Observation Of Etch Pits Research Articles

Observation of Etch-Pits and LAGB Configurations During Ambient Creep of Ti-6Al-4V Alloy

The present work describes the microstructural features of alloy Ti-6Al-4V during constant stress creep at ambient temperature. Samples tested at 800 and 900 MPa stress levels exhibit the presence of etch-pits and/or voids. The ambient creep strain increases with an increase in applied stress due to higher strain rate sensitivity at higher stresses. A high density of low-angle grain boundaries is noticed in and around etch-pits in the creep-tested specimens due to occurrence of slip. The inverse pole figure obtained by EBSD indicates prismatic texture as the main deformation component in the creep-tested specimens.

Contribution of siderite–water interaction for the unconventional generation of hydrocarbon gases in the Solimões basin, north-west Brazil

Hydrocarbon gases with unconventional carbon isotopic signatures were observed in the Solimões sedimentary basin in north-west Brazil. Siderite contents measured with a new Rock-Eval methodology in the drill-cuttings samples of the Famenian source rock were found to decrease with the increase of gas maturity and with the occurrence of the gas isotopic anomalies. Triassic diabase intrusions induced heating of the source rock, which likely resulted in the gradual oxidative dissolution of siderite as suggested by the observation of etch pits on the siderite surfaces. It is proposed that ferrous iron from the carbonate was involved in a redox reaction with water producing ferric iron and H2, then reducing CO2 and yielding an inverse correlation between siderite content and gas maturity. Alternatively, hydrogenation of highly mature kerogen by H2 derived from siderite could explain the production of 13C-rich CH4. Mass balance considerations suggest that these mechanisms may account for a significant fraction of the hydrocarbon gases generated from the Famenian source rock in the Solimões basin.

Xe- and U-tracks in apatite and muscovite near the etching threshold

Ion irradiation of a wedge-shaped Durango apatite backed by a mica detector allows investigating ion track ranges and etching properties at different points along the tracks. Transmission profiles obtained by irradiation with 2×106cm−2 11.1MeV/amu 132Xe and 2×106cm−2 11.1MeV/amu 238U parallel to the apatite c-axis correspond to ranges calculated with SRIM (Xe: 76.3μm; U: 81.1μm). However, the measured profiles show much greater etchable track-length variations than the calculated longitudinal straggles. The probable cause is that the length deficit exhibits significant variation from track to track. The measured length deficit in muscovite is in agreement with most existing data. In contrast, the length deficit in apatite appears to be close to zero, which is in conflict with all earlier estimates. This probably results from the etching properties of the apatite basal face, which permit surface-assisted sub-threshold etching of track sections in the nuclear stopping regime. These sections are not accessible from the opposite direction, i.e. by etching towards the endpoint of the tracks or in the direction of the ion beam. This conclusion is supported by the fact that linear dislocations are revealed in apatite basal faces and by the observation of imperfect etch pits that are separated from the etched ion track channel by a section that appears unetched under the microscope.

Observation of etch pits in Fe-36wt%Ni Invar alloy

To indirectly investigate the dislocation behavior of Fe-36wt%Ni Invar alloy by the etch pit method, polished Invar specimens were etched by a solution containing 4 g copper sulfate, 20 mL hydrochloric acid, and 20 mL deionized water for 2 min. Etch pits in the etched surfaces were observed. All the etch pits in one specific grain exhibited similar shapes, which are closely related to the grain orientations. These etch pits were characterized as dislocation etch pits. It was observed that etch pits arranged along grain boundaries, gathered at grain tips and strip-like etch pit clusters passed through a number of grains in the pure Invar specimens. After the addition of a small amount of alloying elements, the identification of a single dislocation etch pit is challenging compared with the pure Invar alloy. Thus, the observation of etch pits facilitates the investigation on the dislocation behavior of the pure Invar alloy. In addition, alloying elements may affect the densities and sizes of etch pits.

Work Hardening of Magnesium Single Crystals Deformed to Stage B at Room Temperature

Magnesium single crystals of purity (99.8 wt%) deformed to stage B on the work-hardening curve at the temperature of 293 K and at a strain rate of 10−3 s−1 were investigated. The modi ed Bridgman method was used to obtain the crystals of the preferred orientation of (0001)⟨1120⟩ as primary slip system. By using the method based on the experimental gradient matrix, the activity of slip systems was obtained in magnesium single crystals deformed to shear strain 1.2γ, where well developed stage B of work hardening was observed. It was shown that primary (0001)⟨1120⟩ slip system was dominant in the whole investigated range of the examined deformation. The observation and analysis of etch pits on the {1210} plane showed the heterogeneous distribution of dislocations formed during deformation into walls of dislocations perpendicular to the (0001) slip plane. The suggested model of work hardening of magnesium single crystals, which is worth taking into consideration, shows the in uence of the long-range stress eld derivating from the groups of dislocations arranged in dislocation walls.

Etch pits of precipitates in CdZnTe crystals on (1 1 1) B surface

The etch pits of Te-rich and Cd-rich precipitates of the Cd0.94Zn0.04Te crystals situated on (111) B surface were distinguished from the dislocation etch pits and evaluated by using Everson Etching for the first time. By using an IR transmission microscope and a scanning electron microscope (SEM) with an energy-dispersive x-ray spectroscopy (EDX) analytical system, the characteristics of the precipitate etch pits were studied. The etch pit of the Te-rich precipitate which would influence the etch rate of its ambient materials shows the shape of triangle or hexagon with a rough surface different from the cone-shaped triangle etch pit as the dislocation etch pit. The etch pit of the Cd-rich precipitate is always enwrapped by large quantities of dislocation etch pits, which indicates the existence of the damaged layers around the Cd-rich precipitate. Base on the characteristics of the precipitate etch pits, the areal densities of the precipitates with the size larger than 5μm on the substrate surfaces can be measured by the optical microscope with a magnification of 50 and under Nomarski mode. Compared with the conventional measurement method based on the IR transmission microscope (IRTM), the method of the etch pit observation (EPO) is more practical for measuring the areal densities of the precipitates of CdZnTe substrates.

Relationship between grain boundary structures in Si multicrystals and generation of dislocations during crystal growth

We attempted to clarify relationship between grain boundary structures in Si multicrystals and generation of dislocations during crystal growth. Systematic variation of grain boundary structures was realized by employing dendritic nucleation at the initial stage of crystal growth. Etch-pit observation revealed that the contact angle of adjacent dendrite crystals to form a grain boundary affects generation of dislocations. Experimentally observed dislocation density was found to be well correlated with shear stress around the grain boundary calculated by finite element analysis.

PL Imaging Study of In-Grown Stacking Faults in 4H-SiC Epitaxial Layer

Two types of in-grown stacking faults in 4H-SiC epitaxial layers (SFs) were investigated using a new photoluminescence (PL) topographic imaging system, macro/micro PL mapping system, TEM and molten KOH etch pit observation. Shockley type SFs (SSFs) of 3C and 8H inclusion were identified as two different types of triangular PL emission patterns with corner angle of 60° and 30° spreading to the <11-20> down step direction. The peak wavelengths are 423nm and 465nm, respectively. The 60° triangular SSFs are 3C inclusion related with threading edge dislocations. The 30° triangular SSFs are 8H inclusions related with basal plane dislocations. Such SFs are caused by dislocation- related disturbance of the step flow growth resulting in insertion of new cubic sites in between the 4H hexagonal turns. The substrate surface roughness at the early stage of the epitaxial growth and the growth rate may correlate with the might be deeply related in the SFs formation of SFmight be deeply related in the SFs.

Observation of Crystalline Defects Causing pn Junction Reverse Leakage Current

A major crystalline defect which causes a pn junction reverse leakage current has been identified. A faintish stripe defect (FSD), the main cause of the leakage current, was observed in about 90% of the current leak points of our pn diodes. Double shell pits were observed at the edge of the FSD after molten KOH etching, indicating that the FSD is elongated on a basal plane and crosses the epilayer surface. The FSDs are sorted into several groups in terms of the shapes and arrangements of the etch pits. A cross-sectional TEM image of an FSD shows an eight-hold stacked structure, demonstrating that the defect contains a stacking fault. Etch pit observation after repetitive RIE of an epilayer revealed that FSDs originate both in threading dislocations in SiC substrates and from an SiC epitaxial growth process itself.

Solution Growth of Off-Axis 4H-SiC for Power Device Application

Solution growth on off-axis 4H-SiC sublimation substrate as a buffer layer for the subsequent CVD epitaxial growth was investigated. Dislocation conversion and propagation from the substrate to the CVD epitaxial layer through the solution grown buffer layer was inspected by molten KOH etch pit observation. Effective dislocation conversion from BPD to TED as an effect of the buffer layer insertion with no drastic change in the total EPD was confirmed.

Effect of Grain Size on Fatigue Behavior of Pure Copper and Cu-Al Alloys

In order to clarify the grain size dependence on the fatigue behavior of polycrystalline metals including twins from the view point of dislocation theory, pure copper, Cu-3.5at%Al, Cu-6.8at%Al and Cu-14.8at%Al alloys having the average grain sizes ranging from 9 to 122μm were prepared by a strain-annealing method. Fatigue tests at room temperature for each specimen were performed under the constant stress amplitude over a life range of 104 to 107cycles. The fatigue properties at elevated temperatures for Cu-14.8at%Al alloys were confirmed up to 773K, and also the distribution of dislocations close to fatigue cracks was observed by using the etch pit technique. The grain size dependence on the fatigue strength for pure copper and Cu-3.5at%Al alloys disappears beyond 106cycles, whereas the fatigue lives of Cu-6.8at%Al and Cu-14.8at%Al alloys uniformly increase with grain refining over all ranges. Relationship between the fatigue strength at 107cycles and aluminum concentration for Cu-Al alloys of fcc solid solution can be approximately represented by a straight line as well as the shear stress. The fatigue strength of Cu-14.8at%Al alloys markedly decreases with increasing temperature and becomes almost half of that for room temperature at 773K. The results based on the etch pit observation indicate that the dislocations multiplied under cyclic loading pile up against the grain and twin boundaries, where large cracks along both boundaries form and propagate due to the stress concentration.

Photoluminescence analysis of intragrain defects in multicrystalline silicon wafers for solar cells

Structures of intragrain defects were investigated by photoluminescence (PL) mapping tomography in multicrystalline silicon wafers for solar cells. PL dark patterns were observed in short minority carrier diffusion length regions, and we confirmed that the patterns came from the intragrain defects. The tomography revealed that the defects have planelike structures extended to the crystal growth direction. We also found that the growth conditions affect the structures of the defects: slower solidification leads to larger defects with lower density. Origins of the defects were analyzed by low-temperature PL spectroscopy, electron backscatter diffraction pattern measurement and etch-pit observation. We concluded that the defects are metal contaminated dislocation clusters which originate from small-angle grain boundaries.

Etch Pit Observation of Dislocations in Early Deformation of Cu-Al Alloy and Pure Mg Polycrystals

In order to make clear the micro-yielding mechanisms of polycrystalline metals including twins, the movement of dislocations in the surface grains of Cu-6.8at%Al alloy and pure Mg polycrystals during the early stages of deformation was directly observed by using etch pit technique. The fresh dislocations multiply from the Frank-Read sources within the grains, and pile up against the twin and grain boundaries of two kinds of specimens. The pile-up dislocations on the primary and/or secondary slip planes are also confirmed in Cu-6.8at%Al alloys. Especially during the compressive loading for pure Mg, the occurrence of deformation twins is remarkable with an increase of strain rate, whereas the distribution of fresh dislocations tends to decrease in the surface grains. The present results suggest that the effect of twin boundaries on micro-yielding is almost equivalent for that of grain boundaries, which act as barriers to moving dislocations even in the pre-yield deformation.

Structure of In-Grown Stacking Faults in the 4H-SiC Epitaxial Layers

We investigated the structure of the in-grown stacking faults (SFs) in the 4H-SiC epilayers. The in-grown SFs exhibited the photoluminescence (PL) peaks representing phonon replicas with bandgap of 2.710 eV. The in-grown SFs were confirmed to be triangular-shaped by PL mapping and KOH etch pit observation. High-resolution TEM image showed that the in-grown SFs have an identical stacking sequence that differ from single or double Shockley SF. In addition, the density of the in-grown SF depended on growth conditions.

Observation of dislocation etch pits in a sapphire crystal grown by Cz method using environmental SEM

The dislocation etch pits in an as-grown [0 0 0 1] direction sapphire crystal (α-Al 2O 3) produced by Cz method were investigated using an environmental scanning electron microscope for the first time. The clear and stable contrast images of triangular, hexagonal, and quadrilateral etch pits were observed, which demonstrate the structural symmetry of sapphire crystal along [0 0 0 1] direction. The dislocation density we measured is 1–2×10 5/cm 2 and the formation of the etch pits is also discussed.

Back Side Damage Gettering of Cu Using a Cavitating Jet

The effectiveness of the back side damage introduced by a cavitating jet to getter contamination in silicon has been demonstrated. Back side damage required for gettering has been introduced successfully into a silicon wafer, utilizing impacts caused by the cavitating jet. A wafer, which had previously been back side damaged in a selected area, was intentionally contaminated and submitted to a thermal treatment. The effectiveness of gettering was confirmed by the observation of etch pits on the surface, induced by the intentional contamination, other than in regions below which there was back side damage. No etch pits were observed in regions with back side damage.

Preparation of large GaN substrates

A freestanding GaN substrate of over 2-in. size with low dislocation density was prepared by hydride vapor phase epitaxy (HVPE) using GaAs (111)A as a starting substrate. A SiO 2 mask pattern with round openings was formed directly onto the GaAs (111)A substrate. Then, a thick GaN layer was grown with numerous large hexagonal inverse-pyramidal pits constructed mainly by {11–22} facets maintained on the surface. After removing the GaAs substrate and subsequent lapping and polishing, a freestanding GaN about 500 μm in thickness was obtained. Etch pit observation reveals that etch pit groups with etch pit density 2×10 8 cm −2 at the center exist in the matrix area with etch pit density as low as 5×10 5 cm −2. This distribution is due to the effect of large hexagonal pits on collecting dislocations at the bottom of the hexagonal pit. Dislocations propagate into the bottom of the pit mainly in the 〈11–20〉 or 〈1–100〉 direction parallel to (0001).

Growth and characterization of CdSe single crystals by modified vertical vapor phase method

Good quality, large single crystals of CdSe were grown by the modified growth method (i.e., vertical unseeded vapor phase growth with multi-step purification of the starting material in the same quartz ampoule without any manual transfer between the steps). Lower temperature gradients (8–9°C/cm) at the growth interface were used for the crystal growth. As-grown CdSe crystals was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analyzer of X-rays, high-resistance instrument measurement, and etch-pit observation. It is found that there are two cleavage faces of (1 0 0) and (1 1 0) orientations on the crystal, the resistivity is about 10 8 Ω cm, and the density of etch pits is about 10 3–4/cm 2. The crystal was cut into wafers and was fabricated into detectors. The detectors were tested using an 241Am radiation source. γ-ray spectra at 59.5 keV were obtained. The results demonstrated that the quality of the as-grown crystals was good. The crystals were useful for fabrication of room-temperature-operating nuclear radiation detectors. Therefore, the modified growth technique is a promising, convenient, new method for the growth of high-quality CdSe single crystals.

Observation of dislocation etch pits in epitaxial lateral overgrowth GaN by wet etching

This work investigates dislocation etch pits in epitaxial lateral overgrowth (ELO) GaN by wet etching. A mixture of H 2SO 4 and H 3PO 4 was used as an etching solution. SEM and AFM were employed to observe the surface topography. For the as-grown sample, SEM images show the flat, smooth surface without any pits or hillocks. After the chemical etching, hexagonal shaped etch pits were observed at the edge of ELO GaN. AFM observation of etched ELO GaN displayed high densities of etch pits clustered in the “window” region and the coalescent line of two growing fronts. In contrast, the overgrowth region was nearly free of etch pits. Moreover, we observed that different sizes of etch pits dominated in “window” region and coalescent region. This implied different types dislocations dominated in these regions.

Observation of etch pits and defects in diamond single crystals prepared under high temperature–high pressure

As-grown diamond single crystals synthesized under high temperature–high pressure in the presence of FeNi catalyst were directly observed by scanning electron microscopy and transmission electron microscopy (TEM). Etch pits on the (1 1 1) surface of the diamond, which are generated by the screw dislocations meeting the diamond (1 1 1) surface at the points of emergence of dislocations, can be revealed by electrolytic etching and be used to study the motion of dislocations under the action of applied stress. Stacking-fault tetrahedral and stacking faults were investigated by moiré images. The stacking-fault tetrahedral and stacking faults may be derived from supersaturated vacancies generated during rapid cooling from high temperature to room temperature. Dislocation networks and an array of parallel dislocations were directly examined by TEM, which are related to the thermal stress caused by the inclusions in the diamond.