Minority Block Research Articles

Dual Mode Patterning of Fluorine-Containing Block Copolymers through Combined Top-down and Bottom-up Lithography

Integrated nanopatterns were successfully obtained from a combination of high lateral ordering of newly designed self-assembling fluorine-containing block copolymers and degradation of the fluorine-containing polymer nanodomains in e-beam irradiated areas. The fluorine-containing block copolymers of poly(styrene-block-2,2,2-trifluoroethyl methacrylate) (PS-b-PTFEMA) and poly[styrene-block-(methyl methacrylate-co-2,2,2-trifluoroethyl methacrylate)] (PS-b-(PMMA-co-PTFEMA)), which are capable of both top-down and bottom-up lithography, were developed. The reported block copolymers were synthesized by either anionic polymerization or atom transfer radical polymerization (ATRP). Characterization of bulk and thin films were carried out using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS), and these studies revealed the formation of highly ordered self-assembled structures. Lateral ordering of arrays of PS dots was observed in the thin film of PS-b-PTFEMS, in which PS was the minor block, and the thin film of PS-b-(PMMA-co-PTFEMA), in which PS was the major block. These thin films were subjected to conventional lithographic processing using e-beam and deep-UV radiation to create integrated patterns such as “dots in lines”.

In Situ Study of the Breakout Crystallization in the Poly(butadiene)-block-Poly(ε-caprolactone) Thin Film

Despite its wide occurrence in soft confined block co-polymers, breakout crystallization remains poorly understood and is difficult to control. In this work, thin films of cylinder-forming poly(butadiene)-block-poly(ε-caprolactone) (PB-b-PCL) diblock co-polymers, with PCL being the minority block, have been chosen as the study subject. We demonstrate a new route to study the breakout crystallization by obtaining the microphase separation structure within terraced lamellae first and then in situ tracking down the lamellar coalescence, resulting from the development of the crystal growth front. We find that the crystal growth front has sucked materials from the surrounding amorphous lamellae, which lead to the decrease of the lamellar zones and coalescence of the microphase separation structure. Dividing the breakout crystallization into parallel breakout and vertical breakout, we illustrate that it is the crystallization-driven molecular diffusion that make the molecules overcome the topography constraint and grow into large-scale spherulite. Moreover, the results show that the polymer microphase separation structure has a significant influence on the crystal nucleation and greatly retarded the crystal growth rate. With a well-designed microphase separation structure within terraces and an easily tunable atomic force microscopy in situ imaging technique, an intensive study of the breakout crystallization and concomitant microdomain coalescence has been offered.

Dye adsorption, desorption, and distribution in mesoporous TiO2 films, and its effects on recombination losses in dye sensitized solar cells

Recombination rates through bare, partially dyed, and fully dyed mesoporous TiO2 films have been measured, as well as the penetration kinetics of dye molecules into the films. We give evidence that homogeneous partial dye coverage cannot be achieved by short dyeing times or dilute dye solutions, due to the high sticking coefficient of the dyes on TiO2. A new method has been developed which gives homogenous partial dye coverage, based on full dyeing followed by partial desorption. Using this method we show that dyeing with N719, C101, or TG6 dyes provides only minor blocking of recombination, relative to bare TiO2. We also show that recombination rates across the bare TiO2 surface can vary strongly after treatment with mild base, acid, or a Lewis acid/base buffer. We find these treatments can change the density of trap states as well as the conduction band edge potential. We present a method, based on charge extraction, that corrects for changes in trap density when estimating shifts in the conduction band potential. The combined results suggest that the industrially favored fast dyeing procedures can lead to higher recombination rates, especially in the absence of the typical TiCl4 treatment, and under low (e.g. indoor) light levels. The results also explain some anomalous features seen in studies of exciton and hole conduction along partial coverage dye layers which were previously assumed to be homogenous.

Dimensioning the Add/Drop Contention Factor of Directionless ROADMs

Reconfigurable Optical Add/Drop Multiplexers (ROADM) are the optical switching equipment of transparent optical networks. Directionless ROADMs permit the network carriers to change the direction of an added and/or dropped lightpath without the need of a technician on-site intervention in the lightpath end nodes. Colorless ROADMs provide the same versatility for changing the lightpath transmission wavelength. Cost-effective directionless ROADM architectures (colorless or colored) can be built if the maximum number of lightpaths that can be added/dropped using the same wavelength is limited. We name this limit as the node add/drop contention factor, and denote it as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> . In this paper we investigate the network lightpath blocking performance as a function of this add/drop contention factor of the nodes. The scenarios considered are the static planning of a network (i) with unprotected traffic, (ii) with traffic 1+1 protected for single-link failures, and (iii) with traffic 1+1 protected for single-link or single-node failures. Since for these scenarios, the wavelength of an existing lightpath does not have to be dynamically reconfigured, the work in this paper applies to both colorless and colored nodes. An ILP model and an effective heuristic are presented to solve the so-called Add/Drop Contention Aware RWA (ADCA-RWA) planning of the network. Extensive results are reported. In all the cases, an add/drop factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> = 2 is sufficient to provide the same performance as contentionless nodes ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> = ∞). Furthermore, in all the tests a factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> = 1 was also sufficient, or produced a minor lightpath blocking performance degradation (below 0.5% in the unprotected cases, and below 2.5% in the 1 + 1 protected cases).

Nanostructured diblock copolymer films with embedded magnetic nanoparticles

Nanostructured diblock copolymer films with embedded magneticnanoparticles are prepared by solution casting. The diblock copolymerpolystyrene-block-polymethylmethacrylate with a fully deuterated polystyrene block of aweight ratio of 0.22 is used as a structure-directing matrix. Maghemite nanoparticles (γ-Fe2O3) are coated with polystyrene and thus have a selective affinity to the minority block of thediblock copolymer. The hybrid film morphology is investigated as a function ofnanoparticle concentration. The surface structure is probed with atomic force microscopyand scanning electron microscopy. The inner film structure and the structure atthe polymer–substrate interface are detected with grazing incidence small angleneutron scattering (GISANS). Irrespective of the nanoparticle concentration a welldeveloped micro-phase separation structure is present. From the Bragg peaksobserved in the GISANS data a linear nanoparticle concentration dependence of theinter-domain spacing of the micro-phase separation structure is determined. Thesuperparamagnetic and blocking behavior can be explained with a generalizedStoner–Wohlfarth–Néel theory which includes either an elastic torque being exerted onthe nanoparticles by the field or a broad distribution of anisotropy constants.

Preparation and characterization of poly(2‐hydroxyethylme thacrylate)‐b‐P(N‐phenylmaleimide)‐ZnO and poly(2‐hydroxy ethylmethacrylate)‐b‐P(styrene)‐ ZnO micro/nanostructures: micro/nanocomposite particles with core‐shell morphology

AbstractThe present work reports the incorporation of the ZnO doped diblock copolymer matrix and its conversion into a self‐assembled structure. The diblock P(HEMA)80‐b‐P(N‐PhMI)20 and P(HEMA)90‐b‐P(St)10 copolymers consist of a majority (HEMA) and minority (N‐PhMI or St) block. The copolymers were synthesized with a block repeat unit ratio by atom‐transfer radical polymerization (ATRP) using a poly(2‐hydroxyethylmethacrylate)‐Cl/CuBr/bipyridine initiating system. The P(HEMA)‐Cl was prepared by reverse ATRP1. The average theoretical number molecular weight (Mn,th) was calculated from the feed capacity. The composite of the inorganic nanoparticles was achieved at room temperature in the liquid phase, using ZnCl2 precursor dopant and wet chemical processing to convert to ZnO nanoparticle films. Thermal characterization was performed using differential scanning calorimetry (DSC) and thermogravimetry (TG). The proton/area relationship confirmed the block copolymer compositions calculated by elemental analysis, consisting of a majority and minority blocks. Morphology properties of the polymer samples were investigated by scanning electron microscopy (SEM). The microphotographs of the film's surfaces show that the film's upper surfaces were generally smooth with ordered structure morphology. FT‐IR spectroscopy confirmed the association of the ZnCl2 precursor with the majority block and the formation of ZnO, the white SEM showed the morphology of ZnO nanoparticles' films when the surface relief changes principally due to surface loss rather than its orientation. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Ordering kinetics of block copolymers directed by periodic two-dimensional rectangular fields

The ordering kinetics of directed assembly of cylinder-forming diblock copolymers is investigated by cell dynamics simulation of the time-dependent Ginzburg-Landau theory. The directing field, mimicking chemically or topologically patterned surfaces, is composed of a rectangular array of potential wells which are attractive to the minority blocks. The period of the templating fields is commensurate with the hexagonal lattice of the block copolymer domains. The ordering kinetics is described by the time evolution of the defect concentration, which reveals that the rectangular field of [1 m] for a given density multiplication has the best directing effect, and the reversed case of [m 1] has the worst. Compared with a hexagonal directing field, the rectangular field provides a better directing efficiency for a fixed high density multiplication. The difference of the directing effect can be understood by analyzing the ordering mechanisms in the two types of directing fields. The study reveals that the rectangular pattern is an alternative candidate to direct block copolymer assembly toward large-scale ordered domains.

Ellipsometry as a probe of crystallization in binary blends of a sphere-forming diblock copolymer

Ellipsometry is used to measure the crystallization and melting temperature of a bidisperse blend of a crystalline-amorphous diblock copolymer. Binary blends of sphere-forming poly(butadiene-ethylene oxide) (PB-PEO) of two different molecular weights are prepared. The two PB-PEO diblocks that are used share the same amorphous majority PB block length but different crystalline PEO minority block length. As the concentration of higher molecular weight diblock in the blend is increased, the size of the PEO spherical domains swell, providing access to the full range of domain sizes between the limits of the two neat diblock components. The change in domain size is consistent with a monotonic change in both the crystallization and melting temperatures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Staatsfonds als Ankerinvestoren: Eine Note zum Einstieg von Aabar bei Daimler

AbstractThe group of sovereign wealth funds (SWF) is gaining growing importance in the discussion on corporate governance quality as critical success factor for the longrun performance of exchange listed companies. These institutional investors mostly act as long-term oriented minority block holders (anchor investors) in international capital markets. We show for a specific case how capital market participants evaluate SWF investments in exchange listed companies. From the overall stock price reaction we can conjecture that investors expect from this investment of Aabar a positive impact on the corporate governance. However, there is also the alternative explanation that SWF have superior target selection abilities which allow them to detect undervalued companies in an inefficient capital market.

Surface-induced breakout crystallization in cylinder-forming P(I-b-EO) diblock copolymer thin films

We have found very slow crystallization in thin films of cylinder-forming poly(isoprene-b-ethyleneoxide) (P(I-b -EO)) diblock copolymers with PEO being the minority block. The film was crystallized at room temperature after melting at 62 °C. Imaging methods were combined with X-ray reflectometry and grazing-incidence small-angle X-ray scattering and diffraction. Initially, hexagonally packed, amorphous PEO cylinders lie in the film plane. After 148 days, crystallized, finger-like terraces were observed over the entire film surface. The terrace height is 20% higher than the repeat distance in the as-prepared film. Thus, at the film surface, the cylinders have been destroyed by crystalline lamellae lying in the film plane. The PEO chain stems are perpendicular to the substrate surface and are once-folded and fully interdigitated. The substrate-near layers still consist of the hexagonally packed, amorphous PEO cylinders within the PI matrix.

Structural characterization of the Fddd phase in a diblock copolymer thin film by electron microtomography

A 3-dimensional Fddd network structure of a polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer (Mn = 31500, fPI = 0.645) was observed for the first time in real space by transmission electron microtomography (TEMT). In a 650 nm thick film of the PS-b-PI thin film on a silicon wafer, the Fddd phase was developed after annealing at 215 °C for 24 h. The single network structure consists of the connected tripodal units of minor PS block domains. The {111}Fddd plane, the densest plane of the minor PS phase, was found to orient parallel to the film plane. The transitional structure from the wetting layer at the free surface to the internal {111}Fddd plane via a perforated layer structure was also observed.

Dynamics and order–disorder transitions in bidisperse diblock copolymer blends

We employ the dynamic extension of self-consistent field theory (DSCFT) to study dynamics and order–disorder transitions (ODT) in AB diblock copolymer binary mixtures of two different monodisperse chain lengths by imitating the dynamic storage modulus G′ corresponding to any given morphology in the oscillatory shear measurements. The different polydispersity index (PDI) is introduced by binary blending AB diblock copolymers with variations in chain lengths and chain number fractions. The simulation results show that the increase of polydispersity in the minority or symmetric block introduces a decrease in the segregation strength at the ODT, ( χN) ODT, whereas the increase of polydispersity in the majority block results in a decrease, then increase and final decrease again in ( χN) ODT. To the best of our knowledge, our DSCFT simulations, for the first time, predict an increase in ( χN) ODT with the PDI in the majority block, which produces the experimental results. The simulations by previous SCFT, which generally speaking, is capable of describing equilibrium morphologies, however, contradict the experimental data. The polydispersity acquired by properly tuning the chain lengths and number fractions of binary diblock copolymer blends should be a convenient and efficient way to control the microphase separation strength at the ODT.

Directed Assembly of a Cylinder-Forming Diblock Copolymer: Topographic and Chemical Patterns

Using simulations of a coarse-grained model, we examine the ability of topographic and chemical patterns to direct the self-assembly of thin films of copolymers into a defect-free array of vertical cylinders. The topographic pattern is a trench where the diblock is confined, whereas the chemical pattern consists of spots that interact preferentially with the minority block. The self-assembly process is described with Monte Carlo simulations of the standard model of block copolymers. While fully three-dimensional, the simulated systems can include over a hundred domains. By analyzing top views and cross sections of thin films, it is possible to determine the degree of ordering and the properties of individual domains. First, the influence of confinement on ordering perfection is examined. By focusing on the influence of trench width and sidewall selectivity, one can identify conditions that yield defect-free arrays with a high reliability and for which domains exhibit a high degree of uniformity across the...

Magnetostratigraphy and paleomagnetism of early and middle Miocene synorogenic strata: basement partitioning and minor block rotation in Argentine broken foreland

Magnetostratigraphic and paleomagnetic studies on early Andean synorogenic strata (Del Creston Fm.), in the Famatina Belt (28.7°S, 67.5°W) clarify details of chronology that permit calculation of sedimentation rates within the broken foreland of west Argentina. The Del Creston Fm represents the first record of broken foreland sedimentation within the southern Central Andean belt and the earliest retroarc volcanic rocks exposed several hundred kilometers from the trench. Twenty-five out of 49 sites collected along the succession presented a primary remanence, as determined through positive fold and reversal tests. Correlation of the local magnetic polarity section with the global polarity time scale indicates that the sedimentation of Del Creston Fm started at ~16.7 Ma and continued until ~14.5 Ma. The youngest strata are represented by conglomerates bearing abundant Lower Paleozoic granite boulders indicating unroofing of the crystalline basement within the NW Sierras Pampeanas. This result supports the hypothesis of an early broken foreland stage at these latitudes of the Andes, with involvement of the basement in deformation and coeval retroarc volcanism, common attributes of flat-subduction regimes. A mean site paleomagnetic direction of Dec: 6.3°, Inc: −43.6° (α95: 8.0°, N = 24) confirm our earlier intrepretation that the central part of the Famatina Belt within the Sierras Pampeanas did not undergo large vertical axes rotations since the Middle Miocene.

Ordering Dynamics of Directed Self-Assembly of Block Copolymers in Periodic Two-Dimensional Fields

The ordering dynamics of directed self-assembly of cylinder-forming diblock copolymers is studied by cell dynamics simulations. The directing field, mimicking chemically or topologically patterned substrates, is in the form of hexagonally arranged potential wells attractive to minority blocks. Time evolution of the defect concentration is used to characterize the ordering dynamics of the self-assembled cylindrical structures of the block copolymers. When the period of the external potential, Ls, is a small integer multiple of the cylinder-to-cylinder distance, L0, of the block copolymer microphase, the defect concentration decays exponentially. The defect annihilation becomes slower as Ls is increased, and eventually, the exponential decay law is broken. When the ratio Ls/L0 is a square root of an integer, large polycrystalline grains with different orientations are observed. The results are consistent with available experimental and theoretical results.

Tunable morphologies from charged block copolymers

The bulk morphologies formed by a new class of charged block copolymers, 75 vol % fluorinated polyisoprene (FPI) – 25 vol% sulfonated polystyrene (PSS) with 50% sulfonation, are characterized, and the fundamental underlying forces that promote the self-assembly processes are elucidated. The results show how the bulk morphologies are substantially different from their uncharged diblock counterparts (PS-PI) and also how morphology can be tuned with volume fraction of the charged block and the casting solvent. A physical understanding based on the underlying strong electrostatic interactions between the charged block and counterions is obtained using Monte Carlo (MC) and Molecular Dynamics (MD) simulations. The 75/25 FPI-PSS shows hexagonal morphologies with the minority blocks (PSS) forming the continuous phase due to charge percolation and the FPI blocks arranged in hexagonal cylinders. Some long-range order can be sustained even if lipophobicity is increased (addition of water), albeit with lower dimensional structures. However, thermal annealing provides sufficient energy to disrupt the percolated charges and promotes aggregation of ionic sites which leads to a disordered system. Diverse and atypical morphologies are readily accessible by simply changing the number distribution of the charges on the PSS block.

Polymer dynamics under soft confinement in a self-assembled system

Block copolymers that self-assemble into nano-structured melts provide an interesting template for soft confinement. An important question that arises is how the chain dynamics is affected in such self-assembled systems. Here we consider a system composed of poly(isoprene)-b-poly(dimethyl siloxane) (PI6-PDMS30, where the numbers indicate the molecular weight in kg mole−1) having a large asymmetry where the minor PI component block constitutes 19% of the total molecular weight. As shown by small angle neutron scattering (SANS), the system forms hexagonally ordered cylindrical structures composed of a PI phase (with a cylinder radius of about 6.4 nm) in a continuous PDMS matrix. Here we demonstrate using neutron spin-echo spectroscopy and careful H/D contrast matching schemes how the dynamics of single polymer chains (single chain contrast) and the interfacial dynamics of the domains can be resolved independently. This is achieved in the former “single chain contrast” case by matching out the net domain scattering leaving only the intra chain coherent structure factor visible. In the latter “bulk contrast” case, the protonated (h) PI and deuterated (d) PDMS domains are visible and most of the contrast comes from the small interfacial layer where h-PI/d-PDMS segments are intermixed and give rise to a significant contrast by which the fluctuations can be observed. Combining the results from the two contrast conditions, we show that the dynamics can be consistently described in terms of Rouse motion modified by the surface fluctuation and laterally restricted to 2D surface diffusion. Surprisingly, the fluctuations of the interface significantly contribute to the dynamics and the interfacial tension drives the fluctuations of a sizeable portion of the polymer chains while the dynamics is similar to Rouse motion.

Precise placements of metal nanoparticles from reversible block copolymer nanostructures

We demonstrate the fabrication of reversible block copolymer (BCP) templates that can be used to control the spatial location of metal precursors and nanoparticles. A highly ordered polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) micellar array was obtained by solvent annealing. Subsequent immersion of the films in a preferential solvent for the minor component block caused a reorganization of the film to generate a porous structure upon drying. When such reconstructed films were subjected to external stimuli, like solvent vapor or heat, the initial morphology was recovered. These reversible BCP templates were used to control the placement such that, subsequently, oxygen plasma treatment led to the precise placement of metal nanoparticles in a film. By controlling the concentration of the metal precursor solutions, the sizes of the nanoparticles could be tuned.

Use of Sonography in Thoracic Outlet Syndrome Due to a Dystonic Pectoralis Minor

For patients with thoracic outlet syndrome (TOS), it is important to determine the location of the neurovascular compression to achieve effective intervention. The diagnostic workup for a 39-year-old man with TOS included a selective anesthetic block of the pectoralis minor muscle and duplex sonography before and after the block. The subclavian artery peak systolic flow velocity decreased after the block from 208 to 63 cm/s when the arm was in the abduction and external rotation position, indicating a reduction in the severity of focal arterial compression. Also, the arterial diameter increased by 10% after the block (from 0.80 to 0.88 cm). His level of discomfort was reduced from 6 to 2 on a scale of 1 to 10 (66%). The pectoralis minor block resulted in an improvement in subclavian artery blood flow and symptoms and confirmed the diagnosis of pectoralis minor TOS. This suggests that selective anesthetic muscle blocks and duplex sonographic studies may be useful before chemodenervation and surgery.

A Simple Top‐Down/Bottom‐Up Approach to Sectored, Ordered Arrays of Nanoscopic Elements Using Block Copolymers

A top-down/bottom-up approach is demonstrated by combining electron-beam (e-beam) lithography and a solvent annealing process. Micellar arrays of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with a high degree of lateral order can be produced on a surface where sectoring is defined by e-beam patterning. The e-beam is used to crosslink the block copolymer (BCP) film immediately after spin-coating when the BCP is disordered or in a highly ordered solvent-annealed film. Any patterns can be written into the BCP by crosslinking. Upon exposure to a preferential solvent for the minor component block followed by drying, cylindrical nanopores are generated within the nonexposed areas by a surface reconstruction process, while, in the exposed areas, the films remain unchanged. Nickel nanodot arrays can be placed over selected areas on a surface by thermal evaporation and lift-off process.