Two-step Electrochemical Etching Research Articles

Single-Crystal Integrated Photoanodes Based on 4H-SiC Nanohole Arrays for Boosting Photoelectrochemical Water Splitting Activity.

Photoelectrochemical (PEC) splitting of water into H2 and O2 by direct use of sunlight is an ideal strategy for the production of clean and renewable energy, which fundamentally relies on the exploration of advanced photoanodes with high performance. In the present work, we report that single-crystal integrated photoanodes, that is, 4H-SiC nanohole arrays (active materials) and SiC wafer substrate (current collector), are established into a totally single-crystal configuration without interfaces, which was based on a two-step electrochemical etching process. The as-fabricated SiC photoanode showed a rather low onset potential of -0.016 V vs reversible hydrogen electrode (RHE) and a high photocurrent density of 3.20 mA/cm2 vs RHE 1.23 V, which were both superior to those of all reported SiC ones. Furthermore, such a rationally designed photoanode exhibited a fast photoresponse, wide photoresponse wavelength range, and long-term stability, representing its overall excellent PEC performance.

Low cost tips for tip-enhanced Raman spectroscopy fabricated by two-step electrochemical etching of 125 µm diameter gold wires.

Tip-enhanced Raman spectroscopy (TERS) has become a well-applied technique for nanospectroscopy, allowing for single molecule sensitivity with sub-nanometer spatial resolution. The demand for efficient, reproducible and cost-effective probes for TERS is increasing. Here we report on a new electrochemical etching protocol to fabricate TERS tips starting from 125 µm diameter gold wires in a reproducible way. The process is reliable (50% of the tips have radius of curvature <35 nm, 66% <80 nm), fast (less than 2 min) and 2.5 times cheaper than the etching of standard 250 µm diameter wires. The TERS performance of the tips is tested on dyes, pigments and biomolecules and enhancement factors higher than 105 are observed. TERS mapping with a spatial resolution of 5 nm is demonstrated.

Electrochemical etching of lightweight nanotips for high quality‐factor quartz tuning fork force sensor: atomic force microscopy applications

Commercially available quartz tuning forks (QTFs) can be transformed into self-sensing and actuating force sensors by micro-assembling a sharp tip on the apex of a tine. Mass of the tip is critical in determining the quality (Q)-factor of the sensor, therefore, fabrication of the lightweight nanotips is a precondition for high Q-factor QTF sensors. The work reports fabrication of very lightweight tungsten nanotips with a two-step electrochemical etching technique which can be used to develop high Q-factor QTF force sensor. First, a tungsten wire with protective coating at one end (1–2 mm) is etched with a trapezoidal waveform to form a lengthy (∼2–5 mm) and slender (diameter ∼10–40 μm) micro-needle. In the second step, sharp tip apex is fabricated with a direct current etching. High Q-factor (6600–8000) QTF force sensors have been developed with the fabricated nanotips. Atomic force microscope scanning of nano-grating and a triblock copolymer surface validates the scanning performance of the developed sensors.

Wettability control of stainless steel surfaces via evolution of intrinsic grain structures

Wettability control of stainless steel surfaces has wide applicability due to the extensive use of stainless steels in industries that handle liquids. However, previous studies to achieve hydrophobicity on stainless steel surfaces rely on artificial roughness by added particles and residue formation that could compromise mechanical stability of the modified surface. In this study, water-repellent stainless steel surfaces were fabricated via the controlled topographical enhancement of intrinsic grain structures to achieve the required surface roughness. Electrochemical etching was used to control the relative etch rate between grains and grain boundaries by applying an anodic potential to stainless steel 316 (SS316). At low potential (1.2 V vs. Saturated Calomel Electrode), high selectivity between grain and grain boundary etching was observed, which resulted in significant etching at grain boundaries and smooth top grain surfaces. Morphologies with significant microscale roughness, and slight nanoscale roughness, were achieved with intermediate applied potentials (1.3–1.5 V). As the potential increased further (1.8 V), etch selectivity decreased and yielded microscopically smooth surfaces with sponge-like nanoscale roughness; at even higher potentials (2.4 V), electro-polishing was observed with surfaces that are smooth at the nanoscale. Based upon the relationship between anodic potential and topography, we designed a nano/microscale hierarchical SS316 surface by a two-step electrochemical etching combining low and high anodic potentials. The hierarchical SS316 surface resulted in a water contact angle of 137.5 ± 5.0°. Plasma-assisted deposition of a fluorocarbon film further reduced the wettability, with a contact angle of 163.9 ± 1.2° and a roll-off angle of 10.7 ± 1.8° for 4 μL water droplets, thereby rendering the modified SS316 surfaces superhydrophobic. Due to the inherently robust intrinsic grain structure of SS, we expect that this simple approach to generate water-repellent SS316 surfaces will display improved mechanical robustness relative to previous approaches.

Fabrication of high-aspect-ratio platinum probes by two-step electrochemical etching.

In this paper, a two-step AC electrochemical etching process was investigated for the fabrication of platinum probes with controllable aspect ratio from 10 to 30, and tip apex radius less than 300 nm. Experiment results show that the shape of the obtained probes is quite sensitive to the etching time of the first step and the voltage applied in the second step. A graphite crucible was used as the counter electrode during etching. It is proved that the shape of the counter electrode also play a key role for realizing high-aspect-ratio probes. The method presented here provides a simple way in the fabrication of micro-tool for the construction of high-aspect-ratio microstructures, especially for the 3D electrochemical micromachining.

Controlled exfoliation of a heavily n-doped porous silicon double layer electrochemically etched for layer-transfer photovoltaics

We demonstrate the controlled exfoliation of a heavily n-doped mesoporous Si double layer prepared using two-step electrochemical etching, which can be further utilized in Si-epitaxial growth for layer transfer. The first step of electrochemical etching was to apply a lower anodic current density to form self-organized mesoporous silicon with a small pore diameter (≤4.5nm). For the second step, a high anodic current density was applied to create a layer with a higher porosity beneath the first layer, which enables easier detachment from the substrate. Exfoliating the porous double layer was controllable only for heavily n-doped silicon under specific conditions of anodic current density and etching time. The differences in pore morphologies, which depended upon wafer doping levels, were analyzed using two different modes of electrical breakdowns, avalanche and Zener.

A multi-step electrochemical etching process for a three-dimensional micro probe array

We present a simple, fast, and cost-effective process for three-dimensional (3D) micro probe array fabrication using multi-step electrochemical metal foil etching. Compared to the previous electroplating (add-on) process, the present electrochemical (subtractive) process results in well-controlled material properties of the metallic microstructures. In the experimental study, we describe the single-step and multi-step electrochemical aluminum foil etching processes. In the single-step process, the depth etch rate and the bias etch rate of an aluminum foil have been measured as 1.50 ± 0.10 and 0.77 ± 0.03 µm min−1, respectively. On the basis of the single-step process results, we have designed and performed the two-step electrochemical etching process for the 3D micro probe array fabrication. The fabricated 3D micro probe array shows the vertical and lateral fabrication errors of 15.5 ± 5.8% and 3.3 ± 0.9%, respectively, with the surface roughness of 37.4 ± 9.6 nm. The contact force and the contact resistance of the 3D micro probe array have been measured to be 24.30 ± 0.98 mN and 2.27 ± 0.11 Ω, respectively, for an overdrive of 49.12 ± 1.25 µm.

알루미늄 박판의 다단 전해식각 공정을 이용한 3 차원 마이크로 구조물의 제작

본 논문에서는 알루미늄 박판의 다단 전해식각을 공정을 이용한 3 차원 마이크로 구조물 제작방법을 제안한다. 본 공정은 기존 전해가공 공정들에 비해 3 차원 구조물의 대량생산이 용이하며, 기존 3 차원 마이크로 금속 구조물의 제작을 위한 다단 도금방법에 비해 간단하고, 경제적일 뿐만 아니라, 성형된 금속 박판을 이용하므로 구조물의 물성이 안정적이다. 본 논문에서는 단일 전해식각 공정을 통한 2 차원 외팔보 열과 다단 전해식각 공정을 통한 3 차원 마이크로 구조물의 제작을 수행하였다. 단일 전해식각 공정에서 평균 수직방향 식각률 1.50±0.10 ㎛/min 와 평균 수평방향 식각률 0.77±0.03 ㎛/min 을 얻었으며, 이를 이용한 3 차원 마이크로 구조물을 제작한 결과, 수직방향으로 15.5±5.8 %, 수평방향으로 3.3±0.9 % 의 제작오차와 37.4±9.6 ㎚ 의 표면조도를 보였다.

An electrochemical etching procedure for fabricating scanning tunneling microscopy and atom-probe field-ion microscopy tips

A two-step electrochemical etching procedure is developed to control the sharpness and shape of tips used for either scanning tunneling microscopy (STM) or atom-probe field-ion microscopy (APFIM). The formation of a neck near a tip’s apex is controlled by carefully limiting the amount of chemical solution in contact with the area of the neck. Reproducible, atomically sharp, and appropriately tapered tips can be manually produced with this procedure.

Further investigations on CR-39 fast neutron personal dosemeter

A fast neutron personal dosemeter based on CR-39 nuclear track detectors has been developed in as simple a form as possible to be used in routine monitoring. It has been investigated during the last joint irradiation exposures to neutrons organised by EURADOS-CENDOS committee on the application of track detectors in neutron dosimetry. The energy response and the angle dependence of two types of CR-39 material, produced by Pershore Mouldings Ltd (as standard grade material) and American Acrylics (as dosimetry grade material), have been studied using neutron energies ranging from 144 keV up to 66 MeV and the 252Cf neutron spectrum at different angles of incidence, i.e. 0°, 30°, 60° and 85°. Irradiated detectors have been processed using a conventional chemical etching (CE) and a two-step electrochemical etching at low (200 Hz) and high (2 kHz) frequencies (ECE). Under the ECE etching conditions a 80 μSv minimum dose equivalent value is achieved. The response of these detectors to the ambient dose equivalent in the range 0.4–13 mSv has also been studied for monoenergetic neutron beams of 1.2, 5.3 and 15.1 MeV. The dosimetric characteristics of the proposed dosemeter have been much improved by using the ECE conditions. The variations and values of these characteristics approach the required ones in a better way than that given till now in previous works.

Angular response of electrochemically etched CR-39 to protons of 131 to 925 KeV

Solid state nuclear track detectors (SSNTDs) are widely used in fast neutron dosimetry. Latent tracks formed by slowed-down protons resulting from (n,p)-scattering are usually visualized by electrochemical etching (ECE). To estimate the detection efficiency of a SSNTD the proton response and the etching parameters are required. An irradiation device for angular and energy-dependent irradiations using Rutherford backscattering has been constructed. The CR-39 detectors were irradiated with monoenergetic and parallel protons from 131 to 925 keV at 11 different angles of incidence. The critical angle of incidence to protons for a two-step ECE process is presented.

Polycarbonate Track Detectors with a Flat Energy Response for the Measurement of High Energy Neutrons at Accelerators and Airflight Altitudes

For the polycarbonate detector routinely used at FZK, the two-step electrochemical etching was finally optimised after changing the detector thickness from 300 μm to 500 μm and applying a field strength of 42 kV.cm -1 . On the basis of calibrations with monoenergetic neutrons in the neutron energy range from 2 to about 70 MeV the response of Makrofol is now 130 tracks.cm -2 .mSv -1 within ± 30%. The linearity of detector response has been checked. The increase of the track density due to the neutron component of the natural background radiation at ground level has been measured during 1.5 y. Additional calibrations were performed in broad neutron beams at the PSI and CERN. The detector is suitable for monitoring the long-term occupational exposure at high energy particle accelerators and the exposure of the aircrews with a lower limit of detection 0.2 mSv per year. Polycarbonate is the only neutron detector which is insensitive to the high energy proton component of cosmic radiation.

The two-step electrochemical etching technique applied for polycarbonate track etched detectors

The two-step ECE technique was optimized by varying the electrical field strength and applied for Makrofol DE for neutron dosimetry and radon monitoring using an electric field strength of 26.7 kV⋯cm −1 . In comparison with the previously applied combination of chemical and electrochemical etching, the neutron response was increased above a threshold of about 1.5 MeV by a factor of 3 to a value of 52 tracks⋯cm −1 ⋯mSv −1 . The background track density and its standard deviation of (6±2) cm −2 allows to indicate already 0.1 mSv. The alpha energy range was extended from an alpha window of about 1.5 MeV to an alpha energy range from 0.5 to 4 MeV.

Neutron Energy Response and Background of Electrochemically Etched Nuclear Track Detectors: Study of Various CR-39 Materials

The dose equivalent response was investigated for etched track detectors using various CR-39 materials with monoenergic neutrons between 70 keV and 14.8 MeV and a 252 Cf neutron source. A two-step electrochemical etching procedure was employed for all experiments. Results are presented for the energy dependence of the response of the various materials as well as for track background and track diameter distributions

Neutron Dosimetry with CR-39 Track Detectors using Electrochemical Etching: Recent Improvements, Dosimetric Characteristics and Aspects of Routine Application

Recent progress in improving the dosimetric properties of CR-39 etched track detectors is reviewed. With respect to the two-step electrochemical etching (ECE) technique the effects of electrical field strength and various radiator/absorber combinations on the neutron energy response were investigated in the energy range 144 keV to 14 MeV, showing agreement between experimental and theoretical results for the neutron response, if appropriate field strength dependent critical proton angles are used for calculation. Results of international intercomparison experiments show that with respect to energy response the ECE technique has already reached a certain level of optimisation. The energy response, angular dependence, response of CR-39 in contact with (n,a) radiators, dose range and lowest detectable dose are discussed. The results of long-term fading and changes in response and background are presented for commercial CR-39 materials manufactured by American Acrylics and Pershore Mouldings, which were stored over more than one year in air or nitrogen. The high scatter in response and background within the sheet and batch production, and thus the lowest detectable dose and the relatively small dose range, still limit the application of CR-39 in personnel monitoring.

Dosimetric properties of different CR-39 plastics used as neutron recoil track etch detector

Abstract The paper describes the present state of investigations at KfK using CR-39 plastic manufactured by American Acrylics and Pershore. The response of CR-39 to monoenergetic neutrons has been investigated in the range of 0.15 to 14.8 MeV using a two-step electrochemical etching treatment at 50 Hz and 2 kHz. The materials have been found to differ in response up to a factor of 2.5 for energies above 5 MeV. The lower sensitivity of the Pershore plastic is obviously caused by additives in the plastic. Without applying pre-etching the problem of a high unpredictable background still excists.