Exercise #5: Molecular electronics proposals

[As always, I’m not promising this is a good use of your time, but you might find it stimulating.]

Here is a paper from 1983:

In anticipation of the continued size reduction of switching elements to the molecular level, new approaches to materials, memory, and switching elements have been developed. Two of the three most promising switching phenomena include electron tunneling in short periodic arrays and soliton switching in conjugated systems. Assuming a three-dimensional architecture, the element density can range from 1015 to 1018 per cc. In order to make the fabrication of such a molecular electronic device computer feasible, techniques for accomplishing lithography at the molecular scale must be devised. Three approaches possibly involving biological and Langmiur-Blodgett materials are described.

Depending on how you count, the author describes ten or so proposed methods for molecular-level fabrication of electronic devices:

  • Merrifield synthesis: An existing method of amino-acid-by-amino-acid polypeptide synthesis in solution is adapted to build up a network of molecular wires on a lithographically prepared substrate. Later, “switching and control functions are added, adjacent components are bonded together, and the process continued, ultimately forming a three dimensional solid array of active and passive components.”
  • Molecular epitaxial superstructures: Engineer a large flat molecule with edge-edge interactions such that it forms an epitaxial layer with small holes on a substrate; then deposit your desired material so that when you remove your flat molecule, all that’s left is the desired material where there were holes in the original layer.
  • Modulated structures: Heat an insulating film under certain conditions so that small conducting lines, which connect the top and bottom of the film, develop at potentially very close distances to each other, giving you a number of active sites on one surface that can be addressed from the other side of the film.
  • Electron tunnelling: Use a periodic molecular chain to switch electron tunneling from one end to another on and off by modulating the depth of potential wells in the chain so that the electron energy becomes on/off resonance with the wells, making it easy/hard to tunnel across.
  • Soliton switching: Use a propagating soliton in a system of alternating single and double bonds to turn chromophores on and off.
  • Neuraminidase: Use the regular arrangement (when crystallized in two dimensions) of the 10-nanometer spore heads of an influenza virus (or other molecules that form interesting shapes and patterns) to derive useful structures. Maybe use multiple tesselated tiles, like in an Escher drawing.
  • Fractals: Use chemical means to induce self-similar patterns at different scales to bridge the macro and micro scales, like in another Escher drawing.
  • Fiberelectronics: Produce a bundle of long wires of 10 nm diameter by filling a hollow glass rod with metal, heating and pulling out the rod by a factor of 100, bundling many such rods together, then hot drawing by a factor of 100 again.
  • Langmuir-Blodgett films: Modify a known technique for producing a film with a precise number of molecular monolayers, in order to incorporate a pattern of active elements or holes.
  • Monolayer polymerization: Build a device by stitching together monolayers so that interesting things happen at the interfaces.

You can read the paper as deeply as you feel necessary to answer the questions.

  1. What kind of paper is this? Is the author credible? What is he trying to accomplish, and on what timescale?
  2. More specifically: How would you read this paper as a scientist in a field it touches on? As a program officer? As a citizen who wants to understand and encourage innovation effectively?
  3. Which method seems the most experimentally accessible for investigation, from the 1983 perspective or from today’s? [Extra credit: What sort of experiment would you do?]
  4. Which method seems the most speculative in terms of whether it will be ultimately physically/chemically realistic even given advanced experimental techniques?
  5. Which would be the most valuable?
  6. How many of these methods do you think are in use today, almost 35 years later? At what stage of development would they be now, or at what stage were they abandoned? What capabilities will have been achieved by other means? [Extra: Try to determine the actual answers.]

Once you’ve made your effort, check out my follow-up post.

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