10.4 Electrodeposition on Surfaces with Mechanically …
337
10.4 Electrodeposition on Surfaces with Mechanically
Induced Nanoinhomogeneities
In Sect. 10.3, atomic-scale surface inhomogeneities occurring as natural features of
the substrates were discussed from the viewpoint of electrochemical nanomanufacturing. In this chapter, the nanoscale surface modification methods will be presented
where a tip (usually an AFM tip) is contacted to the surface. Although the primary
impact of the tip is mechanical, either the imprint or the scratch line of the tip leads
to a chemical modification by either thinning/removing a surface layer or changing
the crystallinity of the near-surface zone due to the occurrence of dislocations and
other lattice defects. Various nomenclatures can be found in the literature for such
phenomena, including tip-based nanomanufacturing (TBN) or scanning probe lithography (SPL). Concerning the applications of these methods by using techniques other
than electrochemistry, two recent reviews can be recommended [43, 44].
In the methods discussed in this chapter, the tip has no role related to electrochemical phenomena. The cases when a tip is electrochemically active in a nanostructure
preparation method will be presented in Chap. 12 together with other techniques
involving a special electrode arrangement. After a general overview, the mechanical
surface modification opportunities will be listed below roughly in the order of the
strength of the tip impact, which nearly coincides with an incremental order of the
hardness of the surface layer modified. Examples will be mostly restricted to silicon
substrate due to their importance and dominance in the literature, even though the
tip-based modification of metallic surfaces by mechanical action was also studied in
a few cases (see, e.g., Ref. [45]).
A thumb rule for the surface scratching and indentation methods is that the tip
has to be much harder than the surface to be modified. For polymers on graphite, a
normal silicon AFM cantilever is sufficient, while a diamond-coated tip is a standard
choice for oxide-covered silicon surfaces. The shape of a groove depends on the
surface structure, which will be detailed at the surface structure types below. However,
regardless of the specific surface–tip pairs, the increase in both the load of the tip
and the grooving cycle number result is deeper and wider trenches. Therefore, the
tuning of the load is a tool for size adjustment, which can be performed with one
single tip in a limited range.
Another common feature of the metal deposits formed on Si surface is that their
nucleation and growth follows the Volmer–Weber mode. This means that metal nuclei
form in the trenches similarly than at HOPG step edges; i.e., the wires on the surface
are formed as a coalescence of the grains. This trend is valid for both electrochemical
and electroless deposition processes. Since the deposit thickness is mostly in the range
of the characteristic lateral size of the surface feature produced, the deposition time
needed is fairly short, ranging from a few tenths of second to a few seconds only.
Organic molecular layers on silicon single crystals form a soft coating relative to
oxide layers. Therefore, they are quite vulnerable for the grooving by AFM tips. In
spite of their soft nature, they are technologically important because organic layers are
resistant against HF etching and the tip-induced defects in the masking organic layer
337
10.4 Electrodeposition on Surfaces with Mechanically
Induced Nanoinhomogeneities
In Sect. 10.3, atomic-scale surface inhomogeneities occurring as natural features of
the substrates were discussed from the viewpoint of electrochemical nanomanufacturing. In this chapter, the nanoscale surface modification methods will be presented
where a tip (usually an AFM tip) is contacted to the surface. Although the primary
impact of the tip is mechanical, either the imprint or the scratch line of the tip leads
to a chemical modification by either thinning/removing a surface layer or changing
the crystallinity of the near-surface zone due to the occurrence of dislocations and
other lattice defects. Various nomenclatures can be found in the literature for such
phenomena, including tip-based nanomanufacturing (TBN) or scanning probe lithography (SPL). Concerning the applications of these methods by using techniques other
than electrochemistry, two recent reviews can be recommended [43, 44].
In the methods discussed in this chapter, the tip has no role related to electrochemical phenomena. The cases when a tip is electrochemically active in a nanostructure
preparation method will be presented in Chap. 12 together with other techniques
involving a special electrode arrangement. After a general overview, the mechanical
surface modification opportunities will be listed below roughly in the order of the
strength of the tip impact, which nearly coincides with an incremental order of the
hardness of the surface layer modified. Examples will be mostly restricted to silicon
substrate due to their importance and dominance in the literature, even though the
tip-based modification of metallic surfaces by mechanical action was also studied in
a few cases (see, e.g., Ref. [45]).
A thumb rule for the surface scratching and indentation methods is that the tip
has to be much harder than the surface to be modified. For polymers on graphite, a
normal silicon AFM cantilever is sufficient, while a diamond-coated tip is a standard
choice for oxide-covered silicon surfaces. The shape of a groove depends on the
surface structure, which will be detailed at the surface structure types below. However,
regardless of the specific surface–tip pairs, the increase in both the load of the tip
and the grooving cycle number result is deeper and wider trenches. Therefore, the
tuning of the load is a tool for size adjustment, which can be performed with one
single tip in a limited range.
Another common feature of the metal deposits formed on Si surface is that their
nucleation and growth follows the Volmer–Weber mode. This means that metal nuclei
form in the trenches similarly than at HOPG step edges; i.e., the wires on the surface
are formed as a coalescence of the grains. This trend is valid for both electrochemical
and electroless deposition processes. Since the deposit thickness is mostly in the range
of the characteristic lateral size of the surface feature produced, the deposition time
needed is fairly short, ranging from a few tenths of second to a few seconds only.
Organic molecular layers on silicon single crystals form a soft coating relative to
oxide layers. Therefore, they are quite vulnerable for the grooving by AFM tips. In
spite of their soft nature, they are technologically important because organic layers are
resistant against HF etching and the tip-induced defects in the masking organic layer