H.B Groen

Metal–ceramic interfaces studied with high-resolution transmission electron microscopy

Tailoring materials with a desirable set of physical and chemical properties has always been a dream of materials scientists and engineers. It is accurate to say that important properties of materials in high-technology applications are strongly affected or controlled by the presence of solid interfaces. For example, a great deal of the electronic industry is based on the interesting electrical properties of semiconductor interfaces, with ceramic-semiconductor, metal-semiconductor and also metal-ceramic interfaces playing a crucial role. Interfaces are also important in the field of surface engineering. For techniques designed to enhance corrosion resistance of surfaces or to optimise their performance in catalytical or tribological applications, interfaces play a determining role. In the field of semiconductor technology as well as in the area of surface engineering, metal-oxide interfaces are frequently encountered. Despite their obvious technological importance, our basic understanding of interfaces, even relatively simple interfaces like grain-boundaries, is still rudimentary in relation to materials properties. The importance of interfaces is determined primarily by their inherent inhomogeneity, i.e. the fact that physical and chemical properties may change dramatically at or near the interface itself. It should be realised that physical properties, like elastic moduli, thermal expansion or electrical resistivity may differ near interfaces by orders of magnitude from those in bulk regions. As a result of these sharp gradients an isotropic bulk solid may change locally into a highly anisotropic medium. Consequently all processes that are controlled by interface phenomena, such as de-cohesion, segregation, cavitation and diffusion, occur in a very narrow region, of the order of a few lattice spacings, where the two materials join. Thus, the atomic structure of interfaces needs to be understood in order to establish the physical mechanisms of various boundary phenomena. Experimental techniques capable of revealing the structure with atomic resolution are necessary for their investigation. In this work the emphasis is on the understanding of interfaces between metals and oxides at the atomic structure level, using High Resolution (Transmission) Electron Microscopy (HRTEM) as the experimental method.

High-resolution transmission electron microscopy imaging of misfit-dislocation networks at Cu-MgO and Cu-MnO interfaces

Abstract Misfit dislocation networks at Cu-MgO and Cu-MnO {111}metal//{111}oxide interfaces were studied with high-resolution transmission electron microscopy. Experimental results were compared with image simulations of tentative atomic structures of the interface region derived from lattice statics calculations. The calculations take into account the two-dimensional misfit at the interface, which is necessary given the high misfit and short repeat distances at the interfaces. The lattice statics calculations use simplified potentials across the interface which capture essential characteristics that have emerged from recent experimental results and ab-initio calculations. Trigonal networks of edge misfit locations with Burgers vectors ⅙〈112〉 and line direction 〈110〉 follow from these calculations. These misfit-dislocation networks have associated strain fields in the metal, stretching out from the interface with approximately the repeat distance along the interface. These strain fields show up in image s...

Misfit Dislocations at Ag/Mn3O4, Cu/MnO and Cu/Mn3O4 Interfaces

Parallel close-packed plane interfaces between MnO or Mn3O4 and Ag or Cu are studied using high resolution transmission electron microscopy (HRTEM) and atomistic calculations. The study is aimed at determining the network of misfit dislocations at these interfaces. Due to the projective nature of HRTEM, an atomistic model incorporating the displacements associated with the possible misfit–dislocation network appear to be of great value. The following results are obtained. Ag/Mn3O4: an array of dislocations with line direction [11¯0] and alternating Burgers vectors 1/6[112¯] and 1/3[112¯], Cu/MnO: a trigonal network of edge dislocations with Burgers vectors of the 1/6 type and line direction , Cu/Mn3O4: the Burgers vectors with reference to Cu remain of 1/6 type, but due to a slight change in line direction with respect to obtain some screw character.

Atomic structure of interfaces between Mn3O4 precipitates and Ag studied with HRTEM

Abstract Internal oxidation of Ag3 at.% Mn resulted in Mn 3 O 4 precipitates with a “parallel” topotaxy with the metal matrix and an octahedron shape due to {111} facets. Orientation and shape of Mn 3 O 4 in Ag are not in the lowest strain energy state, indicating the dominance of interfacial energy over strain energy. Owing to the tetragonality of Mn 3 O 4 , only a few planes and directions of Ag and Mn 3 O 4 can be parallel simultaneously. The precipitates exhibited a tendency to align {111} planes parallel with the matrix for one pair of facets and then for another pair a tilt of 7.6° occurs which is relieved by ledges in Ag. The dislocation structure at these parallel and tilted {111} interfaces, including phenomena such as stand-off and dissociation of (partial) dislocations, is scrutinized combining HRTEM and atomistic calculations.

Analyses of small facets imaged with scanning-probe microscopy

Two tools for the analysis of facets as detected by scanning-probe microscopy (SPM) images are proposed. One tool is an adaptation of the radial-histogram transform proposed by D. Schleef et al. in Phys. Rev. B. 55, 2535 (1997). In this article the local slopes in the SPM image are in the present version determined by Savitsky–Golay filters with variable lengths [A. Savitsky and M. J. E. Golay, Anal. Chem. 36, 1627 (1964)]. These variable length filters turn out to be important to suppress the influence of noise obscuring the possibility to detect facets and to analyze corrugations with different length scales in SPM images, e.g., surface reconstructions. The other tool allows the direct quantitative determination of the orientation (with a standard deviation) of user-specified parts of facets. It makes use of a Savitsky–Golay filter as well. Both tools were applied to an artificially constructed SPM image and several experimental SFM images showing (ionic) MnO precipitates protruding out of a (metallic) ...

Metal-ZnO interfaces studied by high resolution transmission electron microscopy

This paper reports on investigations of Ag-ZnO and Cu-ZnO interfaces, produced by internal oxidation. ZnO precipitates with the wurtzite structure were found showing mainly one orientation relationship ( OR) with the matrix. However, closely related ORs were found, rotated by small angles from that orientation relation. The atomic structure of several interfaces surrounding these precipitates was studied and compared using high resolution transmission electron microscopy. This paper focuses on interfaces between low index facets of ZnO and vicinal planes of Ag. These interfaces clearly show relaxations. An interpretation of these relaxations in terms of dissociation of partial dislocations at the interface is put forward.