Plan-view Images Research Articles

A Method for Directly Correlating Site-Specific Cross-Sectional and Plan-View Transmission Electron Microscopy of Individual Nanostructures

A sample preparation method is described for enabling direct correlation of site-specific plan-view and cross-sectional transmission electron microscopy (TEM) analysis of individual nanostructures by employing a dual-beam focused-ion beam (FIB) microscope. This technique is demonstrated using Si nanowires dispersed on a TEM sample support (lacey carbon or Si-nitride). Individual nanowires are first imaged in the plan-view orientation to identify a region of interest; in this case, impurity atoms distributed at crystalline defects that require further investigation in the cross-sectional orientation. Subsequently, the region of interest is capped with a series of ex situ and in situ deposited layers to protect the nanowire and facilitate site-specific lift-out and cross-sectioning using a dual-beam FIB microscope. The lift-out specimen is thinned to electron transparency with site-specific positioning to within ≈ 200 nm of a target position along the length of the nanowire. Using the described technique, it is possible to produce correlated plan-view and cross-sectional view lattice-resolved TEM images that enable a quasi-3D analysis of crystalline defect structures in a specific nanowire. While the current study is focused on nanowires, the procedure described herein is general for any electron-transparent sample and is broadly applicable for many nanostructures, such as nanowires, nanoparticles, patterned thin films, and devices.

Effect of grain size on nano-indentation property of Co60Fe20B20 thin film

This study investigates the nano-mechanical properties of Co60Fe20B20 thin films and the effect of the size of the grains on them. These films were sputtered onto glass substrates to thicknesses from 1000Å to 5000Å under the following conditions: (a) substrate temperature maintained at RT, (b) post-annealing at a treatment temperature of 150°C for 1h, (c) post-annealing at a treatment temperature of 250°C for 1h, and (d) post-annealing at a treatment temperature of 350°C for 1h. A plane-view image was captured under a high-resolution transmission electron microscope (HRTEM) to determine the distribution of grains. The selected-area-diffraction (SAD) pattern was obtained using HRTEM. The electron diffraction pattern revealed that the CoFeB thin film had a nano-crystallization body-centered cubic (BCC) CoFeB structure and strong CoFeB (110) crystallization. A higher annealing temperature resulted in a larger grain. The average grain size increased with the thickness of the CoFeB thin film. The hardness and Young’s modulus were obtained using nano-indentation. Results concerning the grain size and the nano-indentation measurement an increase in hardness and Young’s modulus are reasonably inferred from a smaller grain size, consistent with the “Hall–Petch” effect. The nano-indentation microstructure was obtained by scanning electron microscopy (SEM). Annealing increased the area of the nano-indentation triangle. This result is consistent with the results concerning hardness and Young’s modulus. The nano-mechanical properties of the post-annealed CoFeB thin film are worse than those of the as-deposited film.

TEM-study of free-standing self-assembled InSb quantum dots grown on InAs surface

We have investigated the morphology of free-standing self-assembled InSb quantum dots (QDs) grown by liquid-phase epitaxy (LPE) under conventional growth conditions on InAs(001) substrate. Two growth modes, Volmer–Weber for low-density (5×108cm−2) large QDs with 10–12nm in a height and Stranski–Krastanow for high-density (1×1010cm−2) small QDs with a height of 3–4nm, were identified in dependence on a critical growth temperature of InSb QDs formation. Characterization of the sample surface was performed using transmission electron microscopy (TEM) that allowed us to observe some features of the InSb QD shape which transforms from a full dome to truncated one with increasing QD lateral size from 15 to 40nm, respectively. Using pseudo-moiré pattern appearing in plan-view diffraction TEM image the critical size of the InSb QD for plastic deformation was evaluated.

Morphometry of Great Basin pluvial shore landforms: Implications for paleolake basins on Mars

[1] Many basins with relict contributing valley networks and outlet valleys in the Martian highlands indicate past flowing and ponded water on the surface. These likely paleolakes motivate an investigation of pluvial shore landforms in the Great Basin region of the western United States, as confident identification of strandlines on Mars would facilitate analyses of its past hydrology and climate. The purpose of this study is to characterize the scale of Late Pleistocene erosional and depositional shore landforms in an endorheic setting, determine the preservation potential of similar forms from multiple epochs in early Martian history, and identify the data products that would be necessary to detect them. We use Differential Global Positioning System field surveys to measure the dimensions and elevations of shore landforms; compare shore platform widths to theoretical maxima; and note the minimum scale of landforms that have survived since the Late Noachian and Early Hesperian Epochs on Mars. We find that due to impact gardening and aeolian erosion, Martian highland paleolakes like those in the pluvial Great Basin would likely not have well-preserved shore landforms, unless they were unusually large and formed in the Late Hesperian or later. Individual strandlines are often not equally well expressed around an entire basin, so correlating shore landforms in plan view imaging and using their consistency in elevation as a hypothesis test for paleolakes can be challenging. Detection of younger shore landforms like those examined here would require meter-resolution imaging and topography such as stereo digital elevation models.

Seismic geomorphology of a channel reservoir in lower Minghuazhen Formation, Laizhouwan subbasin, China

We apply seismic geomorphology techniques to quantify morphometrics of a Neogene channel system in Bohai Bay, China. The primary goals of this study are to trace and understand the shapes of complex meander channels toward the development of sedimentary models of channel distribution. First, 11 seismic geometrical attributes were extracted to provide large quantities of morphometric data on the channel plan-view images of four fluvial phases. These data were then coanalyzed to yield the desired five morphometric measures: channel width, meander-belt width, meander length, meander-arc height, and sinuosity. Finally, the relationships, if any, among the five geometric measures were assessed to understand channel reservoir distribution in the study area. A bar graph of sinuosity shows three types of dominant grain size transported by the flow in the channel. A cumulative probability curve of channel width helps to estimate the actual reservoir size. Crossplot analyses reveal relationships between pairs of channel morphometric parameters, which in turn provide the key constraints on channel variability for reservoir modeling and flow simulation in the Lower Minghuazhen Formation, Laizhouwan subbasin, Bohai Bay.

Study of defect evolution by TEM with in situ ion irradiation and coordinated modeling

The paper describes a novel transmission electron microscopy (TEM) experiment with in situ ion irradiation designed to improve and validate a computer model. TEM thin foils of molybdenum were irradiated in situ by 1 MeV Kr ions up to ∼0.045 displacements per atom (dpa) at 80°C at three dose rates −5 × 10−6, 5 × 10−5, and 5 × 10−4 dpa/s – at the Argonne IVEM-Tandem Facility. The low-dose experiments produced visible defect structure in dislocation loops, allowing accurate, quantitative measurements of defect number density and size distribution. Weak beam dark-field plane-view images were used to obtain defect density and size distribution as functions of foil thickness, dose, and dose rate. Diffraction contrast electron tomography was performed to image defect clusters through the foil thickness and measure their depth distribution. A spatially dependent cluster dynamic model was developed explicitly to model the damage by 1 MeV Kr ion irradiation in an Mo thin foil with temporal and spatial dependence of defect distribution. The set of quantitative data of visible defects was used to improve and validate the computer model. It was shown that the thin foil thickness is an important variable in determining the defect distribution. This additional spatial dimension allowed direct comparison between the model and experiments of defect structures. The defect loss to the surfaces in an irradiated thin foil was modeled successfully. TEM with in situ ion irradiation of Mo thin foils was also explicitly designed to compare with neutron irradiation data of the identical material that will be used to validate the model developed for thin foils.

Excitation-dependent recombination and diffusion near an isolated dislocation in GaAs

In low-magnification, plan-view photoluminescence images of a nominally lattice-matched, undoped GaAs/GaInP heterostructure, we observe a random distribution of isolated dark spots. We attribute the dark spots to crystal dislocations, where nonradiative recombination is augmented by transitions utilizing defect-related energy levels between the conduction and valence bands. We note that, when the laser excitation intensity is reduced, the darkened regions expand. At lower excitation, the density of photogenerated electrons and holes is reduced, and they are more likely to reach the defective region before encountering a partner for radiative recombination. When we model the behavior with a simulation that allows for Laplacian diffusion and defect-related recombination only through mid-bandgap energy levels, we do not obtain good agreement between experimental and simulated images. But if we allow for an arbitrary distribution of defect levels, such that the occupation of the levels and bands can change independently, we have more flexibility for fitting the density-dependent recombination rates. The more sophisticated model produces results that are more consistent with experimental images.

Investigation of grain boundaries in BaSi2 epitaxial films on Si(1 1 1) substrates using transmission electron microscopy and electron-beam-induced current technique

a-Axis-oriented undoped n-BaSi2 epitaxial films were grown on Si(111) substrates by molecular beam epitaxy, and the crystalline quality and grain boundaries were investigated by means of reflection high-energy electron diffraction, X-ray diffraction, and transmission electron microscopy (TEM). The grain size of the BaSi2 films was estimated to be approximately 0.1–0.3μm, and straight grain boundaries (GBs) were observed in the plan-view TEM images. Dark-field TEM images under a two-beam diffraction condition showed that these GBs consist mostly of BaSi2 {011} planes. The diffusion length of minority carriers in n-BaSi2 was found to be approximately 10μm by an electron-beam-induced current technique.

Atomic Structural Analysis of Nanowire Defects and Polytypes Enabled Through Cross‐Sectional Lattice Imaging

Correlated transmission electron microscopy imaging, electron diffraction, and Raman spectroscopy are used to investigate the structure of Si nanowires with planar defects. In addition to plan-view imaging, individual defective nanowires are imaged in axial cross-section at specific locations selected in plan-view imaging. This correlated characterization approach enables definitive identification of complex defect structures that give rise to diffraction patterns that have been misinterpreted in the literature. Conclusive evidence for the 9R Si polytype is presented, and the atomic structure of this phase is correlated with kinematically-forbidden reflections in Si diffraction patterns. Despite striking similarities between imaging and diffraction data from twinned nanowires and the 9R polytype, clear distinctions between the structures can be made. Finally, the structural origins of ⅓{422} reflections in Si [111] diffraction patterns are identified.

Hysteretic anomalous Hall effect in a ferromagnetic, Mn-rich Ge:Mn nanonet

Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.

Microstructures of GaN Thin Films Grown on Graphene Layers

Plan-view and cross-sectional transmission electron microscopy images show the microstructural properties of GaN thin films grown on graphene layers, including dislocation types and density, crystalline orientation and grain boundaries. The roles of ZnO nanowalls and GaN intermediate layers in the heteroepitaxial growth of GaN on graphene, revealed by cross-sectional transmission electron microscopy, are also discussed.

Seismic geomorphology and high-resolution seismic stratigraphy of inner-shelf fluvial, estuarine, deltaic, and marine sequences, Gulf of Thailand

Pleistocene fluvial, estuarine, marine, and deltaic depositional systems were identified in the uppermost 80 m (262 ft) of the central Gulf of Thailand modern continental shelf, situated approximately 70 m (230 ft) below sea level. Integration of offshore three-dimensional (3-D) seismic reflection data, high-resolution shallow-penetration two-dimensional (2-D) seismic reflection sparker and boomer profiles, and shallow geotechnical borehole measurements enabled the identification of seven depositional sequences. The 3-D plan-view images at successive time slices exhibit single meandering channels (as much as 600 m [1969 ft] wide) and channel belts (as much as 10 km [6.2 mi] wide) deposited in the shelf during times of subaerial exposure. Additional geomorphic features imaged include incised valleys, interfluves, oxbow lakes, neck and chute cutoffs, and point-bar meander scrolls showing evidence of expansion and translation. The high-resolution 2-D profiles, with a tuning thickness of approximately 25 cm (9.8 in.), enabled the discrimination of high-frequency stratigraphic discontinuities (sequence boundaries) and allowed a detailed bed-scale seismic facies characterization of fluvial (point bars), deltaic (clinoforms), estuarine, and marine deposits within a sequence-stratigraphic context. The complete succession shows that most fluvial systems lie within incised valleys in the lower parts of each depositional sequence, fluvial channels show a degradational stacking pattern, and no evidence of fluvial aggradation is observed; aggradation is limited to hemipelagic sedimentation during marine incursions. A shallow (35 m [115 ft]) single-story incised valley was described in detail, placing particular emphasis on the recognition criteria and the controls on valley formation and preservation potential of different systems tracts in an inner-shelf location. The 3-D characterization of this system allowed differentiation of sand-prone point-bar deposits and mud-prone abandonment channel facies. The sinuous but continuous mud-filled channel may act as a lateral muddy barrier or baffle that can potentially subdivide a reservoir system into discrete compartments.

The use of fractals to quantify the morphology of cluster microforms

The emphasis of this paper is on the fractal-analysis of irregular objects like particle clusters that fill the two-dimensional Euclidean space R 2. A common fractal descriptor of such objects is D L (1 < D L < 2), which defines the fractal dimension of the object outline and is determined by the divider method. In this case, an object may possibly exhibit only two statistically self-similar scales, namely ‘structural’ and ‘textural’. The structural fractal dimension describes the form structure (or the degree of convolution) of the object perimeter and the textural describes the crenellations (or edge effects) found on the object perimeter. Recent studies have shown that the D L does not uniquely define the morphology of complex objects like clusters as it does not include the morphologic attributes, associated with the objects enclosed projected area. A key contribution of this work is the recognition that the ‘total areal’ fractal dimension of the object, D AT (1 < D AT < 2) offers a unique description of cluster morphology as it accounts for the collective contributions from the crenellations found on the object perimeter and its form structure, as well as contributions from the object core structure or equivalently object projected area. The D AT , which is theoretically interrelated to D L , satisfies the key self-similarity principle of fractals and is employed here to differentiate among four cluster morphologic groups observed in field and laboratory studies, namely, in-line clusters with elongation ratio, ER < 5 and ER > 5, pseudo-triangle, and -rhomboid. The analysis for this study is performed by applying the box-counting method for analyzing cluster planview images from four groups of cluster morphologies derived from synthetic, laboratory, and field data sets. The D AT is determined via Richardson plots by estimating the slope of the best-fit line over the entire range of box sizes. Doing so, provides a single aggregate dimension that includes the embedded effects from the objects projected area and perimeter. The results show that the average D AT ¯ and its standard deviation can effectively discriminate the four cluster morphologic groups. The D AT ¯ provides a clear demarcation between the nonlinear morphologies and the in-line morphology with ER > 5. The analysis also shows that the in-line clusters with ER < 5 change between pseudo-linear and pseudo-nonlinear morphologies. Moreover, it is found that most morphologies in the field are statistically well represented by the corresponding laboratory and synthetic morphologies. Finally, the analysis of the laboratory cluster data reveals the utility of D AT ¯ for portraying the correspondence between cluster morphology and physical processes responsible for cluster formation and morphologic evolution, such as flow and sediment supply. Future research should build on the knowledge gained on this topic and further examine the links between the fractal dimension of different cluster morphologies and the physical processes that produce the characteristic scale captured by D AT ¯ .

On Morphology and Strain Field of Ge/Si(001) Islands According to TEM Phase Imaging Method

The mechanism driving Germanium islands nucleation and self-assembly is an important effect for opto-electronic applications, still not fully understood. We demonstrate that the new transmission electron microscopy phase imaging method provides insights on the distribution of strain and composition fields in and around the islands on rather large areas. The method consists of retrieving the phase from a focus series of plane view images. The phase image is representative of morphology, composition and strain. The results show that whatever the islands size and shape is, a maximum compressive strain is obtained at the apex of the islands compensated by a maximum tensile strain in the substrate close to the islands perimeter. The maximum compressive strain is associated to a larger Ge concentration. The distribution of tensile strain varies with the shape of the islands: for square base pyramidal "hut" islands, a maximum tensile strain is obtained at the four corners of the pyramid base and for "dome" islands, the tensile strain is less pronounced and affects almost the whole island perimeter. These results are consistent with the higher strain relaxation level of "dome" islands in comparison to those of "hut" islands.

Extended defect structure of a-plane GaN produced by sidewall lateral epitaxial overgrowth

This paper demonstrates the use of Sidewall Lateral Epitaxial Overgrowth (S-LEO) on a-plane GaN thick films on r-plane sapphire by hydride vapor phase epitaxy (HVPE). Comprehensive study of the extended defect microstructure of the a-plane GaN films was carried out using cross-sectional and plan-view transmission electron microscopy (TEM). A very low density of primary threading dislocations and a heterogeneous microstructure can be found in the GaN films. In the window region and N-face wing region, the extended defects included type I 1 and type I 2 basal stacking faults (BSFs), as well as prismatic stacking faults (PSFs) on a-planes. The density of type I 1 BSFs was in the order of ∼2×10 5 cm −1, type I 2 BSFs in the order of ∼10 4 cm −1, and corresponding localized partial dislocation density less than 1.5×10 9 cm −2. PSFs on a-planes were connected to two neighboring type I 1 BSFs with an estimated density of 3×10 2 cm −1 in the plan-view images. In the Ga-face overgrowth regions, the density of BSFs was lower than 10 4 cm −1. However, inversion domains bounded by (1 1̄ 0 2), (1 1̄ 0 2̄), and (1 1̄ 0 0) planes were found in the Ga-face wing regions. The nature of inversion domain boundaries (IDB) on m-planes can be explained by the Auserman-Gehamn model using high-angle annular dark-field TEM images.

TEM analysis of InMnAs layers and dots prepared by low pressure MOVPE

The properties of InMnAs epitaxial layers and quantum dots prepared on (100) GaAs substrates using Metal-Organic Vapor Phase Epitaxy (MOVPE) are reported. Transmission Electron Microscopy (TEM) observation confirmed that the quantum dot structures were plastically relaxed. The degree of relaxation depends on the amount of Mn incorporated in the structure. Moiré fringes at TEM plan view images were used to evaluate strain in the InMnAs quantum dot structures. TEM observation confirmed that the InMnAs dots were uniform and they grew in the zinc-blende structure. The bright field TEM micrographs (cross-sectional) of the epitaxial layers showed the presence of InMnAs precipitates located under the interface between the InMnAs and substrate.

Expanding the possibilities of two-dimensional multielectrode systems, with consideration to earlier geoelectric arrays

Recent two-dimensional multielectrode measurements are restricted to only a few geoelectric arrays. Realizing that specific features of nearly 90 other arrays are totally ignored, all original intentions as published about the development of new geoelectric arrays were reviewed. Apart from arrays, either already applied in two-dimensional geoelectric arrays or impossible to be applied in such systems, 61 forgotten once-developed arrays were found. These provide altogether 102 various solutions, which would be able to increase the efficiency of two-dimensional multielectrode measurements in some respect. 46 array solutions are able to enhance the depth of investigation; 9/11 array solutions give better vertical/horizontal resolution; 17 array solutions provide better planview images; 8 array solutions are worth applying in areas with limited access; 11 array solutions may reduce the effect of near-surface inhomogeneities . By reviving these forgotten arrays, it will be possible to develop versatile multielectrode systems, which are more adaptive to the diverse field needs. ► A historical overview about original intentions of once-developed geoelectric arrays. ► Classification of specific features of 168 array solution techniques. ► Altogether 103 solution techniques (61 arrays) have been found to be relevant. ► Applying these old arrays, 2D multielectrode systems could be improved.

Electrodeposition of Copper and Silver Nanowires in Hierarchical Mesoporous Silica/Anodic Alumina Nanostructures

Copper, silver, and tellurium nanowires were electrodeposited into a hierarchical channel structure formed from columnar silica mesophases inside of anodic alumina membranes. The resulting wires were structurally and spectroscopically characterized within the host matrix, in the partially dissolved matrix, and completely removed from the matrix with electron microscopy methods. Plan view images of wires featuring 10 nm diameter within the intact matrix showed the successful replication of the hexagonal arrangement of the columnar mesoporous system. Dissolving only the alumina while leaving the silica mesophase still intact, the long-range organization of the mesoporous system could be visualized. Finally, by completely dissolving the matrix (both alumina and silica), silver wires in the form of bundles of individual wires of about 10 nm diameter could be obtained.

Velocimetry Measurements of Unstart of an Inlet-Isolator Model in Mach 5 Flow

The dynamics of unstart in a floor-mounted inlet-isolator model in a Mach 5 flow are investigated experimentally using particle image velocimetry and fast-response wall pressure measurements. The inlet compression is obtained with a 6-deg ramp and the isolator is a rectangular straight duct that is 25.4 mm high by 50.8 mm wide by 242.3 mm long. Unstart is initiated from the scramjet mode (fully supersonic in the isolator) by deflecting a motorized flap at the downstream end of the isolator. With the flap fully down, the particle image velocimetry data of the started flow capture the characteristics of the isolator boundary layers and the initial inlet reflected shock system. During unstart, the unstart shock system propagates upstream through the inlet-isolator. The particle image velocimetry data reveal a complex, three-dimensional flow structure that is strongly dependent on viscous mechanisms. Particularly, the unstart shock system propagates upstream and induces significant boundary-layer separation. Side-view particle image velocimetry data show that the locations of strongest separation during unstart correlate with the impingement locations of the initial inlet shock as it reflects down the isolator. For example, in the middle of unstart, the unstart shock system is associated with massive separation of the ceiling boundary layer that begins where the first inlet shock reflection impinges on the ceiling. The observation that separation increases at the inlet shock reflection impingement locations is likely due to the fact that the boundary layers in these locations are subject to larger adverse pressure gradients, thus making them more susceptible to separation. During the unstart process, large regions of separated flow form near the floor and ceiling with reverse flow velocities up to about 0.4U ∞ . These regions of separated, subsonic flow appear to extend to the isolator exit, creating a path by which the isolator exit boundary condition can be communicated upstream. Plan-view particle image velocimetry data show the unstart process begins with separation of the isolator sidewall boundary layers. Overall, the unstart flow structure is highly three-dimensional.

Prospects for 3D imaging of dopant atoms in ceramic interfaces

Expanding upon recent experimental results for a Y-doped Sigma13 alpha-Al(2)O(3) grain boundary, we explore through simulation the extent to which plan-view imaging of buried interfaces may be possible (cf. the more usual cross-section imaging). As we show in detail, that case was significantly aided by the normal to the interface plane being a high-order zone axis orientation, giving the visibility of the Y atoms a remarkable insensitivity to the specimen thickness and the depth of the interface plane. The visibility along lower order zone axis orientations and the visibility of different dopant species are discussed.