Research in the area of CVD single crystal diamond plates of which only
recently has been made commercially available saw significant advancements
during the last decade. In parallel to that, detonation nanodiamond (DND)
particles also now widely made accessible for requisition are provoking a lot
of scientific investigations. The remarkable properties of diamond including its
extreme hardness, low coefficient of friction, chemical inertness,
biocompatibility, high thermal conductivity, optical transparency and
semiconducting properties make it attractive for a number of applications,
among which electronic and micro electrical-mechanical systems devices for
chemical and biological applications are few of the key areas. A detailed
knowledge of diamond devices at the prototypical stage is therefore critical.
The work carried out encapsulated in this thesis describes the employment of
the nanometer-scale diamond structures for the design, fabrication and testing
of electronic devices and micro electrical-mechanical system (MEMS)
structures for chemical sensing applications. Two major approaches are used
to achieve engineering novelty. The first type being devices based on single
crystal diamond substrates, which include state of the art δ-doped single
crystal diamond Ion Sensitive Field Effect Transistor with an intrinsic layer
capping the delta-doped layer for pH sensing and the fabrication and
characterization of a triangular-face single crystal diamond MEMS. A
comprehensive set of characterisations was systematically performed on the
delta ISFET devices. Cyclic Voltammetry has been used to determine the
devices’ potential window determining the limits of the applied potential for the
Current-Voltage measurements. In solutions of different pH levels, an
improved sensitivity of 55mV/pH compared to cap-less design in a previous
study is taken as the salient figure of merit. Electrochemical Impedance
Spectroscopy sheds some light on device performance in terms of flatband
voltages and conduction pathways through circuit modelling. Improved ISFET
characteristics such as lower flat-band voltage at 3.74V, simpler conduction
paths and drain current saturation onsets show the chosen design is correct and advances delta-doped diamond ISFET research and development work.
For the single crystal diamond cantilever, the theoretical modelling supports
the triangular-face design to be a better option, generating 3x greater
deflections in relation to the conventional rectangular-face design, when
operated as a static mode sensor. Based on experimental characterisation
methods such as Raman and Energy Dispersive Spectroscopy, the focusedion
beam only milling technique inflicts minimum damage to the beam
structure.
In the second approach, a novel hybrid device idea was conceived and
implemented using off-the-shelf silicon ISFETs and cantilevers with a coat of
nanodiamond particles on the ‘active area’ surfaces of the respective devices.
These nanodiamond-coated silicon devices exhibit high sensitivity for tracing
threat signatures such as explosive precursors and analogues with the former
in both liquid and vapour medium, and the latter in the vapour phase. The
nanodiamond-gated ISFET shows a voltage response of a commendable
maximum voltage shift of ~90 mV throughout 0 to 0.1M concentration range of
NO2
- and ClO3
- solutions. In the vapour phase detecting 2,4-DNT, a sensitivity
of ~20mV/0.4ppm is observed. The nanodiamond-coated silicon cantilever
demonstrates a performance advantage of 7.4 Hz/ppb to 1.7 Hz/ppb in a
previous study. Fourier Transform Infra-red spectroscopy was carried out on
the nanodiamond surfaces hosted by potassium bromide (KBr) discs to
ascertain the vapour chemisorption. With the fabrication technique simplified,
commercialisation of these proof-of-concept devices should be less time
consuming thus enabling quicker deployment of diamond-based surface
sensing technology