Prognostic Importance of the White Blood Cell Count for Coronary, Cancer, and All-Cause Mortality

Grimm, Richard H.,Neaton, James D.,Ludwig, William MediMedia Korea 1986 JAMA-Korea Vol.1 No.4

Superlattice-induced ferroelectricity in charge-ordered La_1/3Sr_2/3FeO₃

Park, Se Young,Rabe, Karin M.,Neaton, Jeffrey B. National Academy of Sciences 2019 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.116 No.48

<P><B>Significance</B></P><P>Charge-order–driven ferroelectrics are an emerging class of materials with promise for high-frequency electron-dominated polarization switching, distinct from conventional ferroelectrics. However, only a few systems exhibiting this behavior have been experimentally realized thus far. With continued development of layer-by-layer growth techniques with a high level of composition control, the exploration of charge-ordered ferroelectrics can be extended to artificially structured superlattices. Here, we use density-functional theory to explore an experimentally realized bulk perovskite iron-oxide solid solution with robust charge ordering and find that in superlattices formed by layered cation ordering, bulk charge ordering is maintained and can lead to charge-order–driven ferroelectricity. Our results suggest that other broad classes of mixed valence materials may be promising candidates for discovery of electronic ferroelectrics.</P><P>Charge-order–driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La<SUB>1/3</SUB>Sr<SUB>2/3</SUB>FeO<SUB>3</SUB> (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 [Formula]C/[Formula], a significant value arising from electron transfer between [Formula] octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order–induced ferroelectricity.</P>

Length Dependence of Conductance in Aromatic Single-Molecule Junctions

Quek, Su Ying,Choi, Hyoung Joon,Louie, Steven G.,Neaton, J. B. American Chemical Society 2009 NANO LETTERS Vol.9 No.11

<P>Using a scattering-state approach incorporating self-energy corrections to the junction level alignment, the conductance <I>G</I> of oligophenyldiamine−Au junctions is calculated and elucidated. In agreement with experiment, we find <I>G</I> decays exponentially with the number of phenyls with decay constant β = 1.7. A straightforward, parameter-free self-energy correction, including electronic exchange and correlations beyond density functional theory (DFT), is found to be essential for understanding the measured values of <I>both G and</I> β. Importantly, our results confirm quantitatively the picture of off-resonant tunneling in these systems and show that exchange and correlation effects absent from standard DFT calculations contribute significantly to β.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2009/nalefd.2009.9.issue-11/nl9021336/production/images/medium/nl-2009-021336_0005.gif'></P>

Quantitative Current–Voltage Characteristics in Molecular Junctions from First Principles

Darancet, Pierre,Widawsky, Jonathan R.,Choi, Hyoung Joon,Venkataraman, Latha,Neaton, Jeffrey B. American Chemical Society 2012 NANO LETTERS Vol.12 No.12

<P>Using self-energy-corrected density functional theory (DFT) and a coherent scattering-state approach, we explain current–voltage (IV) measurements of four pyridine-Au and amine-Au linked molecular junctions with quantitative accuracy. Parameter-free many-electron self-energy corrections to DFT Kohn–Sham eigenvalues are demonstrated to lead to excellent agreement with experiments at finite bias, improving upon order-of-magnitude errors in currents obtained with standard DFT approaches. We further propose an approximate route for prediction of quantitative IV characteristics for both symmetric and asymmetric molecular junctions based on linear response theory and knowledge of the Stark shifts of junction resonance energies. Our work demonstrates that a quantitative, computationally inexpensive description of coherent transport in molecular junctions is readily achievable, enabling new understanding and control of charge transport properties of molecular-scale interfaces at large bias voltages.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-12/nl3033137/production/images/medium/nl-2012-033137_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl3033137'>ACS Electronic Supporting Info</A></P>

Amine−Gold Linked Single-Molecule Circuits: Experiment and Theory

Quek, S. Y.,Venkataraman, L.,Choi, H. J.,Louie, S. G.,Hybertsen, M. S.,Neaton, J. B. American Chemical Society 2007 NANO LETTERS Vol.7 No.11

Mechanically controlled binary conductance switching of a single-molecule junction

Quek, Su Ying,Kamenetska, Maria,Steigerwald, Michael L.,Choi, Hyoung Joon,Louie, Steven G.,Hybertsen, Mark S.,Neaton, J. B.,Venkataraman, Latha Springer Science and Business Media LLC 2009 Nature nanotechnology Vol.4 No.4

<P>Molecular-scale components are expected to be central to the realization of nanoscale electronic devices. Although molecular-scale switching has been reported in atomic quantum point contacts, single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. To date, switching in single-molecule junctions has been attributed to changes in the conformation or charge state of the molecule. Here, we demonstrate reversible binary switching in a single-molecule junction by mechanical control of the metal-molecule contact geometry. We show that 4,4'-bipyridine-gold single-molecule junctions can be reversibly switched between two conductance states through repeated junction elongation and compression. Using first-principles calculations, we attribute the different measured conductance states to distinct contact geometries at the flexible but stable nitrogen-gold bond: conductance is low when the N-Au bond is perpendicular to the conducting pi-system, and high otherwise. This switching mechanism, inherent to the pyridine-gold link, could form the basis of a new class of mechanically activated single-molecule switches.</P>

Conductance and Geometry of Pyridine-Linked Single-Molecule Junctions

Kamenetska, M.,Quek, Su Ying,Whalley, A. C.,Steigerwald, M. L.,Choi, H. J.,Louie, Steven G.,Nuckolls, C.,Hybertsen, M. S.,Neaton, J. B.,Venkataraman, L. American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.19

<P>We have measured the conductance and characterized molecule−electrode binding geometries of four pyridine-terminated molecules by elongating and then compressing gold point contacts in a solution of molecules. We have found that all pyridine-terminated molecules exhibit bistable conductance signatures, signifying that the nature of the pyridine−gold bond allows two distinct conductance states that are accessed as the gold−molecule−gold junction is elongated. We have identified the low-conductance state as corresponding to a molecule fully stretched out between the gold electrodes, where the distance between contacts correlates with the length of the molecule; the high-conductance state is due to a molecule bound at an angle. For all molecules, we have found that the distribution of junction elongations in the low-conductance state is the same, while in the high-conductance state, the most likely elongation length increases linearly with molecule length. The results of first-principles conductance calculations for the four molecules in the low-conductance geometry agree well with the experimental results and show that the dominant conducting channel in the conjugated pyridine-linked molecules is through the π* orbital.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-19/ja1015348/production/images/medium/ja-2010-015348_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja1015348'>ACS Electronic Supporting Info</A></P>

Molecular-scale quantum dots from carbon nanotube heterojunctions.

Chandra, Bhupesh,Bhattacharjee, Joydeep,Purewal, Meninder,Son, Young-Woo,Wu, Yang,Huang, Mingyuan,Yan, Hugen,Heinz, Tony F,Kim, Philip,Neaton, Jeffrey B,Hone, James American Chemical Society 2009 Nano letters Vol.9 No.4

<P>Carbon nanotube heterojunctions (HJs), which seamlessly connect nanotubes of different chiral structure using a small number of atomic-scale defects, represent the ultimate scaling of electronic interfaces. Here we report the first electrical transport measurements on a HJ formed between semiconducting and metallic nanotubes of known chiralities. These measurements reveal asymmetric IV-characteristics and the presence of a quantum dot (QD) with approximately 60 meV charging energy and approximately 75 meV level spacing. A detailed atomistic and electronic model of the HJ enables the identification of specific defect arrangements that lead to the QD behavior consistent with the experiment.</P>

Enrichment of molecular antenna triplets amplifies upconverting nanoparticle emission

Garfield, David J.,Borys, Nicholas J.,Hamed, Samia M.,Torquato, Nicole A.,Tajon, Cheryl A.,Tian, Bining,Shevitski, Brian,Barnard, Edward S.,Suh, Yung Doug,Aloni, Shaul,Neaton, Jeffrey B.,Chan, Emory M Nature Publishing Group UK 2018 Nature photonics Vol.12 No.7

<P>Efficient photon upconversion at low light intensities promises major advances in technologies spanning solar energy harvesting to deep-tissue biophotonics. Here, we discover the critical mechanisms that enable near-infrared dye antennas to significantly enhance performance in lanthanide-doped upconverting nanoparticle (UCNP) systems, and leverage these findings to design dye-UCNP hybrids with a 33,000-fold increase in brightness and a 100-fold increase in efficiency over bare UCNPs. We show that increasing the lanthanide content in the UCNPs shifts the primary energy donor from the dye singlet to its triplet, and the resultant triplet states then mediate energy transfer into the nanocrystals. Time-gated phosphorescence, density functional theory, singlet lifetimes and triplet-quenching experiments support these findings. This interplay between the excited-state populations in organic antennas and the composition of UCNPs presents new design rules that overcome the limitations of previous upconverting materials, enabling performances now relevant for photovoltaics, biophotonics and infrared detection.</P>

Control of Single-Molecule Junction Conductance of Porphyrins via a Transition-Metal Center

Liu, Zhen-Fei,Wei, Sujun,Yoon, Hongsik,Adak, Olgun,Ponce, Ingrid,Jiang, Yivan,Jang, Woo-Dong,Campos, Luis M.,Venkataraman, Latha,Neaton, Jeffrey B. American Chemical Society 2014 NANO LETTERS Vol.14 No.9

<P>Using scanning tunneling microscope break-junction experiments and a new first-principles approach to conductance calculations, we report and explain low-bias charge transport behavior of four types of metal–porphyrin–gold molecular junctions. A nonequilibrium Green’s function approach based on self-energy corrected density functional theory and optimally tuned range-separated hybrid functionals is developed and used to understand experimental trends quantitatively. Importantly, due to the localized d states of the porphyrin molecules, hybrid functionals are essential for explaining measurements; standard semilocal functionals yield qualitatively incorrect results. Comparing directly with experiments, we show that the conductance can change by nearly a factor of 2 when different metal cations are used, counter to trends expected from gas-phase ionization energies which are relatively unchanged with the metal center. Our work explains the sensitivity of the porphyrin conductance with the metal center via a detailed and quantitative portrait of the interface electronic structure and provides a new framework for understanding transport quantitatively in complex junctions involving molecules with localized d states of relevance to light harvesting and energy conversion.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-9/nl5025062/production/images/medium/nl-2014-025062_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5025062'>ACS Electronic Supporting Info</A></P>