The Solid State Physics Research Unit and its Successors
Nabarro was a great champion of experimental physics. When he was negotiating to come to Wits, his primary concern was what experimental facilities there were and what funding there would be from government and industrial sources for experimental research. The Solid State Physics Research Unit (SSPRU) was established in 1961 with Nabarro as director. Its purpose was coordinating research activities sponsored by the University, the CSIR, Hard Metals Ltd., De Beers DRL and ISCOR. From the outset, the Unit's activities were divided between fundamental physics and projects directly impacting the South African economy. There were originally three main fields of research: the fracture of quartzite, which was primarily carried out by H. Schlon and Tony Ball and research students Ludwig Schog and Hayd le Roux; the strength of hard metal alloys, particularly WC-Co, which Silvana Luyckx, and diamond physics mainly drove. The SSPRU evolved over the years into what is now called the Materials Physics Research Institute (MPRI), and has left its genetic imprint on the DST/NRF Centre of Excellence in Strong Materials.
With Nabarro's retirement at the end of 1984, the SSPRU was closed in line with University policy. Out of its ashes, the Condensed Matter Physics Research Group (CMPRG) was established in January 1985, with Mike Hoch as Head and a significantly reduced research budget compared to the SSPRU, with no research staff positions. Over the years, the CMPRG has established itself as a vigorous and productive entity. On review in 1990, it was elevated to research unit status. The Unit prospered through the 1990s, and in 2000, the significant achievements made by members of the Unit were recognized by granting research institute status. Following Michael Hoch's retirement at the end of 2001, David McLachlan became Director, followed a year later by Darrell Comins, who held the position until his retirement at the end of 2007. Membership of this collective has changed a lot over the years with new appointments, retirements and the passing of several individuals. Recent recruits include Marjorie Mujaji, Karin Pruessner, Jonathan Keartland, Sanjiv Shrivastava and Somnath Bhattacharyya.
The study of materials is by no means confined to physics. It cuts across the boundaries of many of the sciences and branches of engineering. Thus, members of the Physics Department have been drawn into several broader structures, most notably the DST-NRF Centre of Excellence in Strong Materials. This collective brings together a unique team of materials scientists drawn from Wits and the Universities of Johannesburg and Kwazulu-Natal, NMMU, MINTEK and NECSA. It has strong interaction with local industry. Darrell Comins directed the Centre from its inception in 2004 until mid-2007.
Materials Research
The main areas of materials research at Wits over the years have been the following:
Electron Spin Resonance (ESR). ESR at Wits is inseparably associated with the name of J H N (Jan) Loubser. He started at Stellenbosch University and UCT, from where he proceeded to Oxford on a Rhodes Scholarship to research microwave spectroscopy of gases for his D.Phil. From 1948 to 1949, he held a postdoctoral fellowship at Columbia University, where he worked with the future Nobel Laureate Charles Townes. He returned to South Africa to work at the CSIR and then, in 1953, took up the Headship of the Department of Physics at UOFS. In 1962, he was appointed as Chair of Experimental Physics at Wits. He switched his research from microwave spectroscopy of gases to ESR to support the Department's existing interest in solid-state physics. With students and long-time colleague Jan van Wyk and other collaborators, he applied ESR methods to study paramagnetic defects in diamonds. This activity was started partly because of ready access to samples through contacts with De Beers Diamond Research Laboratories (DRL). This work had a fundamental focus related to the fact that diamond is a very special wide-gap semiconductor and a practical goal of importance to the gem trade since ESR is a valuable tool in identifying the colour centres that accompany irradiation and annealing. Loubser passed away in 1994.
Nuclear Magnetic Resonance (NMR). NMR was driven by Mike Hoch, who joined the Wits Physics Dept. at Natal University in 1970. In the early 1970s, a 1.2 Tesla 12-inch high homogeneity Varian electromagnet was acquired for NMR research on condensed matter. With the assistance of Roy Day, he pioneered EPR imaging using an X-band EPR spectrometer, modified to have static magnetic field gradients that could be rotated concerning the sample cavity. The first EPR images ever recorded, showing spatial resolution of small DPPH crystals and two small diamonds, were obtained at Wits.
During a sabbatical year at Cornell in 1986-87, Hoch became involved in metal-insulator work on heavily doped semiconductors. The work was continued at Wits, where postgraduate students used the dilution refrigerator. In collaboration with Johan Prins at the Schonland Centre, a project on the metal-insulator transition in single-crystal diamonds was carried out using high-purity single-crystal diamonds implanted with boron ions, permitting a detailed study of the transition. Several experiments on the Group V semi-metals were also carried out in this period using NQR methods at high pressure. In the mid-1990s, an X-band Bruker spectrometer was purchased and located at the De Beers Diamond Research Laboratories for three years, where it was used for various experiments and was later transferred to Wits. At this time a 5 tesla wide bore superconducting magnet was acquired from Sasol who no longer needed it. At Wits, considerable effort was devoted to developing 13C dynamic nuclear polarization methods in type Ia and Ib diamonds, combining EPR and NMR facilities. Hoch retired at the end of 2001. At present, the NMR lab is managed by Jonathan Keartland.
Low Temperature Physics. This was initiated in 1965 by Professor Frank Nabarro because low-temperature measurement facilities were essential to a modern solid-state research laboratory. At that time, a problem of particular interest to him was the interaction between crystalline dislocations and the vortex lattice in a type II superconductor.
Helium, hydrogen and nitrogen liquefiers were acquired from Oxford University and housed in the so-called Low-Temperature Laboratory, which was run under the guidance of Paul Jackson. John Watts was hired to get the plant operational and was assisted by two new graduate students, Wally Kopp and Ewald Wessels. After many trials and tribulations, the team finally made the first liquid helium in South Africa, about one litre, in 1964. In 1968, a second-hand Collins Model 10 Liquefier was installed in the LTL and became the workhorse of low-temperature physics at Wits. Darrell Comins was one of the first to publish on work done with this liquid He at Wits.
Two graduate students were taken on by Nabarro, Terry Doyle, to work on the experimental aspects of fluxoid dislocation interactions, and Alex Quintanilha to assist him with the theory. Barbara Rothberg worked on the effect of elastic strain on the superconducting phase diagram of super-elastic tin whiskers. Two returning South Africans were recruited: John Brock, an Oxford graduate who had just completed a postdoc in California and David McLachlan, who, after graduating in the States, had worked at the IBM Zurich Research Laboratory for four years. With their arrival, a modern low-temperature laboratory was set up. It included a He3 cryostat and facilities for low-temperature thermal conductivity and high-sensitivity susceptibility measurement. In separate laboratories, Terry Doyle installed facilities for low-temperature magnetic measurements (including a very sensitive, in-house built, vibrating sample magnetometer with a 5T superconducting magnet). Barbara Rothberg had installed a precision micro-straining device for her tin whisker research.
The earliest publications from the 'low-temperature group' were due to McLachlan who succeeded in observing (for the first time recorded) the quantization of the fluxiod. Brock established a research programme to measure the low-temperature thermal conductivity of solids, particularly diamond samples supplied, cut, and polished by de Beers. Jan W Vandersande joined Brock as a graduate student in 1969, and over many years, first as a student and then as a member of staff, was engaged in correlating the conductivity of insulating solids, particularly diamond, with the presence of impurities and other point defects, dislocations and boundaries. Jean-Paul Burger visited the department in 1972, and Mclachlan worked on magnetic alloys of PdMn that were variously doped with atomic hydrogen. Unknowingly, they made some of the first observations on spin glasses at low temperatures, and the original publications in this field appeared shortly before their joint paper.
In 1980, the increasing need for liquid helium in the department and other universities in South Africa necessitated a new Helium liquefier, and a C.T. liquefier was purchased from Afrox, who had found that the commercial market would not support such a plant. This was installed in 1981 and produced sufficient liquid Helium for the departments and other needs, including the first medical MRI scanners in the late 1980s. My experience with this liquefier enabled the departmental team, which consisted of Hoch, Kolk McLachlan, and Peter Ford, to be motivated by purchasing a He3 dilution refrigerator.
With the advent of High Tc Superconductivity, in 1987, McLachlan and Richard Doyle joined the University of Natal and the CSIR to form a team, sponsored by De Beers Industrial Diamond Division, to try to develop new, higher operating temperature materials using De Beers high-pressure know-how, but this effort was not too successful. A Workshop on Low-Temperature Physics was held in 1989 with Bob Richardson of Cornell University as an invited speaker to encourage activities in the low-temperature physics area. It served as the official inauguration of the dilution refrigerator. The proceedings of the Workshop were published in the SA Journal of Physics. In 1991, a Theoretical Summer School on Low Temperature Physics was held at Blydepoort. The proceedings were edited by Hoch and Lemmer and published by Springer. Two speakers, Tony Leggett and Bob Richardson, were later awarded the Nobel prize. Dr Vladimir Gridin joined the department in 1990 and published on high Tc superconductivity, magneto-transport, and heat capacity measurements.
Optical spectroscopy of solids. Leon Vermeulen initiated this in the early 1960s with work on the optical properties of diamonds. He, Roger Farrer and Alun Harris published on several aspects of diamond physics, including counting properties, photoconductivity, defects, magnetoresistance and Hall currents. P T (Pete) Wedepohl joined the Department in 1964 and initiated the then "hot topic" of radiation damage and colour centres in alkali halides, using optical absorption spectroscopy, with Darrell Comins as his Ph D student. Wedepohl also conducted first-principles calculations on defects.
In his career spanning 42 years at Wits, Darrell Comins, together with a number of collaborators and postgraduate students, has built up optical spectroscopy of solids into one of the major fields of research at Wits, with world-class experimental facilities, including the Wits-NRF Raman and Luminescence Laboratory, a National Facility that provides service to academics in various disciplines and also many industrial users. His research has encompassed several distinct areas: radiation damage and ion implantation in multiple materials with A Allen, J Marat-Mendes B Carragher, T Derry, A Davidson (Zululand), S Connell, M Naidoo and G Amolo; fast-ion conductors studied by high-temperature Brillouin and Raman spectroscopy with P Ngoepe, P Mjwara, C Anghel, E Rammutla and M Mujai; ambient and low-temperature Raman and luminescence spectroscopy of diamond with M Fish, S Bradlow, J E Lowther and R Erasmus; site selective spectroscopy with M Mujaji; surface Brillouin scattering (SBS) at ambient and high temperatures as well at high pressure with A Every, P Stoddart, W Pang, X Zhang, J Crowhurst, G Hearne, S Tlali, B Mathe and C Sumanya; high-pressure Raman studies of nanomaterials with G Hearne, M Nieuwoudt and R Erasmus; high-temperature studies of carbon nanotubes with R Shiri and R Erasmus; metallic corrosion studied in situ by Raman spectroscopy with M Nieuwoudt and E M Sherif. His major collaborators abroad have been W Hayes and R Harley (Oxford), R Catlow (Royal Institution), A Chadwick (Kent), S Lefrant and E Rzepka (Nantes), E Balanzat (Caen), N Kristianpoller (Tel Aviv) G Saunders and E Macdonald (Bath), K Schwartz and C Trautmann (Germany), B Hillebrands, T Wittkowski and K Jung (Kaiserslautern) and L Hobbs (MIT).
f-Electron Magnetism and Heavy Fermion Research Programme. Paul de V. DuPlessis joined the Physics Department from RAU in 1993, taking up the Chair of Experimental Physics. He formed the f-Electron Magnetism and Heavy Fermion Research Programme, in which he was joined by his research assistant Andre M Strydom. The research they conducted over the years, much of it with Polish collaborators R Troc and D Kaczorowski and F Steglich in Dresden and postdocs M B Tchoula Tchokonte, L Menon and V H Tran, was mainly concerned with the magnetic and transport properties of rare earth compounds, holmium and dysprosium or otherwise heavy Fermion compounds. Kondo behaviour and antiferromagnetic transitions are some of the issues that came up. Most of their measurements were done in-house in their lab at Wits, but their measurements with neutron scattering had to be done elsewhere. DuPlessis retired from Wits in 2005, and he and Strydom are now at UJ.
Electron Microscopy. The history of electron microscopy at Wits is closely associated with the name of John W Matthews. In 1956, having just graduated with an honours degree in physics, he was appointed Laboratory Assistant in the Department of Physics and given the responsibility for the installation and supervision of the second transmission electron microscope (TEM) to be purchased in South Africa, the first being at the CSIR in Pretoria. Matthews was largely responsible for the maintenance of the microscope while being encouraged to create an interest in electron microscopy throughout the University and develop his field of research. The presence at the CSIR of J T (Koos) Fourie, who had experience in the electron microscopy of thin metal films, and J H van der Merwe at the University of Pretoria, a pioneer in the theory of epitaxy, induced Matthews to work on the electron microscopy of epitaxial deposition. He earned a reputation for undertaking clean and elegant experiments with penetrating discussion. At Wits, an informal grouping comprising Dave Holt, Paul Jackson, Dave Allinson, Rob Caveney, Jim Murphy and Ewald Wessels was formed to promote electron microscopy.
A consequence of Matthews' frequent visits to Charlottesville resulted in increasingly close collaboration with the IBM Watson Research Center. In 1969, he left Wits to take up a position at IBM as manager of a research group heading their thin film research. Matthews' contributions to the field of electron microscopy are recognized through the annual John Matthews Memorial Lectures, which are given at the meetings of the then Electron, now Microscopy Society of Southern Africa (MSSA). Recently, as part of a significant revamp and modernization of the Unit, a number of new microscopes have been purchased, including a focused ion beam scanning electron microscope (FIB) and two atomic force microscopes (AFM).
Mössbauer Spectroscopy. This activity was started by Berend Kolk, who was appointed to the Chair of Experimental Physics at Wits in 1983. At the time, two other groups in the country were doing minimal Mössbauer work. Kolk had been schooled in the technique at the University of Groningen. After obtaining his doctorate, he did post-doctoral work at Rutgers University and then moved to Boston University, where he was based for seven years. On arriving at Wits, Kolk immediately set about establishing a foremost Mössbauer laboratory and also vigorously promoted the benefits of the technique to colleagues in industry and academia around the country. Already in the early stages of the laboratory, both high-temperature and low-temperature (cryogenic) capabilities were implemented. Fundamental physics projects that were tackled included magnetic behaviour and spin dynamics in the vicinity of the spin-ordering temperature of Fe-metal and lattice dynamics aspects of superconductivity in the 'high-Tc' superconductors of the time, namely the so-called A15 compounds, Nb3Sn, V3Sn etc. Those fundamental physics projects formed the core of the research programme in the laboratory.
In 1987, Kolk tragically passed away, and the responsibilities of the MMössbauer laboratory fell to the most senior student, Giovanni Hearne. About two years later, Herman Pollak was recruited to take over the running of the laboratory. His research emphasis and interests differed somewhat from Kolk's, as he was more inclined toward applied and industrial physics project work. This has many applications in the country, especially in mineral processing, metallurgy, and catalysis. During the next several years, Pollak established many linkages with industry, helping cement the place of M-auer spectroscopy as an important analytical tool for iron-bearing materials in the country. After a sabbatical in Israel, Hearne returned to the Department of Physics at Wits in 1995. He continued to assist in guiding activities in the MössbauerLaboratory and establish a new high-pressure research programme based on the knowledge gained during his tenure as a post-doctoral fellow. He is currently the group leader of the Mössbauer Laboratory.
Mechanical Properties of Materials. Despite Nabarro being a theoretician, most of the students he supervised and researchers he interacted with at Wits were experimentalists. Paul Jackson was the first of the students to work on the mechanical properties of metal whiskers. D. B. Holt, a member of the Department in the 1960s, was co-author of an extensive review on the plasticity of pure single crystals with Nabarro and Basinski. C A O Henning obtained his PhD in 1967, supervised by Ludwig Schog, on the growth of gold films on rocksalt in high vacuum. R J (Rob) Caveney obtained his MSc and later a PhD on the vapour growth of CdS crystal platelets.
Research on fractures developed into a substantial activity in 1956 through establishing the Drilling Research Unit with support from the Board and Hardmetal. R M Ferguson of Boart suggested that attention should be paid to improving the performance of rock drills by using 'rock hardness reducers', which lower the energy of the drilling by reducing the stress at which the rock fractures. E T S (Ted) Brown then approached Nabarro, suggesting further investigations into this effect in the laboratory and the field. Helmut Schlon and Ludwig Schog mainly carried out this. Somewhat later, Charlie Levitt obtained his PhD on the impact strength of diamonds under different strain rates by mounting diamonds in a massive pendulum and smashing them against each other. Tony Ball was a member of the Department between 1969 and 1972, working on the fracture of quartz crystals and quartzite.
From the early 1960s, Boart became interested in the fracture of hard metal rock drilling tools, and the Drilling Research Unit launched investigations into mining insert design, internal stress measurements of tungsten carbide, residual stress measurements of braised joints, and the influence of heat treatment on hard metal properties. Much of the drive was to be provided by Silvana Luyckx. In the early 1970s interest shifted from fracture of WC-Co to its magnetic properties. These were exploited in a number of quality control techniques, but were not really understood. Irwin Joffe started work in this field, and his discovery of the role of Co3W microprecipitates is still often quoted today, and used worldwide as a quality control technique. In the mid-1970s, McLachlan built a uniquely large magnetometer for Boart and Hardmetal in Springs, and the effect of inclusions on the strength of hard metal was studied and quantified. In the 1980s, Boart focused on ion implantation's effects, and Luyckx moved the base of her activities to the Schonland Centre.
Biomaterials. Interest in biomaterials in the Physics Department has mainly centered on Nabarro and a number of associates. One of his early biomaterials interests, partly stimulated by Bill Harris and Sheila Saffer, was in applying the ideas of dislocations and disclinations to biological materials. This led to an analysis of the structure of an insect muscle, which appears to have anticipated the ideas of some biologists and, during a sabbatical in Berkeley in 1977, to a successful mechanistic description of the crenation of red blood cells by drugs. With Roger McCarter and C H Wyndham, he published on the reversibility of the length-tension relationship in muscle. In the 1970s, a research program involved the study of insect shells' mechanical strength. The principal investigators were Irwin Joffe in the Physics Department and H R (Randy) Hepburn in the Department of Physiology. In the last months of his life, Nabarro was motivated by the support of biomaterials research and chaired a meeting that brought together interested parties in Gauteng to discuss the desirability of establishing a centre of excellence in biomaterials. The positive outcome led to a National Conference on Biomaterials in September 2006.
