Jongill Hong

Graphene is currently at the forefront of cutting-edge science and technology due to exceptional electronic, optical, mechanical, and thermal properties. However, the absence of a sizeable band gap in graphene has been a major obstacle for application. To open and control a band gap in functionalized graphene, several gapping strategies have been developed. In particular, hydrogen plasma treatment has triggered a great scientific interest, because it has been known to be an efficient way to modi

Abstract The paper presents our simulated results showing the substantial improvement of both switching speed and energy consumption in a perpendicular magnetic tunnel junction (p-MTJ), a core unit of Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM), by the help of additional Spin-Orbit-Torque (SOT) write pulse current (WP SOT ). An STT-SOT hybrid torque module for OOMMF simulation is implemented to investigate the switching behavior of a 20 nm cell in the p-MTJ. We found that the a

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

Low-energy proton irradiation was applied to pattern an array of metallic, ferromagnetic nanoislands through the local phase transformation of an oxidic, paramagnetic phase in a complex superlattice composed of repetitions of an oxidic and metallic layer. The irradiation inflicted minimal damage on the structure, resulting in the absence of unwanted defects and side effects. This nondestructive pattern transfer was clearly confirmed by the contrast between irradiated and unirradiated regions in

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.

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.

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

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

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

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