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Janne Laine - One of the best experts on this subject based on the ideXlab platform.
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Cellulose nanocrystal submonolayers by spin coating.
Langmuir, 2007Co-Authors: Eero Kontturi, Katri S. Kontturi, Päivi Ahonen, Peter C. Thüne, Leena-sisko Johansson, Janne LaineAbstract:Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose Nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of Nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the Nanocrystals is desired. Furthermore, the amount of Nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica su...
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Cellulose nanocrystal submonolayers by spin coating
Langmuir, 2007Co-Authors: Eero Kontturi, Katri S. Kontturi, Päivi Ahonen, Peter C. Thüne, Leena-sisko Johansson, Janne LaineAbstract:Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose Nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of Nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the Nanocrystals is desired. Furthermore, the amount of Nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose Nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose Nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose Nanocrystals. The thicker films of charged Nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose Nanocrystals in the ultrathin regime (
Mariepaule Pileni - One of the best experts on this subject based on the ideXlab platform.
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Hierarchical mechanical behavior of cobalt supracrystals related to nanocrystallinity
Nano Research, 2015Co-Authors: Melanie Gauvin, Zhijie Yang, Nailiang Yang, Imad Arfaoui, Mariepaule PileniAbstract:Here, we report on hierarchical mechanical behavior of 500-nm-thick Co-nanocrystal 3D superlattices (supracrystals) induced by either the crystalline structure (nanocrystallinity) or the length of the coating agent of Co Nanocrystals. Increasing the nanocrystal shape anisotropy of Co Nanocrystals through the control of their nanocrystallinities induces a higher level of ordering with both translational and orientational alignment of Nanocrystals within the supracrystals. The hierarchy in ordering at various scales, i.e., from the atomic lattice within the Nanocrystals to the nanocrystal superlattices within supracrystals, is correlated with marked changes in the Young’s modulus of supracrystals: From 0.7 ± 0.4 to 1.7 ± 0.5 and to 6.6 ± 1.5 GPa as the crystalline structure of Co nanoparticles changes from amorphous-Co to ε-Co and to hexagonal compact packing (hcp)-Co, respectively. Moreover, for supracrystals of 7 nm amorphous Co nanoparticles, the Young’s modulus decreases by one order of magnitude from 0.7 ± 0.4 to 0.08 ± 0.03 GPa upon reducing the alkyl chain length of the ligands coating the Co nanoparticles from C_18 (oleic acid) to C_12 (lauric acid). The hierarchical mechanical behavior is rationalized using a dimensional model of the stress-strain relationship in supracrystals.
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beyond entropy magnetic forces induce formation of quasicrystalline structure in binary nanocrystal superlattices
Journal of the American Chemical Society, 2015Co-Authors: Zhijie Yang, P Bonville, Mariepaule PileniAbstract:Here, it is shown that binary superlattices of Co/Ag Nanocrystals with the same size, surface coating, differing by their type of crystallinity are governed by Co–Co magnetic interactions. By using 9 nm amorphous-phase Co Nanocrystals and 4 nm polycrystalline Ag Nanocrystals at 25 °C, triangle-shaped NaCl-type binary nanocrystal superlattices are produced driven by the entropic force, maximizing the packing density. By contrast, using ferromagnetic 9 nm single domain (hcp) Co Nanocrystals instead of amorphous-phase Co, dodecagonal quasicrystalline order is obtained, together with less-packed phases such as the CoAg13 (NaZn13-type), CoAg (AuCu-type), and CoAg3 (AuCu3-type) structures. On increasing temperature to 65 °C, 9 nm hcp Co Nanocrystals become superparamagnetic, and the system yields the CoAg3 (AuCu3-type) and CoAg2 (AlB2-type) structures, as observed with 9 nm amorphous Co Nanocrystals. Furthermore, by decreasing the Co nanocrystal size from 9 to 7 nm, stable AlB2-type binary nanocrystal superlatt...
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Analogy Between Atoms in a Nanocrystal and Nanocrystals in a Supracrystal: Is It Real or Just a Highly Probable Speculation?
The Journal of Physical Chemistry Letters, 2011Co-Authors: Nicolas Goubet, Mariepaule PileniAbstract:Nanocrystals and supracrystals are arrangements of highly ordered atoms and Nanocrystals, respectively. At the nanometer scale, from face-centered cubic (fcc) tetrahedral subunits, either single fcc Nanocrystals such as cubooctahedra and octahedra or decahedral and icosahedral Nanocrystals are produced. Such Nanocrystals with different shapes are produced by soft chemistry. At the micrometer scale, very surprisingly, supracrystals having shapes similar to those obtained at the nanometer scale are produced. For example, large triangular Nanocrystals as well as supracrystals are produced either by soft chemistry, from nanocrystal diffusion on a surface, or by nanocrystal interactions in solution. The morphologies of Nanocrystals, supracrystals, and minerals, which are similar at various scales (nm and mm), are pointed out, and an explanation of these similarities is undertaken.
Eero Kontturi - One of the best experts on this subject based on the ideXlab platform.
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Cellulose nanocrystal submonolayers by spin coating.
Langmuir, 2007Co-Authors: Eero Kontturi, Katri S. Kontturi, Päivi Ahonen, Peter C. Thüne, Leena-sisko Johansson, Janne LaineAbstract:Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose Nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of Nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the Nanocrystals is desired. Furthermore, the amount of Nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica su...
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Cellulose nanocrystal submonolayers by spin coating
Langmuir, 2007Co-Authors: Eero Kontturi, Katri S. Kontturi, Päivi Ahonen, Peter C. Thüne, Leena-sisko Johansson, Janne LaineAbstract:Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose Nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of Nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the Nanocrystals is desired. Furthermore, the amount of Nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose Nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose Nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose Nanocrystals. The thicker films of charged Nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose Nanocrystals in the ultrathin regime (
Horst Weller - One of the best experts on this subject based on the ideXlab platform.
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CdSe:Te Nanocrystals: Band-Edge versus Te-Related Emission
Journal of Physical Chemistry C, 2007Co-Authors: Thomas Franzl, Thomas A. Klar, And Andrey L. Rogach, Jochen Feldmann, And Dmitri V. Talapin, Josef Muller, Horst WellerAbstract:Strongly luminescent monodisperse CdSe Nanocrystals in which a few Se atoms are substituted with Te atoms (CdSe:Te) provide a model system for studies of both band-edge and trap-related luminescence. Ensemble photoluminescence spectra of CdSe:Te Nanocrystals are asymmetrically broadened and red-shifted in comparison to bare CdSe nanoparticles. Single particle luminescence measurements show that the bare CdSe and the CdSe:Te Nanocrystals emit at distinctly different wavelengths and differ in line shape and line width. Individual CdSe:Te Nanocrystals show two kinds of emission spectra, which have been ascribed by us to particles with one Te and with a few Te atoms per nanocrystal. Single particle measurements furthermore show that a single CdSe:Te nanocrystal can emit either from the band-edge states or from trap state(s) created by the Te atom(s), but not from both.
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The effect of nanocrystal surface structure on the luminescence properties: Photoemission study of HF-etched InP Nanocrystals
The Journal of chemical physics, 2005Co-Authors: S. Adam, Horst Weller, Dmitri V. Talapin, Holger Borchert, A. Lobo, C. Mcginley, A. R. B. De Castro, Markus Haase, T. MöllerAbstract:InP Nanocrystals with narrow size distribution and mean particle diameter tunable from ∼2 up to ∼7nm were synthesized via the dehalosilylation reaction between InCl3 and tris(trimethylsilyl)phosphine. Specific capping of the nanocrystal surface with a shell of organic ligands protects the Nanocrystals from oxidation and provides solubility of the particles in various organic solvents. InP Nanocrystals with enhanced photoluminescence (PL) efficiency were obtained from the initial Nanocrystals by photoassisted etching of the nanocrystal surface with HF. The resulting PL quantum efficiency of InP Nanocrystals dispersed in n-butanol is about three orders of magnitude higher when compared to the nonetched InP samples and approaches ∼40% at room temperature. High-resolution photoelectron spectroscopy with the use of synchrotron radiation was applied to reveal the changes of the nanocrystal surface responsible for the dramatic improvement of the PL efficiency. The analysis of high-resolution P 2p core-level spec...
Daniel R Gamelin - One of the best experts on this subject based on the ideXlab platform.
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anion exchange and the quantum cutting energy threshold in ytterbium doped cspb cl1 xbrx 3 perovskite Nanocrystals
Nano Letters, 2019Co-Authors: Tyler J Milstein, Kyle T Kluherz, Daniel M Kroupa, Christian S Erickson, James J De Yoreo, Daniel R GamelinAbstract:Colloidal halide perovskite Nanocrystals of CsPbCl3 doped with Yb3+ have demonstrated remarkably high sensitized photoluminescence quantum yields (PLQYs), approaching 200%, attributed to a picosecond quantum-cutting process in which one photon absorbed by the nanocrystal generates two photons emitted by the Yb3+ dopants. This quantum-cutting process is thought to involve a charge-neutral defect cluster within the nanocrystal’s internal volume. We demonstrate that Yb3+-doped CsPbCl3 Nanocrystals can be converted postsynthetically to Yb3+-doped CsPb(Cl1–xBrx)3 Nanocrystals without compromising the desired high PLQYs. Nanocrystal energy gaps can be tuned continuously from Eg ≈ 3.06 eV (405 nm) in CsPbCl3 down to Eg ≈ 2.53 eV (∼490 nm) in CsPb(Cl0.25Br0.75)3 while retaining a constant PLQY above 100%. Reducing Eg further causes a rapid drop in PLQY, interpreted as reflecting an energy threshold for quantum cutting at approximately twice the energy of the Yb3+ 2F7/2 → 2F5/2 absorption threshold. These data dem...
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Potentiometric Titrations for Measuring the Capacitance of Colloidal Photodoped ZnO Nanocrystals
Journal of the American Chemical Society, 2016Co-Authors: Carl K. Brozek, Kimberly H. Hartstein, Daniel R GamelinAbstract:Colloidal semiconductor Nanocrystals offer a unique opportunity to bridge molecular and bulk semiconductor redox phenomena. Here, potentiometric titration is demonstrated as a method for quantifying the Fermi levels and charging potentials of free-standing colloidal n-type ZnO Nanocrystals possessing between 0 and 20 conduction-band electrons per nanocrystal, corresponding to carrier densities between 0 and 1.2 × 1020 cm–3. Potentiometric titration of colloidal semiconductor Nanocrystals has not been described previously, and little precedent exists for analogous potentiometric titration of any soluble reductants involving so many electrons. Linear changes in Fermi level vs charge-carrier density are observed for each ensemble of Nanocrystals, with slopes that depend on the nanocrystal size. Analysis indicates that the ensemble nanocrystal capacitance is governed by classical surface electrical double layers, showing no evidence of quantum contributions. Systematic shifts in the Fermi level are also obser...
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redox potentials of colloidal n type zno Nanocrystals effects of confinement electron density and fermi level pinning by aldehyde hydrogenation
Journal of the American Chemical Society, 2015Co-Authors: Gerard M Carroll, Alina M Schimpf, Emily Y Tsui, Daniel R GamelinAbstract:Electronically doped colloidal semiconductor Nanocrystals offer valuable opportunities to probe the new physical and chemical properties imparted by their excess charge carriers. Photodoping is a powerful approach to introducing and controlling free carrier densities within free-standing colloidal semiconductor Nanocrystals. Photoreduced (n-type) colloidal ZnO Nanocrystals possessing delocalized conduction-band (CB) electrons can be formed by photochemical oxidation of EtOH. Previous studies of this chemistry have demonstrated photochemical electron accumulation, in some cases reaching as many as >100 electrons per ZnO nanocrystal, but in every case examined to date this chemistry maximizes at a well-defined average electron density of ⟨Nmax⟩ ≈ (1.4 ± 0.4) × 1020 cm–3. The origins of this maximum have never been identified. Here, we use a solvated redox indicator for in situ determination of reduced ZnO nanocrystal redox potentials. The Fermi levels of various photodoped ZnO Nanocrystals possessing on ave...
