Electrochemical Anodization Method Research Articles

Fabrication and applications of wafer-scale nanoporous GaN near-infrared distributed Bragg reflectors

The wafer-scale, near-infrared, and nanoporous (NP)-GaN distributed Bragg reflectors (DBRs) were fabricated by using an electrochemical anodization method for the first time. The peak reflectivity of the DBR mirrors on the sapphire substrates is ~95% in the range of 550 nm–1750 nm with different stop-band widths. To explore its potential applications, a lead-free all-inorganic perovskite film with a PL emission in the near-infrared region was grown on a DBR mirror. Compared to the reference perovskite film, the photoluminescence intensity of the perovskite film on the DBR substrate presents more than 4-fold enhancement, which is in agreement with the calculated value. The performance enhancement should be contributable to light-coupling enhancement of emission light. The near-infrared NP-GaN DBRs pave the way for developing a range of perovskite devices for broadband and large-area applications.

Distinct band UV–Visible photo sensing property of ZnO-Porous silicon (PS):p-Si hybrid MSM heterostructure

Present article deals with fabrication of UV–Visible radiation sensing photodetector (PD) by architecting planar and sandwiched (PD1 and PD2) electrode configurations on ZnO-PS:p-Si heterostructure. PS:p-Si structure is prepared by electrochemical anodization method. Thin ZnO layer of ~162 nm is deposited on PS:p-Si substrate using pulsed DC magnetron sputtering technique. Gold (Au) is combined with Aluminium (Al) to provide rectifying Schottky contacts to the devices. Prior to device testing it is tested for various conventional characterizations. FESEM studies confirm uniform deposition of nanocrystalline ZnO thin film with mean particle size of ~ 35 nm, whereas its cross section shows uniform interface between ZnO and PS with combined thickness of ~700 nm. Cross sectional EDX analysis confirms diffusion of ZnO particles into PS layer. UV–vis absorption spectrum gives bandgap of ZnO as ~3.3 eV. Reflectance measurement of the heterostructure shows decrease in reflectivity compared to bulk c-Si with ZnO-PS:p-Si showing multiple interference pattern compared to bare ZnO coated on glass within the spectral range 200 nm-800 nm. The pattern is remarkably increased compared to that of PS:p-Si. Photoluminescence study reveals various luminescence bands peaked at ~378 nm, 388 nm, 398 nm, 410 nm, 420 nm, 433 nm, 450 nm, 467 nm, 482 nm 492 nm and 597 nm. Current- Voltage (I–V) measurement for dark current (Id) gives low leakage current of the devices PD1 and PD2 respectively as 6.6×10−8A and 7.5×10−7A at -5V, which is however an order of magnitude more than the ZnO coated one on glass. Both the devices PD1 and PD2 show UV–Visible photoresponse, whereas the ZnO device on glass shows response to UV (375 nm) only. Both the devices show response time ~1 s in visible range which is nearly half the value in UV range.

Synthesis of carbon nanowalls on the surface of nanoporous alumina membranes by RI-PECVD method

This work is devoted to the synthesis of carbon nanowalls on the surface of a nanoporous aluminum oxide membrane by radical-injection plasma enhanced chemical vapor deposition method. Nanoporous alumina oxide membranes with different morphology and thickness, which were obtained by the method of two-stage electrochemical anodization, were used as a substrate. For comparative analysis, carbon nanowalls were also obtained on the surface of a silicon substrate and aluminum foil. The synthesized nanostructures were investigated by using scanning electron microscopy and Raman spectroscopy. The dependence of the morphology and height of carbon nanowalls on the pore size and the thickness of the alumina membrane, respectively, was revealed.

Improved Immunoregulation of Ultra-Low-Dose Silver Nanoparticle-Loaded TiO2 Nanotubes via M2 Macrophage Polarization by Regulating GLUT1 and Autophagy.

IntroductionThe bone regeneration of endosseous implanted biomaterials is often impaired by the host immune response, especially macrophage-related inflammation which plays an important role in the bone healing process. Thus, it is a promising strategy to design an osteo-immunomodulatory biomaterial to take advantage of the macrophage-related immune response and improve the osseointegration performance of the implant.MethodsIn this study, we developed an antibacterial silver nanoparticle-loaded TiO2 nanotubes (Ag@TiO2-NTs) using an electrochemical anodization method to make the surface modification and investigated the influences of Ag@TiO2-NTs on the macrophage polarization, osteo-immune microenvironment as well as its potential molecular mechanisms in vitro and in vivo.ResultsThe results showed that Ag@TiO2-NTs with controlled releasing of ultra-low-dose Ag+ ions had the excellent ability to induce the macrophage polarization towards the M2 phenotype and create a suitable osteo-immune microenvironment in vitro, via inhibiting PI3K/Akt, suppressing the downstream effector GLUT1, and activating autophagy. Moreover, Ag@TiO2-NTs surface could improve bone formation, suppress inflammation, and promote osteo-immune microenvironment compared to the TiO2-NTs and polished Ti surfaces in vivo. These findings suggested that Ag@TiO2-NTs with controlled releasing of ultra-low-dose Ag+ ions could not only inhibit the inflammation process but also promote the bone healing by inducing healing-associated M2 polarization.DiscussionUsing this surface modification strategy to modulate the macrophage-related immune response, rather than prevent the host response, maybe a promising strategy for implant surgeries in the future.

Oxygen vacancy modulation of titania nanotubes by cathodic polarization and chemical reduction routes for efficient detection of volatile organic compounds.

In this work, we have synthesized a highly ordered TiO2 nanotube array by an electrochemical anodization method. Then the oxygen vacancy level of the TiO2 nanotubes was tuned by two different methods: i.e. (i) cathodic polarization by the application of a reverse potential and (ii) chemical reduction using a reducing agent (e.g. hydrazine hydrate) treatment at elevated temperature. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) confirmed there was no morphological deformation of TiO2 nanotubes after the modulation of oxygen vacancies. X-ray diffraction spectroscopy (XRD) and TEM both confirmed the formation of highly crystalline anatase (101). The oxygen vacancy level of all the TiO2 nanotubes was tested progressively with photoluminescence (PL) spectra, Raman spectra, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectra (XPS). All the spectroscopy results confirmed the successful reduction of TiO2 nanotubes with different levels of defects. All the nanotube samples with various oxygen vacancy levels were transformed to Au/TiO2 nanotube/Ti type sandwich structured sensor devices and tested under exposure to 100 ppm of ethanol in air. Highly doped cathodic reduced nanotubes offered very high response magnitudes of 99.64% and 60% under exposure to 100 ppm of ethanol at 200 °C and 50 °C, respectively. Chemically reduced TiO2 nanotubes offered moderate response magnitudes of 75.4% and 80% at 150 °C and 200 °C under exposure to 100 ppm of ethanol, which was found to be the best among all the samples due to the appreciably fast response (155 s) and recovery time (779 s). The developed sensors showed adequate stability and selectivity towards ethanol with a moderate dynamic range (20 to 200 ppm of ethanol) of detection. A general relation was drawn based on the experimental findings of this work to estimate the response magnitude of nanoscale metal oxide gas sensors with various levels of oxygen vacancies.

Formation of TiO2 Nanotubular Layers on Ti-6Al-4V Based Dental Implants for Inhibiting Biofilm Growth

Modification of Ti-6Al-4V through electrochemical anodization method has been investigated on the purpose of generating TiO2 nanotube arrays (TiNTAs) on the surface of Ti-6Al-4V films. The as-anodized samples were calcined in an atmospheric furnace at various temperatures, in the range of 500-800 ºC. The evaluation of biofilm inhibition was performed by an in vitro method with Streptococcus mutans as a bacterium model. FE-SEM imaging confirmed the successful formation of TiO2 nanotube arrays while XRD results implied a phase transformation from anatase to rutile when the calcination temperature was around 600-650 ºC with average crystallite size of 18 nm. Calcination temperature is one of determining factors in the adjustment of crystallinity and morphology of TiO2, which in turn affects its capability to suppress biofilm formation. This study revealed that the best sample for biofilm inhibition was calcined at 600 ºC with a crystallite phase of mostly anatase. This sample managed to improve antibacterial activity of up to five times as compared to the unmodified Ti-6Al-4V. The output of this study is expected to give some insight on a promising alternative for preventing the formation of harmful biofilm on dental implants.

Fabrication of titanium oxide nanotubes by varying the anodization time

The motivation of this work is to develop an efficient and relatively inexpensive material architecture using titanium oxide nanotubes for hydrogen generation. Hydrogen is an environment friendly energy carrier used in the field of transport, power generation, and in various domestic applications. Nano scale materials have many peculiar properties than the bulk ones and have led to break troughs in various fields of science and technology. Titanium oxide nanotubes have attracted much interest in research because of its functional properties such as large surface area. The titanium oxide nanotubes structures are grown and fabricated by electrochemical anodization method at constant DC voltage at different anodization time. Titanium oxide nanotubes formed is characterized by FEG-SEM and the dimensions are analysed. For the first 15 mins of anodization the Nano pores are formed and by increasing the anodization time the size of pores gradually increases. Then finally the titanium oxide nanotubes of 500 nm diameter and length of 50 nm are obtained.

Growth of ZnO nanoflowers: effects of anodization time and substrate roughness on structural, morphological, and wetting properties

Zinc oxide (ZnO) nanoflowers were grown on pure zinc plates through electrochemical anodization. Prior to anodization, zinc plates were artificially roughened by sanding with emery papers #1000, #1500, and #2000 grits so as to obtain varying substrate surface profiles. Thus, the effect of zinc plates’ roughness on the structural, morphological, and wetting properties was investigated by means of anodization time. X-ray diffraction measurements showed that the grown nanostructures were of wurtzite structure. Scanning electron microscope images revealed that anodization time increased the fraction of anodized surface. Additionally, increasing anodization time yields an increase in the aspect ratio of the micrometer long nanoflower spines, as well as, by increasing anodization time, from 0 to 600 s, contact angle gradually decreases for all substrate surface roughness values. The best wettability performance with the lowest contact angle with 13.46° was recorded for the sample with highest roughness (sanded with #1000) and anodized for 600 s. It is expected that the electrochemical anodization method which enables rapid and controlled formation of metal oxide nanostructures can further be a promising way to develop structures with tunable wettability.

Selective Electrocatalytic Water Oxidation to Produce H2O2 Using a C,N Codoped TiO2 Electrode in an Acidic Electrolyte.

Production of hydrogen peroxide (H2O2) via in situ electrochemical water oxidation possesses great potential applications in the energy and environment fields. In this work, for the first time, we reported a C,N codoped TiO2 electrode for selective electrocatalytic water oxidation to produce H2O2 in an acidic electrolyte. An electrochemical anodic oxidation method combined with postcalcination in the presence of urea was applied to fabricate such a C,N codoped TiO2 electrode, which was evidenced by detail structural characterizations. The calcination temperature and urea atmosphere were found to play key roles in its catalytic performances; the optimized 600N sample exhibited an onset potential of 2.66 V (vs Ag/AgCl) and a Tafel slope of 51 mV dec-1 at pH 3. Under the optimal applied potential, the cumulative H2O2 concentration for this sample reached 0.29 μmol L-1 cm-2 h-1. More importantly, a simple recalcination strategy was developed to recover the deactivation electrode. This study proposed an efficient C,N codoped TiO2 electrode toward water oxidation to selectively produce H2O2 in the acidic electrolyte, which could be further used to in situ generate H2O2 for the energy- and environment-related fields with water as the precursor.

Regioselective electrolytic 5,8-difluorination of quinolines

Electrochemical anodic oxidation method for the incorporation of fluorine atom into quinoline ring is described. Our method involves a regioselective 5,8-difluorination of quinolines using HF:pyridine as a reagent/supporting electrolyte in an undivided electrochemical cell equipped with platinum anode and cathode. Various quinoline derivatives were subjected to electrolytic fluorination at room temperature to obtain moderate to good yields in short reaction time.

Condition Monitoring of Transformer Breather Using a Capacitive Moisture Sensor

Ambient air flows into the conventional dehydrating breather due to cyclic loading of transformer. It is the major source of moisture contamination of the transformer oil. Presence of moisture causes failure of insulation strength of the oil. In the proposed work, a moisture sensor-based health monitoring technique of a dehydrating breather is proposed. A parallel plate capacitive sensor to measure and monitor the moisture inside the breather was designed and fabricated by electrochemical anodization method. A phase detection electronics circuit for converting the capacitance change of the moisture sensor to voltage signal was designed and implemented. To maintain the moisture at the desired level in the breather, the power supply of an electric heater of 40 W is controlled by controlling the duty cycle of the pulsewidth modulation (PWM) signal. The duty cycle of the PWM wave is controlled using the designed moisture sensor. Experiments are performed to monitor the moisture of a dehydrating breather of 0.5 kg capacity in the laboratory. The proposed moisture-controlled breather reduces the error due to wrong visual inspections of the moisture level in the drying agent; timely replacement of the drying agent; and the improvement of the operational reliability of the transformer.

Morphological, structural, and functional properties of vertically aligned carbon nanotubes deposited on porous silicon layers by ultrasonic spray pyrolysis

Abstract In this work, we reported the fabrication of hybrid structures by growing the multi-walled carbon nanotubes (MWCNT) on porous silicon (PS) as a template. Aligned multi-walled carbon nanotubes have been successfully synthesized on PS by ultrasonic spray pyrolysis (USP) using a solution of Toluene/Ferrocene as the precursor, while electrochemical anodization method was used to fabricate the PS layers. Au contact was deposited as a metallic contact on the MWCNT layer in order to measure the electrical properties and to analyze the electrical effect of the incorporation of MWCNT on PS. The structural and morphological characteristics of the hybrid structures were investigated by using Field Emission Scanning Electron Microscope (FE-SEM) showing that MWCNT formed a thin film on the PS surface in the form of an aligned array and perpendicular fiber-like structures to the porous surface. High-Resolution Transmission Electron Microscopy (HRTEM) images confirmed the diameter of the CNT between 10 and 30 nm and typically consisted of 10–20 concentric shells of carbon sheets. Raman Microscopy showed three characteristic bands and a high graphitization extent, even it was possible to observe that the carbon structures passivated the PS layer. Consequently, the photoluminescence (PL) spectrum of PS layers significantly was modified by MWCNT. Finally, electrical measurements provided a practical approach to describe how the materials behave under specific conditions that can be used for different applications in electronics or optoelectronics such as diodes or photodetectors. Significant differences were found under darkness, and illumination conditions of current-voltage (I–V) curves implied their possible application in optoelectronics. Moreover, symmetrical rectifying and Ohmic behavior was observed, which rarely has been reported in the literature, even it was possible to fit a transport mechanism, and the capacitance-voltage (C–V) curves presented an un-exponential behavior with interesting effects such as an increase of built-in voltage and negative capacitance. Based on the results obtained, the growth method for MWCNT structures was proposed.

Fabrication of an anodized porous alumina relative humidity sensor with improved sensitivity

Sensitivity is an important parameter of any humidity sensor. In recent times, nanostructure materials have been used to fabricate the capacitive-type humidity sensors to improve the sensitivity. However, for the nanostructure sensors, in most cases, the sensitivity improvement is not guaranteed although extra efforts are made in terms of time and cost. Our aim is to improve the sensitivity of an anodized porous alumina capacitive humidity sensor by a simple method. A nanostructure porous film has been formed on each side of a pure aluminum substrate (99% purity) by an electrochemical anodization method. Two parallel plate capacitors are formed by depositing metal plate on each side of the metal oxide film with bulk aluminum as the common electrode. The sensitivity has been increased by connecting the two parallel plate capacitive sensors in parallel. Thus, two capacitive sensors on single substrate are fabricated and connected in parallel to form the third capacitor, which is used as the humidity sensor. The sensitivity, response time, recovery time, and hysteresis of the sensors are determined with variation in the range from 10% to 99% relative humidity (RH). The sensitivity of the sensor obtained by connecting two capacitors in parallel has been increased by almost two times compared to the sensitivity of an individual sensor fabricated on each side.

Patterned Porous Silicon Prepared by Reactive Ion Etching Technique

A previous study, porous silicon (PSi) have been fabricated by electrochemical anodization method. The PSi surfaces have an inhomogeneous pores size in the range of 95– 1450 nm. In this study, we have prepared patterned PSi using RIE technique in CF4 gas which is activated by RF plasma. Before the RIE process, the surfaces Si was patterned using the photolithography method. Then, the Si surfaces were etched in various etching time to form patterned PSi. The patterned PSi samples were characterized by SEM, Dektak profilometer, and four-point probe equipment. We found the pore sizes and the pore depths for each the etching time were about 5.30 μm and 12.6 nm; 5.19 μm and 19.6 nm; 4.30 μm and 23.8 nm; 3.40 μm and 28.0 nm for 10 min, 20 min, 30 min, and 40 min, respectively. The pores depths increased with increasing the etching time. Meanwhile, the resistivity of patterned PSi increased with increasing the etching time i.e., 1.14×10-4 Ω.cm, 1.79×10-4 Ω.cm, 2.36×10-4 Ω.cm, and 2.60×10-4 Ω.cm for 10 min, 20 min, 30 min, and 40 min, respectively. This indicated that the pore could be considered as defects or dislocation inside material which resist electrons diffuse toward the electrode.

Decoration of copper foam with Ni nanorods and copper oxide nanosheets to produce a high-stability electrocatalyst for the reduction of CO2: Characterization of the electrosynthesis of isonicotinic acid

CuO–Cu 2 O (Cu x O) nanosheets were coated on a copper foam substrate by the electrochemical anodization method in an alkaline solution. Constant current coulometry was performed to electrodeposit Ni nanorods on the surface of a Cu/Cu x O electrode. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) proved that the copper oxide nanosheets were anchored on the copper foam substrate and modified by Ni nanorods (Cu/Cu x O/Ni). The process took place via a facile and inexpensive electrodeposition method. As the results indicate, owing to the synergistic effect of adjacent Cu x O and Ni sites, a Cu/Cu x O/Ni electrode has a very good and stable electrocatalytic activity to reduce CO 2 . As tested in this study, the product of the electrocatalytic reduction of CO 2 (i.e. activated CO 2 , or CO 2 •− ) can be used for the electrocarboxylation of pyridine in mild conditions. Once an electron is transferred from CO 2 •− to pyridine, a pyridine radical anion is formed. Based on the EC'C′CC mechanism, this radical anion reacts with CO 2 •− and produces isonicotinic acid as the main product. In addition, two pyridine radical anions react together and produce a 4,4′-bipyridine dimer. The high stability of the electrocatalyst during the electrolysis process and the simplicity of the workup make the proposed modified electrode appropriate for the electrosynthesis of some organic compounds.

Mechanism investigation on the enhanced photocatalytic oxidation of nonylphenol on hydrophobic TiO2 nanotubes

Enhanced and selective photocatalytic oxidation of nonylphenol (NP), a typical hydrophobic endocrine disrupting chemicals (EDCs), was realized on hydrophobic titanium dioxide nanotubes (H-TiO2NTs), which was fabricated by an electrochemical anodization method, followed by grafting of perfluorooctyl groups. The water contact angle of catalyst surface changed from 21.1° to 128.4° after hydrophobic modification. H-TiO2NTs showed excellent photocatalytic oxidation performance for NP, that it was completely converted in 40 min under irradiation, which was improved for about 17% compared with the hydrophilic TiO2NTs. The enhanced photocatalytic performance of H-TiO2NTs was attributed to the stronger adsorption ability toward NP identified by ATR-FTIR, with an initial adsorption rate of 4 times as higher as that of bare TiO2NTs. Meanwhile, the hydrophobic surface of H-TiO2NTs was beneficial for generation of more hydroxyl radicals. The apparent rate constant of hydroxyl radicals’ generation on H-TiO2NTs, which was the main oxidizing species, could reach 1.83 times that of the hydrophilic TiO2NTs. Both the two factors contributed to the successful competition of NP against the coexistent hydrophilic contaminates in the adsorption and oxidation on the catalyst surface, leading to the selective removal of NP in mixed systems finally.

Morphology dependent field emission from copper sulfide nanosheet arrays tailored with electrolyte concentrations in anodic oxidation process

Vertically oriented copper sulfide nanosheet arrays were successfully fabricated by a simple and manageable electrochemical anodization method at room temperature. By controlling and adjusting the concentrations of sodium sulfide electrolyte to be 0.1 M, 0.5 M, 1.0 M and 1.5 M, respectively, the morphologies of copper sulfide nanosheets (average size, thickness or density of sharp edges) could be well tailored and be more optimized for applications in field emission (FE). As the results showed, for optimal nanostructure of such copper sulfides nanosheet arrays, its turn-on field could be lowered to 2.0 V/μm and the field emission current density would reach up to 4.1 mA/cm2 under an applied field of 6.4 V/μm, and also it can exhibit excellent field emission stability, with a degradation lower than ±4% and a huge field enhancement factor of 8327.

Ceria deposited titania nanotubes for high performance supercapacitors

The present paper reports the application of a rare earth metal oxide – titania nano tube (TNT) composite for supercapacitor applications. Highly ordered arrays of single walled titaniananotubes of length approximately 4 μm were synthesised on titanium metal foil via a modified single step electrochemical anodization method. Nanostructured ceria is deposited on as prepared TNT by simply impregnating in cerous nitrate solution, followed by heat treatment. The characterizations were done by XRD and FE-SEM analysis. Supercapacitive performance is monitored using techniques such as CV, GCD and EIS. The pristine TNT itself shows promising supercapacitive performance (specific capacitance values ~ 6.82 mF/cm2), which is enhanced significantly by coating psuedocapacitive ceria. Among different ceria deposited samples, 0.075 Ce showed the best results with specific capacitance values ~55.28 mF/cm2 at scan rate 5 mV/s, owing to its open porous nanotubular morphology (optimal tube diameter around 20 nm) facilitating smooth charge transport and exposure of enormous amount of active material to the electrolyte, marking an enhancement of about 710% as compared to pristine TNT supercapacitors.

Synthesis and Study of a Polypyrrole–Aluminum Oxide Nanocomposite Film on an Aluminum Surface

Using the method of electrochemical anodization, aluminum oxide porous films are obtained in a sulfuric acid solution. The morphology of the aluminum oxide surface is studied by the method of scanning electron microscopy. The high-quality elemental analysis of the initial and oxidized Al films is performed using the method of electron microprobe analysis. A protective composite polypyrrole-aluminum oxide film is produced on the aluminum surface on top of a porous aluminum oxide film in the galvanostatic oxidation mode by the electrochemical synthesis method. The properties of the polypyrrole–aluminum oxide composite film are studied by the methods of voltammetry, as well as impedance and FTIR spectroscopy.

Controlled synthesis of vertically aligned honeycomb TiO2 nanotube arrays: effect of high-temperature annealing on physical properties

Vertically aligned honeycomb titania (TiO2) nanotube arrays grown on Ti foil were synthesized by electrochemical anodization method. The changing of morphology, crystalline structural, and optical properties of anodic titania nanotube (ATNT) arrays systematically studied. A novel annealing approach is proposed to retain the ATNT arrays at high temperatures ranging from 700 to 900 °C. At 700 and 800 °C, FESEM images showed that the nanotubular structures were preserved from annihilation and the morphology of the structure was a mixture between anatase and rutile. However, the highlight of this research was the successful synthesis of the high-quality rutile ATNT arrays at 900 °C. The X-ray diffractometer measurements proved that the variations in the mean crystallite sizes of anatase and rutile phase occurred during annealing of ATNT samples. The corresponding optical bandgaps were determined by extracting the reflectance values and combining Kubelka–Munk function with the indirect Tauc plot for transition phases of ATNT arrays for high-temperature annealed films.