Molecular substitution produces terahertz switch arrays

By R. Colin Johnson EE Times (04/10/00, 3:35 p.m. EST)

URBANA-CHAMPAIGN, Ill.  Researchers at the University of Illinois have developed a method of prepping single-crystal silicon wafers for organic molecules, which produce molecular switches with atomic precision.

Wafers from existing silicon manufacturing facilities could be used to achieve switching arrays running at 100 terahertz, the researchers said. By attaching arrays of spinning organic molecules to the surface of a standard silicon wafer, the group demonstrated, in principle, how to fabricate molecule memories running at THz speeds.

"The organic molecules are only attached where a single hydrogen atom was removed, so they spin  some as fast as a 100 trillion times a second," said Joseph Lyding, a UI professor of electrical and computer engineering and a researcher at the University of Illinois Beckman Institute for Advanced Science and Technology. "We're working with chemists now who are designing molecules that when attached will act like transistors that can switch at 100 trillion times a second," said Lyding.

Lyding's group removed individual atoms of hydrogen from finished wafers of single crystal silicon, creating "holes" on the silicon surface. The holes create a gradient that attracts any free molecules that happen to float by. By exposing the prepped silicon only to convenient organic molecules, the surface can be automatically populated with arrays of identically spinning memory elements, each emulating a transistor that switches each time it spins.

"If this technology takes hold, we will be returning to the mechanical memories of yesteryear  because we are really just building a mechanical relay, but on a nanotechnology scale. It will be read and written to electrically, but the active element is just a very very small mechanical device," said Lyding.

The researchers' first step was to remove the heavy oxidation that's ordinarily applied to a silicon wafer, thus exposing a perfect silicon surface. Then in very high vacuum, Lyding and fellow researchers Mark Hersam and Nathan Guisinger passivated the pure silicon surface with hydrogen  forming a single-atom-thick layer of hydrogen strongly bonded to the silicon.

The next step involved using a scanning tunneling microscope to dislodge individual hydrogen atoms to attach the spinning organic molecules. The resulting surface was smooth like pure silicon, except for holes where the individual hydrogen atoms had been removed. In terms of gradients, these holes lure molecules toward their "dangling" bonds, spontaneously self-assembling organic molecules, injected in gas phase, into atomically precise arrays.

Atom-sized holes

Atomic precision in punching out single-atom-size holes in the hydrogen surface was accomplished by a feedback loop from the microscope that controlled the tunneling current. When the single atomic bond was broken from the selected hydrogen atom, the feedback signal instantly cut off the tunneling current to prevent further disturbance to the surface. The microscope can also be programmed to move to the next atom when a bond is broken, so that lines of hydrogen atoms can be removed from the silicon surface.

"We are doing things now like writing two non-parallel lines that get closer and closer together  in that way we can gauge just how close we can get lines and still have them remain discrete," said Lyding.

In the end, the researchers impress "templates" atop the silicon surface by scanning the tunneling microscope in chosen patterns. Eventually, they will create arrays of memory or switching elements. But for now the group is trying to perfect procedures. So far, they have tried attaching three organic molecules: norbornadiene, copper phthalocyanine and carbon-60 "buckyballs."

"The advantage of organic molecules is that their ends can be functionalized so that they easily interface with either electronic or nanoscale mechanical devices," said Lyding. The group cautions that it has more work to do to validate its approach before a practical circuit design method can be announced.

-- Nanu (@ .), April 14, 2000

Answers

Looking forward to it. Certainly a 100 terahertz chip would eliminate the delay I presently enounter when Win98 loads. I'd be willing to pay a few extra bucks for that.

-- E.H. Porter (Just Wondering@About.it), April 14, 2000.

The irony, of course, is that Windows will still run slowly on it.

-- (hmm@hmm.hmm), April 14, 2000.

I just never can remember. Is terahertz faster than gigahertz? What is the conversion factor? What about booga-booga hertz?

Anyhow, today was not the day to buy stock in hertzes.

-- Lars (lars@indy.net), April 14, 2000.

Tera is trillion. Giga is billion. A tera- is 1000 times a giga-.

Tera comes from the Greek for "monster" = terus

-- (retard@but.happy), April 14, 2000.

Lars, may you kiss a trillion teratoids.

-- (nemesis@awol.com), April 14, 2000.

I thought that said Billy Joel.

-- Swampthing (in@the.swamp), April 14, 2000.

Hmm:

The irony, of course, is that Windows will still run slowly on it.

I understand the statement; BUT I have one Wintel machine that has been running 2000 for sometime. I predict, that oneday, you will look back and say why can't they make an OS as good as Win98

Just my experience.

Best wishes,,,,,,

-- Z1X4Y7 (Z1X4Y7@aol.com), April 14, 2000.

I agree Z, I put W95 on my wifes 486DX266 so she could run the latest software and compared to W3.1, far slower now. My W98 on my AMD350 runs faster of course, and I will give it this - I have not had a single crash of the operating system since I had it. Of course the usual quirks and lockups of specific Windows programs occurs, especially with the Browsers, but even those are much rarer than with W95.

Have a box of Linux, but haven't got it going yet on another older machine (doesn't reckognise my second HD and a few other devices).

-- FactFinder (FactFinder@bzn.com), April 14, 2000.