1. SmartMembranes GmbH
Dresden, M3d Meeting
05/09/14

2. Production of standard alumina membranes
Samples delivery:
90 pieces (P = 180 ±10 nm, 35 ± 5 nm, 25 ± 5 nm) Neel (2013)
100 pieces (P = 70±10 nm, 35 ± 5 nm) UHAM ( )
Sample delivery of standard high ordered alumina to partners of M3d

3. Production of modulated alumina membranes
Samples delivery:
modulated BII, pore diameter inside  nm, pore diameter outside  nm,
diameter of the membrane 13-15mm, thickness of the membrane up to 70 μm) Neel ( )
- modulated AII and BII, pore diameter inside  nm, pore diameter outside  nm,
diameter of the membrane 13-15mm, thickness of the membrane up to 70 μm FAU ( )
AII
BII
Sample delivery of standard high ordered alumina to partners of M3d
Δ Pa/Pi
40-50 nm
period of modulation
120 nm
Δ Pa/Pi
40-50 nm
period of modulation
140 nm

4. Modulated structures – our approach
(b)
(I)
(II)
New approach:
Concerning Nanotechnology 21 (2010)
(I) switching between MA and HA
(II)
Each pulse consists of four segments of potential ramps defined by the potentials (Uj ) and the time widths (τi j ), where Uj = the potential at the time t j ( j = 1–5), t5 − t1 = the period of a pulse, τi j = t j+1 − t j, and i = the pulse number (i = 1, 2, 3, . . .) (figure 1(b)). An arbitrary form of potential wave (e.g., square, triangle, or sawtooth) can be generated by appropriately varying Uj and τi j . The length of oxide nanopores with a smaller diameter can be controlled by varying the time width τi1 (i.e., the first segment in figure b II), during which the recovery of current takes place. On the other hand, the length and the internal pore geometry of oxide nanopores with a larger diameter can be tuned by appropriately varying the pulse duration and the amplitude, which are defined by (τi2, τi3, τi4) and (U2, U3, U4), respectively
Nanotechnology 21 (2010)
Schematics showing (a) the experimental process for the fabrication of AAO with tailor-made pore structures by pulse anodization of aluminum and (b) a generalized form of a potential pulse employed in pulse anodizations. Uj and τi j define the repeating unit of potential waves, where Uj = the potential at the time t j with U1 = U5 ( j = 1–4), τi j = t j+1 − t j , i = the pulse number (i = 1, 2, 3, . . .).

5. ‘pulse anodization’
- jo and β are the material-dependent constants and
- U/tb is the effective electric field strength (E) across the barrier layer of thickness tb
j = jo exp(βE) = jo exp(ΔU/tb)
for a given electrolyte system, the barrier layer thickness (tb) increases with anodization potential (U) at a rate:
ζ MA ∼ 1.2 nmV−1 ζ HA ∼ 0.6–1.0 nmV−1
switching from HA condition to a lower MA one, the current drops abruptly
gradually increases with time to a steady value corresponding to MA (i.e., current recovery)
the required time for a complete current recovery is dependent on the temperature and the potential difference between MA and HA
increases in the order H2SO4 < H2C2O4 < H3PO4
The current in anodization of aluminum under a potentiostatic condition is related to the passage of ions through the barrier oxide layer at the pore bottom. Previous studies indicate that the anodization current is dependent on the thickness and the chemical composition of the barrier oxide. For a given anodization potential (U), the current density ( j) is inversely proportional to the logarithm of the barrier layer thickness (tb)
through the following equation: j = jo exp(βE) = jo exp(ΔU/tb).
Therefore, when the anodization potential is switched from a higher value satisfying the HA condition (i.e., UHA) to a lower MA one (i.e., UMA), the current drops abruptly to a very small value and then gradually increases with time to a steady value corresponding to UMA (i.e., current
recovery)

6. increase of the ramp between MA / HA (A I)
With increasing of τ11 :
Difference between highest and smallest value of pore diameter (Δ Pa/Pi, pa= pore diameter of the outside, pi= pore diameter of the inside) is increasing
Δ Pa/Pi is a level for the strength of modulation!
period of modulation is increasing too
Δ Pa/Pi
30 nm
40-50 nm
50 nm
period of modulation
160 nm
200 nm
400 nm

7. Influence of temperature
τ11 = 54 s, 1-2°C
τ11 = 54 s, 7-10°C
Influence of the temperature of the electrolyte:
Same profile (τ11 ), but different temperature of the electrolyte during etching.
Δ Pa/Pi is duplicated
period of modulation is increased nearly tenfold for the higher temperature
Δ Pa/Pi
50 nm
90 nm
period of modulation
140 nm
1,2 µm

8. New requirements seperation of the modulation:
diameter of modulations / period of modulation
1 / 10
Influence of the temperature of the electrolyte:
Same profile (τ11 ), but different temperature of the electrolyte during etching.
Δ Pa/Pi is duplicated
period of modulation is increased nearly tenfold for the higher temperature

9. potential difference between segments of HA
current recovery 120s current recovery 600s
100V-140V,
τ11 = 30 s, 2-3°C
no curren flowt at 100V
no influence for pore growing
time for current recoverv too short
- pore splitting,
- pore diameter at 100V is too small

10. potential difference between segments of HA
120V-140V, current recovery 600s V V, current recovery 300s
weak modulations
period = 2,4µm
τ11 = 30 s, 1-3°C
clearly modulations
period = 1,5 µm