Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R64: Optics and Photonics in Polymers and Soft Matter I: Imaging, Characterization and PatterningFocus Live
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Sponsoring Units: DPOLY DSOFT DBIO DAMOP Chair: Chaitanya Ullal, Renesselaer Polytechnic Inst.; Danielle Mai, Stanford Univ |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R64.00001: Phase-shift and Amplitude Analysis Reveal Stages of Nanoparticle-Assisted Photothermal Annealing of Polydimethylsiloxane Maryam Zahedian, Bogdan Dragnea In nanoparticle-assisted photothermal microscopy, absorption of radiation by a nanoparticle is followed by non-radiative relaxation which in turn leads to changes in the surrounding medium temperature, pressure, and density. Under harmonically modulated irradiation, the finite heat diffusion rate causes a phase delay between the thermal oscillation at a location in the medium relative to that at the nanoparticle surface. The phase delay averaged over the probe laser volume can be measured concomitantly with the amplitude of detected probe power modulation. In this study, we show that, in conjunction with the more widespread modulation amplitude measurement, the photothermal phase provides a complementary, sensitive probe of thermally-induced changes in the local medium properties. Moreover, with the help of simulations it is possible to extract from phase/amplitude data the temperature-dependent properties of the medium as shown on a widely used, technologically important polymer resist -- polydimethylsiloxane (PDMS). |
Thursday, March 18, 2021 8:12AM - 8:24AM Live |
R64.00002: Improved characterization of colloidal spheres by modeling effects of spherical aberration in digital holography microscopy Caroline Martin, Brian D Leahy, Vinothan N Manoharan With digital holographic microscopy (DHM), individual colloidal particles can be characterized and tracked in three dimensions and at high frame rates. Recent advances in forward modeling and inference now allow the size, shape, and position of individual particles to be determined much more precisely than in previous approaches based on reconstruction of the hologram. However, current forward models of hologram formation ignore the effects of aberrations in the optical train. We show that spherical aberration at typical levels leads to systematic errors in the inferred parameters that depend on the level of aberration. We develop a model for spherical aberration and fit it to experimental data. We show that this approach reduces the systematic error due to aberration and allows us to recover parameters that are consistent at differing levels of aberration. |
Thursday, March 18, 2021 8:24AM - 8:36AM Live |
R64.00003: Understanding confinement effects on polymer chain conformation using Förster resonance energy transfer Alexander Fortenberry, Zhe Qiang Advancements in nanotechnology demand film thickness to keep shrinking to the size of a molecule, which results in changes in material properties relative to their bulk state. While extensive studies have been pursued to investigate nanoconfinement effects on polymer glassy behaviors, fundamental relations between polymer chain structures and macroscopic film properties still lack a full understanding. This study aims to determine confinement effects on polymer chain conformation using Förster resonance energy transfer (FRET). This technique can detect the distance between a donor and acceptor fluorophore in close proximity at a nanometer length scale by the energy transfer efficiency between the two species. By labeling donor and acceptor fluorophores on polymer chain ends, FRET enables measurement of the averaged polymer chain end-to-end distances at high spatial (nm) and temporal resolutions (~s). We will discuss how to use this technique for investigating chain dimensions as a function of film thickness for polymers of various molecular weights. Furthermore, the conformation of polymer chains under strong confinement will be correlated with their mechanical property deviation compared to the bulk state. |
Thursday, March 18, 2021 8:36AM - 8:48AM Live |
R64.00004: Deactivation wavelength effect on super-resolution in 3 color lithography thin films Sandra A Gutierrez Razo, Nikolaos Liaros, Andrea N Zeppuhar, John S Petersen, John Fourkas The 3 color lithography (3CL) technique has the potential to rival current and emerging lithographic methods by using overlapped beams of visible wavelengths to attain high-resolution features. 3CL uses one beam to excite photoinitiator molecules to a chemically inactive state and a donut-shaped beam to deactivate molecules. The molecules in the dark center of the deactivation beam remain in the chemically inactive excited state. A third beam further excites the molecules that are not deactivated to a different excited state that initiates polymerization. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R64.00005: Super-resolution Interference Lithography using Photochromic Photoresists: Towards bulk volume nanopatterning Hari Vijayamohanan, Adela Habib, Ravishankar Sundararaman, Edmund Palermo, Chaitanya Ullal Inspired from Stimulated Emission Depletion microscopy, two-color photolithography utilizes optically switchable excitation and inhibition pathways for nanopatterning with feature-sizes below the diffraction limit. However, the vast majority of such systems developed thus far, are limited to point-by-point serial writing. Here, we utilize the non-equilibrium kinetics of photochromic spirothiopyran monolayers to develop a super-resolution interference lithography scheme and demonstrate large area nanopatterning with feature sizes below 100 nm using a 2 W 532 nm laser. Extending this technique to the third dimension for nanopatterning in thick photoresists requires overcoming significant challenges due to the multiple process parameters that need to be optimized. In order to facilitate this, we develop an efficient electromagnetic (EM) perturbation theory approach that facilitates fully coupled simulations of EM and chemical kinetics to quantitatively analyze the influence of time dependent optical dynamics such as absorption, diffraction, and intensity modulation on the resist chemical kinetics. This ability to compute the coupled optical and chemical dynamics of such systems allows for the design of optimized exposure strategies for parallel nanopatterning in thick resists. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R64.00006: Designable Non-linear Optics of Light-Responsive, Spiroypyran-Functionalized Hydrogels Amos Meeks, Rebecca Mac, Simran Chathanat, Joanna Aizenberg We demonstrate the potential of spiropyran-functionalized, light-responsive hydrogels to be a promising new platform for nonlinear optical materials. Nonlinear optical behavior in these materials arises from the local swelling/deswelling and resulting refractive index changes that occur due to photoisomerization between the hydrophilic ring-open merocyanine isomer and the hydrophobic ring-closed spiropyran isomer. These materials show an unprecedented combination of reversibility, soft easily processed material, low laser powers, and long-range interactions. These long-range interactions are especially promising for potential applications in all-optical computing or sensing. We show that the long-range interactions can be explained by thermal swelling or deswelling of the gel. Furthermore, the direction and magnitude of a hydrogel’s thermal response can be controlled by changing the gel composition, which allows the behavior of single and multiple beams in these gel materials to be rationally designed over a potentially vast design space. This tunable diversity of behaviors suggests the enormous potential for photoresponsive hydrogels as extremely versatile, rationally designable, soft, nonlinear optical materials. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R64.00007: Excitonic Wave Function Reconstruction from Near-Field Spectra Using Machine Learning Techniques Fulu Zheng, Sidhartha Nayak, Xing Gao, Alexander Eisfeld A general problem in quantum mechanics is the reconstruction of eigenstate wave functions from measured data. In the case of molecular aggregates, information about excitonic eigenstates is vitally important to understand their optical and transport properties. Strong interactions between the transition dipoles of the molecules lead to delocalized excitonic eigenstates where an electronic excitation is coherently shared by many molecules [1]. Here we show that from spatially resolved near field spectra it is possible to reconstruct the underlying delocalized aggregate eigenfunctions [2, 3]. Although this high-dimensional nonlinear problem defies standard numerical or analytical approaches, we have found that it can be solved using a convolutional neural network. For both one-dimensional and two-dimensional aggregates the reconstruction is robust to various types of disorder and noise. The methodology can be easily applied to more complicated cases, promoting information extraction from experimental data in a wide variaty of applications. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R64.00008: Prediction of Effective Optical Properties of Composites via Nonlocal Strong-Contrast Expansions Salvatore Torquato, Jaeuk Kim The preponderance of previous treatments to predict the effective dielectric constant of composites apply to the quasistatic (long-wavelength) regime. Here we derive exact expressions for the nonlocal effective dielectric constants of two-phase composites at intermediate wavelengths by using the "strong-contrast" expansion formalism. From this formalism, we derive a family of series expansions that explicitly incorporate complete microstructural information of the composite via n-point correlation functions and hence accounts for multiple scattering to all orders well beyond the quasistatic regime. The fast convergence of this series enables us to extract an accurate approximation that depends on the two-point correlation function or its Fourier counterpart, called the "spectral density." Our formula thus extends previous quasistatic treatments that typically do not account for nontrivial microstructural information and/or are limited to small phase contrasts. We apply our formula to a variety of disordered models and discuss how to engineer composites with prescribed attenuation properties for electromagnetic waves. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R64.00009: Understanding the Working Mechanism of Vertical Organic Light Emitting Transistors DRONA DAHAL, Raj Kishen Radha Krishnan, Pushpa Paudel, Vikash Kaphle, Bjorn Lussem Vertical Organic Light Emitting Transistors (VOLETs) are a new technology that integrates vertical organic thin film transistors with the organic light emitting diodes into a single device [1]. Their vertical structure and ability to be processed on flexible substrates will create a new horizon for current display technology [2]. Despite their excellent prospects, there are a lot of unexplored areas of VOLETs, both in theory and experiment. Here, we study the operation of VOLETs experimentally and theoretically. In particular, we show that the injection barrier at the source electrode determines the ON/OFF ratio of the transistors and that a significant barrier is needed to reduce the off-currents of these devices. By a comparison of vertical transistors with different semiconductor materials and different injection barriers, we show that a compromise has to be found between large on-currents, requiring a low contact resistance, and large switching ratios. |
Thursday, March 18, 2021 9:48AM - 10:24AM Live |
R64.00010: Visualizing and controlling polymer nanostructures through in situ optical imaging and synthesis Invited Speaker: Muzhou Wang Over the past decade, super-resolution optical microscopy has been an enabling advance in nanoscale characterization, initially for biological problems but now increasingly in the polymer community. Our group is exploring these techniques in a variety of systems including polymer blends, brush polymers, polyelectrolytes, elastomers, and block copolymers. In this talk, we will present several of these studies. As an example, we have been able to measure the persistence length of bottlebrush polymers in the melt for the first time, through fluorescent labeling of single isolated chains mixed with an unlabeled matrix. We have also detected mechanical deformation at the nanoscale by examining local distributions of fluorophore orientation, visualizing regions as small as 15 nm. Finally, we demonstrate time-lapse imaging in solvent-swollen polymer blends, where coarsening behavior and self-assembly is readily observed. |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R64.00011: Super Resolution mediated direct visualization of spatial heterogeneities in bulk PNIPAM hydrogels Gopal Sankar Kenath, Apostolos Karanastasis, Alexander Yepikhin, Chaitanya Ullal Spatial heterogeneities have deleterious effects on the mechanical and transport properties of bulk gels. In the past, insights into the structure of heterogeneities have often been achieved in thermoresponsive gel networks due to their inherently larger length scales within these systems. Here, we report on a super resolution mediated structural study of spatial heterogeneities within bulk PNIPAM hydrogels. Our study reveals new structural insights that diverge from established models for variations in crosslink distributions within heterogeneous thermosresponsive gel systems. These results are expected to provide a more general framework for the description of spatial heterogeneities within such systems. |
Thursday, March 18, 2021 10:36AM - 10:48AM Live |
R64.00012: Resin design for deterministic control of volumetric 3d printing Changda Liu, Charles Michael Rackson, Robert McLeod Volumetric 3D Printing is a type of additive manufacturing in which 2D patterns of light are projected into a rotating volume of photosensitive polymer resin, locally crosslinking the material, resulting in a desired gelled 3D part. Polymerization is typically inhibited below a critical dose in radically-initiated resins due to the presence of dissolved atmospheric oxygen which is consumed prior to significant polymerization. This inhibition threshold is exploited to control which regions solidify in photopolymer 3D printing methods including stereolithography. However, oxygen levels cannot typically be modified, providing limited control over the inhibitory dose. We introduce a resin design scheme that provides deterministic control over the inhibition threshold dose in such resins. Since high resin viscosity is often desirable to limit transport, we show that the existence of a sharp inhibitory threshold sets an upper limit on viscosity through the Smolokowski diffusion limit. |
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