S. Sangiao

Focused Electron and Ion Beam Induced Deposition on Flexible and Transparent Polycarbonate Substrates

The successful application of focused electron (and ion) beam induced deposition techniques for the growth of nanowires on flexible and transparent polycarbonate films is reported here. After minimization of charging effects in the substrate, sub-100 nm-wide Pt, W, and Co nanowires have been grown and their electrical conduction is similar compared to the use of standard Si-based substrates. Experiments where the substrate is bent in a controlled way indicate that the electrical conduction is stable up to high bending angles, >50°, for low-resistivity Pt nanowires grown by the ion beam. On the other hand, the resistance of Pt nanowires grown by the electron beam changes significantly and reversibly with the bending angle. Aided by the substrate transparency, a diffraction grating in transmission mode has been built based on the growth of an array of Pt nanowires that shows sharp diffraction spots. The set of results supports the large potential of focused beam deposition as a high-resolution nanolithography technique on transparent and flexible substrates. The most promising applications are expected in flexible nano-optics and nanoplasmonics, flexible electronics, and nanosensing.

Weak-antilocalization signatures in the magnetotransport properties of individual electrodeposited Bi Nanowires

We study the electrical resistivity of individual Bi nanowires of diameter 100 nm fabricated by electrodeposition using a four-probe method in the temperature range 5–300 K with magnetic fields up to 90 kOe. Low-resistance Ohmic contacts to individual Bi nanowires are achieved using a focused ion beam to deposit W-based nanocontacts. Magnetoresistance measurements show evidence for weak antilocalization at temperatures below 10 K, with a phase-breaking length of 100 nm.

Review of magnetic nanostructures grown by focused electron beam induced deposition (FEBID)

Financial support by several projects is acknowledged: MAT2014-51982-C2-1-R, MAT2014-51982-C2-2-R and MAT2015-69725-REDT from MINECO (including FEDER funding), CELINA COST Action CM1301, Aragon Regional Government through project E26, FP7 Marie Curie Fellowship 3DMAGNANOW, EPSRC Early Career Fellowship EP/M008517/1 and Winton Fellowship.

Control of the spin to charge conversion using the inverse Rashba-Edelstein effect

We show here that using spin orbit coupling interactions at a metallic interface it is possible to control the sign of the spin to charge conversion in a spin pumping experiment. Using the intrinsic symmetry of the “Inverse Rashba Edelstein Effect” (IREE) in a Bi/Ag interface, the charge current changes sign when reversing the order of the Ag and Bi stacking. This confirms the IREE nature of the conversion of spin into charge in these interfaces and opens the way to tailoring the spin sensing voltage by an appropriate trilayer sequence.

Antiferromagnetism at T > 500 K in the layered hexagonal ruthenate SrRu2O6

We report an experimental and computational study of the magnetic and electronic properties of the layered Ru(V) oxide SrRu2O6 (hexagonal, P3¯1m), which shows antiferromagnetic order with a Neel temperature of 563(2) K, among the highest for 4d oxides. Magnetic order occurs both within edge-shared octahedral sheets and between layers and is accompanied by anisotropic thermal expansivity that implies strong magnetoelastic coupling of Ru(V) centers. Electrical transport measurements using focused-ion-beam–induced deposited contacts on a micron-scale crystallite as a function of temperature show p-type semiconductivity. The calculated electronic structure using hybrid density functional theory successfully accounts for the experimentally observed magnetic and electronic structure, and Monte Carlo simulations reveal how strong intralayer as well as weaker interlayer interactions are a defining feature of the high-temperature magnetic order in the material.

Quantitative analysis of the weak anti-localization effect in ultrathin bismuth films

Magnetic-field dependence of conductivity in ultrathin Bi films is measured in applied magnetic fields up to 9 T, in both directions, perpendicular and parallel to the film plane, at temperatures down to 0.4 K, and analyzed in terms of the weak anti-localization theory in two-dimensional systems. With the reduction of film thickness, the classical magnetoresistance effect is completely suppressed, and only the weak anti-localization effect is observed. The parameters extracted from the analysis allow the study of the contribution of the different scattering mechanisms to the electronic transport properties in ultrathin Bi films. In particular, the thickness-independent spin-orbit scattering length indicates that the spin-orbit split surface states dominate the transport in the ultrathin-film limit.

Magnetic properties of optimized cobalt nanospheres grown by focused electron beam induced deposition (FEBID) on cantilever tips

In this work, we present a detailed investigation of the magnetic properties of cobalt nanospheres grown on cantilever tips by focused electron beam induced deposition (FEBID). The cantilevers are extremely soft and the cobalt nanospheres are optimized for magnetic resonance force microscopy (MRFM) experiments, which implies that the cobalt nanospheres must be as small as possible while bearing high saturation magnetization. It was found that the cobalt content and the corresponding saturation magnetization of the nanospheres decrease for nanosphere diameters less than 300 nm. Electron holography measurements show the formation of a magnetic vortex state in remanence, which nicely agrees with magnetic hysteresis loops performed by local magnetometry showing negligible remanent magnetization. As investigated by local magnetometry, optimal behavior for high-resolution MRFM has been found for cobalt nanospheres with a diameter of ≈200 nm, which present atomic cobalt content of ≈83 atom % and saturation magnetization of 106 A/m, around 70% of the bulk value. These results represent the first comprehensive investigation of the magnetic properties of cobalt nanospheres grown by FEBID for application in MRFM.

Fe

In this work we report the growth and structural and magnetic characterization of heteroepitaxial Fe3O4/MgO/Fe junctions. All three layers have been deposited by pulsed laser deposition. Combining high resolution transmission electron microscopy and X-ray results, we have obtained for the heterostructure the epitaxy relation MgO(001) [100]//Fe3 O4 (001)[100]/MgO(001) [100]/Fe(001)[110]. All interfaces appear very sharp with relatively small root-mean square (rms) roughness, ~ 0.2 nm. The magnetic coupling between Fe3O4 and Fe electrodes is also very small, J ~ 0.03 mJ/m2 (MgO barrier thickness of 2 nm). Microfabrication of magnetic tunnel junctions from these heterostructures is in progress.

_{3}

Nascent molecular electronic devices, based on monolayer Langmuir-Blodgett films sandwiched between two carbonaceous electrodes, have been prepared. Tightly packed monolayers of 4-((4-((4-ethynylphenyl)ethynyl)phenyl)ethynyl)benzoic acid are deposited onto a highly oriented pyrolytic graphite electrode. An amorphous carbon top contact electrode is formed on top of the monolayer from a naphthalene precursor using the focused electron beam induced deposition technique. This allows the deposition of a carbon top-contact electrode with well-defined shape, thickness, and precise positioning on the film with nm resolution. These results represent a substantial step toward the realization of integrated molecular electronic devices based on monolayers and carbon electrodes.

O

A detailed description of the use of the focused ion beam (FIB) to grow electrical contacts is presented. The combination of FIB with precursor compounds, which are delivered on the area of interest by means of gas-injection systems, allows the growth of electrical contacts with nanometric resolution on targeted places. The technique has been coined focused ion beam-induced deposition (FIBID). Pros and cons with respect to other existing techniques for contacting are discussed. The FIBID contacts reported in this chapter are based on the use of Pt and W precursors, which result in the growth of deposits with resistivities down to 100 μΩ cm without any post-treatment. A comparison of FIBID with focused electron beam-induced deposition, the sister technique that uses focused electrons instead of ions, is also presented. The steps to follow in order to be successful in the contacting process by means of FIBID are described. Examples of the contacting to individual nanowires and nanoparticles carried out in our laboratory are shown, together with the corresponding four-probe transport measurements. Below 5 K, W deposits are superconducting and can be therefore used for zero-resistance lead contacts, superconductor-based nanocontacts and probing of proximity effects, opening new perspectives as described here.