Microcontact Printing (Stamping) Andrew van Bommel February 7 th, 2006

Formation of Master Stamp Photolithography or micromachining of silicon wafers- desired pattern is etched on substrate h

Polydimethylsiloxane Stamp Elastomeric PDMS stamp fabricated PDMS poured and cured (polymerization)

Inking Molecules (proteins, thiols, lipids) in solvent (toluene, ethanol) placed on stamp PDMS

Stamping Stamp metal (Au, Ag, Cu, Al) PDMS Si metal

Large Area Stamping Large area printing with roller stamp Si

Etching Etching Resists Used as: –Arrays of microelectrodes –Diffractive optical components –Secondary masks (for etching of underlying substrate) Si

Dipping A dipping in a second thiol may lead to contrasts in: –Hydrophobicity –Protein binding Si

Next slides will show… …a more in-depth review of the  CP process and its components!

Master Stamp (Printhead) Usually silicon grid Fabricated from photolithography or micromachining Use of diffraction gratings or TEM grids Surface first silanized with (tridecanfluoro- 1,1,2,2-tetrahydro-octyl)-1-tricholorosilane prior to molding (to ease lift-off) Si

PDMS (Polydimethylsiloxane) Stamp ☺ –Elastomer –Confoms to substrate over large area –Chemically inert –Homogeneous, isotropic, optically transparent –Durable (multiple stamping) –Able to modify surface properties PDMS

PDMS Stamp ☺ –PDMS stamp may be prone to: Pairing Sagging Shrinking PDMS

Ink Thiols, lipids, or proteins in dilute solvent (toluene, ethanol) Species that form SAMs on metal surfaces are chosen (see next slides…) PDMS

Metal Substrate Au: widely used, electrode material Ag: more chemically reactive (easier to etch) and excellent electrical and thermal conductor Transfer of ink results in formation of self- assembled monolayers… Si

SAMs Form spontaneously by chemisorption (in less than 1 sec.) In thiols: S atoms bonded to the gold surface bring the alkyl chains into close contact Si

Nanofeatures Through chemical control of length of alkyl chain, the thickness of SAMs can be controlled to a precision of 0.1 nm Smallest lateral features obtained from the combination of  CP and selective etching: –Etched 35 nm wide trenches –Microcontact printing with hexadecanethiol –Dr. Hans Biebuyck (IBM)

Comparison Photolithography: –Limited by optical diffraction –Expensive –Cannot be easily applied to non-planar surfaces –Provides little control over the chemistry of the patterned surfaces

Comparison Soft lithographic techniques: –Not limited by optical diffraction –Provide alternate route to formation of structures less than 100 nm –New: Types of surfaces Optical Structures Sensors Systems previously difficult to fabricate

Literature Soft Lithography Xia, Y., Whitesides, G. M. Annu. Rev. Mater. Sci : Soft Lithography Xia, Y., Whitesides, G. M. Angew. Chem. Int. Ed : New Approches to Nanofabrication: Molding, Printing, and Other Techniques Gates, B. D., Zu, Q., Stewart, M., Ryan, D., Willson, C. G., Whitesides, G. M. Chem. Rev : Unconventional Methods for Fabricating and Patterning Nanostructures Xia, Y., Rogers, J. A., Paul, K. E., Whitesides, G. M. Chem. Rev : Microcontact Printing Hull, R., Chraska, T., Liu, R., Longo, D. Mater. Sci. Eng :