Orthogonally Spin-Coated Bilayer Films for Photochemical Immobilization and Patterning of Sub-10-Nanometer Polymer Monolayers.

Versatile and spatiotemporally controlled methods for decorating surfaces with monolayers of attached polymers are broadly impactful to many technological applications. However, current materials are usually designed for very specific polymer/surface chemistries and, as a consequence, are not very broadly applicable and/or do not rapidly respond to high-resolution stimuli such as light. We describe here the use of a polymeric adhesion layer, poly(styrene sulfonyl azide-alt-maleic anhydride) (PSSMA), which is capable of immobilizing a 1-7 nm thick monolayer of preformed, inert polymers via photochemical grafting reactions. Solubility of PSSMA in very polar solvents enables processing alongside hydrophobic polymers or solutions and by extension orthogonal spin-coating deposition strategies. Therefore, these materials and processes are fully compatible with photolithographic tools and can take advantage of the immense manufacturing scalability they afford. For example, the thicknesses of covalently grafted poly(styrene) obtained after seconds of exposure are quantitatively equivalent to those obtained by physical adsorption after hours of thermal equilibration. Sequential polymer grafting steps using photomasks were used to pattern different regions of surface energy on the same substrate. These patterns spatially controlled the self-assembled domain orientation of a block copolymer possessing 21 nm half-periodicity, demonstrating hierarchical synergy with leading-edge nanopatterning approaches.

Speed, pacing strategy and aerodynamic drafting in Thoroughbred horse racing.

Choice of pacing strategy and the benefit of aerodynamic drafting are thought to be key determinants of racing performance. These effects have largely been analysed without reference to final outcome, in small datasets with low temporal resolution, and a focus on human swimming, cycling and running. Here, we determined the position and speed of 44,803 racehorses, once per second, in 3,357 races ranging in length from 1006 to 4225 m (50.9-292.9 seconds duration) using a validated radio tracking system. We find that aerodynamic drafting has a marked effect on horse performance, and hence racing outcome. Furthermore, we demonstrate that race length-dependent pacing strategies are correlated with the fastest racing times, with some horses reaching a maximum speed in excess of 19 m s(-1). The higher speeds seen with certain pacing strategies may arise due to the nature of pack racing itself, or may be a reflection of individual capabilities, that is, corresponding to horses that perform well in roles suited to their 'front-running' or 'chaser' personality traits.

Spatial Control of the Self-assembled Block Copolymer Domain Orientation and Alignment on Photopatterned Surfaces.

Polarity-switching photopatternable guidelines can be directly used to both orient and direct the self-assembly of block copolymers. We report the orientation and alignment of poly(styrene-block-4-trimethylsilylstyrene) (PS-b-PTMSS) with a domain periodicity, L0, of 44 nm on thin photopatternable grafting surface treatments (pGSTs) and cross-linkable surface treatments (pXSTs), containing acid-labile 4-tert-butoxystyrene monomer units. The surface treatment was exposed using electron beam lithography to create well-defined linear arrays of neutral and preferential regions. Directed self-assembly (DSA) of PS-b-PTMSS with much lower defectivity was observed on pXST than on pGST guidelines. The study of the effect of film thickness on photoacid diffusion by Fourier transform infrared spectroscopy and near-edge X-ray absorption fine structure spectroscopy suggested slower diffusion in thinner films, potentially enabling production of guidelines with sharper interfaces between the unexposed and exposed lines, and thus, the DSA of PS-b-PTMSS on thinner pXST guidelines resulted in better alignment control.

A new framework for X-ray photon correlation spectroscopy analysis from polycrystalline materials.

We report a new analytical framework for interpreting data from X-ray photon correlation spectroscopy measurements on polycrystalline materials characterized by strong scattering intensity variations at fixed wavevector magnitude (i.e., anisotropic scattering). Currently, no analytical method exists for the interpretation of the time-dependent anisotropic scattering from such materials. The framework is applied to interrogate the dynamics of a spherical micelle-forming diblock copolymer melt below the order-disorder transition, wherein finite size grains of a micellar body-centered cubic structure produce anisotropic scattering. A wealth of analytical information is recovered from a simple measurement, including distributions of relaxation times and speeds associated with micelles within grains. The findings of this study demonstrate the efficacy of this new analytical method, which may be readily adapted for application to a variety of materials and systems.

Characterizing the Interface Scaling of High χ Block Copolymers near the Order-Disorder Transition.

Advancements in the directed self-assembly of block copolymers (BCPs) have prompted the development of new materials with larger effective interaction parameters (χe). This enables BCP systems with phase separation at increasingly small degrees of polymerization (N). Very often these systems reside near the order-disorder transition and fit between the weak and strong segregation limits where the behavior of BCP systems is not as thoroughly understood. Utilizing resonant soft X-ray reflectivity (RSoXR) enables both the BCP pitch (L0) and interface width (wM) to be determined simultaneously, through a direct characterization of the composition profile of BCP lamellae oriented parallel to a substrate. A series of high χe BCPs with χe ranging from ≈0.04 to 0.25 and χeN from 19 to 70 have been investigated. The L0/wm ratio serves as an important metric for the feasibility of a material for nanopatterning applications; the results of the RSoXR measurement are used to establish a relationship between χe and L0/wm. The results of this analysis are correlated with experimentally established limits for the functionality of BCPs in nanopatterning applications. These results also provide guidance for the magnitude of χe needed to achieve small interface width for samples with sub-10 nm L0.

Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers.

The linear viscoelastic behavior of poly(norbornene)-graft-poly(±-lactide) was investigated as a function of grafting density and overall molar mass. Eight sets of polymers with grafting densities ranging from 0 to 100% were synthesized by living ring-opening metathesis copolymerization. Within each set, the graft chain molar mass and spacing between grafts were fixed, while the total backbone length was varied. Dynamic master curves reveal that these polymers display Rouse and reptation dynamics with a sharp transition in the zero-shear viscosity data, demonstrating that grafting density strongly impacts the entanglement molar mass. The entanglement modulus (Ge) scales with inverse grafting density (ng) as Ge ∼ ng1.2 and Ge ∼ ng0 in accordance with scaling theory in the high and low grafting density limits, respectively. However, a sharp transition between these limiting behaviors occurs, which does not conform to existing theoretical models for graft polymers. A molecular interpretation based on thin flexible chains at low grafting density and thick semiflexible chains at high grafting density anticipates the sharp transition between the limiting dynamical regimes.

Dynamics of a Supercooled Disordered Sphere-Forming Diblock Copolymer as Determined by X-ray Photon Correlation and Dynamic Mechanical Spectroscopies.

We report the dynamic behavior of a sphere-forming poly(styrene)-block-poly(1,4-butadiene) (PS-PB) diblock copolymer comprising 20 vol % PB below the order-disorder transition temperature (TODT = 153 °C) using dynamic mechanical spectroscopy (DMS) and X-ray photon correlation spectroscopy (XPCS). A time-temperature transformation diagram was constructed by monitoring the elasticity of the sample as a function of time following rapid quenches of the disordered melt to various temperatures T < TODT. Isothermal frequency spectra acquired prior to nucleation of the ordered BCC phase were time-temperature superposed, and the shift factors were fit using the Williams-Landel-Ferry (WLF) equation. For comparison, XPCS measurements were used to extract relaxation times from the supercooled liquid as a function of the quench temperature. Alignment of the temperature dependence of the XPCS-based relaxation times with that of the WLF shift factors in the range T = 125-140 °C indicates that both techniques probe the fluctuating mesomorphic micelle dynamics mediated by the relaxation modes of individual chains, including interparticle chain exchange. For deeper quench temperatures, TODT - T ≥ 28 °C, departure of the XPCS time constant from WLF behavior is consistent with a jamming transition, analogous to that encountered in concentrated colloidal systems. We postulate that the dominant relaxation mode in the supercooled disordered liquid transitions from ergodic dynamics governed by chain exchange to a nonergodic regime dominated by local rearrangement of micellar particles at T ≈ Terg, where Terg denotes the ergodicity temperature.

Directed Self-Assembly and Pattern Transfer of Five Nanometer Block Copolymer Lamellae.

The directed self-assembly (DSA) and pattern transfer of poly(5-vinyl-1,3-benzodioxole-block-pentamethyldisilylstyrene) (PVBD-b-PDSS) is reported. Lamellae-forming PVBD-b-PDSS can form well resolved 5 nm (half-pitch) features in thin films with high etch selectivity. Reactive ion etching was used to selectively remove the PVBD block, and fingerprint patterns were subsequently transferred into an underlying chromium hard mask and carbon layer. DSA of the block copolymer (BCP) features resulted from orienting PVBD-b-PDSS on guidelines patterned by nanoimprint lithography. A density multiplication factor of 4× was achieved through a hybrid chemo-/grapho-epitaxy process. Cross-sectional scanning tunneling electron microscopy/electron energy loss spectroscopy (STEM/EELS) was used to analyze the BCP profile in the DSA samples. Wetting layers of parallel orientation were observed to form unless the bottom and top surface were neutralized with a surface treatment and top coat, respectively.

Sleep disturbances in patients with post-traumatic stress disorder: epidemiology, impact and approaches to management.

Subjective reports of sleep disturbance indicate that 70-91% of patients with post-traumatic stress disorder (PTSD) have difficulty falling or staying asleep. Nightmares are reported by 19-71% of patients, depending on the severity of their PTSD and their exposure to physical aggression. Objective measures of sleep disturbance are inconsistent, with some studies that used these measures indicating poor sleep and others finding no differences compared with non-PTSD controls. Future research in this area may benefit from examining measures of instability in the microstructure of sleep. Additionally, recent findings suggest that sleep disordered breathing (SDB) and sleep movement disorders are more common in patients with PTSD than in the general population and that these disorders may contribute to the brief awakenings, insomnia and daytime fatigue in patients with PTSD. Overall, sleep problems have an impact on the development and symptom severity of PTSD and on the quality of life and functioning of patients. In terms of treatments, SSRIs are commonly used to treat PTSD, and evidence suggests that they have a small but significant positive effect on sleep disruption. Studies of serotonin-potentiating non-SSRIs suggest that nefazodone and trazodone lead to significant reductions in insomnia and nightmares, whereas cyproheptadine may exacerbate sleep problems in patients with PTSD. Prazosin, a centrally acting alpha1-adrenoceptor antagonist, has led to large reductions in nightmares and insomnia in small studies of patients with PTSD. Augmentation of SSRIs with olanzapine, an atypical antipsychotic, may be effective for treatment-resistant nightmares and insomnia, although adverse effects can be significant. Additional medications, including zolpidem, buspirone, gabapentin and mirtazapine, have been found to improve sleep in patients with PTSD. Large randomised, placebo-controlled trials are needed to confirm the above findings. In contrast, evidence suggests that benzodiazepines, TCAs and MAOIs are not useful for the treatment of PTSD-related sleep disorders, and their adverse effect profiles make further studies unlikely. Cognitive behavioural interventions for sleep disruption in patients with PTSD include strategies targeting insomnia and imagery rehearsal therapy (IRT) for nightmares. One large randomised controlled trial of group IRT demonstrated significant reductions in nightmares and insomnia. Similarly, uncontrolled studies combining IRT and insomnia strategies have demonstrated good outcomes. Uncontrolled studies of continuous positive airway pressure for SDB in patients with PTSD show that this treatment led to significant decreases in nightmares, insomnia and PTSD symptoms. Controlled studies are needed to confirm these promising findings.

Depression as a predictor of perceived social support and demand: a componential approach using a prospective sample of older adults.

This study examined the relationship of the cognitive, mood, and somatic components of depression on perceptions of social support and social demand among older adults (n = 851) over two years. Factor-analyses confirmed the factor structure of our multicomponential model of depression. Results supported our proposal that interpersonal specificity, as measured by depressive cognition about self and others, is important to predicting changes in perceived support and demand over time. Each component of depression was related to social support and social demand cross-sectionally, whereas only the cognitive component of depression predicted changes in support and demand prospectively. Future research should consider the pathways linking depressive cognition to perceived support and demand.

A voice in the wilderness: gay and lesbian religious groups in the Western United States.

The paper describes a study of gay and lesbian religious groups located in the United States between the Mississippi River and the Pacific Ocean between March of 1989 and June of 1993. The researcher found 684 groups to have existed at some time in the region and conducted interviews to document 468 of these groups. While a history of these groups dates back to the 1930s in the region, large groups still existing today did not begin to form until the late 1960s. The six most common goals of the groups were social and support needs, worship, denominational and social politics, community service, and leadership in the gay and lesbian community. Being focused on gay and lesbian issues has an influence on when and how they came into existence (in the beginnings of the gay and lesbian movement, in response to the AIDS crisis, in response to anti-gay legislative initiatives), has an influence on the kinds of key themes addressed (ordination of gay and lesbian people, same-sex marriage, service for people with AIDS, sexual ethics in scripture), and has an influence on relationships with the larger community (shunning or inclusion in the larger society and in the larger religious community). However, the stronger influence is their identity as religious (and, therefore, social) institutions. They experience the same pressures of mainstream religion and as social institutions by facing issues of diversity, gender, age, politics, race, and disease. They face the same challenges as any religious institution today of being prophetic, responsive, changing, traditional, true, relevant, and even noticed. A distinct feature is their role on the fringes. They are on the fringe of religious life and on the fringe of gay and lesbian life.

Photopatterning of Block Copolymer Thin Films.

Block copolymers are potentially useful materials for large-area 2-D patterning applications due to their spontaneous self-assembly into sub-50 nm domains. However, most thin film engineering applications require patterns of prescribed size, shape, and organization. Photopatterning is a logical choice for manipulating block copolymer features since advanced lithography tools can pattern areas as small as a single block copolymer domain. By exposing either the block copolymer or a responsive interfacial surface to patterned radiation, precise control over placement, orientation, alignment, and selective development of block copolymer domains can be achieved. This Viewpoint highlights some of the recent research in photopatterning block copolymer thin films and identifies areas of future opportunity.

Quantifying the Interface Energy of Block Copolymer Top Coats.

Block copolymers (BCPs) have the potential to play a key role in templating materials for nanoscale synthesis. BCP lithography likely will be one of the first examples of BCP-based nanomanufacturing implemented in a production setting. One of the challenges in implementing BCP lithography is that the lamella need to be oriented perpendicular to the substrate. For many systems, this requires control over interfacial energies for both components at the substrate and interface. Top coats can be designed to provide a neutral interface for both blocks on the BCP surface. The preferentiality of the top coat as a function of composition has been determined qualitatively by examining the orientation of a BCP after annealing with a top coat. Measurements of the interfacial width between the top coat and homopolymers allows the interface energy to be quantitatively determined. Resonant soft X-ray reflectivity measurements on top coat/homopolymer pairs were used to extract the Flory-Huggins parameter (χ) and interface energy (γ) as a function of top coat composition. The difference between χ and γ for each top coat/homopolymer pair was minimized at compositions that resulted in the top coat promoting perpendicular orientation. As the composition moved away from the neutral point the difference between χ and γ for each pair grew larger.

Structure, Stability, and Reorganization of 0.5 L0 Topography in Block Copolymer Thin Films.

The structure, stability, and reorganization of lamella-forming block copolymer thin film surface topography ("islands" and "holes") were studied under boundary conditions driving the formation of 0.5 L0 thick structures at short thermal annealing times. Self-consistent field theory predicts that the presence of one perfectly neutral surface renders 0.5 L0 topography thermodynamically stable relative to 1 L0 thick features, in agreement with previous experimental observations. The calculated through-film structures match cross-sectional scanning electron micrographs, collectively demonstrating the pinning of edge dislocations at the neutral surface. Remarkably, near-neutral surface compositions exhibit 0.5 L0 topography metastability upon extended thermal treatment, slowly transitioning to 1 L0 islands or holes as evidenced by optical and atomic force microscopy. Surface restructuring is rationalized by invoking commensurability effects imposed by slightly preferential surfaces. The results described herein clarify the impact of interfacial interactions on block copolymer self-assembly and solidify an understanding of 0.5 L0 topography, which is frequently used to determine neutral surface compositions of considerable importance to contemporary technological applications.

Pattern Transfer of Sub-10 nm Features via Tin-Containing Block Copolymers.

Tin-containing block copolymers were investigated as materials for nanolithographic applications. Poly(4-trimethylstannylstyrene-block-styrene) (PSnS-PS) and poly(4-trimethylstannylstyrene-block-4-methoxystyrene) (PSnS-PMOST) synthesized by reversible addition-fragmentation chain transfer polymerization form lamellar domains with periodicities ranging from 18 to 34 nm. Thin film orientation control was achieved by thermal annealing between a neutral surface treatment and a top coat. Incorporation of tin into one block facilitates pattern transfer into SiO2 via a two-step etch process utilizing oxidative and fluorine-based etch chemistries.

Double-Patterned Sidewall Directed Self-Assembly and Pattern Transfer of Sub-10 nm PTMSS-b-PMOST.

The directed self-assembly (DSA) of two sub-20 nm pitch silicon-containing block copolymers (BCPs) was accomplished using a double-patterned sidewall scheme in which each lithographic prepatterned feature produced two regions for pattern registration. In doing so, the critical dimension of the lithographic prepatterns was relaxed by a factor of 2 compared to previously reported schemes for DSA. The key to enabling the double-patterned sidewall scheme is the exploitation of the oxidized sidewalls of cross-linked polystyrene formed during the pattern transfer of the resist via reactive ion etching. This results in shallow trenches with two guiding interfaces per prepatterned feature. Electron loss spectroscopy was used to study and confirm the guiding mechanism of the double-patterned sidewalls, and pattern transfer of the BCPs into a silicon substrate was achieved using reactive ion etching. The line edge roughness, width roughness, and placement error are near the target required for bit-patterned media applications, and the technique is also compatible with the needs of the semiconductor industry for high-volume manufacturing.

Directed self-assembly of silicon-containing block copolymer thin films.

The directed self-assembly (DSA) of lamella-forming poly(styrene-block-trimethylsilylstyrene) (PS-PTMSS, L0=22 nm) was achieved using a combination of tailored top interfaces and lithographically defined patterned substrates. Chemo- and grapho-epitaxy, using hydrogen silsesquioxane (HSQ) based prepatterns, achieved density multiplications up to 6× and trench space subdivisions up to 7×, respectively. These results establish the compatibility of DSA techniques with a high etch contrast, Si-containing BCP that requires a top coat neutral layer to enable orientation.

Six-month outcomes from a randomized trial augmenting serotonin reuptake inhibitors with exposure and response prevention or risperidone in adults with obsessive-compulsive disorder.

OBJECTIVE: To compare outcomes after 6-month maintenance treatment of adults diagnosed with obsessive-compulsive disorder (OCD) based on DSM-IV criteria who responded to acute treatment with serotonin reuptake inhibitors (SRIs) augmented by exposure and response prevention (EX/RP) or risperidone. METHOD: A randomized trial was conducted at 2 academic sites from January 2007 through December 2012. In the acute phase, 100 patients on therapeutic SRI dose with at least moderate OCD severity were randomized to 8 weeks of EX/RP, risperidone, or pill placebo. Responders entered the 6-month maintenance phase, continuing the augmentation strategy they received acutely (n = 30 EX/RP, n = 8 risperidone). Independent evaluations were conducted every month. The main outcome was the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). RESULTS: Intent-to-treat analyses indicated that, after 6-month maintenance treatment, EX/RP yielded OCD outcomes that were superior to risperidone (Y-BOCS = 10.95 vs 18.70; t40 = 2.76, P = .009); more patients randomized to EX/RP met response criteria (Y-BOCS decrease ≥ 25%: 70% vs 20%; P < .001) and achieved minimal symptoms (Y-BOCS ≤ 12: 50% vs 5%; P < .001). During maintenance, OCD severity decreased slightly in both conditions (Y-BOCS decrease = 2.2 points, P = .020). Lower Y-BOCS at entry to maintenance was associated with more improvement in both conditions (r38 = 0.57, P < .001). CONCLUSIONS: OCD patients taking SRIs who responded to acute EX/RP or risperidone maintained their gains over 6-month maintenance. Because EX/RP patients improved more during acute treatment than risperidone-treated patients, and both maintained their gains during maintenance, EX/RP yielded superior outcomes 6 months later. The findings that 50% of patients randomized to EX/RP had minimal symptoms at 6-month maintenance, a rate double that of prior studies, suggests that EX/RP maintenance helps maximize long-term outcome. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00389493.

Photopatternable Interfaces for Block Copolymer Lithography.

Directly photopatternable interfaces are introduced that facilitate two-dimensional spatial control of block copolymer (BCP) orientation in thin films. Copolymers containing an acid labile monomer were synthesized, formulated with a photoacid generator (PAG), and coated to create grafted surface treatments (GSTs). These as-cast GST films are either inherently neutral or preferential (but not both) to lamella-forming poly(styrene-block-trimethylsilylstyrene) (PS-b-PTMSS). Subsequent contact printing and baking produced GSTs with submicron chemically patterned gratings. The catalytic reaction of the photoacid generated in the UV-exposed regions of the GSTs changed the interfacial interactions between the BCP and the GST in one of two ways: from neutral to preferential ("N2P") or preferential to neutral ("P2N"). When PS-b-PTMSS was thermally annealed between a chemically patterned GST and a top coat, alternating regions of perpendicular and parallel BCP lamellae were formed.