Effect of Mn doping on the microstructures and photoluminescence properties of CBD derived ZnO nanorods

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 525 cm⁻¹ appeared which was significantly enhanced and broadened with the increase of Mn doping concentration.     

Fabrication and characterization of Mn-doped Cu2O thin films grown by RF magnetron sputtering

Two series of Mn-doped Cu₂O diluted-magnetic-semiconductor thin films were prepared by radio-frequency (RF) magnetron sputtering. One is prepared at different deposition temperature with the same Mn doping concentration; the other is deposited at the same temperature but with varying Mn concentration. They were used to find out the ferromagnetic-order zone for the Mn-doped Cu₂O systems. Most of the samples show high (1 1 1) orientation, except low doping concentration (<6 at%). No impurities were found by X-ray diffraction and electron diffraction measurement. The doped Mn ions substituted Cu ions in the Cu₂O lattice and there were about 1.5% cation vacancies. The grains shown in the transmission electron microscopy (TEM) images for all the samples were tiny, i.e. just 5 nm in diameter. A rough phase diagram for the ferromagnetic order existing in the Mn-doped Cu₂O thin films was given with varying Mn doping concentration and deposition temperature.     

Ag掺杂氧化锌纳米材料的制备及高压相变拉曼光谱研究

宽禁带直接带隙半导体材料氧化锌（ZnO）,具有优异的光电性能、机械性能和化学特性。ZnO材料的结构对其性能影响较大,元素掺杂可改变ZnO晶体结构和带隙宽度,是提升ZnO材料性能的有效手段,当前常用Ag掺杂ZnO即为提高光催化反应效率。高压独立于温度、成分,是调控材料结构组织性能的重要手段,是产生新材料、发现新调控原理的重要因素。该研究通过对比纯ZnO晶体和Ag掺杂ZnO晶体的高压相变行为,揭示了元素掺杂对ZnO纳米晶体材料结构性能的影响。研究首先采用水热法辅助制备纯ZnO纳米微球和Ag掺杂ZnO纳米微球（1∶150Ag/ZnO）,表征结果显示水热法合成的纯ZnO和1∶150Ag/ZnO均为六角纤锌矿晶体结构,形貌均为几十纳米尺寸小颗粒堆积形成的微球,ZnO晶格常数随着Ag离子掺杂而变大,Ag掺杂导致ZnO晶格膨胀。随后应用金刚石压腔结合原位拉曼光谱技术测定了纯ZnO和Ag掺杂ZnO的高压结构相变行为。相比于纯ZnO拉曼峰,Ag掺杂ZnO的E₂（high）振动模式439 cm-1拉曼峰峰宽变窄,并呈现向低频方向移动的趋势,与无定形ZnO谱峰相近,表明Ag+取代Zn2+影响了Zn-O键,同时也影响了ZnO晶格结构的长程有序性。随体系压力增大,表征六角纤锌矿结构ZnO的拉曼特征峰439 cm-1出现瞬间弱化和宽化。压力增大至9.0 GPa时,纤锌矿结构ZnO拉曼特征峰439 cm-1消失,585 cm-1处出现新峰,ZnO晶体发生由六角纤锌矿向岩盐矿的结构转变。压力继续增大至11.5 GPa,新的拉曼峰显著增强,峰形变窄,同时向高波数方向移动,相变完成,岩盐矿结构ZnO性能稳定。1∶150 Ag/ZnO从六角纤锌矿结构到立方岩盐结构的相变压力为7.2 GPa,低于纯ZnO。相变压力降低表明晶体结构稳定性下降,可能的原因在于掺杂Ag导致ZnO晶格膨胀,晶体结构松弛,两相相对体积变化增加,从而导致相变势垒降低,使样品在较低压力下发生相变。纳米材料的高压研究揭示了元素掺杂对材料结构稳定性的影响,是纳米材料调控原理的潜在研究手段。     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

Room-Temperature Ferromagnetic ZnMnO Thin Films Synthesized by Plasma Enhanced Chemical Vapour Deposition Method

Room-temperature ferromagnetic Mn-doped ZnO films are grown on Si （001） substrates by plasma enhanced chemical vapour deposition （PECVD）. X-ray diffraction measurements reveal that the Znl-xMn.O films have the single-phase wurtzite structure. X-ray photoelectron spectroscopy indicates the existence of Mn^2＋ ions in Mndoped ZnO films. Furthermore, the decreasing additional Raman peak with increasing Mn-doping is considered to relate to the substitution of Mn ions for the Zn ions in ZnO lattice. Superconducting quantum interference device （SQUID） measurements demonstrate that Mn-doped ZnO films have ferromagnetic behaviour at room temperature.     

Photoluminescence of ZnO and Mn-Doped ZnO Polycrystalline Films Prepared by Plasma Enhanced Chemical Vapour Deposition

ZnO and Mn-doped ZnO polycrystalline films are prepared by plasma enhanced chemical vapour deposition at low temperature （220℃）, and room-temperature photoluminescence of the films is systematically investigated. Analysis from x-ray diffraction reveals that a11 the prepared films exhibit the wurtzite structure of ZnO, and Mndoping does not induce the second phase in the films. X-ray photoelectron spectroscopy confirms the existence of Mn^2＋ ions in the films rather than metalic Mn or Mn^4＋ ions. The emission efficiency of the ZnO film is found to be dependent strongly on the post-treatment and to degrade with increasing temperature either in air or in nitrogen ambient. However, the enhancement of near band edge （NBE） emission is observed after hydrogenation in ammonia plasma, companied with more defect-related emission. Furthermore, the position of NBE shifts towards to high-energy legion with increasing Mn-doped concentration due to Mn incorporation into ZnO lattice.     

Structural stability,electronic structure and mechanical properties of 4d transition metal nitrides TMN (TM=Ru,Rh, Pd)

Ab initio calculations are performed to investigate the structural stability, electronic, structural and mechanical properties of 4d transition metal nitrides TMN (TM=Ru, Rh, Pd) for five different crystal structures, namely NaCl, CsCl, zinc blende, NiAs and wurtzite. Among the considered structures, zinc blende structure is found to be the most stable one among all three nitrides at normal pressure. A structural phase transition from ZB to NiAs phase is predicted at a pressure of 104 GPa, 50.5 GPa and 56 GPa for RuN, RhN and PdN respectively. The electronic structure reveals that these nitrides are metallic. The calculated elastic constants indicate that these nitrides are mechanically stable at ambient condition.     

Effects of doping concentration on properties of Mn-doped ZnO thin films

This paper reports that the radio frequency magnetron sputtering is used to fabricate ZnO and Mn-doped ZnO thin films on glass substrates at 500~°C. The Mn-doped ZnO thin films present wurtzite structure of ZnO and have a smoother surface, better conductivity but no ferromagnetism. The x-ray photoelectron spectroscopy results show that the binding energy of Mn_2p3 / 2 increases with increasing Mn content slightly, and the state of Mn in the Mn-doped ZnO thin films is divalent. The chemisorbed oxygen in the Mn-doped ZnO thin films increases with increasing Mn doping concentration. The photoluminescence spectra of ZnO and Mn-doped ZnO thin films have a similar ultraviolet emission. The yellow green emissions of 4~wt.% and 10~wt.% Mn-doped thin films are quenched, whereas the yellow green emission occurs because of abundant oxygen vacancies in the Mn-doped ZnO thin films after 20~wt.% Mn doping. Compared with pure ZnO thin film, the bandgap of the Mn-doped ZnO thin films increases with increasing Mn content.     

Experimental constraints on the phase diagram of elemental zirconium

The phase diagram of zirconium metal has been studied using synchrotron X-ray diffraction and time-of-flight neutron scattering at temperatures and pressures up to 1273 K and 17 GPa. The equilibrium phase boundary of the α-ω transition has a dT/dP slope of 473 K/GPa, and the extrapolated transition pressure at ambient temperature is located at 3.4 GPa. For the ω-β transition, the phase boundary has a negative dT/dP slope of 15.5 K/GPa between 6.4 and 15.3 GPa, which is substantially smaller than a previously reported value of −39±5 K/GPa in the pressure range of 32-35 GPa. This difference indicates a significant curvature of the phase boundary between 15.3 and 35 GPa. The α-ω-β triple point was estimated to be at 4.9 GPa and 953 K, which is comparable to previous results obtained from a differential thermal analysis. Except for the three known crystalline forms, the β phase of zirconium metal was found to possess an extraordinary glass forming ability at pressures between 6.4 and 8.6 GPa. This transformation leads to a limited stability field for the β phase in the pressure range of 6-16 GPa and to complications of high-temperature portion of phase diagram for zirconium metal.     

Effect of Mn doping on the structural and optical properties of sol-gel derived ZnO nanoparticles

Un-doped and Mn-doped ZnO nanoparticles were successfully synthesized in an ethanolic solution by using a sol-gel method. Material properties of the samples dependence on preparation conditions and Mn concentrations were investigated while other parameters were controlled to ensure reproducibility. It was observed that the structural properties, particle size, band gap, photoluminescence intensity and wavelength of maximum intensity were influenced by the amount of Mn ions present in the precursor. The XRD spectra for ZnO nanoparticles show the entire peaks corresponding to the various planes of wurtzite ZnO, indicating a single phase. The diffraction peaks of doped samples are slightly shifted to lower angles with an increase in the Mn ion concentration, signifying the expansion of the lattice constants and increase in the band gap of ZnO. All the samples show the absorption in the visible region. The absorbance spectra show that the excitonic absorption peak shifts towards the lower wavelength side with the Mn-doped ZnO nanoparticles. The PL spectra of undoped ZnO consist of UV emission at 388 nm and broad visible emission at 560 nm with varying relative peak intensities. The doping of ZnO with Mn quenches significantly the green emission while UV luminescence is slightly affected.     

Synthesis and characterization of Mn-doped ZnO column arrays

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.     

The structural and optical properties of ZnO bulk and nanocrystals under high pressure

The elastic properties of high-quality ZnO crystals and nanopowder of grain size of about 65 nm are studied for both wurtzite (low pressure) and rock-salt high pressure phases. The measured values of bulk moduli for wurtzite and rock-salt phases of bulk ZnO crystals are equal to 156±13 and 187±20 GPa, respectively, and considerably larger for ZnO nanocrystals. The phase transition begins at a pressure of about 9 GPa and it is completed at a pressure of about 13.8 GPa for bulk crystals, whereas the values of pressure at which the phase transition occurs are lower for nanocrystals. A carefull Rietveld analysis of the obtained data does not exhibit the presence of any intermediate phases between low pressure wurtzite and high pressure rock-salt phases of ZnO. The phase transition is accompanied by a strong decrease in the near-band-gap photoluminescence intensity. In addition, the pressure coefficient of the near-band-gap luminescence in ZnO nanocrystals exhibits strong deviation from the linearity observed in bulk crystals. An analysis of the results shows that defects present in the nanopowdered sample are responsible for the observed effects.     

Structural study of Mn-doped ZnO films by TEM

The structural study of diluted magnetic semiconductors is important for interpreting the ferromagnetic behavior associated with the materials. In the present work, a series of low concentration Mn-doped ZnO thin films synthesized by pulsed laser deposition was studied by electron microscopy. All films show the wurtzite structure with (001) preferred growth orientation on the Si substrate. Electron diffraction experiments indicate the deterioration of the growth orientation in some areas of the films with increasing Mn concentration, and the existence of a secondary phase, of Mn₂O₃-type, in the films with larger Mn concentrations. High-resolution electron microscopy images confirm the existence of the secondary phase in the grain boundary of the Mn-doped ZnO phase. The magnetic properties of Mn-doped ZnO are discussed in relation to the structures of the films.     

Synthesis of Mn-doped ZnO diluted magnetic semiconductors in the presence of ethyl acetoacetate under solvothermal conditions

Mn-doped ZnO samples with 5%, 20% and 40% nominal Mn concentrations were prepared in the presence of ethyl acetoacetate under solvothermal conditions. UV absorption spectroscopic analysis discloses that chemical modification was achieved by reaction of Zn or Mn precursor with ethyl acetoacetate in ethanol medium. XRD and HRTEM characterizations indicate that ZnMnO₃ impurity phase was formed in the 20% and 40% Mn-doped ZnO samples while no secondary phase was present in the 5% Mn-doped sample. The 5% Mn-doped sample consists of spheroid-like particles with size of 10-50 nm and has a real Mn concentration of 3.2%. Ferromagnetism and paramagnetism coexist in the 5% Mn-doped ZnO sample at room-temperature, which may arise from ferromagnetic exchange interaction as well as small secondary phases. The 20% and 40% Mn-doped samples show large paramagnetic effects at room temperature. Small paramagnetic secondary phases and clustering of Mn are probably responsible for this.     

Structure of nanocrystalline ZnO up to 85 GPa

The structure of nanocrystalline and bulk polycrystalline ZnO were examined up to 85 GPa and 50 GPa, respectively using synchrotron X-rays and diamond anvil cells at ambient conditions. The transition from the wurtzite to the rock salt phase in the nano-ZnO takes place at 10.5 GPa; this transition pressure is 1.5 GPa higher than in bulk ZnO. A large volume collapse of about 17.5% is observed during the transition in both systems. The rocksalt phase is stable and no structural transitions are observed for both compounds at higher pressures up to the experimental limit. On decompression the rocksalt phase is found to co-exist with the wurtzite phase at ambient conditions for the nano-ZnO.     

An experimental exploration of chemical bond characteristic,bulk modulus and phase stability in ZnO:Cu nanocrystals under high pressure

The high pressure induced phase transitions in Zn_1−x Cu _x O (x=0.005 and 0.011) are investigated by angle-dispersive synchrotron radiation X-ray diffraction. As the pressure increases, phase transformations from the wurtzite structure to the rocksalt structure are observed in both samples, with the transition pressures at 9.8 GPa and 7.9 GPa, respectively. With the increasing of the Cu-doping concentration in ZnO, crystalline parameters, the bulk moduli, and the Zn–O bond lengths all increased, meanwhile, the transition pressures decreased. The results could be explained in terms of the reduction of phase transformation barriers and the lowering of bond energy.     

Impurity effects on the phase transformations and equations of state of zirconium metals

The in situ high P-T X-ray diffraction experiments were conducted at pressures up to 17 GPa and temperatures up to 1273 K to study the phase transformations and equations of state for two grades of zirconium metals. At ambient temperature, our results reveal significant differences in both the transition pressure and kinetics of the α-ω phase transformation between the ultra-pure Zr (35 ppm Hf and <50 ppm O) and impure Zr (1.03 at% Hf and 4.5 at% O). These observations indicate that impurities, particularly oxygen ions, play important roles in the transformation mechanisms as well as crystal stability. On the other hand, impurities have no measurable effects on either the elastic bulk moduli of both α and ω phases or the volume change across the α-ω phase transformation. At elevated temperature, both impure and ultra-pure Zr show similar transition temperatures for the ω-β phase boundary over a pressure range of 6-16 GPa, suggesting that impure oxygen and hafnium ions can only be an α-Zr stabilizer; they do not seem to significantly increase the stability of the ω-Zr relative to the β-Zr.     

Characterizations of n-type ferromagnetic GaMnN thin film grown on GaN/Al2O3 (0 0 0 1) by metal-organic chemical vapor deposition

A high-quality ferromagnetic GaMnN (Mn=2.8 at%) film was deposited onto a GaN buffer/Al₂O₃(0 0 0 1) at 885 °C using the metal-organic chemical vapor deposition (MOCVD) process. The GaMnN film shows a highly c-axis-oriented hexagonal wurtzite structure, implying that Mn doping into GaN does not influence the crystallinity of the film. No Mn-related secondary phases were found in the GaMnN film by means of a high-flux X-ray diffraction analysis. The composition profiles of Ga, Mn, and N maintain nearly constant levels in depth profiles of the GaMnN film. The binding energy peak of the Mn 2p_3/2 orbital was observed at 642.3 eV corresponding to the Mn (III) oxidation state of MnN. The presence of metallic Mn clusters (binding energy: 640.9 eV) in the GaMnN film was excluded. A broad yellow emission around 2.2 eV as well as a relatively weak near-band-edge emission at 3.39 eV was observed in a Mn-doped GaN film, while the undoped GaN film only shows a near-band-edge emission at 3.37 eV. The Mn-doped GaN film showed n-type semiconducting characteristics; the electron carrier concentration was 1.2×10²¹/cm³ and the resistivity was 3.9×10⁻³ Ω cm. Ferromagnetic hysteresis loops were observed at 300 K with a magnetic field parallel and perpendicular to the ab plane. The zero-field-cooled and field-cooled curves at temperatures ranging from 10 to 350 K strongly indicate that the GaMnN film is ferromagnetic at least up to 350 K. A coercive field of 250 Oe and effective magnetic moment of 0.0003 μ_B/Mn were obtained. The n-type semiconducting behavior plays a role in inducing ferromagnetism in the GaMnN film, and the observed ferromagnetism is appropriately explained by a double exchange mechanism.     

Effect of Mn doping on the nanostructure and optical properties of ZnO films synthesized by magnetron sputtering

We investigated the microstructure and optical properties of Zn_1−xMn_xO 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.     

On the paramagnetic behavior of heavily doped Zn1−xMnxO films fabricated by Pechini’s method

Heavily doped Zn_1−xMn_xO (x = 0.3) films were prepared by polymeric precursor method onto glass substrates and their structural, morphological, optical and magnetic properties carefully studied. Undoped ZnO films were also prepared for the purpose of comparison. The polymeric precursor method consists in preparing a coating solution from the Pechini process followed by a three-step thermal treatment of the as deposited films at temperatures up to 550 °C for 30 min. X-ray diffraction (XRD) analysis reveals the typical hexagonal wurtzite structure of the undoped ZnO film. The addition of Mn ions leads to a dramatic reduction of the crystalline quality of film although no evidence of affectation by secondary phases is found. The affectation of the ZnO structure may be due to the formation of Mn clusters and generation of defects such as vacancies and interstitials. Here, the solubility limit of the Mn ions in ZnO should play an important role and it is discussed in the framework of ionic radius and valence states. The scanning electron microscopy (SEM) analysis shows that the surface of the doped sample was affected by the presence of cracks due, probably, to the expansion of the lattice constant of Zn_0.7Mn_0.3O caused by the Mn incorporation in the ZnO lattice. The existence of cluster-type structures on the surface is corroborated by atomic force microscopy (AFM). The EDX analysis, carried out on some areas in the film, yielded Mn/Zn ratios of about 0.3, which points out to an effective Mn incorporation in the film. On the other hand, the absorption edge of the doped films is red shifted to 2.9 eV (3.24 eV for undoped ZnO film) and the absorption edge is less sharp due, probably, to amorphous states appearing in the band gap. No evidence of dilute magnetic semiconductor mean-field ferromagnetic behavior is observed. The temperature dependence of the magnetization follows a Curie law suggesting pure paramagnetic behavior. The very small s-shape behavior of M versus H (without hysteresis) observed at room temperature on selected areas would stem from Mn clusters which are easily formed in transition metal doped ZnO.