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In this work, we report the mechanical reorientationof thiolated ferromagnetic microspheres bridging a pairof gold electrodes under an external magnetic field. Whenan external magnetic field (7 kG) is applied during themeasurement of the current–voltage characteristics of a carboxylferromagnetic microsphere (4 μm diameter) attachedto two gold electrodes by self-assembled monolayers(SAMs) of octane dithiol (C8H18S2), the current signal isdistorted. Rather than due to magnetoresistance, this effectis caused by a mechanical reorientation of the ferromagneticsphere, which alters the number of SAMs between thesphere and the electrodes and therefore affects conduction.To study the physical reorientation of the ferromagneticparticles, we measure their hysteresis loops while suspendedin a liquid solution.Keywords Magnetic microparticles

In this work, we study the long-term aging effect caused by Fe atoms in the superconductor CaLaBa{Cu1 − xFex}3O7 − δ with 0 ≤ x ≤ 0.07. XRD confirms that this system has a YBCO-like structure. The critical temperature (Tc) is strongly affected by aging and depends on the amount of Fe in the structure. Room temperature Mossbauer spectroscopy reveals the presence of the typical species A, B–B ′, C and new species E ′ and F. Interestingly; A, which corresponds to the Fe3 + atom located in the Cu(1) of the chains with spin S z = 3/2, shows a drastic reduction which means migration to the species B, B ′ and C. Species B and B ′ correspond to the Fe3 + in the Cu(2) site forming planar quasi-octahedral and planar square pyramidal, while the C specie is a square pyramidal with O(5) respectively (spin Sz = 3/2 in all these cases). Aging causes loss of superconductivity in the samples with 5 and 7% of iron content.

We report measurements of the tunneling current – distance (I-d) dependence above alkanethiol self-assembled monolayers (SAMs) on Au (111) substrates with high probe voltage. From the semilogarithmic I-d plots of hexanethiol and octanethiol SAMs, a kink in the tunneling current slopes is clearly observed, which shows the point where the STM tip contacts the end of the SAMs. The conductance decay constants of the vacuum layer and the alkanethiol SAMs are estimated from the tunneling current slopes. We also discuss the contact conductance of alkanethiol SAMs.

In the two-junction system of the scanning vibrating probe/ Au dot / vacuum / Si structure, theoretical equations of both the displacement current waveform iD(t) and the mean displacement current ID(VP) due to Coulomb blockade are analyzed by using the orthodox theory. By usingtheoretical iD(t), the single electron motion on a Coulomb island in a period of probe vibration isexplained. Experimental ID(VP) curves due to Coulomb blockade under a constant probe voltage VP clearly show the displacement current staircase and are in good agreement with the theoretical ID(VP) curve. By using this method, the average number of quantized electrons on Au dots is directly measured through the displacement current staircase.

A determination method of the local surface space charge density in thin films on semiconductor surfaces is described. In this method, the displacement current and the tunneling current flow periodically in accordance with the perpendicular vibration of the probe of the scanning tunneling microscopy (STM). The external circuit current is separated into the mean displacement current and the mean tunneling current by using the two-phase lock-in amplifier. The displacement current-probe voltage curve of a p-type silicon with a native oxide layer was measured in a vacuum (>3×10−9 torr). The displacement current-voltage curve has been analyzed taking into account surface space charge. The theoretical displacement current-voltage curve has been fitted to the measurement in order to obtain both the local surface space charge density and the surface potential difference of thin films, and the theory is in good agreement with the measurement in both voltage regions where the majority carriers are accumulated and depleted. We also demonstrate a simple determination method of both the surface space charge density and the surface potential difference of thin films from flat-band conditions in the displacement current-voltage curve.

A new scanning probe method for evaluating the local carrier concentration of semiconductors is presented. The distance between a semiconductor surface and a vibrating tip is changed sinusoidally, and is adjusted to as small as a few nm across which tunneling current IT flows between the semiconductor surface and the vibrating tip. Displacement current ID due to the change in electric flux from the semiconductor surface to the vibrating tip flows periodically in accordance with the vibration of the tip. IT also flows when the distance becomes minimum. Both IT and ID flow simultaneously when a d.c. tip voltage V is applied, and these two currents are separated by using a two-phase lock-in amplifier. ID-V curve is analyzed by taking into account two-dimensional electric flux profile under the tip. In the tip voltage range within which majority carriers are accumulated, ID-V curve is extrapolated by a straight line. On the contrary, the slope of the curve decreases as the tip voltage is reduced from the voltage range of the accumulation, indicating that the majority carriers are depleted at the center of the Si surface. The theoretical ID-V curves are in good agreement with the measurement in the tip voltage region where the majority carriers are both accumulated and depleted. The local carrier concentration is able to be determined by makingthe theoretical ID-V curve fit the experimental results without contacting the semiconductor surface.