Highly Nitridated Graphene–Li2S Cathodes with Stable Modulated Cycles
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Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth
Drs. Anil O. Yalcin
Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
Authors | Anil O. Yalcin, Zhaochuan Fan, Bart Goris, Wun-Fan Li, Rik S. Koster, Chang-Ming Fang, Alfons van Blaaderen, Marianna Casavola, Frans D. Tichelaar, Sara Bals, Gustaaf Van Tendeloo, Thijs J. H. Vlugt, Daniël Vanmaekelbergh, Henny W. Zandbergen and Marijn A. van Huis. Email | m.a.vanhuis@uu.nl
| Application | Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth |
| Authors | Anil O. Yalcin, Zhaochuan Fan, Bart Goris, Wun-Fan Li, Rik S. Koster, Chang-Ming Fang, Alfons van Blaaderen, Marianna Casavola, Frans D. Tichelaar, Sara Bals, Gustaaf Van Tendeloo, Thijs J. H. Vlugt, Daniël Vanmaekelbergh, Henny W. Zandbergen and Marijn A. van Huis. |
| Journal | Nano Letters, 2014 |
| Sample | Nanoparticles |
| Topic | Interface, Diffusion, Growth, hetero-nanoparticle/crystal |
| Field | Material Science, Chemistry, Electronics |
| Techniques | HRSTEM, EDX Mapping |
| Keywords | Colloidal Nanocrystals; Cation Exchange; Molecular Dynamics; Density Functional Theory; In Situ Transmission Electron Microscopy |
| Publication / D.O.I. | Full publication here |
Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth
ABSTRACT: Here, we show a novel solid–solid–vapor (SSV) growth mechanism whereby epitaxial growth of heterogeneous semiconductor nanowires takes place by evaporation-induced cation exchange. During heating of PbSe-CdSe nanodumbbells inside a transmission electron microscope (TEM), we observed that PbSe nanocrystals grew epitaxially at the expense of CdSe nanodomains driven by evaporation of Cd. Analysis of atomic-resolution TEM observations and detailed atomistic simulations reveals that the growth process is mediated by vacancies.
Figure left: HAADF-STEM images and chemical mapping of the nanodumbbells before and after heating. (a) HAADF-STEM image of CdSe-PbSe nanodumbbells. The PbSe tips exhibit brighter contrast than the CdSe nanorods due to Z-contrast. (b,c) Dumbbell HNCs at 160 °C (b) and at 200°C (c), showing gradual extension of PbSe domains at the expense of CdSe. A heating rate of 10 degrees/min was used in the in situ studies and the HNCs were annealed at the indicated temperatures for 5 min before imaging. Dumbbell HNCs with solid arrows transformed totally to brighter contrast with heating. This phenomenon occurred mostly from one side, though it can proceed from both PbSe domains as well (dumbbell with dashed arrows in panel c). (d−o) HAADF-STEM images and corresponding STEM-EDX elemental maps of dumbbell heteronanostructures annealed for 5 min at temperatures of (d−g) 100 °C, (h−k) 170 °C, and (l−o) 200 °C. In panels d−g, HNCs are in original dumbbell state with PbSe tips and CdSe nanorod. In panels h−k, a partially transformed nanorod is present. In panels l−o, two PbSe-CdSe HNCs became full PbSe domains. The Se remains in place during the transformation. Note that the contrast is maximized in each individual image; hence, intensities of different mappings cannot be directly compared. Quantitative analyses are provided in the Supporting Information.
Figure right: Atomic-resolution HAADF-STEM images of CdSe-PbSe HNCs reveals the dynamic growth process. It shows that PbSe has cubic rock salt (RS) crystal structure with a lattice constant(20) of 6.13 Å, whereas CdSe has a hexagonal wurtzite (WZ) crystal structure with lattice parameters(21) a = 4.29 Å and c = 7.01 Å. The CdSe WZ (0002) spacing is 3.5 Å and PbSe RS (200) spacing is 3.1 Å. With heating from 160 °C (a) to 180 °C (b) with a heating rate of 10 degrees/min, WZ CdSe nanorods started to transform to RS PbSe. The insets are Fourier transforms (FTs) taken from the white squares in each image. The spot depicted with an arrow in the inset FT of panel a corresponds to WZ CdSe(0002) spacing. It disappeared in the inset FT of panel b, confirming the WZ to RS transformation. Movie S4 shows the transformation with atomic resolution. (c) HAADF-STEM image of a PbSe-CdSe dumbbell HNC. Stacking faults and a dislocation are present in the CdSe nanorod domain. The interface at the left-hand side is {111}PbSe/{0001}CdSea (panel d), whereas the interface at the right-hand side is {100}PbSe/{0001}CdSe (panel f).
DENSsolutions Comments
Structure evolution across an interface (e.g. diffusion, growth, chemical reaction, etc.) requires not only crystal structure information, but chemical information both to be known. HRSTEM images, combining with EDX mapping, provides analysis tool to investigate samples structure as well as chemical environment changes down to nano/atomic scale. During these analyses, the sample stability at elevated temperature is extremely crucial for achieving reliable/interpretable results, simply because longer time need to be applied for collecting enough signal.
The DENSsolutions heating system provides such an extreme sample stability at the elevated temperature that enables the chemical mapping of this dynamic growth process to be obtained. The researchers use the collect experimental results, as well as detailed atomistic simulations reveal that the growth process is mediated by vacancies.
Download the full publication here at the Nano Letters Journal
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Epitaxial CdSe-Au Nanocrystal Heterostructures by Thermal Annealing
Dr. Albert Figuerola
Istituto Italiano di Tecnologia, Genova, Italy
Author | Albert Figuerola, Marijn van Huis, Marco Zanella, Alessandro Genovese, Sergio Marras, Andrea Falqui, Henny W. Zandbergen, Roberto Cingolani and Liberato Manna.
Email | liberato.manna@iit.it.
| Application | Epitaxial CdSe-Au Nanocrystal Heterostructures by Thermal Annealing (Cited by 59 times) |
| Authors | Albert Figuerola, Marijn van Huis, Marco Zanella, Alessandro Genovese, Sergio Marras, Andrea Falqui, Henny W. Zandbergen, Roberto Cingolani and Liberato Manna. |
| Journal | Nano Lett., 2010, 10 (8), pp 3028–3036 |
| Sample | Nano-Particles |
| Topic | Interface, Diffusion, Catalyst stability |
| Field | Chemistry, Material Science, Electronics |
| Techniques | HRTEM |
| Keywords | Nanorods; nanocrystals; self-assembly; epitaxy; orientation relationship; interface; hybrid nanocrystals; gold; cadmium selenide; annealing |
| Publication | Full publication here – DOI: 10.1021/nl101482q |
Epitaxial CdSe-Au Nanocrystal Heterostructures by Thermal Annealing
ABSTRACT: The thermal evolution of a collection of heterogeneous CdSe−Au nanosystems (Au-decorated CdSe nanorods, networks, vertical assemblies) prepared by wet-chemical approaches was monitored in situ in the transmission electron microscope. In contrast to interfaces that are formed during kinetically controlled wet chemical synthesis, heating under vacuum conditions results in distinct and well-defined CdSe/Au interfaces, located at the CdSe polar surfaces. The high quality of these interfaces should make the heterostructures more suitable for use in nanoscale electronic devices.
FIGURE LEFT: Enlargement and flattening of the CdSe/Au interface (a-c). During heating at a high heating rate (2 K/s), the width of the interface grew by a factor of 3. Images are shown corresponding to temperatures of 150 °C (a), 250 °C (b), and 300 °C (c), respectively. Such an interface reconstruction enables the two crystal lattices to accommodate to each other to maximize the number of covalent bonds between them. various CdSe/Au interfaces with both the CdSe and the Au crystals in identifiable zone axes are shown (d-f) All configurations show the same epitaxial relationship, as indicated in the figure.
DENSsolutions Comments
Colloidal inorganic nanocrystals of semiconductors are promising materials in a variety of applications. For example, in photocatalysis and photovoltaics, the photoinduced generation of charge carriers in nanocrystals can lead to the oxidation/reduction of molecular species or to the generation of clean electrical energy, respectively. In both cases, the performance of the material depends strongly on its charge separation ability and on the construction of suitable nanocrystal-electrode interfaces.
The growth of metallic domains directly on the surface of the semiconductor nanocrystals can help to improve both factors. Thus the nature of the metal-semiconductor nanointerface and its influence on the local electronic structure of the nanorod have become subjects of particular interest in the past decade. Various efforts are devoted to improve the interface between metal and semiconductors.
Using the DENSsolutions heating system, the researchers are able to observe the In-Situ thermal evolution of heterogeneous CdSe-Au nanosystem. The low drift at elevated temperature allows structural and shape transformations in individual nanocrystals that could be imaged in real time with atomic resolution. The researchers showed that such treatment leads to heterostructures with better defined metal-semiconductor interfaces. The high quality of these interfaces should make the heterostructures more suitable for use in nanoscale electronic devices.