Evolution of thickness dependent buckle geometries

Interfaces determine the overall reliability of multi-material components since they have to bear the distinct physical and chemical properties of the different adhering materials. In microelectronic applications, where several materials are implemented at small length scales, the main interest is on identifying the weakest interface, since it dictates the overall reliability of the implemented packages. The focus of the present study is set on a multi-layer stack composed of a rigid Si substrate with dielectric borophosphosilicate glass (BPSG) and a thin TiW film acting as adhesion promoter and diffusion barrier to the copper film, which are finally covered with 6 µm of polyimide (PI). Of main interest is a thorough characterization of the delamination of the various interfaces, which allow for a better understanding of the adhesion and the stress states present in the complex material stack. As a first step to study the interfacial behaviour, a peeling test was carried out to reveal the weakest interfaces resulting in three different delamination zones. Zone 1 delaminated at the BPSG-TiW interface and Zone 2 delaminated at the copper-PI interface (Fig 1a). An intermediate Zone 3 (Fig 1a) was identified, where straight buckles formed in the Cu-TiW layer parallel to the peeling direction at the TiW-BPSG interface (Fig 1b). Using these Zone 3 delaminations, the evolution of the buckle shape as a function of film thickness and layer stress was investigated using atomic force microscopy and X-ray diffraction. Of great interest is that with the Cu layer the buckles have a straight geometry (Fig 1b) indicating an isotropic stress. However, when the Cu layer is removed with chemical etching, the buckle morphology changes to a telephone cord geometry (Fig. 1c), maintaining the outer boundaries from the previous straight buckles shape. The change in geometry could be due to the change in film stress from isotropic to biaxial as well as the fact that the out of plane plasticity is constrained while the copper film is present. Both topics will be further discussed along with how the interfacial adhesion measurements may also be influenced by the change in buckle geometry. Please click Additional Files below to see the full abstract

Productivity and Other Performance Measures in College and University Foodservice

Food, Nutrition and Institution Administratio

Tailoring thin-film mechanical fragmentation properties of hybrid atomic/molecular-layer-deposited materials

Molecular layer deposition (MLD) as the little sister of atomic layer deposition is a strongly emerging thin-film technique for deposition of ultra-thin inorganic–organic hybrid (“metalcone”) coatings directly from the gas phase, even on complex three-dimensional surfaces. Employing tensile testing coupled with in situ optical microscopy, we found [1] that using inorganic metal oxide ALD alone could increase the crack onset strain via nanolaminating amorphous and nanocrystalline film layers, see fig. 1a. This behavior can be attributed to changing residual strains [2] in the overall Al2O3/Y2O3 nanolaminate film and shifted the crack onset strain from 0.67% to 1.1% (and decreased the crack density by a factor 2). However, introducing organic carbon backbones into the inorganic oxide material allows increasing the crack onset strain by an order of magnitude. Please click Download on the upper right corner to see the full abstract

Bioabfallkompost im biologischen Landbau – Auswirkungen auf die Gehalte von bioverfügbaren Schwermetallen im Boden

The accumulation of heavy metals in soils is a potential risk that may keep organic farmers from using biowaste compost. As the ecological effects of metals are related to mobile fractions rather than to total contents in the soil, we measured the total (aqua regia extractable) heavy metal contents, the readily available water soluble and the potentially bioavailable LiCl-extractable fraction of soil heavy metals in a field experiment after ten years with total applications of 95, 175 and 255 t ha-1 biowaste compost (fresh matter). Total soil contents of Cd, Cr, Cu, Ni and Pb in the compost treatments were not significantly higher than in the unfertilized control. Total Zn contents increased in the treatment with the highest application rate. In the mobile fractions Cd and Pb were not detectable. Cr, Ni and Zn contents were in the range published for unpolluted soils in other studies and did not show any differences according to treatment. Easily exchangeable Cu (in LiCl extract) was increased with compost fertilization. In several crops, lower Cd contents were measured with compost fertilization than without fertilization. Potatoes which had received mineral fertilizer had significantly higher Cd contents. Crop Zn contents were increased in the compost treatments. In conclusion, fertilization with high quality biowaste compost at such rates and after ten years of application gives no cause for concern with regard to both total heavy metal contents and available heavy metal fractions

In situ fragmentation analysis of ALD-PVD multilayers on flexible substrates

The deformation behavior of flexible thin film multilayer structures is usually found to be dominated by the most brittle component. Cracks in the brittle layers act as stress concentration points, causing the ductile layers to fracture at very low strains, thereby endangering the mechanical integrity of the multilayer [1]. The extent of the embrittlement often depends on the modulation period (tbrittle + tductile) as well as on the modulation ratio (tbrittle/tductile) [2]. In this work, fundamental deformation mechanisms of brittle/ductile multilayers on flexible polymer substrates are investigated using multilayers of Al / Al2O3 / Al…., produced by a unique combination of atomic layer (ALD, Al2O3) and physical vapor deposition (PVD, Al). Using this ALD/PVD combination, individual film thicknesses can easily differ by one order of magnitude or more. In particular, the ability of operating the ALD/PVD process without breaking vacuum opens up a wide range of otherwise unachievable modulation and thickness ratios. Thickness control with precision down to 0.1 nm can be achieved for the buried Al2O3 layers, well below the native oxide thickness of pure Al films. Figure 1a shows a TEM cross-section of an Al/ Al2O3/Al….multilayer stack (Al 250nm, Al2O3 1-10 nm). For flexible multilayer systems the Al layer thickness is reduced to 50 nm to minimize residual stresses. The Al2O3 layer thickness is varied across the multilayer cross-section (0.1 nm – 10 nm) to study crack onset and propagation as a function of oxide layer thickness. Single layered Al and Al2O3 films are used as reference materials. Ex situ and in situ uniaxial tensile experiments are performed to evaluate the deformation behavior of the flexible thin films using digital image correlation (DIC) to measure strains on the thin film surface. Lateral cracking (Figure 1b) is investigated with scanning election microscopy (SEM), carefully avoiding changes in the deformation behavior by interaction of the electron beam with the polymer substrate. To study cross-sectional crack initiation and growth, focused ion beam (FIB) cross-sections are cut into the film under tension (Figure 1c). The in situ approach avoids crack closure due to relaxation of the polymer substrate after unloading. Primary results show that the multilayer structure has good adhesion between individual layers as well as to the polymer substrate. Grain growth of Al is limited by the Al2O3 layers (Figure 1a), allowing for easy discrimination of individual Al layers necessary for locating the crack onset, and for cross-sectional fragmentation analysis. The Al2O3 layers show increasing stretchability with decreasing film thickness, as a result of being extremely well defined and practically defect free. This study will improve the understanding of the deformation mechanisms in flexible thin film structures and can give useful guidelines for damage tolerant design of flexible thin films systems. Please click Additional Files below to see the full abstract

Metallic Glass Films with Nanostructured Periodic Density Fluctuations Supported on Si/SiO2 as an Efficient Hydrogen Sorber.

Nanostructured metallic glass films (NMGF) can exhibit surface and intrinsic effects that give rise to unique physical and chemical properties. Here, a facile synthesis and electrochemical, structural, and morphologic characterization of Pd-Au-Si based MGs of approximately 50 nm thickness supported on Si/SiO2 is reported. Impressively, the maximum total hydrogen charge stored in the Pd-Au-Si nanofilm is equal to that in polycrystalline Pd films with 1 μm thickness in 0.1 m H2 SO4 electrolyte. The same NMGF has a volumetric desorption charge that is more than eight times and 25 % higher than that of polycrystalline PdNF and Pd-Cu-Si NMGF with the same thickness supported on Si/SiO2 , respectively. A significant number of nanovoids originating from PdHx crystals, and an increase in the average interatomic spacing is detected in Pd-Au-Si NMGF by high-resolution TEM. Such a high amount of hydrogen sorption is linked to the unique density fluctuations without any chemical segregation exclusively observed for this NMGF

Aluminum-Based Composites Reinforced with Ceramic Fibers

The modern transportation industry is in high demand for lightweight structural components with exceptional mechanical properties that can be obtained by a costeffective production process. These specific industrial requirements can be achieved through the attainment of innovative aluminum matrix composites (AMCs) with improved characteristics in accordance with the circular economy. Solid-state recycling is considered a good solution to attain the above-mentioned industrialdemands since it enables the obtainment of usable and inexpensive raw materials with known chemical composition from industrial waste and therefore supports the cost-effective production of structural components. The present research was, therefore, directed toward the repurposing of waste materials derived from the metal industry and the civil engineering sector through a simple and economical solid-state recycling procedure to obtain raw materials for the production of innovative AMCs with required characteristics. The aluminum 2xxx series alloy, i.e. 2024 alloy, in the form of metallic chips generated during the industrial machining was selected for the obtainment of composite base, while basalt fibers derived from stone mineral wool, as waste material in civil engineering, were used to produce the composite reinforcing phase. Basalt, characterized by high strength and low density, provides improved resistance to chemical and mechanical damage, while the 2024 alloy contributes to good fatigue properties of the final fiber-reinforced AMCs. To obtain usable raw materials for the AMCs preparation from the solid industrial waste the basalt fibers were thermally treated, while aluminum-based metallic chips were ballmilled. Treated aluminum alloy powder and basalt fibers were mixed in a 3D tumbler mixer in a 9:1 ratio, isostatically pressed, and sintered in a protective argon atmosphere at 550 °C. Isostatic pressure and sintering duration were varied during the AMCs preparation to determine the optimal processing parameters for the obtainment of AMCs with the required characteristics for a predetermined purpose. The scanning electron microscopic (SEM), energy dispersive spectroscopic (EDS), and X-ray diffraction (XRD) analyses complemented with hardness and density measurements were conducted to characterize starting and final materials. Obtained composites showed improved mechanical properties compared to the starting aluminum alloy, regardless of the processing conditions. The AMCs processed at a higher pressure and for longer sintering times showed higher density and hardness. The results of the presented research undoubtedly indicated that solid-state recycling, as a simple, energy- and cost-efficient process, can be successfully used for the attainment of innovative composites for lightweight structural components in the transportation industry.VII Conference of The Serbian Society for Ceramic Materials, 7CSCS-2023, June 14-16, 2023, Belgrade, Serbi

Electromechanical Behavior of Al/Al2_{2}O3_{3} Multilayers on Flexible Substrates: Insights from In Situ Film Stress and Resistance Measurements

A series of Al and Al/Al$_{2}$O$_{3}$ thin-film multilayer structures on flexible polymer substrates are fabricated with a unique deposition chamber combining magnetron sputtering (Al) and atomic layer deposition (ALD, Al$_{2}$O$_{3}$, nominal thickness 2.4–9.4 nm) without breaking vacuum and thoroughly characterized using transmission electron microscopy (TEM). The electromechanical behavior of the multilayers and Al reference films is investigated in tension with in situ X-ray diffraction (XRD) and four-point probe resistance measurements. All films exhibit excellent interfacial adhesion, with no delamination in the investigated strain range (12%). For the first time, an adhesion-promoting naturally forming amorphous interlayer is confirmed for thin films sputter deposited onto polymers under laboratory conditions. The evolution of Al film stresses and electrical resistance reveal changes in the deformation behavior as a function of oxide thickness. Strengthening of Al is observed with increasing oxide thickness. Significant embrittlement can be avoided for oxide layer thicknesses ≤2.4 nm

Combinatorial Materials Design Approach to Investigate Adhesion Layer Chemistry for Optimal Interfacial Adhesion Strength

A combinatorial material adhesion study was used to optimize the composition of an adhesion promoting layer for a nanocrystalline diamond (NCD) coating on silicon. Three different adhesion promoting metals, namely W, Cr, and Ta, were selected to fabricate arrays of co-sputtered binary alloy films, with patches of seven different, distinct alloy compositions for each combination, and single element reference films on a single Si wafer (three wafers in total; W–Cr, Cr–Ta, Ta–W). Scratch testing was used to determine the critical failure load and practical work of adhesion for the NCD coatings as a function of adhesion layer chemistry. All tested samples eventually exhibit delamination of the NCD coating, with buckles radiating perpendicularly away from the scratch track. Application of any of the presented adhesion layers yields an increase of the critical failure load for delamination as compared to NCD on Si. While the influence of adhesion layers on the maximum buckle length is less pronounced, shorter buckles are obtained with pure W and Cr–Ta alloy layers. As a general rule, the addition of an adhesion layer showed a 75% improvement in the measured adhesion energies of the NCD films compared to the NCD coating without an adhesion layer, with specific alloys and compositions showing up to 125% increase in calculated practical work of adhesion.H2020 Marie Skłodowska-Curie Action