by Merijn Pen | Jul 10, 2017
Florian Niekiel, M.Sc.
Lehrstuhl für Mikro- und Nanostrukturforschung & Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander-Universitaet Erlangen-Nuernberg, Germany Authors | Florian Niekiel, Peter Schweizer, Simon M. Kraschewski, Benjamin Butz and Erdmann Spiecker Email | Erdmann.Spiecker@ww.uni-erlangen.de
| Application |
The Process of Solid-State Dewetting of Au Thin Films Studied by In-situ Scanning Transmission Electron Microscopy |
| Authors |
Florian Niekiel, Peter Schweizer, Simon M. Kraschewski, Benjamin Butz and Erdmann Spiecker |
| Journal |
Acta Materialia, 2015 |
| Keywords |
Solid-state dewetting; Thin films; Morphology; Temporal evolution; Image analysis |
| Publication / D.O.I. |
Full Publication Here |
The Process of Solid-State Dewetting of Au Thin Films Studied by In-situ Scanning Transmission Electron Microscopy
ABSTRACT: Solid-state dewetting describes the transformation of thin films into a set of particles or droplets at temperatures well below the melting temperature of the bulk. In this work in situ scanning transmission electron microscopy has been used to study the dewetting behavior of discontinuous Au thin films (15 nm and 22 nm thick) on amorphous silicon nitride membranes at temperatures ranging from 300°C to 600°C. The combination of microscopic and statistical information enabled not only the qualitative discussion of the observed processes but also the quantification of the kinetics as well as the development of a model of the underlying morphological mechanism. A model-free master curve approach to the temporal evolution of the covered area at different temperatures is used to determine the activation energy of dewetting (1.04 ± 0.14 eV for the 15 nm thick film). A closer inspection reveals a multiple power law behavior, which is discussed in the frame of depercolation. Retraction of finger-like structures is found to be the dominant morphological mechanism based on the observed linear relationship between covered area and boundary length.
FIGURE RIGHT: 15 nm (left) and 22 nm (right) thick Au films in the as-deposited state: (a) plan view HAADF-STEM images, (b) cross sectional TEM bright field images of respective lift-out lamellae.
FIGURE BELOW: Comparison of HAADF images from the in situ STEM experiments on the 15 nm thick Au films. Experiment time t is indicated by red labels.
FIGURE BELOW: Comparison of HAADF images from the in situ STEM experiments on the 22 nm thick Au films. Experiment time t is indicated by red labels.
by Merijn Pen | Jul 10, 2017
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.
by Merijn Pen | Jul 10, 2017
Dr. Bart Goris
EMAT, University of Antwerp, Belgium
Authors | Bart Goris, Marijn A. Van Huis, Sara Bals, Henny W. Zandbergen, Liberato Manna and Gustaaf Van Tendelooi.
Email | sara.bals@ua.ac.be
| Application |
Thermally Induced Structural and Morphological Changes of CdSe/CdS Octapods |
| Authors |
Bart Goris, Marijn A. Van Huis, Sara Bals, Henny W. Zandbergen, Liberato Manna and Gustaaf Van Tendelooi. |
| Journal |
Small 2012, 8, No. 6, 937–942 |
| Publication |
Full Publication Here – DOI: 10.1002/smll.201101897 |
Thermally Induced Structural and Morphological Changes of CdSe/CdS Octapods
ABSTRACT: Branched nanostructures are of great interest because of their promising optical and electronic properties. For successful and reliable integration in applications such as photovoltaic devices, the thermal stability of the nanostructures is of major importance. Here the different domains (CdSe cores, CdS pods) of the heterogeneous octapods are shown to have different thermal stabilities, and heating is shown to induce specific shape changes. The octapods are heated from room temperature to 700 °C, and investigated using (analytical and tomographic) transmission electron microscopy (TEM). At low annealing temperatures, pure Cd segregates in droplets at the outside of the octapods, indicating non-stochiometric composition of the octapods. Furthermore, the tips of the pods lose their faceting and become rounded. Further heating to temperatures just below the sublimation temperature induces growth of the zinc blende core at the expense of the wurtzite pods. At higher temperatures, (500–700 °C), sublimation of the octapods is observed in real time in the TEM. Three-dimensional tomographic reconstructions reveal that the four pods pointing into the vacuum have a lower thermal stability than the four pods that are in contact with the support.
Figure above: a,b) TEM images acquired from non-annealed CdSe/CdS octapods. Four pencil like ended pods and four flat ended pods can be observed. c, d, and e show visualizations of the 3D reconstruction of a non-annealed CdSe/CdS octapod. On these visualizations, the flat ended pods and the pencil-like ended pods are indicated as well as the 6-folded symmetry of the pods. f presents a HAADF-STEM projection of an octapod where the 6-folded symmetry is also visible. The high resolution STEM image in g shows that these 6 facets of the pods correspond to the {10-10} and {11-20} planes. h reports a high resolution STEM image of the cubic CdSe core of the octapod.
Figure above: a,b) TEM images of octapods upon in situ annealing to 300 °C. The pods of the octapod have become rounded. c) HAADF-STEM projection of octapod used to make a tomographic reconstruction. d) Visualization of the tomographic reconstruction confirming that all the pods have become rounded. From the slice through the reconstruction in figure e, it is clear that pure Cd segregates as droplets at the tips and the side of the pods. f) TEM image of an annealed CdSe/CdS octapod where one of these droplets is indicated with an arrow. The elemental maps of S (g) and Cd (h) confirm that the droplet contains pure Cd.
Figure left: Snapshots from in situ annealed CdSe/CdS octapods at a temperature of 600 °C. Rounding of the pods is observed before their sublimation.
by Merijn Pen | Jul 10, 2017
Dr. Chang-Ming Fang
Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
Authors | Chang-Ming Fang, Marijn A. van Huis, Daniël Vanmaekelbergh and Henny W. Zandbergen
Email | m.a.vanhuis@tudelft.nl
| Application |
Energetics of Polar and Nonpolar Facets of PbSe Nanocrystals from Theory and Experiment |
| Authors |
Chang-Ming Fang, Marijn A. van Huis, Daniël Vanmaekelbergh and Henny W. Zandbergen |
| Journal |
ACS Nano, 2010, 4 (1), pp 211–218 |
| Publication |
Full Publication Here – DOI: 10.1021/nn9013406 |
Energetics of Polar and Nonpolar Facets of PbSe Nanocrystals from Theory and Experiment
ABSTRACT: Surface energies of the distinct facets of nanocrystals are an important factor in the free energy and hence determine the nanocrystal morphology, chemical and physical properties, and even interparticle dipole interactions. Here we investigate the stability and atomic structure of polar and nonpolar PbSe surfaces by combining first-principles calculations with high-resolution transmission electron microscopy (TEM). For uncapped surfaces, the calculations predict that the nonpolar {100} surface is the most stable with a surface energy of 0.184 J m2, while the nonpolar {110} and reconstructed {111}-Pb surfaces have surface energies of 0.318 J m2 and 0.328 J m2, respectively. Fully polar {111} surfaces are structurally unstable upon relaxation. These findings are in good agreement with TEM observations showing that capped nanocrystals have a nearly spherical, multifaceted morphology, while cubical shapes with predominantly {100} facets are obtained when the capping molecules are removed through heating in va uum. During this process, however, also multipolar surfaces can temporarily exist just after the removal of the surfactants. These metastable {111} surfaces consist of ribbon-like nanodomains, whereby the ribbons are alternating in polarity. The calculations confirm that these multipolar surfaces are energetically more favorable than fully polar surfaces. The consequences for capped nanocrystals (a dominant Pb-oleate termination) and nanocrystal fusion (a shorter interaction range of dipole interactions) are discussed.
Figure left: Configuration of {100}, {110}, and {111} PbSe surfaces. Full circles indicate surface atoms (top layer) and quasisurface atoms (these atoms are only partially covered; they have at most one atomic bond to the top layer). Empty circles indicate subsurface atoms (having two or more bonds with atoms at an elevated layer). Subfigure (c) shows a fully polar configuration with one Pb-terminated surface and one Se-terminated surface in order to maintain stoichiometry. The bottom two configurations (d,e) are reconstructed {111} surfaces. There is one reconstructed variant {111}-Pb whereby half the Pb atoms are absent in the surface layer, and a domain-wise polar variant {111}2Pb with ribbons of Pb atoms on top of a Se atomic layer. {111}-Se and {111}2Se surfaces can be constructed analogously.
Figure left: High-resolution TEM images showing the morphology of PbSe NCs: (a) PbSe nanocrystals in a [011] projection, so that the {100}, {110}, and {111} surfaces can be observed simultaneously; (b) example of the Wulff diagrams (in this case corresponding to panel a) that were used to derive relative surface energies; (c,d) other PbSe NCs in a [011] projection; (e) other NCs in various orientations; (f) nanowires are formed in low-density areas after annealing at 120 °C; (g) in general, cubical shapes start to dominate after longer annealing times as the surfactants evaporate; the corners of the cubes display {100} nanofaceting, as indicated with white arrows.
by Merijn Pen | Jul 10, 2017
Dr. Marijn A. van Huis
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) |
| Sample |
Nanoparticles |
| 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.
DENSsolutions Comments
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.
