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Register a new userIntermolecular interactions and substrate effects for an adamantane monolayer on the Au(111) surface
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We study theoretically and experimentally the infrared (IR) spectrum of an adamantane monolayer on a Au(111) surface. Using a new STM-based IR spectroscopy technique (IRSTM) we are able to measure both the nanoscale structure of an adamantane monolayer on Au(111) as well as its infrared spectrum, while DFT-based ab initio calculations allow us to interpret the microscopic vibrational dynamics revealed by our measurements. We find that the IR spectrum of an adamantane monolayer on Au(111) is substantially modified with respect to the gas-phase IR spectrum. The first modification is caused by the adamantane--adamantane interaction due to monolayer packing and it reduces the IR intensity of the 2912 cm$^{-1}$ peak (gas phase) by a factor of 3.5. The second modification originates from the adamantane--gold interaction and it increases the IR intensity of the 2938 cm$^{-1}$ peak (gas phase) by a factor of 2.6, and reduces its frequency by 276 cm$^{-1}$. We expect that the techniques described here can be used for an independent estimate of substrate effects and intermolecular interactions in other diamondoid molecules, and for other metallic substrates.
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Pinning single molecules at desired positions can provide opportunities to fabricate bottom-up designed molecular machines. Using the combined approach of scanning tunneling microscopy and density functional theory, we report on tip-induced anchoring of Niphthalocyanine molecules on an Au(111) substrate. We demonstrate that the tip-induced current leads to the dehydrogenation of a benzene-like ligand in the molecule, which subsequently creates chemical bonds between the molecule and the substrate. It is also found that the diffusivity of Ni-phthalocyanine molecules is dramatically reduced when the molecules are anchored on the Au adatoms produced by bias pulsing. The tip-induced molecular anchoring would be readily applicable to other functional molecules that contain similar ligands.
We compute the AC susceptibility of a weakly dipolar-interacting monodisperse assembly of magnetic nanoclusters with oriented anisotropy. For this purpose we first compute the relaxation rate in a longitudinal magnetic field of a single nanomagnet taking account of both dipolar interactions in the case of dilute assemblies and surface anisotropy. We then study the behavior of the real and imaginary components of the AC susceptibility as functions of temperature, frequency, surface anisotropy and inter-particle interactions. We find that the surface anisotropy induces an upward shift of the temperature at the maximum of the AC susceptibility components and that its effects may be tuned so as to screen out the effects of interactions. The phenomenological Vogel-Fulcher law for the effect of dipolar interaction on the relaxation rate is revisited within our formalism and a semi-analytical expression is given for the effective temperature is given in terms of inter alia the applied field, surface anisotropy and dipolar interaction.
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