High-k materials as an alternative dielectric layer for SiC power devices have the potential to reduce interfacial state defects and improve MOS channel conduction capability.Besides,under identical conditions of gate...High-k materials as an alternative dielectric layer for SiC power devices have the potential to reduce interfacial state defects and improve MOS channel conduction capability.Besides,under identical conditions of gate oxide thickness and gate voltage,the high-k dielectric enables a greater charge accumulation in the channel region,resulting in a larger number of free electrons available for conduction.However,the lower energy band gap of high-k materials leads to significant leakage currents at the interface with Si C,which greatly affects device reliability.By inserting a layer of SiO_(2)between the high-k material and Si C,the interfacial barrier can be effectively widened and hence the leakage current will be reduced.In this study,the optimal thickness of the intercalated SiO_(2)was determined by investigating and analyzing the gate dielectric breakdown voltage and interfacial defects of a dielectric stack composed of atomic-layer-deposited Al_(2)O_(3)layer and thermally nitride SiO_(2).Current-voltage and high-frequency capacitance-voltage measurements were performed on metal-oxide-semiconductor test structures with 35 nm thick Al_(2)O_(3)stacked on 1 nm,2 nm,3 nm,6 nm,or 9 nm thick nitride SiO_(2).Measurement results indicated that the current conducted through the oxides was affected by the thickness of the nitride oxide and the applied electric field.Finally,a saturation thickness of stacked SiO_(2)that contributed to dielectric breakdown and interfacial band offsets was identified.The findings in this paper provide a guideline for the SiC gate dielectric stack design with the breakdown strength and the interfacial state defects considered.展开更多
A thermochemical model based on the ion and molecule coexistence theory(IMCT)was developed to calculate thermodynamic data in the CaO-SiO_(2)-Al_(2)O_(3) slag system,considering the influential role of oxide activitie...A thermochemical model based on the ion and molecule coexistence theory(IMCT)was developed to calculate thermodynamic data in the CaO-SiO_(2)-Al_(2)O_(3) slag system,considering the influential role of oxide activities on the thermodynamic properties of slags.Using this model,iso-activity contours were obtained for oxide components CaO,SiO_(2) and Al2O3 in this system at temperatures of 1,873 K and 1,773 K.When compared with the IMCT model,it is found that the predicted activities of oxide components in the CaO-SiO_(2)-Al_(2)O_(3) system using the model developed in this study better matches experimental data from literature in terms of both trend and numerical value.Therefore,the model developed in this study can serve as a robust modeling tool for metallurgical processes,and the thermodynamic data predicted by this new model can be used to improve the metallurgical technology.展开更多
Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde...Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde,followed by its condensation with methanol.This study presents a one-pot method of DMM synthesis from methanol mediated carbon dioxide hydrogenation over novel heterogeneous catalysts.The effect of catalyst pore structure was investigated by synthesizing 3 wt%Ru over novel hierarchical zeolite beta(HBEASX)and comparing against Ru doped commercial zeolite beta(CBEA)and desilicated hierarchical zeolite beta(HBZDS).The results showed that 3%Ru/HBEASX provided the best activity for DMM production due to its large average pore size.It also showed the decisive role of SiO_(2)/Al_(2)O_(3)molar ratio,with SiO_(2)/Al_(2)O_(3)=75 providing the highest DMM yield of 13.2 mmol/gcat.LMeOH with ca.100%selectivity.The activity of 3%Ru/HBEAS3 after 5 recycle steps demonstrated the reusability of this catalyst.展开更多
A series of SAPO-34 molecular sieves with different SiO_(2)/Al_(2)O_(3)ratios have been synthesized for the methanol-to-olefin(MTO)reaction.Their physico-chemical properties are characterized by various techniques suc...A series of SAPO-34 molecular sieves with different SiO_(2)/Al_(2)O_(3)ratios have been synthesized for the methanol-to-olefin(MTO)reaction.Their physico-chemical properties are characterized by various techniques such as X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),Fourier transform infrared spectroscopy(FT-IR)and N2 adsorption-desorption.The results are compared with those of the commercial HZSM-5,which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO_(2)/Al_(2)O_(3)ratio.The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO_(2)/Al_(2)O_(3)ratio of 0.4 exhibits the highest BET surface area.FT-IR spectra indicate that HZSM-5 has both Brǿnsted and Lewis acid sites and Brǿnsted acid sites are stronger,whereas SAPO-34 samples are dominated only by Lewis acid sites.When the SiO_(2)/Al_(2)O_(3)ratio increases,propylene and butylenes become the predominant product of the MTO reaction over HZSM-5.In contrast,the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene.According to the product distribution,the reaction mechanism over HZSM-5 catalysts is proposed.展开更多
基金Project supported by the Key Area Research and Development Program of Guangdong Province of China(Grant No.2021B0101300005)the National Key Research and Development Program of China(Grant No.2021YFB3401603)。
文摘High-k materials as an alternative dielectric layer for SiC power devices have the potential to reduce interfacial state defects and improve MOS channel conduction capability.Besides,under identical conditions of gate oxide thickness and gate voltage,the high-k dielectric enables a greater charge accumulation in the channel region,resulting in a larger number of free electrons available for conduction.However,the lower energy band gap of high-k materials leads to significant leakage currents at the interface with Si C,which greatly affects device reliability.By inserting a layer of SiO_(2)between the high-k material and Si C,the interfacial barrier can be effectively widened and hence the leakage current will be reduced.In this study,the optimal thickness of the intercalated SiO_(2)was determined by investigating and analyzing the gate dielectric breakdown voltage and interfacial defects of a dielectric stack composed of atomic-layer-deposited Al_(2)O_(3)layer and thermally nitride SiO_(2).Current-voltage and high-frequency capacitance-voltage measurements were performed on metal-oxide-semiconductor test structures with 35 nm thick Al_(2)O_(3)stacked on 1 nm,2 nm,3 nm,6 nm,or 9 nm thick nitride SiO_(2).Measurement results indicated that the current conducted through the oxides was affected by the thickness of the nitride oxide and the applied electric field.Finally,a saturation thickness of stacked SiO_(2)that contributed to dielectric breakdown and interfacial band offsets was identified.The findings in this paper provide a guideline for the SiC gate dielectric stack design with the breakdown strength and the interfacial state defects considered.
基金This work was financially supported by the National Natural Science Foundation of China(NSFC 52175352).
文摘A thermochemical model based on the ion and molecule coexistence theory(IMCT)was developed to calculate thermodynamic data in the CaO-SiO_(2)-Al_(2)O_(3) slag system,considering the influential role of oxide activities on the thermodynamic properties of slags.Using this model,iso-activity contours were obtained for oxide components CaO,SiO_(2) and Al2O3 in this system at temperatures of 1,873 K and 1,773 K.When compared with the IMCT model,it is found that the predicted activities of oxide components in the CaO-SiO_(2)-Al_(2)O_(3) system using the model developed in this study better matches experimental data from literature in terms of both trend and numerical value.Therefore,the model developed in this study can serve as a robust modeling tool for metallurgical processes,and the thermodynamic data predicted by this new model can be used to improve the metallurgical technology.
基金Australian Research Council(Grant No.DP170104017)for the financial support of this projectAT and AS received financial support from the Institute for Catalysis,Hokkaido University as part of their Strategic Research Fellowship grant schemesupported by the Cooperative Research Program of Institute for Catalysis,Hokkaido University(Proposal No.19A1005)。
文摘Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde,followed by its condensation with methanol.This study presents a one-pot method of DMM synthesis from methanol mediated carbon dioxide hydrogenation over novel heterogeneous catalysts.The effect of catalyst pore structure was investigated by synthesizing 3 wt%Ru over novel hierarchical zeolite beta(HBEASX)and comparing against Ru doped commercial zeolite beta(CBEA)and desilicated hierarchical zeolite beta(HBZDS).The results showed that 3%Ru/HBEASX provided the best activity for DMM production due to its large average pore size.It also showed the decisive role of SiO_(2)/Al_(2)O_(3)molar ratio,with SiO_(2)/Al_(2)O_(3)=75 providing the highest DMM yield of 13.2 mmol/gcat.LMeOH with ca.100%selectivity.The activity of 3%Ru/HBEAS3 after 5 recycle steps demonstrated the reusability of this catalyst.
基金This research was supported financially by the National High Technology Research and Development Program of China(863 Program)(Grant Nos.2006AA06Z371 and 2008AA06Z324)the Innovation Project of Institute of Process Engineering,Chinese Academy of Sciences(No.082702).
文摘A series of SAPO-34 molecular sieves with different SiO_(2)/Al_(2)O_(3)ratios have been synthesized for the methanol-to-olefin(MTO)reaction.Their physico-chemical properties are characterized by various techniques such as X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),Fourier transform infrared spectroscopy(FT-IR)and N2 adsorption-desorption.The results are compared with those of the commercial HZSM-5,which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO_(2)/Al_(2)O_(3)ratio.The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO_(2)/Al_(2)O_(3)ratio of 0.4 exhibits the highest BET surface area.FT-IR spectra indicate that HZSM-5 has both Brǿnsted and Lewis acid sites and Brǿnsted acid sites are stronger,whereas SAPO-34 samples are dominated only by Lewis acid sites.When the SiO_(2)/Al_(2)O_(3)ratio increases,propylene and butylenes become the predominant product of the MTO reaction over HZSM-5.In contrast,the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene.According to the product distribution,the reaction mechanism over HZSM-5 catalysts is proposed.
