Mark, Lewis Paul (2009) Carbon nanotubes and other highly curved surfaces for field emission and field-promoted ionisation. PhD thesis, University of Warwick.

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Abstract

The thesis describes the development of various novel emitters for the
production of gaseous ions from solutions of non-volatile, thermally labile
samples for the purposes of mass spectrometry.
Nano-electrospray emitters each containing two separated channels running
throughout the length of the emitter were fabricated and evaluated. These
emitters were made from “theta-shaped” borosilicate capillaries, employing a
number of different coating procedures. Loading of different solutions into the
channels demonstrated the possibility of studying solute interactions on ultrashort
timescales. It is proposed that interactions took place in a shared Taylor
cone. The formation of specific adducts from vancomycin and diacetyl-l-lysyld-
alanyl-d-alanine was observed by mass spectrometry. From consideration of
the extent of H/D exchange between vancomycin and deuterated vancomycin, it
was concluded that the interaction times were of the order of 10-5 s.
Underlying theoretical considerations, design and fabrication from carbon
nanotubes (CNTs) of emitters for field desorption and field ionization ion
sources are described and discussed. The emitters fabricated made use of arrays
of vertically aligned multi-walled CNTs with in most cases an average length
and radius of 15 μm and 35 nm respectively. Emitters using dense coverings of
nanotubes and emitters with nanotubes selectively grown so that the height of
each nanotube was twice its separation from its nearest neighbour were investigated. Characterisation of the CNTs by field electron-emission confirmed
their effectiveness as field emitters. Fowler-Nordhein plots indicated fields of
6.14x109 +/- 0.72x109 V/m at a potential of 700 V. Field ionization of He, Ar,
Xe, methane and acetone was achieved with these same CNTs; neither the inert
gases nor methane have been field ionised with conventional activated-wire
emitters. The fields generally accepted to be required for field ionisation of He
and Ar are of the order of several 1010 V/m.
To create emitters which would not need to be removed from vacuum between
experiments, a means of injecting both liquids and gaseous samples directly to
the bottom of the CNTs was devised. This involved drilling 20 μm diameter
holes through the silicon substrate between intended sites of nanotube growth,
but before actually growing the CNTs. It was discovered that the presence of the
holes led to surface migration of the nickel catalysts initiating CNT growth.
Experiments undertaken to achieve mass spectrometric measurements with the
arrays of CNTs as emitters are described and discussed.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Nanotubes -- Research, Mass spectrometry -- Research, Electrospray ionization mass spectrometry
Official Date:	July 2009
Dates:	Date Event July 2009 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Derrick, Peter
Sponsors:	Engineering and Physical Sciences Research Council (Great Britain) (EPSRC) ; Bruker Daltonics (BD)
Format of File:	pdf
Extent:	227 leaves : ill., charts
Language:	eng

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