Photochemical Etching Research Articles

A Novel Approach for Thin 4H-SiC Foil Realization Using Controlled Spalling from a 4H-SiC Wafer

Porosifying the surface of a single crystalline silicon carbide (4H-SiC) wafer with the means of metal assisted photo chemical etching (MAPCE) promotes the adhesion of an electroplated nickel (Ni) layer. By utilizing a mechanical peel-off process, a Ni layer with tailored mechanical stress is peeled off such that also a thin layer of 4H-SiC is teared apart from the wafer as well.

Photochemical wet etching of (0 0 1) plane ß-phase Ga2O3, and its anisotropic etching behavior

The photochemical (PC) wet etching behavior of (001) plane β-phase Ga2O3(β-Ga2O3)single crystal was investigated using potassium hydroxide etchant solution under ultraviolet illumination in the temperature range of 80–95 °C. The etch rate was 1.65 nm/min at 80 °C, and increased up to 4.88 nm/min at 95 °C. The etch rate of the (001) plane β-Ga2O3shows strong temperature dependence with the activation energy of 0.798 eV. The PC wet etching characteristics of the (001) plane β-Ga2O3was compared with those of (2¯01) and (010) plane β-Ga2O3. The etch rates increased in order of the (010), (2¯01), and (001) plane, which is accordance with the increasing surface energy trend. The oval line-shaped grooves aligned along [010] direction were observed on the etched (001) plane β-Ga2O3 crystal surface after 30 min. PC wet etching at 80 °C.

Plasma electrolytic oxidation of AZ31 magnesium stents for degradation rate control

Cardiovascular disease caused by the accumulation of atheroma plaques in the coronary arteries and the subsequent decrease in the blood flow through the affected vessel, known as atherosclerosis, is responsible for a high percentage of deaths worldwide. Angioplasty is practiced to treat atherosclerosis which involves inserting a stent inside the occluded vessel to expand it and restore normal blood flow. In this work, temporary biodegradable stents made of AZ31 magnesium alloy have been fabricated using photo-chemical etching. The stents were coated via plasma electrolytic oxidation (PEO) technique. The radial strength of the stents was evaluated by cyclic compression, and the corrosion protection provided by the PEO coatings was studied by electrochemical and in vitro corrosion tests respectively. The stents showed an optimal maximum radial force of 0.147 N/mm and revealed elastic recuperation lower than 7 % of the total deformation after expansion. The applied PEO coating helped to control the corrosion of the magnesium alloy, delaying its initiation and, once it has started, decreased the degradation rate compared with the bare AZ31 samples. Thus, the stents treated with the PEO coatings developed in this research present promising results for their use as temporary medical devices used in angioplasty.

Study the Effect of Hydrofluoric (HF) Concentration on the Topography of the Porous Silicon Layer Prepared by Sunlight Photochemical Etching (SLPCE)

Silicon nanocrystals have a vast range of potential applications, from improving the efficiency of solar cells and optoelectronic devices to biomedical imaging and drug delivery, wastewater treatment, and antibacterial activities. In this study a photochemical etching technique was used to create layers of porous silicon on a donor silicon wafer with orientation (111) and resistivity equal to 1‑10 ohm·cm. The process involved focusing sunlight onto the samples using a telephoto lens with a suitable focal length of 30cm and a diameter of 90 mm, which provided sufficient energy to complete the chemical etching. By using a constant etching time of 60 minutes and different concentrations of hydrofluoric acid (ranging from 25% to 40%), layers with varying properties were obtained. The resulting surfaces were studied using the atomic force microscope (AFM), revealing the formation of different nanostructures and particles with varying shapes, sizes, and thicknesses depending on the preparation conditions. The average size of the particles was found to be 90.43nm at a concentration of 40% acid, while decreasing to 48.7nm at a concentration of 25% HF acid.

Nucleation of Threading Dislocations in 4H-SiC at Early Physical-Vapor-Transport Growth Stage

In this work, we identify the nucleation mechanism of threading dislocations (TDs) associated with stacking faults (SFs) and 15R-SiC at the early growth stage of 4H-SiC single crystals grown by the physical vapor transport (PVT) technology. By combining molten KOH etching and photochemical etching, we successfully reveal etch pits of TDs and linear etch patterns of SFs on the (112̅0) surface of 4H-SiC single crystals. Systematic investigations based on transmission electron microscopy (TEM) observations and Raman analysis indicate that the Si–C bilayer stacking sequence of SFs is (3, 2) in Zhdanov’s notation. The accumulation of SFs (3, 2) gives rise to the polymorph fluctuation and thus the formation of 15R-SiC at the early PVT growth stage of 4H-SiC single crystals. Quantitative stress analyses indicate that the strain field distributions along the SFs (3, 2) and the 15R-/4H-SiC interfaces are inhomogeneous, which give rise to the nucleation of TDs and low-angle grain boundaries (LAGBs), respectively. The nucleation of LAGBs releases the high stress at the 15R-/4H-SiC interface, which facilities the following 4H-SiC single-crystal growth. Our work indicates that the avoidance of polymorph fluctuation is important to the reduction of TDs at the early growth stage of PVT-grown 4H-SiC single crystals.

Silicon carbide nano-via arrays fabricated by double-sided metal-assisted photochemical etching

Silicon carbide (SiC) has gradually dominated the market of power semiconductor electronic devices because of its excellent electrical properties and chemical stability. However, fabricating micro/nano structures in SiC that are crucial for device functioning has been challenging. In this paper, a novel double-sided metal-assisted photochemical etching (double-sided MAPCE) was proposed to efficiently fabricate SiC nano-via arrays. The experimental results demonstrated that the vertical etching rate of double-sided MAPCE was ∼ 2.2 times higher than that of traditional MAPCE. The etching rate of SiC was found to be closely related to the type of noble metal, the concentration of oxidant (H2O2) and the UV light power density. The mechanism of double-sided MAPCE was disclosed as that the bottom noble metal layer catalyzed the reduction of H2O2, therefore, a built-in electric field was created which separated the photogenerated electron-hole pairs, thus, more photogenerated holes participated in oxidation of SiC resulting in improved SiC etching rate. The proposed method is possible to be used to process wide bandgap semiconductors.

Preparation of porous silicon Wafers using sun light photo chemical etching (SLPCE)

porous Silicon (PS) Layers were prepared by photochemical etching using Sun Light as a Source of energy for the first time instead of industrial Sources of light Such as Lasers, Halogen and tungsten lamps. That was used to preparation (PS) by photochemical etching. Silicon Wafers n-type (100), resistivity (10Ω.cm), (40%) HF Acid, with different illumination intensities(power density) (1758, 3956, 6182 and 8902)mw /cm2 were obtained using different Lenses with different diameters (40, 60, 75 and 90) mm, focal length (13,18,41,45) cm respectively and constant etching time (60min). The morphology of the surface was studied by using an (atomic force microscope) (AFM) and (scanning electron microscope) (SEM) results shows formation of groups of pores and crystals in (nm)size with different diminution are distributed in etched area in wavy forms. The thickness of porous layers ranged from (50.06 3.68, 3.79 and 3.39) nm and the diameter of the particles are(84.06, 59.42, 51.12 and 34.8)nm respectively. The current voltage characteristics for ALthin/n-si/PS/ALthin device fabricated by sun light photochemical etching technique showed a rectifying behavior which improved with increasing light intensity.

Effect of wafer resistivity and light intensity on the topography of porous silicon surfaces produced by photo chemical method

This study includes the effect of wafer resistivity and intensity of light on topography of porous silicon surfaces which produced by photo chemical etching method, the results showed that changing of the resistivity led to change the porosity, where it found the porous silicon layer be less of high value resistivity. 
 Once all the wafers have same resistivity's value that’s found the light intensity effect on porosity, the less value of porosity produced by the less value of intensity light focused.
 The production of Nano crystalline silicon structures and control of their production conditions is the first step to control the properties of the devices (detectors, diodes, solar cells, sensors) and their appropriate applications. Ultimately, this is important in promoting research and development of renewable energy.

Photochemically Etching BiVO4 to Construct Asymmetric Heterojunction of BiVO4 /BiOx Showing Efficient Photoelectrochemical Water Splitting.

BiVO4 as a promising semiconductor candidate of the photoanode for solar driven water oxidation always suffers from poor charge carrier transport property and photo-induced self-corrosion. Herein, by intentionally taking advantage of the photo-induced self-corrosion process, a controllable photochemical etching method is developed to rationally construct a photoanode of BiVO4 /BiOx asymmetric heterojunction from faceted BiVO4 crystal arrays. Compared with the BiVO4 photoanode, the resulting BiVO4 /BiOx photoanode gains over three times enhancement in short-circuit photocurrent density (≈3.2mAcm-2 ) and ≈75mV negative shift of photocurrent onset potential. This is due to the formation of the strong interacted homologous heterojunction, which promotes photo-carrier separation and enlarges photovoltage across the interface. Remarkably, the photocurrent density can remain at ≈2.0mAcm-2 even after 12h consecutive operation, while only ≈0.1mAcm-2 is left for the control photoanode of BiVO4 . Moreover, the Faraday efficiency for water splitting is determined to be nearly 100% for the BiVO4 /BiOx photoanode. The controllable photochemical etching process may shed light on the construction of homologous heterojunction on other photoelectrode materials that have similar properties to BiVO4 .

Identification of subsurface damage of 4H-SiC wafers by combining photo-chemical etching and molten-alkali etching

In this work, we propose to reveal the subsurface damage (SSD) of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching. Under UV illumination, SSD acts as a photoluminescence-black defect. The selective photo-chemical etching reveals SSD as the ridge-like defect. It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion. The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines, which are typical features of scratches. This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers. SSD is incorporated into 4H-SiC wafers during the lapping, rather than the chemical mechanical polishing (CMP).

One‐Step Soft Templated Selective Milling‐Based Circuit Patterning for Eco‐Friendly and High‐Throughput Manufacturing of Flexible Electronics

AbstractOver the past decades, the booming development of flexible electronics in various fields, e.g., Internet of Things and epidermal electronics, requires the support of a reliable manufacturing approach, where circuit patterning is the core. Although the existing circuit patterning methods represented by photochemical etching and direct printing process have shown good performance, they still cannot satisfy today's demands on environmental friendliness and cost‐efficiency concurrently. Here, by regulating the milling force distribution on the flexible workpiece with a grooved soft template, this work presents a milling‐based patterning technique that is compatible with roll‐to‐roll technology, to achieve continuous selective removal of conductive material in one step and hence directly pattern electrical circuits on aluminum clad laminates. Without introducing any chemicals, this new approach generates no emission but recyclable aluminum scraps. Moreover, the process shows a considerable processing speed of 30 m min−1, and costs only commercial aluminum clad laminates. Examples of device fabrication include a radio frequency identification tag and a temperature sensor. Ultimately, this work can bring an eco‐friendly, economic and high‐throughput approach to flexible electronics manufacturing.

QUBIC VII: The feedhorn-switch system of the technological demonstrator

We present the design, manufacturing and performance of the horn-switch system developed for the technological demonstrator of QUBIC (the Q&U Bolometric Interferometer for Cosmology). This system consists of 64 back-to-back dual-band (150 GHz and 220 GHz) corrugated feed-horns interposed with mechanical switches used to select desired baselines during the instrument self-calibration. We manufactured the horns in aluminum platelets milled by photo-chemical etching and mechanically tightened with screws. The switches are based on steel blades that open and close the waveguide between the back-to-back horns and are operated by miniaturized electromagnets. The measured electromagnetic performance of the feedhorns agrees with simulations. In particular we obtained a return loss around –20 dB up to 230 GHz and beam patterns in agreement with single-mode simulations down to –30 dB. The switches for this prototype were designed and built for the 150 GHz band. In this frequency range we find return and insertion losses consistent with expectations (< –25 dB and ∼ –0.1 dB, respectively) and an isolation larger than 70 dB. In this paper we also show the current development status of the feedhorn-switch system for the QUBIC full instrument, based on an array of 400 horn-switch assemblies.

Relationship Between the Rate of Photochemical Metal-Assisted Etching of GaN Layers and Multifractal Parameters of Their Surface Structure

The results of a study of liquid photochemical metal-assisted etching of a series of samples of n-type Ga-polar GaN layers grown by molecular-beam epitaxy with nitrogen plasma activation are presented. Under the chosen conditions of the etching process, it is shown that the etching rate depends mainly on the structural properties of the GaN layers, which manifest themselves in the surface morphology, which can be quantitatively characterized by the multifractal parameters Δq (the degree of ordering and symmetry breaking of the structure under study) and Dq (the Rényi dimension, which depends on the thermodynamic formation conditions). A correlation between the values of the multifractal parameters Δq and Dq of the surface structure and the etching rate of Ga-polar GaN layers is established.

Silicon Carbide Nano-Via Arrays Fabricated by Double-Sided Metal-Assisted Photochemical Etching

Silicon Carbide Nano-Via Arrays Fabricated by Double-Sided Metal-Assisted Photochemical Etching

3D arrangement of epitaxial graphene conformally grown on porousified crystalline SiC

Nanoporous materials represent a versatile solution for a number of applications ranging from sensing, energy applications, catalysis, drug delivery, and many others. The synergy between the outstanding properties of graphene with a three-dimensional porous structure, circumventing the limits of its 2D nature, constitutes therefore a breakthrough for many fields. We report the first three-dimensional growth of epitaxial graphene on a porousified crystalline 4H–SiC(0001). The wafer porosification is performed via a sequence of metal-assisted photochemical and photoelectrochemical etching in hydrofluoric acid based electrolytes. Pore dimensions of the matrix have been evaluated by electron tomography resulting in an average diameter of 180 nm. Graphene growth is performed in an ultra high vacuum environment at a base pressure of 10−11 mbar. The graphene growth inside the pores is uniform as confirmed by Transmission Electron Microscopy (TEM) analysis. Raman spectroscopy confirms the high quality of the graphene with a 2D/G intensity ratio >1 and an average graphene crystal size of ≈ 100 nm. Furthermore, it demonstrates a uniform coverage of graphene across the whole sample area accessible to the Raman probe. The surface-to-volume ratio of this novel material, its properties, the tunability of the pore size and the scalability of the surface porosification process offer a game changing perspective for a large number of applications.

Study of Electrical Properties of Silver Nanoparticles on Porous Silicon

In this paper, porous silicon has been prepared and studied by photochemical etching method using a n-type silicon wafer with electrical resistivity (0.01-0.02 Ω.cm), orientation (100), hydrofluoric acid of 20% HF, current density of 15 mA / cm2 and etching time at (5 min). Silver nanoparticles (AgNPs) have been deposited using laser ablation by drop casting with different laser energy of 400,600 and 800m J. The electrical properties (I-V measurements) of silver nanoparticles on porous silicon have studied in both light and dark conditions. It can be seen the samples behave a rectifier and the current density increases with increase laser energy due to increase in concentration of silver nanoparticles, which lead to a decrease in the values of resistivity as the laser energy increases, this is attributed to the pores are filled with silver nanoparticles and lead to interference between silver and the porous silicon layer. The silver nanoparticles play an important role in forming a homogeneous layer and enhancing the crystal stability of the porous silicon layer.

Efficient Investigation of High‐Performance Perovskite Solar Cells Based on Shadow‐Mask Kits with Uniform Patterning and Antishadowing Capabilities

AbstractIn recent years, there has been increased research and rapid development in perovskite solar cells. Uniformity, repeatability, and reliability of electrode patterns formed by shadow‐mask technologies are factors that play an important role in efficient experimental studies for achieving high‐throughput samples and high‐performance devices. In this study, some new principles of mask design are investigated to overcome the drawbacks of conventional mask. High precision patterns are obtained by fabricating shadow‐masks with stainless steel plates via a photochemical etching process. An assembly concept design is proposed for shadow‐mask kits to improve versatility and avoid edge chamfer. The highly accurate active area and precise replication of the aperture patterns are obtained by improving the alignment between the samples and the mask patterns. The perovskite solar cell arrays are fabricated on a single substrate and a uniform performance is achieved due to the balanced distribution of electrodes. Thin shadow‐masks with smooth surfaces are employed to diminish the shadowing effect and a power conversion efficiency of 20.85% with a high fill factor of 81.6% is obtained in an inverted perovskite solar cell. The versatility and high quality of our shadow‐mask kits can further promote research in the area of thin‐film and photovoltaic technologies.

A Field Guide to Azopolymeric Optical Fourier Surfaces and Augmented Reality

AbstractOptical Fourier surfaces (OFSs) are used for various applications, from diffractive optics to augmented reality (AR). However, the current methods of fabricating OFSs primarily rely on lithographic photochemical reactions and etching. These methods are likely to fabricate digitalized binary reliefs, which cannot match the ideal surface profile of OFSs. Such a profile is the sum of sinusoidal surfaces with various spatial frequencies. As an exception, scanning probe lithography (SPL) is found to be compatible with OFSs. However, the accessible pattern area of the OFSs created via SPL is relatively small owing to the serial feature of the fabrication, which in turn results in an undesired and complicated Fourier spectrum. In this article, the holographic inscription is redesigned for the low‐cost, large‐area, and rapid prototyping of customized OFSs. To this end, an integrative pipeline is established across numerical design, material optimization, and the pragmatic considerations of optical processing. Then, a soft molding strategy is suggested for optically transparent and flexible OFSs and its use for easy‐to‐craft AR devices. Overall, this intuitive framework not only expands the scope of Fourier optics but also acts as a field guide to azopolymeric OFSs and AR technology for experts and newcomers alike.

Ideality factor of Al/nanosilver/PS/Si/Al sandwich structure

In this work, n-type (p-Si) porous Si nanostructures were fabricated by photochemical etching of n-type (p-Si) chips. The etching time of 20 min and the density of current of 20 mA / cm2 were examined to discuss their impact on nanopore array formation. Crystal size was assessed by XRD. AFM confirmed the non-metric size of porous Si showing a rough Si surface increased with etching time and increased the depth and width (diameter) of the surface etching. Colloidal silver nanoparticles were also prepared by laser ablation in liquid (LAL) with Nd: YAG laser pulses and an Ag target submerged in ethanol using laser fluorescence (1.32 J / cm2). The effect of laser flux on the physical properties obtained from this study of Ag nanoparticles has been studied. The energy band gap prepared for the Ag nanoparticles was determined from the optical properties and found between (1.85 eV). Optical constants of deposit film were obtained using transmittance and absorbance spectra. Electrical properties of prepared Al/Ag/PS/p-Si/Al sandwich Solar cells are represented by I-V characteristics under dark conditions.

The Effects of Psi Morphology on the Detection Efficiency of the Au-Nps Hot Spot SERS Sensors

This work is related to the investigation of the effects of porous silicon (PSi) morphologies on the performance of plasmonic gold nanoparticles (Au-NPs) hot spot SERS sensors for the detection of amoxicillin molecules. Two Si wafers with different resistivity values of 10 and 100 Ω.cm were used to synthesize a PSi layer of pores- and mud-like structures, respectively, by pulsed photo chemical etching process. The hot spot SERS sensors were synthesized by incorporating the Au-NPs within the PSi morphologies of pores- and mud- like structures which are characterized by high density of nucleation sites. Plasmonic Au- NPs with different sizes and hot spot regions were incorporated into the porous structures by the ion reduction process. It was recognized that the PSi morphologies have a considerable influence on the fabrication process of the detection sensors and, consequently, on the detection process. The plasmonic Au-NPs hot spot SERS sensor based on the PSi morphology of the mud-like structures shows higher sensitivity than that of pores-like structures, even at very low concentrations of amoxicillin solutions.