This is an experiment with opening my research notebook to the web. I’m keeping my notes in an Evernote notebook, but I’m going to post lightly edited (i.e. remove personally identifiable information from people I talk to unless they give me specific permission).
Keep in mind that these are my raw thoughts for the past two months, with no editing for accuracy. Follow these notes at your own risk.
11/03/2011 (Purchase Notes)
Purchased from Newark ($62.46 + shipping):
* 3 DAC8554 (TSSOP-16 packages) quad 16 bit DAC
* 3 REF02 (DIP-8 packages) precision 5v reference
Purchased from eCrater user fcpcb ($11.44):
* 5 TSSOP-16 to DIP adapters
10/31/2011 (Denver/Boulder Notes)
met L. M. (physicist) at Solid State Depot hackerspace meeting – he built an STM as part of his PhD work:
* L. M.’s STM had a higher cost (and precision) than the chemhacker STM, but a lot of his designs and thoughts can be adapted to fit a cheaper device. Also, he’s excited by the idea of an open source STM project.
* need more bits on the Z DAC
* * 10 bits gives ~17.59 mV/step which is ~2.81 nm /step (at ~0.16 um/volt) that’s so large that the needle will pass into and out of tunneling in only one step.
* * 16 bits gives ~0.2747 mV/step which is ~43.9 pm/step, small enough that you can control tunneling with more than one step.
* * 16bit DAC notes:
* * * DAC8554 from TI is a 4-channel ultralow glitch DAC
* * * $10-15 each: pricey, but handles all four channels at once, not much more expensive than 4 of the microchip DACs I’m using
* * * SPI interface, unsure if it differs from the microchip SPI standard
* * * TI recommends a REF02 precision 5V voltage reference (~$3-4 each) – probably a good idea to try this out
* * * downside: no DIP package available – surface mount only
* probably need a better/faster micro controller
* * suggest that PID loop be accomplished at about 20MHz
* * suggest the Maple from Leaf Labs
* * * 12 bit ADCs (versus 10 bit for arduino/teensy)!
* * * 47 MHz versus 16MHz for arduino/teensy
* * * the IDE looks almost exactly like the arduino IDE.
* * * I’ve spoken to Leaf Labs folks in the past, they’re a good group of quality-focused engineers/artists.
* * * purchased on 10/30/2011 should arrive in a day or so via USPS
* thoughts on the sample bias voltage
* * since sample needs only ~10 millivolts, it’s probably best to just pass the DAC output through a pair of unity inverting amps (don’t remove the DC bias).
* * then, put the two outputs (positive and negative outputs) to a manual switch so the user can choose a positive or negative sample bias (allows future expansion to negative sample bias)
* * with a 16 bit DAC, it’s pretty easy to select ~10mV (just set DAC to ~4 and leave it there)
10/20/2011 (Nanotech conference notes)
Questions for people who know more about SPM than I:
* Is Gwyddion well-regarded in the microscopy arena?
* How do you make HOPG / graphene? Is it at all easy?
* What is an appropriate sample bias for starting? I saw ~10mV today, but I was going to use ~1-2V, that’s bad.
* Is there a market for STM tip-making machines?
* What is the process for making an AFM tip?
10/19/2011 (prototyping notes)
* added 2.5V and 5V voltage regulators to clean up voltage signals
* fixed clipping problems by lowering the gain resistor from 36k (predicted by the formulae) to 27k (as determined experimentally)
* fixed non-symmetrical behavior by applying correct ground to the 2.5v and 5v regulators (their grounds were floating a little higher than true ground)
10/10/2011 (Purchase Notes)
Purchased from Newark ($43.69)
* +9v, -9v, +5v, +2.5v voltage regulators
* piezo elements
* 0.1uf, 1uf, 0.33uf capacitors
* tunneling op-amps
CHEN chapter 11.1: desirable tunneling amp design: 1V/1nA
Idea: change op amp gains such that the electronics use ground, +5v, +12v, -12v >>same as supplied by ATX power supply
Test: test ATX power supply with oscilloscope to check cleanliness of signal (should be pretty clean, right?)
…actually, can use these power supplies now without changing the gains…