Material Sciences Division

Seminars & Conferences

News and Highlights

Join Us!

Home

Electronic, mechanical, and chemical properties of nanoclusters

Atomic scale imaging, manipulation, and spectroscopy Mechanical and electrical properties of molecules in self-assembled films Ambient pressure photoelectron spectroscopy for environnemental sciences Studies of friction, adhesion, and wear at the nanometer scale Electronic, mechanical, and chemical properties of nanoclusters Structure of thin liquid films and wetting Nanoscale material imaging and manipulation (Molecular Foundry) Catalytic and chemical properties of surfaces

Frictional and Dielectric Properties of Nanoclusters in confined geometries

In the Salmeron group, Surface Forces Apparatus (SFA) has been used to investigate the mechanical, tribological, and dielectric properties of organic liquids confined down to few molecular diameters thickness by atomically smooth surfaces of mica. Much of work has been also done to improve the apparatus itself. Current projects are dealing with nanocrystals of various size (1 – 3 nm) and shape (ball, rod, etc) dispersed in organic solvents. It is expected that layering transition will occur when the thickness of the liquid becomes comparable to the size of the nanocrystals. Mechanical, tribological, and dielectric properties of these confined systems will be investigated in order to understand the behavior of nanocrystals in confined states. In SFA, liquids are confined between atomically smooth mica surfaces and squeezed out by applying controlled load. Although the lateral size of the films is several tens of micrometers, their thickness can be controlled very accurately down to subnanometer scale. During the squeezing-out, force-distance curves show the internal ordering of molecules in the liquid. At desired thicknesses, frictional and mechanical properties of the liquids can be studied by applying shear force.

Former Researcher: Sang Hoon Kim

The graph shows the result of squeezing out of OMCTS, a simple round molecule whose diameter is 0.9 nm (black curve). In order to investigate dielectric responses of the samples, small changes (< 1fF) of the capacitance between two silver mirrors on the backsides of mica also measured simultaneously with the thickness of the liquid (red curve in the graph). In case of OMCTS, steps in the change of the capacitance correspond to the steps in the change of the thickness. In case of gold nanocrystals, this simple correlation may not hold any more due to possible interaction between the crystals when they are close enough under high pressure. Layering of OMCTS film between two mica sheets with silver mirrors on backsides. Steps in the liquid thickness (black curve) correspond with steps in the capacitance of the silver mirrors (red curve).