Al2O3 Template Research Articles

Simultaneously manipulating carbon coating layers and void structures in silicon/carbon anode materials via bifunctional templates for lithium-ion batteries

The carbon coating strategies, ameliorating structure instability and reaction kinetics of silicon anodes upon lithiation/delithiation, have been chronically plagued by an electrochemical contradiction between a high specific capacity from a high silicon content and a long cycle life from a high carbon content. Herein, the carbon coating layers and void structures for silicon/carbon composites were simultaneously manipulated through a precisely grown Al2O3 template, which induced a controllable polydopamine polymerization through its mild interfacial interaction with Tris-buffer solution and created abundant void spaces by its residual parts. Particularly, the as-optimized silicon/carbon composite with an ultrahigh silicon content of 89.3 wt% could demonstrate a large initial reversible capacity of 2583 mAh g−1 with an 82.1 % coulombic efficiency at 200 mA g−1, a remarkable cycling durability of 601 mAh g−1 after 990 cycles at 2000 mA g−1, and an excellent rate capability of 887 mAh g−1 at 4000 mA g−1. The uniform void structures could maintain the structural stability/integrity of silicon, boost reaction kinetics across electrode/electrolyte interfaces, and suppress the uncontrollable formation/evolution of solid electrolyte interphases upon cycling. This novel research on synchronously regulating carbon layers and void structures in silicon/carbon composites would enlighten a rational development of high-capacity and long-life silicon anodes.

Design and Characterization of Nanostructured Ag2O-Ag/Au Based on Al2O3 Template Membrane for Photoelectrochemical Water Splitting and Hydrogen Generation

This study considers the progress of our previous study for hydrogen generation depends on the highly ordered metal oxide/plasmonic materials. This study reports the preparation of Ag2O-Ag/Au on the Al2O3 template (Ag2O-Ag/Au/Al2O3) for photocatalytic sewage water splitting and H2 gas production. Ni imprinting, followed by two-step anodization procedures, prepare the Al2O3 template. Ag2O-Ag and Au materials are prepared inside the template using electrochemical deposition and sputter coating methods, respectively. The chemical structure is confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, in which all the peaks characterized by Ag2O, Ag, Au, and Al2O3 are confirmed. The scanning electron microscope (SEM) images confirm the preparation of a highly ordered hexagonal Al2O3 template with a pore wide of about 350 nm. Ag2O-Ag/Au accept the same morphology after the deposition process, in which the materials are deposited inside and on the Al2O3 template, in which the hexagonal pores are still opened after the deposition process. These open pores increase the surface area and then enhance the optical and electrical properties. For the H2 generated from sewage water, the produced Ag2O-Ag/Au on the Al2O3 photoelectrode achieved an incident to photon conversion efficiency (IPCE) of 30%. Additionally, the impact of light wavelength and intensity on photoelectrode performance is evaluated. Under increasing the light total power from 25 to 75 mW.cm−2, the current density (Jph) value goes up from 8.9 to 9.5 mA.cm−2. The current study’s findings show promising results for resolving the issue of energy in remote areas by turning wastewater into hydrogen fuel.

Hexagonal Al2O3/TiO2/TiN Nanotubes‐Based Sensor for CO2 Detection

A hexagonal Al2O3/TiO2/TiN nanotube sensor is prepared using an Al2O3 template. This template is prepared through the Ni imprinting and two‐step anodization technique. After the pore widening process, the pore diameter is 300 nm. The deposition of TiO2 and TiN is conducted through atomic layer deposition and DC sputtering techniques, respectively. The application of Al2O3/TiO2/TiN nanotube sensor for the detection of CO2 gas is carried out under different flow rates of this gas from 50 to 150 SCCM. This application is carried out using electrochemical measurements (Keithley device) to determine the current–voltage and resistance time relations. From the measurements, the sensitivity of the sensor increases from 3.2% to 16.4% with increasing the concentration of the CO2 gas from 50 to 150 SCCM, respectively. Moreover, the prepared sensor has a great response time and recovery time of 3 and 35 s, respectively. This behavior qualifies the sensor for industrial applications. Moreover, the limit of detection is very small (6 SCCM). A simple mechanism is mentioned to explain the physical attraction of CO2 over the sensor surface, in which the greatly prepared tubes play the main role in enhancing the sensitivity and response percent of the sensor to CO2 gas.

FORC-investigation of magnetic properties of Ni nanowire arrays synthesized using Al2O3 templates with different order of pores

FORC-investigation of magnetic properties of Ni nanowire arrays synthesized using Al2O3 templates with different order of pores

Al2O3-assisted synthesis of hollow CuCo2S4 nanospheres with rich sulfur vacancies for hybrid supercapacitor

Preparing hollow materials with a large active surface area is a highlight for energy storage materials. In this work, hollow CuCo2S4 is synthesized via a hard template of commercial Al2O3 at a low cost, and S-vacancies are introduced to enhance the electronic conductivity (rh-CuCo2S4). The template Al2O3 is completely removed by the solvothermal reaction without damaging the hollow structure of CuCo2S4. The rh-CuCo2S4 demonstrates a specific area of 99.5 m2 g–1, higher than that of CuCo2S4 without the Al2O3 template. The rh-CuCo2S4 electrode performs a high specific capacity (247.1 mAh g–1 at 1 A g–1), favorable rate performance, and decent cycling performance (81.1% after 13,000 cycles at 10 A g–1). An asymmetric rh-CuCo2S4//AC hybrid supercapacitor shows an energy density of 77.6 W h kg–1 at the power density of 612 W kg–1 and a maximum power density of 7.3 kW kg–1 at the energy density of 42.5 W h kg–1. The excellent stability of rh-CuCo2S4//AC hybrid supercapacitor is also obtained with a retention of 84.9% after 10,000 cycles at 10 A g–1. The favorable performance of rh-CuCo2S4 is attributed to the increasing charge diffusion channels bases on the hollow morphology and the enhanced electronic conductivity and reaction activity due to S-vacancies. This work provides a low-cost and efficient approach to preparing sulfides with high performance in energy storage applications.

Large-Area Graphene Transfer through Synthesis of an Interfacial Release Layer between Epitaxial Cu(Ni)(111) and Al2O3(0001) Template

As the pioneer two-dimensional material with outstanding properties, graphene is still lacking a CMOS compatible handling process, both for growth and transfer. This restriction slows down the application of large-scale-high-quality monolayer graphene (MLG). The synthesis of wafer-scale single-crystal MLG has matured utilizing a single-crystal Cu(111) deposit epitaxially on c-plane sapphire as a growth template[1,2]. However, the non-straightforward intercalation base transfer process [3] becomes a bottleneck. Hence, an interfacial release layer between Cu and sapphire could provide an alternative route for the graphene transfer process.Here, we report on the synthesis of large-area multilayer graphene at the interface of epitaxial Cu(Ni)(111)/ Al2O3(0001) using atmospheric pressure chemical vapor deposition (CVD). The interfacial carbon layer (ICL) was synthesized by introducing CH4 and H2 gases in the CVD chamber at 1050°C, and characterized by micro-Raman spectroscopy, XRD, and AFM. Carbon layers with thickness up to 80nm were observed at the interface between 500nm thick Cu and Al2O3.The effects of the partial pressure of gases - PH2 and PCH4 – and template substrate on the growth dynamics were investigated systematically by optical microscopy and image analysis. The growth rate and deposition area of ICL are positively correlated with PCH4. In the Cu85Ni15(111) system, ICL coverage is significantly lower compared to Cu(111). This is attributed to the faster growth rate of a top surface MLG, which blocks the access of carbon into the interface of Cu(Ni)/Al2O3. A higher PH2 slows down the MLG growth, leading to a denser ICL deposition in both substrates.The growth mechanism of this ICL is also proposed as the result of two competing effects: 1. The high PCH4 environment drives the decomposed carbon species to the interface from the top surface by diffusion through the bulk of the catalytic metal. 2. The blockage of carbon access to the bulk of metal once the top layer MLG is closed.After process optimization, the ICL could be synthesized simultaneously with top layer high-quality CVD MLG. In the future, this process could provide opportunities to enable CMOS compatible large-scale-high-quality MLG transfer. K. Verguts et al., ECS J. Solid State Sci. Technol., 5, Q3060–Q3066 (2016).M. Huang et al., ACS Nano, 12, 6117–6127 (2018).K. Verguts et al., ACS Appl. Mater. Interfaces, 9, 37484–37492 (2017).

An Increase of Threading Dislocations Filtering Efficiency in Al2O3 Templates with Faceted Surface Morphology During a Growth by Molecular Beam Epitaxy

We present the results of a transmission electron microscopy and X-ray diffractometry investigation of AlN/c-Al2O3 templates with GaN ultrathin insertions grown by plasma-assisted molecular beam epitaxy. It has been shown that AlN buffer layers with faceted surface morphology provide a greater threading dislocation density reduction than smooth layers. The filtering effect of GaN ultrathin insertions has been confirmed.

Comparison of H2O2 screen-printed sensors with different Prussian blue nanoparticles as electrode material

In order to determine hydrogen peroxide condensing from gaseous and liquid phases screen-printed electrodes with controlled and adjustable thickness, shape and size of the working electrode as well as electrode paste composition were investigated. For this purpose Prussian blue (PB) nanoparticles with a different particle size distribution of 20-30 nm (synthesized) and 60-100 nm (commercially available) were mixed with carbon paste and screen-printed on Al2O3 templates to establish H2O2-sensitive electrode. These two types of screen-printed sensors were compared to the commercial one during measurements in H2O2/water solutions at concentrations between 10-5 and 10-2 M H2O2. The linear signal in the investigated concentration range was found only for the sensor with the commercially available PB particles. Thus, this sensor prepared with PB particles of the size 60-100 nm showed the most reproducible and time-stable response versus the analyte in comparison to the others. This result offers the possibility to create sensors with adjustable design adapted to the concrete functionality. Thin films of collecting electrolytes based on agarose gels were printed on the sensor structures. They showed a distinct response on the application of H2O2-containing aerosols and gaseous phase.

Oxygen Incorporation in the Molecular Beam Epitaxy Growth of ScxGa1−xN and ScxAl1−xN

Secondary‐ion mass spectrometry (SIMS) is used to determine impurity concentrations of carbon and oxygen in two scandium‐containing nitride semiconductor multilayer heterostructures: ScxGa1−xN/GaN and ScxAl1−xN/AlN grown by molecular beam epitaxy (MBE). In the ScxGa1−xN/GaN heterostructure grown in metal‐rich conditions on GaN–SiC template substrates with Sc contents up to 28 at%, the oxygen concentration is found to be below 1 × 1019 cm−3, with an increase directly correlated with the scandium content. In the ScxAl1−xN–AlN heterostructure grown in nitrogen‐rich conditions on AlN–Al2O3 template substrates with Sc contents up to 26 at%, the oxygen concentration is found to be between 1019 and 1021 cm−3, again directly correlated with the Sc content. The increase in oxygen and carbon takes place during the deposition of scandium‐alloyed layers.

Повышение эффективности фильтрации прорастающих дислокаций в темплейтах AlN/c-Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- с фасетированной морфологией поверхности во время их роста методом молекулярно-пучковой эпитаксии

The results of transmission electron microscopy study and X-ray diffraction analysis of AlN/c Al2O3 templates with GaN ultrathin insertions grown by plasma-assisted molecular beam epitaxy are presented. It is shown that AlN buffer layers with faceted surface morphology provide a much higher threading dislocations density reduction then with smooth layers. The filtering action of ultrathin GaN insertions is confirmed.

Synthesis of highly reproducible CdTe nanotubes on anodized alumina template and confinement study by photoluminescence and Raman spectroscopy

Many physical characteristics of semiconducting materials can be finely controlled through template-based nanostructure growth, leading to tuning their properties as well. Reproducible through-hole growth of customised semiconducting nanotubes on Al2O3 (AAO) template is challenging; and therefore, their production methods are of utmost importance. An efficient approach is demonstrated here to remove the sensitive barrier layer from micron thick AAO template keeping base aluminium intact, which serves as an ohmic contact. To prove the effectiveness of this approach, high aspect ratio Cadmium telluride nanotubes (CdTe NTs) having controllable diameter were synthesized using DC electrodeposition. FE-SEM and TEM micrographs illustrate the growth of through-hole nanotubes at each stage of barrier layer etching in AAO template. CdTe nanotubes with an average diameter of 80 nm, grown under various electrolyte baths, have been studied using XRD and Raman spectroscopy. Raman study was done at 77 K to check the confinement effect on multiphonon Raman scattering of LO mode in CdTe NTs. As grown nanotubes show strong luminescence in the visible region with enhanced optical bandgap, and high purity demonstrated by X-ray photoelectron spectroscopy. Excellent specific capacitance of 332 F g-1 at scan rate 100 mV s-1 was found for CdTe-NTs in 6 mol L-1 KOH electrolyte. Efficient photoluminescence (PL) emission and the increase in specific capacitance proved to be worthy for its applications in photovoltaics and energy-storage devices.

Synthesis of Co-Fe Alloy 1D Nanocone Array Electrodes with Aluminum Oxide Template for Water Spliting Reaction.

Nanostructured materials have an enormous application potential because of their novel physical and chemical properties which appear upon reduction of the length scales toward a few nanometer. Among the nano-structured materials, nano-cone arrays have received particular attention in the last years. Due to their specific structure and properties, nano-cones are attractive for very different applications. Producing and designing proper nano-crystalline structures could further improve the catalytic properties and replace expensive precious metals (platinum). Hence, the fabrication of Co alloy nano-cones opens the window to promising applications in the field of electrocatalysis Porous anodic aluminum oxide (AAO) is a popular template for synthesis of ordered arrays of nanostructured materials. By the controlling of anodization conditions or applying an appropriate post-anodization treatment the internal pore structure can be changed. Conical pores can be obtained basing on alternating repetition of the anodization and pore widening process during fabrication of AAO. To obtain free standing metallic nanocones the Al2O3 template was chemically etched in dilute phosphoric acid solution. In this case the process of cobalt electrodeposition was carried out in a two-electrode cell. The working electrode was AAO sample, the anode was a platinum plate. Influence of temperature and H3PO4 and H2SO4 solutions in the first step of anodization was examined. An attempt was made to synthesize Co based alloy nanocones. Acknowledgement This work was financially supported by Polish National Science Center (NCN) under grant UMO-2016/23/G/ST5/04058. The authors would like to acknowledge the COST MP1407 Action for networking.

Effect of flattened surface morphology of anodized aluminum oxide templates on the magnetic properties of nanoporous Co/Pt and Co/Pd thin multilayered films

For the first time, nanoporous Al2O3 templates with smoothed surface relief characterized by flattened interpore areas were used in the fabrication of Co/Pd and Co/Pt multilayers (MLs) with strong ...

Magnetic properties of Co/Pd multilayered films on porous Al2O3 templates with developed cell substructure

We studied the structure and magnetic properties of porous multilayered Co/Pd films deposited on the templates of anodized Al2O3 with a specific surface morphology that is characterized by a cellular–porous structure with several pores inside each cell. X-ray diffraction analysis and reflectometry are used to study the peculiarities of the formation of phases in deposited films. The effect of morphological features of porous Co/Pd films on their magnetoanisotropic properties and magnetization reversal processes (magnetization reversal mechanisms, domain structure of films, and coercive field H c ) is revealed by SQUID magnetometry and magnetic force microscopy.

Analysis of interface formation mechanism in GaN double-polarity selective-area growth by metalorganic vapor phase epitaxy

The fabrication of quasi-phase-matching (QPM) crystals by selective-area growth on the two asymmetrically polar surfaces of GaN is examined. We attempted the fabrication of GaN-QPM crystals by one-time growth using a carbon mask. For GaN double-polarity selective-area growth (DP-SAG), we investigated the effect of varied nitriding times of the Al2O3 templates patterned with the carbon mask. We optimized the nitriding conditions for the DP-SAG process, and evaluated the substrate fabricated by the optimized DP-SAG process. In addition, we examined the interface formation mechanism of DP-GaN fabricated by GaN DP-SAG process. We determined that it is possible to fabricate DP-GaN with a sharp interface by optimizing the growth conditions.

Synthesis of copper nanocone array electrodes and its electrocatalytic properties toward hydrogen peroxide reduction

The copper nanocone (Cu-NC) array electrodes were successfully synthesized by metal sputtering on Al2O3/Al substrate with conical nanopores followed by electrodeposition of Cu. To fabricate the conical pores on aluminum substrate, repeated and alternating anodizations and pore widening treatments were performed. Each anodization step was conducted at 45V in a 0.3M oxalic acid solution at 9°C. After that, the holes were widened by immersion in a 5vol% phosphoric acid solution at 30°C. The effect of different number of alternating anodization-etching cycles on the shape, diameter and height of pores in anodic aluminum oxide (AAO) template was studied. After the electrochemical deposition of Cu, free standing Cu-NC arrays were obtained by chemical etching of Al2O3 templates in dilute phosphoric acid. The dimensions of copper nanocones correspond closely with used Al2O3 templates. The morphology and structural characterization of fabricated Al2O3 templates and Cu-NC arrays were performed. The electrocatalytic activity of the Cu-NC array electrodes toward hydrogen peroxide reduction was investigated.

On-substrate fabrication of porous Al2O3 templates with tunable pore diameters and interpore distances

This work is focused on the on-substrate fabrication of porous aluminum oxide templates by anodization of a thin aluminum film deposited directly on the substrate using different concentrations of oxalic acid. These on-substrate templates are used for fabricating supported, free-standing nanorod (NR)-arrays by electrochemical deposition of Pt followed by the removal of the template. The interpore distance of the templates is tuned by varying the concentration of the electrolyte used for anodization and the applied voltage. The diameter of the pores (and thus the NRs of the resulting array) and wall thickness are influenced by modifying the pore opening time during immersion the sample in H3PO4.

Quantized Acoustic-Phonon Modes in Metallic Nanowire Structures

Abstract We conducted a detailed theoretical study on quantized acoustic-phone modes in metallic nanowile structures. Cylindrical metallic nanowire (NW) structures realized from the state-of-the-art nanotechnology, were used to demonstrate Ni NW embedded in Al2O3 template. The phonon modes were examined by solving the wave equations with corresponding boundary conditions. We find that the quantized phonon energy and the energy spacing between different phonon states increase with decreasing of NW radius. The allowed phonon modes lie below the straight line of qzVAl2O3 in the dispersion relation, and such a feature does not vary significantly with altering of NW radius. This study will be pertinent to the applications of metallic NW systems as high-frequency ultrasonic devices.

Bi2Te3 nanowire array preparation and surface polishing by electrochemical deposition

The quantum confinement effect and phonon scattering in low dimensional nanostructure is effective in the improvement of the efficiency of thermoelectric generators. Bi2Te3 nanowire arrays were prepared in Al2O3 templates through the use of electrochemical deposition. Chemical mechanical planarisation was employed to level the upper and lower surfaces of Bi2Te3 samples. The XRD (X-ray Diffractometer) test showed that the crystal grain of Bi2Te3 nanowire was 20–30 nm, attaining a size where the structural properties of the structure induced the quantum confinement effect. It was also indicated that there were dense structures in the fabricated nanowires, the nanowire ends kept at the same level as the hole's edge, solving the problem for the following assembly of thermoelectric transducers. Based on the procedures presented in this paper, there is promise in the future enhancement of the Seebeck coefficient of this nanowire array by introducing nanodoping to the structure.

The enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Role of TiO2 coated on Al2O3 as a novel support for cinchonidine-modified Pd catalysts

The TiO2-coated Al2O3 composites with various TiO2 wt.% loadings were synthesized by the sol–gel method and were used as supports for the Pd-based catalysts to evaluate the enantiomeric excess (ee) of the hydrogenation of (E)-α-phenylcinnamic acid. The physicochemical properties of the composites and the Pd-based catalysts were characterized. The results reveal the strong influence of the TiO2 wt.% loading on the ee value, which is attributed to the effect of pore diffusion. The 5%TiO2/Al2O3 support, which can diminish most of small mesopores in Al2O3 template while remain most of large mesopores, exhibits the highest ee. Our results demonstrate the promising application of mixed oxides as novel supports to improve ee values of the asymmetric hydrogenation of unsaturated prochiral compounds.