B.G. Park

Non-collinear magnetization configuration in interlayer exchange coupled magnetic thin films

Element specific magnetic hysteresis loops of the interlayer exchange coupled CoFeB/Ru/[Co/Ni]4 structure were measured utilizing x-ray magnetic circular dichroism. It was found that the Co/Ni multilayer and the CoFeB layer have Ru thickness dependent oscillatory interlayer coupling. Due to its interlayer coupling with the perpendicularly magnetized Co/Ni multilayer, the CoFeB magnetization direction is slightly tilted out-of-plane from its in-plane magnetic easy axis. Quantitative measurements show that the tilting angle is small (<12°) and that a small in-plane magnetic field (∼50 Oe) applied to this structure will result in a completely in-plane CoFeB magnetization.

Low-energy ion beam treatment of α-Al2O3 (0001) and improvement of photoluminescence of ZnO thin films

A low energy N2− ion beam impinged on a α-Al2O3(0001) single crystal surface in the range of fluence 5×1015/cm2−1×1018/cm2 at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×1015/cm2, only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×1017/cm2 induced Al−O−N bonding at around 403 eV. The occurrence of Al−N bonding was identified at ion fluence higher than 5×1017/cm2 at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al−O−N bonding only, and both Al−O−N and Al−N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al−N−O and Al−O−N layers and relaxation of the interfacial strain between Al2O3 and ZnO.

Synthesis and inhibitory effects of triarylpyrazoles on LPS-induced NO and PGE 2 productions in RAW 264.7 macrophages

The inhibition of nitric oxide and prostaglandin E2 productions is a very interesting research topic in the field of anti-inflammatory drug development. In the current study, a new series of 1,3,4-triarylpyrazole derivatives was synthesized and evaluated for their capabilities to inhibit nitric oxide and prostaglandin E2 productions in lipopolysaccharide-induced RAW 264.7 macrophages. Among all the target analogs, the diarylurea hydroxyl compounds 1f and 1h possessing phenyl and 3-(trifluoromethyl)phenyl terminal moiety, respectively, showed the highest inhibitory effect on the production of prostaglandin E2. Both compounds exerted equal activity to the reference compound NS-398 at 3u2009µM concentration. This effect was due to inhibition cyclooxygenase-2 enzyme activity not inhibition of cyclooxygenase-2 protein expression. The IC50 value of compound 1f against lipopolysaccharide-induced prostaglandin E2 production in the macrophages was 1.12u2009μM. In addition, compound 1j with urea linker, hydroxyl group, and 3,5-bis(trifluoromethyl)phenyl terminal ring was the strongest nitric oxide inhibitor. Western blot study showed that it exerted that effect through inhibition of inducible nitric oxide synthase protein expression.Graphical Abstract

Synthesis, in vitro antiproliferative activity, and kinase inhibitory effects of pyrazole-containing diarylureas and diarylamides

Twenty pyrazole-containing diarylureas and diarylamides were designed and synthesized. They were tested for inxa0vitro antiproliferative activity over a 58-cancer cell line panel at the NCI, USA. The diarylurea derivatives 1b-e and 1g exerted the strongest antiproliferative activity. Among them, compound 1e possessing 3,5-bis(trifluoromethyl)phenyl terminal ring and 3`-methoxy-5`-chlorophenyl ring attached to the central pyrazole ring was the most potent. Its IC50 values were in sub-micromolar range against most of the tested cell lines. It showed superior potency than sorafenib, a reference diarylurea drug, over all the tested cell lines. It was also extremely selective towards cancer cells than non-cancerous cells (IC50 against RAW 264.7 macrophages was higher than 100u202fμM). At molecular level, compound 1e selectively inhibited V600E mutated B-RAF kinase (IC50u202f=u202f0.39u202fμM). It also stimulated caspase 3/7 enzymes in RPMI-8226 leukemia cells (2.79 fold increase at 10u202fμM concentration, EC50u202f=u202f1.52u202fμM). So compound 1e may kill cancer cells through induction of apoptosis. This promising candidate can be considered further for development of new efficient anticancer agents.

Probing spin-polarized tunneling at high bias and temperature with a magnetic tunnel transistor

The magnetic tunnel transistor (MTT) is a three terminal hybrid device that consists of a tunnel emitter, a ferromagnetic (FM) base, and a semiconductor collector. In the MTT with a FM emitter and a single FM base, spin-polarized hot electrons are injected into the base by tunneling. After spin-dependent transmission through the ferromagnetic base they are collected in the conduction band of the semiconductor provided they have the right energy and momentum to overcome the Schottky barrier. Two factors determine the spin-sensitivity of the device: (i) spin-dependent tunneling from the emitter, and (ii) spin-dependent scattering of the hot electrons in the base. Since the magnetocurrent (MC) depends on the tunneling spin polarization, the MTT can be used to study the spin-polarization of ferromagnetic/insulator interfaces at high bias voltage. Moreover, the temperature dependence can be studied using a newly introduced lithographically defined MTT that allows us to probe the tunnel spin-polarization up to room temperature, removing a limitation of the standard technique of tunneling into a superconductor.