There is a saying in the saying: a good saddle with a good horse, a good knife with good steel. The strength of a material is an important indicator of its critical use. In general, the maximum strength of a material is controlled by the breaking behavior of bonds between atoms. In practice, it is often only possible to achieve a theoretical 10% modulus of elasticity or shear modulus. Due to the presence of defects in the material, inelastic relaxation or brittle fracture occurs before the atomic bond reaches its maximum strength.
The maximum elastic tensile strain of a solid material is generally only 0.2-0.4%. In 1958, Brenner achieved a tensile strain of 4% in micron-sized whiskers. Since nanomaterials contain almost no defects, it is of great significance for improving the strength of materials. Therefore, in recent years, researchers who are constantly pursuing stronger materials have turned their attention to nanomaterials. At the same time, atomic and molecular dynamics simulations based on DFT calculations can accurately predict the fracture strength of a perfect crystal and measure the effects of defects and smooth surfaces.
Since CC bonds are the strongest bonds in nature, a large number of carbon-based one-dimensional nanomaterials and two-dimensional nanomaterials have become the focus of research, such as multi-walled carbon nanotubes and graphene.
Figure 1. Strength comparison of various high-strength materials
In view of this, Yang Lu and Wenjun Zhang of the City University of Hong Kong collaborated with Ming Dao of the Massachusetts Institute of Technology and Subra Suresh of Nanyang Technological University of Singapore to report a single crystal nano-diamond with super elastic deformability. Its theoretical limit of 89-98 GPa, the elastic deformation reaches 9%!
Figure 2. Preparation of nanoneedle tip diamond
The researchers first prepared a <111> oriented diamond film by CVD, and then prepared a single crystal nano-tip diamond with a feature size of about 300 nm by a reactive ion etching strategy. The theoretical prediction of the tensile strain is 13%, and the theoretical tensile strength can reach 130 GPa. The actual test shows that the maximum tensile strain (9%) of this single crystal nano-diamond is close to its theoretical elastic limit. Correspondingly, the maximum tensile stress can reach 89-98 GPa, while the tensile strength of bulk diamond is less than 10 GPa. .
As we all know, diamond has extremely high strength, but it does not have elastic deformation ability. If you want to deform the diamond, the only way is to break it. The nano-sized needle-shaped diamond not only has ultra-high strength, but also can be elastically deformed by a large amount.
Figure 3. Superelastic deformation of single crystal nanoneedle tipped diamond
Combined with the computational simulation and characterization tests of the system, the researchers believe that the ultra-high strength and super-elastic deformation of this nano-diamond exist simultaneously. On the one hand, there are few defects in small-volume nano-diamonds, and the other is due to nano-scales. Diamond has a smoother surface than bulk diamond.
Figure 4. Summary of the maximum elastic tensile strain of the material
In summary, this study developed a high-strength material with super-large deformability, opening up new applications of nano-diamonds in microelectronic devices and drug delivery, and for the nanostructure, morphology, elastic strain and physical properties of diamond. The design and optimization brings new inspiration!
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