I have been “hanging out” with a research group at Penn (alas, there is not a more dignified way to describe this relationship .. but at least I am there by invitation and it’s awesome). We needed to create some electrodes that were resistant to electrolytic degradation, and we were interested in some clever alternative to the old (and rather expensive) stand-bys, like platinum and gold.
It turns out that graphite is right up there at the tip-top of the Galvanic series, so it is about the most robust electrode material we could want. However, we also wanted to be able to draw arbitrary electrode geometries and, while graphite is definitely suited to drawing, pencil lines are too resistive and too inconsistent to function as electrodes in our application. Graphite in “bulk” form conducts well (in fact, too well for our needs), and it is hard to machine. We wanted a technique that would let us “draw” relatively conductive lines easily, and it quickly became became apparent that we needed something a little novel. Somehow, I vaguely remembered seeing a few hacks where folks used light-scribe drives to create patterned graphene for super-capacitors, and I got to wondering whether I could make graphene too. I am happy to report that the light-scribe method works as advertised and that it was every bit as easy as I had hoped.
First, I needed graphene oxide (GO). It’s not that hard to make, but the process holds some potential for a devastating explosion, and purchasing the materials could possibly land you on a watch-list. I figured that the risk of getting cheated by an online vendor was more palatable than dying in a fiery explosion as the FBI kicked in my door and my kids looked on in horror, so I rolled the dice and bought some graphene oxide from some-company-I-never-heard-of-before-but-for-all-I-know-it-might-be-some-guy-living-in-his-parents’-basement (in which case, watch out mom and dad — the men in black will be arriving any day now).
I also found a light-scribe drive that I had salvaged a few months before from the corporate dumpster. Then I bought a pack of light-scribe CDs from Office Depot and I was pretty much set. This was definitely a low-buck/high-tech venture … You can buy all of the materials needed to make a few square feet of patterned graphene (GO, Lightscribe Burner and a stack of Lightscribe CDs) for under $150.
I cut some tacky plastic sheeting and stuck it on a light-scribe CD, being careful to leave the light-scribe “hologram” in the middle of the CD unmolested. Then I used a coffee stirrer as a crude dropper to apply a few ml of GO solution to the sheet. I air-dryed my “substrate” and wound up with the thing pictured above — essentially a CD sporting a “hat” adorned with a brown puddle of something purported to be graphene oxide.
I designed a “label”, using the Lightscribe Template software. I just made a template that painted the entire CD black, so that I could disregard the relationship between the puddle and portion to be scribed — i.e. if I scribed everything, I was bound to hit all parts of the puddle. Science!
After 30 minutes of lazoring, the GO had turned from brown to black. I did not measure the resistance at this point, though I should have. I ran the disk through for a second pass and did a quick (not scientific) resistance check by pressing two pennies on the black spot about 20 mm apart and measuring the resistance (575 ohms for what it’s worth, though this particular test has no meaningful, standardized interpretation). After a third pass, my informal resistance test had gone down to 275 ohms (so resistivity was decreasing, it would seem). After a fourth pass, it just nudged down to 225 ohms, so I quit while I was ahead.
I did perform a more meaningful test of resistance of the finished film by taking a sample of my electrode and trimming it to a 6 cm x 2 cm piece, Then I stuck copper foil on the first 2 cm of each end, leaving a 2 cm x 2 cm square in the middle. The resistance across that square was 1200 ohms, so the resistivity of the material’s surface is, at most, 1200 ohms/sq. That’s pretty good for a thin, carbon film whose precise geometry I can control easily with a drawing, and the performance is more than adequate for the application that we are pursuing.
As a bonus, the film is flexible, and it’s reportedly fairly robust when bent — so it may have potential for creating wearable circuits and the like.
With more careful preparation, I think that I can make more consistent films that have somewhat lower resistivity. Even the resistance levels I got on my first attempt are probably usable for MCU circuits that are running at low speed.
I think that it’s pretty a cool prospect — just draw a circuit (with some care, you can even “draw” the resistors and capacitors), toss a GO “blank” in the Laserscribe, print the circuit, glue on a few components and you have a functioning circuit w/o any etching, soldering etc. etc. Plus, it’s pretty “green” from the e-waste perspective. If you use paper or PLA as the substrate, you can pull the chips off and toss the circuit in a landfill, where bacteria will happily eat the substrate and the graphene traces.
There is only one downside as far as I am concerned — the lightscribe method is a little slow. But given the fact that it’s so cheap and easy, I’m not complaining.