Doping Position Research Articles

Electronic transport properties of B/N/P co-doped armchair graphene nanoribbon field effect transistor

On the basis of the Density functional theory (DFT) combined with non-equilibrium Green's function (NEGF), we have investigated the application potential of the boron, nitrogen and phosphorus co-doped seven-atom-wide armchair graphene nanoribbons field effect transistor (7-AGNR-FET). The transfer characteristics indicate that the gate voltage (VG) can modulate the electronic transport properties of 7-AGNR FET, and the ION/IOFF ratio reaches 128.67. When a positive drain voltage (VD) is applied, the device exhibits appreciate working behavior with a saturation drain-source current (IDS) of 76.21 μA. Transmission pathways, transmission spectra and Molecular projection self-consistent Hamiltonian (MPSH) are calculated to explain the variations in current including negative differential resistance (NDR) effect under negative VD. The negative VG affects the height of the channel barrier and causes the rectifying effect. Moreover, band structures and projected density of states (PDOS) shows the performances of devices strongly depend on doping positions. This NPN-doped device simulates the structure of MOSFET as realistically as possible, and it possesses promising applications in memory device and rectifier of carbon-based integrated circuits.

Efficient and accurate atomistic modeling of dopant migration using deep neural network

This paper proposes an efficient and accurate method to model atomistic dopant migration, by leveraging the emerging deep neural network (DNN). By performing nudged elastic band (NEB) simulations of three prototype systems (B-doped Si, Li-doped Si, and C-doped GaN), it is shown that the proposed DNN-based method runs about 104-105 times faster than the widely-used atomistic dopant migration modeling method based on density functional theory (DFT), meanwhile keeping DFT-level high accuracy. Active learning is used to reduce training set redundancy, and the DNN model is further optimized for more accurate NEB calculation. As a result, the dopant atomic position in saddle-point and the dopant migration energy barrier in the migration energy path (MEP) predicted by the proposed DNN-based NEB deviate merely about 10−2 Å and 10−2 eV, respectively, from those predicted by the established DFT-based NEB. Given its efficiency and accuracy, the proposed DNN-based method might be useful to develop future-generation atomic-scale technology computer-aided design (TCAD) tools.

Size Optimization of a N-Doped Graphene Nanocluster for the Oxygen Reduction Reaction.

N-Doped graphene nanoclusters (N-GNCs) are promising electrocatalysts for the oxygen reduction reaction (ORR) at the cathode of fuel cells. In this study, the dependence of the ORR activity on the size of N-GNCs was investigated using first-principles calculations based on density functional theory. The maximum electrode potential (UMax) was estimated from the free energy of the reaction intermediates of the ORR. UMax was predicted to show a volcanic trend with respect to the cluster size. The results suggest that C215H36N with a radius of 13.6 Å is the best candidate for ORRs and is better than platinum in terms of UMax. The volcano-shaped plot of UMax is attributed to the switch of the reaction step that determines UMax, which is caused by the destabilization of reaction intermediates. Such changes in the stability of the intermediates can be explained by the decrease in the local density of states at the reaction site, which is due to the development of the so-called edge state at the zigzag edge. The establishment of experimental techniques to control the cluster size and doping position will be the key to superior catalyst preparation in the future.

Effect of the Dopant Configuration on the Electronic Transport Properties of Nitrogen-Doped Carbon Nanotubes.

Nitrogen-doped carbon nanotubes (N-CNTs) show promise in several applications related to catalysis and electrochemistry. In particular, N-CNTs with a single nitrogen dopant in the unit cell have been extensively studied computationally, but the structure-property correlations between the relative positions of several nitrogen dopants and the electronic transport properties of N-CNTs have not been systematically investigated with accurate hybrid density functional methods. We use hybrid density functional theory and semiclassical Boltzmann transport theory to systematically investigate the effect of different substitutional nitrogen doping configurations on the electrical conductivity of N-CNTs. Our results indicate significant variation in the electrical conductivity and the relative energies of the different dopant configurations. The findings can be utilized in the optimization of electrical transport properties of N-CNTs.

The effects of Pt doping on the optical properties of Au20

We consider the doping of Pt onto small Au20 clusters, identifying the effects that this alloying has upon the optical and static properties of each candidate nanoalloy. By performing real-time time dependent density functional theory calculations, we determine that the electronic structure and, by extension, the optical absorption spectrum strongly depend on the position of a Pt dopant; either as substitutional defect, or as an adsorbed atom on the Au-surface. Indeed, we find that by varying the local positions, we are able to strongly influence the electronic and optical properties of complex nanoalloys. Of particular interest is the profound impact on the HOMO–LUMO gap of Au20 – shrinking or growing depending on the location of a Pt doping. By considering different possible locations and morphologies for the introduced Pt, we identify alloying types which may have a greater probability of supporting collective plasma oscillations.

Engineering ordered arrangements of oxygen vacancies at the surface of superconducting La2CuO4 thin films

We demonstrate how ordered arrangements of oxygen vacancies can be engineered during the growth of superconducting La2CuO4 films by oxide molecular-beam epitaxy. These arrangements are seen using in situ reflection high-energy electron diffraction. Based on qualitative real-time observations, we propose a surface reconstruction mechanism emphasizing the active role of dopants and oxygen vacancies at the film surface. Due to the specific atomic arrangement induced by dopant positions, characteristic surface “stripes” are generated, and they determine the intrinsically heterogeneous structure characterized by distorted checkerboard patterns on the surface. Not only can the surface motif during growth be monitored via characteristic surface reconstructions, but it can also be customized by altering strain, doping, and oxygen activity.

New insights into NO adsorption on alkali metal and transition metal doped graphene nanoribbon surface: A DFT approach

The aim of this article is to investigate the sensing performance of NO gas molecule on the graphene nanoribbon domain for the determination of structural and electronic properties. Effect of an alkali metal (lithium) and a transition metal (iron) on the armchair oriented graphene nanoribbon (ArGNR) surface for the sensing purpose of NO gas has been performed through the quantum mechanics based Density Functional Theory (DFT) calculations. Various configurations of ArGNR doped with Li and Fe atoms such as one-edge doped, center doped, both-edge doped Li-ArGNR and Fe-ArGNR have been simulated, and a detailed comparative study of lithium and iron doping on different configurations of ArGNRs for the adsorption energy, stability analysis, band gap analysis and density of states analysis has been quantitatively evaluated. By comparing the adsorption energy of NO, it is found that Li doping enhances the strength of NO adsorption on the different variants of ArGNR. Computational results predict that the undoped ArGNR is insensitive to the NO gas adsorption with adsorption energy of about −0.41 eV. Our results determine that substitutional doping of Li doping at one edge doped and both-edge doped position increases the adsorption abilities of ArGNRs in these configurations with adsorption energies of approximately −6.92 eV and −9.64 eV that is 16 and 23 times greater than the pristine ArGNR (Pr-ArGNR). Band nature for both type of doping estimates the changing behavior of ArGNRs from semiconductor to metallic transition after the adsorption of NO molecule. It is concluded that the Li doping at one edge and both edge position of ArGNR makes it an excellent potential sensing material for the sensing purpose of NO gas as compared to the Fe doped configurations.

Effect of Sr Doping on Structural and Transport Properties of Bi2Te3.

Search for doped superconducting topological insulators is of prime importance for new quantum technologies. We report on fabrication of Sr-doped BiTe single crystals. We found that Bridgman grown samples have p-type conductivity in the low 10 cm, high mobility of 4000 cmVs, crystal structure independent on nominal dopant content, and no signs of superconductivity. We also studied molecular beam epitaxy grown SrBiTe films on lattice matched (1 1 1) BaF polar surface. Contrary to the bulk crystals thin films have n-type conductivity. Carrier concentration, mobility and c-lattice constant demonstrate pronounced dependence on Sr concentration x. Variation of the parameters did not lead to superconductivity. We revealed, that transport and structural parameters are governed by Sr dopants incorporation in randomly inserted Bi bilayers into the parent matrix. Thus, our data shed light on the structural position of dopant in BiTe and should be helpful for further design of topological insulator-based superconductors.

Effect of iridium doping on electronic structure and optical properties of m-BiVO4 photocatalytic materials: a first principles study

To improve the photocatalytic performance of m-BiVO4 materials, iridium doping in m-BiVO4(0 0 1) crystal was studied using CAmbridge Serial Total Energy Package calculation module based on density functional theory. By calculating the formation energy of Ir doped in m-BiVO4 crystal at different doping positions and different content, model of Bi atom substituted by 6.25% Ir with the Ef of 0.887 eV was selected as a research object. The splitting and transferring of Ir 5d orbit from high localised state to two peaks of state density distributed on sides of conduction band (CB) and valence band (VB) are benefitted for electron transfer and charges redistribution. The band gap value decreased from 2.218 to 1.203 eV after doping Ir element and three hybrid energy bands arised between the VB and CB. The energy range of VB and CB is −5.68∼0.40 eV and 1.90∼7.42 eV, which is mainly the contribution of interaction between O 2p orbit and V 3d orbit, V 3d orbit and Bi 6p orbit, respectively. The iridium doping introduced the impurity levels near the Fermi energy level (EF ), narrowed the band gap and reduced the transition energy barrier of photo-generated electrons and made the electrons transition process more easily.

Understanding the role of lithium bonds in doped graphene nanoribbons as cathode hosts for Li‐S batteries: A first‐principles study

Using first-principles calculations, we investigate a family of doped graphene nanoribbons (GNRs) for their suitability as cathode hosts in lithium-sulfur batteries. We probe the role played by the lone pairs of the dopants in confining the lithium polysulfides (LiPS) to understand the mechanism of binding. Our results show that the Li bond between the polysulfides and the doped GNRs is analogous to a hydrogen bond and also dipole-dipole interactions play a key role in anchoring the polysulfides. A critical donor-Li-acceptor angle of 180° is found to be essential for proper adsorption of LiPS, highlighting the importance of the directionality of lone pairs. The charge lost by the sulfur atom of the polysulfide upon adsorption and shape of the lone pair basins and the value of Electron Localization Function (ELF) at the dopant position can provide a quick estimate of the strength of the bond. Significant contractions in the ELF profiles are also observed upon Li2S adsorption, further providing evidence for the hydrogen bond-like nature of the Li bond. Our results corroborate the fact that all acceptors capable of forming hydrogen bonds can be employed as suitable dopants for carbon-based cathode hosts in Li-S batteries.

Emergent quasi-two-dimensional electron gas betweenLi1±xNbO3andLaAlO3and its prospectively switchable magnetism

Oxide interfaces between insulating perovskites can provide a two-dimensional electron gas (2DEG), which was observed initially beneath polar $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ (LAO) grown on $\mathrm{Ti}{\mathrm{O}}_{2}$-terminated $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$(001). Here, we suggest to use a solid electrolyte $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ (LiNO) instead of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ to create in LAO/LiNO a robustly switchable and magnetic quasi 2DEG (q2DEG). This prospective phenomenon is achieved by charging and discharging lithium niobate while its $n\ensuremath{\rightarrow}p$ doping induces the alteration of magnetic order in LAO/LiNO and, thus, the spin degrees of freedom in q2DEG. On the basis of ab initio calculations and starting from the defectless and insulating LAO/LiNO superlattice, we demonstrate that either a ferromagnetic q2DEG or weakly magnetic quasi-2D hole gas emerge there due to the presence of excessive electrons or holes, respectively. These defects were simulated by one extra Li and a lithium vacancy in LiNO. By varying the $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ thicknesses up to 18 formula units, we found that (i) the spatial extent of q2DEG is 1.5 nm along the stacking direction and that (ii) the dopant position at the Al-terminated interface is energetically preferable by more than 0.5 eV compared to the deep layers. In the context of the advanced design of q2DEG, the out-of-plane electric polarization, which intrinsically appears in multiferroic LAO/LiNO, allows to switch externally the electric-field dependence of the Rashba effect. Moreover, the in-plane charge current via q2DEG may generate there a transverse spin density due to the Rashba-Edelstein effect. We discuss this scenario using the relativistic electronic structures and locally projected density of states which differ remarkably in $\mathrm{L}\mathrm{A}\mathrm{O}/{\mathrm{Li}}_{1+x}\mathrm{N}\mathrm{O}$ and $\mathrm{L}\mathrm{A}\mathrm{O}/{\mathrm{Li}}_{1\ensuremath{-}x}\mathrm{N}\mathrm{O}$.

Heteroatom-doped Clar's goblet: Tunable magnetic order and programmable spin logic gate

Nanographene exhibits manifold magnetic orders depending on its topology. The Clar's goblet, envisioned 50 years ago and synthesized recently, is an emblematic nanographene with an antiferromagnetic ground state induced by topological frustration. Inspired by the significant interest in the designer magnetic order of nanographene, we studied the tunable magnetic order in heteroatom-doped Clar's goblet. Interestingly, the antiferromagnetic to ferromagnetic transition is found in doped Clar's goblet by varying the doping positions. A large exchange-coupling strength of 77 meV is realized in a Clar's goblet doped by two nitrogen atoms. The spin directions and distribution at the connecting atoms determine the magnetic order and exchange-coupling strength. Moreover, the spin logic gate based on Clar's goblet can be converted from XOR (XAND) gate into OR (AND) gate by doping the outer units with nitrogen atoms. The heteroatom-doped nanographene with tunable magnetic order provides a platform for spintronic devices with controllable functions.

Spin thermoelectric effects on aluminum or phosphorus doped zigzag silicene nanoribbons

Based on the density-functional theory (DFT) combined with nonequilibrium Green’s function (NGF), this paper investigates the effects of either single aluminum (Al) or single phosphorus (P) atom substitutions at different edge positions of zigzag-edged silicene nanoribbons (ZGNRs) in the ferromagnetic state on the spin-dependent transport properties and spin thermoelectric effects. It has been found that the spin polarization at the Fermi level can reach 100% or –100% in the doped ZSiNRs. Meanwhile, the spin-up Seebeck effect (for -100% case) and spin-down Seebeck effect (for 100% case) are also enhanced. Moreover, the spin Seebeck coefficient is much larger than the corresponding charge Seebeck coefficient at a special doping position and electron energy. Therefore, the study shows that the Al or P doped ZSiNRs can be used to prepare the ideal thermospin devices.

Investigating optical adsorption properties of lead‐free double perovskite semiconductors Cs2SnI6−xBrx (x = 0–6) via first principles calculation

AbstractIn this work, the properties of the Br− ion‐doped Cs2SnI6 system (Cs2SnI6−xBrx, x = 0–6) are systematically explored via the first principle calculation. The evolution of Cs2SnI6−xBrx crystal structure in the doping process is obtained by regulating the doping positions where I− ions are replaced with Br− ions, and the changing curve of the bandgap is drawn on the basis of the setting of the U value in I 5p and Br 5p orbits and the accurate description of the bandgap of Cs2SnI6−xBrx with HSE06 hybrid functional. Br− ions doping not only improves the stability of the Cs2SnI6−xBrx structure, but also can adjust its bandgap width. In light of the analysis of gain and loss of electrons among ions and electron density difference during the doping process, the introduction of Br− ions enable Cs2SnI6−xBrx to have a stronger ionic crystal character than Cs2SnI6, which indicates that the Cs2SnI6−xBrx is suitable to be applied to photoelectric devices as a carrier transport layer. The further analysis of the distribution of electronic states density of Cs2SnI6−xBrx and the variation trend of its absorption spectra confirms the transition process of electrons among energy bands, which also reveals the main reason why the performance of current photovoltaic devices based on Cs2SnI6 are unsatisfactory. It is notable that we find Cs2SnI6−xBrx, especially Cs2SnI3Br3 is an ideal material for solar‐blind detection.

Exploring the structure of atom-precise silver-palladium bimetallic clusters prepared via improved single-pot co-reduction synthesis protocol.

Designing atom-precise bimetallic clusters with a relatively cost-effective and more abundant metal than Au (i.e., Ag) is desirable for the development of heterogeneous bimetallic cluster catalysts for industrial applications. Atom-precise Ag-based bimetallic clusters, which are analogs of the well-studied Au based clusters, are yet to be fully explored as catalysts. Establishing the Pd loading limit and the position of the Pd dopant in AgPd bimetallic clusters will further give an insight into the structure-activity relationships for these atom-precise AgPd heterogeneous catalysts. In this study, an improved single-pot co-reduction strategy was employed to prepare the bimetallic clusters, which were then characterized by mass spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray absorption spectroscopy (XAS) to identify the loading and position of the dopant metal. Our results show that only a single dopant Pd atom can be incorporated, and in comparison with monometallic Ag25 clusters, the absorption peaks of Ag24Pd1(SPhMe2)18 2- bimetallic clusters are blue shifted due to the incorporation of Pd. The XPS and XAS results show that the Ag24Pd1(SPhMe2)18 2- bimetallic clusters have multivalent Ag(0) and Ag(I) atoms and surprisingly show Pd(II) species with significant Pd-S bonding, despite the prevailing wisdom that the Pd dopant should be in the center of the cluster. The XAS results show that the singly doped Pd atom predominantly occupies the staple position, albeit we cannot unambiguously rule out the Pd atom in an icosahedral surface position in some clusters. We discuss the ramifications of these results in terms of possible kinetically vs thermodynamically controlled cluster formation.

Configuration of phosphorus doping in silicene nanoribbons in the presence of an external electric field

Silicene nanoribbons have been studied a lot in recent years, it is a nanostructure with enormous applications. The doping of another element into the unit cell changes the electrical and magnetic properties of the material, which creates new research directions in materials science. Based on the DFT theory, this work studies the doping phosphorus atoms and in silicene nanoribbons in the presence of an external electric field of about 0.1 V/Angstrom. The work also limited the doping study in two cases: The doping case of one phosphorus atom and the 100% doping configuration. There are two doping positions of a phosphorus atom, the top position, and the valley position, and the formation energy will find the optimal position. The energy band structure and state density will also be drawn, examined, and compared.

The design of a high voltage responsivity terahertz detector based on improved grounding model

AbstractA high voltage responsivity detector in G‐band is designed in this paper. Different grounding models for the terahertz detector are analyzed and designed. Gold wire grounding design is superior to traditional grounding designs, which reduce the influence caused by the doping concentration, position and thickness error of conductive adhesive. Detectors are based on the Virginia Diodes Inc G‐band zero‐bias Schottky diode with low zero‐bias junction capacitance. The voltage responsivity test result of the gold wire grounding detector is about 1800 mV/mW in 210–220 GHz. The development of the detector provides the device basis for the realization of a terahertz focal plane imaging system.

Synthesis and Properties of the Doubly Oxonium-Embedded Picenes as Electron-Deficient Polycyclic Aromatic Hydrocarbons

The doubly oxonium-embedded picenes have been synthesized for the first time. They have a rigid planar electron-deficient core and are stabilized by the pyrylium aromaticity. The doping positions of oxygen atoms influenced their electrochemical and optoelectronic properties because of the different charge distributions in the skeletons. The donor-acceptor-donor-type molecules baring electron-donating triphenylamine moieties exhibited intramolecular charge-transfer absorption at the visible regions, indicating the large impact of the substituents on their electronic properties.

Inorganic electrides of alkali metal doped Zn12O12 nanocage with excellent nonlinear optical response

Finding new materials with exceptionally large nonlinear optical response is an interesting and challenging avenue for scientific research. Here, we report the alkali metal doped Zn12O12 nanocages as inorganic electrides with excellent nonlinear optical response. Density functional theory calculations have been performed for geometric, electronic and nonlinear optical response of exo- and endohedrally alkali metal doped Zn12O12 nanoclusters. For exohedral doping, all different possible doping sites are considered for decoration of alkali metal on the nanocage. The electride nature of the complexes is highly dependent on the position of alkali metal doping. All exohedral complexes except for alkali metal doping on six membered ring (r6) are electride in nature, as revealed from frontier molecular orbital analysis. Interaction energies reveal that all doped nanoclusters except endo-K@Zn12O12 are thermodynamically stable. The exothermic encapsulation of alkali metals in Zn12O12 nanocages is in marked contradiction with other inorganic fullerenes where encapsulation is an endothermic process. The barriers for boundary crossing are also evaluated in order study the interconversion of exo- and endohedral complexes. Doping of alkali metal significantly influences the properties of nanocages. HOMO-LUMO (H-L) gap is reduced significantly whereas hyperpolarizability is increased several orders of magnitude. The NLO response of exohedrally doped complexes is higher than the corresponding endohedral complexes, which is in mark contradiction with the behavior of phosphide or nitride nanocages. The highest first hyperpolarizability of 1.0 × 105 au is calculated for K@r6-Zn12O12 complex. Third order NLO response of these complexes is calculated and compared with the best systems reported in the literature at the same level of theory.

Recent progress in atomistic modelling and simulations of donor spin qubits in silicon

Electron or nuclear spins associated with dopant atoms, such as phosphorus impurities in silicon (Si:P), have been shown to form excellent qubits with promising potential for scale-up towards a fault-tolerant quantum computer architecture. The remarkable progress in the design and characterisation of Si:P qubits and quantum gates has been led by recent experimental demonstrations. Equally importantly, advances in theoretical modelling and simulations over a number of years have underpinned the experimental efforts through the fundamental understanding of dopant physics and by providing crucial interpretation of the experimental evidence. This brief review article provides highlights of our research on developing atomistic theoretical methods and their application to the understanding, characterisation and scale-up of Si:P qubits in silicon. We have established a state-of-the-art theoretical framework which is capable of performing electronic structure simulations over millions of atoms. This includes a comprehensive set of central-cell corrections within atomistic tight-binding theory to simulate dopant energy spectra and electronic wave functions with high precision. When integrated with Bardeen’s tunnelling formalism and Chen’s derivative rule, the theoretical simulations were able to reproduce the measured spatially resolved scanning tunnelling microscope (STM) images of dopant wave functions, providing an unprecedented access to the dopant physics in silicon. A systematic examination of the STM image features (brightness and symmetry) allowed pinpointing of the dopant atom positions in silicon lattice with an exact atom precision and for dopant depths up to 5 nm below the silicon surface. The scale-up of the metrology technique was demonstrated by training a machine learning algorithm such as convolutional neural network. For the design and implementation of high-fidelity two-qubit quantum gates, we investigated exchange interaction between dopant pairs and showed that the application of a small lattice strain could provide a full control in the presence of one-lattice site donor position variations. The state-of-the-art computational capability developed by our team is a culmination of more than five years of research efforts – it has been well-benchmarked against several different experimental measurements and is expected to play an important role in design and characterisation of quantum gates and scale-up architectures in the coming years.