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Dive into the research topics where Torquil Wells is active.

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Featured researches published by Torquil Wells.


Applied Physics Letters | 2001

Very-low-energy electron microscopy of doped semiconductors

M.M. El-Gomati; Torquil Wells

Imaging of As- and B-doped silicon regions has been performed in a scanning electron microscope operated in the cathode lens mode, with incident electron energies (EP) as low as 15 eV. The doped regions of n+ (As, 2.5×1020 cm−3) and p+ (B, 8×1019 cm−3) on n-type silicon (∼1015 cm−3) show distinct contrast with electron energies of about 3 keV. The brightest region is n+ followed by p+, then the n-type substrate. The highest contrast for the p+ and n+ type regions is reached at about EP=300 and 15 eV, respectively. The contrast mechanisms are explained in terms of metal-semiconductor contact assuming an adventitious carbon film at the surface.


IEEE Transactions on Electron Devices | 2004

Why is it that differently doped regions in semiconductors are visible in low voltage SEM

M.M. El-Gomati; Torquil Wells; Ilona Müllerová; Luděk Frank; H. Jayakody

Although doped regions in semiconductors have been shown to give a different secondary electron yield in low-voltage scanning electron microscopy, the basic interpretation of this contrast has been difficult. It is accepted that this contrast stem from electronic phenomenon rather than atomic number differences between differently doped regions. However, the question is whether variations in the patch fields above the sample surface, balancing variations in the inner potentials, or surface coatings and/or surface states are the mechanisms responsible for the observed contrast. The present study reports on comparative experiments of these two models and demonstrates that the image contrast can be controlled by the presence of thin-surface metallic coatings. These results are the first evidence of the adlayer contacts, i.e., the subsurface electric fields instead of the patch fields above the surface, being responsible for the secondary electron contrast of doped semiconductors imaged in low voltage scanning electron microscopes under standard vacuum conditions, and they pave the way for the routine use of this method in semiconductor research and industry.


Proceedings of SPIE, the International Society for Optical Engineering | 2008

The application of carbon nanotube electron sources to the electron microscope

Mark Mann; Mohamed El Gomati; Torquil Wells; W. I. Milne; Ken B. K. Teo

The promising field emission properties of carbon nanotubes, or CNTs, have resulted in them being identified as desirable sources for electron microscopes and other electron beam equipment. A new process to grow single CNTs aligned to the electron-optical axis inside electron source modules has been developed. The process involves putting the entire source-suppressor module inside a plasma-enhanced chemical vapour deposition reaction chamber. This is a process which can be scaled up to mass production. The resultant CNT electron sources were inserted into an electron microscope for imaging. Though current stability was found to be comparable to the tungsten cold-field emitter (with a maximum-minimum variation of 3-7% of the mean current over one hour), the reduced brightness was found to be an order of magnitude greater than a typical Schottky source (at 3×109 Acm2sr-1) with a kinetic energy spread of 0.28 eV. Imaging with a CNT source has produced a marked improvement in resolution when compared to a Schottky source using the same electron-optics. The properties measured show that the CNT source compares favourably with and in some cases improves upon other sources available today. In particular, the CNT source would be of most benefit to low-voltage, high-resolution microscopy.


Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanoengineering and Nanosystems | 2008

Stabilization of carbon nanotube field emitters

Mark Mann; Koon K. Teo; W. I. Milne; M. M. El Gomati; Torquil Wells; T. Tessner; M Ovsyanko

Carbon nanotubes (CNTs) have been determined to be field emitters of high quality, but CNTs produced by chemical vapour deposition can produce emission currents with high instability and noise. This work finds that adsorbates and amorphous carbon deposited during the growth process are the primary contributors to field emission instability, and shows that burning off the amorphous carbon in air at 450°C removes the amorphous carbon, resulting in stabilities of better than 3 per cent over 1 h. This work removes one of the major barriers to the use of CNTs in field emission devices.


Archive | 2005

Low energy scanning analytical microscopy (LeSAM) for Auger and low voltage SEM imaging of semiconductors

V Romanovsky; M.M. El-Gomati; Torquil Wells; J Day

A new low energy scanning analytical microscope (LeSAM), combining scanning electron microscopy (SEM), scanning low energy electron microscopy (SLEEM), Auger electron spectroscopy (AES) and scanning Auger mapping (SAM), was realized using a new mini-electron column in conjunction with a cylindrical mirror analyser (CMA). The SLEEM mode of operation uses a cathode lens in which the specimen is negatively biased. In this arrangement, electrons pass through the microscope at high energy and are decelerated to a low incidental energy at the specimen. A novel 6 segment angular resolved in-lens detector is employed for signal detection. The new mini-electron column in SLEEM mode gives high resolution for primary incident beam energies of a few eV. For AES and SAM modes of operation a 6 segment angular resolved detector is also employed for signal detection.


Physica Status Solidi (a) | 2006

Carbon nanotubes as electron sources

W. I. Milne; K. B. K. Teo; Mark Mann; I. Y. Y. Bu; G.A.J. Amaratunga; N. de Jonge; Myriam Allioux; Jim T. Oostveen; Pierre Legagneux; Eric Minoux; Laurent Gangloff; Ludovic Hudanski; Jean-Philippe Schnell; L. D. Dieumegard; F. Peauger; Torquil Wells; M. El-Gomati


Microelectronic Engineering | 2006

A manufacturable miniature electron beam column

James Spallas; Charles Silver; Lawrence P. Muray; Torquil Wells; M.M. El-Gomati


Archive | 2006

ELECTRON BEAM CONTROL METHOD, ELECTRON BEAM GENERATING APPARATUS, APPARATUS USING THE SAME, AND EMITTER

Shin Fujita; M.M. El-Gomati; Torquil Wells


Microelectronic Engineering | 2010

Controlling the growth of carbon nanotubes for electronic devices

Mark Mann; Y. Zhang; K. B. K. Teo; Torquil Wells; M. M. El Gomati; W. I. Milne


Journal of Nanoscience and Nanotechnology | 2009

Bamboo and herringbone shaped carbon nanotubes and carbon nanofibres synthesized in direct current-plasma enhanced chemical vapour deposition.

Lu Zhang; Li Chen; Torquil Wells; M.M. El-Gomati

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Mark Mann

University of Cambridge

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W. I. Milne

University of Cambridge

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K. B. K. Teo

University of Cambridge

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I. Y. Y. Bu

University of Cambridge

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J Day

University of Bristol

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