Posted on 10/13/2009 9:06:08 PM PDT by neverdem
Researchers from the US and Russia have shown how it is possible to measure the diode properties of a single molecule and how the orientation of the molecule between two electrodes can be controlled. The findings are a significant advance in the expanding field of molecular electronics, which seeks to construct electronic circuits from molecular-scale components, opening the prospect of a new generation of devices that are immensely powerful and efficient yet tiny.
Diodes act as electronic 'check valves' in a circuit, permitting current to flow in one direction only through a process known as rectification. In a molecular circuit, single molecules acting as diodes would form a key component, and ensuring that the diode faces the right way is crucial.
Ismael Díez-Pérez from Arizona State University and his colleagues selected as a candidate molecular diode an asymmetric linear molecule consisting of a pair of pyrimidinyl rings covalently linked to a pair of phenyl rings. The bipyrimidinyl moiety is electron-deficient, while the biphenyl block is electron rich.
To measure the diode properties of the molecule the researchers attached either end to a gold electrode. One electrode consists of a flat gold substrate while the other is the gold-coated tip of a scanning tunnelling microscope (STM). The link between the molecule and the gold is made through a thiol group. To ensure that the molecule is placed in the correct orientation, the thiol group at one end of the molecule is protected by a cyanoethyl group, while the other end is protected by a trimethylsilylethyl group. The molecule is first exposed to the substrate and one of the protecting groups removed so that only one end of the molecule attaches; once in place the second protecting group is removed to enable attachment of the STM tip to the other end of the molecule.
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The team used an asymmetric molecule as to act as the diode, and attached each end to a gold electrode to measure its conductance
© Nature Chemistry
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Measurements of current at the STM tip showed both that contact was made with a single molecule and that the molecule caused a significant rectifying effect.
According to team member Nongjian Tao, 'A general implication is that any molecule with asymmetric electronic properties should have a rectification effect.'
Another member of Díez-Pérez's team, Luping Yu, adds, 'The molecules are designed such that we can sequentially assemble them in a controlled direction. It is like a physical diode device [where] you have mark one end as positive another negative. The difference is that we used chemistry to do that.'
Richard Nichols, an expert in molecular electronics at the University of Liverpool in the UK, is impressed by the study. 'It is a very nice piece of work,' he says. 'They have used a combination of theory, STM and single molecule measurements and have found a way to orient an asymmetric molecule at the junction. Using this strategy it is possible to place things the right way up within a molecular circuit, which is a key consideration.'
And of course in the '60s - '70s we had plenty of schoolbooks warning of the perils of a technology explosion, how we would all become inanimate beings confined to some sort of life support capsules in the vast wasteland of earth, things like that.
And of course there are implications to the idea of all information processing being universally connected about which folks ought to be concerned.
Good or bad? I don't know but certainly each successive generation (not even generation really but a term for a smaller set escapes me) has a different attitude about the extent to which they are willing to embrace and put their affairs into the connected world. For me, I like to think I have control over what I'll freely share with the world and what I'll put forth as needed. But more and more I see what I am trying to maintain be less voluntary and more dictated by someone else (especially government). I don't like it.
The ancient prophecy seems to warn about such a time but that's not central in forming my attitude. I like my debit card, online banking and bill paying, shopping, etc. It is convenient and saves a lot of time, energy, and hassle. I like being able to communicate in near real time with anyone willing about matters of mutual interest. I like having my phone everywhere I go and I like some of the extra things it does. And so on. But at the same time I prefer to be aware of what goes on inside the beast, so to speak, and it is evermore tedious staying up on who has access to what and keeping some manner of control.
And beyond that there is the matter of dependence. The technological infrastructure is not infallible under normal circumstances and certainly it's ripe with soft targets. I don't know if those issues will be resolved in my lifetime and I am prepared to survive in an outage should it occur.
But there, a sort of self healing distributed computing model presents an effective solution to those shortcomings, and the expense would be almost negligible as you say, but what are the other costs?
By “ancient prophesy” you are referring to the bible’s book of revelation?
So in your mind the “beast” of the bible is a super computer or the internet?
I referred to the “ancient prophecy” in my post and I even spelled it correctly. But if you read the whole post you’d know that my concerns about technology are not based on that, but on real here and now things, and that we are in agreement about most of the shortcomings of today and how what is likely to come in the next few years can fix some of those problems.
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