Switching "on" and "off" the adhesion in stimuli-responsive elastomers.

The present work aims at the preparation of dry adhesives with switchable bonding properties by using the reversible nature of the [4πs+4πs] cycloaddition of anthracenes. Photo-responsive hydrogenated carboxylated nitrile butadiene rubber with photo-responsive pendant anthracene groups is prepared by one-pot synthesis. The formation of 3D networks relies on the photodimerization of the anthracene moieties upon UV exposure (λ > 300 nm). Controlled cleavage of the crosslink sites is achieved by either deep UV exposure (λ = 254 nm) or thermal dissociation at 70 °C. The kinetics of the optical and thermal cleavage routes are compared in thin films using UV-vis spectroscopy and their influence on the reversibility of the network is detailed. Going from thin films to free standing samples the modulation of the network structure and thermo-mechanical properties over repeated crosslinking and cleavage cycles are characterized by low-field NMR spectroscopy and dynamic mechanical analysis. The applicability of the stimuli-responsive networks as adhesives with reversible bonding properties is demonstrated. The results evidence that the reversibility of the crosslinking reaction enables a controlled switching "on" and "off" of adhesion properties. The recovery of the adhesion force amounts to 75 and 80% for photo- and thermal dissociation, respectively. Spatial control of adhesion properties is evidenced by adhesion force mapping experiments of photo-patterned films.

Reversibility of temperature driven discrete layer-by-layer formation of dioctyl-benzothieno-benzothiophene films.

Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects.

Thin film growth of aromatic rod-like molecules on graphene.

Research on graphene (Gr) is a vastly expanding field due to its potential for technological applications. Its close structural and chemical relationship to conjugated organic molecules makes it a superior candidate as a transparent electrode material in organic electronics and optoelectronics. The growth of organic thin films-intensively investigated in the past few decades-has demonstrated the complexity in growth and nucleation processes arising from the anisotropy and spatial extension of the molecular building blocks. Choosing the small, conjugated rod-like molecules para-hexaphenyl and pentacene as model representatives for small organic molecules, we review recent findings in organic thin film growth on a variety of Gr substrates. Special attention is paid to the differences in the resulting growth arising from the various methods of Gr fabrication and support that affect both the Gr-molecule interfacing and the involved molecular diffusion processes.

Influence of TiO2(110) surface roughness on growth and stability of thin organic films.

We have investigated the growth and stability of molecular ultra-thin films, consisting of rod-like semiconducting para-hexaphenyl (6P) molecules vapor deposited on ion beam modified TiO2(110) surfaces. The ion bombarded TiO2(110) surfaces served as growth templates exhibiting nm-scale anisotropic ripple patterns with controllable parameters, like ripple depth and length. In turn, by varying the ripple depth one can tailor the average local slope angle and the local step density/terrace width of the stepped surface. Here, we distinguish three types of substrates: shallow, medium, and deep rippled surfaces. On these substrates, 6P sub-monolayer deposition was carried out in ultra-high vacuum by organic molecular beam evaporation (OMBE) at room temperature leading to the formation of islands consisting of upright standing 6P molecules, which could be imaged by scanning electron microscopy and atomic force microscopy (AFM). It has been found that the local slope and terrace width of the TiO2 template strongly influences the stability of OMBE deposited 6P islands formed on the differently rippled substrates. This effect is demonstrated by means of tapping mode AFM, where an oscillating tip was used as a probe for testing the stability of the organic structures. We conclude that by increasing the local slope of the TiO2(110) surface the bonding strength between the nearest neighbor standing molecules is weakened due to the presence of vertical displacement in the molecular layer in correspondence to the TiO2 atomic step height.

Modified energetics and growth kinetics on H-terminated GaAs (110).

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV∕Å(2) measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Mixed permian-triassic fauna, guryul ravine, kashmir.

At Guryul Ravine near Srinagar, Kashmir, a varied fauna of productid brachiopods, including Spinomarginifera, is associated in approximately 15 feet (about 4 meters) of strata with the typical Scythian (Lower Triassic) pelecypod Claraia. These faunas are interpreted as true associations of surviving "Permian" and Lower Triassic faunal elements. Similar mixed associations have previously been identified in the lowest Triassic strata of the Salt Range and Surghar Range of West Pakistan.

Origin of the low-energy emission band in epitaxially grown para-sexiphenyl nanocrystallites.

A comparative study of steady-state and time-resolved photoluminescence of para-sexiphenyl (PSP) films grown by organic molecular beam epitaxy (OMBE) and hot wall epitaxy (HWE) under comparable conditions is presented. Using different template substrates [mica(001) and KCl(001) surfaces] as well as different OMBE growth conditions has enabled us to vary greatly the morphology of the PSP crystallites while keeping their chemical structure virtually untouched. We prove that the broad redshifted emission band has a structure-related origin rather than being due to monomolecular oxidative defects. We conclude that the growth conditions and type of template substrate impacts substantially on the film morphology (measured by atomic force microscopy) and emission properties of the PSP films. The relative intensity of the defect emission band observed in the delayed spectra was found to correlate with the structural quality of PSP crystallites. In particular, the defect emission has been found to be drastically suppressed when (i) a KCl template substrate was used instead of mica in HWE-grown films, and (ii) in the OMBE-grown films dominated by growth mounds composed of upright standing molecules as opposed to the films consisting of crystallites formed by molecules lying parallel to the substrate.

Structure, stresses and stress relaxation of TiN/Ag nanocomposite films.

Morphology, structure and thermal behavior of magnetron sputtered TiN/Ag nanocomposite thin films deposited at 150 degrees C with an Ag content in the range of 7 to 45 at% were characterized. The films were thermally cycled and the relationship between Ag content, film structure and stress development is analyzed. The results indicate that the residual stresses in as-deposited films and the behavior during heating are determined by the film structure and the plastic deformation of the Ag phase. The increasing plastic deformation with increasing Ag content causes significant changes in the stress-temperature behavior. While films with low Ag content show a plateau in compressive stress from deposition temperature up to 280 degrees C followed by stress relaxation, films with higher Ag content exhibit a zero stress level from deposition temperature up to the maximum annealing temperature. During cooling, all films exhibit linear thermo-elastic behavior, where the slope of the stress-temperature curves also depends on the Ag content.

Ion beam sputtered nanostructured semiconductor surfaces as templates for nanomagnet arrays.

The ongoing tendency for increasing the storage densities in magnetic recording techniques requires a search for efficient routes to fabricate and characterize nanomagnet arrays on solid supports. Spontaneous pattern formation in semiconductor heteroepitaxy or under ion erosion of semiconductor surfaces yields nanostructured substrates that can serve as templates for subsequent deposition of magnetic material. The nanostructured morphology of the template can easily be replicated into the magnetic coating by means of the shadow deposition technique which allows one to selectively cover specific areas of the template with magnetic material. Here, we demonstrate that ion bombardment induced hexagonally arranged GaSb dots are suitable templates for fabricating by shadow deposition close-packed nanomagnets with a lateral extension of ≤50 nm, i.e. with a resulting storage density of up to 0.2 Tbit in(-2). Magnetic-force microscopy (MFM) measurements revealed that the individual nanomagnets-which are located on the tops of the semiconductor hillocks-are single domain and show mainly independent magnetization. The coupling behaviour was estimated from correlation function analysis of the MFM data. In addition, magneto-optical Kerr effect measurements demonstrate that the nanomagnets can be magnetized either out-of-plane or in-plane and show remanence at room temperature, with a coercive field of 120 mT.

Fabrication of ion bombardment induced rippled TiO2 surfaces to influence subsequent organic thin film growth.

Control over organic thin film growth is a central issue in the development of organic electronics. The anisotropy and extended size of the molecular building blocks introduce a high degree of complexity within the formation of thin films. This complexity can be even increased for substrates with induced, sophisticated morphology and anisotropy. Thus, targeted structuring like ion beam mediated modification of substrates in order to create ripples, pyramids, or pit structures provides a further degree of freedom in manipulating the growth morphology of organic thin films. We provide a comprehensive review of recent work on para-hexaphenyl (C36H26, 6P) as a typical representative of the class of small, rod-like conjugated molecules and rutile TiO2(1 1 0) as an example for a transparent oxide electrode to demonstrate the effect of ion beam induced nanostructuring on organic thin film growth. Starting from molecular growth on smooth, atomically flat TiO2(1 1 0) (1 × 1) surfaces, we investigate the influence of the ripple size on the resulting 6P thin films. The achieved 6P morphologies are either crystalline nano-needles composed of flat lying molecules or islands consisting of upright standing 6P, which are elongated in ripple direction. The islands' length-to-width ratio can be controlled by tuning the ripples' shape.

Magic Lite Chlamydia immunoassay in urogenital samples and urine versus chlamydial culture.

Magic Lite Chlamydia assay (commercial test kit for the identification of Chlamydia trachomatis) was evaluated on urogenital samples and urine with chlamydial culture as the reference method. The sediment of the transportation buffer of specimens which were Magic Lite positive but culture negative or toxic was investigated for elementary bodies with fluorescein-labelled anti-chlamydial antibodies. The prevalence of chlamydial infection among the 577 men investigated was 13.7% as estimated by culture and direct immunofluorescence and 6.4% among the 173 women. In order to improve the sensitivity a cut-off value below that recommended by the manufacturer was used. The sensitivity of Magic Lite in male urethral specimens was then 60.8% and that in female urethral/cervical specimens 90.9%. The specificity was 99.6% and 100%, respectively. In urine specimens the sensitivity of Magic Lite was 63.3% (men) and 63.6% (women). The specificity was 99.4% and 100%, respectively. The sensitivity of Magic Lite on male urethral specimens was related to the number of inclusion bodies per well in culture and it was higher among men attending with clinical findings of urethritis (69%) than among asymptomatic men sampled as a screening procedure (36%) (P < 0.05). Corresponding differences between the sexes and between those with and without symptoms were not noted for Magic Lite applied on urine samples.

Recent patents on self-organised magnetic nanodot arrays.

As the continuous advance in the process of device miniaturisation reaches down to the nanometre range, fabrication techniques based on self-organisation, i.e., the spontaneous formation of ordered patterns on surfaces, are becoming increasingly attractive as potential, highly efficient alternatives to lithographic methods. In this article we review some of the methodologies that have been developed recently to produce ordered arrays of nanomagnets using self-organised surface templates, and we list the patents that have been filed recently to protect those fabrication procedures. We describe the underlying phenomena giving rise to the appearance of the ordered structures, and discuss their characteristics and the controllable parameters.