Electrical Conduction at the Interface between Insulating van der Waals Materials

Emergent properties of 2D materials attract considerable interest in condensed matter physics and materials science due to their distinguished features that are missing in their bulk counterparts. A mainstream in this research field is to broaden the scope of material to expand the horizons of the research area, while developing functional interfaces between different 2D materials is another indispensable research direction. Here, the emergence of electrical conduction at the interface between insulating 2D materials is demonstrated. A new class of van der Waals heterostructures consisting of two sets of insulating transition‐metal dichalcogenides, group‐VI WSe₂ and group‐IV TMSe₂ (TM = Zr, Hf), is developed via molecular‐beam epitaxy, and it is found that those heterostructures are highly conducting although all the constituent materials are highly insulating. The WSe₂/ZrSe₂ interface exhibits more conducting behavior than the WSe₂/HfSe₂ interface, which can be understood by considering the band alignments between constituent materials. Moreover, by increasing Se flux during heterostructure fabrication, the WSe₂/ZrSe₂ interface becomes more conducting, reaching nearly metallic behavior. Further improvement of the crystalline quality as well as exploring different material combinations are expected to lead to metallic conduction, providing a novel functionality emerging at van der Waals heterostructures.     

Leaching of Lead and Connectivity of Plumbate Networks in Lead Silicate Glasses

The formation of a plumbate network in binary lead silicate glasses was examined based on the leaching behavior of Pb²⁺ in lead silicate glasses over a wide composition region. The effective diffusion coefficient of Pb²⁺ at 40°C was on the order of 10⁻¹⁷ m²/s for PbO<35 mol% glasses, and increased three orders of magnitude for 35–50 mol% PbO contents. Such a steep composition dependence is considered to be because of changes in the medium or longer range structure. That is, it is proposed that the plumbate network forms a percolative 3D network in the composition region to form diffusion paths for the lead ions. In addition, the present results indicate that the lead ion exists as a network former over the entire glass forming composition range of the binary silicate glasses.     

Mechanism of increased serum cytokeratin 19 fragment levels in patients with diabetic nephropathy as a model of chronic renal failure

We examined serum and urinary cytokeratin 19 fragment (CYFRA 21-1) levels in patients with diabetic nephropathy as a model of chronic renal failure, to investigate the mechanism of increased serum CYFRA 21-1 levels in chronic renal failure. Serum and urinary CYFRA 21-1 levels in non-insulin-dependent diabetes mellitus (NIDDM) patients with abnormal urinary immunoglobulin G (IgG) levels (>1.1 mg/g x Cr, n=126) were higher than those with normal urinary IgG levels. In NIDDM patients with normal urinary IgG levels (n=81); the urinary albumin or transferrin levels were not related to serum or urinary CYFRA 21-1 levels. We speculate that the increased serum CYFRA 21-1 levels contribute to metabolic abnormality in the kidney itself rather than the decreased urinary excretion per se, and that increased urinary CYFRA 21-1 levels are found in advanced cases of diabetic nephropathy with destruction of the size barrier.     

Free radicals trapped in polyethylene matrix: 1. Location of the alkyl radicals in irradiated polyethylene

Two types of alkyl radicals were found to be trapped in irradiated crystals grown from polyethylene solution. One of them corresponds to the broad sextet pattern of the e.s.r. spectrum and the other corresponds to the sharp sextet pattern. The free radicals attributed to the broad sextet began to disappear at a lower temperature than the temperature at which the free radicals attributed to the sharp sextet disappeared. When butadiene molecules were brought into contact with the specimen, the decay of the free radicals corresponding to the broad sextet was accelerated. When the specimen was subjected to fuming nitric acid treatment, no broad sextet was observed. The mat of the crystals, was aligned so that the c-axes of its crystallites were perpendicular to its surface. The broad sextet showed no anisotropy when the angle between the direction of applied magnetic field and that of the c-axis of the crystallite was varied. On the other hand, the sharp component of the spectrum showed apparent anisotropy. Consequently, it can be concluded that the broad component comes from the free radicals trapped in the lamellar surface and the sharp component is attributed to the free radicals trapped in the inner part of the crystallite. Hence, the locations of these two types of free radicals have been clarified with much more certainty than before.     

E.s.r. studies on oxidation processes in irradiated polyethylene: 1. Diffusion of oxygen into amorphous parts at low temperatures

Oxidation processes in irradiated polyethylene were studied by e.s.r. By utilization of the characteristic feature of power saturation of the e.s.r. spectrum of peroxide radicals, quantitative measurement of the process of the reaction of oxygen with allylic radicals trapped in the amorphous part of the polyethylene were made and the data were analysed based on the diffusion-controlled process theory. Diffusion equations were solved by computer simulation method. Diffusion of the oxygen into the amorphous part of the polyethylene is discussed and diffusion constants at low temperature are estimated. Related values such as the activation energy of the diffusion process and the solubility constant, are also estimated.     

Structural Study of PbO–B2O3 Glasses by X-ray Diffraction and 11B MAS NMR Techniques

The structure of PbO–B₂O₃ glasses has been investigated in the composition range of 25–80 mol% PbO by using X-ray diffraction and ¹¹B NMR techniques. The well-separated peaks due to Pb–O and Pb–Pb pairs were first observed in the radial distribution function, and peak deconvolution was performed by using a pair function method. The average coordination number of lead atoms was determined to be about 6 in the low-PbO-content region and about 3 in the high-PbO-content region. With an increase of PbO content, the peaks at 0.24 and 0.40 nm shifted to shorter distances, and especially the latter peak drastically increased in intensity in the composition range >50 mol% PbO. It was suggested that PbO is a main glass former in the high-PbO-content region. Based on the results obtained, we propose structural models of lead borate glasses.     

Sperm from mice carrying a targeted mutation of the acrosin gene can penetrate the oocyte zona pellucida and effect fertilization

The physiological function of mammalian sperm acrosin has long been believed to be involved in the limited proteolysis of the oocyte zona pellucida, thus enabling the sperm to penetrate this extracellular matrix and to gain access to the oocyte plasma membrane. Here we show that male mice homozygous for a targeted mutation in the mouse acrosin gene are still fertile in spite of the complete absence of acrosin protease activity in the sperm. In vitro fertilization assays verified that sperm from the homozygous mutant mice penetrate the zona pellucida and effect fertilization. Therefore, acrosin is not essential for both sperm penetration of the zona pellucida and fertilization.     

E.s.r. studies on oxidation processes in irradiated polyethylene: 3. Direct detection of the reaction ROO· + R'H → ROOH + R'· , in urea—polyethylene complexes

Conversion of peroxy radicals into alkyl radicals

$\text{ROO·}\text{+}\text{R′H}\text{→}\text{ROOH}\text{+}\text{R′}$

has been directly observed by the e.s.r. method in the case of polyethylene in a urea—polyethylene complex system. Abstraction of hydrogen atoms was found to be an intramolecular reaction in this case, of activation energy 24.6 kcal/mol. Evidence confirming this was provided by i.r. spectrometry.     

Rhodium‐Catalyzed Addition of α‐Keto Acid Chlorides with Terminal Alkynes

The addition reaction of α‐keto acid chlorides with terminal alkynes proceeds in the presence of (acetylacetonato)dicarbonylrhodium used as catalyst to afford synthetically versatile (Z)‐γ‐chloro‐α‐oxo‐β,γ‐unsaturated ketones regio‐ and stereoselectively.