Chemical Composition Of Films Research Articles

X‐Ray Reflectometry Characterization of Plasma Polymer Films Synthesized from Triallylamine: Density and Swelling in Water

AbstractCommercial membranes suitable for solid alkaline membrane fuel cell (SAMFC) have not proved their competitiveness yet, due to poor ionic conductivity and water and fuel retention. Plasma polymers are however promising candidates to meet the SAMFC requirements. In this work, X‐ray reflectometry has been used to determine the thickness, density and water swelling of plasma polymerized films prepared from triallylamine, leading to a bilayer model for the studied thin films. Both film density and water swelling show a bimodal evolution as a function of the average plasma discharge power, which is directly related to the precursor fragmentation mechanism in the plasma phase and can be correlated with the film chemical composition. magnified image

Effect of using stencil masks made by focused ion beam milling on permalloy (Ni81Fe19) nanostructures

Focused ion beam (FIB) milling is a common fabrication technique to make nanostencil masks which has the unintended consequence of gallium ion implantation surrounding milled features in silicon nitride membranes. We observe major changes in film structure, chemical composition, and magnetic behaviour of permalloy nanostructures deposited by electron beam evaporation using silicon nitride stencil masks made by a FIB as compared to stencil masks made by regular lithography techniques. We characterize the stenciled structures and both types of masks using transmission electron microscopy, electron energy loss spectroscopy, energy dispersive x-ray spectroscopy, magnetic force microscopy and kelvin probe force microscopy. All these techniques demonstrate distinct differences at a length scale of a 1–100 nm for the structures made using stencil mask fabricated using a FIB. The origin of these differences seems to be related to the presence of implanted ions, a detailed understanding of the mechanism however remains to be developed.

Nanoporous SiCOH/CxHy dual phase films with an ultralow dielectric constant and a high Young's modulus

We used plasma-enhanced chemical vapor deposition (PECVD) of allyltrimethylsilane (ATMS), consisting of an allyl group along with three methyl groups attached to silicon, to form a low dielectric constant (low-k) and high modulus SiCOH matrix. We found that the dielectric constant and mechanical properties of the low-k material are strongly affected by the selection of the precursor, processing conditions such as the deposition temperature and post-treatment, the introduction of a second labile phase, and the chemical structure and composition of the films. After porogen (pore generator) treatment with cyclohexene oxide (CHO), the resulting material exhibited a low dielectric constant with excellent mechanical and thermal properties, having k ∼ 2.4 and a Young's modulus of 8.4 GPa. FT-IR and XPS results show that this is caused by the desorption of the labile phase (CxHy), the formation of Si–O cage-like structures, and changes in the chemical composition of films after thermal treatment. SiO2, SiO3, and SiO4 impart greater modulus and hardness to the films by increasing the stable component of Si–O in the SiCOH matrix.

Selective synthesis of α-Fe2O3 thin films and effect of the deposition temperature and lattice oxygen on the catalytic combustion of propene

Pulsed spray evaporation chemical vapour deposition (PSE-CVD), an elaborate CVD process, was employed to synthesize thin films of α-Fe2O3 for the catalytic combustion of propene. According to X-ray diffraction and Raman spectroscopy, the alpha structure type was presented as the unique phase. α-Fe2O3 with fine crystalline structure was revealed by scanning electron microscopy, and probed in depth for the first time by helium ion microscopy. Energy dispersive X-ray microscopy and X-ray photoelectron spectroscopy displayed an overview of the chemical composition of the samples. In situ emission FTIR spectroscopy was used for the accurate determination of the thermal stability of the samples at around 500 °C, and temperature-programmed reduction was performed to correlate the catalytic performance and reduction properties of the obtained α-Fe2O3 thin films. The results showed that the increase of the deposition temperature leads to significant changes of film morphology, chemical composition and reduction properties, with a direct consequence on the catalytic performance. α-Fe2O3 prepared at a low temperature (350 °C) exhibited high activity towards the deep oxidation of propene, which was attributed to its good reducibility and the plate-like structures. The alternate reduction and oxidation of the oxide surface (favored by the bulk oxygen migration towards the surface) and replenishment of bulk oxygen by gas-phase oxygen suggest that the oxidation of propene may proceed according to the Mars van Krevelen mechanism. The morphology and surface composition of the prepared samples remain the same before and after the catalytic test, demonstrating very good stability and reproducibility. We thus conclude that α-Fe2O3 effective in propene conversion can be selectively synthesized with PSE-CVD.

A Comparative Study on Thermal Stability of Two Solid Electrolyte Interphase (SEI) Films on Graphite Negative Electrode

A comparative study is made on thermal stability of two solid electrolyte interphase (SEI) films on a graphite negative electrode. The SEI films are generated by reductive decomposition of two different electrolyte solutions that are prepared by dissolving either lithium hexafluorophosphate (LiPF6) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in ethylene carbonate/diethyl carbonate solvent. The surface film derived from the LiTFSI-containing electrolyte, which is enriched by organic carbon-oxygen species with uniform coverage, remains rather intact in both chemical composition and film morphology after high-temperature (85°C) storage, indicative of a superior thermal stability. As a result, this SEI layer maintains its passivating ability even after the storage. In contrast, the film generated from the LiPF6-containing electrolyte is thermally degraded with a substantial change in both film morphology and chemical composition to lose its passivating ability upon high-temperature exposure. The poorer thermal stability of the latter film has been ascribed to a high population of Li- and F-containing inorganic species and presence of cracks or void spaces in the SEI layer.

Plasma-Enhanced Chemical Vapor Deposition of Si-Rich Silicon Nitride Films Optimized for Waveguide-Based Sensing Applications in the Visible Range

Hydrogenated amorphous silicon nitride (a-SiNx:H) films were deposited by plasma-enhanced chemical vapor deposition (PECVD), an attractive process for integrated optical device fabrication owing to the low temperatures involved (typically 200–400 °C). Two regimes of plasma radio frequency (380 kHz and 13.56 MHz) and a range of plasma powers were studied. Through physical and chemical analyses, we demonstrate the relationship between film optical properties and chemical composition. Films with refractive index close to that of stoichiometric Si3N4 and with very low absorption coefficients owing to the small number of Si–Si bonds, are obtained by low-frequency (LF) PECVD at low powers.

Substrate temperature and electron fluence effects on metallic films created by electron beam induced deposition

Using three different precursors [MeCpPtMe3, Pt(PF3)4, and W(CO)6], an ultra-high vacuum surface science approach has been used to identify and rationalize the effects of substrate temperature and electron fluence on the chemical composition and bonding in films created by electron beam induced deposition (EBID). X-ray photoelectron spectroscopy data indicate that the influence of these two processing variables on film properties is determined by the decomposition mechanism of the precursor. For precursors such as MeCpPtMe3 that decompose during EBID without forming a stable intermediate, the film's chemical composition is independent of substrate temperature or electron fluence. In contrast, for Pt(PF3)4 and W(CO)6, the initial electron stimulated deposition event in EBID creates surface bound intermediates Pt(PF3)3 and partially decarbonylated Wx(CO)y species, respectively. These intermediates can react subsequently by either thermal or electron stimulated processes. Consequently, the chemical composition of EBID films created from either Pt(PF3)4 or W(CO)6 is influenced by both the substrate temperature and the electron fluence. Higher substrate temperatures promote the ejection of intact PF3 and CO ligands from Pt(PF3)3 and Wx(CO)y intermediates, respectively, improving the film's metal content. However, reactions of Pt(PF3)3 and Wx(CO)y intermediates with electrons involve ligand decomposition, increasing the irreversibly bound phosphorous content in films created from Pt(PF3)4 and the degree of tungsten oxidation in films created from W(CO)6. Independent of temperature effects on chemical composition, elevated substrate temperatures (>25 °C) increased the degree of metallic character within EBID deposits created from MeCpPtMe3 and Pt(PF3)4.

Permeability and corrosion in ZrO2/Al2O3 nanolaminate and Al2O3 thin films grown by atomic layer deposition on polymers

The authors studied moisture permeation and corrosion in Al2O3 and Al2O3/ZrO2 nanolaminate (NL) thin films grown by atomic layer deposition (ALD) at 100 °C on polyester substrates. A percolation model accurately described the dependence of permeation on the volume fraction of ZrO2 in the nanolaminates. As the fraction of ZrO2 was reduced to ∼0.5, moisture permeation in the NLs approached the measurement limit ∼1 × 10−4 g-H2O/m2-day, equivalent to Al2O3 with the same total thickness. However, resistance to corrosion by water was modestly better for Al2O3 than for the NL, and we proposed that corrosion in ALD Al2O3 films was associated with hydrogen incorporation and a consequent film chemical composition that is an oxy-hydroxide, AlOx(OH)3−2x. The authors present x-ray diffraction evidence for conversion of ALD Al2O3 to hydroxide corrosion products, AlO(OH) and Al(OH)3, after aging films in damp heat (85 °C/85% relative humidity) for two weeks.

Synthesis and Properties of Sb Layered Te/Cd Stack Prepared by Elemental Stack Method

Sb layered Te/Cd thin films have been prepared by using Stacked Elemental Layer (SEL) method. The presence of mixed phases (CdTe and Sb2Te3) in the films was confirmed by the x-ray diffraction technique. The calculated structural parameters demonstrated the feasibility of Sb doping via SEL method. The topographical and electrical studies of the synthesized thin films depicted the influence of Sb on both surface morphology and conductivity. The values of conductivity of the annealed films were in between 2 x 10-3 and 175 x 10-2 Scm-2. A desired chemical composition of films was confirmed from spectrum shape analysis using energy dispersive x-ray.

Influence of process conditions on chemical composition and electronic properties of AlN thin films prepared by ArF reactive pulsed laser deposition

AbstractAluminium nitride (AlN) thin films were deposited using a reactive ArF excimer pulsed laser ablation (PLD) of a pure Al target in a N2 plasma atmosphere, generated by a RF source, onto p‐Si <100> substrates, at increasing substrate temperatures. A radio‐frequency (13.56 MHz RF) apparatus was introduced with the specific aim of increasing the fraction of excited and/or ionized nitrogen species and, ultimately, to increase its reactivity toward the aluminum atoms, expanding in the plume, and the formation of AlN. We studied the dependence and correlation of structural, compositional and electric properties with the specific experimental conditions. The chemical composition of films, determined by XPS spectroscopy, revealed a trend of increased N2 reactivity, uptake and nitride formation, with deposition temperature. Electrical resistivity, measured by the four‐point‐probe method, has been found to be also strongly dependent on the substrate temperature and nitrogen incorporation. A possible explanation of the correlation of surface conductivity with chemical composition is suggested and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparative Stability Studies of Poly(2-methyl-2-oxazoline) and Poly(ethylene glycol) Brush Coatings

Non-fouling surfaces that resist non-specific adsorption of proteins, bacteria, and higher organisms are of particular interest in diverse applications ranging from marine coatings to diagnostic devices and biomedical implants. Poly(ethylene glycol) (PEG) is the most frequently used polymer to impart surfaces with such non-fouling properties. Nevertheless, limitations in PEG stability have stimulated research on alternative polymers that are potentially more stable than PEG. Among them, we previously investigated poly(2-methyl-2-oxazoline) (PMOXA), a peptidomimetic polymer, and found that PMOXA shows excellent anti-fouling properties. Here, we compare the stability of films self-assembled from graft copolymers exposing a dense brush layer of PEG and PMOXA side chains, respectively, in physiological and oxidative media. Before media exposure both film types prevented the adsorption of full serum proteins to below the detection limit of optical waveguide in situ measurements. Before and after media exposure for up to 2 weeks, the total film thickness, chemical composition, and total adsorbed mass of the films were quantified using variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and optical waveguide lightmode spectroscopy (OWLS), respectively. We found (i) that PMOXA graft copolymer films were significantly more stable than PEG graft copolymer films and kept their protein-repellent properties under all investigated conditions and (ii) that film degradation was due to side chain degradation rather than due to copolymer desorption.

Apatite Deposition on ZrO<sub>2</sub> Thin Films by DC Unbalanced Magnetron Sputtering

Zirconia thin films deposited on 316L stainless-steel substrate were prepared by DC unbalanced magnetron sputtering from a metallic zirconium target at low temperature with the target-to-substrate distance (dt-s) of 100 mm and sputtering power of 180 W. High purity gas of Ar as the working gas and O2 as the reactive gas were used. The depositions were performed for 120 min at a total pressure of 0.5 Pa. The effect of thermal treatment on the HA formation was investigated. The bioactivity was assessed by investigating the formation of hydroxyapatite (HA) on the surface soaked in simulated body fluids (SBF). Films structure, surface morphology and chemical composition of the ZrO2 films and HA formation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and FT-IR spectroscopy. The XRD results demonstrate the ZrO2 films are monoclinic phase. The annealed films show the higher film crystalline due to the rearrangement of film structure. After being immersed the samples in SBF, the bone-like apatite was observed on all ZrO2 films, but a denser and more continuous HA layer were observed on annealed films due to the crystallinity of ZrO2 films.

Effect of Cu addition on properties of Ti-Al-Si-N nanocomposite films deposited by cathodic vacuum arc ion plating

In this paper, detailed properties of Ti-Al-Si-N nanocomposite films doped with Cu additive at various concentrations are studied and followed with careful discussion. Deposited on high speed steel substrates with the assistance of vacuum cathode arc ion plating, the film composition and crystallinity can be controlled by changing the target composition. Then the film structure, chemical and phase composition, mechanical and tribological properties are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), nanoindentation and Rockwell indenter. The results indicate that with increasing copper content in the film systems, a reduction of the grain size and a deterioration of the preferred orientation were detected by XRD and HRTEM. Furthermore the film hardness H and the elastic modulus E decrease from 35±6 to 13±1GPa and from 286±26 to 163±13GPa, respectively. The ratio H3/E2 is calculated on basis of measurements of hardness H and Young's modulus E. The adhesive strength between the film and the substrate is strongly improved, compared to others without Cu additive, as well as the tribological performance of the films. This whole study implies that these Cu-doped nanocomposite films deserve some cautiousness before its application for wear resistance.

Plasma polymerisation of siloxanes at atmospheric pressure

This work deals with the plasma polymerisation of two siloxane precursors, [hexamethyldisiloxane (HMDSO) and tetramethyldisiloxane (TMDSO)] with an atmospheric pressure pseudoglow dielectric barrier discharge operated in argon and an argon–air mixture. The influence of gas composition and precursor type on the physical and chemical properties of the deposited films is examined in detail using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Results clearly show that precursor type as well as gas composition has an profound impact on film growth rate and chemical composition of the deposited films. Plasma polymerisation of both siloxane precursors in argon leads to the formation of hydrophobic polymers consisting of a Si–O–Si backbone, while for deposition in an argon–air mixture, hydrophilic inorganic silica-like coatings are obtained.

Effect of interface energy on abnormal grain growth in pyrite films prepared by sol–gel method

The pyrite films were prepared on quartz and glass substrates by the sol–gel dip coating process and sulfuration treatment. The film microstructure, chemical composition and morphology dependent on sulfuration temperature were investigated. The sulfuration treatment at 773–923 K for the films prepared by the sol–gel dip coating process can prepare pyrite films. Some grains show abnormal growth during sulfuration treatment. The grain size of abnormal growth increased to a limited value with increasing the sulfuration temperature. The grain size in pyrite films has bimodal distribution. The first peak is of Lognormal distribution and the second peak Gauss distribution. By determination of the abnormal grain growth activation energy, it can be concluded that the reduction in interface energy at the interface between the substrate and film should be responsible for the grain abnormal growth.

The surface free energy of pyrite films prepared by sulfurizing the precursive electrodeposited films

The pyrite films were prepared by sulfurizing the precursive films at different temperatures. The microstructure, chemical compositions and surface free energy have been investigated. The results indicate that pyrite films are obtained after the sulfuration process of precursive films. The sulfuration temperature remarkably influences the contact angle. Using Owens and Wendt geometric mean approach, the surface free energy, the dispersive surface free energy and polar surface free energy can be evaluated based on the value of contact angles. It has been found that the surface free energy is significantly dependent on the sulfuration temperature and chemical compositions of films. With the increase of the sulfuration temperature, the dispersive surface free energy decreases but the polar surface free energy keeps basically invariable. A possible relationship between the surface free energy and film quality has been discussed.

Determination of silicon nitride film chemical composition to study hydrogen desorption mechanisms

To go further in the comprehension of hydrogen desorption mechanisms from PECVD (Plasma Enhanced Chemical Vapour Deposited) silicon nitride, a method to determine the chemical composition of amorphous silicon nitride films using fast and non destructive characterization techniques has been developed. In particular, Si H, N H, Si Si and Si N bond concentrations are calculated from Fourier transform infra red spectroscopy, ellipsometry and mass measurement. Next, different PECVD silicon nitride films were annealed at 600 °C during 2 min. Results show that hydrogen desorption from PECVD silicon nitride depends on film mass density and main chemical reactions leading to hydrogen desorption are identified thanks to the determination of Si Si and Si N bond concentrations.

Formation of nano-pores in nano-crystalline diamond films

Various nano-pores in nano-crystalline diamond (NCD) thin films have been fabricated and characterized. Therefore in this work two aspects of NCD thin films synthesized by microwave assisted chemical-vapour-deposition (MWCVD) have been investigated. Firstly, the influence of CVD-growth conditions on the film morphology and chemical grain boundary composition and their impact on the mechanical properties. Second, the formation of nano-pores by selective etching of the non-diamond phase. Freestanding NCD membranes were fabricated and bulged to calculate the Young’s modulus which can reach surprisingly high values (1100GPa) close to single crystal diamond. The presence of nano-pores was verified by electrochemical experiments where ions have been used to detect the porosity.

Passivating Ability of Surface Film Derived from Vinylene Carbonate on Tin Negative Electrode

The passivating ability of surface film derived from vinylene carbonate (VC) is addressed on tin (Sn) negative electrode after a comparative study on the thickness, film growth pattern, chemical composition, and mechanical flexibility of the surface films generated from VC-free and VC-added electrolytes. The surface film derived from the former electrolyte is enriched by inorganic fluorinated and carbonate species, and shows a poor passivating ability to cause a continued electrolyte decomposition, film growth and eventual electrode failure. In contrast, organic carbon-oxygen species are dominant in the film derived from the VC-added electrolyte. Even if this film is thinner than the other, it passivates the Sn electrode surface more effectively. As a result, the film growth and electrode polarization are less significant. The superior passivating ability of organic-rich surface film has been ascribed to a uniform coverage and higher mechanical flexibility.

Low temperature growth of nanocrystalline TiO 2 films with Ar/O 2 low-field helicon plasma

TiO 2 thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO 2 was obtained for ion density on the substrate below 7 × 10 16 m − 3 . Increasing the ion density over 7 × 10 16 m − 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO 2. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO 2 thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.