1. Development of Large-Area Photo-detectors:
U.S. Department of Energy
Development of Large-Area Photo-detectors:
Self Assembled Anodic Aluminum Oxide for MCPs
H. Hau Wang, Argonne National Laboratory
Office of Science
Department of Energy
Abstract
The goal of this R&D program is to develop a family of large-area robust and economical photo-detectors that can be tailored for a wide variety of applications. Micro-channel plate photomultipliers (MCP-PMT’s) combine the virtues of photo-multipliers with a relatively simple planar package construction that can be scaled to large-area detectors. Three major development areas are needed: 1) Nanostructured photocathode for high quantum efficiency, 2) Pore structure with funnel shaped entrance for solving the first strike problem, and 3) Transmission-line anodes with fast waveform sampling to preserve the signal amplitude and shape. This part of the research is to develop anodized aluminum oxide membranes with desired funnel shaped entrance as well as the proper pore diameter. The funnel shaped entrance may be associated with intrinsic AAO pores. We will develop larger AAO pores through various anodization conditions. We will also investigate large AAO pores formation through lithographic fabrication such as focused ion beam and laser writer patterning methods. Our AAO growth studies indicate that surface patterning can facilitate the nanopore formation significantly.
Comparison: MCP, glass plate, and AAO
Results – Intrinsic pore formation
AAO with 280 nm pore-to-pore distance has been demonstrated
5×5 mm AFM image of AAO showing good order with 280 nm pore distance
FFT showing hcp symmetry
AAO with 395 nm pore-to-
pore distance showing non-
uniform lattice.
3.3×3.3 mm AFM image showing the anodization condition has not yet reach equilibrium
Cross section
analysis showing
pore distance
MCP
Glass Plate
AAO
SEM and optical images
Burle 2.3 mm
Incom 10 mm
80 nm pores
Basic 2D pore structure
Hexagonally close packed
Material
PbSiOx
SiO2
Al2O3
Coating feasibility
Yes
Available pore size mm mm nm
Possibility to extend the pore size
Increasingly difficult for smaller pores
due to fiber glass drawing
Larger intrinsic pores are being developed.
mm pores through litho-graphy at CNM
Aspect ratio (L/D)
40-80:1
~40-100:1 :1
Bias angle
0-19° 0°
Funnel shaped entrance No
Possible (intrinsic pores)
Cost for scaling up
Increasingly expensive beyond
a few inches
Relatively inexpensive
Pore formation through lithography
Focused ion beam
direct etching over
Al surface
FIB patterning showing hexagonally close packed array
hcp pattern with 500 nm
pore-to-pore distance
over Al surface
Laser writer
patterning over
a photoresist
layer
Optical micrograph of
a photoresist layer showing
8 mm pores
Procedure for Anodized Aluminum Oxide (AAO) Fabrication
1st anodization
Remove AAO
2nd
anodization
Surface
protection
AAO growth
Remove Al
Remove barrier layer
Remove polymer Al
AFM image of AAO
Pore-to-pore 110 nm
Pore diameter 40 nm
Unique features of AAO membranes
AAO intrinsic pores contains funnel shaped entrance which is beneficial for collecting photo-electrons
Larger pores are feasible
through lithography. The
very high aspect ratio
allows nearly vertical chemical
etching that is hard to accomplish
with conventional Si material.
SEM (left) and AFM (right) images showing
AAO membrane intrinsic pores with
funnel like pore entrance
Ch 1: Yellow Ch 2: Blue
SAXS - AAO growth behavior
1st anodization
AAO removed
In-situ study
Conclusion
AAO intrinsic pores with pore-to-pore distance ~400 nm has been developed. Pore size larger than 400 nm will be studied in the future. Both FIB and laser writer are efficient patterning techniques. Pore diameter between 1 and 10 mm will be fabricated. These samples will be coated with ALD technique and tested for photocathode current amplification.
This work has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.
Pre-patterned growth
The first 6 minutes of AAO growth in oxalic acid at 40 V, showing pattern developed but not ordered.
The first 6 minutes of pre-patterned AAO growth in oxalic acid at 40 V
showing highly ordered hcp pattern.