Iodine-doped Samples Research Articles

Iodine Doping of CdTe and CdMgTe for Photovoltaic Applications

Iodine-doped CdTe and Cd1−x Mg x Te layers were grown by molecular beam epitaxy. Secondary ion mass spectrometry characterization was used to measure dopant concentration, while Hall measurement was used for determining carrier concentration. Photoluminescence intensity and time-resolved photoluminescence techniques were used for optical characterization. Maximum n-type carrier concentrations of 7.4 × 1018 cm−3 for CdTe and 3 × 1017 cm−3 for Cd0.65Mg0.35Te were achieved. Studies suggest that electrically active doping with iodine is limited with dopant concentration much above these values. Dopant activation of about 80% was observed in most of the CdTe samples. The estimated activation energy is about 6 meV for CdTe and the value for Cd0.65Mg0.35Te is about 58 meV. Iodine-doped samples exhibit long lifetimes with no evidence of photoluminescence degradation with doping as high as 2 × 1018 cm−3, while indium shows substantial non-radiative recombination at carrier concentrations above 5 × 1016 cm−3. Iodine was shown to be thermally stable in CdTe at temperatures up to 600°C. Results suggest iodine may be a preferred n-type dopant compared to indium in achieving heavily doped n-type CdTe.

Electrical and thermal transport properties of layered Bi2YO4Cu2Se2

Bi2YO4Cu2Se2 possesses a low thermal conductivity and high electrical conductivity at room temperature, which was considered as a potential thermoelectric material. In this work, we have investigated the electrical and thermal transport properties of Bi2YO4Cu2Se2 system in the temperature range from 300K to 873K. We found that the total thermal conductivity decreases from ~1.8Wm−1K−1 to ~0.9Wm−1K−1, and the electrical conductivity decreases from ~850S/cm to ~163S/cm in the measured temperature range. To investigate how potential of Bi2YO4Cu2Se2 system, we prepared the heavily Iodine doped samples to counter-dope intrinsically high carrier concentration and improve the electrical transport properties. Interestingly, the Seebeck coefficient could be enhanced to ~+80μV/K at 873K, meanwhile, we found that a low thermal conductivity of ~0.7Wm−1K−1 could be achieved. The intrinsically low thermal conductivity in this system is related to the low elastic properties, such as Young's modulus of 70–72GPa, and Grüneisen parameters of 1.55–1.71. The low thermal conductivity makes Bi2YO4Cu2Se2 system to be a potential thermoelectric material, the ZT value ~0.06 at 873K was obtained, a higher performance is expected by optimizing electrical transport properties through selecting suitable dopants, modifying band structures or by further reducing thermal conductivity through nanostructuring etc.

Effect of dopant on thermal properties of polythiophene

Polythiophene (PT) was chemically synthesized, undoped using aqueous ammonia and then re-doped using FeCl3 as well as iodine. Doping concentration was changed by changing the duration of doping process. FTIR results indicate the complex formation between PT and each of the dopants. Elemental analysis of FeCl3 doped samples show that as the duration increases concentration of Fe+ ions increases. In case of iodine doped samples atom equivalent of iodine per thiophene unit increases with doping duration. XRD analysis has been used to calculate crystallinity. It is observed that for FeCl3 and iodine (except 120 min) doped samples there is increase in crystallinity due to doping and crystallinity increases with increase in dopant concentration. TGA analysis shows that FeCl3 doped samples are thermally stable compared to iodine doped samples. Results of DTA as well as DSC indicate that Tg values vary with dopant as well as with dopant concentrations. Reduction in Tg values for all FeCl3 doped samples indicate that FeCl3 acts as plasticizer in PT. In iodine doped samples for low values of dopant concentrations Tg increases indicating anti-plasticizer effect whereas for high concentration of iodine, there is decrease in Tg value indicating plasticizer effect of iodine in PT.

Electrical transport properties of pristine and iodine doped polyetherimides

Electrical conduction behavior of pristine and iodine doped polyetherimides (PEI) has been investigated under both transient and steady state conditions in the operating temperature range 50–200°C at various electric fields of 12–60 kV/cm. The transient currents show the hyperbolic decay character, and the decay exponent p (a measure of current decay rate) decreases with temperature (T) and doping concentration. The origin of transient currents has been attributed to the dipolar nature of carbonyl Open image in new window groups and the ether linkages present in the main chain of PEI. The low field steady state conduction is ohmic in nature. The magnitudes of ionic jump distance (a) values do not favor an ionic type of conduction as a possible conduction mechanism in pristine as well as iodine doped PEI. The Schottky coefficients estimations do not show the possibility of Schottky type or Poole-Frenkel type conduction mechanisms in the low temperature region ( 120°C) there is a certain possibility of Poole-Frenkel type conduction mechanism in both pristine and iodine doped samples. The dual slope in the lgI versus 1/T curves for iodine doped samples indicates the presence of more than one type of trapping levels.

Study on electrical transport and photoconductivity in iodine-doped cellulose fibers

The electrical transport and photoconductivity of pure and iodine-doped cellulose fibers have been studied. The studies were conducted in the temperature range 293–363 K, while the electric field was varied over the range 1–100 V cm−1. The conductivity of the iodine-doped cellulose fibers shows significant enhancement by more than four orders of magnitude as compared to undoped samples. The analysis reveals that the electrical conduction follows Ohm’s law for iodine-doped samples, while for the undoped samples the bulk-limited Pool–Frenkel conduction mechanism is likely to dominate for the steady state current. Especially, the clear photoconduction response at UV and visible region indicates that photoconduction is essential due to band-to-band electron–hole pair’s generation and that doped CF is a good conductor of photogenerated carriers.

Electron paramagnetic resonance study of spin–spin correlation in iodine-doped poly(3-butylthiophene-2, 5-dyle)

Spin dynamics in iodine-doped samples of a poly(thiophene) derivative, poly(3-butylthiophene-2, 5-dyle) (P3BT), was studied by temperature-dependent electron paramagnetic resonance (EPR) measurements. As a result, a change of behavior in the polaron spin–spin correlation was markedly identified in a heavily doped system.

Effects of disorder on the magnetic state of poly(3-hexyl)thiophene

We present EPR magnetic susceptibility measurements as a function of temperature on undoped and iodine-doped samples of regioregular (REPHT) and regiorandom (RAPHT) poly(3-hexyl)thiophene. The regioregular and regiorandom forms of poly(3-hexyl)thiophene show different temperature dependences in both the undoped and the doped states. The results are interpreted in the framework of a spin-pairs model, according to which the number of spins in undoped samples is less than one per two-hundred thiophene rings. In doped samples, the number of spins increases to approximately one per ten thiophene rings. In addition to showing the predominant role of bipolarons, different temperature dependences of the magnetic susceptibility data provide a methodology to investigate mesoscopic disorder.

Structure and physical properties of a hydrogen-bonded self-assembled material composed of a carbamoylmethyl substituted TTF derivative

Crystal structures of the carbamoylmethyl substituted TTF derivative AMET are characterized by polymeric hydrogen bonding between amide groups. As a result, the TTF moieties stack in parallel even in the neutral crystal. The nu;NH absorbtions of neutral AMET at 3426 and 3184cm1 show shifts to lower wavenumber, Delta;k, of 37 and 58cm1, respectively, at 4.1GPa. Therefore the shrinkage of the NH‥O distance is estimated to be ca. 0.04 at this pressure. The pressure dependence of the IR spectra of iodine-doped samples at doping ratios of less than 45 was exactly the same as that for a neutral sample, suggesting that the hydrogen bonding pattern is not affected significantly upon doping.Although crystalline AMET is an insulator in the neutral state (sigma;rt=ca. 108 Scm1), the conductivity is enhanced by a factor of 107 upon iodine doping of 45mol (sigma;rt=1.2101 Scm1). Furthermore, the conductivity increases as a function of the external pressure, and the sigma;rt of a 5 iodine-doped sample increased three-fold at 1.0GPa. The enhanced conductivity of iodine-doped samples may be ascribed to the increase in the overlap between the donor moieties based on the shrinkage of the hydrogen bond of the carbamoylmethyl group.

The effect of partial elimination of methoxy groups in a precursor polymer on the optical absorption and electrical properties of poly(thienylene vinylene).

Films of poly(thienylene vinylene) (PTV) were prepared by thermal elimination of methoxy groups in a precursor polymer in the presence of gaseous hydrochloric acid as a catalyst. The growth of the conjugation length of the polymer during elimination was studied by means of on-line UV-Vis spectroscopy under various conditions of reaction temperature, reaction time and HCl concentration. The optical absorption gap of the polymerś π-π* transition, determined from transmission and reflectivity data, was found to decrease with increasing conjugation length. Measurements of dc electrical conductivity on iodine-doped samples showed a direct connection between chain structure and charge carrier transport. From the temperature dependence of the electrical conductivity (90–300 K) we concluded that the electrical transport in the iodine-doped polymers can be described by a variable-range hopping model proposed by Schäfer-Siebert and Roth.

Electrical conductivity and thermal diffusivity of zinc naphthalocyanine

Naphthalocyanine and its metal complexes are candidate materials for molecular electronic devices such as optical storage media, electrochromic displays and sensors [1,2]. Yanagi et al. [3] have investigated the molecular orientation of vacuum deposited zinc naphthalocyanine (ZnNc) by infrared (IR) spectroscopy, electronic spectroscopy and X-ray diffraction (XRD). Here we report the results of our study on the electrical conductivity and thermal diffusivity of ZnNc and iodine doped ZnNc. ZnNc was synthesized and purified by the method reported by Kaplan et al. [4]. The compound was characterized by elemental analysis, IR and electronic spectra. The data were in agreement with those reported in the literature [3]. ZnNc samples were doped with iodine in the solution phase by stirring 100 mg of powdered ZnNc with a saturated solution of iodine in carbon tetrachloride. The doped material was filtered and washed with carbon tetrachloride to remove excess iodine. This sample was dried at 360 K in vacuo as reported in the case of cobalt phthalocyanine [5]. The samples for measurement were formed into pellets of diameter 5.0 mm and thickness 1.1 mm at a pressure of 2000 kg cm -2. The electrical conductivity was measured in a shielded cell under dynamic vacuum in the temperature range 100-450 K using a Keithley model 617 electrometer. Thermal diffusivity of the pellets was measured by a photoacoustic technique, using 488 nm Ar ÷ laser beam at 26 mW power level. The laser beam was chopped using a Stanford Research System model SR 540 chopper, and front surface illumination was used for finding out the characteristic frequency f~. The schematic diagram of the experimental set up used for determination of the thermal diffusivity by the photoacoustic technique is shown in Fig. 1. The electrical conductivity of pristine ZnNc shows an increase in conductivity with temperature, the Arrhenius plots showing two linear regions of different activation energies, as shown in Fig. 2. The plot does not give any clear indication of a sharp transition. The activation energies in different temperature ranges are given in Table I. Doping with iodine enhances the electrical conductivity. For the iodine doped samples the Arrhenius plot gives two distinct regions with activation energies 0.05 eV and 0.14eV The enhanced electrical conductivity may be due to charge

A novel catalyst system for the production of polyacetylene and of blends of polyacetylene with some silicon‐containing polymers

AbstractDimethyltitanocene, in conjunction with a wide variety of compounds containing SiH bonds, is an excellent catalyst for the polymerization of acetylene to give free standing films. Polymerizations of acetylene in a variety of siloxane and silane matrices using this catalyst system are described. The polyacetylenes produced with a [(MeSiHO)3(Me2Si)17]n random copolymer showed very similar properties to those previously produced by Naarman et al. with a Shirakawa‐type catalyst in a polydimethylsiloxane matrix. Ring, or chain, poly(methylhydrosiloxanes) with higher proportions of (MeSiHO) undergo redistribution in the course of acetylene polymerization to give polyacetylene embedded in an insoluble polysiloxane glass. Polyacetylene produced in a poly(phenylsilane) matrix yielded a 2‐component material from which the polysilane could not be solvent extracted. The electrical conductivity of iodine doped samples of this material is somewhat lower than that of the pure polyacetylene, but its mechanical properties and its resistance to degradative oxidation are superior to those of either of the pure component polymers. © 1994 John Wiley & Sons, Inc.

Various factors affecting the synthesis of highly conducting polyacetylene

The preparative conditions of highly conducting polyacetylene films by acetylene polymerization with a Ti(n-OBu) 4Et 3Al catalyst have been investigated in terms of preparative method of the catalyst, polymerization method, purification method of prepared films and drying method of the films. Highly stretchable films were prepared by the use of a catalyst aged at a temperature higher than 80°C and the stretchability increased with increasing concentration of the catalyst, resulting in higher values of parallel conductivity in the stretch-oriented iodine-doped samples. However, these values were limited to (3–4) × 10 4 S cm −1 due to a decrease in conductivity of the as-prepared films with either increasing aging temperature or concentration of catalyst.

Effect of iodine doping on Bi 2Sr 2Ca 1Cu 2O x charge transfer or interlayer coupling?

A comparative study has been made of iodine-intercalated Bi 2Sr 2Ca 1Cu 2O x single crystal and 1 atm O 2 annealed Bi 2Sr 2Ca 1Cu 1O x single crystal using an AC susceptibility measurement, X-ray photoemission (XPS) and angle-resolved ultraviolet photoemission spectroscopy (ARUPS). The AC susceptibility measurement indicates that O 2 doped samples studied have a T c of 84 K, whereas T c of the iodine-doped samples studied are 80 K. XPS Cu 2p core-level data establish that the hole concentration in the CuO 2 planes is essentially the same for these two kinds of samples. ARUPS measurements show that the electronic structure of the normal states near the Fermi level has been strongly affected by iodine intercalation. We conclude that the dominant effect of iodine doping is to alter the interlayer coupling.

Structure and Conductivity of Iodine-Doped C60 Thin Films

ABSTRACTWe report here the results of our study on the properties of iodine-doped C60 thin films by IR and optical absorption, X-ray diffraction, and electrical conductivity measurements. The results show that there is no apparent structural change in the iodine-doped samples at room temperature in comparison with that of the undoped films. However, in the electrical conductivity measurements, an increase of more that one order of magnitude in the room temperature conductivity has been observed in the iodine-doped samples. In addition, while the conductivity of the undoped films shows thermally activated temperature dependence, the conductivity of the iodine-doped films was found to be constant over a fairly wide temperature range (from 20°C to 70°C) exhibiting a metallic feature.

Possible structure of parathiocyanogen—II. electrochemical synthesis, 13C NMR and conductivity measurements on undoped and iodine doped samples

Parthiocyanogen or polythiocyanogen (SCN) x has been synthesized by the anodic oxidation of NaSCN solutions in methanol. The structure of parathiocyanogen (SCN) x has been studied by means of elemental analysis, IR, UV, 13C NMR and ESR spectroscopy and also by comparison with a triazine-based model compound. All data collected clearly show that parathiocyanogen is structurally different from the triazine-based structure. On the basis of the data collected, the most probable structure should be a linear one, very similar to the one accepted to polysulphur nitride. Upon doping with iodine vapour the specific conductivity of parathiocyanogen increases by several orders of magnitude, as expected from a semi-conductive polymer.

Electrophysical Properties of Iodine Doped Acetylene/Ethylene Copolymers

ABSTRACTA new oxydative-resistant, fusible and processible ethylene/acetylene copolymer has been synthesized. The content of rigid (acetylene) and flexible (ethylene) fragments has been widely varied. The structure of the nascent powders and the films compressed at room temperature have been investigated by SEM and WAXS. DSC has been used for studying the thermal properties. DC conductivity of the iodine doped samples has been measured as a function of temperature. It is shown that the doping leads to arising conductivity in the samples even at 10 Mol % acetylene fragments in copolymer. The conductivity up to 10−3 S/cm is reached for the samples with acetylene fragment concentration about 20 Mol %. It is found that a charge carrier transport in investigated copolymers is caused by doped polyacetylene fragments and described by the hopping Mechanism.

Structural and superconducting properties of iodine-intercalated Bi 2Sr 2Ca 1− xY xCu 2O z

The structual and superconducting properties of Bi 2Sr 2Ca 1− x Y x Cu 2O z intercalated with iodine between the Bi-O bila yers were studied. Formation of the stage-1 compound was verified by X-ray analysis, TG analysis and TEM observation. Expansion of the c-axis, which is caused by increase in the distance of the BiO-BiO layers, decreases with decreasing intercalated iodine concentration down to 60%. The expansion of the c-axis of fully intercalated compounds increases with increasing Y content from 7.2 Å for x=0 to 7.5 Å for x=1.0. The temperature dependence of resistivity showed that iodine-doped samples ( x=0 and 0.4) were more semiconductive than non-doped samples. The T c of the IBi 2Sr 2Ca 1− x Y x Cu 2O z series in the over-doped region was reduced by 2–10 K compared with non-intercalated samples.

The design of polymeric organic metals: structure-property relationships

Oriented, highly conducting polyacetylene was obtained using a thermally aged Shirakawa catalyst. The temperature dependencies of the specific conductivity and the anisotropy of the conductivity of iodine-doped samples are described. The structures of new conducting salts which were obtained by electrochemical and chemical doping, [(CH)(SbF 6) 0.06)], [(CH)(SbF 6) 0.06)] and [(CH)(SbF 6) 0.06)] were characterized by X-ray diffraction experiments.

Electrical conductivity measurements of the plasma-polymerized 1-benzothiophene thin film

D.c. and the real part of a.c. (10 1–10 7 Hz) conductivities of plasma-polymerized 1-benzothiophene (1BT) thin film were measured in the temperature range from 80 to 290 K in order to investigate the conduction mechanism. The iodine-doped sample was also examined. It has been found that d.c. conduction of the pristine sample is ruled by the three-dimensional variable range hopping (3D-VRH) at the lower temperature region (< 160 K) and by the activation process for the nearest-neighbour hopping at the higher temperature region (> 200 K). The quantum-mechanical tunnelling (QMT) process is predominant in a.c. conduction of the pristine sample. The number of a.c. conduction carriers represented by the density of localized states (DOLS) near the Fermi level (that is, N( E F)) has been found in close proximity to the spin concentrations of both the pristine and iodine-doped samples.

Optical and Electrical Properties of Iodine Doped n-Type ZnSe Crystals

We have studied the electrooptical properties of ZnSe single crystals doped with iodine by diffusion at high temperature. The obtained samples are highly conductive. The luminescence at 300 K (RT) is dominated by well known self activated orange emission. At 30 K the blue and orange emission is observed. The ratio of the blue emission peak intensity to the deep 1evel one is much greater for the iodine doped samples than for the undoped intentionally ones.