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
We investigate the intensity and efficiency of a compressed echo, which is important in arbitrary waveform generation（AWG）. A new model of compressed echo is proposed based on the optical Bloch equations, which expo...We investigate the intensity and efficiency of a compressed echo, which is important in arbitrary waveform generation（AWG）. A new model of compressed echo is proposed based on the optical Bloch equations, which exposes much more detailed parameters than the conventional model, such as the time delay of the chirp lasers, the nature of the rare-earth-iondoped crystal, etc. According to the novel model of compressed echo, we find that reducing the time delay of the chirp lasers and scanning the lasers around the center frequency of the inhomogeneously broadened spectrum, while utilizing a crystal with larger coherence time and excitation lifetime can improve the compressed echo＇s intensity and efficiency. The theoretical analysis is validated by numerical simulations.展开更多
A supervised genetic algorithm (SGA) is proposed to solve the quality of service (QoS) routing problems in computer networks. The supervised rules of intelligent concept are introduced into genetic algorithms (GAs) to...A supervised genetic algorithm (SGA) is proposed to solve the quality of service (QoS) routing problems in computer networks. The supervised rules of intelligent concept are introduced into genetic algorithms (GAs) to solve the constraint optimization problem. One of the main characteristics of SGA is its searching space can be limited in feasible regions rather than infeasible regions. The superiority of SGA to other GAs lies in that some supervised search rules in which the information comes from the problems are incorporated into SGA. The simulation results show that SGA improves the ability of searching an optimum solution and accelerates the convergent process up to 20 times.展开更多
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
Surface acoustic wave (SAW) technology has been extensively explored for wireless communication, sensors, microfluidics, photonics, and quantum information processing. However, due to fabrication issues, the frequenci...Surface acoustic wave (SAW) technology has been extensively explored for wireless communication, sensors, microfluidics, photonics, and quantum information processing. However, due to fabrication issues, the frequencies of SAW devices are typically limited to within a few gigahertz, which severely restricts their applications in 5G communication, precision sensing, photonics, and quantum control. To solve this critical problem, we propose a hybrid strategy that integrates a nanomanufacturing process (i.e., nanolithography) with a LiNbO_(3)/SiO_(2)/SiC heterostructure and successfully achieve a record-breaking frequency of about 44 GHz for SAW devices, in addition to large electromechanical coupling coefficients of up to 15.7%. We perform a theoretical analysis and identify the guided higher order wave modes generated on these slow-on-fast SAW platforms. To demonstrate the superior sensing performance of the proposed ultra-high-frequency SAW platforms, we perform micro-mass sensing and obtain an extremely high sensitivity of approximately 33151.9 MHz·mm2·μg−1, which is about 1011 times higher than that of a conventional quartz crystal microbalance (QCM) and about 4000 times higher than that of a conventional SAW device with a frequency of 978 MHz.展开更多
In this paper, the bipolar resistive switching characteristic is reported in Ti/ZrO2/Pt resistive switching memory de- vices. The dominant mechanism of resistive switching is the formation and rupture of the conductiv...In this paper, the bipolar resistive switching characteristic is reported in Ti/ZrO2/Pt resistive switching memory de- vices. The dominant mechanism of resistive switching is the formation and rupture of the conductive filament composed of oxygen vacancies. The conduction mechanisms for low and high resistance states are dominated by the ohmic conduc- tion and the trap-controlled space charge limited current （SCLC） mechanism, respectively. The effect of a set compliance current on the switching parameters is also studied： the low resistance and reset current are linearly dependent on the set compliance current in the log-log scale coordinate; and the set and reset voltage increase slightly with the increase of the set compliance current. A series circuit model is proposed to explain the effect of the set compliance current on the resistive switching behaviors.展开更多
This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the...This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the three-pulse photon echo＇s amplitude and efficiency is analyzed with the Maxwell-Bloch equations solved by finite-difference timedomain method.We demonstrate that the amplitude of three-pulse echo will increase with the increasing of thickness and the optimum thickness to generate three-pulse photon echo is 0.3 cm for Tm^（3＋）：YAG when the attenuation of the input pulse is taken into account.Meanwhile,we find the expression 0.09 exp（α＇L）,which is previously employed to describe the relationship between echo＇s efficiency and thickness,should be modified as 1.3 · 0.09 exp（2.4 ·α＇L） with the propagation of echo considered.展开更多
Highly boron-doped diamond films were deposited on porous titanium substrates by hot filament chemical vapor deposition technique. The morphology variation of highly boron-doped diamond films grown on porous titanium ...Highly boron-doped diamond films were deposited on porous titanium substrates by hot filament chemical vapor deposition technique. The morphology variation of highly boron-doped diamond films grown on porous titanium substrates was investigated, and the effects of carbon concentration on nucleation density and diamond growth were also studied. The continuous change of surface morphology and structure of diamond film were characterized by scanning electron microscopy. The structures of diamond film and interlayer were analyzed by X-ray diffraction. The quality of boron-doped diamond film was confirmed by visible Raman spectroscopy. The experimental results reveal that surface morphology and quality of boron-doped diamond films are various due to the change of carbon concentration. The thickness of intermediate layer decreases with the carbon concentration increasing.展开更多
In this paper, spectral hole depth dependence on temperature below 10 K in Tm^3＋ ：YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on the spectral hole. By using...In this paper, spectral hole depth dependence on temperature below 10 K in Tm^3＋ ：YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on the spectral hole. By using the proposed model, we theoretically deduce the temperature dependence of spectral hole depth. The results are compared with experimental results and they are in good agreement. According to the theoretic results, the optimum temperature in experiment can be found.展开更多
Rare-earth(R)-based materials with large reversible magnetocaloric effect(MCE)are attracting much attention as the promising candidates for low temperature magnetic refrigeration.In the present work,the magnetic prope...Rare-earth(R)-based materials with large reversible magnetocaloric effect(MCE)are attracting much attention as the promising candidates for low temperature magnetic refrigeration.In the present work,the magnetic properties and MCE of DyNiGa compound with TiNiSi-type orthorhombic structure are studied systematically.The DyNiGa undergoes a magnetic transition from antiferromagnetic(AFM)to paramagnetic state with Néel temperature TN=17 K.Meanwhile,it does not show thermal and magnetic hysteresis,revealing the perfect thermal and magnetic reversibility.Moreover,the AFM state can be induced into a ferromagnetic state by a relatively low field,and thus leading to a large reversible MCE,e.g.,a maximum magnetic entropy change(-ΔSM)of 10 J/kg·K is obtained at 18 K under a magnetic field change of 5 T.Consequently,the large MCE without thermal or magnetic hysteresis makes the DyNiGa a competitive candidate for magnetic refrigeration of hydrogen liquefaction.展开更多
In this paper, the physical mechanism of the interaction between electromagnetic wave and spectral-hole burning crystal material is investigated in detail. In the small signal regime, a perturbation theory model is us...In this paper, the physical mechanism of the interaction between electromagnetic wave and spectral-hole burning crystal material is investigated in detail. In the small signal regime, a perturbation theory model is used to analyze the mechanism of spectral-hole burning. By solving the Liouville equation, three-order perturbation results are obtained. From the theoretic analysis, spectral-hole burning can be interpreted as a photon echo of the zero-order diffraction echo when the first optical pulse and the second optical pulse are overlapped in time. According to the model, the spectral-hole width is dependent on the chirp rate of the reading laser. When the chirp rate is slow with respect to the spectral features of interest, the spectral hole is closely mapped into time domain. For a fast chirp rate, distortions are observed. The results follow Maxwell-Bloch model and they are also in good agreement with the experimental results.展开更多
A method of measuring laser frequency stability is proposed by using the spectral-hole-burning technique.The power spectra of the measured laser can be recorded as a spectral hole,and the engraving time of the spectra...A method of measuring laser frequency stability is proposed by using the spectral-hole-burning technique.The power spectra of the measured laser can be recorded as a spectral hole,and the engraving time of the spectral hole is mapped into the frequency of the measured laser.Frequency fluctuation can be expressed by spectral hole frequency variation with different engraving times.By using the proposed method,the frequency stability of the external-cavity diode laser is measured to be 2.22×10^(-9) with an integration time of 20 ms.The frequency stability measurement resolution reaches 14 kHz and the repetition rate is 50 Hz.Compared to the conventional method,it avoids the need for a high stability reference laser source.展开更多
Kelvin probe force microscopy （KFM） technology is applied to investigate the charge storage and loss characteristics of the HfAlO charge trapping layer with various AI contents. The experimental results demonstrate ...Kelvin probe force microscopy （KFM） technology is applied to investigate the charge storage and loss characteristics of the HfAlO charge trapping layer with various AI contents. The experimental results demonstrate that with the increase of AI contents in the HfAIO trapping layer, trap density significantly increases. Improvement of data retention characteristic is also observed. Comparing the vertical charge loss and lateral charge spreading of the HfAIO trapping layers, the former plays a major role in the charge loss mechanism. Variable temperature KFM measurement results show that the extracted effective electron trap energy level increases with increasing AI contents in HfAIO trapping layer, which is in accordance with the charge loss characteristics.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
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
An alternative solution for the simultaneous measurement of temperature and refractive index is presented. A local micro-structured fiber Bragg grating （LMSFBG） is formed as the sensing head, in which a standard gra...An alternative solution for the simultaneous measurement of temperature and refractive index is presented. A local micro-structured fiber Bragg grating （LMSFBG） is formed as the sensing head, in which a standard grating is etched by HF. According to the phase shift theory, the main spectral change of the LMSFBG is the formation of a narrow allowed band, which is strongly dependent on the etching features and the surrounding refractive index. As such, the temperature and refractive index measurements can be achieved by the shifts of the double peaks and narrow allowed band, and their fitting linearity coefficients are 0.996 and 0.994, respectively. Thus, the reflection and transmission peaks of the LMSFBG have a good linear relationshi~ with tem^era,ture and refractive index.展开更多
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Project supported by Special Funds for Scientific and Technological Innovation Projects in Tianjin,China(Grant No.10FDZDGX00400)the Tianjin Research Program of Application Foundation and Advanced Technology,China(Grant No.15JCQNJC01100)
文摘We investigate the intensity and efficiency of a compressed echo, which is important in arbitrary waveform generation（AWG）. A new model of compressed echo is proposed based on the optical Bloch equations, which exposes much more detailed parameters than the conventional model, such as the time delay of the chirp lasers, the nature of the rare-earth-iondoped crystal, etc. According to the novel model of compressed echo, we find that reducing the time delay of the chirp lasers and scanning the lasers around the center frequency of the inhomogeneously broadened spectrum, while utilizing a crystal with larger coherence time and excitation lifetime can improve the compressed echo＇s intensity and efficiency. The theoretical analysis is validated by numerical simulations.
基金China Postdoctoral Foundation (No2005037529)Doctoral Foundation of Education Ministry of China (No2003005607)Tianjin High Education Science Development Foundation (No20041325)
文摘A supervised genetic algorithm (SGA) is proposed to solve the quality of service (QoS) routing problems in computer networks. The supervised rules of intelligent concept are introduced into genetic algorithms (GAs) to solve the constraint optimization problem. One of the main characteristics of SGA is its searching space can be limited in feasible regions rather than infeasible regions. The superiority of SGA to other GAs lies in that some supervised search rules in which the information comes from the problems are incorporated into SGA. The simulation results show that SGA improves the ability of searching an optimum solution and accelerates the convergent process up to 20 times.
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 the National Science Foundation of China(NSFC)(52075162)the Program of New and High-Tech Industry of Hunan Province(2020GK2015 and 2021GK4014)+5 种基金the Excellent Youth Fund of Hunan Province(2021JJ20018)the Key Program of Guangdong(2020B0101040002)the Joint Fund of the Ministry of Education(Young Talents)the Natural Science Foundation of Changsha(kq2007026)the Tianjin Enterprise Science and Technology Commissioner Project(19JCTPJC56200)the Engineering Physics and Science Research Council of the United Kingdom(EPSRC EP/P018998/1).
文摘Surface acoustic wave (SAW) technology has been extensively explored for wireless communication, sensors, microfluidics, photonics, and quantum information processing. However, due to fabrication issues, the frequencies of SAW devices are typically limited to within a few gigahertz, which severely restricts their applications in 5G communication, precision sensing, photonics, and quantum control. To solve this critical problem, we propose a hybrid strategy that integrates a nanomanufacturing process (i.e., nanolithography) with a LiNbO_(3)/SiO_(2)/SiC heterostructure and successfully achieve a record-breaking frequency of about 44 GHz for SAW devices, in addition to large electromechanical coupling coefficients of up to 15.7%. We perform a theoretical analysis and identify the guided higher order wave modes generated on these slow-on-fast SAW platforms. To demonstrate the superior sensing performance of the proposed ultra-high-frequency SAW platforms, we perform micro-mass sensing and obtain an extremely high sensitivity of approximately 33151.9 MHz·mm2·μg−1, which is about 1011 times higher than that of a conventional quartz crystal microbalance (QCM) and about 4000 times higher than that of a conventional SAW device with a frequency of 978 MHz.
基金supported by the National Basic Research Program of China(Grant No.2011CBA00606)the National Natural Science Foundation of China(Grant Nos.61106106,11304237,61376099,and 11235008)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant Nos.20130203130002 and 20110203110012)
文摘In this paper, the bipolar resistive switching characteristic is reported in Ti/ZrO2/Pt resistive switching memory de- vices. The dominant mechanism of resistive switching is the formation and rupture of the conductive filament composed of oxygen vacancies. The conduction mechanisms for low and high resistance states are dominated by the ohmic conduc- tion and the trap-controlled space charge limited current （SCLC） mechanism, respectively. The effect of a set compliance current on the switching parameters is also studied： the low resistance and reset current are linearly dependent on the set compliance current in the log-log scale coordinate; and the set and reset voltage increase slightly with the increase of the set compliance current. A series circuit model is proposed to explain the effect of the set compliance current on the resistive switching behaviors.
基金Project supported by Tianjin Research Program Application Foundation and Advanced Technology,China(Grant No.15JCQNJC01100)
文摘This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works.The influence of thickness on the three-pulse photon echo＇s amplitude and efficiency is analyzed with the Maxwell-Bloch equations solved by finite-difference timedomain method.We demonstrate that the amplitude of three-pulse echo will increase with the increasing of thickness and the optimum thickness to generate three-pulse photon echo is 0.3 cm for Tm^（3＋）：YAG when the attenuation of the input pulse is taken into account.Meanwhile,we find the expression 0.09 exp（α＇L）,which is previously employed to describe the relationship between echo＇s efficiency and thickness,should be modified as 1.3 · 0.09 exp（2.4 ·α＇L） with the propagation of echo considered.
基金Funded by the National Natural Science Foundation of China (No.50972105)the Natural Science Foundation of Tianjin Province(No.10JCYBJC05900)
文摘Highly boron-doped diamond films were deposited on porous titanium substrates by hot filament chemical vapor deposition technique. The morphology variation of highly boron-doped diamond films grown on porous titanium substrates was investigated, and the effects of carbon concentration on nucleation density and diamond growth were also studied. The continuous change of surface morphology and structure of diamond film were characterized by scanning electron microscopy. The structures of diamond film and interlayer were analyzed by X-ray diffraction. The quality of boron-doped diamond film was confirmed by visible Raman spectroscopy. The experimental results reveal that surface morphology and quality of boron-doped diamond films are various due to the change of carbon concentration. The thickness of intermediate layer decreases with the carbon concentration increasing.
基金supported by the National Natural Science Foundation of China (Grant No. 11004152)the Science Fund of Tianjin Education Commission (Grant Nos. 20090715 and 20110704)
文摘In this paper, spectral hole depth dependence on temperature below 10 K in Tm^3＋ ：YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on the spectral hole. By using the proposed model, we theoretically deduce the temperature dependence of spectral hole depth. The results are compared with experimental results and they are in good agreement. According to the theoretic results, the optimum temperature in experiment can be found.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51701130 and 51925605)the Natural Science Foundation of Tianjin,China(Grant Nos.18ZXCLGX00040 and 15JCZDJC38700)the National Key Research and Development Program of China(Grant Nos.2019YFA0704900,2019YFA0705000,2019YFA0705100,2019YFA0705200,and 2019YFA0705300).
文摘Rare-earth(R)-based materials with large reversible magnetocaloric effect(MCE)are attracting much attention as the promising candidates for low temperature magnetic refrigeration.In the present work,the magnetic properties and MCE of DyNiGa compound with TiNiSi-type orthorhombic structure are studied systematically.The DyNiGa undergoes a magnetic transition from antiferromagnetic(AFM)to paramagnetic state with Néel temperature TN=17 K.Meanwhile,it does not show thermal and magnetic hysteresis,revealing the perfect thermal and magnetic reversibility.Moreover,the AFM state can be induced into a ferromagnetic state by a relatively low field,and thus leading to a large reversible MCE,e.g.,a maximum magnetic entropy change(-ΔSM)of 10 J/kg·K is obtained at 18 K under a magnetic field change of 5 T.Consequently,the large MCE without thermal or magnetic hysteresis makes the DyNiGa a competitive candidate for magnetic refrigeration of hydrogen liquefaction.
基金supported by the Special Funds for Scientific and Technological Innovation Projects,Tianjin,China(Grant No.10FDZDGX00400)
文摘In this paper, the physical mechanism of the interaction between electromagnetic wave and spectral-hole burning crystal material is investigated in detail. In the small signal regime, a perturbation theory model is used to analyze the mechanism of spectral-hole burning. By solving the Liouville equation, three-order perturbation results are obtained. From the theoretic analysis, spectral-hole burning can be interpreted as a photon echo of the zero-order diffraction echo when the first optical pulse and the second optical pulse are overlapped in time. According to the model, the spectral-hole width is dependent on the chirp rate of the reading laser. When the chirp rate is slow with respect to the spectral features of interest, the spectral hole is closely mapped into time domain. For a fast chirp rate, distortions are observed. The results follow Maxwell-Bloch model and they are also in good agreement with the experimental results.
基金Supported by the National High-Tech Research and Development Program,the National Natural Science Foundation of China under Grant No 11004152the Funds of Tianjin Education Commission under Grant Nos 20090715,20110704。
文摘A method of measuring laser frequency stability is proposed by using the spectral-hole-burning technique.The power spectra of the measured laser can be recorded as a spectral hole,and the engraving time of the spectral hole is mapped into the frequency of the measured laser.Frequency fluctuation can be expressed by spectral hole frequency variation with different engraving times.By using the proposed method,the frequency stability of the external-cavity diode laser is measured to be 2.22×10^(-9) with an integration time of 20 ms.The frequency stability measurement resolution reaches 14 kHz and the repetition rate is 50 Hz.Compared to the conventional method,it avoids the need for a high stability reference laser source.
基金Supported by the National Basic Research Program of China under Grant Nos 2010CB934200 and 2011CBA00600, the National Natural Science Foundation of China under Grant Nos 61176073 and 60825403, and the Director＇s Fund of Institutes of Microelectronics of Chinese Academy of Sciences.
文摘Kelvin probe force microscopy （KFM） technology is applied to investigate the charge storage and loss characteristics of the HfAlO charge trapping layer with various AI contents. The experimental results demonstrate that with the increase of AI contents in the HfAIO trapping layer, trap density significantly increases. Improvement of data retention characteristic is also observed. Comparing the vertical charge loss and lateral charge spreading of the HfAIO trapping layers, the former plays a major role in the charge loss mechanism. Variable temperature KFM measurement results show that the extracted effective electron trap energy level increases with increasing AI contents in HfAIO trapping layer, which is in accordance with the charge loss characteristics.
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 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 Tianjin Natural Science Foundation(No.11JCYBJC00100)the National Natural Science Foundation of China(Nos.60808004 and 61107052)
文摘An alternative solution for the simultaneous measurement of temperature and refractive index is presented. A local micro-structured fiber Bragg grating （LMSFBG） is formed as the sensing head, in which a standard grating is etched by HF. According to the phase shift theory, the main spectral change of the LMSFBG is the formation of a narrow allowed band, which is strongly dependent on the etching features and the surrounding refractive index. As such, the temperature and refractive index measurements can be achieved by the shifts of the double peaks and narrow allowed band, and their fitting linearity coefficients are 0.996 and 0.994, respectively. Thus, the reflection and transmission peaks of the LMSFBG have a good linear relationshi~ with tem^era,ture and refractive index.
