Ultraviolet light-emitting diodes in water disinfection

Vilhunen, Sari; Särkkä, Heikki; Sillanpää, Mika

doi:10.1007/s11356-009-0103-y

Cited by 188 publications

(85 citation statements)

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“…This disinfection method aims to eliminate microorganisms from the surface of the denture base resin, the major effect occurring via the generation of ROS, which attack both the viruses and bacteria 19,20) . Furthermore, ultraviolet light can directly attack bacterial DNA 21,22) . This causes DNA alterations, usually in the chemical bonding of adjacent thymine bases, which prevents DNA replication and subsequently inactivates microoorganisms 23) .…”

Section: Discussionmentioning

confidence: 99%

Evaluation of denture base resin after disinfection method using reactive oxygen species (ROS)

et al. 2012

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The effects of certain disinfectants on the stability of a polymethyl methacrylate denture base resin were investigated, including those of a novel disinfection method using reactive oxygen species (ROS). The surface roughness and flexural strength were analyzed to assess the effects of the disinfectants on material properties. The following disinfectants were tested: 5% sodium hypochlorite, 70% alcohol, and ROS. Furthermore, the attachment of Candida albicans to the resin surface was investigated. The disinfection method using sodium hypochlorite significantly increased the surface roughness and decreased flexural strength. The surface roughness and flexural strength of the ROS-treated specimens did not significantly differ from those of the control specimens, and the ROS-treated specimens exhibited diminished Candida attachment. These results demonstrate that the ROS disinfection method preserves acceptable material stability levels in polymethyl methacrylate resins.

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Section: Discussionmentioning

confidence: 99%

Evaluation of denture base resin after disinfection method using reactive oxygen species (ROS)

et al. 2012

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“…In 3C-SiC, the crystal has zinc blende structure with all atoms having similar environment of cubic crystal, while in the hexagonal polytypes, there are different inequivalent sites for atoms: h-site or hexagonal site and k-site or quasi-cubic site in 4H-SiC and h, k 1 and k 2 -sites in 6H-SiC. The arrangement of the second nearest neighbor of the h and k-sites in 4H-SiC is similar to that in 2H-SiC and 3C-SiC, respectively (Fig.…”

Section: Common Polytypes Of Sicmentioning

confidence: 99%

“…The band gap of AlGaN increases with increasing of the Al content varying from 3.4 eV for GaN to 6.2 eV for AlN, which corresponds to the changing of wavelength from 365 nm to 200 nm. It was known that light emitting diodes (LEDs) emitting light in the deep-UV spectral region of ~270 nm can be efficiently used for water/air purification and sterilization [1,2]. Therefore, the successful fabrication of high-efficiency deep-UV LEDs and laser diodes (LDs) based on high-Al-content Al x Ga 1-x N (x≥70%) [3][4][5] for replacing low-efficiency and toxic gas lasers and mercury lamps has enormous social impact and attracted much attention.…”

mentioning

confidence: 99%

Electron Paramagnetic Resonance studies of negative-U centers in AlGaN and SiC

Trinh¹

2015

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Silicon (Si) is the most commonly used n-type dopant in AlGaN, but the conductivity of Si-doped Al x Ga 1-x N was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either compensation by deep levels or self-compensation of the so-called DX (or negative-U) center. Understanding the electronic structure of Si and carrier compensation processes is the essential for improving the n-type doping of high-Al-content Al x Ga 1-x N. In our studies of Si-doped AlGaN layers grown by metal-organic chemical vapor deposition, Electron Paramagnetic Resonance (EPR) was used to study the electronic structure of Si in high-Al-content Al x Ga 1-x N.From the temperature dependence of the concentration of the Si donor on the neutral charge state E d determined by EPR, we showed that Si already forms a stable DX center in Al x Ga 1-x N with x ~0.77. However, with the Fermi level locating only ~3 meV below E d , Si still behaves as a shallow donor and high conductivity at room temperature could be achieved in Al 0.77 Ga 0.23 N:Si layers. In samples with the concentration of the residual oxygen (O) impurity larger than that of Si, we observed no carrier compensation by O in Al 0.77 Ga 0.23 N:Si layers, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. The result is presented in paper 1.In paper 2, we determined the dependence of the E DX level of Si on the Al content in Al x Ga 1-x N:Si layers (0.79≤x≤1) with the Si concentration of ~2×10 18 cm -3 and the concentrations of residual O and C impurities of about an order of magnitude lower (~1÷2×10 17 cm -3 ). We found the coexistence of two DX centers (stable and metastable ones) of Si in Al x Ga 1-x N for x≥0.84. For the stable DX center, abruptly deepening of E DX with increasing of the Al content for x≥0.83 was observed, explaining the drastic decrease of the conductivity as often reported in previous transport studies. For the metastable DX center, the E DX level remains close to E d for x=0.84÷1 (~11 meV for AlN).The Z 1 /Z 2 defect is the most common deep level revealed by Deep Level Transient Spectroscopy (DLTS) in 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD). It has previously been shown by DLTS to be a negative-U system which is more stable with capturing two electrons. The center is also known to be the lifetime killer in asiv grown CVD material and, therefore, attracts much attention. Despite nearly two decades of intensive studies, including theoretical calculations and different experimental techniques, the origin of the Z 1 /Z 2 center remains unclear. EPR is known to be a powerful method for defect identification, but a direct correlation between EPR and DLTS is difficult due to different requirements on samples for each technique. Using high n-type 4H-SiC CVD free-standing layers irradiated with lowenergy (250 keV) electrons, which mainly displace carbon atoms creating C vacancies, C interstitials and their associated defects, it was possible...

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“…1-x N .......................................................... Under the exposure of deep-ultraviolet (UV) radiation with wavelength around 260 nm or shorter (such as at 214, 220 or 228 nm) which is often absent in ordinary condition due to the UV absorbance of the ozone shield, DNA or RNA molecules of various micro-organisms are damaged and cannot function or reproduce [1]. Thus, deep-UV radiation can be efficiently used for water/air purification and sterilization [1][2][3]. The short-wavelength deep-UV radiation can be also used for high resolution lithography and high-density optical data storage.…”

Section: Populärvetenskaplig Sammanfattningmentioning

confidence: 99%

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

Trinh¹

2015

Linköping Studies in Science and Technology. Dissertations

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Point defects in semiconductor materials are known to have important influence on the performance of electronic devices. For defect control, knowledge on the model of defects and their properties is required. Information on defects, such as the symmetry and the localization of spins, is essential for identification of defects and understanding their electronic structure. Such information can be obtained from Electron Paramagnetic Resonance (EPR). In many cases, the energy levels of defects can be determined from photoexcitation EPR (photo-EPR) or temperature dependence of the EPR signal. The thesis contains six papers, focusing on the identification and electronic structure investigation of defects and impurities in Al x Ga 1-x N (x~0.7-1) and silicon carbide (SiC) using EPR in combination with other electrical characterizations and density functional theory calculations.The two first papers concern EPR studies of silicon (Si) in AlGaN alloys. Due to its direct and wide band gap which can be tailored from 3.4 eV for GaN to 6.2 eV for AlN, high-Al-content wurtzite Al x Ga 1-x N (x≥0.7) has been considered as a promising material for fabrication of compact, highefficiency and non-toxic deep ultraviolet light-emitting diodes (LEDs) and laser diodes (LDs) for replacing low-efficiency and toxic mercury lamps in water/air purification and sterilization. Si is commonly used for n-type doping in AlGaN and AlN, but the conductivity of Si-doped Al x Ga 1-x N was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either carrier compensation by other deep levels or Si itself when it transforms from a shallow donor to a DX (or negative-U) center which acts as an acceptor. In paper 1, we showed that Si already forms a stable DX center in Al x Ga 1-x N with x ~0.77. However, with the Fermi level locating only ~3 meV below the neutral charge state, E d , Si still behaves as a shallow donor. Negligible carrier compensation by oxygen (O) in Al 0.77 Ga 0.23 N:Si layers was observed, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. In paper 2, we found the coexistence of two Si DX centers, the stable DX1 and the metastable DX2, in Al x Ga 1-x N for x≥0.84. For the stable DX1 center, abrupt deepening of the energy level of the negative charge state DX -, E DX , which determines the ionization energy E a of the Si donor, with increasing of the Al content for x≥0.83 was observed. The dependence of E a on the Al content in Al x Ga 1-x N:Si layers (0.79≤x≤1) was determined. The results explain the drastic decrease of the conductivity as often reported for Al x Ga 1-x N:Si in previous transport studies. For the metastable DX2 center, we found that the E DX level remains close to E d for x=0.84÷1.SiC is a wide band-gap semiconductor having high-thermal conductivity, high breakdown field, and large saturated electron drift velocity which are iv essential properties for high-voltage and high-power devices. In paper 3, the identif...

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Ultraviolet light-emitting diodes in water disinfection

Abstract: This study found UV LEDs to be an optimal method for bacterial disinfection. The emitted wavelength was found to be an essential factor when using LEDs; thus, care should be taken in selecting the proper LED for maximum disinfection.

Cited by 188 publications

References 9 publications

Evaluation of denture base resin after disinfection method using reactive oxygen species (ROS)

Evaluation of denture base resin after disinfection method using reactive oxygen species (ROS)

Electron Paramagnetic Resonance studies of negative-U centers in AlGaN and SiC

Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC

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