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This work presents the preparation of a series of [(PbSe)1+δ]4[TiSe2]4 isomers via a low temperature synthesis approach that exploits precursor nanoarchitecture to direct formation of specific isomers. The targeted isomers formed even when the precursors did not have the correct amount of each element to make a unit cell from each repeating sequence of elemental layers deposited. This suggests that the exact composition of the precursors is less important than the nanoarchitecture in directing the formation of the compounds. The as-deposited diffraction data show that the isomers begin to form during the deposition, and Ti2Se, in addition to PbSe and TiSe2, are present in the specular diffraction patterns. HAADF-STEM images reveal impurity layers above and below an integer number of targeted isomer unit cells. The structural data suggest that Ti2Se forms as Se is deposited on the initial Ti layers and remains throughout isomer self-assembly. During growth, the isomers deplete the local supply of Ti and Pb, creating diffusion gradients that drive additional cations toward the growth front, which leaves surface impurity layers of TiSe2 and TiO2 after the supply of Pb is exhausted. The deposited stacking sequences direct formation of the targeted isomers, but fewer repeating units form than intended due to the lack of material per layer in the precursor and formation of impurity layers. All isomers have negative Hall and Seebeck coefficients, indicating that electrons are the majority carrier. The carrier concentration and conductivity of the isomers increase with the number of interfaces in the unit cell, resulting from charge donation between adjacent layers. The opposite variation of the carrier concentration and mobility with temperature result in minima in the resistivity between 50 and 100 K. The very weak temperature dependence of the carrier concentration likely results from changes in the amount of charge transfer between the layers with temperature.

Solid-state reaction kinetics on atomic length scales have not been heavily investigated due to the long times, high reaction temperatures, and small reaction volumes at interfaces in solid-state reactions. All of these conditions present significant analytical challenges in following reaction pathways. Herein we use in situ and ex situ X-ray diffraction, in situ X-ray reflectivity, high-angle annular dark field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy to investigate the mechanistic pathways for the formation of a layered (Pb0.5Sn0.5Se)1+δ(TiSe2)m heterostructure, where m is the varying number of TiSe2 layers in the repeating structure. Thin film precursors were vapor deposited as elemental-modulated layers into an artificial superlattice with Pb and Sn in independent layers, creating a repeating unit with twice the size of the final structure. At low temperatures, the precursor undergoes only a crystallization event to form an intermediate (SnSe2)1+γ(TiSe2)m(PbS...

Preparing homologous series of compounds allows chemists to rapidly discover new compounds with predictable structure and properties. Synthesizing compounds within such a series involves navigating a free energy landscape defined by the interactions within and between constituent atoms. Historically, synthesis approaches are typically limited to forming only the most thermodynamically stable compound under the reaction conditions. Presented here is the synthesis, via self-assembly of designed precursors, of isocompositional incommensurate layered compounds [(BiSe)1+δ] m[TiSe2] m with m = 1, 2, and 3. The structure of the BiSe bilayer in the m = 1 compound is not that of the binary compound, and this is the first example of compounds where a BiSe layer thicker than a bilayer in heterostructures has been prepared. Specular and in-plane X-ray diffraction combined with high-resolution electron microscopy data was used to follow the formation of the compounds during low-temperature annealing and the subsequent decomposition of the m = 2 and 3 compounds into [(BiSe)1+δ]1[TiSe2]1 at elevated temperatures. These results show that the structure of the precursor can be used to control reaction kinetics, enabling the synthesis of kinetically stable compounds that are not accessible via traditional techniques. The data collected as a function of temperature and time enabled us to schematically construct the topology of the free energy landscape about the local free energy minima for each of the products.

To evaluate optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) measurements in patients with active and quiescent uveitis with and without glaucoma and compare results to the published age-adjusted normative data.Comparative, retrospective pilot study.Consecutive patients with uveitis who underwent OCT RNFL measurements between December 2011 and October 2012 were identified: 76 uveitic eyes without glaucoma and 135 uveitic eyes with glaucoma.We conducted OCT of the RNFL.Global and sectoral RNFL thickness measurements.In 19 nonglaucomatous, uveitic eyes with active inflammation, mean global and all sectoral RNFL measurements were greater than the normative 95th percentile. The mean global RNFL OCT measurement was 140.5 microns in such eyes compared with 107.8 microns in the 57 nonglaucomatous, quiescent, uveitic eyes (P=0.008). These measurements were significantly higher than the average of 95.3 microns reported in normal eyes (P0.001). All mean sectoral measurements except superonasal were significantly higher in active compared with quiescent uveitic eyes (P=0.002-0.05). In glaucomatous eyes with both quiescent and active uveitis, the mean global RNFL measurements on OCT were 92.3 and 95.7 microns, respectively. These measurements were significantly higher than the mean global RNFL thickness (65.3 microns) reported in eyes with the same stage (moderate) of nonuveitic glaucoma.Uveitis is a major confounding factor in assessing the thickness of the RNFL. A significant thickening of the RNFL was found in patients with active uveitis and a greater RNFL thickness than anticipated in patients with uveitic glaucoma. These data raise concerns about the comparative value of RNFL scans as a method to detect and monitor glaucoma in uveitic eyes.

Synthesis and electrical properties of kinetically stabilized (PbSe)1+δ(TiSe2)n thin-film intergrowths are reported for 1 ≤ n ≤ 18. A linear increase in the c-lattice parameter of the intergrowth is observed as n is increased and the slope is consistent with the inclusion of an additional TiSe2 structural unit as n is incremented by 1 and the observed intercept is consistent with the expected thickness of a PbSe bilayer. The charge donated to the TiSe2 constituent from the PbSe is diluted across more layers as n is increased, leading to a systematic increase in the Seebeck coefficient. The room temperature resistivity values of the reported compounds are all on the order of 10−5 Ω m and depend on defect densities that affect the mobility, making the magnitude of the resistivity less sensitive to n. The temperature dependence is metallic for large n, with a slight upturn at low temperatures due to localization of carriers for small n values. The power factor increases with n, including the highest reported for chalcogenide misfit layered and related compounds, showing that nanostructuring and modulation doping are an effective means of tuning the power factor of thermoelectric intergrowth materials. Since these compounds have very low thermal conductivity due to structural anisotropy and misregistration between intergrowth constituents, this suggests that varying their nanoarchitecture is a promising approach to obtain high values of zT.

(SnSe)1.2TiSe2 was found to self-assemble from a precursor containing modulated layers of Sn–Se and Ti–Se over a surprisingly large range of layer thicknesses and compositions. The constituent lattices form an alternating layer superstructure with rotational disorder present between the layers. This compound was found to have the highest Seebeck coefficient measured for analogous TiX2 containing misfit layered compounds to date, suggesting potential for low-temperature thermoelectric applications. Electrical characterization suggests that electrons transferred from SnSe to TiSe2 are responsible for the higher carrier concentration observed relative to bulk TiSe2. The transfer of charge from one constituent to the other may provide a mechanism for doping layered dichalcogenides for various applications without negatively affecting carrier mobility.

Telluride misfit layer compounds are reported for the first time. These compounds were synthesized using a novel approach of structurally designing a precursor that would form the desired product upon low-temperature annealing, which allows the synthesis of kinetically stable products that do not appear on the equilibrium phase diagram. Four new compounds of the [(PbTe)1.17]m(TiTe2)n family are reported, and their structures were examined by a variety of X-ray diffraction techniques.

The method of modulated elemental reactants (MER) is used to prepare the layered compound Ti1+x Se2. Using a thin-film precursor prepared by sequentially depositing elemental titanium and selenium by physical vapor deposition, the binary compound is readily formed by short-duration annealing at 350°C. x-Ray diffraction indicates that TiSe2 layers in the film are highly oriented with the c-axis of the layers perpendicular to the substrate. Temperature-dependent electrical resistivity and Hall coefficient measurements for the MER-prepared specimen reveal temperature dependence that is distinct from crystalline stoichiometric TiSe2 in bulk form. The room-temperature Seebeck coefficient was measured to be −134 μV/K, which is opposite in sign and significantly larger in magnitude than stoichiometric crystalline TiSe2, suggesting that carrier transport in the disordered film is markedly different from the bulk crystalline material.

A homologous series of quasi-2D ([PbSe]1+δ)m(TiSe2)m nanolayered heterostructures are prepared via self-assembly of designed precursors with 1 ≤m≤ 4 and their structures and properties investigated. All heterostructures have the same global composition but vary in their interface density. X-ray diffraction and electron microscopy studies show that the structures consist of rock salt structured PbSe layers alternating with TiSe2 layers, and that grain size increases with m. The compounds are all metallic with upturns in resistivity at low temperature suggesting electron localization, with room temperature resistivity of 1-3 10(-5)Ω m, negative Hall coefficients and Seebeck coefficients between -50 and -100 μV K(-1). A decrease in the mobile carrier concentration with temperature is observed for all m and the rate increases with increasing low-dimensionality. Decreasing the interface density also decreases the average carrier concentration while increasing the electron mobility. The Seebeck coefficients systematically increase in magnitude as m is increased, but the net effect to the power factor is small due to a compensating increase in resistivity. The observed transport behavior is not described by the simple rigid band models with charge transfer between constituents used previously. Charge exchange between constituents stabilizes the intergrowth, but also introduces mobile carriers and interfacial band bending that must play a role in the transport behavior of the heterostructures. As chemical potentials equilibrate in high m heterostructures there is a decrease in total coulombic stabilization as there are fewer interfaces, so m = 1 is likely to be most stable. This rationalizes why the structurally similar misfit layer compounds with m = 1 are often the only intergrowths that can be prepared. Charge transfer and band bending at interfaces should occur in other heterostructures with similar type II broken-gap band alignments and are important considerations regarding both their stability and transport properties.

Thin films of the new title intergrowth compound consisting of a bilayer of SnSe and TiSe2 trilayer are prepared by self-assembly from a precursor containing modulated layers of Sn-Se and Ti-Se, which is synthesized by deposition of elemental layers (annealing at 350 °C).

Telluride misfit layer compounds are reported for the first time. These compounds were synthesized using a novel approach of structurally designing a precursor that would form the desired product upon low-temperature annealing, which allows the synthesis of kinetically stable products that do not appear on the equilibrium phase diagram. Four new compounds of the [(PbTe)1.17]m(TiTe2)n family are reported, and their structures were examined by a variety of X-ray diffraction techniques.

Importance Measurement of retinal nerve fiber layer (RNFL) thickness using optical coherence tomography can aid in the diagnosis and management of glaucoma. We observed a previously unreported phenomenon in eyes with uveitis-associated glaucoma in which paradoxical changes in RNFL thickness were noted. Observations Four eyes of 3 patients with uveitis-associated glaucoma had a relatively normal RNFL measurement on presentation during periods of active uveitis and raised intraocular pressure. Subsequent control of uveitis and intraocular pressure was associated with a paradoxical thinning of the RNFL and increased cupping. Conclusions and Relevance Normal-appearing measurements of RNFL thickness in patients with uveitis should be interpreted cautiously in those with a raised intraocular pressure. Physicians should recognize that continued thinning of the RNFL and increased cupping, despite good intraocular pressure control in such eyes, may be due to resolution of edema of the RNFL.

The title compound is prepared by annealing (350 °C, N2) a system of 28 repetitions of sputtered layer sequences of Ti-Se-Ti-Se-Pb-Se.

The synthesis and characterization of turbostratically disordered (BiSe)1.15TiSe2 is reported. Specular and in-plane x-ray diffraction studies indicate an alternating structure containing two planes of a distorted rock salt structured BiSe and a Se–Ti–Se trilayer of TiSe2 with independent lattices. The title compound was found to be turbostratically (rotationally) disordered about the c-axis, and the BiSe layer displays an orthorhombic in-plane structure with a = 4.562(2) A and b = 4.242(1) A. Temperature dependent electrical resistivity reveals that the disordered compound is metallic, but with less temperature dependence than may be expected for a 3D crystal, which is attributed to the lack of coherent vibrations due to the turbostratic disorder. The room temperature resistivity was found to be ρ = 5.0 × 10−6 Ωm with a carrier concentration of n = 5 × 1021 cm−3. Comparing the carrier concentration to (PbSe)1.16TiSe2 suggests that the bismuth is trivalent and donates an electron to the conduction band of the TiSe2 constituent.

Endothelial progenitor cells (EPCs) can be isolated from adult peripheral and umbilical cord blood. EPCs are thought to originate from bone marrow, circulate in peripheral blood, and migrate to sites of angiogenesis. However, the number of circulating EPCs in peripheral blood is remarkably low, and recent genetic studies show that the contribution of bone marrow derived EPCs to newly formed vascular networks is minimal. Further, while endothelial cells (ECs) derived from vessel walls are widely considered to be differentiated mature ECs, these cells retain extensive proliferative potential and can be passaged for at least 40 population doubling in vitro. Based on these observations, we tested whether EPCs potentially reside in vessel walls utilizing a newly developed single cell deposition assay (Blood, 2004). Analogous to a paradigm established in the hematopoietic cell system, we can utilize this assay to reproducibly identify the following EPCs: (1) high proliferative potential - endothelial colony forming cells (HPP-ECFC), which form macroscopic colonies that form secondary and tertiary colonies upon replating, (2) low proliferative potential - endothelial colony forming cells (LPP-ECFC), which form colonies greater than 50 cells, but do not form secondary colonies upon replating, (3) endothelial cell clusters (EC-clusters) that contain less than 50 cells, and (4) mature terminally differentiated endothelial cells (EC), which do not divide. Utilizing this assay, we compared the clonogenic potential of 1000 single adult human dermal microvascular endothelial cells (HMVECds), human umbilical vein endothelial cells (HUVECs), human umbilical artery endothelial cells (HUAECs), human coronary artery endothelial cells (HCAECs), and human aortic endothelial cells (HAECs) to the potential of adult peripheral and umbilical cord blood derived EPCs. We conducted four independent experiments. Remarkably, we demonstrate that a complete hierarchy of EPCs can be identified in EC populations derived from every vessel wall tested (Table I and n=4). Further, we show that ECs derived from each vessel wall cell population tested contain more proliferative EPCs (LPP-ECFCs and HPP-ECFCs) compared to EPCs derived from adult peripheral blood. Percent of 1,000 Single Cells Plated | | Mature EC | EC-Cluster | LPP-ECFC | HPP-ECFC | |:--------- | --------- | ---------- | -------- | -------- | | HUVEC | 42±6 | 18±2 | 29±9 | 11±5 | | HAEC | 37±3 | 23±8 | 21±4 | 20±6 | | HMVECd | 65±9 | 21±6 | 12±4 | 2±0.6 | | HCAEC | 46±2 | 18±2 | 20±2 | 16±2 | | HUAEC | 41±1 | 10±1 | 27±4 | 21±2 | | Adult EPC | 81±9 | 9±1 | 12±8 | 0.2±0.2 | | Cord EPC | 50±20 | 7±2 | 20±10 | 23±9 | Thus, this study provides evidence that a diversity of EPCs exists in human vessels and provides a new conceptual framework for determining both the origin and function of EPCs in maintaining vessel integrity and contributing to new sites of angiogenesis.