High-Pressure Structural Transformations in Semiconductor Nanocrystals

Tolbert, Sarah H.; Alivisatos, A. Paul

doi:10.1146/annurev.pc.46.100195.003115

Cited by 278 publications

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“…The melting temperatures of metal clusters is size dependent (51). Pressure-induced structural transformations are more facile for smaller clusters and have lower activation energy (52).…”

Section: Studies Of Structural and Electronic Properties Of Metal Nanmentioning

confidence: 99%

“…Pressure-induced structural transformations are more facile for smaller clusters and have lower activation energy (52). The nanocrystals are more perfect, because they cannot support dislocations because of their small size (51). The 2D phase diagram that is applicable to surface systems permits miscibility of metals to form solid solutions that are immiscible in 3 dimensions (53).…”

Section: Studies Of Structural and Electronic Properties Of Metal Nanmentioning

confidence: 99%

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Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

244

187

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The surface science of heterogeneous metal catalysis uses model systems ranging from single crystals to monodispersed nanoparticles in the 1-10 nm range. Molecular studies reveal that bond activation (C-H, H-H, C-C, CAO) occurs at 300 K or below as the active metal sites simultaneously restructure. The strongly adsorbed molecules must be mobile to free up these sites for continued turnover of reaction. Oxide-metal interfaces are also active for catalytic turnover. Examples using C-H and CAO activation are described to demonstrate these properties. Future directions include synthesis, characterization, and reaction studies with 2D and 3D monodispersed metal nanoclusters to obtain 100% selectivity in multipath reactions. Investigations of the unique structural, dynamic, and electronic properties of nanoparticles are likely to have major impact in surface technologies. The fields of heterogeneous, enzyme, and homogeneous catalysis are likely to merge for the benefit of all three.catalytic bond activation ͉ high selectivity catalyst design ͉ molecular ingredients of catalysis M etal containing catalysts are clusters of 1-10 nm in size. These are grouped into three types: heterogeneous catalysts that are embedded in high surface area supports, usually oxides, to optimize their surface area and thus the number of molecules they produce per second and also to optimize their thermal and chemical stability. They are used mostly at high temperatures (400-800 K) and in the presence of vapor phase reactants and product molecules. Enzyme catalysts operate in solution, mostly in water near 300 K, and the metal-containing active sites are surrounded by proteins that maintain structural mobility (1). Homogeneous catalysts function in the same solution in which the reactant and product molecules are dissolved, mostly in organic solvents, and used in the 300-500 K temperature range. Because of the different operating conditions and for reasons of history, the three fields of catalysis developed independently and became separate fields of science within different subdisciplines of chemistry. Heterogeneous catalysis was practiced mostly by physical chemists and chemical engineers, enzyme catalysis by biochemists, and homogeneous catalysis by inorganic and organometallic chemists.Catalytic reactions are distinguished from stoichiometric reactions by having many turnovers per reacting active site producing 10 2 to 10 6 molecules per site. Some of these catalytic reactions are very fast. For instance, the catalytic oxidation of carbon monoxide (CO) produces thousands of CO 2 molecules per metal surface site per second above ignition where the exothermicity of the process makes it self-sustaining in temperature and the reaction rate is only limited by the speed of transport of molecules to and from the catalyst surface (2-4). Ethylene hydrogenation, another exothermic reaction, turns over to produce ethane Ϸ10 times per metal surface site per second at 300 K on Pt(111) (5). The catalytic conversion of n-hexane to benzene or to branched...

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“…The melting temperatures of metal clusters is size dependent (51). Pressure-induced structural transformations are more facile for smaller clusters and have lower activation energy (52).…”

Section: Studies Of Structural and Electronic Properties Of Metal Nanmentioning

confidence: 99%

Section: Studies Of Structural and Electronic Properties Of Metal Nanmentioning

confidence: 99%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

244

187

View full text Add to dashboard Cite

show abstract

“…5 In addition, for some materials there is evidence that the bulk modulus and equation of state depend on crystallite size. 5,6 The Young's modulus of some nanocrystalline materials may be a function of particle size for reasons of porosity. 7 On the other hand, a Mössbauer spectrometry study on nanocrystalline iron ͑␣-Fe͒ has indicated that the grain boundary regions have a bulk modulus approximately 15% of that of the interior crystalline regions.…”

Section: Introductionmentioning

confidence: 99%

Nanocrystalline iron at high pressure

Chen

Penwell

Krüger

et al. 2001

Journal of Applied Physics

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X-ray diffraction measurements were performed on nanocrystalline iron up to 46 GPa. For nanocrystalline ε-Fe, analysis of lattice parameter data provides a bulk modulus, K, of 179±8 GPa and a pressure derivative of the bulk modulus, K′, of 3.6±0.7, similar to the large-grained control sample. The extrapolated zero-pressure unit cell volume of nanocrystalline ε-Fe is 22.9±0.2 Å3, compared to 22.3±0.2 Å3 for large-grained ε-Fe. No significant grain growth was observed to occur under pressure.

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“…A cubic to trigonal structural distortion along a 3-fold rotational axis was discovered by careful and comprehensive analysis of the apparent lattice parameter and full width at half maximum, which are strongly dependent upon the Miller index and crystal size. 1 In the past fifteen years, much attention has been paid to the high pressure behavior of nanomaterials, especially the pressure-induced structural transformations in semiconductor 1O nanocrystals. I -In contrast, there are few reports on structural transformations and distortions in noble metals under high pressure due to their close-packed structures.…”

mentioning

confidence: 99%

Size Dependence of Cubic to Trigonal Structural Distortion in Silver Micro- and Nanocrystals under High Pressure

et al. 2008

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Silver micro-and nanocrystals with sizes of -2-3.5 llm and -50-100 nm were uniaxially compressed under nonhydrostatic pressures (strong deviatoric stress) up to -30 GPa at room temperature in a symmetric diamond-anvil cell and studied in situ using angle-dispersive synchrotron X-ray diffraction. A cubic to trigonal structural distortion along a 3-fold rotational axis was discovered by careful and comprehensive analysis of the apparent lattice parameter and full width at half maximum, which are strongly dependent upon the Miller index and crystal size. 1 In the past fifteen years, much attention has been paid to the high pressure behavior of nanomaterials, especially the pressure-induced structural transformations in semiconductor 1O nanocrystals. I -In contrast, there are few reports on structural transformations and distortions in noble metals under high pressure due to their close-packed structures. It is generally accepted that sub millimeter crystals of silver (~149 !lm) and palladium (~250 Jlll1) are stable in the face-centered cubic (fcc) structure at room temperature up to at least 91. Two samples of conventional, irregularly-structured Ag crystals were purchased from Aldrich and used in our comparative study. They have reported average sizes and purities of2-3.5 Jlll1 and 99.9+%and <100 nm and 99.5%, respectively and are referred to as micro-and nano-Ag powders from hereon. Figure 1 shows representative scanning and transmission electron micrographs (SEM and TEM, respectively) of the Ag samples. These samples were uniaxially compressed under nonhydrostatic pressures up to -30 OPa in a symmetric diamond-anvil cell (DAC) and studied in situ using angle-dispersive synchrotron X-ray diffraction. Two ruby grains, located in the center and at the edge of the samples, respectively, were used for pressure calibration and radial pressure gradient estimation. 17 Detailed experimental procedures are similar to our previous report. 162 Figure 2 shows X-ray diffraction patterns, up to ~30 GPa, for the micro-and nano-Ag powders.From first analysis, it appeared that no phase transfonnations or distortions occurred because no splits, disappearances, or appearances of the diffraction peaks were observed. But when the d-spacing of the (200) peak was carefully compared with that of the (111) The apparent lattice parameters a200 and alll and their ratio a200/al II for the nano-Ag powder are shown in Figure 3a and Figure 3b, respectively. It is well-known that ahkl of Ag with the idealized fcc structure is not dependent upon the Miller index; however, according to Figure 3, it becomes apparent that ahktCP) in the nano-Ag is actually strongly dependent upon the Miller index when P > 1.9 OPa. In general, a200, was always larger than the corresponding alII and the higher the pressure, the larger the relative difference (within the pressure range of 0 to 11.2 GPa). Specifically, the relative difference at ambient pressure was less than 0.03% but increased to 0.37% at a pressure of 11.2 GPa. Beyond 11.2 GPa, this difference d...

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High-Pressure Structural Transformations in Semiconductor Nanocrystals

Cited by 278 publications

References 0 publications

Clusters, surfaces, and catalysis

Clusters, surfaces, and catalysis

Nanocrystalline iron at high pressure

Size Dependence of Cubic to Trigonal Structural Distortion in Silver Micro- and Nanocrystals under High Pressure

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