Hole Doping Research Articles

Rational Regulation of High-Entropy Perovskite Oxides through Hole Doping for Efficient Oxygen Electrocatalysis.

Due to the high configuration entropy, unique atomic arrangement, and electronic structures, high-entropy materials are being actively pursued as bifunctional catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable zinc-air batteries (ZABs). However, a relevant strategy to enhance the catalytic activity of high-entropy materials is still lacking. Herein, a hole doping strategy has been employed to enable the high-entropy perovskite La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 to effectively catalyze the ORR and OER. Hole doping experiments rely on the substitution of Sr2+ for La3+. The optimized La0.7Sr0.3(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 displays remarkable activity for the ORR and the OER, with a low potential difference of 0.880 V between the half-wave potential of the ORR and the OER potential at 10 mA cm-2, exceeding the majority of perovskite bifunctional catalysts. Further analysis of the electronic structures reveals that hole doping could regulate the eg-orbital filling of the transition-metal cations in high-entropy perovskites to an ideal position and thereby generate many highly active sites to promote the redox activity of oxygen. The assembled rechargeable ZAB with the targeted high-entropy perovskite as the cathode affords a specific capacity of 774.5 mAh gZn-1 under 10 mA cm-2 and durability for a period of 300 cycles, comparable to that of the 20%Pt/C + RuO2 ZAB. This work offers an important approach for the advancement of efficient high-entropy perovskites for ZABs.

Intervalence plasmons in boron-doped diamond

Doped semiconductors can exhibit metallic-like properties ranging from superconductivity to tunable localized surface plasmon resonances. Diamond is a wide-bandgap semiconductor that is rendered electronically active by incorporating a hole dopant, boron. While the effects of boron doping on the electronic band structure of diamond are well-studied, any link between charge carriers and plasmons has never been shown. Here, we report intervalence plasmons in boron-doped diamond, defined as collective electronic excitations between the valence subbands, opened up by the presence of holes. Evidence for these low-energy excitations is provided by valence electron energy loss spectroscopy and near-field infrared spectroscopy. The measured spectra are subsequently reproduced by first-principles calculations based on the contribution of intervalence band transitions to the dielectric function. Our calculations also reveal that the real part of the dielectric function exhibits a crossover characteristic of metallicity. These results suggest a new mechanism for inducing plasmon-like behavior in doped semiconductors, and the possibility of attaining such properties in diamond, a key emerging material for quantum information technologies.

Sliding ferroelectricity influenced by charge doping in bilayer antiferromagnetic H–ScO2

Sliding ferroelectricity has been extensively studied as it provides an approach to designing van der Waals ferroelectric materials with nonpolar components. In this work, we demonstrate the sliding ferroelectricity of bilayer H–ScO2, which is formed by an interlayer antiferromagnetic configuration of monolayer H–ScO2 ferromagnetic material. The out-of-plane polarization results from charge transfer between the layers, causing an unequal charge distribution within them and yielding a polarization value of ±1.26 pC/m. We found that increasing the doping concentration suppresses the polarization value. This phenomenon results from the differing occupancy ratios of electrons and holes in the conduction and valence bands after introducing electron or hole doping into the system. The closer the number of electrons in the conduction band is to that in the valence band, the more pronounced the suppression of polarization. Our work offers a perspective for the design of advanced van der Waals ferroelectric materials.

Spontaneous Donor Defects and Voltage-Assisted Hole Doping in Beta-Gallium Oxides under Multiple Epitaxy Conditions

Spontaneous Donor Defects and Voltage-Assisted Hole Doping in Beta-Gallium Oxides under Multiple Epitaxy Conditions

Valley splitting of monolayer Hf3C2O2 by the spin-orbit coupling effect: first principles calculations using the HSE06 methods.

Electrons have not only charge and spin degrees of freedom, but also additional valley degrees of freedom. The search for valleytronic materials with large valley splits is important for the development of valleytronics. In this work, we applied first principles computations to calculate 1 L Hf3C2O2 at the level of HSE06. When the spin-orbit coupling (SOC) effect is considered, 1 L Hf3C2O2 is an indirect bandgap semiconductor with a bandgap of 0.952 eV. Meanwhile, valley splitting occurs between the conduction bands Γ and K, with a valley splitting value as high as 98.228 meV. Bader charge analysis was used to determine that Hf-O and Hf-C are ionic bonds. The computed elastic constants and phonon spectra proved that 1 L Hf3C2O2 is mechanically and dynamically stable. In addition, the Berry curvature of 1 L Hf3C2O2 is non-zero. In the work the effect of the electronic properties of 1 L Hf3C2O2 was also calculated with respect to the biaxial strain. The results show that the biaxial strain can well regulate the band gap and valley splitting. Finally, we calculated the effects of hole and electron doping on the band gap and valley splitting of 1 L Hf3C2O2. The results show that the band gap and valley splitting are linearly related to the doping concentration. Our study shows that 1 L Hf3C2O2 is a promising two-dimensional valleytronics material.

Small molecule doped polymer hole transport layers for all solution processed inverted QLED with using green solvents

Small molecule doped polymer hole transport layers for all solution processed inverted QLED with using green solvents

Reducing the metal-insulator transition temperature of VO2 nanowire by surface molecular adsorption-induced hole doping

Heteroelement doping is one of the most common techniques for decreasing or increasing the phase transition temperature (Tc) of VO2, but it generally suffers from the concomitant deterioration of change...

Pseudogap in electron-doped cuprates: Strong correlation leading to band splitting

The pseudogap phenomena have been a long-standing mystery of the cuprate high-temperature superconductors. The pseudogap in the electron-doped cuprates has been attributed to band folding due to antiferromagnetic (AFM) long-range order or short-range correlation. We performed an angle-resolved photoemission spectroscopy study of the electron-doped cuprates Pr1.3-xLa0.7CexCuO4 showing spin-glass, disordered AFM behaviors, and superconductivity at low temperatures and, by measurements with fine momentum cuts, found that the gap opens on the unfolded Fermi surface rather than the AFM Brillouin zone boundary. The gap did not show a node, following the full symmetry of the Brillouin zone, and its magnitude decreased from the zone-diagonal to (π,0) directions, opposite to the hole-doped case. These observations were reproduced by cluster dynamical-mean-field-theory calculation, which took into account electron correlation precisely within a (CuO2)4 cluster. The present experimental and theoretical results are consistent with the mechanism that electron or hole doping into a Mott insulator creates an in-gap band that is separated from the upper or lower Hubbard band by the pseudogap.

Fluctuating charge-density-wave correlations in the three-band Hubbard model

The high-temperature superconducting cuprates host unidirectional spin- and charge-density-wave orders that can intertwine with superconductivity in nontrivial ways. While the charge components of these stripes have now been observed in nearly all cuprate families, their detailed evolution with doping varies across different materials and at high and low temperatures. We address this problem using nonperturbative determinant quantum Monte Carlo calculations for the three-band Hubbard model. Using an efficient implementation, we can resolve the model's fluctuating spin and charge modulations and map their evolution as a function of the charge transfer energy and doping. We find that the incommensurability of the charge modulations is decoupled from the spin modulations and decreases with hole doping, consistent with experimental measurements at high temperatures. These findings support the proposal that the high-temperature charge correlations are distinct from the intertwined stripe order observed at low-temperature and in the single-band Hubbard model.

Ohmic contact mechanism and charge redistribution of MoS2/Mn+1XnO2 heterostructures

Abstract Several M n+1 X n O2 compounds exhibit work functions higher than those of three-dimensional metals, enabling the formation of Ohmic contact heterostructures with MoS2, which enhances the catalytic activity of MoS2 for the hydrogen evolution reaction. However, the Schottky barrier height (SBH) in these Ohmic contact heterostructures does not adhere to the Schottky-Mott limit, leaving the Ohmic contact mechanism between MoS2 and M n+ 1X n O2 unclear and hindering further investigations into these heterostructures. In this study, we investigate 22 MoS2/M n+ 1X n O2 heterostructures using the unfolding method. Among these, the eight M n+ 1X n O2 compounds—Cr2CO2, Mo2CO2, V2CO2, W2CO2, Cr2NO2, V2NO2, Ti3C2O2 and V4C3O2—form p-type Ohmic contacts with MoS2. In contrast, the twelve compounds—Hf2CO2, Nb2CO2, Ta2CO2, Ti2CO2, Zr2CO2, Mo2NO2, Ti2NO2, Ti3N2O2, Zr3C2O2, Nb4C3O2, Ta4C3O2 and Ti4N3O2—create p-type Schottky contacts, while Hf2NO2 and Zr2NO2 form n-type Schottky contacts with MoS2. In the Ohmic contact heterostructures, out-of-plane orbital states hybridize to form a splitting band, allowing the highest valence band of MoS2 to cross the Fermi level and achieve hole doping. This splitting band not only results in a SBH that does not conform to the Schottky–Mott limit but also redistributes charge density. Notably, the heterostructures formed by Cr2CO2, Mo2CO2, V2CO2, W2CO2, Cr2NO2, V2NO2, V4C3O2, and MoS2 exhibit charge polarity distribution, whereas MoS2/Ti3C2O2 does not demonstrate charge polarity distribution.

Controllable half-metallicity in MnPX3 monolayer

Modulable electronic and magnetic structures significantly extend the properties and applications of two-dimensional (2D) materials. 2D antiferromagnets (AFM) can even become ferromagnets (FM) by various approaches, which ignites growing research interests in 2D AFM. Through first-principles calculations, we find that the adsorption of Li (electron doping) and F (hole doping) on the surface of MnPSe3 can induce half-metallicity with opposite spin polarizations. The adsorption site, concentration, charge transfer, and the exchange energy are investigated in detail, indicating the robustness of half-metallicity. At the interface of MnPS3/Au(111) heterostructure, we find electrons transfer from Au(111) to MnPS3, forming the Ohmic contact and inducing AFM-FM transition. All our results show that ferromagnetic MnPX3 (X = S and Se) monolayer with half-metallicity can be easily obtained, which may be of great significance in 2D spintronic materials and devices.

Two dimensional MoF3 and Janus Mo2F3X3(X = Cl, Br, I): intrinsic ferromagnetic semiconductor, large perpendicular magnetic anisotropy, and hole-induced room-temperature ferromagnetism

Abstract Two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie temperature (T c ) and large perpendicular magnetic anisotropy (PMA) are promising for developing next-generation magnetic storage devices. In this work, we investigated the structural, electronic, and magnetic properties of MoF3 and Janus Mo2F3 X 3 (X = Cl, Br, I) monolayers by first-principles methods. These materials are 2D FM semiconductors with large PMA and half-semiconducting character as both VBM and CBM belonging to the spin-up channel. Biaxial strain can modulate band gap, reverse easy magnetization axis, and induce magnetic phase transitions in MoF3 monolayer and its Janus structures. Compared to MoF3 monolayers, Janus Mo2F3 X 3 monolayers can preserve the structural ability and the FM ground state over a wider range of strain. The magnetic anisotropy energies (MAEs) of these 2D materials can be enhanced to greater than 1 meV/Mo by tensile strains. Intrinsic T c of MoF3 monolayer and its Janus structures are less than 110 K and are insensitive to strain. However, hole doping with a feasible concentration can achieve a room-temperature half-metallicity in these 2D materials. The required hole concentration is lower in Janus Mo2F3 X 3 monolayers than MoF3 monolayer. Our results indicate that MoF3 and Janus Mo2F3 X 3 (X = Cl, Br, I) monolayers are promising candidates for 2D spintronic applications and will stimulate experimental and theoretical broad studies.

Is p-Type Doping in TeO2 Feasible?

Abstract Wide-bandgap two-dimensional (2D) β-TeO2 has been reported as a high-mobility p-type transparent semiconductor [ Nat. Electron. 4 277 (2021)], attracting significant attention. This “breakthrough” not only challenges the conventional characterization of TeO2 as an insulator but also conflicts with the anticipated difficulty in hole doping of TeO2 by established chemical trends. Notably, the reported Fermi level of 0.9 eV above the valence band maximum actually suggests that the material is an insulator, contradicting the high hole density obtained by Hall effect measurement. Furthermore, the detected residual Se and the possible reduced elemental Te in the 2D β-TeO2 samples introduces complexity, considering that elemental Se, Te, and Te1−x Se x themselves are high-mobility p-type semiconductors. Therefore, doubts regarding the true cause of the p-type conductivity observed in the 2D β-TeO2 samples arise. In this Letter, we employ density functional theory calculations to illustrate that TeO2, whether in its bulk forms of α-, β-, or γ-TeO2, or in the 2D β-TeO2 nanosheets, inherently exhibits insulating properties and poses challenges in carrier doping due to its shallow conduction band minimum and deep valence band maximum. Our findings shed light on the insulating properties and doping difficulty of TeO2, contrasting with the claimed p-type conductivity in the 2D β-TeO2 samples, prompting inquiries into the true origin of the p-type conductivity.

Probing Electronic Doping in CVD Graphene Crystals Treated by HNO3 Vapors.

In this work, we present a comprehensive protocol for achieving hole doping in graphene through exposure to nitric acid (HNO3) vapors. We demonstrate gradual p-type surface doping of CVD-grown graphene on a Si/SiO2 substrate by thermally depositing nitric acid molecules to form self-assembled charge transfer complexes. Detailed analysis of charge carrier concentration and Fermi energy shifts was conducted using Raman, X-ray and ultraviolet photoelectron spectroscopies (XPS/UPS). Our methodology, including a novel PMMA coating step, ensures stability and efficiency of the doping process, highlighting its effectiveness in inducing permanent hole doping while maintaining the structural integrity of the graphene.

Hole doping and electronic correlations in Cr substituted BaFe$_{2}$As$_{2}$

Hole doping and electronic correlations in Cr substituted BaFe$_{2}$As$_{2}$

VOC Detection Using p-Type Sm(Fe,Co)O3 Perovskite Oxides

In recent years, there has been concern about the resurgence of sick house syndrome caused by volatile organic compounds (VOCs) emitted from building materials, and there is an urgent need to develop sensors that can continuously detect VOCs with high sensitivity. Our research group is conducting research on VOC detection characteristics using SmFeO3. SmFeO3 is a p-type semiconductor with a perovskite crystal structure and has high oxidation activity against VOCs. However, SmFeO3 has high electrical resistance in air, and sensors using SmFeO3 require heating to a measurable resistance range (approximately 300°C or higher), and also require a measurement system with high input impedance. For this reason, a high cost for apparatus and high power consumption are issues for practical application. Therefore, in this study, we focused on SmFe1-xCoxO3 as the sensing electrode material to operate sensors at reduced temperature. Since SmFeO3 is a p-type semiconductor, Co substitution or hole doping is expected to increase electrical conductivity, and a good redox property of cobalt ion may enhance catalytic activity of VOC decomposition. Regarding the oxidation activity of SmFe1-xCoxO3 powder, the oxidation activity against toluene increased with increasing Co content. T50 = 210oC (x=0), 205 oC (x=0.1), 155 oC (x=0.3), 165 oC (x=0.5). The oxidation activity for ethanol also increased with the amount of substitution, T50 =130oC (x=0), 110 oC (x=0.1), 85 oC (x=0.3), 75 oC (x=0.5). The temperature at which the maximum response value of each sensor was shown is 300℃ (x=0), 250℃ (x=0.1), 250℃(x=0.3), and 200oC (x=0.5). It was found that the Co substitution effectively reduce operating temperature. The response value (RVOC/Rair) in ethanol was results in S=4.6 (x=0 at 300oC), S=6.4 (x=0.1 at 250oC) and the sensor with x=0.1 increased sensor response at reduced temperature. The increase in the response value is thought to be because the sensor with x=0.1 has a higher oxidation activity at 250 oC than that with x=0 at 300 oC, The response of the sensors followed the power law, S=aPVOC n. Here, a and n are constants, and PVOC is the partial pressure of the gas. The constants a and n were determined from the equation log(S)=log(a)+nlog(PVOC), and the response value to 0.1 ppm ethanol was predicted as S=1.11 (x=0), 1.88 (x=0.1), 1.88 (x=0.3), and 1.94 (x=0.5), and it was expected that the response values at 0.1 ppm would increase due to cobalt substitution. Sensor properties mainly depend on material properties and sensor structure (sensing membrane structure). Therefore, it is suggested that higher sensitivity can be achieved by optimizing the sensor structure in the future, and it is considered that the use of cobalt substitutes as a sensor material is useful from the viewpoint of sensitivity.

DFT Calculation on Na Doping Effects on Bismuth Ruthenate-Based Pyrochlore Oxides

Oxygen evolution reaction (OER) is one of the most important electrochemical processes in a wide variety of fields such as water electrolysis, air batteries, electroplating, electrowinning, and others, while the overpotential is known to be 300 mV or more, which results in the increase in energy consumption and the decrease in energy efficiency. One of the authors of this paper has recently found a low overpotential of oxygen nano-catalyst, that is a bismuth ruthenate-based pyrochlore oxide [1]. This novel oxide catalyst contains ca. 5 at% of sodium, which seems to strongly affect the catalytic activity and stability for OER; e.g., the catalyst shows a Tafel slope of 40 mV/dec at 25 oC in 0.1 mol/L KOH solution, which is much lower than those of nickel-based oxide and PGMs investigated as OER catalysts for alkaline water electrolysis, although the mechanism of the fast kinetics has not been clarified. In this paper, we report the results of first-principles calculations of the electronic structure of bismuth ruthenate-based pyrochlore oxides (BRO) and discuss the effects of Na doping on the crystal structure of BRO.Density functional theory (DFT) calculations in the generalized gradient approximation (GGA) were performed using the WIEN2k package [2] for the electronic structure of bismuth ruthenate pyrochlore Bi2Ru2O7 and its Na substituent. We substituted Na for one of the 16 Bi in the unit cell so that the Na content is close to the synthesized Na-doped BRO. Before the electronic structure calculations, structural optimization was performed within DFT with GGA using the VASP package [3-5].We successfully optimized the structures for Bi2Ru2O7 and its Na substituent, and by Na doping, the unit cell exhibits isotropic compression in 0.12% coincident with slight distortion along a [111] direction. While the lattice shrinkage seems inconsistent with a difference in ionic size between trivalent Bi (1.17 Å) and monovalent Na (1.18 Å) [6], the local structure around Na was found to change according to the ionic size; i.e., the BiO8 polyhedron expanded with Na doping, and the NaO8 polyhedron was larger than the BiO8 polyhedron in Bi2Ru2O7 with Na. On the other hand, RuO6 octahedrons shrunk due to the Na substitution, and the degree of shrinkage was higher for the octahedron closer to Na. This shrinkage of the RuO6 octahedron may be due to the hole doping effect. The distributions of the size of the RuO6 octahedron and the electronic state of Ru are reflected in the electronic structure as complicated band dispersion. However, the energy dependence of density of states (DOS) was similar to that of Bi2Ru2O7, so the Na substitution may not have affected the electronic physical property. There is still a potential that some of the RuO6 octahedrons distributed due to the Na substitution induce the enhancement of OER activity by the Na substituent.The authors acknowledge NEDO, Project No. JPNP20003, for their financial support.Ref.1) M. Morimitsu, US Patent No. 11777106-B2 (2023).2) P. Blaha, L. Schwarz, F. Tran, R. Laskowski, G. K. H. Madsen, and L. D. Marks, J. Chem. Phys., 152, 074101 (2020).3) G. Kresse and J. Hafner, Phys. Rev. B, 47, 558 (1993); ibid 49, 14251 (1994).4) G. Kresse and J. Furthmüller, Comput. Mat. Sci., 6, 15 (1996).5) G. Kresse and J. Furthmüller, Phys. Rev. B, 54, 11169 (1996).6) R. D. Shannon, Acta Crystallogr. A, 32, 751 (1976).

Trion sensing of a zero-field composite Fermi liquid.

The half-filled lowest Landau level is a fascinating platform for researching interacting topological phases. A celebrated example is the composite Fermi liquid, a non-Fermi liquid formed by composite fermions in strong magnetic fields1-10. Its zero-field counterpart is predicted in atwisted MoTe2 bilayer (tMoTe2)11,12-a recently discovered fractional Chern insulator exhibiting the fractional quantum anomalous Hall effect13-16. Although transport measurements at ν = -1/2 show signatures consistent with a zero-field composite Fermi liquid14, new probes are crucial to investigate the state and its elementary excitations. Here, by using the unique valley properties of tMoTe2, we report optical signatures of a zero-field composite Fermi liquid. We measured the degree of circular polarization (ρ) of trion photoluminescence versus hole doping and electric field. We found that, within the phase space showing robust ferromagnetism, ρ is near unity for Fermi liquid states. However, ρ is quenched at both integer andfractional Chern insulators, and in a holedoping range near ν = -1/2. Temperature, optical excitation power and electric-field-dependence measurements demonstrate that the quenching of ρ is a direct consequence of an energy gap (pseudogap) for electronic excitations of the Chern insulators (composite Fermi liquid): because the local spin-polarized excitations necessary to form trions are strongly suppressed, trion formation at the corresponding filling factors relies on optically generated unpolarized itinerant holes. Our work highlights a new excitonic probe of zero-field fractional Chern insulator physics, unique to tMoTe2.

Low-frequency noise of MoTe2 transistor: effects on ambipolar carrier transport and CYTOP doping

Low-frequency noise (LFN) characteristics of semiconductor devices pose a significant importance for understanding their working principle, particularly concerning material imperfections. Accordingly, substantial research endeavors have focused on characterizing the LFN of devices. However, the LFN characteristics of the ambipolar transistors have been rarely demonstrated. Herein, we investigate the effects of ambipolar carrier transport and CYTOP-induced p-type doping on low-frequency noise characteristics of MoTe2 transistors. The source of the 1/f noise differs between the n-type (electron transport) and p-type (hole transport) modes. Notably, the influence of contact resistance is more pronounced in the n-type mode. CYTOP doping suppresses the n-type mode by introducing hole doping effects. Furthermore, CYTOP doping mitigates the impact of contact resistance on excess noise.

Lattice study of SU(2) gauge theory coupled to four adjoint Higgs fields

Gauge theories with matter fields in various representations play an important role in different branches of physics. Recently, it was proposed that several aspects of the pseudogap phase of cuprate superconductors near optimal doping may be explained by an emergent SU(2) gauge symmetry. Around the transition with positive hole doping, one can construct a (2+1)−dimensional SU(2) gauge theory coupled to four adjoint scalar fields which gives rise to a rich phase diagram with a myriad of phases having different broken symmetries. We study the phase diagram of this model on the Euclidean lattice using the hybrid Monte Carlo algorithm. We find the existence of multiple broken phases as predicted by previous mean-field studies. Depending on the quartic couplings, the SU(2) gauge symmetry is broken down either to U(1) or Z2 in the perturbative description of the model. We further study the confinement-deconfinement transition in this theory, and find that both the broken phases are deconfining in the range of volumes that we studied. However, there exists a marked difference in the behavior of the Polyakov loop between the two phases. Published by the American Physical Society 2024