Cation Exchange Reactions in Ionic Nanocrystals.

Son, Dong Hee; Hughes, Steven M.; Yin, Yadong; Alivisatos, A. Paul

doi:10.1002/chin.200508244

Cited by 186 publications

(336 citation statements)

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“…In addition, the electron beam-induced phase transformation has also been observed, such as the transformation of Cu 2 S nanorods from low-chalcocite to highchalcocite structures 14 . Meanwhile, cation exchange has also been used for the structure manipulation of inorganic nanocrystals [15][16][17] . However, it should be noted that the composition of the initial nanocrystals will be changed after the cation exchange.…”

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confidence: 99%

“…However, it should be noted that the composition of the initial nanocrystals will be changed after the cation exchange. For instance, hexagonal CdSe nanocrytals can be transformed to cubic Ag 2 Se nanocrystals after cation exchange of Cd 2 þ with Ag þ ions 15 . Importantly, below a critical size, when the surface energy of a nanostructure dominates the total systemic energy, surfactant or solvent molecules can play a critical role in modulating its crystal structure 18,19 .…”

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Surface modification-induced phase transformation of hexagonal close-packed gold square sheets

et al. 2015

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Surface modification-induced phase transformation of hexagonal close-packed gold square sheets

et al. 2015

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“…[1][2][3][4][5][6][7] It is generally assumed that during such an exchange, the anionic framework of the crystal is conserved, while the cations, due to their relatively smaller size and higher mobility, undergo replacement. This has not, however, been experimentally proven or utilized, as only single-phase nanocrystals have so far been transformed using cation exchange.…”

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Nanoheterostructure Cation Exchange: Anionic Framework Conservation

et al. 2010

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In ionic nanocrystals, especially transition metal chalcogenides, the cationic sub-lattice can be replaced with a different metal ion via a fast, simple, and reversible place-exchange, altering the composition of the nanocrystal, while preserving its size and shape. [1][2][3][4][5][6][7] It is generally assumed that during such an exchange, the anionic framework of the crystal is conserved, while the cations, due to their relatively smaller size and higher mobility, undergo replacement. This has not, however, been experimentally proven or utilized, as only single-phase nanocrystals have so far been transformed using cation exchange. Preservation of the anionic framework during cation exchange would enable transformation of multi-component nanoheterostructures, while conserving not only the nanostructure size and shape, but also the compositional interface between the constituents. This would greatly extend the domain of cation exchange to the design of ever more complex nanostructures. In this Communication, we demonstrate that, indeed, the anionic framework is preserved during cation exchange, and that this can be utilized for accessing customized nanoheterostructures.The model heterostructure selected is a seeded rod consisting of a spherical CdSe nanocrystal embedded in a CdS nanorod. [8][9][10] A unique functional feature of such a structural arrangement is the ability to design the relative band alignment of the two semiconductors across the interface, allowing independent tuning of the spatial distribution of electrons and holes along the elongated dimension. [11][12][13][14][15][16] The seeded rod is a canonical example of a nanoheterostructure that allows customization of electronic properties for applications such as force sensing, 17 photocatalysis, 18 optoelectronics, 19-21 and quantum information technology. 22 A 40-nm long CdSe/CdS seeded nanorod synthesized with a 3.9-nm seed (Supporting Information) exhibits absorption features (Fig. 1A) attributable to excitons in the CdSe seed (600 nm and 562 nm) and the CdS rod (460 nm) and strong photoluminescence (PL) due to exciton recombination in the seed (Fig. 1B). Complete cation exchange of the nanorods with Cu + results in the loss of CdS and CdSe excitonic features and the emergence of an absorption band-edge around 850 nm, typical of Cu chalcogenides (indirect bulk band gap ~1.2eV). Back-conversion of the Cu 2 Se/Cu 2 S seeded rod to Cd 2+ recovers all excitonic features of the original structure (Fig 1A, B, and D).The PL peak maximum, due to the confined nature of the emitting exciton in the seed, is known to be highly sensitive to the seed diameter (Fig. 1C). It is noteworthy that following two cycles of exchange, the PL peak recovered with a similar position as that of the initial nanorods. This indicates complete conservation of the selenide seed embedded in the sulfide rod Figure 1. A) Absorbance and B) photoluminescence (PL) spectrum of a 40-nm long CdS nanorod with an embedded 3.9-nm CdSe nanocrystal (top), following complete exchange with Cu ...

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“…In contrast to the reported cation exchange at quantum size by the Alivisatos group, 25 if Ag 2-δ Te is modulated to be crystalline, the ensuing cation exchange reaction will generate polycrystalline CdTe nanosheets (see Supplementary Figure S14). The amorphous state of Ag 2-δ X promoted the motion of Oriented attachment of nanoparticles H Qian et al cations as well as the growth of the quasi-sc domain of CdX due to a reduction of the grain boundary energies.…”

Section: Resultsmentioning

confidence: 62%

“…This unprecedented strategy breaks the deadlock of cation exchange from the colloidal nanoparticle scale to bulk size and synchronously achieves efficient Ag doping in CdX films. 25 It therefore offers the potential for site-fixed growth, complex compositional tailoring and metal ion doping of semiconductor nanosheets/nanobelts on substrates for electrical applications.…”

Section: Xps Depth Profile Analysismentioning

confidence: 99%

Oriented attachment of nanoparticles to form micrometer-sized nanosheets/nanobelts by topotactic reaction on rigid/flexible substrates with improved electronic properties

Zhao

Dai

et al. 2015

NPG Asia Mater

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We report a topotactic reaction strategy to achieve the oriented attachment (OA) of colloidal metal chalcogenide quantum dots into micrometer-sized nanosheets and nanobelts (up to 6-7 μm) on both mechanically rigid and flexible substrates. The nonstoichiometric composition, crystallization and Ag doping were controlled. The strong surface adsorption of cations and thiol ligands facilitated micrometer-scale three-dimensional OA. The cations induced the formation of electrostatic forces, cation passivation on the nanosheet surface and overlap packing of the nanosheets, enabling good contact with the substrates and improved electron transport without severe obstruction of organic insulating barriers. The observation of weak anti-localization phenomena and Hall effect sensitivity (up to 188%) of non-stoichiometric Ag 2-δ Te nanosheet films as well as the improved I-V and photoresponse properties of Ag-doped CdX nanosheet films confirm efficient electron transport. The stable I-V properties of these nanosheet films on flexible substrates, even under bending forces, testify to their potential in flexible device applications.

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Cation Exchange Reactions in Ionic Nanocrystals.

Cited by 186 publications

References 1 publication

Surface modification-induced phase transformation of hexagonal close-packed gold square sheets

Surface modification-induced phase transformation of hexagonal close-packed gold square sheets

Nanoheterostructure Cation Exchange: Anionic Framework Conservation

Oriented attachment of nanoparticles to form micrometer-sized nanosheets/nanobelts by topotactic reaction on rigid/flexible substrates with improved electronic properties

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