Susumu Ichihara

Dual-cantilever AFM probe for combining fast and coarse imaging with high-resolution imaging

This paper presents a new scanning probe concept based on an integrated dual-cantilever device, which has been designed to reduce the tip-wear problem. It consists of two cantilevers, one having a robust blunt tip, the other having a sharp tip. By means of integrated bimorph actuators, such a cantilever can be used to switch between coarse and fast imaging with the blunt tip, and high-resolution imaging with the sharp tip. Hence the delicate sharp tip is used only when high resolution is required, which greatly increases the probes lifetime. A high-sensitivity, constricted piezoresistive strain sensor is used for high-resolution imaging. Imaging with the dual-cantilever probe has been demonstrated successfully.

High Spatial Resolution and Throughput Potential of an Optical Head with a Triangular Aperture for Near-Field Optical Data Storage

A near-field optical head with a triangular aperture has been precisely analyzed on the basis of a three-dimensional finite-difference time-domain method in order to obtain both higher spatial resolution and signal output performance for a near-field optical data storage system. The numerical analysis revealed that in contrast to a conventional aperture, this triangular-shaped aperture can successfully enhance energy distribution intensity at only the side perpendicular to the incident polarization direction, generating an extremely small optical spot not limited by its entire aperture size. The read-out performance was also simulated for the aperture passing over a space-patterned metal medium, resulting in both superior spatial resolution and signal output.

Microfabricated silicon dioxide cantilever with subwavelength aperture.

We have developed a microfabricated SiO2 cantilever with subwavelength aperture for scanning near‐field optical microscopy (SNOM), to overcome the disadvantages of conventional optical fibre probes such as low reproducibility and low optical throughput. The microcantilever, which has a SiO2 cantilever and an aperture tip near the end of the cantilever, is fabricated in a reproducible batch process. The circular aperture with a diameter of 100–150 nm is formed by a focused ion‐beam technique. Incident light is directly focused on the aperture from the rear side of the cantilever using a focusing objective, and high optical throughput (10−2 to 10−3) is obtained. The microcantilever can be operated as a SNOM probe in contact mode or in dynamic mode.

OPTICAL MICROCANTILEVER CONSISTING OF CHANNEL WAVEGUIDE FOR SCANNING NEAR-FIELD OPTICAL MICROSCOPY CONTROLLED BY ATOMIC FORCE

We develop a novel optical microcantilever for scanning near‐field optical microscopy controlled by atomic force mode (SNOM/AFM). The optical microcantilever has the bent channel waveguide, the corner of which acts as aperture with a large tip angle. The resonance frequency of the optical microcantilever is 9 kHz, and the spring constant is estimated to be 0.59 N/m. The optical microcantilever can be operated in contact mode of SNOM/AFM and we obtain the optical resolution of about 200 nm, which is as same size as the diameter of aperture. We confirm that the throughput of optical microcantilever with an aperture of 170 nm diameter would be improved to be more than 10−5.

Signal Readout Using Small Near-Field Optical Head with Horizontal Light Introduction Through Optical Fiber

We have developed a small near-field optical head for high-recording-density data storage applications, to overcome the disadvantage of conventional near-field optical heads, such as large light introduction, low optical throughput, and difficulty in controlling the aperture-medium distance. The optical head structure has miniaturized light introduction using an optical fiber placed horizontally. To decrease the optical loss, an integrated microlens focuses on the aperture tip that has a shortened cut-off region. The fabricated optical head (3.2×3.6×0.9 mm3) with a 200 nm aperture of the same height as the sliders shows a clear readout signal of a 200-nm-wide line and space pattern at a speed of 5.2 MHz. We show that the optical head has the ability to read 4 times the recording density by simulations of the finite difference time domain (FDTD).

High-speed readout using small near-field optical head module with horizontal light introduction through optical fiber

Near-field optics, a super-resolution technique, is expected for optical data storage with high recording density (E. Betzig et al., Appl. Phys. Lett. vol. 61, p. 142, 1992; S. Hosaka et al, Nanotechnology vol. 8, p. A58, 1997). Recently, near- field optical heads using sliders, which can keep the distance between an aperture and a medium surface in proximity, were proposed, and reading from 110-250 nm pattern at the speed of 1.5-7.5 MHz was demonstrated (H. Yoshikawa et al., Opt. Lett. vol. 25, p. 67, 2000; F. Issiki et al., Appl. Phys. Lett. vol. 76, p. 804, 2000; K.T. Yatsui et al., Opt. Lett. vol. 25, p. 1279, 2000). These optical heads use an objective lens above sliders separately, to introduce the focused light to the aperture. However, this large light introduction using the objective lens leads optical heads with actuators to be large. From this perspective, we had proposed a small near-field optical head module with miniaturized light introduction (K. Kato et al., Tech. Dig. ISOM2000, p. 188, 2000). In this paper, we fabricated the proposed optical head module with air-bearing surface, and high speed reading from 200 nm chromium pattern formed on an SiO/sub 2/ disk medium was demonstrated.

Numerical simulation of the near-field optical head with a triangular aperture

1. Introduction Recent rapid advances in information society demand large-capacity and high-speed access capabilities even for optical data storage. Near-field surface recording technology, which utilizes an aperture-mounted head slider, has been vigorously studiedp3 due to its high density recording potential. One of the problems of near-field recording system is its low signal-to-noise ratio, and an optical aperture is required to realize high signal output and high spatial resolution simultaneously. Recently, in order to solve this problem, various configurations of novel near-field aperture have been proposed and their performances are validated in numerical simulationq6. In this paper, we propose a new aperture configuration, a near-field optical head with a triangular aperture, and perform numerical simulations to reveal its optical performance through our developed three-dimensional finite-difference time-domain (3D-FDTD) method. 2. Analysis Model Figure 1 shows the schematic diagram of the analysis model including a triangular aperture head and a metal-coated medium. The shape of the triangular aperture head is a pyramid of an equilateral triangle with a taper angle of 45 degrees, and its shading material is Aluminum. The length of the side of the triangular aperture at the end of the head is 200 nm. Incident light of the linearly polarized plane wave with a wavelength of 680 nm normally illuminates the triangular aperture head. A recording medium, which consists of glass substrate and 40-nm thick Chromium layer having a 100-nm wide space, is placed a few tens of nm (separation: h) apart from the aperture, and moves in lateral direction. The electric energy distribution (=I El *) i s calculated for a measure of the near field energy, and the transmitted optical energy is obtained by integrating the normal Poynting vector component, considering it as a far-field sensed signal. 3. Simulation Results without a Recording Medium First we performed calculations, without considering head-medium interactions to reveal fundamental characteristics of the triangular aperture head. Figure 2 shows the energy distributions of the triangular aperture for X-polarization and Ypolarization on the XY plane just below and 30 nm apart from the aperture. We can see that the energy distribution of the triangular aperture strongly depends on the polarization state, and especially in the case of X polarization, the energy is enhanced at the only one side of the triangular aperture due to the edge enhancement effect. While the circular and rectangular aperture usually show the energy enhancement at both edges of the …

Fabrication of optical micro-cantilever consisting of channel waveguide for scanning near-field optical microscopy controlled by atomic force

We developed a novel optical micro-cantilever for scanning near-field optical microscopy (SNOM), evaluated its mechanical properties, and applied it for SNOM. A cantilever-shaped channel waveguide with an aperture is bent and it is operated in atomic force mode. By combining the conventional lithography techniques and the waveguide bending process, we can fabricate a probe with the shape and the mechanical properties most desirable for given samples and conditions. Our optical micro-cantilever has resonance frequency similar to the conventional optical fiber probe, and it has a spring constant much smaller. We used this optical micro-cantilever for SNOM in contact mode, and confirmed that it gives optical images with a resolution beyond the diffraction limit.