The Sublime World of the Sub-Miniature

in MSE Division Head's Blog
November 23rd, 2011

BISHOP-172At Boston University we have a large and active group of researchers working in MEMS and NEMS.  MEMS are Micro-Electro-Mechanical-Systems and NEMS are Nano-Electro-Mechanical-Systems.  These are devices built at the micrometer and nanometer scale using Silicon VLSI processing with parts and structures that can either move (dynamic systems) or have other functionality enabled by their small sizes.  Basically, in the jargon of today, they are micromachines.

Why is this kind of work interesting and important? 

It turns out that, generally speaking, there are two broad categories of scientists who are rushing towards the nano-world.  There are chemists who traditionally worked with atoms and molecules that entered the nano-world by creating ever larger molecular complexes such as carbon nanotubes and proteins.  They developed the techniques to create, control and understand larger and more complicated molecules and now much of chemistry does this.  Physicists and Electrical Engineers have gotten to the nano-world by following Moore’s law, using the techniques of Silicon VLSI processing to make increasingly smaller structures, down to the nanoscale.  Characterizing chemistry and physics/EE this way is a gross generalization but the high level trends are these.

The reason for this assault on the nano-world is that is where much of the interesting things that biological organisms can do take place.  For example, if you study the mechanical properties of sea shells, their amazing behaviors are due to nano-scale engineering of a kind that we are only just beginning to understand.  Thinking, vision, hearing, smell, taste, touch, these all happen because of structures and functionality at the nano-scale in biological organisms.  Given that biological organisms can do things in these areas that we can’t come even close to imitating with artificial systems, many of us work in this field to let nature teach us.  Sort of a “if you can’t beat them, join them” attitude. 

The nanoworld is interesting because you can combine mechanical functionality with chemical forces and reactions.  In other words, you can make something that moves in a way you can measure that responds to the forces and energies generated by small numbers of atoms and molecules. 

Think about this simple example.  I can use mechanical devices to measure forces.  For example, if I have a swing in a playground, I can make it move by throwing a rock at it.  I can also make it move by throwing a piece of coal at it.  If the rock and the coal are the same size, shape and mass, I won’t be able to tell by the motion of the swing what I hit it with.  There is no chemical selectivity.  If it were important to me to be able to tell if it was coal or a rock, I would be out of luck. 

However, if instead of a human scale swing, I built a nano-scale one, I can functionalize the surface of the swing (geek speak for putting some chemical junk on the surface) that responds differently to rock and coal.  At the nano-scale I would be able to tell whether it was rock or coal by the different chemical responses to the layer of junk and its effect on the mechanical properties of the nano-swing.  The small amount of rock or coal that got left on the large swing wouldn’t affect its behavior enough to measure but it would for the nano-swing.

So you will often see folks like us building nano-swings, nano-guitars, micro-microphones, micro-microscopes, etc.  So in addition to just doing these things to prove to ourselves and others that we are really good at this stuff, there is a larger point to it all.  This larger point is that things at the nano-scale have a sensitivity and functionality that can’t be obtained with human scale devices.  If we want to do the things that the best systems in the world (biological organisms) can do, we need to live and work where they work, at the nano-scale.

In these blogs in the coming months I will be describing some of the ground-breaking research done in this area done by my BU colleagues.  But the larger reason for this entire line of research is that we want to be able to push things to their ultimate limits in terms of performance and biological systems currently rule the roost.  Our eyes, our brains, our ears, our noses, these all work better than artificial systems we can currently create and we are jealous of that type of performance.  Now it took nature 5 billion years to get there and we’ve only been at it for a few decades but we are impatient. 

I don’t think it is very likely I’ll be around for another 5 billion years and so I’m chomping at the bit to see what we can do here in the next decade or so.  If this world fascinates you and you want to join us, either in person or by following us on this site and others at BU, we welcome you.

Cheers,

Dave B.