Carbon nanotubes filled with ferromagnetic metal nanowires (M-CNTs) were synthesized by using chlorine-contained benzene (e.g.trichlorobenzene) as precursor.The wall thicknesses of M-CNTs synthesized by trichlorobenze...Carbon nanotubes filled with ferromagnetic metal nanowires (M-CNTs) were synthesized by using chlorine-contained benzene (e.g.trichlorobenzene) as precursor.The wall thicknesses of M-CNTs synthesized by trichlorobenzene are much thinner than those by precursor without Cl (e.g.benzene).As-synthesized thin-walled M-CNTs exhibit remarkably enhanced field electron emission performance with a low turn-on field of 0.3 V/μm and better field-emission stability.Microwave-absorption coatings were made by dispersing as-synthesized M-CNTs into epoxy resin matrix.It is found that the reflection losses in S-band (2-4 GHz),C-band (4-8 GHz) and X-band (8-12 GHz) are enhanced in the order of FeCoNi-CNTs 【 FeNi-CNTs【 FeCo-CNTs.The areal density of as-prepared coatings is only 2.35 kg/m2 when the coating thickness is 2.0 mm.This demonstrates that M-CNTs are promising to be used as lightweight and wide-band microwave absorbers.展开更多
This paper reports that the nano-sheet carbon films （NSCFs） were fabricated on Si wafer chips with hydrogen- methane gas mixture by means of quartz-tube-type microwave plasma chemical vapour deposition （MWPCVD）. I...This paper reports that the nano-sheet carbon films （NSCFs） were fabricated on Si wafer chips with hydrogen- methane gas mixture by means of quartz-tube-type microwave plasma chemical vapour deposition （MWPCVD）. In order to further improve the field emission （FE） characteristics, a 5-nm Au film was prepared on the samples by using electron beam evaporation. The FE properties were obviously improved due to depositing Au thin film on NSCFs. The FE current density at a macroscopic electric field, E, of 9 V/μm was increased from 12.4 mA/cm2 to 27.2 mA/cm2 and the threshold field was decreased from 2.6 V/μm to 2.0 V/μm for Au-coated carbon films. A modified F-N model considering statistic effects of FE tip structures in the low E region and a space-chavge-limited-current effect in the high E region were applied successfully to explain the FE data of the Au-coated NSCF.展开更多
This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface ...This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/μm corresponding to a current density of about 1μA/cm^2 and a current density of 3.2mA/cm^2 at an electric field of 10V/μm were obtained from the carbon film deposited at CH4 concentration of 8%. The mechanism that the threshold field decreased with the increase of the CH4 concentration and the high emission current appeared at the high CH4 concentration was explained by using the Fowler-Nordheim theory.展开更多
采用微波等离子体化学气相沉积(MPCVD)方法,通过改变CH_4浓度,在单晶Si(100)基底上制备掺氮纳米金刚石(NCD)薄膜,并以所制备的掺氮NCD薄膜为阴极材料,通过场发射扫描电子显微镜(FESEM)、原子力扫描探针显微镜(AFM)、Raman光谱和S波段射...采用微波等离子体化学气相沉积(MPCVD)方法,通过改变CH_4浓度,在单晶Si(100)基底上制备掺氮纳米金刚石(NCD)薄膜,并以所制备的掺氮NCD薄膜为阴极材料,通过场发射扫描电子显微镜(FESEM)、原子力扫描探针显微镜(AFM)、Raman光谱和S波段射频电子枪等测试方法系统地研究了掺氮NCD薄膜的微观结构对微波场发射性能的影响。结果表明:在CH_4浓度(体积比)为4%下,制备的掺氮NCD薄膜的颗粒呈多面体,而且颗粒尺寸和表面粗糙度较大,薄膜中金刚石相含量较高,这些微观结构使得微波场发射性能较高,在电场强度(E_0)为67.7 V·μm^(-1)时,发射电流密度(J0)高达144.8 m A·cm^(-2)。当升高CH_4浓度,所制备的掺氮NCD薄膜的颗粒尺寸减小而且连成条状结构,表面粗糙度也逐渐降低,薄膜中金刚石相减少、非金刚石相增加,这些微观结构的改变使得微波场发射性能逐渐降低。如当CH_4浓度增加至6%时,在电场强度E_0=67.7 V·μm^(-1)时,场发射电流密度降至37.9 m A·cm^(-2)。结果表明:低CH_4浓度下,掺氮NCD薄膜所具有的微观结构有利于微波场发射。展开更多
Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition （MPCVD） in a gas mixture of hydrogen and methane. The structure of the fabricated films is invest...Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition （MPCVD） in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope （FESEM） and Raman spectroscopy. These nano^carbon films are possessed of good field emission （FE） characteristics with a low threshold field of 2.6 V/μm and a high current density of 12.6 mA/cm^2 at an electric field of 9 V/μm. As the FE currents tend to be saturated in a high E region, no simple Fowler-Nordheim （F-N） model is applicable. A modified F N model considering statistic effects of FE tip structures and a space-charge-limited-current （SCLC） effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively.展开更多
The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state(DOS) in the anisotropic photonic band gap(PBG) and the cohe...The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state(DOS) in the anisotropic photonic band gap(PBG) and the coherent control induced by the coupling fields, spontaneous emission can be significantly enhanced when the position of the spontaneous emission peak gets close to the band gap edge. As a result of the closed-loop interaction between the fields and the atom,the spontaneous emission depends on the dynamically induced Autler–Townes splitting and its position relative to the PBG.Interesting phenomena, such as spectral-line suppression, enhancement and narrowing, and fluorescence quenching, appear in the spontaneous emission spectra, which are modulated by amplitudes and phases of the coherently driven fields and the effect of PBG. This theoretical study can provide us with more efficient methods to manipulate the atomic spontaneous emission.展开更多
A simple process to fabricate chain-like carbon nanotube （CNT） films by microwave plasma-enhanced chemical vapor deposition （MPCVD） was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were gro...A simple process to fabricate chain-like carbon nanotube （CNT） films by microwave plasma-enhanced chemical vapor deposition （MPCVD） was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.展开更多
In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition（CVD） over a wide range of experimental parameters. The effects of the microwave power,CH;/H;...In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition（CVD） over a wide range of experimental parameters. The effects of the microwave power,CH;/H;ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope（SEM）, X-ray diffraction（XRD）, Raman spectroscopy and X-ray photoelectron spectroscopy（XPS）. A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH;/H;levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However,diamond film is deteriorated at high CH;/H;ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10 kW and high CH;concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N;or Ar,which is different from other reports. This composite structure has an excellent measured sheet resistance of 10-100 Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission（EFE） properties with a low turn-on field of 2.17 V/μm and β= 3160, therefore it could be a promising alternative in field emission applications.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.50632040,50902080)China Postdoctoral Science Foundation (Grant No.20090450021)
文摘Carbon nanotubes filled with ferromagnetic metal nanowires (M-CNTs) were synthesized by using chlorine-contained benzene (e.g.trichlorobenzene) as precursor.The wall thicknesses of M-CNTs synthesized by trichlorobenzene are much thinner than those by precursor without Cl (e.g.benzene).As-synthesized thin-walled M-CNTs exhibit remarkably enhanced field electron emission performance with a low turn-on field of 0.3 V/μm and better field-emission stability.Microwave-absorption coatings were made by dispersing as-synthesized M-CNTs into epoxy resin matrix.It is found that the reflection losses in S-band (2-4 GHz),C-band (4-8 GHz) and X-band (8-12 GHz) are enhanced in the order of FeCoNi-CNTs 【 FeNi-CNTs【 FeCo-CNTs.The areal density of as-prepared coatings is only 2.35 kg/m2 when the coating thickness is 2.0 mm.This demonstrates that M-CNTs are promising to be used as lightweight and wide-band microwave absorbers.
文摘This paper reports that the nano-sheet carbon films （NSCFs） were fabricated on Si wafer chips with hydrogen- methane gas mixture by means of quartz-tube-type microwave plasma chemical vapour deposition （MWPCVD）. In order to further improve the field emission （FE） characteristics, a 5-nm Au film was prepared on the samples by using electron beam evaporation. The FE properties were obviously improved due to depositing Au thin film on NSCFs. The FE current density at a macroscopic electric field, E, of 9 V/μm was increased from 12.4 mA/cm2 to 27.2 mA/cm2 and the threshold field was decreased from 2.6 V/μm to 2.0 V/μm for Au-coated carbon films. A modified F-N model considering statistic effects of FE tip structures in the low E region and a space-chavge-limited-current effect in the high E region were applied successfully to explain the FE data of the Au-coated NSCF.
文摘This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/μm corresponding to a current density of about 1μA/cm^2 and a current density of 3.2mA/cm^2 at an electric field of 10V/μm were obtained from the carbon film deposited at CH4 concentration of 8%. The mechanism that the threshold field decreased with the increase of the CH4 concentration and the high emission current appeared at the high CH4 concentration was explained by using the Fowler-Nordheim theory.
文摘采用微波等离子体化学气相沉积(MPCVD)方法,通过改变CH_4浓度,在单晶Si(100)基底上制备掺氮纳米金刚石(NCD)薄膜,并以所制备的掺氮NCD薄膜为阴极材料,通过场发射扫描电子显微镜(FESEM)、原子力扫描探针显微镜(AFM)、Raman光谱和S波段射频电子枪等测试方法系统地研究了掺氮NCD薄膜的微观结构对微波场发射性能的影响。结果表明:在CH_4浓度(体积比)为4%下,制备的掺氮NCD薄膜的颗粒呈多面体,而且颗粒尺寸和表面粗糙度较大,薄膜中金刚石相含量较高,这些微观结构使得微波场发射性能较高,在电场强度(E_0)为67.7 V·μm^(-1)时,发射电流密度(J0)高达144.8 m A·cm^(-2)。当升高CH_4浓度,所制备的掺氮NCD薄膜的颗粒尺寸减小而且连成条状结构,表面粗糙度也逐渐降低,薄膜中金刚石相减少、非金刚石相增加,这些微观结构的改变使得微波场发射性能逐渐降低。如当CH_4浓度增加至6%时,在电场强度E_0=67.7 V·μm^(-1)时,场发射电流密度降至37.9 m A·cm^(-2)。结果表明:低CH_4浓度下,掺氮NCD薄膜所具有的微观结构有利于微波场发射。
文摘Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition （MPCVD） in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope （FESEM） and Raman spectroscopy. These nano^carbon films are possessed of good field emission （FE） characteristics with a low threshold field of 2.6 V/μm and a high current density of 12.6 mA/cm^2 at an electric field of 9 V/μm. As the FE currents tend to be saturated in a high E region, no simple Fowler-Nordheim （F-N） model is applicable. A modified F N model considering statistic effects of FE tip structures and a space-charge-limited-current （SCLC） effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively.
基金supported by the National Natural Science Foundation of China(Grant Nos.11447232,11204367,11447157,and 11305020)
文摘The spontaneous emission from a microwave-driven four-level atom embedded in an anisotropic photonic crystal is studied. Due to the modified density of state(DOS) in the anisotropic photonic band gap(PBG) and the coherent control induced by the coupling fields, spontaneous emission can be significantly enhanced when the position of the spontaneous emission peak gets close to the band gap edge. As a result of the closed-loop interaction between the fields and the atom,the spontaneous emission depends on the dynamically induced Autler–Townes splitting and its position relative to the PBG.Interesting phenomena, such as spectral-line suppression, enhancement and narrowing, and fluorescence quenching, appear in the spontaneous emission spectra, which are modulated by amplitudes and phases of the coherently driven fields and the effect of PBG. This theoretical study can provide us with more efficient methods to manipulate the atomic spontaneous emission.
文摘A simple process to fabricate chain-like carbon nanotube （CNT） films by microwave plasma-enhanced chemical vapor deposition （MPCVD） was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.
基金financial support from the Project supported by the National Natural Science Foundation of China(Grant No.51202257)Shenyang Double-Hundreds Project(Z17-7-027,Z18-0-025)
文摘In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition（CVD） over a wide range of experimental parameters. The effects of the microwave power,CH;/H;ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope（SEM）, X-ray diffraction（XRD）, Raman spectroscopy and X-ray photoelectron spectroscopy（XPS）. A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH;/H;levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However,diamond film is deteriorated at high CH;/H;ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10 kW and high CH;concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N;or Ar,which is different from other reports. This composite structure has an excellent measured sheet resistance of 10-100 Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission（EFE） properties with a low turn-on field of 2.17 V/μm and β= 3160, therefore it could be a promising alternative in field emission applications.
