151
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Grünwald M, Dellago C. Transition state analysis of solid-solid transformations in nanocrystals. J Chem Phys 2009; 131:164116. [DOI: 10.1063/1.3253700] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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152
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Sohn JI, Joo HJ, Ahn D, Lee HH, Porter AE, Kim K, Kang DJ, Welland ME. Surface-stress-induced Mott transition and nature of associated spatial phase transition in single crystalline VO2 nanowires. NANO LETTERS 2009; 9:3392-3397. [PMID: 19785429 DOI: 10.1021/nl900841k] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We demonstrate that the Mott metal-insulator transition (MIT) in single crystalline VO(2) nanowires is strongly mediated by surface stress as a consequence of the high surface area to volume ratio of individual nanowires. Further, we show that the stress-induced antiferromagnetic Mott insulating phase is critical in controlling the spatial extent and distribution of the insulating monoclinic and metallic rutile phases as well as the electrical characteristics of the Mott transition. This affords an understanding of the relationship between the structural phase transition and the Mott MIT.
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Affiliation(s)
- Jung Inn Sohn
- Nanoscience Centre, University of Cambridge, Cambridge CB3 0FF, United Kingdom
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153
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Shape evolution of CdSe nanocrystals in vegetable oils: A synergistic effect of selenium precursor. Colloids Surf A Physicochem Eng Asp 2009. [DOI: 10.1016/j.colsurfa.2009.09.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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154
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Frenzel J, Seifert G, Zahn D. Surface Effects in the Pressure-Induced Structural Transformation of a ZnO Nanorod. Z Anorg Allg Chem 2009. [DOI: 10.1002/zaac.200900260] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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155
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Wittenberg JS, Merkle MG, Alivisatos AP. Wurtzite to rocksalt phase transformation of cadmium selenide nanocrystals via laser-induced shock waves: transition from single to multiple nucleation. PHYSICAL REVIEW LETTERS 2009; 103:125701. [PMID: 19792445 DOI: 10.1103/physrevlett.103.125701] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Indexed: 05/28/2023]
Abstract
The behavior of CdSe nanocrystals shocked to stresses of 2-3.75 GPa has been studied. Above 3 GPa a near-complete disappearance of the first excitonic feature and broadening of the low-energy absorption edge were observed, consistent with a wurtzite to rocksalt structural transformation. The transformation pressure is reduced relative to hydrostatic compression in a diamond anvil cell, and the rate increases, attributed to shock induced shear stress along the reaction coordinate. The especially rapid rate observed for a 3.75 GPa shock suggests multiple nucleation events per particle.
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Affiliation(s)
- Joshua S Wittenberg
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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156
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Dong Z, Song Y. Pressure-induced morphology-dependent phase transformations of nanostructured tin dioxide. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.08.060] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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157
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Khalessi AA, Liu CY, Apuzzo MLJ. Neurosurgery and quantum dots: part I--state of the art. Neurosurgery 2009; 64:1015-27; discussion 1027-8. [PMID: 19487880 DOI: 10.1227/01.neu.0000347889.62762.3f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
This article represents the first of a 2-part exploration of quantum dots (Qdots) and their application to neurological surgery. Spanning from materials science to immunology, this initial review traces the marriage of imaging physics to biochemical specificity. Qdot science now stands poised to dramatically advance the diagnosis and therapy of neurosurgical conditions. Qdot research efforts currently involve several disciplines; this comprehensive review therefore considers multiple fields of inquiry. This first installment discusses 1) Qdot physical properties, 2) established biological and in vivo properties, 3) magnetic resonance imaging applications, and (4) existing cardiovascular and oncologic research. Finally, this review establishes the existing bounds of Qdot possibilities. The second concept article details future endovascular diagnostic and therapeutic methods derived from these seminal advances.
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Affiliation(s)
- Alexander A Khalessi
- Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
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158
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Senevirathne K, Tackett R, Kharel PR, Lawes G, Somaskandan K, Brock SL. Discrete, dispersible MnAs nanocrystals from solution methods: phase control on the nanoscale and magnetic consequences. ACS NANO 2009; 3:1129-1138. [PMID: 19358564 DOI: 10.1021/nn900194f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Nanocrystals of thermodynamically stable alpha-MnAs (hexagonal NiAs-type) and metastable beta-MnAs (orthorhombic MnP-type) have been synthesized by the reaction of triphenylarsine oxide (Ph(3)AsO) and dimanganesedecacarbonyl (Mn(2)CO(10)) at temperatures ranging from 250 to 330 degrees C in the presence of the coordinating solvent trioctylphosphine oxide (TOPO). Morphologically, both alpha- and beta-MnAs nanoparticles adopt a core-shell type structure with a crystalline core and low-contrast noncrystalline shell. In contrast to prior studies on MnAs particles, disks, and films, the present bottom-up synthesis yields discrete, dispersible MnAs nanoparticles without a structural support. Even in the absence of epitaxial strain, the lattice parameters of the nanocrystals are decreased relative to bulk MnAs, resulting in a volume decrease of 0.35% in alpha-MnAs and 0.38% in beta-MnAs nanoparticles. In contrast to bulk MnAs, where the ferromagnetic phase transition upon warming through 313-317 K is concomitant with a structure change from ferromagnetic alpha- to paramagnetic beta-MnAs, powder X-ray diffraction studies suggest there is no conversion of alpha-MnAs to beta over the temperature range 298-343 K. Moreover, magnetic measurements suggest that both alpha- and beta-MnAs are ferromagnetic with T(C) approximately 315 K. Partial phase transformation of beta-MnAs nanoparticles into thermodynamically stable alpha-MnAs occurs slowly over time (i.e., months) at room temperature. However, there is no associated change in magnetization, suggesting the ferromagnetism observed in beta-MnAs is intrinsic and cannot be attributed to alpha-MnAs impurities.
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159
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Grünwald M, Dellago C. Nucleation and growth in structural transformations of nanocrystals. NANO LETTERS 2009; 9:2099-2102. [PMID: 19435382 DOI: 10.1021/nl900609d] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Using transition path sampling computer simulations, we reveal the nucleation mechanism of a pressure-induced structural transformation in CdSe nanocrystals. Consistent with experiments, the thermodynamic transition pressure of the transformation increases with decreasing crystal size. Through transition state analysis, we identify the critical nuclei and characterize them by calculating activation enthalpies and volumes. Our simulations reproduce the trends with crystal size observed in experiments. This result supports the observed transformation mechanism, which consists of nucleation on the crystal surface and growth by sliding of parallel crystal planes.
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Affiliation(s)
- Michael Grünwald
- Faculty of Physics and Center for Computational Materials Science, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria.
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160
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Zhao Z, Lin J, Jia T, Sun Z, Wang Z. Optical limiting of niobic tellurite glass induced by self-trapped exciton absorption of the AgCl nanocrystal dopant. Sci Bull (Beijing) 2009. [DOI: 10.1007/s11434-009-0143-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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161
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162
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Rawalekar S, Verma S, Kaniyankandy S, Ghosh HN. Interfacial electron transfer dynamics in quinizarin sensitized ZnS nanoparticles: monitoring charge transfer emission. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:3168-3172. [PMID: 19437781 DOI: 10.1021/la803503c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Water soluble cubic ZnS nanoparticles (NPs) have been synthesized at room temperature by using 3-mercaptopropionic acid (MPA) as a modifier molecule and characterized by X-ray diffraction (XRD), steady-state absorption, and emission spectroscopy. Electron transfer (ET) dynamics have been carried out in ZnS semiconductor nanoparticles and quinizarin (Qz) molecules as studied by picosecond time-resolved fluorescence spectroscopy. We have proposed that electron injection takes place from photoexcited Qz molecules into the surface states of wide band gap ZnS NPs. We have revealed that the formation of a charge transfer complex between the Qz molecule and ZnS nanoparticles facilitates electron injection into the surface states of nanoparticles. In the present investigation, we have detected charge transfer (CT) emission in the Qz-ZnS system as the injected electrons from surface states return back to the parent Qz cation radical. We have determined back ET rates by monitoring the CT emission.
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Affiliation(s)
- Sachin Rawalekar
- Radiation and Photochemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India
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163
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Corrado C, Jiang Y, Oba F, Kozina M, Bridges F, Zhang JZ. Synthesis, Structural, and Optical Properties of Stable ZnS:Cu,Cl Nanocrystals. J Phys Chem A 2009; 113:3830-9. [DOI: 10.1021/jp809666t] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Carley Corrado
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Cruz, California 95064
| | - Yu Jiang
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Cruz, California 95064
| | - Fadekemi Oba
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Cruz, California 95064
| | - Mike Kozina
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Cruz, California 95064
| | - Frank Bridges
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Cruz, California 95064
| | - Jin Z. Zhang
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Cruz, California 95064
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164
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Du YP, Zhang YW, Sun LD, Yan CH. Optically active uniform potassium and lithium rare earth fluoride nanocrystals derived from metal trifluroacetate precursors. Dalton Trans 2009:8574-81. [DOI: 10.1039/b909145a] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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165
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Nanodomain fragmentation and local rearrangements in CdSe under pressure. Proc Natl Acad Sci U S A 2008; 105:19612-6. [PMID: 19052229 DOI: 10.1073/pnas.0805235105] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Structural transformations in extended solids result from local atomic rearrangements and phase growth mechanisms. A broad class of technologically relevant properties critically depends on local structural issues connected with domain sizes, domain boundary geometries, and defects. However, a precise understanding of structural transformation mechanisms and domain formation is still an open question. Here, we demonstrate the feasibility of very detailed mechanistic investigations in real materials as a prerequisite for intelligent property control. We address the problem of domain fragmentation in bulk CdSe under pressure, jointly by molecular dynamics simulations, high-pressure experiments, and HR-TEM imaging. We show that domain fragmentation is taking place in the high-pressure regime, where nucleation events generate both zinc blende (B3) and wurtzite (B4) structural motifs and, in turn, cause the final lamellar appearance observable by high-resolution TEM. A changed nucleation pattern and a modified B3/B4 ratio represents the system's response to modified external stress conditions.
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166
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Epifani M, Pellicer E, Arbiol J, Sergent N, Pagnier T, Morante JR. Capping ligand effects on the amorphous-to-crystalline transition of CdSe nanoparticles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:11182-11188. [PMID: 18729490 DOI: 10.1021/la801859z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Amorphous CdSe nanoparticles were prepared by a base-catalyzed room-temperature reaction between cadmium nitrate and selenourea, with dodecanethiol as a capping ligand. The nanoparticle size could be controlled from 1.9 to 3.6 nm by increasing the water concentration in the reaction. When the nanoparticles were heated in a pyridine suspension, excitonic peaks appeared in the initially featureless optical absorption spectra. By changing the suspension solvent and the capping ligand and its concentration, it was shown that the dynamic surface exchange between the ligand and pyridine controls the crystallization process. This phenomenon was interpreted as a surface rigidity effect imposed by the ligand, whose importance was separately evidenced on the dried nanoparticles by the evolution of X-ray diffraction patterns and Raman spectra. In particular, both techniques showed that a threshold temperature is needed before crystallization occurs, and such a threshold was related to ligand desorption. The surface effect was directly visualized by high-resolution transmission electron microscopy observations of the amorphous particles, where crystallization under the electron beam was observed to start by the formation of a crystalline nucleus in the nanoparticle interior and then to extend to the whole structure.
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Affiliation(s)
- Mauro Epifani
- Consiglio Nazionale delle Ricerche - Istituto per la Microelettronica ed i Microsistemi (C.N.R.-I.M.M.), via Monteroni, I-73100 Lecce, Italy.
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167
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Jørgensen JE, Jensen T, Hanson J. Hydrothermal synthesis of nanocrystalline ZnSe: An in situ synchrotron radiation X-ray powder diffraction study. J SOLID STATE CHEM 2008. [DOI: 10.1016/j.jssc.2008.04.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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168
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ZnSe colloidal nanoparticles synthesized by solvothermal method in the presence of ZrCl4. J Colloid Interface Sci 2008; 322:473-7. [DOI: 10.1016/j.jcis.2008.04.021] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Revised: 03/29/2008] [Accepted: 04/07/2008] [Indexed: 11/16/2022]
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169
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Yang C, Liu Y, Sun H, Guo D, Li X, Li W, Liu B, Zhang X. Pressure-induced transition-temperature reduction in ZnS nanoparticles. NANOTECHNOLOGY 2008; 19:095704. [PMID: 21817686 DOI: 10.1088/0957-4484/19/9/095704] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The study of the structural transition in nanoscale materials is of particular interest for their potential applications. In the present study, we have observed a lower temperature T = 250 °C for the phase transition from the sphalerite structure to the wurtzite structure in ZnS nanoparticles under a pressure of 1 GPa, as compared to those, T = 400 and 1020 °C, for ZnS nanoparticles and bulk ZnS under normal pressure, respectively. The reduced transition temperature is attributed to the applied pressure leading to tight particle-particle contacts, which change the surface (or interfacial) environment of the nanoparticles and thus their surface (or interfacial) energy.
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Affiliation(s)
- Cuizhuo Yang
- State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, 066004 Qinhuangdao, People's Republic of China
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170
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Guo Q, Zhao Y, Mao WL, Wang Z, Xiong Y, Xia Y. Cubic to tetragonal phase transformation in cold-compressed Pd nanocubes. NANO LETTERS 2008; 8:972-975. [PMID: 18237151 DOI: 10.1021/nl0731217] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Pd nanocubes with an average side length of approximately 10 nm were compressed up to 24.8 GPa in a diamond-anvil cell (DAC). In situ synchrotron X-ray diffraction was used to monitor structural changes, and a face-centered cubic (fcc) to face-centered tetragonal (fct) distortion was observed for the first time. This novel discovery not only provides new insights into the pressure-induced behavior of faceted nanocrystals of palladium and other noble metals but also gives guidance for finding new phases in close-packed metals.
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Affiliation(s)
- Qixun Guo
- Los Alamos Neutron Science Center, Los Alamos National Laboratory, NM 87545, USA.
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171
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Zhao Y, Shen T, Zhang J. HighP-TNano-Mechanics of Polycrystalline Nickel. NANOSCALE RESEARCH LETTERS 2007; 2:476-491. [PMID: 21794186 PMCID: PMC3246607 DOI: 10.1007/s11671-007-9095-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Accepted: 09/04/2007] [Indexed: 05/31/2023]
Abstract
We have conducted highP-Tsynchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volume-pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify "micro/local" yield due to high stress concentration at the grain-to-grain contacts and "macro/bulk" yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under highP-Tconditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 Tm) hardens nanocrystalline Ni, leading to an inverse Hall-Petch relationship. We explain this abnormal Hall-Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni.
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Affiliation(s)
- Yusheng Zhao
- LANSCE-LC, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
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172
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Chory C, Neder RB, Korsunskiy VI, Niederdraenk F, Kumpf C, Umbach E, Schumm M, Lentze M, Geurts J, Astakhov G, Ossau W, Müller G. Influence of liquid-phase synthesis parameters on particle sizes and structural properties of nanocrystalline ZnO powders. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/pssc.200775424] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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173
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Li J, Brill T. Kinetics of Solid Polymorphic Phase Transitions of CL-20. PROPELLANTS EXPLOSIVES PYROTECHNICS 2007. [DOI: 10.1002/prep.200700036] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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174
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Peng XH, Alizadeh A, Bhate N, Varanasi KK, Kumar SK, Nayak SK. First-principles investigation of strain effects on the energy gaps in silicon nanoclusters. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2007; 19:266212. [PMID: 21694089 DOI: 10.1088/0953-8984/19/26/266212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
First-principles density functional calculations were performed to study strain effects on the energy gaps in silicon nanoclusters with diameter ranging from 0.6 to 2 nm. Hydrostatic and non-hydrostatic strains have been found to affect the energy gaps differently. For the same strain energy density, non-hydrostatic strain leads to a significantly larger change in the energy gap of silicon clusters compared to that of the hydrostatic strain case. In contrast, hydrostatic and non-hydrostatic strain effects on the energy gaps of bulk Si or larger size Si quantum dots are comparable. Non-hydrostatic strains break the tetrahedral bonding symmetry in silicon, resulting in significant variation in the energy gaps due to the splitting of the degenerate orbitals in the clusters. Our results suggest that the combination of energy gaps and strains permits the engineering of photoluminescence in silicon nanoclusters and offers the possibility of designing novel optical devices and chemical sensors.
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Affiliation(s)
- X-H Peng
- General Electric Global Research Center, Niskayuna, NY 12309, USA. Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
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175
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Li K, Jiang H, Lian G, Wang Q, Zhao X, Cui D, Tao X. Investigation on the key factors in the hydrothermal synthesis of BN: The way of introducing sodium azide. ACTA ACUST UNITED AC 2007. [DOI: 10.1007/s11434-007-0255-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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176
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Zhuang Z, Peng Q, Liu J, Wang X, Li Y. Indium Hydroxides, Oxyhydroxides, and Oxides Nanocrystals Series. Inorg Chem 2007; 46:5179-87. [PMID: 17530840 DOI: 10.1021/ic061999f] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Indium hydroxides, oxyhydroxides, and oxides are important n-type semiconductors and have wide applications in material fields. In this Article, a series of In(OH)(3) and InOOH nanocrystals with different structures and morphologies, such as nanocubes, nanorods, multipods, and nanoparticles, have been synthesized selectively through a liquid-phase reaction, by adjusting the alkalinity and polarity of the solvent. It is found that InOOH multipods are in the orthorhombic phase and their arms grow along nonequivalent faces. Cubic and hexagonal In(2)O(3) can be obtained from In(OH)(3) and InOOH, respectively, while size and morphology can be maintained to a certain extent. Gas sensors were fabricated by using In(2)O(3), and a device based on the multipods shows the best responses to ethanol vapor. XRD, TEM, HRTEM, SEM, and SAED have been used to characterize these nanocrystals. This work provides a preliminary investigation into the structural-based gas-sensing properties of these nanocrystals.
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Affiliation(s)
- Zhongbin Zhuang
- Department of Chemistry, Tsinghua University, Beijing, 100084, Peoples Republic of China
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177
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Zhao Y, Zhang J, Clausen B, Shen TD, Gray GT, Wang L. Thermomechanics of nanocrystalline nickel under high pressure-temperature conditions. NANO LETTERS 2007; 7:426-32. [PMID: 17298011 DOI: 10.1021/nl062685s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We present a comparative study of thermomechanical properties of nano-polycrystalline nickel (nano-Ni) and micrometer-polycrystalline nickel (micron-Ni) by in situ high pressure-temperature (P-T) diffraction experiments. The yield strength of 2.35 GPa for the nano-Ni measured under high-pressure triaxial compression is more than three times that of the micron-Ni value. Contrary to tensile experiments of uniaxial loading, we observe significant work-hardening for the nano-Ni in high-pressure plastic deformation stage, whereas the micron-Ni experiences minor high-pressure work-softening and considerable energy dissipation into heat. The significantly reduced energy dissipation for the nano-Ni during the loading-unloading cycle indicates that the nanostructured materials can endure much greater mechanical fatigue in cyclic loadings. The nano-Ni exhibits steady grain growth during bulk plastic deformation at high-pressure loading, and drastic stress reduction and grain growth occur during the high P-T cycle. Our experiments utilized novel approaches to comparatively study micro- and nanostructured materials revealing recoverability of elastic/plastic deformations, strain corrections by diffraction elasticity ratio, and identifying dominances of stress relaxation, grain growth, and intrinsic residual stresses. The results should be of considerable interest to the fields of materials science, condensed matter, and computational physics.
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Affiliation(s)
- Yusheng Zhao
- LANSCE Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
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178
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Wang X, Li Y. Monodisperse nanocrystals: general synthesis, assembly, and their applications. Chem Commun (Camb) 2007:2901-10. [PMID: 17622427 DOI: 10.1039/b700183e] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This article summarizes the recent advances in the synthesis, assembly and applications of monodisperse nanocrystals, which may be suggestive for the designed synthesis and assemblies of target nanocrystals according to practical requirements.
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Affiliation(s)
- Xun Wang
- Department of Chemistry, Tsinghua University, Beijing, 100084, PR China
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179
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180
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Nicolas D, Masenelli B, Mélinon P, Bernstein E, Dujardin C, Ledoux G, Esnouf C. Structural transition in rare earth oxide clusters. J Chem Phys 2006; 125:171104. [PMID: 17100422 DOI: 10.1063/1.2390693] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Size effects, such as structure transition, have been reported in small clusters of alkali halide compounds. We extend the study to rare earth sesquioxide (Gd(2)O(3)) clusters which are as ionic as the alkali halide compounds, but have a more complicated structure. In a clean and controlled environment (ultra high vacuum), such particles are well crystallized, facetted and tend to adopt a rhombic dodecahedron shape. This indicates the major role of highly ionic bonds in preserving the crystal lattice even at small sizes (a few lattice parameter). Based on both cathodo-luminescence and transmission electron microscopy, we report the existence of a structural transition from bcc to monoclinic at small sizes.
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Affiliation(s)
- D Nicolas
- Université de Lyon, Lyon F-69003, France
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181
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Liu JF, Yin S, Wu HP, Zeng YW, Hu XR, Wang YW, Lv GL, Jiang JZ. Wurtzite-to-Rocksalt Structural Transformation in Nanocrystalline CoO. J Phys Chem B 2006; 110:21588-92. [PMID: 17064112 DOI: 10.1021/jp0648238] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hexagonal CoO nanocrystals are coarsened under hydrothermal conditions to investigate the effect of particle size on phase transformation and stability property. Structural stability and phase transformation of the hexagonal CoO phase have been investigated by X-ray powder diffraction with Rietveld refinement, transmission electron microscopy, X-ray absorption fine structure, and differential scanning calorimeter. It is found that the hexagonal CoO phase is a metastable phase, which increases its grain size from 50 to 250 nm for refluxing times from 1 to 6 h at 200 degrees C. After 12 h, cubic-structured CoO grains with an average grain size of 20 nm are observed, which spread around big hexagonal CoO grains. After about 24 h, only the cubic CoO phase with an average grain size of 25 nm is detected. The onset temperature of hexagonal-to-cubic phase transformation in CoO is estimated to be 378 degrees C by DSC, using a heating rate of 20 deg/min. The results obtained indicate that the hexagonal-to-cubic phase transformation in nanocrystalline CoO is by nucleation and growth mechanism, starting from the surface to the center of the hexagonal grains.
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Affiliation(s)
- J F Liu
- Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China
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182
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Dai Q, Li D, Chen H, Kan S, Li H, Gao S, Hou Y, Liu B, Zou G. Colloidal CdSe Nanocrystals Synthesized in Noncoordinating Solvents with the Addition of a Secondary Ligand: Exceptional Growth Kinetics. J Phys Chem B 2006; 110:16508-13. [PMID: 16913784 DOI: 10.1021/jp063126c] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The addition of a secondary ligand, trioctylphosphine oxide, in the synthesis of cadmium selenide nanocrystals performed in a system with oleic acid as the primary ligand and octadecene as the noncoordinating solvent gives rise to the improvement of nanocrystal size distribution. This phenomenon, which is more significant in the nucleation process than in the growth process, demonstrates that the existence of trioctylphosphine oxide allows for superior nucleation control and permits the facile and reproducible production of extremely small CdSe nanocrystals with narrow size distribution. A systematic study of the nanocrystal formation processes shows that the well-established colloidal nanocrystal growth mechanism, in which nucleation is followed by focusing of size distribution and ended with defocusing of size distribution, cannot be applied to our reactions. Instead, we observed an exceptional type of growth mechanism in which, after nucleation, clear defocusing instead of focusing follows; then slight focusing occurs.
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Affiliation(s)
- Quanqin Dai
- National Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
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183
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Grünwald M, Rabani E, Dellago C. Mechanisms of the wurtzite to rocksalt transformation in CdSe nanocrystals. PHYSICAL REVIEW LETTERS 2006; 96:255701. [PMID: 16907322 DOI: 10.1103/physrevlett.96.255701] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Indexed: 05/11/2023]
Abstract
We study the pressure-driven phase transition from the four-coordinate wurtzite to the six-coordinate rocksalt structure in CdSe nanocrystals with molecular dynamics computer simulations. With an ideal gas as the pressure medium, we apply hydrostatic pressure to spherical and faceted nanocrystals ranging in diameter from 25 to 62 A. In spherical crystals, the main mechanism of the transformation involves the sliding of (100) planes, but depending on the specific surface structure we also observe a second mechanism proceeding through the flattening of (100) planes. In faceted crystals, the transition proceeds via a five-coordinated hexagonal structure, which is stabilized at intermediate pressures due to dominant surface energetics.
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Affiliation(s)
- Michael Grünwald
- Faculty of Physics and Center for Computational Materials Science, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
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184
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Dalpian GM, Chelikowsky JR. Self-purification in semiconductor nanocrystals. PHYSICAL REVIEW LETTERS 2006; 96:226802. [PMID: 16803336 DOI: 10.1103/physrevlett.96.226802] [Citation(s) in RCA: 236] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2006] [Indexed: 05/10/2023]
Abstract
Doping of nanocrystals is an important and very difficult task. "Self-purification" mechanisms are often claimed to make this task even more difficult, as the distance a defect or impurity must move to reach the surface of a nanocrystal is very small. We show that self-purification can be explained through energetic arguments and is an intrinsic property of defects in semiconductor nanocrystals. We find the formation energies of defects increases as the size of the nanocrystal decreases. We analyze the case of Mn-doped CdSe nanocrystals and compare our results to experimental findings.
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Affiliation(s)
- Gustavo M Dalpian
- Center for Computational Materials, Institute for Computational Engineering and Sciences, Department of Physics, University of Texas, Austin, Texas 78712, USA
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185
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Somorjai GA, Contreras AM, Montano M, Rioux RM. Clusters, surfaces, and catalysis. Proc Natl Acad Sci U S A 2006; 103:10577-83. [PMID: 16740668 PMCID: PMC1502274 DOI: 10.1073/pnas.0507691103] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
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, CO) 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 CO 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.
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Affiliation(s)
- Gabor A Somorjai
- Department of Chemistry, University of California, Berkeley, CA 94720, USA.
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186
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Cao H, Wang G, Zhang S, Zhang X, Rabinovich D. Growth and Optical Properties of Wurtzite-Type CdS Nanocrystals. Inorg Chem 2006; 45:5103-8. [PMID: 16780332 DOI: 10.1021/ic060440c] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper reports wurtzite-type CdS nanostructures synthesized via a hydrothermal reaction route using dithiol glycol as the sulfur source. The reaction time was found to play an important role in the shape of the CdS nanocrystals: from dots to wires via an oriented attachment mechanism. This work has enabled us to generate nanostructures with controllable geometric shapes and structures and thus optical properties. The CdS nanostructures show a hexagonal wurtzite phase confirmed by X-ray diffraction and show no evidence for a mixed phase of cubic symmetry. The Raman peak position of the characteristic first-order longitudinal optical phonon mode does not change greatly, and the corresponding full width at half-maximum is found to decrease with the CdS shape, changing from nanoparticles to nanowires because of crystalline quality improvement. The photoluminescence measurements indicate tunable optical properties just through a change in the shape of the CdS nanocrystals; i.e., CdS nanoparticles show a band-edge emission at approximately 426 nm in wavelength, while the CdS nanowires show a band-edge emission at approximately 426 nm as well as a weaker trap-state green emission at approximately 530 nm in wavelength. These samples provide an opportunity for the study of the evolution of crystal growth and optical properties, with the shape of the nanocrystals varying from nearly spherical particles to wires.
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Affiliation(s)
- Huaqiang Cao
- Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
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187
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Chen H, Peng HC, Liu R, Hu S, Jang LY. Local structural characterization of Au/Pt bimetallic nanoparticles. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2005.12.086] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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188
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Nian JN, Teng H. Hydrothermal Synthesis of Single-Crystalline Anatase TiO2Nanorods with Nanotubes as the Precursor. J Phys Chem B 2006; 110:4193-8. [PMID: 16509714 DOI: 10.1021/jp0567321] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Preparation of anatase TiO2 nanorods from solutions in the absence of surfactants or templates has rarely been reported. The present work has found that hydrothermal treatment of titanate nanotube suspensions under an acidic environment resulted in the formation of single-crystalline anatase nanorods with a specific crystal-elongation direction. The nanotube suspensions were prepared by treatment of TiO2 in NaOH, followed by mixing with HNO3 to different pH values. The crystal size of the anatase nanoparticles obtained from the hydrothermal treatment increased with the pH of the suspensions, and nanorods with an aspect ratio up to 6 and a long axis along the anatase [001] were obtained at a pH slightly less than 7. A mechanism for the tube-to-rod transformation has been proposed on the basis of the crystalline structures of the tubes and rods. The local shrinkage of the tube walls to form anatase crystallites and the subsequent oriented attachment of the crystallites have been suggested to be the key steps involved in the nanorod formation.
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Affiliation(s)
- Jun-Nan Nian
- Department of Chemical Engineering and Center for Micro/Nano Technology Research, National Cheng Kung University, Tainan 70101, Taiwan
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189
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Hemraj-Benny T, Banerjee S, Sambasivan S, Balasubramanian M, Fischer DA, Eres G, Puretzky AA, Geohegan DB, Lowndes DH, Han W, Misewich JA, Wong SS. Near-edge X-ray absorption fine structure spectroscopy as a tool for investigating nanomaterials. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2006; 2:26-35. [PMID: 17193550 DOI: 10.1002/smll.200500256] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We have demonstrated near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, surface molecular orientation, degree of order, and electronic structure of carbon nanotubes and related nanomaterials. Specifically, we employ NEXAFS in the study of single-walled carbon nanotube and multi-walled carbon nanotube powders, films, and arrays, as well as of boron nitride nanotubes. We have focused on the advantages of NEXAFS as an exciting, complementary tool to conventional microscopy and spectroscopy for providing chemical and structural information about nanoscale samples.
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Affiliation(s)
- Tirandai Hemraj-Benny
- Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA
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190
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Abstract
The use of high-pressure for the study and elaboration of homogeneous nanostructures is critically reviewed. Size effects, the interaction between nanostructures and guest species or the interaction of the nanosystem with the pressure transmitting medium are emphasized. Phase diagrams and the possibilities opened by the combination of pressure and temperature for the elaboration of new nanomaterials is underlined through the examination of three different systems: nanocrystals, nano-cage materials which include fullerites and group-14 clathrates, and single wall nanotubes. This tutorial review is addressed to scientist seeking an introduction or a panoramic view of the study of nanomaterials under high-pressure.
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Affiliation(s)
- Alfonso San-Miguel
- Université Lyon 1 and CNRS, Laboratoire de Physique de la Matière Condensée et Nanostructures, UMR 5586, 43 Bvd 11 Novembre 1918, 69622 Villeurbanne, France.
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191
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Huo Z, Chen C, Li Y. Self-assembly of uniform hexagonal yttrium phosphate nanocrystals. Chem Commun (Camb) 2006:3522-4. [PMID: 16921432 DOI: 10.1039/b606531g] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a facile chemical route for the synthesis of uniform hexagonal yttrium phosphate hydrate nanocrystals and their assembly into close-packed regular superstructures through noncovalent interactions of long chain molecules attached to the surfaces of inorganic nanocrystals.
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Affiliation(s)
- Ziyang Huo
- Department of Chemistry, Tsinghua University, Beijing, P R China
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192
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Wang Z, Daemen LL, Zhao Y, Zha CS, Downs RT, Wang X, Wang ZL, Hemley RJ. Morphology-tuned wurtzite-type ZnS nanobelts. NATURE MATERIALS 2005; 4:922-7. [PMID: 16284620 DOI: 10.1038/nmat1522] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Accepted: 09/28/2005] [Indexed: 05/05/2023]
Abstract
Nanometre-sized inorganic dots, wires and belts have a wide range of electrical and optical properties, and variable mechanical stability and phase-transition mechanisms that show a sensitive dependency on size, shape and structure. The optical properties of the semiconductor ZnS in wurtzite structures are considerably enhanced, but the lack of structural stability limits technological applications. Here, we demonstrate that morphology-tuned wurtzite ZnS nanobelts show a particular low-energy surface structure dominated by the +/-[210] surface facets. Experiments and calculations show that the morphology of ZnS nanobelts leads to a very high mechanical stability to approximately 6.8 GPa, and also results in an explosive mechanism for the wurtzite-to-sphalerite phase transformation together with in situ fracture of the nanobelts. ZnS wurtzite nanobelts provide a model that is useful not only for understanding the morphology-tuned stability and transformation mechanism, but also for improving synthesis of metastable nanobelts with quantum effects for electronic and optical devices.
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Affiliation(s)
- Zhongwu Wang
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
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193
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Yin L, Bando Y. Semiconductor morphology: optimizing properties by tuning morphology. NATURE MATERIALS 2005; 4:883-4. [PMID: 16319933 DOI: 10.1038/nmat1544] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
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194
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Affiliation(s)
- Carla Molteni
- Physics Department, King's College London, Strand, London WC2R 2LS, UK.
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195
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Zhelev Z, Jose R, Nagase T, Ohba H, Bakalova R, Ishikawa M, Baba Y. Enhancement of the photoluminescence of CdSe quantum dots during long-term UV-irradiation: privilege or fault in life science research? JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2005; 75:99-105. [PMID: 15246356 DOI: 10.1016/j.jphotobiol.2004.05.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2004] [Revised: 05/17/2004] [Accepted: 05/17/2004] [Indexed: 11/25/2022]
Abstract
The present study describes an impressive enhancement of the photoluminescence (PL) intensity of low-temperature synthesized CdSe nanocrystals (75 degrees C) during long-term UV-irradiation. The integrated PL-intensity of CdSe core and CdSe/ZnS core/shell nanocrystals, dispersed in chloroform, enhanced about 3 and 6 times, respectively, during 9 h exposure to UV-light, without any significant changes in the characteristic absorbance spectra and shifting of PL-spectra. After termination of the irradiation a comparatively slow photobleaching was detected with tau(1/2) = 6 h for CdSe core and tau(1/2) = 14 h for CdSe/ZnS core/shell nanocrystals. The most impressive was the effect of UV-irradiation on the photoluminescence of water-soluble CdSe nanocrystals. The integrated PL-intensity enhanced about 10 times during 11 h exposure to UV-light and the improved PL-intensity was preserved during 3 days after termination of the irradiation without any significant photobleaching. The results are discussed in the context of application of CdSe nanocrystals as novel fluorophores in life science experiments.
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Affiliation(s)
- Zhivko Zhelev
- Natural-Substance Composed Materials Group, National Institute for Advanced Industrial Science and Technology, AIST-Kyushu, Tosu, Saga-ken, Japan
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196
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Cococcioni M, Mauri F, Ceder G, Marzari N. Electronic-enthalpy functional for finite systems under pressure. PHYSICAL REVIEW LETTERS 2005; 94:145501. [PMID: 15904072 DOI: 10.1103/physrevlett.94.145501] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Indexed: 05/02/2023]
Abstract
We introduce the notion of electronic enthalpy for first-principles structural and dynamical calculations of finite systems under pressure. An external pressure field is allowed to act directly on the electronic structure of the system studied via the ground-state minimization of the functional E+PV(q), where V(q) is the quantum volume enclosed by a charge isosurface. The Hellmann-Feynman theorem applies, and assures that the ionic equations of motion follow an isoenthalpic dynamics. No pressurizing medium is explicitly required, while coatings of environmental ions or ligands can be introduced if chemically relevant. We apply this novel approach to the study of group-IV nanoparticles during a shock wave, highlighting the significant differences in the plastic or elastic response of the diamond cage under load, and their potential use as novel nanostructured impact-absorbing materials.
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Affiliation(s)
- Matteo Cococcioni
- Department of Materials Science and Engineering, and Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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197
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Yu JH, Joo J, Park HM, Baik SI, Kim YW, Kim SC, Hyeon T. Synthesis of Quantum-Sized Cubic ZnS Nanorods by the Oriented Attachment Mechanism. J Am Chem Soc 2005; 127:5662-70. [PMID: 15826206 DOI: 10.1021/ja044593f] [Citation(s) in RCA: 406] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Quantum-sized ZnS nanocrystals with quasi-spherical and rod shapes were synthesized by the aging reaction mixtures containing diethylzinc, sulfur, and amine. Uniform-sized ZnS nanorods with the average dimension of 5 nm x 21 nm, along with a small fraction of 5 nm-sized quasi-spherical nanocrystals, were synthesized by adding diethylzinc to a solution containing sulfur and hexadecylamine at 125 degrees C, followed by aging at 300 degrees C. Subsequent secondary aging of the nanocrystals in oleylamine at 60 degrees C for 24 h produced nearly pure nanorods. Structural characterizations showed that these nanorods had a cubic zinc blende structure, whereas the fabrication of nanorods with this structure has been known to be difficult to achieve via colloidal chemical synthetic routes. High-resolution TEM images and reaction studies demonstrated that these nanorods are formed from the oriented attachment of quasi-spherical nanocrystals. Monodisperse 5 nm-sized quasi-spherical ZnS nanocrystals were separately synthesized by adding diethylzinc to sulfur dissolved in a mixture of hexadecylamine and 1-octadecene at 45 degrees C, followed by aging at 300 degrees C. When oleic acid was substituted for hexadecylamine and all other procedures were unchanged, we obtained 10 nm-sized quasi-spherical ZnS nanocrystals, but with broad particle size distribution. These two different-sized quasi-spherical ZnS nanocrystals showed different proportions of zinc blende and wurtzite crystal structures. The UV absorption spectra and photoluminescence excitation spectra of the 5 nm ZnS quasi-spherical nanocrystals and of the nanorods showed a blue-shift from the bulk band-gap, thus showing a quantum confinement effect. The photoluminescence spectra of the ZnS nanorods and quasi-spherical nanocrystals showed a well-defined excitonic emission feature and size- and shape-dependent quantum confinement effects.
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Affiliation(s)
- Jung Ho Yu
- National Creative Research Initiative Center for Oxide Nanocrystalline Materials and School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Korea
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198
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Huang F, Banfield JF. Size-Dependent Phase Transformation Kinetics in Nanocrystalline ZnS. J Am Chem Soc 2005; 127:4523-9. [PMID: 15783236 DOI: 10.1021/ja048121c] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nanocrystalline ZnS was coarsened under hydrothermal conditions to investigate the effect of particle size on phase transformation kinetics. Although bulk wurtzite is metastable relative to sphalerite below 1020 degrees C at low pressure, sphalerite transforms to wurtzite at 225 degrees C in the hydrothermal experiments. This indicates that nanocrystalline wurtzite is stable at low temperature. High-resolution transmission electron microscope data indicate there are no pure wurtzite particles in the coarsened samples and that wurtzite only grows on the surface of coarsened sphalerite particles. Crystal growth of wurtzite stops when the diameter of the sphalerite-wurtzite interface reaches approximately 22 nm. We infer that crystal growth of wurtzite is kinetically controlled by the radius of the sphalerite-wurtzite interface. A new phase transformation kinetic model based on collective movement of atoms across the interface is developed to explain the experimental results.
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Affiliation(s)
- Feng Huang
- Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA.
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199
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Son DH, Hughes SM, Yin Y, Paul Alivisatos A. Cation Exchange Reactions in Ionic Nanocrystals. Science 2004; 306:1009-12. [PMID: 15528440 DOI: 10.1126/science.1103755] [Citation(s) in RCA: 723] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Cation exchange has been investigated in a wide range of nanocrystals of varying composition, size, and shape. Complete and fully reversible exchange occurs, and the rates of the reactions are much faster than in bulk cation exchange processes. A critical size has been identified below which the shapes of complex nanocrystals evolve toward the equilibrium shape with lowest energy during the exchange reaction. Above the critical size, the anion sublattice remains intact and the basic shapes of the initial nanocrystals are retained throughout the cation exchange. The size-dependent shape change can also be used to infer features of the microscopic mechanism.
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Affiliation(s)
- Dong Hee Son
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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200
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Senter RA, Pantea C, Wang Y, Liu H, Zerda TW, Coffer JL. Structural influence of erbium centers on silicon nanocrystal phase transitions. PHYSICAL REVIEW LETTERS 2004; 93:175502. [PMID: 15525088 DOI: 10.1103/physrevlett.93.175502] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2003] [Revised: 06/28/2004] [Indexed: 05/24/2023]
Abstract
Two different types of erbium-doped silicon nanocrystals, along with undoped, oxide-capped Si dots, are employed to probe the impact of the impurity center location on phase transition pressure. Using a combination of high pressure optical absorption, micro-Raman, and x-ray diffraction measurements in a diamond anvil cell, it is demonstrated that the magnitude of this phase transition elevation is strongly dictated by the average spatial location of impurity centers introduced into the nanocrystal along with the interfacial quality of the surrounding oxide.
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Affiliation(s)
- Robert A Senter
- Department of Chemistry, Texas Christian University, Fort Worth, Texas 76129, USA
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