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The Journal of Physical Chemistry C 09/2012; 116:22043-22050. · 4.80 Impact Factor
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ABSTRACT: Spontaneous separation of single from polycrystalline 5 nm gold nanocrystals (NCs) is observed in colloidal solution. This segregation takes place upon self-assembling of single crystalline NCs at the air-solvent interface and in precipitated superlattices. Polycrystalline NCs are observed to remain in the suspension. Transmission electron microscopy analysis of the size distribution of NCs issued from the different populations indicates that the NC size does not change from each other, excluding therefore any size segregation in this process. Using both low-frequency Raman scattering and X-ray diffraction provides reliable characterization of nanocrystallinity for each population of NCs, thus confirming the crystallinity segregation. The single crystalline NCs are found by electron diffraction to self-assemble into close-packed superlattices with long-range translational and orientational ordering, while polycrystalline NCs behave like spheres with no preferential orientation. The face-to-face orientational ordering, which is only observed for single crystalline NCs, supports the relevance of the specific crystallinity-related morphologies of these NCs in their better ability to self-assemble. Exploiting this spontaneous segregation would open up a simple alternative to other demanding routes for controlling crystallinity of nanocrystals and optimizing their properties for potential applications.
Nano Letters 09/2012; 12(10):5292-8. · 13.20 Impact Factor
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ABSTRACT: Natural systems give the route to design periodic arrangements with mesoscopic architecture using individual nanocrystals as building blocks forming colloidal crystals or supracrystals. The collective properties of such supracrystals are one of the main driving forces in materials research for the 21st century with potential applications in electronics or biomedical environments. Here we describe two simultaneous supracrystal growth processes from gold nanocrystal suspension, taking place in solution and at the air-liquid interface. Furthermore, the growth processes involve the crystallinity selection of nanocrystals and induce marked changes in the supracrystal mechanical properties.
Journal of the American Chemical Society 02/2012; 134(8):3714-9. · 9.91 Impact Factor
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ABSTRACT: Solutions of LiCl and of NaCl in ultrapure water were studied through Rayleigh/Brillouin scattering as a function of the concentration (molarity, M) of dissolved salt from 0.2 M to extremely low concentration (2 × 10(-17) M). The Landau-Placzek ratio, R/B, of the Rayleigh scattering intensity over the total Brillouin was measured thanks to the dynamically controlled stability of the used Fabry-Perot interferometer. It was observed that the R/B ratio follows two stages as a function of increasing dilution rate: after a strong decrease between 0.2 M and 2 × 10(-5) M, it increases to reach a maximum between 10(-9) M and 10(-16) M. The first stage corresponds to the decrease of the Rayleigh scattering by the ion concentration fluctuations with the decrease of salt concentration. The second stage, at lower concentrations, is consistent with the increase of the Rayleigh scattering by long-lived sub-microscopic bubbles with the decrease of ion concentration. The origin of these sub-microscopic bubbles is the shaking of the solutions, which was carried out after each centesimal dilution. The very long lifetime of the sub-microscopic bubbles and the effects of aging originate in the electric charge of bubbles. The increase of R/B with the decrease of the low salt concentration corresponds to the increase of the sub-microscopic bubble size with the decrease of concentration, which is imposed by the bubble stability due to the covering of the surface bubble by negative ions.
Physical Chemistry Chemical Physics 02/2012; 14(12):4125-32. · 3.57 Impact Factor
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Gopalkrishna M Bhalerao,
Olivier Cambon,
Julien Haines,
Claire Levelut, Alain Mermet,
Sergey Sirotkin,
Bertrand Ménaert,
Jérôme Debray,
Isabelle Baraille,
Clovis Darrigan,
Michel Rérat
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ABSTRACT: Experimental and theoretical studies have been performed to demonstrate the high performance of the novel piezoelectric material GaAsO(4). Hydrothermally grown single crystals of α-quartz phase GaAsO(4) were studied by Brillouin spectroscopy to determine elastic constants. Experimentally obtained values of C(11), C(66), C(33), C(44), C(14) and C(12) are 59.32, 19.12, 103.54, 30.70, 1.7, and 21.1 GPa, respectively. Elastic and piezoelectric tensors were also calculated by a first principles method in this work, leading to a very good agreement with experimental results and confirming the values of elastic components obtained indirectly such as C(14) and the negligible piezoelectric correction for C(11). The thermal behavior of the elastic constant corresponding to the [100] longitudinal L mode (C(11)) was studied up to 1137 K to estimate potential piezoelectric performance. It was found that the thermal behavior is linear up to 1273 K which is just below the thermal decomposition temperature of 1303 K. High thermal stability can be linked to the higher polarizability of large cations Ga and As because of neighboring oxygen atoms. On the basis of thermal behavior, GaAsO(4) is a promising material for high temperature piezoelectric applications.
Inorganic Chemistry 10/2010; 49(20):9470-8. · 4.60 Impact Factor
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ABSTRACT: Au nanocrystals (NCs) with different crystalline structures and related morphologies are unselectively synthesized using an organometallic route. The acoustic vibrations of these NCs are studied by plasmon mediated low-frequency Raman scattering (LFRS). A splitting of the quadrupolar vibration mode is pointed out in the LFRS spectrum. Comparison of the measured frequencies with calculations and careful examination of the NCs morphologies by transmission electron microscopy ascertain this splitting as being an effect of crystallinity. The excitation dependence of the LFRS spectra is interpreted by the shape-selection of the NCs via plasmon-vibration coupling. These results give new insights into the crystallinity influence on both the vibrations of the NCs and their coupling with plasmons and demonstrate the relevance of elastic anisotropy in monodomain NCs.
ACS Nano 06/2010; 4(6):3489-97. · 10.77 Impact Factor
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ABSTRACT: The inelastic scattering of neutrons by nanoparticles due to acoustic vibrational modes (energy below 10 meV) confined in nanoparticles is calculated using the Zemach-Glauber formalism. Such vibrational modes are commonly observed by light-scattering techniques (Brillouin or low-frequency Raman scattering). We also report high-resolution inelastic neutron-scattering measurements for anatase TiO2 nanoparticles in a loose powder. Factors enabling the observation of such vibrations are discussed. These include a narrow nanoparticle size distribution which minimizes inhomogeneous broadening of the spectrum and the presence of hydrogen atoms oscillating with the nanoparticle surfaces which enhances the number of scattered neutrons.
Phys. Rev. B. 12/2008; 78(24).
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ABSTRACT: This Comment corrects some errors which appeared in the calculation of an elastic sphere eigenenergies. As a result, the symmetry of the mode having the lowest frequency is changed. Also a direction for calculating the damping of these modes for embedded elastic spheres is given.
Physical Review E 03/2004; 69(2 Pt 1):023901. · 2.26 Impact Factor
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