Formation of the Electric Field Distribution in Thin Electro-Optic Layers for Precision Correction their Optical Characteristics

A method of making given field distribution within thin electro-optical layers by using narrow band electrodes placed at the same electric potential. A formula for electric field intensity produced by a single band electrode is obtained. Electric field modeling for different band electrode configurations is undertaken. It was shown, by applying piezoresponse force microscopy, that in case of highly inhomogeneous field the polarization of lithium niobate electro-optical film persisted only in the area above the band electrode. Lithium niobate, electro-optical structures, piezoresponse force microscopy, Computer simulation

Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 Substrate by RF Magnetron Sputtering under Electric Field

LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric field to study the self-polarization effect. The films have been characterized crystallographically by x-ray diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization for LiNbO3 thin film

Formation of the Electric Field Distribution in Thin Electro-Optic Layers for Precision Correction their Optical Characteristics

A method of making given field distribution within thin electro-optical layers by using narrow band electrodes placed at the same electric potential. A formula for electric field intensity produced by a single band electrode is obtained. Electric field modeling for different band electrode configurations is undertaken. It was shown, by applying piezoresponse force microscopy, that in case of highly inhomogeneous field the polarization of lithium niobate electro-optical film persisted only in the area above the band electrode. Lithium niobate, electro-optical structures, piezoresponse force microscopy, Computer simulation

Formation of the Microcrystalline Structure in LiNbO3 Thin Films by Pulsed Light Annealing

LiNbO3 thin films with a thickness of 200 nm were deposited onto Al2O3 substrate by RF-magnetron sputtering technique without intentional substrate heating. The results demonstrate that post-growth infrared pulsed light annealing of the amorphous LiNbO3 films leads to the formation of two phases, LiNbO3 and LiNb3O8. After annealing at temperatures of 700 to 800 °C, the percentage of the nonferroelectric phase LiNb3O8 was minimal. The surface composition of the films annealed at different temperatures was examined by X-ray photoelectron spectroscopy. Piezoresponse force microscopy was used to study both the vertical and the lateral polarization and to visualize the piezoelectric inactivity of LiNb3O8 grains. A comparison of the results of PFM and XPS measurements revealed that there is a correlation between the fraction of the piezoelectric phase and the film composition: At an annealing temperature higher than 850 °C, the atomic ratio of lithium to niobium decreases compared to the initial value along with a decrease of the fraction of the piezoelectric phase

Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 Substrate by RF Magnetron Sputtering under Electric Field

LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric field to study the self-polarization effect. The films have been characterized crystallographically by x-ray diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization for LiNbO3 thin film

Моделювання сенсора вібрацій на основі біморфної структури

У дослідженні розроблена математична модель, що описує амплітудно-частотний відгук сенсора або пристрою збору скидної енергії, виготовленого з сегнетоелектричної бідоменної монокристалічної пластини, по відношенню до величини вібраційного збудження. Математична модель дозволяє прогнозувати залежність напруги на електродах від частоти і амплітуди вібраційного збудження, а також резонансної частоти сенсора, що представляє собою прямокутну пластину, в загальному випадку з сейсмічної масою на вільному кінці, який встановлюється на вібраційному столику, параметри коливань якого задаються. Складено відповідне диференційне рівняння, що описує шукані залежності, і отримано його аналітичне рішення. Для перевірки запропонованої моделі був створений монокристалічний біморф за допомогою відпалу підкладки з ніобату літію (LiNbO3) на повітрі для оберненої дифузії літію і формування бідоменної структури, що представляє собою два зустрічно поляризованих домени в одній пластині (так звана структура "голова-до-голови"). Такий кристал аналогічний біморфу, проте на відміну від нього не містить будь-яких міжфазних меж, за винятком міждоменної. Таким чином, виготовлений біморф являє собою не поширену збірну конструкцію, що складається найчастіше з металевої підкладки, до якої прикріплені п'єзоелектричні пластини, як правило, з п'єзокераміки, а однорідне безперервне середовище. Перевага такого біморфу полягає у тому, що, будучи виготовленим з сегнетоелектричного монокристала ніобату (або танталата) літію, сенсор або пристрій збору скидної енергії має великий коефіцієнт перетворення деформації згинання в електричну деформацію, а отже, високу чутливість, а також широкий температурний діапазон застосування та практично повну відсутність гістерезису і старіння. Проведено порівняння результатів моделювання з експериментальними даними, з якого випливає, що запропонована модель добре відповідає результатам експерименту. Показано, що сенсори коливань на бідоменних монокристалічних пластинах мають виключно високу чутливість. Запропонована модель дозволяє оцінювати і прогнозувати параметри сенсорів вібрації, акселерометрів і пристроїв збору скидної енергії на основі бідоменних сегнетоелектричних кристалів.In the current study, we have developed a mathematical model describing the frequency response of a sensor or energy harvester based on a cantilever made of a ferroelectric bidomain single-crystal plate with metal electrodes deposited on opposite faces. The structure is subjected to vibrational excitations. The model allows to predict the dependence of the voltage between the electrodes vs. the vibration frequency and amplitude as well as resonance frequency of the sensor fabricated in form of a rectangular plate, normally with a seismic mass on its free end. The device is placed on a vibration table, whose vibration parameters are set. The relevant differential equation was composed, and an analytic solution describing the required dependencies was obtained. To validate the proposed model, we created a single-crystal bimorph by annealing a lithium niobate (LiNbO3) wafer in air to promote Li out-diffusion and formation of a bidomain ferroelectric structure, i.e. two oppositely polarized domains within the plate (the so called “headto-head” structure). Such a crystal demonstrates a bimorph-like behavior but does not comprise any interface except for an interdomain wall. Thus, our bimorph is not a commonly used structure, typically consisting of two bonded piezoelectric plates (generally made of PZT piezoceramics), but a homogeneous continuous medium. Being made of a lithium niobate (or lithium tantalate) ferroelectric single crystal, the cantilever sensor or energy harvester demonstrates a strong dependence of the voltage between the electrodes on the bending deformations, with almost totally absent hysteresis and ageing in a wide temperature range. The comparison made between the results of the modeling and the experiment shows that the proposed model is in good agreement with the experiment. We have demonstrated that the vibration sensors based on bidomain single-crystal plates possess an exceptionally high sensitivity. The proposed model can be used to estimate and predict the parameters of vibration sensors, accelerometers and waste energy harvesters based on bidomain ferroelectric crystals

2-Pyridylselenenyl versus 2-Pyridyltellurenyl Halides: Symmetrical Chalcogen Bonding in the Solid State and Reactivity towards Nitriles

The synthesis of 2-pyridyltellurenyl bromide via Br2 oxidative cleavage of the Te–Te bond of dipyridylditelluride is reported. Single-crystal X-ray diffraction analysis of 2-pyridyltellurenyl bromide demonstrated that the Te atom of 2-pyridyltellurenyl bromide was involved in four different noncovalent contacts: Te⋯Te interactions, two Te⋯Br ChB, and one Te⋯N ChB contact forming 3D supramolecular symmetrical framework. In contrast to 2-pyridylselenenyl halides, the Te congener does not react with nitriles furnishing cyclization products. 2-Pyridylselenenyl chloride was demonstrated to easily form the corresponding adduct with benzonitrile. The cyclization product was studied by the single-crystal X-ray diffraction analysis, which revealed that in contrast to earlier studied cationic 1,2,4-selenadiazoles, here we observed that the adduct with benzonitrile formed supramolecular dimers via Se⋯Se interactions in the solid state, which were never observed before for 1,2,4-selenadiazoles. © 2021 by the authors

Adducts of 2-Pyridylselenenyl Halides and Nitriles as Novel Supramolecular Building Blocks: Four-Center Se···N Chalcogen Bonding versus Other Weak Interactions

Supramolecular chemistry of chalcogenadiazoles is attracting an increasing attention due to its applications in materials chemistry. Chalcogen bonding allows a fine-tuning of the self-assembly and, therefore, modulation of physical properties when these compounds are employed. Here, we report a facile preparation of a broad scope of 1,2,4-selenadiazoles via coupling of 2-pyridylselenenyl halides with unactivated nitriles, that represent a novel type of supramolecular building blocks which eagerly engage in a variety of chalcogen bonding interactions. The substituent-dependent propensity of novel selenadiazoles for the formation of four-center Se···N chalcogen bonding is analyzed. Other weak interactions, which in some cases outcompete the formation of 2Se-2N squares, are described. The discovery of the adducts derived from α-halogenated nitriles, which form robust dimers featuring a very specific combination of 2Se-2N square, two Hal···Hal, and two Se···Hal noncovalent interactions, is presented. © 2021 American Chemical Society