Explaining how 2-D materials break at the atomic level

January 18, 2017

Cracks sank the 'unsinkable' Titanic; decrease the performance of touchscreens and erode teeth. We are familiar with cracks in big or small three-dimensional (3D) objects, but how do thin two-dimensional (2D) materials crack? 2D materials, like molybdenum disulfide (MoS2), have emerged as an important asset for future electronic and photoelectric devices. However, the mechanical properties of 2D materials are expected to differ greatly from 3D materials. Scientists at the Center for Integrated Nanostructure Physics (CINAP), within the Institute for Basic Science (IBS) published, on Nature Communications, the first observation of 2D MoS2 cracking at the atomic level. This study is expected to contribute to the applications of new 2D materials.

Obviously when a certain force is applied to a material a crack is created. Less obvious is how to explain and predict the shape and seriousness of a crack from a physics point of view. Scientists want to investigate which fractures are likely to expand and which are not .Materials are divided into ductile and brittle: Ductile materials, like gold, withstand large strains before rupturing; brittle materials, like glass, can absorb relatively little energy before breaking suddenly, without elongation and deformation. At the nano-level atoms move freer in ductile materials than in brittle materials; so in the presence of a pulling force (tensile stress) they can go out of position from the ordered crystal structure, or in technical terms - they dislocate. So far, this explanation (Griffith model) has been applied to cracking phenomena in bulk, but it lacks experimental data at the atomic or nano-scale.

In this study, IBS scientists observed how cracks propagate on 2D MoS2 after a pore was formed either spontaneously or with an electron beam. "The most difficult point {of the experiments} was to use the electron beam to create the pore without generating other defects or breaking the sample," explains Thuc Hue Ly, first author of this study. "So we had to be fast and use a minimum amount of energy."

The atomic observations were done using real-time transmission electron microscopy. Surprisingly, even though MoS2 is a brittle material, the team saw atom dislocations 3-5 nanometers (nm) away from the front line of the crack, or crack tip. This observation cannot be explained with the Griffith model.

In order to create conditions that represent the natural environment, the sample was exposed to ultraviolet (UV) light. This caused the MoS2 to oxidize; atom dislocations occurred more rapidly and the stretched region expanded to 5-10 nm from the crack tip.

"The study shows that cracking in 2D materials is fundamentally different from cracking in 3D ductile and brittle materials. These results cannot be explained with the conventional material failure theory, and we suggest that a new theory is needed," explained Professor LEE Young Hee (CINAP).
-end-


Institute for Basic Science

Related Light Articles from Brightsurf:

Light from rare earth: new opportunities for organic light-emitting diodes
Efficient and stable blue OLED is still a challenge due to the lack of emitter simultaneously with high efficiency and short excited-state lifetime.

Guiding light: Skoltech technology puts a light-painting drone at your fingertips
Skoltech researchers have designed and developed an interface that allows a user to direct a small drone to light-paint patterns or letters through hand gestures.

Painting with light: Novel nanopillars precisely control intensity of transmitted light
By shining white light on a glass slide stippled with millions of tiny titanium dioxide pillars, researchers at the National Institute of Standards and Technology (NIST) and their collaborators have reproduced with astonishing fidelity the luminous hues and subtle shadings of 'Girl With a Pearl Earring.'

Seeing the light: Researchers combine technologies for better light control
A new technology that can allow for better light control without requiring large, difficult-to-integrate materials and structures has been developed by Penn State researchers.

A different slant of light
Giant clams manipulate light to assist their symbiotic partner.

New light for plants
Scientists from ITMO in collaboration with their colleagues from Tomsk Polytechnic University came up with an idea to create light sources from ceramics with the addition of chrome: the light from such lamps offers not just red but also infrared (IR) light, which is expected to have a positive effect on plants' growth.

Scientists use light to accelerate supercurrents, access forbidden light, quantum world
Iowa State's Jigang Wang continues to explore using light waves to accelerate supercurrents to access the unique and potentially useful properties of the quantum world.

The power of light
As COVID-19 continues to ravage global populations, the world is singularly focused on finding ways to battle the novel coronavirus.

Seeing the light: MSU research finds new way novae light up the sky
An international team of astronomers from 40 institutes across 17 countries found that shocks cause most the brightness in novae.

Seeing the light: Astronomers find new way novae light up the sky
An international team of researchers, in a paper published today in Nature Astronomy, highlights a new way novae light up the sky: this is shocks from explosions that create the novae that cause most of the their brightness.

Read More: Light News and Light Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.