Impact of electrostatic doping on carrier concentration and mobility in InAs nanowires.

We fabricate dual-gated electric double layer (EDL) field effect transistors based on InAs nanowires gated with an ionic liquid, and we perform electrical transport measurements in the temperature range from room temperature to 4.2 K. By adjusting the spatial distribution of ions inside the ionic liquid employed as gate dielectric, we electrostatically induce doping in the nanostructures under analysis. We extract low-temperature carrier concentration and mobility in very different doping regimes from the analysis of current-voltage characteristics and transconductances measured exploiting global back-gating. In the liquid gate voltage interval from -2 to 2 V, carrier concentration can be enhanced up to two orders of magnitude. Meanwhile, the effect of the ionic accumulation on the nanowire surface turns out to be detrimental to the electron mobility of the semiconductor nanostructure: the electron mobility is quenched irrespectively to the sign of the accumulated ionic species. The reported results shine light on the effective impact on crucial transport parameters of EDL gating in semiconductor nanodevices and they should be considered when designing experiments in which electrostatic doping of semiconductor nanostructures via electrolyte gating is involved.

Physiological and biochemical impacts of graphene oxide in polychaetes: The case of Diopatra neapolitana.

Graphene oxide (GO) is an important carbon nanomaterial (NM) that has been used, but limited literature is available regarding the impacts induced in aquatic organisms by this pollutant and, in particular in invertebrate species. The polychaete Diopatra neapolitana has frequently been used to evaluate the effects of environmental disturbances in estuarine systems due to its ecological and socio-economic importance but to our knowledge no information is available on D. neapolitana physiological and biochemical alterations due to GO exposure. Thus, the present study aimed to assess the toxic effects of different concentrations of GO (0.01; 0.10 and 1.00mg/L) in D. neapolitana physiological (regenerative capacity) and biochemical (energy reserves, metabolic activity and oxidative stress related biomarkers) performance, after 28days of exposure. The results obtained revealed that the exposure to GO induced negative effects on the regenerative capacity of D. neapolitana, with organisms exposed to higher concentrations regenerating less segments and taking longer periods to completely regenerate. GO also seemed to alter energy-related responses, especially glycogen content, with higher values in polychaetes exposed to GO which may result from a decreased metabolism (measured by electron transport system activity), when exposed to GO. Furthermore, under GO contamination D. neapolitana presented cellular damage, despite higher activities of antioxidant and biotransformation enzymes in individuals exposed to GO.

Magnetic and optical bistability in tetrairon(III) single molecule magnets functionalized with azobenzene groups.

Tetrairon(III) complexes known as "ferric stars" have been functionalized with azobenzene groups to investigate the effect of light-induced trans-cis isomerization on single-molecule magnet (SMM) behaviour. According to DC magnetic data and EPR spectroscopy, clusters dispersed in polystyrene (4% w/w) exhibit the same spin (S = 5) and magnetic anisotropy as bulk samples. Ligand photoisomerization, achieved by irradiation at 365 nm, has no detectable influence on static magnetic properties. However, it induces a small but significant acceleration of magnetic relaxation as probed by AC susceptometry. The pristine behaviour can be almost quantitatively recovered by irradiation with white light. Our studies demonstrate that magnetic and optical bistability can be made to coexist in SMM materials, which are of current interest in molecular spintronics.

Magnetic bistability of isolated giant-spin centers in a diamagnetic crystalline matrix.

Polynuclear single-molecule magnets (SMMs) were diluted in a diamagnetic crystal lattice to afford arrays of independent and iso-oriented magnetic units. Crystalline solid solutions of an Fe(4) SMM and its Ga(4) analogue were prepared with no metal scrambling for Fe(4) molar fractions x down to 0.01. According to high-frequency EPR and magnetic measurements, the guest SMM species have the same total spin (S=5), anisotropy, and high-temperature spin dynamics found in the pure Fe(4) phase. However, suppression of intermolecular magnetic interactions affects magnetic relaxation at low temperature (40 mK), where quantum tunneling (QT) of the magnetization dominates. When a magnetic field is applied along the easy magnetic axis, both pure and diluted (x=0.01) phases display pronounced steps at evenly spaced field values in their hysteresis loops due to resonant QT. The pure Fe(4) phase exhibits additional steps which are firmly ascribed to two-molecule QT transitions. Studies on the field-dependent relaxation rate showed that the zero-field resonance sharpens by a factor of five and shifts from about 8 mT to exactly zero field on dilution, in agreement with the calculated variation of dipolar interactions. The tunneling efficiency also changes significantly as a function of Fe(4) concentration: the zero-field resonance is significantly enhanced on dilution, while tunneling at ±0.45 T becomes less efficient. These changes were rationalized on the basis of a dipolar shuffling mechanism and transverse dipolar fields, whose effect was analyzed by using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on SMM behavior and disclose the magnetic response of truly isolated giant spins in a diamagnetic crystalline environment.

One-step covalent grafting of Fe4 single-molecule magnet monolayers on gold.

Iron(III)-based single-molecule magnets have been covalently grafted on Au(111) in one step using 1,2-dithiolan-3-yl side groups. Reaction with the substrate quantitatively affords a monolayer of electronically intact clusters doubly linked to the surface via Au-S bonds, as demonstrated by a combination of STM, XAS/XMCD and XPS studies.

Slow magnetic relaxation from hard-axis metal ions in tetranuclear single-molecule magnets.

We report the synthesis of the novel heterometallic complex [Fe(3)Cr(L)(2)(dpm)(6)]⋅Et(2)O (Fe(3)CrPh) (Hdpm=dipivaloylmethane, H(3)L=2-hydroxymethyl-2-phenylpropane-1,3-diol), obtained by replacing the central iron(III) atom by a chromium(III) ion in an Fe(4) propeller-like single-molecule magnet (SMM). Structural and analytical data, high-frequency EPR (HF-EPR) and magnetic studies indicate that the compound is a solid solution of chromium-centred Fe(3)Cr (S=6) and Fe(4) (S=5) species in an 84:16 ratio. Although SMM behaviour is retained, the |D| parameter is considerably reduced as compared with the corresponding tetra-iron(III) propeller (D=-0.179 vs. -0.418 cm(-1)), and results in a lower energy barrier for magnetisation reversal (U(eff)/k(B)=7.0 vs. 15.6 K). The origin of magnetic anisotropy in Fe(3)CrPh has been fully elucidated by preparing its Cr- and Fe-doped Ga(4) analogues, which contain chromium(III) in the central position (c) and iron(III) in two magnetically distinct peripheral sites (p1 and p2). According to HF-EPR spectra, the Cr and Fe dopants have hard-axis anisotropies with D(c)=0.470(5) cm(-1), E(c)=0.029(1) cm(-1), D(p1)=0.710(5) cm(-1), E(p1)=0.077(3) cm(-1), D(p2)=0.602(5) cm(-1), and E(p2)=0.101(3) cm(-1). Inspection of projection coefficients shows that contributions from dipolar interactions and from the central chromium(III) ion cancel out almost exactly. As a consequence, the easy-axis anisotropy of Fe(3)CrPh is entirely due to the peripheral, hard-axis-type iron(III) ions, the anisotropy tensors of which are necessarily orthogonal to the threefold molecular axis. A similar contribution from peripheral ions is expected to rule the magnetic anisotropy in the tetra-iron(III) complexes currently under investigation in the field of molecular spintronics.

Introduction of ester and amido functions in tetrairon(III) single-molecule magnets: synthesis and physical characterization.

Tetrairon(III) complexes with a propeller-like structure derived from [Fe(4)(OMe)(6)(dpm)(6)] (1) (Hdpm = 2,2,6,6-tetramethylheptane-3,5-dione) are providing a growing class of Single Molecule Magnets (SMMs) displaying unprecedented synthetic flexibility and ease of functionalization. Herein we report the synthesis, crystal structures and magnetic properties of two novel tetrairon(III) SMMs, [Fe(4)(esterC5)(2)(dpm)(6)] (2) and [Fe(4)(amideC5)(2)(dpm)(6)].Et(2)O.4MeOH (3.Et(2)O.4MeOH), in which functionalization of the cluster core is achieved using ester and amido linkages, respectively. To this aim, two new tripodal ligands were prepared by acylation of pentaerythritol (2,2-bis(hydroxymethyl)propane-1,3-diol) and TRIS (2-amino-2-(hydroxymethyl)propane-1,3-diol), namely H(3)esterC5 = RC(O)OCH(2)C(CH(2)OH)(3) and H(3)amideC5 = RC(O)NHC(CH(2)OH)(3) with R = n-butyl. The compounds were structurally investigated by single-crystal XRD, which demonstrated coordination of the tripodal ligands to the cluster core. The products display SMM behavior with anisotropy barriers U(eff)/k(B) congruent with 11 K due to a high-spin (S = 5) ground state and an easy axis anisotropy, described by D = -0.421 cm(-1) in 2 and -0.414 cm(-1) in 3.Et(2)O.4MeOH. The departure of U(eff) from the total splitting of the S = 5 ground multiplet, U/k(B) congruent with 15 K, has to be ascribed to the sizeable rhombic anisotropy that characterizes the two compounds (E = 0.021 cm(-1) in 2 and 0.019 cm(-1) in 3.Et(2)O.4MeOH), as confirmed by master matrix calculations of the temperature-dependent relaxation time.

Redox-driven intramolecular anion translocation between a metal centre and a hydrogen-bond-donating compartment.

Dicationic ligands incorporating two 2,2'-bipyridine units and two imidazolium moieties, [1](2+) and [2](2+), form stable chelate complexes with Cu(II) and Cu(I) in acetonitrile solution. Each Cu(II) complex binds two X(-) ions according to two stepwise equilibria, the first involving the Cu(II) centre and the second involving the bis-imidazolium compartment. Cu(I) complexes are able to host only one NO(3)(-) ion in the bis-imidazolium cavity, while other anions induce demetallation. Thus, in the presence of one equivalent of NO(3)(-), the Cu(II)/Cu(I) redox change makes the anion translocate quickly and reversibly from one binding site to the other within the [Cu(II,I)(1)](4+/3+) system, as demonstrated by cyclic voltammetry and controlled-potential electrolysis experiments.

Synthesis, structures, and magnetic properties of novel mononuclear, tetranuclear, and 1D chain Mn(III) complexes involving three related asymmetrical trianionic ligands.

The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H(3)L(i) (i = 4-6). These ligands are obtained through reaction of salicylaldehyde with "half-units", the latter resulting from monocondensation of different diamines with phenylsalicylate,. Upon deprotonation, L(i) (i = 4-6) possess an inner N(2)O(2) coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor. The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1 crystallizes in the triclinic space group P (No. 2): a = 7.8582(14) A, b = 10.9225(16) A, c = 12.4882(18) A, alpha = 67.231(14) degrees, beta = 72.134(14) degrees, gamma = 82.589(13) degrees, V = 940.6(3) A(3), Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (Nuomicron. 60): a = 23.8283(15) A, b = 11.1605(7) A, c = 26.152(2) A, V = 6954.8(8) A(3), Z = 8, while complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 11.7443(14) A, b = 7.5996(10) A, c = 18.029(2) A, beta = 100.604(10) degrees, V = 1581.6(3) A(3), Z = 4. Owing to hydrogen bonds and pi-pi stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3 are tetranuclear and polymeric (1D chain) species, respectively, owing to the bridging ability of the oxygen atom of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of similarly weak Mn(III)-Mn(III) antiferromagnetic interactions (J = -1.1 cm(-1)). Single ion zero-field splitting of manganese(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J = - 1.1 cm(-1), D(1) = 2.2 cm(-1), D(2) = -2.8 cm(-1)), D(1) and D(2) being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = - 0.2 cm(-1)) operates through pi-pi stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature approximately 7 K) as a result of the spin canting originating from the crystal packing.