Boundary Etching Research Articles

Segmented chip formation during machining under the influence of different atmospheres

Abstract High temperatures and a pronounced segmented chip are characteristic of titanium machining processes. The formation of segmented chips induces an alternating high frequency mechanical load on the tool and thus promotes tool failure. The presence of oxygen triggers a multitude of chemical interactions during the chip forming process. However, the oxygen content’s impact during titanium machining, especially on the chip formation, is unknown. In order to draw conclusions on this process, the machining tests were carried out while varying the oxygen content. The thus produced chips were metallographically examined. The varying degree of segmentation could then be visualized by boundary etching and subsequently be evaluated.

Importance of atmospheric aerosol pollutants on the degradation of Al2O3 encapsulated Al‐doped zinc oxide window layers in solar cells

AbstractAtmospheric aerosol pollutants are considered for the first time for the durability evaluation of non‐metallic photovoltaic materials on the example of pristine and Al2O3‐encapsulated Al‐doped zinc oxide (AZO) window layers. The AZO samples were exposed to a varied temperature and humidity cycle, completed or not by a daily deposition of (NH4)2SO4 or NaCl aerosols, typical pollutants in rural and marine environments, respectively. The samples exposed with and without the pollutants were compared after 1 and 2 weeks of the test. Optical transmittance and conductivity significantly degraded only for the samples exposed with the pollutants. Raman spectroscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy evidenced localized dissolution of the AZO film and chemical modification of the Al2O3 encapsulation. The most severe degradation was caused by (NH4)2SO4, which was attributed to the high stability of soluble [Zn (NH3)42+] complexes. The Al2O3 encapsulation improved chemical and physical stability of AZO in the presence of (NH4)2SO4 but not in the presence of NaCl. The latter can be explained by pitting corrosion of Al2O3. Optical transmission curves are coherent with the AZO layer thinning in the presence of NaCl and very localized AZO dissolution (most likely grain boundary etching) in the presence of (NH4)2SO4. The enhanced degradation of encapsulated AZO in the presence of atmospheric aerosol pollutants suggests that they cannot be neglected in the evaluation of barrier protection capacities of novel encapsulates and, more generally, in the outdoor durability assessment of novel photovoltaic materials and devices.

Development of a Two-Stage Etching Procedure for Grain Analysis of Intermetallic Iron Aluminides (Fe-Al-Ta)

Abstract The present work will introduce a novel two-step etching procedure for grain analysis of intermetallic iron aluminides. A grain boundary etching technique from the literature will be complemented by subsequent grain-contrast etching to visualize different grains in polarized light. The use of an XY-table for the acquisition of MosaiX images also enables grain analysis over the entire cross-section of the sample.

Hydrophobicity and Improved Localized Corrosion Resistance of Grain Boundary Etched Stainless Steel in Chloride-Containing Environment

Localized corrosion of stainless steels by chloride ions in seawater leads to metal degradation while fouling of marine organisms increases the occurrence of localized corrosion. We describe a simple method to increase hydrophobicity of austenitic stainless steel using grain boundary etching that can also inhibit adhesion of bio-organisms present in seawater as well as increase the localized corrosion resistance of stainless steel in chloride-containing aqueous environments. This paper describes the corrosion behavior of stainless steel as a result of grain boundary etching to achieve hydrophobicity. Potentiostatic polarization on stainless steel 316L in a nitric acid solution at an anodic potential of 1.3 V vs. saturated calomel electrode (SCE) results in a grain boundary etched structure and a Cr- and Mo-rich passive film as confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. This modified stainless steel 316L surface exhibits enhanced corrosion resistance to a 0.6 M sodium chloride solution. Specifically, potentiodynamic polarization studies indicate that the breakdown potential increases and the sample-to-sample variability decreases. The modified surfaces show a narrow range of breakdown potentials (0.96 to 1.05 V vs. SCE) compared to as-received stainless steel 316L (0.32 to 0.86 V vs. SCE).

Wettability control of stainless steel surfaces via evolution of intrinsic grain structures

Wettability control of stainless steel surfaces has wide applicability due to the extensive use of stainless steels in industries that handle liquids. However, previous studies to achieve hydrophobicity on stainless steel surfaces rely on artificial roughness by added particles and residue formation that could compromise mechanical stability of the modified surface. In this study, water-repellent stainless steel surfaces were fabricated via the controlled topographical enhancement of intrinsic grain structures to achieve the required surface roughness. Electrochemical etching was used to control the relative etch rate between grains and grain boundaries by applying an anodic potential to stainless steel 316 (SS316). At low potential (1.2 V vs. Saturated Calomel Electrode), high selectivity between grain and grain boundary etching was observed, which resulted in significant etching at grain boundaries and smooth top grain surfaces. Morphologies with significant microscale roughness, and slight nanoscale roughness, were achieved with intermediate applied potentials (1.3–1.5 V). As the potential increased further (1.8 V), etch selectivity decreased and yielded microscopically smooth surfaces with sponge-like nanoscale roughness; at even higher potentials (2.4 V), electro-polishing was observed with surfaces that are smooth at the nanoscale. Based upon the relationship between anodic potential and topography, we designed a nano/microscale hierarchical SS316 surface by a two-step electrochemical etching combining low and high anodic potentials. The hierarchical SS316 surface resulted in a water contact angle of 137.5 ± 5.0°. Plasma-assisted deposition of a fluorocarbon film further reduced the wettability, with a contact angle of 163.9 ± 1.2° and a roll-off angle of 10.7 ± 1.8° for 4 μL water droplets, thereby rendering the modified SS316 surfaces superhydrophobic. Due to the inherently robust intrinsic grain structure of SS, we expect that this simple approach to generate water-repellent SS316 surfaces will display improved mechanical robustness relative to previous approaches.

Synthesis and characterization of hollow mesoporous BaFe12O19 spheres

A facile method is reported to synthesize hollow mesoporous BaFe12O19 spheres using a template-free chemical etching process. Hollow BaFe12O19 spheres were synthesized by conventional spray pyrolysis. The mesoporous structure is achieved by alkaline ethylene glycol etching at 185°C, with the porosity controlled by the heating time. The hollow porous structure is confirmed by SEM, TEM, and FIB-FESEM characterization. The crystal structure and magnetic properties are not significantly affected after the chemical etching process. The formation mechanism of the porous structure is explained by grain boundary etching.

Effect of Formic Acid Vapor <italic>In Situ</italic> Treatment Process on Cu Low-Temperature Bonding

Low-temperature Cu/Cu direct bonding technology using formic acid vapor in situ treatment was developed. Effect of formic acid vapor treatment conditions on Cu surface and bonding was studied. Cu surface oxide was reduced using formic acid vapor in situ treatment at 150 and 200 $^{\circ}{\rm C}$ , respectively. With higher temperature and longer treatment time, surface reduction is more effective. Grain boundary etching was found on chemical mechanical polished Cu film after initial treatment by formic acid. However, Cu surface roughness is minimally influenced by long-time formic acid vapor treatment. Cu film/Cu film direct bonding was realized in ${\rm N}_{2}$ atmosphere with formic acid vapor in situ treatment under temperature below 200 $^{\circ}{\rm C}$ . For lower treatment temperature, longer treatment time is required to achieve good bonding. The bonding strength is about 9.0 MPa when Cu surface is treated at 200 $^{\circ}{\rm C}$ for 10 min.

Evolution of space-efficient and facet-specific ZnO 3-D nanostructures and their application in photocatalysis

We report new structural designs to dramatically increase the surface area of the ZnO nanostructure without compromising the small volume much. Space-efficient and facet-specific ZnO 3-D nanostructures, namely {101}-stacked nanocones and {100}-nanoforest, have been prepared by facet-selective etching and oriented nanocrystal growth, respectively. Grain boundary etching of multiwalled ZnO hexagonal nanocones leads to polar {101} facet-maximized ZnO stacked nanocones and oriented nanocolumn growth on ZnO hexagonal nanocones generates {100} facet maximized ZnO nanoforests. These facet-specific ZnO nanostructures offer opportunities for examination of their facet-dependent photocatalytic properties. Compared to the original ZnO hexagonal nanocone structures, these new ZnO 3-D structures exhibit a much higher photocatalytic property for photodegradation of organic dye, rhodamine B. Specifically, {101} stacked nanocones with a polar {101} plane maximized structure and high density of oxygen vacancies have shown the best performance among structures examined. We also demonstrate a great photocatalytic performance of the Au supported 3-D ZnO nanostructures with well-defined facets and high surface area.

Electrodeposition of nanostructured columnar cobalt for self-lubricant coatings

The preparation of cobalt-perfluoropolyether (PFPE) composite coating with dry lubrication capability is addressed. An original process scheme is proposed involving the electrodeposition of a nanostructured columnar cobalt layer, a grain boundary etching post-deposition treatment of the layer and its further processing by vacuum impregnation with PFPE. The influence of the operating parameters on deposition kinetics and crystal structure of the cobalt layer was investigated in detail, with the objective of identifying the optimum deposition conditions for the growth of a nanocolumnar cobalt film. In particular, the main operating conditions, namely deposition temperature and current density, were analyzed by studying their effect on deposits microstructure and texture. Control of the growth stability of the nanocolumnar structure was achieved in the presence of a suitable concentration of a surfactant. The subsequent steps of grain boundary etching and impregnation with PFPE were successfully implemented completing the planned process scheme. Friction force measurements provided evidence validating the functionality of the Co-PFPE nanocomposite.

Grain Sizes in Electroplated Thin Copper Interconnection Layers

Grain sizes have been observed quantitatively at the surface of thin electroplated copper layers by employing a grain boundary etching technique. In conventional copper layers deposited on TaN barrier layers, the typical grain size in the as-deposited layer is at a thickness of . This size decreases rapidly with decreasing thickness and reaches for thick annealed layers, i.e., grain size is close to the thickness in such a layer. When lower stress layer is electroplated, however, the grain size in the annealed layer increases from for thick ( thick) and from in thick layers, respectively. Deposition of larger grain size copper layers is required in the electroplating of low-resistivity thin copper layers.

Dependence of Oxidation Behavior and Residual Stresses in Oxide Layers on Armco Iron Substrate Surface Condition

Mass gain during oxidation, texture and residual stresses in oxide layers on polycrystalline Armco iron substrates with different surface conditions are investigated using thermogravimetry microscopy and synchrotron X-rays. The mass gain during oxidation in all samples follows a parabolic law. The parabolic oxidation constant increases with increasing roughness of a mechanically ground respectively polished oxide layer. Electrolytic polishing (grain surface etching) reduces while grain boundary etching increases the parabolic oxidation constant compared to the mechanically polished sample. All oxide layers show columnar growth of the magnetite and a moderate fiber texture. The magnetite contains compressive residual stresses. Under the conditions chosen for the oxidation treatment the magnitude of these compressive residual stresses does not depend on the substrate surface condition.

Microstructuring of stainless steel implants by electrochemical etching

The effects of electrochemically enhanced etching on stainless steel coronary stent surfaces have been investigated in respect to their applicability as surface modifications prior drug-coating. Two methods have been investigated, one basing on grain boundary etching with diluted HNO3 and the other one on hydrochloric acid etching. The etching current was in the range of 30–200 mA which accounts for 0.34–2.28 mA/mm² surface. Grain boundary etching produced a micro-furrowed surface providing volume for the coating drug. The theoretical volume offered by the furrows was calculated on the basis of laser perthometry and was determined to be 0.146 mm³/cm². With the hydrochloric acid etching method it was possible to generate an evenly rough, terraced surface. Both surfaces have been coated with Rapamycin in ethanol (20 mg/mL) and examined under SEM after dilatation. It was shown that a uniform drug layer is maintained after dilatation of the stent and little flaking is visible. Quantification of the amount of Rapamycin yielded 21.4 μg/mm² for the electropolished stents, 36.6 μg/mm² for the grain-boundary etched stents and 27.7 μg/mm² for the hydrochloric acid etching after dilatation. For the grain boundary etched stents an improved drug adhesion was found, while the hydrochloric acid etchings resulted in a deterioration of the adhesion properties.

Study on irradiation induced corrosion behavior in austenitic stainless steel using hydrogen-ion bombardment

In order to study the basic factors in irradiation assisted stress corrosion cracking (IASCC) of austenitic steels, the effects of displacement damage on the corrosion behavior of type 304 stainless steel were investigated by means of an ion irradiation technique. Solution-annealed specimens was irradiated using 1 MeV protons to 0.1, 0.5 and 1.0 dpa at about 573, 673 and 773 K. Electrochemical potentiokinetic reactivation (EPR) testing was carried out before and after the ion irradiation to clarify the effects of irradiation on corrosion behavior. The specimens irradiated at 773 K showed clear etching at grain boundaries and relatively high reactivation ratio, however, the specimens irradiated at 573 and 673 K showed no clear grain boundary etching. It was suggested that the higher irradiation temperature enhanced the radiation induced segregation near grain boundaries.

The Dynamics of Cadmium Telluride Etching

AbstractCdTe etching was investigated using variable angle spectroscopic ellipsometry and glancing angle x-ray diffraction. Treatment with HNO3:H3PO4 (NP) based etches was shown to form amorphous-Te surface films which spontaneously crystallize following etching. Br2/methanol (BM) etching forms very thin amorphous-Te films. NP-etched surfaces are stable in ambient air for ∼1 hr before beginning to oxidize, while BM etched films oxidize immediately following treatment. CdTe grain boundary etching by NP was minimized using more acidic etches. Device analysis suggests that a higher Te content produces more stable back contacts by attenuating Cu diffusion. Mechanistic details of NP etching are discussed.

Probenpräparation für hochauflösende Schädigungsuntersuchungen im REM / Sample Preparation for High-Resolution Damage Examinations in the SEM

A systematic study or sequence of preparation steps is presented for a successful quantification of the condition caused by creeping on high-temperature resistant materials. The sequence allows to expose the creep pores already in the stage of formation. To establish the preparation times required, the respective erosion rates are determined by intensive preparation tests on a series of 9-12 % Cr steels. An effort is made to examine the interaction of the microstructure with the kinetics of damage such as pore formation and growth. Therefore, a novel grain boundary etching technique (after Schalk) is presented which makes it possible to excellently image the lath structure of the former austenite grain boundaries and the carbide. This is an absolute prerequisite for the further examinations planned on the interaction between microstructure and the kinetics of damage.

Phosphorus grain boundary segregation in steel 17-4 PH

A correlation between grain boundary etching of a martensitic steel and phosphorus segregation was established. Using metallographic experiments, the phosphorus diffusivity D in the steel and the Gibbs free energy Δ G P of phosphorus grain boundary segregation were determined: D=0.183 −0.174 +3.475×10 −4 exp(−229±19 kJ mol −1/RT) m 2 s −1, Δ G P=−43.1 kJ mol −1.

Phosphorus grain boundary segregation in steel 17-4PH

A correlation between grain boundary etching of a martensitic steel and phosphorus segregation was established. Using metallographic experiments, the phosphorus diffusivity D in the steel and the Gibbs free energy Δ G P of phosphorus grain boundary segregation were determined: D=0.183 −0.174 +3.475×10 −4 exp(−229±19 kJ mol −1/RT) m 2 s −1, Δ G P=−43.1 kJ mol −1.

A novel multicrystalline silicon solar cell using grain boundary etching treatment and transparent conducting oxide

Grain boundary (GB) in multicrystalline silicon (mc-Si) degrades a conversion efficiency of mc-Si solar cell. To reduce the GB effect, we investigated various parameters such as the preferential GB etch, etch time, tin-doped indium-oxide (ITO) electrode, heat treatment, and emitter layer effect. Among various preferential etchants such as Sirtl, Yang, Secco, and Schimmel, a Schimmel etchant illustrated an excellent preferential etching property. We used RF magnetron sputter grown ITO film as a top contact metal. ITO films served as a top electrode as well as an effective AR coating layer. With well-fabricated mc-Si solar cells, we were able to achieve conversion efficiency as high as 16.6% at the input power of 20 mW/cm 2.

A Novel Poly-Si Solar Cell using Grain Boundary Etching Treatment and Transparent Conducting Oxide

ABSTRACTThis paper deals with a novel structure of polycrystalline silicon (poly-Si) solar cell for terrestrial applications. Grain boundary (GB) in poly-Si degrades a conversion efficiency of poly-Si solar cell. To reduce the GB side-effect, we investigated various parameters such as the preferential GB etch, etchtime, ITO electrode, heat treatment, and emitter layer effect. Among various preferential etchants such as Sirtl, Yang, Secco, and Schimmel, a Schimmel etchant illustrated an excellent preferential etching property. We observed a 10μm deep trench along grain boundaries and randomly textured grain surface with pyramid structure. We used rf magnetron sputter grown tin doped indium oxide (ITO) film as a top contact metal. ITO films showed a resistivity of 1.14 ×10-4 Ω-cm and transmittance of 90.5% for the wavelength of 594 nm. ITO films served as a top electrode as well as an effective AR coating layer. ITO film properties were strongly influenced by the preparation temperatures. Substrate temperature of 400oC gave the highest conversion efficiency of poly-Si solar cell. With well-fabricated poly-Si solar cells, we were able to achieve conversion efficiency as high as 16% at the input power of 20 mW/cm2.

Misorientations across etched boundaries in deformed rocksalt: a study using electron backscatter diffraction

Automated electron backscatter diffraction (EBSD) in the scanning electron microscope has been used to collect crystallographic orientation and misorientation data from etched surfaces of deformed synthetic rocksalt. By comparing the misorientation across individual boundaries to the intensity of etching, we have assessed the effectiveness of the etching procedure. High angle (>10°) grain boundaries are typically etched significantly more than low angle subgrain boundaries, and thus they can be easily identified using reflected light microscopy. However, there exists considerable variation in the intensity of etching of subgrain boundaries, independent of their misorientation. The intensity of intragranular boundary etching is controlled by the crystallographic orientation of the etched surface: surfaces close to {100} faces are only lightly etched, while surfaces close to {111} faces are heavily etched. Therefore, whilst reflected light microscopy of etched surfaces of deformed rocksalt remains extremely useful for general microstructural characterisation, fully quantitative techniques such as EBSD are ideal for more detailed microstructural analyses.