Nm In Radius Research Articles

Influence of Particle Size on Mass Transport during the Oxygen Reduction Reaction at Single Silver Particles Using Scanning Electrochemical Cell Microscopy.

Single entity electrochemical measurements enable insight into the electrocatalytic activity of individual particles based on composition, shape, and crystallographic orientation. In addition to structural effects, particle size can further influence electrocatalytic activity and reaction mechanisms through mass transport effects. In this work, electrodeposition was used to grow well-separated silver particles of varying sizes from 100 to 500 nm in radius. Using a multimicroscopy approach of scanning electrochemical cell microscopy combined with scanning electron microscopy, the electrocatalytic current of individual silver particles toward the oxygen reduction reaction was evaluated as a function of their size. It was found that the current density increased with decreasing particle radius, which was correlated to the mass transport of oxygen to the silver particle, demonstrating the importance of size dependent mass transport effects that can occur at the single particle level using scanning electrochemical cell microscopy and opening new opportunities for quantitative electrocatalysis measurements.

Formation of uranium nitride nanoparticles via mechanical alloying of uranium-molybdenum alloy fuels in gaseous nitrogen

Uranium-molybdenum (U-Mo) alloys show promise as a nuclear fuel system due to their high thermal conductivity and fuel loading capability. However, U-Mo systems are susceptible to irradiation induced swelling ultimately affecting the cladding via mechanical and chemical interactions. To address these shortcomings, this research investigated the formation of uranium mononitride (UN) nanoparticles within a 90 wt% U/ 10 wt% Mo (U-10Mo) matrix to act as a prospective defect sink for fission products at nanometric hetero-interfaces. To promote the formation of UN, U-10Mo powders were mechanically alloyed under a high purity nitrogen atmosphere. Variations of the milling process investigated included media size, duration of milling, and number of times the milling jar was re-aerated with nitrogen gas. Characterization of the fuel microstructure was completed using light element analysis, X-ray diffraction, scanning and transmission-electron microscopy, electron energy loss spectroscopy, and atom probe tomography. UN nanoparticles measuring 1–5 nm in radius were observed in the U-Mo matrix as early as 1 h into the mechanical alloying process. Milling time in excess of 10 h was found to lead to deleterious effects induced by the stainless-steel milling media.

Jumping behavior of water nanodroplets on a superhydrophobic surface in high Ohnesorge number (Oh) regime

The coalescence-induced jumping of nanodroplets on superhydrophobic surfaces has recently gained research attention due to its application in energy harvesting, self-cleaning, and cooling of nanoscale electronic devices. This study aims to investigate the jumping behavior of water nanodroplets in a high Ohnesorge number regime, where 0.45 < Oh < 1 and identify the critical size of droplets where jumping terminates. The study utilized molecular dynamics simulations to analyze the jumping characteristics of droplets ranging from 1.5 nm to 7 nm in radius. The findings of this research developed a universal jumping mechanism for droplets of all sizes, identified the lower limit of droplet size, below which coalescence-induced jumping does not occur, and explained a special phenomenon of jumping velocity becoming maximum before it approaches zero. The study also investigated how jumping terminates due to the size difference between droplets. These findings align well with prior micro-scale studies and experimental predictions. Surface energy, viscous dissipation, kinetic energy, and varying surface tension have been identified as the dominating factors influencing nanoscale droplet jumping at such a high Oh regime. The findings will provide insights for developing various applications at this scale.

Hierarchically porous electrospun carbon nanofiber for high-rate capacitive deionization electrodes

Capacitive deionization (CDI) is a promising technology that has gained interest for the desalination of brackish water. Hierarchically porous carbons are commonly used as electrodes for CDI due to their high surface areas and controlled pore size distributions that maximize ion adsorption capacity and rate. Electrospinning is an effective way of generating carbon nanofibers with high inter-fiber macroporosity that can be further modified to improve surface area, total pore volume, and pore size distribution. This work describes the use of sacrificial mesopore formers in tandem with a micropore etching technique to induce hierarchical porosity in electrospun fibers. Mesopores are formed via the dissolution of silica nanoparticles that are introduced into the fibers during the electrospinning step. After mesopore formation, micropores are etched into the resulting surface through KOH impregnation and thermal activation. This sequential technique creates a hierarchical network of pores from the inherent macroporosity of the fiber network, to the mesopores, and finally micropores to simultaneously maximize surface area and accessibility. Micropore formation is optimized to maximize specific surface area while maintaining physical integrity of the fibers. The combination of mesopores and micropores enables fast ion adsorption rates and capacity. Carbon fiber electrodes fabricated in this method achieve specific surface areas exceeding 1400 m2 g−1, with pore volumes exceeding 1.0 cc g−1. The pore size distributions are highly controlled, with 80 % of total pore volume coming from pores <20 nm in radius. In 500 ppm constant voltage CDI tests, these fiber electrodes obtain a salt adsorption capacity of over 14 mg g−1 at a salt adsorption rate of ∼4 mg g−1 min−1, showcasing the high capacity matched with high rate of these easily fabricated, inexpensive materials.

Optimization of synthesis conditions and calibration of water-swellable polyacrylamide microgels

Precipitation Polymerization (PP) and Inverse Emulsion Polymerization (IEP) are the main procedures widely used for the synthesis of microgels from acrylamide derivate monomers, in both academic and industrial spheres. Here, these procedures were optimized for pure acrylamide monomer to synthetize a “model” polyacrylamide microgel targeting a minimized size of approximately 200 nm in radius. For this neutral and non-responsive monomer, the role of the co-solvent in PP and co-surfactant in IEP was discussed. This work demonstrates the crucial step of purification and calibration on microgels physical properties in suspension. In particular, the filtration step has a significant impact on their rheological behaviour, where the flow properties requiring a complex description become analysable with a standard Carreau–Yasuda model. In summary, this paper provides a systematic discussion on the role of each step in the elaboration of model microgel, as a routine checklist to be considered before further physical-chemical studies.

Mathematical modeling of intratumoral immunotherapy yields strategies to improve the treatment outcomes.

Intratumoral injection of immunotherapy aims to maximize its activity within the tumor. However, cytokines are cleared via tumor vessels and escape from the tumor periphery into the host-tissue, reducing efficacy and causing toxicity. Thus, understanding the determinants of the tumor and immune response to intratumoral immunotherapy should lead to better treatment outcomes. In this study, we developed a mechanistic mathematical model to determine the efficacy of intratumorally-injected conjugated-cytokines, accounting for properties of the tumor microenvironment and the conjugated-cytokines. The model explicitly incorporates i) the tumor vascular density and permeability and the tumor hydraulic conductivity, ii) conjugated-cytokines size and binding affinity as well as their clearance via the blood vessels and the surrounding tissue, and iii) immune cells-cancer cells interactions. Model simulations show how the properties of the tumor and of the conjugated-cytokines determine treatment outcomes and how selection of proper parameters can optimize therapy. A high tumor tissue hydraulic permeability allows for the uniform distribution of the cytokines into the tumor, whereas uniform tumor perfusion is required for sufficient access and activation of immune cells. The permeability of the tumor vessels affects the blood clearance of the cytokines and optimal values depend on the size of the conjugates. A size >5 nm in radius was found to be optimal, whereas the binding of conjugates should be high enough to prevent clearance from the tumor into the surrounding tissue. In conclusion, development of strategies to improve vessel perfusion and tissue hydraulic conductivity by reprogramming the microenvironment along with optimal design of conjugated-cytokines can enhance intratumoral immunotherapy.

A novel and economical approach for the synthesis of short rod-shaped mesoporous silica nanoparticles from coal fly ash waste by Bacillus circulans MTCC 6811.

Coal fly ash (CFA) is an industrial byproduct produced during the production of electricity in thermal power plants from the burning of pulverized coal. It is considered hazardous due to the presence of toxic heavy metals while it is also considered valuable due to the presence of value-added minerals like silicates, alumina, and iron oxides. Silica nanoparticles' demands and application have increased drastically in the last decade due to their mesoporous nature, high surface area to volume ratio, etc. Here in the present research work, short rod-shaped, mesoporous silica nanoparticles (MSN) have been synthesized from coal fly ash by using Bacillus circulans MTCC 6811 in two steps. Firstly, CFA was kept with the bacterial culture for bioleaching for 25 days in an incubator shaker at 120rpm. Secondly, the dissolved silica in the medium was precipitated with the 4M sodium hydroxide to obtain a short rod-shaped MSN. The purification of the synthesized silica particle was done by treating them with 1M HCl at 120 °C, for 90min. The synthesized short rod-shaped MSN were characterized by UV-vis spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Particle size analyzer (PSA), Field emission scanning electron microscopy (FESEM), and transmission electron microscope. The microscopic techniques revealed the short rod-shaped mesoporous silica nanoparticles (MSN) for the final nano-silica, whose size varies from 40 to 80nm, with an average size of 36 ± 5nm. The XRD shows the crystalline nature of the synthesized MSN having a crystallite size of 36nm. The FTIR showed the three characteristic bands in the range of 400-1100cm-1, indicating the purity of the sample. The energy dispersive X-ray (EDX) showed 53.04 wt% oxygen and 43.42% Si along with 3.54% carbon in the final MSN. The particle size analyzer revealed that the average particle size is 368.7nm in radius and the polydispersity index (PDI) is 0.667. Such a novel and economical approach could be helpful in the synthesis of silica in high yield with high purity from coal fly ash and other similar waste.

(Invited) Unique Size-Dependent Electrochemistry of Metal Nanoparticles in Aqueous and Hydrogel Environments

Metal nanoparticles (NPs) exhibit unique size-dependent physical and chemical properties, providing many potential applications including sensing, catalysis, optoelectronics, medical diagnostics and disease therapeutics, among others. Here we describe interesting size-dependent metal oxidation, metal reduction, and electrocatalytic properties for Au and other metal nanoparticles that are coated with relatively weak-binding stabilizers, which is necessary for effective electron transfer at the metal NP surface. Metal oxidation potentials decrease dramatically negative with decreasing NP size, especially below 4 nm down to ~1 nm in radius. Electrocatalytic seeded-growth kinetics also depend strongly on the metal NP size (seed size). The thermodynamics of other oxidation/reduction reactions, such as galvanic replacement, also depend dramatically on metal NP size, resulting in unique alloy nanostructures with improved electrocatalytic reactivity and stability. Size-dependent electrophoretic deposition of metal nanoparticles to form thin films also results from size-dependent electrocatalytic properties, allowing metal NP separations based on electrocatalytic activity. These oxidation, reduction, galvanic replacement, and electrocatalytic properties change dramatically when the metal NPs are coated with strong ligand stabilizers or when placed in a viscous hydrogel environment. The effect of the ligand and environment will be described here. A better understanding of size-dependent reactivity of metal NPs as a function of the type of stabilizer and environment is important to realize their potential for tuning the properties to optimize them for a specific application.

Correlation between cellular uptake and cytotoxicity of polystyrene micro/nanoplastics in HeLa cells: A size-dependent matter.

The cytotoxicity of micro/nanoplastics (MNPs) is known to be strongly influenced by particle size, but the mechanism is not clear so far. We reported the ability of polystyrene MNPs to be internalized by HeLa cells could be a reason for the size dependent cytotoxicity of MNPs. We found that small MNPs (10 nm and 15 nm in radius) could be efficiently internalized by HeLa cells, MNPs of 25 nm in radius could be slightly internalized by the cells, and larger MNPs could not enter the cells at all. We showed that only MNPs, which could be internalized by cells, had a toxic effect on cell activity in a dose-dependent manner. In contrast, MNPs, which could not be internalized by cells, showed no cytotoxicity even if at extremely high concentrations. We attributed the correlation between the size-dependent uptake of MNPs and the size-dependent cytotoxicity of MNPs to the enhanced reactive oxygen species (ROS) level and abnormal gene expression. Our study pointed out that cellular uptake is one of the most fundamental mechanisms for the cytotoxicity of MNPs.

In English

Hybrid carbons/metals/metal (metalloid) oxides composites could be effective adsorbents for low– and high–molecular weight compounds, polar and nonpolar, gaseous and liquid. The presence of metal nanocrystallites and carbon nanostructures could provide catalytic properties in redox reactions. For more effective use of hybrid composites, their morphological, structural, textural, and adsorption characteristics should be appropriate for target applications and, therefore, well controlled. Therefore, the aim of this study was to synthesize carbon/metal/silica nanostructured composites with varied content of metal (Ni) to control the mentioned characteristics. Precipitated silica Sipernat 50 was selected as a substrate. Potato starch was used as a carbon precursor. Nickel nitrate (Ni(NO3)2·6H2O) of varied amounts was used as a precursor of Ni nanoparticles reduced upon the starch carbonization. After the starch carbonization and Ni reduction, a set of C/Ni/silica samples was studied using atomic force microscopy, X–ray diffraction, X–ray fluorescence spectroscopy, nitrogen and p-nitrophenol adsorption, thermogravimetry, and Raman spectroscopy. The presence of nickel phase results in the formation of smaller but denser packed char nanoparticles. Estimation of possible contribution of pores accessible for nitrogen molecules in silica globules and outer surface of carbon/Ni particles suggests that the carbon phase is porous that provides a significant part of the specific surface area of the composites. Amorphous silica and char phases are characterized by the presence of certain nuclei of radius (R) &lt; 1 nm and 2 nm &lt; R &lt; 10 nm estimated from the XRD patterns using full peak profile analysis with a self–consistent regularization procedure. Ni crystallites are of several sizes, since particle size distributions include two–three peaks in the range of 3–13 nm in radius. The Raman spectra show that the main changes with increasing Ni content are characteristic to sp3 carbon structures (D line) in contrast to the sp2 structures (G line). The pore size distributions (both differential and incremental) demonstrate complex changes in a broad size range due to increasing Ni content in composites. As a whole, changes in the Ni content in nanostructured C/Ni/silica composites allow one to control the morphological, structural, and textural characteristics of the whole materials.

Effects of h-BN additives on tensile mechanical behavior of Fe matrix: A molecular dynamics study

In this paper, the effect mechanism of h-BN size, strain rate and tensile direction on tensile mechanical properties of Fe matrix in the presence of h-BN inclusions was investigated by molecular dynamics simulations. The results showed that the existence of h-BN inclusions diminished the tensile mechanical properties of Fe, which was attributed to the large variation in Elastic modulus between the inclusions and matrix as well as stress concentration near the interface. When the h-BN inclusions was 1 nm in radius, the results of the CNA analysis showed that the crystal structure changes from ordered to disordered to partially ordered, and the DXA analysis indicated that the dislocation length increased, then decreased, and then increased again. The stress–strain curve showed a double-peak phenomenon. The first peak was caused by the change in the crystal structure, and the second peak aroused due to the regrowth of dislocations. By analyzed the stress–strain curves at different strain rates, it was found that the tensile strength increased with increasing strain rate, while the Elastic modulus was almost unaffected, from the perspective of potential energy, the conclusion was confirmed. The findings of different tensile directions indicated that the material’s tensile strength was affected by the tensile direction. When the h-BN inclusions are parallel to tensile direction, the h-BN inclusions hindered the plastic deformation and a second peak appeared in the stress–strain curve. This study is essential to comprehend the influence of h-BN inclusions on mechanical properties of free-cutting steel.

Enhanced toxicity of 2,2-bis(chloromethyl) trimethylene bis[bis(2-chloroethyl) phosphate] (V6) by nanopolystyrene particles towards HeLa cells

2,2-bis(chloromethyl) trimethylene bis[bis(2-chloroethyl) phosphate] (V6) has been widely used as an additive in a variety of plastics due to its extremely low toxicity. However, we showed in the study that once mixed with nanopolystyrene particles (NPs), the nontoxic V6 could exhibit significant toxicity to HeLa cells. The enhanced toxicity was much higher than the toxicity of NPs alone and was related to the size of NPs. The mixture of V6 and small polystyrene NPs (10 nm and 15 nm in radius) showed obvious toxicity to HeLa cells. The toxicity increased with the concentrations of both V6 and NPs. On the contrary, the mixture of V6 and larger NPs (25 nm, 50 nm, 100 nm, and 500 nm in radius) showed almost no toxicity even at extremely high concentrations (NPs: 100 mg/L; V6: 50 mg/L). The small NPs could enter the cells and accumulated in cytoplasm. However, the larger NPs did not distribute inside the cells. NPs efficiently adsorbed V6 on the surface. The mechanism of the enhanced toxicity was attributed to the increased intracellular reactive oxygen species (ROS) production and the regulation of gene expression concerning apoptosis and ROS scavenging. Our study not only showed that a safe chemical V6 could be turned to be toxic by NPs, but also pointed out a potential risk caused by the joint toxicity of ‘safe’ chemicals and plastic particles with small size.

Microstructure and strengthening mechanisms of Zr-modified Al–Cu–Mg alloy processed by selective laser melting

Zr modification can significantly change the strengthening mechanisms of traditional heat-treatable Al alloys fabricated by selective laser melting (SLM). In this study, the effect of direct aging (DA) treatment on the microstructure and strengthening mechanisms of Zr-modified Al–Cu–Mg alloys fabricated by SLM was analyzed. The fine α-Al grains with an average size of approximately 1.1 μm in the as-fabricated samples were maintained after DA treatment. The S′-Al2CuMg precipitates dissolved, and the secondary Al3Zr-L12, 1.1 nm in radius, precipitated from the α-Al matrix after DA treatment. This led to a larger increase of 29 MPa in the contribution of precipitation strengthening compared with the increase of 5 MPa in the contribution of grain boundary strengthening after the DA treatment. In addition, a large number of Cu–Mg-rich and Cu–Mn-rich particles were found in the DA-treated sample, which offered dispersion strengthening. This work provides valuable insights for the development of Zr-modified 2000 series Al alloys applicable in additive manufacturing.

Capturing Lipid Nanodisc Shape and Properties Using a Continuum Elastic Theory.

Lipid nanodiscs are nanometric bilayer patches enveloped by confining structures, commonly composed of membrane scaffolding proteins (MSPs). To resolve the interplay between MSP geometry, lipid confinement, and membrane material properties on the nanodisc shape, we apply a continuum elastic theory accounting for lipid bending, tilting, and area deformations. The equilibrium nanodisc shape is then determined by minimizing the elastic free energy functional. Analytic expressions derived under simplifying assumptions demonstrate that the nanodisc shape is sensitive to its size, lipid density, and the lipid tilt and thickness imposed at the contact with the MSP. Under matching physical parameters, these expressions quantitatively reproduce the shape of nanodiscs seen in molecular dynamics simulations, but only if lipid tilt is explicitly considered. We further demonstrate how the bending rigidity can be extracted from the membrane shape profile by fitting the numerically minimized full elastic functional to the membrane shape found in simulations. This fitting procedure faithfully informs on the bending rigidity of nanodiscs larger than ca. 5 nm in radius. The fitted profiles accurately reproduce the increase in bending modulus found using real-space fluctuation analysis of simulated nanodiscs and, for large nanodiscs, also accurately resolve its spatial variations. Our study shows how deformations in lipid patches confined in nanodiscs can be well described by a continuum elastic theory and how this fit can be used to determine local material properties from shape analysis of nanodiscs in simulations. This methodology could potentially allow direct determination of lipid properties from experiments, for example cryo-electron microscopy images of lipid nanodiscs, thereby allowing to guide the development of future nanodisc formulations with desired properties.

Predicting chemoevasion potential of cancer cells from statistical chromatin packing behavior.

In malignancy, genetic, metabolic, or environmental insults may remodel chromatin structure, potentially increasing the plasticity of aberrant cell state transitions. Observed alterations to the epigenetic landscape of chromatin include gain-of-function mutations of Polycomb repressor EZH2 that block differentiation. Nucleosome remodeling and higher-order chromatin organization may also increase malignancy, with abnormalities ranging from prevalent mutations of ATP-dependent chromatin remodelers to mixing between transcriptionally active and inactive compartments. However, a universal relationship between chromatin structure and the disease state does not yet exist. Here, using the first principles of physics, we demonstrate that chromatin packing, or the statistical distribution of chromatin density in 4D, is a genome-wide regulator of phenotypic plasticity. The nucleus is a highly crowded, heterogeneous environment where DNA, RNA, proteins, and other macromolecules exert excluded volume effects, altering the kinetics and efficiency of transcription reactions. As chromatin is the major crowder in the nucleus, characterizing the chromatin mass density distribution facilitates a more complete understanding of transcription processes in a realistic nuclear environment. Combining high-resolution chromatin scanning transmission electron microscopy (ChromSTEM) and live-cell, label-free Partial Wave Spectroscopy (PWS) along with polymer physics-based analysis, we identified the existence of spatially separable packing domains, around 80 nm in radius. We then employed our understanding of fundamental chromatin packing to build a chromatin-mediated model of transcription that incorporates two pertinent aspects of phenotypic plasticity: transcriptional malleability, the ability of a cell to upregulate certain genes within a critical time frame, and transcriptional heterogeneity, a cell population's range of functional states. Finally, we extended our transcription model to predict how the average chromatin packing behavior of a cell population contributes directly to cancer cell survival upon chemotherapy treatment. Experimental observations confirmed model predictions, underlying the importance of chromatin packing in chemoevasion processes.

In situ saxs characterization of thermoresponsive behavior of a poly(ethylene glycol)-graft-(poly(vinyl caprolactam)-co-poly(vinyl acetate)) amphiphilic graft copolymer

We report the thermoresponsive assembly and rheology of an amphiphilic thermosensitive graft copolymer, poly(ethylene glycol)-graft-(poly(vinyl caprolactam)-co-poly(vinyl acetate)) (commercial name Soluplus®), which has been investigated for potential biomedical applications. It has received attention due to is ability to solubilize hydrophobic drugs and for its thickening behavior close to body temperature. Through use of the synchrotron at Brookhaven National Lab, and collaboration with the department of energy, the nanoscale structure and properties can be probed in greater detail. Soluplus® undergoes two structural changes as temperature is increased; the first, a concentration independent change where samples become turbid at 32 °C. Increasing the temperature further causes the formation of physically associated hydrogels. This sol-gel transition is concentration dependent and occurs at 32 °C for 40 wt% samples, and increases to 42 °C for 10 wt% samples. From variable temperature SAXS characterization micelles of 20–25 nm in radius can be seen and maintain their size and packing below 32 °C. A gradual increase in the aggregation of micelles corresponding to a thickening of the material is also observed. Close to and above the gelation temperature, micelles collapse and form a physically associated 3D network. A model is proposed to explain these physical effects, where the poly(vinyl caprolactam) group transitions from the hydrophilic corona at room temperature to the hydrophobic core as temperature is increased.

Graphitization by Metal Particles.

Graphitization of carbon offers a promising route to upcycle waste biomass and plastics into functional carbon nanomaterials for a range of applications including energy storage devices. One challenge to the more widespread utilization of this technology is controlling the carbon nanostructures formed. In this work, we undertake a meta-analysis of graphitization catalyzed by transition metals, examining the available electron microscopy data of carbon nanostructures and finding a correlation between different nanostructures and metal particle size. By considering a thermodynamic description of the graphitization process on transition-metal nanoparticles, we show an energy barrier exists that distinguishes between different growth mechanisms. Particles smaller than ∼25 nm in radius remain trapped within closed carbon structures, while nanoparticles larger than this become mobile and produce nanotubes and ribbons. These predictions agree closely with experimentally observed trends and should provide a framework to better understand and tailor graphitization of waste materials into functional carbon nanostructures.

Screening for electrically conductive defects in thin functional films using electrochemiluminescence.

Multifunctional thin films in energy-related devices often must be electrically insulating where a single nanoscale defect can result in complete device-scale failure. Locating and characterizing such defects presents a fundamental problem where high-resolution imaging methods are needed to find defects, but imaging with high spatial resolution limits the field of view and thus the measurement throughput. Here, we present a novel high-throughput method for detecting sub-micron defects in insulating thin films by leveraging the electrochemiluminescence (ECL) of luminol. Through a systematic study of reagent concentrations, buffers, voltage, and excitation time, we identify optimized conditions under which it is possible to detect sub-micron defects at high-throughput. Extrapolating from the signal to background observed for detecting 440 nm wide lines and 620 nm diameter circles, we estimate the minimum detectable features to be lines as narrow as 2.5 nm in width and pinholes as small as 70 nm in radius. We further explore this method by using it to characterize a nominally insulating poly(phenylene oxide) film and find conductive defects that are cross-correlated with high-resolution atomic force microscopy to provide feedback to synthesis. Given this assay's inherent parallelizability and scalability, it is expected to have a major impact on the automated discovery of multifunctional films.

Interphase and fibrous precipitation in a thermomechanically processed V–Nb–Mo microalloyed steel

A novel V–Nb–Mo steel was thermomechanically processed to promote ferrite grain refinement and precipitation during the austenite to ferrite transformation. Transmission electron microscopy and three-dimensional atom probe tomography confirmed the formation of two main types of precipitates: nano-scale interphase precipitates and fibrous precipitates (FP). Both the precipitates had a Baker–Nutting orientation relationship with the ferrite matrix, but with different variants. Interphase precipitates exhibited a disc shape with an average distance between precipitate rows of 15 ± 2 nm and an average Guinier radius of 3.9 ± 1.7 nm, whereas FP had a rod-shape 2.5 ± 0.5 nm in radius and 8–25 nm in length. It appeared that the FP are formed along the plane perpendicular to the interphase precipitates plane.

Orientation effects on near-field radiative heat transfer between complex-shaped dielectric particles

The effect of orientation on near-field radiative heat transfer between two complex-shaped superellipsoid particles of SiO2 is presented. The particles under study are 50 nm in radius and of variable concavity. Orientation is characterized by the degree of rotational symmetry in the two-particle systems, and the radiative conductance is calculated using the discrete system Green's function approach to account for all electromagnetic interactions. The results reveal that the total conductance in some orientations can be up to twice that of other orientations when particles are at a center-of-mass separation distance of 110 nm. Orientation effects are not significantly correlated with system rotational symmetries but are strongly correlated with the minimum vacuum gap distance between particles. As such, orientation effects on near-field radiative heat transfer are a consequence of particle topology, with more extreme topologies leading to a continuation of orientation effects at larger particle center-of-mass separation distances. The concave superellipsoid particles display significant orientation effects up to a center-of-mass separation distance approximately equal to 3.9 times the particle radius, while the convex superellipsoid particles display significant orientation effects up to a center-of-mass separation distance approximately equal to 3.2 times the particle radius. In contrast to previous anisotropic, spheroidal dipole studies, these results of complex-shaped superellipsoid particles suggest that orientation effects become negligible when heat transfer is a volumetric process for all orientations. This work is essential for understanding radiative transport between particles that have non-regular geometries or that may have geometrical defects or abnormalities.