UV Exposure Time Research Articles

The Effects of UV Exposure on Plasma-Enhanced Atomic Layer Deposition ZnO Thin Film Transistor

We investigated the effects of UV treatment on the device properties of a plasma-enhanced atomic layer deposition (PE-ALD) ZnO thin film transistor (TFT). Remote PE-ALD ZnO thin films were used as active layers for bottom-gate TFT devices. The as-deposited PE-ALD ZnO film at a growth temperature of 200°C has an overly small carrier concentration, which produces a TFT device with no modulation by gate voltage sweep. However, after UV light exposure, the device shows proper TFT modulation by gate voltage. The threshold voltage (V th ) of the device can be controlled to the negative direction by increasing the UV exposure time. V th moves from 17.8 to -6.5 V with an increase in UV exposure time from 3 to 120 min.

Patterning on Cyanine-Dye-Doped Conductive Polymer Films by Ink Jet Method

In this study, the conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), doped with a cyanine dye, 5-phenyl-2-(2-{[5-phenyl-3-(3-sulfopropyl)-2-(3H)-benzoxazolylidene]methyl}-l-butenyl)-3-(3-sulfopropyl) benzoxazolium hydroxide, inner salt, compound with triethylamine (NK-1952) was used to fabricate J-type aggregated thin films, using piezoelectric ink jets with desirable shape, size, and patterns on indium tin oxide (ITO) substrates. The effects of the cyanine dye and polymer concentration, UV exposure time, and other fabrication parameters of the ink jet such as nozzle size, pulse voltage, pulse duration, and the second pulses on the J-aggregate formation, spot size, and morphology have been investigated and the related mechanisms have also been discussed.

Spatially controlled hydrogel mechanics to modulate stem cell interactions

Local control of the stem cell microenvironment with biomaterial design is of critical importance for tissue engineering. Matrix mechanics is one aspect of biomaterial design that has received considerable attention recently due to the effect of mechanics on stem cell proliferation, morphology, and differentiation. In order to investigate the effect of locally controlled mechanics on human mesenchymal stem cells (hMSCs), a sequentially crosslinked hyaluronic acid hydrogel system was developed that permits spatial patterning of mechanics (distinct patterns and gradients). Methacrylated hyaluronic acid was synthesized to allow for crosslinking via both Michael-type addition using a dithiol and radical polymerization using light. By varying the initial methacrylate consumption through addition crosslinking, restricting UV light to specified regions, and varying UV exposure time, a wide range of mechanics (from ∼3 kPa to ∼100 kPa) was possible in both uniform and patterned hydrogels. hMSCs exhibited increased spreading and proliferation on stiffer gels compared to cells cultured on softer gels. Furthermore, cells grown on gels with patterned mechanics exhibited spreading and proliferation behavior that correlated with the local mechanics. This method to spatially control matrix mechanics represents a novel hydrogel system to tune the stem cell microenvironment.

Facile synthesis and size control of Ag nanoparticles by a photochemical reduction at room temperature

Facile synthesis and size control of Ag nanoparticles by a photochemical reduction was demonstrated. UV–visible spectra and photographs of the synthesized solutions with and without sodium citrate at different UV exposure times showed that sodium citrate played a crucial role for the growth of Ag nanoparticles. According to UV exposure of the Ag colloidal solutions with 0.250 mM sodium citrate for 0, 7, 15, 30, and 60 min, the average particle sizes were 0, 2.45, 5.58, 7.03, and 11.08 nm, respectively. Ag nanoparticles exhibited great increase in sizes, from 5.71 to 36.43 nm after UV exposure for 60 min, as the sodium citrate concentration increased from 0.125 to 0.500 mM. The photochemical reduction is hypothesized to decompose of citrate ions and result from photoelectron transfer from the neutral Ag atoms to the Ag+ ions to form Ag nanoparticles. These results suggest that the photochemical reduction method can provide Ag nanoparticles in the presence of sodium citrate at room temperature without using a reducing agent.

Photodestruction of BDE-99 in micellar solutions of nonionic surfactants of Brij 35 and Brij 58

Currently, soil contamination by polybrominated diphenyl ethers (PBDEs) at e-waste recycling sites in China is of significant environmental concern and requires the identification of appropriate remediation technologies. In this paper, photodestruction of a model PBDE congener (BDE-99) in selected UV/surfactant systems was investigated, using a RPR-200 Rayonet photochemical reactor equipped with two low-pressure mercury lamps. BDE-99 photodegradation in the micellar solutions of nonionic surfactants of Brij 35 and Brij 58 all followed pseudo first-order kinetics and the photodegradation quantum yields were 1.8–2.4 times as high as that in water alone. The photodegradation was comparably enhanced by Brij 35 and Brij 58, and the quenching effect of dissolved oxygen (DO) was eliminated in their presence. Mono- to tetra-BDEs were identified as one group of BDE-99 photoproducts, indicating that one of BDE-99 photodegradation pathways was through a sequential loss of Br. The pattern of PBDE photoproducts showed the photodebromination of BDE-99 readily occurred on the more heavily substituted phenyl ring. Mono- to tetra-polybrominated dibenzofurans (PBDFs) were identified as another group of photoproducts, indicating BDE-99 can also photodegrade through a dibenzofuran-type ring closure process via an intramolecular elimination of HBr. In addition, the formation of these more toxic photoproducts (PBDFs) was not related to the presence of DO. Finally, the later disappearance of mono-BDEs and mono-BDFs suggested the UV exposure time would be an important technical parameter if the technology of UV photodestruction of PBDEs in surfactant micellar solutions is applied to PBDE-contaminated soil remediation.

Photoimmobilization of unmodified carbohydrates on activated surface

Herein, we demonstrate a simple, versatile and efficient method for immobilization of unmodified carbohydrates onto a solid surface. The method employs a photoreactive-cellulose membrane which is prepared by the introduction of a photoreactive group to a cellulose membrane through 1-fluoro-2-nitro-4-azidobenzene (FNAB). Upon exposure to UV light photo-reactive azido group of the activated cellulose membrane transforms itself into highly reactive nitrene which covalently binds to underivatized carbohydrates through an insertion reaction. Maximum immobilization of carbohydrate is achieved at the UV exposure time of 60min and carbohydrate concentration of 100microg/disk. The immobilized carbohydrate is assayed by affinity binding of biotin-labeled lectins. The amount of Con A required for detecting immobilized carbohydrate ranges from 4-10microg/ml. The binding affinities of the lectin to the immobilized carbohydrates are analyzed by calculating their IC(50) values. Overall, the present work demonstrates an efficient immobilization of underivatized carbohydrate onto cellulose surface and has the potential to be applied to other surfaces.

Long-Range Reverse Transcription as a Useful Tool to Assess the Genomic Integrity of Norovirus

The effects of heat (72°C) and UV-light (254 nm) on the infectivity of murine norovirus-1 (MNV-1) and human norovirus (NoV) are reported. The infectivity of MNV-1 was measured using standard cell-culture plaque assays and was compared with a specific duplex RT-qPCR for MNV-1, which targets two fragments of the MNV genome, one 142 bp (short-range, sRT-qPCR) and a second 4.6 kb (long-range, loRT-qPCR) upstream from the reverse transcription (RT) priming site (poly-A tail). After the heat treatment of MNV neither the sRT- nor loRT-qPCR correlated with decreased infectivity as assessed by the plaque assay. However, after UV-exposure, the lo-qPCR showed decreased qPCR amplification, which became more pronounced with increased UV-exposure time, and reflected decreased infectivity as shown in the plaque assay. The sRT-qPCR amplification was not affected by UV-exposure. Similar results were obtained when challenging non-culturable human GI and GII NoV with UV-light. Using previously published RT-qPCR assays for GI and GII NoV, no decrease in RT-qPCR amplification was seen when using the respective reverse primers of the RT-qPCR assay in the RT reaction, whereas a significant decrease in qPCR amplification occurred when the RT reaction was primed at the poly-A tail about 2.3 kb from the qPCR amplification site. The results indicate that, in contrast to RT-qPCR with a long-range RT, RT-qPCR with a short-range RT does not reflect genomic integrity and therefore viral infectivity. Furthermore, human NoV appears to be highly sensitive to UV-irradiation which could lead to more efficient decontamination procedures.

Thermoluminescence study of UV irradiated Ce doped SrS nanostructures

Thermoluminescence (TL) study and kinetic analysis of UV irradiated Ce doped SrS nanostructures have been presented. Cerium concentration has been tuned to the maximum TL intensity. Cerium (0.5 mol%) doped SrS nanocrystalline phosphor exhibits a broad TL glow curve around 371 K at a heating rate of 10 K/s. We noted that TL intensity increases with UV exposure time in the range 2 min–4 h and saturates between 4 h and 8 h of exposure which may be explained on the basis of track interaction model (TIM) and a high surface to volume ratio for the nanostructures. Further increase in the dose results into a decrease of TL intensity. The effect of different heating rates on the TL glow curve has also been investigated. The trapping parameters namely activation energy ( E), order of kinetics ( b) and frequency factor ( s) for SrS:Ce (0.5 mol%) have been determined using glow curve deconvolution (GCD) functions.

Relationship Between Fiber Gratings Reflectivity and Laser Fabrication Parameters

This study concentrates to investigate the relationship between laser fabrication parameters and reflectivity of fiber gratings. The fiber Bragg grating system, comprising Excimer Laser, Mask Aligner, Optical Spectrum Analyzer and Tunable Laser Source was utilized to fabricate the fiber gratings. A series of experiments were carried out for the fabrication of fiber gratings and to observe the effect of laser fabrication parameters on the reflectivity of fiber gratings. These samples were fabricated with different reflectivitys ranging from 27 to 93% at constant pulse rate i.e. 1Hz. The amount of reflectivity is the extent to which the index modulation in the fiber core changes. The higher the reflectivity of a fiber grating, the more microstructural changes occur within the lattice of the photosensitive core and the more the residual axial stress builds up within the cross section of the fiber. Here, we discussed only two laser fabrications parameters i.e. effect of pulse energy on reflectivity of fiber grating and effect of exposure time on reflectivity of fiber grating/Bragg wavelength. Based on the results of this study, it is inferred that reflectivity is exponentially increased, as the pulse energy increase at constant UV exposure time and attained saturation at pulse energy i.e. 165mJ. The low pulse energy produces a low reflectivity fiber Bragg grating even after a longer UV exposure time. It is also concluded that both reflectivity and Bragg wavelength are increased rapidly in the beginning with the increase of UV exposure time and then become saturated at UV exposure time i.e. 110min, even though pulse energy is constant. It means that the induced index of modulation was increased with the increasing of UV exposure time.

Photostability of phenothiazinyl-substituted ethylenes

Photostability of phenothiazinyl-substituted ethylenes in both solution and in solid state (thin films) was investigated as a function of UV exposure time. Fluorescence intensity and spectral variation measurements in the presence and absence of ambient air were used to determine the effect of oxygen on the degradation of the compounds. The observed reduction in the fluorescence efficiency of air-saturated solutions and thin films subjected to UV was attributed to permanent photo-oxidative degradation. Photostability was higher in the cases of molecules that contained two bulky phenothiazinyl groups as compared to those containing only one phenothiazinyl group and a smaller phenyl substituent. Fully reversible fluorescence intensity decay in the degassed phenothiazine solutions was attributed to photo-isomerization, whereas the partially reversible changes in fluorescence intensity that were observed for films in the absence of air were ascribed to both photoexcited carrier capture by deep-traps acting as exciton quenching centres and degradation imparted by UV-induced bond scission.

Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites

Polyethylene (a 1:1 blend of m-LLDPE and z-LLDPE) double layer silicate clay nanocomposites were prepared by melt extrusion using a twin screw extruder. Maleic anhydride grafted polyethylene (PEgMA) was used as a compatibiliser to enhance the dispersion of two organically modified monmorilonite clays (OMMT): Closite 15A (CL15) and nanofill SE 3000 (NF), and natural montmorillonite (NaMMT). The clay dispersion and morphology obtained in the extruded nanocomposite samples were fully characterised both after processing and during photo-oxidation by a number of complementary analytical techniques. The effects of the compatibiliser, the organoclay modifier (quartenary alkyl ammonium surfactant) and the clays on the behaviour of the nanocomposites during processing and under accelerated weathering conditions were investigated. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), rheometry and attenuated reflectance spectroscopy (ATR-FTIR) showed that the nanocomposite structure obtained is dependent on the type of clay used, the presence or absence of a compatibiliser and the environment the samples are exposed to. The results revealed that during processing PE/clay nanocomposites are formed in the presence of the compatibiliser PEgMA giving a hybrid exfoliated and intercalated structures, while microcomposites were obtained in the absence of PEgMA; the unmodified NaMMT-containing samples showed encapsulated clay structures with limited extent of dispersion in the polymer matrix. The effect of processing on the thermal stability of the OMMT-containing polymer samples was determined by measuring the additional amount of vinyl-type unsaturation formed due to a Hoffman elimination reaction that takes place in the alkyl ammonium surfactant of the modified clay at elevated temperatures. The results indicate that OMMT is responsible for the higher levels of unsaturation found in OMMT-PE samples when compared to both the polymer control and the NaMMT-PE samples and confirms the instability of the alkyl ammonium surfactant during melt processing and its deleterious effects on the durability aspects of nanocomposite products. The photostability of the PE/clay nanocomposites under accelerated weathering conditions was monitored by following changes in their infrared signatures and mechanical properties. The rate of photo-oxidation of the compatibilised PE/PEgMA/OMMT nanocomposites was much higher than that of the PE/OMMT (in absence of PEgMA) counterparts, the polymer controls and the PE–NaMMT sample. Several factors have been observed that can explain the difference in the photo-oxidative stability of the PE/clay nanocomposites including the adverse role played by the thermal decomposition products of the alkyl ammonium surfactant, the photo-instability of PEgMA, unfavourable interactions between PEgMA and products formed in the polymer as a consequence of the degradation of the surfactant on the clay, as well as a contribution from a much higher extent of exfoliated structures, determined by TEM, formed with increasing UV-exposure times.

The Cl + H2 → HCl + H Reaction Induced by IR + UV Irradiation of Cl2 in Solid para-H2: Experiment

We report IR + UV coirradiation photolysis experiments conducted on Cl(2)-doped para-hydrogen (p-H(2)) crystals at 1.8 K, using pulsed 355 nm UV radiation and cw broad-band near-IR light from a FTIR tungsten source. The amount of HCl photoproduct is monitored using FTIR spectroscopy as a function of the IR + UV exposure time. Detailed analysis of the HCl growth kinetics reveals that the reaction Cl + H(2)(v=1,J=0) --> HCl + H is playing a significant (15%) role in the in situ photochemistry. In contrast, UV-only photolysis experiments conducted under similar conditions produce almost exclusively (99%) isolated Cl atom photofragments, indicating the reaction Cl + H(2)(v=0,J=0) --> HCl + H is not readily occurring. This combination of photolysis experiments confirms that under these conditions, the Cl + H(2) reaction probability increases by a factor greater than 25 for Cl atom reactions with H(2)(v=1) versus H(2)(v=0). These results are therefore consistent with the expectation that vibrational excitation of the H(2) reagent lowers the reaction threshold and increases the reaction cross section for the Cl + H(2) reaction. These experimental studies were motivated by and are compared to the quantum model simulations reported by Korolkov, Manz, and Schild in the accompanying paper.

Improving the Wettability of Deep-Groove Polypropylene Fibers by Photografting

This paper presented photografting as a surface modification method to provide permanent wettability improvement to deep-groove polypropylene (PP) fibers. We also evaluated their wettability by testing the dynamic contact angle (DCA) on single fibers and characterized the wicking performance of fiber bundles when polyacrylamide (PAAm) and polyacrylic acid (PAA) were grafted onto the fibers. In this study, the increase in monomer concentration was found more effective than longer UV exposure time in creating higher graft density on deep-groove PP fibers. Acrylic acid (AA) monomers penetrated into the fiber and polymerized inside, but acrylamide (AAm) did not. Fiber dimension changed slightly upon grafting of PAAm, and enlarged significantly after grafting with PAA. DCA results show that the advancing water contact angle on single fibers decreased from 100 to 55° by grafting of PAAm and PAA, and spontaneous wicking of water was observed after surface modification. The wicking amount of the vertically placed fiber bundles showed a linear relationship to the square root of time at early wicking times.

Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum

AbstractAiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, a novel approach to produce luminescent silicon nanoparticles (Si‐NPs) is developed. Single crystalline Si‐NPs are synthesized by pyrolysis of silane (SiH4) in a microwave plasma reactor at very high production rates (0.1–10 g h−1). The emission wavelength of the Si‐NPs is controlled by etching them in a mixture of hydrofluoric acid and nitric acid. Emission across the entire visible spectrum is obtained by varying the etching time. It is observed that the air oxidation of the etched Si‐NPs profoundly affects their optical properties, and causes their emission to blue‐shift and diminish in intensity with time. Modification of the silicon surface by UV‐induced hydrosilylation also causes a shift in the spectrum. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si‐NPs. In addition, the amount of shift depends on the type of organic ligand on the silicon surface and the UV exposure time. The surface modification of Si‐NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si‐NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way towards their commercialization.

The photophysics of singlet, triplet, and degradation trap states in 4,4-N,N′-dicarbazolyl-1,1′-biphenyl

In this paper we report the results of optical characterization of 4,4-N,N(')-dicarbazolyl-1,1(')-biphenyl (CBP), known as a host material for phosphorescent light emitting devices. Using absorption, steady state, and time-resolved spectroscopy, we explore the singlet and triplet states in solid and solution samples of CBP. In solutions we observe two distinct short-lived states with well-resolved emission originating from individual molecule singlet states (at 365 and 380 nm) and "quenching" low energy (LE) states (at 404 and 424 nm). The latter are seen only in saturated solutions and solid samples. Both of those species have different lifetimes. After UV exposure of very concentrated degassed solution the intensities of the LE bands starts to decrease. The longer the solution is exposed to UV, the less emission is seen at 404 and 424 nm, until it is totally gone. The spectrum of the highly concentrated solution is then the same as the spectrum of dilute solution, i.e., only emission at 365 and 380 nm is present. An increase in intensities of the singlet emission peaks correlates with an increase in UV exposure time. Similar behavior is observed in evaporated CBP film. We propose that this behavior is due to chemical instability of the weak N-C bonding of carbazolyl moiety-this creates new degradational species over time which dissociate after exposure to UV. We believe this to be the reason for variation in CBP fluorescence and delayed fluorescence spectra recorded by various research groups. Further, we detected two types of very long-lived states. One of these states (higher energy) is ascribed to molecular phosphorescence emission, the other to emission from low energy triplet trap states which we relate to degradational species. We propose that triplets are more easily caught by these latter sites when their hopping rate increases, and they emit inefficiently from these lower energy sites.

A numerical model of light adjustable lens

We model numerically the mechanical effects of UV induced photo-polymerization in elastomeric artificial lens. The elastomer is originated upon cross-linking of a silicone matrix. UV irradiation of one side of the lens polymerizes selectively a photosensitive macromer, causing local variations of its concentration. The subsequent diffusion of macromers from high concentration to low concentration zones modifies the shape of the lens and thus its dioptric power. In vitro experiments on artificial lens showed that the power change is dependent on UV exposure time, irradiation intensity and light pattern. With the aim to define a numerical tool able to predict the dioptric power adjustment as a function of the UV irradiation parameters, we setup a purely mechanic finite element model of the lens, adopting a hyperelastic material model embedded with eigen-deformations. Numerical simulations of axis-symmetric irradiation closely reproduced the experimental results, in terms of both lens geometry and dioptric power, for positive, negative and lock-in corrections.

EFFECT OF LASER AND MECHANICAL PARAMETERS ON STRENGTH OF FIBER BRAGG GRATINGS

The length of the optical fiber which contains the sensor must be able to withstand the tensile loads that will be placed on it during the duration of its service lifetime. It is important to assess the effect of the UV radiation and removal of coating on the strength of the fiber within the region where the grating has been written. In this study, we have identified the various mechanical and laser fabrication parameters which constrain the strength of fiber gratings. These factors include the laser pulse rate, laser energy per pulse, UV exposure time, methods of coating removal and environmental degradation (moisture). The variation in strength with respect to these factors is discussed in detail. However, it is observed in all the investigations that the average strength of all the fiber grating samples decreased. Finally, the enhancement of mechanical strength of fiber gratings can be achieved by adjusting the laser settings and improving the coating removal methods.

METHOD TO EVALUATE GERMICIDAL EFFICIENCY OF UR-UVGI SYSTEM

UVGI (Ultraviolet Germicidal Irradiation) system is recently considered for the sterilization of indoor air and practically applied to the buildings where need hygienic control mainly in America and Europe. In this study, the factors influencing the germicidal effect such as UV intensity and exposure time were reviewed and the several methods to evaluate the germicidal efficacy of UR (Upper Room)-UVGI system were introduced. The methods mainly use CFD simulation to calculate UV dose, considering the distribution of UV intensity of UR-UVGI system and the air flow induced by air handling system in a room. The methods were applied to a typical 4-patient ward model. Results showed that the positions of UR-UVGI system and supply or exhaust openings are important for UV dose. For example, spatial average UV dose decrease when UR-UVGI system is installed near the exhaust openings. Similar results were shown in the cases that the contaminants assumed to be exhausted from the mouth of patient. In the cases assuming infectious microbe flow in through supply openings or breathing of occupant, the germicidal efficacy of UR-UVGI could be evaluated with the methods.

Twisted liquid crystal pi cell stabilized by polymer-sustained alignment

A uniform π-twist liquid crystal (LC) alignment was stabilized in a pi cell by photopolymerization of a minute amount of monomers without using any chiral material. Controlling UV exposure time can vary the LC pretilt angle to achieve a stabilized π-twist state. This type of π-twisted LC cell made using the polymer-sustained alignment has a pretilt angle estimated to be ∼20°. This cell can quickly transform into a bend state at a low driving voltage and shows excellent brightness and optical contrast, as compared with a conventional pi cell and a chiral-doped cell.

Tuning the Surface Free Energy of Polybenzoxazine Thin Films

A novel approach to manipulate the surface free energy and wettability on polybenzoxazine thin films can be achieved simply by varying the time of thermal treatment or UV exposure. A fraction of the intramolecular hydrogen bonding of the as-cured sample will convert into intermolecular hydrogen bonding upon thermal treatment or UV exposure and, thus, results in an increase in the hydrophilicity and wettability. This UV approach provides a simple method to generate wettability patterns or wettability gradients on the surface of a polybenzoxazine film. In addition, we have applied this technique to the preparation of a large-area periodic array of CdTe colloidal nanocrystals on polybenzoxazine thin films.