Thin Diffusion Research Articles

Collimating lamp with well color mixing of red/green/blue LEDs

A novel light luminaire is proposed and experimentally analyzed, which efficiently mixes and projects the tunable light from red, green and blue (RGB) light-emitting diodes (LEDs). Simultaneous light collimation and color mixing is a challenging task because most collimators separate colors, and most color mixers spread the light beam. Our method is simple and compact; it only uses a short light pipe, a thin diffuser, and a total internal reflection lens. We performed an experimental study to find a balance between optical efficiency and color uniformity by changing light recycling and color mixing.

Grain boundary diffusion in thin films with a bimodal grain boundary structure

Diffusion through different grain boundaries (GBs) in thin films is analyzed by solving the diffusion equations numerically. Supposing a bimodal grain structure, i.e. boundaries with low and high diffusivities, the thin film diffusion problem is solved using the following boundary conditions: one surface is maintained at unit concentration, at the back surface zero flux or fast surface diffusion and the formation of a secondary diffusion source is supposed. In the case of a C kinetic regime, the contributions of the fast and slow boundaries can be separated: the appearance time of the secondary diffusion source is determined by the high diffusivity boundaries, on the other hand, the diffusion broadening of the region in which the grain boundaries are saturated is controlled by the slow GBs. Similarly, the out-diffusion from the secondary diffusion source is also controlled by the slow GBs. From the time evolution of the concentration profiles measured experimentally in the Ta/Co/Si system, Si diffusivities are determined by fitting our numerical solutions. Our results underline the importance of the fitting procedure proposed in this article, i.e. the fitting of the central part of the film can be free of errors due to instrumental broadening around the interfaces.

Preparation of cationic latent initiators containing imidazole group and their effects on the properties of DGEBA epoxy resin

The thermal cationic latent initiators, N-benzyl-3-methylimidazolium hexafluoroantimonate (BMH1) and N-butyl-3-methylimidazolium hexafluoroantimonate (BMH2) were synthesized and applied to the thermal cationic polymerization of diglycidyl ether of bisphenol A (DGEBA). The performance of BMH1 and BMH2 was examined by differential scanning calorimetry (DSC), which showed good thermal latent properties and excelled epoxy resin curing behavior. The morphology, thermal, mechanical, and water sorption properties of DGEBA resin cured by 1 wt% of BMH1 and BMH2 were measured by X-ray diffraction (XRD), scaming electron microscopy (SEM), thermogravimetric analysis (TGA), nanoindentation, and thin film diffusion analysis. The cured DGEBA/BMH1 system showed relatively higher thermal stability than the DGEBA/BMH2 system. The diffusion coefficient and water uptake were 14.2×10−9 cm2/s and 1.15 wt% for the DGEBA/BMH1 system and 11.5×10−9 cm2/s and 1.07 wt% for the DGEBA/BMH2 system, respectively. Therefore, DGEBA/BMH2 showed higher resistance to water sorption than DGEBA/BMH1. On the other hand, hardness and elastic modulus of DGEBA/BMH2 were higher than those of DGEBA/BMH1. This can be attributed to the difference in the end group of initiators as well as the degree of crosslinking in the cured resin network. Open image in new window

Synthesis and characterization of novel UV-Curable PU-Si hybrids: Influence of silica on thermal, mechanical, and water sorption properties of polyurethane acrylates

Organic-inorganic hybrid membranes (HM1-HM4) were synthesized by incorporating 3 wt% (HM1), 5 wt% (HM2), 10 wt% (HM3), and 20 wt% (HM4) of silica precursors into UV-curable polyurethane acrylate (PU) matrix using sol-gel technique. PU, which was prepared by reacting polycaprolactone triol (PCLT) and isophorone diisocyanate (IPDI), was used as the starting organic polymer whereas tetraethoxysilane (TEOS) was used as a precursor for the development of the inorganic phase. The completion of the polymerization reaction of PU and the synthesis of hybrid membranes were confirmed by Fourier transform infrared spectroscopy (FTIR) whereas the morphology was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal, mechanical, and anti-water sorption properties of the hybrid membranes were examined by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), nanoindentator and thin film diffusion analysis, which revealed that HM2 has the highest thermal, mechanical, and anti-water sorption properties. TGA demonstrated that the thermal decomposition temperature (T d10%) of HM2 increased significantly, being 30 °C higher than that of pure PU, whereas DSC indicated that the introduction of 5 wt% of TEOS increased the glass transition temperature from 93.8 to 103 °C. Accordingly, the mechanical and water sorption properties were also enhanced greatly as evidenced by nanoindentation analysis and anti-water sorption data, in which HM2 shows the highest elastic modulus (8.354 GPa), hardness (0.262 GPa), and lowest water sorption capacity. These thermal, mechanical, and anti-water sorption improvements are important for the practical process and applications of PU.

Synthesis and characterization of novel PPC-silica hybrid with improved thermal, mechanical, and water sorption properties

Organic-inorganic hybrids (H1-H5) based on environmentally friendly and biodegradable polymer, poly (propylene carbonate) (PPC) and tetraethoxysilane (TEOS) were synthesized using the sol-gel technique. The synthesized hybrids were characterized structurally and morphologically by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). H1-H5 were examined in term of detailed thermal, mechanical, and anti-water sorption properties using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) nanoindentation, and thin film diffusion analysis, which revealed that H4 has the highest thermal, mechanical, and anti-water sorption properties. H4 greatly increased the thermal decomposition temperature (Td10%) and glass transition temperature, which are 45 and 11 °C higher than that of pure PPC. Accordingly, H4 showed a high storage modulus (2.54 × 109 Pa), elastic modulus (2.601 ± 0.110 GPa), hardness (0.175 ± 0.013 GPa), and lowest water absorption. This improvement in the thermal, mechanical, and anti-water absorption properties of PPC shows that PPC can be used as a packaging and bio-material.

Elongated Membrane Zones Boost Interactions of Diffusing Proteins

Biological membranes are two dimensional, making the discovery of quasi-one-dimensional diffusion of membrane proteins puzzling. Jaqaman et al. (2011) now show that actomyosin and tubulin interact to establish long, thin diffusion corridors, thereby increasing the effective concentration of select membrane proteins to promote their interactions and modulate signaling.

Development of Embedded Heatsinking Layers for Compact Arrays of X-Ray TES Microcalorimeters

Transition-edge sensor microcalorimeter arrays in compact geometries and large formats experience local heating from bias power and x-ray hits that must be dissipated in the frame. For devices on solid, non-perforated silicon substrates, we have introduced an underlying embedded copper heatsinking layer to enhance the ability of the frame to remove this heat. In particular, such a layer can mitigate thermal crosstalk between nearby pixels within the array. Further improvements in array performance, such as decreased magnetic field sensitivity and stray inductance, are possible by turning the heatsinking layer into a superconducting ground plane. In this presentation, we report on the development of heatsinking layers consisting of a 1-2 μm thick high-quality copper layer which is sandwiched between two thin refractory metal-based diffusion barriers. These diffusion barriers are designed to avoid copper migration into the surrounding material over time, especially during our high temperature TES fabrication process which takes place in excess of 400°C . A 0.3-0.5 μm thick PECVD SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cover layer isolates the heatsinking layer from the detector circuit. We present first results on our attempt to tailor the materials forming the diffusion barrier to fabricate both well defined superconducting ground planes and non-superconducting layers with the desired barrier characteristics.

Ignition limits of rapidly expanding diffusion layers: Application to unsteady hydrogen jets

The present paper addresses the ignition problem of a one-dimensional unsteady diffusion layer of fuel and oxidizer, undergoing volumetric expansion. The problem is applied to shock induced diffusion-ignition of pressurized fuel jets that are released into an oxidizing atmosphere. Upon the sudden release of a pressurized gaseous fuel into the ambient atmosphere through a hole, a strong shock wave forms, driven by rapid expansion of the forming jet. The model follows the thin diffusion layer at the head of the jet in Lagrangian coordinates, with its rate of expansion dictated by the local pressure evolution of the surrounding gasdynamic flow. Following the analysis of Radulescu and Law, the latter can be calculated a priori before the ignition event. Hence, the expansion rate is prescribed as a source term in our calculations of the diffusion layer. The calculations, which are performed for hydrogen and air with realistic thermo-chemical data and transport properties of the chemical species, revealed the transient events leading to ignition in this unsteady diffusion layer. Furthermore, the calculations showed that when the rate of expansion was sufficiently strong, which may occur for releases through sufficiently small holes, ignition can be prevented. This illustrates the important role that gasdynamic expansion plays on ignition phenomena. The results of the present model are found to be in very good agreement with previous numerical and experimental results of transient jet release ignition.

Poly( N-methyl aniline) thin films on copper: Synthesis, characterization and corrosion protection

Poly( N-methyl aniline) (PNMA) coatings were synthesized on copper by electrochemical polymerization of N-methyl aniline in aqueous oxalic acid solution by using cyclic voltammetry. The optimum electrodeposition conditions (e.g. upper potential limit, scan rate and cycle number) were determined in order to obtain PNMA coatings to have the best corrosion performance. PNMA coatings were characterized by cyclic voltammetry, Fourier Transform Infrared-Attenuated Total Reflectance spectroscopy and scanning electron microscopy. Redox parameters found after electrochemical tests indicate a thin film character and diffusion controlled electroactive behavior of PNMA. Corrosion test results revealed that PNMA coating appears to enhance protection of copper in 0.1 M H 2SO 4 solution.

A Phase-Field – Finite Element Model for Instabilities in Multilayer Thin Films

ABSTRACTCahn-Hilliard type of phase-field (PF) model coupled with elasticity equations is used to study the instabilities in multilayer thin films. The governing equations of the solid state phase transformation include a 4th order partial differential equation representing the evolution of the conserved PF variable (concentration) coupled to 2nd order partial differential equations representing the mechanical equilibrium. A mixed order Galerkin finite element (FE) model is used including C0 interpolation functions for the displacement, and C1 interpolation functions for the concentration. It is shown that quadratic convergence, expected for conforming elements, is achieved from this coupled mixed-order FE model.Using the PF – FE model, first, we studied the effect of compositional strain on the PF interface thickness and the results of simulations are compared with the analytical solutions of an infinite thin film diffusion couple with a flat interface.Morphological instabilities in binary multilayer thin films are investigated. The alloys with and without intermediate phase are considered, as well as the cases with stable and metastable intermediate phase. Maps of transformations in multilayer systems are carried out considering the effects of initial thickness of layers, compositional strain, and growth of a stable/unstable intermediate phase on the instability of the multilayer thin films. It is shown that at some cases phase transformation, intermediate phase nucleation and growth, or deformation of layers due to high compositional strain can lead to the coarsening of the layers which can result in different mechanical and materials behaviors of the original designed multilayer.

Fabrication of Monolithic RERTR Fuels by Hot Isostatic Pressing

The Reduced Enrichment for Research and Test Reactors (RERTR) program develops advanced nuclear fuels for high-power test reactors. Monolithic fuel design provides higher uranium loading than that of the traditional dispersion fuel design. Hot isostatic pressing is a promising process for low-cost batch fabrication of monolithic RERTR fuel plates for these high-power reactors. Bonding U-Mo fuel foil and 6061-Al cladding by hot isostatic press bonding was successfully developed at Idaho National Laboratory. Because of the relatively high processing temperature, the interaction between fuel meat and aluminum cladding is a concern. Two different methods were employed to mitigate this effect: a diffusion barrier and a doping addition to the interface. Both types of fuel plates have been fabricated by hot isostatic press bonding. Preliminary results show that the direct fuel/cladding interaction during the bonding process was eliminated by introducing a thin zirconium diffusion barrier layer between the fuel and the cladding. Fuel plates were also produced and characterized with a silicon-rich interlayer between fuel and cladding. This paper reports the recent progress of this developmental effort and identifies the areas that need further attention.

M-13 Determination of Wear Behaviour of Titanium Alloys Implant Materials Blasted With Mixture of Zirconia/Silica/Hydroxyapatite Powders

In this research, the effects of thin Al2O3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the high temperature oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings were examined by using isothermal oxidation tests at 1100 °C. Nanostructured YSZ top coat could slightly reduce the double layered TGO growth rate and weight gain of thermal barrier coating systems. However, Al2O3 diffusion barrier layer (consisting of Y-containing small oxide precipitates) could substantially decline the oxidation rate and Ta movement (Ta-enriched oxides formation) in the NiCoCrAlTaY/Al2O3/nanostructured YSZ coating at 1100 °C.

Voltammetric biosensors for the determination of paracetamol at carbon nanotube modified pyrolytic graphite electrode

The voltammetric oxidation of paracetamol on single-walled carbon nanotubes (SWNT) modified edge plane pyrolytic graphite electrode (EPPGE) was explored in phosphate buffer solution by using square wave voltammetry. Cyclic and square wave voltammetry studies indicated the oxidation of paracetamol at the electrode surface through a two-electron reversible step and fundamentally controlled by adsorption. Besides semi-infinite planar diffusion, the role of thin layer diffusion at nanotube modified electrodes is also suggested. The sensitivity at SWNT modified EPPGE is ∼2 times more than that at MWNT modified EPPGE. Paracetamol gave a sensitive oxidation peak at ∼187 mV at pH 7.2 ( μ = 0.5 M) which was used to quantitate the drug in the range of 5–1000 nM with a detection limit of 2.9 × 10 −9 M at SWNT modified EPPGE. The interfering effect of physiologically common interferents on the current response of paracetamol has been reported. The procedure was successfully applied for the assay of paracetamol in pharmaceutical formulations. The applicability of the developed method to determine the drug in human urine samples obtained after 4 h of administration of paracetamol is illustrated.

Determining the diffusion coefficient of Ni in Cu from a Ni/Cu thin film using linear heating, scanning Auger microscopy and a numerical solution of Fick's second law

AbstractIn previous studies, linear temperature ramping was used to determine diffusion coefficients from bulk‐to‐surface segregation experiments of a low concentration solute. Thin film diffusion studies usually employ a classical heating regime, where a sample's annealing time is taken as the time between insertion and removal from a furnace. The aforementioned study type assumes that the time it takes to heat up a sample after insertion is instantaneous, while the sample cools down instantaneously after removal from the furnace. This assumption is incorrect, as it does not compensate for the various mechanisms that govern heat transfer. In order to eliminate the uncertainty, a linear ramping regime is used and samples were annealed inside an ultra high vacuum (UHV) environment with a programmed linear heating scheme. After each anneal, a depth profile was obtained by simultaneously bombarding the sample with Ar+ ions and monitoring the exposed surface with an electron beam which excites Auger electrons, among others. The depth profiles were normalised and the time scale converted to depth. In order to compare the diffusion profiles obtained from classical annealing studies to the linearly ramped studies, the diffusion coefficient obtained for a classical study of Ni diffusing in Cu was inserted into a numerical solution of Fick's second law, modified to include linear temperature ramping. A diffusion coefficient was also obtained from linearly ramped samples. Comparison of the diffusion profiles calculated with the diffusion coefficients obtained from classical heating and linear heating showed a large discrepancy between the profiles. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Reactively Sputtered Nanocrystalline ZrN Film as Extremely Thin Diffusion Barrier between Cu and SiO2

The results of analyses by X-ray diffraction, transmission electron microscopy, and grazing incidence X-ray reflectivity measurement indicate that a 5-nm-thick ZrN film interposed between Cu and SiO2 shows excellent barrier properties, tolerating annealing up to at least 500 °C for 30 min. The X-ray diffraction pattern reveals a decrease in the intensity of the Cu(111) reflection upon annealing at 800 °C, suggesting a failure of the thin barrier due to Cu diffusion through the barrier. We are confident that the formation of a continuous nanocrystalline ZrN film in a uniform fashion in a stable phase with a slightly nitrogen-rich composition is a cause of the excellent features obtained. The formation process of the ZrN film is discussed in terms of the nucleation process of reactive sputtering at a low deposition temperature.

Resonance Properties of a Functionally Gradient Piezoelectric Actuator Based on PNN-PZ-PT Ceramics

A functionally gradient piezoelectric actuator based on PbNi1/3Nb2/3O3-PbZrO3-PbTiO3 (PNN-PZ-PT) system was prepared. The cantilevered actuator consists of a high piezoelectric &amp; low dielectric layer, a low piezoelectric &amp; high dielectric layer and a thin middle diffusion layer. Frequency dependences of impedance were measured from 100Hz to 3MHz. The resonance modes were characterized. A number of low frequency modes were observed and identified as bending resonance. The dimension dependence of resonance frequency of bending resonance was investigated. The results of the measurement were compared with calculated values. There is a good agreement between the determined resonance frequencies and calculated values.

Corrosion Behavior of FBR Structural Materials in High Temperature Supercritical Carbon Dioxide

A key problem in the application of a supercritical carbon dioxide (CO2) turbine cycle to a fast breeder reactor (FBR) is the corrosion of structural material by supercritical CO2 at high temperature. In this study, corrosion test of high-chromium martensitic steel (12Cr-steel) and FBR grade type 316 stainless steel (316FR), which are candidate materials for FBRs, were performed at 400-600°C in supercritical CO2 pressurized at 20MPa. Corrosion due to the high temperature oxidation in exposed surface was measured up to approximately 2000h in both steels. In the case of 12Cr-steel, the weight gain showed parabolic growth with exposure time at each temperature. The oxidation coefficient could be estimated by the Arrhenius function. The specimens were covered by two successive oxide layers, an Fe-Cr-O layer (inside) and an Fe-O layer (outside). A partial thin oxide diffusion layer appeared between the base metal and the Fe-Cr-O layer. The corrosion behavior was equivalent to that in supercritical CO2 at 10MPa, and no effects of CO2 pressure on oxidation were observed in this study. In the case of 316FR specimens, the weight gain was significantly lower than that of 12Cr-steel. Dependency of neither temperature nor exposed time on oxidation was not observed, and the value of all tested specimens was within 2g/m2. Nodule shape oxides which consisted of two structures, Fe-Cr-O and Fe-O were observed on the surface of the 316FR specimen. Carburizing, known as a factor in the occurrence of breakaway corrosion and/or the degradation of ductility, was observed on the surface of both steels.

High Quality NH2SAM (Self Assembled Monolayer) Diffusion Barrier for Advanced Copper Interconnects

AbstractThe trend for future integrated circuits (IC) is decreasing in size beyond the conventional limits. The recent transition from aluminum to copper as the interconnect material for IC is due to copper's higher resistance to electromigration and its lower resistivity. Unfortunately, copper has high mobility in Si and SiO2 and may cause destruction of electrical connections on the chip. Hence, there is a significant necessity in finding ultra thin, thermally stable, high quality and good adhered diffusion barriers. The most widely used barrier is pure Ta films or layer stacks consisting of Ta and TaN. These have excellent conformality, very good uniformity and high thermal stability. But The continuous scaling down of the interconnect dimensions lead to an essential decrease in the barrier layer effective thickness to less than 5nm; coupled with the replacement of silicon oxide by advanced low-k dielectrics it demand further improvements of the diffusion barrier performance. For that reason Self-assembled monolayers (SAMs), with thicknesses of 2nm or less, have been propose for copper diffusion barrier application. By tailoring the structure of these monomolecular organic films, atomic scale properties can be controlled and selective surfaces and interfaces can be engine as desired for a specific application. In the presented work, the quality of an amino-terminated SAM barrier (NH2SAM) is tested. A high density and the absence of pinholes in the barrier layer are essential for a good barrier performance. First, the macroscopic quality of the NH2SAM barrier has been characterized by Water contact angle (CA) and High resolution AFM (HR-AFM). Secondly, the density and the presence and/or absence of pinholes have been tested by Ellipsometry and Cylic Voltametry (CV). Finally, the intrinsic barrier performance in form of Time- dependent dielectric breakdown (TDDB) lifetime has been extracted from planar capacitor structures that permitted to measure the leakage/Cu diffusion through barrier in the vertical direction. The Contact angle of layers formed at different deposition times show a variation of the hydrophilic SiO2 substrate to hydrophobic already with 1min deposited NH2SAM layer. A 15min deposited NH2SAM (~1nm), results in a continuous and pinhole free layer observed by HR-AFM. The refraction index (η) calculated by ellipsometry, indicates an increase in the density of the layer with the deposition time. On the other hand, cyclic voltametry shows inhibition of the electrochemical reduction of Fe3+ specimen to Fe2+ when NH2SAM are formed on ~2nmSiO2/Si electrodes. A decrease in the capacitive current is observed by increasing the layer thickness and density. The intrinsic barrier performance of the NH2SAM barrier by TDDB is demonstrated with an increase of 10 times the capacitor lifetime by comparing with no barrier system.

Interdiffusion and stress development in Ni-Cu thin film diffusion couples

Thin film Ni-Cu diffusion couples (individual layer thicknesses: 50 mn) have been prepared by direct-current magnetron sputtering on silicon substrates. The microstructural development and the stress evolution during diffusion annealing have been investigated employing ex-situ and in-situ X-ray diffraction, transmission electron microscopy and Auger-electron spectroscopy (in combination with sputter-depth profiling). Annealing at relatively low temperatures (175 degrees C to 350 degrees C) for durations up to about 100 hours results in considerable diffusional intermixing. In addition to thermal stresses due to mismatch of the coefficients of thermal expansion of layers and substrate, tensile stress contributions in the sublayers arise during diffusion anneals. The obtained stress data are discussed in terms of possible mechanisms of stress generation.

Water management in direct methanol fuel cells

Water management is an important challenge in portable direct methanol fuel cells. Reducing the water and methanol loss from the anode to the cathode enables the use of highly concentrated methanol solutions to achieve enhanced performances. In this work, the results of a simulation study using a previous developed model for DMFCs are presented. Particular attention is devoted to the water distribution across the cell. The influence of different parameters (such as the cathode relative humidity (RH), the methanol concentration and the membrane, catalyst layer and diffusion media thicknesses) over the water transport and on the cell performance is studied. The analytical solutions of the net water transport coefficient, for different values of the cathode relative humidity are successfully compared with recent published experimental data putting in evidence that humidified cathodes contribute to a decrease on the water crossover. As a result of the modelling results, a tailored MEA build-up with the common available commercial materials is proposed to achieve low methanol and water crossover and high power density, operating at relatively high methanol concentrations. A thick anode catalyst layer to promote methanol oxidation, a thin anode gas diffusion layer as methanol carrier to the catalyst layer and a thin polymer membrane to lower the water crossover coefficient between the anode and cathode are suggested.