Recent advances in preparation of metallic superhydrophobic surface by chemical etching and its applications

In the past few decades,inspired by the superhydrophobic surfaces(SHPS)of animals and plants such as lotus leaves,rose petals,legs of water striders,and wings of butterflies,preparing metal materials with metallic SHPS(MSHPS)have attracted great research interest,due to the great prospect in practical applications.To obtain SHPS on conventional metal materials,it is necessary to construct rough surface,followed by modification with low surface energy substances.In this paper,the action mechanism and the current research status of MSHPS were reviewed through the following aspects.Firstly,the model of wetting theory was presented,and then the progress in MSHPS preparation through chemical etching method was discussed.Secondly,the applications of MSHPS in self-cleaning,anti-icing,corrosion resistance,drag reduction,oil-water separation,and other aspects were introduced.Finally,the challenges encountered in the present application of MSHPS were summarized,and the future research interests were discussed.

Fabrication of Through Micro-hole Arrays in Silicon Using Femtosecond Laser Irradiation and Selective Chemical Etching

We demonstrate a method of fabricating through micro-holes and micro-hole arrays in silicon using femtosecond laser irradiation and selective chemical etching. The micro-hole formation mechanism is identified as the chemical reaction of the femtosecond laser-induced structure change zone and hydrofluoric acid solution. The morphologies of the through micro-holes and micro-hole arrays are characterized by using scanning electronic microscopy, The effects of the pulse number on the depth and diameter of the holes are investigated. Honeycomb arrays of through micro-holes fabricated at different laser powers and pulse numbers are demonstrated.

Achieving a sub-10 nm nanopore array in silicon by metal-assisted chemical etching and machine learning

Solid-state nanopores with controllable pore size and morphology have huge application potential.However,it has been very challenging to process sub-10 nm silicon nanopore arrays with high efficiency and high quality at low cost.In this study,a method combining metal-assisted chemical etching and machine learning is proposed to fabricate sub-10 nm nanopore arrays on silicon wafers with various dopant types and concentrations.Through a SVM algorithm,the relationship between the nanopore structures and the fabrication conditions,including the etching solution,etching time,dopant type,and concentration,was modeled and experimentally verified.Based on this,a processing parameter window for generating regular nanopore arrays on silicon wafers with variable doping types and concentrations was obtained.The proposed machine-learning-assisted etching method will provide a feasible and economical way to process high-quality silicon nanopores,nanostructures,and devices.

GaN hexagonal pyramids formed by a photo-assisted chemical etching method

A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a con-venient photo-assisted chemical （PAC） etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed anal- ysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.

Six million Q factor micro fused silica shell resonator with teeth-like tines released by femtosecond laser-assisted chemical etching

The quality factor(Q factor)is a crucial performance parameter for resonators.In this paper,a novel release method for highquality micro fused silica shell resonators with teeth-like tines with good surface morphology is proposed.This method is based on femtosecond laser-assisted chemical etching.First,the optimal energy range of femtosecond laser modification is obtained through mechanism analysis.Second,the optimal parameters for a straight line and arc pattern are determined by optimizing the average output power,processing speed,and processing spacing.The results demonstrate why edge breakage in rounded corners is easy under different parameters.Finally,according to these conclusions,the processing is performed on a micro fused silica shell resonator with a Q factor exceeding 6 million.In addition,subsurface damage is rare throughout the fabrication process,and the surface roughness of the released cross section reaches the nanometer level.The improved Q factor helps suppress mechanical thermal noise and reduce zero bias and zero bias drift,constituting the primary method for enhancing the performance of the resonant gyroscope.

Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

Fabrication of Submicron-Diameter and Taper Fibers Using Chemical Etching

The thin, long length and high smoothness silica photonic nanowires and taper optical fiber were fabricated using a simple and low cost chemical etching method. A two-steps wet etch process were used consisting of etching with 30% HF acid to remove cladding and 24% HF acid to decrease fiber core diameter. An approach for on-line monitoring of etching using 1300 nm light power transmitted in the optical fiber was used to determine the diameter of the remaining core and showed a transition between two different operation regimes of nanofiber from the embedded regime, where the mode was isolated from the environment, to the evanescent regime. The data indicated that the diameter of the silica fiber decreased linearly for both 30% and 24% HF acid with 1.2 and 0.1/zm/min grad diameter, respectively at room temperature, and more than 70% of the mode intensity could propagate outside fiber when the core diameter was less than 1μm. The results of fiber taper showed that the fiber was tapered by a factor of 20 while retaining a thin core structure and leaving about more than 85% of core structure.

Characterization and Wettability of ZnO Film Prepared by Chemical Etching Method

ZnO thin films were prepared by a chemical etching method and their wettability was investigated. The structure and surface composition structure were characterized by means of scanning electron microscopy, X-ray photoelectronic spectrometry（XPS）, X-ray diffraction（XRD） and Raman spectrometry. These analyses reveal that the etched films were large-scale micro-nanohierarchical structures composed of a Zn core and a ZnO coating. Superhy- drophobic surfaces with water contact angles of over 150~ were obtained by n-octadecanethiol（ODT） modification. The XPS and Raman results indicate that ODT molecules were bound to the ZnO surface with the S head group by forming Zn--S bond.

Plasma-induced chemical etching generating Ni_(3)S_(2) for formaldehyde detection

In this paper,Ni_(3)S_(2)nanosheet(NS)was generated by chemical etching with sodium sulfide directly on the nickel foam(NF),which was induced by dielectric barrier discharge plasma in liquid.Compared with other chemical etching methods of nickel-based nanomaterials,this method was not only rapid(40 min)and mild(at room temperature and atmospheric pressure),but also showed consistent stability and good reproducibility.The Ni_(3)S_(2)NS/NF electrode showed excellent performance in the electrochemical detection of formaldehyde under alkaline conditions.It had a good linear relationship with the concentration of formaldehyde in the range of 0.002-5.45 mmol/L(R^(2)=0.9957)and the limit of detection(LOD)was 1.23μmol/L(S/N=3).The sensitivity was 1286.9μA L mmol^(–1)cm^(–2),and the response time was about 5 s.The plasma-induced chemical etching strategy provides a simple and stable electrode preparation method,which has great application prospects in nonenzymatic electrochemical sensors.

OFHC copper substrates for niobium sputtering:comparison of chemical etching recipes

Purpose Niobium sputtered on copper has been a popular alternative approach for superconducting radio frequency(SRF)community in the last few decades.Comparing to bulk materials of a few millimeters,high-purity niobium of merely a few microns is sufficient to realize superconductivity on the coated surface.Being niobium thin film,it has been widely acknowledged that surface quality of the substrate plays a vital role in obtaining a superior niobium coating with excellent SRF performance.Therefore,proper chemical treatment of the substrate before coating is crucial and the ultimate goal is to create a smooth and defect-free surface.Prior to the design of a cavity etching system,the mechanism of SUBU as well as two industry-used solutions is studied in detail on samples.Methods Copper samples were first pre-treated by mechanical grinding to remove fabrication damages,obvious defects and visible impurities.Two chemical solutions widely used in industries were subsequently chosen to etch the samples.Finally,the established SUBU solution was used independently on these pre-treated samples for comparison.Surface morphology and etching rate were measured accordingly.Results and conclusions Mirror-like copper surface was created by using the SUBU solution thus qualified for subsequent niobium sputtering,while the other two solutions used in industries were less effective with nonideal surface morphology.The chemical reactions,the experimental requisites and the involved processes are extensively elucidated for all three solutions.Limitations for SUBU were examined,and the optimum ratio of the chemical bath volume to sample surface area was also determined.These investigations will serve as an important guidance for the development of a chemical etching system for elliptical copper cavities.

The etching of a-plane GaN epilayers grown by metal-organic chemical vapour deposition

Morphology of nonpolar （1120） a-plane GaN epilayers on r-plane （1102） sapphire substrate grown by low-pressure metal-organic vapour deposition was investigated after KOH solution etching. Many micron- and nano-meter columns on the a-plane GaN surface were observed by scanning electron microscopy. An etching mechanism model is proposed to interpret the origin of the peculiar etching morphology. The basal stacking fault in the a-plane GaN plays a very important role in the etching process.

Studying Different Etching Methods Using CR-39 Nuclear Track Detector

In this research we try to investigate the optimum etching time for the tracks originate in (CR-39) solid state nuclear track detector after irradiated with alpha source (241Am) using three different etching techniques: the traditional method (water bath), microwaves and ultrasound devices. The track etching parameters: bulk etch rate (VB), track etch rate (VT), track etch rate ratio evaluates (V), critical angle (θC), and etching efficiency (η) were calculated in this research. It’s seen that the optimum etching time was ranging with (60 - 150 min), (20 - 30 min) and (60 - 120 min) when etching with water bath, microwave and ultrasound respectively. Also we observed that the critical angle was (24.29) when etching CR-39 detector with microwave. This value is lower than the critical angles values for the detector etched with water bath or ultrasound;thus it can be the optimum magnitude because its decrease leads to increasing the number of the tracks appeared in the detector and the etching efficiency.

Investigation of chlorine-based etchants in wet and dry etching technology for an InP planar Gunn diode

Mesa etching technology is considerably important in the Gunn diode fabrication process. In this paper we fabricate InP Gunn diodes with two different kinds of chlorine-based etchants for the mesa etching for comparative study. We use two chlorine-based etchants, one is HCl-based solution （HC1/H3PO4）, and the other is Cl2-based gas mixture by utilizing inductively coupled plasma system （ICP）. The results show that the wet etching （HCl-based） offers low cost and approximately vertical sidewall, whilst ICP system （C12-based） offers an excellent and uniform vertical sidewall, and the over-etching is tiny on the top and the bottom of mesa. And the fabricated mesas of Gunn diodes have average etching rates of 0.6 p.m/min and 1.2 pm/min, respectively. The measured data show that the current of Gunn diode by wet etching is lower than that by ICP, and the former has a higher threshold voltage. It provides a low-cost and reliable method which is potentially applied to the fabrication of chip terahertz sources.

Characterization of CdZnTeSe Nuclear Detector Chemically Etched in Bromine Methanol

Semiconductor nuclear radiation detectors made from tertiary and quaternary compounds of cadmium telluride (CdTe) can operate at room temperature without cryogenic cooling. One of such materials that have become of great interest is cadmium zinc telluride selenide (CdZnTeSe). Compared to other CdTe-based materials, such as cadmium zinc telluride (CdZnTe), CdZnTeSe can be grown with much less Te inclusions and sub-grain boundary networks. Chemical etching is often used to smoothen wafer surfaces during detector fabrication. This paper presents the characterization of CdZnTeSe that is chemically etched using bromine methanol solution. Infrared imaging shows that the wafer has no sub-grain boundary networks that often limit detector performance. The current-voltage (I-V) characterization experiment gave a resistivity of 4.6 × 1010 Ω-cm for the sample. The I-V curve was linear in the ±10 to ±50 volts range. An energy resolution of 7.2% was recorded at 100 V for the 59.6-keV gamma line of 241Am.

Three-dimensional isotropic microfabrication in glass using spatiotemporal focusing of high-repetition-rate femtosecond laser pulses

To improve the processing efficiency and extend the tuning range of 3D isotropic fabrication,we apply the simultaneous spatiotemporal focusing(SSTF)technique to a high-repetition-rate femtosecond(fs)fiber laser system.In the SSTF scheme,we propose a pulse compensation scheme for the fiber laser with a narrow spectral bandwidth by building an extra-cavity pulse stretcher.We further demonstrate truly 3D isotropic microfabrication in photosensitive glass with a tunable resolution ranging from 8μm to 22μm using the SSTF of fs laser pulses.Moreover,we systematically investigate the influences of pulse energy,writing speed,processing depth,and spherical aberration on the fabrication resolution.As a proof-of-concept demonstration,the SSTF scheme was further employed for the fs laser-assisted etching of complicated glass microfluidic structures with 3D uniform sizes.The developed technique can be extended to many applications such as advanced photonics,3D biomimetic printing,micro-electromechanical systems,and lab-on-a-chips.

Dislocation Analysis for Large-sized Sapphire Single Crystal Grown by SAPMAC Method

In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in large sapphire boule （0001） basal plane was investigated by chemical etchiing, scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6× 10^1-8.0×10^2 cm^2, in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally, the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method.

Growth and Characterization of High-quality LiAlO2 Single Crystal

γ-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by high-resolution X-ray diffraction and chemical etching. The results show that the as-grown crystal has perfect quality with the full width at half maximum （FWHM） of 17.7-22.6 arcsec and etch pits density of （0.3- 2.2）×10^4 cm^-2 throughout the crystal boule. The bottom of the crystal boule shows the best quality. The optical transmission spectra from UV to IR exhibits that the crystal is transparent from 0.2 to 5.5μm and becomes completely absorbing around 6.7μm wavelength, The optical absorption edge in near UV region is about 191 nm.

Effect of Sintering Temperature and Hydrophobic Treatment on the Microstructure and Properties of Copper-Graphite Composites

Copper-graphite composites were prepared by spark plasma sintering(SPS)using coppercoated graphite powder.Hydrophobic surfaces were successfully constructed by chemical etching and surface treatment.The density,metallographic structure,microstructure,Shore hardness,resistivity,water contact angle,and friction/wear properties of the composites were investigated using the Archimedes drainage method,a metallographic microscope,a scanning electron microscope,a hardness tester,a resistometer,a surface science tester,and a friction tester.The results showed that the relative density and Shore hardness of the copper-graphite composites increased slightly from 90.04%and 56 HSD to 92.66%and 59 HSD,respectively,when the sintering temperature increased from 700 to 900℃.The copper and graphite phases in the copper-graphite composites were uniformly distributed with a continuous and network-like structure at various sintering temperatures.The interface between the copper and graphite was in good condition,without any obvious cracks or voids.The optimum process for hydrophobic surface construction included etching with a 1 mol/L K_(2)Cr_(2)O_(7)-H_(2)SO_(4)solution for 1 min,and soaking in a 0.09 mol/L cetylbenzene sulfonic acid alcohol solution for 1 h.The contact angle of the copper-graphite composite reached 130°.Hydrophobic treatment was beneficial for reducing the friction coefficient(from 0.18-0.19 to 0.13-0.15)and the wear rate(from 4.1-6.2×10^(-3)to 1.1-2.1×10^(-3)mm^(3)/(N·m)),demonstrating obvious antifriction and wear-resisting properties.The resistivities of the hydrophobic-treated samples increased slightly,from(4-8)×10^(-7)Ω·m to(5-15)×10^(-7)Ω·m,meeting the resistivity requirements of copper-graphite composite pantograph sliders and current receiver sliders in actual working conditions.

Growth,Dislocation and Morphology of Nd∶GdVO_4 Single Crystal

The neodymium ions doped gadolinium vanadate (Nd∶GdVO_4) single crystals were successfully grown by Czochralski method. Chemical etching technique was used to reveal the dislocation structure of the crystals. An average dislocation density of (100) plane is 600 pits/mm 2. The crystal-morphology can be used to determine crystal orientation accurately with simple optical method.

Ordered silicon nanorod arrays with controllable geometry and robust hydrophobicity

Highly ordered silicon nanorod（Si NR） arrays with controllable geometry are fabricated via nanosphere lithography and metal-assisted chemical etching. It is demonstrated that the key to achieving a high-quality metal mask is to construct a non-close-packed template that can be removed with negligible damage to the mask. Hydrophobicity of Si NR arrays of different geometries is also studied. It is shown that the nanorod structures are effectively quasi-hydrophobic with a contact angle as high as 142°, which would be useful in self-cleaning nanorod-based device applications.