Metal Nanocluster Enhanced Radiation Detection Bruce Hamilton Photon Science Institute

1. Metal Nanocluster Enhanced Radiation Detection Bruce Hamilton Photon Science Institute University of Manchester UK

2. Outline • Context: cancer and the problem of detecting high energy photons (protons). • Photonic detection with wide gap solids • Exploiting high Z atoms • High Z nanoparticle doping: physics of energy transfer • Aims for a future semiconductor/nano-composite 3-D Si technology Cinzia Hadron

3. Context: cancer and the problem of detecting high energy photons. Work in Manchester building high energy particle detectors for the LHC, CERN (ATLAS project) This work aims to build on some of the ideas developed at the LHC; adding in some basic nanoscience to build new detector technology. X-ray and now proton beam therapy are in urgent need of real time (in vivo) dose detecting and imaging technology. This is one of the key challenges for cancer therapy. Cinzia Hadron

4. Context: cancer and the problem of detecting high energy photons. x-ray and (now ) proton beams: highly intense and highly targeted. Proton therapy even worse problem. Beam delivery has developed dramatically (accelerator physics) No checks on what is actually delivered , no information , no feedback , no control. No detection or imaging of beam during therapy. For some key cases, tumours are close to sensitive tissue: chordoma– tumour in the base of skull or spine Treatment plan but patients move, organs move etc. Cinzia Hadron

5. Context: cancer and the problem of detecting high energy photons. What is the problem for detection? We would like to exploit the engineering and materials knowledge of traditional electronic materials e.g. Si Light elements: Si, Al, O, N, C………are poor at stopping high energy particles. Cear high Z advantage is preserved for radiation detection in general. X-ray beam transmission for Si, 0 to 30,000 eV: largely transparent X-ray beam transmission for Au , 0 to 30,000 eVsignificantly less transparent Data CXRO website Cinzia Hadron

6. Photonic detection (of x-rays) with wide gap solids • Alumina (Al2O3) e and h trap at deep states (stable) Blue luminescence signal is a linear function of x-ray photon flux. Visible light used to detect x-radiation electron released, heat or red photon M Hot core hole relaxes, energy dumped into valence band : e-h fs time scale K nucleus Cinzia Hadron

7. Photonic detection (of x-rays) with wide gap solids • Alumina (Al2O3) Blue light pulse proportional to the radiation incident over t seconds Radiation in for t seconds Optical interrogation after t seconds (red) Cinzia Hadron

8. Exploiting high Z atoms to enhance sensitivity How can we exploit high Z atoms ? Moreover, preferably in a integrated thin film technology? AFM nanoporous alumina model system Al2O3 can be made in thin film form by anodisation) of pure Al film; Film few nm to 2 microns thick Pores 5 nm to 70 nm diameter Cinzia Hadron

9. Exploiting high Z atoms to enhance sensitivity How can we exploit high Z atoms ? Moreover, preferably in a integrated thin film technology? energy AFM nanoporous alumina model system X-photon Fill pores with Au by electro-migration X-ray photons absorbed (more efficiently) will produce hot electrons in Au which will transfer to Al2O3 and generate e-h pairs increasing the subsequent blue luminescence Cinzia Hadron

10. Exploiting high Z atoms Did it work? Gold x 2 Gold x 1 No Gold Gold x 3 Yes but not controlled Cinzia Hadron

11. Electro migration depends on existence of micro cracks which allows ionic current to flow • Exploiting high Z atoms • Pore filling by Au electro migration pore Alumina insulator Al metal Cinzia Hadron

12. Exploiting high Z atoms Look carefully at the gold intake into the pore Good luminescence response always associated with nanoparticles (small) Pore filling does not work ….only nanoparticle decoration Cinzia Hadron

13. High Z nanoparticle doping: physics of energy transfer Developed Monte Carlo code for nanoscale geometry X- ray interaction with Au: principal process for energy transfer involves Auger electrons. X-photon absorption produces a cascade of Auger (MNN) electrons, average energy 2050 eV. Calculate the cooling, escape and energy transfer to the surrounding alumina. Use a model system Real system SEM Cinzia Hadron

14. High Z nanoparticle doping: physics of energy transfer 50 electrons , initial locations and flight directions are random within the nanosphere. Initial energy 2050 eV. 200 scattering events, calculation terminated when electron leaves the sphere. 3 nm diameter Au nanoparticle Monte Carlo trajectories indicate high “leakage” of electrons….each able to transfer energy to the alumina. Cinzia Hadron

15. High Z nanoparticle doping: physics of energy transfer 50 electrons , initial locations are random within the nanosphere. Initial energy 2050 eV. 300 scattering events, calculation terminated when electron leaves the sphere. 12 nm diameter Au nanoparticle Monte Carlo trajectories indicate lower “leakage” of electrons. Many lose all energy within the sphere. Cinzia Hadron

16. High Z nanoparticle doping: physics of energy transfer Total energy transfer Sub 10 nm diameter particles are required……….easier technology Cinzia Hadron

17. High Z nanoparticle doping: physics of energy transfer Until the electrons cool significantly, elastic scattering dominates: inelastic elastic Cinzia Hadron

18. High Z nanoparticle doping: physics of energy transfer Size dependent energy spectrum of Au nanoparticles: 5000 electrons with initial random positions 4nm to 6 nm diameter Number out drops, low energy tail broadens 20 nm to 40 nm diameter Number out drops, spectrum unchanged: only the 20nm skin contributes. Cinzia Hadron

19. High Z nanoparticle doping: physics of energy transfer • So now we understand the mechanism for enhancement of detection in terms of the role of the high Z metal X-photons absorbed by the Au release a shower of electrons with energy in the range 1000 eV to 2000 eV “mini e-beams” into the Alumina :e-h production which feeds the detection process A model system but it does correctly predict the effect of high Z nanoparticle doping Cinzia Hadron

20. Aims for a future semiconductor/nano-composite 3-D Si technology n+ sidewall doping Top down processing of “pore” Radial fully depleted diode Radiation hard by virtue of geometry I response not diffusion length limited p- silicon Stack many layers…….position tracking of protons Cinzia Hadron

21. Aims for a future semiconductor/nano-composite 3-D Si technology…..Hadrons The technology gain we seek is dependent on (1) energy transfer from high Z atoms and (2) choice of geometry. Transfer to Si structures depends only on scaling correctly. 3-D adaption Radiation hard by virtue of geometry Response not diffusion length limited BUT enhanced by appropriate pore filling Hadrons Proton energy transfer dependence on atomic number. p- silicon Cinzia Hadron

22. Conclusions We have demonstrated the gain in detection sensitivity for high energy particles using energy transfer from high Z nano materials More than 10X but we know systems not optimised and look for 100X Gain based on geometry and electron energy transfer principles…well understood. Success would impact on the success of cancer beam therapy and radiation detection in general. Cinzia Hadron