Lutetium Oxide Coatings by PVD
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1038-O08-04
Lutetium Oxide Coatings by PVD Stephen G Topping, C H Park, S K Rangan, and V K Sarin Department of Manufacturing Engineering, Boston University, 15 St. Mary's Street, Boston, MA, 02215 ABSTRACT Due to its high density and cubic structure, Lutetium oxide (Lu2O3) has been extensively researched for scintillating applications. Present manufacturing methods, such as hot pressing and sintering, do not provide adequate resolution due to light scattering of polycrystalline materials. Vapor deposition has been investigated as an alternative manufacturing method. Lutetium oxide transparent optical coatings by magnetron sputtering offer a means of tailoring the coating for optimum scintillation and resolution. Sputter deposited coatings typically have inherent stress and defects that adversely affect transparency and emission. The effect of process parameters on the coating properties is being investigated via x-ray diffraction (XRD), scanning electron microscopy (SEM) and emission spectroscopy, and will be presented and discussed. INTRODUCTION Rare earth oxides have been extensively used in the x-ray detector industry for quite some time due to their stability, high density and high atomic number [1]. However, they have generally been limited to small area detectors due to manufacturing limitations. Lutetium Oxide (Lu2O3) doped with Europium Oxide (Eu2O3) has been studied using hot pressing and sintering as an alternative to the industry standard Cesium Iodide doped with Tantalum (CsI:Tl). In terms of optical and scintillating properties, CsI:Tl has a good transparency, density of 4.51g/cc and emits ~60,000 photons per MeV of incident x-rays [2]. Compared to Lu2O3:Eu3+, which has a highly transparent BCC structure, a density of 9.4g/cc and emits ~30,000 photons per MeV [1]. High density and high atomic number of Lu2O3 makes it an ideal scintillator. A viable manufacturing process would expand its market to the large area scintillators. Current manufacturing methods, such as sintering and hot pressing produce a transparent 2-3mm thick disc that must be ground and polished to a thickness close to the desired thickness. It must then be pixelized into 20µm by 20µm square pixels as shown in Figure 1 using a highly labor intensive laser ablation process to reduce light scattering. The top surface is then placed on the CCD camera using optical glue and the back is ground off. [2] Dentistry is one of the applications for such a device and requires approximately 200 microns of Lu2O3, compared to 2mm for CsI, to absorb most of the incoming x-rays. Our proposal is to develop vapor deposited Lu2O3 coatings as an alternative manufacturing method that would enable largescale detector fabrication.
Figure 1. Top surface scanning electron image of a laser pixelized Lutetium Oxide ceramic. [2] EXPERIMENT The radio frequency (R.F.) magnetron sputtering setup used had a 2 inch diameter target angled at 45 degrees with respect to the substrate. The target was made by hot pressing Lu2O3 powder doped with 5 mol% Eu2O3 at 1700◦C usi
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