PROCESS MODELING AND SIMULATION OF FOCUSED ION BEAM MILLING OF WATER ICE IN A CRYOGENIC ENVIRONMENT

Open Access
Author:
Fu, Jing
Graduate Program:
Industrial Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 28, 2008
Committee Members:
  • Sanjay B Joshi, Committee Chair
  • Jeffrey M Catchmark, Committee Member
  • Timothy William Simpson, Committee Member
  • Richard Allen Wysk, Committee Member
Keywords:
  • Microtomy
  • Cryo-EM
  • ion sputtering
  • focused ion beam
  • water ice
  • Cryo-FIB
Abstract:
Focused Ion Beam (FIB) systems, typically based on gallium ions, have become an invaluable tool for sample preparation and fabrication at nano/micro scale. Recently, the application of FIB in a cryogenic environment (Cryo-FIB) has become a potential alternative to cryomicrotome for sectioning frozen biological samples, or as a patterning tool for submicron features on organic materials. However, the interactions of keV gallium ions used in FIB with water ice as the target are still not well understood, impeding the development of this technique for routine use. In this research, FIB milling was investigated in a cryogenic environment to explore the engineering issues for sectioning frozen samples. Thin film samples of amorphous water ice were prepared in the temperature range of 83 to 123 K. Based on different system settings and process parameters, micrometer size features were milled by FIB, and the corresponding sputtering rates were measured by volume loss method. Analytical models, originally limited to astrophysics, were derived to predict the sputtering yield of water ice by FIB. The parameters for gallium ions at keV range were estimated and validated based on the experimental data. Furthermore, the process characteristics of FIB milled water ice were also explored. Different surface morphologies with submicron features that developed during ion bombardment were confirmed using SEM imaging and texture analysis. Experimental results also indicated that the redeposition effect is significant for milling high aspect ratio features on water ice. Results from the experiments were included in a geometric simulation model developed to simulate the milled topology. By investigating process parameters and system settings for Cryo-FIB, feasible plans can now be developed to facilitate reproducibility and ultimately the widespread implementation of Cryo-FIB as a biomedical and nanomanufacturing tool.