Low-temperature Transmission Electron Microscopy Research Articles

Ethosome Containing Ceramide as a Skin Carrier of Active Ingredients.

Numerous formulations have been utilized in the cosmetic and pharmaceutical industries to effectively deliver bioactive ingredients. We selected a well-known liposomal formulation of bilayer lipid vesicles composed of ceramide NP. Ethosomes contain hydrophilic vanillic acid or lipophilic α-bisabolol, and their physicochemical properties were evaluated. Vanillic acid is encapsulated in the aqueous core while α-bisabolol is engaged with the lipid phase. The formulation was prepared by the high-pressure homogenization method at 800 bar for 5 min. The particle size, polydispersity index and zeta potential of the ethosome dispersion were analyzed by dynamic light scattering. In order to measure the skin absorption efficiency from artificial skin, an in vitro assay was performed using the Franz diffusion cell method for 24 hours. In addition, ultracentrifuges for encapsulation efficiency, dialysis membranes for active ingredient release, and low-temperature transmission electron microscopy (TEM) to evaluate the morphology of vesicles were utilized. The particle size of the ethosome containing ceramide NP and vanillic acid was in the range of 80 ~ 130 nm, whereas the particle size of the ethosome containing ceramide NP and α-bisabolol was 150 ~ 170 nm. In the vanillic acid-containing ethosome, increasing the amount of ceramide NP decreased the particle size, whereas the size of the α-bisabolol ethosome did not change. The stability of the prepared ethosome did not change significantly for 4 weeks at 25°C, 4°C, and 45°C. The skin absorption efficiency of ceramide NP and vanillic acid-containing ethosome was increased by about 15% compared to the control group, whereas the ethosome containing α-bisabolol and ceramide NP showed slightly higher skin absorption efficiency than the control group. In addition, encapsulation efficiency evaluation, active ingredient release measurement and cryo-TEM were taken. Based on the results of these studies, we suggest that ethosome formulations containing ceramide NP can be widely used in the cosmetic industry together with other cosmetic formulations.

Metallic Strontium as a Precursor of the Al2O3/SrCO3 Xerogels Obtained by the One-Pot Sol-Gel Method.

Two series of binary xerogel systems of Sr/Al with molar ratios of 0.1, 0.25, 0.5, and 1.0 were synthesized by the sol–gel technique with metallic strontium component as a precursor. The influence of the metallic precursor on the properties of the final xerogel was determined. The properties of the gels were determined on the basis of X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), low temperature nitrogen adsorption, transmission, and scanning electron microscopy with Energy Dispersive X-ray Spectroscopy (TEM, SEM, and SEM/EDS). The Al2O3/SrCO3 xerogels were tested as supports for platinum catalysts. Hydrogen chemisorption was used to determine the platinum dispersion of the Pt/Al2O3-SrCO3 systems. The original method of synthesis allows to obtain highly dispersed and stable strontium carbonate phases that allow for obtaining a high (42–50%) dispersion of platinum nanoparticles.

Microstructure of Lithium Dendrites Revealed by Room-Temperature Electron Microscopy

The uncontrolled deposition/dissolution process of lithium dendrites during electrochemical cycling in batteries limits the large-scale application of Li metal anodes. Investigating the microstructure of Li dendrites is a focal point. Currently, the only way to protect and observe sensitive Li dendrites is through low-temperature transmission electron microscopy (LT-TEM), whereas room-temperature characterization is still lacking. In this work, the room-temperature microstructure of Li dendrites was obtained by TEM using both vacuum- and inert-gas-transfer methods. Detailed comparison between LT- and room-temperature (RT-)TEM characterizations was provided to show the pros and cons of each method. Especially, RT-TEM shows the advantage of flexible incorporation with multifunctional characterizations, such as 3D tomography. By using RT-TEM, microstructural evolution of Li dendrites during the electrodeposition/dissolution process, including increase of the quantity of inorganic Li2O compounds in the solid electrolyte interphase, lateral growth behavior, and two types of inactive Li, has been revealed, enriching the understanding of the structure-property relationship of Li dendrites.

Metallic Calcium as a Precursor for Sol-Gel Synthesis of CaCO3-SiO2 and CaO-SiO2 Systems

A series of binary oxide systems with Ca/Si molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been synthesized by the sol-gel technique from tetraethyl orthosilicate (TEOS) and metallic calcium powder. Upon calcination, a side effect of wollastonite formation as a result of the reaction between the components of the material has been observed in the two calcium-richest systems. The increase in calcium content produces an effect of porosity promotion. At high calcium contents, the homogeneity of the systems is limited by the ability of silica to disperse the calcium component. The properties of these systems are determined by the silica surface coverage with a large amount of the scattered CaCO3 fine microcrystallites (calcite), resulting from the phase segregation. The gels were characterized by X-ray powder diffraction, low temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA), and FT-IR spectra, to describe the parameters important from the point of view of their application as a support for metal-based catalysts.

One-pot synthesis method of SiO2-La2O2CO3 and SiO2-La2O3 systems using metallic lanthanum as a precursor

A series of SiO2-La2O2CO3 and SiO2-La2O3 mixed oxide/carbonate systems with La/Si molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been obtained by the sol–gel technique from tetraethyl orthosilicate (TEOS) and metallic lanthanum powder. For the low lanthanum loading systems (La/Si 0.05 to 0.25) the lanthanum carboxy phase is easily transformed to oxide phase during thermal treatment in the presence of silica. The most important advantage of the proposed method is the possibility of obtaining a mixed oxide/carbonate phase and not directly an oxide phase as in the case of other methods. Depending on the calcination temperature and time, the proposed method can be used for obtaining compositions containing dioxycarbonate, oxide or mixed lanthanum phase.The systems were characterized by X-ray diffraction, low temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA), and FT-IR spectra.

Optical and interface properties of direct InP/Si heterojunction formed by corrugated epitaxial lateral overgrowth

We fabricate and study direct InP/Si heterojunction by corrugated epitaxial lateral overgrowth (CELOG). The crystalline quality and depth-dependent charge carrier dynamics of InP/Si heterojunction are assessed by characterizing the cross-section of grown layer by low-temperature cathodoluminescence, time-resolved photoluminescence and transmission electron microscopy. Compared to the defective seed InP layer on Si, higher intensity band edge emission in cathodoluminescence spectra and enhanced carrier lifetime of InP are observed above the CELOG InP/Si interface despite large lattice mismatch, which are attributed to the reduced threading dislocation density realized by the CELOG method.

An Effect of a Support Nature and Active Phase Morphology on Catalytic Properties of Ni-Containing Catalysts in Hydrogenation of Biphenyl

Ni/Sup catalysts were prepared, where SBA-15, γ-Al2O3, SiO2 were used as supports (Sup). The synthesized catalysts were investigated by the methods of low-temperature nitrogen adsorption, temperatureprogrammed reduction (TPR), and high-resolution transmission electron microscopy. The catalytic properties of the prepared catalysts were tested in liquid phase hydrogenation of biphenyl under conditions of a flow installation at temperatures of 60–100°C, pressure of 4 MPa, volumetric feed rate of 4–10 h–1 and H2: feed ratio of 1500 nM.. A 1 wt % solution of biphenyl in heptane,, as a model mixture, was used. It has been established that the activity of nickel hydrogenation catalysts depends on the nickel content and the type of support. The activity of supported nickel catalysts decreases in the series Ni-12/SBA-15 > Ni-12/SiO2 >> Ni-12/Al2O3. The kinetic characteristics of the biphenyl hydrogenation reaction were determined: the rate constants and activation energy for the hydrogenation of the first and second aromatic rings of the substrate molecule.

The Use of the Ru-Containing Catalyst Based on Hypercrosslinked Polystyrene in the Hydrogenation of Levulinic Acid to γ-Valerolactone

RuO2 particles stabilized in a polymeric matrix of hypercrosslinked polystyrene of MN100 type (5% Ru/MN100) are characterized by physicochemical methods (low-temperature nitrogen adsorption, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy), and the catalytic activity of these particles is studied in the reaction of selective hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). It is shown that synthesized catalyst 5% Ru/MN100 ensures a GVL yield above 99% under mild reaction conditions (90°C; hydrogen partial pressure, 2 MPa) in an aqueous medium and can compete with commercial catalyst 5% Ru/C.

Chemical Vapor Deposition Grown Wafer-Scale 2D Tantalum Diselenide with Robust Charge-Density-Wave Order.

2D metallic transition metal dichalcogenides (MTMDCs) are benchmark systems for uncovering the dimensionality effect on fascinating quantum physics, such as charge-density-wave (CDW) order, unconventional superconductivity, and magnetism, etc. However, the scalable and thickness-tunable syntheses of such envisioned MTMDCs are still challenging. Meanwhile, the origin of CDW order at the 2D limit is controversial. Herein, the direct synthesis of wafer-scale uniform monolayer 2H-TaSe2 films and thickness-tunable flakes on Au foils by chemical vapor deposition is accomplished. Based on the thickness-tunable 2H-TaSe2, the robust periodic lattice distortions that relate to CDW orders by low-temperature transmission electron microscopy are directly visualized. Particularly, a phase diagram of the transition temperature from normal metallic to CDW phases with thickness by variable-temperature Raman characterizations is established. Intriguingly, dramatically enhanced transition temperature from bulk value ≈90 to ≈125 K is observed from monolayer 2H-TaSe2, which can be explained by the enhanced electron-phonon coupling mechanism. More importantly, an ultrahigh specific capacitance is also obtained for the as-grown TaSe2 on carbon cloth as supercapacitor electrodes. The results hereby open up novel avenues toward the large-scale preparation of high-quality MTMDCs, and shed light on their applications in exploring some fundamental issues.

A Generalized Procedure for the Production of High-Grade, Porous Biogenic Silica

Biomasses are a sustainable, CO2 neutral source used in biorefining. Si-accumulating plants can be used for the production of biogenic silica in a biomass valorisation process. This study examines the production of high-grade porous silica from different plant parts like rice, oat and spelt husk, rice straw and horsetail using a generalized procedure for all. The silica materials were produced by a 2-step method. First, the biomasses were pretreated with water and then subjected to leaching with citric acid. As a second step, a sequential burning program was applied. The characterization of the untreated biomasses was carried out by X-ray fluorescence (XRF) analysis and thermal analysis (TG–DTA). The biogenic silica samples were subjected to XRF, carbon content analysis, low temperature nitrogen physisorption, scanning and transmission electron microscopy as well as X-ray diffraction. Independent of the initial composition of the plant part, the established method resulted in amorphous, biogenic silica with up to 99.7% purity, mesopores between 2 and 30 nm with pore volumes of up to 0.46 cm3 g−1 and specific surfaces of up to 303 m2 g−1. It was shown that the generalized method developed works not only for all the biomasses separately, but also if treated in the same batch. The produced biogenic silica can be considered as sustainable alternative to other silica products like precipitated silica, silica gel and fumed silica which are produced in highly energy consuming processes.

New method for the synthesis of Al2O3\u2013CaO and Al2O3\u2013CaO\u2013CaCO3 systems from a metallic precursor by the sol\u2013gel route

A series of binary Al2O3–CaO and Al2O3–CaO–CaCO3 systems with Ca/Al molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been synthesised by the sol–gel technique from aluminium isopropoxide and metallic calcium powder. The rate of the metal reaction is used as a limiting factor to control the binary gel formation. The proposed modification of the traditional sol–gel method was used to examine the influence the effect of the metallic form of the second component as an oxide precursor on the form of the final product. By applying acetic acid instead of mineral acid, calcium acetate is formed and then decomposed to calcium carbonate upon thermal processing. During the synthesis of the binary systems, metallic calcium acts both as a precursor of calcium acetate and as a secondary pH modifier of the gel system. Calcination in air at 600 °C did not produce systems containing only oxides and the calcium carbonate phase was still present. Due to particle size reduction, the CaCO3 to CaO decomposition temperature was lowered. The systems were characterised by X-ray powder diffraction, low-temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA) and FTIR spectra.

Carbon catalysts for electrochemical hydrogen peroxide production in acidic media

Hydrogen peroxide is a commodity chemical, as it is an environmentally friendly oxidant. The electrochemical production of H2O2 from oxygen and water by the reduction of oxygen is of great interest, as it would allow the decentralized, on-site, production of pure H2O2. The ability to run the reaction in an acidic electrolyte with high performance is particularly important, as it would allow the use of polymer solid electrolytes and the production of pH-neutral hydrogen peroxide. Carbon catalysts, which are cheap, abundant, durable and can be highly selective show promise as potential catalysts for such systems. In this work, we examine the electrocatalytic performance and properties of seven commercially available carbon materials for H2O2 production by oxygen electroreduction. We show that the faradaic efficiencies for the reaction lie in a wide range of 18–82% for different carbon catalysts. In order to determine the cause of these differences, we employ prompt gamma ray/neutron activation analysis and XPS measurements to assess the contribution of heteroatoms and defects, as well as low temperature N2-adsorption and transmission electron microscopy to elucidate the particle size, shape, BET surface area and porosity. We find that the surface oxygen groups, nitrogen and sulphur content display effects that are not straightforward, because their chemical state is likely significant. The metal content (when present in the order of magnitude of ∼10 ppm) is not a straightforward indicator of the electrocatalytic performance for this reaction. XPS and BET data indicate that carbons displaying high selectivities for the 2-electron process contain more aliphatic-like, “defect” structures on the surface.

One-pot synthesis of Al2O3-La2O2CO3 systems obtained from the metallic precursor by the sol-gel method

A series of mixed oxide‑carbonate Al2O3-La2O2CO3 systems with the La/Al molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been synthesized by the sol–gel technique from aluminum isopropoxide and metallic lanthanum powder. During the synthesis of Al2O3- La2O2CO3 system, metallic lanthanum acts both as a precursor of lanthanum oxide and as secondary pH modifier of the gel solution. The traditional sol-gel method was modified to provide a better control over the final product surface parameters and structure. The obtained systems were amorphous and highly homogenic. The rate of the metal reaction was used as a limiting factor to control the gel formation. The obtained oxide systems are intended as a support for metallic phase catalysts. Calcination in air at 600°C did not produce systems containing only oxides and the lanthanum (dioxy)carbonate phase was still present. This observation can be explained by the multi stage decomposition process of lanthanum acetate forming during the gel synthesis.The systems were characterized by X-ray powder diffraction, low temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA), and FTIR spectra.

In Ukrainian

Synthesis of mesoporous silicas of MCM-41 type with chemically immobilized β cyclodextrin-containing groups was realized by template sol-gel method in the presence of functional silane. The influence of reaction mixture composition used at β cyclodextrin-silane synthesis (molar ratio β cyclodextrin:3 aminopropyltriethoxysilane: 1,1'-carbonyldiimidazole) on chemical structure and arrangement of mesopores of resulting organosilica materials was proved. The enhancement of ethoxysilyl constituent in β cyclodextrin-silane used in sol-gel condensation leads to the formation of silicas with higher content of chemically immobilizedβ cyclodextrin-containing groups and less arranged mesopores. Structure of obtained materials was determined using chemical analysis, infrared spectroscopy, low-temperature nitrogen adsorption-desorption, X-ray diffraction, and transmission electron microscopy. With the aim to elucidate the contribution of β cyclodextrin-containing groups in the removal of azo dyes, sorption of methyl red and alizarin yellow on synthesized silicas was studied from phosphate buffer solutions in dependence of contact duration, equilibrium concentration, and pH of medium. The results were analyzed using Langmuir, Freundlich and Redlich-Peterson equations. It has been found that equilibrium sorption of methyl red and alizarin yellow on parent silica and silica with chemically immobilized β cyclodextrin containing groups is described by the Redlich-Peterson model.

Surface Properties of Al-Functionalized Mesoporous MCM-41 and the Melting Behavior of Water in Al-MCM-41 Nanopores.

We report an experimental investigation of structural and adhesive properties for Al-containing mesoporous MCM-41 and MCM-41 surfaces. In this work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant. The incorporation of aluminum was evidenced simultaneously without any change in the hexagonal arrangement of cylindrical mesopores. The porous materials were examined by techniques such as low-temperature nitrogen sorption, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Surface properties were determined through X-ray photoelectron spectroscopy, potentiometric titration, and static contact angle measurements. It was shown that an increase in surface acidity leads to an increase in the wetting energy of the surface. To investigate the influence of acidity on the confinement effects, the melting behavior of water in Al-MCM-41 and MCM-41 with the same pore size was determined by using dielectric relaxation spectroscopy and differential scanning calorimetry methods. We found that the melting-point depression of water in pores is larger in the functionalized pores than in pure silica pores of the same pore diameter.

Mixed Metal Oxides of the Type CoxZn1-xFe2O4 as Photocatalysts for Malachite Green Degradation Under UV Light Irradiation.

A combination of thermal and mechanical (high energy ball milling) treatment was applied in an attempt to obtain polycrystalline mixed metal binary and ternary oxides of the type CoxZn1-xFe2O4 (x = 0; 0.25; 0.5; 0.75; 1). The synthetic procedure used successfully produced single-phased, homogeneous ZnFe2O4, CoFe2O4, and Co0.75Zn0.25Fe2O4, as well as mixed oxides, whose composition depended both on the duration of the high energy ball milling and the ratio Zn(II)/Co(II). The formation of spinel-like structures was proved by XRD, Mössbauer spectroscopy and Raman spectroscopy. For the characterization of the samples low-temperature N2 adsorption, UV/Vis spectroscopy and transmission electron microscopy were applied. The energy band gap of the samples was calculated, suggesting they are promising photocatalysts. The decomposition of the Malachite Green in model water solutions under UV-light irradiation was successfully achieved in the presence of the samples as photocatalysts. The highest rate constant was obtained for the sample synthesized at longer milling time in combination with higher Zn(II)/Co(II) ratio. The photocatalytic activity of the ternary mixed oxides was compared with the pure hematite, α-Fe2O3, and the binary ZnFe2O4 and CoFe2O4 ferrites with spinel structure that were treated in the same way. A synergetic effect of α-Fe2O3 and the spinel-like structure on the photocatalytic properties of ternary mixed metal oxides was detected.

Dislocation mediated alignment during metal nanoparticle coalescence

Dislocation mediated alignment processes during gold nanoparticle coalescence were studied at low and high temperatures using molecular dynamics simulations and transmission electron microscopy. Particles underwent rigid body rotations immediately following attachment in both low temperature (500 K) simulated coalescence events and low temperature (∼315 K) transmission electron microscopy beam heating experiments. In many low temperature simulations, some degree of misorientation between particles remained after rigid body rotations, which was accommodated by grain boundary dislocation nodes. These dislocations were either sessile and remained at the interface for the duration of the simulation or dissociated and cross-slipped through the adjacent particles, leading to improved co-alignment. Minimal rigid body rotations were observed during or immediately following attachment in high temperature (1100 K) simulations, which is attributed to enhanced diffusion at the particles' interface. However, rotation was eventually induced by {111} slip on planes parallel to the neck groove. These deformation modes led to the formation of single and multi-fold twins whose structures depended on the initial orientation of the particles. The driving force for {111} slip is attributed to high surface stresses near the intersection of low energy {111} facets in the neck region. The details of this twinning process were examined in detail using simulated trajectories, and the results reveal possible mechanisms for the nucleation and propagation of Shockley partials on consecutive planes. Deformation twinning was also observed in-situ using transmission electron microscopy, which resulted in the co-alignment of a set of the particles' {111} planes across their grain boundary and an increase in their dihedral angle. This constitutes the first detailed experimental observation of deformation twinning during nanoparticle coalescence, validating simulation results presented here and elsewhere.

Understanding the role of mobility of ITO films for silicon heterojunction solar cell applications

Transparent conducting oxides (TCO) are crucial in amorphous/crystalline silicon heterojunction solar cells performance as they have to be highly conductive to ensure the transport of photogenerated charges while remaining highly transparent to the sun spectrum. The key parameter to improve the transparency/conductivity compromise of TCO is mobility, since it allows increasing conductivity without losing transparency in the infrared region. A deep understanding of the factors influencing the mobility is then fundamental, and this is the objective of this paper. For this study, thin films of tin-doped indium oxide (ITO) were prepared by magnetron sputtering with different oxygen content. They were deeply characterized by standard and Low Temperature Hall Effect measurement, scanning and transmission electron microscopy and X-ray diffraction. The impact of oxygen on the microstructure was studied and the electrical properties were deeply investigated. In particular, the different mechanisms impacting the mobility were quantified as a function of oxygen content during ITO deposition.

How the Conditions of Preparation Process Affect the Electrochemical Properties of C/Sn Anode Materials?

How the conditions of preparation process affect the electrochemical properties of C/Sn anode materials? The application of tin in commercially available Li-ion batteries is limited by the poor cyclic performance due to the pulverization caused by cyclic volume changes of elementary cell, during the insertion and extraction processes of lithium ions [1]. Consequently, it results in loss of electrical contact between active material and current collector. One of the ways to overcome this issue is development of tin-carbon nanocomposite, in which nanometric tin grains are encapsulated in a flexible and conductive carbon layers. Such nanocomposites are able to provide appropriate electrochemical properties, only if the formed carbon layer is flexible, has appropriate porosity which featuring local free space to compensate volume changes. The goal of the presented studies is to examine the effects of carbonization temperature as well as origin and content of carbon on the electrochemical performance of carbon-tin nanocomposites. Electrode materials consisted of tin-based nanograins encapsulated in carbon buffer matrix of different origins (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor (SnO2) was prepared using a modified reverse nanoemulsion method (w/o) and then was coated by a various source of carbon (potato starch or modified poly(N-vinylformamide)) [2,3]. The carbon-tin precursors were pyrolyzed, providing formation of tin-based nanograins encapsulated in buffer matrix. The optimal condition for preparation process was studied using thermal analysis method (EGA-TGA/DTG/SDTA). The structure and the morphology of the samples were characterized by X-Ray diffraction analysis (XRD), low-temperature nitrogen adsorption method (N2-BET) and transmission electron microscopy (TEM) as well. The quality of carbon matrix in resulting composites was determined by Raman spectroscopy (RS) measurements. The working electrodes were prepared from a carbon-tin active material and polyvinylidene fluoride (PVDF) binder in N-methylpyrrolidone (NMP) solvent on copper foil. R-2032 coin type cells were assembled using obtained electrodes combined with Li metal discs as a counter electrode. The electrolyte consisted of a solution of 1M LiPF6in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with EC/DEC molar ratio of 1:1. The lithium cells were characterized by cyclic voltammetry (CV), charge-discharge tests (CELL TEST) as well as electrochemical impedance spectroscopy (EIS). The thermal analysis results enabled determination of the optimal carbonization temperature for obtaining carbon-tin anode materials. N2-BET data as well as TEM images indicated that samples, in which the potato starch was used as a carbon source, have high specific surface area and pore volume as well as reveal presence of the opened pores through the composites. The electrochemical tests showed that better encapsutation of tin nanograins in carbon buffer matrix resulted in higher gravimetric capacity and better cell performance. The C/Sn material in which carbon matrix was fabricated from modified polymer exhibited higher gravimetric capacity and better cell performance (589 mAh g-1 after 70 cycles). The authors acknowledge a financial support from the National Science Centre of Poland under research grant No. 2012/07/N/ST8/03725. [1] S. Ding, X.W. Lou, Nanoscale, 3 (2011) 3586[2] M. Molenda, A. Chojnacka, M. Bakierska, R. Dziembaj, Mater. Technol., 29 (2014) A88[3] A. Chojnacka, M. Molenda, M. Bakierska, R. Dziembaj, Procedia Eng., 98 (2014) 2

Observation of spin textures in La1−xSrxMnO3 (x = 0.175)

We have investigated topological spin textures in the ferromagnetic metallic phase of La0.825Sr0.175MnO3 with the centrosymmetric crystal structure by small-angle electron diffraction (SmAED) and low-temperature Lorentz transmission electron microscopy (TEM) experiments. In-situ Lorentz TEM and SmAED experiments revealed that type-I and type-II magnetic bubbles evolved from magnetic stripe domains with the Bloch-type domain wall by applying vertical magnetic field. Type-I magnetic bubbles with left-handed and right-handed spin helicity were randomly distributed and simultaneously type-II magnetic bubbles are formed locally. The important point about type-I and type-II magnetic bubbles is that their emergence depends strongly on whether perpendicular magnetic field is applied parallel to the magnetic easy axis along the [001] direction. Our experimental results suggested that the stabilization of magnetic bubbles should originate from the long-range dipole-dipole interactions, as opposed to the Dzyaloshinskii-Moriya interaction in helical magnets.