Junho Seo

Evidence of the C60/Cu contact formation after thermal treatment

The origin of the lowered electron injection barrier height of C60∕Cu was investigated by in situ ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy (XPS). The onset of the highest occupied molecular orbital level was shifted by 0.2eV toward high binding energy upon the heat treatment, resulting in the improved injection characteristics of the device. Moreover, an unexpected gap state has been observed at 1.2eV below the Fermi level. The XPS core-level spectra revealed that the chemical reaction between C60 and Cu at the interface induced the gap state after heat treatment. The gap state pinned the Fermi level close to the lowest unoccupied molecular orbital of C60. We obtained the complete energy level diagram of C60∕Cu before and after the heat treatment.

Analysis on the Characteristics of Stamped Base for 2.5 in HDD

In this study, we investigate the dynamic characteristics of a cold-rolled steel-plate (SPCC) stamped base for use with a 2.5-in hard disk drive (HDD). A stamped base offers the advantages of a thinner form and lower manufacturing cost compared to die-cast bases. The feasibility of applying a stamped base to a 2.5-in HDD is investigated by considering the various required characteristics. The manufacturing processes for stamped and die-cast bases are compared, revealing several advantages of stamped bases, including room-temperature processing, minimal contamination, fewer processing steps, and faster processing times. Finite element analysis is used to examine the dynamic and magnetic characteristics of the stamped base. The thin stamped base exhibits limited vertical stiffness, shock performance and magnetic force sensitivity. We observe only a slight difference in the temperature characteristics of stamped and die-cast bases. Additionally, internal air-flow analysis indicates an overall similar air velocity distribution in the stamped base compared to the die-cast base.

Application of Herringbone Pattern to a Slim-Type Optical Disk Drive for the Reduction of Warpage and Vibration of the Rotating Disk

A herringbone pattern is applied beneath the top cover of a slim-type optical disk drive to suppress the warpage and vibration of a rotating disk since the pattern can modify the pressure generation over the disk by changing its geometric parameters. The effect of the herringbone geometries on the pressure generation is evaluated for various geometric parameters. The flow field and the pressure distribution in the cavity are calculated by using a commercial program with the k–e model for the turbulent computation. To confirm the numerical results, the axial vibrations of the rotating disk as well as the pressure distribution of the air gap between the disk and the top cover are measured at various points. In this study, the application of the herringbone pattern reduces the disk warpage and axial vibration by 34 and 10% at most, respectively.

A study on dynamic behavior of inner parts with non-operational shock in hard disk drive

Nowadays, function related to anti-vibration and anti-shock of storage devices is required because of portability. Therefore, many hard disk drive (HDD) studies about external shock and vibration have been performed. Especially, many studies are performed with non-operational shock. Most studies have used the fixed condition between spindle system and base when they wanted to analyze dynamic behavior of inner parts in simulation. But spindle system has actually stiffness and damping coefficient. Maybe difference of value would be happened between fixed condition and spring condition. So, we measured FRF of spindle system to know stiffness and damping coefficient in HDD. And we studied on dynamic behavior of inner parts by using calculated stiffness and damping coefficient. As a result, we confirmed the difference as boundary condition of spindle system.

Investigation of unloading performance for change of FDB transient behavior in low temperature

This research investigated unloading performance for change of disk RPM with temperature during emergency parking. First, disk RPM drop was measured by experiment during emergency parking process and simulated by 6-DOF of spindle system. And slider flying attitude variation was investigated by change in the disk RPM drop.

Variation of the dynamic coefficients of the plain journal bearing considering vapor pressure

Fluid dynamic bearings have several advantages that low noise, high rotational stability and low friction. So, early 2000s, the HDD spindle motors have been replaced ball bearings to fluid dynamic bearing. Most of studies apply inner boundary condition that is inside of bearing pressure larger than atmosphere pressure. Therefore, they used Half-Sommerfeld or Reynolds Boundary condition. This paper investigates the dynamic coefficients of the plain journal considered vapor pressure. As a result, it shows that the vapor pressure effect cannot ignore.

Energy level alignment at C 60 /Hf using x-ray and ultraviolet photoelectron spectroscopy

We report the characterization of the interface formation of fullerene (C60) on hafnium (Hf) using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The valence band, C 1s and Hf 4f spectra were measured during the deposition of C60 on a clean Hf surface in a stepwise manner. After enough deposition of C60 layers on Hf, XPS measurements indicate that there is no chemical reaction between C60 on Hf, and band bending exists at the C60/Hf interface. From UPS measurements, the energy level difference between Fermi level of Hf and the onset of the highest occupied molecular orbital of C60 is 2.01 eV. The vacuum level of Hf was shifted toward low binding energy (0.95eV) as the C60 deposition. These valence spectra results indicate that there exist an interface dipole and small electron injection barrier at the C60/Hf interface. We provide the complete energy band diagram of the C60/Hf interface and confirm that a small electron injection barrier can be achieved by inserting a low work function metal in a C60 field-effect transistor.