N-type Semiconductor Characteristics Research Articles

Synthesis, characterization, and double shielding performance for ultraviolet and short-wave blue light of ceria-based materials

In order to extend the photo-shielding range of ceria from the ultraviolet (UV) region (≤ 400 nm) to the high-energy short-wave blue light (BL) region (400–450 nm), three groups of ceria-based materials, including ceria nanoparticles (nano-CeO2), cerium-oxygen-sulfur (Ce-O-S) composites and samarium-cerium-oxygen-sulfur (Sm-Ce-O-S) composites, were prepared from the perspectives of improving the preparation method, non-metal doping and metal/non-metal co-doping. Although the three groups of as-prepared samples have similar phase composition, morphology and pore structure, the Sm-Ce-O-S composites show remarkable double shielding performance for UV light and short-wave BL. Compared with nano-CeO2 and Ce-O-S composites, Sm-Ce-O-S composites that retains the characteristics of n-type semiconductor exhibits a greater degree of lattice distortion, higher concentrations of Ce3+ (41.17%) and oxygen vacancy (77.29%), and narrower band gap (2.71 eV). Through the comparison of the three groups of samples, the order of modification degree from high to low is as follows: metal/non-metal co-doping > non-metal doping > improving the preparation method. This paper provides experimental and theoretical support for breaking through the bottleneck of ceria in the fields of UV shielding agents and catalysts.

Conduction in yttrium iron garnets with nickel dopant: Potential for sensor applications

Doped yttrium iron garnet materials exhibit semiconducting behavior and have potential applications in resistive-based sensors, including thermoresistive and gas sensors. In this study, we synthesized Ni-doped yttrium iron garnet samples using the sol-gel method combined with heat treatment. The crystal structure, morphology, and Ni incorporation into the crystal lattice were investigated using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy. The saturation magnetization of the samples in the ground state was measured in a Physical Property Measurement System (PPMS) at 5K. The experimental magnetic moments deviate significantly from the values calculated based on the cation distribution models, suggesting the occupation of Ni2+ and Fe2+ at the octahedral and tetrahedral sites, respectively, with the latter due to oxygen vacancies. We investigated the resistivity, magnetoresistance effect, and hydrogen sensing properties to elucidate the conduction mechanism. At room temperature, the resistivity of the samples decreased sharply as the oxygen vacancy concentration increased, from ~108 Ωcm in sample x = 0 to ~106 Ωcm in sample x = 0.08. The resistance of the samples increased when exposed to hydrogen gas, supporting the prediction from the magnetization data that the samples exhibit n-type semiconductor characteristics. The samples showed good sensitivity to H2 gas. At 250°C, sample x = 0.08 exhibits a response of S =11.5, the response time (τres. ~8s), and recovery time (τrec. ~22s) at 100 ppm hydrogen concentration.

The electrical properties of nitrogen-doped vanadium dioxide thin films grown by magnetron sputtering

Abstract Vanadium dioxide (VO2) undergoes a reversible semiconductor-metal phase transition near 68°C, and the optical and electrical properties could be changed in femtoseconds. These unique characteristics meet the electro-optic switch applications. In this work, to improve the intrinsic characteristics of VO2, a series of nitrogen-doped vanadium dioxide thin films were prepared by reactive magnetron sputtering. Moreover, the effects of different nitrogen flow rates on the microstructure, surface morphology, electrical properties and phase transition properties of the samples were investigated. The samples are characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), four-point probe system, and Hall effect et al. Sheet resistance variation at room temperature and high temperatures indicates remarkable semiconductor-metal transition characteristics. According to results of Hall effect measurement, when nitrogen flow rate is less than 1 sccm, the samples exhibits p-type semiconductor characteristics. However, while nitrogen flow rate reaches 1 sccm, n-type semiconductor characteristics appear. What’s more, Carrier mobility reaches a maximum at a nitrogen to oxygen flow ratio of 0.3. The results reveal that the samples have a great potential on electro-optic switching applications.

MXene-Enhanced Ionovoltaic Effect by Evaporation and Water Infiltration in Semiconductor Nanochannels.

In recent years, substantial attention has been directed toward energy-harvesting systems that exploit sunlight energy and water resources. Intensive research efforts are underway to develop energy generation methodologies through interactions with water using various materials. In the present investigation, we synthesized sodium vanadium oxide (SVO) nanorods with n-type semiconductor characteristics. These nanorods facilitate the initiation of capillary phenomena within nanochannels, thereby enhancing the interfacial area between nanomaterials and ions. The open-circuit voltage (VOC) was 0.8 V, and the short-circuit current (ISC) was 30 μA, which were continuously monitored at room temperature using a 0.1 M saltwater solution. Additionally, we achieved enhanced energy generation by efficiently converting light energy into thermal energy using MXene, a 2D material. This was accomplished through the photothermal effect, leveraging the inherent semiconductor characteristics. Under light exposure, the system exhibited improved performance attributed to heightened ion diffusion and increased conductivity. This phenomenon was a result of the concerted synergy between ions and electrons facilitated by a semiconductor nanofluidic channel. Ultimately, we demonstrated an application to showcase real-world viability. In this scenario, electricity was harvested through a smart buoy floating on the water, and, based on this, data from the surrounding environment was sensed and wirelessly transmitted.

Unlocking a Type-II CoO@BiVO4 Heterostructure for Wastewater Purification.

Developing a semiconductor-based heterostructure photoanode is crucial in improving the photoelectrocatalytic (PEC) efficiency for degrading refractory organic pollutants. Nevertheless, the PEC performance of the photoanodes is usually restricted by electron/hole pair recombination, oxygen evolution, and slow electron transfer. Herein, a novel CoO@BiVO4 nanowire array film (Ti/CoO@BiVO4) with n-type semiconductor characteristics was prepared via a straightforward hydrothermal method. The optimized Ti/CoO@BiVO4 electrode exhibited excellent PEC decolorization efficiency of active brilliant blue KN-R (∼92.8%) and long-term stability, outperforming recent reports. The insight reason for enhancing the PEC degradation efficiency of the Ti/CoO@BiVO4 electrodes can be attributed to the large electrochemical active area, low charge transfer resistance, and negative flat band potential. The formation of a type-II heterostructure was investigated between CoO and BiVO4 further to promote the generation and separation efficiency of electron/hole pairs, indicating that the optimized Ti/CoO@BiVO4 electrode has the potential for the water PEC degradation ability and superior service life.

Effect of ultraviolet illumination on corrosion resistance of 304 austenitic stainless steel in molybdate-containing solution

This study investigates the effect of ultraviolet (UV) illumination on the corrosion resistance of 304 stainless steel in molybdate-containing solution. The UV illumination was found to reduce the passivation and pitting resistance of the passive films. In addition, the passive film exhibited n-type semiconductor characteristics. Under UV illumination, the content of Cr2O3 within the passive film decreased. Moreover, the formation of a built-in electric field inhibited the absorption of MoO42− on the substrate surface, thereby weakening the corrosion inhibition of Na2MoO4. This leads to a reduction in the corrosion resistance of the passive film.

Influence mechanism of heat treatment on corrosion resistance of Te-containing 15–5PH stainless steel

In this study, the corrosion resistance mechanism of the Te and heat treatments on martensitic stainless steel (15–5PH steel) was investigated. Heat treatment affected the dislocation density of the Te-containing 15–5PH steel and reduced its corrosion tendency. Electrochemical dissolution of the MnS-Te inclusions induced pitting corrosion. Heat treatment significantly affects the potential difference between the Te-modified inclusions and the steel matrix, consequently influencing the emergence of pitting corrosion. Heat treatment improved the anti-corrosion properties of 15–5PH steel by transforming it from an active state to a passive state. The Mott-Schottky test results show that the passive film always exhibits n-type semiconductor characteristics and that the defect density of the passive film is reduced by the heat treatment. Heat treatment facilitated the enrichment of Cr, Te, and TeO3 in the passivation film, resulting in its improved stability and corrosion resistance. The formation of an insoluble or slowly dissolved tellurite film through Te anodic oxidation, along with the self-healing properties of TeO3, improved the repassivation capability of the passivation film of the steel.

Novel Porphyrinic Covalent Organic Polymer with Polarity-Switchable Dual Wavelength for Accurate and Sensitive Photoelectrochemical Sensing.

Herein, we synthesized a novel porphyrinic covalent organic polymer (TPAPP-PTCA PCOP) for constructing a polarity-switchable dual-wavelength photoelectrochemical (PEC) biosensor with ferrocene (Fc) and hydrogen peroxide (H2O2) as regulator and amplifier simultaneously. Interestingly, this new PCOP possessed both n-type and p-type semiconductor characteristics, which thus enabled the appearance of a dual-polarity photocurrent at two different excitation wavelengths. Furthermore, Fc and H2O2 could readily switch the photocurrent of PCOP to the cathode and anode stemming from its efficient electron collection and donation function, respectively. Based on these, a PCOP-based PEC biosensor skillfully integrating dual wavelengths with reliable accuracy and polarity switch with high sensitivity was instituted. As a result, the developed PEC biosensor exhibited a low detection limit down to 0.089 pg mL-1 for the most powerful natural carcinogen aflatoxin M1 (AFM1) assay. Impressively, the target exhibited a completely opposite photocurrent difference to the interfering substances, and the linear correlation coefficient of the assay was improved compared to single-wavelength detection. The PEC sensing platform not only provided a basis for exploring multicharacteristic photoactive material but also innovatively developed the detection mode of the PEC biosensor.

Tuning Dipole Orientation of 2,6-Azulene Units in Conjugated Copolymers by C–H Activation Strategy toward High-Performance Organic Semiconductor

Azulene has aroused widespread interest for constructing optoelectronic materials. However, controlling the dipole orientation of 2,6-azulene units in the conjugated polymer backbone is a significant challenge so far. Herein, by C-H activation strategy, three 2,6-azulene-TPD-based conjugated copolymers with different dipole arrangements were synthesized, where TPD = thieno[3,4-c]pyrrole-4,6-dione. The dipole arrangements of 2,6-azulene units were random for P(AzTPD-1), head-to-head/tail-to-tail for P(AzTPD-2), and head-to-tail for P(AzTPD-3). These polymers exhibited unipolar n-type semiconductor characteristics in organic field effect transistors. Moreover, regioregular polymer P(AzTPD-3) displayed the best device performance with an electron mobility of up to 0.33 cm2 V-1 s-1, which makes P(AzTPD-3) a high-performance n-type polymeric semiconductor. These results demonstrate that incorporation of 2,6-azulene units into the polymeric backbone together with the regulation of the dipole orientation of 2,6-azulene units is an effective strategy for obtaining high-performance organic optoelectronic materials.

Phase control of two-dimensional tin sulfide compounds deposited via atomic layer deposition

Two-dimensional (2D) semiconductor materials are emerging as potential candidates for emerging electronic device applications due to their excellent electrical properties and unique properties such as flexibility and transparency. Among the various potential 2D semiconductor materials, tin sulfide compounds can form polymorphs of different 2D crystals: 2D layered-SnS2 with hexagonal symmetry and 2D layered SnS with orthorhombic symmetry. In addition, since they each have different electrical and optical properties, their controlled growth is important for appropriate target applications. Therefore, we investigated the phase control of tin sulfide compounds deposited via atomic layer deposition according to their deposition temperature and post-annealing conditions. A strategy for controlling the growth of SnS2 or SnS was proposed by investigating phase transition tendencies according to deposition temperature and annealing conditions (temperature, pressure, atmosphere). As a result, it was possible to selectively deposit SnS2 and SnS thin films based on a phase transition study; it was confirmed that SnS2 and SnS thin films exhibited n-type and p-type semiconductor characteristics, respectively.

2D NiCo2S4 decorated on ZnIn2S4 formed S-scheme heterojunction for photocatalytic hydrogen production

The hydrothermal preparation of NiCo2S4/ZnIn2S4 photocatalysts with different mass ratios is studied. Ni-cobalt bimetallic sulfide nanosheets are grown on zinc-indium bimetallic sulfide to form a compact heterojunction. First, both NiCo2S4 and ZnIn2S4 exhibit N-type semiconductor characteristics, a heterojunction formed by both can reduce the surface reaction energy barrier and use its synergy, strengthening the charge self-diffusion between the two semiconductors, it means the formation of a strong electric field. From the electron transfer path and band structure, NiCo2S4/ZnIn2S4 has S-scheme heterojunction characteristics. NiCo2S4 is a reducing photocatalyst (RP), and ZnIn2S4 is an oxidative photocatalyst (OP). Under the action of built-in electric field (BIEF), strong photogenic electrons and holes exist in CB of RP (NiCo2S4) and VB of OP (ZnIn2S4). Thus, the overall redox capacity of the NiCo2S4/ZnIn2S4 heterojunction is enhanced. Using visible light, the composite material can be used for photocatalytic hydrogen production. It is further shown that the composite material has a good effect in photocatalytic hydrogen production under the sensitizer eosin Y (EY) system. The optimal hydrogen production is about 221.75 μmol when the mass ratios of NiCo2S4/ZnIn2S4 is 20%, and the photocatalytic activity of the composite is about 47 times that of ZnIn2S4. Notably, the stability of the composites is the better. A reasonable photo-catalytic mechanism is proposed based on the band gap and photoelectrochemical properties of heterojunction.

Effect of Nb content on the microstructure and corrosion resistance of FeCoCrNiNbx high-entropy alloys in chloride ion environment

In this paper, FeCoCrNiNbx high-entropy alloys were prepared by vacuum arc melting, and their microstructure and corrosion resistance in a chloride ion environment were investigated. The results indicated that FeCoCrNi alloy was a single FCC solid solution and FeCoCrNiNbx alloy was a duplex alloy with FCC phase and Laves phase. FeCoCrNiNb0.15 showed the best corrosion resistance. The corrosion current density of FeCoCrNiNb0.15 decreased by one order compared with 316LSS, and the corrosion rate after the immersion experiment was only one-third of 316LSS. The P-N junction improved the corrosion resistance of the passive film of FeCoCrNiNb0.15, while the passive film of FeCoCrNi mainly exhibited n-type semiconductor characteristics with less obvious p-type semiconductor characteristics.

Versatile TiO2 bandgap modification with metal, non-metal, noble metal, carbon material, and semiconductor for the photoelectrochemical water splitting and photocatalytic dye degradation performance

TiO2 is a flexible material for photocatalytic applications owing to its convenient redox potential, eco-friendliness, and abundance. However, TiO2 requires minor adjustments to improve its absorption ability and to suppress charge carrier recombination. Hence, simple chemical procedures have been used to modify TiO2 by using metals (e.g., Ni), non-metals (e.g., N), noble metals (e.g., Ag), carbon materials (e.g., carbon nanofibers), and semiconductors (Fe2O3) as dopants or by forming composites. The photoelectrochemical (PEC) water splitting and photocatalytic dye degradation performance of the synthesized materials were compared. Fe2O3-TiO2 composite performed admirably in both reactions owing to its unique absorption strength and the formation of the heterojunction interface. Fe2O3-TiO2 demonstrated azo dye degradation efficiency of 94.4%. The Fe2O3-TiO2 photoelectrode in the PEC system exhibited a photocurrent response of 0.244 amp/cm2. This outstanding performance is due to the formation of the heterojunction interface that is attributable to the p-type and n-type semiconductor characteristics of the composite. Moreover, the noticeable absorption strength of Fe2O3-TiO2 enables the generation of additional charge carriers and effectively reduces the recombination rate owing to the formation of the heterojunction interface. Characterization techniques including X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, fluorescence spectroscopy, scanning electron microscopy, and transmission electron microscopy, were used to investigate the photocatalytic characteristics. This study promotes the development of new heterojunction semiconductors and dopants for photocatalytic applications.

Electrochemical corrosion and passive behavior of a new high-nitrogen austenitic stainless steel in chloride environment

In this work, the electrochemical corrosion and passive behavior of a high-nitrogen austenite stainless steel named QN2109 in different NaCl solutions were studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and X-ray photoelectron spectroscopy (XPS). QN2109 stainless steel exhibited a wide passive region and high impedance value in the chloride environment. The high ratio of O2−/OH− made the passive film better self-repair effect, and the passive film is mainly composed of Mo-oxides, Fe-oxides and Cr-oxides, providing excellent pitting corrosion resistance at room temperature. The passive film with p-type and n-type semiconductor characteristics showed a double-layer structure. In addition, the influence of CrN and NH3/NH4+ in passive films was also discussed.

Thermoelectric Transport Properties of Pb(Bi1-xSnx)2Te4 (0≤x≤1) compounds

In this study, the effect of Sb incorporation on the thermoelectric transport properties of tetradymite-type Pb(Bi2-xSbx)Te4 (0≤x≤1) compounds is presented. PbBi2Te4 (x = 0) possesses a high electron concentration of ~1.6×10<sup>20</sup>/cm<sup>3</sup> at room temperature and exhibits n-type degenerate semiconductor behavior, in which electrical conductivity decreases and negative Seebeck coefficient increases almost linearly with increasing temperature. For x = 0.5, the electron concentration decreased to ~5.5×10<sup>19</sup>/cm<sup>3</sup> and n-type semiconductor characteristics was observed. When the Sb content increased to x = 1, the majority charge carrier was found to be hole (p ~ 3.3×10<sup>19</sup>/cm<sup>3</sup>), thus a change in polarity from n-type to p-type semiconductor was observed. It was suggested that the change in polarity with Sb incorporation observed in this study is due to the formation of a p-type antisite defect, which is formed because the electronegativity of Sb is closer to that of Te than that of Bi. Due to the decrease in charge concentration with the increase in Sb content, it was possible to increase the power factor near room temperature for x = 0.5. However, the overall output factor decreased with increasing x. These results are expected to be helpful in efforts to improve the thermoelectric properties of tetradymite-type homologous compounds through antisite defect control.

Synthesis of Group VIII Magnetic Transition-Metal-Doped Monolayer MoSe2.

The limitation on the spintronic applications of van der Waals layered transition-metal dichalcogenide semiconductors is ascribed to the intrinsic nonmagnetic feature. Recent studies have proved that substitutional doping is an effective route to alter the magnetic properties of two-dimensional transition-metal dichalcogenides (TMDs). However, highly valid and repeatable substitutional doping of TMDs remains to be developed. Herein, we report group VIII magnetic transition metal-doped molybdenum diselenide (MoSe2) single crystals via a one-pot mixed-salt-intermediated chemical vapor deposition method with high controllability and reproducibility. The high-angle annular dark-field scanning transmission electron microscopy studies further confirm that the sites of Fe are indeed substitutionally incorporated into the MoSe2 monolayer. The Fe-doped MoSe2 monolayer with a concentration from 0.93% to 6.10% could be obtained by controlling the ratios of FeCl3/Na2MoO4. Moreover, this strategy can be extended to create Co(Ni)-doped MoSe2 monolayers. The magnetic hysteresis (M-H) measurements demonstrate that group VIII magnetic transition-metal-doped MoSe2 samples exhibit room-temperature ferromagnetism. Additionally, the Fe-doped MoSe2 field effect transistor shows n-type semiconductor characteristics, indicating the obtainment of a room-temperature dilute magnetic semiconductor. Our approach is universal in magnetic transition-metal substitutional doping of TMDs, and it inspires further research interest in the study of related spintronic and magnetoelectric applications.

Effects of pH and Cl− Content on Degradation Process of Pre-Passivated Stainless Steels in an Alkaline Solution

The degradation behavior of four prepassivated stainless steels (SSs) in the alkaline solutions with different Cl− concentrations and pH values were investigated by cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis and the X-ray photoelectron spectroscopy (XPS). The results indicated that the pH value and Cl− concentration, together with the phase ratio difference in the microstructure of SS, played a critical role in the degradation process of passive film. At low pH and high Cl− concentration, the passive film gradually enriched in Fe3+ and Cr3+ species and depleted in Fe2+ oxides and its self-regeneration process became more difficult. As the pH decreased, the passive film exhibited clear n-type and p-type semiconductor characteristics more clearly, and the decrease in dopant density well reflected the changes in Fe2+/Fe3+ ratio and electrochemical behavior. Based on the viewpoint of adsorption balance between OH− with inhibitory effect and Cl− with promotion effect on the degradation process, a mechanism for the degradation process of prepassivation film was proposed.

A Highly Luminescent Nitrogen-Doped Nanographene as an Acid- and Metal-Sensitive Fluorophore for Optical Imaging.

Dibenzo[hi,st]ovalene (DBOV) has excellent photophysical properties, including strong fluorescence and high ambient stability. Moreover, the optical blinking properties of DBOV have enabled optical super-resolution single-molecule localization microscopy with an imaging resolution beyond the diffraction limit. Various organic and inorganic fluorescent probes have been developed for super-resolution imaging, but those sensitive to pH and/or metal ions have remained elusive. Here, we report a diaza-derivative of DBOV (N-DBOV), synthesized in eight steps with a total yield of 15%. Nitrogen (N)-bearing zigzag edges were formed through oxidative cyclization of amino groups in the last step. UV–vis and fluorescence spectroscopy of N-DBOV revealed its promising optical properties comparable to those of the parent DBOV, while cyclic voltammetry and density functional theory calculations highlighted its lower orbital energy levels and potential n-type semiconductor character. Notably, in contrast to that of the parent DBOV, the strong luminescence of N-DBOV is dependent on pH and the presence of heavy metal ions, indicating the potential of N-DBOV in sensing applications. N-DBOV also exhibited pH-responsive blinking, which enables pH-sensitive super-resolution imaging. Therefore, N-DBOV appears to be a highly promising candidate for fluorescence sensing in biology and environmental analytics.

Effects of intrinsic defects and doping on SrFe12O19: A first-principles exploration of the structural, electronic and magnetic properties

Effects of intrinsic defects and doping on the M−type strontium hexagonal ferrites (SrFe12O19) has been systematically studied using density functional theory combined with the generalized gradient approximation (GGA) + U method. The energies of possible intrinsic point defects and doping in SrFe12O19 have been determined, and effects of those on the electronic and magnetic properties have been analyzed. The results show that, under an oxygen poor condition, the defects of iron vacancy are difficult to form, while the defects of oxygen vacancy are easy to form. In the case of oxygen rich condition, the defects of iron vacancy are difficult to form when Fermi energy level is close to VBM, however, when Fermi energy level approaches CBM, the defects of iron vacancy in some sublattice sites are tend to form, especially in the 2a sublattice. Meanwhile, under the oxygen rich condition, the defect formation energy of Co substituting for Fe is very low, which indicates that Fe is easy to be substituted by Co, preferentially in 4f2 sublattice, followed by 2a sublattice. The lattice constant of La-Co co-doped is smaller than that of perfect SrFe12O19, meanwhile, the total magnetic moment changes little. The density of states shows that La-Co co-doped SrFe12O19 exhibits n-type semiconductor characteristics.

Carrier Diffusion and Recombination Anisotropy in the MAPbI3 Single Crystal.

MAPbI3, one of the archetypical metal halide perovskites, is an exciting semiconductor for a variety of optoelectronic applications. The photoexcited charge-carrier diffusion and recombination are important metrics in optoelectronic devices. Defects in grain interiors and boundaries of MAPbI3 films cause significant nonradiative recombination energy losses. Besides defect impact, carrier diffusion and recombination anisotropy introduced by structural and electronic discrepancies related to the crystal orientation are vital topics. Here, large-sized MAPbI3 single crystals (SCs) were grown, with the (110), (112), (100), and (001) crystal planes simultaneously exposed through the adjusting ratios of PbI2 to methylammonium iodide (MAI). Such MAPbI3 SCs exhibit a weak n-type semiconductor character, and the Fermi levels of these planes were slightly different, causing a homophylic p-n junction at crystal ledges. Utilizing MAPbI3 SCs, the photoexcited carrier diffusion and recombination within the crystal planes and around the crystal ledges were investigated through time-resolved fluorescence microscope. It is revealed that both the (110) and (001) planes were facilitated to be exposed with more MAI in the growth solutions, and the photoluminescence (PL) of these planes manifesting a red-shift, longer carrier lifetime, and diffusion length compared with the (100) and (112) planes. A longer carrier diffusion length promoted photorecycling. However, excessive MAI-assisted grown MAPbI3 SCs could increase the radiative recombination. In addition, it revealed that the carrier excited within the (001) and (112) planes was inclined to diffuse toward each other and was favorable to be extracted out of the grain boundaries or crystal ledges.