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DOE OSTI2014

Technical Note: Influence of the phantom material on the absorbed-dose energy dependence of the EBT3 radiochromic film for photons in the energy range 3 keV–18 MeV

Purpose: Water is the reference medium for radiation therapy dosimetry, but for film dosimetry it is more practical to use a solid phantom. As the composition of solid phantoms differs from that of water, the energy dependence of film exposed within solid phantoms may also differ. The energy dependence of a radiochromic film for a given beam quality Q (energy for monoenergetic beams) has two components: the intrinsic energy dependence and the absorbed-dose energy dependence f(Q), the latter of which can be calculated through a Monte Carlo simulation of radiation transport. The authors used Monte Carlo simulations to study the influence of the phantom material on the f(Q) of the EBT3 radiochromic film (Ashland Specialty Ingredients, Wayne, NJ) for photon beams with energies between 3 keV and 18 MeV. Methods: All simulations were carried out with the general-purpose Monte Carlo code PENELOPE 2011. The geometrical model consisted of a cylindrical phantom, with the film positioned at different depths depending on the initial photon energy. The authors simulated monoenergetic parallel photon beams and x-ray beams from a superficial therapy system. To validate their choice of simulation parameters, they also calculated f(Q) for older film models, EBT and EBT2, comparing with published results. In addition to water, they calculated f(Q) of the EBT3 film for solid phantom materials commonly used for film dosimetry: RW1 and RW3 (PTW-Freiburg, Freiburg, Germany), Solid Water (Gammex-RMI, Madison, WI), and PMMA. Finally, they combined their calculated f(Q) with published overall energy response data to obtain the intrinsic energy dependence of the EBT3 film in water. Results: The calculated f(Q) for EBT and EBT2 films was statistically compatible with previously published data. Between 10 keV and 18 MeV, the variation found in f(Q) of the EBT3 film for water was within 2.3%, with a standard statistical uncertainty less than 1%. If the quantity dose-to-water in the phantom is considered, which is the common practice in radiation dosimetry, the maximum difference of energy dependence for the solid phantoms with respect to water is about 6%, at an energy of 50 keV. Conclusions: The EBT3 film shows a reasonably constant absorbed-dose energy dependence when irradiated in water. If the dose-to-water in the phantom is considered, the maximum difference of EBT3 film energy dependence with the solid phantoms studied with respect to water is about 6% (at an energy of 50 keV). The reported overall energy dependence of the EBT3 film in water at energies below 100 keV is mainly due to the intrinsic energy dependence.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2015

Correcting scan-to-scan response variability for a radiochromic film-based reference dosimetry system

Purpose: In radiochromic film dosimetry systems, measurements are usually obtained from film images acquired on a CCD-based flatbed scanner. The authors investigated factors affecting scan-to-scan response variability leading to increased dose measurement uncertainty. Methods: The authors used flatbed document scanners to repetitively scan EBT3 radiochromic films exposed to doses 0–1000 cGy, together with three neutral density filters and three blue optical filters. Scanning was performed under two conditions: scanner lid closed and scanner lid opened/closed between scans. The authors also placed a scanner in a cold room at 9 °C and later in a room at 22 °C and scanned EBT3 films to explore temperature effects. Finally, the authors investigated the effect of altering the distance between the film and the scanner’s light source. Results: Using a measurement protocol to isolate the contribution of the CCD and electronic circuitry of the scanners, the authors found that the standard deviation of response measurements for the EBT3 film model was about 0.17% for one scanner and 0.09% for the second. When the lid of the first scanner was opened and closed between scans, the average scan-to-scan difference of responses increased from 0.12% to 0.27%. Increasing the sample temperature during scanning changed the RGB response values by about −0.17, −0.14, and −0.05%/°C, respectively. Reducing the film-to-light source distance increased the RBG response values about 1.1, 1.3, and 1.4%/mm, respectively. The authors observed that films and film samples were often not flat with some areas up to 8 mm away from the scanner’s glass window. Conclusions: In the absence of measures to deal with the response irregularities, each factor the authors investigated could lead to dose uncertainty >2%. Those factors related to the film-to-light source distance could be particularly impactful since the authors observed many instances where the curl of film samples had the potential to cause dose uncertainty in excess of 5%. Two expedients will eliminate the uncertainties: a transparent sheet (preferably glass) placed over the scanned film keeps the film-to-light source distance constant, and an EBT3 reference film included in all scans provides correction factors for measured response values.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2024

Analysis and Design for Sustainable Circularity of Barrier Films Used in Sheet Molding Composites Production

Sheet molding composites (SMC) are thermoset based molding compounds with a global market size of USD 2.1 billion in 2020. SMC is usually processed with multilayer barrier/carrier films to prevent emissions from volatile organic compounds (VOC). The plastic barriers are separated from SMC after the curing process and discarded. To illustrate the high consumption volume of SMC barrier/carrier films, Kohler Co., a company which uses SMC in their bath and showering product lines, alone generates over 1M lb/year of SMC barrier/carrier film waste. Therefore, high amount of SMC barrier/carrier film plastic waste creates a great opportunity for reusing, recycling, or valorization at its end of life. This can be achieved through transition from a linear to a circular supply chain design. However, this transition will not be feasible without overcoming the technical and economic barriers. This project aims to tackle this by making the film circular. Different end of life alternatives will be evaluated experimentally. The reusability of the film will be studied through applying different mechanical and solvent cleaning techniques. The operability concerns regarding the utilization of the cleaned film for long run operations will be addressed by thermally stitching the film. Pelletizing of the cleaned film will also be investigated as a viable technique for recycling or downcycling of the film as molded products. In addition to technical barriers, designing a sustainable circular supply chain for SMC carrier film products requires uncovering the collaboration opportunities between suppliers and users at different stages of the value chain to expand its use to other products. These opportunities will be investigated by finding companies willing to buy or treat the plastic film waste. Finally, the economic viability and environmental impacts of these circular design alternatives will be evaluated through techno-economic assessment (TEA) and life cycle analysis (LCA). Techno-economic and life cycle inventory data for various pathways will also be made available as one of the main outcomes of this project. Preliminary LCA results indicate that the current SMC film supply chain (base case) emits 5.81 tonne CO2 eq. and consumes 104 GJ energy per tonne of SMC film. It is estimated that alternative circular pathways result in 14-20% less CO2 emissions and 34-44% reduction in embodied energy. This project will develop a tool to analyze the circularity and sustainability of hundreds of combinations of alternatives in different life cycle stages. Users of this tool will be able to choose the best combination among these alternatives with respect to the selected economic, environmental and circularity objectives.

circular economy↗

DOE OSTI2019

Evidence of Room Temperature Ferromagnetism in Zn{sub 1−x}Sn{sub x}S Thin Films

Tin (Sn)-doped zinc sulfide (Zn{sub 1−x}Sn{sub x}S) thin films at different tin (Sn) concentrations (= 0.00, 0.02, 0.05, and 0.08) were coated onto Corning 7059 glass substrates using the electron beam evaporation technique. The films were subjected to different characterization techniques to study the physical properties of the thin films. The structural properties of the films were studied using a powder X-ray diffractometer (XRD), and it was found that the films were cubic in structure without any impurity phases. The crystallite size increased with an increase of Sn concentration, and the mean crystallite size was 21 nm. The chemical composition and surface morphology of the films were studied using scanning electron microscopy (FE-SEM) with energy-dispersive analysis of X-rays (EDAX). Optical properties such as transmittance and absorbance were recorded using a diffuse reflectance spectroscope (UV–vis–NIR). All the films exhibited high optical transmittance of 85% in the visible region of the solar spectrum. The band gap of the films was calculated using Tauc’s relation, and it was found that it increased from 3.53 to 3.57 eV with an increase in the Sn doping concentration from x = 0.02 to x = 0.08. The room temperature photoluminescence studies of the films were recorded using a fluorescence spectrophotometer, and it was found that the films exhibited a prominent emission peak at 420 nm. The magnetic properties of the films and glass substrates at room temperature were studied using a vibrating sample magnetometer. From this, it was found that the films were weakly ferromagnetic at room temperature and the strength of magnetization increased with an increase of doping concentration from x = 0.02 to x = 0.05 and decreased at higher doping concentrations (x = 0.08). The films showed high magnetization at x = 0.05. The films at x = 0.05 exhibited the magnetization (M{sub s}), retentivity (M{sub r}), and coercive fields (H{sub c}) 18 × 10{sup − 6} emu/cm{sup 3}, 1.6 × 10{sup − 6} emu/cm{sup 3}, and 91.80 Oe, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Characterizations of Binary FeCr (AISI 430) Thin Films Deposited from a Single Magnetron Sputtering Under Easy Controllable Deposition Parameters

A series of 50-nm binary FeCr martensitic thin films were sputtered from a single source made of commercial AISI 430 ferritic stainless steel under the deposition rates gradually increased from 0.03 to 0.11 nm/s with 0.02 nm/s steps at stationary condition. And, under 0.09 nm/s deposition rate, a second series of the films were also deposited under the rotation speed of their substrates which was chosen at 0, 25, and 45 rpm. As far as we are concerned, this study is the first investigation of properties of the thin films produced from AISI 430. The atomic Fe content in the films increased from 79.3 to 98.6% while atomic Cr content decreased from 20.5 to 1.2% with the increase of deposition rate from 0.03 to 0.11 nm/s. According to compositional analysis, the Fe content increased while Cr content decreased with increasing deposition rate. The reason for this may be attributed to the relatively different bond energy/melting point of metals which have different contents sputtered from source material since this physical parameter is very significant for the sputtering process. And, the Fe content in the films decreased from 84.9 to 79.2 at. % while the Cr content increased from 14.9 to 20.6 at. % when the increase of rotation speed of substrate. The crystal structure of all films was observed to have a body-centered tetragonal phase and the intensity of (110) peak varied with the atomic Fe content. The surface observations of films performed by a scanning electron microscope exposed that the number of surface grains increased with the increase of deposition rate and decreased with the increase of rotation speed. According to surface roughness analysis done by an atomic force microscope, the roughness of the film surfaces increased as the deposition rate increased. And, the roughness of the film surfaces decreased as the rotation speed increased. This has been consistent with the grain size and roughness parameters. Thus, increasing deposition rate and decreasing rotation speed of the substrate caused an increase in grain size and roughness parameters. The magnetic measurements of the films achieved, by a vibrating sample magnetometer at room temperature, displayed that the saturation magnetization, M{sub s}, values increased from 820.1 to 1700.4 emu/cm{sup 3}, the remanence magnetization, M{sub r}, values increased from 293 to 817 emu/cm{sup 3}, and the coercivity, H{sub c}, value also increased from 38 to 107 Oe with the increasing of deposition rate. It is also seen that the magnetic easy axis are in the film plane due to the shape anisotropy. With the increase rotation speed, the values of M{sub s} and M{sub r} increased and the H{sub c} decreased. It was seen that variation of Fe content in the films influences the M{sub s} values and the H{sub c} values are consistent with the surface properties. It was concluded that the deposition rate and the rotation speed of the substrate play a considerable role on the structural and related magnetic properties of the sputtered FeCr thin films, and the properties of the films can be easily controlled by changing production parameters.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Pulsed electrodeposition and characterization of Bi{sub 2}Te{sub 3−y}Se{sub y} films

Highlights: ► Bi{sub 2}Te{sub 3−y}Se{sub y} films synthesized by pulsed electrodeposition. ► The thermoelectric properties of the film were measured at room temperature. ► The films show much better properties then galvanostatically deposited film. -- Abstract: Bi{sub 2}Te{sub 3−y}Se{sub y} films were synthesized by pulsed electrodeposition on indium tin oxide (ITO)-coated glass substrates from aqueous acidic solution at room temperature. The films were deposited at the same average current density but different cathodic current density. The crystal structure, surface morphology and elemental composition of the films were investigated. Smooth and compact Bi{sub 2}Te{sub 3−y}Se{sub y} films were obtained. As the cathodic current density increased, the grain size of the films decreased. The electrical resistivity and Seebeck coefficient of each Bi{sub 2}Te{sub 3−y}Se{sub y} film were measured after the film being transferred onto a non-conductive rubberized fabric support. The films showed n-type conduction, with Seebeck coefficient in the range of ∼−84 to −92 μV/K and electrical resistivity in the range of 102.9–109.4 μΩ m. The films showed much better thermoelectric properties compared with the film galvanostatically deposited at the same average current density.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Confinement and Processing Can Alter the Morphology and Periodicity of Bottlebrush Block Copolymers in Thin Films

Bottlebrush block copolymers (BBCPs) are intriguing architectural variations on linear BCPs with highly tunable structure. Confinement can have a significant impact on polymer assembly, giving rise to changes in morphology, assembly kinetics, and properties like the glass transition. Given that confinement leads to significant changes in the persistence length of bottlebrush homopolymers, it is reasonable to expect that BBCPs will see significant changes in their structure and periodicity relative to the bulk morphology. Understanding how confinement influences assembly will be important for designing BBCPs for thin film applications including membranes, integrated photonic structures, and potentially BCP lithography. In this work, in order to study the effects of confinement on BBCP conformation and morphology, a blade coating was used to prepare films with continuous variation in film thickness. Unlike thin films of linear BCPs, islands/holes were not observed, and instead mixtures of parallel and perpendicular morphologies emerge after annealing. The lamellar periodicity ($L_0$) of the morphologies is found to be thickness dependent, increasing $L_0$ with decreasing film thickness for blade coated films. Films coated out of tetrahydrofuran (THF) resulted in a single well-defined lamellar periodicity, verified through atomic force microscopy (AFM) and grazing incidence small-angle X-ray scattering (GISAXS), which increases dramatically from the bulk value (30.6 nm) and continues to increase as the film thickness decreases. The largest observed $L_0$ was 65.5 nm, and this closely approaches the estimated upper limit of 67 nm corresponding to a fully extended backbone in a bilayer arrangement. Films coated out of propylene glycol methyl ether acetate (PGMEA) resulted in a mixture of perpendicular lamellae and a smaller, likely cylindrical morphology. The lamellar portion of the film shows the same thickness dependence as the lamellae observed in the THF coated films. The scaling of the lamellar $L_0$ with respect to film thickness follows predictions for confined semiflexible polymers with weak excluded volume interactions and can be related to models for confinement of DNA. Spin coated films shows the same reduction in periodicity, although at very different film thicknesses. This result suggests that the material has shallow free-energy barriers to transitioning between different $L_0$ and morphologies, a property that could be taken advantage of for patterning diverse structures with a single material.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Dual mechanical behaviour of hydrogen in stressed silicon nitride thin films

In the present article, we report a study on the mechanical behaviour displayed by hydrogen atoms and pores in silicon nitride (SiN) films. A simple three-phase model is proposed to relate the physical properties (stiffness, film stress, mass density, etc.) of hydrogenated nanoporous SiN thin films to the volume fractions of hydrogen and pores. This model is then applied to experimental data extracted from films deposited by plasma enhanced chemical vapour deposition, where hydrogen content, stress, and mass densities range widely from 11% to 30%, −2.8 to 1.5 GPa, and 2.0 to 2.8 g/cm{sup 3}, respectively. Starting from the conventional plotting of film's Young's modulus against film porosity, we first propose to correct the conventional calculation of porosity volume fraction with the hydrogen content, thus taking into account both hydrogen mass and concentration. The weight of this hydrogen-correction is found to evolve linearly with hydrogen concentration in tensile films (in accordance with a simple “mass correction” of the film density calculation), but a clear discontinuity is observed toward compressive stresses. Then, the effective volume occupied by hydrogen atoms is calculated taking account of the bond type (N-H or Si-H bonds), thus allowing a precise extraction of the hydrogen volume fraction. These calculations applied to tensile films show that both volume fractions of hydrogen and porosity are similar in magnitude and randomly distributed against Young's modulus. However, the expected linear dependence of the Young's modulus is clearly observed when both volume fractions are added. Finally, we show that the stiffer behaviour of compressive films cannot be only explained on the basis of this (hydrogen + porosity) volume fraction. Indeed this stiffness difference relies on a dual mechanical behaviour displayed by hydrogen atoms against the film stress state: while they participate to the stiffness in compressive films, hydrogen atoms mainly behave like pores in tensile films where they do not participate to the film stiffness.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Microstructure of a-C:H films prepared on a microtrench and analysis of ions and radicals behavior

Amorphous carbon films (a-C:H) were prepared on a microtrench (4-μm pitch and 4-μm depth), and the uniformity of film thickness and microstructure of the films on the top, sidewall, and bottom surfaces of the microtrench were evaluated by scanning electron microscopy and Raman spectroscopy. The a-C:H films were prepared by bipolar-type plasma based ion implantation and deposition (bipolar PBII&D), and the negative pulse voltage, which is the main parameter dominating the film structure, was changed from −1.0 to −15 kV. Moreover, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision (PIC-MCC) and Direct Simulation Monte Carlo (DSMC) to investigate the coating mechanism for the microtrench. The results reveal that the thickness uniformity of a-C:H films improves with decreasing negative pulse voltage due to the decreasing inertia of incoming ions from the trench mouth, although the film thickness on the sidewall tends to be much smaller than that on the top and bottom surfaces of the trench. The normalized flux and the film thickness show similar behavior, i.e., the normalized flux or thickness at the bottom surface increases at low negative pulse voltages and then saturates at a certain value, whereas at the sidewall it monotonically decreases with increasing negative voltage. The microstructure of a-C:H films on the sidewall surface is very different from that on the top and bottom surfaces. The film structure at a low negative pulse voltage shifts to more of a polymer-like carbon (PLC) structure due to the lower incident energy of ions. Although the radical flux on the sidewall increases slightly, the overall film structure is not significantly changed because this film formation at a low negative voltage is originally dominated by radicals. On the other hand, the flux of radicals is dominant on the sidewall in the case of high negative pulse voltage, resulting in a deviation from the Raman behavior of a-C:H films deposited by bipolar PBII&D. This tendency intensifies as the negative voltage becomes greater. Also, the energy of incident ions on the sidewall of the trench increases with increasing negative voltage, which causes a shift in the Raman data of the sidewall to the bottom right corner on the figure depicting the relationship of the FWHM(G) and the G-peak position, indicating increased graphitization of a-C:H film.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Optical characteristics of nanocrystalline Al{sub x}Ga{sub 1−x}N thin films deposited by hollow cathode plasma-assisted atomic layer deposition

Gallium nitride (GaN), aluminum nitride (AlN), and Al{sub x}Ga{sub 1−x}N films have been deposited by hollow cathode plasma-assisted atomic layer deposition at 200 °C on c-plane sapphire and Si substrates. The dependence of film structure, absorption edge, and refractive index on postdeposition annealing were examined by x-ray diffraction, spectrophotometry, and spectroscopic ellipsometry measurements, respectively. Well-adhered, uniform, and polycrystalline wurtzite (hexagonal) GaN, AlN, and Al{sub x}Ga{sub 1−x}N films were prepared at low deposition temperature. As revealed by the x-ray diffraction analyses, crystallite sizes of the films were between 11.7 and 25.2 nm. The crystallite size of as-deposited GaN film increased from 11.7 to 12.1 and 14.4 nm when the annealing duration increased from 30 min to 2 h (800 °C). For all films, the average optical transmission was ∼85% in the visible (VIS) and near infrared spectrum. The refractive indices of AlN and Al{sub x}Ga{sub 1−x}N were lower compared to GaN thin films. The refractive index of as-deposited films decreased from 2.33 to 2.02 (λ = 550 nm) with the increased Al content x (0 ≤ x ≤ 1), while the extinction coefficients (k) were approximately zero in the VIS spectrum (>400 nm). Postdeposition annealing at 900 °C for 2 h considerably lowered the refractive index value of GaN films (2.33–1.92), indicating a significant phase change. The optical bandgap of as-deposited GaN film was found to be 3.95 eV, and it decreased to 3.90 eV for films annealed at 800 °C for 30 min and 2 h. On the other hand, this value increased to 4.1 eV for GaN films annealed at 900 °C for 2 h. This might be caused by Ga{sub 2}O{sub 3} formation and following phase change. The optical bandgap value of as-deposited Al{sub x}Ga{sub 1−x}N films decreased from 5.75 to 5.25 eV when the x values decreased from 1 to 0.68. Furthermore, postdeposition annealing did not affect the bandgap of Al-rich films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2012

Linearization of dose-response curve of the radiochromic film dosimetry system

Purpose: Despite numerous advantages of radiochromic film dosimeter (high spatial resolution, near tissue equivalence, low energy dependence) to measure a relative dose distribution with film, one needs to first measure an absolute dose (following previously established reference dosimetry protocol) and then convert measured absolute dose values into relative doses. In this work, we present result of our efforts to obtain a functional form that would linearize the inherently nonlinear dose-response curve of the radiochromic film dosimetry system. Methods: Functional form [{zeta}= (-1){center_dot}netOD{sup (2/3)}/ln(netOD)] was derived from calibration curves of various previously established radiochromic film dosimetry systems. In order to test the invariance of the proposed functional form with respect to the film model used we tested it with three different GAFCHROMIC Trade-Mark-Sign film models (EBT, EBT2, and EBT3) irradiated to various doses and scanned on a same scanner. For one of the film models (EBT2), we tested the invariance of the functional form to the scanner model used by scanning irradiated film pieces with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic film dosimetry system, verification tests have been performed in clinical applications: percent depth dose measurements, IMRT quality assurance (QA), and brachytherapy QA. Results: Obtained R{sup 2} values indicate that the choice of the functional form of the new argument appropriately linearizes the dose response of the radiochromic film dosimetry system we used. The linear behavior was insensitive to both film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMIC Trade-Mark-Sign EBT3 film model are well within {+-}2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. It was also found that criteria of 3%/3 mm for an IMRT QA plan and 3%/2 mm for a brachytherapy QA plan are passing 95% gamma function points. Conclusions: In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic film based reference dosimetry system. In this way, relative dosimetry can be conveniently performed using radiochromic film dosimetry system without the need of establishing calibration curve.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

Radiochromic film calibration for low-energy seed brachytherapy dose measurement

Purpose: Radiochromic film dosimetry is typically performed for high energy photons and moderate doses characterizing external beam radiotherapy (XRT). The purpose of this study was to investigate the accuracy of previously established film calibration procedures used in XRT when applied to low-energy, seed-based brachytherapy at higher doses, and to determine necessary modifications to achieve similar accuracy in absolute dose measurements. Methods: Gafchromic EBT3 film was used to measure radiation doses upwards of 35 Gy from 75 kVp, 200 kVp, 6 MV, and (∼28 keV) I-125 photon sources. For the latter irradiations a custom phantom was built to hold a single I-125 seed. Film pieces were scanned with an Epson 10000XL flatbed scanner and the resulting 48-bit RGB TIFF images were analyzed using both FilmQA Pro software andMATLAB. Calibration curves relating dose and optical density via a rational functional form for all three color channels at each irradiation energy were determined with and without the inclusion of uncertainties in the measured optical densities and dose values. The accuracy of calibration curve variations obtained using piecewise fitting, a reduced film measurement area for I-125 irradiation, and a reduced number of dose levels was also investigated. The energy dependence of the film lot used was also analyzed by calculating normalized optical density values. Results: Slight differences were found in the resulting calibration curves for the various fitting methods used. The accuracy of the calibration curves was found to improve at low doses and worsen at high doses when including uncertainties in optical densities and doses, which may better represent the variability that could be seen in film optical density measurements. When exposing the films to doses > 8 Gy, two-segment piecewise fitting was found to be necessary to achieve similar accuracies in absolute dose measurements as when using smaller dose ranges. When reducing the film measurement area for the I-125 irradiations, the accuracy of the calibration curve was degraded due to the presence of localized film heterogeneities. No degradation in the calibration curves was found when reducing the number of calibration points down to only 4, but with piecewise fitting, 6 calibration points as well as a blank film are required. Variations due to photon energy in film optical density of up to 3% were found above doses of 2 Gy. Conclusions: A modified procedure for performing EBT3 film calibration was established for use with low-energy brachytherapy seeds and high dose exposures. The energy dependence between 6 MV and I-125 photons is significant such that film calibrations should be done with an appropriately low-energy source when performing low-energy brachytherapy dose measurements. Two-segment piecewise fitting with the inclusion of errors in measured optical density as well as dose was found to result in the most accurate calibration curves. Above doses of 1 Gy, absolute dose measurements can be made with an accuracy of 1.6% for 6 MV beams and 5.7% for I-125 seed exposures if using the I-125 source for calibration, or 2.3% if using the 75 kVp photon beam for calibration.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2014

SU-E-T-637: Age and Batch Dependence of Gafchromic EBT Films in Photon and Proton Beam Dosimetry

Purpose: Gafchrmoic films have undergone significant changes in characteristic over time reflected by HS, EBT, EBT2, EBT3 name. Interand intra- EBT film variability have been studied and found to be significant. However, age and lot/batch type have not been studied in various radiation beams that are investigated in this study. Methods: Thirteen sets of films; 2 EBT, 6 EBT2 and 5 EBT3 films with different lot number and expiration date were acquired. Films were cut longitudinally in 3 cm width and sandwiched between two solid water slabs that were placed in a water phantom to eliminate air gap. Each set of films were irradiated longitudinally at dmax with 6 and 15 MV photon beams as well as in reference condition (16 cm range, 10 cm SOBP) in our uniform scanning proton beam. Films were scanned using an Epson flatbed scanner (ES-10000G) after 48 hours to achieve full polymerization. The profiles were compared with the depth-dose measured with ionization chamber and net optical density (net OD) were calculated. Results: The net OD versus dose for EBT, EBT2 and EBT3 films of different age showed similar trend but with different slope. Even after calibration, differences are clearly visible in net OD in proton and photon beams. A net OD difference of nearly 0.5 is observed in photon but this was limited to 0.2–0.3 in proton beam. This relates to 20% and 15% dosimetric difference in photon and proton beam respectively over age and type of film. Conclusion: Net OD related to dose is dependent on the age and lot of the film in both photon and proton beams. It is concluded that before any set of film is used, a calibration film should be used for a meaningful dosimetry. The expired films showed larger OD variation compared to unexpired films.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2015

SU-E-T-386: Evaluation of EBT3 Film Response in Different Batches

Purpose: To investigate the uniformity of film response of EBT3 film of two different film batches. It has been reported that the response of the EBT film family is not homogenous between film batches. The later may have an impact in the dosimetry of small radiotherapy beams. Methods: A solid water phantom was used for dosimetric measurements. EBT3 film irradiation was performed with a 6 MV photon beam at 5 cm depth with a SAD of 100 cm. All irradiations were performed perpendicularly to the film plane covering the dose range 1 to 10 Gy. Three square field sizes were used to analyze the film response energy dependence: 10, 5 and 1 cm{sup 2}. Two batches of film EBT3 were used #A03181302 (B1) and #03031403 (B2). Film read out was carrying out with an Epson Perfection V750-Pro flatbed scanner in transmission mode with a spatial resolution of 72 dpi, with all post-processing and colour management options turned off, using 48 bits RGB colour depth. The scans were analyzed with the red channel. Results: The results shown that there were differences between the film response for each batch. The differences between batches for 1 Gy were 2%, 6% and 12% for 10, 5 and 1 cm2 square field sizes, respectively. The differences found for 10 Gy were 13%, 14% and 13% for 10, 5 and 1 cm{sup 2} square field sizes, respectively. It can be observed that the dependence with field size dismissed for higher doses. The later may be due to film response saturation at 10 Gy. Conclusion: The EBT3 film -as its predecessors-, it suffer for inter-batch variability in the film response. Further research is required to assess the possible impact in small beam dosimetry.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2021

Thin-film chemical expansion of ceria based solid solutions: laser vibrometry study

The chemical expansion of Pr 0.1 Ce 0.9 O 2-δ (PCO) and CeO 2-δ thin films is investigated in the temperature range between 600 °C and 800 °C by laser Doppler vibrometry (LDV). It enables non-contact determination of nanometer scale changes in film thickness at high temperatures. The present study is the first systematic and detailed investigation of chemical expansion of doped and undoped ceria thin films at temperatures above 650 °C. The thin films were deposited on yttria stabilized zirconia substrates (YSZ), operated as an electrochemical oxygen pump, to periodically adjust the oxygen activity in the films, leading to reversible expansion and contraction of the film. This further leads to stresses in the underlying YSZ substrates, accompanied by bending of the overall devices. Film thickness changes and sample bending are found to reach up to 10 and several hundred nanometers, respectively, at excitation frequencies from 0.1 to 10 Hz and applied voltages from 0–0.75 V for PCO and 0–1 V for ceria. At low frequencies, equilibrium conditions are approached. As a consequence maximum thin-film expansion of PCO is expected due to full reduction of the Pr ions. The lower detection limit for displacements is found to be in the subnanometer range. At 800 °C and an excitation frequency of 1 Hz, the LDV shows a remarkable resolution of 0.3 nm which allows, for example, the characterization of materials with small levels of expansion, such as undoped ceria at high oxygen partial pressure. As the correlation between film expansion and sample bending is obtained through this study, a dimensional change of a free body consisting of the same material can be calculated using the high resolution characteristics of this system. A minimum detectable dimensional change of 5 pm is estimated even under challenging high-temperature conditions at 800 °C opening up opportunities to investigate electro-chemo-mechanical phenomena heretofore impossible to investigate. The expansion data are correlated with previous results on the oxygen nonstoichiometry of PCO thin films, and a defect model for bulk ceria solid solutions is adopted to calculate the cation and anion radii changes in the constrained films during chemical expansion. The constrained films exhibit anisotropic volume expansion with displacements perpendicular to the substrate plane nearly double that of bulk samples. The PCO films used here generate high total displacements of several 100 nm’s with high reproducibility. Consequently, PCO films are identified to be a potential core component of high-temperature actuators. They benefit not only from high displacements at temperatures where most piezoelectric materials no longer operate while exhibiting, low voltage operation and low energy consumption.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Low-cost, highly transparent flexible low-e coating film to enable electrochromic windows with increased energy savings

Five Quads of energy are lost through windows annually in the U.S. Low-e coatings are increasingly employed to reduce the wasted energy. Most commonly, the low-e coating is an oxide material applied directly to the glass at high temperature. With over 100,000,000 existing homes, a retrofit product is crucial to achieve widespread energy savings. Low-e films, i.e. coatings on polymeric substrates, are now also available to meet this need. However, the traditional oxide materials and process is incompatible with low temperature plastics. Alternate high performing low-e films typically incorporate materials that limit visible transmission to 35% or less. Further, the cost is high. The objective of this award was to develop a retrofit, integrated low-e/electrochromic window film to dramatically reduce energy lost through windows. While field testing of state-of-the-art electrochromic (EC) windows show the energy savings are maximized if a low-e coating is used in conjunction with the EC, available low-e films have a low visible transmission (~70% or less) that limits the achievable clear state and therefore, appearance and energy savings potential. Comprehensive energy savings models were completed at Lawrence Berkeley National Lab (LBNL). A parametric approach was used to project energy usage for windows with a large range of low-e properties across all U.S. climate zones, without limiting the study to materials that had already been produced commercially or made in a lab. The model enables projection of energy savings for low-e films as well as integrated low-e/EC products. This project developed a novel low-e film, optimized for compatibility with EC windows, using low temperature, high deposition rate processes for the growth of low-e coatings on plastic films by microwave plasma enhanced chemical vapor deposition. Silica films with good density and optical properties were demonstrated at deposition rates as high as 130Å/sec. A simple bi-layer low-e stack of silica and a transparent conductive oxide demonstrated 90% visible transmission with high thermal infrared reflectivity characteristic of conventional low-e coatings. A slightly more complex stack provided high solar infrared reflection without sacrificing visible transmission or thermal infrared reflection. Successful completion of the effort produced a prototype integrated low-e, dynamic window film with characterized energy saving potential. Cost modeling for the passive bi-layer, low-e film projects a manufacturing cost of ~$0.50/ft2 for a plant with 10M ft2/yr capacity. The novel thin film processes developed here enable high deposition rate (low cost), optical quality oxide coatings at low temperatures. When combined with engineered materials, ITN’s coating will result in low-cost, low-e films that reflect a high degree of infrared radiation without substantially reducing the visible transmission. The resultant window film will improve the U-value and achieve SHGC improvements over bare glass. The new low-e coating will be particularly attractive when combined with an electrochromic film. Low-e coating design guided by energy savings modeling allows customization of the product for different climate zones.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2017

Optical-based spectroscopic methods for measuring chemical, optical, and physical properties of thin polymer waveguide films

Non-destructive optical-based spectroscopic methods are needed for analyzing “real world” devices that consist of thin polymer waveguide films. Many applications (e.g., sensors, microelectronics, optics, and biomedical applications, etc.) utilize thin polymer waveguide films, and non-destructive characterization methods based on Fourier transform (FT)-plasmon waveguide spectroscopy (PWR) and scanning angle (SA) Raman spectroscopy are used to extract optical, physical, and chemical properties simultaneously. The FT-PWR method measures reflected light at polymer waveguide interface as both the incident frequency (wavelength) and incident angle are scanned. This method uses p- and s-polarized light to simultaneously extract the polymer waveguide thickness and apparent anisotropic indices of refraction. Polystyrene waveguide films ranging from 360 to 800 nm are used to demonstrate the method and it has an average 0.4% relative error when compared to profilometry and atomic force microscopy measurements. SA Raman spectroscopy is used to measure mixed waveguide polymer films consisting of polystyrene-block-poly(methyl methacrylate) and homopolymer poly(methyl methacrylate) (PS-b-PMMA:PMMA), and poly(2-vinylnapthalene)-block-poly(methyl methacrylate) (P2VN-b-PMMA). PMMA homopolymer is added to the PS-b-PMMA solutions to vary the chemical composition. The chemical composition of each mixed film is quantified (SA Raman peak amplitude ratios) and averaged over all incident angles and is termed the Raman amplitude ratio (rps). This parameter is used to calculate the refractive index of each mixed waveguide polymer film. The refractive index is an input parameter for sum square electric field (SSEF) calculations, which are used to model SA Raman spectra as a function of incident angle to extract the film thickness. The mixed polymer waveguide film thicknesses ranged from 495 to 971 nm, and the SA Raman spectroscopy method has an average 5% difference between the values determined by profilometry. The SA Raman spectroscopy method developed for mixed polymer waveguide films is used to measure the chemical composition and extract interface locations in bilayer and trilayer films consisting of PMMA/PS or PMMA/PS/PMMA, respectively. The rps value is averaged over angle ranges corresponding to waveguide mode 0 and waveguide mode 1 for the bilayer and trilayer films, respectively. Six multilayer films are analyzed and their total thicknesses range from 330 to 1260 nm. Iterative SSEF calculations are used to model the SA Raman spectra as a function of incident angle, and the best fit to the experimental data is used to extract the total thickness and interface location(s). The method has an axial spatial resolution of 7 to 80 nm and provides comparable values to films measured by profilometry with an average 8% and 7% difference for the bilayer and trilayer films, respectively.

36 MATERIALS SCIENCE↗

NASA NTRS2000

The Effect of Radiation on Selected Photographic Film

We conducted this film test to evaluate several manufacturers' photographic films for their ability to acquire imagery on the International Space Station. We selected 25 motion picture, photographic slide, and negative films from three different film manufacturers. We based this selection on the fact that their films ranked highest in other similar film tests, and on their general acceptance by the international community. This test differed from previous tests because the entire evaluation process leading up to the final selection was based on information derived after the original flight film was scanned to a digital file. Previously conducted tests were evaluated entirely based on 8 x 10s that were produced from the film either directly or through the internegative process. This new evaluation procedure provided accurate quantitative data on granularity and contrast from the digital data. This test did not try to define which film was best visually. This is too often based on personal preference. However, the test results did group the films by good, marginal, and unacceptable. We developed, and included in this report, a template containing quantitative, graphical, and visual information for each film. These templates should be sufficient for comparing the different films tested and subsequently selecting a film or films to be used for experiments and general documentation on the International Space Station.

Slater, Richard↗