Fluoride Etching Research Articles

Fluoride etching opens the structure and strengthens the active sites of the layered ZSM-5 zeolite

The NH4F etching is a chemical approach for the preparation of hierarchical zeolites without substantial modification of their framework composition and acidic properties. We employed this approach to modify the 2-dimensional form of ZSM-5 and obtain a catalyst for bulky molecules conversion. The etching conditions were varied in order to obtain hierarchical ZSM-5 with different level of dissolution. Thus, obtained derivatives of 2-dimensional ZSM-5 were thoroughly studied in order to get deep insights into the effect of fluoride treatment. The 2-dimensional ZSM-5 was found unexpectedly stable under etching conditions, which is a consequence of the high quality of zeolite crystals containing a limited number of defect zones and misoriented crystalline domains, in contrast to conventional ZSM-5. Fluoride etching was also used to de-pillar 2-dimensional ZSM-5. The morphology and textural properties of the de-pillared ZSM-5 were very similar to those of the parent layered ZSM-5. Accordingly, amorphous and extra-framework species were dissolved first, resulting in the complete removal of extra-framework Al, thereby strengthening the active sites. In summary, the fluoride etching opens the structure of layered ZSM-5 and strengthens its acid sites when combined with dealumination during calcination.

Encapsulation of NEM Memory Switches for Monolithic-Three-Dimensional (M3D) CMOS⁻NEM Hybrid Circuits.

Considering the isotropic release process of nanoelectromechanical systems (NEMSs), defining the active region of NEM memory switches is one of the most challenging process technologies for the implementation of monolithic-three-dimensional (M3D) CMOS–NEM hybrid circuits. In this paper, we propose a novel encapsulation method of NEM memory switches. It uses alumina (Al2O3) passivation layers which are fully compatible with the CMOS baseline process. The Al2O3 bottom passivation layer can protect intermetal dielectric (IMD) and metal interconnection layers from the vapor hydrogen fluoride (HF) etching process. Thus, the controllable formation of the cavity for the mechanical movement of NEM devices can be achieved without causing any damage to CMOS baseline circuits as well as metal interconnection lines. As a result, NEM memory switches can be located in any place and metal layer of an M3D CMOS–NEM hybrid chip, which makes circuit design easier and more volume efficient. The feasibility of our proposed method is verified based on experimental results.

Making of a single solid-state nanopore on the wall of fused silica capillary.

A channel of nanometre size is an important platform for nanofluidic investigations. In this work, we show that a single solid nanopore can be generated by hydrogen fluoride etching of the outside wall of commercially available fused silica capillary. The geometry, size and the singleness were characterized by various means, including scanning electron microscope, electrolyte conductance measurement and a fluorescent microscope. The generation principle is also discussed. The nanopore thus generated features in low aspect ratio and exhibits typical nanofluidic effects such as ion concentration polarization, rectification and molecular translocation.

Adjustable Silicon Corner Rounding Radius by Wet Technique

Shallow trench isolation (STI) and active area (AA) top cornerrounding is important to device performance. AA top cornerrounding techniques include STI etch [1], linear oxidation [2], H2annealing [3] and wet oxide pull back (PB). However,conventional STI etch will caused AA facet and needs additionalthermal in liner oxidation or H2 annealing processes. Wet oxide PBeasily controls the pad oxide etching amount and reaches thedesired AA top corner top rounding radius. In this study, differentpad oxide PB was achieved by hydrogen fluoride (HF) etching andcorrelated with corner rounding. For high pad oxide PB, additionalhydrogen peroxide (H2O2) with dilute HF (DHF) can optimize theAA top corner profile and enlarge the corner radius.

Wavelength and Phase Detection Based SMS Fiber Sensors Optimized With Etching and Nanodeposition

The development of an optical fiber refractometer by hydrogen fluoride etching and sputtering deposition of a thin-film of indium tin oxide on a single-mode-multimode-single-mode fiber structure has been analyzed with the aim of improving the sensitivity to the changes of the refractive index (RI) of the external medium. The device is sensitive to the RI changes of the surrounding medium, which can be monitored by tracking the spectral changes of an attenuation band or with a fast Fourier transform (FFT) analysis. By using an optical spectrum analyzer combined with a simple FFT measurement technique, the simultaneous real-time monitoring is achieved. The results show that the sensitivity depends on the thin-film thickness. A maximum of 1442 nm/RIU (refractive index unit) in the 1.32–1.35 RIU range has been attained. In addition, a theoretical analysis has been performed, where simulations matched with the experimental results. As a practical application of the developed optical fiber structure, a °Brix (°Bx) sensor has been implemented with a sensitivity of 2.13 nm/°Bx and 0.25 rad/°Bx respectively for wavelength and phase shift detection.

Evaluation of insertion characteristics of less invasive Si optoneural probe with embedded optical fiber

A less invasive Si optoneural probe with an embedded optical fiber was proposed and successfully fabricated. The diameter of the optical fiber was completely controlled by hydrogen fluoride etching, and the thinned optical fiber can propagate light without any leakage. This optical fiber was embedded in a trench formed inside a probe shank, which causes less damage to tissues. In addition, it was confirmed that the optical fiber embedded in the probe shank successfully irradiated light to optically stimulate gene transfected neurons. The electrochemical impedance of the probe did not change despite the light irradiation. Furthermore, probe insertion characteristics were evaluated in detail and less invasive insertion was clearly indicated for the Si optoneural probe with the embedded optical fiber compared with conventional optical neural probes. This neural probe with the embedded optical fiber can be used as a simple and easy tool for optogenetics and brain science.

Fluoride etching of mordenite and its influence on catalytic activity

Due to its structure and high Si/Al ratio, zeolite mordenite has high thermal and acidic stability. Mordenite-type of zeolites have been used as catalysts in many industrially important reactions such as hydrocracking, hydroisomerization, alkylation, acid-catalyzed isomerization of alkanes and aromatics, reforming. In order to overcome the problem of the limited access to the active sites, OSDA-free synthesized mordenite undergoes fluoride etching as a post-synthetic treatment. The post-synthetic treatment is performed with hydrofluoric acid in combination with ammonium fluoride. Thus, the porosity is enhanced additionally without changing considerably the Si/Al ratio of the zeolite framework. All samples have been characterized by X-ray diffraction analysis, nitrogen adsorption, scanning electron microscopy, high-resolution transmission electron microscopy and solid-state nuclear magnetic resonance spectroscopy. The catalytic activity of the samples obtained has been investigated in the reaction of m-xylene transformation. All mordenite samples having undergone post-synthetic treatment exhibit catalytic activity higher than that of the parent sample.

Encasing Si particles within a versatile TiO2−xFx layer as an extremely reversible anode for high energy-density lithium-ion battery

The chemical phenomena occurring at the electrode-electrolyte interfaces profoundly determine the cycle behavior of a lithium ion battery. In this work, we report that silicon-based anodes can attain enhanced levels of capacity retention, rate performance and lifespan when a versatile protective layer of, F-doped anatase (TiO2−xFx), is applied towards taming the interfacial chemistry of the silicon particles. With careful choice of titanium fluoride as a precursor, internal voids can be generated upon in-situ fluoride etching of the native oxide layer and are used to alleviate the mechanical stress caused by volume expansion of silicon during cycling. In the course of F-doping, part of the Ti4+(d0) ions in anatase are reduced to Ti3+(d1), thereby increasing charge carriers in the crystal structure. Hence, the multifunctional F-doped TiO2−x coating, not only minimizes the direct exposure of the Si surface to the electrolyte, but also improves the electronic conductivity via inter-valence electron hopping. The best-performing composite electrode, Si@TiO2−xFx-3, delivered a satisfactory performance in both half-cell and full-cell configurations. Furthermore, we present a study of 1) the Si valence change at the buried interface using synchrotron based hard X-ray photoelectron spectroscopy, and 2) the phase transformation of the electrode monitored in operando using X-ray diffraction. Based on these characterizations, we observe that the Li+ conducting intermediate phase (LixTiO2−xFx) formed inside the surface coating enables deep lithiation and delithiation of the silicon during battery operation, and thus increase the capacity that can be accessed from the electrodes.

An HF-Free Etching of SiO2for Soft Lithography

We show that inorganic fluorides, such as NaF and NH 4 F, can etch SiO 2 in the presence of HCl vapor resulting in a negative tone pattern transfer to a SiO 2 substrate. Using a polydimethylsiloxane stamp, we demonstrate high-quality one-step pattern transfer to a SiO 2 substrate. Compared with traditional HF vapor etching and buffered oxide etching methods, the current approach avoids direct handling of HF and, therefore, significantly reduces the associated safety risks. Our results suggest that fluoride etching could be a general purpose pattern transfer technique for soft lithography of SiO 2 substrates.

New azidation methods for the functionalization of silicon nitride and application in copper‐catalyzed azide‐alkyne cycloaddition (CuAAC)

In this study, a new direct functionalization method of silicon nitride (Si3N4) using azidation and click chemistry is presented. First, amino groups (NHx) were created on a Si3N4 substrate by fluoride etching. These NHx‐terminated Si3N4 surfaces were analyzed by chemical derivatization X‐ray photoelectron spectroscopy with 4‐trifluoromethylbenzaldehyde, and a derivatization yield of 20% was concluded. In the second step, freshly prepared NHx surfaces were transformed into azides, which were used immediately in a click reaction with halogenated alkynes. The presented combination of amination, azidation, and click reaction is a promising alternative for common silane‐based Si3N4 functionalization methods. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous capture, detection, and inactivation of bacteria as enabled by a surface-enhanced Raman scattering multifunctional chip.

Herein, we present a multifunctional chip based on surface-enhanced Raman scattering (SERS) that effectively captures, discriminates, and inactivates pathogenic bacteria. The developed SERS chip is made of a silicon wafer decorated with silver nanoparticles and modified with 4-mercaptophenylboronic acid (4-MPBA). It was prepared in a straightforward manner by chemical reduction assisted by hydrogen fluoride etching, followed by the conjugation of 4-MPBA through AgS bonds. The dominant merits of the fabricated SERS chip include excellent reproducibility with a relative standard deviation (RSD) value smaller than 11.0 %, adaptable bacterial-capture efficiency (ca. 60 %) at low concentrations (500-2000 CFU mL(-1) ), a low detection limit (down to a concentration of 1.0×10(2) cells mL(-1) ), and high antibacterial activity (an antibacterial rate of ca. 97 %). The SERS chip enabled sensitive and specific discrimination of Escherichia coli and Staphylococcus aureus from human blood.

Simultaneous Capture, Detection, and Inactivation of Bacteria as Enabled by a Surface‐Enhanced Raman Scattering Multifunctional Chip

AbstractHerein, we present a multifunctional chip based on surface‐enhanced Raman scattering (SERS) that effectively captures, discriminates, and inactivates pathogenic bacteria. The developed SERS chip is made of a silicon wafer decorated with silver nanoparticles and modified with 4‐mercaptophenylboronic acid (4‐MPBA). It was prepared in a straightforward manner by chemical reduction assisted by hydrogen fluoride etching, followed by the conjugation of 4‐MPBA through AgS bonds. The dominant merits of the fabricated SERS chip include excellent reproducibility with a relative standard deviation (RSD) value smaller than 11.0 %, adaptable bacterial‐capture efficiency (ca. 60 %) at low concentrations (500–2000 CFU mL−1), a low detection limit (down to a concentration of 1.0×102 cells mL−1), and high antibacterial activity (an antibacterial rate of ca. 97 %). The SERS chip enabled sensitive and specific discrimination of Escherichia coli and Staphylococcus aureus from human blood.

Fluoride recovery from spent fluoride etching solution through crystallization of Na3AlF6 (synthetic cryolite)

Fluoride removal by precipitation of calcium fluoride is the most common practice in Taiwan to treat fluoride-containing wastewater in semiconductor or optoelectronic industries. Due to very fine CaF2 precipitates (∼0.1μm), coagulants/flocculants are needed to facilitate sedimentation of CaF2. In turn, large amount of sludge is produced by CaF2 precipitation/sedimentation process. In this study, removal of fluoride from spent fluoride etching solution by cryolite crystallization was investigated. Experimental and chemical equilibrium modeling results show that a good control of reaction pH and Al:F molar ratio is the key to form cryolite successfully. Formation of cryolite is exothermic reaction and formation of cryolite is less favor under elevated temperature. The highest residual fluoride concentration is found at reaction temperature of 90°C while those at 20 and 55°C are similar. Under Al/F molar ratios of 1:3 and 1:6 and pH of 5.5, the precipitates produced at room temperature are very similar to the commercial cryolite according to XRD, SEM, and EDX analysis. Particle size of cryolite precipitates ranges from 3μm to 15μm and is much larger than CaF2 precipitates of 0.1μm, resulting in rapid sedimentation. Cryolite crystallization process produces much less sludge volume than does by CaF2 precipitation.

Electroless deposition of Ru films on Si substrates with surface pretreatments

Electroless Ru depositions on Si substrates undergoing surface pretreatments such as hydrogen fluoride (HF) etching, HF etching and activation, as well as HF etching, sensitization, and activation are explored. The plating bath contains K2RuCl5∙xH2O, NaClO, NaOH, and NaNO2 at appropriate ratios. Continuous electroless Ru film is unable to obtain on the as-received Si wafer because the native oxide inhibits the process of nucleation and growth. In contrast, after surface pretreatments, dense and continuous Ru films are observed at reasonable growth rates. Contact angle measurements indicate a relatively hydrophilic surface after sensitization and activation, which leads to faster Ru film growths and larger surface roughness as compared to the HF-etched sample. X-ray photoelectron spectra confirm the formation of Sn and Pd nuclei and their presence promotes the heterogeneous growth of Ru films as evidenced by images from scanning electron microscope. In addition, depth profiling from Auger electron spectrometer suggests a uniform composition across the film thickness despite part of the Ru exists in an oxidized form.

Direct Photochemical Functionalization of Si(111) with Undecenol

Direct UV photochemical functionalization of H-terminated Si(111) with bifunctional 10-undecen-1-ol was achieved with selective attachment via its vinyl end, resulting in the formation of a compact monolayer with free terminal alcohol groups. This is due to the faster radical propagation mechanism in hydrosilylation with alkene compared to the nucleophilic attack mechanism of alcohol, which is impeded by intermolecular hydrogen bonding present at room temperature. Evidence from X-ray photoelectron spectroscopy, infrared spectroscopy, and resistance to fluoride etching shows that Si-C is the interfacial bond, and atomic force microscopy shows the presence of a smooth, uniform monolayer conforming to the atomic terraces of the Si(111) surface. The application of such a hydroxyl-terminated monolayer was demonstrated by tethering a bromoinitiator through surface esterification and thereafter subjecting the surface to the surface-initiated atom-transfer radical polymerization of butyl methacrylate. The poly(butyl methacrylate) brushes formed were found to be smooth (R(a) < 0.3 nm) and uniform even for a thin film of 4.0 nm.

Resist-less patterning on SiO2 by combination of X-ray exposure and vapor HF etching

We succeeded in a resist-less patterning of SiO2/Si substrates by a combination of X-ray exposure and vapor hydrogen fluoride (HF) etching. A 2 μm thick SiO2 layer was formed on a Si substrate by employing a thermal oxidation process. An X-ray mask consisted of a 1 μm thick Ta absorber on a 2 μm thick Si3N4 membrane mounted on a 1 mm thick Si frame, and a honeycomb pattern where 640 nm diameter circle dots arranged in the corners of a hexagon with a pitch of 960 nm was processed. X-ray exposure experiments were carried out on a beamline BL-4 with a peak photon energy of 2 keV at the TERAS synchrotron radiation (SR) facility. When a dose energy was 750 mAh, the transfer of the patterns was confirmed, although irradiations with different dose energy were also conducted. Moreover, heating temperatures and total etching times of SiO2/Si substrates in vapor HF etching were changed, and the shapes of etched patterns were observed by scanning electron microscope. It was learnt that an appropriate etching time existed between 30 and 60 min. Moreover, we observed discoloration of irradiated area by SR; and this seemed to be caused by changes in the etching rate of SiO2/Si substrates that led to the development of resist-less patterning technique.

Electric field assisted hydrogen fluoride etching of silica

The influence of electric fields on the velocity of the chemical reaction 4HF+SiO 2 →SiF 4 +2H 2 O in aqueous solution is investigated experimentally. The field strengths used were high enough to measure nonlinear effects. The results permit a critical analysis of a theoretical model known in literature. The basic idea of dipole orientation changing the rate of the primary step of the chemical reaction can explain the experimental data, but several important details of the original model had to be changed. The primary step involves two hydrogen fluoride (HF) molecules rather than one, and field screening by mobile ions has a significant influence causing nonlinear effects. The fact that field screening plays an important role implies that electric field-assisted HF etching of silica may by used as an instrument for measuring ion concentrations in highly concentrated electrolytes. The data measured may be well described by a theoretical model based on mean field approximations. The results give an insight into the structure of highly concentrated hydrofluoric acid and also permit a critical analysis of applications of the effect in measuring electric fields written in glass samples by electrothermal poling. The effect may also be used for shaping glass surfaces.

Etching of silicon in fluoride solutions

The development and status of what is commonly called the Gerischer mechanism of silicon etching in fluoride solutions is reviewed. The two most widely used and studied wet etchants of silicon are F − and OH −. Their mechanisms of atom removal share many things in common; in particular, chemical passivation by a hydrogen-terminated surface plays an important role in both. Crucially, however, their initiation steps are different, and this leads to important differences in the structures of the materials produced by the etchants. The initiation of etching by F − is electrochemical in nature, responding to the electronic structure of the Si, and is, therefore, a self-limiting reaction that can produce nanocrystalline porous silicon. Hydroxide etching destroys porous silicon because its initiation step is a catalytic chemical reaction and not a self-limiting process. A number of unanswered questions regarding the dynamics of fluoride etching are highlighted.

Etching of polyvinylidene fluoride with an alkaline solution of potassium permanganate

Kinetics of polyvinylidene fluoride etching with a permanganate alkaline solution used in manufacture of track membranes from hydrogen-containing fluoropolymers, and also products formed in the process, were studied in relation to temperature and relative content of mixture components.

Pre-treatment of GaN template for homoepitaxial growth by radio-frequency molecular beam epitaxy

Effective pre-treatment of metalorganic chemical vapor deposition-grown GaN template for epitaxial growth has been investigated, for the improvement of crystalline quality of homoepitaxial GaN on GaN template by radio-frequency molecular beam epitaxy. Ten-minute buffer hydrogen fluoride etching was the most effective to clean the surface of GaN template from evident improvement of the crystalline quality of homoepitaxial GaN as well as thermal annealing in high vacuum. In addition, changes in crystalline quality were observed from thermally annealed GaN template, which showed narrower I 2-line and clearer radiative recombination of free excitons and shift of these peaks toward higher-energy side in the low-temperature photoluminescence spectrum compared with non-annealed GaN template. This result indicates that re-arrangement of GaN occurred during thermal annealing.