Discrete Dynode Structures Using ALD and Other Techniques for MCPs June 10th, 2010 LAPPD meeting Qing Peng, Anil U. Mane, Jeffrey W. Elam Energy Systems, Argonne National Laboratory

Traditional Discrete Dynode Structures Each stage is biased separately with well-controlled voltage drop Each stage could have its own SEE materials

Traditional Discrete Dynode Structures Functionalized MCP Traditional discrete dynode structures: Each stage is biased separately with well-controlled voltage drop Each stage could have its own SEE materials Can we make a MCP have similar structure as discrete dynode?

Motivation To achieve well-defined strike, especially the first and 2nd strikes, in the operation of MCPs, which could significantly decrease the widths of the transition time spread and single photon charge distributions.

Concept I Discrete dynode: Continuous resistive layer then discrete SEE layer Electrode coating could be putted on before SEE layer High SEE layer Low SEE layer Resistive layer MCP Substrate Electrode

Schematic to Achieve Stripe Coating by ALD Principle Reactants diffuse into the pore and react with along the pore The growth of materials could be selectively blocked by choosing different chemistry, as shown in following scheme. OH Diffusion controlled A deposition XLn O XL Diffusion control YLn YL X Y H2O direction into pore OH OH OH OH X Y

Previous Work of Stripe Coating Results Al2O3 ZnO Owing to large library of ALD chemistry: Stripes of other materials such as MgO could be formed through this method. AAO: aspect ratio >1000. Pore size: <60nm EDAX elemental maps for Zn L following deposition of ZnO stripes in AAO varying only the TMA exposure time J. W. Elam, J. A. Libera, M. J. Pellin etc APPLIED PHYSICS LETTERS 91, 243105 2007

Requirement and Challenge for ALD to form Stripes of SEE Requirement for good stripe coating by ALD The process needs to be in the diffusion controlled region: Reaction rate has to be very fast (sticking coefficient >> diffusion coefficient) Collision rate of molecules to the wall need to be high Diffusion rate has to be slow (Knudson mode) Challenges: It is difficult to control the reaction and diffusion process for the pore size of >10 um, because the mean free path is comparable with the pore size. The diffusion rate is expected to be higher. L/D ratio of glass MCP is ~60, which is small for controlling the diffusion of precursor Due to the concentration gradient along the tube, it is very difficult to form sharp interface between stripe coatings and uncoated parts.

More Effective Way: fabrication of Two Discrete Structure through ALD/PVD or CVD ALD SEE layer Resistive layer MCP substrate High SEE layer By CVD or PVD

Candidate Materials for High SEE Materials with Negative electron affinity, including activated GaP, GaN, GaAs, Diamond, and such. Diamond coating (SEE: <80) Highly crystallized MgO by PVD process (SEE:<25) High quality NaCl, CsI, MgF2, CaF2 (SEE 5-15) MgO film Single crystal MgO

Diamond as High SEE candidate by PECVD Ultrananocrystal Diamond by CNM-ANL At 400C J. Appl. Phys., Vol. 96, No. 4, 15 August 2004, O. Auciello, ANL-MSD www.photek.co.uk

ALD MgF2 and CaF2 APPLIED OPTICS Vol. 47, No. 13 1 May 2008

Proposed Scheme for Dynodes Structure Formation Test SEE of UNCD film by PECVD on Si Test MCPs with UNCD layer only at the top MgO by ALD/PVD/CVD ALD coating for 2 stripes of SEE layers on glass MCP and testing the feasibility for > 2 stripes of SEE layers ALD coating of CaF2 and MgF2 for applications of SEE