Flat-bottomed Pits Research Articles

Incipient Dissolution of Emplaced Forsterite and Fayalite Records the Effects of Climate, Mineral Composition, and Crystallographic Orientation

To investigate the effects of environment, composition, and crystal orientation on incipient surface alteration of forsterite and fayalite in a natural environment, polycrystalline forsterite and fayalite samples were emplaced in Mg/Fe-rich and Al-poor ultramafic soils under subarctic (Tablelands in Newfoundland, Canada; 3.9 ⁰C and ∼120 cm precipitation/year), Mediterranean (Klamath Mountains, California;≤12.8 ⁰C and ∼101-118 cm precipitation/year), and desert (Pickhandle Gulch, Nevada; ∼14.1 ⁰C and ∼14.4 cm/year) climates for one year. Incipient alteration after one year was examined using scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, X-ray photoelectron spectroscopy, and visible and near-infrared reflectance spectroscopy.Alteration features on forsterite surfaces included flat-bottomed pits with steeply dipping walls likely developing on grain faces and representing surface retreat of individual grains and lining features likely developing along grain boundaries. Mg-leached surface layers formed under acidic to slightly alkaline conditions while Mg-enrichment was observed under alkaline conditions. Flat bottomed pit formation preferentially occurs on surfaces within 30° of perpendicular to the b-axis (on the [010] plane) of the olivine crystal lattice. Depth of flat-bottomed pits on forsterite surfaces follows the order Klamath Mountains > Tablelands >> Pickhandle Gulch, reflecting the importance of environmental conditions. Warm, wet, and relatively acidic conditions enhanced forsterite dissolution over cold, wet, and slightly alkaline conditions, with minimal alteration observed under hot but arid and alkaline conditions. Greater surface roughness on flat-bottomed pit floors on Klamath Mountain forsterite surfaces are consistent with less-saturated soil-pore water reaction conditions.In contrast, fayalite disks buried in the Klamath Mountains show no evidence for etch-pit formation despite the warm, wet, and slightly acidic conditions. Elevated Fe/Si ratios from X-ray photoelectron spectroscopy measurements and evidence of M-OH bonds in visual and near infrared spectra are consistent with formation of a Fe-enriched hydroxylated layer limiting fayalite surface area available for water-rock interaction and retarding fayalite dissolution during aqueous alteration under oxidizing conditions. These results differ from previous laboratory experiments that show enhanced dissolution of fayalite relative to forsterite, showing the effect of natural, oxic, unsaturated weathering zones. These results will be helpful for interpreting observations of this widely studied mineral, including from the planet Mars.

Nanosecond laser damage of 532 nm thin film polarizers evaluated by different testing protocols

Different laser damage testing protocols, including 1-on-1, S-on-1, and Raster Scan, were conducted on 532 nm polarizers to evaluate the damage resistance and mechanisms. A comparison of the laser-induced damage thresholds (LIDTs) revealed different damage characteristics and major contributions to film failure for different polarizations. For P polarization, the LIDTs for the three test protocols were nearly the same because of the stabilization of two typical damage morphologies of flat-bottomed pits and mussel damage pits. For S polarization, the LIDTs for multiple pulses were lowest, where absorptive defect-induced damage was revealed. The damage characteristics of 532 nm polarizers and 1064 nm polarizers have been also compared. The mussel damage pits, which are similar to the typical damage morphologies of ultraviolet (UV) laser damage to fused silica, were observed for the first time in coatings of 532 nm polarizers. This suggests that, the polishing-induced subsurface damage of fused silica substrates may tend to be excited by a short-wavelength laser rather than the fundamental wavelength.

Investigation on nano-absorbing precursors in the picosecond regime via the comparative study of HfO2/SiO2 and Ta2O5/SiO2 high-reflectivity coating damage

Laser-induced damage to the final reflective and diffractive optics limits the total output energy of petawatt laser systems with pulse durations ranging from a few hundred femtoseconds (fs) up to a few tens of picoseconds (ps). In this study, the laser damage to HfO2/SiO2 and Ta2O5/SiO2 multilayer dielectric high-reflectivity (HR) coatings induced by a 1053 nm laser with a pulse width of 8.6 ps was studied to investigate the nano-absorbing precursors in ps regimes. The HfO2/SiO2 HR coating exhibited stronger laser resistance than the Ta2O5/SiO2 HR coating. Flat-bottom pits, pinpoints, and funnel pits were the three typical damage morphologies for the experimental HR coatings. The damage to the HfO2/SiO2 HR coating was primarily dominated by flat-bottom pits, whereas dense pinpoints were the most significant damage for the Ta2O5/SiO2 HR coating. The nano-absorbing precursors introduced by the ion-assisted deposition process were proved to be the damage precursors that trigger pinpoints under a strong electric field intensity (EFI). The nano-absorbing precursors located in the second EFI peak of the SiO2 top layer induced the funnel pits. The funnel pits were expected to be the previous stage of the flat-bottom pits. After they grew along the upward-sloping crack and separated from the interface, the flat-bottom pits were formed. In addition, poor-binding interfaces promoted the formation of flat-bottom pits.

Characterizations of etch pits formed on single crystal diamond surface using oxygen/hydrogen plasma surface treatment

Etch pits formed on (001)-oriented single crystal diamond surfaces by O/H plasma etching have been investigated using optical microscopy. Shapes of the formed pits are basically inverted-pyramidal hollows with the edge directions of the 〈110〉, but central areas of these pits have two types of shapes, point-bottom and flat-bottom ones. Depth profiles of the number densities of these two-type pits showed that at an early stage of the etching, a large number of the flat-bottom pits are observed, but disappear to a depth shallower than ~10μm. Compared with the other etching experiment using ion beam sputtering, such flat-bottom pits most likely correspond to the dislocations or microfractures introduced around the surface during surface polishing of the diamond substrates. On the other hand, point-bottom pits still continue to appear even in a deeper region. These correspond to “intrinsic” dislocations included originally inside the diamond substrate. All the tilt angles of the pit between the slope of the pit and top face of the substrate, characterizing the pit shape, were within the range of 3–7° and independent of their sizes in many pits investigated. It was found that the tilt angle and the activation energy of the etch rate obtained in this study are similar to that of an oxygen-gas related etching process.

Interfacial damage in a Ta_2O_5/SiO_2 double cavity filter irradiated by 1064 nm nanosecond laser pulses

The Laser-Induced Damage Threshold (LIDT) and damage morphologies of a Ta(2)O(5)/SiO(2) double cavity filter irradiated by 1064-nm, 10-ns pulses were investigated. The depths of flat bottom pits were examined by an optical profiler and then calibrated according to the Electric-Field Intensity (EFI) distributions and the cross-sectional micrographs obtained using the Focus Ion Beam (FIB) technology. The statistics for depths of 60 damage sites suggested that the Ta(2)O(5) over SiO(2) interface was more vulnerable to Laser-Induced Damage (LID) than the SiO(2) over Ta(2)O(5) interface. After examining the morphologies of interfacial delaminations carefully, we found that the Ta(2)O(5) over SiO(2) interface instead had stronger mechanical strength. So, the higher density of susceptible defects at the Ta(2)O(5) over SiO(2) interface was considered to be the reason that LID was preferentially initiated at this type of interface. Based on the above findings, a phenomenological model was proposed to describe the formation of flat bottom pits.

Growth, chemical and structural analysis of glycine potassium iodate (GPI): A new non-linear optical material

Crystals of glycine potassium iodate (GPI) have been grown from aqueous solution by slow evaporation technique at room temperature. The chemical and structural units have been verified and the crystals were found to be thermally stable up to 210 °C. Comparative IR and Raman studies indicate a molecule with lack of center of symmetry. Habit and cleavage faces treated with glacial acetic acid are seen to produce elongated and flat bottom pits. Thermal evaporation reveals the presence of well defined rhombus shaped pits on cleavage faces heated near 80 °C–100 °C. Partial cleavages, moisture, circular features and glide bands have been observed. UV studies show energy band gap of 5.92 eV in addition to the presence of a wide transparency window. An SHG efficiency of 33.81 times that of standard KDP has been recorded using Kurtz and Perry method. Vickers micro hardness measurements indicate work hardening capacity of 7.78 suitable for applications in optoelectronic setup.

Investigations of impurity striations in potassium bichromate crystals

AbstractImpurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

电子束蒸发制备三倍频分离膜的0.532μm激光预处理效应

The 0.532-\mum laser conditioning of HfO2/SiO2 third harmonic separator fabricated by electron-beam evaporation (EBE) was studied. The laser induced damage threshold (LIDT) of the separator determined by 1-on-1 test is 9.1 J/cm2 and it is 15.2 J/cm2 after laser conditioning determined by raster scanning. Two kinds of damage morphologies, taper pits and flat bottom pits, are found on the sample surface and they show different damage behaviors. The damage onset of taper pits does not change obviously and the laser conditioning effect is contributed to the flat bottom pits, which limits the application of laser conditioning.

Observation of Etch Figures on Protein Crystals by Atomic Force Microscopy

Etch figures on the (110) face of hen egg white lysozyme crystals in aqueous solution were investigated by atomic force microscopy. Three types of etch pits with flat, “deep” flat and point bottoms were observed. All etch pits are elongated to the [-110] direction, similar to the growth of 2D islands. The etch pit density of contaminated crystals, fabricated from a widely used commercial sample, was approximately ten times greater than that of pure crystals. Moreover, the density of “deep” flat bottom pits on contaminated crystals increased with supersaturation, while their density on pure crystals remained almost constant. These results suggest that the impurity molecules incorporated during growth and the line defects, such as edge dislocations, induced by the molecules are the dominant defects in lysozyme crystals grown from commercially available samples.

Etching of (0 0 0 1) habit faces and matched cleavages of flux grown strontium hexaferrite crystals

Results of etching (0 0 0 1) planes of flux grown strontium hexaferrite crystals in 85% H3P04 at 120 °C and 37% HCl at 100 °C are presented. Fractography reveals one-to-one correspondence of cleavage patterns on the two matched (0 0 0 1) cleaved planes. Etch patterns including hexagonal, point-bottomed pits with smooth sloping planes, hexagonal but flat-bottomed pits, geometrically centred hexagonal pits with regularly spaced terracing, eccentric hexagonal pits with irregularly spaced terracing, a large flat-bottomed hexagonal pit with a smaller point-bottomed hexagonal pit within it but having different geometrical centres and flat-bottomed pits with a beak at their centres are illustrated. It is explained that they are indicative of normal, inclined, stepped and bending dislocations in strontium hexaferrite crystals. Pits due to impurity inclusions are also explained. The explanations are supported by the results of mismatchings of etch patterns on matched cleavages.

Dislocation etching of flux grown strontium hexaferrite single crystals (abstract)

Hexagonal hard ferrites like SrFe12O19 are technically interesting materials not only because they are the traditional permanent magnets but also as emerging magnetic recording media and as potential magneto-optic devices. For these reasons the study of dislocations in these samples is quite significant. Flux grown single crystals of SrFe12O19 are etched in 37% HNO3 at 100 °C and 85% H3P4 at 120 °C. These two etchants produce hexagonal pits on (001) planes that are established as dislocation etchants by performing the following experiments: (1) successive etching for prolonged periods resulting in persistent point bottomed etch pits at all the stages; (2) etching of matched (0001) cleavages in similar, as well as dissimilar, etchants which produce 1:1 corresponding point bottomed etch pits on a pair of the matched cleavages; (3) etching of low angle grain boundaries which consist of a grid of equally spaced edge dislocations. An equally spaced row of etch pits is obtained along the grain boundaries. Hexagonal etch pits with smooth sloping planes are normally produced. Among such pits, unusual etch pattern features including pits with rythmically and irrythmically spaced terracings, eccentric pits, small point bottomed pits within a large flat bottomed pit with differing geometrical centers, and flat bottomed pits with beaked centers, are obtained. Unusual deviations from the perfect match of etch patterns on certain matched (0001) cleavages are examined critically. It is thought that these unusual etch patterns are due to bending, branching, and stepping of dislocations. The terracing of pits is attributed to the segregation of impurities along dislocation lines.

Pitting morphology in single crystals of copper during and after cyclic deformation in 0.1 M perchloric acid

The morphologies of corrosion pits produced during cyclic deformation have been studied in copper single crystals exposed to corrosion, and by exposing previously cycled specimens to the same corrosive environment (0.1 M HClO 4), but without cycling. When the previously deformed metal was corroded without cycling, pits formed at moderate and high anodic potentials with 111 facets, and two morphologies were observed; regular octahedral pits with pointed bottoms and others with flat 100 bottoms. The existence of the flat-bottomed pits was justified thermodynamically, and the sharp bottomed pits developed from the other kind because of the mechanism and kinetics of the growth process. The corrosion pits produced during cyclic deformation were not of the conventional octahedral type and showed 110 and 111 facets. The slip steps caused by the cyclic deformation reduced the differences in specific surface energies of the facets, and stimulated the growth kinetics.

Optical microscopic studies on grown and etched surfaces of flux grown LaAlO3 crystals

Surface structures on as-obtained flux-grown crystals of LaAlO3 have been investigated. Strictly oriented square, circular and rhombus shaped pointed, as well as flat-bottomed etch pits are observed. Etch pits along lineage boundaries, intersecting low-angle tilt boundaries and helical dislocations are illustrated and described. Different orientation of etch pits reveal twinning in LaAlO3 crystals. Microdisc patterns and flux inclusions are also observed. The etch patterns on the as-obtained LaAlO3 crystals are explained to be as a result of the flux cleaning operation of crystals in HNO3. Experiments on etching established HNO3 to be a dislocation etchant for LaAlO3 crystals. Dislocation etching kinetics of the HNO3-LaAlO3 surface system are investigated for the freshly identified sites as well as for sites having a previous history of etching. Data obtained on the effects of etching time, etchant concentration and temperature on the dislocation etch rates, are analysed. The results obtained are presented and discussed.

Electrochemical etching

Silver faces with only a few exactly known dislocation emergence points were etched electrochemically. Deep pyramidal etch pits were observed on the screw dislocations whereas flat-bottomed pits arise on the edge dislocations. Qualitatively, this fact corresponds to the results obtained with natural, i.e. as-grown from the vapour phase, {0001}-faces of zinc single crystals. They were etched electrochemically by a new „droplet” technique. Quantitatively, the formation of two-dimensional negative nuclei during the etching of the edge-dislocation emergence points is understood as an atomistic process. Electrochemical etching of zinc was compared with chemical etching. It was concluded that SO4 selective adsorption (from ZnSO4 aqueous solution) changes significantly the polar diagram of the lateral dissolution rate on the basal face of the zinc single crystals and that the electrochemical etching reveals better the actual structure of these crystals.

Electrochemical etching

The formation of two-dimensional negative nuclei (“Hohlkeime”) during the etching of edge dislocation emergence points has been appreciated as an atomistic process. Experimentally, by means of double-pulse potentiostatic method, {0001}-faces of zinc single crystals have been etched electrochemically according to a new “droplet” technique (in 1 N ZnSO 4 water solution). In this way the emergence points of screw and edge dislocations have been distinguished, the former being developed by deep pyramidal etch pits whereas the latter created flat-bottomed pits. By the electrochemical etching we observed ivariably 〈11 2 0〉 pit orientation (and, perhaps, in connection with this the appearance of non-symmetrical etch pits on the emergence points of screw dislocations with the Burgers vector 1 3 〈11 2 3〉). In contrast, the chemical etchant of Rosenbaum and Saffren (alcoholic HCl solution) created 〈10 1 0〉 oriented pits. Anyway, our experiments showed that the addition of SO 2− 4 to this etchant in concentrations exceeding 1:4 changes the azimuthal orientation of the chemically produced etch pits in 〈11 2 0〉 and it was concluded that the SO 2− 4 selective adsorption changes significantly the polar diagram of the lateral dissolution rate.

Cavitation erosion of age-hardenable aluminum alloys

The mechanisms of deformation and failure of age-hardenable aluminum alloys due to ultrasonic cavitation have been investigated. The results indicate that the mode and rate of erosion depend on both composition and heat treatment: increasing the hardness and strength by aging or alloying produces an increase in erosion resistance togetner with a change in failure mode. Alloys of low solute content erode in a manner similar to that of pure FCC metals namely by uniform ductile rupture across the surface. In the samples of 2 to 4.5 pct alloy content, however, material is lost preferentially from apparently random, isolated regions, leaving behind striated, flat-bottomed pits. The fracture surface of these pits resembles those of fatigue failures in aluminum alloys. These pits expand laterally to macroscopic proportions on continued caviation exposure without suffering any changes in their topographical features. Alloys of 9 to 10 pct solute content develop similar striated pits but on a microscopic scale. These different erosion mechanisms are discussed in terms of the microstructure of the alloys and their ability to absorb and attenuate the incident cavitation energy.

Etching models for A {111} diamond surface: Calculation of trigon slopes

A mathematical analysis of the etching of {111} diamond surfaces is developed. The slopes of etch pit faces are computed in terms of the specific rate constants, k 2 and k 3, for removal of two- and three-bonded atoms along 〈1̄10〉 steps and the specific rate constant, k d, for step nucleation at the central initiating defect. Interactions between neighboring steps are neglected. Two limiting etching regimes are found, i.e., one in which the step velocity increases linearly with step length and a regime of constant step velocity. If k d is limited by a no overhang criterion, i.e., nucleation of a new step cannot occur until the prior step has moved out of the way, k d and etch pit slope are functions of the size of the initiating defect. This allows etch pits of vastly different slope to be formed at the same k 2 k 3 ratio. Point bottom pits with shallow (less than 2°) slopes form from small initiating defects, e.g., dislocation outcrops. At the same k 2 k 3 ratio flat bottom pits with steep (70° 32') outer faces are formed by etching from large shallow defects, e.g., ring cracks or inclusions. Some preliminary conclusions are drawn about the chemical environment present during the latter stages of diamond genesis.

TiC single crystals prepared by the radio frequency floating zone process

The growth of TiC single crystals by the radio frequency floating zone process without using seed crystals has been examined. Large, pure, single crystals, 10–12 mm in diameter and 30–40 mm in length, were obtained. The growth direction, lattice parameter and the variation of both the C Ti ratio and the resistivity along the growth direction have been determined. The finer details of pits were observed by a scanning electron microscope and an X-ray microanalyser. It was confirmed that the square and flat-bottomed pits observed in the cleavage plane, (100), were caused by the movement of dislocations rather than by precipitation of carbon.

Dislocation Studies in Bi2Te3 by Etch-Pit Technique

Dislocation studies in Bi2Te3 were made by etch-pit technique. All work was done on c planes. The etch marks the dislocations in the c plane by producing etch grooves, and marks the sites of emergence of dislocations from the surface with pyramidal etch pits. Evidence was found for the presence of networks of dislocations lying predominantly in the c plane. Experimental evidence was also found for bending of the dislocations within the crystal being responsible for different size pyramidal etch pits, and flat bottom pits observed on the etched surfaces. The same mechanism was found to be responsible for bringing out new etch pits on longer etching. The slip traces on the c plane were found by controlled surface-damage studies to be parallel to the binary axes.

Grown-In Dislocations in Calcium Tungstate Crystals Pulled from the Melt

Etch pits on (001) surfaces of calcium tungstate crystals, formed on treatment with hot dilute solutions of hydrochloric acid, were identified to be dislocation etch pits. The technique is able to follow the motion of dislocations during annealing by the formation of new sharp-bottomed pits adjacent to flat-bottomed pits at the initial dislocation positions. Inclusions, both solid and gaseous, are an important source of dislocations in crystals of calcium tungstate grown from the melt.