STM observation of a box-shaped graphene nanostructure appeared after cleavage of pyrolytic graphite
Channel: Rostislav Lapshin
Date: 2015-12-23

Elsevier's Audio Slides
http://audioslides.elsevier.com//ViewerSmall.aspx?source=1&doi=10.1016/j.apsusc.2015.09.222

A short introduction to the research article: R. V. Lapshin, STM observation of a box-shaped graphene nanostructure appeared after mechanical cleavage of pyrolytic graphite, Applied Surface Science, vol. 360, part B, pp. 451-460, 2016 (DOI: 10.1016/j.apsusc.2015.09.222). The article is available for free at the following link: http://www.niifp.ru/staff/lapshin/en/...


Slide 1. Title

Dear Colleagues!
My name is Rostislav Lapshin, I am a research scientist from the Institute of Physical Problems, Zelenograd, Moscow, Russian Federation.
I am going to briefly report on new findings, which are presented in my recent paper “STM observation of a box-shaped graphene nanostructure appeared after mechanical cleavage of pyrolytic graphite” published in Applied Surface Science journal, in September 2015.
Let me remind that graphene is a single monolayer of carbon atoms forming a hexagonal two-dimensional crystal lattice. Actually, graphite crystal can be thought of as a “stack” of graphene sheets.


Slide 2. Box-shaped graphene (BSG) nanostructure

Those who have dealt with graphite know that graphite surface under a scanning tunneling microscope looks “dull” and uniform, as a rule. All you see is usually plain areas of surface of several microns in size bounded by cleaving steps without any features. Just occasionally, you come across something unusual within the familiar “landscape”, say, a carbon fiber, a superlattice or a dislocation network.
The found nanostructure (shown on the left of the slide) looked so extraordinary that it took some time to understand what it actually was. The structure was dramatically different from whatever had previously been observed on graphite. Only some time later, after additional measurements and analysis of the obtained images, it became clear that this was a system of hollow nanosized channels extending along the surface with wall thickness less than 1 nm. The value of thickness estimated as well as the quadrangular cross-section of the channels (shown at the right bottom corner of the slide) unambiguously indicated that the channel walls (or facets) are graphene planes. A schematic view of the box-shaped nanostructure and the typical dimensions of its elements are presented on the right top part of the slide.


Slide 3. Orientation of cleavage front

An image of the upper facet of a nanochannel was obtained with atomic resolution (it is on the left top of the slide). It was then overlaid with the image of the box-shaped nanostructure (the picture on the right bottom). It was easy to reveal that the nanostructure channels were oriented approximately along one of the close-packed directions of graphene. Thus, in order for the box-shaped nanostructure to appear, the cleaving front, which is shown as a rectangle with arrows, should be oriented approximately along one of the close-packed directions of graphite.


Slide 4. Mechanism of nanofold formation

After the geometry and sizes of the found object had been generally clarified, the time came to understand the way the object had been formed. Several hypotheses were suggested, but all of them appeared to be either too complicated or too “fantastic”. Finally, rather simple, if not to say elegant, solution was found which is based on a series of mechanical deformations of graphite, which is layered by its nature.
Briefly, the formation mechanism is apparently the following. During graphite cleavage, a compressive stress directed along the surface appears in the thin surface layer (see position 1). As the cleaving front moves on, the compressive stress causes, first, elastic bending of this layer at a small section A'B (see position 2), and then plastic deformation of the layer with its simultaneous splitting into graphene sublayers (see position 3). The last two transformations result in a nanofold formation.


Slide 5. Simplified formation mechanism of the nanochannel layers

At the final stage, the split graphene sublayers slide in the nanofolds relative to each other resulting in formation of the nanochannels arranged in “stories”. Since the nanochannels have a quadrangular cross-section, the detected graphene nanostructure has been named box-shaped.


Slide 6. Possible applications

Even the preliminary analysis of the box-shaped graphene nanostructure has shown good prospects of its use in various devices. Here are some of the possible applications: ultra-sensitive detectors, high-performance catalytic cells, nanochannels of microfluidic devices (molecular sieving, DNA sequencing and manipulation), high-performance heat sinking surfaces, rechargeable batteries of enhanced performance, nanomechanical resonators, electron multiplication channels in emission nanoelectronic devices, high-capacity sorbents for safe hydrogen storage.


Slide 7. Thank you

Finishing, I wish you all good luck in your research!