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IBM Creates 1st Single Molecule Computer Circuit
Llowfyr writes "Yahoo has reports that IBM researchers have created the first ever single molecule computer circuits which may someday lead to a new class of smaller and faster computers that consume less power than today's machines. The IBM team made a `` voltage inverter '' -- one of the three fundamental logic circuits that are the basis for all of today's computers -- from a carbon nanotube, a tube-shaped molecule of carbon atoms that is 100,000 times thinner than a human hair. IBM scientists will present the achievement today at the 222nd National Meeting of the American Chemical Society being held in Chicago and it appears in the web edition of the ACS' journal Nano Letters."
Gain is a common figure of merit of transistor-based amplifier circuits. The gain of a voltage amplifier is defined as the ratio of the size of the output signal to the size of the input signal. An amplifier that could take a 0.5V amplitude sine wave as its input and produce a 5V amplitude sine wave as its output has a gain of 10. You don't get something for nothing, of course - the amplifier has to be connected to an external power source.
A transistor is a three-terminal device. In a typical computer chip, these three terminals are called the source, the drain, and the gate. For a given voltage between the source and drain, the current that flows into the drain is strongly dependent on the voltage applied to the gate. That's what allows transistors to be used as switches: you can make a transistor that won't let current flow from source to drain unless the gate voltage is turned up past some value.
Achieving actual gain in a single-molecule device is important. Without gain greater than one, it's not possible to efficiently chain large numbers of transistors together to manipulate signals. A strong input would get degraded with each stage of transistor manipulation, eventually falling to a level too small to drive subsequent transistors.
There are *many* problems with the idea of using individual molecules to replace Si devices. Achieving a gain > 1 is a necessary but by no means sufficient step for eventual molecule-based computers. As a physicist, I think it's important to recognize real achievements in this field, but not to buy into the hype unquestioningly.
What IBM need to do now is make an AND gate. The output of an AND gate, fed into a NOT gate (NAND), can form the building block of any digital logic element you care to name (gates, registers, etc.) Then they need to figure out how to join them together, and get signals in and out. Then figure out if a nanotube processor would actually be useful! :> Anyone know the theoretical switching time of these type of devices?
I found the full paper here (that's http://pubs.acs.org/hotartcl/nalefd/nl015606f_rev. html for you paranoid types).
I was just thinking - they say their NOR gate is the size of approx. 1/100,000th the width of a human hair. Well, today's 1.4 GHz chips contain ~22 million transistors. That would make it 220 human hairs wide. That's a lot of power in a small space. I can't wait till the day I can crack RC5 on my cell phone.
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#nohup cat
Your education is shallow and misled.
Diamond is not an ionic compound. It is composed of carbon atoms in the optimal arrangement to form covalent bonds. Tell me diamond isn't a crystal.
Bonds are rarely 100% covalent or 100% ionic. A crystal is a single molecule (but not all single molecules are crystals). These facts are old. Very old. Older than your textbooks. Shame on your school.
I won't get into the semantic argument about solids, liquids, gases, and how any of them can be said to form or be formed by crystals, because that would only confuse you (and because in the more intricate cases I'm bound to forget the details and my book is in another state). Just trust that the definition of "crystal" that you are using here is very inadequate.
Go search on a few things:
Ionic Bond
Covalent Bond
Ionic Character
_General Chemistry_, by Linus Pauling*
--Blair
"We teach chemistry like it's either a foreign language about a dead religion or a way to make the neighborhood kids think we're cool."
P.S. I'd like to thank the Academy for down-modding my original post. It's always nice to see that the forces of intolerant ignorance continue to crawl the planet. It keeps an exterminator of such things in poker money.
* - the Dover 1989 reprint of the 1954 edition only costs like $14. How much did you pay for a semester of your college's misapprehensions?
As classically understood, molecules are fundamental chemical units composed of atoms in precise amounts, types and arrangements. Molecules can't be subdivided without changing their chemical properties.
Crystals are not molecules because their constituents need not appear in precise proportions (a water molecule on the other hand is ALWAYS 2 hydrogen and one water), and because you can break them into chuncks that have identical intensive chemical properties. Crystals have basic units which are molecules or single atoms and combine to form the crystal lattice (often with trace impurties which are important). Crystals are chemcially bonded together, as are many things, but this does not make them molecules (according to the classical definition).
Things like diamond, polymers, DNA, and nanotubes have come to challenge the bounds of what people label as molecules. Many people, news media, and some scientists have come to accept a broader conception of molecules as being any stable, complete (as in not attached to something), and strongly bonded (doesn't usually spontaneously disassociate) compound. Myself and others I know tend to consider this looser definition to be a foolish disregard for the important aspects of the previous definition.
Knowing that what you are studying is the smallest unit with the properties you are interested in is a powerful piece of information. Similarly knowing that this basic unit requires a particular arrangement of certain atomic types grants you the keys to understanding it.
As far as I'm concerned crystals are chemical compounds or chemical aggregates but not molecules. Same for polymers (unless the context makes it important to distinguish 40-unit from 41-unit and every other length of polymer, etc.). DNA is a molecule because every single arrangement is important to how it functions and no piece has the full chemical functionality of the whole. Nanotubes, on the face of it, seem to be polymers and thus not molecules (though I don't have enough depth in the matter to say for sure.)
So we have the first logic process made out of a polymer, but it's not a specific molecule that does the job. I'm glad chemical bonds hold their tubes together and I'm glad they make our standard transistors possible, but chemical bonding != molecule.
Call it what it is, a NOT gate.
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