"PhD Defense: Nanostructuring of nanodevices for nanoscience applications"

Who: Libe Arzubiaga, nanodevices Group, nanoGUNE

Place: CFM Auditorium

Date: Monday, 16 March 2015, 12:00

Thesis supervisor: Dr. Luis Hueso

This thesis is focused on the fabrication of nanostructured devices for applications in different fields of nanoscience, such as plasmonics, spintronics or nanoelectronics.

We first optimised the electron beam lithography process on substrates with different mechanical or electrical properties, such as insulating oxides, pyrex or electron-transparent silicon nitride membranes. We have achieved minimum sizes of around 20 nm for constrictions and nanogaps, which are close to the resolution limit of the employed equipment. We have also prepared electronic devices on graphene, including substrate preparation by physical exfoliation of graphyte flakes at a whole wafer scale. In this case we utilised a high energy electron beam (working at 100 kV), with which we could achieve structures with minimum sizes or around 10 nm.

On the other hand, we optimised the nanostructuring of devices by electromigration, as a technique complementary to electron beam lithography. This technique consists on breaking metallic wires of nanometric cross-section by electrical fatigue, allowing to obtain structures that are beyond the capabilities of most state-of-the-art lithographic techniques. Nanogap electrodes, nanoconstrictions and quantum dots are some examples of the obtained structures.

Finally, we combined all the optimised fabrication methods for obtaining single electron transistors and spintronic devices. On one hand, we obtained palladium-based devices (including pure palladium and nickel palladium alloy) showing single electron transport characteristics at liquid helium temperature. These devices were intended for the study of electronic correlations in metals and alloys. On the other hand, we fabricated lateral spin valves with nanoconstrictions. In these devices pure spin currents are created and transported through a non magnetic metallic channel, which in our case consisted of a constricted copper nanowire. We patterned these constrictions by electron beam lithography and then we further modified them by electromigration. We measured the evolution of the spin current after consecutive electromigration stages, in which the constriction was gradually narrowed. This still unfinished project aims at studying the transport of pure spin currents through nanostructured metallic channels containing either nanoconstrictions, nanogaps or quantum dots.

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