CHAPTER 2
 EXPERIMENTATION


 2.1 Sample Preparation

 Using a Spincoater Model P6700 Series by Specialty Coating Systems, Inc., a 2"

GaAs(001) wafer is spin-coated with 950 molecular weight polymethyl methacrylate

(PMMA) to form a film approximately 400nm thick. The wafer is placed into the

spincoater and is held in place by vacuum force from below on the sample holder. The

sample holder then begins to spin the wafer. The wafer is cleaned before being coated

with PMMA, first with acetone and then with methanol to prevent contamination from

particulates and impurities in the acetone. Once dry, the spinning is stopped to deposit

the PMMA onto the wafer. A pipette is used to draw the PMMA from the center of an

unshaken bottle to avoid any particles that may have settled. The PMMA is deposited

onto the center of the wafer until it covers as much of the wafer as possible without

dripping over the edge also being careful to avoid air bubbles. Spinning is resumed and

continues until the PMMA is evenly distributed over the wafer. When spinning is

complete, the wafer is baked on a hot plate at 1600C for 15 minutes to drive out any

residual solvent. The wafer is then cleaved into quarters for ease of handling and

processing.