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In inelastic light scattering experiments we observe for the first time clearly resolved one dimensional (1D) intersubband spin-density excitations. Together with new structure at energies close to the 2D intersubband transitions, these observations display the formation of 1D subbands. The depolarization shift (W dep ) and the excitonic shift (W xc ) can be deduced approximately from our experiments. These shifts are of special interest because they are related to the direct and exchange-correlation terms of the electron-electron interaction. We find ratios of the shifts (W xc /W dep ) of up to 55%

We have recently developed a spectroscopic technique which allows direct measurement of quantum energy levels. The method is based on observation of the capacitance signal resulting from single electrons tunneling into discrete quantum levels. The electrons tunnel between a metallic layer and confined states of a microscopic capacitor fabricated in GaAs. Charge transfer occurs only for bias voltages at which a quantum level resonates with the Fermi energy of the metallic layer. This creates a sequence of distinct capacitance peaks whose bias positions directly reflect the electronic spectrum of the confined structure. Using this “single-electron capacitance spectroscopy”, we map the magnetic field dependence of the ground state energies of a single quantum dot containing from 0 to 50 electrons. Along with a spectroscopic measurement of the dot's ground states, we probe tunneling rates of electrons to individual quantum states. The experimental spectra reproduce many features of a noninteracting electron model with an added fixed charging energy. However, in detailed observations deviations are apparent: exchange induces a two-electron singlet-triplet transition, self-consistency of the confinement potential causes the dot to assume a quasi two-dimensional character, and features develop which are suggestive of the fractional quantum Hall effect.

Using single-electron capacitance spectroscopy, we map the magnetic field dependence of the ground state energies of a single quantum dot containing from 0 to 50 electrons. The experimental spectra reproduce many features of a noninteracting electron model with an added fixed charging energy. However, in detailed observations deviations are apparent: Exchange induces a two-electron singlet-triplet transition, self-consistency of the confinement potential causes the dot to assume a quasi-two-dimensional character, and features develop which are suggestive of the fractional quantum Hall effect.

This paper presents a technique which permits a quantitative spectroscopy of discrete quantum levels in structures containing as few as one electron. The ground state energy in a quantum dot can be measured for an arbitrary number of electrons and followed as a function of magnetic field. The method involves monitoring the capacitance signal resulting from the tunneling of single electrons. In a microscopic capacitor fabricated in GaAs we study the confined states of a single 1 μm disk to which electrons can tunnel from a nearby metallic layer. Charge transfer occurs only for bias voltages at which a quantum level is resonant with the Fermi energy of the metallic layer. This creates a sequence of distinct capacitance peaks whose bias positions can ve directly converted to an energy scale to determine the electronic spectrum of the confined structure. The evolution of the spectrum in magnetic field allows deduction of the nature of the bound states.

We present a technique which permits a quantitative spectroscopy of discrete quantum levels in semiconductor microstructures. The method involves monitoring the capacitance signal resulting from single-electron tunneling. In a microscopic capacitor fabricated in GaAs we study the confined states of a single 1 μm disk to which electrons can tunnel from a nearby metallic layer. Charge transfer occurs only for bias voltages at which a quantum level is resonant with the Fermi energy of the metallic layer. This creates a sequence of distinct capacitance peaks whose bias positions can be directly converted to an energy scale to determine the electronic spectrum of the confined structure. The evolution of the spectrum in magnetic fields allows deduction of the nature of the bound states.

Recent advances in probe design have led to enhanced resolution (currently as significant as ~ 12 nm) in optical microscopes based on near-field imaging. We demonstrate that the polarization of emitted and detected light in such microscopes can be manipulated sensitively to generate contrast. We show that the contrast on certain patterns is consistent with a simple interpretation of the requisite boundary conditions, whereas in other cases a more complicated interaction between the probe and the sample is involved. Finally application of the technique to near-filed magneto-optic imaging is demonstrated.

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, λ, in the near‐field of the sample (

The optical properties of a one-dimensional (1D) electron gas with only one or two occupied subbands have been studied in semiconductor quantum wires, obtained by electron beam lithography and subsequent low-energy ion bombardment of modulation-doped GaAs quantum wells. Large optical singularities have been observed at the Fermi level, both in optical absorption and emission. They disappear at temperatures comparable to the Fermi energy. The 1D singularities are much larger and sharper than in 2D systems due to the lack of certain hole recoil effects in 1D. The experimental data are in qualitative agreement with theoretical results based on the exact diagonalization of finite chains.

We demonstrate that ballistic electrons in ultra-high mobility two-dimensional electron systems can be controlled in ways analogous to the manipulation of photons in optical systems. Among the electron-optical structures we demonstrate are emitters, detectors, absorbers, and refractors. These advances may enable the design of new types of electronic circuits.

The energy and the wave-vector dispersion of single-particle and collective excitations of the one-dimensional (1D) electron gas in GaAs quantum wires have been determined by resonant inelastic light scattering. In the 1D quantum limit the intrasubband plasmon displays the linear dispersion characteristic of 1D free-electron behavior. Quantitative agreement is found with calculations based on the random-phase approximation. In contrast, collective 1D intersubband excitations appear as dispersion-less and have a negligible shift from the single-particle energy

Modulation-doped quantum wire structures have been fabricated in the extreme quantum limit in which only the lowest one-dimensional (1D) subband is occupied by electrons. A pronounced Fermi edge singularity is observed for the first time in the absorption and emission spectra of the 1D electron gas. It has a strong temperature dependence determined by the Fermi energy and is much sharper than in two dimensions. The experimental results agree qualitatively with exact diagonalization studies of finite Hubbard chains.

Nanometer-scale quantum wires have been directly produced using an epitaxial-growth technique. Modulation of the in-plane lattice constant of a GaAs/GaAlAs quantum well, grown over an InGaAs/GaAs strained-layer superlattice, laterally confines the carriers to one dimension. These novel structures are studied by luminescence and luminescence-excitation spectroscopies and by transmission electron microscopy. Large energy shifts and polarization anisotropy are observed. The results compare very well with a theoretical model based on the effective-mass approximation and elastic and phenomenological deformation-potential theories.

In 1908 (as far as we can ascertain), long before he went to see his ‘old friend’ the Keeper of Geology at South Kensington, some time before he met Teilhard de Chardin, Dawson had in his hands the first piece of the skull of Eoanthropus. This piece, we know, had been chemically treated, by iron sulphate, to produce the brown colour, and in the process the bone had undergone the change in its crystal structure revealed by the X-ray diffraction method. This piece was part of the braincase, the ‘coconut’, smashed by the labourers, according to the story the origins of which are by no means clear. Once again a question faces us which raises sharply and finally the issue of Dawson’s complicity. We might put the question as the ‘Piltdown Riddle’:—Was the pit completely barren at the birth of Piltdown Man or did he begin life there as a burial? Was the cranium genuinely in the gravel or had it been planted where the workmen found it? In the first stages of the investigation, before we fully appreciated the artificiality of the iron-staining, we were inclined to regard the skull-case in the gravel as a genuine though not very ancient fossil. The fluorine values, while not really high, taken with the reduced content of organic matter, certainly gave grounds for accepting a semi-fossilized condition in the cranium. So it was presumed at first that the hoax had been based on a genuine discovery of portions of an ancient skull in the gravel, and that the ape jaw and canine and the other animal remains and implements had been subsequently planted. As the investigations went on, stage by stage, this view became untenable. The iron-staining threw serious doubt on the skull’s derivation from the gravel; the sulphate in the bone, in the form of gypsum, is the result of artificial and deliberate chemical treatment, and gypsum does not occur in the Piltdown or Barcombe Mills gravel. The chemical conditions in the Piltdown subsoil and gravel water are not at all such that this unusual alteration in the bone could have taken place naturally in the gravel.

Towards the end of July 1953 a congress of palaeontologists was held in London under the auspices of the Wenner-Gren Foundation. The problems of fossil man were the subject of its deliberations. Java man, Neanderthal man, Rhodesian man, the South African prehumans—all these were given close attention. But Piltdown man was not discussed. Not surprisingly. He had lost his place in polite society. What more could one usefully say about him? Yet, unofficially, the Dawn Man did manage an appearance. Most of those present had not seen the original fossil specimens, so on a tour of the Natural History Museum these were shown along with others housed there. The sight of the actual fragments provoked the familiar tail-chasing discussion. As always there were those who could not feel that the famous jaw really harmonized with the rest, but there were others who took the opposite view. The enigma remained. At the dinner that night Dr. Oakley remarked casually to Dr. Washburn of Chicago and myself that owing to Dawson’s early death in 1916 the Museum had no record of the exact spot where the remains of the second Piltdown had been found. They knew the place—Sheffield Park—but the actual spot or even the field had never been marked on a map. ‘The fact is’, said Oakley, ‘that all we know about site II is on a postcard sent in July 1915 by Dawson to Woodward, and an earlier letter in that year, from neither of which can one identify the position of Piltdown II.’ This was surprising. The second group of finds had done so much to convince many people that the first Piltdown man was by no means an isolated phenomenon. One had imagined that if it were ever thought worthwhile it would be possible to go and excavate the second site. Now it appeared that this had never been done because the second site could not be located, though Woodward had apparently visited it before the second find. This curious piece of information greatly puzzled me.

Almost any single one of the techniques employed in the investigations suffices to reveal the elaborateness of the deception which was perpetrated at Piltdown. The anatomical examination, the tests for fluorine and nitrogen bear particularly good witness to this; even the radio-activity results taken alone, led the physicists to remark on the ‘great range of activity shown by specimens from this one little site’; ‘it is difficult to avoid the conclusion that the different bones in the Piltdown assemblage have had very different geological and chemical histories’. We have merely to take account of the stained condition of the whole assemblage, to realize the thoroughness of the fraud. From the Vandyke brown colour of the unnaturally abraded canine we infer with certainty that it was deliberately ‘planted’. The superficiality of the iron impregnation, combined with the chromium, tells as much as regards the orang jaw. And it is this iron-staining which finally shows that the rest, human and animal, was without doubt, all ‘planted’. The iron-staining has two peculiar features. It seems probable that ferric ammonium sulphate (iron alum) was the salt employed. This salt is slightly acid. The peculiarity of this salt (and, indeed, of any acid sulphate) is that in bone which contains little organic matter such as the cranium of Piltdown I, or Piltdown II, the beaver bones and hippo teeth, it brings about a detectable change in the crystal structure of the bone. In the apatite in which the calcium of the bone is held, the phosphate is replaced by sulphate to form gypsum. This change is quite unnatural, for neither gypsum nor sufficient sulphate occur in the gravels at Piltdown to bring it about. So the iron-sulphate-staining is an integral part of the forger’s necessary technique. He also used chromium compounds to aid the iron-staining probably because he thought it would assist the production of iron oxide. Chromium compounds are oxidizing. The basic strategy underlying the Piltdown series of forgeries now seems reasonably clear. Two main elements in the plan taken together explain nearly all the features of the affair quite satisfactorily.

The objective evidence for the deception at Piltdown was overwhelming. The frauds extended to every aspect of the discovery—geological, archaeological, anatomical, and chemical—so that proof could be adduced three or four times over. Moreover, every time a new line of investigation was applied, it confirmed, as we have seen, what all previous evidence had established. The two Piltdown ‘men’ were forgeries, the tools were falsifications, the animal remains had been planted. The skill of the deception should not be underestimated, and it is not at all difficult to understand why forty years should have elapsed before the exposure; for it needed all the new discoveries of palaeontology to arouse suspicion, and completely new chemical and X-ray techniques to prove the suspicion justified. Professor Le Gros Clark, Dr. Oakley, and I wrote in our report that ‘Those who took part in the excavation at Piltdown had been the victims of an elaborate and inexplicable deception’. Inexplicable, indeed, for the principals were known to us as men of acknowledged distinction and highly experienced in palaeontological investigation. Woodward, in 1912, was a man of established reputation. Dawson enjoyed a solid esteem. Teilhard de Chardin was, of course, only at the beginning of his palaeontological career. Knowing their place in the world of science, we felt sure that these investigators, whose integrity there was not the slightest reason to question, had been victims—like the scientific world at large—of the deception. Arthur Smith Woodward (who was of an age with Dawson) at the time of the discovery had been Keeper of the Department of Geology at the British Museum since 1901, the year of his election to the Royal Society, and had scores of papers of very great merit to his credit. His work on fossil reptiles and fishes was on a monumental scale, and he had also made discoveries in mammalian palaeontology. He was without doubt the leading authority in his own field. His position was abundantly recognized by many awards and by appointment to many high offices—for example, Secretary, and in the Piltdown years successively Vice-President and President, of the Geological Society.

It is unfortunately not possible to follow in any detail every stage of Smith Woodward’s activities at Piltdown. No diaries or note-books exist of the work done, there is nowhere a complete record of the various finds as they were made. Woodward kept copies of very few of his own letters and we have only the letters written to him and now preserved at the British Museum. When the American palaeontologist Osborn came over in 1920, Woodward dictated some notes which help to allocate the various discoveries. Apart from these notes and the one-sided record of the correspondence, there are only the reports in the scientific literature and popular lectures on Piltdown as primary sources. Woodward does not appear in general to have been a secretive man, but over the Piltdown material he went to some lengths to keep the whole affair as quiet as possible until near the time of the public meeting in December 1912. He did not consult any of his colleagues in the Museum about the finds or about the interpretation he was to place on them. Mr. Hinton says that to his colleagues at South Kensington Woodward’s diagnosis of E. dawsoni came as a surprise mingled with some dismay, for there was much scepticism of the new form amongst his museum colleagues, including Oldfield Thomas and Hinton himself. They would have advised caution, he says. Keith knew nothing of the events in Sussex until rumours reached him in November. He wrote asking for a view of the exciting material, but on his visit on 2 December to the Museum he was received rather coldly and allowed a short twenty minutes. But, judging from Dawson’s letters in 1912, it seems fair to say that Woodward was merely seeking to avoid a premature disclosure, for he had decided early on that Piltdown would indeed prove a sensational event. Woodward did not want any of Dawson’s ‘lay’ friends to come along on his first visit to the gravel when he had yet to make up his mind about the real importance of Dawson’s find and of the necessity for systematic excavation.

On 18 December 1912 Arthur Smith Woodward and Charles Dawson announced to a great and expectant scientific audience the epoch-making discovery of a remote ancestral form of man—The Dawn Man of Piltdown. The news had been made public by the Manchester Guardian about three weeks before, and the lecture room of the Geological Society at Burlington House was crowded as it has never been before or since. There was great excitement and enthusiasm which is still remembered by those who were there; for, in Piltdown man, here in England, was at last tangible, well-nigh incontrovertible proof of Man’s ape-like ancestry; here was evidence, in a form long predicted, of a creature which could be regarded as a veritable confirmation of evolutionary theory. Twenty years had elapsed since Dubois had found the fragmentary remains of the Java ape-man, but by now in 1912 its exact evolutionary significance had come to be invested with some uncertainty and the recent attempt to find more material by the expensive and elaborate expedition under Mme. Selenka had proved entirely unsuccessful. Piltdown man provided a far more complete and certain story. The man from Java, whose geological age was unclear, was represented by a skull cap, two teeth, and a disputed femur. Anatomically there was a good deal of the Piltdown skull and, though the face was missing, there was most of one side of the lower jaw. The stratigraphical evidence was quite sufficient to attest the antiquity of the remains; and to support this antiquity there were the animals which had lived in the remote time of Piltdown man; there was even evidence of the tool-making abilities of Piltdown man. In every way Piltdown man provided a fuller picture of the stage of ancestry which man had reached perhaps some 500,000 years ago. Dawson began by explaining how it came about that he had lighted on the existence of the extremely ancient gravels of the Sussex Ouse: . . . ‘I was walking along a farm-road close to Piltdown Common, Fletching (Sussex), when I noticed that the road had been mended with some peculiar brown flints not usual in the district. . . .

The manifestly fraudulent elements in the man-ape combination called Eoanthropus dawsoni are the filed down molars and canine, the Vandyke brown staining of the latter and the iron-coloration of the jaw. Taken with the massive evidence of the complete incompatibility of jaw and cranium, those fabrications assure us of the enormity of the larger deception, the foisting of a spurious fossil human ancestor on to the world of palaeontology. The plot achieved its great success because it provided in the spurious fossil a self-consistent array of evidence and this fitted well with the presumed antiquity of the gravels of the Sussex Ouse; for that antiquity there was supporting testimony in the presence of palaeolithic tools and remains of animals of the earliest phase of the Ice Age. But now with the centre-piece proved spurious, what of its appurtenances? Since the jaw is no fossil, but a recent intrusion and a deliberate one, can we help but suspect these other objects in the gravel, impressive and persuasive as the fossil animals and implements appear on first sight? The club-like bone implement discovered in 1914 ranks next to the skull as the most remarkable of the discoveries at Piltdown. Implements of bone are well-known to have been used in the late Ice Age, for example, by men of the cave-art period. Not only is the Piltdown specimen entirely unique in its shape, but as a primitive tool, which Dawson and Woodward were confident it was, it would rank as by far the earliest ever used; in the words of the discoverers, ‘their opinion was that the working and cutting of the bone were done when it was in a comparatively fresh state’. Moreover, Woodward had identified the bone as one which in all likelihood had been obtained from the femur of a very early species of elephant. Judging from the other elephant and mastodon remains, such an animal would certainly have been in existence in the times of Piltdown man.

It is common knowledge that Dawson did not command high esteem in the archaeological circle of Lewes. Some local archaeologists, on the basis of their personal feelings about Dawson as well as on their long-held, rather low opinion of his archaeological reliability, came to invest the Piltdown discovery with extreme scepticism from the start; objective evidence to back this up, such as St. Barbe, Morris, or Marriott might have offered, there seems to have been none. It is perhaps as well to indicate how Dawson came to acquire his reputation for ‘unreliability’, since it has a bearing both on the standard of his archaeological work and on the quality of his scientific writing on the Piltdown material, activities which we saw provided grounds for genuine surprise in their vagueness and inaccuracy. The local reasons for Dawson’s unpopularity should be assessed as objectively as possible, for it should not be forgotten how solid a reputation Dawson had made with his Wealden collections at the British Museum and how good his standing was with such men as Keith and Woodward. The deliberate avoidance of the great Piltdown discovery in official local circles is quite undeniable. On my first visit of inquiry in August 1953, I had fully expected to see much made of Piltdown in the local museums. The Borough Museum contained nothing but a small picture of an imaginary Eoanthropus presented by Dr. S. Spokes and some Piltdown eoliths presented by Harry Morris. The Barbican Museum, the home of the Sussex Archaeological Society, hard by the Castle keep, is in the street where once lived the famous Dr. Mantell; and in the same street is Dawson’s home, Castle Lodge. Here, too, there were no specimens of Charles Dawson’s on view, but more flints of Harry Morris, including eoliths from Piltdown. A cast of the well-known reconstruction of Piltdown man was displayed along with three enlarged models of teeth—one the molar from Piltdown II and, for comparison, chimpanzee and human molars. The cast and models (and also the picture in the Borough Museum) had all been presented by Dr. S. Spokes in 1928—fifteen years after the world-famous discovery.

On the basis of our preliminary arguments and our anatomical re-examination of the fragments, Mr. W. N. Edwards, the Keeper of Geology of the Natural History Museum, felt justified in allowing the specimens of mandible, cranium, and teeth to be drilled for much larger samples than could ever have been sanctioned hitherto. These larger samples and the use of improved chemical methods guaranteed a high degree of analytical reliability. The drilling itself gave us an encouraging start. As the drilling proceeded, Dr. Oakley and his assistant perceived a distinct smell of ‘burning horn’ when the jaw was sampled, but they noticed nothing of the sort with any of the cranial borings. This subjective indication of some distinct difference between the constitution of jaw and cranium soon gained objective confirmation. The drilled sample from the jaw proved to be utterly unlike those from the cranium. In keeping with the belief in its fossil or semi-fossilized character, the latter produced a fine particulate granular powder, whereas the jaw yielded little shavings of bone, just as did a fresh bone sampled as a control. Here was the beginning of the series of findings which progressively widened the gulf between jaw and cranium. Very soon Dr. Oakley obtained clear chemical evidence to justify fully the strong suspicion of the modernity of the jaw and of the totally distinct origin of the cranium. An improved technique for estimating small quantities of fluorine produced this decisive result. The cranial fragments of site I were found to contain fluorine in a concentration of 0.1 per cent., a value somewhat similar to that of specimens of known Late Ice Age. The jaw and the three teeth on the contrary gave much lower figures, at levels below 0.03 per cent., values well within the range of known modern and fresh specimens. Indeed, these values are on the borderline of the sensitivity of the method. The fluorine test gave its verdict twice over. For the two cranial fragments from the second Piltdown site contained a fluorine concentration of 0.1 per cent, and the isolated molar which went with these fragments contained less than 0.01 per cent.

In 1941 Mr. F. W. Thomas, on the staff of the News Chronicle and the Star, was advised to evacuate from Seaford and went to live in Lewes where he and his wife stayed with Mr. A. P. Pollard, Assistant Surveyor of the Sussex County Council. One day as they were touring round Chailey they found themselves near the famous Piltdown site. They had some discussion of the gravels and the circumstances of the finds. When his visitor remarked on the great evolutionary importance of the Piltdown man he was extremely surprised at his guide’s reply, which was that there was really nothing in the great discovery, and that he was entirely sceptical of it all. Mr. Pollard did not add anything more at that time. From Mr. Salzman (now President of the Sussex Archaeological Society) I learnt in August 1953 that Mr. Pollard was well acquainted with the gravels and gravel workings in the Lewes region, and that he might be able to help me with my inquiries on the history of Piltdown. When I explained I was interested in the discovery, Mr. Pollard immediately asked me whether I had any reason to distrust the discovery, and on my admitting as much, he said, ‘I am not surprised. I believe it to be a fraud. At least, that is what my old friend Harry Morris used to say.’ What Mr. Pollard had to tell me he had learnt from Harry Morris, a bank clerk and keen amateur archaeologist, whose acquaintance he had first made on taking up his post at Lewes in 1928. Morris and he became close friends, and he was Morris’s executor and saw to the donations of the latter’s collection of eoliths and other flints to the two Lewes museums. Morris in 1912 or 1913, right at the beginning, had come to the conclusion that the flints at Piltdown were not genuine. When he first saw the flints, he at once rejected them because ‘Harry Morris knew every flint bed and gravel bed in the district’.

To Professor Teilhard de Chardin the idea that either Dawson or Woodward was in any way wittingly implicated in this business is completely unthinkable. He holds both of these men in the greatest respect, and indeed is inclined to doubt whether a real hoax occurred at all. It seems to him not impossible that the pit at Barkham Manor was used as a rubbish dump where, over a course of years, all sorts of objects including bones from some discarded collection could have been deposited. The heavily iron-bearing water of the gravel would soon stain the bones dark brown (for Professor Teilhard says that fresh bone left in the water of the Weald does stain easily). To be sure, the queer accumulation must have come from some collector’s hoard! But this suggestion of a rubbish dump leaves, of course, too much unexplained and far too many coincidences. It would be an amazing accident that would bring together an, unusual cranium, the jaw, the remarkable canine, a bone implement of unique character, a number of flints of spurious workmanship (one of which is stained with chromate), and bones partly changed to gypsum and radio-active fossil teeth of a sort never found in England! That all this curious medley, this ‘accidental’ assemblage, should be uncovered in a particular sequence—as Sir Arthur Keith said to us, cas if to confute me personally!’—is straining our acceptance of coincidence too much. Miss Kenward, who lived at Barkham Manor for many years, is positive that the pit was not a general rubbish dump and that the gravel was being dug from an unbroken surface. Lady Smith Woodward, too, rules out the suggestion. There is nothing to commend this rubbish dump theory, for we have seen that hardly anything of the whole collection of material can with certainty be said to have come from gravel originally, although this does not rule out the possibility that at least the cranium, even stained as it is, may not have been genuinely found in the pit and that after treatment it was redeposited in the gravel pit.

Dawson had received widespread recognition, but died too soon to be given any special award from a scientific body. Twenty years later his achievement was commemorated by the erection of a memorial stone at the site of the gravel pit at Barkham Manor. Sir Arthur Smith Woodward had taken the initiative in this and borne most, if not all, of the expense. The unveiling was done, at his request, by his old friend Sir Arthur Keith at the well-attended ceremony on 22 July 1938. Keith gave a brief but eloquent oration. He dwelt on the wonderful achievement of the keen-sighted amateur Dawson, an achievement which he likened in the history of discovery to that of the French lock-keeper, Boucher de Perthes—the first man, three-quarters of a century ago, to recognize clearly the human workmanship of the Ice Age flint hand-axes of the Somme. The discovery at Piltdown ranked worthily, too, with that of Neanderthal man discovered in 1857, the first known of all fossil men. These discoveries had encountered tremendous opposition before acceptance was won. The claims of Perthes had brought incredulity and set the scientific world a momentous problem, and only after years of stormy argument were these claims conceded; the discovery of Neanderthal man likewise brought disagreement and controversy. But this fossil form was accepted in the end. As Keith said, then came Dawson’s discovery, and this brought the greatest problem of all. But Keith did not go on to claim that all was now well with ‘the earliest known representative of man in Western Europe’, of which he had just finished a laborious re-study. A puzzle it had always been and a puzzle it was still. Keith could not hide his underlying doubt, and ten years later he expressed it again in the Foreword which he wrote at Lady Smith Woodward’s request to Woodward’s own book, The Earliest Englishman, published posthumously in 1948. He declared: ‘The Piltdown enigma is still far from a final solution.’ Why should Keith still express such doubt and bewilderment? But it was no longer surprising.

For decades the remains of fossils found in Piltdown, England were believed to come from a "missing link," a creature with a human cranium and an ape's jaw. Dr. Weiner shows how he discovered the truth about these remains, and went on to expose one of the world's greatest scientific frauds.

A hybrid near‐field/fiber laser probe has been developed for high flux, reflection mode optical imaging of surfaces on a subwavelength scale. Spatial resolution of ∼100 nm (i.e., ∼λ/10 at λ=1060 nm) has been achieved simultaneously with signals of ∼1014–1015 photons/s, an improvement of ∼103–104 over earlier designs. The probe thus represents an important step in the development of advanced near‐field transducers for high bandwidth applications such as high density data storage.

Modulation‐doped GaAs/AlGaAs quantum wires have been fabricated using electron‐beam lithography followed by electron‐cyclotron resonance reactive ion etching to selectively deplete the electron gas. This technique has the advantages of low damage to the quantum well, strongly anisotropic etching, and reproducible control over the etch depth. The quantum wires exhibit high photoluminescence efficiencies when etched as close as 200 A to the electron gas. The fundamental gaps show the large optical red shifts associated with strongly spatially indirect transitions. The spacings between one‐dimensional subbands determined from inelastic light scattering measurements are larger than 2 meV.

We demonstrate the use of an ultrathin (≊5 nm) Si layer deposited on InP substrates as a mask in selective area epitaxy of InGaAs by metalorganic molecular beam epitaxy. Patterns of varying shapes and sizes, from 5 to 0.5 μm, were written on the mask by focused Ga ion beam and etched by Cl2. The growth rate of InGaAs was studied by scanning force microscopy using stripes with guard rings spaced as close as 0.5 μm from the stripes. A small increase in the growth rate was detected only when the feature size was lower than 5 μm, and the growth rate was not affected by the presence of the guard rings. This shows that precursor material is being transferred from the slow growing {111}‐planes to the (100)‐plane, and that migration of species from the Si mask to the growing areas is negligible.

A distance regulation method has been developed to enhance the reliability, versatility, and ease of use of near‐field scanning optical microscopy (NSOM). The method relies on the detection of shear forces between the end of a near‐field probe and the sample of interest. The system can be used solely for distance regulation in NSOM, for simultaneous shear force and near‐field imaging, or for shear force microscopy alone. In the latter case, uncoated optical fiber probes are found to yield images with consistently high resolution.

We report the fabrication of strong Bragg reflectors embedded into fiber matched silica on silicon waveguides. First order gratings are dry etched into the waveguide core and are covered with a thin Si3N4 layer prior to cladding deposition. Reflection bands 225 A wide for TE and 193 A wide for TM polarizations are obtained with 200 A Si3N4 cover layers. The TE and TM spectra are overlapping, resulting in nearly polarization independent Bragg reflectors.

Heterostructures of InGaAs/InP have been grown selectively through windows in SiO2‐masked InP substrates using metalorganic molecular beam epitaxy. The structures show high cathodoluminescence efficiency for window sizes down to 5 μm. A significant red shift, consistent with compressive lattice strain, and reduced intensity are observed for smaller features. Anomalous growth is observed near the edges of the windows. Selectively grown InGaAs/InP p‐n junctions and bipolar transistors exhibit excellent electrical characteristics after removal of 1–2 μm of edge material.

We demonstrate the novel application of the scanning tunneling microscope to find and probe the electronic transport properties of single semiconductor nanostructures at temperatures from room temperature to as low as 1.5 K. The current‐voltage characteristics of InGaAs/InAlAs resonant tunneling nanostructures clearly show negative differential resistance. From the dependence of the current on cross‐sectional area the lateral depletion is estimated to be 300 A.

In near-field scanning optical microscopy, a light source or detector with dimensions less than the wavelength (lambda) is placed in close proximity (lambda/50) to a sample to generate images with resolution better than the diffraction limit. A near-field probe has been developed that yields a resolution of approximately 12 nm ( approximately lambda/43) and signals approximately 10(4)- to 10(6)-fold larger than those reported previously. In addition, image contrast is demonstrated to be highly polarization dependent. With these probes, near-field microscopy appears poised to fulfill its promise by combining the power of optical characterization methods with nanometric spatial resolution.

In this article, we review the recent progress on GaAs MOSFET's using in-situ MBE-grown Ga2O3(Gd2O3) as the gate dielectric. Both depletion-mode (D-mode) and inversion-mode (I-mode) GaAs MOSFET's with negligible drain current drift and hysteresis are demostrated. The absence of drain current drift and hysteresis indicates that the excellent stability of the oxide and low oxide/GaAs interface state density have been achieved. The drain current density and transconductance are about one order of magnitude higher than the best previous reported data in the literature for an inversion-mode GaAs MOSFET. Excellent high frequency and power performances were also measured from the depletion-mode devices. These improvements are attributed to the excellent Ga2O3(Ga2O3) oxide properties and novel processing techniques.

We have developed a complete lithographic process combining focused ion beam writing, dry etching, and molecular beam epitaxy for in situ preparation of buried InP‐based microstructures. A focused ion beam is used to locally remove an ultrathin oxide imaging layer grown in situ on the surface of InP. The pattern is transferred into the underlying semiconductor by free Cl2 etching with the patterned oxide layer acting as an etch mask. After removal of the oxide mask, GaInAs/InP heterostructures with excellent morphology and high luminescence efficiency can be grown on the patterned substrate. The entire process of mask formation, lithography, and regrowth can be carried out in situ repeatedly, and used for creating fully buried microstructures.

We have investigated the dependence on the magnetic field of the optical absorption and emission of a one-dimensional (1D) electron gas in GaAs quantum wires with one occupied subband. Spectra show a strong Fermi-edge singularity that narrows as the Fermi energy in the wires is continuously reduced by the enhancement of the effective mass in a perpendicular magnetic field. At high fields, when the cyclotron energy is larger than the 1D subband spacing, the lowest optical transition splits into a doublet due to the spatial modulation of the Landau levels by the wire potential.

Inelastic light scattering spectra of the one-dimensional electron gas in GaAs quantum wires embedded in a strong perpendicular magnetic field show long-wavelength collective excitations and display multiple structures that indicate the magnetoroton density of states. The observed shift of the q∼0 intersubband magnetoplasmons from the cyclotron frequency is the signature of 1D behavior. At low temperatures spin polarization of the 1D system is revealed by the exchange enhancement of spin-flip excitations

We review recent inelastic light scattering studies of elementary excitations of the one-dimensional (1D) electron gas in the quantum limit, when only one or two 1D subbands are occupied by electrons. The light scattering method gives precise determinations of the energies and wavevector dispersions of the excitations. We find that the intrasubband plasmon displays the linear dispersion characteristic of 1D free electron behavior. Quantitative agreement is found with calculations based on the Random Phase Approximation (RPA). In contrast, collective 1D intersubband excitations appear as dispersionless and have energies very close to that of singleparticle excitations. At large wavevectors we observe the anticrossing behavior of the intrasubband plasmon and the intersubband collective mode.

We have fabricated single quantum wires and quantum wire arrays of nanometer scale lateral dimensions. The wires are produced by two steps of epitaxial growth in orthogonal directions. We utilize the concept of pseudomorphic growth of lattice mismatched epitaxial layers to generate strain modulation within the plane of a conventional quantum well. The strain modulation, as large as 2%, modulates the electronic band structure for carrier motion parallel to the quantum well plane. These potential modulations which are of order 0.1 eV, confine carriers laterally to regions comparable in size to the size of a quantum well. We present in this work optical studies of these one dimensional systems by means of low temperature cathodoluminescence, photoluminescence, photoluminescence excitation and time resolved spectroscopies. We analyse our observations using a new multi-band effective mass and deformation potential model. The measured optical transitions and polarization selection rules agree well with the model. In particular, we find that electrons and light holes are laterally confined to the same region while heavy holes are spatially separate from them. Finally, we demonstrate a novel p-i-n linear junction which provides a means to electrically contact these one-dimensional quantum structures.

Modulation doped quantum well wires have been fabricated in the one-dimensional (ID) quantum limit, where only the first ID band is occupied. Novel properties have been found in the optical spectra. Strong Fermi edge singularities are present which markedly differ from the 2D case due to the hole recoil and phase space filling properties unique to ID. The elementary excitations of the ID electron gas have also been investigated, and the ID intraband plasmon dispersion relation has been measured. Very good quantitative agreement is found with the linear dispersion expected for ID systems.

We observe the capacitance signal resulting from single electrons tunneling into discrete quantum levels. The electrons tunnel between a metallic layer and confined states of a single disk in a microscopic capacitor fabricated in GaAs. Charge transfer occurs only for bias voltages at which a quantum level resonates with the Fermi energy of the metallic layer. This creates a sequence of distinct capacitance peaks whose bias positions directly reflect the electronic spectrum of the confined structure. From the magnetic field evolution of the spectrum, we deduce the nature of the bound states.

Selective area growth is used in the fabrication of Si epitaxial devices such as bipolar transistors. This growth technique facilitates the preparation of very complex self-aligned and buried transistor structures. Selective growth has been investigated in the III-V materials, without, however, any significant results pertaining to the optical or electrical quality of the material grown, or device results. In this work, we investigate selective growth of InP and GaInAs on S'02-masked InP substrates using metalorganic molecular beam epitaxy (MOMBE). Group Ill and V elements are derived from triethylgallium and trimethylindium, and AsH3 and PH3 respectively. Excellent selectivity is achieved in the temperature range from 5 10 to 540 deg C.

In near-field scanning optical microscopy (NSOM), a subwavelength source and/or detector of visible light is placed in close proximity (~λ/50) to a sample and raster scanned to generate images with a resolution well beyond the diffraction limit. Our recent development1 of new near-field probes has resulted in a resolution of ~12 nm (~λ/43) concomitant with signals sufficient for dynamic imaging or adapting powerful optical contrast mechanisms to the near-field regime. Both transmission and reflection geometries have been demonstrated, indicating the applicability of NSOM to such diverse areas as pathology and semiconductor characterization. Luminescent and magnetooptic samples have been imaged, as well as phase objects (e.g., photoresist). Such results indicate that the versatility of NSOM should approach that of conventional far-field optical microscopy, because it retains many of the same advantages (e.g., noninvasiveness, informative contrast mechanisms, speed, low cost, and ease of use) while offering unprecedented spatial resolution.

Spatial light modulators (SLMs) designed to replace photomasks for optical lithography have been designed, fabricated, and tested. These microelectromechanical devices are fabricated with alternating polycrystalline Si and sacrificial SiO2 layers that are patterned by a 193nm wavelength scanner to dimensions as small as 150nm. Aerial image simulations were used to define the mechanical requirements of the devices. Piston motion of electrically actuated devices was measured with an optical profilometer. The measurements were fit to a simple equation to within 1nm precision, which is adequate for defining 50nm features lithographically. Transient response measurements show that one version of the SLM responds to actuation as quickly as 20μs, fast enough for current 193nm wavelength excimer laser sources.