Electrochemical Etching Process Research Articles

Investigating Quantum Confinement and Enhanced Luminescence in Nanoporous Silicon: A Photoelectrochemical Etching Approach Using Multispectral Laser Irradiation

This study explores electrochemical etching to form porous silicon (PS), which has diverse biomedical and energy applications. Our objective is to gain new insights and drive significant scientific and technological advancements. Specifically, we study the effect of electrochemical etching of P-type silicon using laser irradiation in a hydrofluoric acid (HF) solution. The formation of the nanoscale PS structure can be successfully controlled by incorporating laser irradiation into the electrochemical etching process. The wavelength and power of the laser influence the formation of nanoporous silicon (NPS) on the surface during the electrochemical etching process. The luminous flux is monitored with the help of a customized integrating sphere system and an LED-based excitation source to find the light flux values distributed across the P-type nanolayer PS wafers. Analysis of the NPS and luminescence characteristics shows that the laser bandwidth controls the band gap energy absorption (BEA) phenomenon during the electrothermal reaction. It is demonstrated that formation of the NPS layer can be controlled in this combined laser irradiation and electrochemical etching technique by adjusting the range of the laser wavelength. This also allows for further precise control of the numerical trend of the luminous flux.

Inserting colloidal quantum dots into GaN mesa-array subsurface porous structures through electrochemical etching for display color conversion application

High-efficiency photon color conversion is an approach of great potential for implementing color display. Inspired by the observation of emission enhancement in a nanoscale cavity, a novel technique to fabricate an array of color converter by mixing colloidal quantum dots (QDs) with the electrolyte of an electrochemical etching (ECE) process is demonstrated. In this process, QDs flow with the electrolyte into the etched subsurface nanoscale porous structure (PS) and settle inside. Since the PS formation and hence QD insertion are controlled by the flow path of the applied electric current in the ECE process, this technique can be used for fabricating any graphic pattern. The nanostructure of such a QD-inserted mesa is examined to confirm QD insertion. Although only single-color mesa arrays are demonstrated in this paper, this technique can be used for fabricating a multiple-color mesa array if a QD or a light-emitting nanoparticle of higher thermal stability is available.

Discrimination of dislocation in highly doped n-type 4H–SiC by combining electrochemical reaction and molten alkali etching

This work proposes an effective etching method for highly doped n-type 4H–SiC by combining electrochemical reactions and molten alkali etching. By employing our developed method, threading mixed dislocation (TMDs) and threading screw dislocations (TSDs) can be distinctly visualized as hexagonal etching pits of varying sizes. The slightly smaller threading edge dislocations (TEDs) appear as roughly circular etching pits, while basal plane dislocations (BPDs) are revealed as characteristic seashell-shaped pits. Additionally, we provide a reaction equation that elucidates the mechanism of the electrochemical etching process, thus sparking a new investigation into the discrimination of dislocations under molten alkali conditions. By applying a positive voltage to the wafer, we ensure a continuous supply of holes crucial for the reaction, thereby maintaining both the etching rate and the selectivity towards defects. This approach not only enhances the efficiency of the etching process but also provides a more accurate and reliable method for characterizing and understanding the dislocation properties of highly doped n-type 4H–SiC wafers.

Vertical InGaN Light-Emitting Diode with Hybrid Distributed Bragg Reflectors.

A vertical-type InGaN light-emitting diode with a resonant cavity was demonstrated with a 9 μm aperture size and a short cavity formed by hybrid distributed Bragg reflectors (DBRs). The approach involved designing epitaxial structures and utilizing an electrochemical etching process to convert heavily doped n-type gallium nitride (n+-GaN) layers into porous GaN layers as a porous-GaN DBR structure. Thirteen pairs of the conductive porous-GaN:Si/GaN:Si DBR structure provided a vertical current path in a vertical-type light-emitting diodes (LED) structure. The LED epitaxial layers were separated from sapphire for membrane-type LED structures through a laser lift-off process. During the free-standing membrane fabrication process, the dielectric DBR deposited on ITO/p-GaN:Mg layers was inverted from top to bottom, thereby establishing the concept of higher reflectivity for the bottom DBR compared to the porous-GaN DBR. The physical cavity length was reduced from about 2.3 μm for the LED membrane to 0.74 μm for the membrane-type LED with the embedded porous-GaN DBR structure. The divergent angles and line width of EL emission light were reduced from 124°/31.7 nm to 44°/3.3 nm due to the resonant cavity effect. The membrane-type LED structures with hybrid DBRs consisted of small divergent angles, narrow line width, and vertical current injection properties that have potential for directional emission light sources and vertical-cavity surface-emitting diode laser applications.

Preparation and properties of two-dimensional Ti2CT x MXene based on electroetching method

The continuous advancements in wearable electronics have drawn significant attention toward 2D MXenes materials for energy storage owing to their abundant availability, adaptability, and distinctive physicochemical properties. Two unresolved concerns currently revolve around environmental pollution by F-containing etching and finite kinetics caused because of re-stacking of nanosheets. In this study, Al was electrochemically etched from porous Ti2AlC electrodes without the use of fluorine, through a selective electrochemical etching process in dilute hydrochloric acid. Subsequently, Ti2CT x MXene was vertically grown on carbon fiber (CF) substrates. The resulting Ti2CT x @CF electrodes are lightweight, thin, and flexible, exhibiting a surface capacitance of 330 mF cm−2 at a constant current density of 1 mA cm−2 after 2000 cycles. They display a surface capacitance retention of 96.16% and a high energy density of 45.3 μWh cm−2 at a power density of 0.497 mW cm−2. These metrics underscore the Ti2CT x @CF electrode’s commendable multifunctionality, electrochemical performance, ion transport efficiency, and charge storage capacity. Moreover, a flexible energy storage electrode material with a high area capacity was developed by combining Ti2CT x MXene nanosheets, possessing a large specific surface area, with a flexible carbon fabric substrate.

Facile and scalable preparation of superhydrophobic brass mesh for efficient and rapid separation of oil and water

A facile method for preparing superhydrophobic brass mesh is proposed based on electrochemical etching and surface modification. The impact of processing time and the electric potential of the electrochemical etching were studied on the contact angle (CA) of the mesh. The samples were examined using scanning electron microscopy, Energy-dispersive X-ray spectroscopy analysis, X-ray diffraction, and Fourier-transform infrared spectroscopy. The electrochemical etching process caused the decrement of wires’ thickness and imposed roughness. Results showed more dissolution of zinc than copper under 3 V of the electric potential and the processing times of 3 and 6 min. The optimum condition of electrochemical etching was obtained under the electric voltage of 3 V for a processing time of 6 min, which led to a CA of 155.5 ± 3.2°. The thickness of the mesh wires decreased by 17.7% due to electrochemical etching in this sample. This sample also showed low adhesion for a water drop. The efficiency of oil/water separation was above 95 for the xylene and ethyl acetate in a batch system. The effect of the flow rate of the oil–water mixture on separation efficiency was also examined. The optimum flow rate was 0.8 ml s−1 with a high separation efficiency of 96.8% for xylene/oil separation.

Alpha particle energy-range studies by a layer removal method in polycarbonate detectors for determining unknown ion energies

The aim of this study is to apply a “layer removal method” for alpha energy-range determination in polycarbonate detectors (PC) compared with SRIM software. This method is a precise chemical pre-etching process by which a layer of a certain thickness is removed from an exposed or unexposed PC detector surface before applying electrochemical etching (ECE). A group of 500 μm thick PC detectors was exposed to alpha particles of known fluence (∼1.0 × 104 alphas.cm−2) and ∼0.3–∼5.0 MeV energy range, followed by a pre-etching process at 12 different time intervals in 70% ethylenediamine solution. After the ECE process, alpha track density and diameter were determined. Track density versus removed layer thickness for each alpha energy follows a Bragg type peak after which approaching zero at a known removed layer thickness corresponding to the alpha range. The results also show a linear increase of the mean track diameter as the removed layer thickness increases for each energy. On the other hand, this study confirms a shift in the energy range registration by increasing the thickness of the removed layer. Using this precise method, an unknown energy can be determined by step-by-step thickness removal process until the track density approaches zero. In conclusion, the upper energy of ions emitted in a PFD can be determined. This method is a precise and simple method for ion energy-range determination studies for passive ion spectrometry.

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 %).

Electrochemical Impedance Spectroscopy Analysis of 45S5 Bioglass Coating on After Oxidation of CoCrW Alloy

Implants and prostheses, which are used to replace a missing or damaged structure in living organisms, must show all the necessary mechanical, tribological, electrochemical and biocompatibility properties together. CoCr alloys are often preferred biometals for their good mechanical strength and wear resistance, especially in dental and orthopedic implants. Although these alloys show good corrosion resistance in terms of electrochemical behavior as well as other good properties, when CoCr alloys come into contact with bone tissue, their surfaces show bioinert properties in terms of tissue formation between the implant and bone tissue. Therefore, both their corrosion behavior and biocompatibility properties need to be improved. In this study, CoCrW alloys produced by selective laser melting were coated with commercial 45S5 bioglass powder, a bioactive material, by electrophoretic deposition method. In order to improve the adhesion after coating, CoCrW alloys were subjected to electrochemical etching process during coating. After the coating process was completed, untreated, oxidized, untreated-coated and oxidized-coated samples were examined by electrochemical impedance spectroscopy (EIS) after open circuit potential measurements to investigate their corrosion behavior. As a result of the corrosion tests, it was determined that the oxidized-coated sample showed the best condition compared to the other samples in EIS analyzes.

The influence of the physicochemical processes on the electrical response of Al/p-Si structure with etched surface

In this paper, the electrochemical etching process is used for surface modification of the p-Si wafer, named as porous silicon (PS), in the metal–semiconductor (MS) type Schottky diode (SD) with a structure of Al/p-Si. Five regions of PS wafer with different etching rates are selected for comparison of them which are called P2, P3, P4, and P5 (P1 is the reference area without porosity). The morphological, structural, and electrical properties of the PS used in the MS-type SD are investigated using field-emission scanning electron microscope (FE-SEM) images, energy dispersive X-ray (EDX) analysis, and current–voltage (I–V) characteristics, respectively. The FE-SEM images show a meaningful effect on the porosity. The EDX spectrum demonstrates the importance of the chemical effects in addition to the physical changes in the porosity process of the p-Si wafer. The reverse-saturation current (I0), ideality factor (n), barrier height at zero-bias (ΦB0), and series/shunt electrical resistances are also computed and compared. Some of these parameters (n, Rs, BH) are determined using different methods, namely Thermionic emission (TE), Cheung functions, and modified Norde, and they exhibit strong agreement with each other. The energy-dependent profiles of surface states (Nss) are estimated from the I–V data by considering the voltage dependence of ΦB (V) and n(V). All the experimental findings indicate that the etching process of the p-Si wafer significantly influences the electrical performance of the Al/p-Si Schottky diode by increasing the extent of etching.

Fabrication of high aspect ratio, non-line-of-sight vias in silicon carbide by a two-photon absorption method

The future of Moore’s Law for high-performance integrated circuits (ICs) is going to be driven more by advanced packaging and three-dimensional (3D) integration than by simply decreasing transistor size. 3D ICs offer low-power consumption, high-performance and a smaller footprint compared to conventional 2D ICs. The key enabling technology to 3D integration is the interposer that provides interconnects to route signals between the chiplets that comprise the IC. However, the fabrication of high-aspect ratio through wafer vias (TWVs), that provide electrical and mechanical connection between chiplets on the top and bottom of the interposer, is one of the important challenges that limit interposer performance. Current fabrication technologies are limited by tapering effects and the need for direct line of sight to the fabrication surface. These limit the possible aspect ratios of vias and require large, complicated surface traces to connect the vias to the chiplets. Here, we demonstrate the fabrication of high-aspect ratio, non-line-of-sight TWVs in silicon carbide (SiC). SiC provides better mechanical, chemical, and thermal performance than silicon (Si). The technique uses an electro-chemical etch process that utilizes two-photon absorption to create any arbitrary 3D structure in SiC allowing for direct, subsurface routing between chiplets.

Alpha radioactivity in Iraqi market foodstuff: Assessing annual effective dose and lifetime cancer risk

In this study, integrated passive radon dosimeters with solid-state nuclear trace detectors (CR-39 and CN-85) were used to determine the annual effective dose and excess cancer risk for 25 different food samples in the Iraqi market. The dosimeters were deployed after four weeks of the required radiological equilibrium between radon and radium in the samples stored in sealed beakers. These caps were then quickly replaced with other caps equipped with detectors and stored for 70 days. After the detectors were removed from the samples, an electrochemical etching process was performed in a water bath and sodium hydroxide solution to reveal the traces of alpha particles on the detector surface. Microscopic observations were performed using an optical microscope to quantify the traces present on the detector surface. The results showed that the average radon concentrations for the CR-39 detectors ranged from 3.80 to 7.32 Bq/kg, with an average of 5.51 Bq/m3, and for the CN-85 detectors ranged from 1.23 to 4.51 Bq/kg, with an average of 2.79 Bq/kg. The radium and uranium concentrations for the CR-39 detector ranged from 0.299 to 0.577 Bq/kg, with an average of 0.434 Bq/kg, and from 3.72 to 7.17 Bq/kg, with an average of 5.40 Bq/kg. Comparing all the results between the two detectors, it was found that the values recorded with the CR-39 were approximately twice those recorded with the CN-85. It is important to note that all recorded values are within internationally permissible limits and do not pose a threat to human health.

Increasing the Light Extraction Efficiency of Organic Light-Emitting Devices by Electrochemically Corroded Patterned Substrates.

A substrate with microstructure can increase the light extraction efficiency of OLEDs. However, the present preparation methods for micro- and nanostructures are not suited for broad-area manufacturing. In this research, we suggested an electrochemical etching approach to patterning Si substrates and effectively generated a vast area of micro-/nanostructures on the surface of Si. We created OLEDs using this patterned substrate. It was discovered through this study that when the current density is 100 mA/cm2, the brightness increases by 1.67 times and the efficiency increases by 1.43 times, over a planar equivalent. In the future, this electrochemical etching process for patterned silicon substrates might give rise to a new approach to the large-scale manufacture of microstructured silicon substrates.

Electrochemical Etching-Assisted Fabrication of Quantum Tunneling Sensing Probes with Controlled Nanogap Width

Quantum tunneling electrical probes, consisting of a pair of nanoelectrodes with a gap width of less than 5 nm, can be used as a robust electrical sensing platform for the detection of various nanoscale objects. To achieve this, stable and gap-width-controllable electrodes are essential. Although various methods, including lithography and electrochemical strategies, have been proposed for the fabrication of tunneling electrodes, the ability to precisely control the gap width and ensure reproducibility is still lacking. Here, we report a feedback-controlled electrochemical etching approach to fabricate the tunneling electrodes with a controlled nanogap. The connected nanoelectrodes, derived from a dual-barrel nanopipette, were subjected to a controlled electrochemical etching process from a short-circuited state to a tunneling gap. The resulting tunneling electrodes exhibited solvent-response current–voltage electrical behavior, which was well fitted with the Simons model, indicating the formation of tunneling electrodes. Overall, a success rate of more than 60% could be achieved to obtain the tunneling gaps. Furthermore, to verify the function of tunneling electrodes, we used the etched-tunneling electrodes for free-diffusing protein detection, showing the potential of etched-tunneling electrodes as single-molecule sensors.

Vegetal melanin-induced radiative recombination centers in porous silicon

Melanin has attracted significant attention in recent years due to its optoelectronic properties exploited in micro and nano-bioelectronic applications. Herein, were report on the photoluminescence tuning of porous silicon (PSi) functionalized with melanin. PSi was prepared through an electrochemical etching process applying a density current of 2.8 mA/cm2 to a silicon wafer using an electrolyte composed of HF and ethanol (1:1). The melanin/PSi heterojunction interface was created by drop casting a melanin solution (0.1 mg/mL in dimethyl sulfoxide) using different volumes of 10, 30 and 50 μl onto a PSi wafer. A remarkable increment of the photoluminescence intensity in the melanin/PSi interface as compared to the pristine PSi was observed through steady-state experiments. Moreover, a pronounced blue-shift (50 nm) of pristine PSi emission maximum as compared to melanin/PSi interfaces was also recorded. This behavior could be ascribed to the generation of radiative recombination centers as indicated by an increment of silicon-hydrogen (Si–H) and silicon-oxygen (Si–O) defects formed in the PSi upon interaction with the melanin, as proven by infrared (FT-IR) experiments. Time-resolved experiments revealed a remarkable decrease in the decay times of the melanin/PSi composites moving from microsecond-time components in the pristine PSi towards nanosecond decay times when the highest amount of melanin was employed, indicative of an increment of radiative recombination centers. Surface morphology changes of the composites were monitored by scanning electron microscopy (SEM), displaying the formation of small grains of melanin on the surface of the PSi up to the appearance of a melanin thin film when low and high amounts of melanin were used, respectively. This study demonstrates the enormous potential of melanin-PSi heterojunctions to provide a novel and sustainable solution for developing (bio)optoelectronic devices.

Cavity Mode-Matching InGaN Aperture-Emitting Device with a Nanoporous GaN Reflector via Ion Implantation

Cavity mode-matching InGaN resonant-cavity light-emitting diodes (RC-LEDs) with aperture size-dependent emission have been demonstrated through nitrogen ion (N+) implantation and electrochemical wet etching processes. The RC-LED structure consisted of 570 nm-depth ion-implanted regions and an embedded 17-pair nanoporous-GaN/n-GaN distributed Bragg reflector (DBR) outside the aperture, while there existed a full 20-pair DBR structure within the aperture regions. Shorter and mode-matching cavity lengths were fabricated, confirmed by transmission electron microscopy and angle-resolved photoluminescence spectra inside the aperture area without subjecting to the N+ implantation. By reducing the aperture sizes, higher current density and narrower far-field electroluminescence emission patterns were observed in the RC-LED with an aperture size of 40 μm-diameter. These results demonstrate that the cavity mode-matching RC-LEDs with optical/electrical confinements and controllable cavity length mismatch features can be applied in a wide range of optoelectronic-based device applications.

Effect of Nanographene Coating on the Seebeck Coefficient of Mesoporous Silicon.

Nanographene-mesoporous silicon (G-PSi) composites have recently emerged as a promising class of nanomaterials with tuneable physical properties. In this study, we investigated the impact of nanographene coating on the Seebeck coefficient of mesoporous silicon (PSi) obtained by varying two parameters: porosity and thickness. To achieve this, an electrochemical etching process on p + doped Si is presented for the control of the parameters (thicknesses varying from 20 to 160 µm, and a porosity close to 50%), and for nanographene incorporation through chemical vapor deposition. Raman and XPS spectroscopies confirmed the presence of nanographene on PSi. Using a homemade ZT meter, the Seebeck coefficient of the p + doped Si matrix was evaluated at close to 100 ± 15 µV/K and confirmed by UPS spectroscopy analysis. Our findings suggest that the Seebeck coefficient of the porous Si can be measured independently from that of the substrate by fitting measurements on samples with a different thickness of the porous layer. The value of the Seebeck coefficient for the porous Si is of the order of 750 ± 40 µV/K. Furthermore, the incorporation of nanographene induced a drastic decrease to approximately 120 ± 15 µV/K, a value similar to that of its silicon substrate.

Ultraviolet-C AlGaN Resonant-Cavity Light-Emitting Diodes with Thermal Stability Pipe-AlGaN-Distributed Bragg Reflectors.

Ultraviolet-C AlGaN resonant-cavity light-emitting diodes with top and bottom pipe-AlGaN-distributed Bragg reflectors (DBRs) have been demonstrated. For the top/bottom DBR structures, 20 pairs of n+-AlGaN:Si/n-AlGaN:Si stack structures were transformed into the pipe-AlGaN:Si/n-AlGaN:Si DBRs through a doping-selective electrochemical wet etching process. The reflectivity of the pipe-AlGaN DBR structure was measured as 90% at 276.7 nm with a 20.9 nm flat stopband width. The anisotropic optical properties of the pipe-AlGaN DBR structure had been analyzed through the polarization-dependent reflectance spectra. For temperature-dependent reflectance spectra, the central wavelengths were slightly redshifted from 275 nm (100 K) to 281 nm (600 K) due to thermal expansion, refractive index increase, and partial strain release phenomena in the pipe-DBR structure. High photoluminescence emission intensity and line-width reducing phenomena were observed at 10 K in the UVC-LED with the resonant-cavity structure, which has potential for high-efficiency UV-C light source applications.

An investigation of photo_electrical properties of silicon nanoparticles/PSi/p-Si hetero structures

In this work, two forms of nanocrystalline, were used (as-prepared macroPorous silicon and silicon nanoparticle) to synthesize hybrid structures for photodetectors applications. The fabrication pathway was carried out through two 2-steps processes. The 1-step was formation of as-prepared silicon nanoparticle (SiNPs), while and the 2-step was creation of low spam of macroPSi size substrate via electrochemical etching process in HF solutions. Specific features of SiNPs and low spam of macroPSi size substrate were explored using scanning electron microscopy SEM, energy-dispersive x-ray (EDX), Atomic Force Microscope (AFM), and photoluminescence (PL) spectroscopy respectively. Dark and photo current characteristics and spectral responsively of photodetectors were investigated for the macPSi layer and the hybrid structure. The performance of the hybrid configuration shows an improvement in the sensitivity of about 0.75 A/W with appearance of new additional peak at 450 nm as compared with the PSi photodetector of about 0.93 A/W. The achieved improvement is related with the appearance of double Heterojunction device between PSi/si and SiNPs/PSi. Also this improvement may be related with the reduction of the reflectd light from the hybrid structure due to the multiple reflection between SiNPs/PSi. The quantum efficiency η of the photodetector in the spectral range 450–700 nm was found to be 65%.

The effective of time etching and different acids on the morphological porous silicon

This paper study the characteristics of nano crystalline silicon prepared with the use of electrochemical etching with etching time (15,20) min for salt and Nitric acid (HNO3) and etching time (15,20) min for Ethanol and Hydrofluoric acid, and study the effect of this solutions on the characteristics of porous silicon (ps) will be produced by electrochemical etching by using electrochemical etching from p-type bulk silicon with resistivity (1-10 Ω.cm) with different time. after that, make a comparison for the morphological properties for porous silicon. Research employing X-ray diffraction and scanning electron microscopy instruments were also performed on the samples that were produced as a result. Micromachining etching uses electrochemical etching of silicon in HF solution. New wafer-etched structures are reported. Wall arrays, hole arrays, meander-shaped structures, spiral-like walls, microtubes, and more are produced. The electrochemical etch process and KOH etching time of the original pattern on final geometries are modelled.