1. 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

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

3. 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?

4. 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.

5. 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

6. 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

7. 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,

8. 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.

9. 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

10. 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

11. 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

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

13. 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