Showing papers on "Doping published in 2018"
TL;DR: The fundamental electromagnetic dynamics governing light matter interaction in plasmonic semiconductor NCs and the realization of various distinctive physical properties made possible by the advancement of colloidal synthesis routes to such NCs are discussed.
Abstract: Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals (NCs) that results in resonant absorption, scattering, and near field enhancement around the NC can be tuned across a wide optical spectral range from visible to far-infrared by synthetically varying doping level, and post synthetically via chemical oxidation and reduction, photochemical control, and electrochemical control In this review, we will discuss the fundamental electromagnetic dynamics governing light matter interaction in plasmonic semiconductor NCs and the realization of various distinctive physical properties made possible by the advancement of colloidal synthesis routes to such NCs Here, we will illustrate how free carrier dielectric properties are induced in various semiconductor materials including metal oxides, metal chalcogenides, metal nitrides, silicon, and other materials We will highlight the applicability and limitations of the Drude model as applied to semiconductors considering the complex band structures
603 citations
TL;DR: This review provides a comprehensive overview of the molecular packing, morphology and charge transport features of organic semiconductor crystals, the control of crystallization for achieving high quality crystals and the device physics in the three main applications.
Abstract: Organic semiconductors have attracted a lot of attention since the discovery of highly doped conductive polymers, due to the potential application in field-effect transistors (OFETs), light-emitting diodes (OLEDs) and photovoltaic cells (OPVs). Single crystals of organic semiconductors are particularly intriguing because they are free of grain boundaries and have long-range periodic order as well as minimal traps and defects. Hence, organic semiconductor crystals provide a powerful tool for revealing the intrinsic properties, examining the structure–property relationships, demonstrating the important factors for high performance devices and uncovering fundamental physics in organic semiconductors. This review provides a comprehensive overview of the molecular packing, morphology and charge transport features of organic semiconductor crystals, the control of crystallization for achieving high quality crystals and the device physics in the three main applications. We hope that this comprehensive summary can give a clear picture of the state-of-art status and guide future work in this area.
537 citations
TL;DR: In this paper, the authors demonstrate the enhanced electrochemical behavior of Ni-rich material LiNi0.8Co0.1O2 (NCM811) coated with a thin ZrO2 layer.
Abstract: One of the major hurdles of Ni-rich cathode materials Li1+x(NixCozMnz)wO2, y > 0.5 for lithium-ion batteries is their low cycling stability especially for compositions with Ni ≥ 60%, which suffer from severe capacity fading and impedance increase during cycling at elevated temperatures (e.g., 45 °C). Two promising surface and structural modifications of these materials to alleviate the above drawback are (1) coatings by electrochemically inert inorganic compounds (e.g., ZrO2) or (2) lattice doping by cations like Zr4+, Al3+, Mg2+, etc. This paper demonstrates the enhanced electrochemical behavior of Ni-rich material LiNi0.8Co0.1Mn0.1O2 (NCM811) coated with a thin ZrO2 layer. The coating is produced by an easy and scalable wet chemical approach followed by annealing the material at ≥700 °C under oxygen that results in Zr doping. It is established that some ZrO2 remains even after annealing at ≥800 °C as a surface layer on NCM811. The main finding of this work is the enhanced cycling stability and lower impedance of the coated/doped NCM811 that can be attributed to a synergetic effect of the ZrO2 coating in combination with a zirconium doping.
404 citations
TL;DR: A good understanding and smart engineering of the defects in MTP have been demonstrated to be a key factor for the fabrication of high-efficiency PSCs and progress on the state-of-the-art defect engineering approaches for the optimization of PSC devices is summarized.
Abstract: The rapid development of solar cells (SCs) based on organic–inorganic hybrid metal triiodide perovskite (MTP) materials holds great promise for next-generation photovoltaic devices. The demonstrated power conversion efficiency of the SCs based on MTP (PSCs for short) has reached over 20%. An MTP material is a kind of soft ionic solid semiconductor. The intrinsic optoelectronic properties of MTP are greatly determined by several factors, such as the crystalline phase, doping type, impurities, elemental composition, and defects in its crystal structure. In the development of PSCs, a good understanding and smart engineering of the defects in MTP have been demonstrated to be a key factor for the fabrication of high-efficiency PSCs. In this review, we start with a brief introduction to the types of defects and the mechanisms for their formation in MTP. Then, the positive and negative impacts of defects on the important optoelectronic features of MTP are presented. The optoelectronic properties mainly include charge recombination, charge transport, ion migration, and structural stability. Moreover, commonly used techniques for the characterization of the defects in MTP are systematically summarized. Recent progress on the state-of-the-art defect engineering approaches for the optimization of PSC devices is also summarized, and we also provide some perspectives on the development of high-efficiency PSCs with long-term stability through the optimization of the defects in MTP.
393 citations
TL;DR: The ultrafast transient absorption and time-resolved photoluminescence (PL) spectroscopy revealed that Ce3+-doping can significantly modulate the PL kinetics to enhance the PL efficiency of doped CsPbBr3 NCs.
Abstract: Inorganic perovskite CsPbBr3 nanocrystals (NCs) are emerging, highly attractive light emitters with high color purity and good thermal stability for light-emitting diodes (LEDs). Their high photo/electroluminescence efficiencies are very important for fabricating efficient LEDs. Here, we propose a novel strategy to enhance the photo/electroluminescence efficiency of CsPbBr3 NCs through doping of heterovalent Ce3+ ions via a facile hot-injection method. The Ce3+ cation was chosen as the dopant for CsPbBr3 NCs by virtue of its similar ion radius and formation of higher energy level of conduction band with bromine in comparison with the Pb2+ cation to maintain the integrity of perovskite structure without introducing additional trap states. It was found that by increasing the doping amount of Ce3+ in CsPbBr3 NCs to 2.88% (atomic percentage of Ce compared to Pb) the photoluminescence quantum yield (PLQY) of CsPbBr3 NCs reached up to 89%, a factor of 2 increase in comparison with the native, undoped ones. The ...
390 citations
304 citations
TL;DR: The structure-performance relationship of these materials is subsequently rationalized and perspectives on developing more efficient and sustainable electrocatalysts from carbon nanomaterials are also suggested.
Abstract: N-doped carbon nanomaterials have rapidly grown as the most important metal-free catalysts in a wide range of chemical and electrochemical reactions. This current report summarizes the latest advances in N-doped carbon electrocatalysts prepared by N mono-doping and co-doping with other heteroatoms. The structure-performance relationship of these materials is subsequently rationalized and perspectives on developing more efficient and sustainable electrocatalysts from carbon nanomaterials are also suggested.
297 citations
TL;DR: Phosphorus-doped graphitic carbon nitrides (P-g-C3N4) have recently emerged as promising visible-light photocatalysts for both hydrogen generation and clean environment applications because of fast charge carrier transfer and increased light absorption.
Abstract: Phosphorus-doped graphitic carbon nitrides (P-g-C3N4) have recently emerged as promising visible-light photocatalysts for both hydrogen generation and clean environment applications because of fast charge carrier transfer and increased light absorption. However, their photocatalytic performances on CO2 reduction have gained little attention. In this work, phosphorus-doped g-C3N4 nanotubes are synthesized through the one-step thermal reaction of melamine and sodium hypophosphite monohydrate (NaH2PO2·H2O). The phosphine gas generated from the thermal decomposition of NaH2PO2·H2O induces the formation of P-g-C3N4 nanotubes from g-C3N4 nanosheets, leads to an enlarged BET surface area and a unique mesoporous structure, and creates an amino-rich surface. The interstitial doping phosphorus also down shifts the conduction and valence band positions and narrows the band gap of g-C3N4. The photocatalytic activities are dramatically enhanced in the reduction both of CO2 to produce CO and CH4 and of water to produce...
292 citations
TL;DR: Control of the roughness of the CIGS surface and the use of a heavily doped organic hole transport layer were crucial to achieve a 22.4% power conversion efficiency in a two-terminal tandem cell with hybrid perovskite/CIGS combination.
Abstract: The combination of hybrid perovskite and Cu(In,Ga)Se2 (CIGS) has the potential for realizing high-efficiency thin-film tandem solar cells because of the complementary tunable bandgaps and excellent photovoltaic properties of these materials. In tandem solar device architectures, the interconnecting layer plays a critical role in determining the overall cell performance, requiring both an effective electrical connection and high optical transparency. We used nanoscale interface engineering of the CIGS surface and a heavily doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layer between the subcells that preserves open-circuit voltage and enhances both the fill factor and short-circuit current. A monolithic perovskite/CIGS tandem solar cell achieved a 22.43% efficiency, and unencapsulated devices under ambient conditions maintained 88% of their initial efficiency after 500 hours of aging under continuous 1-sun illumination.
288 citations
TL;DR: A novel molecular doping of NiOx hole transport layer (HTL) is realized successfully by 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6TCNNQ), offering an extremely promising molecular doping method for inorganic CTLs in PSCs.
Abstract: Both conductivity and mobility are essential to charge transfer by carrier transport layers (CTLs) in perovskite solar cells (PSCs). The defects derived from generally used ionic doping method lead to the degradation of carrier mobility and parasite recombinations. In this work, a novel molecular doping of NiOx hole transport layer (HTL) is realized successfully by 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6TCNNQ). Determined by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, the Fermi level (EF ) of NiOx HTLs is increased from -4.63 to -5.07 eV and valence band maximum (VBM)-EF declines from 0.58 to 0.29 eV after F6TCNNQ doping. The energy level offset between the VBMs of NiOx and perovskites declines from 0.18 to 0.04 eV. Combining with first-principle calculations, electrostatic force microscopy is applied for the first time to verify direct electron transfer from NiOx to F6TCNNQ. The average power conversion efficiency of CsFAMA mixed cation PSCs is boosted by ≈8% depending on F6TCNNQ-doped NiOx HTLs. Strikingly, the champion cell conversion efficiency of CsFAMA mixed cations and MAPbI3 -based devices gets to 20.86% and 19.75%, respectively. Different from passivation effect, the results offer an extremely promising molecular doping method for inorganic CTLs in PSCs. This methodology definitely paves a novel way to modulate the doping in hybrid electronics more than perovskite and organic solar cells.
270 citations
TL;DR: In this article, a high mobility two-dimensional electron gas (2DEG) formed at the β-(AlxGa1-x)2O3/Ga2O 3 interface through modulation doping was demonstrated.
Abstract: In this work, we demonstrate a high mobility two-dimensional electron gas (2DEG) formed at the β-(AlxGa1-x)2O3/Ga2O3 interface through modulation doping. Shubnikov-de Haas (SdH) oscillations were observed in the modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure, indicating a high-quality electron channel formed at the heterojunction interface. The formation of the 2DEG channel was further confirmed by the weak temperature dependence of the carrier density, and the peak low temperature mobility was found to be 2790 cm2/Vs, which is significantly higher than that achieved in bulk-doped Beta-phase Gallium Oxide (β-Ga2O3). The observed SdH oscillations allowed for the extraction of the electron effective mass in the (010) plane to be 0.313 ± 0.015 m0 and the quantum scattering time to be 0.33 ps at 3.5 K. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure lays the foundation for future exploration of quantum physical phenomena and semiconductor device technologies based on the β-Ga2O3 material system.
TL;DR: In this paper, single-atom-level structural investigations reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure, leading to solid-solution-type 2D MoS 2-xOx crystals.
Abstract: The chemical inertness of the defect-free basal plane confers environmental stability to MoS2 single layers, but it also limits their chemical versatility and catalytic activity The stability of pristine MoS2 basal plane against oxidation under ambient conditions is a widely accepted assumption however, here we report single-atom-level structural investigations that reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure The use of scanning tunnelling microscopy reveals a slow oxygen-substitution reaction, during which individual sulfur atoms are replaced one by one by oxygen, giving rise to solid-solution-type 2D MoS2-xOx crystals Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS2 basal plane for the electrochemical H2 evolution reaction
TL;DR: The much smaller energy barrier, longer HSe bond length, and diminished bandgap endow N-MoSe2 /TiC-C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts.
Abstract: Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase- and morphology-modulated N-doped MoSe2 /TiC-C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC-C nanorod arrays serve as the backbone for MoSe2 nanosheets to form high-quality MoSe2 /TiC-C shell/core arrays. Impressively, continuous phase modulation of MoSe2 is realized on the MoSe2 /TiC-C arrays. Except for the pure 1T-MoSe2 and 2H-MoSe2 , mixed (1T-2H)-MoSe2 nanosheets are achieved in the N-MoSe2 by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer HSe bond length, and diminished bandgap endow N-MoSe2 /TiC-C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N-MoSe2 /TiC-C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm-2 , and a small Tafel slope of 32 mV dec-1 . Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.
TL;DR: A solvent-based intercalation method to achieve p-type, n-type and degenerately doped semiconductors in the same parent material at the atomically thin limit is demonstrated and can open a new avenue connecting the previously disparate worlds of integrated circuits andatomically thin materials.
Abstract: Doped semiconductors are the most important building elements for modern electronic devices
1
. In silicon-based integrated circuits, facile and controllable fabrication and integration of these materials can be realized without introducing a high-resistance interface2,3. Besides, the emergence of two-dimensional (2D) materials enables the realization of atomically thin integrated circuits4–9. However, the 2D nature of these materials precludes the use of traditional ion implantation techniques for carrier doping and further hinders device development
10
. Here, we demonstrate a solvent-based intercalation method to achieve p-type, n-type and degenerately doped semiconductors in the same parent material at the atomically thin limit. In contrast to naturally grown n-type S-vacancy SnS2, Cu intercalated bilayer SnS2 obtained by this technique displays a hole field-effect mobility of ~40 cm2 V−1 s−1, and the obtained Co-SnS2 exhibits a metal-like behaviour with sheet resistance comparable to that of few-layer graphene
5
. Combining this intercalation technique with lithography, an atomically seamless p–n–metal junction could be further realized with precise size and spatial control, which makes in-plane heterostructures practically applicable for integrated devices and other 2D materials. Therefore, the presented intercalation method can open a new avenue connecting the previously disparate worlds of integrated circuits and atomically thin materials. Intercalation of copper and cobalt atoms into n-type SnS2 enables seamless integration of metal, and n- and p-type semiconductors in one parent 2D material.
TL;DR: For the first time, oxygen self-doping of solvothermally synthesized g-C3N4 nanospheres with tunable electronic band structure via ambient air exposure is reported for unprecedentedly enhanced photocatalytic performance.
Abstract: As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has attracted much attention for solving the worldwide energy shortage and environmental pollution. In this work, for the first time we report oxygen self-doping of solvothermally synthesized g-C3N4 nanospheres with tunable electronic band structure via ambient air exposure for unprecedentedly enhanced photocatalytic performance. Various measurements, such as XPS, Mott–Schottky plots, and density functional theory (DFT) calculations reveal that such oxygen doping can tune the intrinsic electronic state and band structure of g-C3N4via the formation of C–O–C bond. Our results show that the oxygen doping content can be controlled by the copolymerization of the precursors. As a consequence, the oxygen doped g-C3N4 shows excellent photocatalytic performance, with an RhB photodegradation rate of 0.249 min−1 and a hydrogen evolution rate of 3174 μmol h−1 g−1, >35 times and ∼4 times higher than that of conventional thermally made pure g-C3N4 (0.007 min−1 and 846 μmol h−1 g−1, respectively) under visible light. Our work introduces a new route for the rational design and fabrication of doping modified g-C3N4 photocatalyst for efficient degradation of organic pollutants and H2 production.
TL;DR: It is found that the addition of the alkali metal ions clearly improves the quality of perovskite film: enlarges the grain sizes, reduces the defect state density, passivates the grain boundaries, increases the built‐in potential (V bi), resulting to the enhancement in the power conversion efficiency of pervskite thin film solar cell.
Abstract: Organic-inorganic hybrid halide perovskites are proven to be a promising semiconductor material as the absorber layer of solar cells. However, the perovskite films always suffer from nonuniform coverage or high trap state density due to the polycrystalline characteristics, which degrade the photoelectric properties of thin films. Herein, the alkali metal ions which are stable against oxidation and reduction are used in the perovskite precursor solution to induce the process of crystallization and nucleation, then affect the properties of the perovskite film. It is found that the addition of the alkali metal ions clearly improves the quality of perovskite film: enlarges the grain sizes, reduces the defect state density, passivates the grain boundaries, increases the built-in potential (Vbi), resulting to the enhancement in the power conversion efficiency of perovskite thin film solar cell.
TL;DR: Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor compared to other NDI-based polymers, and the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere.
Abstract: N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide–bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole–dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10–1 S cm–1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 μW K–2 m–1 compared to ...
TL;DR: The investigated nanomanometers/nanothermometers have been successfully applied, as a proof-of-concept of a novel bimodal optical gauge, for the determination of the temperature of the heated system (473 K), which was simultaneously compressed under HP (1.5 and 5 GPa).
Abstract: Upconversion luminescence of nano-sized Yb3+ and Tm3+ codoped rare earth phosphates, that is, LaPO4 and YPO4, has been investigated under high-pressure (HP, up to ∼25 GPa) and high-temperature (293-773 K) conditions. The pressure-dependent luminescence properties of the nanocrystals, that is, energy red shift of the band centroids, changes of the band ratios, shortening of upconversion lifetimes, and so forth, make the studied nanomaterials suitable for optical pressure sensing in nanomanometry. Furthermore, thanks to the large energy difference (∼1800 cm-1), the thermalized states of Tm3+ ions are spectrally well-separated, providing high-temperature resolution, required in optical nanothermometry. The temperature of the system containing such active nanomaterials can be determined on the basis of the thermally induced changes of the Tm3+ band ratio (3F2,3 → 3H6/3H4 → 3H6), observed in the emission spectra. The advantage of such upconverting optical sensors is the use of near-infrared light, which is highly penetrable for many materials. The investigated nanomanometers/nanothermometers have been successfully applied, as a proof-of-concept of a novel bimodal optical gauge, for the determination of the temperature of the heated system (473 K), which was simultaneously compressed under HP (1.5 and 5 GPa).
TL;DR: In this article, a comprehensive review of metal sulfide-based semiconductors for the degradation or decomposition of dyes in wastewater industries with low cost, environment-friendly and sustainable treatment technologies for the environmental protection is presented.
TL;DR: The simultaneous Sr2+ ion doping and surface Cl- ion passivation result in the enhanced photoluminescence quantum yield, elongated emission lifetime, and improved stability of CsPbI3 perovskite NCs.
Abstract: A method is proposed to improve the photo/electroluminescence efficiency and stability of CsPbI3 perovskite nanocrystals (NCs) by using SrCl2 as a co-precursor. The SrCl2 is chosen as the dopant to synthesize the CsPbI3 NCs. Because the ion radius of Sr2+ (1.18 A) is slightly smaller than that of Pb2+ (1.19 A) ions, divalent Sr2+ cations can partly replace the Pb2+ ions in the lattice structure of perovskite NCs and cause a slight lattice contraction. At the same time, Cl- anions from SrCl2 are able to efficiently passivate surface defect states of CsPbI3 nanocrystals, thus converting nonradiative trap states to radiative states. The simultaneous Sr2+ ion doping and surface Cl- ion passivation result in the enhanced photoluminescence quantum yield (up to 84%), elongated emission lifetime, and improved stability. Sr2+ -doped CsPbI3 NCs are employed to produce light-emitting devices with a high external quantum yield of 13.5%.
TL;DR: In this paper, various cation substitutional dopants in Ga2O3 were investigated for the possibility of p-type conductivity using density functional theory and hybrid functional calculations.
Abstract: We investigate the various cation substitutional dopants in Ga2O3 for the possibility of p–type conductivity using density functional theory. Our calculations include both standard density functional theory and hybrid functional calculations. We demonstrate that all the investigated dopants result in deep acceptor levels, not able to contribute to the p–type conductivity of Ga2O3. In light of these results, we compare our findings with other wide bandgap oxides and reexamine previous experiments on zinc doping in Ga2O3.
TL;DR: Doping plays the beneficial role of passivating surface defect states of CsPbI3 nanocrystals, which results in increased photoluminescence quantum yield, elongated emission lifetime, and improved stability of perovskite films.
Abstract: Lead halide perovskite nanocrystals are currently under intense investigation as components of solution-processed light-emitting devices (LEDs). We demonstrate LEDs based on Ag doped–passivated CsPbI3 perovskite nanocrystals with external quantum efficiency of 11.2% and an improved stability. Ag and trilayer MoO3/Au/MoO3 structure were used as cathode and anode, respectively, which reduce the electron injection barrier and ensure the high transparency and low resistance of the anode. Silver ions diffuse into perovskite film from the Ag electrode, as confirmed by the elemental mapping, the presence of Ag 3d peaks in the X-ray photoelectron spectrum, and the peak shift in the X-ray diffraction patterns of CsPbI3. In addition to doping, silver ions play the beneficial role of passivating surface defect states of CsPbI3 nanocrystals, which results in increased photoluminescence quantum yield, elongated emission lifetime, and improved stability of perovskite films.
TL;DR: Electronic spectroscopy indicates the population of midgap states upon air exposure and corroborates intervalence charge transfer between Fe2+ and Fe3+ centers, demonstrating that inducing metal-based mixed valency is a powerful strategy toward realizing high and systematically tunable electrical conductivity in MOFs.
Abstract: Partial oxidation of an iron–tetrazolate metal–organic framework (MOF) upon exposure to ambient atmosphere yields a mixed-valence material with single-crystal conductivities tunable over 5 orders of magnitude and exceeding 1 S/cm, the highest for a three-dimensionally connected MOF. Variable-temperature conductivity measurements reveal a small activation energy of 160 meV. Electronic spectroscopy indicates the population of midgap states upon air exposure and corroborates intervalence charge transfer between Fe2+ and Fe3+ centers. These findings are consistent with low-lying Fe3+ defect states predicted by electronic band structure calculations and demonstrate that inducing metal-based mixed valency is a powerful strategy toward realizing high and systematically tunable electrical conductivity in MOFs.
TL;DR: In this article, the authors studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in β-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods.
Abstract: We have studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in β-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods, including edge-defined film-fed, Czochralski, molecular beam epitaxy, and low pressure chemical vapor deposition. Through simultaneous, self-consistent fitting of the temperature dependent carrier density and mobility, we are able to accurately estimate the donor energy of Si and Ge to be 30 meV in β-Ga2O3. Additionally, we show that our measured Hall effect data are consistent with Si and Ge acting as typical shallow donors, rather than shallow DX centers. The high temperature Hall effect measurement of Fe doped β-Ga2O3 indicates that the material remains weakly n-type even with the Fe doping, with an acceptor energy of 860 meV relative to the conduction band for the Fe deep acceptor. Van der Pauw measurements of Mg doped Ga2O3 indicate an activation energy of 1.1 eV, as determined from the temperature dependent conductivity.
TL;DR: In this paper, the effect of copper doping on crystal structure of ZnO nanoparticles was investigated and the optical band gap of pure and copper-doped ZnOs was calculated from diffuse reflectance spectroscopy (DRS) spectra and was found to decrease from 3.13
Abstract: Pure and copper-doped zinc oxide nanoparticles (NPs) have been synthesized via chemical co-precipitation method where hydrazine is used as reducing agent and aqueous extract of Euphorbia milii plant as capping agent. Main objectives of the reported work are to investigate the effect of copper doping on crystal structure of ZnO nanoparticles; to study the effect of copper doping on optical band gap of ZnO nanoparticles and photoluminescence (PL) study of pure and copper-doped ZnO nanoparticles. To achieve the aforementioned objectives, XRD and SEM tests were performed for the identification and confirmation of crystal structure and morphology of the prepared samples. From XRD data the average grain size for pure ZnO was observed to be 24.62 nm which was first decreased to 18.95 nm for 5 wt% Cu-doped sample and then it was found to increase up to 37.80 nm as the Cu doping was increased to 7 wt%. Optical band gap of pure and Cu-doped ZnO nanoparticles was calculated from diffuse reflectance spectroscopy (DRS) spectra and was found to decrease from 3.13 eV to 2.94 eV as the amount of Cu increases up to 7 wt%. In photoluminescence study, PL technique was used and enhanced visible spectrum was observed. For further characterization FT-IR and EDX tests were also carried out.
TL;DR: In this paper, the electrical conductivity of poly(3-hexylthiophene) (P3HT) thin films doped with small molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was investigated.
Abstract: Doping of thin films of semiconducting polymers provides control of their electrical conductivity and thermopower. The electrical conductivity of semiconducting polymers rises nonlinearly with the carrier concentration, and there is a lack of understanding of the detailed factors that lead to this behavior. We report a study of the morphological effects of doping on the electrical conductivity of poly(3-hexylthiophene) (P3HT) thin films doped with small molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Resonant soft X-ray scattering shows that the morphology of films of P3HT is not strongly changed by infiltration of F4TCNQ from the vapor phase. We show that the local ordering of P3HT, the texture and form factor of crystallites, and the long-range connectivity of crystalline domains contribute to the electrical conductivity in thin films. The thermopower of films of P3HT doped with F4TCNQ from the vapor phase is not strongly enhanced relative to films doped from solution, but the el...
TL;DR: In this paper, a bio-templated porous microtubular C-doped (BTPMC) g-C3N4 with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio template and in-situ carbon dopant.
Abstract: For the first time, the bio-templated porous microtubular C-doped (BTPMC) g-C3N4 with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio-templates and in-situ carbon dopant. Prior to the thermal condensation process, the impregnation strategies (i.e. direct wet and hydrothermal impregnation) of urea on the treated kapok fibre (t-KF) were compared to obtained well-constructed bio-templated porous microtubular C-doped g-C3N4. The details on a physicochemical characteristic of the fabricated samples were comprehensively analyze using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), N2 adsorption-desorption, Thermogravimetric (TGA), and UV–vis spectroscopy. Our finding indicated that the hydrothermal impregnation strategy resulted in well-constructed microtubular structure and more carbon substitution in sp2-hybridized nitrogen atoms of g-C3N4 as compared to the direct wet impregnation. Also, compared to pure g-C3N4, the fabricated BTPMC g-C3N4 exhibited extended photoresponse from the ultraviolet (UV) to visible and near-infrared regions and narrower bandgap. The bandgap easily tuned with the increased t-KF loading in urea precursor which responsible for in-situ carbon doping. Moreover, as compared to pristine g-C3N4, dramatic suppression of charge recombination of the BTPMC g-C3N4 was confirmed through photoluminescence, photocurrent response, and electrochemical impedance spectroscopy. The resultants BTPMC g-C3N4 possesses more stable structure, promoted charge separation, and suitable energy levels of conduction and valence bands for photocatalysis application.
TL;DR: In this paper, the photocatalytic oxidation of As(III) to As(V) by ZnO photocatsalyts doped with Cu was investigated under visible light.
Abstract: In this work, photocatalytic oxidation of As(III) to As(V) by ZnO photocatalyts doped with Cu was investigated under visible light Photocatalysts were successfully prepared by precipitation method The obtained samples were characterized by N2 adsorption at −196 C, X-Ray fluorescence analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV–vis reflectance analysis In particular, according to XRD analysis, all samples showed an hexagonal wurtzite structure with average crystallite sizes approximately in the range 32–33 nm The doping with Cu allowed to obtain a decrease of band gap energy from 32 eV, typical of pure ZnO, to 292 eV Photocatalytic oxidation tests under visible light showed that undoped ZnO is not able to oxidize the As(III) present in solution, while the complete conversion of As(III) to As(V) was achieved in the presence of Cu doped ZnO photocatalyst The best photocatalytic activity was observed with ZnO doped with 108 mol% of Cu (108Cu_ZnO), within 120 min of exposure to visible light irradiation The same result was observed under solar simulated radiation Photocatalytic tests were carried out also in real drinking water and complete oxidation of As(III) to As(V) by 108Cu_ZnO photocatalyst was achieved in 120 min under both visible light (emitted by LEDs) and solar simulated radiation
TL;DR: In this article, the authors studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in $\beta$-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods.
Abstract: We have studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in $\beta$-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods, including edge-defined film-fed (EFG), Czochralski (CZ), molecular beam epitaxy (MBE), and low pressure chemical vapor deposition (LPCVD). Through simultaneous, self-consistent fitting of the temperature dependent carrier density and mobility, we are able to accurately estimate the donor energy of Si and Ge to be 30 meV in $\beta$-Ga2O3. Additionally, we show that our measured Hall effect data are consistent with Si and Ge acting as typical shallow donors, rather than shallow DX centers. High temperature Hall effect measurement of Fe doped $\beta$-Ga2O3 indicates that the material remains weakly n-type even with the Fe doping, with an acceptor energy of 860 meV relative to the conduction band for the Fe deep acceptor. Van der Pauw measurements of Mg doped Ga2O3 indicate an activation energy of 1.1 eV, as determined from the temperature dependent conductivity.