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Abstract

The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant X-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant X-ray emission spectra show depletion of the {\pi} electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the X-ray emission spectra attributed to the {\pi} bands show unambiguous changes of the electronic structure upon protonation. By comparing to X-ray absorption measurements, the chemical bonding and electronic configuration is characterized.

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... The second one of the highest intensity at 285.3 eV relates to the transition to the π* orbital of benzene rings. An appearance of the third π* resonance at 286.7 eV is caused by the chemical shift for the atoms bound directly with the nitrogen atoms [42]. The peaks in the range of 288.0- [41][42][43][44][45]. ...
... An appearance of the third π* resonance at 286.7 eV is caused by the chemical shift for the atoms bound directly with the nitrogen atoms [42]. The peaks in the range of 288.0- [41][42][43][44][45]. A weak feature at 290.0 eV is due to the C1s→ 2π*(C-N) transition. ...
... A weak feature at 290.0 eV is due to the C1s→ 2π*(C-N) transition. Two broad features at 294.0 and 302.0 eV are associated with the σ*(C-C) and σ*(C=C) resonances [42,43]. The resonances at 397.4 and 402.3 eV in the N K edge spectra are related to the π* resonance of the imine and amine groups, respectively [41][42][43]. ...
Article
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The effect of sodium dodecyl sulfate and carbon particles/nanotubes on the electropolymerization of aniline from oxalic acid solution onto a graphite electrode was investigated. The morphology and chemical structure of the as-synthesized polyaniline films were studied by means of SEM, XPS, NEXAFS, FTIR, and Raman spectroscopy. The electrochemical characteristics of the films were also analyzed in sulfuric acid solution. It has been shown that in the presence of sodium dodecyl sulfate, the polymerization rate increases significantly. In the synthesized polyaniline films, all imine groups and most of amine groups are protonated, with dodecyl sulfate ions being intercalated in the polymer. In the presence of sodium dodecyl sulfate, plate-like polyaniline forms large agglomerates with an extended surface and high electrochemical activity. It has been shown that the electrodeposition carried out in the presence of sodium dodecyl sulfate and suspended activated graphite particles or carbon nanotubes favors the formation of composite coatings with high specific capacitance.
... was carried out by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS spectroscopy with its high sensitivity to the nature of chemical bonds has been earlier proved to be extremely applicable to the study of chemical structure of PANI, including mechanisms of its formation and protonation degree [31][32][33][34]. The chemical heterogeneity of PANI was also investigated by means of Raman spectroscopy. ...
... The characteristic changes observed in the carbon K edge NEXAFS spectra for the films at different deposition stages are shown in Fig. 4. The assignment of spectral resonances based on various published data [31][32][33][34][45][46][47][48][49] is given in Table 2. The spectra for t = 25 s and t = 100 s correspond predominantly to iron oxalate layer, with only low-intensity peaks (B) from the polymer. ...
... [17,40,41] 810/840/870 γ (C-H) [17,18,40] 1165 δ (C-H) [41,42] 1220 ν (C-N) [17,18,41] 1250 C-N˙+ def. [41] 1340 ν (C-N + ) [17,18] 1410 Phz [17,18] 1470/1490 ν (C=N) [17,18,41,42] 1560 ν (C-C) Q ring [41,42] 1590 ν (C=C) Q ring [17,18,41,42] 1620 ν (C-C) B ring [17,18,41,42] 1640 ν (C-C) Pho, Phz [17,18] ν, stretching; δ, in-plane bending; γ, out-of-plane bending; Q, quinone ring; B, benzene ring; Pho, phenoxazine; Phz, phenazine; ES, emeraldine salt [31,32,48,49] orbitals. Similar mixed states were observed earlier for iron fluoride complexes [50]. ...
Article
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Chemical structure of polyaniline electrodeposited on iron from oxalic acid solution has been studied by means of NEXAFS, Raman, and XPS spectroscopies. The effect of the duration and synthesis conditions (polarization mode, potentials, stirring of the solution) has been analyzed. The as-formed PANI films have revealed a relatively low degree of protonation. It has been shown that stirring of electrolyte has the greatest effect on the chemical structure of the polymer. The deposition from the stirred solution provides smooth and chemically homogeneous films, whereas the deposition from quiescent solutions favors the precipitation of polyaniline particles enriched in pernigraniline fragments. The obtained XPS results verify the adsorption of the polymer through the N2p-Fe3d donor-acceptor interaction between iron atoms and amine groups of polyaniline chains in the film nuclei. The nitrogen K edge NEXAFS spectra, which are very sensitive to the protonation of chains and electronic delocalization, vary significantly, depending on the conditions of PANI electrodeposition.
... Detailed description of electrodeposition parameters and measuring techniques, including technical characteristics of the beamline, as well as mathematical treatment procedure can be found elsewhere [15,[20][21][22]. [18,19,[23][24][25][26][27][28][29] are shown in Table 1. The main resonances, which are discussed in detail in the paper, are marked with the letters from A to I. The films contain oxalate counterions giving strong spectral contribution (D) which may somewhat mask the changes in the carbon K edge spectra arisen from the molecular orientation in the films. ...
... In the C K edge NEXAFS spectra, changing from grazing incidence to normal one leads to growing the intensity of aromatic rings π* resonances (A and B) with simultaneous slight increase in the intensity of σ*(C-C) resonances (E) and slight weakening the σ*(C-H) resonance (C). In the N K edge NEXAFS spectra, the π* resonance of [26,27], 2π* (C=C) [23,24] 290.0 2π* (C-N) [23,24] 292.7 σ* (C-С) oxalate [27] E 294.0 σ* (C-С) [18,19,23,24] 298.3 σ* (C-O) oxalate [27] 302.6 σ* (C-С) [ imine groups (F and G) is stronger at normal incidence. Relatively weak changes in intensity are also observed for the resonances H and I. Growing the π* resonances intensity in the C K edge NEXAFS spectra points out to predominant upright arrangement of aromatic rings relative to the substrate plane in particles. ...
... In the C K edge NEXAFS spectra, changing from grazing incidence to normal one leads to growing the intensity of aromatic rings π* resonances (A and B) with simultaneous slight increase in the intensity of σ*(C-C) resonances (E) and slight weakening the σ*(C-H) resonance (C). In the N K edge NEXAFS spectra, the π* resonance of [26,27], 2π* (C=C) [23,24] 290.0 2π* (C-N) [23,24] 292.7 σ* (C-С) oxalate [27] E 294.0 σ* (C-С) [18,19,23,24] 298.3 σ* (C-O) oxalate [27] 302.6 σ* (C-С) [ imine groups (F and G) is stronger at normal incidence. Relatively weak changes in intensity are also observed for the resonances H and I. Growing the π* resonances intensity in the C K edge NEXAFS spectra points out to predominant upright arrangement of aromatic rings relative to the substrate plane in particles. ...
Article
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The linear dichroism in the near-edge X-ray absorption fine structure (NEXAFS) spectra measured at the K edges of carbon and nitrogen was used to analyze the molecular orientation in the polyaniline films electrodeposited on iron from oxalic acid solutions under various conditions (cyclic/potentiostatic polarization, potential magnitude, duration, and quiescent/stirred solution). Most of smooth and chemically homogeneous films deposited from stirred solutions did not reveal any dichroism of X-ray absorption, which indicates no specific spatial arrangement of polyaniline molecules in them. Distinct dichroism in the spectra of both absorption edges was observed only for the films containing a great number of particles accumulating on the surface under deposition from quiescent solutions or long-term deposition. The changes observed in the spectra suggest predominant arrangement of most polyaniline chains in-plane the surface with aromatic rings oriented predominantly perpendicular to the surface. The features of molecular arrangement in electrodeposited polyaniline are compared with polypyrrole films. The influence of the observed molecular arrangement on the protective characteristics of the films is also discussed.
... The lone pair electrons on the sp 2 hybrid orbitals of N formed a σ bond with Mo in addition to the dπ−pπ bonding. 67 The dotted line in Figure 8a depicted the CV of the 1%MP composite, which gave the maximum capacitance of 657.5F/g. The shift in the anodic peak from 0.18 to 0.24 V is evident in the CV curves and is due to the formation of the Mo−N bond that is indicated in the IR spectra and confirmed by the XPS spectra. ...
... For electrochemical polymerization, a three-electrode convention in electrochemical cell is used. The working electrode, i.e., the electrode on which the desired reaction takes place, can be an inert metal (e.g., Au, Pt, and Ti) [32][33][34][35][36][37][38], a carbon material (e.g., glassy carbon, GC, pyrolytic graphite, PG, and boron-doped diamond (BDD)) [17,23,[39][40][41][42][43][44][45], a conducting glass (e.g., indium tin oxide (ITO)) [46][47][48], or an alloy. The nature of the working electrode surface [49] influences the ease of the monomer oxidation, the rate of polymerization, and the growth of the polymer films. ...
Chapter
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Advances in molecular electronic devices such as sensors, organic solar cells, and organic light emitting diodes have increased the interest and research on electrosynthetic conducting polymers. This chapter focuses on electrochemical polymerization (or electropolymerization) as a cost-effective and easy-to-use method for the preparation of electrosynthetic conducting polymer films. Electropolymerized materials, characteristically, possess unique morphological, physical, electronic, and electrochemical proprieties which make them amenable to various applications. Electropolymerization is initiated by the oxidation of a monomer in an electrochemical cell, followed by the growth of the polymer film on the surface of the working electrode, which may be a carbonaceous, a metallic, or a conducting glass material. As the oxidation of the monomer is voltage- or current-induced, electrochemical polymerization is, therefore, a green chemistry methodology. Being devoid of the use of toxic oxidants, the technique ensures real-time controlled production of very high purity conducting polymer films. The films exhibit excellent electrical, electronic, magnetic, optical, and rheological properties. Polyaniline films in their pristine and doped forms and the films of other conducting polymers are discussed in this chapter.
... PAni has controlled conductivity and distinct doping interaction, which makes this material suitable for diverse potential applications (10). Both doped, conducting form (emeraldine salt) and de-doped, insulating form (emeraldine base) of PAni exhibit thermal and environmental stability (11)(12)(13)(14). ...
Article
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The addition of polyaniline emeraldine base dissolved in N-methyl-2-pyrrolidone (PAni/NMP) on fullerene C60 whiskers (FW) by direct-mixing technique resulted to the formation of a hybrid material herein called FW/PAni hybrid. The FW/PAni hybrid has a tubular structure with pleated surface texture. It is thinly coated with PAni and has a higher surface area relative to pristine FW and PAni. Beneath the amorphous outer covering, the hybrid shows a crystalline structure as shown by high resolution TEM and selected area electron diffraction. Charge transfer (CT) interaction from electron-rich PAni to electron deficient FW may have resulted to the physical chain entanglement of PAni to FW. The tubular structure of the hybrid is likely caused by the lone pair electrons present in both NMP and PAni causing dissolution inside the whisker. The FW/PAni hybrid having a large surface area and narrow pore size distribution has potential use as hydrogen adsorbent for fuel cell applications, catalysts, and templates for nanofabrication.
... Consequently, for the polymerization charge of 7.9 mAh, and for the theoretical doping degree of 0.5 (two sulfate anions per polymer units) [17,33], available dedoping charge can be estimated to 0.8 mAh, which was in excellent agreement with experimentally obtained value. For the further calculations of the specific values, it was necessary to calculate the as synthesized PANI mass. ...
Article
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The electrochemically synthesized polyaniline and lead sulfate are investigated as a possible active material of the aqueous based hybrid asymmetric supercapacitors. The electrochemical characteristics of polyaniline (doping-dedoping reactions), as well as electrical characteristics (specific capacitance, capacity, energy, and power) of the PbSO4|PANI cell, are determined. Based on the estimated specific energy and power, it is suggested that investigated cell could be classified as “supercapattery” type of electrochemical power sources.
... 17 Figure 2b compares the N 1s XANES spectra of undamaged and substantially damaged PAN. The spectroscopic variations of damaged PAN at the N 1s edge are the decrease of the N 1s ¡ * C'N transition at 399.8 eV and a rise of the pre-edge feature at 398.7 eV, which is attributed to the formation of C=N double bonds, similar to the N 1s ¡ * C=N transitions in polyaniline 40 and in quinoide molecules. 41 Similar N 1s spectroscopic changes were also ob-served in soft X-ray radiation damage to amide functional groups in amino acids 42 and proteins, 20 which attributed the created pre-edge features to the formation of C-N multiple bonds or C=N bonds with different local environments. ...
Article
Soft X-rays induced radiation chemistry in selected Fe molecular compounds and some aliphatic polymers was studied using soft X-ray absorption spectroscopy, and scanning transmission X-ray microscopy. X-ray absorption near-edge structure (XANES) spectroscopy was used to elucidate the radiation chemistry. The results show that damage to the Fe molecular complexes involves Fe-ligand bond breaking, ligand damage and subsequent photoreduction of Fe(III) if it is not tightly bonded to oxygen. Upon radiation damage, polymer PAN primarily undergoes chemical structure changes without mass loss, PECA experiences chemical structure changes as well as small mass loss, while PPC and PEC suffer large mass loss with chemical structure changes. These studies are not only important to X-ray analysis of radiation sensitive materials, but also are valuable to the applications of X-ray lithography and other types of nanofabrication involving photoresist.
... Moreover, the presence of dopants through physico-chemical interactions can control and stabilize the conductivity of polyaniline (Albu et al., 2016). The electronic structure of polyaniline doped with camphor sulfonic acid and 2-propanesulphic acid has been reported by Magnuson et al. (Magnuson, Guo, & Butorin, 1999). It has been shown that the use of sulfuric acid and p-toluene sulfonic acid dopants enhances both ac conductivity and electrochemical properties of polyaniline (Bhandari & Khastgir, 2015). ...
Article
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A series of novel ionic cross-linked chitosan (CS) based hybrid nanocomposites were prepared by using polyaniline/nano silica (PAni/SiO2) as inorganic filler and sulfuric acid as an ionic cross-linking agent. The CS-PAni/SiO2 nanocomposites show enhanced mechanical properties and improved oxidative stabilities. These nanocomposites can be effectively used as environmental friendly proton exchange membranes. Incorporation of PAni/SiO2 into CS matrix enhances water uptake and facilitates the phase separation which enables the formation of hydrophilic domains and improves the proton transport. Moreover, the doped polyaniline also provides some additional pathways for proton conduction. The membrane containing 3 wt% loading of PAni/SiO2 in chitosan (CS-PAni/SiO2-3) exhibits high proton conductivity at 80 °C (8.39 × 10⁻³ S cm⁻¹) in fully hydrated state due to its excellent water retention properties. Moreover, methanol permeability of the ionic cross-linked CS-PAni/SiO2 nanocomposite membranes significantly reduces with the addition of PAni/SiO2 nano particles. The CS-PAni/SiO2-3 composite membrane displays the best overall performance as a polymer electrolyte membrane.
... The electronic properties of a nanotube change in correspondence to its structure; thus armchair nanotubes are metallic, while zigzag and chiral can be either metallic or "semiconducting" [92]. In general, [96][97][98][99] The polyaniline, probably the earliest known synthetic polymer, refer to It has been found that polyaniline can presence in three different state, They are the "leucoemeraldine" oxidation state, the "emeraldine" oxidation state, and the "pernigraniline" oxidation state. Other oxidation states are the result of physical mixture of these oxidation states. ...
Thesis
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ABSTRACT Six different hydrogels were prepared and they were ; (CPG) from crosslinking between chitosan and poly(vinyl alcohol )by glutaraldehyde as crosslinker agent, (CPM) from crosslinking between chitosan and poly (vinyl alcohol) by maleic anhydride, (PPM) from also crosslinking between pectin and poly (vinyl alcohol) by maleic anhydride, (PgA) by grafted polymerization of acrylic acid monomer on poly(vinyl alcohol) backbone under N2 with free radical polymerization, (CgA) synthesis with same method by grafted polymerization of acryl amide monomer on chitosan backbone , and (IPN) by interpenetrating chitosan-poly(acrylic acid-co-acryl amide)hydrogel. The thermal properties of hydrogel were studied by Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and characterization by Fourier Transform Infrared Spectroscopy ( FTIR), X-ray diffraction (XRD), and used Atomic Force Microscopy(AFM) for studying surface topography. Conductive poly aniline was prepared by oxidation of aniline with ammonium persulfate and different nanomatrials were prepared which include, graphene oxide nanosheets (GO) was prepared by Hummer’s method by oxidation of graphite with concentrated H2SO4, NaNO3, KMnO4. Graphene nanosheets (G) were prepared by reduction GO with hydrazine hydride. Fe3O4 MNPs was prepared by co-precipitation method followed by coating with conductive hydrogel (CPG/PANI) which synthesis from crosslinking between chitosan and poly (vinyl alcohol) by glutaraldehyde as crosslinker agent to form (CPG) hydrogel during poly aniline (PANI) polymerization. The coated form (CPG/Fe3O4/PANI) was obtained. This coated magnetite form (CPG/Fe3O4/PANI) has magnetic-electro sensitive. Fe3O4 MNPs pure and coated form (CPG/Fe3O4/PANI) were characterized by XRD, TEM, SEM, AFM & EDS. The average size of nanoparticles was found to be about (11-13) nm for uncoated and (12-14)nm for coated forms. Magnetic properties were studied for coated and uncoated magnetite by vibrating sample magnetometer (VSM) for study hysteresis loop, the hysteresis loop is completely reversible, the hysteresis has an "S" shape where both the descending and ascending loops coincide and yield zero coercivity, indicating that the magnetite nanoparticles are superparamagnetic . Also multiwall carbon nanotube (MWCNTs) was purchased from CheapTubes Company to prepared conductive hydrogel composite. Then was prepared the conductive hydrogels composite which include (hydrogel/PANI), (hydrogel/G) and (hydrogel/MWCNTs). All of hydrogels and hydrogel composite were characterized by FTIR spectroscopy, X-ray diffraction, AFM and some nanocomposite was characterization by SEM. Hydrogel and hydrogel composite were swelled with water at different periods. It was found the PgA hydrogel has the highest degree of swelling equals to S=15.1314, for PANI composite, the PPM/PANI hydrogels composite has the highest degree of swelling (S= 2.2515), for G composite, the PPM/G has the highest degree of swelling (S=5.1151), for MWCNTs composite, the PPM/MWCNTs has the highest degree of swelling (S=11.6776). The conductivity properties for hydrogel and hydrogel composite were studied by LCR meter over the frequencies range (100Hz-100 KHz) at room temperature. LCR measurement indicated that, all hydrogels have insulation electric properties while when they were modified with PANI, G, MWCNTs, they were transformed to be semi conductors. For nanomatrials, MWCNTs has the highest electric conductivity (σ=2.5305 S/m at 100 KHz), while for nanocomposite hydrogels, CPG/MWCNTs has the highest electric conductivity ( σ=1.9669 S/m at 100KHz). The conductive hydrogel nanocomposites were loaded with indigo carmine dye, which was used as drug model and tested for drug release with times by UV-Vis spectrophotometer at room temperature and applied voltages 8V for PANI composite, 2 V for G & MWCNTs composite in phosphate buffer solution (pH=7.4). It was found that CPG composite has the highest value of drug release, the maximum drug release of CPG/PANI was 13.026%, maximum drug release of (CPG/G) was 33.097%, and maximum drug release of CPG/ MWCNTs was 55.072%. Repeat the study of drug release with doxorubicin, methotrexate anticancer drug in addition to indigo carmine was carried for the best composite hydrogel (CPG/PANI), (CPG/Fe3O4/PANI), (CPG/G), & (CPG/MWCNTs) with voltages (3, 5, 8) V for PANI composite, (1,2,3)V for G and MWCNTs nanocomposite and different temperatures (35.5, 37, 38.5ºC). The drug release was increased with increasing voltages for all composite at 37ºC. Doxorubicin hydrochloride loaded on (CPG/MWCNTs) was found to have the highest value of drug release (62.257%) at 2volt and 38.5ºC while Methotrexate loaded on (CPG/MWCNTs) have the highest value of release equal to (43.668%) at 2volt and 38.5ºC. The percentage ratio of drugs release from all nanocomposite hydrogels was found to have the following order: (CPG/MWCNTs) ˃ (CPG/G) ˃(CPG/PANI) ˃(CPG/Fe3O4/PANI).
... For electrochemical polymerization, a three-electrode convention in electrochemical cell is used. The working electrode, i.e., the electrode on which the desired reaction takes place, can be an inert metal (e.g., Au, Pt, and Ti) [32][33][34][35][36][37][38], a carbon material (e.g., glassy carbon, GC, pyrolytic graphite, PG, and boron-doped diamond (BDD)) [17,23,[39][40][41][42][43][44][45], a conducting glass (e.g., indium tin oxide (ITO)) [46][47][48], or an alloy. The nature of the working electrode surface [49] influences the ease of the monomer oxidation, the rate of polymerization, and the growth of the polymer films. ...
... PANI consists of repeat units of benzene rings which are separated by secondary amine groups and a quinoid ring system attached to imine groups [43]. The protonated form of emeraldine is conductive as it can form a semiquinone radical cation [44]. In a study where emeraldine polyaniline was blended with gelatin and then electrospun into nanofibers, the scaffold showed a marked increase in conductivity after incorporation of PANI [45]. ...
Article
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Degenerative neurological disorders and traumatic brain injuries cause significant damage to quality of life and often impact survival. As a result, novel treatments are necessary that can allow for the regeneration of neural tissue. In this work, a new biomimetic scaffold was designed with potential for applications in neural tissue regeneration. To develop the scaffold, we first prepared a new bolaamphiphile that was capable of undergoing self-assembly into nanoribbons at pH 7. Those nanoribbons were then utilized as templates for conjugation with specific proteins known to play a critical role in neural tissue growth. The template (Ile-TMG-Ile) was prepared by conjugating tetramethyleneglutaric acid with isoleucine and the ability of the bolaamphiphile to self-assemble was probed at a pH range of 4 through 9. The nanoribbons formed under neutral conditions were then functionalized step-wise with the basement membrane protein laminin, the neurotropic factor artemin and Type IV collagen. The conductive polymer polyaniline (PANI) was then incorporated through electrostatic and π-π stacking interactions to the scaffold to impart electrical properties. Distinct morphology changes were observed upon conjugation with each layer, which was also accompanied by an increase in Young's Modulus as well as surface roughness. The Young's Modulus of the dried PANI-bound biocomposite scaffolds was found to be 5.5 GPa, indicating the mechanical strength of the scaffold. Thermal phase changes studied indicated broad endothermic peaks upon incorporation of the proteins which were diminished upon binding with PANI. The scaffolds also exhibited in vitro biodegradable behavior over a period of three weeks. Furthermore, we observed cell proliferation and short neurite outgrowths in the presence of rat neural cortical cells, confirming that the scaffolds may be applicable in neural tissue regeneration. The electrochemical properties of the scaffolds were also studied by generating I-V curves by conducting cyclic voltammetry. Thus, we have developed a new biomimetic composite scaffold that may have potential applications in neural tissue regeneration.
... The asymmetric chemical structure of Polyaniline (PANi)(Magnuson et al., 1999) ...
... imine, nitrile and amine which have to be further analyzed in the N K-edge. Here, Fig. 4b, the resonance near 398.6 eV (A′) corresponds most likely to the N 1 s → π* resonance of imine-like N-species 55,62,63 while the intense resonant feature around 399.6 eV (B′) can be attributed to the N 1s → π* transition of nitrile groups (-C≡N). The less intense peak around 401.8 eV (C′) is due to the N 1s → π* transition of amine. ...
Article
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The plasma based synthesis of thin films is frequently used to deposit ultra-thin and pinhole-free films on a wide class of different substrates. However, the synthesis of thin films by means of low temperature plasmas is rather complex due to the great number of different species (neutrals, radicals, ions) that are potentially involved in the deposition process. This contribution deals with polymerization processes in a capacitively coupled discharge operated in a mixture of argon and aniline where the latter is a monomer, which is used for the production of plasma-polymerized polyaniline, a material belonging to the class of conductive polymers. This work will present a particular experimental approach that allows to (partially) distinguish the contribution of different species to the film growth and thus to control to a certain extent the properties of the resulting material. The control of the species flux emerging from the plasma and contributing to the film growth also sheds new light on the deposition process, in particular with respect to the role of the ion component. The analysis of the produced films has been performed by means of Fourier Transform Infrared spectroscopy (FTIR) and Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS).
... This family of polymers is the direct result of the oxidation, under certain conditions, of a combination of monomers. It is one of the most interesting conductive polymers, and has a controllable electrical conductivity which can vary between that of an insulator, a semiconductor and a metal [53], its basic molecular formula consists of 3 (-C6H4 -NH-) benzoid compound unit and one quinoid unit (-N = C6H4 = N-) [54]. ...
... This family of polymers is the direct result of the oxidation, under certain conditions, of a combination of monomers. It is one of the most interesting conductive polymers, and has a controllable electrical conductivity which can vary between that of an insulator, a semiconductor and a metal [53], its basic molecular formula consists of 3 (-C6H4 -NH-) benzoid compound unit and one quinoid unit (-N = C6H4 = N-) [54]. ...
... It is known that PAni is protonated by doping of HCl during the in situ polymerization process and produces a high conductivity ES form [42]. In the doping of PAni with acid, hydrogen ions of acid are added to the chains and bonded to its nitrogen atoms, leading to an increase in polymer conductivity [54,55]. On the other hand, previous researchers have investigated the importance of environmental conditions such as moisture [56][57][58][59]. ...
Article
Complementary resistive switching (CRS) is a suitable method to solve the sneak path problem in passive crossbar arrays. In this work, we fabricated very simple single layered memory devices consisting of indium tin oxide (ITO)/polymer/ITO structures using a conductive polymer, polyaniline (PAni), showing forming-free CRS behavior. The switching mechanism is discussed by the simultaneous protonation/deprotonation process that is a new expression of CRS behavior in memory devices. This mechanism originates from changes in the resistance states between the two different forms of PAni and is influenced only by applying the electric field. For this purpose, PAni nanostructures with different concentrations of hydrochloric acid (HCl) were synthesized, which the structural and morphological characteristics of the specimens confirmed their formation. The electrical conductivity parameter was also discussed, and according to the data obtained from the analyses, increasing the acid concentration reduces the conductivity of PAni nanostructures as a resistive device.
Book
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The engineering and utilization of biocomposites is a research field of major scientific and industrial interest worldwide. Biocomposites include materials that contain at least one biocomponent. The biocomposite area is extensive and spans from structured and solid biocomposites (e.g., reinforced bioabsorbable polymers), films (e.g., antimicrobial barriers), to soft biocomposites (e.g., scaffolds for tissue engineering). Key aspects in this respect are the appropriate engineering and production of biomaterials, nanofibres, bioplastics, their functionalization enabling intelligent and active materials, processes for effective manufacturing of biocomposites and the corresponding characterization for understanding their properties. The current Special Issue Book emphasizes the bio-technological engineering of novel biomaterials and biocomposites, considering also important safety aspects in the production and use of bio- and nanomaterials. It includes: • Synthesis, production, surface modification and applications of novel biomaterials • Hydrogels, films, solid materials • Safety aspects, including cytotoxicity, genotoxicity, immunogenic properties • Microbiological aspects • Scaffolds for tissue engineering • New processing methods, including 3D printing • Encapsulation for controlled release • Characterisation, including structural, physical, chemical, biological and mechanical properties
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Polyaniline doped with CSA/PEO conductive nanofibers were produced by electrospinning. The electrospinning window was determined by using a three level, full factorial experimental design. The combined effects of the humidity, voltage and flow rate on the fiber morphology and diameter were examined demonstrating that the ambient humidity is the critical factor affecting the electrospinning process and determining the electrospinning window for a conductive polymer. Low humidity favors the formation of defect free fibers while high humidity either hinders fiber formation or causes the formation of defects on the fibers either due to jet discharge or due to water absorption and phase separation. High level of doping with CSA led to the formation of crystalline structures. Data fitting was used to explore the behavior of conductive polymers in electrospinning and very good agreement between experimental and theoretical predictions was obtained for only a limited range of experimental conditions, whereas deviation was observed for all other sets of conditions.
Article
The local structure of boron-doped highly oriented graphite films was determined via soft x-ray emission and absorption spectroscopy using synchrotron radiation. Analysis of the BK and CK x-ray emission spectra using the discrete variational-Xalpha molecular orbital method clarified that boron atoms are chemisorbed onto graphite by substituting for carbon atoms in the carbon hexagonal rings. Compared to graphite, boron-doped graphite exhibits spectral differences in the higher edge of the CK x-ray emission spectrum and the CK x-ray absorption edge. Such a spectral profile of boron-doped graphite, which reflects the band structure, is well explained by the chemisorbed boron structure.
Article
Polyaniline (PANI) has been deposited on a carbon template by chemical oxidation of aniline chloride in acidic aqueous medium using sodium persulfate as oxidant. Two kinds of templates were used: array of aligned multiwall carbon nanotubes (CNTs) grown on silicon substrate and ordered mesoporous carbon (OMC) material. Electronic structure of composites was examined using near-edge X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. Analysis of the spectra showed that PANI developed on the CNT surface is mainly protonated while it contains a marked amount of imine (N) nitrogen when deposited into the porous of OMC. Testing of electrochemical cell indicated enhancement of performance of composite electrodes as compared with unsupported PANI. XPS N 1s spectra of composites of PANI with OMC material (PANI/OMC) and aligned multiwall CNTs (PANI/CNT).
Article
The amine headgroup, NH2, in aminothiolate monolayers can often generate unexpectedly rich structures in its N K-edge X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra that are difficult to assign. We have carried out density functional theory (DFT) calculations to study the XPS and NEXAFS of amine headgroup in four different aminothiolate monolayers, namely, aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT), araliphatic 4-aminophenylbutane-1-thiol (APBT), and 3-(4″-amino-1,1′:4′,1″-terphenyl-4-yl)propane-1-thiol (ATPT), with the focus on structure changes caused by protonation, hydrogen bonding, and X-ray damaging. Spectra of all possible saturated and unsaturated species, as well as X-ray damage products, such as imine, nitrile, azo species, and cumulative double bonds, have been thoroughly examined. It is found that extra spectral structures observed in the experimental XPS spectra do not result from protonation but from the formation of a primary ammonium. The X-ray excitation can induce cross-linking between two neighboring molecules to form different complexes that contribute to the π* features in NEXAFS spectra.
Article
Polyaniline (PANI) in its emeraldine salt form was synthesized by chemical method from aniline monomer in the presence of HCl mixed with LiCl and ammonium persulfate as oxidant. Then, a portion of sample was dedoped with NH3 solution and another equal portion was separately postdoped with secondary dopants, such as H2SO4 and HClO4, respectively. Finally, the dried samples of PANI prepared in all its three different forms (emeraldine salt form, undoped emeraldine base, and the two secondary doped forms of PANI) were characterized by UV-visible spectroscopy, cyclic voltammetry (CV) techniques, Fourier transform infrared (FT-IR) spectroscopy, and electrical conductivity measurement. The cyclic voltammograms of PANI in its emeraldine base (PANIEB) determined the electrochemical behavior and the growth mechanisms of the polymer. The FT-IR and UVvis spectra confirmed the expected structural modification up on doping, undoping, and postdoping processes of the polymer. Their measured electrical conductivities were from 0.02 for undoped, 156 for primary doped form, and increasing from 158 to 257 S/cm for those secondary doped PANI. The influence of secondary doping on the electrical conductivity was also investigated from their spectroscopic data which shows dramatic rise in conductivity. The result also shows that secondary doping increased the π conjugation.
Article
Photoemission and atomic force microscopy (AFM) studies have been performed on thin films of polyaniline, carbon nanotubes and nanocomposites made of polyaniline (PANI) and carbon nanotubes (CNT) at different CNT/PANI ratios, in order to characterize their chemical states, as well as to investigate their electronic structure and morphology. Photoemission results show the presence of neutral and charged species in the polymer. The presence of charged species increases with the amount of CNT, indicating that the incorporation of CNT favors the doping level of polyaniline. C1s core level spectra present clear evidence of organization of the nanocomposites films as going from PANI aggregates to more aligned CNT. This observation is corroborated by the AFM results.
Article
An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials.
Article
An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and in operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide material or chemical moiety specific information. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials.
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In this work, single-layered memristors were fabricated with a simple structure based on polyaniline (PAni), and the effect of different concentrations of silver was investigated. Structural analyses confirmed the successful formation of the emeraldine salt (ES) form of PAni as well as the presence of silver in composite samples. In these memristors, a simultaneous protonation/deprotonation process occurred under the influence of applying the electric field that as a new mechanism led to the forming-free complementary resistive switching (CRS) behavior. It was observed that the presence of silver affected not only the switching mechanism, but also the current–voltage (I–V) characteristic of memristor. Accordingly, at the highest concentration, silver changed its behavior from the non-Ohmic to the Ohmic one, thereby reducing the operating voltages of composite devices. Additionally, the retention time and endurance characteristics for 4000 s and 1000 consecutive cycles did not change significantly, indicating the stability of the memristors.
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Fiber Bragg Grating (FBG) sensor coated with PAni was designed as a sensing device in chloroform detection. PAni thin film was synthesized through chemical oxidation method by using aniline (Ani) as a monomer, ammonium persulphate (APS) as an initiator and dioctyl sodium sulfosuccinate (AOT) as a dopant. The chemical structure of PAni thin film was confirmed by using Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectrometer. The conducting behaviour of PAni thin film (1.157 x 10⁻² S/cm) was determined by using four-point probe measurement. In the optical sensor part, FBG was etched in hydrofluoric acid solution (48% HF) to remove the cladding layer on fiber before coated with PAni. The response of this sensor was monitored based on the different of Bragg wavelength shift at ∼1557 nm in an optical spectrum analyzer (OSA) detector. PAni-coated FBG significantly increased in the Bragg wavelength shift (sensitivity = 0.0009) compared with uncoated FBG (sensitivity = 0.0002). The interaction between PAni and chloroform was significantly confirmed by the "polaron peak ratio" (Pf/ Pⁱ) and "quinoid and benzenoid peak ratio" (IQ/ IB) through UV-vis and FTIR spectroscopy analysis. In this study, FBG sensor coated with PAni thin film had been found as an efficient sensor in chloroform detection with fast response time (7 s).
Article
The focus of this paper is on the intermolecular interaction active between polyaniline (PANI) and 10‐camphorsulfonic acid (10CSA). Enantiopure 10CSA, present in the electropolymerization solution, promotes chiral induction in the supramolecular polyaniline polymer (cPANI). Tight integration of experimental data (circular dichroism, CD, near edge X‐ray absorption spectra, NEXAFS, conductive probe atomic force microscopy, CP‐AFM) and theoretical [density functional theory, (DFT)] results allows to unfold the nature of the electronic interaction between PANI and 10CSA and to shed light on the physical interactions inducing the chiral character to bulk pristine non‐chiral PANI: eventually yielding cPANI. The electropolymerization follows a “wet chemistry” method: electrochemical polymerization of aniline in the co‐presence in bulk solution of enantiopure 10‐camphorsulfonic acid (10CSA). The latter is exploited as chirality inductor. The method of integration between experimental results with ab‐initio theoretical calculations, strongly suggests that the chiral induction exerted by the CSA stems from exchange interaction between CSA and PANI. This work studies the camphor sulfonic acid induction of chirality on the supermolecular structure of electropolymerized aniline. The emergence of chirality is also associated to spin filtering properties of the chiral polymer, revealed by conducting probe Atomic Force Microscopy in the presence of a magnetic field. Theoretical results suggest that the chiral induction is due to exchange interaction energy.
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Few-layer graphene on β-SiC(001) functionalized with phenazine dye Neutral Red by means of diazonium chemistry has been studied using X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, photoemission electron microscopy, scanning tunneling microscopy, and density functional theory calculations. The experimental data reveal the formation of a composite phenazine dye/graphene structure with a large energy gap. The molecules in this structure can be oriented both parallel and perpendicular to the graphene surface. According to scanning tunneling spectroscopy and theoretical calculations, the density of electron states in different surface areas depends on the local short-range order and the molecules’ environment. On the other hand, the photoemission spectroscopy study shows that the bottom layers of the few-layer graphene remain intact, which inherently makes the synthesized layered composite a low-dimensional metal/semiconductor heterostructure. In addition, photoemission electron microscopy imaging shows a high homogeneity of the dye-modified graphene on a micrometer scale.
Article
Micro-patterns of conductive polymers are key for various applications in the fields of flexible electronics and sensing. A bottom-up method that allows high-resolution printing without additives is still lacking. Here, such a method is presented based on micro-printing by the laser-induced microbubble technique (LIMBT). Continuous micro-patterning of polyaniline (PANI) was achieved from a dispersion of the Emeraldine base form of PANI (EB-PANI) in n-methyl-2-pyrrolidone (NMP). A focused laser beam is absorbed by the EB-PANI nanoparticles and leads to formation of a microbubble, followed by convection currents, which rapidly pin EB-PANI nanoparticles to the bubble/substrate interface. Micro-Raman spectra confirmed that the printed patterns preserve the molecular structure of EB-PANI. A simple transformation of the printed lines to the conducting Emeraldine salt form of PANI (ES-PANI) was achieved by doping with various acid solutions. The hypothesized deposition mechanism was verified, and the resulting structures were characterized by microscopic methods. The micro-structures displayed conductivity of 3.8×10⁻¹ S/cm upon HCl doping and 1.5×10⁻¹ S/cm upon H2SO4 doping, on par with state-of-the-art patterning methods. High fidelity control over the width of the printed lines down to ~650 nm was accomplished by varying the laser power and microscope stage velocity. This straightforward bottom-up method using low power lasers offers an alternative to current microfabrication techniques.
Article
From genetics to material to behavior Introducing new genes into an organism can endow new biochemical functions or change the patterns of existing functions, but extending these manipulations to structure at the tissue level is challenging. Combining genetic engineering and polymer chemistry, Liu et al. directly leveraged complex cellular architectures of living organisms to synthesize, fabricate, and assemble bioelectronic materials (see the Perspective by Otto and Schmidt). An engineered enzyme expressed in genetically targeted neurons synthesized conductive polymers in tissues of freely moving animals. These polymers enabled modulation of membrane properties in specific neuron populations and manipulation of behavior in living animals. Science , this issue p. 1372 ; see also p. 1303
Article
In the present paper, we report about synthesis of nanostructured organic–inorganic heterojunction of CdS/Polyaniline/CuInSe2 thin films by cost effective chemical route at room temperature, for solar cell application. As such obtained thin films are characterized for structural, compositional, morphological, optical and electrical properties by X-ray diffraction (XRD) pattern, energy dispersive X-ray (EDAX) analysis, scanning electron microscopy (SEM), optical absorbance spectra and I–V response respectively. The XRD reveals the polycrystalline nature of the thin films having tetragonal crystal structure and a crystallite size of 19nm. The presence of observed and expected elements in the EDAX spectra confirms the elemental compositions in CdS/Polyaniline/CuInSe2 thin films. From SEM images it can be inferred that the surface morphology of the Polyaniline thin films exists like clothing fibers, while CdS/CuInSe2 shows granular shape particles distributed over the substrate and the SEM of CdS/Polyaniline/CuInSe2 represents mixing and attachment of circular particles to fiber like structure. The optical absorbance spectra have shown red shift in absorbance strength and energy band gap value of CdS/CuInSe2 from ~1.36eV to ~1.62eV upon formation of CdS/Polyaniline/CuInSe2 thin film. The I–V response of CdS/CuInSe2 and CdS/Polyaniline/CuInSe2 measured under dark and illumination to 100mW/cm2 light, exhibited the solar characteristics from these graphs and the conversion efficiency calculated is observed to be 0.26 and 0.55% for CdS/CuInSe2 and CdS/Polyaniline/CuInSe2 thin films respectively.
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We present the parametrization of nitrogen for use in the valence effective Hamiltonian (VEH) technique. We describe five different parametrization schemes and discuss the quality of the results each of them affords. The VEH method is then applied to the study of the electronic structure of nitrogen containing polymers of interest with regard to the conducting polymers area. These polymers include polypyrrole, poly‐β‐dimethylpyrrole, poly‐N‐methylpyrrole, pyrolized polyacrylonitrile, paracyanogen (polypyrazinopyrazine), and polymethineimine [CH=N]x. Parameters related to the conductivity properties upon doping such as ionization potentials, bandgaps, and bandwidths, are discussed in detail.
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The effect of charge-transfer doping on the geometric and electronic structures of conjugated polymers has been investigated at the ab initio level with explicit consideration of the doping agents. Three systems were chosen for study as prototypical examples of conjugated polymers with nondegenerate ground states: polyparaphenylene, polypyrrole, and polythiophene. As a result of charge transfer with electron-donating dopants, extra charges appear on the polymer chains and induce strong geometry modifications. The lattice evolves from an aromatic structure towards a quinoid-like structure. Charged defects associated with lattice deformations such as spinless bipolarons are formed. The influence on the electronic structure of the polymer chains is such that with respect to the undoped case, new states appear within the gap. For the maximum doping levels experimentally achieved, band-structure calculations demonstrate that the states in the gap overlap to form bipolaron bands, a few tenths of an electron volt wide. The presence of these bipolaron bands is consistent with optical data as well as with magnetic data which suggest that the charge carriers in the highly conducting regime are spinless.
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We present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed optical transitions. These results are in marked contrast with the electronic structure of other doped conducting polymers, in that only one single broad polaron band appears deep in the gap together with a very narrow band nearly degenerate with the conduction-band edge.
Article
It is shown here that poly(p-phenylene vinylene), prepared by way of a solution-processable precursor, can be used as the active element in a large-area LED. The combination of good structural properties of this polymer, its ease of fabrication, and light emission in the green-yellow part of the spectrum with reasonably high efficiency suggest that the polymer can be used for the development of large-area light-emitting displays.
Article
High-resolution ultra-soft X-ray (USX) emission spectra of gaseous aminobenzene (aniline) are presented for the first time. The spectra are excited by an electron beam and recorded with a grazing incidence technique. Interpretation of the spectra is made with the aid of ab initio SCF calculations of the X-ray intensities and electron spectroscopic data. The analysis gives strong support to a previously suggested assignment of the valence photoelectron spectrum. An observed difference in bandwidth between the carbon K and nitrogen K transitions to the outermost valence state is discussed in terms of vibrational excitations.
Article
Solution-state 13C nuclear magnetic resonance spectra are presented for the emeraldine base and leucoemeraldine base forms of polyaniline. The bulk of the leucoemeraldine base sample gives a simple two-line spectrum, which is readily assignable. The emeraldine base samples give spectra of much greater complexity, showing many more lines than there are carbons in the postulated chain repeat unit. This is rationalized in terms of slow interchange of the many conformers available to the emeraldine base form. A quantitative ‘region assignment’ is made. Gel permeation chromatography measurements show that interconversion between the two forms is achieved without either significant crosslinking or chain scission. The minor peaks in the spectrum of the leucoemeraldine base form due to chain defects (including chain ends) are compared with chemical shift values calculated for postulated structures, and some structures can be rejected on the basis of this.
Article
Doped polyacetylene forms a new class of conducting polymers in which the electrical conductivity can be systematically and continuously varied over a range of eleven orders of magnitude. Transport studies and far-infrared transmission measurements imply a metal-to-insulator transition at dopant concentrations near 1%.
Article
Soft x-ray bands in region 50-500A from Li, Be, C, Na, Mg, Al, Si and Ba targets. A 2-meter grazing-incidence spectrograph was used. The bands (except those for Ba) correspond to transitions of outer (or conduction) electrons into a vacant K- or L-shell. The diffuseness of the bands is associated with the energy spread of the filled conduction electron levels. The Ba band is an O-->N transition. The other metal bands extend over a fairly wide wave-length region and each has a sharp short wave-length edge which corresponds to the sharp "surface" of the filled conduction electron levels. The bands of C and Si have a more diffuse head which is connected with their semiconducting property. The energy spread of the metal bands may be calculated approximately from the Sommerfeld theory of metals; this provides a method of determining uniquely the number of conduction-electrons per atom in a metal. But the explanation of the precise shapes of the bands will require a more detailed theory and in particular an investigation of the transition probability of a conduction electron into a K- or L-shell. Some discussion is added on the absolute energies involved in the transitions which give rise to the bands.
Article
The X-ray absorption and electron yield spectra of monomeric pyrrole including derivatives with different substituents, thiazole and oxazole have been investigated. Inductive and mesomeric effects on the spectral features are discussed. Inductive effects create energy shifts of the π∗ resonances: mesomeric effects cause a splitting and energy shifts of the π∗ resonances.
Article
X-ray absorption and photoelectron spectra of polyaniline were investigated in order to characterize the chemical bonding of its nitrogen atoms. The identification of neutral and charged nitrogen groups is of special interest. X-ray absorption near-edge structure (XANES) at the nitrogen K edge shows characteristic resonance structures reflecting transitions from the N1s core-level into unoccupied states. For comparison N1s X-ray photoelectron spectra were recorded representing the initial state of the N1s−12p(π∗σ∗) transitions. Due to the increasing energy differences between the N1s initial state and the unoccupied π and σ states, discrete final states, originating from the different chemical bonding at the nitrogen atom (N, NH+  and NH), were resolved in the N K XANES.
Article
Oscillator strengths for C 1s, N 1s, and O 1s excitation spectra of aniline, nitrobenzene, and the isomeric nitroanilines have been derived from inner-shell electron energy loss spectroscopy recorded under low momentum transfer conditions (> 2.5 keV impact energy and small scattering angle, θ ≤ 2°). Extended Hückel Molecular Orbital (EHMO) calculations carried out within the equivalent core analogy are used to aid spectral interpretation. These spectra are used to investigate the sensitivity of core excitation spectroscopy to charge transfer interactions in aromatic molecules that have both electron-donating and electron-withdrawing substituents. Strong multielectron excitation features were not found, although these had been anticipated from photoemission studies. The C 1s → π* and N 1s (NH2) → π* spectral features of the nitroanilines are found to be strongly dependent on the substitution pattern (ortho, meta, or para). Key words: electronic structure, inner-shell excitation, nitroanilines, EHMO calculations.
Article
The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds. © 1998 American Institute of Physics.
Article
It is shown that the optical transition probabilities for transitions from the conduction levels in metals to the K- and L-levels may vary strongly within the lowest allowed zone, and will also depend on the azimuthal quantum number of the final state. An explanation is given of the form of the x-ray emission bands observed by O'Bryan and Skinner for Li, Be, Mg, Al.
Article
Oscillator strengths for C Is and 0 ls excitation of gas-phase p-benzoquinone, hydroquinone, and phenol have been derived from electron energy loss spectra recorded under electric dipole scattering conditions. Spectral assignments have been aided by extended Huckel (EHMO) calculations carried out within the equivalent core analogy, as well as by comparisons to previously recorded spectra of benzene, acrylic acid, 1,4-cyclohexanedione, and acetone. Two methods of relating EHMO results to experimental core excitation spectra are explored. That derived from the complete charge matrix is found to be preferable. Several features of the C 1s spectrum of p-benzoquinone can be associated with the quinoid structure of this species, namely a second pi* resonance more intense than the first, and a shift of the C ls(C=C) --> pi*LUMO(b2g) transition to 1.6 eV below that of the lowest C ls --> pi* transition in benzenoid species. This shift is associated with the loss of aromatic stabilization. EHMO calculations of p-benzoquinone in nonequilibrium geometries and of related molecules provide further insight into spectral assignments.
Article
X-ray photoelectron spectroscopy has been used to investigate the atomic species, and their bonding, within the conductive polymer polyaniline (PANi). PANi was grown electrochemically using HCl as the electrolyte ion and all three of PANi's oxidation states were investigated. Measurements of the C 1s, N 1s, O 1s and Cl 2p core levels and the valence band have been made on each of these oxidation states. Bond potential model calculations have been used to aid the analysis of the observed spectra. The main findings of this work show that semi-quinone radical cations are the dominant species in the conductive form, and that these are localized. Furthermore, evidence is given to verify that hydrolysis accounts for the principal polymer electrochemical degradation process, and that ring substitution of the halogen counter ion also occurs. Valence band measurements indicate a 30-40 degrees torsion angle between adjacent rings along the polymer backbone. The results are discussed in terms of previously reported oxidation mechanisms.
Article
The first all-organic electronic device to boast the same characteristics as silicon-based ones is reported. Not only does the use of an organic insulating layer result in an increased charge-carrier mobility in the semiconductor, but it also imparts a flexible quality to the whole device which allows it to be rolled up, bent or twisted without reducing performance. The organic-based devices also show remarkable tolerance towards moisture and impurities, production being possible in the normal laboratory environment.
Article
Ultraviolet photoemission spectra were measured for two conducting polymers; PF−6 doped polypyrrole and camphorsulfonic acid doped polyaniline. The valence band structures at the binding energies between 5 eV and 15 eV are attributed to the π and σ bands on both samples. Although the finite spectral intensity at the Fermi level was observed in polypyrrole, that of polyaniline was extremely small. This shows that the electronic state is more metallic in polypyrrole than in polyaniline, which is consistent with the results obtained through magnetic resonance, electrical resistance and X-ray measurements.
Article
The performance of ALS beamline 7.0 is described. This is an integrated system for delivering radiation from a 5 cm period undulator to spectroscopy and microscopy experiments across the range of photon energies from 60 to 1200 eV. The beamline is engineered to deliver the highest possible flux, with negligible deformation of the optic surfaces due to heating. Two experiment stations are served with rapid interchangeability. The measured operational parameters, the resolution and flux delivered, and the refocus of the light into a small spot at the experiment are all discussed. © 1995 American Institute of Physics.
Article
Soft x‐ray emission spectroscopy is a common tool for the study of the electronic structure of molecules and solids. However, the interpretation of spectra is sometimes made difficult by overlaying lines due to satellite transitions or close‐lying core holes. Also, irrelevant inner core transitions may accidentally fall in the wavelength region under study. These problems, which often arise for spectra excited with electrons or broadband photon sources can be removed by using monochromatized synchrotron radiation. In addition, one achieves other advantages as well, such as the ability to study resonant behavior. Another important aspect is the softness of this excitation agent, which allows chemically fragile compounds to be investigated. In this work we demonstrate the feasibility of using monochromatized synchrotron radiation to excite soft x‐ray spectra. We also show new results which have been accomplished as a result of the selectivity of the excitation. The work has been carried out using the Flipper I wiggler beamline at HASYLAB in Hamburg using a new grazing incidence instrument designed specifically for this experiment. The photon flux at the Flipper I station (typically 5×10<sup>1</sup><sup>2</sup> photons per second on the sample with a 1% bandpass) is enough to allow soft x‐ray fluorescence spectra to be recorded at relatively high resolution and within reasonable accumulation times (typically, the spectra presented in this work were recorded in 30 min). The spectrometer is based on a new concept which allows the instrument to be quite small, still covering a large wavelength range (10–250 Å). The basic idea involves the use of several fixed mounted gratings and a large two‐dimensional detector. The grating arrangement provides simple mounting within a limited space and, in particular, large spectral range. The detector can be moved in a three‐axis coordinate system in order to cover the- different Rowland curves defined by the different gratings. The arrangement permits the use of gratings with different radii, which further facilitate the achievement of optimum performance over a large range. Two‐dimensional detection is used to allow a large solid angle, without suffering from loss of resolution due to imaging errors. The detector is based on five 2‐in. MCPs with resistive anode read out. The sensitivity of the detector, which is normally very low for soft x rays, especially at grazing angles, is enhanced by CsI coating and by using an entrance electrode.
Article
In this review paper we present some research results on the use of conjugated polymers for electroluminescence (EL). In the introduction a comparison is made between the relative potential for conjugated polymers and the various other classes of EL material. We then discuss the structure and operation of conjugated polymer based devices and the progress that has been made in enhancing their efficiency. The importance of obtaining balanced carrier injection and transport is demonstrated by the effectiveness of multilayer heterostructure devices. A discussion of the likely non-radiative decay processes competing with EL is possible on the basis of earlier studies of the photophysics of the polymer emissive layers. Specific examples of molecular level polymer engineering in copolymer systems are presented and their use to allow lateral patterning of a film is considered. The range of colours available through tuning the polymer π−π∗ energy gap is reported and a discussion of possible future directions for research is given.
Article
Calculations of NEXAFS (Near-Edge X-ray Absorption Fine Structure) spectra of fluorine substituted benzenes, C6H6−nFn, n = 1–6, and of aniline and phenol have been carried out for the purpose of elucidating systematic trends of these spectra on number, position and strength of substituents. It is found that the differential and average shifts of π∗ NEXAFS spectra for the unconnected carbon atoms are very small, which make these spectra excellent fingerprints for a benzene-ring building block. The excitation energy for the connected carbon π∗ spectra fingerprints the substitution strength and the relative intensity fingerprints the multiplicity of substitution, while the positional dependency of either the connected or the unconnected carbon spectra is too small to fingerprint the isomers. Previous assignments of the spectra are critically examined and in some cases revised. critically examined and in some cases revised.
Article
A method for the reproducible production of isotropic free standing camphorsulfonic acid doped polyaniline with a conductivity of (300 +/- 30) S cm(-1) is described. The paper then goes on to describe a method of stretch orienting such films to enhance the conductivity parallel to the draw direction to (890 +/- 30) S cm(-1). This improvement is attributed to orientation of both the crystal and amorphous phases. The samples produced by this method are the first stress oriented predoped polyaniline specimens reported in the literature. Copyright (C) 1996 Elsevier Science Ltd.
Article
Oxidative chemical polymerization of aniline in hydrochloric acid solution at sub-zero temperatures leads to polyaniline with a molecular weight five to ten times higher than that prepared at room temperature. The optimum polymerization temperature to give a polymer with the highest yield and molecular weight has been determined, and solution state C-13 n.m.r. spectroscopy shows that the improved polyaniline has fewer defect sites compared to the standard polymer. Despite these intrinsic improvements, the conductivity is of the same order of magnitude as standard polyaniline. A solvent-cast film of polyaniline camphorsulfonate had a conductivity of 295 S cm(-1), although this rose to 820 S cm(-1) along the stretch direction after the film had been uniaxially oriented. An oriented film cast from N-methyl-2-pyrrolidone solution and protonated with methanesulfonic acid showed a conductivity of 260 S cm(-1) along the stretch direction and 31 S cm(-1) perpendicular to this. Copyright (C) 1996 Elsevier Science Ltd.
Article
We have prepared and characterized polyaniline in the form of thin free-standing films and films formed by spin coating. The films are formed from solution with chemically prepared base polyaniline (emeraldine) which is dissolved in N-methyl-2- pyrrolidone. The films, as prepared and doped with HCl, have conductivities in the range 60-70 S/cm. Optical reflection spectra reveal metallic-like films. Furthermore, we have been able to align the polyaniline (PANi) chains using uniaxial stress. Elongation ratios of up to 650% have been achieved so far. When doped with HCl these films yield conductivities of up to 350 S/cm and anisotropy sigma-parallel to/sigma- perpendicular to of up to 24. Initial polarized reflection spectra reveal optical anisotropy.
Article
Conductive polyaniline (PANi) films have been prepared via a new route comprising 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPSA) as both the protonating acid and the solvating group, and dichloroacetic acid (DCA) as a solvent. The AMPSA content was varied so that between 30 and 100% of the nitrogen sites on polyaniline could be protonated. The temperature dependence of the conductivity of the films was measured between 15 and 300 K. Above 75-115 K, depending upon the protonation level, a negative temperature coefficient was observed. At 240-260 K a new transition was observed, essentially independent of the protonation level, above which the negative temperature dependency becomes much stronger. The conductivity data were fitted using a simple model employed previously for films of polyaniline camphorsulphonate, and comparisons made between the two systems. Differential scanning calorimetry measurements on a series of films showed an endothermic transition centred at 240-254 K, whose magnitude is dependent upon the AMPSA content. This thermal transition is ascribed to increased motion in the AMPSA anions when heated to above the transition temperature. The AMPSA anion may be considered to behave as a side chain ionically bonded to the PANi backbone, whose particular structure will affect the intrachain molecular dynamics, and hence electrical transport properties of the bulk polymer. The observed thermal transition correlates well with the new transition seen in the conductivity data. It was possible to draw films of uniaxially both at room temperature and at 363 K. The room temperature conductivity along the stretch direction was increased to a maximum value of for a film drawn at 363 K, compared to for an undrawn sample. The films are compared to previous results obtained with polyaniline films protonated with 10-camphorsulphonic acid (CSA).
Article
Wet spinning of fibers from a solution of polyaniline doped with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) is reported. The fibers spun into selected coagulation solvents are inherently electrically conductive and can be cold drawn to extensions of >500 % with a concomitant rise in electrical conductivity of similar to 1500 %. The fibers appear to be void free and, when drawn, the strain-hardened fibers show final breaking strains of the order of 50 MPa. These fibers are stable in air and could be produced cheaply on an industrial scale.
Article
A design of a small size grazing incidence instrument is presented, which offers large spectral range and high resolution without sacrificing luminosity. The instrument is particularly suited for use at synchrotron radiation sources since it can be conveniently attached to existing experiment chambers. The basic idea of the design is the use of fixed mounted gratings of diffent radii and groove densities and a big two-dimensional position sensitive detector mounted on a x−y angle table. The design is discussed in some detail and performance is presented.
Article
The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and nonresonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the {\pi} electron bands in line with symmetry selection and momentum conservation rules. The effect is most vizual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of {\sigma} symmetry and are less frequency dependent.
Article
By exploring the monosubstituted benzene compound aniline, we demonstrate that resonance inelastic x-ray spectroscopy of chemically shifted species is {ital site} {ital selective}. Core-excited levels with distinct, super-electron-volt shifts can be resonantly excited and their x-ray emission spectra analyzed separately. Core-excited levels referring to sites with small, sub-electron-volt, chemical shifts give resonant x-ray spectra that interfere strongly. It is demonstrated that this interference, which is manifested in the one-step model, can be used to monitor chemical shifts in the sub-electron-volt energy region. We show that in the limit when these chemical shifts go to zero some salient symmetry-selective features of the benzene resonant x-ray emission spectrum are restored in the aniline spectra.
Article
Resonantly excited x-ray fluorescence spectra of the benzene molecule are presented and analyzed in terms of symmetry-selective resonant scattering processes. The sharp frequency dependency that is observed can be understood from strict parity and symmetry-selection rules operating in the full ${\mathit{D}}_{6\mathit{h}}$ point group symmetry. The experimental results prove that the electronic symmetry is not broken for the lowest unoccupied level involved in the resonant x-ray emission process.
Article
The x-ray fluorescence and absorption of highly oriented pyrolytic graphite have been measured using monochromatic synchrotron radiation. The spectra can be separated into contributions from pi- and sigma-band components by measuring at different angles of incidence and at different emission angles. The shape of the x-ray fluorescence spectra varies dramatically with excitation energy near the C K edge. This dependence on excitation energy can be interpreted within a resonant-inelastic-scattering formalism. The results are compared with previously published band-structure calculations and photoemission results, and demonstrate the potential for using x-ray fluorescence to obtain symmetry-resolved band information.
Article
We present carbon K emission spectra of diamond excited with high-resolution undulator radiation. The valence-band emission spectra are shown to be strongly dependent on the excitation energy, up to 20-30 eV above the C K edge. It is proposed that the dependence is indicative of the resonant inelastic scattering description of these emission spectra, i.e., the absorption-emission process should be described as a single scattering event where the momenta of the photoelectron and the valence hole in the final state are related by momentum conservation.