Nanomechanical properties of molecular organic thin films

Abstract

Using atomic force microscopy we have studied the nanomechanical response to nanoindentations of surfaces of highly oriented molecular organic thin films (thickness⩽1000 nm). The Young’s modulus E can be estimated from the elastic deformation using Hertzian mechanics. For the quasi-one-dimensional metal tetrathiafulvalene tetracyanoquinodimethane E∼20 GPa and for the α phase of the p-nitrophenyl nitronyl nitroxide radical E∼2 GPa. Above a few GPa, the surfaces deform plastically as evidenced by discrete discontinuities in the indentation curves associated to molecular layers being expelled by the penetrating tip.

Nanoindentation: Toward the sensing of atomic interactions

“…have recently performed nanoindentation experiments with ultrasharp tips on layered molecular organic materials dominated by van der Waals and hydrogen-bonding interactions, much weaker than the electrostatic and covalent bonding (25). In this case, the Hertz model fits well the experimental data despite the fact that R Ϸ ␦, because during penetration, the number of molecules in contact with the tip is continuously increasing.…”

Thin Films of Molecular Metals TTF-TCNQ

“…Finally, the nanomechanical properties of thin films of TTF-TCNQ have been recently determined with AFM, exhibiting Young's modulus of ca. 20 GPa (22).…”

Carrier mediated reduction of stiffness in nanoindented crystalline Si(100)

“…( 2), -------------------------------------------(2) where S intrinsic is the strain caused by the indentation in intrinsic c-Si,  is the stress in the intrinsic sample, and E intrinsic is the apparent elastic modulus. Thus, we define the apparent elastic modulus measured in the heavily doped Si as -------------------------------------------------(3) In order to determine the effect of the carrier concentration on the elastic modulus for c-Si, the mean compressive stress caused by nanoindentation can be estimated to be =F/R, 15 where F is the load of the nanoindentation, R is the radius of the indenter, and  is the penetration depth. If taking F = 5 mN during loading, R 50 nm, and 150 nm (penetration depth corresponding to 5 mN), considering the surface region which can be affected by light and ensuring purely elastic deformation is taking place alone, we estimate   20 GPa.…”