Type Of Etchant Research Articles

Double transition metal MXenes for enhanced electrochemical applications: Challenges and opportunities

AbstractDouble transition metal (DTM) MXenes are a recently discovered class of two‐dimensional composite nanomaterials with excellent potential in energy storage applications. Since their emergence in 2015, DTM MXenes have expanded their composition boundary beyond traditional single‐metal carbide and nitride MXenes. DTM MXenes offer tunable structures and properties through variations in the constituent transition metals and positioning within the layered lattice. These MXenes can exist in two primary forms: ordered DTMs and solid solutions. The compositional versatility of DTM MXenes offers opportunities to enhance their performance in electrochemical energy storage applications. However, the quality, stability, and surface chemistry of DTM MXenes are influenced by several factors, including the etching process, etchant type, and synthesis route. Currently, limited literature is available on experimentally synthesized DTM MXenes, with most studies focusing on carbide‐based MXenes. Most of the articles have dedicated their efforts only to generalized synthesis strategies. Although extensive theoretical studies have explored the suitability of etchants, synthesis parameters, and methods for producing high‐quality MXene with selective terminal functional groups, their stability issues have not been thoroughly examined. This review addresses various types of DTM MXenes, their synthesis techniques, and the impact of these methods on their physicochemical properties and electrochemical performance. Additionally, it provides a critical analysis of the causes of instability in MXenes, particularly DTMs, from synthesis to application. The challenges associated with these materials are discussed, along with opportunities and prospects for enhancing synthesis, structural tuning, surface modification, and applications in electrochemical energy storage.image

Wide-range angle sensing based on mixed variable line spacing gratings

Variable line spacing (VLS) gratings are core components in spatial spectrum and synchrotron radiation facilities due to their merits of self-focusing, aberration correction, and flat focal field. However, optimal design and fabrication of VLS gratings are still required for matching various applications. Scratch-induced selective wet etching has been proven as a robust way for fabricating various nanostructures because of its simplicity, flexibility, and controllability. In this paper, we proposed convenient and maskless methods to fabricate VLS grating based on scratch-induced selective wet etching. During the etching, key factors, including normal load for the scratching, etching time, and types of etchants, were investigated systematically toward optimizing the process. The shapes including sidewall angle and the bottom curvature of the grating elements can be controlled by adjusting the normal load, etching time and/or etching etchants. It is found that the VLS gratings present a wide-range sensing for angle detection based on the reflection spectrum. Furthermore, combining transferring process, the VLS master gratings could be replicated on polydimethylsiloxane (PDMS) surface, which showed great optical performance. This work opened new light to some extent for the application of angle sensing and structural color showing.

Effectiveness of Different Etching Agents on Enamel Surface and Shear Bond Strength: An In Vitro Evaluation.

Background Enamel etching is of utmost importance during the orthodontic bonding procedure. Phosphoric acid, hydrofluoric acid, and citric acid are used in specific concentrations to create surface irregularities on enamel surfaces, enhancing the bond strength of the orthodontic attachment. Therefore, it is essential to evaluate the type of etchant for reliable orthodontic bracket bonding with minimal damage to the enamel surface. Aims and objectives This study aimed to investigate the morphological changes on the enamel surface after treatment with different surface etchants, assess the depth of penetration, and evaluate the shear bond strength (SBS) of orthodontic brackets. Materials and methods One hundred and one extracted premolar teeth were used to investigate morphological changes on the enamel surface treated with 37% phosphoric acid, 11% hydrofluoric acid, and 20% citric acid. It was evaluated on a scanning electron microscope (Jeol Scientific Equipment, Jeol Limited, Akishima, Japan), and the SBS of brackets on enamel treated with different etching agents was evaluated using an Instron Universal Testing Machine (UTM; Instron Model: 5982, Universal Testing Systems, Norwood, MA). Group A had 60 test samples. Group B had 40 test samples. One control without any acid etching was used in both groups. Subgroup A1 (n = 30) was evaluated for surface characteristics of acid-etched enamel. Subgroup A2 was assessed for the penetration depth of various etchants. Group B (n = 40) was tested for SBS. The results were tabulated and analyzed using IBM SPSS Statistics, version 20.0 (IBM Corp., Armonk, NY). Post hoc Tukey HSD test and one-way analysis of variance were used to assess SBS and penetration depth of etchants (P ≤ 0.05). Pearson's correlation test was used to correlate SBS, etching pattern, and penetration depth. The chi-square test was used to test the frequency of types of etching patterns. Results Intergroup correlations between etching depth, etching pattern evaluated on SEM, and SBS evaluated on the UTM showed a high statistical correlation between etching depth & SBS, etching depth & etching pattern, and SBS & etching pattern between A1, A2, and group B (P ≤ 0.001). A highly significant negative correlation between SBS & etching pattern (P = 0.42) was observed among intra-group correlation. Non-significant correlations were found between etching depth & SBS and etching depth & etching pattern within the 20% citric acid etch group (P = 0.370 and 0.141, respectively). Conclusion Penetration depth obtained was highest with 11% hydrofluoric acid, followed by 37% phosphoric acid and20% citric acid. In addition, 11% hydrofluoric acid showed the highest bond strength. Acid etching showed better penetration depth and bond strength than control.

High-Density Nanopatterning of SiGeAsTe Chalcogenide as Ovonic Threshold Switch Selectors for Memory Applications

Cross-point memory architecture involves high-density, fast yet cost-effective storage class memories (SCM). As a result, ovonic threshold switches (OTS) are extensively researched as they are needed in series with the SCM-based memory element for its precise functioning. In addition, these OTS-based devices exhibit the potential to be self-selecting memories too. Hence, its integration-friendly patterning becomes pivotal for large-scale manufacturing. Chalcogenide-based alloys are often the desired candidate for OTS. Here, we study the patterning of one of the widely investigated chalcogenide alloys─SiGeAsTe. While the elements of the alloy generate highly volatile halogenated etch by-products, this material is also prone to severe etch-induced lateral undercuts and material damage. Thus, its high-density patterning is challenging. A conventional method to minimize this undercut damage is to increase the hydrocarbon passivation during the etch process to prevent the exposure of the chalcogenide’s sidewalls (SWs) to any type of etchant. Inherently, this leads to the tapering of the OTS-based pillars, consequently becoming an impediment to their scaling at tighter pitches. Here, we clearly establish that OTS-based devices with well-preserved chemical and morphological properties can be fabricated using lower hydrocarbon passivation by tuning the ion energies during etching. Higher ion energies ensure better etch directionality. Concurrently, a well-controlled high energy ion bombardment is likely to enhance deposition of the passivating hydrocarbon from the etch front on to the chalcogenide’s SWs. This is achieved without any unwanted redeposition from underlying layers in the OTS-based stack. We successfully demonstrate high-density nanopatterning of chalcogenide-based OTS devices of diameter ∼65 nm at 200 nm wide pitch. This is also effectively reproduced on 300 mm semiconductor wafers. The electrically measured devices exhibit low leakage and high endurance. This distinctive yet uncomplicated etch tailoring is also discussed to be scalable for pitches <200 nm and for other chalcogenide compositions.

Assessment of enamel surface roughness and hardness with metal and ceramic orthodontic brackets using different etching and adhesive systems: An in vitro study

BackgroundThis study aimed to evaluate enamel surface roughness and microhardness following the use of different bracket materials (metal or ceramic), etchants (total- and self-etchants), and adhesive systems (precoated or flash-free). MethodA total of 99 extracted human premolars were selected for the analysis. The surface roughness was first assessed (roughness control). One specimen from each subgroup was examined using a scanning electron microscope to illustrate the surface topography. Eighty-eight teeth were prepared using total- or self-etchants and bonded to precoated or flash-free adhesive metal or ceramic brackets. The remaining 11 specimens were not bonded to brackets (microhardness controls). The brackets were debonded after immersion in distilled water for 24 h. The specimens were again scanned for surface roughness and topography imaging. Finally, the microhardness was assessed using a micro-Vickers hardness test at a force of 200 g for 10 s. ResultAn overall statistically significant increase in surface roughness and reduced surface microhardness were observed in all experimental groups when compared with those in the control groups. The etchant type was the only variable found to contribute to the measured surface properties, with increased roughness and reduced microhardness introduced by total-etching compared to those by self-etching. ConclusionOrthodontic brackets introduced a significant increase in enamel surface roughness and reduce microhardness compared with untreated enamel, regardless of the bracket material, etchant type, and adhesive system. The etchant type was the only variable contributing to these changes, with total etching having a more pronounced effect.

Recent advances in titanium carbide MXene-based nanotextures with influential effect of synthesis parameters for solar CO2 reduction and H2 production: A critical review

Photocatalytic solar to energy conversion is considered an attractive approach for overcoming energy crises and environmental concerns. Recently, titanium carbide (Ti3C2) MXenes have been recognized as promising cocatalysts based on their metallic conductivity, excessive active reaction sites, and enlarged surface area. The current review focuses on the properties and applications of Ti3C2 MXenes useful in the field of photocatalysis. More specifically, surface modification of Ti3C2 MXenes by varying synthesis parameters to get pure materials and also composites with the role of functional groups towards solar energy conversion applications is highlighted in this review. The effect of etching and oxidizing pathways to get an efficient cocatalyst has been discussed in detail. Considering the significant effect of parameters, optimum synthesis conditions such as etchant type, concentration, time and type of intercalant in both the Ti3C2 synthesis approaches for improved photoactivity are discussed. Additionally, the surface modification of Ti3C2 through oxidation for TiO2 growth on its surface is deliberated with a detailed discussion on etchant type, concentration, etching time, and environmental factors. The optimum oxidation condition, including temperature, time, and environment for thermal treatment of Ti3C2, were also included. Lastly, the review summarizes the conclusion and future perspectives for solar energy conversion applications.

A remineralizing orthodontic etchant that utilizes calcium phosphate ion clusters.

This study aimed to investigate whether a phosphoric acid (H3PO4) solution containing calcium phosphate ion clusters (CPICs) could minimize enamel damage during long-term bracket bonding by dissolving the enamel surface and promoting enamel remineralization. The experimental design is as follows: first, three experimental etchants (H3PO4, CPICs-incorporated H3PO4 solution-I, and CPICs-incorporated H3PO4 solution-II) and two bonding resins (conventional orthodontic resin and self-adhesive orthodontic resin) were used in combination to create six groups, respectively. Each of these six groups was then divided into two sub-groups based on the presence or absence of thermocycling (TC). Twenty samples were assigned to each of the 12 groups (independent variables), and thus a total of 240 metal bracket-attached human premolars were used in this experiment. Bracket debonding was performed on each of 20 premolars in 12 groups, and shear bond strength (SBS) and adhesive remnant index (ARI) values were measured as dependent variables. Next, the three experimental etchants were applied (independent variables) to each of the three enamel samples, and the remineralization of the enamel surface was investigated as a dependent variable. The enamel surface was observed using electron scanning and atomic force microscopy. Furthermore, X-ray diffraction, energy dispersive spectroscopy (EDX) spectrum X-ray spectroscopy, and elemental mapping were performed, and the Knoop microhardness scale was measured. Therefore, the experiment was performed in two steps: SBS and ARI measurements for 12 groups, followed by observation of the enamel surface and microhardness measurements, according to the three types of etchants. As a result of the experiment, first, when the bracket was debonded, SBS did not decrease, and residual adhesive was hardly observed in the C2A group (before TC), C2A, and C1C groups (after TC) (p < 0.001). Second, the experimental etchant containing CPICs achieved remineralization while demineralizing the enamel. This was verified through SEM/EDX, element mapping, XRD, and AFM. Also, the roughness and microhardness of the enamel surface were better in the remineralized surface by the experimental etchant containing CPICs (p < 0.017). The CPICs-incorporated H3PO4 solution reduced ARI while maintaining SBS during bracket debonding, regardless of whether TC was performed or the type of resin. The etchant containing CPICs was also shown to remineralize the enamel and increase its microhardness.

Automated color etching of aluminum alloys

Abstract Color metallography of aluminum alloys can provide new structural knowledge or extend and refine structural knowledge compared to a black and white image. The basic principle of color metallography is to create a suitable film by etching. On samples coated with a suitable film, light interference is caused by the splitting of the incident light into components reflected at the air-layer interface and the layer-metal interface. The thickness of the film essentially determines at which colors the interference occurs. For films of suitable thickness, interference occurs in the blue, green and yellow regions. The film thickness depends on the chemical composition of the sample material, the chemical composition of the etchant and the etching time. If the etching conditions are kept constant (etchant type, etching time) and the chemical composition of the individual micro-areas changes significantly, it will be possible to distinguish the microareas by color contrast in the bright field. The results of color etching of aluminum alloys in different types of etchants will be presented. Using an automated apparatus, the same etching conditions will be maintained, including time and repeatability of movements in the etching, cleaning and drying process.

Influence of Machining Parameters on Surface Roughness in Chemical Machining of Silicon Carbide (SiC)

This study discussed the influence of chemical machining parameters such as (machining time, type of etchant, etching temperature, and concentration of the solution) on the surface roughness of ceramic material (silicon carbide) as a workpiece in the chemical machining (CHM) process. To achieve the best value for surface roughness. In this research, four levels of factors affecting the chemical etching process were used, the values of etching temperature (60, 80, 100, and 120) °C, the etchant concentration (50, 60, 70, and 80) %, and machining time (30, 50, 70, and 90) min, and two etchant type (HBr, HCl). Experiments proved the best value of surface roughness is obtained (2.933) µm experimentally and (2.958) µm at a predictable program when using hydrochloric acid (HCl) at a temperature (80) °C, time (50) min, and etchant concentration (50) %. The coefficient determination (R-sq) to predict the surface roughness is ((93.7).

Alkali-Treated Alumina and Zirconia Powders Decorated with Hydroxyapatite for Prospective Biomedical Applications.

The alumina and zirconia surfaces were pretreated with chemical etching using alkaline mixtures of ammonia, hydrogen peroxide and sodium hydroxide, and followed with application of the powder layer of Ca-deficient hydroxyapatite (CDH). The influence of etching bath conditions time and concentration on surface development, chemical composition and morphology of medicinal ceramic powders were studied. The following analyses were performed: morphology (scanning electron microscopy), phase composition (X-ray diffraction analysis), changes in binding interactions and chemical composition (FT-Infrared and Energy dispersive spectroscopies). Both types of etchants did not expose the original phase composition changes or newly created phases for both types of ceramics. Subsequent decoration of the surface with hydroxyapatite revealed differences in the morphological appearance of the layer on both ceramic surfaces. The treated zirconia surface accepted CDH as a flowing layer on the surface, while the alumina was decorated with individual CDH aggregates. The goal of this study was to focus further on the ceramic fillers for polymer-ceramic composites used as a biomaterial in dental prosthetics.

2D MXenes: Synthesis, properties, and electrochemical energy storage for supercapacitors – A review

• A detailed view of the synthesis, properties, and applications of MXenes. • The recent trends in MXene synthesis. • The in-depth understanding of the various types of etchants and intercalants that can be used in the formation of MXene. • Understanding the charge storage mechanism of MXenes. • A detailed discussion on the use of MXene composites as supercapacitor electrodes. Supercapacitors are one of the most frequently explored devices for energy storage applications. In comparison with conventional dielectric capacitors, supercapacitors have energy storage capacities several orders of magnitude higher, however much lower than those of secondary batteries. Their long-life cycles, high power densities, and relatively less carbon footprint over their counterparts have encouraged industries to explore and build reliable energy systems for the future. One family of materials that have garnered attention for supercapacitor applications since their discovery in 2011 are 2D transition metal carbides and nitrides (MXenes). Unlike 3D carbon, which possesses complex ion diffusion pathways, 2D nanosheets directly offer large active sites to the electrolyte. With a high surface area, shorter ion diffusion pathways, and high conductivity, MXenes enhance the energy storage characteristics of a supercapacitor. The key to high rate pseudocapacitive energy storage in MXene electrodes is the hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions. In this review, we have explored different types of supercapacitors, charge storage mechanisms, and modified synthesis methods of MXene and its properties. Finally, we discuss the advancement in this field while evaluating future challenges and prospects of MXene composites, which will provide a guide for developing high-performance MXene-based energy storage devices with high throughput and sustainable derivatives.

Influence of machining parameters on material removal rate in chemical machining of silicon carbide (SIC).

This study aims to discuss the effect of chemical etching parameters such as (machining temperature, machining time, etchant type, and concentration of the solution) on the material removal rate and surface roughness of ceramic materials (silicon carbide) as a specimen in chemical machining (CHM) process. This study aims to achieve the best value for the removal rate of the material as well as to obtain the best value for the surface roughness. Four levels of chemical machining process parameters were used in this study: the values of machining time (30, 50, 70, and 90) min, the etchant concentration (50, 60, 70, and 80) % and etching temperature (60, 80, 100, and 120) °C, and two etchant type (HCl, HBr). The results showed that the Taguchi method that has been performed using MINITAB 17 software gave results with good accuracy. The best value of material removal rate is obtained (0.5102) mg/min at experimentally and (0.4816) mg/min at the predictable program, when using hydrochloric acid (HCl) at temperature (100) °C, time (30) min, and etchant concentration (70) %. The best value of surface roughness is obtained (2.933) µm at experimentally and (2.9589) µm at the predictable program, when using Hydrobromic acid (HBr) at temperature (80) °C, time (50) min, and etchant concentration (50) %. The coefficient determination (R-sq.) to predict the material removal rate (MRR) and surface roughness are (91.6) and (93.7) respectively. This means the model is perfect and fit.

Проблемы при использовании травителя KOH-IPA для текстурирования кремниевых пластин

The wet chemical treatment of monocrystalline silicon wafers, said method comprising texturing, represents one of the fundamental steps of manufacturing techniques of high-efficiency solar cells. As part of this work, methods for texturing single-crystal silicon wafers for solar cells were studied.As a result of studies, the optimal parameters of texturing technology for the studied samples were determined. The main type of etchant for texturing processes, which is a solution of KOH with isopropanol, is also determined.

Comparison of Shear Bond Strength Orthodontic Brackets Bonded to Zirconia and Lithium Disilicate Crowns.

Aimof this study was to analyze Shear Bond Strength (SBS) and Adhesive Remnant Index (ARI) of ceramic and metallic orthodontic brackets bonded to zirconia or lithium-disilicate ceramics used for prosthetic restorations, conditioned with hydrofluoric acid (HFA) or phosphoric acid (PhA), as well as to determine the Porcelain Fracture Index (PFI), in order to examine the condition of the ceramic surface after debonding.Material and methodsThe research was conducted on 96 prepared all-ceramic samples divided into 8 groups combined from the type of ceramic material, orthodontic brackets, and surface conditioning. SBS was tested with Universal Testing Machine, and the samples were analyzed using a Scanning Electron Microscope, to determine ARI and PFI. Statistical data were processed using ANOVA, with the level of significance α = 0.05.ResultsLithium-disilicate showed better bond strength in almost all groups. However, no significant difference between the groups was noticed and none of the factors had a significant influence on the mean values of SBS (p>0.05). Nevertheless, ARI significantly depended on the type of bracket (p = 0.005), and PFI significantly depended on the type of etchant (p = 0.029).ConclusionThe use of HFA for surface etching of zirconia and lithium-disilicate, does not cause a significant increase in the SBS values as compared to etching with PhA and silane application. Furthermore, HFA can weaken the surface structure of the ceramic, and considering its toxicity, might not be the best suitable conditioner prior to orthodontic bonding to lithium disilicate, and in particular to zirconia, also taking into account its crystalline structure.

(Invited) High-Temperature Behaviors of MXenes

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) have recently attracted much attention because of their electronic structure and properties that differ from their bulk counterparts [1]. MXenes were first discovered at Drexel University in 2011 [2] by selective chemical etching of aluminum layers from ternary transition metal carbides known as MAX. The general chemical formula of MXene is written as (Mn+1XnTx) [3], where M is an early transition metal (Ti, Nb, Ta, V, Mo, etc.), X is C and/or N, and n = 1- 3 [4]. Due to the chemical synthesis in fluorine-containing solution MXene have surface functional groups (Tx), which can be fluorine (-F), oxygen (-O), or hydroxyl (-OH) groups [3, 4]. Most chemically synthesized MXenes are hydrophilic and some exhibit high electrical conductivity [5, 6]. More than 20 different MXenes have been experimentally synthesized and several more varieties of MXenes have been predicted, rendering MXenes among the most diverse, tunable and fastest growing 2D materials [3]. MXenes have already shown a promising performance in many applications such as energy storage [7], electromagnetic interference shielding [8], water desalination [9], and optoelectronics [10]. However, the moiety and quantity of the surface functional groups have been shown to be dependent on the synthesis conditions [11], and shown to affect the quality and properties of MXene [5, 12]. Here, we systematically study the thermal stability as well as the surface moieties of MXenes, namely (Ti3C2Tx, Mo2CTx, Mo2TiC2Tx and Mo2Ti2C2Tx), using simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) from ambient temperature to 1500 °C. We also discuss the effect of MXene synthesis, that is etchant type and concentration, on surface functional groups. For example, the amount of –OH, –F, and structural water is different and dependent on varying the composition of fluorine-containing etchants. Also, the thermal stability of MXenes strongly depends on their chemical composition. This study sheds lights on the importance of synthesis conditions in controlling MXenes compositions, structure and their surfaces for a variety of potential applications. References Naguib M. Two-dimensional transition-metal carbides and carbonitrides, In: Nanomaterials Handbook, 2ed. Advanced Materials and Technologies Series (Ed. Gogotsi Y.), 2017, Boca Raton: Taylor & Francis Group, CRC Press, pp. 83-103.Naguib M., Kurtoglu M., Presser V., Lu J., Niu J., Heon M., Hultman L., Gogotsi Y., Barsoum M.W. Two-dimensional nanocrystals produced by exfoliation of Ti3AlC2. Adv. Mater. 2011, 23, 4248-4253.Anasori B., Lukatskaya M. R., Gogotsi Y. 2D metal carbides and nitrides (MXenes) for energy storage. Nature Rev. Mater. 2017, 16098, 1-17.Naguib M., Gogotsi Y. Synthesis of two-dimensional materials by selective extraction. Acc. Chem. Res.2015, 48, 128-135.Alhabeb M., Maleski K., Anasori B., Lelyukh P., Clark L., Sin S., Gogotsi Y. Guidelines for synthesis and processing of two-dimensional titanium carbide (Ti3C2Tx MXene). Chem. Mater. 2017 29, 7633-7644.Maleski K., Mochalin V.N., Gogotsi Y. Dispersions of two-dimensional titanium carbide MXene in organic solvents. Chem. Mater. 2017, 29, 1632-1640.Lukatskaya M. R., Kota S., Lin Z., Zhao M.-Q., Shpigel N., Levi M. B., Halim J., Taberna P.-L., Barsoum M. W., Simon P., Gogotsi Y. Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides. Nature Energy 2017, 2, 17105.Shahzad F., Alhabeb M., Hatter C., Anasori B., Hong S. M., Koo C. M., Gogotsi Y. Electromagnetic interference shielding with 2D transition metal carbides (MXenes). Science 2016, 353, 1137-1140.Ren C. E., Hatzell K. B., Alhabeb M., Ling Z., Mahmoud K., Gogotsi Y. Charge- and size-selective ion sieving through Ti3C2Tx MXene membranes. J. Phys. Chem. Lett. 2015, 6, 4026-4031.Jhon Y. I., Koo J., Anasori B., Seo M., Lee J. H., Gogotsi Y., Jhon Y. M. Metallic MXene saturable absorber for femtosecond mode-locked lasers. Adv. Mater. 2017, 29, 1702496 (1-8).Hope M. A., Forse A. C., Griffith K. J., Lukatskaya M. R., Ghidiu M., Gogotsi Y., Grey C. P. NMR reveals the surface functionalisation of Ti3C2 MXene. Phys. Chem. Chem. Phys. 2016, 18, 5099-5102.Sang X., Xie Y., Lin M.-W., Alhabeb M., Van Aken K. L., Gogotsi Y., Kent P. R. C., Xiao K., Unocic R. R. Atomic defects in monolayer titanium carbide (Ti3C2Tx) MXene. ACS Nano, 2016, 10, 9193-9200

Investigation of Microstructure Properties and Quantitative Metallography by Different Etchants in the Service-Exposed Nickel-Based Superalloy Turbine Blade

In this study, the effect of etchant type and etching conditions on the root and airfoil microstructure of a service-exposed IN738 turbine blade has been investigated. The microstructure of superalloy components used at high temperatures, in addition to the usual microstructural changes, experiences deterioration in micrometer dimensions. In order to investigate these changes, electrochemical etching was performed on the samples with the chemical solution including 80% phosphoric acid, solution containing Cr2O3 and 55% glycerol. Chemical etching was performed with marble and etchant solution containing 60% glycerol. The results in terms of specifying the deterioration effects on microstructure of the blade applied at high temperature, the amount of γ′ phase and the best etchant were investigated. Among the solutions used for chemical etching, the solution containing 10 ml HNO3, 50 ml HCl and 60 ml glycerol was appropriate for detection of segregations and dendrites, and among the electrochemical etching solutions, the Cr2O3 solution was found suitable for specifying γ′ precipitates’ morphology by scanning electron microscopy. In this research, the results of the quantitative analysis of the images provided by these etchants were also investigated.

The effect of proanthocyanidin-containing 10% phosphoric acid on bonding properties and MMP inhibition

ObjectivesThis study evaluated the effect of etching using 2% proanthocynidin-containing 10% phosphoric acid 2% PA/10% PhA vs. 35% phosphoric acid 35% PhA on immediate (IM) and 6-months (6M) resin–enamel microshear bond strength (μSBS), resin–dentin microtensile bond strength (μTBS), nanoleakage (NL) and as well as in situ MMP inhibition potential. MethodsThe dentin surface of human were exposed and then etched using 35% phosphoric acid for 15s or 2% PA/10% phosphoric acid for 30s. After rinsing with water, the dentin was bonded with Single Bond Plus (3M ESPE) and composite build-ups were constructed, followed by polymerization. The teeth were sectioned and the bonds were testing for microtensile bond strength (μTBS) and by SEM for NL analysis at IM and 6M. For MMP activity, resin–dentin slices were prepared for in situ zymography, and analyzed under confocal microscopy. For μSBS, others teeth had flattened enamel surfaces etched according the experimental groups and prepared to microshear procedure. The specimens were tested IM and after 6M by microshear bond strength. The data were submitted to two-way repeated measures ANOVA and Tukey's test (α=0.05). ResultsAcid-etching using the 2% PA/10% phosphoric acid did not lower the μTBS in IM (p>0.05) compared to the control 35% phosphoric acid group. However, after 6M, only the 2% PA/10% PhA etched dentin had remained stable the resin–dentin bond strength (p<0.05). Bonds made with 35% PhA showed significant increase in NL% after 6M (p<0.05). Dentin bonds made with 2% PA/10% phosphoric acid showed no increase in NL% after 6 months. The MMP activity within the resin–dentin interface was almost completely reduced after 2% PA/10% PhA etching, while the 35% PhA exhibited intense MMP activity. For μSBS, the type of etchant and the storage period did not affect the resin–enamel bond strengths (p>0.05). SignificanceTen percent phosphoric acid containing 2% PA can produce stable resin–dentin and enamel–resin interfaces, without requiring additional steps in the bonding procedure. Future studies for longer evaluation time are required.

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

A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

Wet anisotropic etching based silicon micromachining is an important technique to fabricate freestanding (e.g. cantilever) and fixed (e.g. cavity) structures on different orientation silicon wafers for various applications in microelectromechanical systems (MEMS). {111} planes are the slowest etch rate plane in all kinds of anisotropic etchants and therefore, a prolonged etching always leads to the appearance of {111} facets at the sidewalls of the fabricated structures. In wet anisotropic etching, undercutting occurs at the extruded corners and the curved edges of the mask patterns on the wafer surface. The rate of undercutting depends upon the type of etchant and the shape of mask edges and corners. Furthermore, the undercutting takes place at the straight edges if they do not contain {111} planes. {100} and {110} silicon wafers are most widely used in MEMS as well as microelectronics fabrication. This paper reviews the fabrication techniques of convex corner on {100} and {110} silicon wafers using anisotropic wet chemical etching. Fabrication methods are classified mainly into two major categories: corner compensation method and two-steps etching technique. In corner compensation method, extra mask pattern is added at the corner. Due to extra geometry, etching is delayed at the convex corner and hence the technique relies on time delayed etching. The shape and size of the compensating design strongly depends on the type of etchant, etching depth and the orientation of wafer surface. In this paper, various kinds of compensating designs published so far are discussed. Two-step etching method is employed for the fabrication of perfect convex corners. Since the perfectly sharp convex corner is formed by the intersection of {111} planes, each step of etching defines one of the facets of convex corners. In this method, two different ways are employed to perform the etching process and therefore can be subdivided into two parts. In one case, lithography step is performed after the first step of etching, while in the second case, all lithography steps are carried out before the etching process, but local oxidation of silicon (LOCOS) process is done after the first step of etching. The pros and cons of all techniques are discussed.

A detailed investigation and explanation of the appearance of different undercut profiles in KOH and TMAH

In wet anisotropic etching, the etched profile of undercut convex corners depends on the type of etchant. A considerable amount of research has been carried out to explain this convex corner undercutting and to identify the orientation of undercut planes. However, it is not clearly understood why differently shaped undercut fronts appear with different etchants. Moreover, there has been no descriptive explanation regarding the distinct shape of the undercut convex corner in both KOH and TMAH. In this work, corner undercutting on the surface of a Si{100} wafer is thoroughly investigated. The undercutting behavior is examined for two different kinds of etchants (KOH and TMAH). The study is performed by analyzing the etching characteristics of different kinds of convex corners on the mask patterns. One type of corner in the mask design is formed by <110 > directions, while other types are formed by the intersection of different directions, which shapes the undercut convex corner profile. Furthermore, the appearance of etchant-dependent beveled directions at convex corners is clearly explained using the contour plot of the etch-rate data of a silicon hemisphere.