Supercritical Fluid Chemical Deposition Research Articles

Improved Electrochemical Performance for High-Voltage Spinel LiNi0.5Mn1.5O4 Modified by Supercritical Fluid Chemical Deposition.

Among candidates at the positive electrode of the next generation of Li-ion technology and even beyond post Li-ion technology as all-solid-state batteries, spinel LiNi0.5Mn1.5O4 (LNMO) is one of the favorites. Nevertheless, before its integration into commercial systems, challenges still remain to be tackled, especially the stabilization of interfaces with the electrolyte (liquid or solid) at high voltage. In this work, a simple, fast, and cheap process is used to prepare a homogeneous coating of Al2O3 type to modify the surface of the spinel LNMO: the supercritical fluid chemical deposition (SFCD) route. This process is, to the best of our knowledge, used for the first time in the battery field. Significantly improved performance was demonstrated vs those of bare LNMO, especially at high rates and for highly loaded electrodes.

Synthesis and Characterization of Ni-Pt Alloy Thin Films Prepared by Supercritical Fluid Chemical Deposition Technique

Ni-Pt alloy thin films have been successfully synthesized and characterized; the films were prepared by the supercritical fluid chemical deposition (SFCD) technique from Ni(hfac)2·3H2O and Pt(hfac)2 precursors by hydrogen reduction. The results indicated that the deposition rate of the Ni-Pt alloy thin films decreased with increasing Ni content and gradually increased as the precursor concentration was increased. The film peaks determined by X-ray diffraction shifted to lower diffraction angles with decreasing Ni content. The deposited films were single-phase polycrystalline Ni-Pt solid solution and it exhibited smooth, continuous, and uniform distribution on the substrate for all elemental compositions as determined by scanning electron microscopy and scanning transmission electron microscopy analyses. In the X-ray photoelectron spectroscopy (XPS) analysis, the intensity of the Pt 4f peaks of the films decreased as the Ni content increased, and vice versa for the Ni 2p peak intensities. Furthermore, based on the depth profiles determined by XPS, there was no evidence of atomic diffusion between Pt and Ni, which indicated alloy formation in the film. Therefore, Ni-Pt alloy films deposited by the SFCD technique can be used as a suitable model for catalytic reactions due to their high activity and good stability for various reactions.

Deposition of Ni-Based Thin Films in Supercritical Carbon Dioxide Solution Via Flow-Type Reaction System

Ni-based films have been extensively studied owing to their potential application in several fields such as metal coatings 1, microelectronic devices 2, magnetic devices 3, and catalysis 4. One of the techniques to deposit Ni thin films is supercritical fluid chemical deposition (SFCD) that offers the potential for the capability of high conformal step coverages and high-aspect-ratio features at materials dimensions 5-6. This technique includes the dissolution of precursor in supercritical fluids, adsorption of precursor and reducing agent onto the substrate surface, the reaction between adsorbed precursor and a reducing agent to its metal or metal oxide form on the substrate surface, and desorption of hydrogenated ligands from the substrate into the supercritical fluids phase. These process steps typically proceed under supercritical carbon dioxide (scCO2) solution due to its relatively moderate critical temperature (31.1°C) and pressure (7.38 MPa) 7 that has high molecular density, high diffusivity, low viscosity and zero surface tension 8.There are two basic type reaction systems for the SFCD technique namely batch-type and flow-type systems 9. In a typical batch-type system, a substrate, a fixed amount of precursor, CO2, and H2 gas are together charged in a closed reactor. The temperature and pressure could ramp up/down because of there is no inlet or outlet in this system. Consequently, the unreacted precursor or the reaction by-product accumulates in the reactor which may make the final product in poor film quality. To overcome this problem, we present here the deposition of Ni thin films in scCO2 solution from Ni(hfac)2 ·3H2O precursor through hydrogen reduction with a variety of independent variables via a flow-type reaction system. In this system, a precursor, CO2, and H2 are continuously supplied at a fixed flow rate, concentration, and pressure into a tubular flow reactor. Furthermore, we also employed the deposition of Ni-Sn alloy thin films with various compositions by flow-type SFCD reaction system, and then their activity was evaluated.The raw materials used in this study were Si(100) wafers having a TiN/SiO2 layer on top, Ni(hfac)2.3H2O, and (i-C3H7)4Sn as Ni and Sn precursor sources respectively, liquid CO2, hydrogen gas, and acetone. Liquid CO2 was cooled and pressurized above a CO2 critical pressure. H2 gas with a certain pressure was added to the scCO2 solution using a gas mixing unit. The precursor solution was added to scCO2 using a high-pressure pump. The substrate was placed inside a tubular flow reactor. And the pressure of this system was adjusted by a back-pressure regulator. All the process parameters of Ni thin film deposition are consisting of precursor concentration, hydrogen concentration, and growth temperature.Ni thin films were successfully deposited onto TiN/SiO2 film by the SFCD technique. Fig. 1 shows the XRD patterns of Ni films deposited at various precursor concentrations and temperatures. This shows that the Ni thin films were highly (111) structure-oriented. For the XRD patterns of Ni-Sn alloy thin films, the Ni(111) and Ni(200) peaks after added an Sn ratio was slightly shifted and became low intensity that might indicate the formation of the Ni-Sn alloys in a wide composition range. Based on the precursor concentration dependence, the curve trend lines in this study indicated Langmuir-Hinshelwood-type adsorption that the Ni growth rate found to be a zero-order reaction. At temperature dependence, the increase in H2 concentration resulted in the Ni growth rate increase, indicating the activation energy decreased with increasing H2 concentration.

Kinetics of Ni thin film synthesis by supercritical fluid chemical deposition

Ni was deposited on TiN films by supercritical fluid chemical deposition (SFCD) through hydrogen reduction of the precursor Ni(hfac)2·3H2O. In this context, the kinetics and reaction mechanism of Ni thin film deposition were studied by using a SFCD flow-type reaction system. The results indicated that the Ni growth rate increased with precursor concentration and then saturated. Based on the Arrhenius plots, the apparent activation energy decreased with increasing H2 concentration, yielding values ranging from 0.90 to 0.61 eV. A kinetics and reaction scheme using the Langmuir–Hinshelwood model, with the surface reaction constituting the rate-determining step, generated a zero-order reaction with respect to precursor concentration. On other hand, the equilibrium constants for the adsorption of precursor and hydrogen in the reaction scheme of Ni thin film deposition decreased with increasing temperature, which indicated that the reaction was exothermic.

Preparation of ceramic materials using supercritical fluid chemical deposition

This paper relates an unconventional technique based on the supercritical fluid technology for manufacturing dense ceramic matrix composites, which is known as the Supercritical Fluid Chemical Deposition process (SFCD). By using a conventional precursor in a solvent above its critical coordinates, it is possible to faster the deposition rate of a SiC-based matrix on fibrous preforms in comparison to the Chemical Vapor Deposition technique for which a low pressure (1–50kPa) is recommended for a similar range of temperatures 800–1000°C (mixture N2: tetramethylsilane 99.2:0.8vol.%). The microstructure of the coating or matrix is characterized by optical microscopy, Spectroscopy Electron Microscopy and Electron Dispersive X-ray spectroscopy. The influence of the main experimental parameters (temperature, pressure, residence time) is studied on the chemical composition of the ceramic deposits. The opportunity to tune the C:SiC molar ratio opens the door towards multilayered interfaces exhibiting multifunctional properties.

A comparative study of copper thin films deposited using magnetron sputtering and supercritical fluid deposition techniques

A comparison of crystallinity, microstructure, surface morphology and electrical conductivity is proposed for the deposition of copper films, using supercritical fluid chemical deposition (SFCD) and RF magnetron sputtering techniques. Both preparation methods yield nanocrystalline Cu films (<100nm) but SFCD gives access to a higher crystallinity for the same AlN substrate temperature during the deposit. Based on the film characteristics, a comparison of the evolution of electrical properties is done for RF magnetron sputtered copper films and SFCD ones with H2 as reducing agent. Uniform strain values are significantly reduced when SFCD technique is used and crystallinity is highly increased leading to lower resistivity values for a same crystallite size. This study demonstrates the viability of the SFCD technique to produce high quality nanostructured copper thin films with low resistivity values.

Supercritical CO2 reactor for wafer-scale thin film deposition: reactor concept, numerical results, and Cu depositio.

Supercritical fluid chemical deposition, frequently abbreviated SFCD, is a thin film deposition technique that employs supercritical fluids. In this deposition technique, a thin film is synthesized from a precursor dissolved in a fluid, along with a reaction reagent if necessary. This paper proposes a novel wafer-scale tool for SFCD. The reactor has a flat cylindrical interior, and the fluid is supplied at the center of the upper face. A porous plate is placed on the bottom face, at the center of which a small fluid outlet is opened. A wafer is placed directly on the porous plate without a holding device, and the diameter of the porous plate is slightly larger than that of the wafer. This reactor has a minimal interior volume and realizes radial and unidirectional flow over the entire wafer. Furthermore, the in-plane pressure distribution is completely uniform, allowing a uniform flow distribution, which was verified by computational fluid dynamics simulations. Cu films were deposited on a 100mm silica glass wafer using Cu(C9H12O2)2 (Cu(dibm)2) as a precursor. The average thicknesses were 75nm at 185°C and 182nm at 200°C,and the standard deviations were 19nm and 14nm, respectively. Basic film characterization was also performed.

Selective Cu filling of nanopores using supercritical carbon dioxide

Supercritical fluid chemical deposition is known for its superior capability of filling metals into nanofeatures. The mechanism behind this filling capability has not been well understood and can be very different from those of other deposition techniques such as chemical vapor deposition. We have proposed a filling mechanism where the precursor condenses preferentially in narrow concave features and then converts into a metal deposit. In accordance with these two sequential phenomena, the narrower the feature is, the better the filling will be achieved. In this article, selective Cu deposition into nanopores of a silica-based porous thin film is described. When the conventional supercritical fluid deposition method was employed, a significant amount of Cu penetrated into the nanopores along with the continuous film formation on the substrate surface. By illuminating UV light before the start of Cu nucleation, Cu deposited selectively only inside the nanopores. During the selective deposition, optical changes in the porous film were investigated by in situ ellipsometry. These results indicate that the precursor condenses preferentially only in the nanopores and converts into a metal deposit.

Formation of zinc oxide thin film using supercritical fluids and its application in fabricating a reliable Cu/glass stack

This paper demonstrates zinc oxide (ZnO) film formation by using supercritical fluid chemical deposition and the application of the ZnO films in improving the adhesion of Cu/glass stacks. Bis(2-methoxy-6-methyl-3,5-heptanedionate)zinc(II) was used as a precursor, and the deposition was carried out at different oxygen contents and temperatures. When oxygen content was high and/or deposition temperature was high, white polycrystalline ZnO films were deposited; otherwise, the films were brown and had a higher carbon content. XPS analyses revealed that the white ZnO films had less carbon contamination. A significant improvement in the adhesion of the Cu/glass stacks was observed when the fabricated ZnO film was inserted between Cu and glass.

Creation of interfaces in composite/hybrid nanostructured materials using supercritical fluids

AbstractBy structuring matter at the nano level using highly versatile nanotechnology approaches and apparatus, multifunctionalities with manifestation of enhanced and/or novel useful properties could be attained. The challenges in nanoengineering are the ability to tune the nano-object characteristics (size, distribution, composition, and surface chemistry) and to have a good control on the possible synergy created at the interfaces, especially in the case of complex multifunctional materials. Surface nanoengineering goes hand in hand with the creation of interfaces between nano-objects – either inorganic or hybrid ones – and a closer look in this direction is essential. The present review aims at presenting the possibilities of surface nanoengineering by versatile approaches, namely supercritical fluids processes. Two main routes of nanostructuration, each containing three concepts, will be discussed: supercritical fluid chemical deposition performed in batch mode and continuous supercritical fluid synthesis. Both approaches can be used to access interesting materials with desired properties, with the choice of process depending on what the readers are pursuing.

Supercritical fluid chemical deposition of Cu in Ru and TiN-lined deep nanotrenches using a new Cu(I) amidinate precursor

We report supercritical fluid chemical deposition (SFCD) of Cu films in Ru- and TiN-lined deep nanotrenches using a new non-fluorinated Cu(I) amidinate precursor. The Cu(I) amidinate precursor dispersed well in an acetone/CO2 solution with molecular hydrogen as the reducing agent at very low temperatures. High-purity Cu films were grown on both Ru and TiN substrates at a lower deposition temperature (140°C) than typical temperatures reported for CuII(hfac)2 and CuII(dibm)2 precursors. The temperature dependence of the growth rate was studied and the growth rates were determined to be 10–14nm/min and 6–13nm/min for Ru and TiN substrates, respectively, in a temperature range of 140–240°C. On the Ru surface, Cu nucleated densely, forming smooth, strongly adherent films. At 140°C, the excellent filling capability of Cu in Ru- or TiN-lined nanotrenches was demonstrated.

Nanohole Coat/Fill with Pt via Chemical Deposition in Supercritical Fluids

This paper demonstrates nanostructure formation performed by supercritical fluid chemical deposition. Pt was deposited through hydrogen reduction of a Pt chelate being dissolved in supercritical carbon dioxide. Pt was deposited conformally inside nanotrences, however Pt did not grow thick due to a very long incubation time for the nucleation. Interestingly, SFCD Pt grew thick on already-existing noble metals. A two-step SFCD process was employed, where a Pt seed layer was deposited first and Pt was grown thicker in the subsequent run. This enabled to fill Pt in nanotrenches and nanoholes.

Cu coating inside small (15 µm) and ultrahigh-aspect-ratio (>130) through-holes using supercritical CO2 fluid

In this article, we describe novel process and equipment for fabricating through-hole interconnects embedded in an interposer. Through-holes are three-dimensionally cranked and have a small diameter (15 µm) and an ultrahigh aspect ratio (>130). This work demonstrated Cu coating inside these through-holes. Cu deposition was carried out by supercritical fluid chemical deposition. The equipment was designed to generate a large differential pressure between the entrance and exit of the through-holes on the basis of the principle of flow reduction. The generated differential pressure assisted the transport of the Cu precursor to the exit of the through-holes. The deposition of Cu inside 1400 through-holes spreading over the glass interposer substrate was successfully demonstrated.

In situ observation of Pt deposition process by using spectroscopic ellipsometry

Supercritical fluid chemical deposition is a technique for depositing films and particles in a supercritical medium. In this article, Pt thin films were grown from the supercritical CO2 that dissolves Pt(hfac)2 and H2, and the temperature dependence was studied using in situ ellipsometry. The temperature needed to form a continuous film was determined from the change of ellipsometric parameters. The determined temperature, about 70°C, was lower than the reported values.

Field Emissions from Organic Nanorods Armored with Metal Nanoparticles

We report the fabrication of organic nanorods with a diameter of approximately 10 nm and a height of 106.8 nm (a high aspect ratio of 10.5) armored by Pt nanoparticles. Our results demonstrate that Pt particles deposited by metalorganic supercritical chemical fluid deposition (MOCFD) covering the entire deposition area play important roles in not only etch resistance, especially in protecting the sidewalls, but also the formation of electroconductive Pt/C composites, which were found to have field emission properties.

Improvement of adhesion and interfacial diffusion behavior in Cu/glass structures using OsOx layers for microelectromechanical systems

We demonstrated that a Cu/Ni/OsOx/glass structure fabricated by using supercritical fluid chemical deposition has high adhesion strength. The adhesion strength was determined with a scratch tester, and the films and interfaces were characterized by transmission electron microscopy. Ni deposition resulted in the reduction of the pre-deposited OsO2 layer, and an OsOx layer formed again during the subsequent post-Ni-deposition annealing. We observed an extreme adhesion improvement. The high adhesion strength originated from the presence or re-formation of the OsOx layer and the diffusion of Cu, Ni, and Si into the OsOx layer.

Supercritical fluid chemical deposition of Pd nanoparticles on magnesium–scandium alloy for hydrogen storage

The deposition of Pd nanoparticles on the binary compound Mg0.65Sc0.35 using the Supercritical Fluid Chemical Deposition (SFCD) method was performed. There, the SFCD operating parameters (co-solvent, temperature, CO2 and hydrogen pressure, reaction time) have been optimized to obtain homogeneous deposition of Pd nanoparticles (around 10nm). The hydrogenation properties of the optimized Pd@Mg0.65Sc0.35 material were determined and compared to those of Mg0.65Sc0.35Pd0.024. The latter compound forms at 300°C and 1MPa of H2 a hydride that crystallizes in the fluorite structure, absorbs reversibly 1.5wt.% hydrogen and exhibits fast kinetics. In contrast, Pd@Mg0.65Sc0.35 compound decomposes into ScH2 and MgH2 during hydrogen absorption under the same conditions. However, reversible sorption reaches 3.3wt.% of hydrogen while keeping good kinetics. The possible roles of Pd on the hydrogen-induced alloy decomposition are discussed.

21203 ZnOを密着層として用いたガラス/CU構造の密着性とナノ組織(OS4-1【機械工学が支援する微細加工技術(1)】)

We studied whether nanometer thick ZnO layer was effective as an adhesion layer between glass and Cu. The adhesion strength was evaluated with a scratch tester and the films and interfaces were characterized with scanning transmission electron microscopy. The Cu films were deposited on ZnO layer by using three methods vacuum deposition, supercritical fluid chemical deposition, and electroless plating. Adhesion strengths of the glass/ZnO/Cu increased when 10 nm thick ZnO layer was used. In addition, when Pd nanoparticles were deposited on ZnO surface before Cu deposition, the adhesion strength increased STEM-EDX analysis revealed that the high adhesion strength was due to the presence of an extremely thin (approximately 10 nm) intermixing layer consisting of Cu, Pd, Zn, O, and Si.

Supercritical Fluid Chemical Deposition as an Alternative Process to CVD for the Surface Modification of Materials

AbstractTaking the desirable attributes of CVD and aqueous plating techniques while minimizing the disadvantages of each, supercritical fluid chemical deposition (SFCD) demonstrates itself to be a promising process alternative to enable the fabrication of nanostructured devices. This paper gives information about the SFCD process for metal deposition as an alternative to CVD through various examples of inorganic deposition (films or nanostructures). In particular, the use of SFCD will be demonstrated for the surface modification of carbon nanotubes (CNTs) and their decoration with palladium nanoparticles.

Chemical Vapor Deposition of GaP and GaAs Thin Films From [nBu2Ga(μ-EtBu2)2GanBu2] (E = P or As) and Ga(PtBu2)3

Low pressure chemical vapor deposition (LPCVD) using the single-source precursors [nBu2Ga(?-EtBu2)2GanBu2] (E = P or As) in the temperature range 723–823 K (0.05 mmHg), gives shiny yellow or silvery gray films of GaP and GaAs, respectively, on silica. The composition and morphology of the deposited materials have been probed via X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray (SEM/EDX), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Raman spectroscopy, revealing crystalline (cubic) GaE with 1:1 Ga/E ratios. The GaP forms nanorods growing perpendicular to the substrate surface and is rougher than the GaAs, which appears to form smaller, densely packed microcrystallites. While the GaAs films produced in this way did not exhibit any significant luminescence, the reflective GaP films obtained by LPCVD were of good electronic quality, revealing photoluminescence comparable to that of a single crystalline GaP reference. LPCVD using Ga(PtBu2)3 gives GaP, although this appears to be an inferior reagent compared to the dimer. Unlike the corresponding [nBu2In(?-EtBu2)2InnBu2] dimers (see Aksomaityte et al., Chem. Mater.2010, 22, 4246) which gave InE films and nanowires from supercritical chemical fluid deposition in sc-CO2/hexane, under the same conditions (773 K, 12 MPa), the gallium dimer precursors mostly failed to give GaE. Instead significant carbon deposition occurred, indicating solvent degradation.