bluuebunny/crossref_metadata_2025 huggingface dataset:
P-N iunctions in semiconductors
Authors: Balkanski M , Wallis R F
Published: November 2023

We have seen in Chapter 5 that impurities of different types can be introduced into bulk intrinsic semiconductors. If the impurity is the source of free charge carriers that are negatively charged electrons, the material is designated n-type, whereas if the impurity is the source of positively charged holes, the material is designated p-type. In n-type material the principal impurities are donors, and the majority carriers are conduction electrons arising primarily from the ionization of donor atoms. In p-type material, the principal impurities are acceptors, and the majority carriers are holes created by the transfer of electrons from the valence band to acceptor atoms leaving positively charged holes in the valence band. In both types of material at nonzero temperature, conduction electrons and holes arising from the excitation of electrons across the energy gap are also present. The thermally excited holes in n-type material and conduction electrons in p-type material are called minority carriers.
Transport properties of heterostructures
Authors: Balkanski M , Wallis R F
Published: November 2023

There are two aspects of heterostructures contammg two-dimensional systems that make their transport properties significantly different from those of three-dimensional structures. First, heterostructures have a large anisotropy of their transport properties in the directions parallel and perpendicular to the growth axis. Second, much higher mobilities can be achieved in such structures.
Symmetries in Quantum Mechanics
Authors: Stancu Fl
Published: November 2023

Group theory is a branch of mathematics appropriate for studying symmetries of physical systems. A symmetry is a natural attribute of the physical world and therefore is the starting point of any physical law. The foundation of dynamics is in Lagrangian theory or equivalently in Hamiltonian theory. A symmetry of a physical system is expressed by the invariance of its Lagrangian or Hamiltonian, or ultimately of its equations of motion, under certain transformations. When these transformations form groups it is convenient and useful to study symmetries through group theory. Group theory can explain observed regularities and helps to simplify and unify the physics of apparently different systems. It is a valuable tool that helps in predicting the behaviour of systems for which a symmetry has been found.
The rectilinear ascent and descent of bodies
Authors: Chandrasekhar S
Published: November 2023

This is an inversion of the common procedure: rectilinear motion in a central field of force is generally (if not always) considered as a special (and a simpler) case that requires a separate treatment since the angular momentum of such motions is zero and there is no constant of areas as a (non-trivial) constraint. Instead, Newton considers rectilinear motion as a limiting case of motion along conic sections and shows how it becomes determinate by an ‘invariant’ form of the law of areas which applies to orbits independently of their eccentricity.
The conservation of energy and the initial-value problem
Authors: Chandrasekhar S
Published: November 2023

Section VIII, including three Propositions XL, XLI, and XLII, represents a watershed in the development of the Principia: it completes the treatment of ‘the motion of bodies in immovable orbits’. But it is very much more than that: in deriving the energy integral (and implicitly the notion of potential energy) and in formulating and solving the initial-value problem in the framework of his dynamics, Newton established for the first time two of the basic tenets of physics. Newton must have been fully aware of the significance of these propositions. But his presentation of them manifests a strange impatience-of this later! Meantime, it will suffice to remark that superficially, Propositions XLI and XLII are presented as straightforward generalizations of Proposition XXXIX and its corollary. And there are, of course, examples of his insight and his craftsmanship.
The two-body problem
Authors: Chandrasekhar S
Published: November 2023

As we have stated in the introduction to the last chapter (§57), a watershed was reached in the development of the Principia at the end of Section IX. In resuming the main development, after a brief pause in Section X, Newton writes: I have hitherto been treating of the attractions of bodies towards an immovable centre; though very probably there is no such thing existent in nature. For attractions are made towards bodies, and the actions of the bodies attracted and attracting are always reciprocal and equal, by Law m; so that if there are two bodies, neither the attracted nor the attracting body is truly at rest, but both (by CoR. IV of the Laws of Motion), being as it were mutually attracted, revolve about a common centre of gravity. And if there be more bodies, which either are attracted by one body, which is attracted by them again, or which all attract each other mutually, these bodies will be so moved among themselves, that their common centre of gravity will either be at rest, or move uniformly forwards in a right line. I shall therefore at present go on to treat of the motion of bodies attracting each other; considering the centripetal forces as attractions; though perhaps in a physical strictness they may more truly be called impulses. But these propositions are to be considered as purely mathematical; and therefore, laying aside all physical considerations, I make use of a familiar way of speaking, to make myself the more easily understood by a mathematical reader.
Attraction by non-spherical bodies
Authors: Chandrasekhar S
Published: November 2023

As Newton stated in his concluding Scholium of Proposition LXXXIV, his next concern was the attraction by non-spherical bodies; but ‘to treat them particularly was not his design’. Even so, Propositions LXXXVII and Corollaries II and III of Proposition XCI stand out. In Proposition LXXXVII, Newton establishes a scaling law for the force exerted at an external point by an arbitrary distribution of mass specified by a density function and the law of centripetal attraction, by the elements of mass of the distribution, is inversely as the nth power of the distance.
On the theory of tides
Authors: Chandrasekhar S
Published: November 2023

But among all the great men who have philosophized about this remarkable effect, I am more astonished at Kepler than at any other. Despite his open and acute mind, and though he has at his fingertips the motions atributed to the earth, he has nevertheless lent his ear and his assent to the moon’s dominion over the waters, to occult properties, and to such puerilities. Concerning the Cause of the tides given by M. Newton, I am by no means satisfied by it, nor by all other Theories that he builds upon his principle of Attraction, which to me seems absurd, ... And I have often wondered how he could have given himself all the trouble of making such a number of investigations and difficult calculations that have no other foundation than this very principle.
The velocity of sound and of long waves in canals
Authors: Chandrasekhar S
Published: November 2023

One can search in vain to find an adequate account of Newton’s investigations on the velocity of sound in Propositions XLVII-XL of Book II. The best that I have been able to find (which is not saying very much in the context) is that of Rayleigh’s:* The first theoretical investigation of the velocity of sound was made by Newton, who assumed that the relation between pressure and density was that formulated in Boyle’s law.
The diatomic molecule
Authors: Sutton Adrian P
Published: November 2023

In this section we shall review some of the mathematical ideas you should have been exposed to in a course on quantum mechanics. If you find that you still do not understand the material described in this section and would like to read more, I suggest you try Chapter 8 of Feynman et al. (1966). It looks weird at first but it is really very simple. You just have to become familiar with it through using it and solving problems. Before we get into quantum mechanics let us take a fresh look at something that we are already familiar with and which is closely related to the mathematics we need to develop, namely vectors. A vector is something that has both magnitude and direction.
Structural stability of compounds
Authors: Sutton Adrian P
Published: November 2023

The notion that particular atomic configurations of molecules and crystals are stabilized by the formation of bonds between particular hybrid states assumes the bonds are saturated, that is, occupied by two electrons each. For example, in our earlier discussion of sp hybrids we assumed that each bond was occupied by two electrons. A saturated single C-C bond has a characteristic length and energy which is almost independent of the types of other atoms bonded to the two C atoms. The properties of a C-C bond depend on the configuration of atoms in the local environment because the configuration determines whether the C-C bond is a single, double, or triple bond. But for a given number and angular disposition of bonds to each C atom the C-C bond is less sensitive to whether other C or H or 0, etc. atoms are bonded to the two C atoms. This is the basis of ‘covalent radii’ for atoms in characteristic bonding topologies. It is as if each saturated bond has a personalized local wave function and properties. In valence bond theory this is known as the ‘perfect pairing approximation’. In molecular orbital theory it is known as the bond orbital approximation, which we discussed on p. 123 in the context of Si.
Cooling Of Large Accelerator Magnet Systems
Authors: Asner Fred M
Published: November 2023

Heat losses and heat in leaks in superconducting magnet systems are due to:resistive losses at varying magnetic fields such as magnetization losses and eddy current losses in the non-superconductive cable parts, in structural parts, current feedthrough, cable splices, end connections, etc. beam losses caused by synchrotron radiation, imaging currents in the beam pipes, continuous losses in the circulating beams, and the relative inefficiency of collimators. In highly irradiated beam regions additional heat is deposited in the mag net cold masses due to absorption of secondary particles. heat in leaks caused by thermal conductivity and radiation losses of magnet parts at ambient and different cryogenic temperatures.
Path Integral Representation
Authors: Kashiwa T , Ohnuki Y , Suzuki M
Published: November 2023

In this chapter path integral formulae in various representations will be derived by starting from the Schrodinger equation. In order to obtain a c-number expression for the time evolution operator given in terms of the momentum and the coordinate, first we need to deal with the issue of operator ordering. Then a discussion on the Euclidean technique, with which path integration can prove its real worth, that is where path integration can be regarded as a powerful tool for acquiring quantum information, will be presented. Further, alternative path integral expressions other than those obtained by using the eigen states of the momentum and the coordinate will be presented by utilizing the coherent states. Path integral formulae for the Fermi system will be finally presented, together with guidance on Grass man numbers, the indispensable rudiments for doing this.
Quantum Monte Carlo Method
Authors: Kashiwa T , Ohnuki Y , Suzuki M
Published: November 2023

The path integral discussed in the preceding chapters can be exactly calculated only in a few restricted systems such as harmonic oscillators. The WKB method and perturbational expansions based on the above path integral method are in fact applicable to systems close to classical ones and weakly interacting systems, respectively. However, in order to study interesting phenomena such as high Tc superconductivity, we have to treat strongly correlated systems in which the quantum effect plays an important role. It is effective in these systems to extract some physically crucial contributions numerically. This will be possible if we use the quantum Monte Carlo method. Although there are many different types of quantum Monte Carlo methods, we explain here mainly the quantum statistical Monte Carlo method based on a Trotter-like formula and on the important sampling method applied to transformed classical systems.
Induced Magnetic Anisotropy
Authors: Chikazumi Sōshin , Graham, Jr C D
Published: November 2023

The induced magnetic anisotropy differs from the ordinary magnetic anisotropy discussed in Chapter 12, in that the induced anisotropy is produced by a treatment (often an annealing treatment) that has directional characteristics. Not only the magnitude but also the easy axis of the anisotropy can be altered by appropriate treatments. We shall discuss various types of induced anisotropy in this section.
Magnetic Domain Structures
Authors: Chikazumi Sōshin , Graham, Jr C D
Published: November 2023

Ferro- and ferrimagnetic materials are divided into multiple domains, in which the spontaneous magnetization takes different orientations. The reason for the existence of domains is that the magnetostatic energy is greatly reduced. In this section we discuss how the magnetostatic energy is reduced by the appearance of domains.
X-RAY And Gamma-Ray Standards For Detector Calibration
Authors: Lorenz A , Nichols A .L
Published: November 2023

The recommended half-life and X- and gamma-ray emission probability data presented here were prepared by members of a Coordinated Research Programme (CRP) on X-ray and Gamma-ray Standards for Detector Calibration under the auspices of the International Atomic Energy Agency (IAEA). This concerted measurement and evaluation effort has resulted in a significant improvement in the accuracy and consistency of the decay parameters required for the efficiency calibration of X- and gamma-ray detectors.
Tunnelling phenomena
Authors: Kelly M J
Published: November 2023

This is the first of three chapters devoted to the new physics that has been made accessible with the advent of semiconductor multilayers. We shall be concerned with the quantum-mechanical phenomenon that an electron of total energy less than that of a thin potential barrier might not be reflected, as would always happen classically, but rather might pass through the barrier with an exponentially small but finite probability. Tunnelling has been an exploitable phenomenon in solid state physics for some time, and Josephson junction technology makes intimate use of superconducting tunnel junctions. In a wider sense, many of the leakage currents that plague high-performance devices have, in fact, come from carriers tunnelling through barriers that are undesirably thin. We are now able to control the tunnel barrier thickness precisely and to engineer the current-voltage characteristics. The subject has received an added boost through the discovery of resonant tunnelling involving two potential barriers: for certain. well-defined energies the tunnelling probability is not exponentially small, but approaches unity. Application of a suitable bias to a double-barrier structure can establish the condition of resonant tunnelling with a high current density. A further increase in bias takes the structure off resonance, and the current falls. This gives rise to a new form of negative differential resistance with attractive attributes that we shall describe below. Although it has taken some time, the device spin-offs are now becoming apparent. In the mean time, many physicists have explored nearly every conceivable aspect of resonant tunnelling.
Quantum wells and their optical properties
Authors: Kelly M J
Published: November 2023

It is arguable that the most widespread and successful applications of semiconductor multilayers to date exploit the optical properties of quantum wells, i.e. thin layers of a narrow-gap semiconductor sandwiched between layers of wider-gap material. This chapter contains a discussion of much of the relevant physics, with the device applications being described in more detail in Chapters 18 and 19. This chapter also completes the trio of chapters on novel physics in multilayers.
Devices I: field-effect and heterojunction bipolar transistors
Authors: Kelly M J
Published: November 2023

Having established the physics and the technology of semiconductor multilayers, in the following four chapters we consider the way in which that physics is being exploited in commercial and advanced research devices. These chapters are not intended to be complete expositions of the devices, which can be found in standard texts (e.g. Sze 1981, 1990). In this chapter we concentrate on transistors used as switches in digital circuits and as amplifiers in analogue circuits. In the next chapter, we focus on two-terminal devices used as sources, detectors, and mixers of microwaves and millimetre waves. These two chapters cover electronic devices with applications in computation and communications (including radar). In Chapter 18, we concentrate on a range of sources, modulators, and detectors of coherent and incoherent optical signals which find their principal application in optical fibre communication links. In Chapter 19 we describe a wider range of optical devices, used as mid- and far-infrared detectors of radiation and in solar cells.
Devices Ill: lasers, modulators, and detectors
Authors: Kelly M J
Published: November 2023

In this chapter we discuss the components required to generate, control, and detect optical signals at wavelengths of order 0.8-1.5 µm. The growth of communication systems based on optical fibre as the transmission medium has been spectacular over the last two decades. In 1993 alone, 80 000 route kilometres of undersea cable was programmed for installation. The bandwidth is enormous when the carrier frequency is of order 300 THz, compared with the c.100 GHz in the last chapter, although one trades off propagation in free space there for that within a fixed link here. The optimum wavelengths for transmission in silica fibres are 1.3 µm and 1.55 µm corresponding respectively to a wavelength where two non-linear effects cancel each other and to a minimum in the absorption, both of which permit long-haul communications without significant distortion or weakenipg of the optical signals {Tsang 1985). This has led to the development of high-performance lasers at both wavelengths. With the discovery that erbium-doped fibres can act as lasers operating at 1.5 µm while pumped at 0.98 µm (Barnes et al. 1989), methods are being sought of pumping fibres with semiconductor lasers at a comparable wavelength. In the first part of this chapter, we describe the subsequent generations of lasers with reference to the GaAs-AIGaAs system (bulk GaAs lases at a wavelength of 0.86 µm determined by the bandgap), and then we apply some of the principles behind these lasers to those operating at longer wavelengths. The storage and reading of data by optical means is another major area of application. At present GaAs-based lasers (costing less than £0.1 each!) are used. The optical systems for writing and reading digital information are limited by diffraction effects, and so ever-shorter wavelengths are required for increased data storage density. GaAllnP-based red lasers are available. Most recently the effort to produce semiconductor laser diodes that operate in the visible has paid off with initial reports of (low-temperature) lasers in the blue and green (Haase et al. 1991, Jeon et al. 1992).
Devices IV: infrared and solar devices
Authors: Kelly M J
Published: November 2023

In the last of these chapters devoted to the applications of multilayer semiconductor structures, we concentrate on two further optical devices, namely infrared detectors and solar cells. The former exploit inter-sub-band absorption in quantum wells, introduced briefly in chapter 10, Section 10.2.6, while the latter use multilayers to increase the absorption from the solar spectrum. Both devices have specialized applications, where the cost of high performance is justified. Thermal imaging and night vision, based on infrared radiation in the 8—14 μm atmospheric window not affected by water vapour, is becoming increasingly exploited outside the military arena for which it was developed, for example in see-through-smoke applications associated with fire fighting, thermal imaging of people buried in collapsed buildings, surveillance and security, etc. The applications have in the past withstood the expense of less stable and convenient materials such as HgCdTe alloys, exploiting a principal bandgap of c.10 pm for an 18 per cent CdTe-82 per cent HgTe alloy (cf. Chapter 1, Fig. 1.8). The prospect of replacing this material with the rather more mature GaAs-AlGaAs system is very attractive, and the pace of development has been particularly rapid in recent years (Levine 1993). In contrast, solar cells for domestic and commercial applications must be cheap before being highly efficient. In space and in other applications where access is difficult (e.g. weather or other monitoring from remote locations, and in some military arenas) one requires a compact, light, and highly efficient method for capturing solar energy and converting it into electricity (Bube 1993).
Radical alternatives
Authors: Kelly M J
Published: November 2023

So far in this text we have dealt with multilayers of conventional III-V and group IV semiconductors, and described what has been the mainstream research in semiconductor science and technology. The rapid advances within this technology have spurred those working in other fields and with other materials to try to match and surpass these achievements. In this closing chapter we introduce some of these radical alternatives to mainstream semiconductor science and technology. While some scientists strive in the vain hope of outperforming Si at what Si is best at, the main advances are likely to be in those areas where the final devices perform functions not available with Si or III-V semiconductors. As mentioned in the early chapters, III-V materials have specific properties, not available in Si, that have allowed them flourish, namely (i) the direct nature of the bandgap, making optical functions efficient, (ii) the turnover in the velocity-field characteristic leading to negative differential resistance and microwave sources, and (iii) the ability of substrates to retain a semi-insulating property after being taken through device processing. Increases in device speed by a factor of 3 in III-V materials compared with Si allow windows of opportunity for III-V digital applications, but in the end Si technology wins out through the greater maturity of its technology. Radical alternative technologies will need distinctive attributes not available with the group IV and III-V materials and devices.
Polymer-polymer interactions in dilute solution
Authors: Selser Jim
Published: November 2023

This chapter deals with interactions between polymers in dilute solution. The chapter does not present a summary either of the results of an extensive search of the relevant literature to date or of a consideration of the behaviours of all possible kinds of polymers under all possible circumstances. Instead, it deals primarily with light scattering studies of interactions in binary systems between non-electrolytic polymer coils, carried out by the author and his coworkers. Two themes emphasized throughout this chapter are: (1) the benefits of using static light scattering (‘SLS’) and the dynamic light scattering technique of photon correlation spectroscopy (‘ DLS’) together to investigate polymer-polymer interactions in dilute solution (see Chapter 8 of ref. 6 and Chapter 13 of this volume), and (2) the interplay between intra-polymer and inter-polymer behaviour in dilute solution.
Scattering from block copolymer micellar systems
Authors: Tuzar Zdeněk , Kratochvil Pavel
Published: November 2023

Block and graft copolymers in solution in selective solvents, that are good for one block and poor for the other, self-associate forming multimolecular micelles, the cores of which consist of insoluble blocks, while the soluble blocks are located in protective shells. A typical association number (i.e. the number of copolymer molecules in a micelle) is from tens to hundreds. These micelles, with a narrow molar mass and size distribution, are in dynamic equilibrium with molecularly dissolved copolymer molecules (unimers). Unlike aqueous micellar systems of soaps and surfactants, block copolymer micellar systems in both organic and aqueous selective solvents have very low, usually imperceptible, critical micelle concentrations (CMC).
Optical waves in vacuum
Authors: Akhmanov S A , Nikitin S YU
Published: November 2023

The electromagnetic nature of light and Maxwell’s theory. Hertz’s experiments. Maxwell’s equations. The wave equation. A plane wave. A spherical wave. Modulated waves and radiation of real sources of light. Spectral expansion of the optical field. The superposition principle.
Classical radiation physics
Authors: Akhmanov S A , Nikitin S YU
Published: November 2023

Hertz’s experiment. The atom as an elementary source of light. The classical model of the atom. Emission from a charge and Emission conditions. Calculation of the vortical component of the field. A rigorous solution of the problem of dipole emission. Harmonic oscillations of a dipole. The total power of dipole radiation. The decay of dipole oscillations due to emission of radiation.
Thermal radiation
Authors: Akhmanov S A , Nikitin S YU
Published: November 2023

The main experimental facts and methods of investigation of thermal radiation. Emissivity and absorptivity of physical bodies. Equilibrium thermal radiation. Kirchhoff’s law. Spectral density of thermal radiation. Thermodynamics of equilibrium thermal radiation. The Rayleigh-Jeans formula. The “ultraviolet catastrophe”. Planck’s formula. The necessity of a quantum-mechanical approach. Thermal radiation laws (Stefan-Boltzmann law, Wien’s displacement law).
Diffraction in the far-field zone
Authors: Akhmanov S A , Nikitin S YU
Published: November 2023

The formation of a stable diffraction pattern in the far-field zone. Fraunhofer diffraction as a spatial Fourier transformation. Fraunhofer diffraction by unidimensional structures—slit diffraction. Fraunhofer diffraction by two-dimensional structures. Diffraction by a rectangular aperture. Diffraction by a round aperture. Diffraction by a Gaussian beam.
The Principles of Monte Carlo Out-of-equilibrium Simulations
Authors: Newman M E J , Barkema G T
Published: November 2023

In Part I of this book we looked at ways of measuring the equilibrium properties of model systems using Monte Carlo simulations. The next few chapters of the book are devoted to systems which are out of equilibrium. In studying these out-of-equilibrium systems we are commonly interested in one of two things. Either we want to know how the system relaxes from an initial state to equilibrium at a particular temperature, or we are studying a system which never reaches equilibrium because it has a driving force which continually pushes it into states which are far from equilibrium. We will see examples of both these types of simulations in the following pages.
Multispin Coding
Authors: Newman M E J , Barkema G T
Published: November 2023

Multispin coding is a programming technique which allows us to speed up some Monte Carlo simulations (or other programs) by a significant factor by making use of the low-level bit manipulation functions provided by the CPU of our computer. These functions include logical operations like AND (∧), OR (v) and exclusive-OR (⊕), as well as things like shifts, additions and subtractions.
Lepton nuclear physics
Authors: Ejiri H
Published: November 2023

The lepton nuclear physics studies the fundamental properties of leptons, weak interactions, and related subjects in the nuclear microlaboratory. Thus, being complementary to the quark nuclear physics as discussed in Chapter 11, it is one of the important new fields in nuclear physics.

Several interesting topics of the lepton nuclear physics are currently under study at RCNP, Osaka. The subjects discussed in the present chapter include neutrinos (v’s) studied by double beta (ββ) decays, spin-coupled dark matter (DM) studied by nuclear elastic and inelastic scatterings, nucleon instabilities and nucleon decays studied by exotic nuclear transitions, and so on. It is interesting to note that charge non-conservation is also studied by searching for exotic X-rays and y-rays.
Over 70 years of neutron scattering
Authors: Willis B T M , Carlile C J
Published: November 2023

In the 1920s James Chadwick undertook a series of experiments in search of the neutron, whose existence had been predicted by Rutherford in his Bakerian lecture to the Royal Society of London in 1920. It was not until 1932 that Chadwick finally achieved his goal, announcing the possible discovery of the neutron (Chadwick, 1932a) and conﬁrming its existence later in the same year (Chadwick, 1932b).
Instrument components
Authors: Willis B T M , Carlile C J
Published: November 2023

In this chapter we shall describe some of the components that are used to tailor the neutron beam to satisfy the requirements of the experimentalist. These components perform such functions as limiting the wavelength range or the degree of collimation of the beam striking the sample. We shall be concerned with unpolarized beams only: the devices for producing polarized beams are described later in Chapter 9.
The powder diffraction method
Authors: Willis B T M , Carlile C J
Published: November 2023

Shortly after the discovery of the diffraction of X-rays by a single crystal, Debye and Scherrer (1916) and Hull (1917) independently showed that a characteristic diffraction pattern is also given by a sample consisting of a polycrystalline powder. This method of examining materials is known as the Powder diffraction Method. Much crystallographic information is lost by condensing the three dimensions of reciprocal space, which are explored in single-crystal diffraction, into the single dimension of the powder pattern. However, for some materials it may not be possible to prepare a suitable single crystal. For example, zeolites, fastion conductors, high-Tc superconductors, fullerenes, etc. may be available only in powder form. Other materials may undergo a series of phase transitions on cooling, making it impossible to retain the integrity of a single crystal. In spite of its inherent limitations, powder diffraction can give not only the detailed atomic arrangement, but also the texture and composition of the sample. It can be used for in situ studies of chemical reactions and processes. With the increasing power of computers, advances in instrumentation, and the trend towards the study of more complex materials, powder diﬀraction has undergone a transformation since the 1980s.
Neutron reflectometry
Authors: Willis B T M , Carlile C J
Published: November 2023

Neutron reflectometry, in which neutrons are reflected from planar structures, is a powerful method for investigating properties of interfaces. It is one of the neutron techniques in most demand today and neutron reflectometers are amongst the first instruments to be commissioned at the new pulsed sources SNS and J-PARC. The technique has been applied to a wide variety of materials, including surfactants adsorbed at solid/liquid interfaces, Langmuir–Blodgett and polymer flims, lipid bilayers in biological cell membranes, and magnetic ultrathin flims and multilayers. By measuring the reflected specular intensity as a function of the incident angle or wavelength, the scattering proﬁle normal to the surface is obtained. Non-specular scattering yields information on the lateral structure of the interface.
Inelastic neutron scattering spectroscopy
Authors: Willis B T M , Carlile C J
Published: November 2023

In the previous chapter, we have seen how coherent inelastic neutron scattering can be used for the study of collective excitations, such as phonons and magnons, in single crystals. This spectroscopic technique was pioneered in the 1950s by the Canadian physicist, Bertram Brock-house, and much of the earlier work was confined to the field of physics. However, the interest today in inelastic neutron scattering (INS) has shifted to include the fields of chemistry, materials science, geology and biology, where work is carried out in areas such as polymers, hydrogen bonding and catalysis. In a paper presented at an IAEA meeting in Trombay (IAEA Bombay 1959), Brockhouse described a time-of-fiight rotating crystal spectrometer, which would nowadays be used for molecular spectroscopy.
Undulator Radiation
Authors: Luchini P , Motz H
Published: November 2023

In this chapter the electromagnetic radiation generated by an electron beam passing through an undulator will be quantitatively determined in the absence of electromagnetic fields other than the undulator's, and neglecting the effect of the field produced by the electrons upon each other. Radiation obtained in this way bears the name of undulator radiation. ('Spontaneous' undulator radiation when it is to be opposed to the 'stimulated' radiation emitted under the influence of an external electromagnetic wave, which we are going to consider in subsequent chapters.)
Saturation
Authors: Luchini P , Motz H
Published: November 2023

With an ever increasing optical field, a point is ev ntually reach d where the linear approximation of the previous chapters fails. The free-electron laser then enters the large-field, non-linear operating regime.
Electronic States Of An Isolated Impurity
Authors: Kamimura Hiroshi , Aoki Hideo
Published: November 2023

In studying doped semiconductors, we start by briefly describing the shallow impurity states of an isolated donor atom in silicon and germanium. Both these elements possess a diamond crystal structure (Fig. 2.l(a)), in which (ns)(np ) valence electrons form covalent bonds between sp hybridized orbitals.
Historical Development Of Localization Theories In Impurity Bands
Authors: Kamimura Hiroshi , Aoki Hideo
Published: November 2023

When an isolated donor atom is doped in Si or Ge, a hydrogen-like ls state is formed just below the conduction band, as seen in Chapter 2. As the concentration of the dopant is increased, the number of such states also increases. James and Ginzbarg (1953) first pointed out that the overlap of wavefunctions of impurities becomes larger with increasing impurity concentration, so that carriers are no longer localized at individual impurities. In the energy spectrum there is a continuous distribution of energy levels, which is called the impurity band (Fig. 3.1). At about the same time, Huang and Gliessman (1950, 1954) experimentally obtained the first evidence for conduction in an impurity band. The wavefunctions for different impurities overlap at higher concentrations in a manner dependent on the spatial distribution of the impurities (Fig. 3.2). In this sense the impurity band is quite different from ordinary energy bands in periodic crystals in which the wavenumber is a good quantum number.
Electron-Electron Interactions In Impurity Bands
Authors: Kamimura Hiroshi , Aoki Hideo
Published: November 2023

As we have seen in Chapter 3, the metal-non-metal transition in doped semiconductors has attracted renewed interest in the light of the localization problem. We mentioned in Chapter 1 that recent theoretical work in the field has followed two main lines of approach. The first approach starts from the nearly free electron picture in the metallic regime and then covers the effect of localization due to disorder. The second line of approach, on the other hand, covers the insulating phase and starts from the Anderson localized regime itself. This approach, which describes the system by a tight-binding picture, is particularly suitable for the donor concentration region where the localization length is of the order of average donor separation. Thus these two approaches for disordered systems may be compared with the two complementary approaches for perfect crystals, i.e. the Bloch electron approach and the tight-binding approach. The final goal of both approaches is of course the same—an accurate description of the metal-non-metal transition.
Defects In Smectics And Columnar Phases
Authors: Gennes P G De , Prost J
Published: November 2023

At a temperature higher than 232°C, the compound is in its isotropic state and the field of view altogether black. Below 232°C, the ̒texture d fils̓ (Schlieren) that we described in Chapter 4 appears. It corresponds, of course, to a nematic phase. Some of the regions may stay perfectly black (homeo- tropic regions) which shows that the system is uniaxial. If we keep on cooling down, below 213.5°C, a new texture appears (Fig. 9.1).
Applications of Multiple Scattering III: Ferromagnetic Alloys And Finite Temperature Magnetism
Authors: Weinberger P
Published: November 2023

This final chapter deals with some applications of multiple scattering to problems of magnetism. Of course only those applications are discussed here which can be viewed in the context of the rest of the book. However, since there are several excellent review articles stating these problems at a fundamental level (in particular see Gyorffy et al. 1985), this does not seem to be a severe restriction. Two cases are chosen to illustrate this rapidly developing field of research: the ab initio calculation of the well known Slater-Pauling curve; and the case of moment formulation within the (still simple) framework of a temperature dependent homogeneous CPA approach. For further applications the reader is referred to Gyorffy et al. (1984) and Staunton et al. (1989).
Open Systems
Authors: Pike frs E R , Sarkar Sarben
Published: November 2023

In the interactions of electromagnetic radiation with matter which we have considered so far, we have almost invariably known accurately the state of the system before interaction. As a result the notion of an open system with an external environment did not have to be systematically discussed. In the quantum electrodynamics of elementary particles, the scattering events are predominantly affected by only few-body interactions and the concepts of temperature and environment are irrelevant. (The resolution of the problem of infra-red divergences is an exception where the environment of soft photons is crucial.) For very small numbers of atoms it may be possible to know the initial state of the system, but in a macroscopic device this is essentially impossible. Although for transitions at optical frequencies the temperature of the environment may be negligible, this will not necessarily be the case for microwave transitions. We have already seen how atomic linewidths can be produced by interactions with the bath of photons at zero temperature. In the general case a quantum-mechanical system will show not only fluctuations due to the non-commutative nature of quantum theory but also thermal fluctuations and dissipation due to interactions with the environment. For complicated systems it will not be possible to know with certainty the initial state of the system, and so the approach of studying the evolution of a state vector through the Schrodinger equation has to be replaced by a consideration of the time evolution of the density operator introduced in Chapter 4. We will formulate a systematic way of treating the dynamics of a quantum-mechanical open system interacting with a heat bath, which will be illustrated with important examples.
The Grand Canonical Formalism
Authors: Cloizeaux Jacques des , Jannink Gerard
Published: November 2023

Whenever the Hamiltonian of a system obeys a global conservation law, like the conservation of energy or of the number of particles, one might be tempted to describe the statistics of the system by giving a well defined value to the conserved quantity. However, such an approach would be clumsy because, in this case, any local fluctuation of the conserved quantity must be compensated elsewhere by fluctuations with the opposite sign, and thus the conservation law would entail correlations devoid of interest and difficult to take into account. In order to break free from these correlations, larger ensembles are used in which a chemical potential or fugacity is associated with each conserved quantity so as to fix only averages of these conserved quantities. Thus, when the energy is conserved in the system, canonical ensembles are used; when, more¬ over, the system consists of particles whose number is also conserved, we use grand canonical ensembles.
Polymers in Solution in Good Solvents: Theoretical Results
Authors: Cloizeaux Jacques des , Jannink Gerard
Published: November 2023

Many theoretical results concerning the behaviour of polymers in good solvents have been found in the framework of the standard continuous model by using perturbation and renormalization techniques. It seems that S.F. Edwards was the first to realize (before 1965) that it is fruitful to use continuous curves to model polymer chains, and he was also the first to understand (around 1965) that interacting polymers in solution screen one another when they overlap. However, this theoretical progress acquired its full meaning only when it was fully recognized (between 1975 and 1985) that a set of long polymers can be considered as a critical system and therefore may have universal properties. Of course, the existence of critical exponents had been accepted much earlier, but the existence of universal functions and universal ratios was really recognized only after 1975. At the same time appeared the concept of semi-dilute solution. Such a solution has a low concentration with a strong chain overlap; the screening effects then play an essential role in agreement with Edwards’s ideas.
Polymers in Good Solvents: Experimental Results
Authors: Cloizeaux Jacques des , Jannink Gerard
Published: November 2023

The structure and the behaviour of polymer chains in solutions have, since the 1930s, been the object of intensive experimental work. The main effort has been carried out on the isolated chain in good solvent, and the swelling caused by repulsive interaction between monomers. The effect had already been predicted by Kuhn, in an article published in 1934, describing the spatial occupancy of chains (RaumerfU/lung). The swelling of a rubber (cross-linked chains) in a solvent can be observed directly with the naked eye. In the case of linear chains, the observation of all aspects of this effect has, however, required the use of instrumentation which has grown heavier, year by year.
Polarization
Authors: Gastmans R , Wu Tai Tsun
Published: November 2023

Beam polarization gives information on the electron’s inclination to behave with aberration. In the preceding chapters, we expounded a convenient way to calculate helicity amplitudes for various processes at high energies. In this chapter, we show how those helicity amplitudes must be combined for the description of processes in which arbitrary spin polarizations occur. We first treat the case of fermion polarization in detail and then analyse the polarization effects for photons and gluons. Throughout this chapter, we again neglect the finite mass effects for simplicity. The positive helicity states for fermions, introduced in Chapter 3 [eqns (3.1)], describe particles with spin polarization along the direction of motion, where as negative helicity states have their spin polarization opposite to the direction of motion. This can be seen as follows.
Fracture Strength of Disordered Solids
Authors: Chakrabarti Bikas K , Gilles Benguigui L
Published: November 2023

For many engineering applications, an important aspect of the choice of the load-bearing material and the engineering design is that the solid material should not fracture or fail in service. As the material contains natural disorders or defects, produced during the preparation or synthesis of the solid, solids contain built-in microcracks (where the interatomic interactions become vanishingly small due to large separation distances etc.) produced due to the defects. Fracture properties of the solids containing these microcracks, under different loading conditions, are therefore of extreme importance in civil and other engineering design problems. We will discuss the statistical aspects of the fracture properties of such solids in this chapter. There are three modes of loading a solid, as shown in Fig. 3.1, where the arrows denote the stress directions. We will mostly discuss here the fracture strength of randomly disordered solids under stress or loading condition in mode I. However, because of the mixing of tensile and shear stresses in disordered systems, the results discussed in this chapter are, in effect, valid for all the modes.
Earthquakes in Model Systems
Authors: Chakrabarti Bikas K , Gilles Benguigui L
Published: November 2023

We discuss in this chapter several model studies for earthquakes. Earthquakes are large scale failures, occurring mainly as a consequence of frictional slips in the upper region of the earth’s crust, to adjust the stress accumulated by the large scale tectonic plate motions over long periods of several decades of years (see e.g. Guttenberg and Richter 1954, Kostrov and Das 1988, Scholz 1990). Like in the cases of fracture or breakdown (discussed in the previous chapters), where the stresses or fields are redistributed within the surviving or unbroken portions of the material, the stresses on the sticking tectonic plates are readjusted after each individual slip in any region (plate). However, unlike in the fracture or breakdown case where a fractured, broken or fused bond is permanently broken and remains unable to sustain any stress any further, the slipped or failed blocks in the earthquake can again stick and participate again in sustaining stresses. An earthquake occurs when a large number of the blocks of the earth’s crust slip simultaneously, releasing a large amount of elastic energy. Such stick-slip frictional instability of a large number of blocks, as in the case of earthquakes, is a typical dynamic failure phenomenon.
Teenage pregnancy policy and practice: the application of evidence
Authors: Dennison Catherine , McCormick Geraldine
Published: November 2023

In recent years there has been increasing recognition of the significance of teenage pregnancy and parenthood as a marker of health and social inequalities, and a risk factor for social exclusion. In addition to public health professionals, the media, politicians of all parties, and family values campaigners have all taken an interest and a position on the topic. Many of these groups have used teenage pregnancy as a vehicle to signify declining moral standards in today’s young people, and as a result it is essential that policy and practice in relation to the issue is firmly evidence based.
Tackling health inequalities at the community level: neighbourhood renewal and the new deal for communities
Authors: Peters Jean , Goyder Elizabeth
Published: November 2023

Reducing health inequalities has been an enduring concern of UK governments. Current policies make explicit the Government’s present commitment to reduce inequalities in health. Such a reduction is also integral to the wider cross-government policies that are addressing issues of poverty and deprivation. However, evidence of what programmes and interventions are most likely to help achieve long-term targets to reduce health inequalities remains uncertain. It is also often difficult to evaluate the contribution made by particular local programmes and initiatives or to tease out the relative impact of individual project contributions within an overall programme.
Public policies and inequalities in health: challenges and lessons from Finland
Authors: Koivusalo Meri
Published: November 2023

Reducing inequalities in health is a broad, long-term, and complex task requiring commitment beyond specific interventions in the health sector. In this chapter we present some issues and points of departure which the Finnish context and situation has raised, and which may also have importance with respect to other countries.