3. Project Description 3.a. Instrument Location and Type ... Application... · Instrument Location and Type Instrument ... construction on a cryocooler based dilution refrigerator

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)


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.


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


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.


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.


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.


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.


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


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).


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


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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3. Project Description 3.a. Instrument Location and Type ... Application... · Instrument Location and Type Instrument ... construction on a cryocooler based dilution refrigerator