Researchers at the Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC) have
initiated multidiscipline efforts to develop nano-based structures and components for insertion into advanced missile,
aviation, and autonomous air and ground systems. The objective of the research is to exploit unique phenomena for the
development of novel technology to enhance warfighter capabilities and produce precision weapons. The key technology
areas that the authors are exploring include nano-based microsensors, nano-energetics, nano-batteries, nano-composites,
and nano-plasmonics. By integrating nano-based devices, structures, and materials into weaponry, the Army can
revolutionize existing (and future) missile systems by significantly reducing the size, weight and cost. The major
research thrust areas include the development of chemical sensors to detect rocket motor off-gassing and toxic industrial
chemicals; the development of highly sensitive/selective, self-powered miniaturized acoustic sensors for battlefield
surveillance and reconnaissance; the development of a minimum signature solid propellant with increased ballistic and
physical properties that meet insensitive munitions requirements; the development of nano-structured material for higher
voltage thermal batteries and higher energy density storage; the development of advanced composite materials that
provide high frequency damping for inertial measurement units' packaging; and the development of metallic
nanostructures for ultraviolet surface enhanced Raman spectroscopy. The current status of the overall AMRDEC
Nanotechnology research efforts is disclosed in this paper. Critical technical challenges, for the various technologies, are
presented. The authors' approach for overcoming technical barriers and achieving required performance is also
discussed. Finally, the roadmap for each technology, as well as the overall program, is presented.
Laser induced Semiconductor Switches (LSS), comprised of a gap antenna deposited on a semiconductor substrate and
photoexcited by a pulsed laser, are the primary source of THz radiation utilized in time-domain spectroscopy (TDS).
THz-TDS applications such as standoff detection and imaging would greatly benefit from greater amounts of power
coupled into free space radiation from these sources. The most common LSS device is based on low temperature-grown
(LT) GaAs photoexcited by Ti:sapphire lasers, but its power performance is fundamentally limited by low breakdown
voltage. By contrast, wide band-gap semiconductor-based LSS devices have much higher breakdown voltage and could
provide higher radiant power efficiency but must be photoexcited blue or ultraviolet pulsed lasers. Here we report an
experimental and theoretical study of 10 wide band-gap semiconductor LSS host materials: traditional semiconductors
GaN, SiC, and ZnO, both pristine and with various dopants and alloys, including ternary and quaternary materials
MgZnO and InGaZnO. The objective of this study was to identify the wide bandgap hosts with the greatest promise for
LSS devices and compare their performance with LT-GaAs. From this effort three materials, Fe:GaN, MgZnO and
Te:ZnO, were identified as having great potential as LSS devices because of their band-gap coincidence with frequency
multiplied Ti:Sapphire lasers, increased thermal conductivity and higher breakdown voltage compared to LT-GaAs, as
well as picoseconds scale recombination times.
Nonstoichiometric ZnO with an excess of Zn atoms (ZnO:Zn) has a long history of use as a green/monochrome
phosphor in electron-excited vacuum fluorescent and field emission displays. The advent of ultraviolet lasers and
light emitting diodes presents the possibility of photoexciting the highly efficient, defect-related green emission
in ZnO:Zn. Here we study experimentally the time-integrated quantum efficiency and the time-resolved photoluminescence
decays of both near band edge and defect emissions in unannealed (ZnO) and annealed (ZnO:Zn)
nanoparticles under femtosecond excitation. A comparison of results using one-photon excitation (excitation
primarily near the particle's surface) versus two-photon excitation (uniform excitation throughout the particle's
volume) elucidates how the quantum efficiencies depend on material properties, such as the spatial distributions
of radiative and nonradiative defects, and on optical effects, such as reabsorption.
The effect of plasma-induced ion damage on the optical properties of ZnO films grown by plasma-assisted molecular
beam epitaxy on a-sapphire substrates and GaN(0001)/c-sapphire templates prepared has been studied using steady-state
and time-resolved photoluminescence. We observed that the deflecting the ions produced by the RF oxygen plasma
away from substrate results in improved excitonic emission and modification of the defect-related PL spectrum. The
intensity of the near-band-edge lines in the photoluminescence spectra from the layers grown with the ion deflection was
found to increase by factors 7 to 20 for the layers grown on GaN(0001)/c-sapphire at a plasma power of 350 W and by 3
to 4 times for ZnO grown on a-sapphire substrates at a plasma power of 265 W as compared to the controls grown
without the ion deflection. The yellow-green spectral range was dominated by different defect bands in the films grown
with and without ion deflection. The effect of RF power on peak positions of the defect band was studied for the films
grown without ion deflection. For the ZnO films grown on a-plane sapphire substrates, time-resolved photoluminescence
showed a significant increase in luminescence decay times both at RT and 89 K. However, for ZnO on GaN(0001)/csapphire
substrates, virtually no improvement in decay time was found at 89 K with only a moderate increase in decay
constant at room temperature.
GaN epitaxial layers grown on SiC and sapphire suffer from high density of line and point defects. To address this
problem, new growth methods using in situ or ex situ nano-network masks as dislocation filters have been introduced
recently. In this work, we report on metalorganic chemical vapor deposition (MOCVD) of GaN layers on 2-inch
sapphire substrates using in situ SiNx nano-networks intended for defect reduction. SiNx interlayers with different deposition times were employed after ~2 &mgr;m GaN grown on sapphire, which was followed by ~3.5 &mgr;m GaN
overgrowth. With increasing SiNx coverage, full width at hall maximum (FWHM) values of (0002) and (101-2) X-Ray
diffraction (XRD) peaks monotonously decrease from 252 arc sec to 217 arc sec and from 405 ar csec to 211 arc sec,
respectively for a 5.5 &mgr;m thick film. Similarly, transmission electron microscopy (TEM) revealed that screw and edge
type dislocation densities as low as 4.4x107 cm-2 and 1.7x107 cm-2 were achieved. The use of SiNx nanonetwork also increases the radiative recombination lifetimes measured by time-resolved photoluminescence to 2.5 ns from less than
0.5 ns in control GaN. We have also fabricated Ni/Au Schottky diodes on the overgrown GaN layers and the diode
performance was found to depend critically on SiNx coverage, consistent with TEM, XRD and TRPL results. A 1.13eV
barrier height was achieved when SiNx layer was used compared to 0.78 eV without any SiNx nanonetwork.
Furthermore, the breakdown voltage was improved from 76 V to 250 V with SiNx nanonetwork.
In this paper some practical observations related to the fabrication of multifocal IOLs are presented from the viewpoint of a diffractive optics design and fabrication group whose experience lies mostly outside the area of ophthalmic optics.
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