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Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films
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Degradation of superconducting Nb/NbN films by atmospheric oxidation
Niobium and niobium nitride thin films are transitioning from fundamental research toward wafer scale manufacturing with technology drivers that include superconducting circuits and electronics, optical single photon detectors, logic, and memory. Successful microfabrication requires precise control over the properties of sputtered superconducting films, including oxidation. Previous work has demonstrated the mechanism in oxidation of Nb and how film structure could have deleterious effects upon the superconducting properties. This study provides an examination of atmospheric oxidation of NbN films. By examination of the room temperature sheet resistance of NbN bulk oxidation was identified and confirmed by secondary ion mass spectrometry. As a result, Meissner magnetic measurements confirmed the bulk oxidation not observed with simple cryogenic resistivity measurements.
Tailoring nanopore formation in atomic layer deposited ultrathin films [Nanopore formation in atomic layer deposited ultrathin films]
Selectivity is a critical attribute of catalysts used in manufacturing of essential and fine chemicals. An excellent way to induce selectivity in catalysts is by using ultrathin films with tailored nanoporosity. For instance, nanopores can be created in atomic layer deposition (ALD) ultrathin over-coatings on supported metal nanoparticles by subjecting the coatings to high temperature annealing. These nanopores expose the active surface of the underlying metal nanoparticles. The dimensions of these nanopores can be tuned to impart shape selectivity: only reactants or products with a specific size or shape can fit inside the pore. In this work, the authors explore the underlying mechanism driving nanopore formation in ALD films. Ultrathin films of ALD TiO 2 (similar to 2.5 nm thick) and ALD Al 2 O 3 (similar to 4.9 nm thick) were deposited on nonporous gamma-Al 2 O 3 nanoparticles. The pore formation and evolution were monitored in situ during thermal annealing using small-angle x-ray scattering (SAXS), and the crystallinity was monitored by in situ x-ray diffraction. A correlation between the nanopore formation and amorphous to crystalline phase transitions in the ALD layers was observed. The authors hypothesize that the pores form through the relaxation of stress induced by densification of the ALD films during the phase transitions. In conclusion, the authors developed a mathematical model to evaluate this hypothesis and found remarkable agreement between the model and the SAXS measurements.
Dual Effect of Structure and Hydration on Magnesium-Ion Insertion into Electrodeposited V 2 O 5 Thin Films
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High-efficiency second harmonic generation of blue light on thin-film lithium niobate
The strength of interactions between photons in a χ (2) nonlinear optical waveguide increases at shorter wavelengths. These larger interactions enable coherent spectral translation and light generation at a lower power, over a broader bandwidth, and in a smaller device: all of which open the door to new technologies spanning fields from classical to quantum optics. Stronger interactions may also grant access to new regimes of quantum optics to be explored at the few-photon level. One promising platform that could enable these advances is thin-film lithium niobate (TFLN), due to its broad optical transparency window and possibility for quasi-phase matching and dispersion engineering. In this Letter, we demonstrate second harmonic generation of blue light on an integrated thin-film lithium niobate waveguide and observe a conversion efficiency of η 0 = 33, 000%/W- cm 2 , significantly exceeding previous demonstrations.
Optical and electrical properties of indium tin oxide films near their laser damage threshold [Electrical and optical properties of indium tin oxide films under multi-pulse laser irradiation at 1064 nm]
In this paper, we investigated whether the optical and electrical properties of indium tin oxide (ITO) films are degraded under laser irradiation below their laser ablation threshold. While performing multi-pulse laser damage experiments on a single ITO film (4.7 ns, 1064 nm, 10 Hz), we examined the optical and electrical properties in situ . A decrease in reflectance was observed prior to laser damage initiation. However, under sub-damage threshold irradiation, conductivity and reflectance of the film were maintained without measurable degradation. This indicates that ITO films in optoelectronic devices may be operated below their lifetime laser damage threshold without noticeable performance degradation.
Controlled exposure of CuO thin films through corrosion-protecting, ALD-deposited TiO 2 overlayers
Ultra-thin film coatings are used to protect semiconductor photoelectrodes from the harsh chemical environments common to photoelectrochemical energy conversion. These layers add contact transfer resistance to the interface that can result in a reduction of photoelectrochemical energy conversion efficiency of the photoelectrode. Here, we describe the concept of a partial protection layer, which allows for direct chemical access to a small fraction of the semiconductor underlayer for further functionalization by an electrocatalyst. The rest of the interface remains protected by a stable, inert protection layer. CuO is used as a model system for this scheme. Atomic layer deposition (ALD)-prepared TiO 2 layers on CuO thin films prepared from electrodeposited Cu 2 O allow for the control of interfacial morphology to intentionally expose the CuO underlayer. The ALD-TiO 2 overlayer shrinks during crystallization, while Cu 2 O in the underlayer expands during oxidation. As a result, the TiO 2 protection layer cracks to expose the oxidized underlying CuO layer, which can be controlled by preceding thermal oxidation. Furthermore, this work demonstrates a potentially promising strategy for the parallel optimization of photoelectrochemical interfaces for chemical stability and high performance.
Diketopyrrolopyrrole-based polymer:fullerene nanoparticle films with thermally stable morphology for organic photovoltaic applications
Polymer:fullerene nanoparticles (NPs) offer two key advantages over bulk heterojunction (BHJ) films for organic photovoltaics (OPVs), water-processability and potentially superior morphological control. Once an optimal active layer morphology is reached, maintaining this morphology at OPV operating temperatures is key to the lifetime of a device. Here we study the morphology of the PDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene}):PC 71 BM ([6,6]-phenyl C 71 butyric acid methyl ester) NP system and then compare the thermal stability of NP and BHJ films to the common poly(3-hexylthiophene) (P3HT): phenyl C 61 butyric acid methyl ester (PC 61 BM) system. Finally, we find that material T g plays a key role in the superior thermal stability of the PDPP-TNT:PC 71 BM system; whereas for the P3HT:PC 61 BM system, domain structure is critical.
Thin Film Approaches to the SRF Cavity Problem Fabrication and Characterization of Superconducting Thin Films
Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory’s CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater performance benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency – 1.5 GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m – there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (≈ 45 MV/m for Nb) where inevitable thermodynamic breakdown occurs. With state of the art Nb based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating-superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio frequency applications. Correlated studies on structure, surface morphology and superconducting properties of epitaxial Nb and MgB2 thin films are presented.
Film thickness measurements on five fluid formulations by the mercury squeeze film capacitance technique
The thinning characteristics of five fluids were studied by measuring film thickness as a function of time. The mercury squeeze film capacitance technique was used. All tests were performed at room temperature. The synthetic hydrocarbon plus a nematic liquid crystal, N-(p-methoxybenzylidene)-p-butylaniline, thinned according to a Newtonian model and retained its bulk viscosity. The synthetic hydrocarbon plus a phosphonate antiwear additive and the synthetic hydrocarbon plus n-hexadecanol produced residual thick films. The synthetic hydrocarbon base fluids and the synthetic hydrocarbon plus a paraffinic resin displayed viscosity increases during thinning, but no residual films were formed.
Thin film growth rate effects for primary ion beam deposited diamondlike carbon films
Diamondlike carbon (DLC) films were grown by primary ion beam deposition and the growth rates were measured for various beam energies, types of hydrocarbon gases and their ratio to Ar, and substrate materials. The growth rate had a linear dependence upon hydrocarbon content in the discharge chamber, and only small dependence on other parameters. For given deposition conditions a threshold in the atomic ratio of carbon to argon gas was identified below which films did not grow on fused silica substrate, but grew on Si substrate and on existing DLC films. Ion source deposition parameters and substrate material were found to affect the deposition threshold and film growth rates.
Room Temperature Thin Film Ba(x)Sr(1-x)TiO3 Ku-Band Coupled MicrostripPhase Shifters: Effects of Film Thickness, Doping, Annealing and Substrate Choice
We report on measurements taken on over twenty Ku-band coupled microstrip phase shifters (CMPS) using thin ferroelectric films of Ba(x)Sr(1-x)TiO3. This CMPS design is a recent innovation designed to take advantage of the high tunability and tolerate the high dielectric constant of ferroelectric films at Ku- and K-band frequencies. These devices are envisioned as a component in low-cost steerable beam phased area antennas, Comparisons are made between devices with differing film thickness, annealed vs unannealed, Mn-doped vs. undoped, and also substrates of LaAlO3 and MgO. A comparison between the CMPS structure and a CPW phase shifter was also made oil the same ferroelectric film.
Nanotube Film Electrode and an Electroactive Device Fabricated with the Nanotube Film Electrode and Methods for Making Same
Disclosed is a single wall carbon nanotube (SWCNT) film electrode (FE), all-organic electroactive device systems fabricated with the SWNT-FE, and methods for making same. The SWCNT can be replaced by other types of nanotubes. The SWCNT film can be obtained by filtering SWCNT solution onto the surface of an anodized alumina membrane. A freestanding flexible SWCNT film can be collected by breaking up this brittle membrane. The conductivity of this SWCNT film can advantageously be higher than 280 S/cm. An electroactive polymer (EAP) actuator layered with the SWNT-FE shows a higher electric field-induced strain than an EAP layered with metal electrodes because the flexible SWNT-FE relieves the restraint of the displacement of the polymeric active layer as compared to the metal electrode. In addition, if thin enough, the SWNT-FE is transparent in the visible light range, thus making it suitable for use in actuators used in optical devices.
Understanding the adsorption and potential tear film stability properties of recombinant human lubricin and bovine submaxillary mucins in an in vitro tear film model
The wetting and adsorption properties for two glycoproteins, recombinant human lubricin and bovine submaxillary mucins (BSM) were evaluated on hydrophilic and hydrophobic glass dome surfaces in a simplified in vitro tear film model. Herein, we show that both recombinant human lubricin (rh-lubricin) and BSM solutions render surfaces hydrophilic and when the fluid films reach 500 nm or less, the fluids resist evaporation-driven breakup through a volumetric flux across the surface, which we believe is due to evaporation-driven solutocapillary flows. rh-Lubricin was able to maintain a wet film without spontaneous breakup for longer periods of time than BSM at lower concentrations, which we attribute to differences in adsorption properties, measured by QCM-D, that result from surface charge and structural differences (confirmed by zeta potential, DLS, and SAXS measurements).
Circularly Polarized Stimulated Emission from a Chiral Cavity Based on Apparent Circular Dichroism Organic Thin-Films
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Influence of piezoelectric strain on the Raman spectra of BiFeO 3 films deposited on PMN-PT substrates
In this study, BiFeO 3 epitaxial thin films were deposited on piezoelectric 0.72Pb(Mg 1/3 Nb 2/3 )O 3 -0.28PbTiO 3 (PMN-PT) substrates with a conductive buffer layer (La 0.7 Sr 0.3 MnO 3 or SrRuO 3 ) using pulsed laser deposition. The calibration of the strain values induced by the electric field applied on the piezoelectric PMN-PT substrates was realised using X-Ray diffraction measurements. The method of piezoelectrically induced strain allows to obtain a quantitative correlation between strain and the shift of the Raman-active phonons, ruling out the influence of extrinsic factors, such as growth conditions, crystalline quality of substrates, or film thickness. Using the Poisson number for BiFeO 3 one can determine the volume change induced by strain, and therefore the Gr neisen parameters for specific phonon modes.