Shape Of Etch Pits Research Articles

Dislocations in monoclinic cadmium tungstate CdWO4

Several types of dislocations were found in CdWO4 single crystals. In-grown dislocations slip on (100) plane parallel to [001]. Dislocation pits were revealed in mechanically polished samples on (100) and (010) planes. Based on the results of chemical etching, it was inferred that the lattice dislocations gliding along < 001 > and < 100 > can split into partial dislocations. In the samples annealed at T = 600ºC for 2 h dislocation density decreased noticeably. After annealing shape and sizes of helical etch pits on (100) and (001) planes transform to those typical of lattice dislocations.

Etching Kinetics of (100) Single Crystal Diamond Surfaces in a Hydrogen Microwave Plasma, Studied with In Situ Low‐Coherence Interferometry

A low‐coherence interferometry (LCI) was used to measure in situ the etch rate (ER) of synthetic single crystal (SC) diamonds in H2 microwave plasma, at substrate temperatures in the broad range of 800–1370 °C. The method allows the collection of the kinetic data on a single sample without switching off the plasma. (100)‐orientated SC plates of CVD and IIa type HPHT diamond were systematically etched in pure hydrogen at pressure p = 130 Torr and microwave power density of ≈300 W cm−3. The activation energies Ea of 42 ± 5 and 32 ± 4 kCal mol−1 have been determined for the CVD and HPHT substrates. An enhanced etching rate of a subsurface defected layer with thickness of ∼1 μm or less, formed upon polishing of the samples, is revealed. Surface morphology, roughness, and the shape of etch pits produced by a selective etching of defects, were characterized with optical profilometry. CH and dimer C2 radicals were detected in the H2 plasma with optical emission spectroscopy, as a result of the diamond etching, and the emission intensity of these species was linked to the substrate etch rate.

Effect of Etchant Composition on Surface Morphology of GaAs during Anisotropic Chemical Etching

Micro-/nanostructures formed on semiconductor substrates have been applied in various devices such as electronic devices and biosensors. In particular, III-V semiconductors (e.g., GaAs, GaN, and InP) have received a great attention for realizing future generation optoelectronic devices owing to their excellent optical and electrical properties including high electron mobility and a direct band gap. Recently, we have reported the fabrication of ordered pore arrays, pillar arrays, and nanowire arrays with a high-aspect-ratio in n-type GaAs (111) B substrate by a combination of anodic etching and subsequent chemical etching [1–3]. The controlled GaAs micro-/nanostructures have potential technological and scientific applications in optoelectronics and chemical sensors that require ordered patterns, high device densities, and high surface-to-volume ratios. In this study, we investigated the effects of etchant composition on the orientation-dependent surface morphology of GaAs during anisotropic chemical etching using various types of etchants. p-type GaAs (111) B was mainly used as a substrate. To control the reactive sites during chemical etching, the photoresist layer with the honeycomb-like openings of 3 μm periodicity was applied as a mask, as described in our previous report [1]. The GaAs substrates coated with a photoresist mask were immersed in various types of etchants consisted of acid (H2SO4, H3PO4, HF) and oxidant (KMnO4 , H2O2) at 20°C. When a mixture of 2 mol dm−3 H2SO4 and 0.05 mol dm−3 KMnO4 was used as an etchant, etch pits having curved bottom and hexagonal aperture were formed (Fig. 1a). The diameter and depth of pits were 1.7 µm and 0.6 µm, respectively. Although pore diameter increased with increasing etching time from 30 s to 150 s, the profile shape of etch pits was not clear (Fig. 1b). However, when KMnO4 concentration increased to 0.2 mol dm−3, anisotropic etching proceeded obviously, resulting in the formation of pit arrays with equilateral-triangular aperture depending on crystal plane of {100} (Fig. 1c). On the other hand, shallow etch pits with hexagonal aperture were formed by chemical etching for 30 s using 0.05 mol dm−3 H2O2 as an oxidant instead of KMnO4 (Fig. 1d). With further chemical etching for 300 s, the diameter of etch pit increased causing lateral etching (Fig. 1e). However, the obtained etch pits were shallower than that of pits formed using KMnO4 of the same concentration despite longtime etching. These results indicate that etching rates for each crystal plane are strongly affected by the type and concentration of oxidants. Correlation between the etchant composition and orientation-dependent surface morphology of GaAs after chemical etching will be discussed in detail. [1] H. Asoh, S. Kotaka and S. Ono, Electrochem. Commun., 13, 458–461 (2011). [2] S. Ono, S. Kotaka and H. Asoh, Electrochim. Acta, 110, 393–401 (2013). [3] H. Asoh, S. Kotaka and S. Ono, Mater. Res. Express, 1 045002 (2014). Figure 1

Experimental study of hydrogen plasma etching of (1 0 0) single crystal diamond in a MPACVD reactor

Hydrogen plasma etching of (100) surfaces of single crystal diamonds were investigated. Etching rates, surface morphology of the etched diamond samples and shape of etch-pits were analyzed. These experiments demonstrated that the etching rate increases exponentially with increasing substrate temperature, strongly depends on crystal surface orientation and increases with an increasing vicinal angle. The activation energy for the etching process on (100) diamond was determined (Ea=45.4±4.5kcal/mol). Hydrogen plasma etching could be used for revealing substrate defects and preparing substrate surface prior to CVD growth.

Influence of Additives on Alkaline Etching of Silicon(111)

Apart from temperature and alkaline concentration, the surface morphology of silicon surfaces after wet chemical etching is also profoundly influenced by the presence of additives in the etchant solution. In this study, the influence of several organic (aprotic, protic, and ionic) additives on the density and shape of etch pits on etched Si-(111) surfaces is investigated using optical microscopy and the Lichtfigur technique. For all the additives used, the number density of the pits increases by 1−3 orders of magnitude. The triangularity of the pit shape, expressed by a dimensionless number, Rab, increases substantially as well. These alterations are attributed to local desolvation of reaction products by the organic additives in a thin “surfactant” layer in the vicinity of the silicon surface. Chemisorption of additive molecules does not play a role in this process.

Thermal Etching of 4H-SiC(0001) Si Faces in the Mixed Gas of Chlorine and Oxygen

4H-SiC (0001)Si faces have been thermally etched at atmospheric pressure in a mixed gas of oxygen (O2) and chlorine (Cl2). Etch pits with definite shapes appeared independently of the conduction type and doping level of SiC. The types of dislocation can be easily identified from the shape of etch pits. Facets in etch pits of screw and edge dislocations consist of specific {110n} pyramidal planes. In dislocation-free areas, etching rate depended on Cl2 flow rate, temperature and the off-angle of the substrate. The activation energy from the Arrhenius plots of etching rate was about 54 kcal/mol, which did not change at O2/Cl2=0-1. After the thermal etching in dislocation-free areas, many concavities were formed. On the basis of these results, etching mechanisms are discussed.

Ion beam modifications of defect sub-structure of calcite cleavages

Experimental investigations on the defect sub-structure and surface modifications, brought about by He+ ion-bombardment of calcite cleavages (100), have been carried out. Optical and scanning electron microscopic investigations revealed drastic modifications on the surface morphology, local symmetry and defect concentration. Additional structural defects on ion-bombardment of calcite surfaces also have been observed. Changes in shape and form of chemical etch pits are found to be a function of ion-beam energy, as studied by optical microscopy. Radiation damage in calcite has been attributed mainly due to desorption of CO −23 ions from the calcite surfaces, on irradiation. Measurements of surface conductivity on irradiated calcite surfaces have been made employing a four-probe technique. Enhancement of surface conductivity has been considered to be due to an increase in concentration of CO −23 ions formed, on ion irradiation and subsequent thermal stimulation. Planar plastic anisotropy has been studied on irradiated calcite cleavages by measurement of microhardness.

Selective Etching of Micropipes During Initial Homoepitaxial Growth Stage on Nearly On-Axis 4H-SiC Substrates

The initial homoepitaxial growth behavior on nearly on-axis 4H-SiC substrates was investigated. We have observed circular etch pits on the surface of on-axis substrate in the presence of source gases. However, there were no circular etch pits on the surface of off-axis substrates. In addition, the surface etched by H2 gas did not show circular etch pits even on nearly on-axis substrates. The shape of the circular etch pits was similar to spiral one. The initial growth behavior of epilayers was also investigated with various C/Si ratios of source gases (0.6&lt;C/Si&lt;2.0). The circular etch pits were observed independent of the source gas ratio. It implies that the source gases promote the selective etching, while the H2 gas etches SiC defect-independent. The spiral shape of etch pits seems to be produced from the screw dislocation with large burgers vector of micropipes. Therefore, the circular shape etch pits were not observed in an off-axis substrate.

The surface topography of GaN grown on Si (1 1 1) substrate before and after wet chemical etching

Surface topography of GaN layer grown on Si (1 1 1) using metalorganic chemical vapor deposition before and after etching were investigated by plan-view transmission electron microscopy and scanning electron microscopy. Different shape of etch pits appeared on GaN with different thickness, and typical pits which reflected the dislocation interaction always occurred at the junction of sub-grains. The mechanism was discussed.

Defect analysis in Czochralski-grown Yb:FAP crystal

Growth-induced defects in Yb:FAP crystals grown by the Czochralski method have been investigated by optical microscopy, chemical etching, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Anisotropic etching features have been observed on two FAP crystal planes: (0 0 0 1) and ( 1 0 1 ¯ 0 ) . The shape of etch pits on the (0 0 0 1) plane is hexagonal, while the etch pits on the ( 1 0 1 ¯ 0 ) plane have a variety of irregular shapes. It is also found that the density of etch pit varies along the boule. Based on the experimental observations, the formation mechanisms of growth defects are discussed, and methods for reducing the growth-induced defect concentration is proposed.

3D computation of the shape of etched tracks in CR-39 for oblique particle incidence and comparison with experimental results

Computation of the shape of etch pits needs to know the varying track etch rate along the particle trajectories. Experiments with alpha particles and 7 Li ions entering CR-39 detectors under different angles showed that this function is not affected by the inclination of the particle trajectory with respect to the normal on the detector surface. Track formation for oblique particle incidence can, therefore, be simulated using the track etch rates determined for perpendicular incidence. 3D computation of the track shape was performed applying a model recently described in literature. A special program has been written for computing the x, y, z coordinates of points on the etch pit walls. In addition, the etch pit profiles in sagittal sections as well as the contours of the etch pit openings on the detector surface have been determined experimentally. Computed and experimental results were in good agreement confirming the applicability of the 3D computational model in combination with the functions for the depth-dependent track etch rates determined experimentally.

The effect of magnetic field on the shape of etch pits of paracetamol crystals

In the present study we investigate the effect of magnetic field on the shape of etch pits of the crystals of p-hydroxyacetanilide (paracetamol), which is widely used in pharmacy as antipyretic, antiphlogistic medicine. It was discovered that the magnetic field (H=0.5 T, τ=15 min) changes the morphology of etch pits and shifts dislocations in paracetamol crystal. Activation energy of the changes induced by the action of the magnetic field was determined to be 63 kJ/mol, which is comparable with the energy of hydrogen bonds in crystal lattice.

ビッカース圧子によるサファイア単結晶の（０００１）および（１０￣１０）面での破壊と変形

Abrasive wear on the contacting surface of machine elements proceeds via penetration or scratch of the sharp asperity tips or wear debris. In order to elucidate the mechanism of wear, it is firstly necessary to have knowledge on the microscopic deformations such as dislocations, minute cracks and slips induced by such penetrations. In the present study, indentation tests using a Vickers indenter were carried out on the (0001) and (1010) crystal faces of Sapphire (Al2O3) single crystals.The diagonal of an indenter was oriented in two ways: parallel and 45° against the [1010] direction on the (0001) face, and against the [0001] direction on the (1010) face respectively. The cleaving faces and directions of propagation of the cracks around an indent were estimated. In addition the shape and distributions of etch pits around an indent were examined.The results obtained are summarized as follows:(1) Radial cracks originate in four directions under comparative lower load of 5.0N, and in six directions under higher load of 10.0N on both of the (0001) and (1010) faces. Raptures that form connections with these cracks are also observed.(2) An average length of cracks on the (0001) is longer about 20% in 0° indentation than that in 45° indentation.(3) Cracks and edges of an indent are formed in a curved pattern due to the anisotropic crystal deformation.(4) Twinnings are observed on the (1010) in both 0° and 45° indentations.(5) Noticeable difference in size of indent was not confirmed in 0° between 45° indentation. An average length of the cracks on the (1010) is about 2.0 times as long as that on the (0001).(6) The area around an indent on the (1010) is corroded by etching in similar figure to individual etch pit.

Dissolution of Baryte (001) Observed by Hydrothermal Scanning Force Microscopy

Scanning force microscopy (SFM) provides in situ access to the microtopography of mineral surfaces and its kinematics during dissolution, with monolayer resolution. Informat ion about not only the mechanism of dissolution, but also quantitative data such as the dissolution rate or activation energy can be acquired. However, the lower limit of dissolution rates that can be studied by SFM lies in the range of 10 -9 mol/m2s. Experiments at elevated temperatures (e.g. those requiring elevated pressure) were not possible using commercial microscopes. Therefore, SFM in situ studies were mainly limited to minerals with dissolution rates higher than 10 -9 mol/m2s at near-room temperature. In order to solve this problem, a pressurizable SFM was constructed (Higgins et al., 1998) which allows examination of dissolution kinetics on mineral surfaces beyond the ambient boiling point of water. Here we present kinetic data on the dissolution of baryte (001). Dissolution and growth of baryte is significant in regulating the abundance of solvated Ba in the hydrosphere and has relevance in baryte scale formation in offshore oil wells (Putnis et al., 1995). In deionized water between 90~ and 125~ baryte (001) dissolves by retreat of steps at (001) terraces. The orientation of the steps is parallel to and [010]. The steps occur such that, in alternating half layers (height: c/2), only steps that retreat either in the positive or negative a-direction are stable. In the case that steps retreat in the positive adirection, the [010] steps are only stable retreating in the negative a-direction, and vice versa. Therefore, steps generated by pits form a triangle pointing in alternating half layers in the positive and negative adirections alternately (Fig. la). This alternating pattern can be attributed to the 21 screw axis parallel to [001] (Putnis et al., 1995). Between 90~ and 125~ steps retreat about twice as fast as [010] steps. Due to these different velocities and the alternating step pattern, etch pits, probably generated by linear defects, have a six-sided shape elongated in [0101 (Fig. lb,c). By measuring step velocities between 90~ and 125~ the activation energy for step retreat (Es) can be determined. On baryte (001) we found Es for retreat of steps to be 34 _+ 4 kJ/mol and for [010] steps to be 31 _+ 6 kJ/mol. Due to the error ranges, different activation energies for different steps cannot be resolved. However, judging by the shape of etch pits at room temperature reported by Putnis et al. (1995), a higher activation energy for the retreat of steps seems to be likely. Considering the step velocities and the slopes of the pit walls, the frequency of generating monolayer pits within deep etch pits can be calculated. By this frequency the dissolution rate of a surface consisting exclusively of pit walls can be determined (Jordan and Rammensee, 1998). At 90~ (1250C) this rate is about 7 x 10 7 mol/m2s (1 x 10 .6 mol/m2s). The rates reasonably agree with literature data determined by solution chemistry (1.12 x 10 -7 mol/m2s, 90~ pH 5.7; Dove and Czank, 1995), bearing in mind that due to the fiat bottoms of the etch pits, our rates must be regarded as maximum rates. Figure 1 d shows the baryte (001) surface during dissolution on a large scale. Low dissolution rate areas cover at least 30% of the surface in this scan area. As in the case of the step velocities, it is possible to calculate the activation energy (Ep) by the temperature dependence of the maximum rates (about 10 kJ/mol). However, Ep is primarily the activation energy for monolayer pit formation within etch pits. If step retreat does not contribute to the macroscopic activation energy for dissolution (Em), as observable e.g. in bulk experiments, Ep reflects Era. However, the actual rate and, therefore, the macroscopic activation energy (Em) are determined by the rate of step formation and the step velocities (via the expansion of fast dissolving areas such as pit walls). In comparison to room temperature (Putnis et al.,

Experimental and Theoretical Treatment of Molecular-scale Mechanisms of Crystal Growth on Baryte

We have used Atomic Force Microscopy in a fluid cell with close to molecular resolution to observe different growth types such as two-dimensional nucleation, anisotropic effects during layer-by-layer growth and spiral growth with structure-induced selfinhibition on different faces of baryte. In combination with computer simulations, we were able to resolve these growth mechanisms and their relative importance for overall growth at an atomic level. This knowledge allows us to critically test the relevance of classical crystal growth theories, specifically the relationship between crystal growth mechanisms and fluid supersaturation as well as the effect of surface crystal structure on growth morphology. According to the classical BurtonCabrera-Frank (BCF) theory, we found that spiral growth is the predominant mechanism at the lowest supersaturation, whereas two-dimensional nucleation prevails at somewhat higher supersaturations. Even though Periodic-Bond-Chain (PBC) theory can explain some of the directions of terminating steps of growth islands, computer simulations involving ionic attachment energies are necessary to explain anisotropic effects into different growth directions and finally explain the sector-like shape of these islands. We also demonstrate that this effect leads to a self-inhibition of spiral growth on baryte, although spiral growth is widely regarded as the most important growth mechanism under near-equilibrium conditions. In order to understand the mechanisms of crystal growth at different conditions (e.g. supersaturation, pH), for different minerals and in the presence of different growth inhibitors/chelators, it is necessary to be able to model these processes by using dynamic molecular modelling techniques. In addition to the deterministic approach that explains the shape of the growth islands, we developed a semistatistical Monte-Carlo model which allows to calculate growth of processes such as dynamic attachment/ dissolution, surface diffusion, relaxation of the surface structure and migration of ions in the nearsurface region. The difference between the different minerals (BaSO4, SrSO4, PbSO4) then only arises from applying the respective sets of ionic potentials that were derived from structural data, elastic properties and phonon frequencies of the respective minerals. Once crystal growth in a pure BaSO4 solution is calculated, we introduced the presence of different organic growth inhibitors and chelators as an additional parameter. These play a crucial role in nature and for geotechnical applications. Molecular modelling techniques can be applied to calculate the surface sites to which the organic molecules will be bonded. These processes influence the rates of growth and dissolution and change the shape of growth islands and etch pits as can be verified by using AFM.

Morphology and surface properties of YBCO and TBCCO thin films: influence of etching processes

Results concerning the study of the morphology and the surface chemical properties of epitaxial YBCO and highly oriented TBCCO films before and after wet etching processes are reported. X-ray photoemission spectroscopy, Auger electron spectroscopy and scanning electron microscopy are employed to get information on the surface contamination and on the defects of the samples. The chemical modifications of surfaces and the shape of etch pits are discussed.

A fractographic study on tensile fracture surface of duplex microstructure TiAl alloy

The mechanical properties of TiAl alloys depend significantly on the microstructure. Introducing duplex microstructure (DM) has improved ambient tensile plasticity and strength of TiAl alloys. To reveal the fracture micromechanism and the function of Lamellar colonies in the process of deformation, detailed fractography and cleavage crystallography are needed. Etch pitting is an efficient method to identify the crystalline features of fracture surfaces, since the shape of etch pits formed on the fracture surface depends on the orientation of the fracture facets and the orientation of the etch pit faces. The relationship between the morphologies of the fracture surface and the orientation of fracture facets in the microstructure can be determined through SEM observation of the fracture surface being etch pitted. The objective of this article is to present the results of a fractographic investigation on tensile fracture surfaces of a DM TiAl alloy through SEM observation and etch pitting technique.

Microtextural controls of weathering of perthitic alkali feldspars

The relationship between the microtexture and dissolution behaviour of fresh, HF acid-etched and naturally weathered alkali feldspar phenocrysts from the Lower Devonian Shap granite has been investigated by SEM and TEM. A novel resin impregnation technique has revealed the three dimensional shape and interconnectivity of etch pits beneath the weathered crystal surface. Further electron microscope work suggests that Shap phenocrysts are representative of the alkali feldspar in the protolith of many soils. Fresh and unweathered Shap feldspars have a complex microtexture, comprising areas of pristine cryptoperthite and lamellar microperthite cross-cut by volumes of microporous altered feldspar or “patch perthites.” Cryptoperthites are made up of <75 nm wide albite exsolution lamellae (platelets) in tweed orthoclase, whereas lamellar microperthites contain >75 nm wide albite films. The platelets are coherent, but albite films have numerous edge dislocations along their interface with orthoclase; (001) and (010) cleavage surfaces intersect ∼2–3 edge dislocations/μm 2. In three dimensions, these edge dislocations form an orthogonal net in the “Murchison plane” of easy fracture, close to (601). Patch perthites are irregular, semicoherent to incoherent intergrowths of albite and irregular microcline subgrains, with ∼0.65-0.70 sub-μm to μm-sized pores/μm 2. Microporous patch perthites form by dissolution-reprecipitation reactions with magmatic or hydrothermal fluids and pores are present before the alkali feldspars enter the weathering regime. Dissolution of Shap feldspars during natural weathering and laboratory acid etching is controlled by their microtexture, especially by dislocations and exsolution lamellae. The core and strain energy associated with dislocation outcrops on (001) and (010) cleavage surfaces promotes rapid dissolution at those sites and formation of nn-sized etch pits after <30 s of laboratory etching with HF acid vapour. With progressive HF etching, crystallographically controlled differences in the reactivity of etch pit walls cause them to expand more rapidly into orthoclase than albite. Naturally weathered feldspars were collected from the glacial erratic boulders, fine gravels surrounding exposed granite surfaces, and from peat soil overlying the granite. During natural weathering, etch pits on microperthites enlarge almost exclusively by dissolution of albite and resin casts demonstrate that they can penetrate ≥15 μm below the cleavage surface, forming an interconnecting, ladder-like grid of submicrometer wide channels in the Murchison plane. Coherent albite platelets and volumes of albite between dislocations in films dissolve uniformly, but faster than orthoclase. This is probably because the albite lamellae have significant elastic coherency strain, but this is much less, per unit volume of albite, than the core and strain energy associated with edge dislocations. Patch perthites etch in HF vapour and weather rapidly in nature to produce a honeycomb-like texture of interconnecting nanometer- to micrometer-sized pits, which nucleate at preexisting micropores or incoherent subgrain boundaries. The size and density of etch pits on microperthite surfaces, which is determined by rates of growth and coalescence, may be a useful progress variable for natural and experimental dissolution. All alkali feldspars are highly heterogeneous materials whose chemical composition and microtexture can vary on a submicrometer scale. These microtextures are critical variables with regard to the origin of surface roughness of fresh and weathered grains, the controls on absolute dissolution rates and why they commonly change over time, the nonlinear variation of dissolution rate with grain size, the ratio of alkali ions released into solution, and disparities between laboratory dissolution rates and those observed in the field.

Atomic force microscopic study of directional SrSO 4(001) surface and its etching property

Different step structures were observed with atomic force microscopy (AFM) on SrSO 4(001) cleaved in air in two ways. Monolayer steps were observed when the crystal was cleaved by wedging open a crack. On the other hand, bilayer steps were observed when it was cleaved by giving a blow on a knife edge placed along the a-axis on a crystal face. In the latter case, the cleavage proceeded under slightly misoriented tensile stress, favoring formation of bilayer cleavage steps due to alternating directions of the bonds connecting (001) ionic layers. Directionality in the arrangement of the ions at the (001) surface was reflected on the shape of etch pits formed by dissolving the surface in electrolyte solutions. Relative stabilities of the steps surrounding the bow-shaped pits are discussed. The directionality of the surface has potential application in constructing two-dimensional assemblies of functional molecules.

Influence of In Atoms on the Shape of Dislocation Etch Pits in LEC In-Doped GaAs Crystals

The shapes of dislocation etch pits formed by molten KOH on {001} LEC GaAs crystal wafers doped with various degrees of In content were investigated. The pit shape was found to change depending on the amount of the doped In. The geometrical relation between the pit shapes and the direction of the composed pit walls is discussed. The formation mechanism of each wall is examined microscopically regarding the explanation of the pit-shape variation. The pit-shape variation is interpreted to be due to an increase in the etch rate in only the Ga{111} planes; this is caused by the In atoms substituting the Ga atoms.