Selective Facet Reactivity during Cation Exchange in Cadmium Sulfide Nanorods

Sadtler, Bryce; Demchenko, D. O.; Zheng, Haimei; Hughes, Steven M.; Merkle, Maxwell G.; Dahmen, U.; Wang, Lin‐Wang; Alivisatos, A. Paul

doi:10.1021/ja809854q

Cited by 386 publications

(530 citation statements)

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“…Examining and understanding these observations suggest a possible growth mechanism for the "barbell" heterostructure: it has been widely accepted that the tips of nanowires usually possess the highest reactivity where the reaction/growth tends to happen first. 25,26 If anhydrous hydrazine is used, the strong reduction environment as well as the high transient concentration of bismuth atoms (reduced from Bi-(NO 3 ) 3 ·5H 2 O by hydrazine) will override the preferred growth on Te nanowire tips so that a nonselective absorption and alloying between Bi and Te nanowire will lead to the uniform conversion into Bi 2 Te 3 nanowires, which has been identified in the previous research. 20,21 Reducing the concentration of hydrazine to 80% and using smaller and smaller amounts slows down the generation of Bi atoms, thus promoting the selective growth of Bi 2 Te 3 plates on the Te nanowire tips.…”

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confidence: 87%

Design Principle of Telluride-Based Nanowire Heterostructures for Potential Thermoelectric Applications

et al. 2012

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We present a design principle to develop new categories of telluride-based thermoelectric nanowire heterostructures through rational solution-phase reactions. The catalyst-free synthesis yields Te−Bi 2 Te 3 "barbell" nanowire heterostructures with a narrow diameter and length distribution as well as a rough control over the density of the hexagonal Bi 2 Te 3 plates on the Te nanowire bodies, which can be further converted to other telluride-based compositionalmodulated nanowire heterostructures such as PbTe−Bi 2 Te 3 . Initial characterizations of the hot-pressed nanostructured bulk pellets of the Te−Bi 2 Te 3 heterostructure show a largely enhanced Seebeck coefficient and greatly reduced thermal conductivity, which lead to an improved thermoelectric figure of merit. This approach opens up new platforms to investigate the phonon scattering and energy filtering.

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confidence: 87%

Design Principle of Telluride-Based Nanowire Heterostructures for Potential Thermoelectric Applications

et al. 2012

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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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confidence: 99%

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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“…Nanoscale heterojunctions 12 and 'barcodes' 13 could further be fabricated by varying the ion concentration.…”

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confidence: 99%