ИССЛЕДОВАНИЕ ТОНКИХ ПЛЕНОК Cu2ZnSnSe4 МЕТОДОМ АТОМНО-СИЛОВОЙ МИКРОСКОПИИ

In comparison to the traditional use of glass substrates, the thin films onto metal substrates offer improved device cooling, economical large-scale roll-to-roll processing, and applicability in lightweight, as well as flexible products. However, unlike glass, metal foils tend to exhibit rough surfaces. This article studies the substrate-type (Mo/glass and Мо-foil) effect on the topographic characteristics of the Cu2ZnSnSe4 films by atomic force microscopy (AFM). Cu2ZnSnSe4 thin films were prepared by the electrodeposition of stack copper/tin/copper/zinc (Cu/Sn/Cu/Zn) precursors, followed by selenization. AFM wasused to study the topographic characteristics of thin films, including grain size, surface roughness, and maximum height of the profile. It is shown that the films obtained on Mo/glass and Mo-foil substrates have similar roughness and in the both cases the grain structure is formed. The Cu2ZnSnSe4 thin films show relatively high surface roughness and maximum roughness profile height compared to Cu-Zn-Sn precursors. The increase in the surface roughness of the films was caused by the growth of grains during annealing and selenization processes.Методом атомно-силовой микроскопии исследовано влияние типа подложки на структуру и шероховатость поверхности пленок Cu2ZnSnSe4, полученных методом селенизации металлических прекурсоров Cu-Zn-Sn на подложках из стекла с подслоем молибдена и молибденовой фольги (Мо/стекло, Мо-фольга). Обнаружено, что пленки Cu2ZnSnSe4 на подложках Мо/стекло и Мо-фольга имеют близкие значения шероховатости и зернистую структуру. Пленки Cu2ZnSnSe4 имеют более высокие значения шероховатости и максимальной высоты неровности профиля, чем металлические прекурсоры Cu-Zn-Sn. Увеличение шероховатости при формировании пленок Cu2ZnSnSe4 из прекурсоров происходит за счет роста зерен в процессе отжига и селенизации

ИЗОТОПНЫЕ ОТНОШЕНИЯ СТРОНЦИЯ 87Sr/86Sr В ВОДЕ РЯДА РЕК ЮЖНОГО УРАЛА

87Sr/86Sr isotopic ratios are widely used to identify strontium sources and study strontium behaviour in(bio)geochemical cycles. 87Sr/86Sr in surface waters can reflect the average composition of bioavailable (i.e. available forfurther absorption by plants and animals) strontium in the catchment specific area. Based on those 87Sr/86Sr ratios, theregional maps of the bioavailable strontium distribution (strontium isoscapes) can be compiled. A complex block structurecharacterizes the Ural mountain system. Individual parts (blocks) are composed of rocks of various ages, genesis andgeochemical characteristics, which can radically change at a distance of several tens of kilometres. Such variability wouldbe reflected in strontium isotopic ratios, thus making it possible to determine the local isotopic signatures of bioavailablestrontium.This work aimed to study 87Sr/86Sr in the water in the rivers of the Southern Urals. We determined the contents andisotopic ratios of strontium in river water samples collected from the territories of the Orenburg and Chelyabinsk regionsand the Republic of Bashkortostan in 2019–2020.For the first time in the surface water of the rivers in the Southern Urals (Ural, Belaya, Tobol, Karagaily-Ayat, Sim, andothers), the 87Sr/86Sr isotopic ratios have been determined, and their variations have been analyzed. 87Sr/86Sr values varyin the range 0.70666–0.71063 (average 0.70908) for the rivers of the Urals basin, 0.70749–0.71058 (average 0.70924)for the Kama-Volga basin, 0.70946–0.71176 (average 0.71071) for the Tobol basin. Such features of the strontium isotopiccomposition may be due to the influence of underlying rocks of the catchment area drained by river water. The dataobtained can be used to identify the sources of strontium input into the water system during hydrological and environmentalstudies; to confirm the authenticity of food products of plant and animal origin; to carry out comparisons in thestudies of the migration of ancient people and animals, as well as to determine the raw material areas for the productionof vegetable and woollen textiles and wooden products in antiquity.Изотопные отношения стронция 87Sr/86Sr широко используются для выявления источниковстронция и исследования его поведения в (био)геохимических циклах, а в поверхностных водах они могут отражатьусредненный состав биодоступного (доступного для дальнейшего поглощения растениями и животными)стронция на конкретной территории водосбора, на основании чего могут быть составлены региональные картыраспределения биодоступного стронция (Sr изоскейпы). Уральская горная система характеризуется блочнойструктурой, отдельные части (блоки) которой сложены разнообразными по возрасту, генезису и геохимическимособенностям горными породами, которые могут радикально изменяться на расстоянии нескольких десятковкилометров. Такая вариативность будет отражаться и в изотопных отношениях стронция, что позволит с достаточновысокой точностью определить локальные метки биодоступного стронция.Целью работы являлось исследование изотопных отношений стронция 87Sr/86Srв воде ряда рек Южного Урала.В образцах речной воды, отобранных в 2019–2020 гг. с территорий Оренбургской и Челябинской областей и РеспубликиБашкортостан, определены содержания (квадрупольная масс-спектрометрия с индуктивно связаннойплазмой) и изотопные отношения стронция (мультиколлекторная масс-спектрометрия с индуктивно связаннойплазмой и термоионизационная масс-спектрометрия после хроматографического выделения стронция).Впервые в поверхностной воде ряда рек Южного Урала (Урал, Белая, Тобол, Карагайлы-Аят, Сим и др.) определеныизотопные отношения 87Sr/86Sr и проанализированы их вариации. Для рек бассейна р. Урал значения87Sr/86Sr варьируются в диапазоне 0.70666–0.71063 (среднее 0.70908), для бассейна р. Кама – 0.70749–0.71058(среднее 0.70924), для бассейна р. Тобол – 0.70946–0.71176 (среднее 0.71071). Подобные особенности изотопногосостава стронция могут быть обусловлены типом подстилающих горных пород водосбора, дренируемых речнойводой. Полученные данные могут быть использованы для выявления источников поступления стронция в воднуюсистему при гидрологических и экологических исследованиях, для подтверждения аутентичности пищевыхпродуктов растительного и животного происхождения, для проведения сопоставлений при исследованияхмиграций древних людей и животных, а также для определения сырьевых ареалов для производства растительногои шерстяного текстиля, деревянных изделий в древности

⁸⁷Sr/⁸⁶Sr ISOTOPE RATIOS IN THE RIVER WATERS OF THE SOUTHERN URALS

87Sr/86Sr isotopic ratios are widely used to identify strontium sources and study strontium behaviour in(bio)geochemical cycles. 87Sr/86Sr in surface waters can reflect the average composition of bioavailable (i.e. available forfurther absorption by plants and animals) strontium in the catchment specific area. Based on those 87Sr/86Sr ratios, theregional maps of the bioavailable strontium distribution (strontium isoscapes) can be compiled. A complex block structurecharacterizes the Ural mountain system. Individual parts (blocks) are composed of rocks of various ages, genesis andgeochemical characteristics, which can radically change at a distance of several tens of kilometres. Such variability wouldbe reflected in strontium isotopic ratios, thus making it possible to determine the local isotopic signatures of bioavailablestrontium.This work aimed to study 87Sr/86Sr in the water in the rivers of the Southern Urals. We determined the contents andisotopic ratios of strontium in river water samples collected from the territories of the Orenburg and Chelyabinsk regionsand the Republic of Bashkortostan in 2019–2020.For the first time in the surface water of the rivers in the Southern Urals (Ural, Belaya, Tobol, Karagaily-Ayat, Sim, andothers), the 87Sr/86Sr isotopic ratios have been determined, and their variations have been analyzed. 87Sr/86Sr values varyin the range 0.70666–0.71063 (average 0.70908) for the rivers of the Urals basin, 0.70749–0.71058 (average 0.70924)for the Kama-Volga basin, 0.70946–0.71176 (average 0.71071) for the Tobol basin. Such features of the strontium isotopiccomposition may be due to the influence of underlying rocks of the catchment area drained by river water. The dataobtained can be used to identify the sources of strontium input into the water system during hydrological and environmentalstudies; to confirm the authenticity of food products of plant and animal origin; to carry out comparisons in thestudies of the migration of ancient people and animals, as well as to determine the raw material areas for the productionof vegetable and woollen textiles and wooden products in antiquity

Size-dependent photocurrent switching in chemical bath deposited CdSe quantum dot films

Size-dependent photocurrent switching has been investigated in chemical bath deposited CdSe quantum dot (QD) films with band gaps 2.26, 2.09, and 1.81 eV (corresponds to nanoparticles’ average diameter of 4, 5, and 10 nm). CdSe films generate only anodic photocurrent (exhibit n-type semiconductor behavior) in the solution which contains only acceptor of photoholes (SO3 2− anions), whereas cathodic photocurrent (corresponding to p-type behavior) arises after immersionof the films in polyselenide electrolyte (containing Sen 2− /Se 2− redox system). Appearance of the cathodic photocurrent is related to chemisorptions of Se 2− and Sen 2− anions, as revealed by the cadmium underpotential deposition (UPD). Photocurrent switching from anodic to cathodic becomes more pronounced with decreasing of CdSe nanoparticle size because small quantum dots with their broadened band gaps have more favorable conduction band energy for electron injection to polyselenide anions. On the contrary, particle size does not play a significant role for the injection of photoholes into the electrolyte because the position of the valence band is weakly size-dependent, and anodic photocurrent is determined primarily by the real surface area of the electrode, which was found to be greater than the geometrical one by 1–2 orders of magnitude from cadmium UPD. Effective charge separation at the highly developed CdSe-electrolyte interface contributes to high incident photon-to-current conversion efficiency of photocurrent (IPCE ~40 %)

Fabrication of CdS/CdTe-Based thin film solar cells using an electrochemical technique

Thin film solar cells based on cadmium telluride (CdTe) are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i- and p-type CdTe can be grown easily by electroplating. These material layers consist of nano- and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n → p or p → n conversion upon heat treatment. The general trend of CdCl2 treatment is to gradually change the CdTe material’s n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV) effect as well as making use of IR photons from the surroundings when fully optimised

Mosaicism in preimplantation human embryos

Since the very first publications on preimplantation genetic testing, researchers have faced a serious problem — a high mosaicism level in the preimplantation human embryos obtained by means of in vitro fertilization cycles. The nature of this mosaicism and its high impact on embryo development draws attention to this issue. In this research we studied the cells from different parts of preimplantation human embryos with mosaicism in the trophectoderm cells detected using Next-generation Sequencing (NGS). Six human blastocysts with mosaicism in their trophectoderm cells were each sectioned in three parts: two containing only trophectoderm cells and one predominantly inner cell mass. These parts were then analyzed individually. Our data indicate that the proportion of aneuploid cells in bioptate taken for preimplantation genetic testing does not necessarily reflect the true chromosomal status of the whole embryo and cannot be extrapolated to that in the embryoblast cells. The results of our study strongly suggest that mosaicism revealed in blastocyst reduces the likelihood of finding the euploid chromosome set in the other parts of the embryo. Karyotypes of cells from different parts of mosaic embryos show low concordance. Chromosomal abnormalities in mosaic embryos are unpredictably diverse, which may lead not only to loss of conception, but also to the development of genetic disease in the offspring. According to our data, the mosaic rate tends to increase in the samples containing trophectoderm adjacent to the embryoblast, which may have physiological significance for the implantation. Comparative studies focused on the concordance of mosaicism level of and the type of chromosomal abnormalities detected in different parts of preimplantation human embryos will improve clinical recommendations regarding the transfer of mosaic embryos