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Today's circuit technology requires low-power transistors and diodes to extend Moore's law. While research has been focused on reducing power consumption of transistors, low-power diodes have not been widely studied. Here, we report a low-power, thus steep-slope Schottky diode, with a “cold metal” source. The Schottky barrier between metal electrode and bulk MoS2 enabled the diode behavior, and the steep-slope diode IV curve originated from the change in the density of states of a graphite (cold metal) source with a bias voltage. The MoS2 Schottky diode with a cold metal exhibits an ideality factor (η) 8). The realization of a steep-slope Schottky diode paves the way to the improvement in low-power circuit technology.

Nonmagnetic phase assisted low temperature phase MnBi bulk magnetic materials, i.e., MnBi/NaCl and MnBi/C magnets, were fabricated by hot pressing mixtures of MnBi and NaCl or C powders. The effects of nonmagnetic NaCl or C on the magnetic and physical properties of the MnBi bulks were investigated in detail. Identifications of phase stability and decomposition rate during the mixing and hot pressing processes were analyzed using the Rietveld refinement method. It was found that the coercivities (Hc) of the bulk magnets significantly increase with increasing content of NaCl or C: Hc of the MnBi bulks with NaCl of 5 wt. % and C of 5 wt. % reach 9041 Oe and 7054 Oe, respectively, which are higher than the pure MnBi bulk of 6272 Oe. This means that the addition of a small amount of NaCl and C in the MnBi bulks could be one of the promising routes to enhance their magnetic properties.Nonmagnetic phase assisted low temperature phase MnBi bulk magnetic materials, i.e., MnBi/NaCl and MnBi/C magnets, were fabricated by hot pressing mixtures of MnBi and NaCl or C powders. The effects of nonmagnetic NaCl or C on the magnetic and physical properties of the MnBi bulks were investigated in detail. Identifications of phase stability and decomposition rate during the mixing and hot pressing processes were analyzed using the Rietveld refinement method. It was found that the coercivities (Hc) of the bulk magnets significantly increase with increasing content of NaCl or C: Hc of the MnBi bulks with NaCl of 5 wt. % and C of 5 wt. % reach 9041 Oe and 7054 Oe, respectively, which are higher than the pure MnBi bulk of 6272 Oe. This means that the addition of a small amount of NaCl and C in the MnBi bulks could be one of the promising routes to enhance their magnetic properties.

We explore the photoluminescence (PL) properties of hexagonal boron nitride (h-BN) quantum emitters embedded within atomically thin graphene/h-BN heterostructures fabricated by mechanical transfer. Stable light emission could be observed from h-BN emitters which due to the local presence of multilayer h-BN are not subject to fluorescence quenching by graphene. By using graphene as a top gate contact, the PL emission can be tuned by up to 24 meV per V/nm, with a high robustness of the emitters over several voltage sweep cycles. Two different types of h-BN emitters were observed, one with a quadratic and the other one with a linear Stark shift. Moreover, the vertical electric field leads to an asymmetric modulation of both the fluorescence intensity and lifetime between the negative and positive gate voltage regimes. The overall behavior can be well explained by a model involving different rates for electron and hole tunneling between the h-BN and graphene layers. Our findings suggest ultrathin van der Waals heterostructures as valuable platforms for fine tuning the optoelectronic properties of atomic defect-based quantum emitters.

Little is known about the physical properties of Mn4C for which is unstable and difficult to prepare. We herein report on the unusual thermomagnetic properties of high purity Mn4C powders obtained by plasma melting and magnetic separation processes. The saturation magnetization of Mn4C increases linearly with increasing temperature in the range of 50 K–590 K and remains stable at temperatures below 50 K. The anomalous magnetization increases of Mn4C with increasing temperature can be considered in terms of the Neel's P-type ferrimagnetism. At temperatures above 590 K, the Mn4C decomposes into Mn23C6 and Mn, which would be partially oxidized into manganosite when exposed to air. The remanent magnetization of Mn4C varies little with temperature. The Curie temperature of Mn4C is around ∼870 K. The positive temperature coefficient (∼0.0072 Am2 kg−1 K−1) of magnetization in Mn4C makes it potentially important in controlling the thermodynamics of magnetization in magnetic materials.

The effects of elemental doping of Si and Fe on the ε→τ phase transformation and the magnetic properties of MnAl were studied. The magnetic powders of Si- and Fe-doped MnAl were prepared by using induction melting followed by water-quenching, annealing, and salt-assisted ball-milling. The Fe-doped MnAl powders are mainly composed of the L10-structured τ-phase, while the Si-doped MnAl are composed of τ-phase and a small fraction of γ2- and β-phases. A unique thin leaves-like morphology with thickness of several tens of nanometers and diameter size up to 500 nm were observed in the Si-doped MnAl powders. The Fe-doped MnAl powders show irregular shape with much larger dimensions in the range from several to 10 μm. The morphology difference of the samples was ascribed to the variation of the mechanical properties affected by different doping elements. The phase transformation temperatures of the ε-phase of the samples were measured. The doping of Fe decreases the onset temperature of the massive phase transformation in MnAl, while the Si-doping increases the massive phase transformation temperature. Both Fe and Si increase the Curie temperature of MnAl. A substantially enhanced coercivity up to 0.45 T and 0.42 T were observed in the ball-milled MnAl powders doped with Si and Fe, respectively.

To investigate the structural effect on the ferroelectric electron emission, the electric field distribution in a two-dimensional structure was calculated as a function of thickness and upper electrode diameter, and the switching charge density and emission charge were measured simultaneously. The simulation results of the electric field distribution showed that an asymmetric electrode structure caused a stray field on the bare surface of the ferroelectric cathode near the edge of upper electrode. The distance of the stray field from the electrode edge increased with increasing ferroelectric thickness, but it did not depend on the upper electrode diameter. The switching charge density increased more on the cathode with thicker ferroelectric and smaller upper electrode diameter. This was attributed to the difference of field distribution on the bare ferroelectric surface near the electrode edge. The expanded stray field for the thicker ferroelectric cathode enhanced polarization switching near the electrod...

The correlation between the channel thickness and the carrier mobility is investigated by conducting static and low frequency (LF) noise characterization for ambipolar carriers in multilayer MoTe2 transistors. For channel thicknesses in the range of 5–15 nm, both the low-field carrier mobility and the Coulomb-scattering-limited carrier mobility (μC) are maximal at a thickness of ∼10 nm. For LF noise, the interplay of interface trap density (NST), which was minimal at ∼10 nm, and the interfacial Coulomb scattering parameter (αSC), which decreased up to 10 nm and saturated above 10 nm, explained the mobility (μC) peaked near 10 nm by the carrier fluctuation and charge distribution.

The dielectric and piezoelectric properties of sol–gel derived (x)Pb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr1/2Ti1/2)O3[(x)PMN–(1−x)PZT] thin films were investigated as a function of PMN content (x=0–1). For all compositions in the (x)PMN–(1−x)PZT thin films, a well-developed perovskite phase with (111) preferred orientation was obtained at the annealing temperature range of 700–800 °C. With increasing PMN content, the dielectric constant increased, while the remnant polarization and coercive field decreased. The enhanced dielectric properties were shown in the region of x=0.2. At this composition, the dielectric constant and remnant polarization were 1750 and 12.75 μC/cm2, respectively, which indicate that the morphotropic phase boundary (MPB) exists near the composition of x=0.2. The transverse piezoelectric coefficient (d31) showed a maximum value of −84 pC/N at x=0.2. These results confirmed that enhancement of the dielectric constant and remnant polarization improved the piezoelectric properties at the MPB.

We have calculated the electronic structure of MnB using first-principles calculations based on the density functional theory within the local-spin-density approximation. The temperature dependence of saturation magnetization [Ms(T)] was calculated by mean field approximation. The calculated density of states (DOS) shows that the energy region near the Fermi energy (EF) is mostly attributed to the d bands of Mn. The saturation magnetizations (Ms) of MnB were calculated to be 964.5 emu/cm3 (1.21 T) at 0 K and 859.3 emu/cm3 (1.08 T) at 300 K. The calculated Ms at 300 K is in good agreement with experimental Ms of 851.5 emu/cm3.

We have calculated electronic structures of nanocrystalline Fe90−xCuxSi10−yBy using first principles calculations based on density functional theory (DFT) to obtain saturation magnetic flux density (Bs). The Bs of crystalline (Fe3Si) and amorphous (Fe-B) phases in Fe90−xCuxSi10−yBy were separately calculated, and the total Bs of Fe90−xCuxSi10−yBy was derived by the summation of the Bs for the Fe3Si and Fe-B phases. The calculated Bs of Fe3Si is 1.35 T, and that of Fe-B varies from 2.08 to 2.22 T based on Fe to B ratios. Therefore, a total Bs higher than 1.80 T can be obtained with y ≥ 4 for both x = 1 and 2 in Fe90−xCuxSi10−yBy.

0.2Pb(Mg1/3Nb2/3)O3–0.8Pb(Zr0.5Ti0.5)O3 (0.2PMN–0.8PZT) thin films were deposited on Pt(111)/Ti/SiO2/Si [Pt(111)] and Pt(200)/SiO2/Si [Pt(200)] substrates by a sol–gel method, and the effect of orientation on the piezoelectric and dielectric properties of 0.2PMN–0.8PZT thin films was investigated. The 0.2PMN–0.8PZT thin films on Pt(111) and Pt(200) showed strong (111) and (100) preferred orientations, respectively. The spontaneous polarization of the (111) oriented film was higher than that of the (100) oriented film. However, the (100) oriented film showed a higher dielectric constant (K) and transverse piezoelectric coefficients (d31) than the (111) oriented film. Because the spontaneous polarization direction of the (100) oriented film is more tilted away from the normal to the film surface than that of the (111) oriented film, the dielectric constant and the transverse piezoelectric coefficient (d31) of the (100) oriented film were enhanced.

We calculate the electronic structures of FePt and Fe0.5Mn0.5Pt using first-principles calculations based on density functional theory within the local-spin-density approximation. The Curie temperature (Tc) was calculated by mean field approximation. Composition dependence of the Cure temperature (Tc(x)) of Fe1−xMnxPt was used to identify a composition to meet the desired Tc in the range of 600–650 K. The identified composition (0.0294 ≤ x ≤ 0.0713) gives saturation magnetization (Ms) in the range of 1041–919 emu/cm3 and magnetocrystalline anisotropy constant (K) in the range of 9.96–8.36 × 106 J/m3 at 0 K. Temperature dependent M(T) and K(T) of Fe1−xMnxPt (0.0294 ≤ x ≤ 0.0713) were calculated using the Brillouin function and Callen-Callen experimental relation, respectively. Fe1−xMnxPt (0.0294 ≤ x ≤ 0.0713) shows 930–800 emu/cm3 of Ms and 7.18–5.61 × 106 J/m3 of K at 300 K, thereby satisfying desired magnetic properties for heat-assisted magnetic recording media to achieve 4 Tb/in.2 areal density.

The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues.

We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from −22.9 to −9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range.

We have studied soft M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite for T-DMB (terrestrial digital media broadcasting) antenna applications. The effect of magneto-dynamic properties on antenna size, bandwidth, and radiation efficiency was investigated. The soft M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite (Co/Ti-substituted BaM) was synthesized by a combination of ball-milling and two-step sintering processes. Permeability and loss tan δµ of the Co/Ti-substituted BaM were measured to be 4.5 and 0.039 at 200 MHz, respectively. The Wheeler cap method and network analyzer were used to evaluate antenna radiation efficiency and measure return losses, respectively. Our experimental results show that the low-loss Co/Ti-substituted BaM is an excellent soft magnetic material for VHF (very high frequency: 30–300 MHz) miniature antenna applications.

Magnetic properties and ferromagnetic resonance (FMR) frequency of Ni0.7Mn0.3−xCoxFe2O4 ferrites (NiMnCo: x = 0.00, 0.04, 0.06, and 0.10) were controllable with the concentration of cobalt (Co). The measured saturation magnetization remains almost constant at 57 emu/g in the studied range of the Co content. However, the coercivity increased to 72 Oe (x = 0.10) from 12 Oe (x = 0.00). Ferromagnetic resonance frequency increased from 129 MHz to the GHz frequency with increasing the Co content from x = 0.00 to x = 0.10, but the real part of permeability decreased to 1.6 from 16.7. This is because FMR frequency increases with the magnetocrystalline anisotropy (Hk) of the Co according to fr = (γ/2π)Hk. The permeability decreased with the Co content by µ = 1 + (4πMs/Hk). Temperature coefficient, in the range of 20–100 °C, was 0.002 for Ni0.7Mn0.3Fe2O4 (x = 0.00) and 0.008 for Ni0.7Mn0.2Co0.1Fe2O4 (x = 0.10). The results suggest that Ni0.7Mn0.3−xCoxFe2O4 ferrites have excellent temperature stability, and also are...

Here we report the directed growth of ZnO nanowires on multilayer graphene films (MGFs) without the use of metal seed materials. The ZnO source substance was diffused onto the MGF surface, where nanowires tended to grow in the high surface energy sites. This property was exploited to fabricate top-gate structural nanowire transistors with ZnO nanowires grown in the direction of the exposed sides of 6 × 4 μm patterned MGFs with a SiO2 capping layer. The devices showed an on-current of 160 nA, a threshold voltage of −2.27 V, an on-off current ratio of 3.98 × 105, and a field effect mobility of ∼41.32 cm2/V·s.

Low magnetic and dielectric loss Co2Z (Ba3Co2Fe24O41)–glass composite in the frequency range of 1–3 GHz is reported. Co2Z–glass composite was prepared by firing a mixture of 40 h shake-milled Co2Z hexaferrite powder and borosilicate glass at 950 °C for 1 h. The real part of permeability decreased slightly from 2.29 to 1.96 at 2.4 GHz as the glass content increased from 0 to 4 wt. %, but magnetic loss decreased less than 0.02. On the other hand, the real part of permittivity was 7.29 at 0 wt. % and 7.28 at 4 wt. % glass and dielectric loss was less than 0.01 at 2.4 GHz. The 3D peak gain of Co2Z–glass composite chip antenna was measured to be 3.32 dBi at 2.35 GHz. These results imply that the Co2Z–glass composite is an underpinning magnetodielectric material for gigahertz antenna applications.

Single crystals of Zr-substituted Zn-Y (Zr–ZnY; Ba2Zn2ZrxFe12−xO22) were grown from the flux system of BaCO3 and B2O3 by a high temperature slow cooling flux method. X-ray diffraction pattern confirmed the crystal structure with Zn–Y composition. The single crystals were characterized for magnetic and microwave properties. The measured anisotropy field (HA) and the in-plane magnetization (σs) are 13 kOe and 52.0 emu/g, respectively. Ferrimagnetic resonance measurements show 18 Oe of linewidth (ΔH) at 9 GHz. The combination of low ΔH with a high HA in Zr–ZnY hexaferrite is suitable for microwave devices, which can operate with low external biasing field.

Model exchange coupled composite media, namely [Co/Pd]5/Pd(t)/[Co/Ni]3/Co multilayers, deposited onto prepatterned substrates have been investigated for potential use in bit patterned recording. Optimizing the thickness of the Pd interlayer allows decreasing the switching field (HC) and switching field distribution (σSFD) while maintaining thermal stability. The dependence of the remanent coercivity on the external field angle indicates that the gain in HC and σSFD originates from the incoherent magnetization reversal introduced by slightly decoupling the hard and soft multilayer stacks. This tendency is confirmed by further reductions in HC and σSFD, when inserting another Pd interlayer within the hard [Co/Pd]5 stack.

This paper deals with analytical approach of operational power defined as load power and rotor loss represented as eddy current loss for applying a permanent magnet (PM) synchronous motor/generator to the high-power flywheel energy storage system. The used model is composed of a double-sided Halbach magnetized PM rotor and coreless three-phase winding stator. For one such motor/generator structure, we provide the magnetic field and eddy current with space and time harmonics via magnetic vector potential in two-dimensional (2D) polar coordinate system. From these, the operational power is estimated by backelectromotive force according to the PM rotor speed, and the rotor loss is also calculated from Poynting theorem.

This paper presents analytical methods to predict the magnetic field distribution, electrical parameters, and output characteristics of a high speed synchronous generator equipped with surface-mounted permanent magnet. In order to analyze the magnetic field distribution and to estimate the electrical parameters, electromagnetic transfer relation (TR) theorem is employed. Moreover, output characteristics for variable resistive load and the operating speed are also obtained by solving the permanent magnet machine’s equivalent circuit equation. The analytical results are validated extensively by nonlinear finite element analysis and experimental results.

In this paper, the rotor losses in the high-speed permanent magnet (PM) synchronous motor are discussed. In particular, the influence of different load conditions is highlighted in developed PM synchronous motor. On the basis of analytical field analysis, two-dimensional fast Fourier transformation, and the Poynting theorem, the flux harmonics and rotor losses are predicted and validated by finite element method. Moreover, the difference of rotor losses between the motor with rated- and overload conditions is made quantitatively clear in this work.

We investigated the effect of annealing a polymeric dielectric film in the presence of an oscillating electric field on its dielectric constant. Films were prepared with the vertical structure of electrode/poly(4-vinylphenol)/electrode and annealed at a temperature above the glass transition temperature while applying an ac electric field ranging from 0to6V at various frequencies in the hope of altering the arrangement of polymer chains through conformational transitions influenced by the orientational polarization of the polar phenol groups. It was found that the dielectric constant increased significantly by about 30% when the annealing frequency corresponded to that at which dielectric relaxation takes place effectively.

The authors report on the electrical reliabilities of poly-4-vinyl phenol (PVP) and SiO2 gate dielectrics for pentacene thin-film transistors (TFTs). SiO2 films were grown by dry oxidation and PVP films were prepared by spin coating and subsequent cross-linking at 175°C for 15min. The pentacene TFTs with the PVP cured for 15min exhibited a large hysteresis and an abnormal drain-current increase under a gate bias stress over time, while the other TFT with SiO2 displayed a small hysteresis but its drain current decreases with time. The hysteresis behaviors induced by PVP and SiO2 were opposite to each other in the gate bias swing direction, due to the difference in hysteresis mechanism between the two types of TFTs. Comparing their hysteresis behavior, the authors fabricated a far more reliable pentacene TFT with PVP by extending the PVP curing time to 1h. Our improved device with PVP exhibited no hysteresis and persistent toughness to the gate bias stress.

We report on the fabrication of pentacene-based thin-film transistors (TFTs) with poly-4-vinylphenol (PVP)/yttrium oxide (YOx) double gate insulator films. The minimum PVP and YOx layer thicknesses were chosen to be 45 and 50nm, respectively. The PVP and YOx double dielectric layers with the minimum thicknesses exhibited a high dielectric capacitance of 70.8nF∕cm2 and quite a good dielectric strength of ∼2MV∕cm at a leakage current level of ∼10−6A∕cm2 while the leakage current from either PVP or YOx alone was too high. Our pentacene TFTs with the 45nm thin PVP∕50nm thin YOx films operated at −5V showing a high field effect mobility of 1.74cm2∕Vs and a decent on/off current ratio of 104. Our work demonstrates that the PVP∕YOx double layer is a promising gate dielectric to realize low-voltage high-mobility organic TFTs.

We report on the tetracene-based photo-thin-film transistors (photo-TFTs) which adopt thin poly-4-vinylphenol (PVP)/aluminum oxide (AlOx) bilayer for a gate dielectric and two different source/drain (S∕D) electrodes: semitransparent NiOx and Au. Our tetracene-based TFT with NiOx S∕D electrode exhibited quite good field effect mobility (μ=∼0.23cm2∕Vs), high on/off current ratio (Ion∕Ioff) of ∼105, and good photo-to-dark current ratio (Iph∕Idark=∼104) under an ultraviolet (364nm) illumination while that with Au S∕D electrodes showed much lower device performance (μ=∼0.08cm2∕Vs, Ion∕Ioff=∼104, and Iph∕Idark=∼20), although the both TFTs operated at a low voltage of −8V. With the hole-injection and light-reception advantages of NiOx electrode, our tetracene photo-TFT demonstrated good dynamic optical gating.

We have fabricated the flexible semitransparent pentacene-based thin-film transistors (TFTs) with poly-4-vinylphenol (PVP) dielectric layers which were deposited by spin coating on a thermostable plastic substrate with a conductive film. For the source∕drain (S∕D) electrodes of our flexible pentacene TFTs both Au and semitransparent NiOx have been tested. It was found that NiOx was better matched to the pentacene channel for the S∕D contacts than Au. Our flexible pentacene TFTs with semitransparent NiOx contacts exhibited mobility of ∼0.24cm2∕Vs higher than that achieved with Au contacts (∼0.14cm2∕Vs) and also demonstrated a higher initial drain current.

This paper presents the practical parameter estimation for a slotless air-cored permanent magnet linear synchronous motor (PMLSM) using an analytical method and experiment. In the analytical method, the linkage flux is calculated through the generalized magnetic vector potential obtained by the space harmonics and transfer relation with each region of permanent magnet (PM) mover, air gap, and winding stator. This linkage flux is used to estimate the dynamic parameters such as magnetization inductance, backemf, and thrust constant. Also, the resistance and self-inductance with one phase are obtained by the experiment. Therefore, dynamic simulation of a linear synchronous motor composed of dynamic parameters is performed by the nonrotating (d-q) voltage equation. In good agreement with the estimated parameter values, the experimental results confirm the validity of the analysis method and simulation.