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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Technical Note: On GAFChromic EBT-XD film and the lateral response artifact

Purpose: The new radiochromic film, GAFChromic EBT-XD, contains the same active material, lithium-10,12-pentacosadiynoate, as GAFChromic EBT3, but the crystalline form is different. This work investigates the effect of this change on the well-known lateral response artifact when EBT-XD film is digitized on a flatbed scanner. Methods: The dose response of a single production lot of EBT-XD was characterized by scanning an unexposed film plus a set of films exposed to doses between 2.5 and 50 Gy using 6 MV photons. To characterize the lateral response artifact, the authors used the unexposed film plus a subset of samples exposed to doses between 20 and 50 Gy. Digital images of these films were acquired at seven discrete lateral locations perpendicular to the scan direction on three Epson 10000XL scanners. Using measurements at the discrete lateral positions, the scanner responses were determined as a function of the lateral position of the film. From the data for each scanner, a set of coefficients were derived whereby measured response values could be corrected to remove the effects of the lateral response artifact. The EBT-XD data were analyzed as in their previous work and compared to results reported for EBT3 in that paper. Results: For films scanned in the same orientation and having equal responses, the authors found that the lateral response artifact for EBT-XD and EBT3 films was remarkably similar. For both films, the artifact increases with increased net response. However, as EBT-XD is less sensitive than EBT3, a greater exposure dose is required to reach the same net response. On this basis, the lower sensitivity of EBT-XD relative to EBT3 results in less net response change for equal exposure and a reduction in the impact of the lateral response artifact. Conclusions: The shape of the crystalline active component in EBT-XD and EBT3 does not affect the fundamental existence of the lateral response artifact when the films are digitized on flatbed scanners. Owing its lower sensitivity, EBT-XD film requires higher dose to reach the same response as EBT3, resulting in lesser impact of the lateral response artifact. For doses >10 Gy, the slopes of the EBT-XD red and green channel dose response curves are greater than the corresponding ones for EBT3. For these two reasons, the authors prefer EBT-XD for doses exceeding about 10 Gy.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Nanomechanical properties of platinum thin films synthesized by atomic layer deposition

The nanomechanical properties of Pt thin films grown on Si (100) using atomic layer deposition (ALD) were investigated using nanoindentation. Recently, atomic layer deposition (ALD) has successfully demonstrated the capability to deposit ultra-thin films of platinum (Pt). Using (methylcyclopentadienyl) trimethylplatinum (MeCpPtMe3) as chemical platinum precursor and oxygen (O2) as the oxidizing agent, the ALD synthesis of Pt can be achieved with high conformity and excellent film uniformity. The ALD process window for Pt films was experimentally established in the temperature range between 270 °C and 320 °C, where the sheet conductance was constant over that temperature range, indicating stable ALD Pt film growth rate. ALD growth of Pt films exhibits very poor nucleation and adhesion characteristics on bare Si surfaces when the native oxide was removed by 2% HF etch. Pt adhesion improves for thermally oxidized Si wafers and for Si wafers covered with native oxide. Three ALD Pt films deposited at 800, 900, and 1000 ALD deposition cycles were tested for the structural and mechanical properties. Additionally, the sample with 900 ALD deposition cycles was further annealed in forming gas (95% N2 and 5% H2) at 450 °C for 30 min in order to passivate dangling bonds in the grain boundaries of the polycrystalline Pt film. Cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscope (SEM) were employed to characterize the films' surface structure and morphology. Nanoindentation technique was used to evaluate the hardness and modulus of the ALD Pt films of various film thicknesses. The results indicate that the films depict comparable hardness and modulus results; however, the 800 and 1000 ALD deposition cycles films without forming gas annealing experienced significant amount of pileup, whereas the 900 ALD deposition cycles sample annealed in forming gas resulted in a smaller pileup.

Mamun, M.A.↗
NASA NTRS1992

Molecular films associated with LDEF

The molecular films deposited on the surface of the Long Duration Exposure Facility (LDEF) originated from the paints and room-temperature-vulcanized (RTV) silicone materials intentionally used on the satellite and not from residual contaminants. The high silicone content of most of the films and the uniformity of the films indicates a homogenization process in the molecular deposition and suggests a chemically most favored composition for the final film. The deposition on interior surfaces and vents indicated multiple bounce trajectories or repeated deposition-reemission cycles. Exterior surface deposits indicated a significant return flux. Ultraviolet light exposure was required to fix the deposited film as is indicated by the distribution of the films on interior surfaces and the thickness of films at the vent locations. Thermal conditions at the time of exposure to ultraviolet light seems to be an important factor in the thickness of the deposit. Sunrise facing (ram direction) surfaces always had the thicker film. These were the coldest surfaces at the time of their exposure to ultraviolet light. The films have a layered structure suggesting cyclic deposition. As many as 34 distinct layers were seen in the films. The cyclic nature of the deposition and the chemical uniformity of the film one layer to the next suggest an early deposition of the films though there is evidence for the deposition of molecular films throughout the nearly six year exposure of the satellite. A final 'spray' of an organic material associated with water soluble salts occurred very late in the mission. This may have been the result of one of the shuttle dump activities.

Crutcher, E. R.↗
NASA NTRS2003

Experiments on the Flow of a Thin Liquid Film Over a Horizontal Stationary and Rotating Disk Surface

Experiments on characterization of thin liquid films flowing over stationary and rotating disk surfaces are described. The thin liquid film was created by introducing deionized water from a flow collar at the center of an aluminum disk with a known initial film thickness and uniform radial velocity. Radial film thickness distribution was measured using a non-intrusive laser light interface reflection technique that enabled the measurement of the instantaneous film thickness over a finite segment of the disk. Experiments were performed for a range of flow rates between 3.01pm and 15.01pm, corresponding to Reynolds numbers based on the liquid inlet gap height and velocity between 238 and 1,188. The angular speed of the disk was varied from 0 rpm to 300 rpm. When the disk was stationary, a circular hydraulic jump was present in the liquid film. The liquid-film thickness in the subcritical region (down-stream of the hydraulic jump) was an order of magnitude greater than that in the supercritical region (upstream of the hydraulic jump) which was of the order of 0.3 mm. As the Reynolds number increased, the hydraulic jump migrated toward the edge of the disk. In the case of rotation, the liquid-film thickness exhibited a maximum on the disk surface. The liquid-film inertia and friction influenced the inner region where the film thickness progressively increased. The outer region where the film thickness decreased was primarily affected by the centrifugal forces. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. At high rotational speeds, spiral waves were observed on the liquid film. It was also determined that the angle of the waves which form on the liquid surface was a function of the ratio of local radial to tangential velocity.

Ozar, B.↗
NASA NTRS2003

Collaboration of the NASA Glenn Research Center and Rolls-Royce Developed Thin Film Multilayered Dielectrics for Harsh Environments

The use of thin films to electrically insulate thin film sensors on engine components minimizes the intrusiveness of the sensors and allows a more accurate measurement of the environment. A variety of insulating films were investigated for preventing electrical shorting caused by insulator failure between the sensor and the component. By alternating layers of sputtered high-temperature ceramics, a sequence of insulating layers was devised that (1) prevents pinholes from forming completely through the insulator and (2) maintains high electrical resistivity at high temperatures. The total thickness is only a fraction of that needed for conventional insulating techniques. The Sensors and Electronics Technology Branch of the NASA Glenn Research Center has an in-house effort to develop thin film sensors for surface measurement in propulsion system research. Thin film sensors do not require special machining of the components on which they are mounted, and they are considerably thinner (less than 10 mm thick) than wire or foil sensors. The thin film sensors are thus much less disturbing to the operating environment and have a minimal impact on the physical characteristics of the supporting component. To further this research, NASA Glenn and Rolls-Royce (Derby, UK), with assistance from the Ohio Aerospace Institute (OAI) and the Akima Corporation, pursued a joint investigation using multilayered thin film dielectrics as a reliable insulator in harsh environments. The use of a multilayered scheme is thought to be promising for the fabrication of electrically insulating thin films. A major cause of conduction in thin film dielectrics is the presence of defects, such as pinholes, that propagate through the film to the underlying substrate surface. By alternating the insulating material, each new growth pattern would deviate from the previous one, eliminating direct pathways for conduction to the substrate. The film depositions and testing were conducted in the Instrument Research Laboratory at Glenn. The multilayered insulator test samples were made from alumina and stainless steel shims that were first covered with a sputtered underlayer of either yttria-stabilized zirconia or chromium carbide, and then overcoated with a sputtered top layer of alumina. An example of a test sample is shown in the following photograph. Each multilayered insulator sample was 5 mm thick, at least an order of magnitude thinner than conventional insulators. The insulating properties of the samples were tested in a high-temperature air oven to determine their suitability. The multilayer insulators tested showed a stabilized film at temperatures in excess of 800 C (1472 F). The underlying materials in these multilayers allow thermal expansion stresses produced during the heating to be graded. The chromium carbide-alumina multilayer had the best adhesion at high temperatures, presumably from the induced chemical bonding between the substrate and the chromium carbide underlayer. However, the zirconia-alumina multilayer proved to have slightly better insulating properties when adhering. The application of the zirconia-alumina insulator has been demonstrated on a nickel-alloy fan blade, as shown. The insulators using thin film sensors still need to be tested in a relevant high-temperature combustion environment.

Wrbanek, John D.↗
DOE OSTI2013

Gafchromic EBT2 film dosimetry in reflection mode with a novel plan-based calibration method

Purpose:A dosimetric system formed by Gafchromic EBT2 radiochromic film and Epson Expression 10000XL flatbed scanner was commissioned for dosimetry. In this paper, several open questions concerning the commissioning of radiochromic films for dosimetry were addressed: (a) is it possible to employ this dosimetric system in reflection mode; (b) if so, can the methods used in transmission mode also be used in reflection mode; (c) is it possible to obtain accurate absolute dose measurements with Gafchromic EBT2 films; (d) which calibration method should be followed; (e) which calibration models should be used; and (f) does three-color channel dosimetry offer a significant improvement over single channel dosimetry. The purpose of this paper is to help clarify these questions. Methods: In this study, films were scanned in reflection mode, the effect of surrounding film was evaluated and the feasibility of EBT2 film dosimetry in reflection mode was studied. EBT2's response homogeneity has been reported to lead to excessive dose uncertainties. To overcome this problem, a new plan-based calibration method was implemented. Plan-based calibration can use every pixel and each of the three color channels of the scanned film to obtain the parameters of the calibration model. A model selection analysis was conducted to select lateral correction and sensitometric curve models. The commonly used calibration with fragments was compared with red-channel plan-based calibration and with three-channel plan-based calibration. Results: No effect of surrounding film was found in this study. The film response inhomogeneity in EBT2 films was found to be important not only due to differences in the fog but also due to differences in sensitivity. The best results for lateral corrections were obtained using absolute corrections independent of the dose. With respect to the sensitometric curves, an empirical polynomial fit of order 4 was found to obtain results equivalent to a gamma-distributed single hit model based on physical assumptions. Three-channel dosimetry was found to be substantially superior to red-channel dosimetry. Conclusions: Reflection mode with Gafchromic EBT2 radiochromic film was found to be a viable alternative to transmission mode. The same methods that are used in transmission mode can be followed in reflection mode. A novel plan-based method was developed for calibration and multichannel dosimetry. This novel method offers increased robustness against film response inhomogeneities and reduces considerably the time required for calibration.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Study of Electrical Transport and Magnetic Properties of Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Nd{sub 0.8}Na{sub 0.2}MnO{sub 3} Bilayer Thin Films

Bilayer films of Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Nd{sub 0.8}Na{sub 0.2} MnO{sub 3} were grown on 001-orientated LaAlO{sub 3} substrate by using RF magnetron sputtering. The thickness of the Nd{sub 0.8}Na{sub 0.2}MnO{sub 3} (NNMO) film was kept fixed at 120 nm while that of the Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3} (NSMO) film was varied from 12 to 100 nm. X-ray diffraction patterns confirm the growth of films along the (001) direction, and the out-of-plane lattice constant of the NSMO film decreases with an increase in film thickness. The bilayer films are found to undergo out-of-plane tensile strain, and the lattice strain is found to decrease with an increase in film thickness. The ferromagnetic transition temperature is found to increase with an increase in the NSMO film thickness. M–H loops recorded at 50 K show a systematic increase in saturation magnetisation with an increase in film thickness. Metal–insulator transition has been observed for the film thickness of 30 nm and above, and the transition temperature is found to increase with an increase in film thickness. The electrical resistivity data in the metallic region were explained based on electron–electron and electron–magnon scattering mechanism by including a weak localisation effect at low temperature. The electrical resistivity data in the insulating region follow the Mott-variable range hopping model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tuning of Magnetic and Optical Properties of Co{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} Spinel Ferrite Thin Films Based on Post Annealing Temperature

This paper is dedicated to deposit zinc substituted cobalt ferrite (Co{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4}) thin films on glass substrate using electron beam deposition technique. The effect of post annealing temperature on structural, magnetic, and optical properties of thin films has been investigated. Thin films have been characterized using x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), vibrating sample magnetometer (VSM), UV-VIS spectroscopy, and spectroscopic ellipsometry (SE) analysis. The as-deposited thin films are amorphous in nature. After deposition, these thin films post annealed at different temperature ranges from 200 to 500 {sup ∘}C to enhance the crystallinity of films. The film post annealed at 200 {sup ∘}C is also amorphous in nature. As the post annealing temperature increases, the thin films become more crystalline. X-ray diffractometer and Raman analysis confirm the formation of cubical inverse spinel structure of thin films. The saturation magnetization of the thin films decreases with the annealing temperature due to the sites occupancy of cations between tetrahedral and octahedral. The reduction in coercivity is correlated with the anisotropy constant, but the anisotropy value is still high which is suitable to form stable magnetic storage memories. The band gap energy are decreased which is mainly attributed due to increase in grain size of the film. It is noted that the band gap energy of these thin films are higher than that of bulk material, so these may be suggested for use in wide band gap applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of RF Power on Structural, Magnetic, and Optical Properties of CoFe{sub 2}O{sub 4} Thin Films

The thin films of CoFe{sub 2}O{sub 4} were deposited on glass substrates by radio-frequency (RF) sputtering. The effect of RF power variation from 60–120 W on the structure, magnetic, and optical properties of the as-deposited films and films annealed at 500 °C was studied. The magnetic parameters of the film, i.e., in-plane coercivity (H{sub c}), saturation magnetization (M{sub s}), and remanence (M{sub r}) increase as RF power is increased from 60 to 80 W followed by a decreasing trend with further increase in RF power to 120 W. Annealing of the film significantly improves the magnetic properties. The largest grain size and the best crystallinity of the film are obtained for the film deposited at 80 W of RF power. The thin films exhibited 70–80% optical transmittance. Optical band gap (E{sub g}) depends on the RF power and grain size, and it varies between 2.08 and 2.16 eV for the as-deposited films and between 2.16 and 2.30 eV for the annealed films. The study shows that RF power used for depositing the film has strong effect on the microstructure and properties of the film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Microstructural dependence of defect formation in iron-oxide thin films

In this report passivating iron-oxide films are grown atop iron films simulating the corrosion process in a nuclear reactor environment. Two oxide films grown via physical vapor deposition at 600 °C and room temperature exhibited dense-epitactic and columnar-polycrystalline, microstructures respectively. A third oxide film grown in open air at 600 °C exhibited an eqiuaxed, porous morphology. Cubic maghemite and magnetite phases in each oxide film were identified via grazing incidence X-ray diffraction. Positron annihilation spectroscopy was used to characterize point defects and measure their depth and size distributions in each oxide layer and showed a range of average positron lifetimes from 0.23 ns in the high temperature, vapor deposited film, 0.35 ns in the room temperature-grown film, and 0.31 ns in the thermally grown oxide. These data indicate that the film morphology, which varies greatly in these films, leads to very different defect content. Finally, four-dimensional scanning transmission electron microscopy was used to measure the internal stress of each film and was correlated to the strain state presented in the X-ray diffraction spectra. The defect formation in each film is reasoned through using a thin film growth model.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Magnetron sputtered nanostructured cadmium oxide films for ammonia sensing

Nanostructured cadmium oxide (CdO) films were deposited on to glass substrates by reactive dc magnetron sputtering technique. The depositions were carried out for different deposition times in order to obtain films with varying thicknesses. The CdO films were polycrystalline in nature with cubic structure showing preferred orientation in (1 1 1) direction as observed by X-ray diffraction (XRD). Field-emission scanning electron microscope (FE-SEM) micrographs showed uniform distribution of grains of 30–35 nm size and change in morphology from spherical to elliptical structures upon increasing the film thickness. The optical band gap value of the CdO films decreased from 2.67 to 2.36 eV with increase in the thickness. CdO films were deposited on to interdigitated electrodes to be employed as ammonia (NH{sub 3}) gas sensor. The fabricated CdO sensor with thickness of 294 nm has a capacity to detect NH{sub 3} as low as 50 ppm at a relatively low operating temperature of 150 °C with quick response and recovery time. - Highlights: • Nanostructured CdO films were deposited on to glass substrates using magnetron sputtering. • Deposition time was varied in order to obtain films with different thicknesses. • The CdO films were polycrystalline in nature with preferred orientation along (1 1 1) direction. • The optical bandgap values of the films decreased on increasing the thickness of the films. • CdO films with different thickness such as 122, 204, 294 nm was capable to detect NH{sub 3} down to 50 ppm at operating temperature of 150 °C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Large-scale fabrication of linear low density polyethylene/layered double hydroxides composite films with enhanced heat retention, thermal, mechanical, optical and water vapor barrier properties

Novel LDH intercalated with organic aliphatic long-chain anion was large-scale synthesized innovatively by high-energy ball milling in one pot. The linear low density polyethylene (LLDPE)/layered double hydroxides (LDH) composite films with enhanced heat retention, thermal, mechanical, optical and water vapor barrier properties were fabricated by melt blending and blowing process. FT IR, XRD, SEM results show that LDH particles were dispersed uniformly in the LLDPE composite films. Particularly, LLDPE composite film with 1% LDH exhibited the optimal performance among all the composite films with a 60.36% enhancement in the water vapor barrier property and a 45.73 °C increase in the temperature of maximum mass loss rate compared with pure LLDPE film. Furthermore, the improved infrared absorbance (1180–914 cm{sup −1}) of LLDPE/LDH films revealed the significant enhancement of heat retention. Therefore, this study prompts the application of LLDPE/LDH films as agricultural films with superior heat retention. - Graphical abstract: The fabrication process of LLDPE/LDH composite films. - Highlights: • LDH with basal spacing of 4.07 nm was synthesized by high-energy ball milling. • LLDPE composite films with homogeneous LDH dispersion were fabricated. • The properties of LLDPE/LDH composite films were improved. • LLDPE/LDH composite films show superior heat retention property.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Preparation and characterization of RF magnetron sputtered CuO/CaTi{sub 4}O{sub 9} thin films with enhanced third-order nonlinear optical properties

The titanate, is a material of interest for various energy applications, including photovoltaics, catalysts, and high-rate energy storage devices. Herein, its related materials, CuO/CaTi{sub 4}O{sub 9} [CCTO] thin films, were successfully fabricated on SrTiO{sub 3} (100) substrates by RF magnetron sputtering assisted with subsequent oxygen annealing. This obtained CCTO thin films were then systemically studied by X-ray powder diffraction (XRD), atomic force microscopy (AFM), scan electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). It was found that CuO and CaTi{sub 4}O{sub 9} (001) particles were closely accumulated together on the surface of the substrate in the annealing process after comparing with that of the as-prepared thin film, which was verified by SEM and AFM results. Furthermore, we investigated the third-order nonlinear optical (NLO) properties of the as-prepared and annealed CCTO thin film by means of the Z-scan technique using 650 nm femtosecond laser pulse. Post-deposition oxygen annealing was found to modify the morphological characteristics of the films, resulting in enhancing their NLO properties. The observation of NLO performance of annealed CCTO thin film indicates that RF magnetron sputtering is a feasible method for the fabrication of optical thin films, which can be expanded to fabricate other NLO materials from the corresponding dispersions. Naturally, we concluded that the CCTO thin film occupy a better NLO property, and thus enlarge its application in nonlinear optics. - Highlights: • The CCTO thin film was prepared using the RF magnetron sputtering and oxygen annealing. • The film was prepared on the SrTiO{sub 3}(100) substrates with a Ca{sub 2}CuO{sub 3} target. • The oxygen annealing was found can effectively enhance the film quality and NLO property. • The film was characterized using XPS, SEM, AFM, TEM, XRD and Z-scan techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Measurement of valence band structure in arbitrary dielectric films

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structural and optical characterization of high-quality ZnO thin films deposited by reactive RF magnetron sputtering

Highlights: ► High-quality ZnO thin films were deposited at room temperature. ► Effect of O{sub 2} flow and RF sputtering voltages on properties of ZnO films were studied. ► O{sub 2}/Ar ratios played a key role in controlling optical properties of ZnO films. ► Photoluminescence intensity of the ZnO films strongly depended on O{sub 2}/Ar ratios. ► Crystallite size, stress and strain strongly depended on O{sub 2}/Ar ratios. - Abstract: ZnO thin films were deposited onto quartz substrates by radio frequency (RF) reactive magnetron sputtering using a Zn target. The structural and optical properties of the ZnO thin films were investigated comprehensively by X-ray diffraction (XRD), ultraviolet–visible and photoluminescence (PL) measurements. The effects of the oxygen content of the total oxygen–argon mixture and sputtering voltage in the sputtering process on the structural and optical properties of the ZnO films were studied systemically. The microstructural parameters, such as the lattice constant, crystallite size, stress and strain, were also calculated and correlated with the structural and optical properties of the ZnO films. In addition, the results showed that the crystalline quality of ZnO thin films improved with increasing O{sub 2}/Ar gas flow ratio from 2:8 to 8:2. XRD and PL spectroscopy revealed 800 V to be the most appropriate sputtering voltage for ZnO thin film growth. High-quality ZnO films with a good crystalline structure, tunable optical band gap as well as high transmittance could be fabricated easily by RF reactive magnetron sputtering, paving the way to obtaining cost-effective ZnO thin films transparent conducting oxides for optoelectronics applications.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Wet chemical synthesis of quantum confined nanostructured tin oxide thin films by successive ionic layer adsorption and reaction technique

Graphical abstract: - Highlights: • Quantum confined SnO{sub 2} thin films were synthesized at 80 °C by SILAR technique. • Film formation mechanism is discussed. • Films with snow like crystallite morphology offer high specific surface area. • The blue-shifted value of band gap confirmed the quantum confinement effect. • Present synthesis has advantages – low cost, low temperature and green friendly. - Abstract: Quantum confined nanostructured SnO{sub 2} thin films were synthesized at 353 K using ammonium chloride (NH{sub 4}Cl) and other chemicals by successive ionic layer adsorption and reaction technique. Film formation mechanism is discussed. Structural, morphological, optical and electrical properties were investigated and compared with the as-grown and annealed films fabricated without NH{sub 4}Cl solution. SnO{sub 2} films were polycrystalline with crystallites of tetragonal structure with grain sizes lie in the 5–8 nm range. Films with snow like crystallite morphology offer high specific surface area. The blue-shifted value of band gap of as-grown films confirmed the quantum confinement effect of grains. Refractive index of the films lies in the 2.1–2.3 range. Films prepared with NH{sub 4}Cl exhibit relatively lower resistivity of the order of 10{sup 0}–10{sup −1} Ω cm. The present synthesis has advantages such as low cost, low temperature and green friendly, which yields small particle size, large surface–volume ratio, and high crystallinity SnO{sub 2} films.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Chemical bonding and optoelectrical properties of ruthenium doped yttrium oxide thin films

Graphical abstract: IR transmittance of various transparent conductive materials (RYO films grown under RT, 400 °C and 600 °C, ITO films [2], Carbon Nano tube films [11], metal/dielectric multilayers [12]). - Highlights: • Y{sub 2}O{sub 3}:Ru (RYO) films were prepared on ZnS substrates by reactive magnetron sputtering. • Ru doping significantly decreases the resistivity and extends the transparent range. • Optical and electrical properties of RYO films can be tuned by substrate temperatures. • The RYO films exhibit excellent far-IR transmittance and electrical property. - Abstract: Highly infrared transparent conductive ruthenium doped yttrium oxide (RYO) films were deposited on zinc sulfide and glass substrates by reactive magnetron sputtering. The structural, optical, and electrical properties of the films as a function of growth temperature were studied. It is shown that the sputtered RYO thin films are amorphous and smooth surface is obtained. The infrared transmittance of the films increases with increasing the growth temperature. RYO films maintain greater than ∼65% transmittance over a wide wavelength range from 2.5 μm to 12 μm and the highest transmittance value reaches 73.3% at ∼10 μm. With increasing growth temperature, the resistivity changed in a wide range and lowest resistivity of about 3.36 × 10{sup −3} Ω cm is obtained at room temperature. The RYO thin films with high conductivity and transparency in IR spectral range would be suitable for infrared optical and electromagnetic shielding devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructural, optical, and electrical properties of Ni–Al co-doped ZnO films prepared by DC magnetron sputtering

Graphical abstract: - Highlights: • Ni–Al co-doped ZnO (NiAl:ZnO) composite thin films were deposited by DC magnetron sputtering at room temperature. • All films showed a highly preferential (0 0 2) c-axis orientation. • XPS revealed the presence of metallic Ni, NiO, and Ni{sub 2}O{sub 3} states, and Ni atoms were successfully doped in the NiAl:ZnO films. • NiAl:ZnO (3 wt% Ni) film showed the lowest electrical resistivity of 2.59 × 10{sup −3} Ω cm. • Band gap widening (4.18 eV) was observed in the NiAl:ZnO films with 5 wt% Ni. - Abstract: Ni–Al co-doped ZnO (NiAl:ZnO) films with fixed Al content at 2 wt% and different Ni contents (2.5, 3, and 5 wt%) were deposited by DC magnetron sputtering in an argon atmosphere at room temperature. X-ray diffraction revealed that all films showed a highly preferential (0 0 2) c-axis orientation. XPS revealed the presence of metallic Ni, NiO, and Ni{sub 2}O{sub 3} states, and Ni atoms were successfully doped in NiAl:ZnO films, which did not result in a change in ZnO crystal structure and orientation. The electrical resistivity of NiAl:ZnO film was decreased to 2.59 × 10{sup −3} Ω cm at a Ni doping concentration of 3 wt% compared with undoped Al-doped ZnO film (5.58 × 10{sup −3} Ω cm). The mean optical transmittance in the visible range was greater than 80% for all films. Band gap widening (4.18 eV) was observed in the NiAl:ZnO films with 5 wt% Ni, attributed to the Burstein–Moss shift due to the increase of carrier concentration.

36 MATERIALS SCIENCE↗