Nanoprobe Staff (Back): Dr. John Moreland,
Eric Langlois, Li-anne Liew, Dong-Hoon Min,
and Elizabeth Mirowski. (Front): Daniel Porpora
and Shawn Liu.
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Technical Accomplishments
Project Goals
This project develops scanned-probe microscopy (SPM) and micro-electromechanical
systems (MEMS) for nanometer-scale magnetic measurements in support
of the magnetic data storage industry. Project members perform research
to understand and relate SPM images and MEMS magnetometer measurements
to the performance of magnetic materials and devices for future
recording technologies. The project is currently focusing on ultra-small
magnetic-force-microscopy tips for imaging recording heads and media
at a resolution of 10 nanometers. Quantitative field mapping of
heads and media is based on electromechanical detection of magnetic
resonance. MEMS magnetometers with integrated specimens and high
sensitivity are being developed. Over the next few years, the
project will work on a "magnetic resonance spectrometer on a chip"
to achieve magnetic-resonance imaging resolution of 1 nanometer on
ferromagnetic thin films. Recent research includes the development
of new ferromagnetic resonance spectrometers based on calorimetry,
torque, and transfer of spin angular momentum. Such sensors can
be integrated with atomic-force microscopes for imaging of local
DC and RF magnetic fields. The project also develops manipulation
and measurement techniques for isolating and probing the behavior
and structure of single molecules. Finally, the project is developing
microfabricated Cs vapor cells and cantilever-based magnetic detectors
for a chip-scale atomic clock.
Customer Needs
The Information Storage Industry Consortium recently drafted a
recording-head metrology roadmap that calls for high-resolution,
quantitative magnetic microscopes and magnetometers that go beyond
the limitations of current technology. Magnetic measurement systems
have be-come increasingly complex. Our expertise in magnetism, probe
microscopy, and cleanroom microfabrication techniques helps move
instruments from the development stage to routine operation in
the industrial laboratory and on the factory floor.
Industry also looks to NIST for fundamental constants and representations
of magnetic units as it pushes to smaller time and length scales.
The physics of nanometer-scale magnetism must be explored so that
industry can make the right choices for recording at densities of
over 100 gigabits per square centimeter.
In order to improve upon magnetic microscopes, our project is focusing
on specialized magnetic-force-microscope (MFM) tips for imaging
heads and media. Ultra-small tips are being developed for magnetic
image resolution of 10 nanometers. We are looking at new technologies
for making very sharp probe tips and for controlling nano-scale
magnetic structure near the tip. In addition, more sensitive MFM
instruments are being developed. Quantitative field mapping of heads
and media can be done with tiny field probes based on electromechanical
detection of magnetic resonance. We are developing ways to attach
submicrometer magnetic resonance particles to ultra-sensitive cantilevers
and to position particles a few nanometers from the sample surface.
Instrumentation will also be adapted to a new class of microwave
probe stations that use micromachined probe chips to extend voltage
and current probe measurements on microwave circuits with submicrometer
spatial resolution in the 100 gigahertz range.
The project also develops single-molecule manipulation and measurement
(SM3) techniques. This program will advance single-molecule metrology
by developing a novel platform, based on bio-nano-electromechanical
systems, that integrates electrical, optical and spectroscopic technologies.
Specifically, we are developing SM3 technologies to address significant
inaccuracies in the base-pair ordering inferred from current gene-sequencing
tools, affecting such efforts as the Human Genome Project. Our pro-gram
is an effort to ensure the integrity of such bio-informatic databases
through the development and utilization of a high-throughput SM3
platform to directly manipulate and measure the structure and dynamics
of single RNA or DNA molecules. By directly working with an individual
molecule of DNA, many of these sources of error are eliminated.
Currently, the lack of measurement tools and methods for isolating,
manipulating and probing the behavior and structure of single molecules
prevents such an effort. This is a collaboration among divisions
in EEEL, the Physics Laboratory, the Chemical Science and Technology
Laboratory, and the Information Technology Laboratory.
We are also working with the Physics Laboratory to develop a chip-scale
atomic clock (CSAC). The most common type of passive frequency standard
is the vapor-cell frequency reference. In these clocks the atoms
are part of a thermal vapor contained inside a cell. The atomic
vapor cell is placed inside a microwave cavity resonant at the atomic
transition frequency. Light from a laser or discharge lamp, resonant
with an optical transition in the atoms, optically pumps the atoms
into one of the hyperfine ground states. Microwaves, usually synthesized
from a crystal oscillator, are then injected into the cavity. When
their frequency exactly equals the atomic transition frequency,
a change of atomic state occurs, which is measured by the change
in absorption of the laser. This change in absorption is used to
correct the local oscillator frequency and lock it to the atomic
transition.
What is the smallest size for an atomic clock? The difficulty associated
with the large size of the microwave cavity can be overcome by using
an all-optical excitation method based on coherent-population-trapping
(CPT) resonances. In the CPT clock, no microwaves are applied directly
to the atoms. Instead, an optical field is modulated at the atomic
hyperfine frequency, resulting in two optical fields separated by
the atomic oscillation frequency. Due to the CPT effect, the absorption
of these two optical fields is altered when the separation frequency
exactly equals the atomic hyperfine splitting. This change in absorption
can be used to lock the local oscillator frequency to the atomic
transition. Thus, the fundamental limit to the clock size is the
wavelength of the optical radiation, which is of the order of 1
micrometer.
The CSAC research will help protect satellite transmissions, including
global positioning systems, from being jammed. We expect that one
of the first spin-offs of the research program will be the development
of compact, accurate magnetometers based on the Zeeman shift of
Cs atoms.
Technical Strategy
We are developing new tools for measurements of nanoscale magnetic
phenomena and representations of magnetic units for the next generation
of data-storage devices. We are developing MEMS magnetometers with
integrated magnetic samples that can offer tremendous gains in magnetic-moment
sensitivity. Our micromachining facility is at the state of the
art, providing the tools necessary for bulk and surface micro-machining
on Si wafers. Our plans over the next four years are to demonstrate
new metrology instrumentation based on MEMS devices that will enable
us to create instruments that have superior performance compared
to current magnetic-measurement methods.
Scanning Probe Development
In order to improve upon scanning probe microscopes, such as MFM,
and keep pace with industry needs, we are focusing on specialized
MFM tips for imaging heads and media. Ultra-small tips are currently
being developed for magnetic-image resolution of 20 nanometers.
We are looking at new technologies for fabricating, controlling
and measuring nanometer-scale magnetic structures near the probe
tip. In particular, MFM resolution can improve only with the development
of more sensitive cantilevers for measuring the small magnetic forces
associated with nanometer-scale magnetic probe tips. Conventional
MFM is not an intrinsically quantitative technique. However, quantitative
field mapping can be done with tiny field probes based on mechanical
detection of magnetic resonance in the probe. We are developing
ways to fabricate small magnetic-resonance particles on ultra-sensitive
cantilevers and position the particles a few nanometers from the
sample surface for field mapping with 1 nanometer resolution.
Deliverables
- Characterize MEMS high-frequency sensors with integrated magnetic
and microwave structures for microwave probing. Develop nanoscale
magnetic recording scanning stand based on SPM. (FY 2003)
- Develop probes based on direct mechanical coupling between microwave
fields and the magnetic moment of a 100 nanometer magnetic particle
fabricated near the tip of an atomic force microscope (AFM) cantilever.
Compare MFM, scanning electron microscopy with polarization analysis
(SEMPA), and Lorentz microscopy on prototype magnetic imaging
standards for mag-netic-recording applications. (FY 2004)
MEMS Magnetometer Development
Micrometer and submicrometer-scale magnetic measurements have proven
to be a challenge for conventional magnetometers, and new methods
are being employed to probe magnetism on this scale. Conventional
measurements are made on arrays of micromagnetic dots. However,
due to fabrication limitations, the results are clouded by statistical
variations in dot shape, size and spacing. Thus, more sensitive
detectors are needed that can measure magnetic properties of individual
dots.
In particular, there is a need to understand atomic-scale spin damping
in ferromagnetic systems in order to improve the switching speed
of magnetic devices. For example, data-transfer rates for commercial
disk drives will soon require operational bandwidths in excess of
1 gigahertz. For switching times less than 1 nanosecond, gyromagnetic
effects dominate. One way to understand damping is to investigate
size effects as magnetic devices are reduced to sub-micrometer dimensions.
Studies of magnetic nanodots will give a better understanding of
spin damping and therefore aid in the development of faster disk
drives.
We will provide new magnetometers based on highly specialized MEMS
chips fabricated at NIST. The instruments will be inexpensive, since
MEMS can be batch-fabricated in large quantities. In addition, large-scale
magnetic wafer properties can be transferred to smaller MEMS magnetometers
so that nanometer-scale measurements can be calibrated with reference
to fundamental units. In particular, our focus will be the development
of torque and force magnetometers, magnetic-resonance spectrometers,
and magnetic-resonance imaging (MRI) microscopes on MEMS chips.
Over the long term, we expect that this technology will lead to
atomic-scale magnetic instrumentation for the measurement and visualization
of fundamental magnetic phenomena.
Deliverables
- Perform ferromagnetic resonance (FMR) spectroscopy using MEMS
detectors on isolated submicrometer dots to measure spin decay.
Correlate decay with size effects, spinwave spectra, and phonon
spectra. (FY 2003)
- Develop high-gradient micro-electromagnets and micro-RF coils
for MRI based on a MEMS sensor. Integrate microcoils and torsion
oscillator sensor for pulsed-field-gradient MRI. Demonstrate conventional
MRI by replacing the inductive pickup coil with a torsion oscillator
for measuring spin decay. (FY 2004)
- Demonstrate a fully integrated MRI microscope on a chip. (FY
2005)
Single-Molecule Manipulation and Measurement
The semiconductor electronics industry has driven the development
of fabrication tools that are capable of patterning structures on
the order of 100 nanometers, smaller than cellular dimensions. Using
MEMS, it is possible to create three-dimensional structures that
are commensurate with the size of biomolecules.
Interactions of single molecules with nanoscale mechanical structures,
restriction elements, and other single molecules will be probed
by electronic, electromechanical and optical techniques. The effort
will result in a well characterized SM3 platform integrated with
AFM, fluorescence resonance energy transfer (FRET), optical microscopy,
and electronics, thereby enabling a wide variety of single-molecule
studies. Determination of DNA structure will be performed by directly
interrogating ordered bases as they are threaded through a well
characterized nanopore.
Deliverables
- Fabricate magnetic nanofluidic capture cell and demonstrate
capture-and-release of magnetic nanobeads. Develop methods to
attach DNA to beads. Demonstrate magnetic bead position control
with fluid-cell MFM. (FY 2003)
- Fabricate prototype nanofluidic SM3 platform. (FY 2004)
- Fabricate and test magnetic random access array sorter. (FY
2005)
- Integrate SM3 measurement chips with nanofluidic SM3 platform.
(FY 2006)
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Concept of magnetic trap for single-magnetic-bead manipulation
in a microfluidic cell. Bio-molecules will be attached to
the beads for single-molecule manipulation and measurements.
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Chip-Scale Atomic Clock
The main thrust of the CSAC project is to develop a Cs vapor cell
with submillimeter dimensions and to study the effect of the vapor
cell wall coatings and buffer gases on the intrinsic line width
of the Cs atomic transitions. The challenges for developing a microfabricated
atomic-clock vapor cell are threefold. First, the process must be
performed at the wafer level in order to take advantage of batch
fabrication of the cells. Second, the process must provide a means
for evacuating and subsequently backfilling the cell with Cs or
Rb without the need for microvalve technology or glass tubing connections
to the cell. Third, the process must allow for the introduction
of cell coatings or buffer gases to minImize size-effect spectral
broadening. We are currently investigating several approaches to
cell microfabrication based on wafer bonding and bulk and surface
micromachining techniques of Si. In addition, we will be investigating
schemes that rely on direct magnetic coupling between a mechanical
micro-oscillator and the Cs vapor, thus eliminating the need for
external feedback control.
Deliverables
- Design and fabricate submillimeter Cs/Rb gas cells using MEMS.
Develop methods for cell filling and sealing. (FY 2003)
- Develop wall coating for Cs/Rb cells. Optimize Cs/Rb gas cell
process for batch fabrication. (FY 2004)
- Integrate cells with clock components. Design prototype chip-scale
clock. Transfer the technology. (FY 2005)
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