Effect Of Iodine Doping Research Articles

Effects of iodine doping on structural and electrical characteristics of solution-processed indium oxide thin-film transistors and its potential application for iodine sensing

Effects of iodine doping on structural and electrical characteristics of solution-processed indium oxide thin-film transistors and its potential application for iodine sensing

(Invited) Record-High Charge Carrier Mobilities in 2D Covalent- and Metal- Organic Frameworks

Organic based 2D layered materials (2DLMs) including 2D covalent and metal organic frameworks (COFs and MOFs) are promising candidates for traditional applications in gas storage and separation as well as catalysis. This is due to the long-range crystalline order that can be achieved in them as well as their tunable porosity and chemistry. Synthetic chemistry efforts aiming an enhanced coupling between their building block constituents have recently led to the design of (semi-)conducting MOFs and COFs displaying high conductivities and record charge carrier mobilities. These achievements have opened the path for their application in opto-electronics. Yet, despite being a critical aspect for the development of 2DLM based electronics, understanding the true nature of charge transport in these novel materials by stabilising reliable structure-property-function relations is largely unexplored.Here I will present time-resolved high-frequency (terahertz) conductivity studies of state-of-the-art organic based 2DLMs materials revealing semiconducting behaviour and record charge carrier mobilities. First, I will present a detailed characterization for the electronic properties of Zn– and Cu–phthalocyanine-based pyrazine-linked 2D COFs [1,2]. These 2D COFs, synthesized by condensation of metal–phthalocyanine (M = Zn and Cu) and pyrene derivatives, are obtained as polycrystalline-layered semiconductors displaying p-type doping and a band gap of ∼1.2 eV. Hall effect measurements (dc limit) and terahertz (THz) spectroscopy (ac limit) in combination with density functional theory (DFT) calculations demonstrate that varying metal center from Cu to Zn in the phthalocyanine moiety has a negligible effect in the conductivity (∼5 × 10–7 S/cm), charge carrier density (∼1012 cm–3), charge carrier scattering rate (∼3 × 1013 s–1), and effective mass (∼2.3m0) of majority carriers (holes). However, both samples reveal slightly different mobilities that can be attributed to charge carrier localization at crystalline grain boundaries. Furthermore we analyse the effect of iodine doping on the Zn based 2D COFs. The resultant 2D c-COF ZnPc-pz-I2 maintains its structural integrity and displays enhanced conductivity by 3 orders of magnitude, as a result of improved charge carrier concentrations. Hall effect reveal a charge carrier mobility reaching ∼22 cm2/Vs for ZnPc-pz-I2, which represent a record value for 2D c-COFs. An improved mobility upon doping can be traced to an increase in scattering time for free charge carriers, indicating that scattering mechanisms limiting the mobility are mitigated by doping.In the second part of my talk, I present the results concerning a Fe3(THT)2 (THT=2,3,6,7,10,11-hexathioltriphenylene) 2D MOFs [3]. The π-d conjugated samples, synthesized through interfacial method at room temperature, are obtained as a large-area, free-standing films with tunable geometry (size and thickness). The Fe3(THT)2 films are porous (specific surface area of 526±5 m2/g) and semiconducting (with a ~250 meV direct bandgap), and remarkably display band-like charge transport. This finding is directly demonstrated from the Drude-type high-frequency (terahertz) photo-conductivity response obtained in the samples; revealing free-moving, delocalized charge carriers displaying ~220 cm2/Vs mobilities at room temperature; a record charge carrier mobility for MOFs. The temperature dependence of the mobility reveals that the main scattering mechanism limiting the mobility and hence band-like charge transport in this material is related to impurity scattering, so that material improvements may further increase the mobility.The demonstration of band-like charge transport and record-high mobilities in semiconducting 2D COFs and MOFs reveal the potential of (porous) electrically conductive 2DLMs to be employed as active materials in opto-electronics devices.

Cobalt Iodate Microparticles for Highly Sensitive Acetone Gas Sensor Applications

Introduction Acetone is well known as a breath gas biomarker of diabetes patient, at concentration level greater than 1.8 ppm in exhaled breath gases1. Thus, the precise and selective detection of a low concentration (sub-ppm level) of acetone in breath gases containing over 1,000 kinds of gas species can characterize the diagnosis of diabetes. Therefore, reliable acetone gas sensors with highly sensitive and selective acetone response are essential for diagnosis of diabetes. Metal oxide semiconductor (MOS) is one of the most popular acetone gas sensing materials because of their high sensitivity, fast response, and low-cost fabrication2. In an effort to improve the selectivity and sensitivity, decoration of catalysts on MOS materials has been suggested. In this study, we used iodine as catalysts on cobalt oxide-based materials and fabricated gas sensors using sol-gel derived cobalt iodate [Co(IO3)2] which has a good sensitivity and selectivity toward a low concentration of acetone gas. We also thoroughly characterized the materials using scanning electron microscope (SEM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), and polarization-electric field characteristics to figure out the gas sensing mechanism. Method Co(IO3)2 micro-particles were synthesized by precipitation method from aqueous solutions of Co(CH3COO)2·4H2O and HIO3 as precursors. For evaluation of effect of iodine doping on cobalt oxide-based materials on gas sensing performance, Co3O4 micro-particles were also synthesized by the same method using NH4OH precursor instead of HIO3. The obtained precipitates were washed with distilled water and ethanol, followed by drying step. We used the structure of interdigitated (IDT) electrodes for sensor fabrication, described in our previous work3. These powders were dispersed in DI water (1 wt%) and drop-casted on the IDT electrodes on a hot plate at 100 °C. After evaporation of the solvent, the devices were eventually calcined in air at various temperatures. Sensing measurements were done in a gas sensing system varying operating temperatures using a power supply. The gas concentrations were controlled diluting target gases with dry air. We tested gas responses by monitoring changes in resistances of Rg/Ra or Ra/Rg, where Rg is a resistance during exposure to the target gas, and Ra is a resistance in air, respectively. Results and Conclusions Figure 1(a) represents gas responses of samples based on Co(IO3)2 and Co3O4 toward 1.8 ppm of acetone at operating temperature of 250 °C. The gas responses of the Co3O4 sample are much smaller than that of Co(IO3)2 sample. Accordingly, iodine in a high concentration could play a beneficial role in acetone sensing processes for the sensors. Figure 1(b) shows gas responses for the Co(IO3)2 sample annealed at 300 °C toward various gases of 1.8 ppm such as acetone, toluene, NO2, NH3, H2, and H2S at 250 °C, representing a good selectivity. The optimum operating temperature is found to be 250 °C. Acknowledgments J.-S. Park was partially supported by the ATC program (Grant No. 10076984) from MOTIE of the Rep. of Korea. References C. Deng, J. Zhang, X. Yu, W. Zhang, and X. Zhang, J. Chromatogr. B, 810, 269–275 (2004).2. Y. Li, M. Zhang, and H. Zhang, Phys. B, 29, 90702 (2020) http://cpb.iphy.ac.cn.S. Nundy et al., Ceram. Int., 46 (2020). Figure 1

Structural and optical characteristics of charge transfer complex of plasma deposited 2-(diethylamino)ethyl methacrylate thin films and iodine

The effect of iodine doping on the optical and structural characteristics of plasma polymerized 2-(diethylamino)ethyl methacrylate (PPDEAEMA) thin films are described in this paper. Scanning electron micrographs show that both as-deposited and iodine doped PPDEAEMA thin films are homogeneous. Thermogravimetric analysis demonstrates the stability temperature as 560 K for iodine doped PPDEAEMA. The degradation temperature of iodine doped PPDEAEMA is slightly greater than that of as deposited PPDEAEMA. Fourier transform infrared spectroscopy shows shifts in absorption bands due to the incorporation of iodine in PPDEAEMA. The absorption coefficient and allowed direct and indirect transition energy gaps were calculated from the ultraviolet–visible absorbance spectra. The energy band gap value decreases due to iodine doping. Urbach energy, steepness parameter and extinction coefficient were calculated as well for the PPDEAEMA thin films of thicknesses 100, 200 and 300 nm which were iodine doped for 45, 360 and 720 min.

Effects of Iodine Doping on Electrical Characteristics of Solution-Processed Copper Oxide Thin-Film Transistors.

In order to implement oxide semiconductor-based complementary circuits, the improvement of the electrical properties of p-type oxide semiconductors and the performance of p-type oxide TFTs is certainly required. In this study, we report the effects of iodine doping on the structural and electrical characteristics of copper oxide (CuO) semiconductor films and the TFT performance. The CuO semiconductor films were fabricated using copper(II) acetate hydrate as a precursor to solution processing, and iodine doping was performed using vapor sublimated from solid iodine. Doped iodine penetrated the CuO film through grain boundaries, thereby inducing tensile stress in the film and increasing the film’s thickness. Iodine doping contributed to the improvement of the electrical properties of the solution-processed CuO semiconductor including increases in Hall mobility and hole-carrier concentration and a decrease in electrical resistivity. The CuO TFTs exhibited a conduction channel formation by holes, that is, p-type operation characteristics, and the TFT performance improved after iodine doping. Iodine doping was also found to be effective in reducing the counterclockwise hysteresis in the transfer characteristics of CuO TFTs. These results are explained by physicochemical reactions in which iodine replaces oxygen vacancies and oxygen atoms through the formation of iodide anions in CuO.

Effect of iodine doping on the electrical, thermal and mechanical properties of SnSe for thermoelectric applications.

We report the evolution of the thermoelectric and mechanical properties of n-type SnSe obtained by iodine doping at the Se site. The thermoelectric performance of n-type SnSe is detailed in the temperature range starting from 150 K ≤ T ≤ 700 K. The power factor of 0.25% iodine doped SnSe is found to be 0.33 mW m-1 K-2 at 700 K, comparable to that of the other monovalent doped n-type SnSe. The temperature-dependent electrical conductivity of the undoped and iodine doped SnSe samples is corroborated by using the adiabatic small polaron hopping model. A very low value of thermal conductivity, 0.62 W m-1 K-1, is obtained at 300 K and is comparable to that of SnSe single crystals. The low thermal conductivity of n-type polycrystalline SnSe is understood by taking into account the anharmonic phonon vibrations induced by the incorporation of heavy iodine atoms at the Se sites as well as the structural hierarchy of the compound. Besides, iodine doping is found to improve the reduced Young's modulus and hardness values of SnSe, which is highly desirable for thermoelectric device applications.

Elemental mercury removal by I−-doped Bi2WO6 with remarkable visible-light-driven photocatalytic oxidation

In this work, I–-doped Bi2WO6 composites were synthesized using a one-step hydrothermal method, and the effect of iodine doping on their photocatalytic efficiency in gas-phase elemental mercury removal was evaluated under visible-light irradiation. The results showed that 1.0 wt.% iodine doped Bi2WO6 exhibited the optimal Hg0 removal efficiency of 87.6 % and 97.5 % under N2+O2+CO2 and N2+O2+CO2+SO2+NO conditions, respectively. The improved photocatalytic activity of Bi2WO6 can be ascribed to the reduction in the potential energy of its conduction band and recombination rate of electron-hole pairs, as well as the acceleration of charge transfer. The density functional theory calculations showed that iodine was doped in the (WO4)2– layer and oxidized HgO can be adsorbed on the surface of I– doped Bi2WO6. The OBi site was found to be exhibit weak adsorption with respect to HgO, implying that most conducive to the desorption of HgO. Finally, the photocatalysis mechanisms was elaborated.

Dual-iodine-doped BiOIO3: Bulk and surface co–modification for enhanced visible-light photocatalytic removal of bisphenol AF

Developing effective and feasible treatment methods to address high-risk emerging contaminants is a tremendous and persistent challenge to environmental safety. Bisphenol AF (BPAF), one of the most often used bisphenol A (BPA) alternatives, has a higher lethality, estrogenic activity, and developmental toxicity than BPA, and is difficult to decompose, yet studies to remove BPAF are very limited. Herein, by analysis and design of band structure, single bulk-doped, single surface-doped, and bulk and surface dual-iodine-doped BiOIO3 photocatalysts are fabricated via modifying pristine BiOIO3 using ion exchange or/and in situ reduction strategies. The respective role and synergistic effect of iodine doping at different locations of BiOIO3 are then discussed. As dual doping mode affords a high iodine content, rich oxygen vacancies, and more dispersed band structure, the as-synthesized dual-iodine-doped BiOIO3 exhibits strong visible-light absorption (from UV to ~ 750 nm), strong oxidation ability (valence band potential of 2.68 V), and efficient charge separation kinetics, resulting in an excellent visible-light photocatalytic activity for BPAF degradation. After 2 h of photoreaction, the degradation percentage and TOC reduction of BPAF reach 96.5% and 94.0%, respectively, which far exceed those of BiOIO3, BiOI, or single iodine-doped BiOIO3. The radical trapping experiments and EPR analysis reveal that h+, e−, O2−, OH, and 1O2 are all involved in the catalytic process. The reaction intermediates are identified, and a reasonable photocatalytic mechanism is proposed. In addition, the synthetic dual-iodine-doped photocatalyst maintains stability during photoreaction and is successfully applied to a real wastewater sample, demonstrating its potential in practical applications.

Synergistic effect of iodine doping and platinum loading on boosting the visible light photocatalytic activity of BiOBr

Platinum loaded BiOBr with iodine doping photocatalyst (Pt/I-BiOBr) was synthesized to further improve the photocatalytic activity of BiOBr. The photocatalytic test showed the bisphenol A degradation efficiency of Pt/I-BiOBr under visible light was about 93% within 20 min, about 5.8, 1.5 and 1.3 times that of BiOBr, iodine doped BiOBr and platinum loaded BiOBr, respectively. The composition, morphology, optical property and dominant active radical were investigated. Based on the results, a possible mechanism was proposed. Iodine doping and platinum loading played a synergetic effect on broadening the visible light absorption range and increasing the photo-induced carrier separation efficiency of BiOBr.

Effect of iodine doping on photoelectric properties of perovskite-based MOS devices

In this article, the PVK based metal-oxide-semiconductor (MOS) capacitor structures were fabricated and the photoelectric performance of the capacitor was carried out to study the intrinsic electrical characteristic of PVK with iodine doped. The electrical hysteresis of the capacitor after iodine doping becomes larger in the dark state, which indicates that the hysteresis behavior of the PVK is caused by the mobile iodine ions. The photocurrent of iodine-doped PVK is significantly greater than that of undoped PVK under illumination, which suggests that the capacitor has better response to light and the photodetectors efficiency also increase after iodine doping. Our results provide a theoretical basis for the potential application of memory devices such as memristors under dark. Meanwhile, it provides a method to improve photodetector performance by adding an appropriate amount of iodine to the PVK precursor solution.

Understanding the effects of iodine doping on the thermoelectric performance of n-type PbTe ingot materials

The superior performance of p-type PbTe has generated excitement toward discovering an n-type PbTe recipe to meet the manufacturing requirements for thermoelectric devices. PbI2 is a well-known dopant for n-type PbTe alloys fabrication. For the halogen family, the sintering process involves a common densifying strategy used to reduce the lattice thermal conductivity, which unfortunately causes strong deviations from nominal composition. Thus, to precisely determine the effects of iodine on PbTe’s electrical properties, PbI2-doped ingots were fabricated and characterized in this work. We found that the ingot samples exhibited high electrical conductivity, high power factors, and low lattice thermal conductivity when x equaled 0.004 and 0.005, especially at low temperatures, which was comparable with previous reports.

Effect of iodine doping on the characteristics of polythiophene thin films prepared by aerosol assisted plasma jet polymerization at atmospheric pressure

Iodine-doped polythiophene thin films are prepared by aerosol assisted plasma jet polymerization at atmospheric pressure and room temperature. The doping of iodine was carried out in situ by employing iodine crystals in thiophene monomer by weight mixing ratios of 1%, 3%, 5% and 7%. The chemical composition analyses of pure and iodine-doped and heat-treated polythiophene thin films are carried out by FTIR spectroscopy studies. The optical band gaps of the films are evaluated from absorption spectrum studies. Direct transition energy gaps are determined from Tauc plots. The structural changes of polythiophene upon doping and the reduction of optical band gap are explained on the basis of the results obtained from FTIR spectroscopy, UV–VIS absorption studies, X-ray diffraction and atomic force microscope (AFM) analysis. The energy band gap will be different according to the concentration of polythiophene iodine. It can be concluded that iodine-doped polythiophene thin films can be prepare by aerosol assisted plasma jet polymerization and control the optical energy band gap regulars by controlling the thiophene -iodine weight mixing ratios.

Effects of Iodine Doping on Carrier Behavior at the Interface of Perovskite Crystals: Efficiency and Stability

The interface related to the polycrystalline hybrid perovskite thin film plays an essential role in the resulting device performance. Iodine was employed as an additive to modify the interface between perovskite and spiro-OMeTAD hole transport layer. The oxidation ability of iodine significantly improved the efficiency of charge extraction for perovskite solar cells. It reveals that the Open Circuit Voltage (Voc) and Fill Factor (FF) of perovskite solar cells were improved substantially due to the dopant, which is mainly attributed to the interfacial improvement. It was found that the best efficiency of the devices was achieved when the dopant of iodine was in equivalent mole concentration with that of spiro-OMeTAD. Moreover, the long-term stability of the corresponding device was investigated.

Structural, optical, and magnetic studies of iodine-doped CdO nanopowders and films

Iodine-doped CdO powders of different iodine contents have been synthesized by thermal dissociation of Cd complex. In addition, I-doped CdO thin films have been grown on glass substrates by a physical vapor deposition method. The effects of iodine doping on the structural, magnetic, and optical properties of the host CdO powder and film were systematically studied. The X-ray diffraction study shows that the incorporated I−-ions most likely occupy oxygen vacancies (VO) created naturally in CdO lattice as point defects during synthesis. Thus, I-doping increases the unit-cell volume of host CdO, causes bandgap narrowing, and removing the weak d0 ferromagnetic (FM) component of CdO. Therefore, the weak FM component of undoped (d0) CdO is defect-induced phenomenon or induced by the created oxygen vacancies (VO). In the present fundamental investigation, real experimental connection between active VO, I-doping, and magnetic properties of I-doped CdO was observed and discussed. Structural, optical and magnetic Study of iodine-doped CdO nanocomposite ceramic

Effect of iodine doping in the deposition solution and iodine vapor pressure in the sensitization treatment on the properties of PbSe films

Effect of iodine-doping in the deposition solution and iodine vapor pressure during the sensitization process on the morphological, microstructural, electrical, and optical properties of PbSe films was studied. Undoped and iodine-doped PbSe films of polycrystalline particles were coated on thermally oxidized silicon substrates by chemical bath deposition. The PbSe films were oxidized at 380°C for 30 min and then iodinated at different iodine vapor pressures at 380°C for 5 min. When the iodine vapor pressure was below 20 Pa, PbSeO3 was the main phase formed on the surface of PbSe microcrystals for both undoped and iodine-doped films. As the iodine vapor pressure was increased above 20 Pa, Pb3I2O2 and PbI2 phases were formed in both types of films and PbSeO3 disappeared in the undoped film. Only the iodine-doped films showed photo response. The sheet resistance and IR signal-to-noise ratio had maximum values at the iodine vapor pressure of 17.5 Pa in the iodine-doped film. The x-ray diffraction spectra, scanning electron microscopy morphologies, and EDS analyses of the sensitized PbSe films show that the main role of iodine in the sensitization is helping solid-state sintering of PbSe microcrystals which may lead to redistribution of oxygen atoms in the effective atomic sites.

Effects of Iodine Doping on Optoelectronic and Chemical Properties of Polyterpenol Thin Films.

Owing to their amorphous, highly cross-liked nature, most plasma polymers display dielectric properties. This study investigates iodine doping as the means to tune optoelectronic properties of plasma polymer derived from a low-cost, renewable resource, i.e., Melaleuca alternifolia oil. In situ exposure of polyterpenol to vapors of electron-accepting dopant reduced the optical band gap to 1.5 eV and increased the conductivity from 5.05 × 10−8 S/cm to 1.20 × 10−6 S/cm. The increased conductivity may, in part, be attributed to the formation of charge-transfer complexes between the polymer chain and halogen, which act as a cation and anion, respectively. Higher levels of doping notably increased the refractive index, from 1.54 to 1.70 (at 500 nm), and significantly reduced the transparency of films.

Polymerization mechanisms in plasma polyallylamine

This is a study about the polymerization mechanisms of plasma polyallylamine (PAl). This polymer is studied in the reconnection of the communications in the spinal cord after a severe lesion and it has been recognized that the iodine doping increases the reconnecting effect in laboratory rats; however, there are no chemical studies about the effect of iodine doping in the polymerization mechanisms, so analyses of undoped and iodine-doped PAl chemical structures by XPS were carried out in this work to know the plasma polymerization mechanisms. The results indicated that six different carbon chemical states were formed during the polymerization of allylamine with percentages that depend on the power of synthesis. The most active point in the chemical reactions was identified in the CH2=C segment of allylamine molecule, which disappeared in the polymers to form single, double, and triple bond structures. PAl without iodine doping has a structure with preference for single bonds (up to 62 %) and doped PAl had a preference for double-bond structures (up to 54 %) in the power of synthesis studied. The participation of triple bonds segments reached up to 4 % in PAl and up to 7 % in iodine-doped PAl. In general terms, the dopant had a catalyst role in the polymerization increasing the dehydrogenation and almost disappearing in the final polymers.

Effects of iodine doping on small molecule organic semiconductors for high charge carrier mobility and photoconductivity

Here we report the effects of iodine doping on small molecule organic semiconductors. Thin films of semiconducting p-DTS(FBTTh2)2 doped with 1–5 wt% iodine were fabricated and their photo-physical, crystallographic, morphological, and electrical properties were systematically analyzed. The doping significantly increased the energetic distance between the highest occupied molecular orbital (HOMO) and Fermi level of p-DTS(FBTTh2)2, typical for p-type doping. In addition, depletion mode transistor measurements showed an increase in the hole concentration with increasing dopant concentration. From grazing incidence X-ray diffraction (GIXD) analyses of iodine-doped p-DTS(FBTTh2)2 films, we observed significant changes in the crystal orientation at the optimal doping ratio of 1 wt%. Atomic force microscopy (AFM) analyses showed morphological changes with respect to dopant concentrations, which were in good agreement with the GIXD results. As a result, accumulation mode transistor measurements demonstrated an increase in the hole mobility by 54% at the optimized doping concentration compared to an undoped device. Furthermore, photoconductive device operation revealed that iodine-doping can induce dramatically enhanced photo-responsivity as high as 2.08 A/W. We demonstrate that iodine doping can be a simple and effective method for enhancing the performance of small molecule-based electronic devices, by optimizing the energy level configuration as well as enhancing intermolecular interactions.

Enhanced electrical and optical properties of iodine doped LDPE films

In this study, an attempt has been made to dope Low Density Polyethylene (LDPE) with iodine and to study the effect of iodine doping on the optical band gap of LDPE films. The DC conductivity measurements and UV/Vis spectral studies are employed to characterize the samples. Iodine treatment induces colour change in the polymer film which supports the interaction between iodine molecules and polyethylene chains. I2 molecule links the polymer chains electronically and provides conducting path ways by forming DA complexes. The absorption band of complex films has extended to the visible and near infrared region of the spectrum. Further there are discernible shifts found in the energy gap and band edge towards lower energies on doping with iodine. This is essentially due to the formation of strong DA complexes upon iodine doping which improves the conducting behaviour.

Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers

Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m−1 K−1 near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion.