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New evidence of the paired end-bridge configuration in the room-temperature adsorption geometries of C 2 H 2 molecules on Si(0 0 1) is presented by scanning tunneling microscopy (STM) and ab initio pseudopotential calculations. The distinct four-leaved feature occupying two adjacent Si dimer sites in the experimental empty-state STM images are well reproduced by simulations of the paired end-bridge adsorption configuration. Calculated energetics suggests that the Si(0 0 1) surface is covered by paired end-bridge structures at the saturation coverage of 1 ML, in agreement with the existing experiments.

The structure of a clean Si(100) and a Ni-contaminated si(100) was investigated using scanning tunneling microscopy. The clean Si (100) shows the 2 × 1 reconstruction with a surface dimer vacancy density less than 2%. The major defects on the clean surface are a single dimer vacancy and the C defect. A small amount of Ni on the surface drastically changes the surface structure and produces 2 × n reconstructions. The formation of vacancy clusters is favored. A rebonded SB step is preferred on the clean Si(100) while a nonrebonded SB step with a split-off dimer is mainly observed on the Ni-contaminated Si(100) and in the vicinity of dimer vacancies of the lower terrace on the clean Si(100).

The atomic structure at monatomic-height ${\mathit{S}}_{\mathit{B}}$ steps on clean Si(001) and a Ni-contaminated Si(001) was investigated using high-resolution scanning tunneling microscopy at room temperature. Rebonded ${\mathit{S}}_{\mathit{B}}$ steps are dominant on clean Si(001). Nonrebonded ${\mathit{S}}_{\mathit{B}}$ steps with split-off dimers are favored on the Ni-contaminated Si(001) and in the vicinity of dimer vacancies on clean Si(001). The nonrebonded step with the split-off dimer is generated by the strain due to dimer vacancies. A buckled dimer was observed in the vicinity of a kink of ${\mathit{S}}_{\mathit{B}}$ step edges on clean Si(001). \textcopyright{} 1996 The American Physical Society.

Dimer-vacancy defects on clean Si(001)-2\ifmmode\times\else\texttimes\fi{}1 and Ni-contaminated Si(001)-2\ifmmode\times\else\texttimes\fi{}n surfaces are investigated by scanning tunneling microscopy (STM). The clean Si(001) surface shows the 2\ifmmode\times\else\texttimes\fi{}1 reconstruction irrespective of cooling rates faster than 150 \ifmmode^\circ\else\textdegree\fi{}C/sec. On the Si(001)-2\ifmmode\times\else\texttimes\fi{}1 surface with a surface dimer-vacancy density of 1.7%, the most abundant dimer-vacancy defect is a randomly distributed one dimer vacancy (1-DV) of the Wang-Arias-Joannopoulos model. Appreciable amounts of (1+2)-DV and 2-DV are observed. The ordered defects on the Si(001)-2\ifmmode\times\else\texttimes\fi{}n surface are mainly composed of (1+2)-DV and 2-DV. The real-space STM images reveal that the dimer adjacent to the unrebonded side of 2-DV is depressed by more than 0.5 \AA{}, representing the highly asymmetric characteristics. A small amount of Ni contamination on Si(001) drastically increases the dimer-vacancy density from below 2% to above 20%.

Eddy current probes were designed to be suitable for the test of fin tubes. Fin tubes, often used for heat exchangers, have uneven outer and inner surfaces to enhance the heat emission. The surface roughness makes it difficult to detect flaws employing eddy current test (ECT). In order to overcome the difficulties we performed two kinds of works, one is the development of ECT probes, and the other is the signal processing including fast Fourier transform and digital filtering. In the development of ECT probes, we adopted empirical design method. Our ECT probes for the fin tubes are inside type. And we are specially concerned about geometric features such as the widths of the coils composing an ECT probe. We fabricated four probes with various coil widths. Eddy current test was performed using those ECT probes on artificially flawed specimens. After analyzing the output signals, we found that, for the effective testing, the width of a coil should be determined considering the pitch of the fins of a tube. And we also learned that the frequency filtering could improve the s/n.

Green's function is used in order to derive the analytical solution for the change in impedance due to a presence of the flaws in a conductor. This solution is applied to a cylindrical flaw and a spherical flaw whose radii are much smaller than the radius of the test coil. For both cases, the change in impedance is obtained within Born's limit.

The impedance of a single-turn coil which surrounds a conducting cylinder with a flaw is calculated employing Green's function technique. The Born approximation is used in order to know how the impedance change due to the presence of a flaw depends on the conductivity and size of a flaw.

The eddy current tests of ferromagnetic materials are theoretically analyzed employing a Globus model for the magnetization process, and the impedance change of a coil due to the presence of flaws contained in a magnetic conductor is derived employing Green’s function technique. The results show that for an excitation field which is lower than the critical field, the impedance change is maximum when the residual magnetization (or the dc magnetic field applied for the magnetic saturation of the conductor) is absent but for a large field the impedance change becomes maximum when the appropriate dc magnetic field in which the differential permeability reaches its maximum value is applied. For small surface flaws, the volume inhomogeneity mainly contributes to the reactance change of the coil whereas the discontinuity in magnetic permeability contributes to both real and imaginary parts of the impedance change. The dependence of the impedance change on flaw shape is shown explicitly in the derived formula.

The impedance of a test coil was measured as a function of the dc current of an electromagnet, and the determination method of magnetization level with the normalized impedance diagram is discussed. An eddy current test for the outer side of a steel tube wall was also performed. Test results show that the impedance change of the test coil is brought about by the eddy current perturbation and the change of magnetization level. These effects on the flaw inspection are also analyzed.

Magnetic effects in eddy current nondestructive method are studied employing an extension of the general ideas of Globus for the magnetization processes of polycrystalline materials. The reversible permeability depends on the residual magnetization of the material. The relation between these two quantities is derived from the Globus model. An expression is derived for the impedance of a single‐turn coil above a ferromagnetic conducting half‐space. From this expression, flaw effects and liftoff effects are analyzed, and theoretical treatment for the evaluation of residual magnetization is described.