Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W52: Thin Film Coatings and Applications |
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Sponsoring Units: DCMP Chair: Daniel Dougherty, North Carolina State University Room: Mile High Ballroom 1E |
Friday, March 6, 2020 8:00AM - 8:12AM |
W52.00001: Growth of Conformal Thin Film Si Coatings on Terraced Substrates Using Subsequent Oblique Incidence Xe+ Ion Bombardment Emmett Randel, Carmen Susana Menoni, Richard M Bradley Using a Si surface pre-patterned with a 500 nm pitch sinusoidal profile, it is demonstrated that ordered terraced topographies with sub-nanometer scale roughness on the facets develop under oblique incidence 1500 eV Xe+ broad beam ion bombardment. Bi-layers of SiO2/Si were then deposited onto the terraced substrate using ion beam sputtering. Following the deposition of each Si layer, the oblique incidence Xe+ bombardment was repeated to restore the terraced structure. This work was performed in tandem with theory in an effort to refine models, showing agreement in selection of terraced slopes and the development of transverse roughness along the facets. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W52.00002: Amorphous oxides to improve the coatings of future gravitational wave detectors Gabriele Vajente, Mariana Fazio, Le Yang, Alena Ananyeva, GariLynn Billingsley, Ashot Markosyan, Riccardo Bassiri, Martin M. Fejer, Carmen Susana Menoni Amorphous oxides like tantala and titania-doped-tantala have been used as high index material for high reflectivity coatings in many applications, including the mirrors of current gravitational wave detectors. The sensitivity of those detectors is currently limited by coating Brownian noise, which is related to elastic energy loss in the coatings, as shown by the Fluctuation-Dissipation Theorem. This motivates a wide range search of an alternative amorphous material with lower mechanical loss, that could provide a substitute for the high refractive index currently used, namely titania-doped-tantala. |
Friday, March 6, 2020 8:24AM - 8:36AM |
W52.00003: Wide survey of Ta2O5-based mixed oxide coatings for gravitational wave detectors Mariana Fazio, Le Yang, Gabriele Vajente, Alena Ananyeva, GariLynn Billingsley, Ashot Markosyan, Riccardo Bassiri, Martin M. Fejer, Carmen Susana Menoni Thermal noise is a fundamental limitation in optical interferometry experiments as thermally driven fluctuations cause variations in the optical path. The sensitivity of gravitational wave detectors, such as Advanced LIGO and Advanced Virgo, is affected by the thermal noise in the high-reflectivity mirrors of the end masses. These mirrors are multilayer stacks of alternating layers of TiO2:Ta2O5 and SiO2, with the main source of thermal noise being the mechanical loss of TiO2:Ta2O5. |
Friday, March 6, 2020 8:36AM - 8:48AM |
W52.00004: Dielectrowetting of nematic liquid crystal films Ensela Mema, Linda Cummings, Lou Kondic We consider a mathematical model that describes the flow of a Nematic Liquid Crystal (NLC) film placed on a surface that contains interlaced electrodes (which generate an electric field that varies in the plane of the substrate). We assume that the NLC film is thin relative to the inter-electrode spacing. Under the usual long-wave scaling, a partial differential equation that describes the time evolution of the thin film is obtained. Due to the dielectric nature of NLC molecules, this equation is coupled to a boundary value problem that describes the interaction between the nematic director and the electric field potential. After validating our fully nonlinear simulations by linear stability analysis, we discuss the influence of an applied electric field on the stability of the NLC film. |
Friday, March 6, 2020 8:48AM - 9:00AM |
W52.00005: Sound velocity study in multilayer ultrathin films using wavelet transform Saeed Yousefi Sarraf, Robbyn Trappen, Navid Mottaghi, Alan Bristow, Mikel Holcomb Ultrafast spectroscopy of thin films reveals mechanisms responsible for relaxation of charge carriers’ energy to lower energy states. In the case of a strong enough excitation pump pulse, a shock wave will travel with the sound velocity, longitudinally in the thin film. Due to the interference effect, the shock wave superimposes a sinusoidal wave on the transient reflectivity, which can be used to calculate the sound velocity. In lower thicknesses, this sinusoidal behavior is not analyzable by Fourier transforms. Wavelet transforms, which use scalable wavelets localized in time and space, are perfect tools to analyze these fast-vanishing oscillations. Wavelet analysis has been applied to the residual sinusoidal TR to extract information related to different oscillatory modes, in multilayer ultrathin films. This approach can isolate the location of various oscillatory modes with close energy ranges, at the surface, interface and in the bulk of the heterostructures. As a result, implementation of wavelet transforms provided information regarding the sound velocity and acoustic phonons in multilayer thin films. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W52.00006: Mixture and nanolaminate – a pathway to understand coating mechanical loss Le Yang, Mariana Fazio, Gabriele Vajente, Alena Ananyeva, GariLynn Billingsley, Ashot Markosyan, Riccardo Bassiri, Martin M. Fejer, Carmen Susana Menoni Composite oxides in the form of mixture and nanolaminate are extensively used in optical coatings and as dielectric materials. Tunable properties accessible through mixing and nanolayering have drawn great attention to these composite thin films. TiO2-Ta2O5 mixture coating has been shown to reduce the mechanical loss compared to pure Ta2O5 coating thereby improving the sensitivity of the Advanced LIGO gravitational wave detector. In this work, reactive biased target ion beam deposition was used to grow mixture and nanolaminate coatings of SiO2-Ta2O5 and TiO2-Ta2O5. Different mechanisms of mechanical loss reduction through heat treatment are observed. Ta2O5-SiO2 mixtures annealed at 750°C show diffraction only from the crystallized orthorhombic Ta2O5 phase, indicating an immiscibility of SiO2 in Ta2O5. Additionally, Ta2O5-SiO2 nanolayers remained separate by sharp interface after annealing. On the contrary, mixing identified by blurring of interfaces is observed in Ta2O5-TiO2 nanolaminate after annealing at 650°C. This behavior resembles the mixture coating. This work brings out new understanding of the physical mechanism of coating mechanical loss reduction at room temperature. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W52.00007: Monitoring structural changes in steel thin films in electrolyte in situ by X-ray standing waves Debi Garai, Ilaria Carlomagno, Axel Wilson, Carlo Meneghini, Vladyslav Solokha, Christian Morawe, Ajay Gupta, Jorg Zegenhagen Ultra-thin stainless steel films were deposited on Ru/B4C multilayers using DC magnetron sputtering and characterised by synchrotron X-rays. The X-ray standing wave (XSW) technique revealed the metal distribution with depth. Typical for stainless steel [1], the near surface region was free of nickel. The oxidation states of Cr, Ni and Fe were determined by X-ray near edge absorption structure (XANES) under XSW condition. Nickel was found to be largely metallic whereas Fe and Cr where oxidized in the surface region, forming an about 2 nm passive layer. Exposure to 0.1M KCl at cathodic potential of -0.6 V vs Ag/AgCl resulted in expansion of the steel film due to in-diffusion of hydrogen. Using XSW/XANES, structural and chemical changes of the steel film were further traced in situ as a function of electrode potential up to +0.8 V. Results will be presented in the talk. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W52.00008: Deformation profile and interface-mediated defect interaction in Cu/CuZr nanolaminates: An effective-temperature description Michael Tong, Charles Lieou, Irene Beyerlein Both simulations and experiments have suggested that Cu/CuZr nanolaminates are stronger and more ductile than their individual constituents due to interface-mediated interactions between plasticity carriers. We use the effective-temperature theories of dislocation and amorphous shear-transformation-zone (STZ) plasticity to study amorphous-crystalline interface (ACI)-mediated plasticity in Cu/CuZr nanolaminates under mechanical straining. The model is shown to capture reasonably well the measured deformation response when strained either in tension parallel to or in compression normal to the amorphous-crystalline interface. Our analysis indicates that increasing CuZr or decreasing Cu layer thickness increases the maximum flow stress for both perpendicular and parallel loading cases. In all slip strain analyses, maximum slip strain occurs at the ACI, thus indicating that plasticity carriers accumulate at the interface and are absorbed there. These findings indicate a significant anisotropy in strength with greater sensitivity to layer thickness for the case of tensile loading parallel to the ACI. Further findings signify that slip strain is more sensitive when the nanolaminate is compressed perpendicular to the ACI. |
Friday, March 6, 2020 9:36AM - 9:48AM |
W52.00009: The Search for an Amorphous Coating with Low Mechanical Loss and High Refractive Index Kiran Prasai, Sagada I Penano, Jun Jiang, Alec Mishkin, Hai-ping Cheng, Riccardo Bassiri, Martin M. Fejer The next major upgrade to gravitational wave detector LIGO, called Advanced LIGO+ or A+, is planned to operate at room temperature and requires 4 times improvement in coating mechanical loss to meet its design sensitivity. The coatings are made up of alternating layers of high and low refractive index materials to make the mirrors highly reflective. The current coatings have amorphous silica as the low index layer and titania-doped tantala as the high index layer. The mechanical loss of high index layer dominates the coating loss and the thermal noise requirement for A+ could be met by finding a high index layer with low enough mechanical loss. In this talk, I will describe the research efforts aimed at finding such a coating. In particular, I will talk about how the atomic structure measurements and modeling of amorphous oxides are being used to guide the coating development process. I will highlight some interesting correlations in the structure and loss measurements and draw some empirical conclusions. Finally, I will discuss the thermally activated relaxation processes (TARP) in amorphous oxides based on atomic simulations of two-level systems (TLSs). TARP is believed to be the source of mechanical loss in amorphous materials. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W52.00010: Addressing the Achilles’ Heels of Amorphous Carbon Overcoats with Doping: Mechanisms of Thermal and Oxidative Degradation Filippo Mangolini, Brandon Krick, Tevis D.B. Jacobs, Subarna R. Khanal, Frank Streller, J. Brandon McClimon, James Hilbert, Somuri V. Prasad, Thomas Scharf, James Ohlhausen, Jennifer R. Lukes, W. Gregory Sawyer, Robert W Carpick Harsh environments pose materials durability challenges across different sectors. While amorphous carbon materials have been used as coatings in environmentally-demanding applications owing to their unique properties, their limited thermal stability and high reactivity in oxidizing environments have inhibited their use in many technologies. Silicon- and oxygen-containing hydrogenated amorphous carbon (a-C:H:Si:O) films are promising for several applications because of their higher thermal stability and lower residual stress compared to hydrogenated amorphous carbon (a-C:H). However, an understanding of their superior thermo-oxidative stability compared to a-C:H is lacking. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W52.00011: capillarity-enhanced thin-film mineral coating in 3D-printed porous micromodel Hongxia Li, Aikifa Raza, TieJun Zhang In subsurface-related applications such as hydrocarbon recovery, carbon geo-sequestration and water filtration, 3D-printed porous media, usually polymer-based material, are quite different from natural rocks. It is highly desireable to functionalize 3D-printed models in mimicking the surface chemistry of natural rocks. Here, we propose a surface-coating approach by seeding calcite nanoparticles (CalNPs) followed by in-situ growth of calcite crystals along the inner surfaces of as-printed 3D micromodels. Notably, suface coating inside porous media is quite challangeing compared to the flat surfaces due to the capillary effect in the irregular pores/throats. To guarantee the coating uniformity, we tuned the properties of coating solutions for a lower surface tension, lower viscosity and higher volatility. In this way, we promote the formation of an ultra-thin liquid film in confined space of porous media. The stability of the coating layer, specifically the CalNPs, was also investigated using water-flush experiments. The capillary-rise enhanced nanoparticle stability is revealed from atomic force microscope (AFM) analysis. Through this work, we provide guidance on thin-film coating in porous media, where the effect of capillarity is a critical issue and requires careful attention. |
Friday, March 6, 2020 10:12AM - 10:24AM |
W52.00012: Effects of substrate bias on current for varying argon intensity in a low-pressure hydrogen/argon plasma in chemical vapor deposition. Bhavesh Ramkorun, Kallol Chakrabarty, Sumner B Harris, Shane A Catledge Studies have shown that in CVD, low substrate temperature often favors amorphous materials growth over crystalline. In a hydrogen/argon plasma acting on a negatively DC-biased silicon substrate, hydrogen alpha and bias current due to ion bombardment were monitored for temperature <1000oC. The temperature was controlled through microwave power of 0.6kW, and pressure of 10 – 30 torr. The flow rate of argon was varied between 0 sccm and 500 sccm, and hydrogen's was 500 sccm. Optical Emission Spectroscopy (OES) of hydrogen line was found to be influenced by argon flow rate. Current was recorded for several values of the applied bias voltage from 100V to 340V. A decrease in current with decreasing hydrogen emission for glow discharge systems has been reported in the literature. Our results substantiate these results, and further show a peak in current at 10 and 20 torr. OES data was used to estimate the plasma electron temperature to be constant at approximately 0.5 eV. This suggests that the observed peak in current may be due to variation in plasma density as Ar flow changes between 0 sccm and 500 sccm. These results may be used to correlate plasma emission characteristics with substrate bias conditions in order to better predict and control MPCVD grown materials. |
Friday, March 6, 2020 10:24AM - 10:36AM |
W52.00013: Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces using Graphene-enhanced Raman Spectroscopy (GERS)-based Stark-shifts Haotian Shi, Bofan Zhao, Steve Cronin We report spectroscopic measurements of the local electric fields and charge densities at electrode surfaces using graphene-enhanced Raman spectroscopy (GERS) based on the Stark-shifts of surface-bound molecules (CuPc) and the G band frequency shift in graphene. The shifts in vibrational frequencies of the graphene G band and CuPc are obtained simultaneously and correlated. The 1531 cm-1 peak exhibits Stark-shifts and can, thus, be used to report the local electric field strength at the electrode surface under electrochemical working conditions. Computational simulations using density functional theory (DFT) predict similar Stark shifts and provide a detailed atomistic picture of the electric field-induced perturbations to the surface-bound CuPc molecules. |
Friday, March 6, 2020 10:36AM - 10:48AM |
W52.00014: Ferroelectric polarization rotation through He irradiation induced uniaxial strain Andreas Herklotz, Robert Roth, Kathrin Dorr, Niranjan Ramakrishnegowda, Yogesh Sharma, Alessandro Mazza, Thomas Zac Ward The physical properties of ferroic thin films are typically dominated by their domain configurations and their responses to external fields. A central prerequisite to domain engineering and harnessing functionalities of ferroelectric thin films is thus the control of the polarization orientation. Historically, the direction of ferroelectric polarization in thin films has been mainly tailored by heteroepitaxial in-plane strain or a variation of growth conditions inducing defects. |
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