Function Of Bilayer Thickness Research Articles

A two-step mechanism for the binding of the HIV-1 MPER epitope by the 10E8 antibody onto biosensor-supported lipid bilayers.

HIV-1 antibodies targeting the carboxy-terminal area of the membrane-proximal external region (ctMPER) are close to exerting viral pan-neutralization. Here, we reconstituted the ctMPER epitope as the N-terminal extremity of the Env glycoprotein transmembrane domain helix and immobilized it onto biosensor-supported lipid bilayers. We assessed the binding mechanism of anti-MPER antibody 10E8 through Surface Plasmon Resonance, and found, through equilibrium and kinetic binding analyses as a function of bilayer thickness, peptide length, and paratope mutations, that 10E8 engages first with the epitope peptide (encounter), limited by ctMPER helix accessibility at the membrane surface, and then inserts into the lipid bilayer assisted by favorable Fab-membrane interactions (docking). This mechanistic information may help in devising new strategies to develop more efficient MPER-targeting vaccines.

Evolution of the metallic state in LaNiO3/LaAlO3 superlattices measured by Li8β -detected NMR

Using ion-implanted $^8$Li $\beta$-detected NMR, we study the evolution of the correlated metallic state of LaNiO$_3$ in a series of LaNiO$_3$/LaAlO$_3$ superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of 6.55 T reveal two equal amplitude components: one with metallic ($T$-linear) $1/T_{1}$, and a second with a more complex $T$-dependence. The metallic character of the slow relaxing component is only weakly affected by the LaNiO$_3$ thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing towards low $T$) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed.

Structural and electrical characterization of multilayer Al2O3/ZnO nanolaminates grown by atomic layer deposition

Nanolaminates formed by several bilayers of Al2O3 and ZnO (AZA), grown by atomic layer deposition from Trimethyl aluminum, Diethyl zinc and water as co-reactants, were deposited on n-type (100) silicon substrates. A set of 5 nanolaminates with a total thickness of about 100nm, containing several Al2O3/ZnO bilayers with thicknesses of 0.28, 0.38, 2, 10 and 20nm, were prepared. XRD shows an evolution from amorphous to crystalline structure as a function of bilayer thickness. Capacitance-Voltage (C-V) and Current-Voltage (I-V) electrical characterization was carried out in order to evaluate the potential of the nanolaminates for microelectronic applications. Dielectric constant values between 8.3 and 9.6 were obtained, depending on bilayer thickness. The MOS capacitors exhibited net equivalent oxide thickness values between 44 and 38nm.

Thermal conductivity of amorphous Al2O3/TiO2 nanolaminates deposited by atomic layer deposition

The thermophysical properties of Al2O3/TiO2 nanolaminates deposited by atomic layer deposition (ALD) are studied as a function of bilayer thickness and relative TiO2 content (0%–100%) while the total nominal thickness of the nanolaminates was kept at 100 nm. Cross-plane thermal conductivity of the nanolaminates is measured at room temperature using the nanosecond transient thermoreflectance method. Based on the measurements, the nanolaminates have reduced thermal conductivity as compared to the pure amorphous thin films, suggesting that interfaces have a non-negligible effect on thermal transport in amorphous nanolaminates. For a fixed number of interfaces, we find that approximately equal material content of Al2O3 and TiO2 produces the lowest value of thermal conductivity. The thermal conductivity reduces with increasing interface density up to 0.4 nm−1, above which the thermal conductivity is found to be constant. The value of thermal interface resistance approximated by the use of diffuse mismatch model was found to be 0.45 m2 K GW−1, and a comparative study employing this value supports the interpretation of non-negligible interface resistance affecting the overall thermal conductivity also in the amorphous limit. Finally, no clear trend in thermal conductivity values was found for nanolaminates grown at different deposition temperatures, suggesting that the temperature in the ALD process has a non-trivial while modest effect on the overall thermal conductivity in amorphous nanolaminates.

Refractive index and bandgap variation in Al2O3-ZnO ultrathin multilayers prepared by atomic layer deposition

This research focuses on the study of the refractive index and bandgap behavior in ultrathin multilayer films of Al2O3-ZnO bilayers grown via atomic layer deposition (ALD) technique on Si(100) substrates. The multilayer configuration stack consists in alternate layers of constant thickness Al2O3 (2 nm) and varying thickness ZnO films in order to obtain a total thickness of ∼100 nm. A set of 10 samples based on bilayers with various 2:X thickness ratios were prepared, where X refers to the ZnO layer thickness. X is proportional to the number of cycles (N) of the ZnO precursor, varying from 1 to 100. The sample morphology was studied via Atomic Force Microscopy and the results show that the surface roughness of the multilayers varies from 0.2 to 1.2 nm, as the ZnO layer thickness increases. In all cases, the roughness values remain below 2% of the total thickness of the multilayer. The refractive index n(λ) and optical bandgap, Eg, of each multilayer sample were studied via spectroscopic ellipsometry (SE). A General Oscillator optical model was utilized to fit the experimental data in order to obtain the total thickness, refractive index and absorption coefficient. Cross-sectional mode scanning electron microscope images verified the multilayer total thickness and corroborated the accuracy of the optical model. The refractive index varies significantly from values close to the Al2O3 refractive index when the bilayer thickness is small, up to values corresponding closely to ZnO for thicker bilayers. The refractive index, as a function of bilayer thickness, varies between 1.63 and 2.3, for λ = 370 nm (UV region), showing high sensitivity. In addition, the optical bandgap energy, Eg, determined using the Tauc model, decreases when the bilayer thickness increases, with a maximum variation of ΔEg ∼1.6 eV. These results reveal that the refractive index and optical bandgap of Al2O3-ZnO material can be modulated systematically as a function of the bilayer thickness. Such behavior is of great importance for optoelectronics applications, in particular for the development of devices with response in the UV spectral range.

The Antimicrobial Peptide Gramicidin S Permeabilizes Phospholipid Bilayer Membranes Without Forming Discrete Ion Channels

We examined the permeabilization of lipid bilayers by the β-sheet, cyclic antimicrobial decapeptide gramicidin S (GS) in phospholipid bilayers formed either by mixtures of zwitterionic diphytanoylphosphatidylcholine and anionic diphytanoylphosphatidylglycerol or by single zwitterionic unsaturated phosphatidylcholines having various hydrocarbon chain lengths, with and without cholesterol. In the zwitterionic bilayers formed by the phosphatidylcholines, without or with cholesterol, the peptide concentrations and membrane potentials required to initiate membrane permeabilization vary little as function of bilayer thickness and cholesterol content. In all the systems tested, the GS-induced transient ion conductance events exhibit a broad range of conductances, which are little affected by the bilayer composition or thickness. In the zwitterionic phosphatidylcholine bilayers, the effect of GS does not depend on the polarity of the transmembrane potential; however, in bilayers formed from mixtures of phosphatidylcholines and anionic phospholipids, the polarity of the transmembrane potential becomes important, with the GS-induced conductance events being much more frequent when the GS-containing solution is positive relative to the GS-free solution. Overall, these results suggest that GS does not form discrete, well-defined, channel-like structures in phospholipid bilayers, but rather induces a wide variety of transient, differently sized defects which serve to compromise the bilayer barrier properties for small electrolytes.

Fabrication and electrical characterization of Si-based rolled-up microtubes

Freestanding SiGe:B∕Si:B tubes are fabricated by rolled-up technology. Linear I-V curves are measured both for unreleased and rolled-up films. The bilayer resistance increases after release from the substrate. The electrical resistance of tubes with diameters varying in the range of 0.8−2.2μm, scales from 110to9kΩ as a function of bilayer thickness. Rapid thermal annealing is used to investigate the effect of B activation and Si–Ge interdiffusion on structural and electrical properties of unreleased and rolled-up films.

The antimicrobial peptide gramicidin S permeabilizes phospholipid bilayer membranes without forming discrete ion channels

We examined the permeabilization of lipid bilayers by the β-sheet, cyclic antimicrobial decapeptide gramicidin S (GS) in phospholipid bilayers formed either by mixtures of zwitterionic diphytanoylphosphatidylcholine and anionic diphytanoylphosphatidylglycerol or by single zwitterionic unsaturated phosphatidylcholines having various hydrocarbon chain lengths, with and without cholesterol. In the zwitterionic bilayers formed by the phosphatidylcholines, without or with cholesterol, the peptide concentrations and membrane potentials required to initiate membrane permeabilization vary little as function of bilayer thickness and cholesterol content. In all the systems tested, the GS-induced transient ion conductance events exhibit a broad range of conductances, which are little affected by the bilayer composition or thickness. In the zwitterionic phosphatidylcholine bilayers, the effect of GS does not depend on the polarity of the transmembrane potential; however, in bilayers formed from mixtures of phosphatidylcholines and anionic phospholipids, the polarity of the transmembrane potential becomes important, with the GS-induced conductance events being much more frequent when the GS-containing solution is positive relative to the GS-free solution. Overall, these results suggest that GS does not form discrete, well-defined, channel-like structures in phospholipid bilayers, but rather induces a wide variety of transient, differently sized defects which serve to compromise the bilayer barrier properties for small electrolytes.

Characterization of Hall-Petch relation on microstructural parameter of softer sublayer and the hardness in nanomultilayers

Scale dependent microstructures and plastic deformation in Ni/Al nanomultilayers with different modulated ratio has been investigated as a function of bilayer thickness by X-ray diffraction and nanoindentation. Experimental results show that the hardness and the related microstructural parameter in the softer sublayer exhibited the similar variation tendency, which indicated the sensitivity of plastic behaviors on the microstructural constraints in softer sublayer. Further investigation showed that in the nanometer regime, by adopting a new parameter r in softer sublayer (r=Lsub/d, where Lsub is the sublayer thickness and d is the grain size), the competing grain-boundary and interface-boundary strengthening mechanisms could be unified. Moreover, within the overall scale, the deformation of nanomultilayers could follow the Hall-Petch relation with decreasing characteristic length scales.

Thermodynamics of mechanosensitivity

Mechanosensitivity of ion channels is conventionally interpreted as being driven by a change of their in-plane cross-sectional area Amsc. This, however, does not include any factors relating to membrane stiffness, thickness, spontaneous curvature or changes in channel shape, length or stiffness. Because the open probability of a channel is sensitive to all these factors, we constructed a general thermodynamic formalism. These equations provide the basis for the analysis of the behaviour of mechanosensitive channels in lipids of different geometric and chemical properties such as the hydrophobic mismatch at the boundary between the protein and lipid or the effects of changes in the bilayer intrinsic curvature caused by the adsorption of amphipaths. This model predicts that the midpoint γ1/2 and the slope1/2 of the gating curve are generally not independent. Using this relationship, we have predicted the line tension at the channel/lipid border of MscL as ∼10 pN, and found it to be much less than the line tension of aqueous pores in pure lipid membranes. The MscL channel appears quite well matched to its lipid environment. Using gramicidin as a model system, we have explained its observed conversion from stretch-activated to stretch-inactivated gating as a function of bilayer thickness and composition.

A Comparison of Pseudomorphic Bcc Phase Stability in Zr/Nb and Ti/Nb Thin Film Multilayers

A series of Nb-rich Zr/Nb and Ti/Nb multilayers were sputter deposited. Upon a reduction in thickness, a pseudomorphic bcc phase was stabilized in the Zr and Ti layers. X-ray and electron diffraction techniques were used to confirm these phase transformations. The change in phase stability was modeled by the competition between volumetric and interfacial components of the total free energy of a unit bilayer representing the multilayer. An outcome of this model is the ability to plot phase stability diagrams for multilayers, referred to as biphase diagrams, as a function of bilayer thickness and volume fraction. A comparison of the phase stability boundary between hcp/bcc and bcc/bcc for these two systems has shown that the bcc Ti’s pseudomorphic phase stabilization is maintained for a much larger layer thickness as compared to Zr. Atom probe compositional profiles of the Ti/Nb multilayers have indicated that the Nb layers interdiffused into the Ti layers thus helping to facilitate the bcc Ti phase stability in the Ti/Nb multilayers.

A Comparison of Pseudomorphic Bcc Phase Stability in Zr/Nb and Ti/Nb Thin Film Multilayers

A series of Nb-rich Zr/Nb and Ti/Nb multilayers were sputter deposited. Upon a reduction in thickness, a pseudomorphic bcc phase was stabilized in the Zr and Ti layers. X-ray and electron diffraction techniques were used to confirm these phase transformations. The change in phase stability was modeled by the competition between volumetric and interfacial components of the total free energy of a unit bilayer representing the multilayer. An outcome of this model is the ability to plot phase stability diagrams for multilayers, referred to as biphase diagrams, as a function of bilayer thickness and volume fraction. A comparison of the phase stability boundary between hcp/bcc and bcc/bcc for these two systems has shown that the bcc Ti’s pseudomorphic phase stabilization is maintained for a much larger layer thickness as compared to Zr. Atom probe compositional profiles of the Ti/Nb multilayers have indicated that the Nb layers interdiffused into the Ti layers thus helping to facilitate the bcc Ti phase stability in the Ti/Nb multilayers.

Bi induced layer-by-layer growth in the homoepitaxial growth of Fe on Fe (1 0 0)-c(2×2)O reconstruction surface

We have investigated the effect of Bi on the homoepitaxial growth of Fe(100) by means of reflection high-energy electron diffraction (RHEED). It was clearly found that Bi induces layer-by-layer growth of Fe on Fe(100)-c(2×2)O reconstruction surface. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there exist optimum amount of Bi surfactant layer that induces smoother layer-by-layer growth. The surface segregation effect of Bi was studied by Auger electron spectroscopy. A strong surface segregation of Bi was found at the top of surface and Bi atoms acted as a surfactant by promoting the interlayer transport.

Proton Transfer in Gramicidin Channels is Modulated by the Thickness of Monoglyceride Bilayers

The thickness of monoglyceride planar bilayers has significant effects on the transfer of protons in both native gramicidin A (gA) and in covalently linked SS- and RR-dioxolane-linked gA proteins. Planar bilayers with various thicknesses were formed from an appropriate combination of monoglyceride with various fatty acid lengths and solvent. Bilayer thicknesses ranged from 25 Å (monoolein in squalene) to 54 Å (monoeicosenoin in decane). Single-channel conductances to protons ( g H) were measured in the concentration range of 10–5000 mM HCl. In native gA as well as in RR channels, the shape of the log( g H)-log([H +]) relationships was nonlinear and remained basically unaltered in monoglyceride bilayers with various thicknesses. For both native gA and RR channels, g H values were systematically and significantly larger in thin than in thick bilayers. By contrast, the shape of the log( g H)-log([H +]) relationships in the SS channel was linear (with a slope considerably smaller than 1) in thick (>37 Å) bilayers. However, in thin (<37 Å) bilayers these plots became nonlinear and g H values approached those obtained in native gA channels. The linearization of the log-log plots in the SS channel in thick bilayers is a consequence of a dramatic increase (instead of a decrease as in native gA and RR channels) of g H in these bilayers in [H +] <1 M. The gating characteristics of the various gA channels as a function of bilayer thickness followed the same pattern as described previously. It was noticed, however, that in the thickest monoglyceride bilayer used in this study, both the SS- and RR-dioxolane-linked channels opened in a mode of bursting activity instead of remaining in the open state as in thin bilayers. It is proposed that the thickness of monoglyceride bilayers modulates proton transfer in native gA channels by a combination of factors including the access resistances of channels to H +, and fluctuations in both the structure of the lipid bilayer and in the distance between gA monomers. The differential effects of relatively thick monoglyceride bilayers on proton transfer in both dioxolane-linked gA channels must relate to distinct interactions between the bilayers and the SS and RR dioxolanes.

Bismuth-Induced Layer-by-Layer Growth in the Homoepitaxial Growth of Fe(100)

ABSTRACTWe have investigated the effect of Bi on the homoepitaxial growth of Fe(100) by means of reflection high-energy electron diffraction (RHEED). It was clearly found that Bi induces layer-by-layer growth of Fe on Fe(100)-c(2×2)O reconstruction surface. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is optimum amount of Bi surfactant layer that induces the smoother layer-by-layer growth. A strong surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport.

Surfactant Mediated Epitaxial Growth of Co on Au(111) Surface

ABSTRACTWe have chosen Bi as the surfactant atom in the heteroepitaxial growth of Co on Au(111). It was found that Bi induces layer-by-layer (LBL) growth at room temperature. With pre-deposition of 0.2 ∼ 0.8Å Bi on Au(111) prior to the evaporation of Co, more long-lasting RHEED intensity oscillations were observed and this implies that it induces the LBL growth of Co film. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is a suitable amount of Bi surfactant layer that induces the smoother LBL growth. A surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport.

Magnetic properties of ordered CoPt/SiO 2 multilayer films

The magnetic properties of L1 0 multilayer Co 47Pt 53/SiO 2 films have been studied as a function of bilayer thickness and SiO 2 fraction. Under identical annealing conditions, coercivities were found to decrease significantly with decreasing bilayer thickness and decreased with increasing SiO 2 fraction. Measurements on single-layer CoPt films with and without SiO 2 bottom and top layers suggest that the SiO 2 inhibits ordering.

Effect of intermixing on self-propagating exothermic reactions in Al/Ni nanolaminate foils

Exothermic reactions can self-propagate rapidly in multilayered foils, and the properties of these reactions depend strongly on the heat of reaction, the average atomic diffusion distance, and the degree of intermixing at the layer interfaces prior to ignition. By performing low-temperature anneals on sputter-deposited Al/Ni nanolaminate foils, the thickness of the intermixed region between layers was increased and its effects on the heats and velocities of reactions were measured. The intermixed region consisted of the metastable Al9Ni2 phase while the final phase of the foil was Al3Ni2. Analytical and empirical models were used to predict reaction velocities as a function of bilayer thickness and intermixing thickness, and the predictions are in good agreement with the experimental results. Increasing the average thickness of the intermixed region from 2.4 to 18.3 nm reduced the reaction velocity for all of the foils but was most significant for the foils with bilayer thicknesses less than 25 nm. The results indicate that the reaction velocity can be separated into two distinct regimes. The first regime occurs for thicker bilayers in which the average atomic diffusion distance is large. In this regime, reaction temperatures are high and reducing the bilayer thickness increases the reaction velocity. The second regime occurs for thinner bilayers where reaction velocity is dominated by the reduction in available energy due to intermixing. In this regime, reducing bilayer thickness results in a decrease in reaction velocity.

Microcrack toughening in two-phase multilayered media

This work presents a numerical model of the toughening behavior exhibited when a Mode I macrocrack propagates through alternating tough and brittle layers of a composite. The toughening occurs due to microcracking in brittle layers. Microcracks form at periodic flaw sites in brittle layers when the stress at a site is sufficient to propagate a crack within the layer. An established microcrack is modeled by a dislocation dipole, with Burgers vector chosen to render the normal component of stress equal to zero at the dipole midpoint. R-curves for layered media are predicted as a function of bi-layer thickness, volume fraction, density of flaw sites, and inhomogeneity in fracture toughness and elastic modulus. A critical combination of properties for the onset of R-curve behavior is identified, and features which optimize the upper plateau of the R-curve are discussed in light of experimental observations.

Permeation of Halide Anions through Phospholipid Bilayers Occurs by the Solubility-Diffusion Mechanism

Two alternative mechanisms are frequently used to describe ionic permeation of lipid bilayers. In the first, ions partition into the hydrophobic phase and then diffuse across (the solubility-diffusion mechanism). The second mechanism assumes that ions traverse the bilayer through transient hydrophilic defects caused by thermal fluctuations (the pore mechanism). The theoretical predictions made by both models were tested for halide anions by measuring the permeability coefficients for chloride, bromide, and iodide as a function of bilayer thickness, ionic radius, and sign of charge. To vary the bilayer thickness systematically, liposomes were prepared from monounsaturated phosphatidylcholines (PC) with chain lengths between 16 and 24 carbon atoms. The fluorescent dye MQAE ( N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide) served as an indicator for halide concentration inside the liposomes and was used to follow the kinetics of halide flux across the bilayer membranes. The observed permeability coefficients ranged from 10 −9 to 10 −7 cm/s and increased as the bilayer thickness was reduced. Bromide was found to permeate approximately six times faster than chloride through bilayers of identical thickness, and iodide permeated three to four times faster than bromide. The dependence of the halide permeability coefficients on bilayer thickness and on ionic size were consistent with permeation of hydrated ions by a solubility-diffusion mechanism rather than through transient pores. Halide permeation therefore differs from that of a monovalent cation such as potassium, which has been accounted for by a combination of the two mechanisms depending on bilayer thickness.