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This paper proposes a robust to defects and short length device (RDSLD), a newly in-plane resonant tunneling diode (RTD), and its ac-modeling with the minimum length of 3 nm. The proposed structure has robust performance in the presence of defects. It also has a high degree of flexibility in tuning electronic specifications. By using bipolar doping and a special h-boron nitride barrier pattern, these unique features are obtained. The simulation results verify that the proposed structure has the potential for replacing conventional RTD diodes. Such that the peak-to-valley ratio (PVR) and the maximum current of 4500, 450 nA for perfect bowtie and 3.45, 1256 nA for rhombic barrier shape structure are obtained, respectively. Also, negative differential resistance (NDR) is observed in all of the structures with vacancy and impurity defects. The effect of the geometrical parameters on the charge transmission of the device is another issue that is addressed in this paper. Furthermore, the analytical and numerical capacitance model parameters are presented. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride encapsulation significantly improves carrier transport in graphene. This paper investigates the benefit of implementing the encapsulation technique in graphene field-effect transistors (GFETs) in terms of their intrinsic radio frequency (RF) performance, adding the effect of the series resistances at the terminals. For such a purpose, a drift-diffusion self-consistent simulator is prepared to get the GFET electrical characteristics. Both the mobility and saturation velocity are obtained by an ensemble Monte Carlo simulator upon considering the relevant scattering mechanisms that affect carrier transport. RF figures of merit are simulated using an accurate small-signal model. Results reveal that the cutoff frequency could scale up to the physical limit given by the inverse of the transit time. Projected maximum oscillation frequencies, in the order of few terahertz, are expected to exceed the values demonstrated by InP and Si-based RF transistors. The existing tradeoff between power gain and stability and the role played by the gate resistance are also studied. High power gain and stability are feasible even if the device is operated far away from current saturation. Finally, the benefits of device unilateralization and the exploitation of the negative differential resistance region to get negative-resistance gain are discussed. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of field-effect transistors (FETs) based on chemical vapor deposited (CVD) graphene encapsulated between few layer CVD boron nitride (BN) sheets with complementary metal–oxide–semiconductor (CMOS) compatible nickel edge contacts. Noncontact terahertz time-domain spectroscopy (THz-TDS) of large-area BN/graphene/ BN (BN/G/BN) stacks reveals average sheet conductivity >1 mS/sq. and average mobility of 2500 cm2/V $\cdot $ s. Improved output conductance is observed in dc measurements under ambient conditions, indicating the potential for radio frequency (RF) applications. Moreover, we report a maximum voltage gain of 6 dB from a low-frequency signal amplifier circuit. RF characterization of the GFETs yields an ${f}_{T}\times {L}_{g}$ product of 2.64 GHz $\cdot ~\mu \text{m}$ and an ${f}_{{\textsf {Max}}}\times {L}_{g}$ product of 5.88 GHz $\cdot ~\mu \text{m}$. This paper presents for the first time THz-TDS usage in combination with other characterization methods for device performance assessment on BN/G/BN stacks. The results serve as a step toward scalable, all CVD 2-D material-based FETs for CMOS compatible future nanoelectronic circuit architectures. [ABSTRACT FROM AUTHOR]

In 2-D van der Waals heterostructures, interactions between atomic layers dramatically change the vibrational properties of the hybrid system and demonstrate several interesting phenomena that are absent in individual materials. In this paper, we have investigated the vibrational properties of the heterostructure between transition metal dichalcogenide (TMD) and hexagonal boron nitride (hBN) on gold film at low- and high-frequency ranges by Raman spectroscopy. Nineteen Raman modes have been observed from the sample, including a new interlayer coupling mode at 28.8 cm−1. Compared to reported experimental results of tungsten disulfide (WS2) on SiO2/Si substrates, the Raman spectrum for WS2 on hBN/Au emerges a blue shift of about 8 cm−1. Furthermore, a remarkable enhancement of Raman intensity can be obtained when tuning hBN thickness in the heterostructure. Through systematic first-principles calculations, numerical simulations, and analytical calculations, we find that the 28.8 cm−1 mode originates from the shearing motion between monolayer TMD and hBN layers. In addition, the gold substrate and hBN layers form an optical cavity and the cavity interference effects enhance the obtained Raman intensity. This paper demonstrates the novel vibrational modes of 2-D van der Waals heterostructure as an effective tool to characterize a variety of such heterostructures and reveals a new method to enhance the Raman response of 2-D materials. [ABSTRACT FROM AUTHOR]

Surface discharge can lead to the failures of insulation materials in LN2, especially when the bubbles are generated during the quenching process. In this paper, the surface discharge properties of polypropylene (PP)/boron nitride (BN) nanocomposites were investigated in the normal and quench conditions. The results showed that the surface discharge voltage was improved in the normal condition as the BN filler content was increased from 5 wt% to 10 wt%. But it was reduced as the BN filler content was 15 wt%. As the filler content was less than 10 wt%, the free charges were captured by traps, which were with deeper trap energy level. In quench condition, the bubbles were decreased as the BN filler content increased, which were associated with the higher thermal conductivity of BN to rapidly release the joule heat. Therefore, the surface discharge voltage was increased with the BN filler content. The research has the potential to restrain the surface discharges and extent the lifetime of insulation materials in high-temperature superconducting devices. [ABSTRACT FROM AUTHOR]

This paper examines the effect of Co60 gamma-ray irradiation to a maximum total dose of 1000 kGy on the charge transport in polyethylene based micro/nanocomposites. Micron sized hexagonal boron nitride (BN) and nano size silica (SiO 2) fillers are used in this work. Surface potential decay measurement are used to evaluate the charge transport in the composite samples. Scanning electron microscopy, Fourier transform infrared spectrum, differential scanning calorimetry, and gel content techniques are used to understand the irradiation induced variations in the microstructure of the composites. The results indicate that the carrier trap center becomes shallower and the carrier mobility tends to increase with increasing gamma ray dose and this effect is mitigated with the addition of fillers. It is suggested that the radiation induced reduction in the crystallinity and the appearance of voids and the formation of carbonyl groups are responsible for the observed effect. The micron- and the nano-size particles hinder the penetration of oxygen, thereby reducing oxidation, and the gamma-ray irradiation induces increased charge transport in the composites. [ABSTRACT FROM AUTHOR]

The standard procedure for neutron reactor dosimetry is based on neutron irradiation of a target and its post-irradiation analysis by Gamma and/or X-ray spectrometry. Nowadays, the neutron spectra can be easily characterized for thermal and fast energies (respectively 0.025 eV and > 1~\MeV). In this paper we propose a new target and an innovating post-irradiation technique of analysis in order to detect the neutron spectra within the energy of 1 keV to 1 MeV. This paper will present the calculations performed for the selection of a suitable nuclear reaction and isotope, the results predicted by simulations, the irradiation campaign that is proposed, and the post-irradiation technique of analysis. [ABSTRACT FROM PUBLISHER]

The purpose of this paper is to demonstrate 92,94Zr application in neutron reactor dosimetry. We aim to detect neutron flux in 1-keV to 1-MeV energy range by irradiating 92,94Zr samples under boron nitride (BN) filter. The presence of BN is needed in order to cut off thermal neutron contribution. This paper describes Zr irradiation and experimental results that were obtained by $\gamma $ spectrometry and accelerator mass spectrometry. In parallel, Zr irradiation is modeled with Monte Carlo-based code for neutron transport—TRIPOLI-4v10 developed by CEA (Saclay). Experimental values of 95Zr activity and 93Zr/92Zr ratio are compared to calculation results. Since crosssection values are necessary for the neutron flux determination, we present here the comparison between several nuclear data libraries for radiative capture on 92,94Zr. Uncertainties for calculation/experience (C/E) ratios are obtained combining both experimental and nuclear data ones. This paper shows the feasibility of 1-keV to 1-MeV neutron detection by using 92,94Zr (n, $\gamma $ ) reaction and introduces a postirradiation analysis for reactor dosimetry based on accelerator mass spectrometry. It also reveals that more precise evaluation of 92,94Zr (n, $\gamma $ ) cross section is required in order to improve C/E values. [ABSTRACT FROM AUTHOR]

In this article, silicone rubber (SiR) is filled with industry preferred micro-silica and specialty hexagonal boron nitride (h-BN) nanosheets, by varying the ratio between the two fillers, while keeping the filler to matrix ratio the same in all three composites. The fillers are added to SiR using an electrostatic disperser which aids in homogenizing the filler-polymer mixture by means of shearing force along with elongation. The performance of synthesized silicone composites are evaluated using thermal, erosion resistance, morphological, mechanical, and high-temperature dielectric properties. Addition of as low as 5 wt% h-BN fillers significantly improved the thermal properties; 6%–20% improvement in thermal conductivity and in less than half the weight loss compared to only silica filled composites with laser erosion. The morphological and mechanical analyses showed improved filler dispersion and filler to silicone matrix interaction owing to good filler dispersion achieved through the electrostatic dispersing method. The dielectric properties measured in wide frequency range, between 10−4 and 103 Hz and at elevated temperatures (up to 175 °C) showed a negligible effect of increase in h-BN content. Thus, this article implies that low amounts of h-BN in silica-silicone composites improve thermal conductivity and erosion resistance significantly and not altering the dielectric responses of these hybrid composites even at elevated temperatures. Hence these composites can find applications both in the high voltage industry and as electronic packaging materials. [ABSTRACT FROM AUTHOR]

Polymeric insulated cable with high ampacity and good thermal performance is the core of the new fast charging technology for electric vehicles (EVs). Advanced materials with both good thermal and electrical properties to improve the performance of EVs charging cable are proposed in this paper. Two sample cables were manufactured with ethylene-propylene-diene (EPDM) insulation and a chlorosulfonated polyethylene rubber (CSM) sheath. Both the insulation and sheathing materials were modified by hybrid boron nitride (BN) to improve the thermal conductivity (TC). The test results show that the modified EPDM insulation has good electrical and mechanical properties. For the temperature characteristics of these two cables, the adoption of high TC EPDM insulation and CSM sheath can improve the heat dissipation capability and the temperature distribution in the cable. In addition, the theoretical ampacity of the cable was calculated showing a significant improvement. The employment of high TC insulation and sheath appears to be of great benefit to the reduction of temperature and increase in ampacity of EV charging cables. [ABSTRACT FROM AUTHOR]

To reduce the electric field distortion and increase the thermal conductivity of the dielectric materials in cable accessories, this paper proposes a method to prepare composites with good nonlinear electrical conductivity and high thermal conductivity. Silver nanoparticles grown on hexagonal boron nitride (AgNPs/BN) were prepared as a powder and introduced into ethylene propylene diene monomer (EPDM) to obtain AgNPs/BN/EPDM composites. The nonlinear electrical conductivity, thermal conductivity and breakdown field strength of the composites were investigated at different temperatures. The nonlinear electrical conductivity and thermal conductivity of the composites increased with increasing AgNPs content grown on BN. Moreover, the breakdown field strength decreased with increasing AgNPs, and exhibited a weaker temperature dependence than neat EPDM. Simulations showed that the composites could improve the electric field distribution in a cable accessory. [ABSTRACT FROM AUTHOR]

In this paper, design aspects of the output system of a 170-GHz/1.5-MW continuous wave gyrotron operating in the TE28,12 mode is presented for testing the latest version of gyrotron design suite (GDS.V3.2014), which has been equipped with new features. The output system has been incorporated and showcased here considering the design aspects of the output system of this specific gyrotron as a case study. A nonlinear up-taper has been designed using a multiobject particle swarm evolutionary algorithm and the design of an advanced dimpled-wall launcher is carried out using launcher optimization tool. Single-disk chemical vapor deposition (CVD) diamond and CVD boron nitride windows have been designed to take out the output power. Besides, the reconstruction of the wave phase at different planes outside the tube is calculated by an iterative phase retrieval algorithm. The Gaussian mode content achieved by the launching system is 99.5%. In addition, design of a matching optics unit has also been done considering a very recent approach for off-axis incident beams. [ABSTRACT FROM PUBLISHER]

For several decades, Hall-effect thrusters (HETs) are being used in several applications, such as orbiting satellites, deep space missions, etc. This article studies the effect of several parameters, namely, thruster geometry, magnetic field, wall material, and different propellants that significantly influence thruster performance. It was reported that annular thrusters are preferred for deep space missions, whereas, cylindrical thrusters are widely used in low power applications, such as station keeping of satellites. The lifespan of HET is a crucial parameter that is decided by the erosion of the thruster wall. Magnetically shielded thrusters are preferred not only to reduce the erosion but also the secondary emission of electrons. The overall effect of magnetic shielding is the improvement in thruster performance and its lifespan. Boron nitride and mixture of boron nitride and silica (borosil) were found to be the most appropriate thruster wall materials due to their lowest electron emission and reduced ion–wall interaction. Over the years, Xenon has been the best choice among several propellants for the HET operation. Other potential propellants include Krypton, Bismuth, Iodine, etc. [ABSTRACT FROM AUTHOR]

An optical-phonon-limited velocity model has been employed to investigate high-field transport in a selection of layered 2-D materials for both, low-power logic switches with scaled supply voltages, and high-power, high-frequency transistors. Drain currents, effective electron velocities, and intrinsic cutoff frequencies as a function of carrier density have been predicted, thus providing a benchmark for the optical-phonon-limited high-field performance limits of these materials. The optical-phonon-limited carrier velocities for a selection of multi-layers of transition metal dichalcogenides and black phosphorus are found to be modest compared to their n-channel silicon counterparts, questioning the utility of biasing these devices in the source-injection dominated regime. h-BN, at the other end of the spectrum, is shown to be a very promising material for high-frequency, high-power devices, subject to the experimental realization of high carrier densities, primarily due to its large optical-phonon energy. Experimentally extracted saturation velocities from few-layer MoS2 devices show reasonable qualitative and quantitative agreement with the predicted values. The temperature dependence of the measured v{\mathrm{sat}} is discussed and compared with the theoretically predicted dependence over a range of temperatures. [ABSTRACT FROM AUTHOR]

A moderate-pressure microwave plasma is used to deposit boron nitride (BN) films by employing boron trifluoride as a source gas. In the deposition conditions, the ion flux onto a negatively biased substrate is measured to be on the order of 1016 cm−2s−1 depending upon the bias voltage. The films consisting of both hexagonal BN and cubic BN (cBN) phases are deposited on silicon substrates by applying a bias voltage ranging from −85 to −200 V. The film deposited at −85 V shows the higher crystallinity and larger roughness and grains of cBN due to a decrease in mean ion impact energy. The results suggest that the bias voltage for cBN phase formation is lowered by increasing the ion to depositing boron flux ratio even in collisional moderate-pressure conditions. [ABSTRACT FROM AUTHOR]

Band gap size of armchair graphene nanoribbons (AGNRs) can be tuned by implementing topological antidotes or boron/nitride (BN) atoms at the middle of ribbons. By imposing such modulated patterns on certain regions of AGNRs, double barrier quantum well structures can be produced. According to this procedure, this paper proposes a new method for constructing resonant tunneling diodes (RTDs) by using AGNRs while the widths of the ribbons remain constant. Different structures of modulated AGNR-RTDs are constructed by introducing hexagonal antidotes, hexagonal BN doping atoms, and the combination of antidotes and BN doping atoms at the middle of pristine AGNRs. It is found that in general, antidote AGNR-RTDs present negative differential resistance with better performance in comparison with other modulated AGNR-RTDs. In addition, the effects of dimensional parameters such as the length of channel, the length of barrier, and the distance between antidotes on the performance of antidote AGNR-RTDs are investigated. It is extracted that the peak to valley ratio, power dissipation, and other properties can be modified by tuning the dimensional parameters to appropriate values. Numerical tight-binding model along with nonequilibrium Green’s function formalism is applied to study the electronic properties of devices. [ABSTRACT FROM AUTHOR]

This paper presents the reflectivity and insertion loss characteristics of Boron Nitride (BN) and Sapphire RF windows for a 95-GHz Gaussian RF beam of a 100-kW gyrotron. The design of an RF window has been carried out using Fresnel’s formula for reflection and transmission of Gaussian electromagnetic wave at the boundary between two media. The return loss of the RF windows of 95 GHz was found to be less than −46.8 dB for BN and less than −57.8 dB for Sapphire, and the transmission loss of the RF windows was better than −0.06 dB for BN and better than −0.01 dB for Sapphire. Furthermore, the heat load due to RF power absorption over the disk surface has been calculated. The Sapphire RF windows have been found with lower heat load and deflection, and higher tensile stress than that of BN. The allowable stress level for Sapphire is higher than that of BN; therefore, using Sapphire is structurally safer to use. [ABSTRACT FROM PUBLISHER]

Conventional designs of the extensively studied resistive-random access-memory (RRAM) cell involve one transistor and one RRAM—“1T1R,” i.e., two separate devices thereby constraining its integration density. In this work, we overcome this longstanding limitation by experimentally demonstrating a novel memory architecture that combines the 1T and 1R into a single hybrid device by uniquely leveraging both lateral and vertical van der Waals (vdW) heterostructures. This ultracompact device, which can be considered as a “0.5T0.5R” memory cell, reduces the device count by half—the first of its kind in RRAM technology history, and simultaneously allows higher lateral as well as vertical (3-D) integration density w.r.t. the conventional 1T1R architecture. The unique “smart” device that can retain information after power is turned off is structurally designed by utilizing a shared graphene edge-contact and resistively switchable hexagonal boron nitride (h -BN) insulator. Aided by design optimization, record performance (< 10 ns switching-speed), energy- (~0.07 pJ/bit), and area-efficiency (smallest footprint among all reported vdW-material-based RRAM memory units), as well as great retention (106 s) and endurance (>1000), benchmarked against current vdW-material-based RRAM devices, have been achieved by this 0.5T0.5R memory cell. Moreover, the RRAM’s fine tunability with ultrashort pulsewidth, pulse amplitude, and gate voltage, enables synaptic plasticity and makes it an integrated three-terminal RRAM with considerable potential for neuromorphic and in-memory computing applications. [ABSTRACT FROM AUTHOR]

In this research, the mesomorphic properties, thermal conductivity, and dielectric strength of a liquid-crystalline epoxy resin with hybrids of cellulose nanofiber and boron nitride nanosheet are studied. The thermal conductivity of LCER with hybrid fillers at a loading of 30 wt% demonstrated approximately 387% of that of the neat LCER and 246% of that of the nanocomposites with single BNNS fillers. The hybrid nanocomposite also demonstrates comparable dielectric strength and greater water contact angles in contrast to nanocomposites with single BNNS fillers. Furthermore, the nanocomposites with hybrid fillers show greater resistance to electrical erosion during the breakdown testing due to the greater thermal conductivity induced by enhanced filler dispersion. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the influence of different types of nanoparticles on thermal and dielectric properties along with the relation between them. Boron nitride (BN) nanoparticles with high thermal conductivity and ferriferrous oxide (Fe3O4) nanoparticles as a typical magnetic oxide were dispersed into transformer oil to form different types of nanooil. Thermal and dielectric properties of the nanooil with different mass fractions were measured. Thermal conductivity and thermal diffusivity under different temperature were measured for each type of the nanooil in order to investigate the effect of nanoparticles on thermal property. Dielectric property experiments were performed in accordance with IEC standard. Relative permittivity, dissipation factor and electrical resistivity tests for the nanooil were conducted along with ac and dc breakdown strength in a range of temperature. It is found that both types of the nanooil showed improved thermal property compared with non-modified oil. The nanooil exhibits different performance in dielectric property due to the different properties of the nanoparticles. The obtained results show significant improvement in heat transfer process with increasing the mass fraction of BN nanoparticles while the oil modified by Fe3O4 nanoparticles shows considerable enhancement in dielectric breakdown strength. Through further comparison between the two types of nanooil, it is proposed that the improved thermal property contributes to the enhancement of the breakdown strength. [ABSTRACT FROM AUTHOR]

Transformer oil is widely used in electric transformers serving the dual functions as insulating medium and cooling material. However, safety and stability of power system is interrupted due to the operation failure of electric transformers in certain case. Therefore efforts should be focused on improving the property of transformer oil for the stable operation of insulating system. The purpose of this paper is to obtain a new type of nanomodified transformer oil with improved dielectric and thermal properties. Boron nitride (BN) nanoparticles with high thermal conductivity were dispersed into transformer oil to form the nanooil. Dielectric and thermal properties of the samples before and after modification were measured. Dielectric property experiments were performed in accordance with IEC standard. Discharge phenomenon in breakdown process was captured by a high speed CCD camera. In order to investigate the effect of BN nanoparticles on thermal property, temperature change and heat distribution of the samples in heat transfer process were measured by an infrared thermal imager and a temperature sensor. It is found that the nanooil has higher dielectric breakdown strength and lower dissipation factor which indicate better dielectric property compared with nonmodified oil. Obtained results show significant improvement in heat transfer process with increasing the concentration of BN nanoparticles. It is proposed that the nanoparticles create an interfacial region which contributes to the enhancement of dielectric strength. For thermal property the ballistic phonon transport of the nanoparticles acts as the key factor in the remarkable improvement. Furthermore, the improved thermal property of the nanooil has an inhibitory effect on the breakdown process according to the bubble theory. [ABSTRACT FROM AUTHOR]

In this paper, we presented a new strategy for fabrication of polymeric composites combined with low dielectric loss and desirable thermal conductivity. With the incorporation of hyperbranched polyborosilazane (hb-PBSZ) into bisphenol A cyanate ester (BADCy) matrix, the modified hb-PBSZ/BADCy resin with 4 wt% hb-PBSZ possessed a low dielectric constant (?) value of 2.37 and relatively low dielectric loss tangent value of 0.008 at 1MHz. Furthermore, by integrating micrometer boron nitride particles (mBN) into hb-PBSZ/BADCy matrix, the mBN/hb-PBSZ/BADCy composites presented relatively low ? of 3.09, desirable thermally conductive coefficient (? of 0.63 W/(m?K)) and thermal diffusivity (? of 0.42 mm2/s) values. It provides an important perspective for designing dielectric and thermally conductive polymeric composites for electrical packaging and energy storage fields. [ABSTRACT FROM PUBLISHER]

Silicone rubber (SiR) is widely employed as an insulating material in transmission lines because of its excellent electrical properties and superior performance under wet and polluted conditions. However, the discharges that occur during operation can cause electrical erosion on the surface of silicone rubber insulators. The thermal conductivity of insulators has a correlation with the resistance to tracking and erosion. This study attempts to clarify whether the addition of boron nitride (BN) particles can improve the resistance to tracking and erosion of SiR by increasing its thermal conductivity. Before the tests, specimens were prepared by dispersing nano-BN particles into room temperature vulcanizing (RTV) silicone rubber at different loadings. In this paper, the dc test has been developed from the current IEC 60587 inclined plane tracking and erosion test to compare the phenomena occurring during the tests. Temperature distribution was observed by an infrared thermal imager. The experimental results indicate that the filled specimens have a lower degree of surface damage than the unfilled specimens. In addition, with the increase in content of fillers from 0 to 7 wt%, the thermal dissipation is improved and both the erosion depth and the weight loss show a decreasing trend, which proves the resistance of silicone rubber to tracking and erosion is improved. [ABSTRACT FROM AUTHOR]

Epoxy is widely used in electronic and electrical devices because of its excellent insulation properties. The addition of nanoparticles to epoxy could change the material structure and then charge behaviors are altered as a consequence. The accumulation of surface charge may cause electric field distortion, which would lead to surface flashover. In this paper, the samples were made by dispersing nano-scale boron nitride (BN) particles in Epoxy with the weight ratios of 5, 10, 20, 30, 40 wt%. The samples were charged by a dc corona triode system using needle-plate electrodes. The distribution of charges was measured with an electrostatic voltmeter and the effect of nanoparticles on charge accumulation and decay behavior was studied. A flashover test was carried out under a dc stress between two finger-type electrodes. The effect of nanoparticles on flashover characteristics and the relation between surface charging and surface flashover were also investigated. The results showed that the traps between nanoparticles and the polymer, which were introduced by the added nanoparticles, could cause surface charge accumulation. In addition, the flashover occurred at a lower voltage because of the accumulated charge on the sample surface. [ABSTRACT FROM AUTHOR]

We present the characterization of ballistic graphene field-effect transistors (GFETs) with an effective oxide thickness of 3.5 nm. Graphene channels are fully encapsulated within hexagonal boron nitride, and self-aligned contacts are formed to the edge of the single-layer graphene. Devices of channel lengths ( LG) down to 67 nm are fabricated, and a virtual-source transport model is used to model the resulting current–voltage characteristics. The mobility and source-injection velocity as a function of LG yields a mean-free-path, ballistic velocity, and effective mobility of 850 nm, 9.3\times 10^7 cm/s, and 13 700 cm2/Vs, respectively, which are among the highest velocities and mobilities reported for GFETs. Despite these best-in-class attributes, these devices achieve transconductance ( gm) and output conductance ( $g_{{\mathrm{ds}}}) of only 600 and 300 \mu \textS/\mu \textm , respectively, due to the fundamental limitations of graphene’s quantum capacitance and zero-bandgap. g_m values, which are less than those of comparable ballistic silicon devices, benefit from the high ballistic velocity in graphene but are degraded by an effective gate capacitance reduced by the quantum capacitance. The $g_{{\mathrm{ds}}}$ values, which limit the effective power gain achievable in these devices, are significantly worse than comparable silicon devices due to the properties of the zero-bandgap graphene channel. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the electrical behavior of transistors based on a vertical graphene-hexagonal boron nitride (hBN) heterostructure, using atomistic multiphysics simulations based on density-functional theory and non-equilibrium Green's function formalism. We show that the hBN current-blocking layer is effective and allows modulation of the current by five orders of magnitude, confirming experimental results. We also highlight—through accurate numerical calculations and simplified analytical modeling—some intrinsic limitations of vertical heterostructure transistors. We show that the overlap between gate contacts and source/drain leads screens the electric field induced by the gates and is responsible for the excessive degradation of the sub-threshold swing, the ION/IOFF ratio, and the cut-off frequency. [ABSTRACT FROM AUTHOR]

Recently, quantum dots-converted white light-emitting diodes (QDs-WLEDs) are attracting numerous attention due to their high luminous efficiency and excellent color quality. As for color conversion material, the quantum dots (QDs) are commonly embedded into a low-thermal-conductivity polymer matrix. In this case, their generated heat during the photoluminescence process can hardly be dissipated into the heat sink, leading to a high working temperature and reduced lifetime. Adding particles with high thermal conductivity to the QDs layer can enhance its thermal conductivity, and thus reduce QDs’ working temperature. At the same time, these particles may affect the optical properties of QDs. However, this problem has still not been deeply studied. In this article, we systematically investigated the effects of the highly thermal-conductive hexagonal boron nitride sheets (hBNSs) on the optothermal performances of QDs/phosphor film in white light-emitting diodes (WLEDs). The thermal conductivity of QDs/phosphor film was significantly increased by 24% after adding 5wt% of 45- $\mu \text{m}$ -diameter hBNS. As for the optical performance, the transparency of the silicone gel film with 45- $\mu \text{m}$ -diameter hBNS was much better than that with 6–9- $\mu \text{m}$ -diameter hBNS under the same weight fraction. Furthermore, the scattering effect of hBNS plays a more important role in enhancing the light conversion performance of QDs than that of phosphor. At last, a color stability test showed the increasing rate of correlated color temperature (IRCCT) of hBNS-added WLEDs are 21% smaller than that of common WLEDs after working 153 h, meaning a better QDs stability in hBNS-added WLEDs. [ABSTRACT FROM AUTHOR]

From a novel empirical power law between the DC breakdown field and DC conductivity, an analysis of the trapping characteristics in polyimide/boron nitride (PI/BN) nanocomposites is presented based on space-charge-limited current (SCLC) measurements. The impact of the total trap density H t enhancement (increasing up to 1.1×1017 cm−3) induced by the BN nanoparticles on the space charge attenuation, the DC conductivity reduction and the DC breakdown field increase is clearly reported. This work proves that an efficient control of the trapping parameters allows huge enhancement of the insulating properties of PI nanocomposites. High temperature thermal breakdown can be delayed by free carrier reduction through deep trap formation caused by nanofiller addition. [ABSTRACT FROM AUTHOR]

Structures with pores having diameters of several nanometers can be used for distinguishing nucleotides in DNA. A 2-D material such as a thin membrane is expected to enhance precise molecule recognition. Here, we present the nanopore fabrication to thin 2-D membranes using He ion microscopy (HIM). We transferred three 2-D materials, chemical vapor deposition (CVD) graphene, CVD boron nitride, and peel-off MoS2, to the submicrometer pore of freestanding SiO2 membranes on a silicon substrate. The number of atomic layers of the 2-D materials was confirmed via Raman spectroscopy and X-ray photoelectron spectroscopy. We examined the reproducibility and accuracy of nanopore fabrication as a function of the focal position and beam irradiation intensity of the HIM system. Reproducible nanopores having diameters of less than 10 nm were realized by optimizing the intensity and focal position. We achieved 1.5-nm-diameter nanopores in a single layer of graphene using this HIM technique. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) has re-emerged as a promising layered material with significant potential for future nanoelectronic applications. Several recent studies have demonstrated an improvement in the transport properties of BP channels when insulated from SiO2 substrates using hexagonal boron nitride (hBN) (or when fully encapsulated). This improvement is typically characterized using extractions of mobility based on the empirical relationship between conductivity and carrier density. However, this does not provide insight into the transport mechanisms, nor it allows accounting for differences in intrinsic (e.g., bandgap and effective mass) and extrinsic (e.g., trap density/distribution and Schottky barrier heights) properties in the analysis. Here, we present a modeling approach for Schottky-barrier MOSFETs with low-dimensional channel materials based on the Landauer theory. To analyze transport improvement in hBN-insulated BP channels we fabricate and measure BP Schottky-barrier-MOSFETs with and without the hBN insulating layer. Our analysis demonstrates ~80% improvement in low-field effective channel mobility and an (energy averaged) scattering mean free path that is >5 times larger for BP devices with an underlying hBN layer compared to devices with BP directly on SiO2. [ABSTRACT FROM AUTHOR]

In this work, in order to investigate the effects of thermal conductivity on arcing resistance from the view of thermal accumulation under pulse strength, a range of polyethylene (PE) based composites filled with micro or hybrid boron nitride (BN) particles at different loadings (0, 3, 6 and 9 wt%) were prepared. Thermal conductivity and relative permittivity were measured to characterize the basic properties of various samples. Influences of thermal conductivity on thermal accumulation and arcing resistance were discussed through surface dielectric breakdown test. Obtained results show that the thermal conductivity of BN filled PE composite is obviously improved and the relative permittivity could maintain a relatively low value. At the same pulse frequency, with increasing filler concentration from 0 to 40 wt%, thermal conductivity and the time to surface dielectric breakdown all present increase trend, whereas sample surface maximum temperature and damage degree reflect the opposite tendency. It implies that the increased thermal conductivity contributes to reduce thermal accumulation during arcing discharge, which can help to promote the resistance to arcing discharge. Moreover, PE/hybrid-BN composite presents a higher thermal conductivity, a longer time to surface dielectric breakdown and a lower surface damage degree at the same filler content. It is concluded that adding hybrid-BN filler into PE resin can suppress thermal accumulation and improve arcing resistance more effectively. [ABSTRACT FROM PUBLISHER]

The electrical conduction and dielectric breakdown of polyimide/boron nitride (PI/BN) are investigated in a large temperature range up to 350 °C. This work shows that BN nanofillers act as deep traps for mobile ions. Below 150 °C, the nanostructuration of PI slightly improves the DC conductivity and the breakdown field. On the contrary above 150 °C, while neat PI exhibits ionic space charge contribution on the charging currents, PI/BN nanocomposites show a return to normal polarization currents. In such combined high field and high temperature ranges, the nanostructuration of PI allows increasing the mean free path of ions by decreasing the ionic hopping distance. The consequence of the improvement of the total trap density is a huge decrease (5 orders of magnitude) in the steady state currents and an increase (factor 2) in the breakdown field of PI/BN. This study proves the possibility to extend both the electric field and temperature ranges of PI films thanks to an adequate nanostructuration. [ABSTRACT FROM PUBLISHER]

In this work, a range of polypropylene (PP) based composites filled with micro or nano sized boron nitride (BN) particles at different loadings (0, 3, 6 and 9 wt%) were manufactured to investigate effects of thermal conductivity on surface dielectric breakdown (SDB). In addition to thermal conductivity measurement of various samples, thermal dissipation was also discussed to analyze the relationship between them. Meanwhile, in order to evaluate SDB strength of the manufactured samples, time to SDB, erosion depth and weight loss of the polymeric samples were measured through the test. Obtained results show that thermal conductivity of the doped PP composite is obviously improved. The increased thermal conductivity results in improvement of thermal dissipation ability, which contributes to inhibition of SDB occurrence. Thermal conductivity, thermal dissipation ability and SDB strength all represent positive correlation to filler loading level. More importantly, compared with nano-BN filled PP samples, PP/micro-BN samples can obtain higher thermal conductivity, better thermal dissipation ability and higher SDB strength at the same filler content. Experimental validation was also conducted with dc bulk dielectric breakdown (BDB) measurement of various samples. It is concluded that introduction of nano-BN filler into base resin favors improvement of BDB strength evidently, while the sample coated micro-BN exhibits a lower BDB strength than the base resin in any filler loadings investigated. [ABSTRACT FROM AUTHOR]

A unique configuration of the magnetic field and channel geometry near the wall of Hall thrusters, called magnetic shielding, has recently demonstrated the ability to significantly reduce the erosion of the boron nitride (BN) walls and extend the life of Hall thrusters by orders of magnitude. The ability of magnetic shielding to minimize interactions between the plasma and the discharge chamber walls in regions where erosion typically occurs has for the first time enabled the replacement of insulating walls with conducting materials without loss in Hall thruster performance. It is important to note that this is not a thruster with anode layer (TAL) where the walls are at or near cathode potential, but is a Hall thruster configuration where the walls are near the anode potential. The BN rings in the 6-kW H6 Hall thruster were replaced with graphite that self-biased to near the anode potential during operation. The thruster efficiency remained over 60% (within 2% of the baseline BN configuration) with a small decrease in thrust and increase in Isp typical of magnetically shielded Hall thrusters. The graphite wall temperatures decreased significantly compared with both shielded and unshielded BN configurations, leading to the potential for higher power operation. Eliminating ceramic walls makes it simpler and less expensive to fabricate a thruster to survive launch loads, and the graphite discharge chamber radiates more efficiently, which increases the power capability of the thruster compared with conventional Hall thruster designs. [ABSTRACT FROM PUBLISHER]

In [1], the first name of the third author in the byline under the title of the paper [1, p. 3257] as well as in the biography of the third author [1, p. 3261] should read “Rengaswamy” instead of “Ramaswamy.” [ABSTRACT FROM PUBLISHER]

Boron nitride (BN) thin film was deposited over Al substrate and used as a heatsink for high-power LED. The rise in junction temperature ( \(T_{J}\) ) was evaluated from transient cooling curve and observed as a low value for BN coated substrates rather than for bare and thermal paste (TP) applied substrate measured at 700 mA. Total thermal resistance ( \(R_{\rm thtexttot}\) ) was also observed as a low value for BN samples. The BN thin film interface influenced the wavelength peak shift toward a higher value. Noticeable increment on luminosity of the LED was also observed for BN coated Al substrate with respect to driving currents. The observed results were suggested the use of BN thin film as thermal interface materials as an alternative for TP. [ABSTRACT FROM PUBLISHER]

Two-dimensional atomic sheets of graphene represent a new class of nanoscale materials with potential applications in electronics. However, exploiting the intrinsic characteristics of graphene devices has been problematic due to impurities and disorder in the surrounding dielectric and graphene/dielectric interfaces. Recent advancements in fabricating graphene heterostructures by alternately layering graphene with crystalline hexagonal boron nitride (hBN), its insulating isomorph, have led to an order of magnitude improvement in graphene device quality. Here, recent developments in graphene devices utilizing boron–nitride dielectrics are reviewed. Field-effect transistor (FET) characteristics of these systems at high bias are examined. Additionally, existing challenges in material synthesis and fabrication and the potential of graphene/BN heterostructures for novel electronic applications are discussed. [ABSTRACT FROM PUBLISHER]

The performance of an extreme ultraviolet (EUV) photoelectron spectroscopy (EUPS) as a detector of tin (Sn) contamination on ultralow-level surface is studied using a 4.86-nm photon which is generated from boron-nitride plasma. The signal at 130 ns is normalized by the valence band signal at 105 ns to compensate for possible fluctuation of EUV intensity, which shows that Sn debris by laser ablation often shots cover the whole surface of a Si wafer. The intensity of the 130-ns peak decreased as the Sn coverage is decreasing. The Sn 4d electron peak having a binding energy of 25 eV was a good indicator of Sn contamination. The EUPS is proved to be sensitive to one atomic-layer contamination and have detect ability of several-percent coverage Sn contamination or 0.3% reflectivity drop. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIMs) are used in electronics cooling application to decrease the thermal contact resistance between surfaces in contact. A methodology to determine the optimal volume fraction of filler particles in TIMs for minimizing the thermal contact resistance is presented. The method uses finite element analysis to solve the coupled thermo-mechanical problem. It is shown that there exists an optimal filler volume fraction which depends not only on the distribution of the filler particles in a TIM but also on the thickness of the TIM layer,. the contact pressure and the shape and the size of the filler particles. A contact resistance alleviation factor is defined to quantify the effect of these parameters on the contact conductance with the use of TIMs. For the filler and matrix materials considered--platelet-shaped boron nitride filler particles in a silicone matrix--the maximum observed enhancement in contact conductance with the use of TIMs was by a factor of as much as 9. [ABSTRACT FROM AUTHOR]

The authors have developed a new technique to synthesize Fe nanoparticles encapsulated by boron nitride (BN) nanolayers. Starting materials--Hematite (α-Fe[sub2]O[sub3]) and boron (B) powders--are annealed at 1273-1473 K for 2 h in a nitrogen (N[sub2]) atmosphere. Hematite is reduced during annealing and Fe particles coated with BN are synthesized. It is revealed that the average diameter of the particles is 320 nm and the thickness of the coating layers is several nanometers from the observation using a high-resolution transmission electron microscope. The nanoparticles exhibit soft magnetic properties and the saturation magnetization depends on the weight ratio of hematite to boron in the starting materials. [ABSTRACT FROM AUTHOR]

The aim of this research is to find a way to achieve the epoxy composites with high thermal conductivity and acceptable dielectric breakdown (BD) strength. A value 12.3 W/m-K is the highest thermal conductivity obtained for epoxy composite in Part I. Dielectric breakdown performances such as short-time dielectric breakdown strength (BD strength), partial discharge (PD) resistance and BD time for composites were investigated in the Part II. In general, micro filler inclusion will increase thermal conductivity and decrease dielectric breakdown performance. Influencing factors are considered to be the orientation of filler, the content of void space, the content ratio in the case of co-mixing, the addition of nano filler, and filler surface modification. Twenty six kinds of composites were prepared in consideration of the above influencing factors. There are two options for most appropriate ones among the composites evaluated in the research. One is an epoxy/ conglomerated h-BN composite with co-loaded nano SiO2 and micro AlN filler. It has 12.3 W/m-K in thermal conductivity, 75.1 kVpeak/mm in BD strength and 260 % of BD time for neat epoxy. It is most suitable when low BD strength and high thermal conductivity is needed. The other one is an epoxy/ h-BN composite with co-loaded nano silica and AlN filler for requirement of very high BD strength but lower thermal conductivity. Optimum thermal conductivity is obtained if flaky h-BN filler is oriented in parallel to heat flow. Since it is difficult to realize full orientation, the use of conglomerated h- BN filler is a suitable option. Optimum BD performance is obtained if void space is reduced by certain methods such as co-dispersion of different size fillers and addition of nano filler. [ABSTRACT FROM PUBLISHER]

The aim of this research is to find a way to achieve the epoxy composites with both high thermal conductivity and acceptable dielectric breakdown (BD) strength. As high thermal conductivity, low permittivity and low thermal expansion coefficient of filler can endow composite with higher thermal conductivity, higher BD strength and lower thermal expansion coefficient respectively, BN (boron nitride) with high thermal conductivity, low permittivity and low thermal expansion coefficient was adopted as main filler in the research. Thermal conductivity was investigated in this part. The BD strength of samples will be discussed in Part II. Neat epoxy and other 25 kinds of epoxy/BN composites were prepared by a hot press method. Most of BN fillers were surface modified with silane coupling agent through ethanol/water reflux method to improve thermal conductivity. The values of 2.91 W/m???K, 3.95 W/m???K and 10.1 W/m???K as thermal conductivity were obtained for the composites that was singleloaded with h-BN(hexagonal boron nitride), c-BN (cubic boron nitride) or conglomerated h-BN, respectively. They were further improved to 5.26 W/m???K, 5.94 W/m???K and 12.3 W/m???K, respectively, by adding extra smaller AlN (aluminum nitride) to fill the voids in sample. Thermal conductivity of samples changes with the ratio of c- BN and h-BN when c-BN and h-BN were co-loaded. A value of 5.74 W/m???K as maximum was obtained at their ratio of 1 to 1 when total filler content is 80 wt%. A much higher value of 7.69 W/m???K was obtained by adding extra AlN. From the experiment data, it is concluded that the filler orientation in vertical direction of sample surface and the decrease of voids in sample are very important to obtain high thermal conductivity, and that the filler surface modification is also necessary to improve thermal conductivity especially for epoxy/ c-BN composites, and addition of nano silica in small amount can also increase thermal conductivity if sample is prepared a ppropriately. [ABSTRACT FROM PUBLISHER]