Enhanced blue-green response of nanoarray AlGaAs photocathodes for underwater low-light detection.

Underwater optical communication and low-light detection are usually realized via blue-green laser sources and blue-green light-sensitive detectors. Negative-electron-affinity AlGaAs photocathode is an ideal photosensitive material for ocean exploration due to its adjustable spectrum range, long working lifetime, and easy epitaxy of materials. However, compared with other photocathodes, the main problem of AlGaAs photocathode is its low quantum efficiency. Based on Spicer's three-step photoemission model, nanoarray structures are designed on the surface of AlGaAs photocathode to improve its quantum efficiency from two aspects of optical absorption and photoelectron transport. Through simulation, it is concluded that the cylinder with diameter of 120 nm and height of 600 nm is the best nanoarray structure, and its absorptance is always greater than 90% in the 445∼532 nm range. Moreover, the absorptance and quantum efficiency of the cylinder nanoarray AlGaAs photocathode are less affected by the incident angle. When the angle of incident light reaches 70°, the minimum absorptance and quantum efficiency are still 64.6% and 24.9%. In addition, the square or hexagonal arrangement pattern of the nanoarray has little effect on the absorptance, however, a reduction in the overall emission layer thickness will decrease the absorptance near 532 nm.

Hybrid thermionic-photovoltaic converter with graphene-on-semiconductor heterojunction anode for efficient electricity generation.

Thermionic energy converters are solid-state heat engines to produce electricity with significant potential, whereas the output voltage is constrained by the work function difference between cathode and anode. In this work, we originally apply a graphene-on-semiconductor heterojunction anode to a thermionic-photovoltaic (TIPV) converter to output additional voltage. Thermionic electrons are injected into the graphene layer and then recombined with photogenerated holes. Photogenerated electrons are extracted from the conduction band and reinjected into the cathode through an external load. A proof-of-concept demonstration of the TIPV converter is developed with barium surface-engineered cathode and anode. Open-circuit voltage is increased from ∼0.9 to ∼1.9 V by comparing with an identical configuration without graphene layer. The TIPV converter yields a power generation density of 2.7 kW/m2 with an electronic efficiency of ∼27%. This work paves the way for the development of TIPV converter toward high power density.

City Brand Image Building and Its Impact on the Psychological Capital of New Entrepreneurs Following Cultural Construction.

The purpose of the study is to provide effective direction and ideas for urban modernization and promote the development of the city innovation economy and the stability of the employment rate. First, the main contents and influencing factors of urban culture construction are introduced. Second, the construction of city cultural images and the social capital of new entrepreneurs are discussed, and the relationship between the two is analyzed. Then, Interpretative Structural Modeling Method (ISM) is put forward, and five influencing factors of city entrepreneurial environments are expounded. A questionnaire survey is designed based on the ISM model, and a nationwide survey of new entrepreneurs is carried out. The survey results show that entrepreneurs of different genders, ages, and educational levels have different degrees of concern for the city image. Among them, the entrepreneurs with different educational levels have the most obvious difference in their attention to the cultural image of the city (p < 0.05). In addition, public transportation, educational conditions, tourism resources, air quality, and image orientation are the most obvious factors affecting the construction of city brand images (p < 0.05). The influence of the educational level of residents and investment environment on new entrepreneurs is more prominent. This shows that in the process of shaping the city brand image, the improvement of city culture is helpful for new enterprises. The more perfect the city culture is, the more attractive it will be for highly educated entrepreneurs. The study can help relevant decision-makers to plan the future development direction of the city more accurately and realize the stable development of city brand images.

Spectral response characteristics of the transmission-mode aluminum gallium nitride photocathode with varying aluminum composition.

In order to research spectral response characteristics of transmission-mode nanostructure aluminum gallium nitride (AlGaN) photocathodes, the AlGaN photocathodes materials with varied aluminum (Al) composition were grown by metalorganic chemical vapor deposition (MOCVD) and its optical properties were measured. The Al compositions of each AlGaN film of the photocathodes were analyzed from their adsorption properties curves; their thickness was also calculated by the matrix formula of thin-film optics. The nanostructure AlGaN photocathodes were activated with the Caesium-Oxygen (Cs-O) alternation, and after the photocathode was packaged in vacuum, their spectrum responses were measured. The experimental results showed that the trend of spectrum response curves first increased and then decreased along with the increasing of the incident light wavelength. The peak spectrum response value was 17.5 mA/W at 255 nm, and its quantum efficiency was 8.5%. The lattice defects near the interface of the AlGaN heterostructure could impede the electron motion crossing this region and moving toward the photocathode surface; this was a factor that reduces the electron emission performance of the photocathodes. Also, the experimental result showed that the thickness of each AlGaN layer affected the electron diffusion characteristics; this was a key factor that influenced the spectrum response performance.

Research on quantum efficiency for reflection-mode InGaAs photocathodes with thin emission layer.

In order to understand the photoemission mechanism of the reflection-mode InGaAs photocathode with a thin emission layer, the formula describing reflection-mode quantum efficiency is revised by solving the one-dimensional continuity equation, in which the electrons generated in the GaAs buffer layer are considered. Compared with the conventional formula, the revised formula is proved to be more suitable for the reflection-mode InGaAs photocathode with a thin emission layer. In experiment, the InGaAs sample goes through two-step surface preparation including a wet chemical cleaning process and a heat treatment process. Then the sample is activated by Cs/O and the experimental quantum efficiency curves are measured simultaneously every other hour. The measured results show that the shapes of the quantum efficiency curves degrade with time because of the contamination of residual gases in the vacuum system. All the quantum efficiency curves are well fitted by the revised formula.

Photoemission performance of thin graded structure AlGaN photocathode.

In order to research a high-efficiency AlGaN photocathode, the AlGaN photocathodes with varied Al composition (0.68 and 0.4) and uniform Al composition (0.24) were grown. The photocathodes were activated by Cs adsorption and received their spectral response via multi-information system. Results show that the absorption rate of the AlGaN photocathode with varied Al composition is half of the AlGaN photocathode with uniform Al composition, but the quantum efficiency of the photocathode with varied Al composition is approximately 29% higher than that of the photocathode with uniform Al composition. The built-in field within the emission layer of the AlGaN photocathode with varied Al composition is much higher than that of the photocathode with uniform Al composition, which is the main factor that promotes the photoelectron movement toward the photocathode surface and improves photoemission performance of the AlGaN photocathode.

Effect of surface cleaning on spectral response for InGaAs photocathodes.

Photocathode surface treatment aims to obtain high sensitivity, where the key point is to acquire an atomically clean surface. Various surface cleaning methods for removing contamination from InGaAs photocathode surfaces were investigated. The atomic compositions of InGaAs photocathode structures and surfaces were measured by x-ray photoelectron spectroscopy and Ar ion sputtering. After surface cleaning, the InGaAs surface is arsenoxide-free, however, a small amount of Ga2O3 and In2O3 still can be found. The 1:1 mixed solution of hydrochloric acid to deionized water followed by thermal annealing at 525°C has been demonstrated to be the best choice in dealing with the surface oxides. After the Cs/O activation, a surface model was proposed where the oxides on the surface will lead to a positive electron affinity, adversely affecting low-energy electrons escaping to the vacuum, which is reflected by the photocurrent curves and the spectral response curves.

Effect of Cs adsorption on the photoemission performance of GaAlAs photocathode.

The effect of Cs adsorption on the photoemission performance of a reflection-mode GaAlAs photocathode in an ultrahigh vacuum chamber has been investigated. The experiments for Cs/O activation, multiple recaesiation, and degradation are performed on a GaAlAs photocathode. Meanwhile, the Cs/O activated and recaesiated photocurrent curves, degraded photocurrent curves, and spectral response curves are measured and analyzed. Besides, the performance parameters of the photocathodes are obtained by using the formula to fit with the experimental quantum efficiency curves. The results show that the Cs atoms not only make the atomically clean surface form the negative electron affinity, but also make the degraded photocathode recover to a good level. The quantum efficiency and the lifetime of GaAlAs photocathode become lower with increasing the recaesiation times.

Influence of Al fraction on photoemission performance of AlGaN photocathode.

To research the photoemission performance of a transmission-mode Al(1-x)Ga(x)N photocathode, Al0.24Ga0.76N and GaN photocathodes with the same structure were activated, their spectral responses were measured using a multi-information measurement system at room temperature, and the photocathode parameters were obtained by fitting quantum efficiency curves. The results showed that both the reflective-mode and transmission-mode spectral responses of the AlGaN photocathode were lower than those of the GaN photocathode. Compared with the GaN photocathode, the short-wavelength spectral response of the Al0.24Ga0.76N photocathode was less seriously affected by lattice defects between the buffer and emission layers. The Al atom at the AlGaN photocathode surface could affect the optimal Cs adsorption position, which mainly affects the surface electron escape probability of the photocathode.

Stability of negative electron affinity Ga0.37Al0.63As photocathodes in an ultrahigh vacuum system.

The stability of negative electron affinity Ga0.37Al0.63As photocathodes in an ultrahigh vacuum system has been investigated. The degraded photocurrents of the Cs/O activated Ga0.37Al0.63As photocathodes under illumination with different intensity are recorded in real time, and the quantum efficiencies are measured after the degradation. The degraded quantum efficiencies of the photocathode under no illumination are measured at regular intervals. Multiple activations are performed on the Ga0.37Al0.63As photocathode, after that the quantum efficiencies and the degraded photocurrents are measured. The results indicate that the lifetime of the Ga0.37Al0.63As photocathode increases as the intensity of illumination decreases, and is longer than that of the GaAs photocathode in the case of no illumination. Besides, the Ga0.37Al0.63As photocathode performed after the second activation would obtain optimal stability.

Attenuation performance of reflection-mode AlGaN photocathode under different preparation methods.

To research the attenuation performance of the AlGaN photocathode, three samples with the same structures grown by metalorganic chemical vapor deposition were activated with three different activation methods, which are called Cs-only, Cs-O, and Cs-O-Cs activation, respectively. The spectral responses and attenuated photocurrents of the three AlGaN photocathodes were measured. The results show that the Cs-O activated AlGaN photocathode exhibits the lowest attenuation speed in the first few hours, and the attenuation speed of the Cs-only activated one is fastest. After attenuating for 90 min, the attenuation photocurrent curve of the Cs-O-Cs activated sample is coincident with that of the Cs-O activated one. The main factor affecting the photocurrent attenuation is related to Cs atoms desorbed from the photocathode surface.

[The clinical staging and tissue bacterial quantification in the diagnosis of burn wound sepsis].

OBJECTIVE: To investigate and re-evaluate the relationship between burn wound sepsis and tissue bacterial quantity. METHODS: Thirty-two patients admitted during past 5 years were enrolled in the study. Bacterial isolation and quantity in burn wound tissue were carried out. Meanwhile clinical signs were evaluated for the staging of burn wound sepsis. RESULTS: 1) Bacterial invasion could be identified in 123 pieces of tissue samples from 32 patients. Samples with tissue bacterial quantity > or = 10(5)/g were found in 82 subeschar tissue samples, and 41 samples with bacteria <10(5)/g. Subeschar tissue samples with bacterial quantity > or = 10(5)/g could be determined in 68 samples from 18 patients, and < 10(5)/g in 20 samples from 5 cases. In addition, samples of subeschar tissue with bacterial quantity > or = 10(5)/g could only be found in some of the samples form 9 cases. 2) Burn wound sepsis could be classified into I-IV stages according to tissue bacterial quantification and clinical signs. CONCLUSION: Burn wound sepsis could be established by identification of bacterial invasion into living tissue with clinical symptoms of toxemia.