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Plasmonics based sensing, using the surface plasmon resonance of metal nanoparticles, has been effectively demonstrated in various applications. Extending this methodology to cell and artificial lipid bilayer membranes is extremely beneficial in enhancing the sensitivity of the detection of binding and cellular transport of molecules across such membranes. Here, the creation of an artificial plasmonic biomembrane template is demonstrated and used to show the enhanced detection sensitivity of certain widely used biomarker molecules. The efficacy of these templates is explained in terms of the ability of the hydrophobic polymer grafted gold nanoparticles used to organize, penetrate, and fluidize the membranes. The enhancement of photoluminescence of the dye molecules used occurs over a reasonably large spectral range as compared to the plasmon resonance of gold nanoparticles. The results could, possibly, be extended to cellular membranes with relevant modifications, as well as to the detection of any other biological molecule appropriately labeled with fluorescent dye molecules, and demonstrate the versatility of these plasmonic bioinspired platforms as potential biochemical sensors.

Nanotechnology 27(42), 425702(2016). doi:10.1088/0957-4484/27/42/425702, We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the[001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots., Published by IOP Publ., Bristol

We report on X-ray reflectivity experiments of thin liquid heptane films. The films were examined using X-ray reflectivity and modelled both as a layered system using the Parratt algorithm and using a ´phase guessing´ inversion method. Our results combined with simulations of films of shrinking thickness show that small temperature instabilities during the investigation can cause artifacts in the electron density profile. These can easily be mistaken for density os cillations near the interface as might be expected for liquid molecules near a hard wall.

We present a real-time X-ray scattering study of the growth modes in organic molecular-beam epitaxy. We have studied the model system 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) on Ag(111) and find a temperature-dependent transition from layer-by-layer growth to islanding. The transition smears out for low substrate temperatures, T, implying that the degree of the layer-by-layer growth of the wetting layer decreases with decreasing T. This behavior has been analyzed quantitatively and reproduced by kinetic Monte Carlo simulations. The implications and consequences of our findings for the understanding of the organic molecular-beam epitaxy are discussed.

Liquid octamethylcyclotetrasiloxane (OMCTS) films have been prepared between two flat silicon substrates with varying nanometer-sized gaps which correspond to two to three molecular diameters of OMCTS. These extremely confined liquid films have been investigated using X-ray scattering methods as a function of applied pressure, in particular by observing the specular reflectivity and the diffuse scattering. For the first time, scattering methods show that the gap size cannot be changed continuously with changing pressure. Instead, the gap is quantized due to ordering effects of the OMCTS molecules. The use of scattering methods has enormous future implications as they allow very detailed investigations of confined liquids at a molecular level.

We have employed a new experimental configuration to measure ferromagnetic X-ray resonance exchange scattering (XRES) from a EuS single crystal. Using polarisation analysis we could achieve a magnetic-scattering intensity stronger than charge scattering resulting in an asymmetry ratio as large as Ra = 0.67 at the EuLII edge. By a combined refinement of the dependencies of the scattered intensity on the energy and the applied magnetic field we could uniquely determine spectroscopic information such as the 5d conduction band exchange splitting = 0.27(1) eV.

Dendrimers are highly branched polymeric nanoparticles whose structure and topology, largely, have determined their efficacy in a wide range of studies performed so far. An area of immense interest is their potential as drug and gene delivery vectors. Realizing this potential, depending on the nature of cell surface-dendrimer interactions, here we report controlled model membrane penetration and reorganization, using a model supported lipid bilayer and poly(ether imine) (PETIM) dendrimers of two generations. By systematically varying the areal density of the lipid bilayers, we provide a microscopic insight, through a combination of high resolution scattering, atomic force microscopy and atomistic molecular dynamics simulations, into the mechanism of PETIM dendrimer membrane penetration, pore formation and membrane re-organization induced by such interactions. Our work represents the first systematic observation of a regular barrel-like membrane spanning pore formation by dendrimers, tunable through lipid bilayer packing, without membrane disruption.

We have performed X-ray specular and off-specular measurements of free-standing polystyrene thin films as a function of molecular weight and thickness. The results show films thicker than a few radii of gyration (R-g) are well fit by a simple liquid model. This confirms the assumption that the anomalies previously reported in the scattering intensity from polymer films of comparable thickness were mostly due to confinement by long-ranged interactions with the substrate rather than a fundamental property of viscoelastic fluids. The simple liquid model was found to be insufficient to fit the transverse diffuse data for films thinner than a few R-g. Longitudinal diffuse scattering data demonstrated that the roughness at the two interfaces is highly correlated when the film thicknesses are approximately 2R(g). Hence, very thin films do not exhibit liquidlike behavior, and higher-order elastic terms may have to be included into models to describe their rheological behavior.

Recent x-ray and neutron scattering studies have revealed static diffuse scattering due to polarons in the paramagnetic phase of the colossal magnetoresistive manganites La2-2xSr1+2xMn2O7, with x = 0.40 and 0.44. We show that the polarons exhibit short-range incommensurate correlations that grow with decreasing temperature, but disappear abruptly at the combined ferromagnetic and metal-insulator transition in the x = 0.40 system because of the sudden charge delocalization, while persisting at low temperature in the antiferromagnetic x = 0.44 system. The "melting" of the polaron ordering as we cool through T-C occurs with the collapse of the polaron scattering itself in the x = 0.40 system. This short-range polaron order is characterized by an ordering wave vector q = (0.3,0,1) that is almost independent of x for x greater than or equal to 0.38, and is consistent with a model of disordered stripes. (C) 2001 American Institute of Physics.

We report on the first results of a structural and magnetic investigation of Fe 1-x Co x /Mn/Fe 1-x Co x trilayers (x = 0-0.75). In situ low energy electron diffraction shows that Mn grows epitaxially on bcc Fe 1-x Co x (x ≤ 0.75) with a good crystallinity up to 30 A. Reflectivity and small angle diffuse scattering of synchrotron radiation reveal sharp interfaces, each of them having two lateral characteristic lengths in the height-height correlation function that differ by one order of magnitude. The long-range height-height correlation function is vertically correlated and the short-range one is not. From magneto-optical Kerr effect measurements, evidence for non-collinear coupling between Fe 1-x Co x layers (x = 0 and 0.5) was found for Mn spacer thicknesses below 12 A. Polarized neutron reflectometry performed at 300 K reveal a net magnetization of 0.8 ± 0.3 μ B /at in the Mn layer in Fe 0.5 Co 0.5 /Mn/Fe 0.5 Co 0.5 and no net magnetization in the Mn layer in Fe/Mn/Fe.

We review our recent x-ray and neutron scattering studies that reveal static diffuse scattering due to polarons in the paramagnetic phase of the colossal magnetoresistive manganites La 2-2x Sr 1+2x Mn 2 O 7, with x=0.40 and 0.44. We show that the polarons exhibit short-range incommensurate correlations that grow with decreasing temperature, but disappear abruptly at the combined ferromagnetic and metal-insulator transition in the x=0.40 system because of the sudden charge delocalization, while persisting at low temperature in the antiferromagnetic x=0.44 system. The "melting" of the polaron ordering as we cool through TC occurs with the collapse of the polaron scattering itself in the x=0.40 system. The polaron order is characterized by an ordering wave vector q=(0.3,0,1) that is almost independent of x for x≥0.40, and is consistent with a model of disordered stripes.

The effect of confinement on the surface structure of thin polymer films is investigated by specular and diffuse X-ray scattering. It will be shown to what extent information of the film surfaces and the substrate/film interactions can be obtained. In the case of polymer and liquid films predictions for correlation functions exist which may be quantitatively compared with scattering data.

X-ray and neutron scattering measurements directly demonstrate the existence of polarons in the paramagnetic phase of optimally doped colossal magnetoresistive oxides. The polarons exhibit short-range correlations that grow with decreasing temperature, but disappear abruptly at the ferromagnetic transition because of the sudden charge delocalization. The ``melting'' of the charge ordering as we cool through ${T}_{C}$ occurs with the collapse of the quasistatic polaron scattering, and provides important new insights into the relation of polarons to colossal magnetoresistance.

Physical review letters 81(13), 2731 - 2734 (1998). doi:10.1103/PhysRevLett.81.2731, Surfaces of thin dewetted polyethylene-propylene films were investigated by atomic force microscopy (AFM) and x-ray scattering. The AFM images show the mesoscopic island structure but do not give information about the microscopic roughness of the polymer surface. Together with the AFM data we were able to identify capillary waves on the island surfaces by their specific power laws in the diffuse x-ray scattering signal. The wave number spectrum of these waves is modified by a cutoff introduced by the van der Waals substrate-film interactions., Published by APS, College Park, Md.

Amorphous silicon films with thicknesses ranging from about 20 \AA{} to 2000 \AA{} were evaporated onto silicon substrates. The surface and interfaces were then investigated by specular and diffuse x-ray scattering experiments in the region of total external reflection. A model of self-affine interfaces was used for the refinement. The rms roughness \ensuremath{\sigma} and the in-plane correlation length \ensuremath{\xi} vs film thickness follow power laws with exponents of $\ensuremath{\beta}=0.1\ifmmode\pm\else\textpm\fi{}0.05$ and $1/z=0.6\ifmmode\pm\else\textpm\fi{}0.2,$ and the average Hurst parameter is $h=0.23\ifmmode\pm\else\textpm\fi{}0.05.$ The resulting parameters are compatible with growth models based on the Kardar-Parisi-Zhang equation.

X-ray reflectivity is now a common tool for investigating density profiles of thin films and multilayers in a nondestructive manner. In contrast to the specularly reflected beam the nonspecular diffuse intensity is sensitive to the lateral structure of rough interfaces. The most reliable results are obtained from simultaneous fits of all available data (i.e. reflectivity together with all diffuse scans) with a single set of parameters. It turns out that diffuse scattering experiments from a large class of systems can be described by correlation functions of self-affine fractal surfaces. Two layer systems serve as test cases: (1) A CoSi2/Si-layer system grown by molecular beam epitaxy (MBE) and (2) Langmuir—Blodgett films. The analysis within the distorted-wave Born approximation (DWBA) of the scattering from the silicide sample gives a large amount of information, e.g. strong vertical correlations. For the topmost surface a comparison between scanning tunneling microscopy (STM) and X-ray results leads to very good agreement. Nine and eleven monolayer Langmuir—Blodgett films with high defect concentrations also can be successfully analyzed with the fractal model. The lateral lengths obtained from the diffuse scattering and grazing-incidence diffraction (GID) agree.

Four samples with different numbers of Si/Ge-bilayers were grown at the same time by high vacuum vapor deposition onto Si(111)-substrates at room temperature. Diffuse scattering experiments within the region of total external reflection were carried out to investigate the mesoscopic roughness of the interfaces. The data are explained quantitatively using the distorted wave Born approximation (DWBA) for correlated layer systems with self-affine interfaces. Because all samples were grown under identical conditions the interface parameters of the simpler systems were used for the more complex samples in order to reduce the number of free parameters in the refinement. The resulting trends for the roughness amplitude and the in-plane correlation lengths are compared to predictions from different growth models.

Physical review / B 65(18), 184207 (2002). doi:10.1103/PhysRevB.65.184207, Published by Inst., Woodbury, NY

X-ray specular and off-specular reflectivity studies have been carried out to study the density modulations in liquids confined between two smooth silicon mirrors. The special technique as well as the advantages of using high energy and high brilliance synchrotron x-ray beams for carrying out such experiments will be discussed. Results will be presented on the ordering of octamethyl-cyclotetrasiloxane (OMCTS) as a function of the confining pressure, where we find evidence of layering as the gap is decreased from macroscopic down to a few nanometers.

Physical review letters 83(3), 564 - 567 (1999). doi:10.1103/PhysRevLett.83.564, The surfaces of thermally annealed thin polystyrene films on silicon were investigated by specular and diffuse x-ray scattering. The data cannot be interpreted satisfactorily with capillary wave calculations assuming attractive van der Waals substrate film interactions. The analysis shows that polystyrene films coated on silicon substrates are in a strongly confined state even for film thicknesses much larger than the radius of gyration, possibly due to strong confinement that arises from the interaction at the polymer/substrate interface and the viscoelastic behavior of the thin films., Published by APS, College Park, Md.

We combine the extended finite element method with simulations of diffracted x-ray intensities to investigate the diffusely scattered intensity due to dislocations. As a model system a thin PbSe epitaxial layer grown on top of a PbTe buffer on a CdTe substrate was chosen. The PbSe film shows a periodic dislocation network where the dislocations run along the orthogonal ⟨110⟩ directions. The array of dislocations within this layer can be described by a short range order model with a narrow distribution.

Langmuir monolayers of two artificial cyclic peptides with an alternating sequence of L-glutamic acid and 3-aminobenzoic acid subunits, a cyclohexapeptide (C6G) and a cyclooctapeptide (C8G), were investigated using a variety of techniques, including π–A isotherms, in situ surface sum-frequency generation (SFG) and Brewster angle microscopy. The monolayers were also transferred onto a solid substrate by the Langmuir–Blodgett technique and characterized by grazing incident X-ray diffraction (GIXD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The investigations indicated that C6G forms 2D crystallite structures at the air–water interface, whereas no such structures were observed for C8G. Being amphiphilic, both peptides attain a horizontal orientation on the water surface after spreading. Surface compression causes the molecules to flip to a perpendicular state, thus minimizing the molecular area. The measurements also indicate that, in the perpendicular state, self-assembly of C6G leads to a tubular arrangement of the peptide rings. According to GIXD and TEM data, pairs of tubes arrange in a well defined and oriented order producing 2D crystals. Surface vibrational spectroscopic methods (sum-frequency generation and polarization modulation IR reflection–absorption) combined with molecular modeling gave insight into the arrangement of individual C6G molecules in the tubes. Overall, our results indicated that the tubular assembly of C6G is most likely due to intermolecular H-bonding between the CO group in the glutamic acid side chains and peptide NH group of a neighboring peptide ring.

We show that the x-ray surface scattering from a freestanding polymer film exhibits features that cannot be explained by the usual stochastic formalism for surfaces with random height fluctuations. Instead, a geometric description of the film morphology assuming two curved surfaces characterized by a radius of curvature and a lateral cutoff length successfully accounts for the phase difference between the Kiessig fringes of the nominal "specular" and "off-specular" components of the scattering. The formalism allows one to distinguish unambiguously between conformal and anticonformal curvature morphologies at long length scales.

The striking anisotropy observed in Huang scattering distributions near the intense Bragg reflections of ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ is shown to be the result of orbitally polarized polarons in the paramagnetic insulating state above ${T}_{C}.$ X-ray single-crystal diffuse scattering patterns from this bilayered colossal magnetoresistive manganite are calculated in terms of the polaronic local structure and compared with experimental measurements. At 300 K, the polaronic ${e}_{g}$ electrons occupy ``out-of-plane'' (i.e., ${3z}^{2}\ensuremath{-}{r}^{2})$ orbitals, leading to ${\mathrm{MnO}}_{6}$ octahedra that are Jahn-Teller elongated along the c axis, perpendicular to the perovskite layers. Between 300 K and ${T}_{C},$ however, the ``orbital polarization'' is shown to shift into the $\mathit{a}\ensuremath{-}\mathit{b}$ plane (i.e., ${3x}^{2}\ensuremath{-}{r}^{2}$ and ${3y}^{2}\ensuremath{-}{r}^{2}$ orbitals), allowing the formation of nanoscale polaron correlations above ${T}_{C}.$