High-resolution Scanning Transmission Electron Microscopy Research Articles

The Drosophila blood–brain barrier invades the nervous system in a GPCR-dependent manner

The blood–brain barrier (BBB) represents a crucial interface between the circulatory system and the brain. In Drosophila melanogaster, the BBB is composed of perineurial and subperineurial glial cells. The perineurial glial cells are small mitotically active cells forming the outermost layer of the nervous system and are engaged in nutrient uptake. The subperineurial glial cells form occluding septate junctions to prevent paracellular diffusion of macromolecules into the nervous system. To address whether the subperineurial glia just form a simple barrier or whether they establish specific contacts with both the perineurial glial cells and inner central nervous system (CNS) cells, we undertook a detailed morphological analysis. Using genetically encoded markers alongside with high-resolution laser scanning confocal microscopy and transmission electron microscopy, we identified thin cell processes extending into the perineurial layer and into the CNS cortex. Interestingly, long cell processes were observed reaching the glia ensheathing the neuropil of the central brain. GFP reconstitution experiments highlighted multiple regions of membrane contacts between subperineurial and ensheathing glia. Furthermore, we identify the G-protein-coupled receptor (GPCR) Moody as negative regulator of the growth of subperineurial cell processes. Loss of moody triggered a massive overgrowth of subperineurial cell processes into the CNS cortex and, moreover, affected the polarized localization of the xenobiotic transporter Mdr65. Finally, we found that GPCR signaling, but not septate junction formation, is responsible for controlling membrane overgrowth. Our findings support the notion that the Drosophila BBB is able to bridge the communication gap between circulation and synaptic regions of the brain by long cell processes.

Failure of adhesive bonding unveiled by in-situ strain testing by high-resolution scanning transmission electron microscopy

The nano-scale failure behaviors of adhesive interfaces were investigated through in-situ straining testing to observe real-time crack propagations under a scanning transmission electron microscope (STEM). Two different loading modes were applied to thin sections of adhesive interfaces: crack-opening mode applied to pre-cracks made at the interface and shear mode. The failure of aluminum alloy (Al6061) and a second-generation acrylic adhesive (SGA) was examined, enabling observation of the growth of crazing in the adhesive layer, which has a phase-separated structure, preceding the macroscopic failure of the interfaces. Furthermore, the failure of a direct joint of thermoplastic and Al was investigated, with a comparison made to that observed in the adhesive interface. The generation and propagation of cracks near the interface, attributed to the adhesive's phase separation, contribute to the toughness of the adhesive interface. Both the direction of stress acting on the interface and the interface's strength influence the initiation and growth of cracks throughout the adhesive layer.

The Defects Genome of Janus Transition Metal Dichalcogenides.

Two-dimensional (2D) Janus Transition Metal Dichalcogenides (TMDs) have attracted much interest due to their exciting quantum properties arising from their unique two-faced structure, broken-mirror symmetry, and consequent colossal polarisation field within the monolayer. While efforts have been made to achieve high-quality Janus monolayers, the existing methods rely on highly energetic processes that introduce unwanted grain-boundary and point defects with still unexplored effects on the material's structural and excitonic properties Through High-resolution scanning transmission electron microscopy (HRSTEM), density functional theory (DFT), and optical spectroscopy measurements; this work introduces the most encountered and energetically stable point defects. It establishes their impact on the material's optical properties. HRSTEM studies show that the most energetically stable point defects are single (VS and VSe) and double chalcogen vacancy (VS -VSe), interstitial defects (Mi), and metal impurities (MW) and establish their structural characteristics. DFT further establishes their formation energies and related localized bands within the forbidden band. Cryogenic excitonic studies on h-BN-encapsulated Janus monolayers offer a clear correlation between these structural defects and observed emission features, which closely align with the results of the theory. The overall results introduce the defect genome of Janus TMDs as an essential guideline for assessing their structural quality and device properties. This article is protected by copyright. All rights reserved.

Improved electrochemical performance of hydrothermally synthesized Zn-Ni-S/rGO nanocomposite as an electrode for supercapacitor application

This present work reports on the hydrothermal synthesis of zinc-nickel sulfide with reduced graphene oxide (Zn-Ni-S/rGO) nanocomposite for supercapacitor applications. The synthesized samples are evaluated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), and high-resolution scanning transmission electron microscopy (HR-TEM), which are employed to examine the structure, morphology, and chemical composition of the Zn-Ni-S/rGO nanocomposite. The XRD results indicates the presence of high crystalline Zn-Ni-S with rGO. FE-SEM equipped with an EDX spectrum, illustrates a spherical morphology of Zn-Ni-S combined with a thin layer of rGO in the form of composite nature. Furthermore, the elemental composition of Zinc, Nickel, Sulfur and Carbon presence in the EDS spectra further supports the formation of the Zn-Ni-S/rGO nanocomposite. The electrochemcial properties of ZnS and the Zn-Ni-S/rGO nanocomposite are studied through cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. A high specific capacitance of 284F/g is obtained at 11 mA g−1 current density. The Zn-Ni-S/rGO nanocomposite demonstrates exceptionally high capacitance retention of 96 % over 3,000 charging and discharging cycles. The potential application of the Zn-Ni-S/rGO nanocomposite as an efficient electrode material for pseudocapacitors is supported by its favourable performance.

Magnetic coupling in La2/3Sr1/3MnO3/SrRuO3 heterostructures grown on SrTiO3 (111) substrates with abrupt interface

We report on the magnetic coupling behavior in all-ferromagnetic La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) heterostructures deposited on the SrTiO3 (111) substrate, where the interface leads to an enhanced exchange field as compared to the one deposited on SrTiO3 (001). Importantly, high-resolution scanning transmission electron microscopy reveals distinct interface structures of the (111) heterostructures depending on the growth sequence. The heterostructure with an SRO bottom layer shows an atomically flat and abrupt interface, while the one with an LSMO bottom layer shows a deformed interface due to the surface roughening of LSMO deposited directly on SrTiO3 (111). As a result, the heterostructure with an abrupt interface exhibits a robust antiferromagnetic coupling between LSMO and SRO, while the one with a rough interface shows negligible magnetic coupling. Our results demonstrate the key role of an abrupt interface in determining the magnetic properties of oxide heterostructures.

Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 3 – Cluster growth and crystal nucleation

This Part 3 focuses on the detailed study of the nanostructures forming in amorphous microwires which were previously received and described in the Part 2. The clustering process was studied at long-term DC Joule heating’s much lower the crystallization temperature. Particular attention is paid to the study of the redistribution of the components of the initial stage of crystallization. The studies were carried out using the Atom Probe Tomography method (APT), which allows for the identification of individually considered atoms. A description and analysis of APT data processing techniques are provided for studying the cluster structure and distribution of elements in the amorphous matrix and crystalline phases. To identify crystalline phases, data obtained using High-Resolution Transmission Electron Microscopy (HR-TEM) and Scanning Transmission Electron Microscopy (STEM), as well as X-Ray Powder Diffraction (XRPD) with synchrotron radiation source were used. The applied techniques made it possible to establish that the formation of nuclei of crystalline phases is preceded by three stages of the amorphous microwire matrix evolution. At the first stage, clusters of the first and second coordination spheres appear. At the second stage, the clusters coagulate and become more than 2nm in diameter, the stage ends with the predominance of Co-rich and silicide Me-Si clusters. At the third stage, they grow to an average diameter of 4.5nm, the predominance of clusters of this type remains, and the formation of nuclei of crystalline phases α-Co and Co2Si, with a size of about 8nm, occurs. This stage is characterized by high stable soft magnetic properties. With a further increase in the heat treatment temperature, a gradual deterioration of the soft magnetic properties and further structural transformation occur – structures of joint crystalline phases from two crystalline phases α-Co and Co2Si are formed in the amorphous matrix, and crystallization occurs with the alternation of these two phases. This leads to a significant redistribution of alloy components. As a result, an amorphous barrier layer is formed in the amorphous matrix near the surface of the growing two-phase substructures, enriched in chromium and silicon; this layer affects the growth of crystalline phases, slowing it down.

Microstructure and mechanical properties of a hypereutectic Al–Si–Cu alloy manufactured by laser powder bed fusion

A novel Al–Si–Cu alloy was designed for additive manufacturing of automotive components, such as pistons and supercharger rotors, requiring a combination of elevated temperature properties and high cycle fatigue strength. The alloy was designed with an Al–Si hypereutectic chemistry to exploit the formation of primary Si nucleants to enable an equiaxed as-printed microstructure during laser powder bed fusion (LPBF). The alloy design space was assessed using a combined integrated computational materials engineering (ICME) approach with melt-spinning experiments to select a chemistry exhibiting primary Si nucleants acting as heterogeneous grain nucleation sites. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) of the LPBF as-printed samples revealed primary Si particles with a fully equiaxed grain structure and no apparent texturing as evaluated using electron backscatter diffraction (EBSD). High-resolution scanning transmission electron microscopy (STEM) revealed sub-micron Si particles and Al2Cu θ-phase precipitates which result in enhanced room and elevated temperature mechanical strength (room temperature: UTS: 449 ± 10 MPa, YS: 336 ± 12 MPa) as compared to commercial Al10SiMg (UTS: 417 ± 3 MPa, YS: 236 ± 6 MPa).

Observation of broad triangular Frank-type stacking faults and characterization of stacking faults with emission wavelengths below 430 nm in 4H–SiC epitaxial layers

Frank-type stacking faults in 4H–SiC epitaxial layers were investigated using room-temperature photoluminescence mapping and high-angle annular dark-field high-resolution scanning transmission electron microscopy. Remarkably, the intrinsic Frank-type stacking fault (5,2) and intrinsic multilayer Frank-type stacking fault (4,2), which have been reported to have elongated triangular shapes to date, were found to have broader triangular shape, which was typical shape of Shockley-type stacking faults. The shaping of stacking faults could be explained based on the directions of the partial dislocations bounding the stacking faults. Formation models for the intrinsic (5,2) and (4,2) stacking faults were proposed. In addition, we observed Frank-type stacking faults (3,2,2,3) and (3,3) and Shockley-type stacking faults (3,3,3,2,3,2) and (3,2,3,3,3,2), which were not reported before. All of these stacking faults were composed with the stacking numbers 2 and 3 in the Zhdanov notation and showed very close characteristic photoluminescence emission wavelengths of 427–428 nm. Formation models for the stacking faults of (3,2,2,3), (3,3), (3,3,3,2,3,2), and (3,2,3,3,3,2) were proposed, also. Based on the proposed formation models of (4,2) and (3,3) stacking faults, formation models for the Frank-type stacking faults (4,1) and (3,2) were discussed. Finally, we pointed out that the (4,1) Frank-type stacking fault should be the intrinsic not the extrinsic fault, and the (3,2) Frank-type stacking fault is the extrinsic fault.

Chiroplasmonic DNA Scaffolded "Fusilli" Structures.

DNA is an ideal template for the design of nanoarchitectures with molecular-like features. Here, we present an optimized assembly strategy for the concatenation of DNA quasi-rings into long scaffolds. Ionic strength, which played a major role during self-assembly, produced the expected high quality only at 15 mM MgCl2. Atomic force microscopy (AFM) characterization showed several micrometer long tubular structures that were used as templates for the positioning of plasmonic nanoparticles (NPs) along a three-dimensional helical path using DNA tethers. As imaged by high-resolution scanning transmission electron microscopy (HR-STEM) and modeled by theoretical calculations, the NPs distributed into a "fusilli" fashion (i.e., a helical pasta shape), displaying chiroptical activity as revealed by a bisignated CD absorption, centered at the plasmon resonance wavelength. The present structures contribute to enrich the ever-developing arena of chiroplasmonic DNA-based nanomaterials and demonstrate that large assemblies are attainable for their future application to develop metamaterials.

Probing Surface Transformations of Lanthanum Nickelate Electrocatalysts during Oxygen Evolution Reaction.

Monitoring the spontaneous reconstruction of the surface of metal oxides under electrocatalytic reaction conditions is critical to identifying the active sites and establishing structure-activity relationships. Here, we report on a self-terminated surface reconstruction of Ruddlesden-Popper lanthanum nickel oxide (La2NiO4+δ) that occurs spontaneously during reaction with alkaline electrolyte species. Using a combination of high-resolution scanning transmission electron microscopy (HR-STEM), surface-sensitive X-ray photoelectron spectroscopy (XPS), and soft X-ray absorption spectroscopy (sXAS), as well as electrochemical techniques, we identify the structure of the reconstructed surface layer as an amorphous (oxy)hydroxide phase that features abundant under-coordinated nickel sites. No further amorphization of the crystalline oxide lattice (beyond the ∼2 nm thick layer formed) was observed during oxygen evolution reaction (OER) cycling experiments. Notably, the formation of the reconstructed surface layer increases the material's oxygen evolution reaction (OER) activity by a factor of 45 when compared to that of the pristine crystalline surface. In contrast, a related perovskite phase, i.e., LaNiO3, did not show noticeable surface reconstruction, and also no increase in its OER activity was observed. This work provides detailed insight into a surface reconstruction behavior dictated by the crystal structure of the parent oxide and highlights the importance of surface dynamics under reaction conditions.

“Invisible” radioactive cesium atoms revealed: Pollucite inclusion in cesium-rich microparticles (CsMPs) from the Fukushima Daiichi Nuclear Power Plant

Understanding radioactive Cs contamination has been a central issue at Fukushima Daiichi and other nuclear legacy sites; however, atomic-scale characterization of radioactive Cs in environmental samples has never been achieved. Here we report, for the first time, the direct imaging of radioactive Cs atoms using high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In Cs-rich microparticles collected from Japan, we document inclusions that contain 27 – 36 wt% of Cs (reported as Cs2O) in a zeolite: pollucite. The compositions of three pollucite inclusions are (Cs1.86K0.11Rb0.19Ba0.22)2.4(Fe0.85Zn0.84X0.31)2.0Si4.1O12, (Cs1.19K0.05Rb0.19Ba0.22)1.7(Fe0.66Zn0.32X0.41)1.4Si4.6O12, and (Cs1.27K0.21Rb0.29Ba0.15)1.9(Fe0.60Zn0.32X0.69)1.6Si4.4O12 (X includes other cations). HAADF-STEM imaging of pollucite, viewed along the [111] zone axis, revealed an array of Cs atoms, which is consistent with a simulated image using the multi-slice method. The occurrence of pollucite indicates that locally enriched Cs reacted with siliceous substances during the Fukushima meltdowns, presumably through volatilization and condensation. Beta radiation doses from the incorporated Cs are estimated to reach 106 – 107 Gy, which is more than three orders of magnitude less than typical amorphization dose of zeolite. The atomic-resolution imaging of radioactive Cs is an important advance for better understanding the fate of radioactive Cs inside and outside of nuclear reactors damaged by meltdown events.

Characterization of Mn5Ge3 Contacts on a Shallow Ge/SiGe Heterostructure.

Mn5Ge3 is a ferromagnetic phase of the Mn-Ge system that is a potential contact material for efficient spin injection and detection. Here, we investigate the creation of Mn5Ge3-based contacts on a Ge/SiGe quantum well heterostructure via solid-state synthesis. X-ray diffraction spectra fitting indicates the formation of Mn5Ge3-based contacts on bulk Ge and Ge/SiGe. High-resolution scanning transmission electron microscopy imaging and energy dispersive X-ray spectroscopy verify the correct Mn5Ge3-based phase formation. Schottky diode measurements, transmission line measurements, and Hall measurements reveal that Mn5Ge3-based contacts serve as good p-type contacts for Ge/SiGe quantum well heterostructures due to having a low Schottky barrier height of 0.10eV (extracted from a Mn5Ge3/n-Ge analogue) and a contact resistance in the order of 1 kΩ. Furthermore, we show that these electrical characteristics have a gate-voltage dependence, thereby providing tunability.

A method to synthesize specific active Cu sites of single-atom catalysts with high stability for acetylene hydration

Single-atom catalysts (SACs) have received much attention in the realm of energy and catalytic conversion due to their maximum atomic efficiency. Herein, we report a cascade anchoring strategy for the preparation of a Cu-S1O2 species of single-atom catalyst attached to a carbon carrier containing P and S (Cu-S1O2 SA/CPS) with a content of 12.4 wt%. Over the Cu-S1O2 SA/CPS catalyst, the conversion of 95.8% and selectivity of 87.2% for acetylene hydration could still be achieved at 70 h (T = 200°C, GHSV(C2H2) = 90 h−1 and VH2O/VC2H2 = 4). X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) tests reveal that the Cu atoms of Cu-S1O2 SA/CPS are predominantly coordinated in a trinary manner (Cu-S1O2). Based on high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), it is demonstrated that the Cu single-atom sites are highly dispersed in Cu-S1O2 SA/CPS. It is evident from the scanning electron microscopy (SEM) that Cu-S1O2 SA/CPS has a two-dimensional layered structure. The specific structure of the active site Cu is primarily attributed to the coordination of S and O atoms, resulting in its superior stability for acetylene hydration towards the synthesis of acetaldehyde. Density functional theory (DFT) calculations confirm that the formation of the Cu-S1O2 site facilitates the activation of acetylene, which is a pivotal step in the acetylene hydration process and considered as the rate-determining step. This article not only introduces an innovative strategy in the synthesis of Cu SACs but also represents a significant breakthrough in the stability of Cu SACs in acetylene hydration.

Impact of varied zeolite materials on nickel catalysts in CO2 methanation

Ni catalysts supported on 4A, 5A, 13X, ZSM-5, and BEA zeolites were prepared using the vacuum-heating method for CO2 methanation. These support materials play a pivotal role in shaping the catalysts' properties and their catalytic performance. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) mappings suggest a significant concentration of Ni nanoparticles situated on the external surfaces of catalysts with low Si/Al ratios zeolites (Ni-4A, Ni-5A, and Ni-13X). These Ni nanoparticles exhibit characteristics of weaker metal-support interaction, lower metal reduction temperatures, and moderate H2 adsorption activity. Moreover, these low Si/Al ratio zeolites demonstrate robust CO2 adsorption activity. These properties endow Ni-5A and Ni-13X catalysts with heightened CO2 conversion (70.4–70.9%) and methane selectivity (92.4–96.4%). In contrast, high Si/Al ratio zeolite-based catalysts (Ni-ZSM-5 and Ni-BEA) exhibit smaller Ni particles, strong metal-support interaction and weaker CO2 adsorption activity, resulting in reduced CO2 methanation activity and decreased methane selectivity (71.2–73.4%). The normalized CO2 conversion rate presents a correlation with the average Ni particle size.

Mapping orthorhombic domains with geometrical phase analysis in rare-earth nickelate heterostructures

Most perovskite oxides belong to the Pbnm space group, composed of an anisotropic unit cell, A-site antipolar displacements, and oxygen octahedral tilts. Mapping the orientation of the orthorhombic unit cell in epitaxial heterostructures that consist of at least one Pbnm compound is often needed for understanding and controlling the different degrees of coupling established at their coherent interfaces and, therefore, their resulting physical properties. However, retrieving this information from the strain maps generated with high-resolution scanning transmission electron microscopy can be challenging, because the three pseudocubic lattice parameters are very similar in these systems. Here, we present a novel methodology for mapping the crystallographic orientation in Pbnm systems. It makes use of the geometrical phase analysis algorithm, as applied to aberration-corrected scanning transition electron microscopy images, but in an unconventional way. The method is fast and robust, giving real-space maps of the lattice orientations in Pbnm systems, from both cross section and plan-view geometries, and across large fields of view. As an example, we apply our methodology to rare-earth nickelate heterostructures, in order to investigate how the crystallographic orientation of these films depends on various structural constraints that are imposed by the underlying single crystal substrates. We observe that the resulting domain distributions and associated defect landscapes mainly depend on a competition between the epitaxial compressive/tensile and shear strains, together with the matching of atomic displacements at the substrate/film interface. The results point toward strategies for controlling these characteristics by appropriate substrate choice.

Latent ion tracks were finally observed in diamond

Injecting high-energy heavy ions in the electronic stopping regime into solids can create cylindrical damage zones called latent ion tracks. Although these tracks form in many materials, none have ever been observed in diamond, even when irradiated with high-energy GeV uranium ions. Here we report the first observation of ion track formation in diamond irradiated with 2–9 MeV C60 fullerene ions. Depending on the ion energy, the mean track length (diameter) changed from 17 (3.2) nm to 52 (7.1) nm. High resolution scanning transmission electron microscopy (HR-STEM) indicated the amorphization in the tracks, in which π-bonding signal from graphite was detected by the electron energy loss spectroscopy (EELS). Since the melting transition is not induced in diamond at atmospheric pressure, conventional inelastic thermal spike calculations cannot be applied. Two-temperature molecular dynamics simulations succeeded in the reproduction of both the track formation under MeV C60 irradiations and the no-track formation under GeV monoatomic ion irradiations.

High-pressure phase transitions in a laser directed energy deposited Fe-33Cu Alloy

Additively manufactured Fe-Cu alloys contain both equilibrium face-centered cubic (FCC) and metastable body-centered cubic (BCC) crystal structure Cu precipitates depending on their size. However, the stability of these nanoscale precipitates under extreme conditions such as high pressures has not been reported. This study investigates the phase transformations and microstructural stability of laser directed energy deposition (DED-LB) made Fe67Cu33 alloy (nominal composition in at.%) under high static pressure deformation using in-situ synchrotron X-ray diffraction under pressure, postmortem high-resolution scanning transmission electron microscopy (HR-STEM), and molecular dynamics (MD) simulations. In-situ XRD results reveal a reversible phase transformation from BCC to the hexagonal close-packed (HCP) structure in the Fe grains at an onset pressure of 16.4 GPa, significantly higher than reported in the literature for pure Fe. Although no high-pressure phase transition was observed in the FCC Cu grains through XRD, HR-STEM analysis uncovers a phase transition to the HCP structure in nanoscale metastable BCC Cu precipitates within the BCC Fe matrix. After decompression, the Fe matrix reverted back to the BCC structure with periodic lath martensite, while regions of the nanoscale BCC Cu precipitates retained the metastable HCP structure. MD simulations support the BCC → HCP transition in the embedded nanoscale coherent Cu precipitates, consistent with the classical Burgers mechanism. Thus, by leveraging in-situ XRD observation, postmortem high-resolution S/TEM microscopy, and MD simulations, this study offers profound insights into the distinctive phase transformations induced by high pressure in DED-LB Fe67Cu33 alloy, which is distinguished by its hierarchical microstructure.

Insights into structural defect formation in individual InP/ZnSe/ZnS quantum dots under UV oxidation

InP/ZnSe/ZnS quantum dots (QDs) stand as promising candidates for advancing QD-organic light-emitting diodes (QLED), but low emission efficiency due to their susceptibility to oxidation impedes applications. Structural defects play important roles in the emission efficiency degradation of QDs, but the formation mechanism of defects in oxidized QDs has been less investigated. Here, we investigated the impact of diverse structural defects formation on individual QDs and propagation during UV-facilitated oxidation using high-resolution (scanning) transmission electron microscopy. UV-facilitated oxidation of the QDs alters shell morphology by the formation of surface oxides, leaving ZnSe surfaces poorly passivated. Further oxidation leads to the formation of structural defects, such as dislocations, and induces strain at the oxide-QD interfaces, facilitating In diffusion from the QD core. These changes in the QD structures result in emission quenching. This study provides insight into the formation of structural defects through photo-oxidation, and their effects on emission properties of QDs.

Growth mechanisms of eta phase in 718Plus alloy

Growth mechanisms of eta phase in 718Plus alloy were investigated by high-resolution scanning transmission electron microscopy. The results demonstrated the nucleation and growth of the η platelets were arranged along the {111}γ habit planes. The fine lamellae γ phase, enveloped in the η platelets blocks, was determined. The possible occurrence of interfacial misfit dislocations could effectively release the mismatch strain, and enhance the ledges nucleation on the {0001}η plane. Analysis of the experimental observations, and possible mechanisms of growth were also addressed.

Stimulation of microvesicle secretion in Trichomonas vaginalis

Trichomonas vaginalis is an extracellular flagellate protozoan and the etiological agent of human trichomoniasis, a sexually transmitted infection (STI) with a high incidence. Several reports have shown that this protozoan releases microvesicles into the culture medium, which show high potential in modulating cell-to-cell communication and the host response to infections. However, the biogenesis of these vesicles has not been analyzed in detail. In the present study, high-resolution ion scanning microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the surface of control cells and cells incubated in the presence of Ca2+ alone or with A 23187 calcium ionophore. Two different strains of T. vaginalis were analyzed. Most control cells displayed relatively smooth surfaces, whereas cells incubated with Ca2+ had many surface projections of variable shape and size (from 40 nm to around 1 μm). Quantitative analyses were performed directly in the scanning electron microscope and showed a significant increase in the number of cells with surface projections after incubation in the presence of calcium. TEM showed that treated cells presented several cytoplasmic multivesicular structures, suggesting membrane fusion and exosomes in the extracellular medium. The amount and size of the released vesicles were quantitatively analyzed using light scattering and TEM on negatively stained samples.The observations show that incubation of both parasite strains in the presence of Ca2+ significantly increased the release of microvesicles into the extracellular medium in a time-dependent process. Sequential incubation in the presence of Ca2+ and the calcium ionophore A23187 increases the presence of vesicles on the parasite surface only at a short incubation time (5 min). Transmission electron microscopy showed that at least part of the vesicles are originated from cytoplasmic multivesicular structures. This information contributes to a better understanding of the biogenesis of extracellular vesicles secreted by T. vaginalis.