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This paper reviews the recent advances in reaction-ion etching (RIE) for application in high-aspect-ratio microfabrication. High-aspect-ratio etching of materials used in micro- and nanofabrication has become a very important enabling technology particularly for bulk micromachining applications, but increasingly also for mainstream integrated circuit technology such as three-dimensional multi-functional systems integration. The characteristics of traditional RIE allow for high levels of anisotropy compared to competing technologies, which is important in microsystems device fabrication for a number of reasons, primarily because it allows the resultant device dimensions to be more accurately and precisely controlled. This directly leads to a reduction in development costs as well as improved production yields. Nevertheless, traditional RIE was limited to moderate etch depths (e.g., a few microns). More recent developments in newer RIE methods and equipment have enabled considerably deeper etches and higher aspect ratios compared to traditional RIE methods and have revolutionized bulk micromachining technologies. The most widely known of these technologies is called the inductively-coupled plasma (ICP) deep reactive ion etching (DRIE) and this has become a mainstay for development and production of silicon-based micro- and nano-machined devices. This paper will review deep high-aspect-ratio reactive ion etching technologies for silicon, fused silica (quartz), glass, silicon carbide, compound semiconductors and piezoelectric materials.

Lithium niobate on insulator is being established as a versatile platform for a new generation of photonic integrated devices. Extensive progress has been made in recent years to improve the fabrication of integrated optical circuits from a research platform towards wafer-scale fabrication in commercial foundries, and optical losses have reached remarkably low values approaching material limits. In this context, argon etching of lithium niobate waveguides has been shown to provide the best optical quality, yet the process is still challenging to optimise due to its physical nature. Namely, the micro-masking effects introduced by the material redeposition and a close to one etch mask selectivity for deep etches. We present a workflow to identify the parameter set offering the best etching results independent of the plasma system being used. We show how to reach the redeposition-free regime and propose three methods to achieve redeposition-free lithium niobate etching with good quality sidewalls without need of wet chemistry for cleaning.

In this work, the surface modification using a two-steps plasma etching has been developed for enhancing energy conversion performance in polytetrafluoroethylene (PTFE) triboelectric nanogenerator (TENG). Enhancing surface area by a powerful O 2 and Ar bipolar pulse plasma etching without the use of CF 4 gas has been demonstrated for the first time. TENG with modified surface PTFE using a sequential two-step O 2 /Ar plasma has a superior power density of 9.9 Wm −2 , which is almost thirty times higher than that of a pristine PTFE TENG. The synergistic combination of high surface area and charge trapping sites due to chemical bond defects achieved from the use of a sequential O 2 /Ar plasma gives rise to the intensified triboelectric charge density and the enhancement of power output of PTFE-based TENG. The effects of plasma species and plasma etching sequence on surface morphologies and surface chemical species were investigated by a field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The correlation of surface morphology, chemical structure, and TENG performance was elucidated. In addition, the applications of mechanical energy harvesting for lighting, charging capacitors, keyboard sensing and operating a portable calculator were demonstrated.

An experimentally obtained precise technology for forming a controlled profile of aluminum conductive paths with the given resistance is presented. The technology is based on anisotropic plasma-chemical etching of aluminum in a BCl 3 –Cl 2 gas mixture, followed by precise adjustment of the track resistance using the dry plasma-chemical method. It is shown that in order to ensure the highest quality plasma-chemical etching of aluminum with minimal underetching under the photoresist mask, with the minimal slope of the aluminum conductive path profile, and the absence of defects in the etching pattern and etched areas, it is necessary to use a multistage iterative technological process with technological operations of surface preparation before etching and operations of removing the polymer and photoresist after etching.

In this study, we analyzed the morphological changes and molecular structure changes on the surface of single-walled carbon nanotube (SWCNT) films during oxygen plasma (O2) etching of SWCNT surfaces formed by the spray method and analyzed their potential use as electrochemical electrodes. For this purpose, a SWCNT film was formed on the surface of a glass substrate using a self-made spray device using SWCNT powder prepared with DCB as a solvent, and SEM, AFM, and XPS analyses were performed as the SWCNT film was O2 plasma etched. SEM images and AFM measurements showed that the SWCNT film started etching after about 30 s under 50 W of O2 plasma irradiation and was completely etched after about 300 s. XPS analysis showed that as the O2 plasma etching of the SWCNT film progressed, the sp2 bonds representing the basic components of graphite decreased, the sp3 bonds representing defects increased, and the C–O, C=O, and COO peaks increased simultaneously. This result indicates that the SWCNT film was etched by the O2 plasma along with the oxygen species. In addition, electrochemical methods were used to verify the damage potential of the remaining SWCNTs after O2 plasma etching, including cyclic voltammetry, Randles plots, and EIS measurements. This resulted in a reversible response based on perfect diffusion control in the cyclic voltammetry, and an ideal linear curve in the Randles plot of the peak current versus square root scan rate curve. EIS measurements also confirmed that the charge transfer resistance of the remaining SWCNTs after O2 plasma etching is almost the same as before etching. These results indicate that the remaining SWCNTs after O2 plasma etching do not lose their unique electrochemical properties and can be utilized as electrodes for biosensors and electrochemical sensors. Our experimental results also indicate that the ionic conductivity enhancement by O2 plasma can be achieved additionally.

Plasma etching treatment is an effective strategy to improve the electrocatalytic activity, but the improvement mechanism is still unclear. In this work, a nitrogen‐doped carbon nanotube‐encased iron nanoparticles (Fe@NCNT) catalyst is synthesized as the model catalyst, followed by plasma etching treatment with different parameters. The electrocatalytic activity improvement mechanism of the plasma etching treatment is revealed by combining the physicochemical characterizations and electrochemical results. As a result, highly active metal–nitrogen species introduced by nitrogen plasma etching treatment are recognized as the main contribution to the improved electrocatalytic activity, and the defects induced by plasma etching treatment also contribute to the improvement of the electrocatalytic activity. In addition, the prepared catalyst also demonstrates superior ORR activity and stability than the commercial Pt/C catalyst. This work studies the electrocatalytic activity improvement mechanism of the plasma etching treatment on oxygen reduction reaction catalysts, which reveals that the highly active metal‐nitrogen species induced by nitrogen plasma treatment is the main active contributor of the improved electrocatalytic activity.

In this work, SiNx/a-Si/SiNx caps on conductive coplanar waveguides (CPWs) are proposed for thin film encapsulation of radio-frequency microelectromechanical systems (RF MEMS), in view of the application of these devices in fifth generation (5G) and modern telecommunication systems. Simplification and cost reduction of the fabrication process were obtained, using two etching processes in the same barrel chamber to create a matrix of holes through the capping layer and to remove the sacrificial layer under the cap. Encapsulating layers with etch holes of different size and density were fabricated to evaluate the removal of the sacrificial layer as a function of the percentage of the cap perforated area. Barrel etching process parameters also varied. Finally, a full three-dimensional finite element method-based simulation model was developed to predict the impact of fabricated thin film encapsulating caps on RF performance of CPWs.

In this paper, we report oxidation time effect on highly porous silver oxide nanowires thin films fabricated using ultrasonic spray pyrolysis and oxygen plasma etching method. The NW’s morphological, electrical, and optical properties were investigated under different plasma etching periods and the number of deposition cycles. The increase of plasma etching and oxidation time increases the surface roughness of the Ag NWs until it fused to form a porous thin film of silver oxide. AgNWs based thin films were characterized using X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoemission spectroscopy, and UV–Vis spectroscopy techniques. The obtained results indicate the formation of mixed mesoporous Ag 2 O and AgO NW thin films. The Ag 2 O phase of silver oxide appears after 300 s of oxidation under the same conditions, while the optical transparency of the thin film decreases as plasma etching time increases. The sheet resistance of the final film is influenced by the oxidation time and the plasma application periodicity. Graphic abstract

Atmospheric pressure plasma (APP) etching has been developed recently into a manufacturing technique for silicon-based materials used for large optical lenses. However, there are few reports published regarding APP etching of non-silicon-based materials. We report here the development of an APP process using SF6 for the etching of Ti-6Al-4 V metal alloy. Ti-6Al-4V is extensively used in aerospace and biomedical fields for its excellent properties; however, these properties also make it difficult to machine. Current techniques such as precision grinding and laser polishing can be slow, energy intensive, and cause damages and defects which reduce the lifetime of vital components. The results in this paper demonstrate effective material removal and little surface damage by APP etching of Ti-6Al-4V. Material removal rates between 0.5 and 2 mm3 min−1 were obtained, and the proposed material removal mechanism is through the formation of volatile VFx and TiF4. These results show that APP etching is a promising technique for surface finishing of Ti-6Al-4V, particularly for large- and complex-shaped components.

Effective hotspot engineering with facile and cost-effective fabrication procedures is critical for the practical application of surface-enhanced Raman spectroscopy (SERS). We propose a SERS substrate composed of a metal film over polyimide nanopillars (MFPNs) with three-dimensional (3D) volumetric hotspots for this purpose. The 3D MFPNs were fabricated through a two-step process of maskless plasma etching and hydrogel encapsulation. The probe molecules dispersed in solution were highly concentrated in the 3D hydrogel networks, which provided a further enhancement of the SERS signals. SERS performance parameters such as the SERS enhancement factor, limit-of-detection, and signal reproducibility were investigated with Cyanine5 (Cy5) acid Raman dye solutions and were compared with those of hydrogel-free MFPNs with two-dimensional hotspots. The hydrogel-coated MFPNs enabled the reliable detection of Cy5 acid, even when the Cy5 concentration was as low as 100 pM. We believe that the 3D volumetric hotspots created by introducing a hydrogel layer onto plasmonic nanostructures demonstrate excellent potential for the sensitive and reproducible detection of toxic and hazardous molecules.