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Large unsaturated magnetoresistance (XMR) with magnitude about 1000% is observed in topological insulator candidate TaSe3 from our high field (up to 38 T) measurements. Two oscillation modes, associated with one hole pocket and two electron pockets in the bulk, respectively, are detected from our Shubnikov-de Hass (SdH) measurements, consistent with our first-principles calculations. With the detailed Hall measurements performed, our two-band model analysis exhibits an imperfect density ratio n_h/n_e closing 0.9 at T< 20 K , which suggests that the carrier compensations account for the XMR in TaSe3.

The high performance Mn1.2Co1.5Ni0.3O4 (MCN) ceramic materials are successfully fabricated using nanoparticles which are synthesized by the reverse microemulsion method. The morphology, crystal structure and particle size distribution of MCN nanoparticles are characterized by the XRD, SEM, TEM and HRTEM. The results show the well single tetragonal spinel structure and the narrow particle size distribution about 40 nm. As the sintering temperature increasing from 1000 to 1250 °C, all the MCN ceramic samples prepared by above-mentioned nanoparticles show the same single tetragonal spinel structure. The thermal sensitive properties with high values of ρ25, B25/100, Ea, and α25 of MCN ceramics at different sintering temperatures are in the range of 68,805–497,730 Ω cm, 4578–5159 K, 0.395–0.445 eV, and −5.2 to −5.8 %/K, respectively. These features indicate that the microstructure and electrical properties of MCN ceramics are relevant to the sintering temperature.

Topological semimetals characterize a unique class of quantum materials hosting Dirac/Weyl fermions. The important features of topological fermions can be exhibited by quantum oscillations. Here, we report the magnetoresistance and Shubnikov-de Haas (SdH) quantum oscillation of longitudinal resistance in the single crystal of topological semimetal candidate Ta3SiTe6 with a magnetic field up to 38 T. The periodic amplitude of the oscillations shows related information about the Fermi surface. The fast Fourier transformation spectra represent a single oscillatory frequency. The analysis of the oscillations shows the Fermi pocket with a cross sectional area of 0.13 A−2. Combining magneto-transport measurements and the first-principles calculation, we find that these oscillations come from the hole pocket. Hall resistivity and the SdH oscillations recommend that Ta3SiTe6 is a hole dominated system.

The development of hydrogen compatibility is crucial for its being a new key energy source. A study of hydrogen fuse based on Pd break junction method is presented to explore the limit of sensitivity. The critical part of this device was fabricated from a Pd nanowire electrode (80 ± 20 nm) made by electron beam lithography (EBL) method. Subsequent electromigration technique is utilized to develop a controllable break junction on the nanowire (1–2 nm). This device shows reversible response cycles of hydrogen in an ultralow pressure range below 0.1±0.002 Pa and fuse-like response above 10 Pa at room temperature. The results show that the relationship between quantum conductance with hydrogen pressure was kept linear because of hydrogen absorption induced expansion of break junction. When the expansion exceeds the threshold value, the break junction gap is closed and becoming conductive. This method opens up a possibility to detect hydrogen under ultralow partial pressure.

Mn-Co-Ni-O ultrafine ceramic nanoparticles are successfully synthesized by the reverse microemulsion method in a triton X-100/n-hexanol/cyclohexane system. The thermal decomposition process, crystallinity and crystal structure of Mn-Co-Ni-O powders are investigated and characterized by thermogravimetric-differential scanning calorimetry (TG/DSC), Fourier Transform Infrared (FT-IR), X-ray powders diffraction (XRD) and High Resolution Transmission Electron Microscope (HRTEM), respectively. The TGA/DSC, FT-IR and XRD results show that the reverse microemulsion method can effectively reduce the calcination temperature to 600 degrees C for synthesizing cubic spinel phase Mn-Co-Ni-O ceramic particles. Furthermore, the XRD and HRTEM images reveal that the particles are highly crystalline and have a narrow and uniform particle size distribution. These findings indicate that Mn-Co-Ni-O nanoparticles prepared via reverse microemulsion process meet demands for obtaining better microstructure and performance of Mn-Co-Ni-O materials.

Mn1.56Co0.96Ni0.48O4±δ thin films are fabricated by Pulsed Laser Deposition process at different oxygen partial pressure. The X-ray diffraction shows that the preferential orientation of the films changes from (4 0 0) plane to (1 1 3) as the oxygen pressure increases. The resistance of the (1 1 3)-oriented films is found to decrease compared to those of the (4 0 0)-oriented ones. Meanwhile, the activation energy Ea increases dramatically. A detailed X-ray photoemission spectroscopy study of the lattice oxygen content and Mn cation distribution is performed. The results reveal that higher oxygen partial pressure during deposition should be responsible for the preferred (1 1 3) plane growth and the greatly elevated amount of Mn3+ and Mn4+, which can result in significantly different electrical properties of Mn1.56Co0.96Ni0.48O4±δ spinel films.

Single (100)-oriented Mn1.56Co0.96Ni0.48O4 thin films were achieved on SrTiO3 (100) substrate using laser molecular beam epitaxy technique. The effects of growth temperature and oxygen partial pressure on crystal quality and negative temperature coefficient characteristics were studied by XRD, RHEED, AFM, SEM, resistance-temperature measurements and impedance spectrum. The results showed that the growth direction (400) of epitaxial Mn1.56Co0.96Ni0.48O4 thin films was parallel to SrTiO3 (100) substrate and the best NTC characteristic with B value of about 3000 K was found in the Mn1.56Co0.96Ni0.48O4 thin films grown at 500 degrees C with Po-2 = 5 x 10 (3) Pa for 3 h. Such thin films are desirable for a wide range of practical applications in the NTC thermistors. (C) 2014 Elsevier B. V. All rights reserved.

The recent discovery of a Weyl semimetal in TaAs offers the first Weyl fermion observed in nature and dramatically broadens the classification of topological phases. However, in TaAs it has proven challenging to study the rich transport phenomena arising from emergent Weyl fermions. The series MoxW1−xTe2 are inversion-breaking, layered, tunable semimetals already under study as a promising platform for new electronics and recently proposed to host Type II, or strongly Lorentz-violating, Weyl fermions. Here we report the discovery of a Weyl semimetal in MoxW1−xTe2 at x=25%. We use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe a topological Fermi arc above the Fermi level, demonstrating a Weyl semimetal. The excellent agreement with calculation suggests that MoxW1−xTe2 is a Type II Weyl semimetal. We also find that certain Weyl points are at the Fermi level, making MoxW1−xTe2 a promising platform for transport and optics experiments on Weyl semimetals., A Type II Weyl fermion semimetal has been predicted in Mo x W1−x Te2, but it awaits experimental evidence. Here, Belopolski et al. observe a topological Fermi arc in Mo x W1−x Te2, showing it originates from a Type II Weyl fermion and offering a new platform to study novel transport phenomena in Weyl semimetals.

Recently, the picture of type-II energy dispersion with broken Lorentz invariance has been adapted from Weyl to Dirac fermions. It is demonstrated in PdTe${}_{2}$ in this paper by extensive evidence from electrical transport, de Haas--van Alphen oscillations, first-principles calculations, and angle-resolved photoemission spectroscopy. The type-II Dirac cone looks like a pinnacle in momentum space. It may be cut by the Fermi level with the result of a pair of Dirac pockets (of $p$/$n$ type), whose sizes change dramatically with the Fermi level. The nontrivial Berry phase of the hole pocket is also displayed. This also means a nonvanishing density of states in the whole Dirac cones, which makes PdTe${}_{2}$ an improved platform for possible topological superconductors and Majorana fermions

Atomic defects are easily created in the single-layer electronic devices of current interest and cause even more severe influence than in the bulk devices since the electronic quantum paths are obviously suppressed in the two-dimensional transport. Here we find a drop of chemical solution can repair the defects in the single-layer MoSe2 field-effect transistors. The devices’ room-temperature electronic mobility increases from 0.1 cm2/Vs to around 30 cm2/Vs and hole mobility over 10 cm2/Vs after the solution processing. The defect dynamics is interpreted by the combined study of the first-principles calculations, aberration-corrected transmission electron microscopy, and Raman spectroscopy. Rich single/double Selenium vacancies are identified by the high-resolution microscopy, which cause some mid-gap impurity states and localize the device carriers. They are found to be repaired by the processing with the result of extended electronic states. Such a picture is confirmed by a 1.5 cm−1 red shift in the Raman spectra. Defects can heavily influence the electrical transport properties of three-dimensional materials. But their impact becomes even more pronounced in low-dimensional systems. Fengqi Song and colleagues use a combination of calculations and experiments to show that a simple drop of a chemical solution can repair the selenium vacancies in field-effect transistors made from single layer molybdenum diselenide. By reducing the number of vacancies, which localize the electronic transport, the authors increased the carrier mobilities to nearly the intrinsic value by 2–3 orders of magnitude. The defect dynamics is visualized by the high resolution electron microscopy and multislice simulations. Such an approach could provide a route for enabling practical devices to be made from these relatively fragile materials.

The discovery of a new type-II Dirac semimetal in Ir1-x Ptx Te2 with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level close to the Dirac point. The type-II Dirac dispersion in Ir1-x Ptx Te2 is confirmed by angle-resolved photoemission spectroscopy and first-principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir1-x Ptx Te2 is an ideal platform for further studies on the exotic properties and potential applications of type-II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics.

We report the low-temperature magneto-transport in the bulk-insulating single crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S. Shubnikov-de Haas oscillations appear with their reciprocal frequency proportional to cos θ, demonstrating the dominant transport of topological surface states. While the magnetic field rotates on the sample surface, the planar Hall effect arises with sizeable oscillations following a relation of cos θ sin θ. Its amplitude reaches the maximum at the lowest temperature and drops to nearly zero at temperature higher than 100 K. All these evidences consolidate such planar Hall oscillations as another golden criterion on the topological surface transport.

The electron storage characteristics of Ge/Si hetero-nanocrystal metal-oxide-semiconductor field-effect transistor memory are investigated by computer simulation. Owing to the Ge/Si hetero-energy bands, the retention time increases several orders compared with that of Si nanocrystal memory, and the programming time achieves the order of μs. The trade-off between the high-speed programming and the long retention time could be solved efficiently with the present Ge/Si hetero-nanocrystal structure.

The spin-orbit coupling strength of graphene can be enhanced by depositing iridium nanoclusters. Weak localization is intensely suppressed near zero fields after the cluster deposition, rather than changing to weak anti-localization. Fitting the magnetoresistance gives the spin relaxation time, which increases by two orders with the application of a back gate. The spin relaxation time is found to be proportional to the electronic elastic scattering time, demonstrating the Elliot–Yafet spin relaxation mechanism. A sizeable Kane–Mele-like coupling strength of over 5.5 meV is determined by extrapolating the temperature dependence to zero.

The characteristics of low-frequency noise in n-metal–oxide–semiconductor field-effect transistors with ultranarrow channels have been investigated through random telegraph signals and low-frequency noise spectroscopy. Random telegraph signals with very large amplitude (∼70%) are observed in weak inversion at room temperature. Low-frequency noise spectra having both 1/fn and Lorentzian type are found separately in the same channel at various gate bias voltages. The observations strongly suggest that the low-frequency noise is dominated by carrier mobility fluctuation in weak inversion and by carrier number fluctuation under high-field conditions in an ultranarrow channel.

The characteristics of low-frequency (LF) noise in n-metal oxide semiconductor field effect transistors (n-MOSFET) with ultra-narrow channels have been investigated. LF noise spectra having both 1/f/sup n/ and Lorentzian type are found separately in the same narrow channel at different gate bias voltage, while only 1/f/sup n/ noise is observed in relative wide channels. Furthermore, random telegraph signals (RTSs) with very large amplitude are observed in the devices with narrow channels at room temperature. The observations strongly suggest that LF noise in weak inversion dominantly suffer from carrier mobility fluctuation rather than carrier number fluctuation in narrow channels.

A GaN-based metal–insulator–semiconductor (MIS) structure has been fabricated by using ferroelectric Pb(Zr0.53Ti0.47)O3 instead of conventional oxides as insulator gate. Because of the polarization field provided by ferroelectric and the high dielectric constant of ferroelectric insulator, the capacitance–voltage characteristics of GaN-based metal–ferroelectric–semiconductor (MFS) structures are markedly improved compared to those of other previously studied GaN MIS structures. The GaN active layer in MFS structures can reach inversion just under the bias of smaller than 5 V, which is the generally applied voltage used in semiconductor-based integrated circuits. The surface carrier concentration of the GaN layer in the MFS structure is decreased by one order compared with the background carrier concentration. The GaN MFS structures look promising for the practical application of GaN-based field effect transistors.

The films with the discrete diamond-like-carbon nanoparticles were prepared by the deposition of the carbon nanoparticle beam. Their morphologies were imaged by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nanoparticles were found distributed on the silicon (100) substrate discretely. The semisphere shapes of the nanoparticles were demonstrated by the AFM line profile. EELS was measured and the sp3 ratio as high as 86% was found. The field-induced electron emission of the as-prepared cascade (nanoDLC/ Si) was tested and the current density of 1mA/cm2 was achieved at 10.2V/{\mu}m.