Diffusion bonding of zirconia to austenitic stainless steel

Technische MateriaalwetenschappenMechanical, Maritime and Materials Engineerin

New avenues for residual stress analysis in ultrathin atomic layer deposited free-standing membranes through release of micro-cantilevers

The fabrication of thinnest, yet undeformed membrane structures with nanometer resolution is a prerequisite for a variety of Microelectromechanical systems (MEMS). However, functionally relevant thin films are susceptible to growth-generated stress. To tune the performance and reach large aspect ratios, knowledge of the intrinsic material properties is indispensable. Here, we present a new method for stress evaluation through releasing defined micro-cantilever segments by focused ion beam (FIB) milling from a predefined free-standing membrane structure. Thereby, the cantilever segment is allowed to equilibrate to a stress-released state through measurable strain in the form of a resulting radius of curvature. This radius can be back-calculated to the residual stress state. The method was tested on a 20 nm and 50 nm thick tunnel-like ALD Image 1 membrane structure, revealing a significant amount of residual stress with 866 MPa and 6104 MPa, respectively. Complementary finite element analysis to estimate the stress distribution in the structure showed a 97% and 90% agreement in out-of-plane deflection for the 20 nm and 50 nm membranes, respectively. This work reveals the possibilities of releasing entire membrane segments from thin film membranes with a significant amount of residual stress and to use the resulting bending behavior for evaluating stress and strain by measuring their deformation

Correlating laser energy with compositional and atomic-level information of oxides in atom probe tomography

International audienceAtom probe tomography (APT) is a 3D analysis technique that offers unique chemical accuracy and sensitivity with sub-nanometer spatial resolution. There is an increasing interest in the application of APT to complex oxides materials, giving new insight into the relation between local variations in chemical composition and emergent physical properties. However, in contrast to the field of metallurgy, where APT is routinely applied to study materials at the atomic level, complex oxides and their specific field evaporation mechanisms are much less explored. Here, we perform APT measurements on the hexagonal manganite ErMnO 3 and systematically study the effect of different experimental parameters on the measured composition and structure. We demonstrate that both the mass resolving power (MRP) and compositional accuracy can be improved by increasing the charge-state ratio (CSR) working at low laser energy (< 5 pJ) for a given fixed detection rate. Furthermore, we observe a substantial preferential retention of Er atoms, which is suppressed at higher CSRs. We explain our findings based on fundamental field evaporation concepts, expanding the knowledge about the impact of key experimental parameters and the field evaporation process in complex oxides in general

Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer

The monolithic integration of wurtzite GaN on Si via metal amp; 8722;organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single layer graphene as an atomically thin buffer layer for c axis oriented growth of vertically aligned GaN nanorods mediated by nanometer sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene covered Si 111 as well as Si 100 . High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro Raman, and cathodoluminescence measurements supported by finite difference time domain simulations. Current amp; 8722;voltage characteristics revealed high vertical conduction of the as grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN based heterojunction device concept