A PEO/CrAlSi composite coating of similar to 10 mu m thick on Zr-2 alloy was prepared by duplex plasma electrolytic oxidation (PEO) and filtered cathode vacuum arc deposition (FCVAD) techniques. The high temperature steam oxidation behavior of bare and PEO/CrAlSi-coated Zr alloys was performed in 1000-1200 degrees C. Their morphologies, microstructures, compositions and phase components were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and glow discharge optical emission spectrometer (GDOES). The effects of Al and Si elements on multilayers microstructure evolution of coated Zr-2 alloy at steam atmosphere were discussed. It was found that the composite coating significantly improved the high-temperature steam oxidation resistance of Zr-2 alloy. The mass gains of the PEO/CrAlSi-coated Zr-2 alloy after 3600 s exposure in 1000 degree celsius, 1100 degrees C and 1200 degrees C steam were 28 %, 29 % and 44 % of the bare alloy. Through the oxidations, Al diffused both inward and outward to the substrate and the surface regions, respectively. Formation of a top oxide layer (Al2O3, Cr2O3) greatly suppressed the inward oxygen diffusion. The Si enrichment in the PEO interlayer formed a Zr2Si layer, which inhibited the Cr-Zr interdiffusion at 1000 degree celsius and 1100 degree celsius. At 1200 degree celsius, the Zr2Si layer was oxidized and the CrZr2 phase was formed in the Zr alloy substrate especially at the beta-Zr/alpha-Zr(O) interface.

The initial discharge process of pulsed plasma electrolytic oxidation (PEO) on the 60% SiCp/2009 aluminum metal matrix composite (Al MMC) in silicate solution was monitored by acoustic emission (AE) technique. Parameters and correlations of AE signals on the Al MMC sample and under water were analyzed, and their generation mechanism was discussed. It was found that the peak amplitudes of AE signals and AE hits during the pulse time quickly increased with the increase of micro-discharge intensity, and the absolute energy of AE signals improved several orders of magnitude. Moreover, different from the peak amplitude, duration and rise time, the duration and count had a strong correlation. Elastic stress waves resulted from the microjet of plasma bubble collapse, the inner-surface friction inside discharge channel, the expansion-shrinkage process of plasma bubbles and micro-crack propagation during rapid solidification of melt are sources of AE signals on the Al MMC sample during the pulse time. However, the expansion-shrinkage process of plasma bubbles plays a key role in the generation of underwater AE signals. In the pause time of one pulse period, the bursting and moving of vapor bubbles result in weak AE signals. It is demonstrated that the AE technique can effectively characterize the features of micro-discharges within a pulse period.

Fiber components form the standard not only in modern telecommunication but also for future quantum information technology. For high-performance single-photon detection, superconducting nanowire single-photon detectors (SPDs) are typically fabricated on a silicon chip and fiber-coupled for easy handling and usage. The fiber-to-chip interface hinders the SPD from being an all-fiber device for full utilization of its excellent performance. Here, we report a scheme of SPD that is directly fabricated on the fiber tip. A bury-and-planar fabrication technique is developed to improve the roughness of the substrate for all-fiber detectors’ performance for single-photon detection with amorphous molybdenum silicide (MoSi) nanowires. The low material selectivity and universal planar process enable fabrication and packaging on a large scale. Such a detector responds to a broad wavelength range from 405 nm to 1550 nm at a dark count rate of 100 cps. The relaxation time of the response pulse is ~ 15 ns, which is comparable to that of on-chip SPDs. Therefore, this device is free from fiber-to-chip coupling and easy packaging for all-fiber quantum information systems.

Facing the demand for applications such as wide-area terrain mapping and space-based atmospheric measurements, there is an urgent need to develop miniaturized single-photon detection systems with low power consumption that can be adapted to airborne platforms. Superconducting nanowire single-photon detectors (SNSPDs) have been applied to quantum information, bioimaging, deep space communication and long-range lidar with the advantages of high quantum efficiency, low dark count rate and fast detection rate. However, traditional SNSPD usually operates at 2.1 K or even lower, and the required cryogenic systems are large in size and weight, which are not easy to apply to airborne platforms. Up to now, there has been no report on SNSPD applied to airborne platforms. How to apply SNSPD to airborne platforms is an urgent problem to be solved.In this work, we design and make an SNSPD with an operating temperature of 4.2 K. The superconducting detector chip is a four-channel photon-number-resolving device with a photosensitive area of 60 μm × 60 μm, which is coupled to a 200-μm-diameter fiber by a beam compression system with a quantum efficiency of 50% at 1064 nm and a temperature of 4.2 K. Finally, the time characteristics of a single channel are tested in response to different photon numbers. The timing jitter of four-photon response is smallest, and the half-height width is 110 ps. This work not only supports airborne applications, but also has positive implications for promoting the development of general-purpose miniaturized SNSPD systems and their applications.

In this paper, oxide coatings were prepared on Ti-48Al-2Cr-2 V alloy in 50 vol% glycerin solution by cathodic plasma electrolytic oxidation (CPEO) at 300 V-340 V for 5 min. The morphologies, microstructure and phase components of CPEO coatings were analyzed. Air acoustical and sample vibrational signals during the CPEO process were collected and their frequency spectra were analyzed. The electron temperature and electron concentration in plasma discharge envelope was calculated on the basis of optical emission spectroscopy (OES). The thickness and microhardness of oxide coating on gamma-TiAl alloy at 340 V reached to 26 mu m and 765 HV. The surface energy of CPEO coatings reduced to 24-28 mJ/m2 from 32.56 mJ/m2 of bare gamma-TiAl alloy. The CPEO coatings were composed of Al2TiO5, anatase, rutile and alpha-Al2O3 phases. The average electron temperature in plasma discharge zone was about 5500 K, which greatly enhanced the growth of CPEO coating on gamma-TiAl alloy. Furthermore, the frequency spectra of air acoustic and sample vibrational signals were related to the voltagetime and current-time evolutions in the CPEO process. The sample vibration is more sensitive than the air acoustic in diagnosing the spark discharge of CPEO process on the gamma-TiAl alloy cathode.

The purpose of this study was to indicate the effect of the presence of the carbon and nitrogen diffusion zone below the boride layers of Q235 low-carbon steel. The boride layers were produced by cathodic plasma elec-trolysis treatment (PET). Based on the results, the boride layer thickness on the treated samples at 260 V and 300 V varied from 10 mu m to 22 mu m. The XRD and GDOES analysis demonstrate that the boride layer on the treated samples mainly consists of single Fe2B phase, and the top loose layer mainly contain Fe2O3, Fe3C, Fe4N, and BN phases. The boride layers exhibited excellent scratch resistance compared to the bare Q235 steel. In addition, the plasma electron temperature was around 3000-4500 K, and the frequency spectra of acoustic signals were related to the voltage-time and current-time curves. At the high temperature and strong electric field, the decomposition reaction of electrolyte and the growth mechanism of the boride layers were discussed.

Superconducting nanowire single-photon detector (SNSPD) is one of the most mainstream single-photon detectors at present, which possesses excellent comprehensive performance, including low time jitter, high efficiency, low dark count, and wide spectrum. However, the traditional single-pixel SNSPD suffers a lack of spatial resolution and a small photosensitive surface, which becomes a bottleneck associated with optical coupling efficiency. In addition, a single-pixel detector has no ability to resolving the photon number, whose working speed cannot be further improved due to the existence of dead time. While array devices can make up for the above deficiencies. Therefore, the development of a large-area SNSPD array is the key to free-space photon detection and other applications. In recent years, the relevant researches have been conducted and great progress has been achieved. However, the large-area SNSPD array is facing some intractable problems, including complex process, low yield, and difficult fabrication, owing to the photosensitive surface consisting of a large number of superconducting nanowires. Photons imaging is verified with this device. At present, in the existing studies mainly used is the three-dimensional technology with complicated process steps to fabricate large array SNSPDs. How to simplify the process has become a research focus. In this work, we design an ultra-large area nanowire array structure and propose an innovative plane process. Taking advantage of the property that the electron beam resists HSQ (hydrogen silsesquioxane polymer) forming a silicon oxide electrical isolation layer after exposure, we fabricate a large array SNSPD with a simplified two-dimensional process and realize dimensionality reduction for the traditional three-dimensional process of a multilayer structure. By measurement in parallel, the devices enjoy high yield with no bad points found. In addition, a full-superconducting electrode is adopted in our design to reduce the thermal effect of resistors. We add series and parallel resistors in the pixels to divide the bias current evenly and expand the array scale optionally. At the same time, we also offer the design details of array SNSPDs, the related simulation of hot spots to verify the rationality of the design, the optimization of the preparation conditions of array devices, measurement scheme formulation, and other related work. This work provides an idea for designing and fabricating ultra-large array SNSPD, which is expected to be applied to the fabrication of megapixel array SNSPDs. Combined with an efficient readout circuit, a focal plane photon detection and imaging system with both a large field of view and high sensitivity can be realized.

Purpose The authors designed those experiments to test the sensitivity of graphene when it is exposed to NO2 gas, to find a way to decrease the recovery time of graphene and to find the difference effect between monolayer and bilayer graphene in the experiments. Design/methodology/approach The authors transferred graphene from film on Cu foil to NO2 sensor sample and measured the resistances of on monolayer and bilayer graphene when they were exposed to NO2 gas under different concentration; then, the authors obtained the results. Findings The results show that monolayer graphene exhibits a linear response when the NO2 concentration is below 20 ppm. But the monolayer graphene will not be so sensitive to NO2 gas when the concentration continues to reduce. The desorption time of monolayer graphene is longer when compared with bilayer graphene. It shows faster recovery time and higher response of bilayer graphene under low NO2 concentration. And the limit detectable NO2 concentration of bilayer graphene is 50 ppb. Desorption time of bilayer graphene is shortened to below 20 s under UV light. Originality/value The authors found a reliable way to decrease the recovery time of graphene when it is exposed NO2 gas and got the concrete data.

A NO2 sensor based on novel SnO2/graphene nanocomposite materials was proposed. Monolayer graphene was decorated with fin oxide via drop-casting and vacuum annealing, and the monolayer graphene was prepared using the chemical vapor deposition (CVD) method. The nanocomposites were characterized by Raman spectroscopy and a scanning electron microscope (SEM). The gas sensing capabilities of the SnO2/graphene nanocomposites for NO2 gas were investigated. Compared with the pure graphene sensor, the sensitivity of the SnO2/graphene sensor is higher and the recovery time is shorter. Moreover, the recovery time of the sensor is clearly further shortened using transient UV light irradiation. The SnO2/graphene sensor augmented with transient UV irradiation can achieve fast response/recovery with NO2. The sensor was demonstrated to have huge potential for real-time detection of NO2 at room temperature (25 degrees C).

Surface acoustic wave (SAW) devices show promising applications for highly sensitive gas sensors for continuously monitoring of hazardous and flammable gases when integrating with specifically designed sensing materials. Improving the SAW sensor’s responses by using nanostructure sensing materialshas become a research hot topic in recent years. In this work, we presented a SAW room temperature NO2 gas sensor with high sensitivity using one-dimensional (1D) Bi2S3 Nanobelts as the sensing materials. SAW devices with thecentral frequency of ~200 MHz were fabricated on ST-cut quartz substrate as the sensing platform. The Bi2S3 Nanobelts were synthesized by solvothermal method and deposited onto SAW sensors using a spin-coating technology. The response of the prepared SAW gas sensors was 2 kHz when subjected to 10 ppm NO2 even at room temperature. Moreover, the sensor shows good selectivity, reversibility, and stability. The sensing mechanism of one-dimensional Bi2S3 nanobelts-based SAW sensors for NO2 detection was also be discussed.

Colloidal quantum dots (CQDs) have shown their advantages in gas-sensing applications due to their extremely small particle size and facile solution based processes. In this study, a high sensitivity of surface acoustic wave (SAW) NO2 sensor was demonstrated using SnS CQDs as the sensing layer. The delay line based SAW device with a resonant frequency of 200 MHz were fabricated on ST-cut quartz substrate. The SnS CQDs with average sizes of 5.0 nm were synthesized and deposited onto SAW sensors using a spin-coating method. The fabricated SAW sensor was capable of detecting a low concentration of NO2 gas at room temperature with a good efficiency and selectivity e.g., with a 1.8 kHz decrease of center frequency of the SAW delay line when exposed to 10 ppm NO2 at room temperature.

针对石墨烯气体传感器的恢复过程长的问题,研究了在浓度为(10～230)×10-6之间的二氧化氮(NO2)环境中,加热对石墨烯的性能影响,结果表明:加热能有效地加快石墨烯气体传感器的恢复过程,且加热对石墨烯自身的阻值和响应均有一定影响.

Purpose - Graphene is a two-dimensional material. Its use has many advantages in gas sensing, but its long desorption process is problematic. The aim of this paper is to design a graphene-based gas sensor, study the response to NO2 gas concentrations and find ways to accelerate the desorption process.Design/methodology/approach - In one group, the sensor was placed in air to measure its initial resistance. Then, it was exposed to the NO2 gas at a certain concentration. Finally, the sensor was exposed to light immediately after NO2 gas exposure was ended. In another group, the sensor was heated using a heating plate at a stable temperature, before taking the measurements. Then the adsorption and desorption experiments were carried on.Findings - Illumination and heating at a suitable temperature can expedite desorption of NO2 molecules on graphene.Originality/value - In the paper, two main methods are introduced to accelerate the desorption process when the NO2 gas is absorbed on graphene. Through a series of experiments and analysis, the authors found that the recovery time could be reduced observably and the recovery performance of the graphene-based NO2 sensor could be improved effectively.

Properties of the gas sensing and the method of the desorption about graphene have been discussed. By analyzing the response and desorption time of the NO2 molecule on graphene,we discussed the gas sensing proper?ties of graphene. In the experiments,the graphene has fast and high response to NO2 gas,while the recovery prog?ress is quite slow,that is to say the desorption time is very long. The analysis states that by heating and illumina?tion, the desorption time could be decreased effectively,and the adsorption property would be improved.

To improve nanotube production, we developed a novel optical control technique, based on the shape of the visible plasma zone created between the anode and the cathode in the direct current (DC) arc process. For a given inert gas, we adjust the anode to cathode distance (ACD) in order to obtain strong visible vortices around the cathode. This enhance anode vaporization, which improve nanotubes formation. In light of our experimental results, we focus our discussion on the relationship between plasma parameters and nanotube growth. Plasma temperature control during arc process is achieved using argon, helium, and their mixtures as a buffer gases. The variation of the gas mixture from pure argon to pure helium changes plasma temperature. As a consequence, the microscopic characteristics of nanotubes as diameter distribution is changed moving from smaller values for argon to higher diameters for helium. We also observe a dependence of the macroscopic characteristics of the final products as Brunauer-Emmett-Teller (BET) surface area.