Non-isothermal crystallization kinetics and nucleation behavior of isotactic polypropylene composites with micro-talc

Journal of Thermal Analysis and Calorimetry - The current investigation has presented a new synthesis technique to prepare pentaethylene glycol-treated graphene nanoplatelets (PEG-GnP) and...     

Surface plasmons reveal spin crossover in nanometric layers

Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale.     

Fe(II)(TRIM)(2)]F(2), the First Example of Spin Conversion Monitored by Molecular Vibrations

The new [Fe(II)(TRIM)(2)]F(2) spin-crossover complex (TRIM = 4-(4-imidazolylmethyl)-2-(2-imidazolylmethyl)imidazole) has been synthesized, crystallizing in the monoclinic system, space group P2/n, with Z = 2, a = 9.798(2) ?, b = 8.433(2) ?, c = 14.597(3) ?, and beta = 90.46(1) degrees. The structure was solved by direct methods and refined to conventional agreement indices R = 0.032 and R(w) = 0.034 with 1378 unique reflections for which I > 3sigma(I). The molecular structure consists of [Fe(TRIM)(2)](2+) complex cations hydrogen-bonded to six fluoride anions. The crystal packing results from this highly symmetrical and dense 3D network of hydrogen bonds. The coordination geometry of the iron(II) center can be described as a weakly distorted octahedron, including six nitrogen atoms originating from the two TRIM ligands coordinated to Fe(II) through their imine nitrogen atoms. Investigation of [Fe(II)(TRIM)(2)]F(2) by magnetic susceptibility measurements and M?ssbauer spectroscopy as a function of temperature indicates a 5% thermal variation of the spin fraction between 50 and 150 K, at variance with all previous litterature data. The spin conversion is gradual with 6% LS fraction below 50 K and less than 1% above 150 K. A theoretical approach based on the Ising-like model, completed with harmonic oscillators associated with the 15 vibration modes of the FeN(6) coordination octahedron, successfully fits the data with an energy gap of approximately 40 K between the lowest LS and HS electrovibrational states, an average vibration frequency omega(LS) of 232 K in the LS state, and an average omega(LS)/omega(HS) ratio of 1.3. Taking these results into account, the computed molar entropy change DeltaS associated with a complete conversion between the HS and LS states of Fe(II)(TRIM)(2)F(2) ( approximately 40 J.K(-)(1).mol(-)(1)) is in fair agreement with the expected value.     

Light induced excited spin state trapping in the binuclear spin crossover compound [Fe(bpym)(NCS)2]2(bpym) exhibiting a high-spin ground state

A photo-magnetic effect is evidenced using near-infrared light in the binuclear complex [Fe(bpym)(NCS)₂]₂(bpym). This compound has a ⁵T_2g–⁵T_2g ground state and exhibits no thermal spin crossover – in contrast to the analogous [Fe(bpym)(NCSe)₂]₂(bpym). The estimated photo-conversion ratio is ca. 30%. By means of magnetic susceptibility measurements as well as Raman and infrared absorption spectroscopies, the nature of the photo-induced phase was established as the ⁵T_2g–¹A_1g state, which means that only one iron center is converted to low-spin. The photo-induced state was completely converted back to the ground state either by visible light excitation or by heating.     

On bistability in molecular systems: Photomagnetic studies of inorganic complexes

Photo‐induced effects have been detected by magnetic measurements, Mössbauer spectroscopy and reflectivity. The LIESST effect has been achieved in the spin‐crossover system [Fe_xCo_1-x(btr)₂(NCS)₂]·H₂O. We investigated the purely photo‐induced magnetism of a Prussian Blue analogue Rb_0.52Co[Fe(CN)₆]_0.84, 2.31 H₂O, involving an optical electron transfer from Fe^II to Co^III. Inherent aspects of photomagnetic experiments are described: bulk and surface effects, magnetic and electronic metastabilities of the photo‐excited state.     

Fabrication and characterization of 1.55 μm single transverse mode large diameter electrically pumped VECSEL

We report on the design, fabrication, and characterization of InP-based 1.55 μm wavelength large diameter (50 μm) electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs). The hybrid device consists of a half vertical cavity surface emitting laser (1/2-VCSEL) structure assembled with a concave dielectric external mirror. The 1/2-VCSEL is monolithically grown on InP substrate and includes a semiconductor Bragg mirror and a tunnel junction for electrical injection. Buried (BTJ) and ion implanted (ITJ) tunnel junction electrical confinement schemes are compared in terms of their thermal and electrical characteristics. Lower thermal resistance values are measured for BJT, but reduced current crowding effects and uniform current injection are evidenced for ITJ. Using the ITJ technique, we demonstrate Room-Temperature (RT) continuous-wave (CW) single transverse mode laser operation from 50-μm diameter EP-VECSEL devices. We show that the experimental laser optical output versus injected current (L–I) curves are well-reproduced by a simple analytical thermal model, consistent with the thermal resistance measurements performed on the 1/2-VCSEL structure. Our results indicate that thermal heating is the main mechanism limiting the maximum CW output power of 50-μm diameter VECSELs, rather than current injection inhomogeneity.