Tuesday, May 31, 2022

Drawing on a plasma display with a laser pointer

An orange plasma display will retain an image caused by incident near-UV light. This is an interesting visual combination of photoelectric, hot carrier injection, plasma, and charge trapping effects.



Correction: The orange display is running at 700Hz, 130V in the video.
  I realize that I may have conflated the issues of one-resistor-per-pixel and the display's ability to maintain an image throughout row scanning. They are separate problems that are both addressed by designing the panel to work on AC. Each pixel can maintain its state (on or off) by being supplied constantly with a lower "sustaining" voltage, and can be set or cleared by giving it a momentary higher or lower amplitude. The sustaining voltage allows the pixel to be emitting light or not, and its state remains because of its own impedance until updated on the next scan. In color plasma displays, separate electrodes are used for sustaining and addressing pixels, and the discharge may be sustained between coplanar electrodes instead of plane-to-plane, as in this display.

It's also a possibility that the dielectric and MgO layer only exists on one electrode (the metal), and the ITO is bare. I don't know. On this display, if all rows are electrically connected together, and all columns are connected together, and AC is applied to rows and columns, this effect does not work -- no light is emitted at all! At least some of the electrodes (ie every other column) must be left floating to emit any light, and to show this memory effect. So, driving AC plasma panels requires more waveform tricks that I do not fully understand.

Prior art patents: https://patents.google.com/patent/US7283301B2/en https://patents.google.com/patent/US20060132716A1/en


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Saturday, April 9, 2022

Silver nanoprisms grown into structural colors by high power LEDs



How to chemically synthesize silver nanoparticles, then grow them into triangular nanoprisms with light from a variety of LEDs. Each color LED creates a different size nanoprism, which has its own characteristic color.

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CMDITR video: https://www.youtube.com/watch?v=agD5jfXua-o 
Multispectral LED driver on Github: https://github.com/benkrasnow/MultiSpectLED 
Chemicals sourced from Amazon/eBay 
20ml glass vials with PTFE lined cap (do not use metal-lined): Environmental Express APC1675P Already gone from Amazon 
pH pen (this cost more than I remember, but it works really well, and has lasted many years. Cheaper pH pens are often pretty bad) https://www.amazon.com/gp/product/B01ESYG6B0/ 
Comparison of CD, DVD, Blu-ray discs with electron microscope: https://twitter.com/BenKrasnow/status/615327472909840385 
Great way to find related papers: https://www.connectedpapers.com/ 

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Monday, November 22, 2021

X-ray timelapse of fluid movement in plants, stop-motion animation, sensor teardown/repair

I repaired a large digital x-ray detector and used it to record timelapse and stop-motion animations of plants, a clock, and a camera lens.



Applied Science X-ray backscatter imaging system: https://www.youtube.com/watch?v=H7ldYhzKAp4
Applied Science CT scanner: https://www.youtube.com/watch?v=hF3V-GHiJ78 
Octave (open source MATLAB alternative): https://www.gnu.org/software/octave/index 
Mouse movement recorder software: https://sourceforge.net/projects/mousecontroller/ 
Thank you for your support on Patreon: https://www.patreon.com/AppliedScience 
Thank you, Amir, for the X-ray sensor and software!

Saturday, September 25, 2021

Underwater laser cutting and silver sintering to make ceramic circuit boards

 

Thermal stress cracking can be completely avoided by CO2 laser cutting thin alumina sheets underwater.  I also show how to formulate and apply silver paste, then sinter in a kiln to produce double-sided ceramic printed circuit boards with conductive vias.

60W CW CO2 laser at 80% power.  10mm/sec.  Standard lens focal length (50mm).  2mm water above ceramic.  180 passes to cut through 0.75mm thick alumina.  

Silver paste: 97% silver powder, 3% glass powder by mass.  Particle size 1 micron or less. Add poly vinyl alcohol mold release until desired consistency reached.

Paste applied with 4 mil thick vinyl stencil.  Dried in air 10 minutes, then rapidly brought up to 900*C, held for 10 minutes, then rapidly brought back down to room temperature.  Total cycle about 45 minutes.

I measured electrical conductivity of the finished traces from my process with vinyl stencils: 4 milliohms per square at 10 micron final thickness.  This is pretty close to the Dupont published spec ( less than 2 milliohm/sq at 16 micron thick)

Underwater CO2 laser cutting reference: https://sci-hub.se/10.1016/J.JEURCERAMSOC.2011.06.015
Raspberry Pi picoReflow oven controller: https://apollo.open-resource.org/mission:resources:picoreflow

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