Mn Films Research Articles

Structural and optical properties of an undoped and Mn doped ZnO nanocrysatlline thin film

In this study a ZnO:Mn nano structured film doped with manganese of different concentrations is deposited on glass substrates by the sol-gel dip coating method. Characterization techniques of XRD, SEM with EDAX and UV-Visible spectra measurements were done to investigate the effect of an Mn doping concentration on the optical and structural properties of a ZnO:Mn nanostructured thin film. XRD patterns of all nanostructured thin film show crystallization behavior and have a hexagonal wurtzite structure. Optical studies show that the band gap of ZnO:Mn decreases because of the d electron of Mn atom and band carriers of the host material. Full text: PDF

Preparation and structural characterization of Zn1−xMnxSe thin films

Undoped and Mn doped ZnSe nanoparticles thin films of thickness ranging from 20 to 120 nm have been successfully synthesized via inert gas condensation (IGC) technique with constant Argon gas flow rate and deposition temperature 300 K. The energy dispersive X-ray analysis (EDX) for freshly deposited Zn1−xMnxSe thin films were carried out and revealed that Mn contents (x) were 0, 0.05, 0.16 and 0.25. The as-prepared deposited thin films of different thickness were examined using transmission electron microscope (TEM) and showed that all films were nanocrystalline with particle size ranging from 4.1 to 6.6 nm. The grazing incident in-plane X-ray diffraction (GIIXD) patterns verified nanocrystalline single phase zinc blende structure for 80 nm film thickness for all examined Zn1−xMnxSe compound films. A broadening of main characteristic lines (111), (220) and (311) of cubic phase was observed and was attributed to the lower particle size in nanocrystalline examined Zn1−xMnxSe compound films.

Structural and magnetic phase diagrams of epitaxial Cr–Mn alloy thin films

We report here a systematic study of Cr–Mn alloy films that have been epitaxially stabilized on GaSb (100) using molecular beam epitaxy. The crystal structural transition between the α-Cr-type and the α-Mn-type for the Cr–Mn alloy films is observed along with changes in growth temperature, film thickness, and the ratio of Cr to Mn. Ferrimagnetism is observed in the Cr–Mn films containing the α-Mn-type phase based on the magnetic field-dependent anomalous Hall effect hysteresis and is corroborated by the magnetization hysteresis. The α-Mn-type CrMn phase at the expanded lattice parameter induces the observed ferrimagnetic ordering. The magnetic moments of Cr–Mn films can be tuned by adjusting the growth temperature, film thickness, and the ratio of Cr to Mn. Eventually, new structural and magnetic phase diagrams of the epitaxial Cr–Mn alloy films are established. The results of this study can prove helpful in both forming a comprehensive understanding of Cr–Mn alloys and in finding new applications for it in spintronic devices.

Structural analysis and luminescent study of thin film zinc germanate doped with manganese

Thin films of zinc germanate doped with manganese (Zn 2GeO 4:Mn) were fabricated by radio frequency magnetron sputtering, and their structural characteristics and luminescent properties were studied. The Zn 2GeO 4:Mn films exhibited a pronounced absorption edge at around 271 nm and a high optical transparency in the visible wavelength region with a peak transmittance of 0.927 at 691 nm. While the as-deposited Zn 2GeO 4:Mn films had an amorphous structure, the annealed films possessed a rhombohedral polycrystalline structure with a random crystallographic orientation of grains. The broad-band photoluminescence (PL) emission was observed from the annealed Zn 2GeO 4:Mn films. The PL emission spectrum showed a peak maximum at around 537 nm in the green range, which was accounted for by the intrashell transition of 3 d 5 orbital electrons from the 4T 1 lowest excitation state to the 6A 1 ground state in the divalent manganese ions. Two discrete peaks were observed in the PL excitation spectrum at 256 and 296 nm, which are considered to be associated with the band-to-band absorption of the host and the sub-band absorption from defect states, respectively. The green cathodoluminescence (CL) emission was obtained from the annealed Zn 2GeO 4:Mn films with a peak centered at around 534 nm, analogous to the PL emission spectrum.

Structure, optical, and magnetic properties of Mn-doped ZnO films prepared by sputtering

The microstructural, optical, and magnetic properties and room-temperature photoluminescence (PL) of Mn-doped ZnO thin films were studied. The chemical compositions were examined by energy dispersive X-ray spectroscopy (EDS) and the charge state of Mn ions in the ZnO:Mn films was characterized by X-ray photoelectronic spectrometry (XPS). From the X-ray diffraction (XRD) data of the samples, it can be found that Mn doping does not change the orientation of ZnO thin films. All the films prepared have a wurtzite structure and grow mainly along the c-axis orientation. The grain size and the residual stress were calculated from the XRD results. The optical transmittance of the film decreases with the increase of manganese content in ZnO. The room-temperature photoluminescence of the films shows that the intensity of near band energy (NBE) emission depends strongly on the Mn content. The hysteresis behavior indicates that the films with the Mn content below 9at% are ferromagnetic at room temperature.

Composition and Temperature Dependence of Electronic and Optical Properties in Manganese Doped Tin Dioxide Films on Quartz Substrates Prepared by Pulsed Laser Deposition

Manganese-doped tin dioxide (SnO2:Mn) films (grain size of about 16 nm) with different composition x from 2.5 to 15% have been grown on quartz substrates by pulsed laser deposition. X-ray diffraction analysis show that the films are polycrystalline and an impurity phase appears until the x is up to 15%. The optical functions in the photon energy range of 0.5−6.5 eV have been extracted by fitting the transmittance spectra at room temperature with the Adachi’s dielectric function model (Adachi, S. Phys. Rev. B 1987, 35, 7454). The refractive index generally decreases with the doping composition except for the film doped with 15% Mn because of the variation in crystalline formation and electronic energy band structure. Because of the repelling effect of 2p−3d hybridization and its perturbation on O 2p-like bands, the optical band gap linearly decreases and can be well expressed by (4.26−3.8x) eV. The transmittance spectra of the film doped with 2.5% Mn at the temperature varied from 5.3 to 300 K have been recorded and a redshift trend of the absorption edge with increasing the temperature can be observed. The results indicate that the dielectric functions decrease with the temperature at the photon energies above the fundamental band gap. Moreover, the optical band gap is shrinked from 4.30 to 4.20 eV with increasing the temperature because of the modification of the electron−phonon interactions. The band gap narrowing coefficient of the SnO2:Mn film with 2.5% Mn is estimated to be about −5.74 × 10−4 eV/K at room temperature.

Spinodal decomposition to control magnetotransport in (Ge,Mn) films

Changing the morphology of the growing surface and the nature of residual impurities in (Ge,Mn) layers dramatically changes nanospinodal decomposition, i.e., the morphology of ferromagnetic Mn-rich inclusions. By this way, we are able to control the magnetotransport properties of (Ge,Mn) films. By using different substrates and substrate preparation, we have indeed obtained $p$-type layers with nanocolumns, either parallel or entangled, and $n$-type layers with spherical clusters. Holes exhibit an anomalous Hall effect and electrons exhibit a tunneling magnetoresistance, both with a clear dependence on the magnetization of the Mn-rich inclusions; holes exhibit orbital MR and electrons show only the normal Hall effect, and an additional component of magnetoresistance due to weak localization, all three being independent of the magnetic state of the Mn-rich inclusions. Identified mechanisms point to the position of the Fermi level of the Mn-rich material with respect to the valence band of germanium as a crucial parameter for the control and the optimization of magnetotransport in such hybrid layers.

Optical and ferromagnetic characteristics of Mn doped ZnO thin films grown by filtered cathodic vacuum arc technique

Mn doped ZnO (ZnO:Mn) thin films with ~ 10 at.% of Mn were grown on quartz substrates by filtered cathodic vacuum arc (FCVA) technique at low substrate temperature (≤ 200 °C). The influence of substrate temperature and oxygen flow rate on the optical, electrical and magnetic properties of the ZnO:Mn thin films was studied. Both room temperature ferromagnetism and ultraviolet photoluminescence were observed in all films. A maximum saturation moment of 2.9 × 10 − 24 A m 2/Mn can be achieved for the films grown in an optimum condition. This suggests that the fabrication of high-quality ZnO:Mn films by FCVA technique has the potential to realize efficient magneto-optic devices operating at ultraviolet regime.

Exchange constant and domain wall width in (Ga,Mn)(As,P) films with self-organization of magnetic domains

The incorporation of Phosphorus into (Ga,Mn)As epilayers allows for the tuning of the magnetic easy axis from in-plane to perpendicular-to-plane without the need for a (Ga,In)As template. For perpendicular easy axis, using magneto-optical imaging a self-organized pattern of up- and down-magnetized domains is observed for the first time in a diluted magnetic semiconductor. Combining Kerr microscopy, magnetometry and ferromagnetic resonance spectroscopy, the exchange constant and the domain wall width parameter are obtained as a function of temperature. The former quantifies the effective Mn-Mn ferromagnetic interaction. The latter is a key parameter for domain wall dynamics. The comparison with results obtained for (Ga,Mn)As/(Ga,In)As reveals the improved quality of the (Ga,Mn)As$_{1-y}$P$_y$ layers regarding domain wall pinning, an increase of the domain wall width parameter and of the effective Mn-Mn spin coupling. However, at constant Mn doping, no significant increase of this coupling is found with increasing P concentration in the investigated range.

Fabrication and Performance of ACTFEL Display Devices Using Manganese-Doped Zinc Germanate as a Green-Emitting Electroluminescent Layer

Alternating-current thin-film electroluminescent (ACTFEL) display devices fabricated using manganese-doped zinc germanate (Zn2GeO4:Mn) as a green-emitting electroluminescent layer material are described. The ACTFEL display devices were fabricated with a standard bottom emission structure having a multilayer stack of thin films in the metal/semiconductor/insulator/ metal (MSIM) configuration. The device was constructed on a transparent Corning glass substrate through which the emitted EL light passed. The Zn2GeO4:Mn emission layer was synthesized by using a RF magnetron sputter deposition method, followed by post-annealing at 700 C in air ambient for 1 hour. The obtained Zn2GeO4:Mn films were found to be polycrystalline with a rhombohedral crystal structure. A green emission spectrum with a maximum at approximately 538 nm was produced from the fabricated device. The chromaticity color coordinates of the EL emission were measured to be x = 0.308 and y = 0.657. The device demonstrated a sharp increase in the intensity of green EL emission upon increasing the AC peak voltage applied to the device above a threshold of 148 V.

Growth and magnetic order of Mn films onFe(001)−p(1×1)Ostudied by spin-polarized scanning tunneling microscopy

Mn films show improved layer-by-layer growth on the $\text{Fe}(001)\text{\ensuremath{-}}p(1\ifmmode\times\else\texttimes\fi{}1)\text{O}$ surface compared to the clean Fe(001) surface. From Auger electron spectroscopy the surfactant role of the oxygen was confirmed. A layerwise antiferromagnetic order in the Mn films is preserved as seen from the magnetic contrast between adjacent Mn layers in spin-polarized scanning tunneling microscopy while the surface spin polarization is enhanced by a factor 2 compared to Mn films grown on the clean Fe(001) surface. Further, topologically induced magnetic frustrations of the Mn layer above buried Fe steps appear wider than without oxygen.

A new reactive sputtering technique for the low temperature deposition of transparent light emitting ZnS:Mn thin films

The temperature sensitive nature of the substrates used in the flexible displays market necessitates a low temperature deposition technique for processing them. ZnS:Mn exhibiting high intensity photoluminescence (PL) and good crystallinity has been deposited onto Si wafers, glass microscope slides and polymeric substrates using a new reactive sputtering technology referred to as HiTUS. This technique enables very high deposition rates and requires no substrate heating. When incorporated as part of a complete EL device, as-deposited ZnS:Mn films are seen to exhibit stable electroluminescence on Si, glass and planarised PET substrate materials. Post annealing of the devices on Si and glass at temperatures of up to 600 °C show that the HiTUS films perform better than equivalent ZnS:Mn films deposited using RF magnetron sputtering.

Epitaxial growth and ferrimagnetic properties of Mn film on GaSb(100)

We report on the epitaxial stabilization and magnetic properties of Mn films on GaSb(100) using molecular beam epitaxy, a follow-up to our previous work on the growth of Mn films on GaAs(100) [Phys. Rev. B 79, 045309 (2009)]. A strong ferrimagnetic ordering was observed which was attributed to the largely expanded lattice parameter resulting from the lattice mismatch with substrate and the enhanced thermal energy with increasing growth temperature. The observed magnetic moment of 1.16μB/Mn atom was several times larger than that observed in the Mn/GaAs(100) films due to the lattice constant difference of substrates. The in-plane magnetoresistance behavior demonstrated the magnetic anisotropy that might result from the slightly distorted cubic structure of α-Mn phase under low-dimensional growth.

Effect of hydrogen on interface of metal–semiconductor Schottky diode

The effect of hydrogen on p-type Si/Mn and Si/Co Schottky diode has been investigated in present studies. The variations of I– V characteristics suggested that the rectifying act of these diodes change with variation of hydrogen pressure, which is due to the diffusion of hydrogen through the Mn and Co metal films up to Si surface or a creation of surface states at the interface. It is also observed that the effect of hydrogen found to be reverse in order for forward as well as reverse direction of current in Mn and Co deposited films on Si substrate, corresponding to anionic and protonic model of hydrogen interaction with metals. One can say that hydrogen plays an amphoteric role to neutralize either donors or acceptors level in semiconductors and metals. The Raman spectra of Si/Mn and Si/Co are taken and stoke lines link with the presence of hydrogen is observed. In this paper, we are presenting the role of hydrogen pressure on I– V characteristics at the interface of metal–semiconductor structure.

Irradiation induced modifications in morphology and magnetic property of Mn/Si structure

Mn films of ∼50 nm has been deposited by electron beam evaporation technique on cleaned and etched Si [(1 0 0), 8–10 Ω cm] substrates to realize a Mn/Si interfacial structures. The structures have been irradiated from energetic (∼100 MeV) ion beam from Mn side. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry, magnetic force microscopy, and vibrating sample magnetometer facilities. It has been found that surface/interfacial granular silicide phases (of Mn x Si y ) are formed before and after the irradiation with a irradiation induced modifications of surface morphology and magnetic property. The surface/interface roughness has been found to increase on the irradiation from the atomic force microscopy data. The magnetic property on the irradiation shows an interesting and significant feature of an increased coercivity and a ferromagnetic like behavior in the Mn–Si structure. The observed increased coercivity has been related to the increased roughness on the irradiation. The ferromagnetism after the irradiation is a curious phenomenon which seems due to the formation of Mn–C–Si compound from the carbon dissolved in silicon.

Preparation and photoemission investigation of bulklikeα-Mnfilms on W(110)

We report the successful stabilization of a thick bulk-like, distorted $\alpha$-Mn film with (110) orientation on a W(110) substrate. The observed $(3\times3)$ overstructure for the Mn film with respect to the original W(110) low-energy electron diffraction pattern is consistent with the presented structure model. The possibility to stabilize such a pseudomorphic Mn film is supported by density functional total energy calculations. Angle-resolved photoemission spectra of the stabilized $\alpha$-Mn(110) film show weak dispersions of the valence band electronic states in accordance with the large unit cell.

Role of carrier and spin in tuning ferromagnetism in Mn and Cr-doped In2O3 thin films

Mn and Cr-doped In2O3 films with Sn codoping were deposited on sapphire substrate by pulsed laser deposition. The ferromagnetism of Mn-doped In2O3 films shows reversible behavior, which can be switched between “on” and “off” states by controlling the carrier density via varying Sn concentration. The enhanced ferromagnetism in Cr-doped In2O3 films is observed due to the significant increase in the carrier density with Sn doping, and the saturation magnetization can reach 2.10 μB/Cr. Most importantly, both of the experiment results reveal that the carrier density and the net spin are two crucial factors for producing and tuning ferromagnetism.

Opto–magnetic interaction between electrochemiluminescent CdS : Mn film and Fe3O4 nanoparticles and its application to immunosensing

This work firstly reports an opto-magnetic interaction-induced enhancement of electrochemiluminescence (ECL) from CdS : Mn nanocrystals (NCs) film by superparamagnetic Fe(3)O(4) nanoparticles and its application to sensitive immunosensing.

Effect of oxygen pressure on room-temperature ferromagnetism of Al co-doped Mn doped ZnO thin films prepared by pulsed laser deposition

Thin films of Al and Mn doped ZnO (Zn0.97Mn0.02Al0.01O) were made using Pulsed Laser Deposition technique (PLD) on Si substrates maintained at a constant temperature of 400°C, under varying pressures of oxygen (O2) and at a fixed pressure of 400 μbar nitrogen (N2) atmospheres. X-ray diffraction (XRD) patterns of the deposited films indicated that they are predominantly oriented in the [002] direction. Magnetisation measurements as a function of field on these samples showed that the magnetic moment is sensitive to the O2 pressure and the film deposited at 400 μbar of O2 pressure shows significantly increased magnetic moment (4.44 μB/Mn) compared to other films. Depositing the film in N2 atmosphere or changing the O2 pressure to higher or lower values affected the magnetisation adversely. Magnetisation measurement, as a function of temperature, done on 400 μbar O2 deposited film further confirmed its room temperature ferromagnetic behaviour (RTF).

(Ge,Mn): A ferromagnetic semiconductor for spin injection in silicon

Spin injection in semiconductors has been a long-standing issue in the field of spintronics for nearly 10 years. Only at the end of the 1990s, electrical spin injection in III-V semiconductors could be demonstrated using spin-light emitting diodes as spin detectors. Although silicon is the key material of microelectronics, spin injection in silicon could be achieved only recently in 2007. For this purpose, we have developed a new ferromagnetic semiconductor (Ge,Mn) that may be suitable for spin injection in silicon. Indeed this material is compatible with mainstream silicon technology and is predicted as a half-metallic ferromagnet. We have used low temperature molecular beam epitaxy to grow germanium films doped with manganese. Growth temperatures as well as Mn concentrations were kept low in order to avoid phase separation due to the low solubility of Mn in Ge. Careful structural and chemical analyses showed that (Ge,Mn) films are not diluted magnetic semiconductors. We rather observe high-TC ferromagnetic self-assembled nanocolumns in the germanium film with magnetic properties strongly dependent on growth parameters. We could clearly identify four different magnetic phases in Ge1−xMnx films: diluted paramagnetic Mn atoms in the germanium matrix, low TC ( 400 K) and Ge3Mn5 clusters. The relative weight of each phase mainly depends on the growth temperature and to a lesser extent to Mn concentration. In parallel, we have developed methods to detect spin injection in silicon. Using a ferromagnetic metal with perpendicular magnetisation we could perform spin injection in silicon in the tunnelling regime through an alumina barrier. Spin detection was optically achieved using a SiGe/Si spin-light emitting diode without applying a magnetic field.