Friday, September 12, 2008

Work Experience - or 'slave labour'?

Work experience student Paul Randall - from Thornden School - has been helping me this week with Outreach work at the University of Southampton's School of Physics and Astronomy. I've asked Paul to tell you what he got up to - when I let him off photocopying duty...

"I am a year 11 student doing a two-week work experience placement here at the School of Physics and Astronomy. After being accepted I was very excited and anticipant - since my placement began I have delved into nanoscience, learnt endless pieces of new and interesting information and have always had my views and opinions asked for and taken seriously.

On my first day I was asked to help improve both a nanotechnology poster and a Year 10 prospectus (both of which are being sent to schools round Hampshire) and was also shown both the Holography and the nanotechnology fabrication labs and the equipment they use. Not only has my work experience been helpful and interesting, it has allowed me to meet new people and learn about aspects of science I never new existed.

Creating a two dimensional image with a layer of gold.

With the help of Zondy Webber, one of the technicians, I was taken to the ‘clean room’ - to be inducted into the ways of lithography.

First Zondy coated a centimetre square piece of wafer in a photo resist, a thermo-setting plastic (PMMA). To create a thin film of the liquid on the square we used a spin coater which span at 4000RPM forming an almost perfectly flat layer of about 350nm thick.

Once heated to 1200C the plastic set and a spectrophotometre was used to measure the thickness of the plastic layer (by reflecting light off the surface). The equipment works by literally splitting a beam of visible light in two and sending one half to a sample (used as a control) and the other to the silicon wafer (the reference material). Fortunately in this instance the results revealed the wafer to be suitable to work with.

Using a scanning electron microscope (SEM) we exposed an area of the water to an electron beam that works using a high electric charge (10KV) to accelerate and focus a beam of electrons at the target. The diameter of the beam is a mere 25 nanometres and so is but 1/1600th of the width of a human hair.

This electron beam exposes the PMMA and breaks the molecular bond within it; this creates a groove of weakened PMMA - the depth can be altered by different levels of exposure. Once removed from the SEM the wafer is placed in a solvent to remove the exposed PMMA, it is then placed in a thermal evaporator chamber which melts first chrome and then gold to form vapours which coat the wafer, the grooves and the whole of the chamber. Because the whole wafer is coated in a thin layer of chrome and gold a different solvent is used to remove the unexposed PMMA, leaving only the gold in the grooves as a thin but still visible layer.

We produced the name ‘Paulus’ at 5 different exposure levels to allow us to discover the best level for this thickness of PMMA. The first was ¼ of the recommended exposure which came out as an illegible lump, the second was at ½ of the recommended exposure and was considerably clearer, then at full exposure which was legible and well shaped except for small abnormalities on the second ‘u’. We also tested both double and quadruple recommended exposure levels produced better quality but thicker lettering.

It was amazing to have my name written so clearly at such a small scale that isn’t even close to being visible to the human eye. Looking at the wafer one can only just make out the comparatively giant scratch (which is larger than the size of the words and the even bigger spaces between them) to the upper right of the 5 names. The words are only half the height of a human hair and each letter but ¼ as wide, and each word took an average of less than 10 seconds to complete.

I also worked with Pearl John helping her to create multiple holograms of different objects.


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