Atomic Layer Deposition Layers Research Articles

Micromachining of Al2O3 thin films via laser drilling and plasma etching for interfacing copper

Due to their chemical inertness and high-temperature stability, atomic layer deposited (ALD) oxide thin films emerged as an attractive copper encapsulation, passivation, and protection technology. Several types of high-k dielectrics, which are robust insulators, can be deposited by ALD. Hence, a successful encapsulation process electrically isolates the underlying film and active elements from the environment, as a side effect. To electrically interface such encapsulated structures, a reliable method that selectively and locally removes the encapsulation film is required. Here, the study focused on the effectiveness of laser drilling and plasma etching of Al2O3 thin films deposited via ALD, both in silico and experimentally. Results have shown that the CO2 laser drilling alone is insufficient to remove the Al2O3 thin films. However, plasma etching successfully removes the encapsulation layer, providing a clean interface for conductive vias. Results are essential for future ALD layer applications in the encapsulation of copper and other critical components in semiconductor fabrication processes.

Atomic Layer Deposition on Polymer Thin Films: On the Role of Precursor Infiltration and Reactivity.

Inorganic barriers grown by atomic layer deposition (ALD) can overcome the stability issues originating from the permeation of foreign species (water and oxygen) into polymer thin films. Alternatively, infiltration of ALD species into the bulk of the polymer can be used to modify its characteristic properties. In this study, the feasibility of growing an inorganic barrier with ALD on polystyrene, poly(methyl methacrylate), and poly(ethylene terephthalate glycol) thin films is evaluated. The nucleation and growth of the ALD layer, including the infiltration into the polymer thin film, are monitored in situ using spectroscopic ellipsometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy for Al2O3-ALD with trimethylaluminum as the Al precursor and H2O as the reactant. The results show that the deposition temperature and the presence and location of functional groups in the polymer chain exert the strongest influence on the infiltration behavior and as such allow us to manipulate (i.e. to prevent or expedite) the infiltration into the polymer thin film.

The roles of atomic layer deposition (ALD) coatings on the stability of FeF3 Na-ion cathodes

Atomic layer deposition (ALD) has been used to stabilize Na-ion battery (SIB) electrodes but the role of ALD coatings and the mechanism of the improvements remain unclear, particularly in conversion-type cathodes. Here, we study for the first time the influence of alumina and titania (Al2O3 and TiO2) ALD coatings on conversion FeF3 cathodes in SIBs. Post-mortem analysis revealed that active material in both samples developed a small fraction of iron oxyfluoride (FeOF) during cycling. Similarly, the in-situ fluorination of both ALD oxide coatings led to the formation of aluminum and titanium oxyfluorides. The aluminum oxyfluoride formed a conformal passivating layer that was well adhered to the cathode electrolyte interphase (CEI). As a result, the Al2O3 coating reduced direct contact between the active material and the liquid electrolyte, minimized active material dissolution and significantly improved the overall electrochemical performance of FeF3 cathodes in SIBs. In contrast, the in-situ fluorination of the TiO2 ALD layer failed to produce a defect-free passivating layer and was inefficient in preventing side reactions, leading to the inferior performance.

Structure and Properties of TiO2/nanoTiO2 Bimodal Coatings Obtained by a Hybrid PVD/ALD Method on 316L Steel Substrate.

This paper presents the synergy of the effect of two surface engineering technologies—magnetron sputtering (MS-PVD) and atomic layer deposition (ALD) on the structure and properties of 316L steel. Recent studies indicate that PVD coatings, despite their thickness of a few micrometers, have many discontinuities and structural defects, which may lead to pitting corrosion after time. Applying an ALD layer to a PVD coating seals its structure and contributes to extending the service life of the coating. Investigations of the structure and morphology of the produced layers were carried out using a scanning electron microscope (SEM) and atomic force microscope (AFM). In addition, the structure of the coatings was investigated on the cross-section using a scanning-transmission electron microscope S/TEM. The tribological properties of the materials studied were determined by the ball-on-disc method. The corrosion resistance of the tested materials was determined by the electrochemical potentiodynamic method by recording the polarization curves of the anodes. Additional information about the electrochemical properties of the tested samples, including the quality, their tightness, and their resistivity, was obtained by electrochemical impedance spectroscopy (EIS). In addition, the main mechanisms of corrosion and tribological wear were determined by SEM observations after corrosion tests and after tribological tests. The study showed that the fabrication of hybrid layers by MS-PVD and ALD techniques allows obtaining coatings with electrochemical properties superior to those of layers fabricated by only one method.

Ultraflat Sub-10 Nanometer Gap Electrodes for Two-Dimensional Optoelectronic Devices.

Two-dimensional (2D) materials are promising candidates for building ultrashort-channel devices because their thickness can be reduced down to a single atomic layer. Here, we demonstrate an ultraflat nanogap platform based on atomic layer deposition (ALD) and utilize the structure to fabricate 2D material-based optical and electronic devices. In our method, ultraflat metal surfaces, template-stripped from a Si wafer mold, are separated by an Al2O3 ALD layer down to a gap width of 10 nm. Surfaces of both electrodes are vertically aligned without a height difference, and each electrode is ultraflat with a measured root-mean-square roughness as low as 0.315 nm, smaller than the thickness of monolayer graphene. Simply by placing 2D material flakes on top of the platform, short-channel field-effect transistors based on black phosphorus and MoS2 are fabricated, exhibiting their typical transistor characteristics. Furthermore, we use the same platform to demonstrate photodetectors with a nanoscale photosensitive channel, exhibiting higher photosensitivity compared to microscale gap channels. Our wafer-scale atomic layer lithography method can benefit a diverse range of 2D optical and electronic applications.

Atomic layer deposition of hafnium and zirconium oxyfluoride thin films

Hafnium and zirconium oxyfluoride films may act as effective protective coatings during plasma processing. The low molar volume expansion/contraction ratios and the small estimated strain values versus fluorination/oxidation suggest that hafnium and zirconium oxyfluorides can serve as protective coatings in both fluorine and oxygen plasma environments. To demonstrate the procedures for depositing these films, hafnium and zirconium oxyfluorides with tunable stoichiometry were grown using atomic layer deposition (ALD) at 150 °C. Tetrakis(dimethylamido)hafnium and tetrakis(ethylmethylamido)zirconium were used as the metal precursors. H2O and HF were employed as the oxygen and fluorine precursors, respectively. MOxFy (M = Hf and Zr) films were grown using two deposition mechanisms: the nanolaminate method and the HF exchange method. In situ quartz crystal microbalance studies were employed to monitor the MOxFy growth. Both deposition methods observed a linear MOxFy growth at 150 °C. The nanolaminate method is defined by the sequential deposition of MOx ALD and MFy ALD layers. Compositional tunability was achieved by varying the ratio of the number of MOx ALD cycles to the number of MFy ALD cycles in the nanolaminate. The HF exchange method is based on the thermodynamically favorable fluorination reaction of MOx by HF. Variable oxygen-to-fluorine concentrations in these films were obtained either by changing the HF pressure or by varying the thickness of the underlying MOx ALD layers. Ex situ Rutherford backscattering spectroscopy measurements were utilized to determine the composition of the various MOxFy thin films. Both deposition techniques displayed a wide range of compositional tunability from HfO2 to HfF4 and ZrO2 to ZrF4. In addition, the physical sputtering rates of MOxFy films were estimated from the film removal rates during ex situ x-ray photoelectron spectroscopy depth profiling. The physical sputtering rates increased with F concentration in the MOxFy films.

Surface passivation of organometal halide perovskites by atomic layer deposition: an investigation of the mechanism of efficient inverted planar solar cells.

Interface passivation plays a pivotal role in achieving high-efficiency organic metal halide perovskite solar cells (PSCs). It has been recently revealed that atomic layer deposition (ALD) of wide-band gap oxides shows great potential to effectively passivate defects at the interface, and ALD is also of great technological promise for industrial upscaling. However, the conflicting observations of ALD passivation are often reported in the literature, even with very similar ALD conditions. To unveil the involved crucial mechanism, this work carefully investigates the evolution of a representative MAPbI3 perovskite surface during the ALD of Al2O3, by employing the technique of in situ X-ray photoelectron spectroscopy. The ALD at 125 °C was found to cause significant degradation of the perovskite; lowering the deposition temperature can largely minimize the degradation, and 75 °C was found to be the best ALD temperature. Following this conclusion, inverted planar perovskite solar cells were prepared in ambient conditions with ALD Al2O3 interlayers. Indeed, cells with the interlayer deposited at 75 °C exhibited a significantly enhanced power conversion efficiency from 18.8% (champion 19.2%) to 20.0% (champion 20.4%). Photoluminescence measurements further evidence that the ALD layer can effectively passivate defect states at the perovskite surface. Considering the great representativeness and broad applicability of MAPbI3 and ALD Al2O3, the mechanism and strategy reported herein should be of significant value for the perovskite interface engineering in general.

Flexible to rigid: IR spectroscopic investigation of a rhenium-tricarbonyl-complex at a buried interface.

This work explores the solid-liquid interface of a rhenium-tricarbonyl complex embedded in a layer of zirconium oxide deposited by atomic layer deposition (ALD). Time-resolved and steady state infrared spectroscopy were applied to reveal the correlations between the thickness of the ALD layer and the spectroscopic response of the system. We observed a transition of the molecular environment from flexible to rigid, as well as limitations to ligand exchange and excited state quenching on the embedded complexes, when the ALD layer is roughly of the same height as the molecules.

(Invited) ALD Enabling High-Efficiency Solar Cells

Atomic layer deposition (ALD) can synthesize materials with atomic-scale precision. The ability to tune the material composition, film thickness with excellent conformality, low-temperature processing, and in-situ real-time monitoring makes this technique very appealing for a wide range of applications. In this contribution, we will show that ALD is already widely used in the manufacturing of industrial silicon solar cells, where ALD aluminum oxide is used for the passivation of the rear of PERC (Passivated Emitter and Rear Contact) solar cells. ALD aluminum oxide layers can also be used to reduce the contact resistance and firing temperature for phosphorous diffused surfaces. We will show that ALD layers can also avoid potential induced degradation (PID, a possible failure mode for large photovoltaic systems) at the solar cell level. ALD capping layers can also be used to reduce light and elevated temperature induced degradation (LeTID), which is a recently identified failure mode for high-efficiency solar cells, by acting as a blocking layer for hydrogen. Finally, we will show that ALD layers are enabling world-record CZTS (copper-zinc-tin-sulphide) solar cells.

Single and Multilayer Atomic Layer Deposition on and into Mesoporous Silicon Layers

Surface functionalization and pore filling of porous layers are essential key aspects for successful application of complex porous matrices. Atomic layer deposition (ALD) in deep macroporous trenches with high aspect ratio using different coating materials was investigated for a wide field of applications, such as energy storage, catalysis, and membrane technology1-3. Experimental data for ALD into mesopores, especially in the low mesoporous range (up to 20 nm) are rare4, 5. ALD on and into mesoporous silicon layers has different functions: 1st Surface passivation (sealing) of the underlying mesoporous structures, such as electrical barrier, diffusion barrier or corrosion protection. In this case complete pore filling is necessary to avoid transport processes through the passivated mesoporous interface. 2nd Pore size reduction (narrowing), i.e. adjustment of pore size for mesoporous membranes or single pores, e.g. for universally applicable, label-free, and nanopore-based sensor systems for the detection of small molecules in the nanofiltration range. Additionally, pore narrowing can be used for fine tuning of porous silicon-based sensors or optical filter properties5. 3rd Surface functionalization, e.g. in biomimetic or bioinspired systems or in fuel cells as catalytic layer.This contribution gives an extensive investigation of single and multi-layer depositions on and into mesoporous silicon layers and analyzes the material distribution and penetration profile of the corresponding atomic compositions.Mesoporous silicon layers were fabricated using highly doped (0.01-0.02 Ωcm) p-type substrates. Electrochemical etching (anodization) was performed in a mixture of 50 m% HF and absolute ethanol in volume ratio 1:1, to generate a 5 µm thick mesoporous layer. A current density of 70 mA/cm2 was used. 48 % porosity was measured by gravimetric technique. Nitrogen adsorption-desorption isotherms were measured in a Belsorp-mini from Rubotherm/Bel GmbH at 77 K using native porous silicon layers. Pore radius (rp) and pore radius distribution were evaluated using Barrett-Joyner-Halenda (BJH) theory. An average pore size radius of 4.68 nm, and pore radius range up to 12 nm were measured. However, surface oxidation will change the layer morphology, especially the pore size, porosity, and specific surface area.The layer deposition process was carried out with different ALD single layers, such as thermal Al2O3, plasma TiO2, thermal HfO2, thermal ZnO, and layer combinations as multilayer ALD, such as plasma Al2O3/TiO2 in an Oxford FlexAl reactor. Typical ALD cycle consists of two half-cycles, sequential precursor and co-reactant doses, which are separated by purge and pump steps, leading to self-limited layer growth6. Co-reactants and oxidizers are typically oxygen sources (H2O or oxygen plasma). When using an oxygen-containing medium, vacuum oxidation occurs, which leads to partial oxidation of the huge inner surface of the mesoporous layer5.Characterization of ultrathin layer deposited in complex 3D mesoporous structures is challenging and demands special analysis methods. In our experiments the penetration depth and depth distributions of atomic compositions for different ALD single and multilayers were measured using secondary neutral mass spectrometry (SNMS). Fig. 1 shows one example of the material distribution for Al2O3 atomic compositions on silicon substrate (Fig. 1a) and on and into mesoporous silicon substrate (Fig. 1b) with the same nominal Al2O3 layer thickness of 96.89 nm, which was measured on the silicon substrate with a Woollan M-2000FTM ellipsometer. The influence of both half-cycles of the ALD process must be considered at the evaluation, both the deposition effect on and into mesoporous silicon layers, and the transformation of the inner pore surface by oxidation. In the mesoporous layer the Al atomic composition profile follows the initial Al atomic profile up to 110 nm and subsequently shows a decreasing tendency up to 225 nm. The O atomic composition shows a decreasing tendency from 125 nm to 225 nm, and a saturation at 3.5 atomic percent. The existence of O in the deeper (>250 nm) mesoporous layers (Fig. 1b) indicates the partial oxidation of the underlying mesoporous layer occurring mainly during the H2O dose half-cycle process sequence. Penetration depths and profiles will be presented for the investigated single ALD layer. Further experimental results show that for multilayer ALD, e.g. with Al2O3/TiO2 layer combination, the first ALD-layer of the multilayer and its specific properties are dominating in the pore filling of the mesoporous layer.

Electrical Characteristics of Atomic Layer Deposited Y-Silicate Dielectrics

Introduction High k dielectric materials are widely used for scaling the equivalent oxide thickness (EOT) of various very large integrated devices. Rare-earth silicates maintain their amorphous structure within the temperature range of typical semiconductor processes [1] , making them suitable for high-k dielectrics. Rare-earth silicates are easily formed by thermal processes, but their formation consumes Si at the interface. The consumption of Si at the interface is disadvantageous for micro-structured devices such as three-dimensional structures. One of the methods to suppress Si consumption at the interface is to supply Si atoms in the deposited film to form silicates without reacting with the channel material. In this work, we focused on the formation of yttrium silicate (Y-silicate) dielectrics, a typical rare-earth silicate [2] , so that the formation process can be easily extended to other rare-earth silicates, including La-silicate [3] .Y-silicate films were formed by cyclic deposition of Y2O3 and SiO2 based on atomic-layer deposition (ALD). Experiments Firstly, Y2O3/SiO2 multi-stacked layer（call it stacked-layer from now on）with a thickness of 16 nm without annealing process was analyzed by x-ray photoelectron spectroscopy (XPS) to confirm forming of Y-silicates. Next, MOS capacitor was fabricated by stacked-layer with a thickness 5 nm were deposited on the n-Si substrates by ALD at 200oC. Fig. 1 shows the schematic structure of the fabricated MOS capacitors. The cycles are determined to have the Y/Si atomic ratio of the stacked-layer to be 1:1. Then, W gate electrodes and TiN layer are deposited by RF sputtering. Al contact layers were deposited on the backside of the samples by thermal evaporation. The capacitors were then annealed at 800oC in forming gas (N2: H2=97%:3%) ambient for 30 min. [4] Finally, the metal-insulator-metal (MIM) capacitor, 10-nm-thick stacked-layer were also fabricated aim to no interfacial layer. Result Fig.2 shows the results of XPS analysis. The shift in the binding energy indicates that most of the Y atoms are in the form of silicate. Suggesting that the stacked layer is readily transformed in the form of Y-silicate during ALD process. The bandgap of the stacked-layer was estimated to be 6.4 eV. Fig. 3 shows the XPS depth profile of the stacked-layer obtained by Ar etching. The atomic ratio of Y, Si and O remained constant throughout the film at almost 2:2:7 until the Si substrate appeared. From the results, it is confirmed that a uniform Y2Si2O7 layer can be obtained by the multi-stacking of Y2O3/SiO2 ALD process. Fig. 4 shows the C-V characteristics of the n-Si capacitors with a 5-nm-thick Y-silicate layer. After annealing, the capacity of Y-silicate layer capacitor doesn’t increase. This result indicating little reaction at Y-silicate/Si interface. Finally, from the C-V and J-V measurements of MIM capacitor, A k-value of the stacked-layer is calculated to be 8.5, break down field of MIM capacitor is 6.6MV/cm. The k-value of the Y-silicate layer is also reasonable considering the k-values of SiO2 of 3.9 and Y2O3 of 13. [5] Conclusion Low temperature formation of Y-silicate layer has been confirmed by cyclic deposition of stacked-layer of Y2O3 and SiO2 ALD layers. The target composition of Y2Si2O7 and the formation of Y-O-Si bonds have been confirmed by XPS. Bandgap, breakdown field and k-value of Y-silicate dielectrics were determined to be 6.4eV, 6.6MV/cm, 8.5 respectively.

Effect of reactant dosing on selectivity during area-selective deposition of TiO2 via integrated atomic layer deposition and atomic layer etching

A key hallmark of atomic layer deposition (ALD) is that it proceeds via self-limiting reactions. For a good ALD process, long reactant exposure times beyond that required for saturation on planar substrates can be useful, for example, to achieve conformal growth on high aspect ratio nanoscale trenches, while maintaining consistent deposition across large-area surfaces. Area-selective deposition (ASD) is becoming an enabling process for nanoscale pattern modification on advanced nanoelectronic devices. Herein, we demonstrate that during area-selective ALD, achieved by direct coupling of ALD and thermal atomic layer etching (ALE), excess reactant exposure can have a substantially detrimental influence on the extent of selectivity. As an example system, we study ASD of TiO2 on hydroxylated SiO2 (Si–OH) vs hydrogen-terminated (100) Si (Si–H) using TiCl4/H2O for ALD and WF6/BCl3 for ALE. Using in situ spectroscopic ellipsometry and ex situ x-ray photoelectron spectroscopy, we show that unwanted nucleation can be minimized by limiting the water exposure during the ALD steps. Longer exposures markedly increased the rate of nucleation and growth on the desired non-growth region, thereby degrading selectivity. Specifically, transmission electron microscopy analysis demonstrated that near-saturated H2O doses enabled 32.7 nm thick TiO2 patterns at selectivity threshold S > 0.9 on patterned Si/SiO2 substrates. The correlation between selectivity and reactant exposure serves to increase fundamental insights into the effects of sub-saturated self-limiting surface reactions on the quality and effectiveness of ASD processes and methods.

Vacuum outgassing characteristics of unpigmented 3D printed polymers coated with atomic layer deposited alumina

3D printing offers enormous potential for fabricating custom equipment for space and vacuum systems, but in order to do this at low costs, polymers are necessary. Historically, polymers have not been suitable for these applications because of outgassing, but if coated with a conformal, inorganic film introduced with atomic layer deposition (ALD), then outgassing can be reduced. Previous work on coating ALD layers showed promise with heavily outgassing carbon black containing 3D printed polymers. In this study, ALD aluminum oxide and a commercially available vacuum sealant resin were used to coat clear, acrylonitrile butadiene styrene, polycarbonate, and polypropylene. Characterization of the films included spectroscopic ellipsometry for thickness, microstructure analysis with scanning electron microscopy, chemical analysis with energy-dispersive x-ray spectroscopy, and residual gas analysis to study relative change in outgassing. ALD-coated samples registered lower pressures than the resin-coated ones. The results showed that the ALD coatings could effectively inoculate unpigmented 3D printed plastics, which could be used in contamination-sensitive environments such as semiconductor processing systems and space environments.

Simple electrochemical method for monitoring the time-dependent dissolution behavior of layers deposited by atomic layer deposition

Spectroscopic and microscopic techniques are not suitable for the rapid monitoring of time-dependent dissolution behavior (particularly, pinhole changes) of a layer deposited by atomic layer deposition (ALD). Here, we present a simple electrochemical method that provides information on the dissolution mechanism including pinhole generation and thickness change. Because indium tin oxide (ITO) electrodes exhibit flat capacitive currents and good (electro)chemical stability, they are selected as ideal underlying substrates for the electrochemical monitoring of the ALD layers even under harsh conditions. Two ALD layers (Al 2 O 3 and TiO 2 layers) that exhibit opposite dissolution behaviors are chosen as model layers because the as-deposited Al 2 O 3 layers are pinhole-free but unstable in aqueous solutions, whereas the as-deposited TiO 2 layers are not pinhole-free but stable in aqueous solutions. The combination of capacitive current level (in an electrolyte solution containing no redox-active species) and electrochemical blocking behavior (in an electrolyte solution containing a redox-active species such as Ru(NH 3 ) 6 3+ and ferrocenemethanol) obtained from cyclic voltammograms enables us to verify whether the dissolution of an ALD layer occurs, to evaluate the dissolution rate, and to identify the plausible dissolution mechanism. The electrochemical results reveal that the Al 2 O 3 layers are dissolved in biological buffers, along with pinhole generation, and that the TiO 2 layers are stable with no pinhole generation. The difference in electrochemical blocking behavior between Ru(NH 3 ) 6 3+ and ferrocenemethanol provides information on the approximate size of the pinholes. The present method is appealing for practical use because even an ALD layer with a thickness of only a few nanometers can be tested to monitor the dissolution behavior and because any ALD layer that can be readily deposited on ITO electrodes can be easily examined using this method. • Stability comparison of Al 2 O 3 and TiO 2 layers deposited by atomic layer deposition. • Indium tin oxide electrodes are ideal underlying substrates for the comparison. • The combination of capacitive current level and electrochemical blocking behavior allows for evaluating dissolution. • Al 2 O 3 layers are dissolved in biological buffers, along with pinhole generation.

22‐1: Formation of Silicon‐Based Thin‐Film Encapsulation for Fabrication of Highly Flexible OLED Devices

The commercialized OLED display is one of the most attractive display in the 21st century. The OLED display is able to manufacture as a deformable display then before, such as foldable, rollable, and stretchable. Manufacturing the deformable display requires thinner and/or more flexible layers in the inner display. To make a high performance barrier preventing moisture and oxygen for the thinner thin film encapsulation (TFE), we have studied the process for inorganic layer by ALD (Atomic layer deposition) and organic layer by CVD (Chemical vapor deposition). In this study, we evaluated the OLED device deposited by ALD and CVD encapsulation layers. The method introduced in this study confirmed the same level of encapsulation characteristics even in a thickness of about 35% thinner than the conventional thin films encapsulation layer. To perform the evaluation according to the bending radius, a flexibility evaluation of 200,000 cycles was performed at room temperature. Finally, we were confirmed that this encapsulation layer by above process was thinner and more flexible while maintain the encapsulation characteristic rather than conventional encapsulation layer.

Development of polarity inversion in a GaN waveguide structure for modal phase matching

In this work, we report on the fabrication of a GaN/AlGaN waveguiding structure dedicated to modal phase matching, where GaN waveguide has planar polarity inversion. First, we optimized the growth conditions for the AlGaN epilayer. Second, on top of the AlGaN epilayer, we fabricated the waveguiding structure starting with the growth of the Ga-polar GaN epilayer followed by atomic layer deposition (ALD) of an Al $$_{2}$$ O $$_{3}$$ layer, then, continuing with the growth of N-polar GaN epilayer. We tested several layer thicknesses, but with 20 nm we managed to inverse the GaN polarity from Ga to N. To confirm the N-polarity, we etched the GaN epilayer surface in aqueous KOH solution. We performed out-of-plane (0002) and in-plane (11–20) X-ray diffraction and rocking curve measurements to estimate the crystalline quality of the AlGaN epilayer, Ga- and N-polar GaN epilayer. Atomic force microscopy measurement lets us evaluate the epilayer surface morphology and roughness. Optical and scanning electron microscopy inspection revealed characteristic hexagonal N-polar GaN epilayer surface. We used high-resolution transmission electron microscopy to investigate the crystallinity and orientation of the Ga- and N-polar GaN epilayer, also the Al $$_{2}$$ O $$_{3}$$ ALD layer, the interface quality of the waveguide structure.

Comparing physiologically relevant corrosion performances of Mg AZ31 alloy protected by ALD and sputter coated TiO2

The utilization of Mg alloys for biomedical applications is so far underexplored due to the accelerated corrosion hampering patient recovery post implantation. Here, we explore the effectiveness of corrosion reduction of an AZ31 alloy in Simulated Body Fluid when coated with a 40 nm sputtered TiO2 layer and compare it to a similar coating made by Atomic Layer Deposition (ALD). Potentiodynamic polarization and hydrogen evolution experiments were performed on coated samples having different surface roughness and 3D topologies. Interestingly, ALD layers reduce corrosion current density by 94% on Ra = 118.6 ± 5.1 nm and 93% on Ra = 4794.3 ± 49.4 nm, whereas sputtered only by 84% on Ra = 118.6 ± 5.1 nm and 60% on Ra = 4794.3 ± 49.4 nm. Particularly on 3D aspects, the ALD coatings are superior, where a scaffold of 85% porosity with 1 mm pore sizes released 68% lower hydrogen compared to the sputtered counterparts. We relate these observations to the higher surface integrity, adhesion strength and lower line-of-sight restrictions of ALD compared to sputter deposition. The results can be interesting for researchers and practitioners aiming to make Mg alloys more commonplace as temporary metallic implant materials.

Protective coatings for front surface silver mirrors by atomic layer deposition.

The problem of protection of the front surface silver mirrors is a very important one for a number of applications. The atomic layer deposition (ALD) technique provides an efficient way to form a coating, protecting the sensitive surface of silver from a corrosive and oxidizing environment. Moreover, the ALD layer provides extremely high conformality (even when deposited over high aspect ratio features) and has high integrity, efficiently blocking foreign species diffusion to the silver-overcoat interface. We tested the efficiency of the protection of silver mirrors against oxygen plasma exposure by the ALD-deposited Al2O3 layers by combining spectroscopic ellipsometry, reflection measurements and pulsed glow-discharge optical emission spectroscopy (GD-OES) profiling. We have found that for optimal protection, the thickness of the ALD deposited layer should exceed at least 15 nm (about 150 ALD cycles at 150°C). We have also demonstrated that the deposition of 15 nm of a protective ALD-deposited Al2O3 layer does not affect the absolute reflectivity of a silver mirror in the spectral range 320 -2500 nm.

Optimizing the Atomic Layer Deposition of Alumina on Perovskite Nanocrystal Films by Using O2 As a Molecular Probe

AbstractEncapsulation methods have shown to be effective in imparting improved stability to metal‐halide perovskite nanocrystals (NCs). Atomic layer deposition (ALD) of metal oxides is one of the promising approaches for such encapsulation, yet better control on the process parameters are required to achieve viable lifetimes for several optoelectronic and photocatalytic applications. Herein, we optimize the ALD process of amorphous aluminum oxide (AlOx) as an encapsulating layer for CsPbBr3 NC thin films by using oxygen (O2) as a molecular diffusion probe to assess the uniformity of the deposited AlOx layer. When O2 reaches the NC surface, it extracts the photogenerated electrons, thus quenching the PL of the CsPbBr3 NCs. As the quality of the ALD layer improves, less quenching is expected. We compare three different ALD deposition modes. We find that the low temperature/high temperature and the exposure modes improve the quality of the alumina as a gas barrier when compared with the low temperature mode. We attribute this result to a better diffusion of the ALD precursor throughout the NC film. We propose the low temperature/high temperature as the most suitable mode for future implementation of multilayered coatings.

Atomic layer deposition of titanium oxide and nitride on vertically aligned carbon nanotubes for energy dense 3D microsupercapacitors

This work demonstrates the use of ALD coatings in a full-cell 3D microsupercapacitor (MSC) device for the first time. The novel device design described herein has potential to be exploited for rapid and scalable manufacturing of on-chip MSCs integrated with other electronic devices in standard semiconductor fabs or foundries. In this study, atomic layer deposition (ALD) was used to deposit conformal pseudocapacitive coatings of titanium oxide (TiO2) and titanium nitride (TiN) onto CVD-grown vertically aligned carbon nanotubes (VACNTs) to increase the area-specific capacitance (by 240× and 74× at 0.1 Vs−1 versus the as-deposited VACNT electrode and full-cell VACNT device, respectively) and thus energy density for microscale energy storage applications. The study indicated that combining TiO2 and TiN ALD layers resulted in a multilayered composite coating rich in oxygen vacancies with enhanced capacitance relative to a single TiO2 or TiN layer due to a dynamic surface chemistry that developed during charge-discharge cycling. A key component of this multilayered coating was the formation of titanium oxynitride (TiON) which we attributed to the improved performance. Further, we demonstrated that controlling the thickness and stoichiometric ratio of the TiN-TiO2 composite coating was key to enabling functionality and optimizing the symmetric 3D MSC device performance.