Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B33: Advanced Materials for Applications: Fabrication, Lithography and InstrumentationFocus
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Sponsoring Units: FIAP Chair: Ronald Warzoha Room: BCEC 204B |
Monday, March 4, 2019 11:15AM - 11:27AM |
B33.00001: Thermal Transport Analysis of Strained Polymer Films Andrew Borgdorff, Edward Gorzkowski, Ronald Warzoha, Brian Donovan Strained polymer films are commonly used as dielectric materials in high energy density capacitors, and processed such that they have significant anisotropy in a variety of materials parameters. In order to interrogate the influence of this anisotropy in thermal transport characteristics, we use the Transient Electro Thermal Technique (TET). TET enables characterization of novel materials with micrometer dimensions, without necessitating bulk production, reducing the time and cost of materials research. Using TET, we are able to obtain resolution of anisotropy in strained polymer films simply by modifying the orientation of the measurement. We compare the results of this thermal diffusivity obtained via TET analysis to the expected enhancement in thermal diffusivity results, from molecular dynamics modeling, of mechanically strained polymers. These findings demonstrate the utility of this for use in novel, laboratory-scale, polymer-based dielectric film fabrication. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B33.00002: Origin of long-lived photostriction in molecular ferroelectrics Xuanyuan Jiang, Xiao Wang, Andy Clark, Shashi Poddar, Le Yu, Anthony DiChiara, Xuemei Cheng, Xiaoshan Xu Croconic Acid (CA) exhibits ferroelectricity due to proton displacement between molecules. Utilizing Time resolved x-ray spectroscopy under UV irradiation, we were able to observe lattice dilation effect with time scale over few seconds indicative of a long-lived metastable structure. The origin of the lattice dilation cannot be attributed to thermal effects due to its anisotropic characteristics. To elucidate the photon-induced electron structure change, current measurements were performed under different irradiation wavelengths of which only UV light exposure gives second-long excitation and relaxation time. Since the energy of the UV radiation is comparable to the bandgap in CA, the origin of photostriction could be solely attributed to the localized proton transfer between adjacent CA molecules. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B33.00003: Theory and simulation of charge injection at metal-polymer interfaces YIYUAN WANG, Arash A Mostofi, Mikael Unge High voltage direct current (HVDC) technology is widely used in long-distance power transmission from remote energy sources. Insulators used in HVDC components such as capacitors and transformers undergo electrical degradation, which can result from charge injection at the metal-polymer interface. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B33.00004: Unravelling The Behaviour in a TCNQ Based Molecular Solid Adam Berlie, Ian Terry, Marek Szablewski Molecular solids present many advantages over their inorganic counterparts, however their more work is needed to bring our understanding up to that of other types of materials. One interesting problem is using organic based compounds to create functional materials, pairing the existence of magnetism and electrical behaviour. Within this talk, I will focus on triethylammonium 7,7,8,8-tetracyanoquinodimethane (TEA(TCNQ)2), a quasi-1D system where an electron is shared between two TCNQ molecules creating a delocalised radical anion. Dielectric measurements have shown anomalies at two temperatures and these match with both a structural and magnetic phase transition. Our recent study has shown that the system enters a 3D Ising ground state and not simply undergoing a spin-transition as was previously thought. This is helping to further our knowledge of the system and highlight it's potential as a functional material. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B33.00005: Ultrafast photoexcited carrier dynamics in violanthrone-79 thin films Kateryna Kushnir, Taylor Trottier, Patrick Devin Fitzgerald, Andrew Mendizabal, Christopher R Lambert, Lyubov Titova Violanthrone-79 (VO-79) is a promising organic semiconductor, molecules of which consist of large aromatic cores and aliphatic side chains. Strong π - π interactions promote stacking of individual molecules and forming nanoaggregates in solutions when dissolved in polar solvents like toluene and chloroform. Introduction of small amount of poor solvents such as hexane enhances aggregation and results in highly crystalline morphology. We have studied optical and electronic properties of VO-79 thin films prepared from VO-79/chloroform solution at a concentration above the aggregation threshold, as well as those prepared from VO-79 solutions in chloroform/hexane mix. Using optical pump – THz probe spectroscopy, we have demonstrated that delocalization of π electrons in the film results in band-like carriers that remain free within individual aggregates for tens of picoseconds after photoexcitation. We correlate carrier dynamics in films containing VO-79 nanoaggregates with their morphology and optical properties as revealed by the photoluminescence spectroscopy. Observation of long-lived free, mobile photocarriers suggests possible applications of VO-79 in organic optoelectronic and solar energy conversion devices. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B33.00006: Ferroelectric switching kinetics of large area Croconic acid thin films Shashi Poddar, Xuanyuan Jiang, Yifan Yuan, Xiaoshan Xu In the present work, large area ferroelectric thin films of Croconic acid with thickness ranging from 10-50 nm has been fabricated by physical vapor deposition on ITO substrates at – 30 C. The films on being annealed up to room temperature show excellent wetting forming polycrystalline films. The AFM morphology exhibits stable grains with lateral dimensions of 50-200 nm often exhibiting a monodomain polar states which can be reversibly switched as evidenced by piezoresponse force microscopy. Since the switching mechanism here solely relies on the proton tautomerism localized in the -OH- hydrogen bonds, studying local switching kinetics of the individual polar grains may unveil a novel mechanism of domain nucleation and switching in these molecular ferroelectric systems. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B33.00007: Metal-semicoductor contact effects and temperature-dependence of carrier transport in large-grain organic semiconductor thin film transistors Jing Wan, Yang Li, Jonatan Hollin, Adam Whalley, Randall Headrick The pen-writer solution deposition method is used to deposit 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor thin films and also polymer dielectric layers. Organic transistors with source/drain contact layers either below or on top of the semiconductor layer and with or without surface treatment are investigated. Contact resistance produces a pronounced non-linearity in the output characteristics at low drain voltage, which is found to be consistent with a Schottky Barrier model. By treating the Au electrode with pentafluorobenzenethiol (PFBT) in a bottom contact geometry, the contact resistance is greatly reduced. An optimized geometry is obtained by using pen-written CytopTM dielectric in a top-gate/bottom-contact structure, which exhibits a near-intrinsic average mobility, up to 9.0 cm2/V-s for C8-BTBT thin films deposited at high writing speed (25mm/s) and deposition on a heated substrate (60°C). We will report temperature-dependent carrier transport results for individual devices with both a top gate (with cytop dielectric) and bottom gate (with silicon dioxide dielectric) to compare results at both interfaces of the same C8-BTBT thin film. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B33.00008: Entropic elasticity and negative thermal expansion in ScF3 Igor Zaliznyak, David Wendt, Emil Bozin, Katharine L. Page, Joerg Neuefeind, Brent T Fultz, Alexey Tkachenko Negative thermal expansion (NTE) is common in polymers and biomolecules, where its origin can be traced to entropic elasticity, but is rare in solids where it is desirable for applications. We report pair distribution function (PDF) analysis of neutron total scattering tracking the local structure and relative atomic positions in ScF3 as it shrinks with increasing temperature. In agreement with previous Xray studies1,2, we find that Sc-F bond slightly expands on warming, while the lattice spacing decreases. The correlation in positions of the neighbor F atoms rapidly fades on warming, consistent with simple model of F transverse thermal motion constrained only by the rigid Sc-F bond. This indicates that entropic stiffness rendered by strong Sc-F bond is at the origin of NTE in ScF3. We thus observe universality of the NTE phenomenon across hard and soft matter, which opens new avenues for predictive modelling of this effect in solids. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B33.00009: Atomic Calligraphy: A MEMS Based Nanomanufacturing Technique Lawrence Barrett, Richard Lally, Thomas Stark, Jeremy Reeves, David John Bishop Atomic Calligraphy is a nanomanufacturing technique with the potential to combine resolutions below 10 nm with high throughputs. It works by combining two technologies, stencil lithography which is essentially shadow masking a flux atoms and microelectromechanical systems (MEMS). Stencil lithography is useable over large areas, inexpensive to implement, useable with fragile materials and on fragile surfaces. However, it has several challenges including: clogging of the stencil, limited resolution due to the dimensions of the evaporation source and the distance to the target, and imprecise alignment between stencil and target. Here, we present on overcoming these challenges using a variety of MEMS technologies including joule heating, precision springs, capacitive sensing and capacitive actuation. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B33.00010: Focused Electrohydrodynamic Printing Technology by Incorporating an Einzel Lens Matthew Strohmayer, Atul Dhall, Pujhitha Ramesh, Natalya Tokranova, James Castracane, Carl Ventrice Additive manufacturing (AM) shows great promise for both research and industrial applications. The main advantages of AM include limited waste and the ability to build complicated structures. The most common techniques for AM are fused deposition manufacturing, digital light printing, and ink jetting. All of these techniques suffer from resolution and material limitations. Recently, a cost-effective, versatile method of high-resolution printing called electrohydrodynamic (EHD) printing has been introduced. This method allows for spatial resolution in the hundreds of nanometers. This method works similarly to a typical ink jetting system, except instead of the ink/polymer being pushed out of a tip, it is pulled out by an applied electric field. This allows for the resultant droplet to be smaller than the needle diameter. Coulomb’s law limits the ultimate resolution of this technique. To overcome this resolution limitation, we have incorporated an Einzel lens into the system to focus the droplets. This helps the droplets overcome the repulsive force from Coulomb’s law and leads to better spatial resolution. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B33.00011: Superalloy Radiative Heat Transfer in Additive Manufacturing Erin Curry, Rainer Hebert, Pamir Alpay, Sanjubala Sahoo, Jason Hancock Direct Laser Metal Sintering (DLMS) is a layer-by layer additive manufacturing process using a high power focused source such a laser or electron beam. As the metal powder melts, the melt pool experiences non-equilibrium thermalization processes involving convection, evaporation, plasma creation and radiative cooling, expected to be most important at high temperature. Developing a fundamental understanding of the melt pool cooling rate through the radiative cooling is invaluable to controlling microstructure of the final product. In DLMS a high energy melting source is focused to a small spot size on the build plate and travels across the powder layer at a high velocity, all of which parameters make in-situ measurements of melt pool temperature from radiative cooling difficult. We discuss approaches to spatially resolved temperature analysis of the DLMS melt pool as well as a combined experimental and theoretical optical property investigation of superalloys typically used in DLMS. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B33.00012: Cathodoluminescence-based nanoscopic thermometry in a lanthanide-doped phosphor Clarice D Aiello, Andrea D Pickel, Edward Barnard, Rebecca Wai, Christian Monachon, Edward Wong, Shaul Aloni, Frank Ogletree, Chris Dames, Naomi Ginsberg Crucial to analyze phenomena as varied as plasmonic hot spots and the spread of cancer in living tissue, nanoscale thermometry is challenging: probes are usually larger than the sample under study, and contact techniques may alter the sample temperature itself. Many photostable nanomaterials whose luminescence is temperature-dependent, such as lanthanide-doped phosphors, have been shown to be good non-contact thermometric sensors when optically excited. Using such nanomaterials, in this work we accomplished the key milestone of enabling far-field thermometry with a spatial resolution that is not diffraction-limited at readout. We explore thermal effects on the cathodoluminescence of lanthanide-doped NaYF4 nanoparticles. Whereas cathodoluminescence from such lanthanide-doped nanomaterials has been previously observed, here we use quantitative features of such emission for the first time towards an application beyond localization. We demonstrate a thermometry scheme that is based on cathodoluminescence lifetime changes as a function of temperature that achieves ∼ 30 mK sensitivity in sub-μm nanoparticle patches. The scheme is robust against spurious effects related to electron beam radiation damage and optical alignment fluctuations. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B33.00013: Modeling Performance of Ultra-Sensitive In-Orbit Infrared Telescopes William Atkinson This paper evaluates considerations in minimizing disruptions of scientific data in ultra-sensitive Infrared (IR) spaced-based telescopes by charged particles in space radiation. The particles modeled are protons, alphas, and heaver ions with an atomic number as high as that of iron. Performance results of proposed designs are based on a model developed at Boeing. The components modeled are the spectra of the ion species in cosmic rays and solar flares, the transport of the primary ions and secondary particles produced including neutrons, the generation electron hole pairs (EHPs) by the particles penetrating the focal point array (FPA), and a component modeling transfer of EHPs from generation to recombination. Results indicate noise levels above 100 EHPs by secondary particles alone per pixel in in intense space weather events; these observations agree with empirical data sources. Space based IR astronomical observatories now have a noise level of 100 electrons/pixel indicating the need of detailed radiation transport models; in near future designs where the pixel pitch reduces from 25 to 5 microns, the radiation model component becomes even more significant. Measures reducing the number of electrons per pixel below the threshold are discussed. . |
Monday, March 4, 2019 1:51PM - 2:03PM |
B33.00014: Revisiting the Non-linear transport behaviors in conducting polymer Jiawei Wang, Ling Li, Ming Liu The non-linear transport in conducting polymers usually refers to the non-ohmic current-voltage (IV) relationship at low temperature, and are widely reported in both molecular doped and field effect doped polymers, power-law dependence of conductance on temperature, at low voltage (eV<<kBT) and current on voltage, at high voltage (eV>>kBT) are universally observed in the non-linear regime. |
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