Excellent Thickness Control Research Articles

Atmospheric-pressure atomic layer deposition: recent applications and new emerging applications in high-porosity/3D materials.

Atomic layer deposition (ALD) is a widely recognized technique for depositing ultrathin conformal films with excellent thickness control at Ångström or (sub)monolayer level. Atmospheric-pressure ALD is an upcoming ALD process with a potentially lower ownership cost of the reactor. In this review, we provide a comprehensive overview of the recent applications and development of ALD approaches emphasizing those based on operation at atmospheric pressure. Each application determines its own specific reactor design. Spatial ALD (s-ALD) has been recently introduced for the commercial production of large-area 2D displays, the surface passivation and encapsulation of solar cells and organic light-emitting diode (OLED) displays. Atmospheric temporal ALD (t-ALD) has opened up new emerging applications such as high-porosity particle coatings, functionalization of capillary columns for gas chromatography, and membrane modification in water treatment and gas purification. The challenges and opportunities for highly conformal coating on porous substrates by atmospheric ALD have been identified. We discuss in particular the pros and cons of both s-ALD and t-ALD in combination with their reactor designs in relation to the coating of 3D and high-porosity materials.

Ionic Liquid-Mediated Route to Atomic Layer Deposition of Tin(II) Oxide via a C-C Bond Cleavage Ligand Modification Mechanism.

Atomic layer deposition (ALD) is a technologically important method to grow thin films with high conformality and excellent thickness control from vapor phase precursors. The development of new thermal ALD processes can be limited by precursor reactivity and stability: reaction temperature and precursor design are among the few variables available to achieve higher reactivity in gas-phase reactions, unlike in solution synthesis, where the use of solvent and/or a catalyst can promote a desired reaction. To bridge this synthesis gap between vapor-phase and solution-phase, we demonstrate the use of an ultrathin coating layer of a vapor phase-compatible solvent─an ionic liquid (IL)─on our growth substrate to perform ALD of SnO. Successful SnO deposition is achieved using tin acetylacetonate and water, a process that otherwise would require a stronger counter-reactant such as ozone. The presence of the layer of IL allows a solvent-mediated reaction mechanism to take place on the growth substrate surface. We report a growth per cycle of 0.67 Å/cycle at a deposition temperature of 100 °C in an IL comprising 1-ethyl-3-methylimidazolium hydrogen sulfate. Characterization of the ALD films confirms the SnO film composition, and 1H and 13C NMR are used to probe the solvent-mediated ALD reaction, suggesting a solvent-mediated addition-elimination-type mechanism which breaks a C-C bond in acetylacetonate to form acetone and acetate. Density functional theory calculations show that the IL solvent is beneficial to the proposed solvent-mediated mechanism by lowering the C-C bond cleavage energetics of acetylacetonate compared to the vapor phase. A general class of ligand modification reactions for thermal ALD is thus introduced in this work.

Flexible and high-intensity photoacoustic transducer with PDMS/CSNPs nanocomposite for inspecting thick structure using laser ultrasonics

Laser ultrasonic technique has been increasingly implemented for nondestructive testing and structural health monitoring. However, the poor signal-to-noise ratio (SNR) and low amplitude of laser generated ultrasonic signals under thermoelastic regime severely restrict its applications. In this paper, we propose a method for fabricating flexible, high-intensity and readily transplantable photoacoustic transducer (PAT) comprised of candle soot nanoparticles (CSNPs) and polydimethylsiloxane (PDMS), and utilize it to generate high SNR and amplitude ultrasonic signals for inspecting thick structures. A robotic-arm based layer-by-layer automatic scanning strategy is developed to realize candle soot nanoparticles (CSNPs) deposition with excellent homogeneity and thickness controllability, and the optimal thickness of PDMS/CSNPs nanocomposite layer to achieve high SNR and amplitude ultrasonic signal is obtained. In addition, a novel method for optimizing the PAT's structure to generate distinguishable and pure longitudinal ultrasonic signals is proposed, with amplitude over 100 times, and with center frequency (13.5 MHz) and −6 dB bandwidth (20.1 MHz) 29.8% and 35.8% higher than those generated without PAT. The optimized PAT is eventually combined with laser ultrasonic technique to successfully inspect and visualize the internal defects with various sizes (4, 2, 0.8 mm in diameter) of an aluminum component with thickness of 50 mm. With the merits of flexible and high-intensity nanocomposite PAT, the laser ultrasonics can be promisingly implemented for inspecting structure with large thickness and complex geometry under thermo-elastic mechanism.

In Situ Plasma‐Grown Silicon‐Oxide for Polysilicon Passivating Contacts

AbstractLarge‐scale manufacturing of polysilicon‐based passivating contacts for high‐efficiency crystalline silicon (c‐Si) solar cells demands simple fabrication of thermally stable SiOx films with well controlled microstructure and nanoscale thickness to enable quantum‐mechanical tunneling. Here, plasma‐dissociated CO2 is investigated to grow in situ thin (<2 nm) SiOx films on c‐Si wafers as tunnel‐oxides for plasma‐deposited, hole‐collecting (i.e., p‐type) polysilicon contacts. It is found that such plasma processing offers excellent thickness control and superior structural integrity upon thermal annealing at 1000 °C, compared to state‐of‐the‐art wet‐chemical oxides. As a result, p‐type polysilicon contacts are achieved on n‐type c‐Si wafers that combine excellent surface passivation, resulting in an implied open‐circuit voltage exceeding 700 mV, with a contact resistance as low as 0.02 Ω cm2.

Corrosion protection of Cu by atomic layer deposition

Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0–14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5–7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade.

Pulsed Laser Deposition Assisted van der Waals Epitaxial Large Area Quasi‐2D ZnO Single‐Crystal Plates on Fluorophlogopite Mica

AbstractThere are still challenges in growth of transferable large area orientated ultrathin high‐melting‐point metal oxide single crystals with conventional methods. Herein, a new pathway to produce high quality single‐crystal ZnO nanoplates with more than 400 µm crystal size is revealed by using the van der Waals epitaxy (vdWE) combined with pulsed laser deposition (PLD) method on fluorophlogopite mica. The quasi‐2D ZnO plates as thin as 5 nm on fluorophlogopite mica without transition layer are achieved, showing an excellent thickness and orientation control while maintaining the excellent crystalline. ZnO nanoplates grown on conducting graphite and insulating hexagonal boron nitride (h‐BN) 2D substrates are also obtained through PLD assisted vdWE. The transfer of 15 nm thick quasi‐2D ZnO plates with 8 mm × 8 mm area onto a SiO2/Si substrate is successfully demonstrated. Based on the ZnO nanoplates, semitransparent self‐powered ultraviolet (UV) photodetectors and light‐emitting diodes centered at 400 nm UV region are demonstrated. This research highlights that the PLD assisted vdWE method is a fascinating way to fabricate high coverage ultrathin 2D ZnO plates with precisely thickness control for optoelectronic applications and may have enormous inspiration for other 2D nanomaterials growth.

69‐3: Distinguished Paper: Large‐Area Spatial Atomic Layer Deposition of Amorphous Oxide Semiconductors at Atmospheric Pressure

Indium Gallium Zinc Oxide (IGZO) films are deposited using plasma‐enhanced spatial Atomic Layer Deposition (sALD) on substrates as large as 32 cm x 35 cm. Excellent uniformity and thickness control leads to high‐performing and stable co‐planar top‐gate self‐aligned (SA) thin‐film transistors (TFTs), demonstrating the viability of atmospheric spatial ALD as a novel deposition technique for the flat‐panel display industry.

Large‐area spatial atomic layer deposition of amorphous oxide semiconductors at atmospheric pressure

AbstractIndium gallium zinc oxide (IGZO) is deposited using plasma‐enhanced spatial atomic layer deposition (sALD) on substrates as large as 32 × 35 cm2. Excellent uniformity and thickness control leads to high‐performing and stable coplanar top‐gate self‐aligned (SA) thin‐film transistors (TFTs). The integration of a sALD‐deposited aluminum oxide buffer layer into the TFT stack further improves uniformity and stability. The results demonstrate the viability of atmospheric sALD as a novel deposition technique for the flat‐panel display industry.

High performance few-layer MoS2 transistor arrays with wafer level homogeneity integrated by atomic layer deposition

Wafer-level integration of 2D transition metal disulfide is the key factor for future large-scale integration of the continuously scaling-down devices, and has attracted great attention in recent years. Compared with other ultra-thin film growth methods, atomic layer deposition (ALD) has the advantages of excellent step coverage, uniformity and thickness controllability. In this work, we synthesized large-scale and thickness-controllable MoS2 films on sapphire substrate by ALD at 150 °C with molybdenum hexcarbonyl and hexamethyldisilathiane (HMDST) as precursors followed by high-temperature annealing in sulfur atmosphere. HMDST is introduced for the first time to enable a toxic-free process without hazardous sulfur precursors such as H2S and CH3SSCH3. The synthesized MoS2 retains the inherent benefits from the ALD process, including thickness controllability, reproducibility, wafer-level thickness uniformity, and high conformity. Finally, field-effect transistor (FET) arrays were fabricated based on the large-area ALD MoS2 films. The top-gate FETs exhibited excellent electrical performance such as high on/off current ratio over 103 and peak room-temperature mobility up to 11.56 cm2 V−1 s−1. This work opens up an attractive approach to realize the application of high-quality 2D materials with wafer scale homogeneity.

BaTiO3 Thin Films from Atomic Layer Deposition: A Superlattice Approach

A superlattice approach for the atomic layer deposition of polycrystalline BaTiO3 thin films is presented as an example for an effective route to produce high-quality complex oxide films with excellent thickness and compositional control. This method effectively mitigates any undesirable reactions between the different precursors and allows an individual optimization of the reaction conditions for the Ba–O and the Ti–O subcycles. By growth of nanometer thick alternating Ba(OH)2 and TiO2 layers, the advantages of binary oxide atomic layer deposition are transferred into the synthesis of ternary compounds, permitting extremely high control of the cation ratio and superior uniformity. Whereas the Ba(OH)2 layers are partially crystalline after the deposition, the TiO2 layers remain mostly amorphous. The layers react to polycrystalline, polymorph BaTiO3 above 500 °C, releasing H2O. This solid-state reaction is accompanied by an abrupt decrease in film thickness. Transmission electron microscopy and Raman spect...

Synthesis of single-walled carbon nanotubes from atomic-layer-deposited Co3O4 and Co3O4/Fe2O3 catalyst films

We have investigated the synthesis of single-walled carbon nanotubes (SWCNTs) employing Co3O4 films prepared by atomic layer deposition (ALD). These films dewet into Co catalyst nanoparticles in the furnace before starting CNT growth by chemical vapor deposition (CVD). The facile Co3O4 ALD process allows for excellent film thickness control and very reproducible growth of high quality SWCNTs even from ultrathin, single-digit cycle ALD films. We demonstrate CNT growth on planar and 3-dimensional geometries. A detailed study using a combination of Raman spectroscopy as well as scanning and transmission electron microscopy reveals that the density and diameter distribution of the catalyst particles and resulting CNTs can be controlled by the number of ALD cycles. Moreover, we demonstrate straightforward preparation of Fe/Co bimetallic catalysts by mixing ALD processes of Co3O4 and Fe2O3. Finally, the wide temperature window of Co3O4 ALD allows for patterning of the catalyst via standard electron-beam lithography, as the deposition temperature is low enough to prevent resist reflowing. We conclude that ALD is an ideal technique to deposit Co3O4 catalyst films for SWCNT synthesis in a well-controlled manner, with several advantages over other materials and deposition techniques.

Modeling and in Situ Probing of Surface Reactions in Atomic Layer Deposition.

Atomic layer deposition (ALD) has matured into a preeminent thin film deposition technique by offering a highly scalable and economic route to integrate chemically dissimilar materials with excellent thickness control down to the subnanometer regime. Contrary to its extensive applications, a quantitative and comprehensive understanding of the reaction processes seems intangible. Complex and manifold reaction pathways are possible, which are strongly affected by the surface chemical state. Here, we report a combined modeling and experimental approach utilizing ReaxFF reactive force field simulation and in situ real-time spectroscopic ellipsometry to gain insights into the ALD process of Al2O3 from trimethylaluminum and water on hydrogenated and oxidized Ge(100) surfaces. We deciphered the origin for the different peculiarities during initial ALD cycles for the deposition on both surfaces. While the simulations predicted a nucleation delay for hydrogenated Ge(100), a self-cleaning effect was discovered on oxidized Ge(100) surfaces and resulted in an intermixed Al2O3/GeOx layer that effectively suppressed oxygen diffusion into Ge. In situ spectroscopic ellipsometry in combination with ex situ atomic force microscopy and X-ray photoelectron spectroscopy confirmed these simulation results. Electrical impedance characterizations evidenced the critical role of the intermixed Al2O3/GeOx layer to achieve electrically well-behaved dielectric/Ge interfaces with low interface trap density. The combined approach can be generalized to comprehend the deposition and reaction kinetics of other ALD precursors and surface chemistry, which offers a path toward a theory-aided rational design of ALD processes at a molecular level.

Metal-Insulator-Metal Single Electron Transistors with Tunnel Barriers Prepared by Atomic Layer Deposition

Single electron transistors are nanoscale electron devices that require thin, high-quality tunnel barriers to operate and have potential applications in sensing, metrology and beyond-CMOS computing schemes. Given that atomic layer deposition is used to form CMOS gate stacks with low trap densities and excellent thickness control, it is well-suited as a technique to form a variety of tunnel barriers. This work is a review of our recent research on atomic layer deposition and post-fabrication treatments to fabricate metallic single electron transistors with a variety of metals and dielectrics.

Fabrication of hollow TiO2 nanotubes through atomic layer deposition and MWCNT templates

Titanium oxide (TiO2) nanotubes were synthetized by atomic layer deposition (ALD) coating multiwalled carbon nanotubes (MWCNTs) template. Thick wall (20nm) TiO2 tubes were fabricated by coating directly the bare MWCNTs surface with TiO2 ALD. For thinner wall tubes (10nm), very thin Al2O3 buffer layer was inserted to enhance the structural stability of the TiO2 tubes. Coatings were carried out at 100°C in a hot-walls pulsed-bed ALD reactor. Trimethyl-aluminum (TMA) and Tetrakis(dimethylamino)titanium (TDMAT), where used as metal precursors and water as oxygen source. Wall thickness of TiO2 tubes was controlled by adjusting the number of ALD-cycles, as seen Transmission Electron Microscopy (TEM) images. Chemical characteristics of both uncoated and coated MWCNTs were analyzed through a XPS and a FTIR. Templates were removed by thermal oxidation, monitored by thermogravimetric analysis (TGA) up to 800°C, finding thicker TiO2 layers shift up the degradation temperature of the templates. EDXS line scan in TEM confirmed the coatings retained the concentric structure of the parent templates while attaining excellent wall thickness control. XRD, Raman spectroscopy and SAED confirm that TiO2 anatase is the only crystalline phase present after template removal.

Hybrid Film Deposition for High-Aspect-Ratio Structures with Functional Surfaces

Thin film deposition is one of the most significant issues in the fabrication of nano structures. Especially it is difficult to achieve conformal films on high-aspect ratio nanostructures, such as nanoholes and nanochannels. Though there are various thin film deposition processes, atomic layer deposition (ALD) has attracted due to its extreme surface conformality and excellent thickness controllability. Because ALD is a chemical gas phase thin film deposition method based on sequential and self-saturating surface reactions, it can be used for coating of nano structures with high-aspect ratio. Sputtering process is one of the popular film deposition techniques due to its relative simplicity of process and fast deposition speed. However, film depositions by sputtering technique are less conformal compared to those by ALD, because of ions directionality sputtered by plasma. Therefore it is difficult to form films on the surfaces perpendicular to substrate by sputtering process. However, if ALD and sputtering processes are combined, hybrid thin films deposition which different films are deposited on selectively different surfaces (eg. surfaces perpendicular and parallel to substrate). In this poster, I will present the results of hybrid films deposition on nano holes/channels structures with high-aspect ratio. For different functionalities (hydrophilicity and hydrophobicity) of surfaces, Al2O3 and Pt films were grown on nanochannel structures. Al2O3 films deposition on the vertical surfaces (inner surfaces of nanochannels) was controlled precisely in nanometer scale by using ALD process. Pt films were formed on horizontal surfaces (outer surfaces of nanochannels) by using DC magnetron sputtering.

Plasma - Assisted ALD of Lipo(N) for Solid State Batteries

Present-day planar thin-film solid state Li-ion batteries provide an excellent power density and improved safety over their liquid counterparts. However, their energy density remains typically low. For this reason the transition to a 3D thin film battery is presently being explored. This preserves the extreme power characteristics associated with the usage of thin films while increasing the amount of active material and therefore the energy density. Key to the realization of such battery is the possibility to coat these large surface area structures in a conformal and defect free way1. This aspect is especially critical for the solid electrolyte which provides electronic insulation between the two electrodes. Nitrogen-doped lithium phosphate glass or LiPON, is the solid state electrolytes of choice for planar thin-film batteries. This is attributed to its good electronic insulating properties, its wide electrochemical window (0 - 5.5V vs Li+/Li) and reasonable ionic conductivity (~10-6 S/cm). The ionic resistance of the LiPON is still below 100 Ω.cm2 when the film thickness is kept below 1 μm. It was shown recently that LiPON layers can provide electronic insulation down to 15 nm.2 Atomic layer deposition (ALD), which is a vapor based technique with sequential and self-limiting reactions, is known to provide excellent conformality and thickness control (down to sub-nm level). Hence, it is ideally suited for the deposition of the solid electrolyte in thin film battery applications. Recently both thermal and plasma assisted ALD of LiPON was shown3,4. In this work we report the deposition of Li3PO4 and LixPOyNz using LiOtBu and TMPO as precursors and H2O (or O2 plasma) and N2 plasma as reactants. The effect of these different processing conditions on the stoichiometry is studied by a combination of Elastic Recoil Detection (ERD) and X-ray Photoelectron Spectroscopy (XPS). As expected, nitrogen is incorporated in the Li3PO4 layers by sequentially exposing the layers to a N2plasma. For the first time the electrical and electrochemical properties were investigated for a range of different material compositions and thicknesses in detail. Large varieties in ionic conducitivity (between 10-14 – 10-7 S/cm) and activation energy were measured by impedance spectroscopy for the different processing conditions. DC-polarization measurements showed good electronic insulating properties for films below 50 nm (ρ ~ 1015 Ω.cm). Such thin films lead to a minimal ionic resistance (on the order of 1.5 Ω.cm2for the thinnest layer), which can facilitate extreme charging and discharging kinetics. Finally, the deposition of these layers was tested in high aspect ratio pillar arrays and in Li-ion half cells comprising TiO2/LiPO(N) and LiMn2O4/LiPO(N). The layers fabricated here can serve as electrolyte in the all solid state 3D batteries. However, they also hold potential as buffer layer to stabilize electrodes in a classical wet battery. Vereecken et al., ECS transactions, 58, 111-118, 2013Put et al., ACS Applied materials & interfaces, 8, 7060–7069, 2016Kozen et al., Chemistry of materials, 27, 5324-5331, 2015Nisula et al., Chemistry of materials, 27, 6987–6993, 2015 Figure Caption: Figure 1: Complex plane plot of a Li3PO4 layer showing the characteristic semi-circle associated with Li-ion conductivity through the layer. The inset shows the conformal coating of a high aspect-ratio pillar array. Figure 1

Interface Engineering of Next Generation Lithium Metal Anodes

Protection of lithium metal is of significant interest to the battery community: as the lightest and most electropositive alkali metal, lithium has a low density, resulting in an extremely high specific capacity value of 3.86Ah/g and energy density of 11,701Wh/kg, making it the holy grail of battery anodes. However, due to the extreme reactivity of lithium metal surfaces, controlled protection and characterization are extremely difficult. We have developed a bespoke integrated deposition, transfer, and characterization system capable of coating lithium metal anodes using Atomic layer deposition (ALD), characterizing the surface chemistry using XPS/SEM/UPS/Auger spectroscopy, and transfer directly from UHV into an Ar glovebox for battery assembly, disassembly, and electrochemical testing. After testing, the metal anodes can be transferred directly back to the XPS/SEM/UPS/Auger system for characterization. Protection coatings for lithium metal require the coatings be conformal, easily deposited at low temperature, and stable against organic electrolytes. Preventing direct contact of the lithium metal surface with the electrolyte and any dissolved species that would ordinarily react will ensure that the lithium atoms are oxidized in a reversible manner, rather than losing ions/electrons to highly stable, low ionic conductivity surface species such as Li2CO3. Lithium metal protection may allow the relaxation of purity requirements for both electrolytes and, in the case of Li-O2 batteries, cathode gas purity. To date, Li metal protection has been demonstrated with coatings of chlorosilanes[1] and other polymeric[2], organic[3], and inorganic coatings, but ALD has not been applied directly to lithium metal anodes for the purposes of protection. Known for conformality, low temperature deposition, excellent thickness control, ALD serves as an excellent permeation barrier, suggesting that it can be pinhole-free a promising technique for this application. We have developed ALD processes suitable for the protection of Li metal, and we assess the behavior of these functional ALD coatings electrochemically using over-potential studies and electrochemical impedance spectroscopy measurements. Surface characterization by semi in-situ XPS of protected and pristine lithium metal subjected to both gaseous environments and electrolytes with controlled/measured H2O content will be discussed, where the surface characterization is accomplished without ambient air exposure. We show that protection of lithium metal is not only possible with ALD, but that it is effective at preventing the tarnishing of the lithium metal surface due to reaction with atmospheric H2O and CO2. Using our unique capabilities, we are able to probe the chemistry of both protected and unprotected lithium metal, while using in-situ gas dosing we can decouple and characterize the interface chemistry and reactions. We demonstrate as a proof of concept that a 14 nm thick, ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Furthermore, using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles. This work has implications and impact on the metallic lithium anode battery systems Li-O2, Li-S and Li-NMC. Additionally, it is promising to pursue corresponding protection layers for Mg ad Na, where similar deleterious surface reactions may apply. Fundamental understanding of the controlled surface protection of lithium by ALD coatings could be extended to these other next-generation metal anode battery systems, and indeed could have a beneficial impact on the cyclability and storage lifetimes of lithium metal anode batteries.

Graphene and monolayer transition-metal dichalcogenides: properties and devices

Abstract

Interface Engineering of Next Generation Lithium Metal Anodes Using Atomic Layer Deposition

Protection of lithium metal is of significant interest to the battery community: as the lightest and most electropositive alkali metal, lithium has a low density, resulting in an extremely high specific capacity value of 3.86Ah/g and energy density of 11,701Wh/kg, making it the holy grail of battery anodes. However, due to the extreme reactivity of lithium metal surfaces, controlled protection and characterization are extremely difficult. We have developed a bespoke integrated deposition, transfer, and characterization system capable of coating lithium metal anodes using Atomic layer deposition (ALD), characterizing the surface chemistry using XPS/SEM/UPS/Auger spectroscopy, and transfer directly from UHV into an Ar glovebox for battery assembly, disassembly, and electrochemical testing. After testing, the metal anodes can be transferred directly back to the XPS/SEM/UPS/Auger system for characterization. Protection coatings for lithium metal require the coatings be conformal, easily deposited at low temperature, and stable against organic electrolytes. Preventing direct contact of the lithium metal surface with the electrolyte and any dissolved species that would ordinarily react will ensure that the lithium atoms are oxidized in a reversible manner, rather than losing ions/electrons to highly stable, low ionic conductivity surface species such as Li2CO3. Lithium metal protection may allow the relaxation of purity requirements for both electrolytes and, in the case of Li-O2 batteries, cathode gas purity. To date, Li metal protection has been demonstrated with coatings of chlorosilanes[1] and other polymeric[2], organic[3], and inorganic coatings, but ALD has not been applied directly to lithium metal anodes for the purposes of protection. Known for conformality, low temperature deposition, excellent thickness control, ALD serves as an excellent permeation barrier, suggesting that it can be pinhole-free a promising technique for this application. We have developed ALD processes suitable for the protection of Li metal, and we assess the behavior of these functional ALD coatings electrochemically using over-potential studies and electrochemical impedance spectroscopy measurements. Surface characterization by semi in-situ XPS of protected and pristine lithium metal subjected to both gaseous environments and electrolytes with controlled/measured H2O content will be discussed, where the surface characterization is accomplished without ambient air exposure. We show that protection of lithium metal is not only possible with ALD, but that it is effective at preventing the tarnishing of the lithium metal surface due to reaction with atmospheric H2O and CO2. Using our unique capabilities, we are able to probe the chemistry of both protected and unprotected lithium metal, while using in-situ gas dosing we can decouple and characterize the interface chemistry and reactions. We demonstrate as a proof of concept that a 14 nm thick, ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Furthermore, using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles. This work has implications and impact on the metallic lithium anode battery systems Li-O2, Li-S and Li-NMC. Additionally, it is promising to pursue corresponding protection layers for Mg ad Na, where similar deleterious surface reactions may apply. Fundamental understanding of the controlled surface protection of lithium by ALD coatings could be extended to these other next-generation metal anode battery systems, and indeed could have a beneficial impact on the cyclability and storage lifetimes of lithium metal anode batteries.

Hybrid Films Deposition for Nanochannel Membranes with Functional Surfaces

Thin film deposition is one of the most significant issues in the fabrication of nano structures. Especially it is difficult to achieve conformal films on high-aspect ratio nanostructures, such as nanochannel membranes. Though there are various thin film deposition techniques, atomic layer deposition (ALD) has attracted due to its extreme surface conformality and excellent thickness controllability. Because ALD is a chemical gas phase thin film deposition method based on sequential and self-saturating surface reactions, it can be used for coating of nano structures with high-aspect ratio. Sputtering process is one of the popular film deposition techniques due to its relative simplicity of process and fast deposition speed. However, film depositions by sputtering technique are less conformal compared to those by ALD, because of ions directionality sputtered by plasma. Therefore it is difficult to form films on the surfaces perpendicular to substrate by sputtering process. However, if ALD and sputtering techniques are combined, hybrid thin films deposition which different films are deposited on selectively different surfaces (eg. surfaces perpendicular and parallel to substrate). In this poster, I will present the results of hybrid films deposition on nanochannel membranes with high-aspect ratio. For different functionalities (hydrophilicity and hydrophobicity) of surfaces, Al2O3 and Pt films were grown on nanochannel membranes. Al2O3 films deposition on the vertical surfaces (inner surfaces of nanochannels) was controlled precisely in nanometer scale by using ALD process. Pt films were formed on horizontal surfaces (outer surfaces of nanochannels) by using DC magnetron sputtering. In addition, I will also present the ionic seperation in NaCl solution using fabricated nanochannel membranes by hybrid deposition process and using electrcal bias on Pt films.