Usgaocar, Ashwin R.
Integration of electrodeposited PdNi alloys with silicon and carbon nanotube electronics.
University of Southampton, School of Electronics and Computer Science,
This thesis investigates the electrodeposition of PdNi films with controllable composition
and their suitability as electrical contacts in electronic and spintronic devices based on
Silicon and Carbon nanotubes (CNTs). The electrodeposition process and characterisation
of the electrical and magnetic properties of the deposited PdNi films are described. PdNi
films with a wide composition range can be deposited from the same bath by changing
the deposition potential. Electrical characterisation shows the formation of high quality
PdNi-Si Schottky barriers while magnetic measurements prove the ferromagnetic nature of
the PdNi films. Electrodeposited PdNi films are thus shown to be suitable contacts for
electronic and spintronic devices.
Hydrogen sensors comprising back to back electrodeposited PdNi-Si Schottky barriers
are fabricated and characterised. The back to back architecture ensures low current operation
at all biases. Palladium causes the Hydrogen molecules to dissociate and be absorbed
by the film, while Nickel makes the sensor resistant to repeated cycling in the Hydrogen
environment. The sensors exhibit extremely low idle currents, large percentage current increases
on Hydrogen exposure and high selectivity for Hydrogen. These factors, in addition
to the simplicity of fabrication and easy integration with conventional electronics show that
electrodeposited PdNi-Si Schottky barriers are well suited for use as Hydrogen sensors.
The workfunction change in PdNi films exposed to Hydrogen is used to characterise
CNTs contacted by electrodeposited PdNi. The PdNi contacted CNTs exhibit ohmic characteristics,
which change on exposure to Hydrogen. Examining this change allows differentiation
between semiconducting and metallic CNTs. Raman spectroscopy is used to
characterise the same CNTs and the results are compared with the electrical characterisation
in Hydrogen. The electrical and Raman analysis experimentally verify the theoretically
assigned CNT Raman features.
The fabrication and electrical characterisation of CNT transistors incorporating electrodeposited
PdNi contacts are presented. The CNTs are spin coated from a 1,2-dichlorobenzene
dispersion and contacted with electrodeposited PdNi. The PdNi-Si Schottky barrier is used
to suppress the current through the Silicon substrate during electrical characterisation. The
operating restrictions imposed by the direct PdNi-Si contact and methods to overcome the
same are discussed. The characteristics of the CNT transistor in a changing magnetic field
at room temperature are presented.
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