A new push‐pull sample design for microscale mode 1 fracture toughness measurements under uniaxial tension

The miniaturization of microelectronic devices and the use of thin hard coatings have led to an increased demand for knowledge on the fracture behaviour of microscopic structures. A new geometry called Micro-SENT is proposed in this work that allows performing experiments in uniaxial tension on the microscale using a standard flat punch indenter by making use of a symmetric push-pull sample design. This enables the measurement of mode 1 fracture toughness under uniform tensional far-field loading as opposed to current state of the art approaches based on cantilever bending or micropillar splitting. Please click Additional Files below to see the full abstract

Micro-shear of silicon: Elastic strain analysis using digital image correlation

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Deformation and fracture mechanisms in nanocomposite and nanolaminate thin films revealed through combinatorial design and nanomechanical testing

We’ve integrated an atomic layer deposition (ALD), a physical vapor deposition (PVD) and a nanoparticle inert gas condensation (NP) deposition system into a single vacuum chamber. This combined system allows for PVD sputtering of micrometer thick films and incorporation of size filtered nanoparticles and/or controlled deposition of mono-layer highly conformal film coatings within a multilayer structure. In this way, unique model thin film microstructures can be architectured. We designed three thin films to understand the basic mechanism of plasticity and fracture in thin films: a) Al2O3 oxide films were deposited on combinatorial libraries of the ternary noble metal alloys with full compositional range to understand interfacial adhesion between oxide and noble metal alloys b) monosized tungsten nanoparticles were deposited at the interface of Cu/Ni multilayers to understand how thin film hardness and thermal stability can be engineered, c) ultrathin monolayers of Al2O3 layers were sandwiched between sputtered Al layers and micropillar compression was used to understand dislocation transmission and fracture across ultrathin ceramic layers. Please click Additional Files below to see the full abstract

Temperature-dependent dynamic plasticity of micro-scale fused silica

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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

Room Temperature Viscous Flow of Amorphous Silica Induced by Electron Beam Irradiation

The increasing use of oxide glasses in high‐tech applications illustrates the demand of novel engineering techniques on nano‐ and microscale. Due to the high viscosity of oxide glasses at room temperature, shaping operations are usually performed at temperatures close or beyond the point of glass transition Tg. Those treatments, however, are global and affect the whole component. It is known from the literature that electron irradiation facilitates the viscous flow of amorphous silica near room temperature for nanoscale components. At the micrometer scale, however, a comprehensive study on this topic is still pending. In the present study, electron irradiation inducing viscous flow at room temperature is observed using a micropillar compression approach and amorphous silica as a model system. A comparison to high temperature yielding up to a temperature of 1100 °C demonstrates that even moderate electron irradiation resembles the mechanical response of 600 °C and beyond. As an extreme case, a yield strength as low as 300 MPa is observed with a viscosity indicating that Tg has been passed. Those results show that electron irradiation‐facilitated viscous flow is not limited to the nanoscale which offers great potential for local microengineering

Data_2023_Bruns_AdvSci_RT-Visc-Flow

Research and raw data to publication: Bruns S, Minnert C, Pethö L, Michler J, Durst K. Room Temperature Viscous Flow of Amorphous Silica Induced by Electron Beam Irradiation. Adv Sci (Weinh). 2023:e2205237. https://doi.org/10.1002/advs.202205237

Fracture of Silicon: Influence of rate, positioning accuracy, FIB machining, and elevated temperatures on toughness measured by pillar indentation splitting

ISSN:0264-1275ISSN:1873-419

Orientation-dependent extreme shear strain in single-crystalline silicon - from elasticity to fracture

Measuring strain accurately at small length scales poses a significant challenge, making it difficult to obtain precise elastic properties of small materials. This becomes particularly pronounced for test geometries beyond micro-pillars and for materials with high elastic limits and high Peierls stresses. This study investigates the elastic strain limits and strain distribution in micro double shear tests conducted on single-crystalline silicon with different crystallographic orientations. In situ scanning electron microscopy images were used to obtain full-field strain maps using digital image correlation. This local strain analysis approach revealed that the shear zones of the test geometry are not solely under pure shear conditions, but also experience superimposed bending. The local strain analysis approach increases the precision of measured elastic properties to ±15% of the literature value compared to deviations of 75-80% using the traditional global strain analysis approach. This study highlights the limitations of the global strain analysis approach in complex specimen geometries and demonstrates the effectiveness of digital image correlation in accurately determining elastic strain at the small length scale. Furthermore, both the low defect density in the samples as well as the small length scales allow for the exploration of orientation dependent strength levels close to the theoretical limit.ISSN:0264-1275ISSN:1873-419

Nanomechanical test specimen preparation techniques by microfabrication and two‐photon lithography to avoid FIB induced Ga implantation damage

Traditional mechanical test specimen preparation methods require a subtractive approach to define the structure out of the bulk material. The most commonly used technology, focused ion beam patterning, leaves a modified specimen surface by gallium implantation resulting in for instance an altered grain structure. In this work, purely chemical approaches and an additive manufacturing technique are introduced to define test specimen. Compression pillars have been fabricated out of single crystal silicon and glass. The developed silicon process is crystalline orientation independent; consists of optical lithography, reactive ion etching via an alternating fluorine plasma and polymer passivation, surface oxidation and HF wet etching for sidewall planarization. High aspect ratio structures are achievable with a sub-50 nm surface roughness and parallel sidewalls. Glass pillar microfabrication requires a hard metallic mask due to the relatively low selectivity of any etchant plasma. Sputtered aluminum is patterned by photolithography and a chlorine based dry etch. The glass is reactively etched in a fluorine based plasma via this mask. The aluminum is then selectively removed by wet etching. The process has been demonstrated on a fused silica substrate with an average of 84º sidewall angle, although a wide variety of glasses may be used. Glass purity influences the sidewall angle. Please click Additional Files below to see the full abstract