Gram-negative bacteria are an increasingly serious source of antibiotic-resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir–Blodgett and Langmuir–Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The nanoscale magnetic structure of FeRh epilayers has been studied by polarized neutron reflectometry. Epitaxial films with a nominal thickness of 500 Å were grown on MgO ͑001͒ substrates via molecular-beam epitaxy and capped with 20 Å of MgO. The FeRh films show a clear transition from the antiferromagnetic ͑AF͒ state to the ferromagnetic ͑FM͒ state with increasing temperature. Surprisingly the films possess a FM moment even at a temperature 80 K below the AF-FM transition temperature of the film. We have quantified the magnitude and spatial extent of this FM moment, which is confined to within ϳ60-80 Å of the FeRh near the top and bottom interfaces. These interfacial FM layers account for the unusual effects previously observed in films with thickness Ͻ100 Å. Given the delicate energy balance between the AF and FM ground states we suggest a metastable FM state resides near to the interface within an AF matrix. The length scale over which the FM region resides is consistent with the strained regions of the film.

Organic photovoltaic devices (OPVs) based on conjugated polymers and fullerene blends offer an attractive method to produce renewable energy. It has been demonstrated that they can be manufactured on fl exible substrates and at low cost over large areas using the high volume technique of roll-to-roll printing. [1][2][3] Whilst much work has been devoted to the donoracceptor system P3HT:PCBM (poly(3-hexylthiophene):[6,6]-phenyl-C 61 -butyric acid methyl ester), attention is now turning to the use of donor materials which have a reduced energy gap (permitting more of the sun's spectral emission to be harvested) and an increased ionization potential (leading to an increased open-circuit voltage and thus greater power conversion effi ciency [ 4 , 5 ] ).One promising new donor polymer for OPV applications is PCDTBT (poly [N-9 ′ -heptadecanyl-2,7-carbazole-alt-5,5-(4 ′ ,7 ′ -di-2-thienyl-2 ′ ,1 ′ ,3 ′ -benzothiadiazole)] whose chemical structure is shown in Figure 1 . [ 4 ] When PCDTBT is blended with the fullerene acceptor PC 70 BM, OPV devices have been created having a power conversion effi ciency of ∼ 6%, [ 6 ] one of the highest OPV effi ciencies to date. A marked difference in the fabrication process of these devices compared to the benchmark P3HT:PCBM system is the requirement for thermal annealing. It has been established that thermal annealing at ∼ 150 ° C [ 7 ] (between the glass transition and melting temperatures of P3HT) is required to drive the crystallization of the two components to form nanoscale, phase-separated domains. [8][9][10] Without such a thermal anneal process, the power conversion effi ciency (PCE) of P3HT:PCBM is limited to around 1%-2% [ 11 ] -a value that is improved to between 4 and 5% in an annealed device. [ 7 , 11 ] Recently we have established that this thermal anneal also modifi es the vertical structure of P3HT:PCBM thin fi lms. [ 12 ] In as-cast P3HT:PCBM fi lm, the surface is relatively depleted in PCBM. However by annealing the fi lm, PCBM is driven to the fi lm surface, an effect that we believe improves the electronic functionality of the device. In PCDTBT:PCBM OPVs however, a high temperature annealing process has been reported to be detrimental to device effi ciency. [ 6 ] Rather a low-temperature anneal/ drying stage at 70 ° C appears suffi cient to fully optimize device effi ciency although the benefi t of this stage has not been explicitly quantifi ed. Devices incorporating a TiO x optical spacing layer are also subsequently annealed at 80 ° C. [ 6 ] In this paper, we use neutron refl ectivity (NR) and grazing incidence wide-angle X-ray scattering (GI-WAXS) to explore the nanoscale structures formed in freshly cast PCDTBT:PCBM thin fi lms and those that have been annealed at a relatively low temperature. We make two main fi ndings. Firstly, we fi nd that the surface of freshly cast PCDTBT:PCBM fi lms is relatively enriched in PCBM with a negative concentration gradient existing away from the fi lm surface. Secondly, thermal annealing at 70 ° C does not signifi cantly m...

We present an unreported magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 (x ∼ 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn(3+)/Mn(4+) to an enriched Mn3+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e(g) orbital (d(3)z(2)-r(2). This reconstruction may provide a mechanism for coupling the Mn3+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.

No abstract

Superconducting spintronics has emerged in the past decade as a promising new field that seeks to open a new dimension for nanoelectronics by utilizing the internal spin structure of the superconducting Cooper pair as a new degree of freedom 1,2 . Its basic building blocks are spin-triplet Cooper pairs with equally aligned spins, which are promoted by proximity of a conventional superconductor to a ferromagnetic material with inhomogeneous macroscopic magnetization 3 . Using low-energy muon spin-rotation experiments we find an unanticipated e ect, in contradiction with the existing theoretical models of superconductivity and ferromagnetism: the appearance of a magnetization in a thin layer of a non-magnetic metal (gold), separated from a ferromagnetic double layer by a 50-nm-thick superconducting layer of Nb. The e ect can be controlled either by temperature or by using a magnetic field to control the state of the remote ferromagnetic elements, and may act as a basic building block for a new generation of quantum interference devices based on the spin of a Cooper pair.The ability to manipulate the spin degree of freedom of charge carriers is key to realizing future spin-based electronics. Integrating superconductors into spintronic devices can greatly enhance performance 1 and allows the transport of spin over long distances without the dissipation of heat 2 . To achieve the alignment of electron spins, ferromagnetic materials are used. Superconductivity and ferromagnetism are, however, antagonistic states of matter, and the interplay between these two states results in the conversion of conventional spin-singlet into spin-triplet pair correlations 3 . Whereas spin-singlet pairs have spin angular momentum S = 0, spin-triplet pairs have S = 1, with three possible spin projections s z = −1, 0, +1. The realization of such spin-triplet pairs in mesoscopic systems containing interfaces between superconducting (S) and ferromagnetic (F) layers has attracted much interest from both the theoretical and experimental communities. Interaction of spin-singlet superconductivity with collinear ferromagnetism leads to oscillations and suppression of the pair correlation at a short distance ξ f due to the exchange magnetic field in the ferromagnet, which tends to align the spins of electrons parallel 4-7 . However, to create longer-range penetration of spin-triplet superconductivity into the ferromagnet, interaction with a non-collinear magnetism is required [8][9][10] , motivating the discovery of superconducting currents through ferromagnetic metals over distances far longer than the singlet penetration length ξ f (refs 11-13). These long-range triplet components (LRTC) have parallel spin projections (s z = ±1), and are not suppressed by the exchange field. Theory predicts that the conversion into spin-triplet pairs should also give rise to an induced magnetic moment in the superconductor, decaying away from the interface [14][15][16] , often called the inverse or magnetic proximity effect. For diffusive systems this induced m...

We report the structural and magnetic study of Cr-doped Bi2Se3 thin films using x-ray diffraction (XRD), magnetometry and polarized neutron reflectometry (PNR). Epitaxial layers were grown on c-plane sapphire by molecular beam epitaxy in a two-step process. Highresolution XRD shows the exceptionally high crystalline quality of the doped films with no parasitic phases up to a Cr concentration of 12% (in % of the Bi sites occupied by substitutional Cr). The magnetic moment, measured by SQUID magnetometry, was found to be ∼2.1 μB per Cr ion. The magnetic hysteresis curve shows an open loop with a coercive field of ∼10 mT. The ferromagnetic transition temperature was determined to be 8.5 K analyzing the magnetizationtemperature gradient. PNR shows the film to be homogeneously ferromagnetic with no enhanced magnetism near the surface or interface.

Yttrium iron garnet has a very high Verdet constant, is transparent in the infrared and is an insulating ferrimagnet leading to its use in optical and magneto-optical applications. Its high Q-factor has been exploited to make resonators and filters in microwave devices, but it also has the lowest magnetic damping of any known material. In this article we describe the structural and magnetic properties of single crystal thin-film YIG where the temperature dependence of the magnetisation reveals a decrease in the low temperature region. In order to understand this complex material we bring a large number of structural and magnetic techniques to bear on the same samples. Through a comprehensive analysis we show that at the substrate -YIG interface, an interdiffusion zone of only 4–6 nm exists. Due to the interdiffusion of Y from the YIG and Gd from the substrate, an addition magnetic layer is formed at the interface whose properties are crucially important in samples with a thickness of YIG less than 200 nm.