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Impact of Alkyl Side Chain Length on Doping Kinetics, Thermopower and Charge Transport Properties in Highly Oriented F4TCNQ-Doped PBTTT films
摘要： Doping of polymer semiconductors such as PBTTT with acceptor molecules such as F4TCNQ is widely used to tune the charge transport and thermoelectric (TE) properties in thin films. However, the mechanism of dopant insertion in the polymer matrix, the insertion kinetics and the ultimate doping levels reached have been investigated only marginally. This contribution addresses the impact of alkyl side chain length on the doping mechanism of a series of PBTTTs with linear side chains ranging from n-octyl to n-octyldecyl. The study focuses on thin films oriented by high temperature rubbing and sequentially doped in F4TCNQ solution. Structure-property correlations are established as a function of side chain length by a combination of Transmission Electron Microscopy, polarized UV-Vis-NIR spectroscopy and charge transport / thermopower measurements. Intercalation of F4TCNQ into the layers of side chains results in the expansion of the lattice along the side chains and the contraction along the π-stacking direction for all polymers. The extent of lattice expansion decreases with increasing side chain length. UV-vis-NIR spectroscopy demonstrates integer charge transfer for all investigated PBTTTs. The doping kinetics and final doping level depend on both the side chain length and packing. Highly disordered n-octyl and crystalline n-octyldecyl side chain layers tend to hamper dopant diffusion in the side chain layers contrary to n-dodecyl side chains that can host the highest proportion of dopants. Consequently, the best TE properties are observed for C12-PBTTT films. Alignment of the polymers enhances significantly the TE performance by increasing the charge conductivity and the thermopower along the rubbing direction. Aligned films of C12-PBTTT show charge conductivities of 193 S/cm along the rubbing direction and power factors of approximately 100 μW.m-2.K-1 versus a few μW.m-2.K-1 for non-oriented films.
关键词： Thin films,Structure,Organic Thermoelectric,Conducting Polymers,Doping.
更新于2025-09-23 15:22:29
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Trap-assisted enhanced bias illumination stability of oxide thin film transistor by praseodymium doping
摘要： Praseodymium-doped indium zinc oxide (PrIZO) have been employed as the channel layer of thin film transistors (TFTs). The TFTs with Pr doping exhibited a remarkable suppression of the light induced instability. A negligible photo-response and remarkable enhancement in negative gate bias stress under illumination (NBIS) were achieved in the PrIZO-TFTs. Meanwhile, the PrIZO-TFTs showed reasonable characteristics with a high field effect mobility of 26.3 cm2/Vs, SS value of 0.28 V/decade, and Ion/Ioff ratio of 108. X-ray photoelectron spectroscopy (XPS), microwave photoconductivity decay (Micro-PCD) and photoluminescence spectra (PL) were employed to analyze the effects of the Pr concentrations on the performance of PrIZO-TFTs. We disclosed that acceptor-like trap states induced by Pr ions might lead to the suppression of photo-induced carrier in conduction band, which is a new strategy for improving illumination stability of amorphous oxide semiconductors. Finally, a prototype of fully transparent AMOLED display was successfully fabricated to demonstrate the potential of Pr-doping TFTs applied in transparent devices.
关键词： Praseodymium doping,negative bias illumination stress,metal oxide,thin film transistor,photo-response
更新于2025-09-23 15:22:29
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Preparation of hollow yttrium-doped TiO<sub>2</sub> microspheres with enhanced visible-light photocatalytic activity
摘要： Using melamine-formaldehyde polymer microspheres as templates, yttrium-doped TiO2 hollow spheres (Y-TiO2HS) were successfully prepared via a sol-gel method. The as-synthesized samples were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-Vis diffuse reflectance spectrum, luminescence spectrum, specific surface area (BET) analysis and porosity analysis. The results indicate that Y doping could increase the thermal stability, reduce the band gap and enhance photocatalytic activity of the TiO2. When the Y doping molar ratio was 1.5%, the Y-TiO2HS presented high surface area (62.651 m2 /g) and photocatalytic degradation rate (about 70%). The corresponding BET value and photocatalytic degradation rate of Y-TiO2HS increased by 3 times and 50%, respectively, compared with those of un-doped TiO2HS.
关键词： synthesis,yttrium doping,hollow microspheres,photocatalytic activity,TiO2
更新于2025-09-23 15:22:29
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High-voltage regrown nonpolar m-plane vertical p-n diodes: A step toward future selective-area-doped power switches
摘要： We report high-voltage regrown nonpolar m-plane p-n diodes on freestanding GaN substrates. Secondary-ion mass spectroscopy (SIMS) measurements indicate O and Si spikes at the regrowth interfaces with maximum concentration ~ 5×1017 cm-3, which is similar to previously published c-plane studies. A high blocking voltage of 540 V at ~ 1 mA/cm2 (corresponding to an electric field of E ~ 3.35 MV/cm), turn-on voltages between 2.9-3.1 V, specific on-resistance of 1.7 mΩ.cm2 at 300 A/cm2, and a minimum ideality factor of 1.7 were obtained for the regrown diodes. Our results suggest that Si, O and C interfacial impurity levels up to 2×1017 cm-3, 8×1017 cm-3, and 1×1019 cm-3, respectively, at the metallurgical junction of m-plane p-n diodes do not result in very early breakdown in the reverse bias, although the off-state leakage current in forward bias is affected. The impact of growth interruption/regrowth on diode performance is also investigated.
关键词： Selective-area doping,GaN,Specific on-resistance,Impurity incorporation,Avalanche breakdown,Leakage currents,Ideality factor,Nonpolar,SIMS,Vertical p-n diodes
更新于2025-09-23 15:22:29
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Effect of codoping Ce <sup>3+</sup> on the luminescence properties of Sr <sub/>9</sub> Mg <sub/>1.5</sub> (PO <sub/>4</sub> ) <sub/>7</sub> :Eu <sup>2+</sup> orange-yellow phosphor
摘要： Sr9Mg1.5(PO4)7:Eu2+ has recently been reported as a promising blue light-excited orange-yellow phosphor that can be used in white LED device. Here, Ce3+-codoping is found to be an effective strategy to improve the luminescence performance of Sr9Mg1.5(PO4)7:Eu2+ phosphor. The coexistence of Eu2+ and Eu3+ ions has been verified via photoluminescence spectral analysis. The reduction of Eu3+ to Eu2+ in Sr9Mg1.5(PO4)7 lattice cannot be completed in a reducing atmosphere, but can be promoted through codoping with Ce3+ ions to a great extent, which finally increase the effective concentration of Eu2+ in the crystal lattice. The Eu3+–Eu2+ reduction mechanism is analyzed using a charge compensation model. This work not only achieves enhanced luminescence of the Sr9Mg1.5(PO4)7:Eu2+ phosphor by codoping with Ce3+ ions, but also provides new insights into the design of Ce3+/Eu2+ codoped luminescent materials.
关键词： optical materials,defects,doping,LED,europium
更新于2025-09-23 15:22:29
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Metaheuristic <i>Ab Initio</i> Optimum Search for Doping Effects in Nanocarbons
摘要： We have developed a combined approach of metaheuristic optimization algorithms (MOA), such as the genetic algorithm, with an ab-initio materials simulation engine. Concurrent run of the ab-initio calculations with each different parameter set selected by the MOA searches the optimum condition within a given input-parameter space. Using this methodology, the optimum dopant and its position/structure at a graphene edge are found to be a multiple N-atoms doping at graphitic sites, which predicts to lead to better charging/discharging performance when it is used as an anode material of Li-ion battery.
关键词： genetic algorithm,lithium-ion battery,nano-carbon,ab-initio simulation,doping effect
更新于2025-09-23 15:22:29
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Enhanced up-conversion luminescent properties of KYb2F7:Er3+ by Sc3+ doping
摘要： In the field of up-conversion materials, Yb3+ is usually used as sensitizer. In this work, KYb2F7 is synthesized by hydrothermal method using Yb3+ as a part of the matrix material, and at the same time, the luminescent center Er3+ and the non-luminescent center Sc3+ are co-doped therein. It was found that Yb3+ can be introduced into the matrix material with improved luminescence properties. In addition, with the doping of Sc3+, the luminescence intensity of the material can be increased by up to five times. This testified that the doping of an appropriate amount of non-luminescent center Sc3+ can significantly improve the up-conversion luminescence intensity of up-conversion material.
关键词： Doping,KYb2F7,Nanoparticles,Sc3+,Up-conversion materials
更新于2025-09-23 15:22:29
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Carrier concentration and transport in Be-doped InAsSb for infrared sensing applications
摘要： Accurate p-type doping of the active region in III-V infrared detectors is essential for optimizing the detector design and overall performance. While most III-V detector absorbers are n-type (e.g., nBn), the minority carrier devices with p-type absorbers would be expected to have relatively higher quantum efficiencies due to the higher mobility of minority carrier electrons. However, there are added challenges to determining the hole carrier concentration in narrow bandgap InAsSb due to the potential for electron accumulation at the surface of the material and at its interface with the layer grown directly below it. Electron accumulation layers form high conductance electron channels that can dominate both resistivity and Hall-effect transport measurements. Therefore, to correctly determine the bulk hole concentration and mobility, temperature- and magnetic-field-dependent transport measurements in conjunction with Multi-Carrier Fit analysis were utilized on a series of p-doped InAs0.91Sb0.09 samples on GaSb substrates. The resulting hole concentrations and mobilities at 77 K (300 K) are 1.6×1018 cm-3 (2.3×1018 cm-3) and 125 cm2 V-1 s-1 (60 cm2 V-1 s-1), respectively, compared with the intended Be-doping of ~2×1018 cm-3. A surface treatment experiment is conducted to associate one of the electron conducting populations to the surface. Variable temperature (15 – 390 K) measurements confirmed the different carrier species present in the sample and enabled the extraction of the bulk heavy hole, interface carriers and surface electron transport properties. For the bulk carrier, a thermal activation of intrinsic carriers is identified at high temperatures with a bandgap of EG ~ 258 meV and the low temperature data suggests an activation energy of EA ~ 22 meV for the Be dopant atoms. Finally, temperature analysis confirms a surface carrier electron with resulting mobilities and sheet concentrations at 30 K (300 K) of 4500 cm2 V-1 s-1 (4300 ± 100 cm2 V-1 s-1) and 5.6×1010 cm-2 (6×1010 ± 2×1010 cm-2), respectively.
关键词： Hall-effect measurements,magneto-transport,beryllium doping,III-V infrared detectors,InAsSb
更新于2025-09-23 15:21:21
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An Investigation into the Stability of Graphitic C <sub/>3</sub> N <sub/>4</sub> as a Photocatalyst for CO <sub/>2</sub> Reduction
摘要： The increasing CO2 concentration in the atmosphere exerts a significant influence on global warming and climate change. The capture and utilization of CO2 by conversion to useful products is an area of active research. In this work, the photo-driven reduction of CO2 was investigated using graphitic carbon nitride (g-C3N4) as a potential photocatalyst. The photocatalytic reduction of CO2 was investigated with g-C3N4 powder immobilized on a glass support in a batch gas phase photoreactor. The experiments were carried out under UV-Vis irradiation at 70°C and an initial pressure of 2.5 bar. The only gas phase product detected during the irradiation of the g-C3N4 in the presence of CO2 was CO, and the rate of production was observed to decrease over time. Oxygen doped g-C3N4 was also tested for CO2 reduction but had lower efficiency that the parent g-C3N4. Repeated cycles of photocatalytic CO2 reduction showed a decline in the activity of the g-C3N4. In the absence of CO2 some CO generation was also observed. Characterization of used and unused materials, using FTIR and XPS, showed an increase in the oxygen functional groups following UV-Vis irradiation or thermal treatment. While others report the use of g-C3N4 as a photocatalyst, this work highlights the important need for replicates and control testing to determine material stability.
关键词： CO2 reduction,photocatalysis,oxygen doping,graphitic carbon nitride,material stability,g-C3N4
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Structural characterization and emission properties of phosphorus-doped NCD films
摘要： Phosphorus-doped NCD films were grown on n-type silicon substrate by plasma-enhanced CVD with H2, CH4, and PH3 gas mixture for cold cathode application. The structure properties were characterized by Raman spectroscopy with a green laser of 532 nm at room temperature, scanning electron microscope, transmission electron microscope, and electron energy-less spectroscopy. Grown films show a good conductivity and have a typical structure with a combination of sp3 diamond gains with size around 20-100 nm and sp2 grain boundaries. The electron emission properties were characterized as comparing with single crystal, NCD film, and tip-array NCD. The tip-array NCD shows good emission properties with lower threshold electric filed and higher saturation current.
关键词： Structural characterization,Nano crystal diamond (NCD),PECVD,electron emitter,Phosphorus doping
更新于2025-09-23 15:21:21