@article{17511, author = {Marques, Gabriela A. and Liu, Jia and Matilla, José Manuel Zorrilla and Haiman, Zoltán and Bernui, Armando and Novaes, Camila P.}, issn = {1475-7516}, journal = {Journal of Cosmology and Astroparticle Physics}, number = {06}, publisher = {IOP Publishing}, title = {{Constraining neutrino mass with weak lensing Minkowski Functionals}}, doi = {10.1088/1475-7516/2019/06/019}, volume = {2019}, year = {2019}, } @article{17512, abstract = {The localization of stellar-mass binary black hole mergers using gravitational waves is critical in understanding the properties of the binaries’ host galaxies, observing possible electromagnetic emission from the mergers, or using them as a cosmological distance ladder. The precision of this localization can be substantially increased with prior astrophysical information about the binary system. In particular, constraining the inclination of the binary can reduce the distance uncertainty of the source. Here, we present the first realistic set of localizations for binary black hole mergers, including different prior constraints on the binaries’ inclinations. We find that prior information on the inclination can reduce the localization volume by a factor of 3. We discuss two astrophysical scenarios of interest: (i) follow-up searches for beamed electromagnetic/neutrino counterparts and (ii) mergers in the accretion discs of active galactic nuclei.}, author = {Corley, K Rainer and Bartos, Imre and Singer, Leo P and Williamson, Andrew R and Haiman, Zoltán and Kocsis, Bence and Nissanke, Samaya and Márka, Zsuzsa and Márka, Szabolcs}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {4459--4463}, publisher = {Oxford University Press}, title = {{Localization of binary black hole mergers with known inclination}}, doi = {10.1093/mnras/stz2072}, volume = {488}, year = {2019}, } @article{17530, abstract = {Based on the cosmic shear data from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), Kilbinger et al. (2013) obtained a constraint on the amplitude of matter fluctuations of σ8(Ωm/0.27)0.6=0.79±0.03 from the two-point correlation function (2PCF). This is ≈3σ lower than the value 0.89±0.01 derived from Planck data on cosmic microwave background (CMB) anisotropies. On the other hand, based on the same CFHTLenS data, but using the power spectrum, and performing a different analysis, Liu et al. (2015) obtained the higher value of σ8(Ωm/0.27)0.64=0.87+0.05−0.06. We here investigate the origin of this difference, by performing a fair side-by-side comparison of the 2PCF and power spectrum analyses on CFHTLenS data. We find that these two statistics indeed deliver different results, even when applied to the same data in an otherwise identical procedure. We identify excess power in the data on small scales (ℓ>5,000) driving the larger values inferred from the power spectrum. We speculate on the possible origin of this excess small-scale power. More generally, our results highlight the utility of analysing the 2PCF and the power spectrum in tandem, to discover (and to help control) systematic errors.}, author = {Lu, Tianhuan and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {5033--5042}, publisher = {Oxford University Press}, title = {{The matter fluctuation amplitude inferred from the weak lensing power spectrum and correlation function in CFHTLenS data}}, doi = {10.1093/mnras/stz2931}, volume = {490}, year = {2019}, } @article{17533, abstract = {The origins of the stellar-mass black hole mergers discovered by LIGO/Virgo are still unknown. Here we show that if migration traps develop in the accretion disks of active galactic nuclei (AGNs) and promote the mergers of their captive black holes, the majority of black holes within disks will undergo hierarchical mergers—with one of the black holes being the remnant of a previous merger. 40% of AGN-assisted mergers detected by LIGO/Virgo will include a black hole with mass ≳50⁢𝑀⊙, the mass limit from stellar core collapse. Hierarchical mergers at traps in AGNs will exhibit black hole spins (anti)aligned with the binary’s orbital axis, a distinct property from other hierarchical channels. Our results suggest, although not definitively (with odds ratio of ∼1), that LIGO’s heaviest merger so far, GW170729, could have originated from this channel.}, author = {Yang, Y. and Bartos, I. and Gayathri, V. and Ford, K. E. S. and Haiman, Zoltán and Klimenko, S. and Kocsis, B. and Márka, S. and Márka, Z. and McKernan, B. and O’Shaughnessy, R.}, issn = {0031-9007}, journal = {Physical Review Letters}, number = {18}, publisher = {American Physical Society}, title = {{Hierarchical black hole mergers in active galactic nuclei}}, doi = {10.1103/physrevlett.123.181101}, volume = {123}, year = {2019}, } @article{17541, abstract = {In recent years, the discovery of massive quasars at z~7 has provided a striking challenge to our understanding of the origin and growth of supermassive black holes in the early Universe. Mounting observational and theoretical evidence indicates the viability of massive seeds, formed by the collapse of supermassive stars, as a progenitor model for such early, massive accreting black holes. Although considerable progress has been made in our theoretical understanding, many questions remain regarding how (and how often) such objects may form, how they live and die, and how next generation observatories may yield new insight into the origin of these primordial titans. This review focusses on our present understanding of this remarkable formation scenario, based on discussions held at the Monash Prato Centre from November 20--24, 2017, during the workshop "Titans of the Early Universe: The Origin of the First Supermassive Black Holes."}, author = {Woods, Tyrone E. and Agarwal, Bhaskar and Bromm, Volker and Bunker, Andrew and Chen, Ke-Jung and Chon, Sunmyon and Ferrara, Andrea and Glover, Simon C. O. and Haemmerlé, Lionel and Haiman, Zoltán and Hartwig, Tilman and Heger, Alexander and Hirano, Shingo and Hosokawa, Takashi and Inayoshi, Kohei and Klessen, Ralf S. and Kobayashi, Chiaki and Koliopanos, Filippos and Latif, Muhammad A. and Li, Yuexing and Mayer, Lucio and Mezcua, Mar and Natarajan, Priyamvada and Pacucci, Fabio and Rees, Martin J. and Regan, John A. and Sakurai, Yuya and Salvadori, Stefania and Schneider, Raffaella and Surace, Marco and Tanaka, Takamitsu L. and Whalen, Daniel J. and Yoshida, Naoki}, issn = {1323-3580}, journal = {Publications of the Astronomical Society of Australia}, publisher = {Cambridge University Press}, title = {{Titans of the early universe: The prato statement on the origin of the first supermassive black holes}}, doi = {10.1017/pasa.2019.14}, volume = {36}, year = {2019}, } @article{17543, abstract = {Massive black-hole (MBH) binaries, which are expected to form following the merger of their parent galaxies, produce gravitational waves which will be detectable by Pulsar Timing Arrays at nanohertz frequencies (year periods). While no confirmed, compact MBH binary systems have been seen in electromagnetic observations, a large number of candidates have recently been identified in optical surveys of AGN variability. Using a combination of cosmological, hydrodynamic simulations; comprehensive, semi-analytic binary merger models; and analytic AGN spectra and variability prescriptions; we calculate the expected electromagnetic detection rates of MBH binaries as periodically variable AGN. In particular, we consider two independent variability models: (i) Doppler boosting due to large orbital velocities, and (ii) hydrodynamic variability in which the fueling of MBH accretion disks is periodically modulated by the companion. Our models predict that numerous MBH binaries should be present and distinguishable in the existing data. In particular, our fiducial models produce an expectation value of 0.2 (Doppler) and 5 (hydrodynamic) binaries to be identifiable in CRTS, while 20 and 100 are expected after five years of LSST observations. The brightness variations in most systems are too small to be distinguishable, but almost 1% of AGN at redshifts z≲0.6 could be in massive binaries. We analyze the predicted binary parameters of observable systems and their selection biases, and include an extensive discussion of our model parameters and uncertainties.}, author = {Kelley, Luke Zoltan and Haiman, Zoltán and Sesana, Alberto and Hernquist, Lars}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {2}, pages = {1579--1594}, publisher = {Oxford University Press}, title = {{Massive BH binaries as periodically variable AGN}}, doi = {10.1093/mnras/stz150}, volume = {485}, year = {2019}, } @article{17556, abstract = {The abundance of molecular hydrogen (H2), the primary coolant in primordial gas, is critical for the thermodynamic evolution and star-formation histories in early protogalaxies. Determining the photodissociation rate of H2 by an incident Lyman-Werner (LW) flux is thus crucial, but prohibitively expensive to calculate on the fly in simulations. The rate is sensitive to the H2 rovibrational distribution, which in turn depends on the gas density, temperature, and incident LW radiation field. We use the publicly available cloudy package to model primordial gas clouds and compare exact photodissociation rate calculations to commonly-used fitting formulae. We find the fit from Wolcott-Green et al. (2011) is most accurate for moderate densities n~10^3 cm^{-3} and temperatures, T~10^3K, and we provide a new fit, which captures the increase in the rate at higher densities and temperatures, owing to the increased excited rovibrational populations in this regime. Our new fit has typical errors of a few percent percent up to n =<10^7 cm^{-3}, T =< 8000K, and H2 column density NH2 =<10^{17} cm^{-2}, and can be easily utilized in simulations. We also show that pumping of the excited rovibrational states of H2 by a strong LW flux further modifies the level populations when the gas density is low, and noticeably decreases self-shielding for J_21 > 10^3 and n < 10^2 cm^{-3}. This may lower the "critical flux" at which primordial gas remains H2-poor in some protogalaxies, enabling massive black hole seed formation.}, author = {Wolcott-Green, J and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {2}, pages = {2467--2473}, publisher = {Oxford University Press}, title = {{H2 self-shielding with non-LTE rovibrational populations: Implications for cooling in protogalaxies}}, doi = {10.1093/mnras/sty3280}, volume = {484}, year = {2019}, } @article{17565, abstract = {The coalescence of a compact object with a 104−107M⊙ supermassive black hole (SMBH) produces mHz gravitational waves (GWs) detectable by the future Laser Interferometer Space Antenna (LISA). If such an inspiral occurs in the accretion disc of an active galactic nucleus (AGN), the gas torques imprint a small deviation in the GW waveform. Here we present two-dimensional hydrodynamical simulations with the moving-mesh code DISCO of a BH inspiraling at the GW rate in a binary system with a mass ratio q=M2/M1=10−3, embedded in an accretion disc. We assume a locally isothermal equation of state for the gas (with Mach number M=20) and implement a standard α-prescription for its viscosity (with α=0.03). We find disc torques on the binary that are weaker than in previous semi-analytic toy models, and are in the opposite direction: the gas disc slows down, rather than speeds up the inspiral. We compute the resulting deviations in the GW waveform, which scale linearly with the mass of the disc. The SNR of these deviations accumulates mostly at high frequencies, and becomes detectable in a 5-year LISA observation if the total phase shift exceeds a few radians. We find that this occurs if the disc surface density exceeds Σ0≳102−3gcm−2, as may be the case in thin discs with near-Eddington accretion rates. Since the characteristic imprint on the GW signal is strongly dependent on disc parameters, a LISA detection of an intermediate mass ratio inspiral would probe the physics of AGN discs and migration.}, author = {Derdzinski, A M and D’Orazio, D and Duffell, P and Haiman, Zoltán and MacFadyen, A}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {2}, pages = {2754--2765}, publisher = {Oxford University Press}, title = {{Probing gas disc physics with LISA: simulations of an intermediate mass ratio inspiral in an accretion disc}}, doi = {10.1093/mnras/stz1026}, volume = {486}, year = {2019}, } @article{17567, abstract = {The growing number of stellar-mass binary black hole mergers discovered by Advanced LIGO and Advanced Virgo are starting to constrain the binaries' origin and environment. However, we still lack sufficiently accurate modeling of binary formation channels to obtain strong constraints, or to identify sub-populations. One promising formation mechanism that could result in different black hole properties is binaries merging within the accretion disks of Active Galactic Nuclei (AGN). Here we show that the black holes' orbital alignment with the AGN disks preferentially selects heavier black holes. We carry out Monte Carlo simulations of orbital alignment with AGN disks, and find that AGNs harden the initial black hole mass function. Assuming an initial power law mass distribution M−βbh, we find that the power law index changes by Δβ∼1.3, resulting in a more top-heavy population of merging black holes. This change is independent of the mass of, and accretion rate onto, the supermassive black hole in the center of the AGN. Our simulations predict an AGN-assisted merger rate of ∼4Gpc−3yr−1. With its hardened mass spectra, the AGN channel could be responsible for 10−50% of gravitational-wave detections.}, author = {Yang, Y. and Bartos, I. and Haiman, Zoltán and Kocsis, B. and Márka, Z. and Stone, N. C. and Márka, S.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, publisher = {American Astronomical Society}, title = {{AGN disks harden the mass distribution of stellar-mass binary black hole mergers}}, doi = {10.3847/1538-4357/ab16e3}, volume = {876}, year = {2019}, } @article{17603, abstract = {Weak gravitational lensing is one of the most promising cosmological probes of the late universe. Several large ongoing (DES, KiDS, HSC) and planned (LSST, Euclid, WFIRST) astronomical surveys attempt to collect even deeper and larger scale data on weak lensing. Due to gravitational collapse, the distribution of dark matter is non-Gaussian on small scales. However, observations are typically evaluated through the two-point correlation function of galaxy shear, which does not capture non-Gaussian features of the lensing maps. Previous studies attempted to extract non-Gaussian information from weak lensing observations through several higher order statistics such as the three-point correlation function, peak counts, or Minkowski functionals. Deep convolutional neural networks (CNN) emerged in the field of computer vision with tremendous success, and they offer a new and very promising framework to extract information from 2D or 3D astronomical data sets, confirmed by recent studies on weak lensing. We show that a CNN is able to yield significantly stricter constraints of (σ8, Ωm) cosmological parameters than the power spectrum using convergence maps generated by full N-body simulations and ray-tracing, at angular scales and shape noise levels relevant for future observations. In a scenario mimicking LSST or Euclid, the CNN yields 2.4–2.8 times smaller credible contours than the power spectrum, and 3.5–4.2 times smaller at noise levels corresponding to a deep space survey such as WFIRST. We also show that at shape noise levels achievable in future space surveys the CNN yields 1.4–2.1 times smaller contours than peak counts, a higher order statistic capable of extracting non-Gaussian information from weak lensing maps.}, author = {Ribli, Dezső and Pataki, Bálint Ármin and Zorrilla Matilla, José Manuel and Hsu, Daniel and Haiman, Zoltán and Csabai, István}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {2}, pages = {1843--1860}, publisher = {Oxford University Press}, title = {{Weak lensing cosmology with convolutional neural networks on noisy data}}, doi = {10.1093/mnras/stz2610}, volume = {490}, year = {2019}, } @article{17915, abstract = {The construction of self-assembled iron phthalocyanine (FePc) systems on gold electrodes modified by self-assembled monolayers (SAMs) is becoming an interesting strategy for obtaining electrocatalytic molecular building blocks for the oxygen reduction reaction (ORR). In this work, we have measured the conductance of pyridiniums axial ligands at the single molecule level using the scanning tunneling microscope-based break-junction method (STM-Break Junction) to study the role of the axial ligand on the activity of the self-assembled FePc systems on a gold electrode surface. The electron-pulling effect of pyridinium axial ligands is known to increase the electrocatalytic activity of FePc for the oxygen reduction reaction (ORR). We have used these systems as a platform for carrying out a comparative study for understanding the real influence of the proximal axial ligands. Further, these ligands act as molecular wires between the gold electrode surface and the FePc molecule. The pyridinium molecules were synthesized following a series of structural variations using a basic molecular backbone. From conductance measurements obtained for each pyridinium molecule, it was possible to establish that electron transport through each pyridinium does not influence the activity of FePc for ORR in alkaline media. In addition, the DFT calculations shows that the axial ligand in FePc modifies its catalytic activity by decreasing the binding energy of O2 to the Fe site.}, author = {Gutiérrez-Ceron, Cristian and Oñate, Rubén and Zagal, José H. and Pizarro, Ana and Silva, J. Francisco and Castro-Castillo, Carmen and Rezende, Marcos Caroli and Flores, Marcos and Cortés-Arriagada, Diego and Toro-Labbé, Alejandro and Campos, Luis M. and Venkataraman, Latha and Ponce, Ingrid}, issn = {0013-4686}, journal = {Electrochimica Acta}, publisher = {Elsevier}, title = {{Molecular conductance versus inductive effects of axial ligands on the electrocatalytic activity of self-assembled iron phthalocyanines: The oxygen reduction reaction}}, doi = {10.1016/j.electacta.2019.134996}, volume = {327}, year = {2019}, } @article{17916, abstract = {Electric fields have been proposed as having a distinct ability to catalyze chemical reactions through the stabilization of polar or ionic intermediate transition states. Although field-assisted catalysis is being researched, the ability to catalyze reactions in solution using electric fields remains elusive and the understanding of mechanisms of such catalysis is sparse. Here we show that an electric field can catalyze the cis-to-trans isomerization of [3]cumulene derivatives in solution, in a scanning tunneling microscope. We further show that the external electric field can alter the thermodynamics inhibiting the trans-to-cis reverse reaction, endowing the selectivity toward trans isomer. Using density functional theory-based calculations, we find that the applied electric field promotes a zwitterionic resonance form, which ensures a lower energy transition state for the isomerization reaction. The field also stabilizes the trans form, relative to the cis, dictating the cis/trans thermodynamics, driving the equilibrium product exclusively toward the trans.}, author = {Zang, Yaping and Zou, Qi and Fu, Tianren and Ng, Fay and Fowler, Brandon and Yang, Jingjing and Li, Hexing and Steigerwald, Michael L. and Nuckolls, Colin and Venkataraman, Latha}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Directing isomerization reactions of cumulenes with electric fields}}, doi = {10.1038/s41467-019-12487-w}, volume = {10}, year = {2019}, } @article{17917, abstract = {A single-molecule method has been developed based on the scanning tunneling microscope (STM) to selectively couple a series of aniline derivatives and create azobenzenes. The Au-catalyzed oxidative coupling is driven by the local electrochemical potential at the nanostructured Au STM tip. The products are detected in situ by measuring the conductance and molecular junction elongation and compared with analogous measurements of the expected azobenzene derivatives prepared ex situ. This single-molecule approach is robust, and it can quickly and reproducibly create reactions for a variety of anilines. We further demonstrate the selective synthesis of geometric isomers and the assembly of complex molecular architectures by sequential coupling of complementary anilines, demonstrating unprecedented control over bond formation at the nanoscale.}, author = {Zang, Yaping and Stone, Ilana and Inkpen, Michael S. and Ng, Fay and Lambert, Tristan H. and Nuckolls, Colin and Steigerwald, Michael L. and Roy, Xavier and Venkataraman, Latha}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {45}, pages = {16008--16012}, publisher = {Wiley}, title = {{In situ coupling of single molecules driven by gold‐catalyzed electrooxidation}}, doi = {10.1002/anie.201906215}, volume = {58}, year = {2019}, } @article{17918, abstract = {The single-molecule conductance of silanes is suppressed due to destructive quantum interference in conformations with cisoid dihedral angles along the molecular backbone. Yet, despite the structural similarity, σ-interference effects have not been observed in alkanes. Here we report that the methyl substituents used in silanes are a prerequisite for σ-interference in these systems. Through density functional theory calculations, we find that the destructive interference is not evident to the same extent in nonmethylated silanes. We find the same is true in alkanes as the transmission is significantly suppressed in permethylated cyclic and bicyclic alkanes. Using scanning tunneling microscope break-junction method we determine the single-molecule conductance of functionalized cyclohexane and bicyclo[2.2.2]octane that are found to be higher than that of equivalent permethylated silanes. Rather than the difference between carbon and silicon atoms in the molecular backbones, our calculations reveal that it is primarily the difference between hydrogen and methyl substituents that result in the different electron transport properties of nonmethylated alkanes and permethylated silanes. Chemical substituents play an important role in determining the single-molecule conductance of saturated molecules, and this must be considered when we improve and expand the chemical design of insulating organic molecules.}, author = {Garner, Marc H. and Li, Haixing and Neupane, Madhav and Zou, Qi and Liu, Taifeng and Su, Timothy A. and Shangguan, Zhichun and Paley, Daniel W. and Ng, Fay and Xiao, Shengxiong and Nuckolls, Colin and Venkataraman, Latha and Solomon, Gemma C.}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {39}, pages = {15471--15476}, publisher = {American Chemical Society}, title = {{Permethylation introduces destructive quantum interference in saturated silanes}}, doi = {10.1021/jacs.9b06965}, volume = {141}, year = {2019}, } @article{17919, abstract = {The adsorption geometry and the electronic structure of a Blatter radical derivative on a gold surface were investigated by a combination of high‐resolution noncontact atomic force microscopy and scanning tunneling microscopy. While the hybridization with the substrate hinders direct access to the molecular states, we show that the unpaired‐electron orbital can be probed with Ångström resolution by mapping the spatial distribution of the Kondo resonance. The Blatter derivative features a peculiar delocalization of the unpaired‐electron orbital over some but not all moieties of the molecule, such that the Kondo signature can be related to the spatial fingerprint of the orbital. We observe a direct correspondence between these two quantities, including a pronounced nodal plane structure. Finally, we demonstrate that the spatial signature of the Kondo resonance also persists upon noncovalent dimerization of molecules.}, author = {Patera, Laerte L. and Sokolov, Sophia and Low, Jonathan Z. and Campos, Luis M. and Venkataraman, Latha and Repp, Jascha}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {32}, pages = {11063--11067}, publisher = {Wiley}, title = {{Resolving the unpaired‐electron orbital distribution in a stable organic radical by Kondo resonance mapping}}, doi = {10.1002/anie.201904851}, volume = {58}, year = {2019}, } @article{17920, abstract = {Stable organic radicals have potential applications for building organic spintronic devices. To fulfill this potential, the interface between organic radicals and metal electrodes must be well characterized. Here, through a combined effort that includes synthesis, scanning tunneling microscopy, X-ray spectroscopy, and single-molecule conductance measurements, we comprehensively probe the electronic interaction between gold metal electrodes and a benchtop stable radical—the Blatter radical. We find that despite its open-shell character and having a half-filled orbital close to the Fermi level, the radical is stable on a gold substrate under ultrahigh vacuum. We observe a Kondo resonance arising from the radical and spectroscopic signatures of its half-filled orbitals. By contrast, in solution-based single-molecule conductance measurements, the radical character is lost through oxidation with charge transfer occurring from the molecule to metal. Our experiments show that the stability of radical states can be very sensitive to the environment around the molecule.}, author = {Low, Jonathan Z. and Kladnik, Gregor and Patera, Laerte L. and Sokolov, Sophia and Lovat, Giacomo and Kumarasamy, Elango and Repp, Jascha and Campos, Luis M. and Cvetko, Dean and Morgante, Alberto and Venkataraman, Latha}, issn = {1530-6992}, journal = {Nano Letters}, number = {4}, pages = {2543--2548}, publisher = {American Chemical Society}, title = {{The environment-dependent behavior of the Blatter radical at the metal–molecule interface}}, doi = {10.1021/acs.nanolett.9b00275}, volume = {19}, year = {2019}, } @article{17921, abstract = {The promise of the field of single-molecule electronics is to reveal a new class of quantum devices that leverages the strong electronic interactions inherent to subnanometer scale systems. Here, we form Au–molecule–Au junctions using a custom scanning tunneling microscope and explore charge transport through current–voltage measurements. We focus on the resonant tunneling regime of two molecules, one that is primarily an electron conductor and one that conducts primarily holes. We find that in the high bias regime, junctions that do not rupture demonstrate reproducible and pronounced negative differential resistance (NDR)-like features followed by hysteresis with peak-to-valley ratios exceeding 100 in some cases. Furthermore, we show that both junction rupture and NDR are induced by charging of the molecular orbital dominating transport and find that the charging is reversible at lower bias and with time with kinetic time scales on the order of hundreds of milliseconds. We argue that these results cannot be explained by existing models of charge transport and likely require theoretical advances describing the transition from coherent to sequential tunneling. Our work also suggests new rules for operating single-molecule devices at high bias to obtain highly nonlinear behavior.}, author = {Fung, E-Dean and Gelbwaser, David and Taylor, Jeffrey and Low, Jonathan and Xia, Jianlong and Davydenko, Iryna and Campos, Luis M. and Marder, Seth and Peskin, Uri and Venkataraman, Latha}, issn = {1530-6992}, journal = {Nano Letters}, number = {4}, pages = {2555--2561}, publisher = {American Chemical Society}, title = {{Breaking down resonance: Nonlinear transport and the breakdown of coherent tunneling models in single molecule junctions}}, doi = {10.1021/acs.nanolett.9b00316}, volume = {19}, year = {2019}, } @article{17922, abstract = {Gold–thiol contacts are ubiquitous across the physical and biological sciences in connecting organic molecules to surfaces. When thiols bind to gold in self-assembled monolayers (SAMs) the fate of the hydrogen remains a subject of profound debate—with implications for our understanding of their physical properties, spectroscopic features and formation mechanism(s). Exploiting measurements of the transmission through a molecular junction, which is highly sensitive to the nature of the molecule–electrode contact, we demonstrate here that the nature of the gold–sulfur bond in SAMs can be probed via single-molecule conductance measurements. Critically, we find that SAM measurements of dithiol-terminated molecular junctions yield a significantly lower conductance than solution measurements of the same molecule. Through numerous control experiments, conductance noise analysis and transport calculations based on density functional theory, we show that the gold–sulfur bond in SAMs prepared from the solution deposition of dithiols does not have chemisorbed character, which strongly suggests that under these widely used preparation conditions the hydrogen is retained.}, author = {Inkpen, Michael S. and Liu, Zhen–Fei and Li, Haixing and Campos, Luis M. and Neaton, Jeffrey B. and Venkataraman, Latha}, issn = {1755-4349}, journal = {Nature Chemistry}, number = {4}, pages = {351--358}, publisher = {Springer Nature}, title = {{Non-chemisorbed gold–sulfur binding prevails in self-assembled monolayers}}, doi = {10.1038/s41557-019-0216-y}, volume = {11}, year = {2019}, } @article{17924, abstract = {We demonstrate that imidazole based π–π stacked dimers form strong and efficient conductance pathways in single-molecule junctions using the scanning-tunneling microscope-break junction (STM-BJ) technique and density functional theory-based calculations. We first characterize an imidazole-gold contact by measuring the conductance of imidazolyl-terminated alkanes (im-N-im, N = 3–6). We show that the conductance of these alkanes decays exponentially with increasing length, indicating that the mechanism for electron transport is through tunneling or super-exchange. We also reveal that π–π stacked dimers can be formed between imidazoles and have better coupling than through-bond tunneling. These experimental results are rationalized by calculations of molecular junction transmission using non-equilibrium Green's function formalism. This study verifies the capability of imidazole as a Au-binding ligand to form stable single- and π-stacked molecule junctions at room temperature.}, author = {Fu, Tianren and Smith, Shanelle and Camarasa-Gómez, María and Yu, Xiaofang and Xue, Jiayi and Nuckolls, Colin and Evers, Ferdinand and Venkataraman, Latha and Wei, Sujun}, issn = {2041-6539}, journal = {Chemical Science}, number = {43}, pages = {9998--10002}, publisher = {Royal Society of Chemistry}, title = {{Enhanced coupling through π-stacking in imidazole-based molecular junctions}}, doi = {10.1039/c9sc03760h}, volume = {10}, year = {2019}, } @article{17925, abstract = {Recent years have seen tremendous progress towards understanding the relation between the molecular structure and function of organic field effect transistors. The metrics for organic field effect transistors, which are characterized by mobility and the on/off ratio, are known to be enhanced when the intermolecular interaction is strong and the intramolecular reorganization energy is low. While these requirements are adequate when describing organic field effect transistors with simple and planar aromatic molecular components, they are insufficient for complex building blocks, which have the potential to localize a carrier on the molecule. Here, we show that intramolecular conductivity can play a role in controlling device characteristics of organic field effect transistors made with macrocycle building blocks. We use two isomeric macrocyclic semiconductors that consist of perylene diimides linked with bithiophenes and find that the trans-linked macrocycle has a higher mobility than the cis-based device. Through a combination of single molecule junction conductance measurements of the components of the macrocycles, control experiments with acyclic counterparts to the macrocycles, and analyses of each of the materials using spectroscopy, electrochemistry, and density functional theory, we attribute the difference in electron mobility of the OFETs created with the two isomers to the difference in intramolecular conductivity of the two macrocycles.}, author = {Ball, Melissa L. and Zhang, Boyuan and Fu, Tianren and Schattman, Ayden M. and Paley, Daniel W. and Ng, Fay and Venkataraman, Latha and Nuckolls, Colin and Steigerwald, Michael L.}, issn = {2041-6539}, journal = {Chemical Science}, number = {40}, pages = {9339--9344}, publisher = {Royal Society of Chemistry}, title = {{The importance of intramolecular conductivity in three dimensional molecular solids}}, doi = {10.1039/c9sc03144h}, volume = {10}, year = {2019}, }