Project Objectives
Design a nitrogen gas distributor that can effectively disperse the excess charge which builds on the surface of biological specimens when being imaged by a Scanning Electron Microscope.
High Priority Objectives
New nozzle that provides full gas coverage of large samples (up to 1mmx1mm)
Compatible with different sample sizes and geometries(square, rectangular, trapezoidal), most likely via swappable nozzle heads
Mechanism functions for thousands of repeated images over months of continuous use
Second Priority Objectives (not fulfilled)
A more elegant retraction mechanism than what currently exists (in the current product, the sample slicer just pushes the nozzle out of the way while it’s cutting).
Other constraints and issues
The nozzle has to be made of a vacuum safe, conductive material, and cannot emit so much gas that it disrupts the vacuum inside the SEM.
Fits within the very small size constraints of the SEM (4mm tall)
Major Risks and Concerns
Microscope testing takes a long time
Conditioning takes hours to prepare
Inconsistent testing samples -- size and material varies
Each test takes 1 to 2 hour to complete
Gas leakage between top piece and bottom piece
Current design requires epoxy adhesive to attach top piece to the bottom piece
Seal depends on how well epoxy is applied and the finish between surfaces
Misalignments between top piece and bottom piece
Although clearance and error are considered in the design, there is still a high risk of misalignment and care must be taken when manufacturing (tolerance of ± 50 μm)
Space limitation due to installed Gatan Backscatter detector
Risk Reduction Strategy
Narrowed material options for nozzle, anchor, and nozzle support
Designed experiment to calculate gas flow rate and optimal nozzle shape
Calculated maximum allowable pressure at nozzle exit and pressure force on nozzles to estimate anchor force required