Effect Of Electron Doping Research Articles

Promoted room temperature NH3 gas sensitivity using interstitial Na dopant and structure distortion in Fe0.2Ni0.8WO4

The demand for gas-sensing operations with lower electrical power and guaranteed sensitivity has increased over the decades due to worsening indoor air pollution. In this report, we develop room-temperature operational NH3 gas-sensing materials, which are activated through electron doping and crystal structure distortion effect in Fe0.2Ni0.8WO4. The base material, synthesized through solid-state synthesis, involves Fe cations substitutionally located at the Ni sites of the NiWO4 crystal structure and shows no gas-sensing response at room temperature. However, doping Na into the interstitial sites of Fe0.2Ni0.8WO4 activates gas adsorption on the surface via electron donation to the cations. Additionally, the hydrothermal method used to achieve a more than 70-fold increase in the surface area of structure-distorted Na-doped Fe0.2Ni0.8WO4 powder significantly enhances gas sensitivity, resulting in a 4-times increase in NH3 gas response (Rg/Ra). Photoluminescence and XPS results indicate negligible oxygen vacancies, demonstrating that cation contributions are crucial for gas-sensing activities in Na-doped Fe0.2Ni0.8WO4. This suggests the potential for modulating gas sensitivity through carrier concentration and crystal structure distortion. These findings can be applied to the development of room-temperature operational gas-sensing materials based on the cations.

Electrode-Dependent and Tunable Sub-to-Super-Linear Responsivity in Mott Material-Enabled Near-Infrared Photodetectors for Advanced Near-Sensor Image Processing.

Brain-like intelligence is ushering humanity into an era of the Internet of Perceptions (IoP), where the vast amounts of data generated by numerous sensing nodes pose significant challenges to transmission bandwidth and computing hardware. A recently proposed near-sensor computing architecture offers an effective solution to reduce data processing delays and energy consumption. However, a pressing need remains for innovative hardware with multifunctional near-sensor image processing capabilities. In this work, Mott material (vanadium dioxide)-based photothermoelectric near-infrared photodetectors are developed that exhibit electrode-dependent and tunable super-linear photoresponse (exponent α > 33) with ultralow modulation bias. These devices demonstrate an opto-thermo-electro-coupled phase transition, resulting in a large photocurrent on/off ratio (>105), high responsivity (≈500 A W-1), and well detectivity (≈3.9× 1012 Jones), all while maintaining rapid response speeds (τr = 2 µs and τd = 5 µs) under the bias of 1V. This electrode-dependent super-linear response is found to arise from the electron doping effect determined by the polarity of the Seebeck coefficient. Furthermore, the work showcases intensity-selective near-sensor processing and night vision pattern reorganization, even with noisy inputs. This work paves the way for developing near-sensor devices with potential applications in medical image preprocessing, flexible electronics, and intelligent edge sensing.

Indirect-To-Direct Bandgap Crossover and Room-Temperature Valley Polarization of Multilayer MoS2 Achieved by Electrochemical Intercalation.

Monolayer (1L) group VI transition metal dichalcogenides (TMDs) exhibit broken inversion symmetry and strong spin-orbit coupling, offering promising applications in optoelectronics and valleytronics. Despite their direct bandgap, high absorption coefficient, and spin-valley locking in K or K' valleys, the ultra-short valley lifetime limits their room-temperature applications. In contrast, multilayer TMDs, with more absorptive layers, sacrifice the direct bandgap and valley polarization upon gaining inversion symmetry from the bilayer structure. It is demonstrated that multilayer molybdenum disulfide (MoS2) can maintain 1) a structure with broken inversion symmetry and strong spin-orbit coupling, 2) a direct bandgap with high photoluminescence (PL) intensity, and 3) stable valley polarization up to room temperature. Through the intercalation of organic 1-ethyl-3-methylimidazolium (EMIM+) ions, multilayer MoS2 not only exhibits layer decoupling but also benefits from an electron doping effect. This results in a hundredfold increase in PL intensity and stable valley polarization, achieving 55% and 16% degrees of valley polarization at 3 K and room temperature, respectively. The persistent valley polarization at room temperature, due to interlayer decoupling and trion dominance facilitated by a gate-free method, opens up potential applications in valley-selective optoelectronics and valley transistors.

Influence of Mg doping on structure and optical properties of red-emitting phosphor Li2TiO3:Mn4+

Li2TiO3:Mn4+ has been previously identified as a potential candidate to replace commercial red-emitting Eu2+-activated phosphors. Its luminescent efficiency is limited by the presence of defects and the sensitivity of Mn4+ to redox processes. A series of co-doped Li2TiO3: x Mg2+, 0.01 Mn4+ samples were prepared to gain insight on the effect of electron doping on the structure and photoluminescent properties, through characterization by powder X-ray diffraction, elemental analysis, and optical spectroscopy. As Mg2+ substitutes for Li+, the ordered arrangement of cations within the honeycomb layers in the parent structure (Li2SnO3-type, an ordered derivative of rocksalt) gradually transforms to a more disordered arrangement. The increased cation site disorder leads to less intense and broader emission peaks as well as lower quantum yields.

Enhanced Performance of P-Channel CuIBr Thin-Film Transistor by ITO Surface Charge-Transfer Doping.

The process development and optimization of p-type semiconductors and p-channel thin-film transistors (TFTs) are essential for the development of high-performance circuits. In this study, the Br-doped CuI (CuIBr) TFTs are proposed by the solution process to control copper vacancy generation and suppress excess holes formation in p-type CuI films and improve current modulation capabilities for CuI TFTs. The CuIBr films exhibit a uniform surface morphology and good crystalline quality. The on/off current (ION/IOFF) ratio of CuIBr TFTs increased from 103 to 106 with an increase in the Br doping ratio from 0 to 15%. Furthermore, the performance and operational stability of CuIBr TFTs are significantly enhanced by indium tin oxide (ITO) surface charge-transfer doping. The results obtained from the first-principles calculations well explain the electron-doping effect of ITO overlayer in CuIBr TFT. Eventually, the CuIBr TFT with 15% Br content exhibits a high ION/IOFF ratio of 3 × 106 and a high hole field-effect mobility (μFE) of 7.0 cm2 V-1 s-1. The band-like charge transport in CuIBr TFT is confirmed by the temperature-dependent measurement. This study paves the way for the realization of transparent complementary circuits and wearable electronics.

Large anomalous Nernst conductivity of L10-ordered CoPt in CoPt composition-spread thin films

We demonstrate a high-throughput experimental characterization of anomalous Nernst conductivity ( αxyA ) of L10-ordered CoPt using Co1–x Pt x composition-spread thin films on MgO(100) substrates. The compositional dependence of the anomalous Nernst effect, anomalous Hall effect (AHE) and Seebeck effect is systematically measured. As increasing the Pt concentration, the crystal structure in the composition-spread film grown at 500 °C changes from face-centered cubic (fcc) Co, A1-disordered CoPt, L10-ordered CoPt, A1-CoPt to fcc Pt. The largest αxyA of 2.52 A m–1 K–1 is obtained in L10-CoPt for Pt-rich composition of x = 70%, which is larger than that for an additionally fabricated nearly stoichiometric L10-Co48Pt52 reference uniform film. The contribution from direct conversion of a temperature gradient to a transverse charge current through αxyA is dominant to the total anomalous Nernst coefficient compared to the AHE-related contribution. From a scaling analysis of the AHE, the intrinsic contribution is found to be dominant for x = 70%. A theoretical calculation for αxyA of L10-Co50Pt50 agrees with the experimental αxyA value for the nearly stoichiometric reference film by considering on-site Coulomb interaction for Co atoms. We also point out the possible electron doping effect by the addition of Pt in L10-CoPt, which could explain the larger αxyA for the off-stoichiometric Pt-rich composition than that for the nearly stoichiometric one. Our experimental and theoretical results suggest the potential of L10-CoPt with a large αxyA originating from the intrinsic mechanism for future thermoelectric applications.

Design strategy to simultaneously enhance electrical conductivity and strength: Cold-drawn copper-based composite wire with in-situ graphene

We proposed a unique wire-production process by rolling up and drawing chemical vapor deposition copper/graphene (Cu/Gr) foils, and a good strength-conductivity trade-off was achieved originating from the dispersed Gr in Cu matrix and the high-quality heterointerfaces. The 1.14 mm cold-drawn composite wire exhibited a tensile strength of 455 ± 5 MPa and a conductivity of 98.18 ± 0.16 % of the International Annealed Copper Standard (IACS), and the tensile strength was 250 ± 2 MPa with a satisfied electrical conductivity of 101.68 ± 0.52 % IACS upon annealing. The microstructure involution during the preparing process was revealed, and the reinforcement mechanisms in the yield strength and conductivity due to the introduced Gr were clarified. The results indicated that the Gr plays a role in pinning dislocations and preventing grain boundary movement during deformation and the subsequent annealing, thereby enhancing the strength of the Cu matrix. Meanwhile, the Cu-Gr coupling interfaces exhibited an electronic doping effect, enhancing the conductive properties. Our work presented a feasible method for preparing Cu/Gr composite wire with comprehensive electrical conductivity and strength optimization.

The coexistence and competition of charge-density wave and superconductivity in the electron-doped H- MX2 (M = Mo, W and X=S, Se)

In the group VI transition metal dichalcogenides (TMDs), an insulator family with two-dimensional structure, MoS2 has recently demonstrated to be involved in charge-density wave (CDW) and superconductivity (SC). Nevertheless, there is a lack of a cohesive theoretical framework and fragmentation in the existing theoretical models of the relationship between CDW and SC for this system. Base on first-principles calculations, the effects of electron doping on the electronic properties, electron-phonon interaction and SC are investigated comprehensively for monolayer H- MX2 (M = Mo, W and X = S, Se) here. We confirmed that two CDW phases, 23×23 and 2 × 2, are originated from Fermi surface nesting (FSN) and electron-phonon coupling (EPC), respectively. A complicated phase diagram of doping concentration dependencies of CDW and SC critical temperatures (TC) is created, by SC coexisting with 23×23 CDW phase while competing with 2 × 2 CDW phase. The physical mechanisms of such coexistence and competition are also explained here. Our results extend the theoretical investigation by providing a comprehensive and in-depth analysis of CDW and SC in the group VI TMDs, and open up an alternative path for the exploration and regulation of collective phases of two-dimensional materials.

Superconductivity and charge density wave in Cu0.06TiSe2: A low-temperature STM/STS investigation

As one of the earliest discovered two-dimensional materials possessing charge density wave (CDW), TiSe2 has attracted wide attention due to its superconductivity induced by Cu intercalation. Until now, the relationship between superconductivity and CDW remains unclear, largely due to insufficient research at extremely low temperatures and magnetic fields. In this study, spatially resolved electronic density of states (DOS) of Cu0.06TiSe2 is investigated using low-temperature scanning tunneling microscopy/spectroscopy measurements. It is found that short-ranged commensurate CDW coexists with a homogeneous superconductivity exhibiting an anisotropic s-wave gap with an amplitude of 0.5 meV. Compared to the parent compound TiSe2, the spectra of Cu0.06TiSe2 exhibit a clear electron doping effect, as evidenced by a 70 meV shift of Fermi energy. Interestingly, the DOS is found to be strongly modified near the Fermi energy, despite its overall rigid band nature. These findings suggest that it is the remnant electron–hole coupling that sustains the short-ranged CDW, while the doping enhanced DOS facilitates superconductivity. This reveals a momentum space competition between the two microscopically coexistent orders.

Quantification of the sheet resistance between two-dimensional semiconductors and semi-metals by a contact-end-resistance method

Semi-metal presents an extremely promising method for establishing an ohmic contact with near-quantum-limit contact resistance (Rc) in two-dimensional material (2DM) transistors. However, the physical mechanisms occurring at the interface between 2DMs and semi-metals, which contribute to Rc reduction, are not yet well understood. Leveraging on the contact-end-resistance model applied to the transfer length method structure, we conduct a quantitative and comprehensive characterization of the molybdenum disulfide (MoS2) contact interface with various contact metals. The sheet resistance beneath the semi-metal contact (Rsk) is found to be two orders of magnitude smaller than the sheet resistance of the channel (Rsh), validating the electron doping effect of semi-metals on MoS2 contact areas. Among semi-metals studied, including bismuth (Bi), antimony (Sb), and their alloy, Bi results in the highest electron doping density and the lowest Rsk of 764 Ω/◻, leading to an improvement in Rc down to 526 Ω μm. This work provides a perspective toward the physical mechanisms beneath the semi-metal induced Rc reduction, setting a strong foundation for devising strategies to lower the Rc in 2D-based devices.

Atomic construction and spectroscopic characterization of FeSe-derived thin films on SrTiO3 substrates

Controllably fabricating low-dimensional systems and unraveling their exotic states at the atomic scale is a pivotal step for the construction of quantum functional materials with emergent states. Here, by utilizing the elaborated molecular beam epitaxy growth, we obtain various FexSey phases beyond the single-layer FeSe/SrTiO3 films. A synthetic strategy of lowering substrate temperature with superfluous Se annealing is implemented to achieve various stoichiometric FeSe-derived phases, ranging from 1:1 to 5:8. The phase transitions and electronic structure of these FexSey phases are systematically characterized by atomic resolution scanning tunneling microscopy measurements. We observe the long-ranged antiferromagnetic order of the Fe4Se5 phase by spin-polarized signals with striped patterns, which is also verified by their magnetic response of phase shift between adjacent domains. The electronic doping effect in insulating Fe4Se5 and the kagome effect in metallic Fe5Se8 are also discussed, where the kagome lattice is a promising structure to manifest both spin frustration of d electrons in a quantum-spin-liquid phase and correlated topological states with flat-band physics. Our study provides promising opportunities for constructing artificial superstructures with tunable building blocks, which is helpful for understanding the emergent quantum states and their correlation with competing orders in the FeSe-based family.

Crystal structure, magnetism, electronic structure and effect of electron doping in ThCrAsN: An ab-initio study

In this work, we use first principles methods, to predict a mechanically and dynamically stable crystal structure of ThCrAsN which is iso-structural to ThXAsN (X = Mn,Fe,Co,Ni). We have investigated its mechanical, thermal, magnetic and electronic properties. Our calculation reveals that the magnetic ground state of ThCrAsN is G-AFM. Bader charge analysis reveals a significant inter-layer charge transfer between ThN and CrAs layers. Electronic structure of ThCrAsN is thoroughly investigated by evaluation of density of states, band structure and FSs for NM as well as G-AFM phases. Our calculation predicts a metallic behaviour for both the phases. Existence of FS pockets, consisting of multiple Cr-d orbitals at different parts of the Brillouin zone is observed. The influence of electron correlation effects on the electronic structure of ThCrAsN has been investigated using the Hubbard model. We also evaluate Lindhard response function to study the FS nesting which indicate a stronger FS nesting along Γ-X direction as compared to the Γ-M direction. Furthermore, we have examined the alterations in the density of states resulting from the partial substitution of Cr atom with Mn atom in ThCrAsN. Our findings suggest the occurrence of a metal-insulator transition in ThCrAsN upon Mn doping.

Electron-hole asymmetry in the phase diagram of carrier-tuned CsV3Sb5

In this work, we study the effect of electron doping on the kagome superconductor CsV3Sb5. Single crystals and powders of CsV3Sb5−xTex are synthesized and characterized via magnetic susceptibility, nuclear quadrupole resonance, and x-ray diffraction measurements, where we observe a slight suppression of the charge density wave transition temperature and superconducting temperature with the introduction of electron dopants. In contrast to hole doping, both transitions survive relatively unperturbed up to the solubility limit of Te within the lattice. A comparison is presented between the electronic phase diagrams of electron- and hole-tuned CsV3Sb5.

Structural, electronic and magnetic properties of electron-doped CrAs

We report the effect of electron doping in binary transition metal-pnictide compound CrAs in polycrystalline compositions (Cr0.85T0.15)As (T = Fe, Co, Ni). Room temperature powder x-ray diffraction measurements show that the impurity-free doped samples crystallize in the orthorhombic MnP-type crystal structure with space group Pnma. Electrical resistivity ρ(T) data of all three compositions exhibit metallic behaviour with the room temperature ρ of about 1 mΩ cm, which is close to the values observed in single-crystal and polycrystalline samples of CrAs. Magnetic susceptibility χ(T) data of all three compositions show paramagnetic behaviour and show no evidence any magnetic ordering down to 1.8 K. The ρ(T) and χ(T) results collectively reveal that the antiferromagnetic ordering observed at Néel temperature TN ≈ 270 K in CrAs is absent in the doped samples.

Wearable Sensors Based on Atomically Thin P‐Type Semiconductors

Abstract2D materials have exceptional physical and chemical characteristics, which makes them attractive for wearable technology. These characteristics include high carrier mobility, outstanding mechanical performance, abundant chemistry, and excellent electrostatic tunability. However, due to the high electron doping effect of interfacial charge impurities and intrinsic defects, most reported 2D materials are n‐type. Complementary electronic devices and high‐performance wearable sensors necessitate the development of p‐type 2D semiconductors, which have superior electrocatalytic performance in oxidative processes compared to their n‐type counterparts. This review paper thoroughly accounts for recent advancements in 2D p‐type semiconductor‐based wearable sensors, covering basic understandings, synthesis and fabrication, functional devices, and sensor performance insights. Finally, challenges and future opportunities for 2D p‐type semiconductor‐based wearable sensors are discussed.

Thermodynamics Properties of (6, 6, 12)-Graphyne Structure Due to Biaxial Strain and Magnetic Field Effects

In this paper, we apply a tight binding Hamiltonian model in the presence of magnetic field for investigation of the electronic and transport properties of (6, 6, 12)-graphyne layer. We have also considered the effects of in-plane biaxial strain on the electronic behavior of (6, 6, 12)-graphyne layer. Moreover the impact of strains on magnetic susceptibility and specific heat of the structure has been studied. Specially, the temperature dependence of static thermal conductivity of (6, 6, 12)-graphyne layer has been studied due to magnetic field and strain effects. We have exploited the linear response theory and Green’s function approach to obtain the temperature behavior of thermal conductivity, electrical conductivity and Seebeck coefficient. Our numerical results indicate, thermal conductivity increases upon increasing the temperature in the low amounts region. This fact comes from the increasing of thermal energy of charge carriers and excitation of them to the conduction bands. The temperature dependence of Seebeck coefficient shows that the thermopower of undoped (6, 6, 12)-graphyne layer gets positive sign on the whole range of temperatures in the absence of strain effects. The effects of both electron doping and magnetic field factors on temperature behavior of electrical conductivity of (6, 6, 12)-graphyne have been investigated in details. Moreover the effects of biaxial strain on thermal conductivity of single layer (6, 6, 12)-graphyne have been addressed.

Biaxial ([110]) strain influence on the n-type half-metallicity and Curie temperature of Tc-doped Janus MoSSe monolayer

2D materials having stable half-metallic (HM) ferromagnetism are pivotal for multifunctional spintronic devices such as non-volatile random access magnetic memories and magnetic sensors. Using ab-initio calculations, we theoretically demonstrate that the electron-doped (Tc-doping at Mo site) Janus MoSSe monolayer (ML) is an n-type HM ferromagnetic (FM) with a charge carrier density of 2.9 × 1012 cm−2, which is thermally, mechanically, and dynamically stable. In addition, the large HM energy band gap of 1.63 eV is high enough to establish the long spin mean free path, high spin-filtering performance, and to avoid thermally excited spin-flip transition. Simultaneously, the calculated Curie temperature (TC) using a classical 2D Heisenberg model is 175 K, which indicates that Tc-doped MoSSe ML could be a stable FM structure. Interestingly, it is revealed that TC approaches to room temperature value for Fe 3d transition metals doping at Mo site, which makes the Fe-doped MoSSe ML highly desired for device application. Moreover, a direct-to-indirect band gap transition occurs in the pristine MoSSe ML for a biaxial ([110]) compressive/tensile (comp./tens.) strain of ≥−/+2%. It is also predicted that the n-type HM nature of the Tc-doped ML is very sensitive against applied strains and can be preserved under the -3% comp. to +2% tens. strain range. Along with this, the system undergoes a transition from FM to a non-magnetic state at a critical tensile strain of ＋ 5%, while the FM state remains robust under applied comp. strains. Correspondingly, it is also proposes that TC can be enhanced when a moderate compr. strain is adjusted. Hence, the present work are supposed to trigger further experimental studies to probe HM FM behavior in various Janus MLs by the combined effect of electron doping and strain engineering.

Electron doping of SmNiO3 via interfacial charge transfer: A first-principles study

SmNiO3 is a representative quantum material exhibiting the antidoping behavior, where the conductivity of the material is reduced rather than increased by electron doping. Recent experimental and theoretical works have demonstrated a phase transition of SmNiO3 with large conductance changes via chemical methods. However, the effect of electron doping via interfacial charge transfer in SmNiO3 is much less studied. In this work, the first-principles density functional theory (DFT)+U method is employed to investigate the SmNiO3/YTiO3 superlattice, in which the YTiO3 layer acts as the electron donor. Compared with the chemical doping in SmNiO3, several interesting physical phenomena have been predicted in SmNiO3/YTiO3 superlattices due to the lattice and electronic reconstructions. First, at a doping concentration of 1e− per Ni, i.e., (SmNiO3)1/(YTiO3)1 superlattice, all Ni3+ are converted to Ni2+, resulting in a Mott-insulating phase, similar to the chemical doping in the pristine material. Interestingly, such a Mott gap can be efficiently modulated by tuning the stacking orientation. Second, at a doping concentration of 12e− per Ni, i.e., [001]-orientated (SmNiO3)2/(YTiO3)1 superlattice, the electronic structure associated with charge ordering depends on the concrete magnetic order, giving rise to magnetism-dependent electronic behavior. In addition, as the doping concentration further decreases (i.e., a doping concentration of 13e−/Ni), a metallic state is predicted in a [001]-orientated (SmNiO3)3/(YTiO3)1 superlattice, which is quite different from the case of chemical doping.

Magnetocaloric effect in the Ising model with RKKY interaction on the Shastry–Sutherland lattice

The classical Monte Carlo method is used to examine effects of electron and hole doping on the magnetocaloric effect in the generalized 2D Ising model with the long-range RKKY interaction on the Shastry–Sutherland lattice. The electron and hole doping in this model is controlled by deviations of the Fermi wave vector kF from the initial value kF=2π/1.24 which models the most realistically situation in the undoped metallic Shastry–Sutherland rare-earth tetraboride TmB4. For the undoped case we have found a heating hill (the entropy change ΔS>0) occurring in the vicinity of metamagnetic transitions and a cooling depression in the paramagnetic phase which is in a very good qualitative agreement with experimental measurements in TmB4. In the case of small electron doping (kF=2π/1.26), a significant decrease of the maximum of −ΔS is observed, while in the strongly hole (electron) doped case kF=2π/1.17 (kF=2π/1.43) the maximum of −ΔS is considerably enhanced against the undoped system, which points to the fact that some of doped systems could have better cooling properties than the undoped one. This is confirmed independently by calculations of relative cooling power for a wide range of parameter kF, where we have found two intervals kF∈〈2π/1.15,2π/1.21〉 and kF∈〈2π/1.39,2π/1.5〉 with much larger relative cooling power in comparison to the undoped case.

Electron doping induced stable ferromagnetism in two-dimensional GdI3 monolayer

As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM–FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d–4f hybridization. Moreover, the shortened Gd–Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.