Font Size: a A A

Investigation of NbNx thin films and nanoparticles grown by pulsed laser deposition and thermal diffusion

Posted on:2014-10-05Degree:Ph.DType:Dissertation
University:Old Dominion UniversityCandidate:Hassan Farha, AshrafFull Text:PDF
GTID:1450390005494984Subject:Engineering
Abstract/Summary:
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 (lambda = 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 -Nb 2N and cubic delta-NbN phases to single hexagonal beta- Nb 2N. 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 delta-NbN with a strong (111) orientation. A correlation between surface morphology, electronic, and superconducting properties was found. The highly-textured delta-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 beta-Nb 2N. 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 1.3x10-3 Pa, showed the formation of an alpha phase. As pressure increased to 0.13 Pa, an alpha-NbN phase mixed with beta-Nb 2N 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 delta-NbN phase. The femtosecond laser-nitrided samples were prepared by different laser fluences of 0.1--1.3 mJ/cm2 at 4.0x104 Pa nitrogen pressure. NbNx samples with mixedalpha, beta and delta phases were observed. The cubic delta-NbN structure is dominated over the other two phases.
Keywords/Search Tags:Laser, Films, Nbnx, Deposition, PLD, Niobium nitride, Grown, Cubic delta-nbn
Related items