CHEM 146C Experiment 7 Soft Lithography Patterning Yat Li Department of Chemistry Biochemistry University of California Santa Cruz Objective In this laboratory experiment we will learn 1 The principle of soft lithography and the fabrication of poly dimethylsiloxane PDMS stamp 2 Microcontact printing technique to create patterned metal electrodes or interesting features on a substrate Micro and nanofabrication Microfabrication through its role in microelectronics and optoelectronics is an indispensable contributor to information technology Photolithoghaphy 1 micrometer resolution limited by difraction of light E beam lithography 50 nm Photo or E beam resists lithography Develop Lift of Metal evaporation Drawback expensive time consuming e beam poorly suited for patterning nonplanar surface Soft lithography Soft lithography represents a nonphotolithographic strategy based on self assembly and replica molding for carrying out micro and nanofabrication 1 Generate patterns and structures with feature sizes ranging from 30 nm to 100 m 2 Convenient efective and low cost Xia Y N and Whitesides G M Soft Lithography Annu Rev Mater Sci 28 153 184 1998 Poly dimethylsiloxane PDMS Poly dimethylsiloxanes 1 A unique combination of properties resulting from the presence of an inorganic siloxane backbone and organic methyl groups attached to silicon 2 Very low glass transition temperatures and hence are fluids at room temperature 3 Can be readily converted into solid elastomers by cross linking PDMS SYLGARD 184 SILICONE ELASTOMER KIT base cure Mechanism of cross linking Dean J Campbell Katie J Beckman Preparation of PDMS elastomeric block Xia Y N and Whitesides G M Soft Lithography Annu Rev Mater Sci 28 153 184 1998 Dean J Campbell Katie J Beckman Microcontact printing The concept of microcontact printing is use the relief pattern on the surface of a PDMS stamp to form patterns of SAMs on the surfaces of substrates by contact For example alkylthiol on Au and Ag surfaces Simple and suitable for non planar substrates Xia Y N and Whitesides G M Soft Lithography Annu Rev Mater Sci 28 153 184 1998 Making metal thin films Typical methods to make high quality metal films Sputtering Tollens process Ag NH3 2 reducing agent Solution A a mixture of AgNO3 and NH4NO3 Solution B NaOH Solution C Glucose C6H12O6 Evaporation Ag film Making metal electrodes by microcontact printing Gerber R W and Oliver Hoyo M T Selective Etching via Soft Lithography of Conductive Multilayered Gold Films with Analysis of Electrolyte Solutions Journal of Chemical Education 85 1108 1111 2008