Two-photon Lithography for 3D Magnetic Nanostructure Fabrication

Ferromagnetic materials have been utilised as recording media within data storage devices for many decades. Confinement of the material to a two dimensional plane is a significant bottleneck in achieving ultra-high recording densities and this has led to the proposition of three dimensional (3D) racetrack memories that utilise domain wall propagation along nanowires. However, the fabrication of 3D magnetic nanostructures of complex geometry is highly challenging and not easily achievable with standard lithography techniques. Here, by using a combination of two-photon lithography and electrochemical deposition, we show a new approach to construct 3D magnetic nanostructures of complex geometry. The magnetic properties are found to be intimately related to the 3D geometry of the structure and magnetic imaging experiments provide evidence of domain wall pinning at a 3D nanostructured junction

Batch fabrication of scanning microscopy probes for thermal and magnetic imaging using standard micromachining

We present a process for batch fabrication of a novel scanning microscopy probe for thermal and magnetic imaging using standard micromachining and conventional optical contact lithography. The probe features an AFM-type cantilever with a sharp pyramidal tip composed of four freestanding silicon nitride nanowires coated by conductive material. The nanowires form an electrical cross junction at the apex of the tip, addressable through the electrodes integrated on the cantilever. The cross junction on the tip apex can be utilized to produce heat and detect local temperature changes or to serve as a miniaturized Hall magnetometer enabling, in principle, thermal and magnetic imaging by scanning the probe tip over a surface. We have successfully fabricated a first probe prototype with a nanowire tip composed of 140 nm thick and 11 μ m long silicon nitride wires metallized by 6 nm titan and 30 nm gold layers. We have experimentally characterized electrical and thermal properties of the probe demonstrating its proper functioning. ©2010 IEEE

FABRICATION AND CHARACTERIZATION OF MESOSCALE PROTEIN PATTERNS USING ATOMIC FORCE MICROSCOPY (AFM)

A versatile AFM local oxidation lithography was developed for fabricating clean protein patterns ranging from nanometer to sub-millimeter scale on octadecyltrichlorosilane (OTS) layer of Si (100) wafer. This protein patterning method can generate bio-active protein pattern with a clean background without the need of the anti-fouling the surface or repetitive rinsing. As a model system, lysozyme protein patterns were investigated through their binding reactions with antibodies and aptamers by AFM. Polyclonal anti-lysozyme antibodies and anti-lysozyme aptamer are found to preferentially bind to the lysozyme molecules on the edge of a protein pattern before their binding to the interior ones. It was also demonstrated that the topography of the immobilized protein pattern affects the antibody binding direction. We found that the anti-lysozyme antibodies binding to the edge lysozyme molecules on the half-buried pattern started from the top but the binding on the extruded pattern started from the side because of their different spatial accessibility. In addition, after incubating lysozyme pattern with anti-lysozyme aptamer in buffer solution for enough long time, some fractal-shaped aptamer fibers with 1-6nm high and up to tens of micrometers long were formed by the self-assembling of aptamer molecules on the surface. The aptamer fibers anchor specifically on the edge of protein patterns, which originates from the biospecific recognition between the aptamer and its target protein. Once these edge-bound fibers have formed, they can serve as scaffolds for further assembly processes. We used these aptamer fibers as templates to fabricate palladium and streptavidin nanowires, which anchored on the pattern edges and never cross over or collapse over each other. The aptamer fiber scaffold potentially can lead to an effective means to fabricate and interface nanowires to existing surface patterns

AFM manipulation of gold nanowires to build electrical circuits

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters , copyright © American Chemical Society after peer review and technical editing by the publisher. To acces final work see “AFM Manipulation of Gold Nanowires To Build Electrical Circuits”, Nano Letters 19.8 (2019): 5459-5468, https://doi.org/10.1021/acs.nanolett.9b01972We introduce scanning-probe-assisted nanowire circuitry (SPANC) as a new method to fabricate electrodes for the characterization of electrical transport properties at the nanoscale. SPANC uses an atomic force microscope (AFM) to manipulate nanowires to create complex and highly conductive nanostructures (paths) that work as nanoelectrodes, allowing connectivity and electrical characterization of other nano-objects. The paths are formed by the spontaneous cold welding of gold nanowires upon mechanical contact, leading to an excellent contact resistance of ∼9 ω/junction. SPANC is an easy to use and cost-effective technique that fabricates clean nanodevices. Hence, this new method can complement and/or be an alternative to other well-established methods to fabricate nanocircuits such as electron beam lithography (EBL). The circuits made by SPANC are easily reconfigurable, and their fabrication does not require the use of polymers and chemicals. In this work, we present a few examples that illustrate the capabilities of this method, allowing robust device fabrication and electrical characterization of several nano-objects with sizes down to ∼10 nm, well below the current smallest size able to be contacted in a device using the standard available technology (∼30 nm). Importantly, we also provide the first experimental determination of the sheet resistance of thin antimonene flake

Electronic transport properties of silicon nanowires synthesized by laser ablation

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Johannesburg, 2015.In this thesis electron transport properties of silicon nanowires are studied. The devices are synthesized using a laser ablation technique. The catalysts used in the synthesis are nickel nanoparticles. The silicon nanowires are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Dielectrophoresis is used to align and contact nanowires across two electrodes to create two-terminal devices. In addition four-terminal devices are fabricated using PMMA lift-off based electron beam lithography. Electron transport properties of the fabricated devices have been studied using dc measurement techniques. Resistance of the silicon nanowires has been measured as a function of temperature and magnetic field. These measurements have been accomplished using a Cryogenics system at low temperature, and high magnetic field. Temperature dependent studies reveal that Arrhenius type thermally activated transport behavior is the dominant transport mechanism in measurements at zero magnetic field. Magnetic field dependent measurements show a weak positive linear magnetoresistance. There are also strong oscillations in magnetoresistance curves. The temperature and field independence of the oscillations has been attributed to quantum interference effects

Nanowires fabricated by Focused Ion Beam

This thesis reports research on nanowires fabricated by FIB lithography with experiments to understand their mechanical, electrical and hydrodynamic properties. Au nanowires fabricated on Si$_3$N$_4$ membranes with width below 50nm exhibit liquid like instabilities and below $\sim$20nm the instabilities grow destroying the nanowires due to the Rayleigh- Plateau instability. Stability is better in the case for Si substrates than for the insulators Si0$_2$ and Si$_3$N$_4$. A series of 4-terminal resistance measurements were carried out on a "platinum" nanowire grown by FIB-induced decomposition of an organometallic precursor. Such nanowires are found to be a two phase percolating system, containing up to 70% by volume carbon. They have unexpected temperature behaviour which is explained using a percolation model with Kirkpatrick conduction in the presence of temperature induced strain. Au nanowire bridges of very small diameter were probed using AFM to investigate their deformation and fracture strength. Below a diameter $\sim$50nm, the mechanical properties are consistent with liquid-like behaviour. After reaching the fracture, the gold molecules from the bridge retract towards the fixed ends; rebinding of the gold causing reforming of the nanowire bridge can occur. FIB fabrication was also used to form a thermal bimorph MEMS cantilever which was investigated by AFM during actuation