Triangular Pits Research Articles

Observed Performance of a Large-Scale Deep Triangular Excavation in Shanghai Soft Clays

An 18.4-m-deep triangular foundation pit with in-plane excavation area of approximately 10,000 m2 was constructed in soft clay. The excavation located at Hongqiao comprehensive transportation hub center in Shanghai, in which an energy gallery, many underground pipelines, and viaduct piers exist. Deformation characteristics of the foundation pit and the impact on the adjacent buildings and structures were observed by a monitoring system during excavation. Field data including wall deflections, vertical wall movements, ground subsidence, as well as vertical column movements were analyzed and compared with other excavations of metro stations or rectangular excavations in Shanghai. This excavation exhibited different deformation characteristics from other excavations because of its triangular shape with acute corners. The deformation law of this special excavation was beneficial for the design and construction of special-shaped foundation pit in complex environment.

Directional Oxidation of Pyrite in Acid Solution

This study aimed to investigate the oxidation mechanism of pyrite crystallographic direction by cutting pyrite samples to expose their (100), (110), and (111) planes. Differences in the oxidation rates of pyrite planes in acid solution were determined. The morphological changes of pyrite were evaluated by scanning electron microscopy and hyperdepth-3D microscopy. The oxidation products of pyrite were examined by Raman spectroscopy and X-ray photoelectron spectroscopy. Results showed that the aqueous oxidation of pyrite produced Fe(OH)3, Fe2O3, Fe2(SO4)3, and S8 on the surface. Moreover, the morphologies of corrosion patterns differed from one crystal plane to another: square, rectangular, and triangular etch pits were found on the (100), (110), and (111) planes, respectively. The corrosion patterns reflected the symmetrical arrangement of the crystallographic planes in the lattice on which they formed.

Dynamics and Molecular Mechanism of Phosphate Binding to a Biomimetic Hexapeptide.

Phosphorus (P) recovery from wastewater is essential for sustainable P management. A biomimetic hexapeptide (SGAGKT) has been demonstrated to bind inorganic P in P-rich environments, however the dynamics and molecular mechanisms of P-binding to the hexapeptide still remain largely unknown. We used dynamic force spectroscopy (DFS) to directly distinguish the P-unbound and P-bound SGAGKT adsorbed to a mica (001) surface by measuring the single-molecule binding free energy (Δ Gb). Using atomic force microscopy (AFM) to determine real-time step retreat velocities of triangular etch pits formed at the nanoscale on the dissolving (010) face of brushite (CaHPO4·2H2O) in the presence of SGAGKT, we observed that SGAGKT peptides promoted in situ dissolution through an enhanced P-binding driven by hydrogen bonds in a P-loop being capable of discriminating phosphate over arsenate, concomitantly forming a thermodynamically favored SGAGKT-HPO42- complexation at pH 8.0 and relatively low ionic strength, consistent with the DFS and isothermal titration calorimetry (ITC) determinations. The findings reveal the thermodynamic and kinetic basis for binding of phosphate to SGAGKT and provide direct evidence for phosphate discrimination in phosphate/arsenate-rich environments.

Degradation behaviors and mechanisms of MoS2 crystals relevant to bioabsorbable electronics

Monolayer molybdenum disulfide (MoS2) exhibits unique semiconducting and bioresorption properties, giving this material enormous potential for electronic/biomedical applications, such as bioabsorbable electronics. In this regard, understanding the degradation performance of monolayer MoS2 in biofluids allows modulation of the properties and lifetime of related bioabsorbable devices and systems. Herein, the degradation behaviors and mechanisms of monolayer MoS2 crystals with different misorientation angles are explored. High-angle grain boundaries (HAGBs) biodegrade faster than low-angle grain boundaries (LAGBs), exhibiting degraded edges with wedge and zigzag shapes, respectively. Triangular pits that formed in the degraded grains have orientations opposite to those of the parent crystals, and these pits grow into larger pits laterally. These behaviors indicate that the degradation is induced and propagated based on intrinsic defects, such as grain boundaries and point defects, because of their high chemical reactivity due to lattice breakage and the formation of dangling bonds. High densities of dislocations and point defects lead to high chemical reactivity and faster degradation. The structural cause of MoS2 degradation is studied, and a feasible approach to study changes in the properties and lifetime of MoS2 by controlling the defect type and density is presented. The results can thus be used to promote the widespread use of two-dimensional materials in bioabsorption applications.

Homogeneous surface oxidation and triangle patterning of monolayer MoS2 by hydrogen peroxide

Atomically thin monolayer molybdenum disulfides (MoS2) with tunable electronic structure has promising applications in opto-electronic devices and sensors. In this work, unique nano-patterning and surface oxidation of monolayer MoS2 was achieved based on hydrogen peroxide (H2O2) treatment. It was found that the exfoliated monolayer MoS2 can be uniformly oxidized when exposed to low-concentration H2O2, forming an intermediate phase composed of MoSxOy. In addition, patterned triangular pits with well-defined edges can be formed under high-concentration H2O2 condition. The band gap of monolayer MoS2 could be effectively modulated by H2O2 treatment as verified by photoluminescence spectra. This work shows that simple H2O2 treatment can be an alternative approach for both surface functionalization and band gap modulation of MoS2 flake, and it also provides an alternatively simple way to obtain patterned MoS2 nanostructures without complicated standard lithography processes.

Controllable etching of MoS2 basal planes for enhanced hydrogen evolution through the formation of active edge sites

The catalytic activity of molybdenum disulfide (MoS2) is associated with active sites located along the edges, whereas the MoS2 basal plane is regarded to be inert. However, it is a great challenge to develop a rational way for producing active edges efficiently. Herein, we report a novel, cost-effective top-down process in which we can create a high density of active edge sites on MoS2 basal plane by selective steam etching. The results show that the etched structure is strongly sensitive to the temperature, which creates 1D nano-channels, 2D in-plane triangular pits and 3D vertical hexagonal cavities on the MoS2 basal planes by elevating the temperature. The edge configuration is revealed to exhibit a distinct crystallographic orientation. Furthermore, we evaluate the corresponding enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) by measurements of the single etched MoS2 samples in an electrochemical microcell, where the Tafel slope decrease by 49%, confirming the increased the density of active sites. In addition, the method is not limited to 2D materials in a flat geometry alone, but is also demonstrated on 0D MoS2 particles by in-situ transmission electron microscopy. The steam etching reported here offers an alternative avenue to engineer the surface structures of MoS2 facilitating the electrocatalytic applications of MoS2 for hydrogen production.

Interface-Confined Doubly Anisotropic Oxidation of Two-Dimensional MoS2.

Despite their importance, chemical reactions confined in a low dimensional space are elusive and experimentally intractable. In this work, we report doubly anisotropic, in-plane and out-of-plane, oxidation reactions of two-dimensional crystals, by resolving interface-confined thermal oxidation of a single and multilayer MoS2 supported on silica substrates from their conventional surface reaction. Using optical second-harmonic generation spectroscopy of artificially stacked multilayers, we directly proved that crystallographically oriented triangular oxides (TOs) were formed in the bottommost layer while triangular etch pits (TEs) were generated in the topmost layer and that both structures were terminated with zigzag edges. The formation of the Mo oxide layer at the interface demonstrates that O2 diffuses efficiently through the van der Waals (vdW) gap but not MoO3, which would otherwise sublime. The fact that TOs are several times larger than TEs indicates that oxidation is greatly enhanced when MoS2 is in direct contact with silica substrates, which suggests a catalytic effect. This study indicates that the vdW-bonded interfaces are essentially open to mass transport and can serve as a model system for investigating chemistry in low dimensional spaces.

Zn vacancies creation via (2 × 2) surface reconstruction

Zinc vacancies have been incorporated in ZnO via (2 × 2) surface reconstruction during the epitaxy growth. Evolution of in situ reflection high-energy electron diffraction (RHEED) patterns indicate Zn-polar surface (2 × 2) reconstruction was realized under extreme O-rich conditions. Atom sized triangular pits and islands were presented by the high resolution scanning tunneling microscopy (STM) images, which stand for a single Zn vacancy per (2 × 2) surface unit cell. The neutral acceptor-bound exciton (A0,X), peak located at 3.344 eV, and red luminescence (RL), maximum emission intensity at ~1.76 eV, which related to Zn vacancy, have been studied by variable-temperature/power steady-state photoluminescence (PL) spectroscopy.

Correlation of Etch Pits and Dislocations in As-grown and Thermal-Cycle-Annealed HgCdTe(211) Films

This paper reports observations of the different types of etch pits and dislocations present in thick HgCdTe (211) layers grown by molecular beam epitaxy on CdTe/Si (211) composite substrates. Dislocation analysis for as-grown and thermal cycle-annealed samples has been carried out using bright-field transmission electron microscopy. Triangular pits present in as-grown material are associated with a mixture of Frank partials and perfect dislocations, while pits with fish-eye shapes have perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector. The dislocations beneath skew pits are more complex as they have two different crystallographic directions, and are associated with a mixture of Shockley partials and perfect dislocations. Dislocation analysis of samples after thermal cycle annealing (TCA) shows that the majority of dislocations under the etch pits are short segments of perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector while the remainder are Shockley partials. The absence of fish-eye shape pits in TCA samples suggests that they are associated with mobile dislocations that have reacted during annealing, causing the overall etch pit density to be reduced. Very large pits with a density ∼2×103 cm−2 are observed in as-grown and TCA samples. These defects thread from within the CdTe buffer layer into the upper regions of the HgCdTe layers. Their depth in as-grown material is so large that it is not possible to locate and identify the underlying defects.

Atomic process of oxidative etching in monolayer molybdenum disulfide

The microscopic process of oxidative etching of two-dimensional molybdenum disulfide (2D MoS2) at an atomic scale is investigated using a correlative transmission electron microscope (TEM)-etching study. MoS2 flakes on graphene TEM grids are precisely tracked and characterized by TEM before and after the oxidative etching. This allows us to determine the structural change with an atomic resolution on the edges of the domains, of well-oriented triangular pits and along the grain boundaries. We observe that the etching mostly starts from the open edges, grain boundaries and pre-existing atomic defects. A zigzag Mo edge is assigned as the dominant termination of the triangular pits, and profound terraces and grooves are observed on the etched edges. Based on the statistical TEM analysis, we reveal possible routes for the kinetics of the oxidative etching in 2D MoS2, which should also be applicable for other 2D transition metal dichalcogenide materials like MoSe2 and WS2.

Correlation of Etch Pits and Dislocations in As-grown and Thermal Cycle-Annealed HgCdTe(211) Films

This paper reports observations of the different types of etch pits and dislocations present in thick HgCdTe (211) layers grown by molecular beam epitaxy on CdTe/Si (211) composite substrates. Dislocation analysis for as-grown and thermal cycle-annealed samples has been carried out using bright-field transmission electron microscopy. Triangular pits present in as-grown material are associated with a mixture of Frank partials and perfect dislocations, while pits with fish-eye shapes have perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector. The dislocations beneath skew pits are more complex as they have two different crystallographic directions, and are associated with a mixture of Shockley partials and perfect dislocations. Dislocation analysis of samples after thermal cycle annealing (TCA) shows that the majority of dislocations under the etch pits are short segments of perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector while the remainder are Shockley partials. The absence of fish-eye shape pits in TCA samples suggests that they are associated with mobile dislocations that have reacted during annealing, causing the overall etch pit density to be reduced. Very large pits with a density ∼2×103 cm−2 are observed in as-grown and TCA samples. These defects thread from within the CdTe buffer layer into the upper regions of the HgCdTe layers. Their depth in as-grown material is so large that it is not possible to locate and identify the underlying defects.

Characterization of Alkali-Induced Quartz Dissolution Rates and Morphologies

A number of studies have investigated the impact of alkali cations on quartz dissolution to increase the understanding of natural rock weathering and enhance the predictability of silica behaviour in reservoir systems. However, there are few evidences for how alkali cations approach the quartz surface. Thus, this study is an attempt to provide empirical evidence on the interaction of electrolytes (\(\hbox {Na}^{+}, \hbox {K}^{+}, \hbox {Ca}^{2+})\) with quartz surface. Bulk quartz grains and clean-faced single quartz crystals were dissolved/etched in varying pH solutions of acidic, near-neutral/neutral and alkali solutions (KOH, NaOH, KCl, NaCl, \(\hbox {CaCl}_{2}, \hbox {CH}_{3}\hbox {COOH}\), HCl). The amount of dissolved silica was measured with molybdate spectrophotometry method, while variations in quartz surface morphology were studied using scanning electron microscopy attached with EDX. Quartz dissolution rates varied with pH, hydrated radius and hydrolysis constants of alkali cations in the order: \(\hbox {Ca}^{2+}<\hbox {Na}^{+}<\hbox {K}^{+}\). Relatively deeper triangular etch pits were observed in quartz dissolved in KOH and NaOH solutions, while shallower pits formed in neutral solutions, and exsolution faces and lamellae were formed in quartz dissolved in low-pH solutions. The results also showed that interfacial secondary phases of cationic silicates play a key role in quartz dissolution.

Deep-sea chitons of the genus &lt;i&gt;Stenosemus&lt;/i&gt; (Mollusca: Polyplacophora) from Fiji and Solomon Islands

Three new species of the genus Stenosemus collected near Fiji and Solomon Islands of the central Pacific are described here. Stenosemus fijiensis sp. nov. from Fiji differs from the congeneric species by a unique sculpture of the central areas of tegmentum, consisting of triangular pits and light brown spots on valves. S. philippei sp. nov. and S. solomonensis sp. nov., both from the Solomon Islands, differ from other the species of the genus by having a head of major lateral tooth of radula bicuspidate with small outer denticle, shape and sculpture of dorsal spicules and sculpture of tegmentum.

Polygonal pits on silicon surfaces that are created by laser-assisted chemical etching

Laser-assisted chemical etching was conducted for creating periodic textures on silicon surfaces. Silicon plates with the (111) surface orientation were immersed in an aqueous solution of potassium hydroxide, and a pulsed laser beam (532 nm wavelength, 5 ns duration, 10 pulse/s) was irradiated on their surface to promote anisotropic etching. The laser beam was patterned by using a glass capillary plate that contained a hexagonal array of micropores (10μm diameter, 12μm period). The focused beam projected the hexagonal image on the silicon surface, creating bright spots of 4μm period. During the laser irradiation process of 3 min, both laser-induced ablation and chemical etching took place at these bright spots. After stop of laser irradiation, the chemical etching progressed further, and consequently, a periodic array of triangular or hexagonal pits emerged on the silicon surface. The direction of the triangular pits changed by rotation of the silicon plate. When a silicon plate with the (100) surface orientation was used, diamond or rectangular pits were created on its surface. The mechanism of this polygonal texturing was explained by using the normal and intersecting vectors of the (100), (110), and (111) planes that exhibited different etching rates.

화학적 polishing 및 etching을 통한 RE : YAG (RE = Nd3+, Er3+, Yb3+) 단결정의 표면 결함 분석

Czochralski 법으로 성장한 RE : YAG (<TEX>$RE=Nd^{3+}\;,Er^{3+}\;,Yb</TEX><TEX>^{3+}$</TEX>) 단결정의 표면 결함을 측정하는 chemical polishing 및 etching 조건에 대하여 조사하였다. 최적의 chemical polishing 조건은 시편을 수직 방향으로 고정하고 85 % <TEX>$H_3PO_4$</TEX> 용액에서 <TEX>$330^{\circ}C$</TEX>, 30분 동안 진행한 것이었다. 또한 최적의 chemical etching 조건은 85 % <TEX>$H_3PO_4$</TEX> 용액에서 <TEX>$260^{\circ}C$</TEX>, 1시간 동안 진행한 것이었고, (111) 면에 <TEX>$70~80{\mu}m$</TEX> 크기의 삼각형 etch pit들이 관찰되었다. 결함 밀도 분석 결과, Nd(1 %) : YAG는 <TEX>$1.9{\times}10^3$</TEX>개/<TEX>$cm^2$</TEX>, Er(7.3 %) : YAG는 <TEX>$4.3{\times}10^2$</TEX>개/<TEX>$cm^2$</TEX>, Yb(15 %) : YAG는 <TEX>$5.1{\times}10^2$</TEX>개/<TEX>$cm^2$</TEX>로 측정되었다. The conditions for chemical polishing and etching technique were investigated to reveal surface defects in RE : YAG (<TEX>$RE=Nd^{3+},\;Er^{3+},\;Yb^{3+}$</TEX>) single crystals grown by Czochralski method. The optimal condition for chemical polishing was in 85 % <TEX>$H_3PO_4$</TEX> solution at <TEX>$330^{\circ}C$</TEX> for 30 minutes with a specimen fixed in the vertical direction. In addition, the optimal condition for chemical etching was in 85 % <TEX>$H_3PO_4$</TEX> solution at <TEX>$260^{\circ}C$</TEX> for 1 hour, and <TEX>$70{\sim}80{\mu}m$</TEX> sized triangular etch pits were observed on (111) face. As a result of defect density analysis, <TEX>$1.9{\times}10^3/cm^2$</TEX> for Nd(1 %) : YAG, <TEX>$4.3{\times}10^2/cm^2$</TEX> for Er(7.3 %) : YAG, and <TEX>$5.1{\times}10^2/cm^2$</TEX> for Yb(15 %) : YAG were measured.

Current mapping of nonpolar a-plane and polar c-plane GaN films by conductive atomic force microscopy

Nonpolar (11-20) a-plane GaN and polar (0001) c-plane GaN films have been grown by metal organic chemical vapor deposition on r-plane (1-102) and c-plane (0001) sapphire substrates, respectively. Conductive atomic force microscopy (C-AFM) has been used to investigate the local conductivity of the films. C-AFM shows enhanced current conduction within the etch pits of c-plane GaN and triangular pits of a-plane GaN. The results indicate that the off-axis planes are more electrically active than c-plane and a-plane. Surprisingly, the C-AFM values in triangular pit of the a-plane GaN are much smaller than that in etch pits of the c-plane GaN. The dislocations type related current leakage mechanism is revealed for polar c-plane and nonpolar a-plane GaN films.

Large area synthesis, characterization, and anisotropic etching of two dimensional tungsten disulfide films

Emergent properties of tungsten disulfide at the quantum confinement limit hold promise for electronic and optoelectronic applications. Here we report on the large area synthesis of atomically thin tungsten disulfide films with strong photoluminescence properties via sulfurization of the pre-deposited tungsten films. Detailed characterization of the pre-deposited tungsten films and tungsten disulfide films are performed using microscopy and spectroscopy methods. By directly heating tungsten disulfide films in air, we have shown that the films tend to be etched into a series of triangular shaped pits with the same orientations, revealing the anisotropic etching behavior of tungsten disulfide edges. Moreover, the dimensions of the triangular pits increase with the number of layers, suggesting a thickness dependent behavior of etching in tungsten disulfide films. This method offers a promising new avenue for engineering the edge structures of tungsten disulfide films.

Triangular Si3N4 Nano-scale Pits On The Stepped Si (553) Surface By Ion Induced Reaction

Triangular nano-scale pits (TNPs) of Si3N4 are fabricated by reactive nitrogen ion sputtering using low energy nitrogen ions on the Si (553) surface at 500 °C. The electronic structure of the developing Si3N4 interface was monitored in-situ by Auger Electron Spectroscopy (AES) while the ion beam induced surface reaction was analysed via X-Ray and Ultraviolet photoemission spectroscopy (XPS & UPS), Photoluminescence and Raman spectroscopy. The morphological development of nanoscale pit structures was observed by Scanning Electron Microscopy (SEM). The formation of Si3N4 was identified by AES, with the appearance of the characteristic reacted Si(LVV) peak at 83 eV, while photoemission spectroscopy confirmed the stoichiometry of Si3N4. The valence band maximum was observed to be located at 2.4 eV below the Fermi level. SEM images showed uniformly distributed Si3N4 TNPs with size varying between 250 to 600 nm (length) and 200 to 400 nm (width). Our work underlines the influence of ion energy and substrate temperature and establishes the conditions for the growth of Si3N3 TNPs by ion induced reactive sputtering. Copyright © 2015 VBRI Press.

Morphological and Microstructural Evolution and Related Impurity Incorporation in Non-Polar a-Plane GaN Grown on r-Sapphire Substrates **Supported by the National Natural Science Foundation of China under Grant No 61204006, and the Fundamental Research Funds for the Central Universities under Grant No K50511250002.

Effects of the growth temperature on morphological and microstructural evolution of a-plane GaN films grown on r-plane sapphires by metal organic chemical vapor deposition are investigated by atomic force microscopy and secondary ion mass spectroscopy (SIMS). Surface morphology, structural quality and related impurity incorporation are very sensitive to the growth temperature. A significant difference of yellow luminescence is observed and attributed to the incorporation of carbon into GaN films, which is confirmed by SIMS analysis. Our results show that the sample with triangular-pit morphology has significantly higher concentrations of oxygen than the other sample with pentagon-like pit morphology, which is induced by the existence of an N-face in triangular pits.

Petrographic Studies of Pb-Zn Ore Deposits of Rajpura-Dariba-Bethumni Belt in District Udaipur (Rajasthan) India

The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. In the present work, rock samples taken from Outcrop and Underground Mine of Sindeskar Kalan, Vedanta Group, Rajpura-Dariba-Bethumni Belt which are located at a distance of 76 Kms from Udaipur District (Rajasthan) have been studied. The chief litho units of the group are identified which contain sulfide-bearing calc-silicate and graphite mica schist, dolomite marble, calc-biotite schist and quartzite. Importance to the ore minerals like galena and sphalerite which have been reported in association with the buffer minerals like pyrite and pyrrhotite occurr in the host rocks of the study area. Ore petrography denotes two types of sphalerites, 1) highly deformed and dark brown colour, 2) less deformed and with light yellow colour. Galena shows high reflectance and a network of triangular pits. Pyrite shows high reflectance and anomalous anisotropism because of high brittleness.