Topographic Contrast Research Articles

Quantitative Analysis of Nanorod Aggregation and Morphology from Scanning Electron Micrographs Using SEMseg.

General methods to achieve better physical insight about nanoparticle aggregation and assembly are needed because of the potential role of aggregation in a wide range of materials, environmental, and biological outcomes. Scanning electron microscopy (SEM) is fast and affordable compared to transmission electron microscopy, but SEM micrographs lack contrast and resolution due to lower beam energy, topographic contrast, edge effects, and charging. We present a new segmentation algorithm called SEMseg that is robust to the challenges inherent in SEM micrograph analysis and demonstrate its utility for analyzing gold (Au) nanorod aggregates. SEMseg not only supports nanoparticle size analysis for dispersed nanoparticles, but also discriminates between nanoparticles within an aggregate. We compare our algorithm to those incorporated into the commonly used software ImageJ and demonstrate improved segmentation of aggregate structures. New physical insight about aggregation is demonstrated by the introduction of an order parameter describing side-by-side structure in nanoparticle aggregates. We also present the segmentation and fitting algorithms included in SEMseg within a user-friendly graphical user interface. The resulting code is provided with an open-source interface to provide quantitative image processing tools for researchers to characterize both dispersed nanoparticles and nanoparticle assemblies in SEM micrographs with high throughput.

Late Pleistocene-Holocene landscape evolution in the lower Peixe river, Brazil: A meandering river valley

This study investigated the lower terrace and floodplain formation in the lower Peixe River in southeastern Brazil. Morphologic, sedimentologic and geochronologic analyses in this meandering tributary of the Paraná River allowed an integrated approach to reconstructing fluvial changes from the late Pleistocene. Geomorphic units were mapped with Global Navigation Satellite System, satellite imagery and digital surface model interpretation, and sedimentary facies and radiocarbon (14C) dating analyses were performed on palaeochannels and backswamps. The palaeochannels on the lower terrace indicate fluvial activity during the late Pleistocene, torrential flows during the Northgrippian stage, and abandonments during the Meghalayan stage. The backswamp evaluated on the lower terrace documents the depositional change from oxbow lake abandonment in the Greenlandian stage to tributary flow, which passes flows over the palaeodrainage during flood episodes, while another backswamp in the floodplain highlights an intense morphodynamic removal of terrace deposits. An incisive phase during the Meghalayan stage is the main event responsible for establishing the current fluvial landscape, which promotes the formation of the lower terrace and floodplain. Local variations (i.e., tributary flows) in the degradation process on the terraces results in a topographical and morphological contrast between corresponding geochronologic units. Therefore, adjustment stages in the fluvial relief drive wetland variability in the fill terraces, which are fundamental to understanding degradational processes and formulating environmental management policies.

Garnet-Type Li7La3Zr2O12 / Lithium Metal Interface: Microstructure and Electrochemical Properties in Solid State Batteries

All-solid-state lithium ion batteries may overcome safety issues in future energy storage systems, when a non-flammable solid electrolyte instead of a liquid electrolyte is applied. Garnet-type Li7La3Zr2O12 (LLZO) is an encouraging choice due to its high Li+ conductivity and its chemical stability against lithium metal [1]. However, low-resistance LLZO/Li interfaces are deteriorated by incomplete adhesion of lithium metal onto LLZO and by surface contamination [2]. The resulting inhomogeneous distribution of contact areas may be more prone to dendrite formation. Previous studies [3,4] indicate that LLZO/Li interface quality is significantly improved by metallic buffer layers.In this study, we aim for a reliable preparation of low-resistance interfaces between solid electrolyte and lithium metal. At first, magnetron sputtering is applied to deposit an indium buffer layer of 50 to 500 nm thickness onto the polished and cleaned electrolyte surface. For cell assembly, lithium foil is put on both sides of an In-coated LLZO pellet and the test cell is heated to 220°C in argon atmosphere. After that, microstructure and electrochemical properties of the symmetric cells are analyzed. We improved cross-section sample preparation to inspect the quality of LLZO/In/Li interfaces over hundreds of µm. Scanning electron microscopy (SEM, cf. figure 1) confirms excellent adhesion between lithium and LLZO. We use a dry inert atmosphere during preparation, handling and transfer of our samples to avoid artifacts and sample degradation. The FEI Helios G4 FX microscope enables correlative SEM imaging by simultaneous acquisition of up to four different detector signals for interface topography and material contrast. Local chemical composition at the interface is analyzed by energy dispersive X-ray spectroscopy and electron-beam damage is minimized for SEM imaging by selecting optimum electron energies.Electrochemical impedance spectroscopy (EIS) followed by data evaluation via the distribution of relaxation times (DRT) and equivalent circuit modelling [5] deliver the proportional contributions of grain, grain boundaries and interfaces to the total impedance of symmetric cells (Li/In/LLZO/In/Li). Interface microstructures and EIS measurements are correlated for samples with different buffer layer characteristics to allow targeted optimization. We compare the pristine state of the test cells to samples that have been cycled with different current densities.

Multiple scattering in scanning helium microscopy

Using atom beams to image the surface of samples in real space is an emerging technique that delivers unique contrast from delicate samples. Here, we explore the contrast that arises from multiple scattering of helium atoms, a specific process that plays an important role in forming topographic contrast in scanning helium microscopy (SHeM) images. A test sample consisting of a series of trenches of varying depths was prepared by ion beam milling. SHeM images of shallow trenches (depth/width < 1) exhibited the established contrast associated with masking of the illuminating atom beam. The size of the masks was used to estimate the trench depths and showed good agreement with the known values. In contrast, deep trenches (depth/width > 1) exhibited an enhanced intensity. The scattered helium signal was modeled analytically and simulated numerically using Monte Carlo ray tracing. Both approaches gave excellent agreement with the experimental data and confirmed that the enhancement was due to localization of scattered helium atoms due to multiple scattering. The results were used to interpret SHeM images of a bio-technologically relevant sample with a deep porous structure, highlighting the relevance of multiple scattering in SHeM image interpretation.

Multiscale analysis of viscoelastic properties, topography and internal structure of a biodegradable thermo-responsive shape memory polyurethane

In this paper, the effect of the temperature on viscoelastic properties of the thermo-responsive biodegradable shape memory polyurethane (SMPU) is presented. Comprehensive micro and nano mechanical and morphological studies were performed to assess the behavior of the considered material in the form of 3D-printed fibers. For this purpose, specimen's topography, nano-mechanical and macro-mechanical characterization of the material were carried out. Data obtained from the temperature-dependent AFM indentation test was used to quantify nanoscale viscoelastic properties of the investigated material. Power-law rheology (PLR) was chosen as constitutive viscoelastic relaxation model describing behavior of the investigated material at different temperatures. Topography and phase contrast studies done in the nanoscale exposed bi-phasic structure of heated SMPU polymer - soft and hard domains corresponding with structural composition of the material were detected. The applied fitting procedure enabled for the identification of the viscoelastic properties of the revealed phases identified as the hard and the soft domains.

Observation of diffraction contrast in scanning helium microscopy

Scanning helium microscopy is an emerging form of microscopy using thermal energy neutral helium atoms as the probe particle. The very low energy combined with lack of charge gives the technique great potential for studying delicate systems, and the possibility of several new forms of contrast. To date, neutral helium images have been dominated by topographic contrast, relating to the height and angle of the surface. Here we present data showing contrast resulting from specular reflection and diffraction of helium atoms from an atomic lattice of lithium fluoride. The signature for diffraction is evident by varying the scattering angle and observing sharp features in the scattered distribution. The data indicates the viability of the approach for imaging with diffraction contrast and suggests application to a wide variety of other locally crystalline materials.

Evaluation and zoning of environmental climatic parameters for tourism feasibility in northwestern Iran, located on the western border of Turkey

The purpose of this study is to evaluate and seasonally map the tourism climate of northwestern Iran using the Tourism Climate Index (TCI). In this study, climate data from 22 synoptic stations of northwestern Iran during 26 years (1993–2018) were prepared to evaluate climate comfort from a tourism perspective. In this system model, seven parameters were used: mean maximum temperature, mean temperature, mean minimum relative humidity, average relative humidity, monthly precipitation, daily mean sunshine and wind speed. For data processing, the TCI index was used to map the tourism climate map for four seasons using ArcGIS. The TCI index was used to process the data and the tourist climate map was drawn up using GIS for 12 months. The results showed that the TCI of the northwest is varied due to topography contrast throughout the year. The months of April, May, June, July, August, September and October have good to ideal conditions with a rating of 60–99 for climatic comfort. The months of November, December, January, February, and March provide inappropriate conditions with a range of 24–52. The areas (Parsabad Moughan and Jolfa) have a favourable climate in the cold months of the year and there is an inappropriate condition for tourism during the warm months. September is the most favourable month with ratings from 78 to 99 and journey is the most inappropriate month for tourism in the northwest with the rank of 24–52. Northwest of Iran, having plenty of tourist attractions, can be a source of domestic and foreign tourists. In addition to the introduction of this region to attract tourists, employment can also be achieved by the planning and management of tourism.

Late Pleistocene hominin settlement patterns and population dynamics in the Zagros Mountains: Kermanshah region

The Middle and Upper Palaeolithic artifacts of the Zagros Mountains are relatively better understood than those in other parts of the Iranian Plateau. However, settlement systems, land use and Palaeolithic population dynamics for this region have received less attention. Here we present research on the study of human behavior that contributes to a better understanding of the early human colonization of Eurasia. Specifically, we focus on the Kermanshah region of the west-central Zagros to evaluate hominin dispersal and adaptation by investigating hominin settlement patterns and behavioral responses to the new and diverse environments and topography of this part of the Zagros region. Our survey in Kermanshah documented over 260 new Palaeolithic localities, enabled us to draw Middle and Upper Palaeolithic site distribution patterns and population dynamics which reveal that this part of the Zagros was intensively populated in both the Middle and Upper Palaeolithic. This research demonstrates that the Zagros in general, and the Kermanshah area in particular, were by no means impassable but include intermountain plains connected to each other by valleys associated with permanent water and raw material sources. Middle Palaeolithic settlements are most abundant in areas with high topographic contrast that contain high mountains, flat plains, and diverse resources. Eventually, the Zagros was one of a handful of important interglacial refugia in south-western Asia for hominins during the Upper Pleistocene and may have served as a core area from which colonizations and recolonizations of Eurasia occurred during multiple dispersals.

Imaging low-dimensional nanostructures by very low voltage scanning electron microscopy: ultra-shallow topography and depth-tunable material contrast

We demonstrate the implications of very low voltage operation (<1 kV) of a scanning electron microscope for imaging low-dimensional nanostructures where standard voltages (2–5 kV) involve a beam penetration depth comparable to the cross-section of the nanostructures. In this common situation, image sharpness, contrast quality and resolution are severely limited by emission of secondary electrons far from the primary beam incidence point. Oppositely, very low voltage operation allows reducing the beam-specimen interaction to an extremely narrow and shallow region around the incidence point, enabling high-resolution and ultra-shallow topographic contrast imaging by high-angle backscattered electrons detection on the one hand, and depth-tunable material contrast imaging by low-angle backscattered electrons detection on the other. We describe the performance of these imaging approaches on silicon nanowires obtained by the vapor-liquid-solid mechanism. Our experimental results, supported by Monte Carlo simulations of backscattered electrons emission from the nanowires, reveal the self-assembly of gold-silica core-shell nanostructures at the nanowire tips without any ad-hoc thermal oxidation step. This result demonstrates the capacity of very low voltage operation to provide optimum sharpness, contrast and resolution in low-dimensional nanostructures and to gather information about nanoscaled core-shell conformations otherwise impossible to obtain by standard scanning electron microscopy alone.

Angular and Energy Characteristics of Backscattered Electrons and Allowing for Them in the Three-Dimensional Visualization of Microstructures in Scanning Electron Microscopy

The main angular characteristics and resulting semi-empirical equations for back-scattered electrons of medium energy (1–30 kV) are calculated. The results from an analysis are used to develop an optimized detector system of back-scattered electrons for scanning electron microscopes to visualize subsurface microstructures and improve topographic contrast. These results contribute to solving problems of the three-dimensional visualization of surface topography and selective tomography of the subsurface architecture of micro-objects.

Seasonal Variation in Residence Times of Two Neighboring Bays with Contrasting Topography

Residence time is an important parameter for evaluating the physical and biochemical characteristics of estuaries and bays. The residence times of two neighboring South Korean bays with contrasting topographies, Gwangyang Bay and Jinju Bay, were calculated for winter and summer using a three-dimensional model. Gwangyang Bay, with considerable industrial development nearby, has a relatively large volume and depth, whereas Jinju Bay is shallow and is primarily used for aquaculture. River discharge in the two bays is high in summer and low in winter, in part due to the influence of the East Asian Monsoon. Temperature and salinity in both bays are vertically homogeneous during winter but stratified in summer. The mean residence time in Gwangyang Bay is more than 20 days in winter due to its large volume, but less than 5 days in summer due to increased gravitational circulation driven by large volumes of river discharge and a horizontal density gradient. However, the mean residence time of Jinju Bay is less than 5 days in both seasons due to its small volume and shallow depth. These results reveal that Gwangyang Bay is vulnerable to industrial pollution during winter, but that it may remove pollutants efficiently in summer. The shallower Jinju Bay is likely to remain free from anthropogenic eutrophication caused by nutrient inputs from aquaculture due to its short residence time throughout the year.

Optimization and Characterization of Si3N4 Layer for Wear Resistant Ti-Al-N/Si3N4 Nano- Composite Coatings

Machining Custom 465 steel at high speeds usually at 20-30% lower than ordinary stainless steel leads to excessive tool wear and thereby affecting the tool life. In such case tool life can be increased by coating a nano-composite layer of Ti-Al-N/Si3N4 which exhibits high strength, hardness, toughness, resistance to oxidation and thermal shock. Particularly, Si3N4serves as an interfacial phase in nano-composite layer is thermodynamically stable phase at high temperatures up to 1850˚C along with high oxidation resistance which might reduce the heat flow between tool-workpiece interfaces leading to high thermal stability of cutting tool. Physical vapor deposition techniques can be used to develop Ti-Al-N/Si3N4 nano-composite coating which involves typically 81 trial depositions in order to obtain optimized process parameters for Si3N4. Here we attempt to reduce the number of trails by design and optimization of process parameters which was efficiently achieved at faster rate by applying the Taguchi design. In present work, we used Taguchi orthogonal (L9) array to conduct the 9 experiments and obtained optimum process parameters for Si3N4 coating. Based on the design we deposited Si3N4nanocoating using RF magnetron sputtering process with 4 factor and 3 level process parameters namely, Ar:N2 gas mixture, RF Power, deposition time, and deposition pressure on high speed steel (HSS), tungsten carbide (WC) and Si (100) substrates. Atomic Force Microscopy (AFM) studies were carried for surface roughness, topography, and phase contrast imaging. Glancing incidence X-ray diffraction (GIXRD) studies were performed for the identification and quantification of crystalline and amorphous phase. Field Emission Scanning Electron Microscopy (FE-SEM) studies were performed for the film thickness and grain size of Si3N4layers.

An adaptive-coherence light source for hyperspectral, topographic, and flow-contrast imaging.

Colorectal cancer accounts for an estimated 8% of cancer deaths in the United States with a five-year survival rate of 55-75%. The early detection and removal of precancerous lesions is critical for reducing mortality, but subtle neoplastic growths, such as non-polypoid lesions, often go undetected during routine colonoscopy. Current approaches to flat or depressed lesion detection are ineffective due to the poor contrast of subtle features in white light endoscopy. Towards improving colorectal lesion contrast, we present an endoscopic light source with custom laser channels for multimodal color, topographic, and speckle contrast flow imaging. Three red-green-blue laser units, paired with laser speckle reducers, are coupled into endoscopic fiber optic light guides in a benchtop endoscope. Tissue phantom topography is reconstructed using alternating illumination of the laser units and a photometric stereo endoscopy algorithm. The contrast of flow regions is enhanced in an optical flow phantom using laser speckle contrast imaging. Further, the system retains the ability to offer white light and narrow band illumination modes with improved power efficiency, a reduced size, and longer lifetimes compared to conventional endoscopic arc lamp sources. This novel endoscopic light source design shows promise for increasing the detection of subtle lesions in routine colonoscopy screening.

Structural analysis of interfacial dislocations and expanded single Shockley-type stacking faults in forward-current degradation of 4H-SiC p-i-n diodes

The structure of interfacial dislocations (IDs) formed at different depth and expansion of single Shockley-type stacking faults (1SSF) from the IDs in forward-current degradation of 4H-SiC p-i-n diodes were investigated. IDs showing different contrast in X-ray topography (XRT) were formed during p-i-n diode fabrication processes. From a high-resolution observation using a transmission electron microscopy, it was clarified that IDs observed by different contrast in XRT were different in the formation interface although they had the same Burgers vector of and Si-core type. The ID with brighter contrast in XRT were formed at the shallower interface between p+ anode and n− drift layers, whereas darker contrast ones were formed at the deeper interface between n− drift and n+ buffer layers. Expansion of the 1SSFs originated from the IDs which were formed at the shallower interface occurred under the condition of lower stress-current density than 25 A cm−2, whereas that originated from ID which were formed at the deeper interface was caused under the condition of higher stress-current density than 1200 A cm−2. These results indicated that IDs were formed at different depths during device processes, and 1SSF expanded from these IDs under various stress-current conditions.

Fabrication and Characterization of a High-Performance Multi-Annular Backscattered Electron Detector for Desktop SEM.

Scanning electron microscopy has been developed for topographic analysis at the nanometer scale. Herein, we present a silicon p-n diode with multi-annular configuration to detect backscattering electrons (BSE) in a homemade desktop scanning electron microscope (SEM). The multi-annular configuration enables the enhancement of the topography contrast of 82.11 nA/μm as compared with the commercial multi-fan-shaped BSE detector of 40.08 nA/μm. Additionally, we integrated it with lateral p-n junction processing and aluminum grid structure to increase the sensitivity and efficiency of the multi-annular BSE detector that gives higher sensitivity of atomic number contrast and better surface topography contrast of BSE images for low-energy detection. The responsivity data also shows that MA-AL and MA p-n detectors have higher gain value than the MA detector does. The standard deviation of measurements is no higher than 1%. These results verify that MA p-n and MA-AL detectors are stable and can function well in SEM for low-energy applications. It is demonstrated that the multi-annular (MA) detectors are well suited for imaging in SEM systems.

RESULTS OF NON-INVASIVE ACTIVATION MAPPING OF THE HEART IN “IDIOPATHIC” VENTRICULAR ARRHYTHMIAS IN COMPARISON WITH STRUCTURAL CHARACTERISTICS OF MYOCARDIUM BY MAGNETIC RESONANCE IMAGING

Aim.To compare the results of non-invasive activational mapping in patients with “idiopathic” ventricular arrhythmias (IVA) with the data on myocardial structure obtained by late enhancement magnetic resonance tomography (MRI).Material and methods.Twenty eight IVA patients, mean age 37 y. o. [26; 45], with ventricular arrhythmias of the heart (VA) of 2nd or higher grade by Lown, and 5 healthy volunteers (HV), mean age 29 [29; 30], underwent surface epiand endocardial non-invasive mapping (SEENIM) of the heart with the system for noninvasive electrophysiological investigation of the heart “Amicard 01C” with the analysis of duration of the activation-recovery interval (ARI) of the ventricles, and high resolution MRI (voxel 1,25x1,25x2,5mm) with delayed contrasting.Results.The number of VA in IVA group was 20196 [11479; 29834] for 24 hours. In 11 patients there were episodes of non-sustained ventricular tachycardia (VT). By SEENIM, predominating morphological type of ventricular ectopic activity in 22 patients sourced from the right ventricle myocardium (RV), of those in 20 from outflow tract of the LV (OTLV). There was significantly prolonged ARI in OTLV patients with IVA comparing to HV (p&lt;0,05). In IVA and non-sustained ventricular tachycardia patients, by contrast MRI of the heart, in LV myocardium there were small foci of contrast retention found. There was no correlation of the areas of contrast retention and topography of VA sources.Conclusion.In most of IVA patients the source of VA was outflowing tract of the RV. The revealed prolongation of the ARI of this area in IVA patients can be an important factor of IVA onset. Small foci of LV fibrosis, found in late enhancement MRI of the heart and episodes of so called idiopathic VT, might be the earliest presentation of the “tachycardiopathy” at the step of pathology development when there are no signs of LV dilation.

Low-voltage SEM contrasts of steel surface studied by observations and electron trajectory simulations for GEMINI lens system.

Scanning electron microscopy (SEM) is a powerful tool for observing the surface of materials. Modern SEM systems have multiple detectors with different geometries. Consequently, the SEM image contrast depends on the instrument and experimental conditions even for the same sample. Understanding the SEM imaging mechanism is necessary to clarify SEM contrast. In this paper, low-voltage (LV)-SEM image contrast is investigated by comparing LV-SEM images and electron trajectory simulation results. Surface observations of oxides on a steel surface, positive charging contrast and topographic contrast in the image systematically changed with the working distance (WD). The electron trajectory simulation revealed the sharing of emitted electrons by the in-lens and Everhart-Thornley detectors, and systematic changes in the electron sharing caused by changes in WD. The image contrast was reasonably explained by the kinetic energy and take-off angle (acceptance plots) of the detected electrons derived by the electron trajectory simulations. This approach is essential to understanding the SEM image contrast obtained by SEM systems with multiple detectors. Thorough image simulations based on acceptance plots are required in future work.

Space rocks and optimising scanning electron channelling contrast

Forescatter electron imaging is a popular microscopy technique, especially for scanning electron microscopes equipped with an electron backscatter diffraction detector. In principal, this method enables qualitative imaging of microstructure but quantitative assessment can be limited due to limited information about the contrast afforded. In this work, we explore forescatter electron imaging and demonstrate that imaging can be optimised for topographic, phase, and subtle orientation contrast imaging through appropriate sample and detector positioning. We demonstrate the relationship between imaging modes using systematic variation in detector positioning and compare this with pseudo-forescatter electron images, obtained from image analysis of diffraction patterns, to explore and confirm image contrast modes. We demonstrate these contrast mechanisms on a map obtained from a sample of the Gibeon meteorite.

Proton irradiation damage in cold worked Nb-stabilized 20Cr-25Ni stainless steel

Micro-scale damage with a topographical contrast has been observed in cold-worked Nb-stabilised 20%Cr-25%Ni stainless steel, following irradiation with 2.2 MeV protons at 400 °C and a dose rate of ∼10−5 dpa/s. After an irradiation dose of 3 and 5 dpa, microstructural changes were found to a depth of 22 μm below the irradiated surface, coincident with the estimated mean range of protons in the material as predicted by the TRIM code. Large variations of intragranular mis-orientations, in combination with a depletion of chromium at grain boundaries, were observed in the proton-irradiated layer. This was accompanied by an increase in nano-hardness, which was linked to a partial transformation of tangled dislocation networks into dislocation loops. Such visible microstructural changes have not been reported before in the absence of post-irradiation annealing treatments.

Daily Monitoring of Shallow and Fine-Grained Water Patterns in Wet Grasslands Combining Aerial LiDAR Data and In Situ Piezometric Measurements

The real-time monitoring of hydrodynamics in wetlands at fine spatial and temporal scales is crucial for understanding ecological and hydrological processes. The key interest of light detection and ranging (LiDAR) data is its ability to accurately detect microtopography. However, how such data may account for subtle wetland flooding changes in both space and time still needs to be tested, even though the degree to which these changes impact biodiversity patterns is of upmost importance. This study assesses the use of 1 m × 1 m resolution aerial LiDAR data in combination with in situ piezometric measurements in order to predict the flooded areas at a daily scale along a one-year hydrological period. The simulation was applied over 663 ha of wet grasslands distributed on six sites across the Marais Poitevin (France). A set of seven remote sensing images was used as the reference data in order to validate the simulation and provide a high overall accuracy (76–94%). The best results were observed in areas where the ditch density was low, whereas the highly drained sites showed a discrepancy with the predicted flooded areas. The landscape proportion index was calculated for the daily steps. The results highlighted the spatiotemporal dynamics of the shallow flooded areas. We showed that the differences in the flooding durations among the years were mainly related to a narrow contrast in topography (40 cm), and occurred over a short period of time (two months).