Effect of the Substrate Crystallinity on Morphological and Magnetic Properties of Fe70Pd30 Nanoparticles Obtained by the Solid-State Dewetting

Advances in nanofabrication techniques are undoubtedly needed to obtain nanostructured magnetic materials with physical and chemical properties matching the pressing and relentless technological demands of sensors. Solid-state dewetting is known to be a low-cost and “top-down” nanofabrication technique able to induce a controlled morphological transformation of a continuous thin film into an ordered nanoparticle array. Here, magnetic Fe70Pd30 thin film with 30 nm thickness is deposited by the co-sputtering technique on a monocrystalline (MgO) or amorphous (Si3N4) substrate and, subsequently, annealed to promote the dewetting process. The different substrate properties are able to tune the activation thermal energy of the dewetting process, which can be tuned by depositing on substrates with different microstructures. In this way, it is possible to tailor the final morphology of FePd nanoparticles as observed by advanced microscopy techniques (SEM and AFM). The average size and height of the nanoparticles are in the ranges 150–300 nm and 150–200 nm, respectively. Moreover, the induced spatial confinement of magnetic materials in almost-spherical nanoparticles strongly affects the magnetic properties as observed by in-plane and out-of-plane hysteresis loops. Magnetization reversal in dewetted FePd nanoparticles is mainly characterized by a rotational mechanism leading to a slower approach to saturation and smaller value of the magnetic susceptibility than the as-deposited thin film.

Controlling Equilibrium Morphologies of Bimetallic Nanostructures Using Thermal Dewetting via Phase-Field Modeling

Herein, we report a computational model for the morphological evolution of bimetallic nanostructures in a thermal dewetting process, with a phase-field framework and superior optical, physical, and chemical properties compared to those of conventional nanostructures. The quantitative analysis of the simulation results revealed nano-cap, nano-ring, and nano-island equilibrium morphologies of the deposited material in thermal dewetting, and the morphologies depended on the gap between the spherical patterns on the substrate, size of the substrate, and deposition thickness. We studied the variations in the equilibrium morphologies of the nanostructures with the changes in the shape of the substrate pattern and the thickness of the deposited material. The method described herein can be used to control the properties of bimetallic nanostructures by altering their equilibrium morphologies using thermal dewetting.

Multidimensional Aligned Nanowires Array: Toward Bendable and Stretchable Strain Sensors

Micropatterns based on the oriented nanowires have attracted research interests for their unique physicochemical advantages in various applications of electric microdevices. Here, we proposed a facile fibrous dewetting strategy by spreading and dewetting of the silver nanowire (AgNW) solution on the vertical aligned carbon nanotube array (ACNTs) for preparing multidimensional aligned nanowires array, based on the elastocapillary coalescence. The unidirectional shrinking of the liquid film on the top of ACNTs happens during the dewetting process, as a result of the elastocapillary coalescence of ACNTs, which drives the AgNWs aligned along normal direction of liquid film shrinkage on the top of ACNTs. Thus, a multidimensional aligned NWs array was prepared, composing of the horizontally oriented NWs of top layer and vertical ACNT bundles of under layer connected by CNT yarns. A bendable flexible electrode was prepared using the as-prepared multidimensional aligned nanowires array, showing high stability during bending cycles (1800 cycles). Moreover, the multidimensional aligned nanowires array is also applicable for fabricating strain sensors, which show stable resistance response under strain. We envision that the as-developed approach shed new light on easy manufacture NW-based micropatterns.

Solid-State Dewetting Dynamics of Amorphous Ge Thin Films on Silicon Dioxide Substrates

We report on the dewetting process, in a high vacuum environment, of amorphous Ge thin films on SiO2/Si (001). A detailed insight of the dewetting is obtained by in situ reflection high-energy electron diffraction and ex situ scanning electron microscopy. These characterizations show that the amorphous Ge films dewet into Ge crystalline nano-islands with dynamics dominated by crystallization of the amorphous material into crystalline nano-seeds and material transport at Ge islands. Surface energy minimization determines the dewetting process of crystalline Ge and controls the final stages of the process. At very high temperatures, coarsening of the island size distribution is observed.

Droplet Formation of an Anisotropic Liquid

The process of formation of new morphologies by confinement in nano-droplets, created from a dewetting process, was simulated. The obtained structures showed a great similarity with the experimental results present in the literature. The developed model captures the fundamental interactions that determine the dynamics of the phase separation process of a copolymer system confined between a rigid substrate and a free surface. Furthermore, its numerical resolution is highly efficient as a result of the implementation of Eyre algorithm.

Analysis of catalyst surface wetting: the early stage of epitaxial germanium nanowire growth

In several nanotechnological applications the dewetting process is crucial. Although not all phenomena of dewetting are fully understood yet, especially with regard to metallic fluids, it is clear that the formation of nanoparticles, -droplets, and -clusters and their movement is strongly linked to their wetting behaviour. For this reason, the thermodynamic stability of thin metal layers (0.1 – 100 nm) with respect to its free energy is examined here. The decisive factor for the theoretical consideration is the interfacial energy. In order to achieve a better understanding of the interface interactions, three different models for the estimation of this energy are presented: i. fully theoretical, ii. empirical and iii. semi-empirical. The formation of nanometre-sized gold particles on silicon and silicon oxide is investigated in detail, elucidating the strengths and weaknesses of the three models, comparing the different substrates, and verifying the possibility of further processing of the gained particles as nanocatalysts. The importance of a persistent thin communication wetting layer between the particles and its effects on their size and number also becomes clear. In particular, the intrinsic reduction of the Laplace pressure of the system by material re-evaporation and Ostwald ripening is considered to describe the theoretically predicted and experimentally found effects. Thus dewetting phenomena of thin metal layers can be well-directed used for the manufacturing of nanostructured devices. From this viewpoint, the behaviour of gold droplets as catalysts to grow germanium nanowires on different substrates is described.

Antifungal Properties of Pure Silver Films with Nanoparticles Induced by Pulsed-Laser Dewetting Process

Silver particles were prepared by dewetting Ag films coated on glass using a fiber laser. The size of the particles was controlled in the range of 92 nm–1.2 μm by adjusting the thickness of the Ag film. The structural properties and surface roughness of the particles were evaluated by means of scanning electron microscopy. In addition, the antifungal activity of the Ag particles was examined using spore suspensions of Colletotrichum gloeosporioides. It is shown that particles with a size of 1.2 μm achieved 100% inhibition of conidia growth of C. gloeosporioides after a contact time of just 5 min. Furthermore, the smaller particles also achieved good antifungal activity given a longer contact time. Similar results were observed for spore germination and pathogenicity tests performed on mango fruit and leaves. Overall, the results confirm that Ag particles have an excellent antifungal effect on C. gloeosporioides.