National Institute Of Materials Physics - Romania

A theoretical relationship for the dissolution kinetics of thin chalcogenide films is proposed. The influence of light irradiation on the film dissolution is taken into account. The theoretical curves are in good agreement with the experimental dissolution results obtained for As2S3 thin amorphous films.

We report the formation of stable C-70 aggregate forms in o-dichlorobenzene/N-methyl-2-pyrrolidinone (DCB/NMP) and o-dichlorobenzene/acetonitrile (DCB/ACN) mixtures and their characterization by UV-VIS absorption spectroscopy and photoluminescence. As NMP acts on C-70 both as a solvent and reactant due to the unpaired electrons of the amidic nitrogen atom, molecular complexes (C-70/NMP) that aggregate slowly are formed by the binding of the NMP molecule to the fullerene cage. This interaction is seen in the UV-VIS absorption spectra of C-70 in DCB/NMP solvent mixtures by a gradual modification of the absorption spectra when increasing the NMP concentration. On the other hand, DCB and ACN combined form it typical solvent/non-solvent mixture favoring an intense aggregation of fullerenes. This yields to the C-70 clusters formations, having different size, similar to a precipitation process. Their characteristic is an abrupt variation in the absorbance appearing when the ACN is used in a greater extent. This different behavior of C-70 aggregation in DCB/NMP and DCB/ACN mixtures is also seen in their luminescence spectra recorded at different excitation wavelengths. While the PL spectra of C-70 solvated in DCB/NMP solution keeps almost the same modified shape irrespective the NMP concentration, the luminescence spectra Of C-70 in DCB/ACN mixture partially regains the powder C-70 PL signature as the ACN concentration is increased.

Hybrid material based on PbI2 intercalated with 2,2'-bypiridine (BIPY) was investigated by correlated studies of photoluminescence. infrared absorption and Raman spectroscopy. The PbI2(BIPY) intercalated compound has been synthesized by the chemical reaction of K1 and Pb(NO3)(2) in aqueous BIPY solution The optical studies reveal different properties for the hybrid material in comparison with those of pure PbI2 and BIPY. In the photoluminescence spectrum of the intercalated compound. recorded at liquid nitrogen temperature a new intense hand emission with maximum at 2 07 eV is observed. The excitation spectrum reveals it broad hand featured by several maxima at 2.77, 3.34 and 3 70 eV. New absorption bands at about 1589, 1489, 1435, 1312, 1009 cm(-1) are observed in the IR spectrum of PbI2(BIPY). The Raman spectrum of intercalated compound discloses new lines at 67, 83, 127 cm(-1) and the shift of two Raman lines from 994 cm(-1) to 1010 cm(-1) and from 1045 cm(-1) to 1060 cm(-1). A charge transfer process, leading to the formation of lead-BIPY coordination complexes. is considered its responsible for the strong host-guest interaction revealed by almost all experimental data

The structure of nano-carbon objects (ball-like, nanotubes, defected graphenes) has been modeled by a Monte-Carlo computer procedure. The structure of nano-chalcogenides objects based on two-dimensional network of arsenic sulphide has been modeled. The results were compared to the experimental data whenever possible. The structural modelling was proved as a powerful method for predicting new nano-structural elements in various low-dimensional materials.

We show that an anisotropic periodic structure can shape an incident optical beam with a large angular divergence. This is a new application of photonic crystals, which does not require any additional energy source, such as an electric field

Measurements by optical microscopy and spectroscopy were performed on different textile materials (yarn, woven, knitted materials) in order to get their characterization. Thus, using non-specialized classical equipment, the value of the yarn diameter can be estimated. The yarn behavior during the stretching can be directly observed. The observation of the water imbibition by following the shape and stability of a water droplet placed onto the textile material was also developed; in this way the wetting kinetics of different textile materials was obtained. In addition, the spectral properties of woven materials allowed for the study of the modifications induced by different treatments of the woven materials.

Functionalization of PbI2 with polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES) is demonstrated by Raman spectroscopy. Two functionalization methods were used: electrochemical polymerization of aniline onto the PbI2 modified Pt electrode and the mechanico-chemical reaction between PANI and PbI2. The functionalization induces changes in the Raman spectrum of PbI2 that consist in the appearance of new Raman lines with the peaks at 80, 144 and 170 cm(-1) The first line is the signature of the "stacking faults" that disrupt the stacking sequence of layers I-Pb-I atomic layers along the c crystalline axis by the intercalation of polymer molecules The bands at 144 and 170 cm(-1) are attributed to a vibrational mode associated to the Pb-NHR"(2) (R" = C6H4) bond.

The combination of the unique properties of carbon nanotubes (CNTs) with conjugated polymers makes their combined composite materials interesting as multifunctional systems with great potential. Supercapacitors, lithium rechargeable batteries, sensors, photovoltaic cells and photodiodes, optical limiting devices, solar cells, high-resolution printable conductors, electromagnetic absorbers and advanced transistors are among the most promising applications. Knowledge of the molecular structure of such compounds is essential for a better use, and for that reason vibrational spectroscopies are fruitful techniques. Therefore, this feature article presents recent progress in the characterization of composites based on conjugated polymers and carbon nanotubes. The contribution of Raman scattering and FTIR spectroscopy to establish the type of interaction between the two constituents will be discussed for different cases, i.e. bi-layers of polymers and carbon nanotubes, doped conjugated polymers with carbon nanotubes and covalently functionalized carbon nanotubes with conjugated polymers. In addition, surface enhanced Raman scattering (SERS) has also proven to be a suitable technique for characterization by providing signal enhancements, allowing for instance the detection of reactions at interfaces or the exploitation of properties associated with nanostructures. As an example, an extra increase of the Raman signal of a polymer deposited on a carbon nanotube thin film demonstrates the generation of surface plasmons in metallic tubes.

A switching unit can be defined as the smallest unit that preserves the property of switching in memory materials. Atomic switching unit is discussed, molecular switching units are described and supramolecular units in phase change materials are evidenced and discussed. The "commuton", as basic switching unit, could give more insight into the particular properties of the switching phenomena in various solid materials.

The phase change materials are the most important materials in the class of chalcogenides (combination of chalcogens (S, Se and Te) with metalloids or metals). The outstanding property of these materials is the switching from a high electrical resistivity state to low electrical resistivity state and back under a moderate voltage. The thin film materials are used in computer memories, CD and DVD devices with performing speed and storage capacity. We have studied several thin solid films made of Ge-Sb-Te in order to assess the switching quality of different compositions. In order to systemize the whole class of chalcogenide phase change materials we have investigated the correlation between different crystallo-chemical parameters and the ionicity of the elements. Binary and ternary compounds are distributed into several distinct groups. The most favorable phase change materials are situated in a specific range of mean ionicity and mean glass formation ability. The results give the possibility to design new compositions with better switching properties.