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Mn-doped ZnO samples, Zn1–xMnxO (x = 0, 0.01, 0.03 and 0.05; mole fraction), were successfully synthesized by sonochemical method. The undoped and Mn-doped ZnO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. XRD patterns of all products are identified to hexagonal wurtzite ZnO structure and their three main peaks shift toward lower diffraction angles due to the incorporation of Mn²⁺ into ZnO crystal lattice. The morphologies of Zn1–xMnxO (x = 0, 0.01, 0.03 and 0.05) were examined by SEM and TEM. The undoped ZnO sample shows large-scale uniform microflowers which are broken into nanorods and nanoparticles by Mn dopant. Their magnetic properties were investigated by a vibrating sample magnetometer at room temperature. The magnetization-applied field behavior of undoped ZnO defines its weak ferromagnetic behavior. The 3 mol% Mn-doped ZnO shows the highest saturation magnetization of 51.73 × 10⁻³ mA·m²·g⁻¹, and the 5 mol% Mn-doped ZnO has suppressed ferromagnetic property due to the formation of Mn clusters inside.
Polycrystalline Mn doped ZnO (MZO) semiconductor thin films were deposited onto glass substrates employing different number of dipping at room temperature using Successive Ionic Layers by Adsorption Reaction (SILAR) technique. The thin film deposition conditions were optimized by altering the various deposition parameters based on their structure. The structural study was carried out using X-ray diffractometer (XRD). The XRD analysis indicated that there is no change in the structure of ZnO thin films due to Mn doping. The films exhibited hexagonal wurtzite structure. The structural studies on Mn doped samples revealed that the predominant orientation is (002) lattice plane and the position of this orientation shifted toward lower angle during doping. The intensity of photoluminescence (PL) emission of ZnO is found to be augmented for Mn doped samples. The room temperature Raman spectra measurements revealed the presence of additional modes. The Vibrating Sample Magnetometer (VSM) studies show that MZO thin film has ferromagnetic properties.
One-dimensional nanostructures exhibit interesting electronic and optical properties due to their low dimensionality leading to quantum confinement effects. ZnO has received lot of attention as a nanostructured material because of unique properties rendering it suitable for various applications. Amongst the different methods of synthesis of ZnO nanostructures, the hydrothermal method is attractive for its simplicity and environment friendly conditions. This review summarizes the conditions leading to the growth of different ZnO nanostructures using hydrothermal technique. Doping of ZnO nanostructures through hydrothermal method are also highlighted.
For the first time the bulk oriented single crystals ZnO:Mn are obtained and the polarized Raman spectra are studied at excitation in the visible and near infrared regions. The resonance enhancing of the Raman scattering by Mn-related modes is found at the visible excitation due to the extra optical absorption in ZnO at the addition of Mn. It is shown that the resonance-enhanced overtone of Mn-related silent modes may be responsible for an appearance of anomalous modes of the A1 symmetry at 500–600 cm−1. A Fermi resonance between the overtone and one-phonon mode is analyzed.
We present a systematic analysis of the structural properties of Mn implanted ZnO by Raman scattering and complementary methods in the Mn composition range 0.2–8 at.% (relative to Zn) with an implantation step profile of about 300 nm depth. Mn ions are substitutionally incorporated on Zn sites in the ZnO wurtzite lattice and no secondary phases are detected. Beside the common eigenmodes of the ZnO host lattice, we observe additional modes related to the Mn implantation, which are studied for different Mn concentrations and annealing procedures. We distinguish between implantation damage and impurity induced disorder, and also show that the spectral feature which is often assigned to a Mn local vibrational mode (LVM) in ZnO consists of two separate modes. We present evidence that only one of these features is a candidate for a LVM.
We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga1-xMnxAs using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature TC with respect to the IR spectral weight are examined using a sum-rule analysis of IR conductivity spectra. We find nonmonotonic behavior of trends in TC with the spectral weight to effective Mn ratio, which suggest a strong double-exchange component to the FM mechanism, and highlights the important role of impurity states and localization at the Fermi level. Spectroscopic features of the IR conductivity are tracked as they evolve with temperature, doping, annealing, As-antisite compensation, and are found only to be consistent with a Mn-induced IB scenario. Furthermore, our detailed exploration of these spectral features demonstrates that seemingly conflicting trends reported in the literature regarding a broad mid-IR resonance with respect to carrier density in Ga1-xMnxAs are in fact not contradictory. Our study thus provides a consistent experimental picture of the magnetic and electronic properties of Ga1-xMnxAs.
ZnO nanowires were deposited on the Si(1 0 0) substrate via vapor–liquid–solid process with flowing Ar gas current for 90 s. The morphology, structure, and optical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and Raman spectrum, respectively. The results showed that the as-deposited ZnO nanowires had hexagonal wurzite structure. The Raman spectrum showed oxygen defects in ZnO nanowires due to the existence of the Ar gas during the growth process, leading to the dominant green band peak and the weak UV peak in the PL spectrum. And blue shift of the Raman peaks was attributed to the lattice distortion and piezoelectric effect of the nanostructures. Finally, the biaxial compressive stress within the c-axis oriented ZnO nanowires was estimated to 0.365 GPa, which was also responsible for the frequency shift of the E2 (high) mode of the Raman spectra.
Mn-doped ZnO column arrays were successfully synthesized by conventional sol–gel process. Effect of Mn/Zn atomic ratio and reaction time were investigated, and the morphology, tropism and optical properties of Mn-doped ZnO column arrays were characterized by SEM, XRD and photoluminescence (PL) spectroscopy. The result shows that a Mn/Zn atomic ratio of 0.1 and growth time of 12 h are the optimal condition for the preparation of densely distributed ZnO column arrays. XRD analysis shows that Mn-doped ZnO column arrays are highly c-axis oriented. As for Mn-doped ZnO column arrays, obvious increase of photoluminescence intensity is observed at the wavelength of ∼395 nm and ∼413 nm, compared to pure ZnO column arrays.
Magnetic properties of Mn-doped ZnO (Zn0.98Mn0.02O) bulk materials prepared by the solid state reaction method were investigated by measuring magnetization as functions of temperature and magnetic field. The results indicate that the samples sintered in Ar gas show ferromagnetic behavior at room temperatures, but it disappears in samples sintered in air. Even for ferromagnetic samples, the obtained saturation value of magnetization is much smaller than theoretical value, suggesting the possibility of that there was a strong anti-ferromagnetic exchange coupling in this kind of compounds.
We investigate the temperature dependent Raman spectra of Mn implanted (Ga,Mn)N samples with five Mn implantation doses. A small shoulder at 572.4cm−1 on the high energy side of the main Raman peak E2H has been attributed to the Mn-related local vibrational mode (LVM). It is found that with the increase of Mn implantation dose the intensity ratio of LVM to that of the E2H(ILVM/IE2H) increases at first and tends to saturate at high implantation dose. In addition, at high temperature or after rapid thermal anneal treatment, the value of ILVM/IE2H decreases significantly, explaining the reason why it is difficult to observe Mn-related LVM reported in the literature.
High density Mn-doped ZnO nanorod arrays were vertically grown on ITO substrate via hydrothermal reaction at relatively low temperature of 95 °C. The microstructure and magnetism of the arrays have been examined. Field emission scanning electron microscopy shows that the nanorods of 100 nm diameter and 1 μm length grow along the  direction. X-ray photoemission spectroscopy demonstrates that Mn is successfully doped into the nanorods. Meanwhile, all the Mn-doped ZnO nanorod arrays are ferromagnetic at room temperature. It is also found that the value of the saturation magnetization (Ms) of the ZnO nanorod arrays firstly increases with increasing the Mn concentration and then decreases. The higher Ms value is 0.11emu/g, which is obtained in the 5 at.% Mn-doped ZnO nanorod arrays. The ferromagnetism comes from the ferromagnetic interaction between the Mn ions, which partly replace Zn ions.
Mn-doped ZnO nanorods were synthesized from aqueous solutions of zinc nitrate hexahydrate, manganese nitrate and methenamine by the chemical solution deposition method (CBD). Their microstructures, morphologies and optical properties were studied in detail. X-ray diffraction (XRD) results illustrated that all the diffraction peaks can be indexed to ZnO with the hexagonal wurtzite structure. Scanning electron microscope (SEM) results showed that the average diameter of Mn-doped ZnO nanorods was larger than that of the undoped one. Photoluminescence (PL) spectra indicated that manganese doping suppressed the emission intensity and caused the blue shift of UV emission position compared with the undoped ZnO nanorods. In the Raman spectrum of Mn-doped ZnO nanorods, an additional mode at about 525cm−1 appeared which was significantly enhanced and broadened with the increase of Mn doping concentration.
Large-scale chestnut-like ZnO and Zn–ZnO hollow nanostructures on Si substrates were prepared without catalyst by a one-step chemical vapor deposition technique. The morphology, composition, and phase structure of as-prepared products were characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and X-ray diffraction, respectively. The ZnO consists of chestnut-like nanostructures with hollow interior and a lot of nanoneedles aligning on the surface of the hollow structure in a radial way, whereas the Zn–ZnO shows that long nanowires grew on the chestnut-like hollow structure with a hexagonal flower-like structure on the top layer. A vapor–solid (VS) growth mechanism for the chestnut-like ZnO and Zn–ZnO hollow nanostructures was proposed. The photoluminescence (PL) of ZnO and Zn–ZnO shows a large number of oxygen vacancy defects appeared in the novel hollow nanostructures.
A mixture of bi(acetylacetonato) zinc(II)hydrate and tris(acetylacetonato) manganese(III) complexes was thermally co-dissociated to synthesize Mn-doped ZnO powders. In order to examine the effect of oxygen vacancies on the ferromagnetic coupling of Mn ions, two preparation routes were used: in route (I) the preparation was done in an open environment, whereas in route (II) the preparation was done in a closed environment. The X-ray diffraction (XRD) and the X-ray fluorescence (XRF) measurements indicate that the Mn content in the three samples are 3.9% (I), 3.3% (II) and 4.2% (II). The XRD results showed that the Mn ions were incorporated in the ZnO crystal and that a Zn1−xMnxO solid solution has formed. The magnetic characterization indicated that only samples prepared via route (II) exhibited a room temperature ferromagnetic component of magnetization. Furthermore, magnetic analysis showed that the magnetic moment per dopant ion in the samples examined was in the range of 4.2–6.1μB/Mn. The percentages of coupled Mn atoms to the total number of Mn atoms were found to be extremely small (less than 0.1%), which by itself cannot explain the observed RT hysteresis loops. Thus, in order to produce long-range ferromagnetic order in these samples, the FM coupling has to be mediated via defects. The observed FM in this study may be attributed to the presence of oxygen vacancies, which mediate the ferromagnetic exchange between the coupled Mn ions. This is consistent with the bound magnetic polarons (BMP) model where defects like oxygen vacancies cause the polarons to overlap and give rise to a long-range ferromagnetic order in dilute magnetic semiconductors (DMS).
Semiconducting zinc oxide nanowires (NWs) and nanobelts (NBs) are a unique group of quasi-one-dimensional nanomaterial. This review mainly focuses on the rational synthesis, structure analysis, novel properties and unique applications of zinc oxide NWs and NBs in nanotechnology. First, we will discuss rational design of synthetic strategies and the synthesis of NWs via vapor phase and chemical growth approaches. Secondly, the vapor–solid process for synthesis of oxide based nanostructures will be described in details. We will illustrate the polar surface dominated growth phenomena, such as the formation of nanosprings, nanorings and nanohelices of single-crystal zinc oxide. Third, we will describe the unique and novel electrical, optoelectronic, field emission, and mechanical properties of individual NWs and NBs. Finally, we will illustrate some novel devices and applications made using NWs as ultra-sensitive chemical and biological nanosensors, solar cell, light emitting diodes, nanogenerators, and nano-piezotronic devices. ZnO is ideal for nanogenerators for converting nano-scale mechanical energy into electricity owing to its coupled piezoelectric and semiconductive properties. The devices designed based on this coupled characteristic are the family of piezotronics, which is a new and unique group of electronic components that are controlled by external forces/pressure.
Different molar ratios of Zn(NO3)2 to NaOH were dissolved in de-ionized water, mixed to form solutions with different pH values and heated using 180W microwave power (80°C) in ambient atmosphere for 20min. Wurtzite ZnO nanostructure was detected using an X-ray diffractometer (XRD) and a selected area electron diffraction (SAED) technique. The patterns were in accordance with those of the simulation. Scanning and transmission electron microscopes (SEM and TEM) revealed their nanostructures with different morphologies controlled by molar ratios of the starting agents as well as pH values of the solutions. High resolution transmission electron microscopic (HRTEM) technique shows that the crystallographic planes are aligned in lattice array. Seven different Raman wavenumbers at 334, 378, 410, 440, 541, 575 and 660cm−1 were used to specify that the products were wurtzite structured ZnO. Photoluminescence (PL) spectra show their emission peaks at 385–394nm due to the recombination process of free excitons.
Hexagonal ZnO nanostructure flowers were successfully synthesized from a 1:15 molar ratio of Zn(CH3COO)22H2O to KOH using 180 W microwave radiation for 20 min. The product phase was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED). A diffraction pattern was also simulated and was found to be in accordance with those of the experiment and the JCPDS database. Raman spectrometry revealed the presence of four vibration peaks at 337.85, 381.13, 437.54 and 583.30 cm−1. The product, spear-shaped nanorods in flower-like clusters, was characterized using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). High resolution TEM (HRTEM) showed that growth of the spear-shaped nanorods was in the  direction, which was normal to the (002) planes composing a lattice fringe of the nanorods. A formation mechanism of hexagonal ZnO nanostructure flowers was also proposed.
ZnO nanoparticles and nanorods were synthesized from Zn(NO3)2·6H2O and NaOH in H2O and in different molecular weights (MWs) of polyethylene glycol (PEG) using 180W microwave radiation. The phase was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED). The diffraction pattern was in accordance with that obtained by simulation. Scanning and transmission electron microscopy (SEM and TEM) revealed the presence of nanoparticles with an average size of 12.7±2.7nm in water; these gradually changed into nanorods in PEG with different MWs. Four Raman vibrations were detected, with the strongest intensity at 439cm−1, specified as the optical phonon E2H high frequency mode. Luminescence emission was detected at 366–374nm, caused by the recombination of free excitons in the products. Emission intensity was highest for the product synthesized in PEG600.
We investigated the microstructure and optical properties of Zn1−xMnxO films synthesized by the magnetron sputtering technique. Structural analyses suggest that Mn occupied the Zn sites successfully and did not change the wurtzite structure of ZnO. In addition, nanoscale columnar grain arrays were found in the Mn-doped ZnO films. The experimental results indicate that moderate Mn doping could enhance the photoluminescence emission of ZnO. The possible origin of the emissions from our samples was also explored.
Flower-like manganese (Mn) doped ZnO nanorods were fabricated by a chemical vapor deposition method using zinc and MnCl2 powders as source materials of Zn and Mn, respectively. Raman scattering and cathodoluminescence (CL) are used to study the influence of Mn on the lattice dynamics and optical properties of ZnO. A local vibrational mode located at about is observed, which is related to Mn dopants. In addition, the presence of a new Raman mode centered at about as well as the enhancement and redshift of the A1(LO) mode is caused by the lattice defects and disorder induced by Mn doping. CL spectra mapping as well as monochromatic CL imaging shows that the ultraviolet emission from the surface is much weaker than that from the interior of the Mn-doped ZnO nanorod, while the green emission from the surface is much stronger than that from the interior.
A facile approach to fabricate Mn-doped ZnO hollow nanospheres is reported. Zn2+ and Mn2+ cations were adsorbed onto the surface of carbon template to form a core/shell structure in solution. Subsequent calcination of the core/shell structure would lead to the formation of Mn-doped ZnO hollow nanospheres. The magnetic properties of the hollow spheres were dependent on the calcination temperature. The room-temperature ferromagnetism was obtained when the temperature was less than 900 °C. However, the ferromagnetic behavior disappeared when the temperature was elevated to 1200 °C. The possible reason is the short-ranged ferromagnetic spin–spin interaction between neighboring Mn atoms by forming a bridge bond by Hi.
The x–y spatially-resolved mappings of polarized Raman scattering spectra from a single tetrapod-like ZnO nanostructure were proposed and performed with different polarized scattering configurations by utilizing the intrinsic geometry configuration. The ZnO nanostructures were synthesized by rapid thermal evaporation of metal zinc without metal catalyst and graphite additive. The sharp spectral peaks from all Raman active phonon modes have been distinctly observed. However, no pronounced quantum confinement effect has been observed for the tetrapod-like nanostructure with diameter of 50 nm. In addition, larger red shifts of longitudinal-optical phonon scattering peaks, compared with bulk ZnO, were observed in the single tetrapod-like nanostructure, which were primarily attributed to laser-induced heating or/and the phonon localization effects.
Mn-doped ZnO diluted magnetic semiconductor nanoparticles are prepared by an ultrasonic assisted solgel process. Transmission
electron microscopy shows pseudo-hexagonal nanoparticles with an average size of about 24 nm. From the analysis of X-ray diffraction,
the Mn-doped ZnO nanoparticles are identified to be a wurtzite structure without any impurity phases. The magnetic properties
are measured by using superconducting quantum interference device. For the ZnO with 2% Mn doping concentration, a good hysteresis
loop indicates fine ferromagnetism with a Curie temperature higher than 350 K.
The unique water/PVP (polyvinylpyrrolidone)/ n -pentanol interface has been developed to prepare the ZnO particles with hexagonal bilayer structure. By modifying the interface through varying the amount of PVP and water, one can readily tune the particle size and change the particle shape from hexagonal bilayer to capped potlike to hemispherical features. The study of the growth dynamics and extinction spectra suggests that the bilayer structure arises from the selective adsorption of PVP on the ZnO crystallographic planes. Both the photoluminescence and extinction spectra show that the band gap of the hexagonal bilayer ZnO particles shrinks with increasing particle size.
Mn-doped ZnO nanorods (composition: Mn0.046Zn0.954O) were grown by a simple solvothermal technique. The morphological, structural and optical properties of the as-prepared nanorods were investigated by means of transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and photoluminescence. The results showed that the sample had rod-like morphology and that the preferential growth direction was along the c-axis. The doping of Mn2+ ions has significant influences on the optical properties of ZnO nanorods. Low-temperature photoluminescence spectra of Mn-doped ZnO nanorods exhibit a strong near band-edge emission at 370.8 nm and a weak deep-level emission around 525 nm, indicating the concentrations of the defects responsible for deep-level emissions are reduced on doping. The dynamic process of the UV emission for Mn-doped ZnO nanorods was discussed.
Undoped and manganese doped zinc oxide (ZnO) thin films were prepared by pyrolytic decomposition of aqueous solution onto glass substrates. The structural properties studied using X-ray diffraction showed that the undoped ZnO films exhibit hexagonal wurtzite structure with strong c-axis orientation, however Mn doped ZnO films were polycrystalline. The surface morphological studies from SEM depicted the formation of clusters like structure of undoped ZnO while the Mn doped film showed the nanocrystalline grains on the surface. From the optical studies, the transmittance in the wavelength range 350–850 nm was found to be decreased after doping of Mn. The optical band gap was found to be 3.3 eV for undoped ZnO film and 3.10 eV for Mn doped films. From the electrical resistivity measurement, it is found that the Mn doping significantly caused to increase the room temperature resistivity from 104 to 106 Ω cm.
Mn doped ZnO nanowires have been synthesized using a simple autocombustion method. The as-synthesized Mn doped ZnO nanowires were characterized by X-ray diffraction and transmission electron microscopy. An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Mn concentration. Optical absorption studies show an increment in the band gap with increasing Mn content, and also give evidence for the presence of Mn2+ ions in tetrahedral sites. All Zn1−xMnxO (0≤x≤0.25) samples are paramagnetic at room temperature. However, a large increase in the magnetization is observed below 50 K. This behavior, along with the negative value of the Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicate ferrimagnetic behavior. The origin of ferrimagnetism is likely to be either the intrinsic characteristics of the Mn doped samples, or due to some spinel-type impurity phases present in the samples that could not be detected.
This paper reports the fabrication of highly-sensitive cholesterol biosensor based on cholesterol oxidase (ChOx) immobilization on well-crystallized flower-shaped ZnO structures composed of perfectly hexagonal-shaped ZnO nanorods grown by low-temperature simple solution process. The fabricated cholesterol biosensors reported a very high and reproducible sensitivity of 61.7 microA microM(-1)cm(-2) with a response time less than 5s and detection limit (based on S/N ratio) of 0.012 microM. The biosensor exhibited a linear dynamic range from 1.0-15.0 microM and correlation coefficient of R=0.9979. A lower value of apparent Michaelis-Menten constant (K(m)(app)), of 2.57 mM, exhibited a high affinity between the cholesterol and ChOx immobilized on flower-shaped ZnO structures. Moreover, the effect of pH on ChOx activity on the ZnO modified electrode has also been studied in the range of 5.0-9.0 which exhibited a best enzymatic activity at the pH range of 6.8-7.6. To the best of our knowledge, this is the first report in which such a very high-sensitivity and low detection limit has been achieved for the cholesterol biosensor by using ZnO nanostructures modified electrodes.
Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena
in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic
interactions that lead to a Curie temperature (T
C) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition
metals in 1950, can explain T
C of Ga1−
xMnxAs and that of its II-VI counterpart Zn1−
xMnxTe and is used to predict materials with T
Cexceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
Synthesis and band gap of ZnO particles with hexagonal bilayer structure