Dan Haneman died in Sydney as a result of Parkinson's disease on 13 December 2002. He made fundamental contributions to the study of clean semiconductor surfaces from the beginning of such studies in the 1950s. Perhaps his most important contributions were the Haneman model for semiconductor surfaces and the invention of novel experimental methods for the study of surfaces produced by cleavage in ultrahigh vacuum. Numerous PhD students benefited from his careful supervision over many years.
Dan Haneman's father, Samuel Haneman, was born in Memel, in what is now Lithuania, and completed a medical degree at the University of Breslau (then a city under German control but now Wroclaw, a city of Poland). His mother Lena (Gantman) was born in Minsk, in what is now called Belarus ('White Russia') and moved to Germany as a girl when her family fled the Bolshevik revolution. Dan Haneman was born on 20 March 1931 in Berlin, where his father had a medical practice. As a result of the situation with the Nazis and Jew-baiting in Germany, which was already quite ugly by the early 1930s, Dan's parents decided that hope for a future in Germany was misplaced and it was better to lose everything and to emigrate. Other members of their family had also been early refugees from Germany, settling in Australia, and they were able to arrange the necessary papers. Consequently, Dan arrived in Sydney in 1934 with his parents.
In 1934 Australia was in the midst of an economic depression and, in addition, the British Medical Association (forerunner in Australia of the not-yet-established Australian Medical Association) persuaded the government not to register foreign doctors. Therefore the only source of income for the Haneman family was from other refugees who patronized their own doctors (including Dan's father) who worked without official permission to practise. Dan remembered an occasion when he was six years old, playing at a friend's place when his friend's mother, learning Dan had come from Germany, told him to get out, screaming 'We don't want any Germans here'. His friend Alfie tried to interpose 'He's a German Jew' (whatever he thought that meant) but she replied 'I don't care, I don't want any Germans'. Ignorance in Australia was widespread. Indeed the Australian authorities, when the war started, interned all 'enemy aliens', including both Jewish refugees and German Nazi supporters, in the same camps.
When Japan entered the war, many doctors were called up and a shortage of doctors in country areas developed. Under this pressure, the government decided to allow foreign, mostly refugee, doctors to sit for the final examinations at the University of Sydney. His father sat and passed the examination and was then sent to practise in Burren Junction in outback New South Wales and later in Wee Waa where the living conditions were slightly better, for example there was electricity. Dan had to board in Sydney while he attended Sydney Boys High School. His brother John was born before the family left Sydney and his sister Sylvia when the family was living in Wee Waa.
On leaving high school in 1948, Dan was awarded an Exhibition Scholarship at the University of Sydney (one of 100 non-means-tested scholarships that were available). By his second year at university, he had saved enough from working during summer vacations to buy a BSA 125 cc Bantam motorcycle. To his delight, his father gave him enough additional money to buy instead a BSA 250 cc, which was a much better machine. Thus he became the proud owner of a motorcycle, which greatly eased the irritating transport problems from Bondi to Chippendale and enabled him to make longer trips to Melbourne and to Adelaide. Dan was involved in five accidents with the motorcycle in his first year but none in the following four years of riding. That was fortunate because, in those days, helmets for riders were not known.
At the University of Sydney, he progressed to the 4th (Honours) year in 'Theoretical Physics', which consisted of the entire Physics honours course plus the Applied Mathematics honours course. During his undergraduate years, Dan was active in student politics, believing in the need to fight discrimination, exploitation and the like. This was a principle to which he adhered throughout his life. His honours year was the year in which Prime Minister Menzies tried to ban the Communist Party. The entire political left, led by the leader of the Labor Party, Dr H. V. Evatt, mobilized against Menzies. Although Dan spent a lot of time in political campaigning against the decisions of the Menzies Government at that time, he still was awarded First Class Honours. The 1952 honours class in Physics at the University of Sydney was an exceptionally strong class with four students who later became Fellows of the Australian Academy of Science (Neville Fletcher, Dan Haneman, Brian Robinson and Stuart Turner).
In 1953, Dan continued his studies by enrolling in an MSc at the University of Sydney. Study at the PhD level was not available at the time, the normal course being for the best students to go to England for the purpose. After completing his MSc in 1953, Dan was appointed to a Research Officer position in the Radiophysics Division at CSIRO. He was directly responsible to Lou Davies [who later also became a Fellow of the Australian Academy of Science and for whose biographical memoir see Rigby (2003)] in the newly established transistor section, led by Brian Cooper. After work he and a friend, Ralph Loughead, furthered their study by working through the analytical mathematics text by Whittaker and Watson. Two afternoons a week, he went to Dovey's gym in Darlinghurst where he engaged in body building, and he maintained an interest in physical fitness throughout his life. Earlier in his life, he had been forbidden from participating in sporting activities following a series of operations to his abdomen following a burst appendix when he was ten years old.
Soon after Harry Messel took up the position as Head of the School of Physics at the University of Sydney during 1952, it became possible to enrol in a PhD programme there. Nevertheless, Dan decided to go to England for that purpose. He was awarded an Admiralty Scholarship at the University of Reading to study under the supervision of E. W. J. Mitchell. The stipend was 600 pounds, regarded as large for that position. By that time, Dan was engaged to be married to Rose Anush, and she accompanied him to England where they married in London on 31 July 1955. They had a flat in the upper half of a house belonging to George Blair, then head of the Rheology section of the National Institute for Research in Dairying, in the Reading area of Berkshire. They were pleased and impressed with the standards of courtesy and behaviour that they encountered in the Reading area and generally in England. Nevertheless, England in 1955 was still not free of the aftermath of the war and, compared with the economic boom they had left in Australia, it seemed to them somewhat backward economically. Dan recalled working hard at his studies during this period, assisted, he said, by the generally wretched weather that was not conducive to outdoor activities. His thesis topic was to measure photoelectron emission from semiconductor surfaces, and it was during this period that he developed his lifelong interest in the surfaces of solids and of semiconductors in particular. One of his achievements during his PhD study was to pioneer measurements on semiconductor surfaces obtained by cleavage in ultrahigh vacuum [8] and he continued using that method wherever possible throughout his career. The study of surfaces requires good vacuum systems, which were all glass at that time. It was still the practice, and indeed the necessity, to make nearly everything oneself, including ionization gauges, devices to manipulate samples under vacuum, and so on. Each time a sample was changed, it was necessary to break open and then rejoin the glass vacuum system. Consequently Dan became a skilful glass blower, a talent that he later put to good use, especially when the time came to establish a surface physics laboratory when he returned to Australia.
On their way to a holiday in Europe, to be followed by a conference in Germany, Dan and Rose had a car accident as a result of which both of them ended up in hospital in Redhill in Surrey, Rose with a badly broken arm and Dan, having been projected through the windscreen--there were of course no seat belts at the time – with concussion and facial injuries. After three weeks they were both out of hospital and able to continue by train to the conference at Garmisch-Partenkirchen, which Dan described as 'a much-needed morale restorative'. At the end of three years at Reading, Dan attended a conference in Brussels and met H. E. (Charles) Farnsworth who offered him a postdoctoral position at Brown University in Providence, Rhode Island, USA. Thus, after completing his PhD at the University of Reading in 1958, Dan was fortunate to be able to join Farnsworth's laboratory, one of the leading surface physics laboratory in the United States at the time, especially in the application of the new technique of low-energy electron diffraction to the study of clean surfaces. From 1958 to 1960, he performed experiments on clean and gas-exposed semiconductor surfaces using state-of-the-art equipment for the new technique of low-energy electron diffraction (LEED). During this period Dan's practice was to work in the laboratory in the mornings, to go home for lunch and a nap, and then to return to work through the afternoon and into the evening. Dan had the greatest respect for H. E. Farnsworth and for many years he displayed a photograph of his mentor in his office. Dan and Rose loved Providence and the affluent life in the USA. Their daughter Daphne was born there in the midst of a serious snowstorm that required Dan to struggle to the hospital through deep snow, on foot, to obtain medical assistance.
The main experimental results of Dan's postdoctoral work were published in 1961 in a long and widely cited paper in Physical Review [17] in which he also proposed the first detailed model of the reconstruction of semiconductor surfaces. The low-energy surface of the elemental semiconductors Si and Ge is the (111) surface, which means there is ideally one broken or 'dangling' sp3-orbital on each surface atom [at least, that was and is the conventional wisdom, which Dan was to challenge in 1988 (164)]. Dan's model proposed that the dangling surface orbitals would rehybridize. He suggested that some of the dangling orbitals would become more p-like leading to more sp2-like, and therefore more planar, bonds to the subsurface atoms. Thus those surface atoms would contract towards the surface and the second-layer atoms would move laterally apart. He argued that strain in the second layer would be relieved if the dangling bonds of the remaining surface atoms became more s-like, so the bonds to the subsurface atoms would be more p-like with smaller bond angles than sp3. Thus those surface atoms would move away from the surface. The 'rumpling' or 'buckling' of the surface due to the two types of surface atoms explained the larger surface unit cells. The same model could be applied to other surfaces that Dan had studied, including the (111) surfaces of GaSb [16] and the (100) surface of InSb [17]. A couple of years later Lander, Gobeli and Morrison (1963) proposed alternative surface models based on LEED data they had obtained and analysed at Bell Telephone Laboratories at Murray Hill, New Jersey. In their model of the cleaved surface structure, pairs of surface atoms moved closer together within the surface layer so that the dangling bonds could pair up to form a double bond. Interest in the Si surface had been stimulated by the discovery by Schlier and Farnsworth (1959) that, on annealing above about 500 K, the Si(111) surface exhibited a huge surface unit cell involving 49 surface atoms, which became known as the Si(111)-7 ¥ 7 surface structure. The discovery of the Si(111)-7 ¥ 7 structure is sometimes wrongly attributed to Lander, as Dan has had occasion to point out [153]. Lander, Gobeli and Morrison (1963) proposed that the 7 ¥ 7 structure was the result of vacancy migration on the surface while Dan adapted his basic model to explain the results. Much of Dan's future research would be directed towards devising experiments capable of providing evidence for or against the surface model he had proposed.
After two years at Brown University, Dan was offered a Senior Lectureship in Physics at the newly established University of New South Wales (UNSW) in Sydney. Dan and Rose were both keen to see their families in Australia again so they returned to Sydney and Dan took up the position at the beginning of 1961. With financial assistance from his parents, Dan purchased a cottage in the Rose Bay area, conveniently located near UNSW. Twin sons, Andrew and Neal, were born in 1962 and a couple of years afterwards Dan bought a larger house in nearby Dover Heights, also overlooking the ocean.
Initially he was a little surprised at the huge contrast between the Physics Department at Brown University and that at UNSW, which was trying to make the difficult transition from a technical college to a university. He noted that there appeared to be a certain amount of friction at the time between academic staff and administrators who, Dan felt, misunderstood their positions compared with their counterparts in USA.
Dan relished the opportunity to establish his own laboratory and he built up significant research facilities in surface physics with limited funds (this preceded the establishment of the Australian Research Grants Committee) and managed to maintain a brisk publishing rate. At that time his laboratory occupied a large area on the bottom floor of the first building built on the UNSW campus and was on the floor below what had been the first office of the Vice-Chancellor and the first University Council Chambers. His initial experimental research in Australia concentrated on the changes in surface morphology of semiconductors during annealing in ultrahigh vacuum [18, 19, 21]. Several glass vacuum systems had to be constructed in-house for the purpose. Dan also constructed a glass vacuum system to continue research involving LEED. On the theoretical side, in conjunction with Norm Hansen, an existing staff member at UNSW, he showed that his surface model was capable of fitting the experimental LEED data on the Ge(111) surface [23].
In addition to the research just mentioned, Dan compensated for the lack of funds and facilities, compared with overseas laboratories working in the rapidly developing field of surface physics, by embarking on innovative methods for the study of clean and gas-exposed semiconductor surfaces (as well as pursuing conventional experimental techniques like LEED). The use of completely novel experimental techniques was a hallmark of Dan's career. The first was the 'surface mating technique', which involved creating a small partial split in a block-shaped semiconductor single crystal in ultrahigh vacuum and monitoring the conductivity across the block as the wedge that created the crack was removed. The prediction was that the conductivity would be restored towards its initial value because the two surfaces created by the split would at least partially rebond perfectly if Dan's surface model, involving no lateral surface-atom movement, was correct. On the other hand, if the surface reconstruction involved lateral atomic displacements, as in the Lander and Morrison model, the surfaces would not be able to rebond. In order to produce partial splits in brittle materials like Si and Ge, it was necessary to construct an elaborate system of motion reduction levers in the ultrahigh vacuum system to transmit very small pressures to the top of the wedge. The skill of laboratory technician Dave Roots was an important element in achieving a successful experimental set up that showed, indeed, that atom-on-atom closure occurred at the bases of partial cleavages made in ultrahigh vacuum in germanium and silicon [36].
A second innovative experiment involved the behaviour of semiconductor surfaces subjected to ion bombardment and annealing. The method was based on the differences in sputtering yield, for a given energy, between material previously damaged by a higher-energy bombardment and material previously undamaged. The change in yield when all the previously damaged material was eroded away marked the depth of this region. The problem of how to measure the tiny changes in sputtering yield was solved by growing thin germanium films on a piezoelectric quartz crystal and monitoring the change in the resonant frequency of the crystal as the surface of the semiconductor film was sputtered away. The detection method was sensitive to mass changes of 4 ¥ 10-10 g/cm2 [32, 33]. This project was the thesis topic of Ron MacDonald who was the first of Dan's PhD students to submit his thesis and who later became Deputy Vice-Chancellor (Research) at the University of Newcastle, New South Wales.
Yet another new technique pioneered at this time was to prepare extremely thin semiconductor samples and to measure, using laser interferometry, the change in bending of the samples as the upper surface was cleaned in ultrahigh vacuum by ion bombardment and annealing [37]. All these projects involved students studying for PhDs under Dan's supervision and in fact a key to Dan's success was his ability to inspire and enthuse the many postgraduate students who studied under his guidance over the years.
If Dan's rumpled-surface model for semiconductors was correct, each surface atom possessed a 'dangling' orbital, either more s-like or more p-like than sp3, that ideally would be occupied by one electron. One might expect to obtain an electron paramagnetic resonance (EPR) signal from the unpaired electrons in those dangling orbitals on the surface atoms. Indeed, it was known that Si crushed in air or partial vacuum did show a strong EPR signal but it was reported in 1964 that no EPR had been obtained from Si crushed in ultrahigh vacuum [Muller et al. (1964)]. That result appeared to support the Lander and Morrison model of surface reconstruction, in which the dangling bonds paired up, so Dan decided to repeat the experiment with M. F. Chung who had come to Australia from Hong Kong to pursue a PhD. The experiment involved evacuating and sealing off a glass vacuum system in which the Si could be crushed and the powder transferred to a quartz tube suitable for EPR measurements while continuously under vacuum. Sometimes a large glass bulb containing pure oxygen or hydrogen had been attached to the sealed-off vacuum system, and separated from the Si sample by a breakable seal, so that the powders could be exposed to gases while the Si sample was in the EPR spectrometer. Chung and Haneman [31] found an EPR signal from the Si surface prepared in ultrahigh vacuum and studied its properties before and after exposure to various gases. The first experiments were performed at the University of Sydney on an EPR spectrometer made available by Professor Albert Alexander. In 1965 Dan was awarded funds to purchase his own EPR spectrometer in the first round of grants from the newly established Australian Research Grants Committee, and he was able to continue for many years a successful and innovative research programme in EPR from various clean and gas-exposed semiconductor surfaces using this instrument.
In 1964 Dan was promoted to Associate Professor (later with a special salary). Throughout his career at UNSW, Dan used his regular periods of sabbatical leave to keep up to date with developments elsewhere and often to embark on new lines of research. In 1966, Dan was made a US National Science Foundation Senior Foreign Scientist Fellow and spent his first sabbatical leave mainly at Brown University with H. E. Farnsworth and at the University of California at Berkeley. The day before he was to leave, his students filled his office with balloons and when Dan slid back the door to his office he was engulfed in a colourful torrent. The main achievement during his sabbatical was to advance the surface EPR work by performing measurements on cleaved single crystal surfaces rather than crushed powders. This involved constructing an ultrahigh vacuum system in which single-crystal Si could be cleaved into several pieces that were then transferred and aligned in an 11 mm diameter quartz tube suitable for EPR measurement. While still under ultrahigh vacuum, the quartz tube was manoeuvred into the EPR cavity by lowering the whole vacuum system by about 12 cm by rotating four threaded support legs. Because of the reduced surface area, the EPR signal was at the limit of the sensitivity of the EPR spectrometer even after employing signal accumulation, but Dan obtained the EPR signal from the cleaved surfaces and was able to measure its properties before and after controlled exposure to various gases. Apart from its inherent difficulty, the experiment is noteworthy for the extreme care that Dan took to ensure that the surfaces were clean and that nothing other than the cleaved Si – that is, no Si chips – contributed to the EPR signal. The results were analysed in detail and reported in another long paper in Physical Review after his return from leave [42]. He completed his sabbatical with two months at the Hebrew University in Jerusalem with A. Many and Y. Margoninski, who had co-authored the first major textbook in the developing field of surface physics. It was just after the Six-Day War and there was a heady atmosphere in Israel. Unusually, it snowed in Jerusalem and Dan remembered seeing the traffic chaos and wondering where the efficiency was that had disposed of several Arab armies so quickly.
The next significant development in producing experimental evidence for his rumpled surface model of semiconductor surfaces was the discovery with PhD student John Ridgway that the Si(111)- 7 ¥ 7 structure could be observed within a few seconds of cleavage at room temperature [53]. Previously the 7 ¥ 7 structure had only been obtained after high temperature annealing (for example, at 600 K or above for the order of minutes) of the Si(111) surface. This discovery obviously counted against models of the 7 ¥ 7 structure that involved vacancies, and the suggestion that by then had been made that the 7 ¥ 7 structure was stabilized by impurities.
Throughout his career, Dan combined experimental work with theoretical work directly related to experiments. His theoretical work had involved the detailed explanation of the EPR spectrum from semiconductor surfaces. With students Gus Taloni [40] and David Heron [54], he had been involved in numerical computations on the energy of restructuring of semiconductor surfaces. Dan was not interested in theoretical work that involved approximations so extreme (for example, so-called 'model calculations') that the theoretical results could not be related to current experimental results or problems. Nevertheless, he was prepared to become interested in fairly esoteric theoretical investigations provided they showed potential for explaining experimental results. One problem that arose in the laboratory around 1970 was that calculations with PhD student David Heron [44] showed that electrons in the dangling bonds in Dan's rumpled-surface model ought to form narrow bands and therefore the spins ought to be mostly paired, resulting in a negligible EPR signal. Although the Hubbard model first proposed in 1963 to explain the properties of electrons in narrow bands is now an industry in itself, in 1970 its significance was only just beginning to be recognised by the physics community. In work with PhD students, Dan used the Hubbard model to show that an EPR signal could be expected from electrons in narrow surface bands [64].
Meanwhile, the experimental techniques Dan had begun a decade earlier continued to be developed and to bear further fruit. The surface EPR investigations continued and by this time included spectra from oxygen adsorbed on III-V semiconductor surfaces at 77 K, which exhibited hyperfine structure due to the interaction with surface atoms [57]. The theoretical interpretation of the hyperfine structure allowed conclusions to be drawn about the hybridization of the wave functions of the surface atoms and later led to more detailed surface structure models for III-V surfaces [92, 99]. In 1970-1971 Dan's expertise in the surface EPR area was recognised when he was one of relatively few scientists outside the USA to be appointed a NASA Lunar Sample Principal Investigator, in his case to perform EPR and mass spectrometry measurements on rock samples brought back from the NASA lunar expedition [60].
The work on partial splits in semiconductors was also still being pursued [38, 43, 45, 47, 48, 50, 63, 66]. Dan and students had found that the back-to-back surface barriers that formed at the partially healed splits constituted junctions that exhibited electroluminescence in various semiconductors. In 1973, in work with a student from Pakistan enrolled in a PhD, R. U. Kohkar, Dan reported, from partial splits in CdSe, the highest light generation efficiencies yet achieved in that material [69].
On the personal front, another son, Jeremy, was born in 1971. Dan was awarded a DSc by the University of Sydney in 1973. He spent his next sabbatical, in 1974, at the University of California at Berkeley in the Laboratory for Chemical Biodynamics of Nobel laureate Melvin Calvin. It was during that year that he began a completely new research interest, namely solar energy, which had come to the forefront as a result of the sudden increase in the price of oil. He concentrated on photoelectrochemical cells, reasoning that the lower cost could compensate for the much lower efficiency than single crystal silicon (15%-efficient silicon solar cells were already available at that time but were a relatively expensive source of energy).
It is said that Berkeley leaves few persons unchanged, and Dan certainly appreciated the high standards of science, intellect and activity there. After returning from Berkeley, he renewed his resolve to spend more time on creative research and to avoid, as far as possible, the pitfalls of what he termed the pseudo-satisfaction of sitting on university committees. In retrospect, he never regretted that decision.
In 1978, the origin of the EPR signal from Si surfaces was finally laid to rest with a careful study with PhD student Bruno Lemke resulting in the conclusion that the signal was due to microcracks that inevitably formed in the preparation of the surface, whatever method – crushing, cleavage or abrasion – was used [89]. Dan then turned to more novel paramagnetic resonance techniques, including photoconductive resonance and spin-dependent resonance, leading to the discovery over the next several years of new centres at the Si-SiO2 interface [88, 101, 103, 106, 114].
On his next sabbatical year in 1981, Dan began yet another new avenue of research. He spent the year at the Xerox Palo Alto Research Center in the USA working with R. Street, D. Biegelsen and R. Nemanich on amorphous hydrogenated silicon and related matters. This was an area that he was to pursue for many years, along with the existing programmes on photoelectrochemical cells and clean semiconductor surfaces.
There was no avenue for further promotion at UNSW except for appointment to a personal chair. There had been no appointments to personal chairs at UNSW for many years, presumably because the then Vice-Chancellor, Rupert Myers, was opposed to such appointments. After Myers retired, the policy was changed and appointment to a personal chair became possible although very difficult to achieve. Dan was appointed to a personal chair in Physics in 1983. Nowadays, of course, the situation has eased with a regular promotion avenue to professorial rank.
Dan continued with the various research programmes involving both fundamental surface physics and the development of solar cells. His research continued to be aided by substantial Australian Research Council (ARC) support. The solar-cell research required an understanding of the interface between semiconductor/metal and liquid. Dan's investigations with postdoctoral workers led to the first general theory of current flow at an illuminated surface barrier liquid-junction and metal-junction interface without restrictive approximations [115]. This was followed up by application of the theory to the experimental derivation of charge transfer parameters at the semiconductor-electrolyte interface [117, 122]. With the understanding gained from those and other [111, 112] fundamental investigations, Dan and co-workers concentrated on making practical solar cells. The first stable photoelectrochemical cell made from non-single-crystal material was reported from polycrystalline CuInSe2 in 1985 [141], followed by thin-film CuInSe2 in 1986 [145]. It was hoped that the latter material in particular would be the basis of a stable, cost-effective solar cell. By the end of the 1980s, the solar-cells research had produced 8%-efficient solar cells, with a good cost-benefit advantage over more conventional solar cells. Unfortunately there were durability problems that Dan and co-workers identified as being due to interaction with the electrolyte [169]. This was a problem it appeared impossible to overcome and so Dan eventually decided to stop that research programme.
The next major discovery Dan made was with D. H. Zhang from the Department of Physics at Shandong University. They found a field-enhanced conductivity (FEC) in doping-modulated superlattices of amorphous hydrogenated silicon consisting of repetitions of layers of n-type, intrinsic and p-type doped material that are sometimes called nipnip... structures. The FEC consisted of an increase in the conductivity by three orders of magnitude after application of low electric fields (20-100 Vcm-1) [149]. The nipnip... structures were grown in Dan's laboratory by radio-frequency decomposition of silane doped with phosphine or diborane for the n and p layers, respectively, and were about ten times larger than previous structures grown by others. A series of papers on various aspects of amorphous hydrogenated silicon ensued [150, 152, 154-158, 161, 168, 171, 173, 174, 179, 182, 184, 199, 200, 205, 224].
Dan's first marriage came to an end in 1987. The following year, he spent a period of sabbatical leave, with assistance from the USSR-Australia Scientific Exchange Agreement, with A. A. Chernov at the USSR Academy of Sciences Institute of Crystallography in Moscow. After surmounting some bureaucratic difficulties, he married his second wife, Tamara Golubeva, whom he had met earlier in Moscow while at an anti-nuclear-weapons conference to which he had been invited by the office of Premier Gorbachev. During this part of his sabbatical leave, Dan performed calculations in collaboration with A. A. Chernov on the energy required for the conversion between the different structures on Si surfaces [170].
The latter part of his 1988 sabbatical was spent as a Brittingham Visiting Professor at the University of Wisconsin in Madison, working with Max Lagally. There a daughter Alice was born, also in a snowstorm. The sabbatical at the University of Wisconsin provided Dan with the opportunity to return to his lifelong interest: the study of cleaved semiconductor surfaces, particularly using LEED. For the Si(001) surface, the then currently favoured model was one involving double bonds between the surface atoms that had been proposed by Pandey (1981). For other Si surfaces, Dan's original rumpled-surface model was still a viable option. In all cases there were still experimental data that were difficult to fit to any of the models. With Max Lagally, Dan proposed a radical solution for the (111) surfaces, namely the 'three-bond scission model' [165]. The (111) planes in the diamond and zinc-blende semiconductors consist of pairs of planes coupled by a single bond alternating with pairs of planes that are coupled by three bonds. It had always been assumed that these semiconductors cleaved by breaking the single bonds between a pair of (111) planes of the first type. Haneman and Lagally argued that it was energetically favourable for the surfaces joined by three bonds to be exposed by cleavage. They noted that this type of rupture regularly occurs in the formation of dislocations in those semiconductors and gave other arguments in support of their contention. The (111) surfaces exposed by breaking the three bonds would have a different atomic arrangement from the surfaces exposed by breaking a single bond, which led them to propose new models for the (111) surfaces of the diamond and zinc-blende semiconductors. The models they proposed for the surface structure resembled a model proposed many years earlier by Seiwatz (1964) but it now followed naturally from the different surface arrangement on a (111) surface exposed by the three-bond scission and did not require the migration of adatoms as proposed by Seiwatz. During his time at Wisconsin, Dan also performed further LEED measurements on the Si(111) surface cleaved and measured at elevated temperatures [172] that shed light on calculations he had been performing in collaboration with A. A. Chernov on the conversion between the different structures on the Si surface in the earlier part of his sabbatical year.
After his return to Australia in 1989, Dan continued his previous interest in amorphous Si and the completion of the work on polycrystalline materials for photoelectrochemical solar cells. In 1990, he was elected to the Fellowship of the Australian Academy of Science. Dan also continued his interest in cleaved semiconductor surfaces, this time by conceiving an entirely novel method of obtaining more information about the rearrangement of atoms on the two new surfaces created by the cleavage. The motivation of the experiment was that the surface reconstructions predicted by either Dan's rumpled-surface model or Pandey's model involved changes in bond energies and it was reasonable to suppose that some of the energy might be released in the form of electromagnetic radiation. In 1991 he and postdoctoral fellow Neil McAlpine set about finding out whether, indeed, the cleavage of single-crystal Si in vacuum was accompanied by the emission of light. The amount of radiation emitted was very small and the experimental detection and confirmation of the origin of the cleavage luminescence was an experimental challenge, but one they were able to meet. Thus a significant innovation in the study of cleaved semiconductor surfaces was reported in early 1991 [176]. This method was used over the next few years to measure for the first time the indirect surface-state band gap on Si(111) [194] (the direct band gap was known from more conventional experiments) and was extended to other semiconductor surfaces [187, 198]. The cleavage of Si was further investigated by the observation of a voltage produced by the cleavage of Si [204], a temperature rise on cleavage [221] and the emission of ions and electrons on cleavage [231].
Apart from pursuing his work on cleaved semiconductor surfaces, Dan received considerable funding from the ARC during the 1990s to study the potential for producing efficient electroluminescence in Si from structures formed by processing the Si surface by new methods. He obtained promising results from porous Si (produced by anodic oxidation of Si in hydrogen fluoride solution) [188, 202, 203, 216, 232, 241-245], lightly spark-processed Si [212, 223, 227, 233], laser-grooved Si [229] and mechanically damaged Si [230].
Dan's next period of six months' sabbatical leave was spent in Berlin, working with H. Tributsch at the Hahn-Meitner-Institut. There he made his first scanning tunnelling microscopy measurements on semiconductor surfaces. Also, he was able to see the house in which he was born, because it was one of the few pre-war buildings left standing in Berlin.
In 1995 he spent another six months' sabbatical leave at Berkeley, this time working with G. Somorjai. In 1996 Dan turned 65 but did not feel the slightest interest in retirement, as he remained interested in science, was active and successful in publications, conferences and research grants, and felt that he was providing useful training to research students (although, to his regret, not enough Australian ones). The Australian Government had introduced legislation making forced retirement at the age of 65 illegal. Some universities had mounted a court challenge to the legislation and Dan was pleased that they had lost. He did reduce his undergraduate teaching at this time by using funds to 'buy out' some teaching and marking duties, but he retained some lecturing duties. He continued to minimize local bureaucratic involvements, which not only consumed time but, it seemed too him, 'had a noticeable ageing effect on those who were significantly involved in that way'.
Although Dan continued to look after his fitness, eventually advancing Parkinson's disease led to his retirement in 1998 from the university in which he had been employed for thirty-seven years. He died on 13 December 2002, survived by his sister Sylvia and brother John, his first wife Rose and their daughter Daphne, twin sons Andrew and Neal and son Jeremy, and his second wife Tamara and their daughter Alice and son Bernard.
Apart from the research described above, Dan's professional life was notable for his role in postgraduate supervision. He usually had several PhD students working in his laboratory at any one time. On most days, he would spend time with each student in turn, turning his mind to the problems of their particular project somewhat like a grand master playing multiple boards at a chess exhibition. The following is a partial list of PhD students whom he supervised: Ron MacDonald, Mui Fatt Chung, Graeme Russell, Gus Taloni, John Grant, Rahmat Kohkar, John Ridgway, David Miller, David Wheeler, Bruno Lemke, Bob Calvert, George Mendz, K. de Silva, Steven Hinckley, Joseph Szot, Rita Kristensen, Chris Kaalund, Bo (Hebei) Chen, Reza Dariani, Dongguanng Li, Mohammed Jafar, Siyong Wu, Wei Li, V. A. Kuztnetsov, Jinning Yuan.
Dan made significant contributions to his discipline in other ways. He was a member of the international advisory committees and steering committees for the meetings of the two major conferences related to surface physics from their inception: the International Conference on Solid Films and Surfaces (ICSFS) that met every three and later every two years from 1978, and the International Conference on the Structure of Surfaces (ICSOS) that met every three years beginning in 1984. He organized ICSFS-3 in Sydney in 1984. He was also a member of the international advisory committees of various meetings of the International Conference on Thin Films, the International Conference on Superlattices, Microstructures and Microdevices and the International Symposium on Atomically Controlled Surfaces and Interfaces. He was the Australian representative on the Surface Science Division of the International Union of Vacuum Science Techniques and Applications (IUVSTA) and an elected member of the IUVSTA Solid State Division Committee in 1984 and 1986. He was Chair of the Solid State Division of the Royal Australian Chemical Institute, 1982-1984. He served as a member of the Australian Academy of Science's National Committee for Physics from 1987 to 1993. He was a member of the editorial board of the journal Physics of Low-Dimensional Structures from 1992. Dan also left a legacy to the scientific community through the invited review articles that he wrote covering each of the main research areas in which he worked, including the clean surfaces of semiconductors [76, 125, 151] resonance techniques in the study of surfaces [74, 75, 80, 135] and materials for photoelectrochemical solar cells [96, 107, 159]. His review of the Si(111)-7 ¥ 7 structure [151] was referred to in the history of twentieth century physics published by the American Physical Society and the Institute of Physics (Cochran 1995: p. 470).
As already mentioned, Dan received recognition of his achievements in a number of ways, including Fellow of the Australian Academy of Science (1990); Official Guest of the USSR Academy of Sciences (1983); Official Guest of the Chinese Academy of Sciences (1986); Fellow of the Australian Institute of Physics; and Fellow of the Royal Australian Chemical Institute.
Dan is remembered by his colleagues and his many postgraduate students as a practical, 'down-to-earth' physicist who seemed to have a knack for asking the right question. Sometimes his questions were asked to stimulate new lines of enquiry to pursue, and an immediate answer was not expected. But if Dan felt that a question could be answered now, he was not afraid either in colloquia or in conversation to persist with that question. This would often elicit a very enlightening explanation of the physics and the problems involved, to the benefit of all present. In persisting with his questions, as well as by his research and teaching, Dan did a lot to promote a deeper understanding of physics among his colleagues and students.
This memoir was originally published in Historical Records of Australian Science, vol.18, no.1, 2007. It was written by:
The authors acknowledge the assistance of Andrew Haneman who also supplied a biographical memoir written by Dan Haneman. The memoir was invaluable in the preparation of this article and in some places the present article closely follows the wording of the memoir.
© 2024 Australian Academy of Science
