Search

Low-noise amplifier is one of the most attractive applications of graphene transistors in the RF area. In this letter, a graphene amplifier MMIC is fabricated on the quasi-free-standing bilayer epitaxial graphene grown on SiC (0001) substrate. In order to realize both the high gain and low return loss, Au matching lines are designed as the input and output impedance match networks. The fabricated graphene amplifier MMIC shows a small-signal power gain of 3.4 dB at 14.3 GHz and a minimum noise figure of 6.2 dB. This letter is a significant step forward for graphene electronics in low-noise amplifier and demonstrates graphene’s potential in RF applications for future high-speed electronics.

2D material of graphene has inspired huge interest in fabricating of solid state gas sensors. In this work, epitaxial graphene, quasi-free-standing graphene, and CVD epitaxial graphene samples on SiC substrates are used to fabricate gas sensors. Defects are introduced into graphene using SF6 plasma treatment to improve the performance of the gas sensors. The epitaxial graphene shows high sensitivity to NO2 with response of 105.1% to 4 ppm NO2 and detection limit of 1 ppb. The higher sensitivity of epitaxial graphene compared to quasi-free-standing graphene, and CVD epitaxial graphene was found to be related to the different doping types of the samples.

The excellent electrical properties of graphene make it have broad application in electronic devices [1–2]. Grain boundaries and wrinkles will greatly scatter charge carriers of graphene [3–4]. Graphene with less gain boundaries and wrinkles are highly demanded. At present, the chemical vapor deposition (CVD) of graphene on Cu foil/Cu-Ni surfaces has been known as the simplicity and low cost way to prepare large-sized high-quality graphene films. However, the suppressing nucleation density method also leads to a low growth rate. Here we demonstrate a surface oxygen supply strategy for the Cu Ni substrate on sapphire to form a Cu-Ni-O surface. With the Cu-Ni-O surface, the growth rate of graphene is greatly increased to 240 μm/min. The as-synthesized graphene has less wrinkles, and a small 2D peaks FWHM of 25.2 cm−1. The room temperature sheet resistance reaches 267 Ω/square. This study provides a meaningful method to time-saving synthesis of high-quality graphene.

High-quality graphene materials and high-performance graphene transistors have attracted much attention in recent years. To obtain high-performance graphene transistors, large single-crystal graphene is needed. The synthesis of large-domain-sized single-crystal graphene requires low nucleation density; this can lead to a lower growth rate. In this study, a Ni-foam assisted structure was developed to control the nucleation density and growth rate of graphene by tuning the flow dynamics. Lower nucleation density and high growth rate (∼50 μm min−1) were achieved with a 4 mm-gap Ni foam. With the graphene transistor fabrication process, a pre-deposited Au film as the protective layer was used during the graphene transfer. Graphene transistors showed good current saturation with drain differential conductance as low as 0.04 S mm−1 in the strong saturation region. For the devices with gate length of 2 μm, the intrinsic cut-off frequency fT and maximum oscillation frequency fmax were 8.4 and 16.3 GHz, respectively, with fmax/fT = 1.9 and power gain of up to 6.4 dB at 1 GHz. The electron velocity saturation induced by the surface optical phonons of SiO2 substrates was analyzed. Electron velocity saturation and ultra-thin Al2O3 gate dielectrics were thought to be the reasons for the good current saturation and high power gain of the graphene transistors.

In this work, we present a graphene amplifier Monolithic Microwave Integrated Circuit (MMIC) operating at X-Band. The graphene field effect transistor (FET) was fabricated on quasi-free-standing bilayer epitaxial graphene on SiC (0001) substrate by a self-aligned fabrication procedure. The small-signal equivalent circuit model of 2× 15 μm graphene FET with 200 nm T-gates was deduced from the measured small-signal S-parameters. The modeled S-parameters show good agreement with experiments from 1 GHz to 20 GHz. Based on the model, the X-band amplifier MMIC was designed and fabricated with independent bias component and impedance matching network composing of inductance and transmission line. A small-signal gain of 2.6 dB and a noise figure of 6.1 dB were achieved in the fabricated amplifier.

Vulnerability to poverty refers to the risk of an individual or household falling below the poverty line. A partial vulnerability to poverty ordering is defined to indicate when a situation characterized by uncertainty means that people are more vulnerable to poverty than in another situation. The family of expected poverty indices used in this context contains versions under vulnerability of many well-known poverty indices. The ordering resembles the Hardy et al. result on the Lorenz partial ordering. A separate ordering for the expected income gap ratio is also investigated. First-order stochastic dominance is used to indicate when the expected value of the censored returns from the states increases.

Owing to its ultra high carrier mobility, graphene transistor shows great application potential as high-frequency electronics. Intrinsic cutoff frequency ( f T ) of 427 GHz has been reported. But the maximum oscillation frequency ( f max ) remains low, limiting its use in practical radio-frequency (RF) circuits. Here, we report an ultra clean self-aligned graphene transistors fabrication by pre-deposition of gold film on graphene as protection layer. This improved self-aligned fabrication keeps graphene away from any possible contamination, which makes our graphene transistors show good gate coupling and less parasitics, thus good dc and RF performances. The 100 nm gate-length graphene transistor exhibits a f max of 105 GHz. Our study shows a pathway to fabrication of high-performance graphene transistors for future application in RF circuits.

Hydrogenated diamond MOSFETs with self-oxidized alumina as a gate dielectric are fabricated. The diamond MOSFETs show a high maximum drain current density of 466 mA/mm at VGS = −6 V, a transconductance of 58 mS/mm, and an off-state breakdown voltage of −53 V. The maximum output power density reaches 745 mW/mm at 2 GHz continuous wave, which is the highest reported value for diamond transistors measured at 2 GHz. The output power value measured is lower than that estimated. Pulse I-V analysis shows that the main factor that affects the output power of the diamond MOSFETs is the traps in the channel.

We investigated the magnetotransport properties of a bilayer graphene Hall bar sample epitaxially grown on Si-terminated silicon carbide. Integer quantum Hall effect and weak localization effect were observed. From the weak localization effect, the carrier scattering and phase coherence were extracted. The extracted phase coherence length is 0.5 μm at 2 K, which is comparable with that of the exfoliated graphene. The temperature dependence of the phase coherence rate shows that electron–electron interaction is the main inelastic-scattering factor and direct Coulomb interaction also exists. Compared with exfoliated bilayer graphene, no sign of weak antilocalization was observed at such high carrier concentration of 1013 cm−2 due to the strong intervally scattering. Both the strong intervally scattering and Coulomb interaction of phase coherence are due to the large amount of atomically sharp defects in epitaxial graphene on Si-terminated SiC.

In order to better blend green plum wine and study aromatic components of green plum wine, a qualitative analysis on aromatic components of soaked base liquor, green plum soaked wine, green plum juice, and fermented wine of green plum juice by Head Space Solid-phase Microextraction (HS-SPME) and Gas Chromatograph Mass Spectrometer (GC-MS) was studied in this paper. Experiment results indicated that 14，32，17，and 46 kinds of aromatic components were identified respectively from four samples. Different aromatic components determined the special flavor and taste of green plum wine. Unique aromatic components generated in soaking process include benzaldehyde, 1-butanol, 2-methyl-, S-(-), benzoic acid ethyl ester, and 5-(hydroxymethyl). Special aromatic components in green plum juice were furfural, phenylethyl alcohol, and benzyl alcohol. The aromatic components in fermented wine of green plum juice mainly included phenylethyl alcohol (6.941%, relative content of peak area, same below), 1-butanol, 3-methyl- (6.940%), octanoic acid, ethyl ester (3.734%), decanoic acid, ethyl ester (2.590%), hexanoic acid, ethyl ester (2.479%), ethyl 9-decenoate (2.080%), and 5-hydroxymethyl (1.756%). This study was expected to provide scientific basis and data reference for quality improvement of green plum wine.

Considering its high carrier mobility and high saturation velocity, a low-noise amplifier is thought of as being the most attractive analogue application of graphene field-effect transistors. The noise performance of graphene field-effect transistors at frequencies in the K-band remains unknown. In this work, the noise parameters of a graphene transistor are measured from 10 to 26 GHz and noise models are built with the data. The extrinsic minimum noise figure for a graphene transistor reached 1.5 dB, and the intrinsic minimum noise figure was as low as 0.8 dB at a frequency of 10 GHz, which were comparable with the results from tests on Si CMOS and started to approach those for GaAs and InP transistors. Considering the short development time, the current results are a significant step forward for graphene transistors and show their application potential in high-frequency electronics.

In this letter, we report the first wafer-scale epitaxial graphene field-effect transistor (FET) grown and fabricated on 2-inch sapphire (0001) substrate by chemical vapor deposition (CVD) without a metal catalyst. The monolayer structure of the epitaxial graphene was confirmed by Raman spectra. Room temperature Hall effect mobility was 1,500 cm2/V·s. The maximum drain source current (I ds ) of 0.78 A/mm and peak transconductance of 0.13 S/mm were obtained at V ds = −1 V for the graphene FET with gate length of 100 nm. The cutoff frequency (f T ) and maximum oscillation frequency (f max ) reached 24 GHz and 26 GHz after de-embedding, respectively, which are the first epitaxial graphene-on-sapphire FET showing RF performance. Our work proves out the promise of epitaxial graphene on sapphire substrate.

The service life of the piston head and the stability of a large diesel engine are greatly affected by the wear resistance of the groove of the piston head. Conventional high-frequency quench-and-temper treatment results in several deleterious effects that may impair the anti-friction and wear properties of the groove of the piston head. Laser surface quenching is a new candidate technique. In this study, based on orthogonal experimental design, the effect of the surface condition, the laser power, the traverse speed, the incident angle and the gas flow rate on the quenched zone of 40CrNiMoA steel was investigated systematically. The profile, hardness and microstructure of the quenched zone vary with the surface condition, the laser power, the incident angle and the traverse speed. However, they are not significantly affected by the gas flow rate. The optimum processing parameters are obtained for the laser quenching of the groove of the piston head. Using the optimum processing parameters, quenched zones with not only sufficient case depth and greater hardness but also of a suitable profile and a finer microstructure, are obtainable. The hardness of the laser quenched zone is substantially higher than that resulting from conventional high-frequency quench-and-temper treatment.

In hot forging, the effect of temperature on the process is great. The temperature variation has a strong effect on both the die and the workpiece: in the high-speed hot-forging process in particular there exists a significant increase in the billet temperature, which can induce microstructural modifications that alter the flow resistance of the material and other mechanical properties, as well as affecting shortcomings. In this paper, a numerical simulation technique has been employed to study the thermal behavior of the high-speed forging of an AISI1045 disk. Useful information on the temperature distribution in the entire die—workpiece domain can be provided. The influences of the forming speed and the die temperature are also investigated. It is found that die-chilling and some forging parameters have a key effect on the forging process and even on the final product shape. Through the optimization of the forging parameters, an optimum forming processing can be selected before the component is put into production.