Australian overturns 15 years of nano-science doctrine

Tuesday, 08 April, 2003

Dr John Sader, at the University of Melbourne's Department of Mathematics and Statistics, and Particulate Fluids Processing Centre, used established mechanical principles to prove that the popular V-shaped cantilever inadvertently degrades the performance of the instrument and delivers none of its intended benefits.

Sader's research was published in the April issue of Review of Scientific Instruments.

In atomic force microscopy, small cantilevers are used to profile surface topography and structure. Shortly after the invention of the AFM, almost two decades ago, V-shaped cantilevers were introduced to minimise the effect of lateral forces on image quality, a problem faced by the original rectangular design. Sader's research reveals that this attempt to rectify the lateral force problem was based on a false assumption.

Instead of increasing the resistance to twisting, V-shaped micro-cantilevers actually maximise twist and degrade the performance of the instrument.

"This finding is surprising and counterintuitive, contradicting accepted practice and manufacturing standards worldwide where the V-shaped cantilever is the standard due to its alleged advantages," says Sader.

Users of the atomic force microscope have long put up with the geometric complexity of the V-shaped micro-cantilever, with resulting difficulties in calibration and interpretation, to gain improved lateral performance.

Sader's calculations establish that the simple cantilever design of a straight beam proposed for the original atomic force microscope offers greatly improved performance over the V-shape while facilitating calibration and measurement interpretation.

This finding has the potential to revolutionise the industry by setting a single universal standard and improving the performance of the instrument, while greatly simplifying its operation.

"Although the V-shape certainly offers strength and stability in the construction industry, its misuse has had a detrimental effect in the field of nano-science," says Sader.

Atomic force microscopy

Since its invention in 1986, the AFM has been the instrument of choice for three dimensional measurements at the atomic scale.

The all-important cantilevers are placed in light contact with a sample and moved across its surface, detecting any change in surface topography. Cantilever calibration is a fundamental issue in the use of the instrument. There are several techniques in existence. Sader has devised one of these techniques, which is used commercially and by researchers worldwide.

The AFM is suitable for studies such as cell biology, polymer materials, biomaterials, materials science, food science, colloids, surfactants and coatings. The AFM is also capable of operation in liquids, a necessity for examining cells, tissues and other biological specimens immersed in liquid.

Measurements made from AFMs have revolutionised the way scientists quantitatively observe and think about the chemical, biological and physical world.

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