148
8 Nanofabrication on Reactive Block Copolymer Film …
of both the orientation and lateral ordering of the nanoscopic domains is essential to
fully realize the potential of these materials. This requires the use of external fields,
such as electric fields [1], mechanical shear [2], temperature gradients [3], crystallization [4], or the use of prepatterned substrates (graphoepitaxy) [5]. For various
possible future applications, block copolymer films should constitute what may be
called a nanoperiodic chemically functionalized surface, i.e., a heterogeneous surface
exhibiting an ordered array of nanoscopic areas of different chemical composition
and thus different chemical reactivity [4].
Such nanoperiodic chemically functionalized surfaces have been reported
primarily for polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) systems
owing to the similarity of the surface tensions of the two blocks [6]. Lopes et al.
successfully deposited gold nanoparticles on PS-b-PMMA diblock copolymer scaffolds [7]. Morkved et al. also discussed the mesoscopic self-assembly of gold
nanoparticles on symmetric PS-b-PMMA and asymmetric PS-b-P2VP [8]. In addition, very recently spin-coated block copolymer films have been used to control the
deposition of proteins and other biomolecules on nanometer length scales [9]. Kumar
et al. exploited unspecific interactions (physisorption) to immobilize various proteins
on microphase-separated domains of PS-b-PMMA ultrathin films. However, since
the biomolecules are bound only via weak unspecific interactions, these assemblies
can be expected to be unstable.
As sketched in the introductory chapters, nanoperiodic chemically functionalized surfaces could also be exploited in conjunction with scanning probe lithography (SPL) approaches [10] to prepare platforms for screening of (bio)molecular
interactions, surface reactions [11], and cell–surface interactions [12], among other
possible applications. Two possible advantages can be considered for these patterned
nanoreactive PtBA platforms compared to further miniaturized reactive microcontact
printing (following the approaches discussed in Chap. 7 to smaller stamp features),
if ultimately nanometer precision is required for such arrays:
(a) The immobilization of (bio)molecules is confined to the nanoreactive PtBA
islands, thereby the pattern is defined by the template structure of the reactive
film;
(b) Compared to nanospotting [13] or nanocontact printing [14] on unpatterned
films, diffusion may be better controlled because of the inert PS matrix around
the reactive islands.
The reactivity of the PtBA block has been treated in detail in various preceding
chapters and the combination of these versatile and robust platforms with top-down
patterning methodologies (reactive microcontact printing) showed that patterns down
to the 300 nm range can be fabricated. However, in these experiments the inherent
microphase separation of diblock copolymers has not been utilized. In fact, reactions
were carried out on the PtBA skin layer. For the creation of chemically functionalized
surfaces with periodicities on the sub-100 nm length scale, the microphase separation of these diblock copolymers will be exploited. Hence in this final experimental
chapter, the first steps toward the fabrication of such platforms based on ultrathin
8 Nanofabrication on Reactive Block Copolymer Film …
of both the orientation and lateral ordering of the nanoscopic domains is essential to
fully realize the potential of these materials. This requires the use of external fields,
such as electric fields [1], mechanical shear [2], temperature gradients [3], crystallization [4], or the use of prepatterned substrates (graphoepitaxy) [5]. For various
possible future applications, block copolymer films should constitute what may be
called a nanoperiodic chemically functionalized surface, i.e., a heterogeneous surface
exhibiting an ordered array of nanoscopic areas of different chemical composition
and thus different chemical reactivity [4].
Such nanoperiodic chemically functionalized surfaces have been reported
primarily for polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) systems
owing to the similarity of the surface tensions of the two blocks [6]. Lopes et al.
successfully deposited gold nanoparticles on PS-b-PMMA diblock copolymer scaffolds [7]. Morkved et al. also discussed the mesoscopic self-assembly of gold
nanoparticles on symmetric PS-b-PMMA and asymmetric PS-b-P2VP [8]. In addition, very recently spin-coated block copolymer films have been used to control the
deposition of proteins and other biomolecules on nanometer length scales [9]. Kumar
et al. exploited unspecific interactions (physisorption) to immobilize various proteins
on microphase-separated domains of PS-b-PMMA ultrathin films. However, since
the biomolecules are bound only via weak unspecific interactions, these assemblies
can be expected to be unstable.
As sketched in the introductory chapters, nanoperiodic chemically functionalized surfaces could also be exploited in conjunction with scanning probe lithography (SPL) approaches [10] to prepare platforms for screening of (bio)molecular
interactions, surface reactions [11], and cell–surface interactions [12], among other
possible applications. Two possible advantages can be considered for these patterned
nanoreactive PtBA platforms compared to further miniaturized reactive microcontact
printing (following the approaches discussed in Chap. 7 to smaller stamp features),
if ultimately nanometer precision is required for such arrays:
(a) The immobilization of (bio)molecules is confined to the nanoreactive PtBA
islands, thereby the pattern is defined by the template structure of the reactive
film;
(b) Compared to nanospotting [13] or nanocontact printing [14] on unpatterned
films, diffusion may be better controlled because of the inert PS matrix around
the reactive islands.
The reactivity of the PtBA block has been treated in detail in various preceding
chapters and the combination of these versatile and robust platforms with top-down
patterning methodologies (reactive microcontact printing) showed that patterns down
to the 300 nm range can be fabricated. However, in these experiments the inherent
microphase separation of diblock copolymers has not been utilized. In fact, reactions
were carried out on the PtBA skin layer. For the creation of chemically functionalized
surfaces with periodicities on the sub-100 nm length scale, the microphase separation of these diblock copolymers will be exploited. Hence in this final experimental
chapter, the first steps toward the fabrication of such platforms based on ultrathin