Layers Of Different Thicknesses Research Articles

Toward a quantitative definition of mechanical units: New techniques and results from an outcropping deep-water turbidite succession (Tanqua-Karoo Basin, South Africa)

The physical properties of reservoirs are strongly influenced by distributed fracture fields. Outcrop studies are commonly used to determine them but have provided unsatisfactory results because the definition of mechanical units, i.e., (groups of) layers displaying homogeneous fracture patterns, is difficult and typically conducted in a qualitative manner. We have developed a systematic methodology to acquire and process fracture patterns in outcrops and to define their relation with stratigraphy. We dedicate particular attention to the vertical distribution of fractures in a sedimentary succession, commonly composed of layers of different thicknesses and compositions. The method makes full use of geographic information system technologies and allows for direct digital acquisition in the field leading to time-efficient acquisition. Data are processed with a newly developed routine that permits an objective description of the changes of fracture characteristics along the stratigraphy of the outcrop. The operator is then able to define the most suitable fracture stratigraphy. The integration of results from different outcrops is thought to provide a tool for predicting fracture distributions in subsurface target areas.

Mixed-mode interface toughness of wafer-level Cu–Cu bonds using asymmetric chevron test

Characterization of interfacial adhesion is critical for the development of wafer bonding processes to manufacture microsystems with high yield and reliability. It is imperative that the test method used in such adhesion studies corresponds to the loading conditions present during processing and operation of the devices. In most applications in which wafers and die are bonded, the interface experiences a combination of shear and normal loading (i.e. mixed-mode loading) with the relative magnitude of the Mode I and II components varying in different scenarios. In the current work, the toughness of Cu–Cu thermocompression bonds, which are of interest for the fabrication of three-dimensional integrated circuits, is analyzed using a bonded chevron specimen with layers of different thickness that allows for the application of interfacial loading with variable mode mixity. The phase angle (a function of the degree of mode mixity at the interface) is varied from 0° to 24° by changing the layer thickness ratio from 1 to 0.48. The Cu–Cu bond toughness increases from 2.68 to 10.1 J/m 2, as the loading is changed from Mode I (pure tension) to a loading with a phase angle of 24°. The energy of plastic dissipation increases with increasing mode mixity, resulting in the enhanced interface toughness. The Mode I toughness of Cu–Cu bonds is minimally affected by plasticity, and therefore, provides the closest estimate of the interfacial work of fracture under the bonding conditions employed.

Finite-Elemente-Analyse einer zementierten, keramischen Femurkomponente unter Berücksichtigung der Einbausituation bei künstlichem Kniegelenkersatz / Finite element analysis of a cemented ceramic femoral component for the assembly situation in total knee arthroplasty

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.

Thickness-dependent dc conductivity of lithium borate glasses

Amorphous lithium borate films are prepared by ion-beam sputtering using a $0.2\phantom{\rule{0.3em}{0ex}}{\mathrm{Li}}_{2}\mathrm{O}∙0.8\phantom{\rule{0.3em}{0ex}}{\mathrm{B}}_{2}{\mathrm{O}}_{3}$ glass as a target material. The films of a thickness between 7 and $700\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ are deposited onto silicon substrates between two metallic AlLi electrodes serving as electrical contacts. dc conductivities of the glass layers of different thicknesses are determined by temperature-dependent impedance measurements. An increase of the specific dc conductivity of about 3 orders of magnitude is observed, when the thickness of the layers decreases from 120 down to $7\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. This conductivity increase in the case of very thin films leads to an absolute conductance per unit area of $0.32\phantom{\rule{0.3em}{0ex}}{\ensuremath{\Omega}}^{\ensuremath{-}1}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ at $25\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, which is sufficient for technical application of the glass layers in solid-state ionic devices. Three alternative explanations are suggested to explain this nontrivial conductivity increase: structural modifications at the interfaces, the formation of space-charge regions, and the existence of randomly distributed ion-conducting channels.

Size Determination of (Bio)conjugated Water-Soluble Colloidal Nanoparticles: A Comparison of Different Techniques

The size of inorganic colloidal nanoparticles coated with organic layers of different thickness has been measured with different techniques, including transmission electron microscopy, gel electrophoresis, size exclusion chromatography, fluorescence correlation spectroscopy, and thermophoresis. The results are critically compared, and the advantages and disadvantages of the respective methods are discussed.

Stable Field Emission Property of Patterned MgO Coated Carbon Nanotube Arrays

Aligned carbon nanotubes (CNTs) in a specific pattern were synthesized by catalytic thermal chemical vapor deposition (CVD) technique. The carbon nanotubes were then coated with MgO layer of different thicknesses to improve the field emission property. Field emission with high stability and low turn-on voltage of about 116 V was observed for the aligned nanotubes coated with a MgO layer of thickness 10 nm compared to that of uncoated CNTs. The current fluctuation for 8 h was found to be as low as 9% for MgO (10 nm) coated nanotubes. The field emission image indicated a very uniform emission from the whole area of the deposited CNTs on the substrate for the 10-nm-MgO-coated CNTs.

Displacements and stresses in composite multi-layered media due to varying temperature and concentrated load

This paper deals with the determination of the thermo-elastic displacements and stresses in a multi-layered body set up in different layers of different thickness having different elastic properties due to the application of heat and a concentrated load in the uppermost surface of the medium. Each layer is assumed to be made of homogeneous and isotropic elastic material. The relevant displacement components for each layer are taken to be axisymmetric about a line, which is perpendicular to the plane surfaces of all layers. The stress function for each layer, therefore, satisfies a single equation in absence of any body forces. The equation is then solved by integral transform technique. Analytical expressions for thermo-elastic displacements and stresses in the underlying mass and the corresponding numerical codes are constructed for any number of layers. However, the numerical comparison is made for three and four layers.

Wetting and sealing of interface between 7056 Glass and Kovar alloy

This study examines the wetting and sealing of Kovar alloy with 7056 Glass. First, the Kovar alloy underwent pre-oxidization treatment at three different temperatures (700, 800 and 900 °C) and for seven different isothermal holding periods (0, 3, 5, 10, 15, 30 and 60 min), producing oxide layers of different thickness on the surface of the alloy. Then the wetting experiment was conducted at 925 °C for 15 min to observe the wettability of 7056 Glass on the underlying Kovar alloy discs. Finally, Kovar alloy and 7056 Glass were joined at thermal treatment temperature of 825–1000 °C with isothermal holding for 15 min at every interval of 25 °C. The wetting phenomenon and interface structure were observed under optical microscope and elemental analysis was also conducted on the glass-to-metal junction using an electron probe micro-analyzer. Experimental results reveal that Kovar alloy pre-oxidized at 700 °C and held isothermally for 5–15 min would have a denser and more compact oxide layer of 4–7 μm thick showing good adherence. Kovar alloy pre-oxidized at 700 °C and 10 min isothermal holding and heated in furnace filled with nitrogen only would obtain good wettability. Finally, thermal treatment temperature of 900 °C and 15 min isothermal holding resulted in a bigger surface area of the reaction layer and high-quality glass-to-metal junction.

Nanogranular Au films deposited on carbon covered Si substrates for enhanced opticalreflectivity and Raman scattering

Electroless deposition of gold has been carried out on Si(100) surfaces precoated with laserablated carbon layers of different thicknesses, and the resulting substrates have beencharacterized by a host of techniques. We first established the porous nature of the amorphouscarbon layer by Raman and profilometric measurements. The Au uptake from the platingsolution was optimal at a carbon layer thickness of 90 nm, where we observed nanogranules of∼60–70 nm, well separated from each other in the carbon matrix (mean interparticle spacing∼7 nm). We believe that the observed nanostructure is a result ofAu3+ electroless reduction on the Si surface through porous channels present in theamorphous carbon matrix. Importantly, this nanostructured substrate exhibited highreflectivity in the near IR region besides being effective as a substrate for surfaceenhanced Raman scattering (SERS) measurements with enhancement factors up to107.

Effect of CeO 2 buffer layer thickness on the structures and properties of YBCO coated conductors

Biaxially textured YBa 2Cu 3O 7− x (YBCO) films were grown on inclined-substrate-deposited (ISD) MgO-textured metal substrates by pulsed laser deposition. CeO 2 was deposited as a buffer layer prior to YBCO growth. CeO 2 layers of different thickness were prepared to evaluate the thickness dependence of the YBCO films. The biaxial alignment features of the films were examined by X-ray diffraction 2 θ-scans, pole-figure, ϕ-scans and rocking curves of Ω angles. The significant influence of the CeO 2 thickness on the structure and properties of the YBCO films were demonstrated and the optimal thickness was found to be about 10 nm. High values of T c = 91 K and J c = 5.5 × 10 5 A/cm 2 were obtained on YBCO films with optimal CeO 2 thickness at 77 K in zero field. The possible mechanisms responsible for the dependence of the structure and the properties of the YBCO films on the thickness of the CeO 2 buffer layers are discussed.

A continuum-based model capturing size effects in polymer bonds

It is known from applications that the mechanical behaviour of polymer bonds does not only depend on the properties of the polymer itself but also on the substrate. Therefore, the mechanical behaviour, i.e. the stiffness, of a polymer joint becomes thickness dependent. In the present work we describe experiments performed on polymer joints and we develop a continuum-based model which is able to describe the experimentally observed size effects without suggesting the microstructure in detail. The continuum mechanical model is enhanced by a scalar-valued structure parameter which describes all the effects taking place in the boundary layer which arises near the substrate. It is shown that the model parameters can be determined on the basis of simple shear experiments performed on polymer layers of different thickness.

Implementation of diffractive optical element in four-wave mixing scheme for ex situ characterization of hydride vapor phase epitaxy-grown GaN layers

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.

Bulk and interfacial effects in exchange bias systems

In this work we report on an extensive and detailed study of exchange bias systems consisting of two ferromagnetic layers deposited with an antiferromagnetic layer of IrMn between them. Systems with two different ferromagnetic layers have been studied in which sample 1 had CoFe layers of different thicknesses and sample 2 had not only ferromagnetic layers of different thicknesses but also the composition of the upper ferromagnetic layers was changed from CoFe to NiFe. In both the samples the antiferromagnetic layer thickness was maintained constant at 5 nm, NiCr seed and capping layers (5 nm) were used on all samples. Such a system is of considerable interest as the properties of each ferromagnetic layer are affected by the same antiferromagnet. However differences in behaviour will occur due to the nature of the interfaces between the different layers as well as other parameters such as the ferromagnetic layer thickness. We have conducted a study of thermal activation effects in these systems where both or a single ferromagnetic layer can be reversed whilst the system is heated. We find that we can differentiate between bulk and interface effects indicating that the role of spin disorder at the interface is crucial in determining the final value of the exchange bias.

Two-dimensional model of heat flow in broad-area laser diode mounted to a non-ideal heat sink

An analytical, two-dimensional, stationary model of heat distribution in a broad-area laser is discussed. In the model the laser is treated as a stack of layers of different thicknesses and thermal conductivities. We show how to adjust the geometry of such a stack to take into account a non-ideal heat sink (made of material of finite thermal conductivity) and thus obtain reliable values of the device temperature. The calculated and measured thermal resistances of an exemplary laser series are compared. Our experiment is based on the analysis of a spectral shift of the laser radiation, which provides information about the mean temperature of the active region. A discussion of different types of bonding imperfections and their influence on the obtained results is provided.

Properties of compositionally graded Ba (1− x) Sr xTiO 3 self-standing thick films

Compositionally graded self-standing thick films (0.4 mm) have been fabricated using the airflow deposition method. Films were made of five layers with different composition Ba (1− x) Sr x TiO 3 (BST, x = 0, 0.1, 0.2, 0.3 and 0.4). The layers of different thicknesses, ranging from 80 to 30 μm, presented similar Vickers microhardness of about 0.25 GPa. The average particle size of deposited layers was finer than 500 nm and the density of as-deposited films was about 80% of theoretical. After sintering at 1350 °C samples presented increased-density (>90%) and maintained a compositional gradient. When compared to single-composition BST ceramics, permittivity of graded films was much less dependent on temperature over a wide range, from −50 to 250 °C. In addition, the films displayed polarization offset when driven by an alternating field and heated above 50 °C.

Discrimination between Doppler-shifted and non-shifted light in coherence domain path length resolved measurements of multiply scattered light

We show a novel technique to distinguish between Doppler shifted and unshifted light in multiple scattering experiments on mixed static and dynamic media. With a phase modulated low coherence Mach- Zehnder interferometer, optical path lengths of shifted and unshifted light and path length dependent Doppler broadening are measured in a two-layer tissue phantom, with a superficial static layer of different thickness covering a semi-infinite dynamic medium having identical optical properties. No Doppler broadening is observed until a certain optical path length depending on the thickness of the superficial static layer. From the minimum optical path length corresponding to the Doppler-shifted light the thickness of the static layer that overlies the dynamic layer can be estimated. Validation of the experimentally determined thickness of the static layer is done with the Doppler Monte Carlo technique. This approach has potential applications in discriminating between statically and dynamically scattered light in the perfusion signal and in determining superficial burn depths.

Characterization of Ag/Pt core-shell nanoparticles by UV–vis absorption, resonance light-scattering techniques

The water-soluble Ag/Pt core-shell nanoparticles were prepared by deposition Pt over Ag colloidal seeds with the seed-growth method using K 2PtCl 4 with trisodium citrate as reduced agent. The Ag:Pt ratio is varied from 9:1 to 1:3 for synthesizing Pt shell layer of different thickness. A remarkable shift and broadening of Ag surface plasmon band around 410 nm was observed. The contrast of TEM images of Ag/Pt colloids has been obtained. Various techniques, such as transmission electron microscopy (TEM), UV–vis absorption and resonance light-scattering spectroscopy were used to characterize nanoparticles. The data of TEM, UV–vis and resonance light-scattering spectrum all confirm formation of Ag/Pt core-shell nanoparticles. Resonance light-scattering and emission spectrum show the Ag and Ag/Pt core-shell nanoparticles have a nonlinear light-scattering characteristic.

Achievement of 4.51% conversion efficiency using ZnO recombination barrier layer in TiO2 based dye-sensitized solar cells

The authors report the use of chemically deposited ZnO recombination barrier layer for improved efficiency of TiO2 based dye-sensitized solar cells. The ZnO layers of different thicknesses were deposited on spin coated porous TiO2. The presence of ZnO over TiO2 was confirmed by x-ray diffraction, electron dispersive x-ray analysis, and supported by x-ray photoelectron spectroscopy, proved inherent energy barrier between the porous TiO2 electrode and lithium iodide electrolyte. They found that TiO2 based dye-sensitized solar cell with 30nm ZnO layer thickness showed 4.51% efficiency due to the formation of efficient recombination barrier at electrode/electrolyte interface. Further increase in ZnO barrier thickness may leak the electrons injected from the dye due to its low electron effective mass of 0.2me.

Ferromagnetic interlayer exchange coupling in semiconductor SbCrTe∕Sb2Te3∕SbCrTe trilayer structures

Semiconductor trilayer structures with ferromagnetic Sb2−xCrxTe3 layers separated by a nonmagnetic Sb2Te3 layer of different thickness have been fabricated by molecular beam epitaxy. Ferromagnetic out-of-plane exchange coupling between the SbCrTe layers was found and the coupling strength, which can be represented by a saturation field HS, depends on both the Sb2Te3 spacer thickness and temperature.

FRACTAL CRACK PATTERNS IN LAPONITE FILMS AND THEIR SCALING BEHAVIOR

We study crack patterns in laponite films of different thickness. The patterns show a self-similarity under coarse-graining, the fractal dimension determined by box-counting has a value around 1.66, independent of film thickness. The cracks on layers of different thickness show a remarkable scaling bahavior. We have measured the cumulative area covered by the cracks versus minimum crack-width resolved. Curves representing crack area for different thickness collapse onto a single curve, when the crack widths are scaled by the film thickness.