MIDP

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ATMOSPHERIC ELECTRON X-RAY SPECTROMETER (AEXS)
FOR IN-SITU ELEMENTAL ANALYSIS
The AEXS is a miniature X-Ray Fluorescence (XRF)
instrument for in situ elemental surface analysis
with short (minute) spectrum acquisition times
and variable spatial resolution (from several cm-
to sub mm-size).
Funding Profile (K) and Milestones
PI Jaroslava Z. Wilcox
Co-Investigators E. Urgiles, T. George, M.
Buehler, R. Toda Science Joy Crisp Rover
Accommodation E. Baumgartner
FY03 Construction of a stand-alone electron
source FY04 Construction of the AEXS instrument
head FY05 Accommodation of the AEXS instrument
onto a rover platform
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FY04 Tasks and Milestones

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• Task 1. Vacuum-Encapsulation of the Electron
  Source
• The Thomas Electronics gun will be encapsulated
  using a glass-to-metal-to-Si transition The
  electron source vacuum will be maintained by an
  external vacuum pump at this stage of the
  development
• Task 2. Environmental Chamber Testing
• XRF measurements investigating the effect of
  simulated Mars atmosphere and AEXS operating
  parameters (beam current, voltages, geometry) on
  spectra acquisition will be performed using an
  environmental chamber
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• Task 3. Environmental Robustness of the
  Encapsulated Source
• Thermal cycling and mechanical vibration and
  shock testing will be performed to assess the
  robustness of the encapsulated electron source
• Task 4. Stand-alone Electron Source
• The electron source will be isolated from the
  external vacuum pump to create the stand-alone
  electron source

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Technical Accomplishments

• The Environmental Chamber has been adapted for
  testing the 20 keV Electron Gun
• The encapsulation process for vacuum-sealing the
  electron gun has been developed.
• Thomas Electronics tubes were procured mounted
  on a 7052 glass stem containing an evacuation
  port
• Glass enclosures that envelop the electron-optics
  column of the electron gun were fabricated
• The membrane-bearing Silicon chip was anodically
  bonded to the Pyrex/Kovar exit aperture parts
• The membrane/Pyrex/Kovar subassembly was
  laser-welded to the Kovar/7052 transition

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Technical Accomplishments

• The Environmental Chamber has been adapted for
  the 20 keV Electron Gun

• The effects of the atmosphere are significant.
• An environmental chamber with the ability to
  control the pressure and atmospheric content of
  the sample atmosphere to better understand the
  atmosphere. It is capable of holding high vacuum
  levels (2e-6 Torr) or regulating to a set
  pressure (simulating Martian atmosphere)
• The chamber was used to collect XRF data using a
  10 keV electron gun. Is is being adapted for the
  20 keV gun.

Photo
Rendering Cross-section
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Technical Accomplishments
The Encapsulation Process for Vacuum-Sealing the
Electron Gun
Exploded view of the the Thomas Electronics gun.
The mount is supplied on a 7052 boro-silicate
glass stem containing an evacuation port, is
vacuum sealed by (I) glass blowing a glass
envelope, (ii) anodic bonding of the
membrane-bearing Silicon chip to the Pyrex/Kovar
exit aperture assembly, and (iii) laser-welding
the assembly to the Kovar/7052 transition
Anodic Bonding
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Significant Events
Vacuum-Isolation of the Electron Source
Kovar transition
Glass Envelope

• In-situ operation of the AEXS instrument relies
  on the use of a vacuum-isolated electron source
  with a thin micro-fabricated SiN membrane that is
  transparent to the source electrons yet robust
  enough to isolate the source vacuum
• Our encapsulation procedure consists of
• Fabrication of a glass enclosure that envelops
  the electron optics column
• Double-anodic bonding of the membrane-bearing
  Silicon chip to a Pyrex-Kovar subassembly
• Laser Welding of the Pyrex/Kovar subassembly to a
  Kovar/Glass transition
• Gun evacuation, baking and pinching off the
  evacuation port

Silicon chip
Vacuum-Isolated Thomas Electronics 20keV Electron
gun
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Plans for Next Quarters

• Membrane Optimization to improve Membrane
  Robustness and Yield
• JPL-pioneered double thickness membrane
  fabrication process
• Electron-Optics Optimization for Beam Focusing
• Anode Electrode re-design in co-operation with
  Thomas Electronics Inc
• Robustness Tests
• Vacuum Isolation
• Thermal Robustness
• Mechanical Vibrations Robustness
• Environmental Chamber Testing
• Operating Parameters
• XRF Data Acquisition
• Stand-Alone Electron Gun Testing

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Financial Status Obligations Cost
MIDP MIDP-102162-13.0
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BACKGROUD INFORMATION
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Comparison of EDS AEXS Spectra in Air Using a
10 keV gun Waspaloy NIST Standard Reference
Material 1243
Characteristic X-ray spectra were acquired from
various mineral standards and NIST traceable
alloy materials using the encapsulated 10 keV
electron gun
NIST Certified Composition
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10 keV Electron Gun Breadboard Instrument
Enabling Component SiN membrane window etched
into a silicon frame. Anodic bonding was used to
encapsulate the electron gun with the
membrane-bearing Si chip

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Sealed 10 keV gun in the AEXS apparatus.
Cross-section of the electron gun