Séminaire d'Institut

Vendredi 21 Juin 2019 à 14h00.

Mapping Nanowire Junction Potentials with Particle Beams

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Semiconductor nanowire (NW) junctions are being studied using a well-known electron holography (EH) technique available with existing transmission electron microscopes. The minimum required capabilities are a coherent electron beam, provided by field-emission electron guns, and a beam-splitting electrical biprism placed in a convenient location in the electron optical column. The electron hologram gives the phase and amplitude of the beam after it passes through the sample and through this information junction potentials can be imaged with 10 nm lateral resolution. Results from EH for Si, GaAs, and InGaP NW systems will be described showing the effects of growth direction, and dopant type or composition on the resulting p-n junctions. [1] Greater resolution could be feasible with a smaller wavelength radiation such as might be provided by keV helium (He) ion beams. The lesser-known He ion microscope (HIM) is similar to a scanning electron microscope (SEM) but applies a focussed He+ ion beam to generate secondary electron images with sub-nanometer resolution. The spatial coherence of this beam is likely to be significant, since the He ions field ionize from the last atom of a tungsten tip. However, the spatial coherence has not been measured. We will describe results from focussed ion beam channeling through Si nanomembranes - the first step towards the demonstration of He ion diffraction and transmission helium ion microscopy (THIM).

[1] Three-dimensional imaging of beam-induced biasing of InP/GaInP tunnel diodes, Cristina Cordoba, Xulu Zeng, Daniel Wolf, Axel Lubk, Enrique Barrigon, Magnus T. Borgström, and Karen L. Kavanagh, Nano Letters (2019) May 9th.
Corresponding author email: Karen L. Kavanagh, kavanagh@sfu.ca, www.sfu.ca/kavanaghlab

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