directly fabricate metal and semiconductor nanostructures [89]. It has been suggested that the application of the bias between the tip and substrate lead to better
stability of the structure. The meniscus in this case contains metal salts that can be
dissolved in water and it leads to deposition of the metal on the substrate from the
meniscus electrolyte by cathodic reduction. As an example 30 nm wide, 0.4 nm
high lines of Pt have been drawn on H-passivated P-type Si (100) wafers using 2
wt% H 2 PtCl 6 as the electrolyte.
It has been demonstrated that DPN can be used to create nanostructures on a
surface which can then be used for directed assembly of nanoparticles [90]. In this
application also the basic patterning by DPN was done with MHA as ink on an
Au substrate. Subsequently, alkylamine-modified DNA was coupled to the MHA
nanopatterns so created. By creating an ordered pattern of two distinct oligonucleotide sequences it was possible to create an ordered assembly of two different
nanoparticles from a randomly dispersed system.
21.6
Use of Scanning Probe Microscopy in Nanomanipulation
The field of nanolithography is intimately connected with nanomanipulation. In
nanomanipulation generally a preformed nanoparticle, nanotube or a nanowire
is manipulated to place it at a predetermined site. The most widely used tool for
nanomanipulation is the cantilever of the AFM that provides a ‘‘robotic’’ arm to
place the nano-objects in predetermined sites. A nanoparticle weakly adsorbed on a
substrate can be moved by an AFM tip when it works in contact mode. This is not
wanted but if the particle is ‘‘selected’’ and then moved by the AFM then it becomes a useful tool. The AFM-based manipulation turns the unwanted aspect to
an advantage. For instance if one wants to place a nanowire between two electrodes
an AFM cantilever can be used to image the wire and push it between the two
electrodes. The advantage of the cantilever is that a predetermined force can be
applied and also the same instrument can image it. The basic idea behind SPMbased nanomanipulation is shown in Figure 21.17.
The STM tip can also be used for nanomanipulation. In fact the first atomic level
nanomanipulation was done by STM only [91]. However, in more recent context,
by nanomanipulation we generally imply use of an AFM cantilever to manipulate
nano-objects. This field, however, is in its early stages and there is a need to
understand the physics of the manipulation in terms of the basic forces that are
involved in this process. It is realized that it is different from what one sees in
micromanipulation. There are three main road blocks that need to be solved effectively before this field can mature. First, there is the need to understand the basic
physical and chemical processes that take place at the scale of a few nanometers,
including the mechanics. Second, one need to develop effective hardware as well as
control that has resolution and reproducibility of manipulation at this level. Third,
there is a need for effective automation and software. Interestingly, these road21 Nanolithography and Nanomanipulation
716
stability of the structure. The meniscus in this case contains metal salts that can be
dissolved in water and it leads to deposition of the metal on the substrate from the
meniscus electrolyte by cathodic reduction. As an example 30 nm wide, 0.4 nm
high lines of Pt have been drawn on H-passivated P-type Si (100) wafers using 2
wt% H 2 PtCl 6 as the electrolyte.
It has been demonstrated that DPN can be used to create nanostructures on a
surface which can then be used for directed assembly of nanoparticles [90]. In this
application also the basic patterning by DPN was done with MHA as ink on an
Au substrate. Subsequently, alkylamine-modified DNA was coupled to the MHA
nanopatterns so created. By creating an ordered pattern of two distinct oligonucleotide sequences it was possible to create an ordered assembly of two different
nanoparticles from a randomly dispersed system.
21.6
Use of Scanning Probe Microscopy in Nanomanipulation
The field of nanolithography is intimately connected with nanomanipulation. In
nanomanipulation generally a preformed nanoparticle, nanotube or a nanowire
is manipulated to place it at a predetermined site. The most widely used tool for
nanomanipulation is the cantilever of the AFM that provides a ‘‘robotic’’ arm to
place the nano-objects in predetermined sites. A nanoparticle weakly adsorbed on a
substrate can be moved by an AFM tip when it works in contact mode. This is not
wanted but if the particle is ‘‘selected’’ and then moved by the AFM then it becomes a useful tool. The AFM-based manipulation turns the unwanted aspect to
an advantage. For instance if one wants to place a nanowire between two electrodes
an AFM cantilever can be used to image the wire and push it between the two
electrodes. The advantage of the cantilever is that a predetermined force can be
applied and also the same instrument can image it. The basic idea behind SPMbased nanomanipulation is shown in Figure 21.17.
The STM tip can also be used for nanomanipulation. In fact the first atomic level
nanomanipulation was done by STM only [91]. However, in more recent context,
by nanomanipulation we generally imply use of an AFM cantilever to manipulate
nano-objects. This field, however, is in its early stages and there is a need to
understand the physics of the manipulation in terms of the basic forces that are
involved in this process. It is realized that it is different from what one sees in
micromanipulation. There are three main road blocks that need to be solved effectively before this field can mature. First, there is the need to understand the basic
physical and chemical processes that take place at the scale of a few nanometers,
including the mechanics. Second, one need to develop effective hardware as well as
control that has resolution and reproducibility of manipulation at this level. Third,
there is a need for effective automation and software. Interestingly, these road21 Nanolithography and Nanomanipulation
716