Doping Mechanism Research Articles

Controlling ions and electrons in aqueous solution: an alternative point of view of the charge-transport behavior of eumelanin-inspired material

Humidity- and pH-dependent current–voltage and impedance/dielectric spectroscopy shows that an electrochemical doping mechanism can dominate eumelanin's charge transport.

Intrinsic point defects and the n- and p-type dopability in α- and β-Bi2O3 photocatalysts.

In this work, all kinds of intrinsic point defects, unintentional N and H impurities and possible complex defects between impurities and native defects in α- and β-Bi2O3 with different growth conditions are systematically investigated using hybrid density functional calculations. And then, the n- or p-type doping mechanisms in α- and β-Bi2O3 are explored and discussed. It is found that α-Bi2O3 presents the n-type conductivity under O-poor conditions. The unintentional H interstitials as the shallow donors should be majorly responsible for the n-type conductivity character. While under O-rich conditions, α-Bi2O3 displays the p-type conductivity, and the unintentional complex defects VBi1 + 2H as the shallow acceptors should be the primary origins of the p-type conductivity. The hydrogenation of the Bi vacancy in α-Bi2O3 not only significantly lowers the formation energy of the Bi vacancy but also markedly decreases its acceptor transition level. This well explains the experimental observation that α-Bi2O3 changes from n-type to p-type conductivity with increasing O partial pressure. Compared to α-Bi2O3, β-Bi2O3 always presents the n-type conductivity behaviour regardless of the growth conditions. The native O1 vacancies (VO1) and unintentional H interstitials in β-Bi2O3 are shallow and excellent donors. They are responsible for the n-type conductivity and further perfectly explain the observed unintentional n-type conductivity character in β-Bi2O3 experiments. Understanding the defect physics in α- and β-Bi2O3 could inspire more significant studies on developing Bi2O3-based photocatalysts.

Efficient n-Type Surface Doping in Diamond

Conventional doping in diamond is challenging for its application in electronic devices, which could be overcome by an alternative method of surface-transfer doping. In this study, efficient surface n-type conductivity is obtained on the N-terminated diamond surface doped with decamethylcobaltocene (DMC) and cobaltocene (CoCp2) molecules having low ionization energy values by first-principles calculation. By the surface-transfer doping mechanism, electrons are transferred from the dopants to diamond, and then electron accumulation occurs on the diamond surface. For DMC- and CoCp2-doped diamond surfaces, the areal electron density values are 4.822 × 1013 and 4.519 × 1013 cm–2, and the carrier mobility values are 357 and 108 cm2 V–1 s–1 at 298 K, respectively. Moreover, after DMC and CoCp2 molecular adsorption, the optical absorption coefficient increases in the visible region. This study will promote investigations for two-dimensional electron gas on the diamond surface.

Stabilizing Cobalt‐free Li‐rich Layered Oxide Cathodes through Oxygen Lattice Regulation by Two‐phase Ru Doping

AbstractThe application of Li‐rich layered oxides is hindered by their dramatic capacity and voltage decay on cycling. This work comprehensively studies the mechanistic behaviour of cobalt‐free Li1.2Ni0.2Mn0.6O2 and demonstrates the positive impact of two‐phase Ru doping. A mechanistic transition from the monoclinic to the hexagonal behaviour is found for the structural evolution of Li1.2Ni0.2Mn0.6O2, and the improvement mechanism of Ru doping is understood using the combination of in operando and post‐mortem synchrotron analyses. The two‐phase Ru doping improves the structural reversibility in the first cycle and restrains structural degradation during cycling by stabilizing oxygen (O2−) redox and reducing Mn reduction, thus enabling high structural stability, an extraordinarily stable voltage (decay rate <0.45 mV per cycle), and a high capacity‐retention rate during long‐term cycling. The understanding of the structure‐function relationship of Li1.2Ni0.2Mn0.6O2 sheds light on the selective doping strategy and rational materials design for better‐performance Li‐rich layered oxides.

Stabilizing Cobalt-free Li-rich Layered Oxide Cathodes through Oxygen Lattice Regulation by Two-phase Ru Doping.

The application of Li-rich layered oxides is hindered by their dramatic capacity and voltage decay on cycling. This work comprehensively studies the mechanistic behaviour of cobalt-free Li1.2 Ni0.2 Mn0.6 O2 and demonstrates the positive impact of two-phase Ru doping. A mechanistic transition from the monoclinic to the hexagonal behaviour is found for the structural evolution of Li1.2 Ni0.2 Mn0.6 O2, and the improvement mechanism of Ru doping is understood using the combination of in operando and post-mortem synchrotron analyses. The two-phase Ru doping improves the structural reversibility in the first cycle and restrains structural degradation during cycling by stabilizing oxygen (O2- ) redox and reducing Mn reduction, thus enabling high structural stability, an extraordinarily stable voltage (decay rate <0.45 mV per cycle), and a high capacity-retention rate during long-term cycling. The understanding of the structure-function relationship of Li1.2 Ni0.2 Mn0.6 O2 sheds light on the selective doping strategy and rational materials design for better-performance Li-rich layered oxides.

Sulfur-Doped Carbon for Potassium-Ion Battery Anode: Insight into the Doping and Potassium Storage Mechanism of Sulfur.

The sulfur doping strategy has been attracting extensive interest in potassium-ion battery carbon anodes for the dual potential of improving the capacity and kinetics of carbon anodes. Understanding the doping and potassium storage mechanism of sulfur is crucial to guide the structural design and optimization of high-performance sulfur-doped carbon anodes. Herein, presenting a laboratory-synthesized sulfur-doped hard carbon (SHC) with a sulfur content of 6.4 at. % as an example, we clarify the sulfur doping mechanism and reveal the role of sulfur in potassium storage. The high sulfur content of SHC stems from the selective substitution of sulfur for carbon and the residual trace of sulfur molecular fragments after sulfurization. As a result, thanks to the multifaceted roles of doped sulfur in potassium storage, about twice as much capacity, rate capability, and cycling stability is achieved for SHC against S-free hard carbon at the same test conditions. Furthermore, potassium-ion hybrid capacitors assembled based on an SHC anode demonstrate high energy/power density (139 Wh kg-1/7.3 kW kg-1), along with an extraordinary cycling stability.

Anion‐Modulated Chemical Doping of Organic Hole Conductor Boosts Efficiency and Stability of Perovskite Solar Cells

AbstractChemical doping of organic semiconductors enables significant progress in improving their optoelectronic performance. However, the correlation between doping counter ions and charge‐transport mechanism has not been yet well‐understood. In this study, it is discovered that the anion‐dependent degree of delocalization (DOD) of lithium‐based dopants significantly determines the doping kinetics as well as the conductivity of organic hole transport layer (HTL), leading to large variation in solar cell efficiency and device stability. Specifically, the incorporation of bis(pentafluoroethanesulfonyl) imide (PFSI−) as the anion with a high DOD results in one order of magnitude higher film conductivity and thus an elevated power conversion efficiency (PCE) exceeding 22.1%, much higher than the state‐of‐the‐art lithium bis(trifluoromethane)sulfonimide (LiTFSI) (21.1%) and lithium hexafluorophosphate (LiPF6) (20.0%). Moreover, the dopant LiPF6 with a smaller DOD produces higher doping yield of HTL accompanied by stronger light‐induced PCE fluctuation. Structural analysis reveals anion‐modulated ion exchange kinetics determine the hole‐transport mechanism and device photostability. To mitigate these detrimental effects, a versatile strategy of Li+ solvation is developed to modulate the anion dissociation, enabling simultaneous improvement of device efficiency and stability. This study elucidates an intriguing and generally applicable doping mechanism, and envisages a bright future to further developing efficient and stable organic electronics.

In-Situ Spectro-Electrochemistry of Conductive Polymers Using Plasmonics to Reveal Doping Mechanisms.

Conducting polymers are a key component for developing wearable organic electronics, but tracking their redox processes at the nanoscale to understand their doping mechanism remains challenging. Here we present an in-situ spectro-electrochemical technique to observe redox dynamics of conductive polymers in an extremely localized volume (<100 nm3). Plasmonic nanoparticles encapsulated by thin shells of different conductive polymers provide actively tuned scattering color through switching their refractive index. Surface-enhanced Raman scattering in combination with cyclic voltammetry enables detailed studies of the redox/doping process. Our data intriguingly show that the doping mechanism varies with polymer conductivity: a disproportionation mechanism dominates in more conductive polymers, while sequential electron transfer prevails in less conductive polymers.

Synergic and competitive effect of A-site substitution on structure and electric property in BaTiO3-based ceramics

Sites engineering has been extensively investigated in BaTiO3-based lead-free materials. Although the effect of A or B site substitution on structure and electric properties have been researched adequately, the synergic and competitive impacts of doping element have received little attention, which has become an urgent issue for further optimizing performance. Here, three groups BT-based ceramics [0.6(Ba0.9Ca0.1)TiO3-0.4Ba(Sn0.2Ti0.8)O3, B(Ca)TS, 0.6(Ba0.9Ca0.05Sr0.05)TiO3-0.4Ba(Sn0.2Ti0.8)O3, B(Ca,Sr)TS, and 0.6(Ba0.9Sr0.1)TiO3-0.4Ba(Sn0.2Ti0.8)O3, B(Sr)TS] are synthesized by normal sintering, revealing the synergic and competitive mechanism of A site doping on structure and properties. The effect of Ca2+ and Sr2+ are quite different on the structure, especially the phase structure and grain size, and the evolution of electric properties (e.g., d33, Strain, and Temperature stability) results from structure caused by the synergic and competitive effect of Ca2+ and Sr2+. For example, a large d33 (∼950 pC/N) is obtained in B(Sr)TS due to its closer R-O-T phase structure compared to B(Ca)TS and B(Ca,Sr)TS ceramics, which is superior to some previous BT-based studies. Therefore, exploring of doping mechanism can further tune the microscopic structure and thus enhance electric properties, accelerating the practical process of lead-free ceramics.

One step activation by ammonium chloride toward N-doped porous carbon from camellia oleifera for supercapacitor with high specific capacitance and rate capability

In recent years, various biomasses (such as coconut, cotton, wheat straw, basswood, bamboo, etc.) have been utilized to prepare porous carbon materials (PCMs) through carbonization and/or physical/chemical activation. Most of these carbon materials are limited by the electric double-layer capacitance, resulting in a limited specific capacitance. Moreover, the preparation processes are often complicated and the carbon yield is low. Therefore, from the perspective of green and sustainable preparation of PCMs with high carbon yield and high performance, in this study, N-doped porous carbon electrodes were prepared by one-step activation carbonization method using camellia oleifera branches as raw material and NH 4 Cl as the activator. The N-doped NCW-2 sample has a rational hierarchical porous structure and high N doping amount (3.35 at. %) and exhibited optimal rate performance with a specific capacitance of 250 F g −1 at 50 A g −1 . The symmetrical device also presented excellent performance with a capacitance retention of 93.7 % after cycling 30,000 times at 20 A g −1 and delivered superior rate performances of 22.3 W h kg −1 @100 W kg −1 to 11.8 W h kg −1 @4800 W kg −1 . This work may provide a certain reference for the preparation of N-doped biomass-derived PCMs and widen its practical application in supercapacitor devices. • The self-supporting N-doped porous carbon can be directly used without posttreatment. • The mechanism of doping and activation are preliminarily proposed. • The as-prepared material has a high nitrogen doping of 3.35 at. %. • Electrodes exhibited a high specific capacitance of 250 F g −1 even at 50 A g −1 . • The symmetrical device showed a capacitance retention of 93.7 % after 30,000 cycles.

Polymer and composite based thermoelectrics: Basics, scopes and issues

AbstractLow thermal conductivity of polymeric materials along with their ability for nonconventional process ability, light weight, and flexibility makes them possible candidates for low‐power thermo electrical applications. However, it requires the development of both Seebeck coefficient and electrical conductivity simultaneously. This viewpoint addresses some of the concepts in the literature to reach this by taking into consideration the intricacies and interconnectivities of diverse thermoelectric parameters. Particularly, the applicability of the Wiedemann–Franz rule as well as DOS engineering by combination two semiconductors, suitable in inorganic, is reviewed for polymeric systems. One of the major advantages of polymeric semiconductors is that their thermal conductivity is mostly phononic (lattice thermal conductivity) and remains low with increasing charge carrier concentrations, as needed for TE applications. The momentum in polymer artificial strategies has to be joined with the studies on doping effectiveness and doping mechanisms to overcome the bottlenecks in polymeric thermoelectric.

Multimodal Encapsulation to Selectively Permeate Hydrogen and Engineer Channel Conduction for p-Type SnOx Thin-Film Transistor Applications.

It has been challenging to synthesize p-type SnOx (1 < x < 2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band. Herein, we report on the multifunctional encapsulation of p-SnOx to limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnOx channel for thin-film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements identified that ultrathin SiO2 as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnOx and selectively diffused hydrogen across the entire thickness of the channel. Encapsulated p-SnOx-based TFTs demonstrated much enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current (on/off ratio > 103), field effect mobility of 3.41 cm2/(V s), and threshold voltages of ∼5-10 V. The fabricated devices show minimal deviations as small as ±6% in the TFT performance parameters, which demonstrates good reproducibility of the fabrication process. The relevance between the TFT performance and the effects of hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. Density functional theory calculations reveal that hydrogen-related impurity complexes are in charge of the enhanced channel conductance with gate biases, which further supports the selective permeation of hydrogen through a thin SiO2 encapsulation.

DFT calculations and experiments of oxidation resistance research on B, N, and Si multi-doped diamond films

The oxidation resistance of diamond films is essential in maintaining their good performance in high-temperature applications. Although numerous experiments have proved that doping can improve diamond films' oxidation resistance properties, the theoretical explanation still needs to be discussed. In this study, the density functional theory (DFT) method is used to elucidate the influence mechanism of multiple doping, including B, N, and Si elements doping, on the oxidation resistance of diamond films and obtain the doped diamond films with the optimal oxidation resistance. These include the confirmation of the different doped diamond (111) models, the adsorption site of the O atoms on the various doped diamond surfaces, and the subsequent reaction process of O2 molecules with the C atom. The results show that the multi-doped diamond model has the most considerable activation energy due to the synergistic effect of the three elements, which represents better oxidation resistance properties. In addition, eight kinds of diamond films are fabricated on the silicon substrate. Their weight loss at high temperatures is conducted to evaluate oxidation resistance, indicating that multiple doping can effectively reduce the high-temperature oxidation rate of diamond films, and the experimental results are consistent with the theoretical calculations.

Enhancing the Performance of N-Type Thermoelectric Devices via Tuning the Crystallinity of Small Molecule Semiconductors.

In the development of high-performance organic thermoelectric devices, n-type materials, especially with small molecule semiconductors, lags far behind p-type materials. In this paper, three small molecules are synthesized based on electron-deficient naphthalene bis-isatin building blocks bearing different alkyl chains with the terminal functionalized with 3-ethylrhodanine unit and studied their aggregation and doping mechanism in detail. It is found that crystallinity plays an essential role in tuning the doping behavior of small molecules. Molecules with too strong crystallinity tend to aggregate with each other to form large crystalline domains, which cause significant performance degradation. While molecules with weak crystallinity can tolerate more dopants, most of them exhibit low mobility. By tuning the crystallinity carefully, organic thermoelectric devices based on C12NR can maintain high mobility and realize effective doping simultaneously, and a high power factor of 1.07 µW m-1 K-2 at 100°C is realized. This delicate molecular design by modulating crystallinity provides a new avenue for realizing high-performance organic thermoelectric devices.

Oxygen-doped carbon nanofiber nonwovens as an effective interlayer towards accelerating electrochemical kinetics for lithium-sulfur battery

Introduction of hydrophilic groups like oxygen/nitrogen groups is considered as a favorite solution to guarantee the functionality for interlayer in lithium-sulfur battery. However, the contributions of different oxygen containing groups was less studied especially when carbon nanofibers are used as interlayer. Herein, a bifunctional electrospun carbon nanofiber nonwoven (xO-CM) derived from coal tar pitch was prepared, followed by acid impregnation. The species and amount of oxygen groups could be finely regulated by changing the acid oxidation time. When xO-CM was adopted as interlayer, increased lithiophilicity on account of oxygen doping enables a larger flux and a uniform release of lithium ions. Ex-situ EIS analysis revealed that the addition of xO-CM in the cell could accelerate the conversion between polysulfides, especially for the liquid–solid and solid–solid reaction. Besides, the oxygen doping facilitated the nucleation of Li2S. Cells with 30O-CM (acid dipping for 30 min) possessed the best facilitation with relatively low solid electrolyte interface resistance and charge transfer resistance. Even at 2C, the cell achieved an ultralow capacity decay rate of 0.06 %, demonstrating its efficatively anchoring and accelerating effect for polysulfides. This work manifested the effective mechanism of oxygen doping for lithium-sulfur battery by adopting pitch-based carbon nanofibers as carrier.

Unraveling the diagnostic phase of 99mTc-doped iron oxide nanoprobe in sarcoma bearing mice

Most current single photon emission computed tomography (SPECT) nano-tracers are designed via a chelator-based radiolabeling approach which requires sophisticated optimization and faces limited in-vivo stability. Here, 99mTc can be intrinsically interchelated to the core of iron oxide nanoparticles (IO-NPs) providing a promising alternative radiolabeling approach to develop 99mTc-doped IO nanoplatform for tumor diagnosis without using an organic chelator or temperature dependent procedure. 99mTc-doped IO nanoplatform was prepared via a validated one-step radiochemical doping mechanism during the polyvinyl pyrrolidone capped IO-NPs (IO-PVP-NPs) co-precipitation synthesis where stannous chloride concentration and pH adjustment played a vital role. It was synthesized with high radiolabeling efficiency 96.5 ± 0.79%, convenient hydrodynamic size 12.54 ± 2.54 nm, reasonable biocompatibility profile and appropriate in-vitro stability up to 24 h. The in-vivo evaluation in sarcoma bearing mice revealed reduced RES's organs uptake, lustrous tumor accumulations (26.5 ± 1.17 and 69.32 ± 0.97% ID/g at 60 and 30 min post i.v. and i.t., respectively) and sparkling target/non-targeting ratios at all the experimental time points with magnitude 31.17 and 62.17 at 60 min post i.v. and i.t., respectively. Hence, this IO-NPs based in-situ radiochemical doping mechanism could open a plethora of novel SPECT based nano-tracers for convenient cancer diagnosis.

On the dissolution and enhancement mechanisms of Cr doping in Mo2FeB2-based cermets

In this work, the effect of Cr doping on the mechanical properties of Mo2FeB2-based cermets was studied. The results indicated that the hardness was continuously enhanced with the Cr contents, while the transverse rupture strength increased and then decreased. With the increase of Cr contents, the decreased binder deteriorated the fracture toughness. In the Mo2FeB2 particles of the cermets, Cr atoms mainly substituted the large-size Mo atoms instead of Fe. However, the first-principles calculation results showed that when the Cr atoms occupied the sites of Fe, the Cr-doped Mo2FeB2 were more thermodynamically stable. Based on the elemental composition of Cr-doped Mo2FeB2 bulks, the sites of Cr in Mo2FeB2 were mainly determined by the contents of Mo and Fe. In the Mo-depleted Mo2FeB2 bulk, Cr atoms preferred to substitute the Mo atoms, while Cr atoms occupied the sites of Fe in the Fe-depleted Mo2FeB2 bulk. Hence, the relatively lower content of Mo in Mo2FeB2-based cermets resulted in the substitution of Mo with Cr atoms. The intrinsic hardening of Mo2FeB2 induced by Cr doping contributed to the enhanced hardness of Mo2FeB2-based cermets. Besides, the decreased bulk modulus and shear modulus were conducive to the improvement of the transverse rupture strength.

Mechanism of carrier doping induced magnetic phase transitions in two-dimensional materials

Electrically tuning long-range magnetic orders has been realized in two-dimensional (2D) semiconductors via electrostatic doping. On the other hand, the observations are highly diverse: the transition can be realized by either electrons or holes or both depending on specific materials. Moreover, doped carriers seem to always favor the ferromagnetic (FM) ground state. The mechanism behind those diverse observations remains uncovered. Combining first-principles simulations, we analyze the spin superexchange paths of the correlated d/f orbitals around band edges and assign 2D magnetic semiconductors into three types by their projected density of states (PDOS). We find that each type of PDOS corresponds to a specific carrier-driven magnetic phase transition and the critical doping density and type of carriers can be quantitatively obtained by calculating the superexchange coupling strength. The model results are in good agreements with first-principles calculations and available measurements. After understanding the mechanism, we can design heterostructures to realize the FM to antiferromagnetic transition, which has not been realized before. This model is helpful to understand diverse measurements and expand the degrees of freedom to control long-range magnetic orders in 2D semiconductors.

Study of the mechanism of nitrogen doping in carbon supports on promoting electrocatalytic oxygen reduction reaction over platinum nanoparticles

Nitrogen-doped carbons (Nano-NC) are often employed as functional supports for boosting oxygen reduction reaction (ORR) over Pt-based catalysts, however, the mechanism of N doping on the adsorption and activation of molecular oxygen on Pt active sites is still not clear. Herein, Nano-NCs as the supports were prepared by a facile NH3 antipyretic method, which allowed to tune the kinds of nitrogen species in carbon matrix and their contents by adjusting the NH3 antipyretic temperatures. With such an exquisite control, the Pt nanoparticles loaded on the as-obtained Nano-NC showed an optimal Pt particle size (2.10 nm), a higher content of Pt0, a large electrochemically active surface area, and fast electron transport ability. As a consequence, the Pt/Nano-NC-800 catalyst with the optimal N-doping showed an outstanding ORR performance with half-wave potential of 0.80 V vs. RHE, limit diffusion current of 5.37 mA/cm2 and improved methanol/CO anti-poisoning, which is superior to the commercial Pt/C catalyst (20%, JM), and most of previously reported Pt-based catalysts. This work may pave a way for the design of the advanced supports for Pt-based catalysts for the ORR applications.

Tuning of carrier concentration and superconductivity in high-entropy-alloy-type metal telluride (AgSnPbBi)(1-)/4In Te

High-entropy-alloy-type (HEA-type) compound superconductors have been drawing much attention as a new class of exotic superconductors with local structural inhomogeneity. NaCl-type (Ag,In,Sn,Pb,Bi)Te is a typical HEA-type superconductor, but the carrier doping mechanism had been unclear. In this study, we synthesized (Ag,In,Sn,Pb,Bi)Te with various In concentration using high-pressure synthesis: the studied system is (AgSnPbBi)(1-x)/4InxTe (x = 0-0.4). Single-phase samples were obtained for x = 0-0.3. A semiconductor-like temperature dependence of resistivity was observed for x = 0, while superconductivity appeared for the In-doped samples. The highest transition temperature (Tc) was 3.0 K for x = 0.3. The Seebeck coefficient decreases with increase of x, which suggests that In3+ generates electron carriers in (AgSnPbBi)(1-x)/4InxTe. Tuning of carrier concentration and superconducting properties of (Ag,In,Sn,Pb,Bi)Te would be useful for further investigation of exotic superconductivity in the HEA-type compound.