Osaaki Watanuki

Characteristics of photon scanning tunneling microscope read‐out

A semimicroscopic approach based on linear response theory is applied to analysis of the near‐field‐reading process, both for an isolated recording bit and for bits periodically arranged by means of photon scanning tunneling microscopy (PSTM). The polarization effects and typical characteristics of super‐resolution are shown by simulation. The results are valid not only for the read‐out process in optical storage, but also for sensing of local indices of refraction or absorption in samples observed with PSTM, in general. Some theoretical results are compared with experimental data in terms of the resolving power.

Small magnetic patterns written with a scanning tunneling microscope

The authors present a technique for writing submicron magnetic bit patterns on double-layered perpendicular recording media by using a scanning tunneling microscope (STM) with an amorphous magnetic tip and observing them with a magnetic force microscope (MFM). The proposed technique provides a very small tip-to-medium spacing on the order of angstroms. It is shown that the magnetization of the extremity of an amorphous tip can be reversed by switching the external field. The possibility of writing magnetic bit patterns in double-layered perpendicular media at a high areal density equivalent to 1 Gb/in/sup 2/ or more by means of this technology is demonstrated. >

Floating-point on-line arithmetic: Algorithms

For effective application of on-line arithmetic to practical numerical problems, floating-point algorithms for on-line addition/subtraction and multiplication have been implemented by introducing the notion of quasi-normalization. Those proposed are normalized fixed-precision FLPOL (floating-point on-line) algorithms.

Polarization-dependent contrast in near-field optical microscopy

This article presents a simple modeling and simulation of experiments with a near-field optical microscope or a photon scanning tunneling microscope (PSTM) in the sub-100-nm range. The simulation employs a semimicroscopic and perturbative approach based on field propagator and linear response theory. A probe tip and sample are approximated as nanometric spheres in order to clarify the behavior of the near-field and far-field signal intensities, I, and the contrast, i.e., visibility, (Imax−Imin)/(Imax+Imin), for s and p polarization of incident light and three scanning methods: constant height, constant intensity, and constant distance. The signal intensity then becomes a function of the taper angle of the fiber probe tip θ or the numerical aperture of the collecting lens, in addition to the variables mentioned above. Note that the signal intensity I(θ=90°) corresponds to that for the near-field. The simulated polarization-dependent intensity and contrast are in good qualitative agreement with the experime...

Floating-point on-line arithmetic: Error analysis

The properties of redundant number system in mantissa representation are studied and the range of the redundant mantissa is derived. From the range of the mantissa and the absolute error of on-line operations, the MRRE (maximum relative representation error) is defined and analyzed for redundant floating-point numbers.

Speaker-independent isolated word recognition using label histograms

In this paper, a simple and fast method for speaker-independent isolated word recognition is presented. This method is regarded as simplification of the approach based on the Hidden Markov Model (HMM). In the proposed method, all training and decoding data are transformed into label strings by vector quantization. By segmenting the label strings of utterances into N pieces with equal duration, label histograms are computed in the training mode. In recognition, the label string of an input word is also divided into equal N segments, and the likelihood is computed with the corresponding histogram. It will be shown that the computational cost of this method is relatively low. This method is applied to the recognition of 32-Japanese-word vocabulary, and achieved a recognition accuracy comparable to or better than that of the conventional approaches.

Magnetic-force-sensing STM: novel application of STM for simultaneous measurement of topography and field gradient of magnetic recording heads

Abstract We present a technique for simultaneously measuring the topography and the field gradient of recording heads using a scanning tunneling microscope with a cantilever-shaped magnetic tip. The field from the recording head excited by an alternating current vibrates the tip of the STM, and this causes modulation in tunneling current. This modulated signal is detected by a lock-in amplifier and is processed to obtain a magnetic-force image. The low-frequency components of the tunneling current represent the topography of the air-bearing surface of the recording head in a normal STM mode. The effects of the head current and the tunneling voltage upon the field gradient were also investigated.

Direct measurement of side fringe field and two-dimensional head field using high-resolution inductive loop

A method is described to measure side fringing fields and two-dimensional head field distribution using a high-resolution inductive loop. To study the side fringing effects, measurements are performed with thin film heads.

Polarization-Dependent Contrast of Near-Field and Far-Field-Propagating Signal Intensities in C-Mode Scanning Near-Field Optical Microscopy/ Photon Scanning Tunneling Microscopy*

A recent paper by Nayaet al. (Opt. Commun.124 (1996) 9) presented high-resolution imaging results obtained in the sub-100-nm range with a collection-mode near-field optical microscope. The images exhibit apparent polarization dependence. A simple modeling and calculation based on the experiment, using a semi-microscopic and perturbative approach, showed that the far-field-propagating signal intensity converted from the near-field can qualitatively explain the polarization dependence of the experiment if the taper angle of the probe tip is taken into account.

Matteucci effect of an amorphous alloy tip used for high‐density magnetic recording with a scanning tunneling microscope

This paper presents a study of the Matteucci effect of a Co–Fe–Si–B amorphous alloy tip used for magnetic recording with a scanning tunneling microscope (STM). The Matteucci effect is a phenomenon in which a pulse‐shaped alternating current (ac) voltage is induced between the ends of a torsionally stressed magnetostrictive wire when the magnetization of the core domain is switched by application of an external ac magnetic field parallel to the wire axis. The influence on the tip‐to‐medium spacing using the above tip is investigated experimentally. Quantitative results for various coil currents and frequencies are obtained. The observed Matteucci pulse voltage is less than 10% of the bias voltage of the STM, and the Matteucci pulse width is approximately 1 μs. The influence of the Matteucci effect on the feedback system of the STM is also discussed.