Three-dimensional electrochemical microfabrication of n-GaAs using l-cystine as a scavenger

The confined etchant layer technique (CELT) was used to fabricate complex three-dimensional (3D) microstructures on gallium arsenide (n-GaAs). The design of an appropriate chemical etching system is needed in order to realize successful microfabrication. In this study, Br₂ was electro-generated at the mold surface and used as an efficient etchant for n-GaAs. The use of l-cystine as a scavenger to replace the toxic scavenger H₃A_SO₃ was explored. The resolution of the fabricated microstructure depended strongly on the composition of the electrolyte, and especially on the concentration ratio between l-cystine and KBr. A well-defined and polished Pt micro-cylindrical electrode with a diameter of ∼50 μm was employed as one kind of mold for CELT. By inspecting the deviation of the sizes of the etching spots from the real diameter of the microelectrode, the thickness of confined etchant layer (CEL) can be estimated and thus the composition of electrolyte can be optimized for better etching precision. By choosing an appropriate concentration ratio between l-cystine and KBr, complex microstructures were fabricated successfully on n-GaAs. The etched patterns on n-GaAs were approximately negative copies of the mold, and the precision of duplication could easily reach the submicrometer scale, which was better than that achieved with H₃A_SO₃. The experimental results indicated that l-cystine is a good scavenger for microfabrication on n-GaAs by CELT. This technique avoids severe pollution of the environment, which will help to extend its future application in industry.     

Electrochemical behaviour of the surface treated composite-electrolyte/electrode interface

The effect of surface treatment of the solid electrolyte 50 wt% (4.7 mol% Sc₂O₃+95.3 mol % ZrO₂)+ 50 wt % Al₂O₃ (used in the SIRO₂ low temperature oxygen sensor) on its electrochemical behaviour has been studied by complex impedance spectroscopy. Two techniques, namely, preferential etching of alumina from the surface by a suitable etchant and cosintering of a thin layer of an alumina free electrolyte composition were used. The electrode/electrolyte interfaces prepared by using surface treated electrolyte samples had much lower electrode resistance (by a factor of 3–6) compared with the untreated surfaces. The decrease in the interfacial impedance is attributed mainly to the absence of alumina at the interface (an insulator phase) at which no oxygen exchange reactions could take place.     

A potential method for electrochemical micromachining of titanium alloy Ti6Al4V

The micromachining of complex three-dimensional microstructures (bulk micromachining) on metals can be applied to fabricate many novel devices for micro electromechanical system (MEMS), which will greatly benefit the development of MEMS. In this paper, a new electrochemical micromachining method named the confined etchant layer technique (CELT) was explored on the micromachining of the titanium alloy. Micro-scale trapezoidal slots were replicated on titanium alloy by using a mold with the corresponding negative microstructures (trapezoidal teeth). The machining resolution reached 0.503 μm. The electrochemical mechanisms involved in the process are analyzed and the parameters that influenced the machining resolution are discussed. A. Attia is on leave from Physical Chemistry Department, National Research Centre, El-Tahrir St., Dokki, Cairo, Egypt.     

Three-dimensional micromachining for microsystems by confined etchant layer technique

The micromachining of GaAs with three different truly three-dimensional (3D) molds were performed by the confined etchant layer technique (CELT). The etched patterns were found, approximately, to be the negative copy of the 3D molds. The general comparison of CELT with the existing micromachining techniques, such as two-dimensional (2D) projection lithography and electro-discharge machining, was made. The replication of the complex microstructures down to micrometer scale has been done by CELT in a single step. The photoresist layer, together with the procedures of exposure, developing and removal of resist, could be eliminated. The advantages of CELT over the existing lithography techniques and its potential applications are discussed briefly. It has been shown that CELT could be developed as a complementary technique to the existing micromachining techniques in fabricating microdevices for microsystems.     

Micromachining of CVD diamond by RIE for MEMS applications

Reactive Ion Etching (RIE) is an effective method for etching of diamond films. In this paper, the influences of maskant, gas pressure and the composition of reactive gas on the etch rate and etched surface of diamond are studied. The patterned metal film used as hard mask plays an important role in etching process, it can be sputtered and re-deposited as metal oxides on the etched surface of diamond, acting as a micromask on the bottom face and a passivating layer on its sidewall. Trying to enhance the sidewall passivation and destroy the micromask on the bottom of the etched trench, the diamond film can be precisely patterned into smooth, steep and straight microstructures with inerratic and integrated boundaries and well kept dimensions of patterns as well. This is the so-called sidewall passivation mechanism for micromachining of CVD diamond. A gas mixture of oxygen and argon is used as the etching gas, with the concentration of argon being in the range of 0% to 100% (V/V), and the etching result reveals that increase in argon always leads the etch rate to going down, thus it is not necessary. The gas pressure influences the etched surface and etched contours of fabricated diamond microstructures remarkably.     

Interface layers of fiber reinforced composites with transcrystalline morphology

Summary In fiber reinforced polymer composites with transcrystalline structure, an interface layer can exist between the fiber and the transcrystalline area. Polymer chains orient along the fiber when the matrix consists of liquid crystalline polymers and form row structures on the fiber surface. The interface layer is not oriented and consists of crystalline aggregates, when the matrix is a flexible polymer. The interface layer can be easily etched by a chemical etchant or by ion etching, whereas the transcrystalline areas are revealed by controlling the degree of etching. As a result, the interface layer and the transcrystalline area can be well distinguished from each other by using scanning electron microscopy (SEM).     

Vibration etching,a method of evaluation of photoresist characteristics

A new method of etching is described, the principle of which is the vibration of the sample being etched within the etchant. Because only small samples can be used this method is not suitable for commercial etching. As a test procedure however it has several advantages: a small volume of etchant (about 100 cc) is sufficient, the pressure of etchant attack can be varied and measured continuously, and the temperature can easily be controlled. Examples are given to demonstrate that vibration etching can be applied for characterization as well as for control of photoresist giving data of etch resistance, etch factor, adhesion, flexibility. Also the characteristics of different etchants and the etch behavior of different metal substrates can easily be compared.     

Cycle of two-step etching process using ICP for diamond MEMS applications

Inductively coupled plasma (ICP) etching was performed to etch diamonds, and a new diamond etching technique was established in order to obtain the high selective etching rate of diamond with respect to the silicon oxide etching mask and the smooth etched surface. Scanning electron microscope (SEM) observations and energy dispersive X-ray (EDX) characterizations of the etched diamond surfaces show that the silicon oxide etching mask particles were re-deposited on the fresh etched diamond surface. This results in un-intentional whisker formation. In order to obtain both the high selectivity and the smooth etched surface, a sequential cycle of ICP etching was, for the first time, applied for diamond. Diamond is etched with O₂ plasma during the first step and, in the second step, silicon oxide was removed using (CF₄ + O₂) plasma. Both the selective etching rate of diamond to silicon oxide was improved and the smooth surface was obtained. By applying the two-step etching process, diamond gene-surgery tips for atomic force microscopy (AFM) have been fabricated.     

The role of silanol groups on the reaction of SiO2 and anhydrous hydrogen fluoride gas

It is essential to etch SiO₂ for producing silica glass components, semiconductor devices, and so on. Although wet-etching with hydrogen fluoride (HF) solutions is usually employed for this purpose, it faces a drawback that microstructures stick during the drying of the solution. To overcome this problem, we have developed a dry-etching technique with gaseous HF at high temperatures. In the present study, an interesting phenomenon was found that silicon thermal oxides were much less etched than vitreous silica by gaseous HF. Such difference had not been found in wet- or humid HF gas etching. Because their bulk chemical formulae are the same (SiO₂), it was suggested that the surface species affected the reaction rate. In fact, preprocessing with water vapor plasma remarkably increased the etching rate on the thermal oxides layer, and vacuum heating almost completely suppressed the reaction on the vitreous silica and the plasma-treated thermal oxides. These results indicate that the surface silanol groups enhance the reaction between SiO₂ and gaseous HF. Based on the results, a model of chain reaction for SiO₂ and gaseous HF was proposed, where the surface silanol groups act as the reaction center.     

Alpha-hydroxy glycolic acid for root dentin etching: Morphological analysis and push out bond strength

The purpose of this study was investigated the use of α-hydroxy glycolic acid as a dentin etchant for adhesive procedures in the root canal. The etching pattern of glycolic acid and mineral content distribution of root canal dentin were assessed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The effect of glycolic acid surface etching on the push out bond strength of fiber post to root dentin was assessed using three adhesive systems: Single Bond Universal [SBU], Scotchbond Multipurpose [SBMP], and Ambar [AM]. The 37% phosphoric acid was used as a control group. The bond strength values were statistically compared using ANOVA/Fisher LSD tests (α = 0.05). SEM revealed similar etching patterns for phosphoric acid and glycolic acid. Both acids also shared similar interfacial morphology of the hybrid layer. EDS showed similar levels of Ca and Mg after treatment with glycolic acid when compared with phosphoric acid. When the P level was compared, it was observed that phosphoric acid caused greater removal of P. The push out bond strengths were statistically similar between glycolic acid and phosphoric acid in all groups (p > 0.05). Comparisons using post hoc Fisher LSD test showed that the bond strengths in the SBU and SBMP groups were not significantly different from each other (p > 0.05). The bond strength in the AM group was similar to that in the SBMP group (p > 0.05); however, it was significantly lower than that in the SBU group (p < 0.05). It can be concluded that the glycolic acid effectively etched root dentin surfaces, resulting in a surface pattern, hybrid layer, and push out bond strength similar to those produced by traditional phosphoric acid. Therefore, glycolic acid may be recommended as a suitable root dentin surface etchant for adhesive restorative procedures.     

Aerosol etching by low-pressure impaction

Low-pressure impaction technology has been applied to a new etch process using aerosol, called aerosol jet etching (AJE). Fine droplets (0.1 to 0.3 urn) produced by spray-evaporation-condensation method impinge on a substrate in low-pressure impactor and etches its surface. Investigations were carried out on the control of etchant droplet size, the critical diameter for impaction and the performance of AJE on patterned etching. The patterned etching on SiO₂ film reveals some advantages over conventional wet etching: the economic use of etchant, the reduction of waste disposal and the increase in controllability of etching. To make maximum use of the advantage of AJE, techniques of further decreasing the droplet size and depositing this small droplets on substrates need to be developed.     

Influence of different etching protocols on the reliability of resin bonding to CAD/CAM feldspathic porcelain

ObjectivesTo evaluate the effects of different acid etching times on the mechanical strength of dental porcelain as well as the influence on the reliability of resin bonded CAD/CAM porcelain veneer.Material and MethodsRectangular CAM/CAM feldspathic porcelain (Mark II, Vita Zahnfabrik) specimens (12 mm×10 mm×4 mm) were prepared and polished with silicon carbide abrasive paper under running water. All the samples were randomly divided into four groups according to the corresponding etching protocols: control group (without any treatment), group A (etched with a gel etchant containing 5% hydrofluoric acid for 30 s and rinsed with de-ionized water), group B (etched for 1 min and rinsed), group C (etched for 2 min and rinsed). After silanization, resin stubs were adhered on porcelain surface. There are 25 resin–porcelain samples prepared in each group and subjected to the shear bond strength testing. Weibull analysis was conducted to evaluate of the reliability of resin–porcelain bonding. For each of the etching method, eight additional porcelain samples (3 mm×2 mm×10 mm) were prepared and etched. Then, surface roughness (R_a), microhardness (Vickers Hardness) and biaxial flexural strengths were measured on these porcelain specimens. Energy dispersive X-ray spectrometry technique was used to assess the changes in surface chemical composition after etching and the surface topography was recorded under atomic force microscope (AFM) and scanning electron microscopy (SEM).ResultsThe reliability of resin to CAD/CAM porcelain bonding was decreased with the increase in HF etching time. The application of HF etching for 30 s decreased the Vickers hardness number (HV) significantly from 651.6 (control group) to 488.7 (group A). With the extension of etching time, the Vickers hardness number was further reduced to 430.1 (group B) and 305.7 (group C). However, the biaxial flexural strengths of these four groups were not statistically significant different (p>0.05). AFM revealed the porous structures on the porcelain surface at microscopic level.ConclusionsThe application of HF to etch the CAD/CAM feldspathic porcelain surface reduced the microhardness number. Etching with 5% hydrofluoric acid on dental porcelain for more than 1 min might impair the reliability of resin bonded porcelain veneer.     

A New Surface Etching Method Using MnO2/H2SO4 Colloid for Adhesion Improvement of Epoxy Polymer

Abstract

A new surface etching method using MnO₂/H₂SO₄ as the etchant to improve the adhesion between an epoxy polymer surface and a metallic layer, was studied. The effects of bath temperature, etching time and H₂SO₄ concentration on the surface topography and chemical properties were investigated. After the etching treatment of the MnO₂–H₂SO₄ colloid, not only did the surface roughness increase remarkably, but also the surface of epoxy became hydrophilic and the contact angle of the epoxy surface was also decreased from 93.5° to about 8.0°. The X-ray photoelectron spectroscopy analysis indicated that as a result of the etching treatment, hydroxyl, carbonyl and carboxylic acid groups formed on the epoxy surface. The adhesion strength was markedly enhanced with the appropriate etching treatment, which was attributed to the improvement of the surface roughness and the increased hydrophilicity.     

Robust,low haze and graded porous anti-reflective glass by Tailoring the Nanostructures

Low haze and anti-reflective glass has high potential applications in automobile and optoelectronic fields. Etching is a novel and effective method to fabricate gradient refractive index anti-reflective layer on glass surface. However, the gradient layer on glass surface prepared by the etching method usually characterizes rough porous structure, and the structural defect results in high haze and low abrasion resistance to restrict its applications. In this paper, a hydrothermal etching method has been explored to prepare anti-reflective glass. It has demonstrated to be a new and facile method successfully to tailor the porous nanostructure of gradient refractive index layer and largely decrease the haze of the glass, by adding complex compound in the etching solution. Compared with the etching solution containing NaOH, adding the complex compound of C₆H₅Na₃O₇ in the etching solution has the advantage to overcome the defects. The grain diameter of the graded porous anti-reflective film decreases from ~63 nm to ~18 nm, the etched film thickness increases from 0.44 μm to 1.55 μm, the haze decreases drastically from 23.76% to 1.00%, the reflectivity decreases from 5.88% to 1.08% and the abrasion resistance greatly increases. However, when changing the complex compound from C₆H₅Na₃O₇ to Na₂HPO₄, the haze is 23.44% and has no effect on decreasing haze. Structural characterizations show that the grain size in the porous gradient layer can be easily tailored by changing the ion radius of complex anion in the etching solution, and the optical properties can be controlled. The paper provides new insights into the nanostructures and the preparation approach of anti-reflective glass.     

Electroplating onto inorganic glass surfaces - Part II: Mechanical treatment to improve adhesion‡

The metallization of glass surfaces was carried out using chemical and mechanical methods to achieve a roughened surface. Comparable to ABS polymers, where chemical treatment resulted in a selective etching of the chemically weaker phase and the adhesion mechanism was due to mechanical keying of the metal into the etched caverns, a finely structured glass surface must be properly prepared to ensure metal anchoring. For chemical treatment, melts of sodium and potassium hydroxide and potassium hydrogen sulfate were used. The treatment did not result in a finely roughened surface structure and no improvement in adhesion could be achieved. A mechanical treatment (using abrasive blast with Al₂O₃ of various grain sizes) produced a uniformly roughened glass surface but only with a combination of mechanical and chemical treatment, crevices comparable to the caverns produced in ABS-electroplating were attained. For chemical treatment, solutions of ammonium hydrogen fluoride of various concentrations were used. Soda-lime glass could be etched more easily than the borosilicate glass and gave higher peel-strengths.     

Effects of the surface modification of poly(amino acid)/hydroxyapatite/calcium sulfate biocomposites on the adhesion and proliferation of osteoblast‐like cells

In this study, we focused on the surface modification of a novel poly(amino acid) (PAA)/hydroxyapatite/calcium sulfate composite and the effect of its surface modification on cellular responses. The surface modification was performed by sandblasting (sample S2), calcium chloride ethanol saturated solution etching (sample S3), and formic acid etching (sample S4) followed by in vitro culturing of osteoblast‐like cells. The obtained results indicate that a new interface of the composite was formed during the modification, and the modified surface was changed with respect to its surface morphology by physical abrasion. The calcium chloride ethanol saturated solution etchant etched PAA selectively whereas forming rich calcium‐phosphate (Ca–P) apatite on the surface of S3. The formic acid etchant attacked the inorganic component without changing the PAA state. Cell attachment and cell proliferation were improved by the treatments of S2 and S3 in comparison with no treatment and the treatment of S4 © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42427.     

Low-damage direct patterning of silicon oxide mask by mechanical processing

To realize the nanofabrication of silicon surfaces using atomic force microscopy (AFM), we investigated the etching of mechanically processed oxide masks using potassium hydroxide (KOH) solution. The dependence of the KOH solution etching rate on the load and scanning density of the mechanical pre-processing was evaluated. Particular load ranges were found to increase the etching rate, and the silicon etching rate also increased with removal of the natural oxide layer by diamond tip sliding. In contrast, the local oxide pattern formed (due to mechanochemical reaction of the silicon) by tip sliding at higher load was found to have higher etching resistance than that of unprocessed areas. The profile changes caused by the etching of the mechanically pre-processed areas with the KOH solution were also investigated. First, protuberances were processed by diamond tip sliding at lower and higher stresses than that of the shearing strength. Mechanical processing at low load and scanning density to remove the natural oxide layer was then performed. The KOH solution selectively etched the low load and scanning density processed area first and then etched the unprocessed silicon area. In contrast, the protuberances pre-processed at higher load were hardly etched. The etching resistance of plastic deformed layers was decreased, and their etching rate was increased because of surface damage induced by the pre-processing. These results show that etching depth can be controlled by controlling the etching time through natural oxide layer removal and mechanochemical oxide layer formation. These oxide layer removal and formation processes can be exploited to realize low-damage mask patterns.     

Highly Porous SiOC Bulk Ceramics with Water Vapor Assisted Pyrolysis

Micro/mesoporous SiOC bulk ceramics with the highest surface area and the narrowest pore size distribution were prepared by water‐assisted pyrolysis of polysiloxane in argon atmosphere at controlled temperatures (1100°C–1400°C) followed by etching in hydrofluoric acid (HF) solution. Their pyrolysis behaviors, phase compositions, and microstructures were investigated by DSC, FTIR, XRD, and BET. The Si–O–Si bonds, SiO₂‐rich clusters, and SiO₂ nanocrystals in the pyrolyzed products act as pore‐forming species and could be etched away by HF. Water injection time and pyrolysis temperature have important effects on phase compositions and microstructures of the porous SiOC bulk ceramics, which have a maximum‐specific surface area of 2391.60 m²/g and an average pore size of 2.87 nm. The porous SiOC ceramics consist of free carbon phase, silicon carbide, and silicon oxycarbide.     

Fabrication of nanoporous copper ribbons by dealloying of Al-Cu alloys

Nanoporous copper (NPC) ribbons were synthesized by free corrosion dealloying of Al-Cu alloy ribbons prepared by single-roller melt spinning processing equipment for precursor samples. The components and microstructures of NPC were characterized by utilizing X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDS) analysis. The results show that, the microstructures of the NPC ribbons strongly depend upon the phase constitutions of the starting Al-Cu alloys. In dealloying, Al atoms in the ??-Al phase and Al₂Cu phase can be easily etched off, resulting in the formation of NPC with a homogeneous porous structure, while the AlCu phase can hardly be eroded. Moreover, etching solution and annealing process also have important effects on the dealloying process and morphology of the NPC ribbons.     

Fouling Resistance on Chemically Etched Hydrophobic Surfaces in Nucleate Pool Boiling

Chemical etching, liquid phase deposition, and dipping techniques were utilized to fabricate highly hydrophobic micro‐ and nanoscale coating surfaces on stainless‐steel substrates. Heat transfer and fouling characteristics on these surfaces in pool boiling of deionized water and CaSO₄ solution were studied. High roughness and hydrophobicity of coated surfaces were obtained on chemically etched substrates. Compared to the polished stainless‐steel surface, the chemically etched coating surface provided a three times enhanced nucleate boiling coefficient at high heat flux. Obvious decrease of CaSO₄ fouling resistance was obtained on chemically etched surfaces due to the higher roughness and hydrophobicity before the fouling resistance reaches the asymptotic value. Slightly high asymptotic fouling resistance was observed compared with coating surfaces without chemical etching of substrates.