T Gnanavel

Tomographic nanofabrication of ultrasharp three-dimensional nanostructures

We present the extension of electron tomography from a pure characterization technique into a three-dimensional nanofabrication technique using focused electron beams in the scanning transmission electron microscope. Two-dimensional surface patterning techniques are insufficient to achieve full three-dimensional nanosculpting, instead, multiple sample rotations under the beam are required. We demonstrate fabrication of ultrafine tips and hollow structures with applications in scanning probe microscopy, atom probe tomography, or in magnetoconductance of nanobridges. A sharpened tip radius of <3 nm is achieved, an order of magnitude finer than with standard methods.

Ni and W nanotips: fabrication and characterisation

Etching techniques are used to fabricate nickel and tungsten tips suitable as probes for in-situ SEM and TEM experiments. The smallest tip radius achieved is 10nm for Ni and 1.5 nm for W. Depending on the electrolyte concentration and speed of tip movement during etching, the macroscopic morphology can be changed between conical and concave shapes and the tip end can be modified. HREM and EELS characterisation is used to determine oxide layer thickness. For Ni the oxide layer is found to be extremely thin, while for W various thicknesses can be achieved. The particular amorphous WO3 layer is imaged by plasmon resonance mapping in EELS, which turns out to be a sensitive and discriminative technique exploiting the much larger plasmon peak width of the oxide compared to the pure metal.

Nanoscale sculpting of ferromagnetic structures by electron beam ablation

We report an electron beam (e-beam) fabrication method to produce sub-5 nm structures, e.g. nanohole-arrays, nanojunctions and nanotips inside a TEM. The method is demonstrated using ferromagnetic nickel cross-sectional TEM specimens as well as electrochemically etched nickel tips. Different e-beam shapes and electron guns are compared, including point versus line focus and field-emission versus LaB6 guns. As an extension of this 2-D patterning of nanostructures, a 3-D nanofabrication technique has been introduced using a high tilt tomographic holder. An electrochemically etched nickel tip of initially 18 nm in radius is sculpted down to sub-5 nm diameter. In some cases, mostly in 3-D nanofabrication, a protrusion during hole drilling was observed and confirmed by EELS as pure nickel.

A novel tripod-driven platform for in-situ positioning of samples and electrical probes in a TEM

We present a design for a novel coarse positioning system based on a tilting platform which is positioned using linear slip/stick motors. The design differs from common arrangements of stacked x, y, and z motors, and also ball mounted slip/stick motors, by allowing easy access along the central axis of the microscope holder. The drive motors are highly compact and co-linear and may be easily incorporated in an off-axis configuration, leaving a central cylindrical region with an approximate diameter of 3mm which is available to accommodate screened electrical wiring and optical fibres. We show that the tripod can be used to manoeuvre two metallic tips towards each other in-situ in a TEM in nanometre-scale lateral steps.

Hybrid tomography for structural and chemical 3D imaging on the nanoscale

Electron tomograms can be reconstructed from a variety of projection imaging techniques in TEM, some of which are sensitive to the surface or the bulk, to the structure or chemistry, or operate under different resolution regimes. We introduce a concept of combining two acquisition series using two different complementary modes to form a single hybrid tomogram. As the main application, composite nanoobjects are presented for which a low-resolution 3D chemical mapping mode for the object interior can be combined with a high-resolution surface sensitive mode to precisely define the object exterior shape.

Nanoporous structures from anodisation of non-planar aluminium surfaces

We report about a novel combination of two etching techniques for generating nanostructures, which individually are well established: (i) metal tip etching in NaOH, as e.g. used for STM or atom probe tip making, and (ii) anodic oxidation of aluminium for the generation of self-organised ordered pores. The non-planar geometry in both these etching processes allowed us to follow the electric field mediated orientation of pattern growth observable in the SEM. Surface-near porosity is found from both etching processes, however only anodisation leads to continued growth of deep channel-like pores. FIB cross-sections of the cone and tip regions are found suitable to study the oxide-metal interface distribution and their dependence with anodisation time and current, even grain boundaries between the two opposite regions of deep pores are observed.

Nanofabrication of ferromagnetic nanotips and nanobridges by 2D and 3D electron-beam cutting

Electron beam nanofabrication is a powerful technique to generate finest structures by atom ablation while concurrently observing the progress by TEM imaging [1–3].