Mn Films Research Articles

Scanning tunneling microscopy studies of the formation and coarsening of manganese silicides on Si(111)

Solid-phase epitaxial growth of manganese silicides on a Si(111)-7×7 surface at temperatures between room temperature and ∼750 °C has been studied using scanning tunneling microscopy. The as-deposited Mn film of ∼0.6–1 ML shows an ordered honeycomb structure with each Mn cluster occupying a half of the 7×7 unit cell. The Mn clusters begin to react with the Si substrate to form silicides at ∼250 °C. Two types of silicides, the three-dimensional (3D) and tabular islands, which correspond to Mn-rich silicides and monosilicide MnSi, respectively, coexist on the Si(111) surface at annealing temperatures between 250 and 500 °C. At 500 °C annealing, all 3D islands convert into tabular islands and MnSi is the only Mn silicide phase. Above 600 °C, the tabular islands convert into large 3D islands that are likely to be Si-rich manganese silicides. With increasing annealing temperature and time, the number density of silicide islands decreases, while the average size (area) of the remaining islands increases. The growth of large islands is a result of the dissolution of small ones, which can be understood in the context of Ostwald ripening mechanism.

Mn-doped ZnO transparent conducting films deposited by DC magnetron sputtering

Abstract Mn-doped zinc oxide (ZnO:Mn) thin films with low resistivity and relatively high transparency were firstly prepared on glass substrate by direct current (DC) magnetron sputtering at room temperature. Influence of film thickness on the properties of ZnO:Mn films was investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that all the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c -axis perpendicular to the substrate. As the thickness increases from 144 to 479 nm, the crystallite size increases while the electrical resistivity decreases. However, as the thickness increases from 479 to 783 nm, the crystallite size decreases and the electrical resistivity increases. When film thickness is 479 nm, the deposited films have the lowest resistivity of 2.1 × 10 − 4 Ω cm and a relatively high transmittance of above 84% in the visible range.

Room temperature paramagnetism of ZnO:Mn films grown by RF-sputtering

ZnO:Mn transparent thin films (thickness < 1 μm) with the Mn contents ranging from 1.8 to 3.25 at.% were grown by RF magnetron co-sputtering. The films are nanocrystalline, with wurtzite-structure grains of a typical size of 20 nm and with a preferential orientation of the c-axis perpendicular to the surface. According to the Raman spectroscopy data, Mn mostly substitutes Zn in the lattice sites. In spite of these factors, the nanostructure and the Mn(Zn) substitution, that are considered favorable for ferromagnetism in this material, both magnetic resonance and Faraday effect measurements show paramagnetic behavior of the ZnO:Mn films and the absence of ferromagnetic order at room temperature.

Influence of Mn incorporation on the structural and optical properties of sol gel derived ZnO film

Undoped and manganese doped ZnO (ZnO:Mn) films were prepared by sol gel method using spin coating technique. The effect of Mn incorporation on the structural and optical properties of the ZnO film has been investigated. The crystalline structure and orientation of the films have been investigated by using their X-ray diffraction spectra. The films exhibit a polycrystalline structure. Mn incorporation led to substantial changes in the structural characteristics of the ZnO film. The scanning electron microscopy (SEM) images of the films showed that the surface morphology of the ZnO film was affected by the Mn incorporation. The transparency of the ZnO film decreased with the Mn incorporation. The optical band gap and Urbach energy values of the ZnO and ZnO:Mn films were found to be 3.22, 3.19 eV and 0.10, 0.23 eV, respectively. The optical constants of these films, such as refractive index, extinction coefficient and optical dielectric constants were determined using transmittance and reflectance spectra. The refractive index dispersion curve of the films obeys the single oscillator model with dispersion parameters. The oscillator energy, E o , and dispersion energy, E d, of the films were determined 5.30 and 16.26 eV for ZnO film and 5.80 and 12.14 eV for ZnO:Mn film, respectively.

ZnO:Mn nanorods and ZnO/ZnO:Mn core/shell structures: Synthesis and local atomic structure

Investigation on local atomic structure of ZnO:Mn nanorods, thin films and nanoscale core/shell structures ZnO nanorods/ZnO:Mn film (10% Mn concentration) has been performed. The structures are synthesized with high pressure pulsed-laser deposition (PLD) method. Synthesis and growth of the studied structures have been considered in detail for the determination of Mn embeddings and impurities in ZnO host lattice. Theoretical analysis of experimental data have been carried out using a self-consistent real space multiple scattering method (FEFF8.4 code) and a finite difference method (FDMNES2008 code). Local structure parameters have been refined using multidimensional interpolation approach on the basis of fitting XANES spectra (Fitit2.0 code). The samples synthesized under certain condition may contain both Mn embeddings and secondary phases. It is found that the most probable model of the Mn embeddings is the structure where Mn atoms substitute for Zn atoms but a part of Mn atoms is located in interstitial sites in ZnO host lattice.

Percolation ferromagnetism and spin waves in Ge:Mn thin films

We studied magnetic properties of thin Ge:Mn films obtained by implantation of Mn+ ions into a single crystalline bulk germanium. In the net magnetic moment we were able to separate contributions originating from dispersed Mn2+ ions, ferromagnetic Mn5Ge3 precipitates, and regions of the germanium matrix enriched with diluted manganese -MnmGen alloys. In the subsystem of dispersed Mn2+ ions we observed a percolation transition into the ferromagnetic state at T13 K. Collective excitations, standing spin waves, were also detected below this temperature. The main parameters of the exchange interaction obtained from the analysis of the experimental spin-wave resonance data are consistent with results acquired from static magnetic measurements as well as with theoretical estimations for a percolation ferromagnet. Thus, we demonstrate that low-temperature magnetic properties of group IV magnetic semiconductor can be successfully explained within a magnetic polaron model.

Phase transformations in Mn/Fe(001) films: Structural and magnetic investigations

The solid-phase synthesis in epitaxial Mn/Fe(001) bilayer film systems with 24 at % of Mn has been shown to start at a temperature of 220°C with the formation of a γ-austenite lattice and the Mn and Fe films react completely under annealing to 600°C. In the sample cooling process after annealing below 220°C, the γ austenite undergoes a martensitic transformation to an oriented ∈(100) martensite. When the annealing temperature is increased above 600°C, Mn atoms migrate from the γ-lattice, which becomes unstable, and the film is partially again transformed to the epitaxial Fe(001) layer. The solid-phase synthesis in Mn/Fe(001) bilayer nanofilms and multilayers is assumingly determined by the inverse e → γ martensitic transformation in the Mn-Fe system. The existence of a new low-temperature (∼220°C) structure transition in the Mn-Fe system with a high iron content is assumed.

Influence of Mn-oxide Nanoclusters on the Electric Properties ofZnO:Mn Films

Polycrystalline ZnO:Mn films have been deposited on Si substrates by using ultrasonic spray pyrolysis methods. ZnO:Mn (3%) films show hysteretic behaviors in the I-V curves and these behaviors are related to charging and discharging of Mn-oxide nanoclusters. The conditions for hysteresis to appear depend on the sizes of the formed Mn-oxide nanoclusters close to the electrode interfaces.

Low-Temperature Growth of Nanocrystalline Mn-Doped ZnS Thin Films Prepared by Chemical Bath Deposition and Optical Properties

ZnS:Mn thin films were deposited on quartz, Si (polycrystalline), and glass substrates using a chemical bath deposition (CBD) method in an aqueous solution containing ethylene diamine tetra acetic acid disodium salt (Na2EDTA) as the complexing agent for zinc ions and thioacetamide (TAA) as the sulfide source at temperatures ranging from 50 to 80 °C. ZnS:Mn thin films with thicknesses ranging from 60 to 450 nm were synthesized at various Mn2+/Zn2+ molar ratios ranging from 1 to 4. The effects of the process parameters on the properties of ZnS:Mn films were investigated. The films were characterized by energy-dispersive X-ray spectrometer (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-AES), Rutherford backscattering (RBS), secondary ion mass spectrometry (SIMS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FE-SEM), ultraviolet -visible light (UV−vis) spectroscopy, and photoluminescence (PL) spectroscopy. The results showed that the deposition time, temperature, and Mn doping concentration can affect the composition, surface morphology, crystallinity, thickness, grain size, and hence, the photoluminescence and transmission spectra of the films. UV−vis transmission spectroscopy showed that the prepared films were highly transparent (>80%) in the visible region. X-ray diffraction showed that the films consisted of small ZnS:Mn nanocrystallites, 3.0−4.7 nm in size, showing quantum size effects. FE-SEM revealed a homogeneous morphology, dense nanostructures, and a narrow grain size distribution.

Magnetism in strained pseudomorphic ultrathin films of fcc 3d-transition metals (Cr, Mn, Fe, Co and Ni) with lateral lattice parameters of bulk fcc- [formula omitted

Pseudomorphic ultrathin (1–4 ML) free standing films, overlayers, and sandwiches of Cr, Mn, Fe, Co and Ni on fcc-Cu ( 0 0 1 ) are investigated using spin-polarized ab-initio calculations. All free standing thin films have quite high magnetic moment, with the exception of the 2 ML Mn film which has zero magnetic moment. Sandwiches show the same magnetic behavior as overlayers, but with reduced magnetic moments. The 3 ML overlayer of Fe has a different structure than any other overlayer structure. Sandwiches built of monolayers of Ni and Cr in Cu have zero magnetic moment. The ultrathin free standing films, overlayers and sandwiches of Cr, Mn and Fe exhibit an oscillating magnetic moment depending upon the number of layers. We attribute this to alternating ferromagnetic and antiferromagnetic coupling. On the contrary, thin films of Co and Ni always show a ferromagnetic coupling, with a magnetic moment per atom converging towards a constant value. The magnetic moment induced in Cu atoms at the interface is significant for Mn, Fe, and Co (0.02– 0.07 μ B ), while it is zero for the Ni/Cu interface.

Room-temperature ferromagnetism and in-plane magnetic anisotropy characteristics of nonpolar GaN:Mn films

Diluted magnetic nonpolar GaN:Mn films have been fabricated by implanting Mn ions into nonpolar a-plane ( 1 1 2 ¯ 0 ) p-type GaN films and a subsequent rapid thermal annealing process. The ferromagnetism properties of the films were studied by means of superconducting quantum interference device (SQUID). Clearly in-plane magnetic anisotropy characteristics of the sample at 10 K were revealed with the direction of the applied magnetic field rotating along the in-plane [0 0 0 1]-axis. Moreover, obvious ferromagnetic properties of the sample up to 350 K were detected by means of the temperature-dependent SQUID.

Highly efficient transparent Zn 2SiO 4:Mn 2+ phosphor film on quartz glass

Highly efficient transparent Zn 2SiO 4:Mn 2+ film phosphors on quartz substrates were deposited by the thermal diffusion of sputtered ZnO:Mn film. They show a textured structure with some preferred orientations. Our film phosphor shows, for the best photoluminescence (PL) brightness, a green PL brightness of about 20% of a commercial Zn 2SiO 4:Mn 2+ powder phosphor screen. The film shows a high transmittance of more than 10% at the red-color region. The excellence in PL brightness and transmittance can be explained in terms of the textured crystal growth with a continuous gradient of Zn 2SiO 4: Mn 2+ crystals.

Electrical and magnetic properties of Mn-doped Si thin films

Abstract We have studied electrical and magnetic properties of x at% Mn-doped Si thin films with high Mn concentrations (x at%=7.5, 9.1, and 11.3), which were prepared by molecular beam epitaxy. Our data reveals that the films are p-type semiconductors at room temperature, and their hole density is about 1020 cm−3. When temperature increases from 5 to 300 K, the resistivity of 7.5 at% Mn film decreases and can be described by Mott's variable-range-hopping model. The resistivity of 9.1 at% Mn film does not change remarkably. In contrast, the resistivity of 11.3 at% Mn film increases, indicating metallic characteristics at temperatures below 240 K. Magnetic measurements reveal that the films exhibit the low-temperature ferromagnetic ordering, which is largely related to the presence of secondary phase.

Ferromagnetic ordering in Mn induced by thermal strain

We report that the thermal strain due to the thermal-expansion difference between a Mn film and a semiconductor substrate is strong enough to overcome the thermal energy for a paramagnetic (PM) state and also to break antiferromagnetic (AF) magnetic symmetry, inducing ferromagnetic (FM) ordering at high temperatures. A Mn film on GaAs (100) showed FM ordering up to $9000\text{ }\text{\AA{}}$ with a Curie temperature $({T}_{C})$ of over 750 K and a net magnetic moment of $0.33{\ensuremath{\mu}}_{B}/\text{Mn}$, instead of AF (N\'eel temperature, ${T}_{N}=95\text{ }\text{K}$) and PM orderings in bulk.

Activation of room-temperature ferromagnetism in Mn doped ZnO thin films by N codoping

Mn doped ZnO films with and without N codoping have been fabricated by oxidative annealing of sputtered Zn:Mn and Zn2N3:Mn films on silicon substrates in flowing O2 ambient. It was found that the ZnO:Mn films show very weak ferromagnetic behavior, while for those with N codoping, significant ferromagnetism with a moderate saturation magnetization of about 0.23—0.61 μB per Mn2+ ion was observed at room temperature. It suggests that significant ferromagnetism in ZnO:Mn films could be activated by N codoping. The results indicate that holes are favorable for ferromagnetic ordering of the doped Mn2+ ions in ZnO, in agreement with the recent theoretical studies.

Growth of Epitaxial ZnO:Mn/ZnO:V Heterostructures and Ferroelectric-ferromagnetic Characterization

AbstractThe wide band gap semiconductor ZnO is well known for its multifunctionality in the form of ferromagnetism (FM), piezoelectricity, and magneto optics. ZnO has been found to grow with intrinsic oxygen deficiencies which in turn are believed to give ferromagnetism and high conductivity in this material. Doping Zn2+ sites by V5+ ions creates a mixed valency as well as strain in the original ZnO hexagonal structure because of the reduced ionic size of vanadium. The mixed valency creates charge polarity between Zn-O and V-O bonds. This charge polarity and the rotation of the nonlinear V-O bonds with respect to Zn-O bonds under electric field have been shown to produce ferroelectricity. Furthermore, Mn doping of ZnO has also shown enhancement in ferromagnetic properties in ZnO. For this material to be a viable ferromagnetic material the magnetic properties should not be from segregated phases. In the present study we have grown undoped, Mn, and V doped ZnO thin films using pulsed laser deposition (PLD). ZnO target with 2% atomic Mn doping and a target with 0.5% atomic V doping were prepared by solid state reactions and sintering. Films were grown both epitaxially on sapphire substrates and in polycrystalline form on silicon substrates. Magnetization measurements by the PPMS showed M vs. H hysteresis loops with saturation for all ZnO: Mn films. V doped films showed high saturation polarization for film deposited at high pressures. We have also fabricated epitaxial bilayers of ZnO:V/ZnO:Mn on sapphire substrates. Ferroelectric and ferromagnetic properties of these heterostructures are presented.

On the defect induced ferromagnetic ordering above room-temperature in undoped and Mn doped ZnO thin films

AbstractEvidence for long range ferromagnetic order above room-temperature, RTFM, in pristine ZnO, In2O3, TiO2 nanoparticles and thin films, containing no nominal magnetic elements have been reported recently. This could question the origin of RTFM in doped dilute alloys if for example the ZnO matrix itself develops a defect induced magnetic order with a significant moment per unit cell. In this presentation we report a systematic study of the film thickness dependence of RTFM in pure ZnO deposited by DC Magnetron Sputtering. We observe a maximum in the saturation magnetization, MS, value of 0.62 emu/g (0,018 μB/unit cell), for a ˜480 nm film deposited in an oxygen ambience of appropriate pressure. Above a thickness of around 1 μm the films are diamagnetic as expected. We thus see a sequential transition from ferromagnetism to para- and eventual diamagnetism as a function of film thickness in ZnO. We also find that in such a ZnO matrix with a maximum intrinsic defect induced moment, on doping with Mn the maximum enhanced MS value of 0.78 emu/g is obtained for 1at.% Mn doping. With this approach of appropriate doping in a defect tailored matrix, we routinely obtain RTFM in both undoped and Mn- doped ZnO thin films.

Suppression of conductivity in Mn-doped ZnO thin films

We studied the dopant concentration distribution and conductivity in ZnO:Mn films grown by metalorganic chemical vapor deposition. The ion beam, surface, and microstructural properties of undoped ZnO films were compared with Mn-doped ZnO films. Suppression of ZnO conductivity was observed for Mn doping up to ∼4.5 at. %. The presence of Mn2+, confirmed by x-ray photoelectron spectroscopy, is correlated with the reduction in conductivity. Variable-temperature Hall effect measurements yield an activation energy of 170 meV, consistent with deep donors in the bulk or at the interface. The results suggest that the incorporation of substitutional Mn suppresses the formation of native defects such as oxygen vacancies.

Physicochemical factors that affect the pseudocapacitance and cyclic stability of Mn oxide electrodes

Manganese (Mn) oxide was prepared by anodizing metallic Mn film that was electrodeposited in n-butylmethylpyrrolidinium bis(trifluoromethylsulfony)imide (BMP–NTf 2) ionic liquid. Different anodization courses, namely potentiostatic and cyclic voltammetric methods, led to variations in physical and chemical characteristics of the Mn oxides, and therefore in their pseudocapacitive performance. Evolution of the microstructure, residual weight, and chemical state of the Mn oxides with the charge–discharge cycling number was studied using a scanning electron microscope (SEM), an atomic absorption spectroscope, and an X-ray photoelectron spectroscope, respectively. The analytical results indicate that the electrochemical stability of Mn oxide is mainly determined by its microstructure; the more fibrous (or porous) oxide had a greater durability against cyclic charge–discharge. Moreover, the chemically hydrous state was found to be the most crucial factor that governed the mass specific capacitance of Mn oxide.

Annealing Effect of Mn thin Films on GaAs

Thin Mn films were deposited on GaAs(100) surfaces at room temperature by a thermal evaporation system followed by annealing at 500 °C for times ranging from 2 to 8 h in nitrogen atmosphere. X-ray diffraction shows that for samples annealed at 500 °C, the interfacial reaction results in the formation of different phases such as Mn2As, MnAs and Mn3Ga. Rutherford Backscattering Spectrometry indicates a diffused layer of Mn–Ga–As system along with some minor oxygen content. Magnetization study done at 10 K shows M–H curve comprising a ferromagnetic and antiferromagnetic part and M–T measurement done from 10 to 300 K shows a transition around 45 K which may be related to the presence of GaMnAs alloy along with the presence of the above binary phases.