Thin Film Deposition Techniques Research Articles

Molecular Layer Deposition of Titanicone over Lithium Silicide Anode

The increasing demands for more advanced consumer electronics, electric vehicles, and stationary facilities call for the next generation of rechargeable batteries with higher specific energy (energy per mass) and energy density (energy per volume) than the current generation of lithium ion batteries (LIBs), which largely use lithium metal oxide (LMO) positive electrodes and graphite negative electrode.Si has become one of the most highly investigated materials for LIB negative electrodes because of its ability to accommodate 3.75 moles of Li per mole of Si (Li15Si4) for a theoretical capacity of 3579 mA h g−1 at room temperature. Despite Si inherent advantages, progress towards a commercially viable Si anode has been impeded by Si rapid capacity fade, poor rate capability, and low coulombic efficiency (CE). Si exhibits volume changes of ~300% upon lithium alloying and de-alloying, leading to material degradation and presenting a major problem for electrochemical performance. This high volume expansion and contraction is too large to be controlled by currently developed coating technologies.As the electrode matrix fractures, the continuous exposure of fresh nano-Si surface to the liquid electrolyte causes parasitic formation of a solid-electrolyte interphase (SEI) leading to irreversible charge loss and low CE. The volume fluctuation, also causes a damage of the electrical contact between Si and the current collector.One of the main front-end strategies established for the realization of such an approach is coating nano-Si particles with flexible materials in order to attempt to accommodate the volumetric changes of the particles. In order to address the challenge of Si dramatic volumetric change, we carried out a surface modification, in which Molecular layer deposition (MLD) was utilized to grow a mechanically robust, flexible coating, producing high-capacity Si nanocomposite anodes.MLD is a thin film deposition technique where hybrid organic–inorganic films are grown by exposing the substrate to subsequent, self-limiting, metal–organic precursor gases. The processes used here is based on TiCl4 as the titanium precursor. TiCl4 is a relatively small molecule, and when combined with the larger organic reactants it leads to high growth rates which are mainly limited by steric hindrance caused by the organic reactants.The composition of the films was studied using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope-Energy-dispersive X-ray spectroscopy (SEM-EDX). Multiple characteristic absorption modes for both carbon and titanium related groups can be observed in the FTIR spectrum, Figure 1. The combination of both the carbon related groups and the Ti absorptions provides evidence for the successful deposition of a hybrid organic–inorganic film containing titanium.The electrochemical performance of the LixSi coated with titanicone used as an anode was investigated by Cyclic Voltammetry (CV). Typical voltammograms of the half cell in the first scan show the formation of the SEI. In the subsequent scans these peaks disappears.We successfully show the deposition of titanicone on LixSi electrode and an initial electrochemical assessment of this electrode. Figure 1

Spray Pyrolysis Strategy for Preparation of Cathode-Supported Protonic Ceramic Fuel Cells

Since the discovery of proton conducting ceramic materials many research efforts have been focused into overcoming processing difficulties that hinder long-term stability and high performance of protonic ceramic fuel cells (PCFCs). Notably, high processing temperatures exceeding 1600 °C are often required to meet the microstructural demand of a dense proton conducting electrolyte membrane [1-2]. At this temperature range most potential electrode materials are chemically incompatible and therefore preclude the fabrication of electrode supported structures. In addition, for barium-based electrolytes (e.g. BaZr1-xYxO3-d) barium loss is anticipated resulting in lower conductivities and formation of structural defects. To overcome this major challenge thin film deposition techniques can be employed[3-4].Spray pyrolysis is a cost effective and simple deposition technique for preparation of ultra-thin films (i.e.<5μm) enabling the reduction of operating and processing temperatures of fuel cells [5]. Microstructures and electrochemical performance of multi-layered thin film PCFCs fabricated at exceptional low temperatures of 950 °C, are investigated. Large area 5x5cm2 cathode substrates of (La0.8Sr0.2)0.95MnO3-d prepared by tape casting were used for mechanical support of the cells. To modify and reduce the surface porosity of the substrate Ce0.9Gd0.1O3-d was coated to facilitate the deposition of the BaZr0.9Y0.1O3-d (BZY) thin electrolyte. Subsequently, the anode electrode was sprayed in two stages comprised by a nano-porous layer of BZY and infiltrated Ni particles. Characterization of the cathode-supported PCFCs was performed by electrical measurements operating up to 600°C and scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) techniques.[1] Shanwen Tao and John T.S. Irvine, Adv. Mater., 18, 1581-1584, (2006).[2] Peter Babilo and Sossina M. Haile, J. Am. Ceram. Soc., 88 2362-2368, (2005).[3] Kiho Bae et al., Adv. Energy Mater., 8, 1801315, (2018).[4] Georgios Tsimekas et al., ECS J. Solid State Sci. Technol.,6(8), P553-P560, (2017).[5] Georgios Tsimekas et al., ECS Trans., 70(1), 205-212, (2015).

Physical Supercritical Fluid Deposition: Patterning Solution Processable Materials on Curved and Flexible Surfaces.

We provide the initial demonstration of a general thin film deposition technique that leverages the unique solubility properties of supercritical fluids. The technique is the solution-phase analogue of physical vapor deposition and allows thin films of a semiconducting polymer to be grown without the need for in situ chemical reactions. Film growth is approximately linear with time, indicating that film thickness can be controlled in a straightforward manner by varying the time of deposition. To further demonstrate the flexibility of the technique, we demonstrate precise control over the location of material deposition using a combination of photolithography and resistive heating. The potential for scalable manufacturing is demonstrated by use of a master to control deposition onto a flexible polymer film. Finally, we demonstrate a unique deposition capability of this technique by depositing patterns onto the curved interior of a hemisphere made from a silicone elastomer. This capability is not possible with any printing or line-of-sight deposition technique. More generally, the ability to control the deposition of solution processed materials with high accuracy provides the long sought after bridge between top-down and bottom-up self-assembly.

Operating pressure influences over micro trenches in exposure time introduced atomic layer deposition

Tremendous interest has been placed on the atomic layer deposition (ALD) process as a thin film deposition technique capacity to deposit quality thin films. However, further comprehension of the ALD process is mandatory to increase the probability of achieving the necessary improvement, which can have a substantial impact on devices’ requiring properties that involve size, performance, and durability. It has been reported that pressure tends to impact growth per cycle. However, little has been done to investigate the specific effects of the – operating pressure on the mechanistic, species transport and reaction rates. Moreover, the effect of these prior properties due to complex topology elements, such as micro-trenches, has rarely been investigated. Hence, this study focuses on numerically investigating the effect between 1 and 10 Torr operating pressure along the ALD process using the computational fluid dynamic approach. A two-dimensional numerical simulation producing Al2O3 ALD thin film over a surface with micro-trenches is studied. Trimethyl-Aluminium and Ozone were utilized as the metal and oxidation source reactants. To assist in the precursor reaction process, a 2.5 s exposure time is added within the ALD sequence. The findings illustrated the fluid flow velocity, surface coverage, mass fraction, deposition rate and growth of the thin-film process.

Impact of growth kinetics on the interface morphology and magnetization in La1/3Sr2/3FeO3/La2/3Sr1/3MnO3 heterostructures

The ability to create atomically perfect, epitaxial heterostructures of correlated complex perovskite oxides using state-of-art thin film deposition techniques has generated new physical phenomena at engineered interfaces. Here we report on the impact of growth kinetics on the magnetic structure and exchange coupling at the interface in heterostructures combining layers of antiferromagnetic La1/3Sr2/3FeO3 (LSFO) and ferromagnetic La2/3Sr1/3MnO3 (LSMO) on (0 0 1)-oriented SrTiO3 (STO) substrates. Two growth orders are investigated, (a) LSMO/LSFO/STO(0 0 1) and (b) LSFO/LSMO/STO(0 0 1), where the LSFO layer is grown by molecular beam epitaxy and the LSMO layer by high oxygen pressure sputtering. The interface has been investigated using electron microscopy and polarized neutron reflectometry. Interdiffusion over seven monolayers is observed in LSMO/LSFO (a) with an almost 50% reduction in magnetization at the interface and showing no exchange coupling. However, the exchange bias effect ( mT at 10 K) could be realized when the interface is atomically sharp, as in LSFO/LSMO (b). Our study therefore reveals that, even for well ordered and lattice-matched structures, the kinetics involved in the growth processes drastically influences the interface quality with a strong correlation to the magnetic properties.

Atomic Layer Deposition on Dental Materials: Processing Conditions and Surface Functionalization to Improve Properties - a Critical Review

Atomic Layer Deposition (ALD) is a well-established thin film deposition technique. It is being used for surface functionalization in different technologies and biological related applications. In the current work, ALD is elaborated as a promising method for surface modification of dental materials. Different aspects of conventional dental materials that can be enhanced using ALD are discussed. Also, the influence of different ALD thin films and their microstructure on the surface properties, corrosion-resistance, antibacterial activity, biofilm formation, and osteoblast compatibility are addressed. Depending on the stage of advancement for the studied materials reported in the literature, these studies are then categorized into four stages: fabrication & characterization, in vitro studies, in vivo studies, and human tests. Materials coated with ALD thin films with potential dental applications are also presented here and they are categorized as stage 1. The current study can serve as a guide for future work on using ALD for surface functionalization and resulting property tuning of materials in real world dental applications.

Study on optimization of nano-coatings for ultra-sensitive biosensors based on long-period fiber grating

Bio-chemical sensors are expected to offer high sensitivity and specificity towards the detection of an analyte. It has been found that optical sensors based on long period fiber gratings (LPFGs) meet most of these requirements, particularly when coated with thin and high-refractive index overlays with proper bio-functionalization. In this paper, the influence of properties of the overlay material on the sensitivity of LPFG sensors to bio-analytes is analyzed. It has been observed that the sensitivity of a particular cladding mode of LPFG can be changed drastically with the adhesion of few tens of ‘nm’ of bio-layers to the surface of LPFG. “Volume refractive index sensitivity” and “add-layer sensitivity” of a particular cladding mode, dynamic range, and limit of detection of the sensors have been investigated in the context of overlay materials, bio-functionalization steps, and surrounding buffer medium. The selection criteria of the thin-film deposition technique are discussed with the aim of designing highly sensitive sensors for biological and chemical applications. Concept of optimum overlay thickness has been redefined and an effective case-specific design methodology is proposed.

ZnO-CuO core-shell heterojunction nanowires for optoelectronic applications

Nowadays, core-shell nanowires have attracted a great scientific interest due to their unique physical properties and advanced functionalities leading to applications in optoelectronic area [1]. Combining ZnO, an n type semiconductor with a band gap of 3.3 eV [2] and CuO, an p type semiconductor with a band gap of 1.2 eV [3], into core-shell radial heterojunction nanowires, a type II heterojunction alignment can be acquired, with a good control of the separation and recombination of the charge carriers at the interface between the two semiconductors. In this context, the ZnO-CuO core-shell heterojunction nanowire arrays were synthesized by thermal oxidation in air and radiofrequency magnetron sputtering (Figure 1). The ZnO-CuO core-shell nanowire arrays were investigated by the morphological, structural, optical, compositional and surface chemistry point of views. In order to assessed their optoelectronic properties, individual ZnO-CuO core-shell nanowires were contacted using photolithography, electron beam lithography and thin film deposition techniques. Exhibiting a rectifying behavior (Figure 2), typical for n-p diodes, these single ZnO-CuO core-shell nanowires can be used in UV photodetectors applications, such as radiation detection, air purification, advanced communications etc.

Challenges in Sr2FeMoO6−δ Thin Film Deposition

This work reviews some fundamental issues that are relevant for the fabrication of stable‐phase strontium ferromolybdate thin films. The main challenges for strontium ferromolybdate thin film deposition arise from the sensitivity of the material's magnetic properties to point defect formation: i) Antisite defect formation and oxygen nonstoichiometry should be avoided by precise composition control during film manufacturing; ii) a highly ordered state of the correct phase and B‐site cation valence will be obtained only in a very narrow window of growth conditions; iii) to avoid additional antisite disorder with decreasing synthesis temperature, the effective temperature at the film surface should be increased by an energy flux to the growing film surface. Since thin film deposition is nonequilibrium in nature, the review starts with the consideration of equilibrium phase stability. Cation and oxygen stoichiometries are analyzed with regard to their effect on key magnetic properties. Film strain formed due to thermal and lattice mismatch is of great concern since it influences the choice of the substrate. Finally, thin film deposition techniques are valued for their benefits in strontium ferromolybdate thin film technology.

Development of a Faraday cup fast ion loss detector for keV beam ions.

The development and testing of a Faraday cup fast-ion loss detector capable of measuring sub 100 keV particles is documented. Such measurement capabilities play an important role in the assessment of particle confinement of nuclear fusion experiments. The detector is manufactured using thin-film deposition techniques, building upon previous work using discrete foils. This new manufacturing method allows the form factor of the sensor to become that of essentially a microchip. Analysis of the diagnostic response is performed using Monte-Carlo particle simulations. These simulations show peaks in the detector response at 40 and 70 keV. The sensor is then tested in a tunable linear accelerator capable of accelerating protons from 20 to 120 keV. The detector response was found to be well matched to simulations. Improvements to the design to facilitate robustness are discussed.

Atomic Layer Deposition of Al2O3 with Alcohol Oxidants for Impeding Substrate Oxidation

Atomic layer deposition (ALD) is a vapor phase thin film deposition technique based on self-limited surface reaction. ALD processes consist of two (or more than) half-reactions. The first half-reaction is the self-limiting adsorption of precursor molecules which contain core metal atoms; the second half reaction is the self-limiting reaction between surface adsorbed precursor molecules and reactants. Since ALD could deposit thin films with high quality, good uniformity, high conformality, and sub-nanometer thickness controllability, [1-3] ALD has been regarded as one of the most suitable deposition technologies for semiconductor device fabrication. Since thin films of alumina (Al2O3) have wide range of applications such as high-k dielectric material for electronic devices, mechanical and chemical protective coatings, diffusion barriers, and optical coatings, [4-7] ALD of Al2O3 process is the mostly and thoroughly studied. For the deposition of Al2O3, trimethylaluminum (TMA) have been the most widely used for Al precursor due to its high vapor pressure and reactivity. And water (H2O) is widely utilized as the oxygen source in ALD Al2O3 processes, because since H2O often shows facile ligand exchange reaction during ALD. However, ALD Al2O3 processes with H2O reactant showed undesirable substrate oxidation issue. For example, there was an unwanted interface oxide between ALD deposited Al2O3 film and Si substrate. The interface oxide could reduce the dielectric constant of the deposited thin films and increase leakage current density. [8-9] Especially, the oxidation of substrate is critical issue for 2 dimensional (2D) transition-metal dichalcogenides (TMDCs) based field effect transistors (FETs). From our previous results, the oxidation of MoS2 by H2O considerably degraded device performance. [10-11] To avoid the oxidation of substrates and improve device performance, it is necessary to develop a new ALD process by using oxidants with lower oxidation potential than that of H2O. Despite its technical importance, ALD Al2O3 processes with weaker oxidants such as alcohols have rarely been investigated. [8] For this reason, the chemical reaction mechanism between surface adsorbed precursor and reactant has not been clearly identified. In this work, we fundamentally investigated ALD process Al2O3 on Si substrate, using TMA and various alcohol oxidants (methanol (MeOH), ethanol (EtOH), and n-propanol (n-PrOH)). Furthermore, we investigate the reaction mechanism of various alcohol oxidants during ALD of Al2O3 with TMA. Density functional theory (DFT) calculations at B97D3 level of theory were performed using Gaussian 09 suite of programs. Our developed ALD processes showed typical ALD growth characteristics. The saturated growth rates with MeOH, EtOH and n-PrOH were 0.10, 0.96, and 0.74 Å/cycle, respectively. From the calculation results, we revealed that the beta-hydrogen transfer reaction of EtOH and n-PrOH could easily oxidize surface methyl group into surface hydroxyl. The results could be applicable to highly integrated semiconductor devices fabrication and 2D TMDC based FET fabrication processes.

High-Speed Vapor Transport Deposition of Perovskite Thin Films.

Intensive research of hybrid metal-halide perovskite materials for use as photoactive materials has resulted in an unmatched increase in the power conversion efficiency of perovskite photovoltaics (PVs) over the last couple of years. Now that lab-fabricated perovskite devices rival the efficiency of silicon PVs, the next challenge of scalable mass manufacturing of large perovskite PV panels remains to be solved. For that purpose, it is still unclear which manufacturing method will provide the lowest processing cost and highest quality solar cells. Vapor deposition has been proven to work well for perovskites as a controllable and repeatable thin-film deposition technique but with processing speeds currently too slow to adequately lower the production costs. Addressing this challenge, in the present work, we demonstrate a high-speed vapor transport processing technique in a custom-built reactor that produces high-quality perovskite films with unprecedented deposition speed exceeding 1 nm/s, over 10× faster than previous vapor deposition demonstrations. We show that the semiconducting perovskite films produced with this method have excellent crystallinity and optoelectronic properties with 10 ns charge carrier lifetime, enabling us to fabricate the first photovoltaic devices made by perovskite vapor transport deposition. Our experiments are guided by computational fluid dynamics simulations that also predict that this technique could lead to deposition rates on the order of micrometers per second. This, in turn, could enable cost-effective scalable manufacturing of the perovskite-based solar technologies.

Reduction of Interfacial Polarization between Inorganic Solid Electrolyte and Li Anode By Using a Metallic Interlayer

In early 1990s, rechargeable batteries using inorganic ionic conductors as solid electrolytes have been proposed. Because of their improved safety features, solid state batteries have received great attention recently. Among several inorganic ionic conductors, Garnet-structured Li7La3Zr2O12 (LLZO) show adequate ionic conduction and excellent structural stability when used as the solid electrolyte for Li battery applications. Using Li metal as anode has been a long-term target Moreover, LLZO exhibits superior reduction stability against metallic Li. However, the poor contact/adhesion between Li and LLZO has caused large interface polarization between LLZO and Li metal. Several metals and oxides have been used as the interlayer between LLZO and Li metal and shown improved interface behaviour with lower polarization. Sputtering has been an excellent thin-film deposition technique for obtaining metallic and oxide thin film. Thus, the main objective of this study is to (i) investigate the feasibility of using metallic thin film as an interlayer for inorganic solid state battery using Li as anode, (ii) to evaluate the interface polarization with and without interlayer; (iii) to determine the effect of interlayer thickness on interface polarization, (iv) to analyse and understand the process and behaviour of Li insertion into metal thin film layer, (v) to demonstrate the effectiveness of metallic interlayer on reduction of interface polarization based on Li stripping/plating and full cell tests. In this study, LLZO will be densified to >95% dense using nanosized powder. Gold thin film will be first deposited on the polished surface of LLZO using rf magnetron sputtering. Secondly, Li metal will be placed on top of Au film under heating near melting point of Li. Li stripping and plating will be conducted under constant current with monitoring of applied voltage. Impedance resulted from interface variation will be measured using Electrochemical impedance spectroscopy (EIS). XRD analysis and SEM observation will be performed for possible alloy forming processing. Finally, a full cell based on Li/Au (interlayer)/LLZO/LCO will be tested and compared with the one without Au interlayer to show the effectiveness of metallic interlayer.

Thin-Film Processing Routes for Combinatorial Materials Investigations-A Review.

High-throughput combinatorial investigations are transforming materials discovery, phase diagram development, and processing optimization. Thin-film deposition techniques are frequently used to fabricate sample libraries employed in these studies. Various adaptations of well-known thin-film chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques utilized for the synthesis of inorganic combinatorial thin-film materials libraries are reviewed, with novel processing approaches being highlighted. Methods for developing gradients in composition of other film properties are described. Issues and considerations specific to thin-film processing of combinatorial materials libraries are discussed, with some emphasis on catalytic applications.

Vinyl and phenyl terminated octasilsesquioxane thin films: Evidence for π-stacking induced self-organization of the spherically symmetrical molecules

Organosilicon compounds are surprising in the diversity of their applications as a result of the enormous diversity in their structure. Of particular interest are the self-assembling possibilities of silsesquioxane molecules leading to the formation of thin films with thicknesses not exceeding tens of nanometers. To date, only cases of self-organization of molecules with a strongly asymmetrical shape have been known. This study is aimed at obtaining confirmation of self-organization of silsesquioxane molecules in which the π-stacking interaction between arranged spherically symmetrical aromatic rings leads to the formation of a new smectic phase not observed for bulk material. For this purpose, the morphology of growth and the structure of thin octasilsesquioxane layers substituted either with vinyl or phenyl groups was compared. Due to the use of molecular beam technique for thin-film deposition under ultra-high vacuum conditions, any undesirable external influences as well as those associated with the solvent were avoided. The main measurement techniques were the X-Ray Reflectometry and Atomic Force Microscopy, which provided the final proof of the key role of aromatic rings in the self-assembly of these spherically symmetrical molecules.

New Trend in Thin Film Composite Coating Deposition: A Mini Review

The need for new materials for manufacturing application has become a necessity in the material world. Thus, in an attempt to provide innovative materials that have an astonishing blend of chemical, mechanical and physical properties, this study critically looks into the recent advances in thin film deposition. The terminologies used in film deposition were defined, the thin film deposition techniques were highlighted and some applications which showed the new trends in thin film deposition were reviewed and discussed. The overview shows that advances in thin film deposition are evolving and enormous, thus, few of the applications were discussed in course of this study. Examples of advances in thin film deposition application discussed in this review include the application of thin film deposition in storage, electronic semiconductor devices, detectors and sensors, energy and optoelectronics application, resistance to wear, corrosion, abrasion and thermal stability.

Editors' Choice—Review—Cobalt Thin Films: Trends in Processing Technologies and Emerging Applications

Cobalt metallic films are the subject of an ever-expanding academic and industrial interest for incorporation into a multitude of new technological applications. This report reviews the state-of-the art chemistry and deposition techniques for cobalt thin films, highlighting innovations in cobalt metal-organic chemical vapor deposition (MOCVD), plasma and thermal atomic layer deposition (ALD), as well as pulsed MOCVD technologies, and focusing on cobalt source precursors, thin and ultrathin film growth processes, and the resulting effects on film composition, resistivity and other pertinent properties.

Overview of thin film deposition techniques

Surface properties of the material can affect the efficiency and behavior of the material when in service. Modifying and tuning these surface properties to meet the specific demand for better performance is feasible and has been vastly employed in a different aspect of life. This can be achieved by coating the surface via deposition of the thin film. This study provides a review of the existing literature of different deposition techniques used for surface modification and coating. The two major areas of interest discussed are physical and chemical vapor deposition techniques, and the area of applications of surface coating was briefly highlighted in this report.

Synthesis of Doped, Ternary, and Quaternary Materials by Atomic Layer Deposition: A Review

In the past decade, atomic layer deposition (ALD) has become an important thin film deposition technique for applications in nanoelectronics, catalysis, and other areas due to its high conformality on 3-D nanostructured substrates and control of the film thickness at the atomic level. The current applications of ALD primarily involve binary metal oxides, but for new applications there is increasing interest in more complex materials such as doped, ternary, and quaternary materials. This article reviews how these multicomponent materials can be synthesized by ALD, gives an overview of the materials that have been reported in the literature to date, and discusses important challenges. The most commonly employed approach to synthesize these materials is to combine binary ALD cycles in a supercycle, which provides the ability to control the composition of the material by choosing the cycle ratio. Discussion will focus on four main topics: (i) the characteristics, benefits, and drawbacks of the approaches that currently exist for the synthesis of multicomponent materials, with special attention to the supercycle approach; (ii) the trends in precursor choice, process conditions, and characterization methods, as well as underlying motivations for these design decisions; (iii) the distribution of atoms in the deposited material and the formation of specific (crystalline) phases, which is shown to be dependent on the ALD cycle sequence, deposition temperature, and post-deposition anneal conditions; and (iv) the nucleation effects that occur when switching from one binary ALD process to another, with different explanations provided for why the growth characteristics often deviate from what is expected. This paper provides insight into how the deposition conditions (cycle sequence, temperature, etc.) affect the properties of the resultant thin films, which can serve as a guideline for designing new ALD processes. Furthermore, with an extensive discussion on the nucleation effects taking place during the growth of ternary materials, we hope to contribute to a better understanding of the underlying mechanisms of the ALD growth of multicomponent materials.

Kinetic Monte Carlo Study of the Atomic Layer Deposition of Zinc Oxide

Atomic layer deposition (ALD) has emerged as an important technique for thin-film deposition in the last two decades. Zinc oxide thin films, usually grown via diethylzinc (DEZ) and water process, h...