We report conductivity measurements of Cr-doped V2O3 using a variable pressure technique. The critical behavior of the conductivity near the Mott insulator to metal critical endpoint is investigated in detail as a function of pressure and temperature. The critical exponents are determined, as well as the scaling function associated with the equation of state. The universal properties of a liquid-gas transition are found. This is potentially a generic description of the Mott critical endpoint in correlated electron materials.

We have performed in-plane transport measurements on the two-dimensional organic salt κ-(BEDT-TTF)2Cu[N(CN)2]Cl. A variable (gas) pressure technique allows for a detailed study of the changes in conductivity through the insulator-to-metal transition. We identify four different transport regimes as a function of pressure and temperature (corresponding to insulating, semiconducting, "bad metal", and strongly correlated Fermi liquid behaviours). Marked hysteresis is found in the transition region, which displays complex physics that we attribute to strong spatial inhomogeneities. Away from the critical region, good agreement is found with a dynamical mean-field calculation of transport properties using the numerical renormalization group technique.

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We report here the development of stable aqueous suspensions of biocompatible superparamagnetic iron oxide nanoparticles (SPIONs). These so-called ferrofluids are useful in a large spectrum of modern biomedical applications, including novel diagnostic tools and targeted therapeutics. In order to provide prolonged circulation times for the nanoparticles in vivo, the initial iron oxide nanoparticles were coated with a biocompatible polymer poly(ethylene glycol) (PEG). To permit covalent bonding of PEG to the SPION surface, the latter was functionalized with a coupling agent, 3-aminopropyltrimethoxysilane (APS). This novel method of SPION PEGylation has been reproduced in numerous independent preparations. At each preparation step, particular attention was paid to determine the physico-chemical characteristics of the samples using a number of analytical techniques such as atomic absorption, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, transmission electron microscopy (TEM), photon correlation spectroscopy (PCS, used for hydrodynamic diameter and zeta potential measurements) and magnetization measurements. The results confirm that aqueous suspensions of PEGylated SPIONs are stabilized by steric hindrance over a wide pH range between pH 4 and 10. Furthermore, the fact that the nanoparticle surface is nearly neutral is in agreement with immunological stealthiness expected for the future biomedical applications in vivo.

We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit cobalt oxides results from the addition of a spin entropy contribution to an enlarged electronic one.

High quality vanadium sesquioxide V2O3 films (170–1100Å) were grown using the pulsed laser deposition technique on (0001)-oriented sapphire substrates, and the effects of film thickness on the lattice strain and electronic properties were examined. X-ray diffraction indicates that there is an in-plane compressive lattice parameter (a), close to −3.5% with respect to the substrate and an out-of-plane tensile lattice parameter (c). The thin film samples display metallic character between 2 and 300K, and no metal-to-insulator transition is observed. At low temperature, the V2O3 films behave as a strongly correlated metal, and the resistivity (ρ) follows the equation ρ=ρ0+AT2, where A is the transport coefficient in a Fermi liquid. Typical values of A have been calculated to be 0.14μΩcmK−2, which is in agreement with the coefficient reported for V2O3 single crystals under high pressure. Moreover, a strong temperature dependence of the Hall resistance confirms the electronic correlations of these V2O3 thin film samples.

n‐Type‐doped polymers are key elements to fabricate all‐polymer thermoelectric generators but they are challenging to produce. Herein, a new strategy is proposed, which is based on polarity switching upon doping of a donor–acceptor (D–A) copolymer based on diketopyrrolopyrrol (DPP) and quintethiophene (5T) with FeCl3. Polarity switching from p‐type to n‐type is observed upon increasing the doping concentration of FeCl3. An analysis based on nonmonotonic density of states is proposed, which accounts for the main experimental trends and demonstrates that the polarity switch is governed by the electronic band filling that is determined by the dopant concentration. The influence of the curvature of the density of states is in addition discussed and a complete description of the doping induced transport regimes is proposed. This polarity switching depends on the molecular weight Mn of the polymer and shifts to higher FeCl3 concentrations with increasing Mn. This behavior is attributed to the change of the width of the density of states with Mn. The combination of polarity switching and alignment is a means to produce n‐type‐like oriented and conducting polymers with enhanced power factors up to 10 µW K−2 m−1 along the chain direction.

We report a one-pot synthesis protocol for highly efficient and stable covalent binding of both the fluorescent drug doxorubicin (DOX) and the biocompatible polymer poly(ethylene glycol) (PEG) to the surface of superparamagnetic iron oxide nanoparticles (SPIONs). The final aim is to obtain a biocompatible, injectable nanosystem combining anticancer activity (magnetically targeted drug delivery) and nondestructive imaging of the treated cancer cells and tissues by means of fluorescence and magnetic resonance imaging (MRI). Our protocol employs silane and epoxide chemistry, which could also be useful to bind other molecules possessing a primary or secondary amine group, such as drugs, proteins, and fluorescent labels. The suspensions of SPIONs-DOX-PEG (iron concentration of 17 mg/L) obtained in this study are stable at physiological pH values. This stability coupled with the PEG surface neutrality makes these nanoparticles compatible with their application in vivo, via systemic administration. Efficient binding of DOX to the SPIONs surface via the amine group of the sugar moiety of the drug, i.e., outside of the aromatic pharmacophore-fluorophore, preserves the fluorescence activity of DOX. Confocal fluorescence spectral imaging of treated MCF7 cancer cells indicates that, in spite of the accumulation of SPIONs-DOX-PEG in the cytosol, only a minor fraction of the drug reaches the nucleus in 24 h. As a result, no in vitro cytotoxicity against MCF7 cancer cells was detected (the highest iron and drug concentrations were 2.7 mg/L and 8.1 µM, respectively). Interestingly, SPIONs-DOX particles noncoated with PEG were cytotoxic. We conclude that cellular enzymes can cleave the amine drug-particle linkage, but the PEG shell hinders the cleavage, possibly by sterical repulsion. Therefore, the developed chemistry is useful for stable coating of SPIONs with polymers and fluorescent labels, while an alternative strategy will be needed for more efficient drug release.