Self-organized Sr leads to solid state twinning in nano-scaled eutectic Si phase.

A new mechanism for twin nucleation in the eutectic Al-Si alloy with trace Sr impurities is proposed. Observations made by sub-angstrom resolution scanning transmission electron microscopy and X-ray probing proved the presence of <110> Sr columns located preferentially at twin boundaries. Density functional theory simulations indicate that Sr atoms bind in the Si lattice only along the <110> direction, with preferential positions at first and second nearest neighbors for interstitial and substitutional Sr, respectively. Density functional theory total energy calculations confirm that twin nucleation at Sr columns is energetically favorable. Hence, twins may nucleate in Si precipitates after solidification, which provides a different perspective to the currently accepted mechanism which suggests twin formation during precipitate growth.

Direct writing of CoFe alloy nanostructures by focused electron beam induced deposition from a heteronuclear precursor.

Recently, focused electron beam-induced deposition has been employed to prepare functional magnetic nanostructures with potential in nanomagnetic logic and sensing applications by using homonuclear precursor gases like Fe(CO)5 or Co2(CO)8. Here we show that an extension towards the fabrication of bi-metallic compounds is possible by using a single-source heteronuclear precursor gas. We have grown CoFe alloy magnetic nanostructures from the HFeCo3(CO)12 metal carbonyl precursor. The compositional analysis indicates that the samples contain about 80 at% of metal and 10 at% of carbon and oxygen. Four-probe magnetotransport measurements are carried out on nanowires of various sizes down to a width of 50 nm, for which a room temperature resistivity of 43 µΩcm is found. Micro-Hall magnetometry reveals that 50 nm × 250 nm nanobars of the material are ferromagnetic up to the highest measured temperature of 250 K. Finally, the transmission electron microscopy (TEM) microstructural investigation shows that the deposits consist of a bcc Co-Fe phase mixed with a FeCo2 O4 spinel oxide phase with nanograins of about 5 nm diameter.

The influence of beam defocus on volume growth rates for electron beam induced platinum deposition.

Electron beam induced deposition (EBID) is a versatile method for the controlled fabrication of conducting, semi-conducting and non-conducting structures down to the nanometer scale. In contrast to ion beam induced deposition, EBID processes are free of sputter effects, ion implantation and massive heat generation; however, they have much lower deposition rates. To push the deposition efficiency further towards its intrinsic limits, the individual influences of the process parameters have to be explored. In this work a platinum pre-cursor is used for the deposition of conducting nanorods on highly oriented pyrolytic graphite. The study shows the influence of a beam defocus during deposition on the volume growth rates. The temporal evolution of volume growth rates reveals a distinct maximum which is dependent on the defocus introduced, leading to an increase of deposited volumes by a factor 2.5 after the same deposition times. The observed maximum is explained by an increasing and saturating electron yield contributing to the final deposition process and constantly decreasing diffusion abilities of the pre-cursor molecules toward the tip of the nanorods, which is further supported by dwell time experiments.