single Crystal and a Pressed Pellet

There exists a need to measure optical constants n and k for many materials, especially organic solids in the infrared spectral region, but at present, there are only two established methods for making such measurements: single-angle (SA) reflectance and infrared spectroscopic ellipsometry (IRSE). The former derives the n/k vectors via measurement of the change in the amplitude of light reflected from the sample and then uses the Kramers–Kronig transform, while the latter measures the change in polarization of the reflected light from the sample to derive n/k. Here we make a direct comparison between the n/k vectors derived from SA measurements of a sucrose single crystal and the n/k values obtained after the crystal had been crushed, ground to powder, and pressed into a pellet form. The pellet was measured not only by SA but also via the IRSE method, and we found that pressing specular-quality pellets was critical, especially for the SA data. The n/k values of this typical organic molecule all agree to within 0.04 root-mean-square error, confirming that a pressed pellet can be used instead of a crystal to derive the intrinsic n/k vectors. In conclusion, this result is important for the many organic materials that, unlike sugar, do not have centimeter-sized crystals readily available.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Combined Spatially Resolved Characterization of Antireflection and Antisoiling Coatings for PV Module Glass

Characterization of photovoltaic (PV) module materials throughout different stages of service life is crucial to understanding and improving the durability of these materials. Currently the large-scale of PV modules (>1 m 2 ) is imbalanced with the small-scale of most materials characterization tools (= 1 cm 2 ). Furthermore, understanding degradation mechanisms often requires a combination of multiple characterization techniques. Here, we present adaptations of three standard materials characterization techniques to enable mapping characterization over moderate sample areas (=25 cm 2 ). Contact angle, ellipsometry, and UV-Vis spectroscopy are each adapted and demonstrated on two representative samples: a commercial multi-functional coating for PV glass and an oxide combinatorial sample library. Best practices are discussed for adapting characterization techniques for large area mapping and combining mapping information from multiple techniques.

14 SOLAR ENERGY↗
DOE OSTI2024

Tunable Collective Excitations in Epitaxial Perovskite Nickelates

The formation of plasmons through the collective excitation of charge density has generated intense discussions, offering insights to fundamental sciences and potential applications. While the underlying physical principles have been well-established, the effects of multibody interactions and orbital hybridization on plasmonic dynamics remain understudied. Here, in this work, we present the observation of conventional metallic and correlated plasmons in epitaxial La 1-x Sr x NiO 3 (LSNO) films with varying Sr doping concentrations (x = 0, 0.125, 0.25), unveiling their intriguing evolution. Unlike samples at other doping concentrations, the x = 0.125 intermediate doping sample does not exhibit the correlated plasmons despite showing high optical conductivity. Through experimental investigation using spectroscopic ellipsometry and X-ray absorption spectroscopy, that is further supported by theoretical calculations, the O2p-Ni3d orbital hybridization for x = 0.125 is found to be significantly enhanced, alongside a considerable weakening of its effective interaction comprising long-range Coulomb and variable interaction, U*. These factors account for the absence of correlated plasmons and the high optical conductivity observed in LSNO(0.125). Our findings highlight the significant impact of orbital hybridization on the electronic structures and the formation of quasiparticles in strongly correlated systems, opening new paths for plasmonic-based engineering research.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Influence of Substrate Temperature on the Transformation Front Velocities That Determine Thermal Stability of Vapor-Deposited Glasses

Stable organic glasses prepared by physical vapor deposition transform into the supercooled liquid via propagating fronts of molecular mobility, a mechanism different from that exhibited by glasses prepared by cooling the liquid. In this paper, we show that spectroscopic ellipsometry can directly observe this front-based mechanism in real time and explore how the velocity of the front depends upon the substrate temperature during deposition. For the model glass former indomethacin, we detect surface-initiated mobility fronts in glasses formed at substrate temperatures between 0.68T g and 0.94T g . At each of two annealing temperatures, the substrate temperature during deposition can change the transformation front velocity by a factor of 6, and these changes are imperfectly correlated with the density of the glass. We also observe substrate-initiated fronts at some substrate temperatures. By connecting with theoretical work, we are able to infer the relative mobilities of stable glasses prepared at different substrate temperatures. Finally, an understanding of the transformation behavior of vapor-deposited glasses may be relevant for extending the lifetime of organic semiconducting devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Inferring relative dose-dependent color center populations in proton irradiated thoria single crystals using optical spectroscopy

In this work, we have utilized photoluminescence spectroscopy and optical ellipsometry to characterize the dose-dependence of the photoluminescence emission intensity and changes in optical absorption of thoria single crystals subject to irradiation with energetic protons at room- and elevated-temperatures. The photoluminescence peaks and the optical absorption bands are attributed to creation of new electronic states emerging from defects resulting from displacement damage. These bands are most likely associated with electrons trapped at the oxygen vacancy sites similar to color centers formed in other irradiated oxides and halides. Our experimental observations are supported by a standard density functional theory calculation of the electronic structure in pristine and oxygen vacancy-bearing thoria crystals. The dose-dependence of the intensity of the photoluminescence peaks is used to parameterize a rate theory model that estimates the concentration of color centers in the irradiated crystals. This parameterization provides optimized migration barrier parameters for oxygen interstitials and vacancies that simultaneously capture the optical response of the crystals irradiated at room- and elevated-temperature. These optical spectroscopy techniques offer a promising pathway to characterize the population of color centers formed at the sites of oxygen anion vacancies, particularly in irradiated nuclear fuels, where atomic-level defects cannot be readily imaged using electron microscopy. When combined with other direct and indirect characterization tools, our approach can provide new insight into defect formation and accumulation in energy materials over single atomic to extended length scales.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The A-site driven phase transition procedure of (Pb{sub 0.97}La{sub 0.02})(Zr{sub 0.42}Sn{sub 0.40}Ti{sub 0.18})O{sub 3} ceramics: An evidence from electronic structure variation

The transition of (Pb{sub 0.97}La{sub 0.02})(Zr{sub 0.42}Sn{sub 0.40}Ti{sub 0.18})O{sub 3} (PLZST) ceramic has been investigated by temperature-dependent X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). The rhombohedral and tetragonal symmetries are confirmed by XRD analysis. Two interband transitions (E{sub cp1} and E{sub cp2}) located at about 3.7 and 5.2 eV can be derived from the second derivative of the complex dielectric functions using the standard critical point (SCP) model. Except for the negative temperature coefficient parts, the transitions present additional parts corresponding to appearance of the antiferroelectric (AFE) phase. The phenomena can be attributed to variation of the electronic structure during A-site driven phase transition.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Electron effective mass in Al{sub 0.72}Ga{sub 0.28}N alloys determined by mid-infrared optical Hall effect

The effective electron mass parameter in Si-doped Al{sub 0.72}Ga{sub 0.28}N is determined to be m{sup ∗}=(0.336±0.020) m{sub 0} from mid-infrared optical Hall effect measurements. No significant anisotropy of the effective electron mass parameter is found supporting theoretical predictions. Assuming a linear change of the effective electron mass with the Al content in AlGaN alloys and m{sup ∗}=0.232 m{sub 0} for GaN, an average effective electron mass of m{sup ∗}=0.376 m{sub 0} can be extrapolated for AlN. The analysis of mid-infrared spectroscopic ellipsometry measurements further confirms the two phonon mode behavior of the E{sub 1}(TO) and one phonon mode behavior of the A{sub 1}(LO) phonon mode in high-Al-content AlGaN alloys as seen in previous Raman scattering studies.

36 MATERIALS SCIENCE↗