Nanometer Scale Research Articles

Development of a Versatile Nanostructured Lipid Carrier (NLC) Using Design of Experiments (DoE)-Part II: Incorporation and Stability of Butamben with Different Surfactants.

Nanostructured lipid carriers (NLCs) are typically composed of liquid lipids, solid lipids, and surfactants, enabling the encapsulation of lipophilic drugs. Butamben is a Class II anesthetic drug, according to the Biopharmaceutical Classification System (BCS); it has a log P of 2.87 and is considered a 'brick dust' (poorly water-soluble and poorly lipid-soluble) drug. This characteristic poses a challenge for the development of NLCs, as they are not soluble in the liquid lipid present in the NLC core. In a previous study, we developed an NLC core consisting of a solid lipid (CrodamolTM CP), a lipophilic liquid with medium polarity (SRTM Lauryl lactate), and a hydrophilic excipient (SRTM DMI) that allowed the solubilization of 'brick dust' types of drugs, including butamben. In this study, starting from the NLC core formulation previously developed we carried out an optimization of the surfactant system and evaluated their performance in aqueous medium. Three different surfactants (CrodasolTM HS HP, SynperonicTM PE/F68, and CroduretTM 40) were studied and, for each of them, a 23 factorial design was stablished, with total lipids, % surfactant, and sonication time (min) as the input variables and particle size (nm), polydispersity index (PDI), and zeta potential (mV) as the response variables. Stable NLCs were obtained using CrodasolTM HS HP and SynperonicTM PE/F68 as surfactants. Through a comparison between NLCs developed with and without SRTM DMI, it was observed that besides helping the solubilization of butamben in the NLC core, this excipient helped in stabilizing the system and decreasing particle size. NLCs containing CrodasolTM HS HP and SynperonicTM PE/F68 presented particle size values in the nanometric scale, PDI values lower than 0.3, and zeta potentials above |10|mV. Concerning NLCs' stability, SBTB-NLC with SynperonicTM PE/F68 and butamben demonstrated stability over a 3-month period in aqueous medium. The remaining NLCs showed phase separation or precipitation during the 3-month analysis. Nevertheless, these formulations could be freeze-dried after preparation, which would avoid precipitation in an aqueous medium.

Nanoscale intracellular ultrastructures affected by osmotic pressure using small-angle X-ray scattering

Although intracellular ultrastructures have typically been studied using microscopic techniques, it is difficult to observe ultrastructures at the submicron scale of living cells due to spatial resolution (fluorescence microscopy) or high vacuum environment (electron microscopy). We investigate the nanometer scale intracellular ultrastructures of living CHO cells in various osmolality using small-angle X-ray scattering (SAXS), and especially the structures of ribosomes, DNA double helix, and plasma membranes in-cell environment are observed. Ribosomes expand and contract in response to osmotic pressure, and the inter-ribosomal correlation occurs under isotonic and hyperosmolality. The DNA double helix is not dependent on the osmotic pressure. Under high osmotic pressure, the plasma membrane folds into form a multilamellar structure with a periodic length of about 6 nm. We also study the ultrastructural changes caused by formaldehyde fixation, freezing and heating.

Design of Holographic Condenser Lens for Visible Light Lithography

Photolithography with visible light at λ = 405 nm utilizing the concept of nonlinear saturable absorption effect where the size of the spot is diminished to the nanometer scale as proposed by several researchers is an alluring proposition for cost-effective projection lithography. Costly conventional condenser lenses can be replaced by monochromatic aberration-free and cost-effective volume phase holographic lenses for visible light photolithography with enhanced resolution utilizing the concept of off-axis illumination. However, the diffraction efficiency of holographic lenses depends on the wavelength of illuminating light and the angle of illumination. Angular and spectral characteristics of volume phase holograms can be controlled by optimizing processing parameters. The results on the theoretical optimization of three important processing parameters, namely fringe spacing ( ∧ ), thickness of the film ( d ), and refractive index modulation ( Δ n ) in the light of coupled wave theory for recording holographic lenses of high diffraction efficiency at λ = 405 nm are presented. It is pointed out that a properly designed single holographic lens can be used for off-axis illumination of a photomask with a parallel beam of light, whereas a system of two identical holographic lenses cemented together has to be used to realize a condenser lens similar to a converging lens.

Tuning ZnSe nanostructures for enhanced ammonia sensing at room temperature

Nanostructured materials, defined by their distinctive physicochemical properties at the nanometer scale, facilitate the innovation of sophisticated applications through their inherent size-dependent phenomena and surface characteristics. In this study, we explore the synthesis of ZnSe nanostructures with distinct spherical and flower-like morphologies by varying the concentration of Ethylenediamine tetraacetic acid (EDTA). Our findings reveal that higher concentrations of EDTA facilitate flower-like morphologies, which provide a large surface area desired for gas sensing applications. Herein, the as-synthesized ZnSe nanostructures were applied for ammonia (NH3) sensing at room temperature at different concentrations to evaluate their performance. The results obtained indicate that ZnSe nanostructures with flower-like morphology exhibit superior sensing capabilities, demonstrating a good response (ΔR/Rair)% of 71 % compared to the 61 % response observed for spherical ZnSe nanostructures for 20 ppm NH3 gas, measured at room temperature. Additionally, the flower-like ZnSe nanostructures show significantly enhanced response and recovery times, demonstrating their potential as efficient materials for NH3 detection at room temperature.

A novel 3D instance segmentation network for synapse reconstruction from serial electron microscopy images

Synapses are fundamental components of how neurons communicate with each other and have attracted widespread attention from neuroscientists. Due to the rapid development of electron microscopy (EM) technology, imaging synapses at nanometer scale has become possible. However, the automation and efficacy of the synapse detection algorithm have not yet met expectations. The most popular approach involves a two-step process in which binary segmentation masks are first obtained and then connected components are used to produce reconstruction results. In this paper, an intelligent system to detect and segment synapses from serial section EM images is proposed. Specifically, a novel 3D instance segmentation network that can predict the synapses end-to-end is presented. The network can exploit and summarize features consistent with the biological structures of synapses, which is similar to the process of manual annotation. A block-wise inference strategy that adapts well to large-scale EM images is then introduced. Finally, two public datasets are used to evaluate our method. Experimental results demonstrate the superiority of the proposed approach, thus enabling computer-assisted analysis of synapses for neuroscientists.

Combination of scanning electron microscopy and digital image correlation for micrometer-scale analysis of shear-loaded adhesive joints

ABSTRACT To understand adhesive bonds and their macroscopic behavior, a new experimental method is presented in this paper that allows to investigate micromechanical effects down to nanometer scale under load. The method combines ion milled cross sections, low-voltage scanning electron microscopy (SEM), digital image correlation, and a miniaturized testing machine in the SEM-chamber. Experimental results from shear-loaded adhesively bonded carbon fiber-reinforced polymer specimens illustrate the method’s benefits. Through a plasma etching process, the specimen cross section is textured, creating a stochastically distributed speckle pattern visible in SEM images. A miniaturized testing machine placed in the SEM is used to apply a load to the specimens while capturing images simultaneously. The resulting image series can be analyzed by image correlation algorithms. This method enables precise statements regarding strain distribution on the specimen at micro- and nanometer scales. While conventional coupon tests on bonded specimens can only depict the effects of a composite in a homogenized manner, the new method allows to gain additional insights into the underlying mechanisms.

Nano particle distribution in blood via electroosmotic peristaltic flow in a non-uniform wavy membrane base capillaries

ObjectiveThe primary purpose of this article is to undertake a mathematical investigation into the electro osmotically thermally driven transport of solute particles, which are typically on a micro to nano-meter scale, suspended in blood. The study is conducted within a non-uniform porous channel for a Williamson fluid. The main objective of this research is to explore the interactions and consequences of solute particles and nanoparticles in the Esophagus, particularly regarding their potential applications in drug delivery and biomedical engineering, especially in the context of electroosmotic non-Newtonian fluids. SignificanceThis research also has significant implications for microscale physiological phenomena. In this investigation, blood serves as the base fluid, and a nanofluid is created by introducing Nickel and Cobalt nanoparticles into the blood. Both nanoparticles have critical medical applications, especially in drug delivery and cancer treatment. To delve deeper into the study of nanomedicine delivery, Nickel and Cobalt nanoparticles are introduced into the blood alongside other smaller solute particles. MethodologyThe mathematical modeling is conducted in a rectangular coordinate system, and the governing flow equations are linearized using approximations that consider low Reynolds numbers and large wavelengths. The numerical solution is computed for a coupled set of nonlinear equations that describe the profiles of fluid-particle velocity, temperature, and fluid-particle composition. The study explores the influence of various key parameters and presents these effects through graphical representations. FindingsIt is observed that an increase in the suspension concentration and the Williamson fluid parameter leads to higher fluid velocity, while the temperature distribution exhibits the opposite trend. The introduction of nanoparticles into the fluid decelerates the flow and raises the temperature.

Petrographic and chemical characterization and carbon and nitrogen isotopic compositions of cometary IDPs and their GEMS amorphous silicates

GEMS (glass with embedded metal and sulfides) are the dominant carrier of amorphous silicates in anhydrous interplanetary dust particles (IDPs) and one of the most suitable materials to study early solar system processes. Amorphous silicates in 105 GEMS from eight IDPs were analyzed regarding texture and chemical composition to reassess GEMS formation theories and genetic relationships to amorphous silicate material in meteorites. Petrography of bulk IDPs was investigated to understand GEMS’ relationships to other IDP components. Furthermore, carbon and nitrogen isotopic compositions were measured. Nearly all GEMS are aggregates of several subgrains with variable amount of nanophase inclusions and different Mg- and Si-contents, while single GEMS are rare. The subgrains within aggregates are typically surrounded by one or more carbon rims with high density. The chemical compositions of GEMS amorphous silicates are subsolar for all major element/Si ratios but exhibit wide heterogeneity. This is not influenced by silicon oil from the capturing process of IDPs as assumed before, as a penetration of the silicon oil is excluded by high resolution EELS (electron energy loss spectroscopy) areal density maps of silicon. Furthermore, low Fe-content in GEMS amorphous silicates shows that these are not altered by aqueous activity on the parent body as it is the case for amorphous silicate material in primitive meteorites. The subsolar element/Si ratios and the wide chemical heterogeneity point to a non-equilibrium fractional condensation origin either in the early solar nebula or in a circumstellar environment and are not in agreement with homogenization via sputtering in the ISM. The close association with carbon around GEMS subgrains and as double-rims around GEMS aggregates argue for a multi-step aggregation after formation of the smallest GEMS subgrains in the ISM or the early solar nebula. Carbon acting as matrix material connecting GEMS and other IDP components has lower areal density as seen from carbon EELS areal density maps and isotopic anomalies varying at the nanometer scale, pointing to different origins and processing of materials to varying extent or at changing temperatures.To balance GEMS’ subsolar element/Si ratios, a supersolar component in IDPs was assumed to account for the overall chondritic composition of bulk IDPs. Nevertheless, our bulk IDP analyses revealed subsolar, but variable, element/Si ratios for complete particles as well, depending on type and amount of mineral phases in each particle. Pyroxenes in the investigated particles can occur as elongated euhedral crystals, but are overall rare. The dominant crystalline fraction in the investigated IDP samples are equilibrated aggregates (EAs) that show the same chemical compositions as GEMS, indicating that the EAs are recrystallized GEMS grains and formed after GEMS formation as secondary phases.

Can the laws of physics be circumvented? On methods of super-resolution fluorescence microscopy

Biological sciences are increasingly uncovering the foundations of life in greater detail, made possible by the development of research methods enabling exploration at the nanometer scale. Optical microscopy, a field with a significant contribution to current knowledge, is inherently limited by the Abbe limit, stemming from the fundamental wave properties of light. Through the efforts of scientists, this limit can be circumvented, as evidenced by STED and MINFLUX techniques. STED allows imaging with a resolution down to 40 nm, while MINFLUX enables resolution as fine as 2 nm. Both techniques require labelling of biological molecular targets with fluorescent markers and enable imaging in living cells, facilitating the study of dynamic biological processes. This article provides an introduction to super-resolution techniques STED and MINFLUX, demonstrating their utility through the example of studying kinesin movement along microtubules using the MINFLUX technique.

Optimizing alkaline hydrothermal treatment for biomimetic smart metallic orthopedic and dental implants

Orthopedic and dental implant failure continues to be a significant concern due to localized bacterial infections. Previous studies have attempted to improve implant surfaces by modifying their texture and roughness or coating them with antibiotics to enhance antibacterial properties for implant longevity. However, these approaches have demonstrated limited effectiveness. In this study, we attempted to engineer the titanium (Ti) alloy surface biomimetically at the nanometer scale, inspired by the cicada wing nanostructure using alkaline hydrothermal treatment (AHT) to simultaneously confer antibacterial properties and support the adhesion and proliferation of mammalian cells. The two modified Ti surfaces were developed using a 4 h and 8 h AHT process in 1 N NaOH at 230 °C, followed by a 2-hour post-calcination at 600 °C. We found that the control plates showed a relatively smooth surface, while the treatment groups (4 h & 8 h AHT) displayed nanoflower structures containing randomly distributed nano-spikes. The results demonstrated a statistically significant decrease in the contact angle of the treatment groups, which increased wettability characteristics. The 8 h AHT group exhibited the highest wettability and significant increase in roughness 0.72 ± 0.08 µm (P < 0.05), leading to more osteoblast cell attachment, reduced cytotoxicity effects, and enhanced relative survivability. The alkaline phosphatase activity measured in all different groups indicated that the 8 h AHT group exhibited the highest activity, suggesting that the surface roughness and wettability of the treatment groups may have facilitated cell adhesion and attachment and subsequently increased secretion of extracellular matrix. Overall, the findings indicate that biomimetic nanotextured surfaces created by the AHT process have the potential to be translated as implant coatings to enhance bone regeneration and implant integration.Graphical

Application of nanoscale metal–organic frameworks in tumor immunotherapy

Application of nanoscale metal–organic frameworks in tumor immunotherapy

Nanoscale dark-field imaging in full-field transmission X-ray microscopy

The dark-field signal uncovers details beyond conventional X-ray attenuation contrast, which is especially valuable for material sciences. In particular, dark-field techniques are able to reveal structures beyond the spatial resolution of a setup. However, its implementation is limited to the micrometer regime. Therefore, we propose a technique to extend full-field transmission X-ray microscopy by the dark-field signal. The proposed method is based on a well-defined illumination of a beam-shaping condenser, which allows to block the bright field by motorized apertures in the back focal plane of the objective lens. This method offers a simple implementation and enables rapid modality changes while maintaining short scan times, making dark-field imaging widely available at the nanometer scale.

Investigation of Cyrene organosolv fractionation of softwood biomass and alkaline post-incubation

Cyrene organosolv fractionation effectively extracted 78 % of lignin from recalcitrant softwood biomass pine at a mild temperature of 120 °C. However, the enzymatic conversion of the fractionated cellulose-rich solid did not improve significantly. Alkali post-incubation of the fractionated cellulose fraction notably enhanced the glucan conversion. This phenomenon has also been observed in other organosolv processes, but how this approach transforms pretreated biomass has not yet been comprehensively investigated. In this study, small-angle X-ray scattering (SAXS) was employed to understand the structural changes in biomass during fractionation and post-incubation at the nanometer scale. No lignin aggregation was found on the microfibrils, whereas the distance between the microfibrils increased after pretreatment and decreased after alkaline post-incubation. These results suggests that the Cyrene molecules remained between the microfibrils and were removed by post-incubation. In addition, the pine lignin recovered after pretreatment was characterized by NMR to understand the impact of Cyrene pretreatment on the lignin structure.

An intelligent and self-assembled nanoscale metal organic framework (99mTC-DOX loaded Fe3O4@FeIII-tannic acid) for tumor targeted chemo/chemodynamic theranostics

BackgroundRecent advances in clinical transformation research have focused on chemodynamic theranostics as an emerging strategy for tackling cancer. Nevertheless, its effectiveness is hampered by the tumor's glutathione antioxidant effect, poor acidic tumor microenvironment (TME) and inadequate endogenous H2O2. Hence, we designed an activatable theranostics (99mTc-DOX loaded AA-Fe3O4@FeIII-TA) that effectively boost the catalytic efficiency of the Fenton-reaction-induced ROS production and augment the chemotherapeutic efficacy combined with diagnostic action.ResultsA cross-linked matrix of tannic acid-ferric salt (FeIII-TA) as a pH-responsive shell onto ascorbic acid-decorated iron-oxide nanoparticles (AA-Fe3O4NPs) was prepared demonstrating a metal–organic- framework (MOF) nanostructure, followed by loading of 99mTc-labelled DOX. The platform (99mTc-DOX loaded AA-Fe3O4@FeIII-TA) displayed suitable physical–chemical properties, including 69.8 nm particle size, 94.8 nm hydrodynamic size, − 21 mV zeta potential, effective FeIII-TA shell crosslinking onto AA-Fe3O4NPs and 94% loading efficiency for 99mTc-DOX. The results of the in-vitro release investigations showed that the platform exhibited a pH-dependent release manner with 98.3% of the 99mTc-DOX being released at pH 5 (simulating the tumor’s pH) and only 10% being released at the physiological pH (pH 7.4). This indicates that there was negligible payload leakage into the systemic circulation during the platform's passive accumulation inside tumor. Due to the acidic TME nature, the MOF shell might be degraded releasing free FeIII, TA and a sustained release of 99mTc-DOX. Besides its chemotherapeutic impact and capacity to raise intracellular H2O2 content, the released 99mTc-DOX might be used as SPECT imaging tracer for concurrent tumor diagnosis. Furthermore, the mild acidity of the tumor may be overcome by the released TA, which might raise the acidification level of cancer cells. The released FeIII, TA and the endogenous GSH could engage in a redox reaction that depletes GSH and reduces FeIII to FeII ions which subsequently catalyze the elevated concentration of H2O2 to reactive •OH via Fenton-like reaction, increasing the effectiveness of chemodynamic therapy. Moreover, the in-vivo evaluation in tumor-bearing mice showed significant radioactivity accumulation in the tumor lesion (16.8%ID/g at 1 h post-injection) with a potential target/non-target ratio of 8.ConclusionsThe 99mTc-DOX loaded AA-Fe3O4@FeIII-TA could be introduced as an effective chemo/chemodynamic theranostics.Graphical

Solvent-Dependent Dynamics of Cellulose Nanocrystals in Process-Relevant Flow Fields.

Flow-assisted alignment of anisotropic nanoparticles is a promising route for the bottom-up assembly of advanced materials with tunable properties. While aligning processes could be optimized by controlling factors such as solvent viscosity, flow deformation, and the structure of the particles themselves, it is necessary to understand the relationship between these factors and their effect on the final orientation. In this study, we investigated the flow of surface-charged cellulose nanocrystals (CNCs) with the shape of a rigid rod dispersed in water and propylene glycol (PG) in an isotropic tactoid state. In situ scanning small-angle X-ray scattering (SAXS) and rheo-optical flow-stop experiments were used to quantify the dynamics, orientation, and structure of the assigned system at the nanometer scale. The effects of both shear and extensional flow fields were revealed in a single experiment by using a flow-focusing channel geometry, which was used as a model flow for nanomaterial assembly. Due to the higher solvent viscosity, CNCs in PG showed much slower Brownian dynamics than CNCs in water and thus could be aligned at lower deformation rates. Moreover, CNCs in PG also formed a characteristic tactoid structure but with less ordering than CNCs in water owing to weaker electrostatic interactions. The results indicate that CNCs in water stay assembled in the mesoscale structure at moderate deformation rates but are broken up at higher flow rates, enhancing rotary diffusion and leading to lower overall alignment. Albeit being a study of cellulose nanoparticles, the fundamental interplay between imposed flow fields, Brownian motion, and electrostatic interactions likely apply to many other anisotropic colloidal systems.

The Synthesis of Y-zeolite-modified CaCO3-ZnO Nanocomposites as an Antibacterial Agent

The ability of inorganic antibacterial agents like metal oxides and nanoscale inorganic materials to inhibit bacterial growth rates has yet to receive much research attention. In this study, CaCO3-ZnO/Y-zeolite nanocomposites were created utilizing coprecipitation and impregnation techniques with Ca(CH3COO)2, Zn(CH3COO)2 2H2O, Y-zeolite precursors. Physical and chemical characteristics of nanocomposites have been investigated using XRD, FTIR, and SEM-EDX characterizations. The agar-well diffusion method tested the substance for antibacterial activity against gram-positive and gram-negative bacteria. Nanocomposites have a crystal size range of 35.46-36.53 nm and a crystallinity of 35-37 %, according to the results of XRD analysis. The carbonate groups are visible in FTIR data at wave numbers 1433, 875, and 712 cm-1. The Zn-O absorption band was verified at wave numbers 600-400 cm-1. The Y-zeolite absorption bands at wave numbers 1012-997 cm-1 and 745-746 cm-1 were confirmed. The particle morphology is cube-shaped with irregular sizes. The EDX result showed that the composition consists of 35.92 % calcium, 1.68 % zinc, 44.81 % oxygen, and 13.79 % carbon as elements. With the addition of 2.5 % Y-zeolite, the antibacterial activity of nanocomposites showed the best results, with an inhibition zone diameter of 7.62 mm against Escherichia coli and 6.56 mm against Staphylococcus aureus bacteria.

Effectively detecting cardiac myoglobin by use of bound states in the continuum in silicon nitride gratings

Optical biosensors with their sensitivity, compact design, and reliability stand out as versatile tools capable of detecting a wide range of analytes. Recently, nanophotonic structures supporting bound states in the continuum (BIC) modes have been actively studied, which is especially interesting for biosensing applications due to their high quality (Q) factor and strongly localized electric field, achieving favorable interaction between field and nanometer scale analyte on the sensing surface. Herein, we demonstrate an optical label-free sensing by accidental or Friedrich–Wintgen (FW) BIC supported on silicon nitride gratings. We compared the sensing performance in terms of bulk, and surface sensitivity, and figure of merit with FW-BIC in the leaky regime and with a symmetry-protected (SP) BIC, which are also supported by the studied platform. We exploit the fact that for FW-BIC a high-Q factor up to 498 comparable to that of SP-BIC (up to 425) retains for a much larger set of interrogation angles, providing excellent interrogation stability. We observed that FW-BIC has slightly higher bulk sensitivity than SP-BIC [186 and 158 nm/RIU (refractive index unit), respectively], but at the same time similar characteristics in terms of surface sensitivity and figure of merit. In addition, we show that both BIC resonances are significantly superior in all respects to the leaky regime due to better field confinement. Finally, the surface of sensing device was also functionalized to detect a cardiac biomarker, myoglobin, exhibiting the limit of detection of 49 ng/ml with clinically relevant level.

Preparation of Fibrous Three-Dimensional Porous Materials and Their Research Progress in the Field of Stealth Protection.

Intelligent and diversified development of modern detection technology greatly affects the battlefield survivability of military targets, especially infrared, acoustic wave, and radar detection expose targets by capturing their unavoidable infrared radiation, acoustic wave, and electromagnetic wave information, greatly affecting their battlefield survival and penetration capabilities. Therefore, there is an urgent need to develop stealth-protective materials that can suppress infrared radiation, reduce acoustic characteristics, and weaken electromagnetic signals. Fibrous three-dimensional porous materials, with their high porosity, excellent structural adjustability, and superior mechanical properties, possess strong potential for development in the field of stealth protection. This article introduced and reviewed the characteristics and development process of fibrous three-dimensional porous materials at both the micrometer and nanometer scales. Then, the process and characteristics of preparing fibrous three-dimensional porous materials through vacuum forming, gel solidification, freeze-casting, and impregnation stacking methods were analyzed and discussed. Meanwhile, their current application status in infrared, acoustic wave, and radar stealth fields was summarized and their existing problems and development trends in these areas from the perspectives of preparation processes and applicability were analyzed. Finally, several prospects for the current challenges faced by fibrous three-dimensional porous materials were proposed as follows: functionally modifying fibers to enhance their applicability through self-cross-linking; establishing theoretical models for the transmission of thermal energy, acoustic waves, and electromagnetic waves within fibrous porous materials; constructing fibrous porous materials resistant to impact, shear, and fracture to meet the needs of practical applications; developing multifunctional stealth fibrous porous materials to confer full-spectrum broadband stealth capability; and exploring the relationship between material size and mechanical properties as a basis for preparing large-scale samples that meet the application's requirement. This review is very timely and aims to focus researchers' attention on the importance and research progress of fibrous porous materials in the field of stealth protection, so as to solve the problems and challenges of fibrous porous materials in the field of stealth protection and to promote the further innovation of fibrous porous materials in terms of structure and function.

Theoretical limits of magnetic detection of structural surface defects at the nanometre scale

ABSTRACT We present a theoretical study on the magnetic signals of structural surface defects like cracks or indents combined with inhomogeneities on the surface or subsurface inclusions of soft ferromagnetic metals like body-centred cubic Fe or amorphous CoFeB. We discuss limits of early detection of small surface defects on the basis of calculated magnetic stray fields few tens of nm above the surface. The considered surface imperfections have extensions of a few nm which correspond to low multiples of the magnetic exchange lengths of Fe or CoFeB. The detection of such small inhomogeneities requires that the sensor is about as close to the surface as the size of the inhomogeneity is. Furthermore, the step width of a scanning sensor must be of the same size as well. Both these requirements may be fulfilled for instance by scanning microscopy with diamond nitrogen-vacancy-centre quantum sensors.

Insight into the influence of alloying elements on the secondary corrosion protection of Fe-base alloys by means of atom probe tomography

Breakaway corrosion of Fe-base alloys remains a challenge in applications operated in harsh conditions. The material lifetimes are often determined by the corrosion propagation after breakaway. Nevertheless, detailed microstructural studies, linking the protective properties of the Fe-rich oxides formed after breakaway, are scarce. This study utilizes APT to investigate the Fe-rich oxides formed after breakaway, i.e., the secondary corrosion protection, of four Fe-based model alloys chosen to exhibit good and poor secondary protection at 600 °C. The APT investigation shows that the inward-growing scale is heterogeneous at the nanometer scale and that Fe-enriched regions form on the poorly protective oxides.