Shinya Aoki

Neutral-ionic transition in dimethyl-TTF-chloranil

Abstract We report on a new mixed-stack organic charge-transfer crystal of 2,6-dimethyltetrathiafulvalene- p -chloranil (DMTTF-CA), which undergoes a temperature-induced neutral-ionic transition (TINIT). The discontinuous change in molecular ionicity was found to occur at 65K. A most striking feature of the TINIT in DMTTF-CA was that a neutral-ionic coexisting phase appeared at lower temperatures, unlike the homogeneous ionic phase observed for the TINIT of TTF-CA. The pressure-induced transition in DMTTF-CA was found to occur at 1.2 GPa. The transition characteristics of DMTTF-CA are discussed in comparison with those of TTF-CA.

Composition for hard tissue repair

The materials requirements for composites for biomedical applications include all the usual mechanical property requirements for general engineering composites of stiffness, strength, toughness, and so on. However, there are additional biological requirements, the materials have to be biocompatible, that is, not produce a disadvantageous biological response in the required application [1,2] including in the case of degradable materials the degradation products must also be biocompatible. An additional desirable property is that the material should be bioactive, that is, it should produce a beneficial response in the appropriate application [1,2]. Bioactive means that the body’s cells react beneficially with the material, and in the case of hard tissue applications, the bone cells, instead of producing a layer of fibrous tissue between the patient’s own bone and the implant, produce new bone directly on the implant. This direct bone–implant contact leads to a mechanically stronger interface and thus a stronger and more durable bone–implant structure. From a mechanical point of view, bone has two major functions, to provide a stiff skeleton against which the muscles can contract to provide locomotion and secondly to protect the major organs such as the brain, protected by the skull, and the heart and lungs, protected by the rib cage (Fig. 1). Biologically, bone provides a store of calcium and phosphate ions that are essential for biological function, while the marrow is the source for red and white blood cells [3]. At the macroscopic scale, there are two types of bone. The first type of bone is known as cortical, which is a nearly solid material, making up the outer surfaces of all bones, with a porosity of <3% in normal people [3]. The second type of bone is porous, is called either cancellous or trabecular bone, being a foam of bone made up of small struts called trabeculae. Cancellous bone is found throughout the middle of bones such as the ribs and the skull and at the end of long bones below the joint surface. The porosity ranges from 30% to 90%, depending on the position in the body, age, and activity level of the person. Both cortical and cancellous bones become more porous with age and conditions, such as osteoporosis that particularly affects postmenopausal women. At the structural and microstructural levels, cortical and cancellous bones have different structures in the form of osteons in cortical bone and trabeculae in cancellous bone. At the nanostructural level, all bone material is a composite of collagen, a natural polymer, filled with a calcium phosphate mineral, thus a particulate-reinforced composite. There are three major types of bone cells, osteoblasts that

Structural study of neutral-ionic transition in DMTTF-CA

Abstract Dimethyltetrathiafulvalene-p-chloranil (DMTTF-CA), showing a particular neutral(N)-ionic(I) transition from a N phase into a NI coexisting phase by cooling, was structural analyzed by X-ray at 29K, 48K, 109K and 293K. Below Tc of 65K, changes observed in unit cell parameters, bond lengths and anisotropic temperature factors indicate 1) a increase in degree of charge transfer(CT) from a DMTTF donor to a CA acceptor and 2) a formation of a molecular dimerization, in I part of the coexisting phase. A possible staging superlattice was not observed.

Metal/organic junction characteristics of vacuum-evaporated films of charge transfer complexes

Abstract Several donor-acceptor charge transfer (CT) complexes, having different degrees of charge transfer (ϱ) and different CT absorption bands(νCT), were successfully evaporated onto SiO2/n-Si substrates, yielding the device structures of metal/CT complex /SiO2/Si. The metal/organic junction characteristics were then investigated by measuring the displacement currents(Id), which are ascribale to the changes in charge densities for the devices, with respect to applying ac biases at low frequency. Different carrier injection behaviors were observed for the complexes examined. Perylene(Per)-TCNQ exhibited a predominantly electron-injective property, while for Dimethylphenazine (M2P)-TCNQ and Phenothiazine (PTZ)-TCNQ; whose absorption energies were much smaller than ca. 0.6 eV, both electron- and hole-injective characteristics were found. The results can be explored by taking into account the participation of charge carriers injected from metal electrodes. Also the carriers stem from thermal excitation within the CT complexes.

Strained Lattice Organic Thin Film Growth by Molecular Beam Epitaxy

Abstract Strained lattice organic thin film which possessed distinct lattice structure from the bulk crystal was formed by molecular beam epitaxy (MBE). In situ infrared (IR) spectroscopic characterization was carried out to clarify the as-grown film structure under several growth conditions. The growth condition for parallel orientation of the flat molecules was discussed under the interrelation between the molecule-substrate interactions and the intermolecular interactions.