홍종일 교수

The wettability of graphene has been extensively studied and successfully modified by chemical functionalization. Nevertheless, the unavoidable introduction of undesired defects and the absence of systematic and local control over wettability by previous methods have limited the use of graphene in applications. In addition, microscale patterning, according to wettability, has not been attempted. Here, we demonstrate that the wettability of graphene can be systematically controlled and surface pa

We have developed spin valves with thin oxide reflective layers, which exhibit a greatly improved magnetoresistance (MR) performance while keeping other good properties, such as an exchange bias field of over 1000 Oe and a coercivity and an interlayer coupling field of less than 10 Oe. The giant magnetoresistance (GMR) values reached over 12% for the spin valve with a single specular layer and over 15% for the spin valve with double specular layers. The oxide reflective layers helped improve MR

Diluted magnetic semiconductor Cd1−xMnxTe-CdTe superlattices with x=0.069, 0.13, 0.15, and 0.20 and various layer thicknesses were grown by molecular-beam epitaxy for optical and magnetic studies of dimensional crossover. X-ray diffraction patterns, low-temperature photoluminescence spectra, and ac magnetic susceptibility measurements were used to verify the integrity of these structures. In particular, the magnetic studies showed the spin-glass transition present in the thicker magnetic layers

We developed a spin valve with oxide specular layers that shows a giant magnetoresistance value of 20%. The spin valve also showed an exchange bias field of over 1000 Oe. The giant magnetoresistance was mainly due to an increase in the sheet resistance change and resulted from additional specular reflection at the interface of the free layer. The method we used was to modify specularly reflective oxide layers of the free and the capping layers.

Appropriate oxide capping on a spin valve significantly improved electrical and magnetic properties. The interlayer exchange coupling oscillated in the thickness range of a Cu spacer (between 20 and 30 Å). The coupling was antiferromagnetic and it allowed us to reduce the Cu spacer down to 20 Å without sacrificing the good properties of the spin valve. The improvement is due to enhanced specular reflection at the interface between the magnetic and the oxide layer and to less current shunting thr

Thin films consisting of granular dispersions of cobalt nano-particles in a hydrocarbon matrix are fabricated by simultaneous sputtering of cobalt and plasma induced polymerization of hydrocarbon monomers. It is confirmed that cobalt nano-particles with a hexagonal close-packed (hcp) structure are uniformly distributed throughout the amorphous hydrocarbon matrix. In-plane magnetic hysteresis loops obtained by MOKE (Magneto-Optic Kerr Effect) magnetometry measurements show significant differences

Recurrence of ptosis after frontalis suspension using silicone rod was associated with physical changes of implanted silicone rods, including positional migration, weakened tensile strength, and micromorphological changes in combination with patients' characteristics.

A 100 Mb/s experimental multilevel Decision Feedback Equalization read channel has been designed and prototyped in discrete-components. The analog forward equalizer consists of two bi-quads, based on the maximization of inner eye versus noise power plus uncancelled ISI at the input to the detector. The feedback equalizer consists of a 6-tap filter plus an RC exponential decay network which helps reduce hardware complexity. The digitally implemented timing/gain/dc-offset loops are adjusted only w

We controlled interlayer coupling from ferromagnetic to antiferromagnetic by appropriately capping spin valves with thin oxides. The interlayer coupling field was -16.6 Oe at a Cu-spacer thickness of 30 /spl Aring/. The sign of coupling changed at a Cu-spacer thickness of 20 /spl Aring/. The antiferromagnetic coupling achieved in this way allowed a reduction of thickness of the Cu spacer down to 20 /spl Aring/ without loss of good magnetic and electrical properties, and this led to a significant

Preventing or reducing side effects caused by defects created during patterning processes has long posed a major challenge to device fabrications. Such defects on the surfaces and at the boundaries can fatally impair device performance. This is particularly the case for graphene-based devices because graphene is a surface itself, and its surface states exclusively determine the properties. Here, we show that our hydrogenated patterning of graphene can be a breakthrough in electrical patterning f

An experimental 180 Mbit/s partial-response maximum-likelihood (PRML) channel was developed in order to investigate various technical issues arising in very high speed magnetic disk recording systems. The channel was implemented with discrete analog and logic components. A thin-film 10-turn write head and an experimental high-resolution magnetoresistive read head were used with a high coercivity, thin-film disk. Linear densities of 4000 fc/mm were achieved at 45 m/s and 100 nm flying height. The

High moment FeRhN films with soft magnetic properties have been fabricated by reactive RF sputtering. The magnetic properties and microstructures of the FeRhN films are similar to those of FeN films, but the sputtering parameters for the minimum coercivity are somewhat shifted. The addition of Rh results in slightly increased saturation magnetostriction at a given N/sub 2//Ar flow rate ratio. It is confirmed by High Resolution Transmission Electron Microscopy (HREM) that small grains are importa

In‐situ Raman spectroscopy was performed on chemical vapor deposited graphene microbridge (3 μm × 80 μm) under electrical current density up to 2.58 × 10 8 A/cm 2 in ambient conditions. We found that both the G and the G′ peak of the Raman spectra do not restore back to the initial values at zero current, but to slightly higher values after switching off the current through the microbridge. The up‐shift of the G peak and the G′ peak, after switching off the electrical current, is believed to be

In an examination of near-edge x-ray absorption fine structure spectra and magnetoresistance responses of a spin valve with a partially oxidized Co90Fe10 layer, we found that oxygen preferentially reacted with the solute Fe rather than with the solvent Co, and the very oxidized Fe likely enhanced specular reflections leading to an increase in the magnetoresistance value. Most Fe oxides transformed into α-Fe2O3, which further improved the magnetoresistance response after the spin valves were anne

Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin-orbit-related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low-energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co<sub>3