Graphene-oxide-semiconductor planar-type electron emission device

Graphene was used as the topmost electrode for a metal-oxide-semiconductor planar-type electron emission device. With several various layers, graphene as a gate electrode on the thin oxide layer was directly deposited by gallium vapor-assisted chemical vapor deposition. The maximum efficiency of the electron emission, defined as the ratio of anode current to cathode current, showed no dependency on electrode thickness in the range from 1.8 nm to 7.0 nm, indicating that electron scattering on the inside of the grapheneelectrode is practically suppressed. In addition, a high emission current density of 1–100 mA/cm2 was obtained while maintaining a relatively high electron emission efficiency of 0.1%–1.0%. The graphene-oxide-semiconductor planar-type electron emission device has great potential to achieve both high electron emission efficiency and high electron emissioncurrent density in practical applications

Initial Surgical Versus Conservative Strategies in Patients With Asymptomatic Severe Aortic Stenosis

AbstractBackgroundCurrent guidelines generally recommend watchful waiting until symptoms emerge for aortic valve replacement (AVR) in asymptomatic patients with severe aortic stenosis (AS).ObjectivesThe study sought to compare the long-term outcomes of initial AVR versus conservative strategies following the diagnosis of asymptomatic severe AS.MethodsWe used data from a large multicenter registry enrolling 3,815 consecutive patients with severe AS (peak aortic jet velocity >4.0 m/s, or mean aortic pressure gradient >40 mm Hg, or aortic valve area <1.0 cm2) between January 2003 and December 2011. Among 1,808 asymptomatic patients, the initial AVR and conservative strategies were chosen in 291 patients, and 1,517 patients, respectively. Median follow-up was 1,361 days with 90% follow-up rate at 2 years. The propensity score–matched cohort of 582 patients (n = 291 in each group) was developed as the main analysis set for the current report.ResultsBaseline characteristics of the propensity score–matched cohort were largely comparable, except for the slightly younger age and the greater AS severity in the initial AVR group. In the conservative group, AVR was performed in 41% of patients during follow-up. The cumulative 5-year incidences of all-cause death and heart failure hospitalization were significantly lower in the initial AVR group than in the conservative group (15.4% vs. 26.4%, p = 0.009; 3.8% vs. 19.9%, p < 0.001, respectively).ConclusionsThe long-term outcome of asymptomatic patients with severe AS was dismal when managed conservatively in this real-world analysis and might be substantially improved by an initial AVR strategy. (Contemporary Outcomes After Surgery and Medical Treatment in Patients With Severe Aortic Stenosis Registry; UMIN000012140

Antiferromagnetic superexchange via 3d states of titanium in EuTiO3 as seen from hybrid Hartree-Fock density functional calculations

A superexchange mechanism between Eu^2+ 4f spins via the 3d states of nonmagnetic Ti^4+ ions is proposed through first-principles calculations based on a hybrid Hartree-Fock density functional approach to explain G-type antiferromagnetism in EuTiO3. This mechanism is supported by systematic calculations for related Eu2+-based perovskite oxides. In EuTiO3, the competition between the antiferromagnetic superexchange and an indirect ferromagnetic exchange via the Eu 5d states leads to a delicate balance between antiferromagnetic and ferromagnetic phases. The superexchange mechanism involving the Ti 3d states hints at the microscopic origin of the strong spin-lattice coupling in EuTiO3

Ferromagnetism induced by lattice volume expansion and amorphization in EuTiO[3] thin films

Lattice volume expansion or amorphization renders EuTiO[3] ferromagnetic, although the stable phase of crystalline EuTiO[3] is an antiferromagnet. The lattice volume expansion is induced into the crystalline EuTiO[3] thin film by utilizing the lattice mismatch between the thin film and a substrate. The magnetization at low temperatures monotonically increases with an increase in lattice volume for the crystalline EuTiO3 thin film, coincident with the results of calculations based on the hybrid Hartree–Fock density functional approach. The ferromagnetic interaction between Eu[2+] ions is enhanced by the amorphization as well; the amorphous EuTiO[3] thin film becomes a ferromagnet, and the Curie temperature is higher for amorphous Eu[2]TiO[4] than for its crystalline counterpart. The phenomenon, that is, the volume expansion- and amophization-induced ferromagnetism, is explained in terms of the competition between ferromagnetic and antiferromagnetic interactions among Eu[2+] ions

Current Voltage Characteristics through Grains and Grain Boundaries of High‐k Dielectric Thin Films Measured by Tunneling Atomic Force Microscopy

Leakage current distributions of high‐k dielectric thin films (8 nm HfSixOy and 5 nm ZrO2) were measured by tunneling atomic force microscopy (TUNA). In contrast to the thick HfSixOy film, where grains and grain boundaries can be seen by TUNA topography maps, ZrO2 films show no topography roughness. But large leakage current fluctuations can be seen for both dielectrics by TUNA current images. Higher leakage currents were found to flow through the grain boundaries of both analyzed high‐k dielectric films. Furthermore, local current voltage (I‐V) characteristics could successfully be measured precisely localized at grains and at grain boundaries, respectively, of the ZrO2 film. The obtained local I‐V curves showed significant differences between grains and grain boundaries, respectively. In the case of the ZrO2 film, the leakage current through the grain boundaries was up to 8 times larger than that through the grains at a substrate voltage of −3.5 V