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Nanoscale hybrid inorganic–organic multilayers are attractive for accessing emergent phenomena and properties through superposition of nanomolecularly-induced interface effects for diverse applications. Here, we demonstrate the effects of interfacial molecular nanolayers (MNLs) of organo-diphosphonates on the growth and stability of titania nanolayers during the synthesis of titania/MNL multilayers by sequential atomic layer deposition and single-cycle molecular layer deposition. Interfacial organo-diphosphonate MNLs result in ∼20–40% slower growth of amorphous titania nanolayers and inhibit anatase nanocrystal formation from them when compared to amorphous titania grown without MNLs. Both these effects are more pronounced in multilayers with aliphatic backbone-MNLs and likely related to impurity incorporation and incomplete reduction of the titania precursor indicated by our spectroscopic analyses. In contrast, both MNLs result in two-fold higher titania nanolayer roughness, suggesting that roughening is primarily due to MNL bonding chemistry. Such MNL-induced effects on inorganic nanolayer growth rate, roughening, and stability are germane to realizing high-interface-fraction hybrid nanolaminate multilayers. [ABSTRACT FROM AUTHOR]

Experimental and theoretical approaches are used to understand the role of nanomorphology on exciton dissociation and charge collection at dilute donor–acceptor (D–A) organic heterojunctions (HJs). Specifically, two charge transfer (CT) states in D–A mixed HJs comprising nanocrystalline domains of tetraphenyldibenzoperiflanthene (DBP) as the donor and C70 as the acceptor are unambiguously related to the nanomorphology of the mixed layer. Alternating DBP:C70 multilayer stacks are used to identify and control the optical properties of the CT states, as well as to simulate the dilute mixed heterojunctions. A kinetic Monte Carlo model along with photoluminescence spectroscopy and scanning transmission electron microscopy are used to quantitatively evaluate the layer morphology under various growth conditions. As a result, we are able to understand the counterintuitive observation of high charge extraction efficiency and device performance of DBP:C70 mixed layer photovoltaics at surprisingly low (∼10%) donor concentrations. [ABSTRACT FROM AUTHOR]

Single conical nanopores were functionalised layer by layer with weak polyelectrolytes. We studied their influence on the ionic diode properties We have considered different couples of polyelectrolytes: poly-L-lysine/poly(acrylic acid) and poly(ethyleneimine)/poly(acrylic acid) as well as the influence of cross-linking. The results show that the nanopores decorated with poly(ethyleneimine)/poly(acrylic acid) exhibit an interesting behavior. Indeed, at pH 3, the nanopore is open only at the low salt concentration, while at pH 7, it is already open. The nanopores functionalized with poly-L-lysine/poly(acrylic acid) do not show an inversion of ionic transport properties with the pH as expected. After cross-linked to prevent large conformational changes, the ionic diode properties are dependent on the pH. [ABSTRACT FROM AUTHOR]

Laser pulses induce spin-selective charge flow that we show to generate dramatic changes in the magnetic structure of materials, including a switching of magnetic order from antiferromagnetic (AFM) to transient ferromagnetic (FM) in multisub-lattice systems. The microscopic mechanism underpinning this ultrafast switching of magnetic order is dominated by spin-selective charge transfer from one magnetic sublattice to another. Because this spin modulation is purely optical in nature (i.e., not mediated indirectly via the spin–orbit interaction) this is one of the fastest means of manipulating spin by light. We further demonstrate this mechanism to be universally applicable to AFM, FM, and ferri-magnets in both multilayer and bulk geometry and provide three rules that encapsulate early-time magnetization dynamics of multisub-lattice systems. [ABSTRACT FROM AUTHOR]

Honeycomb structure endows graphene with extraordinary properties. But could a honeycomb monolayer superlattice also be generated via self-assembly of colloids or nanoparticles? Here we report the construction of mono- and multilayer molecular films with honeycomb structure that can be regarded as self-assembled artificial graphene (SAAG). We construct fan-shaped molecular building blocks by covalently connecting two kinds of clusters, one polyoxometalate and four polyhedral oligomeric silsesquioxanes. The precise shape control enables these complex molecules to self-assemble into a monolayer 2D honeycomb superlattice that mirrors that of graphene but on the mesoscale. The self-assembly of the SAAG was also reproduced via coarse-grained molecular simulations of a fan-shaped building block. It revealed a hierarchical process and the key role of intermediate states in determining the honeycomb structure. Experimental images also show a diversity of bi- and trilayer stacking modes. The successful creation of SAAG and its stacks opens up prospects for the preparation of novel self-assembled nanomaterials with unique properties. [ABSTRACT FROM AUTHOR]

Polyelectrolyte multilayers (PEMs) are of great interest as cell culture surfaces because of their ability to modify topography and surface energy and release biologically relevant molecules such as growth factors. In this work, fibroblast growth factor 2 (FGF2) was adsorbed directly onto polystyrene, plasma-treated polystyrene, and glass surfaces with a poly(methacrylic acid) and poly-l-histidine PEM assembled above it. Up to 14 ng/cm² of FGF2 could be released from plasma-treated polystyrene surfaces over the course of 7 days with an FGF2 solution concentration of 100 µg/mL applied during the adsorption process. This release rate could be modulated by adjusting the adsorption concentration, decreasing to as low as 2 ng/cm² total release over 7 days using a 12.5 µg/mL FGF2 solution. The surface energy and roughness could also be regulated using the adsorbed PEM. These properties were found to be substrate- and first-layer-dependent, supporting current theories of PEM assembly. When released, FGF2 from the PEMs was found to significantly enhance fibroblast proliferation as compared to culture conditions without FGF2. The results showed that growth factor release profiles and surface properties are easily controllable through modification of the PEM assembly steps and that these strategies can be effectively applied to common cell culture surfaces to control the cell fate. [ABSTRACT FROM AUTHOR]

Multilayer superstructures based on stacked layered nanomaterials offer the possibility to design three-dimensional (3D) nanopores with highly specific properties analogous to protein channels. In a layer-by-layer design and stacking, analogous to molecular printing, superstructures with lock-and-key molecular nesting and transport characteristics could be prepared. To examine this possibility, we use molecular dynamics simulations to study electric field-driven transport of ions through stacked porous graphene flakes. First, highly selective, tunable, and correlated passage rates of monovalent atomic ions through these superstructures are observed in dependence on the ion type, nanopore type, and relative position and dynamics of neighboring porous flakes. Next, enantioselective molecular transport of ionized l- and d-leucine is observed in graphene stacks with helical nanopores. The outlined approach provides a general scheme for synthesis of functional 3D superstructures. [ABSTRACT FROM AUTHOR]

We present a combination of self-consistent field theory simulations and experimental results to explore the mechanism behind the orientational preference of second-layer cylinders in nanomeshes formed by two consecutive steps of the self-assembly of block copolymers (BCPs). Incommensurability of the top-layer cylinder spacing with that of the bottom-layer features is found to dictate orientation preference, and this mismatch can be controlled by either the film height or the nanomesh spacing ratio via the molecular weight of the polymers used. When the space available within the film does not accommodate the hexagonal packing of the parallel orientation, the system will favor orthogonal alignment of the second-layer cylinders. This behavior is robust: it is consistently observed in many experimental systems and verified here by the comparison of free energies of both states obtained from simulations. We also discuss the impact of substrate selectivity and air-polymer interface selectivity on these energies and therefore their effect on the orientational selection. [ABSTRACT FROM AUTHOR]

The emergence of polymer-free water surface in a Langmuir polymer film at conditions where a homogeneous coverage has been expected previously is explained on the basis of the surface tensions of polymer and water, Υpv and Υwv, respectively, as well as the interfacial tension between the two materials, Υpw. The polymer molecules considered are 22-residue poly(Υ-benzyl-l-glutamate) (PBLG) peptides in α-helical conformation. Values for Υpv and Υpw derived from MD simulations are consistent with values inferred from experiments considering the emergence of polymer-free surface area for ultrathin films studied using the surface forces apparatus in earlier work. Based on these surface properties, the behavior of individual PBLG peptides at the air-water interface, the dimerization of PBLG peptides, the equilibrium height and width of fibers with given cross section, and the lateral fusion of fibers are described. We show that a prerequisite for the emergence of multilayer structures, which appear locally in domains of sizes of tens to hundreds of micrometers in the considered Langmuir polymer film, is that the condition Υpv + Υpw - Υwv > 0 holds true. [ABSTRACT FROM AUTHOR]

Using grazing-incidence small-angle scattering (GISAXS) with computed tomography (CT), we have individually reconstructed the spatial distribution of a thin gold (Au) layer buried under a thin poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) layer. Owing to the difference between total reflection angles of Au and PS-b-P2VP, the scattering profiles for Au nanoparticles and self-assembled nanostructures of PS-b-P2VP could be independently obtained by changing the X-ray angle of incidence. Reconstruction of scattering profiles allows one to separately characterize spatial distributions in Au and PS-b-P2VP nanostructures. [ABSTRACT FROM AUTHOR]

This Letter reports on the unusual diffusion behavior of Ge during oxidation of a multilayer Si/SiGe fin. It is observed that oxidation surprisingly results in the formation of vertically stacked Si nanowires encapsulated in defect free epitaxial strained SixGe1-x. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows that extremely enhanced diffusion of Ge occurs along the vertical Si/SiO2 oxidizing interface and is responsible for the encapsulation process. Further oxidation fully encapsulates the Si layers in defect free single crystal SixGe1-x (x up to 0.53), which results in Si nanowires with up to -2% strain. Atom probe tomography reconstructions demonstrate that the resultant nanowires run the length of the fin. We found that the oxidation temperature plays a significant role in the formation of the Si nanowires. In the process range of 800-900 °C, pure strained and rounded Si nanowires down to 2 nm in diameter can be fabricated. At lower temperatures, the Ge diffusion along the oxidizing Si/SiO2 interface is slow, and rounding of the nanowire does not occur, while at higher temperatures, the diffusivity of Ge into Si is sufficient to result in dilution of the pure Si nanowire with Ge. The use of highly selective etchants to remove the SiGe could provide a new pathway for the creation of highly controlled vertically stacked nanowires for gate all around transistors. [ABSTRACT FROM AUTHOR]

The surface morphology and organization of poly(ionic liquid)s (PILs), poly[1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir-Blodgett (LB) monolayers at the air-water and air-solid interfaces is demonstrated. The hydrophobic bis(trifluoromethylsulfonyl)imide (Tf2N-) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films. [ABSTRACT FROM AUTHOR]

The ability to control the growth of materials with nanosized precision as well as a complex hollow morphology provides rationale for the study of systems comprising both characteristics. This study explores the design of TiO2 hollow nanotube shells deposited by atomic layer deposition (ALD) on vertically aligned SnO2 nanorods grown using the vapor-liquid-solid technique. The sacrificial template approach in combination with highly conformal coating advantages of ALD resulted in a highly reproducible method to create a large surface area covered by TiO2-protected SnO2 nanorods, which are about 60-100 nm in diameter and approximately 1 μm in length. ZnO was used as a sacrificial layer to create a 30 nm gap between SnO2 nanorods and 10 nm of TiO2 shells. Chemical etching of the sacrificial layer was used to create the desired hollow nanocomposite. A coin half-cell battery has been assembled using the TiO2-protected SnO2 nanorods as an anode electrode and lithium foil as a counter electrode and tested for lithium storage during 70 cycles of charge/discharge in a range of 0.5-2.5 V. The TiO2 hollow shell functioned as a good and robust enhancer for both absolute capacity and current rate capabilities of vertically aligned SnO2 nanorods; an improvement in cyclic stability was also observed. This advanced self-standing hollow configuration provides several unique advantages for energy storage device applications including enhanced lithiation for superior energy storage performance. [ABSTRACT FROM AUTHOR]

In the present work, polyelectrolyte multilayers (PEMs) and graphene sheets are applied to sequentially coat on the surface of hollow carbon spheres/sulfur composite by a flexible layer-by-layer (LBL) self-assembly strategy. Owing to the strong electrostatic interactions between the opposite charged materials, the coating agents are very stable and the coating procedure is highly efficient. The LBL film shows prominent impact on the stability of the cathode by acting as not only a basic physical barrier, and more importantly, an ion-permselective film to block the polysulfides anions by Coulombic repulsion. Furthermore, the graphene sheets can help to stabilize the polyelectrolytes film and greatly reduce the inner resistance of the electrode by changing the transport of the electrons from a "point-to-point" mode to a more effective "plane-to-point'' mode. On the basis of the synergistic effect of the PEMs and graphene sheets, the fabricated composite electrode exhibits very stable cycling stability for over 200 cycles at 1 A g-1, along with a high average Coulombic efficiency of 99%. With the advantages of rapid and controllable fabrication of the LBL coating film, the multifunctional architecture developed in this study should inspire the design of other lithium-sulfur cathodes with unique physical and chemical properties. [ABSTRACT FROM AUTHOR]

The effects of CaCl2, MgCl2, and Na2SO4 on the swelling response and the thermal transition of poly(diallyldimethylammonium chloride)/poly(styrenesulfonate) (PDAC/PSS) layer-by-layer (LbL) assemblies are investigated. For MgCl2 and CaCl2, two swelling regimes are observed depending on the salt concentration of the overlying solution. Below 0.17 M MgCl2 or CaCl2, swelling appears to arise from electrostatic repulsion within the multilayer. Above 0.17 M MgCl2 or CaCl2, the multilayer swells linearly with the concentration of the overlying solution due to doping; the degree of swelling in this linear regime depends on the hydration shell of the doping ions. Alternatively, swelling with no concentration dependence was observed for Na2SO4. Unlike the swelling behavior, the thermal transition temperature observed in hydrated films shifts to higher temperatures with increasing concentration of Na2SO4. However, when hydrated with CaCl2 or MgCl2 solutions, the transition remains relatively constant within error. Results are discussed in terms of the salt ion's hydration shell and Donnan exclusion. [ABSTRACT FROM AUTHOR]

We created both a superhydrophilic polymer surface and a superhydrophobic surface by using the poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) multilayers with the synchronously generated hierarchical porous surface structures. The formation of surface and pore structures induced at acidic pH values is subject to the composition, distribution, and molecular weights of polyelectrolytes in the layer-by-layer (LbL) assembled film, leading to a variety of unique surface topographies and porous structures located on different scales. During the porous induction at pH 2.0, both nano- and microscaled features synchronously developed on the surface as a result of the unique combination of high-molecular-weight PAH (900K g/mol) and low molecular weight PAA (15K g/mol), along with a much reduced deposition time of 1 min. Although thermally cross-linked, the porous surface with hierarchical structure could achieve superhydrophilicity due to the remaining free amine and carboxylate groups on the porous structures. A complete switch from the superhydrophilic to the superhydrophobic surface was achieved via a simple chemical vapor deposition of trichloro(1H,1H,2H,2H-perfluoro-octyl)silane. In this work, the effects of molecular weight of polyelectrolytes (15K-900K g/mol), deposition time (10-900 s) during the LbL assembly, and pH (1.8 to 2.4) for the porous induction on the surface topography, pore structures, and wetting behavior were investigated in detail. A variety of unique porous surface structures on different length scales were systematically studied by controlling the above parameters. [ABSTRACT FROM AUTHOR]

A study is presented of the effects of sample temperature on the sputter depth profiling of two organic materials, NPB ( N,N′-Di(1-naphthyl)- N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine) and Irganox 1010, using a 5 keV Ar cluster ion beam and analysis by secondary ion mass spectrometry. It is shown that at low temperatures, the yields increase slowly with temperature in accordance with the Universal Sputtering Yield equation where the energy term is now modified by Trouton's rule. This occurs up to a transition temperature, T , which is, in turn, approximately 0.8 T , where T is the sample melting temperature in Kelvin. For NPB and Irganox 1010, these transition temperatures are close to 15 °C and 0 °C, respectively. Above this temperature, the rate of increase of the sputtering yield rises by an order of magnitude. During sputtering, the depth resolution also changes with temperature with a very small change occurring below T . At higher temperatures, the depth resolution improves but then rapidly degrades, possibly as a result first of local crater surface diffusion and then of bulk inter-diffusion. The secondary ion spectra also change with temperature with the intensities of the molecular entities increasing least. This agrees with a model in which the molecular entities arise near the crater rim. It is recommended that for consistent results, measurements for organic materials are always made at temperatures significantly below T or 0.8 T , and this is generally below room temperature. [ABSTRACT FROM AUTHOR]

We report approaches to the design of covalently crosslinked and physically stable surface coatings with chemically labile and dynamic surface features based on the functionalization of azlactone-containing materials with alcohol-, thiol-, and hydrazine-based nucleophiles. Past studies demonstrate that residual azlactone groups in polymer multilayers fabricated by the reactive layer-by-layer assembly of poly(2-vinyl-4,4-dimethylazlactone) and branched poly(ethylenimine) can react with amine-based nucleophiles to impart new surface and bulk properties through the creation of chemically stable amide/amide-type bonds. Here, we demonstrate that the azlactone groups in these covalently crosslinked materials can also be functionalized using less nucleophilic alcohol- or thiol-containing compounds, using an organic catalyst, or converted to reactive acylhydrazine groups by direct treatment with hydrazine. These methods (i) broaden the pool of molecules that can be used for post-fabrication functionalization to include compounds containing alcohol, thiol, or aldehyde groups and (ii) yield surface coatings with chemically labile amide/ester-, amide/thioester-, and amide/imine-type bonds that make possible the design of new dynamic and stimulus-responsive materials (e.g., surfaces that release covalently bound molecules or undergo changes in extreme wetting behaviors in response to specific chemical stimuli). Our results expand the range of functionality that can be installed in, and thus the range of new functions that can be imparted to, azlactone-containing coatings beyond those that can be accessed using primary amine-based nucleophiles. The chemical approaches demonstrated here using model polymer-based reactive multilayer coatings are general and should thus also prove useful for the design of new responsive surfaces based on other types of azlactone-functionalized materials. [ABSTRACT FROM AUTHOR]

Selective deposition of peptides from liquid solutions to n- and p-doped silicon has been demonstrated. The selectivity is governed by peptide/silicon adhesion differences. A noninvasive, fast characterization of the obtained peptide layers is required to promote their application for interfacing silicon-based devices with biological material. In this study we show that spectroscopic ellipsometrya method increasingly used for the investigation of biointerfacescan provide essential information about the amount of adsorbed peptide material and the degree of coverage on silicon surfaces. We observed the formation of peptide multilayers for a strongly binding adhesion peptide on p-doped silicon. Application of the patterned layer ellipsometric evaluation method combined with Sellmeier dispersion led to physically consistent results, which describe well the optical properties of peptide layers in the visible spectral range. This evaluation allowed the estimation of surface coverage, which is an important indicator of adsorption quality. The ellipsometric findings were well supported by atomic force microscopy results. [ABSTRACT FROM AUTHOR]

Supported membranes on top of polymer cushions are interesting models of biomembranes as cell membranes are supported on a polymer network of proteins and sugars. In this work lipid vesicles formed by a mixture of 30% 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 70% 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) are assembled on top of a polyelectrolyte multilayer (PEM) cushion of poly(allylamine hydrochloride) (PAH) and poly(styrene sodium sulfonate) (PSS). The assembly results in the formation of a bilayer on top of the PEM as proven by means of the quartz crystal microbalance with dissipation technique (QCM-D) and by cryo-transmission electron microscopy (cryo-TEM). The electrical properties of the bilayer are studied by electrochemical impedance spectroscopy (EIS). The bilayer supported on the PEMs shows a high resistance, on the order of 107 Ω cm², which is indicative of a continuous, dense bilayer. Such resistance is comparable with the resistance of black lipid membranes. This is the first time that such values are obtained for lipid bilayers supported on PEMs. The assembly of polyelectrolytes on top of a lipid bilayer decreases the resistance of the bilayer up to 2 orders of magnitude. The assembly of the polyelectrolytes on the lipids induces defects or pores in the bilayer which in turn prompts a decrease in the measured resistance. [ABSTRACT FROM AUTHOR]

We study the 2D rheological properties of hydrogen-bonded polymer multilayers assembled directly at dodecane-water and air-water interfaces using pendant drop/bubble dilation and the double-wall ring method for interfacial shear. We use poly(vinylpyrrolidone) (PVP) as a proton acceptor and a series of polyacrylic acids as proton donors. The PAA series of chains with varying hydrophobicity was fashioned from poly(acrylic acid), (PAA), polymethacrylic acid (PMAA), and a homemade hydrophobically modified polymer. The latter consisted of a PAA backbone covalently grafted with C12 moieties at 1% mol (referred to as PAA-1C12). Replacing PAA with the more hydrophobic PMAA provides a route for combining hydrogen bonding and hydrophobic interactions to increase the strength and/or the number of links connecting the polyacid chains to PVP. This systematic replacement allows for control of the ability of the monomer units inside the absorbed polymer layer to reorganize as the interface is sheared or compressed. Consequently, the interplay of hydrogen bonding and hydrophobic interactions leads to control of the resistance of the polymer multilayers to both shear and dilation. Using PAA-1C12 as the first layer improves the anchoring energy of a few monomers of the chain without changing the strength of the monomer-monomer contact in the complex layer. In this way, the layer does not resist shear but resists compression. This strategy provides the means for using hydrophobicity to control the interfacial dynamics of the complexes adsorbed at the interface of the bubbles and droplets that either elongate or buckle upon compression. Moreover, we demonstrate the pH responsiveness of these interfacial multilayers by adding aliquots of NaOH to the acidic water subphase surrounding the bubbles and droplets. Subsequent pH changes can eventually break the polymer complex, providing opportunities for encapsulation/release applications. [ABSTRACT FROM AUTHOR]

Weak polyelectrolyte multilayers (PEMs) prepared by the layer-by-layer technique have attracted a great deal of attention as smart responsive materials for biological and other applications in aqueous medium, but their dynamic behavior as a function of exposure to a wide temperature range is still not well understood. In this work, the thermally dependent swelling behavior of PEMs consisting of branched poly(ethylenimine) and poly(acrylic acid) is studied by temperature controlled in situ spectroscopic ellipsometry. Because of diffusion and interpenetration of polyelectrolytes during film deposition, the PEMs densify with increasing bilayer number, which further affects their water uptake behavior. Upon heating to temperatures below 60 °C, the worsened solvent quality of the PEM in water causes deswelling of the PEMs. However, once heated above this critical temperature, the hydrogen bonds within the PEMs are weakened, which allows for chain rearrangement within the film upon cooling, resulting in enhanced water uptake and increased film thickness. The current work provides fundamental insight into the unique dynamic behavior of weak polyelectrolyte multilayers in water at elevated temperatures. [ABSTRACT FROM AUTHOR]

Graphene layers are known to stack in two stable configurations, namely, ABA or ABC stacking, with drastically distinct electronic properties. Unlike the ABA stacking, little has been done to experimentally investigate the electronic properties of ABC graphene multilayers. Here, we report on the first magneto optical study of a large ABC domain in a graphene multilayer flake, with ABC sequences exceeding 17 graphene sheets. ABC-stacked multilayers can be fingerprinted with a characteristic electronic Raman scattering response, which persists even at room temperatures. Tracing the magnetic field evolution of the inter Landau level excitations from this domain gives strong evidence for the existence of a dispersionless electronic band near the Fermi level, characteristic of such stacking. Our findings present a simple yet powerful approach to probe ABC stacking in graphene multilayer flakes, where this highly degenerated band appears as an appealing candidate to host strongly correlated states. [ABSTRACT FROM AUTHOR]

The effects of number of graphene layers (n) and size of multilayer graphene sheets on thermal conductivities (TCs) of their epoxy composites are investigated. Molecular dynamics simulations show that the in-plane TCs of graphene sheets and the TCs across the graphene/epoxy interface simultaneously increase with increasing n. However, such higher TCs of multilayer graphene sheets will not translate into higher TCs of bulk composites unless they have large lateral sizes to maintain their aspect ratios comparable to the monolayer counterparts. The benefits of using large, multilayer graphene sheets are confirmed by experiments, showing that the composites made from graphite nanoplatelets (n < 10) with over 30 µm in diameter deliver a TC of ~1.5 W m-1 K-1 at only 2.8 vol %, consistently higher than those containing monolayer or few-layer graphene at the same graphene loading. Our findings offer a guideline to use cost-effective multilayer graphene as conductive fillers for various thermal management applications. [ABSTRACT FROM AUTHOR]

Superior mechanical properties of nanolayered structures have attracted great interest recently. However, previously fabricated multilayer metallic nanostructures have high strength under compressive load but never reached such high strength under tensile loads. Here, we report that our microalloying-based electrodeposition method creates a strong and stable Ni/Ni-Au multilayer nanocrystalline structure by incorporating Au atoms that makes nickel nanowires (NWs) strongest ever under tensile loads even with diameters exceeding 200 nm. When the layer thickness is reduced to 10 nm, the tensile strength reaches the unprecedentedly high 7.4 GPa, approximately 10 times that of metal NWs with similar diameters, and exceeding that of most metal nanostructures previously reported at any scale. [ABSTRACT FROM AUTHOR]

Large-scale growth of high-quality hexagonal boron nitride has been a challenge in two-dimensional-material-based electronics. Herein, we present wafer-scale and wrinkle-free epitaxial growth of multilayer hexagonal boron nitride on a sapphire substrate by using high-temperature and low-pressure chemical vapor deposition. Microscopic and spectroscopic investigations and theoretical calculations reveal that synthesized hexagonal boron nitride has a single rotational orientation with AA' stacking order. A facile method for transferring hexagonal boron nitride onto other target substrates was developed, which provides the opportunity for using hexagonal boron nitride as a substrate in practical electronic circuits. A graphene field effect transistor fabricated on our hexagonal boron nitride sheets shows clear quantum oscillation and highly improved carrier mobility because the ultraflatness of the hexagonal boron nitride surface can reduce the substrate-induced degradation of the carrier mobility of two-dimensional materials. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of a cross-linkable, cinnamic acid functionalized, hole-transporting polyfluorene-triarylamine (PF-PTAA) copolymer. Irradiation with light induces [2 + 2] cycloaddition and renders thin films of this polymer insoluble. Spin-coated films of the polymer and their light-induced cross-linking were investigated by atomic force and electron microscopy. In a proof-of-principle multilayer OLED device the polymer was applied as hole-transport layer (HTL) with commercially available F8BT as emitting layer (EML). Compared to the reference device without HTL we observe a significant increase in OLED performance. These results promise progress in cost-effective large area fabrication of polymer-based multilayer OLEDs with superior performance. [ABSTRACT FROM AUTHOR]

The preparation of thin melanin films suitable for applications is challenging. In this work, we present a new alternative approach to thin melanin-type films using oxidative multilayers prepared by the sequential layer-by-layer deposition of cerium(IV) and inorganic polyphosphate. The interfacial reaction between cerium(IV) in the multilayer and 5,6-dihydroxyindole (DHI) in the adjacent aqueous solution leads to the formation of a thin uniform film. The oxidation of DHI by cerium(IV) proceeds via known melanin intermediates. We have characterized the formed DHI-melanin films using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-vis spectroscopy, and spectroelectrochemistry. When a five-bilayer oxidative multilayer is used, the film is uniform with a thickness of ca. 10 nm. Its chemical composition, as determined using XPS, is typical for melanin. It is also redox active, and its oxidation occurs in two steps, which can be assigned to semiquinone and quinone formation within the indole structural motif. Oxidative multilayers can also oxidize dopamine, but the reaction stops at the dopamine quinone stage because of the limited amount of the multilayer-based oxidizing agent. However, dopamine oxidation by Ce(IV) was studied also in solution by UV-vis spectroscopy and mass spectrometry in order to verify the reaction mechanism and the final product. In solution, the oxidation of dopamine by cerium shows that the indole ring formation takes place already at low pH and that the mass spectrum of the final product is practically identical with that of commercial melanin. Therefore, layer-by-layer formed oxidative multilayers can be used to deposit functional melanin-type thin films on arbitrary substrates by a surface-controlled reaction. [ABSTRACT FROM AUTHOR]

9-(Bis-p-tert-octylphenyl)-amino-perylene-3,4-dicarboxy anhydride (BOPA-PDCA) is a strongly dipolar molecule representing a group of asymmetrically substituted perylenes that are employed in dye-sensitized solar cells and hold great promise for discotic liquid crystal applications. Thin BOPA-PDCA films with orientated dipole moments can potentially be used to tune the energy-level alignment in electronic devices and store information. To help assessing these prospects, we here elucidate the molecular self-assembly and electronic structure of BOPA-PCDA employing room temperature scanning tunneling microscopy and spectroscopy in combination with ultraviolet and X-ray photoelectron spectroscopies. BOPA-PCDA monolayers on Au(111) exclusively form in-plane antiferroelectric phases. The molecular arrangements, the increase of the average number of molecules per unit cell via ripening, and the rearrangement upon manipulation with the STM tip indicate an influence of the dipole moment on the molecular assembly and the rearrangement. A slightly preferred out-of-plane orientation of the molecules in the multilayer induces a surface potential of 1.2 eV. This resembles the giant surface potential effect that was reported for vacuum-deposited tris(8-hydroxyquinoline)aluminum and deemed applicable for data storage. Notably, the surface potential in the case of BOPA-PDCA can in part be reversibly removed by visible light irradiation. [ABSTRACT FROM AUTHOR]

In this work, the structure of solid-supported lipid multilayers exposed to increased hydrostatic pressure was studied in situ by X-ray reflectometry at the solid-liquid interface between silicon and an aqueous buffer solution. The layers' vertical structure was analyzed up to a maximum pressure of 4500 bar. The multilayers showed phase transitions from the fluid into different gel phases. With increasing pressure, a gradual filling of the sublayers between the hydrophilic head groups with water was observed. This process was inverted when the pressure was decreased, yielding finally smaller water layers than those in the initial state. As is commonly known, water has an abrasive effect on lipid multilayers by the formation of vesicles. We show that increasing pressure can reverse this process so that a controlled switching between multi- and bilayers is possible. [ABSTRACT FROM AUTHOR]

A long-standing dream in the large scale application of solar energy conversion is the fabrication of solar cells with high-efficiency and long-term stability at low cost. The realization of such practical goals depends on the architecture, process and key materials because solar cells are typically constructed from multilayer heterostructures of light harvesters, with electron and hole transporting layers as a major component. Recently, inorganic-organic hybrid lead halide perovskites have attracted significant attention as light absorbers for the fabrication of low-cost and high-efficiency solar cells via a solution process. This mainly stems from long-range ambipolar charge transport properties, low exciton binding energies, and suitable band gap tuning by managing the chemical composition. In our pioneering work, a new photovoltaic platform for efficient perovskite solar cells (PSCs) was proposed, which yielded a high power conversion efficiency (PCE) of 12%. The platform consisted of a pillared architecture of a three-dimensional nanocomposite of perovskites fully infiltrating mesoporous TiO2, resulting in the formation of continuous phases and perovskite domains overlaid with a polymeric hole conductor. Since then, the PCE of our PSCs has been rapidly increased from 3% to over 20% certified efficiency. The unprecedented increase in the PCE can be attributed to the effective integration of the advantageous attributes of the refined bicontinuous architecture, deposition process, and composition of perovskite materials. Specifically, the bicontinuous architectures used in the high efficiency comprise a layer of perovskite sandwiched between mesoporous metal-oxide layer, which is a very thinner than that of used in conventional dye-sensitized solar cells, and hole-conducting contact materials with a metal back contact. The mesoporous scaffold can affect the hysteresis under different scan direction in measurements of PSCs. The hysteresis also greatly depends on the cell architecture and perovskite composition. In this Account, we will describe what we do with major aspects including (1) the film morphology through the development of intermediate chemistry retarding the rapid reaction between methylammonium or formamidinium iodide and lead halide (PbI2) for improved perovskite film formation; (2) the phase stability and band gap tuning of the perovskite layer through the materials engineering; (3) the development of electron and hole transporting materials for carrier-selective contacting layers; and (4) the adoption of p-i-n and n-i-p architectures depending on the position of the electron or hole conducting layer in front of incident light. Finally, we will summarize the recent incredible achievements in PSCs, and finally provide challenges facing the future development and commercialization of PSCs. [ABSTRACT FROM AUTHOR]

The powerful host-guest chemistry of cucurbit[8]uril (CB[8]) was employed to obtain photoresponsive polyelectrolyte multilayer films for the reversible and photocontrolled binding and release of an organic guest molecule. For this purpose, we designed and synthesized a polyelectrolyte with azobenzene side groups. Then, CB[8] was associated with the azo side group to obtain a supramolecular host-guest complex that was further used as building block in order to prepare photoresponsive and CB[8]-containing polyelectrolyte multilayer films. Ultraviolet spectroscopy and a dissipative quartz crystal microbalance are employed to monitor the formation of the host-guest complex and the layer-by-layer self-assembly of the multilayer films, respectively. We demonstrate that the photoresponsive properties of the azo side groups are maintained before and after host-guest complexation with CB[8] in solution and within the multilayer films, respectively. A guest molecule was then specifically included as second binding partner into the CB[8]-containing multilayer films. Subsequently, the release of the guest was performed by UV light irradiation due to the trans-cis isomerization of the adjacent azo side groups. Re-isomerization of the azo side groups was achieved by VIS light irradiation and enabled the rebinding of the guest into CB[8]. Finally, we demonstrate that the photocontrolled binding and release within CB[8]-containing multilayer films can reliably and reversibly be performed over a period of more than 2 weeks with constant binding efficiency. Therefore, we expect such novel type of photosensitive films to have promising future applications in the field of stimuli-responsive nanomaterials. [ABSTRACT FROM AUTHOR]

We investigate the electro-optic properties of black phosphorus (BP) thin films for optical modulation in the mid-infrared frequencies. Our calculation indicates that an applied out-of-plane electric field may lead to red-, blue-, or bidirectional shift in BP's absorption edge. This is due to the interplay between the field-induced quantum-confined Franz-Keldysh effect and the Pauli-blocked Burstein-Moss shift. The relative contribution of the two electro-absorption mechanisms depends on doping range, operating wavelength, and BP film thickness. For proof-of concept, simple modulator configuration with BP overlaid over a silicon nanowire is studied. Simulation results show that operating BP in the quantum-confined Franz-Keldysh regime can improve the maximal attainable absorption as well as power efficiency compared to its graphene counterpart. [ABSTRACT FROM AUTHOR]

Cross-linked layer-by-layer (LbL) assemblies with a precisely tuned surface ?-potential were fabricated to control the adsorption of proteins, mammalian cells, and bacteria for different biomedical applications. Two weak polyions including a synthesized polyanion and polyethylenimine were assembled under controlled conditions and cross-linked to prepare three robust LbL films as model surfaces with similar roughness and water affinity but displaying negative, zero, and positive net charges at the physiological pH (7.4). These surfaces were tested for their abilities to adsorb proteins, including bovine serum albumin (BSA) and lysozyme (LYZ). In the adsorption tests, the LbL films bind more proteins with opposite charges but less of those with like charges, indicating that electrostatic interactions play a major role in protein adsorption. However, LYZ showed higher nonspecific adsorption than BSA, because of the specific behavior of LYZ molecules, such as stacked multilayer formation during adsorption. To exclude such stacking effects from experiments, protein molecules were covalently immobilized on AFM colloidal probes to measure the adhesion forces against the model surfaces utilizing direct protein molecule-surface contacts. The results confirmed the dominating role of electrostatic forces in protein adhesion. In fibroblast cell and bacteria adhesion tests, similar trends (high adhesion on positively charged surfaces, but much lower on neutral and negatively charged surfaces) were observed because the fibroblast cell and bacterial surfaces studied possess negative potentials. The cross-linked LbL films with improved stability and engineered surface charge described in this study provide an excellent platform to control the behavior of different charged objects and can be utilized in practical biomedical applications. [ABSTRACT FROM AUTHOR]

Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11-20) and semipolar (11-22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced. The underlying defect reduction mechanisms include epitaxial growth through the MSN covered template, island nucleation via nanogaps in the MSN, and lateral overgrowth and coalescence above the MSN. InGaN/GaN multiple quantum wells structures grown on a nonpolar GaN/MSN template show more than 30-fold increase in the luminescence intensity compared to a control sample without the MSN. This self-assembled MSN technique provides a new platform for epitaxial growth of nitride semiconductors and offers unique opportunities for improving the material quality of GaN grown on other orientations and foreign substrates or heteroepitaxial growth of other lattice-mismatched materials. [ABSTRACT FROM AUTHOR]

Inspired by nature, in particular by the marine mussels adhesive proteins (MAPs) and by the tough brick-and-mortar nacre-like structure, novel multilayered films are prepared in the present work. Organic-inorganic multilayered films, with an architecture similar to nacre based on bioactive glass nanoparticles (BG), chitosan, and hyaluronic acid modified with catechol groups, which are the main components responsible for the outstanding adhesion in MAPs, are developed for the first time. The biomimetic conjugate is prepared by carbodiimide chemistry and analyzed by ultraviolet-visible spectrophotometry. The buildup of the multilayered films is monitored with a quartz crystal microbalance with dissipation monitoring, and their topography is characterized by atomic force microscopy. The mechanical properties reveal that the films containing catechol groups and BG present an enhanced adhesion. Moreover, the bioactivity of the films upon immersion in a simulated body fluid solution is evaluated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. It was found that the constructed films promote the formation of bonelike apatite in vitro. Such multifunctional mussel inspired LbL films, which combine enhanced adhesion and bioactivity, could be potentially used as coatings of a variety of implants for orthopedic applications. [ABSTRACT FROM AUTHOR]

A series of polyanions and polycations have been synthesized from atactic, syndiotactic, and isotactic forms of poly(methyl methacrylate) and used to construct polyelectrolyte multilayers (PEMs). Polymer tacticity has been found to have a large influence on film growth but only a slight effect on H2/N2 permeation selectivities and no significant influence on CO2/N2 permeation selectivities. The permeances of H2, CO2, and N2 across those PEMs exhibiting the highest H2/N2 selectivities were found to vary by as much as factors of 3, 6, and 5, respectively, depending on the tacticities employed. A simple model that accounts for the strong dependency of film growth on tacticity is presented. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries have recently attracted considerable attention as a promising alternative to lithium-ion batteries owing to the natural abundance and low cost of sodium compared with lithium. Among all proposed anode materials for sodium-ion batteries, antimony is a desirable candidate due to its high theoretical capacity (660 mA h g-1). Herein, an antimony/multilayer graphene hybrid, in which antimony is homogeneously anchored on multilayer graphene, is produced by a confined vapor deposition method. The chemical bonding can realize robust and intimate contact between antimony and multilayer graphene, and the uniform distribution of antimony and the highly conductive and flexible multilayer graphene can not only improve sodium ion diffusion and electronic transport but also stabilize the solid electrolyte interphase upon the large volume changes of antimony during cycling. Consequently, the antimony/multilayer graphene hybrid shows a high reversible sodium storage capacity (452 mA h g-1 at a current density of 100 mA g-1), stable long-term cycling performance with 90% capacity retention after 200 cycles, and excellent rate capability (210 mA h g-1 under 5000 mA g-1). This facile synthesis approach and unique nanostructure can potentially be extended to other alloy materials for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

A multilayer three-dimensional (3D) structure made of hydrophobic stainless steel mesh has been designed for in situ continuous oil/water separation. The hydrophobic stainless steel mesh was prepared via a facile and environmental friendly method by etching with FeCl3 solution and coating with n-octadecylthiol. The as-prepared mesh allows oils (gasoline, diesel oil, engine oil) and organic solvents (hexane, liquid paraffin) to pass through and repels water. A separation device equipped with the multilayer 3D structure can continuously separate the aforementioned oils from oil-water mixtures. The separation efficiency of continuous separation is more than 99.0 wt % and shows little decrease after 10 cycles. [ABSTRACT FROM AUTHOR]

Phase separation of all-conjugateddonor–acceptor blockcopolymers is more difficult to achieve compared to classical coil–coilsystems owing the intrinsic similarity of the two blocks having bothrigid conjugated backbones and alkyl side chains and their generallylow degrees of polymerization. Here we demonstrate that side chainfluorination of a poly(carbazole-alt-dithienylbenzothiadiazole)segment (SF-PCDTBT), to be used as electron acceptor block in combinationwith poly(3-hexylthiophene) P3HT as donor block in all-conjugateddonor–acceptor block copolymers of type SF-PCDTBT-b-P3HT, strongly increases dissimilarity between P3HT and SF-PCDTBTleading to phase separation for already moderate molar masses. Keyto the successful synthesis of a new TBT-monomer with semifluorinatedside chains is a direct arylation step that elegantly bypasses classicalcross-coupling reactions in which the semifluorinated side chain causeslow yields. Suzuki polycondensation of the semifluorinated TBT monomerwith a suitable carbazole comonomer and in situ termination by P3HT-Bris optimized extensively with respect to the yield of the end-cappingefficiency and molar mass control of the PCDTBT segment. When thefluorinated side chains are replaced by hydrogen (H-PCDTBT) or by n-hexyl chains (hex-PCDTBT), the tendency for phase separationwith covalently connected P3HT is much reduced as shown by differentialscanning calorimetry and grazing incidence small-angle scatteringmeasurements on thin films. Favorably, of all the block copolymersmade only SF-PCDTBT-b-P3HT is microphase separated,exhibits face-on orientation of P3HT domains, and additionally displayssurface segregation of the SF-PCDTBT segment at the polymer/air interface.All of these properties are beneficial for single layer single componentsolar cells. SF-PCDTBT-b-P3HT exhibits the best solarcells performance with a high open-circuit voltage of 1.1 V and apower conversion efficiency of ∼1% which largely outperformsdevices based on the analogous H-PCDTBT-b-P3HT andhex-PCDTBT-b-P3HT. [ABSTRACT FROM AUTHOR]

The host–guest chemistry ofcucurbit[8]uril (CB[8]) and the layer-by-layer self-assembly techniqueare combined to obtain a molecular imprinted polyelectrolyte multilayerfilm for the recognition and binding of a guest molecule. Cucurbit[8]urilas a ready-made binding site is first associated with a polyelectrolyteand then assembled into a polyelectrolyte multilayer film via layer-by-layerdeposition. A cationic guest is subsequently included into the nanocontainerdue to specific host–guest interactions. The quantitative analysisof both CB[8] and the included guest molecule in dependence of thesurface charge of the multilayer film identifies a high nanocontainerdensity as well as good to excellent binding efficiencies, thereforeyielding a promising imprinted nanomaterial with potential applicationsin filtration or sensor technology. The investigation of the guestmolecule uptake kinetics reveals two processes on different time scales,respectively, which are again related to the charge of the multilayerfilm surface. The combination of the results obtained from both ultravioletspectroscopy and dissipative quartz crystal microbalance enables usto describe a full picture of several simultaneous processes initiatedby the guest molecule. [ABSTRACT FROM AUTHOR]

Multilayersof 1-octyl-3-methylimidazolium tetrafluoroborate [C8C1Im][BF4] have been deposited on aCu(111) surface by evaporation in UHV. XPS shows that [C8C1Im][BF4] adsorbs without decomposition forsubstrate temperatures < 300 K. XPS and UPS data indicate thationic liquid (IL) deposition onto a 120 K Cu(111) surface resultsin the IL forming multilayers by a simultaneous-multilayer growthprocess. IL deposition onto a room temperature Cu(111) surface resultsin a different arrangement where at a coverage of one monolayer theIL forms droplets of about 100 Å height covering only about 1/10thof the surface. Multilayers deposited at 120 K convert to the roomtemperature arrangement upon heating. Further heating above room temperaturecauses the IL multilayer droplets to desorb leaving an IL monolayerof ≈6 Å thickness at ≈430 K. At higher temperatures,this monolayer reacts with the surface and BF3is emitted,leaving products containing C, N, and some F on the surface. We proposea surface reaction where [BF4]−ionsreact to form chemisorbed fluorine (Cu–F) and gaseous BF3, with the remaining [C8C1Im]+decomposing on the Cu(111) in an unidentified manner. [ABSTRACT FROM AUTHOR]

We report a layer-by-layer approachto the fabrication of thinpolymer-based multilayers that release DNA rapidly in physiologicallyrelevant environments. This approach exploits the properties of aweak anionic polyelectrolyte [poly(acrylic acid); PAA] to disruptionic interactions and promote disassembly in coatings that otherwiseerode slowly. We investigated this approach using multilayers fabricatedfrom plasmid DNA and linear poly(ethylenimine) (LPEI), a model syntheticcationic polymer used widely for DNA delivery. LPEI/DNA multilayerserode and release DNA slowly over ∼4 days when incubated inPBS buffer. In contrast, substitution of every other layer of DNAwith PAA lead to thin films that released DNA rapidly, with >60%beingreleased in the first 5 min. These quick-release coatings releasebioactive DNA and can be used to fabricate uniform coatings on a varietyof objects, including the tips of inflatable balloon catheters. Wedemonstrate that these coatings can promote high levels of cell transfectionin vitro and the robust contact transfer and expression of DNA invascular tissue in vivo using a rat model of vascular injury. Thesematerials provide useful alternatives to multilayers and other coatingsthat promote the prolonged release of DNA. More broadly, approachesthat depart from the use of degradable polymers to promote film erosioncreate opportunities to design new gene delivery coatings using abroader range of polymer-based building blocks designed for othergene delivery applications. With further development, this approachcould thus provide a new and useful platform for the rapid contacttransfer of DNA to cells and tissues of interest in a range of fundamentaland applied contexts. [ABSTRACT FROM AUTHOR]

Using the Boltzmann–Peierlsequation for phonon transportapproach with the inputs of interatomic force constants from the self-consistentcharge density functional tight binding method, we calculate the room-temperaturein-plane lattice thermal conductivities kof multilayergraphene (up to four layers) and graphite under different isotropictensile strains. The calculated in-plane kof graphite,finite monolayer graphene and 3-layer graphene agree well with previousexperiments. For unstrained graphene systems, both the intrinsic kand the extent of the diffusive transport regime presenta drastic dimensional transition in going from monolayer to 2-layergraphene and thereafter a gradual transition to the graphite limit.We find a peak enhancement of intrinsic kfor multilayergraphene and graphite with increasing strain with the largest enhancementamplitude ∼40%. Competition between the decreased mode heatcapacities and the increased lifetimes of flexural phonons with increasingstrain contribute to this kbehavior. Similar kbehavior is observed for 2-layer hexagonal boron nitridesystems. This study provides insights into engineering kof multilayer graphene and boron nitride by strain and into thenature of thermal transport in quasi-two-dimensional and highly anisotropicsystems. [ABSTRACT FROM AUTHOR]

The self-assemblyof mixed vesicles of zwitterionic phosphatidylcholine(PC) and anionic phosphatidylserine (PS) phospholipids on top of polyelectrolytemultilayers (PEMs) of poly(allylamine hydrochloride) (PAH), as a polycation,and polystyrenesulfonate (PSS), as a polyanion, is investigated asa function of the vesicle composition by means of the quartz crystalmicrobalance with dissipation (QCM-D), cryo-transmission electronmicroscopy (Cryo-TEM), atomic force microscopy (AFM), and atomic forcespectroscopy (AFS). Vesicles with molar percentages of PS between50% and 70% result in the formation of lipid bilayers on top of thePEMs. Vesicles with over 50% of PC or over 80% of PS do not assemblyinto bilayers. AFS studies performed with a PAH-modified cantileverapproaching and retracting from the lipid assemblies reveal that themain interaction between PAH and the lipids takes place through hydrogenbonding between the amine groups of PAH and the carboxylate and phosphategroups of PS and with the phosphate groups of PC. The interactionof PAH with PS is much stronger than with PC. AFS measurements onassemblies with 50% PC and 50% PS revealed similar adhesion forcesto pure PS assemblies, but the PAH chains can reorganize much betteron the lipids as a consequence of the presence of PC. QCM-D experimentsshow that vesicles with a lipid composition of 50% PC and 50% PS donot form bilayers if PSS is replaced by alginate (Alg) or poly(acrylicacid) (PAA). [ABSTRACT FROM AUTHOR]

We report on the effect of salt ondiffusion of polyelectrolyte(PE) chains within electrostatically assembled polyelectrolyte multilayers.Layer-by-layer (LbL) films were assembled using poly(methacrylic acid)(PMAA) as a polyanion and quaternized poly(2-(dimethylamino)ethylmethacrylate) as a polycation. Fluorescence recovery after photobleachingand neutron reflectometry were used to monitor the center-of-massdiffusion of PMAA chains in directions parallel and perpendicularto the substrate (D∥and D⊥, respectively). Film intermixing andpolymer chain diffusion in the direction perpendicular to the substrateexhibit an unusual dependence on the PMAA molecular weight, with dramaticallystronger diffusional response to salt annealing for the films formedby PMAA with the lowest molecular weight of 7 kDa. Films assembledwith this lowest molecular weight PMAA reveal that both diffusioncoefficients of PMAA chains (D∥and D⊥) depend exponentiallyon the concentration of salt in the annealing solutions, with muchfaster diffusion in the direction parallel to the substrate. [ABSTRACT FROM AUTHOR]

Fibroblasts cultured on polyelectrolytemultilayers, PEMUs, madefrom poly(diallyldimethylammonium), PDADMA, and poly(styrene sulfonate),PSS, showed a variety of attachment modes, depending on the chargeof the last layer and deposition conditions. PEMUs terminated withPDADMA (cationic) were cytotoxic when built in 1.0 M NaCl but cytophilicwhen built in 0.15 M NaCl. Cells adhered poorly to all PSS-capped(anionic) films. PEMUs built in 0.15 M NaCl but terminated with alayer of PSS in 1.0 M NaCl induced most cells to form spherical clustersafter about 48 h of culture. These clusters still interrogated thesurface, and when they were replated on control tissue culture plastic,cells emerged with close to 100% viability. Differences between thevarious surfaces were probed in an effort to identify the mechanismresponsible for this unusual behavior, which did not follow acceptedcorrelations between substrate stiffness and cell adhesion. No significantdifferences in roughness or wetting were observed between cluster-inducingPSS-capped multilayers and those that did not produce clusters. Whenthe surface charge was assayed with radiolabeled ions a strong increasein negative surface charge was revealed. Viewing the multilayer asa zwitterionic solid and comparing its surface charge density to thatof a cell membrane yields similarities that suggest a mechanism forpreventing protein adhesion to the surface, a necessary step in theintegrin-mediated mechanotransduction properties of a cell. [ABSTRACT FROM AUTHOR]

Graphene-like two-dimensional (2D)materials not only are interesting for their exotic electronic structureand fundamental electronic transport or optical properties but alsohold promises for device miniaturization down to atomic thickness.As one material belonging to this category, InSe, a III–VIsemiconductor, not only is a promising candidate for optoelectronicdevices but also has potential for ultrathin field effect transistor(FET) with high mobility transport. In this work, various substratessuch as PMMA, bare silicon oxide, passivated silicon oxide, and siliconnitride were used to fabricate multilayer InSe FET devices. Throughback gating and Hall measurement in four-probe configuration, thedevice’s field effect mobility and intrinsic Hall mobilitywere extracted at various temperatures to study the material’sintrinsic transport behavior and the effect of dielectric substrate.The sample’s field effect and Hall mobilities over the rangeof 20–300 K fall in the range of 0.1–2.0 × 103cm2/(V s), which are comparable or better thanthe state of the art FETs made of widely studied 2D transition metaldichalcogenides. [ABSTRACT FROM AUTHOR]