UV Photodiode Research Articles

Large Area Visible Blind 4H-SiC p+/N UV Photodiode Obtained by Aluminium Implantation

4H-SiC junction photodiodes, obtained by aluminium (Al) ion- implantation on low doped n-type epilayers are widely characterized observing an extremely low dark current density < 1 nA/cm2 at -100 V up to 90°C, a peak responsivity of 0.11 A/W at 280 nm corresponding to a quantum efficiency of 50% and a visible blindness > 103. The absence of optically active defects and pairs recombination centers was monitored by electro-optical and Emission Microscopy measurements.

Simultaneous determination of amlodipine and telmisartan from pharmaceutical products by way of capillary electrophoresis

Abstract A rapid, simple and sensitive capillary zone electrophoresis method was developed for the simultaneous determination of amlodipine besylate and telmisartan, in fixed-dose combinations, through the utilization of a UV photodiode array detector. Electrophoretic parameters such as buffer concentration and pH, system temperature, applied voltage and injection parameters, were optimized in order to improve the efficiency of the separation. The best results were obtained when employing fused silica capillary (48 cm length X 50 μm ID) and 50 mM phosphate buffer electrolyte at pH 4.50, + 25 kV applied voltage, as well as 25°C system temperature. The separation was achieved in approximately 3 minutes, with a resolution of 4.90, while the order of migration was amlodipine followed by telmisartan. The analytical performance of the method was verified with regard to linearity, precision and robustness. In addition, the limit of detection and the quantification were calculated.

Visible-blind ultraviolet photodiode fabricated by UV oxidation of metallic zinc on p-Si

A UV photodiode fabricated by the UV oxidation of a metallic zinc thin film on p-Si has manifested unique photoresponse characteristics. The electron concentration found by the Hall measurement was 3 × 1016 cm−3, and such a low electron concentration resulted in a low visible photoluminescence. UV illumination enhances the oxidation at low temperatures and decreases the concentration of the oxygen vacancies. The I-V characteristic showed a good rectification with a four-order magnitude difference in the forward and reverse currents at 2 V, and its linear and frequency independent C−2–V characteristic confirmed an abrupt pn junction. The photoresponse showed a visible blindness with a responsivity ratio of UV and visible light as high as 100. Such a visible-blind photoresponse was attributed to the optimum thickness of the SiO2 formed on the Si surface during the UV oxidation at 400 °C. A lower potential barrier to holes at the ZnO/SiO2 interface facilitates Fowler-Nordheim tunneling of the photo-generated holes during the UV illumination, while a higher potential barrier to electrons efficiently blocks transport of the photo-generated electrons to the ZnO during the visible light illumination. The presence of oxide resulted in a slow photoresponse to the turn-on and off of the UV light. A detailed analysis is presented to understand how the photo-generated carriers contribute step by step to the photocurrent. In addition to the slow photoresponse associated with the SiO2 interfacial layer, the decay of the photocurrent was found extremely slow after turn-off of the UV light. Such a slow decay of the photocurrent is referred to as a persistent photoconductivity, which is caused by metastable deep levels. It is hypothesized that Zn vacancies form such a deep level, and that the photo-generated electrons need to overcome a thermal-energy barrier for capture. The ZnO film by the UV oxidation at 400 °C was found to be rich in oxygen and deficient in zinc.

Simultaneous determination of aliskiren, amlodipine and hydrochlorothiazide in spiked human plasma and urine by high performance liquid chromatography

A reversed-phase (RP) liquid chromatographic technique for the simultaneous determination of aliskiren (ALS), amlodipine (AMD) and hydrochlorothiazide (HCT) in spiked human plasma and urine is presented. The method employs a gradient elution using 10 mM orthophosphoric acid containing 0.1% triethylamine (pH 2.5, v/v) and acetonitrile and an RP-C18 column (4.6 mm × 250 mm, 5 μm, Phenomenex) at 1 mL/min of flow rate, with a UV photo diode array detector at 271 nm. The linear ranges were 0.01–10 μg/mL in plasma and 0.05–10 μg/mL in urine for both ALS and AMD. The linearty of HCT was in the range of 0.0125–2.5 μg/mL in plasma and urine. Correlation coefficients (r2) were higher than 0.9983 for all of the analytes, indicating good linear relationship. The method validation was performed with respect to linearity, recovery, accuracy, precision and stability. The developed method could be applied in the routine clinical analysis.

Optimization and validation of an HPLC-photodiode array detector method for determination of organic acids in vinegar.

A novel isocratic RP-HPLC method with UV photodiode array detection for the determination of seven organic acids in vinegar samples was developed and optimized. Samples were analyzed on a C18 (150 × 4.6 mm id, 5 μm) analytical column. Methanol-0.010 M sodium dihydrogen phosphate buffer adjusted with H3PO4 to pH 2.80 (2 + 98, v/v), was used as the mobile phase. The column oven temperature was optimized at 23.0°C, the flow rate was 0.80 mL/min, and the detection wavelength was 210 nm. Matrix-matched calibration curves were prepared for all analytes, and the correlation coefficients were greater than 0.99. LOD and LOQ ranged from 0.10 to 10.0 and 0.30 to 30.0 μg/mL, respectively. The results for interday and intraday precision and accuracy fell within the ranges specified. Vinegar samples were quantified by the standard addition method. The main advantages of this method are its selectivity, which is one of the main weaknesses of most methods when determining organic acids in complex matrixes, and its simplicity since little sample preparation is needed. Moreover, it is safe and inexpensive with low organic solvent usage.

Highly sensitive fast-response UV photodiode fabricated from rutile TiO2 nanorod array on silicon substrate

An ultraviolet photodiode based on rutile TiO2 nanorods, which were grown on p-type Si substrate seeded with a TiO2 layer, was synthesized by radiofrequency reactive magnetron sputtering. Chemical bath deposition was performed to grow rutile TiO2 nanorods. X-ray diffraction and field emission-scanning electron microscopy were conducted to determine the structural and optical properties of the sample. The synthesized TiO2 nanorods exhibited tetragonal rutile structure. The device showed 3.79×102 sensitivity when it was exposed to 325nm light (1.6mW/cm) at 5V bias voltage. In addition, the internal gain of the photosensor was 4.792 and the photoresponse peak was 460mA/W. The photocurrent was 6.09×10−4A. The response and recovery times of the PD were 50.8 and 57.8ms, respectively, upon illumination of a pulsed UV light (325nm, 1.6mW/cm2) at 5V bias voltage.

Improved two-dimensional responsivity physical model of a CMOS UV and blue-extended photodiode

A CMOS UV and blue-extended photodiode is presented and fabricated for light detection in the ultraviolet/blue spectral range. An octagon homocentric ring-shaped geometry is used to improve the ultraviolet responsivity and suppress edge breakdown. This paper has established a two-dimensional responsivity physical model for the presented photodiode and given some numerical analyses. The dead layer effect, which is caused by the high-doping effects and boron redistribution, is considered when analyzing the distribution of the current of the proposed UV and blue-extended photodiode. In the dead layer, the boron doping profile decreases towards the surface. Simulated results illustrate that the responsivity in the UV range is obviously decreased by the effect of the dead layer, while it is not affected in the visible and near-infrared part of the spectrum. The presented photodiode is fabricated and the silicon tested results are given, which agree well with the simulated ones.

Phenolic Profile of Tunisian Opuntia Ficus Indica Thornless form Flowers via Chromatographic and Spectral Analysis by Reversed Phase-High Performance Liquid Chromatography-UV-Photodiode Array and Electrospray Ionization-Mass Spectrometer

The qualitative and quantitative analysis of phenolic compounds of the methanol extract of Tunisian thornless form Opuntia ficus indica flowers was described. Reversed phase high-performance liquid chromatography UV photodiode array analysis detected four peaks at 320 nm, attributed to phenolic acids; three of them were quantified to 141 mg.kg−1 of fresh plant material. Electrospray ionization mass spectrometer analysis detected 8 glycosylated flavonols at 350 nm, identified among 11 chromatographic peaks. The amount of flavonoids was 4980 mg.kg−1 of fresh plant material, with isorhamnetin glycosylated derivatives as the main flavonoid components (55.1%), quercetin derivatives as the second (23.7%), and kaempferol derivatives as the third (8.4%).

Specificity of Lipoxygenase Pathways Supports Species Delineation in the Marine Diatom Genus Pseudo-nitzschia

Oxylipins are low-molecular weight secondary metabolites derived from the incorporation of oxygen into the carbon chains of polyunsaturated fatty acids (PUFAs). Oxylipins are produced in many prokaryotic and eukaryotic lineages where they are involved in a broad spectrum of actions spanning from stress and defense responses, regulation of growth and development, signaling, and innate immunity. We explored the diversity in oxylipin patterns in the marine planktonic diatom Pseudo-nitzschia. This genus includes several species only distinguishable with the aid of molecular markers. Oxylipin profiles of cultured strains were obtained by reverse phase column on a liquid chromatograph equipped with UV photodiode detector and q-ToF mass spectrometer. Lipoxygenase compounds were mapped on phylogenies of the genus Pseudo-nitzschia inferred from the nuclear encoded hyper-variable region of the LSU rDNA and the plastid encoded rbcL. Results showed that the genus Pseudo-nitzschia exhibits a rich and varied lipoxygenase metabolism of eicosapentaenoic acid (EPA), with a high level of specificity for oxylipin markers that generally corroborated the genotypic delineation, even among genetically closely related cryptic species. These results suggest that oxylipin profiles constitute additional identification tools for Pseudo-nitzschia species providing a functional support to species delineation obtained with molecular markers and morphological traits. The exploration of the diversity, patterns and plasticity of oxylipin production across diatom species and genera will also provide insights on the ecological functions of these secondary metabolites and on the selective pressures driving their diversification.

P-N Junction of NiO Thin Film for Photonic Devices

The development of a short-wavelength p-n junction device is essentially important for the realization of transparent electronics for next-generation optoelectronics. Nickel oxide (NiO) thin films with a tunable electrical conductivity of both p-type and n-type under the optimized growth conditions using RF sputtering technique with high optical transmission in the visible region have been fabricated. The room-temperature conductivities for n-type and p-type NiO thin films were about 5.91 × 101 and 1.9 ×10-2 S·cm-1, respectively. A p-n junction of NiO thin film has been realized, successfully exhibiting good rectifying behavior with efficient UV photodiode characteristics, providing suitable solution for low-cost visible blind UV photodetector application.

Oligonucleotide Bioanalysis: Sensitivity Versus Specificity

Oligonucleotide Bioanalysis: Sensitivity Versus Specificity

Validation of a Capillary Electrophoresis Method for the Simultaneous Determination of Amlodipine Besylate and Valsartan in Pharmaceuticals and Human Plasma

A rapid, simple, and sensitive capillary electrophoresis (CE) method was developed and validated for the simultaneous determination of amlodipine (AML) and valsartan (VAL) in pharmaceuticals and human plasma using a UV photodiode array detector. Electrophoretic conditions were optimized to improve separation, sensitivity, and rapidity. The optimal conditions were 25 mM phosphate buffer at pH 8.0, injection time 10.0 s, voltage 25 kV, and column temperature 25 degrees C, with detection at 214 nm. The method was found to be linear in the range of 1.0-35 and 1.0-350 mg/L, with weighted regression 0.9999 and 0.9994, for AML and VAL, respectively. Validation of the method showed acceptable intraday and interday accuracy (85.5-95.3%) and precision (RSD 1.64-4.2%) in pharmaceutical formulation and human plasma analysis. The sensitivity of the method was enhanced by both optimization of the CE procedure and preconcentration performed by liquid-liquid extraction. The LOD for both AML and VAL was 0.03 mg/L, which allows analysis at the level of the drugs possibly found in human plasma. Therefore, the proposed method is suitable for QC in pharmaceutical laboratories and therapeutic drug monitoring in clinical laboratories.

UV and MS Identification of Urolithins and Nasutins, the Bioavailable Metabolites of Ellagitannins and Ellagic Acid in Different Mammals

Urolithins are microbial metabolites produced from ellagic acid after the intake of dietary ellagitannins by different animals. Urolithin metabolites have distinct UV spectra that enable their detection and differentiation by HPLC coupled with UV photodiode array detectors. Correlations between structural characteristics, including conjugation, with the UV spectra and retention times are established. The production of urolithin derivatives in different animals feeding on ellagitannins, including rodents (rats and mice), humans, pigs, squirrels, beavers, sheep, bull calves, birds, and insects, was investigated. All mammals produced urolithins, and their glucuronyl and sulfate conjugates were the main metabolites detected in plasma and urine. Unconjugated urolithins were detected in feces, ruminal content, and beaver castoreum. Different urolithin hydroxylation patterns were observed for different animal species, suggesting that the microbiota responsible for the metabolism of ellagitannins in each animal species produces dehydroxylases for the removal of specific hydroxyls from the ellagic acid residue. Metabolites were characterized using HR HPLC-TOF-MS and ion trap MS/MS. Insects and birds feeding on ellagitannin-containing foods did not produce urolithins, although they released ellagic acid. Beavers and pigs were able to produce dehydroxyellagic acid derivatives (nasutin A), showing that in some cases the removal of hydroxyl groups from the ellagic acid nucleus can be carried out before the lactone ring is opened to produce urolithins.

Simple and Rapid RP-HPLC Method for Simultaneous Determination of Acyclovir and Zidovudine in Human Plasma

Combination therapy with acyclovir and zidovudine is used for the treatment of herpes-infected immunocompromised patients. In the view of the optimal drug concentrations (minimum effective concentrations) for viral suppression and avoidance of drug toxicity, monitoring of drug levels has been considered essential to determine drug concentrations in plasma after administration of a dose of acyclovir and zidovudine. A simple, precise, and rapid RP-HPLC method has been developed for this purpose. Chromatographic separation was performed using methanol-water (50 + 50, v/v), pH 2.5 adjusted with orthophosphoric acid, as an isocratic mobile phase at a flow rate of 0.8 mL/min with an Inertsil ODS (C18) column (5 microm particle size, 250 x 4.60 mm id). Detection was carried out using a UV photo diode array detector at 258 nm. The plasma samples were prepared by a protein precipitation method. The retention time for acyclovir and zidovudine was 3.5 +/- 0.2 and 6.2 +/- 0.3 min, respectively. The method was linear in the range of 200-1800 and 400-3600 ng/mL with LOQ of 200 ng (SD = +/-1.4) and 400 ng (SD = +/-0.9) for zidovudine and acyclovir, respectively, in plasma. The mean accuracy was 98.0 and 96.4%, with average extraction recovery of 64.8 +/- 2.1 and 77.5 +/- 1.7% for lower nominal concentrations of acyclovir and zidovudine, respectively.

Simultaneous identification of glucosinolates and phenolic compounds in a representative collection of vegetable Brassica rapa

Brassica rapa rapa group is widely distributed and consumed in northwestern Spain. The consumption of Brassica vegetables has been related to human health due to their phytochemicals, such as glucosinolates and phenolic compounds that induce a variety of physiological functions including antioxidant activity, enzymes regulation and apoptosis control and the cell cycle. For first time in Brassica crops, intact glucosinolates and phenolic compounds were simultaneously identified and characterized. Twelve intact glucosinolates, belonging to the three chemical classes, and more than 30 phenolic compounds were found in B. rapa leaves and young shoots (turnip greens and turnip tops) by LC–UV photodiode array detection (PAD)–electrospray ionization (ESI). The main naturally occurring phenolic compounds identified were flavonoids and derivatives of hydroxycinnamic acids. The majority of the flavonoids were kaempferol, quercetin and isorhamnetin glycosylated and acylated with different hydroxycinnamic acids. Quantification of the main compounds by HPLC-PAD showed significant differences for most of compounds between plant organs. Total glucosinolate content value was 26.84 μmol g −1 dw for turnip greens and 29.11 μmol g −1 dw for turnip tops; gluconapin being the predominant glucosinolate (23.2 μmol g −1 dw). Phenolic compounds were higher in turnip greens 51.71 μmol g −1 dw than in turnip tops 38.99 μmol g −1 dw, in which flavonols were always the major compounds.

HPLC method validation for measurement of sulforaphane level in broccoli by‐products

A simple and specific analytical method was developed and tested for the determination of sulforaphane in broccoli by-products. The method includes the optimization of the conversion of glucoraphanin to sulforaphane, followed by purification of extracts using solid-phase extraction and high-performance liquid chromatography (HPLC) analysis. The response surface methodology was used to find optimum conditions for the preparation and purification procedure. Chromatographic conditions for reversed-phase HPLC with UV photodiode array detection were as follows: column, Exil ODS C(18), 25 x 0.46 cm, 5 microm; column temperature, 36 degrees C; mobile phase, a 30 : 70 (v/v) mixture of acetonitrile:water; flow rate, 0.6 mL/min. The detection wavelength was UV 202 nm. Under these conditions, excellent linearity was obtained (r(2) = 1), and the overall recovery was 97.5 and 98.1% for fresh florets and lyophilized florets, respectively. The precision results showed that the relative standard deviation of the repeatability for florets fresh and lyophilized was 3.0 and 4.0%, respectively. Sulforaphane contents were determined in the edible portion of fresh broccoli, and broccoli crop remains.

Rapid seed oil analysis using UPLC for quality control and authentication

AbstractWithout derivatization and halogenated solvent, various seed oil samples were rapidly characterized using a UPLC (Ultra Performance LC) equipped with UV photodiode array and mass spectrometer detectors. The method acquires multiple types of data in a single injection to authenticate seed oil, analyze triacylglycerol composition, and evaluate seed oil oxidation. It can, for example, identify olive oil samples adulterated with <1% of other seed oils. Compared with conventional high‐performance liquid chromatography methods, the UPLC solution shortens analysis time, reduces solvent usage, and provides more information, resulting in cost benefit. The reduction in analysis time and solvent usage align with the principles of green chemistry.

Schottky Barrier Lowering in 4H-SiC Schottky UV Detector

The Schottky barrier lowering in 4H-SiC interdigit Schottky-type UV photodiode is investigated in the presence of a thermally grown oxide layer on the exposed active area. Gain photocurrent is observed and correlated with the presence of the oxide and with the charge traps at the semiconductor/oxide interface. Photo-thermally stimulated current measurements evidenced that interface charge accumulation is optically promoted. Rise and fall photo-current measurements provided the time parameter of the trapping phenomenon.

Performance optimization of a membrane assisted passive sampler for monitoring of ionizable organic compounds in water

A thin-walled silicone rubber hollow fibre membrane has been developed as a passive sampler. The inside of the tube is filled with an aqueous solution at an appropriate pH. The tube is sealed at both ends and then immersed in a water sample. In order for the ionizable permeating compounds to be trapped in the aqueous receiving phase, the pH is adjusted such that the compounds are ionized and trapped. The major advantages are its simplicity, low cost and high selectivity, since only ionizable organic compounds are trapped. Additionally, the sampler uses no organic solvent. By adjusting the pH of the acceptor phase, it is possible to control the extraction process and whether the sampler is used in the kinetic or equilibrium regime. Since it is very selective, no further clean-up of the extract is required. The membrane assisted passive sampler has been tested for extraction of chlorophenols under laboratory conditions. The extraction process was found to be linear over a 72 h sampling period. Selectivity of the passive sampler in river water was demonstrated and the extraction process was independent of sample concentration, even at lower concentration levels of analytes. However, the sample matrix in some river water samples led to incomplete trapping, thereby reducing the amount trapped in the acceptor phase. Detection limits (three times signal to noise ratio) were dependant on sample matrix and type of detection system and ranged from 0.05 microg L(-1) to about 1 microg L(-1) with a UV photodiode detector in water samples from one river and 1.0 microg L(-1) to 20 microg L(-1) in another but with an ordinary UV detector. The enrichment factors in river water were 28 for 2-chlorophenol and 44 for 2,4-dichlorophenol over a 72 h sampling period. 4-chlorophenol was poorly extracted and its enrichment factor was 3.

UV Bandpass Optical Filter for Microspectometers

This paper describes the design and modeling of a UV bandpass optical filter for microspectrometers. The materials used for fabricating the multilayer UV filter are: silicon dioxide (SiO2), titanium dioxide (TiO2) and yttrium oxide (Y2O3). The optical filter shows a bandpass response wavelength in the range 230-280 nm, with a transmittance higher than 80%. Such a device is extremely suitable for optical detection of biological molecules with optical absorption or/and fluorescence in the UV spectral range. This UV optical filter can be built using post- processing after integrated-circuit and UV photodiode fabrication in a bipolar or CMOS technology. The dielectric multi-layer stack can be deposited on top of the UV photodiode after the standard technology process has been completed. The number of layers was optimized for 11 with all layers of a thickness acceptable for reproducible fabrication. The materials used for fabricating the UV filter are silicon compatible. Applications presented are in DNA solutions (to measure the optical density of these solutions at 260 nm) and in the detection of a gas flame in the presence of ambient light based on the different emission spectra in the UV.