Row Reconstruction Research Articles

Modeling the phase boundaries in Cu(100)-(2√2 × √2)R45°-O missing row reconstruction (MRR) structure

Although the structure of Cu(100)-(22×2)R45°-O missing row reconstruction (MRR) has been well-established for decades, the detailed structure of its various boundaries remains an untilled area due to the difficulties in obtaining atomically resolved images. Herein, atomic arrangement of the phase boundaries existing in MRR structure was modeled on the basis of scanning tunneling microscopy (STM) investigations. By determining the periodicity and unit structure of MRR in STM images and extending them to boundary region, several types of phase boundaries were identified, resulted respectively from: (1) the mismatch between c(2 × 2)-O patches, (2) the regulation by step edges, and (3) the mismatch between Cu missing rows (MRs). With the modeled structure, it was revealed that the types of the c(2 × 2)-O mismatch induced phase boundaries (OMIPBs) are mainly dominated by the oxygen exposure and in-diffusion barrier. The step edge regulated phase boundaries (SERPBs) are always terminated with Cu-O chain and may represent an intermediate growth stage to larger MRR structure. Comparatively, Cu MRs mismatch is often reconciled by the differently oriented domains between them. As a result, the Cu MRs mismatch induced phase boundaries (CMRMIPBs) are only occasionally observed as Cu-O chains between mismatched Cu MRs that encounter shoulder-to-shoulder. For all studied boundaries, the surrounding MRR domains exhibit obvious orientation preference through inclined packing along the SP direction with the degree closely related with the width of the boundaries.

The relevance of structural variability in the time-domain for computational reflection anisotropy spectroscopy at solid–liquid interfaces

In electrochemistry, reactions and charge-transfer are to a large extent determined by the atomistic structure of the solid–liquid interface. Yet due to the presence of the liquid electrolyte, many surface-science methods cannot be applied here. Hence, the exact microscopic structure that is present under operating conditions often remains unknown. Reflection anisotropy spectroscopy (RAS) is one of the few techniques that allow for an in operando investigation of the structure of solid–liquid interfaces. However, an interpretation of RAS data on the atomistic scale can only be obtained by comparison to computational spectroscopy. While the number of computational RAS studies related to electrochemical systems is currently still limited, those studies so far have not taken into account the dynamic nature of the solid–liquid interface. In this work, we investigate the temporal evolution of the spectroscopic response of the Au(110) missing row reconstruction in contact with water by combining ab initio molecular dynamics with computational spectroscopy. Our results show significant changes in the time evolution of the RA spectra, in particular providing an explanation for the typically observed differences in intensity when comparing theory and experiment. Moreover, these findings point to the importance of structural surface/interface variability while at the same time emphasising the potential of RAS for probing these dynamic interfaces.

STM study of surface restructuring of oxidized Cu(100)

The Cu(100) surface offers a model platform for the investigation of the copper oxidation process. Starting from clean Cu(100), we characterized oxidized surfaces with varying oxygen exposure, sample temperature, and post-oxidation annealing conditions. Scanning tunneling microscopy was used to characterize the surfaces with atomic resolution imaging at 78 K. Annealing in O2 (P∼ 5·10−6 mbar) at 80-260 °C led to the (2√2 x √2) R45°Cu(100)-O missing row reconstruction (MRR), which self-limited at monolayer coverage and was relatively insensitive to exposure or temperature in this range. Further annealing of the MRR surface in UHV (PO2 < 10−9 mbar) at 160 °C resulted in large scale reorganization of the surface into MRR areas with a higher degree of step-bunching, coexisting with facet-like hills. The facets are decorated by terraces with a quasi-hexagonal lattice that we attribute to a Cu(110) c(6 × 2) oxygen induced reconstruction.

Double row reconstruction of achilles tendon (speedbridge technique) for haglund syndrome results in early weight bearing

BackgroundReconstruction of tendoachilles (TA) tendon using double row reconstruction (speedbridge technique) following excision of haglund deformity is relatively newer technique. The purpose was to assess the clinical outcome and effects of early postoperative mobilization with speedbridge technique. MethodsThis was a prospective observational study performed between January 2018 to February 2019. All the patients underwent open excision of haglund deformity after complete detachment of TA tendon. Reconstruction of TA tendon was done using fibretape and 4.75 mm biocomposite Swivelock [ArthrexAchilles SpeedBridge Convenience Pack (AR-8928 BC-CP)].Clinical evaluation was done using American Orthopedic Foot and Ankle Society (AOFAS) Hind Foot Score (HFS) and Visual Analogue Scale (VAS). Patients were followed at 6weeks, 6 months,12 months,18 months and 2 years. Results11 female and 2 male patients (16 feet) with mean age of 53.00 ± 4.93 years were analyzed. Full weight bearing mobilization was started on an average of 10 days postoperatively.The mean postoperative HFS, at 24 months of postoperative period, was 87.61 ± 4.69 compared to mean preoperative HFS of 53.07 ± 5.93. ConclusionHaglund deformity excision and reconstruction of Tendoachilles using double row technique is an agile construct for early mobilization with an excellent clinical outcome.

Reconstruction of Lateral Rows of the Late Cambrian and Early Ordovician Active Continental Margin Structures in the Paleozoids of Northern Kazakhstan

A comprehensive study of the Upper Cambrian and Lower Ordovician complexes of Northern Kazakhstan was carried out, their ages were substantiated, the structures and compositions of the rocks were investigated. It has been ascertained that the Upper Cambrian formations comprise coarse clastic strata, mafic alkaline effusive rocks and gabbro, while felsic volcanic rocks and granites are represented only by boulders in conglomerates. The Lower Ordovician rocks contain basalt-rhyolite series, felsic alkaline volcanic rocks, and granitoids. The lateral rows of structures of the active continental margin have been reconstructed for the Late Cambrian and Early Ordovician. In the Late Cambrian, the lateral series includes only the structures of the rear extension region, where complexes with the within-plate geochemical characteristics were formed. In the lateral series of the Early Ordovician structures, the frontal volcanic area with the island-arc volcanic rocks and the rear extension area with the intraplate felsic volcanic rocks and granites, were revealed. It is assumed that the differences in the lateral rows of structures may be associated with a change in the tectonic mode of the active continental margin at the Cambrian–Ordovician boundary, when the transform mode with no evidence of suprasubduction magmatism was replaced by convergent magmatism accompanied by the wide distribution of island-arc volcanic rocks.

Polar surface of ferroelectric nanodomains in GeTe thin films

Ferroelectrics have polar surfaces that can undergo large structural and stoichiometric modifications to be neutral. These changes can have major implications on the surface stability and physicochemical properties. We have studied the growth and structure of ferroelectric GeTe thin films on Si(111) by a combination of scanning tunneling microscopy, low-energy electron microscopy, and low-energy electron diffraction. We show that GeTe growth occurs with a single epitaxy and proceeds via a step-flow mode hindered by the advance of electrically neutral step edges exhibiting triangular notches. We demonstrate the presence of ferroelectric nanodomains with in-plane components of polarization and a complex restructuring of their polar surface. $2\ifmmode\times\else\texttimes\fi{}2$ surface reconstruction, missing row reconstruction and extended 2D modulations of the surface structure are demonstrated on these nanodomains. We show that these structures stabilize the surface termination of the low-symmetry polar nanodomains.

Uneven Oxidation and Surface Reconstructions on Stepped Cu(100) and Cu(110).

How defects such as surface steps affect oxidation, especially initial oxide formation, is critical for nano-oxide applications in catalysis, electronics, and corrosion. We posit that surface reconstruction, a crucial intermediate oxidation step, can highlight initial oxide formation preferences and thus enable bridging the temporal and spatial scale gaps between atomistic simulations and experiments. We investigate the surface-step-induced uneven surface oxidation on Cu(100) and Cu(110), using atomic-scale in situ environmental transmission electron microscopy experiments with dynamical gas control and advanced data processing. We show that the Cu(100)-O (2√2 × √2)R45° missing row reconstruction strongly favors upper terraces over lower terraces, while Cu(110)-O (2 × 1) "added row" reconstructions indicate slight preferences for upper or lower terraces, depending on oxygen concentration. The observed formation site preference and its variation with surface orientation and oxygen concentration are mechanistically explained by Ehrlich-Schwöbel barrier differences for oxygen diffusion on stepped surfaces.

Effects of lattice strain on noble metal (110) surface: Missing row reconstruction and adsorption properties

Strain engineering of noble metals may optimize their adsorption properties and catalytic performance. On the other hand, while it has been shown that lattice strain may change surface reconstruction for some crystals, it remains to be seen whether strain-induced surface phase transition will modify the adsorption and catalysis properties. In this contribution, we address this issue by density functional methods. We show that 4d elements of Rh, Pd, and Ag change from unreconstruction to 1 × 2 missing row reconstruction under negative strains, while 5d ones including Ir, Pt, and Au change from reconstruction to unreconstruction under positive strains. Strain-induced surface phase transition results in abrupt changes in hydrogen adsorption strength. The present results imply that it is important to consider possible modifications in surface reconstruction to understand catalytic performance of strained noble metals.

Pentacene growth on the (111) surface of the 1/1 Au-Al-Tb approximant: Influence of surface geometry on adsorption

Molecular adsorption on both quasicrystalline and approximant substrates has produced a number of pseudomorphic films, and has led to a deeper understanding of the chemistry of the surfaces of these materials. Here, the recently reported reconstructed (111) surface of the 1/1 Au-Al-Tb Tsai-type approximant has been used as a template for pentacene (Pn) adsorption, which is investigated using scanning tunneling microscopy. This surface provides unique varieties of adsorption sites compared to a normal metal surface. After room-temperature deposition, the Pn molecules are mobile yet exhibit a structure which indicates a bond with the Tb atoms of the surface, while reflecting the twofold symmetrical nature of the reported Au/Al row reconstruction. Postdeposition annealing shows a linear arrangement of molecules in a specific adsorption geometry, likely corresponding to the most favorable energetic configuration.

First-principles calculations of metal surfaces. II. Properties of low-index platinum surfaces toward understanding electron emission

The stability of low-index platinum surfaces and their electronic properties is investigated with density functional theory, toward the goal of understanding the surface structure and electron emission, and identifying precursors to electrical breakdown, on nonideal platinum surfaces. Propensity for electron emission can be related to a local work function, which, in turn, is intimately dependent on the local surface structure. The $(1\ifmmode\times\else\texttimes\fi{}N)$ missing row reconstruction of the Pt(110) surface is systematically examined. The $(1\ifmmode\times\else\texttimes\fi{}3)$ missing row reconstruction is found to be the lowest in energy, with the $(1\ifmmode\times\else\texttimes\fi{}2)$ and $(1\ifmmode\times\else\texttimes\fi{}4)$ slightly less stable. In the limit of large $(1\ifmmode\times\else\texttimes\fi{}N)$ with wider (111) nanoterraces, the energy accurately approaches the asymptotic limit of the infinite Pt(111) surface. This suggests a local energetic stability of narrow (111) nanoterraces on free Pt surfaces that could be a common structural feature in the complex surface morphologies, leading to work functions consistent with those on thermally grown Pt substrates.

First-principles characterization of Mg low-index surfaces: Structure, reconstructions, and surface core-level shifts

In this paper, first-principles calculations provide structural characterization of three low-index Mg surfaces - Mg(0001), Mg(1010), and Mg(1120) - and their respective surface core-level shifts (SCLSs). Inspired by the close similarities between Be and Mg surfaces, we also explore the reconstruction of Mg(1120). Through the calculation of surface energies and the use of the angular-component decomposed density of states, we show that reconstructions are likely to occur at the Mg(1120) surface, similarly to what was found earlier for Be(1120). Indeed, the surface energy of some of the explored reconstructions is slightly lower than that of the unreconstructed surface. In addition, because of lattice symmetry, the morphology of the unreconstructed surface (1120) results in a steplike zig-zag chain packing, with topmost chains supporting a resonant, quasi-one-dimensional (1D), partially filled electronic state. As the presence of partially filled quasi-1D bands is a necessary condition for Peierls-like dimerization, we verify that the undimerized surface chain remains stable with respect to it. Some of the reconstructions, namely, the 2×1 and 3×1 added row reconstructions, induce a stronger relaxation of the topmost chains, increasing the coupling with lower layers and thus significantly damping the quasi-1D character of this state. The original approach followed offers a common and general framework to identify quasi-1D bands - even in the case of resonant electronic surface states - and to meaningfully compare calculated and measured SCLSs even in the presence of multicomponent peak contributions. (Less)

Carbon Monoxide Oxidation Promoted by a Highly Active Strained PdO Layer at the Surface of Au30Pd70(110)

The evolution of the Au30Pd70(110) surface was studied by coupling grazing incidence X-ray diffraction and mass spectrometry under oxygen-rich conditions at moderate temperatures (300 to 470 K). This allows us to correlate the depth profile of its structure to its catalytic properties for carbon monoxide (CO) oxidation. Under increasing pressure from ultrahigh vacuum up to 100 mbar, both oxygen and CO induce Pd segregation, even at room temperature. However, in pure oxygen the surface is reorganized with a (1 × 2) missing row reconstruction, whereas in pure CO it is strongly roughened. When oxygen pressure is increased a phase corresponding to the initial step of the oxidation with oxygen dissolution in the subsurface region appears at first. Then, from about 400 K onward, an oxidized thin Pd layer (≤1 nm) is formed growing in the [100]PdO direction. This PdO phase is strained and does not coincide with the P42/mmc structure usually observed for this oxide under ambient conditions. It is more probably con...

Leaf Area Estimation of Reconstructed Maize Plants Using a Time-of-Flight Camera Based on Different Scan Directions

The leaf area is an important plant parameter for plant status and crop yield. In this paper, a low-cost time-of-flight camera, the Kinect v2, was mounted on a robotic platform to acquire 3-D data of maize plants in a greenhouse. The robotic platform drove through the maize rows and acquired 3-D images that were later registered and stitched. Three different maize row reconstruction approaches were compared: reconstruct a crop row by merging point clouds generated from both sides of the row in both directions, merging point clouds scanned just from one side, and merging point clouds scanned from opposite directions of the row. The resulted point cloud was subsampled and rasterized, the normals were computed and re-oriented with a Fast Marching algorithm. The Poisson surface reconstruction was applied to the point cloud, and new vertices and faces generated by the algorithm were removed. The results showed that the approach of aligning and merging four point clouds per row and two point clouds scanned from the same side generated very similar average mean absolute percentage error of 8.8% and 7.8%, respectively. The worst error resulted from the two point clouds scanned from both sides in opposite directions with 32.3%.

Nanoscale investigation of Si nanoribbon growth on Ag(110)

The authors present a nanoscale investigation by means of scanning tunneling microscopy of Si nanostructure growth on the anisotropic silver (110) surface, in the submonolayer range. Four types of Si nanostructures are studied statistically as a function of the substrate temperature in the range 300–500 K: isolated single and double nanoribbons, which differ only by a factor of 2 in their width, and their respective bidimensional counterparts in the self-assembly regime. Their observations highlight different growth regimes controlled by kinetics. Below 320 K, the Si adatoms diffuse along the easy [11¯0] direction, forming essentially isolated single nanoribbons randomly distributed on the silver terraces. At higher temperatures, transverse diffusion along the [001] direction is activated and a competition between the growth of self-assembled single nanoribbons and isolated double nanoribbons is observed. Above 440 K, a transition from one- to two-dimensional double nanoribbon growth is evidenced. At 490 K, the Si deposition results in the formation of massively self-assembled double nanoribbons. Based on Arrhenius analyses, activation barriers are found to be (125 ± 15) and (210 ± 20) meV for the formation of isolated Si nanoribbons and self-assembled Si double nanoribbons, respectively. Their results allow for a better understanding of the kinetic limiting processes which determine the submonolayer morphology and illustrate the role played by the missing row reconstruction of the Ag(110) surface in the formation of extended Si nanoribbon arrays.

Reflectance anisotropy spectroscopy of Fe3O4 (110): Anisotropic strain

We present a study of (110)-terminated magnetite using a range of surface-sensitive techniques, the foremost of those being reflectance anisotropy spectroscopy (RAS). The anisotropic optical response of the as-polished and row-reconstructed terminations are investigated. The responses are interpreted to result from termination-induced anisotropic shifts in energy of the bulklike optical transitions. Density functional theory (DFT) calculations demonstrate that the row reconstruction of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$(110) exhibits anisotropic strain in its terminating layers, and this strain is concluded to be the origin of the RAS response. X-ray photoelectron spectroscopy measurements demonstrate that the row reconstruction is reduced and the stoichiometry in the surface region is relatively easily altered by in situ preparation procedures. This is correlated to altered surface electronic properties identified by scanning tunneling spectroscopy measurements. RAS is sensitive to this change in surface structure, with the magnitude of the RAS response being altered.

Biomechanical evaluation of an arthroscopic transosseous repair as a revision option for failed rotator cuff surgery

BackgroundThe number of revision rotator cuff cases is increasing. The literature is lacking guidance or biomechanical evaluation for fixation strength in a revision case scenario. Therefore, the aim of the study was to provide biomechanical data investigating primary fixation strength of a transosseous technique after anchor pullout failure of a single row reconstruction. It was hypothesized that an arthroscopic transosseous repair system as a procedure for rotator cuff revisions is providing equivalent stability compared to a primary single row suture anchor fixation due to change of fixation site.MethodsEight matched pairs (n = 16) of fresh frozen human shoulders were tested. The paired specimen shoulders were randomly divided into two repair groups (A single row and B primary transosseous repair). The potted specimens were mounted onto the Servohydraulic test system. Both groups were tested under cyclic loading followed by load to failure testing. Suture anchor repair shoulders (group A) that were tested to failure underwent a revision transosseous repair and were subsequently tested again using the same setup and protocol (group C).ResultsThe mean native footprint areas did not show a significant difference between groups. The reconstructed footprint area showed a significantly greater coverage in favor of the transosseous repair. Ultimate load to failure of reconstructions with the primary anchor fixation (344.73 N ± 63.19) and the primary transosseous device (375.36 N ± 70.27) was not significantly higher compared to the revision repair (332.19 N ± 119.01 p = 0.45, p = 0.53).ConclusionThe tested transosseous anchor device is a suitable option to widely used suture anchors, providing equivalent fixation properties even in a revision case scenario.Level of evidenceBasic Science Study, Biomechanics.

Segregation induced order-disorder transition in Cu(Au) surface alloys

Using in-situ transmission electron microscopy and atomistic simulations, we report atomic-scale observations of segregation-induced structure changes in the surface and subsurface region of a Cu(Au) solid solution in both reductive and oxidative environments. In a H2 atmosphere, Au segregation induces the formation of a two-atomic-layer thick ordered surface alloy with an L10 terminated surface layer. By switching to an O2 atmosphere, the outermost surface develops into an Au-missing row reconstruction and simultaneously the second layer experiences an order-disorder transition via intralayer atomic exchanges. The chemical disordering then propagates to the outermost surface, driven by oxygen-adsorption induced Cu surface segregation. This transforms the L10 missing-row reconstruction into a non-reconstructed, oxygenated surface. These observations provide a mechanistic detail regarding the evolution of the surface and subsurface of this alloy in response to environmental stimuli, and are relevant to a wide range of technologically relevant processes.

3-D reconstruction of maize plants using a time-of-flight camera

Point cloud rigid registration and stitching for plants with complex architecture is a challenging task, however, it is an important process to take advantage of the full potential of 3-D cameras for plant phenotyping and agricultural automation for characterizing production environments in agriculture. A methodology for three-dimensional (3-D) reconstruction of maize crop rows was proposed in this research, using high resolution 3-D images that were mapped into the colour images using state-of-the art software. The point cloud registration methodology was based on the Iterative Closest Point (ICP) algorithm. The incoming point cloud was previously filtered using the Random Sample Consensus (RANSAC) algorithm, by reducing the number of soil points until a threshold value was reached. This threshold value was calculated based on the approximate number of plant points in a single 3-D image. After registration and stitching of the crop rows, a plant/soil segmentation process was done relying again on the RANSAC algorithm. A quantitative comparison showed that the number of points obtained with a time-of-flight (TOF) camera, compared with the ones from two light detection and ranging (LIDARs) from a previous research, was roughly 23 times larger. Finally, the reconstruction was validated by comparing the seedling positions as ground truth and the point cloud clusters, obtained using the k-means clustering, that represent the plant stem positions. The resulted maize positions from the proposed methodology closely agreed with the ground truth with an average mean and standard deviation of 3.4 cm and ±1.3 cm, respectively.

A Low-Cost Approach to Automatically Obtain Accurate 3D Models of Woody Crops.

Crop monitoring is an essential practice within the field of precision agriculture since it is based on observing, measuring and properly responding to inter- and intra-field variability. In particular, “on ground crop inspection” potentially allows early detection of certain crop problems or precision treatment to be carried out simultaneously with pest detection. “On ground monitoring” is also of great interest for woody crops. This paper explores the development of a low-cost crop monitoring system that can automatically create accurate 3D models (clouds of coloured points) of woody crop rows. The system consists of a mobile platform that allows the easy acquisition of information in the field at an average speed of 3 km/h. The platform, among others, integrates an RGB-D sensor that provides RGB information as well as an array with the distances to the objects closest to the sensor. The RGB-D information plus the geographical positions of relevant points, such as the starting and the ending points of the row, allow the generation of a 3D reconstruction of a woody crop row in which all the points of the cloud have a geographical location as well as the RGB colour values. The proposed approach for the automatic 3D reconstruction is not limited by the size of the sampled space and includes a method for the removal of the drift that appears in the reconstruction of large crop rows.

Benzene adsorption on two-dimensional silica films – Benzene on silicatene

The kinetics of benzene adsorption on monatomic crystalline silica films (silicatene) was studied, employing temperature programmed desorption (TPD). In addition, the precursor of the silica film formation, a Mo(112)-p(1×3)-O missing row reconstruction, and Mo(112) were considered. Benzene adsorbed molecularly on all surfaces. Judged by the desorption temperatures, the adsorption on the Mo oxygen phase is stronger than on silica. Two binding sites were evident for the oxygen induced reconstruction, but only one for silica. Thus, the adsorption kinetics on the support and the monoatomic thin silica film were quite different. In addition, the surfaces were characterized by Auger electron spectroscopy and low energy electron diffraction (LEED).