[en] A method is presented that enables the template assisted electrochemical deposition of tens of micrometer thick, compact and stoichiometric Bi₂Se₃ micropillars. This is achieved by modifying the acidic electrolyte that contains 1 M HNO₃ with potassium chloride salt and introducing resting pulses during the plating process. We demonstrate the successful deposition into photoresist templates with mold diameters down to 30 µm and thicknesses up to 45 µm. Cross-sectional EDX line measurements confirm an optimal stoichiometry of Bi:Se 40:60 along the growth direction, independent of the micropillar diameter. XRD and Raman measurements after electrochemical deposition point to a primarily orthorhombic structure. To illustrate the potential of this electrochemical method for thermoelectric applications, Seebeck coefficient and electrical conductivity of 45 µm thick orthorhombic Bi₂Se₃ pillars with 30 and 50 µm diameter are measured for five different electrodeposition runs. An average electrical conductivity of 8.6 S/m (SD = 4.5 S/m) and a high average negative Seebeck coefficient of -162 µV/K (SD = 32 µV/K) was determined. The process presented here is highly promising for the reliable synthesis of Bi₂Se₃ micropillars, which can be integrated in thermoelectric micro generators or sensors.

[en] Recent advances in nanorobotic manipulation of ferromagnetic nanowires bring new avenues for applications in the biomedical area, such as targeted drug delivery, diagnostics or localized surgery. However, probing a single nanowire and monitoring its dynamics remains a challenge since it demands high precision sensing, high-resolution imaging, and stable operations in fluidic environments. Here, we report on a novel method of imaging and sensing magnetic fields from a single ferromagnetic nanowire with an atomic-scale sensor in diamond, i.e. diamond nitrogen-vacancy (NV) defect center. The distribution of static magnetic fields around a single Co nanowire is mapped out by spatially distributed NV centers and the obtained image is further compared with numerical simulation for quantitative analysis. DC field measurements such as continuous-wave ODMR and Ramsey sequence are used in the paper and sub Gauss level of field sensing is demonstrated. By imaging magnetic fields at a single nanowire level, this work represents an important step toward tracking and probing of ferromagnetic nanowires in biomedical applications. (paper)

[en] A magnetic hyperthermia cancer treatment strategy that does not operate by means of conventional heating mechanisms is presented. The proposed approach consists of injecting a gel with homogeneously distributed magnetic nanowires into a tumor. Upon the application of a low-frequency rotating or circularly polarized magnetic field, nanowires spin around their center of viscous drag due to torque generated by shape anisotropy. As a result of external rotational forcing and fluid friction in the nanoparticle's boundary layer, heating occurs. The nanowire dynamics is theoretically and experimentally investigated, and different feasibility proofs of the principle by physical modeling, which adhere to medical guidelines, are presented. The magnetic nanorotors exhibit rotations and oscillations with quite a steady center of gravity, which proves an immobile behavior and guarantees a time-independent homogeneity of the spatial particle distribution in the tumor. Furthermore, a fluid dynamic and thermodynamic heating model is briefly introduced. This model is a generalization of Penne's model that for this method reveals theoretic heating rates that are sufficiently high, and fits well into medical limits defined by present standards.

[en] Rh-Fe nanoparticles (NPs) with variable Rh/Fe ratios have been obtained by direct current electrodeposition onto Au-metalized Si/Ti substrates from an electrolyte containing Rh(III) and Fe(III) chloride salts. NP mean diameter could be varied in the range of 20–80 nm by playing with the applied current density (−j = 0.5–2 mA cm⁻²) and deposition times (t = 200–3200 s). NPs were very well adhered to the substrate and became progressively enriched in Fe as the absolute value of the current density increased. X-ray photoelectron spectroscopy analyses revealed that the NPs are mostly metallic. The oxygen signal detected at surface level is relatively high but reduces down to less than 1 at% after 1 min Ar ions sputtering. The as-deposited Rh-Fe NPs are active toward hydrogen evolution reaction in alkaline medium. Different values of the onset potential for water reduction have been observed depending on the j and t values applied for NPs growth. Cycling stability tests reveal that NPs do not suffer from excessive deterioration of their electrocatalytic activity with time.

[en] Highlights: • Cobalt-indium (Co-In) multilayered films are produced by direct current electrodeposition from a single electrolyte. • A periodicity of 175 ± 25 nm has been observed from the cross-section of the films. • Each layer exhibits a columnar microstructure and well-defined compositionally different (In-rich and Co-rich) regions. • Magnetic force microscopy measurements reveal the occurrence of a cross-sectional stripe-like magnetic patterning. Micrometer-thick cobalt-indium (Co-In) films consisting of self-assembled layers parallel to the cathode plane, and with a periodicity of 175 ± 25 nm, were fabricated by electrodeposition at a constant current density. These films, which exhibit spatio-temporal patterns on the surface, grow following a layer-by-layer mode. Films cross-sections were characterized by electron microscopies and electron energy loss spectroscopy. Results indicate the spontaneous formation of nanolayers that span the whole deposit thickness. A columnar structure was revealed inside each individual nanolayer which, in turn, was composed of well-distinguished In- and Co-rich regions. Due to the dissimilar magnetic character of these regions, a periodic magnetic nanopatterning was observed in the cross-sectioned films, as shown by magnetic force microscopy studies.

[en] Pseudo-ordered macroporous iron-phosphorous (Fe-P) films have been electrodeposited potentiostatically from a citrate-sulfate bath onto Au surfaces pre-patterned with a colloidal crystal mask of polystyrene spheres of 350 nm in diameter. The electrolyte contained sodium hypophosphite as the P source, enabling the incorporation of 6–14 at.% P. For comparative purposes, continuous films have been obtained galvanostatically on unpatterned Au surfaces. In both cases, the P content could be varied to a certain extent by adjusting the deposition potential or current density. Tunable microstructure and magnetic response was observed due to the dissimilar chemical composition, with coercivity values being larger in the macroporous films. Additionally, wettability analyses showed that these were more hydrophobic, reaching contact angle values of about 130^∘. In spite of their hydrophobic character, the samples were catalytic toward oxygen evolution reaction (OER) in alkaline media. The macroporous Fe-P films showed faster kinetics for OER than their nonporous counterparts. Our results show that electrodeposited porous Fe-P based materials show an interesting combination of properties which make them appealing for applications including water cleaning, soft-magnetic components, or electrocatalytic production of oxygen, to name a few.

[en] Highlights: • Functionalized alginate hydrogels for pH controlled drug release are synthesized. • Functionalization is designed to allow sustained drug release only at pH lower than 4.5. • Hydrogels are applied on magnetically steerable devices able to navigate human body. • Hydrogel coating onto microrobots create drug carriers that can reach specific target sites. • Hydrogel coating functionalization can guarantee the release of drugs only in the target site. Targeted drug delivery is currently emerging as a promising approach to overcome the limits of currently employed administration techniques. The most convenient methodology to control drug delivery is the application of stimuli-responsive materials, which can release drugs only when required, to remotely controlled microdevices able to navigate human body. Thanks to this synergy, release can be controlled both spatially and temporally. Spatial control is guaranteed by the maneuverability of the devices, which can be precisely guided to release in targeted locations. Temporal control, conversely, is guaranteed by the functionalization introduced in the stimuli-responsive material. In this context, the present work describes the coating of magnetically controlled microdevices with functionalized alginate-based hydrogels able to release drugs at pH values lower than 4.5. Hydrogels are functionalized binding the drug with either an azidoethyl ester bond or an amidic bond, following an innovative synthesis route. After fabrication, release from hydrogel coated microdevices as a function of the environmental pH is characterized. Finally, devices are magnetically actuated and the possibility to achieve spatially and temporally controlled release is demonstrated. The functional microtransporters described in the present work are particularly promising for in-vivo applications in environments where pH differences are present, like the digestive apparatus.