Triangular Etch Pits Research Articles

Microrelief of Rounded Diamond Crystals as an Indicator of the Redox Conditions of Their Resorption in a Kimberlite Melt

We conducted a detailed study of the morphology of diamond crystals partially dissolved in a water-bearing kimberlite melt at pressure of 6.3 GPa, temperature of 1400 °C, and two oxygen fugacities (fO2) corresponding to the Re-ReO2 buffer and near the magnetite–hematite (MH) buffer. The triangular etch pits on the {111} faces, which formed during experimental diamond dissolution, were found to completely correspond to negative trigons on natural diamond crystals in the shape and sidewalls inclination angle. Furthermore, two experimental fO2 values were associated with two relief types of the rounded tetrahexahedroid surfaces typical of natural rounded diamonds. Therefore, the surface microrelief on rounded natural diamond crystals was concluded to be an indicator of the redox conditions of natural diamond resorption.

Microscopic Kinetics of Heat-Induced Oxidative Etching of Thick MoS2 Crystals

We have studied the kinetics of microscopic heat-induced oxidative etching in the case of thick, mechanically exfoliated, geological MoS2 crystals in air. We have measured spatial dimensions of microscopically obtained triangular etch pits during a series of sample heating increments at a given temperature. The data has been collected for the samples heated at 320, 350, 370 and 390 °C. Using our data we have extracted an Arrhenius apparent activation energy, Ea = 1.15 ± 0.25 eV, as well as an Arrhenius kinetic constant, A= 10x s-1 with x = 9,09 ± 2,03. The obtained value of Ea compares extremely well with another study of oxidative etching, but done via in situ Raman spectroscopy on an collection of thin MoS2 flakes. We notice that apparent activation energy relates to a weighted average of microscopic Arrhenius-like processes. It might need a correction due to yet unknown fractions of removed MoOx species at the investigated temperatures. Based on the existing literature the most expected reaction is a s...

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.

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.

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.

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.

Chlorite topography and dissolution of the interlayer studied with atomic force microscopy

The weathering of rocks is a process important for the understanding of soil formation as well as a general understanding of the interaction between litho- and hydrosphere. Phyllosilicates in general are of special importance for the understanding of weathering processes due to their abundance in rocks and soils. A common phyllosilicate in soils is chlorite, which has a structure composed of a combination of two distinct layers, the tetrahedral-octahedral-tetrahedral (TOT) and the interlayer (i.e., the octahedral layer between TOT layers). In this study, the morphology and dissolution of chlorite in pure water has been visualized using atomic force microscopy. Upon cleavage, the TOT layer shows atomically flat terraces and steps, while the interlayer presents strips and voids. In pure water, dissolution channels and equilateral, mono-oriented triangular etch pits form in the interlayer and lead to progressively increased solubilization. Dissolution channels are proposed to originate from structural defects, while a conceptual model is discussed to explain the presence of triangular etch pits. In this model, their formation is driven by the different reactivity of the two octahedral configurations along the etch pits. It is not currently known which of these is the most stable configuration, however we propose arguments that point toward a specific orientation. The conceptual model is supported by experimental data and is potentially applicable to all mineral structures constituted by continuous octahedral layers.

Anisotropic Etching of Atomically Thin MoS2

Exposure to oxygen at 300–340 °C results in triangular etch pits with uniform orientation on the surfaces of atomically thin molybdenum disulfide (MoS2), indicating anisotropic etching terminating on lattice planes. The triangular pits grow laterally with oxidation time. The density of pits scarcely depends on oxidation time, temperature, and MoS2 thickness but varies significantly from sample to sample, indicating that etching is initiated at native defect sites on the basal plane surface rather than activated by substrate effects such as charged impurities or surface roughness. Raman spectroscopy confirms that oxygen treatment produces no molybdenum oxide (MoO3) below 340 °C. However, upon oxidation above 200 °C, the Raman A1g mode upshifts and the linewidth decreases, indicating p-type doping of MoS2. Oxidation at 400 °C results in complete conversion to MoO3.

SiOx nanostructures grown under atmospheric pressure

Using a vapor liquid solid method with Au as the catalyst and a Si substrate as the Si source, high temperature annealing under atmospheric pressure resulted in a series of SiOx nanoflowers and nanobangles. The growth process and mechanism were investigated by comparing the morphologies of the nanoflowers grown using different annealing conditions. Triangular etch pits over ten micrometers in size were found scattered on the substrates, around which different SiOx nanoflowers had developed dozens of micrometers away. Photoluminescence measurements of the nanoflowers demonstrated that the luminous intensities increased with the increasing length and amount of the nanoflowers' petals.

Analysis of thermal cycle-induced dislocation reduction in HgCdTe/CdTe/Si(211) by scanning transmission electron microscopy

High threading dislocation densities limit the operability of infrared focal plane arrays based on large lattice-mismatched heterostructures such as HgCdTe/CdTe/Si. Recently it has been shown that post-growth thermal cycle annealing can routinely reduce the surface etch pit density from >5×106cm−2 to as low as 9×105cm−2. To fully exploit the procedure, a deeper understanding of the inherent dislocation dynamics is needed. In this work, we employ scanning transmission electron microscopy to analyze cross-sectional samples of HgCdTe/CdTe/Si prepared using site-specific focused ion beam milling. A key factor in this work is the use of defect decorated samples, which has allowed for a correlation of surface etch pits to dislocation segments observed in cross-section images. We have observed that the previously reported oval-shaped etch pits are likely associated with Shockley partial type dislocations, and that triangular etch pits are associated with perfect dislocations. This suggests the likelihood that interaction between mobile Shockley partial and other dislocation types are responsible in part for the observed reduction in top surface etch pit density. These studies provide a deeper understanding of dislocation reduction processes which are critical for the realization of high performance infrared detectors based on low-cost, lattice-mismatched substrates.

Crystal growth and optical studies on a semi organic nonlinear optical material for laser blue-green generation

In recent days amino acid single crystals are gaining importance due to good optical behavior. The title compound l-alanine lithium chloride (LAL), a semi-organic nonlinear optical material has been grown by slow evaporation technique. The material was characterized by single crystal XRD and FT-IR spectroscopic analysis. The growth mechanism and surface features are investigated by optical microscopic techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM). The etching study indicates the occurrence of different types of etch pit patterns like striations, triangular etch pits and step like pattern. The UV–Vis transmittance spectrum shows that it has a good transmittance in the entire visible region with the lower cutoff wavelength at 252nm. Fluorescence spectral studies were carried out for LAL crystal. The SHG conversion efficiency and laser damage threshold were measured using an Nd:YAG laser (1064nm).

Cobalt‐Mediated Crystallographic Etching of Graphite From Defects

Herein is reported a study of Co-assisted crystallographic etching of graphite in hydrogen environment at temperatures above 750 °C. Unlike nanoparticle etching of graphite surface that leaves trenches, the Co could fill the hexagonal or triangular etch-pits that progressively enlarge, before finally balling-up, leaving well-defined etched pits enclosed by edges oriented at 60° or 120° relative to each other. The morphology and chirality of the etched edges have been carefully studied by transmission electron microscopy and Raman analysis, the latter indicating zigzag edges. By introducing defects to the graphite using an oxygen plasma or by utilizing the edges of graphene/graphite flakes (which are considered as defects), an ability to define the position of the etched edges is demonstrated. Based on these results, graphite strips are successfully etched from the edges and graphitic ribbons are fabricated which are enclosed by purely zigzag edges. These fabricated graphitic ribbons could potentially be isolated layer-by-layer and transferred to a device substrate for further processing into graphene nanoribbon transistors.

Microscopic Study of Hydroxyapatite Dissolution As Affected by Fluoride Ions

Fluoride ions play a critical role in preventing tooth decay. We investigated the microscopic effects of fluoride ions on hydroxyapatite (100) surface dissolution using in situ atomic force microscopy. In the presence of 10 mM NaF, individual surface step retraction velocities decreased by about a factor of 5 as compared to NaF-free conditions. Importantly, elongated hexagonal etch pits, which are characteristic of (100) surface dissolution, were no longer observed when NaF was present. The alteration of pit shape is more distinct at a higher NaF concentration (50 mM) where triangular etch pits evolved during dissolution. Furthermore, in a fluoride concentration typical for tap water (10 μM), we observed roughening of individual step lines, resulting in the formation of scalloped morphologies. Morphological changes to individual steps across a wide range of fluoride concentrations suggest that the cariostatic capabilities of fluoride ions originate from their strong interactions with molecular steps.

Characteristics of the dislocations in CdZnTe crystals revealed by etch pits

The configurations and distributions of triangular pyramid etch pits on the (1 1 1)B face of CdZnTe revealed by Everson etch were studied using a scanning electron microscope (SEM), an optical microscope and a confocal laser scanning microscope (CLSM). Six types of triangular pyramid etch pits with different configurations were observed, one for the first time. These etch pits correspond to threading dislocations in the materials. By measuring the depths and orientations of the pit tips as well as the side lengths of the triangular pits on the surface, the orientations of the dislocations were determined. They are 〈2̄ 1̄ 1〉, 〈1̄ 3̄ 1̄〉, 〈1̄ 1̄ 1〉, 〈1 5̄ 1〉, 〈0 3̄ 1〉 and 〈1̄ 1̄ 0〉 for the six types of triangular pyramid etch pits. Among them, dislocations with 〈2̄ 1̄ 1〉, 〈1̄ 1̄ 1〉, 〈1 5̄ 1〉 and 〈0 3̄ 1〉 orientations have higher densities in CdZnTe materials. It was also found that the proportion of triangular pyramid etch pit to total etch pits is variable for different CdZnTe wafers and related to the stoichiometry of CdZnTe melt. These results show that Everson etch can reveal more information of CdZnTe materials than etch pit density (EPD).

Etching and Micro-Topographical Studies of Barium Oxalate Crystals Grown in Agar Gel

In the present study, the selection of an etchant for a particular crystal was purely made on empirical basis. The gel grown barium oxalate crystals were etched by HCl, HNO3, BaCl2, NH4Cl, and NH4Cl-HCl solutions. Micro-topographical studies have been made and it was found that elongated triangular etch pits and pits within pits were formed. Rectangular growth layers in the form of staircase and leaf like dendrite pattern were seen. Kinetics of etching was studied. Quantitative estimation of dissolved crystals in etchants was used for the determination of activation energy of reaction and pre-exponential factor with the help of Arrhenius equation.

In situ Atomic Force Microscopy study of dissolution of the barite (0 0 1) surface in water at 30 °C

The dissolution behavior of the barite (0 0 1) surface in pure water at 30 °C was investigated using in situ Atomic Force Microscopy (AFM), to better understand the dissolution mechanism and the microtopographical changes that occur during the dissolution, such as steps and etch pits. The dissolution of the barite (0 0 1) surface started with the slow retreat of steps, after which, about 60 min later, the < hk0> steps of one unit cell layer or multi-layers became two-step fronts (fast “f” and slow “s” steps) with a half-unit cell layer showing different retreat rates. The “f” step had a fast retreat rate (≈(14 ± 1) × 10 −2 nm/s) and tended to have a jagged step edge, whereas the “s” step (≈(1.8 ± 0.1) × 10 −2 nm/s) had a relatively straight front. The formation of the “f” steps led to the formation of a new one-layer step, where the front of the “s” step was overtaken by that of the immediate underlying “f” step. The “f” steps also led to the decrease of the < hk0> steps and the increase in the percentage of stable steps parallel to the [0 1 0] direction during the dissolution. Etch pits, which could be observed after about 90 min, were of three types: triangular etch pits with a depth of a half-unit cell, shallow etch pits, and deep etch pits. The triangular etch pits were bounded by the step edges parallel to [0 1 0], [1 2 0], and [ 1 2 ¯ 0 ] and had opposite orientations in the upper half and lower half layers. Shallow etch pits that had a depth of two or more half-unit cell layers had any two consecutive pits pointing in the opposite direction of each other. The triangular etch pit appeared to grow by simultaneously removal of a row of ions parallel to each direction from the three step edges. At first, deep etch pits were elongated in the [0 1 0] direction with a curved outline and then gradually developed to an angular form bounded by the {1 0 0}, {3 1 0}, and (0 0 1) faces. The retreat rate of the (0 0 1) face was much slower than those of the {1 0 0} and {3 1 0} and tended to separate into two rates ((0.13 ± 0.01) × 10 −2 nm/s for the deep etch pits derived from a screw dislocation and (0.07 ± 0.01) × 10 −2 nm/s for those from other line defects). The changes in the dissolution rate of a barite (0 0 1) surface during the dissolution were estimated using the retreat rates and densities of the various steps as well as the growth rates, density, and areas of the lateral faces of the deep etch pits that were obtained from this AFM analysis. Our results showed that the dissolution rate of the barite (0 0 1) surface gradually increased and approached the bulk dissolution rate because of the change in the main factor determining the dissolution rate from the density of the steps to the growth and the density of the deep etch pits on the surface.

Fluorite dissolution at acidic pH: In situ AFM and ex situ VSI experiments and Monte Carlo simulations

Dissolution of the fluorite (1 1 1) cleavage surface was investigated by means of in situ atomic force microscopy (AFM) and ex situ vertical scanning interferometry (VSI) experiments at pH range 1–3 in HCl solutions. Surface retreat was quantified at different pH values, yielding dissolution rates that were used to derive an empirical rate law for fluorite dissolution: Rate fluorite ( mol m - 2 s - 1 ) = 2.0 ± 0.4 × 10 - 6 · ( a H + ) 0.38 ± 0.07 where a H + is the proton activity. The influence of Δ G on fluorite dissolution rate at pH 2 was investigated by means of AFM and VSI surface measurements and flow-through experiments with powdered fluorite. The fluorite dissolution rate decreases non-linearly with increasing Gibbs energy (Δ G) and a dissolution plateau is obtained at Δ G ⩽ −7 kcal mol −1. This Δ G effect can be expressed with a rate law of the form Rate fluorite mol m - 2 s - 1 = k · a H + n 1 - exp - 4.7 × 10 - 2 · | Δ G | RT 1.41 ± 0.24 An alternative form based on a formulation making use of a Temkin number is also possible Rate fluorite mol m - 2 s - 1 = k · a H + n 1 - exp Δ G 8 RT Dissolution proceeds by formation of equilateral triangular etch pits with trigonal pyramidal morphology and emanation of stepwaves that are responsible for the surface retreat. The results of Monte Carlo simulations are consistent with this reaction mechanism.

Morphological and chemical optimization of ex situ NH4F (40%) conditioned Si(111)-(1×1):H

Synchrotron radiation photoelectron spectroscopy was employed to investigate the chemical state of Si(111) surfaces upon anisotropic etching in concentrated NH4F solution. Minute amounts of oxidized silicon were detected and attributed to the fast Si–H–OH formation at atomic steps. Combining in situ optical and scanning probe techniques, consecutive chemical treatments were developed to achieve optimized morphological and chemical surface properties. Native oxides and a stressed SiO2/Si layer are removed by a two-step NH4F treatment leading to a terraced surface without triangular etch pits; subsequently, silicon in the Si1+/2+/3+ valence states is dissolved by HF (50%) while the surface topography is preserved.

Dissolution of Brucite on the (001) Surface at Neutral pH: in situ Atomic Force Microscopy Observations

AbstractThe dissolution of brucke, Mg(OH)2, on the (001) surface was investigated using in situ atomic force microscopy in solutions at near-neutral pH. Dissolution proceeded by the formation of crystallographically oriented triangular etch pits with monolayer step and expansion of the pits. The sides of the triangle are parallel to the [100], [110] and [010] directions of the brucite structure, and the orientation of lines from the center of the triangle to the three apices are along the [210], [1¯10]$[\bar 110]$ and [1¯2¯0]$[\bar 1\bar 20]$ directions. This orientation may produce pit edges where OH groups coordinate to two Mg2+. Although triangular etch pits with monolayer depth formed mostly at random on the (001) surface, concentric pits penetrating several layers were also observed. Etch pits with spiral steps were rarely observed. Coalescence of the pits resulted in stranded terraces that diminished in size rapidly and formed a rounded irregular form. The step-retreat velocity around the triangular pit is 0.015–0.04 nm/s at pH 5–8. The retreat velocity around the stranded terraces was about three times more rapid than that around the triangular etch pits.