Search Results - (Author, Cooperation:L. E. Brus)
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1Latest Papers from Table of Contents or Articles in PressX. Roy ; C. H. Lee ; A. C. Crowther ; C. L. Schenck ; T. Besara ; R. A. Lalancette ; T. Siegrist ; P. W. Stephens ; L. E. Brus ; P. Kim ; M. L. Steigerwald ; C. Nuckolls
American Association for the Advancement of Science (AAAS)
Published 2013Staff ViewPublication Date: 2013-06-08Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsPublished by: -
2Articles: DFG German National LicensesBawendi, M. G. ; Carroll, P. J. ; Wilson, William L. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1992Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: We use time-, wavelength-, temperature-, polarization-resolved luminescence to elucidate the nature of the absorbing and "band edge'' luminescing states in 32 A(ring) diameter wurtzite CdSe quantum crystallites. Time-resolved emission following picosecond size-selective resonant excitation of the lowest excited state shows two components—a temperature insensitive 100 ps component and a microsecond, temperature sensitive component. The emission spectrum, showing optic phonon vibrational structure, develops a ∼70 wave number red shift as the fast component decays. Photoselection shows the slow component to be reverse polarized at 10 K, indicating this component to be the result of a hole radiationless transition. The 100 ps emitting state is repopulated thermally as temperature increases from 10 to 50 K. All available data are interpreted by postulating strong resonant mixing between a standing wave molecular orbital delocalized inside the crystallite and intrinsic surface Se lone pair states. The apparent exciton transition is assigned to a ∼130 wave number wide band of eigenstates with the hole localized principally on the surface. The band contains strongly emitting "doorway'' states and weakly emitting "background'' states. The hole becomes mobile among these states as T increases to 50 K. It is suggested that such resonant mixing may be general in II–VI and III–V crystallites.Type of Medium: Electronic ResourceURL: -
3Articles: DFG German National LicensesBawendi, M. G. ; Kortan, A. R. ; Steigerwald, M. L. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1989Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: X-ray powder patterns obtained from three different types of 35–40 A(ring) CdSe nanoclusters are analyzed. We simulate the effects of thermal fluctuations, stacking faults, surface reconstructions, and bond compressions on powder patterns of CdSe clusters using the Debye formula. We find that the spectra of capped and annealed CdSe particles grown in inverse micelles are best fit by a mixture of crystalline structures intermediate between zinc-blende and wurtzite. We describe a new preparation for CdSe clusters, the structure of which appears to be well-defined wurtzite with, on average, less than one stacking fault per cluster. Thermal effects are found to be important and to mask the subtle effects of likely surface and core reconstructions.Type of Medium: Electronic ResourceURL: -
4Articles: DFG German National LicensesAlivisatos, A. P. ; Harris, T. D. ; Carroll, P. J. ; Steigerwald, M. L. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1989Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: The resonance Raman spectrum of 45(+−3) A(ring) diameter CdSe clusters was measured. The incident photons were resonant with the HOMO–LUMO transition in the clusters. At low temperature, one mode at 205 cm−1 is observed, as well as two overtones, with the integrated areas under these peaks in the ratio of 9:3:1. This mode is assigned as the longest wavelength longitudinal optical vibration of the cluster. The strength of the coupling between the lowest electronic excited state and the LO vibration is found to be 20 times weaker in these clusters than in the bulk solid. The CdSe cluster resonance Raman spectrum is shown to be consistent with the recently measured homogeneous cluster absorption spectrum.Type of Medium: Electronic ResourceURL: -
5Articles: DFG German National LicensesAlivisatos, A. P. ; Harris, T. D. ; Brus, L. E. ; Jayaraman, A.
College Park, Md. : American Institute of Physics (AIP)
Published 1988Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: The pressure dependence of the HOMO–LUMO transition energy and the frequency of the longest wavelength longitudinal optical vibration of 45 A(ring) diameter CdSe clusters in methanol–ethanol solution have been measured up to 50 Kbar. The LO mode shifts to higher frequency at a rate of 0.43 cm−1/Kbar, which corresponds to a Grüneisen parameter of 1.1. The HOMO–LUMO transition shifts to higher energy at 4.5 meV/Kbar, yielding a deformation potential of 2.3 eV. The pressure dependence of these properties closely resemble those of the corresponding bulk solid, confirming the point of view that the lattice properties of these clusters resemble those of the bulk, even though the optical properties are quite distinct.Type of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesAlivisatos, A. P. ; Harris, A. L. ; Levinos, N. J. ; Steigerwald, M. L. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1988Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: The homogeneous (single-cluster) and inhomogeneous contributions to the low temperature electronic absorption spectrum of 35–50 A(ring) diameter CdSe clusters are separated using transient photophysical hole burning. The clusters have the cubic bulk crystal structure, but their electronic states are strongly quantum confined. The inhomogeneous broadening of these features arises because the spectrum depends upon cluster size and shape, and the samples contain similar, but not identical, clusters. The homogeneous spectrum, which consists of a peak 140 cm−1 (17 meV) wide, with a phonon sideband and continuum absorption to higher energy, is compared to a simple molecular orbital model. Electron–vibration coupling, which is enhanced in small clusters, contributes to the substantial broadening of the homogeneous spectrum. The inhomogeneous width of the lowest allowed optical transition was found to be 940 cm−1, or seven times the homogeneous width, in the most monodisperse sample.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesStaff View
ISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: The ground state resonance Raman spectra of β-carotene, in fluid isopentane at 293 and 119 K, show saturation and near-Lorentzian broadening as a function of fluence, using intense ∼30 ps visible laser pulses. There are no lines assignable to transient species. A two-pulse, two-color pump-and-probe Raman experiment shows that the broadening is due to high optical field, and not due to unrelaxed internal excitation in the molecule. The broadening is a manifestation of nonlinear resonance Raman scattering, previously predicted (but not observed) in molecules when the Rabi energy becomes larger than the vibrational dephasing linewidth. Our data can be semiquantitatively explained using a model by Dick and Hochstrasser. The saturation represents population loss from the vibrationally relaxed ground electronic state, and is consistent with lowest excited singlet lifetime on the order of 10 ps.Type of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesChestnoy, N. ; Hull, R. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1986Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: Metal selenide clusters have been made and characterized, using the arrested precipitation colloidal technique. A comparison of sulfide and selenide spectra enables observation of the effect of changes in the highest occupied molecular orbitals upon cluster electronic properties. The first and second excited electronic states are both observed as a function of size in ZnSe clusters. The systematic dependence of the spectra lead to assignment of the higher state to a 1S-type hole based upon the split-off valence band. It is shown that the energy spectrum of discrete hole states is controlled by the spin-orbit energy and the isotropic hole mass in small, highly symmetrical clusters. This result contrasts with the heavy hole and light hole states observed for planar confinement. In (approximately-equal-to) 20 A(ring) diameter ZnS clusters, there is a strong vibronic temperature dependence in the excited state spectra, while in clusters of smaller gap materials such vibronic effects are very minor. We conjecture that lifetime broadening is severe in clusters of small gap materials.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesRossetti, R. ; Hull, R. ; Gibson, J. M. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1985Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: Tiny single PbS crystals of ∼25 A(ring) diameter are synthesized and studied optically in low-temperature colloidal solutions. Electron microscopic examination shows a simple cubic rock salt structure with a lattice constant unchanged, within experimental error, from the bulk value. These crystallites lack the near infrared electronic absorption characteristic of bulk PbS. The small crystallite absorbance in the visible rises more steeply than does the bulk absorbance. These results reflect electron and hole localization if one considers the variation in effective mass across the band structure. A simple discussion of localization anywhere in the Brillouin zone is given. For the first time, crystallite syntheses are carried out in solvent mixtures that form transparent glasses upon cooling. The PbS spectra are independent of temperature (at current experimental resolution) down to 130 K, in contrast to earlier results for quantum size exciton peaks in ∼20 A(ring) ZnS crystallites. Previously published observations of size dependence in the excited state electronic properties of AgI and AgBr are explained as consequences of electron and hole localization in the small crystallites. AgBr appears to be the first indirect gap semiconductor to be examined in the regime where bulk properties are not fully formed.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesRossetti, R. ; Hull, R. ; Gibson, J. M. ; Brus, L. E.
College Park, Md. : American Institute of Physics (AIP)
Published 1985Staff ViewISSN: 1089-7690Source: AIP Digital ArchiveTopics: PhysicsChemistry and PharmacologyNotes: Very small ZnS and CdS crystallites are made and stabilized in aqueous and methanolic media without organic surfactants. Low temperature (−77 °C) synthesis in methanol produces the smallest crystallites, (approximate)30 A(ring) diameter cubic CdS and 〈20 A(ring) diameter cubic ZnS. The crystallites are characterized by transmission electron microscopy and in situ optical spectroscopy (λ(approximately-greater-than)200 nm). The crystallites are too small to exhibit bulk band gaps in their optical spectra. In the band gap region, the small crystallites show a higher energy absorption threshold with a resolved spectral feature (quantum size exciton peak), not present in the spectra of larger crystals. The far ultraviolet spectra are unaffected by size at present resolution. These results can be understood in terms of the crystallite molecular orbitals, and an elementary confined electron and hole model.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesNirmal, M. ; Dabbousi, B. O. ; Bawendi, M. G. ; Macklin, J. J. ; Trautman, J. K. ; Harris, T. D. ; Brus, L. E.
[s.l.] : Nature Publishing Group
Published 1996Staff ViewISSN: 1476-4687Source: Nature Archives 1869 - 2009Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsNotes: [Auszug] In Fig. la we show a fluorescence image of single 21-A-radius CdSe nanocrystals, embedded in a thin polyvinylbutyral film, at room temperature. The streaks in the image are a consequence of raster scanning the sample across a diffraction-limited laser spot, and arise due to the discrete turning on ...Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesTrautman, J. K. ; Macklin, J. J. ; Brus, L. E. ; Betzig, E.
[s.l.] : Nature Publishing Group
Published 1994Staff ViewISSN: 1476-4687Source: Nature Archives 1869 - 2009Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsNotes: [Auszug] In Fig. 1 are shown a schematic view of the experiment and a near-field fluorescence image of individual dil molecules (Molecular Probes) on a thin film of polymethylmethacrylate (PMMA). As an imaging microscope, the present configuration is similar to that recently reported8 for observing single ...Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesDameron, C. T. ; Reese, R. N. ; Mehra, R. K. ; Kortan, A. R. ; Carroll, P. J. ; Steigerwald, M. L. ; Brus, L. E. ; Winge, D. R.
[s.l.] : Nature Publishing Group
Published 1989Staff ViewISSN: 1476-4687Source: Nature Archives 1869 - 2009Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsNotes: [Auszug] C. glabrata and S. pombe respond to Cd salts by synthet y-glutamyl peptides7'8. Cytoplasmic cadmium ions are sequestered within complexes containing these y-Glu pep-tides7'9. Related metal- y-peptide complexes are found in metal-exposed plants and Euglena gracilis10'12. The metal-peptide complexes ...Type of Medium: Electronic ResourceURL: