News Release

Under the Microscope: How an atomistic puzzle gets resolved

Scientists monitor the evolution of crystal irregularities called "dislocations" in a silicene sheet in real time after adding silicon atoms to it

Peer-Reviewed Publication

Japan Advanced Institute of Science and Technology


image: Top panel: Transformation of epitaxial-silicene on ZrB2 from domain structure to single-domain. The labels a,b,c and d represent four different shifts of the silicene lattice resulting from the presence of the dislocations. Silicon atoms in the domains, boundaries and on top of Zr are blue, yellow and red respectively. The Topmost Zr atoms are colored grey. The dark grey Zr atoms are used to visualize the shifts of the domains visualized by the positions of red atoms. They correspond to the positions of red Si atoms for a single-domain a. The green lines compare the positions of the Si atoms before and after merging of four successive domains into a single-domain a through the reaction of 4 dislocations. A row of Si atoms (colored in pink) can then be incorporated into the resulting gap. Bottom panel: STM images showing the path found by nature to resolve this atomistic puzzle. Left: Nucleation of a single-domain island through the stepwise reaction of dislocations. The circles denote a Si cluster that disappears together with domain c which indicates that Si atoms were integrated in the silicene sheet at this stage of the transformation. Right: Propagation of a single domain after its nucleation. The blue lines indicate the interface between the single-domain and the domain structure. The circles point to the same group of Si clusters. The time intervals between the captures of the STM images are indicated. view more 

Credit: Antoine Fleurence from JAIST

Ishikawa, Japan - We might imagine crystals to be perfect structures, but they are, in fact, often plagued with “defects.” Curiously enough, such defects often appear due to atoms undergoing reorganization to lower the energy of the system and attain stability.

“Dislocations can strongly affect the physical and chemical properties of a crystal. Moreover, they can undergo “reactions” when for instance strain is applied on the crystal or atoms are added to its surface. Studying how dislocations react can, therefore, provide crucial insights on how to cure these crystal defects. Silicene on zirconium diboride (ZrB2) provides a perfect test bed for that. This two-dimensional form of silicon features an array of dislocations which disappear when few Si atoms are deposited on top of it. This transformation, that suppresses the high cost of energy caused by the presence of unbounded Si atoms on the surface, requires the reaction of four dislocations to create the room necessary to accommodate the deposited atoms in the silicene sheet. As this needs the motion of a large number of atoms and to overcome the repulsive interaction between the dislocations, this transformation looked very unlikely at first glance: It is a veritable atomistic puzzle which has to be solved to integrate the deposited atoms!,” says Senior Lecturer Antoine Fleurence from Japan Advanced Institute of Science and Technology (JAIST), Japan, who works on 2D materials.

In a new study published in 2D Materials, Dr. Fleurence and his colleague, Prof. Yukiko Yamada-Takamura from JAIST, monitored using scanning tunneling microscopy (STM) the evolution of dislocations in a silicene sheet in real time after depositing silicon (Si) atoms on it.

Through this real time monitoring the trick used by the nature to integrate the deposited Si atoms and obtain a dislocation-free silicene sheet could be determined: the silicene sheet experiences a sequence of dislocation reactions during which the integration of Si atoms within the silicene sheet occurs. Locally "nucleated" single-domain islands then propagate across the entire silicene sheet to eventually result in a dislocation-free, single-domain structure.

“The information on dislocation dynamics provided by this study could be used to find solutions to heal structural defects in similar 2D materials, interfaces, and a wide range of nanomaterials,” comments Dr. Fleurence.



Title of original paper:

Adatom-induced dislocation annihilation in epitaxial silicene


2D Materials




About Japan Advanced Institute of Science and Technology, Japan

Founded in 1990 in Ishikawa prefecture, the Japan Advanced Institute of Science and Technology (JAIST) was the first independent national graduate school in Japan. Now, after 30 years of steady progress, JAIST has become one of Japan’s top-ranking universities. JAIST counts with multiple satellite campuses and strives to foster capable leaders with a state-of-the-art education system where diversity is key; about 40% of its alumni are international students. The university has a unique style of graduate education based on a carefully designed coursework-oriented curriculum to ensure that its students have a solid foundation on which to carry out cutting-edge research. JAIST also works closely both with local and overseas communities by promoting industry–academia collaborative research.  


About Dr. Antoine Fleurence from Japan Advanced Institute of Science and Technology, Japan

Dr. Antoine Gilles Valery Fleurence is a Senior Lecturer of solid-state physics at the Japan Advanced Institute of Science and Technology. His areas of expertise include applied physics, surface sciences and 2D nanomaterials. He has 40 publications which have over 1700 citations and 5000 reads. As a teacher he believes the best way to improve learning capability of students is to generate curiosity and allow them to undertake autonomous hands-on experimental work. He also encourages his students to develop communication skills alongside their scientific research abilities for a better future in professional as well as personal life.

Funding information:

 The study is funded by JSPS KAKENHI Grant Number 26790005.

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