Biomedical Engineering Reference
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Figure 7. (A) AFM image of a crater-like hole formed by ink jetted ethanol drops. A series of drops
(5 pL for each) is deposited onto a PVP film with a thickness of 500 nm. The depth of the hole
corresponds to the thickness. A ridge is created at the rim of the hole and the height is greater than
1 µm. (B) Schematic profile of the crater along the dashed black line. (C) Micrograph of inkjet-printed
via-holes with an increasing number of ethanol drops (horizontal) and with a series of different drop
volumes (vertical). Different colours represent different thickness. The colours show that via holes
through a 500 nm thick film are formed with deposition of 5 to 7 drops. [Reprinted figure from:
Kawase, T.; Sirringhaus, H.; Friend, R. H.; Shimoda, T., Advanced Materials 2001 , 13, (21), 1601.
Copyright (2001) by Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.]
insulating material was preferentially re-deposited at the TPCL, resulting in a de-
crease of thickness in the central area and in the formation of a ridge at the former
TPCL. When the deposition of a drop was repeated at the same position, the hole
became deeper and the ridge higher, and after several repetition steps a via-hole
was formed. The AFM image of such hole (Fig. 7A) confirms this. Holes could
be formed with different numbers of solvent drops (horizontal direction) and with
different drop volumes (vertical direction). The etching depth is indicated by the
colour generated by light interference, and the via-hole is attained after 5-7 drop
depositions. Further deposition of solvent drops after reaching the bottom of the
film does not change the shape or diameter of the hole.
The process of hole formation can be explained by the action of a number of
processes already mentioned above: (i) the solvent dissolves part of the polymer, so
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