Combinatorial thin film synthesis of scintillation materials
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June 12, 2007 The University of Tennessee Materials Science and Engineering 1 Combinatorial thin film synthesis of scintillation materials Development of a high throughput technique for new scintillator discovery Jonathan D. Peak, Charles L. Melcher, Philip D. Rack Scintillation Materials Research Center Department of Materials Science University of Tennessee
Transcript of Combinatorial thin film synthesis of scintillation materials
June 12, 2007The University of Tennessee
Materials Science and Engineering 1
Combinatorial thin film synthesis of scintillation materials
Development of a high throughput techniquefor new scintillator discovery
Jonathan D. Peak, Charles L. Melcher, Philip D. RackScintillation Materials Research Center
Department of Materials ScienceUniversity of Tennessee
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Outline
Background of combinatorial methodsThin film methodsOur groups previous work
Deposition systemModelingBenchmarking
Lu2O3 to SiO2 gradient with constant cerium dopingLu2SiO5 (LSO) with cerium doping gradient
Conclusions and future work
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Combinatorial methods – thin films
H. Koinuma and I. Takeuchi, "Combinatorial solid-state chemistry of inorganic materials," Nature Materials, vol. 3, pp. 429 - 438, July 2004 2004.
Composition spreadKennedy, et al., 1965Hanak, 1970ChristenYamamoto, et al.
Spatial addressableXiang and Schultz, 1995
Layer-by-layer arrayKoinuma and Takeuchi
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Combinatorial thin films - modeling, synthesis, rapid characterization Cr-Fe-Ni phase diagram determinationCu-Ni carbon nanofiber catalysts for PECVDBulk metallic glass alloy developmentYAG:Gd solid state UV emittersLuminescent materials
Gd doped, yttrium oxideYAG:Gd and YAG:Cr
Our groups previous work
SEM micrograph of multilayer SEM micrograph of multilayer GdGd doped YAG thin filmsdoped YAG thin films
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Sputter system
AJA International ATC-200V RF magnetron sputter systemFour rf magnetron Gunsrf/dc substrate bias Rotating substrate holderHeater: RT–800°C (+/- 1°C)Base pressure below 10-9 torrInert gas injection at sourceReactive gas injection at substrate
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Sputter system
Si
Lu
Substrate
Ce
Chamber during Lu and Si deposition
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Sputter deposition
( ) ( )cosI Iθ θ=
Target
0
45
90
Target
Dark space
Positive Glow
V010
V
Self
bias
Ar+ Ar+
Substrate Angular Distribution
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Process modeling
{ } ( )360 32.7
0 01[ ] 360 90
3 30 0
21 1 1 1
cos sin1 cos cos
sin
2
nP
j k j ki i
total ij i j ij
i j
d d PtSC nVqd d
n n rr
θ θ φ θφ θ
θ φ θθ
π
= == =
= = = =
⎡ ⎤⎡ ⎤⎧ ⎫⎢ ⎥⎧ ⎫⎢ ⎥⎪ ⎪ +⎨ ⎬⎨ ⎬⎢ ⎥⎢ ⎥
⎩ ⎭⎪ ⎪⎢ ⎥⎢ ⎥⎡ ⎤ ⎩ ⎭⎢ ⎥⎢ ⎥= = Δ Δ⎢ ⎥ ⎢ ⎥⎢ ⎥⎣ ⎦⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎣ ⎦⎣ ⎦
∫ ∫∫ ∫∑ ∑ ∑ ∑
Ф
θsubstrate
r
Input variables:Source power, voltage, current
Material sputter yieldSource tilt angle
Substrate positionSource time
Determines substrate composition as a function of position
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MATLab process modelBinary Composition Profile
Al
ZrCu
Ternary Composition Profile
AlZr
Cu
Thickness Modeling
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Benchmarking
Development of a high throughput techniquefor new scintillator discovery
1. Thin film processing methods2. Characterization methods of thin film samples
Samples:1. Lu2O3 to SiO2 with constant cerium doping2. Lu2SiO5 (LSO) with a gradient of cerium doping
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Lu2O3-SiO2 with constant ceriumProcedure:
Sputter deposit multilayer Lu2O3-SiO2/Ce films, 5.3 at% CeAnneal: N2, 1400°C, 10 hours
Diffuse cerium, crystallize structureCharacterization:
Photoluminescence, x-ray excitation, x-ray diffraction, scanning electron microscopy
Alumina Substrate
Lu Si
1 μm
.5 mm
Deposited structure
material Lu to Si gradient ceriumtime 5 layers, 15min each 4 layers, 200s eachrf power Lu - 200W, Si - 100W Ce - 25Wpressure 3 mtorr 3 mtorrgas flow 25 sccm Ar, 2 sccm O2 25 sccm Arrotation 0 RPM 20 RPM
Processing parameters:
cerium
4.5 nm
Lu Si
Lu Si
Lu Si
Lu Si
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0.96 μmceriumlayers
as deposited
Substrate
Scanning electron micrographs
1.41 μm
annealed
Substrate
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LPS + SiO2
LSO + LPS
Lu2O3 + LSO
1 3 5 7 9
liquid
Lu2O3 SiO2
X-ray diffraction
LSOLu2O3
2 theta16.2 17.2
1cm - Lu rich3cm5cm7cm9cm - Si rich
30.5 31.534 35
Lu2Si2O7(LPS)
0200400600800
1000
20 25 30 35 40 45 50 55 602 theta
Inte
nsity
As deposited vs. annealed
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Photoluminescence excitation and emission spectra. Insert - integrated emission intensity.
Photoluminescence and x-ray excitation results
0
100
200
300
400
500
600
250 300 350 400 450 500nm
2cm - Lu rich4cm6cm8cm - Si rich
Inte
nsity
020406080
0 2 4 6 8 10cm from high Lu end
0
500
1000
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200 300 400 500 600 700nm
1cm - Lu rich4cm6cm9cm - Si rich
Inte
nsity
0
100200
300
400
0 2 4 6 8 10cm from Lu rich end
Optimum composition was found to be LSO
X-ray excitation spectra. Insert –integrated emission intensity.Bulk LSO spectra
00.20.40.60.8
1
250 300 350 400 450 500nm
EmissionExcitation
Inte
nsity
Bulk LSO spectra
00.20.40.60.8
1
250 300 350 400 450 500nm
EmissionExcitation
Inte
nsity
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Lu2SiO5 (LSO) with cerium gradientProcedure:
Sputter deposit multilayer LSO/Ce-gradient films – Ce gradient 2.5-8.5 at% Anneal: N2, 1400°C, 10 hours
Diffuse cerium, crystallize structureCharacterize:
Photoluminescence, x-ray excitation, x-ray diffraction, scanning electron microscopy
Alumina Substrate
LSO
LSO
LSO
LSO
LSO
cerium
1 μm
.5 mm
Deposited structure
material LSO cerium gradienttime 5 layers, 15min each 4 layers, 200s eachrf power Lu - 200W, Si - 100W Ce - 25Wpressure 3 mtorr 3 mtorrgas flow 25 sccm Ar, 2 sccm O2 25 sccm Arrotation 20 RPM 0 RPM
Processing parameters:
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Scanning electron micrographsLSO:Ce
.92 μm
as deposited
1.21 μm
annealedcathodoluminescence image
Substrate
Substrate
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Photoluminescence excitation and emission spectra. Insert -integrated emission intensity.
X-ray excitation spectra. Insert –integrated emission intensity.
Photoluminescence and x-ray excitation results
0
200
400
600
800
1000
250 300 350 400 450 500nm
1cm - Ce low3cm5cm - middle7cm9cm - Ce high1
Inte
nsity
04080
120
0 2 4 6 8 10cm low Ce end
0
400
800
1200
1600
2000
200 400 600nm
1cm - Ce low5cm9cm - Ce high
Inen
sity
240260280300320
0 2 4 6 8 10cm low Ce end
.
Inte
nsity
Peak photoluminescence intensity at 6.7 at% cerium
Bulk LSO spectra
00.20.40.60.8
1
250 300 350 400 450 500nm
EmissionExcitation
Inte
nsity
Bulk LSO spectra
00.20.40.60.8
1
250 300 350 400 450 500nm
EmissionExcitation
Inte
nsity
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Conclusion
Used combinatorial thin film deposition to investigate scintillatorsDemonstrated synthesis of scintillator libraries via thin film sputter deposition; example: (Lu2O3)x - (SiO2)(1-x)
Identified various phases in Lu2O3-SiO2 system with XRD and correlated with emission spectra Peak LSO photoluminescence intensity at 6.7 at% Ce
Identified thin film characterization techniques
Further refinement of technique is in progress
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Future work
Investigate interaction of thin film with substrate Further refine relationship to bulk materialsInvestigate new scintillator material systemsGrow bulk single crystal samples of potential new scintillator materials
Combinatorialscreening
Bulk crystalgrowth
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Acknowledgements
Siemens Medical Imaging
Jung-Won Park, Kan Yang, Merry Spurrier, Piotr Szupryczynski, and Harold Rothfuss from the University of TennesseeJames Fitz-Gerald from the University of Virginia
