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Research projects and
goals
Popular articles:
Overview of current
reseach:
Our
group
focuses on development and application of nanoscale magnetic
resonance imaging and spectroscopy. We are currently working on two
major research topics: Ultrasensitive force microscopy and nanoscale
magnetic imaging with single spins in diamond (see Techniques).
Our goal is to use
these
techniques for three-dimensional microscopy of biological
macromolecules and for chemical identification of materials with
nanometer resolution. We are also interested in the underlying
fundamental physics that makes these experiments possible.
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Diamond
crystals host
a number
of fluorescent defects. One
of these defects, the so-called nitrogen-vacancy (NV) color center, has
a
single electronic spin associated with it. This spin
can be controlled
individually based on optically detected magnetic resonance, can be
implemented
in nanodiamonds less than ten nanometers in size, and can thus be used
as
sensitive magnetic detector with nanometer spatial
resolution. This
"scanning diamond magnetometry"
was proposed
only very recently and is a genuine idea from our lab. See highlight
in
Nature Nanotechnology, June 2008 (link,
pdf).
In
our lab, we intend to
integrate high-quality NV centers
into scanning probes, so that we can apply them for directly mapping
electron
and nuclear spins on surfaces with nanometer resolution. Combination
with
magnetic resonance spectroscopy may then permit full chemical analysis
of materials
and study of surface dynamics.
On
this
chart
you see how the sensitivity of diamond sensors compares to other
nanoscale
magnetic sensors.
- Papers: C.
L. Degen, "Scanning magnetic field microscope with a diamond
single-spin sensor", Appl. Phys. Lett. 92, 243111 (2008). (link)
See also: J. R. Maze et al., Nature 455, 644 (2008) (link)
and G.
Balasubramanian et al., Nature 455, 648 (2008) (link).
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One
of our main goals is the
application of nanoscale spin
detection to the 3D imaging of important biological structures by MRI.
The main
obstacles to these experiments are sensitivity and spatial resolution.
Nanomechanical force sensors have, in the latest demonstration
experiments,
pushed the resolution of MRI to about 5 nm and enabled
three-dimensional
imaging of individual virus particles (a roughly 1000x improvement
compared to
conventional MRI techniques).
Our
objective is to make these methods
more widely
applicable and to apply them to 1-100 nm-sized biological objects. Many
of
these objects are of extraordinary relevance to biology, including, for
example, single virus particles, functional cellular units (like the
ribosome),
or Amyloid fibrils (implicated in Alzheimer’s disease). Our
aim
is to use Nano-MRI
for resolving their superstructure and eventually locating specific
functional
units using isotopic labeling techniques. Another strategy is the
combination
with atomistic data from X-ray analysis (that is generally incomplete
for large
molecules), with the aim of reconstructing full atomic structures.
- Papers: C.
L. Degen, M. Poggio, H. J. Mamin, C. T. Rettner, and D. Rugar,
"Nanoscale magnetic resonance imaging", PNAS 106, 1313 (2009). (link)
- See also: The
New York Times, January 13, 2008, on
page D3 (link
to the online version), and the News & Views article by Chris
Hammel: P. C. Hammel,
Nature 458, 844 (2009). (link)
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Sensitive
detection of magnetic
forces requires mechanical
structures that can measure very small forces. Some of the best
sensitivities
are achieved with micromechanical cantilevers, which reach detection
limits in
the range of Attonewtons (1e-18 N). Making even more sensitive
mechanical
structures is important not only for nanoscale spin detection, but also
for
mass sensing or testing of fundamental laws in, e.g., gravity.
Our
lab explores limitations to
these detectors. This
includes studies of the various dissipation mechanisms. We are also
interested
in resonators made from new materials. These might not only offer
better force
sensitivity, but by studying their behavior we also learn more about
the
material’s fundamental properties.
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Local
chemical
characterization of nanostructured surfaces,
especially when working
with organic
materials like self-assembled monolayers or thin polymer films, is
currently
very hard or not possible. Due to the chemical specificity of magnetic
resonance, it may be possible to apply spectroscopy techniques (like
NMR) for
exactly that purpose. Our lab’s objective is to adopt such
techniques so as to
simultaneously image a surface's chemical composition (using
spectroscopy), spin
density
(using Nano-MRI) and topography (using the sensor in force microscopy
mode) with nanometer resolution. This application is also very
interesting
for semiconductor devices as well as for a variety of nanostructured
surfaces
in material and energy science, like catalysts.
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The
physics of microscopic spin
ensembles can be distinctly
different from that of macroscopic ensembles. For example, in volumes
of
nuclear spins smaller than about < (100 nm)3, random spin flips
generate a
fluctuating polarization that exceeds the typical thermal (or
Boltzmann)
polarization. These spin fluctuations are a major source of dephasing
in
solid-state quantum systems, and their control is an important
prerequisite for
nanometer-scale magnetic resonance imaging (MRI) and spectroscopy. In
our lab
we focus on the fundamental physics that goes into these experiments on
small
numbers of spins. We also try to understand
“back-action”
effects from the
detector on dynamics of spins as they become strongly coupled to, for
example,
a nanomechanical resonator.
- Papers:
C. L. Degen, M. Poggio, H. J. Mamin, and D.
Rugar, Nuclear
spin relaxation
induced by a mechanical
resonator", Phys.
Rev. Lett. 100, 137601 (2008). (link)
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©
2009 Massachusetts Institute of Technology
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