Antiferromagnetic ferromagnetic transition in zigzag graphene nanoribbons induced by substitutional doping

Using first-principles calculations based on density functional theory, we show that the ground state of zigzag-edged graphene nanoribbons（ZGNRs） can be transformed from antiferromagnetic（AFM） order to ferromagnetic（FM） order by changing the substitutional sites of N or B dopants. This AFM–FM transition induced by substitutional sites is found to be a consequence of the competition between the edge and bulk states. The energy sequence of the edge and bulk states near the Fermi level is reversed in the AFM and FM configurations. When the dopant is substituted near the edge of the ribbon, the extra charge from the dopant is energetically favorable to occupy the edge states in AFM configuration. When the dopant is substituted near the center, the extra charge is energetically favorable to occupy the bulk states in FM configuration. Proper substrate with weak interaction is necessary to maintain the magnetic properties of the doped ZGNRs. Our study can serve as a guide to synthesize graphene nanostructures with stable FM order for future applications to spintronic devices.

Substitutional doping in 2D transition metal dichalcogenides

Two-dimensional(2D)van der Waals transition metal dichalcogenides(TMDs)are a new class of electronic materials offering tremendous opportunities for advanced technologies and fundamental studies.Similar to conventional semiconductors,substitutional doping is key to tailoring their electronic properties and enabling their device applications.Here,we review recent progress in doping methods and understanding of doping effects in group 6 TMDs(MX2,M=Mo,W;X=S,Se,Te),which are the most widely studied model 2D semiconductor system.Experimental and theoretical studies have shown that a number of different elements can substitute either M or X atoms in these materials and act as n-or p-type dopants.This review will survey the impact of substitutional doping on the electrical and optical properties of these materials,discuss open questions,and provide an outlook for further studies.

In-situ neutron-transmutation for substitutional doping in 2D layered indium selenide based phototransistor

Neutron-transmutation doping(NTD)has been demonstrated for the first time in this work for substitutional introduction of tin(Sn)shallow donors into two-dimensional(2D)layered indium selenide(InSe)to manipulate electron transfer and charge carrier dynamics.Multidisciplinary study including density functional theory,transient optical absorption,and FET devices have been carried out to reveal that the field effect electron mobility of the fabricated phototransistor is increased 100-fold due to the smaller electron effective mass and longer electron life time in the Sn-doped InSe.The responsivity of the Sn-doped InSe based phototransistor is accordingly enhanced by about 50 times,being as high as 397 A/W.The results show that NTD is a highly effective and controllable doping method,possessing good compatibility with the semiconductor manufacturing process,even after device fabrication,and can be carried out without introducing any contamination,which is radically different from traditional doping methods.

Controllable substitutional vanadium doping in wafer-scale molybdenum disulfide films

Substitutional atomic doping of transition metal dichalcogenides(TMDs)in the chemical vapor deposition(CVD)process is a promising and effective strategy for modifying their physicochemical properties.However,the conventional CVD method only allows narrow-range modulation of the dopant concentration owing to the low reactivity of the precursors.Moreover,the growth of wafer-scale monolayer TMD films with high dopant concentrations is much more challenging.Herein,we report a facile doping approach based on liquid precursor-mediated CVD process for achieving high vanadium(V)doping in the MoS_(2)lattice with excellent doping uniformity and stability.The lateral growth of the host MoS_(2)lattice and the reactivity of the V precursor were simultaneously improved by introducing an alkali metal halide as a reaction promoter.The metal halide promoter enabled the wafer-scale synthesis of V-incorporated MoS_(2)monolayer film with excessively high doping concentrations.The excellent wafer-scale uniformity of the highly V-doped MoS_(2)film was confirmed through a series of microscopic,spectroscopic,and electrical analyses.

Doping Mn into(Li_(1-x)Fe_x)OHFe_(1-y)Se superconducting crystals via ion-exchange and ion-release/introduction syntheses

We report the success in introducing Mn into（Li1-xFex）OHFe1-y Se superconducting crystals by applying two different hydrothermal routes, ion exchange（1-step） and ion release/introduction（2-step）. The micro-region x-ray diffraction and energy dispersive x-ray spectroscopy analyses indicate that Mn has been doped into the lattice, and its content in the 1-step fabricated sample is higher than that in the 2-step one. Magnetic susceptibility and electric transport properties reveal that Mn doping influences little on the superconducting transition, regardless of 1-step or 2-step routes. By contrast, the characteristic temperature T^＊, at which the negative Hall coefficient reaches its minimum, is significantly reduced by Mn doping.This implies that the hole carriers contribution is obviously modified, and hence the hole band might have no direct relationship with the superconductivity in（Li1-xFex）OHFe1-y Se superconductors. Our present hydrothermal methods of ion exchange and ion release/introduction provide an efficient way for elements substitution/doping into（Li1-xFex）OHFe1-y Se superconductors, which will promote the in-depth investigations on the role of multiple electron and hole bands and their interplay with the high-temperature superconductivity in the FeSe-based superconductors.

Doping engineering of iron oxide nanoparticles towards high performance and biocompatible T_(1)-weighted MRI contrast agents

Extremely small-sized iron oxide nanoparticles(IONPs) are of great interest in magnetic resonance imaging(MRI) due to their biosafety as an alternative to clinical gadolinium(Ⅲ) complexes-based contrast agents.Especially when the particle size is less than 10 nm,it has strong diffusion ability and deep penetration distance in tumor tissue.Substitution doping can significantly enhance the T_(1)contrast effect of nanoparticles by regulating the surface exposed atoms.However,the nucleation and growth processes of multi-component synthesis systems are complex and difficult to be accurately controlled,leading to great challenges in the synthesis of ultra-small-sized nanoparticles with different components and sizes.Here,extremely smallsized superparamagnetic gadolinium-doped iron oxide nanoparticles(GdIONPs,Gd_(x)Fe_(3-x)O_(4) NPs) with adjustable doping amount and controllable size in the range of 3.5-7.5 nm were synthesized by thermal decomposition.Then,as-synthesized GdIONPs were surface modified with a highly water-soluble and biocompatible carboxyl-polyethylene glycol-phosphoric acid ligand with high binding affinity.Gd_(0.65)Fe_(2.35)O_(4) NPs exhibited very high r_(1) relaxivity of 10.6 mmol^(-1)·L·s^(-1) in terms of all metal concentrations and 49.0 mmol^(-1)·L·s^(-1) in terms of gadolinium alone,respectively,3 and 14 times higher than clinical T_(1) contrast agents(Gd-DTPA).GdIONPs can continuously obtain high resolution images of blood vessels,and can be used as an efficient and multifunctional contrast agent for MR T_(1)imaging.This stable and efficient doping strategy provides an easy and effective method to individually optimize the magnetic properties of complex oxides and their relaxation effects for a variety of biomedical applications.

Structural,electronic,and magnetic behaviors of 5d transition metal atom substituted divacancy graphene：A first-principles study

Structural, electronic, and magnetic behaviors of 5d transition metal（TM） atom substituted divacancy（DV） graphene are investigated using first-principles calculations. Different 5d TM atoms（Hf, Ta, W, Re, Os, Ir, and Pt） are embedded in graphene, these impurity atoms replace 2 carbon atoms in the graphene sheet. It is revealed that the charge transfer occurs from 5d TM atoms to the graphene layer. Hf, Ta, and W substituted graphene structures exhibit a finite band gap at high symmetric K-point in their spin up and spin down channels with 0.783 μB, 1.65 μB, and 1.78 μB magnetic moments,respectively. Ir and Pt substituted graphene structures display indirect band gap semiconductor behavior. Interestingly, Os substituted graphene shows direct band gap semiconductor behavior having a band gap of approximately 0.4 e V in their spin up channel with 1.5 μB magnetic moment. Through density of states（DOS） analysis, we can predict that d orbitals of 5d TM atoms could be responsible for introducing ferromagnetism in the graphene layer. We believe that our obtained results provide a new route for potential applications of dilute magnetic semiconductors and half-metals in spintronic devices by employing 5d transition metal atom-doped graphene complexes.