SEARCH · Engineering Papers

Results for “FILMS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

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

At least 1,153 records · Page 64

All sources NASA NTRS DOE OSTI

NASA NTRS1965

Dry film lubricants

The Space Age has necessitated accelerated development of many technologies which have direct application to commercial, earthbound hardware. One striking example is dry film lubrication. The stimulus for the development of dry film lubricants was provided by the unsatisfactory condition created when commercial liquid lubricants were exposed to the multiple environs of space. In the search for a satisfactory solution to lubrication in space, dry films were investigated. The dry film lubrication concept has proven most desirable for space, and a natural fallout is the potential shown by such films for consumer item application. On the acceptance that the coefficient of friction of dry films is not equivalent to that of a liquid lubricant under ideal conditions, this paper discusses how the ideal condition for liquid lubrication is rarely achieved in practical applications. Comparisons are made between the performance of dry film and liquid lubricants as a function of temperature, environmental pressure, and life. Furthermore, consideration is given to the comparative costs of liquid versus dry film lubricants to show the practicality and desirability of dry film lubrication to consumer items. Although no data on the performance of consumer items lubricated with dry films are presented, the comparisons clearly establish the potential of dry film lubricants in a competitive consumer market.

SOLID LUBRICANT↗

DOE OSTI2026

Delamination of Multilayer Plastic Films to Recover Polyethylene with Favorable Mechanical Properties

Multilayer plastic films play a critical role in packaging, with each polymer layer contributing specific properties to the multilayer film. Multilayer plastic films are not currently recyclable due to the bound polymers. With multilayer film production of about 20 million metric tons in 2024 and rising, endof- life treatment becomes pressing. This work presents a scalable solvent-based delamination recycling process that is applied to commercial postindustrial multimaterial films to unbind the materials within a multilayer film by dissolving only the adhesive layer and recover polyethylene (PE) as an intact solid film. Solventbased delamination is a simple process that allows the complete recovery of materials and solvents used in the process. The delaminating solvent, 88% formic acid in water, induces delamination of PE/PEI/PET and PE/PU/PET films at 70 °C in under an hour. Recovered PE has no contamination detected by Fourier transform infrared spectroscopy and mechanical properties on par with those of virgin resin. The recovery of high-quality solid PE film fit for reprocessing, at low operating temperatures and with closed-loop solvent reuse, promotes delamination as a low energy consumption and environmentally friendly recycling process. PE recovered from delamination can be reused in equivalent products, promoting circularity of multimaterial films.

chemical recycling↗

DOE OSTI2024

Characterization of MoS 2 films via simultaneous grazing incidence X-ray diffraction and grazing incidence X-ray fluorescence (GIXRD/GIXRF)

Physical vapor deposited (PVD) molybdenum disulfide (nominal composition MoS 2 ) is employed as a thin film solid lubricant for extreme environments where liquid lubricants are not viable. The tribological properties of MoS 2 are highly dependent on morphological attributes such as film thickness, orientation, crystallinity, film density, and stoichiometry. These structural characteristics are controlled by tuning the PVD process parameters, yet undesirable alterations in the structure often occur due to process variations between deposition runs. Nondestructive film diagnostics can enable improved yield and serve as a means of tuning a deposition process, thus enabling quality control and materials exploration. Grazing incidence X-ray diffraction (GIXRD) for MoS 2 film characterization provides valuable information about film density and grain orientation (texture). However, the determination of film stoichiometry can only be indirectly inferred via GIXRD. The combination of density and microstructure via GIXRD with chemical composition via grazing incidence X-ray fluorescence (GIXRF) enables the isolation and decoupling of film density, composition, and microstructure and their ultimate impact on film layer thickness, thereby improving coating thickness predictions via X-ray fluorescence. We have augmented an existing GIXRD instrument with an additional X-ray detector for the simultaneous measurement of energy-dispersive X-ray fluorescence spectra during the GIXRD analysis. This combined GIXRD/GIXRF analysis has proven synergetic for correlating chemical composition to the structural aspects of MoS 2 films provided by GIXRD. We present the usefulness of the combined diagnostic technique via exemplar MoS 2 film samples and provide a discussion regarding data extraction techniques of grazing angle series measurements.

MoS2↗

DOE OSTI2017

Electrochemical Growth of Copper Hydroxy Double Salt Films and Their Conversion to Nanostructured p-Type CuO Photocathodes

New electrochemical synthesis methods were developed to produce copper hydroxy double salts (Cu-HDS) films with four different intercalated anions (NO 3 - , SO 4 2- , Cl - , and dodecyl sulfate (DS)) as pure crystalline films as-deposited (Cu 2 NO 3 (OH) 3 , Cu 4 SO 4 (OH) 6 , Cu 2 Cl(OH) 2 , and Cu 2 DS(OH) 3 ). These methods are based on p-benzoquinone reduction, which increases the local pH at the working electrode and triggers the precipitation of Cu 2+ and appropriate anions as Cu-HDS films on the working electrode. The resulting Cu-HDS films could be converted to crystalline Cu(OH) 2 and CuO films by immersing them in basic solutions. Since Cu-HDS films were composed of 2D crystals due to the atomic level layered structure of HDS, the CuO films prepared from Cu-HDS films have unique low dimensional nanostructures, creating high surface areas, which cannot be obtained by direct deposition of CuO that has a 3D atomic level crystal structure. Here, the resulting nanostructures allowed the CuO films to facilitate electron-hole separation and demonstrate great promise for photocurrent generation when investigated as a photocathode for a water splitting photoelectrochemical cell. Electrochemical synthesis of Cu-HDS films and their facile conversion to CuO films will provide new routes to tune morphologies and properties of the CuO electrodes that may not be possible by other synthesis means.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Microstructural Evolution of the Thin Films of a Donor–Acceptor Semiconducting Polymer Deposited by Meniscus-Guided Coating

Crucial to the development and refinement of organic electronics is a fundamental understanding of how deposition processes affect the active material’s resulting microstructure in the thin film. Meniscus-guided coating (MGC) methods are attractive because of their amenability to high-throughput, industrially relevant continuous processes like roll-to-roll deposition, but the mechanism of solid film formation has not been elucidated and is valuable for the precise control of thin-film morphology and thus ultimate device performance. Here, in this work, we investigate the microstructural evolution of thin films of a diketopyrrolopyrrole–terthiophene donor–acceptor polymer semiconductor using both in situ and ex situ X-ray diffraction methods. On the basis of a comparison of disorder between the film bulk and the top surface and a depth profiling of the out-of-plane orientation of crystallites, we find that faster coating speeds introduce more disorder into the resulting films because the stochastic nucleation of disordered crystallites at the meniscus air–liquid interface becomes more dominant than substrate-mediated nucleation. Our results suggest that there exist three separate deposition regimes—namely the shear-dominate, disorder-dominate, and Landau–Levich–Derjaguin regimes—revealed by observing both polymer alignment via dry film thickness and optical dichroism, a property sensitive to the flow and shear fields. At low coating speeds, the shear strain imparted upon the solution directly induces polymer alignment, causing an increase in dichroism as a function of coating speed. When solvent evaporation becomes too rapid as coating speeds increase, a decrease in the dichroic ratio is observed before the classical Landau–Levich–Derjaguin regime occurs at the highest coating speeds, resulting in isotropic films. The preservation of out-of-plane crystalline texture throughout the thickness of the films is seen only for lower coating speeds, and a study of different deposition temperatures similarly indicates that the lower overall solvent evaporation is conducive to this process. Increased paracrystalline disorder (i.e., peak broadening) is observed by grazing-incidence wide-angle X-ray diffraction at the top interface of the dry films and at higher coating speeds. Together, these results indicate that more rapid solvent evaporation at higher coating speeds causes increased disorder, which can cause the nucleation of misaligned crystallites, affect the dichroic ratio, and may frustrate the alignment of polymer molecules in the amorphous regions of the film. Finally, because the polymer studied and the deposition technique used are representative models, these results are likely general for aggregating, semicrystalline donor–acceptor polymers deposited with MGC.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Characterizing Hygroscopic Films of Polyzwitterions in Electric Fields Using Neutron and X-ray Reflectometries: Electrostriction or Mass Loss?

Herein we study responses of thermally annealed ultrathin films deposited on silicon substrates and containing polyzwitterions to applied electric fields by using specular neutron reflectometry (NR). In particular, we applied 7 kV under vacuum at 150 °C on the films containing poly(1-(3-sulfonatopropyl)-2-vinylpyridinium) (P2VPPS) and its blends with either a deuterated ionic liquid (EMIMBF 4 - d 11 ), potassium bromide (KBr), or deuterated sodium polystyrenesulfonate (NaPSS-d 7 ). The voltage was applied over an air gap, and the in situ neutron reflectivity measurements allowed us to measure changes in the films. In all the cases, we measured decreases in thicknesses of the films, which varied up to ~8% depending on the added salt. Posteriori X-ray reflectivity (XRR) measurements on the same films at room temperature reveal that these films were highly hygroscopic, which led to the presence of water in these films. Analysis of the NR and the XRR revealed that the decrease in the thickness of the films in the neutron reflectivity experiments on heating resulted from the loss of water and the ionic liquid but not from electrostrictive effects. The in situ NR and posteriori XRR experiments revealed not only the hygroscopic nature of these films but also depth-resolved structural rearrangements due to the applied electric fields in the films containing electrolytes and polyelectrolytes. This work shows that a combination of NR and XRR can be used to distinguish between mass loss and electrostriction in films containing charged polymers such as polyzwitterions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Electrochemical Characterization and Catalytic Application of Gold-Supported Ferrocene-Containing Diblock Copolymer Thin Films in Ethanol Solution

This study reports the electrochemical behavior and catalytic property of electrode-supported thin films of polystyrene- block -poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PS- b -PAEFc) in an ethanol (EtOH) solution. The electrochemical properties of PS- b -PAEFc films with different PAEFc volume fractions (f PAEFc = 0.47, 0.30, and 0.17) in 0.1 M ethanolic sodium hexafluorophosphate were compared with those in an acetonitrile (MeCN) solution of 0.1 M tetrabutylammonium hexafluorophosphate. Pristine PS- b -PAEFc films did not afford significant faradaic currents in the EtOH solution because EtOH is a nonsolvent for both PS and PAEFc. However, the films could be rendered redox-active in the EtOH solution by applying potentials in the MeCN solution to induce the redox-associated incorporation of the supporting electrolytes into the films. Atomic force microscopy images verified the stability of PAEFc microdomains upon electrochemical measurements in these solutions. Cyclic voltammograms measured in the EtOH solution for PS- b -PAEFc with the larger f PAEFc were diffusion-controlled regardless of ellipsometric film thickness (23 – 152 nm) at relatively slow scan rates, in contrast to those in the MeCN solution that were controlled by surface-confined redox species. The electron propagation efficiency in the EtOH solution was significantly lower than that in the MeCN solution due to the poorer swelling of the films, which limited the migration of counter ions and the collisional motions of the ferrocene moieties. PS- b -PAEFc films were applied as electrochemically-responsive heterogeneous catalysts based on the ferrocenium moieties for Michael addition reaction between methyl vinyl ketone and ethyl 2-oxocyclopentanecarboxylate (E2OC) in 0.1 M NaPF 6 /EtOH. The catalytic activities of thin films were similar regardless of f PAEFc , suggesting that the catalytic reaction took place for the reactants that could penetrate through the film and reach PAEFc microdomains communicable with the underlying electrode. Interestingly, the permeability of PS-b-PAEFc films provided a means to control the reaction selectivity, as suggested by negligible reaction of E2OC with trans -4-phenyl-3-buten-2-one.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Effects of Oxygen Modification on the Structural and Magnetic Properties of Highly Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films

Abstract La 0.7 Sr 0.3 MnO 3 , a strong semi-metallic ferromagnet having robust spin polarization and magnetic transition temperature ( T C ) well above 300 K, has attracted significant attention as a possible candidate for a wide range of memory, spintronic, and multifunctional devices. Since varying the oxygen partial pressure during growth is likely to change the structural and other physical functionalities of La 0.7 Sr 0.3 MnO 3 (LSMO) films, here we report detailed investigations on structure, along with magnetic behavior of LSMO films with same thickness (~30 nm) but synthesized at various oxygen partial pressures: 10, 30, 50, 100, 150, 200 and 250 mTorr. The observation of only ( 00 l ) reflections without any secondary peaks in the XRD patterns confirms the high-quality synthesis of the above-mentioned films. Surface morphology of the films reveals that these films are very smooth with low roughness, the thin films synthesized at 150 mTorr having the lowest average roughness. The increasing of magnetic T C and sharpness of the magnetic phase transitions with increasing oxygen growth pressure suggests that by decreasing the oxygen growth pressure leads to oxygen deficiencies in grown films which induce oxygen inhomogeneity. Thin films grown at 150 mTorr exhibits the highest magnetization with T C = 340 K as these thin films possess the lowest roughness and might exhibit lowest oxygen vacancies and defects. Interpretation and significance of these results in the 30 nm LSMO thin films prepared at different oxygen growth pressures are also presented, along with the existence and growth pressure dependence of negative remanent magnetization (NRM) of the above-mentioned thin films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

Extraordinary optical transmission in nanopatterned ultrathin metal films without holes

In this study, we experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller than the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2017

Orbital orientation mapping of V 2 O 5 thin films

We report the effects of growth methods on the orbital orientation in vanadium pentoxide (V 2 O 5 ) thin films, an important factor to consider when selecting growth techniques for highly selective catalysts and devices. Thermal evaporation and sol-gel methods were used to synthesize the V 2 O 5 films. The surface morphology, roughness, and orientation of the films were characterized by atomic force microscopy and x-ray diffraction. Surface electronic properties and oxidation states were assessed by x-ray photoemission spectroscopy. Polarized x-ray absorption spectroscopy demonstrated that the thermally evaporated film [which was in the (001) orientation] exhibited greater anisotropy than the (100) oriented sol-gel film. The observed increase in anisotropy agrees well with computational findings which revealed that more vanadyl bonds are present at the surface of the thermally evaporated film than at the surface of the sol-gel film. The same computational study also found that the orientation of these bonds is more parallel to the film surface in the thermally evaporated film than in the sol-gel film. Finally, the data suggest that the method of growth may be used as a controlled variable to select key film characteristics for potential applications.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Microstructure, mechanical and electrical properties of nanocrystalline W-Mo thin films

The effect of sputtering pressure on the surface/interface microstructure, crystal phase, mechanical properties and electrical characteristics of nanocrystalline W-Mo films is reported. The W-Mo films (≈300 nm) with variable microstructure were deposited under variable argon (Ar) sputtering pressure (P Ar ), which is varied in the range of 3-19 mTorr. X-ray diffraction analyses indicate that the W-Mo films crystallize in thermodynamically stable α-phase of W. However, the crystal-quality degradation occurs for W-Mo films deposited at higher P Ar due to difference in the adatom mobilities. The average grain size (d) of the W-Mo films was in the range of 11-24 nm; grain size decreases with increasing P Ar . The effect of P Ar and associated microstructure are significant on the mechanical characteristics; the hardness (H) and modulus of elasticity (E r ) of W-Mo films deposited at lower P Ar were higher but decreases continuously with increasing P Ar . The W-Mo films deposited under optimum sputtering pressure exhibit superior mechanical characteristics: H=40 GPa, E r =275 GPa, H/E r =0.8, and H 3 /E r 2 =0.145 GPa, which are higher compared to pure, α-phase W-films. The W-Mo films deposited at P Ar =3-9 mTorr exhibit high resistivity≈350-400 μΩ-cm, which decreases to 150-200 μΩ-cm for films deposited at higher P Ar . Based on the results, structure-mechanical-electrical property correlation in W-Mo films is established.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Optimization of electrical treatment strategy for surface roughness reduction in conducting thin films

The surface roughness of deposited conducting thin films is responsible for various materials reliability problems in nanoelectronics and nanofabrication technologies. In this work, we report a modeling and simulation study that aims at optimizing the electrical surface treatment of deposited conducting thin films as a physical processing strategy for their surface roughness reduction. Our research is based on a continuum model of film surface morphological evolution that accounts for the residual stress in the deposited conducting thin film, the film’s wetting of the substrate layer that it is deposited on, film texture and surface diffusional anisotropy, and surface electromigration. Through systematic linear stability analysis and dynamical simulation protocols, we examine in detail the effects of film surface crystallographic orientation and applied electric field direction toward minimizing the electric field strength required for film surface smoothening. We believe that the critical electric field strength requirement for surface roughness reduction on {110}, {100}, and {111} surfaces of face-centered cubic crystalline conducting thin films exhibits a very strong dependence on the applied electric field direction, expressed as the electric field misalignment with respect to the principal residual stress directions in the film and the fast surface diffusion directions. Due to these findings, we optimize the electrical treatment strategy for surface roughness reduction of conducting thin films with respect to all relevant processing and material parameters.

42 ENGINEERING↗

DOE OSTI2012

Novel wide band gap materials for highly efficient thin film tandem solar cells. Final report

Tandem solar cells (TSCs), which use two or more materials to absorb sunlight, have achieved power conversion efficiencies of >25% versus 11-20% for commercialized single junction solar cell modules. The key to widespread commercialization of TSCs is to develop the wide-band, top solar cell that is both cheap to fabricate and has a high open-circuit voltage (i.e. >1V). Previous work in TSCs has generally focused on using expensive processing techniques with slow growth rates resulting in costs that are two orders of magnitude too expensive to be used in conventional solar cell modules. The objective of the PLANT PV proposal was to investigate the feasibility of using Ag(In,Ga)Se 2 (AIGS) as the wide-bandgap absorber in the top cell of a thin film tandem solar cell (TSC). Despite being studied by very few in the solar community, AIGS solar cells have achieved one of the highest open-circuit voltages within the chalcogenide material family with a Voc of 949 mV when grown with an expensive processing technique (i.e. Molecular Beam Epitaxy). PLANT PV's goal in Phase I of the DOE SBIR was to (1) develop the chemistry to grow AIGS thin films via solution processing techniques to reduce costs and (2) fabricate new device architectures with high open-circuit voltage to produce full tandem solar cells in Phase II. PLANT PV attempted to translate solution processing chemistries that were successful in producing >12% efficient Cu(In,Ga)Se 2 solar cells by replacing copper compounds with silver. The main thrust of the research was to determine if it was possible to make high quality AIGS thin films using solution processing and to fully characterize the materials properties. PLANT PV developed several different types of silver compounds in an attempt to fabricate high quality thin films from solution. We found that silver compounds that were similar to the copper based system did not result in high quality thin films. PLANT PV was able to deposit AIGS thin films using a mixture of solution and physical vapor deposition processing, but these films lacked the p-type doping levels that are required to make decent solar cells. Over the course of the project PLANT PV was able to fabricate efficient CIGS solar cells (8.7%) but could not achieve equivalent performance using AIGS. During the nine-month grant PLANT PV set up a variety of thin film characterization tools (e.g. drive-level capacitance profiling) at the Molecular Foundry, a Department of Energy User Facility, that are now available to both industrial and academic researchers via the grant process. PLANT PV was also able to develop the back end processing of thin film solar cells at Lawrence Berkeley National Labs to achieve 8.7% efficient CIGS solar cells. This processing development will be applied to other types of thin film PV cells at the Lawrence Berkeley National Labs. While PLANT PV was able to study AIGS film growth and optoelectronic properties we concluded that AIGS produced using these methods would have a limited efficiency and would not be commercially feasible. PLANT PV did not apply for the Phase II of this grant.

14 SOLAR ENERGY↗

DOE OSTI2010

Recovery Act: "Near-Single-Crystalline Photovoltaic Thin Films on Polycrystalline, Flexible Substrates" (Final Report)

III-V photovoltaics have exhibited efficiencies above 40%, but have found only a limited use because of the high cost of single crystal substrates. At the other end of the spectrum, polycrystalline and amorphous thin film solar cells offer the advantage of low-cost fabrication, but have not yielded high efficiencies. Our program is based on single-crystalline-like thin film photovoltaics on polycrystalline substrates using biaxially-textured templates made by Ion Beam-Assisted Deposition (IBAD). MgO templates made by IBAD on flexible metal substrate have been successfully used for epitaxial growth of germanium films. In spite of a 4.5% lattice mismatch, heteroepitaxial growth of Ge was achieved on CeO 2 that was grown on IBAD MgO template. Room temperature optical bandgap of the Ge films was identified at 0.67 eV indicating minimal residual strain. Refraction index and extinction coefficient values of the Ge films were found to match well with that measured from a reference Ge single crystal. GaAs has been successfully grown epitaxially on Ge on metal substrate by molecular beam epitaxy. RHEED patterns indicate self annihilation of antiphase boundaries and the growth of a single domain GaAs. The GaAs is found to exhibit strong photoluminescence signal and, an existence of a relatively narrow (FWHM~20 meV) band-edge excitons measured in this film indicates a good optoelectronic quality of deposited GaAs. While excellent epitaxial growth has been achieved in GaAs on flexible metal substrates, the defect density of the films as measured by High Resolution X-ray Diffraction and etch pit experiments showed a high value of 5 x 10 8 per cm 2 . Cross sectional transmission electron microscopy of the multilayer architecture showed concentration of threading dislocations near the germanium-ceria interface. The defect density was found decrease as the Ge films were made thicker. The defects appear to originate from the MgO layer presumably because of large lattice mismatches between the various layers. The defect density in GaAs was reduced by a factor of five by adding a step of in-situ deposition of Ge by MBE on the sputtered Ge prior to GaAs growth. We have investigated device design strategies that would support development of high-efficiency devices in presence of dislocation densities of 10 8 cm -2 present in our epitaxial GaAs films. Results from modeling work show that with a proper emitter, base and doping selection, the modeled efficiency of a GaAs cells with dislocation densities of 10 9 and 10 8 cm -2 could be increased from 1% and 7% to 11% and 17% respectively. Under AM0, this single junction GaAs solar cell, has optimized value of emitter and base thickness of around 0.7 and 1.7 microns respectively, to give a maximum efficiency of 24.2%. We have fabricated complete GaAs solar cells using our Ge films on metal substrates. Pattern resolution of few microns with well-defined grid line of 30 microns has been realized on few cm square flexible templates. The ability to grow single-crystalline-like Ge films on flexible, polycrystalline substrates by reel-to-reel tape processing now provides an immense potential to fabricate high quality III-V photovoltaics on flexible, inexpensive substrates.

14 SOLAR ENERGY↗

DOE OSTI2013

Investigation of NbN x Thin Films and Nanoparticles Grown by Pulsed Laser Deposition and Thermal Diffusion

Niobium nitride films (NbN x ) were grown on Nb and Si (100) substrates using pulsed laser deposition (PLD), laser heating, and thermal diffusion methods. Niobium nitride films were deposited on Nb substrates using PLD with a Q-switched Nd: YAG laser (λ = 1064 nm, 40 ns pulse width, and 10 Hz repetition rate) at different laser fluences, different nitrogen background pressures and deposition temperatures. The effect of changing PLD parameters for films done by PLD was studied. The seen observations establish guidelines for adjusting the laser parameters to achieve the desired morphology and phase of the grown NbN x films. When the fabrication parameters are fixed, except for laser fluence, surface roughness, deposition rate, nitrogen content, and grain size increases with increasing laser fluence. Increasing nitrogen background pressure leads to change in the phase structure of the NbN x films from mixed -Nb 2 N and cubic δ-NbN phases to single hexagonal β-Nb 2 N. A change in substrate temperature led to a pronounced change in the preferred orientation of the crystal structure, the phase transformation, surface roughness, and composition of the films. The structural, electronic, and nanomechanical properties of niobium nitride PLD deposited at different nitrogen pressures (26.7-66.7 Pa) on Si(100) were investigated. The NbN x , films exhibited a cubic δ-NbN with a strong (111) orientation. A correlation between surface morphology, electronic, and superconducting properties was found. The highly-textured δ-NbN films have a T c up to 15.07 K. The film was deposited at a nitrogen background pressure of 66.7 Pa exhibited improved superconducting properties and showed higher hardness values as compared to films deposited at lower nitrogen pressures. NbN nanoclusters that were deposited on carbon coated Cu-grids using PLD at laser fluence of 8 J/cm 2 were observed. Niobium nitride is prepared by heating of Nb sample in a reactive nitrogen atmosphere (133 Pa) at a temperature of 900 °C. The results suggest that the niobium nitride was crystalline in the single phase of hexagonal β-Nb 2 N. As heating time increased, film growth continued with improvement in hardness and modulus. The XRD of samples prepared by a thermal diffusion method at low nitrogen pressure and high temperatures were reported. The samples were prepared at temperatures ranging from 1250-1500 °C. 2D-XRD images of samples, processed at temperature range from 1250 -1500 °C at pressure of 1.3×10 -3 Pa, showed the formation of an α phase. As pressure increased to 0.13 Pa, an α-NbN phase mixed with β-Nb 2 N phase appeared. Niobium nitride samples were prepared by laser nitridation using a Q-switched Nd: YAG nanosecond laser and Ti: sapphire femtosecond lasers. The effects of laser fluence on the formed phase, surface morphology, and electronic properties of the NbN x were investigated. Samples were prepared using Nd: YAG laser are of NbN x in the cubic δ-NbN phase. The femtosecond laser-nitrided samples were prepared by different laser fluences of 0.1-1.3 mJ/cm 2 at 4.0×10 4 Pa nitrogen pressure. NbN x samples with mixedα, β and δ phases were observed. The cubic δ-NbN structure is dominated over the other two phases.

Farha, Ashraf Hassan↗

DOE OSTI2020

Water-Dependent Blending of Pectin Films: The Mechanics of Conjoined Biopolymers

Biodegradable pectin polymers have been recommended for a variety of biomedical applications, ranging from the delivery of oral drugs to the repair of injured visceral organs. A promising approach to regulate pectin biostability is the blending of pectin films. To investigate the development of conjoined films, we examined the physical properties of high-methoxyl pectin polymer-polymer (homopolymer) interactions at the adhesive interface. Pectin polymers were tested in glass phase (10–13% w/w water content) and gel phase (38–41% w/w water content). The tensile strength of polymer-polymer adhesion was measured after variable development time and compressive force. Regardless of pretest parameters, the adhesive strength of two glass phase films was negligible. In contrast, adhesion testing of two gel phase films resulted in significant tensile adhesion strength (p < 0.01). Adhesion was also observed between glass phase and gel phase films—likely reflecting the diffusion of water from the gel phase to the glass phase films. In studies of the interaction between two gel phase films, the polymer-polymer adhesive strength increased linearly with increasing compressive force (range 10–80 N) (R 2 = 0.956). In contrast, adhesive strength increased logarithmically with time (range 10–10,000 s) (R 2 = 0.913); most of the adhesive strength was observed within minutes of contact. Fracture mechanics demonstrated that the adhesion of two gel phase films resulted in a conjoined film with distinctive physical properties including increased extensibility, decreased stiffness and a 30% increase in the work of cohesion relative to native polymers (p < 0.01). Scanning electron microscopy of the conjoined films demonstrated cross-grain adhesion at the interface between the adhesive homopolymers. These structural and functional data suggest that blended pectin films have emergent physical properties resulting from the cross-grain intermingling of interfacial pectin chains.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

NASA NTRS1987

Mechanical strength and tribological behavior of ion-beam deposited boron nitride films on non-metallic substrates

An investigation was conducted to examine the mechanical strength and tribological properties of boron nitride (BN) films ion-beam deposited on silicon (Si), fused silica (SiO2), gallium arsenide (GaAs), and indium phosphide (InP) substrates in sliding contact with a diamond pin under a load. The results of the investigation indicate that BN films on nonmetallic substrates, like metal films on metallic substrates, deform elastically and plastically in the interfacial region when in contact with a diamond pin. However, unlike metal films and substrates, BN films on nonmetallic substrates can fracture when they are critically loaded. Not only does the yield pressure (hardness) of Si and SiO2 substrates increase by a factor of 2 in the presence of a BN film, but the critical load needed to fracture increases as well. The presence of films on the brittle substrates can arrest crack formation. The BN film reduces adhesion and friction in the sliding contact. BN adheres to Si and SiO2 and forms a good quality film, while it adheres poorly to GaAs and InP. The interfacial adhesive strengths were 1 GPa for a BN film on Si and appreciably higher than 1 GPa for a BN film on SiO2.

Miyoshi, Kazuhisa↗

NASA NTRS1987

Mechanical strength and tribological behavior of ion-beam-deposited boron nitride films on non-metallic substrates

Miyoshi, Kazuhisa↗