Junho Kim

Fabrication of a High-Throughput Cantilever-Style Aperture Tip by the Use of the Bird's-Beak Effect

A fabrication technique for a high-throughput cantilever-style aperture tip is described. Using the birds-beak effect due to the stress caused by Si3N4 film in the field oxidation of silicon, we fabricated a near-field aperture with a diameter of about 100 nm which has a throughput of more than 1000 times that of the pyramidal pit.

Simulation study on heat conduction of a nanoscale phase-change random access memory cell.

We have investigated heat transfer characteristics of a nano-scale phase-change random access memory (PRAM) cell using finite element method (FEM) simulation. Our PRAM cell is based on ternary chalcogenide alloy, Ge2Sb2Te5 (GST), which is used as a recording layer. For contact area of 100 x 100 nm2, simulations of crystallization and amorphization processes were carried out. Physical quantities such as electric conductivity, thermal conductivity, and specific heat were treated as temperature-dependent parameters. Through many simulations, it is concluded that one can reduce set current by decreasing both electric conductivities of amorphous GST and crystalline GST, and in addition to these conditions by decreasing electric conductivity of molten GST one can also reduce reset current significantly.

Scanning near-field optical microscope study of Ag nanoprotrusions fabricated by nano-oxidation with atomic force microscope

We investigate light transmission of Ag nano protrusions with a scanning near-field optical microscope (SNOM) to study the surface plasmon (SP) in metallic films. A Ag nanoprotrusion whose height is ~20 nm is fabricated by the deposition of Ag on the Ti nano-protrusion template which is made by nano-oxidation with an atomic force microscope (AFM). It is found that through several scans, the tip is coated with Ag from the sample, and this modified tip shows apparent undulation patterns in SNOM imaging, while a fresh tip does not. The undulation pattern in the SNOM image is observed only along the direction of polarization light close to the expected undulation period. This result indicates that local launching of SP is effective with an Ag-coated tip and the SP launching characteristic is consistent with the so-called cos 2? SP distribution. By finite domain time difference (FDTD) simulations, it is confirmed that light transmission is enhanced in the Ag-coated tip compared to the fresh tip. Our results imply that local illumination with a noble-metal-coated cantilever probe tip is desirable for obtaining more detailed features in SNOM images involved with SP. Our results also indicate that a nano protrusion fabricated by AFM-based nano-oxidation can be applied to an optical element using surface plasmon.

Local excitation of surface plasmon in structured Au films by atomic force anodic oxidation

We used a near field scanning optical microscopy (NSOM) to locally excite and detect surface plasmon (SP) in structured Au films by a consecutive process of anodic oxidation of atomic force microscope (AFM) and Au deposition process. Different types of interference patterns with the period close to a half of SP wavelength around and on the array of Au line protrusions are observed in NSOM optical transmission images, depending on the polarization direction of the incident light, which suggests a successful excitation of SP on fabricated nanostructures. The NSOM probes are believed to be somewhat coated with Au during the scans, and these probes are found to be more efficient in exciting SP than uncoated probes. Our result shows that NSOM combined with the AFM anodic oxidation technique provides an efficient and inexpensive method to study the SP excitation on metallic nanostructures.

Improvement of scanning speed in NSOM-based data storage device

Near-field optical storage using cantilever aperture tip is a promising way for next generation optical data storage. To enhance the speed of reading and writing data, gap between tip and media should be controlled fast and precisely within near field region. In this paper, several PZT actuators are analyzed for constructing dual servo control algorithm: coarse actuators (stack PZT, bimorph PZT) for media surface inclination and fine actuator (film PZT) for media surface roughness. Dynamic analysis of stack PZT, bimorph PZT, and film PZT are performed through the frequency response. Based on the frequency response and mathematical model, fast analog controller is designed and experimented. From experimental results, analog control of film PZT is 50 times faster than conventional stage. We get the 0.1 msec over 800nm step.

Fabrication of a high throughput apertured tip by the use of birds beak effect: a potential fabrication technique for near-field optical data storage

An optical recording device with an atomic force microscope (AFM) tip, having a sub wavelength aperture, has been considered as one of candidates for Th/in/sup 2/ data density in near-field optical storage technology. However, the low optical throughput of a near field aperture limits the practical use of the near-field optical storage technique. This limit can be avoided by the enhancement of the throughput of the near-field apertured tip and the development of new recording media with low phase change temperature. To increase the optical throughput of an AFM/near field apertured tip, several fabrication techniques have been proposed so far. In this paper we present a simple fabrication process of a near-field high throughput apertured tip using a birds beak effect. Using the birds beak effect and field oxidation, a higher throughput aperture and larger cone angled tip are fabricated, simultaneously.