BBC Home

Explore the BBC

Front Page

Life | The Universe | Everything | Advanced Search
 
Front PageReadTalkContributeHelp!FeedbackWho is Online

Click here to complete your registration.

 
3. Everything / Maths, Science & Technology / Engineering

Make Yourself a Scanning Tunnelling Microscope

A scanning tunnelling microscope, or STM, is a device that allows us to see individual atoms. It's generally thought that they must be ridiculously complex pieces of equipment, but nothing could be further from the truth. Here is a simple step-by-step guide to building your own.

Site Location

Before you begin construction, consider your position carefully. While they're not complex, STMs are sensitive so positioning your electron microscope next to a motorway is possibly a bad move. Even a corridor next to the apparatus will give you large amounts of noise, and talking should be kept to a minimum. It'll also help if you plonk the whole thing in a bell jar to keep vibrations out.

The Electron 'Needle'

The STM works by using a fine needle as an electrode, placed a tiny distance from any surface. It seems obvious that you'll need a very fine needle; but what's obvious is not always true. Even at top research universities, the needles are remade every day; not because of accuracy problems, but because it's a ridiculously simple process.

Building Your Needle

  1. Get a piece of electrical wire.

  2. Take a single thread of it, so it's about 1mm wide.

  3. Get some pliers.

  4. Cut end of wire at a 45° angle.

That's it - you've made a needle for your STM!

Power Supply

To get electrons to jump a gap, you usually need to use a high voltage. In fact, classically1, you shouldn't get any jumping. Most people think you need a couple of tera-volts2 to get an STM to work, whereas in practice about 6 volts are used. Whack this up to a massive 9V3and connect one end of the power supply to the needle (the uncut end) and don't connect the other end to anything. But do earth4 whatever you are trying to scan.

Looking at Something Very Small

To make your STM work, you actually have to give it something to scan and tunnel. Get the tip to hover above the surface you want to scan so that a constant current passes through it; this ensures it's always a constant distance from the sample. This involves using a piezo-electric crystal5 to produce very fine movements in the needle. Send this to a PC and you are on your way to seeing atoms.

Other Essentials

The whole thing needs to be performed in air, not in a vacuum... it makes tunnelling6 more likely. Also, your object needs to be electrically conducting and to do this you can coat an object with silver if it isn't electrically conducting on its own.

Using Your New Toy

Once everything is hooked up, program your computer to scan along the sample. Record the information on the PC and marvel at the roughness of polished steel.

The Professionals

DFM have a nice if somewhat technical page on Scanning Probe Microscopes - the family of microscopes to which the STM belongs.


1 Classical science is what physicists knew in the 18th Century and what you learned in school.
2 A tera-volt is 1012V.
3 For this you can use a standard smoke-alarm battery
4 That is, connect it to the electrical earth, sometimes known as 'ground'.
5 A piezo-electric crystal changes shape when you run voltage across it, and produces a voltage difference when you change its shape.
6 Tunnelling is when an electron crosses the needle-sample gap.

Discuss this Entry  People have been talking about this Guide Entry. Here are the most recent Conversations:

STM in air? and more..
(Last Posting: Feb 24, 2002)

Vibrations
(Last Posting: May 5, 2000)

building one
(Last Posting: May 5, 2000)

The problems IMHO
(Last Posting: Jul 27, 2001)

<No subject>
(Last Posting: May 5, 2000)




Add your Opinion!

There are tens of thousands of h2g2 Guide Entries, written by our Researchers. If you want to be able to add your own opinions to the Guide, simply become a member as an h2g2 Researcher. Tell me More!

 
Entry Data
Entry ID: A275942 (Edited)

Written and Researched by:
The Cow
Gert

Edited by:
26199


Date: 16   March   2000


Text only
Like this page?
Send it to a friend


Referenced Sites
DFM
Scanning Probe Microscopes

Please note that the BBC is not responsible for the content of any external sites listed.

Most of the content on this site is created by h2g2's Researchers, who are members of the public. The views expressed are theirs and unless specifically stated are not those of the BBC. The BBC is not responsible for the content of any external sites referenced. In the event that you consider anything on this page to be in breach of the site's House Rules, please click here to alert our Moderation Team. For any other comments, please start a Conversation below.
 


Front PageReadTalkContributeHelp!FeedbackWho is Online

Most of the content on h2g2 is created by h2g2's Researchers, who are members of the public. The views expressed are theirs and unless specifically stated are not those of the BBC. The BBC is not responsible for the content of any external sites referenced. In the event that you consider anything on this page to be in breach of the site's House Rules, please click here. For any other comments, please start a Conversation above.


About the BBC | Help | Terms of Use | Privacy & Cookies Policy