There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Handbook of Chemistry and Physics

The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.

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Towards a definition of inorganic nanoparticles from an environmental, health and safety perspective

Keywords: Surface Electronic and Atomic Structure ; Spectroscopy ; Spin-Polarized STM Reference LNS-ARTICLE-1990-002doi:10.1103/PhysRevB.42.9307 Record created on 2009-04-14, modified on 2017-05-12

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Scanning tunneling microscopy observations on the reconstructed Au(111) surface: Atomic structure, long-range superstructure, rotational domains, and surface defects

This review paper illustrates the main normal and superconducting state properties of magnesium diboride, a material known since the early 1950s but only recently discovered to be superconductive at a remarkably high critical temperature Tc = 40 K for a binary compound. What makes MgB2 so special? Its high Tc, simple crystal structure, large coherence lengths, high critical current densities and fields, and transparency of grain boundaries to current promise that MgB2 will be a good material for both large-scale applications and electronic devices. During the last seven months, MgB2 has been fabricated in various forms: bulk, single crystals, thin films, tapes and wires. The largest critical current densities, greater than 10 MA cm−2, and critical fields, 40 T, are achieved for thin films. The anisotropy ratio inferred from upper critical field measurements is yet to be resolved as a wide range of values have been reported, γ = 1.2–9. Also, there is no consensus on the existence of a single anisotropic or double energy gap. One central issue is whether or not MgB2 represents a new class of superconductors, which is the tip of an iceberg awaiting to be discovered. To date MgB2 holds the record for the highest Tc among simple binary compounds. However, the discovery of superconductivity in MgB2 revived the interest in non-oxides and initiated a search for superconductivity in related materialss; several compounds have since been announced to be superconductive: TaB2, BeB2.75, C–S composites, and the elemental B under pressure.

https://iopscience.iop.org/article/10.1088/0953-2048/14/11/201/pdf

Review of the superconducting properties of MgB2

This article reviews quantum cluster theories, a set of approximations for infinite lattice models which treat correlations within the cluster explicitly, and correlations at longer length scales either perturbatively or within a mean-field approximation. These methods become exact when the cluster size diverges, and most recover the corresponding mean-field approximation when the cluster size becomes 1. Although quantum cluster theories were originally developed to treat disordered systems, they have more recently been applied to the study of ordered and disordered correlated systems, which will be the focus of this review. After a brief historical review, the authors provide detailed derivations of three cluster formalisms: the cluster perturbation theory, the dynamical cluster approximation, and the cellular dynamical mean-field theory. They compare their advantages and review their applications to common models of correlated electron systems.

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Quantum cluster theories

A simple theory is presented for various fundamental properties of small clusters. In particular, we calculate the cohesion, the magic numbers, bond contraction, stability of atomic structures, and alloy formation as a function of cluster size, and determine also the Coulomb explosion of small multiply charged clusters.

Simple theory for the electronic and atomic structure of small clusters

The size and structural dependence of magnetic properties of small ${\mathrm{Cr}}_{\mathrm{n}}$, ${\mathrm{Fe}}_{\mathrm{n}}$, and ${\mathrm{Ni}}_{\mathrm{n}}$ clusters are determined by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment \ensuremath{\mu}${\ifmmode\bar\else\textasciimacron\fi{}}_{n}$, local magnetic moments, and magnetic ordering at T=0. We obtain for ${\mathrm{Fe}}_{\mathrm{n}}$ (n\ensuremath{\le}15) that \ensuremath{\mu}${\ifmmode\bar\else\textasciimacron\fi{}}_{n}$ varies as a function of n due to the interplay between the changes in coordination number and bond length as a function of cluster size, which may be related to recent experiments. The dependence of the structural cluster stability on magnetism is discussed. Results are also given for the cohesive energy, average bond length, and local densities of states.

Size and structural dependence of the magnetic properties of small 3d-transition-metal clusters.

The effect of a dense electron-hole plasma on the stability of the diamond lattice of the crystalline group-IV elemental semiconductors C, Si, and Ge is examined with use of a tight-binding model. Such a plasma may result, for example, from a short, intense laser pulse. We find that the transverse-acoustic phonons of Si become soft if about 9% of the electrons are excited from the valence band into the conduction band. At higher densities of the electron-hole excitations the cubic symmetry of the diamond lattice is destroyed within less than 100 fs after the creation of the electron-hole plasma. This is much shorter than the time needed for the crystal to melt. The instability of the lattice then leads directly to a very rapid melting of the crystal structure. Our results are in agreement with recent experiments using pulsed lasers to induce disorder in crystalline Si surfaces. We obtain for C and Ge essentially the same theoretical results as for Si.

Theory for the instability of the diamond structure of Si, Ge, and C induced by a dense electron-hole plasma.

We extend our previous analysis of the ultrafast laser-induced instability of the diamond structure of semiconductors by including longitudinal optical-phonon distortions in addition to the instability of the transverse acoustic phonons. Generally, longitudinal optical distortions enhance the instability of the transverse acoustic phonons, increasing the kinetic energy of the atoms and the final lattice temperature. These phonons make a transition to a centrosymmetric structure of GaAs with metallic properties possible. We present results for the time dependence of the instability of Si for the case where 15% of the valence electrons have been excited into the conduction band. Thus, already 100 fsec after the excitation of the plasma the atoms are displaced about 1 \AA{} from their equilibrium position and their kinetic energy has increased to approximately 0.4 eV. Collisions between the atoms then lead to a rapid melting of the crystal. These results are in good agreement with recent experiments performed on Si and GaAs.

Time dependence of the laser-induced femtosecond lattice instability of Si and GaAs: Role of longitudinal optical distortions.

The physical mechanisms for damage formation in graphite films induced by femtosecond laser pulses are analyzed using a microscopic electronic theory. We describe the nonequilibrium dynamics of electrons and lattice by performing molecular dynamics simulations on time-dependent potential energy surfaces. We show that graphite has the unique property of exhibiting two distinct laser-induced structural instabilities. For high absorbed energies ( $g3.3\phantom{\rule{0ex}{0ex}}\mathrm{eV}/\mathrm{atom}$) we find nonequilibrium melting followed by fast evaporation. For low intensities above the damage threshold ( $g2.0\phantom{\rule{0ex}{0ex}}\mathrm{eV}/\mathrm{atom}$) ablation occurs via removal of intact graphite sheets.

K. H. Bennemann

Papers

Simple theory for the electronic and atomic structure of small clusters

Size and structural dependence of the magnetic properties of small 3d-transition-metal clusters.

Theory for the instability of the diamond structure of Si, Ge, and C induced by a dense electron-hole plasma.

Time dependence of the laser-induced femtosecond lattice instability of Si and GaAs: Role of longitudinal optical distortions.

Theory for the Ultrafast Ablation of Graphite Films