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Elemental homeopathy

(published 20 July 2011)

Yesterday I set out on a voyage to draw a picture of silicon. I had wanted to draw the silicon atom (and to subsequently work up to the crystal structure) whilst envisaging the positions of the electrons / their orbitals, as I wish to come to a degree of understanding about semiconductors; the freedom, or not, of electrons from the silicon atoms in its crystal lattice appears to be of some import in that regard. 

Semiconductors can conduct a little bit of electricity (more than insulators, less than metals) as a result of loosely bound electrons in their chemical structures that can be liberated by absorption of energy from the environment in the form of heat; with increasing temperature intrinsic semiconductors become more conductive. I had been reading about semiconductor doping, this being a mechanism whereby semiconductor materials (for example silicon) can be altered through the addition of tiny amounts of other chemicals (the dopants) in order to make them more conductive. It’s kind of like elemental homeopathy. The doping materials can either be such as to add electrons to the semiconductor, making it more negative and hence called n-type dopants, or to stick some of the free electrons that exist in the semiconductor more securely into the chemical structure, effectively making it more positive and thus called p-type. P- and n- doping are fundamental processes in silicon photonics where they are used on a precise and minuscule scale to manipulate the passage of current through chips and wafers, etc. I had been fascinated to read that the addition of a single arsenic atom per million atoms of silicon increases the conductivity of the latter by 100,000 times. The arsenic atom has one free electron that it lends to the process (it is an n-type dopant), and yet this tiny addition accounts for such significant changes in the behaviour of the material. And so off I set onto the sea of electrons.

My journey took me deep into the world of angular momentums and exclusion principles, illuminations of virtual photons lighting my way, as I floated on surfaces of identical electron particle/waves. I had a smooth crossing of the Dirac Sea, since there was nothing there to cause wind or heavy weather, although the negativity got hard to bear towards its infinitely distant shores. Luckily the outcome from such monotonous negativity can only be positive, and all of a sudden the antimatter positron popped into existence. I journeyed on through radiant matter, and passed a few anomalous magnetic moments. Many hours of incomprehension further into the books and pages, all the while trying to assess which bits of this science are knowledge and which are model. I know that people have focussed beams of electrons for one reason or another, but no one has ever actually seen an electron, so know not what they have focussed. I read words telling me that an electron has a mass of about 0.00000000000000000000000000009 g, has an electric charge of -0.00000000000000000016 coulombs and a spin of a half. But I am also informed that electrons have no substructure and are hence assumed to be a point particle with a point charge and no spatial extent. I’m not sure how I can draw no spatial extent.

In order to see anything it seems that we need an illumination source that has a shorter wavelength than the dimensions of the thing we are endeavouring to see. For example, we can see using light since it bounces off the surface of visible things in such a manner as to convey surface texture and colour of objects, etc., to our eyes. Using a classic light microscope we can visualise objects with a resolution of down to about a tenthousandth of a millimetre, at which point the wavelength of visible light is getting to be of a similar scale to what we are looking at and it ceases to be able to discriminate surface variations. With an electron microscope the smallest dimensions visible are in the low nm range, about a hundred or so times smaller than things that can be seen under a light microscope. In order to look at an electron or a photon we need (a) for them to have a physical existence, and (b) something that can visualise down to the range of their physical size. 

And so I am back at wondering how, in the name of Art, to depict silicon’s electrons. Mentioning my problem to M later in the day she suggests that I simply put forward blank sheets of paper, and since she is an Art Historian I think I’ll take her advice.

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