article posted 07 April 2016
Günter Möbus has specialised for over a decade into research applying advanced electron microscopy methods to oxide glasses and nanomaterials, both for characterisation and for in-situ-modification and fabrication purpose. Particular highlights include speciation of coordination and oxidation states in glasses via EELS, shape reconstructions of glass particles and internal precipitates in 3D via tomography, and observation of single-atom dynamical movements on oxide surfaces, along with multiple studies on irradiation response of crystalline and glassy materials on the nanoscale.
Electron Beam Patterning of Glasses via Metal Nanoparticle Precipitation
Mohammed M. Sabri, Russell J. Hand & Günter Möbus*
University of Sheffield, Dept. Materials Science & Engineering, Sheffield S1 3JD, UK.
A variety of borosilicate (BS) glasses loaded with functional cations are exposed to focused beam electron irradiation in a transmission electron
microscope (TEM). The work is aimed at the generation of spatially localised regions of nanoparticle precipitation while the glass remains unchanged outside
the region of electron beam impact. This corresponds to a nm-resolution analogue to the well-established laser- irradiation patterning research field. Three glass
chemistries with large variation of target metal concentration are presented and compared: (i) a Zn-BS glass (60mol% ZnO) for Zn-metal patterning represents a
type of glass where the precipitate comes from a majority constituent, which is network forming (ZnO); (ii) a Cu loaded BS- glass (20mol% CuO) represents an example
with medium concentration of the target metal species, not considered network forming; and (iii) an Ag loaded cerium- borosilicate glass with only 2mol% Ag2
represents a glass with small dopant contribution, where the extra Ce doping offers the opportunity to study Ag-Ce redox interaction during precipitation. The
work is aimed at illustrating future possibilities of glass surface (and refractive index) engineering with respect to reflectivity, wave guiding, nano-plasmonic
light coupling, and potentially catalysis. The experiments undertakenfrom also provide insight into multi-component glass behaviour under irradiation relevant
to nuclear waste immobilisation.
In all three glass types it was possible to form metallic nano-precipitates under the electron beam at pre-selected positions, however the pattern quality varied.
Challenges include (i) speed of precipitation (which needs to be high enough to give high particle densities in line-scans, and low enough to prevent premature-formation
during image focusing), (ii) localisation, i.e. avoidance of particles forming mainly on the outside of the beam, leading to double-lines and circle-patterns,
(iii) fabrication of metal particles in the interior rather than on the glass surfaces, and (iv) avoidance of excessive glass matrix ablation (glass thinning)
during patterning. Interesting side effects observed include formation of self-ordered particle-chains, concurrent occurrence of precipitation, phase separation,
and cation migration, and (expanding
on earlier work) the transformation of sharp glass corners into rounded shapes via radiation induced flow (RIF). Evidence of all of these effects will be presented.