Semiconductor-metal transition in BiSe caused by impurity doping.

Doping a typical topological insulator, BiSe, with Ag impurity causes a semiconductor-metal (S-M) transition at 35 K. To deepen the understanding of this phenomenon, structural and transport properties of Ag-doped BiSe were studied. Single-crystal X-ray diffraction (SC-XRD) showed no structural transitions but slight shrinkage of the lattice, indicating no structural origin of the transition.

Strain-Controlled Spin Transition in Heterostructured Metal-Organic Framework Thin Film.

Metal-organic framework (MOF) thin films have recently attracted much attention as a new platform for surface/interface research, where unconventional structural and physical properties emerge. Among the many MOFs as candidates for fabrication of thin films, Hofmann-type MOFs {Fe(pz)[M(CN)]} [pz = pyrazine; M = Ni (), M = Pt ()] are attractive, because they undergo spin transitions with concomitant structural changes. Here, we demonstrate the first example of a strain-controlled spin transition in heterostructured MOF thin films.

Fabrication of ring oscillators using organic molecules of phenacene and perylenedicarboximide.

Organic field-effect transistors (FETs) can be applied to radio-frequency identification tags (RFIDs) and active-matrix flat-panel displays. For RFID application, a cardinal functional block is a ring oscillator using an odd number of inverters to convert DC voltage to AC. Herein, we report the properties of two ring oscillators, one formed with [6]phenacene for a p-channel FET and ,'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) for an n-channel FET, and one formed with 3,10-ditetradecylpicene ((CH)-picene) for a p-channel FET and PTCDI-C8 for an n-channel FET.

Confined water-mediated high proton conduction in hydrophobic channel of a synthetic nanotube.

Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. As a representative system, water-filled carbon nanotubes (CNTs) are generally studied, but direct observation of the crystal structure and proton transport is difficult for CNTs due to their poor crystallinity and high electron conduction. Here, we report the direct observation of a unique water-cluster structure and high proton conduction realized in a metal-organic nanotube, [Pt(dach)(bpy)Br](SO)·32HO (dach: (1R, 2R)-(-)-1,2-diaminocyclohexane; bpy: 4,4'-bipyridine).

Improving grazing-incidence small-angle X-ray scattering-computed tomography images by total variation minimization.

Grazing-incidence small-angle X-ray scattering (GISAXS) coupled with computed tomography (CT) has enabled the visualization of the spatial distribution of nanostructures in thin films. 2D GISAXS images are obtained by scanning along the direction perpendicular to the X-ray beam at each rotation angle. Because the intensities at the positions contain nanostructural information, the reconstructed CT images individually represent the spatial distributions of this information ( size, shape, surface, characteristic length).

A highly crystalline oriented metal-organic framework thin film with an inorganic pillar.

We report a step-by-step route to fabricate the first example of a crystalline oriented metal-organic framework thin film having an anionic inorganic pillar ligand, {Cu(4,4'-bipyridyl)(SiF)}. X-ray study and sorption analysis revealed its high crystallinity and porous character.

Extended Polymorphism of Two-Dimensional Material.

When controlling electronic properties of bulk materials, we usually assume that the basic crystal structure is fixed. However, in two-dimensional (2D) materials, atomic structure or polymorph is attracting growing interest as a controlling parameter to functionalize their properties. Various polymorphs can exist in transition metal dichalcogenides (TMDCs) from which 2D materials are generated, and polymorphism has drastic impacts on the electronic states.

Fabrication and Structural Characterization of an Ultrathin Film of a Two-Dimensional-Layered Metal-Organic Framework, {Fe(py)[Ni(CN)]} (py = pyridine).

We report the fabrication and characterization of the first example of a tetracyanonickelate-based two-dimensional-layered metal-organic framework, {Fe(py)Ni(CN)} (py = pyridine), thin film. To fabricate a nanometer-sized thin film, we utilized the layer-by-layer method, whereby a substrate was alternately soaked in solutions of the structural components. Surface X-ray studies revealed that the fabricated film was crystalline with well-controlled growth directions both parallel and perpendicular to the substrate.

Visualization of Individual Images in Patterned Organic-Inorganic Multilayers Using GISAXS-CT.

Using grazing-incidence small-angle scattering (GISAXS) with computed tomography (CT), we have individually reconstructed the spatial distribution of a thin gold (Au) layer buried under a thin poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) layer. Owing to the difference between total reflection angles of Au and PS-b-P2VP, the scattering profiles for Au nanoparticles and self-assembled nanostructures of PS-b-P2VP could be independently obtained by changing the X-ray angle of incidence. Reconstruction of scattering profiles allows one to separately characterize spatial distributions in Au and PS-b-P2VP nanostructures.

Mixed-Valence Nickel Bis(azamacrocycle) Compounds with Ghost-Leg-type Sheets.

The fabrication of so-called ghost-leg sheets and their electronic properties is reported. This unique sheet structure is composed of one-dimensional mixed-valence nickel chains, which are linked with one another by bis(azamacrocycle) ligands. They are also topologically unique Ni /Ni mixed-valence complexes, as confirmed by X-ray and optical measurements.

An Electrically Conductive Single-Component Donor-Acceptor-Donor Aggregate with Hydrogen-Bonding Lattice.

An electrically conductive D-A-D aggregate composed of a single component was first constructed by use of a protonated bimetal dithiolate (complex 1H). The crystal structure of complex 1H has one-dimensional (1-D) π-stacking columns where the D and A moieties are placed in a segregated-stacking manner. In addition, these segregated-stacking 1-D columns are stabilized by hydrogen bonds.

Guest-Induced Two-Way Structural Transformation in a Layered Metal-Organic Framework Thin Film.

Fabrication of thin films made of metal-organic frameworks (MOFs) has been intensively pursued for practical applications that use the structural response of MOFs. However, to date, only physisorption-induced structural response has been studied in these films. Chemisorption can be expected to provide a remarkable structural response because of the formation of bonds between guest molecules and reactive metal sites in host MOFs.

Ultrafine Metal-Organic Right Square Prism Shaped Nanowires.

We report the structural design and control of electronic states of a new series of ultrafine metal-organic right square prism-shaped nanowires. These nanowires have a very small inner diameter of about 2.0 Å, which is larger than hydrogen and similar to xenon atomic diameters.

A three-dimensional accordion-like metal-organic framework: synthesis and unconventional oriented growth on a surface.

We describe the synthesis and sorption properties of a new metal-organic framework (MOF), Fe(H2O)2(bpy)[Pt(CN)4]·H2O (bpy = 4,4'-bipyridine), with a three-dimensional accordion-like structure. Although crystalline oriented MOF thin films reported to date have been mainly limited to a layer-type structure, we succeeded in the fabrication of its crystalline oriented thin film.

Crystalline coordination framework endowed with dynamic gate-opening behaviour by being downsized to a thin film.

The fabrication of porous coordination frameworks in thin-film forms has been investigated intensively with a view to using their structural response to external stimuli and guests for potential nanotechnological applications, for example as membranes for gas separation. Here we report a coordination framework that exhibits a dynamic guest-sorption behaviour in a nanometre-sized thin-film form (16 nm thick), yet shows no guest uptake in the bulk. Highly oriented crystalline thin films of this coordination framework--which consists of interdigitated two-dimensional layers of {Fe(py)2[Pt(CN)4]} (py, pyridine)--were fabricated through liquid-phase layer-by-layer synthesis.

Neutral-Type One-Dimensional Mixed-Valence Halogen-Bridged Platinum Chain Complexes with Large Charge-Transfer Band Gaps.

One-dimensional (1D) electronic systems have attracted significant attention for a long time because of their various physical properties. Among 1D electronic systems, 1D halogen-bridged mixed-valence transition-metal complexes (the so-called MX chains) have been thoroughly studied owing to designable structures and electronic states. Here, we report the syntheses, structures, and electronic properties of three kinds of novel neutral MX-chain complexes.

Remarkable Lattice Shrinkage in Highly Oriented Crystalline Three-Dimensional Metal-Organic Framework Thin Films.

Highly oriented crystalline thin films of metal-organic frameworks (MOFs) have promising practical applications, such as in gas separation, catalysis, and sensing. We report on the successful fabrication of highly oriented crystalline thin films of three-dimensional porous MOFs, Fe(pz)[M(CN)4] (M = Ni, Pd; pz = pyrazine). Synchrotron X-ray diffraction studies reveal not only the highly oriented crystalline nature but also the remarkable shrunken structure of the thin films (∼3-7% volume shrinkage) compared with bulk samples.

A compact planar low-energy-gap molecule with a donor-acceptor-donor nature based on a bimetal dithiolene complex.

We present the first report of a compact, planar and low-energy-gap molecule based on a π-conjugated bimetal system comprising a tetrathiooxalate (tto) skeleton. The observed low HOMO-LUMO energy gap (1.19 eV) is attributed to its donor-acceptor-donor (D-A-D) nature because the skeleton acts as an electron acceptor as well as a tiny and noninnocent bridging moiety.

Atomic and electronic structures of an extremely fragile liquid.

The structure of high-temperature liquids is an important topic for understanding the fragility of liquids. Here we report the structure of a high-temperature non-glass-forming oxide liquid, ZrO2, at an atomistic and electronic level. The Bhatia-Thornton number-number structure factor of ZrO2 does not show a first sharp diffraction peak.

Controlling charge-density-wave states in nano-thick crystals of 1T-TaS2.

Two-dimensional crystals, especially graphene and transition metal dichalcogenides (TMDs), are attracting growing interests because they provide an ideal platform for novel and unconventional electronic band structures derived by thinning. The thinning may also affect collective phenomena of electrons in interacting electron systems and can lead to exotic states beyond the simple band picture. Here, we report the systematic control of charge-density-wave (CDW) transitions by changing thickness, cooling rate and gate voltage in nano-thick crystals of 1T-type tantalum disulfide (1T-TaS2).

Hierarchical dielectric orders in layered ferroelectrics Bi2SiO5.

Electric dipole engineering is now an emerging technology for high electron-mobility transistors, ferroelectric random access memory and multiferroic devices etc. Although various studies to provide insight into dipole moment behaviour, such as phase transition, order and disorder states, have been reported, macroscopic spontaneous polarization has been mainly discussed so far. Here, visualization of the electric dipole arrangement in layered ferroelectrics Bi2SiO5 by means of combined analysis of maximum entropy charge density and electrostatic potential distribution analysis based on synchrotron radiation X-ray powder diffraction data is reported.

Evidence of electronic polarization of the As ion in the superconducting phase of F-doped LaFeAsO.

Understanding the nature of superconductivity in iron-based compounds is essential in the development of new strategies to increase T c. Using a charge density analysis based on synchrotron radiation X-ray powder diffraction data, we found that the charge carriers only accumulated in the iron layer of the superconducting phase of LaFeAsO1 - x F x at low temperatures. Analysis of the electrostatic potential distribution revealed the concerted enhancement of the electronic polarization of the As ions and the carrier redistribution.

Variable-rung design for a mixed-valence two-legged ladder system situated in a dimensional crossover region.

Ladder systems situated in a crossover from one dimensionality to two dimensionalities have been an attractive research target, because the physical properties, which are associated with dimensionality, are strongly dependent on the number of constituent legs. However, control of the intraladder configuration and electronic properties based on the substitution of structural components remain challenging tasks in materials science. On the other hand, structural design using coordination chemistry offers crucial advantages for architectural and electronic variations through substitutions of metal-organic building blocks.

A twisted bi-icosahedral Au(25) cluster enclosed by bulky arenethiolates.

Ligation of 2,6-diphenylbenzenethiol (DppSH) onto Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) and subsequent core etching yielded a single cluster Au25(SDpp)11. High-energy X-ray diffraction measurement showed that Au25 constitutes a core in Au25(SDpp)11. We propose a bi-icosahedral Au25 core whose 22 Au surface atoms are capped directly by 11 bulky arenethiolates.

Network topology for the formation of solvated electrons in binary CaO-Al2O3 composition glasses.

Glass formation in the CaO-Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO-Al2O3 glasses using combined density functional theory-reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O-Ca and O-Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings.