Atomically-thin metallic Si and Ge allotropes with high Fermi velocities

Silicon and germanium are the well-known materials used to manufacture electronic devices for the integrated circuits but they themselves are not considered as promising options for interconnecting the devices due to their semiconducting nature. We have discovered that both Si and Ge atoms can form unexpected metallic monolayer structures which are more stable than the extensively studied semimetallic silicene and germanene, respectively. More importantly, the newly discovered two-dimensional allotropes of Si and Ge have Fermi velocities superior to the Dirac fermions in graphene, indicating that the metal wires needed in the silicon-based integrated circuits can be made of Si atom itself without incompatibility, allowing for all-silicon-based integrated circuits.Comment: 10 pages, 3 figures, 1 tabl

Vildagliptin vs liraglutide as a second-line therapy switched from sitagliptin-based regimens in patients with type 2 diabetes: A randomized, parallel-group study

Introduction: A step-up strategy for dipeptidyl peptidase (DPP)-4 inhibitor-based regimens has not yet been established. In addition, similarities and differences between DPP-4 inhibitors and glucagon-like peptide (GLP)-1 receptor agonists remain to be elucidated in humans. We investigated the pleiotropic effects of vildagliptin vs liraglutide in patients with type 2 diabetes on sitagliptin-based regimens in an open-label, randomized, clinical trial. Materials and Methods: A total of 122 patients with type 2 diabetes that was inadequately controlled by sitagliptin-based regimens were randomly assigned to either vildagliptin (50 mg, twice daily) or liraglutide treatment (0.9 mg, once daily) for 12 weeks. The primary outcomes were glycated hemoglobin and body mass index. Results: Both vildagliptin and liraglutide significantly lowered glycated hemoglobin within 12 weeks after switching from sitagliptin, but liraglutide produced a greater reduction (-0.67 ± 0.12% vs -0.36 ± 0.53%). Liraglutide lowered body mass index, whereas vildagliptin did not affect body mass index. Vildagliptin lowered fasting C-peptide immunoreactivity, but liraglutide did not. Vildagliptin increased serum levels of adiponectin, arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid, whereas liraglutide had no effect on these levels. Quality of life, assessed using the diabetes treatment satisfaction questionnaire, was not impaired in either group. The most common adverse events were gastrointestinal symptoms, which occurred with similar frequencies in both groups. Conclusions: Vildagliptin-mediated improvements in glycemic control did not correlate with indices for insulin secretion and insulin sensitivity. Switching from sitagliptin to liraglutide is useful in managing hyperglycemia and weight. Each agent exerts unique pleiotropic effects. This trial was registered with the University Hospital Medical Information Network Clinical Trials Registry (no. 000004953). © 2014 The Authors. Journal of Diabetes Investigation published by Asian Association of the Study of Diabetes (AASD) and Wiley Publishing Asia Pty Ltd

Progress in the materials science of silicene

In its freestanding, yet hypothetical form, the Si counterpart of graphene called silicene is predicted to possess massless Dirac fermions and to exhibit an experimentally accessible quantum spin Hall effect. Such interesting electronic properties are not realized in two-dimensional (2D) Si honeycomb lattices prepared recently on metallic substrates where the crystal and hybrid electronic structures of these 'epitaxial silicene' phases are strongly influenced by the substrate, and thus different from those predicted for isolated 2D structures. While the realization of such low-dimensional Si π materials has hardly been imagined previously, it is evident that the materials science behind silicene remains challenging. In this contribution, we will review our recent results that lead to an enhanced understanding of epitaxial silicene formed on diboride thin films, and discuss the remaining challenges that must be addressed in order to turn Si 2D nanostructures into technologically interesting nanoelectronic materials

Growth of single-crystalline zirconium diboride thin film on sapphire

Conducting and reflecting thin film of ZrB_2, which has lattice mismatch of only 0.6% to GaN, was grown epitaxially on sapphire substrate [α-Al_2O_3(0001)] via thermal decomposition of Zr(BH_4)_4. In situ reflection high energy electron diffraction and ex situ x-ray diffraction analyses indicate that the epitaxial relationship is singular, i.e., ZrB_2[0001]∥Al_2O_3[0001] and ZrB_2[110]∥Al_2O_3[100]. X-ray photoelectron spectroscopy and scanning tunneling microscopy revealed that the oxide-free surface could be recovered by heating the film at approximately 750 °C under ultrahigh vacuum, which demonstrates its suitability as a template for the growth of nitride semiconductors

Competing magnetism in π-electrons in graphene with a single carbon vacancy

[[abstract]]One intriguing finding in graphene is the vacancy-induced magnetism that highlights the interesting interaction between local magnetic moments and conduction electrons. Within density functional theory, the current understanding of the ground state is that a Stoner instability gives rise to ferromagnetism of π-electrons aligned with the localized moment of a σ dangling bond and the induced π magnetic moments vanish at low vacancy concentrations. However, the observed Kondo effect suggests that π-electrons around the vacancy should antiferromagnetically couple to the local moment and should carry nonvanishing moments. Here we propose that a phase possessing both significant out-of-plane displacements and π bands with antiferromagnetic coupling to the localized σ moment is the ground state. With the features we provide, it is possible for spin-resolved scanning tunneling microscopy, scanning tunneling spectroscopy, and angle-resolved photoelectron spectroscopy measurements to verify the proposed phase.[[notice]]補正完

Hidden mechanism for embedding the flat bands of Lieb, kagome, and checkerboard lattices in other structures

[[abstract]]The interplay of hopping parameters that can give rise to flat bands in consequence of quantum interference in electronic, photonic, and other interesting materials has become an extensively studied topic. Most of the recognized structures having flat bands are lattices that can be understood by the mathematical theory of line graphs, such as the Lieb, kagome, and checkerboard lattices. Here, we demonstrate that the structures that can realize the same kinds of flat bands given by those well-known lattices hosting exotic quantum phases are more flexible. The flat bands belonging to the recognized structures can be ideally embedded into new structures that cannot be considered as the original ones in terms of a unitary transformation. The uncovered mechanism enriches the understanding of physics behind the localized quantum states and broadens the choice of materials that can be used for designing electronic and photonic devices from the zero band dispersion.[[notice]]補正完