Direct visualization of the thermomagnetic behavior of pseudo–single-domain magnetite particles
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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Atomic Resolution Imaging and Spectroscopy of Barium Atoms and Functional Groups on Graphene Oxide
Dr. Chris B. Boothroyd
Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Germany Authors | C.B. Boothroyda, M.S. Morenob, M. Duchampa, A. Kovácsa, N. Mongec, G.M. Moralesc, C.A. Barberoc, R.E. Dunin-Borkowskia Email | c.boothroyd@fz-juelich.de
| Application | Atomic Resolution Imaging and Spectroscopy of Barium Atoms and Functional Groups on Graphene Oxide |
| Authors | C.B. Boothroyda, M.S. Morenob, M. Duchampa, A. Kovácsa, N. Mongec, G.M. Moralesc, C.A. Barberoc, R.E. Dunin-Borkowskia |
| Journal | Ultramicroscopy Journal, 2014 |
| Sample | Graphene |
| Topic | Contamination Free, 2D Materials, Soft Matter, E-Beam Sensitive Imaging |
| Techniques | HRTEM, HRSTEM, EELS, Diffraction |
| Keywords | Graphene oxide; Functional groups; Scanning transmission electron microscopy; Transmission electron microscopy; Spectrum imaging; Atomic resolution; Single atom imaging |
| Publication / D.O.I. | Full Publication Here |
Atomic Resolution Imaging and Spectroscopy of Barium Atoms and Functional Groups on Graphene Oxide
ABSTRACT: We present an atomic resolution transmission electron microscopy(TEM) and scanning TEM(STEM) study of the local structure and composition of graphene oxide modified with Ba2+. In our experiments, which are carried out at 80kV,the acquisition of contamination-free high-resolution STEM images is only possible while heating the sample above 400C using a highly stable heating holder. Ba atoms are identified spectroscopically in electron energy-loss spectrum images taken at 800C and are associated with bright contrast in high-angle annular dark-field STEM images. The spectrum images also show that Ca and O occur together and that Ba is not associated with a significant concentration of O. The electron dose used for spectrum imaging results in beam damage to the specimen, even at elevated temperature. It is also possible to identify Ba atoms in high-resolution TEM images acquired using shorter exposure times at room temperature, thereby allowing the structure of graphene oxide to be studied using complementary TEM and STEM techniques over a wide range of temperatures.
FIGURE ABOVE: HAADF STEM images acquired at a specimen temperature of 800 C (a) before and (b) after recording the spectrum image (the total time of spectrum imaging is 800s). The area of spectrum imaging is marked by the box. While the area surrounding the box is relatively unchanged after acquiring the spectrum image (except for a small drift and local distortion), the area from which the spectrum image was acquired has changed significantly.
FIGURE ABOVE: Color images created from a selection of the spectrum images which were acquired from graphene oxide with Ba imaged at a temperature of 800 C by using STEM spectrum imaging method. The images show the spatial relationships between the elements, corresponding to the following colours: (a) Ba red and C cyan; (b) O red and C cyan; (c) Ca red and C cyan; (d) Ba red, Ca green and C blue. The spectrum image shows that Ba, O and Ca are present mostly in the areas where the C is thinnest and that Ca and O have very similar distributions.
DENSsolutions Comments:
Graphene, graphene-like two dimensional and other soft-mater materials attract increasing research efforts. Characterization of these type of materials in TEM, however, suffers contamination problems and e-beam damage.
Contamination, referring to the build-up of decomposed carbon on a specimen, heavily influences the quality of electron microscopy imaging. Graphene and graphene-like two dimensional materials suffer contamination the most because of two reasons 1. these materials are ultrathin, with low image contrast, the build up contamination contrast blur the original contrast easily; 2. these materials are with large surface area, easier to absorb hydrocarbon, water to form contamination under e-beam.
DENSsolutions heating system provides the opportunity to image these samples free of contamination at elevated temperature, without sacrificing the quality/resolution of imaging. The extreme high stability of DENSsolutions heating system (sample spatial drift less than 0.5nm/min) can even allow the researchers using a long exposure time (5s-8s) to image the individual carbon atoms for improving the contrast. Furthermore, the low drift allows chemical sensitive spectrum imaging to be carried down to atomic level.
Download the full publication here at the Ultramicroscopy (2014) Journal
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Controllable Atomic Scale Patterning of Freestanding Monolayer Graphene at Elevated Temperature
Dr. Qiang Xu
Kavli Institute of Nanoscience, Delft University of Technology,The Netherlands Authors | Qiang Xu, Meng-Yue Wu, Grégory F. Schneider, Lothar Houben, Sairam K. Malladi, Cees Dekker, Emrah Yucelen, Rafal E. Dunin-Borkowski and Henny W. Zandbergen. Email | h.w.zandbergen@tudelft.nl
| Application | Controllable Atomic Scale Patterning of Freestanding Monolayer Graphene at Elevated Temperature |
| Authors | Qiang Xu, Meng-Yue Wu, Grégory F. Schneider, Lothar Houben, Sairam K. Malladi, Cees Dekker, Emrah Yucelen, Rafal E. Dunin-Borkowski and Henny W. Zandbergen. |
| Journal | ACS Nano, 2013, 7 (2), pp 1566–1572 |
| Sample | Graphene |
| Topic | Contamination Free, 2D Materials, Soft Matter, E-Beam Sensitive Imaging |
| Field | Material Science, Chemistry, Electronics, Life Science |
| Techniques | HRTEM, HRSTEM, EELS, Diffraction |
| Keywords | Graphene; Controlled Sculpting; Nondestructive Imaging; Nanopatterning; Self-repair |
| Publication / D.O.I. | Full Publication Here – DOI: 10.1021/nn3053582 |
Controllable Atomic Scale Patterning of Freestanding Monolayer Graphene at Elevated Temperature
ABSTRACT: In order to harvest the many promising properties of graphene in (electronic) applications, a technique is required to cut, shape, or sculpt the material on the nanoscale without inducing damage to its atomic structure, as this drastically influences the electronic properties of the nanostructure. Here, we reveal a temperature-dependent self-repair mechanism that allows near-damage-free atomic-scale sculpting of graphene using a focused electron beam. We demonstrate that by sculpting at temperatures above 600 C, an intrinsic self-repair mechanism keeps the graphene in a single-crystalline state during cutting, even though the electron beam induces considerable damage. Self-repair is mediated by mobile carbon ad-atoms that constantly repair the defects caused by the electron beam. Our technique allows reproducible fabrication and simultaneous imaging of single-crystalline free-standing nanoribbons, nanotubes, nanopores, and single carbon chains.
FIGURE ABOVE: Annular dark field STEM images of graphene ribbon arrays sculpted in a reproducible way by using a script-controlled electron beam at elevated temperature. After the first sculpting process, the patterns were imaged as shown in (a). Next, each ribbon was reduced in width precisely, and image (b) was acquired. Intensity line profiles across the ribbon outlined by the white frames in (a) and (b) are shown in (c) and (d), respectively. The width of the ribbon is estimated to be 4.0 nm after initial sculpting and 1.9 nm after final sculpting.
DENSsolutions Comments
Objective & Goal
Graphene, carbon nanotube and other soft-mater materials suffers irradiation damage caused by high energy electron beam during TEM characterization. The e-beam damage limits the observation time or observation electron beam condition, thus requiring a way to prevent. Moreover, application of graphene needs to patterning graphene into various functional devices with nano-size geometry. The e-beam induced damage can be utilized for creating a lithography method for graphene patterning. Achieving control of e-beam damage of graphene becomes an essential topic.
Benefit
DENSsolutions heating system provides the extreme high stability of sample at elevated temperature (sample spatial drift less than 0.5nm/min) At the elevated temperature, the e-beam induced defects of the sample can be repaired with a corresponding speed, therefore, provides an extra parameter for control of e-beam damage.