Nano Trees

In my reading up on silicate crystals, I stumbled upon this…

Aren’t these just beautiful? These tiny trees are only a couple of microns tall. They’re made from silicon carbide (one of the toughest substances known) and were grown on a wafer of silicon.

They’re made by chemical vapour deposition. In other words, they condense straight from gas into these crystalline forms — not unlike the way snowflakes form. Amazingly, the growth of these tiny structures can actually be controlled by varying the temperature and pressure of the chemical vapour.

They were made by Ghim Wei Ho, now an assistant professor at the University of Singapore. When she was studying her PhD at Cambridge, it seems she made quite a few other little nanostructures.


About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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7 Responses to Nano Trees

  1. Yes, there is a formula that is used to calculate the kinetic energy, and I think I have it in my report and powerpoint presentation — although I’d have to double check.
    If you want, I can message you first and then you can message me with your email.

  2. invaderxan says:

    Ooo! Yes please! If you could send me both of those that would be brilliant!
    I’ll send you a message with my e-mail.
    So essentially it’s all down to having enough kinetic energy to knock an atom away… And I’m guessing an ion is easier to accelerate too. That makes perfect sense. Is there any way to calculate how much kinetic energy you’d need for a given atom?
    Thank you very much for taking the time out, here! :)

  3. I guess it depends on the type of sputtering you’re wanting to do. For the sputtering I work with — that is, to make thin-films on various substrates — one of the main things you need is weight. It sounds a bit cliche’ but you know how people say that those people with weight can push it about? The same is somewhat true for sputtering too. With sputtering in general, you’re relying both on kinetic and thermodynamic processes for the sputtering to occur, but the weight comes into play with the kinetic parts of the sputtering. The heavier the atom you use to bombard the sputtered material with, the easier it will be to knock off the material you wish to sputter.
    For example, you can use Nitrogen to sputter most materials – like Al, Si, Ti, Au, just to name a few. However, for the heavier metals (especially Ag or Au), it’s to your advantage to use a heavier Noble gas such as Argon, as the argon (which does require more kinetic energy to get it moving) will be able to transfer more kinetic energy to the material being sputtered so that they are released from the bulk more readily. So, generally — as I’ve worked with sputtering, you use ionized atoms, rather than electrons, to sputter because of the weight issue.
    As for high energy photons, there might be a manner that this used, but I am not aware of it. Usually I’ve only heard of high energy photons being used as you’ve described with with XPS and Auger Spectroscopy.
    Oh! If you want, I can send you a Powerpoint file I have for when I did a comparative study of CVD vs Sputtering back for my Surface Chemistry class four years ago. I think it’ll give you a good overview, and if you want more details I can send you the research paper I wrote in conjunction with it.

  4. invaderxan says:

    Haha! Fair point! :)
    So… I was wondering about the actual mechanism involved in sputtering. I know sputtering is typically caused by bombardment by energetic ions or electrons — But can it be caused by high energy EM photons? I was thinking, a similar mechanism to x-ray photoelectron or auger electron emission.
    See, they’re both candidate physical processes that could (and probably do) affect interstellar dust grains… ;)

  5. Some of us don’t get to be quite so picky.
    Technically, I can’t be picky either. When you join a lab that already has $1 millon of Reactive Magnetron Sputtering equipment, you really don’t get to chose CVD over that. ;)
    Sure, feel free to ask me sputtering questions whenever you have them. Both CVD and Sputtering have their +s and -s when it comes to thin film deposition, so it’s good to know about both.

  6. invaderxan says:

    Heh… Some of us don’t get to be quite so picky. By all rights, I should really know about both. ;)
    Though I don’t really know that much about sputtering. Do you mind if I ask you some stupid questions from time to time…?

  7. Boo! Down with CVD!
    (Sorry, CVD is the main competition for sputtering – another method to do thin film deposition. Those of us in thin film deposition are fiercely loyal to one method or another.)
    But very pretty anyway! ;)

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