Etching Agents Research Articles

Hybrid chemical etching of femtosecond irradiated 3D structures in fused silica glass

We report on the fabrication of 3D micro-structures in fused silica glass using chemical etching along femtosecond laser irradiated zones. In particular, we exploited a novel approach combining two different etching agents in successive steps: the hydrofluoric acid, which provides fast volume removal, and potassium hydroxide, which exhibits high selectivity. We demonstrated that this hybrid approach enables a more easy prototyping and fabrication of complex geometries for microfluidic devices.

Finishing works after welding of structures made of rust-resistant, high-alloy steels

In this paper, problems that occur when working with welds formed of high-alloy steels to restore their passive layers, damaged as a result of temperature impact, are discussed. Particular attention was paid to the procedures concerning aggressive etching agents during and after completion of the passivation processes (waste neutralization and utilization).

A simple transformation from silica core–shell–shell to yolk–shell nanostructures: a useful platform for effective cell imaging and drug delivery

Silica-based yolk–shell nanostructures (SYSNs) are a potential platform of bioimaging and drug delivery for cancer diagnosis and therapy. Herein, a simple, flexible, green and controlled route to SYSNs is developed, in which structurally different silica core–shell–shell nanospheres are firstly prepared via a single step, and then their more porous interlayers are selectively etched by a mild agent (Na2CO3), resulting in the transformation of these silica core–shell–shell nanospheres to SYSNs. In this process, no complicated synthetic processes, special surfactants, corrosive etching agents or high-temperature treatments are involved; moreover, the size, shell thickness, shape and void space of the SYSNs are controllable by simply tuning the synthetic parameters. For cell imaging and drug delivery, the surface of the formed SYSNs is functionalized with fluorescein isothiocyanate (FITC) and polyethylene glycol (PEG), which show excellent biocompatibility and possess sustained drug release properties. Furthermore, the drug loaded nanocomposites can induce breast cancer cell death efficiently, and exhibit a long-term cytotoxicity in vitro, indicating their promising properties as drug carriers for cell imaging and cancer chemotherapy.

CoO octahedral nanocages for high-performance lithium ion batteries

Pure-phase CoO octahedral nanocages were successfully fabricated by a novel simple method. The coordination etching agents play key roles in the formation of these non-spherical hollow structures. When tested as anode materials in lithium ion batteries (LIBs), these nanocages showed excellent cycling performance, good rate capability and enhanced lithium storage capacity.

Main laws of the formation of composite membranes made of palladium alloys on a carrier made of corrosion-resistant steel with directional porosity

The main stages of formation of thin-film membranes with a functional layer of palladium-ruthenium alloy on a foil carrier made of corrosion-resistant steel with directed pores are studied. Selective etching agents and etching modes are determined, and a project of a technological route for the production of such composite hydrogen-permeable membranes is developed.

Experiments on the Release of CMOS-Micromachined Metal Layers

We present experimental results on the release of MEMS devices manufactured using the standard CMOS interconnection metal layers as structural elements and the insulating silicon dioxide as sacrificial layers. Experiments compare the release results of four different etching agents in a CMOS technology (hydrofluoric acid, ammonium fluoride, a mixture of acetic acid and ammonium fluoride, and hydrogen fluoride), describe various phenomena found during the etching process, and show the release results of multilayer structures.

Geometry and surface damage in micro electrical discharge machining of micro-holes

Geometry and subsurface damage of blind micro-holes produced by micro electrical discharge machining (micro-EDM) is investigated experimentally to explore the relational dependence with respect to pulse energy. For this purpose, micro-holes are machined with various pulse energies on plastic mold steel samples using a tungsten carbide tool electrode and a hydrocarbon-based dielectric liquid. Variations in the micro-hole geometry, micro-hole depth and over-cut in micro-hole diameter are measured. Then, unconventional etching agents are applied on the cross sections to examine micro structural alterations within the substrate. It is observed that the heat-damaged segment is composed of three distinctive layers, which have relatively high thicknesses and vary noticeably with respect to the drilling depth. Crack formation is identified on some sections of the micro-holes even by utilizing low pulse energies during machining. It is concluded that the cracking mechanism is different from cracks encountered on the surfaces when machining is performed by using the conventional EDM process. Moreover, an electrically conductive bridge between work material and debris particles is possible at the end tip during machining which leads to electric discharges between the piled segments of debris particles and the tool electrode during discharging.

Halogen-Assisted Copper Atom Abstraction: A Computational Perspective

ion reactions of copper from a (111) surface using halogen (F, Cl, and Br) atoms are studied as benchmark processes involving halogen-based etching agents. Reaction energetics are discussed, as well as potential energy surfaces that were created from ab initio energy calculations as functions of the center of mass and interatomic separation of the desorbing copper monohalide molecule. We support these results with a simple quantum dynamics model for the reaction leading to the desorption of CuF, which shows very high abstraction reaction probabilities. We also comment on analogous reactions on a Cu-terminated CuO surface.

Synthesis of Hollow Co Structures with Netlike Framework

Hollow Co structures with the size of 4-10 microm were fabricated by a simple solvothermal process using stearic acid as surfactant. Cobalt stearate formed at the initial stage and further self-assembled to micelles as a soft template. This precursor controlled the growth rate of Co crystal to form the primary nanorods attaching on the surface of the micelles. These nanorods then assembled into hollow Co spheres with a dense shell. Because of the acidic etching effect of stearic acid, however, the hollow Co spheres were further developed to Co nests constructed by netlike frameworks. Stearic acid acted as structure-directing and acidic etching agents in the formation of these novel hollow structures constructed by nanorods. The Co nests showed quite promising catalytic performance in hydrogenolysis of glycerol, demonstrating the potential application in heterogeneous catalysis.

Dual roles of stearic acid in the synthesis of Co nanomaterials in polyol

The role of stearic acid in the synthesis of Co nanostructures in polyol was demonstrated to be structure directing and acidic etching agents. Lower concentration of stearic acid favors the formation of Co nanowires with the diameter of 10 nm and the length up to 1000 nm through the structure directing effect, whereas higher concentration of stearic acid tends to produce Co nanoparticles with size of 10–50 nm mainly because of the acidic etching effect. Both the nanowires and the nanoparticles can effectively catalyze hydrogenolysis of glycerol to propylene glycol, giving quite promising activity and selectivity under very mild conditions.

A new environmentally friendly process for the recovery of gold from electronic waste

A new method for the recovery of precious metals, in particular gold, from electronic waste is proposed. This work focused on the research of an easily renewable etching agent, in order to make an environmentally friendly process possible. Two well known hydrometallurgical etching agents, FeCl3 and CuCl2, were evaluated in terms of efficiency and kinetics, testing solutions with different concentration of etchant and hydrochloric acid. The recovery of spent etching solutions was evaluated: promising results were found in the case of CuCl2, which can be completely restored by oxidation of the cuprous chloride formed during the etching using atmospheric oxygen.

Comparison of Different Etching Agents and Repair Materials Used on Feldspathic Porcelain

When fractures of fixed partial dentures occur, they cause an aesthetic and functional dilemma both for the patient and the dentist. Re-make of the entire restoration is an option, but not always desirable. Previous studies have provided several options for ceramic reparation, but there is limited consensus about this issue. The aim of this study was to test the shear bond strength due to four different etching agents for ceramic repair. The goal was to find a substitute for hydrofluoric acid as etching agent with less toxicity. Ideally, the repair of ceramics must meet both functional and aesthetic requirements. A total of 70 square shaped feldspathic porcelain disks of dimensions 10 mm × 10 mm × 3 mm were produced and embedded in cylindrical polyethylene walled poly(methyl methacrylate) (PMMA) blocks (16 mm diameter and 12 mm thick). All specimens were wet-ground with silicon carbide papers down to P4000. For one of the groups ten cylindrical ceramic specimens (diameter 5 mm and 2.5 mm high) were made and wet-ground to P4000. The blocks were divided into 7 groups with 10 specimens for each group. In six of the groups composite cylinders were bonded to the porcelain with different pretreatments of the porcelain. As etching agents 9% hydrofluoric acid (HF), 35% phosphoric acid (PO), 15% hydrochloric acid (HCl) and 15% potassium fluoride/hydrogen fluoride (KF·HF) were tested. This study compared a one-part (activated) silane and a new two-part silane. In one group two porcelain specimens were bonded with composite veneer cement. All the specimens were thermocycled for 5000 cycles from 5°C to 55°C before shear bond test. The best overall result was obtained in group 6 (two porcelain specimens bonded with veneer cement), and the mean shear bond strength was 24.5 MPa. The lowest values were obtained in group 4 with 35% phosphoric acid, and group 5 with 15% hydrochloric acid as the etching agent (6.5 and 0.8 MPa, respectively). Pretreatment with either 9% HF or 15% KF·HF as the etching agent combined with two-part silane gave good adhesion for porcelain reparations.

MgO nanobelts using a reactive and auto-removed ZnO nanobelt template

A newly developed chemical conversion route has been used to manufacture MgO nanobelts by using prefabricated ZnO nanobelts as a template. The converted MgO nanobelts are composed of small nanocrystals with an average diameter of 12 nm. Room-temperature photoluminescence measurement shows two emission bands centered at 392 and 478 nm which are attributed to various structural defects with different densities in the MgO nanobelts. Our approach here is effective and facile without additional etching agents being introduced. Other novel MgO nanostructures may be further fabricated by this method, depending on the morphologies of ZnO nanostructure templates.

Crystal growth vs. conventional acid etching: A comparative evaluation of etch patterns, penetration depths, and bond strengths

The present study was undertaken to investigate the effect on enamel surface, penetration depth, and bond strength produced by 37% phosphoric acid and 20% sulfated polyacrylic acid as etching agents for direct bonding. Eighty teeth were used to study the efficacy of the etching agents on the enamel surface, penetration depth, and tensile bond strength. It was determined from the present study that a 30 sec application of 20% sulfated polyacrylic acid produced comparable etching topography with that of 37% phosphoric acid applied for 30 sec. The 37% phosphoric acid dissolves enamel to a greater extent than does the 20% sulfated polyacrylic acid. Instron Universal testing machine was used to evaluate the bond strengths of the two etching agents. Twenty percent sulfated polyacrylic acid provided adequate tensile bond strength. It was ascertained that crystal growth can be an alternative to conventional phosphoric acid etching as it dissolves lesser enamel and provides adequate tensile bond strength.

Microcontact printing pattern as a mask for chemical etching: A scanning photoelectron microscopy study

Synchrotron-based scanning photoelectron spectromicroscopy and microspectroscopy were used to monitor the outcome of the etching process involving the transfer of a lithographic pattern produced by microcontact printing (μCP) of self-assembled monolayers (SAMs) to the underlying metal (gold) substrate. As a test system, octadecanethiolate (ODT) SAMs on gold substrates were chosen. The μCP ODT SAMs were found to protect the underlying gold against the wet-chemical etching, ensuring the effective transfer of the μCP pattern to the substrate. These SAMs exhibited only a slight degradation upon their exposure to the Au-etching solution. In contrast, a significant degradation of the edges of the printed features was observed. This degradation was predominantly related to a lateral diffusion of the active etching agents across these edges, along the SAMs-Au interface. This process can result in a blurring and narrowing of the printing features of a μCP SAM pattern at its transfer to the underlying substrate.

An evaluation of the otolith characteristics ofConger congerduring metamorphosis

A sample of 20 metamorphosing conger eelConger congerleptocephali were collected from the Minho River, Portugal, in February 1999 and their sagittal otoliths were analysed by scanning electron microscopy. Four different etching agents were applied along both sagittal and frontal sections during otolith preparation to examine the microstructural growth in this species. Otolith growth increments were visible throughout the increment countable zone using all four treatments, but a permanent peripheral diffuse zone, where the daily increments were unclear, appeared on all otoliths, preventing accurate age estimation. To understand more about the nature of the diffuse zone, otoliths of 10 other metamorphosing leptocephali reared in aquaria were marked by immersion in tetracycline hydrochloride. The distance between the fluorescent marks and otolith edge, measured over a fixed period of time, was used to estimate the otolith growth rate. The application of this technique led to an anomalously high estimated otolith growth rate, probably as a result of the capture, marking and handling stress.

Kinetics of cuprous oxide etching with β-diketones in Supercritical CO 2

Cuprous oxide films (Cu 2O) supported on Cu or on SiO 2 were etched using solutions of β-diketones including 1,1,1,5,5,5-hexafluoroacetylacetone, 2,2,6,6-tetramethyl-3,5-heptanedione and 2,2,7-trimethyl-3,5-octanedione (TMOD) in supercritical carbon dioxide at temperatures between 80 and 150 °C and pressures between 20 and 27.5 MPa. The films and etched substrates were analyzed by X-ray photoelectron spectroscopy depth profiling, field emission scanning electron microscopy and spectroscopic ellipsometry. Each of the etching agents was effective. Etching kinetics using TMOD were measured at 100, 125 and 150 °C. At 150 °C the etch rate was 1.5 nm/min. Based on the activation energy obtained from the studies (66 kJ/mol), etching rates of greater than 10.0 nm/min can be obtained at 200 °C.

Environmental risk assessment of hydrofluoroethers (HFEs)

Hydrofluoroethers (HFEs) are being used as third generation replacements to chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and perfluorocarbons (PFCs) because of their nearly zero stratospheric ozone depletion and relatively low global warming potential. HFEs have been developed under commercial uses as cleaning solvents (incl., HFE-7500, C 7F 15OC 2H 5; HFE-7200, C 4F 9OC 2H 5; HFE-7100, C 4F 9CH 3; HFE-7000, n-C 3F 7OCH 3), blowing agents (incl., HFE-245mc, CF 3CF 2OCH 3; HFC-356mec, CF 3CHFCF 2OCH 3), refrigerants (incl., HFE-143a, CF 3OCH 3; HFE-134, CHF 2OCHF 2; HFE-245mc, CF 3CF 2OCH 3), and dry etching agents in semiconductor manufacturing, (incl., HFE-227me, CF 3OCHFCF 3). From the environmental, ecological, and health points of view, it is important to understand their environmental risks for these HFEs from a diversity of commercial applications and industrial processes. This paper aims to introduce these HFEs with respect to physiochemical properties, commercial uses, and environmental hazards (i.e. global warming, photochemical potential, fire and explosion hazard, and environmental partition). Further, it addresses the updated data on the human toxicity, occupational exposure and potential health risk of commercial HFEs. It is concluded that there are few HFEs that still possess some environmental hazards, including global warming, flammability hazard and adverse effect of exposure. The partition coefficient for these HFEs has been estimated using the group contribution method; the values of log K ow for commercial HFEs have been estimated to be below 3.5.

Chemical Reduction and Wet Etching of CeO2 Thin Films

Cerium oxide is stable to commonly used aqueous etching agents and can be reliably etched only by a combination of chlorine and fluorine plasma. This hinders practical applications of pure and doped ceria thin films in bulk and surface micromachining. In the present work, the reasons for the chemical stability of cerium oxide in aqueous media were analyzed and two etching solutions were investigated. In the absence of stirring, the etching rate dropped with time. In an ultrasonic bath, etching was isotropic with a constant rate of ∼10 nm/min. This permits patterning of ceria films using chromium as a mask and demonstrates practical applicability of the proposed etching solutions. © 2005 The Electrochemical Society. All rights reserved.

Photographic appraisal of crystal lattice growth technique

Concept of creating mechanical retention for bonding through crystal growth has been successfully achieved in the present study. By using polyacrylic acid, sulphated with sulphuric acid as etchant, abundant crystal growth was demonstrated. Keeping in view the obvious benefits of crystal growth technique, the present SEM study was aimed to observe and compare the changes brought about by different etching agents (phosphoric acid, polyacrylic acid and polyacrylic acid sulphated) and to evaluate their advantages and disadvantages in an attempt to reduce iatrogenic trauma caused due to surface enamel alteration. Control and experimental groups were made of 24 and 30 premolars, respectively, for scanning electron microscopic appraisal of normal unetched and etched enamel surface and fracture site and finished surface evaluation. When compared with conventional phosphoric acid and weaker polyacrylic acid, investigations indicated that crystal growth treatment on enamel surface caused minimal iatrogenic trauma and surface alteration were restored to the original untreated condition to a large extent.