The aim of this project is to make high grade all diy AFM.
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3D shape to create nano sized tip
Standard Tesselated Geometry - 35.82 kB - 07/18/2023 at 14:39
3D shape to create nano sized tip
Standard Tesselated Geometry - 38.56 kB - 07/18/2023 at 14:39
This basically DAC which takes input from I2C. In my case this is Arduino nano as a master.
All other connections are the output and other configurations of the DAC chip. (Like reference,gain etc.)
The next step will be making Arduino and DAC talk over I2C and watch for change on A,B,C and D outputs.
Actually, this stage of I2C or Arduino to DAC went smoothly even beyond my expectations.
All I had to do is to disable input code (since we are not going to use same input) and change LDAC pin (since we are using nano) and vaila!
Here is simple code
And the output:
The next step is to connect converter from 0-5v to (-12) - (+12)v but it's very technical and I don't expect any trouble with that.
As expected, connecting the op-amp was quite straightforward. Although I found bug in OpenAFM schematic (or my coping it), the gain of DAC should be connected to 5v so the total output should be from 0 to 2*Vref. Plus connecting the power supply we get this:
The output is not simetrical around 0v but this can be fixed by changing reference voltage for op-amp. Voltage is not fully rail-to-rail, but it can be fixed by taking bigger resistors as feedback. The problem is that I have that noise (the thick line) I believe it's due to the fact that I use bread board and not PCB with suggested layout.
I think I done with this part of the project
Started with charge pump as it was most tricky part in my opinion in power supply circuit.
Other power supply components I've already worked with such as LM7805 and they are pretty straightforward.
This oddly looking thing is the LTC3260 with all capacitors and resistors connected
And the result is negative voltage compared to GND.
The next steps are creating downsteping from 24v to 12v and 5v.
As expected it was quite straightforward
In my case it gets 24v DC and convert to 12v DC and 5DC.
The outputs of 12v and 5v seems very flat signals, although I am not quite sure how to measure it.
Well that's is another milestone
Since there is a lot of space on this bread board I thought to dense both the power supply and charge pump. This way 12v, 5v, and -12,12v from the same board.
Got messy just the way I like it 🤣
The schematic is much simpler
Got the components but it turns out that they too small to work with. My CNC machine cannot go beyond 1mm resolution.
So now waiting for converter from 0.5mm to DIP-16, from Poland.
My first try to solder this tiny components ended up by soldering all together 😕 but second was more successful.
TADA 🎉 !!!
Now I can proceed to building the power supply for this project.
Not so fast...
I was trying to connect this IC to the 5v and I couldn't find GND terminal. What?!
It turns out that GND is underneath the chip. I could resolder it but the connector doesn't have GND pad. I guess I should make a hole in the connector PCB and connect. This is another setback.
I guess I should find the components by myself but this reference got lots of good ideas. I guess it worth the pain.
Luckily I have CNC machine, after gently curving through PCB I got this
The GND terminal is exposed! Hopefully I didn't break anything in the process.
One of the reasons I feel this project is feasible is some nice open sources. One of them is OpenAFM, it holds lots if valuable information like electronic schematics. It's power supply and piezoelectric controller looks interesting. It took me time to find the software which will conver schematic to eagle files. I got those:
Power supply board
Now it's only to buy all the components and try to connect them. Fingers crossed 🤞
Although it might look scary a bit at first but after some researching the components and you get this simplified schematic
Some pictures from openAFM (converted to Eagle files)
This will help to reduce noise in the final layout
I've suspecting that my tips are not optimal.
One of the problems with my prototype was that the wires were hard to bend into the right position. Now I made this assembly to hold everything in a much easier fashion and use suspended ring. Another reason is this configuration doesn't require Tungsten wire to be connected to as cathod, thus we can make it extremely short while it's connected to Quartz tunning fork.
The idea is to have a springs, by pushing springs down get solution into the small ring.
Once the Tungsten wire snaps it will cut electric current this making the tip much sharper (in my previous design I had to stop the current manually. This short time might de-sharpen the tip)
It should run like this
And the result is (after about 90 minutes)
Again I've managed to bump (twice) this sensitive needle into the ring(after I've crushed quartz fork)[Sometimes I am a disaster]. As a result the tip was bent. But we clearly can see the tiny tip much smaller than my previous one. Actually this is a design problem. The ring is held by lower holder and the Tungsten on the upper. I should redesign so both the ring and Tungsten holder are attached to the lower part.
You can find the STL files on https://github.com/100dollarhacker/atomic_force_microscope/blob/main/AFM_tiip_creator_part1.stl
Third time ice cream, with the new part it was much easier
And the result
Now that is what I call thin! (The wide part is only 0.2mm)
It think I should change project main picture 😄
It's hard to admit but this time I think I got stuck.
I think this is one of the hardest parts except building the Tungsten needle.
Well the good news is that I was able to run Quartz crystal fork. Using AD9833 signal generator and NE5532 based attenuator.
The yellow is 32.000KHz AD9833 signal and blue is QTF 32.768KHz. The problem is once QTF encapsulation removed, signal disappears. The next step would be using two rail power supply and more sensitive electronics. So yeah, I guess I will have to use LTSPICE to debug it. (It much faster than buying bunch of components and trying to debug it)
Once we have quartz fork, we would like to glue Tungsten wire.
The problem is that it's extremely difficult to glue something so small. The easiest solution was to use syringe.
Now is just a meter of retracting Tungsten wire back put some glue on tip of the wire. Push wire forward and wait for few hours.
After couple hours of drying up, we get
The next step is to use Quartz fork. I've bought sime 2x8mm 32KHz Quartz oscillators. Now the tricky part is to gently remove enclosed without breaking the Quartz fork. I've preferred to use small file to remove metallic encapsulation. (Although it's tempting to put Quartz fork into something like a drill, I was afraid that centrifugal force will damage this tiny fork)
Another run, this time I got much better results.
Same technique, this time didn't drop the tip and turn electrolyte process once it finished
Here we can see the tip with x250 magnification
And here with OpenFlex microscope and x1000 magnification. The tip looks quite sharp.
You can buy nanometer tips but they are pricey. Each tip costs about $100 and you must buy a pack of ten.
I would like to go some other way, much cheaper. (As I don't know if I could make one)
The cheapest way to fabricate AFM-tip is using Tungsten wire and NaOH solution.
I bought 100mg of Sodium hydroxide (NaOH)
100ml of tap water and 8mg of NaOH(two tea spoons), and we have a solution, yeah!
Place it in some unused glass cup, made a anod using copper loop of diameter about 2cm anod (copper wire of 1.3mm).
Attached about inch of Tungsten wire(0.25mm diameter) (cathod) and dipped cathod and anod into the solution.
Connect Tungsten wire to plus and copper loop to minus. (If you see a lot of bubbles and 100mA you probably connected wrong polarity) In my case I see a little bit of bubbles only on copper side. After 30 minutes I got some results. (Clumsy me, I managed to drop it when inserting to a microscope, so the tip looks bend)
Will continue next week to get better results.
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