Changes In Film Structure Research Articles

Influence of annealing temperature on thermal stabilities of hydrogenated amorphous carbon on silicon nitride balls

Hydrogenated amorphous carbon films were synthesized on silicon, silicon nitride (Si3N4) ceramic balls and SUS304 by using linear ion beam deposition technology. To investigate the annealing effect on the thermal stabilities of the films on Si3N4 balls, Raman spectroscopy, Fourier transformation infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, stylus profiler and ball-on-disk friction test were adopted. The results showed that the annealing temperatures had no significant influence on the structure, mechanical and tribological properties of the films until 200 °C. When the temperature was above 200 °C, the film structure changes as effusion of hydrogen and graphitization leading to poor mechanical and tribological properties. Roles of the tribochemical reactions occurred on Si3N4 ball surface during the friction in the tribological properties of hydrogenated amorphous carbon films were discussed.

Accelerated weathering studies on the bioplastic, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The effect of accelerated weathering exposure time on the bioplastic, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was studied. The chemical structure and thermophysical property changes of solvent cast PHBV films were examined by a combination of optical microscopy, size exclusion chromatography, FTIR and 1H NMR spectroscopies, tensile testing, and differential scanning calorimetry (DSC). The exposed PHBV surfaces experienced surface crazing upon weathering. The molar mass of weathered PHBV was shown to decrease due to chain scission which was dominant over the crosslinking reaction mechanism, and compositional analysis showed the polymer degradation was non-random between the hydroxybutyrate-hydroxyvalerate units. The degree of crystallinity for PHBV was shown to increase significantly (by about 20%) upon weathering. Tensile tests showed that the weathered PHBV exhibited reduced ultimate strength and elongation to break, while the Young's modulus increased ascribing to an increase in crystallinity. Different degradation mechanisms (Norrish I/II, radical initiation, crosslinking, and hydrolysis) of PHBV are proposed and confirmed based on the experimental findings. This study provides degradation insight for PHBV exposed to both UV radiation and moisture.

Phase-Controlled Electrochemical Activity of Epitaxial Mg-Spinel Thin Films.

We report an approach to control the reversible electrochemical activity (i.e., extraction/insertion) of Mg(2+) in a cathode host through the use of phase-pure epitaxially stabilized thin film structures. The epitaxially stabilized MgMn2O4 (MMO) thin films in the distinct tetragonal and cubic phases are shown to exhibit dramatically different properties (in a nonaqueous electrolyte, Mg(TFSI)2 in propylene carbonate): tetragonal MMO shows negligible activity while the cubic MMO (normally found as polymorph at high temperature or high pressure) exhibits reversible Mg(2+) activity with associated changes in film structure and Mn oxidation state. These results demonstrate a novel strategy for identifying the factors that control multivalent cation mobility in next-generation battery materials.

Mechanical Properties and Microstructural Characterization of Amorphous SiCxNy Thin Films After Annealing Beyond 1100°C

The effect of thermal annealing on structure and mechanical properties of amorphous SiCxNy (y ≥ 0) thin films was investigated up to 1500°C in air and Ar. The SiCxNy films (2.2–3.4 μm) were deposited by reactive DC magnetron sputtering on Si, Al2O3 and α‐SiC substrates without intentional heating and at 600°C. The SiC target with small excess of carbon was sputtered at various N2/Ar gas flow ratios (0–0.48). The nitrogen content in the films changes in the range 0–43 at.%. Hardness and elastic modulus (nanoindentation), change in film thickness, film composition, and structure (Raman spectroscopy, XRD) were investigated in dependence on annealing temperature and nitrogen content. All SiCxNy films preserve their amorphous structure up to 1500°C. The hardness of all as‐deposited and both air‐ and Ar‐annealed SiCxNy films decreases with growth of nitrogen content. The annealing in Ar at temperatures of 1100°C–1300°C results in noticeable hardness growth despite the ordering of graphite‐like structure in carbon clusters in nitrogen free films. Unlike the SiC, this graphitization leads to hardness saturation of SiCN films starting above 900°C, especially for films with higher nitrogen content (deposited at higher N2/Ar). This indicates the practical hardness limit achievable by thermal treatment for SiCxNy films deposited on unheated substrates. The ordering in carbon phase is facilitated by the presence of nitrogen in the films and its extent is controlled by the N/C atomic ratio. The suppression of graphitization was observed for N/C ranging between 0.5–0.7. Films deposited at 600°C show higher hardness and oxidation resistance after annealing in comparison with those deposited on unheated substrates. Hardness reaches 40 GPa for SiC and ~28 GPa for SiCxNy (35 at.% of nitrogen). Such a high hardness of SiC film stems from its partial crystallization. Annealing of SiCxNy film (35 at.% of N) in Ar at 1400°C is accompanied by formation of numerous hillocks (indicating heterogeneous structure of amorphous films) and redistribution of film material.

Initial stages of growth and the influence of temperature during chemical vapor deposition of sp2-BN films

Knowledge of the structural evolution of thin films, starting by the initial stages of growth, is important to control the quality and properties of the film. The authors present a study on the initial stages of growth and the temperature influence on the structural evolution of sp2 hybridized boron nitride (BN) thin films during chemical vapor deposition (CVD) with triethyl boron and ammonia as precursors. Nucleation of hexagonal BN (h-BN) occurs at 1200 °C on α-Al2O3 with an AlN buffer layer (AlN/α-Al2O3). At 1500 °C, h-BN grows with a layer-by-layer growth mode on AlN/α-Al2O3 up to ∼4 nm after which the film structure changes to rhombohedral BN (r-BN). Then, r-BN growth proceeds with a mixed layer-by-layer and island growth mode. h-BN does not grow on 6H-SiC substrates; instead, r-BN nucleates and grows directly with a mixed layer-by-layer and island growth mode. These differences may be caused by differences in substrate surface temperature due to different thermal conductivities of the substrate materials. These results add to the understanding of the growth process of sp2-BN employing CVD.

Graphene-enhanced intermolecular interaction at interface between copper- and cobalt-phthalocyanines.

Interfacial electronic structures of copper-phthalocyanine (CuPc), cobalt-phthalocyanine (CoPc), and graphene were investigated experimentally by using photoelectron spectroscopy. While the CuPc/graphene interface shows flat band structure and negligible interfacial dipole indicating quite weak molecule-substrate interaction, the CuPc/CoPc/graphene interface shows a large interfacial dipole and obvious energy level bending. Controlled experiments ruled out possible influences from the change in film structure of CuPc and pure π-π interaction between CoPc and CuPc. Analysis based on X-ray photoelectron spectroscopy and density functional theory reveals that the decrease in the work function for the CuPc/CoPc/graphene system is induced by the intermolecular interaction between CuPc and CoPc which is enhanced owning to the peculiar electronic properties at the CoPc-graphene interface.

Experimental study on molecular arrangement of nanoscale lubricant films—A review

In order to understand lubrication mechanism at the nanoscale, researchers have used many physical experimental approaches, such as surface force apparatus, atomic force microscopy and ball-on-disk tribometer. The results show that the variation rules of the friction force, film thicknessand viscosity of the lubricant at the nanoscale are different from elastohydrodynamic lubrication (EHL). It is speculated that these differences are attributed to the special arrangement of the molecules at the nanoscale. However, it is difficult to obtain the molecular orientation and distribution directly from the lubricant molecules in these experiments. In recent years, more and more attention has been paid to use new techniques to overcome the shortcomings of traditional experiments, including various spectral methods. The most representative achievements in the experimental research of molecular arrangement are reviewed in this paper: The change of film structure of a liquid crystal under confinement has been obtained using X-ray method. The molecular orientation change of lubricant films has been observed using absorption spectroscopy. Infrared spectroscopy has been used to measure the anisotropy of molecular orientation in the contact region when the lubricant film thickness is reduced to a few tens of nanometers. In situ Raman spectroscopy has been performed to measure the molecular orientation of the lubricant film semi-quantitatively. These results prove that confinement and shear in the contact region can change the arrangement of lubricant molecules. As a result, the lubrication characteristics are affected. The shortages of these works are also discussed based on practicable results. Further work is needed to separate the information of the solid-liquid interface from the bulk liquid film.

The role of gas direction in a modified Grimm-type glow discharge for controlling the degree of crystallinity in brass alloy thin films

Sputter-deposition rates in different gas directions were used for growing brass thin films in the modified Grimm-type direct current glow discharge. The sputtering and deposition rates were significantly improved by changing the direction of the argon gas flow. The degree of crystallinity and the nanoparticle size of the deposited thin films could also be controlled. Optimal operating conditions such as the gas pressure, applied power, deposition time, and distance from the substrate to the target surface were employed. The degree of crystallinity of the films was determined via the X-ray diffraction technique. Sequence changes in the brass thin film structure to nanocrystalline phases were obtained based on the direction of the Ar gas. However, in all cases, the obtained nanocrystalline films had polycrystalline or single crystalline structure with the normal and the new proposed gas flow direction respectively. Wavelength dispersive X-ray fluorescence analysis confirmed that the films had the same elemental compositions as that of the cathode material. Semi-amorphous and polycrystalline brass thin films were also easily obtained using the normal gas direction. Moreover, the new proposed gas direction in the modified Grimm-type glow discharge resulted in the successful deposition of single crystal thin films with controlled nanoparticle sizes.

Time-resolved detection of structural change in polyethylene films using mid-infrared laser pulses

Some of the vibrational modes of crystalline organic polymers are known to be sensitive to the structural change from the crystalline phase to the amorphous phase, and vice versa. Using a mid-infrared (mid-IR) pulse from a free-electron laser as a probe, we demonstrate the time-resolved detection of structural change in crystalline polymer (polyethylene) films upon laser heating by a Q-switched Nd:YAG laser. Transmittance of the resonant mid-IR pulse almost instantaneously changes before and after the Nd:YAG laser pulse if its fluence is sufficient to induce the structural change in the film. The developed technique would be useful to study the time-dependent dynamics of the structural change in various materials.

Thermogravimetric study of water affinity of gelatin materials

Gelatin materials in the form of thin films were prepared using film-forming gelatin solutions with pH value of 2.5–6.8; interaction of gelatin with water in the films and in the solutions was studied. Thermogravimetric analysis at temperature up to 200 °C was used to identify and characterize free and bound water present in dried films. To simulate the water–gelatin interaction and to interpret thermogravimetric data, quantum chemical calculations along with the studies on the films swelling were performed. For both free water and bound water, the parameters of thermal desorption process were found to be affected by pH of film-forming solution. The observed changes in content of free and bound water and in apparent activation energies of water thermal desorption may be attributed to the growth of the quantity of negatively charged groups in gelatin molecules upon pH increase and to the changes in film structure and water affinity resulting from the charged groups interaction. Thus, by varying pH of the solution, one may influence the affinity of the films with respect to water and change the properties and usability of gelatin materials.

Structural and surface characterization of magnetron sputtered In1−xAlxN films grown on GaAs substrates

This paper reports the structural and surface features of In1−xAlxN films grown on GaAs substrates with ZnO buffer layer by using reactive magnetron co-sputtering of Al and In targets in Ar–N2 at 100°C. The Al sputtering power was varied between 100W and 300W with respect to the fixed In power (50W) to obtain different compositions of the films. X-ray diffraction (XRD) studies revealed the formation of nanostructured In1−xAlxN films along (0002) and (101¯1) planes with composition ‘x’ ranging from 0.4 to 0.9. Intensity of the diffraction peaks and crystallite size were decreased with increase of the Al contents in the film. Field emission scanning electron microscopy (FESEM) results indicated that a compact film structure changes into a relatively loose structure by increasing the Al power.

TiO2 thin films with rutile phase prepared by DC magnetron co-sputtering at room temperature: Effect of Cu incorporation

The thin films for pure TiO2 and that incorporated with Cu ion were deposited by DC magnetron co-sputtering with Ar gas. The crystal texture, surface morphology, energy gap and optical properties of the prepared films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrometer (XPS), UV–vis spectrophotometer, and Raman spectroscopy. The results show that as-deposited TiO2 film mainly possesses anatase structure at room temperature with pure Ar gas, but the introduction of Cu can alter the phase structure of crystallite TiO2. XRD patterns and Raman spectra indicate that the Cu incorporation with high concentration (ACu/ATi+ACu≈20%) favors the formation of rutile phase. Moreover, the Cu incorporation into TiO2 lattice induces band gap narrowing. Band structures and density of states have been analyzed based on density functional theory (DFT) and periodic models in order to investigate the influence of the Cu incorporation on the electronic structure of TiO2. Both experimental data and electronic structure calculations evidence the fact that the change in film structure from the anatase to the rutile phase can be ascribed to the possible incorporation of Cu1+ in the sites previously occupied by Ti4+, and the presence of Cu results in important effect on the electronic states, which is mainly related to the 3d Cu orbitals in the gap and in the vicinity of the valence band edges for TiO2.

On the HiPIMS benefits of multi-pulse operating mode

High power impulse magnetron sputtering (HiPIMS) technology is particularly interesting for its high ionization efficiency of the sputtered target elements. However, one of its major drawbacks is the typically lower deposition rate, compared to direct current magnetron sputtering (DCMS), mainly due to the metal ion back-attraction. Using HiPIMS with very short pulses (less than 5 µs), it is possible to partially overcome the deposition rate limitation. In this contribution our focus is the optimization of the HiPIMS process with respect to DCMS, based on the physical understanding of the plasma state when using sequences of pulses, instead of general single high power pulse. Sequences of consecutive very short high-power pulses significantly increase the deposition rate compared to standard HiPIMS (s-HiPIMS), as proven by quartz crystal microbalance measurements and by scanning electron microscopy cross section images of the deposited films. Tailoring the sequences of multi-pulses (m-HiPIMS), experimental results undoubtedly show that tungsten deposition rate is at least 50% higher than in the s-HiPIMS, for the same average power. This finding is explained via tuneable diode laser absorption spectroscopy measurements of the sputtered W atoms correlated with electrostatic probe ion detection and time evolution of the plasma potential measured at the substrate position. Moreover, poly-crystalline thin film structure changes to a mainly preferential orientation (2 0 0) and film roughness is drastically reduced as provided by x-ray diffraction and atomic force microscopy, respectively.

Unexpected Redox Enhancement and Electrochemical Pseudo-capacitance Performance of Polyaniline/poly(vinyl alcohol) (PAn/PVA) Composite Films

We report significant improvement, though unexpected contrary to intuition, of the redox behaviour and electrochemical pseudo-capacitance of polyaniline (PAn) conducting polymer composited with non-conducting poly(vinyl alcohol) (PVA). Redox and film composition characterizations were carried out using a combination of in situ electrochemical and nanogravimentric techniques. Film structural changes due to the presence of PVA in the matrix of PAn have been studied with FT-IR and XRD as well as thermal analysis techniques such as TGA and DSC. The increase in PAn/PVA film redox responses compared to pure PAn film was observed to be a factor of ca. 2 while electrochemical capacitance enhancement was obtained to be ca. 40% increase (ca. 130 F g−1 for PAn/PVA composite film compared to ca. 94 F g−1 for PAn). These drastic improvements of composite film's redox behaviour were attributed to the increase in film chain-chain interactions due to the presence of multiple hydrogen bonding created by the introduction of PVA chain segments in the bulk of PAn film and thus enhancing the rate of film redox conversions. Redox enhancement was also associated to the increase in composite film's ion doping capacity.

Change of diamond film structure and morphology with N2 addition in MW PECVD apparatus with linear antenna delivery system

Deposition of nano‐crystalline diamond (NCD) over large areas is of high interest for industrial applications. For instance NCD is an excellent substrate for cell growth but it is also interesting for photonic applications associated with nitrogen‐vacancy (NV) centres. There have been many studies on the effect of nitrogen addition on the growth of diamond using conventional resonance cavity microwave plasmas (both H and Ar based) but none using MW PECVD apparatus with linear antenna delivery system (MW‐LA‐PECVD). In this work, we show that an ultra nano‐crystalline diamond (UNCD) type of morphology can be prepared upon N2 addition to H2CO2CH4 plasmas at low pressures (0.3 mbar) and low temperature (520 °C); however, these films despite their UNCD character show sp3 dominated Raman spectra and highly isolating behavior. The crystalline structure and morphology of the films were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, grazing angle X‐ray diffraction, and transmission electron microscopy. Diamond films' composition was evaluated from thermal neutron depth profiling. Films were also characterized by photoluminescence spectroscopy to study the incorporation of luminescent NV centre. Addition of nitrogen increases deposition rate and dramatically changes surface morphology and crystalline structure from well faceted diamond crystals to UNCD like morphology.

Swelling dynamics and swelling induced structural changes of polyelectrolyte ultrathin films

Swelling dynamics and swelling induced structural evolution of spin coated poly(sodium-4-styrenesulfonate) (NaPSS) ultrathin films in presence of water vapor have been studied using X-ray scattering and AFM techniques. Swelling dynamics of the films has been modelled in terms of the swelling of gyration ellipsoid of polyelectrolyte chains. In presence of water vapor swelling of these gyration ellipsoids is found to be independent of the film thickness. In presence of water vapor not only the thickness of the film increases but their in-depth and in-plane structures undergo continuous modification; that being different for thinner and thicker films. In–plane structural studies of the films indicate that undulations or faceting are present on film surface and contribution from each facet shows an oscillating behaviour with swelling time for thinner films. While for thicker films in-plane modification was unidirectional. The structural changes of the films in presence of water vapor are found to be permanent in nature for both thinner and thicker films and overall film quality diminishes on prolonged swelling. Pre and post annealing XRR data shows that rather than stress relaxation, solvent–molecule interaction is mainly responsible for the structural evolution of the polyelectrolyte films.

Tuning of soft magnetic properties in FeCoHfO thin films by various sputtering power and pressure

FeCoHfO thin films with soft magnetic properties were deposited on Si (100) substrates using radio frequency reactive magnetron sputtering in Ar+O2 gases. During the deposition process, the partial pressure of oxygen was fixed at 3%. Sputtering power and sputtering pressure varied from 50 to 350 W and from 0·2 to 1 Pa respectively. In the condition of stationary sputtering gases pressure of 0·4 Pa, it was found that the film electrical resistivity ρ decreases steeply with the increasing sputtering power, and the natural ferromagnetic resonant frequency fr and static anisotropy field Hk increase with increase in power from 50 to 250 W, and then decrease when power exceeded 250 W. The coercivity of films had a contrary trend compared with fr. At 250 W sputtering powers, the optimal properties with fr≈3·02 GHz, saturation magnetisation 4πMs≈19·6 kGs, coercivity Hc≈2 Oe and ρ≈2200 μΩ cm were obtained. In the condition of fixed sputtering power of 250 W, fr, 4πMs and Hk decreased with the increases in sputtering pressure; Hc and ρ had an opposite trend. The physical nature of the effect was suggested to be related to the structure and composition changes in films.

Titanium dioxide thin films: a study of film morphology and structural changes upon photocatalytic degradation of methylene blue

TiO2 thin films were deposited by reactive DC-magnetron sputtering at different Ar/O2 ratios in the gas mixture. The photocatalytic activity (under UV light irradiation) of these films was evaluated upon degradation of aqueous solutions of methylene blue (MB), a model organic pollutant. Upon photocatalysis, the TiO2 films showed structural, morphological and compositional changes that were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and energy dispersive X-ray (EDX).

Electronic structure changes of TiO2 thin films due to electrochromism

Titanium dioxide thin films were deposited by metal–organic chemical vapor deposition (MOCVD) on soda–lime and indium tin oxide (ITO) coated glass substrates at 400°C. X-ray diffraction (XRD) studies revealed that the deposited films have a pure anatase phase. Thickness of the film was measured by scanning electron microscopy (SEM). Atomic force microscopy was used to study the morphology of the deposited films. Depth profiling was monitored by using secondary ion mass spectroscopy (SIMS). Cyclic voltammetry indicates that the transport of Li ions in the TiO2 thin film is diffusion limited. Chronoamperometry and its corresponding optical modulation measurements show that the increase of the quantity of inserted charge causes the appearance of two absorption bands, and a blueshift of the TiO2 film absorption edge. The observed optical changes were attributed to band gap broadening.

Evaluation of metal cation effects on galvanic corrosion behavior of the A5052 aluminum alloy in low chloride ion containing solutions by electrochemical noise impedance

The effects of metal cations on the galvanic corrosion behavior of the A5052 aluminum alloy in low chloride ion containing solutions (tap water) were examined by electrochemical noise impedance. The electrochemical noise impedance and conductance were calculated by the power spectral density (PSD) of the galvanic current and potential. The oscillations in the galvanic current correlate well with the oscillations in the potential. The total charge (summation of galvanic current) during galvanic corrosion tests was suppressed by the addition of Ca2+, while it was increased with Mg2+ addition. Only a small effect on mean impedance and conductance was observed in solutions with Cu2+ and Mg2+, while addition of Ca2+ strongly influences both the mean impedance and conductance. These results may be explained by the passive film structure changes due to the metal cations. The results obtained in this study indicate that metal cations play a very important role in the corrosion behavior of A5052 aluminum alloys in tap water.