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Nano Courses

A repository of courses and units are available for instructors who want to incorporate NSE into their existing course or desire to create a new course. Each Nanocourse or unit contains an introduction, main concepts, notes, lectures and accompanying homework assignments or in-class activities. All materials on the NanoEd Resource Portal are peer-managed and covered by a creative-commons attribution, non-commercial share-alike type licensing.

 
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What Can Electrons Do? - Electron Microscopy
J.G. Zheng and
Prof. V.P. Dravid
Northwestern University, IL, USA


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Unconventional Patterning at the Nanoscale    »» Main Menu


NANOSCALE TOOLS

Fabrication of Masters | Preparation of PDMS Stamps | Cleaving Si Wafers


Preparation of PDMS Stamps

(PDMS - POLY DIMETHYLSILOXANE)   » More about PDMS

An elastomeric stamp is the key element of soft lithography. It is usually prepared by replica molding, by casting the liquid pre-polymer of an elastomer over a master that has patterned relief structures on its surface.

WHY USE PDMS?

It is the unique surface behavior of PDMS that allows for most of the applications. The surface energy is a manifestation of intermolecular forces. The organic portion in PDMS is the methyl group, which has almost the weakest intermolecular forces. The inorganic siloxane backbone, one of the most flexible polymer backbone, allows the methyl groups to be arranged such that PDMS has almost the lowest surface energies known (expensive fluorocarbon polymers have the least surface energy).

ATERIALS:

  • Sylgard 184 elastomer (consists of pre-polymer and curing agent)
  • Dessicator
  • An oven capable of reaching 70°C
  • Master that has patterned relief structures (CD / DVD)
  • Plastic cup, Plastic fork, Sharp scalpel, petri dish

PROCEDURE: (Click on pictures to view the videos)

*You will need QuickTime Player installed on your computer to view the videos.
 Download Player: For Mac | For PC

movie1-pdms

In a plastic cup, weigh 10 parts (by weight, ~ 20 g) of Sylgard 184 pre-polymer and 1 part (~ 2g) of curing agent.

 
movie2-pdms

Mix the above vigorously for a couple of minutes until the entire mixture is filled with bubbles.

 
movie3-pdms

Place the cup in a dessicator to degas (allow bubbles to rise out) for 20 minutes.

 
movie4-pdms

Pour the mixture slowly into a petri dish that has prepatterned structure (DVD/CD). Avoid bubbles and make sure that the master is lying flat on the bottom of the petri dish. It should cover the CD/ DVD masters completely. The PDMS layer should be about 2 mm (you may not use all of the polymer).

 
movie5-pdms

Place the petri dish in an oven and cure it at 70°C for an hour.

 
pdms-scalp

Using a sharp scalpel, evenly and gently cut around the pattern.

 
pdms-cut

Remove the stamp using a tweezer. The movie depicts a small stamp being cut from the much larger polycarbonate master of the CD.

 

 » More about PDMS

 

 

 

 

 

 

Authors:
Prof. Teri W. Odom,
Dr. M. Viswanathan and Y. Babayan

Institution:
Northwestern University
Evanston, IL USA

Level:
College and above

In the classroom:
This Course is a video lab manual for hands on fabrication and characterization of materials at the nanoscale. Materials requirements range from simple chemicals, benchtop tools and CDs to necessary access to advanced characterization equipment such as an Scanning Tunneling Microscope.