Novel SnO₂ based optical sensor for detectin of low ammonia concentration in water at room temperatures

In the work, presented are preliminary experimental results on the capability of a metal oxide (MO) based optical sensor to perform ammonia detection in water environment at room temperature. The electro-spray pyrolysis technique was used to deposit SnO₂ films on the distant end of standard silica optical fiber (SOF). Reflection spectra of the studied samples were preliminarily characterized in the range of 1520 to 1620 nm by using a tunable laser and an optical spectrum analyzer. Single wavelength reflectance measurements were carried out to test the sensing performances for detecting the ammonia of concentration from 4 to 20 ppm. High sensitivity to the target analyte and fast response times were observed. From the results obtained, the detection limit close to a sub-ppm level was achieved

Optical and electrical properties of Zn1-xBexSe grown by molecular beam epitaxy

Journal of Physical Studies, 8(4): pp. 384–388. Retrieved September 19, 2006 from http://www.ece.drexel.edu/mml/pubs/jps_paper.pdfThe dopant behaviour in the n-type ZnBeSe:Cl and p-type ZnBeSe:N grown by Molecular Beam Epitaxy (MBE) is investigated. All the samples have been grown on (001) GaAs substrates (conducting or semi-insulating). For the experimental investigation the photoluminescence (PL), Raman Scattering, photoconductivity and I–V measurements are used. From the temperature (9 K–300 K) and exitation intensity dependent on PL measurements it will be shown that donor and acceptor impurities exhibit a somewhat different behaviour and/or properties from those in ZnSe. We argue that (i) the activation energy of both the N acceptor and Cl donor increases in ZnBeSe as concentration of Be increases; (ii) all the indoped and n-type samples exhibit high (>180 K) temperature PL associated with shallow impurity of acceptor type, which also show an increase in the binding energy with Be composition; Raman scattering experiments have shown that at low Be concentrations (x < 0.04) one can use LO photon energy in ZnSe in the analyses of PL spectra from ZnBeSe. From photoconductivity and I–V measurements we show that (i) there are a number of carrier traps in ZnBeSe:Cl; (ii) some of the ZnBeSe samples with Be concentrations over 1% exhibit photoconductivity behaviour associated with the presence of DX centres or other deep trap, i. e., we observe persistent photoconductivity; (iii) volt-ampere dependencies (with and without irradiation) are different for the samples grown on conducting and semi-insulating substrates

Theory of cultural resilience as an instrument for interpretation of cultural changes in North-Western Black Sea region on the Pleistocene-Holocene boundary under the global climate change

Рассматривается теория упругости культуры как инструмент интерпретации культурных изменений в Северо-Западном Причерноморье на рубеже плейстоцена и голоцена под влиянием глобальных изменений климата.This article summarizes the contemporary postulates of the cultural resilience theory and examines the possibility of its application for the studies of human response to the global climate change in the Early Prehistoric societies. Evolution of the subject field of the resilience concept is demonstrated through the broad range of natural, social and environmental sciences. Subject of special attention of the author is the essence of cultural resilience notion and its application in the prehistoric studies, particularly, for the hunter-gatherers societies. The article particularly focuses on the transformation of livelihood and subsistence strategy of the population of the North-Western Black sea region which took place on the Pleistocene-Holocene boundary in connection with the Black Sea level rise and the coastline migration and possibility of its further explanation on the base of the cultural resilience theory. As the result, the culture resilience theory is conceptualized as an important component of the contemporary methodology of the conceptualization of human and nature interaction in historical retrospection, applied for explanation of the durability and the scale of changes in the mode of life, subsistence strategy and social networking background. In this context the special emphasis in the cultural resilience studies should be made on the everyday routine activities of prehistoric population, which helped this cultural group to survive without any principal transformations

MODELLING OF RAPID STAGE DECAY OF SIGNAL OF OPTICAL SENSOR BASED ON HETEROSTRUCTURE CdS-Cu2 S

The work is devoted to modeling and calculation of the spatial distribution of the concentration of charge localized in the space charge region (SCR) heterojunction, this distribution changes with time at different initial filling of deep traps centers nonequilibrium holes. Within the framework described model the theoretical calculation of two characteristic stages of relaxation current, compliance with the calculated and experimentally obtained dependencies was demonstrated

ЕЛЕКТРОКАТАЛІЗАТОРИ ДЛЯ КИСНЕВИХ СЕНСОРІВ НА ОСНОВІ ГЕТЕРОМЕТАЛІЧНИХ M/Mn(II) (M= Cо(III), Cu(II)) ОКСАЛАТНО-АМІННИХ КОМПЛЕКСІВ

In this work are explored studies of the optical absorption and photoluminescence of nanocristals sulfide cadmium, synthesed by method sol-gel technologies in food and photographic gelatine. It is shown that under equal condition of the syntheses in food gelatine are formed nanocristals greater size, than in photographic gelatine. It is made conclusion that, factor, defining size nanocristals sulfide cadmium, is viscosity gelatines, which is directly connected with presence of the impurites.Синтезированы электрокатализаторы восстановления кислорода на основе активированного угля СИТ-1, промотированного продуктами пиролиза гетерометаллического комплекса [CoL][Mn(C2 O4 )2 ]Clx3H2 O, где L = три-(2-аминоэтилметиленамин)-амин и [Cu(Еn)2 ] [Mn2 (С2 О4 )3 ] x6H2 O. Методом термогравиметрического анализа и масс-спектрометрией ионизирующих частиц определены продукты пиролиза и установлен механизм разложения комплекса. Установлены оптимальные условия синтеза катализаторов, влияющие на эффективность электровосстановления кислорода. Синтезовані електрокаталізатори відновлення кисню на основі активованого вугілля СІТ-1, промотованого піролізованним гетерометалічним комплексом [CoL][Mn(C2 O4 )2 ]Clx3H2 O, де L = три-(2-аміноетилметиленамін)-амін та [Cu(Еn)2 ] [Mn2 (С2 О4 )3 ]x6H2 O. Методом термогравіметричного аналізу та мас-спектрометрією іонізуючих частин виявлені продукти піролізу та встановлений механізм розкладу комплексу. Встановлені оптимальні умови синтезу каталізаторів, що впливають на ефективність електровідновлення кисню.

РЕЛАКСАЦІЯ СИГНАЛУ В СЕНСОРІ ЗОБРАЖЕННЯ НА БАЗІ НЕІДЕАЛЬНОГО ГЕТЕРОПЕРЕХОДУ

In this article is discribed the results of the research of the processes of relaxation of a nonequilibrium charge in the barrier region of a nonideal heterojunction. A sensor based on this heterojunction, even at room temperature, can store a latent image long enough, as it is formed by a nonequilibrium charge occupied in deep traps in the space charge region where occur a significant recombination barrier.The research of relextation of the signal after the excitation light was turned off was accomplished at four points of the sensor. It is established that at different points the signal decreases with the same indicative relaxation time, but it differs in absolute magnitude. It is evidence that the heterogeneity of the sensor to photosensitivity is caused by a significant change along the surface of the concentration of trap centers with the same parameters that determine the probability of thermal emission.Исследованы процессы релаксации неравновесного заряда в барьерной области неидеального гетероперехода. Сенсор на основе такого гетероперехода даже при комнатной температуре может достаточно долго хранить скрытое изображение, так как оно сформировано неравновесным зарядом, захваченным на глубокие ловушки в области пространственного заряда, где имеется значительный рекомбинационный барьер. Исследование релаксации сигнала после выключения возбуждающего света было выполнено в четырех точках сенсора. Установлено, что в разных точках сигнал убывает с одним и тем же характерным временем релаксации, однако сильно отличается по абсолютной величине. Это свидетельствует о том, что неоднородность сенсора по фоточувствительности вызвана существенным изменением вдоль поверхности концентрации ловушечных центров с одними и теми же параметрами, определяющими вероятность термического выброса.Досліджено процеси релаксації нерівноважного заряду в бар’єрній області неідеального гетероперехода. Сенсор на базі такого гетеропереходу навіть при кімнатній температурі може досить довго зберігати сховане зображення, тому що воно сформовано нерівновагим зарядом, захопленим на глибокі пастки в області просторового заряду, де мається значний рекомбінаційний бар’єр. Дослідження релаксації сигналу після вимикання збудливого світла було виконано в чотирьох точках сенсора. Установлено, що в різних точках сигнал убуває з тим самим характерним часом релаксації, однак сильно відрізняється по абсолютній величині. Це свідчить про те, що неоднорідність сенсора по фоточутливості викликана істотною зміною уздовж поверхні концентрації пасткових центрів з тими самими параметрами, що визначають імовірність термічного викиду

Synthesis of CdS Nanocrystalsin the Gelatin Matrix with Different рН Values and their Optical Properties

We have investigated the influence of solution pH on the formation of nanocrystals and their size in the process of synthesis. We have analyzed the optical absorption spectra and luminescence of colloidal solutions of NC CdS.Nanocrystals of cadmiumsulphide were obtained by sol-gel technology in gelatin solution which has different pH values (6 ÷ 10). A decrease was observed in the average size of the nanocrystals from 8 till 3.5 nm while reducing pH from 10 to 6. There has been established the dependence of the contour of luminescence spectra from pH values