Alena L. Bogoslovtseva

Structural features of aluminum nitride thin films, which are important for applications as a piezoelectric material, are studied. The films are grown by pulsed magnetron sputtering at deposition temperatures from 60 °C to 300 °C and a magnetron power of 300 W. The powder XRD analysis indicates textured growth of films along the c axis and a microstrain decrease with increasing deposition temperatures. The growth rate also decreases and the refractive index increases with increasing deposition temperature. The obtained patterns are explained by the ordering of the microstructure of the films with increasing deposition temperature due to increased mobility of atoms adsorbed on the substrate. It is shown by transmission electron microscopy and electron diffraction that the sample prepared at 200 °C is characterized by a lower disorientation of crystallites relative to the c axis than the samples deposited at 100 °C and 300 °C. For the sample prepared at 200 °C, the highest piezoresponse is qualitatively detected by piezoresponse force microscopy. The films exhibit two photoluminescence bands, the position and intensity of which do not depend on the growth temperature. The nature of defects corresponding to these bands is discussed.

Работа посвящена исследованию важных для применений в качестве пьезоэлектрического материала особенностей строения тонких плёнок нитрида алюминия, выращенных методом импульсного магнетронного распыления при температурах осаждения от 60 до 300 °C и мощности магнетрона 300 Вт. Рентгенофазовый анализ показывает текстурированный рост пленок в направлении оси c и уменьшение микронапряжений с увеличением температуры осаждения. Увеличение температуры осаждения также приводит к уменьшению скорости роста и увеличению показателя преломления. Полученные закономерности объясняются упорядочением микроструктуры пленок с ростом температуры осаждения благодаря увеличению подвижности адсорбированных на подложку атомов. С помощью просвечивающей электронной микроскопии и электронной дифракции выявлено, что образец, осажденный при 200 °C, обладает наименьшей разориентацией кристаллитов относительно оси c по сравнению с образцами, осажденными при 100 и 300 °C. Для этого образца методом силовой микроскопии пьезоотклика качественно обнаружен наибольший пьезоотклик. Установлено присутствие в пленках двух полос фотолюминесценции, положение и интенсивность которых не связаны с изменением температуры роста. Обсуждается природа дефектов, соответствующих этим полосам.

The purpose of the present work is the investigation of mechanical stress variation in the AlN films deposited by pulsed DC magnetron sputtering under changing of substrate temperature and magnetron power. It has been revealed for the first time that the deposition of AlN films with low mechanical stresses is possible under low values of substrate temperature and magnetron power. A remarkable decrease in mechanical stresses in films from −2.5 GPa to values less than ±300 MPa was found in the case of increasing the film deposition temperature from 60 °C to 300 °C. Comparison of the data obtained by the optical method of measuring the substrate curvature and the XRD method showed that the stress values according to the x-ray diffraction results for films grown at low temperatures (60 °C–100 °C) are significantly higher than those measured by the optical method. This difference can be explained by an increased content of defects for low-temperature films that are shown by results of FTIR spectroscopy, where the absorbance intensity of the E ₁ (TO) mode peak increases with temperature. At the same time, with an increase in the deposition temperature to 275 °C–300 °C, the differences between the XRD and optical data vanish, and the mechanical stresses become small enough and satisfactory for the fabrication of multilayer film bulk acoustic wave resonators.

The chemical composition, structure, and physical properties of aluminum nitride (AlN) films obtained using pulsed DC reactive magnetron sputtering in asymmetric bipolar mode have been studied. X-ray diffraction and electron diffraction confirmed the composition of c–axis textured hexagonal AlN films required for piezoelectric applications. The surface of the films obtained is quite smooth; the arithmetic average roughness does not exceed 2 nm. Transmission electron microscopy has shown the presence of a transition layer at the film–substrate interface. Transmission electron microscopy and X-ray photoelectron spectroscopy depth profile analysis have shown that the films have an oxidized surface layer which has an influence on the optical model of the films derived from ellipsometric data. However, it does not significantly influence the films’ piezoresponse. Piezoelectric force microscopy indicated a piezoelectric effect in the films that is uniform over their surface.

The possibility of changing the silicon surface morphology at certain glow discharge parameters is shown. It is established that oxidation is the main process influencing the surface morphology during glow discharge plasma treatment. As a result of processing in the investigated parameter range, various stages of the surface oxidation process are observed: the formation of a uniform oxide layer and the formation of nano- and microstructures of silicon oxide. It is shown that these processes lead to surface modification, which acquires stable hydrophilic and superhydrophilic properties.

In this work, membranes were synthesized by depositing fluoropolymer coatings onto metal meshes using the hot wire chemical vapor deposition (HW CVD) method. By changing the deposition parameters, membranes with different wetting angles were obtained, with water contact angles for different membranes over a range from 130° ± 5° to 170° ± 2° and a constant oil contact angle of about 80° ± 2°. These membranes were used for the separation of an oil–water emulsion in a simple filtration test. The main parameters affecting the separation efficiency and the optimal separation mode were determined. The results reveal the effectiveness of the use of the membranes for the separation of emulsions of water and commercial crude oil, with separation efficiency values that can reach over 99%. The membranes are most efficient when separating emulsions with a water concentration of less than 5%. The pore size of the membrane significantly affects the rate and efficiency of separation. Pore sizes in the range from 40 to 200 µm are investigated. The smaller the pore size of the membranes, the higher the separation efficiency. The work is of great economic and practical importance for improving the efficiency of the membrane separation of oil–water emulsions. It lays the foundation for future research on the use of hydrophobic membranes for the separation of various emulsions of water and oil products (diesel fuel, gasoline, kerosene, etc.).