Scanning tunnelling microscope (STM)

Function: Lets users study the surface of nanostructures. 

Maximum magnification: Approximately 90,000,000x. 

Best for:

• Looking at individual atoms.

• Looking at the surface of nanostructures. 

Disadvantages:

• Only a few nanometres of a sample can be seen at a time.

• Requires very clean and stable surfaces. 

Video: Professor Richard Haverkamp of Massey University explains how a scanning tunnelling microscope works, accompanied by views of the device in use.

Transcript

Dr Richard Haverkamp

A scanning tunnelling microscope and an atomic force microscope are two related techniques. 

I've got two of these machines, and they can be either scanning tunnelling or atomic force. So the basic machinery is the same except for a little attachment you put on them. So the scanning tunnelling microscopy is where you are imaging using a little sharp needle, usually a platinum wire, and you’re passing a current between that wire and your sample. So the closer it is to the sample, the more current will flow. And so by measuring that current, you can work out how close it is to the sample. This distance you can measure, you can judge that distance down to incredibly small amounts, so the fraction of the size of an atom. 

With this machine, you can't look through an eye piece. You have to see it through the computer. You’re doing it by touch, so the computer is poking with a little needle and feeling the height and recording a number, and it gives it to the computer and then you get the computer graphics to draw it up. So what you are seeing is generated by the computer from touch. So it’s a blind person’s drawing really. And you can use colours to show heights. You can make some beautiful looking pictures, but none of the colours relate to what you are looking at.

Acknowledgements
Professor Richard Haverkamp, Massey University