| 1. |
- Balmes, Olivier, et al.
(författare)
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Cryo-TEM observation of 3-dimensionally ordered aggregates of 5-nm gold particles in organic solvents
- 2004
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Ingår i: Journal of Nanoparticle Research. - : Springer Science and Business Media LLC. - 1572-896X .- 1388-0764. ; 6:6, s. 569-576
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we show evidence for the assembly of ordered 3-dimensional aggregates of 5-nm gold particles in toluene, 1-octanol, n-decane, and chloroform. The use of plunge-freezing allows to freeze the solution containing the aggregates at a rate which does not allow reorganisation of the particles during sample preparation. The samples were then observed using cryo-transmission electron microscopy (cryo-TEM) showing that most of the particles were part of ordered aggregates, thus proving that organisation already exists in solution. In some cases, the stability of the sample under the electron beam made it possible to record several pictures of the same aggregate at different angles and build animated tilt series.
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| 2. |
- Balmes, Olivier, et al.
(författare)
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Homogeneous surface-enhanced Raman scattering observed from self-assembled gold nanoparticle films deposited from the liquid-liquid interface
- 2005
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Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031. ; 37:2, s. 189-193
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembled gold nanoparticle film deposited from the liquid-liquid interface has been fabricated, and homogeneous surfaceenhanced Raman scattering (SERS) of R6G molecules on the film has been observed. The SERS enhancement factor of the film is estimated to be in the range 10(8)-10(10). Occasionally, there are some sudden jumps in the Raman signal, where the signal is increased a few times. Such jumps are probably caused by single-molecule SERS in some extremely "hot" sites. (c) 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Balmes, Olivier, et al.
(författare)
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Imaging atomic structure in metal nanoparticles using high-resolution cryo-TEM
- 2006
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Ingår i: Microscopy and Microanalysis. - 1435-8115. ; 12:2, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown, by imaging gold (200) planes, that it is possible to achieve better than 0.20-nm structural resolution in cryo-transmission electron microscopy (cryo-TEM). This has been done using commercially available cryo equipment and using a 300-kV field emission gun (FEG) TEM. The images of 15-nm gold particles embedded in amorphous frozen water clearly show the (111) planes (separated by 0.235 nm) in gold. Fourier transform demonstrates the presence of (200) planes in the image, proving a resolution of better than 0.20 nm. The experimental results are Supported by image simulations using the multislice method. These simulations suggest that it should be possible to achieve the same resolution even in smaller particles and particles of lighter elements. The crucial experimental problem to overcome is keeping the thickness of the amorphous film low and to work at low electron dose conditions.
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| 4. |
- Balmes, Olivier, et al.
(författare)
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Self-healing and self-organized gold nanoparticle films at a water/organic solvent interface
- 2006
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 0000-0000. ; 6:1, s. 130-134
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Tidskriftsartikel (refereegranskat)abstract
- Gold nanoparticles (5 nm and 20 nm) have been synthesized and stabilized with mercaptoundecanol. These particles, although insoluble in water or common organic solvents, spread as a thin film at the liquid-liquid interface between a water phase and an organic phase. Films of these gold nanoparticles have been observed both by conventional transmission electron microscopy of deposited samples and by cryo-transmission electron microscopy of plunge-frozen samples. The film can be monolayered and extend over centimeter-sized areas. The particle films spontaneously re-assemble and self-organize at the interface when disrupted. This self-healing capacity of the film should make it possible to build a device for continuous production and deposition of the film.
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| 5. |
- Carlsson, A, et al.
(författare)
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The first structure determination of nanosized colloidal particles of Pd3P by high-resolution electron microscopy
- 1998
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Ingår i: Angewandte Chemie (International edition). - 1433-7851. ; 37:9
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Tidskriftsartikel (refereegranskat)abstract
- The exact three-dimensional structure of a nanosized colloidal particle of Pd3P was determined directly from high-resolution transmission electron microscopy (HRTEM) images that were recorded in several crystallographic directions. An HRTEM image recorded along [011] is shown on the right. The cores of the particles were excluded from the analysis because of severe multiple diffraction.
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| 6. |
- Chen, Wei, et al.
(författare)
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Crystal field, phonon coupling and emission shift of Mn2+ in ZnS:Mn nanoparticles
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89, s. 1120-1129
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Tidskriftsartikel (refereegranskat)abstract
- The Mn2+ emission wavelengths are at 591, 588, 581 and 570 nm, respectively, for the similar to 10, similar to4.5, similar to3.5 nm sized nanoparticles and the ZnS:Mn nanoparticles formed in an ultrastable zeolite-Y. To reveal the cause for the shift, the crystal field and phonon coupling were investigated. The results show that the predominant factor for the shift is the phonon coupling, whose strength is size dependent and is determined by both the size confinement and the surface modification of the nanoparticles. Although the crystal field strength decreases with the decreasing of the particle size, its change has little contribution to the emission shift of Mn2+ in ZnS:Mn nanoparticles. (C) 2001 American Institute of Physics.
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| 7. |
- Chen, Wei, et al.
(författare)
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Energy structure and fluorescence of Eu2+ in ZnS:Eu nanoparticles
- 2000
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Ingår i: Physical Review B. - 1098-0121. ; 61:16, s. 11021-11024
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Tidskriftsartikel (refereegranskat)abstract
- Eu2+-doped ZnS nanoparticles with an average size of around 3 nm were prepared, and an emission band around 530 nm was observed. By heating in air at 150 degrees C, this emission decreased, while the typical sharp line emission of Eu3+ increased. This suggests that the emission around 530 nm is from intraion transition of Eu2+: In bulk ZnS:Eu2+, no intraion transition of Eu2+ was observed because the excited states of Eu2+ are degenerate with the continuum of the ZnS conduction band. We show that the band gap in ZnS:Eu2+ nanoparticles opens up due to quantum confinement, such that the conduction band of ZnS is higher than the first excited state of Eu2+, thus enabling the intraion transition of Eu2+ to occur.
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| 8. |
- Chen, W, et al.
(författare)
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Full-Color Emission and Temperature Dependence of the Luminescence in Poly-P-phenylene ethynylene-ZnS/Mn2+ Composite Particles
- 2003
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:27, s. 6544-6551
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a nanocomposite material composed of anionic poly(phenylene ethynylene) (aPPE) polymer particles and ZnS/Mn2+ nanoparticles is described, and its luminescence properties are investigated. aPPE particles have two emissions, one in the blue (460 nm) and the other in the green (490 nm), that are assigned to the 0-0 transition and an excimer, respectively. ZnS/Mn2+ nanoparticles have an emission at 596 nm that is due to the T-4(1)-(6)A(1) transition of Mn2+ and an emission at 706 nm that is ascribed to defect-related luminescence. The blue, green, yellow, and red emissions make the composite a potential material for full-color displays. More interestingly, the relative intensities of the different emissions may be varied by changing the excitation energy. Infrared spectra reveal that interactions exist between the two particles; however, photoluminescence excitation and emission spectra as well as observations of luminescence lifetimes indicate that there is negligible energy transfer from the polymer particles to the ZnS/Mn2+ nanoparticles. Temperature studies reveal that the ZnS/Mn2+ particles in the nanocomposite have a significantly reduced thermal quenching energy relative to that of bare ZnS/Mn2+ nanoparticles. In addition, between room temperature and 90 degreesC, the luminescence of the ZnS/Mn2+ nanoparticles at 596 nm increases in intensity with increasing temperature. This surprising phenomenon is attributed to thermoluminescence and thermal curing of the particle surface upon heating.
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| 9. |
- Chen, W, et al.
(författare)
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Size dependence of Eu2+ fluorescence in ZnS:Eu2+ nanoparticles
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:5, s. 2671-2675
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Tidskriftsartikel (refereegranskat)abstract
- The emission bands of the 4.2, 3.2 and 2.6 nm sized ZnS:Eu2+ nanoparticles are peaking at 670, 580 and 520 nm, respectively. The emission of the 4.2 nm sized nanoparticles originates from the recombination of the Eu2+-bound exciton, while the emission of the 3.2 and 2.6 nm sized nanoparticles is from the Eu2+ intra-ion transition of 4f(6)5d(1)(t(2g))-4f(7). Possible mechanisms for the size dependence of the 4f(6)5d(1)(t(2g))-4f(7) transition of Eu2+ in ZnS:Eu2+ nanoparticles were investigated, and it was concluded that the decreases in the electron-phonon coupling and in crystal field strength upon a decrease in size are the two major factors responsible for the shift. (C) 2001 American Institute of Physics.
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| 10. |
- Chen, W, et al.
(författare)
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Structure, luminescence, and dynamics of Eu2O3 nanoparticles in MCM-41
- 2002
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:28, s. 7034-7041
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Tidskriftsartikel (refereegranskat)abstract
- The structure, luminescence spectroscopy, and lifetime decay dynamics of Eu2O3 nanoparticles formed in MCM-41 have been investigated. Both X-ray diffraction and high-resolution transmission electron microscopic observations indicate that Eu2O3 nanoparticles of monoclinic structure are formed inside channels of MCM-41 by heating at 140 degreesC. However, heat treatment at 600 or 700 degreesC causes migration of Eu2O3 from the MCM-41 channels, forming nanoparticles of cubic structure outside the MCM-41 channels. After heating to 900 degreesC, some of the cubic Eu2O3 particles change to monoclinic Eu2O3, and the MCM-41 structure breaks down and a different or disordered phase is formed. The feature of the hypersensitive D-5(0) --> F-7(2) emission profile of Eu3+ is used to follow the structural changes. In the luminescence spectrum of the sample prepared at 140 degreesC, the emission spectrum is dominated by peaks at 615 and 623 nm, while in the other samples a peak at 612 nm is prevalent. Photoluminescence lifetimes show the existence of short (<1 mus) and long (microsecond to millisecond) components for each sample. The fast decay is attributed to quenching by surface states of the nanoparticles or energy transfer to the MCM-41, while the longer time decays show the effects of concentration quenching. The monoclinic sample prepared at 140 degreesC shows a higher luminescence intensity than the cubic samples or the bulk powder. These observations indicate that MCM-41 as a template can be used for making and stabilizing monoclinic rare earth oxides, which normally are stable only at high temperatures and high pressures. More importantly, the nanophase Eu2O3/MCM-41 composite materials formed at low temperatures might represent a new type of efficient luminescence material with fast response, with potential applications in lighting and displays.
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