Coherent effects in synchrotron radiation (SR) have been observed for the first time from 180-MeV short electron bunches of 2.4 mm using the Tohoku 300-MeV Linac. The intensity of the coherent SR was about ${10}^5$ times as strong as that of incoherent SR in the wavelengths of 0.4–2.2 mm. This enhancement factor corresponds to the number of electrons in a bunch. The SR intensity showed a quadratic dependence on the electron beam current. The radiation was mainly polarized in the orbital plane. The possibility of induced rf in a vacuum chamber was excluded experimentally.

Access to the MHD second stability regime has been achieved in the ATF torsatron. Experimental β values (${\beta }_0$≤3%, with fast ions contributing ≊(1/3 of the pressure at high β) are well above the theoretical transition value (${\beta }_c$≊1.3% for ideal modes) required to reach this regime. The relatively low ${\beta }_c$ results from operation with peaked pressure profiles. The measured magnetic fluctuations decrease with increasing β, and the pressure profile broadens. This behavior is consistent with theoretical predictions for β self-stabilization of resistive interchange modes.

Synchrotron x-ray diffraction has been used to analyze the (√3×√3)R30° reconstruction of B/Si(111). Excellent agreement is obtained with in-plane data for a model in which boron sits in every third site of threefold symmetry. Out-of-plane diffraction, however, is only consistent with boron below the surface in the fivefold-coordinated substitutional site under a silicon ${\mathrm{T}}_4$ adatom. The structure is confirmed by the growth behavior under room-temperature Si deposition in which the silicon adatom is displaced from its ordered site leaving boron in a two-dimensional ordered substitutional array.

We have investigated the incorporation of boron into the Si(111) (√3×√3)R30° surface from low boron concentration up to (1/3 monolayer, using tunneling microscopy and spectroscopy and first-principles total-energy calculations. Surprisingly, we find that a (√3×√3)R30° structure composed almost entirely of Si adatoms on a Si double layer can be stabilized by boron doping in near surface layers. Moreover, when boron atoms are in the surface layers, the adatom site is unfavorable compared with the site underneath the adatom, unlike other group-III elements adsorbed on the Si(111) surface.

Adsorption of B induces a (√3 × √3 )R30° reconstruction on Si(111). By combining scanning tunneling microscope topographs and spectra with first-principles calculations we are able to follow the different stages of B incorporation in the Si surface and the corresponding changes to the surface electronic states. We find that the thermodynamically stable configuration consists of a B substitutional atom directly below a Si adatom at a $T_4$ site. The stability of this configuration is due to the relief of subsurface strain by the short B-Si bonds and the passivation of the surface obtained through charge transfer from the Si adatom to the substitutional B.

Two superstructures of adsorbed sulfur coexisting on the stepped Cu(11 1 1) surface are identified by scanning tunneling microscopy. A p(2×2) and a c(4×2) structures are atomically resolved and their interaction with the steps investigated. The direction taken by a step edge is found to be strongly correlated with the sulfur arrangement on the adjacent terraces. The origin of this two-dimensional faceting phenomenon is discussed.

Consider surfaces being brought into contact. It is proposed that atomic layers can collapse or avalanche together when the interfacial spacing falls below a critical distance. This causes a discontinuous drop in the adhesive binding energy. Avalanche can occur regardless of the stiffness of external supports. A simple understanding of the origin of this phenomenon is provided. A numerical calculation has been carried out for adhesion in Ni. A new wear mechanism due to avalanche is suggested.

Using first-principles calculations, in conjunction with modeling techniques, we show that the top layer of the Au(100) surface will transform to a close-packed structure while that of Ag(100) will not. Our calculations provide some insight into the microscopic origin of the difference in stability between 4d and 5d fcc metal (100) surfaces.

A one-to-one correspondence of silicide interface dislocations to Si(111) surface steps has been discovered for epitaxial silicide layers grown at room temperature. This has allowed the examination, by transmission electron microscopy, of the topography of large areas of the Si surface after various treatments. Growth modes of molecular-beam epitaxy (MBE) at different temperatures and growth rates are clearly displayed and explained. A change of step character from 〈112¯〉 to 〈11¯2〉 at the initial stage of MBE is observed and is attributed to the stabilities of the two types of steps in relationship to the 7×7 structure.

It is shown that the mean-field approach to irreversible aggregation (Smoluchowski’s coagulation equation) leads to incorrect predictions at large times for dimensions d≤$d_c$, where the upper critical dimension $d_c$ is model dependent, nd may be arbitrarily large. The value of $d_c$ is calculated for a large class of aggregation models. Estimates for the time $t_D$, at which the Smoluchowski approach breaks down , are given. The behavior of the system for t≳$t_D$ is discussed.

The kinetics of electrochemical doping of polyaniline films has been studied using in situ ESR experiments. It has been found that the kinetics and the doping level achieved during a potential-reading step depend on the previous electrochemical events undergone by the sample. It is shown that slow relaxation process takes place in the polymer film while it is maintained in the neutral state. Possible relations to hysteresis effects are discussed.

We obtain the Fermi contact term of the electron-nuclear effective Hamiltonian describing the coupling between the planar Cu(2) nucleus and the O(2,3) nuclei on the one hand, and the effective degrees of freedom of the one band t-J (or Heisenberg Hubbard) model on the other. The details of the resulting couplings suggest that the copper and oxygen relaxation rates are sensitive to antiferromagnetic correlations in different degree. In the insulating phase we predict that the effective dynamical critical exponent for O(2,3) is reduced by two from that of Cu(2).

Deuteron-deuteron fusion, detected via the 3-MeV protons produced, is shown to occur when singly charged clusters of 25 to 1300 ${\mathrm{D}}_2$O molecules, accelerated to 200 to 325 keV, impinge on TiD targets. The energy and cluster-size dependence of the fusion rate are discussed. The fusion events are shown to originate from the cluster-ion impacts rather than from ${\mathrm{D}}^{+}$ or ${\mathrm{D}}_2$${\mathrm{O}}^{+}$ ions in the beam. The observed rates may be correlated with the compressions and high energy densities created in collision spikes by cluster-ion impacts.

We consider Finkelshtein’s model for a disordered Fermi liquid. We show that logarithmic terms at two-loop order suppress the fixed point proposed by Castellani et al. Spin transport slows down dramatically, and in d=2+ε a sizable scaling region exists. We show that in the scaling region the apparent conductivity exponent is zero to all orders in a loop expansion. This implies that the charge transport is unaffected by the crossover in the spin system. Experiments compare favorably with this scenario. Further measurements of the Wilson ratio are proposed.

Monte Carlo simulation has been performed on a previously proposed model of oxygen ordering in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{z}}$: A two-dimensional Ising model with isotropic first-neighbor and anisotropic second-neighbor effective pair interactions in the ‘‘chain plane.’’ At low temperatures, states of partial order are observed in agreement with experimental findings. Such states of quasi-one-dimensional order are a consequence of the asymmetric nature of the interactions.

Measurements of LVV Auger-electron spectra from a Si(111) surface before and after Ge deposition reveal that atoms at the surface have a qualitatively different Auger line shape than atoms in the bulk. In particular, the redistribution of electron density at the Si(111) surface enhances the ratio of pp to sp contributions to the LVV line shape. This surface effect is expected to be a general property of LVV spectra from all surfaces, which must be considered when comparing theory to experimental data.

Experiments on small superconducting tunnel junctions in a Giaever-Zeller-plus-SQUID geometry clearly show an I(V) feature due to Josephson supercurrent in a regime where single-electron charging effects are dominant. The I(V) data exhibit marked oscillations with gate voltage characteristic of single-electron charging. The Josephson feature shows both this effect and SQUID-related oscillations with applied magnetic field. The behavior can be understood through the usual model for charging effects in such circuits, extended to include two-electron transitions.

Low-temperature magnetic susceptibility measurements were made during illumination of n-${\mathrm{Al}}_2$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As with DX centers to investigate the microscopic origin of persistent photoconductivity. Experiments using a dc SQUID magneto-optic microsusceptometer revealed the change of electronic susceptibility as a function of illumination time and temperature. The results indicate that the DX center is a paramagnetic donor with one unpaired electron.

We suggest that weak electron tunneling between layers is responsible for the experimentally observed dramatic deviations from two-dimensional behavior in the magnetoresistance in the metallic phase of the quasi-two-dimensional conductors (TMTSF${)}_2$${\mathrm{ClO}}_4$ and (TMTSF${)}_2$${\mathrm{PF}}_6$. We predict a fine structure due to resonances in open orbits between motion parallel and perpendicular to the planes.

A new quantum Bogoliubov–De Gennes (BdeG) formalism is developed to study the self-consistent motion of holes on an antiferromagnetic background within the generalized t-J model. The local distortion of spin configurations and the renormalization of the hole motion due to virtual excitations of the distorted spin background are treated on an equal footing. The hole wave function and its spectrum, as well as the effective mass for a propagating hole are calculated explicitly.