Papers by Keyword: Ultraviolet

Abstract: The far-UVC band (200–240 nm) is highly attractive for germicidal and solar-blind detection. To address limited surface carrier collection in epitaxial SiC phototransistors, we designed fully ion-implanted lateral phototransistors by combining transistor physics with CMOS-compatible processing. The lateral base width was systematically varied from 1 to 8 μm to investigate its influence on carrier transport and gain. A narrower base significantly enhanced photocurrent amplification, with the 1 μm device reaching 100.7 A/W at 200 nm and 60.0 A/W at 240 nm, while maintaining amplification up to the ~380 nm cutoff. Moreover, dark currents remained as low as 10⁻¹¹ A, confirming the advantage of structural engineering for high-performance far-UVC SiC phototransistors.

Abstract: Titanium dioxide (TiO₂) is excellently used in various applications including wastewater treatment. It is known to have superb pigmentary properties, high adsorption in the ultraviolet (UV) region, and high stability. The objective of this paper is to study the effect of contact time of seawater desalination in the photocatalytic reaction. The hybrid TiO₂ catalysts; a mixture of TiO₂ and biomass ash, was synthesized via wet impregnation and calcined at 800 °C. The photocatalyst was then characterized by using Scanning Electron Microscopy (SEM) and Braunauer-Emmett-Teller (BET). The investigation was carried out in a photoreactor equipped with UV light operated for up to six hours with catalyst to seawater weight ratio of 1:400 and stirring speed of 600 rpm. The salt concentration, turbidity and pH of the water were determined prior and after the investigation. The result indicates that the salt concentration gradually decreased more than 25% as the contact time increased up to six hours. However, there is no significant change on pH value of the water. It can be concluded that the hybrid TiO₂ is able to reduce the seawater salinity effectively.

Abstract: 4H-SiC ultraviolet photodetectors based on Schottky barriers have been formed on lightly doped n-type epitaxial layers grown by chemical vapor deposition method on industrial substrates. The diode structures were irradiated at 25°C with 167 MeV Xe ions at a fluence of 6x10⁹ cm^-2. Comparative studies of the optical and electrical properties of initial and irradiated structures with Schottky barriers were carried out in temperature range 23-180°C. Swift heavy ion stimulated changes in photosensitivity and electrical characteristics of the initial and irradiated detectors are explained in terms of the fluctuation traps model with the subsequent thermal dissociation.

Abstract: Studies were carried out in order to investigate the sensitivity of some thin films, to ultraviolet light, based on barium stearate and carbon nanotubes structures. A three – five monolayers structures were developed using the Langmuir – Blodgett technique onto ceramic substrate. Obtained Langmuir – Blodgett complex thin films shows sensitivity to ultra violet light radiation, taking into consideration the presence of carbon nanotubes that facilitates the charge carriers transport. Also the investigations performed, revealed the properties of carbon nanotubes and point out the fine chemistry of these materials. Based on this premise we proceed to investigate and characterize the photo – electrical behavior of the obtained structures.

Abstract: According to the characteristics of high altitude and strong ultraviolet radiation in Tibet, this paper do ultraviolet irradiation experiment research to different strength grades of concrete blocks in a closed laboratory, it is found that ultraviolet rays has promoting effect to early strength growth of test block, but the growth became slow along with the time.

Abstract: With the living standards improvement of rural residents, people pay more attention to the safety of drinking water in China. As the final step in drinking water treatment, disinfection technology has received much attention. At present, drinking water disinfection process is mainly involved in chlorine disinfection, chlorine dioxide disinfection, chloramine disinfection, disinfection of potassium permanganate, ozone disinfection and ultraviolet disinfection. However, due to limitations in rural economic conditions and management level, only ozone disinfection and ultraviolet disinfection are suitable for rural areas in China. This paper described some of the application problems and limitations in drinking water disinfection process, as well as the select principle in rural areas. The principle, research status, trends and issues in application of ozone and ultraviolet disinfection technology were emphatically introduced. Finally, the development of drinking water disinfection technologies was discussed.

Abstract: In this study, the formation of trihalomethanes (THMs) during chlorination or chloramination after different pretreatments including single nanoTiO₂ adsorption, single UV treatment or the combination of UV/TiO₂ under the same pH, TiO₂ dose and humic acid concentrations were evaluated. Effect of different pretreatments on the reduction of non-purgeable organic carbon (NPOC) and UV₂₅₄ before the disinfection was investigated. The result showed that single UV and single TiO₂ adsorption to reduce NPOC and UV₂₅₄ values is negligible, and the combination of UV/TiO₂ removed 45% of NPOC and 72% of UV₂₅₄ after 480min reaction. For the formation of the THMs during the followed chlorination, it was found that the combination pretreatment of UV/TiO₂ resulted in a parabolic trend for the formation of the THMs while single UV pretreatment increased steadily and single TiO₂ pretreatment kept stable. Chlorination generated higher concentrations of total THMs than chloramination. The total THMs produced by chloramination only represented <5% of that of chlorination.

Abstract: The modeling of aluminum gallium nitride (AlGaN) p-i-n photodetectors response in the very narrow ultraviolet A (UV-A) range is reported in this paper. To obtain narrow-band response and high short wave rejection ratio, two AlGaN buffer layer with Al-content higher than that of the absorption region were designed between the substrate and un-doped AlGaN absorption layer to act under backside illumination as filter for short wavelength radiation. The band-pass of these a structure depends on the buffer layer Al-content. Electronic-band-structure calculations show that the blocking layer is the crucial parameter to achieve both a high short wave rejection ratio and a low dark current.

Abstract: To distinguish the ultraviolet (UV) photoresponse of Ohmic and Schottky contact devices, we have fabricated symmetrical and nonsymmetrical devices by standard lithography based on a single WO₃ nanowire. For the Ohmic contact device, the photocurrent can change from 100 nA to 300 nA. Even 200 s under UV illumination, nonsaturated photocurrent can be observed, and the fall time is more than 1000 s. But for the Schottky contact device, the rise and fall time are faster than that of Ohmic device. The barrier height of Schottky device can be easily controlled through the oxygen adsorption and desorption on the junction region, which can be served as a ‘‘gate’’ that effectively tunes the conductance of the device. Therefore, the Schottky barrier plays a very important role in the rapid-response of UV photodetector.

Abstract: In recent years, MgZnO alloy becomes one of the most suitable materials for the fabrication of ultraviolet detectors. In this paper, we have fabricated three metal semiconductor metal (MSM) photodetectors on Mg_0.42Zn_0.58O film grown by radio frequency magnetron sputtering. The interdigital electrodes are 500 um long and 5 um wide with an interelectrode spacing 2, 5 and 10 um, respectively. The structural, electrical and optical properties of epilayers were characterized by various techniques. At 5 V bias, a peak responsivity of 1.09 mA/W was achieved at 283 nm for the device with 2 um interelectrode spacing. The peak responsivity at 283 nm increased with the reduction of the finger pitch for three devices and the ultraviolet-visible rejection ratio (R283 nm/R400 nm) was more than one order of magnitude at 5 V bias.