Nanoelectronics and Nano Materials in Space Extreme Environments
The heavy ion component of the solar wind poses an especially dangerous hazard to electronic and
human operations in inter-planetary space and on the lunar surface because these high-mass, highly charged (fully stripped) particles penetrate all but
the most massive shielding. The Michigan State University Facility for Rare Isotope Beams (FRIB) (formerly the National Superconducting Cyclotron Laboratory)
is one of the few facilities that can deliver fully stripped heavy-ion beams with an extended energy range that makes it possible to reproduce 99% of the
space radiation spectrum. Beam-time awards to Dr. Ayres and collaboration with expert FRIB beam physicists enable pioneering investigations of nanomaterials
and real-time nanocircuit operation under accurately simulated space radiation duress.
a. GaN nanoFETS Under Real-time Space Irradiation at FRIB (NSCL)
Primary beams of fully stripped Krypton-78, and Xenon-124 with 140 MeV per nucleon energies were used
to generate realistic space conditions for two separate real-time long duration (30 minutes) investigations of GaN nanoFET physical and electronic performance.
Two important findings to date are: heavy ion interactions consistently produce amorphous surface plumes along GaN nanowires rather than conventional radiation
tracks that go all the way through. The observation that damage was restricted to the surface is consistent with our second finding, that normal nanoFET
function was maintained during real time heavy ion irradiation followed by electrical stress tests at 72 h post-rad. Our current goal is to determine
whether it is reduced dimensionality, or a previously reported metallic response to ion impact on bulk GaN surfaces, that is responsible for the surface
b. Nanocircuit Contacts Under Real-time Space Irradiation
Nanowire and nanotube nanocircuits operate as unconventional Schottky barrier devices, in which field
effect transistor (FET) functionality is achieved through barrier, not channel, manipulation. This decouples these devices from the capacitive changes that
disable conventional on junction FETs under space radiation conditions. Furthermore, the reduced dimensionality nanomaterials themselves display inherent
radiation resilience from quantum energy and momentum constraints.
Any changes to the Schottky barrier control in a radiative environment are therefore significant.
The general theory for Schottky barriers is commonly used in one of its mathematically tractable regimes, thermionic emission ‘over’ the barrier or ohmic
contact (ﬁeld emission) tunneling through the barrier. However, the high current densities reported in reduced dimensionality devices, including ours,
correspond to barrier transport in the thermionic field emission (TFE) mixed regime. TFE analysis is difﬁcult due to its multivariate nature.
Ayres’ group has developed a novel self-consistent mathematical stability approach that enables determination of the major TFE ﬁtting parameters.
One immediate goal is to complete and publish an Application Note for the freeware release of this code.
Using the TFE stability code described above, we reported the ﬁrst-time analyses of the barrier heights,
tunneling probabilities and potential drops for the long-duration exposure GaN nanoFETs and obtained a new result: barrier heights and widths both decreased
as their initial radiation response, which implies improved transport, and then slowly recovered their pre-rad values. Investigations of speciﬁc interface
charge models that can produce the observed behavior are underway. GaN has recently become the material of choice for terrestrial 5G communication systems,
and all communications providers are interested in extension to space qualification.
c. Ni, Co and Ni-Co Nanowires
Through ongoing collaborative work with a UK group, we have discovered conditions for growth of
highly crystalline Ni, Co and layered Ni-Co nanowires from a novel combination of high-speed turbulent flow electrodeposition (HSTFE) with a thin
hydrocarbon layer on an oxidized substrate These are single crystal nanowires rather than the usual poly-nanocrystalline. Our new results indicate that
HSTFE breaks an applied hydrocarbon film into an array of carbon catalyst particles and oxygen radicals while enhancing local ion concentrations and
trajectories in ways that result in templateless nanowire growth via an “ion vapor”-liquid-solid mechanism. This work is significant because synthesis
of high-melting point metallic nanowires has proved especially challenging, and they are highly sought after for applications in magnetic storage,
magnetic sensing, optical sensing, plasmonic resonance sensing, as micro polarizers and as supercapacitors. Ni nanowires have also been used to
non-chemo-toxically induce apoptosis in pancreatic cancer cells, a potentially breakthrough application as pancreatic cancer has a high mortality rate
and few good treatment options. Our next step is to transition these results by extending our collaboration to include physical and biological
d. Carbon Onion Nano-lubricants
This work was initiated in collaboration with Tokyo Institute of Technology, Japan, where Dr.
Ayres has had the honor of serving as a Chair of International Cooperation with a time-specific grant of permanent resident citizenship. Nano-carbons
are a promising approach to lubrication challenges in space that include vacuum, radiation and temperature extremes. Planar graphite, while an excellent
lubricant on earth, undergoes knock-on collision amorphitization by heavy ions in space and structural collapse in vacuum.
The responses of carbon onions with increasing graphite layer character due to increasing
temperature growth conditions were investigated under heavy ion irradiation at FRIB (NSCL). Primary beams of fully stripped Calcium-48,
and Argon-40 with 140 or 70 MeV per nucleon energies were used to generate realistic space conditions. Stored elastic energy and layer number
were investigated through analysis of pre- and post- irradiation HRTEM images. Our work demonstrated the new result, that as the radiation dose
increased, carbon onion mechanical energy storage counterintuitively increased due to a decrease in disorder. A stored energy range that correlates
with a radiation-induced conversion to planar graphite was identified. The allowed dynamics of radiation-induced defect propagation in radial (carbon onion)
versus planar graphene layers were shown to be causative. The practical consideration is that our results indicate that for space lubrication applications,
“less perfect” lower temperature grown carbon onions may be more resilient to heavy ion space radiation. We are currently exploring collaborative partnerships
for lunar surface applications.