by Merijn Pen | Apr 13, 2017
Drs. Kuang He
Department of Materials, University of Oxford Authors | Kuang He, Alex W. Robertson, Ye Fan, Christopher S. Allen, Yung-Chang Lin, Kazu Suenaga, Angus I. Kirkland and Jamie H. Warner. Email | jamie.warner@materials.ox.ac.uk
| Application |
Temperature Dependence of the Reconstruction of Zigzag Edges in Graphene |
| Authors |
Kuang He, Alex W. Robertson, Ye Fan, Christopher S. Allen, Yung-Chang Lin, Kazu Suenaga, Angus I. Kirkland and Jamie H. Warner. |
| Journal |
ACS Nano, 2015 |
| Publication |
Full Publication Here – DOI: 10.1021/acsnano.5b01130 |
Temperature Dependence of the Reconstruction of Zigzag Edges in Graphene
ABSTRACT: We examine the temperature dependence of graphene edge terminations at the atomic scale using an in situ heating holder within an aberration-corrected transmission electron microscope. The relative ratios of armchair, zigzag, and reconstructed zigzag edges from over 350 frames at each temperature are measured. Below 400 C, the edges are dominated by zigzag terminations, but above 600 C, this changes dramatically, with edges dominated by armchair and reconstructed zigzag edges.
We show that at low temperature chemical etching effects dominate and cause deviation to the thermodynamics of the system. At high temperatures (600 and 800 C), adsorbates are evaporated from the surface of graphene and chemical etching effects are significantly reduced, enabling the thermodynamic distribution of edge types to be observed. The growth rate of holes at high temperature is also shown to be slower than at room temperature, indicative of the reduced chemical etching process. These results provide important insights into hthe role of chemical etching effects in the hole formation, edge sputtering, and edge reconstruction in graphene.
Figure above: Edge behavior at room temperature (∼25 C). (ac) Three typical HRTEM images of graphene holes at that temperature. The edges are color-coded to differentiate the types of edge configurations. Red represents armchair; yellow is zigzag, and green is Rec. 57; white indicatesmixed or unidentified edge types. The inset in (a) and (b) shows typical long-ordered zigzag and armchair configurations at this temperature. The statistics for three examples are shown in (d); the percentages of edges occupied by different types of edges are ranked accordingly: black columns represent panel (a), red columns panel (b), and blue columns panel (c). (e,f) Long-ordered zigzag edge from both bulk of graphene and edge of a nanoribbon, respectively. (g) Representative long-ordered armchair edge found at this temperature. The o iginal image ofwhich (eg) are cropped fromthose shown in Figure S1ac of Supporting Information. All scale bars are 1 nm.
by Merijn Pen | Apr 13, 2017
Dr. Sairam K. Malladi
Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands. Authors | Sairam K. Malladi, Qiang Xu, Marijn A. van Huis, Frans D. Tichelaar, K. Joost Batenburg, Emrah Yücelen, Beata Dubiel, Aleksandra Czyrska-Filemonowicz, and Henny W. Zandbergen. Email | H.W.Zandbergen@tudelft.nl.
| Application |
Real-Time Atomic Scale Imaging of Nanostructural Evolution in Aluminum Alloys |
| Authors |
Sairam K. Malladi, Qiang Xu, Marijn A. van Huis, Frans D. Tichelaar, K. Joost Batenburg, Emrah Yücelen, Beata Dubiel, Aleksandra Czyrska-Filemonowicz, and Henny W. Zandbergen. |
| Journal |
Nano Lett., 2014, 14 (1), pp 384–389 |
| Sample |
FIB lamella, Metal |
| Topic |
Heat Treatment, Aging, Precipitation |
| Field |
Materials Science, Micro Electronics |
| Techniques |
HRTEM, EDX mapping |
| Keywords |
In situ (S)TEM; precipitation; aluminum alloys |
| Publication |
Full Publication Here – DOI 10.1021/nl404565j |
Real-Time Atomic Scale Imaging of Nanostructural Evolution in Aluminum Alloys
ABSTRACT: We present a new approach to study the three dimensional alloys during heat treatments such as commonly used for improving overall material properties. It relies on in situ heating in a high-resolution scanning transmission electron microscope (STEM). The approach is demonstrated using a commercial Al alloy AA2024 at 100−240 °C, showing in unparalleled detail where and how precipitates nucleate, grow, or dissolve. The observed size evolution of individual precipitates enables a separation between nucleation and growth phenomena, necessary for the development of refined growth models. We conclude that the in situ heating STEM approach opens a route to a much faster determination of the interplay between local compositions, heat treatments, microstructure, and mechanical properties of new alloys.
FIGURE ABOVE: STEM imaging and EDX maps obtained at each of the intermediate stages of heat-treatment. These maps are obtained with a frame size of 512×512 pixels2 and a frame time of 100 s, averaged over three frames. Notice the Cu redistribution associated with the precipitation at grain boundaries and precipitation in the matrix during the heat-treatment processes. The lath-like nanoprecipitates are enriched with Cu and Mg, suggesting S-phase-type compositions. Throughout the heat-treatment process, the Mn-rich precipitates remained as they are at room temperature.
DENSsolutions Comments:
Most commercial engineering alloys undergo heat treatments to change their intrinsic microstructural properties, such as elemental distribution and precipitate density, to enhance their extrinsic physical properties such as mechanical strength. Despite the key importance of these treatments, studies of the compositional and structural evolution of alloys undergoing heat treatments are fragmented and time consuming as they have been carried out on a set of different samples taken at intermediate stages, which are postmortem data that do not show the evolution of the same area. Achieving in situ TEM observation of heat treatment process at atomic scale enable a full understanding of the relation among process, structure and properties.
The DENSsolutions heating system provides the minimal specimen drift at elevated temperature, allowing a novel in situ method to investigate the aging hardening process that the structural and compositional evolution of alloys can be directly analyzed with time and temperature down to atomic scale.
