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 E02: Developments in Reflectivity for Thin Film CharacterizationFocus Live
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Sponsoring Units: DPOLY DBIO DSOFT Chair: Daniel Sunday, National Institute of Standards and Technology |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E02.00001: Solvent vapor annealing of diblock copolymer thin films with a solvent mixture Invited Speaker: Christine Papadakis Solvent vapor annealing (SVA) is an attractive method to control the morphology of block copolymer thin films. Using mixtures of vapors from solvents having different selectivities for the blocks enhances the possibilities greatly. We used a setup with two bubblers to investigate thin films from a cylinder-forming polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer in mixtures of the vapors of toluene, which is nearly non-selective for the PS matrix and the PDMS cylinders, and n-heptane, which is selective for PDMS [1]. We varied the vapor composition in a stepwise manner and monitored the overall film thickness in-situ using spectral reflectance. The film morphologies were determined using in-situ real-time grazing-incidence small-angle X-ray scattering (GISAXS). In dependence on the mixing ratio of the two solvent vapors, randomly or hexagonally ordered cylinders and lamellae were observed. This novel type of experiments allows probing trajectories in the state diagram of the PS-b-PDMS/n-heptane/toluene mixture, which are drawn in dependence on the polymer volume fraction ΦP and the effective volume fraction of the swollen PDMS nanodomains, feff. These are determined from the overall degree of swelling and from the intensity of a Bragg reflection in the 2D GISAXS maps. Comparing the trajectories from several protocols of swelling and vapor exchange [2], we find that, apart from the solvent vapor composition, the mobility of the PS blocks forming the matrix is a key factor for the time scales of re-structuring and for the sequence of morphologies. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E02.00002: Introducing the CANDOR polychromatic reflectometer David Hoogerheide, Alexander Grutter, Brian Maranville, Charles Majkrzak The new CANDOR neutron reflectometer at the NIST Center for Neutron Research marries the advantages of time-of-flight polychromatic reflectometers, such as those commonly employed at pulsed neutron sources, to the high time-averaged flux of a reactor neutron source. CANDOR’s unique energy dispersive detector, currently comprising 108 individual wavelength-sensitive neutron detectors operating at over 90% efficiency, allows simultaneous detection of cold neutrons in the 4 Å to 6 Å wavelength range. In this talk, I will describe the instrument features of CANDOR and compare its performance to that of conventional reflectometers. In particular, CANDOR’s 20-fold speed increase over NIST’s monochromatic reflectometers enables faster measurement, smaller sample sizes, and improved sensitivity to small effects. These features will be demonstrated in combination with CANDOR’s full neutron polarization capabilities for magnetic thin film samples. For solid/liquid interfaces, CANDOR’s measurement speed increase and intrinsic background rejection allows routine measurement to at least twice the scattering vector, and hence resolution, of conventional measurements. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E02.00003: Characterization of anisotropic organic layered films by resonant soft x-ray reflectivity Luca Pasquali, Raffaella Capelli, Matteo Bonfatti, Francesco Mezzadri, Emanuele Galligani, Adriano Verna, Alessandro Ruocco, Nicola Mahne, Stefano Nannarone Reflectivity is typically carried out in the hard X-rays, where electron density contrast is exploited. In the soft X-rays, reflectivity at resonance provides additional advantages in terms of atomic and depth-resolved investigation of the chemical, structural and magnetic properties. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E02.00004: Probing Buried Interfaces in Polymers with Soft X-ray Reflectivity Daniel Sunday, Jacob L Thelen, Chun Zhou, Jiaxing Ren, R. Joseph Kline, Paul F Nealey Studies on lamellar forming block copolymers (BCPs) organized parallel to a substrate are important for understanding assembly in confined conditions and the impact of surface effects. These have typically been conducted using either hard X-rays or neutron reflectivity where the contrast mechanism makes it difficult to distinguish depth dependent structural variations. Using soft X-rays the optical constants of a material can be controlled by varying the energy near an atomic absorption edge. As you approach the edge, the real and imaginary components can change dramatically as a function of functional group type, concentration and orientation. Additionally, unlike hard X-rays or neutrons, the absorption is no longer negligible and shifting energies can significantly change the depth profile of the electromagnetic field, providing additional control over sensitivity as a function of film depth. This technique is applied to two systems of BCP multilayers with different affinities for a surface. Strong interactions with the substrate lead to interface broadening due to the distribution of adsorbed positions along the chain. Near the free surface the interface width is reduced due to the suppression of capillary wave fluctuations. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E02.00005: Development of spin-contrast-variation neutron reflectometry for structural analysis of multilayer films Takayuki Kumada, Kazuhiro Akutsu, Daisuke Miura, Jun-ichi Suzuki, Naoya Torikai The spin-contrast-variation neutron reflectometry technique was developed for the structural analysis of multilayer films. Polarized-neutron reflectivity curves of film samples vary according to their proton polarization (PH). The PH-dependent reflectivity curves of a polystyrene monolayer film were precisely reproduced using a common set of structural parameters and the PH-dependent neutron scattering length density of polystyrene, ensuring that these curves are not deformed by inhomogeneous PH but can be used for structural analysis. Unpolarized reflectivity curves of poly(styrene-block-isoprene) films were reproduced a lot of models. The global fit of the PH-dependent multiple reflectivity curves severely restrict the models. In this manner, the spin-contrast-variation neutron reflectometry technique determines the structure of multiple surfaces and interfaces of film samples while excluding the incorrect structure that accidentally accounts for a single unpolarized reflectivity curve only. |
Tuesday, March 16, 2021 9:24AM - 10:00AM Live |
E02.00006: Information Content and Experimental Design in Neutron Reflectometry Invited Speaker: Frank Heinrich Optimal design of a scattering experiment seeks to maximize the information content of a measurement with respect to features of interest. This process includes choosing the best sample composition, measurement procedure, and instrument configuration. While there is a great flexibility in designing a scattering experiment, a quantitative measure for assessing which implementation maximizes the gain in information has been lacking and the community largely follows empirical best-practices. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E02.00007: Determining Lamellar Structure with Soft X-ray Reflectivity Whitney Loo, Hongbo Feng, Daniel Sunday, Paul F Nealey Nanostructured polymer thin films have been studied for a variety of applications including electronic transistors, membranes for separations, and bit-patterned media. The formation of the nanostructure is dependent on three polymer properties: the composition of the block copolymer, fA, the interaction parameter between the homopolymer components, χ, and overall chain length of the polymer, N. While composition and chain length can be easily tuned during polymer synthesis, χ is dependent on copolymer chemistry and, therefore, is difficult to tune. We have devised a model block copolymer system to systematically tune χ through use of modular A-b-(B-r-C) copolymers. The nanostructure can be tuned by changing the chemical identities of blocks B and C, as well as the volume fraction of component B to C, φ. Through resonant soft X-ray reflectivity (RSoXR), we have determined the effect of φ on the self-assembly of lamellar thin films through measurements of the interface width. The thin-film measurements are compared with predictions from bulk using strong segregation theory. Our results provide insights into the effect of molecular structure on block copolymer self-assembly to help enable predictive design of nanostructured materials. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E02.00008: Depth profiling molecular orientation with polarized resonant soft X-ray reflectivity Thomas Ferron, Jacob L Thelen, Kushal Bagchi, Marie Fiori, Mark Ediger, Dean DeLongchamp, Daniel Sunday Organic molecules often exhibit complex molecular packing that results in anisotropic behaviors. Advances in thin-film processing make it feasible to harness this asymmetry and fabricate devices with superior properties. For instance, vapor deposition of glassy molecules can produce OLEDs with increased charge transport and light-outcoupling when components are aligned ‘face-on’ to the substrate. While many measurements are capable of investigating bulk orientation, few can simultaneously interrogate buried or free interfaces. Here we will discuss progress in developing polarized resonant soft X-ray reflectivity (P-RSoXR) for molecular orientation depth profiling in soft matter thin-films. P-RSoXR derives orientation contrast by probing near-edge X-ray absorption fine structure dipole moments allowing for continuous depth profiling of molecular orientation. We will demonstrate such capabilities by investigating orientationally inhomogeneous bilayers comprised of a model glassy molecule, TCTA, where P-RSoXR reveals a buried layer with a distinct orientation compared to the bulk. Modeling methodologies will be discussed along with future opportunities in systems with composition and orientation heterogeneity. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E02.00009: Probing interactions at the polymer thin film/substrate interface using Kelvin probe force microscopy Jill Wenderott, Ban Dong, Jojo Amonoo, Peter F Green Interfacial interactions between a thin polymer film and substrate influence a myriad of thickness-dependent physical properties of polymers, including glass transition temperature, dynamics, and phase transitions. Direct quantification of these interfacial interactions has been challenging because this interface is buried. Here, we utilized Kelvin probe force microscopy (KPFM) to better understand interactions at the polymer thin film/substrate interface. KPFM yields contact potential difference (CPD), determined by the polarities of the materials and processing conditions. We investigated different polymer thin film systems: polystyrene (PS), supported by gold (Au) and silicon (SiOx/Si) substrates, and tetramethyl bisphenol-A polycarbonate (TMPC), supported by Au and SiOx/Si substrates. We found CPDs of the polymer films were dependent on both thickness of the film and substrate. The CPD of TMPC on SiOx/Si increased significantly with decreasing film thickness (<100 nm), whereas for PS on SiOx/Si and for PS and TMPC on Au, the CPDs increased modestly as thicknesses increased. These observations are rationalized in terms of local interfacial the bonding environments between polymers and substrates and the relation to key thickness-dependent physical properties. |
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