Abstract Recently, engineering researchers in Columbia, USA, found that graphene has excellent hardness properties even if it is made up of many small graphene grains. This finding solves some of the contradictions between previous theoretical simulations and experiments; the previous theory called the hardness of the grain boundaries is strong, and...
Recently, engineering researchers in Columbia, USA, found that graphene has excellent hardness properties even if it is made up of many small graphene grains. This finding solves some of the contradictions between previous theoretical simulations and experiments; the previous theory stated that the grain boundary hardness of graphene is strong, and the test predicts that the hardness of small-grain graphene is much weaker than that of intact graphite. Alkenyl lattice. The study was recently published in the journal Science. 
Experiments have shown that the commonly used CVD growth graphene post-treatment method tends to weaken the hardness of the grain boundary. The Columbia research team invented a new processing method that prevented the resulting graphene from receiving any effects and damage during the migration process. Gwan-Hyoung Lee said, “We replaced one of the corrosive agents and found a test example without affecting the graphene. The experiment clearly corrected the previous misunderstanding—the grain boundary hardness of graphene It is very weak.†This conclusion is of extraordinary significance, and it provides more opportunities for research and industrial applications in basic disciplines.
In the complete crystal form, graphene (a single-atom thick carbon layer) is by far the hardest substance in the world. In the first phase of the experiment, the team obtained a small, structurally complete graphene sheet from the graphite crystal by mechanical stripping. However, mechanical stripping is a very time consuming process that is far from meeting the scale of industrial production of graphene applications.
Now, scientists can use chemical vapor deposition to grow a single layer of graphene on a copper substrate in a high temperature furnace. One of the first applications of graphene is the conductive layer of flexible displays that are nowadays popular.
Since CVD graphene is made up of many small grains that are bonded to the grain boundary surface, they are put together like a quilt, which causes the grain boundary to have certain defects in atomic structure; Kysar says that it consists of small grains of graphene. If the grain boundary is more easily broken than the intact graphene lattice, it will greatly limit the strength of the large-area graphene material. In view of this, it is necessary to understand and study in depth the strength of these small graphene grains.
The Columbia engineering research team wanted to figure out exactly what could weaken the hardness of CVD graphene. During the manufacturing process of the test samples, the staff found that some of the chemicals commonly used to remove copper substrates affected graphene and severely reduced its hardness properties.
It has been found that the hardness of the large-grain CVD graphene is comparable to that of the graphene obtained by mechanical stripping, which indicates that the lattice of the CVD graphene is intact. What is even more surprising is that small-grain CVD graphene, even when tested on a single grain boundary, has a hardness of up to 90%.
“This is a welcome finding for graphene applications in the future. Because the anomalous hardness of atomic-scale graphene grains can show superior performance in a variety of cases,†says Hone, “as scientists have developed With new flexible electronic devices and super-hard composite materials, the hardness value of small graphene grains will be more excellent."
Graphite materials with high strength and large area will be widely used in various facilities such as flexible electronic products, and can potentially enhance the performance of their components. Flexible TV screens that can be rolled up like posters, super-hard composites that can replace carbon fiber; researchers predict, or, like space elevators, sci-fi applications that use CVD graphene sheets to connect orbiting satellites to the Earth, It is also likely to become a reality in the future, because only graphene (including its similar products such as carbon nanotubes) can meet the high-strength hardness performance requirements.
The research team is also interested in the research and application of graphene as a two-dimensional material. Kysar said, "There is little knowledge about the grain boundaries of two-dimensional materials; our research shows that the grain boundaries of two-dimensional materials are more sensitive to the processing flow than three-dimensional materials because the graphene atoms themselves are in place. On the surface of graphene, therefore, the surface effect caused by processing may be minimal for the hardness of three-dimensional materials, but it can greatly destroy and reduce the hardness of two-dimensional materials. Of course, as long as appropriate processing methods are taken to avoid damage to the surface of the material. The grain boundary of a two-dimensional material such as graphene is simply a superhard material with no regrets.
The study was supported by the US Air Force Research Office and the National Science Foundation. (Compiled from Science Daily; translation: Wang Xian)
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