Surfaces that present expansion instead of relaxation?

In summary, the conversation discusses the phenomenon of surface relaxation in solids, where external layers are usually closer to the next layer. However, there are also cases of surface expansion, such as in Aluminium (111), which is claimed to exhibit this behavior. Theoretical explanations suggest that the Lennard-Jones potential can lead to this type of relaxation, although it was considered unfavorable for metals. The speaker is seeking more information on this topic.
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voila
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Since there are no bonds at the other side of the surface, external layers of solids are usually closer to the next layer. This process is called relaxation. (Example in picture a here).

However, at a lecture I attended the other day it was mentioned that some surfaces present expansion, instead of the more common relaxation. I haven't been able to find anything on the topic. Anyone knows about it?
 
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  • #2
Aluminium (111) is claimed to exhibit surface expansion here and here
 
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Theoretically , I recall that Lennard -Jones potential leads to outer-surface relaxation (i.e. expansion). This is one reason why it was considered a bad interaction potential for metals.
 

1. What are surfaces that present expansion instead of relaxation?

Surfaces that present expansion instead of relaxation are materials that exhibit an increase in surface area when subjected to stress or pressure rather than a decrease. This phenomenon is known as negative Poisson's ratio or auxetic behavior.

2. What causes a surface to present expansion?

The unique structure of materials with a negative Poisson's ratio allows for the expansion of the surface when stretched. This is due to the arrangement of the material's internal structure, which allows for the movement of particles in a direction perpendicular to the applied force instead of parallel.

3. What are some examples of surfaces that present expansion?

Some common examples of surfaces that exhibit negative Poisson's ratio include auxetic foams, certain types of rubber, and biological materials such as tendon and cartilage. These materials have been found to have various practical applications, such as in protective gear and medical implants.

4. How is the negative Poisson's ratio measured?

The negative Poisson's ratio, also known as Poisson's ratio of expansion (PRE), is typically measured by subjecting a material to a uniaxial stress and measuring the resulting strain in the perpendicular direction. The ratio between the two values is then calculated to determine the PRE value.

5. What are the potential applications of surfaces that present expansion?

Materials with a negative Poisson's ratio have shown promising properties for use in various industries, including aerospace, automotive, and biomedical. Some potential applications include impact-resistant structures, more efficient energy absorption, and improved flexibility and durability in medical devices.

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