Thin Metal Films Research Articles

Development of L10-ordered FePt with low damping and large perpendicular magnetic anisotropy by engineering the nanostructure

THz spintronics is an emergent area of research aimed at bridging the gap between fifth- and sixth-generation wireless telecommunications by utilizing spintronic devices such as magnetic spin torque oscillators as a source of low powered THz emission. The realization of such devices using ferromagnetic metal thin films however requires magnetic materials with both large perpendicular magnetic anisotropy (PMA) and low Gilbert damping constants. In this Letter, we report on the development of L10-ordered FePt with an effective Gilbert damping constant as low as 0.033. Using time-resolved magneto-optical Kerr effect, we characterized the magnetization dynamics of continuous L10-ordered FePt grown on MgO and SrTiO3 substrates. By changing the substrate on which FePt is grown, the lattice mismatch and subsequent number of misfit dislocations at the interface and L10-ordering can be controlled. We found that fewer misfits and improved ordering in FePt lead to a reduced Gilbert damping constant due to reduced electron scattering but that FePt grown on SrTiO3 also shows robust perpendicular magnetic anisotropy. Importantly, these results demonstrate the ability to control the damping in FePt and similar materials by changing the number of misfit dislocations at the interface and the smaller damping in FePt opens up the possibility of using this material in spintronic materials in the THz wave range.

Vapour phase deposition of phosphonate-containing alumina thin films using dimethyl vinylphosphonate as precursor.

Phosphorous-containing materials are used in a wide array of fields, from energy conversion and storage to heterogeneous catalysis and biomaterials. Among these materials, organic-inorganic metal phosphonate solids and thin films present an interesting option, due to their remarkable thermal and chemical stability. Yet, the synthesis of phosphonate hybrids by vapour phase thin film deposition techniques remains largely unexplored. In this work, we present successful deposition of phosphonate-containing films using dimethyl vinylphosphonate (DMVP) as a phosphonate precursor. Two processes have been studied, being a three-step process comprising alternating exposure to trimethylaluminum (TMA), water (H2O) and DMVP (ABC process), and a four-step process with an extra O3 step following the DMVP pulse (ABCD process). The O3 treatment is employed for in situ functionalisation of the adsorbed phosphonate precursor, transforming the vinyl group into a carboxylic acid end group. For both processes, good precursor saturation was found, with the ABCD process exhibiting a more stable growth per cycle (0.54-0.38 Å per cycle) in the investigated temperature range (100-250 °C). Phosphonate features were visible in FTIR spectra for both films, with the ABCD films also exhibiting a carboxylate signal. XPS showed a higher P incorporation in the ABCD films deposited at 250 °C, although still moderate (P/Al = 0.27), consistent with an alumina structure with phosphonate inclusions. The film stability upon immersion in water was tested, showing a slow oxidation over the course of a week. Finally, annealing experiments in air demonstrated stable films up to 400 °C.

An Investigation of the Indentation Elastic Modulus for Metal Films on Flexible Substrates Considering the Substrate Effect.

The accurate measurement of the elastic modulus of thin metal films on flexible substrates is critical for understanding the mechanical reliability of flexible electronics. However, conventional methods, such as the Oliver-Pharr model, often underestimate the modulus due to substrate effects, particularly with low-modulus substrates like polyimide (PI). In this study, we propose an improved weighting model that replaces the empirical weighting factor with a variable X to better account for substrate contributions. Nanoindentation experiments were performed on Cu and Al films with thicknesses of 0.5, 1, and 1.5 μm, deposited on PI and silicon substrates. The results show a significant underestimation of the elastic modulus when traditional methods were applied, especially on PI substrates, where values decreased by up to 95%. Using the proposed X-based model, the corrected elastic modulus aligned with the inherent properties of the films, with errors reduced to within 2%. A finite element analysis (FEA) validated the stress and displacement distributions, demonstrating the substrate's influence on indentation behavior. This study provides a robust framework for accurately measuring the elastic modulus of thin films on flexible substrates, paving the way for a more reliable mechanical characterization in flexible electronics.

Hydride formation in open thin film metal hydrogen systems: Cahn-Hilliard-type phase-field simulations coupled to elasto-plastic deformations

Hydride formation in open thin film metal hydrogen systems: Cahn-Hilliard-type phase-field simulations coupled to elasto-plastic deformations

Spectral SPR effect in thin films of high-conductive metals and features of SPR-biosensors implementation in chromatic mode

In this paper, we have evaluated the application of various types of highly conductive metals for implementing the effect of spectral surface plasmon resonance (SPR) within a visible spectrum range to achieve more efficient and productive registration of biomolecules in a liquid medium using tricolor RGB cameras. Thin films of gold, silver, copper, and aluminum, as well as a bimetallic coating of silver with a gold superlayer on a glass substrate, are considered. Detailed calculations of the spectral characteristics of reflection at SPR excitation in the Kretschmann geometry are performed, particularly when a thin dielectric film is formed on the metal surface that imitates a layer of biomolecules. For each of the specified metals, the width of the region of implementation of the full-fledged SPR effect in the visible range of the spectrum is determined, and the sensitivity of the optical response to the influence of an external dielectric layer is assessed.

A Hydrodynamic Finite-Difference Time-Domain Model of Spatial Dispersion and Surface Modes in Metallic Thin Films

A Hydrodynamic Finite-Difference Time-Domain Model of Spatial Dispersion and Surface Modes in Metallic Thin Films

A Novel Approach to Fabricate Fe-based Thin Film Metallic Glass With Commercial Boron Carbide and AISI M42 Tool Steel

In this study, we report a Fe-based thin film metallic glass (Fe-Cr-Mo-C-B-X TFMG) fabricated by magnetron sputtering with commercial boron carbide (B4C) target and AISI M42 tool steel pellets. Varied number of M42 pellets were co-sputtered with B4C target, resulting in Fe content ranged from 48.1 at% to 62.8 at%. X-ray diffraction and transmission electron microscopy confirmed that all sample films were amorphous. All samples showed glass transition and crystallization in differential scanning calorimetry (DSC), similar to typical metallic glasses. However, glass transition was barely observable in B4m owing to its high oxygen content. The sample films also had extremely low surface roughness of 0.14 – 0.26 nm. The sample films also showed tribological properties comparable to conventionally deposited TFMG, where the highest hardness and reduced modulus obtained was 9.0 GPa and 150.8 GPa respectively. The sample films also demonstrated specific wear rate K0 as low as 1.6 × 10-5 mm3Nm-1. Our work demonstrates a more cost-effective and sustainable way of fabricating Fe-based TFMG, in which both AISI M42 are readily available and can be easily recycled after use.

Gap plasmonic properties of NPOM structures composed of gold nanoparticles and thin films

Metal nanoparticles have attracted great interest because of their unique near-field enhancement properties, and have important applications in many fields, such as surface-enhanced Raman scattering (SERS), fluorescence enhancement, solar cell efficiency enhancement and so on. In this paper, we use the finite element method to study the local field enhancement characteristics of the coupling system in which the gold ellipsoidal nanoparticles (GENP) on a mirror. In the coupling system, a hot spot will be formed at the gap between the GENP and the mirror under the appropriate incident light excitation. Based on the structural characteristics of GENP, we systematically study the local electric field produced by placing ellipsoids vertically and horizontally on the mirror. Under the excitation of the same polarized incident light, the maximum local electric field of the vertical GENP is 2200 (V/m), while that of the horizontal GENP is more than 9400 (V/m). Our proposed gap coupling system based on metal nanoparticles and thin films may open a new field of interest in the fields of plasmon, sensing, optical limitation and enhancement.

Research on Stability of Removal Function in Figuring Process of Mandrel of X-Ray-Focusing Mirror with Variable Curvature.

Over the past 30 years, researchers have developed X-ray-focusing telescopes by employing the principle of total reflection in thin metal films. The Wolter-I focusing mirror with variable-curvature surfaces demands high precision. However, there has been limited investigation into the removal mechanisms for variable-curvature X-ray mandrels, which are crucial for achieving the desired surface roughness and form accuracy, especially in reducing mid-spatial frequency (MSF) errors. It is essential to incorporate flexible control in deterministic small-tool polishing to improve the tool's adaptability to curvature variations and achieve stable, Gaussian-like tool influence functions (TIFs). In this paper, we introduce a curvature-adaptive prediction model for compliance figuring, based on the Preston hypothesis, using a compliant shaping tool with high slurry absorption and retention capabilities. This model predicts the compliance figuring process of variable-curvature symmetrical mandrels for X-ray grazing incidence mirrors by utilizing planar tool influence functions. Initially, a variable-curvature pressure model was developed to account for the parabolic and hyperbolic optical surfaces' curvature characteristics. By introducing time-varying removal functions for material removal, the model establishes a variable-curvature factor function, which correlates actual downward pressure with parameters such as contact radius and contact angle, thus linking the variable-curvature surface with a planar reference. Subsequently, through analysis of the residence time distribution across different TIF models, hierarchical filtering, and PSD distribution, real-time correction of the TIFs was achieved to enable customized variable-curvature polishing. Furthermore, by applying a time-varying deconvolution algorithm, multiple rounds of flexible polishing iterations were conducted on the mandrels of a rotationally symmetric variable-curvature optical component, and the experimental results demonstrate a significant improvement in form accuracy, surface quality, and the optical performance of the mirror.

Understanding the Dynamics of Cobalt Nitride-Based Thin Films for Electrocatalytic Oxygen Reduction

In both acidic and alkaline hydrogen fuel cells, platinum is the benchmark cathode catalyst, exhibiting high activity for the oxygen reduction reaction (ORR). Despite platinum’s exceptional performance, its low abundance and high cost are major factors limiting the widespread adoption of hydrogen fuel cells—a critical technology for the decarbonization of our energy systems. Cobalt nitrides (CoNx) along with cobalt-nitrogen-carbon macrocyclic compounds (Co-N-C) have emerged in literature as a promising subset of active, low-cost ORR catalysts in both acidic and alkaline media. However, the most active of these materials are carbon-supported nanoparticles or single atom catalysts with complex, non-uniform active sites, making it difficult to disentangle the impact of each element within the catalyst (Co, N, C, etc.) on performance. Additionally, the pH- and potential-dependent material stability of these materials is not well-understood.To broaden our fundamental understanding of the activity and dynamics of non-precious ORR electrocatalysts, we have devised a synthesis procedure for well-defined metallic and bimetallic X-ide (nitride, oxide, sulfide, etc.) thin film catalysts. Following a two-step procedure, we have used physical vapor deposition followed by thermal ammonia treatments to form CoxSbyNz films of various compositions. To develop a holistic understanding of the factors influencing ORR electrocatalysis on these materials, we utilize ex situ characterization along with in situ techniques to probe time- and potential-dependent material stability and selectivity during catalysis. With depth-profiling x-ray photoelectron spectroscopy, we observe uniform incorporation of N at approximately 10 atomic percent throughout the NH3-treated films below a native oxide layer. X-ray diffraction indicates that untreated films have a hexagonal close packed structure matching a Co standard, and the NH3-treated films have a hexagonal structure similar to Co3N.To understand catalyst dynamics in situ, we use on-line inductively coupled plasma mass spectrometry (ICP-MS) to measure Co and Sb dissolution, electrochemical mass spectrometry (EC-MS) to probe nitride degradation, and a rotating ring disk electrode (RRDE) to monitor peroxide selectivity. With each of these in situ techniques, we couple cyclic voltammetry experiments, demonstrating that activity and stability are dependent on catalyst composition, electrolyte pH, and the upper and lower potential limits. We find that the stability of CoxSbyNz is limited by Co dissolution in acidic electrolyte and nitride degradation in alkaline electrolyte. The individual incorporation of Sb and N help to prevent the anodic dissolution of cobalt in acidic media, and the metastable incorporation of N improves activity at both pH extremes. Although it is often too difficult to deconvolute the role of individual elements within highly active non-oxide electrocatalysts, our multistep synthesis procedure and comprehensive in situ and ex situ characterization techniques allow us to probe the impact of each element in various CoxSbyNz films on material stability and product-specific activity. Our results impart wisdom that will be useful in the development of low-cost, high-performance electrocatalysts across a broad set of reactions and applications.

(Invited) Atomic Layer Deposited Sulfides As (Pre)Catalysts for Electrochemical Water Splitting

Electrocatalysis is projected to play a key role in building a sustainable world based on renewable energy. Electrochemical water splitting produces H2 on the cathode (hydrogen evolution reaction, HER), which can be used as a fuel and reactant in diverse industries. The oxygen evolution reaction (OER) producing O2 at the anode is a complex reaction that limits the overall efficiency of water electrolyzers. Active, stable, and affordable catalysts are required for both reactions. The range of potential catalysts has expanded from metals and oxides to others, sulfides having become one of the most actively studied material groups. Our work focuses on understanding inherent activity and structural changes under HER and OER conditions.Different water electrolyzer technologies subject the catalysts to different operating conditions, which limits the available catalyst materials. For proton exchange membrane electrolyzers featuring an acidic environment, platinum group metals are currently used. However, several earth abundant catalysts have been identified for HER in acid. Among these, molybdenum sulfides in both amorphous (a-MoSx) and crystalline (c-MoS2) forms have attracted attention.1 We developed a plasma-enhanced ALD (PEALD) process that can deposit both amorphous MoSx with adjustable S/Mo ratio (2.8–4.7) and crystalline MoS2 with different crystallinity, morphology, and electrical properties.2 Electrochemical measurements in 0.5 M H2SO4 combined with ex situ and quasi in situ XPS revealed a-MoSx films to transform into highly active a-MoS2. C-MoS2 films were less active and did not show structural changes under HER conditions.3 Alkaline electrolyzers and anion exchange membrane electrolyzers operate under alkaline conditions and use earth abundant Fe/Co/Ni based catalysts. Most if not all materials based on these metals convert to oxyhydroxides under the highly oxidizing OER conditions and readily incorporate iron present in electrolytes.4,5 Thus, the as-deposited OER catalysts are best described as precatalysts. We developed new ALD processes to deposit NiSx and Co9S8,6,7 while oxide, metal, and hydroxide thin films were deposited for comparison using different methods. Extensive electrochemical measurements in 0.1 M KOH electrolyte with controlled Fe impurities combined with ex situ XPS revealed that in absence of iron all the Ni-based precatalysts convert to an OER-active oxyhydroxide, yet at substantially different rates (NiSx ≈ Ni(OH)2 >> Ni > NiO).8 However, good OER activity and stability was only achieved in the presence of Fe impurities. The highest amount of iron incorporation and the best OER performance was found for the NiSx and Ni(OH)2 precatalysts, which convert the fastest into the active oxyhydroxide form. Studies on Co-based OER precatalysts are currently ongoing, including use of operando characterization methods.Our studies on ALD sulfides as both HER and OER catalysts showcase the importance of understanding catalyst structure and its changes under catalytic conditions. Armed with this knowledge and unique capabilities of ALD, catalysts with higher performance in electrolyzer applications can be designed and engineered.

Realization of a Long-Lifespan Thin Li Metal Batteries Capable of Self-Recovery with a Functional Separator

Due to the rapid expansion of the electric vehicles (EVs) market, the demand for large-scale batteries is increasing. Particularly, EVs face several limitations in terms of battery volume and weight. Therefore, achieving high energy density in limited spaces requires a significant reduction in the volume of the anode. Recently, the research is underway on batteries that employ thin Li metal anodes, typically around 20-25μm thick, as the next generation of lithium-ion batteries. However, thin Li anodes present various challenges regarding their cycle life. Compared to Li metal, thin Li metal faces scarcity in lithium sources. Furthermore, due to the unstable formation and destruction of the Solid Electrolyte Interphase (SEI) during the plating-stripping process in Li metal anode charging and discharging, lithium ions and electrolyte are constantly consumed. These side reactions lead to decreased capacity and deteriorated lifespan characteristics. To maintain stable charging and discharging properties, it is necessary to minimize electrolyte decomposition by forming a stable SEI in the early cycle and continuously supplying consumed Li ions throughout the cycling process. Commonly used methods to supplement the limited lithium source of the thin Li anode and replenish consumed Li ions during charging and discharging represent the employing the high-concentration electrolytes (HCE). However, HCE have limits on the dissolved concentration of salts in the electrolyte, and the method of dissolving salts in the entire electrolyte is not attractive a cost perspective. Additionally, as the electrolyte concentration increases, viscosity also increases, leading to a decrease in ion mobility.In this study, high-concentration lithium bis(fluoromethanesulfonyl)imide (LiFSI) salts are coated onto commercial separators to provide a locally high-concentration environment at the electrode/electrolyte interface. This coating layer dissolves as Li ions are consumed, replenishing the depleted Li ions. Furthermore, the presence of high-concentration Li ions in the electrolyte eliminates free solvent. Reducing free solvent suppresses electrolyte consumption further. Additionally, by adopting LiFSI as the salt, rapid decomposition of anions in the initial cycle facilitates the formation of a stable LiF layer. The densely formed LiF layer exhibits high mechanical strength and electrochemical stability, aiding in achieving long-term characteristics.Li||Li symmetric cells were tested using commercial electrolytes, including 1M LiFSI in diethylene glycol dimethyl ether (DME) and 1M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/ diethylene carbonate (EC/DEC). Both electrolytes showed improved cycle stability and lower polarization in cells using an ionically conductive salt-coated separator (SDL) compared to polyethylene (PE) separators. Particularly, the nucleation polarization observed during the initial charging process, when Li ions are deposited onto bare lithium metal, significantly decreased in SDL cells, indicating better Li ion affinity on the lithium surface of SDL cells. Tafel plots were used to analyze the exchange current at the electrode/electrolyte interface. The exchange current for PE was 1.09 mA/cm2, while for SDL, it was 1.52 mA/cm2, suggesting faster interfacial kinetics in SDL compared to PE. The results were also evident in rate capability tests, with the largest capacity difference observed at 5C. Scanning electron microscope (SEM) images revealed distinctly different Li ion deposits on the Cu foil. PE showed vigorous dendrite growth with many voids, while SDL exhibited dense Li deposition, attributed to the presence of high-concentration salts at the interphase, suppressing dendrite growth and inducing uniform Li ion flux. The stable interfacial characteristics were analyzed using X-ray photoelectron spectroscopy (XPS). After 100 cycles, PE showed a high proportion of electrolyte decomposition components, while SDL exhibited a higher proportion of LiF formation. These results demonstrate coated separator with LiFSI effectively suppressed electrolyte decomposition. Additionally, boehmite was pre-coated on the PE separator to endow with coating adhesion, resulting in improved surface morphology. When various commercial electrolytes were applied after salt coating, significantly enhanced wettability was observed compared to PE. Ultimately, half-cells were constructed using thin-film Li metal for galvanostatic charge-discharge tests, achieving superior cycle stability of over 200 cycles with SDL. Figure 1

Investigating Activity and Stability of Mixed-Metal Oxides (M-NiO) for Anion Exchange Membrane Electrolysis

Recent experimental studies suggest mixed oxides of Ni, Co, and Fe operated in basic media may be the strongest alternative to iridium.1, 2 However, the efficiency of these catalysts is strongly synthesis-dependent and there is no established understanding of the role of the different metals in operation with ionomers. Notably, Trotochaud, et al. observed catalyst efficiency in the order Ni0.9Fe0.1Ox > NiOx > NiyCo1-y, whereas Morales-Guio, et. al. ranked FeNiOx, CoFeNiOx > CoNiOx > NiOx.1, 2 Anderson et al. found in their RDE studies of commercial catalysts that NiFe2O4outperformed NiO, Co3O4 by 7 times kinetically. In low concentrations, these mixed-oxide materials may behave more closely to doped-catalysts, where dopants can increase activity, change selectivity, and even improve resistance to poisoning of active sites.3-6 Understanding how and why these catalysts work, and do not work, is critical to enabling these materials to achieve the Hydrogen Shot goal of $1/kg H2 in 1 decade. For our theoretical model, we limited our mixed material model to a single dopant to fully examine the geometric and electronic effects of a nearby transition metal e.g., Fe and Co dopants. Plane-wave density functional theory calculations elucidated the dopant-effects on both activity (the oxygen evolution reaction) and stability in anion exchange membrane electrolysis in the presence of experimentally-relevant ionomers (Georgia Tech, Nafion, Versogen, and Sustainion).(1) Trotochaud, L.; Ranney, J. K.; Williams, K. N.; Boettcher, S. W. Solution-cast metal oxide thin film electrocatalysts for oxygen evolution. Journal of the American Chemical Society 2012, 134 (41), 17253-17261.(2) Morales-Guio, C. G.; Liardet, L.; Hu, X. Oxidatively electrodeposited thin-film transition metal (oxy) hydroxides as oxygen evolution catalysts. Journal of the American Chemical Society 2016, 138 (28), 8946-8957.(3) Ha, M.-A.; Dadras, J.; Alexandrova, A. Rutile-deposited Pt–Pd clusters: A hypothesis regarding the stability at 50/50 ratio. ACS Cat. 2014, 4(10), 3570-3580.(4) Baxter, E. T.; Ha, M.-A.; Cass, A. C.; Alexandrova, A. N.; Anderson, S. L. Ethylene Dehydrogenation on Pt4, 7, 8 Clusters on Al2O3: Strong Cluster Size Dependence Linked to Preferred Catalyst Morphologies. ACS Cat. 2017, 7 (5), 3322-3335.(5) Ha, M.-A.; Baxter, E. T.; Cass, A. C.; Anderson, S. L.; Alexandrova, A. N. Boron switch for selectivity of catalytic dehydrogenation on size-selected Pt clusters on Al2O3. Journal of the American Chemical Society 2017, 139 (33), 11568-11575.(6) Halder, A.; Ha, M.-A.; Zhai, H.; Yang, B.; Pellin, M. J.; Seifert, S.; Alexandrova, A. N.; Vajda, S. Oxidative Dehydrogenation of Cyclohexane by Cu vs Pd Clusters: Selectivity Control by Specific Cluster Dynamics. ChemCatChem 2020, 12 (5), 1307-1315. DOI: 10.1002/cctc.201901795. Figure 1

Experimental Insights into the Reaction Intermediates-Selectivity Relationship for Electrochemical CO2 Reduction Reaction

Since the industrial revolution, the use of fossil fuels has increased CO2 concentration in the atmosphere, which has caused global warming to become a serious problem [1]. Thus, to realize a "carbon neutral" society, Electrochemical CO2 Reduction Reaction (CO2RR) has attracted attention. However, there are several challenges to the practical application of CO2RR, one of which is the improvement of product selectivity: the standard electrode potential of each reaction to various products is overlapped [2], and its large overpotential [3], making it difficult to selectively produce a specific product. In the pioneering study by Hori and co-workers, various metal electrodes were investigated and classified into four groups based on their primary reaction product: HCOO–-forming metals, CO-forming metals, hydrocarbon-forming metals, and CO2RR inactive metals (hydrogen-producing metals) [4]. Since the adsorption strength of the reaction intermediates has been considered the primary descriptor for the differences in reaction products, most studies have focused mainly on the adsorption energy. In recent years, more studies have focused on aspects other than the adsorption energies of O-bound and C-bound adsorbates to further improve product selectivity. Rossmeisl et al. suggest that the binding energy of H-bound adsorbates, in addition to O-bound and C-bound adsorbates, is an essential factor in explaining the final product [5]. Furthermore, the focus now expands to electrolyte properties, such as pH [ 6], cations [ 7], and anions [ 8] to control the stability of the reaction intermediates. As such, it is critical to experimentally probe the state of the reaction intermediates in situ to accurately understand the effect of the strategies mentioned above on the reaction pathway.In this study, we experimentally probe the reaction intermediates at various metal electrodes with different product selectivity using operando surface-enhanced infrared spectroscopy (SEIRAS). For the operando SEIRA measurements, we used a metal working electrode composed of a thin metal film electrodeposited on a Si prism coated with a Pt surface enhancement layer. Carbon rods were used as the counter electrode, Ag/AgCl as the reference electrode, and 1 M KHCO3 as the electrolyte. To compare the reactivity of reaction intermediates on different metal electrodes, we conducted linear sweep voltammetry (LSV) from 0.50 to –0.90 V vs RHE and probed the reaction intermediates during the potential sweep using SEIRAS. The result confirms the potential-dependent change in the reaction intermediates as well as the metal-dependent change in the composition of the reaction intermediates, suggesting successful observation of the CO2RR intermediates in different metal catalysts. Through this study, we attempted to interpret the correlation between the reactivity of each electrode and the properties of the reaction intermediates.Reference[1] Choi, S. et al, ChemSusChem 2009, 2, 796-854.[2] Jouny, M. et al, Ind. Eng. Chem. Res. 2018, 57, 2165–2177.[3] Yoo, J. S. et al, ChemSusChem 2016, 9, 358-363.[4] Hori, Y. et al, Modern Aspects of Electrochemistry 2008, 42, 89–189.[5] Bagger, A. et al, ChemPhysChem 2017, 18, 3266–3273.[6] Varela, A.S. et al, Catal. Today 2016, 260, 8-13.[7] Resasco, J. et al, J. Am. Chem. Soc. 2017, 139, 11277-11287.[8] Dunwell, M. et al, J. Am. Chem. Soc. 2017, 139, 3774-3783.

Effect of Carbon Addition and Passivation on the Mechanical Behavior of Freestanding Al Thin Films

Thin films are widely used as functional and structural elements in micro-electronic devices. Therefore, understanding the mechanical behavior of thin films at different length scales and environmental conditions is essential for the design of reliable devices. However, it is difficult to precisely measure the properties of small-scale materials with the methods that are employed for bulk materials; probing micro/nano scale samples is challenged by the inherent difficulties associated with fabricating and handling of extremely small specimens. For several decades, much work has been dedicated to characterizing the mechanical behavior of thin metal films and it has been observed that the mechanical properties of thin films can be very different to those of their bulk counterparts. In addition, passivated metal thin films showed interesting features such as higher strain hardening rate and enhanced failure strain. In this presentation, the effect of carbon addition and passivation on the microstructure and mechanical behavior of freestanding Al thin films will be discussed. Tensile specimens with sub-micron thickness were fabricated via sputter deposition followed by standard Si-based microfabrication techniques. Mechanical characterization was carried out by performing micro-tensile tests and membrane deflection tests. Supersaturated Al-C thin films containing 10.3at% C exhibit yield strength of about 400 MPa, over three times the yield strength of pure Al thin films. This strengthening can be explained by the role of interstitial C atoms which block dislocations movement inside the Al matrix. In addition, an upper yield followed by drop in stress was observed in Al-C thin films which implies the formation of the Cottrell atmosphere. For passivated films, a large increase in the failure strain was observed when an ultra-thin layer (< 10 nm) is deposited, which is attributed to delay in the strain localization due to constraint imposed by the passivation layer.

Zr-Based Thin Film Metallic Glasses As High-Efficiency Materials for Electrocatalysis of the Hydrogen Evolution Reaction

The production of hydrogen through water electrolysis is a major limiting step in the implementation of hydrogen-based energy storage. Currently used materials for catalyzing the hydrogen evolution reaction require large overpotentials, reducing the efficiency of hydrogen production. Metallic glasses are of interest for use in electrocatalysis due to their high activity and diversity of catalytic sites. However, only a small selection of metallic glass compositions can be manufactured into bulk parts, necessitating the use of metallic glass coatings. In this research, a Zr-based metallic glass was produced as a thin film using sputtering deposition. Combinatorial co-sputtering was used to produce a library of quaternary Zr-based metallic glasses to enable high-throughput characterization of the anode material and electrochemical testing. Metallic glass surfaces were characterized prior to and after electrochemical testing using a range of techniques to explore the physiochemical properties of the catalytic surface. Nano-structured metallic glass coatings are a promising material for catalysis of the hydrogen evolution reaction.This work is funded by ARPA-e under DE-AR0001697. JRH is funded as a fellow under the NSF GRFP.

Synthesis and Characterization of Advanced Thin-Film Metallic Glass Anodes for Lithium Metal Batteries

Instability of the solid-electrolyte interphase (SEI) formed on the surface of the anode is a major cause of capacity degradation in Li-ion and Li metal batteries. High-capacity anode materials which form a stable SEI are desirable for improving the lifetime performance of batteries made using these technologies. One such class of materials that has been suggested are Si-based metallic glasses. Si alloys have a high theoretical capacity, and the amorphous structure has been shown to improve capacity. The SEI layer that forms on these anodes is thin and highly stable. In this research, a genetic algorithm method was used to locate optimal compositions of Si-based metallic glasses for use in Li metal batteries. Sputtering was then employed as a high-throughput, combinatorial method to produce a library of compositions for initial characterization and electrochemical testing. Nanostructured metallic glass anodes with improved capacity and high electrochemically active surface area were then synthesized. The capacity and stability of these anode materials were tested in Li metal batteries. After battery testing, the SEI formed on the anode was characterized to understand its chemistry and structure.This work is funded by NASA under grant 80NSSC19M0152. JRH is funded as a fellow under the NSF GRFP.

Disintegration of Thin Liquid Metal Films Engendered by Aluminum Corrosion.

Liquid metals (LMs) illustrate a fantastic future. Thus, great endeavors are made to earn a comprehensive understanding of this fluid and carve it into a niche. Herein, by revisiting the combination of Ga-based LMs and aluminum (Al), a new phenomenon, namely the disintegration of LM films on encountering water, is identified. Deviating from previous investigations where the LM generally took the form of bulk puddles, the LM-Al slurry is spread as thin films here. In this case, Al debris embedded in the LM matrix hydrolyzes and therefore can exert disjoining pressure strong enough to split the thin film into countless tiny LM droplets. Based on this mechanism, transient circuits independent of substrate decomposition are realized. Furthermore, taking advantage of the portfolio strategy of pure LM and the LM-Al slurry, novel concepts of flood warning and information storage and encryption are demonstrated. Integrating these functions all in one demonstrates the versatility of the disintegration of thin LM films engendered by Al corrosion, which provides a scientific insight into ephemeral art and makes the Ga─Al combination more illuminating.

Wafer-level metal thin film thickness scanning based on multiple probe wavelengths nanosecond transient thermoreflectance

The present metal film thickness (dMetal) measurement methods (e.g., profiler and electron microscope) are not able to simultaneously achieve non-invasion, wide measurement range, high-resolution, and wafer-level scanning. In this work, a dMetal measurement method based on multiple probe wavelengths transient thermoreflectance (MW-TTR) is developed. Through a systematic sensitivity discussion, the guidance for reliable dMetal measurement is illustrated theoretically. The realization of measuring different types of metals (Au, Al, Ni, Ti) is achieved with different wavelengths of probe lights. After the rigorous comparison with profiler and picosecond acoustic measurement, the accuracy of measuring nanosized film is verified (∼1% difference). The fitting uncertainties of dMetal are < 5 % for Au and Al metals. The high-throughput wafer-level scanning measurement, with a spatial resolution of ∼ 50 μm, is also realized by integrating automatic displacement control and deep learning fast predicting model into MW-TTR. Spatial mapping of dMetal is consistent with profiler measurement (∼5% deviation in 2000 μm length).

High temperature evolution of interfacial metal film bonding two 4H-SiC substrates

The high temperature behavior of thin metal films (tungsten and titanium) confined between two off-axis single crystal SiC substrates is investigated. Through the application of transmission and scanning transmission electron microscopy, scanning electron microscopy, and X-ray scattering techniques, we examine the phase and morphology changes induced by high temperature annealing in thin layers consisting of these materials, as well as at their interfaces with SiC. Upon high-temperature annealing, a uniform and continuous W film formed by low-temperature deposition undergoes a transition to an array of discontinuous domains surrounded by a direct SiC/SiC interface. In contrast, a Ti film remains continuous with a strong thickness alteration. In parallel to step-bunching process of the internal SiC surfaces, both materials transform into new crystalline phases which contain Si and/or C atoms and achieve an epitaxial relationship with the SiC structures. The experimental findings are discussed in terms of dewetting phenomena and analyzed in light of potential chemical and structural reactions that may occur during interface reconstructions.