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Periodontitis is a chronic inflammatory disease, and periodontal ligament cells (PDLCs) are pivotal for osteogenesis. Circular RNAs (circRNAs) can regulate disease progression via targeting miRNA/mRNA axis. The purposes of this study were to explore the function and mechanism of circ_0138959 in periodontitis.Periodontitis cell model was established by lipopolysaccharide (LPS) treatment in PDLCs. RNA expression was determined by quantitative reverse transcription-polymerase chain reaction assay. Cell proliferation was detected using 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide assay. Wound healing and cell apoptosis were examined by wound healing assay and flow cytometry. Inflammatory cytokines were measured via Enzyme-linked immunosorbent assay. Osteogenic differentiation was assessed by Alkaline phosphatase and Alizarin red S staining assays. Western blot was used for protein detection. The target interaction was validated by dual-luciferase reporter assay.Circ_0138959 was overexpressed in periodontitis tissues and LPS-treated PDLCs. Downregulation of circ_0138959 attenuated LPS-induced inhibition of proliferation, wound healing and osteogenic differentiation but promotion of apoptosis and inflammation. Circ_0138959 acted as a miR-495-3p sponge, and the regulatory role of circ_0138959 in LPS-induced cell injury was achieved by sponging miR-495-3p. Additionally, miR-495-3p targeted TNF Receptor Associated Factor 6 (TRAF6) and miR-495-3p protected against LPS-induced cell dysfunction by targeting TRAF6. Circ_0138959 upregulated TRAF6 level via inhibiting miR-495-3p.This study suggested that circ_0138959 upregulated the TRAF6 expression by binding to miR-495-3p, consequently aggravating LPS-induced cell damages in PDLCs. Circ_0138959 might be a probable target for treatment of periodontitis.

Photocatalysis-assisted chemical mechanical polishing, in which the photocatalysis oxidation and silica abrasives polishing are combined, is a novel finishing technique for 4H–SiC wafer. This paper characterizes the effect of pressure and abrasives on the MRR and surface quality and discusses mechanical and chemical interaction based three slurries that resulted in maximum material removal rate (1.18 μm/h) with PCMP slurry. The polished silicon carbide wafer was examined with atomic force microscope, transmission electron microscope and X-ray photoelectron spectroscopy for surface quality and material removal mechanism. The results show that an atomically smooth and flat 4H–SiC (0001) surface (Ra about 0.247 nm) was obtained by PCMP. The interface of crystal and amorphous layer of 4H–SiC wafer was flat without introducing crystallographic subsurface damage, and the atoms and lattice fringes of the crystal layer are arranged in regular order. The existence of a thin silicon oxycarbide layer, which are various forms of functional groups such as Si–C, Si–C–O, Si–O, Si4C4O4, C–O, and C = O, at the interface. And, it also demonstrates that the amorphous layer is composed of oxide layer (4–6 nm) and distorted layer. The silicon carbide surface is mechanically activated, oxidized and mechanically removed in turn, which is the main method of material removal.

The unique properties of SiC not only originally promise superior electrical performances of SiC power devices, but also offer more margins in power devices designing. For example, different combinations of doping concentration and thickness of N-drift layer of SiC IGBT can be used to block same high-voltage. However, in the optimization of N-drift layer, we typically only consider the maximum breakdown voltage and carrier lifetime related performances, and the influences of doping concentration and thickness of N-drift layer are usually ignored. In this paper, we comprehensively study their influences on both static and dynamic performances of 15kV SiC IGBT by TCAD simulations. It is found that a lower N-drift doping concentration can achieve better trade-off between VON and Eoff, and enlarge the RBSOA. Nevertheless, it also causes higher voltage slop (dv/dt) and current slop (di/dt), thus more electromagnetic interference (EMI) related issues. Therefore, it is necessary to reconsider optimizing N-drift layer for high-performance SiC IGBTs.

Objective: Acne is a chronic skin disease that involves four key pathogenic factors: excess sebum production, ductal epidermal hyperproliferation, Propionibacterium acnes (P. acnes) colonization, and skin inflammation. Mangostins are well-known for their anti-bacterial and anti-inflammatory effects, suggesting that mangostins may have therapeutic potential for acne. The present study aimed to explore the anti-acne effects of mangostins from the perspective of multiple pathogenic mechanisms of acne. Methods: The effects of α- and γ-mangostins on the growth of P. acnes and lipase activity were analyzed. Their effects on P. acnes-induced keratinocyte proliferation were examined by CCK-8. The expression of inflammatory genes and activation of NF-κB and MAPK signaling pathways were detected by quantitative real-time PCR and western blotting, respectively. Results: Alpha- and γ-mangostins not only inhibited the growth of P. acnes, but also reduced the proliferation of keratinocytes induced by heat-killed P. acnes. Furthermore, α- and γ-mangostins were able to suppress P. acnes-induced expression of pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6 in keratinocytes by inhibiting the activation of NF-κB and MAPK signaling pathways. Discussion and conclusions: Mangostins appeared to possess multiple anti-acne activities, including the inhibition of P. acnes growth, regulation of keratinocytes proliferation, and attenuation of skin inflammatory reaction. Hence, mangostins might be developed into a potential therapeutic agent for the treatment of acne.

High-quality VO 2 films have been successfully synthesized on SiO 2 /Si substrates by a simple and efficient method in a tube furnace. The as-synthesized VO 2 films were structurally uniform and single-crystalline. These films show a large resistance change of more than four orders of magnitude with a 5 K width of the hysteresis loop as the temperature is cycled through the phase transition. VO 2 thin-film devices have been fabricated by reactive ion etching (RIE) and deposition processes. The current response of devices under light illumination and bias exhibited a higher sensitivity and a much wider pressure range than that without light illumination. Experimental data also revealed that the current response of a VO 2 film device shows an approximately linear dependence on the logarithm of air pressure. These high-quality VO 2 thin films with excellent properties have potentially promising application in vacuum sensor.

The electron emission model of a negative electron affinity graded-bandgap AlGaAs/GaAs electron-injection cathode was developed from two-dimensional continuity equations. The emission current was obtained from a simulation of the model, and the emission current efficiency and emission current per unit length were calculated. Based on the simulation results and preparation conditions, the range of optimum parameters for the cathode structure were determined. The ranges of optimum thickness for the p-AlGaAs and the graded-bandgap p-AlGaAs layers were 0.05–0.15 μm and 0.1–0.3 μm, respectively. The optimum width of the base electrode ranged from 1 to 4 μm, and the optimum molar ratios of Al in the p-AlGaAs and the n-AlGaAs layers were 0.2–0.3 and 0.4–0.5, respectively. This abrupt PN heterojunction inhibited the hole current and increased the emission current efficiency, with a maximum value of 25.3%. According to the emission current per unit length, the optimum range of width of emission unit surface was 6 to 10 μm, and the peak emission current per unit length reached 43.2 μA/μm.

SiC GTO is one of the most powerful power devices and very promising in high power applications such as HVDC and MW traction. However, the die size of SiC GTO is limited by the material defects, resulting in small current handling capability of discrete devices. Different from the situation in Si GTOs that parallel operation is never practically feasible, it is potential for paralleled SiC GTOs to balance their static currents naturally owing to the exhibited positive temperature coefficient of on-resistance in their temperature-dependent forward current-voltage characteristics according to our recent study. This paper focuses on analyzing the parallel operation of SiC GTOs. The temperature-dependent forward conduction characteristic and dynamic current sharing characteristics of SiC GTO is firstly investigated. And then the turn-off process is analyzed to explain the reason why turn-off failure occurs. Some possible solutions have also been proposed and verified to solve the turn-off failure problem. Therefore, the feasibility of parallel operation of SiC GTOs is demonstrated, and this will further help improve the power handling capability of SiC GTO based power electronics systems.

In this brief, an evaluation is made on the steady-state and dynamic electrical characteristics of high voltage Silicon Carbide (SiC) Insulated Gate Bipolar Transistor (IGBT). Through two-dimensional (2-D) numerical simulation, the impact of the key parameters of the device cell on the performance trade-off between dynamic switching noise and power dissipation is studied. With carrier lifetime in the drift layer enhanced, the generation of high dv/dt noise can be suppressed to a certain extent, but the slowdown of turn-off transient and the resulting increased turn-off power loss weakens device’s maximum operation frequency. It is revealed that the width of JFET region is important for the design of forward voltage drop V on and onstate power loss as a narrow JFET greatly limits the carrier transport into drift region. The introducing of Current Enhancement Layer (CEL) is shown to be an effective way to control carrier injection at the emitter side, though its extension will get the turn-off loss E off increased. With a CEL of moderate doping concentration and extension of approximately 1 μm, the voltage rising rate of SiC IGBT under punch through can be reduced while the frequency capability keeps almost unaffected.

A photoemission model of graded band-gap AlGaAs/GaAs wire NEA photocathode is developed based on the numerical solution of coupled Poisson and continuity equations. The emission current density and integral sensitivity of graded band-gap AlGaAs/GaAs wire photocathode as a function of incident light wavelength, Al composition range, and wire length, are simulated according to the model. The simulation results show that, compared with the GaAs (Al composition 0) wire photocathode, the peak integral sensitivities for the photocathodes with wire width of 1 µm and linearly graded Al composition ranges of 0 to 0.1, 0.2, 0.3, and 0.4 increase by 29.5%, 38.5%, 42.1%, and 43.8%, respectively. The optimum wire lengths are 4.7, 5.9, 7.1, and 8.4 µm for the wire photocathodes with Al composition ranges of 0 to 0.1, 0.2, 0.3, and 0.4, respectively.

The extremely high dv/dt of 4H-SiC insulated gate bipolar transistor (IGBT) becomes the major concern in its next-generation large-volume power conversion applications because severe electromagnetic interference (EMI) is induced. However, the root reason for its high dv/dt and the method of suppressing EMI have not been extensively investigated yet. In this paper, we proposed a novel physical model for SiC IGBT to identify the major limiting device design parameters of dv/dt during switching transients. The influences of SiC IGBT’s design parameters on its dv/dt and power dissipation are quantitatively analyzed by means of the physical model. Comparisons between the theoretical predictions and technology computer-aided design simulation results validate the physical model. The results on design optimization of a 18 kV n-channel SiC IGBT shows that 80% reduction of dv/dt and 60% reduction in turn-off power dissipation are achieved simultaneously without sacrificing its forward voltage drop.

A GaN-based pin neutron detector with a 6LiF conversion layer was fabricated, and can be used to detect thermal neutrons. Measurement of the electrical characteristic of the GaN-based pin neutron detector showed that the reverse leakage current of the neutron detector was reduced significantly after deposition of a 6LiF conversion layer on the detector surface. The thermal neutrons used in this experiment were obtained from an 241Am–Be fast neutron source after being moderated by 100-mm-thick high-density polyethylene. The experimental results show that the detector with 16.9-μm thick 6LiF achieved a maximum neutron detection efficiency of 1.9% at a reverse bias of 0 V, which is less than the theoretical detection efficiency of 4.1% calculated for our GaN neutron detectors.

Schottky diode nuclear radiation detectors based on semi-insulating gallium-arsenide (GaAs) wafers were fabricated. The minimum leakage current and current density of the detectors were 7.8 nA and 2.5 × 10−7 A/cm2, respectively, at a reverse bias of 100 V. The Schottky GaAs detectors were subjected to 10 MeV electron irradiation with a radiation dose of 0 to 200 kGy. Pre- and post-irradiation detectors were characterized by current–voltage, charge collection efficiency (CCE), and alpha-particle pulse-height spectroscopy. The detection efficiency of all detectors improved after irradiation, which may be attributed to defects induced by high-energy electron irradiation increasing the inhomogeneity of semi-insulating GaAs wafers. However, the energy resolution and CCE of the post-irradiation detectors decreased. After electron irradiation, the post-irradiation detectors were annealed at 200 °C for 5 min in nitrogen. The CCE of the annealed detectors improved, which suggests that the damages caused by high-dose electron irradiation can be repaired partially by annealing at 200 °C.

With the development of the energy internet, the integrated energy system that takes the power system as the main body and integrates heat energy, natural gas and other energy forms has gradually become a new situation of energy utilization. In view of the uncertainty of wind power and load, an integrated electricity and natural-gas energy system scheduling model considering multi-energy storage systems was established in this paper. Finally, testing results verify the effectiveness of the proposed method.

Schisandrin B (Sch B), an active extract of Schisandra chinensis, has demonstrated antioxidant activity in a number of in vitro and in vivo models. In the present study, the capacity of Sch B to protect against oxidative injury in keratinocytes using the human keratinocyte‑derived HaCaT cell line was investigated. To induce oxidative injury, tert‑Butyl hydroperoxide (tBHP) was employed. The results indicate that Sch B efficiently reduced tBHP‑induced cell death, reactive oxygen species (ROS) generation, protein oxidation, lipid peroxidation and DNA damage. Sch B also effectively attenuated the loss of mitochondrial membrane potential (MMP), and restored adenosine triphosphate (ATP) levels in tBHP‑injured HaCaT cells. Furthermore, Sch B enhanced the expression of key antioxidant enzymes, including catalase, heme oxygenase‑1, glutathione peroxidase, and superoxide dismutase, and further engaged the nuclear factor‑erythroid 2‑related factor 2 (Nrf2) signaling pathway by modulating its phosphorylation through activating multiple upstream kinases, including protein kinase B, adenosine monophosphate‑activated protein kinase and mitogen‑activated protein kinases (MAPKs). The present study suggests that Sch B provides a protective effect in keratinocytes in response to oxidative injury via reinforcing the endogenous antioxidant defense system. Therefore, it may be applied as an adjuvant therapy or in health foods to delay the skin aging process and the onset of skin diseases caused by oxidative stress.

The device-related parameters of 0.5eV Ga0.75In0.25Sb TPV cell were analyzed by considering the effects of carrier recombination and incident radiation spectra. Regarding the investigated device, we had demonstrated that the optimum structure of the device consisted of a 0.2-0.5μm n-type baser and a 4.5-6μm p-type emitter with a doping concentration of 1-3×1017cm-3. The Auger recombination sets an ultimate limit on performance of the device; however, it needs a dislocation density of Nt 6Ω/cm2 to approach the Auger-limited performance. An analysis on incident radiation spectra showed that the energy conversion efficiency can be improved by increasing the temperature of the radiator and the sub-bandgap photo recirculation efficiency.

The modulation transfer function (MTF) of graded band-gap AlGaAs/GaAs reflection-mode photocathodes was determined using two-dimensional Poisson and continuity equations through numerical method. Based on the MTF model, we calculated the theoretical MTF of graded and uniform band-gap reflection-mode photocathodes. We then analyzed the effects of Al composition, wavelength of incident photon, and thicknesses of AlGaAs and GaAs layer on the resolution. Calculation results show that graded band-gap structures can increase the resolution of reflection-mode photocathodes. When the spatial frequency is 800 lp/mm and wavelength is 600 nm, the resolution of graded band-gap photocathodes generally increases by 15.4–29.6%. The resolution improvement of graded band-gap photocathodes is attributed to the fact that the built-in electric field in graded band-gap photocathodes reduces the lateral diffusion distance of photoelectrons.

A photodetection model for AlGaAs/GaAs nanowire photodetectors with graded composition is developed based on the numerical solution of coupled Poisson and continuity equations. Photocurrents and spectral sensitivities of nanowire photodetectors have been simulated as a function of Al content range, the wavelength of the incident light, the length of the nanowire, and contact types. The results demonstrate Ohmic–Schottky devices have the highest sensitivities among the four types of nanowire devices, which can be attributed to the strong built-in electric field induced by the graded composition and the dominant unidirectional built-in electric field due to the Schottky barrier. Schottky–Schottky devices show the lowest sensitivities due to the additional blocking effect of the Schottky barrier. The optimum nanowire length in which an Ohmic–Schottky structured nanowire photodetector can achieve maximum sensitivity is 7.4 μm for a nanowire with a linearly graded Al content range of 0–0.4 (x Al = 0.4). The optimum nanowire lengths for Ohmic–Ohmic (x Al = 0.3), Schottky–Schottky (x Al = 0.1), and Schottky–Ohmic (x Al = 0.0) nanowire devices are 6.5, 3.5, and 11 μm, respectively.

The nuclear factor of activated T-cells (NFAT) is a family of transcription factors, essential for T-cell activation. Norisoboldine (NOR), an isoquinoline alkaloid from Radix linderae, has been demonstrated to possess anti-inflammatory activity.This study examines NOR's effect on NFAT activation and its therapeutic potential for atopic dermatitis (AD).The transcriptional activity of NFAT was examined with luciferase reporter assay, using K562-luc cells, stimulated with 20 ng/mL PMA plus 1 μM ionomycin. NFAT dephosphorylation was examined by immuno-blotting in K562-luc cells and Jurkat cells. Interleukin-2 (IL-2) expression in Jurkat cells was examined by real-time PCR. A mouse model of dermatitis, induced by 2,4-dinitrochlorobenzene (DNCB), was used to test NOR's therapeutic potential for AD.NOR, dose-dependently, inhibited PMA and ionomycin-induced NFAT reporter gene expression in K562-luc cells in the range of 2-50 μM. NOR also inhibited PMA and ionomycin-induced NFAT dephosphorylation in K562-luc cells and Jurkat cells. Consequently, NOR suppressed PMA plus ionomycin-induced IL-2 expression in Jurkat cells. The administration of NOR (10 mg/kg, i.p.), alleviated DNCB-induced dermatitis in mice, by the reduction of ear swelling and attenuation of inflammatory infiltration into ear tissue. Moreover, mRNA levels of INF-γ, TNF-α, IL-4 and IL-6 in ears of NOR-treated mice were reduced by 78.4, 77.8, 72.3 and 73.9%, respectively, compared with untreated controls.This study demonstrates that NOR inhibits NFAT activation in T-cells and alleviates AD-like inflammatory reaction in a DNCB-induced dermatitis model, highlighting NOR as a potential therapeutic agent for AD.

We reported a method combining the gas–liquid interface method and inductively coupled plasma (ICP) to fabricate highly-ordered nanowire arrays on a 2 inch GaAs substrate. A large-area and highly-ordered SiO2 nanosphere monolayer was fabricated and the GaAs nanowire array was etched by ICP. The flow rates and ratios of the etching gases were studied. Finally, highly-ordered GaAs nanowire arrays with high quality surface morphology were obtained with the volumetric flow rates at 9 sccm and 21 sccm for BCl3 and N2 gases, respectively. Reflectance of the samples was found to be consistently below 10%, the lowest being 3%.

The resolution model of graded doping and graded composition reflection-mode AlGaAs/GaAs photocathode is solved numerically from the two-dimensional continuity equations. According to the model, the theoretical modulation transfer functions (MTFs) of different structure reflection-mode photocathodes were calculated, and the effects of doping concentration, Al composition, AlGaAs and GaAs layer thickness on the resolution of cathodes were analyzed. The simulation results show that both graded composition and graded doping structures can increase the resolution of photocathode, and the effect of graded composition structure is more pronounced. The resolution improvement is attributed to the built-in electric field induced by a graded composition or doping structure. The simulation results also show that the MTFs of cathodes are affected by the AlGaAs and GaAs layer thickness.

Two types of negative electron affinity gallium arsenide (GaAs) wire array photocathodes were fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material. High density GaAs wire arrays with high periodicity and good morphology were verified using scanning electron microscopy, and photoluminescence spectra confirmed the wire arrays had good crystalline quality. Reflection spectra showed that circular GaAs wire arrays had superior light trapping compared with square ones. However, after Cs/O activation, the square GaAs wire array photocathodes showed enhanced spectral response. The integral sensitivity of the square wire array photocathodes was approximately 2.8 times that of the circular arrays.

Objective The aim of the study was to evaluate the responses and toxicities of liposome encapsulated paclitaxel (LEP) plus cisplatin (DDP) (LP regimen) and paclitaxel (TAX) plus DDP (TP regimen) in the treatment of advanced non-small cell lung cancer (NSCLC).

Scanning photocurrent microscopy is a powerful tool for investigating charge transfer and internal fields, which strongly influence carrier statics and dynamics in semiconductor nanowires. We performed comprehensive numerical modeling of the carrier dynamics of graded-composition and graded-doping AlGaAs nanowires to achieve a greater understanding of these nanowires. The simulation results indicated that the built-in electric field changes the shape of the scanning photocurrent microscopy profiles, which helped us to judge the dopant level, Al composition range and doping type of the material. The simulation results also assess the potential of the scanning photocurrent techniques in graded-doping and graded-composition nanowire properties.

The quantum efficiency equations of two kinds of reflcetion-mode GaAs photocathodes (GaAs-GaAs and AlGaAs-GaAs) with back interface recombination velocity have been solved from the diffusion equations. According to these quantum efficiency equations, the integral sensitivities as a function of active layer thickness, electron diffusion length and back interface recombination velocity for both kinds of cathodes are simulated. Through the theoretical simulation, we found the active layer thickness for AlGaAs-GaAs cathodes has an optimum value at which the cathodes achieve the maximum sensitivity. Under most conditions, the theoretical integral sensitivities of AlGaAs-GaAs cathodes are greater than that of GaAs-GaAs cathodes. This is attributed to that AlGaAs-GaAs interface barrier reflects most photoelectrons back into the active layer. The theoretical spectral response of both kinds of cathodes is also simulated. We found that the increase in integral sensitivity of AlGaAs-GaAs cathodes mainly reflects in the increase of spectral response of long wavelength photons.

Negative electron affinity GaAs wire-array photocathodes have been fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material followed by Cs-O activation. Scanning electron microscope has revealed that the thus obtained high-density GaAs wire arrays had high periodicity, large height, and good morphology. Photoluminescence spectra indicated the wire arrays were of good crystalline quality and free from any obvious damage. Compared to the original GaAs wafer, the photoluminescence peak positions of the wire arrays were somewhat red-shifted, which may be attributed to the temperature effect and strain relaxation. The wire-array structures showed significantly reduced light reflection compared with the original wafer due to the excellent light-trapping effect. Cs-O activation experiments of the GaAs wire arrays have been performed to reveal the effect of incident angle on quantum efficiency. The results show that maximum quantum efficiency was obtained at about 30°. Given these unique electrical and optical properties, a GaAs wire-array photocathode is an attractive alternative to its planar-structured counterpart.

The effects of AlGaAs/GaAs layer thickness and Al composition range on the spectral response and integral sensitivities of reflection-mode graded band-gap AlGaAs/GaAs photocathodes have been investigated and simulated. The experimental results demonstrate that the spectral response over the wavelength region of interest for graded band-gap photocathodes is greater than that for uniform band-gap cathodes, and the increase in long-wavelength response is more pronounced. These results can be attributed to the built-in electric field in the graded band-gap AlGaAs layer. We established a spectral response model of graded band-gap photocathodes based on the numerical solution of coupled Poisson and continuity equations. According to the model, we calculated the theoretical spectral response and sensitivities of graded band-gap cathodes, and found the optimum Al(x)Ga(1-x)As layer thicknesses are 6, 10, 16, and 22 μm for the reflection-mode cathodes with linearly graded Al composition x ranges of 0 to 0.1, 0.2, 0.3, and 0.4, respectively.

Gallium arsenide (GaAs) nanowire array (NWA) photocathodes have unique electrical and optical properties. Based on studies about photon absorption, band structure, and electron transport properties of GaAs nanowire, a photoemission model for GaAs NWA photocathodes is established. According to the model, we simulate and analyze the photocurrent, spectral response, and absorption properties of ordered GaAs NWA photocathodes. The results present a very interesting phenomenon; the photocurrent and spectral response peak at incident angles of 20° and 30°, respectively. These special properties of NWA cathodes differentiate them from their thin film counterparts. We also analyze the effects of nanowire length and diameter on the photocurrent of NWA cathodes, and find the optimum height of the nanowires is 10 μm. This study shows that NWAs exhibit higher absorbance and excellent charge transport. Thus, GaAs NWA photocathodes are excellent candidates for electron sources.

The resolution model of a graded doping and graded composition transmission-mode AlGaAs/GaAs photocathode is solved numerically from the two-dimensional continuity equations. According to the model, we calculate the theoretical modulation transfer function (MTF) of different graded doping and graded composition structures. The simulation results show that both graded composition and graded doping structures can increase the resolution of the photocathode. The exponentially doping and linear composition photocathode has the maximum resolution among the possible graded doping and graded composition photocathodes. The resolution improvement is attributed to the built-in electric field induced by a graded composition or graded doping structure. The simulation results also show that the MTFs of AlGaAs/GaAs cathodes increase as the AlGaAs layer thickness decreases, or the incident light wavelength increases.

By calculating the energy distributions of electrons reaching the photocathode surface and solving the Schrödinger equation for an electron tunneling through the surface potential barrier, we have obtained an equation to calculate the energy distributions of electrons emitted from reflection-mode Cs-covered GaAs photocathodes based on a two-minima diffusion model. According to the equation, we studied the effects of incident photon energies, diffusion lengths, and surface potential barrier on the electron energy distributions. The equation was also used to fit the measured electron energy distribution curves and the cathode performance parameters were obtained from the fitting. The Γ and L peaks in the theoretical curves are in agreement with the peaks in the experimental curves. The fitted barrier thickness 1.7 Å exactly reflects the GaAs-Cs dipole layer thickness.

The quantum efficiency equations of two different structure reflection-mode GaAs photocathodes with back interface recombination velocity have been solved from the diffusion equations. One structure consists of GaAs substrate and an epitaxial GaAs active layer (GaAs-GaAs) and another structure consists of GaAs substrate, an epitaxial AlGaAs buffer layer, and a GaAs active layer (AlGaAs-GaAs). The experimental results show that the quantum efficiency of long-wavelength photons and the integral sensitivities for GaAs-GaAs cathodes both increase with the increase in the active layer thickness, which is due to the increase of electron diffusion length. The quantum efficiency of long-wavelength photons and the integral sensitivity of AlGaAs-GaAs cathodes are greater than those of GaAs-GaAs cathodes with an identical active layer thickness, which is attributed to the AlGaAs buffer layer. The buffer layer can reflect electrons and improve the quality of the GaAs active layer. Through the theoretical simulation, we found the active layer thickness for AlGaAs-GaAs cathodes has an optimum value at which the cathodes achieve the maximum sensitivity.