Nanomechanical testing technique for millimeter-sized and smaller molecular crystals.

Area of Science:

• Materials Science
• Crystallography
• Mechanical Engineering

Background:

• Developing reliable mechanical testing methods for small molecular crystals is crucial.
• Existing nanoindentation techniques face challenges with surface effects and sample size limitations.

Purpose of the Study:

• To develop and validate a nanoindentation testing technique for millimeter-sized and smaller molecular crystals.
• To compare the accuracy and reliability of elastic versus elastic-plastic indentation methods.
• To determine the mechanical properties (Young's modulus and hardness) of griseofulvin.

Main Methods:

• Utilized large crystals as controls for technique development.
• Employed both elastic and elastic-plastic nanoindentation methods.
• Tested the model material griseofulvin.

Main Results:

• Elastic-plastic indentations yield more accurate elastic modulus measurements than elastic indentations, which are sensitive to surface conditions.
• Similar hardness values were observed for both small and large crystals, indicating comparable defect content.
• Young's modulus and hardness of griseofulvin were determined to be 11.5 GPa and 0.4 GPa, respectively.

Conclusions:

• The developed nanoindentation technique is suitable for characterizing small molecular crystals.
• Elastic-plastic indentation is preferred for accurate mechanical property assessment of small crystals.
• Small molecular crystals can be reliably compared to larger ones in terms of hardness.