Study of the evolution of the conductivity of iodine-doped poly(N-vinylcarbazole) as a function of annealing treatment

Electron spin resonance (ESR) and d.c. conductivity measurements on iodine-doped poly(N-vinylcarbazole) (PVK) as a function of annealing treatment was performed. When doped at room temperature as at 370 K, the appearance of an ESR signal and the increase of the conductivity can be explained by CT complex formation between iodine and PVK. The correlation between conductivity σ and spin density N_s was observed as a function of the annealing temperature. At higher annealing temperature, the decrease of the conductivity and of the ESR signal is attributed to the PVK degradation and to the formation of a new conjugated polymer. All these results and their discussion are in good agreement with X-ray diffraction, Raman diffusion, and earlier studies. © 1996 John Wiley & Sons, Inc.     

Tuning PL emission energy and bandgap with Ni dopant of MgO thin films

In this study, for the first time, the effect of Nickel (Ni) additive on Magnesium oxide (MgO) thin films produced by using successive ionic layer adsorption and reaction technique (SILAR) was investigated. Absorption, photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) measurements were executed to examine how the optical, structural and morphological properties of the samples were affected by the addition of Ni. In the absorption analysis, it was noted that the band gaps of the MgO samples decreased from 4 eV to 3.5 eV with the increase of Ni dopant concentrations. Also, the transmittance values of MgO nanostructures decreases with the increase of Ni contribution, and in the same way, the reflection measurements show that the reflection of MgO decreases with the increase of Ni doping. PL measurements revealed that the fabricated structures radiate around 410 nm and 730 nm. According to XRD measurements, besides the cubic structure of the samples, NiO formations were detected inside the MgO thin film samples due to the increase in Ni dopant. XPS measurements have proven the presence of Ni doping in MgO. SEM measurements showed that all samples exhibited nanowall structure. All these results demonstrate that Ni doping on MgO thin films can be achieved by using SILAR deposition technique.     

Defect induced magnetic transition in Co doped CeO2 sputtered thin films

Cobalt-doped cerium dioxide thin films exhibit room temperature ferromagnetism due to high oxygen mobility in doped CeO₂ lattice. CeO₂ is an excellent doping matrix as there is a possibility of it losing oxygen while retaining its structure. This leads to increased oxygen mobility within the fluorite CeO₂ lattice, leading to formation of Ce³⁺ and Ce⁴⁺ species. Magnetic ceria materials are important in several applications from magnetic data storage devices to magnetically recoverable catalysts. In this paper, the room temperature ferromagnetism of rf sputtered Co doped CeO₂ thin films is reported whereas undoped CeO₂ thin films exhibit paramagnetic behavior. The ferromagnetic properties of the Co doped films were explained based on oxygen vacancies created by Co ions in Ce sites. This is further supported by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman. Change in surface morphology due to Co doping of the samples were analyzed using atomic force microscopy (AFM).     

X-ray photoelectron spectroscopy investigation on the interaction of polyvinylcarbazole and fullerene

Summary Using X-ray Photoelectron Spectroscopy (XPS) technique, the interaction mechanism between polyvinylcarbazole (PVK) and fullerene (C₆₀) in photoconductive PVK film doped with C₆₀ was studied. PVK and fullerene can form electron transfer complex according to the molar ratio of PVK unit and C₆₀ being about 2:1 in room temperature, and the formation and dissociation of the complex are reversible with the change of temperature. The formation of complex is the key to improve the photoconductivity of PVK.     

Properties of poly(tetrabromo‐p‐phenylenediselenide) doped with IBr,H2SO3, and CH3COOH acids

Poly(tetrabromo‐p‐phenylenediselenide) (PBrPDSe) has been doped by IBr, H₂SO_3, and CH₃COOH acids. The samples have been studied by X‐ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). Conductivity measurements have also been performed on pressed pellet samples. It has been shown by XPS and ESR that, after doping, positive charges are localized on Se atoms. The conductivity of the acid‐doped PBrPDSe exhibits an increase by about four orders of magnitude. However, the limit of 10⁻⁷ Ω⁻¹ cm⁻¹ appears difficult to overcome. This saturation effect could be attributed not only to charge localization on Se atoms but also to steric hindrance related to the substituent introduced on the backbone of the polymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2511–2517, 2000     

Influence of low concentration Sm doping on optical and catalytic performance of titania

The work focuses on exploring the effect of the concentration of Sm dopant (0.2–0.6 at.%) on structural, optical and photocatalytic properties of the spin coated titania based thin films annealed at different temperatures. The optical interpretation involves the influence of Sm doping on optical constants and luminescence behaviour of the samples. The comprehensive work on optical bandgap, Urbach energy and electron-phonon interaction strength was conducted for Sm doped samples. The optical band gap was found to increase with the increasing concentration of Sm, but decreased with high temperature annealing. Using ellipsometry measurement, refractive index of the samples was obtained. The orbital level information was gathered using X-Ray Photoelectron Spectroscopy (XPS) study with a special emphasis on the evolution of physico-chemical properties as function of Sm doping. The XPS study confirms the presence of Sm in the titania host material and it helped in estimating defects induced by Sm doping. The photocatalytic study of Sm doped titania thin films was carried out by using methylene blue (MB) and Rhodamine B (RhB) dye and we have found an enhanced photocatalytic activity for the 0.4 at.% Sm doped samples.     

Poly(9‐vinylcarbazole)/silver composite nanotubes and networks formed at the air–water interface

Silver‐nanoparticle‐doped poly(9‐vinylcarbazole) (PVK) nanocomposites were prepared via the reduction of Ag⁺ ions and the self‐assembly of PVK on AgNO₃ aqueous solution surfaces. The formed composite nanostructures depended strongly on the experimental temperature. Thick round disks of PVK surrounded by discrete Ag nanoparticles and/or with irregular holes formed at room temperature; nanotubes and micronetworks doped with Ag nanoparticles formed at about 30–40°C, and networks formed at higher temperature. Further investigation revealed that the nanotubes were transformed from thin round disks. The length of the PVK/Ag composite nanotubes were longer than 10 μm, and the average size of the embedded Ag nanoparticles was found to be about 3.5 nm. The composite networks were composed of round pores with diameters of several hundred nanometers and fine silver nanoparticles embedded in the thin polymer films that covered the pores. The formation of the nanotubes was a very interesting self‐assembly phenomenon of the polymer at the air–water interface that has not been reported before. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

XPS and ESR studies of electrochemically synthesized polycarbazole post‐doped with iodine

Polycarbazole powders obtained by electrochemical oxidation of carbazole thin films or of carbazole in solution in the electrolyte have been post‐doped with iodine and characterized by room temperature electrical conductivity, X‐ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR). Similar results are obtained with polymers saturated with iodine at room temperature after 6 weeks and with polymers doped at 383 K for 24 h. The polymers obtained from carbazole thin films have a higher electrical conductivity (ς ∼ 10⁻⁴ Ω⁻¹ cm⁻¹) and a higher spin density (9.9 10²¹ spins mol⁻¹ g⁻¹), which corresponds to 71 atom % of ionic iodine. The polymer radicals are located on the nitrogen, and the percentage of N⁺ is 40 atom %. The electrical conductivity of the polymers obtained from carbazole in solution in the electrolyte is two order of magnitude smaller. The percentage of N⁺ is only 25 atom % with an ionic iodine percentage of 13 atom %. So, the most important parameter is not the iodine percentage introduced after doping into the polymers but the percentage of ionic iodine present in the polymers. The differences that are put in evidence can be explained by a better polymerization efficiency of the carbazole when it is deposited on thin film form by vacuum evaporation before electrochemical oxydation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 115–124, 1999     

Boron-doped hydrogenated amorphous carbon films grown by surface-wave mode microwave plasma chemical vapor deposition

We report the effects of boron (B) doping on optical and structural properties of the hydrogenated amorphous carbon thin films grown by surface-wave mode microwave plasma (SW-MWP) chemical vapor deposition (CVD) on n-type silicon and quartz substrates at room temperature. Argon and acetylene were used as a carrier and carbon source gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy were employed to investigate the properties of the films. Low atomic concentration of B (0.08 at.%) was found in the doped film. The optical band gap of the undoped film was 2.6 eV and it decreased to 1.9 eV for the B-doped film. Structural property shows the crystalline structure of the film and it has changed after incorporating B as a dopant. The structural modifications of the films leading to being more graphite in nature were confirmed by the Raman and FT-IR characterization.     

Study on the effect of acid‐ or iodine‐doping on the properties of copolymer C1–4poly‐phenylene‐vinylene‐ether

In this article, the new red‐colored copolymer, referred to as C_1–4poly‐phenylene‐vinylene‐ ether (C_1–4PPV‐ether) is built as a PPV polymer with some conjugated links (? CH?CH? ) that are changed into ethylic‐ether links (? CH₂? O? CH₂? ) and whose modified phenyl ring is grafted, respectively, in two and five positions with methoxy and butoxy groups. The C_{1– 4}PPV‐ether is doped with protonic acid or iodine. The infrared absorption (IR), optical density, X‐ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR) show that there is a charge transfer complex formed between the copolymer and the doping species (iodine or acidic dopants). From IR, XPS, and ESR analysis, we deduced that the doping mechanism of the copolymer is, respectively, a protonation of the double links in PPV in the case of the protonic acid doping process and a grafting of the iodine to the ether links in the case of iodine‐doping process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1858–1866, 2002     

Soluble conducting polypyrrole doped with DBSA–CSA mixed acid

Soluble conductive polypyrrole (PPy) with room temperature conductivity (2–18 S/cm) has been synthesized by doping polypyrrole with mixed acid containing camphor sulfonic acid (CSA) and dodecyl benzene sulfonic acid (DBSA). The solubility and the room temperature conductivity of PPy doped with mixed acid were measured as a function of component of CSA–DBSA mixed acid, and the structure of PPy was characterized by Fourier transform infrared (FTIR), ultraviolet–visible (UV-vis) spectra, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). PPy doped with DBSA–CSA mixed acid is soluble in m-cresol although PPy doped only by CSA is completely insoluble in any solvent. The solubility of PPy doped with mixed acid increases with an increase in the fraction of DBSA in the mixed acid, while the room temperature conductivity of the PPy increases with increasing CSA molar fraction. The UV-vis spectra and electron spin resonance (ESR) measurements showed that both polaron and bipolaron are the charge carrier in the doped PPy with mixed acid. It was proposed that the contribution of CSA to the solubility of PPy doped with mixed acid is to decrease the interaction among PPy chains due to the large molecular size of CSA, while DBSA contributes to the solubility by its good solvating effect derived from its long alkyl chain. These may be a reason that both the solubility and conductivity of PPy are improved by the presence of CSA compared with those of PPy doped only with DBSA. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 68: 1277–1284, 1998     

Influence of yttrium doping on the structural,morphological and optical properties of nanostructured ZnO thin films grown by spray pyrolysis

This study reports on the deposition of highly transparent, n-type ZnO thin films on glass substrate at 450?°C using spray pyrolysis processing, with the simultaneous insertion of yttrium (Y) at different percentages (0, 2, 5, 7?at%) as a dopant. The effect of Y doping on the structure, morphology and optical properties of Y doped ZnO (ZnO:Y) was investigated for optoelectronic applications. The obtained thin films were characterized by means of X-ray diffraction, field-emission scanning electron microscopy (FESEM), UV–visible absorbance measurements, photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. The as-prepared films exhibit well-defined hexagonal wurtzite structure grown along [002]. Field emission scanning electron microscope micrographs of the pure ZnO and ZnO:Y showed that the films acquired a dominance of hexagonal-like grains, the morphology was influenced by Y incorporation. All the films showed high transparency in the visible domain with an average transmittance of 83%. The band gap energy, E_g, increased from 3.12?eV to 3.18?eV by increasing the Y doping concentration up to 5?at% and then decreased to 3.15?eV for 7?at% Y content. The PL and CL measurements reveal a strong ultraviolet (UV) emission, suggesting that the as-prepared ZnO:Y thin films can potentially be used in optoelectronic devices.     

Synthesis, fabrication and characterization of poly[3-3′(vinylcarbazole)] (PVK) Langmuir-Schaefer films

Poly[3-3′(vinylcarbazole)] (PVK) was synthetized with N-vinylcarbazole as monomer by oxidative polymerization with ferric chloride. The resulting polymer was then deposited on various solid supports by using Langmuir-Schaefer (LS) method. The pressure-area isotherm of PVK revealed the possibility of compact monolayer formation at air-water interface. Different layers of PVK were doped with iodine vapours. Both scanning probe microscopy and optical microscopy images indicated a good uniformity of the films. The morphology and the thickness of PVK films were investigated using atomic force microscopy. The voltammetric investigation of I₂ doped PVK showed a distinctive electrochemical behaviour. The photoinduced charge transfer across a donor/acceptor (D/A) hybrid interface provided an effective method to study the photoelectrochemical properties of the composite LS films.     

Chemical solution deposition of pure and Gd-doped ceria thin films: Structural,morphological and optical properties

High quality smooth, uniform and crack-free ceria and gadolinium doped ceria (GDC) thin films were prepared on Si and Si/YSZ substrates by chemical solution deposition. The thermal behavior of Gd-Ce-O precursor was investigated by TG-DSC measurements. The phase purity and structure of deposited films were evaluated using X-ray diffraction (XRD) analysis and Raman spectroscopy. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the estimation of surface morphological features. Oxidation state of Ce ions in fabricated films was analyzed by X-ray photoelectron spectroscopy (XPS). Optical properties were evaluated by diffuse reflectance UV–vis spectrometry. Thickness of the films can be controlled by applying a certain number of spin coating cycles. A linear relation between the thickness of the films and the number of deposited layers was observed. The single-layer thickness was determined to be approximately 20 nm. The influence of annealing temperature and Gd content on the film structure, morphology and optical properties was studied and discussed. The dependence of an optical band gap as a function of grain size was demonstrated.     

Photoconductivity of poly(N-vinylcarbazole) (PVK) doped with the metallofullerene Dy@C82 and the fullerenes C84 and C60

Photoconductivity has been measured on films of pure poly(Nvinylcarbazole) (PVK) and PVK doped with the metallofullerene Dy@C₈₂ and the fullerenes C₈₄ and C₆₀. The photo-induced discharge rate of the PVK film increased dramatically when doped with the metallofullerene or the fullerenes. Comparatively, the film doped with Dy@C₈₂ displayed better photoconductivity than that doped with C₈₄, which is attributed to the Dy@C₈₂ being a better electron acceptor than C₈₄. However, the film doped with C₆₀ showed the best photoconductivity. This is attributed to the better electron accepting ability of excited C₆₀* or the better miscibility of the hollow fullerenes with the PVK polymer and organic solvents.     

Iodine doping of amorphous diamond-like carbon films

Amorphous diamond-like carbon (a:DLC) films have been doped by incorporation of iodine during the films deposition. XPS and AES analysis shows the existence of iodine atoms with constant concentration of 0.9% along the iodine doped DLC film (a:I-DLC). The optical and electronic properties of the doped films were studied. Optical measurements in the visible light show that iodine affects the interband absorption of the a:DLC films. Iodine causes decreasing of the optical energy gap, from 1.07 to 0.78 eV and affects the density of states at the conducting band. Like the optical measurements, electrical measurements show that iodine also decreases the activation energy of the films from 0.34 to 0.22 eV. This shows that although both gaps decrease, the optical energy gap remains different from that of electrical gap, also after doping.     

Structural and electrochemical characterisation of [Pd(salen)]-type conducting polymer films

The oxidative polymerisation of four structurally-related [Pd(salen)] complexes and characterisation of the resulting polymeric films by cyclic voltammetry (CV), UV-visible transmission spectroscopy, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) is reported. The voltammetric technique gives insight into the electrochemical properties of the polymeric films whereas UV-visible spectroscopy is used to characterise the electronic structure of Pd electroactive films, of particular relevance to the type of charge carriers. X-ray techniques (supported by density functional theory, DFT) provide information related to composition and structural features of [Pd(salen)] precursors and the resulting polymers. Characterisation of poly[Pd(salen)] films shows that the electrochemical response of these supramolecular systems is ligand-based and dependent upon substituents in the diimine bridge and aldehyde moieties. XAS measurements near the Pd K-edge demonstrate that polymerisation of the Pd complexes does not change the coordination sphere of the Pd centre; this is consistent with the coupling of monomers units via phenyl rings. As further evidence of ligand-based electrochemical responses, polymer doping does not impart any changes at the Pd centre or its coordination sphere. Compositional analysis by XPS confirms that C: Pd, N: Pd and O: Pd surface atomic ratios do not change significantly from monomer to undoped or doped polymer, except for small variations associated with incorporation of electrolyte and solvent upon polymerisation and polymer oxidation. Overall, the data provide a picture of a polyaromatic delocalised electroactive system, in which the metal atom plays a templating (rather than electroactive) role.     

Effect of nickel doping on structural,optical, electrical and ethanol sensing properties of spray deposited nanostructured ZnO thin films

Undoped and nickel (Ni)-doped ZnO thin films were spray deposited on glass substrates at 523 K using 0.1 M of zinc acetate dihydrate and 0.002–0.01 M of nickel acetate tetrahydrate precursor solutions and subsequently annealed at 723 K. The effect of Ni doping in the structural, morphological, optical and electrical properties of nanostructured ZnO thin film was investigated using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–vis Spectrophotometer and an Electrometer respectively. XRD patterns confirmed the polycrystalline nature of ZnO thin film with hexagonal wurtzite crystal structure and highly oriented along (002) plane. The crystallite size was found to be increased in the range of 15–31 nm as dopant concentration increased. The SEM image revealed the uniformly distributed compact spherical grains and denser in the case of doped ZnO thin films. All the films were highly transparent with average transmittance of 76%. The measured optical band gap was found to be varied from 3.21 to 3.09 eV. The influence of Ni doping in the room temperature ethanol sensing characteristics has also been reported.     

Improved photostability of a CuO photoelectrode with Ni-doped seed layer

In this study, we examined the growth of copper oxide (CuO) photoelectrodes using nickel-doped copper oxide seed layers with various doping concentrations. We investigated the effects of the seed layer doped with various amounts of nickel on the morphological, structural, optical and photoelectrochemical properties of the CuO photoelectrode by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and potentiostat/galvanostat measurements, respectively. We found that doping the seed layer with nickel affects properties such as the surface roughness, surface area, crystallinity and photostability. As a result, we obtained a maximum photostability of 46.2% using a 10 at% nickel-doped seed layer.     

Effect of working conditions on the morphology of electrosynthesized polyfuran

The influence of electrolyte and deposition potential on polyfurane doped/undoped electrogenerated films was analyzed by potentiodynamic profiles and current–time transients. The films were formed on platinum electrodes from the monomer and tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, or tetraethylammonium perchlorate in acetonitrile. Results were also discussed with the aid of X‐ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), and primarily by scanning electron microscopy (SEM). It was shown that there is some oxygen contamination not only after ClO₄ doping. However, it was shown by XPS and EPMA that C? O? C bonds are present in the films, which confirmed that there was no destruction of the furan ring during electropolymerization. SEM study showed film morphology evolution with monomer concentration, and with the electrolyte or the dopant used. The undoping effect was also visualized, showing that doped polyfuran was more homogeneous than the respective undoped deposits. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1346–1354, 2004