Thin films block copolymer

In the region of an external interface, differences in the surface-free energy or affinity of each block toward the substrate 

Parallel domain alignment at an interface will propagate into the bulk of a copol5fmer film to a degree dependent on the magnitude of the substrate affinity asymmetry or surface field Ay. TEM studies on a PS-b-PMMA lamellar system found a critical thickness (linearly dependent on Ay) below which surface fields are enough to cause the entire film to adopt an L alignment [11]. For example, the critical thickness was 10 lamellar periods when 

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Gong, Y., Huang, H., Hu, Z., Chen, Y, Chen, D Wang, Z. and He, X. (2006) Inverted to normal phase transition in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films. Macromolecules, 39, 3369-3376. 

This review will discuss two types of patterning approaches that can be employed with patternable block copolymers. Due to the fact that most practical applications require block copolymer thin films with large-domain ordered patterns, particular attention is paid to the optimization of bottom-... 

In addition to the previously mentioned driving forces that determine the bulk state phase behavior of block copolymers, two additional factors play a role in block copolymer thin films the surface/interface energies as well as the interplay between the film thickness t and the natural period, Lo, of the bulk microphase-separated structures [14,41,42], Due to these two additional factors, a very sophisticated picture has emerged from the various theoretical and experimental efforts that have been made in order to describe... 

The self-assembly of block polymers, in the bulk, thin film and solution states, produces uniformly sized nanostructured patterns that are very useful for nanofabrication. Optimal utilization of these nanoscopic patterns requires complete spatial and orientational control of the microdomains. However, the microdomains in the bulk state normally have grain sizes in the submicron range and have random orientations. In block copolymer thin films, the natural domain orientations are generally not desirable for nanofabrication. In particular, for composition-asymmetric cylindrical thin films, experimental... 

In block copolymer thin films, the perpendicular orientation of microdomains relative to the substrate cannot be achieved by the shear methods developed in the bulk case. Based on the additional variables (film thickness and surface/interface interactions) in block copolymer thin films, as described in Sect. 2.1.2, three different strategies are generally applied for orienting block copolymer thin films ... 

Unlike the bulk morphology, block copolymer thin films are often characterized by thickness-dependent highly oriented domains, as a result of surface and interfacial energy minimization [115,116]. For example, in the simplest composition-symmetric (ID lamellae) coil-coil thin films, the overall trend when t>Lo is for the lamellae to be oriented parallel to the plane of the film [115]. Under symmetric boundary conditions, frustration cannot be avoided if t is not commensurate with L0 in a confined film and the lamellar period deviates from the bulk value by compressing the chain conformation [117]. Under asymmetric boundary conditions, an incomplete top layer composed of islands and holes of height Lo forms as in the incommensurate case [118]. However, it has also been observed that microdomains can reorient such that they are perpendicular to the surface [ 119], or they can take mixed orientations to relieve the constraint [66]. 

Fig. 2 Schematic representation of control of block copolymer thin film orientations by adjusting polymer-substrate interactions neutral interfaces...

Fig. 3 Schematic representation of control over block copolymer thin film orientation by applying an electric field to orient PS-6-PMMA cylinders perpendicular to the substrate (taken from [43])...

Fig. 6 Schematic representation of controlling the block copolymer thin film orientations by using top-down lithography-defined chemically patterned heterogeneous sin-face...

Nealey and coworkers [75,76,146] took a similar approach and applied lithographically defined self-assembled monolayers as substrates to direct the orientation of block copolymer thin films. After EUV interferometic lithography on octadecyltrichlorosilane (OTS) or phenylethyltrichlorosilane (PETS) monolayers, PS-fr-PMMA block copolymers were deposited and annealed on the substrates. Due to the selective wetting of PS and PMMA on the unexposed and exposed regions, respectively, they were able to obtain large areas of perpendicular lamella when the commensurate condition was fulfilled. 

Fig. 10 Schematic representation of the nanoreplication processes from block copolymers, a Growth of high-density nanowires from a nanoporous block copolymer thin film. An asymmetric PS-fc-PMMA diblock copolymer was aligned to form vertical PMMA cylinders under an electric field. After removal of the PMMA minor component, a nanoporous film is formed. By electrodeposition, an array of nanowires can be replicated in the porous template (adapted from [43]). b Hexagonally packed array of aluminum caps generated from rod-coil microporous structures. Deposition of aluminum was achieved on the photooxidized area of the rod-coil honeycomb structure (Taken from [35])...

Fig. 7 2D thickness-surface energy gradient library for mapping the effects of these parameters on the self-assembly of PS-b-PMMA block copolymer thin films. See text for a fuU description. Lq is the equilibrium self-assembly period and h is the film thickness. Dashed white lines delineate the neutral surface energy region, which exhibits nanostructures oriented perpendicular to the substrate plane. (Derived from [18] with permission)... 

Zhang X, Berry BC, Yager KG, Kim S, Jones RL, Satija S, Pickel DL, Douglas JE, Karim A (2008) Surface morphology diagram for cylinder-forming block copolymer thin films. ACS Nano 2 2331-2341... 

Fasolka MJ, Mayes AM (2001) Block copolymer thin films physics and applications. Annu Rev Mater Res 31 323-355... 

Binder WH, Kluger C, Straif CJ, Eriedbacher G. Directed nanoparticle binding onto microphase-separated block copolymer thin films. Macromolecules 2005 38 9405-9410. 

Shenhar R, Jeoung E, Srivastava S, Norsten TB, Rotello VM. Crosslinked nanoparticle stripes and hexagonal networks obtained via selective patterning of block copolymer thin films. Adv Mater 2005 17 2206-2210. 

To achieve in-plane alignment in a lamellar block copolymer thin film, the lamellae have to be oriented perpendicular to the plane of the film in the first place. As we have shown earlier, in the block copolymer system S47H10M4382 perpendicular alignment of the lamellae is achieved spontaneously at zero electric field [9, 17]. In short, a thin brush layer of the block copolymer is adsorbed onto the (polar) substrate via the PHEMA middle block, resulting in a stripe pattern of the two majority components PS and PMMA. In thicker films, this brush layer seems to serve as a template for perpendicular lamellae [21, 22], This can be seen in Fig. 2a, which shows SFM images of a thin S47H10M4382 film annealed for... 

Olszowka V et al (2006) Large scale alignment of a lamellar block copolymer thin film via electric fields a time-resolved SFM study. Soft Matter 2(12) 1089-1094... 

Olszowka V, Kuntermann V, Boker A (2008) Control of orientational order in block copolymer thin films by electric fields a combinatorial approach. Macromolecules 41 5515-5518... 

Tsarkova L et al (2006) Defect evolution in block copolymer thin films via temporal phase transitions. Langmuir 22(19) 8089-8095... 

Nanopattem Evolution in Block Copolymer Thin Films... 

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