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Polystyrene-b-polyisoprene-b-poly(methylmethacrylate) (PS-b-PI-b-PMMA) triblock copolymer was synthesized by sequential anionic polymerization. The as-synthesized triblock copolymer contains side products of inadvertently terminated PS and PS-b-PI precursors. The side products can be effectively removed by semi-prep scale liquid chromatography using multiple injection method to obtain pure PS-b-PI-b-PMMA. It was found that the removed side product contains another polymer species, coupled PS-b-PI, which could not be recognized by size exclusion chromatography (SEC) analysis since the elution peak of the coupled product overlaps with that of PS-b-PI-b-PMMA. This study demonstrates that the size based separation of SEC is often not good enough to characterize complex polymers precisely and interaction chromatography can render unique advantage over SEC analysis.

Intensive focusing of Rayleigh waves was realized by the fabrication of a curved PZT (Pb(Zr 2 Ti)O 3 ) piezoelectric element having a new shape. Two- and three-dimensional beam profiles of the focusing transducer employing the curved PZT element were obtained by a contact scan on a steel block with flat bottom holes. The beam intensity was higher, about 35 dB, at the focal distance and the signal-to-noise ratio was higher, about 17 dB, than the focusing transducer employing a flexible PVDF (polyvinylidene fluoride) film in the earlier study. The −6 dB and −3 dB lateral widths at the focal point were 0.61 mm and 0.46mm, and the −6 dB and −3 dB axial widths were about 5.5mm and 4.0mm, respectively. The axial stress field showed a good agreement with the overall pattern estimated by a simplified model. The ratio of the detected smallest flaw size to the wavelength of Rayleigh waves for the center frequency was about 0.29. As an application, a single time scan was performed along the flat bottom holes (FBHs) at the focal distance, and an image to show sharp peaks with amplitude depending on the size of the FBHs was obtained. The focusing transducer showed the characteristics of a narrow lateral resolution, high energy, and high signal-to-noise ratio, and was practical for the detection of surface flaws smaller than the wavelength.

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.

In conventional ultrasonic testing of a thin layer with thickness less than about twice the wavelength, successive echo signals become inseparable. Recently, a new time-domain analysis technique to determine the thickness or the wave velocity of a thin plate was developed and through-transmission experiments were reported. We have studied the validity of the technique and its applicability to contact testing under a reflection field system. We found a mistake in the derivation of the reconstructed reflection field equation reported, and a correction has been made. We performed the experiment in a reflection field system using contact type transducers of centre frequency 1, 2.25, and 5 MHz with water layers of thickness ranging from 0.06 to 1.44 mm (0.04 ≤ thickness/wavelength h ∗ λ ) larger than about 0.4, 3% for h ∗ λ larger than 0.8, and 1% for h ∗ λ larger than 2. The time domain technique with our corrected equation was applicable to the evaluation of a thin layered medium under reflection system using contact type transducers.

A phase diagram was constructed for a polystyrene-block-polyisoprene (PS-b-PI, M(W) = 32 700, f(PI) = 0.670) in thin films on Si wafer as a function of film thickness over the range of 150-2410 nm (7-107L(0) (L(0): domain spacing)). The PS-b-PI exhibits a variety of ordered phases from hexagonally perforated lamellar (HPL) via double gyroid (DG) to hexagonally packed cylinder (HEX) before going to the disordered (DIS) phase upon heating. The morphology of the PS-b-PI in thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography. In thin film, the phase transition temperature is difficult to be determined unequivocally with in situ heating processes since the phase transition is slow and two phases coexist over a wide temperature range. Therefore, in an effort to find an "equilibrium" phase, we determined the long-term stable phase formed after cooling the film from the DIS phase to a target temperature and annealing for 24 h at the temperature. The temperature windows of stable ordered phases are strongly influenced by the film thickness. As the film thickness decreases, the temperature window of layer-like structures such as HPL and HEX becomes wider, whereas that of the DG stable region decreases. For the films thinner than 160 nm (8L(0)), only the HPL phase was found. In the films exhibiting DG phase, a perforated layer structure at the free surface was found, which gradually converts to the internal DG structure. The relief of interfacial tension by preferential wetting appears to play an important role in controlling the morphology in very thin films.

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%.

Atomic structures of Ga and As atoms on GaAs(110) were examined employing a first-principles pseudopotential method. Both Ga and As atoms reside in the center of a triangle consisting of a surface Ga and two surface As atoms in the single-atom chemisorbed state. Adsorption energies for Ga and As atoms are 3.1 and 3.5 eV, respectively. Energy barrier heights of Ga and As atoms for the migration along the path through the interstitial channel were found to be 0.6 and 1.0 eV, respectively. Simulations on the deposition of two atoms reveal that a pair formation is stable against separate single-atom chemisorptions.

A simple procedure for the fabrication of sub-10 nm scale Si nanopillars in a 2-D array using reactive ion etching with 8 nm Co nanoparticles as etch masks is demonstrated. The obtained Si nanopillars are single crystalline tapered pillar structures of 5 nm (top) x 8 nm (bottom) with a density of approximately 4 x 10(10) pillars cm(-2) on the substrate, similar to the density of Co nanoparticles distributed before the ion etching process. The uniform spatial distribution of the Si nanopillars can also be patterned into desired positions. Our fabrication method is straightforward and requires mild process conditions, which can be extended to patterned 2-D arrays of various Si nanostructures.

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.

Positron annihilation spectroscopy is a relatively new NDE technique for characterizing the atomic scale lattice defects like vacancies and dislocations. Positron annihilation lifetime and Doppler broadening line-shape were measured and analyzed in cold rolled low carbon steel. Both positron lifetime and Doppler broadening line shape reflect the change in the microstructure and the substructure of the specimens sensitively.

Recently developed austempered ductile irons have good mechanical properties. Comparing the austempered ductile irons with the normal ductile irons the austempered ductile irons have about two times or higher tensile strength than the normal ductile irons at the same level of elongation as shown in Fig.l [1]. Austempered ductile irons are made from ductile cast irons by austempering heat-treatment. Ideally, during austempering, the ductile cast irons are cooled rapidly from the austenitizing temperature to the temperature range for bainite formation, avoiding the zone of pear-lite formation. However, wide spread use of austempered ductile irons have not yet occurred. The main problem is in the difficulties of identifying and controlling the austempering heat-treat — ment parameters to achieve optimum properties consistently [1]. Those heat-treatment parameters are austenitizing temperature, austempering temperature, and austempering holding time. Austempering reaction of ductile cast irons is usually divided into two stages. First stage is toughening stage. Austenite decomposes into bainitic ferrite and carbon riched austenite. These two phase mixture of bainitic ferrite and austentie is the reason for the outstanding mechanical properties of austempered ductile irons.