HF-based Etching Research Articles

Experimental Study on Evolution of Chemical Structure Defects and Secondary Contaminative Deposition during HF-Based Etching

Post-processing based on HF etching has become a highly preferred technique in the fabrication of fused silica optical elements in various high-power laser systems. Previous studies have thoroughly examined and confirmed the elimination of fragments and contamination. However, limited attention has been paid to nano-sized chemical structural defects and secondary precursors that arise during the etching process. Therefore, in this paper, a set of fused silica samples are prepared and undergo the etching process under different parameters. Subsequently, an atomic force microscope, scanning electron microscope and fluorescence spectrometer are applied to analyze sample surfaces, and then an LIDT test based on the R-on-1 method is applied. The findings revealed that appropriate etching configurations will lead to certain LIDT improvement (from initial 7.22 J/cm2 to 10.76 J/cm2), and HF-based etching effectively suppresses chemical structural defects, while additional processes are recommended for the elimination of micron- to nano-sized secondary deposition contamination.

Ultra-Efficient Synthesis of Nb4 C3 Tx MXene via H2 O-Assisted Supercritical Etching for Li-Ion Battery.

Nb4 C3 Tx MXene has shown extraordinary promise for various applications owing to its unique physicochemical properties. However, it can only be synthesized by the traditional HF-based etching method, which uses large amounts of hazardous HF and requires a long etching time (> 96h), thus limiting its practical application. Here, an ultra-efficient and environmental-friendly H2 O-assisted supercritical etching method is proposed for the preparation of Nb4 C3 Tx MXene. Benefiting from the synergetic effect between supercritical CO2 (SPC-CO2 ) and subcritical H2 O （SBC-H2 O）, the etching time for Nb4 C3 Tx MXene can be dramatically shortened to 1h. The as-synthesized Nb4 C3 Tx MXene possesses uniform accordion-like morphology and large interlayer spacing. When used as anode for Li-ion battery, the Nb4 C3 Tx MXene delivers a high reversible specific capacity of 430mAhg-1 at 0.1Ag-1 , which is among the highest values achieved in pure-MXene-based anodes. The superior lithium storage performance of the Nb4 C3 Tx MXene can be ascribed to its high conductivity, fast Li+ diffusion kinetics and good structural stability.

Safe Synthesis of MAX and MXene: Guidelines to Reduce Risk During Synthesis

MXenes are proven to be promising materials for a wide variety of applications, from electrochemical energy storage to environmental remediation, leading to their increasing popularity in research. With an influx of new researchers focused on MXenes, it is increasingly important to ensure the safe and reliable production of these materials. Herein, we describe the safe synthesis of MXenes, from their precursors (MAX) to the final product (delaminated MXene), focusing on HF-based etching approaches. Using the synthesis of Ti3C2Tx MXene as an example, we discuss safety risks associated with each step of the procedure and demonstrate necessary precautions for the safe, reproducible, and reliable synthesis of MXenes. Finally, we overview the most updated research on MXene safety from a cytotoxicity aspect.

Alternative HF-free etching solution for aluminum induced texturing of glass surface with improved haze

Aluminum induced texturing (AIT) is a promising surface conditioning method applied on glass substrates. In conventional AIT process, the reaction products (i.e., Al2O3 and Si) are stripped off the glass surface using an HF-based solution, rendering the process sensitive to etch duration. In this study, an alternative, HF-free chemistry is compared to conventional HF-based etching. We show that newly proposed alkaline-based solution leads to significantly improved diffused transmission, of up to 80%. In addition, the etchant does not interact with the glass surface, enabling effective process control.

Hydrofluoric acid-based etching effect on surface pit, crack, and scratch and laser damage site of fused silica optics.

In a large-scale, high-power laser facility, fused silica optics plays an irreplaceable role to transmit extremely intense lasers. However, the surface fractures, such as surface pit, crack, and scratch and laser damage site, of fused silica optics will shorten the lifetime of the optics and thus limit the output performance of the laser facility. In this work, besides experimental study, finite difference time domain (FDTD) simulation is performed to study hydrofluoric acid-based (HF-based) etching effect on the surface fractures. The effect of local surface curvature on etching rate is discussed and an explicit local-curvature-dependent etching model is proposed. Based on this model, the result from FDTD simulation qualitatively agrees very well with that of the experiment. It is demonstrated that the FDTD simulation is efficient to predict the morphological evolution of the surface fractures during etching. In addition, it is found that the surface fractures will be passivated and HF-based etching can greatly suppress the laser-damage growth of laser-induced damage to the surface site of fused silica optics.

Capping a glass thin layer on the etched surface via plasma chemical vapor deposition for improving the laser damage performance of fused silica.

Buffered HF-based etching can effectively improve the laser damage resistance of the fused silica, but deep etching would cause the deteriorations in surface roughness and hardness, and decrease the laser-induced damage threshold. Capping a glass thin layer on the etched surface via plasma chemical vapor deposition in one step could overcome those deteriorations. We found that the deposition of the glass thin layer can further reduce the impurity element contamination and the PL intensity while retaining the low subsurface defect density as well as for the deeply etched sample. The surface quality, surface hardness and the laser damage resistance of the fused silica can be significantly improved by the glass thin layer, which reveals the potential application in high power laser facility.

Laser-induced damage characteristics in fused silica surface due to mechanical and chemical defects during manufacturing processes

Mechanical and chemical defects incurred by grinding and polishing as well as post-processing have been recognized as the most influential culprits that hamper the elevation of laser power/energy in high peak power/energy laser systems. In order to find out the causes for limiting the operational power of laser systems, the effects of these defects on laser damage and removal and mitigation of the defects were investigated in detail in the article. Cracks and scratches were created, annealed, etched and damaged so as to reveal the likely effects of mechanical defects on damage and potential techniques to reduce their influence. The results show that HF-based etching can open and smooth cracks/scratches, improving laser-induced damage threshold (LIDT) at scratches by up to >250%. Thermal annealing did heal, to some extent, cracks but the LIDT is little improved. Both HF-etching and leaching proves to be effective in removing metallic contamination during polishing process and handling of optics, which can “contribute” to damage/damage density in fused silica. However, HF-based etching may degrade surface roughness, from <1nm to >20nm under some conditions when >20µm material was etched away while the surface roughness was perceptibly altered by leaching (<1nm to 1–2nm). Although the LIDT might not be directly correlated to each individual kind of metallic contaminants or surface roughness, it is found that the surfaces with the highest LIDT's have some distinguished characteristics: clean surface (almost no metallic contamination) plus very smooth surface (RMS surface roughness: <5nm). By removing metallic contamination and scratches, surface damage threshold of fused silica can exceed >30J/cm2 (355nm @3ns, beam diameter ~400µm @1/e2), a significant progress.

Combination of reaction ion etching and dynamic chemical etching for improving laser damage resistance of fused silica optical surfaces.

In this Letter, an effective combined process of reaction ion etching (RIE) and dynamic chemical etching (DCE) is applied for significantly improving the damage resistance of fused silica optics, while minimizing the removal amount. By optimizing the combination process and removal depth, a near-perfect optical surface of fused silica with relatively low roughness (<0.7 nm) is created with 1μm RIE pretreatment and 3μm DCE retreatment. In this case, the sample has a 2.4 times enhanced 0% probability damage threshold compared to the original sample. We show that the optimized combining process with a low removal amount is superior to a conventional HF-based etching process with a high removal amount in enhancing damage resistance and controlling the surface shape and roughness of fused silica. The results advance our understanding of a key factor influencing the RIE-DCE matching relationship and can lead to further optimization of associated applications, ranging from material processing to high-power laser systems.

Laser induced damage characteristics of fused silica optics treated by wet chemical processes

Laser damage to fused silica continues a main issue of high-power/energy laser systems. HF-based etching technique is known to mitigate laser damage initiation and growth under UV laser illumination. The responses of material surface properties, especially surface damage characteristics to various etching parameters are questioned in the article. Fused silica was submerged into HF-based etchants (HF, NH4F:HF, HF:HNO3 with diverse concentrations) in an attempt to improve its laser-induced damage threshold (LIDT). The results have evidenced that the LIDT relies on, to a greater degree, the etched thickness and the etchant composition. The secondary ion mass spectrometer (SIMS) testing was aimed at relating the LIDT to certain metallic contaminant; however, the LIDT exhibits weak direct correlation with Ce, La, Ca, Fe contaminants. The surfaces with the highest LIDT are, more often than not, such that the surface roughness is <10nm RMS and few metallic impurities are present. In addition, we tried to link the LIDT to the hardness and Young's modulus of fused silica, but no testing data show that there exists direct dependence of the LIDT on hardness and Young's modulus, which are actually independent of the removed thickness.

Acid etching combined with ultrasonic for improving laser damage threshold of fused silica

In order to improve the laser damage resistance of fused silica optical surfaces, the appearance of smoothed fused silica surface defect and the effect of wiping off etching contamination are researched on HF-based etching processes under ultrasonic. And the experimental parameters are determined with SEM microscopy and atomic force microscopy to record face appearance and with one pulse laser incidence to measure laser damage threshold. Results show that it is advantageous to use HF-based etching processes under ultrasonic to smooth the defected surfaces and wipe off micrometer contamination particles. By experimental measurement, the parameters of HF-based etching processes under ultrasonic are obtained for different kinds of fused silica optics. The present research is very important for improving laser damage resistance of fused silica.

HF-based clad etching of fibre Bragg grating and its utilization in concentration sensing of laser dye in dye–ethanol solution

This paper presents a fibre Bragg grating (FBG) based sensor to study the concentration of laser dye in dye–ethanol solution. The FBG used in this experiment is indigenously developed using 255 nm UV radiations from copper vapour laser. The cladding of the FBG was partially removed using HF-based etching to make FBG sensitive to changes in the surrounding refractive index. The experimental results on the shift of the Bragg peak wavelength with HF etching and different dye concentration in ethanol are presented. The Bragg wavelength shifted from 1534.670 nm to 1534.225 nm in 30 min and from this point to 1533.97 in the next 2 min. The clad-etched Bragg peak shifted almost linearly from 1534.056 nm to 1534.162 nm as surrounding dye concentration in ethanol changes from 0 mM to 1.5 mM. It was observed that sensitivity depends on the concentration of the solution and found to be 70 pm/mM.

Subsurface defects characterization and laser damage performance of fused silica optics during HF-etched process

Subsurface defects of fused silica optics would vary with HF-etched process. In this paper, the subsurface defects characteristics of HF-etched fused silica optics and their effects on laser induced damage were investigated. The results suggest that most of metal impurities defects (especially Ce element) of fused silica optics can be dissolved in strong acid solution. Subsurface damage can be removed by submerging fused silica optics in HF-based etchants. Laser damage resistance is improved through the removal of metal impurities and subsurface damage. Optical thermal absorption describes the laser absorption characterization of fused silica subsurface layer. A good correlation between optical thermal absorption and laser-induced damage performance is shown in this paper. Laser damage performance deteriorates when the HF-based etching depth exceeds one value, which can be explained by the impurities redeposition and surface roughness increase. Research results have a guiding significance for HF-based etching process technology of fused silica optics.

A cobalt-coated needle-type microelectrode array sensor for in situ monitoring of phosphate

In this paper, a new cobalt-coated needle-type microelectrode array sensor for in situ measurements of phosphate has successfully been designed, fabricated and characterized. MEMS technologies were used to fabricate microelectrode arrays with a small tip size. An HF-based etching technique was used to taper and sharpen three-dimensional glass probes. A cobalt thin film was electroplated on a gold conductive layer using a cobalt sulfate electrolyte and then was oxidized to form CoO on the surface. The microelectrode array (MEA) was packaged on a designed printed circuit board (PCB) for electrical connections. The MEA sensors were fully characterized with potassium sulfate solution in the concentration range of 1 × 10−5.1−1 × 10−3 M at pH 7.5. The repeatable phosphate-selective potentials with a sensitivity of ∼96 mV per decade were exhibited with less than 30 s response times and good signal stability. This sensitivity is the highest value among the reported cobalt-based phosphate sensors to date. Ultimately, in the long term, we envision extension of this MEA sensor to include additional sensors for multi-analyte, rapid, accurate and reliable in situ sensing in biological applications.

Processing and morphology of permeable polycrystalline silicon thin films

It is known that thin films of polycrystalline silicon, deposited under the right conditions, can be permeable to HF-based etching solutions. While these films offer unique capabilities for microfabrication, both the poor reproducibility of the permeable film properties and the lack of a detailed physical understanding of the material have limited their application. This work provides a methodical study of the relationship between process, microstructure, and properties of permeable polycrystalline silicon thin films. It is shown that the permeability is a result of small pores, on the order of 10 nm, between the 100–200-nm hemispherical grains characteristic of the permeable film morphology. This morphology occurs only in nearly stress-free films grown in a narrow temperature range corresponding to the transition between tensile and compressive film growth regimes. This result strongly suggests that the monitoring of residual film stress can provide the process control needed to reliably produce permeable films. A simple kinetic model is proposed to explain the evolution of the morphology of the permeable films.