Mn Nanowires Research Articles

The Effect of Oxidation of Vicinal Au Surface on the Magnetic Properties of Surface‐Supported Mn Nanowires

It is well‐established that oxidation of a stepped surface can lead to the formation of 1D metal oxide nanowires along the steps. However, it is still uncertain how the extent of surface oxidation impacts the characteristics of these nanowires. Ab initio study of the effect of the oxidation state of a nonmagnetic vicinal Au surface on the magnetic properties of 1D Mn nanowires formed on the step edge is presented. Herein, the magnetic properties and electronic structure of two different types of nanowires are investigated: 1D manganese oxides (MnO) and 1D dioxides (MnO2), which correspond to different levels of oxidation of the substrate surface.

Preparation, Characterization, and Magnetic Resonance Imaging of Mn@SiO2 Nanowires.

The deposition time was controlled to prepare Mn nanowires of different lengths and diameters on templates of anodic aluminum oxide (AAO) with different pore sizes. The surface of as-prepared Mn nanowires was modified with SiO2 using the sol-gel method to improve their dispersion in aqueous solution. The effects of the diameter and length of the as-prepared Mn nanowires coated with SiO2 on the relaxivity were investigated. It was found that the Mn@SiO2 nanowires have smaller diameters and a higher longitudinal relaxivity (r1) with an increased length. Mn3@SiO2 nanowires had the highest r1 value of 5.8 mM-1 s-1 among the Mn@SiO2 nanowires (Mn3 nanowires have a diameter of about 30 nm and a length of about 0.5 μm length). Additionally, the biocompatibility and in vivo imaging ability of the Mn3@SiO2 nanowires were evaluated. The Mn3@SiO2 nanowires had good cytotoxicity and biocompatibility, and the kidney of SD rats showed a positive enhancement effect during small animal imaging at 1.5 T. This study showed that the Mn3@SiO2 nanowires could potentially become contrast agents (CAs) of longitudinal relaxation time (T1).

Magnetic properties of oxide Mn nanowires on vicinal Au surface

The development of quantum computing or magnetic storage systems requires the search for magnetic nanostructures with multiple magnetic configurations with controllable quantum spin states. The study of the magnetic properties of metal oxide nanowires is of particular importance for the development of these technological implementations. The present work is devoted to an ab initio study of the magnetic properties of Mn and Mn oxide (MnO) nanowires on vicinal Au surfaces with different step edge geometries. The existence of ferromagnetic and antiferromagnetic configurations of Mn and MnO nanowires on vicinal Au surfaces was found. The effect of oxidations and surface geometry on the appearance of ferromagnetic or antiferromagnetic properties of the nanowire was revealed. The ground state of pure Mn nanowires was shown to be dependent on the surface structure. At the same time, the ground state of oxide Mn nanowires is antiferromagnetic on all studied vicinal surfaces and did not depend on the surface structure. We observed an increase in the exchange interaction energy in nanowires under surface oxidation. The exchange interaction between manganese atoms in MnO nanowires is much stronger than in pure Mn nanowires.

Thermoelectric-Powered Supercapacitors Based on Ni–Mn Nanowires Driven by Quadripartite Electrolyte

Thermal energy is copiously available, especially low-grade heat which is typically wasted as a byproduct without use. Tapping into this immense energy reservoir with cost-effective technologies may become a key element for an energy-sustainable economy and society. The utilization of this waste thermal energy holds great potential in space applications for generating electric energy without using a solar panel. With this approach of harvesting heat energy, Ni–Mn composite nanowire-based electrodes synthesized via the electrochemical deposition technique are used to assemble a thermoelectric-powered supercapacitor. For charging purpose, the thermoelectric phenomenon of a quadripartite gel electrolyte [K3Fe(CN)6 + K4Fe(CN)6 + KOH + PVA] is tested. High-grade flexible copper tape used as a substrate can withstand high temperature and is perfectly suitable for thermoelectric devices. The fabricated symmetric device attained a high specific capacitance of 556 F/g at 4 mA in addition to a high energy density of 173.75 W h/kg at 3 kW/kg. Moreover, the fabricated thermoelectric-powered device attains a maximum voltage of ∼60 mV as a result of a temperature difference in the range of 8–10 °C. The proposed supercapacitor offers opportunities for the development of future devices that simultaneously harvest and store energy.

Mn-dopant induced Octahedral Configuration Strongly Stabilizes Ni12P5 Nanowires for Battery-Supercapacitor Hybrid Devices

Transition metal phosphides (TMPs) have recently emerged as an important type of electrode materials for supercapacitors due to their intrinsically outstanding specific capacity and high conductivity. Herein, we report Mn doped Ni12P5 nanowires (Mn-Ni12P5-3) as an advanced cathode material for hybrid supercapacitors, which delivers a high specific capacity of 808 C g−1 at 1 A g−1 (560 C g−1 at 10 A g−1) and good cyclic stability (capacity retention of 87% after 1000 cycles at 10 A g−1). Meanwhile, the First-principle Calculation results reveal that the Mn-doping can form an octahedral supporting structure between Mn atoms and P atoms to enhance the structure stability. The assembled Mn-Ni12P5-3//AC hybrid device demonstrates good capacity retention of 67.3% after 5000 cycles at 2 A g−1. This research brings a new implication to the development of supercapacitors.

Synthesis, magnetism and photoluminescence of Mn doped AlN nanowires

Manganese doped aluminum nitride (AlN:Mn) nanowires were fabricated by direct nitridation of Al and Mn mixed powders. The as-synthesized AlN:Mn nanowires were characterized by X-ray diffraction, Raman, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The measurements reveal the successful incorporation of Mn2+ ions into AlN nanowires. The magnetic and optical properties of the AlN:Mn nanowires were studied using vibrating sample magnetometer and photoluminescence spectroscopy. The AlN:Mn nanowires exhibit room temperature ferromagnetic behavior and a red emission band centered at 597 nm corresponding to the 4T1(4G)-6A1(6S) transition of Mn2+. The abnormal thermal quenching behavior and long afterglow feature are investigated through the temperature dependent emission and the afterglow spectrum. The thermoluminescence curve shows that AlN:Mn nanowires have the plentiful traps, which leads to the abnormal thermal quenching behavior and persistent luminescence. Multifunctional AlN:Mn nanowires with magnetic and luminescence properties are expected to be used in spintronic and optoelectronic nanodevices.

Two-Dimensional SnSe Composited with One-Dimensional Mn Nanowires: A Promising Thermoelectric with Ultrahigh Power Factor

Two-dimensional (2D) SnSe is a promising candidate for thermoelectric applications. In this work, we have explored an optimization strategy for thermoelectric conversion in two-dimensional monolaye...

Self-organization of various “phase-separated” nanostructures in a single chemical vapor deposition

Chemical vapor deposition (CVD) is one of the most versatile techniques for the controlled synthesis of functional nanomaterials. When multiple precursors are induced, the CVD process often gives rise to the growth of doped or alloy compounds. In this work, we demonstrate the self-assembly of a variety of ‘phase-separated’ functional nanostructures from a single CVD in the presence of various precursors. In specific, with silicon substrate and powder of Mn and SnTe as precursors, we achieved self-organized nanostructures including Si/SiOx core-shell nanowire heterostructures both with and without embedded manganese silicide particles, Mn11Si19 nanowires, and SnTe nanoplates. The Si/SiOx core-shell nanowires embedded with manganese silicide particles were grown along the direction of the crystalline Si via an Au-catalyzed vapor-liquid-solid process, in which the Si and Mn vapors were supplied from the heated silicon substrates and Mn powder, respectively. In contrast, direct vapor-solid deposition led to particle-free -oriented Si/SiOx core-shell nanowires and -oriented Mn11Si19 nanowires, a promising thermoelectric material. No Sn or Te impurities were detected in these nanostructures down to the experimental limit. Topological crystalline insulator SnTe nanoplates with dominant {100} and {111} facets were found to be free of Mn (and Si) impurities, although nanoparticles and nanowires containing Mn were found in the vicinity of the nanoplates. While multiple-channel transport was observed in the SnTe nanoplates, it may not be related to the topological surface states due to surface oxidation. Finally, we carried out thermodynamic analysis and density functional theory calculations to understand the ‘phase-separation’ phenomenon and further discuss general approaches to grow phase-pure samples when the precursors contain residual impurities.

Ab initio investigation of supported Au–Mn nanowires

We present an ab initio study of surface supported Au–Mn nanowires. Three different substrates are discussed: Cu(110), stepped Cu(111) and Si(001) surface. The emergence of stable antiferromagnetic (AFM) solutions in Au–Mn nanowires was found in all three cases. We found the nonzero magnetic moments of Mn atoms, however, the bulk of manganese is paramagnetic. The critical temperature of the Au–Mn wires is calculated by means of kinetic Monte Carlo simulation. The strong size-effect of the critical temperature is demonstrated.

Unusual magnetic properties of Au–Mn nanowires on copper and silicon substrates

The quantum properties of bimetallic supported Au–Mn nanowires on copper and silicon substrates were studied. As a result of ab initio calculations it was found that Au–Mn nanowires are antiferromagnetic in the ground state. The strong dependence of magnetic properties of supported Au–Mn nanowires on the substrate geometry and component composition was revealed. Analysis of wire geometry shows that Mn atoms are embedded into the silicon substrate. Results of our study show the strong suppressing of exchange interaction in Au–Mn nanowire on nonmetal silicon substrate in comparison to copper ones. A significant decrease was found for the energy difference ΔE between antiferromagnetic and ferromagnetic states of the supported Au–Mn nanowires in comparison to freestanding nanowires as the result of nanowire–substrate interaction.

Noncollinear magnetism of Mn nanowires on Fe(1 1 0)

Magnetic properties of Mn linear nanochains on a bcc Fe(1 1 0) surface have been studied using the first-principles real space-linear muffin-tin orbital atomic sphere approximation (RS–LMTO–ASA) method. We have considered up to nine Mn atoms deposited on bcc Fe(1 1 0). Our ab initio calculations reveal the competition between the antiferromagnetic Mn–Mn and Mn–Fe couplings, presenting a behavior which is very different from Mn nanowires on Fe(0 0 1), as shown in a previous publication. Due to this competition and non-negligible Dzyaloshinskii–Moriya interaction, noncollinear magnetic structures are stabilized as ground states for the Mn nanochains on Fe(1 1 0).

Magnetic characteristics of Au–Mn nanowires

The quantum properties of Au–Mn nanowires are analyzed theoretically from first principles. The emergence of magnetic properties in these nanowires, consisting of nonmagnetic elements, is demonstrated. It is shown that the manganese atoms carry fairly large magnetic moments (∼4.3 μB), although crystalline Mn is a paramagnet. Analysis of the electronic structure of these bimetallic nanowires indicates that the magnetic moments at the Mn atoms arise owing to the formation of a complicated structure of hybrid orbitals. Furthermore, it is found that the antiferromagnetic state in Au–Mn nanowires is stabilized by the occurrence of indirect exchange interaction between Mn atoms.

Magnetic and electronic structure of Mn nanostructures on Ag(111) and Au(111)

We present results of the electronic and magnetic structure of Mn nanowires adsorbed on Ag(111) and Au(111) surfaces. For finite Mn nanowires on Ag(111) and Au(111) surfaces, our ab initio results show that the large difference between the spin-orbit splitting of these two surfaces leads to completely different magnetic configurations. The magnetic ordering for Mn nanowires adsorbed on Ag(111) is governed by the strong exchange interaction between Mn adatoms. For Mn nano-chains on Au(111), the competition between Heisenberg and Dzyaloshinskii-Moriya interactions leads to a complex magnetic structure of the clusters considered here. Among the more conspicuous results we note a spin-spiral helical type for the nanowire with seven atoms, and a complex magnetic configuration incommensurate with the substrate lattice for a double-sized Mn wire. The effect of the structural relaxation is also investigated, showing sensitivity of the exchange interactions to the bond distance to the substrate. We also demonstrate that small changes in the band filling of these Mn chains results in drastically different changes of the interatomic exchange. Finally, we show that dispersion of the electronic energy spectrum is possible even in nanostructures with bounded spatial extension.

The Oxygen Vacancies Correlated Ferromagnetism in Transition Metal-Doped ZnO Nanowires

Dilute magnetic semiconductors (DMSs) have attracted much attention over the last decades due to their possibility of manipulating charge and spin degrees of freedom in a single substance. Extensive experimental investigations on ferromagnetism (FM) in transition metal (TM) doped ZnO have been concentrated on thin film and nanograin systems. However, up to now the debate on the origin of FM in TM doped ZnO still exists. Recently, there are some experimental report on the FM of transition metal doped ZnO with the one-dimensional nanowires, nanotubes and nanobelts. For examples, the ferromagnetism with low Curie temperature T c <50K has been observed in Mn-doped ZnO nanowires synthesized by vapor-phase or chemical vapor deposition methods. Room temperature FM has been oberved in Mn or Co-doped ZnO nanowires prepared by solution phase method. In this work, in order to understand the role of oxygen vacancies in TM doped ZnO nanowires, ab initio calculations on the magnetism of V, Cr and Mn-doped ZnO NWs with oxygen vacancies are performed, in comparison with case without oxygen vacancies.

Magnetic exciton relaxation and spin-spin interaction by the time-delayed photoluminescence spectra of ZnO:Mn nanowires.

ZnO:Mn nanostructures are important diluted magnetic materials, but their electronic structure and magnetic origin are still not well understood. Here we studied the time-delayed and power-dependent photoluminescence spectra of Mn(II) doped ZnO nanowires with very low Mn concentration. From the time-delayed emission spectra, we obtained their electronic levels of single Mn ion replacement of Zn ions in ZnO nanowire. The high d-level emissions show up unusually because of the stronger p-d hybridization than that in ZnS, as well as the spin-spin coupling. After increasing Mn doping concentration, the ferromagentic cluster of the Mn-O-Mn with varied configurations can form and give individual emission peaks, which are in good agreement with the ab initio calculations. The presence of clustered Mn ions originates from their ferromagnetic coupling. The lifetimes of these d levels show strong excitation power-dependent behavior, indication of strong spin-dependent coherent emission. One-dimensional structure is critical for this coherent emission behavior. These results indicate that the d state is not within Mn ion only, but a localized exciton magnetic polaron, Mn-O-Mn coupling should be one source of ferromagnetism in ZnO:Mn lattice, the latter also can combine with free exciton for EMP and produce coherent EMP condensation and emission from a nanowire. This kind of nanowires can be expected to work for both spintronic and spin-photonic devices if we tune the transition metal ion doping concentration in it.

CL from ZnO nanowires and microneedles Co-doped with N and Mn

Cathodoluminescence (CL) was used to study the luminescence emission of ZnO : N, Mn nanowires and microneedles grown by thermal evaporation. CL spectra acquired at room temperature showed the presence of near band edge and defect-related emissions. The defect related emission comprised two bands centered at 2.28 and 2.5 eV. The first component was attributed to the formation of spinel ZnMn2O4 and the second to the well-known ZnO green emission. CL spectra acquired at 100 K showed two emissions centered at 3.22 and 3.25 eV that were attributed to donor–acceptor pair (DAP) and FA transitions, respectively. It was proposed that substitutional nitrogen (NO) and zinc interstitial (Zni) were acceptor and shallow-donor centers in the DAP transition.

Magneto-optical spectrum and the effective excitonic Zeeman splitting energies of Mn and Co-doped CdSe nanowires

The electronic structure of Mn and Co-doped CdSe nanowires are calculated based on the six-band k·p effective-mass theory. Through the calculation, it is found that the splitting energies of the degenerate hole states in Mn-doped CdSe nanowires are larger than that in Co-doped CdSe nanowires when the concentration of these two kinds of magnetic ions is the same. In order to analysis the magneto-optical spectrum of Mn and Co-doped CdSe nanowires, the four lowest electron states and the four highest hole states are sorted when the magnetic field is applied, and the 10 lowest optical transitions between the conduction subbands and the valence subbands at the Γ point in Mn and Co-doped CdSe nanowires are shown in the paper, it is found that the order of the optical transitions at the Γ point almost do not change although two different kinds of magnetic ions are doped in CdSe nanowires. Finally, the effective excitonic Zeeman splitting energies at the Γ point are found to increase almost linearly with the increase of the concentration of the magnetic ions and the magnetic field; meanwhile, the giant positive effective excitonic g factors in Mn and Co-doped CdSe nanowires are predicted based on our theoretical calculation.

Room temperature ferromagnetism in Mn doped CdS nanowires

CdS:Mn (0%, 1.9% and 3%) nanowires with significant room-temperature ferromagnetism have been synthesized by chemical vapor deposition method using Au as catalyst. The X-ray diffraction, Raman spectroscopy and transmission electron microscopy analyses of these samples showed the formation of impurity free crystals with wurtzite CdS structure. SEM results reveal a uniform size distribution of the nanowires throughout the substrate. Photoluminescence spectra of undoped CdS reveals a weak band edge emission and a strong red emission related to surface defects. The luminescence is found to be decreased with Mn doping. Quenching of red emission intensity observed with the doping of Mn ions into CdS confirmed the changed defect structure in Mn doped CdS lattice. The enhancement of room temperature ferromagnetism was observed with increasing Mn doping concentration.

Experimental and first-principles study of ferromagnetism in Mn-doped zinc stannate nanowires

Room temperature ferromagnetism was observed in Mn-doped zinc stannate (ZTO:Mn) nanowires, which were prepared by chemical vapor transport. Structural and magnetic properties and Mn chemical states of ZTO:Mn nanowires were investigated by X-ray diffraction, superconducting quantum interference device (SQUID) magnetometry and X-ray photoelectron spectroscopy. Manganese predominantly existed as Mn2+ and substituted for Zn (MnZn) in ZTO:Mn. This conclusion was supported by first-principles calculations. MnZn in ZTO:Mn had a lower formation energy than that of Mn substituted for Sn (MnSn). The nearest neighbor MnZn in ZTO stabilized ferromagnetic coupling. This observation supported the experimental results.

Synthesis of polypyrrole coated manganese nanowires and their application in hydrogen peroxide detection

This study focuses on the synthesis and application of polypyrrole coated manganese nanowires (Mn/PPy NWs) as an enzyme-less sensor for the detection of hydrogen peroxide (H2O2). The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results confirm a core–shell structure with the Mn nanowires encapsulated by the PPy. An electrochemical sensor based on the Mn/PPy NWs for amperometric determination of H2O2 is prepared. The electrochemical behaviour of H2O2 is investigated by cyclic voltammetry with the use of modified glassy carbon electrode (GCE) with Mn/PPy NWs film. The modified glassy carbon electrode (GCE) with Mn/PPy NWs shows enhanced amperometric response for the detection of H2O2. This is due to the high available surface area of Mn/PPy NWs which can provide a suitable area for the reaction of H2O2. The detection limit and limit of quantification (S/N = 3) for two linear segments (low and high concentration of H2O2) are estimated to be 2.12 μmol L−1, 7.07 μmol L−1 and 22.3 μmol L−1, 74.5 μmol L−1, respectively. In addition, the sensitivity for these two linear segments is 0.4762 μA mM−1 and 0.0452 μA mM−1 respectively.