ICMCTF2013 Session TSP: Syposium TS Poster Session

In the present study, resin-base masking technique is proposed as an initial patterning procedure onto DLC coated mold-die substrates. Spectroscopic measurement and Langmuir probe method are combined not only to describe the population of activated oxygen species but also to measure the transients of electron density in plasmas. Through optimization of processing conditions, high etching rate was attained up to 8 to 10 micro-meter per hour, or, 2.2 to 3.0 nm/s. Both line and grid patterns were first employed to describe anisotropic etching behavior via SEM and leaser-microscopic measurement, and, to discuss this microscopic etching with reference to reactive ion etching process. In addition, macroscopic etching behavior was also in-situ monitored by spectroscopic plasma diagnosis for rational termination of etching when the monitored peak intensity became minimum. This termination of etching provided us the stepwise depth profile of micro- and nano-grooves and grids as the three dimensional pattern onto DLC coating.

In final, this etching method was applied to make three dimensional micro-grid patterning onto DLC-coated WC (Co) mold dies. Geometric accuracy of 5.2 x 5.2 μm squared grid as well as the depth of 5 μm was attained onto the 50 x 10 mm² mold-surface of DLC coated WC (Co) through SEM observation and laser reflection profilometer. This surface-engineered mold die was applid to duplicate these patterns onto aluminum shee via mold-stamping and to fabricate heat-radiation devices.

Zirconia-based plasma-sprayed coatings are widely used in jet and land-based engines as thermal barriers coatings (TBCs) for protecting and insulating gas turbine metal components from the extreme temperature in the hot gas thus extending the engine life capabilities and service performances as well as to reduce fuel consumption. Zirconia-based thermal barrier coatings (TBCs) of nominal chemical composition 8 wt% Y₂O₃–ZrO₂ and 25.5 wt% CeO₂–2.5 Y₂O₃–ZrO₂ were prepared by means of atmospheric plasma spray (APS) and low pressure plasma spray (LPPS) and thermal treated at different temperature (up to 1460°C, treatment time 200 hours). The heated materials have been then fractured and the resulting surfaces have been studied by means of X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) combined with energy dispersive spectrometry (EDS) and secondary ion mass spectrometry (SIMS) in order to study the surface micro-chemical composition and morphology The results disclose the variation of the stabilising oxides amount, the occurrence of valence states modifications of cerium, impurities segregation phenomena and sintering. These information confirm that chemical and morphological aspects in plasma sprayed TBCs must be known in order to understand and predict relationships between the parameters of plasma spray process and TBC features, properties and performances for a better design of reliable TBCs.

Bismuth oxide thin films were deposited by magnetron sputtering using an α-Bi₂O₃ target, under an Ar/O₂ (80:20) atmosphere. The power and substrate temperature were varied from 100-180 W and 125-250 ^oC. The films were simultaneously deposited on glass and silicon substrates; therefore spectroscopic optical characterization was done by both transmittance and ellipsometry. The film structure was studied by X-ray diffraction, obtaining strong differences in the predominant phase (mainly delta, beta and alpha) as the power or substrate temperatures were increased, which were also reflected in the deposition rate, the variations in the structure were also confirmed by Raman spectroscopy. The XPS analysis confirms that for all the conditions the composition was nearly 2:3 (Bi:O), except for minor traces of metallic bismuth found in some samples.

The electrical properties of the films were measured in planar mode for samples deposited on glass using two concentrical Pt electrodes. The measurements were done as a function of the temperature from RT to 600 ^oC. It was clearly shown that for all samples, the resistivity decreased as the T increased, showing an Arrhenius variation which allow us to estimate the values of the activation energy (optical gap) and the intrinsic surface conductivity. The results from the electrical properties are correlated to both the deposition conditions and the structure of the samples.

Acknowledgement: The research leading to these results has received funding from the European Community Seven Framework Programme (FP7-NMP-2010-EU-MEXICO) and CONACYT under grant agreements nº 263878 and 125141, respectively.

A facile approach to disperse and stabilize high loading of multi-walled carbon nanotubes (CNTs) in polyimide (PI) matrix is presented. PI/CNT nanocomposite films were synthesized by in situ polymerization of pyromellitic acid dianhydride (PMDA) and 4,4'-oxydianiline (ODA) in N,N'-dimethyl acetamide (DMAc) with the presence of various amounts of CNTs and the surfactant polyvinylpyrrolidone (PVP) and sodium dodecyl benzene sulfonate (SDBS). The FTIR spectroscopy proved that the surfactant did not hinder the polymerization of PI. The experimental results showed that the dispersion of CNT was significantly improved by increasing the ultrasonication temperature to 60 ^oC. Accordingly, The electrical conductivity of PI/CNT was increased to 41.5 S/m for the hybrid film containing 40 wt% of CNT.

A series of advanced anticorrosive hybrid films comprising of polyimide (PI) or poly(amide-imide) (PAI) matrix dispersed with various content of graphene oxide (GO) nanosheets have been successfully synthesized through the solution dispersion process of GO in PI or PAI. PAI was synthesized by mixing 4,4'-oxydianiline (ODA), 3,3'-4,4'-benzophenonetetracarboxylic dianhydride (BTDA), trimellitic anhydride chloride (TMAC) in N-Methyl-2-pyrrolidone ( NMP ) solvent. The content of hydroxyl groups in PAI affects the dispersion of GO in PAI matrix. The water-vapor-transmission-rate (WVTR), oxygen-transmission-rate (OTR) and corrosion resistance in saline condition of PAI/GO films were comprehensively studied and correlated with the content of GO. The PAI/GO nanocomposite films exhibit improved corrosion inhibition compared to pure PI and PAI .

The kinetics of spinodal decomposition are affected by several factors including the alloy composition and the depression of the coherent spinodal below chemical spinodal within the miscibility gap. Within the spinodal, phase separation leads to the formation of characteristic composition wavelengths from a solid solution. In the gold-nickel (Au-Ni) alloy system, nanolaminates were used to initially create an artificial composition fluctuation with unique nanoscale wavelengths. Although the decomposition reaction has been well documented for Au-Ni in the literature, the direct measurement of the diffusivities at low temperatures, i.e. at room temperature, would require time durations on the order of several decades. This has been accomplished by now examining sputter deposited films that were synthesized in a thermalized condition 25 years ago. In addition to the aging at room temperature, the effects of strain energy are accounted for in accommodating lattice misfit in this superlattice system. For this purpose, the results of x-ray diffraction to assess the state of short-range order at grazing incidence angles are compared with scans at high angle reflections that evidence the effects of lattice distortions.

In this work, a process with ammonia replaced by sodium citrate was employed for producing a more continuous, compact, homogeneous CdS thin film with controlled thickness. Cadmium acetate, instead of cadmium chloride, was used for its low-cost and not under regulation. First, Cd(OH)₂ particles were deposited on the substrate, thiourea was then added to the solution and the CdS uniform thin film was formed finally. Phase determination was carried out by X-ray diffraction (XRD). It was reported that the CdS synthesized using cadmium chloride had a preferred (002) hexagonal orientation and the crystal quality produced by cadmium acetate was not as good. However, an (002) hexagonal crystal orientation was obtained in this work applying cadmium acetate by controlling the pH value in the beginning of reaction. Surface morphology of the films was observed by scanning electron microscopy (SEM). Hall measurement and optical transmission spectroscopy will be applied to determine the carrier mobility and band gap. The reaction mechanism will be discussed in this paper and the as-formed CdS films are expected to be beneficial for solar cell applications for its probable high carrier mobility and reduced carrier recombination.

It is known that ohmic metal contact is essential for solar cell devices application. However, few studies has been reported for pyrite thin film devices. Schieck et al. [1] reported that platinum showed good ohmic contact characteristic on thick pyrite crystal film and R. J. Soukup et al. found the low-cost Ni metal also showed ohmic characteristic on pyrite thin film with higher resistivity. In order to get good and cheaper ohmic metal contacts for our ultrathin pyrite films, various metals were tested and stability study will be performed for the best electrode obtained in this report.

Various metals including Au, Mo, Cu, Ag, and Ni were tried in this study to find out their ohmic contact characteristic on our pyrite ultrathin films. The metal layers with thickness of 1 μm were deposited onto glass substrates by direct current magnetron sputtering under argon atmosphere. Pyrite thin film with ~50 nm thickness produced by spin coating pyrite nanoparticles ink was covered on these metal layers. Layers stacked by this sequence may avoid the destruction of the pyrite absorption layer resulted from the post deposited metal layers. For optimal choice of contact metal, a current-voltage (I-V) measurement was employed on sandwich-structured electrodes. The top metal electrodes were sputtered on the pyrite film applying a mini-pores mask so as to eliminate the plasma damage to the absorption layer. The devices were then annealed at 400 °C in sulfur ambient to improve the crystallinity of the spin-coated pyrite thin films.

Grazing incidence x-ray diffraction (GIXRD) diffractometer will be utilized to detect if phases other than pyrite and metals are present. The metal with best I-V characteristic will be adopted for further interface diffusion study. Depth profiles from nano Auger will reveal the interface diffusion between the metal layer and pyrite thin film after prolonged annealing.

Reference:

[1] R. Schieck, A. Hartmann, S. Fiechter, R. Konenkamp, and H. Wetzel, J. Mater. Res., 5 (1990) 1567.

It has been reported that the size and shape of the pores depend on the structure of the base metal, the type of electrolyte and the conditions of the anodizing process. The paper presents thin Al2O3 oxide layer formed under hard anodizing conditions on a plate made of EN AW-5251aluminium alloy. The oxidation of the ceramic layer was carried out for sixty minutes in a three-component SFS electrolyte at a temperature of 303K, electric charge 180A*min and the current density of 3A/dm2. Presented images taken with a scanning microscope for: base material (aluminium alloy), breakdown voltage, beginning of the oxidation, five, ten and sixty minutes layer growth. A computer analysis of the binary images showed the average surface of a pore and different shapes as: triangle, rhombus, pentagon and hexagon. The structure of ceramic Al2O3 layers is one of the main factors determining chemical, physical, surface and mechanical properties. The resistance to wear of polymer-oxide coating layer depends on porosity, morphology and roughness of the ceramic layer surface. A 3D oxide coating model, based on the computer analysis of images from a scanning electron microscope (SEM), was proposed. Special computer program that shows morphology of the layer was programmed in C++ language.

A number of substrates that have coefficients of thermal expansion covering a range of values different to that of the coating material have been considered to assess the potential role of thermal misfit as mechanism in improving the coating performance. Both the as-coated and stress annealed conditions (40% of the respective melting temperatures) have been investigated.

The different annealing temperatures influence the final coating microstructural properties [1,2]. Depth resolved studies of the in-plane residual stresses in the coatings and substrates have been investigated using, X-ray, synchrotron and neutron diffraction techniques in con-junction with sub millimetre sized gauge volumes [1-3]. The abrasive wear performance of the coatings were characterised using an ASTM-G65 three body abrasive wear machine. Steep stress gradients have been observed in the near surface regions of all the as-coated substrates, extending to approximately 0.5 mm from the interface. It has been identified to originate primarily from the shot blast surface preparation step. Annealing had the effect of completely removing the cold work contribution and triggering the differences in the CTE’s between coating and substrates that introduced beneficial residual stresses. Differences ob-served in the wear behaviour are related to the residual stresses resulting in the coatings ow-ing to the thermal mismatch between the coatings and substrates.

[1] O.P Oladijo. A.M. Venter, L.A. Cornish, N. Sacks, X-ray diffraction Measurement of Residual Stress in WC-Co Thermally Sprayed Coatings onto Metal Substrates, Surface & Coatings Technology (2012) 206 4725

[2] A.M. Venter, T. Pirling, T. Buslaps, O.P. Oladijo, A. Steuwer, T.P. Ntsoane, L.A. Cornish, N. Sacks, Systematic investigation of the residual strains associated with WC-Co coatings thermal sprayed onto metal substrates, Surface & Coatings Technology (2012) 206 4011

[3] V. Luzin, A.M Venter, O.P. Oladijo, L.A. Cornish, N. Sacks, Residual stress in WC-Co coated systems studied by high resolution neutron diffraction, 5th Asian Thermal Spray Conference, 26 –28 November 2012, Japan. To be submitted to Journal of Thermal Spray Technology

A common technique to enhance the adhesion of hydrogenated amorphous carbon (a-C:H) coatings especially on steel substrates is the use of adhesion layers based on different elements like W, Cr or Si. These layers normally show a complex microstructure with chemical gradients and their thickness is less than one micron. Relating the local chemical composition to the microstructure and the mechanical properties is therefore not an easy task.

In this work two a-C:H coating systems with an Si-based adhesion layer deposited with different process parameters on steel substrates were investigated in terms of chemical composition, local mechanical properties and residual stresses. Nanoindentations across small angle cross-sections of the coating systems result in a complex hardness and Young`s modulus depth profile over the adhesion layer. Additionally, auger electron spectroscopy revealed the corresponding chemical composition. A direct correlation between the local mechanical properties and the chemical composition of the two different adhesion layers was observed.

In addition, residual stresses of the two a-C:H coating on steel substrates were determined by means of focused ion beam (FIB) milling and digital image correlation (DIC). For this a H-bar geometry which is commonly used for TEM lamella preparation was FIB milled in the a-C:H coating which causes the residual stresses to relax locally. The residual stresses can be quantified by tracking the relaxation strain with DIC. At this the H-bar geometry enables a simple evaluation of the residual stresses using Hooke’s law. For the two a-C:H coatings similar residual compressive stresses of about - 2 to -3 GPa were found.