Date of Award

Winter 2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Hani Elsayed-Ali

Committee Member

Helmut Baumbart

Committee Member

Gon Namkoong

Committee Member

Ganapati Myneni

Abstract

Niobium nitride films (NbNx) were grown on Nb and Si (100) substrates using pulsed laser deposition (PLD), laser heating, and thermal diffusion methods. Niobium nitride films were deposited on Nb substrates using PLD with a Q-switched Nd: YAG laser (λ = 1064 nm, 40 ns pulse width, and 10 Hz repetition rate) at different laser fluences, different nitrogen background pressures and deposition temperatures. The effect of changing PLD parameters for films done by PLD was studied. The seen observations establish guidelines for adjusting the laser parameters to achieve the desired morphology and phase of the grown NbNx films.

When the fabrication parameters are fixed, except for laser fluence, surface roughness, deposition rate, nitrogen content, and grain size increases with increasing laser fluence. Increasing nitrogen background pressure leads to change in the phase structure of the NbNx films from mixed -Nb2N and cubic δ-NbN phases to single hexagonal β- Nb2N. A change in substrate temperature led to a pronounced change in the preferred orientation of the crystal structure, the phase transformation, surface roughness, and composition of the films.

The structural, electronic, and nanomechanical properties of niobium nitride PLD deposited at different nitrogen pressures (26.7-66.7 Pa) on Si(100) were investigated. The NbNx, films exhibited a cubic δ-NbN with a strong (111) orientation. A correlation between surface morphology, electronic, and superconducting properties was found. The highly-textured δ-NbN films have a Tc up to 15.07 K. The film was deposited at a nitrogen background pressure of 66.7 Pa exhibited improved superconducting properties and showed higher hardness values as compared to films deposited at lower nitrogen pressures. NbN nanoclusters that were deposited on carbon coated Cu-grids using PLD at laser fluence of 8 J/cm2 were observed.

Niobium nitride is prepared by heating of Nb sample in a reactive nitrogen atmosphere (133 Pa) at a temperature of 900 °C. The results suggest that the niobium nitride was crystalline in the single phase of hexagonal β-Nb2N. As heating time increased, film growth continued with improvement in hardness and modulus.

The XRD of samples prepared by a thermal diffusion method at low nitrogen pressure and high temperatures were reported. The samples were prepared at temperatures ranging from 1250–1500 °C. 2D-XRD images of samples, processed at temperature range from 1250 –1500 °C at pressure of 1.3×10-3 Pa, showed the formation of an α phase. As pressure increased to 0.13 Pa, an α-NbN phase mixed with β-Nb2N phase appeared.

Niobium nitride samples were prepared by laser nitridation using a Q-switched Nd: YAG nanosecond laser and Ti: sapphire femtosecond lasers. The effects of laser fluence on the formed phase, surface morphology, and electronic properties of the NbNx were investigated. Samples were prepared using Nd: YAG laser are of NbNx in the cubic δ-NbN phase. The femtosecond laser-nitrided samples were prepared by different laser fluences of 0.1–1.3 mJ/cm2 at 4.0×104 Pa nitrogen pressure. NbNx samples with mixedα, β and δ phases were observed. The cubic δ-NbN structure is dominated over the other two phases.

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DOI

10.25777/8tmf-wg54

ISBN

9781303570247

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