1. EFFECT OF THE ALUMINIUM SURFACE MORPHOLOGY ON THE BARRIER TYPE ANODIC FILM GROWTH
KOLÁŘ Jakub, SVATOŠ Vojtěch, HUBÁLEK Jaromír, MOZALEV Alexander
CEITEC - Central European Institute of Technology,
Brno University of Technology, Technicka 10, Brno, Czech Republic
Prezentace v rámci udržitelnosti projektu NANOTEAM: , VUT v Brně, Technická 10
Nanocon 2015
October 14-16, 2015, Brno, Czech Republic
Originaly presented at:

2. Projekt OPVK NANOTEAM,reg. č. projektu CZ.1.07/2.3.00/09.0224
Seminář v rámci udržitelnosti projektu OPVK NANOTEAM

3. Porous anodic alumina and its application
Self-organized nanostructured material grown by anodization of Al 
Regular structure with narrow size distributions of pore diameters and interpore spacing
Tuneable size
Easy, cheap and well described preparation process

4. Porous anodic alumina and its application
Self-organized nanostructured material grown by anodization of Al 
Regular structure with narrow size distributions of pore diameters and interpore spacing
Tuneable size
Easy, cheap and well described preparation process
Range of applications
Resistive switching
Photovoltaics
Template for nanowires/nanotubes
Kolář et al., J. Mat. Chem. C, 2 (2013) 349.
Kapadia et al., Nano Energy, 1 (2012) 132.
Proenca et al., Nanoscale Res. Lett., 7 (2012) 280.

5. Porous anodic alumina and its application
Self-organized nanostructured material grown by anodization of Al 
Regular structure with narrow size distributions of pore diameters and interpore spacing
Tuneable size
Easy, cheap and well described preparation process
Range of applications
The importance of PAA could be extended by applying the anodizing technique to thin Al films
Mozalev A. et al., J. Mater. Chem. C., 2. (2014) 4847

6. vs anodic aluminium oxide
Porous type
barrier type
Structure
Inner layer- thin, compact barrier type Outer layer - thick and porous
Thin, compact, non-porous structure
Thickness
Depends on current density and on time of anodizing
Depends on maximal potential applied
Typical electrolyte
Sulphuric, phosphoric, oxalic and chromic acid
Borate buffer, citric acid
Main processes
Ion migration, dissolution, stress, pore formation
Ion migration

7. vs anodic aluminium oxide
Porous type
barrier type
Complex
Fundamental
Structure
Inner layer- thin, compact barrier type Outer layer - thick and porous
Thin, compact, non-porous structure
Thickness
Depends on current density and on time of anodizing
Depends on maximal potential applied
Typical electrolyte
Sulphuric, phosphoric, oxalic and chromic acid
Borate buffer, citric acid
Main processes
Ion migration, dissolution, stress, pore formation
Ion migration

8. Why to study specificity of Al thin film anodizing?
The structure and morphology of Al thin films differ from those of Al foils.
The structure and morphology of thin films depend significantly on the deposition technique and deposition conditions.
The use of a two step anodizing is quite limited in the case of Al thin films.
Our aim:
To reveal the influence of thin Al film structure and morphology on electrochemical response and oxide formation during anodizing, in order to be able to prepare high quality thin film porous anodic aluminium oxide.
This talk:
Minor part of our recent research focused on investigation of the influence of Al thin film surface roughness on the electrochemical response during barrier type anodizing.

9. Experimental part - scheme
Ion beam deposition
Magnetron sputtering
Thermal evaporation
Al foil
anodizing
Surface profile
Surface roughness
SEM
Stylus profilometry

10. Prepared films – SEM images and roughness
SEM images of samples prepared by various techniques.
Sample a) IBD 3, b) MS 1 and c) TE 2
Summary of surface roughness of all investigated Al thin films
Sample
deposition technique
sample number
initial film roughness (mm)
IBD 1
0.006 2
0.03 3 MS
0.01
0.009
0.06 TE
0.003
The variety of surface structure and morphology of the deposited Al films is clearly visible from the SEM images.
Each of the Al thin film samples was measured by stylus profilometry and the surface roughness was evaluated

11. Anodizing response of Al thin films and comparison with Al foil
Current recorded during barrier type anodizing of A) the sample IBD 2 and B) the Al foil
Anodizing done in borate buffer V, 0.1 V/s, current density limited to 2.3 mA/cm2
Barrier type anodizing of Al thin films reveals typical breakdown, which occurs at a much lower potential than in the case of Al foil.
The barrier type anodizing response reveals good reproducibility and differs for various Al films.

12. Anodized films – roughness data
Sample
deposition technique
sample number
initial film roughness (mm)
anodic oxide film roughness (mm)
ratio after/before anodizing
breakdown potential (V)
IBD 1
0.006
0.09
15.0
101 2
0.03
1.0
136 3
0.04
1.3
140 MS
0.01
0.16
16.0
142
0.009
0.11
12.2
117
0.06
0.07
1.2
112 TE
0.003
0.05
16.7
137
0.02
2.0
150

13. Anodized films – roughness data
Sample
deposition technique
sample number
initial film roughness (mm)
anodic oxide film roughness (mm)
ratio after/before anodizing
breakdown potential (V)
IBD 1
0.006
0.09
15.0
101 2
0.03
1.0
136 3
0.04
1.3
140 MS
0.01
0.16
16.0
142
0.009
0.11
12.2
117
0.06
0.07
1.2
112 TE
0.003
0.05
16.7
137
0.02
2.0
150
In several Al thin films the surface roughness change after barrier type anodizing is significant

14. Anodized films – roughness data
Sample
deposition technique
sample number
initial film roughness (mm)
anodic oxide film roughness (mm)
ratio after/before anodizing
breakdown potential (V)
IBD 1
0.006
0.09
15.0
101 2
0.03
1.0
136 3
0.04
1.3
140 MS
0.01
0.16
16.0
142
0.009
0.11
12.2
117
0.06
0.07
1.2
112 TE
0.003
0.05
16.7
137
0.02
2.0
150
In several Al thin films the surface roughness change after barrier type anodizing is significant
For the other Al thin films the surface roughness change after barrier type anodizing is minor

15. Anodized films – roughness data
Sample
deposition technique
sample number
initial film roughness (mm)
anodic oxide film roughness (mm)
ratio after/before anodizing
breakdown potential (V)
IBD 1
0.006
0.09
15.0
101 2
0.03
1.0
136 3
0.04
1.3
140 MS
0.01
0.16
16.0
142
0.009
0.11
12.2
117
0.06
0.07
1.2
112 TE
0.003
0.05
16.7
137
0.02
2.0
150
In several Al thin films the surface roughness change after barrier type anodizing is significant
For the other Al thin films the surface roughness change after barrier type anodizing is minor
There is no relation between the surface roughness change and breakdown potential
The surface roughness change is significant for samples with the initially lower roughness

16. Surface of the anodic oxide film after anodizing
SEM observation:
Al thin films with significant surface roughness change – the surface of the anodic oxide film was seriously damaged
Al thin films without significant surface roughness change – the surface remains flat
The breakdown phenomenon occurs for both sample types
The surface damage is not responsible for the breakdown phenomenon
Surface of the anodic oxide of sample
a) MS1 and b) IBD 2 after anodizing

17. The surface roughness change during anodizing
Several pieces of sample TE 1 (a typical example of sample with significant surface change) were anodized to a different potential and then their surface roughnesses were measured
The breakdown phenomenon is not caused by the serious surface damage
The shift between the breakdown phenomenon and surface damage was observed
Evaluation of the surface roughness during anodizing.

18. Discussion
During the potentiodynamic anodizing, an electric breakdown occurs at a certain potential
The breakdown is not caused by a serious destruction of the anodic oxide film.
The breakdown could be related to generation of defect sites in the anodic films. [1].
The further potential increase causes, at least partially, the growth of defects and/or gas evaluation [2]. Finally, the processes lead to serious surface damage.
The bigger initial surface roughness seems to provide more space for the defect expansion and stress dissipation.
[1] Shimizu K. et al., Electrochim. Acta., 25 (1980) 1481.
[2] Li Y. et al., J. Electrochem. Soc., 144 (1997) 866.

19. Summary
The effect of surface roughness of the aluminium films on their electrochemical response during barrier type anodizing was investigated.
The importance of surface roughness on the anodizing response was recognized.
The mechanism of the observed behaviour was suggested.
The nature of such defects, their behavior and their elimination will be the subject of a future work.

20. ACKNOWLEDGEMENTS
Research leading to these results was supported by a grant from the Czech Science Foundation (GA ČR) no S. For part of this research, the infrastructure of SIX Research Centre was used.