Northwestern University
Internal competition for limited submission to NSF Major Research Instrumentation Program (MRI-R2)
ID: Nanoscale Spatial and Time Resolved Microwave Characterization at
Variable Temperatures and Magnetic Fields
Venkat Chandrasekhar, Physics and Astronomy, PI
Dmitriy Dikin, Mechanical Engineering, co-PI
Matthew Grayson, EECS, co-PI
Chang Liu, Mechanical Engineering, co-PI
Bruce Wessels, Materials Science and Engineering, co-PI
John Ketterson, Physics and Astronomy, co-PI
Radio (RF) and microwave (MW) frequency measurements have proved to be a powerful tool to
characterize state-of-the-art electronic devices and to probe the dynamic characteristics of a number of
fundamental physical phenomena. Many institutions have well-developed programs in RF and MW
measurement, but the equipment and expertise for such measurements does not exist at Northwestern,
apart from a few decades-old instruments in various individual laboratories. The goal of this proposal is
to develop a state-of-the-art cryogenic RF and MW measurement facility that will enable researchers to
push the frontier of measurement techniques. While RF and MW instruments are commercially available,
integration of this equipment with the cryogenic low temperature instrumentation is not trivial, and forms
the bulk of the development work proposed here. The facility we will develop will be located in Tech
FG19, a space that was designed during Tech reconstruction almost 15 years ago as a low vibration and
low noise laboratory, and the project will involve the modification of two existing low temperature
cryostats, both equipped with superconducting magnets. Development of the instrument is expected to
take three years, and will involve two graduate students in addition to the senior personnel. Availability
of this facility will also provide training to graduate and undergraduate students in an area of expertise
that is currently not available at Northwestern.
Research
In addition to the projects listed below, the instrument is expected to benefit research programs in a
number of departments across Northwestern, and will also involve collaborations with other institutions
in the US and abroad. It will immediately impact ongoing research programs, and make possible new
projects that explicitly require RF and MW measurement capabilities. Apart from the faculty on the
proposal, others who have expressed great interest in this system and who may contribute to its
development and future use include Mark Hersam, Vinayak Dravid, Scott Barnett (MSE), Horacio
Espinosa and Cheng Sun (Mech. Engineering), Mercouri Kanatzidis, Tobin Marks, Chad Mirkin, Teri
Odom, Michael Wasielewski and Emily Weiss (Chemistry).
(a) RF and MW scanning probe microscopy (Chandrasekhar, Liu, Dikin)
Scanning probe microscopy in its various manifestations is now routinely used as a characterization
tool for nanometer scale samples, and there are a number of scanning probe microscopes available for use
at Northwestern. However, scanning probe microscopy in extreme environments such as at low
temperatures and high magnetic fields is still a challenge. Furthermore, scanning probe microscopes that
probe the RF and MW properties of samples with nanometer scale resolution are still primarily in the
development stage. In collaboration with Pavel Kabos at NIST Boulder, we propose to develop a low
temperature RF and MW scanning probe microscope to investigate the dynamical properties of samples
on the nanometer scale, building on the low temperature multimode scanning probe microscope already
developed in Chandrasekhar’s group. This effort will be enhanced by the capability in Liu’s group of
making custom scanning probe cantilevers.
(b) Nanomagnetics (Ketterson, Chandrasekhar) Nanosize magnets are essential constituents of spintronic
devices and promise to be used in future magnetic storage elements. While the static magnetic properties
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Northwestern University
Internal competition for limited submission to NSF Major Research Instrumentation Program (MRI-R2)
of submicron size ferromagnets have been studied extensively, the high-frequency dynamical properties
still remain a subject of intensive investigation. Apart from the potential commercial interest in making
high-speed magnetic devices, the fundamental physics of how the size and shape of a magnetic particle
affects its dynamic magnetic properties is also of interest. With this instrument, we will be able to probe
the spin-wave properties of magnetic nanoparticles using RF and MW electrical transport techniques, as
well as the spatial variation of the spin wave modes using the RF and MW scanning probe microscope
described above.
(c) Luttinger liquids in one-dimensional quantum wires (Grayson, Chandrasekhar) A versatile GHz
microwave experimental system could explore time-of-flight measurements along a Luttinger liquid to
calibrate the interaction constants of these and other one-dimensional systems. These Luttinger liquids
can be fabricated from cleaved-edge growth semiconductor heterostructures, as has been done in
Grayson’s group.
(d) Quantum mechanics on a chip (Chandrasekhar, Liu, Dikin) Precision RF and MW measurements of
mesoscopic devices are at the forefront of the exploration of fundamental quantum phenomena in solidstate systems. Examples include solid-state analogues of atomic systems, quantum computation and
quantum cryptography. Three problems are of immediate interest here. The first involves persistent
currents in normal metal rings. Many important questions, including verification of the expected sign of
the persistent current, the temperature dependence of the amplitude, the effect of electron-electron
interactions, can be addressed by precise measurements at microwave frequencies. Since the signals are
small, we will be collaborating with Joe Aumentado of NIST, Boulder, to use NIST’s ultra-low noise
microwave SQUID amplifiers at a frequency of 6 GHz to perform these measurements. The second
problem is associated with exploring the quantum properties of mechanical oscillators. Using the NEMS
techniques being developed in Liu’s group, one can fabricate mechanical oscillators with resonant
frequencies in the GHz regime. At low enough temperatures, we expect to reach the regime where only a
few quantum modes are excited. The third problem involves the investigation of noise in mesoscopic
systems. Measurement of electrical noise in nanometer scale devices provides information not available
by conventional dc electrical transport measurements, such as quantum correlations between charge
carriers. However, measuring noise using low frequency techniques is famously difficult. Highfrequency techniques provide improved signal-to-noise due to the larger measurement bandwidth. We
will measure noise in superconducting systems, as well as new materials systems such as carbon
nanotubes and graphene.
(e) Non-linear optical waveguide devices for nanophotonics (Wessels) We are interested in the
development of non-linear optical waveguide devices. Of particular interest are ultra-wideband thin film
electro-optic modulators. This work builds on our recent demonstration of thin film ferroelectrics with
electro-optic coefficients more than an order of magnitude greater than lithium niobate, the current
standard. Thin film strip-loaded waveguide devices will be fabricated for ultra-wideband frequency
operation. Factors limiting bandwidth will be determined through modeling and testing using the
instrumentation requested in this proposal.
(f) Nanowires (Dikin, Espinosa, Lauhon) Carbon nanotubes and Si-based nanowires are considered as
possible options for the next generation of interconnects and high-integration-density structures.
Although extensive research is progress on the structural, mechanical, and optical properties and
applications of these materials, very little is known about their behavior in another important frequency
range, from a few megahertz to tens of gigahertz. We are developing non-invasive measurement
technology that allows separating the behavior of the nanostructures of interest from that of their
environment.
(g) Nanocomposites and Metamaterials (Dikin, Sun) In recent years there has been increased interest in
the development of nanocomposite materials and artificial structures with properties that differ
significantly from the properties of standard materials. Among those are the band-gap materials for
different frequency ranges and the so-called "negative index" materials that support the propagation of
electromagnetic waves with opposite phase and group velocities. Due to their special properties many
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Northwestern University
Internal competition for limited submission to NSF Major Research Instrumentation Program (MRI-R2)
challenges in the tailored material design will have to be mastered. With a new instrumentation these
challenges will be possible to address.
Description of the equipment/facility
The proposed system will consist of: (1) high-frequency equipment; (2) custom developed scanning
probe microscopy platform (hardware, electronics, and software); (3) custom developed sample pucks; (4)
variable temperature cryostats equipped with superconducting magnets.
Major concept of the equipment/facility: The facility will provide a unique combination of
experimental conditions and modularity for multiple projects. Our goal is to achieve flexibility without
sacrificing the performance of each module. Following this approach, different modules may be added at
any time depending on the availability of funding and users’ interest.
(1) High-frequency equipment (1MHz-50GHz range): a. Network Analyzer. The availability of a
network analyzer is critical for the characterization of microwave circuits in any experiment involving
high frequencies. b. A Signal Generator is critical for frequency modulation, pulse generation and other
signal modulation techniques. c. Spectrum Analyzer. For detailed analysis of signals, a spectrum
analyzer is extremely useful, and provides capabilities not available with only a network analyzer. d.
High Frequency Oscilloscope. For some of the experiments the ability to visualize the real-time behavior
of the signals coming from the devices is critical. A multi-channel oscilloscope would also enable us to
make direct measurements of noise (both autocorrelation and cross-correlation).
(2) Scanning probe microscope (hardware, electronics, and software): Hardware: We have already
built and tested a low temperature scanning probe microscope (SPM) based on compact linear piezo
stages made by Attocube and force sensors based on a tuning fork transducer. We will design (in
collaboration with C. Liu/ME and P. Kabos/NIST) special probes for spatial and spectral bandwidth MW
near-field measurements and imaging. Electronics – We have most of the controllers available, some
will be custom made. Software – We have a combination of commercial open platform and custom built
software. Additional custom software components will also be developed.
(3) Custom sample pucks with multiple electrical leads for sample connections, with integrated heater
and thermometer, and passive thermal expansion compensation layout will be designed, and made.
(4) Variable temperature cryostat: Two existing cryostats will be modified for use in this facility. The
first is a top-loading Oxford TLM dilution refrigerator equipped with a 12 T magnet currently in
Ketterson’s group. This refrigerator is capable of going down to 50 mK, and is already partially wired for
high-frequency measurements. The second is a Janis helium 3 system that can be inserted into two
dewars, one equipped with a 3T/1T dual axis superconducting magnet, and the second with a 6 T axial
solenoid. Both cryostats will be moved into FG19.
Project and management plans
We are going to build an innovative, complex state-of-the-art instrument. The focus of this system is on
intensive, long-term fundamental research projects that require continuous use of expensive equipment
and also development of new educational programs for students with a major in physics, material science,
or engineering.
Prof. Dmitriy Dikin (Research Assistant Professor with a joint appointment in the Physics and ME
Departments) will be responsible for supervising the construction of the instrument, and also supervising
the two graduate students whose PhD projects will be related to the development of this system. Dikin
will also be responsible for the day-to-day operation of the instrument.
Dikin has a Master’s degree in cryogenic engineering and electronics, and a PhD in the physics of
superconductivity. He has 20+ years experience in low temperature and high vacuum technologies, 6+
years of experience in nano manipulation, piezo devices, and all types of microscopy. Dikin designed and
constructed a number of devices for experimental low temperature physics, nano mechanics, and high
frequency measurements (see his CV).
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Northwestern University
Internal competition for limited submission to NSF Major Research Instrumentation Program (MRI-R2)
Development plan
The first year of the project will be devoted to careful analysis of the major system components, their
selection and acquisition. At the same time the graduate students and undergraduate students involved
will obtain a background education in cryogenic technologies, scanning probe microscopy, RF and
microwave measurements, LabView programming, digital signal processing, etc. We will also complete
the installation of the two cryostats in FG19 in the first year.
The second year of the project will be mostly devoted to engineering, manufacturing and testing of the
variable temperature scanning probe microscope, microwave setup and special evanescent microwave
probes. A second major task for this year will be the installation of major components and their testing.
In the second year, we also propose to commence electrical transport and noise experiments that do not
require scanning probe techniques.
The third year of the project will be primarily devoted to developing, debugging and testing of the
entire system. At this time we expect to introduce this system to other researchers and students across NU
with the goal to invite a few more active contributors to the development of this complex system tailored
to their own research goals and technical requirements. We also expect to gain the first physical results
for NSF and other agencies’ supported research projects.
Maintenance, operation, and technical support of the facility
We believe that this complex and modular system can serve as a platform for many years of advanced
research in physics and material science at the nanoscale, as well as becoming an important part of a
broad range of educational programs for Weinberg and McCormick. Once the instrumentation is in place,
the major cost of operation is in cryogens (nitrogen and helium), which will be provided by the individual
grants of the investigators. The facility will be supervised by Prof. Dikin. As the technical requirements
of the experiments that will be carried out in this facility are expected to differ from experiment to
experiment, technical assistance and training for new students will be provided by Prof. Dikin and other
regular users of the instrument on a case-by-case basis.
Summary budget
This development proposal requires a high level of technical expertise. An estimated total budget of
$991K for 3 years will be requested to support two graduate students ($40K per student per year or
$240K total), one research professor (D. Dikin, 6 months per year, $180K total), for purchasing major
components (listed below), for materials, fabrication, and testing ($60K total).
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Tentative list of major components of the system, and salaries
High-frequency equipment
Agilent Network Analyzer
Calibration module
Signal Generator
Spectrum Analyzer
Oscilloscope
Low temperature microwave amplifiers
Scanning probe microscope (components)
Custom sample pucks (components)
Variable temperature cryostat
Superconducting Magnets
Materials, fabrication and testing expenses including cryogenic liquids
Salaries
Total:
Estimated cost, $
490,500
85,000
13,500
161,000
92,000
124,000
15,000
15,000
5,000
0
0
60,000
420,000
990,500
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