Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands.
Authors | Marijn A. van Huis, Lucas T. Kunneman, Karin Overgaag, Qiang Xu, Gregory Pandraud, Henny W. Zandbergen and Daniël Vanmaekelbergh. Email | M.A.vanHuis@uu.nl
|Application||Low-Temperature Nanocrystal Unification through Rotations and Relaxations Probed by In-situ Transmission Electron Microscopy|
|Authors||Marijn A. van Huis, Lucas T. Kunneman, Karin Overgaag, Qiang Xu, Gregory Pandraud, Henny W. Zandbergen and Daniël Vanmaekelbergh.|
|Journal||Nano Lett., 2008, 8 (11), pp 3959–3963 (cited 79 times)|
|Topic||Self assembly, Sintering, Stability of Catalyst|
|Techniques||Materials Science, Chemistry, Electronics|
|Publication||Full publication here DOI: 10.1021/nl8024467e|
Low-Temperature Nanocrystal Unification through Rotations and Relaxations Probed by In-situ Transmission Electron Microscopy
ABSTRACT: Through the mechanism of “oriented attachment”, small nanocrystals can fuse into a wide variety of one- and two-dimensional nanostructures. This fusion phenomenon is investigated in detail by low-temperature annealing of a two-dimensional array of 10 nm-sized PbSe nanocrystals, in situ in the transmission electron microscope. The researchers have revealed a complex chain of processes; after coalescence, the connected nanocrystals undergo consecutive rotations in three-dimensional space, followed by drastic interfacial relaxations whereby full fusion is obtained.
FIGURE RIGHT: Schematic representation of the entire fusion process indicated by experimental data: (i) attachment due to surfactant evaporation, (ii) rotations to a planar alignment, (iii) subsequent rotation to a nearly full 3D alignment, and (iv) relaxations resulting in removal of the defective interface in order to achieve complete fusion.
FIGURE LEFT: Stills of in situ TEM recordings, showing the evolution PbSe quantum dots (QDs) during three fusion events. The scale bars indicate 4 nm. In general, one QD is centered in the field of view because it is not known beforehand with which other QD it will fuse. (a-h) First event, two 10 nm PbSe QDs fuse into a single crystal at a temperature of 120 °C. Panels a-d: Rotation over 6° in the plane of view, establishing alignment of the (111) planes in panels d and e. Panels e-h: Subsequent rotation of the central nanocluster perpendicular to the field of view. A third QD attaches at the bottom in image h. (i-m) Second event, two 10 nm QDs with hexylamine capping fusing at a temperature of 120 °C. Panels k and l: A rotation of 7° removes the misalignment between the (022) planes, 3D alignment is obtained in panel m where the fused crystal is projected along (011). (n-w) Multisized PbSe QDs fusing into a nanorod. Panels n-u: The small nanocluster no. 3 rotates to align with the larger dot at its left. Movie 3 in the Supporting Information shows that the rotation is not smooth, but irregular as a function of time. Panel v: Four dots have fused into a 4 dot single crystal. The small dot that rotated has been assimilated into the rod. Panel w: The rod has rotated around its own axis, changing the projection of the crystal.
Orientation attachment is one of self-assembly process, in which the components of a system assemble themselves spontaneously via an interaction to form a larger functional unit. The ability to assemble nanoparticles into well-defined configuration in space is crucial to the development of electronic devices that are small but can contain plenty of information. The spatial arrangements of these self-assembled nanoparticles can be potentially used to build increasingly complex structures leading to a wide variety of materials that can be used for different purposes. Moreover this process is also crucial for understanding of traditional sintering process, which heavily influences the catalysis activity of nanoparticles at elevated temperature.
The DENSsolutions heating system provides accurate temperature environment that enable this dynamic process in a controlled manner such that the whole process can be visualized at atomic level, leading to an intuitive understanding.