Rhenium Films Research Articles

Superconducting Polycrystalline Rhenium Films Deposited at Room Temperature

Superconducting Polycrystalline Rhenium Films Deposited at Room Temperature

Formation of Thin Rhenium Films on Nickel Plate by its Chloride Electrolysis

Formation of Thin Rhenium Films on Nickel Plate by its Chloride Electrolysis

The potential––pH diagram for rhenium

The aqueous chemistry of rhenium is of importance for the hydrometallurgical processes involving rhenium alloys, for the leaching of rhenium from its ores and alloys, and for the electrochemical deposition of thin rhenium films. This study aims to present the chemical and electrochemical equilibria in the Re – H2O system in the form of the Pourbaix diagram. The existing variants of the Pourbaix diagrams for rhenium available in the literature were reviewed; it was shown that they significantly differ from each other in the composition and the values of the thermodynamic activities of rhenium species. The thermodynamic properties of aqueous rhenium species, including the standard Gibbs energies of formation and the standard electrode potentials of half-cell reactions involving it, were collected and analysed. The compounds of rhenium (+7) and rhenium (+6) not isolated in the free aqueous state, and rhenium hydride compounds were discussed. The self-consisted set of thermodynamic data for further calculations was obtained. Using these data, the basic chemical and electrochemical equilibria involving aqueous rhenium species at the temperature of 298 K and the air pressure of 1 bar were calculated. For the first time the potential – pH diagram for the Re – H2O system at the temperature of 298 K, the air pressure of 1 bar and the different activities of rhenium species in the solution were constructed. The influence of thermodynamic activities of aqueous rhenium compounds on the stability of rhenium oxides was discussed. It was shown that rhenium trioxide ReO3 is thermodynamically stable only in concentrated solutions (at the activities of rhenium species not less than 10–6 М), rhenium dioxide ReO2 loses the stability at the activities of rhenium species less than 10–8 М, and rhenium sesquioxide Re2O3 does so at the activities of rhenium species not less than 10–14 М. The necessity of the measurement of the stability constants of ortho- and mesorhenate anions, as well as nonahydridorhenates for a deeper understanding of the aqueous rhenium chemistry was discussed.

Thermal atomic layer deposition of rhenium nitride and rhenium metal thin films using methyltrioxorhenium.

The growth of rhenium nitride and rhenium metal thin films is presented using atomic layer deposition (ALD) with the precursors methyltrioxorhenium and 1,1-dimethylhydrazine. Saturative, self-limiting growth was determined at 340 °C for pulse times of ≥4.0 s for methyltrioxorhenium and ≥0.1 s for 1,1-dimethylhydrazine. An ALD window was observed from 340 to 350 °C with a growth rate of about 0.60 Å per cycle. Films grown at 340 °C revealed a root mean square surface roughness of 2.7 nm for a 70 nm thick film and possessed a composition of ReN0.14 with low O and C content of 1.6 and 2.6 at%, respectively. Enhanced nucleation on in situ grown TiN, relative to thermal SiO2, enabled a conformality of 98% on high aspect ratio trenched structures. Subjecting the ReN0.14 thin films to thermal or chemical and thermal treatments reduced the nitrogen content to ≤1.6 at%, yielding a film purity of about 96 at% rhenium and resistivities as low as 51 μΩ cm. The Re metal film thicknesses on the trenched structures remained intact during the post-deposition annealing treatments and the films did not delaminate from the substrate surfaces.

Grain growth and superconductivity of rhenium electrodeposited from water-in-salt electrolytes

The relationship between superconductivity and the film preparation conditions, i.e., the thickness and annealing process, in electrodeposited rhenium (Re) films is studied in order to understand the effect of grain size and impurities on the film's superconducting transition temperature, Tc. A water-in-salt electrolyte was used to mitigate embrittlement by reducing hydrogen evolution at the cathode where Re is deposited. The as-deposited films exhibit a highly disordered atomic structure and superconductivity up to a temperature of Tc > 5.8 K, consistent with that expected from amorphous films. A reduction of the critical temperature of superconductivity is found to accompany grain growth. However, for film thicknesses less than 300 nm the grain growth is inhibited. This leads to a retention of the critical temperature upon annealing these thin films. A reduction of impurities in Re films is found to accompany annealing, and significant grain growth is found to proceed rapidly at temperatures of 220 °C in inert atmospheres. The introduction of hydrogen in the annealing ambient further facilitates this grain growth.

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition

AbstractRhenium is both a refractory metal and a noble metal that has attractive properties for various applications. Still, synthesis and applications of rhenium thin films have been limited. We introduce herein the growth of both rhenium metal and rhenium nitride thin films by the technologically important atomic layer deposition (ALD) method over a wide deposition temperature range using fast, simple, and robust surface reactions between rhenium pentachloride and ammonia. Films are grown and characterized for compositions, surface morphologies and roughnesses, crystallinities, and resistivities. Conductive rhenium subnitride films of tunable composition are obtained at deposition temperatures between 275 and 375 °C, whereas pure rhenium metal films grow at 400 °C and above. Even a just 3 nm thick rhenium film is continuous and has a low resistivity of about 90 μΩ cm showing potential for applications for which also other noble metals and refractory metals have been considered.

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition.

Rhenium is both a refractory metal and a noble metal that has attractive properties for various applications. Still, synthesis and applications of rhenium thin films have been limited. We introduce herein the growth of both rhenium metal and rhenium nitride thin films by the technologically important atomic layer deposition (ALD) method over a wide deposition temperature range using fast, simple, and robust surface reactions between rhenium pentachloride and ammonia. Films are grown and characterized for compositions, surface morphologies and roughnesses, crystallinities, and resistivities. Conductive rhenium subnitride films of tunable composition are obtained at deposition temperatures between 275 and 375 °C, whereas pure rhenium metal films grow at 400 °C and above. Even a just 3 nm thick rhenium film is continuous and has a low resistivity of about 90 μΩ cm showing potential for applications for which also other noble metals and refractory metals have been considered.

Electrodeposition of rhenium with suppressed hydrogen evolution from water-in-salt electrolyte

The electrodeposition of rhenium was studied using a “water-in-salt” type of electrolyte with a superhigh concentration of lithium chloride to suppress the proton activity. Cyclic voltammetry and DC plating were carried out on rotating disc electrodes to characterize the electrolyte and to prepare thin films. Electrolytes without metal cations were also studied, where the cathodic reduction of proton was significantly suppressed when the concentration of supporting salt approached the solubility limit. Film cracks were eliminated for rhenium films deposited from this superhigh ionic strength electrolyte.

Electrodeposition of Superconducting Rhenium with Water-in-Salt Electrolyte

Superconductive rhenium films were electrodeposited from a water-in-salt type electrolyte with superhigh concentration of LiCl. Rhenium free electrolytes were also studied with linear sweep voltammetry to further understand the effects of LiCl salt concentration on the ion activity and side reactions. The morphology, crystallographic structures and superconductivity of the electrodeposited Re films were characterized. The hydration of LiCl resulted in a depletion of free water molecules and a decrease of proton reduction. While cracks were ubiquitously observed in films electrodeposited from traditional electrolyte, such cracks are eliminated when water-in-salt is used. An increased critical temperature of 6 K with an improved stability was observed for the Re film deposited from this new type of electrolyte.

Epitaxial Rhenium Microwave Resonators

We have fabricated rhenium microwave resonators from epitaxial films. We have used thin films of different structural quality depending on their growth conditions. The resonators were coupled to a microwave transmission line which allows the measurement of their resonance frequencies and internal quality factors. From the resonance frequency at low temperature , the effective penetration depth and the London penetration depth of the rhenium film are extracted.

Numerical ellipsometry: Examination of growing nickel and rhenium thin films using n–k plane analysis and effective numerical substrates

Abstract Useful thin film information may be obtained using ellipsometry data recorded during film growth. In cases in which the growing film overlies a substrate already coated with other films, it is possible to use a model which includes prior knowledge of the optical properties and layer thicknesses of all underlying films and the substrate. However, accuracy of the analysis is limited by imprecision in knowledge of the underlying structure and is not possible if the underlying material structure is unknown. These problems may be addressed by substituting a four-variable “numerical substrate” in place of the underlying materials. The “numerical substrate” exactly mathematically replaces a model of the physical substrate. It is represented by two effective optical indices which are independent of the growing film and dependent only upon light incidence angle and wavelength. The method may be implemented with a set of five measurements at a single wavelength and incidence angle or a set of three measurements at each of two incidence angles. Measurements may be made in-situ during film growth or ex-situ using “step deposited” films of different thicknesses. The work presented here is to demonstrate the method for nickel and rhenium films deposited on a BK7 substrate by Yamamoto using ion sputtering.

Synthesis of ReN3 Thin Films by Magnetron Sputtering

In this work ReNx films were prepared by reactive magnetron sputtering at room temperature and deposited on a silicon wafer. It was found that the diffractograms of the nitrogen-rich rhenium film are consistent with those produced by high-pressure high-temperature methods, under the assumption that the film is oriented on the substrate. Using density functional calculations it was found that the composition of this compound could be ReN3, instead of ReN2, as stated on previous works. The ReN3 compound fits in the Ama2 (40) orthorhombic space group, and due to the existence of N3 anions between Re layers it should be categorized as an azide. The material is exceptionally brittle and inherently unstable under indentation testing.

Photoelectrochemical reduction of nitrate on p-Si coated with metallic Re thin films

In this study we examined the rhenium electrodeposition process onto p-Si(100) from acidic media. The study was carried out by means of cyclic voltammetry and the potential-steps method from which the corresponding nucleation and growth mechanism were determined. Both methods were performed under illumination using a solar simulator for electron photogeneration. A 3D progressive nucleation, diffusion-controlled growth of rhenium films was found. Likewise, a morphologic analysis was completed for the deposits obtained at different potential values by means of atomic force microscopy. An energetic characterization through capacitance measurements (Mott–Schottky plots and parallel capacitance) of the p-Si/NO 3 − and p-Si/Re/NO 3 − interfaces was done. The photoelectrochemical reduction of nitrate ions, PERN, on the different p-Si/Re electrode systems synthesized was studied. An overpotential decrease of 0.3 V and a photocurrent increase for the PERN on p-Si(100)/Re electrode systems compared with p-Si(100) and metallic Re was found. Finally, the kinetic parameters of the cathodic reactions in the p-Si and p-Si/Re acidic media were estimated using intensity modulated photocurrent spectroscopy. A brief analysis from this technique was done. According to these results, the p-Si/Re electrode system could be a potential photoelectrocatalyst for the PERN.

Deposition and characterization of few-nanometers-thick superconducting Mo–Refilms

We report on the fabrication and investigation of few-nanometers-thick superconductingmolybdenum–rhenium (Mo–Re) films intended for use in nanowire single-photonsuperconducting detectors (SSPDs). Mo–Re films were deposited on sapphiresubstrates by DC magnetron sputtering of an Mo(60)–Re(40) alloy targetin an atmosphere of argon. The films 2–10 nm thick had critical temperatures(Tc) from 5.6 to 9.7 K. HRTEM (high-resolution transmission electron microscopy)analysis showed that the films had a homogeneous structure. XPS (x-rayphotoelectron spectroscopy) analysis showed the Mo to Re atom ratio to be0.575/0.425, oxygen concentration to be 10%, and concentration of other elements to be 1%.

Electrochemical Deposition and Characterization of Mixed-Valent Rhenium Oxide Films Prepared from a Perrhenate Solution

Cathodic electrodeposition of mixed-valent rhenium oxides at indium tin oxide, gold, rhenium, and glassy carbon electrodes from acidic perrhenate solutions (pH = 1.5 +/- 0.1) prepared from hydrogen peroxide and zerovalent rhenium metal is described. Cyclic voltammetry, variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), UV-vis spectroelectrochemistry, and electrochemical quartz crystal microbalance (EQCM) data indicate that the chemical nature of the electrodeposited rhenium species depends mainly upon the potential and supporting electrolyte. The presence of SO4(2-) as a supporting electrolyte inhibits the adsorption of perrhenate, ReO4-, at non-hydrogen adsorbing electrode materials. However, in acidic perrhenate solutions containing only protons and ReO4- anions, strong adsorption of ReO4- at potentials preceding hydrogen evolution occurs. This leads to the formation of an unstable ReIII2O3 intermediate which catalytically disproportionates to form mixed-valent rhenium films consisting of 72% ReIVO2 and 28% Re0. During the hydrogen evolution reaction (HER), hydrogen polarization causes the principle deposit to be more reduced, consisting of roughly 64% ReIVO2 and 36% Re0. Conclusively, metallic rhenium can be deposited at potentials preceding the HER at non-hydrogen adsorbing electrode materials, especially in the absence of SO4(2-) anions.

Rhenium electrodeposition process onto p-Si(1 0 0) and electrochemical behaviour of the hydrogen evolution reaction onto p-Si/Re/0.1 M H 2SO 4 interface

In this study we examined the rhenium electrodeposition process onto p-Si(1 0 0). The study was carried out by means of cyclic voltammetry (CV) and the potential-steps method from which the corresponding nucleation and growth mechanism (NGM) were determined. Both methods were performed under illumination for electron photogeneration. A 3D progressive nucleation, diffusion-controlled growth of rhenium films was found (PN3D Diff). Furthermore, the photocurrent–time transients were fitted with an equation that takes into account redox reactions occurring simultaneously on the rhenium film surface, in this case proton reduction. Likewise, a morphologic analysis was completed for the deposits obtained at different potential values by means of atomic force microscopy (AFM). Finally, the hydrogen evolution reaction, HER, on different electrode systems was studied. An overpotential decrease of 0.2 V and a photocurrent increase by one order of magnitude for the HER on p-Si(1 0 0)/Re electrode system compared with p-Si(1 0 0) and metallic Re was found. According to these effects, this electrode system could be a photoelectrocatalyst for the HER.

Oxygen transport and reaction mechanisms in rhenium gate contacts on hafnium oxide films on Si

Oxygen transport and incorporation were investigated following postdeposition annealing of metal-oxide-semiconductor structures having ultrathin rhenium films as metal electrode and HfO2 films as dielectric on Si(001). Isotopic tracing, nuclear reaction analysis, narrow resonant nuclear reaction profiling, and x-ray photoelectron spectroscopy were used to pursue this investigation. For annealing temperatures below 400°C, oxygen from the gas phase incorporates mainly in near-surface regions of the overlying Re cap. Significant oxygen incorporation into the HfO2 films is observed only after annealing at 500°C. The present results are discussed considering that supplying oxygen to the metal/dielectric interface can cause device threshold voltage shifts.

Study of the electrodeposition of rhenium thin films by electrochemical quartz microbalance and X-ray photoelectron spectroscopy

Rhenium thin films were prepared by electrodeposition from an aqueous solution containing 0.1 M Na 2SO 4+H 2SO 4, pH 2 in presence of y mM HReO 4. As substrates polycrystalline gold ( y=0.75 mM HReO 4) and monocrystalline n-Si(100) ( y=40 mM HReO 4) were used. The electrochemical growth of rhenium was studied by cyclic voltammetry and electrochemical quartz microbalance on gold electrodes. The results found in the potential region before the hydrogen evolution reaction (her) showed that ReO 3, ReO 2 and Re 2O 3 with different hydration grades can be formed. In the potential region where the her is occurring, either on gold or n-Si(100) the electrodeposition of metallic rhenium takes place. On both substrates, rhenium films were formed by electrolysis at constant potential and X-ray photoelectron spectroscopy technique was used to characterise these deposits. It was concluded that the electrodeposited films were of metallic rhenium and only the uppermost atomic layer contained rhenium oxide species.

An XPS study of the oxidation and reduction of the rhenium-platinum system under atmospheric conditions

The oxidation and reduction of the platinum-rhenium system has been studied by using X-ray photoelectron spectroscopy (XPS). Rhenium films about 10 layers thick were formed by evaporation onto a platinum foil under vacuum. These samples were sequentially exposed to 1 atm of oxygen at different temperatures and then reduced with 1 atm of H 2. XP spectra were taken after each high pressure experiment. A mixture of rhenium oxides was formed after oxidation at above 475 K, and depletion of the surface rhenium due to the formation of the volatile Re 2O 7 was observed after treatments above 575 K. Subsequent hydrogen treatment did not completely reduce these oxides, and a remaining low oxidation state rhenium, perhaps ReO, could be detected by XPS. The behavior of alloys of platinum-rhenium after similar treatments was also studied. Oxidation for this system was even more facile than for the rhenium overlayers, but almost complete reduction to the metallic state was achieved by hydrogen treatment of the oxides, indicating that platinum may catalyze this rhenium reduction step.

ChemInform Abstract: “Transparent” Metals: Preparation and Characterization of Light‐Transmitting Palladium, Rhodium, and Rhenium Films.

AbstractPd, Rh, and Re films being more transparent to visible, near UV and IR light than the dense metal films at equal metal loading are obtained by photoelectrodeposition onto p‐InP(100) photocathodes from 5·10‐5 M solutions of the metal in 1 M HClO4 under mass‐transport limited conditions.