Infrared and Raman studies of the phase transition in the organic conductor (TTM-TTP)I3

We report the polarized IR reflectance as well as Raman scattering investigations of the organic charge transfer salt (TTM-TTP)I₃ as a function of temperature, below and above the metal–insulator phase transition at T = 160 K. The IR reflectance was measured in the frequency region from 600 to 10,000 cm⁻¹, for the electrical vector of the polarized light parallel and perpendicular to the TTM-TTP stacking axis. For the polarization parallel to stacks the IR spectra are typical for semiconducting charge transfer salts. The electronic part of IR spectra was analysed in terms of a Lorentz model and temperature dependence of the optical transport parameters was determined. For the polarization perpendicular to the stacks we observed two electronic bands at about 5000 and 8000 cm⁻¹. The phase transition at 160 K has nearly no influence on the IR spectrum. The Raman scattering for different excitations (λ = 514.5, 632.6 and 785 nm) was mainly studied within the region of CC stretching vibrations. In this frequency range, three Raman lines at 1426, 1453 and 1486 cm⁻¹ attributed to TTM-TTP molecules are observed. Below 160 K a splitting of the band 1486 cm⁻¹ into two peaks at about 1488 and 1498 cm⁻¹ is found. The intensity and temperature behaviour of the split band at 1498 cm⁻¹ is strongly dependent on sample. The observed spectral modifications are related to an asymmetric deformation of TTM-TTP. Taking into account temperature dependence of bands attributed to the CH stretching and SCH₃ bending vibrations, we suggest that the TTM-TTP deformation can exist also above the phase transition temperature. Above 160 K molecules fluctuate between distorted and symmetrical state forming non-stable domains (pre-transitional effects), but below 160 K the molecular distortion and domains are stable. The existence of electronic band at 5000 cm⁻¹ for the polarization perpendicular to TTM-TTP supports this picture.     

Infrared and Raman studies of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene as a model compound in polyacetylene

The FT-infrared (IR) and Raman spectra of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene (DP₁₀⁻), a polyene molecule with five conjugated CC bonds, were observed in vacuum condition. The IR absorption spectrum for ionic species of polyene molecule was observed for the first time in the experimental method. The CC stretching band of IR absorption has the weak at 1591–1603 cm⁻¹, while the Raman band has the two intense peaks at 1533 and 1574 cm⁻¹. In IR absorption, the in-plane CH bending has the several strong bands between 1448 and 1551 cm⁻¹, whereas the Raman has a strong band used as a marker of negatively charged polyene at 1272 cm⁻¹. The origin of IR and Raman spectra of DP₁₀⁻ is discussed in terms of a polaron model compound in polyacetylene.     

Superconductivity in acenes

The vibronic coupling between the lowest unoccupied molecular orbital (LUMO) and molecular vibrations is calculated and analyzed with respect to a series of acenes. The Raman active CC stretching modes of 1400–1600 cm⁻¹ have large coupling constants in small acenes, while both low Raman active modes of 200–300 cm⁻¹ and CC stretching modes of 1400–1600 cm⁻¹ play an important role in the electron–phonon coupling in large acenes. The possible superconducting transition temperatures of the monoanions of benzene (C₆H₆) and acenes are roughly estimated, on the basis of the hypothesis that vibronic interactions between the LUMO and intramolecular vibrations would play an essential role in the occurrence of superconductivity in these molecules.     

The effect of phosphorus and nitrogen co-doped on the synthesis of diamond at high pressure and high temperature

The synthesis of phosphorus and nitrogen co-doped diamond is investigated in the NiMnCo–C system by adding P₃N₅ or carbonyl iron powders mixed with phosphorus powders under high pressure and high temperature. Experimental results show that the color distribution in diamond crystals with low concentration of P₃N₅ additive is not uniform. The color becomes deep green with the increase of P₃N₅ additive. The optical images and FTIR spectra reveal that the nitrogen atoms are more easily incorporated via {111} than {100} in the same conditions. In addition, the result of FTIR spectra of synthesized diamond indicates that the hydrogen atoms in the form of sp³–CH₂– are more likely to enter the diamond lattice in the P/N co-doped system, compared with the single N-doped system. The absorption peak at 3107 cm^− 1 attributed to vibration of H-related point defects (sp²–CHCH–) is observed in diamonds, which is often found in natural diamonds. The Raman shifting to lower frequency and FWHM value becoming wider are due to the doping of phosphorus atoms.     

Effect of boron doped fullerene C60 film coating on the electrochemical characteristics of silicon thin film anodes for lithium secondary batteries

In this work, boron doped fullerene (B:C₆₀) films were prepared by the radio frequency plasma assisted thermal evaporation technique for use as a coating material for the silicon thin film anode in lithium secondary batteries. Raman and XPS analyses revealed that the boron atoms were well inserted into the fullerene film lattices. The effect of the B:C₆₀ film on the electrochemical characteristics of the silicon thin film was studied by charge–discharge tests, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The B:C₆₀ coated silicon film exhibited a high reversible capacity of more than 1200 mAh g^?1 when cycled 50 times between 0 and 2 V at a current density of 1200 μA cm^?2 (1.5 C). The film also showed good rate capacity at different current densities and a more improved coulombic efficiency of 87.7% in the first cycle in comparison with that of the C₆₀ coated film electrode.     

Structural characterization of poly-para-phenylenediamine–montmorillonite clay nanocomposites

The structure of the poly-(para-phenylenediamine) (PpPD) formed by oxidative polymerization of 1,4-phenylenediamine (p-PD) into the galleries of the Montmorillonite (MMT) clay was determined by different spectroscopic techniques. According to X-ray diffraction (XRD) pattern the polymer is formed between the clay layers. In addition, the composite morphology, visualized by electron microscopy (SEM), is similar to the pristine clay. The UV–vis–NIR data of PpPD–MMT sample shows strong absorption bands at 620 and 670 nm, being related to groups with protonated phenazine-like rings. The resonance Raman spectrum of PpPD–MMT displays bands at 1179, 1201, 1347, 1412, and 1630 cm^?1, which are related to phenazine-like rings modes. X-ray absorption (XANES) at Nitrogen K edge of PpPD–MMT confirms the presence of azo, hydrazo and phenazinic nitrogens. The intercalated material is EPR silent, confirming that the charge carriers, responsible for the conductivity of ca. 10^?4 S cm^?1, have diamagnetic behavior. Hence, the results confirm that when aniline or its derivates are polymerized in confined environments, it causes preferentially the formation of diamagnetic segments having protonated phenazine and azo segments.     

Synthesis of potential capacitive Poly 4, 4′-diaminodiphenyl sulphone–metal nanocomposites and their characterizations

4, 4′-Diaminodiphenyl sulphone was polymerized (with lithium/cobalt/lithium–cobalt salts) by chemical oxidation method using potassium perdisulphate. The solubility of the chemically prepared polymer–metal nanocomposite was ascertained and it showed good solubility in DMF, chloroform, trichloroethylene and DMSO. The PDDS–Li/Co/Li–Co nanocomposites were characterized by UV–vis and FTIR spectral studies. Amine and imine vibrations observed at 1593 and 1503 cm^?1 were shifted to lower wave numbers when the polymer–metal composites were formed. A single absorption peak due to the N–H stretching vibration of the imino groups of polymer–metal nanocomposite is observed around 3459 cm^?1 and it suggests the participation of NH group during polymerization. The X-ray diffraction studies revealed the formation of nano sized (82 nm) crystalline polymer. The conductivity of the PDDS–Li–Co nanocomposite was determined to be 6.26 × 10^?2 S cm^?1. SEM analysis showed mixed granular nature of the polymer–metal nanocomposite. The capacitance (159.04 μF) of chemically synthesized PDDS–Li–Co nanocomposite is suggested as a potential capacitive material.     

Enhanced third-order nonlinear optical property of poly(3-decayl)thiophene films modified by N+ ion implantation

Poly(3-decayl)thiophene (P3DT) films implanted by 30 keV nitrogen ions (N⁺) with the dose range of 10¹⁵–10¹⁷ ions/cm² were characterized by FTIR-ATR spectra, which showed that the C–H bonds of the P3DT films were largely broken and new bonds like CC, CN and CN were formed as the increasing ion fluences. The third-order nonlinear optical susceptibilities (χ⁽³⁾) were measured by degenerate four-wave mixing (DFWM) technique at 532 nm. The results demonstrated that the (χ⁽³⁾) value of P3DT films was maximized to 2.61 × 10^?9 esu at an ion dose of 5.73 × 10¹⁶ ions/cm², which was almost four times larger than that of the pristine film. The enhanced third-order nonlinear properties may attribute to the enlarged expansion coefficient of the bombarded films at proper N⁺ ions dose.     

Covalent linking of ethylene amine functionalized single-walled carbon nanotubes to cobalt (II) tetracarboxyl-phthalocyanines for use in electrocatalysis

In this paper, we report on the use of ethylene amine (EA) side-wall functionalized single-walled carbon nanotubes (SWCNT) in the synthesis of covalently linked cobalt (II) tetracarboxyl-phthalocyanine complex (CoTCPc–EA–SWCNT(linked)), the characterization of the linked complex and the application of this complex in the electrocatalytic oxidation of amitrole. UV–vis, FTIR, TEM, Raman and XRD spectroscopies were used in characterization of CoTCPc–EA–SWCNT complex, while cyclic voltammetry, rotating disc electrode (RDE) voltammetry, chronoamperometry and electrochemical impedance spectroscopy were used during the characterization of amitrole on the modified glassy carbon electrode. Thermogravimetric analysis (TGA) was used to confirm the extend of functionalisation of of SWCNTs. The catalytic rate constant was 1.2 × 10³ M^?1 s^?1 and the apparent electron rate transfer constant was 3.0 × 10^?5 cm s^?1. The linear dynamic range was 1.0 × 10^?5–1.6 × 10^?4 M, with a sensitivity of ～0.76 A mol^?1L cm^?2 and a limit of detection of 0.1 μM using the 3δ notation.     

Spectroscopic investigation of the interactions between emeraldine base polyaniline and Eu(III) ions

The interactions of emeraldine base form of polyaniline (EB-PANI) and Eu(III) ions in 1-methyl-2-pyrrolidinone (NMP) solution and in films have been investigated by UV–vis–NIR, resonance Raman, luminescence and electron paramagnetic resonance (EPR) spectroscopies. These spectroscopic techniques allowed to characterize quinone and semiquinone segments in the polymeric chains, and the oxidation state of europium ions in Eu-PANI samples. For high values of Eu(III)/N molar ratio (24/1) the presence of a weak polaronic absorption band at 980 nm in UV–vis–NIR spectrum and the observation of bands at 1330 and 1378 (ν_C–N+) cm^?1 due to emeraldine salt in the Raman spectrum at 1064 nm indicate a low doping degree. Oxidation of EB-PANI to pernigraniline base (PB-PANI) occurs in diluted solutions. The experimental data showed that the solvent plays an important role on the nature of formed species. The narrow EPR signal at g = 2.006 (line width 8G) confirms the presence of PANI radical cations in Eu-PANI film. The absence of broad signal characteristic of Eu(II) in EPR spectrum suggested that europium ions are primarily at Eu(III) oxidation state. The luminescence spectra of Eu-PANI film presented emission bands at 405 and 418 nm assigned to PANI moieties and bands at 594, 615 and 701 nm assigned to ⁵D₀ → ⁷F_J (J = 1, 2 and 4, respectively) transitions of Eu(III). EPR and photoluminescence data confirm that europium ions are mainly in Eu(III) oxidation state in Eu(III)/PANI films.     

A Novel cathode material based on polyaniline used for lithium/sulfur secondary battery

Polyaniline polysulfide (SPAn) was prepared for high energy secondary lithium batteries as cathode material. Polyaniline was synthesized via a classical chemical oxidation way, and then HCl was used to substitute the H atoms on the 6 member rings, so that polyaniline chloride (CPAn) was gained. The SPAn was prepared by way of substitute the Cl atoms on the aromatic rings of CPAn by S atoms in assistant of Na₂S and element sulfur. Element analysis tests proved that there are more than 7 S atoms on each aniline structural group. FT-IR, Raman and XPS (X-ray photoelectron spectroscopy) analysis were used to confirm the SPAn's configuration. Button type battery was assembled, and charge–discharge test shows an initial discharge capacity of more than 980 mAh g^?1, which is a grafting value.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Solid-state oxidation of aniline hydrochloride with various oxidants

Aniline hydrochloride was oxidized in the solid state with three different oxidants: ammonium peroxydisulfate, iron(III) chloride, and silver nitrate. Polyaniline salt was obtained after a few hours when ammonium peroxydisulfate was used as an oxidant. The polymerization of aniline hydrochloride with silver nitrate leads to polyaniline only after several days; in the case of iron(III) chloride, aniline oligomers were obtained. The conductivity of the polyaniline was 0.21 S cm^?1 when ammonium peroxydisulfate was applied; it is comparable with the conductivity of a ‘standard’ polyaniline. The oxidation with silver nitrate yields a composite material, polyaniline salt and silver particles, with conductivity 1.5 × 10^?3 S cm^?1. Photoacoustic spectroscopy was employed to study the kinetics of the oxidation reaction. Infrared and UV–vis spectra were efficient tools to characterize the final products, and to compare their molecular structure with that of the polyaniline prepared under ‘standard’ conditions in aqueous medium.     

Novel properties of polyaniline nanofibers coated with polycatechol

Polyaniline nanofibers coated with polycatechol, FcPAn/polycatechol, have been prepared with two steps by using repeated potential cycling. First, aniline in a solution containing ferrocenesulfonic acid (Fc) was polymerized on a platinum electrode to form polyaniline nanofibers (FcPAn); second, catechol was polymerized on the polyaniline nanofibers to form FcPAn/polycatechol. The scanning electron microscopy (SEM) images show that the diameters of FcPAn and FcPAn/polycatechol fibers are in the range of 40–60 and 70–90 nm, respectively. The IR and XPS spectra of FcPAn/polycatechol indicate that OH groups and ferrocenesulfonic acid are contained in FcPAn/polycatechol. FcPAn/polycatechol has a good electrochemical activity in the wide pH range. The cyclic voltammogram identifies that FcPAn/polycatechol in the Na₂SO₄ solution with pH 11.0 still has the electrochemical activity at the scan rate of 60 mV s⁻¹. The conductivity of FcPAn/polycatechol is 0.48 S cm⁻¹, which is slightly affected by water. FcPAn/polycatechol nanofibers with the diameter of 70–90 nm have a higher catalytic activity to the electrochemical oxidation of ascorbic acid, compared with FcPAn/polycatechol fibers with the diameter of 140–210 nm.     

The carbonization of granular polyaniline to produce nitrogen-containing carbon

Polyaniline (PANI) was prepared by the oxidative polymerization of aniline. The deprotonated product, a PANI base, was carbonized in an inert atmosphere at temperatures up to 800 °C for various times. The mass decreased to 40–50 wt.% at temperatures above 600 °C. The progress of molecular structure during carbonization was followed by infrared and Raman spectroscopies. The carbonization at 650 °C for 1 h is suggested for the optimum conversion of PANI to carbon. The product retained the original globular structure of PANI. The conductivity of the carbonized material was low for carbonizations below 600 °C, <10^?10 S cm^?1, and increased to 10^?4 S cm^?1 after treatment at 800 °C. The content of nitrogen, ～10 wt.%, was not affected appreciably by the carbonization.     

Corrosion mechanism of a NiCoCrAlTaY coated Mar-M247 superalloy in molten salt vapour

A mechanism of corrosion is proposed relating to a NiCoCrAlTaY coated Mar-M247 superalloy exposure in molten Na₂SO₄ salt vapour at 900 °C. The corrosion process indicates the parabolic “diffusion controlled” region I at rate of 4.6 × 10^?6 mg² cm^?4 s^?1, the combination of parabolic and linear “reaction–diffusion controlled” region II at rate of 2.28 × 10^?5 mg² cm^?4 s^?1 and 4.35 × 10^?5 mg cm^?2 s^?1, and finally the complete “reaction controlled” region III at the same rate of 3.92 × 10^?4 mg cm^?2 s^?1 as the uncoated superalloy. The corrosion kinetics of each region and of the whole process are formulated rationally associated with the corrosion mechanism.     

Properties of single-walled carbon nanotube-based aerogels as a function of nanotube loading

Here, we present the synthesis and characterization of low-density single-walled carbon nanotube-based aerogels (SWNT-CA). Aerogels with varying nanotube loading (0–55 wt.%) and density (20–350 mg cm^?3) were fabricated and characterized by four-probe method, electron microscopy, Raman spectroscopy and nitrogen porosimetry. Several properties of the SWNT-CAs were highly dependent upon nanotube loading. At nanotube loadings of 55 wt.%, shrinkage of the aerogel monoliths during carbonization and drying was almost completely eliminated. Electrical conductivities are improved by an order of magnitude for the SWNT-CA (55 wt.% nanotubes) compared to those of foams without nanotubes. Surface areas as high as 184 m² g^?1 were achieved for SWNT-CAs with greater than 20 wt.% nanotube loading.     

The reduction of silver nitrate to metallic silver inside polyaniline nanotubes and on oligoaniline microspheres

Polyaniline (PANI) reduces silver nitrate to metallic silver. Composites based on conducting polymer and silver have been prepared with equimolar proportions of reactants. Polyaniline bases having different morphologies – granular or nanotubular – and oligoaniline microspheres have been left to react with silver nitrate in acidic, neutral, and alkaline media. The content of silver, typically 20–30 wt.%, was determined by thermogravimetric analysis. Clusters of 40–80 nm silver particles are produced in the granular form of PANI. The formation of silver inside PANI nanotubes has been observed. With oligoaniline microspheres, silver was produced on their surface, and on PANI agglomerates accompanying them. The highest conductivity, 943 S cm^?1, was found with silver reduced by nanotubular PANI base in 0.1 M nitric acid at 17.3 wt.% silver content. The standard granular PANI, used as a reference material, yielded a composite having a much lower conductivity of 8.3 × 10^?5 S cm^?1 at 24.3 wt.% Ag. There is no simple correlation between the conductivity and silver content. Infrared and Raman spectroscopies have been used to study the changes in the molecular structure of the PANI bases of various morphologies before and after reaction with silver nitrate.     

Alkali doped poly(vinyl alcohol) for potential fuel cell applications

Optical transparent, chemically stable alkaline solid polymer electrolyte membranes were prepared by incorporation KOH in poly(vinyl alcohol) (PVA). The distributions of oxygen and potassium in the membrane were characterized by XRD and SEM–EDX. It is demonstrated that combined KOH molecules may exist in the PVA matrix, which allow it to be an ionic conductor. In particular, the chemical and thermal stabilities were investigated by measuring changes of ionic conductivities after conditioned the membrane in various alkaline concentrations at elevated temperatures for 24 h for potential use in fuel cells. The membranes were found very stable even in 10 M KOH solution up to 80 °C without losing any membrane integrity and ionic conductivity due to high dense chemical cross-linking in PVA structure. The measured ionic conductivity of the membrane by AC impedance technique ranged from 2.75 × 10^?4 S cm^?1 to 4.73 × 10^?4 S cm^?1 at room temperature, which was greatly increased to 9.77 × 10^?4 S cm^?1 after high temperature conditioning at 80 °C. Although, a relatively higher water uptake, the methanol uptake of this membrane was one-half of Nafon 115 at room temperature and 6 times lower than that of Nafion 115 after conditioned at 80 °C. The membrane electrolyte assembly (MEA) fabricated with PVA–KOH in direct methanol fuel cell (DMFC) mode showed an initial power density of 6.04 mW cm^?2 at 60 °C and increased to 10.21 mW cm^?2 at 90 °C.     

SERS spectroscopy studies on the electrochemical oxidation of single-walled carbon nanotubes in sulfuric acid solutions

Surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV) were used to investigate oxidation–reduction processes of single-wall carbon nanotube (SWNT) films deposited on Au supports in 0.5 M H₂SO₄ solutions. In the potential range (0; +1000) and (0; +1500) mV versus saturated calomel electrode (SCE), the oxidation–reduction reactions of SWNT films are quasi-reversible and irreversible, respectively. Anodic polarization of SWNT films until +1000 mV versus SCE produced compounds similar to the bisulfate intercalated graphite. Regardless of excitation wavelength, i.e. 1064 or 676.4 nm, variation in the Raman spectra exhibited a decrease in the intensity of the bands associated with the radial breathing mode (RBM) situated in the 120–240 cm⁻¹ spectral range. Also an increase in the intensity of the D band is accompanied an up-shift of this band. A gradual decrease of the Breit–Wigner–Fano component was observed at λ_exc=676.4 nm. Partial restoration of the Raman spectra was achieved by a subsequent alkaline solution treatment. Potentials higher than +1000 mV versus SCE resulted in SWNTs breakage and fragments of different length were formed such as closed-shell fullerene. This was observed in the SERS spectrum by: (i) the disappearance of the RBM band, (ii) the increased D-band shifted to ca. 1330 cm⁻¹ and (iii) the appearance of a new band at 1494 cm⁻¹, frequently observed also in the Raman spectrum of fullerenes on the type C₇₀, C₈₄, C₁₁₉, as well as in its derivative compounds (e.g. C₆₀O, clathrates, etc.). Appearance and increase in the intensity of the Raman band at 1494 cm⁻¹ as result of an anodic polarization of the SWNT film in solution of H₂SO₄ 0.5 M in 1-butanol is a further evidence of the nanotubes breakage.