Low Mn Doping Research Articles

Mapping the Identity of Transition Metal Doping and Surface Passivation in Indium Phosphide with Theoretical Calculation.

Understanding the electronic structure of doped InP quantum dots (QDs) is essential to optimize the material for specific optoelectronic applications. However, current synthesis approaches are often tedious and unfavorable for rational tunning. Herein, a combination of experimental and computational studies was conducted to address the doping mechanism and surface passivation of InP QDs. The successful dopant introduction requires low Cu doping concentration and heavy Mn doping, while the Ag doping amount is relatively moderate. This may correspond to the theoretical doping formation energy presented as Cu (-2.52 eV) < Ag (-1.76 eV) < Mn (-0.38 eV). As for surface passivation, inorganic ions and shell-like ZnS are unraveled through simulational investigation. Chloride ion promotes oriented growth toward tetrahedron morphology while nitrate-passivated InP QDs exhibit blurry transmission electron microscope (TEM) morphology. Correspondingly, the binding energy of chloride ion with (111) facet is -2.13 eV significantly lower than those of (110) and (100) facets. Further, the additional Zn 3d bands are more involved in the formation of conduction band, which optimized the Mn-doped InP with a 0.32 eV bandgap. These experimental and model results provide more microscopic details of doped InP, which can motivate theoretically exact control of guest ion stoichiometry with optimized characteristics for electrical devices.

Effect of low amount Mn doping on structural and magnetic properties of SrFe12O19: Effective magnetic anisotropy study by Stoner - Wohlfarth model

A series of strontium hexaferrites (Sr-HF) compounds, doped with a low amount of manganese SrFe12-xMnxO19 (where x = 0.00, 0.03 and 0.05), were prepared by a sol-gel method. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM) in order to determine some basic properties such as lattice parameters and particles size. Moreover, magnetic properties of the samples were measured in a temperature range from 2 to 900 K. The results show that the transition temperature (TC) decreases from 764 to 721 K with Mn doping at x = 0.05 content. Also, temperature and doping effects on the coercivity (Hc), the remanent magnetization (Mr) and the magnetization of saturation (MS) were discussed considering the Stoner - Wohlfarth model. A slight improvement of the magnetic properties (Hc =5.56 kOe, Mr =49.99 emu/g, MS =101.9 emu/g (i.e. 19.37 μB/u.f)) for low content (x = 0.03) is evidenced, yielding to promising material for permanent magnet devices. This improvement was explained by the relationship between the microstructure and to the effective magnetic anisotropy.

Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs

Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs was demonstrated in α- and β-TCP polymorphs prepared by wet precipitation method under identical conditions and annealed at 700 °C. Calcium phosphates with Mn doping level in the range from 1 to 5 mol% were studied and the formation of desired polymorph was controlled by varying Mn content in as-prepared precipitates. It was found that increasing Mn content resulted in the formation of β-TCP, while α-TCP was obtained with low Mn doping level, whereas a mixture of two polymorphs was obtained for intermediate Mn concentrations. Moreover, doping with Mn ions allowed the synthesis of β-TCP at relatively low temperature (700 °C). Synthesized compounds were characterized by X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and colorimetric MTT assay.

0.6ST-0.4NBT thin film with low level Mn doping as a lead-free ferroelectric capacitor with high energy storage performance

Srx(Na0.5Bi0.5)1−xTi0.99Mn0.01O3 (x = 0.2, 0.4, 0.6, and 0.8) relaxor ferroelectric thin films were grown on Pt/Ti/SiO2/Si substrates by the Sol-Gel method. The influence of the Sr content on the microstructures, ferroelectric properties, and energy-storage performances of the thin films were investigated in detail. The Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3 thin film exhibits very slim hysteresis loops with the highest electric breakdown field strength due to reduced oxygen vacancies. Owing to the high breakdown field strength of 3134.3 kV/cm, the Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3 thin film shows a giant recoverable energy-storage density of 33.58 J/cm3. These results indicate that the Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3 thin film is promising for applications of advanced capacitors with high energy-storage density.

Influence of Mn Substitution on Mössbauer and Magnetic Properties of Ni-Zn Ferrite Nanoparticles

Series of Mn-substituted Ni-Zn ferrite compositions were synthesized and characterized using XRD, IR, TEM, and Mossbauer studies. The lattice parameter was found to increase with an increase in Mn substitution. The FTIR spectra of ferrites show two principal absorption bands in the regions 580–630 and 390–420 cm−1. The 57Fe Mossbauer spectra recorded at room temperature were fitted with three sextets corresponding to Fe3+ ions at A and B sites and a superparamagnetic doublet. The saturation magnetization shows an initial increase at lower Mn doping and decreases with a further increase in Mn concentration. The coercivity was found to decrease with Mn substitution.

Terahertz emission characteristics of GaMnAs dilute magnetic semiconductor under 650 mT external magnetic field

We investigate the effects of an externally applied magnetic field on the terahertz (THz) emission of Gallium Manganese Arsenide (GaMnAs) films grown via molecular beam epitaxy (MBE). Results show that low Mn-doping in GaMnAs resulted to increased THz emission as compared with a SI-GaAs substrate. Further increase in Mn-doping content resulted to a comparably less THz emission, which is attributed to reduced crystallinity and higher free-carrier absorption. Under an external magnetic field, the contributions of the Bup and Bdown-related THz emission were observed to be asymmetric: possibly due to intrinsic magnetic properties of GaMnAs.

(Invited) Red-Emitting Manganese-Doped Aluminum Nitride Phosphor

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N2 in a reducing environment results in nitrogen deficiency, as revealed by diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86±0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol%. The principal Mn2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn. Figure 1

Red-emitting manganese-doped aluminum nitride phosphor

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900°C, 10atmN2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650°C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254nm excitation (Q.E.=0.86±0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06mol.%. The principal Mn2+ decay of 1.25ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn.

X-ray absorption spectroscopy of Mn doped ZnO thin films prepared by rf sputtering technique

A set of r.f. sputter deposited ZnO thin films prepared with different Mn doping concentrations have been characterised by Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Spectroscopy (XANES) measurements at Zn, Mn and O K edges and at Mn L2,3 edges apart from long range structural characterisation by Grazing Incident X-ray Diffraction (GIXRD) technique. Magnetic measurements show room temperature ferromagnetism in samples with lower Mn doping which is however, gets destroyed at higher Mn doping concentration. The results of the magnetic measurements have been explained using the local structure information obtained from EXAFS and XANES measurements.

Peculiarly strong room-temperature ferromagnetism from low Mn-doping in ZnO grown by molecular beam epitaxy

Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO thin films grown by molecular beam epitaxy. Very low Mn doping concentration is investigated, and the measured magnetic moment is much larger than what is expected for an isolated ion based on Hund's rules. The ferromagnetic behavior evolves with Mn concentration. Both magnetic anisotropy and anomalous Hall effect confirm the intrinsic nature of ferromagnetism. While the Mn dopant plays a crucial role, another entity in the system is needed to explain the observed large magnetic moments.

Effect of Mn doping on the temperature-dependent anomalous giant dielectric behavior of CaCu3Ti4O12

We report dielectric properties and dielectric relaxation behaviors of Mn-substituted CaCu${}_{3}$Ti${}_{4}$O${}_{12}$ (CCTO) on Cu sites. While CCTO exhibits the giant dielectric constant and low dielectric loss in a wide temperature range, drastic suppression of the dielectric constant in Mn-doped CCTO (CCMTO) samples have been observed in temperature and frequency dependencies of dielectric properties with two possible origins as Mn doping increases. The observed suppression of dielectric response in the low Mn doping differs from the heavy doping of Mn in CCMTO samples. The low-Mn-doped CCMTO samples ($x=0.01$ and 0.02) show that the relaxation time and the activation energy ${E}_{a}$ were slightly reduced due to a decreased contribution from the density of the dipolar effect. However, in heavily doped CCMTO samples ($x=0.03$, 0.04, and 0.05), the dielectric response, relaxation time, and ${E}_{a}$ were significantly decreased, suggesting Mn doping plays a significant role in the destruction of the intrinsic dipolar effect.

Structural, Optical and Photocatalytic Photodegradation Properties of Zn1−xMnxO Prepared by the Sol-Gel Process

Effect of Mn doping on the structural, photoluminescence and photocatalytic photodegradation properties of Zn1−xMnxO have been studied. The Zn1−xMnxO powders and thin films were synthesized by the sol-gel, spin coating and high temperature annealing processes. The samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), photoluminescence and UV-visible (UV-Vis) spectroscopy. XRD analysis showed that Zn1−xMnxO can keep a single phase of wurtzite structure at low Mn doping. UV-Vis spectra of Mn-doped samples showed that Mn doping can enhance the decolorization efficiency of methyl orange at optimal Mn doping levels.

Synthesis and Physical Properties of Mn Doped ZnO Dilute Magnetic Semiconductor Nanostructures

Mn doped ZnO nanostructures have been prepared using low temperature simple, quick, and versatile synthesis approach. The structural, microstructural, and vibrational investigations reveal that as prepared nanostructures with low Mn doping concentration have single hexagonal phase and are grown along the preferred c-axis. The X-rays photoelectron spectroscopy demonstrates that the Mn ions are in mixed oxidation states for high doping concentration of Mn, while are in 2+ oxidation state for low concentration into ZnO lattice. The photoluminescence spectrum (PL) exhibits a significant red-shift of 22 nm in the optical band gap of doped ZnO and shows the improved luminescence properties, which makes it potential for its use in the photocatalyst, optoelectronics and solar cell nanodevices. Furthermore, the magnetic measurement of Mn doped ZnO nanostructures exhibits the ferromagnetism at room temperature.

Element-resolved orbital polarization in (III,Mn)As ferromagnetic semiconductors fromK-edge x-ray magnetic circular dichroism

Using x-ray magnetic circular dichroism (XMCD), we determine the element-specific character and polarization of unoccupied states near the Fermi level in (Ga,Mn)As and (In,Ga,Mn)As thin films. The XMCD at the $\text{As}\text{ }K$ absorption edge consists of a single peak located on the low-energy side of the edge, which increases with the concentration of ferromagnetic Mn moments. The XMCD at the $\text{Mn}\text{ }K$ edge is more detailed and is strongly concentration dependent, which is interpreted as a signature of hole localization for low Mn doping. The results indicate a markedly different character of the polarized holes in low-doped insulating and high-doped metallic films, with a transfer of the hole orbital magnetic moment from Mn to As sites on crossing the metal-insulator transition.

Study of the substitution effect of Mn doped in ZnO matrix

Zn1-xMnxO (x = 0.01, 0.02, 0.05, 0.1, and 0.15) powders were prepared by solid-state reaction processes. The structural and magnetic properties of the powders were investigated. X-ray diffraction (XRD) analysis of the samples indicates the presence of wurtzite crystal structure similar to pure ZnO and absence of any other secondary phase till 5% Mn doping. This suggests that doped Mn2+ ions substitute Zn2+ sites. However, Raman results revealed the presence of secondary phase even at very low Mn doping (2%), which demonstrates that Mn does not incorporate completely the ZnO lattice. The powders exhibit ferromagnetism at low temperatures and paramagnetic at room temperature. Transition from ferromagnetic to paramagnetic is highlighted by measurements at 230 K.

Preparation and Dielectric Properties of Mn-Doped Ba 0.6Sr 0.4TiO 3-MgTiO 3 Composite Ceramics

Barium strontium titanate (Ba 0.6Sr 0.4TiO 3, BST) nano-powders were prepared using Ba(NO 3) 2, Sr(NO 3) 2, oxalic acid dehydrate, and tetrabutyl titanate (Ti(OC4H9)4) as precursors by the chemical co-precipitation method. The product was characterized by thermogravimetry-differential scanning calorimetry (TG-DSC) thermal analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results indicated that the resulting Ba 0.6Sr 0.4TiO 3 nano-powders were homogeneous with agglomerated nature. The Ba 0.6Sr 0.4TiO 3-MgTiO 3 (BST-MT) bulk composite ceramics doped by Mn were obtained by the traditional solid phase method. The XRD patterns demonstrated that Mn-doped BST was unable to change the perovskite crystalline structure of BST materials. SEM photographs revealed that the crystalline grains became larger with increasing the content of doping Mn (<1.5% (x, molar fraction)) and then the size of grains decreased after the Mn content exceeded 1.5% in the BST ceramics, suggesting the effect of Mn doping on the morphologies of BST-MT composites. The dielectric properties of BST-MT composite ceramics doped with 0.1%-2.0% (x) Mn were investigated systematically. Two effects of Mn doping on the dielectric properties of the BST-MT composite ceramics were observed. At low Mn doping concentrations (<1.5%), Mn mainly acted as an acceptor dopant to replace Ti at the B site of ABO3 perovskite structure, leading to a diffused phase transition. It was also observed that the grain size increased drastically as the Mn content increased and thus caused the decrease of dielectric loss. At higher Mn doping concentrations (>1.5%), the grain size decreased and the suppression of permittivity and the drastic increase of the dielectric losses were observed, which indicated a “composite” mixing effect.

Structure of MnxGe1－x dilute magnetic semiconductor films

The structure of MnxGe1-x dilute magnetic semiconductor thin films prepared by magnetron co-sputtering has been studied by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) techniques. The XRD results show that in the MnxGe1-x thin film with low Mn doping concentration (x=0.070), only diffraction peaks attributed to crystalline Ge can be observed. In samples with high Mn doping concentrations (x=0.250, 0.360), the secondary phase Ge3Mn5 appears, and its content enhances with Mn doping concentration. The XAFS results indicate that for the Mn0.07Ge0.93 thin film, Mn atoms are mainly incorporated into the Ge lattice and located at the substitutional sites of Ge atoms with the ratio of 75%, while for the Mn0.25Ge0.75 and Mn0.36Ge0.64 samples, most of the Mn atoms are aggregated to form Ge3Mn5.

Phase separation inLa1.85−1.5xSr0.15+1.5xCu1−xMnxO4

In this paper, we report the occurrence of phase separation and the influence of phase separation on the conductivity in the ${\mathrm{La}}_{1.85\ensuremath{-}1.5x}{\mathrm{Sr}}_{0.15+1.5x}{\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{O}}_{4}$ system. At low Mn doping range, the resistivity increases sharply with increasing $x$ due to the magnetic scattering effect. The phase separation occurs in the intermediate doping regime $0.33\ensuremath{\leqslant}x&lt;0.5$. When the phase separation occurs, the resistivity decreases unexpectedly. This result indicates that the phase separation enhances the motion of itinerant charge carriers.

Mn doping effect on structure and magnetism of epitaxial (FePt)1−xMnx films

We study the structure and perpendicular magnetism of molecular beam epitaxy grown (FePt)1−xMnx films with doping concentration x=0, 1%, 2%, 3%, 4%, and 5%. The (FePt)1−xMnx films were made by multilayers growth of [Fe/Pt/Mn]×N at 100 °C and annealed at 600 °C. X-ray diffraction scans indicate that relatively better L10 ordered structure for low Mn doping (x&amp;lt;2%). The (001) and (003) superstructure peaks decrease with the increase of the Mn doping for x⩾2%, and a significant (111) peak appears for x&amp;gt;3%. The perpendicular magnetic anisotropy effect of the (FePt)1−xMnx films tends to decrease with the increase of Mn doping for x&amp;gt;1%. However, the x=1% doped films possess slightly better perpendicular magnetic anisotropy effect than the zero doped film. The perpendicular magnetic anisotropy constant are of about 1.3×107 and 1.6×107 erg/cm3 for x=0% and x=1%, respectively.