arXiv subjects

C. J. Edgcombe

Publications and source records attributed to C. J. Edgcombe.

3 recordsLinked to original sources

arXiv2019

Analysis of a capped carbon nanotube (CNT) with linear-scaling density-functional theory

The apex region of a capped (5,5) carbon nanotube (CNT) has been modelled with the DFT package ONETEP, using boundary conditions provided by a classical calculation with a conducting surface in place of the CNT. Results from the DFT solution include the Fermi level and the physical distribution and energies of individual Kohn-Sham orbitals for the CNT tip. Application of an external electric field changes the orbital number of the highest occupied molecular orbital (the HOMO) and consequently changes the distribution of the HOMO on the CNT.

physics.app-ph↗

arXiv2013

Imaging of weak phase objects with a Zernike phase plate

Analysis of the imaging of some simple distributions of object phase by a phase plate of Zernike type shows that sharp transitions in the object phase are well transmitted. The low-frequency components of the complete object function are attenuated by the plate. The behaviour can be characterised by a cut-on parameter defined as the product of the cut-on frequency of the plate and a characteristic dimension of the object. When this parameter exceeds a value of the order of unity, a sharp boundary in the object is imaged by a Zernike plate as a dark lining inside the boundary with a white outline or halo outside the boundary, in agreement with reported observations. The maximum diameter of objects that can be imaged accurately is inversely proportional to the diameter of the hole for beam transmission in the phase plate.

physics.ins-det↗

arXiv2012

Characterisation of Ferromagnetic Rings for Zernike Phase Plates using the Aharonov-Bohm effect

Holographic measurements on magnetised thin-film cobalt rings have demonstrated both onion and vortex states of magnetisation. For a ring in the vortex state, the difference between phases of electron paths that pass through the ring and those that travel outside it was found to agree very well with Aharonov-Bohm theory within measurement error. Thus the magnetic flux in thin-film rings of ferromagnetic material can provide the phase shift required for phase plates in transmission electron microscopy. When a ring of this type is used as a phase plate, scattered electrons will be intercepted over a radial range similar to the ring width. A cobalt ring of thickness 20 nm can produce a phase difference of pi/2 from a width of just under 30 nm, suggesting that the range of radial interception for this type of phase plate can be correspondingly small.

physics.ins-det↗