Microfluidics:Catalytic Pumping Systems
Paul Longwell
Hollidaysburg Area High School
Summer 2005
Catalytic?
See movies of working nano-devices:
http://www.mrsec.psu.edu/News/nugget3.html
Penn State researchers havebuilt several nano-devices thatmove when place in a hydrogenperoxide solution.
The platinum serves as acatalyst, helping the hydrogenperoxide decompose andproduce oxygen gas bubbles.
During this process, extraelectrons are passed from theplatinum to the gold andreleased into the solution.
The Catalytic Pump Idea
Using silver in place of gold,Penn State’s Jeffrey Catchmarkdesigned the device (pictured) tosee if a pumping effect could beproduced.
Based on flow patterns observedwhen testing previous devices,Dr. Catchmark believed theelectrons would cause watermolecules to be pulled alongsidethe conducting wire.
The RET Project
As a participant of Penn State’s Research Experience for Teachersprogram, I worked under Dr. Catchmark to construct catalytic pumpsusing several different designs.
These designs varied in the size and shape of the silver and goldplates as well as the thickness of the conducting wire.
The Fabrication Process
Building the catalytic pump involved the following steps:
1.Mapping out the structure of the devices.
2.Creating masks (patterns) to use in creating each component ofthe devices.
3.Applying the first-layer pattern on a silicon wafer.
4.Depositing/Lift-off of gold using first-layer pattern.
5.Applying the second-layer pattern over the first pattern.
6.Depositing/Lift-off of silver using second-layer pattern.
7.Applying a dielectric coating over the entire device.
8.Using the third-layer pattern to open “windows” to the silver/gold.
Creating the MasksThe Material
After Dr. Catchmark designed the devices, the next stepwas to construct a template for each layer of materialneeded for the pumping device.
The mask was made on afive-inch piece of soda-limeglass coated with chromium.
Creating the MasksWriting the Pattern
Using a laser-writer, three separate masks were created.Each mask contained the pattern for one of the threelayers of the pumping device.
Here, the quartz squareis loaded into the laserwriter.
The bottom of the writer.
Creating the MasksDeveloping the Pattern
After being patterned by the laser writer, each mask mustbe developed using a Chromium Etch chemical. In thisprocess, the chemical dissolves the chromium accordingto the pattern created by the laser.
1st Layer - GoldPhotolithography
To begin building the pumping device, the pattern fromthe mask must be transferred onto a circular 3-inchsilicon wafer.
1st Layer - GoldPhotolithography
The LOR 1A is baked on before a second photoresist(SPR 3008) is applied and baked.
1st Layer - GoldPhotolithography
Now coated with light-sensitive photoresist, the wafer isexposed to light through the first mask pattern.
1st Layer - GoldPhotolithography
After one final bake, the exposed wafer is soaked in CD-26 developer and the photoresist is removed from thepatterned areas.
1st Layer - GoldGold Deposition
Using an electron-gun evaporator, the wafers are coatedwith 150 Angstroms of chrome and then 1000 Angstromsof gold.
1st Layer - GoldGold Lift-Off
All gold outside of the patterned area is etched away withacetone and CD-26 developer.
2nd Layer - SilverPhotolithography
As done previously with the first pattern, a layer of LOR1and SPR-3008 photoresist are applied on top of the goldso that the silver features can be added.
2nd Layer - SilverAlignment
For the device to function properly, it is extremelyimportant that the new silver features matchup with thegold features as designed.
Improper alignment resultsin defects in a device.
2nd Layer - SilverSilver Deposition
This time silver is evaporated and deposited on thewafers.
2nd Layer - SilverSilver Lift-off
Using acetone and CD-26 again, the silver is removedfrom everywhere except the patterned locations.
3rd Layer - DielectricFinal Layer
To electrically insulate all of the components except forone gold window and one silver window, a layer of Spin-On Glass was applied on top of the wafer.
The Final ProductReady for Testing
TestingIn Hydrogen Peroxide Solution
For testing, devices were taken to the chemistry lab ofPh.D. student Tim Kline.
TestingIn Hydrogen Peroxide Solution
The devices were tested in a 5% solution of hydrogenperoxide. Polystyrene microspheres and gold nanorodswere used to assess the performance of the device.
Results
The polystyrene spheres indicated no discernible flowpattern in the fluid surrounding the device.
However…
Results
The nanorods showed an attraction toward the silvermetal even though the wire on this particular device wasdisconnected.
Conclusion
The geometry of the pumping device seemed to beinsignificant in affecting if/how the catalysis occurred.
In fact, the reaction seemed to occur regardless ofwhether or not a direct connection was present betweenthe silver and gold. (Assuming the amount of goldcontained in the lead connected to the silver wassignificant to sustain the reaction.)
Further research may reveal other factors (such as thesubstrate itself) that affect the nature of the reaction.
Thank You
The staff at the Penn State Nanofabrication Facilitywere extremely helpful throughout this RET project.
Jeff Catchmark, Operations Manager
John McIntosh, Process Engineer
Joseph Lonjin, Process Technician
Guy Luvalee, Process Engineer
Andrzej Mieckowski, Process Engineer
Michael Rogosky, Process Engineer