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Aluminium-copper alloys of the 2xxx type receive their excellent mechanical properties by the formation of copper-rich precipitates during hardening. Size, distribution and crystal structure of the formed precipitates determine the final strength of those alloys. Adding traces of certain elements, which bind to vacancies, significantly influences the decomposition behaviour, i.e. the diffusion of the copper atoms. For high-purity ternary alloys (Al-1.7 at.% Cu-X), we investigate the interaction of copper and trace element atoms (X=In, Sn, and Pb) with quenched-in vacancies by Positron Annihilation Lifetime Spectroscopy (PALS). By employing Vickers microhardness, Differential Scanning Calorimetry (DSC) and Small Angle X-Ray Scattering (SAXS) we obtain a comprehensive picture of the decomposition process: opposite to predicted binding energies to vacancies by ab-initio calculations we find during ageing at room and elevated temperature a more retarded clustering of copper in the presence of In rather than for Sn additions, while Pb, having the highest predicted binding to vacancies, shows nearly no retarding effect compared to pure Al-Cu. If the latter would be due to a limited solubility of lead, it had to be below 2 ppm. Transmission Electron Microscopy (TEM) as imaging method complements our findings. Annealing the quenched Al-1.7 at.% Cu-X-alloys containing 100 ppm In or Sn at $$150\,^\circ {\text {C}}$$ 150 ∘ C leads to finely distributed $$\theta \, '$$ θ ′ -precipitates on the nanoscale, since due to the trace additions the formation temperature of $$\theta \, '$$ θ ′ is lowered by more than $$100\,^\circ {\text {C}}$$ 100 ∘ C . According to TEM small agglomerates of trace elements (In, Sn) may support the early nucleation for the $$\theta \, '$$ θ ′ -precipitates.

Nanocrystalline Nickel-based alloys were investigated as catalysts for the oxygen evolution reaction (OER) at industrial operation conditions for alkaline water electrolysis. Different alloys were prepared by rapid solidification and subsequent high-energy milling. Regarding OER activity, the best efficiency was obtained for a nanocrystalline Ni Fe alloy in 29.9 wt.-% KOH at 298 K. However, at elevated temperature (333 K), comparable activities were determined in short-term experiments for nanocrystalline Ni Fe and Ni alloys as well as for polycrystalline Ni. This initially incomprehensible outcome can be explained by the incorporation of Fe, which is present as impurity in the reagent grade KOH solution, into the NiOOH anode surface layer. However, after a long-term operation, the nanocrystalline Ni Fe alloy shows a significantly better activity, in particular, at altering current density of up to 1 A cm−2. As a result, the nanocrystalline Ni Fe alloy exhibits a very high efficiency and excellent long-term activity (375 mV overpotential at 0.3 A cm−2) after 95 h of operation at different loads.

For the assessment of the precipitation state in aluminum-based alloys by transmission electron microscopy (TEM), the sample must have an orientation in the [100] direction of the matrix. TEMs equipped with objective lenses that are optimized for high resolution are mostly characterized by limited sample tilt angles. The required crystal orientation must thus be taken into account during sampling. A favorably oriented grain was chosen in a coarse-grained material using electron backscatter diffraction and prepared in a suitable direction applying the in-situ lift-out method in the focused ion beam device. After that, the final correction of the orientation in the TEM amounts to less than 12°.

Deep trenches, as essential elements of silicon chips used in electronic high-power and high-frequency devices, are known as starting points for dislocation generation under the influence of internal mechanical stresses resulting mainly from the difference in the thermal expansion coefficients between silicon and silicon dioxide. Since the electrical insulation of the devices requires a sequence of mechanical, chemical, and high-temperature processes during the preparation of the deep trenches, including the formation of an amorphous SiO2 edge layer, the emergence of the internal stresses is hardly avoidable. The method of cross correlation backscattered electron diffraction in the scanning electron microscope is used here to quantitatively determine the magnitude and local distribution of internal stresses in silicon around the deep trenches after four different process steps. For this purpose, Kikuchi diffraction images are recorded of the wafer cross section areas along lines perpendicular and parallel to the deep trenches. After Fourier transformation, these images are cross correlated with the Fourier transform of the diffraction image from a stressfree reference sample site. The well-established numerical evaluation of cross correlation functions provides the complete distortion tensor for each measuring point of the line scan, from which the stress tensor can be calculated using Hooke's law. It is found that the in-plane normal stress component s11 perpendicular to the long edges of the deep trench is larger than the other stress components. That means it essentially determines the magnitude of the von-Mises stress, which was determined as a general stress indicator for all measuring points, too. A characteristic feature is the local distribution of the stress component s11 with maximum tensile stresses of some hundred megapascals at transition between Si and amorphous SiO2 on the long edges of the deep trench, and with even higher maximum compressive stresses immediately below the bottom of the deep trench. At a distance of about 2 mm from the edges of a single deep trench, all stress components decrease to negligibly small values so that steep stress gradients occur. The range and distribution of tensile and compressive stresses are in accordance with finite element simulations; however, the measured stresses are higher than expected for all investigated states so that dislocation formation seems to be possible. The influence of the electron acceleration voltage on the determination of the internal stresses is discussed as well.

Combining stainless steel with zirconia components by powder technological shaping routes for manufacturing of multifunctional parts is an advantageous and promising one-step method making expensive and time-consuming additional joining steps redundant. However, several requirements for co-shaping and co-sintering of the very different compound partners have to be met. The microstructural and chemical constitution of the interface between both materials plays an important role for the mechanical properties, durability and corrosion resistance of the manufactured parts. In the present study, different shaping techniques for co-shaping of stainless steel and zirconia are introduced. The microstructure and the interphase properties of metal/ceramic hybrid parts have been investigated for samples made by tape casting, subsequent lamination and co-sintering. Nevertheless, the results of this study are valid for components made by other hybrid shaping processes as well. The interfaces were characterized by TEM, FESEM, EDX, and X-ray diffraction. Furthermore, the hydrothermal stability of the material compound was investigated.

As the new generation of microelectronics is pushed into smaller spaces and the yield production is pushing to lower the unoccupied spaces on chips, the local variation of stress has an influence on the component’s performance. This stress comes mainly from different thermal and mechanical properties of the materials used especially in 3D integrations like through silicon via (TSV) technology [1]. Through finite element simulation [2] the internal strain profile was modelled and based on these findings we devised a simulation model for a large area chunk lift out, to preserve the stress inside the material. Standard preparation method for strain measurement is to use a wafer dicing saw and subsequently focused ion beam (FIB) milling, to create lamellae with a defined geometry, close to the desired TSV. This method requires different equipment and knowledge base to achieve a lamella which is still contaminated by Gallium. Therefor we developed our own method based on an FE model of a large chunk lift out, where only a Xenon Plasma FIB is utilized until the local stress measurement using convergent beam electron diffraction (CBED) is measured in a transmission electron microscope (TEM).

Silicon carbide ceramics have found widespread use due to their high corrosion stability. Both solid state-sintered silicon carbide, which has an extremely high corrosion resistance, and silicon-infiltrated silicon carbide are used for various applications. The latter material contains SiC as well as free silicon, which is less stable. Hence, in the present work, the corrosion behavior of silicon-infiltrated silicon carbide ceramics was investigated in NaOH solutions. Long-term corrosion experiments were conducted, and a method for analyzing the corrosion behavior in short-term experiments was developed. The short-term method is based on the accurate measurement of the corrosion depth by laser scanning microscopy on polished surfaces. The results of both methods were in good agreement. The advantage of the short-term method is that it provides information on changes in corrosion mechanisms and corrosion rates in the initial period and as a function of the impurities present. Preferential corrosion of Si at the interface to SiC was observed. TEM investigations revealed that this enhanced corrosion was caused by the segregation of impurities.

We present an experimental investigation of the immiscible alloy system Mo–Na with different Na concentrations between 1 and 8 at.%. These non-equilibrium alloys were created by mechanical alloying utilizing high-energy ball milling for up to 75 h. The different microstructures, particle-size distributions, and Na contents of the as-milled powder have been studied using transmission electron microscopy and scanning electron microscopy combined with energy-dispersive X-ray analysis. The maximum Na concentration incorporated into the Mo–Na alloy is identified to be 2 at.%. In addition, the thermal stability of the alloy was examined by analyzing the Na content after annealing at different temperatures and annealing times. While after milling with 1 at.% Na, the establishment of a solid solution was proved previously, the formation of a solid solution is limited to about 1.2 at.% if more Na is used. The residual incorporated Na is segregated at pores, defects, and grain boundaries.

We report a combined experimental and first principles study of an extremely immiscible alloy of Mo with 1 and 2 at.% Na, which was produced by high-energy ball milling. The microstructure of the as-milled and annealed state were examined by various methods, including atom-probe tomography (APT), transmission electron microscopy, and energy-dispersive (EDX) analysis. Despite the complete immiscibility of the Mo-Na system in the solid and even in the liquid state, APT measurements clearly evidence the formation of a true nanocrystalline solid-solution microstructure with insignificant Na clustering for samples with 1 at.% Na. In agreement with our x-ray diffraction experiments, first principles calculations expose that the Na atoms do not expand the Mo lattice, which is in contrast to predictions using Vegard's rule. Heating at 700 °C induces only slight grain growth while the solid solution remains remarkably stable without any decomposition. On the contrary, after annealing at 900 °C first Na segregations at triple junctions and significant grain growth are observable, although the solid solution still retains most of the dissolved Na.

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element drift-diffusion simulations reveal that both leakage current suppression and polarity control can also be achieved at highly scaled geometries, providing solutions for future energy-efficient systems.

The effect of titanium addition beyond the solubility limit was investigated in order to proof the precipitation hardening possibility of the Cantor alloy CoCrFeMnNi. As high entropy alloys are currently in the focus of interest, this method is a highly suitable possibility to further improve their remarkably properties. After appropriate heat treatment consisting of homogenisation, solution and precipitation annealing a significant increase in hardness was detected. The high hardness was caused by nanometer sized precipitates, which were identified by TEM-analysis.

The transport properties of novel device architectures depend strongly on the morphology and the quality of the interface between contact and channel materials. In silicon nanowires with nickel silicide contacts, NiSi 2–Si interfaces are particularly important as NiSi 2 is often found as the phase adjacent to the silicide–silicon interface during and after the silicidation. The interface orientation of these NiSi 2–Si interfaces as well as the ability to create abrupt and flat interfaces, ultimately with atomic sharpness, is essential for the properties of diverse emerging device concepts. We present a combined experimental and theoretical study on NiSi 2–Si interfaces. Interfaces in silicon nanowires were fabricated using silicidation and characterized by high-resolution (scanning) transmission electron microscopy. It is found that {111} interfaces occur in ⟨110⟩ nanowires. A tilted interface and an arrow-shaped interface are observed, which depends on the nanowire diameter. We have further modeled NiSi 2–Si interfaces by density functional theory. Different crystallographic orientations and interface variations, e.g., due to interface reconstruction, are compared with respect to interface energy densities. The {111} interface is energetically most favorable, which explains the experimental observations. Possible ways to control the interface type are discussed.

In the vicinity of a through silicon via (TSV) used in 3D chip integration, the effect of dedicated strain engineering to enhance the carrier mobility in the channel of metal oxide semiconductor field effect transistors (MOSFETs) is superposed by a strain caused by cooling down from high process temperatures to room temperature. This additional strain influences the transistor characteristics, and consequently the product performance. The measurement of strain with high spatial resolution requires TEM-based methods. In this paper, convergent beam electron diffraction (CBED) is used for strain measurement. The strain state is significantly changed during the preparation of the TEM lamellae. The exact sample geometry and accurate materials parameters were used in FE modelling and strain simulation based on a physical model. The strain in silicon at several distances from the TSV were determined experimentally using TEM-CBED and compared with numerical simulations. High-quality sample preparation is crucial for reliable and reproducible TEM-based strain data, i.e., it is a necessary precondition for strain release correction based on FE modelling and simulation.

Germanium is a promising material for future VLSI devices, due to its high hole mobility. However, due to the low bandgap of 0.66 eV Ge based devices typically suffer from high reverse junction leakage und therefore high static power dissipation. In this paper, we apply a nanowire structure with multiple independent gates to suppress the leakage in off-direction to achieve off-current levels below 10−9 A/μm. In addition, the polarity of the same doping-free device can be dynamically switched between unipolar p- and n-type function, without the use of any dopants. This feature offers a variety of disrupting circuit design possibilities not accessible with CMOS, for example in the area of hardware security [l].

Superhard silicon carbide-bonded diamond materials were synthesized by liquid silicon infiltration of diamond-containing preforms. The properties of the materials were strongly influenced by the strength of the interfaces between the diamond and the silicon carbide. Interface formation was investigated through local analysis of the microstructure in the interface regions using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) as well as X-ray diffraction (XRD). The results of these experiments revealed a pronounced orientation relationship between SiC and diamond at their interfaces and, as a result, strong bonding of the diamond particles to the ceramic matrix. There was also an orientation relationship between the nano-sized SiC grains, which were embedded in residual silicon near the diamond interfaces, and diamond. Additionally, the different morphologies and phenomena occurring in the microstructures of the diamond-SiC composites and their dependence on the infiltration temperature were studied.

The time dependent dielectric breakdown (TDDB) in copper/ultra-low-k on-chip interconnect stacks of integrated circuits has become one of the most critical reliability concerns in recent years. In this paper, a novel experimental in situ microscopy approach using transmission X-ray microscopy (TXM) and scanning transmission electron microscopy (STEM) is proposed to study TDDB degradation and failure mechanisms. It combines electrical testing and imaging techniques. Low-dose bright field (BF) STEM inserting a small condenser aperture is chosen to reduce the beam damage of the dielectric material, while the electron spectroscopic imaging technique is used for the chemical analysis to detect the migration path of Cu atoms. This new experimental approach will contribute to an improved understanding of the TDDB effect.

Within a DFM type of methodology, the application of physics-based models for a multi-scale simulation of mechanical stress in 3D TSV-stacked products was proposed in [1]. Highly accurate multi-scale materials data are needed as input for this approach of simulation and for model validation. This paper focuses on the set of materials data for wafer-level and package-level structures, needed to feed a materials database that comprises the input parameters for simulation. Particularly the generation of materials data such as (local and effective) Young's modulus, Poisson ratio and (effective) coefficients of thermal expansion (CTE) on several scales will be described. The nanoindentation method was developed further to measure local and effective elastic modulus values and Poisson ratio for micro-bump, TSV and BEoL stacks. TCAD simulations show significant influence of the copper microstructure on the charge carrier mobility in transistors [2]. To consider the orientation dependence of elastic properties of copper, nanoindentation with extremely low penetration depths was applied. A high-resolution in-situ technique was developed to determine “composite CTE” values for BEoL stacks. A free-standing cantilever containing the region of interest was extracted using the FIB technique, and imaged in a SEM at several temperatures. For model validation and calibration, local stress measurements are needed to determine the effect of the TSV/package-induced stress on the transistor performance. Due to the high resolution needed, the only direct technique to measure strain in transistor channels is TEM. For the first time, the strain in transistor channels will be reported as a function of the distance from the TSV, based on Convergent Beam Electron Diffraction (CBED) data.

The effect of point defects, dislocations and grain boundaries on the electron scattering in molybdenum thin films having a constant thickness of 500 nm was described quantitatively in form of a dependence of the electrical resistivity on the concentration of impurity atoms, stress-free lattice parameter, microstrain and grain size. The concentration of impurity atoms and the dislocation density were modified by depositing the Mo thin films using different techniques (DC magnetron sputtering, pulsed DC magnetron sputtering and RF magnetron sputtering) and by varying the substrate temperature (25 °C, 150 °C, 250 °C and 350 °C). As expected, the electrical resistivity of the Mo films decreased with decreasing density of microstructure defects. For all deposition methods, the dislocation density decreased with increasing substrate temperature, which led to an overall decrease of the measured resistivity with increasing substrate temperature. Due to the deposition equipment constraints during the RF sputtering, up to 3 at.% of Fe, Cr and Ni were incorporated at the regular lattice positions in the crystal structure of molybdenum, which increased the resistivity of the Mo films nearly two times as compared to the DC and pulsed DC sputtered films.

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. The aggressive scaling of feature sizes, on both devices and interconnects, poses serious challenges to ensure the required product reliability. Conventional reliability tests and postmortem failure analysis provide only limited information about the physics of failure mechanisms and degradation kinetics. Therefore, it is necessary to develop new experimental approaches and procedures to study the time-dependent failure mechanisms and degradation kinetics, in particular. In this paper, comprehensive transmission electron microscopy (TEM), particularly an in situ experimental methodology, is demonstrated to investigate the TDDB degradation and failure mechanisms in Cu/low-k interconnect stacks. A dedicated “tip-to-tip” test structure is designed in the 32-nm complementary metal–oxide–semiconductor (CMOS) technology node, to restrict the failure site, and is the key basis for the in situ and ex situ TEM investigations. High-quality imaging and chemical analysis are used to identify the failure mechanism and study the kinetic process. The in situ electrical test is also integrated into the in situ TEM investigation, to provide an elevated electric field to the dielectrics. Electron tomography is utilized to characterize the directed Cu diffusion in the insulating dielectrics. These experimental approaches open a different possibility to study the TDDB failure mechanism in interconnect stacks of microelectronic products, and it could also be extended to other structures in active devices.

A novel approach to deposit GaN layers directly on a sapphire substrate by Hydride Vapor Phase Epitaxy is presented. The two-step deposition process includes the growth of GaN nucleation layers at intermediate temperatures in the range of 750 – 900 °C and subsequent high-temperature overgrowth at about 1040 °C. Closed and non-closed nucleation layers with a thickness of up to 2 μm were produced and characterized by scanning and transmission electron microscopy, micro-Raman spectroscopy and X-ray diffraction. A growth temperature of 780 °C is found to be optimal with respect to density and size distribution of nucleation islands. Raman measurements performed on the nucleation layers reveal nearly zero residual stress indicating effective stress relaxation on cooling down from growth temperature. The results of first overgrowth experiments demonstrate the possibility to grow 10 μm thick, crack-free GaN layers of high crystalline quality on the nucleation layers. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of the carbon ion energy applied in a pulsed arc deposition process on the morphology of the interface between Cr layers and subsequently deposited tetrahedral bonded carbon (ta-C) coatings was investigated. The carbon ion energy was varied through the bias voltage between ~ 25 and 500 eV. Small-angle and wide-angle X-ray scattering (SAXS and WAXS), high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) were used as the central experimental methods for microstructure analysis. In order to improve the scattering power of the ta-C/Cr interfaces for SAXS, the samples were prepared in the form of ta-C/Cr multilayers. SAXS revealed density and thickness of individual layers in the multilayer stack, and the roughness and morphology of the ta-C/Cr interfaces. The density of ta-C layers ranged between 2.72 and 3.15 g/cm 3 , which was related to the amount of sp 3 bonds between 37% and 71%. The amount of the sp 3 bonds calculated from the density of the ta-C layers agreed well with the amount of the sp 3 bonds determined using EELS. HRTEM confirmed both the increase of the interface roughness with increasing carbon ion energy and the changes in the correlation of the interface corrugations observed by SAXS. Furthermore, HRTEM approved the crystallinity of Cr layers revealed by WAXS.

TiCxN1-x base layers with Al2O3 top layers, both grown by chemical vapour deposition (CVD), are state-of-the-art in metal cutting with cemented carbide inserts. In order to influence the microstructure and properties of the base layer, five different TiCxN1-x coatings were grown by medium-temperature CVD with increasing CO fractions in the TiCl4–CH3CN–H2–N2–CO feed gas using an industrial-scale low-pressure CVD system. With the CO fraction in the feed gas rising up to 2.2 vol.%, oxygen contents of 2.2. at.% could be detected, which are distributed homogeneously over the coating thickness. The originally equiaxed TiCxN1-x grains with preferred {110} orientation obtained without CO addition change to randomly distributed plate-like grains, while the grain size decreases to the sub-micron range. Also the surface roughness decreases with rising CO addition. The incorporation of oxygen leads to a homogenous distribution of dislocations within the TiCxN1-x grains and to an increasing density of twin boundaries. The residual tensile stress shows a minimum of 200 ± 47 MPa, while the hardness increases to 29.1 ± 1.3 GPa and the elastic modulus reaches a maximum 569 ± 29 GPa for CO fractions of 1.5 vol.% in the feed gas.

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. The aggressive scaling of feature sizes, both on devices and interconnects, leads to serious challenges to ensure the required product reliability. Standard reliability tests and post-mortem failure analysis provide only limited information about the physics of failure mechanisms and degradation kinetics. Therefore it is necessary to develop new experimental approaches and procedures to study the TDDB failure mechanisms and degradation kinetics in particular. In this paper, an in situ experimental methodology in the transmission electron microscope (TEM) is demonstrated to investigate the TDDB degradation and failure mechanisms in Cu/ULK interconnect stacks. High quality imaging and chemical analysis are used to study the kinetic process. The in situ electrical test is integrated into the TEM to provide an elevated electrical field to the dielectrics. Electron tomography is utilized to characterize the directed Cu diffusion in the insulating dielectrics. This experimental procedure opens a possibility to study the failure mechanism in interconnect stacks of microelectronic products, and it could also be extended to other structures in active devices.

Dense nanocomposites consisting of titanium nitride (TiN) and 1.7–8.1 mol% silicon nitride (a-Si3N4) have been prepared by high-pressure sintering at 6.5 GPa and at temperatures up to 1300 °C. Microstructure, hardness, indentation fracture toughness, elastic modulus and the correlation of these parameters to the silicon nitride content of the obtained TiN–Si3N4 ceramics have been determined. The results demonstrate that even the addition of small amounts of Si3N4 leads to a considerable increase in Vickers hardness to HV500 g ∼ 25 GPa and indentation fracture toughness up to 6 MPa m½. This significant enhancement of mechanical properties can be related to interfacial bonds between titanium nitride crystals strengthened by nano-size effects and amorphous silicon nitride forming an intergranular matrix. Realignment and rotation of such interlocked titanium nitride crystallites under deformational stress is suppressed and crack propagation reduced by a crack deflection mechanism.

Display Omitted We studied the TDDB-induced damage mechanism in Cu/ULK structures in-situ.The methodology combined TEM imaging, ESI analysis and in-situ electrical testing.Three major TDDB-induced damage mechanisms were observed.The breakdown spot depends on the materials, geometry and the degradation effects.The results highlight the importance of the quality of the deposition process for the Ta-based barrier. The time-dependent dielectric breakdown (TDDB) mechanism in Cu/ultra-low-k (ULK) on-chip interconnect structures has been raising serious reliability concerns for state-of-the-art microelectronic devices in recent years. An advanced experimental methodology, which combines transmission electron microscopy (TEM) imaging and an in-situ electrical test using a Hysitron PI95 TEM holder, was used to study TDDB-induced damage mechanisms and degradation kinetics in Cu/ULK interconnect structures. In flawless Cu/ULK interconnect structures with locally very thin Ta-based barriers, slow but massive Cu migration into the SiO2 layer was observed at the bottom corner of the M1 metal after the TaN/Ta barrier had been firstly ruptured by the Ta migration, driven by the high electrical field. More importantly, it was found that both the high electric field and the massive metal migration into the SiO2 can contribute to the final breakdown of the Cu/ULK interconnect structures. The final breakdown spot could be located either at the interface of the SiCN layer and the ULK material or in the SiO2 layer, which depends on the geometry, the kind of dielectric materials (particularly ULK) and the driving force (the high electric field). The results also highlight the importance of the quality of TaN/Ta barrier deposition process, especially at the bottom corner of the M1 metal, to ensure the functionality of the TaN/Ta barriers during the product lifetimes.

The present study describes the application of hot deformation experiments and microstructure investigations in order to predict the deformation behaviour of uncoated and TBC-coated superalloys NiCr22Co12Mo9 and CoCr22Ni22W14. Estimating parameters like dislocation density and carbide spacing by transmission electron microscopy (TEM), the hot tensile, creep and relaxation behaviour has been connected with the evolution of microstructure. The results of mechanical tests and the TEM-investigations have been used as input data into two models (an effective stress model and a modified constitutive model by Kocks–Mecking), which describe the deformation behavior. The deterioration in the creep properties of the alloy NiCr22Co12Mo9 as a result of coating was a result both of the degraded state of the M 23 C 6 -precipitate in the substrate metal, and of the weakening of the solid solution- and precipitation hardening mechanisms responsible for the creep strength of the material, in the region of the boundary surface.

Relaxation of residual stresses in metallic materials is caused by diffusion of inhomogeneously distributed solved alloying elements and by microstructural mechanisms like rearrangements of dislocation structure and precipitation processes, respectively. Both processes are often linked with each other. Therefore, the description and the modelling of stress relaxation on a microstructural basis is very complicated. The aim of this study was to demonstrate some models for stress relaxation in metallic materials. The paper presents the relaxation of tensile loading stresses in Ni-based and Co-based superalloys at high temperatures. In stress relaxation tests the microstructure development was connected with a rearrangement of the dislocation structures and by a decreasing dislocation density. The stress relaxation in carbide strengthened superalloys is a typical case of dislocation relaxation in the presence of precipitations. By including the determined microstructure parameters, the effective stress model and also a constitutive model yields to qualitatively correct predictions of the tensile and relaxation behaviour.

This paper presents the application of an effective stress model for modelling the creep and tensile behaviour of superalloys in a large range of temperature and strain rates. It is the aim of the microstructure investigations to estimate parameters like dislocation density and particle spacing for a microstructure related modelling using physical equations. A common log g3-log σ plot of tensile and creep data shows a systematic shift of about 10% towards higher stresses in tension compared to creep. The dislocation densities measured by TEM, agree quite well with those, determined by the evolution equation of the model, introducing a time dependent term. The simulation of creep and tensile curves shows satisfying results. With this model, it is possible to describe quite well the type of the primary creep curves as well as the starting point of the steady-state region.

The present study describes the application of hot tension experiments in order to predict the creep and tensile behaviour of the highly loaded superalloy CoCr 2 2Ni 22 W 14 . The results of mechanical tests and transmission electron microscopy (TEM) investigations have been used as input data in a model which describes the high temperature plastic deformation. A common log ɛ - log σ plot of tensile and creep data shows a systematic shift of about 10% towards higher stresses in the case of tensile loading. In creep tests the dislocation densities reach their steady-state values at the points of minimal strain rates, whereas in tensile tests the dislocation densities increase at any given time until the tensile strength is reached at significantly higher strains. Under the condition of equal true stresses subgrain formation is more pronounced after tensile than after creep deformation. By including the experimentally determined dislocation densities, the constitutive model yields qualitatively correct predictions of the creep and tensile behaviour.

This study captures the time-dependent dielectric breakdown kinetics in nanoscale Cu/low-k interconnect structures, applying in-situ transmission electron microscopy (TEM) imaging and post-mortem electron spectroscopic imaging (ESI). A “tip-to-tip” test structure and an experimental methodology were established to observe the localized damage mechanisms under a constant voltage stress as a function of time. In an interconnect structure with partly breached barriers, in-situ TEM imaging shows Cu nanoparticle formation, agglomeration and movement in porous organosilicate glasses. In a flawless interconnect structure, in-situ TEM imaging and ESI mapping show close to no evidence of Cu diffusion in the TDDB process. From the ESI mapping, only a narrow Cu trace is found at the SiCN/OSG interface. In both cases, when barriers are breached or still intact, the initial damage is observed at the top interface of M1 between SiCN and OSG.

Numerous metallurgical investigations require the detailed microstructural characterisation of the surface regions of a sample by transmission electron microscopy (TEM). To carry out such analysis, the region of interest must be thinned down to a thickness of only a few hundred nanometres, through which the electron beam can pass. Thus, for each combination of materials to be examined, the optimum method of preparation must be found to produce the electron transparent specimen (disc) required. The preparation of the disc consists of numerous individual manual and sometimes complicated instrumental steps, each of which must be optimised to deal efficiently with the broad range of materials possible. It is however most important that each step in the preparation carried out by the TEM laboratory is modular and compatible with both the previous and subsequent steps. The development of a preparation programme for a particular material is thus reduced to determining the optimum preparation route. As examples of this, various different routes are discussed by which the following samples were prepared for TEM-examination: The cobalt based super-alloy CoCr22Ni22W14 after creep, a plasma sprayed thermal insulation coating applied to the nickel based super-alloy NiCr22Co12Mo9, a TiAIN-PVD coating, the surface layer region of a shot-blast SAE 1045 steel specimen after fatigue, and individual defects in vertically gradient-freeze solidified GaAs.

One possibility of evaluating the primary creep behaviour of the alloy CoCr22Ni22W14 is presented using the microstructural data obtained from TEM experiments. Due to the complex precipitation behaviour of the alloy at 1123 K it is necessary to investigate the evolution of the mean free path of the dislocations caused by forest dislocations and precipitations. Measured and modelled dislocation densities and the simulated creep curves are presented for creep under constant loading at 1123 K. The model used has no requirement for a weighting factor of strengthening caused by particles or dislocations and differs from Kocks and Mecking's approach using microstructural data from TEM.

Vacuum annealing is a widely used method to increase the electric conductivity of SrTiO3 single crystals. The induced oxygen vacancies act as intrinsic donors and lead to n-type conductivity. Apart from the changed electronic structure, however, also crystal structure modifications arise from this treatment. Hence, electronic properties are determined by the interplay between point defects and line defects. The present paper provides a survey of the real structure of commercially available SrTiO3 single crystals and the changes induced by reducing vacuum heat-treatment. Therefore, all investigations were performed ex situ, i.e., after the annealing process. Used characterization methods include atomic force microscopy, transmission electron microscopy, spectroscopic ellipsometry, infrared spectroscopy, and photoluminescence spectroscopy. Besides the expected variation of bulk properties, especially surface modifications have been detected. The intrinsic number of near-surface dislocations in the samples was reduced by vacuum annealing. X-ray photoelectron spectroscopy proves the existence of a layer of adsorbed molecules, which influences the SrTiO3 work function. Also, the interaction between adsorbates and surface point defects as well as laser annealing due to local oxygen absorption are discussed.

Thermal barrier coatings (TBC) have the potential to improve considerably the efficiency of stationary gas or aircraft turbines by increasing the operating temperature. This report describes the use of creep experiments and microstructure investigations in order to predict the deformation behavior of uncoated and TBC-coated superalloys NiCr22Co12Mo9 and CoCr22Ni22W14. The results of mechanical tests and transmission electron microscopy investigations have been used as input data into two models in order to describe the hot deformation behavior. The deterioration in the creep properties of the superalloy NiCr22Co12Mo9 as a result of coating was due to the degraded state of the M 23 C 6 precipitates in the substrate metal, as well as to the weakening of the solid solution- and precipitation-hardening mechanisms responsible for the creep strength of the material, in the region of the boundary surface.