다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.

/pdf/reticular-synthesis-and-the-design-of-new-materials-lazbx7tdux.pdf

Reticular synthesis and the design of new materials

Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

We have developed a microspectroscopy technique for measuring gate-modulated reflectance to probe excitonic states in two-dimensional transition metal dichalcogenides. Successfully observing excited states of excitons from cryogenic to room temperature showed that this method is more sensitive to excitonic signals than traditional reflectance spectroscopy. Our results demonstrated the potential of this reflectance spectroscopy method in studying exciton physics in two-dimensional transition metal dichalcogenides and their heterostructures.

Gate-modulated reflectance spectroscopy for detecting excitonic species in two-dimensional semiconductors

Ultrathin lateral heterostructures of monolayer MoS 2 and WS 2 have successfully been realized with the metal-organic chemical vapor deposition method. Atomic-resolution HAADF-STEM observations have revealed that the junction widths of lateral heterostructures range from several nanometers to single-atom thickness, the thinnest heterojunction in theory. The interfaces are atomically flat with minimal mixing between MoS 2 and WS 2 , originating from rapid and abrupt switching of the source supply. Due to one-dimensional interfaces and broken rotational symmetry, the resulting ultrathin lateral heterostructures, 1~2 mixed-dimensional structures, can show emergent optical/electronic properties. The MOCVD growth developed in this work allows us to access various ultrathin lateral heterostructures, leading to future exploration of their emergent properties absent in each component alone. a STEM EDS elemental mapping is performed by using JED-2300.

Two-dimensional atomic-scale ultrathin lateral heterostructures

Missing Small‐Bandgap Metallofullerenes: Their Isolation and Electronic Properties.

We have investigated the energetics and electronic structure of monolayer MoS2 with periodic structural corrugations by density functional theory. The total energy of corrugated MoS2 slightly increases with increasing corrugation height, which indicates that the MoS2 sheet intrinsically and extrinsically possesses nanometer scale structural corrugation. The corrugation causes an upward shift of the valence band edge and a downward shift of the conduction band edge owing to the local strain at the wrinkle peak. Accordingly, by injecting holes using the external electric field, the corrugation leads to a one-dimensional conducting channel in the MoS2 sheet. This indicates that corrugation is a plausible procedure to control the dimensionality of the electrons and holes in two-dimensional materials without implementing one-dimensional boundary conditions.

Formation of a one-dimensional hole channel in MoS2 by structural corrugation

We investigate the valley coherence in high and low-quality monolayer MoSe2 by polarization-resolved photoluminescence spectroscopy. The observed valley coherence is on the order of 10% regardless of the sample quality, proving that the suppression of extrinsic effects does not improve the valley coherence. The valley decoherence time estimated based on the valley coherence time and exciton lifetime is sub-picosecond at the longest, which suggests that intrinsic scattering sources, such as phonons, strongly limit the valley coherence.

/pdf/assessment-of-valley-coherence-in-a-high-quality-monolayer-2pzhh11s.pdf

Ryo Kitaura

Papers

Gate-modulated reflectance spectroscopy for detecting excitonic species in two-dimensional semiconductors

Two-dimensional atomic-scale ultrathin lateral heterostructures

Missing Small‐Bandgap Metallofullerenes: Their Isolation and Electronic Properties.

Formation of a one-dimensional hole channel in MoS2 by structural corrugation

Assessment of valley coherence in a high-quality monolayer molybdenum diselenide