Effect Of Chemical Doping Research Articles

The effect of chemical doping on the lithiation processes of the crystalline Si anode ‒ A first-principles study.

We employed first-principles calculations to investigate the effect of chemical doping on the lithiation kinetics and dynamic properties of the c-Si anode. Our abinitio molecular dynamics simulations reveal that phosphorous/arsenic doping can greatly enhance the lithiation kinetics of c-Si, whereas boron doping is unable to produce such an improvement. Our calculations also show that boron doping could enhance Li insertion into c-Si, but phosphorous/arsenic doping tends to increase the insertion energy of Li ions. Although the migration energy barriers of Li ions may slightly increase (decrease) in the boron-(phosphorus-/arsenic-)doped c-Si, these changes were only effective within the range of the nearest-neighbor distance from dopants. Furthermore, it was found that the phosphorus-/arsenic-doped Si can be more ductile and can more easily undergo plastic deformation upon lithiation, while the c-Si matrix becomes more brittle and stiffer when doped with boron. Our simulation results also demonstrate that phosphorous- and arsenic-doping can effectively speed up the Li-induced structural amorphization of c-Si while boron doping appears to severely slow it down. These findings unambiguously indicate that the induced mechanical softening of the c-Si bond network can be the primary factor that leads to the enhanced lithiation kinetics in the n-type doped c-Si anodes.

Effect of Chemical Doping on Ion Transport in Sulfide Solid Electrolytes

Rechargeable solid-state batteries (SSBs) offer tremendous promise as a safe and energy-dense storage technology for use in electric transportation, robotics, and portable electronics. Lithium argyrodites (e.g., Li7PS6, and its halogen-doped derivatives) have emerged as a lucrative class of solid-state electrolytes (SSEs) for SSBs owing to their high Li-ion conductivity (~10-3 S/cm), good elastic stiffness (~30 GPa), and low flammability. Meanwhile, sulfide-based solid electrolytes such as Na3SbS4 (NSS) also showcase substantial potential for SSBs with their high theoretical specific capacity, enhanced safety, and abundance of resources. Despite their promise, both lithium and sodium-based SSBs remain far from commercialization due to lack of atomic-scale understanding of ion-conduction, charge transport, structural evolution, and interfacial reactions (e.g., dendrite growth, electrolyte decomposition etc.). Here we employ a combination of density functional theory calculations, ab initio molecular dynamics simulations, and nudged elastic band calculations to understand ion transport mechanism in chemically doped lithium argyrodites and NSS.In lithium-based systems, using accurate materials modeling, we design fluorine-containing argyrodite electrolytes that offers enhanced Li-ion conduction facilitated by unique Li-disorder induced by fluorine and other halogen co-dopants. Our results show the opening up of new pathways for Li inter-cage hops in these fluorine -containing argyrodite electrolytes which increases the Li-ion conductivity. In the case of sodium-based systems, we focus on atomic-scale mechanisms underlying Na-ion conduction in the presence of cation dopants. Ab initio molecular dynamics simulations reveal the significant impact of cation dopants on NSS, where the introduction of charge-compensating Na-vacancies enhances Na-ion conduction. The size of the cation dopant is found to be a critical factor, with examples such as Ca-doped NSS (rCa2+ / rNa+ = 0.98) showing a conductivity approximately 10 times that of pristine NSS, while larger Ba2+ as a dopant (rBa2+ / rNa+ = 1.35) hinders Na-ion hops due to local strain, resulting in a Na-ion conductivity ~5 times that of NSS. We will discuss these results in the context of accelerating design of novel solid-state electrolytes for long-lived, stable, and high-energy density SSBs.

Quantum emitters in aluminum nitride induced by heavy ion irradiation

The integration of solid-state single-photon sources with foundry-compatible photonic platforms is crucial for practical and scalable quantum photonic applications. This study explores aluminum nitride (AlN) as a material with properties highly suitable for integrated on-chip photonics and the ability to host defect-center related single-photon emitters. We have conducted a comprehensive analysis of the creation of single-photon emitters in AlN, utilizing heavy ion irradiation and thermal annealing techniques. Subsequently, we have performed a detailed analysis of their photophysical properties. Guided by theoretical predictions, we assessed the potential of Zirconium (Zr) ions to create optically addressable spin defects and employed Krypton (Kr) ions as an alternative to target lattice defects without inducing chemical doping effects. With a 532 nm excitation wavelength, we found that single-photon emitters induced by ion irradiation were primarily associated with vacancy-type defects in the AlN lattice for both Zr and Kr ions. The density of these emitters increased with ion fluence, and there was an optimal value that resulted in a high density of emitters with low AlN background fluorescence. Under a shorter excitation wavelength of 405 nm, Zr-irradiated AlN exhibited isolated point-like emitters with fluorescence in the spectral range theoretically predicted for spin-defects. However, similar defects emitting in the same spectral range were also observed in AlN irradiated with Kr ions as well as in as-grown AlN with intrinsic defects. This result is supportive of the earlier theoretical predictions, but at the same time highlights the difficulties in identifying the sought-after quantum emitters with interesting properties related to the incorporation of Zr ions into the AlN lattice by fluorescence alone. The results of this study largely contribute to the field of creating quantum emitters in AlN by ion irradiation and direct future studies emphasizing the need for spatially localized Zr implantation and testing for specific spin properties.

Ethanol Solvation of Polymer Residues in Graphene Solution-Gated Field Effect Transistors.

The persistence of photoresist residues from microfabrication procedures causes significant obstacles in the technological advancement of graphene-based electronic devices. These residues induce undesired chemical doping effects, diminish carrier mobility, and deteriorate the signal-to-noise ratio, making them critical in certain contexts, including sensing and electrical recording applications. In graphene solution-gated field-effect transistors (gSGFETs), the presence of polymer contaminants makes it difficult to perform precise electrical measurements, introducing response variability and calibration challenges. Given the absence of viable short to midterm alternatives to polymer-intensive microfabrication techniques, a postpatterning treatment involving THF and ethanol solvents was evaluated, with ethanol being the most effective, environmentally sustainable, and safe method for residue removal. Employing a comprehensive analysis with XPS, AFM, and Raman spectroscopy, together with electrical characterization, we investigated the influence of residual polymers on graphene surface properties and transistor functionality. Ethanol treatment exhibited a pronounced enhancement in gSGFET performance, as evidenced by a shift in the charge neutrality point and reduced dispersion. This systematic cleaning methodology holds the potential to improve the reproducibility and precision in the manufacturing of graphene devices. Particularly, by using ethanol for residue removal, we align our methodology with the principles of green chemistry, minimizing environmental impact while advancing diverse graphene technology applications.

Enhanced oxide ion conductivity in sodium niobate-based ceramics

Doping of Mg2+ and Ga3+ leads to the transition of electrical conduction mechanism of NaNbO3 from mixed oxide ion and electron conduction to oxide ion dominated conduction.

Effects of pressure and doping on Ruddlesden-Popper phases Lan+1NinO3n+1

Recently, the discovery of superconductivity with a critical temperature Tc up to 80 K in Ruddlesden–Popper phases Lan+1NinO3n+1 (n = 2) under pressure has garnered considerable attention. Up to now, the superconductivity was only observed in La3Ni2O7 single crystal grown with the optical-image floating zone furnace under oxygen pressure. It remains to be understood the effect of chemical doping on superconducting La3Ni2O7 as well as other Ruddlesden–Popper phases. Here, we systematically investigate the effect of external pressure and chemical doping on polycrystalline Ruddlesden–Popper phases. Our results demonstrate that the application of pressure and doping effectively tunes the transport properties of Ruddlesden–Popper phases. We find pressure-induced superconductivity up to 86 K in La3Ni2O7 polycrystalline sample, while no signatures of superconductivity are observed in La2NiO4 and La4Ni3O10 polycrystalline samples under high pressure up to 50 GPa. Our study sheds light on the exploration of high-Tc superconductivity in nickelates.

Nanostructure, optical, electronic, photoluminescence and magnetic properties of Co-doped ZrO2 sol–gel films

ZrO2 is a fascinating metal oxide with rich physical phenomenon and promised applications. In this study, the effects of chemical doping with Co+2 ions on nanostructure, electronic, optical, photoluminescence (PL), and magnetic properties of Zr1-xCoxO2 thin films (x = 0.0, 0.05, 0.1, and 0.15) prepared by sol–gel spin-coating method were investigated. The films exhibited a tetragonal structure with crystallinity improved with Co doping. Pure ZrO2 film showed a smooth surface morphology consisting of small particle size of 22 nm. The Co-doped ZrO2 films exhibited well-ordered holes, and their size and number increased with Co doping up to x = 0.1 and then decreased at x = 0.15. Root-mean-square roughness increased from 1.1 nm for pure ZrO2 to 16.5 nm for film x = 0.15. The Co ions in the films existed in a 2 + valence state. Energy band gap decreased with Co doping and had values of 4.40, 4.396, 4.392, and 4.170 eV for the films with x = 0.0, 0.05, 0.1, and 0.15, respectively. The PL spectra of films x = 0.00 and 0.05 are mainly comprised of two emission peaks; intense peak centred at 370 nm and broad peak centred about 500 nm. As the Co concentration increased, two intense and sharp emission peaks emerged at 335 and 373 nm. The films showed soft hysteresis loop, and their magnetization was enhanced with the increase of Co content.

Signatures of a gapless quantum spin liquid in the Kitaev material Na3Co2−xZnxSbO6

The honeycomb-lattice cobaltate Na$_3$Co$_2$SbO$_6$ has recently been proposed to be a proximate Kitaev quantum spin liquid~(QSL) candidate. However, non-Kitaev terms in the Hamiltonian lead to a zigzag-type antiferromagnetic~(AFM) order at low temperatures. Here, we partially substitute magnetic Co$^{2+}$ with nonmagnetic Zn$^{2+}$ and investigate the chemical doping effect in tuning the magnetic ground states of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. X-ray diffraction characterizations reveal no structural transition but quite tiny changes on the lattice parameters over our substitution range $0\leq x\leq0.4$. Magnetic susceptibility and specific heat results both show that AFM transition temperature is continuously suppressed with increasing Zn content $x$ and neither long-range magnetic order nor spin freezing is observed when $x\geq0.2$. More importantly, a linear term of the specific heat representing fermionic excitations is captured below 5~K in the magnetically disordered regime, as opposed to the $C_{\rm m}\propto T^3$ behavior expected for bosonic excitations in the AFM state. Based on the data above, we establish a magnetic phase diagram of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. Our results indicate the presence of gapless fractional excitations in the samples with no magnetic order, evidencing a potential QSL state induced by doping in a Kitaev system.

Effect of ZnO dimers on the thermoelectric performance of armchair graphene nanoribbons.

Enhancing the thermoelectric performance in engineered graphene nanoribbons is used to produce thermoelectric nanodevices, which are important in many applications. By using a chemical doping method, armchair graphene nanoribbons (AGNRs) can have thermoelectric properties that are tunable. We predicted that changing the number and geometrical pattern of zinc oxide (ZnO) dimers in an AGNR can engineer thermoelectric properties, so we used density functional-based tight binding (DFTB) combined with the non-equilibrium Green's function (NEGF) to investigate the geometric, electronic, and thermoelectric properties of the AGNR with and without various dopants of ZnO dimers. With three forms of ZnO dimers, ortho, meta, and para dimers, different concentration ratios of Zn and O atoms are used. Our results indicate that the electronic features of AGNR are influenced not only by the concentrations of ZnO dimers but also by the geometrical pattern of ZnO dimers in the AGNR. These results are helpful in better understanding the effect of chemical doping on the transport properties of AGNRs and in motivating nanodevices to improve their thermoelectric performance.

Effect of hydrostatic pressure on the unconventional charge density wave and superconducting properties in two distinct phases of doped kagome superconductors CsV3−xTixSb5

Recent studies on the kagome metal ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ have revealed an intricate interplay between unconventional charge density waves (CDWs) and superconductivity (SC). Substitutions of Ti for V can perturb the CDW and produce two distinct SC phases with different pairing symmetries in the series of $\mathrm{Cs}{\mathrm{V}}_{3\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{Sb}}_{5}$. Here, we performed a comprehensive high-pressure study on Ti-doped $\mathrm{Cs}{\mathrm{V}}_{3\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{Sb}}_{5}$ ($x=0.04,0.15$) samples to elucidate the combined effects of physical pressure and chemical doping on the coexistence of CDWs and SC. Under high pressures, the M-shaped double superconducting dome observed in the parent ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ is retained but very weakened for $x=0.04$, and it is replaced by a single broad superconducting dome for $x=0.15$. Accordingly, the optimal superconducting ${T}_{\mathrm{c}}$ under high pressures decreases gradually with increasing Ti-doping level. On the other hand, the upper critical field first exhibits an obvious rise with enhanced flux pinning effects by disorders for $x=0.04$ and then is suppressed upon further increasing Ti doping. The constructed $T\text{\ensuremath{-}}P$ phase diagrams of $\mathrm{Cs}{\mathrm{V}}_{3\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{Sb}}_{5}$ reveal the competition and coexistence of CDWs and SC. Our results provide more insight into the intertwined competing electronic orders in the Ti-doped kagome superconductors $\mathrm{Cs}{\mathrm{V}}_{3\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{Sb}}_{5}$.

Synergistic Effect of Solvent Vapor Annealing and Chemical Doping for Achieving High-Performance Organic Field-Effect Transistors with Ideal Electrical Characteristics.

Contact resistance and charge trapping are two key obstacles, often intertwined, that negatively impact on the performance of organic field-effect transistors (OFETs) by reducing the overall device mobility and provoking a nonideal behavior. Here, we expose organic semiconductor (OSC) thin films based on blends of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8) with polystyrene (PS) to (i) a CH3CN vapor annealing process, (ii) a doping I2/water procedure, and (iii) vapors of I2/CH3CN to simultaneously dope and anneal the films. After careful analysis of the OFET electrical characteristics and by performing local Kelvin probe force microscopy studies, we found that the vapor annealing process predominantly reduces interfacial shallow traps, while the chemical doping of the OSC film is responsible for the diminishment of deeper traps and promoting a significant reduction of the contact resistance. Remarkably, the devices treated with I2/CH3CN reveal ideal electrical characteristics with a low level of shallow/deep traps and a very high and almost gate-independent mobility. Hence, this work demonstrates the promising synergistic effects of performing simultaneously a solvent vapor annealing and doping procedure, which can lead to trap-free OSC films with negligible contact resistance problems.

Ultrahigh tunability of resistive switching in strongly correlated functional oxide

Vanadium dioxide (VO2) is a strongly correlated material that undergoes reversible resistive switching. However, the underlying mechanism of such resistive switching is still under debate. In this work we report an ultrahigh decrease in the VO2 switching threshold-voltage by more than 35 V and a giant 680% change by modifying the material stoichiometry through tungsten (W) doping. This remarkable effect of chemical doping on the resistive switching characteristics of VO2 illuminates on the fundamental mechanism of the insulator-to-metal transition, which reveals that such abrupt resistive switching is attributed to the electro-thermal actuation process. Furthermore, we report ultralow voltage spontaneous electrical oscillation in W-doped VO2 for the first time. Advances achieved here through the design of a new class of transition metal oxide based strongly correlated materials are of paramount importance for emerging electronics.

Effect of intentional chemical doping on crystallographic and electric properties of the pyrochlore Bi2Sn2O7

The development of p-type oxide semiconductors is challenging owing to the localized nature of the valence band maximum (VBM), which primarily comprises O 2p orbitals. Although some Sn2+-based pyrochlore-type oxides (A2B2O7) with VBMs comprising spatially spread Sn 5s orbitals show p-type semiconducting properties, these properties cannot be tuned by an intentional chemical doping owing to the instability of their valence states. Herein, the influence of chemical doping on the crystal structure and electrical properties of Bi2Sn2O7, whose VBM is composed of valence-stable ions with Bi 6s orbitals, in the VBM is investigated. X-ray absorption spectroscopy reveals that In3+ is doped substitutionally at the Sn4+ site. Although the doped In3+ ions are expected to act as acceptors, their electrical properties always show n-type character. Simultaneously, extended X-ray absorption fine structure reveals the formation of oxygen vacancies in BiOBi bonds contributing to the VBM, whereas negligible changes are observed in the SnO6 octahedra, suggesting that the generated holes are electrically compensated by electrons because of the oxygen vacancies. P-type electric properties can be observed under oxidizing conditions, providing a critical design concept for the realization of hole conduction in acceptor-doped Bi2Sn2O7.

Ni-doping effect on thermoelectric properties of c-axis-oriented CuFeO2 ceramics

The combined effect of chemical doping and grain orientation on the thermoelectric properties of delafossite-type CuFeO2 ceramics was investigated. Ni was chosen as the dopant, whereas the reactive templated grain growth method was used for the fabrication of grain-oriented bulk ceramics. Nanorods of Ni-doped α-FeOOH with a nominal Ni content of up to 5 mol% were synthesized by the hydrothermal method and were then used as the template to fabricate Ni-doped CuFeO2 ceramics with a preferred c-axis orientation. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the Ni-doped CuFeO2 ceramics along the in-plane direction (perpendicular to the orientation axis) were measured at temperatures between 300 and 1100 K. Ni doping was found to effectively increase the electrical conductivity and decrease the thermal conductivity, whereas it maintained a high Seebeck coefficient of around 400 μV K−1. Consequently, the c-axis-oriented CuFeO2 ceramics doped with 1 and 3 mol% Ni showed an enhanced dimensionless figure of merit of 0.08 at 900 K.

Effect of chemical doping on memristive behavior of VO2 microcrystals

Strongly correlated oxides, such as vanadium dioxide that undergoes a sharp metal-insulator transition when triggered by different stimuli, are of high relevance for novel electronic devices. In this work, we show the variation in threshold voltage of memristor behavior with systematic doping of tungsten (W) in VO2 crystals grown by the vapor transport method. Chemical doping effects on metal insulator transition are further correlated with Raman spectroscopy studies and differential scanning calorimetry studies. Furthermore, bi-polar threshold switching of VO2 memristor behavior is demonstrated in VO2 microcrystals with different contents of W. Threshold voltage for electrical triggering in W doped VO2 is reduced to about 0.547 V from 2.27 V of undoped VO2.

Synergistic Effect of Micro-Nano-Hybrid Surfaces and Sr Doping on the Osteogenic and Angiogenic Capacity of Hydroxyapatite Bioceramics Scaffolds.

BackgroundThe synergistic effect of chemical element doping and surface modification is considered a novel way to regulate cell biological responses and improve the osteoinductive ability of biomaterials.MethodsHydroxyapatite (HAp) bioceramics with micro-nano-hybrid (a mixture of microrods and nanorods) surfaces and different strontium (Sr) doping contents of 2.5, 5, 10, and 20% (Srx-mnHAp, x: 2.5, 5, 10 and 20%) were prepared via a hydrothermal transformation method. The effect of Srx-mnHAp on osteogenesis and angiogenesis of bone marrow stromal cells (BMSCs) was evaluated in vitro, and the bioceramics scaffolds were further implanted into rat calvarial defects for the observation of bone regeneration in vivo.ResultsHAp bioceramics with micro-nano-hybrid surfaces (mnHAp) could facilitate cell spreading, proliferation ability, ALP activity, and gene expression of osteogenic and angiogenic factors, including COL1, BSP, BMP-2, OPN, VEGF, and ANG-1. More importantly, Srx-mnHAp (x: 2.5, 5, 10 and 20%) further promoted cellular osteogenic activity, and Sr10-mnHAp possessed the best stimulatory effect. The results of calvarial defects revealed that Sr10-mnHAp could promote more bone and blood vessel regeneration, with mnHAp and HAp bioceramics (dense and flat surfaces) as compared.ConclusionThe present study suggests that HAp bioceramics with micro-nano-hybrid surface and Sr doping had synergistic promotion effects on bone regeneration, which can be a promising material for bone defect repair.

Disentangling the effect of doping chemistry on the energy storage properties of barium titanate ferroelectrics using data science tools

Using data science tools including machine learning and statistical analysis, the effects of multiple chemical doping on the energy storage performance of barium titanate based ceramics are investigated from both quantitative and qualitative perspectives.

Anisotropic magnetoresistance and planar Hall effect in correlated and topological materials

This article reviews the recent progress in understanding the anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in two classes of quantum materials, the strongly correlated oxides and topological materials. After introducing the phenomenological description, we give a comprehensive survey of the experimental results, including the effects of temperature, magnetic field, strain, chemical doping, and electric field effect tuning. The material systems of interest include single-phase bulk and thin film materials, artificial nanostructures, surfaces and heterointerfaces, as well as superlattices. We focus on the critical information revealed by the AMR and PHE about the complex energy landscape in these emergent materials, elucidating their connection with magnetocrystalline anisotropy, charge correlation, spin-orbit coupling, band topology, and interface coupling.

Multi-scale modeling of 2D GaSe FETs with strained channels

Electronic devices based on bidimensional materials (2DMs) are the subject of an intense experimental research, that demands a tantamount theoretical activity. The latter must be hold up by a varied set of tools able to rationalize, explain and predict the operation principles of the devices. However, in the broad context of multi-scale computational nanoelectronics, there is currently a lack of simulation tools connecting atomistic descriptions with semi-classical mesoscopic device-level simulations and able to properly explain the performance of many state-of-the-art devices. To contribute to filling this gap we present a multi-scale approach that combines fine-level material calculations with a semi-classical drift-diffusion transport model. Its use is exemplified by assessing 2DM field effect transistors with strained channels, showing excellent capabilities to capture the changes in the crystal structure and their impact into the device performance. Interestingly, we verify the capacity of strain in monolayer GaSe to enhance the conduction of one type of carrier, enabling the possibility to mimic the effect of chemical doping on 2D materials. These results illustrate the great potential of the proposed approach to bridge levels of abstraction rarely connected before and thus contribute to the theoretical modeling of state-of-the-art 2DM-based devices.

Slow oxidation of magnetite nanoparticles elucidates the limits of the Verwey transition

Magnetite (Fe3O4) is of fundamental importance for the Verwey transition near TV = 125 K, below which a complex lattice distortion and electron orders occur. The Verwey transition is suppressed by chemical doping effects giving rise to well-documented first and second-order regimes, but the origin of the order change is unclear. Here, we show that slow oxidation of monodisperse Fe3O4 nanoparticles leads to an intriguing variation of the Verwey transition: an initial drop of TV to a minimum at 70 K after 75 days and a followed recovery to 95 K after 160 days. A physical model based on both doping and doping-gradient effects accounts quantitatively for this evolution between inhomogeneous to homogeneous doping regimes. This work demonstrates that slow oxidation of nanoparticles can give exquisite control and separation of homogeneous and inhomogeneous doping effects on the Verwey transition and offers opportunities for similar insights into complex electronic and magnetic phase transitions in other materials.