Palladium Films Research Articles

Irradiation effects of swift heavy ions on palladium films deposited on 6H-SiC substrate

The irradiation effect of swift heavy ions on palladium (Pd) films deposited on 6H-SiC was investigated. The samples were irradiated by Xe26+ ions with the energy of 167 MeV at fluences of 1 × 1013 cm−2 and 3 × 1014 cm−2 at room temperature. Phase identification, residual stress and surface morphology were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that the as-deposited sample was composed of Pd and SiC with no evidence of a reaction between Pd and SiC. No reaction was observed for the lower irradiation fluence, only an increase in the Pd peak intensities was observed indicating improvement in the crystallinity of the material. A reaction between Pd and SiC forming PdSi and Pd2Si was observed after irradiation at a fluence of 3 × 1014 cm−2. The stress measurements indicated that the films were having tensile and biaxial stress not exceeding 200 MPa. A decrease in stress values was observed with an increase in irradiation fluence. The surface morphology of the as-deposited was flat and composed of small granules. There was an increase in granule sizes due to irradiation at 1 × 1013 cm−2. Irradiating at 3 × 1014 cm−2 caused grain agglomeration and clustering.

Pd films on soft substrates: a visual, high-contrast and low-cost optical hydrogen sensor

For the rapid development of the hydrogen economy, a reliable and low-cost hydrogen sensor appears to be extremely important. Here, we first show that a palladium film deposited on polydimethylsiloxane (PDMS) can obtain an exceedingly high-reflectance contrast of 25.78 over the entire visible band upon exposure to 4 vol% hydrogen gas (H2) mixed with nitrogen gas. This high-reflectance contrast results from the surface deformation induced by the volume inflation after exposure to H2, leading to the transition of the near-specular surface to a diffusing surface. In addition, a change in brightness is readable by naked eye upon exposure to H2 with various concentrations from 0.6 to 1 vol% under the illumination of a fluorescent tube. Furthermore, this sensor possesses an excellent recyclability and quick response time of a few seconds. Compared with Pd nanostructure-based hydrogen sensors, this visual, high-contrast and low-cost sensor is of great potential for practical hydrogen sensing.

On the Synthesis of PdO−RuO2 Solid-Solution Thin Films by Thermal Oxidation and Investigation of Their Gas-Sensing Properties

The phase and structural transformations that Pd–Ru(7 at %) solid solution thin films undergo during thermal oxidation in oxygen in the temperature range 570–1070 K are studied by transmission electron microscopy, high-energy electron diffraction, and reflection high-energy electron diffraction. With increasing oxidation temperature, the phase composition is found to change in the order: Pd–Ru(7 at %) solid solution → Pd–Ru(7 at %) + PdO + RuO2 → PdO + RuO2 → PdO–RuO2 solid solution. We show that the complete oxidation of Pd–Ru(7 at.%) thin films to form single-phase films of the PdO–RuO2 solid solution takes place at a temperature of 100 K higher compared to pure palladium films. The resistance sensor response of the prepared PdO−RuO2 oxide films to ozone in air is studied for the first time. The results suggest that this is a promising material for use in gas-sensing applications.

Fabrication and Morphological Control of a Palladium Film with a Three-Dimensional Nano-Network Structure as a Hydrogen Gas Sensing Material using Organic Acid Chelation

ABSTRACTNano-porous palladium (Pd) thin films could potentially be applied to hydrogen gas sensing materials with high sensitivity and selectivity. In our previous study, a nano-porous Pd film was fabricated with a three-dimensional network structure from an AlPd mother alloy film by a dealloying method using the chelating ability of an organic acid. This process was simple and environmentally friendly because it only required organic acid in a ppm concentration, and did not exhaust a strong acid waste solution, including heavy metal ions. This method was modified to improve the Pd purity of the dealloyed specimen, reaction rate, and morphology control. In this study, the existence of a composition undulation pattern was shown in the AlPd mother alloy film, and its effects on the morphology of the dealloyed specimen were evaluated. Furthermore, this pattern could be controlled by N2 gas addition to the Ar sputtering gas during the preparation of the AlPd mother alloy film.

Effect of hydriding induced defects on the small-scale plasticity mechanisms in nanocrystalline palladium thin films

Nanoindentation tests performed on nanocrystalline palladium films subjected to hydriding/dehydriding cycles demonstrate a significant softening when compared to the as-received material. The origin of this softening is unraveled by combining in situ TEM nanomechanical testing with automated crystal orientation mapping in TEM and high resolution TEM. The softening is attributed to the presence of a high density of stacking faults and of Shockley partial dislocations after hydrogen loading. The hydrogen induced defects affect the elementary plasticity mechanisms and the mechanical response by acting as preferential sites for twinning/detwinning during deformation. These results are analyzed and compared to previous experimental and simulation works in the literature. This study provides new insights into the effect of hydrogen on the atomistic deformation and cracking mechanisms as well as on the mechanical properties of nanocrystalline thin films and membranes.

High performance hydrogen sensor based on Pd/TiO2 composite film

Hydrogen sensors with fast response and recovery rate based on nanoporous palladium (Pd) and titanium dioxide (TiO2) composite films supported by anodic aluminum oxide (AAO) template have been demonstrated. Nanoporous TiO2 film was sprayed on the porous AAO templates, followed by Pd film deposited on TiO2 layer by DC magnetron sputtering. We have researched the detection performance of the hydrogen sensors depending on different thickness of TiO2 layer from 6 to 30 nm with keeping the thickness of Pd as 30 nm. The results have demonstrated the sensors with 10 nm thickness of TiO2 achieve the best performance with a response/recovery time as short as 4/8s at 0.8% and 0.4% hydrogen concentration, respectively. The sensors exhibited very good performance under hydrogen concentrations from 0.4% to 1.8%.

Apparatus for combined nanoscale gravimetric, stress, and thermal measurements

We present an apparatus that allows for the simultaneous measurement of mass change, heat evolution, and stress of thin film samples deposited on quartz crystal microbalances (QCMs). We show device operation at 24.85 ± 0.05 °C under 9.31 ± 0.02 bars of H2 as a reactive gas. Using a 335 nm palladium film, we demonstrate that our apparatus quantifies curvature changes of 0.001 m-1. Using the QCM curvature to account for stress induced frequency changes, we demonstrate the measurement of mass changes of 13 ng/cm2 in material systems exhibiting large stress fluctuations. We use a one-state nonlinear lumped element model to describe our system with thermal potentials measured at discrete positions by three resistance temperature devices lithographically printed on the QCM. By inputting known heat amounts through lithographically defined Cr/Al wires, we demonstrate a 150 μW calorimetric accuracy and 20 μW minimum detectable power. The capabilities of this instrument will allow for a more complete characterization of reactions occurring in nanoscale systems, such as the effects of hydrogenation in various metal films and nanostructures, as well as allow for direct stress compensation in QCM measurements.

Investigation of a Rayleigh-Like Instability During the Solid-State Dewetting of Single-Crystal Nickel and Palladium Films

We report the results of an investigation of the Rayleigh-like instability during the solid-state dewetting of stripe patches patterned from 30-nm-thick single-crystal Ni(100) and Pd(100) films. The stability of the dewetting lines is shown to be highly anisotropic, leading to a strong dependence of the interspacing of the dewetted particles on the crystallographic orientations of the patches. The dewetting lines are most stable against the Rayleigh-like instability in the or the direction, resulting in maximum interparticle spacing. The stability of the and that of the lines are observed to increase under the condition in which oxygen adsorption on the film’s surface decreases and increases, respectively. The mean interspacing of the particles can be controlled by using artificial perturbations along the patch edges, and its dispersion is significantly narrowed in the direction in which the spontaneous wavelength is comparable to or greater than the characteristic length scale of a given artificial perturbation.

A happy couple

Pairing electrosynthetic anode and cathode processes (either convergent or divergent) is essential to maximize energy usage/sustainability and to minimize waste. New approaches to pairing in electrosynthesis are needed and the use of a palladium film membrane by Berlinguette and co-workers represents an effective paired reactor prototype that couples electrosynthesis with chemical catalysis.

Accurate Coulometric Quantification of Hydrogen Absorption in Palladium Nanoparticles and Thin Films

We report here an electrochemical method for precise and accurate quantification of hydrogen absorption in palladium materials. We demonstrate that conventional chronocoulometry over-reports adsorbed hydrogen due to charge from the accompanying hydrogen oxidation reaction (HOR). We designed and built a bespoke electrochemical flow cell that mitigates the concurrent HOR reaction and consequently provides improved accuracy and reproducibility relative to other existing electrochemical techniques. The efficacy of this technique is demonstrated experimentally for a series of palladium sample types: a 100 nm electron-beam deposited thin film, a 20 μm electrodeposited palladium film, a casting of 21 nm edge-length cubic nanoparticles, and a casting of 27 nm edge-length octahedral nanoparticles. We contend that this method is the most effective for measuring hydrogen uptake in different palladium samples.

Asymmetry of Hydrogen Transfer through a Composite Membrane

Hydrogen mass transfer through a composite membrane represented by a film of palladium (or its alloys) applied onto a porous substrate has been studied. The hydrogen flux through the composite membrane has been shown to be governed by the ratio between the diffusion permeabilities of the film and the porous substrate, the mechanism of the transfer through the film, and the external pressure. It has been found that the intensity of hydrogen transfer through the composite membrane may depend on the transfer direction. The transfer is most asymmetric when the diffusion permeabilities of both layers are close and the hydrogen transfer in the film is limited by diffusion. At the same time, the transfer asymmetry effect does not arise when the hydrogen transfer in the film is limited by adsorption processes on its surface.

Temperature dependence of photoinduced hydrogen production and simultaneous separation in TiO2 nanotubes/palladium bilayer membrane

Temperature dependence of photoinduced hydrogen production and simultaneous separation was examined in a bilayer membrane comprised by an anodized TiO2 nanotube array (TNA) and a palladium layer. This membrane was fabricated by transferring a TNA embedded in a titanium sheet onto an electroless-plated palladium film. Sacrificial water splitting with methanol was photocatalytically performed under ultraviolet (UV) irradiation and only generated hydrogen gas was concurrently separated with the Pd layer. The H2 production rate (rH2) with the membrane at various temperatures was evaluated by using a home-made characterization system. The measured rH2 showed larger values at higher temperature of the membrane and increased abruptly after several hours of UV irradiation. This inflection behavior appeared earlier at the higher temperature of the membrane, which can be related to the permeation and adsorption characteristics of hydrogen in the Pd layer.

Interfacial microstructure and mechanical reliability of the Sn-Ag-Cu/Au/Pd(xP)/Ni(P) reactive system: P content effects

Electroless deposition of a palladium film, e.g., pure Pd or Pd(P), between Au and Ni(P) films has received a great deal of attention from the microelectronic industry over the past decade. We investigated the effect of P on the solderability and the corresponding mechanical reliability of the Sn-3Ag-0.5Cu/Au/Pd(xP)/Ni(P)/Cu joint system, where x = 0, 3, and 4.5 wt%. Analyses of electron probe X-ray microanalysis and field-emission transmission electron microscopy showed that a trilayer of (Cu,Ni)6Sn5/(Ni,Cu)3Sn4/Ni3P intermetallic structure grew at the interface at x = 0 wt%, and the growth of (Ni,Cu)3Sn4 was replaced by that of Ni2SnP at x = 3 and 4.5 wt%. In high-speed ball shear testing, the microstructure transition induced by P addition would cause a fracture mode change from brittle to ductile, and increased the shear resistance of solder joints. These findings indicated that the P content in the Pd(P) film is a crucial factor in interfacial strength, and an appropriate amount of P is beneficial to the solderability of the Au/Pd(xP)/Ni(P) surface finish.

Palladium nanostructure incorporated cupric oxide thin film with strong optical absorption, compatible charge collection and low recombination loss for low cost solar cell applications

Cupric oxide (CuO) is one of the most promising and low-cost materials for solar cell application, but its power conversion efficiency is limited by discrepancy between short carrier diffusion length and optical absorption length, low charge collection efficiency, and high recombination rate. We present a novel optical absorbing CuO film to simultaneously address all of these issues by combining thin films of palladium (Pd) nanoparticles-incorporated CuO (CuO:Pd), nitrogen-doped CuO (CuO:N), and nitrogen-doped cuprous oxide (Cu2O:N). Incorporation of Pd nanoparticles significantly increases photo-generated charge collection efficiency and enhances optical absorption over the wide range of solar spectrum. Graded refractive index and step distribution of carrier concentration of Cu2O:N/CuO:N thin films reduce optical reflectance and build high potential into optical absorbing thin film. The Cu2O:N/CuO:N/CuO:Pd/CuO thin film increases charge collection efficiency and reduces recombination rates. Using this design, record high short circuit current density (Jsc) and efficiency (η) of around 28.5 mA cm−2 and 8.3 are achieved, respectively, for heterojunction solar cell using Cu2O:N/CuO:N/CuO:Pd/CuO thin film on titanium (Ti) passivated n-type silicon (Si) substrate (p-(Cu2O:N/CuO:N/CuO:Pd/CuO)/Ti/n-Si). Jsc and η for p-(Cu2O:N/CuO:N/CuO:Pd/CuO)/Ti/n-Si solar cell are around 14 and 40 times higher than the control p-CuO/n-Si solar cell, respectively. This work provides a novel approach to achieve high efficiency CuO-based thin film solar cells.

Optical investigation of palladium(II) phthalocyanine including an aromatic group

Peripherally β-naphthoxy unit substituted palladium(II) phthalocyanine was synthesized from corresponding phthalonitrile compounds. The palladium (II) phthalocyanine was characterized with ultraviolet–visible spectroscopy (UV-Vis), fourier transform- infrared spectroscopy (FT-IR), mass and elemental analyses techniques. Thin films of palladium (II) phthalocyanine were prepared using different organic solvents by spin coating technique. Transmittance and absorbance spectra of the thin films were studied in the wavelength range of 200–1000 nm. Optical band gaps of palladium (II) phthalocyanine thin films were also calculated.

Unexpected Behavior of the Hydrogen Oxidation Reaction on Palladium in Alkaline Solution: A Feasible Kinetic Explanation

The hydrogen oxidation reaction was studied on a thin film palladium electrode supported on a gold substrate in alkaline solution. The hydrogen absorption process was analyzed by open circuit potential transient and the current - overpotential dependences were obtained by chronoamperometry at different rotation rates in a solution saturated with hydrogen. The results obtained show an unexpected profile at low overpotentials, where current decreases as rotation rate increases. A kinetic mechanism was proposed to interpret this behavior and the corresponding equations were derived. They were used to correlate the results, with a good agreement between the experimental and fitted curves.

Influence of the selective layer morphology on the permeation properties for Pd-PSS composite membranes prepared by electroless pore-plating: Experimental and modeling study

Abstract This work analyzes the relationship between hydrogen permeation behavior and palladium layer morphology, particularly taking into account the palladium introduction into the pores for composite membranes prepared by Electroless Pore-Plating (ELP-PP) over porous stainless steel supports. Fully dense membranes have been achieved with hydrogen permeances in the range 7 - 18 · 10 - 5 mol / m 2 s Pa 0.5 by varying the hydrazine concentration used for the palladium plating. Permeation measurements for pure gases and mixtures have been carried out at different conditions: pressure driving force, temperature and feed composition. Both morphology and permeation properties are clearly influenced by the concentration of hydrazine, used as reducing agent during the ELP-PP process. In this manner, higher hydrazine concentrations provoke the formation of thicker external palladium films and, consequently, the reduction of both external porosity and roughness. On the other side, lower hydrazine concentrations reduce the required amount of palladium to obtain a fully dense membrane. In the last case, however, part of palladium is introduced into the pores of the support in a huger extension. This fact, in turns, generates an additional hydrogen permeation resistance, which diminishes the permeation flux and introduces a threshold in the minimum trans-membrane pressure value required for a hydrogen permeate flux. A new mathematical model, based on the classical Sieverts’ law, is proposed to predict this particular behavior by including a new fitting parameter defined as the ratio of the gas-palladium surface in both retentate and permeate sides of the membrane. This new parameter has been denoted as η , achieving good accuracy between both predicted and experimental data when considering the gap in the trans-membrane pressure. Therefore, the presented model can be used in multiple cases to design and optimize membranes modules, whereas the retentate and permeate gas-palladium surface ratio will be different, as for instance in case of palladium is introduced partially into the pores of supports.

Antibacterial Efficacy of Sacrifical Anode Thin Films Combining Silver with Platinum Group Elements within a Bacteria‐Containing Human Plasma Clot

Silver (Ag) dots arrays (64 and 400 dots per mm2) are fabricated on a continuous platinum (Pt), palladium (Pd), or iridium (Ir) thin film (sacrifical anode systems for Ag) and for comparison on titanium (Ti) film (non‐sacrifical anode system for Ag) by sputter deposition and photolithographic patterning. The samples are embedded within a tissue‐like plasma clot matrix containing Staphylococcus aureus (S. aureus), cultivated for 24 h. Bacterial growth is analyzed by fluorescence microscopy. Among platinum group sacrifical anode elements and a dense Ag sample, only the high Ag ion releasing Ag–Ir system is able to inhibit the bacterial growth within the adjacent plasma clot matrix. This study demonstrates that the antibacterial efficiency of Ag coatings is reduced under tissue‐like conditions. However, the new sacrificial anode based Ag–Ir system can overcome this limitation.

FMR Studies of Ultra-Thin Epitaxial Pd0.92Fe0.08 Film

Magnetic anisotropies of 20 nm epitaxial film of palladium–iron alloy Pd0.92Fe0.08 grown on the (001) MgO substrate were studied. Ferromagnetic resonance (FMR) spectroscopy and vibrating sample magnetometry (VSM) were exploited to determine magnetic parameters of the film. It was found that the synthesized film reveals cubic anisotropy with tetragonal distortion. The simulated magnetic hysteresis loops, obtained utilizing the magnetic anisotropy constants taken from the FMR spectra analysis, agree well with those measured by VSM.

Catalytic Palladium Film Deposited by Scalable Low-Temperature Aqueous Combustion.

This article describes a novel method for depositing a dense, high quality palladium thin film via a one-step aqueous combustion process which can be easily scaled up. Film deposition of Pd from aqueous solutions by conventional chemical or electrochemical methods is inhibited by hydrogen embrittlement, thus resulting in a brittle palladium film. The method outlined in this work allows a direct aqueous solution deposition of a mirror-bright, durable Pd film on substrates including glass and glassy carbon. This simple procedure has many advantages including a very high deposition rate (>10 cm2 min-1) and a relatively low deposition temperature (250 °C), which makes it suitable for large-scale industrial applications. Although preparation of various high-quality oxide films has been successfully accomplished via solution combustion synthesis (SCS) before, this article presents the first report on direct SCS production of a metallic film. The mechanism of Pd film formation is discussed with the identification of a complex formed between palladium nitrate and glycine at low temperature. The catalytic properties and stability of films are successfully tested in alcohol electrooxidation and electrochemical oxygen reduction reaction. It was observed that combustion deposited Pd film on a glassy carbon electrode showed excellent catalytic activity in ethanol oxidation without using any binder or additive. We also report for the first time the concept of a reusable "catalytic flask" as illustrated by the Suzuki-Miyaura cross-coupling reaction. The Pd film uniformly covers the inner walls of the flask and eliminates the catalyst separation step. We believe the innovative concept of a reusable catalytic flask is very promising and has the required features to become a commercial product in the future.