Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P17: Organic Interfaces from Single Molecules to Thin FilmsFocus
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Sponsoring Units: DMP Chair: Wai-Lun Chan, University of Kansas Room: LACC 306A |
Wednesday, March 7, 2018 2:30PM - 3:06PM |
P17.00001: Electronic Structure and Spin Texture at Organic Semiconductor Interfaces Invited Speaker: Oliver Monti Interfaces of organic semiconductors with inorganic solids are notoriously difficult to understand and tailor due to fundamentally different perspectives when describing the electronic structure of each side in isolation. Considerable progress has been made for physisorptive weakly interacting systems, as well as in select more strongly interacting instances. For the latter, general approaches are however still missing. Here, I will show how both electronic structure and magnetic texture can be tailored and understood by judicious choice of the organic semiconductor. I will discuss several case studies of chemisorption that use designer molecule-surface interactions at organic-metal and organic-topological insulator interfaces to control electronic interactions and spin texture. This opens a pathway towards an improved understanding of organic semiconductor interfaces even in strongly interacting cases. |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P17.00002: Tuning of Interface Properties of Transition Metal Phthalocyanines on Metal Surfaces by Graphene: Ionization Potential and Graphene-Substrate Coupling Heiko Peisert, David Balle, Thomas Chassé
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Wednesday, March 7, 2018 3:18PM - 3:30PM |
P17.00003: Observation of novel gapped phases in potassium doped single layer p-terphenyl on Au (111) Mingqiang Ren, Wei Chen, Chen Chen, Qin Liu, Yanjun Qiao, Yijing Chen, Gang Zhou, zhenhua Li, Tong Zhang, Yajun Yan, Donglai Feng Recently superconductivity in potassium (K) doped p-terphenyl (C18H14) has been suggested by Meissner effect and subsequent photoemission study, sparking the research of doped phenyl materials. Here we report a low temperature STM study on K-doped single layer p-terphenyl films grown on Au (111). We observe several ordered phases with different morphologies and electronic behaviors, in two of which a sharp and symmetric low-energy gap of about 11 meV opens below 50 K. In particular, the gap shows no obvious response to a magnetic field up to 11 Tesla, which rule out the possibility of a superconducting gap. Such gapped phases are rarely (if ever) observed in single layer hydrocarbon molecular crystals, several candidates for its origin are discussed but still need further investigation. Our work also paves the way for fabricating doped two-dimensional (2D) hydrocarbon materials, which will provide a platform to search for novel emergent phenomena. |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P17.00004: Atomic Scale Control in Driving a Dipolar Supramolecular Nanocar Kyaw Zin Latt, Sanjoy Sarkar, Yuan Zhang, Ryan Tumbleson, Yang Li, Mersad Raeisi, Kotturi Kondalarao, K. Perumal, Ramin Rabbani, Eric Masson, Saw Hla The ability to control the nanoscale structure at the atomic level is important for the advancement of nanotechnology. We have developed a molecular vehicle that can be driven on materials surfaces by an electric field applied from a scanning tunneling microscope (STM) tip. Our nano-vehicle dubbed "Bobcat Nanowagon" is composed of an H shape frame with four Cucurbit[7]uril wheels attached. We used our nano vehicle to enter the first international nanocar race held in France on 29 April 2017. The nano vehicles were deposited onto atomically clean Au(111) surface across the Au(111) surface at 5 K substrate temperature. Moreover, we have competed the nanocar race by manipulating the STM remotely from France. This was the first time demonstration of atomic scale manipulation from one quarter of the globe distance, i.e. across Atlantic, and thus it was considered to be the world record. The nano vehicles can be driven by both electric field polarity. From the manipulation experiments, we determine the energy required to operate the nano vehicles as 800 meV. |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P17.00005: Electronic Structure and Electrical Properties of Single Crystal Dinaphthothienothiophene (DNTT) Sujitra Pookpanratana, Emily Bittle, Christina Hacker, Steven Robey, Ruslan Ovsyannikov, Erika Giangrisostomi Dinaphthothienothiophene (DNTT), a thienoacene, has demonstrated carrier mobilities approaching 10 cm2/(V s) when integrated into a solid state device.1 Thin-film DNTT-based field effect transistors are air-stable2 and durable against accelerated temperatures and humidity conditions.3 While there are numerous device studies that establish DNTT and other related thienoacenes for a variety of applications, detailed electronic and chemical structure studies are much fewer. Here, electronic band structure measurements using a novel angle-resolved time-of-flight electron spectrometer are performed on single crystalline DNTT (SC-DNTT). Characterization is accomplished by both laboratory- and synchrotron-based photoemission spectroscopies with the assistance of a continuous wave blue laser source to increase the surface conductivity. Multiple highest occupied molecular orbitals are resolved of varying widths, and high-resolution x-ray photoelectron spectroscopy resolve the shake-up satellite features from the S 2p core electrons. Electrical measurements on SC-DNTT have also been performed, and will be presented. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P17.00006: Vertical tunneling transport and nonlinear access resistance in layered single-crystal organic transistors Takamasa Hamai, Shunto Arai, Hiromi Minemawari, Satoru Inoue, Tatsuo Hasegawa Organic semiconductors (OSCs) are the key materials for flexible printed electronics with the suitability for solution processes under ambient conditions. Recent studies revealed that high layered crystallinity of OSCs is quite essential for providing highly uniform crystalline films and high performance organic thin-film transistors (TFTs) [1]. In the materials, substitutions with normal alkyl chains is used to improve both solvent solubility and layered crystallinity. However, these alkyl chains should exhibit insulating nature due to the lack of pi electrons, which may affect the transport properties. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P17.00007: A high-throughput method for probing exciton dissociation at organic donor-acceptor interfaces Bhupal Kattel, Tika Ram Kafley, Liang Qin, Wai Lun Chan In the organic molecular solids, electrons and holes are bound together to form excitons. Effective dissociation of these excitons at interfaces is critical for applications such as photovoltaics and photosensing. Here, we develop an interface-sensitive ultrafast spectroscopy method that utilizes a graphene field effect transistor as an ultrafast electric-field sensor to measure the exciton dissociation dynamics at organic donor-acceptor interfaces. Compared to other interface-sensitive techniques such as time-resolved non-linear optical spectroscopy, our method has a much-reduced measurement time and can be easily adapted to a large variety of interfaces. Hence, it can be developed into a high throughput screening tool to evaluate the effectiveness of charge separation in a large number of interfaces. Using a typical organic donor-acceptor interface, ZnPc/C60, as an example, we demonstrate how this method can be used to distinguish the coherent charge separation from delocalized CT excitons and the thermal-activated charge separation from bound, localized CT excitons. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P17.00008: Mobility of Non-fullerene Acceptors Using a Time of Flight Method Natalie Mica, Stuart Thomson, Ifor D. Samuel Fullerene acceptors such as PC71BM have shown wide-use and success in organic solar cells partially due to their good electron transport properties. However, the cost of synthesis and poor absorption limit scale-up and device performance. In order to replace these materials, new non-fullerene molecules require an accurate measure of their electron mobility and a better understanding of their charge transport properties. Here we used two acceptors, ITIC and IDTBR, and studied their mobility using a time of flight (TOF) method. This method allowed for the observation of either the hole or electron mobility separately, while also revealing some in-film charge dynamics such as trapping and disorder. With a zero-field electron mobility of 3.5 x 10-4 cm2/Vs for ITIC in a blend with PTB7-Th, and 6.0 x 10-5 cm2/Vs for IDTBR in a P3HT blend, these non-fullerene acceptors have slower electron transport compared to fullerenes. However, electron mobility values of this magnitude match the hole mobility of the donor material, minimizing charge build up and recombination. This balance leads to efficient charge extraction and power conversion in solar cells, making these materials a competitive replacement for fullerenes. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P17.00009: Local Electric Fields, Solvation, and Frustration at Interfaces Directly Probed by Vibrational Spectroscopy Jahan Dawlaty It is widely understood that the molecular-scale structure and the corresponding local electric fields near an interfaces are crucial for controlling and optimizing interfacial processes. Yet, very little is known about the interface from direct spectroscopic observations. Most of our understanding, especially about local fields, is based on inferences from net transport data. We report advances in understanding interfaces using vibrational Stark shift probes at the surface and measured by Sum Frequency Generation Spectroscopy. We report three new developments. First, a new solvation model, as the interfacial analog of the bulk Onsager solvation theory, will be presented along with experimental support. Second, the extent of validity of the Guoy-Chapman-Stern (GCS) model and its variants as examined by Stark shift spectroscopy will be discussed. Our finding demands a new theoretical description of local fields under non-equilibrium conditions. Finally, we present result on the concept of Frustrated Lewis Acid-Base pairs (FLP) near the surface. We report creation of FLPs on metal surfaces and use vibrational spectroscopy to measure the extent of interfacial frustration. We argue that the above concepts will shed new light on the physics and chemistry of surfaces. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P17.00010: Reduced Conductance Attenuation in Cyanine Dye Molecular Junctions Daniel Hernangomez-Perez, Suman Gunasekaran, Iryna Davydenko, Seth Marder, Ferdinand Evers, Latha Venkataraman Charge transport properties of molecular wires are determined not only by the properties of the molecular junction (i.e. contact geometry or relative level alignment of frontier molecular orbitals with the Fermi level of the metal electrodes) but can also be influenced by the external environment. Here, we study conductance trends in single-molecular junctions of polymethine dyes fabricated with the scanning tunneling microscope based break-junction technique. These junctions are shown to present very low attenuation of conductance with the molecular length, with the trend being tunable (either positively or negatively) by the choice of solvent. Supported by a Hückel model and ab-initio quantum transport calculations, we argue that the unusually low attenuation factor and solvent-induced modifications in the conductance trends can be related to reduced bond-length alternation (BLA) in the wire. This work details on the impact that BLA has on single-molecular junctions, which could lead to improved design for efficient nanoscale electron transport devices. |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P17.00011: Abstract Withdrawn
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Wednesday, March 7, 2018 5:06PM - 5:18PM |
P17.00012: Abstract Withdrawn
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Wednesday, March 7, 2018 5:18PM - 5:30PM |
P17.00013: Microscopic mechanism of the helix-to-layer transformation in elemental selenium Dan Liu, David Tomanek Using ab initio calculations, we study the microscopic |
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