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Frank E Osterloh

Publications and source records attributed to Frank E Osterloh.

10 recordsLinked to original sources
PubMed2006

Effect of additives on LiMo3Se3 nanowire film chemical sensors.

Here we investigate the effect of lithium iodide and cetyltrimethylammonium (CTA) bromide additives on the ability of LiMo(3)Se(3) nanowire film sensors to bind and detect organic solvents electrically. Both additives decrease the electrical conductivity of the films. Lithium iodide increases the response of the films to both polar and nonpolar analytes. CTA increases the response of the films to nonpolar analytes but reduces the response to polar analytes. Quartz crystal microbalance measurements show that the modified electrical sensitivities of the films are due to altered analyte adsorption abilities of the films. These results show that the Li(+) ions are involved in analyte binding in native LiMo(3)Se(3) films and that a programming of LiMo(3)Se(3) nanowire film sensors is possible by replacing lithium cations with other receptors.

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PubMed2006

Planar gold nanoparticle clusters as microscale mirrors.

Dispersible microscale mirror particles were synthesized by linkage of citrate-coated gold nanoparticles and 3-aminopropylsilyl-modified Ca2Nb3O10 perovskite nanoplates. The mirror particles reflect 14-19% of light in the 500-800 nm wavelength interval with retention of polarization. Due to their directional reflection properties, laser-irradiated micromirror dispersions in solvents exhibit Brownian motion-driven multicolor blinking behavior.

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PubMed2006

Molecular adsorption to LiMo3Se3 nanowire film chemiresistors.

Thin films of metallic nanowire bundles derived from the Chevrel compound LiMo3Se3 undergo reversible increases of their electrical resistance (up to 70%) upon exposure to vapors of organic solvents (Qi, X. B.; Osterloh, F. E. J. Am. Chem. Soc. 2005, 127 (21), 7666-7667). Using quartz crystal microbalance measurements with four analytes, we demonstrate here that the temporal and steady-state resistance changes of the films depend on the time following the adsorption and on the number of molecules that adsorb to the nanowire films at a given pressure. The adsorption ability of the films and the corresponding film resistance increase in the row: hexane < THF < ethanol < DMSO, closely following the polarities of the solvents. On average, approximately 10(5) analyte molecules per LiMo3Se3 unit are required to produce a measurable electrical response. Atomic force microscopy scans on nanowire films reveal that analytes deposit on top of the nanowire bundles and cause the films to swell by approximately 6% in volume. The temporal and steady-state resistance data of the LiMo3Se3 chemiresistors can be explained by assuming that coating of the nanowire bundles with analyte molecules reduces the interwire charge transport in the films.

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PubMed2005

Planar polarized light emission from CdSe nanoparticle clusters.

This paper describes synthesis and optical properties of planar clusters of CdSe nanocrystals. The clusters emit linearly polarized light in the plane of the cluster. The emission wavelength of the clusters can be adjusted between 568 and 639 nm with the size of the CdSe nanocrystals. Planar CdSe microclusters were synthesized by reaction of trioctylphosphine oxide-coated CdSe/CdS nanocrystals with 3-aminopropylsilyl-modified Ca(2)Nb(3)O(10) nanosheets in THF. The clusters are 3.92 +/- 1.18 mum length/width and 91 +/- 37 nm thickness, and they consist of alternating layers of Ca(2)Nb(3)O(10) to which CdSe nanocrystals are attached with densities of 5300 +/-310 particles per side of a single Ca(2)Nb(3)O(10) sheet. The chemical inertness of the clusters in coordinating solvents suggests covalent interactions between the aminopropyl groups and CdSe nanocrystals. Upon excitation at lambda(exc) = 400 nm, the clusters emit green (568 nm), orange (589 nm), or red (639 nm) light, depending on the size of the CdSe crystals. The light is emitted preferentially in the cluster plane and it is linearly polarized along the cluster edges. Combined fluorescence microscopy and atomic force microscopy reveal that the directional emission efficiency depends linearly on the thickness of the clusters, which varies between 70 and 180 nm. The ability to manipulate the direction and polarization of the photoemission of CdSe nanoparticles via assembly into 2D structures is of interest for applications of these and similar structures in advanced optical materials and devices.

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PubMed2005

Fe3O4-LiMo3Se3 nanoparticle clusters as superparamagnetic nanocompasses.

A scaleable chemical approach to functional nanoscale analogues of the magnetic compasses in magnetotactic bacteria is described. LiMo(3)Se(3)-Fe(3)O(4) nanowire-nanoparticle composites were synthesized by a reaction of 3-iodopropionic acid treated LiMo(3)Se(3) nanowire bundles with oleic acid-stabilized Fe(3)O(4) nanoparticles of 2.8, 5.3, and 12.5 nm size in tetrahydrofuran. Transmission electron micrographs show that the composite consists of Fe(3)O(4) nanoparticles attached to the surfaces of the 4-6 nm thick nanowire bundles. UV/vis spectra reveal absorptions from the nanowire (506 nm) and magnetite components (280-450 nm), and IR spectra show characteristic bands for the propionic acid linkers and for the residual oleic acid ligands on the magnetite particles. In the presence of excess oleic acid, the nanocomposites undergo rapid disassembly, suggesting that Fe(3)O(4) nanoparticles are bonded to nanowires via carboxylate groups from the linkers. Ultrasonication of a dispersion of the composite in THF produces individual LiMo(3)Se(3)-Fe(3)O(4) clusters, which are 340 +/- 107 nm long and 20 +/- 5 nm thick, depending on the sonication time and Fe(3)O(4) nanoparticle size. Field cooled and zero-field cooled magnetization measurements reveal that the blocking temperature (T(B) = 100 K) of the clusters with 5.3 nm Fe(3)O(4) is increased as compared to the free nanoparticles (T(B) = 30 K). Directional dipolar interactions in the clusters lead to magnetic anisotropy, which makes it possible to align the clusters in a magnetic field (900 Oe).

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PubMed2005

ZnO-CdSe nanoparticle clusters as directional photoemitters with tunable wavelength.

Reaction of 3-aminopropylsilyl-modified ZnO microrods with trioctylphosphineoxide-coated CdSe/CdS core/shell nanocrystals in THF produces rod-shaped nanoparticle clusters that show directional photoemission that can be tuned with the size of the CdSe nanocrystals. The observed waveguiding effect of these microstructures is due to total internal reflection of light at the cluster-air interface.

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PubMed2005

Synthesis and real-time magnetic manipulation of a biaxial superparamagnetic colloid.

Superparamagnetic colloidal plates were synthesized from tetrabutylammonium stabilized Ca(2)Nb(3)O(10) nanosheets and oleic acid-stabilized Fe(3)O(4) nanoparticles. Modification with 3-aminopropyltrimethoxysilane produces amine-terminated Ca(2)Nb(3)O(10) with an amine concentration of 0.43 +/- 0.06 groups per Ca(2)Nb(3)O(10) unit as follows from spectroscopic quantification with trinitrobenzenesulfonic acid as a dye. Treatment of the modified sheets in THF/ethanol with 5.3 nm oleic acid-stabilized magnetite nanoparticles yields pseudo-2D assemblies that consist of 2 nm thick nanosheets decorated on both sides with a dense collection (9.3 +/- 0.5 x 10(3) particles per square micrometer per side) of magnetite particles. In noncoordinating or weakly coordinating solvents, these composite particles further aggregate into stacked aggregates with a mean edge length of 1.6 +/- 0.7 microm and a thickness of 79 +/- 30 nm. The colloidal plates were characterized by elemental analysis, X-ray powder diffraction, and infrared and UV/vis spectroscopy. SQUID measurements show that films of the aligned particles are superparamagnetic at room temperature. The magnetic hysteresis that is observed at 5 K reveals that the plates have a magnetic anisotropy with the easy axis in the plane of the plates and the hard axis perpendicular to it. Calculations show that the magnetic anisotropy is a direct consequence of the two-dimensional distribution of the magnetic nanoparticles on the sheets. Optical microscopy reveals that when suspended in ethanol or THF, the colloidal plates can be rotated in real time with a variable external magnetic field (200 Oe). Magnetic alignment of the particles in suspensions also produces asymmetric light scattering patterns and magnetic birefringence. These effects and the observed magneto-orientational properties make the biaxial colloids interesting as components in displays and as magnetic actuators.

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PubMed2005

Chemical sensing with LiMo3Se3 nanowire films.

Thin films (4-150 nm) of metallic LiMo3Se3 nanowires respond to chemical vapors of molecular analytes (2-400 mTorr) with rapid (<20 s) and mostly reversible changes of their resistance (DeltaR/R0 approximately 1-70%). Measurements show that the effect is concentration-dependent, and that it depends on the molecular properties of the analytes.

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PubMed2002

Solution self-assembly of magnetic light modulators from exfoliated perovskite and magnetite nanoparticles.

Covalent linkage of oleic acid ligated Fe3O4 spheres (9 nm) with sheetlike [H1-xCa2Nb3O10] particles (300 x 300 x 2 nm) yields, depending on conditions, submicro- or microscale stacks, which on their surfaces are decorated with magnetite nanoparticles. Due to the optical anisotropy of the sheetlike Ca2Nb3O10 building blocks and due to the superparamagnetic nature of the Fe3O4 components, the nanostructured composites exhibit magnetically controllable birefringence and light-scattering properties in solution.

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