NEW HORIZONS — Gold and medical research

The ability of gold atoms to stick together even when beaten into gossamer-thin layers has been known since ancient Egyptian times. Now, researchers have produced an even thinner layer of gold — no thicker than one gold atom. This super-thin, super-smooth gold is being used in a special microscope to study living molecules.

Its most immediately useful application is for determining the structure of biological molecules using the scanning tunnelling microscope. Gold is ideal for this microscope because the substrate must be conductive, cannot react with the sample and has to be very smooth.

The scanning tunnelling microscope works by moving the tip of a metallic needle over a sample, much like the needle of a record player moves over the groove of a vinyl record. The tip moves up and down over each atom on the surface. An electric current through the needle is kept constant as it moves along a 2-dimensional representation of the surface. By repeating these scans in parallel, a 3-dimensional representation of the atoms on the surface is obtained.

Physicists evaporate gold in a vacuum onto a specially prepared drawn-glass surface, then peel off the gold. When a virus, bacteria or organic molecule is placed on this atomically flat gold surface, the tunnelling microscope will reveal its structure, atom by atom. With the structure thus revealed, ways to deal with the desirable or undesirable properties of the virus, bacteria or organic molecule can be identified more easily.

There are a wide range of uses for optically flat gold surfaces. Gold is not only the best infrared reflector (and so, has become the material of choice for infrared telescopes and microscopes), but it is dense enough to reflect x-rays, making it suitable for use in x-ray mirrors. The new super-smooth gold provides x-ray microscopes with a precision of reflection not possible with other metals.

Precise thickness measurements on an atomic level will be welcomed by electronics manufactures. The perfectly smooth gold layer provides a reference surface essential to the ellipsometer, a device the monitors precisely how many layers of atoms have been grown on a surface. This is of critical importance to manufacturers of microelectric circuitry, where minimizing circuit length and size can increase computer speed.

Under study is the potential of using the gold substrate for measuring the strength of forces that hold atoms together. Besides providing a reference for understanding the interatomic forces in surfaces, such data is also essential to research into high-strength adhesives.

— The preceding is an excerpt from “Gold News,” published by the Washington, D.C.-based Gold Institute.