Showing papers in "Contemporary Physics in 1981"
TL;DR: In this paper, the authors present a method for writing patterns in thin films of electron sensitive material using a finely focused (sub-micrometre diameter) electron beam, which can be generated with great accuracy by combining electrical scanning with interferometrically monitored mechanical motion.
Abstract: Electron beam lithography means writing patterns in thin films of electron sensitive material using a finely focused (sub-micrometre diameter) electron beam. By combining electrical scanning with interferometrically monitored mechanical motion, very complex patterns can be generated with great accuracy; for example, a pattern containing one-micrometre features can extend over 100 mm with a positional accuracy of 025 μm. In the manufacture of integrated circuits this technique is used for generating masks which are then projected optically onto silicon wafers which are coated with photosensitive resists. For making circuits with sub-micrometre features the resist-coated wafer can be exposed directly with the electron beam; however this is slow because the electron beam exposure is point-by-point and there are limits to electron beam intensity and resist sensitivity. Overcoming this limit is possible using techniques which allow the exposure of many points simultaneously but such techniques are not...
129 citations
TL;DR: In this article, the authors present an overview of the essential features of the laser systems used to generate such plasmas followed by a summary of some concepts in plasma physics necessary for their proper interpretation, and the theory of the evolution of the plasma is presented in terms of a hydrodynamic model and the relationship between laser irradiance and plasma temperature is discussed.
Abstract: When the output of a typical Q-switched laser is focused onto a solid target, a short-lived, localized plasma, characterized by very high ion and electron densities and by very high temperatures, is formed. The present article begins with an outline of the essential features of the laser systems used to generate such plasmas followed by a summary of some concepts in plasma physics necessary for their proper interpretation. The theory of the evolution of the plasma is presented in terms of a hydrodynamic model and the relationship between laser irradiance and plasma temperature is discussed. Several of the more important methods used for studying plasma properties, including inter-ferometry, mass-spectrometry and optical and X-ray spectroscopy, are described and the results for some typical plasmas are presented.
76 citations
TL;DR: A simple physical explanation for the formation of Cooper pairs in a superconducting metal, for the origin of the attractive force causing the binding of the pairs, and for the forming of a degenerate Bow gas by the Cooper pairs was given in this article.
Abstract: A simple physical explanation is given for the formation of Cooper pairs in a superconducting metal, for the origin of the attractive force causing the binding of the pairs, for the forming of a degenerate Bow gas by the Cooper pairs, for the finite energy gap that prevents the ensemble of electrons from changing its quantum state at low temperatures, and for the existence of permanent currents in a superconducting wire.
63 citations
TL;DR: The phenomenon of lattice relaxation, namely, that the atomic configuration surrounding a localized center in solids changes with its change of electronic state, leads to various forms of multiphon as discussed by the authors.
Abstract: The phenomenon of lattice relaxation, namely, that the atomic configuration surrounding a localized centre in solids changes with its change of electronic state, leads to various forms of multiphon...
49 citations
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TL;DR: In this paper, experimental and theoretical work on the spectrum of ice has been carried out, and two features arising from translational lattice vibrations and symmetric O-H stretching have received much attention.
Abstract: This article reviews experimental and theoretical work on the spectrum of ice. Its features in the radiofrequency region arise from the reorientation of water molecules at lattice sites where strong thermal excitations of a molecular vibration produce a defect. The large permittivity and relaxation time in ice are consistent with our knowledge of its structure. The microwave region has been less extensively studied, but enough information is available to determine how the molecular polarizability of a water molecule in ice depends upon temperature and volume. In the infrared region, two features, arising from the translational lattice vibrations and symmetric O-H stretching, have received much attention, and progress is being made towards understanding them theoretically. The visible and ultraviolet regions show no distinctive features, and the absorptivity in this region is small. The entire spectrum of ice is, of course, useful for studies of many natural phenomena, but the features in the radi...
26 citations
TL;DR: In this article, a simple theoretical formulation, based on the coupled Maxwell-Schrodinger equations, is described, and simple expressions for observable output parameters are given, valid in experimentally relevant regimes.
Abstract: This article reviews the present status of superradiance in atoms and molecules. The introductory section describes the important physical properties of superradiant emission, and presents the important experimental features. A simple theoretical formulation, based on the coupled Maxwell-Schrodinger equations, is described. Simple expressions for observable output parameters are given, valid in experimentally relevant regimes. These results are compared with superradiance experiments performed at a wide range of wavelengths in numerous laboratories since 1973. While the principal features of superradiance are generally agreed upon, details of the initiation of the radiation process and of the observed ringing are still under study.
14 citations
TL;DR: In this paper, the development of optical pumping from the ideas first elaborated by Kastler in 1950 is traced, including the general characteristics of optical pump, the optical magnetization of gases and vapours, spin exchange, metastability exchange, orientation by collision, multiple quantum resonances, atomic coherences, quantum beats and dressed atoms.
Abstract: This article traces the development of optical pumping from the ideas first elaborated by Kastler in 1950. It deals with the general characteristics of optical pumping, the optical ‘magnetization’ of gases and vapours, spin exchange, metastability exchange, orientation by collision, multiple quantum resonances, atomic coherences, quantum beats, and dressed atoms: and concludes with a note on laser spectroscopy.
12 citations
TL;DR: In this article, the authors describe the principles behind the first NSE spectrometer (at the Institute Laue-Langevin, Grenoble, France) and, as an example of one of its applications on polymer chain dynamics are presented.
Abstract: The neutron spin-echo (NSE) spectrometar provides the highest energy resolution available in neutron scattering experiments. The article describes the principles behind the first NSE spectrometer (at the Institute Laue-Langevin, Grenoble, France) and, as an example of one of its applications, some recent results on polymer chain dynamics are presented.
11 citations
TL;DR: In this paper, the tunnelling-state model was used to explain low-temperature thermal properties of amorphous materials, including the thermal conductivity and thermal capacity.
Abstract: This brief review of the tunnelling-state model explains the observed low-temperature thermal properties of amorphous materials. Below 1.0 K, the amorphous materials have, over and above contribution by phonons, a specific heat capacity c that varies almost linearly with temperature; and the thermal conductivity k is approximately proportional to T2 , becoming almost independent of T above 1.0 K. This behaviour is very different from that of crystalline materials, for which c α T 3 and k α T 3 in this range. A broad band of localized excitations is apparently an intrinsic characteristic of the amorphous state. The tunnelling-state model for these localized excitations can explain qualitatively the various unusual low-temperature properties found in amorphous materials, even though no physical description of the tunnelling entity for any material is available.
10 citations
TL;DR: The electron microscope was conceived and built in the Technical University of Berlin some 50 years ago as discussed by the authors, and further development took place in university laboratories, where significant contributions came to be made in the Cavendish in respect of high voltage operation and the improvement of resolution.
Abstract: The electron microscope was conceived and built in the Technical University of Berlin some 50 years ago. Much of its further development took place in university laboratories. Some significant contributions came to be made in the Cavendish in respect of high voltage operation and the improvement of resolution. and in microanalytical instrumentation. Part I (Vol. 22, no. (1), pp. 3–36), covering the years 1946–60, included some account of the prehistory of the subject, the exploration of the operation and applications of the first commercial models, the development of an X-ray microscope and, from it, the scanning microprobe analyser. Part II now continues the story, through the two following decades, the conception and construction of a high voltage electron microscope, and then its extension to an instrument capable of atomic resolution.
9 citations
TL;DR: In this article, the authors deal with primary particles of the highest known energies, i.e. 1017-1020eV and deal with the evidence for their existence, their nature and their origin.
Abstract: There falls on the Earth's atmosphere a rain of particles and photons the high energy part of which is termed the Cosmic Radiation. This article is concerned specifically with primary particles of the highest known energies, i.e. 1017-1020eV and deals with the evidence for their existence, their nature and their origin. Such particles are very rare but because they produce many millions of secondaries in the atmosphere they can be readily detected by large counter arrays at ground level. Some of the principal arrays in the world will be described including the giant array at Haverah Park, near Harrogate, England. The latest results on the energy spectrum and the incident directions of the primaries will be given and their astronomical significance critically assessed. Finally, an account will be given of a novel array which promises to make a substantial contribution to our knowledge of primaries of energies even above 1020 eV.
TL;DR: In this paper, the authors describe the mechanisms of electron production and the fundamental properties of the resultant discharge, as seen mainly from the viewpoint of an electricity supply industry, and show that electric discharges can be of great use to mankind or may cause serious problems.
Abstract: The conduction of electricity through a gas manifests itself in various forms. The current in visible. self-sustaining electrical discharges may be as small as micro-amperes for coronas or as large as mega-amperes for arcs. The transformation of a gas from being a good insulator to being a good conductor of electricity occurs when electrons are liberated from neutral gas molecules and liquid or solid surfaces. The article describes the mechanisms of such electron production and the fundamental properties of the resultant discharge. Electrical discharges can be of great use to mankind or may cause serious problems; examples of both are given, as seen mainly from the viewpoint of an electricity supply industry.
TL;DR: The free surface of a solid represents the most radical discontinuity in its structure that one can envisage with crystalline solids and specific surface properties that arise involve a number of challenging physical problems as well as providing opportunities for exploitation in the electronics and chemical industries as discussed by the authors.
Abstract: The free surface of a solid represents the most radical discontinuity in its structure that one can envisage With crystalline solids the specific surface properties that arise involve a number of challenging physical problems as well as providing opportunities for exploitation in the electronics and chemical industries For convenience one may divide these surface characteristics into atomic, electronic and macroscopic effects but, in fact, they are all interrelated As far as atomic structure is concerned the atomic spacing of the surface layer is usually different from that of the bulk Further, the atomic arrangement itself may be different (reconstruction) These differences affect the surface Debye temperature as well as the detailed processes involved in the adsorption of vapours or other deposited species Because the electronic wave-functions are discontinued at the free surface, the electrons have energy states at the surface which are not the same as in the bulk These surface energy s
TL;DR: This paper reviewed the structure of mature tropical cyclones and discussed the physical processes that are important in their genesis and maintenance, and summarized the operational prediction of actual tropical storms by statistical and dynamical methods.
Abstract: Over the past two decades, observational studies using aircraft and satellite data to supplement conventional surface and upper air data have revealed much about the structure of tropical cyclones. During this same period, numerical weather prediction models have been developed to study the dynamics and energetics of these intense, destructive storms. This article reviews the structure of mature tropical cyclones and discusses the physical processes that are important in their genesis and maintenance. Some examples of computer simulation models are presented. Finally, the operational prediction of actual tropical storms by statistical and dynamical methods is summarized.
TL;DR: The radial distributions of the nuclear charge and nuclear matter, or equivalently of the neutrons and protons, are among the most basic of nuclear properties, and substantial advances in our knowledge of these distributions have been made in recent years, both experimental and theoretical as mentioned in this paper.
Abstract: The radial distributions of the nuclear charge and nuclear matter, or equivalently of the neutrons and protons, are among the most basic of nuclear properties. Substantial advances in our knowledge of these distributions have been made in recent years, both experimental and theoretical. Experimentally, the accurate measurements of the differential cross-sections for electron elastic scattering and of the energies of muonic atom transitions, analysed by model-independent techniques, have given very precise charge distributions for many nuclei. At the same time, the elastic scattering of energetic protons by nuclei have been analysed by the Glauber theory and by the optical potential method of Kerman, McManus and Thaler to yield nuclear matter distributions of somewhat lower accuracy.
TL;DR: Transmission computerized tomography and ultrasonic imaging made an initial impact on the diagnostic use of radioisotopes, but since the latter measure and make a visual display of organ function rather than anatomical structure, their use is likely to continue growing.
Abstract: Radioactive isotopes have been increasingly used for medical diagnosis since the late 1940s. The number in common use is surprisingly limited with a few, like 99rnTc1 being used to label several different pharmaceuticals that concentrate in specific organs. Imaging of such organs is probably now the main diagnostic clinical use of radioisotopes but other tests such as bone mass measurement, immunoassay, blood volume determination, neutron activation analysis and whole body radioactivity measurement also require them. Most tests can be satisfactorily performed with a radiation dose to the patient of only about 10 mGy. Transmission computerized tomography and ultrasonic imaging made an initial impact on the diagnostic use of radioisotopes, but since the latter measure and make a visual display of organ function rather than anatomical structure, their use is likely to continue growing.
TL;DR: In this article, the authors consider the global distribution of earthquakes, their size and their frequency of occurrence, and seek the migration patterns and temporal patterns of seismic activity as a means of defining the locations of future seismic hazard.
Abstract: Earthquake risk is the combination of three factors: the earthquake hazard, the loss potential and the vulnerability. To examine the risk it is first necessary to consider the global distribution of earthquakes, their size and their frequency of occurrence. Migratory trends and temporal patterns of activity are sought as a means of defining the locations of future seismic hazard. It is important also to appreciate the kind of damage that is brought about by an earthquake, including the social and economic effects that can follow. Where loss potential is high, in areas of high population density, and where there is a known hazard from earthquakes, it is vital to mitigate the risk by reducing the vulnerability so far as possible. This can best be achieved through earthquake-resistant construction of buildings and other structures, but there are limits to what can be achieved. Consequently earthquake prediction may prove an alternative, complementary approach that could at least save lives. A range ...
TL;DR: A broad general survey of the physics of planetary interiors in these terms, without concentrating in detail on any particular planetary body, is given in this article, highlighting significant areas which could repay future study, as well as to explain what is already understood.
Abstract: Data from space missions of various kinds coupled with those from Earth-based observatories have allowed us to pass beyond the separate study of individual planets to the study of the Solar System as a composite physical system. We can identify those physical principles which are characteristic of planetary bodies over the full range of possible sizes. This article offers a broad general survey of the physics of planetary interiors in these terms, without concentrating in detail on any particular planetary body. The aim is to highlight significant areas which could repay future study, as well as to explain what is already understood. Magnetism will not be included nor will matters involving possible origins of the Solar System.
TL;DR: The 12 member states of the European high energy physics laboratory CERN are considering the construction of a huge new accelerator as mentioned in this paper, which will enable some of their mysteries to be explained.
Abstract: The 12 member states of the European high energy physics laboratory CERN are considering the construction of a huge new accelerator. This article outlines our understanding of the fundamental forces of nature and the subnuclear structure of matter, and describes the accelerator that will enable some of their mysteries to be explained.
TL;DR: The need to minimize the chance of accidents with serious consequences led to pursuit of safety by siting, by containment and by automatic built-in safety mechanisms; these are discussed in this article.
Abstract: The article concentrates mainly on the developing pattern of safety thinking and safety practices which have been brought about by, and in turn have influenced, the growth of modern industrial technology, particularly in the nuclear field. The need to minimize the chance of accidents with serious consequences led to pursuit of safety by siting, by containment and by automatic built-in safety mechanisms; these are discussed. Codes of practice and safety guidelines are becoming linked with more quantitative goals to achieve desired objectives in safety and reliability. This is particularly important in the assessment of major hazards.
TL;DR: In this paper, the authors trace the development of synchrotrons from early cyclotrons, pausing to describe the main principles of their operation as they emerge, and explain in more detail how such large machines are designed, drawing together a consistent whole from a diversity of technical components.
Abstract: This paper is concerned with the synchrotrons and storage rings which accelerate protons and electrons for high energy physics. First we trace the development of these machines from early cyclotrons, pausing to describe the main principles of their operation as they emerge. After briefly introducing the reader to the present generation of synchrotrons, we explain in more detail how such large machines are designed, drawing together a consistent whole from a diversity of technical components. We make no attempt to describe the construction phase but move to the running in where component systems must be made to work together and design principles are put to the test.
TL;DR: The William Herschel Telescope (WHT) as discussed by the authors is the largest optical telescope in the world, with a diameter of 4.2m and a length of 1.5m. But it is not suitable for astronomy applications.
Abstract: Astronomers in Britain have until very recently found it hard to obtain observing time on large optical telescopes. The success of observational X-ray and radio astronomy has revealed an urgent need for first-class telescopes on excellent sites. That need is now being met in Australia and at the new observatory on the island of La Palma, where the Royal Greenwich Observatory is providing three telescopes for the Science Research Council. The largest of these, 4.2m in diameter, is to be named the William Herschel Telescope in commemoration of the great telescope builder and observer.