Pemmaraju C.D.,Molecular Foundry |
Pemmaraju C.D.,Lawrence Berkeley National Laboratory |
Copping R.,Lawrence Berkeley National Laboratory |
Wang S.,Lawrence Berkeley National Laboratory |
And 6 more authors.
Inorganic Chemistry | Year: 2014
We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands. © 2014 American Chemical Society.
Altman A.B.,University of California at Berkeley |
Pemmaraju C.D.,Chemical science Division |
Camp C.,University of California at Berkeley |
Arnold J.,University of California at Berkeley |
And 4 more authors.
Journal of the American Chemical Society | Year: 2015
Polarized aluminum K-edge X-ray absorption near edge structure (XANES) spectroscopy and first-principles calculations were used to probe electronic structure in a series of (BDI)Al, (BDI)AlX2, and (BDI)AlR2 coordination compounds (X = F, Cl, I; R = H, Me; BDI = 2,6-diisopropylphenyl-β-diketiminate). Spectral interpretations were guided by examination of the calculated transition energies and polarization-dependent oscillator strengths, which agreed well with the XANES spectroscopy measurements. Pre-edge features were assigned to transitions associated with the Al 3p orbitals involved in metal-ligand bonding. Qualitative trends in Al 1s core energy and valence orbital occupation were established through a systematic comparison of excited states derived from Al 3p orbitals with similar symmetries in a molecular orbital framework. These trends suggested that the higher transition energies observed for (BDI)AlX2 systems with more electronegative X1- ligands could be ascribed to a decrease in electron density around the aluminum atom, which causes an increase in the attractive potential of the Al nucleus and concomitant increase in the binding energy of the Al 1s core orbitals. For (BDI)Al and (BDI)AlH2 the experimental Al K-edge XANES spectra and spectra calculated using the eXcited electron and Core-Hole (XCH) approach had nearly identical energies for transitions to final state orbitals of similar composition and symmetry. These results implied that the charge distributions about the aluminum atoms in (BDI)Al and (BDI)AlH2 are similar relative to the (BDI)AlX2 and (BDI)AlMe2 compounds, despite having different formal oxidation states of +1 and +3, respectively. However, (BDI)Al was unique in that it exhibited a low-energy feature that was attributed to transitions into a low-lying p-orbital of b1 symmetry that is localized on Al and orthogonal to the (BDI)Al plane. The presence of this low-energy unoccupied molecular orbital on electron-rich (BDI)Al distinguishes its valence electronic structure from that of the formally trivalent compounds (BDI)AlX2 and (BDI)AlR2. The work shows that Al K-edge XANES spectroscopy can be used to provide valuable insight into electronic structure and reactivity relationships for main-group coordination compounds. © 2015 American Chemical Society.
Pascal T.A.,Molecular Foundry |
Wujcik K.H.,CA Technologies |
Wujcik K.H.,University of California at Berkeley |
Velasco-Velez J.,Material Science Division |
And 12 more authors.
Journal of Physical Chemistry Letters | Year: 2014
The X-ray absorption spectra (XAS) of lithium polysulfides (Li 2Sx) of various chain lengths (x) dissolved in a model solvent are obtained from first-principles calculations. The spectra exhibit two main absorption features near the sulfur K-edge, which are unambiguously interpreted as a pre-edge near 2471 eV due to the terminal sulfur atoms at either end of the linear polysulfide dianions and a main-edge near 2473 eV due to the (x -2) internal atoms in the chain, except in the case of Li 2S2, which only has a low-energy feature. We find an almost linear dependence between the ratio of the peaks and chain length, although the linear dependence is modified by the delocalized, molecular nature of the core-excited states that can span up to six neighboring sulfur atoms. Thus, our results indicate that the ratio of the peak area, and not the peak intensities, should be used when attempting to differentiate the polysulfides from XAS. © 2014 American Chemical Society.
Forster J.D.,Molecular Foundry |
Harris S.J.,Lawrence Berkeley National Laboratory |
Urban J.J.,Molecular Foundry
Journal of Physical Chemistry Letters | Year: 2014
We demonstrate confocal Raman microscopy as a general, nonperturbative tool to measure spatially resolved lithium ion concentrations in liquid electrolytes. By combining this high-spatial-resolution technique with a simple microfluidic device, we are able to measure the diffusion coefficient of lithium ions in dimethyl carbonate in two different concentration regimes. Because lithium ion transport plays a key role in the function of a variety of electrochemical devices, quantifying and visualizing this process is crucial for understanding device performance. This method for detecting lithium ions should be immediately useful in the study of lithium-ion-based devices, ion transport in porous media, and at electrode-electrolyte interfaces, and the analytical framework is useful for any system exhibiting a concentration-dependent Raman spectrum. © 2014 American Chemical Society.
Kim K.,Lawrence Livermore National Laboratory |
Kim K.,University of California at Berkeley |
Geng J.,Lawrence Livermore National Laboratory |
Geng J.,University of California at Merced |
And 7 more authors.
Nano Letters | Year: 2014
We report the measurements of transport of ions and uncharged species through carbon nanotube (CNT) porins-short segments of CNTs inserted into a lipid bilayer membrane. Rejection characteristics of the CNT porins are governed by size exclusion for the uncharged species. In contrast, rejection of ionic species is governed by the electrostatic repulsion and Donnan membrane equilibrium. Permeability of monovalent cations follows the general trend in the hydrated ion size, except in the case of Cs+ ions. © 2014 American Chemical Society.
McLeod A.S.,Molecular Foundry |
Schuck P.J.,Molecular Foundry |
Neaton J.B.,Molecular Foundry
Optics InfoBase Conference Papers | Year: 2010
We present analytic models describing the optical properties of the noble metals at frequencies from 5-7eV. With a single finite difference time domain calculation, these models enable a complete spectral description of plasmonic nano-structure properties. © 2010 Optical Society of America.
Altoe V.,Molecular Foundry |
Martin F.,Lawrence Berkeley National Laboratory |
Martin F.,University of California at Berkeley |
Katan A.,Lawrence Berkeley National Laboratory |
And 4 more authors.
Nano Letters | Year: 2012
Transmission electron microscopy was used to determine the structure of molecular films of self-assembled monolayers of pentathiophene derivatives supported on various electron transparent substrates. Despite the extreme beam sensitivity of the monolayers, structural crystallographic maps were obtained that revealed the nanoscale structure of the film. The image resolution is determined by the minimum beam diameter that the radiation hardness of the monolayer can support, which in our case is about 90 nm for a beam current of 5 × 10 6 e -/s. Electron diffraction patterns were collected while scanning a parallel electron beam over the film. These maps contain uncompromised information of the size, symmetry and orientation of the unit cell, orientation and structure of the domains, degree of crystallinity, and their variation on the micrometer scale, which are crucial to understand the electrical transport properties of the organic films. This information allowed us to track small changes in the unit cell size driven by the chemical modification of the support film. © 2012 American Chemical Society.
Zaia E.W.,University of California at Berkeley |
Sahu A.,Molecular Foundry |
Zhou P.,Molecular Foundry |
Gordon M.P.,Molecular Foundry |
And 5 more authors.
Nano Letters | Year: 2016
This work demonstrates the first method for controlled growth of heterostructures within hybrid organic/inorganic nanocomposite thermoelectrics. Using a facile, aqueous technique, semimetal-alloy nanointerfaces are patterned within a hybrid thermoelectric system consisting of tellurium (Te) nanowires and the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Specifically, this method is used to grow nanoscale islands of Cu1.75Te alloy subphases within hybrid PEDOT:PSS-Te nanowires. This technique is shown to provide tunability of thermoelectric and electronic properties, providing up to 22% enhancement of the system's power factor in the low-doping regime, consistent with preferential scattering of low energy carriers. This work provides an exciting platform for rational design of multiphase nanocomposites and highlights the potential for engineering of carrier filtering within hybrid thermoelectrics via introduction of interfaces with controlled structural and energetic properties. © 2016 American Chemical Society.
De Oteyza D.G.,Molecular Foundry |
Perera P.N.,Molecular Foundry |
Schmidt M.,University of California at Berkeley |
Falch M.,Molecular Foundry |
And 6 more authors.
Nanotechnology | Year: 2012
Pattern collapse of small or high aspect ratio lines during traditional wet development is a major challenge for miniaturization in nanolithography. Here we report on a new dry process which combines high resolution resist exposure with selective laser ablation to achieve high resolution with high aspect ratios. Using a low power 532nm laser, we dry develop a normally negative tone methyl acetoxy calix(6)arene in positive tone to reveal sub-20nm half-pitch features in a ∼100nm film at aspect ratios unattainable with conventional development with ablation time of 12s per laser pixel (∼600nm diameter spot). We also demonstrate superior negative tone wet development by combining electron beam exposure with subsequent laser exposure at a non-ablative threshold that requires far less electron beam exposure doses than traditional wet development. © 2012 IOP Publishing Ltd Printed in the UK & the USA.
PubMed | Molecular Foundry
Type: Journal Article | Journal: Nanotechnology | Year: 2012
Pattern collapse of small or high aspect ratio lines during traditional wet development is a major challenge for miniaturization in nanolithography. Here we report on a new dry process which combines high resolution resist exposure with selective laser ablation to achieve high resolution with high aspect ratios. Using a low power 532nm laser, we dry develop a normally negative tone methyl acetoxy calix(6)arene in positive tone to reveal sub-20nm half-pitch features in a 100nm film at aspect ratios unattainable with conventional development with ablation time of 1-2s per laser pixel (600nm diameter spot). We also demonstrate superior negative tone wet development by combining electron beam exposure with subsequent laser exposure at a non-ablative threshold that requires far less electron beam exposure doses than traditional wet development.