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In seismically active regions, high-filled embankment slopes on liquefiable soils tend to damage after strong earthquakes. Therefore, post-seismic damages should be estimated as soon as possible to mitigate potential losses. Fragility function is an efficient tool for assessing the seismic vulnerability conditions of structures, which links the probability of exceeding different limit states to seismic intensity. An embankment slope on liquefiable soils at Yading Airport in China was selected as the study object, and a series of numerical analyses of the embankment-foundation system utilizing the finite element method were conducted. Advanced dynamic constitutive models considering liquefaction and hysteresis characteristics were also adopted to simulate the nonlinear stress–strain behavior of soils under cyclic loadings. The post-seismic stability of embankment slopes was assessed using the strength reduction method (SRM) based on the stress–strain analysis. On this basis, the permanent ground deformation (PGD) at the ground-free field conditions was selected as the intensity measure (IM), while the factor of safety (FoS) of the slopes was selected as the damage measure (DM). Then, a procedure was presented for deriving seismic fragility functions with different damage states in light of incremental dynamic analysis (IDA). This paper aims to investigate the effects of different embankment typologies, such as the thickness of liquefiable soils and slope inclination, on the post-seismic vulnerability of embankment slopes. The fragility curves constructed in this study may soon be helpful for predicting the post-seismic damage of similar high-filled embankment slopes on liquefiable soils, which enables efficient traffic control and rapid disaster response.

Plasma enhanced atomic layer deposition (PEALD) SiN gate dielectric is performed on AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT). The fabricated MIS-HEMTs with 5 nm SiN gate dielectric layer exhibits a tiny threshold voltage hysteresis (~ 0.04 V), sufficiently decreased leakage current of ~10−9 A/mm at ${V}_{\text {GS}} =-{60}$ V and good threshold voltage ( ${V}_{\text {TH}}$ ) stability even measured at 200 °C. The increased mobility of 2-D electron gas (2-DEG) and suppressed current collapse are demonstrated, thereby producing a power density of 7.05 W/mm with an associated 34.0 % power-added efficiency (PAE) and a peak PAE of 51.4 % in a continuous-wave mode at 30 GHz.

A Ka -band AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) with SiN gate dielectric grown by plasma-enhanced atomic layer deposition (PEALD) is demonstrated. The gate reverse leakage current in a controlled HEMT is reduced by about three orders of magnitude by the PEALD-SiN, contributing to an improved breakdown voltage of 92.5 V (source–drain separation of $2.0~\mu \text{m}$ ) in the fabricated MIS-HEMTs. The MIS-HEMTs also feature small threshold voltage hysteresis in dc transfer and capacitance–voltage characterizations, suggesting a good PEALD-SiN/AlGaN interface. The fabricated MIS-HEMTs deliver a high output power density of 7.16 W/mm and a peak power-added efficiency of 60.3%, respectively, at ${V}_{\text {DS}} =30$ V and ${V}_{\text {DS}} =10$ V in pulse mode at 28 GHz. PEALD-SiN could be a compelling gate dielectric for fabrication of high-power and high-efficiency MIS-HEMTs.

Low damage atomic layer etching (ALE) gate recess is developed for fabrication of millimeter-wave AlGaN/GaN high-electron-mobility transistors (HEMTs). Plasma ion induced bombardments to the AlGaN barrier is effectively suppressed by the ALE recess, contributing to a well-controlled recessed surface morphology. The suppressed lattice damage to AlGaN/GaN heterostructure is also reflected by a significantly reduced gate leakage as well as an invisible threshold voltage shift associated with damage induced traps. With a 0.15- $\mu \text{m}$ T-gate fabrication technology, a high power-gain cutoff frequency ${f}_{\text {MAX}}$ of 205 GHz has been achieved. The ALE-recessed AlGaN/GaN HEMTs exhibits a record high power-added-efficiency (PAE) of 43.6% at 40 GHz in a continuous-wave mode. The associated gain and output power density are also remarkably improved compared with controlled HEMTs with conventional gate recess process.

Rockburst is a common geological hazard in underground mining and excavating, constituting a serious threat to the safety of workers and equipment. Rockburst liability prediction is of crucial significance to the prevention of rockburst hazards. Multi-criteria decision-making approach is an effective tool to predict rockbursts. In this paper, five empirical factors (strength-stress ratio, Russenes criterion, brittleness index, strain energy storage index, and integrity index) were used to construct the standard of rockburst liability. A novel analytic hierarchy process (AHP) was proposed to determine the weight of these factors, and then a cloud model was established for rockburst liability prediction on this basis. In the new AHP, the random errors induced by the pairwise comparison matrices of decision-makers were corrected according to the Bayesian theories. Nine cases from engineering projects in China were collected to validate the proposed model for rockburst liability prediction, and the prediction results were consistent with the field status. The quantitative index (Euclidean distance) indicates that the novel analytic hierarchy process has better performance than the original analytic hierarchy process in the weight calculation of factors; the new proposed cloud model is also superior to the original cloud model and the technique for order preference by similarity to an ideal solution model in the prediction of rockburst liability.

Based on the Darcy's law and water balanceprinciple,some infiltration models have been proposed,but most of these models are not suitable for simulating infiltration into layered soils during unsteady rainfall. In this paper, a simple modelfor simulating water infiltration into the two-layer soil slopesduring unsteadyrainfallwasproposed, combined with the limit equilibrium methodto analyze the stability of thetwo-layer soil slope.The water infiltration rate of slopes depends on rainfall intensity and the actual infiltration capacity of soils. The proposedmodelhas been successfully applied to three cases (steady rainfall and homogeneous slope, unsteady rainfall and homogeneous slope,unsteady rainfall and two-layer soil slope), and it can be also combined with probabilistic methods to calculate the failure probability of slopes.Compared with the Richards model, the combination of the proposed model and the random field method can quickly obtain the failure probability of the slope.

Dimethyl ether (DME) can be directly synthesized from carbon dioxide and hydrogen by mixing methanol synthesis catalysts and methanol dehydration catalysts. The activity and selectivity of the catalyst can be greatly affected by the promoter; herein, we presented a series of CuO-ZnO-Ga

Mechanical properties and geometries of printed products have been extensively studied in metal 3D printing. However, chemical properties and catalytic functions, introduced by metal 3D printing itself, are rarely mentioned. Here we show that metal 3D printing products themselves can simultaneously serve as chemical reactors and catalysts (denoted as self-catalytic reactor or SCR) for direct conversion of C1 molecules (including CO, CO2 and CH4) into high value-added chemicals. The Fe-SCR and Co-SCR successfully catalyze synthesis of liquid fuel from Fischer-Tropsch synthesis and CO2 hydrogenation; the Ni-SCR efficiently produces syngas (CO/H2) by CO2 reforming of CH4. Further, the Co-SCR geometrical studies indicate that metal 3D printing itself can establish multiple control functions to tune the catalytic product distribution. The present work provides a simple and low-cost manufacturing method to realize functional integration of catalyst and reactor, and will facilitate the developments of chemical synthesis and 3D printing technology., Metal 3D printing is a very promising technology to revolutionize catalytic systems. Here the authors show that metal 3D printing products themselves can simultaneously serve as chemical reactors and catalysts for conversion of C1 molecules into high value-added chemicals.

In this letter, a high-temperature (HT) gate recess technique is implemented into the fabrication of high-performance millimeter-wave AlGaN/GaN high-electron-mobility transistors (HEMTs). By virtue of the low damage feature of the HT recess, a high extrinsic transconductance of 422 mS/mm, a three-terminal breakdown voltage of 134 V with a source–drain separation of 2.4 $\mu \text{m}$ , and a remarkable low Schottky gate leakage current of $1.6\times 10^{-6}$ A/mm at ${V}_{\textsf {GS}} = -\textsf {60}$ V are achieved, which is at least two orders of magnitude lower than the HEMTs with gate recessed at room temperature. By employing a 0.2- $\mu \text{m}$ T-shaped gate technology, a current-gain cutoff frequency ${f}_{T}$ of 81 GHz and a unit-power-gain frequency ${f}_{\textsf {MAX}}$ of 194 GHz are realized. The current collapse in the HT-recessed AlGaN/GaN HEMTs is significantly suppressed, contributing to a record high power-added-efficiency of 42.8%, as well as high output power density of 5.1 W/mm at 35 GHz in a continuous-wave mode.

Superior iron-based Fischer-Tropsch synthesis (FTS) catalysts (Fe/NMCs) were developed by impregnating high amount of iron (40 wt%) over nitrogen-rich mesoporous carbons (NMCs) with high porosities. The large pore volumes and specific surface areas of NMCs realized the high loadings and proper dispersions of iron while the nitrogen-containing groups enhanced the basicities of the catalysts. Weak metal-support interactions were observed in Fe/NMCs, which improved the reduction, carburization of iron, and further the FTS activities. FTS tests indicated a medium amount of nitrogen (≤8.3 wt%) did not show obvious effect on the activity of the catalyst, but a much higher amount of nitrogen (≥16.5 wt%) could result in a significant decrease of activity. Nitrogen-containing groups could effectively suppress the methane selectivity and improve the lower olefins selectivity in the FTS reaction. The hydrocarbon productivity of the Fe/NMCs was up to 0.62 g HC/(h·g cat.) at 260 °C, 1 MPa, and H2/CO ratio of 1, much higher than that of any other iron catalyst reported under similar conditions. As a result of the superior performance, Fe/NMCs could be one of ideal candidates for iron-based FTS catalysts in the future.

Iron-based Fischer-Tropsch synthesis (FTS) has received renewable interests due to the gradual depletion of crude oil resources and its flexible product adjustment from lower olefins to long-chain hydrocarbons. However, one of the main challenges of iron-based FTS catalysts is the relative lower activity or productivity (per gram catalyst) at low or middle temperature. In this work, ultra-active iron-based FTS catalysts (Fe/SMC) were developed by loading iron over spherical mesoporous carbon (SMC) with huge porosity. The large pore volume (2.22 cm 3 /g) and high specific surface area (767 m 2 /g) of SMC allowed the high iron loading (up to 50 wt%) with proper dispersion. Weak C-Fe interaction was observed in the Fe/SMC catalysts, which was favorable for the reduction of iron and its further carburization to form more active sites of FTS. Activity tests showed that the Fe/SMC catalysts exhibited ultra-high activities in FTS. With the increase of iron loadings (30–50 wt%), the FTS rates (FTY, mmol CO/(h·g cat.)) of Fe/SMC catalysts increased due to the larger iron surfaces exposed at higher iron loadings. Small amount of K promoter significantly enhanced the FTY and apparent turnover frequency (TOF, S −1 ) of the Fe/SMC catalysts. The hydrocarbon productivity of K-promoted catalyst (40FeK/SMC) was up to 0.91 g HC/(h·g cat.) (260 °C, H 2 /CO = 1, 2 MPa), much higher than that of any other supported or unsupported iron-based FTS catalysts reported at similar reaction conditions. The results obtained in this work will open a new avenue for the development of highly active iron-based FTS catalysts.

The infiltration process in slopes is an essential issue in geotechnical engineering. A new Green-Ampt model for describing the two-stage infiltration in slopes based on fractional derivatives was proposed in this paper. The Green and Ampt (1911) ’s model, and Chen and Young (2006) ’s model are two special cases of the proposed model. A 1D loess soil column test in the literature as well as a laboratory rainfall test of loess slope were used to validate the proposed model. The travel curve of wetting front obtained by the proposed model was obviously closer to the actual test value than that obtained by the Chen and Young’s model, indicating that the performance of the proposed model is superior to the Chen and Young’s model due to the use of fractional derivatives. The proposed Green-Ampt model was combined with a rigorous 3D limit equilibrium method to obtain the real-time safety factor of the slope during rainfall. The calculated failure time of the loess slope by the proposed method is close to the actual failure time of the laboratory test, while the corresponding of Chen and Young’s model is obviously shorter than the actual status. Six parameters are included in the proposed model, and sensitivity analysis shows that the fractional derivative has the most significant impact on the wetting front depth, followed by the permeability coefficient, moisture content difference, suction head, rainfall intensity, and slope angle.

In this contribution, the efficient hydrogenation of dimethyl oxalate (DMO) to ethanol was achieved over a series of cerium promoted Cu/SiO2 (xCe-Cu/SiO2) catalysts prepared by a urea-assisted gelation approach. As a promoter, Ce played a crucial role in improving the structure, properties and catalytic performance of the Cu/SiO2 catalysts. The structure and chemical properties of the synthesized catalysts were characterized by XRD, FT-IR, in situ XRD, TEM, STEM-EDX mapping, N2O titration, H2-TPR, H2-TPD, XPS, XAES, etc. The characterization results disclosed that the addition of a Ce promoter to the Cu/SiO2 catalysts remarkably increased the Cu dispersion and retarded the sintering of small-sized Cu species. The strong interaction between the Ce promoter and Cu species substantially changed the redox properties of xCe-Cu/SiO2 catalysts and made the Cu2+ species easy to reduce. In addition, the activation ability of H2 species was significantly improved in the xCe-Cu/SiO2 catalysts, as evidenced by H2-TPD studies. Among these synthesized catalysts, the 1Ce-Cu/SiO2 catalyst with a 1.0 wt% Ce loading exhibited the highest catalytic activity (100% DMO conversion), ethanol selectivity (91.8%) and stability. This enhancement of catalytic activity, ethanol selectivity and stability is very promising for the development of an alternative route for the production of ethanol by hydrogenation of DMO from syngas.

Mesoporous Ni-Mg-Al and Ni-Al catalysts were facilely synthesized via evaporation-induced self-assembly (EISA) method and employed for coupled reforming reaction consisting of dry reforming of methane (DRM) and partial oxidation of methane (POM) to produce syngas (H 2 + CO). The Ni-Mg-Al and Ni-Al catalysts with encapsulated nickel nanoparticles were directly synthesized in one-pot way. For comparison, Ni/Al 2 O 3 as reference catalyst was also prepared by general impregnation method. Characterization by BET, XRD and H 2 -chemisorption revealed that the Ni-Mg-Al catalyst owned larger surface area and higher Ni dispersion as well as smaller metallic Ni particles size compared to Ni-Al and Ni/Al 2 O 3 catalysts. CO 2 -TPD demonstrated that the Ni-Mg-Al catalyst presented stronger basicity due to Mg incorporation. H 2 -TPR confirmed that the reduction of Ni-based species to Ni 0 was performed in high temperature due to the formed NiAl 2 O 4 phase. Activity tests indicated that this Ni-Mg-Al catalyst, due to its excellent physicochemical property, exhibited higher CH 4 conversion, H 2 selectivity, and H 2 /CO ratio in the coupled DRM-POM reaction. XRD, SEM and TG-DTA analyses of the used catalysts disclosed that the Mg-modified Ni-Mg-Al catalyst for syngas production using coupled DRM-POM reaction exhibited robust resistance to coke deposition. Consequently, by the synergistic cooperation between the coupled DRM-POM reaction and Mg-modified Ni-Mg-Al catalyst, high catalytic activity and stability could be accomplished to produce syngas.

Silicalite-1 zeolite coating was coated on the honeycomb-like monolithic SiC foam via hydrothermal synthesis method. The as-made Silicalite-1-coated SiC (S-1/SiC) was used as catalyst support to prepare a novel supported Ni monolith catalyst (Ni/S-1/SiC) by impregnation method. The Ni/S-1/SiC monolith catalyst was characterized by X-ray diffraction (XRD), N 2 physical adsorption, scanning electron microscope (SEM), thermogravimetry (TG), etc. The analysis results of XRD and SEM disclosed that Silicalite-1 coating successfully grew in situ on the SiC surface under the employed hydrothermal conditions. The Ni/S-1/SiC monolith catalyst was employed for syngas production in a combined reforming reaction consisting of CO 2 dry reforming of methane (CDRM) and partial oxidation of CH 4 (POM). Activity results indicated that the Ni/S-1/SiC monolith catalyst exhibited better catalytic activity than Silicalite-1 supported Ni catalyst (Ni/S-1) and SiC supported Ni (Ni/SiC) catalyst. The Silicalite-1 coating on the Ni/S-1/SiC catalyst combined the SiC support and Ni-based species tightly, leading to the enhanced catalytic performance of Ni/S-1/SiC catalyst. The stability test indicated that the Ni/S-1/SiC monolith catalyst also presented excellent stability and strong resistance to carbon deposition, which was attributed to the high heat conductivity of SiC, the presence of Silicalite-1 being coated on SiC as well as the combined reforming reaction of CDRM-POM. Furthermore, the H 2 /CO molar ratio of syngas generated in the combined CDRM-POM reaction over Ni/S-1/SiC catalyst could be tuned facilely by adjusting the proportion of O 2 coexisting in feed gas.

A silicon carbide (SiC) foam monolith decorated with a carbon nanofibers (CNFs) layer was employed as the catalyst support for Ni-based catalyst preparation, used for the CO2 dry reforming of methane (DRM) reaction. The loading amount of CNFs on the SiC foam monolith was 6.6 wt.%, which obviously increased the surface area of the pristine SiC foam from 4 m2/g to 24 m2/g. The prepared CNFs layer strongly attached to the pristine SiC surface and was considerably stable even after 100 h time on stream (TOS) DRM reaction. The CNFs decorated SiC composite support provided more anchorage sites for improving the dispersion of the Ni particles and enhanced the metal-support interaction compared to the pristine SiC support. Compared with other catalysts such as Ni/SiC and Ni/CNFs, the Ni/CNFs-SiC catalyst exhibited not only the highest activity but also remarkable stability during DRM reaction. The XPS and SEM-EDS results showed that the carbon deposition over the nickel surface of Ni/CNFs-SiC catalyst was much less than those of Ni/SiC and Ni/CNFs catalysts. In addition, the XRD analysis verified that almost no sintering of nickel particle was detected over the Ni/CNFs-SiC catalyst, which was prepared with CNFs-SiC composite as catalyst support, even after 100 h TOS DRM reaction at 750 °C.

The upgrading and reforming of coal-derived liquids are necessary for the application of high value-added liquid fuels, but the processing is difficult due to the amounts of impurities. In this paper, the catalytic cracking of 4-(1-naphthylmethyl)bibenzyl (NMBB) as a model reaction was studied deeply under sub- and supercritical water environment. Water might serve as a cheap and environmental H donor, which was more efficient than the supplied H2 in the processing of coal-derived liquids upgrading. Meanwhile, sub- and supercritical water could provide a homogeneous reaction environment for NMBB cracking as special solvents. The NMBB conversion under subcritical water was much higher than that under supercritical water. Furthermore, for H2 atmosphere, NMBB conversion was higher than that of N2 atmosphere, indicating that the process of in-situ H2 formation from subcritical water was more easily. Therefore, the cracking of NMBB under subcritical water and H2 atmosphere could be regarded as a reasonable reaction condition.

This study focused on the synthesis of hydrocarbon fuel containing a high iso-paraffin and very low oxygen content from palm oil using a mixed acid–base catalyst. The catalysts were characterized by nitrogen adsorption–desorption, X-ray diffraction, hydrogen-temperature programmed reduction, carbon dioxide- and ammonia-temperature programmed desorption as well as thermogravimetric analysis. Solid base (MgO, CaO, SiO2, and Na2SiO3) and solid acid (HY, H-beta, HZSM5, and Al2O3) catalysts were individually evaluated for their catalytic activity in a semi-batch reactor in terms of the deoxygenation level of palm oil product. The best acid and alkali catalyst were then selected for mixing at different weight ratios and re-tested for their tandem catalytic performance in terms of the deoxygenation activity. Finally, the reaction temperature (400–460 °C), pressure in a nitrogen or hydrogen gas atmosphere and residence time were optimized. The main components in the liquid product obtained were normal paraffins, iso-paraffins, olefins and aromatics. For the single base catalysts, a liquid yield of higher than 65 wt% was obtained at a 460 °C using MgO catalyst, which also realized an excellent oxygen removal through decarboxylation and decarbonylation. For the single acid catalysts, the zeolite beta catalysts reached a liquid yield of around 55 wt% with high iso-paraffin content. The optimal MgO:beta zeolite weight ratio for the acid–base hybrid catalyst was 3:1, which resulted in a low oxygen content in the products with a high iso-paraffin (35%) content.

Benzene as an important raw material for production of industrial chemicals is generally synthesized from petroleum and coal tar. Here, we realized the synthesis of benzene from greenhouse CO2 and H2 with two connected reactors by a tandem catalysis reaction comprising CO2 methanation and CH4 aromatization. The Ni/SiO2 catalyst loaded in the first reactor was used to convert CO2 to CH4, and the formed CH4 was sequentially converted to benzene on the Mo/HZSM-5 catalyst in the second reactor. The benzene formation rate reaches 0.68 μmol g−1 min−1 accompanied by a high CO2 conversion of 92%. This concept will provide a new pathway for the direct synthesis of benzene and CO2 utilization.

The application of rice-bran catalysts containing “biopromoters”, from rice bran, in the production of synthetic oil was investigated. Trace minerals such as K, Mg, and Mn from rice bran were successfully incorporated into Fe@C microspherical cores and played a cooperative promotional role on the iron species. The yield of the hydrocarbons was strikingly higher than that obtained with the unpromoted catalyst. Further, rice bran is a natural carbon source, not a chemical carbon source, that can be used to fabricate the carbon microsphere support. This concept opens a new avenue for recycling and boosts the value of abundant waste biomass in nature.

Heteroatom doping is a promising approach to improve the properties of carbon materials for customized applications. Herein, a series of Cu catalysts supported on boron-doped carbon nanotubes (Cu/xB-CNTs) were prepared for the hydrogenation of dimethyl oxalate (DMO) to ethanol. The structure and chemical properties of boron-doped catalysts were characterized by XRD, TEM, N2 O pulse adsorption, CO chemisorption, H2 temperature-programmed reduction, and NH3 temperature-programmed desorption, which revealed that doping boron into CNT supports improved the Cu dispersion, strengthened the interaction of Cu species with the CNT support, introduced more surface acid sites, and increased the surface area of Cu0 and especially Cu+ sites. Consequently, the catalytic activity and stability of the catalysts were greatly enhanced by boron doping. 100 % DMO conversion and 78.1 % ethanol selectivity could be achieved over the Cu/1B-CNTs catalyst, the ethanol selectivity of which was almost 1.7 times higher than that of the catalyst without boron doping. These results suggest that doping CNTs with boron is an efficient approach to improve the catalytic performance of CNT-based catalysts for hydrogenation of DMO. The boron-doped CNT-based catalyst with improved ethanol selectivity and catalytic stability will be helpful in the development of efficient Cu catalysts supported on non-silica materials for selective hydrogenation of DMO to ethanol.

In this letter, we report high-performance enhancement-mode (E-mode) Al2O3/AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) fabricated with high-temperature low-damage gate recess technique. The high-temperature gate recess is implemented by increasing the substrate temperature to 180 °C to enhance the desorption of chlorine-based etching residues during the dry etching of AlGaN barrier. High-crystal-quality Al2O3 gate dielectric was grown by atomic-layer deposition using O3 as the oxygen source to suppress hydrogen-induced weak bonds. The fabricated E-mode MIS-HEMTs exhibit a threshold voltage of 1.6 V, a pulsed drive current of 1.13 A/mm, and very low OFF-state standby power of $6.8 \times 10^{\mathrm {-8}}$ W/mm at $V_{\mathrm {GS}} =0$ V and $V_{\mathrm {DS}} =30$ V. At 4 GHz and in pulse-mode operation, the output power density and power-added efficiency were measured to be 5.76 W/mm and 57%, both of which are the highest for GaN-based E-mode MIS-HEMTs reported to date.

Low-pressure chemical vapor deposition (LPCVD) technique is utilized for SiN x passivation of AlGaN/GaN high-electron-mobility transistors (HEMTs). A robust SiN x / AlGaN interface featuring high thermal stability and well-ordered crystalline structure is achieved by a processing strategy of “passivation-prior-to-ohmic” in HEMTs fabrication. Effective suppression of surface-trap-induced current collapse and lateral interface leakage current are demonstrated in the LPCVD-SiN x passivated HEMTs, as compared with conventional plasma-enhanced chemical vapor deposition-SiN x passivated ones. Energy dispersive X-ray spectroscopy mapping analysis of SiN x /AlGaN interfaces suggests the interface traps are likely to stem from amorphous oxide/oxynitride interfacial layer.

PurposeThe purpose of this paper is to report upon high power, internally matched GaN high electron mobility transistors (HEMTs) at Ku band with 1.5 GHz bandwidth, which employ a simple and cost‐effective lossless compensated matching technique.Design/methodology/approachTwo 4 mm gate periphery GaN HEMTs are parallel combined and internally matched with multi‐section reactive impedance transformers at the input and output networks. The output matching network is designed at the upper frequency of the design band for a flat power of the circuit, while the input matching network is designed at the upper frequency for a flat gain.FindingsWith the reactively compensated matching technique, the internally matched GaN HEMTs exhibit a flat saturated output power of 43.2+0.7 dBm and an average power added efficiency of 15 per cent over 12 to 13.5 GHz.Originality/valueThis paper provides useful information for the internally matched GaN HEMTs.

An obvious increase in the gate leakage current has been commonly observed in GaN HEMTs, after Plasma-enhanced chemical vapor deposition (PECVD) SiN passivation has been observed to obviously increase. This paper presents an Al/SiN stack layer passivation structure. The high gate leakage current in GaN HEMTs caused by the PECVD SiN passivation is distinctly reduced by 2 to 3 orders of magnitude by introducing a thin Al layer. It is mainly attributed to the Al layer blocking and minimizing the damage for the (Al)GaN surface in the build-up of the luminance process of PECVD SiN and then reducing the surface trap density. TEM mapping and SRIM software simulation reveal that neither damage nor inter-diffusion is demonstrated at the Al/AlGaN interface, where a continuous crystalline region is observed. The moderate current collapse suppression and 32.8% improvement in VBR are achieved in GaN HEMTs with Al/SiN passivation.

This letter reports a 0.2- μm gate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with an AlN/SiNx (4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. The AlN/SiNx-passivated HEMTs exhibit a high maximum drain current of 930 mA/mm, an three-terminal OFF-state breakdown voltage (BVDS) of 119 V, and a small threshold voltage shift of 130 mV in a wide drain bias range (VDS=3-24 V). Owing to the additional positive polarization charge in the AlN passivation layer, the access resistance Rs in the GaN-on-Si HEMTs is significantly reduced while maintaining small parasitic gate-drain capacitance Cgd, contributing to a high power-gain cutoff frequency fMAX of 182 GHz and a high Johnson's figure of merit of BVDS × f T of 6.43 × 1012 V/s simultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters.

This paper concentrates on the impact of SiN passivation layer deposited by plasma-enhanced chemical vapor deposition (PECVD) on the Schottky characteristics in GaN high electron mobility transistors (HEMTs). Three types of SiN layers with different deposition conditions were deposited on GaN HEMTs. Atomic force microscope (AFM), capacitance–voltage (C–V), and Fourier transform infrared (FTIR) measurement were used to analyze the surface morphology, the electrical characterization, and the chemical bonding of SiN thin films, respectively. The better surface morphology was achieved from the device with lower gate leakage current. The fixed positive charge Q f was extracted from C–V curves of Al/SiN/Si structures and quite different density of trap states (in the order of magnitude of 1011–1012 cm−2) was observed. It was found that the least trap states were in accordance with the lowest gate leakage current. Furthermore, the chemical bonds and the %H in Si–H and N–H were figured from FTIR measurement, demonstrating an increase in the density of Q f with the increasing %H in N–H. It reveals that the effect of SiN passivation can be improved in GaN-based HEMTs by modulating %H in Si–H and N–H, thus achieving a better Schottky characteristics.

A C-band linear power amplifier is successfully developed with a one-chip 2 mm AlGaN/GaN high electron mobility transistors (HEMTs). Two kinds of matching circuits for the linear power amplifier are compared. Besides, stabilization methods for the amplifier are also discussed. At 5.4 GHz, the developed GaN HEMTs linear power amplifier delivers a 37.2 dBm (5.2 W) cw P1 dB output power with 9 dB linear gain and 55.7% maximum power-added efficiency (PAE) with a drain voltage of 25 V. To our best knowledge, the achieved PAE is the state-of-the-art result ever reported for 2 mm gate width single die GaN-based hybrid microwave integrated power amplifier at C-band.

Cytoplasmic male sterility (CMS) is essential for sunflower hybridproduction. CMS-GIG2, a new sunflower CMS type, was furtherconfirmed by crossing with the maintainer and restorer lines for theCMS-PET1, both of which maintain the male sterility of CMS-GIG2.Meiotic division in CMS-GIG2 was observed with 4¢6-diamidino-2-phenylindole dihydrochloride staining, indicating that microsporeformation was disrupted before the meiotic cytokinesis was com-pleted. Light microscopy observation showed that both middle layerand tapetal cells expand radially rather than degrade over time,followed by failure to form tetrads and normal microspores. Thismorphological defect leading to male sterility in CMS-GIG2 differsfrom that observed in the PET1 CMS type. CMS-GIG2 will certainlyprovide additional genetic diversity for sunflower hybrid breedingprogrammes. Key words: Helianthus annuus L. — cytoplasmic male sterility— microsporogenesis — meiotic divisionCytoplasmic male sterility (CMS) is a maternally inheritedtrait that has been described in more than 150 plant species,and is characterized by the inability to produce functionalpollen grains, but both vegetative and female development areunaffected (Kaul 1988). The FAO Technical Consultation ofthe European Cooperative Research Network on Sunflowerreported 72 male-sterile sunflower sources of different origins(Serieys 2005), including (i) mutants spontaneously occurringin nature, such as ANN1, ANN2, ANN3 and ANN4(Serieys 1984); (ii) interspecific cross progeny such as ARG3(Christov 1992), CMG1, CMG2 and CMG3 (Whelan andDedio 1980); (iii) intraspecific crosses progeny such as ANT1(Vranceanu et al. 1986), ANL2 (Heiser 1982) and ANL1(Anashchenko et al. 1974) and (iv) MUT1 and MUT2 frommutagenesis of two maintainer lines for the PET1 cytoplasm(Christov 1993). SunflowerCMS-PET1wasfirstidentifiedintheprogeny of the interspecific cross Helianthus petiolaris ·Helianthus annuus (Leclercq 1969), which is the only sourceextensively used in oilseed hybrid production. In addition toidentifying new sources of CMS and corresponding fertilityrestorers to broaden the genetic diversity of hybrid seedproduction, more research work has been focused on theabortionmechanismaswellasthechimericgenesrelatedtoCMS.The observation of microsporogenesis development inCMS-PET1, with the cytoplasm of H. petiolaris and nucleusof H. annuus, indicates that the anther abortion is due totapetum degeneration and disintegration after meiosis II(Horner 1977, Laveau et al. 1989). In some crops, such asPennisetum glaucum L., Triticum aestivum L., Brassica napus L.and Zea mays L., different CMS cytoplasm genotypes with thesame nuclear genotype display various abortion stages,abortion process of microspore development or abnormaltapetum (Li and Sun 1996, Chhabra et al. 1997, Zhou et al.1997, Long et al. 2005). Therefore, the observation ofmicrospore development in different sunflower CMS typeswill extend our knowledge of the important cytoplasmic effectsoccurring during pollen production.The objectives of this study were to compare the antherdevelopment of CMS-GIG2 with HA 89, a public oilseedsunflower inbred maintainer line to confirm the abortion stageof the new CMS, meanwhile, we can primarily identify a newCMS type different from PETl (H. petiolaris cytoplasm andH. annuus nucleus) based on its different reflects in themicrospore abortion as well as cross with some identified linesfor PET1.

This paper presents an X-band high gain and high power three-stage PHEMT monolithic microwave integrated circuit (MMIC) power amplifier (PA). Based on 0.15-μm GaAs power PHEMT technology, this PA is fabricated on a 2-mil thick wafer. While operating under 7.2 V and 3300 mA dc bias condition, the characteristics of 29.2-dB small signal gain, 11.7-W output power, and 42.2% power added efficiency at 9.2 GHz can be achieved.

Temperature-dependent ON-state breakdown (BV ON ) loci of AlGaN/GaN high-electron-mobility transistors (HEMTs) were experimentally demonstrated for the first time. With gate-current extraction technique, impact ionization was revealed to be responsible for the ON-state breakdown in our device as the HEMTs is marginally turned on. The characteristic electric-field E i of impact ionization was extracted exhibiting an U-shaped temperature dependence from 40 to -30 o C, with minimum E i occurs at -10 o C. Such anomalous temperature dependence of E i together with the kink effect observed in our devices stem from coulomb scattering effect of the acceptor-like traps in AlGaN/GaN heterostructures.

We have performed constant voltage stress (CVS) tests on GaN-on-SiC HEMT to investigate the drain current drift. Two kinds of current drift behavior are observed in CVS. The off-state drain voltage step stress tests are carried out to confirm the electric field dependent current drift. A critical voltage for drain current recovery is observed. We suggest that the recovery of drain current is due to holes generation near the heterojunction interface or the detrapping of acceptors in the barrier layer. The drain current drift is balanced by the current degradation and recovery mechanism.

We use near-field scanning optical microscopy (NSOM) operating in collection mode to map the optical field distribution of continuous wave infrared light propagating along an air-bridged W3 silicon photonic crystal (PC) slab multimode waveguide in a subwavelength resolution. The detected near-field optical intensity distribution patterns show very different longitudinal propagation features and transverse field profiles at different wavelength ranges. We have analyzed the dispersion of the guided modes in the PC waveguide and the corresponding eigenfield profile for each guided mode by means of the three-dimensional plane-wave expansion simulations. It is found that the experimentally observed complex while interesting near-field pattern features can be well explained by the field profiles of the multiple waveguide modes and their superposition at different excitation wavelengths. The detection and analysis of this multimode PC slab waveguide via NSOM could help us to understand complex wave propagation behavior and to further design novel PC devices.

A high quality superconducting Li0.68NbO2 polycrystalline sample was prepared by deintercalation of Li ions from Li0.93NbO2. The field-dependent resistivity and specific heat were measured down to 0.5 K. The temperature dependence of the upper critical field is determined. A notable specific-heat jump is observed at the superconducting transition temperature T-c similar to 5.0 K at zero field. Below T-c, the electronic specific heat shows a thermal activated behavior and agrees well with the theoretical result for the BCS s-wave superconductor. It indicates that the superconducting pairing in Li0.68NbO2 has s-wave symmetry.

The out-of-plane resistivity (rho(c)) and magnetoresistivity (MR) are studied in antiferromangetic (AF) Nd2-xCexCuO4 single crystals, which have three types of noncollinear antiferromangetic spin structures. The apparent signatures are observed in rho(c)(T) measured at the zero-field and 14 T at the spin structure transitions, giving a definite evidence for the itinerant electrons directly coupled to the localized spins. One of the striking features is an anisotropy of the MR with a fourfold symmetry upon rotating the external field (B) within ab plane in the different phases, while twofold symmetry at spin reorientation transition temperatures. The intriguing thermal hysteresis in rho(c)(T,B) and magnetic hysteresis in MR are observed at spin reorientation transition temperatures.

In-plane (rho(ab)) and c-axis (rho(c)) resistivities and magnetoresistivity of NaxCoO2 with x=0.7, 0.5, and 0.3 and superconducting Na(0.3)CoO(2)center dot 1.3H(2)O single crystals were studied. A dimensional crossover from 2 to 3 occurs with decreasing Na concentration from 0.7 to 0.3. A striking feature is that intercalation of water leads to a reentrance of two dimensions (2D) in superconducting crystal. It suggests that the 2D plays an important role in superconductivity as the case of cuprates. The anisotropic magnetoresistivity with a d-wave-like symmetry at 2 K gives evidence for the existence of a special spin ordering like the stripes below 20 K in Na0.5CoO2.

We report the magnetization, specific heat, and transport measurements of a high quality Na0.85CoO2 single crystal in applied magnetic fields up to 14 T. At high temperatures, the system is in a paramagnetic phase. It undergoes a magnetic phase transition below similar to20 K. For the field H parallel to c, the measurement data of magnetization, specific heat, and magnetoresistance reveal a metamagnetic transition from an antiferromagnetic state to a quasiferromagnetic state at about 8 T at low temperatures. However, no transition is observed in the magnetization measurements up to 14 T for H perpendicular to c. The low temperature magnetic phase diagram of Na0.85CoO2 is determined.

High quality Al2O3 film grown by atomic layer deposition (ALD), with ozone (O3) as oxygen source, is demonstrated for fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Significant suppression of Al–O–H and Al–Al bonds in ALD-Al2O3 has been realized by substituting conventional H2O source with O3. A high dielectric breakdown E-field of 8.5 MV/cm and good TDDB behavior are achieved in a gate dielectric stack consisting of 13-nm O3-Al2O3 and 2-nm H2O-Al2O3 interfacial layer on recessed GaN. By using this 15-nm gate dielectric and a high-temperature gate-recess technique, the density of positive bulk/interface charges in normally-off AlGaN/GaN MIS-HEMTs is remarkably suppressed to as low as 0.9 × 1012 cm−2, contributing to the realization of normally-off operation with a high threshold voltage of +1.6 V and a low specific ON-resistance RON,sp of 0.49 mΩ cm2.

The effects of interface oxidation on the transport behavior of the 2-D electron gas (2DEG) in AlGaN/GaN heterostructures by plasma-enhanced-atomic-layer-deposited AlN (PEALD-AlN) passivation were investigated using temperature-dependent Hall-effect and X-ray photoelectron spectroscopy (XPS) characterizations. AlGaN/GaN heterostructure with a 4-nm-thick PEALD-AlN passivation exhibits good 2DEG transport behavior and stability at moderately high temperature (e.g., 275 °C). However, serious oxidation of the AlN/GaN (cap layer) interface occurs as the sample is heated up to 400 °C in low-pressure atmosphere, as verified by an increased Ga-O bond in Ga 3d core-level spectra. The oxidation leads to a significant reduction of 2.47 × 1012 cm−2 in the 2DEG density in the channel. A modified AlN passivation structure with Al2O3/AlN (10/4 nm) stack is shown to be able to effectively suppress the oxidation of the AlN/GaN interface, demonstrating an enhanced 2DEG density and high-temperature stability even when the sample is heated up to 500 °C. Based on XPS and 2DEG recovery experiments, it is suggested that acceptor-like deep levels have been generated in the near-surface region of AlGaN/GaN heterostructure because of the oxidation, and trapping of these deep levels results in significant depletion of the 2DEG in the channel. The effects of PEALD-AlN passivation on the strain in the AlGaN barrier of AlGaN/GaN heterostructures are also evaluated with high-resolution X-ray diffraction technique.