(A) Principal Investigator’s Laboratory (Department of Chemical Engineering and Materials Science)
Approximately 2400 square feet of laboratory space is available for this research. The following equipment is available in the PI’s laboratory:
UHV sputter deposition system:
This is a commercial system based on a modified version of the Kurt J. Lesker CMS 18. The deposition system consists of a UHV (< 10-9 Torr) main chamber and a HV load lock chamber. The main chamber has a dry pumping system, the primary pump being a magnetically-levitated turbomolecular pump. The main process chamber has six confocal deposition sources (DC or RF), an oxygen compatible heater stage (up to 850 C), two mass flow channels (Ar and O2) and a residual gas analyzer. The load lock chamber is set up for annealing or cooling in an oxygen pressure up to 500 Torr. Sputtering is possible in total gas pressures up to about 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 entire system, including source shutters, mass flow control, heater stage temperature, and source power supplies, allows for completely automated growth of compounds, alloys, multilayers, and superlattices.
High pressure oxygen sputter deposition system:
To the best of our knowledge this is the only system of its kind at a US university. Based on the Julich design, it is a three source sputter system designed to operate in pure oxygen at pressures up to several Torr. The unique design almost eliminates oxygen induced re-sputtering problems 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 the 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, etc.
UHV molecular beam epitaxy system:
This is a home-built UHV metal MBE system with a base pressure below 10-10 Torr.
The system incorporates a large ion pump, titanium sublimation pumps, sorption pumps (for roughing), a set of cryopanels, a residual gas analyzer, and a UHV (10-9 Torr) load lock chamber with in situ plasma etching capability. Deposition sources include a four-source linear electron beam evaporator and three thermal cells, which can be energized simultaneously for alloy growth. Growth can be monitored via two quartz crystal monitors and a sophisticated deposition controller capable of controlling rates down to 0.025 Ås-1, as well as alloy growth from two sources. 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.
Sulfide reactive deposition system:
A home-built 3 source HV sputtering system for the reactive deposition of transition metal disulfides. 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 the growth of thin films of CoS2 and FeS2.
Electrical transport and magnetotransport measurement system:
A 10 T superconducting magnet with variable temperature insert operating from 1.25 to 325 K. 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) transport measurements. Using combined temperature control on the variable temperature insert and the sample stage heater temperature stability of order 1 mK can be achieved at 10 K. The system is capable of measuring resistivity, Hall effect, magnetoresistance and photoconductivity (via an optical fiber), and has a second probe which enables sample rotation in both planes. One probe is wired with sub-miniature stainless steel coaxial cables to enable low noise, high impedance measurements. A home-built oven insert provides access to temperatures up to 1000 K (in an O2 atmosphere if required) for high temperature transport measurements. In addition to this system we also have a high-throughput transport probe where resistivity measurements (using a second AC resistance bridge) can be made from 4.2 - 300 K by insertion in a helium dewar.
Oxygen plasma etcher:
A home-built vacuum system for oxygen plasma etching. The system is based on a turbomolecular pumped high vacuum chamber equipped with a 300 W dense gas plasma source and a custom designed sample mount capable of RF bias up to 100 W. Control over the pressure of oxygen gas or an oxygen/argon mix, combined with the application of substrate bias voltage, enables controlled directionality etching of polymer membranes for fabrication of nanoscale deposition masks. This system can also be used for pre-deposition cleaning and surface treatment of substrates.
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.
Physical property measurement system:
A cryogen-free Quantum Design PPMS (Physical Property Measurement System) with a 1.7 to 400 K temperature range and a 9 T magnet. The system is equipped with a VSM (Vibrating Sample Magnetometry) option enabling high throughput magnetometry from 1.7 to 1000 K. Electronics required for other measurement options is pre-installed, meaning that the shared 3He, AC susceptibility, heat capacity, torque magnetometry, and AC transport options available in the UMN Physics Department (see section (D) below) can be used in this system. A “break-out box” has also been installed, enabling transport measurements with a wide variety of other electronics for DC and AC transport measurements.
This is an additional 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 transport measurements.
Bulk fabrication equipment:
In addition to the major items listed above we have a number of other items, primarily used for bulk sample preparation. These include three fume hoods, one laminar flow hood, four standard box furnaces (up to 1200 C), a high temperature muffle furnace (up to 1600 C), an 1100 C tube furnace (1”), and a 1200 C tube furnace (3”) with a HV pumping and gas flow manifold for oxygen, a three zone 1350 C tube furnace (used for single crystal growth via chemical vapor transport), two glove boxes, a vacuum oven with liquid nitrogen trap, a powder press, and a high vacuum annealer (1 x 10-8 Torr, 800 C, 500 Oe magnetic field).
(B) UMN College of Science and Engineering Characterization Facility
The University of Minnesota College of Science and Engineering Materials Characterization Facility is extensively used in the PIs research. The facility provides access to a wide variety of characterization techniques.
High resolution X-ray diffractometer:
The high-resolution (primarily thin film) diffractometer (a Panalytical X’Pert Pro) is used extensively in the PIs research. 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.
Wide angle X-Ray diffraction:
Four additional diffractometers, two general purpose systems, one with multi sample capability, two with wide-range temperature control, and two with line/area detectors. The latter enable high-throughput characterization and are particularly useful for polycrystalline thin films. The complete temperature range covered is from liquid helium to 1400 K.
Two microdiffractometers with 2D area detectors are available. In addition to small samples, these systems are ideal for thin film polycrystals, and for orientation/mapping of single crystals. Texture and single crystallinity can be easily verified in these systems. 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 Agilent systems), featuring contact and tapping mode atomic force microscopy, scanning tunneling microscopy, conductive probe, Kelvin probe, etc., some with variable temperature capability.
Scanning electron microscopy:
Four units are available for SEM, all based on field-emission guns. Energy dispersive spectroscopy, electron back-scatter diffraction, and cathodoluminescence are all available.
Transmission Electron Microscopy:
Four units are available, an FEI Tecnia T12 TEM, an FEI Tecnai G2 F30 cryo scanning TEM, an FEI Tecnai G2 F30 scanning TEM, and the recently acquired FEI Titan G2 60-300 X-FEG aberration-corrected scanning TEM. These systems cover conventional TEM imaging, Z-contrast STEM imaging, EDX and EELS. The PI collaborates with Prof. Andre Mkhoyan at the University of Minnesota on TEM imaging and analysis, as well as Prof. Maria Varela of Oak Ridge National Lab/Universidad Complutense Madrid.
Other spectroscopic / 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, Fourier transform infra-red spectroscopy, Raman spectroscopy and microscopy, and visible light microscopy.
(C) University of Minnesota Nano Center (MNC)
The University of Minnesota maintains a state-of-the-art nanofab facility, spanning two buildings and 8000 square feet of clean space, with additional support labs. Equipment items used by the PI include:
Electron beam lithography system: This is a new Vistec EBPG 5000+ 100 kV lithography system capable of sub-10 nm linewidths and large area patterning.
Photolithography systems: 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), CVD, and 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.
Neutron Scattering Facilities
The group is also a frequent user of several national user facilities, particularly neutron sources. We use and collaborate with: