We develop a model based on the idea of dangling-bond-mediated attractive electron-electron interactions to describe the metastably reconstructed 2×1 Si(111) surface and its elimination with increasing annealing temperature. It is found that the resultant picture is able to correlate a considerable amount of experimental data.

We propose that Si-H-Si three-center bonds exist in hydrogenated amorphous silicon. These centers give rise to states in the energy gap which have a negative effective electronic correlation energy, $U$. Our model can explain many of the known properties of this material. We make suggestions about how to obtain materials which may prove useful in electronic device applications.

We have developed a method for solving the Green's-function equations describing an isolated localized defect in an otherwise perfect crystal. It yields a charge density in sufficinet detail to allow recalculation of the potential and iteration to self-consistency. The method is applied to the ideal (unrelaxed) vacancy in silicon, in the ionic-pseudopotential, local-exchange-correlation approximation.

We report the development of a method to calculate self-consistently the electronic structure of neutral point defects in semiconductors. The method is an adaptation of the original Koster-Slater idea. Calculations become feasible, practical, and accurate at the level of current band-structure and surface calculations when an LCAO basis set is used instead of Wannier functions. A detailed study of the isolated vacancy is Si is used to illustrate the method.

Pure, perfect, single-crystal Zr${\mathrm{V}}_2$ does not undergo a structural phase transformation but all other sample modifications, including twinned single crystal, do transform (∼100 K) from the cubic to a rhombohedral phase. All samples exhibit, in addition, an electronic instability (also ∼100 K). An anomaly in the ultrasonic velocity occurs at higher temperatures (∼150-180 K) for pure polycrystalline Zr${\mathrm{V}}_2$ samples.

A molecular-dynamics calculation of the work of introducing a charge in a polarizable fluid leads to about twice the value predicted by the Born continuum model. The screened Coulomb field reaches its macroscopic limit about three molecular diameters from the charge but is larger than the continuum dielectric prediction because of higher-order polarizability corrections. The diffusion coefficient leads to a Stokes radius that corresponds roughly to a singly ionized particle and its solvation shell diffusing as a unit.

The superconducting transition temperature $T_c$ and its width $\Delta T_c$ were determined for neutron-irradiated ${\mathrm{V}}_3$Si for various fluences $\varphi t$, using heat-capacity and resistivity measurements. It was found that, although the two determinations do not give identical results, in both cases $\Delta T_c$ increases with fluence indicating the inhomogeneous nature of the damage.

At low temperatures we have observed a strong microwave absorption in Na $\beta$-alumina which increases with decreasing temperature below 4 K. At electromagnetic intensities $I\underset{\simeq }{<}0.1$ mW/${\mathrm{cm}}^2$ saturation occurs. This absorption is ascribed to low-energy tunneling states which are associated with the Na ions.

We propose a method by which it is possible to narrow the energy distribution of relativistic protons. The method is based on the conversion of relativistic hydrogen ions into neutral hydrogen atoms, consequent velocity-selective excitation of relativistic hydrogen atoms by the $1S-2P$ transition, and photoionization of the selectively excited atoms. The method can be realized using existing lasers on present accelerators.

We have searched the missing-mass spectrum of the reaction $\mathrm{pp}\to K^{+}{K}^{+}X$ for a narrow six-quark resonance in the mass range 2.0-2.5 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$. No narrow structure was observed. Upper limits for the production cross section of such a state depend upon mass and vary from 30 to 130 nb.

Measurements of the polarization parameter and angular distributions in $\mathrm{pp}$ elastic scattering at incident energies of 100 and 300 GeV are reported. The data cover the kinematic range $0.18<-t<\mathrm{}2.0\mathrm{}$ ${\mathrm{GeV}}^2$. They are found to be consistent with absorption-model predictions.

We have measured the reaction ${\pi }^{-}p\to K^{+}{K}^{-}{K}^{+}{K}^{-}n$ at 22.6 GeV/c and detect strong $\varphi$ signals in the $K^{+}{K}^{-}$ effective-mass plots. We do not observe the expected Okubo-Zweig-Iizuka-rule suppression of the $\varphi \varphi n$ final state and conclude that the rule is working poorly in the observed production processes.

Following the idea of Sterman and Weinberg, we calculate the jet angular radius of a gluon jet and its energy dependence in the framework of perturbative quantum chromodynamics. The result is free of infrared and mass singularities and does not depend on the gluon fragmentation function. We find that the gluon jet spreads much more (i.e., less jetlike) than a quark jet; this renders the detection of gluon jets very difficult.

A method is developed to determine average lifetimes of continuum gamma rays following heavy-ion compound-nucleus reactions. The resulting enhancement factors for $E2\mathrm{}$ transitions depopulating states in the spin-(30-50) regions are of the same order of magnitude as for ground-state rotational bands of deformed nuclei. This shows for the first time that these high-spin states decay through strongly collective bands.

On the basis of new data on pionic atoms, it is argued that the criticality condition for the existence of strongly bound $\pi$-nuclear states is likely to be met in most nuclei. Numerical solutions for ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ are reported, with the conclusion that the widths of such $\pi$ states are generally prohibitively large for their observability except, possibly, in heavy nuclei.

A rotating relativistic electron beam, charge but not current neutralized and exceeding the Alfvén limit, has been propagated down a closed metal tube in the absence of an external guide field. The radial equilibrium is determined by the self-fields of the beam and the induced wall currents. The 100-nsec duration beam, upon leaving the system, induces plasma currents that maintain a field-reversed configuration for 18 μsec.

We have applied the Kruskal-Oberman energy principle to a simple model of an anisotropic tokamak in which the pressure varies around flux surfaces. We show that the weighting of pressure towards regions of favorable curvature leads to a significant stabilization of the high-$n$ ballooning modes.R ballooning modeql

Electron spin relaxation times in surface collisions were deduced from measurements on superconductors of the NMR Knight shift, critical magnetic fields, and tunneling conductance as well as from measurements on normal metals by conduction-electron spin resonance. The relaxation times ${\tau }_{\mathrm{so}}$ as determined by the various methods are consistent and depend on the atomic number of the metal in a manner similar to that proposed by Abrikosov and Gor'kov.

We report the results of high-resolution studies of the effect of uniaxial stress on the bound-multiexciton-complex luminescence lines in phosphorus-doped silicon. Our results differ significantly from those contained in two previous studies which attempted to rule out the bound-multiexciton-complex explanation of these lines, and instead strongly support Kirczenow's shell model of the structure of the bound-multiexciton complexes. In addition, new lines are observed which are interpreted as stress-induced two-electron transitions of the bound exciton.

We report the first measurements of the distribution function $f$ of quasiparticles in a nonequilibrium superconductor. For a wide range of quasiparticle-injection energies, $f\left(E\right)\mathrm{}\simeq {[1+\exp (\frac{(E-{\mu }^{*})}{k{T}^{*}}\left)\right]}^{-1\mathrm{}}$, where ${\mu }^{*}$ and $T^{*}$ depend on the injection energy. Novel results include a negative ${\mu }^{*}$, a $T^{*}$ greater than the transition temperature, and a totally unanticipated bump in $f$ at an energy of $3\Delta$, where $\Delta$ is the energy gap. This last result shows that detailed balance is violated in nonequilibrium states.