Electrochemical Etching Research Articles

Potential monitoring during Ge electrochemical etching: Towards tunable double porosity layers

Porous Germanium (PGe) has emerged as a promising material for applications such as substrate engineering, sensing, and energy storage, thanks to its uniquely versatile and tunable properties. The bipolar electrochemical etching (BEE) method is widely regarded as the go-to approach for producing high-quality PGe layers. However, the lack of profound understanding of BEE process limits its use to a few well-studied morphological structures, hindering the development of more complex multi-layered structures with variable morphologies. In this work, we introduce potentiometric measures of the system as a means of monitoring the BEE process. We establish a correlation between the potential response and the reactions occurring during the BEE process, as well as their evolution over time. This approach enables elucidating the importance of the passivation, and how to shape the double-layered PGe structures. These findings bring new opportunities for controllable BEE with process monitoring and fabrication of tunable PGe multilayers for advanced applications.

Photo-driven electrochemical etching to construct porous structures with oxygen vacancies on ZnO photoanodes for efficient solar water splitting

Fast charge separation and oxidation kinetics are the key issues for photoelectrochemical (PEC) water splitting. Herein, photo-driven electrochemical etching (PEE) was applied to modify the morphology and surface properties of ZnO photoanodes to improve PEC performance. By regulating the applied potential and treatment time, the PEE generated a lotus root like porous structure with a pore diameter of 20–30 nm and depth of about 300 nm, and produced a large amount (30.1 %) of oxygen vacancies (Ov) on ZnO photoanode. PEE treated-ZnO array demonstrated a charge separation efficiency of 87 %, and achieved 1.8 times larger photocurrent (1.26 mAcm−2 at 1.23 VRHE) with a cathodic shift of onset potential of 0.12 VRHE than pristine ZnO. The introduced Ov and the shortened charge transport distance of porous microstructures by PEE treatment improved the electrode/electrolyte interface charge transfer and water oxidation kinetics. DFT calculations indicate that the construction of oxygen defects on the catalyst surface can reduce the overpotential of oxygen evolution reaction (OER) and further promote the catalytic activity of OER. Moreover, electrode surface pore structure can be tailored by adjusting illumination parameters and electrolytes. This work illustrates a novel and effective approach to tunable photo-corrodible electrode materials for solar water splitting.

Micro/nano manufacturing aircraft surface with anti-icing and deicing performances: An overview

Abstract The aircraft surface is prone to icing when flying under windward conditions. It is required to protect the aircraft surface from icing for flight safety. The anti-/deicing performance of aircraft surface is affected by the surface morphology and surface wettability. The hydrophobicity of aircraft surface with anti-/deicing performance is closely related to the surface energy. To satisfy the requirements of anti-/deicing surface processing, the micro/nano manufacturing technologies have been developed to fabricate anti-/deicing functional aircraft surfaces. The icing time and deicing efficiency for aircraft surfaces fabricated with micro/nano manufacturing technologies are dozens of times more than those manufactured by conventional anti-/deicing methods. In this study, the recent technologies of micro/nano manufacturing of anti-/deicing functional surfaces are reviewed. First, the extreme conditions during aircraft flight and the huge potential safety hazards of icing are introduced. Then, the principle of aircraft icing and mechanism of both anti-icing and deicing are summarized. Then, the current micro/nano manufacturing technologies for preparing anti-icing and deicing surfaces, including electrochemical, chemical, laser and wire-cut etching chemical, electrochemical, vapor and plasma deposition, and other processing methods are described. By summarizing the advantages and disadvantages of different preparation methods, guidance is provided for new methods of preparing anti-icing and deicing surfaces, in order to avoid disadvantages and promote advantages. Fabrication and characterization of nanocomposite materials and composite coatings/thin films with anti-icing and deicing properties are discussed. Finally, the development trend and application prospect of micro/nano manufacturing in the field of anti-icing and deicing are presented.

Porous silicon microneedle patches for delivery of polymyxin‐based antimicrobials

AbstractThere is a global trend of increasing antibiotic resistance to Gram‐negative bacteria and the medical research community is looking for alternative antibiotics. Antibiotics such as polymyxin B (PMB) show excellent efficacy and low resistance rates against Gram‐negative bacteria. The topical administration of PMB, however, has clinical limitations such as minimal residence time, making it difficult for its use to treat skin infections. Here, we present porous silicon microneedle (pSi MN) patches to deliver PMB to the skin. pSi MN patches are fabricated by, first, generating the projections by dry Si etching techniques, followed by an electrochemical etching to create porous layers around the MNs. After loading PMB into the porous layer, the antibacterial activity of pSi MNs is determined by measuring the inhibition zone of Gram‐negative Escherichia coli. Next, PMB is efficiently delivered into the epidermal layer of ex vivo skin models, as confirmed by chemical mapping using matrix‐assisted laser desorption/ionization mass spectrometry imaging (MALDI‐MSI). The results demonstrate that pSi MN patches are an efficient and versatile tool for the transdermal delivery of PMB with maintained bioactivity and antimicrobial efficacy, thus expanding the possibilities of current transdermal drug delivery systems.

Electrochemical etching strategy for shaping monolithic 3D structures from 4H-SiC wafers

Silicon Carbide (SiC) is an outstanding material, not only for electronic applications, but also for projected functionalities in the realm of spin-based quantum technologies, nano-mechanical resonators and photonics-on-a-chip. For shaping 3D structures out of SiC wafers, predominantly dry-etching techniques are used. SiC is nearly inert with respect to wet etching, occasionally photoelectrochemical etching strategies have been applied. Here, we propose an electrochemical etching strategy that solely relies on defining etchable volumina by implantation of p-dopants. Together with the inertness of the n-doped regions, very sharp etching contrasts can be achieved. We present devices as different as monolithic cantilevers, disk-shaped optical resonators and membranes etched out of a single crystal wafer. The high quality of the resulting surfaces can even be enhanced by thermal treatment, with shape-stable devices up to and even beyond 1550°C. The versatility of our approach paves the way for new functionalities on SiC as high-performance multi-functional wafer platform.

Study of electrochemical etching surface of ultrafine-grained nickel using scanning tunneling microscopy

An approach that allows a qualitative and quantitative analysis of the grain structure of ultrafine grained nickel by electrochemical etching surface is proposed. The data on the etching relief of ultrafine grained nickel obtained by scanning tunneling microscopy have been analyzed. The bimodality of the structure was revealed, which was confirmed by statistical analysis.

In-situ fabricated porous Ni-Co-Mo based nanosheet array electrodes for hybrid supercapacitors with long-cycle stability

The porous NiCoMo-based ternary nanosheet arrays have been synthesized on carbon cloth (CC) substrate by a simple hydrothermal process combined with electrochemical assisted template etching method. CC@ZnO@NiCoMo composite exhibits charge/discharge activation phenomenon and holds a capacitance of 8.84 F cm−2 after 3000 cycles at 8 mA cm−2. The porous electrode structure formed by etching ZnO template not only makes it easier for the electrolyte to permeate and exposes the active point as much as possible, but also reduces the charge transfer impedance from 1.32 to 0.92 Ω. As expected, Asymmetric supercapacitors assembly with CC@ZnO@NiCoMo composite achieves a high energy density of 0.64 mWh cm−2 at 3.2 mW cm−2 and ultra-high cycle stability of 181 % after 10,000 cycles. The excellent electrochemical properties of the electrode material is mainly attributed to the synergistic effect between the multi-components of the nanosheets and the enrichment of Zn2+ formed by template etching in the solution, which helps to maintain the relatively stable morphology of Ni-Co-Mo based nanosheets.

Simulation and fabrication of titanium dioxide thin films for supercapacitor electrode applications

Nanostructured thin-film electrode materials are proposed for supercapacitors due to their outstanding performance over bulk materials. In this work, we fabricated a TiO2 nanotube film over a titanium foil using a top-down approach for supercapacitor electrodes. We noticed that the fabricated nanotubes are uniform and well aligned, confirmed by FESEM; the TiO2 nanotube parameters were further simulated using COMSOL Multiphysics. Simulations show an areal capacitance of 1.19393 pF/cm2 with oxidation and reduction peak currents of 6.18921×10[Formula: see text] A and −6.0320×10[Formula: see text] A, respectively, at 10 mV/s scan rate. The as-prepared nanotubes show a poor areal capacitance of 1.0193 F/cm2, which is improved to 12.8764 F/cm2 at a scan rate of 10 mV/s, that is approximately 12.63 times with oxidation and reduction peak currents of 0.129 mA/cm2 and −0.105 mA/cm2, respectively, by performing an electrochemical etching. Further, the surface roughness of both as-prepared and etched samples is studied to comment on their surface area changes. The effect of the etched sample is studied, compared and validated with simulation, which reveals that the etched TiO2 nanotubes thin-film sample shows considerable similarity with the simulation results.

Surface reconstruction of copper foil via electrochemical etching to proliferate CH4 production from CO2 electroreduction

Electrocatalytic CO2 reduction (eCO2R) to CH4 is a prospective approach for producing high value-added fuels. In this work, an effective approach was proposed by surface reconstruction using copper foil to facilitate eCO2R to CH4. The copper foil surface reconstruction was achieved via electrochemical etching in dilute phosphoric acid. Comprehensive characterizations suggested that the crystallinity and chemical binding energy states of the copper foil were well preserved after surface reconstruction, but the arrangement of copper atoms on the surface was adjusted. Etching time for 80 s was the most preferable condition, obtaining a uniform valley pattern structure with abundant grain boundaries, reporting the highest CH4 Faraday efficiency of 68.84% which was an order of magnitude higher compared to green foil counterpart. The relevant partial current density, CH4 production rate, and half-cell power conversion energy were measured to be −16.32 mA cm−2, 0.174 μmol s−1 cm−2, and 28.8% respectively from eCO2R at −1.3 V (vs. RHE). The in-situ ATR-IR spectroscopy confirmed that the surface reconstructed copper foil can significantly strengthen the adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH4 instead of dimerization to give C2 products. This work expanded the method of surface modification for copper foil via electrochemical etching and realized the regulation of geometric morphology on catalyst surface to obtain the desired performance for CO2 electroreduction reaction.

Porous pseudo-substrates for InGaN quantum well growth: Morphology, structure, and strain relaxation

Strain-related piezoelectric polarization is detrimental to the radiative recombination efficiency for InGaN-based long wavelength micro-LEDs. In this paper, partial strain relaxation of InGaN multiple quantum wells (MQWs) on the wafer scale has been demonstrated by adopting a partially relaxed InGaN superlattice (SL) as the pseudo-substrate. Such a pseudo-substrate was obtained through an electro-chemical etching method, in which a sub-surface InGaN/InGaN superlattice was etched via threading dislocations acting as etching channels. The degree of strain relaxation in MQWs was studied by x-ray reciprocal space mapping, which shows an increase of the in-plane lattice constant with the increase of etching voltage used in fabricating the pseudo-substrate. The reduced strain in the InGaN SL pseudo-substrate was demonstrated to be transferable to InGaN MQWs grown on top of it, and the engineering of the degree of strain relaxation via porosification was achieved. The highest relaxation degree of 44.7% was achieved in the sample with the porous InGaN SL template etched under the highest etching voltage. Morphological and structural properties of partially relaxed InGaN MQWs samples were investigated with the combination of atomic force and transmission electron microscopy. The increased porosity of the InGaN SL template and the newly formed small V-pits during QW growth are suggested as possible origins for the increased strain relaxation of InGaN MQWs.

Achieving porous germanium from both p- and n-type epitaxial Ge-on-Si via bipolar potentiostatic etching

Due to the large surface specific area, tunable porosity and refractive index, porous germanium (Ge) has wide applications in optoelectronics, photovoltaics, anode materials in batteries. Electrochemical etching is the most used approach to fabricate porous Ge. However, previous work focused on bulk Ge wafer etching, which is not suitable for device integration on a Si substrate, and illumination had to be used for n-type porous Ge formation. In this paper, we show that by using bipolar potentiostatic etching, porous Ge with the thickness of more than 100 nm and the pore diameter in the range of 10 to 100 nm, can be obtained from both p- and n-type Ge-on-Si layers without illumination. The pore formation mechanism is interpreted by hydrogen evolution effect and Space Charge Region (SCR) model where pore nucleation, growth and dissolution are determined by the total etching time. Our work paves the way for porous Ge applications in Si based integrated photonics and microelectronics.

Controlled and Fast Fabrication for P-Type Porous Silicon Structures with a High Aspect Ratio by Electrochemical Etching

Controlled and Fast Fabrication for P-Type Porous Silicon Structures with a High Aspect Ratio by Electrochemical Etching

Thermal strain relaxation of GaAs overgrown on nanovoid based Ge/Si substrate

The integration of high quality III-V materials-based devices on the Si platform is considered as an enabling path towards achieving the long-standing goal of creating low-cost/high-performance devices. However, the heteroepitaxy of III-V compounds on a Si substrate generates high stress due to the difference in thermal expansion coefficient leading notably to crack generation. Here, we report on the reduction of the thermal strain of GaAs and Ge deposited on a Si substrate. The method is based on the formation of buried high density nanovoids by electrochemical etching of Ge/Si virtual substrate followed by direct epitaxial growth of Ge and GaAs. The thermal strain has been investigated for GaAs epilayer by High-Resolution X-Ray Diffraction and Raman spectroscopy showing a 30% decrease in strain. The strain reduction relies on the nanovoids-mediated thermal strain accommodation. Furthermore, photoluminescence measurements showed a 10-fold increase of the intensity, resulting in an improved optical and crystalline quality, making this virtual substrate promising for III-V based devices on Silicon.

Effect of surface engineering methods on refrigerant evaporating flow characteristics in annular tubes: Experimental approach

Techniques such as mechanical, electrochemical, and chemical etching are recognized as functional strategies for modifying surface roughness, which in turn manipulates surface energy. This research aims to delve into the influence of these factors on the heat transfer and pressure drop characteristics of two-phase R134a refrigerant flow during boiling inside horizontal annular concentric tubes with internal heat flux. The study scrutinizes the heat transfer coefficient and frictional pressure drop for R134a evaporating flow in an annular tube featuring an inner diameter of 28.6 mm and an outer diameter of 42 mm. The exploration spans a broad range of parameters, which include vapor quality from 0.15 to 0.8, mass flux from 6.72 to 20.16 kg/m2s, internal heat flux from 0.608 to 2.432 kW/m2, and varying surface characteristics. The results show that escalating surface roughness via mechanical techniques introduces greater resistance to flow shear stress in comparison to other methods. Moreover, an increase in surface roughness contributes to a reduction in contact angle and an expansion of the heating area, thereby enhancing both heat transfer coefficient and pressure drop. However, the implementation of low-energy coating holds an insignificant influence on R134a heat transfer characteristics, potentially due to its diminutive surface tension. This results in minor variations in the refrigerant contact angle in relation to the coatings. Performance evaluation criteria have been employed to assess the optimal thermal performance of the surface engineering method, with peak performance achieved at a mass flux of 20.16 Kg/m2s and an internal heat flux of 2.432 kW/m2. Ultimately, the study corroborates the experimental procedure by comparing the observed outcomes with established empirical correlations for R134a flow boiling.

Surface reconstruction enabled o-PdTe@Pd core-shell electrocatalyst for efficient oxygen reduction reaction

Palladium-based alloy catalysts have been employed as one of the potential candidates for oxygen reduction reaction (ORR), but the dissolution of transition metal hinders their application. Herein, structure ordered PdTe intermetallic with Pd shell (o-PdTe@Pd) are synthesized via an electrochemical etching driven surface reconstruction strategy. The surface reconstruction could tune the electronic structure, weaken the adsorption energy of reaction intermediates on o-PdTe@Pd, resulting in enhanced electrocatalytic activity for ORR. The mass activity of o-PdTe@Pd is about 3.3 and 2.7 times higher than that of Pd/C in acid and alkaline, respectively. Besides, the half-potentials for ORR decay only about 44 mV and 12 mV after 30 k cycles accelerated durability test in acid and alkaline media, respectively. The enhanced durability originates from the resistance of Te atoms dissolve in the ordered PdTe intermetallic core and the core-shell structure. When assembled in a Zn-air battery, o-PdTe@Pd electrode delivers a higher specific capacity (794 mAh/g) and better cycling stability than Pt/C.

Facile electrochemical surface-alloying and etching of Au wires to enable high-performance substrates for surface enhanced Raman scattering

Surface-enhanced Raman Spectroscopy (SERS) is a nondestructive technique for rapid detection of analytes even at the single-molecule level. However, highly sensitive and reliable SERS substrates are mostly fabricated with complex nanofabrication techniques, greatly restricting their practical applications. A convenient electrochemical method for transforming the surface of commercial gold wires/foils into silver-alloyed nanostructures is demonstrated in this report. Au substrates are treated with repetitive anodic and cathodic bias in an electrolyte of thiourea, in a one-pot one-step manner. X-rays absorption fine structure (XAFS) spectroscopy confirms that the AuAg alloy is induced at the surface. The unique AuAg alloyed surface nanostructures are particularly advantageous when served as SERS substrates, enabling a remarkably sensitive detection of Rhodamine B (a detection limit of 10−14 ​M, and uniform strong response throughout the substrates at 10−12 ​M).

Impact of electroplating salt (AgNO3) concentration on the morphological, optical, electrical and thermoelectric properties of silver assisted electrochemically etched silicon nanowires (SINWs)

Silicon nanowires (SINWs) are fabricated through silver assisted electrochemical etching route at room temperature. Very high yield vertically aligned SINWs are obtained through this electrochemical etching route. The effect of electroplating salt concentration on the properties of SINWs is investigated. Surface morphology shows grass like structures with increase of length and decrease of diameter with increasing salt concentration. Atomic force microscopy reveals increased surface roughness. UV–Visible spectra show reduced reflectivity enabling the material to be efficient for antireflection coatings. Photoluminescence spectra exhibit multiband transitions. Raman spectra show asymmetric peak broadening with peak downshift. Electrical properties display enhancement of SINWs current with higher AgNO3 concentration due to increased surface mediated effects. Current - voltage characteristics follow thermionic emission model. Samples exhibit space charge limited conduction at higher bias voltages due to presence of traps or crystal imperfections. Prepared samples are also investigated for thermoelectric properties and the results show enhanced Seebeck coefficient with increasing AgNO3 concentration.

Optimization of process parameters for preparing the hydrophobic surface of aluminum alloy by laser-assisted electrochemical composite etching based on response surface method

To explore the influence of electrolyte concentration, single pulse energy, current density and scan times on the hydrophobic properties of laser-assisted electrochemical composite etching 2024 aluminum alloy surface, the experimental platform of laser-assisted electrochemical composite etching is built. Based on the results of the single-factor experiments, the response surface method (RSM) is chosen to optimize the process parameters. The optimum combination of process parameters is obtained, and the accuracy of the regression equation is verified by experiments. Through residual analysis, the established regression model fits well. By analysis of variance (ANOVA), the sequence of influence of the factors on apparent contact angle (from large to small) is single pulse energy, scan times, electrolyte concentration, and current density. With the maximum apparent contact angle as the goal, the combination of process parameters adjusted after optimization is: electrolyte concentration 2.0 mol/L, single pulse energy 20µJ, current density 18 mA, and scan times 15. Under these conditions, the experimental values of apparent contact angle is 157°, which is close to the predicted value (158°) by the models. The relative errors is 0.6%. It indicates that the regression model is accurate and reliable. This study shows that RSM is an effective method to optimize the process parameters and obtain the ideal experimental results.

Role of etching parameters on the performance of porous silicon based photodetector devices

This work demonstrates the high speed porous silicon (P–Si) based photodetector with varying the etching parameters. The P–Si samples were fabricated using electrochemical etching. The microstructural characterization was performed using SEM, contact angle, FTIR and Raman spectroscopy. Further, these nanostructured samples were tested as photodetectors in the visible wavelength spectrum. The optimized sample based photodetector shows a higher photo to dark current ratio (PDCR) of 1.27 × 103 and less dark current as compared to the other tested photodetectors. Moreover, it also offers a higher detectivity of 5.97✕1011 Jones and rise/fall time of 0.017/0.010 s. The developed nanostructures and photodetectors are shown to have excellent process scalability and repeatability. These results demonstrate the potential applications of P–Si photodetectors for optoelectronic devices.

Development and Isolation of Dot LEDs for Display Applications through Electrochemical Etching and Sonochemical Separation

AbstractThis paper presents a top‐down fabrication and an isolation process for producing billions of multifunctional dot light‐emitting diodes (LEDs) without a sacrificial layer. The process involves a combination of electrochemical etching (ECE) of an n‐GaN layer and sonochemical separation of an etched porous layer to isolate the dot LEDs. The structure of the developed dot LEDs can be expressed as Au/indium tin oxide (ITO)/p‐GaN/multiple quantum well (MQW)‐InGaN/n‐GaN@SiO2. The nanopore size, separation ratio, and emission characteristics of dot LEDs produced by ECE are investigated, as well as the solvent type on ultrasonic separation in the sonochemical process. Blue electroluminance devices fabricated in a vertical structure using dot LEDs exhibit a peak external quantum efficiency (EQE) of 6.21% at an applied voltage of 4.0 V, and a luminous efficacy of 1070 cd m−2, at an applied voltage of 10.0 V. Although the current technology for blue dot LEDs may not produce a higher EQE than the existing display technologies, it is essential to consider that the development of dot LED displays is still in its early stages. Furthermore, the findings show that the dot LEDs have the potential to significantly reduce material costs and provide new opportunities for nanoscale GaN‐based LED displays.