Atomic Force Microscopy Study of Cross-Sections of Perovskite Layers

Improvement of methods for imaging of the volume structure of photoactive layers is one of the important directions towards development of highly efficient solar cells. In particular, volume structure of photoactive layer has critical influence on perovskite solar cell performance and life time. In this study, a perovskite photoactive layer cross-section was prepared by using Focused Ion Beam (FIB) and imaged by Atomic Force Microscopy (AFM) methods. The proposed approach allows using advances of AFM for imaging structure of perovskites in volume. Two different types of perovskite layers was investigated: FAPbBr3 and MAPbBr3. The heterogeneous structure inside film, which consist of large crystals penetrating the film as well as small particles with sizes of several tens nanometers, is typical for FAPbBr3. The ordered nanocrystalline structure with nanocrystals oriented at 45 degree to film surface is observed in MAPbBr3. An optimized sample preparation route, which includes FIB surface polishing by low energy Ga ions at the angles around 10 degree to surface plane, is described and optimal parameters of surface treatment are discussed. Use of AFM phase contrast method provides high contrast imaging of perovskite structure due to strong dependence of phase shift of oscillating probe on materials properties. The described method of imaging can be used for controllable tuning of perovskite structure by changes of the sample preparation routes

Структурные особенности формирования цинкосодержащих наночастиц, полученных методом ионной имплантации в Si(001) и последующим термическим отжигом

This work deals with structural transformations in the near− surface layers of silicon after  ion beam synthesis of zinc−containing nanoparticles. Phase formation after  Zn + ion implantation and  two−stage O+ and Zn+ ion implantation followed by thermal annealing in a dry oxygen atmosphere was studied. To avoid amorphization, we heated the substrate to 350 °C during the implantation. After implantation, we annealed the samples for 1 h in a dry oxygen  atmosphere at 800  °C. The structure of the surface silicon layers was examined by X−ray diffraction and transmission electron microscopy. We show that a disturbed near  surface layer with a large  concentration of radiation induced defects appears as  a result  of 50 keV Zn+ ion implantation. In the  as−implanted specimens, metallic  Zn nanoparticles about 25 nm in size formed at a depth of 40 nm inside  the damaged silicon layer. Subsequent annealing at 800 °C in a dry oxygenatmosphere produced structural changes in the defect layer, formed Zn2SiO4 nanoparticles at a depth of 25 nm with an average size of 3 nm and oxidized the existing Zn particles to form the Zn2SiO4  phase. The oxidation  of the metallic  Zn nanoparticles starts from the surface of the particles and leads to the formation of particles with a “core−shell” structure. Analysis of the phase composition of the silicon layer after O+ and  Zn+ ion two−stage implantation showed that Zn and  Zn2SiO4 particles formed in the  as−implanted state. Subsequent annealing at 800 °C in a dry oxygen  atmosphere increases the particle  size but does not change the phase composition of the near surface layer. ZnO nanoparticles were  not observed under the  experimental ion beam synthesis conditions.. Исследованы структурные превращения в приповерхностных слоях кремния после ионного  синтеза цинкосодержащих наночастиц. Рассмотрены процессы фазообразования после имплантации ионов Zn+ и двухстадийной последовательной имплантации ионами O+ и Zn+ с последующим термическим отжигом в атмосфере сухого кислорода. Для предотвращения аморфизации в процессе имплантации мишень подогревали до температуры 350 °С. После имплантации образцы подвергали термообработке в течение 1 ч в атмосфере сухого кислорода при температуре 800  °С. Структура поверхностных слоев кремния исследована методами рентгеновской дифрактометрии и просвечивающей электронной микроскопии. Показано, что в результате имплантации ионов Zn+ с энергией 50 кэВ в подложку монокристаллического кремния на поверхности образуется нарушенный слой с большой концентрацией радиационных дефектов. В приповерхностном слое кремния на глубине 40 нм формируются наночастицы металлического Zn размером порядка 25 нм. Последующий отжиг при температуре 800 °C в атмосфере сухого кислорода обуславливает структурные изменения в дефектном слое и образование в приповерхностном слое кремния на глубине 25 нм частиц Zn2SiO4  со средним размером 3 нм, а также окисление уже имеющихся частиц Zn с формированием фазы Zn2SiO4. Окисление наночастиц Zn начинается с поверхности и приводит к образованию частиц со структурой типа «ядро—оболочка». Исследование фазового состава приповерхностного слоя кремния после последовательной имплантации ионами О+ и Zn+ показало, что при таком способе имплантации сразу образуются частицы  двух фаз: Zn и Zn2SiO4. Последующий отжиг при температуре 800 °С в атмосфере сухого кислорода приводит к увеличению размеров частиц, но не изменяет фазового состава поверхностного слоя кремния. При данных условиях эксперимента в результате ионного  синтеза не наблюдали образования частиц ZnO

MarkHub Cloud Online Editor as a modern web-based book creation tool

The main criterion for the competitiveness of a teacher or expert in the field of science is a good ability to present their knowledge to students in an interactive form without spending a lot of time in preparation. The purpose of the study is to analyze modern editors to create educational information content in the modern educational space and to present a modern tool for creating web books based on the latest IT technologies. Modern editors of web material creation have been analyzed, statistics of situations on mastering of knowledge by listeners, using interactive methods of information submission have been investigated. Using the WYSIWYG concept and analyzing modern information tools for presenting graphic material, an effective tool for teaching interactive web material was presented. An adapted version of the MarkHub online editor based on cloud technologies is presented. Using MarkHub cloud-based online editor for the unified development of educational content can significantly increase the author’s productivity in the content creation process. At the same time, the effects of reducing the time spent on formatting the external presentation of the content, making synchronous changes to different versions of the content, tracking the versions of the content, organizing remote teamwork in the network environment are achieved

Structural properties of the formation of zinc-containing nanoparticles obtained by ion implantation in Si (001) and subsequent thermal annealing

This work deals with the study of structural transformations in the near-surface layers of silicon after ion beam synthesis of zinc-containing nanoparticles. Phase formation after implantation of Zn+ ions and two-stage implantation of O+ and Zn+ ions with subsequent thermal annealing in an atmosphere of dry oxygen has been considered. We heated the substrate to 350 °C during the implantation to avoid amorphization. After implantation, the specimens were annealed for 1 h in a dry oxygen atmosphere at 800 °C. Investigation of the structure of surface silicon layers has been carried out by X-ray diffractometry and transmission electron microscopy. We show that a damaged layer with a large concentration of radiation induced defects forms near the surface as a result of the implantation of Zn+ ions with an energy of 50 keV. In the as-implanted state, nanoparticles of metallic Zn with a size of about 25 nm form at a depth of 40 nm inside the damaged silicon layer. Subsequent annealing at 800 °C in a dry oxygen atmosphere leads to structural changes in the defect layer and the formation of Zn2SiO4 nanoparticles at a depth of 25 nm with an average size of 3 nm, as well as oxidation of the existing Zn particles to the Zn2SiO4 phase. The oxidation of the metallic Zn nanoparticles starts from the surface of the particles and leads to the formation of particles with a “core-shell” structure. Analysis of the phase composition of the silicon layer after two-stage implantation with O+ and Zn+ ions showed that Zn and Zn2SiO4 particles form in the as-implanted state. Subsequent annealing at 800 °C in a dry oxygen atmosphere leads to an increase in the particle size but does not change the phase composition of the near-surface layer. ZnO nanoparticles were not observed under these experimental conditions of ion beam synthesis

Model-independent measurement of the charge density distribution along an Fe atom probe needle using off-axis electron holography without mean inner potential effects

The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electric field and electrostatic potential around the needle with ∼10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness

Extending the Limits of Fast Acquisition in TEM Tomography and 4D-STEM

Both transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) experiments profit from recording two-dimensional camera images at very high readout speeds. This includes, but is not limited to, tomography in TEM and ptychography in STEM. The pnCCD (S)TEM camera uses a direct detecting, radiation hard pnCCD with a minimum readout speed of 1 000 full frames per second (fps) with a size of 264x264 pixels [1]. It features binning and windowing modes, which allow to further increase the frame rate substantially. For example, 4-fold binning in one direction, i.e. 66x264 pixels, yields a readout speed of 4 000 fps. Up to 20 000 fps are possible in windowing modes. Further applications that benefit from the high readout speed range from imaging on the micro- and millisecond timescale to strain analysis or electric and magnetic field mapping.Typical tomographic reconstructions use tilt series of fewer than 100 images which are recorded in 15 to 60 minutes with conventional cameras running at speeds below 40 fps. The series are recorded by stepwise rotation of the goniometer and taking a camera image after each rotation step. These long acquisition times restrict the acquisition of tomographic series for beam sensitive samples. We have recorded a tilt series containing 3 487 images of an inorganic nanotube in only 3.5 s with the pnCCD camera [2]. Due to the high readout speed it was possible to rotate the goniometer continuously over a tilt range of −70 ° to +30 ° in an FEI Titan 60–300, operated at 60 keV beam energy. The short acquisition time and the high sensitivity of the camera allowed to reduce the cumulative electron dose to about 8 electrons per Å2, i.e. about an order of magnitude lower than conventionally used for low dose tomography. A 3D reconstruction of the nanowire is shown in Figure 1. The acquisition time was not limited by the readout of the camera, but rather by the rotation speed of the goniometer.Combining the high readout speed with the scanning mode makes 4D-STEM imaging feasible, a powerful imaging technique where a two-dimensional image is recorded for each probe position of a two-dimensional STEM diffraction pattern. With the pnCCD (S)TEM camera, a 4D data cube consisting of 256x256 (i.e. 65 536) probe positions with a 132x264 pixel detector image (using 2-fold binning) for each probe position can be recorded in about 35 s. Several measurements have been performed to prove the capability of the camera for 4D-STEM imaging, including strain analysis, magnetic domain mapping and electron ptychography. The latter is a 4D-STEM technique that was described theoretically already in 1993 [3] but was so far limited experimentally by the low readout speed of existing cameras. In electron ptychography, the intensity distribution in the bright field disk is recorded in 2D for each STEM probe position. In an electron wave-optical approach the phase and amplitude information is extracted from the recorded intensity images. The reconstructed phase image (Figure 2a) shows enhanced image contrast compared to the simultaneously acquired conventional annular dark field image (Figure 2b). Measurements with the pnCCD (S)TEM camera were carried out using a JEOL ARM200-CF to investigate different samples with the ptychographic phase reconstruction technique.In conclusion, the pnCCD camera enables new techniques in TEM and STEM. Various fields of application benefit from recording two-dimensional detector images at high speeds. With its direct detection, high readout speed and radiation hardness the pnCCD (S)TEM camera permits the recording of tomographic tilt series and large 4D-STEM data cubes in short times and thus paves the way for new science