Optical Properties and Durability of Al2O3-NiP/Al Solar Absorbers Prepared by Electroless Nickel Composite Plating

A simple and low-cost method, electroless nickel composite plating, was used to deposit an Al₂O₃-NiP composite coating on an Al substrate to form an Al₂O₃-NiP/Al solar absorber. The effects of the Al₂O₃ content in the Al₂O₃-NiP composite coating, the thickness of the coating, and the use of a double-layer Al₂O₃-NiP composite coating and a TiO₂ antireflection (AR) layer on the optical characteristics of the Al₂O₃-NiP/Al absorbers were studied. The absorptance (α) and thermal emittance (ε) of the Al₂O₃-NiP/Al absorbers increased with the Al₂O₃ content in the Al₂O₃-NiP composite coating and decreased as the thickness of the coating increased. A double-layer Al₂O₃-NiP/Al absorber with 2:1 thickness ratio of the top layer (Al₂O₃-NiP with 25 vol.% Al₂O₃) to the inner layer (Al₂O₃-NiP with 7 vol.% Al₂O₃) had the best optical properties (α/ε = 0.746/0.103). The optimal double-layer Al₂O₃-NiP/Al absorber with a 106-nm-thick TiO₂ AR layer achieved absorptance of 0.893 and thermal emittance of 0.111. The results of a thermal stability test and a condensation test revealed that the TiO₂-coated double-layer Al₂O₃-NiP/Al absorbers had excellent thermal stability, and their failure time in the condensation test exceeded 100 h.     

Flat band voltage modulation of AlGaN/GaN MOS capacitor with stacked Al2O3/La2O3 high dielectric structures

AlGaN/GaN metal-oxide-semiconductor (MOS) capacitor structures using atomic layer deposited high-dielectric-constant (High-k) Al₂O₃/La₂O₃ bilayer films as dielectric have been investigated using high-frequency capacitance-voltage measurement. The stable thickness and uniform surface morphology of the bilayer films with different La/Al deposition cycle ratio (La/Al ratio) were observed after rapid thermal annealing by spectroscopic ellipsometry and atomic force microscopy, respectively. We have found that with a decrease of the La/Al ratio, the dipole layer observed by X-ray photoelectron spectroscopy at Al₂O₃/La₂O₃ interfaces is close to the surface of semiconductor and the flat band voltage shifts to the negative direction. Furthermore, the dramatic drop in dielectric constant of the films as La/Al ratio decrease was caused by the formation of La(OH)₃ in La₂O₃. Finally, the reason for the flat band voltage shifts, which is based on the dielectric constant of Al₂O₃ and La₂O₃ comprising the position of dipole layer in the dielectric films, is proposed.     

UV light activated gas sensor for NO2 detection

In the present study, UV light activated gas sensor was investigated for Al/Al₂O₃/p-Si and Al/TiO₂/Al₂O₃/p-Si samplesby atomic layer deposition method (ALD). Generally, in order to obtain the sensing performance, traditional metal oxide semiconductor gas sensors are operated at 100–400 °C. However, this temperature range limits their applications to flammable gases, and causes high power consumption. It is important to note that sensing performance experiments should have been performed at room temperature. With the support of UV light, gas sensors do not need to be heated and they can work at room temperature easily. For this purpose, electrical measurements have been performed on sensing performance with and without UV irradiation for dedection of NO₂ gas. With the help of UV irradition, we obtained good sensitivity at the room temperature for Al/TiO₂/Al₂O₃/p-Sistructure but under the same conditions no result was obtained for Al/Al₂O₃/p-Si structure. Without UV irradiation, there was no sensitivity for both.We observed that increasing of sensitivities at the room temperature show a direct effect of the light on the adsorbed oxygen ions. According to the relation of photocatalytic reaction and photoactivated gas sensing process, we concluded that TiO₂ might be an acceptable sensor for detection of nitrogen dioxide (NO₂) at room temperature under UV illumination.     

A novel gate insulator for flexible electronics

Field effect transistors using a poly(triaryl amine) p-channel organic semiconductor in conjunction with anodised aluminium oxide as the gate insulator (Al₂O₃ on Al) are demonstrated. Anodised films are pinhole-free, homogenous oxide layers of precisely controlled thickness. The anodisation process requires no vacuum steps; anodised Al₂O₃ is insoluble in organic solvents, and Al films are cheaply available as laminates on flexible substrates. Anodised Al₂O₃ is confirmed to have high gate capacitance (≈60 nF/cm²) and electric breakdown strength (>3 MV/cm in the working device). This property profile answers to the demands on gate insulators for flexible electronics applications.     

Parameters of metal one-electron transistors based on various materials

Limiting parameters (operating temperature and cutoff frequency) and current-voltage characteristics of one-electron transistors based on various metal compounds (Al/AlO_x/Al, Al/SiO₂/Al, Au/Al₂O₃/Au, Nb/Al₂O₃/Nb, Ti/TiO_x/Ti, Cr/Cr₂O₃/Cr, and Nb/NbO_x/Nb) were theoretically studied. Practical recommendations for the choice of materials and structure sizes were formulated. The characteristics were calculated using a SET-NANODEV software package based on the effect of one-electron tunneling and developed for structure simulation according to a technique for estimating the limiting parameters and a two-dimensional numerical model of the metal one-electron transistor.     

Single-domain nickel films for production of graphene

A technique for depositing single-domain heteroepitaxial nickel films onto sapphire substrates is presented. It is demonstrated that high-temperature annealing of these substrates in oxygen alters their near-surface layer in a way that enables the growth of single-domain heteroepitaxial (111) Ni films on a (0001) Al₂O₃ substrate. Single-domain heteroepitaxial (111) Ni films on a (0001) Al₂O₃ substrate, which can be taken as the basis for a technique for fabrication of large-area single-crystalline graphene films, were synthesized for the first time.     

Stack engineering of low-temperature-processing Al2O3 dielectrics prepared by nitric acid oxidation for MOS structure

The electrical characteristics of low-temperature-processing Al₂O₃ films were studied. With an anodization SiO₂ film as a buffer layer, Al₂O₃ dielectric was grown on it by oxidizing an ultra-thin aluminum film in nitric acid, followed by a surface DAC-ANO compensation. The significant development is, when the Al₂O₃ film fabrication of this experiment was repeated, which means one more same Al₂O₃ layer deposition, the sample demonstrated satisfactory electrical properties.     

Study on ta diffusion barrier in Al/Si system

The property of Ta as a diffusion barrier is studied for Al/Ta/Si structure. Interfacial reactions of Al(180 nm)/Ta(130 nm)/Si and Al(180 nm)/Ta(24 nm)/Si, in the temperature range 450∼600°C for 30 min, have been investigated. In Al/Ta(130 nm)/Si system, which is Ta-excess case, Al₃Ta is formed at 500°C. At 575°C, TaSi₂ is formed at the interface of Ta Si. At 600°C, after Al₃Ta decomposes at the interface of Al₃Ta TaSi₂, free Ta is bonded to TaSi₂ with the supply of Si from Si substrate and free Al diffuses through TaSi₂, resulting in Al spiking. In Al/Ta(24 nm)/Si system, which is Al-excess case, Al₃Ta is formed at 500°C. At the same temperature of 500°C, after Al₃Ta decomposes at the interface of Al₃Ta/Si, free Ta reacts with Si to form TaSi₂ and free Al diffuses to Si substrate, resulting in Al spiking. The results of interfacial reactions can be understood from the calculated Al-Si-Ta ternary phase diagram. It can be concluded that the reaction at Al/Ta should be suppressed to improve the performance of Ta diffusion barrier in Al/Si system.     

Highly Conductive Few‐Layer Graphene/Al2O3 Nanocomposites with Tunable Charge Carrier Type

An ex situ strategy for fabrication of graphene oxide (GO)/metal oxide hybrids without assistance of surfactant is introduced. Guided by this strategy, GO/Al₂O₃ hybrids are fabricated by two kinds of titration methods in which GO and Al₂O₃ colloids are utilized as titrant for hybrids of low and high GO content respectively. After sintered by spark plasma sintering, few‐layer graphene (FG)/Al₂O₃ nanocomposites are obtained and GO is well reduced to FG simultaneously. A percolation threshold as low as 0.38 vol.% is achieved and the electrical conductivity surpasses 10³ Sm^?1 when FG content is only 2.35 vol.% in FG/Al₂O₃ composite, revealing the homogeneous dispersion and high quality of as‐prepared FG. Furthermore, it is found that the charge carrier type changes from p‐ to n‐type as graphene content becomes higher. It is deduced that this conversion is related to the doping effect induced by Al₂O₃ matrix and is thickness‐dependent with respect to FG.     

Improved Performance in FeF2 Conversion Cathodes through Use of a Conductive 3D Scaffold and Al2O3 ALD Coating

FeF₂ is considered a promising conversion compound for the positive electrode in lithium‐ion batteries due to its high thermodynamic reduction potential (2.66 V vs Li/Li⁺) and high theoretical specific capacity (571 mA h g^?1). However, the sluggish reaction kinetics and rapid capacity decay caused by side reactions during cycling limit its practical application. Here, the fabrication of Ni‐supported 3D Al₂O₃‐coated FeF₂ electrodes is presented, and it is shown that these structured electrodes significantly overcome these limitations. The electrodes are prepared by iron electrodeposition on a Ni support, followed by a facile fluorination process and Al₂O₃ coating by atomic layer deposition. The 3D FeF₂ electrode delivers an initial discharge capacity of 380 mA h g^?1 at a current density of 200 mA g^?1 at room temperature. The 3D scaffold improves the reaction kinetics and enables a high specific capacity by providing an efficient electron pathway to the insulating FeF₂ and short Li diffusion lengths. The Al₂O₃ coating significantly improves the cycle life, probably by preventing side reactions through limiting direct electrode–electrolyte contact. The fabrication method presented here can also be applied for synthesis of other metal fluoride materials on different 3D conductive templates.     

STUDY OF THE ANODIZATION OF Al FILM ON InP SUBSTRATE AND ITS PROPERTIES

The anodization of Al film on InP substrate and properties of anodic Al_2O_33/InPhave been investigated by AES,DLTS,I-V,C-V and ellipsometer.The results show that theanodic oxide Al_2O_3 has a permittivity of 11～12 and a resistivity of 1.3×10~(13) ohm-cm.Interfacestate density at Al_2O_3/InP is about 10~(11) cm~(-2)·eV~(-1).DLTS reveals that there is a continuouslydistributed interface electron traps at Al_2O_3/InP interface.Anodic Al_2O_3 exhibits good stabilityand electrical properties and could be used for passivation,diffusion mask and gate insulator,etc.     

High‐Performance,Transparent Thin Film Hydrogen Gas Sensor Using 2D Electron Gas at Interface of Oxide Thin Film Heterostructure Grown by Atomic Layer Deposition

A high‐performance, transparent, and extremely thin (<15 nm) hydrogen (H₂) gas sensor is developed using 2D electron gas (2DEG) at the interface of an Al₂O₃/TiO₂ thin film heterostructure grown by atomic layer deposition (ALD), without using an epitaxial layer or a single crystalline substrate. Palladium nanoparticles (≈2 nm in thickness) are used on the surface of the Al₂O₃/TiO₂ thin film heterostructure to detect H₂. This extremely thin gas sensor can be fabricated on general substrates such as a quartz, enabling its practical application. Interestingly, the electron density of the Al₂O₃/TiO₂ thin film heterostructure can be tailored using ALD process temperature in contrast to 2DEG at the epitaxial interfaces of the oxide heterostructures such as LaAlO₃/SrTiO₃. This tunability provides the optimal electron density for H₂ detection. The Pd/Al₂O₃/TiO₂ sensor detects H₂ gas quickly with a short response time of <30 s at 300 K which outperforms conventional H₂ gas sensors, indicating that heating modules are not required for the rapid detection of H₂. A wide bandgap (>3.2 eV) with the extremely thin film thickness allows for a transparent sensor (transmittance of 83% in the visible spectrum) and this fabrication scheme enables the development of flexible gas sensors.     

Formation of aluminum oxide films from aluminum hexafluoroacetylacetonate at 350–450° c

A study of the thermally activated decomposition of Al(hfa)₃ (aluminum hexafluoroacetylacetonate) from the gas phase to form Al₂O₃ on silicon substrates is reported. The decomposition process was carried out in an open tube atmospheric pressure reactor in either argon or oxygen/argon mixtures in the temperature range, 350–450° C. The chemical vapor deposition process resulted in the formation of aluminum oxide films in all instances. The dielectric strength of Al/Al₂O₃/Si capacitors which received a post-metal anneal, but did not receive a high temperature annealing treatment, with aluminum oxide films prepared from Al(hfa)₃ in argon, was found to be in the range 2–6 MV/cm. The difference between the flatband voltage of the MOS structures and the metal-silicon work function difference was positive, indicative of a net negative oxide charge with a density of approximately 3 × 10¹¹ – 3 × 10¹² cm^-2, assuming the charge is located at the oxide-silicon interface. Decomposition of Al(hfa)₃ was also carried out in oxygen/argon mixtures with the oxygen concentration in the range 10–60 vol %. This process led to the deposition of aluminum oxide films with breakdown fields in the range 8–9 MV/cm. However, the flatband voltages of the Al/Al₂O₃/Si capacitors were even more positive than those obtained with Al₂O₃ formed in pure argon. High temperature (800–1000° C) oxygen or nitrogen annealing treatments of alumina films deposited in either argon or oxygen/argon mixtures were evaluated from the point of view of their influence on the oxide film properties. In particular, an annealing process in oxygen at 1000° C for 15 min was found to result in a reduction of the net negative oxide charge, and an improvement of the dielectric strength of films deposited in argon. Films formed in oxygen/argon mixtures did not change appreciably following oxygen annealing, as far as breakdown fields are concerned, but the oxide net negative charge was reduced. As in an earlier study by the authors, of copper film deposition from Cu(hfa)₂, it was found that essentially carbon free films could be obtained under appropriate conditions.     

Ultrastrong Hierarchical Porous Materials via Colloidal Assembly and Oxidation of Metal Particles

Porous materials are useful as lightweight structures, bone substitutes, and thermal insulators, but exhibit poor mechanical properties compared to their dense counterparts. Biological materials such as bone and bamboo are able to circumvent this trade‐off between porosity and mechanical performance by combining pores at multiple length scales. Inspired by these biological architectures, a manufacturing platform that allows for the fabrication of Al₂O₃ foams and Al₂O₃/Al composites with hierarchical porosity and enhanced mechanical properties is developed. Macroscale pores are formed through the assembly of aluminum particles around templating air bubbles in wet foams, whereas the thermal oxidation of the metal particles above 800 °C generates porosity at the micrometer scale. After elucidating the mechanism of pore formation under different sintering conditions at the microscale, the mechanical performance of the resulting hierarchical foams using compression experiments and finite element simulations is evaluated. Porous materials manufactured via this simple approach are found to reach unparalleled mechanical properties with near‐zero sintering shrinkage and minimum loss in mechanical strength. The ability to produce macroscopic objects with ultrahigh strength at porosities up to 95% makes this an attractive manufacturing technology for the fabrication of high‐performance lightweight structures or advanced thermal and acoustic insulators.     

Nanoscale Film Thickness Gradients Printed in Open Air by Spatially Varying Chemical Vapor Deposition

Nanoscale films are integral to all modern electronics. To optimize device performance, researchers vary the film thickness by making batches of devices, which is time-consuming and produces experimental artifacts. Thin films with nanoscale thickness gradients that are rapidly deposited in open air for combinatorial and high-throughput (CHT) studies are presented. Atmospheric pressure spatial atomic layer deposition reactor heads are used to produce spatially varying chemical vapor deposition rates on the order of angstroms per second. ZnO and Al₂O₃ films are printed with nm-scale thickness gradients in as little as 45 s and CHT analysis of a metal-insulator-metal diode and perovskite solar cell is performed. By testing 360 Pt/Al₂O₃/Al diodes with 18 different Al₂O₃ thicknesses on one wafer, a thicker insulator layer (≈7.0 nm) is identified for optimal diode performance than reported previously. Al₂O₃ thin film encapsulation is deposited by atmospheric pressure chemical vapor deposition (AP-CVD) on a perovskite solar cell stack for the first time and a convolutional neural network is developed to analyze the perovskite stability. The rapid nature of AP-CVD enables thicker films to be deposited at a higher temperature than is practical with conventional methods. The CHT analysis shows enhanced stability for 70 nm encapsulation films.     

A Novel Pd Precursor Loaded γ-Al2O3 with Excellent Adsorbent Performance for Ultra-Deep Adsorptive Desulfurization of Benzene

Fabricating highly water-soluble and chlorine-free precursors from Pd complexes remains challenging. Here, a novel Pd precursor (ammonium dinitrooxalato palladium(II) ((NH₄)₂[Pd(NO₂)₂(C₂O₄)]·2H₂O)) is synthesized to address this challenge. Additionally, a Pd/Al₂O₃ adsorbent is prepared using γ-Al₂O₃ as a base material to host Pd. The ligand action of the Pd complex forms single Pd atoms and Pd sub-nano clusters on the surface of γ-Al₂O₃. Pd/Al₂O₃-4 as an adsorbent is evaluated using the benzene ultra-deep desulfurization procedure, wherein thiophene is used as a probe molecule. The sulfur adsorption capacity of Pd/Al₂O₃-4 is 1.76 mg g⁻¹ for the ultra-deep adsorptive desulfurization of benzene at a sulfur concentration of 50 ppm. The sulfur adsorption capacity of the new Pd/Al₂O₃-4 adsorbent is 21.8% higher than that of a commercial Pd/Al₂O₃ adsorbent. In addition, the stability and durability of Pd/Al₂O₃-4 are investigated at a sulfur concentration of 1 ppm. The Pd/Al₂O₃-4 adsorbent achieves ≈100% thiophene removal after 434 h, which is 62 h more than the time required by the commercial Pd/Al₂O₃ adsorbent. The novel Pd precursor shows excellent potential for industrial applications, and the Pd/Al₂O₃-4 adsorbent can be produced on a mass scale of 500 kg per batch.     

Effects of Metal Work Function and Contact Potential Difference on Electron Thermionic Emission in Contact Electrification

Triboelectric nanogenerator (TENG) is a direct measure of the surface charge density, thus providing a novel and powerful tool to study the essential mechanism of contact electrification (CE). A variety of TENGs including a Pt‐Al₂O₃ TENG, Au‐Al₂O₃ TENG, Ti‐Al₂O₃ TENG, Al‐Al₂O₃ TENG, and SiO₂‐Al₂O₃ TENG are prepared in this study. After introducing initial charges on the Al₂O₃ surface of the TENGs, the long‐term evolution of surface charge quantity is investigated at different temperatures. The results show that charge variation of all the TENGs is analogous to exponential decay and is in accord with the thermionic emission model, verifying the electron transfer dominated mechanism of CE. Additionally, it is explored for the first time that the potential barrier of materials can be regulated by changing the contacting metals or dielectrics. Regulation of the barrier at high temperatures fully excludes the influence of ions from moisture and functional groups, which further indicates the dominant role played by electron transfer in CE. Surface state models for explaining barrier regulation during CE for both metal–dielectric and dielectric–dielectric pairs are proposed. This study provides a new perspective of the exploration of CE, and a novel method for further increasing or rapidly eliminating electrification of charged materials.     

Structural and Electrical Properties of Atomic Layer Deposited Al‐Doped ZnO Films

Structural and electrical properties of Al‐doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD‐AZO films exhibit a unique layer‐by‐layer structure consisting of a ZnO matrix and Al₂O₃ dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al₂O₃ dopant layer deposited during one ALD cycle could provide ≈4.5 × 10¹³ cm^?2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD‐AZO films when the interval between the Al₂O₃ layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD‐AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.     

Pt/Al stacked metals gate MESFET

A new InP MESFET structure both with a gate structure of stacked metal and with a active channel of stacked layer is proposed. The gate metals are constituted by a double metal structure, Pt/Al. It improves the barrier height and reduces the reverse leakage current in the MFSFET. This is due to the formation of Al₂O₃, and becoming a Pt/Al/Al₂O₃/InP, metal-insulating-semiconductor structure in the gate region of the transistor. The conductive channel is constituted by a stack-layered structure, a n-InP layer and an i-InP layer. A transfer characteristics of excellent pitch off, and transconductance of 93 mS/mm is derived. It also shows a negative differential resistance effect on the MESFET. The illumination and temperature effect of the transistor are brought into discussed.     

Magnetic,Multilayered Nanotubes of Low Aspect Ratios for Liquid Suspensions

This work presents a synthesis route for low‐aspect‐ratio nanotubes consisting of a layer of magnetite (Fe₃O₄) sandwiched between SiO₂ layers. In this template‐based strategy, self‐ordered porous alumina membranes are combined with the atomic layer deposition of SiO₂ and Fe₂O₃. An optimized electrochemical setup yields nanoporous Al₂O₃ membranes on 4‐inch Al substrates, which serve as templates for the large‐scale fabrication of nanotubes. A selective chemical etching step releases the magnetic tubes for suspension in a carrier fluid and permits recycling of the underlying aluminum foils for the fabrication of subsequent nanotube batches. The nanotubes consisting of an iron oxide layer protected by a silica shell are magnetically characterized in suspensions as well as in dried form on a substrate. High‐resolution transmission electron imaging reveals a polycrystalline, magnetite spinel structure of iron oxide, with the proper stoichiometry proven by the presence of the Verwey transition. Furthermore, field‐dependent viscosity measurements show an enhancement of the magnetoviscosity, thus demonstrating the technological potential of nanotube suspensions as a new class of ferrofluidic solutions. Owing to the tubular shape being closed at one end, these nanoparticles might additionally function as magnetic containers for targeted drug‐delivery or as chemical nanoreactors.