Owing to the low p-type doping efficiency in the hole injection layers(HILs)of GaN-based ultra-violet(UV)vertical-cavity surface-emitting laser(VCSEL),effective hole injection in multi-quantum wells(MQW)is not achieve...Owing to the low p-type doping efficiency in the hole injection layers(HILs)of GaN-based ultra-violet(UV)vertical-cavity surface-emitting laser(VCSEL),effective hole injection in multi-quantum wells(MQW)is not achieved,significantly limiting the photoelectric performance of UV VCSELs.We developed a slope-shaped HIL and an EBL structure in AlGaN-based UV VCSELs.In this study,by improving hole in-jection efficiency,the hole concentration in the HIL is increased,and the hole barrier at the electron barrier layer(EBL)/HIL interface is decreased.This minimises the hindering effect of hole injection.A mathematic-al model of this structure was established using a commercial software,photonic integrated circuit simulator in three-dimension(PICS3D).We conducted simulations and theoretical analyses of the band structure and carrier concentration.Introducing polarisation doping through the Al composition gradient in the HIL en-hanced the hole concentration,thereby improving the hole injection efficiency.Furthermore,modifying the EBL eliminated the abrupt potential barrier for holes at the HIL/EBL interface,smoothing the valence band.This improved the stimulated radiative recombination rate in the MQW,increasing the laser power.There-fore,the sloped p-type layer can enhance the optoelectronic performance of UV VCSELs.展开更多
There is nonradiative recombination in waveguide region owing to severe carrier leakage,which in turn reduces output power and wall-plug efficiency.In this paper,we designed a novel epitaxial structure,which suppresse...There is nonradiative recombination in waveguide region owing to severe carrier leakage,which in turn reduces output power and wall-plug efficiency.In this paper,we designed a novel epitaxial structure,which suppresses carrier leakage by inserting n-Ga_(0.55)In_(0.45)P and p-GaAs_(0.6)P_(0.4) between barriers and waveguide layers,respectively,to modulate the energy band structure and to increase the height of barrier.The results show that the leakage current density reduces by 87.71%,compared to traditional structure.The nonradiative recombination current density of novel structure reduces to 37.411 A/cm^(2),and the output power reaches 12.80 W with wall-plug efficiency of 78.24%at an injection current density 5 A/cm^(2) at room temperature.In addition,the temperature drift coefficient of center wavelength is 0.206 nm/℃at the temperature range from 5℃to 65℃,and the slope of fitted straight line of threshold current with temperature variation is 0.00113.The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.展开更多
Metal single atom catalysts(SACs)have been attracting increasing attention in recent years owing to their incredibleperformance in several key catalytic reactions such as the oxygen reduction reaction and CO oxidation...Metal single atom catalysts(SACs)have been attracting increasing attention in recent years owing to their incredibleperformance in several key catalytic reactions such as the oxygen reduction reaction and CO oxidation.The construction of well dis-persed stable SACs can not only make it possible to understand the catalytic reactions on the atomic scale,but is also important for developing novel industrial catalysts.Recent efforts have been focused on dispersing metal SACs on carbon substrates rather than on metals or metal oxides for improved catalytic behavior.Especially,graphene-based materials have proven to be excellent candidates for supporting SACs due to their unique structural and electronic properties.Nevertheless,the anchoring mechanism between metal SACs and carbon substrates is not well understood.Here we review the many roles of carbon materials as the support of SACs and highlight the anchoring mechanism.We also propose some suggestions to improve the experimental and theoretical research methods to expand the number of applications and realize industrial applications.展开更多
The deoiled asphalt as the carbon source and the ferrocene as the metal source and the catalyst precursor were chosen to synthesize iron-containing carbon microparticles through co-carbonization at the temperature of ...The deoiled asphalt as the carbon source and the ferrocene as the metal source and the catalyst precursor were chosen to synthesize iron-containing carbon microparticles through co-carbonization at the temperature of about 450℃ for 3 h. The resulting products were treated at 2 000 ℃ for 2 h. All samples were examined by high resolution transmission electron microscopy （HRTEM） and X-ray diffraction （XRD）. The results show that the iron particles in the heat-treated material are completely coated by carbon. In addition to the fully filled carbon microparticles as well as hollow carbon ones, also form carbon fibers with hollow centers. The formation mechanism of the as-prepared products was discussed briefly.展开更多
An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn...An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.展开更多
Joints between sintered silicon carbide （SSiC） were produced using a polysiloxane silicon resin YR3370 （GE Toshiba Silicones） as joining material. Samples were heat treated in a 99.99% nitrogen flux at temperature...Joints between sintered silicon carbide （SSiC） were produced using a polysiloxane silicon resin YR3370 （GE Toshiba Silicones） as joining material. Samples were heat treated in a 99.99% nitrogen flux at temperatures ranging from 1 100 ℃ to 1 300 ℃. Three point bending strength of the joint reached the maximum of 179 MPa as joined at 1 200℃. The joining layer is continuous, homogeneous and densified and has a thickness of 2 μm -5μm. The joining mechanism is that the amorphous silicon oxycarbide （SixOyCz） ceramic pyrolyzed from silicon resin YR3370 acts as an inorganic adhesive to SSiC substrate, which means the formation of the continuous Si-C bond structure between SixOyCz structure and SSiC substrate. Life prediction of the ceramic joint can be realized through the measurement of the critical time of the joint after the cyclic loading test.展开更多
Iridium(Ⅲ)complexes with 2−phenylpyridine(ppy)have been demonstrated as a type of promising phosphorescence dopant in emitting layers of organic light emitting diodes(OLEDs).In most iridium(III)complexes,there exist ...Iridium(Ⅲ)complexes with 2−phenylpyridine(ppy)have been demonstrated as a type of promising phosphorescence dopant in emitting layers of organic light emitting diodes(OLEDs).In most iridium(III)complexes,there exist the strong spin−orbit coupling betweenπ−orbitals of cyclometalated ligands and 5d orbitals of the centric iridium.We study a novel iridium(Ⅲ)complex(ppy)2Ir(4−TfmBTZ)with ppy as cyclometalated ligands and 2-(4-trifluoromethyl-2-hydroxylphenyl)benzothiazole(4-TfmBTZ)as an ancillary ligand using the Gaussian 03 program.The geometries,electronic structures and spectroscopic properties of this iridium(Ⅲ)complex are investigated by density functional theory(DFT)and time−dependent density functional theory(TD-DFT).The results show that the spin-orbit coupling occurs not only between ppy and iridium atom but also between 4-TfmBTZ and iridium atom in this complex.The highest occupied molecular orbital is dominantly localized on the Ir atom and 4-TfmBTZ ligand,while the lowest unoccupied molecular orbital on 4-TfmBTZ ligand.The triplet lowest-lying transition is attributed to the Ir-to-4-TfmBTZ charge-transfer(3MLCT)transition while the sub−low-lying transitions are assigned to the 3MLCT transitions of Ir(ppy)2.The nature of the lowest unoccupied orbital changes from ppy−localized to 4-TfmBTZ-localized and reveals that phosphorescent color of Ir(Ⅲ)complex can be controlled by the ancillary ligand and substituent.展开更多
文摘Owing to the low p-type doping efficiency in the hole injection layers(HILs)of GaN-based ultra-violet(UV)vertical-cavity surface-emitting laser(VCSEL),effective hole injection in multi-quantum wells(MQW)is not achieved,significantly limiting the photoelectric performance of UV VCSELs.We developed a slope-shaped HIL and an EBL structure in AlGaN-based UV VCSELs.In this study,by improving hole in-jection efficiency,the hole concentration in the HIL is increased,and the hole barrier at the electron barrier layer(EBL)/HIL interface is decreased.This minimises the hindering effect of hole injection.A mathematic-al model of this structure was established using a commercial software,photonic integrated circuit simulator in three-dimension(PICS3D).We conducted simulations and theoretical analyses of the band structure and carrier concentration.Introducing polarisation doping through the Al composition gradient in the HIL en-hanced the hole concentration,thereby improving the hole injection efficiency.Furthermore,modifying the EBL eliminated the abrupt potential barrier for holes at the HIL/EBL interface,smoothing the valence band.This improved the stimulated radiative recombination rate in the MQW,increasing the laser power.There-fore,the sloped p-type layer can enhance the optoelectronic performance of UV VCSELs.
文摘There is nonradiative recombination in waveguide region owing to severe carrier leakage,which in turn reduces output power and wall-plug efficiency.In this paper,we designed a novel epitaxial structure,which suppresses carrier leakage by inserting n-Ga_(0.55)In_(0.45)P and p-GaAs_(0.6)P_(0.4) between barriers and waveguide layers,respectively,to modulate the energy band structure and to increase the height of barrier.The results show that the leakage current density reduces by 87.71%,compared to traditional structure.The nonradiative recombination current density of novel structure reduces to 37.411 A/cm^(2),and the output power reaches 12.80 W with wall-plug efficiency of 78.24%at an injection current density 5 A/cm^(2) at room temperature.In addition,the temperature drift coefficient of center wavelength is 0.206 nm/℃at the temperature range from 5℃to 65℃,and the slope of fitted straight line of threshold current with temperature variation is 0.00113.The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.
基金National Natural Science Foundation of China(51372160,51242007 and 51501124)Basic Research Project in Shanxi Province(2015011037 and 2015021071)Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province~~
文摘Metal single atom catalysts(SACs)have been attracting increasing attention in recent years owing to their incredibleperformance in several key catalytic reactions such as the oxygen reduction reaction and CO oxidation.The construction of well dis-persed stable SACs can not only make it possible to understand the catalytic reactions on the atomic scale,but is also important for developing novel industrial catalysts.Recent efforts have been focused on dispersing metal SACs on carbon substrates rather than on metals or metal oxides for improved catalytic behavior.Especially,graphene-based materials have proven to be excellent candidates for supporting SACs due to their unique structural and electronic properties.Nevertheless,the anchoring mechanism between metal SACs and carbon substrates is not well understood.Here we review the many roles of carbon materials as the support of SACs and highlight the anchoring mechanism.We also propose some suggestions to improve the experimental and theoretical research methods to expand the number of applications and realize industrial applications.
基金National Basic Research Program of China (2004CB217808)National Natural Science Foundation of China (20471041, 90306014)+1 种基金Natural Science Foundation of Shanxi Province (20051018)Shanxi Research Fund for Returned Scholars (200428)
文摘The deoiled asphalt as the carbon source and the ferrocene as the metal source and the catalyst precursor were chosen to synthesize iron-containing carbon microparticles through co-carbonization at the temperature of about 450℃ for 3 h. The resulting products were treated at 2 000 ℃ for 2 h. All samples were examined by high resolution transmission electron microscopy （HRTEM） and X-ray diffraction （XRD）. The results show that the iron particles in the heat-treated material are completely coated by carbon. In addition to the fully filled carbon microparticles as well as hollow carbon ones, also form carbon fibers with hollow centers. The formation mechanism of the as-prepared products was discussed briefly.
基金the National Natural Science Founda- tion of China (No. 20671068 and 20471041)
文摘An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.
基金National Key Fundamental R&D Plan (2004CB217808)National Natural Science Foundation of China (20271037)
文摘Joints between sintered silicon carbide （SSiC） were produced using a polysiloxane silicon resin YR3370 （GE Toshiba Silicones） as joining material. Samples were heat treated in a 99.99% nitrogen flux at temperatures ranging from 1 100 ℃ to 1 300 ℃. Three point bending strength of the joint reached the maximum of 179 MPa as joined at 1 200℃. The joining layer is continuous, homogeneous and densified and has a thickness of 2 μm -5μm. The joining mechanism is that the amorphous silicon oxycarbide （SixOyCz） ceramic pyrolyzed from silicon resin YR3370 acts as an inorganic adhesive to SSiC substrate, which means the formation of the continuous Si-C bond structure between SixOyCz structure and SSiC substrate. Life prediction of the ceramic joint can be realized through the measurement of the critical time of the joint after the cyclic loading test.
基金by the National Natural Scientific Foundation of China under Grant Nos 60976018 and 21071108Key Program of Science and Technology of Ministry of Education(207015)+1 种基金Program for Changjiang Scholar and Innovative Research Team in University(IRT0972)Shanxi Natural Scientific Foundation(2008011008).
文摘Iridium(Ⅲ)complexes with 2−phenylpyridine(ppy)have been demonstrated as a type of promising phosphorescence dopant in emitting layers of organic light emitting diodes(OLEDs).In most iridium(III)complexes,there exist the strong spin−orbit coupling betweenπ−orbitals of cyclometalated ligands and 5d orbitals of the centric iridium.We study a novel iridium(Ⅲ)complex(ppy)2Ir(4−TfmBTZ)with ppy as cyclometalated ligands and 2-(4-trifluoromethyl-2-hydroxylphenyl)benzothiazole(4-TfmBTZ)as an ancillary ligand using the Gaussian 03 program.The geometries,electronic structures and spectroscopic properties of this iridium(Ⅲ)complex are investigated by density functional theory(DFT)and time−dependent density functional theory(TD-DFT).The results show that the spin-orbit coupling occurs not only between ppy and iridium atom but also between 4-TfmBTZ and iridium atom in this complex.The highest occupied molecular orbital is dominantly localized on the Ir atom and 4-TfmBTZ ligand,while the lowest unoccupied molecular orbital on 4-TfmBTZ ligand.The triplet lowest-lying transition is attributed to the Ir-to-4-TfmBTZ charge-transfer(3MLCT)transition while the sub−low-lying transitions are assigned to the 3MLCT transitions of Ir(ppy)2.The nature of the lowest unoccupied orbital changes from ppy−localized to 4-TfmBTZ-localized and reveals that phosphorescent color of Ir(Ⅲ)complex can be controlled by the ancillary ligand and substituent.
