First-Principles Study of Magnetic Properties of 3d Transition Metals Doped in ZnO Nanowires

Effect of ZnO nanorods and nanotubes on the electrical and optical characteristics of organic and perovskite light-emitting diodes

Due to their suitable electrical and optical properties, ZnO nanostructure-based organic light-emitting diodes (LEDs) and perovskite LEDs can be utilized in the optoelectronics industry. A combination of ZnO nanorods and nanotubes with various types of polymers or hybrid perovskites leads to better waveguides and transportation of carriers. Therefore, more efficient LEDs are offered to the industry. In this research, four devices, including ZnO nanorod (nanotube)/MEH-PPV (CH3NH3PbI3) LEDs are simulated by SILVACO TCAD software. To provide deeper understanding of the impact of applying nanorods and nanotubes in hybrid heterostructures, an ab initio study has been conducted and the electronic structure, density of states, absorption coefficient and dielectric function of each of these nanostructures have been scrutinized. Subsequently, the obtained data have been utilized in the SILVACO simulation, and characteristics such as the current-voltage curve, light power-voltage curve, electroluminescence (EL) spectra and radiative recombination rate of four devices have been investigated. By employing a combination of a perovskite layer and ZnO nanotubes, the turn-on voltage of the simulated devices has been decreased from 13.7 V to 1.1 V. Moreover, a drastic increment in ultraviolet emission from devices based on ZnO nanotubes can be seen, which stems from occurrence of the whispering gallery mode and low defects of nanotubes compared to nanorods. A redshift caused by a reduction in the band gaps of the nanostructures can also be observed in the EL spectra.

Effects of Se substitution and transition metal doping on the electronic and magnetic properties of a MoSxSe2-x/h-BN heterostructure

The van der Waals heterostructures created by stacking two monolayer semiconductors have been rapidly developed experimentally and exhibit various unique physical properties. In this work, we investigate the effects of Se atom substitution and 3d-TM atom doping on the structural, electronic, and magnetic properties of the MoSe2/h-BN heterostructure, by using first-principles calculations based on density functional theory (DFT). It is found that Se atom substitution could considerably enhance the band gaps of MoSe2/h-BN heterostructures. With an increase in the substitution concentration, the energy band changes from an indirect to a direct band gap when the substitution concentration exceeds a critical value. For 3d-TM atom doping, it is shown that V-, Mn-, Fe-, and Co-doped systems exhibit a half-metallic state and magnetic behavior, while there is no spin polarization in the Ni-doped case. The results provide a theoretical basis for the development of diluted magnetic semiconductors and spin devices based on the MoSxSe2-x/h-BN heterostructure.

The structural, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe, Co and Ni) hetero-nanostructure

The magnetic transition-metal (TM) @ oxide nanoparticles have been of great interest due to their wide range of applications, from medical sensors in magnetic resonance imaging to photo-catalysis. Although several studies on small clusters of TM@oxide have been reported, the understanding of the physical electronic properties of TM_n@(ZnO)₄₂ is far from sufficient. In this work, the electronic, magnetic and optical properties of TM_n@(ZnO)₄₂ (TM = Fe, Co and Ni) hetero-nanostructure are investigated using the density functional theory (DFT). It has been found that the core-shell nanostructure Fe₁₃@(ZnO)₄₂, Co₁₅@(ZnO)₄₂ and Ni₁₅@(ZnO)₄₂ are the most stable structures. Moreover, it is also predicted that the variation of the magnetic moment and magnetism of Fe, Co and Ni in TM_n@ZnO₄₂ hetero-nanostructure mainly stems from effective hybridization between core TM-3d orbitals and shell O-2p orbitals, and a magnetic moment inversion for Fe₁₅@(ZnO)₄₂ is investigated. Finally, optical properties studied by calculations show a red shift phenomenon in the absorption spectrum compared with the case of (ZnO)₄₈.

Structural, optical, and magnetic studies of manganese-doped zinc oxide hierarchical microspheres by self-assembly of nanoparticles

In this study, a series of manganese [Mn]-doped zinc oxide [ZnO] hierarchical microspheres [HMSs] are prepared by hydrothermal method only using zinc acetate and manganese acetate as precursors and ethylene glycol as solvent. X-ray diffraction indicates that all of the as-obtained samples including the highest Mn (7 mol%) in the crystal lattice of ZnO have a pure phase (hexagonal wurtzite structure). A broad Raman spectrum from as-synthesized doping samples ranges from 500 to 600 cm-1, revealing the successful doping of paramagnetic Mn2+ ions in the host ZnO. Optical absorption analysis of the samples exhibits a blueshift in the absorption band edge with increasing dopant concentration, and corresponding photoluminescence spectra show that Mn doping suppresses both near-band edge UV emission and defect-related blue emission. In particular, magnetic measurements confirm robust room-temperature ferromagnetic behavior with a high Curie temperature exceeding 400 K, signifying that the as-formed Mn-doped ZnO HMSs will have immense potential in spintronic devices and spin-based electronic technologies.

Synthesis and magnetic properties of Zr doped ZnO Nanoparticles

Zr doped ZnO nanoparticles are prepared by the sol-gel method with post-annealing. X-ray diffraction results show that all samples are the typical hexagonal wurtzite structure without any other new phase, as well as the Zr atoms have successfully entered into the ZnO lattices instead of forming other lattices. Magnetic measurements indicate that all the doping samples show room temperature ferromagnetism and the pure ZnO is paramagneism. The results of Raman and X-ray photoelectron spectroscopy indicate that there are a lot of oxygen vacancies in the samples by doping element of Zr. It is considered that the observed ferromagnetism is related to the doping induced oxygen vacancies.

Wet chemical synthesis and magnetic properties of single crystal Co nanochains with surface amorphous passivation Co layers

: In this study, for the first time, high-yield chain-like one-dimensional (1D) Co nanostructures without any impurity have been produced by means of a solution dispersion approach under permanent-magnet. Size, morphology, component, and structure of the as-made samples have been confirmed by several techniques, and nanochains (NCs) with diameter of approximately 60 nm consisting of single-crystalline Co and amorphous Co-capped layer (about 3 nm) have been materialized. The as-synthesized Co samples do not include any other adulterants. The high-quality NC growth mechanism is proposed to be driven by magnetostatic interaction because NC can be reorganized under a weak magnetic field. Room-temperature-enhanced coercivity of NCs was observed, which is considered to have potential applications in spin filtering, high density magnetic recording, and nanosensors. PACS: 61.46.Df; 75.50; 81.07.Vb; 81.07.

Metal-functionalized single-walled graphitic carbon nitride nanotubes: a first-principles study on magnetic property

The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage.

Low-Temperature Preparation of Superparamagnetic CoFe(2)O(4) Microspheres with High Saturation Magnetization

Based on a low-temperature route, monodispersed CoFe(2)O(4) microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe(2)O(4) MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe(2)O(4) MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.

Magnetic Properties of Ni-doped ZnO Nanocombs by CVD Approach

The search for above room temperature ferromagnetism in dilute magnetic semiconductors has been intense in recent year. Arrays of perpendicular ferromagnetic nanowire/rods have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple low-temperature chemical vapor deposition (CVD) to create self-assembled comb-like Ni-/undoped ZnO nanostructure arrays. The phases, compositions, and physical properties of the studied samples were analyzed by different techniques, including high-resolution X-ray diffraction/photoelectron spectroscopy/transmission electron microscopy, photoluminescence, and MPMS. In particular, the Ni-doped ZnO nanocombs (NCs) with ferromagnetic and superparamagnetic properties have been observed whereas undoped ZnO NCs disappear. The corresponding ferromagnetic source mechanism is discussed, in which defects such as O vacancies would play an important role.

Influence of Cobalt Doping on the Physical Properties of Zn0.9Cd0.1S Nanoparticles

Zn0.9Cd0.1S nanoparticles doped with 0.005-0.24 M cobalt have been prepared by co-precipitation technique in ice bath at 280 K. For the cobalt concentration >0.18 M, XRD pattern shows unidentified phases along with Zn0.9Cd0.1S sphalerite phase. For low cobalt concentration (≤0.05 M) particle size, dXRDis ~3.5 nm, while for high cobalt concentration (>0.05 M) particle size decreases abruptly (~2 nm) as detected by XRD. However, TEM analysis shows the similar particle size (~3.5 nm) irrespective of the cobalt concentration. Local strain in the alloyed nanoparticles with cobalt concentration of 0.18 M increases ~46% in comparison to that of 0.05 M. Direct to indirect energy band-gap transition is obtained when cobalt concentration goes beyond 0.05 M. A red shift in energy band gap is also observed for both the cases. Nanoparticles with low cobalt concentrations were found to have paramagnetic nature with no antiferromagnetic coupling. A negative Curie-Weiss temperature of -75 K with antiferromagnetic coupling was obtained for the high cobalt concentration.