Non-doped System Research Articles

Adsorption of Zn atoms by monolayer WS2 doped with different atoms X (X = O, Se, N, P, F, Cl): first principles study.

The effect of X (X = O, Se, N, P, F, Cl) doping on the adsorption of Zn atoms by WS2 was investigated based on first principles. The electronic structure and optical properties of the adsorbed system after atomic doping were calculated. It is found that the Zn atom adsorbed on the W top (Tw) site has the most stable structure. When an S atom is replaced with an X atom based on the adsorption system, where the adsorption energy decreases after doping of O, P, F, and Cl atoms compared to the undoped system, it means that each system is more stable after doping of these atoms; charge transfer shows that the adsorption system after P-atom doping the system around the Zn atom loses electrons while S-atom gains electrons, which indicates that P-atom doping is favorable for the adsorption of Zn by WS2, N, P-atom is introduced as p-type doping and F, Cl-atom is introduced undoped by n-type doping, and the band gap of the doped system is less than that of the undoped one. With the introduction of different dopant atoms, certain impurity energy levels are introduced into the adsorption system. The prohibited bandwidth around the Fermi energy level reduces the density of states, causing the doped system's density of states to shift to lower energies, among which the shifts of N, P, F, and Cl are more pronounced. The P-doped adsorption system shows a new peak near the energy of - 11 eV. In addition, the study of optical properties showed that the peak reflections of both doped and non-doped systems adsorbing Zn atoms appeared in the ultraviolet region; the absorbance coefficient of the doped system is moved in the lower energy direction and red-shifted after atom doping; in addition, the absorption coefficients and reflectance of the P, Se doped systems are enhanced in the wavelength range of 200-300 nm compared with that before doping, the dielectric function and CBM and VBM positions were also calculated further indicating the potential of Se-doped systems in improving photocatalytic efficiency. In this paper, the structure optimization of X (X = O, Se, N, P, F, Cl) doping on WS2 adsorbed Zn atom model is performed based on the CASTEP module in Materials-Studio software under the first principles using GGA and PBE generalized function. The corresponding binding energies, bond lengths, bond angles, charge densities, energy band structures, densities of states, and optical properties were also analyzed. The Monkhorst-Pack particular K-point sampling method is used in the calculations; the K-point grid is 6 × 6 × 1, and the cutoff energy for the plane wave expansion is 500 eV. After geometric optimization, the iterative accuracy converges to a value of less than 1 × 10-5 eV/atom for the total energy of each atom and less than 0.03 eV/Å for all atomic forces. The thickness of the vacuum layer was set to 20 Å to avoid the effect of interlayer interaction forces. In this paper, 27 atoms were used to form a 3 × 3 × 1 supercellular tungsten disulfide system consisting of 18 S atoms and 9 W atoms.

Theoretical study of a Ti4 cluster interacting with B-doped and non-doped multivacancy graphene

A density functional theory study was performed to understand the interactions of a small Ti4 cluster with multi-vacancy graphene. We also consider the effect produced by the B-doping of the vacancy defect. In this sense, we analyze the binding mechanisms of the metal cluster. The focus is set on its stability on the substrate, geometrical structure and the interactions participating between the cluster and graphene substrate. A qualitative study of the principal bonds was carried out employing overlap population and bond order chemical descriptors. Additionally, as an attempt to comprehend better the electronic structure and related properties, we performed total density of states, band structure and magnetic moment calculations to characterize the electrical and magnetic properties of the B-doped and non-doped systems.

Intramolecular hydrogen bonding-induced conformation-locked multifunctional emitters for non-doped OLEDs

Organic multifunctional triplet-harvesting emitters based organic light emitting diodes (OLEDs) are a relatively unexplored area, primarily due to the challenging requirements of achieving high rates of intersystem crossing (ISC; kISC > 107 s−1), reverse intersystem crossing (RISC; kRISC > 106 s−1), radiative decay (kr > 107 s−1), and low non-radiative decay (knr < 106 s−1) within non-doped systems. In this study, we synthesized three asymmetric heavy-atom-free (HAF) multifunctional triplet-harvesting emitters. The incorporation of intramolecular hydrogen bonding (IHB) induced conformational locking and distortion, resulting in a quasi-planar structure that effectively reduces reorganization energy (λ). Consequently, Qx-Py-2DMAC exhibited improved radiative characteristics with high quantum yields (0.94) in neat film state. Significantly, the existence of IHB interactions was confirmed through various methods, including DFT calculations, single-crystal XRD, and 2D-GIWAXD measurements, which verified the effect in both single molecules and solid states. Subsequently, the IHB-induced conformation-locked structure exhibited a preferred orientation with a large coherence length (Lc) for dense packing and efficient emission in aggregated state. Consequently, due to the IHB-induced unique aggregation properties, Qx-Py-2DMAC realized significant multifunctionality of aggregation-induced emission (AIE), mechanochromic luminescence (MCL), thermally activated delayed fluorescence (TADF), and room-temperature phosphorescence (RTP) in solid state. In this regard, non-doped OLEDs were successfully realized.

Insights into the Effect of Lithium Doping on the Deep Eutectic Solvent Choline Chloride:Urea.

Choline-based deep eutectic solvents (DESs) are potential candidates to replace flammable organic solvent electrolytes in lithium-ion batteries (LIBs). The effect of the addition of a lithium salt on the structure and dynamics of the material needs to be clarified before it enters the battery. Here, the archetypical DES choline chloride:urea at 1:2 mole fraction has been added with lithium chloride at two different concentrations and the effect of the additional cation has been evaluated with respect to the non-doped system via multinuclear NMR techniques. 1H and 7Li spin-lattice relaxation times and diffusion coefficients have been measured between 298 K and 373 K and revealed a decrease in both rotational and translational mobility of the species after LiCl doping at a given temperature. Temperature dependent 35Cl linewidths reflect the viscosity increase upon LiCl addition, yet keep track of the lithium complexation. Quantitative indicators such as correlation times and activation energies give indirect insights into the intermolecular interactions of the mixtures, while lithium single-jump distance and transference number shed light into the lithium transport, being then of help in the design of future DES electrolytes.

Nitrogen Fixation at the Edges of Boron Nitride Nanomaterials: Synergy of Doping.

Synthesis of ammonia at ambient conditions is very demanding yet challenging to achieve due to the production of ammonia fuel, which is considered to be a future fuel for sustainable energy. In this context, computational studies on the catalytic activity of the edge sites of boron nitride nanomaterials for possible nitrogen reduction into ammonia have been investigated. Geometrical and electronic properties of zigzag and armchair B-open edges of BN sheet (BOE) models have been unraveled to substantiate their catalytic nature. Results reveal that BOE sites exhibit very high potential determining steps (PDS) of 2.0 eV. Doping of carbon (C) at the nitrogen center, which is vicinal to the BOE site reduces the PDS of the N2 reduction reaction (NRR) (to 1.18–1.33 eV) due to the regulation of charge distribution around the active BOE site. Further, the NRR at the C doped at various edge sites of a boron nitride sheet (BNS) has also been studied in detail. Among the 12 new C-doped defective BNS models, 9 model catalysts are useful for nitrogen activation through either chemisorption or physisorption. Among these, ZC N , AC N , and ZC BV models are efficient in catalyzing NRR with lower PDS of 0.86, 0.88, and 0.86 eV, respectively. The effect of carbon doping in tuning the potential requirements of NRR has been analyzed by comparing the relative stability of intermediates on the catalyst with and without carbon doping. Results reveal that C-doping destabilizes the intermediates compared to non-doped systems, thereby reducing the possibility of catalyst poisoning. However, their interactions with catalysts are good enough so that the NRR activity of the catalyst does not decrease due to C-doping.

Pt-doped armchair graphene nanoribbon as a promising gas sensor for CO and CO2: DFT study

Abstract In this work, four armchair graphene nanoribbon (AGNR) based sensor materials were built using Atomistic ToolKit Virtual NanoLab (ATK-VNL) and utilized to detect carbon monoxide (CO) and carbon dioxide (CO2) gases. First, the effect of passivating AGNR on the sensing performance toward CO and CO2 gases has been investigated, where AGNR was passivated with hydrogen (H-AGNR) and nitrogen (N-AGNR). The obtained results reflected no significant changes in the adsorption parameters of CO and CO2 molecules on H-AGNR and N-AGNR. Particularly, the adsorption energies between H-AGNR and N-AGNR systems and CO were found to be −0.446 and −0.436 eV, while for the case of CO2, the adsorption energies were found to be −0.426 and −0.432 eV, respectively. To enhance the sensing performance, both H-AGNR and N-AGNR systems were doped with platinum (Pt) forming another two systems: Pt–H-AGNR, and Pt–N-AGNR. After doping, the results revealed a significant increase in the adsorption energy to almost 9 times than the non-doped systems for the cases of CO on Pt–N-AGNR as well as CO2 on both Pt–H-AGNR and Pt–N-AGNR. Moreover, an increase of almost 13 times was observed in the adsorption energy for the case of CO on Pt–H-AGNR. Besides to the adsorption energy ( E a d s ), the adsorption distance (( D ), charge transfer ( Δ Q ), the density of states (DOS), as well as the band structure have been examined to confirm the adsorption of CO and CO2 on the four systems.

Preparation of Ruthenium Olefin Metathesis Catalysts Immobilized on MOF, SBA-15, and 13X for Probing Heterogeneous Boomerang Effect

Promoted by homogeneous Ru-benzylidene complexes, the olefin metathesis reaction is a powerful methodology for C-C double bonds formation that can find a number of applications in green chemical production. A set of heterogeneous olefin metathesis pre-catalysts composed of ammonium-tagged Ru-benzylidene complexes 4 (commercial FixCat™ catalyst) and 6 (in-house made) immobilized on solid supports such as 13X zeolite, metal-organic framework (MOF), and SBA-15 silica were obtained and tested in catalysis. These hybrid materials were doped with various amounts of ammonium-tagged styrene derivative 5—a precursor of a spare benzylidene ligand—in order to enhance pre-catalyst regeneration via the so-called release-return “boomerang effect”. Although this effect was for the first time observed inside the solid support, we discovered that non-doped systems gave better results in terms of the resulting turnover number (TON) values, and the most productive were hybrid catalysts composed of 4@MOF, 4@SBA-15, and 6@SBA-15.

Magnetic Properties of Hole-Doped Pyrochlore Iridate (Y&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;&lt;sub&gt;-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;y&lt;/sub&gt;&lt;/i&gt;Cu&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Ca&lt;i&gt;&lt;sub&gt;y&lt;/sub&gt;&lt;/i&gt;)&lt;sub&gt;2&lt;/sub&gt;Ir&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;

We report the results of studies on the electronic state of the hole-doped Y-based pyrochlore iridate, (Y1-x-yCuxCay)2Ir2O7. We carried out the resistivity, Muon Spin Relaxation (μSR), X-ray Photoemission Spectroscopy (XPS) measurements and Density Functional Theory (DFT) calculations on the non-doped (x=y=0) and doped (x=0.05, y=0.15) systems. We found in the non-doped system that the magnetic ordering of Ir spins which was accompanied by the metal-insulator transition (MIT) occurred at around 157 K and disappeared in the doped system in which MIT seems to disappear or smeared out. We suggest from the current study that a quantum critical point which shows a change in the electronic ground state from insulating to metallic to exist between those two systems.

DFT study of boron doped MgH2: Bonding mechanism, hydrogen diffusion and desorption

The impact of boron doping on MgH2 bonding mechanism, hydrogen diffusion and desorption was calculated using density functional theory (DFT). Atomic interactions in doped and non-doped system and its influence on hydrogen and vacancy diffusion were studied in bulk hydride. Slab calculations were performed to study hydrogen desorption energies from (110) boron doped surface and its dependence on the surface configuration and depth position. To study kinetics of hydrogen diffusion in boron vicinity and hydrogen molecule desorption activation energies from boron doped and non-doped (110) MgH2 surface Nudged Elastic Band (NEB) method was used. Results showed that boron forms stronger, covalent bonds with hydrogen causing the destabilization in its first and second coordination. This leads to lower hydrogen desorption energies and improved hydrogen diffusion, while the impact on the energy barriers for H2 desorption from hydride (110) surface is less pronounced.

Solution-processed multilayer green electrophosphorescent devices with self-host iridium dendrimers as the nondoped emitting layer: achieving high efficiency while avoiding redissolution-induced batch-to-batch variation.

Self-host Ir dendrimers have been adopted as the nondoped emitting layer for the successful construction of multilayer green phosphorescent organic light-emitting diodes (PhOLEDs) prepared via layer-by-layer solution processing with orthogonal solvents. Unlike previous doped systems, the risk of small-molecular-phosphor redissolution by alcohols and the resultant serious batch-to-batch variation can be eliminated. Consequently, a record-high external quantum efficiency of 21.2% together with good reproducibility is achieved for the green-emitting Ir dendrimer G2, which displays sufficient alcohol resistance owing to the effective encapsulation from the second generation dendritic wedge. The obtained performance is highly competitive with those of doped devices, while avoiding the unwanted redissolution-induced batch-to-batch variation simultaneously, representing an important development in the solution fabrication of multilayer PhOLEDs based on a nondoped system.

Electronic properties and fermi surface for new Fe-free layered pnictide-oxide superconductor BaTi2Bi2O from first principles

Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which has the highest TC (about 4.6 K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi2Bi2O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electronic factors, which can be responsible for the increased transition temperature for BaTi2Bi2O (as compared with related pnictide-oxides BaTi2As2O and BaTi2Sb2O), are discussed.

Tin Dioxide Nanowires: Evolution and Perspective of the Doped and Nondoped Systems

SnO2 semiconductor nanowire is an extremely important technological material for use in nanophotonic and nanoelectronic devices. These semiconductor nanowires of desirable property can be achieved through a bottom-up approach to the controlled synthesis in a pure or doped state. Each of the synthetic methods offers materials with broad range structural, morphological, optical, and electrical properties. Selective doping of the SnO2 nanowires by normal, transition or inner transition elements offer a broad variation in the optical and electrical properties and are open for further theoretical exploration of the properties as well as necessary changes possible for the improvement of the material properties. The properties of SnO2 nanowires can be tuned either in the pure state by structural modification or doping during nanowire growth or after growth to meet most of the requirements.

Fluctuation Conductivity of La0.5RE0.5BaCaCu3O7−d (RE=Y, Sm, Dy) Superconductor

We report production, conductivity fluctuation and magnetoconductivity fluctuation measurements of the system La0.5RE0.5BaCaCu3O7−δ RE=(Y,Sm,Dy) high-temperature superconductors. Samples were synthesized by the standard solid state reaction recipe. By Rietveld-like refinement of X-ray diffraction patterns we determined that the material crystallizes in a tetragonal structure. DC resistivity measurements show a bulk critical temperature Tc (71, 72 and 72 K for RE=Y, Sm, Dy, respectively) for the analyzed samples. In order to examine the effect of substitution of rare earth into the lanthanum structural sites on the pairing mechanism close to Tc, we performed conductivity fluctuation analysis by using the method of logarithmic temperature derivative of the conductivity excess. We found the occurrence of Gaussian and genuinely critical fluctuations. Our results are in agreement with reports on non-doped systems, but we observe minor values of the coherence length of the fluctuation regimes for the doped case. Correlations of critical exponents with the dimensionality of the fluctuation system for Gaussian regimes were made by using the Aslamazov–Larkin theory. The genuinely critical exponent was interpreted by the 3D-XY.

Superconductivity in ionic-Hubbard model on honeycomb lattice

To consider the origin of superconductivity (SC) in layered nitride superconductors, we study an ionic-Hubbard model on a honeycomb lattice, which consists of two sublattices with a level offset, using an optimization variational Monte Carlo method. The parameter values for the Coulomb interaction and the level offset, to realize a band insulator, is evaluated in the non-doped system. In carrier-doped band insulating systems, a spin singlet d-wave SC state is stabilized. The spin fluctuation remains relatively strong even for large level offsets. We find that a renormalization effect of the energy band primarily contributes to the spin fluctuation.

Effect of impurities on the electronic and magnetic properties of zinc oxide nanostructures

Electronic and magnetic properties of carbon-, sulfur-, and non-doped ZnO clusters are investigated using density functional theory (DFT). It is found that in the case of non-doped systems a planar graphitic-like reconstruction is necessary for the observation of a magnetic moment; carbon impurities could promote ferromagnetism; and sulfur impurities at the surface of ZnO nanoparticles hamper any magnetic state and open the HOMO–LUMO gap. Our findings suggest that the experimentally observed magnetic properties of ZnO systems are driven by competition in the structural conformation and are extremely sensitive to the surface and interfaces.

The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

Rare-earth ( RE) doped Ba(Zr,Ti)O 3 (BZT) thin films were prepared by rf-magnetron sputtering from a Ba 0.90 Ln 0.067Zr 0.09Ti 0.91O 3 ( Ln=La, Nd) target. The films were deposited at a substrate temperature of 600 °C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a 〈001〉 epitaxial crystal growth on Nb-doped SrTiO 3, 〈001〉 and 〈011〉 growth on single-crystal Si, and a 〈111〉-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100 nm for 30 min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0–3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2 p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO 3-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO 6-octahedra distortion ( M=Ti, Zr) and, thereby, modifying the Ti–O binding length. Polarization-electric field hysteresis loops on Ag/ RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.

Phosphorescent Organogels via “Metallophilic” Interactions for Reversible RGB−Color Switching

A trinuclear Au(I) pyrazolate complex bearing long alkyl chains (1) in hexane self-assembles via a Au(I)-Au(I) metallophilic interaction, to form a red-luminescent organogel (lambda(em) = 640 nm, lambda(ext) = 284 nm). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis of an air-dried gel with 1 show the presence of heavily entangled fibers, each consisting of a rectangularly packed columnar assembly of 1. Doping of the organogel with a small amount of Ag(+) results in a blue luminescence (lambda(em) = 458 nm, lambda(ext) = 370 nm) without disruption of the gel, while removal of doped Ag(+) with cetyltrimethylammonium chloride results in complete recovery of the original red-luminescent gel. Upon heating, these organogels undergo gel-to-sol transition due to the destabilization of the metallophilic interactions, where the red luminescence of the nondoped system becomes hardly visible, while the blue luminescence of the Ag(+)-doped system turns green (lambda(em) = 501 nm, lambda(ext) = 370 nm). On cooling, these solutions undergo gelation and synchronously recover the original luminescences. The observed RGB (red-green-blue) luminescences are all long-lived (3-6 micros) and assigned to electronic transitions from triplet-excited states.

Ferromagnetism in the two-dimensional periodic Anderson model

Using the constrained-path Monte Carlo method, we studied the magnetic properties of the two-dimensional periodic Anderson model for electron fillings between 1/4 and 1/2. We also derived two effective low energy theories to assist in interpreting the numerical results. For 1/4 filling we found that the system can be a Mott or a charge transfer insulator, depending on the relative values of the Coulomb interaction and the charge transfer gap between the two non-interacting bands. The insulator may be a paramagnet or antiferromagnet. We concentrated on the effect of electron doping on these insulating phases. Upon doping we obtained a partially saturated ferromagnetic phase for low concentrations of conduction electrons. If the system were a charge transfer insulator, we would find that the ferromagnetism is induced by the well-known RKKY interaction. However, we found a novel correlated hopping mechanism inducing the ferromagnetism in the region where the non-doped system is a Mott insulator. Our regions of ferromagnetism spanned a much smaller doping range than suggested by recent slave boson and dynamical mean field theory calculations, but they were consistent with that obtained by density matrix renormalization group calculations of the one-dimensional periodic Anderson model.