Pd Films Research Articles

Metallic Glass Films with Nanostructured Periodic Density Fluctuations Supported on Si/SiO2 as an Efficient Hydrogen Sorber.

Nanostructured metallic glass films (NMGF) can exhibit surface and intrinsic effects that give rise to unique physical and chemical properties. Here, a facile synthesis and electrochemical, structural, and morphologic characterization of Pd-Au-Si based MGs of approximately 50 nm thickness supported on Si/SiO2 is reported. Impressively, the maximum total hydrogen charge stored in the Pd-Au-Si nanofilm is equal to that in polycrystalline Pd films with 1 μm thickness in 0.1 m H2 SO4 electrolyte. The same NMGF has a volumetric desorption charge that is more than eight times and 25 % higher than that of polycrystalline PdNF and Pd-Cu-Si NMGF with the same thickness supported on Si/SiO2 , respectively. A significant number of nanovoids originating from PdHx crystals, and an increase in the average interatomic spacing is detected in Pd-Au-Si NMGF by high-resolution TEM. Such a high amount of hydrogen sorption is linked to the unique density fluctuations without any chemical segregation exclusively observed for this NMGF.

Effect of bulk and surface modification of SnO2 thin films with PdO catalyst on CO gas sensing characteristics prepared by vacuum evaporation process

We have investigated various approaches of PdO addition on to SnO2 thin films for efficient detection of CO gas molecules. Bulk-doped and surface-decorated PdO/SnO2 thin films were prepared by the thermal oxidation of vacuum evaporated metal films in ambient air. For bulk-doping, Pd and Sn metals were co-evaporated followed by thermal oxidation. PdO surface-decoration was done by thermal oxidization of either Pd/Sn metal bilayer or Pd/SnO2 films. The SnO2 thin films are characterized with rutile crystalline structure and porous surface morphology. X-ray photoelectron spectroscopy confirms the dominant presence of PdO on SnO2 surface for the doped films. Pristine SnO2 film exhibited a maximum sensitivity of about 13% for 915 ppm of calibrated CO molecules in nitrogen gas with a response/recovery time of 69/49 s. The PdO bulk-doping in SnO2 film marginally increased the CO sensitivity, whereas, two to four-fold increase is achieved for PdO surface-decorated SnO2 thin films. It is also found that the Pd film thickness plays a critical role in determining the CO sensitivity and is optimized to be 4 nm. A maximum CO sensitivity of 52% with a lowest response/recovery time of 34/46 s is obtained for PdO/SnO2 structure formed through direct oxidation of Pd metal on SnO2 films. A possible gas sensing mechanism based on PdO/SnO2 hetero-junction is discussed.

Fiber-Tip Polymer Microcantilever for Fast and Highly Sensitive Hydrogen Measurement.

Hydrogen as an antioxidant gas has been widely used in the medical and biological fields for preventing cancer or treating inflammation. However, controlling the hydrogen concentration is crucial for practical use due to its explosive property when its volume concentration in air reaches the explosive limit (4%). In this work, a polymer-based microcantilever (μ-cantilever) hydrogen sensor located at the end of a fiber tip is proposed to detect the hydrogen concentration in medical and biological applications. The proposed sensor was developed using femtosecond laser-induced two-photon polymerization (TPP) to print the polymer μ-cantilever and magnetron sputtering to coat a palladium (Pd) film on the upper surface of the μ-cantilever. Such a device exhibits a high sensitivity, roughly -2 nm %-1 when the hydrogen concentration rises from 0% to 4.5% (v/v) and a short response time, around 13.5 s at 4% (v/v), making it suitable for medical and environmental applications. In addition to providing an ultracompact optical solution for fast and highly sensitive hydrogen measurement, the polymer μ-cantilever fiber sensor can be used for diverse medical and biological sensing applications by replacing Pd with other functional materials.

Localized Surface Plasmon Resonance Studies on Pd/C Nano-Composite System: Effect of Metal Concentration and Annealing Temperature.

The effects of metal concentration and annealing temperature on the localized surface plasmon resonance (LSPR) properties of the Pd nanoparticles (NP) dispersed in carbon were investigated. The Pd/C nano-composite thin films with 7 to 39 atomic % concentration of metal content were deposited using the atom beam co-sputtering techniques and subjected to annealing at temperature varying from 300 °C to 600 °C. The UV-vis spectroscopy studies on as-prepared films displayed a Mie scattering profile, but not well-defined LSPR bands were observed for all the values of Pd concentration. This is attributed to the smaller size (3-4 nm) of Pd NPs and rough Pd/C interface, as confirmed from TEM studies. When samples were annealed at a temperature of 300 °C, three broad LSPR absorption bands in the visible region, along with a sharp peak at 210 nm, were observed and the effect of Pd concentration variation was insignificant on their position. The multiple LSPR bands were observed due to agglomeration NPs, which is consistent with earlier reports and is also observed in the TEM images. When annealing temperature was subsequently increased to 500 °C, a blue shift in the LSPR peak position with an increase in the Pd concentration was observed, which phenomena is attributed to the formation of bigger NPs with the formation of sharp NPs-interface at high temperature upon annealing. A monotonic increase in the magnitude and decrease in the FWHM with an increase in concentration suggested change in the dielectric function of sample due to the growth of NPs. This is further confirmed from XRD studies, where strain relaxation and grain growth were observed. The intensity of the SPR peak decreased with an increase in the annealing temperature. The LSPR peak disappeared on annealing at a temperature of 600 °C, suggesting the formation of continuous polycrystalline thin films of Pd. In summary, NPs size, metalmatrix interface, and concentration of metal play key roles in the tailoring the LSPR properties of the Pd.

Positive vs negative resistance response to hydrogenation in palladium and its alloys

Resistive solid state sensors are widely used in multiple applications, including molecular and gas detection. The absorption or intercalation of the target species varies the lattice parameters and an effective thickness of thin films, which is usually neglected in the analyses of their transport properties in general and the sensor response in particular. Here, we explore the case of palladium-based thin films absorbing hydrogen and demonstrate that the expansion of thickness is an important mechanism determining the magnitude and the very polarity of the resistance response to hydrogenation in high resistivity films. The model of the resistance response that takes into account the modifications of thickness was tested and confirmed in three Pd-based systems with variable resistivity: thin Pd films above and below the percolation threshold, thick Pd–SiO2 granular composite films with different contents of silica, and Pd-rich CoPd alloys where resistivity depends on the Co concentration. The superposition of the bulk resistivity increase due to hydride formation and the decrease in the film resistance due to the thickness expansion provides a consistent explanation of the hydrogenation response in both continuous and discontinuous films with different structures and compositions.

Influence of Pd(P) thickness on the Pd-free solder reaction between eutectic Sn-Ag alloy and Au/Pd(P)/Ni(P)/Cu multilayer

Autocatalytic plating deposition of a Pd(P) film over a Ni(P) metallization pad, such as Au/Pd(P)/Ni(P) (electroless nickel/electroless palladium/immersion gold, ENEPIG), has been widely used in microelectronic industry for the past decade. However, the data regarding its soderability with eutectic Sn-Ag (Sn-3.5Ag) is still lacking in the literature. We investigated the effects of Pd(P) thickness (δPd(P)) on the interfacial reaction between Sn-3.5Ag and ENEPIG and the mechanical reliability of the joint system. A slight increase in δPd(P) from 0 μm to 0.2 μm caused the nucleation of a pronounced amount of (Pd,Ni)Sn4 in the solder matrix after reflow, which gradually migrated to the joint interface and formed a (Pd,Ni)Sn4/Ni3Sn4 dual layer after subsequent solid-state aging. The formation of the (Pd,Ni)Sn4 dense layer slowed the growth of Ni3Sn4, facilitated the depletion of the Ni(P) film, and seriously deteriorated the mechanical characteristics of the solder joints. This (Pd,Ni)Sn4-induced embrittlement in solder joints (termed the “Pd-embrittlement phenomenon”) had never been found previously in the Sn-Ag reaction system. The formation and migration of (Pd,Ni)Sn4 was dictated by thermodynamics and could be rationalized using a Pd-Ni-Sn isotherm. The above observations indicated that δPd(P) was an important factor of the ENEPIG solderability and should be strictly controlled to be 0.1 μm or less to prevent the undesired Pd-embrittlement phenomenon in Sn-Ag micro joints.

Ultrasonic Bonding of Ag and Ag-Alloy Ribbon—An Innovative Alternative for High Power IC Packages

With the development of automotive power electronics and high-power integrated circuits, ribbon bonding is currently in the spotlight for its superior properties to those of traditional heavy wire bonding. In this article, innovative ribbon materials made of Ag and Ag–4Pd are introduced. The ultrasonic bonding of Ag and Ag-alloy ribbons on direct bonded copper (DBC) substrates metallized with Ni/Pd/Au films was evaluated as replacements for Al and Cu ribbons. A continuous bonding interface with satisfactory pull strength can be obtained from substrates metallized with Pd and Au films due to their similar metallurgical properties and softer surface conditions. The footprint study of bond residuals after pull tests correlated with the failure codes and bond strengths of the modules. The reliability of Ag and Ag–4Pd ribbons with regard to pull strength after high-temperature storage tests (HTSTs) at 150 °C for 1000 h was slightly increased, and the bond interface remained unchanged. The results showed that Ag and Ag-alloy ribbons made specifically for power electronics are feasible and can be an attractive alternative to aluminum ribbons.

Relationships between electroless plating temperature, Pd film thickness and hydrogen separation performance of Pd-coated Al2O3 hollow fibers

The present work aims to study the formation of Pd thin film at different electroless plating temperatures and optimize the operating conditions to increase the hydrogen permeation performances of Pd-coated Al2O3 hollow fibers. Deposition of Pd thin films on the structured Al2O3 hollow fiber substrate was systematically investigated at different electroless plating temperatures (30 °C, 40 °C, and 50 °C). Herein, we present data about the effects of the electroless plating temperature on the hydrogen separation properties over a wide temperature range from 350 °C to 450 °C. The Pd thin film thickness is an inverse function of the bath temperature, and the hydrogen flux is primarily dependent on the thickness. The hydrogen fluxes increase with increasing electroless plating temperature.

Site-Selective Functionalization of Polydopamine Films via Aryl Azide-Based Photochemical Reaction

Although the post functionalization of versatile polydopamine (pD) films enables the expression of functional groups of interest on target substrates, their immobilization generally lacks site-selectivity within a surface platform. In this paper, we report a site-selective conjugation method to functionalize pD films based on the combination of simple photolithographic techniques. The essence of the chemical functionalization strategy was the use of the aryl azide group, whose photolysis induces the generation of reactive nitrene groups that functionalize hydrocarbon networks of pD films. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses indicated that the pD film was functionalized primarily with aryl azide groups under UV irradiation and the introduction of a photomask enabled the pattern generation of the initiator that was tethered with the aryl azide group. A subsequent surface-initiated polymerization on their substrates produced a patterned polymer brush, expressing their own functionality on the surface platform.

Hydrogen detection using membrane-type surface stress sensor

This study shows a possibility of the application of a membrane-type surface stress sensor (MSS) with a Pd film to a hydrogen sensor. It was able to detect hydrogen concentrations from 5 to 40000 ppm in a nitrogen gas mixture. In the case of a conventional sensor using a hydrogen-occluding material, it is necessary to wait for a state of saturation. In contrast, the proposed method can detect hydrogen quickly by the initial rate of hydrogen absorption. The relationship between the initial absorption rate and hydrogen concentration is explained by considering the two-step reaction kinetics of hydrogen absorption into bulk Pd via Langmuir dissociative adsorption on surface.

Reaction Acceleration of Nanoporous High-Purity Pd Film Formation by Dealloying of Al-Pd-N Film in pH-Controlled EDTA Solution

AbstractMetallic palladium (Pd) is used for hydrogen storage and detection. Fabrication of a nanoporous (NP) Pd structure can increase the specific surface area leading to a significant improvement in the sensitivity. In our previous study, we succeeded in forming a NP-Pd film by dealloying an Al-Pd alloy film using citric acid as a chelating agent. This method was environmentally friendly but had a long reaction time and a considerable amount of Al remained after dealloying; hence, the Pd purity was reduced. In this study, we succeeded in forming a higher purity NP-Pd film faster by dealloying the nitrogen-containing Al-Pd (Al-Pd-N) film using ethylene-diamine-tetraacetic-acid (EDTA) as a chelating material.

Microstructure and Nanoscopic Porosity in Black Pd Films

Microstructure and Nanoscopic Porosity in Black Pd Films

Modelling the combined effects of hydrogen traps and surface films on hydrogen permeation in ferritic steels

PurposeThe purpose of this study is to develop a model extending Oriani’s formula by introducing a normalised concentration to simulate hydrogen diffusion in a multi-material system such as coated steels, under the presence of traps.Design/methodology/approachImplemented through the finite element method based on the analogy between mass diffusion and heat transfer, the governing equation was applied to investigate the combined effects of hydrogen traps and surface oxide films on hydrogen permeation in ferritic steels.FindingsThis study shows that the effective diffusivity varies over several orders of magnitude depending on the traps and films. This explains the divergence of measured hydrogen diffusivities in steels. It is revealed that hydrogen permeation in steels with Pd or Ni film is a trapping-dominant transport process, while hydrogen permeation in steel with oxide film is a process controlled by both trapping effect and retarding effect of oxide film. The oxide film enhances total hydrogen concentration within the steel substrate and is therefore detrimental. The Pd or Ni film has a little influence on total hydrogen concentration distribution depending on trapping energy.Originality/valueHydrogen flux curves and transient hydrogen concentration distributions can be directly obtained through the developed model. The proposed approach can also be extended to investigate other interstitial (i.e. carbon, oxygen and nitrogen) diffusion with traps revisited in complex systems.

Switching of magnetism via modifying phase shift of quantum-well states by tailoring the interface electronic structure

We demonstrate control of the magnetism of Pd(100) ultrathin films, which show d-electron quantum-well induced ferromagnetism, via modulation of the interface electronic state using density functional calculation. From an analysis based on the phase model, forming the Au/Pd(100) interface induces hybridization of the wave function of d-electron quantum-well states, and modulates the term of the scattering phase shift as a function of the reciprocal lattice point. In contrast, forming the Al interface, which has only s-electrons at the Fermi energy, cannot modify the scattering phase shift. Our finding indicates the possibility of modifying the phase shift by tailoring the interface electronic states using hybridization of the wave function, and this efficiently changes the density of states near the Fermi energy of Pd films, and the switching between paramagnetism and ferromagnetism occurs based on the condition for ferromagnetism (Stoner criterion).

Room-temperature sensing performance of hydrogen using palladium-based film by optical setup

H2 sensing performance of novel Pd–Pt alloy films has been compared with those obtained by using Pd films and H2-reducted PdO films. Two different detecting systems were used to measure the hydrogenation and de-hydrogenation phases with a H2 concentration of both 5% v/v nitrogen and 1% v/v nitrogen at room temperature. The sensitivity loss observed for the Pd–Pt alloy and H2-reducted PdO samples with respect to pure Pd samples can be explained in terms of the reduction in the lattice constant and interstitial volume due to the Pt addition, which determine a decrement of hydrogen atoms penetrating in the films. On the other hand, results show an improvement in time -response for Pd–Pt alloy and H2-reducted PdO films with respect to pure Pd ones, presumably due to the increase of its permeability to H2. Moreover, the sensing measurements repeated after 60 days show that the Pd–Pt alloy films, unlike the Pd-based ones, fully preserve their performances, demonstrating the advantage of the Pt inclusion for stability purposes when the samples are stored upon humidity.

Structure and Orientation Variations during Growth of Films of Pd–5 at % Pb Solid Solution

This article is devoted to studying morphological, structural, and orientation transformations and variations of elemental composition during growth of films of Pd–Pb solid solution upon magnetron sputtering of Pd–5 at % Pb target in an Ar environment (10–1 Pa); the initial vacuum is 10–3 Pa; growth rate is 4 nm/s; magnetron power during growth of thin films is 630–650 W and of thick films is 750–790 W. It is established that nucleation and growth of films of Pd–Pb solid solution take place according to the Volmer–Weber growth mode and are accompanied by collective recrystallization. The stage of labyrinth morphology is achieved at an average thickness of 10 nm. This stage is characterized by nanocrystalline structure and uniaxial texture 〈 111〉 . Existence of the second component (Pb) suppresses multiple twinning peculiar to Pd island films. The elemental composition in the film bulk is characterized by a decrease in Pb concentration.

Mesoporous Au3Pd Film on Ni Foam: A Self-Supported Electrocatalyst for Efficient Synthesis of Ammonia.

As a promising alternative approach to industrial N2 fixation process, electrocatalytic N2 reduction reaction (NRR) can achieve efficient, sustainable, and eco-friendly ammonia production under ambient conditions. Developing efficient NRR catalysts is critical for the electrochemical ammonia synthesis. Herein, self-supported mesoporous Au3Pd film on Ni foam (mAu3Pd/NF) has been in situ synthesized via a micelle-assisted replacement strategy. Combination of bimetallic compositions, interconnected mesoporous structure, and binder-free characteristic, the mAu3Pd/NF shows a superior NRR performance in 0.1 M Na2SO4. This micelle-assisted replacement route is very important to construct efficient self-supporting mesoporous films for the NRR and other fields.

A compact hydrogen sensor based on the fiber-optic Fabry-Perot interferometer

We report an optical fiber hydrogen sensor based on the Fabry-Perot interferometer formed by inserting two ceramic ferrules, one with a flat fiber end facet and the other with a commercial Pd film on their tip, into a matched ceramic sleeve. The response time and sensitivity of the proposed hydrogen sensor are investigated both theoretically and experimentally. A response time of 185 s and a sensitivity of 1.44 nm/% have been obtained. In addition, the resolution and repeatability are investigated experimentally. A resolution of 500 ppm and a good repeatability have been demonstrated. The proposed sensor is compact, easy in fabrication, low cost and has a high potential for hydrogen detection.

Realizing stable high hydrogen permeation flux through BaCo0.4Fe0.4Zr0.1Y0.1O3-δ membrane using a thin Pd film protection strategy

Hydrogen (H2)-selective membrane is an enabling technology for high purity H2 production from natural gas. Here, we demonstrate the feasibility to apply BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY), a widely studied MPEC composition with high electronic conductivity as H2 permeation membrane by sputtering thin Palladium (Pd) films on its feed and permeate surfaces as a protective layer to prevent BCFZY reduction upon long-term exposure to reducing H2. Pd thin film also acts as a catalytic layer to enhance H2 dissociation in the feed surface and H association in the permeate surface. Pd-sputtered BCFZY (Pd|BCFZY|Pd) membrane displayed exceptionally high H2 flux that varies from 0.101 rise to 0.213 mL min−1 cm−2 (450 °C–650 °C) under the 10% H2-90% N2/Argon (Ar) gradient. The attainment of significant H2 permeability below 500 °C shown here indicates the possibility to lower the operating temperature for H2 permeation using MPEC materials. Pd|BCFZY|Pd membrane also demonstrated stable, high H2 flux that fluctuates more or less 0.138 mL min−1 cm−2 during the continuous operation over 225-h duration.

Photoresponse of wafer-scale palladium diselenide films prepared by selenization method

Palladium diselenide (PdSe2) films exhibit a high charge carrier mobility and sensitivity in photodetection. In this work, wafer-scale PdSe2 thin films with controllable thickness have been synthesized by the selenization of Pd films. A PdSe2-based photodetector can detect a broad wavelength ranging from 420 nm to 1200 nm. The responsivity and detectivity can reach 1.96 × 103 A W−1 and 1.72 × 1010 W Hz−1/2 at VSD = 3 V, respectively. The figure of merit of the photodetection are comparable to the mechanically exfoliated PdSe2 based photodetector. This work demonstrated that selenization is a facile method to synthesize PdSe2 films in large scale and the films are promising for broadband photodetection.