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New Probe Microscope Measures to Levels Less than a Nanometre

Dr Liu with the device
Dr Liu with the device
Originally Published 5 November 2001

It is increasingly important for manufacturers of high tech materials and coatings to understand exactly what is going on at the surface of their products right down to the nanometre level. It has been possible to get individual measurements of friction, hardness, elasticity, and surface shape but until now it has not been so easy to get all four measurements and exactly correlate those measurements against each other. Now a researcher at the University of Warwick's Centre for Nanotechnology and Microengineering has designed a device - a multi-function Tribological Probe Microscope (TPM) - that solves that problem.

Dr Ping Liu's Tribological Probe Microscope is able, in one pass, to measure an area of 100 by 100 micrometres of surface and give an accurate measurement of the surface topography (shape), friction, Young’s modulus (surface elasticity), and hardness. These four simultaneous surface measurements can then be accurately correlated in space and in time.

The device uses a diamond tip (Berkovich tip with a 100nm – nanometre - radius) mounted on a silica rod a few millimetres long, fixed on a thin beryllium/Copper (Cu/Be) foil acting as a flexible spring. On the other side of the beam, is attached a small permanent magnet, surrounded by a coil. The force with which the tip contacts the sample surface is controlled by passing a current in this coil, which delivers a constant force in a range of 0.01- 30mN (millinewtons).

The tip slides along the sample measuring the shape or topography of the sample surface down to a resolution of 0.1nm (nanometres). At the same time the friction of the surface causes the probe tip to tilt and by measuring the amount of tilt the device is able to get a measure of the surface's friction properties. Finally as the tip exerts a downward force the probe records the depth of penetration of the probe as a measure of the surface hardness at that point. It then records how far the depressed surface recovers to its original shape after the applied force has been removed as a measure of the surface's elasticity.

Dr Liu received a commendation for her work on this device at the "Metrology for World Class Manufacturing Awards" last month.

For further information please contact:

Dr Ping Liu, Dept of Engineering
Centre for Nanotechnology and Microengineering
University of Warwick: Tel: 024 7652 3136