AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency(RF) magnetron sputtering method.The post-processing is carried out under the cooling conditions including high vacuu...AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency(RF) magnetron sputtering method.The post-processing is carried out under the cooling conditions including high vacuum,low vacuum under deposition gas ambient and low vacuum under dynamic N2 ambient.Structures and morphologies of the films are analyzed by X-ray diffraction(XRD) and atomic force microscopy(AFM).The hardness and Young's modulus are investigated by the nanoindenter.The experimental results indicate that the(100) and(110) peak intensities decrease in the XRD spectra and the root-mean-square of roughness(Rrms) of the film decreases gradually with the increase of the cooling rate.The maximum values of the hardness and Young modulus are obtained by cooling in low vacuum under deposition gas ambient.The reason for orientation variation of the films is explained from the perspective of the Al-N bond formation.展开更多
Cr-doped ZnO thin films are prepared on glass substrates by the magnetron sputtering technique. An X-ray diffraction (XRD) is used to analyze the structural properties of the thin films. It indicates that all the thin...Cr-doped ZnO thin films are prepared on glass substrates by the magnetron sputtering technique. An X-ray diffraction (XRD) is used to analyze the structural properties of the thin films. It indicates that all the thin films have a preferential c-axis orientation. The peak position of the (002) plane shifts to the higher 2θ value, and the peak intensity decreases with the increase of Cr doping. The results of the scanning electron microscopy (SEM) show that the surface morphology becomes loose with the increase of Cr doping. Besides, it is found from the photoluminescence (PL) measurement at room temperature that the ultraviolet emission peak and green emission band are located at 375 nm and 520 nm, respectively, and both intensities of them decrease with the increase of the Cr doping concentration, while the band gap of the ultraviolet emission shifts to the lower wavelength. The experimental results confirm that the optimal Cr doping concentration is 2 at. %.展开更多
The carrier recombination was one of the factors limiting the further improvement of the Cu2ZnSnS4(CZTS)thin film solar cells.In this paper,a proper bandgap structure was designed to solve this problem.The effects of ...The carrier recombination was one of the factors limiting the further improvement of the Cu2ZnSnS4(CZTS)thin film solar cells.In this paper,a proper bandgap structure was designed to solve this problem.The effects of the different bandgap structure on the CZTS thin film solar cells were studied by the solar cell performance simulation software wx AMPS.A graded bandgap structure was designed and optimized.The bandgap with a front bandgap gradient and a flat bandgap gradient had a favorable effect on the CZTS thin film solar cells.Finally,the fill factor(FF)and conversion efficiency(η)of the CZTS thin film solar cell were increased from 36.41% to 42.73% and from 6.85% to 10.03%,respectively.In addition,the effect of donor and acceptor defect densities in CZTS absorber layer near the Cd S/CZTS interface on the device performance was studied,ηof the CZTS thin film solar cell was increased from 5.99% to 7.55% when the acceptor defect concentration was 10^(12)—10^(13) cm^(-3).Moreover,the thicknesses of the CZTS absorber layer were optimized.The FF andηof the CZTS thin film solar cell were increased to 63.41% and 15.04%,respectively.展开更多
Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly affect the radiation efficiency and bandwidth of the antenna.Here,a wideband non-uniform wavy microstrip line for co...Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly affect the radiation efficiency and bandwidth of the antenna.Here,a wideband non-uniform wavy microstrip line for complex impedance in automotive radar frequency range is proposed.Unlike the gradient transmission line,the wavy structure is composed of periodically semi-circular segments.By adjusting the radius of the semi-circular,the surface current is varied and concentrated on the semi-circular segments,allowing a wider tunability range of the resonant frequency.The results reveal that the bandwidth of the loaded wavy transmission line antenna improves to 9.37 GHz,which is 5.81 GHz wider than that of the loaded gradient line.The gain and the half power beam width of the loaded antenna are about 14.69 dB and 9.58°,respectively.The proposed non-uniform microstrip line scheme may open up a route for realizing wideband millimeter-wave automotive radar applications.展开更多
A triple-band miniaturized end-fire antenna based on the odd modes of spoof surface plasmonic polariton(SSPP)waveguide resonator is proposed in this paper.To meet the ever increasing demand for more communication chan...A triple-band miniaturized end-fire antenna based on the odd modes of spoof surface plasmonic polariton(SSPP)waveguide resonator is proposed in this paper.To meet the ever increasing demand for more communication channels and less antenna sizes,multi-band antennas are currently under intensive investigation.By a novel feeding method,three odd modes are excited on an SSPP waveguide resonator,which performs as an end-fire antenna operating at three bands,7.15-7.26 GHz,11.6-12.2 GHz and 13.5-13.64 GHz.It exhibits reasonably high and stable maximum gains of 5.26 dBi,7.97 dBi and 10.1 dBi and maximum efficiencies of 64%,92%and 98%at the three bands,respectively.Moreover,in the second band,the main beam angle shows a frequency dependence with a total scanning angle of 19°.The miniaturized triple-band antenna has a great potential in wireless communication systems,satellite communication and radar systems.展开更多
Cu(In,Ga)Se2(CIGS)thin films are prepared by a single-stage process and a three-stage process at low temperature in the co-evaporation equipment.The quite different morphologies of CIGS thin films deposited by two met...Cu(In,Ga)Se2(CIGS)thin films are prepared by a single-stage process and a three-stage process at low temperature in the co-evaporation equipment.The quite different morphologies of CIGS thin films deposited by two methods are characterized by scanning electron microscopy(SEM).The orientation of CIGS thin films is identified by X-ray diffraction(XRD)and Raman spectrum,respectively.Through analyzing the film-forming mechanisms of two preparation processes,we consider the cause of such differences is that the films deposited by three-stage process at low temperature evolve from Cu-poor to Cu-rich ones and then back to Cu-poor ones.The three-stage process at low temperature results in the CIGS thin films with the(220)/(204)preferred orientation,and the ordered vacancy compound(OVC)layer is formed on the surface of the film.This study has great significance to large-scale industrial production.展开更多
Boron nitride （BN） films for high-frequency surface acoustic wave （SAW） devices are deposited on Ti/AI/Si（111） wafers by radio frequency （RF） magnetron sputtering. The structure of BN films is investigated by ...Boron nitride （BN） films for high-frequency surface acoustic wave （SAW） devices are deposited on Ti/AI/Si（111） wafers by radio frequency （RF） magnetron sputtering. The structure of BN films is investigated by Fourier transform infrared （FrlR） spectroscopy and X-ray diffraction （XRD） spectra, and the surface morphology and piezoelectric properties of BN films are characterized by atomic force microscopy （AFM）. The results show that when the flow ratio of nitrogen and argon is 2：18, the cubic BN （c-BN） film is deposited with high purity and c-axis orientation, and when the flow ratio of nitrogen and argon is 4：20, the hexagonal BN （h-BN） film is deposited with high c-axis orientation. Both particles are uniform and compact, and the roughnesses are 1.5 nm and 2.29 nm, respectively. The h-BN films have better piezoelectric response and distribu- tion than the c-BN films.展开更多
C-axis oriented ZnO films are deposited on polished diamond substrates in various O2/(O2+Ar) ratios using the radio frequency(RF) magnetron sputtering technique and are subsequently annealed in oxygen ambience under t...C-axis oriented ZnO films are deposited on polished diamond substrates in various O2/(O2+Ar) ratios using the radio frequency(RF) magnetron sputtering technique and are subsequently annealed in oxygen ambience under the same conditions.Structural,morphologic and electrical properties of ZnO films are characterized by X-ray diffraction(XRD),high-resistance instrument,energy dispersive X-ray spectroscopy(EDS) and scanning electronic microscopy(SEM).As the O2/(O2+Ar) ratio increasing from 1/12 to 5/12,the crystallinity of the as grown ZnO films becomes better and the electrical resistivity increases slowly.After annealing,the ZnO films deposited in O2/(O2+Ar) =1/12 and 3/12 are improved greatly in crystallinity,and their electrical resistivity is enhanced by two orders of magnitude,while those deposited in O2/(O2+Ar) =5/12 are scarcely changed in crystallinity,and their resistivity is only increased by one order.In addition,the ZnO films deposited in O2/(O2+Ar) =3/12 and annealed in oxygen are with the best crystal quality and the highest resistivity.展开更多
In this paper, we propose and experimentally demonstrate a compact optical fiber sensor based on a Mach-Zehnder in- terferometer （MZI） cascaded with fiber Bragg grating （FBG） for simultaneous measurement of refrac...In this paper, we propose and experimentally demonstrate a compact optical fiber sensor based on a Mach-Zehnder in- terferometer （MZI） cascaded with fiber Bragg grating （FBG） for simultaneous measurement of refractive index （RI） and temperature. In order to get a proper spectrum, we discuss the effects of different structure parameters of MZI. Using the resonant wavelength of the FBG （DipFBG） and the interference dip of the MZI （Dipl）, the RI and tempera- ture of the surrounding medium can be determined. The sensor has good operation linearity. The experimental results show that the distinctive spectral sensitivities are 0.071 75 nm/℃and -91.766 67 nm/RIU （refraction index unit） for Dip1 and 0.009 09 nm/℃ for DipFBG.展开更多
In this paper, the silver nanoparticle ink and ink-jet printing technology are used to manufacture the surface acoustic wave(SAW) filters. The characteristics of three common substrate piezoelectric materials of ST-qu...In this paper, the silver nanoparticle ink and ink-jet printing technology are used to manufacture the surface acoustic wave(SAW) filters. The characteristics of three common substrate piezoelectric materials of ST-quartz, Y36°-LiTaO3 and Y128°-LiNbO3 are evaluated. The experimental results show that Y128°-LiNbO3 matches the ink much better than others. The printed SAW filter with Y128°-LiNbO3 as piezoelectric substrate is realized, and its center frequency and bandwidth are 18.4 MHz and 500 kHz, respectively.展开更多
ZnO:Cu/ZnO core/shell nanocrystals are synthesized by a two-step solution-phase process. The morphology, structure and optical properties of the samples are detected by scanning electron microscopy, Raman, absorption ...ZnO:Cu/ZnO core/shell nanocrystals are synthesized by a two-step solution-phase process. The morphology, structure and optical properties of the samples are detected by scanning electron microscopy, Raman, absorption and luminescence spectroscopy. The increase of particle size confirms the growth of ZnO shell. The segregation of CuO phase observed in ZnO: Cu core is not detected in ZnO:Cu/ZnO core/shell nanocrystals from Raman spectra. It is suggested that some Cu ions can be segregated from ZnO nanocrystals, and the separated Cu ions can be incorporated inside ZnO shell after the growth of ZnO shell. The visible emission mechanism is discussed in detail, and the photoluminescence analysis indicates that the core/shell structure helps to eliminate the surface-related emission.展开更多
Multi-π-phase-shifted fiber Bragg gratings and π-phase-shifted sampled fiber Bragg gratings(SFBGs) with dual wavelength filtering properties are compared.Results show that both of these gratings have the dual wavele...Multi-π-phase-shifted fiber Bragg gratings and π-phase-shifted sampled fiber Bragg gratings(SFBGs) with dual wavelength filtering properties are compared.Results show that both of these gratings have the dual wavelength reflective spectra.However,the side lobe of the reflective spectrum of π-phase-shifted SFBGs is lower than that of multi-π-phaseshifted gratings.By adjusting the duty cycle in the range of 0.66-0.80,the filtering properties of π-phase-shifted SFBGs are optimized,and the side lobe suppression ratio(SLSR) is the lowest when the duty cycle is 0.75.The application of the π-phase-shifted SFBGs in the dual-wavelength laser is also demonstrated.展开更多
In this paper, a long-period waveguide grating was fabricated in x-cut lithium niobate substrate by patterned annealed proton exchange waveguide fabrication process. The waveguide mode characteristic was evaluated usi...In this paper, a long-period waveguide grating was fabricated in x-cut lithium niobate substrate by patterned annealed proton exchange waveguide fabrication process. The waveguide mode characteristic was evaluated using a charge-coupled device(CCD) camera. It shows that the waveguide is single mode transmission at a wavelength of1 550 nm. The transmission spectra of the long period waveguide gratings were measured by optical spectrum analyzer(OSA) and show an extinction ratio of ~17 dB and a 3 dB bandwidth of ~10 nm at the resonant wavelength. The resonant wavelength moves toward to the long wavelength direction as the waveguide width-difference increases in the same period, and also shifts toward to the long wavelength direction with the increase of the period in the case of the same waveguide width-difference. The method of fabricating a long period waveguide grating based on a patterned annealed proton exchange technique simplifies the fabrication process, and at the same time, reduces the fabrication cost.展开更多
As for the Domino effect dv/dt and electromagnetic interference during the rapid switching course of single-chip switching power supply,this article firstly analyzes electromagnetic interference source,and then diagno...As for the Domino effect dv/dt and electromagnetic interference during the rapid switching course of single-chip switching power supply,this article firstly analyzes electromagnetic interference source,and then diagnoses the essential interaction relationship between interference and switching activity based on the timely and area measured waveform,analyzes and studies the production mechanism and coupling path of interference mode,and sets up circuit model according to the features of transverse mode interference and common mode interference.Put forward different suppression methods finally.展开更多
Active constellation expansion(ACE) and iterative clipping and filtering(ICF) are simple and effective techniques for reducing the peak-to-average ratio(PAPR) in coherent optical orthogonal frequency division multiple...Active constellation expansion(ACE) and iterative clipping and filtering(ICF) are simple and effective techniques for reducing the peak-to-average ratio(PAPR) in coherent optical orthogonal frequency division multiplexing(CO-OFDM) systems, but effective PAPR suppression requires a lot of iterations. To overcome this shortcoming, a joint algorithm based on improved active constellation expansion(IACE) and ICF(IACE-ICF) is proposed. The simulation results show that at the complementary cumulative distribution function(CCDF) of 10-4, the PAPR of IACE-ICF(G=4, iter=4) algorithm is optimized by 1.507 d B, 1.13 d B and 0.204 d B compared with that of the IACE, ICF(iter=4) and ICF-IACE(G=4, iter=4) algorithms, respectively. Meanwhile, when the bit error rate(BER) is 10-3, the optical signal to noise ratio(OSNR) of the proposed scheme is optimized by 2.04 d B, 1.75 d B and 1.4 d B compared with that of clipping, ICF(iter=4) and ICF-IACE(G=4, iter=4) algorithms, respectively. On the other hand, the proposed scheme can reduce the number of complex multiplications by 14.29% and complex additions by 28.57% compared with the ICF(iter=14) scheme.展开更多
In order to reduce the noises affixed to the signals when testing high frequency devices,a single-port test mode(S11) is used to test frequency response of high frequency(GHz) and dual-port surface acoustic wave devic...In order to reduce the noises affixed to the signals when testing high frequency devices,a single-port test mode(S11) is used to test frequency response of high frequency(GHz) and dual-port surface acoustic wave devices(SAWDs) in this paper.The feasibility of the test is proved by simulating the Fabry-perot model.The frequency response of the high-frequency dual-port resonant-type diamond SAWD is measured by S11 and the dual-port test mode(S21),respectively.The results show that the quality factor of the device is 51.29 and the 3 dB bandwidth is 27.8 MHz by S11-mode measurement,which is better than the S21 mode,and is consistent with the frequency response curve by simulation.展开更多
The free-standing diamond films are deposited on molybdenum substrate by direct current jet chemical vapor deposition (DCJCVD). X-ray diffraction,Raman spectroscopy and cathodoluminescence (CL) measurement are used to...The free-standing diamond films are deposited on molybdenum substrate by direct current jet chemical vapor deposition (DCJCVD). X-ray diffraction,Raman spectroscopy and cathodoluminescence (CL) measurement are used to investigate the films structure and defects related to electron transition properties of the diamond films. The X-ray diffraction spectrum reveals that the diamond films have the polycrystalline cubic structure with diffraction peaks at 43.88o and 75.24o. A sharp peak at 1331.8 cm-1 and a broad band at about 1250-1550 cm-1 from Raman spectrum are attributed to diamond phase and sp2-type carbons,respectively. Two emission peaks at 440 nm and 530 nm,associated with dislocation defects and nitrogen and vacancy complexes respectively,are observed in cathodoluminescence spectrum. In addition,in order to understand both emission processes,a simple energy level scheme is suggested.展开更多
A Mach-Zehnder interferometer(MZI)based on two spherical structures is proposed and temperature and humidity are measured simultaneously.The device is fabricated by inserting two spherical structures into a single mod...A Mach-Zehnder interferometer(MZI)based on two spherical structures is proposed and temperature and humidity are measured simultaneously.The device is fabricated by inserting two spherical structures into a single mode optical fiber(SMF).The results of the experiment indicate that the temperature sensitivities are 0.079 nm/℃and 0.090 nm/℃from 10℃to 60℃,respectively.When the humidity changes from 30%to 70%,the humidity sensitivities are0.148 nm/%RH and 0.06 nm/%RH,respectively.Therefore,temperature and humidity are measured simultaneously by the sensitive matrix.The new structure is demonstrated to be a particularly useful approach to detect temperature and humidity.展开更多
In order to further study doping-free asymmetric heterojunction(DASH) solar cells,we used AFORS-HET software to optimize the structure of Al/SnO_(2)/a-Si:H(i)/c-Si(p)/a-Si:H(i)/NiO_(x)/Ag.In a certain adjustment range...In order to further study doping-free asymmetric heterojunction(DASH) solar cells,we used AFORS-HET software to optimize the structure of Al/SnO_(2)/a-Si:H(i)/c-Si(p)/a-Si:H(i)/NiO_(x)/Ag.In a certain adjustment range,a series of simulations were carried out on the band gap,electron affinity,thickness and work function(WF) of NiO_(x),thickness and WF of SnO_(2),and the thickness of a-Si:H(i).After the above optimization,21.08% efficiency was obtained at 300 K.This study shows that the solar cells with this structure have good light absorption properties in a very wide spectrum.The present simulation provides instructive suggestions for follow-up experiments of DASH solar cells.展开更多
A tunable erbium-doped fiber（EDF） laser with a cascaded structure consisting of in-line Mach-Zehnder interferometer（MZI） and traditional MZI is proposed. The transmission spectrum of the in-line MZI is modulated b...A tunable erbium-doped fiber（EDF） laser with a cascaded structure consisting of in-line Mach-Zehnder interferometer（MZI） and traditional MZI is proposed. The transmission spectrum of the in-line MZI is modulated by the traditional MZI, which determines the period of the cascaded structure, while the in-line MZI＇s transmission spectrum is the outer envelope curve of the cascaded structure＇s transmission spectrum. A stable single-wavelength lasing operation is obtained at 1 527.14 nm. The linewidth is less than 0.07 nm with a side-mode suppression ratio（SMSR） over 48 d B. Fixing the in-line MZI structure on a furnace, when the temperature changes from 30 ℃ to 230 ℃, the central wavelength can be tuned within the range of 12.4 nm.展开更多
基金supported by the National Natural Science Foundation of China (No.50972105)Tianjin Natural Science Foundation (Nos.09JCZDJC16500,08JCZDJC22700 and 10SYSYJC27700)
文摘AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency(RF) magnetron sputtering method.The post-processing is carried out under the cooling conditions including high vacuum,low vacuum under deposition gas ambient and low vacuum under dynamic N2 ambient.Structures and morphologies of the films are analyzed by X-ray diffraction(XRD) and atomic force microscopy(AFM).The hardness and Young's modulus are investigated by the nanoindenter.The experimental results indicate that the(100) and(110) peak intensities decrease in the XRD spectra and the root-mean-square of roughness(Rrms) of the film decreases gradually with the increase of the cooling rate.The maximum values of the hardness and Young modulus are obtained by cooling in low vacuum under deposition gas ambient.The reason for orientation variation of the films is explained from the perspective of the Al-N bond formation.
基金supported by Tianjin Natural Science Foundation (No.06YFJZJC00100)
文摘Cr-doped ZnO thin films are prepared on glass substrates by the magnetron sputtering technique. An X-ray diffraction (XRD) is used to analyze the structural properties of the thin films. It indicates that all the thin films have a preferential c-axis orientation. The peak position of the (002) plane shifts to the higher 2θ value, and the peak intensity decreases with the increase of Cr doping. The results of the scanning electron microscopy (SEM) show that the surface morphology becomes loose with the increase of Cr doping. Besides, it is found from the photoluminescence (PL) measurement at room temperature that the ultraviolet emission peak and green emission band are located at 375 nm and 520 nm, respectively, and both intensities of them decrease with the increase of the Cr doping concentration, while the band gap of the ultraviolet emission shifts to the lower wavelength. The experimental results confirm that the optimal Cr doping concentration is 2 at. %.
基金supported by the National Natural Science Foundation of China(No.61804108)。
文摘The carrier recombination was one of the factors limiting the further improvement of the Cu2ZnSnS4(CZTS)thin film solar cells.In this paper,a proper bandgap structure was designed to solve this problem.The effects of the different bandgap structure on the CZTS thin film solar cells were studied by the solar cell performance simulation software wx AMPS.A graded bandgap structure was designed and optimized.The bandgap with a front bandgap gradient and a flat bandgap gradient had a favorable effect on the CZTS thin film solar cells.Finally,the fill factor(FF)and conversion efficiency(η)of the CZTS thin film solar cell were increased from 36.41% to 42.73% and from 6.85% to 10.03%,respectively.In addition,the effect of donor and acceptor defect densities in CZTS absorber layer near the Cd S/CZTS interface on the device performance was studied,ηof the CZTS thin film solar cell was increased from 5.99% to 7.55% when the acceptor defect concentration was 10^(12)—10^(13) cm^(-3).Moreover,the thicknesses of the CZTS absorber layer were optimized.The FF andηof the CZTS thin film solar cell were increased to 63.41% and 15.04%,respectively.
基金Supported by the National Natural Science Foundation of China( 61974104)。
文摘Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly affect the radiation efficiency and bandwidth of the antenna.Here,a wideband non-uniform wavy microstrip line for complex impedance in automotive radar frequency range is proposed.Unlike the gradient transmission line,the wavy structure is composed of periodically semi-circular segments.By adjusting the radius of the semi-circular,the surface current is varied and concentrated on the semi-circular segments,allowing a wider tunability range of the resonant frequency.The results reveal that the bandwidth of the loaded wavy transmission line antenna improves to 9.37 GHz,which is 5.81 GHz wider than that of the loaded gradient line.The gain and the half power beam width of the loaded antenna are about 14.69 dB and 9.58°,respectively.The proposed non-uniform microstrip line scheme may open up a route for realizing wideband millimeter-wave automotive radar applications.
基金supported in part by the Natural Science Foundation of Tianjin(No.19JCYBJC16100)the Tianjin Innovation and Entrepreneurship Training Program(No.202210060027)。
文摘A triple-band miniaturized end-fire antenna based on the odd modes of spoof surface plasmonic polariton(SSPP)waveguide resonator is proposed in this paper.To meet the ever increasing demand for more communication channels and less antenna sizes,multi-band antennas are currently under intensive investigation.By a novel feeding method,three odd modes are excited on an SSPP waveguide resonator,which performs as an end-fire antenna operating at three bands,7.15-7.26 GHz,11.6-12.2 GHz and 13.5-13.64 GHz.It exhibits reasonably high and stable maximum gains of 5.26 dBi,7.97 dBi and 10.1 dBi and maximum efficiencies of 64%,92%and 98%at the three bands,respectively.Moreover,in the second band,the main beam angle shows a frequency dependence with a total scanning angle of 19°.The miniaturized triple-band antenna has a great potential in wireless communication systems,satellite communication and radar systems.
基金supported by the National High Technology Research and Development Program of China(No.2012AA050701)
文摘Cu(In,Ga)Se2(CIGS)thin films are prepared by a single-stage process and a three-stage process at low temperature in the co-evaporation equipment.The quite different morphologies of CIGS thin films deposited by two methods are characterized by scanning electron microscopy(SEM).The orientation of CIGS thin films is identified by X-ray diffraction(XRD)and Raman spectrum,respectively.Through analyzing the film-forming mechanisms of two preparation processes,we consider the cause of such differences is that the films deposited by three-stage process at low temperature evolve from Cu-poor to Cu-rich ones and then back to Cu-poor ones.The three-stage process at low temperature results in the CIGS thin films with the(220)/(204)preferred orientation,and the ordered vacancy compound(OVC)layer is formed on the surface of the film.This study has great significance to large-scale industrial production.
基金supported by the National Natural Science Foundation of China (Nos.50972105 and 60806030)the Tianjin Natural Science Foundation (Nos. 09JCZDJC16500 and 08JCYBJC14600)
文摘Boron nitride （BN） films for high-frequency surface acoustic wave （SAW） devices are deposited on Ti/AI/Si（111） wafers by radio frequency （RF） magnetron sputtering. The structure of BN films is investigated by Fourier transform infrared （FrlR） spectroscopy and X-ray diffraction （XRD） spectra, and the surface morphology and piezoelectric properties of BN films are characterized by atomic force microscopy （AFM）. The results show that when the flow ratio of nitrogen and argon is 2：18, the cubic BN （c-BN） film is deposited with high purity and c-axis orientation, and when the flow ratio of nitrogen and argon is 4：20, the hexagonal BN （h-BN） film is deposited with high c-axis orientation. Both particles are uniform and compact, and the roughnesses are 1.5 nm and 2.29 nm, respectively. The h-BN films have better piezoelectric response and distribu- tion than the c-BN films.
基金supported by the National Natural Science Foundation of China (No. 50972105)Tianjin Natural Science Foundation (No.09JCZDJC16500)
文摘C-axis oriented ZnO films are deposited on polished diamond substrates in various O2/(O2+Ar) ratios using the radio frequency(RF) magnetron sputtering technique and are subsequently annealed in oxygen ambience under the same conditions.Structural,morphologic and electrical properties of ZnO films are characterized by X-ray diffraction(XRD),high-resistance instrument,energy dispersive X-ray spectroscopy(EDS) and scanning electronic microscopy(SEM).As the O2/(O2+Ar) ratio increasing from 1/12 to 5/12,the crystallinity of the as grown ZnO films becomes better and the electrical resistivity increases slowly.After annealing,the ZnO films deposited in O2/(O2+Ar) =1/12 and 3/12 are improved greatly in crystallinity,and their electrical resistivity is enhanced by two orders of magnitude,while those deposited in O2/(O2+Ar) =5/12 are scarcely changed in crystallinity,and their resistivity is only increased by one order.In addition,the ZnO films deposited in O2/(O2+Ar) =3/12 and annealed in oxygen are with the best crystal quality and the highest resistivity.
基金supported by the National High Technology Research and Development Program of China(No.2013AA014200)the National Natural Science Foundation of China(No.11444001)the Municipal Natural Science Foundation of Tianjin(No.14JCYBJC16500)
文摘In this paper, we propose and experimentally demonstrate a compact optical fiber sensor based on a Mach-Zehnder in- terferometer （MZI） cascaded with fiber Bragg grating （FBG） for simultaneous measurement of refractive index （RI） and temperature. In order to get a proper spectrum, we discuss the effects of different structure parameters of MZI. Using the resonant wavelength of the FBG （DipFBG） and the interference dip of the MZI （Dipl）, the RI and tempera- ture of the surrounding medium can be determined. The sensor has good operation linearity. The experimental results show that the distinctive spectral sensitivities are 0.071 75 nm/℃and -91.766 67 nm/RIU （refraction index unit） for Dip1 and 0.009 09 nm/℃ for DipFBG.
基金supported by the Project of the Science&Technology Pillar Program of Tianjin(No.12ZCZDJC35500)the Natural Science Foundation of Tianjin(No.13JCQNJC01300)
文摘In this paper, the silver nanoparticle ink and ink-jet printing technology are used to manufacture the surface acoustic wave(SAW) filters. The characteristics of three common substrate piezoelectric materials of ST-quartz, Y36°-LiTaO3 and Y128°-LiNbO3 are evaluated. The experimental results show that Y128°-LiNbO3 matches the ink much better than others. The printed SAW filter with Y128°-LiNbO3 as piezoelectric substrate is realized, and its center frequency and bandwidth are 18.4 MHz and 500 kHz, respectively.
基金supported by the National Natural Science Foundation of China (Nos.60877029,10904109,60977035 and 60907021)the Natural Science Foundation of Tianjin (No.09JCYBJC01400)the Tianjin Key Subject for Materials Physics and Chemistry
文摘ZnO:Cu/ZnO core/shell nanocrystals are synthesized by a two-step solution-phase process. The morphology, structure and optical properties of the samples are detected by scanning electron microscopy, Raman, absorption and luminescence spectroscopy. The increase of particle size confirms the growth of ZnO shell. The segregation of CuO phase observed in ZnO: Cu core is not detected in ZnO:Cu/ZnO core/shell nanocrystals from Raman spectra. It is suggested that some Cu ions can be segregated from ZnO nanocrystals, and the separated Cu ions can be incorporated inside ZnO shell after the growth of ZnO shell. The visible emission mechanism is discussed in detail, and the photoluminescence analysis indicates that the core/shell structure helps to eliminate the surface-related emission.
基金supported by the National Natural Science Foundation of China (No.60808004)the Fund of New Century Excellent Talents in University (No.NCET-07-0611)Tianjin Natural Science Foundation (No.08JCYBJC14500)
文摘Multi-π-phase-shifted fiber Bragg gratings and π-phase-shifted sampled fiber Bragg gratings(SFBGs) with dual wavelength filtering properties are compared.Results show that both of these gratings have the dual wavelength reflective spectra.However,the side lobe of the reflective spectrum of π-phase-shifted SFBGs is lower than that of multi-π-phaseshifted gratings.By adjusting the duty cycle in the range of 0.66-0.80,the filtering properties of π-phase-shifted SFBGs are optimized,and the side lobe suppression ratio(SLSR) is the lowest when the duty cycle is 0.75.The application of the π-phase-shifted SFBGs in the dual-wavelength laser is also demonstrated.
基金supported by the National Natural Science Foundation of China(No.61377075)the New Century Excellent Talents in University(No.NCET-07-0611)the Training Program for Leading Talents of Universities in Tianjin
文摘In this paper, a long-period waveguide grating was fabricated in x-cut lithium niobate substrate by patterned annealed proton exchange waveguide fabrication process. The waveguide mode characteristic was evaluated using a charge-coupled device(CCD) camera. It shows that the waveguide is single mode transmission at a wavelength of1 550 nm. The transmission spectra of the long period waveguide gratings were measured by optical spectrum analyzer(OSA) and show an extinction ratio of ~17 dB and a 3 dB bandwidth of ~10 nm at the resonant wavelength. The resonant wavelength moves toward to the long wavelength direction as the waveguide width-difference increases in the same period, and also shifts toward to the long wavelength direction with the increase of the period in the case of the same waveguide width-difference. The method of fabricating a long period waveguide grating based on a patterned annealed proton exchange technique simplifies the fabrication process, and at the same time, reduces the fabrication cost.
基金Tianjin Natunal science Foundation of China(No:05YFSYSF033)
文摘As for the Domino effect dv/dt and electromagnetic interference during the rapid switching course of single-chip switching power supply,this article firstly analyzes electromagnetic interference source,and then diagnoses the essential interaction relationship between interference and switching activity based on the timely and area measured waveform,analyzes and studies the production mechanism and coupling path of interference mode,and sets up circuit model according to the features of transverse mode interference and common mode interference.Put forward different suppression methods finally.
基金supported by the Natural Science Foundation of Tianjin(No.18JCYBJC86300)。
文摘Active constellation expansion(ACE) and iterative clipping and filtering(ICF) are simple and effective techniques for reducing the peak-to-average ratio(PAPR) in coherent optical orthogonal frequency division multiplexing(CO-OFDM) systems, but effective PAPR suppression requires a lot of iterations. To overcome this shortcoming, a joint algorithm based on improved active constellation expansion(IACE) and ICF(IACE-ICF) is proposed. The simulation results show that at the complementary cumulative distribution function(CCDF) of 10-4, the PAPR of IACE-ICF(G=4, iter=4) algorithm is optimized by 1.507 d B, 1.13 d B and 0.204 d B compared with that of the IACE, ICF(iter=4) and ICF-IACE(G=4, iter=4) algorithms, respectively. Meanwhile, when the bit error rate(BER) is 10-3, the optical signal to noise ratio(OSNR) of the proposed scheme is optimized by 2.04 d B, 1.75 d B and 1.4 d B compared with that of clipping, ICF(iter=4) and ICF-IACE(G=4, iter=4) algorithms, respectively. On the other hand, the proposed scheme can reduce the number of complex multiplications by 14.29% and complex additions by 28.57% compared with the ICF(iter=14) scheme.
基金supported by the National Natural Science Foundation of China (Nos.50972105 and 60806030)Tianjin Natural Science Foundation (Nos.09JCZDJC16500,08JCYBJC14600 and ZD200709)
文摘In order to reduce the noises affixed to the signals when testing high frequency devices,a single-port test mode(S11) is used to test frequency response of high frequency(GHz) and dual-port surface acoustic wave devices(SAWDs) in this paper.The feasibility of the test is proved by simulating the Fabry-perot model.The frequency response of the high-frequency dual-port resonant-type diamond SAWD is measured by S11 and the dual-port test mode(S21),respectively.The results show that the quality factor of the device is 51.29 and the 3 dB bandwidth is 27.8 MHz by S11-mode measurement,which is better than the S21 mode,and is consistent with the frequency response curve by simulation.
基金supported by the Natural Science Foundation of Tianjin (No. 06YFJZJC00100)
文摘The free-standing diamond films are deposited on molybdenum substrate by direct current jet chemical vapor deposition (DCJCVD). X-ray diffraction,Raman spectroscopy and cathodoluminescence (CL) measurement are used to investigate the films structure and defects related to electron transition properties of the diamond films. The X-ray diffraction spectrum reveals that the diamond films have the polycrystalline cubic structure with diffraction peaks at 43.88o and 75.24o. A sharp peak at 1331.8 cm-1 and a broad band at about 1250-1550 cm-1 from Raman spectrum are attributed to diamond phase and sp2-type carbons,respectively. Two emission peaks at 440 nm and 530 nm,associated with dislocation defects and nitrogen and vacancy complexes respectively,are observed in cathodoluminescence spectrum. In addition,in order to understand both emission processes,a simple energy level scheme is suggested.
基金supported by the National Youth Natural Science Foundation of China(No.11704283)the Natural Science Foundation of Tianjin(No.18JCYBJC86300)the Tianjin Municipal Education Commission Scientific Research Project(No.2018KJ132)。
文摘A Mach-Zehnder interferometer(MZI)based on two spherical structures is proposed and temperature and humidity are measured simultaneously.The device is fabricated by inserting two spherical structures into a single mode optical fiber(SMF).The results of the experiment indicate that the temperature sensitivities are 0.079 nm/℃and 0.090 nm/℃from 10℃to 60℃,respectively.When the humidity changes from 30%to 70%,the humidity sensitivities are0.148 nm/%RH and 0.06 nm/%RH,respectively.Therefore,temperature and humidity are measured simultaneously by the sensitive matrix.The new structure is demonstrated to be a particularly useful approach to detect temperature and humidity.
基金supported by the National Natural Science Foundation of China (Nos.62074084 and No.62074165)。
文摘In order to further study doping-free asymmetric heterojunction(DASH) solar cells,we used AFORS-HET software to optimize the structure of Al/SnO_(2)/a-Si:H(i)/c-Si(p)/a-Si:H(i)/NiO_(x)/Ag.In a certain adjustment range,a series of simulations were carried out on the band gap,electron affinity,thickness and work function(WF) of NiO_(x),thickness and WF of SnO_(2),and the thickness of a-Si:H(i).After the above optimization,21.08% efficiency was obtained at 300 K.This study shows that the solar cells with this structure have good light absorption properties in a very wide spectrum.The present simulation provides instructive suggestions for follow-up experiments of DASH solar cells.
基金supported by the National High Technology Research and Development Program of China(No.2013AA014201)the Tianjin Youth Science Foundation(No.13JCQNJC01800)the State Key Laboratory on Integrated Optoelectronics of China(No.IOSKL2015KF06)
文摘A tunable erbium-doped fiber（EDF） laser with a cascaded structure consisting of in-line Mach-Zehnder interferometer（MZI） and traditional MZI is proposed. The transmission spectrum of the in-line MZI is modulated by the traditional MZI, which determines the period of the cascaded structure, while the in-line MZI＇s transmission spectrum is the outer envelope curve of the cascaded structure＇s transmission spectrum. A stable single-wavelength lasing operation is obtained at 1 527.14 nm. The linewidth is less than 0.07 nm with a side-mode suppression ratio（SMSR） over 48 d B. Fixing the in-line MZI structure on a furnace, when the temperature changes from 30 ℃ to 230 ℃, the central wavelength can be tuned within the range of 12.4 nm.
