Argon Plasma Etching Research Articles

Morphological Study before and after Thermal Treatment of Polymer-Polymer Mixed-Matrix Membranes for Gas Separations.

A good integration of the polymer materials that form a mixed-matrix membrane (MMM) for gas separation is essential to reaching interesting permselective properties. In this work, a porous polymer network (PPN), obtained by combining triptycene and trifluoroacetophenone, has been used as a filler, which was blended with two o-hydroxypolyamides (HPAs) that act as polymer matrices. These polymer matrices have been thermally treated to induce a thermal rearrangement (TR) of the HPAs to polybenzoxazoles (β-TR-PBOs) through a solid-state reaction. For its structural study, various techniques have been proposed that allow us to undertake a morphological investigation into the integration of these materials. To access the internal structure of the MMMs, three different methods were used: a polishing process for the material surface, the partial dissolution of the polymer matrix, or argon plasma etching. The argon plasma technique has not only revealed its potential to visualize the internal structure of these materials; it has also been proven to allow for the transformation of their permselective properties. Force modulation and phase contrast in lift-mode techniques, along with the topographic images obtained via the tapping mode using a scanning probe microscope (SPM), have allowed us to study the distribution of the filler particles and the interaction of the polymer and the filler. The morphological information obtained via SPM, along with that of other more commonly used techniques (SEM, TGA, DSC, FTIR, WASX, gas adsorption, and permeability measurements), has allowed us to postulate the most probable structural configuration in this type of system.

Comparative study on the activation of peroxymonosulfate and peroxydisulfate by Ar plasma-etching CNTs for sulfamethoxazole degradation: Efficiency and mechanisms

Sulfamethoxazole (SMX), a widely utilized antibiotic, was continually detected in the environment, causing serious risks to aquatic ecology and water security. In this study, carbon nanotubes (CNTs) with abundant defects were developed by argon plasma-etching technology to enhance the activation of persulfate (PS, including peroxymonosulfate (PMS) and peroxydisulfate (PDS)) for SMX degradation while reducing environmental toxicity. Obviously, the increase of ID/IG value from 0.980 to 1.333 indicated that Ar plasma-etching successfully introduced rich defects into CNTs. Of note, Ar-90-CNT, whose Ar plasma-etching time was 90 min with optimum catalytic performance, exhibited a significant discrepancy between PMS activation and PDS activation. Interestingly, though the Ar-90-CNT/PDS system (kobs = 0.0332 min−1) was more efficient in SMX elimination than the Ar-90-CNT/PMS system (kobs = 0.0190 min−1), Ar plasma-etching treatment had no discernible enhancement in the catalytic efficiency of MWCNT for PDS activation. Then the discrepancy on activation mechanism between PMS and PDS was methodically investigated through quenching experiments, electron spin resonance (ESR), chemical probes, electrochemical measurements and theoretical calculations, and the findings unraveled that the created vacancy defects were the ruling active sites for the production of dominated singlet oxygen (1O2) in the Ar-90-CNT/PMS system to degrade SMX, while the electron transfer pathway (ETP), originated from PDS activation by the inherent edge defects, was the central pathway for SMX removal in the Ar-90-CNT/PDS system. Based on the toxicity test of Microcystis aeruginosa, the Ar-90-CNT/PDS system was more effective in alleviating environmental toxicity during SMX degradation. These findings not only provide insights into the discrepancy between PMS activation and PDS activation via carbon-based materials with controlled defects regulated by the plasma-etching strategy, but also efficiently degrade sulfonamide antibiotics and reduce the toxicity of their products.

Argon nonthermal plasma etching of poly(L-lactic acid) films: Tunning the local surface degradation and hydrolytic degradation rate

Plasma technology is widely used in the industry for the surface modification of polymeric materials, improving the adhesion of paints in polymeric packaging and cellular adhesion on polymers' surfaces without using hazardous chemicals. Plasma etching is a fast way to modify polymers, creating new nanostructure surfaces and adding chemical groups for new applications like antimicrobial surfaces. Poly(L-lactic acid) (PLLA) is a biodegradable polymer with exciting properties for biomedical, tissue engineering, food packaging, and other applications. In many cases, these products must undergo plasma surface treatments to meet the technical requirements of their function. Herein, we evaluated the effects of surface modification of PLLA using Argon nonthermal plasma etching. The results from Gel Permeation Chromatography (GPC), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Excited Photoelectron Spectroscopy (XPS), and Matrix-assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF-MS) show that increasing the plasma exposure time causes an enhancement in bulk and local surface degradation, crystallization kinetics and susceptibility to hydrolytic degradation for PLLA. Atomic Force Microscopy (AFM) show that the PLLA films present the highest surface roughness after 60 s of plasma etching times. Our findings suggest that plasma etching can be a suitable tool to adjust the polymer degradation rate to design intracorporeal devices with controlled degradation kinetics.

Deposition and Characterisation of a Diamond/Ti/Diamond Multilayer Structure

In this work, a diamond/Ti/diamond multilayer structure has been fabricated by successively following thin-film CVD and PVD routes. It has been found that a combined pre-treatment of the silicon base substrate, via argon plasma etching for creating surface roughness and, thereafter, detonation nanodiamond (DND) seeding, helps in the nucleation and growth of well-adherent CVD diamond films with a well-defined Raman signal at 1332 cm−1, showing the crystalline nature of the film. Ti sputtering on such a CVD-grown diamond surface leads to an imprinted bead-like microstructure of the titanium film, generated from the underlying diamond layer. The cross-sectional thickness of the titanium layer can be found to vary by as much as 0.5 µm across the length of the surface, which was caused by a subsequent hydrogen plasma etching process step of the composite film conducted after Ti sputtering. The hydrogen plasma etching of the Ti–diamond composite film was found to be essential for smoothening the uneven as-grown texture of the films, which was developed due to the unequal growth of the microcrystalline diamond columns. Such hydrogen plasma surface treatment helped further the nucleation and growth of a nanocrystalline diamond film as the top layer, which was deposited following a similar CVD route to that used in depositing the bottom diamond layer, albeit with different process parameters. For the latter, a hydrogen gas diluted with PH3 precursor recipe produced smaller nanocrystalline diamond crystals for the top layer. The titanium layer in between the two diamond layers possesses a very-fine-grained microstructure. Transmission electron microscopy (TEM) results show evidence of intermixing between the titanium and diamond layers at their respective interfaces. The thin films in the composite multilayer follow the contour of the plasma-etched silicon substrate and are thus useful in producing continuous protective coatings on 3D objects—a requirement for many engineering applications.

Physical feature exploration of nanocrystalline FeSi2 surface with argon plasma etching under varying power

Nanocrystalline (NC) FeSi2 films were created on Si(111) wafers via direct-current sputtering with facing targets at an ambient temperature, then the films were etched by Ar plasma generated through microwave source at different powers of 50, 100, and 150 W. The surface morphology of the as-coated NC FeSi2 films showed numerous small uniform crystallites and root-mean-square roughness of 4.65 Å. The surface for each etched NC FeSi2 film showed appearance of holes and slight increase in the roughness as the power increased. X-ray photoelectron spectra showed that the etching decreased the content of hydrophobic carbon and increased the presence of polar oxide group on the NC FeSi2 films as the power increased. These changes should be the factor behind the shift from hydrophobic state to hydrophilic state. The contact angle of the unetched NC FeSi2 film surface was 100.55°, which is hydrophobic. The NC FeSi2 film's surface reached a minimum contact angle of 35.65°, which belong to hydrophilic state, when the etching power was increased to 150 W. The mechanical properties of NC FeSi2 films rarely affect by Ar plasma. The change in surface state to nearly superhydrophilic after plasma etching indicate possibility to develop NC FeSi2 into a self-cleaning surface coating material.

Bioinspired Antimicrobial PLA with Nanocones on the Surface for Rapid Deactivation of Omicron SARS-CoV-2.

Bioinspired bactericidal surfaces are artificial surfaces that mimic the nanotopography of insect wings and are capable of inhibiting microbial growth by a physicomechanical mechanism. The scientific community has considered them an alternative method to design polymers with surfaces that inhibit bacterial biofilm formation, suitable for self-disinfectant medical devices. In this contribution, poly(lactic acid) (PLA) with nanocone patterns was successfully produced by a novel two-step procedure involving copper plasma deposition followed by argon plasma etching. According to reverse transcription-quantitative polymerase chain reaction tests, the bioinspired PLA nanostructures display antiviral performance to inactivate infectious Omicron severe acute respiratory syndrome coronavirus 2 particles, reducing the amount of the viral genome to less than 4% in just 15 min due to a possible combined effect of mechanical and oxidative stress. The bioinspired antiviral PLA can be suitable for designing personal protection equipment to prevent the transmission of contagious viral diseases, such as Coronavirus Disease 2019.

Fabrication of Low Loss Lithium Niobate Rib Waveguides Through Photoresist Reflow

We present lithography and argon plasma etching of lithium niobate on insulator (LNOI) rib waveguides using reflowed photoresist etch masks and 405 nm photolithography. Melting the photoresist at temperatures greatly exceeding its glass transition temperature while minimizing feature distortion through photoresist adhesion control reduces sidewall surface roughness and allows the photoresist to be used both as the pattern mask and the hard etch mask. Waveguide sidewall surfaces exhibiting sub-nm root mean square roughness are fabricated. Dependence of sidewall roughness and angle on feature width, and propagation loss on thermal annealing of the fabricated devices is characterized. Measured quality factors on fabricated microresonators exceed one million. LNOI rib waveguides and resonators with low propagation loss increase nonlinear optical conversion efficiencies and are useful for efficient electro-optic modulation. Photolithography compatible fabrication of low loss LNOI photonic integrated circuits facilitates scalable commercialization.

Variation in nanopillar surface on plasma-etched stainless steel owing to the crystal phase and composition

Argon (Ar) plasma etching of stainless steel leads to the formation of nanopillars that function as an antibacterial surface. This study investigated the influences of the crystal phase and composition of steel on nanopillar characteristics, aiming to produce an effective antibacterial surface. Nanopillars on the ferritic stainless steel surface with a body-centered cubic (BCC) structure showed a higher number density, compared with the austenitic case with a face-centered cubic structure. In addition, the number density of the pillars decreased in the cases of lower C and higher Cr contents of the stainless steel. Such differences were dominated by the behavior of carbide precipitation, which acted as a template for etching. Stainless steels with BCC structures and a low Cr content are advantageous for carbide formation; in contrast, a low C content is a disadvantage for the formation of nanopillars owing to the absence of a carbide source. The nanopillar surfaces exhibited antibacterial activity against the gram-positive Staphylococcus epidermidis species, but the effect was mitigated for stainless steel with a reduced number density. The crystal structure and chemical composition of stainless steels influence their antibacterial activity; hence, plasma etching conditions must be optimized for stainless steel to produce an effective antibacterial surface.

Fully vertical gallium nitride trench MOSFETs fabricated with metal-free gate first process

We report on the fabrication and characterization of fully vertical gallium nitride trench metal oxide semiconductor field effect transistors on native substrates with a metal-free gate first process and a chlorine-free trench etching method. Trenches were fabricated using sulfur hexafluoride and argon plasma etching in combination with alkaline wet etching posttreatment to create crystal oriented trenches along the a- and m-planes. Low pressure chemical vapor deposited silicon dioxide was used as gate dielectric with a poly-silicon gate contact. The metal-free gate structure was separated by a silicon dioxide passivation from any subsequent metal containing contact formation processing steps. The breakdown robustness of the gate structure was examined in the forward direction and no temperature dependence was observed up to 450 K. Fabricated trench MOSFETs showed only small hysteresis effects during transfer characterization but a positive threshold shift was observed. An inversion channel carrier field effect mobility of ≈10 cm2/V s was extracted. The area specific on resistance was calculated to be 5.8 mΩ cm2. Results for devices with differently oriented trenches were comparable and no significant performance difference was observed.

Fabrication of antibacterial nanopillar surface on AISI 316 stainless steel through argon plasma etching with direct current discharge

The present study demonstrated that argon (Ar) plasma etching with direct current (DC) discharge leads to the formation of antibacterial nanopillars on AISI 316 stainless steel with a comparatively short processing duration. Small protrusions appeared initially, and then transformed into nanopillars of hundreds of nanometers in size with prolonged plasma etching durations up to 60 min. The dimensions of the nanopillars could be controlled by adjusting the applied current to generate the plasma. The height and the base and cap diameters of the nanopillars increased with increasing applied current, whereas an excessively high current reduced the density of the nanopillars. The fabricated nanopillars functioned as an antibacterial surface, which reduced the survival rates of bacterial strains; however, the reduction in the survival rate of gram-positive Staphylococcus epidermidis was mitigated compared to that of gram-negative Escherichia coli. Moreover, the degree of antibacterial activity varied depending on the dimensions of the nanopillars. In conclusion, Ar plasma etching with DC discharge is an effective method for the rapid fabrication of antibacterial nanopillars with optimal dimensions on AISI 316 stainless steel surfaces.

Monolithic integration of MoS2-based visible detectors and GaN-based UV detectors

With the increasing demand for high integration and multi-color photodetection for both military and civilian applications, the research of multi-wavelength detectors has become a new research hotspot. However, current research has been mainly in visible dual- or multi-wavelength detectors, while integration of both visible light and ultraviolet (UV) dual-wavelength detectors has rarely been studied. In this work, large-scale and high-quality monolayer MoS2 was grown by the chemical vapor deposition method on transparent free-standing GaN substrate. Monolithic integration of MoS2-based visible detectors and GaN-based UV detectors was demonstrated using common semiconductor fabrication technologies such as photolithography, argon plasma etching, and metal deposition. High performance of a 280 nm and 405 nm dual-wavelength photodetector was realized. The responsivity of the UV detector reached 172.12 A/W, while that of the visible detector reached 17.5 A/W. Meanwhile, both photodetectors achieved high photocurrent gain, high external quantum efficiency, high normalized detection rate, and low noise equivalent power. Our study extends the future application of dual-wavelength detectors for image sensing and optical communication.

Low-loss waveguides on Y-cut thin film lithium niobate: towards acousto-optic applications.

We investigate the dependence of photonic waveguide propagation loss on the thickness of the buried oxide layer in Y-cut lithium niobate on insulator substrate to identify trade-offs between optical losses and electromechanical coupling of surface acoustic wave (SAW) devices for acousto-optic applications. Simulations show that a thicker oxide layer reduces the waveguide loss but lowers the electromechanical coupling coefficient of the SAW device. Optical racetrack resonators with different lengths were fabricated by argon plasma etching to experimentally extract waveguide losses. By increasing the oxide layer thickness from 1 µm to 2 µm, we were able to reduce propagation loss of 2 µm (1 µm) wide waveguide from 1.85 dB/cm (3 dB/cm) to as low as 0.37 dB/cm (0.77 dB/cm). Resonators with a quality factor greater than 1 million were demonstrated as well. An oxide thickness of approximately 1.5 µm is sufficient to significantly reduce propagation loss, due to leakage into the substrate and simultaneously attain good electromechanical coupling in acoustic devices. This work not only provides insights on the design and realization of low-loss photonic waveguides in lithium niobate, but also, most importantly, offers experimental evidence of how the oxide thickness directly impacts losses and guides its selection for the synthesis of high-performance acousto-optic devices in Y-cut lithium niobate on insulator.

Pronounced effects of argon plasma etching on photoluminescence and Schottky contact properties of Pt/ZnO nanorods

Vertically well-aligned ZnO nanorods (NRs) with good crystallization quality and obvious UV photoluminescence (PL) characteristics were grown by hydrothermal method and Ar plasma etching. Schottky diodes were made by evaporating Pt dots on these ZnO NRs. The effects of Ar plasma etching on the PL and Schottky properties of the prepared ZnO NRs were investigated. Compared with the as-grown ZnO NRs, the UV and visible peak area ratio in the PL spectra increased from 3.8 to 840 with decreased reverse current from 10−3 A to 10−6 A, and increased current on/off ratio of the ZnO NRs Schottky diode from 1 to 102 after 60-min Ar plasma etching. The results suggest that the low-energy Ar plasma etching is an effective method to promote the performance of the Pt/ZnO NRs diode by improving the crystallization quality of the ZnO NRs.

Electrochemical Performance of All-Solid-State Li-Ion Batteries Based on Garnet Electrolyte Using Silicon as a Model Electrode

Owing to improved safety, all-solid-state batteries based on the garnet Ta-substituted Li7La3Zr2O12 solid electrolyte are promising alternatives to conventional Li-ion batteries with organic electrolytes. However, to date, the viability of such all-solid-state batteries is uncertain because their performance is limited by the problematic electrode–electrolyte interface. Herein, we report the viability to use Si anodes facilitated by enhancement of this interface. Before depositing Si as a thin film electrode (50 nm) on the smooth surface of the solid electrolyte, we treated the electrolyte surface by argon plasma etching to reduce the amount of resistive species. This approach enabled the cycling of Si/garnet/Li all-solid-state cells, achieving an initial capacity of ∼2700 mAh/g followed by partial fading and stabilization for more than 100 cycles. Electrochemical measurement, coupled with morphological and chemical investigations, demonstrate that Si is a viable anode in combination with garnet electroly...

Argon plasma etching of fused silica substrates for manufacturing high laser damage resistance optical interference coatings

The laser damage resistance of an optical element in high power laser systems depends significantly on the surface quality of the optical substrate. In this experiment, commercially polished fused silica substrates were etched in argon plasma generated by a RF source and their surface roughness, flatness and optical properties were investigated. This method can be applied in a vacuum chamber prior to deposition of the multilayer coatings without breaking the vacuum. It was shown that by etching the resistance to 355 nm, laser radiation could be improved more than 8 times. However, it strongly related with primary substrate quality. The etching depth from 100 nm suggests the optimum performance of surface quality in terms of surface low roughness, high flatness, and high laser damage threshold. These results are of significant importance for the manufacture of high quality laser optics on fused silica substrates. As an example of an application of our technology, anti-reflective and polarizing optical interference coatings were deposited on etched substrates and the increase of their resistance to laser radiation was measured.

Rf-sputtered aluminium doped zinc oxide films: Enhanced damp heat stability by means of plasma etching treatment

Abstract ZnO:Al films, obtained by RF-sputtering and textured by wet etching, have been subjected to argon plasma etching treatment in order to stabilize their electrical properties over time, being well known the electrical degradation of these transparent conductive films when exposed to air. Specifically focused on photovoltaic application as front electrode, the effect of argon plasma treatment on long-term electrical stability of ZnO:Al thin film was monitored by performing damp heat degradation cycles in environmental test chamber. There was evidence for strong slowdown of electrical degradation when ZnO surface had been subjected to Ar plasma treatment. Different etching times have been used and it has been observed that surface modification induced by plasma treatment gave its more pronounced beneficial effect after the first 10 min of the process. In particular, for no-plasma treated samples the carrier mobility worsening is about three times larger than that related to Ar-treated samples after long-lasting aging test. The stabilization mechanism of the electrical properties was investigated by studying the main modifications of the plasma etched materials in terms of optical, chemical, morphological and structural properties. Structural analysis revealed that crystalline rearrangement occurs down to 30 nm depth below the plasma treated film surface, where a thin nanocrystalline layer forms. PL analysis revealed a different distribution of deep defect centres for plasma treated film surface compared to untreated one. In particular, donor-like lattice defects (Vo and Zni) decreased whereas Vzn defects became predominant. Crystalline rearrangement and change of type and/or amount of deep defect centres inside the plasma modified top layer have been hypothesized as responsible for the enhancement of the electrical stability.

Nanotextured Shrink Wrap Superhydrophobic Surfaces by Argon Plasma Etching.

We present a rapid, simple, and scalable approach to achieve superhydrophobic (SH) substrates directly in commodity shrink wrap film utilizing Argon (Ar) plasma. Ar plasma treatment creates a stiff skin layer on the surface of the shrink film. When the film shrinks, the mismatch in stiffness between the stiff skin layer and bulk shrink film causes the formation of multiscale hierarchical wrinkles with nano-textured features. Scanning electron microscopy (SEM) images confirm the presence of these biomimetic structures. Contact angle (CA) and contact angle hysteresis (CAH) measurements, respectively, defined as values greater than 150° and less than 10°, verified the SH nature of the substrates. Furthermore, we demonstrate the ability to reliably pattern hydrophilic regions onto the SH substrates, allowing precise capture and detection of proteins in urine. Finally, we achieved self-driven microfluidics via patterning contrasting superhydrophilic microchannels on the SH Ar substrates to induce flow for biosensing.

The study of FTO surface texturing fabrication using Argon plasma etching technique for DSSC applications

This paper is aimed to investigate the fabrication of the fluorine-doped tin oxide (FTO) texturing by using Argon (Ar) plasma etching. The pressure and temperature of Ar gas during plasma etching were 1.6 mbar and 240-285oC, respectively. The plasma etching time was varied from 3 and 10 min. We also prepared without etching samples as reference. UV-Vis spectrophotometer showed that the transmittances of etching samples are higher than the without etching samples. The root mean square roughness (Rq) of etching samples are lower than the without etching samples. It is considered that the Ar ions bombardment can modify the FTO surfaces. However, the etching time does not significantly affect the FTO surfaces for 3 min and 10 min. The Rq of the without etching sample, the etching sample for 3 min, and the etching sample for 10 min are 11.697 nm, 9.859 nm, and 9.777 nm, respectively. These results are good agreement with the four point probe measurement that indicated that the sheet resistance (RS) for each the without sample, the etching sample for 3 min, and the etching sample for 10 min are 16.817 Ωsq, 16.067 Ω/sq, and 15.990 Ω/sq. In addition, the optical transmittance of the etching sample for 3 min and the etching sample for 10 min at wavelengths of 350 - 850 nm are almost similar. This is evidence that the etching time below 10 min cannot significantly change the morphology, optical and electrical properties.

Formation mechanism of graphite hexagonal pyramids by argon plasma etching of graphite substrates

A new graphite crystal morphology has been recently reported, namely the graphite hexagonal pyramids (GHPs). They are hexagonally-shaped crystals with diameters ranging from 50 to 800 nm and a constant apex angle of 40°. These nanostructures are formed from graphite substrates (flexible graphite and highly ordered pyrolytic graphite) in low pressure helicon coupling radiofrequency argon plasma at 25 eV ion energy and, purportedly, due to a physical etching process. In this paper, the occurrence of peculiar crystals is shown, presenting two hexagonal orientations obtained on both types of samples, which confirms such a formation mechanism. Moreover, by applying a pretreatment step with different time durations of inductive coupling radiofrequency argon plasma, for which the incident ion energy decreases at 12 eV, uniform coverage of the surface can be achieved with an influence on the density and size of the GHPs.

Fabrication of porous boron-doped diamond electrodes by catalytic etching under hydrogen–argon plasma

Porous boron-doped diamond (BDD) was prepared by hydrogen–argon plasma etching using electrodeposited Ni nanoparticles as a catalyst. The etching process and formation mechanism of porous BDD were investigated by changing the etching time from 30s to 300s. Pores were produced due to the C atoms around Ni nanoparticles are easy to react with hydrogen plasma and form methane. With the increase of etching time, the pore size increased, the pore density decreased, and the pore depth first increased and then maintained unchanged. The sp2-bonded graphitic carbons existing on the surface of BDD increase with increasing etching time due to the increase of surface area. No preferential etching was observed due to the high energy of argon plasma. The electrochemical behaviors of the pristine and porous BDD electrodes were characterized by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results showed that the porous BDD electrode exhibited high specific capacitance, which is attributed to its high electrical conductivity and large specific surface area. The highest specific capacitance of porous BDD electrode is 9.55mFcm−2, which is 22 times higher than that of pristine BDD electrode. The specific capacitance retention of the porous BDD electrode reduced to 98.2% of the initial capacitance after 500 cycles and then increased to 120.0% after 10,000 cycles. For the first 500 cycles, the reduction of capacitance can be attributed to the dissolution of Ni nanoparticles that attached on the porous BDD surface or buried in the shallow layer. The capacitance increase after 10,000 cycles is due to the better contact of the electrolytic solution with the residual Ni with the increase of cycle number.