Deposition Window Research Articles

Phase-selective growth of κ- vs β-Ga2O3 and (InxGa1−x)2O3 by In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy

Its large intrinsic polarization makes the metastable κ-Ga2O3 polymorph appealing for multiple applications, and the In-incorporation into both κ and β-Ga2O3 allows us to engineer their bandgap on the low-end side. In this work, we provide practical guidelines to grow thin films of single phase κ-, β-Ga2O3 as well as their (InxGa1−x)2O3 alloys up to x = 0.14 and x = 0.17, respectively, using In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy (MEXCAT-MBE). The role of substrate temperature, oxidizing power, growth rate, and choice of substrate on phase formation and In-incorporation is investigated. As a result, the κ phase can be stabilized in a narrow deposition window irrespective of the choice of substrate [(i) α-Al2O3 (0001), (ii) 20 nm of (2̄01) β-Ga2O3 on α-Al2O3 (0001), and (iii) (2̄01) β-Ga2O3 single crystal]. Low growth rates/metal fluxes as well as growth temperatures above 700 °C tend to stabilize the β-phase independently. Lower growth temperatures and/or O-richer deposition atmospheres allow to increase the In-incorporation in both polymorphs. Finally, we also demonstrate the possibility to grow (2̄01) β-Ga2O3 on top of α-Al2O3 (0001) at temperatures at least 100 °C above those achievable with conventional non-catalyzed MBE, opening the road for better crystal quality in heteroepitaxy.

Process parameters selection for multi-layer friction surfacing of 7075 aluminium alloy

The effect of deposition parameters on the microstructure and mechanical properties are studied in multi-layer friction surfacing of 7075 aluminium alloy. These multi-layer structures were successfully manufactured after a parametric study which allows the generation of a deposition window, including an interface quality comparison. A higher rotational speed leads to a larger grain sizes. The coarse precipitates size and volume fraction decrease along the build direction in correlation with the thermal cycles’ profile. The top layer has a higher hardness after deposition, while bottom layers are in annealed state due to the growth of the strengthening phases. Fracture surface analysis revealed that transversal cracks are due to interlayer decohesion and that voids nucleated on the coarse precipitates.

Study of selective etching of TaN with respect to SiOCH dielectrics using SiF4 plasma processes

TaN is used as a Cu diffusion barrier during metal interconnect formation to enable modern chip fabrication. In this study, the selective removal of TaN with respect to SiOCH dielectrics is explored using neutral dominant plasmas containing pure SiF4 or with O2 or H2 additives. SiF4 is studied because the Si-containing gas has been historically used to deposit Si-based films, but the gas also contains F capable of volatilizing Ta. This work explores the possibility of enabling both selective etching of TaN and selective deposition on SiOCH. SiF4 discharges are impacted by the addition of O2 and H2 gases; exhibiting significantly different deposition and etching regimes. The substrate temperature plays a critical role in modulating the TaN etching versus deposition window compared to SiOCH. Through this work, selective etching of TaN with respect to SiOCH is achieved.

Plasma-enhanced atomic layer deposition of silicon nitride thin films with different substrate biasing using Diiodosilane precursor

In this work, we report on Plasma-Enhanced Atomic Layer Deposition (PE-ALD) of SiNx films using Diiodosilane (DIS) precursor and N2-H2 plasma. Systematic studies as a function of DIS dosing time, plasma duration, plasma composition and deposition temperature are investigated. The material properties have been studied using X-ray photoelectron spectroscopy (XPS), X-Ray Reflectometry (XRR), Atomic Force Microscopy (AFM) and High-Resolution Transmission Electron Microscopy (HR-TEM). The optimal deposition parameters for achieving high-quality SiNx with a high growth per cycle (GPC) are first determined. We show that DIS offers a wide temperature window for SiNx deposition starting from 110 °C up to 300 °C, paving the way for a large choice of SiN-based applications. The impact of substrate biasing on SiNx film deposition and properties is also investigated. We show that high ion energies during the nitridation step can cause surface damage and void formation, thus affecting the SiNx quality. Overall, these results highlight the importance of this novel precursor for growing SiNx using PE-ALD and the possible swapping of the material properties by fine control of the substrate biasing, which can help to go far beyond the existing SiNx limitations.

Modeling the influence of the duration of water vapor pulses on the properties of hafnium oxide synthesized by atomic layer deposition method

The work experimentally and theoretically analyzes the process of atomic layer deposition of hafnium oxide with the participation of water vapor as an oxidizing agent. The study of infrared absorption, Auger spectroscopy and luminescence shows that with increasing water pulse duration, the concentration of oxygen vacancies decreases and the composition tends to stoichiometric, which is given by the formula HfO2. Modeling of gas dynamics and kinetics of film synthesis by atomic layer deposition was performed, which showed the dependence of the coverage of the film surface with oxygen on the pulse duration and deposition temperature. A comparison of calculations with experimental results made it possible to estimate the magnitude of the kinetic coefficients of the synthesis processes that describe the observed experimental dependences and to show that the larger of the two temperatures of the atomic layer deposition window is associated with water desorption.

Suppressing interfacial nucleation competition through supersaturation regulation for enhanced perovskite film quality and scalability.

The growing interest in cost-effective and high-performing perovskite solar cells (PSCs) has driven extensive research. However, the challenge lies in upscaling PSCs while maintaining high performance. This study focuses on achieving uniform and compact perovskite films without pinholes and interfacial voids during upscaling from small PSCs to large-area modules. Competition in nucleation at concavities with various angles on rough-textured substrates during the gas-pumping drying process, coupled with different drying rates across the expansive film, aggravates these issues. Consequently, substrate roughness notably influences the deposition window of compact large-area perovskite films. We propose a supersaturation regulation approach aimed at achieving compact deposition of high-quality perovskite films over large areas. This involves introducing a rapid drying strategy to induce a high-supersaturation state, thereby equalizing nucleation across diverse concavities. This breakthrough enables the production of perovskite photovoltaics with high efficiencies of 25.58, 21.86, and 20.62% with aperture areas of 0.06, 29, and 1160 square centimeters, respectively.

Co-deposition of TaC and SiC by chemical vapor deposition: A systematical thermodynamic exploration

A systematical thermodynamic analysis on the co-deposition of TaC and SiC via the chemical vapor deposition (CVD) is performed using the TaCl5-SiCl4-CH4-H2 system as the representative precursors system to guide experiments. The optimal deposition window for co-depositing TaC and SiC and tailoring their ratio is determined. The results show that temperature and pressure have limited influence on the content of TaC but mainly affect the mole fraction of SiC and graphite at equilibrium. CH4/(TaCl5 + SiCl4) ratios between 0.5 and 0.85 and H2/(TaCl5 + SiCl4) ratios of >5 favor the formation of the two-phase region of TaC + SiC. Medium temperatures (1000–1400 °C) are conducive to the co-deposition of TaC and SiC. Other condensed species will deposit at CH4/(TaCl5 + SiCl4) ratios below 0.6. By adjusting the ratios of CH4/(TaCl5 + SiCl4) and SiCl4/TaCl5, the mole fractions of TaC in the deposit can be regulated.

Atomic Layer Deposition Growth and Characterization of Al2O3 Layers on Cu-Supported CVD Graphene

The deposition of thin uniform dielectric layers on graphene is important for its successful integration into electronic devices. We report on the atomic layer deposition (ALD) of Al2O3 nanofilms onto graphene grown by chemical vapor deposition onto copper foil. A pretreatment with deionized water (DI H2O) for graphene functionalization was carried out, and, subsequently, trimethylaluminum and DI H2O were used as precursors for the Al2O3 deposition process. The proper temperature regime for this process was adjusted by means of the ALD temperature window for Al2O3 deposition onto a Si substrate. The obtained Al2O3/graphene heterostructures were characterized by Raman and X-ray photoelectron spectroscopy, ellipsometry and atomic force and scanning electron microscopy. Samples of these heterostructures were transferred onto glass substrates by standard methods, with the Al2O3 coating serving as a protective layer during the transfer. Raman monitoring at every stage of the sample preparation and after the transfer enabled us to characterize the influence of the Al2O3 coating on the graphene film.

Spatiotemporal Observation of Monosodium Urate Crystals Deposition in Synovial Organoids Using Label-Free Stimulated Raman Scattering.

Gout, a common form of arthritis, is characterized by the deposition of monosodium urate (MSU) crystals in joints. MSU deposition in synovial tissues would initiate arthritis flares and recurrence, causing irreversible joint damage. However, the dynamic deposition of MSU crystals in tissues lacks experimental observation. In this study, we used chemical-specific, label-free stimulated Raman scattering (SRS) microscopy to investigate the spatiotemporal deposition and morphological characteristics of MSU crystals in human synovial organoids. Our findings revealed a critical 12-h window for MSU deposition in the lining layer of gouty synovium. Moreover, distinctive inflammatory reactions of the lining and sublining synovial layers in gout using SRS microscopy were further verified by immunofluorescence. Importantly, we identified a crucial proinflammatory role of sublining fibroblast-like synoviocytes, indicating a need for targeted medication treatment on these cells. Our work contributes to the fundamental understanding of MSU-based diseases and offers valuable insights for the future development of targeted gout therapies.

Computational thermodynamic study on CVD of silicon oxynitride films from Si–O–N–H and Si–O–N–H–Cl systems

High-throughput thermodynamic analysis of chemical vapor deposition of silicon oxynitride films from the Si–O–N–H and Si–O–N–H–Cl systems are performed based on the CALPHAD (CALculation of PHAse Diagram) approach. The considered deposition conditions are 800 °C, 200 Pa, NH3/SiH4 ratios of 0.05–50 and NH3/N2O ratios of 0.05–10. The influence of precursor composition on the phase and composition of the coatings as well as the optimal window for obtaining high-purity Si2N2O are discussed. The formation of SiO2 favors low NH3/N2O ratios and its fraction decreases with increasing NH3/N2O ratio. The content of Si2N2O increases monotonously with increasing NH3/N2O ratio until reaching 100 at.%. Free Si is suppressed to almost 0 at.% when the NH3/SiH4 ratio is greater than 1. The introduction of Cl in the precursor can not only reduce the formation of free Si but also expand the deposition window for preparing pure Si2N2O. Our calculated results agree well with available experimental data.

Low-Pressure Cold Spray Deposition Window Derived from a One-Dimensional Analytical Model

Low-pressure cold spray (LPCS) coating deposition requires the consideration of multiple parameters to define spraying conditions. The use of a parameter window provides an integral approach to achieving this goal. In this work, an LPCS deposition window for zinc powders was obtained through the development of a one-dimensional analytical model of fluid and particle interaction. The model considers powder particle injection downstream of the nozzle and follows the particle from injection to impact. The model equations relate the particle velocity (vp) to the process parameters, such as the gas pressure (P0) and temperature (T0), particle size (dp) and stand-off distance (SoD). The values of the particle velocity (vp) at the nozzle exit and during the “free-jet”, as well as the drag coefficient (Cd), were calculated using experimental spraying conditions for Cu and Al that have previously been documented in LPCS studies. The model’s accuracy and applicability to other materials were confirmed upon comparing the results with those in the aforementioned studies. Moreover, the definition of the model equations allowed for the identification of three new parameters: (γ) the maximum ideal particle velocity, (β) the capacity to accelerate the powder particle inside the nozzle and (α) the deceleration of the particle in the free-jet zone. These parameters have not previously been published and allow for comparative evaluation between LPCS processes.

A study of the parameters affecting the particle velocity in cold-spray: Theoretical results and comparison with experimental data

Within coating applications, cold-spray is nowadays an extended technique commonly used in environments such as the additive manufacturing or repair industries. The differential factor that leads this approach to be chosen over others is its low deposition temperature. The need for ensuring the resistance and durability of the free-standing components has led to the development of models that can predict the kinetic energy of the particles, which is the main driving parameter affecting the deposit performance. In this study, an optimisation theoretical model, previously developed by the authors, is validated with the experimental exit particle velocity data taken from commercial geometries and using Fluent simulations available in literature. The aim of this work is to relate fundamental parameters in the cold-spray process such as the stagnation conditions, nozzle geometry, powder size or particle velocity. This objective is achieved by creating novel interdependent maps connecting these pivotal data by virtue of the model presented. Several graphs describing the final particle velocity depending on the stagnation pressure and temperature are obtained along with the optimal geometry for a wide range of materials (aluminium, titanium, steel, Inconel 625 and copper). In addition, the analytical model is able to hand over a deposition window of particle sizes and velocities that can be achieved using a specific cold-spray equipment. Both set of maps combined together can be a powerful tool which users and manufacturers can benefit from on the grounds that they do not only provide information about whether a deposition can be achieved or not with a cold-spray equipment but also about the stagnation conditions needed. The results obtained with this methodology reflect the limitations of low and medium-pressure equipment in terms of the maximum particle diameter that can be deposited and constitute a novel advance in the state of art of cold-spray. Moreover, the fundamental parameter regarding the geometry, namely the ratio between the nozzle exit and the nozzle throat diameters, is represented as a function of the above-mentioned parameters.

Process optimisation of cold spray additive manufacturing of FeCoNiCrMn high-entropy alloy

ABSTRACT The deposition window of cold spray additive manufacturing (CSAM) a high-entropy alloy (HEA) was optimised by investigating processing parameters on deposition efficiency and porosity. The optimal parameters were obtained with helium as the driving gas, gas inlet temperature was at 700°C, and spray distance at 25 mm, at which the deposit was the thickest and of the lowest porosity. The type of driving gas is critical as it affects the porosity and deposition efficiency, and helium is required to obtain high-quality HEA deposits. With it, gas inlet temperature and spray distance have a minimal effect. Furthermore, higher gas temperature and moderate spraying distance were selected to increase particle deformation and reduce the effect of shock waves at the plate front.

On the optimal process window for powder-based laser-directed energy deposition of AA7050 under different robot programs and scanning strategies

Powder-based laser-directed energy deposition (L-DED) has drawn lots of attention during the last years because of the multiple application areas, such as coating, repairing, and building 3D structures. One challenge in L-DED is the limited variety of applicable materials, especially in the case of aluminum alloys. To broaden the material spectrum, the processability and the optimal process window of high-strength Al-alloy AA7050 are investigated in the present study. Besides the process parameters, special emphasis was paid to the scanning strategy and the robot program controlling. The present results show a strong effect of scanning strategy and robot program on buildability, geometrical accuracy, melt pool visibility, porosity level, and crack initiation. Hot cracks can be reduced or eliminated by choosing an appropriate combination of scanning strategy and robot program. Meanwhile, the geometrical accuracy of specimens with any height was well maintained. Based on the systematic experimental study, appropriate L-DED process parameters were identified for the deposition of structures up to 24 layers with a lower porosity level (about 3.7 ± 0.8 %) and lower amount of hot cracks, which are comparable with that in the 12-layer structure.

Plasma-enhanced atomic-layer-deposited indium oxide thin film using a DMION precursor within a wide process window

In this study, we developed a new liquid indium precursor, dimethyl[N-(tert-butyl)-2-methoxy-2-methylpropan-1-amine] indium (DMION), to deposit indium oxide films using the plasma-enhanced atomic layer deposition (PEALD) method. The indium oxide films were deposited using DMION and Ar/O2 plasma as the precursor and reactant, respectively, with relatively high growth per cycle (GPC, ∼1.2 Å/cycle) within a wide atomic layer deposition (ALD) window (35–300 °C). Impurities such as carbon and nitrogen were not detected regardless of the deposition temperature. The crystallinity of the films had a bixbyite cubic structure within the ALD window and facets could be controlled by deposition temperature modulation; (400) facets were dominant at low deposition temperatures (35 and 100 °C), whereas (222) facets were dominant at high deposition temperatures (200 and 300 °C). The dominant facets and orientations of the indium oxide crystal were maintained until 400 °C in the post-annealing process. The thin-film transistors (TFTs) using indium oxide deposited at 200 °C exhibited high field-effect (∼32.1 cm2/Vs) mobility with a reasonable threshold voltage (∼1.8 V) and subthreshold voltage swing (∼0.48 V/decade).

Self-healing Growth of LaNiO3 on a Mixed-Terminated Perovskite Surface.

Developing atomic-scale synthesis control is a prerequisite for understanding and engineering the exotic physics inherent to transition-metal oxide heterostructures. Thus, far, however, the number of materials systems explored has been extremely limited, particularly with regard to the crystalline substrate, which is routinely SrTiO3. Here, we investigate the growth of a rare-earth nickelate─LaNiO3─on (LaAlO3)(Sr2AlTaO6) (LSAT) (001) by oxide molecular beam epitaxy (MBE). Whereas the LSAT substrates are smooth, they do not exhibit the single surface termination usually assumed necessary for control over the interface structure. Performing both nonresonant and resonant anomalous in situ synchrotron surface X-ray scattering during MBE growth, we show that reproducible heterostructures can be achieved regardless of both the mixed surface termination and the layer-by-layer deposition sequence. The rearrangement of the layers occurs dynamically during growth, resulting in the fabrication of high-quality LaNiO3/LSAT heterostructures with a sharp and consistent interfacial structure. This is due to the thermodynamics of the deposition window as well as the nature of the chemical species at interfaces─here, the flexible charge state of nickel at the oxide surface. This has important implications regarding the use of a wider variety of substrates for fundamental studies on complex oxide synthesis.

Tin and zinc microparticle impacts above the critical adhesion velocity

In cold spray, the critical adhesion velocity, or the point at which microparticles start to adhere to the substrate upon impact, defines the lower bound of the velocity window over which deposition can occur. Less information is available on the upper bound of this deposition window, which has previously been connected to both melting and hydrodynamic penetration processes that can lead to erosion. In this study, we examine impacts of tin microparticles on a tin substrate and zinc microparticles on a zinc substrate across a range of velocities above the critical adhesion velocity. We observe a variety of phenomena that occur as impact velocity is increased, including jetting, melting, fragmentation, and hydrodynamic penetration. Using laser scanning confocal microscopy and scanning electron microscopy, we quantify the net amount of material deposited at each impact site for each material. We use these measurements to understand the circumstances under which an erosive condition is met at high velocities, in which net deposition of microparticle material to the substrate no longer occurs. • Impact-induced melting occurs in both tin and zinc single microparticle impacts. • Confocal microscopy can be used to quantify erosion onset at high velocities. • Erosion in cold spray is caused by melting, penetration, and/or fragmentation. • Jetting, fragmentation, melting, & penetration occur at material-specific speeds.

Features of ceramic nanoparticle deformation in aerosol deposition explored by molecular dynamics simulation

The deformation and bonding of particles in Aerosol Deposition (AD) is a topic of growing technological interest for solid-state coating and additive manufacturing with ceramic materials. The core feature of the AD process is the unexpected plasticity of ceramics at high strain rates and small length scales, which is also a topic of general interest for understanding the response of intrinsically brittle materials to dynamic deformation. We explore this feature through computational analysis of the impact of ceramic particles – modelled based on a Lennard-Jones description of submicron TiO2-anatase particles in a two-dimensional molecular-dynamics system – onto a substrate at a range of impact velocities (100–800 m/s). The deformation behaviour of the particle for each impact velocity was analysed with respect to the evolution of the stress, strain, and temperature fields. The results reveal indications of dislocation-based plasticity within a certain velocity regime. This velocity regime, which becomes narrower with increasing the particle size, coincides incidentally with bonding of particles to the substrate in AD. The results also show that outside this regime, the impact is associated predominantly with either rebounding (at lower velocities) or particle fracture (at higher velocities). The simulation results are interpreted in view of a phenomenological model of fragmentation, considering the interplay between the material properties, such as the fracture energy, and the kinetic energy of particles upon impact. Based on the simulations and the analytical model, a window of deposition is proposed for AD.

In situ ellipsometry aided rapid ALD process development and parameter space visualization of cerium oxide nanofilms

Process development in atomic layer deposition (ALD) is often time-consuming, requiring optimization of saturation curves and temperature windows for controlled deposition rates. Any ALD process should be self-limiting in nature, exhibiting a temperature window of nominal deposition and a linear deposition rate. Meeting these criteria usually requires several ALD experiments, followed by film characterization, which are generally time, cost, and labor-intensive. Against this backdrop, we report a methodology using in situ ellipsometry to rapidly develop the ALD process for cerium oxide using Ce(iPrCp)2(N-iPr-amd) and water. The entire optimized process was realized in ten experiments of sequential pulsing as a function of temperature, requiring less than a day. In the traditional approach, tens of experiments and ex situ characterization may be required. The approach reported here generated a contour visualization of the time-temperature-thickness parameter space delineating the optimal deposition conditions. The cerium oxide deposition rate deposited in the ALD temperature window was ∼0.15 nm/cycle; the deposited film was further characterized using x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy to probe the film composition and quality further.

Selective Deposition of Copper on Self-Assembled Block Copolymer Surfaces via Physical Vapor Deposition.

Block copolymer (BCP) self-assembly produces chemically and topographically patterned surfaces which are used to guide the formation of Cu nanostructures by exploiting differences in the mobility of vapor-deposited species on each microdomain. Cu metal films a few nm thick were deposited on three different BCP surfaces self-assembled from poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP). For PS-b-PMMA, the effects of chemical heterogeneity dominate over the effects of the 2 nm peak-to-valley topography, and sputtered Cu preferentially wets the PS block. PS-b-P2VP has greater chemical and topographical contrast and shows a wider process window for selective deposition. Cu grown by evaporation has less surface mobility, and shadowing effects are believed to dominate pattern formation. The hierarchical self-assembly process of thin metal films on BCP surfaces provides a route to fabricating heterogeneous metallic nanostructures.