Search

A method is introduced to measure friction on small, free standing objects, specifically microfabricated silicon plates, based on atomic force microscopy (AFM). An AFM tip is brought into contact with the plate resting on a substrate. The substrate is displaced laterally and, provided the AFM tip does not slide over the plate, the twisting of the AFM cantilever is used to measure the friction of the underlying plate-substrate interface. The method can measure nano-Newton to micro-Newton forces (both friction and applied load) and provides a means to measure friction of macroscopic structures at low load.

A cantilever has been microfabricated for use in non-contact Atomic Force Microscopy (AFM) using a very thick magnetic film to actuate the cantilever motion. The thick magnetic block is deposited electrochemically over a defined area of the cantilever. This cantilever is particularly suitable for driving stiff AFM cantilevers in a liquid environment. Clean mechanical resonances are easily observed. Examples are given of a hard (CoPt) magnet of dimension 29 × 21 × 6 μm(3) electroplated on Silicon cantilevers of stiffness ~22 N/m, giving a static displacement of ~0.2 nm in an applied field of 10(-3) T.

We use conducting atomic force microscopy (AFM) in ultra high vacuum to measure the thermoelectric power of Au, Pt, and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) films. Tips coated with thick (1200 nm) Pt films or highly doped diamond film give reproducible data. The thermoelectric power of metal junctions formed with diamond tips is high but dominated by the diamond material thus making diamond tips of limited applicability in thermovoltage AFM. Pt coated tips on Au or Pt films gives small thermovoltage signal, making quantitative analysis of the thermopower on metal sample problematic. The thermovoltage AFM technique appears best suited to study organic thin films and the thermoelectric power of 1.5 nm and 2 nm thick PTCDA deposited on Au measured with Pt tips is −342 and −372 μV/K, respectively. The negative sign indicates that the lowest unoccupied molecular orbital level dominates electrical transport.