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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of oxygen vacancies and Ag deposition on the magnetic properties of Ag/N co-doped TiO2 single-crystal films

Highlights: • Photochemical deposition method to prepare Ag-doped TiO{sub 2} samples. • TiO{sub 2} single crystal films are used for studying room temperature ferromagnetism origin. • Ag element is deposited on TiO{sub 2} single crystal films surface in the form of Ag particles. • Oxygen vacancies and Ag particles synergy influence the ferromagnetism in samples. - Abstract: We employ TiO{sub 2} single-crystal films as a substrate and use a photochemical deposition method to prepare Ag-doped and Ag/N co-doped TiO{sub 2} single-crystal films. We also investigate the optical and magnetic properties of the samples using various measurements. No diffraction peaks related to silver oxide appear in the X-ray diffraction (XRD) spectra, which implies the existence of Ag atoms in Ag-doped TiO{sub 2} single-crystal films. X-ray photoelectron spectroscopy (XPS) spectra indicate the existence of Ti{sup 4+} and Ag° in Ag/N co-doped TiO{sub 2} single-crystal films. It is found that Ag is deposited on a TiO{sub 2} single-crystal film surface in the form of Ag particles. Meanwhile, Ag particles can slightly enhance ferromagnetism in Ag-doped TiO{sub 2} single-crystal films compared with the TiO{sub 2} single-crystal film sample. Oxygen vacancies and Ag particle synergy influence ferromagnetism in Ag/N co-doped TiO{sub 2} single-crystal films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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 OSTI2016

Scanning angle Raman spectroscopy: A nondestructive method for simultaneously determining mixed polymer fractional composition and film thickness

A scanning angle (SA) Raman spectroscopy method was developed to simultaneously measure the chemical composition and thickness of waveguide mixed polymer films with varying fractional compositions. In order to test the method, six films of polystyrene-block-poly(methyl methacrylate), some mixed with poly(methyl methacrylate) homopolymer (PS-b-PMMA:PMMA), and two films of poly(2-vinylnapthalene)-block-poly(methyl methacrylate) (P2VN-b-PMMA) were prepared. The film thickness ranged from 495 to 971 nm. The chemical composition and thickness of PS-b-PMMA:PMMA films was varied by the addition of the PMMA homopolymer and annealing the films in toluene. SA Raman peak amplitude ratios (1001 cm -1 for PS, 812 cm -1 for PMMA, and 1388 cm -1 for P2VN) were used to calculate the refractive index of the polymer film, an input parameter in calculations of the sum square electric field (SSEF). The film thickness was determined by SSEF models of the experimental Raman amplitudes versus the incident angle of light. The average film thickness determined by the developed SA Raman spectroscopy method was within 5% of the value determined by optical profilometry. In conclusion, SA Raman spectroscopy will be useful for in situ label-free analyses of mixed polymer waveguide films.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Structural and Electrocatalytic Studies of Pulsed Laser Deposited Epitaxial RuO 2 Thin Films

Two sets of high-quality epitaxial ruthenium oxide (RuO 2 ) thin films with different thicknesses were synthesized in situ on cost-competitive sapphire substrates by using a pulsed laser deposition technique. The first set of films, with a thickness of 40 nm and a sheet resistance of 15.7 Ω/□, was prepared using 2100 laser pulses, while the second set of films, with a thickness of 87 nm and a sheet resistance of 6.7 Ω/□, was prepared using 4800 laser pulses. All other deposition parameters were kept the same. The post-deposition structural and morphological measurements showed that both sets of films grew at the same growth rate, had the same crystallinity, similar grain boundary density, and slightly different surface roughness. The thicker RuO 2 films achieved an overpotential of 280 mV for the oxygen evolution reaction at a current density of 100 μA/cm 2 , comparable to or exceeding the performance of films grown on more expensive substrates. Comparatively, the thinner RuO 2 films, which have a significantly higher charge transfer resistance (250 Ω versus 100 Ω for thick films), display a higher overpotential of 320 mV. These results indicate that the lower electrical resistance of thicker films promotes charge transfer through the film body, leading to superior electrocatalytic properties.

charge-transfer↗
DOE OSTI2011

Influence of Al/CuO reactive multilayer films additives on exploding foil initiator

An investigation on the influence of Al/CuO reactive multilayer films (RMFs) additives on exploding foil initiator was performed in this paper. Cu film and Cu/Al/CuO RMFs were produced by using standard microsystem technology and RF magnetron sputtering technology, respectively. Scanning electron microscopy characterization revealed the distinct layer structure of the as-deposited Al/CuO RMFs. Differential scanning calorimetry was employed to ascertain the amount of heat released in the thermite reaction between Al films and CuO films, which was found to be 2024 J/g. Electrical explosion tests showed that 600 V was the most matching voltage for our set of apparatus. The explosion process of two types of films was observed by high speed camera and revealed that compared with Cu film, an extra distinct combustion phenomenon was detected with large numbers of product particles fiercely ejected to a distance of about six millimeters for Cu/Al/CuO RMFs. By using the atomic emission spectroscopy double line technique, the reaction temperature was determined to be about 6000-7000 K and 8000-9000 K for Cu film and Cu/Al/CuO RMFs, respectively. The piezoelectricity of polyvinylidene fluoride film was employed to measure the average velocity of the slapper accelerated by the explosion of the films. The average velocities of the slappers were calculated to be 381 m/s and 326 m/s for Cu film and Cu/Al/CuO RMFs, respectively, and some probable reasons were discussed with a few suggestions put forward for further work.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Large area ceramic thin films on plastics: A versatile route via solution processing

A new general route for large area, submicron thick ceramic thin films (crystalline metal oxide thin films) on plastic substrates is presented, where the crystallization of films is guaranteed by a firing process. Gel films are deposited on silicon substrates with a release layer and fired to be ceramic films, followed by transferring onto plastic substrates using adhesives. The ceramic films thus fabricated on plastics exhibit a certain degree of flexibility, implying the possibility of the technique to be applied to high-throughput roll-to-roll processes. Using this technique, we successfully realized transparent anatase thin films that provide high optical reflectance and transparent indium tin oxide thin films that exhibit electrical conductivity on polycarbonate and acrylic resin substrates, respectively. Crystallographically oriented zinc oxide films and patterned zinc oxide films are also demonstrated to be realized on acrylic resin substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructural evolution of thin film vanadium oxide prepared by pulsed-direct current magnetron sputtering

Vanadium oxide (VO{sub x}) thin films have been deposited by pulsed-DC magnetron sputtering using a metallic vanadium target in a reactive argon and oxygen environment. While the process parameters (power, total pressure, oxygen-to-argon ratio) remained constant, the deposition time was varied to produce films between 75 {+-} 6 and 2901 {+-} 30 A thick, which were then optically and electrically characterized. The complex dielectric function spectra ({epsilon} = {epsilon}{sub 1} + i{epsilon}{sub 2}) of the films from 0.75 to 5.15 eV were extracted by ex situ, multiple-angle spectroscopic ellipsometry (SE) measurements for the series of varied thickness VO{sub x} samples. Significant changes in {epsilon} and resistivity occur as a function of thickness, indicating the correlations exist between the electrical and the optical properties over this spectral range. In addition, in situ measurements via real time SE (RTSE) were made on the film grown to the largest thickness to track optical property and structural variations during growth. RTSE was also used to characterize changes in the film occurring after growth was completed, namely during post sputtering in the presence of argon and oxygen while the sample is shielded, and atmospheric exposure. RTSE indicates that the exposure of the film to the argon and oxygen environment, regardless of the shutter isolating the target, causes up to 200 A of the top surface of the deposited film to become more electrically resistive as evidenced by variations in {epsilon}. Exposure of the VO{sub x} thin film to atmospheric conditions introduces a similar change in {epsilon}, but this change occurs throughout the bulk of the film. A combination of these observations with RTSE results indicates that thinner, less ordered VO{sub x} films are more susceptible to drastic changes due to atmospheric exposure and that microstructural variations in this material ultimately control its environmental stability.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Lattice mismatch-induced evolution of microstructural properties in FePt films

FePt (10, 20, 40, and 60 nm) films were fabricated on four different single crystal substrates [MgO (001), KTaO{sub 3} (001), SrTiO{sub 3} (001), and LaAlO{sub 3} (001)], and the effects of lattice mismatch on the microstructure and magnetic properties of FePt films were systematically investigated. The X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results showed that the different lattice mismatch between the substrates and FePt films resulted in the different crystallographic texture and microstructure of the FePt films. Under the tensile strain between the FePt and substrates (MgO, KTaO{sub 3}, SrTiO{sub 3}), the FePt films preferred to form L1{sub 0} FePt (001) texture. The perpendicular anisotropy of the FePt films grown on MgO was larger than that grown on KTaO{sub 3} and SrTiO{sub 3}. For the FePt films grown on the LaAlO{sub 3} substrate, both FePt (110) and (001) orientations were found, which indicated the presence of tensile and compressive strain, respectively. With the reduction of the lattice mismatch between the FePt (10 nm) and substrate from 5.8% (MgO) to 2.4% (KTaO{sub 3}), and 0.1% (SrTiO{sub 3}), the microstructure of the FePt films changed gradually from granular to continuous films (SEM and TEM results). The microstructure of the 10 nm FePt film grown on LaAlO{sub 3} substrate showed granular structure.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Characterization of reactively sputtered molybdenum oxide films for solar cell application

Molybdenum oxide (MoO{sub 3}) thin films were prepared via Radio Frequency (RF) sputtering at different ambient composition and post-deposition annealing. The effects on the structural, optical, and surface properties of the deposited films were investigated. The ambient oxygen concentration O{sub 2}/(O{sub 2} + Ar) was varied from 10% to 100% at 10 mTorr. Post deposition anneals were performed in Ar at 300-500 Degree-Sign C. The films were analyzed using glancing incidence x-ray diffraction (GIXRD), UV/Vis/NIR spectrophotometry, and x-ray photoelectron spectroscopy (XPS). As-deposited films have amorphous structures, independent of the oxygen partial pressure. Annealing at 300 Degree-Sign C in air resulted in crystallization of the molybdenum oxide films to the monoclinic {beta}-MoO{sub 3} phase. Samples annealed at 400 and 500 Degree-Sign C were identified as pure orthorhombic {alpha}-MoO{sub 3} phase with (020) preferred orientation. High resolution XPS studies showed the presence of Mo{sup 6+} (MoO{sub 3}) and Mo{sup 5+} (Mo{sub 4}O{sub 11}) oxidation states at the surface of as deposited and low temperature (300 Degree-Sign C) annealed films, and the Mo{sup 6+} to Mo{sup 5+} did not change much with deposition oxygen partial pressure. Annealing at 400-500 Degree-Sign C suppressed the oxygen deficiency at the surface, resulting in films with composition close to stoichiometric phases. UV/Vis/NIR spectrophotometry revealed that all films have a high optical transmittance (>80%) in the visible range, followed by a steep drop at {lambda} Almost-Equal-To 400 nm indicating a strong absorption due to band-to-band transition. Increasing the oxygen partial pressure had no significant effect on optical transmittance of the films, and the bandgaps in the range of 2.6 eV to 2.9 eV were obtained. Annealing at 300 Degree-Sign C had a negligible effect on the optical properties of the MoO{sub 3} films, but samples annealed at 400 Degree-Sign C and 500 Degree-Sign C exhibited wider bandgaps within the range of 3.1-3.4 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructure after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Enhanced ferroelectric and dielectric properties of (111)-oriented highly cation-ordered PbSc{sub 0.5}Ta{sub 0.5}O{sub 3} thin films

Cation-ordered (111)-oriented epitaxial PbSc{sub 0.5}Ta{sub 0.5}O{sub 3} (PST) thin films were deposited by pulsed laser deposition on SrRuO{sub 3}-electroded SrTiO{sub 3} (111) substrates at three different temperatures of 525 °C, 550 °C, and 575 °C. All the films were well crystalline and (111)-oriented at all the three growth temperatures; however, the films deposited at the temperatures other than 550 °C exhibited the presence of a pyrochlore phase. X-ray diffraction analysis and transmission electron microscopy measurements revealed that the films were epitaxial and highly cation-ordered. In comparison to (001)-oriented PST films, (111)-oriented films on SrRuO{sub 3}/SrTiO{sub 3} (111) exhibited enhanced ferroelectric and dielectric properties with a broad size distribution of cation-ordered domains (5–100 nm). At a measurement temperature of 100 K, the remnant polarization of PST (111) films is almost √3 times larger than the remnant polarization observed for (001)-oriented PST films, which is attributed to the (111) orientation of the films, as the spontaneous polarization in PST lies close to the [111] direction. The observed dielectric constant and loss at 1 kHz were around 1145 and 0.11, respectively. The dielectric constant is thus almost three times higher than for previously reported (001)-oriented PST thin films, most probably due to the enhancement in cation-ordering.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Annealing effects on structural, electrical and optical properties of antimony-tinoxide thin films deposited by sol gel dip coating technique

Antimony-doped tin dioxide possess interesting physical and chemical properties. These properties have a wide range of applications such as catalysis and optoelectronic devices. In the present study, antimony-doped tin oxide (SnO2:Sb) thin films were deposited on the quartz substrates by sol-gel dip coating technique. The films were annealed at temperatures 350°C, 550°C and 850°C in air for 2 hours. The structure and surface morphologies were observed by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). XRD patterns shows tetragonal structure for the SnO2:Sb films annealed at different temperatures. Crystallite size increased from 6 to 14 nm as annealing temperature increased from 350°C to 850°C. SEM studies reveals crack free and smooth surface for all the films. The grains are found to be homogenously distributed for films annealed at higher temperature. The electrical conductivity of the films annealed at 350°C and 550°C decreased and increased for the films annealed at 850°C. The optical properties of the films were investigated in the UV-visible-NIR region (200-900 nm) using UV spectra. The transmittance of the films decreased for films annealed at higher temperature. The optical energy band gap values (4.13 eV-4.83 eV) increased with the increase in annealing temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Morphology and structure evolution of Cu(In,Ga)S{sub 2} films deposited by reactive magnetron co-sputtering with electron cyclotron resonance plasma assistance

Cu(In,Ga)S{sub 2} (CIGS) films were deposited on Mo coated soda lime glass substrates using an electron cyclotron resonance plasma enhanced one-step reactive magnetron co-sputtering process (ECR-RMS). The crystalline quality and the morphology of the Cu(In,Ga)S{sub 2} films were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy, and X-ray fluorescence. We also compared these CIGS films with films previously prepared without ECR assistance and find that the crystallinity of the CIGS films is correlated with the roughness evolution during deposition. Atomic force microscopy was used to measure the surface topography and to derive one-dimensional power spectral densities (1DPSD). All 1DPSD spectra of CIGS films exhibit no characteristic peak which is typical for the scaling of a self-affine surface. The growth exponent β, characterizing the roughness R{sub q} evolution during the film growth as R{sub q} ∼ d{sup β}, changes with film thickness. The root-mean-square roughness at low temperatures increases only slightly with a growth exponent β = 0.013 in the initial growth stage, while R{sub q} increases with a much higher exponent β = 0.584 when the film thickness is larger than about 270 nm. Additionally, we found that the H{sub 2}S content of the sputtering atmosphere and the Cu- to-(In + Ga) ratio has a strong influence of the morphology of the CIGS films in this one-step ECR-RMS process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Poole-Frenkel effect on electrical characterization of Al-doped ZnO films deposited on p-type GaN

This paper presents the electrical properties of Al-doped ZnO (AZO) films directly grown on two types of p-type GaN thin films. The low-pressure p-GaN thin films (LP-p-GaN) exhibited structural properties of high-density edge-type threading dislocations (TDs) and compensated defects (i.e., nitrogen vacancy). Compared with high-pressure p-GaN thin films (HP-p-GaN), X-ray photoemission spectroscopy of Ga 3d core levels indicated that the surface Fermi-level shifted toward the higher binding-energy side by approximately 0.7 eV. The high-density edge-type TDs and compensated defects enabled surface Fermi-level shifting above the intrinsic Fermi-level, causing the surface of LP-p-GaN thin films to invert to n-type semiconductor. A highly nonlinear increase in leakage current regarding reverse-bias voltage was observed for AZO/LP-p-GaN. The theoretical fits for the reverse-bias voltage region indicated that the field-assisted thermal ionization of carriers from defect associated traps, which is known as the Poole-Frenkel effect, dominated the I-V behavior of AZO/LP-p-GaN. The fitting result estimated the trap energy level at 0.62 eV below the conduction band edge. In addition, the optical band gap increased from 3.50 eV for as-deposited AZO films to 3.62 eV for 300 °C annealed AZO films because of the increased carrier concentration. The increasing Fermi-level of the 300 °C annealed AZO films enabled the carrier transport to move across the interface into the LP-p-GaN thin films without any thermal activated energy. Thus, the Ohmic behavior of AZO contact can be achieved directly on the low-pressure p-GaN films at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Crossover of electron-electron interaction effect in Sn-doped indium oxide films

We systematically study the structures and electrical transport properties of a series of Sn-doped indium oxide (ITO) films with thickness t ranging from ∼5 to ∼53 nm. Scanning electron microscopy and x-ray diffraction results indicate that the t ≲ 16.8 nm films are polycrystalline, while those t ≳ 26.7 nm films are epitaxially grown along [100] direction. For the epitaxial films, the Altshuler and Aronov electron-electron interaction (EEI) effect governs the temperature behaviors of the sheet conductance σ{sub □} at low temperatures, and the ratios of relative change of Hall coefficient ΔR{sub H}/R{sub H} to relative change of sheet resistance ΔR{sub □}/R{sub □} are ≈2, which is quantitatively consistent with Altshuler and Aronov EEI theory and seldom observed in other systems. For those polycrystalline films, both the sheet conductance and Hall coefficient vary linearly with logarithm of temperature below several tens Kelvin, which can be well described by the current EEI theories in granular metals. We extract the intergranular tunneling conductance of each film by comparing the σ{sub □}(T) data with the predication of EEI theories in granular metals. It is found that when the tunneling conductance is less than the conductance of a single indium tin oxide (ITO) grain, the ITO film reveals granular metal characteristics in transport properties; conversely, the film shows transport properties of homogeneous disordered conductors. Our results indicate that electrical transport measurement can not only reveal the underlying charge transport properties of the film but also be a powerful tool to detect the subtle homogeneity of the film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nanostructured and wide bandgap CdS:O thin films grown by reactive RF sputtering

In this study, CdS:O thin films were prepared from a 99.999% CdS target by reactive sputtering in a Ar:O{sub 2} (99:1) ambient with different RF power at room temperature. The deposited films were studied by means of XRD, SEM, EDX, Hall Effect and UV-Vis spectrometry. The incorporations of O{sub 2} into the films were observed to increase with the decrease of deposition power. The cryatallinity of the films were reduced, whereas the band gaps of the films were increased by the increase of O{sub 2} content on the films. The films were found in nano-structured grains with a compact surface. It has been seen that the highest carrier density is observed in the film with O{sub 2} at.% 21.10, while the values decreased with the further increase or decrease of O{sub 2} content on the films; indicating that specific amount of donor like O{sub 2} atoms substitute to the S atoms can improve the carrier density of the CdS:O thin film.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Proposed linear energy transfer areal detector for protons using radiochromic film

Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured at a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated LET with the LET measured using radiochromic film at the pixel level over extended areas. Failure rates using gamma analysis are calculated for areas in the dose distribution using parameters of 25% of MC LET and 3 mm. The processed dose distributions find 5%–10% failure rates for the narrow 12.5 and 15 cm proton ranges and 10%–15% for proton ranges of 15, 17.5, and 20 cm and modulated by 5 cm. It is found through gamma analysis that the measured proton energy deposition in radiochromic film and TPS can be used to determine LET. This modified film dosimetry provides an experimental areal LET measurement that can verify MC calculations, support LET point measurements, possibly enhance biologically based proton treatment planning, and determine the polymerization process within the radiochromic film.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Strong visible electroluminescence from silicon nanocrystals embedded in a silicon carbide film

We report the strong visible light emission from silicon (Si) nanocrystals (NCs) embedded in a Si carbide (SiC) film. Compared to Si NC light-emitting diode (LED) by employing the Si nitride (SiN{sub x}) film as a surrounding matrix, the turn-on voltage of the Si NC LED with the SiC film was significantly decreased by 4 V. This was attributed to a smaller barrier height for injecting the electrons into the Si NCs due to a smaller band gap of SiC film than a SiN{sub x} film. The electroluminescence spectra increases with increasing forward voltage, indicating that the electrons are efficiently injected into the Si NCs in the SiC film. The light output power shows a linear increase with increasing forward voltage. The light emission originated from the Si NCs in a SiC film was quite uniform. The power efficiency of the Si NC LED with the SiC film was 1.56 times larger than that of the Si NC LED with the SiN{sub x} film. The Si NCs in a SiC film show unique advantages and are a promising candidate for application in optical devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗