Search

Precise measurement of the potential of mean force is necessary for a fundamental understanding of the dynamics and chemical reactivity of a biological macromolecule. The unique advantage provided by the recently developed constant-information approach to analyzing time-dependent single-molecule fluorescence measurements was used with maximum entropy deconvolution to create a procedure for the accurate determination of molecular conformational distributions, and analytical expressions for the errors in these distributions were derived. This new method was applied to a derivatized poly(L-proline) series, P(n)CG3K(biotin) (n = 8, 12, 15, 18, and 24), using a modular, server-based single-molecule spectrometer that is capable of registering photon arrival times with a continuous-wave excitation source. To account for potential influence from the microscopic environment, factors that were calibrated and corrected molecule by molecule include background, cross-talk, and detection efficiency. For each single poly(L-proline) molecule, sharply peaked Förster type resonance energy transfer (FRET) efficiency and distance distributions were recovered, indicating a static end-to-end distance on the time scale of measurement. The experimental distances were compared with models of varying rigidity. The results suggest that the 23 angstroms persistence length wormlike chain model derived from experiments with high molecular weight poly(L-proline) is applicable to short chains as well.

Ferroelectric/dielectric materials are useful for a variety of different applications. Addition of small amounts of different dopants often dramatically improves the materials performance. The conventional approach to exploring new materials is to make and characterize samples of discrete composition one at a time. In an effort to accelerate this process, we fabricate a combinatorial materials chips containing 256 differently doped (Ba, Sr)TiO3 thin films. From this study, we found that tungsten doping in this class of materials greatly reduces the dielectric loss and does not significantly affect the tunability of these materials. As the result, the overall figures of merit of the materials are greatly improved.

Lead perovskite compounds possess very rich and complex phase diagrams. They also have great potential in a variety of commercial applications. However, due in part to the very complicated nature of these materials, very few systematic studies of their ternary phase diagrams with respect to electrical properties have been performed. In this letter, we report the microwave dielectric property mapping of a ternary Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 composition spread using a scanning evanescent microwave probe. We identified composition regions with dielectric constants higher than 600 at 1 GHz.

Dielectric Ba0.6Sr0.4TiO3 thin films were epitaxially grown on (001) MgO by using pulsed laser ablation. Microstructure studies from x-ray diffraction and electron microscopy suggest that the as-grown films are c-axis oriented with an interface relationship of 〈100〉BSTO//〈100〉MgO. A room temperature coupled microwave phase shifter has been developed with a phase shift near 250° at 23.675 GHz under an electrical field of 40 V/μm and a figure of merit of ∼53°/dB. The performance of the microwave phase shifter based on the epitaxial Ba0.6Sr0.4TiO3 thin films on (001) MgO is close to that needed for practical applications in wireless communications.

The combinatorial material chip strategy is used to study the ferroelectric-paraelectric phase boundary of the Ba1−xSrxTiO3 thin film system. The electro-optic (EO) effect at different compositions is measured using a modified direct-current/alternating-current birefringence EO measurement technique. We find that Ba1−xSrxTiO3 thin films exhibit relaxor like behavior with diffused ferroelectric domains existing well past the previously defined ferroelectric-paraelectric boundary (x>0.3).

While electron microscopes and AFMs are capable of high resolution imaging to molecular leve ls, there is an ongoing problem in integrating these results into the larger scale structure and functions of tissue and organs within a complex organism. Imaging biological samples with optical microscopy is predominantly done with histology and immunohistochemistry, which can take up to a several weeks to prepare, are artifact prone and only available as individual 2D images. At the nano resolution scale, the higher resolution electron microscopy and AFM are used, but again these require destructive sample preparation and data are in 2D. To bridge this gap, we describe a rapid non invasive hierarchical bioima ging technique using a novel lab based x-ray computed tomography to characterize complex biological organism in mult iscale- from whole organ (mesoscale) to calcified and soft tissue (microscale), to subcellular structures, nanomaterials and cellular-scaffold interaction (nanoscale). While MicroCT (micro x-ray computed tomography) is gaining in popularity for non invasive bones and tissue imaging, contrast and resolution are still vastly inadequate compared to histology. In this study we will present multiscale results from a novel microCT and nanoCT (nano x-ray tomography system). The novel MicroCT can image large specimen and tissue sample at histology resolution of submicron voxel resolution, ofte n without contrast agents, while the nanoCT using x-ray optics similar to those used in synchrotron radiation facilities, has 20nm voxel resolution, suitable for studying cellular, subcellular morphology and nanomaterials. Multiscale examples involving bo th calcified and soft tissue will be illustrated, which include imaging a rat tibia to the indi vidual channels of osteocyte canaliculli and lacunae and an unstain ed whole murine lung to its alveoli. Th e role of the novel CT will also be discussed as a possib le means for rapid virtu al histology using a biopsy of a human regenerated bone sample done without contrast agents and that of other soft tissues with contrast agents. Comparison between histolog y, SEM and MRI will be given. Keywords: Multiscale bioimaging, hierarchical framework bioimaging , microCT, nanoCT, nanotomography, 50 nm resolution, virtual histology, osteo cyte lacunar-canaliculi network, cancellous bones, cartilage, alveoli, tissue regeneration, PLGA resorbable bioscaffold, contrast agents

X-ray computed tomography (XCT) is a powerful nondestructive 3D imaging technique, which enables the visualization of the three dimensional structure of complex, optically opaque samples. High resolution XCT using Fresnel zone plate lenses has been confined in the past to synchrotron radiation centers due to the need for a bright and intense source of x-rays. This confinement severely limits the availability and accessibility of x-ray microscopes and the wide proliferation of this methodology. We are describing a sub-50nm resolution XCT system operating at 8 keV in absorption and Zernike phase contrast mode based on a commercially available laboratory x-ray source. The system utilizes high-efficiency Fresnel zone plates with an outermost zone width of 35 nm and 700 nm structure height resulting in a current spatial resolution better than 50 nm. In addition to the technical description of the system and specifications, we present application examples in the semiconductor field.

The recent development of methods for generating libraries of solid-state compounds has made it possible to apply combinatorial approaches to the discovery of materials. A library of 128 members containing different compositions and stoichiometries of Ln x M y CoO δ , where Ln = Y or La and M = Pb, Ca, Sr, or Ba, was synthesized by a combination of thin-film deposition and physical masking techniques. Large magnetoresistance has been found in La x (Ba,Sr,Ca) y -CoO δ samples, whereas Y-based samples exhibit much smaller magnetoresistive effects. The magnetoresistance of the Co-containing compounds increases as the size of the alkaline earth ion increases, in sharp contrast to Mn-containing compounds, in which the magnetoresistance effect increases as the size of the alkaline earth ion decreases.

A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO(3), Bi(2)O(3), CaO, CuO, PbO, SrCO(3), and Y(2)O(3) were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.

Optical and microwave impedance and magnetic mapping of continuous phase diagram of thin film ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ was achieved on a single chip. The optical and microwave impedance images obtained by charge-coupled device camera and scanned evanescent microwave probe showed abrupt variations in visible wavelength reflectance and microwave impedance as functions of composition at room temperature. The low-temperature magnetic order probed by scanning superconducting quantum interference device microscope is directly correlated with the room-temperature electrical impedance variation. Most of these variations may arise from remnant electronic orbital ordering persisting to room temperature in these compounds. We also observed a narrow singular stripe in composition with dramatically increased conductivity.

A quaternary combinatorial masking strategy was used in conjunction with photolithography to generate compositionally diverse thin-film phosphor libraries containing 1024 different compositions on substrates 2.5 centimeters square. A parallel imaging system and scanning spectrophotometer were used to identify and characterize compositions in the library with interesting luminescent behavior. Optimal compositions were identified with the use of gradient libraries, in which the stoichiometry of a material was varied continuously. This process led to the identification of an efficient blue photoluminescent composite material, Gd 3 Ga 5 O 12 /SiO 2 . Experimental evidence suggests that luminescence in this material may arise from interfacial effects between SiO 2 and Gd 3 Ga 5 O 12 .

We describe a novel x-ray computer tomography (CT) system for high contrast, non invasive 3D imaging of internal structures of functional ceramics, composites and polymeric membranes. System is capable of multi-length scale imaging from mm to sub 50 nm spatial resolutions and requires little or no sample preparation or staining. Relatively large samples with thickness from several mm to several microns may be imaged at high resolution. Examples using functional composites and membranes from SOFC (solid oxide fuel cell) and PEM (proton exchange membranes) fuel cell to derive direct information such as porosity and catalytic membrane degradation will be discussed. The key to the novel laboratory CT technology lies in utilizing proprietary x-ray optics with Fresnel Zone plates, and innovative high resolution, high contrast detectors.