Youngsuk Kim

Ultrahigh density array of epitaxial ferroelectric nanoislands on conducting substrates.

An ultrahigh density array of epitaxial PbTiO(3) (PTO) nanoislands with uniform size was fabricated on a single-crystalline Nb-doped SrTiO(3) (100) substrate over a large area (cm(2) scale) by simple but robust method utilizing polystyrene-block-poly(4-vinylpridine) copolymer micelles. Each nanoisland has an average volume of 2.6 x 10(3) nm(3) (a height of 7 nm and a diameter of 22 nm). Because of uniform nanoislands over a large area, a synchrotron X-ray diffraction experiment was successfully employed to analyze the domain structures of PTO nanoislands. They showed well-defined epitaxy on the substrate, which was also confirmed by high-resolution transmission electron microscopy. All of the nanoislands existing in the entire area showed distinct piezoresponse that confirms the existence of ferroelectricity at this size. The results indicate that the critical size of ferroelectrics could be scaled-down further, thereby much increasing the density of ferroelectric devices.

Association between a genetic variation of CC chemokine receptor-2 and atopic asthma

excellent correlation was found between ACT score and eNO (r 1⁄4 0.7, P 1⁄4 0.001) as the higher was ACT score, the lower was eNO. A good correlation was also seen between eNO and GINA grade of severity, whereas FEV1 did not correlate with GINA classes (data not shown). Despite FEV1 reliably reflecting the degree of bronchial obstruction, in our naive patients it correlated neither with the ACT self-assessed score nor with the GINA class of severity. This fact may be explained by the well-known individual variability in the perception of symptoms. On the other hand, eNO displayed a good correlation with the considered clinical parameters. It is difficult, based on the present data, to provide a satisfactory explanation of this latter fact, although a correlation between perceived symptoms and inflammatory markers has been described previously (5), and the role of reactive nitrogen species as markers of asthma has been suggested (6). We can postulate that the degree of bronchial inflammation is more sensitively detected by eNO than by FEV1, and that symptom and medication usage depends first on inflammation itself. As an adjunct observation, the ACT proved to be a valid tool for assessing the degree of asthma control. Our data further confirm that the diagnosis and follow-up of asthma should be based on an integrated approach that involves clinical aspects, functional parameters and biomarkers of inflammation. In this regard, eNO and reactive nitrogen products (3, 6) are promising candidates for the assessment and follow-up of inflammation.

High density array of multiferroic nanoislands in a large area

We report the innovative fabrication of a high density array of multiferroic BiFeO3 (BFO) nanoislands on a conductive substrate in a large area. The anodic aluminum oxide (AAO) template has widely been used to fabricate highly arranged nanostructures, because of easy control of pore size and perfect hexagonal pore packing. The existing AAO mask-assisted pulsed laser deposition (PLD) method is limited to fabricating a nanoisland array in a small area. To supplement the shortcoming of this method, a thick AAO membrane in a large area was electrochemically detached and floated on polystyrene (PS) film without crack. Then, a nanoporous polystyrene (PS) template was prepared by dry etching with the thick AAO membrane mask, followed by spin coating of the BFO precursor on the PS template. After removing the PS template at high temperature, we prepared a high density array of multiferroic BFO nanoislands in a large area epitaxially grown on an STO:Nb (100) substrate. A high density array of BFO nanoislands in a large area showed both ferroelectricity of individual nanoislands obtained by piezoresponse force microscopy (PFM) and macroscopic magnetism measured by a superconducting quantum interference device (SQUID) based magnetic property measurement system (MPMS). A high density array of BFO nanoislands could be employed as a next-generation memory device capable of electric writing and magnetic reading (or vice versa).

Towards the limit of ferroelectric nanostructures: switchable sub-10 nm nanoisland arrays

Ultrahigh density arrays of ferroelectric PbTiO3 (PTO) nanoislands with various feature sizes were epitaxially grown by utilizing block copolymer micelles. Piezoresponse and ferroelectric properties were clearly observed in the PTO nanoislands by band excitation piezoresponse force microscopy. In particular, PTO nanoislands were fully switchable even with a volume as small as 79 nm3. Accordingly, it is expected that the volume of the switchable ferroelectric nanoislands can be further decreased. The obtained results show that an areal density of over 10 Tb in−2 for the ferroelectric memory devices would be possible.

Separation of Acetylene from Carbon Dioxide and Ethylene by a Water‐Stable Microporous Metal–Organic Framework with Aligned Imidazolium Groups inside the Channels

Separation of acetylene from carbon dioxide and ethylene is challenging in view of their similar sizes and physical properties. Metal-organic frameworks (MOFs) in general are strong candidates for these separations owing to the presence of functional pore surfaces that can selectively capture a specific target molecule. Here, we report a novel 3D microporous cationic framework named JCM-1. This structure possesses imidazolium functional groups on the pore surfaces and pyrazolate as a metal binding group, which is well known to form strong metal-to-ligand bonds. The selective sorption of acetylene over carbon dioxide and ethylene in JCM-1 was successfully demonstrated by equilibrium gas adsorption analysis as well as dynamic breakthrough measurement. Furthermore, its excellent hydrolytic stability makes the separation processes highly recyclable without a substantial loss in acetylene uptake capacity.

Triazenyl Radicals Stabilized by N-Heterocyclic Carbenes

Notwithstanding the notable progress in the synthesis of N-heterocyclic carbene-stabilized radicals, aminyl radicals, supported by NHCs or otherwise, have been scarcely studied due to synthetic challenges. Triazenyl radical is a particular form of aminyl radical that contains three adjacent nitrogen atoms, and offers intriguing possibilities for unique reactivity and physical properties stemming from expected delocalization of the spin density over the NNN moiety and its conjugated substituents. Here, we report the synthesis and full characterization of the first NHC-stabilized triazenyl radicals, obtained by one-electron reduction of the corresponding triazenyl cations with potassium metal. These radicals reversibly oxidize back to the cations upon treatment with transition metal sources or electrophiles, and abstract H atom from xanthene to form a new N-H bond at the center nitrogen atom. Potential application of the redox couple between triazenyl cation and triazenyl radical was demonstrated as cathode active materials in lithium ion batteries.

Oxime Ether Radical Cations Stabilized by N-Heterocyclic Carbenes

N-heterocyclic carbene (NHC) nitric oxide (NHCNO) radicals, which can be regarded as iminoxyl radicals stabilized by NHCs, were found to react with a series of silyl and alkyl triflates to generate the corresponding oxime ether radical cations. The structures of the resulting oxime ether radical cations were determined by X-ray crystallography, along with EPR and computational analysis. In contrast, lutidinium triflate produced a 1:1 mixture of [NHCNO+ ][OTf- ] and [NHCNHOH+ ][OTf- ] upon the reaction with NHCNO. This study adds an important example of stable singlet carbenes for stabilizing main-group radicals because of their π-conjugating effect, the synthesis and structures of which have not been reported previously.

Stable Organic Radicals Derived from N-Heterocyclic Carbenes

Over the past decade, numerous stable organic and main-group radicals have been synthesized from N-heterocyclic carbenes (NHCs). The structure of NHCs, in particular, offers electronic stabilization that helps to delocalize the unpaired electron over the molecule. In addition, the sterically bulky substituents of NHCs protect the radical center to prevent detrimental reactions such as dimerization. These advantages enable the straightforward synthesis and characterization of various interesting organic radicals starting from NHCs, which are, these days, widely available. NHCs have enabled the structural characterization of various organic radicals over the past decade, including α-carbonyl, propargyl, oxyallyl, and triazenyl radicals as notable examples. This minireview summarizes the advances in this field, mainly focusing on the preparation and stability as well as the properties and applications of NHC-derived organic radicals.