Metal Fluoride Films Research Articles (Page 1)

High purity aluminum in its bulk form has intrinsicallyhigh reflectancein the far-ultraviolet (FUV) regime and finds utility in astrophysicalinstrumentation applications. However, bulk Al oxidizes rapidly inthe atmosphere, and its native oxide strongly absorbs and severelydegrades the observed FUV properties relative to bare Al. Varioustechniques have been investigated to produce coatings that inhibitaluminum oxide formation and lead to high FUV mirror reflectance.This work examines the development and use of a uniquely modified,hybrid plasma-enhanced atomic layer deposition (PEALD) system to passivatealuminum mirrors with metal fluoride films. This system combines twoplasma sources in a commercial atomic layer deposition (ALD) reactor.The first is a conventional inductively coupled plasma (ICP) sourceoperated as a remote plasma, and the second is an electron beam (e-beam)driven plasma near the mirror surface. To establish the operatingconditions for the in situ e-beam plasma source, the effects of samplegrounding, SF6/Ar flow, and sample temperature on resultingAlF3 films were investigated. Optimal operating conditionsproduced mirrors with excellent FUV reflectivity, 92% at 121 nm and42% at 103 nm wavelengths, which is comparable to state-of-the-artAlF3-based passivation coatings and matches that of previouslyreported ex situ e-beam plasma-processed mirrors. This optimized insitu e-beam process, along with XeF2 passivation, is thenexplored to produce a clean seed layer (unoxidized Al surface) forsubsequent PEALD of AlF3. Both approaches are demonstratedas valid pretreatments before PEALD of AlF3, showing apromising pathway for the deposition of other fluoride-based layers,such as MgF2 or LiF, with ALD or PEALD.

1.Introduction Alkaline water splitting, a low-cost and simple hydrogen production method, has been attracting attention to the realization of a sustainable society. However, the overpotential of the oxygen evolution reaction (OER) on the anode is high and the hydrogen production efficiency is low. Catalysts containing Fe, Co, and Ni are expected to be promising candidates for electrodes materials [1]. Recently, we succeeded in fabricating FeNi and FeNiCo alloy electrodes covered with a porous metal fluoride film by anodizing, which exhibited better OER activity and durability than OER catalysts [2]. We reported that the metal fluoride films synthesized by anodizing in fluoride-containing organic electrolytes converted to metal oxyhydroxide during OER in KOH aqueous solution. However, the physical properties of the films and electrode characteristics, which are the factors responsible for the high OER activity of this electrode, remain unclear.In this study, various commercial FeNiCo and FeNi alloys (Kovar: Fe-17 mass% Co-29 mass% Ni, 42-Invar: Fe-42 mass% Ni, 45-Permalloy: Fe-45 mass% Ni, 78-Permalloy: Fe-78 mass% Ni) were anodized to fabricate highly active OER electrodes and applied to in-situ Raman spectroscopic characterization to understand the activation mechanism of the anodized alloy electrodes.2.Experimental Commercial FeCoNi and FeNi alloys were used for electrode preparation. The electrolytes used for anodizing were ethylene glycol containing 0.54 M NH4F and 2.5 M H2O for Kovar, 45-Permalloy, and 42-Invar, and ethylene glycol containing 0.08 M NH4F and 0.02 M H2O for 78-Permalloy. The anodizing process was performed at 10 V for 60 min at 293 K in an ethylene glycol-based electrolyte, and platinum was used as the counter electrode. The surface morphology and composition of the OER electrodes were measured using field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. In-situ Raman measurements were conducted using laboratory-made cells. The measurement was performed using a three-electrode system with a platinum counter electrode and an Hg/HgO electrode as the reference electrode under a flow of 1 M KOH aqueous solution at 24.0 mL min-1. In-situ Raman spectra were measured under potentiostatic conditions every 0.2 V from 1.13 V vs. RHE.3.Results and discussion【morphology and compositional characterization】 The surface morphology of the films was highly dependent on the composition of the FeCoNi and FeNi alloys. A uniform and smooth film with an average thickness of 200 nm was observed in the anodized 78-Permalloy electrode, and non-uniform films with an average thickness of 1 µm were observed in the anodized 45-Permalloy and 42-Invar electrodes. The anodized Kovar electrode exhibited a non-uniform and wide crack film with an average thickness of 2.5 µm. The cationic composition of the films was also dependent on the composition of the commercial FeCoNi and FeNi alloys. The anodized 78-Permalloy electrode showed the lowest Fe content in the film.【Raman measurement】 The ex-situ Raman measurements revealed the presence of mixed phases of spinel oxide and metal oxyhydroxide for all electrodes after OER, indicating that the metal fluoride films were completely converted to metal oxide and metal oxyhydroxide. Then, in-situ Raman measurements were conducted under the controlled potential in 1 M KOH aqueous solution. The peak intensity of spinel oxides decreased and that of metal oxyhydroxides increased with increasing applied potential. Because the spinel oxide peaks disappeared and those of metal oxyhydroxide were only observed at the OER onset potential for all electrodes, the in-situ measurements revealed that metal oxyhydroxide is an active phase for OER in the electrolysis system. Interestingly, when the electrode potential was returned to negative, the film structure reverted to the mixed phases of spinel oxide and metal oxyhydroxide. Therefore, we confirmed that the anodized electrodes possess structural reversibility. However, since no trend was observed in the correlation between structural change behaviors and the order of OER activities of the electrodes, other factors would also contribute to OER activities in addition to the formation of the metal-oxyhydroxide structure.

The precisely tailored refractive index of optical materials is the key to utilizing and manipulating light during its propagation through the matrix, thereby improving their application performances. In this paper, mesoporous metal fluoride films with engineered composition (MgF2 :LaF3 ) are demonstrated to achieve finely tunable refractive indices. These films are prepared using a precursor-derived one-step assembly approach via the simple mixing of precursor solutions (Mg(CF3 OO)2 and La(CF3 OO)3 ); then pores are formed simultaneously during solidification owing to the inherent instability of La(CF3 OO)3 . The mesoporous structures are realized through Mg(CF3 OO)2 and La(CF3 OO)3 ions, which interacted with each other based on their electrostatic forces, providing a wide range of refractive indices (from 1.37 to 1.16 at 633 nm). Furthermore, it is systematically several MgF2(1-x) -LaF3(x) layers with different compositions (x=0.0, 0.3, and 0.5) to form the graded refractive index coating that is optically consecutive between the substrate and the air for broadband and omnidirectional antireflection. An average transmittance of ≈98.03% (400-1100nm) is achieved with a peak transmittance of ≈99.04% (at 571nm), and the average antireflectivity is maintained at ≈15.75% even at an incidence of light of 65° (400-850nm).

The present study describes atomic layer deposition (ALD) processes and characterization of CoF2, NiF2, and HoF3 thin films. For CoF2 deposition CoCl2(TMEDA) (TMEDA = N,N,N',N'-tetramethylethylenediamine) and NH4F were used as precursors. CoF2 deposition was studied at 180-275 °C, resulting in a growth per cycle (GPC) of 0.7 to 1.2 Å. All the films consist of tetragonal CoF2 according to XRD. The impurity contents were measured with ToF-ERDA and less than 1 at% of N and Cl were detected in the films, indicating effective reactions. In addition, the F/Co ratio is close to 2 as measured by the same method. The saturation of the GPC with respect to precursor pulses and purges was verified at 250 °C. The common feature of ALD metal fluoride films - remarkable roughness - is encountered also in this process. However, the films became smoother as the deposition temperature was increased. CoF2 deposition was also demonstrated on graphite substrates. NiF2 deposition was studied at 210-250 °C by using Ni(thd)2 and TaF5 or a new fluoride source NbF5 as the precursors. Tetragonal NiF2 was obtained, but the oxygen and hydrogen contents in the films were remarkable, up to ∼11 at%, as measured by ToF-ERDA. This was observed also when the films were in situ capped with YF3. NbF5 was shown to be a potential fluoride precursor by combining it with Ho(thd)3 to deposit HoF3 films. Orthorhombic HoF3 was obtained at deposition temperatures of 200-275 °C. The films deposited at 235-275 °C are pure, and the Nb contents in films deposited at 250 and 275 °C are only 0.21 and 0.15 at%. The main impurity in both films is oxygen, but the contents are only 1.5 and 1.6 at%. The saturation of the GPC with respect to precursor pulses was verified at 250 °C. The GPC is ∼1 Å.

In this work, the reaction mechanism in the atomic layer deposition (ALD) process of AlF3 thin films is studied with in situ quartz crystal microbalance and quadrupole mass spectrometer. The depositions are done with AlCl3 and TiF4 as precursors. Similar to many metal fluoride films deposited by ALD, the growth rate of the AlF3 is strongly temperature dependent. In addition, at low temperatures, the growth rate is exceptionally high for a traditional ALD process. In this study, the reasons behind these characteristics are studied and a detailed step-by-step mechanism for the AlF3 film growth process is presented.

The injection and transporting characteristics of an Al/metal fluoride (or Alq3: Cs2CO3)/Alq3/Al electron-only device are determined by the dark injection space-charge-limited current (DI-SCLC)method. The deviation from the ratio of peak current density JDI to the steady-state current density JSS for the ideal ohmic contact, which should be 1.21, was obtained to compare the effects of modifications by four metal fluoride films and Alq3 doped with Cs2CO3 on the injection of electrons. The value of JDI/JSS, 1.29, for the device modified by 0.5 nm LiF approaches the ideal value of 1.21, confirming the formation of quasic-ohmic contact between the organic layer and cathode, although the deviation increases significantly with the thickening of the film. The value of JDI/JSS for the device modified by NaF remains stable within 1.6 in a wide NaF film thickness range of 0–2 nm. The minimum value of JDI/JSS, for Alq3:Cs2CO3 doped film is 1.24, which means that the theoretical ohmic contact between the organic layer and cathode is formed. These characterization results are consistent with the observations in steady-state current–voltage(J–V) experiments. The great electron injection enhancements in the devices pave the way for an application of the cathodic injection in the preparation of OLEDs which are confirmed by doping Alq3 with Cs2CO3.

Conventional and Pulsed Liquid Injection MOCVD processes (C-MOCVD and PLI-MOCVD) have been explored as synthetic routes for the growth of BaMgF4 on Si (100) and single crystalline SrTiO3 (100) substrates. For the two applied approaches, the volatile, thermally stable β-diketonate complexes Ba(hfa)2tetraglyme and Mg(hfa)2(diglyme)2(H2O)2 have been used as single precursors (C-MOCVD) or as a solution multimetal source (PLI-MOCVD). Structural characterization through X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) analyses confirmed the formation of epitaxial BaMgF4 films on SrTiO3 substrates. Energy dispersive X-ray (EDX) analyses have been used to confirm composition and purity of deposited films. The impact of process parameters on film properties has been addressed, highlighting the strong influence of precursor ratio, deposition temperature and oxygen partial pressure on composition, microstructure and morphology of the films. Both methods appear well suited for the growth of the BaMgF4 phase, but while PLI-MOCVD yields a more straightforward control of the precursor composition that reflects on film stoichiometry, C-MOCVD provides easier control of the degree of texturing as a function of temperature.

The “AlPO4” coating has been shown to improve the electrochemical performance of LiCoO2 batteries. We previously showed that the “AlPO4” coating promotes the formation of metal fluorides, which could act as a stable surface film and protect LiCoO2 from continuous degradation upon cycling. In this work, we removed the fluorine source in the LiPF6 salt by using the LiClO4 salt and investigated the effectiveness of the “AlPO4” coating. Interestingly, the “AlPO4” coating was found to improve the voltage efficiency and capacity retention when cycling in the LiPF6 electrolyte, but was detrimental when cycling in the LiClO4 electrolyte. XPS revealed that the “AlPO4” coating promotes the formation of metal fluoride in both electrolytes, with the surface film formed in LiClO4 being more electrically resistive compared to that formed in LiPF6. The source of fluorine in the coated electrode cycled in LiPF6 is largely attributed to the LiPF6 salt whereas the source of fluorine in the coated electrode cycled in LiClO4 is the binder PVDF. We believe that the coating could react with HF impurity in the LiPF6 electrolyte or from the binder PVDF and form stable metal fluoride films on the surface.

Voltammetric investigations on the transition between dissolution, passivation and deposition characteristics of Ni, Cu and their alloys in fluorine based ionic liquid

The voltammetric responses of copper and silver had been extensively studied and compared in a variety of non-aqueous solvents such as acetonitrile (AN), propylene carbonate (PC) and sulfolane containing two different supporting electrolytes namely triethylaminetrishydrogen fluoride (TEA.3HF) and tetrabutylammonium tetrafluoroborate (TBABF4). The dissolution rate and surface transformation on the electrode surfaces as a result of anodic polarization was investigated using atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM), respectively. In solvent-free TEA.3HF medium, the copper electrode shows high charge recovery ratio (Q c/Q a), and the difference between the initial anodic and cathodic potentials, obtained at a current density of 2 mA cm−2, is around 0.11 V, suggesting that in this medium, Cu can certainly serve as reference electrode. On the other hand, on Ag electrode, substantial dissolution was observed leading to very high anodic (Q a) and cathodic (Q c) charges, and the surface morphology after the cyclic polarization results in roughened surface with large pores. The effects of incorporating AN and water as additives in TEA.3HF on the solubility and stability of these metal fluoride films are also reported. The dissolution pattern and film formation behavior of these two metals in the different solvents containing fluoride and fluoroborate ionic species have several qualitative similarities, as noted from cyclic voltammetry responses and SEM morphology. Anodic dissolution and precipitation process for both Cu and Ag depends significantly on the nature of supporting electrolytes as well as solvents. In AN containing 0.1 M TEA.3HF, the dissolution of Cu and Ag electrodes was very high. Fluoride salts of Cu show lesser solubility than Ag in those solvents, while fluoroborate salts exhibit the reverse trend. The AAS data suggest that for a particular salt, which may be either fluoride or fluoroborate of Cu and Ag, the relative solubility decreases in the order AN > PC > sulfolane.

On the mechanism of polytetrafluoroethylene ablation using a synchrotron radiation-induced photochemical process

Metal fluoride films were prepared from trifluoroacetate sols by a spin-coating method. Effects of preparation conditions on the deposition of fluoride films have been examined in order to control the thickness and the refractive index of the films. It was suggested that the fluoride was formed by the thermal decomposition of the trifluoroacetate sols generating gaseous phases such as (CF3CO)2O, CO and CO2. This reaction mechanism seemed to largely effect the deposition of the fluoride films in terms of the formation of pores. Characteristics of the fluoride films could be changed by varying the heat treatment. The refractive index of the MgF2 films decreased with increasing heating temperature, which might result from the increased porosity of the films. Drying the film before the heat treatments was effective in the control of the refractive index.

ABSTRACTThe properties of metal fluoride films (MgF2 CeF3, LaF3 CaF2 and SrF2) deposited using cw laser and electron-beam evaporation were compared. The differences in film properties were subtle, but important. Films obtained by laser evaporation have lower losses in the UV (185–250 nm) and slightly better crystallinity than the films deposited by e-beam evaporation. Other optical and mechanical properties were independent of preparation method. Differences in the film properties were tentatively attributed to the higher proportion of dissociated species in the évaporant plume of the laser-evaporated materials.

Abstract Metals form protective metal fluoride films upon exposure to fluorine. The utilization of the metal fluoride films as catalysts for surface polymerization of tetrafluoroethylene is described. The process consists of a two‐step synthesis: (1) gas phase fluorination of a metal sample to produce a fluoride film on the metal surface and, (2) gas phase polymerization to form a polymeric coating. The fluorocarbon films formed on the metal substrates by the Toy process are fairly adherent, continuous and flexible, except that it is somewhat porous depending on the conditions of fluorination, polymerization, metal compositions, and metal surface preparations. The possible mechanisms of surface‐polymerization are discussed.