Stephen Topping

January 2012
Vapor Deposited Lu2o3:Eu3+ For X-Ray Imaging Applications
Committee Members: Advisor: Vinod Sarin, MSE/ME, Soumendra N. Basu, MSE/ME;
Srikanth Gopalan, MSE/ME; Charles Brecher, ALEM Associates; Chair: Thomas Bifano,
MSE/ME

Abstract: Lutetium oxide doped with europium oxide (Lu2O3:Eu3+) has been established to be an unparalleled bright, dense scintillator material with limitless potential in both medical and high resolution X-ray imaging applications.  Unfortunately its commercial viability has been completely restricted due to the cost of manufacturing the material and the post treatment costs associated with device fabrication. This research was aimed at the development of two vapor deposition techniques; chemical and physical vapor deposition (CVD and PVD), to produce coatings of Lu2O3:Eu3+ for various x-ray imaging applications. A unique CVD process to co-deposit Lu2O3 and Eu2O3 was developed using lutetium and europium chloride (LuCl3 and EuCl3) precursors and reacting with carbon dioxide (CO2) and hydrogen (H2). An in-depth study was performed by systematically varying process parameters to explore the deposition kinetics, and to identify rate limiting steps and their effects on the growth morphology using both cold and hot wall CVD reactors. The activation energy for the kinetically limited deposition of Lu2O3 from the LuCl3 – Ar – CO2 – H2 system was identified to be approximately 140 kJ/mol, which is significantly lower than expected. The predominant growth orientations were identified to be {111} and {100}, depending on the deposition conditions. As the temperature is increased, the growth orientation preference decreases to produce a randomly oriented growth. The scintillation properties and x-ray imaging characteristics of a co-deposited Lu2O3:Eu3+ thin film with a {100} orientation were measured, confirming the feasibility and applicability of the CVD system to produce thick scintillator x-ray imaging devices. A fundamental study of the PVD process and its effect on oxide scintillators was performed by sputtering of Lu2O3:Eu3+ using a single target magnetron sputtering gun. Systematic variations of the deposition parameters were used to understand the effect of ejected flux kinetic energies and deposition rate on the deposit density, stress, optical and scintillation properties. The deposition system was subsequently optimized for rapid, dense growth of a 10 μm thick Lu2O3:Eu3+ coating at elevated temperatures. The optical, scintillation and x-ray imaging properties were measured and the results yielded a ~1 μm resolution with the potential for an x-ray imaging resolution of 0.5 μm with further optimization, a resolution never before attained.