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Research Paper

Optimization Based Geometric Modeling of Nano/Micro Scale Ion Milling of Organic Materials for Multidimensional Bioimaging

[+] Author and Article Information
Jing Fu

Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australiajing.fu@eng.monash.edu.au

Sanjay Joshi

Department of Industrial and Manufacturing Engineering, Pennsylvania State University, University Park, PA 16802sjoshi@psu.edu

J. Nanotechnol. Eng. Med 1(3), 031003 (Aug 10, 2010) (8 pages) doi:10.1115/1.4001851 History: Received April 13, 2010; Revised May 19, 2010; Published August 10, 2010; Online August 10, 2010

Focused ion beam (FIB) instruments have recently started to be seen in applications to organic materials such as polymers and biological samples. FIB provides a novel tool for sectioning biological samples for electron microscope based imaging or microfabrication with environment friendly materials. The modeling of nano/micro scale geometry accurately sculptured by FIB milling is crucial for generating the milling plan and process control, and for computer simulation based prediction and visualization of the milled geometry. However, modeling of the milled geometry on compound materials, especially for high aspect ratio feature, is still difficult due to the complexity of target material, as well as multiple physical and chemical interactions involved. In this study, a comprehensive model of ion milling with organic targets is presented to address the challenges in using a simulation based approach. At each discrete point of the milled front, the depth is the dynamic result of aggregate interactions from neighboring areas, including physical sputtering and chemical reactions. Instead of determining the exact interactions, the parameters of the proposed model are estimated by studying a number of preliminary milling results followed by a nonlinear optimization model. This platform has been validated by milling different features on water ice in a cryogenic environment, and the simulation and experiment results show great consistency. With the proliferation of nanotechnology in biomedical and biomaterial domains, the proposed approach is expected to be a flexible tool for various applications involving novel and heterogeneous biological targets.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Bacteria cluster (Acetobacter xylinum) (a) imaged by optical microscope and (b) by SEM after FIB milling a micrometer sized cross section at liquid nitrogen temperature (−190°C). (c) Schematic diagram of the setup for FIB milling and SEM viewing.

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Figure 2

Proposed framework for investigating novel material milled by FIB

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Figure 3

Schematic diagram of modeling material removal process in ion milling

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Figure 4

Schematic diagram of the sputtering and redeposition model for simulation

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Figure 5

Schematic diagram of modeling dynamic effects of the sputtered species with target material upon arriving

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Figure 6

Schematic diagram of updating points after one iteration

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Figure 7

Simulation of cross section geometry of different values of x with all other settings remain the same

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Figure 8

Schematic diagram of measurements for performance measure

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Figure 9

SEM images (tilted 45 deg) of the 2 μm trenches on water ice and the simulation results (right)

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Figure 10

SEM image of 300 nm trenches milled on water ice and the simulation result (dashed line represents the depths by constant erosion)

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Figure 11

SEM images of the cross sections of cylindrical features milled on water ice and the simulation result at right (dashed lines shows the regular milled geometry). (a) Fluence of 0.25 nC/μm2. (b) Fluence of 0.76 nC/μm2.

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Figure 12

Diagram of the consistency level of simulated depths versus nominal aspect ratio R

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Figure 13

Comparison of aspect ratio R¯ and nominal aspect ratio R of milled geometry on water ice and silicon

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