Electron Microscopy Investigations Research Articles

A study of the spinodal decomposition of AgC[sbnd]u alloy films using in situ transmission electron microscopy

We performed in situ transmission electron microscopy (TEM) investigations to understand spinodal decomposition in AgCu alloy thin films. The decomposition of a homogeneous nanocrystalline morphology into a heterogeneous two-phase structure when annealed in situ from room temperature to 400 °C was investigated with different imaging modes in the TEM. These studies reveal phase transformation proceeds in stages: between 180 and 200 °C, onset of phase separation via spinodal decomposition is observed. Then, prominent phase separation occurs between 200 and 250 °C with minimal grain growth. Next, between 250 and 300 °C, grain growth primarily occurs via coalescence, with no apparent phase separation. From 300 to 350 °C, we observe significant phase separation and Ostwald Ripening. Finally, between 350 and 400 °C, further coarsening occurs via coalescence. STEM-HAADF mode reveals the onset of phase separation from domains as small as 5 nm and these results are also supported by electron diffraction and compositional mapping.

Physics and chemistry from parsimonious representations: image analysis via invariant variational autoencoders

Electron, optical, and scanning probe microscopy methods are generating ever increasing volume of image data containing information on atomic and mesoscale structures and functionalities. This necessitates the development of the machine learning methods for discovery of physical and chemical phenomena from the data, such as manifestations of symmetry breaking phenomena in electron and scanning tunneling microscopy images, or variability of the nanoparticles. Variational autoencoders (VAEs) are emerging as a powerful paradigm for the unsupervised data analysis, allowing to disentangle the factors of variability and discover optimal parsimonious representation. Here, we summarize recent developments in VAEs, covering the basic principles and intuition behind the VAEs. The invariant VAEs are introduced as an approach to accommodate scale and translation invariances present in imaging data and separate known factors of variations from the ones to be discovered. We further describe the opportunities enabled by the control over VAE architecture, including conditional, semi-supervised, and joint VAEs. Several case studies of VAE applications for toy models and experimental datasets in Scanning Transmission Electron Microscopy are discussed, emphasizing the deep connection between VAE and basic physical principles. Python codes and datasets discussed in this article are available at https://github.com/saimani5/VAE-tutorials and can be used by researchers as an application guide when applying these to their own datasets.

Invited: Mimicking Biological Synapse Activity with LDH-Based Memristor

Memristors, mimicking biological synapse response, are believed to have a great potential for use as an adaptive memory unit in future neuromorphic computing systems. Here we report on fabrication of two-dimensional memristor comprised of layered double hydroxide (LDH) material, covered with graphene layer, serving as a terminal for connecting to electrodes. We demonstrated nonvolatile resistive switching of LDH memristor. Device performance is studied upon replacing graphene semimetal with alternative 2D materials. Comprehensive characterization of the memristor materials was performed with correlated Raman, Electron, and Scanning Probe Microscopy methods.ACKNOWLEDGMENTThis work was supported by the US Department of Defense (Contract #W911QY2220006), 2DCC-MIP NSF cooperative agreement DMR-2039351. Work was performed at JSNN, a member of the Southeastern Nanotechnology Infrastructure Corridor (SENIC) and National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the NSF (ECCS-1542174)

(Invited) Electron Microscopy Investigation of PEM Electrolyzer Degradation at Low Iridium Loadings

The employment of hydrogen as an energy carrier provides a promising solution toward zero carbon emission and battling climate change. To meet the DOE’s Hydrogen Shot goal of $1 per kilogram of hydrogen by 2031, proton exchange membrane (PEM) water electrolysis is a key technology of hydrogen production from renewable energy sources. Successful deployment of PEM electrolyzers requires reducing cost while simultaneously improving performance and lifetime. While cost reduction is expected from a variety of strategies including scaling up, operation optimization, and advanced manufacturing, it remains vital to reduce the use of noble-metal catalyst due to its scarcity and vulnerable supply chain subject to market disturbance. [1]Reducing the loading of iridium catalyst on the anode while maintaining electrolyzer performance and durability is of great challenge. In this talk, we discuss issues in PEM electrolyzer component development and advanced manufacturing of electrode layers related to catalyst loading reduction with an emphasize on analytical electron microscopy which provides valuable insight on materials morphology, crystalline structure, and chemical compositions. The batch-to-batch variance of catalyst morphology and elemental composition/distribution from commercial suppliers will be examined for catalyst down-selection. We then analyze the effect of reducing Ir loading on the electrode layer structure and ionomer distribution. These results are correlated with electrochemical measurements in the electrolyzer cell, which help elucidate the effect of low catalyst loading on electrolyzer performance. Morphologies of degraded low-loading anode catalyst layer and gas recombination layers will be investigated, and the dissolution and migration of iridium will be studied. We will also examine impact of different roll-to-roll manufacturing strategies for low-loading catalyst layers and on electrolyzer durability. Last but not least, we analyze MEAs subject to cation contamination and recovery procedure with electron microscopy. [2]References[1] Alia, S.M., Current Opinion in Chemical Engineering 2021, 33:100703.[2] Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Evidence for a Giant Magneto-Electric Coupling in Bulk Composites with Coaxial Fibers of Nickel–Zinc Ferrite and PZT

This report is on magneto-electric (ME) interactions in bulk composites with coaxial fibers of nickel–zinc ferrite and PZT. The core–shell fibers of PZT and Ni1−xZnxFe2O4 (NZFO) with x = 0–0.5 were made by electrospinning. Both kinds of fibers, either with ferrite or PZT core and with diameters in the range of 1–3 μm were made. Electron and scanning probe microscopy images indicated well-formed fibers with uniform core and shell structures and defect-free interface. X-ray diffraction data for the fibers annealed at 700–900 °C did not show any impurity phases. Magnetization, magnetostriction, ferromagnetic resonance, and polarization P versus electric field E measurements confirmed the ferroic nature of the fibers. For ME measurements, the fibers were pressed into disks and rectangular platelets and then annealed at 900–1000 °C for densification. The strengths of strain-mediated ME coupling were measured by the H-induced changes in remnant polarization Pr and by low-frequency ME voltage coefficient (MEVC). The fractional change in Pr under H increased in magnitude, from +3% for disks of NFO–PZT to −82% for NZFO (x = 0.3)-PZT, and a further increase in x resulted in a decrease to a value of −3% for x = 0.5. The low-frequency MEVC measured in disks of the core–shell fibers ranged from 6 mV/cm Oe to 37 mV/cm Oe. The fractional changes in Pr and the MEVC values were an order of magnitude higher than for bulk samples containing mixed fibers with a random distribution of NZFO and PZT. The bulk composites with coaxial fibers have the potential for use as magnetic field sensors and in energy-harvesting applications.

Adapting Conductivity and Mechanical Properties through Layer Thickness Variation in Copper Niobium Laminated Metallic Composites

Cu/Nb laminated metallic composites (LMCs) exhibit extraordinary mechanical strength while electrical conductivity is maintained at a high level. In this research, Cu‐based LMCs with varying volume fraction of niobium are produced via accumulative roll bonding (ARB) and additionally cold‐rolled and heat‐treated to identify the role of these heterogeneous phase boundaries on the overall sheet properties. Deformation structures in these layered materials are studied through scanning transmission electron microscopy investigations. The existence of an interface‐affected zone at the phase boundaries and mechanical intermixing is attributed to decreasing electrical and increasing mechanical properties, especially in very thin layered LMCs. Atom probe tomography measurements show that mechanical alloying occurs due to severe plastic deformation during ARB processing of the laminates. An additional subsequent heat treatment leads to chemical demixing at the interfaces of the phase boundaries.

Comparison of kink-band structures and specificities of cell wall polysaccharides in modern and ancient flax fibres

Flax (Linum usitatissimum L.) is a plant of industrial importance, its fibres being presently used for high-value textile applications, composite reinforcements as well as natural actuators. Human interest in this fibre-rich plant dates back several millennia, including to Ancient Egypt where flax was used extensively in various quotidian items. While the recent technical developments of flax fibres continue to diversify through scientific research, the historical use of flax also has rich lessons for today. Through careful examination of ancient Egyptian and modern flax fibres, this study aims to conduct a multi-scale characterization from the yarn to the fibre cell wall scale, linking differences in structure and polysaccharide content to the mechanical performance and durability of flax. Here, a multi-scale biochemical study is enriched by scanning electron microscopy and nanomechanical investigations. A key finding is the similarity of cellulose features, crystallinity index and local mechanical performances between ancient and modern fibres. Biochemically speaking, monosaccharides analysis, deep-UV and NMR investigations demonstrate that ancient fibres exhibit less pectins but a similar hemicellulosic content, especially through uronic acids and galactose, suggesting the sensitivity of these non-crystalline components.

Microstructural and mechanical properties of Al-Al2O3 micro and nanocomposite fabricated by stir casting

ABSTRACT The current study examines the relationship between the microstructure and tribological characteristics of Al-Si alloy composites reinforced by secondary phase nano SiC particulates synthesis via the stir casting process. The results of wear testing of stir-cast SiC metal matrix composites including up to 12 weight percent fine (75–100 µm) and coarse (125–150 µm) size particles were obtained from cast aluminium alloy. It was discovered via microstructural investigation that the aluminium alloy and SiC particles have good interface bonding. However, at greater amounts (12 wt.%) of fine size reinforcement, clustering of reinforced particles is observed. In addition, results state that finer size particles agglomerate more in the matrix than coarser size particles at greater reinforcement levels. In addition, increasing the amount of SiC particles in the matrix enhanced the hardness of the base alloy. However, when the size of the SiC particles was reduced, the hardness of the composite increased dramatically. Better wear resistance was observed for higher SiC reinforcement levels, while higher forces were also associated with a corresponding increase in wear rate. A combined mode of adhesive and abrasive wear mechanisms is responsible for composite wear, according to a scanning electron microscopy (SEM) investigation of worn surfaces.

Compressive behavior of thermoplastic polyurethane with an active agent foaming for 3D-printed customized comfort insoles

The primary objective of this study was to investigate the compressive behavior of 3D-printed specimens made of a thermoplastic polyurethane filament, specifically colorFabb varioShore TPU, which incorporates a foaming agent. The foaming technology makes it possible to manipulate 3D prints' properties by adjusting process parameters that affect the level of expansion, such as printing temperature, printing speed or flow ratio. This capability opens new possibilities for 3D-printed personalized foot orthotics or for static comfort-oriented applications by tailoring the stiffness of the print based on the application requirements. Since infill density and infill pattern also affect the compressive characteristics of 3D prints, this research took these two parameters into account as independent variables, alongside the printing temperature. Thus, the specimens with printing temperatures set at 190 °C, 220 °C, and 240 °C, gyroid and honeycomb patterns, and infill variations from 10 % to 35 % in 5 % increments were experimentally investigated in compression testing. The evaluation was conducted to determine the influence of these factors on the stiffness of prints at 10 % and 20 % strains, in accordance with established standard. The findings had an important practical value as they provide data for adjusting the variable stiffness based on peak plantar pressure measurement data when developing tailored foot orthoses (insoles), which was the second objective of the research. The most influential factor affecting the compressive strength was the printing temperature, followed by infill density and pattern type. The difference in compression modulus between 10 % and 20 % strains did not exhibit statistical significance. Moreover, the main effects plots indicated minimal variations in compression modulus effects at 220 °C and 240 °C, whereas an important difference was observed at 190 °C printing temperature, which was confirmed by scanning electron microscopy investigations showing foamed layers at 220 °C and unfoamed layers at 190 °C. Furthermore, interaction plots revealed no significant interaction effect among the studied variables. Additionally, a comparison of samples’ sizes and densities before and two months after testing indicated no observable modifications When applied to custom orthotics (five pairs of insoles were customized and tested), the experimental findings documented variations in the reduction and distribution of peak plantar pressure based on the infill variability.

Atomistic phase transition mechanism of zero-strain electrode material: Transmission electron microscopy investigation of Li4Ti5O12 spinel lattice upon lithiation

The lithiation mechanism of electrode materials is important for understanding the basic reactions in Li-ion batteries. In particular, zero-strain materials have garnered interest owing to their stable charge–discharge performances. In this study, we investigated the atomistic phase transition mechanism of spinel Li4Ti5O12, a well-known zero-strain material, using high-resolution transmission electron microscopy. A single-crystalline Li4Ti5O12 (100) specimen was prepared and observed in situ at a lattice resolution under electron-beam-assisted lithiation. The lattice fringes originating from the Li plane of the spinel crystal were anisotropically altered during phase transition, suggesting the asymmetrical site shifting of Li atoms during lithiation. This spontaneous symmetry-breaking mechanism for the phase transition is considered essential for the lithiation of spinel lattice.

Teak leaf biochar production for sustainable forest waste management at low temperatures

This study investigates the possibilities of producing biochar from teak leaves as an environmentally beneficial approach to managing forest waste in a sustainable manner. Teak leaves, a readily available forest by-product, were converted into biochar through a low-temperature pyrolysis process using a top-lit updraft mechanism. The results demonstrate the efficiency of this approach, yielding a substantial biochar output of 37.4 wt%, with its thermal field modelled perfectly via Levenberg-Marquardt algorithm in ANN topology. Elemental analysis of the teak leaf biochar revealed a high carbon content of 64.40%, positioning it as a valuable carbon-rich material suitable for various applications. Textural properties analysis indicated a significant surface area of 371.78 m2/g and a total pore volume of 0.175 cm³/g, enhancing its potential for various applications. Scanning Electron Microscopy (SEM) investigations showed a diverse network of pores and a rough surface structure, reinforcing the biochar’s versatility. This study shows the environmental benefits of low-temperature teak leaf biochar production, because it provides a carbon-content-preserving, sustainable alternative for handling forest wastes.

Microstructure and mechanical response of as-built and solution-annealed LPBF Hastelloy X under high-temperature fatigue loading

This study investigates the microstructural characteristics and the high-temperature mechanical behavior of Hastelloy X, fabricated via laser powder-bed fusion (LPBF) technology. Hastelloy X, a solid solution-strengthened nickel-based superalloy known for its high strength and oxidation resistance at elevated temperatures, has gained significant interest for the fabrication of complex aerospace components through LPBF technology. The study initially focuses on the impact of solution annealing heat treatment at 1227 °C on the alloy microstructure, based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. It then explores the fatigue and cyclic deformation response of the alloy at 750 °C across different strain ranges, comparing the as-built and solution-annealed conditions. To understand the observed differences in the cyclic mechanical response of as-built and solution-annealed LPBF HX, for a particular condition, a set of dedicated tests have been performed and interrupted at selected numbers of cycles in the different stages of the mechanical response. At each interruption point, specimens have been examined by TEM to provide an in-depth understanding of the effect of dislocation microstructural evolution on the high-temperature cyclic mechanical response of the alloy.

Effects of aging on the microstructure and mechanical properties of metastable β-type Ti-23.6Nb-5.1Mo-6.7Zr alloy with low elastic modulus

In this study, the influence of thermomechanical treatments on the microstructure and mechanical properties of a new metastable β-titanium Ti-23.6Nb-5.1Mo-6.7Zr alloy was assessed. The objective was to determine if the alloy is a potential candidate for a future fabrication of orthopedic implants, in particular prosthetic hip stems with a functional gradient of mechanical properties. Two thermomechanical processing routes were investigated: (a) 90% cold-rolled, (b) 90% cold-rolled, followed by annealing at 950 °C for 1 h. After these initial processing steps, samples were aged between 300 °C and 500 °C from 0.5 h to 4 h. Microstructural characterization was conducted by optical microscopy, transmission electron microscopy and x-ray diffraction. Young's modulus and microhardness were measured. Young's modulus of the sample annealed after cold rolling is lower than that after the cold rolled one. Aging was effective at increasing hardness but also increasing Young's modulus. The hardening during aging resulted from fine ωiso and α precipitation. The transmission electron microscopy investigations indicated that an aging treatment at 500 °C leads to a fine (α + β) microstructure, avoiding brittle ωiso precipitation. For these reasons, this alloy is a potential candidate for the manufacture of a hybrid hip prosthetic stem by employing localized aging treatment at 500 °C in the neck region, creating a functional strength gradient and maintaining a low Young's modulus in the distal part, which is needed to mitigate the stress shielding of the bone.

Gomphonemavancampianum sp. nov. (Gomphonemataceae, Bacillariophyceae), a new large Gomphonema species from Europe.

During a French biomonitoring survey of the lakes in the region Rhône-Méditerranée-Corse, a large, unknown Gomphonema taxon was observed in a lake in the vicinity of the City of Lyon (Département du Rhône, France), that could not be identified using the currently available literature. Detailed light and scanning electron microscopy investigations revealed the presence of two types of valves, one bearing a thick marginal crest and valves lacking the crest. Following comparison with similar, mostly tropical Gomphonema species, the unknown taxon is described as new: Gomphonemavancampianum sp. nov. Discriminating features of the new species include the peculiar valve shape resembling a Chinese spoon, the broad upper valve part with acuminate tip, the presence of shallow depressions in the axial area, distinctly punctate striae and the occasional presence of the marginal crest. The new species was observed in several samples collected in an oligo- to mesotrophic, calcium-carbonate rich lake with a high ecological quality.

Wettability and reactivity of liquid aluminium and highly deformed steel

The high-temperature liquid Al - solid S355J2N steel interaction was studied using a modified wettability test. A sessile drop method with a capillary purification procedure was employed for the first time, involving non-contact aluminium isothermal heating followed by the dropping of a pure liquid Al drop onto the severely deformed steel substrate and isothermal contact heating of Al with steel. The calculated contact angles and wetting kinetics curves demonstrated a good spreading and wetting of the investigated system. Scanning electron microscopy investigations played an important role in interpretation of the microstructural characteristics of the specimen, especially those located at the drop/substrate interface. The electron backscattered diffraction measurements allowed to characterize the microstructure of the interface zone to obtain more detailed information about the grain size, type of the intermetallic phases: θ-Al13Fe4, Fe2Al5, FCC Al and ferrite and their distribution in the neighborhood of the interface zone. These intermetallics were also confirmed via transmission electron microscopy studies coupled with energy-dispersive X-ray spectroscopy analysis of the drop/substrate interface. Research findings provide valuable insights into the liquid Al and steel interaction during the explosive welding process, where the local melting of metal takes place at the interface of colliding plates, strongly deformed due to the collision.

Synergistic and potential antifungal properties of tailored, one pot multicomponent monoterpenes co-delivered with fluconazole encapsulated nanostructure lipid carrier

Frequent and variant infections are caused by the virtue of opportunistic fungi pathogens. Candidiasis, aspergillosis, and mucormycosis are pathogenic microorganisms that give rise to vast fungal diseases that alternate between moderate to fatal in severity. The use of fluconazole as an antifungal drug was limited due to the acquired resistance in some types of Candida and other fungal species. This study aims to consolidate fluconazole’s biological effectiveness against several pathogenic fungi. Six active monoterpenes (MTs) of carvacrol, linalool, geraniol, α-terpinene, citronellal, and nerolidol were selected and encapsulated in nanostructure lipid carrier (NLC) with (NLC-Flu-MTs) and/without (NLC-MTs) fluconazole in one nanoformulation to determine if they will act synergistically or not? The synthesized nanoformulation NLC-Flu-MTs and NLC-MTs exhibited very good particle size of 144.5 nm and 138.6 nm for size and zeta potential values of (− 23.5 mV) and (− 20.3 mV), respectively. Transmission electron microscope investigation confirmed that the synthesized NLCs have regular and spherical shape. The abundance and concentration of the six released monoterpenes were determined, as a novel approach, using GC–MS with very good results and validity. In-vitro antifungal screening was done before and after nano co-delivery against seven pathogenic, and aggressive fungi of Candida tropicalis, Candida krusei, Candida glabrata, Geotrichum Candidum, Candidaalbicans, Aspergillus Niger, and mucor circinelloides. Inhibition Zone diameter (IZD) and the minimum inhibitory concentration (MIC) were measured. Nanoformulations NLC-Flu-MTs and NLC-MTs manifested potential and unique biological susceptibility against all the tested microorganisms with reduced (MIC) values, especially against Candida Tropicalis (MIC = 0.97 µg/ml) which represents 16-fold of the value shown by NLC-MTs (MIC = 15.6 µg/ml) and 64-fold of fluconazole free before nanoformulation (MIC = 62.5 µg/ml). The efficiency of nanomaterials, particularly NLC-Flu-MTs, has become evident in the diminishing value of MIC which affirmed the synergism between fluconazole and the other six monoterpenes.

Gomphonema beaugerianum, a new Gomphonema species (Bacillariophyta) found in a historic William Smith sample from the Auvergne (France)

A large, unknown Gomphonema taxon belonging to the G. truncatum group was observed in a historic sample collected by William Smith during his 1854 excursion in the Auvergne (France). The unknown species presented sufficient differences with all known taxa in the truncatum-capitatum group to warrant further morphological investigations. Detailed light and scanning electron microscopy investigations in comparison with all published literature revealed that the unknown species had a unique combination of morphological (uniseriate striae, lack of well-develop headpole) and morphometric (large valve width) features. Therefore, the species is described as new: Gomphonema beaugerianum sp. nov. The new species was observed in Lac de Guéry, an oligotrophic, almost circumneutral lake in the Auvergne with a high ecological quality.

Deeper Insights into the Morphology Effect of Na2Ti3O7 Nanoarrays on Sodium-Ion Storage.

Na2Ti3O7-based anodes show great promise for Na+ storage in sodium-ion batteries (SIBs), though the effect of Na2Ti3O7 morphology on battery performance remains poorly understood. Herein, hydrothermal syntheses is used to prepare free-standing Na2Ti3O7 nanosheets or Na2Ti3O7 nanotubes on Ti foil substrates, with the structural and electrochemical properties of the resulting electrodes explored in detail. Results show that the Na2Ti3O7 nanosheet electrode (NTO NSs) delivered superior performance in terms of reversible capacity, rate capability, and especially long-term durability in SIBs compared to its nanotube counterpart (NTO NTs). Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations, combined with density functional theory calculations, demonstrated that the flexible 2D Na2Ti3O7 nanosheets are mechanically more robust than the rigid Na2Ti3O7 nanotube arrays during prolonged battery cycling, explaining the superior durability of the NTO NSs electrode. This work prompts the use of anodes based on Na2Ti3O7 nanosheets in the future development of high-performance SIBs.

Improving photocatalytic efficiency of ZnO nanoflowers through gold incorporation for Rhodamine B photodegradation

In this study, we reported the synthesis and characterization of Au-doped ZnO hybrid nanostructures via a wet chemical approach and assessed their photocatalytic efficiency for the removal of Rhodamine (Rh–B). X-ray powder diffraction (XRD) has been done to verify the crystal structure, i.e. phase identification, crystallite size, texture, stress, and strain. The XRD patterns demonstrate that the wurtzite structure has been retained and that Au nanoparticles were effectively ingested into the ZnO nanoflowers lattice. This demonstrates that Au nanoparticles are effectively absorbed into the ZnO nanoflowers lattice, considering that peaks shifted in the direction of smaller Bragg's angles. As a result, the size of the crystallites increases from (20.7–25.3) nm, and their microstrain decreases from (0.92–0.72) x 10−3 A0 for pure-ZnO to Au-doped ZnO heterostructures, respectively. Scanning Electron Microscopy (SEM) investigation reveals flower-like structures of pure ZnO while a further closed look indicates that these flowers are made up of a variety of oriented, thorn-like branched NWs with diameters ranging from (50–90) nm and lengths ranging from a few microns. The corresponding EDS evaluation of pure ZnO nanoflowers and Au-doped ZnO heterostructures clearly shows that the noble metal Au NPs are deposited, and enormously safeguard the surface of ZnO nanoflowers. Reducing the Au-doped ZnO band gap which generated a red shift in light absorption, was confirmed by the PL spectra which in turn increased the photocatalytic efficiency and reduced the dye degradation time of Rh–B. The photocatalytic ability of Au-doped ZnO heterostructures considerably increased the photodegradation efficiency of Rh–B molecules from 28 min for pure ZnO to 10 min for Au-doped ZnO heterostructures. Due to their wide surface area and distinct morphology as compared to pure ZnO nanoflowers.

Grain boundary chemistry and increased thermoelectric performance in Bi2Se3–Fe3O4 nanocomposites

The addition of Fe3O4 nanoparticles to Bi2Se3 nanocomposites resulted in a significant increase of the thermoelectric figure of merit zT at room temperature from 0.14 in Bi2Se3 to 0.21 in Bi2Se3 with added 5 % volume of Fe3O4 nanoparticles. The main contributor to the improved zT is the large increase in carrier concentration, hence increased electrical conductivity. Electron microscopy investigation revealed chemical changes in the Bi2Se3 leading to segregation of Bi to the interface with the Fe3O4 nanoparticles. The fact that the altered Bi/Se proportion was constrained close to the grain boundaries resulted in a mild reduction of the Seebeck coefficient, less than what is expected from simple band structure models for the same increase in carrier density. The addition of Fe3O4 in relatively small volume fraction allowed to both decrease the thermal conductivity and increase the power factor in a Bi2Se3 material, the latter more intensely than usual substitution methods.