A complete quantum mechanical model for GaAs/AlGaAs quantum well infrared photodetectors(QWIPs) was presented. The photocurrent was investigated by the optical transition(absorption coefficient)between the ground stat...A complete quantum mechanical model for GaAs/AlGaAs quantum well infrared photodetectors(QWIPs) was presented. The photocurrent was investigated by the optical transition(absorption coefficient)between the ground state and the excited states due to the nonzero component of the radiation field along the sample growth direction. By studying the inter diffusion of the Al atoms across the GaAs/AlGaAs heterointer faces, the mobility of the drift diffusion carriers in the excited states was calculated. As a result, the measurement results of the dark current and the photocurrent spectra are explained theoretically.展开更多
The effect of metal （Ti, Ni, and Au） electrodes on humidity sensing properties of electrospun TiO2 nanofibers was investigated in this work. The devices were fabricated by evaporating metal contacts on SiO2 layer th...The effect of metal （Ti, Ni, and Au） electrodes on humidity sensing properties of electrospun TiO2 nanofibers was investigated in this work. The devices were fabricated by evaporating metal contacts on SiO2 layer thermally grown on silicon substrate. The separation between the electrodes was 90 μm for all sensors. The sensors were tested from 40% to 90% relative humidity （RH） by AC electrical characterization at room temperature. When sensors are switched between 40% and 90% RH, the corresponding response and recovery time are 3 s and 5 s for Ti-electrode sensor, 4 s and 7 s for Ni-electrode sensor, and 7 s and 13 s for Au-electrode sensor. The hysteresis was 3%, 5% and 15% for sensitivity of Ti, Ni, and Au-electrode sensors are Ti-, Ni-, and Au-electrode sensor, respectively. The 7.53 MΩ/%RH, 5.29 MΩ/%RH and 4.01 MΩ/%RH respectively at 100 Hz. Therefore Ti-electrode sensor is found to have linear response, fast response and recovery time and higher sensitivity as compared with those of Ni- and Au-electrode sensors. Comparison of humidity sensing properties of sensors with different electrode material may propose a compelling route for designing and optimizing humidity sensors.展开更多
A complete quantum mechanical model for GaAs?AlGaAs quantum well infrared photodetectors(QWIPs) is presented here. The model consisted of four parts: (1) Starting with the description of the electromagnetic field of t...A complete quantum mechanical model for GaAs?AlGaAs quantum well infrared photodetectors(QWIPs) is presented here. The model consisted of four parts: (1) Starting with the description of the electromagnetic field of the infrared radiation in the QWIP, effective component of the vector potential <| A z |> along the QWIP growth direction ( z axis) due to the optical diffraction grating was calculated. (2) From the wave transmissions and the occupations of the electronic states, it was discussed that the dark current in the QWIP is determined by the drift diffusion current of carriers thermally excited from the ground sublevel in the quantum well to extended states above the barrier. (3) The photocurrent was investigated by the optical transition (absorption coefficient between the ground state to excited states due to the nonzero <| A z |> ). (4) By studying the inter diffusion of the Al atoms across the GaAs?AlGaAs heterointerfaces,the mobility of the drift diffusion carriers in the excited states was calculated, so the measurement results of the dark current and photocurrent spectra can be explained theoretically. With the complete quantum mechanical descriptions of (1 4), QWIP device design and optimization are possible.展开更多
Anodic oxidization （AO） is one of the most important methods available for fabricating mesoporous Al2O3 , which can be conducted at either high potential or low potential; however, the need for an external electrici...Anodic oxidization （AO） is one of the most important methods available for fabricating mesoporous Al2O3 , which can be conducted at either high potential or low potential; however, the need for an external electricity power source limits its applications. In this work, a novel self-powered electrochemical anodic oxidization （SPAO） system was introduced for preparing mesoporous Al2O3 , by using newly-invented triboelectric nanogenerator （TENG） arrays driven by wind power. Using the controllable voltage output of the TENG arrays, the SPAO system was shown to regulate the pore depth and pore size of the mesoporous Al2O3 . In contrast to traditional AO systems, this technique takes advantage of the high output voltage of TENG arrays without any additional energy costs. In addition, the SPAO system can be used for the preparation of other mesoporous materials.展开更多
Nano-composite, perovskite Ba(1- x - y)Sr(x)TiFe(y)O3, denoted as (BSTFe) in powder form was derived via sol-gel (SG) method followed by sintering at fixed temperature 750℃ for one hour. The chemical composition, mor...Nano-composite, perovskite Ba(1- x - y)Sr(x)TiFe(y)O3, denoted as (BSTFe) in powder form was derived via sol-gel (SG) method followed by sintering at fixed temperature 750℃ for one hour. The chemical composition, morphology and structure of the powder samples were investigated by using X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The XRD characterization indicates formation of a cubic crystalline phase in the pure BST. A well defined perovskite phase with nano-crystallite sizes equal to about 34 nm was achieved from XRD for B10ST3F sample, while TEM study confirmed the obtained XRD results giving the following crystallite size value about 33.75 nm for the same sample. The dielectric A.C. conductivity was evaluated as a function of temperature and frequency ranging from 42 Hz up to 1 MHz.展开更多
In this study, novel nickel oxide (NiO) flowers like nanostructures were fabricated onto gold coated glass substrate by hydrothermal method using high alkaline pH medium. The structural study of nickel oxide nanostruc...In this study, novel nickel oxide (NiO) flowers like nanostructures were fabricated onto gold coated glass substrate by hydrothermal method using high alkaline pH medium. The structural study of nickel oxide nanostructures was performed by scanning electron microscopy (SEM) and X-ray differaction (XRD) techniques. Nickel oxide nanostructures are highly dense, uniform and possess good crystalline quality. The so prepared structures were investigated for their electrochemical properties by cyclic voltammetry and amperometric techniques. The nickel oxide flower like morphology has shown good electrochemical performances for the oxidation of glucose. The presented sensing material was able to detected glucose in a wide range of concentration of 0.001 mM to 8 mM with a high sensitivity (123 μmA/mM) and regression coefficient of 0.99. Moreover, the NiO nanostructures based sensor is highly reproducible, stable, exhibiting a fast response time and selective in the response. All the obtained results indicate the potential use of this material in the development of enzyme free sensors for the detection of glucose.展开更多
We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy （MBE）, The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current-...We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy （MBE）, The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current-voltage （l-V） measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49 ± 0.03 eV and capture cross-section of 8,57 ×10^-18 cm^2. Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy （SIMS） of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO,展开更多
Wurtzite hexagonal ZnO semiconductor nano-rods (NRs) thin films were grown on silicon substrates and silver wire with diameter equal 68 nm. Sol gel (SG) and aqueous chemical growth (ACG) methods by two steps of prepar...Wurtzite hexagonal ZnO semiconductor nano-rods (NRs) thin films were grown on silicon substrates and silver wire with diameter equal 68 nm. Sol gel (SG) and aqueous chemical growth (ACG) methods by two steps of preparation (seed layers and nano-rod growth) are used for samples preparation. The structural and morphological properties are evaluated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The proposed iron ion sensor has shown good linearity for a wide concentration range from 0.078 M/L to 0.26 M/L of iron ions. The results show that the electrode is highly sensitive to iron ions with a slope around 47.8 mV/decade with a regression coefficient R2 = 0.96.展开更多
We have studied the optical spectra of low-dimensional semiconductor systems by calculating all possible optical transitions between electronic states. Optical absorption and emission have been obtained under differen...We have studied the optical spectra of low-dimensional semiconductor systems by calculating all possible optical transitions between electronic states. Optical absorption and emission have been obtained under different carrier population conditions and in different photon wavelengths. The line-shapes of the peaks in the optical spectrum are determined by the density of electronic states of the system, and the symmetries and intensities of these peaks can be improved by reducing the dimensionality of the system. Optical gain requires in general a population inversion, whereas for a quantum-dot system, there exists a threshold value of the population inversion.展开更多
Per-and polyfluorinated alkyl substances(PFASs)have been used since the 1950s as chrome mist suppressant(CMS)in the electroplating industry.In this study,various samples within an electroplating factory,the related wa...Per-and polyfluorinated alkyl substances(PFASs)have been used since the 1950s as chrome mist suppressant(CMS)in the electroplating industry.In this study,various samples within an electroplating factory,the related wastewater treatment facilities and surrounding environment at Hangzhou Bay in Southeast China were investigated for the occurrence and removal of PFASs.PFOS and 6:2 Cl-PFAES are predominant compounds in the samples.The PFASs in the bath solution of the workshops had some differences from the final releases,partly because of the historic usage and memory effects.PFOS and 6:2 Cl-PFAES were found in high concentration(5500 and 154.5 mg/L in influent,795 and 985 mg/L in effluent)in the electroplating Wastewater Treatment Plant(WWTP).The ultrafiltration and reverse osmosis(RO)treatment had a significant removal efficiency(74%e100%).On the other hand the reduction,precipitation and anaerobic/anoxic/oxic(A2/O)treatment had poor removal efficiency for PFASs.The receiving river samples had levels of PFASs between 300 and 1500 ng/L,and the concentrations of PFOS and 6:2 Cl-PFAES decreased with increasing distance to the municipal WWTP outlet due to dilution.The concentrations of PFOA in the river water samples were also high but might originate from other sources.The relevant ecological risk is noteworthy,especially for PFOS and PFOA for which limits have been defined.There is an urgent need to control plating industries in China and worldwide.Currently a GEF project related to Stockholm Convention implementation has reduced and possibly eliminated PFOS use and release in the plating industry in China.In addition,it will be important to evaluate and control the alternatives used.展开更多
文摘A complete quantum mechanical model for GaAs/AlGaAs quantum well infrared photodetectors(QWIPs) was presented. The photocurrent was investigated by the optical transition(absorption coefficient)between the ground state and the excited states due to the nonzero component of the radiation field along the sample growth direction. By studying the inter diffusion of the Al atoms across the GaAs/AlGaAs heterointer faces, the mobility of the drift diffusion carriers in the excited states was calculated. As a result, the measurement results of the dark current and the photocurrent spectra are explained theoretically.
基金support of the Higher Education Commission(HEC),Pakistan
文摘The effect of metal （Ti, Ni, and Au） electrodes on humidity sensing properties of electrospun TiO2 nanofibers was investigated in this work. The devices were fabricated by evaporating metal contacts on SiO2 layer thermally grown on silicon substrate. The separation between the electrodes was 90 μm for all sensors. The sensors were tested from 40% to 90% relative humidity （RH） by AC electrical characterization at room temperature. When sensors are switched between 40% and 90% RH, the corresponding response and recovery time are 3 s and 5 s for Ti-electrode sensor, 4 s and 7 s for Ni-electrode sensor, and 7 s and 13 s for Au-electrode sensor. The hysteresis was 3%, 5% and 15% for sensitivity of Ti, Ni, and Au-electrode sensors are Ti-, Ni-, and Au-electrode sensor, respectively. The 7.53 MΩ/%RH, 5.29 MΩ/%RH and 4.01 MΩ/%RH respectively at 100 Hz. Therefore Ti-electrode sensor is found to have linear response, fast response and recovery time and higher sensitivity as compared with those of Ni- and Au-electrode sensors. Comparison of humidity sensing properties of sensors with different electrode material may propose a compelling route for designing and optimizing humidity sensors.
文摘A complete quantum mechanical model for GaAs?AlGaAs quantum well infrared photodetectors(QWIPs) is presented here. The model consisted of four parts: (1) Starting with the description of the electromagnetic field of the infrared radiation in the QWIP, effective component of the vector potential <| A z |> along the QWIP growth direction ( z axis) due to the optical diffraction grating was calculated. (2) From the wave transmissions and the occupations of the electronic states, it was discussed that the dark current in the QWIP is determined by the drift diffusion current of carriers thermally excited from the ground sublevel in the quantum well to extended states above the barrier. (3) The photocurrent was investigated by the optical transition (absorption coefficient between the ground state to excited states due to the nonzero <| A z |> ). (4) By studying the inter diffusion of the Al atoms across the GaAs?AlGaAs heterointerfaces,the mobility of the drift diffusion carriers in the excited states was calculated, so the measurement results of the dark current and photocurrent spectra can be explained theoretically. With the complete quantum mechanical descriptions of (1 4), QWIP device design and optimization are possible.
基金Acknowledgements We thank the financial support from the National Natural Science Foundation of China （NSFC） （Nos. 21173017, 51272011, and 21275102）, the Program for New Century Excellent Talents in University （No. NCET-12-0610）, the Science and Technology Research Projects from Education Ministry （No. 213002A）, National ＂Twelfth Five-Year＂ Plan for Science ＆ Technology Support （No. 2013BAK12B06）, the ＂thousands talents＂ program for pioneer researcher and his innovation team, China, National Natural Science Foundation of China （Nos. 51432005 and Y4YR011001）, Beijing Municipal Commission of Science and Technology （Nos. Z131100006013004 and Z131100006013005）.
文摘Anodic oxidization （AO） is one of the most important methods available for fabricating mesoporous Al2O3 , which can be conducted at either high potential or low potential; however, the need for an external electricity power source limits its applications. In this work, a novel self-powered electrochemical anodic oxidization （SPAO） system was introduced for preparing mesoporous Al2O3 , by using newly-invented triboelectric nanogenerator （TENG） arrays driven by wind power. Using the controllable voltage output of the TENG arrays, the SPAO system was shown to regulate the pore depth and pore size of the mesoporous Al2O3 . In contrast to traditional AO systems, this technique takes advantage of the high output voltage of TENG arrays without any additional energy costs. In addition, the SPAO system can be used for the preparation of other mesoporous materials.
文摘Nano-composite, perovskite Ba(1- x - y)Sr(x)TiFe(y)O3, denoted as (BSTFe) in powder form was derived via sol-gel (SG) method followed by sintering at fixed temperature 750℃ for one hour. The chemical composition, morphology and structure of the powder samples were investigated by using X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The XRD characterization indicates formation of a cubic crystalline phase in the pure BST. A well defined perovskite phase with nano-crystallite sizes equal to about 34 nm was achieved from XRD for B10ST3F sample, while TEM study confirmed the obtained XRD results giving the following crystallite size value about 33.75 nm for the same sample. The dielectric A.C. conductivity was evaluated as a function of temperature and frequency ranging from 42 Hz up to 1 MHz.
文摘In this study, novel nickel oxide (NiO) flowers like nanostructures were fabricated onto gold coated glass substrate by hydrothermal method using high alkaline pH medium. The structural study of nickel oxide nanostructures was performed by scanning electron microscopy (SEM) and X-ray differaction (XRD) techniques. Nickel oxide nanostructures are highly dense, uniform and possess good crystalline quality. The so prepared structures were investigated for their electrochemical properties by cyclic voltammetry and amperometric techniques. The nickel oxide flower like morphology has shown good electrochemical performances for the oxidation of glucose. The presented sensing material was able to detected glucose in a wide range of concentration of 0.001 mM to 8 mM with a high sensitivity (123 μmA/mM) and regression coefficient of 0.99. Moreover, the NiO nanostructures based sensor is highly reproducible, stable, exhibiting a fast response time and selective in the response. All the obtained results indicate the potential use of this material in the development of enzyme free sensors for the detection of glucose.
文摘We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy （MBE）, The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current-voltage （l-V） measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49 ± 0.03 eV and capture cross-section of 8,57 ×10^-18 cm^2. Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy （SIMS） of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO,
文摘Wurtzite hexagonal ZnO semiconductor nano-rods (NRs) thin films were grown on silicon substrates and silver wire with diameter equal 68 nm. Sol gel (SG) and aqueous chemical growth (ACG) methods by two steps of preparation (seed layers and nano-rod growth) are used for samples preparation. The structural and morphological properties are evaluated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The proposed iron ion sensor has shown good linearity for a wide concentration range from 0.078 M/L to 0.26 M/L of iron ions. The results show that the electrode is highly sensitive to iron ions with a slope around 47.8 mV/decade with a regression coefficient R2 = 0.96.
文摘We have studied the optical spectra of low-dimensional semiconductor systems by calculating all possible optical transitions between electronic states. Optical absorption and emission have been obtained under different carrier population conditions and in different photon wavelengths. The line-shapes of the peaks in the optical spectrum are determined by the density of electronic states of the system, and the symmetries and intensities of these peaks can be improved by reducing the dimensionality of the system. Optical gain requires in general a population inversion, whereas for a quantum-dot system, there exists a threshold value of the population inversion.
基金the Major Science and Technology Program for Water Pollution Control and Treatment in China(Grant Nos.2017ZX07202001 and 2017ZX07202004).
文摘Per-and polyfluorinated alkyl substances(PFASs)have been used since the 1950s as chrome mist suppressant(CMS)in the electroplating industry.In this study,various samples within an electroplating factory,the related wastewater treatment facilities and surrounding environment at Hangzhou Bay in Southeast China were investigated for the occurrence and removal of PFASs.PFOS and 6:2 Cl-PFAES are predominant compounds in the samples.The PFASs in the bath solution of the workshops had some differences from the final releases,partly because of the historic usage and memory effects.PFOS and 6:2 Cl-PFAES were found in high concentration(5500 and 154.5 mg/L in influent,795 and 985 mg/L in effluent)in the electroplating Wastewater Treatment Plant(WWTP).The ultrafiltration and reverse osmosis(RO)treatment had a significant removal efficiency(74%e100%).On the other hand the reduction,precipitation and anaerobic/anoxic/oxic(A2/O)treatment had poor removal efficiency for PFASs.The receiving river samples had levels of PFASs between 300 and 1500 ng/L,and the concentrations of PFOS and 6:2 Cl-PFAES decreased with increasing distance to the municipal WWTP outlet due to dilution.The concentrations of PFOA in the river water samples were also high but might originate from other sources.The relevant ecological risk is noteworthy,especially for PFOS and PFOA for which limits have been defined.There is an urgent need to control plating industries in China and worldwide.Currently a GEF project related to Stockholm Convention implementation has reduced and possibly eliminated PFOS use and release in the plating industry in China.In addition,it will be important to evaluate and control the alternatives used.
