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At least 1,621 records · Page 90
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DOE OSTI2014

Characterization of nanocrystalline ZnO:Al films by sol-gel spin coating method

Nanocrystalline ZnO films doped with aluminium by sol-gel spin coating method have been investigated using optical transmittance UV-Vis and X-ray diffraction (X-RD) measurements. ZnO films were prepared using zinc acetate dehydrate (Zn(CH{sub 3}COO){sub 2}@@‡2H{sub 2}O), ethanol, and diethanolamine (DEA) as a starting material, solvent, and stabilizer, respectively. For doped films, AlCl{sub 3} was added to the mixture. The ZnO:Al films were deposited on a transparent conductive oxide (TCO) substrate using spin coating technique at room temperature with a rate of 3000 rpm in 30 sec. The deposited films were annealed at various temperatures from 400°C to 600°C during 60 minutes. The transmittance UV-Vis measurement results showed that after annealing at 400°C, the energy band gap profile of nanocrystalline ZnO:Al film was a blue shift. This indicated that the band gap of ZnO:Al increased after annealing due to the increase of crystalline size. As the annealing temperature increased the bandgap energy was a constant. In addition to this, there was a small oscillation occurring after annealing compared to the as–grown samples. In the case of X-RD measurements, the crystalinity of the films were amorphous before annealing, and after annealing the crystalinity became enhance. Also, X-RD results showed that structure of nanocrystalline ZnO:Al films were hexagonal polycrystalline with lattice parameters are a = 3.290 Å and c = 5.2531 Å.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Bandgap tailoring of in-situ nitrogen-doped TiO₂ sputtered films intended for electrophotocatalytic applications under solar light

We report on a reactive RF-sputtering process permitting the in-situ nitrogen doping of TiO₂ films in order to shift their photoactivity from UV to visible range. By carefully controlling the relative nitrogen-to-argon mass flow rate ratio (within the 0%–25% range) in the sputter deposition chamber, TiO₂:N films were grown with nitrogen contents ranging from 0 to 6.2 at. %, as determined by high-resolution X-ray spectroscopy measurements. A systematic investigation of the crystalline structure of the TiO₂:N films, as a function of their N content, revealed that low N contents (0.2–0.3 at. %) induce crystallization in the rutile phase while higher N contents (≥1.4 at. %) were accompanied with the recovery of the anatase structure with an average crystallite size of ~35 nm. By using both UV-Vis absorption and spectroscopic ellipsometry measurements, we were able to quantitatively determine the bandgap (E{sub g}) variation of the TiO₂:N films as a function of their N content. Thus, we have demonstrated that the E{sub g} of the TiO₂:N films effectively narrows from 3.2 eV down to a value as low as ~2.3 eV for the optimal N doping concentration of 3.4 at. % (higher N incorporation does not translate into further red shifting of the TiO₂:N films' E{sub g}). The photoactivity of the TiO₂:N films under visible light was confirmed through electro-photocatalytic decomposition of chlortetracycline (CTC, an emerging water pollutant) under standard 1.5AM solar radiation. Thus, CTC degradation efficiencies of up to 98% were achieved with 2 hours process cycles under simulated solar light. Moreover, the electro-photocatalytic performance of the TiO₂:N films is shown to be directly correlated to their optoelectronic properties (namely their bandgap narrowing).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Physical properties of electron beam evaporated CdTe and CdTe:Cu thin films

In this paper, we report on physical properties of pure and Cu doped cadmium telluride (CdTe) films deposited onto corning 7059 microscopic glass substrates by electron beam evaporation technique. X-ray diffraction study showed that all the deposited films belong to amorphous nature. The average transmittance of the films is varied between 77% and 90%. The optical energy band gap of pure CdTe film is 1.57 eV and it decreased to 1.47 eV upon 4 wt. % of Cu addition, which may be due to the extension of localized states in the band structure. The refractive index of the films was calculated using Swanepoel method. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, and oscillator energy (E{sub o}) of CdTe and CdTe:Cu films were calculated and discussed in detail with the light of possible mechanisms underlying the phenomena. The variation in intensity of photoluminescence band edge emission peak observed at 820 nm with Cu dopant is due to the change in surface state density. The observed trigonal lattice of Te peaks in the micro-Raman spectra confirms the p-type conductive nature of films, which was further corroborated by the Hall effect measurement. The lowest resistivity of 6.61 × 10{sup 4} Ω cm was obtained for the CdTe:Cu (3 wt. %) film.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Anisotropy of electrical and magnetic transport properties of epitaxial SrRuO{sub 3} thin films

SrRuO{sub 3} (SRO) thin films with different thickness (2–70 nm) have been grown on (001), (110), and (111) SrTiO{sub 3} substrates. The (001)-SRO films (2–8 nm) exhibited smooth flat surfaces whereas the (110)- and (111)-SRO films featured a faceted island structure. Room temperature resistivity and residual resistivity are the lowest for the (111)-SRO films (30–70 nm). Over all thicknesses, we observed enhanced magnetization in the (111)-SRO films (∼4 μ{sub B}/Ru) compared with that for the (001)- and (110)-SRO films (∼2 μ{sub B}/Ru and ∼3 μ{sub B}/Ru, respectively), suggesting a low-spin state t{sub 2g}(3↑,1↓), high-spin state t{sub 2g}(3↑)e{sub g}(1↑), and mixed low- and high-spin states for the (001)-, (111)-, and (110)-SRO films, respectively. The dependence of resistivity on temperatures near T{sub C} follows a power law with exponent β = 0.312 and β = 0.363 for the (110)- and (111)-SRO films, respectively. These critical exponents are consistent with magnetic data with scaling law M = C (T{sub C} − T){sup β}. At low temperatures, dM/dT and dρ/dT show a linear relationship in the temperature range for the Fermi liquid. These results suggest that the intrinsic electrical and magnetic transport properties are coupled.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Ferromagnetic properties of fcc Gd thin films

Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature T{sub S} and film thickness x. Gd fcc samples were obtained when T{sub S} = 763 K and x = 10 nm, while the hcp structure was stabilized for lower T{sub S} (300 K) and thicker film (20 nm). The fcc structure is formed on the Ta buffer layer, while the hcp phase grows on the fcc Gd layer as a consequence of the lattice relaxation process. Spin reorientation phenomenon, commonly found in bulk Gd species, was also observed in the hcp Gd thin film. This phenomenon is assumed to cause the magnetization anomalous increase observed below 50 K in stressed Gd films. Magnetic properties of fcc Gd thin films are: Curie temperature above 300 K, saturation magnetization value of about 175 emu/cm{sup 3}, and coercive field of about 100 Oe at 300 K; features that allow us to classify Gd thin films, with fcc structure, as a soft ferromagnetic material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Improved ferroelectric polarization of V-doped Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films prepared by a chemical solution deposition

We prepared V-doped Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films on Pt/Ti/SiO{sub 2}/Si (100) substrates by using a chemical solution deposition route and investigated the doping effect on the microstructure, dielectric, leakage, and ferroelectric properties of Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films. The Bi{sub 5.97}Fe{sub 2}Ti{sub 2.91}V{sub 0.09}O{sub 18} thin film exhibits improved dielectric properties, leakage current, and ferroelectric properties. The incorporation of vanadium resulted in a substantially enhanced remnant polarization (2P{sub r}) over 30 μC/cm{sup 2} in Bi{sub 5.97}Fe{sub 2}Ti{sub 2.91}V{sub 0.09}O{sub 18} thin film compared with 10 μC/cm{sup 2} in Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin film. It is demonstrated that the improved properties may stem from the improvement of crystallinity of the films with the contribution of suppressed oxygen vacancies and decreased mobility of oxygen vacancies caused by the V-doping. The results will provide a guidance to optimize the ferroelectric properties in Bi{sub 6}Fe{sub 2}Ti{sub 3}O{sub 18} thin films by chemical solution deposition, which is important to further explore single-phase multiferroics in the n = 5 Aurivillius thin films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Deposition of high permeability FeCoN films on mica substrates

In this study, sheet mica was explored as an alternative substrate for thin film deposition due to its unique layered structure and atomically flat surface. Static magnetic properties and microwave permeability of sputtered FeCoN films on mica with and without SiO{sub 2} under-layer were examined. In-plane isotropy and a large coercivity of 70 Oe were observed for the film directly deposited on mica substrate. With the insertion of 40 nm SiO{sub 2} under-layer between the film and mica substrate, well-defined in-plane anisotropy is formed due to the significant reduce in film residual stress, associated with a 3 Oe coercive force along easy axis. As a result, excellent microwave properties have been achieved and are comparable with the same film on Si substrate. Moreover, the permeability spectra are surprisingly stable from room temperature up to 390 K. Mica is proved as a promising substrate for magnetic films with high microwave performance, which is a great advantage for practical applications. Furthermore, our results provide an effective way to reduce the residual stress in sputtered films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Electrical and optical properties of molybdenum doped zinc oxide films prepared by reactive RF magnetron sputtering

Molybdenum doped zinc oxide (MZO) films were deposited on to glass substrates held at temperatures in the range from 303 to 673 K by reactive RF magnetron sputtering method. The chemical composition, crystallographic structure and surface morphology, electrical and optical properties of the films were determined. The films contained the molybdenum of 2.7 at. % in ZnO. The films deposited at 303 K were of X-ray amorphous. The films formed at 473 K were of nanocrystalline in nature with wurtzite structure. The crystallite size of the films was increased with the increase of substrate temperature. The optical transmittance of the films was in the visible range was 80–85%. The molybdenum (2.7 at %) doped zinc oxide films deposited at substrate temperature of 573 K were of nanocrystalline with electrical resistivity of 7.2×10{sup −3} Ωcm, optical transmittance of 85 %, optical band gap of 3.35 eV and figure of merit 30.6 Ω{sup −1}cm{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanocomposites biodegradable coating on BOPET films to enhance hot seal strength properties

The coating technology is a strategic solution to improve the properties of flexible packaging films. Indeed, additional functional layers are often designed and added as coating on the substrate, in order to improve the characteristic of the flexible packaging and to meet the requirements for the desired gas or vapour barrier, for adhesion and sealing, or for improving the film printability, its aesthetics and durability. Moreover, this technology allows to functionalize a polymeric substrate applying materials with different chemistry, rheology, thermal and structural characteristics. BOPET films are widely used for food packaging applications thanks to their good gas barrier and mechanical properties, high transparency and for the excellent printability. In regard to sealing performance, BOPET films show poor sealing properties so they are mostly submitted to lamination processes with polyethylene. Nevertheless, this solution compromises the PET recyclability and influences the gas permeability of the multilayer PET based structures. The aim of this work is to investigate on the effect of nanocomposite biodegradable coatings for BOPET substrates in enhancing the heat sealing strength of eco-compatible PET/PLA films. At this regards, different percentages of Cloisite C30B (0%, 2% and 4%{sub wt/wt}) have been added to PLA by solution intercalation technique and the nanocomposite biodegradable materials produced have been applied on BOPET commercial films by casting. The BOPET coated films have been characterized in order to evaluate the heat sealing strength and the mechanical, gas permeability and surface properties. The results have shown that the addition of nanoclay in PLA coating significantly enhance the hot tack properties of the PET/PLA system produced, while the oxygen and water vapour permeability are slightly increased if compared to pure BOPET films.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Coupling of microwave magnetic dynamics in thin ferromagnetic films to stripline transducers in the geometry of the broadband stripline ferromagnetic resonance

We constructed a quasi-analytical self-consistent model of the stripline-based broadband ferromagnetic resonance (FMR) measurements of ferromagnetic films. Exchange-free description of magnetization dynamics in the films allowed us to obtain simple analytical expressions. They enable quick and efficient numerical simulations of the dynamics. With this model, we studied the contribution of radiation losses to the ferromagnetic resonance linewidth, as measured with the stripline FMR. We found that for films with large conductivity of metals the radiation losses are significantly smaller than for magneto-insulating films. Excitation of microwave eddy currents in these materials contributes to the total microwave impedance of the system. This leads to impedance mismatch with the film environment resulting in decoupling of the film from the environment and, ultimately, to smaller radiation losses. We also show that the radiation losses drop with an increase in the stripline width and when the sample is lifted up from the stripline surface. Hence, in order to eliminate this measurement artefact, one needs to use wide striplines and introduce a spacer between the film and the sample surface. The radiation losses contribution is larger for thicker films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Thermal transport in Cu{sub 2}ZnSnS{sub 4} thin films

The stability of kesterite Cu{sub 2}ZnSnS{sub 4} (CZTS) under a range of compositions leads to the formation of a number of stable defects that appear to be necessary for high efficiency photovoltaic applications. In this work, the impact of the presence of these defects on the thermal conductivity of CZTS thin films has been explored. Thermal conductivities of CZTS thin films, prepared by pulsed laser deposition with differing compositions, were measured from 80 K to room temperature using the 3ω-method. The temperature dependence of the thermal conductivity indicates that the phonon mean free path is limited by strain field induced point defect scattering from sulfur vacancies in sulfur deficient thin films. The sulfurization of these films in a 10% N{sub 2} + H{sub 2}S ambient at 500 °C increased the sulfur content of the films, reducing the concentration of sulfur vacancies, and produced a negligible change in grain size with an unexpected factor of 5 increase in phonon boundary scattering. This, along with anisotropies in the x-ray diffraction peak profiles of the sulfurized films, suggests that the phonon mean free path in sulfurized films is limited by the presence of cation exchange induced stacking faults. The resulting room temperature thermal conductivities for sulfurized and sulfur deficient thin films were found to be 4.0 W/m K and 0.9 W/m K, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Direct growth of nano-crystalline graphite films using pulsed laser deposition with in-situ monitoring based on reflection high-energy electron diffraction technique

We report an experimental method to overcome the long processing time required for fabricating graphite films by a transfer process from a catalytic layer to a substrate, as well as our study of the growth process of graphite films using a pulsed laser deposition combined with in-situ monitoring based on reflection high-energy electron diffraction technique. We monitored the structural evolution of nano-crystalline graphite films directly grown on AlN-coated Si substrates without any catalytic layer. We found that the carbon films grown for less than 600 s cannot manifest the graphite structure due to a high defect density arising from grain boundaries; however, the carbon film can gradually become a nano-crystalline graphite film with a thickness of approximately up to 5 nm. The Raman spectra and electrical properties of carbon films indicate that the nano-crystalline graphite films can be fabricated, even at the growth temperature as low as 850 °C within 600 s.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Properties of RF sputtered cadmium telluride (CdTe) thin films: Influence of deposition pressure

Influence of deposition pressure on structural, morphology, electrical and optical properties of CdTe thin films deposited at low substrate temperature (100°C) by RF magnetron sputtering was investigated. The formation of CdTe was confirmed by low angle XRD and Raman spectroscopy. The low angle XRD analysis revealed that the CdTe films have zinc blende (cubic) structure with crystallites having preferred orientation in (111) direction. Raman spectra show the longitudinal optical (LO) phonon mode peak ∼ 165.4 cm{sup -1} suggesting high quality CdTe film were obtained over the entire range of deposition pressure studied. Scanning electron microscopy analysis showed that films are smooth, homogenous, and crack-free with no evidence of voids. The EDAX data revealed that CdTe films deposited at low deposition pressure are high-quality stoichiometric. However, for all deposition pressures, films are rich in Cd relative to Te. The UV-Visible spectroscopy analysis show the blue shift in absorption edge with increasing the deposition pressure while the band gap show decreasing trend. The highest electrical conductivity was obtained for the film deposited at deposition pressure 1 Pa which indicates that the optimized deposition pressure for our sputtering unit is 1 Pa. Based on the experimental results, these CdTe films can be useful for the application in the flexible solar cells and other opto-electronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

The annealing temperature dependences of microstructures and magnetic properties in electro-chemical deposited CoNiFe thin films

CoNiFe thin films with various compositions had been successfully fabricated using electro-chemical deposition method. The crystal structure of Co{sub 65}Ni{sub 15}Fe{sub 20}, Co{sub 62}Ni{sub 15}Fe{sub 23}, and Co{sub 55}Ni{sub 15}Fe{sub 30} thin films was fcc, bcc-fcc mix, and bcc, respectively. The difference crystal structure results the difference in magnetic properties. The saturation magnetic flux density (Bs) of Co{sub 65}Ni{sub 15}Fe{sub 20}, Co{sub 62}Ni{sub 15}Fe{sub 23}, and Co{sub 55}Ni{sub 15}Fe{sub 30} thin films was 1.89 T, 1.93 T, and 2.05 T, respectively. An optimal annealing temperature was determined for controlling the microstructure and magnetic properties of CoNiFe thin films. Depending on annealing temperature, the ratio of bcc and fcc structure varied without changing the film composition. By annealing at temperature of T ≥ 350°C, the intensity ratio of X-ray diffraction peaks for bcc(110) to fcc(111) increased. The increase of phase ratio of bcc(110) to fcc(111) caused the increase of Bs, from 1.89 T to 1.95 T. Coercivity (Hc) also increased after annealing, from 2.6 Oe to 18.6 Oe for fcc phase thin films, from 2.0 Oe to 12.0 Oe for fcc-bcc mix phase thin films, and 7.8 Oe to 8 Oe for bcc phase thin films. The changing crystal structures during annealing process indicated that the thermal treatment at high temperature cause the changing crystallinity and atomic displacement. The TEM bright-field images with corresponding selected-area electron diffraction (SAED) patterns showed that there are strongly effects of thermal annealing on the size of fcc and bcc phase crystalline grain as described by size of individual spot and discontinuous rings. The size of crystalline grains increased by thermal annealing. The evolution of bcc and fcc structures of CoNiFe during annealing is though to be responsible for the change of magnetic properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Role of target-substrate distance on the growth of CuInSe{sub 2} thin films by pulsed laser ablation technique

CuInSe{sub 2} thin films have been deposited on corning glass substrates by pulsed laser ablation technique. The chamber pressure and substrate temperature was maintained at 1 × 10{sup −6} torr and 550°C respectively during deposition of the films. The influence of target to substrate (T-S) distance on the structural and optical properties of thin films have been investigated by grazing incidence x-ray diffraction, Raman spectroscopy, scanning electron microscope and UV-Vis-NIR spectroscopy. The study reveals that thin films crystallized in a chalcopyrite structure with highly preferential orientation along (112) plane. Optimum T-S distance has been attained for the growth of thin films with large grain size. An intense Raman peak at 174 cm{sup −1} corresponding to dominant A{sub 1} vibration mode is gradually shifted to smaller wavenumber with the increase in T-S distance. The optical bandgap energy of the films was evaluated and found to vary with the T-S distance. The bandgap tailing was observed to obey the Urbach rule and the Urbach energy was also calculated for the films. Scanning electron micrographs depicts uniform densely packed grains and EDAX studies revealed the elemental composition of CuInSe{sub 2} thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Thickness dependent structural, magnetic and magneto-transport properties of epitaxial Nd{sub 0.50}Sr{sub 0.50}MnO{sub 3} thin films

We report the thickness-dependent structural, magnetic and magneto-transport properties in epitaxial Nd{sub 0.50}Sr{sub 0.50}MnO{sub 3} thin films (10 to 300nm) prepared by DC magnetron sputtering technique on single crystalline (001) oriented substrate LaAlO{sub 3}. X-ray diffraction pattern reveals the epitaxial growth of all the films and the out-of-plane lattice parameter of films were found to increase with thickness. As thickness of the film increases the paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature (T{sub C}), charge ordered transition temperature (T{sub CO}) and magnetic moment were found to increase with a strong bifurcation in ZFC-FC magnetization. The asymmetry in the coercivity seen in field dependent magnetization loops (M-H loops) suggests the presence of exchange bias (EB) effect. While temperature dependent resistivity of films show the semiconducting nature for thickness 10-200nm in temperature range from 5-300K, the film of thickness 300nm shows the insulator to metal transition with transition temperature (T{sub IM}) at 175K. Temperature dependent low field magnetoresistance (LFMR) measured at 4kOe found to decrease with thickness and for high field magnetoresistance (HFMR) at 40kOe and 60kOe also show similar dependence and a crossover at intermediate temperature range in the magnitude of MR between 10nm and 200nm films at constant field. Colossal increase in magnetoresistance observed for 10nm film at low temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Simultaneous determination of the residual stress, elastic modulus, density and thickness of ultrathin film utilizing vibrating doubly clamped micro-/nanobeams

Measurement of ultrathin film thickness and its basic properties can be highly challenging and time consuming due to necessity of using several very sophisticated devices. Here, we report an easy accessible resonant based method capable to simultaneously determinate the residual stress, elastic modulus, density and thickness of ultrathin film coated on doubly clamped micro-/nanobeam. We show that a general dependency of the resonant frequencies on the axial load is also valid for in-plane vibrations, and the one depends only on the considered vibrational mode. As a result, we found that the film elastic modulus, density and thickness can be evaluated from two measured in-plane and out-plane fundamental resonant frequencies of micro-/nanobeam with and without film under different prestress forces. Whereas, the residual stress can be determined from two out-plane (in-plane) measured consecutive resonant frequencies of beam with film under different prestress forces without necessity of knowing film and substrate properties and dimensions. Moreover, we also reveal that the common uncertainties in force (and thickness) determination have a negligible (and minor) impact on the determined film properties. The application potential of the present method is illustrated on the beam made of silicon and SiO{sub 2} with deposited 20 nm thick AlN and 40 nm thick Au thin films, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural and magnetic studies of Cr doped nickel ferrite thin films

We have studied the structural and magnetic properties of Cr doped nickel ferrite thin films deposited on Si (100) and Si (111) using pulsed laser deposition technique. The films were deposited under vacuum and substrate temperature was kept at 700°C. X-ray diffraction analysis revealed that films on both substrates have single phase cubic spinel structure. However, the film grown on Si (111) shows better crystalline behavior. Fourier transform infrared spectroscopy suggests that films on both substrates have mixed spinel structure. These films show magnetic hysteresis behavior and magnetization value of film on Si (100) is larger than that on Si (111). It turns out that structural and magnetic properties of these two films are correlated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗