Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A45: Photophysics and Pattern Formation in Thin FilmsFocus
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Sponsoring Units: DCMP Chair: Radwan Elzein, University of South Florida Room: BCEC 211 |
Monday, March 4, 2019 8:00AM - 8:12AM |
A45.00001: Photoresponsive thin film based on photochromic diarylethene blended with thermoplastic elastomer: Structural and morphological analysis Maroua LOUATI, Sophie Barrau, Jean-François Tahon, Stéphane Aloise, Michinori Takeshita An increasing attention has been paid to photo-deformable polymeric materials that can convert light energy into mechanical energy without contact or electrical wires, using photoresponsive molecules. Diarylethenes known for their thermal stability and their fatigue resistance are one of the best studied compounds that exhibit photomechanical response. Upon alternating irradiation with UV and visible light, a change in molecular volume occurs between open- and close-ring during the photochromic reaction which induces photomechanical motions. In order to develop a light-driven polymer actuator, we investigate a novel system based on the mixture of a derivative diarylethene (Ureidopyrimidinone-functionalized diarylethene denoted UPy-DTE) and a thermoplastic elastomer (Ureidopyrimidinone -functionalized poly(ethylene-co-butylene) denoted UPy-PEB). In solution, the UPy-DTE/UPy-PEB system leads to a supramolecular assembly via quadrupole hydrogen bonding. The thin films are elaborated using different techniques such as drop casting or melt molding. Under illumination, a photomechanical response of the film is observed. Our strategy is to establish a correlation between the structural and morphological properties responsible for the macroscopic deformations. |
Monday, March 4, 2019 8:12AM - 8:24AM |
A45.00002: Singlet fission and exciton dynamics in vapor deposited rubrene films Drew Finton, Elizabeth DeJong, Vincent Zoutenbier, Ivan Biaggio In rubrene single crystals, singlet excitons can efficiently transition into two independent triplet excitons through a process called singlet fission. Photoluminescence in single crystals is a result of the singlet exciton’s radiative decay and both geminate and non-geminate triplet pair recombination. This process has been well documented, although a precise description of the intermediate steps is still an active area of research. In more disordered systems, such as amorphous films of rubrene, the singlet fission process is greatly hindered and the likelihood of non-geminate triplet recombination is effectively zero. As a result, photoluminescence measurements show only the radiative decay of the singlet exciton, as no singlet fission can occur. The effect of molecular ordering and the photoluminescence dynamics of amorphous rubrene samples will be addressed. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A45.00003: Defect Engineering for Modulating the Trap States in Two-dimensional Photoconductor Jie Jiang, Chongyi Ling, Tao Xu, Wenhui Wang, Xianghong Niu, Amina Zafar, Zhenzhong Yan, Xiaomu Wang, Yumeng You, Litao Sun, Junpeng Lu, Jinlan Wang, Zhenhua Ni Defect induced trap states are essential in determining the performance of semiconductor photodetectors. The de-trap time of carriers from a deep trap could be prolonged by several orders of magnitude as compared to shallow trap, resulting in additional decay/response time of the device. Here, we demonstrate that the trap states in two-dimensional ReS2 could be efficiently modulated by defect engineering through molecule decoration. The deep traps that greatly prolong the response time could be mostly filled by Protoporphyrin (H2PP) molecules. At the same time, carrier recombination and shallow traps would in-turn play dominant roles in determining the decay time of the device, which can be several orders of magnitude faster than the as-prepared device. Moreover, the specific detectivity of the device is enhanced (as high as ~1.89×1013 Jones) due to the significant reduction of dark current through charge transfer between ReS2 and molecules. Defect engineering of trap states therefore provides a solution to achieve photodetectors with both high responsivity and fast response. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A45.00004: Photothermoelectric detection of gold oxide non-thermal decomposition and related studies Xifan Wang, Charlotte Evans, Mahdiyeh Abbasi, Douglas Natelson Controlling morphology and composition via nanoscale structuring gives opportunities to improve the thermoelectric properties of materials for energy conversion and photodetection. In this study, we report the detection of the decomposition of metastable gold oxide via open circuit photothermoelectric voltage detection on thin-film Au nanowire devices as a function of the position of an optical heat source. A focused laser beam is used to locally heat the metal nanostructure. The first-scan enhanced photovoltage correlates with a reduction of the electrical resistance of the nanostructure back to pre-oxygen-exposure levels. These experiments demonstrate that combined optical and electronic measurements can provide a window on surface-sensitive photochemical processes. Besides the photothermoelectric voltage detection of gold oxide, we also report preliminary data on the thermoelectric properties of Au nanowires via other surface modification methods includes self-assembled monolayer formation. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A45.00005: Formation of gold nanoparticles by laser annealing and enhanced terahertz beam by plasmonics Dong Ho Wu The plasmonic effect increases photocurrents substantially. There are considerable efforts to exploit this phenomenon for various applications, such as a high-efficiency photovoltaic cell, photodetector, etc. In this presentation, we will report gold nanoparticles on a photoconductive antenna and substantial terahertz power enhancement by the plasmonics. A laser annealing process creates the gold nanoparticles, and the plasmonic effect occurs when the gold nanoparticles interact with the femtosecond laser beam. The photoconductive antenna contains a pair of Schottky electrodes, which are fabricated by depositing shallow titanium-gold layers on a semi-insulating GaAs substrate. After the fabrication, the photoconductive antenna is exposed to a rather intense femtosecond laser beam exceeding 130 mW while applying a 70 V AC bias voltage to the electrodes. This laser annealing process generates about 1 mW of terahertz beam, which is nearly stable until the annealing time past 60 minutes when terahertz power abruptly jumps more than 20 -30%. This sudden power enhancement is coincident with the formation of gold nanoparticles and dendrites in a tiny area around the electrodes. We found that the plasmonic effect enhances the photocurrents of more than one order of magnitude. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A45.00006: The Influence of Fractional Surface Coverage on Core-Core Separation in Monolayers of Thiol-Ligated Gold Nanoparticles Morgan Reik, Stuart A Rice, Binhua Lin, Melanie S Calabro, Sean Griesemer, Sophie Macfarland The way in which thiol-ligated gold nanoparticles self-assemble into ordered monolayers when deposited on a surface is contingent on the thiol's length and concentration. The influence of ligand composition on the properties of nanoparticle films is well-reported. However, the understanding of the molecular and structural origins of these properties is incomplete, particularly when examining the number of ligands on a nanoparticle surface. It has been assumed that the concentration of ligands in solution, within typical ranges, always generates the maximum possible nanoparticle surface packing. We demonstrate through Grazing Incidence X-Ray Diffraction and Transmission Electron Microscopy that the nanoparticle separation and correlation length of these films increases linearly with thiol concentration in solution, indicating that the bulk thiol is in equilibrium with thiol on the core surface. Our findings thus challenge the assumption that the free energy of binding of an alkanethiol to a gold nanoparticle is so large that its surface is consistently saturated with ligands. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A45.00007: Laser-induced Detuning of Quartz Crystal Microbalances in Adsorbing and Non-adsorbing Environments Samuel Kenny, Jacqueline Krim Light induced modifications in frictional behavior of films of adsorbed molecules constitute an area of current interest in nanotribology, and are potentially observable at room temperature by means of a quartz crystal microbalance (QCM). In order for such studies to be viable, the impact of laser light on a QCM must be established. We report here an investigation of the response of a QCM to green laser light in vacuum, nitrogen, and ethanol gas. Measurements of frequency and amplitude responses of the QCMs were performed, for samples with electrodes composed of AuNi alloys with varying degrees of Ni content. For the adsorbing ethanol films, we observed that the frequency response upon green laser irradiation initially strongly decreased with pressure, but recovered slowly up to the vapor pressure. This effect was more pronounced in electrodes with higher Ni content. QCMs exposed to non-adsorbing nitrogen produced responses of similar magnitude regardless of Ni content, however, we noticed marked changes in the initial response behavior upon illumination. The effects can be explained within the context of the effects of mass uptake, desorption and laser heating [1]. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A45.00008: Interferometric Measurements of High Quality Acoustic Microcavities (MCs) on Anisotropic Surfaces Madeleine Msall, Paulo Santos Applications that couple high frequency surface acoustic waves (SAW) to quasi 0-D systems require high-Q acoustic MCs. We use optical interferometry to measure the surface displacement patterns between pairs of interdigital transducers (IDTs) configured to form resonant MCs with Q ~ 1800. Our focusing Al/Ti IDT with 0.6 rad (34○) aperture and wavelength Λ=5.6 μm emits a SAW beam along the [110] direction on GaAs with focusing comparable to the predicted 1.2Λ beam waist and 8Λ Rayleigh length. Reflections from the anisotropy corrected outer edges of the IDT fingers play an important role in performance. Previous assumptions of parabolic dispersion overcorrect for anisotropy and move the device focus closer to the IDT. Our resonant MC is created by placing additional floating fingers to form a 2.5Λ cavity around the focus. Since the inner cavity fingers are in the near field of the beam focus, their positions must also be adjusted to account for the Gouy phase shift. The resulting IDT + MC system shows highly localized elastic strain at frequencies within the electrical resonance band of the driving IDT. These 514 MHz, 5.6 µm devices should scale well to the submicron wavelength and GHz frequency domain appropriate to quantum dot applications. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A45.00009: Resonant Scattering as a Rapid and Site-Specific Spatiochemical Probe of Patterned Interfaces Isvar Cordova, Guillaume Freychet, Christopher Chi, Wei Xu, Alexander Hexemer, Cheng Wang The advent of highly precise nanofaborication tools has enabled the development of a new generation of mesoscale materials with potential across a variety of applications, but concomitant progress in the characterization techniques is also required. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A45.00010: Effect of titanium adhesion layer on iridium thin film optical properties Nicole Pfiester, Margaret Stevens, Thomas Vandervelde, Kevin Grossklaus The refractory metal iridium is useful for highly reflective mirrors for x-ray astronomy and high temperature plasmonic applications like selective emitters. However, the deposition conditions of the thin film can produce very different optical properties which will affect the final performance of the optical device. In this study, we report on the optical properties, crystal structures, and surface roughness of Ir thin films produced by dc magnetron sputtering. The chamber pressure was varied from 10 mTorr to 25 mTorr with a constant plasma power of 160 W. Films deposited on a titanium adhesion layer or directly on a silicon substrate will be compared. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A45.00011: Pattern formation on a bubble: Capillary waves on surfactant-laden interfaces Li Shen, Fabian Denner, Neal Morgan, Daniele Dini On a surface-tension-driven liquid interface, the behaviour of the capillary wave is often a bellweather of the overall motion of the system. Consequently, understanding how capillary waves behave is crucial in various interfacial flows at the edge of instability, such as capillary-driven breakup, liquid bridges and pattern formation phenomena. Examining the dynamics of the capillary waves on a surfactant-laden interface, the role of critical wavenumber (at which the capillary wave transitions from the dispersive underdamped regime to the non-dispersive overdamped regime) is explored in the context of the onset behaviour of pattern formation instabilities observed experimentally. Moreover, we look at the effect of the convective-diffusive transport of insoluble surfactants along the interface on the critical wavenumber and the overall dynamics of the capillary waves. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A45.00012: Active control of thin liquid film flows: beyond reduced-order models Radu Cimpeanu, Susana N Gomes A thin liquid film flowing down an inclined plane is a canonical setup in fluid mechanics and pertains to a wide range of industrial applications. In some cases it is desirable to maintain the liquid-gas interface flat (e.g. coating problems), whereas other contexts (e.g. heat transfer) benefit from increased interfacial area. Ultimately, there is a strong need to reliably manipulate the flow in this mathematically rich system. Control theory has recently been applied successfully by A.B. Thompson et al. (Physics of Fluids 28, 012107, 2016) for an extended range of long-wave models such as the Benney and weighted residual equations, forming a hierarchy of complexity in which the effect of the control is well understood. The subject of this talk relates to the transition from controls on reduced dimensional systems to full Navier-Stokes solutions of this setup. A state-of-the-art volume-of-fluid methodology is used for the direct numerical simulation of the target flow, with control techniques informed by the modelling framework. We study both distributed and localised controls and analyse the robustness of these strategies, bringing us closer to their integration into real-life engineering designs. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A45.00013: How to control the morphology of a multiple-liquid system via direct mixing? Tao Li Arrested composites can be created via the stabilization of convoluted fluid-fluid interfaces, which applies to multiple immiscible liquid systems containing dispersed colloidal particles. Such systems can form various morphologies, including the conventional Pickering emulsions, multiple emulsions, Janus droplets and non-spherical droplets. Moreover, the jamming of interfacial particles provides a promising route to create even more elaborate arrested states. For instance, the bijels (bicontinuous interfacially jammed emulsion gels)! All these structures exhibit novel properties and can lead to numerous applications in drug delivery, food, energy conversion and functional materials. Part I of this talk will focus on the viscosity effect on the formed structures in a binary liquid system, which reveals the formation mechanism of bijels created by direct mixing, and fills an important gap between the phase behaviors in low molecular weight liquids and that in bulk polymers. When mixing three immiscible liquids, the morphology development becomes more complex. In Part II, I will introduce both the formation mechanism and the stability mechanism of Janus emulsions, which can be a combined effect of multiphase immiscibility, interfacial tensions and surface stabilization. |
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