Facilities
Overview
The growth of large and pristine single crystals of new materials is central to our research program. We produce most of the single and polycrystalline materials that we study with scattering techniques, either ourselves or in collaboration with leading crystal growers internationally. This allows us to set up long term and systematic studies of entire families of materials, and to explore certain themes in condensed matter physics. I prefer to have all my graduate students gain experience with both growing crystals and characterizing them afterwards, often with neutron and x-ray scattering methods.
We carry out our neutron and x-ray experiments at the facility which is the best match to our particular science interests and needs. Working at these large national and international facilities we develop excellent collaborations. Grad students and postdocs benefit from close interaction with the world’s best neutron and x-ray scientists with whom we collaborate.
McMaster Labs
Crystal Growth Laboratory
The cornerstones of our crystal growth effort are two Floating Zone Image Furnaces. Polycrystalline starting material of the desired composition, or material close to the desired composition, is placed near one of the common focii in a 2 or 4 elliptical mirror cavity. Halogen light bulbs placed at the other elliptical mirror focii ensure that light is focused at the sample position, producing a “hot spot” which is only a few mm across. Depending on how well the material absorbs the light, the “hot spot” may be locally heated up to as high as 2200 C, which is enough to melt most materials. A molten zone is then formed at the common focus, and it is held in place by the surface tension of the molten material. Then, either the polycrystalline sample, or the mirror assembly, or both, can be translated such that the molten zone passes along the polycrystalline rod. The polycrystalline rods are placed in a sealed quartz tube, so that the crystal growth can be carried out in specialized oxidizing or reducing, or inert atmospheres – up to 10 atmospheres. If everything works well, a zone refined single crystal is left behind the passing molten zone, and a high quality single crystal of approximate dimensions 5mm diameter by 50 mm long is produced.
These furnaces are particularly well suited to growing large single crystals of transition metal oxides. Our recent successes have been the cubic pyrochlores Yb2Ti2O7, Er2Ti2O7, Tb2Ti2O7, Ho2Ti2O7 ; kagome staircase materials Co3V2O8; high temperature superconductors La(2-x)Ba(x)CuO4, Bi2Sr2CaCu2O8; and quantum magnets SrCu2(BO3)2 and CuGeO3.
A very important prerequisite for all single crystal growth is the capacity to make the polycrystalline materials which are the starting point. We have extensive facilities for the accurate weighing, mixing, and annealing of polycrystalline materials, as well as infrastructure, such as x-ray diffraction capabilities, which allow us to assess whether or not the starting polycrysyalline material is what we think it is.
We also perform some Flux Growth which involves slow cooling of a melt, and single crystals are then cut out of the resulting boule. We have the capacity for performing Growths from supersaturated solution, Bridgeman growths, Czochralski growths, as well as Tri-Arc growths for intermetallic materials.
Taken together, the infrastructure for both crystal growth and for the assessment of crystalline materials in the Centre for Crystal Growth is the most sophisticated and extensive of its type in Canada, and one of the most sophisticated in North America. This infrastructure underpins our entire program in the advanced characterization of materials with exotic ground states.
The X-ray Scattering Laboratory:
The X-ray scattering laboratory at McMaster University features a high power Cu – rotating anode x-ray source, which feeds a very versatile 4-circle diffractometer. We can mount both a low temperature displex for sample temperatures between 2.8 K and 325 K, and a 3He fridge which allows us access to sample temperatures as low as 0.3 K. This latter capability, to perform x-ray measurements at temperatures as low as 0.3 K, is very unusual worldwide.
Prof. Gaulin’s X-ray scattering laboratory at McMaster is also home to a Laue X-ray camera, that is used primarily to assess single crystal quality and to orient and mount single crystals in advance of experiments at large scale neutron and x-ray scattering facilities. The strategy is to be able to perform all of our single crystal sample preparation ourselves, in advance of the large scale facility experiments, so that we do not waste any valuable beam time at the large scale facility.
We have also recently been funded for a new modern X-ray powder diffractometer which will replace an existing, old diffractometer. The new powder diffractometer will be co-located with the rotating anode single crystal diffractometer and the Laue diffractometer, and all three will comprise a comprehensive forefront capability for university X-ray beam science.
The Canadian Neutron Beam Laboratory
Under our leadership, McMaster is creating a national neutron beam user facility at the McMaster Nuclear Reactor (MNR) to provide access to these versatile and irreplaceable probes of materials for researchers at the University and all over Canada. MNR is currently home to two neutron scattering beamlines. These two beamlines are to open as user facilities soon, with three more to be completed over the next several years. The latter three are newly funded through the CFI 2020 Innovation Fund project “Building a Future for Canadian Neutron Scattering,” a national collaboration of 17 universities. (https://nuclear.mcmaster.ca/neutron-beams/)
Major X-Ray & Neutron Sources
Spallation Neutron Source at Oak Ridge National Lab (USA)
The Spallation Neutron Source (SNS) at Oak Ridge National Lab is the world’s brightest pulsed neutron source, designed to operate at 1.4 MW. We have played a major leadership role in this facility by contributing to development of two state-of-the-art neutron instruments at SNS – SEQUOIA, a high-resolution chopper instrument, and VULCAN, a powder diffractometer optimized for the study of engineering materials. Our work to date has focused on the inelastic chopper spectrometers SEQUOIA, ARCS, and CNCS. With figures-of-merit for instruments exceeding those at other sources by factors of 10 – 100, we will continue to pursue our most challenging experiments at SNS. Oak Ridge National Lab is in East Tennessee, and is about a 12 hour drive from McMaster. (http://neutrons.ornl.gov/)
The ISIS Neutron and Muon Source (UK)
The ISIS pulsed neutron facility at the Rutherford Appleton Laboratory in the UK. This is a very well developed spallation neutron source with advanced and sophisticated instrumentation. ISIS has completed the installation and commissioning of their Second Target Station, which significantly expands their capability for cold neutron research. Our group has been a significant user of the OSIRIS and MAPS chopper spectrometers. The Rutherford Appleton Lab is in Oxfordshire, UK, about a 90 minute drive west of Heathrow airport. (http://www.isis.rl.ac.uk/)
NIST Center for Neutron Research (USA)
We have been major users of the Disk Chopper Spectrometer, the SPINS and MACS cold triple axis spectrometers, as well as SANS diffraction instruments. NIST is located just northwest of Washington, DC, about a 9 hour drive from McMaster. (http://www.ncnr.nist.gov/)
Canadian Light Source
The Brockhouse Sector at the Canadian Light Source (CLS) is a state-of-the-art sector of beamlines devoted to scattering studies at the CLS in Saskatoon. This sector is based at a straight section of the CLS with two insertion devices (one undulator, one wiggler) which will feed three or more experimental stations for simultaneous scattering experiments. It provides the capacity for very sophisticated resonant and non-resonant x-ray scattering studies of new materials under a host of extreme environments, including low temperatures and high magnetic fields. (http://www.lightsource.ca/)
Advanced Photon Source at Argonne National Lab (USA)
The Advanced Photon Source (APS) at Argonne National Lab: We have made extensive use of two insertion device beamlines at the APS to carry out very high-resolution scattering studies on a number of topical problems in new materials. We conduct time-resolved x-ray scattering measurements on exotic magnets in pulsed magnetic fields. We have developed a very exciting capability to make x-ray measurements on exotic new magnetic materials as they experience an ultra-high magnetic field, pulsed from 0 to ~ 30 or 40 T over a few milliseconds and have used it to study giant magnetoelastic effects in geometrically frustrated magnets. The APS, just outside of Chicago, is about a 9 hour drive from McMaster. (http://www.aps.anl.gov/)
