Facilities

(A) PI’s Laboratory

Approximately 2400 square feet of laboratory space is available for the PI’s research. The following equipment is available:

UHV sputter deposition system: This is a modified version of a Kurt J. Lesker CMS 18. The system consists of a UHV (~10^-9 Torr) main chamber and HV load lock. The main chamber has a dry pumping system with a magnetically-levitated turbomolecular pump, six confocal deposition sources (DC or RF), an O₂ compatible heater stage (to 850 °C), two mass flow channels (Ar and O₂), a wedge grower, and a residual gas analyzer. The load lock enables annealing or cooling in O₂ up to 500 Torr. Sputtering is possible in total pressures up to ~150 mTorr, with 30 mTorr of O₂. The deposition sources are powered by three (switchable) power supplies (two DC and one RF). Computer control over the system, including source shutters, mass flow control, heater stage, and source power supplies, enables automated growth of compounds, alloys, multilayers, etc. The system is currently used for growth of various metals, as well as binary metal oxides. 

High pressure oxygen sputter deposition system: To the best of our knowledge, this is the only such system at a US university. Based on the Jülich design, it is a three-source sputter system designed to operate in pure O₂ at pressures up to several Torr. The unique design almost eliminates oxygen-induced re-sputtering by thermalizing O ions via collisions with other ions in the dense plasma. The system is capable of deposition temperatures up to 1000 °C and films can be cooled, post-deposition, in one atmosphere of O₂. The system has demonstrated capability for deposition of high quality epitaxial films of cuprates, manganites, cobaltites, ferrites, titanates, stannates, etc. The system is currently used exclusively for growth of complex oxides.

UHV molecular beam epitaxy (MBE) system: This is a home-built UHV (~10^-11 Torr) metal MBE system. The system incorporates a large ion pump, titanium sublimation pumps, sorption pumps (for roughing), cryopanels, a residual gas analyzer, and a UHV (10^-9 Torr) load lock chamber. Deposition sources include two four-source linear electron beam evaporators and three K-cells, for a total of 11 deposition materials. Growth can be monitored via two quartz crystal monitors and a sophisticated deposition controller, enabling alloy, multilayer, and superlattice growth, at rates down to 0.025 Ås^-1. The system also includes a rotating x-y-z growth stage capable of temperatures up to 1200 °C. In situ structural characterization is achieved by RHEED (Reflection High Energy Electron Diffraction) with a 15 kV electron gun, beam rocking capability, and k-Space image acquisition and analysis software. Most recently, an ion source has been added to the load lock to provide in situ etching capability, of high utility in multi-step lithographic processes. The system is used exclusively for metal deposition, particularly for magnetism and spin transport research.

Sulfide reactive deposition system:  This is a home-built three-source HV sputtering system for the reactive deposition of metal sulfides. The system has three 2” magnetron sources, a HV load lock chamber, a residual gas analyzer, a 700 °C substrate heater, and a gas flow system capable of handling a H₂S/Ar mix as a reactive gas. The latter involves an exhausted gas cabinet, double-walled delivery lines, a corrosive series turbomolecular pump, a N₂ dilution system, a rough pump in a fume hood, and a H₂S detection system. This chamber has been used for growth of films of CoS₂, FeS₂, Cu₂ZnSnS₄, and Co₃Sn₂S₂.  

Additional synthesis/processing equipment: In addition to the four deposition systems described above, we have a number of other tools, primarily for bulk sample preparation and processing. Two three-zone furnaces are available for CVT (Chemical Vapor Transport) growth of bulk single crystals, primarily sulfides. These systems are set up in fume hoods; the lab has three of the latter, in addition to two laminar flow hoods. For bulk polycrystalline ceramic synthesis and sputter target fabrication we have a suite of furnaces, including two tube furnaces for up to 1200 °C (with a manifold enabling the use of high vacuum, O₂, forming gas, N₂, or Ar), four standard box furnaces (up to 1200 °C), and a high temperature muffle furnace (up to 1600 °C). A powder press, two glove boxes, a pumping/flame sealing station for quartz crystal growth tubes, and a vacuum oven with a liquid nitrogen trap are also available. Finally, we have a high vacuum magnetic annealer that can achieve 10^-8 Torr and 800 °C in a 500 Oe magnetic field. 

Janis magnetotransport measurement system: This is a 9 T Janis superconducting magnet with a 1.25 to 325 K variable temperature insert. The system is equipped with calibrated high field thermometers, temperature controller, level meter, pumps, and electronics for DC (current source, voltage source, nanovoltmeter, and source/measure unit) and AC (resistance bridge or lock-in) measurements. Using combined temperature control on the variable temperature insert and sample stage heater, stability of order 1 mK can be achieved at 10 K. The system measures resistivity, Hall effect, magnetoresistance and photoconductivity (via an optical fiber), and has a second probe that enables sample rotation in both planes. One probe is wired with sub-miniature stainless steel coax to enable low noise, high impedance measurements. A home-built oven insert provides access to temperatures to 1000 K (in an O₂ atmosphere if required) for high temperature measurements.

Physical property measurement system (PPMS): This is a cryogen-free (Evercool-II) Quantum Design PPMS with a 1.7 to 400 K standard temperature range and 9 T magnet. The following options are available: VSM (Vibrating Sample Magnetometer) with extended 1.7 to 1000 K temperature range; DC transport; heat capacity (by relaxation calorimetry); torque magnetometry. A home-built break-out system has also been added, enabling transport measurements with a wide variety of other electronics for DC and AC measurements (see above). 

SQUID magnetometer: This is a Quantum Design XL7 MPMS with a 7 T, 1.7 K field/temperature platform. The system has an oven insert (up to 800 K), a sample rotator (horizontal and vertical rotation), AC susceptibility capability, ultra-low-field operation, and a reciprocating sample option for higher throughput/sensitivity.

He-3 cryostat/magnet: The group recently commissioned a new 9 T superconducting magnet system (American Magnetics) equipped with a ³He insert (Cryo Industries of America). The insert reaches a base temperature of 265 mK, and features a sample rotator. The whole system includes a temperature controller, AC resistance bridge, DC measurement electronics (via a source-measure unit), level meters, pumps, etc. 

Cryocooler/electromagnet: This is a transport and magnetotransport measurement system based on a closed-cycle refrigerator with a base temperature of 8 K, mounted within a 1.5 T electromagnet. The cryocooler has optical windows to enable photoconductivity measurements, while the electromagnet is mounted on a rotating table for angle-dependent magnetotransport measurements. Electronics are available for both DC and AC measurements.

Liquid nitrogen cryostat/electromagnet: This is a transport and magnetotransport measurement system based on a liquid nitrogen flow cryostat mounted within a 1.5 T electromagnet. The cryostat has a temperature range of 65 to 500 K. The system has dedicated electronics for DC and AC transport measurements, including an AC resistance bridge.

Additional transport probe: In addition to the above systems, we also have a high-throughput transport probe where resistivity measurements (both DC and AC (via a resistance bridge)) can be made from 4.2 - 300 K by insertion in a helium dewar. 

Helium recovery system: This is a high pressure recovery system used to recover helium gas from the three “wet” cryogenic systems in the lab. This helium gas is then transported to the University of Minnesota School of Physics and Astronomy to be liquefied in the high capacity liquefier system in the Physics and Nanotechnology building.  This renders the PI's lab essentially closed-cycle with respect to helium usage.

(B) University of Minnesota Characterization Facility
The University of Minnesota Characterization Facility is extensively used in the PIs research. The facility provides access to a wide variety of materials characterization techniques, including, but not limited to:

High-resolution X-ray diffraction: This high-resolution (primarily thin film) diffractometer (a Rigaku Smartlab SE) is used extensively by the PIs group. This instrument is capable of high-resolution wide-angle diffraction, rocking curves, grazing-incidence reflectometry, grazing-incidence in-plane diffraction, pole figures, and reciprocal space mapping. An area detector (HyPix 3000) allows for greatly accelerated reciprocal space mapping, for example, while temperature and environmental control is also possible, between -180 and 1100 °C, with electrical access and in various gases.    

Wide-angle X-Ray diffraction: Five additional diffractometers are available: a high-resolution system (Panalytical X’Pert pro), a variable temperature powder system (Rigaku SmartLab XE), a microdiffractometer (Bruker D8 Discover 2D), and two general-purpose systems (Bruker D8 Advance, Bruker AXS D5005). Several of these systems have 2D detectors. The Rigaku SmartLab XE features a temperature range of 12 – 310 K. A real-time Laue system is also available for alignment of single crystals. 

Scanning probe microscopy: Four multimode scanning probe microscopes are available (two Bruker and two Keysight systems), featuring contact and tapping mode atomic force microscopy, scanning tunneling microscopy, conductive probe, Kelvin probe, etc., some with variable temperature/environment capability.   

Scanning electron microscopy: Three field-emission-gun units are available for SEM. Energy dispersive spectroscopy, electron back-scatter diffraction, and cathodoluminescence are all available, along with temperature control. An FEI Helios G4 UX dual beam focused ion beam (FIB/SEM) is also available. 

Transmission Electron Microscopy (TEM): Five units are available, an FEI Tecnai T12 TEM, an FEI Tecnai G2 F30 cryo scanning TEM, an FEI Tecnai G2 F30 scanning TEM, and the FEI Titan G2 60-300 X-FEG aberration-corrected scanning TEM. These systems cover conventional TEM imaging, Z-contrast STEM imaging, energy dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS).   

Other spectroscopy/microscopy methods: Also available at the Characterization Facility are Auger electron spectroscopy, ion beam analysis (including Rutherford backscattering spectroscopy and particle-induced X-ray emission), spectroscopic ellipsometry, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Fourier transform infra-red spectroscopy, Raman spectroscopy and microscopy, and visible light microscopy.

(C) Minnesota Nano Center (MNC)
The University of Minnesota maintains a state-of-the-art nanofab facility in the NNCI network, spanning two buildings and 8000 square feet of clean space, with additional support labs. Equipment items used by the PI include:   

Electron beam lithography: This is a Vistec EBPG 5000+ 100 kV lithography system capable of sub-10 nm linewidths and large area patterning.

Photolithography: Full suite of photolithographic patterning tools including mask making capabilities for feature sizes down to 0.5 microns, as well as a direct-write optical lithography system.   

Etching Tools: Multiple reactive ion etch, deep trench etch, and ion mill tools, and a focused ion beam tool. 

Deposition Tools: Several evaporators (thermal and electron beam), sputtering systems (RF and DC), chemical vapor deposition (CVD), and atomic layer deposition (ALD) tools, in addition to various spin coating systems. These systems enable deposition of metals, insulators, oxides, nitrides, etc. 

Additional miscellaneous items: These include a confocal microscope, a wirebonder, rapid thermal anneal systems, ellipsometers, profilometers, wafer saws, etc.