Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S35: Surface Science of Organic Molecular Solids, Films, and Nanostructures III |
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Sponsoring Units: DMP Room: 298 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S35.00001: Transient Mobility on Submonolayer Island Growth: An Exploration of Asymptotic Effects in Modeling Josue Morales-Cifuentes, Theodore L. Einstein, Alberto Pimpinelli In studies of epitaxial growth, modeling of the smallest stable cluster (i+1 monomers, with i the critical nucleus size), is paramount in understanding growth dynamics. Our previous work has tackled submonolayer growth by modeling the effect of ballistic monomers, \textit{hot-precursors,} on diffusive dynamics \footnote{J. R. Morales-Cifuentes, T. L. Einstein, and A. Pimpinelli. Phys. Rev. Lett. 113, 246101 (2014)}. Different scaling regimes and energies were predicted, with initial confirmation by applying to para-hexaphenyl submonolayer studies \footnote{L. Tumbek & A. Winkler, Surf. Sci. 606, L55 (2012)}. Lingering questions about the applicability and behavior of the model are addressed. First, we show how an asymptotic approximation based on the growth exponent, $\alpha$ ($N \propto F^\alpha$) allows for robustness of modeling to experimental data; second, we answer questions about non-monotonicity by exploring the behavior of the growth exponent across realizable parameter spaces; third, we revisit our previous para-hexaphenyl work and examine relevant physical parameters, namely the speed of the hot-monomers. We conclude with an exploration of how the new asymptotic approximation can be used to strengthen the application of our model to other physical systems. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S35.00002: Tuning Interfacial States Using Organic Molecules as Spin Filters Andrew DeLoach, Jingying Wang, Christopher M. Papa, Mykhaylo Myahkostupov, Felix N. Castellano, Daniel B. Dougherty, Wei Jiang, Feng Liu Organic semiconductors are known to have long spin relaxation times which makes them a good candidate for spintronics(1). However, an issue with these materials is that at metal-organic interfaces there is a conductivity mismatch problem that suppresses spin injection(2). To overcome this, orbital mixing at the interface can be tuned with an organic spacer layer to promote the formation of spin polarized interface states(3,4). These states act as a ``spin filters'' and have been proposed as an explanation for the large tunneling magnetoresistance seen in devices using \textit{tris}-(8-hydroxyquinolate)-aluminum(Alq$_{\mathrm{3}})$(3). Here, we show that the spin polarized interface states can be tuned from metallic to resistive by subtle changes in molecular orbitals. This is done using spin polarized scanning tunneling microscopy with three different tris-(8-hydroxyquinolate) compounds: aluminum, chromium, and iron. Differences in d-orbital mixing results in different mechanisms of interfacial coupling, giving rise to metallic or resistive interface states. (1)J. Devkota \textit{et al.} Adv. Funct. Mater. 26,22 (2016). (2)G. Schmidt \textit{et al.} Phys. Rev. B 62,8 (2000). (3)C. Barraud \textit{et al.} Nat Phys 6,8 (2010). (4)V. A. Dediu, Nat Phys 9,4 (2013). [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S35.00003: Spinterface between tris(8-hydroxyquinoline)metal(III) molecules and magnetic surfaces: a first-principles study W. Jiang, Jingying Wang, Daniel Dougherty, Feng Liu Using first-principles calculations, we have systematically investigated the hybridization between tris(8-hydroxyquinoline)metal(III) (Mq$_{\mathrm{3}}$, M $=$ Fe, Cr, Al) molecules and magnetic substrates (Co and Cr). Mq$_{\mathrm{3}}$ with different central metal elements but the same organic framework has dramatically different interaction with different magnetic substrates, which affect the interface state significantly. AFM coupling was observed between magnetic Mq$_{\mathrm{3}}$ molecules and ferromagnetic (Co) as well as antiferromagnetic (Cr) substrate, manifested with a superexchange and direct exchange interaction, respectively. Such strong magnetic interfacial coupling may open a gap around the Fermi level and significantly change interface transport properties. Nonmagnetic Alq$_{\mathrm{3}}$ molecule was found to enhance the interface spin polarization due to hybridization between the lowest unoccupied molecular orbitals (LUMO) of Alq$_{\mathrm{3}}$ and metallic surface state. These findings will help better understand spinterface and shed new light on future application of Mq$_{\mathrm{3}}$ molecules in spintronics devices. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S35.00004: STM STUDY OF QUASI-1D C$_{\mathrm{\mathbf{60}}}$ NANOSTRUCTURES ON RIPPLED GRAPHENE Chuanhui Chen, Husong Zheng, Adam Mills, James Heflin, Chenggang Tao As two nanostructured allotropes of carbon, both graphene and fullerene exhibit fascinating physical properties and have numerous applications. A particularly interesting arrangement of C$_{\mathrm{60}}$ is the quasi-one-dimensional (1D) structure, an excellent model system and prototype of quantum confinement of electronic states. However, quasi-1D C$_{\mathrm{60}}$ nanostructures have been rarely realized experimentally due to their highly anisotropic configuration. I will report our experimental realization of quasi-1D C$_{\mathrm{60}}$ nanostructures on rippled graphene by utilizing the linear periodic potential in grapheme. Through careful control of the subtle balance between the linear periodic potential of rippled graphene and the C$_{\mathrm{60}}$ intermolecular interaction, we demonstrated that C$_{\mathrm{60}}$ molecules can be arranged into a novel 1D C$_{\mathrm{60}}$ chain structure with widths of two to three molecules. At a higher annealing temperature, the 1D chain structure transitions to a more compact hexagonal close packed quasi-1D stripe structure. This first experimental realization of 1D C$_{\mathrm{60}}$ structures on rippled graphene may pave a way for fabricating new C$_{\mathrm{60}}$/graphene hybrid structures for future applications in electronics, spintronics and quantum information. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S35.00005: Strongly-hybridized C$_{60}$-decorated copper surfaces enable giant current rectification Jeffrey R. Guest, Joseph A. Smerdon, Pierre Darancet Building on previous rectification demonstrations of strong electron-blocking character of pentacene/C$_{60}$ layers on Cu(111) [1], we demonstrate hole-blocking and rectification ratios ($RR$) of over 1000 at biases of 1.3~V in bilayers of C$_{60}$ deposited on copper [2]. Using scanning tunneling spectroscopy and first-principles calculations, we show that the strong coupling between C$_{60}$ and the Cu(111) surface leads to the metallization of the bottom C$_{60}$ layer, while the molecular orbitals of the top C$_{60}$ are essentially unaffected. Due to this substrate-induced symmetry-breaking and to a tunneling transport mechanism, the system behaves as a hole-blocking layer, with a spatial dependence of the onset voltage on intra-layer coordination. This work further demonstrates the potential of strongly-hybridized, C$_{60}$-coated surfaces to harness the electrical functionality of molecular components. [1] J. A. Smerdon {\it et al.}, Nano Letters {\bf 16}, 2603 (2016); [2] J. A. Smerdon {\it et al.}, { \it submitted}. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S35.00006: Electronic Structure of Single Crystal $\alpha $-Perylene S. J. Pookpanratana, K. P. Goetz, R. Ovsyannikov, E. Giangrisostomi, E. G. Bittle, O. D. Jurchescu, S. W. Robey, C. A. Hacker In organic electronics, the highest estimated charge mobility in a device is typically achieved when the organic semiconductor is a single crystal. However, the measurement of the electronic and chemical structure of organic single crystals by photoemission lags far behind of the thin-film counterpart. The measurement challenge is due to two reasons: the insulating nature of the crystal surface and relatively small size of the crystals (millimeter to a few hundred micrometers). X-ray and ultraviolet-based photoemission measurements are achievable on single crystal $\alpha $-perylene with measurement assistance from a blue light emitting laser to enhance photoconductivity of the crystal surface. We are able to clearly resolve multiple highest molecular orbitals and determine the ionization energy of $\alpha $-perylene. We are able to obtain high-resolution C 1s spectrum which we can clearly distinguish contribution from carbon atoms in the two inequivalent sites and shake-up satellite features. Electronic ``band'' structure measurements of $\alpha $-perylene are realized using a novel angle-resolved time-of-flight electron spectrometer and the complete $\alpha $-perylene electronic structure and impact on electrical performance will be discussed. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S35.00007: Polarization dependent photo-induced bias stress effect in organic transistors. Vitaly Podzorov, Hyun Ho Choi, Hikmet Najafov, Danila Saranin, Nikolai A. Kharlamov, Denis V. Kuznetzov, Sergei I. Didenko, Kilwon Cho, Alejandro L. Briseno Photo-induced charge transfer between a semiconductor and a gate insulator that occurs in organic transistors operating under illumination leads to a shift of the onset gate voltage in these devices. Here we report an observation of a polarization dependent photo-induced bias-stress effect in two prototypical single-crystal organic field-effect transistors, based on rubrene and TPBIQ. We find that the rate of the effect is a periodic function of polarization angle of a linearly polarized photoexcitation, with a periodicity of $\pi $. The observed phenomenon provides an effective tool for addressing the relationship between molecular packing and parameter drift in organic transistors under illumination. [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S35.00008: Thiol-Ene Networks for Photon Upconversion Joseph Lott, Abagail Jentsch Photon upconversion via the mechanism of triplet-triplet annihilation (TTA) offers the prospect of employing low-power and non-coherent excitation sources to drive the upconversion process. Solid-state materials capable of TTA present several significant challenges including limited solubility of the required chromophores and reduced molecular diffusion. Owing to the wide range of chemical compositions, tunable mechanical properties, and the ease of processing, polymeric materials have been at the forefront of solid-state materials for TTA. This study focuses on the use of thiol-ene `click' chemistry to create elastomeric films for TTA. Functionalized derivatives of 9,10-diphenylanthracene bearing two vinyl groups were synthesized and covalently incorporated into thiol-ene films, along with palladium (II) octaethylporphine as a sensitizing chromophore. Both emitter and sensitizer concentrations were systematically varied. The network formation was monitored using FTIR measurements and leaching experiments were conducted to quantify the amount of emitter chromophores not bonded into the network. The thermal and mechanical properties of the films were characterized using TGA, DSC, and DMTA. The upconverting performance was gauged using steady-state photoluminescence and lifetime measurements. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S35.00009: Adhesion of Blended Polymer Films. Christopher Staszel, Suman Sinha-Ray, Alexander L. Yarin, Behnam Pourdeyhimi The adhesive energy of blended and monolithic PCL and PCL-N6 surfaces was measured by blister method and linked to the surface composition of the blended samples. It was shown that PCL does not adhere to N6 after heat-treatment at 55 C, while the monolithic PCL films adhered to the blended samples solely via the PCL islands at the surface. The surface concentration of PCL in the blended samples was established using the novel staining method. It was shown that the surface concentration of PCL differs from its bulk content in the blended samples. The measurements also revealed that the surface concentration of PCL is practically linearly proportionality to the normalized adhesion energy between the blended PCL-N6 samples and monolithic PCL films. Several statistical characteristics of the surfaces of the blended samples were used to characterize their uniformity/non-uniformity. It was shown that increasing the surface uniformity of the adhering component in the blended samples (PCL), one increases the adhesion energy. Moreover, at about 70{\%} of PCL at the surface, the adhesion energy of blended samples to monolithic PCL films could reach the value characterization of the adhesion between two monolithic PCL samples. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S35.00010: Simple Coarse-grained modeling of regioregularity controlled P3HT molecules YongJoo Kim, Hyeong Jun Kim, Jin-Seong Kim, Yeon Sik Jung, Bumjoon J. Kim Conjugate polymers have been evaluated as the active component in organic electronics due to their great potential in the mass production of large area, light-weight and flexible electronic devices by cost-effective solution processing. Among them, poly(3-hexylthiophene) (P3HT) represents most widely investigated model system due to its high performances in various organic electronics. Among the various factors that affects the intrinsic properties of P3HTs, regio-chemical control over head-to-tail (HT) coupling between thiophene rings, defined by regioregularity (RR), has been considered most critical factor for the primary crystalline structure and resulting optoelectronic properties. Alkyl side chains in irregularly substituted head-to-head (HH) linkages causes a sterically driven twist of thiophene rings, resulting in a loss of conjugation and crystallinity. In this study, we suggest highly efficient coarse-grained model of RR controlled P3HT to study thermodynamical properties. We found that our P3HT model successfully predicts crystalline temperature as a function of RR and phase diagram of solution assembled RR controlled P3HT. We believe that our model can be efficiently used for designing various organic electronic devices based on RR controlled P3HT. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S35.00011: Hierarchical Patterning of Hydrogels by Replica Molding of Impregnated Breath Figures Leads to Superoleophobicity. Vijay John, Jaspreet Arora, Noshir Pesika The surface chemistry and topography govern the spreading of liquids on a solid. Adding roughness to an inherently oleophobic surface enhances its oil dewetting characteristics and can lead to superoleophobicity. Here, we introduce the concept of a two-tier hierarchical roughness on the surface of soft materials such as hydrogels by forming the patterned inverse replica of breath figure polymer films impregnated with nanoparticles. The directed deposition of nanoparticles in the breath figure pores is accomplished by an aerosol assisted technique that exclusively leads to deposition within the pores and filling of the pores. The inverse replica of such impregnated films exhibits a close packed hexagonally structured second tier of surface roughness which directly leads to a superoleophobic surface. Since these structures have well defined geometries, it is possible to estimate the contact angle by assuming a partial wetting of the oil drop in a `fakir' state on the rough surface. While the work demonstrates a facile method to impart superoleophobicity to a hydrogel surface, it also demonstrates new methods to imbue breath figure pores with functional materials that can be easily transferred to the pores of the inverse replica. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S35.00012: Role of residual hydrogen on the XPS of organic molecules on surfaces Aran Garcia-Lekue, Ane Sarasola, Mikel Abadia, Giacomo Lovat, Luca Floreano, Celia Rogero It is a well-known experimental issue that residual H is abundant in a seemingly ideal UHV environment, which might have a significant effect on STM and XPS measurements. For example, additional XPS peaks are often observed when evaporating organic molecules on a surface.[1,2] In this work, a set of DFT based tools is employed to elucidate the influence of chemical and surface-induced changes on the core-level shifts (CLSs) of XPS experiments. The capabilities of our tools are demonstrated by unraveling the origin of an unpredicted component in the N 1s XPS spectra of metal phthalocyanine molecules on a metal surface. On one hand, we prove that surface effects, such as LUMO splitting and surface screening, cannot account for the huge experimental CLSs. On the other hand, we show that, when adsorbed at low temperatures, these molecules capture residual H atoms from the surface, giving rise to hydrogenated molecular species without demetalation of the molecule and, thus, to an extra component in the molecular CLS spectra.[3] [1] A. Garcia-Lekue et al., J. Phys. Chem C 116, 15378 (2012). [2] G. Lovat et al., Phys. Chem. Chem. Phys. 17, 30119 (2015). [3] A. Sarasola et al. (submitted) [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S35.00013: Metallic Transport Behavior in a Two-Dimensional Metal Organic Framework: Copper Benzene Hexathiol (Cu-BHT) Ryuichi Tsuchikawa, Neda Lotfizadeh, Nabajit Lahiri, Janis Louie, Vikram Deshpande Two-dimensional (2D) metal organic frameworks (MOF) have flexibilities in controlling the material properties owing to their bottom-up synthesis process and to the selectivity of metal species. We synthesized layers of 2D MOF, Copper benzene hexathiol (Cu-BHT), of thickness less than 100nm and investigated its electronic transport properties. In particular, the resistance of our highly crystalline samples decreased as the temperature was lowered, showing a metallic temperature dependence. This metallic behavior has not been observed in many organic conductors and is a prerequisite to superconductivity that can be realized in the 2D MOFs. Finally our capability of synthesizing high quality 2D MOFs paves a way to the realization of organic topological insulators [1] [2]. [1] Z.F. Wang, Zheng Liu, Feng Liu, Nature commun. 4, 1471 (2013) [2] Z.F. Wang, Ninghai Su, Feng Liu, Nano lett. 13, 2842 (2013) [Preview Abstract] |
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