Effect of Sinusoidal Surface Roughness and Energy on the Orientation of Cylinder-Forming Block Copolymer Thin Films

We explore the relative stability of three possible orientations of cylinder-forming di-block copolymer on a sinusoidally corrugated substrate. The cylinders can be aligned either parallel to the substrate, with their long axis being oriented along or orthogonal to the corrugation trenches, or perpendicular to the substrate. Using self-consistent field theory, we investigate the influence of substrate roughness and surface preference on the phase transition between the three orientations. When the substrate preference, $u$, towards one of components is small, increasing the substrate roughness induces a phase transition from parallel to perpendicular cylindrical phase. However, when $u$ is large, the parallel orientation is more stable than the perpendicular one. Within this parallel phase, increasing the substrate roughness leads to a transition of cylinder orientation changing from being orthogonal to parallel to the trench long axis. Increasing the substrate preference leads to an opposite transition from parallel to orthogonal to the trenches. Furthermore, we predict that the perpendicular cylinder phase is easier to be obtained when the unidirectional corrugation is along the longer unit vector of the hexagonal packing than when it is along the shorter unit vector. Our results qualitatively agree with previous experiments, and contribute towards applications of the cylinder-forming block copolymer in nanotechnology.Comment: 9 pages, 7 figure

Etude de l'auto-organisation de films minces de copolymères diblocs en vue d'applications pour la microélectronique

The aim of this work is to understand how PS-b-PMMA thin films presenting vertically oriented cylindrical PMMA nanodomains self-assemble. These films are used to organize discrete nano-objects with small dimensions (diameter ~ 20 nm) and in high density (~1011/cm ²). It is shown that the vertical cylinder phase is indirectly formed during thermal annealing starting from a homogeneous phase. First, a disordered cylinder phase is created within the film, followed by the nucleation and growth of the vertical cylinder phase . This implies the presence of defects at the grain boundaries so that the obtained films present an hexatic order according to KTHNY theory. For defect sites, the unit cell could adopt an anisotropic configuration due to the stress of the lattice. In this case, in order to minimize the free energy of the system, the PMMA domain deforms commensurately with the unit cell and adopts an elliptical or a lozenge-like cross section, in good agreement with strong segregation considerations. However, these strained configurations reveal to be metastable so that thermal fluctuations could induce a transition from a distorted column to two other circular columns. This phenomenon has been used to explain the motion of dislocations. Finally, we use these films as a mask to realize, by etching plasma, Si/SiGe nano-pillars or MOS capacities with Pt nanocristals.L'objectif de ce travail est de comprendre comment s'auto-organisent les films minces de PS-b-PMMA présentant des nanodomaines cylindriques de PMMA orientés verticalement. Ces films sont ensuite utilisés pour organiser des nano-objets discrets de faibles dimensions (diamètre ~ 20 nm) et en forte densité (~1011/cm²).Il est montré que la phase de cylindres verticaux se forme de façon indirecte pendant le recuit thermique à partir d'une phase homogène. Tout d'abord, il se forme une phase de cylindres désordonnés au sein du film sur laquelle la phase de cylindres verticaux s'établie par un mécanisme de nucléation-croissance, menant à la présence de défauts aux joints de grains. L'élimination des défauts dans le réseau nécéssite une diffusion de ces derniers. Après avoir montré expérimentalement et théoriquement que les sites heptacoordinés adoptent une morphologie distordue en raison de la contrainte du réseau, nous proposons un mécanisme de diffusion des dislocations basé sur la division des nanodomaines distordus. Nous montrons que les films réalisés possédent un ordre hexatique selon la théorie KTHNY. Finalement, nous utilisons ces films en tant que masque pour réaliser, par gravure plasma, des nano-piliers en Si/SiGe ou bien des capacités MOS à nanocristaux de P

Etude de l auto-organisation de films minces de copolymères diblocs en vue d applications pour la microélectronique

L objectif de ce travail est de comprendre comment s auto-organisent les films minces de PS-b-PMMA présentant des nanodomaines cylindriques de PMMA orientés verticalement. Ces films sont ensuite utilisés pour organiser des nano-objets discrets de faibles dimensions (diamètre ~ 20 nm) et en forte densité (~1011/cm ). Il est montré que la phase de cylindres verticaux se forme de façon indirecte pendant le recuit thermique à partir d une phase homogène. Tout d abord, il se forme une phase de cylindres désordonnés au sein du film sur laquelle la phase de cylindres verticaux s établie par un mécanisme de nucléation-croissance, menant à la présence de défauts aux joints de grains. L élimination des défauts dans le réseau nécéssite une diffusion de ces derniers. Après avoir montré expérimentalement et théoriquement que les sites heptacoordinés adoptent une morphologie distordue en raison de la contrainte du réseau, nous proposons un mécanisme de diffusion des dislocations basé sur la division des nanodomaines distordus. Nous montrons que les films réalisés possédent un ordre hexatique selon la théorie KTHNY. Finalement, nous utilisons ces films en tant que masque pour réaliser, par gravure plasma, des nano-piliers en Si/SiGe ou bien des capacités MOS à nanocristaux de PtThe aim of this work is to understand how PS-b-PMMA thin films presenting vertically oriented cylindrical PMMA nanodomains self-assemble. These films are used to organize discrete nano-objects with small dimensions (diameter ~ 20 nm) and in high density (~1011/cm ). It is shown that the vertical cylinder phase is indirectly formed during thermal annealing starting from a homogeneous phase. First, a disordered cylinder phase is created within the film, followed by the nucleation and growth of the vertical cylinder phase . This implies the presence of defects at the grain boundaries so that the obtained films present an hexatic order according to KTHNY theory. For defect sites, the unit cell could adopt an anisotropic configuration due to the stress of the lattice. In this case, in order to minimize the free energy of the system, the PMMA domain deforms commensurately with the unit cell and adopts an elliptical or a lozenge-like cross section, in good agreement with strong segregation considerations. However, these strained configurations reveal to be metastable so that thermal fluctuations could induce a transition from a distorted column to two other circular columns. This phenomenon has been used to explain the motion of dislocations. Finally, we use these films as a mask to realize, by etching plasma, Si/SiGe nano-pillars or MOS capacities with Pt nanocristals.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Self-assembling study of a cylinder-forming block copolymer via a nucleation-growth mechanism

Block copolymer materials form self-assembling structures at a nanometric scale, of interest in nanotechnology. The organization process of asymmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) copolymer thin films is studied. In a first step it is demonstrated that two consecutive mechanisms lead to the formation of a well-ordered phase. The first mechanism is the local segregation of blocks, which leads to a metastable disordered cylinder phase (C-d). The second mechanism is a transformation of the C-d phase to a vertical cylinder phase via a nucleation-growth mechanism. The influence of film thickness and surface tension on the organization is also studied. Above the natural cylinder monolayer height, h(1), the kinetics of the cylinder organization strongly depends on the initial film thickness, and below h(1) the film splits into terraces. By varying the interactions between the substrate surface and the different blocks, a disordered phase can be formed instead of terraces

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Block Copolymer Systems: From Single Chain to Self-Assembled Nanostructures

Recent advances in the field of macromolecular engineering applied to the fabrication of nanostructured materials using block copolymer chains as elementary building blocks are described in this feature article. By highlighting some of our work in the area and accounting for the contribution of other groups, we discuss the relationship between the physical-chemical properties of copolymer chains and the characteristics of nano-objects originating from their self-assembly in solution and in bulk, with emphasis on convenient strategies that allow for the control of composition, functionality, and topology at different levels of sophistication. In the case of micellar nanoparticles in solution, in particular, we present approaches leading to morphology selection via macromolecular architectural design, the functionalization of external solvent-philic shells with biomolecules (polysaccharides and proteins), and the maximization of micelle loading capacity by the suitable choice of solvent-phobic polymer segments. The fabrication of nanomaterials mediated by thin block copolymer films is also discussed. In this case, we emphasize the development of novel polymer chain manipulation strategies that ultimately allow for the preparation of precisely positioned nanodomains with a reduced number of defects a block-selective chemical reactivity. The challenges facing the soft matter community, the urgent demand to convert huge public and private investments into consumer products, and future possible directions in the field are also considered herein

Non-Native Block Copolymer Thin Film Nanostructures Derived From Iterative Self-Assembly Processes

Nanostructured block copolymer thin films constitute an elegant tool to generate complex periodic patterns with periodicities ranging from a few nanometers to hundreds of nanometers. Such well-organized nanostructures are foreseen to enable next-generation nanofabrication research with potent applications in the design of functional materials in biology, optics or microelectronics. This valuable platform is, however, limited by the geometric features attainable from diblock copolymer architectures considering the thermodynamic drive force leaning toward the formation of structures minimizing the interface between the blocks. Therefore, strategies to enrich the variety of structures obtained by block copolymer self-assembly processes are gaining momentum and this progress report reviews the opportunities inherent to iterative BCP self-assembly by considering the emerging strategies for the generation of "non-native" morphologies

Nano-Organization of Amylose- b -Polystyrene Block Copolymer Films Doped with Bipyridine

International audienceThis paper discusses the self-assembly of rod-coil amylose-b-polystyrene (Mal-b-PS) block copolymer thick and thin films. The nano-organization falls in an interdomain spacing d of about 10 am, much smaller than flexible-flexible petrol block copolymer systems. Additionally, hydrogen-bonding interactions between carbohydrate rods (amylose) and 4',4-bipyridine (bipy) molecules induces phase transitions. Indeed, adding bipy in maltooctadecaose-block-polystyrene (Mal18-b-PS) copolymers results, at room temperature, in the formation of a lamellar phase having Mal18 bipy-rich nanodomains instead of hexagonal close-packed (HCP) of cylinders made of Mal18, whereas a coexistence of Mal7bipy-rich cylindrical and spherical nanodomains are formed from maltoheptaose-b-polystyrene (Mal7-b-PS) copolymers instead of a poorly organized array of Mal7-based cylinders. On heating, the Mal7bipy-b-PS system shows more rich phase behavior as compared to the Mal7-b-PS one due to weakening of hydrogen bonding with temperature. Such a system is of great interest in developing active layers in light-emitting diodes (LEDs) or in photovoltaic cells to realize devices with an optimal structure, that is, having large interface area and domain size with similar exciton diffusion length (10 nm)

Periodic Bicontinuous Structures Formed on the Top Surface of Asymmetric Triblock Terpolymer Thick Films

The combination of the nonsolvent-induced phase separation (NIPS) process with a solvent vapor annealing (SVA) treatment is used to produce asymmetric and hydrophobic thick films having different long-range ordered network nanostructures, which are inaccessible via currently available membrane fabrication methods. We show that the disordered phase generated by NIPS on the material top surface can be transformed into a highly ordered bicontinuous network nanostructure during the SVA process without disrupting the substructure morphology. For instance, by using a straightforward blending approach, either a triply periodic alternating diamond (D-A) structure or a core-shell perforated lamellar (PL) phase was demonstrated on the skin layer of fully hydrophobic poly(1,1-dimethyl silacyclobutane)-block-polystyrene-block-poly(methyl methacrylate) (PDMSB-b-PS-b-PMMA) thick films. Such a material fabrication method, enabling the formation of a sponge-like substructure topped by a network phase having an excellent long-range order, provides an appealing strategy to facilitate the manufacture of next-generation membranes at large scale since these bicontinuous morphologies obviate the need of the nanochannel alignment