Traditional mirrors at optical wavelengths use thin metalized or dielectric layers of uniform thickness to approximate a
perfect electric field boundary condition. The electron gas in such a mirror configuration oscillates in response to the
incident photons and subsequently re-emit fields where the propagation and electric field vectors have been inverted and
the phase of the incident magnetic field is preserved. We proposed fabrication of sub-wavelength-scale conductive
structures that could be used to interact with light at a nano-scale and enable synthesis of the desired perfect magneticfield
boundary condition. In a magnetic mirror, the interaction of light with the nanowires, dielectric layer and ground
plate, inverts the magnetic field vector resulting in a 0 degree phase shift upon reflection. Geometries such as split ring
resonators and sinusoidal conductive strips were shown to demonstrate magnetic mirror behavior in the microwave [1]
and then in the visible [2]. Work to design, fabricate and test a magnetic mirror began in 2007 at the NASA Goddard
Space Flight Center (GSFC) under an Internal Research and Development (IRAD) award. Our initial nanowire geometry
was sinusoidal but orthogonally asymmetric in spatial frequency, which allowed clear indications of its behavior by
polarization. We report on the fabrication steps and testing of magnetic mirrors using a phase shifting interferometer and
the first far-field imaging of an optical magnetic mirror.
Observations of the Earth are extremely challenging; its large angular extent floods scientific instruments with high flux
within and adjacent to the desired field of view. This bright light diffracts from instrument structures, rattles around and
invariably contaminates measurements. Astrophysical observations also are impacted by stray light that obscures very
dim objects and degrades signal to noise in spectroscopic measurements. Stray light is controlled by utilizing low
reflectance structural surface treatments and by using baffles and stops to limit this background noise. In 2007 GSFC
researchers discovered that Multiwalled Carbon Nanotubes (MWCNTs) are exceptionally good absorbers, with potential
to provide order-of-magnitude improvement over current surface treatments and a resulting factor of 10,000 reduction in
stray light when applied to an entire optical train. Development of this technology will provide numerous benefits
including: a.) simplification of instrument stray light controls to achieve equivalent performance, b.) increasing
observational efficiencies by recovering currently unusable scenes in high contrast regions, and c.) enabling low-noise
observations that are beyond current capabilities. Our objective was to develop and apply MWCNTs to instrument
components to realize these benefits. We have addressed the technical challenges to advance the technology by tuning
the MWCNT geometry using a variety of methods to provide a factor of 10 improvement over current surface treatments
used in space flight hardware. Techniques are being developed to apply the optimized geometry to typical instrument
components such as spiders, baffles and tubes. Application of the nanostructures to alternate materials (or by contact
transfer) is also being investigated. In addition, candidate geometries have been tested and optimized for robustness to
survive integration, testing, launch and operations associated with space flight hardware. The benefits of this technology
extend to space science where observations of extremely dim objects require suppression of stray light.
A carbon nanotube (CNT) field emission electron gun has been fabricated and assembled as an electron impact
ionization source for a miniaturized time-of-flight mass spectrometer (TOF-MS). The cathode consists of a patterned
array of CNT towers grown by catalyst-assisted thermal chemical vapor deposition. An extraction grid is precisely
integrated in close proximity to the emitter tips (20-35 μm spacing), and an anode is located at the output to monitor the
ionization beam current. Ultra-clean MEMS integration techniques were employed in an effort to achieve three
improvements, relative to previous embodiments: reduced extraction voltage during operation to be resonant with gas
ionization energies, enhanced current transmission through the grid, and a greater understanding of the fundamental
current fluctuations due to adsorbate-assisted tunneling. Performance of the CNT electron gun will be reported, and
implications for in situ mass spectrometry in planetary science will be discussed.
We are implementing nano- and micro-technologies to develop a miniaturized electron impact ionization mass
spectrometer for planetary science. Microfabrication technology is used to fabricate the ion and electron optics, and a
carbon nanotube (CNT) cathode is used to generate the ionizing electron beam. Future NASA planetary science
missions demand miniaturized, low power mass spectrometers that exhibit high resolution and sensitivity to search for
evidence of past and present habitability on the surface and in the atmosphere of priority targets such as Mars, Titan,
Enceladus, Venus, Europa, and short-period comets. Toward this objective, we are developing a miniature, high
resolution reflectron time-of-flight mass spectrometer (Mini TOF-MS) that features a low-power CNT field emission
electron impact ionization source and microfabricated ion optics and reflectron mass analyzer in a parallel-plate
geometry that is scalable. Charged particle electrodynamic modeling (SIMION 8.0.4) is employed to guide the iterative
design of electron and ion optic components and to characterize the overall performance of the Mini TOF-MS device via
simulation. Miniature (< 1000 cm3) TOF-MS designs (ion source, mass analyzer, detector only) demonstrate simulated
mass resolutions > 600 at sensitivity levels on the order of 10-3 cps/molecule N2/cc while consuming 1.3 W of power and
are comparable to current spaceflight mass spectrometers. Higher performance designs have also been simulated and
indicate mass resolutions ~1000, though at the expense of sensitivity and instrument volume.
The lifetime of a patterned carbon nanotube film is evaluated for use as the cold cathode field emission ionization source
of a miniaturized mass spectrometer. Emitted current is measured as a function of time for varying partial pressures of
nitrogen gas to explore the robustness and lifetime of carbon nanotube cathodes near the expected operational voltages
(70-100 eV) for efficient ionization in mass spectrometry. As expected, cathode lifetime scales inversely with partial
pressure of nitrogen. Results are presented within the context of previous carbon nanotube investigations, and
implications for planetary science mass spectrometry applications are discussed.
Solar system exploration and the anticipated discovery of biomarker molecules is driving the development of a new
miniature time-of-flight (TOF) mass spectrometer (MS). Space flight science investigations become more feasible
through instrument miniaturization, which reduces size, mass, and power consumption. However, miniaturization of
space flight mass spectrometers is increasingly difficult using current component technology. Micro electro mechanical
systems (MEMS) and nano electro mechanical systems (NEMS) technologies offer the potential of reducing size by
orders of magnitude, providing significant system requirement benefits as well. Historically, TOF mass spectrometry
has been limited to large separation distances as ion mass analysis depends upon the ion flight path. Increased TOF MS
system miniaturization may be realized employing newly available high speed computing electronics, coupled with
MEMS and NEMS components. Recent efforts at NASA Goddard Space Flight Center in the development of a
miniaturized TOF mass spectrometer with integral MEMS and NEMS components are presented. A systems overview,
design and prototype, MEMS silicon ion lenses, a carbon nanotube electron gun, ionization methods, as well as
performance data and relevant applications are discussed.
A cold cathode field emission electron gun (e-gun) based on a patterned carbon nanotube (CNT) film has been fabricated
for use in a miniaturized reflectron time-of-flight mass spectrometer (RTOF MS), with future applications in other
charged particle spectrometers, and performance of the CNT e-gun has been evaluated. A thermionic electron gun has
also been fabricated and evaluated in parallel and its performance is used as a benchmark in the evaluation of our CNT
e-gun. Implications for future improvements and integration into the RTOF MS are discussed.
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