Substitutional Doping Research Articles

Nucleation‐Controlled Doping of II–VI Semiconductor Nanocrystals Mediated by Magic‐Sized Clusters

Doping quantum‐confined semiconductor nanocrystals offers an effective way to tailor their unique properties. However, the inherent challenges of nanoscale doping processes, such as the low probability of successful doping, have hindered their practical applications. Nucleation‐controlled doping has emerged as a potential solution, but a comprehensive mechanistic understanding of this process is lacking. Herein, the nucleation‐controlled doping process facilitated by magic‐sized cluster intermediates is elucidated. This approach enables the synthesis of 2D ZnSe quantum nanoribbons with two distinct doping sites. Remarkably, the identity of the dopants plays a critical role in determining the chemical pathways of nucleation‐controlled doping. Substitutional doping of magic‐sized clusters with Mn2+ ions leads to successful substitutional doping of the final 2D nanocrystals. Conversely, Co2+ ions, initially occupying substitutional positions in the magic‐sized cluster intermediates, relocate to alternative sites, such as interstitial sites, in the final nanocrystals. First‐principle calculations of dopant formation energies support these experimental findings, demonstrating the thermodynamic favorability of specific dopant site preferences. Moreover, a consistent tendency is observed in CdSe nanocrystals, suggesting that the proposed doping mechanism is generally applicable to II–VI semiconductors. This study will advance the controlled synthesis of various doped semiconductor nanocrystals using nucleation‐controlled doping processes.

Unveiling the Impact of Substitutional Doping on the Oxidation Behavior of MoAlB: A Comprehensive First-Principles Study

Unveiling the Impact of Substitutional Doping on the Oxidation Behavior of MoAlB: A Comprehensive First-Principles Study

Emerging new phases in correlated Mott insulatorCa2RuO4.

The Mott insulator Ca2RuO4is a paradigmatic example among transition
metal oxides, where the interplay of charge, spin, orbital, and lattice degrees of freedom leads to competing quantum phases. In this paper, we focus on and review some key aspects, from the underlying physical framework and its basic properties, to recent theoretical efforts that aim to trigger unconventional quantum ground states, using several external parameters and stimuli. Using first-principle calculations, we demonstrate that Ca2RuO4shows a spin splitting in the reciprocal space, and identify it as an altermagnetic candidate material. The non relativistic spin-splitting has an orbital selective nature, dictated by the local crystallographic symmetry. Next, we consider two routes that may trigger exotic quantum states. The first one corresponds to transition metal substitution of the 4d4Ru with isovalent 3d3ions. This substitutional doping may alter the spin-orbital correlations favoring the emergence of negative thermal expansion. The second route explores fledgling states arising in a nonequilibrium steady state under the influence of an applied electric field. We show that the electric field can directly affect the orbital density, eventually leading to strong orbital fluctuations and the suppression of orbital imbalance, which may, in turn, reduce antiferromagnetism. These aspects suggest possible practical applications, as its unique properties may open up possibilities for augmenting existing technologies, surpassing the limitations of conventional materials.

Precise p-type and n-type doping of two-dimensional semiconductors for monolithic integrated circuits

The controllable fabrication of patterned p-type and n-type channels with precise doping control presents a significant challenge, impeding the realization of complementary metal-oxide-semiconductor (CMOS) logic using a single van der Waals material. However, such an achievement could offer substantial benefits by enabling continued transistor scaling and unprecedented interlayer interconnect technologies. In this study, we devise a precise method for two-dimensional (2D) semiconductor substitutional doping, which allows for the production of wafer-scale 2H-MoTe2 thin films with specific p-type or n-type doping. Notably, we extend this approach to the synthesis of spatially selective doped 2H-MoTe2 thin films via a one-step growth method, facilitating the monolithic integration of p-type and n-type semiconductor channels. Leveraging this advancement, we successfully fabricate a chip-sized 2D CMOS inverter array that demonstrates excellent device performance and yield. Collectively, these findings represent a significant stride towards the practical incorporation of 2D semiconductors in very large-scale integration technology.

High-performance p-type field-effect transistors using substitutional doping and thickness control of two-dimensional materials

High-performance p-type field-effect transistors using substitutional doping and thickness control of two-dimensional materials

P-type doped AlxGa1-xAs nanowire photocathode: A theoretical perspective on structural and optoelectronic properties

In this work, the effect of p-type doping on the structural, electronic, and optical properties of AlxGa1-xAs nanowires are investigated by first-principles calculations. Different doping elements (Be, Mg, Zn), doping methods (interstitial and substitution doping) and doping concentration are considered. The calculations of formation energy suggest that the structural stability of p-type AlxGa1-xAs nanowires is gradually weaken as the rise of doping concentration and Al composition. Besides, the difficulty of forming substitution doping for different doping elements obeys the following order: Be<Mg<Zn. In addition, the substitution doping atom tends to replace Ga atom rather than Al atom to form substitution doping structure. After substitution doping, all energy bands shift to higher energy region due to the orbital hybridization of electronic states induced by impurity atom and nanowire atoms. Moreover, the substitution doping leads to the Fermi level entering into the valence band, resulting in obviously p-type conductivity. The p-type modulation doping is indeed effective in the axial type AlxGa1-xAs nanowires with p-type carrier concentration varying between 1.85×1020 cm-3 and 4.42×1020 cm-3, and the conductivity will be further enhanced with increasing substitution doping concentration or Al composition. Finally, the optical absorption of AlxGa1-xAs nanowire photocathodes can be effectively enhanced through BeGa doping. Our findings not only present a comprehensive understanding of p-type doping mechanism of AlxGa1-xAs nanowires, but also provide a theoretical basis for preparing AlxGa1-xAs nanowire based photoelectric devices with p-type properties.

Significant enhancement in the magnetic properties of Cr2Te3 nanosheets by atom substitution doping.

Ferromagnetic Cr2Te3 nanocrystals, with their high spin-orbit coupling and low symmetry, have attracted considerable attention as rare-earth-free magnetic nanomaterials due to their potential to achieve high magnetic anisotropy. However, their relatively low values of remanence (Mr) and saturation (MS) magnetisation limit their energy product, making them unsuitable for practical applications. Herein, we report a straightforward one-pot heat-injection technique for the synthesis of high-remanence hexagonal Cr2Te3 nanosheets by heterogeneous doping with atoms of M (M = V, Mn and Se). The doped materials provide enhanced Mr and MS at an unchanged Curie temperature (TC), resulting in excellent hard magnetic properties. With Mn doping, the Mr of the matrix increases significantly, reaching 18.38 emu g-1 at 5 K, far exceeding the original undoped Cr2Te3 nanosheets. The nearly square hysteresis loop makes it valuable for many low temperature applications. These results provide a valuable case for tuning the magnetism of ferromagnetic Cr2Te3 by substitutional doping.

Self-supported electrochemical sensor based on uniform palladium nanoparticles functionalized porous graphene film for monitoring H2O2 released from living cells.

Graphene film has been considered a promising material for the construction of self-supported electrodes due to its favorable flexibility and high conductivity. However, the film fabricated from pristine graphene or conventional graphene sheet reduced graphene oxide processes limited electrocatalytic performance. Decorating active metal species or incorporating heteroatoms intothegraphene framework have been proved to be effective methods to enhance the electrocatalytic efficiency of graphene film-based self-supported electrodes. Herein, we present a freestanding electrode composed of uniform Pd nanoparticles decorating N,S co-doped porous graphene film (Pd/NSPGF) and explore its practical application in differentiating various human colon cell types by in situ tracking the amount of H2O2 secreted from live cells. Our findings reveal that, on the one hand, the NSPGF has abundant surface and inner pores, which promote active site exposure, and mass diffusion during electrochemical reactions; on the other hand, the substitutional doping ofthe graphene framework with heteroatoms (e.g., N or S) can tailor its electronic and chemical properties, and facilitate the uniform loading of high-density Pd nanoparticles. Moreover, the intrinsic activity of Pd/NSPGF is regulated by the interaction of Pd nanoparticles withtheNSPGF support. Taking the advantages of morphology and composition, the self-supported Pd/NSPGF electrode displays remarkable electrochemical performance with a wide linear range up to 2.0mM, low detection limit of 0.1μM (S/N = 3), high sensitivity of 665 µA cm-2mM-1, and good selectivity. When applied in real-time trackingofthe H2O2 released from normal human colon epithelial cells and human colorectal cancer cells, the Pd/NSPGF-based electrochemical sensing system can distinguish the cell types by testing the number of extracellular H2O2 molecules released per cell, which holds considerable potential for early detection and monitoring of disease-related clinical specimens.

Effective Screening of Metal Dopants for In2O3 Catalyst to Tune Catalytic Performance of CO2 Hydrogenation to Formic Acid

The metal doping is an effective strategy to adjust catalytic performance for indium oxide catalyst in CO2 hydrogenation. In current work, a series dopant, Co, Fe, Ni, Pd, Pt, Rh and Ru, are selected and examined in CO2 hydrogenation to formic acid by DFT based microkinetic simulation. It is found that substitutional doping is local effect which mainly promotes the reactivity of adjacent oxygen atoms. The calculations of both CO2 adsorption and hydrogen molecule dissociation certify the positive effects induced by doping, and the adsorption energy of CO2 has a linear relation with the transferred charges for all investigated catalysts which helps to explain the C‐O bond activation mechanism. Two pathways, Formate and Carboxyl, are investigated under same footing. It is noted that doping significantly reduces the hydrogenation barriers on two pathways compared with undoped surfaces. Moreover, the calculated TOF of formic acid formation is greatly increased on doped surfaces and Pt, Pd, Ru are identified as the most active dopants. In the end, it is concluded that reaction obeys Carboxyl mechanism and a valid descriptor of trans‐HCOOH* and H* formation energy is proposed for the screening of effective dopants.

Impact of Dual Functionalities of Mo‐Doped BiFeO3 Decorated with Bi4MoO9 Heteroatoms for Piezo‐Photocatalytic Activity

AbstractPiezocatalysts have shown great promise for effcient hydrogen generation. However, their application is limited by the rapid charge recombination and sluggish charge transfer rate of piezo‐induced charge carriers. This work aims to address the preceding limitations by controlled synthesis of a representative piezocatalyst, BiFeO3 doped with Mo atoms and decorated with Bi4MoO9 (BMO) heteroatoms using sol‐gel method. The substitutional doping of Mo on BFO (BFMO) was shown to induce a shallow energy level near the conduction band that acted as a trapping state, to suppress recombination of charge carriers, enhance charge mobility for transport to the surface, modulate band alignment, and lower the energy barrier for surface reaction. The formation of BFMO/BMO heterostructures induced electrical band bending, leading to the electric potential gradient, hence promoting charge carrier separation and transfer. The BFMO/BMO with 0.5 mol % Mo (Mo‐5) demonstrated four times faster piezocatalytic Rhodamine B (RhB) dye degradation rate (k of 0.032 min−1) compared to pristine BFO (0.009 min−1). Further, the Mo‐5 exhibited a 45% higher piezocatalytic H2 production rate (14.4 µmol/g/h) compared to pristine BFO (9.8 µmol/g/h) while being cocatalyst‐free. Coupling piezocatalysis with photocatalysis was found to reduceperformance relative to the individual processes, which is attributed to Auger recombination which impedes any potential synergistic effect.

Effect of substitutional Sb doping on the structural stability, half-metallicity, elastic properties, electronic properties, and magnetism of the Co₂MnSn full Heusler compound

We conducted Density Functional Theory (DFT) calculations using the full potential linearized augmented plane wave (FP-LAPW) method to modify the Fermi level by introducing Sb doping into Co2MnSn.This was done through the Generalized Gradient Approximation (GGA) and modified Becke-Johnson (mBJ-GGA) formalisms to enhance spin polarization and suggest signs of half-metallicity. For both ferromagnetic and paramagnetic phases, lattice optimization was performed to identify the stable magnetic structure. The results designate that the doped alloys are stable in a ferromagnetic phase with L21 structure. The calculated elastic constants suggest that the doped alloys meet the criteria for mechanical stability. The magnetism in these compounds is primarily due to the localized moments on the Mn and Co atoms. According to mBJ-GGA calculations, the total magnetic moment slightly increases with Sb doping. Analysis of the optical constants revealed the optoelectronic properties, confirming semiconducting behavior. Doping elements to achieve half-metallicity is demonstrated to be an effective method for discovering new materials suitable for spintronics applications.

The interstitial Ru dopant induces abundant Ni(Fe)[sbnd]Ru cooperative sites to promote ampere-level current density for overall water splitting

Directionally induced interstitial Ru dopant rather than ordinary substitutional doping is a challenge. Furthermore, DFT calculations revealed that compared with the substituted Ru dopants, the interstitial Ru dopants induce abundant Ni(Fe)Ru cooperative sites, greatly expediting the reaction kinetics for HER and OER. Inspired by these, the interstitial Ru-doped NiFeP/NF electrode is constructed by the ’quenching doped Ru-phosphorization’ strategy. Relevant physical characterizations confirmed that interstitial Ru dopants promote electron reset in the Ni(Fe)Ru synergistic sites, effectively avoiding metal atom dissolution and encouraging more Ni (Fe)OOH active species. As expected, the Ru-NiFeP/NF||Ru-NiFeP/NF electrolyzer only need as low as 1.54 V to yield a current density of 1 A cm−2. In summary, this work innovatively constructs the phosphide electrode with ampere-level current density from the perspective of regulating the doping position of Ru. This provides a new design idea for optimizing the Ru doping strategy.

Atomic Nb-doping of WS2 for high-performance synaptic transistors in neuromorphic computing

Owing to the controllable growth and large-area synthesis for high-density integration, interest in employing atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for synaptic transistors is increasing. In particular, substitutional doping of 2D materials allows flexible modulation of material physical properties, facilitating precise control in defect engineering for eventual synaptic plasticity. In this study, to increase the switch ratio of synaptic transistors, we selectively performed experiments on WS2 and introduced niobium (Nb) atoms to serve as the channel material. The Nb atoms were substitutionally doped at the W sites, forming a uniform distribution across the entire flakes. The synaptic transistor devices exhibited an improved switch ratio of 103, 100 times larger than that of devices prepared with undoped WS2. The Nb atoms in WS2 play crucial roles in trapping and detrapping electrons. The modulation of channel conductivity achieved through the gate effectively simulates synaptic potentiation, inhibition, and repetitive learning processes. The Nb-WS2 synaptic transistor achieves 92.30% recognition accuracy on the Modified National Institute of Standards and Technology (MNIST) handwritten digit dataset after 125 training iterations. This study’s contribution extends to a pragmatic and accessible atomic doping methodology, elucidating the strategies underlying doping techniques for channel materials in synaptic transistors.

Study on the effect of rare earth elements La, Ce, Y and Sc doping on the mechanical properties of aluminum–lithium alloys

In this paper, the effects of rare earth elements La, Ce, Sc, and Y on the bond strength of the aluminum–lithium alloy δ’ (Al3Li)/Al interface are investigated using first-principles calculations. The results show that the interfacial energy decreases after substitutional doping of Al atoms on both sides of the interface by rare earth elements, respectively, with values ranging from −2.0664 eV/Å2 to −1.9720 eV/Å2. The interfacial energy decreased by 2.0841 eV/Å2 and 2.0709 eV/Å2 when Ce and Sc elements replaced Al in the matrix, respectively. Uniaxial interfacial tensile simulations of Al/ Al3Li showed that the strain elongation of the material increased from 24 % to 42 % for the pure interface after doping with Sc elements at the interface. The same tensile tests yielded a maximum elongation at break of 3.25 % for Al-Li alloy after artificial aging at 0.6 % Sc content. Observation of the microstructure of the materials before and after rare earth doping using TEM reveals that the content of nanoscale Al3(Sc, Li) composite particles increases with the increase of Sc content after artificial aging at 185 °C for 10 h. Moreover, the presence of Al3Sc refines the precipitated phase of the alloy and improves the plastic toughness of the material.

Formation, Structure, Electronic, and Transport Properties of Nitrogen Defects in Graphene and Carbon Nanotubes.

The substitutional doping of nitrogen is an efficient way to modulate the electronic properties of graphene and carbon nanotubes (CNTs). Therefore, it could enhance their physical and chemical properties as well as offer potential applications. This paper provides an overview of the experimental and theoretical investigations regarding nitrogen-doped graphene and CNTs. The formation of various nitrogen defects in nitrogen-doped graphene and CNTs, which are identified by several observations, is reviewed. The electronic properties and transport characteristics for nitrogen-doped graphene and CNTs are also reviewed for the development of high-performance electronic device applications.

Two-Dimensional Magnetic Semiconductors by Substitutional Doping of Monolayer PtS2

Two-Dimensional Magnetic Semiconductors by Substitutional Doping of Monolayer PtS₂

Substitutional Cu doping at the cation sites in Ba2YNbO6 toward improved visible-light photoactivity—A first-principles HSE06 study

Artificial photosynthesis holds immense promise for sustainable clean energy harvesting, with recent strides in material engineering with the earth abundant elements enabling efficient utilization of the visible solar spectrum for photoelectrochemical catalytic water splitting. Here, we have investigated the impact of substitutional Cu doping at all three cation sites in Ba2YNbO6 (BYN) using density functional theory calculations at the Heyd-Scuseria-Ernzerhof-06 level. One of the key findings is that the defect formation energy follows the hierarchy Nb &amp;gt; Ba &amp;gt; Y. The presence of an oxygen vacancy (OV) enhances the co-solubility of Cu substitution of Nb, particularly when placed outside the CuO6 unit, while it has a contrary effect for Y substitution. Cu replacement reduces the bandgap as Nb &amp;gt; Y ≫ Ba vis-à-vis pure BYN, while extending it into the visible part of the solar spectrum for Nb and Y replacement cases, albeit with OV causing a slight blue shift to them, without reducing the oxidation state of Cu due to strong charge-delocalization. Cu doping at Y and Nb sites retains the direct band transition character of BYN, a feature removed by OV. While all the bare Cu doped systems exhibit formation of a weak electron polaron, the placement of OV tends to annihilate this except for the system comprising first nearest neighbor placement of an OV relative to the Cu substitution at an Nb site. Notably, Cu doping at the Nb site significantly enhances optical activity, particularly ∼2.0–2.5 eV, resulting in promising candidates for photoelectrochemical catalysts.

Observation of anomalous excitonic emission in V-doped WS2 QDs synthesized by hydrothermal method and subsequent mechanical exfoliation

This study focuses on synthesizing vanadium (V) doped 2H phase WS2 via a facile hydrothermal method and subsequent liquid phase mechanical exfoliation of the material into QD-like nanostructures. An increment in dopant percentage from 1 % to 7 % red shifted the band gap of WS2 from 4.15 eV to 3.78 eV. The nanostructures show electronic transition due to B, A, and defect-bound excitons and demonstrate modulation of excitonic behavior with V doping. Low V doping provides the WS2 material with a reduced B/A excitonic peak intensity ratio because of the nonradiative pathways favoring the relaxation of high energy B excitons to A excitons. High V doping results in anomalous emission behavior marked by an increased B/A ratio, attributed to positive trion formation as a result of excess free hole concentration due to the p-type vanadium. The study suggests that V-doped WS2 nanostructures hold potential for technological applications, particularly in spintronics and photonics, emphasizing the importance of engineering exciton dynamics in two-dimensional materials using p-type substitutional dopants.

Insight into insulation degradation mechanism of Al2O3 involved with positive and negative defects

Al2O3 with the desired electrical insulating properties and thermal shock resistivity has been extensively applied in the field of solid oxide fuel cells and oxygen sensors. However, degradation of the insulating Al2O3 layer is an intractable issue in practical applications. In this study, different point defect structures of Al2O3 were realized with the substitutional doping effect of ZrO2 and MgO. The MgO dopant provides positively charged oxygen vacancies, whereas the ZrO2 dopant tends to trigger negatively charged vacancy formation at Al3+ sites. The oxygen vacancy concentration of Al2O3 exhibits the following trend: MgO-doped Al2O3 > Al2O3 > ZrO2-doped Al2O3. Furthermore, the densification morphology, insulating properties, and oxygen vacancy migration of Al2O3 have been confirmed to be largely affected by the extrinsic factors. This study indicates that oxygen vacancy migration depends on the applied electric field at high temperatures. As the voltage and temperature increase, oxygen vacancy migration shows obvious electric-field-dependent characteristics, and its aggregation macroscopically shows hole defects. The defect position of Al2O3 is nonstoichiometric Al2O3-x with poor crystallinity. Therefore, it is believed that the oxygen vacancy migration triggered by the second phase directly determines the insulation performance and causes the degradation of Al2O3 materials.

Saturation degree in dopant monolayers as modulator of Al-doping of ZnO by the Atomic Layer Deposition-supercycle approach

Transparent conductive oxides are trending topic in science and technology due to counterintuitive properties: optical transparency and high electrical conductivity. ZnO is a promising example with optoelectronic properties enhanced by supervalent doping. Al-doped ZnO (AZO) has emerged as leading candidate to replace environmentally hazardous In-doped SnO2. However, an ongoing debate exists regarding whether Al-doping improves its optoelectronic properties by substitutional doping or by promoting active defects. Here, we focused on Al-doping of ZnO by atomic layer deposition (ALD) applying the supercycle approach, showing that, decreasing Zn precursor dosing during dopant cycles, the decreasing saturation degree of Zn-species monolayers leads to morphological and microstructural changes that negatively impact optoelectronic properties, whereas Al content remains invariant. Our results demonstrate that unsaturated surfaces after decreasing Zn precursor dosing play a crucial role in Al incorporation, suggesting that, to maximize the effect of doping, complete oxide substitution reactions rather than those of conventional ALD must control growth, while crystallinity must remain. These findings could impact strategy designing for optimization of optoelectronic properties of AZO films deposited by ALD by inclining the debate towards the hypothesis that electrical properties are determined by Al substitutional doping together with active defects formed due to substitutional doping itself.