Co-deposited Films Research Articles

(Keynote) Controlling CO2 Electrolyzer Reactivity Using Alloy and Polymer-Modified Electrodes

This talk addresses the reactivity associated with CO2 reduction. Electrodeposition of metals from plating baths containing 3,5-diamino-1,2,4-triazole (DAT) as an inhibitor yields highly porous materials exhibiting enhanced activity for electrochemical reactions. Electrodeposition of Cu or CuAg and CuSn, alloy films from such plating baths yields high surface area catalysts for the active and selective electroreduction of CO2 to multi-carbon hydrocarbons and oxygenates. EXAFS shows the co-deposited alloy film to be homogenously mixed. Alloy films containing Sn exhibit the best CO2 electroreduction performance, with the Faradaic efficiency for C2H4 and C2H5OH production reaching nearly 60 and 25%, respectively, at a cathode potential of just –0.7 V vs. RHE and a total current density of ~–300 mA/cm2. Alloy films containing Sn exhibit greater efficiency for CO production relative to either Cu alone or CuAg at low overpotentials. In-situ Raman and electroanalysis studies suggest the origin of the high selectivity towards C2 products to be a combined effect of the enhanced destabilization of the Cu2O overlayer and the optimal availability of the CO intermediate due to the Ag or Sn incorporated in the alloy. Sn-containing films exhibit less Cu2O relative to either the Ag-containing or neat Cu films, likely due to the increased oxophilicity of the admixed Sn. Additionally, modification of the Cu electrode with certain polymers (Figure 1) yields substantially enhanced reactivity, due in part to control of the Cu2O layer and elevated surface pH, measured in situ. These electrodes exhibit enhance ethanol production. Polymer-composite electrodes exhibit enhanced reactivity over a wide range of proton-involved electrochemical reactions, such as methanol oxidation and oxygen reduction.

Effect of exposure of W-D co-deposited films to air on deuterium content in the films

Effect of exposure of W-D co-deposited films to air on deuterium content in the films

Cooperative Fe-Sites in Nickel and Cobalt Oxyhydroxides

With incorporated iron, nickel and cobalt oxyhydroxides display the highest known oxygen evolution activities of any catalyst in alkaline media. To leverage this high activity in low temperature electrolysis systems, a comprehensive understanding of where Fe-based active sites form, their local chemical structure, and how this structure evolves under electrochemical conditioning is critical. Here we show that incorporation of Fe into NiOxHy and CoOxHy films during constant potential chronoamperometry yields NiFeOxHy and CoFeOxHy catalysts with extremely high TOFs of up to ~40 s-1 and 0.7 s-1, respectively, at 350 mV overpotential. Further, we discover that the TOF of these materials is linearly related to the amount of Fe incorporated with this method. We propose a mechanism involving cooperative catalysis involving multiple Fe sites to explain this linear dependence. Density functional theory calculations are used to show this cooperativity may arise from increased ability to delocalize oxidative charge in active sites comprised of neighboring FeOxHy monomers. We then show that cycling these films lowers the per-Fe TOF substantially, to a level similar to that of co-deposited NiFe and CoFe films. This loss of activity during cycling and similarity to co-deposited films in which Fe occupies intraplanar lattice sites is consistent with migration of high activity Fe clusters initially adsorbed at surface edges and defects during chronoamperometry to less active sites within the oxyhydroxide lattice via cycling-driven dynamic substrate behavior. Further evidence for this Fe relocation into bulk lattice sites is provided using the redox features of adsorbed Ni2+ and Co2+ as probes for monitoring the extent to which ions are incorporated into the bulk of NiOxHy and CoOxHy.

Effects of processing parameters on the morphologies of complex sesquioxide thin films

Controlling and predicting the morphology of lanthanide sesquioxides in thin film form is vital to their use in current applications. In the present study, single and codeposited Sm2O3, Er2O3, and Lu2O3 thin films were grown on yttria-stabilized zirconia (8%) substrates by radio frequency magnetron sputtering at room temperature and 500 °C. The effect of two different substrate temperatures and altering the oxide cation on the structural and morphological properties of the films was analyzed. The thin films were characterized by profilometry, scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The single-component Lu2O3 and Sm2O3 films obtained were of the cubic phase, and the Er2O3 was a mix of cubic and monoclinic phases. It was observed for both the Er2O3 and Lu2O3 films that increasing the substrate temperature to 500 °C resulted in larger grained polycrystalline films. In contrast, large grained polycrystalline films were obtained at both room temperature and 500 °C for Sm2O3 and uneven granularity increased as temperature increased. Codeposition of Lu2O3 and Sm2O3, and Lu2O3 and Er2O3 resulted in a cubic bixbyite phase (the C phase of the lanthanide sesquioxide) solid solution. It was observed that the structure and morphology of the films can be controlled by manipulating deposition parameters. Both substrate temperature and altering the oxide cation contributed to changes in crystallinity and grain structure, which can modify the chemical and physical properties of the films for their applications.

Effect of helium presence on tungsten-deuterium co-deposited films

Effect of helium presence on tungsten-deuterium co-deposited films

Microstructure and Mechanical Properties of Co-Deposited Ti-Ni Films Prepared by Magnetron Sputtering

Ti-Ni films with various Ni contents (16.5, 22.0, 33.5 at. %) were deposited on Al alloy substrates using DC magnetron co-sputtering. The effects of Ni target power and substrate bias (−10, −70, −110 V) on morphologies, crystallography, nanomechanical properties and scratch behavior of films were studied. All the deposited Ti-Ni films exhibited a BCC structure of β-Ti (Ni). The Ti-Ni films grew with a normal columnar structure with good bonding to substrates. When increasing the Ni target power and substrate bias, the grain size grew larger and the surface became denser. The as-deposited Ti-Ni films significantly improved the hardness (>4 GPa) of the Al alloy substrate. With the increase of bias voltage, the hardness and modulus of the film increased. The hardness and modulus of the Ti-22.0Ni film prepared at −70 V bias were 5.17 GPa and 97.6 GPa, respectively, and it had good adhesion to the substrate.

Deuterium to protium isotope exchange in W-D co-deposited films below 200°C

Deuterium to protium isotope exchange in W-D co-deposited films below 200°C

Magnetism and microstructure of co-deposited yttrium iron garnet-barium titanate films

Yttrium iron garnet (YIG) and barium titanate (BTO) were co-deposited on (001)-orientated gadolinium gallium garnet substrates by pulsed laser deposition with composition determined by the ratio of laser shots ablating each target. With increasing shot ratios of YIG/BTO = 2.5/1, 4/1, 20/1, and 30/1, the majority phase in the film changes from textured polycrystalline perovskite to epitaxial garnet. Cross-sectional STEM characterization of the YIG-rich films reveals three distinct sublayers: the bottom layer is a coherent epitaxial garnet layer with higher unit cell volume than that of YIG; the second layer is garnet exhibiting crystalline defects and misorientation; and the upper layer is amorphous. Highly defective regions within the second layer are richer in Ba, suggesting that the microstructure is promoted by the insolubility of Ba in YIG. Temperature-dependent magnetization measurements fitted to a super-exchange dilution model indicate the presence of nonmagnetic Ti and vacancies in both octahedral and tetrahedral sites.

Growth behaviors and emission properties of Co-deposited MAPbI3 ultrathin films on MoS2

Hybrid organic–inorganic perovskite thin films have attracted much attention in optoelectronic and information fields because of their intriguing properties. Due to quantum confinement effects, ultrathin films in nm scale usually show special properties. Here, we report on the growth of methylammonium lead iodide (MAPbI3) ultrathin films via co-deposition of PbI2 and CH3NH3I (MAI) on chemical-vapor-deposition-grown monolayer MoS2 as well as the corresponding photoluminescence (PL) properties at different growing stages. Atomic force microscopy and scanning electron microscopy measurements reveal the MoS2 tuned growth of MAPbI3 in a Stranski–Krastanov mode. PL and Kelvin probe force microscopy results confirm that MAPbI3/MoS2 heterostructures have a type-II energy level alignment at the interface. Temperaturedependent PL measurements on layered MAPbI3 (at the initial stage) and on MAPbI3 crystals in averaged size of 500 nm (at the later stage) show rather different temperature dependence as well as the phase transitions from tetragonal to orthorhombic at 120 and 150 K, respectively. Our findings are useful in fabricating MAPbI3/transition-metal dichalcogenide based innovative devices for wider optoelectronic applications.

Tailoring of Multisource Deposition Conditions towards Required Chemical Composition of Thin Films.

The model to tailor the required chemical composition of thin films fabricated via multisource deposition, exploiting basic physicochemical constants of source materials, is developed. The model is experimentally verified for the two-source depositions of chalcogenide thin films from Ga–Sb–Te system (tie-lines GaSb–GaTe and GaSb–Te). The thin films are deposited by radiofrequency magnetron sputtering using GaSb, GaTe, and Te targets. Prepared thin films are characterized by means of energy dispersive X-ray analysis coupled with a scanning electron microscope to determine the chemical composition and by variable angle spectroscopic ellipsometry to establish film thickness. Good agreement between results of calculations and experimentally determined compositions of the co-deposited thin films is achieved for both the above-mentioned tie-lines. Moreover, in spite of all the applied simplifications, the proposed model is robust to be generally used for studies where the influence of thin film composition on their properties is investigated.

Growth and characterization of W thin films with controlled Ne and Ar contents deposited by bipolar HiPIMS

This work is focused on controlling and optimizing the inclusion of neon (Ne) and argon (Ar) impurities in tungsten (W) reference coatings. A tungsten target has been sputtered in monopolar and bipolar High Power Impulse Magnetron Sputtering (HiPIMS) operation modes, in Ar-Ne gas mixture. It has been found that the process of noble gas retention in W thin layers is strongly dependent on both ion energy and average flux to the substrate. The ion energy can be accurately controlled by the amplitude of the positive voltage pulse while the average ion flux can be controlled by the duration of the negative pulse. Measurements of the plasma potential in front of the substrate and the ion saturation current at the substrate position allow explaining the mechanism of ion acceleration and the control of ion energy and flux. The effect of the pulsing configuration on the microstructure of the co-deposited films has been investigated by X-ray Diffractometry, Scanning Electron Microscopy and Atomic Force Microscopy, while the amount of noble gas enclosed in the coatings has been measured by Non-Rutherford Backscattering Spectrometry. Ne and Ar amount in the W co-deposited layers increases up to 3.0 at.% each as the amplitude of the positive pulse increases to + 300 V or the negative pulse duration decreases to 3 µs. The highest film crystallinity, with W(1 1 0) preferential growth, has been obtained for a positive pulse voltage of + 200 V and a negative pulse duration of 5 µs. The thickness of the deposited layers ranges between 350 nm in bipolar HiPIMS with a positive pulse voltage of + 300 V and 550 nm in monopolar HiPIMS.

220 keV Ag ion irradiation-induced surface plasmon resonance shift of gold nanoparticles in fullerene C60 matrix

• Synthesis of Au-C 60 nanocomposites utilizing the co-evaporation technique. • Irradiation with 220 keV silver ion beam. • A ∼34 nm red shift in the Surface plasmon resonance wavelength and then a ∼67 nm blue shift with increasing dose. • Growth of gold nanoparticles with increasing dose. The effect of 220 keV Ag ion beam irradiation on the optical and structural properties of thermally co-deposited Au-C 60 nanocomposite thin films on a quartz substrate is investigated by irradiating samples at different doses. To determine the exact gold (Au) concentration in the film and thickness of the film, Rutherford Backscattering Spectrometry (RBS) was utilized on the as-deposited film. The Surface Plasmon Resonance (SPR) of Au nanoparticles embedded into the fullerene C 60 matrix was seen at 721 nm in the as-deposited sample. A ∼34 nm redshift in SPR wavelength was obtained at a dose of 1 × 10 14 ions/cm 2 which was mainly due to the increase in the size of Au nanoparticles with irradiation. At higher doses, a blue shift of ~67 nm was obtained at a dose of 1 × 10 16 ions/cm 2 which was due to the transformation of fullerene C 60 matrix into amorphous carbon with a much lower dielectric constant at higher doses. The progressive transformation of fullerene C 60 into amorphous carbon with increasing doses was confirmed by Raman spectroscopy. The size of Au nanoparticles in the highest dose irradiated sample was found to be ∼3.9 nm by High-Resolution Transmission Electron Microscopy (HRTEM) bright-field measurements. The size modifications of nanoparticles and SPR wavelength tuning of these nanoparticles are very much needed to use them in organic solar cell.

Compositionally-Driven Formation Mechanism of Hierarchical Morphologies in Co-Deposited Immiscible Alloy Thin Films.

Co-deposited, immiscible alloy systems form hierarchical microstructures under specific deposition conditions that accentuate the difference in constituent element mobility. The mechanism leading to the formation of these unique hierarchical morphologies during the deposition process is difficult to identify, since the characterization of these microstructures is typically carried out post-deposition. We employ phase-field modeling to study the evolution of microstructures during deposition combined with microscopy characterization of experimentally deposited thin films to reveal the origin of the formation mechanism of hierarchical morphologies in co-deposited, immiscible alloy thin films. Our results trace this back to the significant influence of a local compositional driving force that occurs near the surface of the growing thin film. We show that local variations in the concentration of the vapor phase near the surface, resulting in nuclei (i.e., a cluster of atoms) on the film’s surface with an inhomogeneous composition, can trigger the simultaneous evolution of multiple concentration modulations across multiple length scales, leading to hierarchical morphologies. We show that locally, the concentration must be above a certain threshold value in order to generate distinct hierarchical morphologies in a single domain.

Aggregate formation in crystalline blends of α-sexithiophene and para-sexiphenyl

Earlier reports on rod-like conjugated molecules of similar shape and size such as α-sexithiophene (6T) and para-sexiphenyl (6P) indicated mixed crystal growth in equimolar blends. The spectral overlap between the 6P fluorescence and 6T absorption might there give rise to resonant energy transfer between the two species. In marked contrast to H-type aggregation found for 6T bulk crystals, isolated monolayers of 6T as well as 6T monolayers sandwiched between 6P multilayers have been reported to show pronounced green (instead of red) fluorescence, which has been attributed to J-type aggregation. Here, we investigate whether these altered optical properties of 6T translate from the monolayer to a bulk equimolar blend with 6P. Insight into the mixed crystal structure for vacuum co-deposited films of 6T + 6P is provided by using synchrotron grazing-incidence x-ray diffraction on different substrates. By correlating the optical properties of the pure and the mixed systems using absorption and photoluminescence spectroscopy we identify the green emission known from 6T monolayers to prevail in the blend. Our analysis indicates the formation of aggregates which are promoted by the molecular arrangement in the mixed crystal structure highlighting that the remarkable optical properties of 6T/6P heterostacks translate into mixed crystalline films. This study underlines that tuning the opto-electronic properties of organic semiconductors by blending species of similar shape but distinct opto-electronic properties is a promising pathway to achieve altered material properties.

Multiphysics approaches for modeling nanostructural evolution during physical vapor deposition of phase-separating alloy films

Physical vapor deposition of phase-separating alloy films yields a rich variety of distinct self-assembled nanostructures depending on the deposition rate and temperature. However, the role of grain boundaries, elastic imhomogeneity, and anisotropy, and surface tension, in the formation of such nanostructures is currently not well understood. Here, we employ a phase-field approach that couples the multiphysics of elemental diffusion, elastic misfit and anisotropy, surface tension, and grain boundaries with processing parameters, namely deposition rate and temperature, to investigate phase separation and grain boundary evolution in binary alloy films. We develop phase-field deposition models of increasing complexity to isolate and analyze the influence of processing parameters on nanostructural transitions in vapor co-deposited films. While it is found that such transitions are primarily guided by a minimization of total free energy, our simulation-based insights strongly indicate the phenomena of nanostructure selection at faster deposition rates. It is anticipated that the insights gained from this study will provide the much-required knowledgebase for establishing nanostructure-level control in the physical vapor deposition of alloy films.

Thin film growth of phase-separating phthalocyanine-fullerene blends: A combined experimental and computational study

Blended organic thin films have been studied during the last decades due to their applicability in organic solar cells. Although their optical and electronic features have been examined intensively, there is still lack of detailed knowledge about their growth processes and resulting morphologies, which play a key role for the efficiency of optoelectronic devices such as organic solar cells. In this study, pure and blended thin films of copper phthalocyanine (CuPc) and the Buckminster fullerene (C60) were grown by vacuum deposition onto a native silicon oxide substrate at two different substrate temperatures, 310 K and 400 K. The evolution of roughness was followed by in-situ real-time X-ray reflectivity. Crystal orientation, island densities and morphology were examined after the growth by X-ray diffraction experiments and microscopy techniques. The formation of a smooth wetting layer followed by rapid roughening was found in pure CuPc thin films, whereas C60 shows a fast formation of distinct islands at a very early stage of growth. The growth of needle-like CuPc crystals loosing their alignment with the substrate was identified in co-deposited thin films. Furthermore, the data demonstrates that structural features become larger and more pronounced and that the island density decreases by a factor of four when going from 310 K to 400 K. Finally, the key parameters roughness and island density were well reproduced on a smaller scale by kinetic Monte-Carlo simulations of a generic, binary lattice model with simple nearest-neighbor interaction energies.

Compositionally-Driven Formation Mechanism of Hierarchical Morphologies in Co-Deposited Immiscible Alloy Thin Films

Co-deposited immiscible alloy systems will form hierarchical microstructures under specific processing parameters that accentuate the difference in constituent element mobility. The formation mechanism of these unique hierarchical morphologies during the deposition process is hard to identify since the characterization of these structures is typically done post-deposition. The present work employs a combination of phase-field modeling for the evolution of microstructure during deposition with microscopy characterization of experimentally-deposited thin films to reveal the origin of the formation mechanism of hierarchical morphologies in co-deposited immiscible alloy thin films. Our results show the significant influence of a local compositional driving force that triggers the simultaneous evolution across multiple length scales, necessary for hierarchical formation. We reveal that there must be a threshold local phase concentration near the surface of the thin film in order to generate distinct hierarchical morphologies in a single domain.

Corrosion Behavior of Electrodeposited Nickel Coating Reinforced by Cr<sub>2</sub>O<sub>3</sub> Particles

The objective of this work is the characterisation of the composite deposits Ni-Cr2O3 on copper substrate; these deposits are obtained from bath of electro-deposition of Nickel watts. The different electrodeposited layers are characterized by various analytical techniques such as adhesion quality, corrosion tests, Vickers microhardness, morphology by scanning electron microscopy Followed by EDX microanalysis and X-ray diffraction. The corrosion tests are realized in a solution of 3.5 % NaCl using lost mass method, polarization and impedance spectroscopy techniques. It was found that the composite coatings Ni-Cr2O3 have an homogeneous and compact morphology, well crystallized and exhibit a high degree of codeposition of Cr2O3 particles incorporated in the nickel matrix. The co-deposited films have very good hardness, adhere perfectly to the substrate and are more resistant to corrosion.

Ordered Donor–Acceptor Complex Formation and Electron Transfer in Co-deposited Films of Structurally Dissimilar Molecules

The electrical and optoelectronic properties of organic semiconductor thin films can be tailored by mixing two molecular materials, e.g., by co-deposition. Possible resulting morphologies include p...

Isotope exchange in Li-D co-deposited layers at temperatures below 200 °C

Abstract Hydrogen-deuterium isotope exchange in Li-D co-deposited films was studied as a method of removal of heavy hydrogen isotopes from Li films deposited in fusion devices. The total H and D retention was measured using in-vacuo thermal desorption spectroscopy. Co-deposited Li-D films were kept in H2 gas at 1 Pa and 105 Pa at room temperature, 100 °C, and 200 °C. Some reduction of the D content was observed even at RT, while nearly full isotope substitution was achieved at 200 °C after 1 day at 105 Pa in H2 gas.