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Ge – Sb – Te alloys are widely used for data recording based on the rapid and reversible amorphous-to-crystalline phase transformation that is accompanied by increases in the optical reflectivity and the electrical conductivity. However, uncertainties about the optical band gaps and electronic transport properties of these phases have persisted because of inappropriate interpretation of reported data and the lack of definitive analytical studies. In this paper we characterize the most widely used composition, Ge2Sb2Te5, in its amorphous, face-centered-cubic, and hexagonal phases, and explain the origins of inconsistent or unphysical results in previous reports. The optical absorption in all of these phases follows the relationship αhν∝(hν−Egopt)2, which corresponds to the optical transitions in most amorphous semiconductors as proposed by Tauc, Grigorovici, and Vancu [Tauc et al., Phys. Status Solidi 15, 627 (1966)], and to those in indirect-gap crystalline semiconductors. The optical band gaps of the amorphous, face-centered-cubic, and hexagonal phases are 0.7, 0.5, and 0.5eV, respectively. The subgap absorption in the amorphous phase shows an exponential decay with an Urbach slope of 81meV. We measured the photoconductivity of amorphous Ge2Sb2Te5 and determined a mobility-lifetime product of 3×10−9cm2∕V. The spectral photoconductivity shows a threshold at about 0.7eV, in agreement with our analysis of the optical band gap. The face-centered-cubic and hexagonal phases are highly conductive and do not show freeze-out; even at 5K the density of free carriers remains at 1019–1020cm−3, so these are degenerate semiconductors in which the Fermi level resides inside a band. In the hexagonal phase, the effect of free electrons on the Hall coefficient is significant at high temperatures. When the Hall data are fitted using the two-carrier analysis, the hole mobility is found to decrease slowly with temperature, as expected. The considerations discussed in this paper can be readily applied to study related chalcogenide materials.

in Wiley InterScience (www.interscience.wiley.com).The evaporation behavior of urea-water-solution (UWS) droplet was investigated for application to urea-selective catalytic reduction (SCR) systems. A number of experiments were performed with single UWS droplet suspended on the tip of a fine quartz fiber. To cover the temperature range of real-world diesel exhausts, droplet ambient temperature was regulated from 373 to 873 K using an electrical furnace. As a result of this study, UWS droplet revealed different evaporation characteristics depending on its ambient temperature. At high temperatures, it showed quite complicated behaviors such as bubble formation, distortion, and partial rupture after a linear D 2 -law period. However, as temperature decreases, these phenomena became weak and finally disappeared. Also, droplet diminishment coefficients were extracted from transient evaporation histories for various ambient temperatures, which yields a quantitative evaluation on evaporation characteristics of UWS droplet as well as provides valuable empirical data required for modeling or simulation works on urea-SCR systems.

The hepatocyte-specific contrast agent gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) was developed to improve the detection and characterization of focal liver lesions at magnetic resonance (MR) imaging. Approximately 50% of the injected dose is taken up into the functional hepatocyte and is excreted via the biliary system. Because of this property, Gd-EOB-DTPA has the potential to be a biliary contrast agent. When combined with T2-weighted MR cholangiography, Gd-EOB-DTPA-enhanced MR imaging can allow morphologic and functional assessment of the biliary system. Gd-EOB-DTPA-enhanced MR cholangiography could be effective in evaluation of biliary anatomy, differentiation of biliary from extrabiliary lesions, diagnosis of cholecystitis, assessment of bile duct obstruction, detection of bile duct injury including leakage and stricture, evaluation of biliary-enteric anastomoses, postprocedure evaluation, differentiation of biloma from other pathologic conditions, and evaluation of sphincter of Oddi dysfunction. However, the clinical applications of this imaging technique have not yet been fully explored, and further investigations are needed to determine the utility of Gd-EOB-DTPA-enhanced MR cholangiography in a clinical setting.

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A series of dual stimuli responsive synthetic polymer bioconjugate chimeric materials, poly(N-isopropylacrylamide)55-block-poly(L-histidine)n [p(NIPAM)55-b-p(His)n] (n=50, 75, 100, 125), have been synthesized by employing reversible addition-fragmentation chain transfer polymerization of NIPAM, followed by ring-opening polymerization of α-amino acid N-carboxyanhydrides. The dual stimuli responsive properties of the resulting biocompatiable and membrenolytic p(NIPAM)55-b-p(His)n polymers are investigated for their use as a stimuli responsive drug carrier for tumor targeting. Highly uniform self-assembled micelles (∼55 nm) fabricated by p(NIPAM)55-b-p(His)n polymers display sharp thermal and pH responses in aqueous media. An anticancer drug, doxorubicin (Dox), is effectively encapsulated in the micelles and the controlled Dox release is investigated in different temperature and pH conditions. Antitumor effect of the released Dox is also assessed using the HepG2 human hepatocellular carcinoma cell lines. Dox molecules released from the [p(NIPAM)55-b-p(His)n] micelles remain biologically active and have stimuli responsive capability to kill cancer cells. The self-assembling ability of these hybrid materials into uniform micelles and their efficiency to encapsulate Dox makes them a promising drug carrier to cancer cells. The new chimeric materials thus display tunable properties that can make them useful for a molecular switching device and controlled drug delivery applications needing responses to temperature and pH for the improvement of cancer chemotherapy.

A series of synthetic polymer bioconjugate hybrid materials consisting of poly(2‐hydroxyethyl methacrylate) (p(HEMA)) and poly(l‐histidine) (p(His)) are synthesized by combining atom transfer radical polymerization of HEMA with ring opening polymerization of benzyl‐N‐carboxy‐L‐histidine anhydride. The resulting biocompatible and membranolytic p(HEMA)25‐b‐p(His)n (n = 15, 25, 35, and 45) polymers are investigated for their use as pH‐sensitive drug‐carrier for tumor targeting. Doxorubicin (Dox) is encapsulated in nanosized micelles fabricated by a self‐assembly process and delivered under different pH conditions. Micelle size is characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM) observations. Dox release is investigated according to pH, demonstrating the release is sensitive to pH. Antitumor activity of the released Dox is assessed using the HCT 116 human colon carcinoma cell line. Dox released from the p(HEMA)‐b‐p(His) micelles remains biologically active and has the dose‐dependent capability to kill cancer cells at acidic pH. The p(HEMA)‐b‐p(His) hybrid materials are capable of self‐assembling into nanomicelles and effectively encapsulating the chemotherapeutic agent Dox, which allows them to serve as suitable carriers of drug molecules for tumor targeting.