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Electromigration occurs when a high current density drives atomic motion from the cathode to the anode end of a conductor, such as a metal interconnect line in an integrated circuit. While electromigration eventually causes macroscopic damage, in the form of voids and hillocks, the earliest stage of the process when the stress in individual micron-sized grains is still building up is largely unexplored. Using synchrotron-based x-ray microdiffraction during an in-situ electromigration experiment, we have discovered an early prefailure mode of plastic deformation involving preferential dislocation generation and motion and the formation of a subgrain structure within individual grains of a passivated Al (Cu) interconnect. This behavior occurs long before macroscopic damage (hillocks and voids) is observed.

Electromigration during accelerated testing can induce plastic deformation in apparently undamaged Al interconnect lines as recently revealed by white beam scanning x-ray microdiffraction. In the present article, we provide a first quantitative analysis of the dislocation structure generated in individual micron-sized Al grains during an in situ electromigration experiment. Laue reflections from individual interconnect grains show pronounced streaking during the early stages of electromigration. We demonstrate that the evolution of the dislocation structure during electromigration is highly inhomogeneous and results in the formation of unpaired randomly distributed dislocations as well as geometrically necessary dislocation boundaries. Approximately half of all unpaired dislocations are grouped within the walls. The misorientation created by each boundary and density of unpaired individual dislocations is determined. The origin of the observed plastic deformation is considered in view of the constraints f...

Scanning X-ray microdiffraction (microSXRD) combines the use of high-brilliance synchrotron sources with the latest achromatic X-ray focusing optics and fast large-area two-dimensional-detector technology. Using white beams or a combination of white and monochromatic beams, this technique allows for the orientation and strain/stress mapping of polycrystalline thin films with submicrometer spatial resolution. The technique is described in detail as applied to the study of thin aluminium and copper blanket films and lines following electromigration testing and/or thermal cycling experiments. It is shown that there are significant orientation and strain/stress variations between grains and inside individual grains. A polycrystalline film when investigated at the granular (micrometer) level shows a highly mechanically inhomogeneous medium that allows insight into its mesoscopic properties. If the microSXRD data are averaged over a macroscopic range, results show good agreement with direct macroscopic texture and stress measurements.

In their comment (M. Lagos et al., Scripta Mater. (2012), http://dx.doi.org/10.1016/j.scriptamat.2012.04.018 ), Lagos et al. propose a two-dimensional plasticity model based on grain boundary sliding to explain the deformation behavior of ultrathin Cu and Ta/Cu film systems on polyimide substrates. Here, we critically discuss their comments and include new results obtained by peak profile analysis of the original in situ diffraction data; they strongly suggest that the deformation behavior of the different film systems is very likely not self-similar as claimed by Lagos et al.

The availability of high brilliance third generation synchrotron sources together with progress in achromatic focusing optics allows us to add submicron spatial resolution to the conventional century-old x-ray diffraction technique. The new capabilities include the possibility to map in situ, grain orientations, crystalline phase distribution, and full strain/stress tensors at a very local level, by combining white and monochromatic x-ray microbeam diffraction. This is particularly relevant for high technology industry where the understanding of material properties at a microstructural level becomes increasingly important. After describing the latest advances in the submicron x-ray diffraction techniques at the Advanced Light Source, we will give some examples of its application in material science for the measurement of strain/stress in metallic thin films and interconnects. Its use in the field of environmental science will also be discussed.

Metallic reactive multilayers are known as high energy-density storage systems. Conventionally, these multilayers are tailored for high reaction rates with the purpose to achieve high maximum reaction temperatures and explosive-like behavior upon mixing. However, in some instances such as neutralization of biological hazards or chemical energy-storage systems, a low heat flow rate is desired. In the present work, we show that Nb-alloying presents an efficient approach to stabilize the as-deposited state and to form a diffusion barrier in situ, effectively reducing the heat flow rate by more than 50%. The validation of the concept is carried out by a comparative study of thermally induced phase reactions in Ni/Al and (Nb-Ni)/Al reactive multilayers. Kinetics of the phase reactions in these systems were followed by differential scanning calorimetry, analytical scanning transmission electron microscopy, and in situ electron diffraction analysis. The results confirm alloying as a design strategy for tailoring...

Currently, the focus of additive manufacturing (AM) is shifting from simple prototyping to actual production. One driving factor of this process is the ability of AM to build geometries that are not accessible by subtractive fabrication techniques. While these techniques often call for a geometry that is easiest to manufacture, AM enables the geometry required for best performance to be built by freeing the design process from restrictions imposed by traditional machining. At the micrometer scale, the design limitations of standard fabrication techniques are even more severe. Microscale AM thus holds great potential, as confirmed by the rapid success of commercial micro-stereolithography tools as an enabling technology for a broad range of scientific applications. For metals, however, there is still no established AM solution at small scales. To tackle the limited resolution of standard metal AM methods (a few tens of micrometers at best), various new techniques aimed at the micrometer scale and below are presently under development. Here, we review these recent efforts. Specifically, we feature the techniques of direct ink writing, electrohydrodynamic printing, laser-assisted electrophoretic deposition, laser-induced forward transfer, local electroplating methods, laser-induced photoreduction and focused electron or ion beam induced deposition. Although these methods have proven to facilitate the AM of metals with feature sizes in the range of 0.1-10 µm, they are still in a prototype stage and their potential is not fully explored yet. For instance, comprehensive studies of material availability and material properties are often lacking, yet compulsory for actual applications. We address these items while critically discussing and comparing the potential of current microscale metal AM techniques.

Improving the esthetics of Ti-based dental implants is the last challenge remaining in the optimization process. The optical issues were recently solved by the application of highly and selectively reflective coatings on Ti implants. This work focuses on the mechanical durability of these esthetic ceramic based coating systems (with and without adhesion layers). The coating systems (Ti-ZrO2, Ti-Al-ZrO2, Ti-Ti-Al-ZrO2, Ti-Ag-ZrO2, Ti-Ti-Ag-ZrO2, Ti-Bragg and Ti-TiO2-Bragg) were subjected to nanoindentation experiments and examined using scanning electron microscopy and focused ion beam cross sectional analysis. Three coating systems contained adhesion layers (10nm of Ti or 60nm of TiO2 layers). The fracture toughness of selected samples was assessed applying two different models from literature, a classical for bulk materials and an energy-based model, which was further developed and adjusted. The ZrO2 based coating systems (total film thickness

Patterning of ultra-dense, large-area lines down to 11 nm half-pitch using extreme ultraviolet (EUV) interference lithography with two types of inorganic photoresist is shown. The resist patterns are transferred using plasma etching into silicon (Si) for both types of resist. 14 nm half-pitch silicon nanowires with 1∶1 aspect ratio and square cross-sectional profile using a hafnium oxide based resist was achieved. For a silicon oxide based resist, the etching selectivity was shown to be critical, and a variety of etching strategies to overcome this deficiency are discussed.

Recent demonstrations of light emission from group IV materials such as Ge and its alloy with Sn renew the vision for the realization of an all group IV based opto-electronic platform. We compare some of these approaches to our strain method and mention rewarding research to further improve materials and concepts.

Journal of Synchrotron Radiation, 21 (1), ISSN:0909-0495, ISSN:1600-5775

Ion-beam irradiation is conventionally used to tune the electronic properties of semiconductors or as a "surrogate" for the study of radiation damage. Recently, it has also been employed for microstructure engineering, namely non-selective and selective grain growth. An even more interesting phenomenon is ion-induced crystal or texture rotation in thin metallic films. This couples an extensive crystal rotation with no significant modification of the grain/film morphology. The present work concentrates on the study of microstructural mechanisms of the phenomenon. A combination of in situ transmission electron microscopy irradiation experiments and finite element simulations reveals that the effect stems from a directional motion of gliding dislocations that is driven by the anisotropic stress field induced in the material surrounding the ion track. The hindrance of dislocation glide at the grain boundaries forces the crystal to relax through a crystal rotation. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Since the pioneering work of Turing on the formation principles of animal coat patterns [Turing AM (1952) Phil Trans R Soc Lond B 237(641):37-72], such as the stripes of a tiger, great effort has been made to understand and explain various phenomena of self-assembly and pattern formation. Prominent examples are the spontaneous demixing in emulsions, such as mixtures of water and oil [Herzig EM, et al. (2007) Nat Mater 6:966-971]; the distribution of matter in the universe [Kibble TWB (1976) J Phys A: Math Gen 9(8):1387]; surface reconstruction in ionic crystals [Clark KW, et al. (2012) Nanotechnol 23(18):185306]; and the pattern formation caused by phase transitions in metal alloys, polymer mixtures and binary Bose-Einstein condensates [Sabbatini J, et al. (2011) Phys Rev Lett 107:230402]. Photoactivated pattern formation in functional polymers has attracted major interest due to its potential applications in molecular electronics and photoresponsive systems. Here we demonstrate that photoactivated pattern formation on azobenzene-containing polymer films can be entirely explained by the physical concept of phase separation. Using experiments and simulations, we show that phase separation is caused by an instability created by the photoactivated transitions between two immiscible states of the polymer. In addition, we have shown in accordance with theory, that polarized light has a striking effect on pattern formation indicated by enhanced phase separation.

At the Advanced Light Source in Berkeley we have instrumented a beam line that is devoted exclusively to X-ray micro-diffraction problems. By micro-diffraction we mean those classes of problems in Physics and Materials Science that require X-ray beam sizes in the sub-micron range. The instrument is for instance, capable of probing a sub-micron size volume inside micron-sized aluminum metal grains buried under a silicon dioxide insulating layer. The resulting Laue pattern is collected on a large area CCD detector and automatically indexed to yield the grain orientation and deviatoric (distortional) strain tensor of this sub-micron volume. A four-crystal monochromator is then inserted into the beam, which allows monochromatic light to illuminate the same part of the sample. Measurement of the diffracted photon energy allows for the determination of d spacings. The combination of white and monochromatic beam measurements allow for the determination of the total strain/stress tensor (6 components) inside each sub-micron-sized illuminated volume of the sample.

A deep understanding of the appearance and distribution of residual stresses in ZnO is of high importance as mechanical stresses directly influence its electrical and optical properties. In this paper we investigate the correlation between residual stresses and the plastic deformation below a micro indent placed on a prism plane of a ZnO single crystal. The residual stress field was mapped by means of confocal Raman microscopy. A cross section was studied by transmission electron microscopy and cathodoluminescence to visualize defect structures. In the Raman measurement bands of residual stresses were observed. The analysis of the defect structure showed that the residual stress distribution corresponds to crystallographic directions which are known to be the preferred directions for plastic deformation. The preparation of lamellae by FIB strongly alters both the residual stress state as well as the defect density caused by plastic deformation.

Electron/hole lifetimes in thermally strained Ge layers on Si are deduced from time-resolved infrared pump-probe transmission spectroscopy. A doping scheme with n-doped Ge on intrinsic Ge yields maximum lifetimes of approximately 3 ns.

We present a stressor-free fabrication approach for creating 3.1% uniaxial tensile strain in Ge layers resulting in a 25× increase in PL intensity. 460 cm-1 gain is predicted for aforementioned strain and 1×1019 cm-3 n-doping.

Tensile strain is a widely discussed means for inducing a direct bandgap in Ge for the realization of a semiconductor laser compatible with Si microelectronics. We present a top down fabrication approach for creating high uniaxial tensile stress in suspended Ge structures which enhances by a factor of more than 20 the strain induced by thermal mismatch of Ge layers grown on silicon or silicon on insulator substrates. Strain values up to 3.1 are measured using Raman spectroscopy in excellent agreement with simulations using a biaxial thermal strain of 0.15. As expected from the high value of strain a 210 meV peak energy shift in the emission with respect to bulk Ge and a strong increase (×25) in the integrated photoluminescence intensity are observed. Although 3.1 uniaxial strain does not transform Ge into a direct gap material our model calculation predicts an optical gain of 460 cm 1 for 1 × 10 19 cm 3 n doped structures at an electron hole injection density of 3 × 10 19 cm 3. © 2013 Macmillan Publishers Limited. All rights reserved.

Journal of Nanoparticle Research, 15 (3), ISSN:1388-0764, ISSN:1572-896X

Heterogeneous composite materials with variable local stiffness are widespread in nature, but are far less explored in engineering structural applications. The development of heterogeneous synthetic composites with locally tuned elastic properties would allow us to extend the lifetime of functional devices with mechanically incompatible interfaces, and to create new enabling materials for applications ranging from flexible electronics to regenerative medicine. Here we show that heterogeneous composites with local elastic moduli tunable over five orders of magnitude can be prepared through the site-specific reinforcement of an entangled elastomeric matrix at progressively larger length scales. Using such a hierarchical reinforcement approach, we designed and produced composites exhibiting regions with extreme soft-to-hard transitions, while still being reversibly stretchable up to 350%. The implementation of the proposed methodology in a mechanically challenging application is illustrated here with the development of locally stiff and globally stretchable substrates for flexible electronics.

Structural colors have drawn wide attention for their potential as a future printing technology for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realize robust colors with a scalable fabrication technique is still lacking, hampering the realization of practical applications with this platform. Here, we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless, ultra-thin dielectric coatings. By using theory and experiments, we show how subwavelength dielectric coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network, generating the formation of saturated structural colors that cover a wide portion of the spectrum. Ellipsometry measurements support the efficient observation of these colors, even at angles of 70°. The network-like architecture of these nanomaterials allows for high mechanical resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technology for real-world, large-scale commercial applications., Light: Science & Applications, 6, ISSN:2047-7538

The ultimate aim of this study is to construct polymer nanocomposite patterns by dip-pen nanolithography (DPN). Recent investigations have revealed the effect of the amount of ink (Laplace pressure) on the mechanism of liquid ink writing. In this study it is shown that not only the amount of ink, but also physisorption and surface diffusion are relevant. After a few writing steps, physisorption and surface diffusion outweigh the influence of the amount of ink, allowing consistent patterning governed by dwell times and writing speeds. Polymer matrices can be utilized as a delivery medium to deposit functional particles. DPN patterning of polymer nanocomposites allows for local tuning of the functionality and mechanical strength of the written patterns in high resolution, with the benefit of pattern flexibility. Typically polymer matrices with volatile components are used as a delivery medium for nanoparticle deposition, with subsequent removal of loosely bound matrix material by heating or oxygen plasma. In our study, nanocomposite patterns were constructed, and the differences between polymer and nanocomposite patterning were investigated. Cross-sectional SEM and TEM analysis confirmed that nanoparticles can be deposited with the liquid-polymer ink and are evenly distributed in the polymer matrix.

Strained Si nanowires are among the most promising transistor structures for implementation in very large scale integration due to of their superior electrostatic control and enhanced transport properties. Realizing even higher strain levels within such nanowires are thus one of the current challenges in microelectronics. Here we achieve 4.5 of elastic strain (7.6 GPa uniaxial tensile stress) in 30 nm wide Si nanowires which considerably exceeds the limit that can be obtained using SiGe based virtual substrates. Our approach is based on strain accumulation mechanisms in suspended dumbbell shaped bridges patterned on strained Si on insulator and is compatible with complementary metal oxide semiconductor fabrication. Potentially this method can be applied to any tensile prestrained layer provided the layer can be released from the substrate enabling the fabrication of a variety of strained semiconductors with unique properties for applications in nanoelectronics photonics and photovoltaics. This method also opens up opportunities for research on strained materials. © 2012 Macmillan Publishers Limited. All rights reserved.

We investigate tensile strained Ge/Si 1 − x Ge x ( x = 0.87) multiple quantum wells (MQW) on a Ge virtual substrate abruptly grown on Si for integration in CMOS technology. Two schemes are discussed – Scheme A in situ growth of the MQW stack combined with post-growth rapid thermal annealing (RTA) and Scheme B re-growth of the MQW stack on an RTA strain optimized Ge-VS. Samples are characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning transmission electron microscopy, Brewster transmission and photo-reflectance spectroscopy. The strain in the as-grown virtual substrate of Scheme A , measured with Raman spectroscopy and XRD, increases from 0.17% to 0.24% after RTA to 850 °C. XRD reveals an activated inter-diffusion of the MQWs and, at the highest temperatures ( T RTA > 750 °C), a structural relaxation. The MQWs of Scheme B appear to be of inferior quality. The inter-band transitions in this material are comparatively blue shifted and broad, which is attributed to relaxation induced dislocations at the interface between the virtual substrate and the multiple quantum wells.

We have used scanning white beam x-ray microdiffraction to study microstructural evolution during an in situ electromigration experiment on a passivated Al(Cu) test line. The data show plastic deformation and grain rotations occurring under the influence of electromigration, seen as broadening, movement, and splitting of reflections diffracted from individual metal grains. We believe this deformation is due to localized shear stresses that arise due to the inhomogeneous transfer of metal along the line. Deviatoric stress measurements show changes in the components of stress within the line, including relaxation of stress when current is removed.

The availability of high brilliance synchrotron sources, coupled with recent progress in achromatic focusing optics and large area 2D detector technology, have allowed us to develop an X-ray synchrotron technique capable of mapping orientation and strain/stress in polycrystalline thin films with submicron spatial resolution. To demonstrate the capabilities of this instrument, we have employed it to study the microstructure of aluminum thin film structures at the granular and subgranular level. Owing to the relatively low absorption of X-rays in materials, this technique can be used to study passivated samples, an important advantage over most electron probes given the very different mechanical behavior of buried and unpassivated materials.

Highly porous Pt/Al thin film electrodes on yttria-stabilized zirconia electrolytes were prepared by dealloying of co-sputtered Pt/Al films. The oxygen reduction capability of the resulting electrodes was analyzed in a solid oxide fuel cell setup at elevated temperatures. During initial heating to 523 K, exceptionally high performances compared to conventional Pt thin film electrodes were measured. This results from the high internal surface area and large three phase boundary length obtained by the dealloying process. Exposure to elevated temperatures of 673 or 873 K gave rise to degradation of the electrode performance, which was primarily attributed to the oxidation of remaining Al in the thin films.

Applying focused ion beam (FIB) nanotomography and Rutherford backscattering spectroscopy (RBS) to dealloyed platinum-aluminum thin films an in-depth analysis of the dominating physical mechanisms of porosity formation during the dealloying process is performed. The dynamical porosity formation due to the dissolution of the less noble aluminum in the alloy is treated as result of a reaction-diffusion system. The RBS analysis yields that the porosity formation is mainly caused by a linearly propagating diffusion front, i.e. the liquid/solid interface, with a uniform speed of 42(3) nm/s when using a 4M aqueous NaOH solution at room temperature. The experimentally observed front evolution is captured by the normal diffusive Fisher-Kolmogorov-Petrovskii-Piskounov (FKPP) equation and can be interpreted as a branching random walk phenomenon. The etching front produces a gradual porosity with an enhanced porosity in the surface-near regions of the thin film due to prolonged exposure of the alloy to the alkaline solution., Comment: 4 pages, 5 figures

The seed-mediated method in presence of high concentrations of CTAB is frequently implemented in the preparation of high aspect ratio gold nanorods (i.e., nanorods with aspect ratios of 5 or more); however, the reproducibility has still been limited. We rendered the synthesis procedure simpler, decreased the susceptibility to impurities, and improved the reproducibility of the product distribution. As a result of the high aspect ratios, longitudinal plasmon absorptions were shifted up to very high absorption maxima of 1955 nm in UV-vis-NIR spectra (since this band is completely covered in aqueous solution by the strong absorption of water, the gold species were embedded in poly(vinyl alcohol) films for UV-vis-NIR measurements). Finally, the directed particle growth in (110) direction leads to the conclusion that the adsorption of CTAB molecules at specific crystal faces accounts for nanorod growth and not cylindrical CTAB micelles, in agreement with other observations., Journal of Nanomaterials, 2011, ISSN:1687-4129, ISSN:1687-4110

JOM, 62 (12), ISSN:1047-4838, ISSN:0148-6608, ISSN:1543-1851

Applied Physics A, 100 (1), ISSN:0947-8396, ISSN:1432-0630, ISSN:0340-3793

Raman microscopy provides the unique possibility to measure stresses in a fast and uncomplicated way in the sub-micrometer range. The maximal lateral resolution is determined by the laser wavelength. In a Raman spectrum of a deformed or strained material, peak positions are shifted relative to the peak positions of stress-free material. Quantifying these shifts allows the determination of sign and magnitude of internal stresses. Depending on the Raman tensor and therefore on the material’s crystal structure, several components of the stress tensor can be measured. Hence, it is not always possible to analyze complicated stress states just by means of Raman microscopy without making adequate assumptions. For transparent Raman-active materials, three-dimensional stress fields can be measured. This chapter will outline the principles of Raman stress measurements and present case studies on ceramics, semiconductors and polymers.

In situ synchrotron radiation diffraction and confocal light microscopy is used to study fragmentation and buckling of thin brittle Ta layers with thicknesses of 50 nm, 100 nm and 200 nm on polyimide substrates. Synchrotron‐based stress measurements confirm that cracking leads to relaxation of tensile stress. Simultaneously, compressive stress arises in transverse direction, which finally leads to buckling. This behavior can be explained quantitatively by a two‐dimensional shear lag model. It is well established that the properties of the coating‐substrate interface determine the processes of coating fragmentation and delamination. A possible approach for influencing and controlling these processes is given by the incorporation of a ductile interlayer. It can be observed that the presence of Cu interlayers with thicknesses of 5 nm, 20 nm and 50 nm reduces the fracture strength of brittle Ta coatings on polyimide substrates, whereas the resistance to buckling is increased significantly.

Journal of Materials Research, 24 (6), ISSN:0884-2914, ISSN:2044-5326

A nanowire is an extremely thin wire with a diameter on the order of a few nanometers and with lengths orders of magnitude larger than its diameter. The physical properties of nanowires at this scale are expected to deviate significantly from the bulk metal, due to confinement and surface effects. For example, the electrical conductivity of the wires changes considerably, due to the drastic increase in the surface-to-volume ratio, which can be exploited for sensing. Mechanical properties, such as the yield strength, are important parameters that need to be characterized for applications like flexible circuits. In order to study the nanowire properties one needs to arrange them on a surface in a controlled way.

The resistivities of individual multiwalled pure and boron-doped carbon nanotubes have been measured in the temperature range from 25 to 300 °C. The connection patterns were formed by depositing two-terminal tungsten wires on a nanotube using focused-ion-beam lithography. A decrease of the resistivity with increasing temperature, i.e., a semiconductor-like behavior, was found for both B-doped and pure carbon nanotubes. B-doped nanotubes have a reduced room-temperature resistivity (7.4×10−7–7.7×10−6 Ωm) as compared to pure nanotubes (5.3×10−6–1.9×10−5 Ωm), making the resistivity of the doped tubes comparable to those along the basal plane of graphite. The activation energy derived from the resistivity versus temperature Arrhenius plots was found to be smaller for the B-doped (55–70 meV) than for the pure multiwalled nanotubes (190–290 meV).

Phase analysis of highly out-of-plane textured specimens using x-ray diffraction is usually complicated due to the disappearance of most of the x-ray peaks in a common theta/2 theta diffraction geometry. In this paper, we propose a technique, where powderlike spectra of textured samples are obtained by multiaxial x-ray diffraction scans. This technique is a simple, yet powerful method which allows for significant improvement in thin film characterization and provides several types of information about the samples, such as the rapid qualitative identification of phases using common powder x-ray diffraction spectra databases, texture distribution, and quantitative residual stress analysis.

We present novel modified lift-off processes for the fabrication of large-area, uniform metal nanowire arrays. In all processes, dense line arrays with periods in the 50-100nm range were obtained in photoresist films with Extreme Ultraviolet Interference Lithography (EUV-IL). The critical problem of preparing lift-off masks with a negative resist profile is solved by the use of either a bilayer resist stack of HSQ/PMMA or deposition of a metal layer at oblique angles on top of the patterned resist lines. As an added benefit, the metal deposition step enables fine-tuning of the width of the nanowires. Using the developed processes, Au and Cr nanowires with 8nm-70nm linewidth were obtained.

In the present work reflectance anisotropy spectroscopy (RAS) is evaluated as a new tool for the mechanical characterization of metallic thin films on viscoelastic substrates. Cu and Cu–Zn thin films of thicknesses in the range from 50 to 1000 nm were sputter-deposited onto a viscoelastic polyimide substrate and subjected to uniaxial tensile loading. The changes in the mechanical, electrical and optical response of the films upon loading were monitored by simultaneous acquisition of total strain, electrical resistance and the RA-signal. The RA-spectrum of pure copper reveals a feature at a photon energy of ~4.0 eV that linearly increases with strain at the beginning of loading (elastic regime) and saturates at later stages (plastic regime). Post-mortem SEM studies of samples loaded to different strain values confirmed that this saturation corresponds to the onset of plastic deformation, defined by the appearance of slip lines. Concurrent measurements of the electrical resistance confirmed the absence of cracking at the onset of the 4.0 eV RA-signal saturation. Therefore we claim that the RAS technique can be employed for yield point determination. Besides the applicability of the RAS technique for pure metals, chemical sensitivity of RAS in terms of peak position was observed in the case of Cu–Zn thin films.

In this study we show the influence of surface roughness on gecko adhesion on both the nano- and macroscales. We present experimental data for the force necessary to pull off single spatulae from hard rough substrates and also detail observations on living geckos clinging to various surfaces. Both experiments consistently show that the effective adhesion shows a minimum for a root mean square roughness ranging from 100 to 300 nm.

The Scanning X-Ray Submicron Diffraction (μ-SXRD) technique using focused synchrotron radiation white beam developed in the Beamline 7.3.3 at the ALS Berkeley Lab has been used to study the microstructural evolution at granular level of Cu polycrystalline lines during electromigration. Plastic deformation was observed in damascene Cu interconnect test structures during this in situ electromigration experiment and before the onset of visible microstructural damage (voiding, hillock formation). We show here that the extent of this electromigration-induced plasticity is dependent on the line width. In wide lines, plastic deformation manifests itself as grain bending and the formation of subgrain structures, while only grain rotation is observed in the narrower lines. The analysis of the Laue reflections allow for the determination of the geometrically necessary dislocation density in individual grains as well as for the misorientation angles between small angle boundaries generated by polygonization. The deformation geometry leads us to conclude that dislocations introduced by plastic flow lie predominantly in the direction of electron flow and may provide additional easy paths for the transport of point defects. Furthermore, we observe that the rotation axis of this plastic deformation coincides with one of the line directions of the known slip systems for FCC crystal, and that it is always very close (within a few degrees) to the direction of the electron flow. This finding suggests a correlation of the proximity of certain line directions to the direction of electron flow with the occurrence of plastic behavior. One important practical implication of this particular finding is that the grain texture of the line might thus play an important role in giving higher resistance towards early plastic response of the Cu line upon the electromigration loading.

In the present paper the evolution of the dislocation structure during electromigration in different regions along the Al(Cu) interconnect line is considered. It is shown that plastic deformation increases in the regions close to cathode end of the interconnect line. A coupling between the dissolution, growth and re-precipitation of Al2Cu precipitates and the electromigration-induced plastic deformation of grains in interconnects is observed. Possible mechanism of the Cu doping effect on the improved electromigration resistance of the Al(Cu) interconnects is discussed.

A novel synchrotron-based X-ray diffraction technique is presented by which it is possible to characterize the evolution of stresses in polycrystalline metallic films thinner than 100 nm. The film under investigation is deposited on a flexible polyimide substrate which is subjected to a uniaxial tensile test. The evolutions of longitudinal and transverse elastic strains in the film are monitored simultaneously by means of a high-resolution area detector. The strain resolution is better than 10−4. The samples are typically subjected to 6 % total strain and subsequently unloaded. First experiments carried out on Au films in the thickness range between 20 nm and 1000 nm show the usefulness and the power of this new technique.

In the past years the concept of measuring strain by x-rays has changed significantly. The combination of 3rd generation synchrotron sources, advanced focusing techniques and large area detectors has made it possible to probe volumes smaller than a cubic micron. This devolopment has made it possible to probe microstrains directly without having to rely on highly sophisticated models to evaluate peak broadening effects. This paper will provide a review of the state of art of local strain measurements by x-rays, discuss their limitations, provide an outlook of where the field may be going within the next years and address the most important issues to be solved. Examples will be given for the current limits in terms of resolution in time, space, strain and intensity.