Rhodium Films Research Articles

Rhodium and Rhodium-Alloy Films and Nanoparticles: Part II

Part I of this review covered the synthesis methods for synthesis of rhodium films and nanoparticles (). In Part II, we review the literature on the current and potential applications of rhodium and rhodium alloy films and nanoparticles in catalysis, components for the glass, chemical and electronic industries, thermal sensors and anticancer drugs.

Rhodium and Rhodium-Alloy Films and Nanoparticles: Part I

Noble metals are key to various research fields and noble metal nanomaterials are directly relevant to optics, catalysis, medicine, sensing and many other applications. Rhodium-based nanomaterials have been less studied than metals such as gold, silver or platinum. There have been many improvements in characterisation tools over the years and knowledge about rhodium chemistry and nanomaterials is growing rapidly. Rhodium nanoparticles are widely used as catalysts for automotive emissions control and for hydrogen and oxygen precipitation reactions in electrolytic cells. Novel applications in electronics, anticancer drugs and aerospace are being revisited. In Part I of this two-part review, we cover different strategies for the synthesis of rhodium films and nanoparticles.

Investigation of iridium, ruthenium, rhodium, and palladium binary metal oxide solid solution thin films for implantable neural interfacing applications

Metal oxide solid solution thin films containing binary mixtures of iridium, ruthenium, rhodium, and palladium were combinatorially synthesized by DC reactive magnetron sputtering to investigate the compositional dependence of properties relevant to neural interfacing applications. The binary metal oxides studied included Ir(1-x)MxOy where M = Pd, Rh, and Ru. The properties of the binary metal oxides are compared to that of their single metal oxide endmembers which include palladium oxide (PdOx), ruthenium oxide (RuOx), rhodium oxide (RhOx), and iridium oxide (IrOx). The binary metal oxides exceed the electrochemical performance of their respective single metal oxide endmembers (as measured by cyclic voltammetry) at film thicknesses generally greater than 700 nm. The binary metal oxide concentrations which produce robust microstructures and exceptional electrochemical performance have been identified to be but are not limited to x ≥ 0.5 for Ir(1-x)RhxOy, x ≥ 0.34 for Ir(1-x)RuxOy, and x ≥ 0.14 for Ir(1-x)Pdx Oy. XPS analyses suggest that the electrochemical enhancements observed are at least partly due to the presence of higher oxidation states in the binary metal oxides when compared to that of the corresponding single metal oxide endmembers.

Electrochemical enhancement of reactively sputtered rhodium, ruthenium, and iridium oxide thin films for neural modulation, sensing, and recording applications

Implantable neural interfacing devices are able to diagnose, monitor, and treat many conditions through modulating and recording electrical signals to and from neural tissue. The efficacy of treatment can be limited by a lack of specificity in targeting of neural tissue. To improve specificity and functionality, the electrodes and microelectrode arrays in these devices must be further miniaturized and must possess exceptional charge exchange characteristics. In this study, rhodium oxide (RhxOy), ruthenium oxide (RuOx), and iridium oxide (IrOx) thin films were synthesized using pulsed-DC reactive magnetron sputtering. The effect of sputtering chamber working pressure (WP) on the morphology, crystal structure, chemical composition, and electrochemical properties of the subsequent metal oxide thin films were investigated. The cathodic charge storage capacity (CSCc) and impedance of films were measured via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Results show that CSCc increases, and the overall impedance decreases with increasing WP in all oxide systems. The enhanced electrochemical performance of these films has been attributed in large part to the morphological changes that occur with increasing WP resulting in an apparent increase in the porosity. This study reviews the electrochemical properties of IrOx, and also demonstrates the viability of RhxOy and RuOx as possible electrode coatings for neural interfacing applications.

Direct Self-Assembly of Hierarchically Grown Rhodium Thin Films for Electrocatalytic Hydrogen Evolution Reaction

Thin films of metallic rhodium (Rh) are developed on two different supports, nickel foam (NF) and titanium foil (Ti), and evaluated for electrochemical hydrogen evolution reaction (HER). The electrodes are prepared by aerosol-assisted chemical vapor deposition technique using a Rh diethyldithiocarabamte precursor for three distinct time periods of 40, 80, and 120 min at 500 °C. The film consists of phase pure metallic Rh with hierarchical flower-like morphology. The structural features of such nanostructures can be modulated by adjusting the growth time. The HER catalytic performance data for the optimized films (i.e., with the deposition time of 80 min) suggest that the Rh deposited on Ti foil (Rh/Ti) catalyze the reaction substantially faster than Rh deposited on Ni foam (Rh/NF). To produce current density of 100 mA cm−2, the Rh/NF needed over potential of 263 mV, while the Rh/Ti electrode required only 175 mV. In spite of lower electrical conductivity, caused by the bare Ti foil, the Rh/Ti electrode exhibits superior HER performance. The Tafel slopes of Rh/NF and Rh/Ti electrodes are determined to be 52 and 42 mV dec−1, while the turnover frequencies are estimated to be 1.1 and 37.3 s−1 at over potential of 260 mV.

Phosphorus modulation of a mesoporous rhodium film for enhanced nitrogen electroreduction.

Electrochemical reduction of nitrogen to ammonia has received considerable attention for sustainable nitrogen fixation, but the sluggish kinetics results in unsatisfactory activity and efficiency. Designing electrocatalytic active centers for nitrogen adsorption and activation is highly desired. Herein, we present an electrodeposition method for the synthesis of a phosphorus-doped mesoporous rhodium film on nickel foam for the electrochemical synthesis of ammonia. Due to the unique combination of components and structure, the obtained catalyst not only shows excellent catalytic performance (NH3 yield: 32.57 μg h-1 mg-1cat.; faradaic efficiency: 40.86%), but also exhibits almost no decrease in activity after the durability test. This research work can provide a facile synthesis strategy for non-metal-doped porous metal based catalysts, which would be promising for the electrochemical synthesis of ammonia.

Study on the influence of the thickness of nanostructured rhodium films toward electrooxidation of adsorbed carbon monoxide

Carbon-supported rhodium thin films with various thicknesses are grown by varying the number of laser pulses, Nlp (from 5000 to 50,000) under 2 Torr of He background atmosphere using the pulsed laser deposition method. The thin films are characterized for their morphological features and structural properties. It is observed that smooth dense 2D nanosheets of Rh are obtained with 5000 Nlp, whereas higher Nlp yields to highly porous Rh films. X-ray photoelectron spectroscopy reveals that both metallic Rh and Rh3+ are present at the surface of the Rh films. Nevertheless, the amount of metallic Rh increased as the Nlp increased. The influence of the thickness of the Rh films on the tolerance to CO, a poison that strongly adsorbs on the surface of catalysts in fuel cells reactions, was investigated through anodic stripping voltammetry. It is found that Rh film deposited with 50,000 Nlp exhibits the highest electroactive surface area (27.90 cm2 vs. 1.20 cm2 of Pt), the lowest onset potential of CO electrooxidation (0.47 V vs. 0.60 V Pt), and a net charge corresponding to electrooxidation of the CO adlayer of 424 μC cm−2 (vs. 358 μC cm−2 of Pt). Such high tolerance to CO poisoning is explained on the basis of the elevated porosity and roughness of the Rh surface. Indeed, a roughness factor of 90.5 for Rh against about 3.8 for Pt grows under analogous deposition conditions of pressure and number of laser pulses.

Високотемпературні відбивальні покриття для носіїв довготривалого зберігання даних

The results of the analysis of technologies of creation and properties of high-temperature reflective coatings for long-term storage media are presented. It is shown that promising materials for such coatings are thin films based on nitrides of transition metals and platinum group metals. The particular attention is paid to physical methods of obtaining high-temperature optically homogeneous coatings. It is demonstrated that magnetron sputtering of chromium film and nitride Cr, Ti, Zr and Hf can be used as reflective coatings for optical media. To obtain a certain value of the read signal, most optical media use metal reflective coatings, the characteristics of which significantly affect the life of the media. Optical media with silver and aluminum reflective coatings, which are used on most CDs, cannot provide long-term storage of the recorded information. To create long-term data storage media that use substrates of high-stable materials (sapphire, quartz, etc.), special high-temperature reflective coatings should be used to withstand the short-term effects of elevated temperatures of the order of 1000 ° C. The analysis of scientific and technical literature showed that promising materials for heat-resistant reflective coatings are metal films of rhodium, platinum alloys, chromium, and transition metal nitrides. It is proposed to use ZrPt3 films to create high-temperature reflective coatings. The choice of this intermetallic compound to create a reflective coating is due to its high melting point (> 2190 °C). Based on ZrPt3, high-temperature and oxidation-resistant coatings have been created for carbon composites widely used in the aerospace industry. Currently, oxidation-resistant coatings are unfortunately not capable of withstanding extreme temperatures (> 2000 ° C) .Chromium films are widely used as reflective coatings. The chrome coating can effectively protect Zr tubes from high temperature oxidation in air for one hour. In such a coating, oxidation at a temperature of 1100 ° C forms an oxide layer of Cr2O3 with a thickness of 5 μm, which prevents the further penetration of oxygen into the coating. Tabl.: 1. Fig.: 2. Refs: 24 titles.

The influence of current density and bath temperature on electrodeposition of rhodium film from sulfate–phosphate aqueous solutions

Rhodium films were electrodeposited galvanostatically on copper–zinc alloy substrates from sulfate–phosphate aqueous solutions, in order to obtain a smooth, dense, and thick Rh film for electrical contacts. The influence of current density and bath temperature on phases, crystal structure, microstructure, and deposition rate of the film was studied. The phases and crystal structure, as well as microstructure of the film were determined by X-ray diffraction and scanning electron microscopy, respectively. The results showed that the current density and bath temperature had a significant influence on electrodeposition of rhodium film. The particles or aggregates on the surface evolved from fine to coarse and large with the increase of current density and bath temperature. By adjusting the deposition conditions, the optimized current density and bath temperature were 6.4–12.7 mA cm−2 and 50 °C, respectively. The film was composed of polycrystalline phase with monometallic form. The film was uniform and dense at low current density. The thickness of the film was up to 1.38–2.1 μm. At the optimal temperature of 50 °C, the surface of the film was smooth and fine. At the same time, the electrodeposition mechanism of the film was discussed. Rhodium films were electrodeposited from sulfate–phosphate aqueous solutions. The influence of current density and bath temperature on electrodeposition of the film was studied, and at the same time, the electrodeposition mechanism of the film was addressed.

Fuzzy nanostructure growth on precious metals by He plasma irradiation

Growth of helium bubbles near the surface of metals leads to various morphology changes when sufficient helium ions are continuously implanted on the surface. In this study, low energy (< 100 eV) helium plasma irradiations to various noble metals were conducted, and consequent surface morphology changes were analyzed. It was found that fiberform nanostructures were formed by the helium plasma irradiation on rhodium and ruthenium thin films, which were deposited by magnetron sputtering, and on platinum and iridium wires. Growth of fiberform structures were not identified on gold, silver, and palladium samples exposed to helium plasmas even though the irradiations were conducted at various surface temperatures, though pinholes were observed on palladium surface. We discussed the relation between the morphology changes and material properties.

Centimeter-Sized Single-Orientation Monolayer Hexagonal Boron Nitride With or Without Nanovoids

Large-area hexagonal boron nitride (h-BN) promises many new applications of two-dimensional materials, such as the protective packing of reactive surfaces or as membranes in liquids. However, scalable production beyond exfoliation from bulk single crystals remained a major challenge. Single-orientation monolayer h-BN nanomesh is grown on 4 in. wafer single crystalline rhodium films and transferred on arbitrary substrates such as SiO2, germanium, or transmission electron microscopy grids. The transfer process involves application of tetraoctylammonium bromide before electrochemical hydrogen delamination. The material performance is demonstrated with two applications. First, protective sealing of h-BN is shown by preserving germanium from oxidation in air at high temperatures. Second, the membrane functionality of the single h-BN layer is demonstrated in aqueous solutions. Here, we employ a growth substrate intrinsic preparation scheme to create regular 2 nm holes that serve as ion channels in liquids.

XPS Study of Nanostructured Rhodium Oxide Film Comprising Rh4+ Species

Studies of highly oxidized rhodium species as potential active sites in catalytic oxidation reactions are of great interest. In this work, we investigated the properties of highly oxidized nanostructured rhodium film prepared by radio frequency discharge in an oxygen atmosphere. The charge states of Rh in RhOx particles, their thermal stability, and reactivity toward CO were analyzed in comparison with the properties of thermally prepared Rh2O3 oxide. The formation of Rh4+ species in a composition of Rh4+/Rh3+ oxyhydroxide structures was shown to take place in plasma-synthesized films. The highly oxidized rhodium species was stable up to 150 °C and demonstrated reactivity in a CO oxidation reaction at 100 °C. The reoxidation of a partially reduced Rh/RhOx film was observed at 100 °C under treatment with molecular O2. However, Rh4+ species were not recovered under such conditions.

Structural, electronic and adsorption properties of Rh(111)/Mo(110) bimetallic catalyst: A DFT study

Geometric and electronic characterizations of one monolayer rhodium with Nishiyama-Wassermann (NW) structure on Mo(110) substrate have been performed by density functional theory (DFT) calculations. In the NW structure the Rh atoms form a wavy structure propagating along the [001] direction, characterized by an amplitude of 0.26Å in the [110] direction and by 0.10Å in the [110] direction of the Mo(110) substrate. Strain and ligand effects operating in the rhodium film are distinguished and found to be manifested in the downward shift of the d-band center of the electron density of states (DOS) by 0.11eV and 0.18eV, respectively. The shift in the d-band center of Rh DOS predicts a decrease in the surface reactivity toward CO adsorption, which has been verified by detailed calculations of bond energies of CO located at on-top, bridge and hollow adsorption sites. The CO adsorption energies are decreased by about 35% compared to those reported for pure Rh(111), offering novel catalytic pathways for the molecule. An in-depth analysis of the charge transfer and the partial DOS characters upon CO adsorption on the NW-structured Rh(111)/Mo(110) bimetallic catalyst and on the pure Rh(111) surface sheds light on the bonding mechanism of CO and on the governing factors determining its lowered bond energy on the bimetallic surface.

Laser cleaning of diagnostic mirrors from tungsten–oxygen tokamak-like contaminants

This paper presents a laboratory-scale experimental investigation about the laser cleaning of diagnostic first mirrors from tokamak-like contaminants, made of oxidized tungsten compounds with different properties and morphology. The re-deposition of contaminants sputtered from a tokamak first wall onto first mirrors’ surfaces could dramatically decrease their reflectivity in an unacceptable way for the proper functioning of plasma diagnostic systems. The laser cleaning technique has been proposed as a solution to tackle this issue. In this work, pulsed laser deposition was exploited to produce rhodium films functional as first mirrors and to deposit onto them contaminants designed to be realistic in reproducing materials expected to be re-deposited on first mirrors in a tokamak environment. The same laser system was also used to perform laser cleaning experiments, exploiting a sample handling procedure that allows one to clean some cm2 in a few minutes. Cleaning effectiveness was evaluated in terms of specular reflectance recovery and mirror surface integrity. The effect of different laser wavelengths (, 266 nm) on the cleaning process was also addressed, as well as the impact of multiple contamination/cleaning cycles on the process outcome. A satisfactory recovery of pristine mirror reflectance (⩾90%) was obtained in the vis–NIR spectral range, avoiding at the same time mirror damaging. The results here presented show the potential of the laser cleaning technique as an attractive solution for the cleaning of diagnostic first mirrors.

Enhanced dispersion and the reactivity of atomically thin Rh layers supported by molybdenum oxide films

The behavior of rhodium layers deposited on oxidized, 0.15–20.0 ML thick Mo films formed on a nearly stoichiometric TiO2(110) single crystal was characterized by AES, TPD and work function (WF) measurements. The oxidation of 0.15–2.7 ML thick Mo deposits was performed via the redox reaction with the titania support at 1000K. Molybdenum oxide supports of MoO3 and MoO2 surface composition were formed by the oxidation of 20 ML thick Mo multilayers by O2 at 650K and 1000K, respectively. Rh grows in a layer-by-layer fashion on a mixed titanium-molybdenum oxide produced in the reaction between titania and 0.15 ML Mo, corresponding to a considerably enhanced dispersion of rhodium as compared with that on the clean TiO2(110). The surface reactivity of Rh layers supported by molybdenum oxides as a function of pre-annealing temperature was followed by carbon monoxide adsorption–desorption cycles. The CO uptake of a 0.4 ML thick Rh film formed on the MoO3 support was strongly suppressed at 300K, indicating the encapsulation of rhodium with MoOX species of low surface free energy. The CO adsorption capability of rhodium particles supported by both MoO3 and MoO2 layers was eliminated due to pre-annealing at 600K, related to the extended decoration of metal particles by MoOX moiety. The encapsulation of the rhodium films proceeded above 600K on both supports, and annealing to 1000K resulted in nearly equal WF values, indicating the formation of MoOX overlayers of similar surface composition close to MoO2. AES depth profiles revealed that the 0.4 ML thick Rh deposits covered by MoOX at 1000K preserved their island structure.

Laser cleaning of diagnostic mirrors from tokamak-like carbon contaminants

This paper presents a laboratory-scale experimental investigation of laser cleaning of diagnostic First Mirrors (FMs). Redeposition of contaminants sputtered from tokamak first wall onto FMs surface could dramatically decrease their reflectivity in an unacceptable way for the functioning of the plasma diagnostic systems. Laser cleaning is a promising solution to tackle this issue. In this work, pulsed laser deposition was exploited to produce rhodium films functional as FMs and to deposit onto them carbon contaminants with tailored features, resembling those found in tokamaks. The same laser system was also used to perform laser cleaning experiments by means of a sample handling procedure that allows to clean some cm2 in few minutes. The cleaning effectiveness was evaluated in terms of specular reflectivity recovery and mirror surface integrity. The effect of different laser wavelengths (λ=1064, 266nm) on the cleaning process is also addressed.

Effect of deuterium ion beam irradiation onto the mirror-like pulsed laser deposited thin films of rhodium

The effect of deuterium ion beam irradiation on the reflectivity of mirror-like pulsed laser deposited (PLD) thin film of rhodium is reported. The deposition parameters; target-substrate distance and background helium gas pressure were optimized to obtain the good quality rhodium films, of higher thickness, oriented preferentially in (111) plane. The rhodium thin films deposited at optimum PLD parameters were exposed to 10, 20, and 30keV deuterium ion beam. The changes in surface morphology and UV–Visible–FIR reflectivity of mirror-like rhodium thin films, as a function of energy of deuterium ion beam, after exposure are reported.

Transfer hydrogenation of ketones catalyzed by new rhodium and iridium complexes of aminophosphine containing cyclohexyl moiety and photosensing behaviors of rhodium and iridium based devices

The reaction of [Rh(μ-Cl)(cod)]2 and Ir(η5-C5Me5)(μ-Cl)Cl]2 with aminophosphine ligands Cy2PNHCH2–C4H3X (X: O; S) gave a range of new monodendate [Rh(Cy2PNHCH2–C4H3O)(cod)Cl], (1), [Rh(Cy2PNHCH2–C4H3S)(cod)Cl], (2), [Ir(Cy2PNHCH2–C4H3O)(η5-C5Me5)Cl2], (3) and [Ir(Cy2PNHCH2–C4H3S)(η5-C5Me5)Cl2], (4) complexes, which were characterized by analytical and spectroscopic methods. The new rhodium(I) and iridium(III) catalysts were applied to transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with high activity (up to 99%) under mild conditions. Notably, [Rh(Cy2PNHCH2–C4H3O)(cod)Cl] complex (1) is much more active than the other analogous complexes in the transfer hydrogenation. Moreover, organic–inorganic rectifying contacts were fabricated forming rhodium(I) and iridium(III) complex thin films on n-Si semiconductors and evaporating Au metal on the structures. Electrical properties of the contacts including ideality factor, barrier height and series resistance were determined using their current–voltage (I–V) data. The photoelectrical characteristics of the devices were examined under the light with 40–100 mW/cm2 illumination conditions. It was seen that light had strong effects on I–V characteristics of the devices and the ones fabricated using 3 and 4 complexes had unusually forward and reverse bias photoconducting behavior.

Deuterium plasma exposure of rhodium films: Role of morphology and crystal structure

The behavior of rhodium film mirrors with different crystal structure and morphology toward a deuterium plasma is presented. The specular reflectivity of rhodium films was monitored before, during and after exposure. To understand the reflectivity behavior of the rhodium films during exposure, samples were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Crystal structure and morphology of rhodium films strongly affect the change of the specular reflectivity during deuterium plasma exposure. In particular, films with few nm crystallite size and granular-like morphology prevent the reflectivity degradation, probably as a consequence of the inhibition of rhodium deuteride sub-superficial layer formation.

Fabrication and calibration of Pt–10%Rh/Pt thin film thermocouples

Platinum–10% rhodium vs. platinum thin film thermocouples with multi-layer structure were prepared on the nickel based superalloy substrates. The samples were calibrated in a thermocouple calibrating furnace in temperature range from 200°C to 950°C. The influences of anneal on the Seebeck coefficient and the relative sensitivity coefficient were investigated in detail. The results show that the Seebeck coefficient of the samples annealed in air is degenerated from 7.7μV/°C down to 7.32μV/°C and the sensitive coefficient is degenerated from 0.742 to 0.647 in average. However, the samples annealed in vacuum is improved from 7.7μV/°C to 8.28μV/°C and the sensitive coefficient is improved from 0.742 to 0.911 in average. The error was limited to 11°C from 200°C to 1000°C. The loss efficacy time of all the samples is less than 20h in our test condition.