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Project Description - 1
3. Project Description 3.a. Instrument Location and Type Instrument Location: Millennium Science Complex, Pennsylvania State University, University Park
Instrument Code: MRI-21 Microscopes
3.b. Research Activities: The proposed instrument, complementing the world-class instrumentation already available in Penn
State’s Materials Characterization Lab, will form a unique platform for the nanoscale characterization of
structured materials and devices. It will combine a flexible scanning probe microscope (SPM) head,
capable of both scanning tunneling microscopy (STM) and atomic force-based measurements, with a
sample holder enabling in-situ, simultaneous transport measurement and sample control (e.g., through
gating or through strain applied using piezoelectric substrates for thin film samples). Its open design will
allow for multiple paths of optical access to the tip-sample junction, enabling both optical excitation
spectroscopies as well as optically guided, precision (micron length scale) tip positioning. Meanwhile,
construction on a cryocooler based dilution refrigerator will allow temperature dependent measurements
across a wide temperature range (50 mK to room temperature).
This unique combination of features will make the proposed instrument an invaluable resource for the US
materials research community, both as a tool and as a template for future instrument development. At
Penn State it will greatly expand many projects funded by NSF under individual and multi-investigator
grants, including MRSEC, CAREER, Materials World Network and Industry/University Cooperative
Research Center programs. In Table 1 we list senior personnel, internal and external to Penn State, who
will be significantly involved in the development of the instrument and make substantial use of it once
constructed.
Although the instrument we propose will enable a large amount of diverse work in science and
engineering, we focus here on research that will take full advantage of the many capabilities of the
instrument, nanoscale investigations of 1) sheets and nanoribbons, 2) nanowires and 3) interfaces.
NAME RANK DEPT. PD G U URM W
Moses Chan (Co-PI) Prof. Phys 2 2 2 0 2
Suman Datta Prof. EE 1 14 1 0 2
*Renee Diehl Prof. Phys 0 4 4 0 2
Venkatraman Gopalan Prof. MatSci 2 6 0 0 4
Roman Engel-Herbert (Co-PI) Asst. Prof. MatSci 0 1 2 0 0
Eric Hudson (PI) Assoc. Prof. Phys 0 2 2 0 2
Ying Liu Prof. Phys 0 6 1 0 2
*Qi Li Prof. Phys 0 4 1 0 0
Thomas Mallouk (Co-PI) Prof. Chem 1 3 1 0 3
*Joan Redwing (Co-PI) Prof. MatSci 3 4 0 1 1
Nitin Samarth Prof. Phys 2 8 2 0 3
Oliver Schaff CTO SPECS 0 2 4 0 0
Peter Schiffer Prof. Phys 1 4 1 0 2
Vladimir Shvarts Sr. Scientist Janis 0 0 0 0 0
Humberto Terrones Visiting Prof. Phys 0 0 0 0 0
Mauricio Terrones Prof Phys/MS 5 8 3 3 5
*Jun Zhu Asst. Prof. Phys 1 3 1 0 1
Table 1 Senior personnel (*indicates women) with rank, department and current numbers of postdocs (PD),
graduate students (G), undergraduates (UG), underrepresented minorities (UM) and women (W)
Project Description - 2
3.c. Description of the Research Instrumentation and Needs
Brief Instrumentation Description:
The scientific goals described in section 3.b require the development of a versatile instrument. In this
section we will briefly outline the capabilities of the proposed instrument. In the next we will describe
various aspects of the instrument in more detail, connecting them to specific scientific needs.
At the heart of the instrument lies a scanning probe microscope (SPM) based on the SPECS Tyto head61
(Schaff), capable of both atomic force-based and scanning tunneling microscopy measurements, using
position registered, in-situ sensor exchange. Multiple sample contacts enable simultaneous sample
characterization, for example using electrical and thermal transport measurements, as well as sample
modification, for example through gating or through strain applied using piezoelectric substrates for thin
film samples. Head and chamber design allow for multiple paths of optical access to the tip-sample
junction, enabling both optically guided, precision tip positioning, and optical excitation spectroscopies.
Precision temperature control over a wide temperature range (50 mK to room temperature) without the
common problems of short hold times and project-dominant liquid helium expenses is provided by a
cryogen free dilution refrigerator, based on designs by Janis Research (Shvarts) and one of the PIs
(Chan). In addition, a superconducting magnet system (Janis) will provide fields to 10 T.
Integrated into the instrument are sample preparation and characterization tools, including several crystal
cleavers, argon ion sputtering, e-beam evaporation, LEED and Auger. These tools enable the study of a
wide variety of materials and devices, guaranteeing that whether produced in neighboring labs or around
the world we will be able to prepare and characterize surfaces suitable for SPM study.
Science-Enabling Technology
A core research strength of the chemistry, condensed matter physics, electrical engineering and materials
science groups at Penn State, as represented in our team, lies in the fabrication and characterization of
nanostructured materials and devices. All aspects of the proposed instrument are designed to interface
with and expand upon these capabilities by providing a unique combination of measurement technologies.
Scanning Probe Microscope (SPM) SPECS’s new Tyto scan head (Fig. 1)61 provides the base of these new
technologies. Its innovative sensor mount enables the use of any kind of
electrical sensor, such as tunneling tips for scanning tunneling microscopy
(STM), and tuning fork or piezoelectric/piezoresistive type sensors for force
based microscopies. Thus, while STM has unparalleled sub-pm resolution50 and
the capability of mapping materials’ local electronic density of states, for
systems like nanowires, nanoribbons or nanodevices situated on insulating
substrates, the ability to first locate the conducting structure using an atomic
force (AFM) is crucial (STM tips typically crash on insulating surfaces).
Furthermore, the wide array of force based scanning probe microscopies will
enable nanoscale characterization of other material properties, including
topographic (AFM), magnetic (MFM), chemical (CFM), ferroelectric
(piezoresponse PFM), work function (Kelvin probe KPFM), and thermal
(SThM), to mention a few.
Kinematic sample and sensor mounts (Fig. 2), combined with accurate position
sensors (5 nm resolution), allow different sensors to access identical locations on
Fig. 1 Tyto head, with
optically open design.
Project Description - 3
a sample and to reliably return to those locations, further
reducing the barrier to sensor swapping for integrated
(multi-technique) studies. Sample swapping is also
possible, for example for insertion of a sensor calibration
target in the middle of an experiment, useful for verifying
that phase transition driven changes are due to real physics
and not sensor (tip) changes.
We will guide the Tyto’s coarse positioning capabilities (a
5 mm XY range, 10 nm resolution) optically, using a long
distance microscope, such as the Questar QM200 (1.25 m
resolution at working distance62), attached to a video CCD,
to move sample features within the sensor fine scan range
(22 m at room temperature, 4m at low temperatures).
This optically guided sensor positioning is crucial for quickly finding features across the range of systems
described in our planned research activities, from nanoribbons to nano-devices, and in particular for
reliably landing the tip on the edge of thin films for cross-sectional STM (XSTM) studies of interfaces. It
will replace the time consuming “step and scan” process currently used by most SPM groups to find small
samples (for example, groups studying graphene with more traditional STMs can take days to find the
sample) and thus improve our operating efficiency.
Multiple paths of optical access to the sensor-sample junction also allow the
study of, for example, opto-electronic coupling at the nanoscale in systems such
as inhomogeneous colossal magnetoresistive materials (Li63), semiconductor
microdots (Samarth Fig. 3a64) and in nanowire arrays for solar energy
conversion (Mallouk, Redwing Fig. 3b65,66). Finally, these paths allow easy
future upgrades by the addition of evaporators in order to dose the sample in situ.
Although we do not have immediate plans to do this, ports will be positioned to
take advantage of the optically open design of the Tyto head (Fig. 1).
Multiple Sample Contacts We will further enhance the capabilities of the SPM by wiring multiple
connections to the sample, as opposed to the single sample connection typical of
STM measurements. Many of our proposed research activities will take
advantage of this novel capability. Very generally, for the study of phase
transitions, whether driven by temperature, magnetic field, strain, or some other
external control parameter, having simultaneous “bulk” transport measurements
will allow us better tuning through the transition, and thus give us a better understanding of any phase
transition associated changes we observe in local probe measurements.
In addition, multiple sample contacts will enhance our study of nanowire
(Chan, Mallouk, Samarth) or, more generally, nano-device (Datta,
Redwing, Liu, Zhu) properties, as the capability of making simultaneous
transport measurements will enable probes of local voltage profiles (using
Kelvin probe force microscopy67) and current profiles (using scanning gate
microscopy68). The sensor can also serve as a second, movable, nanowire
contact, either in tunneling (STM) or contact (conducting tip AFM) mode, allowing transport
measurements on localized, precisely controllable segments of the device.
Fig. 2 Tyto Kinematic Mount. The empty
mount (a) closed and (b) open and ready to
accept a sensor. (c) Sensor packages are held
firmly by three claws.
Fig. 3 Optical Materials
(a) GaAs/GaAlAs dots;
(b) p-n silicon nanowire
Fig. 4 Mesoscopic Al (Liu)
b
a
a
b
c
Project Description - 4
Beyond enhancing measurement capabilities through simultaneous transport measurements, the presence
of additional contacts at the sample also allows sample modification, for example through control of gate
voltages or local heating elements. Our most immediate use of this capability will be in the study of strain
induced multiferroic properties34 in titanate thin films grown on piezoelectric substrates (Gopalan,
Hudson, Schiffer), allowing us to smoothly sweep through strain driven phase transitions. More broadly
speaking, multiple sample contacts fulfill our desire, as experimentalists, to have more knobs to turn, the
effects of which we can change from sample to sample depending on our wiring of the sample holder. We
are excited by the myriad possibilities.
Environmental Controls The nature of SPM demands clean surfaces, thus the instrument will be operated in ultrahigh vacuum,
with a base pressure <10-10 mbar in the prep chamber and <10-11 mbar at room temperature in the
measurement chamber (immeasurably better when cold). All systems, including the dilution refrigerator,
are bakeable, and pressure will be maintained by several ion pumps, which are particularly useful for
SPM applications due to their mechanical and acoustic silence.
One major improvement of our instrument over all other SPMs currently in use at Penn State is the
extended temperature range afforded by a dilution refrigerator (DR) – from 50 mK to room temperature.
Only a handful of SPMs in the world work at dilution refrigerator temperatures,69–76 (mostly STMs) yet
lower temperatures both improve STM spectral energy resolution (~4kBT) and make available a wide
variety of interesting phenomena. Liu, for example, in an NSF-MWN funded project, is studying the
effects of sample geometry on nanoscale mesoscopic superconductors77 (Fig. 4), and in particular in
unconventional, p-wave, superconductors78. Combining the ultra-low temperature and atomic scale
density of state mapping capabilities of this instrument would greatly contribute to current transport
measurements.
Beyond simply adding a DR, however, we will use a “dry” (cryocooler powered) DR. The recently
skyrocketing cost of the liquid helium required for low temperature refrigeration has generated a
tremendous amount of interest in the development of cryocoolers. Although tremendous gains have been
made in cryocooler technology, the low vibration performance necessary for SPMs is still a work in
progress (we discuss our approach to this problem in our management plan, section 3.e). In addition to
significant operational savings (in excess of $30K/year compared to typical DR setups), the use of a
cryocooler also eliminates the need for liquid Helium transfers, which in most low temperature
instruments interrupt operations on the one day to one week time scale. This will allow data acquisition
timing to be driven by scientific need rather than cryogenic schedules, and enables more complex,
lengthier measurements.
In addition to low temperatures, high magnetic fields allow us to explore other regions of phase space.
For studying magnetic properties the dimensionless quantity µBB/kBT (µB is the Bohr magneton and kB
the Boltzmann constant) is a good figure of merit for an STM’s spectral capabilities, as the Zeeman
energy, µBB, sets the energy scale to be resolved at the temperature T. For our proposed system, with 10
T at 50 mK, that quantity is 130. To our knowledge, this is second to only one system currently operating
in the world, the 10 mK, 15 T STM at NIST76 (co-designed by Shvarts). At the same time, our proposed
system will have other advantages relative to that system, most notably sensor flexibility (for force
microscopy as well as STM), multiple sample contacts, and the use of dry refrigeration.
Project Description - 5
The use of a magnetic field is critical for several of our initially planned research activities. A key
question in Liu’s nanoscale mesoscopic superconductors77 is how the interplay of magnetic fields and
sample geometry control superfluid velocity.79 Magnetic fields will also prove useful for Engel-Herbert
and Hudson’s study of novel superconductivity at oxide interfaces. Vortices, the study of which this
instrument enables in both planar and cross-sectional geometries, are a powerful probe of a wide variety
of superconducting properties, particularly for unconventional superconductors.80 For example, by STM
mapping of vortex core states Hudson was able to directly image and accurately measure the
superconducting coherence length in the cuprate superconductor Bi2Sr2CaCuO8+x.81 The unique ability of
the proposed instrument to bring both STM and MFM to bear not only on the same sample but also at the
same location under the same widely tunable conditions could revolutionize our understanding of the
interplay of electronic and magnetic vortex properties in exotic superconductors. Such understanding is
not only of scientific interest, but also of huge technological import, as high current use of
superconducting wires demands vortex control (through pinning).
Sample Preparation and Characterization In order to open this instrument to as broad a range of samples as possible, robust, integrated sample
preparation and characterization facilities are essential. All scanning probe microscopies rely on a clean
sample surface; we will make available a variety of methods for obtaining such surfaces. For the study of
bulk samples and thin films, cleavage, revealing a fresh layer immediately prior to instrument insertion, is
often a useful technique. We will construct both post (in which a post glued to the sample is knocked off,
peeling off several layers of the sample with it) and knife edge cleavers, and will temperature control
them in order to enable the study of materials where cleavage temperature can have a significant impact
on surface quality, such as the cuprate superconductor YBCO (Hudson82) and quasicrystals (Diehl83).
For nanostructured materials and devices prepared elsewhere, less destructive surface preparation
techniques are required. One method is to, at the completion of sample growth or device fabrication,
cover the surface with a capping layer which will later be removed in our prep chamber. Many capping
materials may be burned off, so we will construct both a substrate heater (where heat comes to the sample
surface through the sample) and an e-beam heater, where the capping layer can be directly heated. For
other capping systems, and for general cleaning of other systems, repeated cycles of Ar-ion sputtering
followed by annealing will be necessary. Further sample preparation tools will include a set of e-beam
evaporators, for example for surface impurity studies such as those proposed by Terrones and Terrones.
In addition to preparing sample surfaces, ensuring that they are properly prepared is also crucial. Among
other techniques we will use Auger electron spectroscopy (AES) to verify surface chemical composition
and low energy electron diffraction (LEED) to verify surface structure.
Project Description - 6
Impact on Research and Training Infrastructure
Attracting Students and Researchers:
As described in section 3.b, the development of the proposed instrument will greatly impact many single
and multi-investigator research projects, leading to increased interdisciplinary collaboration, and hence to
an exciting scientific environment with which to attract new students and researchers. We consider the
training of young scientists to be one of the most important goals of the research enterprise. All senior
members of the team have strong records in mentoring and nurturing post-docs and graduate students in
furthering their scientific careers. They are also active in involving undergraduate students in their
research activities (Table 1). The co-PIs each regularly host and mentor one or two undergraduate
students in their laboratories (the five of us have worked with over 30 undergraduates over the past five
years). During the summer this research is often funded by Penn State’s Research Experience for
Undergraduates and Teachers Program (REU-RET) in Condensed Matter Physics and Interdisciplinary
Research, under PIs Chan (1990-1992, 2004-2011) and Li (1998-2004) We have published multiple
papers with undergraduates as co-authors,84–105 helping propel the great majority of them into graduate
programs. In addition benefitting our research and the undergraduates themselves, their involvement in
the lab also provides important mentoring opportunities for graduate students and post-docs.
The fabrication we propose provides the opportunity for a post-doc and students to receive rigorous
experimental training and the opportunity to work with faculty members of different and complementary
expertise in SPM and low temperature physics in building and testing the instrument. Both they and those
involved in its subsequent use will become members of the Materials Research Institute (MRI), which
coordinates and promotes interdisciplinary materials research at Penn State with the goal of enabling
faculty, researchers, students, and industry partners to link disciplinary expertise with shared facilities and
trained staff to advance multidisciplinary research at the cutting edge of science and technology.
Research Training: SPM Tutorials
The impact of this instrument will reach beyong those directly using it. Exposure to a variety of
fabrication and characterization tools is a crucial part of materials research education. Our Materials
Science and Engineering Department and Materials Characterization Lab (MCL) offer many courses with
this focus (including some taught by Redwing). The breadth of surface preparation and characterization,
scanning probe and transport techniques integrated in the proposed instrumentation make it an excellent
educational resource. We will develop a new course, describing the techniques united in this instrument
and providing raw data from our instrument-wide test runs along with a framework for analyzing and
understanding the interconnected nature of that data. This will not only help students understand a
specific set of materials characterization technques, but also engender in them an appreciation of the
importance of taking an integrated approach when trying to understand new material systems.
Broader Impact: Women and Underrepresented Minorities
We firmly believe in the importance of increasing the diversity of the STEM community, and have
worked to attract and involve a diverse student body in our individual research groups. We have been
reasonably successful at improving gender balance (Table 1), a focus of Diehl, who was awarded the
2006 Outstanding Service Award from the Women in the Sciences and Engineering Institute for her work.
She has been an active advisor for the WISER program (Women in Science and Engineering Research),
aimed at attracting and retaining women in their first year of undergraduate studies – mentoring five
women through this program in her lab in the past four years (and leading to three publications). We will
partner with WISER to ensure that our female undergraduates are encouraged to participate in the unique
research activities enabled by the development of the proposed instrument.
Project Description - 7
Individually, we have had less recent success recruiting underrepresented minority (URM) students to our
groups. We will work collectively to improve this. Penn State has a number of programs designed to
increase URM involvement in research, in which we will fully participate. For example, the Summer
Research Opportunities Program (SROP) is an eight week program designed to interest talented
undergraduate students from underrepresented groups in academic careers and to enhance their
preparation for graduate study through intensive research experiences with faculty mentors. REU
programs run by our MRSEC, our node of the NNIN, and the Departments of Physics and Materials
Science and Engineering each have strong records of attracting undergraduate students from across the
United States, with emphasis on recruiting underrepresented groups in engineering and science
disciplines. We also have a very strong Upward Bound Math and Science (UBMS) Center, which works
with URM students from some of the poorest performing high schools around Pennsylvania and drives
impressive results, with 100% of their students being accepted into postsecondary education, and 76% of
their students going on to graduate with a math or science degree. As part of their UBMS experience,
about 30 students a year participate in a summer research program on our campus. The highly
collaborative and interdisciplinary nature of the research to be enabled by our proposed instrument will
create an excellent summer research environment for students from all of these programs.
Beyond providing an exciting and educational research environment for their students, we will also work
with these programs and our departments to identify areas for improvement, in particular through
interdisciplinary program collaboration. Hudson has just arrived from MIT where he was awarded the
inaugural "MIT Excellence Award for Fostering Diversity and Inclusion," based in part on his work
redesigning the MIT Summer Research Program, which more than doubled URM participation in the
subsequent three years, and his work both within the physics department (where he was the minority
advisor for 8 years) and institute wide to increase successful graduate school URM applications.
Broader Impact: Exciting the Next Generation of Science and Engineering Students
In addition to a strong record of educating and involving in research a diverse body of current
undergraduates, graduate students and post-docs, we also believe in the importance of developing the next
generation of STEM students. Chan and Mallouk played major roles in initiating a science museum
show program in 2000, as part of the inauguration of the Penn State Materials Research Science and
Engineering Center (MRSEC), of which they are Associate Directors. In this program, MRSEC partners
with the Franklin Institute of Philadelphia and develops hands-on, cart-based interactive demonstration
kits and modules on the science of materials targeted for middle school students. Ideas and designs of
modules have been developed through a series of workshops bringing together Penn State faculty and
graduate students and Franklin Institute staff members. These modules aim to connect the microscopic
structure of material with its macroscopic properties through hands-on illustrations and examples. Since
2001, four demonstration kits, “Materials Matter,” “Zoom in on Life,” “Small Wonders” and “Hidden
Power” have been duplicated and distributed to 22 science museums around the United States and
Canada. They have proven to be very popular with children. A conservative estimate puts the number of
children who have visited the shows to be close to a million. These shows are also presented to students
visiting from nearby schools and for the visitors of the Central Pennsylvania Festival of Arts in State
College. We will partner with the Penn State MRSEC and the Franklin Institute to develop a new
interactive kit “CryoCOOL” both discussing the idea of temperature (and low temperatures) and
illustrating the working principles of scanning probe microscopes and how they can characterize the
atomic structure of materials.
Project Description - 8
3.e. Management Plan
Materials Characterization Laboratory:
The proposed instrument will be housed in Penn State’s Millennium Science Complex (MSC) research
building, which has just come online this year. This 275,600 gross sq. ft. interdisciplinary building brings
together materials and life sciences research activities in the central campus and in close proximity to all
key academic departments. It will be situated in the Materials Characterization Suite, a collection of labs
housing instrumentation complementary to the one proposed here, including scanning and transmission
electron microscopes (SEMs and TEMs). For noise reduction, the suite is located underground, beneath,
but in close proximity to, growth facilities, including Engel-Herbert’s MBE system, and our class
100/1000 Nanofabrication Laboratory Cleanroom. A room within the suite has been specifically designed
to satisfy the stringent requirements of a scanning probe instrument such as the one proposed here.
Instrument space meets the most stringent class E vibration standard (floor velocity under 3 m/s) and is
acoustically and structurally isolated, using a double wall, isolated slab construction, from both a control
room, where operators will be located, and a service corridor, where acoustic sources such as pumps and
the cryocooler compressor will be placed.
Development Schedule:
Chan and Hudson will oversee development as co-Project Managers. Upon acknowledgment of the
success of this proposal, our first goal will be to hire a postdoctoral researcher with experience in low
temperature SPM. Ideally the candidate will have experience in design and construction, however because
of the limited number of home built systems around the world, a successful candidate may only have
extensive experience in SPM use. The purpose of hiring a post-doc is multi-fold. First of all, although our
team already shares the experience required to successfully bring the proposed instrument online, having
another team member who, along with Chan and Hudson, will be focused on the successful development
of the entire instrument and who, as opposed to we senior researchers, will have no responsibilities
outside of this instrument development, will help ensure smooth and rapid progress. This post-doc will
also be responsible for coordinating the efforts of any students who are involved, particularly during the
construction and testing phases. A second reason to involve a postdoctoral researcher in this instrument
development is to help in the education of the next generation of instrumentalists. Design of this
instrument will require and hence help the post-doc further develop a large range of skills, ranging from
generic scientific skills such as collaborative team management and student mentoring, to specific
techniques, such as ultra-low temperature, UHV and SPM techniques. A third reason to hire a post-doc is
to help ensure transference of knowledge gained during the development to the broader community.
Yr Exp. Activity Deliverables
0.5 $60K Design all systems; Order SPM & analysis systems Hired Postdoc
1 $790K Order cryostat; Begin component construction SPM, Analytic, Tables & Optics
1.5 $935K Assemble and test subsystems Cryostat (Dry DR)
2 $50K Test/improve vibration isolation, other systems Magnet, Isolation System
2.5 $35K Assemble and test complete instrument Instrument, Vibration Article
3 $35K Final commissioning Test results, Overview RSI
Table 2. Estimated construction schedule, including semi-annual expenditures, activities and deliverables
Project Description - 9
Although our goal would be to bring on this researcher as soon as possible, we expect that it may take up
to half a year to identify and hire a suitable candidate, perhaps not until near the completion of the design
phase, described below. Estimated cost: $50K per year for three years.
Design Phase We have assembled a team with expertise in all aspects of the proposed instrumentation. For the purpose
of development, we will subdivide the instrument into three key parts: 1) the cryogenic system and
magnet, 2) the SPM system, and 3) the preparation and characterization instrumentation. Design of the
cryogenic systems will be led by Chan, who has designed and constructed a half dozen dilution
refrigerators (DRs) over the past several decades, including most recently a cryogen-free DR.106 He will
work in close collaboration with Shvarts, who has a decade of experience as a senior R & D scientist at
Janis Research in the development of liquid cooled and cryogen-free DRs, including, recently, a special
model for the DR-based STM system at the National Institute for Standards and Technology (NIST)
which, in the world, is most similar in scope to our proposed design.76
The cryogenic system is the most central and perhaps complex piece of the entire instrument. The
technological demands of the system are not unusual for “dry” (cryocooler based) DRs – a base
temperature of 20 mK (to ensure 50 mK at the SPM head), and a cooling power of 200 W at 100 mK,
coupled with a 10 T magnet. Janis has delivered many systems with even more cooling power, higher
fields and lower base temperatures (we limited our demands in part to reduce the overall instrument cost).
However, much of the cryostat design is dictated by the requirements of the SPM system and in particular
by the need for both mechanical access to the SPM, for sensor and sample exchange, and for optical
access to the sensor-sample junction during operation. This will necessitate, for example, the use of a
split-coil magnet. Another crucial part of the cryostat design is vibration isolation. This isolation will take
place in multiple stages, from the room level – isolating the cryocooler compressor structurally and
acoustically in the service corridor – to the instrument level – isolating the cryocooler cold head from the
main chamber. The final stage of vibration isolation – between the cold stage and the SPM – will be
handled by the SPM team. Finally, because of the need for clean surfaces in the SPM, the entire system
will be ultra-high vacuum (UHV) compatible.
Chan, Hudson and Shvarts have years of experience in these design issues,76,106–109 and estimate that it
will take roughly six months to design the cryostat and that it will have a roughly one year lead time from
Janis, primarily because of the high field magnet. Given the planned flexibility of the design, with the
magnet relatively easily removable, we plan to receive the bulk of the cryostat six months earlier, so that
we may move to the construction and testing phases as soon as possible. Estimated cryostat cost,
including UHV chamber, dry DR, gas handling system, thermometry and temperature controllers,
feedthroughs and wiring (as specified by the SPM team) and magnet: $900K.
Design of the SPM system will be headed by Hudson. He has designed, constructed and used multiple
STM and AFM systems, including both a 240 mK system108 and one integrated with surface preparation
and analysis instruments as we propose to include here.109 He will work in close collaboration with Zhu,
who has designed and constructed two low temperature SPM systems (AFM110 and STM), and Schaff,
who as the CTO of SPECS has over a decade of experience in the design and construction of SPM
systems, and who was instrumental in the design of the Tyto head61 features crucial to our scientific
needs, such as optical access to the sensor-sample junction and easily exchangeable sample and sensors.
Here, the basic system including the head and control electronics (Nanonis111), is already commercially
available, and we will immediately place an order for this system (estimated cost $250K, lead time 6
months to one year).
Project Description - 10
Thus, design work by Hudson, Schaff and Zhu will, aside from making some head modifications, for
example to allow for multiple electrical contacts to the sample and sensor and to allow for better
temperature measurement and control, focus primarily on integrating the SPM into the cryostat. In
particular, we will develop an appropriate low temperature vibration isolation stage, to shield the SPM
head from any remnant vibrations in the cold head, while maintaining good thermal contact. This has
been a focus of Hudson’s previous instrument development,107–109 and was a central part of his design
enabling the maintenance of atomic registration during temperature variations,91 essential for the
measurement of thermal phase transitions.
Design of the ancillary surface preparation and analysis systems will be headed by Engel-Herbert, in
close collaboration with Mallouk and Redwing. As materials growth experts drawing from different
backgrounds and techniques (respectively MBE, chemical and, primarily, CVD), this team brings together
decades of experience in the use of surface analytic techniques for the characterization of a broad range of
material systems. This aspect of the development is the most collaborative of the three, as its purpose is to
ensure that the instrument will be able to effectively interface with as many different types of sample
systems as possible. So while Hudson and Zhu, for example, bring experience of preparing layered
materials for SPM by cleavage, Engel-Herbert, Mallouk and Redwing will explore a broader variety of
techniques for preparing samples produced elsewhere for study in this instrument, including the use of
capping layers which may be removed by flash heating, and the elimination of contaminants by repeated
sputtering and annealing. After discussion with all team members to determine the needs of the
preparation and analysis chamber, they will design and order it. Estimated cost: $400K, with a design plus
lead time of approximately one year.
In addition to the above systems, a support structure also needs to be designed and purchased. An
additional benefit of using a dry DR is that the weight of the system does not change constantly due to the
evaporation of liquid helium. This enables the use of isolators like those from MinusK,112 which are more
sensitive to weight but which otherwise outperform air-based isolators (and are significantly less
expensive than active systems). Two separate vibration isolation tables, one for the cryostat and one for
the surface preparation and analysis system, will be used to support and separately isolate work in the two
subsystems. Once the other systems have been designed, the design and lead time for these tables is
minimal. Estimated expense: $50K.
Construction and Testing Phase Once the designs have been completed (6 months to 1 year), construction and testing of home built
components will immediately begin. For the cryostat team this includes a variety of small components
such as radiation shields and a low temperature sample storage system (allowing rapid exchange of
multiple samples and, for example, field emission targets for STM tip cleaning). For the SPM team this
includes the low temperature vibration isolation system as well as a room temperature test bed. And for
the analysis team this includes two different cleaver systems, one for layered (graphite-like) systems, and
one with a knife edge for semiconductor and cross-sectional SPM studies, as well as a sample heating
stage. External wiring (from the control room and the service corridor to the instrument room) will also
need to be completed. We estimate that construction of these home-built components will be completed
by the arrival date of the purchased components, from one (for the analysis) to one and a half (for the
cryostat) years into the project. Estimated expense: $25K.
Once the subsystems have been separately assembled, testing may begin. Vibrations at the DR cold stage
are our largest concern, as this aspect of the project, mounting a sub-atomic resolution SPM on a dry DR,
is the most technologically ground breaking and challenging. So far, surprisingly few measurements of
Project Description - 11
pulse tube cryocooler vibration levels have been published, either in the literature or in commercial
application notes, though “nanometer scale displacements” is a common (not entirely scientific) sales
statement. We will measure vibration levels at the cold stage along all three axes using Oyo Geospace
geophones,113 compact, UHV compatible accelerometers which continue to work at dilution refrigerator
temperatures. We will also characterize the transfer function of our low temperature vibration isolation
system. Based on known performance levels of top STM systems around the world, our goal is a
broadband acceleration spectral density of under 220 nm s Hz at the STM head, particularly near the
head resonance frequency of roughly 10 kHz. Based on our experience with low temperature vibration
isolation (Hudson91,107) we are confident that we will achieve these levels. However, if problems arise our
isolation design will allow us to sacrifice cooling power and base temperature of the SPM head to gain
stability by reducing mechanical contact to the cold stage. As characterization of dry DR vibration levels
and suitable ultra-low temperature vibration isolation systems do not currently exist in the literature,
publishing the methodology and results of this testing will be of great service to the community.
Once satisfied with testing results from the three sub-systems, including SPM room temperature tests, we
will complete assembly of the entire instrument (estimated completion at 2.5 years into the project).
Risk Mitigation Because the unique aspect of our instrument lies in its particular combination of features, rather than
dramatic, previously untested capabilities, this is a relatively low risk, high reward project. Aside from the
technical challenges regarding vibration isolation, the mitigation of which is detailed above, major project
risks are cost increases due to inflation and schedule. The Project Managers will ensure that critical path
activities are performed as scheduled, controlling both of these possible issues. Contingency funds (~5%
of project cost) are available internally from Hudson’s startup funds. Schedule contingency of 25%-30%
for all purchase lead times is included in the project schedule.
Operation and Maintenance Because of the complexity of operating an ultra-low temperature, UHV SPM, we have chosen an
operation model between that of a user facility and the more typical SPM lab model (external sample
providers, internal users). All research on the instrument will be done in collaboration with instrument
experts, either postdocs or senior graduate students from the Hudson group. These experts will not only
take care of general maintenance of the instrument (the use of a cryogen-free system dramatically reduces
operating costs) but will also train collaborators in all aspects of instrument usage, and will work with
them throughout the data acquisition and analysis process. “Users” (collaborators), will not be charged
any specific fee for use of the instrument, though they will be responsible for minimal costs (typically
<$100/month) directly associated with their research. More importantly, collaborators will also be
expected to have one or two personnel who will be trained and will actively participate in that use during
the full three months to a year that research projects such as those described in section 3.b will likely take.
This model will ensure enough personnel to maintain efficient 24 hour a day, seven day a week usage of
the instrument.
Project selection will be made by the development team in in bi-yearly meetings, drawing from both
internal and external proposals (temporary housing and office space is available for collaborators from
outside the State College area). This will ensure that the unique capabilities of the proposed instrument
will be shared broadly by the materials research community both at Penn State and beyond.
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