Nanocrystal quantum dots (QDs) are attractive materials for applications as laser media because of their bright, size-tunable emission and the flexibility afforded by colloidal synthesis. Nonradiative Auger recombination, however, hampers optical amplification in QDs rapidly depleting population gain-active multiexciton states. In order to elucidate role recombination QD lasing isolate its influence from other factors that might affect gain, we study two types CdSe/CdS core/shell with same...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTArene-Bridged Diuranium Complexes: Inverted Sandwiches Supported by δ BackbondingPaula L. Diaconescu, Polly Arnold, Thomas A. Baker, Daniel J. Mindiola, and Christopher C. CumminsView Author Information Department of Chemistry Room 2-227 Massachusetts Institute Technology Cambridge, 02139-4307 Cite this: Am. Chem. Soc. 2000, 122, 25, 6108–6109Publication Date (Web):June 9, 2000Publication History Received23 December 1999Published online9 June...

Luminescent solar concentrators (LSCs) can be utilized as both large-area collectors of radiation supplementing traditional photovoltaic cells well semitransparent "solar windows" that provide a desired degree shading and simultaneously serve power-generation units. An important characteristic an LSC is concentration factor (C) thought coefficient effective enlargement (or contraction) the area cell when it coupled to LSC. Here we use analytical numerical Monte Carlo modeling in addition...

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control physical properties needed. Here we report four terpolymers prepared from two distinct alkene monomers that predictively tuned in glass transition, molecular...

Radical-closed shell and radical-radical intermolecular interactions are less well-understood than those between closed species. With the objective of gaining additional insight, this work reports a generalization absolutely localized molecular orbital (ALMO) energy decomposition analysis (EDA) to open fragments, described by self-consistent field methods, such as standard density functional theory. The ALMO-EDA variationally partitions an interaction into three separate contributions;...

Anion [CMo(N[R]Ar)3]- (R = C(CD3)2CH3 or tBu, Ar 3,5-C6H3Me2) containing one-coordinate carbon as a terminal substituent and related molecules have been studied by single-crystal X-ray crystallography, solution solid-state 13C NMR spectroscopy, density functional theory (DFT) calculations. Chemical reactivity patterns for investigated, including the kinetics of proton-transfer self-exchange involving HCMo(N[R]Ar)3, carbidomolybdenum anion's conjugate acid. While Mo⋮C bond lengths in...

We report the first systematic theoretical study of oxidative self-coupling methanol to form ester, methylformate, on atomic-oxygen-covered Au(111) using density functional theory calculations. The step in process—dissociation O−H bond methanol—has a lower barrier for transfer proton adsorbed oxygen than H gold, consistent with experimental observations that O is necessary initiate reaction. computed formation methoxy (CH3O) and OH 0.41 eV, compared 1.58 eV calculated clean Au surface....

Recently, gold has been intensely studied as a catalyst for key synthetic reactions. Gold is an attractive because, surprisingly, it highly active and very selective partial oxidation processes suggesting promise energy-efficient "green" chemistry. The underlying origin of the high activity Au controversial subject since metallic commonly thought to be inert. Herein, we establish that one catalysis extremely reactive nature atomic oxygen bound in 3-fold coordination sites on gold. This...

We report the first scanning tunneling microscope (STM) investigation, combined with density functional theory calculations, to resolve controversy regarding bonding and structure of chlorine adsorbed on Au(111). STM experiments are carried out at 120 K overcome instability caused by mobile species upon adsorption room temperature. Chlorine initially lifts herringbone reconstruction. At low coverages (<0.33 ML), binds top Au(111)-(1 x 1) surface leads formation an overlayer (square root(3)...

Preparation of the terminal nitrido anion -[NNb(N[iPr]Ar)3] and niobazene trimer {(μ-N)Nb(N[iPr]Ar)2}3 (iPr = CH(CH3)2 or CH(CD3)2, Ar 3,5-C6H3Me2) entails cooperative splitting dinitrogen upon reduction heterobimetallic paramagnetic complex (Ar[R]N)3Mo(μ-N2)Nb(N[iPr]Ar)3 (R tBu C(CD3)2 CH3).

We present evidence for the formation of transient hydroxyls from reaction water with atomic oxygen on Au(111) and investigate effect adsorbed hydrogen bonding water. Water is evolved in peaks at 175 195 K temperature programed experiments following adsorption oxygen-covered Au(111). The peak ascribed to sublimation multilayers water, whereas associated oxygen-stabilized or a water-hydroxyl surface complex. Infrared reflection absorption spectra are consistent presence molecular over entire...

We study the equilibrium structures for adsorption of atomic oxygen on Au(111) surfaces containing defects such as vacancies and steps, using first-principles density functional theory calculations. considered gold−oxygen interaction a function surface vacancy concentration, with 1,2 4 gold adatoms (the latter number arranged in groups that represent 2D or 3D islands), at finally, effect strain. find there is an attractive between atoms surface, which lowers cost to create by 0.20 eV, but...

We report theoretical evidence from first-principles density functional theory (DFT) calculations that the bonding between Cl and Au(111) surface is primarily covalent in character, which contrast to generally held view of halogens metal surfaces ionic. observe transfer charge into region interacting Au atoms, would not be expected case Cl- anion formation (symmetric accumulation on Cl). Importantly, we also find a clear directionality dz2 orbitals atoms pointing adsorbed mixing electronic...

The interaction of alkali metals—specifically, lithium—with polycyclic aromatic hydrocarbons (PAHs) was studied using a variety electronic structure methods. Electron transfer from lithium to PAH depends on the size and method used. In some cases, we observe an artificial when density functional theory (DFT) due self-interaction error, whereas Hartree−Fock underestimates amount charge overlocalization. Our results have interesting implications for validity DFT calculations metal−PAH in Li...

The Au(111) surface is the prototypical inert metal substrate, whose interaction with oxygen remains a controversial issue. Here, we study effect of dosing temperature and coverage on absorption atomic this surface, using ab initio molecular dynamics high-resolution electron energy loss spectroscopy. Two vibrational peaks are observed experimentally at 380 580 cm−1. lower frequency peak predominant low coverages, while higher grows more pronounced increasing coverage. Our simulations...

Electron emission from individual Au nanorods deposited on indium–tin–oxide (ITO) following excitation with femtosecond laser pulses near the rod longitudinal plasmon resonance is studied via scanning photoionization microscopy. The measured electron signal observed to strongly depend polarization and wavelength. Correlated secondary microscopy (SEM) dark-field (DFM) studies of same unambiguously confirm that maximum results (i) aligned long axis (ii) wavelength resonant localized surface...

Tanya L. Williams, Erica Jackson, Amanda Carritte, and Tania A. Baker Department of Chemistry, Biology, Howard Hughes Medical Institute, Massachusetts Institute Technology, Cambridge, 02139 USA

Minimal structural changes accompany the oxidation of paramagnetic uranium(V) anion [U(dbabh)6]− to neutral, diamagnetic counterpart [U(dbabh)6] (see structure). These two Th-symmetric complexes, which were synthesized starting from 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene (Hdbabh), are first isolable homoleptic hexakisamido complexes and (VI).

This work investigates plasmon-enhanced multiphoton scanning photoelectron emission microscopy (SPIM) of single gold nanorods under vacuum conditions. Striking differences in their photoemission properties are observed for deposited either on 2 nm thick Pt films or 10 indium tin oxide (ITO) films. On a support, the Au display fourth-order photoionization when excited at 800 nm, wavelength corresponding to plasmon resonance aqueous solution. A cos(8)(θ) dependence flux laser polarization...

The ground state restricted Hartree Fock (RHF) wave function of C(60) is found to be unstable with respect spin symmetry breaking, and further minimization leads a significantly contaminated unrestricted (UHF) solution (<S(2)> = 7.5, 9.6 for singlet triplet, respectively). nature the breaking in relative radicaloid fullerene, C(36), assessed by energy lowering UHF solution, <S(2)>, unpaired electron number. We conclude that high value each these measures not attributable strong correlation...

We investigate the effects of Cl and O coverage on atomic structure Au(111) surface using density functional theory calculations. find that release incorporation gold atoms in adsorbate layer becomes energetically favorable only at high coverages either or (&amp;gt;0.66 ML (monolayer) for &amp;gt;0.33 Cl), whereas adsorption without is lower coverages. The bonding between substrate changes significantly with coverage, becoming more covalent (less ionic) higher coverage. This based fact there...

Photoionization studies of single Au and Ag metal nanostructures are presented, using a scanning multiphoton photoionization microscope (SPIM) with single-electron detection capability. Four-photon photoemission following ultrafast excitation at around 840 nm two-photon 420 yield high signal-to-noise 2D photoelectron images for variety sample materials. By way test demonstration the technique, we present results obtained from SPIM imaging photolithographically patterned gold nanostructures,...

Chlorine is an important element in promoting oxidation on noble metal surfaces. Here, we report a comprehensive theoretical study of chlorine interaction with defects the Au(111) surface, using density functional theory calculations and periodic slabs to model surface. We find that binds preferentially steps, vacancies, gold adatoms. The increase binding energy per atom, compared flat, defect-free 0.29 eV when atom top adatom, 0.38 it at edge step, 0.19 next single surface vacancy. An...