Nuclear Magnetic Resonance Force Microscopy Using Ultrasensitive
Oscillators, Phase II
Army Research Office, STTR Phase II
Project, Start Date: July 23, 2002
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Xidex and UT Austin have pushed the room-temperature limits for
magnet-on-oscillator scanning mode using a "semi-infinite" sample, and
obtained the highest resolution room-temperature NMR, and certainly the
best room-temperature z-resolution (200 nm) to date. We again demonstrated
submicron resolution on a 0.3-micron-thick polymer film. We also observed
resonance using an ADP sample and verified its NMR origin. Using e-beam
lithography, we obtained our first double-sided etch micro-oscillators.
The first generation were somewhat thicker than hoped for, providing force
sensitivities around 10-16
N/Hz1/2 at room temperature, and matched our
existing sensitivity limits for silicon oscillators. We fabricated carbon
nanotube oscillators with a projected force sensitivity of
2.6x10-20
(N/Hz1/2) at 0.3 K, which would be adequate for
detection of a single
nuclear spin. We demonstrated a 7.2 nm diameter spherical iron magnet with
a magnetic field gradient of 3x106 (T/m) at 10
nm, or 2x107 T/m at 5 nm,
satisfying the main requirement for magnets for single-nuclear-spin
detection. We built and tested X-Y-Z stages for fiber positioning and
sample positioning that provide independent motion in each spatial
dimension with sub-nanometer resolution and have an immense range of many
millimeters. We also designed and constructed a dual fiber-interferometer
system to contribute to the single-spin NMRFM project.
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Nuclear Magnetic Resonance Force Microscopy Using Ultrasensitive
Oscillators, Phase I
Army Research Office, STTR Phase I
Project, Start Date: July 23, 2002
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Xidex Corporation and UT Austin demonstrated the feasibility of our high-Q
torsional oscillator method for detection of single proton spins using
nuclear magnetic resonance force microscopy. The advantage of torsional
oscillators over cantilevers is precisely this "more sensitive but more
robust" architecture. Together with current magnet technology, a stable
and sensitive scanning and motion-feedback stage, and implementation of
now-standard techniques for lower interferometer power. Other achievements
in our supporting research in carbon nanotube oscillators could provide
enhancements which would increase the bandwidth of single-spin nuclear
magnetic resonance microscopy scans. This would increase imaging and
quantum-spin-processing speeds, essential for resolving complex structures
or performing intensive quantum algorithms.
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Nuclear Magnetic Resonance Force Microscopy for Subcellular Imaging,
Phase I
National Science Foundation, SBIR Phase I Project,
Start Date: July 1, 2003
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This Small Business Innovation Research (SBIR) Phase I project
demonstrated the feasibility of a nuclear magnetic resonance force
microscope (NMRFM) that will make it possible for the first time ever to
routinely image intracellular diffusion properties, relaxation times, and
hydrogen densities of live cells with sub-optical spatial resolution, down
to a volume resolution of 0.1 micron on a side. The hypothesis is that an
NMRFM technique can be used for NMR-based imaging of living eucaryotic and
procaryotic cells with sub-optical resolution, thereby allowing
measurement of diffusion properties, relaxation times, and hydrogen
(proton-spin) densities of the cell itself and its larger internal
structures (e.g. nucleus, cytoplasm, plasma membrane, and mitochondria).
The commercial applications of this project will be in the research
instrumentation market. Prospective customers include biologists, medical
researchers, clinical practitioners, and others interested in functional
and structural imaging of living cells and acellular tissue samples.
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Ultra-Sensitive Torsional Oscillators for Scanning Probe Microscopes,
Phase I
National Institute of Standards and Technology, SBIR
Phase I Project, Start Date: July 15, 1999
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Xidex and UT Austin developed a new type of ultrasensitive force sensor
suitable for use with scanning probe microscopes. Ultrasensitive force
detection was enabled by using high-Q silicon multiple torsional
oscillators. Our strategy to attain and surpass a force sensitivity of
10-16 N/Hz1/2, which
is required to measure extremely small electro-dynamic forces, involves
two main thrusts: (1) utilizing double- and multiple-torsional oscillator
modes, which can enhance oscillator quality factor Q by a factor of 100 or
more, and (2) replacing ultrathin silicon-nitride (amorphous) cantilevers
with single-crystal silicon structures, which can further enhance the Q by
a similar or greater factor. Further work will focus on improving the
repeatability and scalability of the batch fabrication process, thus
enabling incorporation of ultra-sensitive cantilevers into planed OEM
modules and sale of cantilevers themselves to end-users of scanned probe
microscopy tools and instruments.
Targeted commercial applications include magnetic force microscopy
(MFM), magnetic force resonance microscopy (MRFM), lateral force
microscopy (LFM), and scanning potentiometry. Two commercial embodiments
of the technology will be evaluated: (1) sensing components, bundled with
appropriate software, for sale to OEMs of laboratory instrumentation, and
(2) integration of the technology into our own stand-alone tools for sale
directly to end users. The channel we pick will depend on the application
or applications that have the greatest commercial potential.
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Magnetic Resonance Force Microscopy Using High-Q Multiple Torsional
Mechanical Oscillators, Phase II
Army Research Office, STTR
Phase I Project, Start Date: September 1, 1999
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Xidex and UT successfully demonstrated the feasibility of developing a
magnetic resonance force microscope for single proton imaging. Force
detection experiments enabled us to conclude that NMRFM single-sweep
sensitivity as low as 1 x 1016
N/Hz½ can be achieved at room temperature with
our probe and that a force detection sensitivity of 3 x
10-18 N/Hz½ can be
achieved at 0.3 kelvin. For planned field gradients, this makes our
results comparable to the single electron spin sensitivity of others, but
only at about Signal/Noise ~ 1 for nuclear spins. Our approach uses
high-sensitivity measurement of the magnetic force using the high-Q mode
of a multiple torsional oscillator fabricated from single crystal silicon
as the sensing element. We have built the required hardware for doing
NMRFM, including a 3He system capable of 0.3 K, a 9T magnet, an
in-house-developed digital feedback controller for scanning probe tools
and a lithography tool for oscillator fabrication. Cobalt micromagnets
with moments below 10-12 J/T were fabricated,
characterized, and modeled, and the magnetic forces were measured. A
prototype NMRFM probe was set-up for imaging single biological cells.
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Magnetic Resonance Force Microscopy Using High-Q Multiple Torsional
Mechanical Oscillators, Phase I
Army Research Office, STTR
Phase I Project, Start Date: August 19, 1998
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Xidex Corporation and The University of Texas at Austin demonstrated the
feasibility of developing a magnetic resonance force microscope for single
proton imaging. The proposed device will achieve high-precision,
high-sensitivity measurement of the magnetic force using the high-Q mode
of multiple torsional oscillators fabricated from silicon as the sensing
element. The UT Austin research group has already attained the spatial
resolution required for single proton imaging by abandoning inductive
detection schemes (NMR pickup coils, etc.) in favor of the multiple
torsional oscillator system. This is the only group known to be actively
pursuing magnetic resonance force microscopy with this approach. A factor
of 100,000 improvement in signal-to-noise has been demonstrated in the
laboratory. We now propose to extend the technique to its ultimate goal:
single proton imaging. The target magnetic moment sensitivity of 2 x
10-28 J/T will easily permit single proton
imaging (Mproton = 1.4 x
10-26 J/T). The achievement will be demonstrated
by non-intrusive detection of individual hydrogen atoms on surfaces. The
project was directed at demonstration of oscillators with a force
sensitivity of Fmin = 5 x
10-16 N at room temperature and 2 x
10-19 N at 4 K.
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