Al2O3/CrAlSiN multilayer coating deposited using hybrid magnetron sputtering and atomic layer deposition

In this study, Al₂O₃/CrAlSiN multilayer coatings with various periods were prepared using a hybrid process involving overlapping magnetron sputtering of CrAlSiN and atomic layer deposition (ALD) of Al₂O₃. The influence of the number of Al₂O₃ layers on the mechanical properties, corrosion behavior and oxidation characteristics of the coatings was studied using nano/micro indentation, electrochemical corrosion, and high temperature static oxidation tests. The results show that the multilayer structure can effectively prevent crack propagation during the coating and subsequently increase the coating toughness. A substantial improvement in the resistance to electrochemical and oxidation corrosion was observed in the Al₂O₃/CrAlSiN multilayer coatings and increasing the number of Al₂O₃ layers dramatically increases the corrosion durability. The Al₂O₃ ALD layers are expected to inhibit the diffusion of corrosive substances such as ions and oxygen and the increase of the Al₂O₃ layer number decreases the diffusion fluxes of the coating elements to the surface and limit the oxide growth, resulting in the evolution of the oxidation produces from irregular particles to nano-walls/fibers. It is supposed that the PVD/ALD hybrid process may open a new hard coating design concept by providing a superior toughness and corrosion/oxidation resistance.     

Atomic layer deposition of Al2O3 thin films on diamond

Atomic layer deposition (ALD) of aluminum oxide thin films on diamond was demonstrated for the first time, and the film properties as a gate insulator for diamond field effect transistor (FET) were examined. The interface between the aluminum oxide and the diamond was abrupt, and the ratio of aluminum to oxygen in the film was confirmed to be stoichiometric by Rutherford back scattering. Even a bumpy surface of polycrystalline diamond film was conformally covered by the Al₂O₃ films. To evaluate the feasibility of the film for FET gate insulator, the electrical characteristics of the Al₂O₃ films deposited by ALD on diamond were measured using metal–insulator–semiconductor structure. It was found that the Al₂O₃ films deposited by ALD were better than those deposited by conventional methods, which indicates that the ALD-Al₂O₃ films are feasible for gate insulators of diamond FETs.     

Electrical characterization of ZnO-based thin film nanodiodes fabricated through atomic layer deposition: Effect of electron beam irradiation on interfacial property

ZnO thin films were deposited onto p-type (P-Si) Si wafers using atomic layer deposition. The rectifying performance of the deposited ZnO thin films was confirmed by current–voltage characteristics. P-Si/ZnO-based nanodiodes were subjected to electron irradiation. Depending on the irradiation conditions, the diode performance changed significantly. At 0.8 MeV, the diode was degraded in terms of both forward and reverse currents. At 2.5 MeV, the reverse current in the nanodiode decreased and the forward current increased, leading to significant enhancement in the current ratio. The electrical response was monitored using impedance spectroscopy. Impedance analysis indicated that depletion regions are significantly affected by electron irradiation.     

Atmospheric pressure spatial ALD of Al2O3 thin films for flexible PEALD IGZO TFT application

Atmospheric pressure spatial atomic layer deposition (AP S-ALD)-derived Al₂O₃ films were investigated on the growth temperatures (100 °C ～ 200 °C) and demonstrated as the gate insulator for IGZO thin film transistor (TFT) applications. When the growth temperature increases to 200 °C, growth per cycle (GPC) and refractive index of the Al₂O₃ films were 1.33 Å/cycle and 1.63, respectively. The film density also increased from 2.55 g/cm³ to 2.79 g/cm³ on the growth temperature, which decreasing the carbon impurities of the Al₂O₃ film (100 °C: 3.57 at%, 150 °C: 1.73 at%, 200 °C: N/A). In addition, the impurity and low growth temperature may degrade not only film surface roughness, but also electrical characteristics. As the buffer and gate insulator Al₂O₃ layers, the IGZO TFT were fabricated on a polyimide substrate. The IGZO TFTs with the Al₂O₃ layers showed excellent device performances: 52.48 cm²/V.sec of field effect mobility, ?3.09 ± 0.14 of threshold voltage, and 0.14 ± 0.01 subthreshold swing. In addition, the TFT exhibited excellent bias reliability and mechanical bending stability. This highly stability will be attributed to AP S-ALD Al₂O₃ acting as an excellent insulator.     

Fabrication of graphene oxide reinforced plasma sprayed Al2O3 coatings

Graphene oxide (GO) reinforced Al₂O₃ ceramic coatings were prepared on the surface of medium carbon steel by plasma spraying. The microstructure of the raw materials and coatings were characterized and analyzed by XPS, XRD, Raman and SEM. The bonding strength of the coatings was studied using a scratch method. The wear resistance of the coatings was assessed by the sliding test. The results showed that, after adding GO, the porosity of the coating reduced by about 31%, the hardness increased by approximately 10%, the bonding strength improved by 250%, and the wear rate reduced by 81% (Load: 30 N) and 84% (Load: 60 N), respectively.     

Atomic layer deposition of Al2O3 on porous polypropylene hollow fibers for enhanced membrane performances

Porous polypropylene hollow fiber (PPHF) membranes are widely used in liquid purification.However,the hydrophobicity of polypropylene (PP) has limited its applications in water treatment.Herein,we demonstrate that,for the first time,atomic layer deposition (ALD) is an effective strategy to conveniently upgrade the filtration performances of PPHF membranes.The chemical and morphological changes of the deposited PPHF membranes are characterized by spectral,compositional,microscopic characterizations and protein adsorption measurements.Al2O3 is distributed along the cross section of the PP hollow fibers,with decreasing concentration from the outer surface to the inner surface.The pore size of the outer surface can be easily turned by altering the ALD cycles.Interestingly,the hollow fibers become much more ductile after deposition as their elongation at break is increased more than six times after deposition with 100 cycles.The deposited membranes show simultaneously enhanced water permeance and retention after deposition with moderate ALD cycle numbers.For instance,after 50 ALD cycles a 17％ increase in water permeance and one-fold increase in BSA rejection are observed.Moreover,the PP membranes exhibit improved fouling-resistance after ALD deposition.     

Effect of graphene addition on the mechanical and electrical properties of Al2O3-SiCw ceramics

This paper presents a study on graphene-reinforced Al₂O₃-SiCw ceramic composites and the relationship between graphene oxide (GO) loading and the resulting mechanical and electrical properties. Well-dispersed ceramic-GO powders were fabricated using a colloidal processing route. Dense composites were obtained via spark plasma sintering, a technique that has the ability to reduce GO to graphene in situ during the sintering process. The mechanical properties of the sintered composites were investigated. The composite with only a small amount of graphene (0.5 vol.%) showed the highest flexural strength (904 ± 56 MPa), fracture toughness (10.6 ± 0.3 MPa·m^1/2) and hardness (22 ± 0.8 GPa) with an extremely good dispersion of graphene within the ceramic matrix. In addition to these exceptional mechanical properties, the sintered composites also showed high electrical conductivity, which allows the compacts to be machined using electrical discharge machining and thus facilitates the fabrication of ceramic components with sophisticated shapes while reducing machining costs.     

Induction of ferroelectricity in nanoscale ZrO2 thin films on Pt electrode without post-annealing

Large stable ferroelectricity in nanoscale undoped zirconia (ZrO₂) thin films prepared without post-annealing has been demonstrated for the first time. Remanent polarizations up to 12 μC cm⁻² were obtained in the as-deposited ZrO₂ thin films prepared by remote plasma atomic layer deposition at 300 °C substrate temperature on the Pt electrode. Ferroelectric crystallization of the films was achieved without post-annealing, which is highly beneficial to the application of the films in non-volatile memories and ultralow-power nanoelectronics. The existence of the ferroelectric orthorhombic phase with noncentrosymmetric space group Pbc2₁ in the as-deposited ZrO₂ thin films was confirmed by high-resolution transmission electron microscopy.     

Low temperature atomic layer deposition of SiO2 thin films using di-isopropylaminosilane and ozone

Silicon dioxide (SiO₂) films are deposited by atomic layer deposition (ALD) at low temperatures from 100 to 200 °C using di-isopropylaminosilane (SiH₃N(C₃H₇)₂, DIPAS) as the Si precursor and ozone as the reactant. The SiO₂ films exhibit saturated growth behavior confirming the ALD process, showing a growth rate of 1.2 Å/cycle at 150 °C, which increases to 2.3 Å/cycle at 250 °C. The activation energy of 0.24 eV, extracted from temperature range of 100–200 °C, corresponds to the reported energy barrier for reaction between DIPAS and surface –OH. The temperature dependence of the growth rate can be explained in terms of the coverage and chemical reactivity of the thermally activated precursor on the surface. The ALD-SiO₂ films deposited at 200 °C show properties such as refractive index, density, and roughness comparable to those of conventionally deposited SiO₂, as well as low leakage current and high breakdown field. The fraction of Si–O bond increases at the expense of Si–OH at higher deposition temperature.     

Electronic properties of thermally formed thin iron oxide films

The oxide layer, present between an organic coating and the substrate, guarantees adhesion of the coating and plays a determinating role in the delamination rate of the organic coating. The purpose of this study is to compare the resistive and semiconducting properties of thermal oxides formed on steel in two different atmospheres at 250 °C: an oxygen rich atmosphere, air, and an oxygen deficient atmosphere, N₂. In N₂, a magnetite layer grows while in air a duplex oxide film forms composed by an inner magnetite layer and a thin outer hematite scale. The heat treatment for different amounts of time at high temperature was used as method to sample the thickness variation and change in electronic and semiconducting properties of the thermal oxide layers. Firstly, linear voltammetric measurements were performed to have a first insight in the electrochemical behavior of the thermal oxides in a borate buffer solution. Electrochemical impedance spectroscopy in the same buffer combined with the Mott-Schottky analysis were used to determine the semiconducting properties of the thermal oxides. By spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), respectively, the thickness and roughness of the oxide layers were determined supporting the physical interpretation of the voltammetric and EIS data. These measurements clearly showed that oxide layers with different constitution, oxide resistance, flatband potential and doping concentration can be grown by changing the atmosphere.     

Degradation of La0.6Sr0.4CoO3-based cathode performance in solid oxide fuel cells due to the presence of aluminum oxide deposited through atomic layer deposition

Aluminum oxide was deposited into the porous cathode compartment of the (Sc,Al)-doped ZrO₂ electrolyte cell through atomic layer deposition involving trimethyl aluminum and water as aluminum and oxygen sources, respectively. The deposited aluminum oxide had a detrimental effect on the cell performance of the zirconia-based SOFC unit cells in terms of the output power but did not change the open-cell voltage. Based on impedance spectroscopy, the open-cell voltage, and the output performance, the resultant degradation is attributed to the geometrical blockade of functional triple phase boundaries in La_0.6Sr_0.4CoO₃ (LSCo)-based cathode materials of mixed ionic electronic conduction, indicating that there is a disruption at the interface between the charge collector and cathode that is proportional to the amount of deposited Al₂O₃.     

Comparative study of the electrical characteristics of ALD-ZnO thin films using H2O and H2O2 as the oxidants

ZnO thin films were deposited via atomic layer deposition (ALD) using H₂O and H₂O₂ as oxidants with substrate temperatures from 100°C to 200°C. The ZnO films deposited using H₂O₂ (H₂O₂-ZnO) showed lower growth rates than those deposited with H₂O (H₂O-ZnO) at these temperature range due to the lower vapor pressure of H₂O₂, which produces fewer OH⁻ functional groups; the H₂O₂-ZnO films exhibited higher electrical resistivities than the H₂O-ZnO films. The selection of H₂O₂ or H₂O as oxidants was revealed to be very important for controlling the electrical properties of ALD-ZnO thin films, as it affected the film crystallinity and number of defects. Compared to H₂O-ZnO, H₂O₂-ZnO exhibited poor crystallinity within a growth temperature range of 100-200°C, while H₂O₂-ZnO showed a strong (002) peak intensity. Photoluminescence showed that H₂O₂-ZnO had more interstitial oxygen and fewer oxygen vacancies than H₂O-ZnO. Finally, both kinds of ZnO thin films were prepared as transparent resistive oxide layers for CIGS solar cells and were evaluated.     

High temperature failure modes of In2O3 thin films and improved thermal stability using Al2O3/ZrO2 protective layers

The limiting temperature of an In₂O₃ thin film sensor is much lower than its melting point. Herein, the failure modes of In₂O₃ thin films at high temperatures, including sublimation and changes in composition, have been studied. The edge and surface layer sublimation rates increased dramatically at 1350 °C, indicating that it is the limiting temperature of no-protection In₂O₃ films. In addition, oxygen atoms will escape from In₂O₃ thin films at high temperatures, forming oxygen vacancies. As the main current carrier type in In₂O₃, the increasing number of oxygen vacancies affects the resistance of In₂O₃ thin film sensors. To solve these problems and promote the high temperature performance of In₂O₃ thin films, protection methods based on Al₂O₃ and ZrO₂ layers have been investigated. The ZrO₂ protective layer alleviated the serious considerable sublimation of In₂O₃ thin films at high temperatures, and the Al₂O₃ protective layer was beneficial for reduction the escape of oxygen atoms. Finally, different protection layers were evaluated by in-situ resistivity measurements of In₂O₃ thin films at high temperatures. The resistance of the In₂O₃ thin film resistor with a protective multilayer consisting of Al₂O₃ and ZrO₂ remained stable at 1360 °C, verifying the protection method effectively increased the thermal stability of In₂O₃ thin films.     

Influence of substrate temperature on the properties of (AlGa)2O3 thin films prepared by pulsed laser deposition

(AlGa)₂O₃ thin films were deposited on (0001) sapphire substrates by pulsed laser deposition at different substrate temperatures. The influence of substrate temperature on surface morphology, optical properties, and crystal quality has been systematically investigated by atomic force microscope, transmission spectra, X-ray diffraction, and Raman spectroscopy. The results reveal that all the (AlGa)₂O₃ films have smooth surface and high transmittance. The (AlGa)₂O₃ film with the good crystal quality can be obtained at a substrate temperature of 400 °C. Our results provide an experimental basis for realizing the Ga₂O₃-based quantum well.     

Enhancing the thermoelectric properties of super-lattice Al2O3/ZnO atomic film via interface confinement

Aluminum oxide (Al₂O₃)/zinc oxide (ZnO) thin films deposited via atomic layer deposition (ALD) are demonstrated to enhance their thermoelectric properties by manipulating them with a nano-thick Al₂O₃ interface. The overall superlattice structure is tuned by varying the ZnO ALD sequence and the Al₂O₃ ALD sequence while maintaining the same composition. An aluminum-doped zinc oxide (AZO) thin film is deposited at 250 °C, and the Al₂O₃ thickness in the superlattice is gradually increased from 0.13 nm to 1.23 nm. The total film composition is fixed at 2% AZO. We observe that an efficient superlattice structure is made with a specific Al₂O₃ thickness. The thermal conductivity is significantly decreased from 0.57 W/mK to 0.26 W/mK as the thickness of the Al₂O₃ layer is increased. Additionally, the absolute Seebeck coefficient is increased from 14 μV/K to 65 μV/K. This may be caused by the interface confinement effect and interface scattering between the ZnO layer and the Al₂O₃ layer. The figure of merit ZT value is 0.14 for the most efficient structure.     

Tailoring UV emission from a regular array of ZnO nanotubes by the geometrical parameters of the array and Al2O3 coating

Self-aligned and equal-spaced zinc oxide (ZnO) nanotube arrays were fabricated with anodic aluminum oxide (AAO)-assisted growth and the ALD technique. The near band-edge (NBE) emission was strongly affected by the nanotube's geometrical parameters, such as a packing density and thickness of the nanotube walls. The NBE emission was further enhanced with Al₂O₃ coating. The effect was analyzed by X-ray photoelectron spectroscopy (XPS) and ascribed to the surface defect passivation and a ZnAl₂O₄ spinel formation. The NBE emission enhancement was greater in ZnO nanotubes with thicker walls. A smaller UV enhancement factor was explained by less uniform and integral Al₂O₃ coverage of the ZnO nanotubes with thinner walls; this, possibly induced a variation of the Al₂O₃ refractive index along the nanotubes. As a result, the optical conditions at the ZnO/Al₂O₃/air interfaces was changed and the light extraction efficiency was reduced in the latter samples.     

AC,DC conduction and dielectric behaviour of solid and liquid phase sintered Al2O3-15 mol% V2O5 pellets

Microstructural and dielectric characterization of porous Al₂O₃-V₂O₅ pellets sintered under both solid (600 °C) and liquid phase (850 °C) conditions are reported. The low temperature solid state sintering (SSS) leaves a very porous network of dense alumina particles surrounded by smaller facetted vanadia, whereas under liquid phase sintering (LPS), the V₂O₅ melts and recrystallizes over the relatively inert Al₂O₃, leading to a connected network structure. The ac conductivity and dielectric parameters of the pellets investigated from room temperature (RT) to 400 °C exhibited both universal dielectric (diffusive) behaviour at low frequencies and nearly constant loss (sub-diffusive) regimes at low temperatures. Activation energies calculated for dc/ac conduction at different frequencies suggests a composite conduction mechanism controlled by the Vanadia phase: at low frequencies, the calculated energies (E_a≈0.5 eV) compare with ionic diffusion of vanadium in V₂O₅, while at high frequencies and low temperatures an additional (E_a≤0.16 eV) polaronic hopping mechanism is seen. This cross-over frequency is significant for the LPS specimen indicating that the vanadia connected network assists conduction by providing a continuous (but disordered) diffusion route. Impedance and modulus spectral analysis show the presence of distributed time constants arising from electrodes, pore/matrix and phase interfaces and GBs.     

Atomic layer deposition and characterization of Bi1Se1 thin films

Van der Waals (vdWs) heterostructured materials have attracted considerable interest due to their intriguing physical properties. Here, we report on the deposition of BiSe by atomic layer deposition (ALD) using Bi(NMe₂)₃ and Se(SnMe₃)₂ as volatile and reactive Bi and Se precursors, respectively. The growth rate varies from 1.5 to 2.0 Å/cycle in the deposition temperature range of 90–120 °C. Higher deposition temperatures lead to increased grain sizes and enhanced crystallinity of resulting films. Further microstructure characterization reveals the formation of crystalline domains with varying orientations and nanotwinned boundaries. The presence of Bi-Bi zigzag bilayers and the formation of the BiSe phase were confirmed by the existence of the Bi-Bi binding energy peak in the XPS spectra and Raman spectra. Furthermore, the electrical conductivity of BiSe ranged from 1420 to 1520 S/cm due to the ultrahigh carrier concentration (2–3.5 × 10²¹ cm⁻³), which is the highest among undoped bismuth selenide-based materials.     

The effect of homogeneously dispersed few-layer graphene on microstructure and mechanical properties of Al2O3 nanocomposites

Fully dense few-layer graphene (FG)/Al₂O₃ nanocomposites with homogeneously dispersed FG in matrix are prepared by using a heteroaggregation method followed by spark plasma sintering. It is found that the two dimensional FG has great ability to restrain grain growth in comparison to other inclusions. In addition, the morphology of grain in composite is modified by the addition of FG during densification process compared with monolithic alumina. Thanks to the greatly decreased grain size, the composites are almost as hard as monolithic alumina at low sintering temperature (1573 K) even if graphene content is as high as 1.2 vol.%. However, at higher sintering temperature (1673 K), the hardness of composites decreases further but the change in elastic modulus is very limited. The decline of hardness and elastic modulus mainly arises from the sliding feature of FG, low modulus of reduced graphene oxide in both in-plane and out-of-plane directions.     

Nonlinear growth of zinc tin oxide thin films prepared by atomic layer deposition

Zinc tin oxide (ZTO) thin films can be deposited by atomic layer deposition (ALD) with adjustable electrical, optical and structural properties. However, the ternary ALD processes usually suffer from low growth rate and difficulty in controlling film thickness and elemental composition, due to the interaction of ZnO and SnO₂ processes. In this work, ZTO thin films with different Sn levels are prepared by ALD super cycles using diethylzinc, tetrakis(dimethylamido)tin, and water. It is observed that both the film growth rate and atom composition show nonlinear variation versus [Sn]/([Sn]+[Zn]) cycle ratio. The experimental thickness measured by spectroscopic ellipsometry and X-ray reflectivity are much lower than the expected thickness linearly interpolated from pure ZnO and SnO_x films. The [Sn]/([Sn]+[Zn]) atom ratios estimated by X-ray photoelectron spectroscopy have higher values than that expected from the cycle ratios. Hence, to characterize the film growth behavior versus cycle ratio, a numerical method is proposed by simulating the effect of reduced density and reactivity of surface hydroxyls and surface etching reactions. The structure, electrical and optical properties of ZTO with different Sn levels are also examined by X-ray diffraction, atomic force microscope, Hall measurements and ultraviolet–visible–infrared transmittance spectroscopy. The ZTO turns out to be transparent nanocrystalline or amorphous films with smooth surface. With more Sn contents, the film resistivity gets higher (>1 Ω cm) and the optical bandgap rises from 3.47 to 3.83 eV.