Reactive Ion Etching Technique Research Articles

THERMOREGULATION SYSTEM FOR BIOSENSORS BASED ON FIELD-EFFECT TRANSISTORS WITH A NANOWIRE CHANNEL

In this work we present an automatic thermoregulation system for biosensors based on field-effect transistors with a nanowire channel, which provides full control on the required temperature regime in bioanalytical analises. The system elements, including field-effect transistors with a nanowire channel, temperature sensors and heaters, were fabricated on a single silicon cristal using electron beam lithography, reactive ion etching and high-vacuum deposition techniques. Unicue electronics have been developed to control and maintain temperature. The dependence of thermometer readout on heating power was measured, which is in good agreement with the results of numerical simulation. A demonstration of a thermoregulation system with PID-feedback was carried out, ensuring the establishment of a desiered temperature in the range of 30-70◦ C in 18 s in liquid. A demonstration of a thermoregulation system for detecting nucleic acids was carried out using synthetic single-stranded DNA, which is a gene fragment from the bacterium Escherichia coli. The minimal detectable response was observed for a sample with a concentration of 3 fM.

Praseodymium-Doped Ge20In5Sb10Se65 Films Based on Argon Plasma Cosputtering for Infrared-Luminescent Integrated Photonic Circuits.

In this paper, we report on the infrared luminescence of amorphous praseodymium-doped Ge20In5Sb10Se65 waveguides, which can be used as infrared sources in photonic integrated circuits on silicon substrates. Amorphous chalcogenide thin films were deposited by radiofrequency magnetron cosputtering using an argon plasma whose deposition parameters were optimized for chalcogenide materials. The micropatterning as ridge waveguides of the chalcogenide cosputtered films was performed using photolithography and plasma-coupled reactive ion etching techniques. The influence of the rare earth concentration within those thin films on their optical properties and rare earth spectroscopic properties was investigated. Using an excitation wavelength of 1.55 μm, the mid-infrared luminescence of Pr3+ ions from 2.5 to 5.5 μm was clearly demonstrated for studied chalcogenide materials. A wide range of waveguide widths and doping ratios were tested, assessing the ability of the cosputtering technique to preserve the luminescence properties of the rare earth ions initially observed in the bulk glass through the thin-film deposition and patterning process.

Large area nanoscale patterning of functional materials using organosilicate ink based nanotransfer printing

This paper presents a versatile nanotransfer printing method for achieving large-area sub-micron patterns of functional materials. Organosilicate ink formulations combined with effective release layers have been shown to facilitate patterning of materials through the commonly used patterning approaches—lift off, physical etching and chemical etching. In this paper, we demonstrate that organosilicate ink formulations function as an effective resist owing to its superior physico-chemical stability whereas the release layers ensure clean removal of the resist post patterning. We successfully demonstrate patterning of sub-micron structures (800 nm feature sizes) of chromium metal through the lift off approach, silicon through reactive ion etching technique and silicon dioxide through wet chemical etching technique illustrating the versatility of the reported method. This patterning methodology represents a significant advancement in enabling nanostructure fabrication within resource-constrained laboratories. The approach requires nothing more than a master mold containing the desired structures, a spin coater, a low-temperature hotplate, and a desktop reactive ion etch tool.

Polystyrene microspheres with ultra-rough surfaces engineered using RIE technique and applied using SERS.

In this study, we successfully fabricated two ultra-rough surfaces based on polystyrene (PS) microspheres by employing the reactive ion etching (RIE) technique. Elemental analysis confirmed a stable AlF3 composition of the structures of these surfaces. We proposed the mechanism of the formation of these surfaces and performed SERS-related tests; the prepared substrates exhibited excellent SERS performance.

Shape tuning of large area silicon nanotip arrays through reactive ion etching

Nanostructures formed in silicon form an important class of structures that span a broad spectrum of application areas. Of these, columnar structures of silicon featuring tiplike apexes have their own niche applications. The ability to afford shape tunability for these structures further enhances their application potential. In this paper, we present our findings on the large area fabrication of silicon nanotips defined through microsphere lithography and shape tuned through a combination of different reactive ion etching (RIE) techniques. The self-sharpening mechanism of the tips when using nonplanar etch masks (microspheres) under anisotropic etching conditions is elucidated. We further show that depending on the manner of etching (continuous versus discrete multistep etch), identical anisotropic etching recipes produce vastly different tip morphologies. Hourglass-shaped silicon tips were obtained when silicon was subjected to anisotropic followed by isotropic etching conditions. Sharp silicon tips with tip apex radii on the order of 2 nm have been successfully realized when the RIE shape tuned tips were subjected to a series of oxidative sharpening steps.

A polarization converter array based on microcavity patterned hydrophobic layer induced twisted-radial liquid crystals

We report a facile method to prepare an array of liquid-crystal polarization converters (LCPCA) based on hydrophobic microcavity arrays. The reactive ion etching (RIE) technique was chosen to treat the homeotropic polyimide (PI⊥) layers through a metal mask with a through-hole array. Under the selective RIE treatment, a hydrophobic–hydrophilic pattern is obtained due to the increase in surface energy in the etched area from ∼34.6 to ∼73.2 mN/m. The etched area forms a microcavity with a diameter of 520 μm, depth of ∼23 nm, and center distance of 690 μm, which is consistent with the dimensions of the metal mask. Since the walls of the microcavity retain hydrophobicity, the liquid-crystal (LC) molecules show a radial arrangement in the microcavity. Combining a substrate covered by a parallel rubbed homogeneous polyimide (PI∥) layer with the substrate covered by a microcavity-patterned PI⊥ layer can form a “sandwich” structure. The LC molecules in the microcavities are arranged in a twisted-radial texture, which can convert linearly polarized light to radially or azimuthally polarized light depending on the polarization direction of the incident light. The proposed method has the merits of simple steps, controllable size, and easy to fabricate large-area arrays. Our LCPCA has potential applications in tight focus, material processing, biological tissue analysis, particle capture, and optical data storage.

Mechanobactericidal Nanotopography on Nitrile Surfaces toward Antimicrobial Protective Gear.

We have much to learn from other living organisms when it comes to engineering strategies to combat bacterial infections. This study describes the fabrication of cicada wing-inspired nanotopography on commercially pure (CP) nitrile sheets and nitrile gloves for medical use using the reactive ion etching (RIE) technique. Antibacterial activity against P. aeruginosa was tested using two different surface morphologies. It was observed that the etched nitrile surfaces effectively minimized bacterial colonization by inducing membrane damage. Our findings demonstrate a single-step dry etching method for creating mechanobactericidal topographies on nitrile-based surfaces. These findings have utility in designing next-generation personal protective gear in the clinical setting and for many other important applications in the age of antimicrobial resistance.

Room temperature single-photon emission from InGaN quantum dot ordered arrays in GaN nanoneedles

GaN-based single-photon sources have received immense attention for applications in quantum technologies. An isolated semiconductor quantum dot (QD) is an attractive and proven choice. Most experimental demonstrations involve epitaxial growth or etching of the QD embedded in a vertical nanopillar/nanowire structure. Here, we demonstrate room-temperature single-photon emission from an InGaN QD embedded in a GaN nanoneedle. The nanoneedle is tapered at the bottom and is formed by a succession of inductively coupled plasma reactive ion etching and crystallographic direction-dependent wet etching techniques. The nanofabrication process steps yield reproducible and uniform-sized QDs in the needle structures. Cross-sectional SEM images show needles are centered at the center of a hexagonal base, which confirms a good crystalline property of the QD. Micro-photoluminescence measurements on a single QD manifest a short time constant for radiative decay channels without any prominent non-radiative decay path. Second-order correlation measurements confirm the antibunching of the emitted photons. Higher spectral purity and smaller value of the second-order correlation are maintained up to a good excitation power, indicating the usefulness of the methodology for quantum technologies.

Effect of microarchitectural surface of polycaprolactone modified by reactive ion etching on osteogenic differentiation

The surface topology of a bioimplantable material is considered to be the most important influencing factor on the cytocompatibility and function. The aim of this study was to compare the cytocompatibility and osteogenic differentiation of polycaprolactone (PCL) surfaces with spiky and hill-and-valley (H-a-V) topologies fabricated by the Plasma reactive ion etching (RIE) technique. The RIE process was performed at a plasma power of 100 W and pressure of 100 mTorr using an oxygen flow rate of 100 sccm for 3 min (for Spiky) and 5 min (for H-a-V). The surface roughness and wettability of PCL were improved with the increase in the RIE treatment time. The focal cell adhesion, migration, and proliferation were increased in the H-a-V group compared to the Spiky group. The cell differentiation values (alkaline phosphatase (ALP) and Alizarin-red staining) were statistically significantly improved in H-a-V compared to those of Spiky. A western blot analysis demonstrated that H-a-V promoted cell differentiation compared to Spiky. These results suggest that the H-a-V topology is more favorable for cytocompatibility and osteogenic differentiation over the Spiky topology.

Simply structured polarization-independent high efficiency multilayer dielectric gratings.

A polarization-independent multilayer dielectric diffraction grating with a low aspect ratio and high diffraction efficiency was designed and fabricated. The diffraction grating designed with a grating density of 1200 lines/mm had an aspect ratio of 0.59, mean polarization-independent diffraction efficiency in the Littrow angle of ±2.5∘, and 1030-1080 nm wavelength range of 97.2%. The designed grating was fabricated using ion assisted deposition and reactive ion etching techniques. The mean polarization-independent diffraction efficiency of the fabricated grating was 96.1%, and its standard deviation was 0.68%. The fabricated diffraction grating was irradiated with a 1064 nm cw laser, with a power density of 30kW/cm2, for 1 min to measure the temperature change before and after the laser application. It was verified that the temperature variation of the diffraction grating without heat treatment was 8.8°C, and the temperature variation after heat treatment at 400°C decreased to 2.3°C.

Tailoring InSb Nanowires for High Thermoelectric Performance Using AAO Template-Assisted Die Casting Process.

Herein, we demonstrate a facile technique for the fabrication of one-dimensional indium antimonide (InSb) nanowires using anodic aluminium oxide (AAO) template-assisted vacuum die-casting method. The filling mechanism of the vacuum die-casting process is investigated on varying AAO pore structures through different electrolytes. It is found that the anodizing electrolytes play a vital role in nanowire growth and structure formation. The as-obtained InSb nanowires from the dissolution process show a degree of high crystallinity, homogeneity, and uniformity throughout their structure. The TEM and XRD results elucidated the InSb zinc-blende crystal structure and preferential orientation along the c-axis direction. The thermoelectric characteristics of InSb nanowires were measured with a four-electrode system, and their resistivity, Seebeck coefficient, power factor, thermal conductivity, and ZT have been evaluated. Further, surface-modified nanowires using the reactive-ion etching technique showed a 50% increase in thermoelectric performance.

A carbon nanotube@silicon-based three-dimensional porous photo-supercapacitor for self-powered UV detection

Miniaturized self-powered energy devices are indispensable units for next-generation portable electronics. Photo-supercapacitors (PSCs), as a reliable energy harvesting device, have been explored for self-powered applications by utilizing the photovoltaic effect of micro-supercapacitors. In this paper, we propose a self-powered PSC with bulk micro-machined three-dimensional (3D) porous asymmetric electrodes with a high-aspect ratio via deep reactive-ion etching (DRIE) technique for the detection of ultra-violet (UV) radiance. The as-fabricated porous CNT@TiC/CNT@TiO2 PSC delivers an areal capacitance of 2.69 mF/cm2 (@5 mV/s) and 7.35 mF/cm2 (@20 μA/cm2) before and after photo-charge process, respectively. The optical response of the PSC is linearly proportional to the UV power intensity with a photoresponsivity of 14.8 mA/W. A photocurrent density of 354 μA/cm2 and a photo-to-dark current ratio of 12 are experimentally obtained under a UV power intensity of 15 mW/cm2. The as-prepared PSCs are further integrated on-chip to implement a UV leakage warning system that can drive a white LED for more than 60 s under a UV power intensity of 10 mW/cm2, fully demonstrating the practical application of the 3D silicon-based device in UV monitoring systems.

Influence of the Available Surface Area and Cell Elasticity on Bacterial Adhesion Forces on Highly Ordered Silicon Nanopillars.

Initial bacterial adhesion to solid surfaces is influenced by a multitude of different factors, e.g., roughness and stiffness, topography on the micro- and nanolevel, as well as chemical composition and wettability. Understanding the specific influences and possible interactive effects of all of these factors individually could lead to guidance on bacterial adhesion and prevention of unfavorable consequences like medically relevant biofilm formation. On this way, the aim of the present study was to identify the specific influence of the available surface area on the adhesion of clinically relevant bacterial strains with different membrane properties: Gram-positive Staphylococcus aureus and Gram-negative Aggregatibacter actinomycetemcomitans. As model surfaces, silicon nanopillar specimens with different spacings were fabricated using electron beam lithography and cryo-based reactive ion etching techniques. Characterization by scanning electron microscopy and contact angle measurement revealed almost defect-free highly ordered nanotopographies only varying in the available surface area. Bacterial adhesion forces to these specimens were quantified by means of single-cell force spectroscopy exploiting an atomic force microscope connected to a microfluidic setup (FluidFM). The nanotopographical features reduced bacterial adhesion strength by reducing the available surface area. In addition, the strain-specific interaction in detail depended on the bacterial cell’s elasticity and deformability as well. Analyzed by confocal laser scanning microscopy, the obtained results on bacterial adhesion forces could be linked to the subsequent biofilm formation on the different topographies. By combining two cutting-edge technologies, it could be demonstrated that the overall bacterial adhesion strength is influenced by both the simple physical interaction with the underlying nanotopography and its available surface area as well as the deformability of the cell.

High efficiency TOPCon solar cells with micron/nano-structured emitter for a balance of light-trapping and surface passivation

At present, conventional micron-pyramid texture is imperfect for further reducing optical reflection loss and improving photoelectric conversion efficiency (PCE) of tunnel oxide passivating contact (TOPCon) solar cells. Herein, reactive ion etching technique is used to fabricate nanopores on top of pre-formed micron-pyramid silicon surface, called NPP structure. The equivalent medium layer with graded refractive index appeared on NPP textures makes the absorption of almost all incident light independent of the wavelength and angle. However, serious Auger recombination and surface recombination associated with NPP structure is detrimental to emitter passivation, usually counteracting the photocurrent gain. To identify an appropriate balance of light-trapping and surface passivation, we investigate the impact of different radio-frequency power (PRF) on the optical and electrical properties of TOPCon solar cells and discusses the underlying structural causes behind these observed improvements. Finally, we demonstrate NPP TOPCon solar cells with an average short-circuit current density of 41.44 mA/cm2 and an average PCE of 23.55% at the PRF of 600 W. Besides, the external quantum efficiency results under various incident angles from 0° to 70° exhibited excellent wide-angle spectral absorption capability, which is significant for solar cells working in an outdoor environment.

New Fabrication Method of Silicon Sub-Micron Beams with Monolithic Contacts for Thermoelectric Transport Properties Analysis.

Micromachined devices were developed and fabricated using complementary metal-oxide-semiconductor (CMOS)/micro-electro-mechanical systems (MEMS) technology allowing for the analysis of transport properties of silicon sub-micron beams having monolithic contacts. The beams were fabricated by a combination of deep reactive ion etching (RIE) and potassium hydroxide (KOH) etching techniques on standard p and n silicon bulk and silicon-on-insulator (SOI) wafers. Simultaneous fabrication of many devices on one wafer allows for the extraction of statistical information to properly compare the different layers and contacts. Fabricated devices are presented, underlining the feasibility of the proposed microdevice. The methods used to manipulate the geometry and the surface roughness of the single crystalline silicon beams are described. The presented measurement device offers the possibility to determine simultaneously all the main transport values, thermal, and electrical conductivities as well as the Seebeck coefficient.

Laser-induced morphology-switchable slanted shape memory microcones for maneuvering liquid droplets and dry adhesion

Slanted micro-/nano-structures play pivotal roles in a diversity of fields, including water-proof engineering and fogdrop collection. In light of recent advances in fabricating slanted microstructures by using photolithography or reactive ion etching techniques, however, a complex, environmentally unfavorable, and tedious fabrication process makes them far from practical in application. Herein, we present a viable strategy to prepare a slanted shape memory microcone array (SSMMA) by combining the femtosecond laser oblique microfabrication and replica-mold method. Thanks to its fast temperature-responsive feature, SSMMA enables the transition of adhesion forces to effectively control the sliding of droplet on the surface. The underlying principle of the adjustable migration behavior of droplet is that SSMMA switches between the slanted and collapsed states. Moreover, we systematically studied the influence of the microcone spacing/height together with the microcone bending angle on the wetting performance of water droplet. More significantly, the resulted SSMMA analogous to a “machine hand” is experimentally demonstrated to be competent for the grab and transfer of fragile and smooth objects (e.g., coverslip) with a maximum adhesion force of ∼19.404 mN. The current study opens up an avenue for rapidly fabricating functional slanted microstructures for practical usage.

Investigation into the effect of distinct nanostructures on silicon reflectivity for solar cells

Considering the future importance of unconventional energy sources, improving the efficiency of photovoltaic devices is vital. This study investigates the effect of different cross-sectional nanogratings on reflectivity of silicon surface. The nanostructures dimesions were optimized thorugh simulation and further validated using spectrophotometer. Electron Beam Lithography and Reactive Ion Etching techniques were used to fabricate nanogratings on silicon surface and characterized to confirm dimensions. The fabricated rectangular nanogratings on silicon surface helps to reduce the reflectance by 31.44% owing to the gradual change in refractive index of the surface.

Ultra-Low-Reflective, Self-Cleaning Surface by Fabrication Dual-Scale Hierarchical Optical Structures on Silicon

An integrated functional anti-reflective surface is of great significance for optical and optoelectronic devices. Hence, its preparation has attracted great attention from many researchers. This study combined wet alkaline etching approaches and reactive ion etching (RIE) techniques to create a dual-scale hierarchical anti-reflective surface on silicon substrates. The effect of RIE time on surface morphology and optical performance was investigated using multiple characterization forms. The optimal parameters for the fabrication of dual-scale structures by the composite etching process were explored. The silicon surface with a dual-scale structure indicated excellent anti-reflective properties (minimum reflectivity of 0.9%) in the 300 to 1100 nm wavelength range. In addition, the ultra-low reflection characteristic of the surface remained prominent at incident light angles up to 60°. The simulated spectra using the finite difference time domain (FDTD) method agreed with the experimental results. Superhydrophobicity and self-cleaning were also attractive properties of the surface. The functionally integrated surface enables silicon devices to have broad application prospects in solar cells, light emitting diodes (LEDs), photoelectric detectors, and outdoor equipment.

Silicon Metalens Fabrication from Electron Beam to UV-Nanoimprint Lithography.

This study presents the design and manufacture of metasurface lenses optimized for focusing light with 1.55 µm wavelength. The lenses are fabricated on silicon substrates using electron beam lithography, ultraviolet-nanoimprint lithography and cryogenic deep reactive-ion etching techniques. The designed metasurface makes use of the geometrical phase principle and consists of rectangular pillars with target dimensions of height h = 1200 nm, width w = 230 nm, length l = 354 nm and periodicity p = 835 nm. The simulated efficiency of the lens is 60%, while the master lenses obtained by using electron beam lithography are found to have an efficiency of 45%. The lenses subsequently fabricated via nanoimprint are characterized by an efficiency of 6%; the low efficiency is mainly attributed to the rounding of the rectangular nanostructures during the pattern transfer processes from the resist to silicon due to the presence of a thicker residual layer.

Improving the performance of a laser-driven flyer with a diffractive optical element of high wavefront distortion tolerance

To improve the performance of a laser-driven flyer (LDF), we design and fabricate a diffractive optical element (DOE) to convert a laser pulse with nonuniform energy into a flat-topped beam, with 77.05% diffraction efficiency and 55.45% mean square error (MSE). The DOE has a high tolerance for wavefront distortion. Within the maximum 3λ phase fluctuation, the diffraction efficiency of the flat-topped spot maintains around 77.05% and the MSE is 57.47%. In the experiment, the designed DOE has been well achieved through the photolithography and the reactive ion etching technique, and the DOE displays a diffraction efficiency of 75.15% and a MSE of 64.78%. When combining with the LDF, a flyer with high velocity and integrity has been demonstrated experimentally, where the flyer velocity is increased by about 1.16 ∼ 1.52 times due to the generation of high-uniform laser beam from DOE.