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Determination of the elastic behavior of silicon nanowires within a scanning electron microscope
(2016)
Three-point bending tests were performed on double-anchored, <110> silicon nanowire samples inside a scanning electron microscope (SEM) via a micromanipulator equipped with a piezo-resistive force sensor. Representing the upper and lower boundaries achievable in a consistent manner, silicon nanowires with widths of 35 nm and 74 nm and a height of 168 nm were fabricated. The nanowires were obtained monolithically along with their 10-m-tall supports through a top-down fabrication approach involving a series of etching processes. Hence, no interface compliance was introduced between supports and nanowires. Exact nanowire dimensions and cross-sectional features were determined by transmission electron microscopy (TEM) following sample preparation through focused ion beam (FIB) machining. Conducting the experiments inside an SEM chamber further raised the opportunity of the direct observation of any deviation from ideal loading conditions such as twisting, which was taken into consideration in simulations. Measured force-displacement behavior was observed to exhibit close resemblance to simulation results obtained by finite element modeling, when the bulk value of 169 GPa was taken as the modulus of elasticity for <110> silicon. Hence, test results show neither any size effect nor evidence of residual stresses for the considered nanoscale objects. The increased effect of the native oxide with reduced nanowire dimensions was captured as well. Thus this very simple in-situ testing method was found to be an alternative to elaborate AFM measurements on geometrically formidable nanostructures. The results demonstrate the applicability of the developed fabrication approach to the incorporation of silicon nanowires in functional micromechanical devices.
The objective of the present work was to study the impact of Focused Ion Beam (FIB) machining parameters on the thickness of the damaged layer within a thin film PZT. Therefore, different Ga+- ion doses and ion energies were applied to a standard PZT film (80/20 lead zirconium titanate) under two beam incidence angles (90° and 1°). The thicknesses of the corresponding Ga+-implanted layers were then determined by cross-sectional TEM in combination with energy dispersive spectroscopic (EDS) line-scans and correlated with polarisation hysteresis loops. The results show a decrease of Ga+-implanted layer thickness with decreasing inclination angle, whereas ion energy and ion dose could be correlated with gallium concentration in the implanted layers.. Under the most unfavorable conditions the depth of the affected zone was 26 nm, it was only 2 nm for the most favorable conditions.
A combined methodical approach is tested with respect to the characterization of the inner structure of porous TiO2 layers as typically used in modern dye sensitized solar cells (DSSC). Their performance is directly linked to the surface area of the pore network. The micrometer thick layer employed was manufactured by screen-printing of a starting TiO2 powder constituted of shape-controlled, bipyramidal anatase nanoparticles on FTO/glass substrates. The analytical methods exploited in our study are Focused Ion Beam (FIB) slicing followed by 3D reconstruction as well as the new approach transmission Kikuchi diffraction (TKD) technology in the scanning electron microscope (SEM). Size and shape distribution of the TiO2 NPs within the layer can be extracted. SEM in transmission mode and atomic force microscopy (AFM) have been used to verify the dimensional data obtained by the new combined methodical approach. Its analytical benefits but also the challenges and limitations are highlighted.
A combined methodical approach is tested for the first time with respect to the characterization of the inner structure of porous TiO2 layers infiltrated with ruthenium molecular sensitizer as typically used in modern dye sensitized solar cells (DSSC). Their performance is directly linked to the surface area ‘offered’ by the pore Network to the dye. The micrometer thick layer employed was manufactured by screen-printing of a starting TiO2 powder constituted of shape-controlled, bipyramidal anatase nanoparticles (NPs) on FTO/glass substrates. The
analytical methods exploited in our study are Focused Ion Beam (FIB) slicing followed by 3D reconstruction as well as the new approach transmission Kikuchi diffraction (TKD) technology in the scanning electron microscope (SEM). While the first method results in the visualization of the 3D pore network within the TiO2 layer, the second one can be successfully applied to analyze the crystal orientation of grains (i.e. NPs in our case) in nanometer resolution. Moreover, size and shape distribution of the TiO2 NPs within the layer can be extracted.
SEM in transmission mode and atomic force microscopy (AFM) have been used to verify the dimensional data obtained by the new combined methodical approach. Its analytical benefits but also the challenges and limitations
are highlighted.