Catalyst-free graphene films has been synthesized by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) using hydrogenated carbon source on silicon substrates at low temperature (500℃). The synt...Catalyst-free graphene films has been synthesized by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) using hydrogenated carbon source on silicon substrates at low temperature (500℃). The synthesized process is simple, low-cost and possible for application on transparent electrodes, gas sensors and thin film resistors. Analytical methods such as Raman spectroscopy, transmission electron microscopy (TEM) and four points prove resistivity measurement and UV-VIS-NIR spectroscopy were employed to characterize properties of the graphene films. The formation of multilayer of graphene on silicon substrate was confirmed by Raman spectroscopy and TEM. It is possible to grow graphene directly on silicon substrate (without using catalyst) due to high radical density of MW SWP CVD. In addition, we also observed that the hydrogen had significant role for quality of graphene.展开更多
A method has been devised to analyze multilayer electrically thick circular mi-crostrip antenna excited by a probe.The current on the probe is taken to be uniform.Thismethod was verified by analysis and experiment of ...A method has been devised to analyze multilayer electrically thick circular mi-crostrip antenna excited by a probe.The current on the probe is taken to be uniform.Thismethod was verified by analysis and experiment of an electrically thick circular microstrip an-tenna with an air gap.Based on the free space electric dyadic Green’s function,the field expressionof an horizontal electric dipole(HED),which is located at any point of the multilayer media andpoints in any direction,has been derived.By using this field expression and the Richmond re-action equation,an integral equation in terms of electric current on the patch is formulated.Byproperly choosing current expansion modes,this method can be used for an electrically thick mi-crostrip antenna.The theoretical results agree very well with experimental data for an electricallythick circular microstrip antenna with an air gap.展开更多
The diamond film on single crystal silicon substrate in threekinds of substrate is deposited by pre- treatment method usingmicrowave plasma, the diamond film is analyzed using SEM and Raman,the reasons why substrate p...The diamond film on single crystal silicon substrate in threekinds of substrate is deposited by pre- treatment method usingmicrowave plasma, the diamond film is analyzed using SEM and Raman,the reasons why substrate pretreatment affects nucleation and growthare probed. The results show that substrate pretreatment di- rectlyaffects nucleation and growth of diamond film, ho- mogeneousnucleation and growth can be formed only in suitable pretreatmentmethod.展开更多
为了探究国产低温共烧陶瓷(Low Temperature Co-fired Ceramic,LTCC)材料的工程应用前景,促进LTCC材料国产化进程,文中从工程应用的角度出发,使用国产LTCC材料制作了微波基板并进行了相应的测试和研究。研究内容主要包括国产LTCC材料的...为了探究国产低温共烧陶瓷(Low Temperature Co-fired Ceramic,LTCC)材料的工程应用前景,促进LTCC材料国产化进程,文中从工程应用的角度出发,使用国产LTCC材料制作了微波基板并进行了相应的测试和研究。研究内容主要包括国产LTCC材料的匹配性能以及基于国产LTCC材料的微波基板的性能和可靠性。研究结果表明,国产LTCC材料的匹配性能满足要求,基于国产LTCC材料研制的微波基板的性能和可靠性与基于进口LTCC材料研制的微波基板相当,满足X波段T/R组件技术要求。展开更多
Glass-free MgO-based microwave dielectric ceramics(1-x)wt%(0.98 MgO-0.02 Al2O3)-x wt%LiF(x=0.5,1,2,3,4)were synthesized where LiF and Al2O3 were utilized as sintering additive and reinforcement phase in MgO matrix res...Glass-free MgO-based microwave dielectric ceramics(1-x)wt%(0.98 MgO-0.02 Al2O3)-x wt%LiF(x=0.5,1,2,3,4)were synthesized where LiF and Al2O3 were utilized as sintering additive and reinforcement phase in MgO matrix respectively.It was found that ion substitution is apt to occur between LiF and MgO,leading to the formation of oxygen vacancies and MgF2.Nevertheless,different from ordinary liquidphase sintering,morphologies of ceramics were distinctly altered with grains changing from polyhedron to sphere-like shape and densities underwent obvious decrease when excessive amount of LiF was introduced and we call it excessive liquid-phase sintering.Grain boundary weakening caused by this circumstance would exert an adverse effect on physical properties.Moreover,LiF addition dramatically reduced dielectric breakdown strength and altered the dielectric breakdown behavior of MgO-based ceramics,which is dominated by electrical breakdown mechanism.Combination of good properties were achieved in 1 wt%LiF modified MgO-based ceramics sintered at 950℃ which exhibited superior microwave properties(εr=9.56,tanδ=9.2×10^(-5),Qf=124,600 GHz),high flexural strength(184.5 MPa),high thermal conductivity(21.3 W/(m,K)),high coefficient of thermal expansion(-12 ppm/℃)and moderate electrical properties(Eb=35.9 kV/mm,r=4.9×10^(12) U cm).展开更多
文摘Catalyst-free graphene films has been synthesized by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) using hydrogenated carbon source on silicon substrates at low temperature (500℃). The synthesized process is simple, low-cost and possible for application on transparent electrodes, gas sensors and thin film resistors. Analytical methods such as Raman spectroscopy, transmission electron microscopy (TEM) and four points prove resistivity measurement and UV-VIS-NIR spectroscopy were employed to characterize properties of the graphene films. The formation of multilayer of graphene on silicon substrate was confirmed by Raman spectroscopy and TEM. It is possible to grow graphene directly on silicon substrate (without using catalyst) due to high radical density of MW SWP CVD. In addition, we also observed that the hydrogen had significant role for quality of graphene.
文摘A method has been devised to analyze multilayer electrically thick circular mi-crostrip antenna excited by a probe.The current on the probe is taken to be uniform.Thismethod was verified by analysis and experiment of an electrically thick circular microstrip an-tenna with an air gap.Based on the free space electric dyadic Green’s function,the field expressionof an horizontal electric dipole(HED),which is located at any point of the multilayer media andpoints in any direction,has been derived.By using this field expression and the Richmond re-action equation,an integral equation in terms of electric current on the patch is formulated.Byproperly choosing current expansion modes,this method can be used for an electrically thick mi-crostrip antenna.The theoretical results agree very well with experimental data for an electricallythick circular microstrip antenna with an air gap.
基金The research was supported by the Major Research Plan of Wuhan City(961001005-1)the Open Fund of State Key Laboratory for SimulationDie Technology in Huazhong Univ.of Sci.&Tech.(99-7)
文摘The diamond film on single crystal silicon substrate in threekinds of substrate is deposited by pre- treatment method usingmicrowave plasma, the diamond film is analyzed using SEM and Raman,the reasons why substrate pretreatment affects nucleation and growthare probed. The results show that substrate pretreatment di- rectlyaffects nucleation and growth of diamond film, ho- mogeneousnucleation and growth can be formed only in suitable pretreatmentmethod.
文摘为了探究国产低温共烧陶瓷(Low Temperature Co-fired Ceramic,LTCC)材料的工程应用前景,促进LTCC材料国产化进程,文中从工程应用的角度出发,使用国产LTCC材料制作了微波基板并进行了相应的测试和研究。研究内容主要包括国产LTCC材料的匹配性能以及基于国产LTCC材料的微波基板的性能和可靠性。研究结果表明,国产LTCC材料的匹配性能满足要求,基于国产LTCC材料研制的微波基板的性能和可靠性与基于进口LTCC材料研制的微波基板相当,满足X波段T/R组件技术要求。
基金supported by National Natural Science Foundation of China(Grant No.11774366)International Partnership Program of Chinese Academy of Sciences(Grant No.GJHZ1821)。
文摘Glass-free MgO-based microwave dielectric ceramics(1-x)wt%(0.98 MgO-0.02 Al2O3)-x wt%LiF(x=0.5,1,2,3,4)were synthesized where LiF and Al2O3 were utilized as sintering additive and reinforcement phase in MgO matrix respectively.It was found that ion substitution is apt to occur between LiF and MgO,leading to the formation of oxygen vacancies and MgF2.Nevertheless,different from ordinary liquidphase sintering,morphologies of ceramics were distinctly altered with grains changing from polyhedron to sphere-like shape and densities underwent obvious decrease when excessive amount of LiF was introduced and we call it excessive liquid-phase sintering.Grain boundary weakening caused by this circumstance would exert an adverse effect on physical properties.Moreover,LiF addition dramatically reduced dielectric breakdown strength and altered the dielectric breakdown behavior of MgO-based ceramics,which is dominated by electrical breakdown mechanism.Combination of good properties were achieved in 1 wt%LiF modified MgO-based ceramics sintered at 950℃ which exhibited superior microwave properties(εr=9.56,tanδ=9.2×10^(-5),Qf=124,600 GHz),high flexural strength(184.5 MPa),high thermal conductivity(21.3 W/(m,K)),high coefficient of thermal expansion(-12 ppm/℃)and moderate electrical properties(Eb=35.9 kV/mm,r=4.9×10^(12) U cm).
