Etching Technique Research Articles

Enhancement of titanium surfaces using different acid solutions at room temperature to improve bone cell responses

Background/purposeEarly osseointegration of titanium (Ti) dental implants relies on the surface topography. Surface modification of Ti seeks to enhance bone regeneration around implants. Acid etching is the simple, less technique sensitive and cost-effective technique for surface treatment. The purpose of this study was to elucidate the simplified acid etching technique at room temperature lies in its capacity to enhance both physical properties and biological reactions relevant to bone. Materials and methodsUtilizing sulfuric acid (H2SO4) and hydrochloric acid (HCl), five distinct acid solutions were prepared, and the acid etching process was executed at five different time points at room temperature. The surface characterization of nanoscale modified titanium disks encompassed surface characteristics analysis, wettability and roughness tests. The biocompatibility evaluation involves tests that assess cell attachment, proliferation, alkaline phosphatase activity (ALP), and mineralization. ResultsThe surface modified by HCl exhibited the most significant alterations, characterized by an elevated roughness value and reduced hydrophilicity properties. The surface treated with a mixture of HCl and H2SO4 for 24 h (TH5) displayed a hydrophilic surface and high surface energy. Acid etched surfaces showed the greater cell attachment with long pseudopodia. The cell proliferation rate and ALP reaction rate of TH5 is the highest at day 7. Cells mineralization of Ti surface treated with 37% HCl for 24 h (TC5) shows the lowest and TH5 shows the greatest on day 21. ConclusionThe proposed acid etching at room temperature utilizing a combination of H2SO4 and HCl demonstrated improved physical properties while fostering favorable biological responses.

Fabrication of lateral diamond MOSFET with buried pn-junctions by diamond surface planarization based on carbon solid solution into nickel

New fabrication processes for buried p+-type diamond using etching techniques based on the solid-solution reaction of carbon with nickel were proposed and demonstrated. Specifically, an inversion-channel diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with source and drain regions buried in the body were fabricated, and their operation were confirmed. An etching process using etching techniques based on the solid-solution reaction of carbon with nickel was applied to realize trench formation and planarization after the growth of a p+-type diamond. The fabricated MOSFET exhibited drain current density equivalent to that of conventional MOSFET with source and drain p+-type regions deposited as islands on an n-type body, and ideal field-effect transistor characteristics with linear and saturation regions, and the drain current density was controlled by the gate voltage. However, the surface protrusion structure owing to the incomplete planarization process limited the device characteristics. The proposed fabrication processes for buried layers are expected to function as an important selective doping technique for diamond electronic devices such as ion implantation.

Facile synthesis of RGO/TiO2 heterojunction on SiNWs on Si chip for near infrared detector

Here, a ternary nanostructure-based heterojunction was developed for the detection of infrared (IR) radiation in near wavelength range. During materials synthesis process, silicon nanowires (SiNWs) were developed using metal assisted chemical etching (MACE) technique whereas reduced graphene oxide (RGO) sheets and TiO2 nanoparticles were synthesized by chemical vapour deposition (CVD) and solvothermal method, respectively. Thereafter, RGO/TiO2 nanostructure was deposited over SiNWs to form a heterojunction. To analyse the stoichiometry, morphology, and internal structure, various characterization techniques were performed such as scanning electron microscope (SEM), transmission electron microscope (TEM), Energy dispersive spectrometer (EDS), X-Ray Diffractometer (XRD), UV–Vis spectrophotometer and X-Ray Photoelectron Spectrometer (XPS). The RGO/TiO2@SiNWs nanostructure-based heterojunction was used for the detection of near IR radiation where the responsivity (R) was found to be 17.22 × 10−3 A/W and detectivity (D) was measured to be 0.23 × 1011 Jones with response time < 1 s and recovery time < 3 s. These results were found comparatively better than pristine RGO@Si and RGO@SiNWs nanostructure-based sensors used for the near IR detection under same conditions. The photocurrent response was also recorded with 5 ON/OFF cycles which depicted a good reproducibility of the prepared detector. Hence, the SiNWs on Si chip based highly sensitive and selective photodetector can be used to set a new milestone for various near IR applications.

Synthesis of hierarchically porous Cu-BTC through phase-controlled etching

To enhance diffusion channels and boost active sites within microporous metal–organic frameworks, hierarchically porous structures are indispensable. This study pioneered phase-controlled acetic acid etching techniques, encompassing solution etching and steam etching resulting in the successful synthesis of a series of hierarchically porous Cu-BTC (HP-Cu-BTC). In contrast to etching with an acetic acid solution, acetic acid steam etching offers advantages in terms of reduced etchant usage and minimized damage to the original microporous structure. Noteworthy, by employing steam-controlled recovery etching technology, it is possible to regulate both the steam concentration and the etching degree, while also facilitating the recovery of etchant. The prepared HP-Cu-BTC exhibits adjustable pore sizes (15–45 nm), and mesopore volume (0.14–0.23 cm3/g). Compared to the original Cu-BTC, the well-engineered HP-Cu-BTC demonstrates an 81 % increase in ethylene diffusion rates. The phase-controlled synthesis of HP-MOFs serves as a valuable source of inspiration for the future preparation of hierarchical porous structures.

Evaluation of adhesive bond strength of restorative materials to hard tissues of deciduous teeth based on adhesion technique

Relevance. Treating caries in deciduous teeth remains one of the most complex challenges in pediatric dentistry. The bond strength between the enamel and dentin of deciduous teeth and restorative materials is crucial for the durability of hard tissue restorations in these teeth. This article evaluates the adhesive strength of restorative materials to the enamel and dentin of deciduous teeth using a universal adhesive system, both with and without prior etching with orthophosphoric acid.Purpose. To assess the adhesive bond strength of dental filling materials to the hard tissues of deciduous teeth, contingent upon the enamel and dentin etching techniques used with a universal adhesive system.Materials and methods. This study measured the adhesive strength of a composite filling material to the enamel and dentin of deciduous teeth using a universal adhesive system. The methods included both the absence of preliminary etching with 37% orthophosphoric acid (self-etch technique) and the application of preliminary etching of enamel and dentin with 37% orthophosphoric acid (total-etch technique). Sixty extracted deciduous teeth from children aged 6-8 years were used. Adhesive strength was assessed using the shear test of the filling material in cylinder form against the substrate surface.Results. Significant differences were observed in the adhesive bond strength of the composite material to the hard tissues of deciduous teeth when using 37% orthophosphoric acid before applying the adhesive system (total-etch technique) compared to no preliminary etching (self-etch technique). When filling carious lesions in deciduous teeth, if the defect is within the enamel, etching the surface with 37% orthophosphoric acid significantly (by two-fold) enhances the adhesive strength of the bond with the composite material using a universal adhesive. However, when repairing defects located deeper than the enamel layer in deciduous teeth, no statistically significant differences were observed in the adhesive strength with or without dentin etching. The optimal adhesive bond strength of composite materials to the hard tissues of deciduous teeth under laboratory conditions was attained by selectively etching the enamel with 37% orthophosphoric acid, followed by the application of a universal adhesive system to both the enamel and dentin.

A Precursor-Derived Ultramicroporous Carbon for Printing Iontronic Logic Gates and Super-Varactors.

A liquid precursor for 3D printing ultramicroporous carbons (pore width <0.7nm) to create a novel in-plane capacitive-analog of semiconductor-based diodes (CAPodes) is presented. This proof-of-concept integrates functional EDLCs into microstructured iontronic devices. The working principle is based on selective ion-sieving, controlling the size of the electrolyte ions, and the nanoporous sieving carbon's pore size. By blocking bulky electrolyte ions from entering the sub-nanometer pores, a unidirectional charging characteristic with controllable ion flux is achieved, leading to diodic U-I characteristics with a high rectification ratio. The liquid precursor approach enables successful printing of miniaturized in-plane CAPodes. A combination of inkjet and extrusion printing techniques with suitable inks is explored to fabricate electrode materials with engineered porosity. Deliberate fine-tuning of the ultramicroporous carbon's porosity and surface area is achieved using a customized carbon precursor and CO2 etching techniques. Electrochemical evaluation of the printed CAPodes demonstrates successful miniaturization compared with macroscopic film assembly. 3D manufacturing and miniaturization allow for the integration of CAPodes into logic gate circuits (OR, AND). For the first time, these switchable devices are used as variable capacitors in a high-pass filter application, adjusting the cut-off frequency of applied alternating voltage analogous to an I-MOS varactor.

Noninvasive characterization methods for ultra-short laser pulse induced volume modifications

We present two noninvasive characterization methods to investigate laser induced modifications in bulk fused silica glasses. The methods discussed are immersion microscopy and scanning acoustic microscopy (SAM). SAM shows merits in measuring the distance from sample surface to the first detectable density change of the modification, while immersion microscopy offers a look into the modification. Both noninvasive methods are preferred over conventional polishing or etching techniques due to the facts, that multiple investigations can be done with only one sample and lower time expenditure. The type II modifications were introduced by focusing laser pulses with high repetition rates into the fused silica.

Wafer-scale porous germanium bilayer structure formation by fast bipolar electrochemical etching

Recently, porous Germanium (PGe) structures have gained significant attention as a promising engineering material for a broad range of applications due to the versatility of its intrinsic physical and chemical properties. The Conventional Bipolar Electrochemical Etching (CBEE) technique favours a cost-effective and controlled synthesis of PGe layers, to tune the structural properties. However, some challenges still persist. Specifically, the etch rate of these layers remains low limited, resulting in extended process times. Achieving low porosity layers (< 40 %) remains unclear, and addressing the development of a non-sponge morphology is necessary for various fields, such as batteries. In this work, we investigate the impact of the anodic current density and electrolyte ratio on tubular single PGe layer (T-PGe) morphology with low porosities using a Fast Bipolar Electrochemical Etching (FBEE) process. We have demonstrated T-PGe structures with no parasitic sponge-like layer on top, providing insights to control their occurrence. We establish the feasibility of such layers as a template for the formation of tubular bilayers on the wafer's scale. This approach emphasizes the fast synthesis of promising T-PGe structures with low porosities (< 40 %).

Ordered silicon nanocone fabrication by using pseudo-Bosch process and maskless etching

Nanocone arrays are widely employed for applications such as antireflection structures and field emission devices. Silicon nanocones are typically obtained by an etching process, but the profile is hard to attain because anisotropic dry etching generally gives vertical or only slightly tapered sidewall profiles, and isotropic dry plasma etching gives curved sidewalls. In this work, we report the fabrication of cone structures by using masked etching followed by maskless etching techniques. The silicon structure is first etched using fluorine-based plasma under the protection of a hard metal mask, with a tapered or vertical sidewall profile. The mask is then removed, and maskless etching with an optimized nonswitching pseudo-Bosch recipe is applied to achieve the cone structure with a sharp apex. The gas flow ratio of C4F8 and SF6 is significantly increased from 38:22 (which creates a vertical profile) to 56:4, creating a taper angle of approximately 80°. After subsequent maskless etching, the sidewall taper angle is decreased to 74°, and the structure is sharpened to give a pointed apex. The effect of an oxygen cleaning step is also studied. With the introduction of periodic oxygen plasma cleaning steps, both the etch rate and surface smoothness are greatly improved. Lastly, it was found that the aspect ratio-dependent etching effect becomes prominent for dense patterns of cone arrays, with a greatly reduced etch depth at a 600 nm pitch array compared to a 1200 nm pitch array.

High throughput clogging free microfluidic particle filter by femtosecond laser micromachining.

In recent decades, driven by the needs of industry and medicine, researchers have been investigating how to remove carefully from the main flow microscopic particles or clusters of them. Among all the approaches proposed, crossflow filtration is one of the most attractive as it provides a non-destructive, label-free and in-flow sorting method. In general, the separation performance shows capture and separation efficiencies ranging from 70% up to 100%. However, the maximum flow rate achievable (µL/min) is still orders of magnitude away from those suitable for clinical or industrial applications mainly due to the low stiffness of the materials typically used. In this work, we propose an innovative hydrodynamic-crossflow hybrid filter geometry, buried in a fused silica substrate by means of the femtosecond laser irradiation followed by chemical etching technique. The material high stiffness combined with the accuracy of our manufacturing technique allows the 3D fabrication of non-deformable channels with higher aspect ratio posts, while keeping the overall device dimensions compact. The filter performance has been validated through experiments with both Newtonian (water-based solution of microbeads) and non-Newtonian fluids (blood), achieving separation efficiencies of up to 94% and large particles recovery rates of 100%, even at very high flow rates (mL/h).

Wide-Size Range and High Robustness Self-Assembly Micropillars for Capturing Microspheres.

Capillary force driven self-assembly micropillars (CFSA-MP) holds immense promise for the manipulation and capture of cells/tiny objects, which has great demands of wide size range and high robustness. Here, we propose a novel method to fabricate size-adjustable and highly robust CFSA-MP that can achieve wide size range and high stability to capture microspheres. First, we fabricate a microholes template with an adjustable aspect ratio using the spatial-temporal shaping femtosecond laser double-pulse Bessel beam-assisted chemical etching technique, and then the micropillars with adjustable aspect ratio are demolded by polydimethylsiloxane (PDMS). We fully demonstrated the advantages of the Bessel optical field by using the spatial-temporal shaping femtosecond laser double-pulse Bessel beams to broaden the height range of the micropillars, which in turn expands the size range of the captured microspheres, and finally achieving a wide range of capturing microspheres with a diameter of 5-410 μm. Based on the inverted mold technology, the PDMS micropillars have ultrahigh mechanical robustness, which greatly improves the durability. CFSA-MP has the ability to capture tiny objects with wide range and high stability, which indicates great potential applications in the fields of chemistry, biomedicine, and microfluidics.

Dynamic process of wet etching using BOE solutions to control the etch rate, roughness, and surface morphology of a Z-cut α-quartz wafer

Quartz is a widely used material in the field of microelectromechanical systems (MEMS) for fabricating devices such as substrates, probes, and lenses; it is also indispensable as a resonator or oscillator for frequency control in communication and network technologies. However, its development is limited because it is difficult to fabricate an ideal profile for implementation in complex structures. In practice, wet etching is the most effective and extensive method for achieving the expected structure, although dry etching and other special machining techniques have also been investigated. In this study, the dynamic wet etching process was recorded using different ratios of buffered oxide etcher (BOE) solutions as the etchant to reveal the etching mechanism. The experiments were first designed considering the fabrication of samples, experimental conditions, and measurement indicators. Subsequently, the corresponding etch rate, roughness, and surface morphology were investigated to control the process parameters during wet etching. Different etchants exhibit varying etching rates and roughness properties. A smaller proportion of hydrofluoric acid in the BOE solution results in lower etch rate, and vice versa. The roughness (Ra) in the stable stage was not completely consistent with the tendency of the etch rate, whereas the surface morphology and dimensions of the pyramids rationally complied with the roughness trend. Additionally, the results suggested that the three following stages exist during the wet etching process of the z-cut α-quartz wafer; smooth, incremental, and stable. The analysis of the dynamic wet etching process in this study is beneficial for the structural design, manufacturing, and performance of quartz MEMS devices.

Three-dimensional core shell InGaN/GaN heterostructure for color tunable emitters on the aspect ratio controlled GaN nanorods

In the pursuit of developing red, green and blue emitters, comprehension of color tunability in relation to the nanostructure properties is imperative. Hence, we present a systematic study for the fabrication of color tunable emitters based on GaN nanorods (NRs) prepared via two-step etching technique. In the essence of tunable emission wavelength, aspect ratio controlled GaN NRs were employed for the growth of core shell heterostructure of InGaN/GaN multiple quantum wells (MQWs) using MOCVD and the impact of aspect ratio regulation on the emission wavelength modulation was studied. To analyze the role of the GaN NRs aspect ratio in facilitating the tunable emission wavelength, we employed metrological as well as optical characterizations. Photoluminescence spectra results established a direct relation of the aspect ratio to the emission profile of the GaN NRs. Furthermore, power-dependent photoluminescence (PL) and cathodoluminescence (CL) studies clarified the source of the emission, providing confirmation of the active region's exclusive growth on non-polar sidewalls and the absence of polarization-induced fields. Tunneling microscope measurements revealed a direct relation of the GaN NRs aspect ratio to the emission wavelength profile. In conclusion, we studied comprehensively the impact of aspect ratio regulation for the tunable emission wavelength.

Wetting Properties of Black Silicon Layers Fabricated by Different Techniques

The wettability of black silicon (BSi) layers fabricated by reactive ion etching (RIE), metal‐assisted chemical etching (MACE), and laser‐induced etching (LIE) techniques is studied. The contact angles of wetting on the samples with deionized water and methylammonium iodide‐based perovskite solutions are determined. It is found that the element composition and the enlargement area factor of BSi layers have a significant effect on their wettability. When tested with water, the RIE and MACE BSi layers exhibit hydrophobic properties, while the LIE BSi layer demonstrates hydrophilic properties due to the SiOx‐rich surface structures. It is also shown that aging leads to a decrease in the water contact angle. Upon exposure to perovskite solution droplets, BSi layers become highly lyophilic. Based on the Wenzel and Cassie–Baxter models, the mechanisms responsible for the wetting states of the fabricated samples are identified. In the results obtained, valuable insights are provided into the potential of using these layers in tandem perovskite/silicon solar cells.

Plasma activated titanium-based bonding for robust and reliable Si–Si and Si-glass integration

The exceptional biocompatibility of Ti/Ti bonding technology makes it highly significant for the sealing of implantable devices. However, achieving highly reliable Ti/Ti bonding at low temperatures is challenging due to the facile formation of a native oxide film, which hinders the diffusion of interfacial atoms. This paper develops a low-temperature Ti/Ti bonding process based on plasma activation, resulting in a remarkable bonding strength of 17.5 MPa at 300 °C, which can be used for Si–Si homogeneous and Si-glass heterogeneous integration. After optimizing the processes, the surface oxides of Ti can be partially reduced through Ar/H2 plasma activation to form unsaturated chemical bonds, thereby overcoming the limitation of film thickness in Ti/Ti bonding. The results indicate that plasma activation can realize high strength Ti/Ti bonding in the film thickness range of 10–50 nm. It is worth noting that the Ti/Ti bonding area and strength remain stable after immersion experiments in DI water and normal saline for 7 days, which proves that Ti/Ti bonding has good corrosion resistance. In addition, the microcavity structures were prepared using photolithography and etching techniques. The Ti/Ti bonding technology enables direct bonding of microcavity structures with plate Ti, and an intact bonding interface near the microcavity was obtained. This low-temperature Ti/Ti bonding technology is suitable for the three-dimensional integration of various substrate materials, and its excellent corrosion resistance makes it promising for application in the sealing of BioMEMS.

Hierarchically porous electrospun carbon nanofiber for high-rate capacitive deionization electrodes

Capacitive deionization (CDI) is a promising technology that has gained interest for the desalination of brackish water. Hierarchically porous carbons are commonly used as electrodes for CDI due to their high surface areas and controlled pore size distributions that maximize ion adsorption capacity and rate. Electrospinning is an effective way of generating carbon nanofibers with high inter-fiber macroporosity that can be further modified to improve surface area, total pore volume, and pore size distribution. This work describes the use of sacrificial mesopore formers in tandem with a micropore etching technique to induce hierarchical porosity in electrospun fibers. Mesopores are formed via the dissolution of silica nanoparticles that are introduced into the fibers during the electrospinning step. After mesopore formation, micropores are etched into the resulting surface through KOH impregnation and thermal activation. This sequential technique creates a hierarchical network of pores from the inherent macroporosity of the fiber network, to the mesopores, and finally micropores to simultaneously maximize surface area and accessibility. Micropore formation is optimized to maximize specific surface area while maintaining physical integrity of the fibers. The combination of mesopores and micropores enables fast ion adsorption rates and capacity. Carbon fiber electrodes fabricated in this method achieve specific surface areas exceeding 1400 m2 g−1, with pore volumes exceeding 1.0 cc g−1. The pore size distributions are highly controlled, with 80 % of total pore volume coming from pores <20 nm in radius. In 500 ppm constant voltage CDI tests, these fiber electrodes obtain a salt adsorption capacity of over 14 mg g−1 at a salt adsorption rate of ∼4 mg g−1 min−1, showcasing the high capacity matched with high rate of these easily fabricated, inexpensive materials.

Enhancing thermal stability of Nd:GGG WGM microdisk lasers via silica integration

Abstract Whispering gallery mode (WGM) resonators, as an integral component of integrated photonics, have attracted considerable attention due to their high Q factor, small footprint, and small mode volume, making them widely applied as microlasers. In this work, Nd:GGG crystal was prepared into a Nd:GGG film with thickness of 1.8 μm through ion implantation-enhanced etching (IIEE) technique, and subsequently, the Nd:GGG film was partened by focused ion beam (FIB) technology to generate a microdisk with diameter of 20 μm. For high-power microcavity lasers, heat generation during laser operation was inevitable. We placed the microdisk on a silica holder and a silica wafer, respectively. The microdisk placed on the silica holder and silica wafer exhibited laser thresholds of 32 μW and 17 μW, respectively. Moreover, due to different heat dissipation conditions, the microdisk placed on the silica holder exhibited a mode shift of 0.13 nm/mW, while the microdisk placed on the silica wafer showed a more stable laser output state with a mode shift of 0.02626 nm/mW.

Rapid Detection and Elimination of Subsurface Mechanical Damage for Improving Laser-Induced Damage Performance of Fused Silica

The fabrication of SSD-free fused silica optics is a crucial objective for high-power laser applications. To treat the surface of polished fused silica, a combination of RIE/RIBE and deep-controlled etch (DCE) techniques are typically employed. Currently, it is important to consider and study the ideal etching depth and precision while using combined etching techniques to remove the identified SSD. Herein, we present a novel approach to identify the distribution of SSD in fused silica, which corresponds to a specific grinding/polishing process condition. Our method involves using a mobile RIBE to perform cone cutting and remove material from the polished fused silica surface. Afterward, we etch the optical element’s surface with HF to visualize the subsurface cracks and understand their relationship with the RIBE depth. Through a systematic investigation of the combined etching technique, we establish a correlation between the depth of RIBE and DCE and the performance of laser damage. The combined etching technique can be implemented as a dependable approach to treat the surface/subsurface defects in fused silica and has the potential to improve laser damage resistance significantly.

Silicon flow stop frame for encapsulation of CMOS microsensor chips by wet anisotropic etching in KOH

Bulk micromachining in silicon is governed by the etching process where anisotropic (wet) etching in KOH can yield complex structures beyond that achievable with isotropic (dry) etching techniques. One example is the miniaturised frame reported herein with an area of 2.9 to 7.5 mm2, walls that are 1/10 mm thick, a height of 525 μm equipped with sloping walls that takes advantage of the 54.7° angle of the (111) planes to the horizontal (100) top surface of the wafer. Convex corners liable to damage are protected by sacrificial bridge structures which are etched thin to a point where the frame can be easily removed from the bulk substrate material. Frames made from isotropic (dry) etching processes have been made for comparison. Although the frame structure has different applications in microfabrication, the intended use is a flow stop barrier preventing liquid resins from entering the active area of a CMOS chemical sensor chip during encapsulation for use in aqueous or gaseous media. Beyond this specific proof-of-concept, the strategy is expected to be of general interest for all who treasures KOH etching and wants to explore new avenues based on this process.

Versatile Titanium Carbide MXene Thin-Film Memristors with Adaptive Learning Behavior.

With the advent of the modern era, there is a huge demand for memristor-based neuromorphic computing hardware to overcome the von Neumann bottleneck in traditional computers. Here, we have prepared two-dimensional titanium carbide (Ti3C2Tx) MXene following the conventional HF etching technique in solution. After confirmation of Ti3C2Tx properties by Raman scattering and crystallinity measurements, high-quality thin-film deposition is realized using an immiscible liquid-liquid interfacial growth technique. Following this, the memristor is fabricated by sandwiching a Ti3C2Tx layer with a thickness of 70 nm between two electrodes. Subsequently, current-voltage (I-V) characteristics are measured, revealing a nonvolatile resistive switching property characterized by a swift switching speed of 30 ns and an impressive current On/Off ratio of approximately 103. Furthermore, it exhibits endurance through 500 cycles and retains the states for at least 1 × 104 s without observable degradation. Additionally, it maintains a current On/Off ratio of about 102 while consuming only femtojoules (fJ) of electrical energy per reading. Systematic I-V results and conductive AFM-based current mapping image analysis are converged to support the electroforming mediated filamentary conduction mechanism. Furthermore, our Ti3C2Tx memristor was found to be truly versatile as an all-in-one device for demonstrating edge computation, logic gate operation, and classical conditioning of learning by the brain in Psychology.