Integration of electrodeposited PdNi alloys with silicon and carbon nanotube electronics

Abstract

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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Identifiers

ORCID for C.H. de Groot: orcid.org/0000-0002-3850-7101

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