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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis and optical properties of MoS2 and isomorphous nanoclusters in the quantum confinement regime (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 7934-7944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly crystalline nanoclusters of hexagonal (2H polytype) MoS2 and several of its isomorphous Mo and W chalcogenides have been synthesized with excellent control over cluster size down to ∼2 nm. These clusters exhibit highly structured, bandlike optical absorption and photoluminescence spectra which can be understood in terms of the band-structures for the bulk crystals. Key results of this work include: (1) strong quantum confinement effects with blue shifts in some of the absorption features relative to bulk crystals as large as 4 eV for clusters ∼2.5 nm in size, thereby allowing great tailorability of the optical properties; (2) the quasiparticle (or excitonic) nature of the optical response is preserved down to clusters (approximately-less-than)2.5 nm in size which are only two unit cells thick; (3) the demonstration of the strong influence of dimensionality on the magnitude of the quantum confinement. Specifically, three-dimensional confinement of the carriers produces energy shifts which are over an order of magnitude larger than those due to one-dimensional (perpendicular to the layer planes) confinement emphasizing the two-dimensional nature of the structure and bonding; (4) the observation of large increases in the spin-orbit splittings at the top of the valence band at the K and M points of the Brillouin zone with decreasing cluster size, a feature that reflects quantum confinement as well as possible changes in the degree of hybridization of the electronic orbitals which make up the states at these points; and (5) the observation of photoluminescence due to both direct and surface recombination. Several of these features bode well for the potential of these materials for solar photocatalysis. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365367
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  • 2
    Electronic Resource
    Electronic Resource
    Photoluminescence from nanosize gold clusters (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9137-9143 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have observed visible light emission from nanosize gold clusters. Liquid chromatographic analysis of the metal clusters shows that relatively intense photoluminescence occurs only when the size of the metal nanocluster is sufficiently small (〈5 nm). The emission is strongly Stokes shifted and is assigned to radiative recombination of Fermi level electrons and sp- or d-band holes. The electron and/or hole states are perturbed by surface states, as indicated by the dependence of the emission spectrum on the nature of the cluster surface. Finally, we found that large, nonemitting gold clusters can also be made luminescent by partial dissolution using KCN. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476360
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  • 3
    Electronic Resource
    Electronic Resource
    Electron transfer dynamics in MoS2 nanoclusters: Normal and inverted behavior (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4978-4987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photophysics and electron transfer (ET) dynamics of quantum confined MoS2 nanoclusters have been studied using static and time resolved emission spectroscopy. The MoS2 nanoclusters consist of a single S–Mo–S trilayer, having diameters of ∼2.5 or 4.5 nm. Two types of electron acceptors are adsorbed on these nanoclusters: 2,2′-bipyridine (bpy) and 4,4′,5,5′-tetramethyl-2,2′-bipyridine (TMB). The ET reaction exothermicities may be varied by changing the electron acceptor or by varying the size of the MoS2 nanocluster. TMB is harder to reduce, and thus has a smaller ET driving force than bpy. The smaller nanoclusters have a higher energy conduction band, and thus have a larger ET driving force. In all cases, the ET driving force may be calculated from bulk MoS2 properties and quantum confinement theory. Both "normal'' and "inverted'' behaviors are observed. A reorganization energy of 0.40 eV is calculated from energy dependent ET rates. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471128
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  • 4
    Electronic Resource
    Electronic Resource
    Statics and dynamics of concentration fluctuations in nonionic micellar solutions (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4684-4691 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of the angular distribution of light scattered from a nonionic surfactant, C12E6, are used to obtain the divergence of the static correlation length and isothermal compressibility near the critical point. The dependence of the apparent diffusion coefficient on momentum transfer yields a dynamic correlation length which agrees closely with the static values for the temperature regime (Tc−4 °C)〈T〈Tc. Outside this regime the scattering measurements are consistent with micelle growth. Dynamic scaling holds for this system near Tc but a significant background contribution to the diffusion coefficient is present due to the large micelle size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452709
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  • 5
    Electronic Resource
    Electronic Resource
    Optical properties of gold and silver nanoclusters investigated by liquid chromatography (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 998-1008 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report high-pressure liquid chromatography (HPLC) and transmission electron microscopy studies of the size-dependent absorbance properties of Au and Ag nanoclusters dispersed in organic solvents. These nanosize metal clusters are synthesized by an inverse micelle synthetic technique at room temperature in inert oils and those investigated range in diameter from 1.3–8 nm. HPLC allows us to separate the clusters from all other chemicals and size select to a resolution of ±2 Å. We use an on-line photodiode array to study the size-dependent absorbance properties of these clusters. For both Au and Ag clusters in the size range d=8 to d=1.5 nm, the plasmon linewidth broadens following a 1/R linewidth size dependence whose slope is greatest for Au. The peak asymmetry in the plasmon band shape is greatest for Au and increases with decreasing size for both Au and Ag clusters. The plasmon peak energy blue shifts with decreasing size for Au clusters while in the case of Ag nanoclusters a red shift is observed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380374
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  • 6
    Electronic Resource
    Electronic Resource
    Performance of a high-resolution, synchrotron-based, small-angle x-ray scattering instrument (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3021-3034 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the construction and performance of a small-angle x-ray scattering (SAXS) instrument which we have used on several beam lines at the National Synchrotron Light Source. The analyzer crystal was a channel cut Si(1,1,1) designed for use at λ=1.54 A(ring) with a measured efficiency of 60% and an angular resolution full width at half maximum of 0.001°. In the case of strongly scattering samples (i.e., powders), momentum transfer q between 1×10−4 A(ring)〈q〈0.1 A(ring)−1 could be studied with over eight decades of dynamic intensity range. We demonstrate the versatility of this instrument by performing scattering experiments on a variety of spherical latex samples spanning the size range from 50 to 800 nm, liquid crystal samples with sharp, asymmetrical Bragg peaks, and metal clusters with sizes less than 10 nm. Small-angle x-ray scattering data for the larger polystyrene samples is compared with light scattering data and theoretical structure factors, and the relative roles of instrument smearing, sample polydispersity, and interparticle interference are elucidated. In the case of the liquid crystal samples, the high resolution of the instrument allows structural features to be observed that were previously obscured by the instrumental resolution in other small-angle neutron and synchroton-based Kratky camera data taken on the same samples. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147424
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of isotopic substitution on the critical behavior of aqueous solutions of n-dodecylhexaoxyethylene glycol monoether (C12E6) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1909-1917 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The critical behavior of a nonionic surfactant, n-dodecylhexaoxyethylene glycol monoether (C12 E6) in D2O, is examined using static and dynamic light scattering and small angle neutron scattering (SANS). Modification of the short-range attractive interactions responsible for phase separation by substitution of D2O for H2O has no effect on the measured universal critical exponents describing the divergence of the correlation length (ν=0.6±0.05) and the isothermal compressibility (γ=1.2±0.1) although such substitution results in a reduction of both the nonuniversal amplitudes and critical temperatures. The measured exponents are the same as those of binary molecular fluids. However, in contrast to binary fluids, significant deviations from the Ornstein–Zernike form are observed at intermediate length scales in SANS measurements near the critical point. Isotopic substitution also preserves the dynamic scaling of the Kawasaki form for the measured Rayleigh linewidth, as found previously for H2 O (Ref. 1). However, this scaling is restricted to a more limited range of distance from the critical point than the static scaling. A maximum in compressibility at the critical isochore is reflected in the concentration dependence of both the compressibility and diffusion coefficient even large distances (∼25 °C) from the coexistence curve. Estimates of micelle size, shape, and polydispersity are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456032
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  • 8
    Electronic Resource
    Electronic Resource
    Tailorable, visible light emission from silicon nanocrystals (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3164-3166 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Crystalline, size-selected Si nanocrystals in the size range 1.8–10 nm grown in inverse micellar cages exhibit highly structured optical absorption and photoluminescence (PL) across the visible range of the spectrum. The most intense PL for the smallest nanocrystals produced (∼2 nm) was in the blue (∼365 nm) with a radiative lifetime of ∼1 ns and is attributed to direct recombination at zone center. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124096
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  • 9
    Electronic Resource
    Electronic Resource
    Phase behavior and metastability in a nonionic surfactant-water-electrolyte system (1990)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 94 (1990), S. 7588-7596 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100382a052
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  • 10
    Electronic Resource
    Electronic Resource
    Optical properties of gold colloids formed in inverse micelles (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9933-9950 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We discuss the formation of gold metal colloids in a variety of surfactant/solvent systems. Static and dynamic light scattering, small angle x-ray and neutron scattering, TEM analysis, and UV-visible absorbance are used to characterize the kinetics of formation and final colloid stability. These gold colloids exhibit a dramatic blueshift and broadening of the plasmon resonance with decreasing colloid size. Several types of reduction method are discussed and differences between micelle (water-free) or microemulsions as reaction media are compared. Use of inverse micelles allows smaller clusters to be formed with greater long-term stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464320
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