MnO3 Thin Films Research Articles

Monitoring the growth of SrTiO3 and La0.66Sr0.33MnO3 thin films using a low-pressure Reflection High Energy Electron Diffraction system

Oxides display a variety of electronic phenomena, including ferroelectricity, magnetism or multiferroicity. Recently, a large interest has raised from the interfaces between two oxides of few unit cells, which show unexpected electronic properties such as superconductivity or magnetism. Thus, the structural quality of interfaces as well as a precise control of the thickness are main challenges for researchers who grow oxide films. To achieve such a high quality interface and a careful control of the growth, Reflection High Energy Electron Diffraction in-situ monitoring, is often used and mounted in a pulsed laser ablation system. While high pressure is widely utilized, low pressure is rarely utilized for oxides except when coupled to a molecular beam epitaxy (MBE) chamber. Here, the preparation of high-quality oxide thin films is reported and the different factors which affect the reliability of such an approach are presented, i.e. the correlation between the observed intensity oscillations and the deposited thickness. It is shown that oxides thin films grown on SrTiO3 single crystals, in a low-pressure environment with the laser-MBE system, possess extremely high physical characteristics (magnetoresistance, ferroelectricity, ferromagnetism, metal/insulating transition) very close to the bulk values and that the interface is nearly perfect, of the same quality as found for semiconductors.

(Invited) Wafer Level Fabrication Process of High Performance Micro-Supercapacitors

Nowadays, miniaturized power sources are key devices for providing autonomy to smart and connected sensors. To reach this goal, the current trend is to fabricate micro-storage unit such as microbatteries (MB) or microsupercapacitors (MSC) at the wafer level. According to the limited surface of such device, the metrics should be reported as normalized to the footprint area (mF, µWh and mW per cm2). With such metrics, the average energy density of most of MSC1,2 (Onions like carbon, graphene) is found to be close to 1 µWh/cm2which is not enough to get autonomous miniaturized and connected sensors. Within this study, two different approaches will be reported to significantly improve the performances of MSC. One attractive way to improve the areal energy density of MSC is to enhance the material mass loading while keeping low the footprint area. To meet this requirement3, on chip fabrication of 3D MSC is proposed. Wafer level fabrication process on high area enlargement factor 3D scaffold (AEF # 50) is achieved. Step conformal deposition of MnO2 thin film (electrophoretic deposition) on this 3D template is performed and the MSC are tested either in aqueous electrolyte (0.5M Na2SO4) or in EMI-TFSI aprotic ionic liquids (AILs). The areal energy density of the proposed micro-device is close to 10 µWh/cm2 while maintaining high areal power density of 10 mW/cm2. Carbon derived carbide (CDC) based MSC is the second followed way to propose on chip high performance device. The fine-tuned chlorination of TiC thin films deposited and patterned as interdigitated planar electrodes is performed in the framework of this study4. CDC based MSC were directly fabricated on silicon wafer. The corresponding areal energy density is around 1 µWh/cm2 for aqueous based device (1M H2SO4) and higher than 20 µWh/cm2 for MSC tested in organic electrolyte (2M EMI-BF4 in ACN). The power density is measured to be close to 100 mW/cm2. Finally, MSC based on vanadium nitride5 thin films grown either by sputtering technique (for planar MSC) or by atomic layer deposition technology (for 3D MSC) will be reported. The objective of these studies is to clearly find the suitable technology allowing to propose the fabrication of high areal energy density, small footprint area MSC and to move toward solid state configuration.

High Zr doping effects on the microstructural and optical properties of Mn3 O4 thin films along with ethanol sensing

Transition metal oxides as transparent conducting oxides (TCOs) films, with high optical transparency (≥82%), various valence states and p-type conductivity are used in a several physical domains. This work covers the physical study of Zr doped Mn3O4 semiconductor thin films using a spray pyrolysis method where Zr content varies in starting solutions from 0 to 20at.%. The impact of this work is to offer some understanding of microscopic effects of relatively high doping Zr and then correlate these effects with the macroscopic properties for interesting applications especially gas sensor. In fact, the addition of Zr ions pointed out the reduction of crystallite size (24.1 (nm)) with 20at.% doping allowing a better adsorption of gas molecules. In addition, it promotes the increase of optical gap (2.92eV) with 6at.% doping which is a useful parameter for some optical devices. X-ray diffraction (XRD), Raman spectroscopy, FTIR spectroscopy, atomic force microscopy (AFM) and EDAX techniques were used. It is found that these films crystallized in spinel type tetragonal hausmmanite structure. The gas sensing activity of these thin films (0, 6, 12 and 20at.% Zr) was examined with Ethanol. The performances of these last four sensing layers were compared. All the tests were performed at different working temperatures Twork=125, 150, 175 and 225°C and under two gas concentrations: 0.1% and 0.5% ethanol using dry air as carrier gas. The films exhibited noticeably ethanol sensing especially the sample doped with 6% of zirconium exhibits the most excellent sensing performance since it showed a clear response already at a low ethanol concentration of 0.1%.

Superconductor-ferromagnet-superconductor nanojunctions from perovskite materials

The lateral superconductor-ferromagnet–superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa2Cu3Ox (YBCO) and half-metallic ferromagnet La0.67Sr0.33MnO3 (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga3+ focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO2.

Effect of Terraces at the Interface on the Structural and Physical Properties of La0.8Sr0.2MnO3 Thin Films**Supported by the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB07030200, the National High-Technology Research and Development Program of China under Grant No 2014AA032607, and the National Natural Science Foundation of China under Grant No 11404380.

Employing atomic force microscopy, transmission electron microscopy and the second harmonic generation technique, we carefully explore the structural properties of 6-unit-cell-thick La0.8Sr0.2MnO3 films grown on SrTiO3 with atomically fat TiO2-terminated terraces on the surface. The results clearly demonstrate that the terraces on the surface of TiO2-terminated SrTiO3 can improve the layer-by-layer epitaxial growth of the manganite films, which results in uniform film coverage at the beginning of growth and thus reduces the substrate-induced disorder at or near the interface. Comparing the magnetic and transport properties of La0.8Sr0.2MnO3 films with the thicknesses varying from 6 unit cells to 80 unit cells grown respectively on as-received SrTiO3 and TiO2-terminated SrTiO3, it is found that these atomically flat terraces on the surface of TiO2-terminated SrTiO3 can greatly enhance the Curie temperature and conductivities of the ultrathin La0.8Sr0.2MnO3 films with thickness less than 50 unit cells, while no obvious difference is detected in the magnetic and transport properties of the 80 unit-cell thick films.

Effects of strain on the magnetic and transport properties of the epitaxial La0.5Ca0.5MnO3 thin films

The epitaxial strain can considerably modify the physical properties of thin films compared to the bulk. This paper reports the effects of substrate-induced strain on La0.5Ca0.5MnO3 (LCMO) thin films, grown on (100) SrTiO3 (STO) and LaAlO3 (LAO) substrates by pulsed laser deposition technique. Transport and magnetic properties were found to be strongly dependent on strain type. It is also shown that compressive (tensile) strain leads to the increase (decrease) in the magnetization of the films. Moreover, it was observed that all LCMO films deposited on both LAO and STO substrates behave as an insulator, but LCMO/LAO thin films with compressive strain have lower resistivity than LCMO/STO thin films with tensile strain. Applying magnetic field to LCMO/STO thin films with thickness of 25 and 50nm leads to very small change in the resistivity, while the effects of magnetic field on the sample with thickness of 125nm leads to an insulator–metal transition. For LCMO/LAO thin films, the magnetic field has a strong impact on the resistivity of samples. The results show that the magnetoresistance (MR) is enhanced by increasing film thickness for LCMO/LAO samples, due to the relatively stronger phase separation. For LCMO/STO thin films MR is drastically decreased by reduction of film thickness, which is attributed to the enhancement of the charge–orbital order (CO–O) accompanying the complex spin order (the so-called CE type). The changes of the antiferromagnetic structure from the CE to C type and the enhancement of the CE type could be attributed to the in-plane compressive and tensile strain, respectively.

Effect of Film Thickness in Electrical Resistivity and Magnetic Properties of Nd0.7Sr0.3MnO3 Thin Films

Nd0.7Sr0.3MnO3 thin films of different thicknesses were deposited on (001)-MgO substrate by using a radio frequency-magnetron sputtering system. These films were divided into two batches and were post-annealed separately in an air and oxygen environment, respectively, at 700 °C. Analysis of X-ray diffraction patterns shows that these films crystallise in cubic structure with a typical lattice constant a = 3.847 Ȧ and it expands with increase in film thickness. Both air- and oxygen-annealed films exhibit ferromagnetic transition and the transition temperature gradually rises as the film thickness is increased. Magnetisation loops recorded at 50 K show that all the prepared thin films show ferromagnetic behaviour with a maximum saturation magnetisation value (3.6 μB) comparable to that of bulk sample. The anisotropy constant (K) estimated from the analysis of initial magnetisation curve is found to decrease with increase in film thickness. Metal-insulator transition has been observed and the resistivity data in the insulating region were analysed based on variable range hopping model.

Ethanol sensing properties and photocatalytic degradation of methylene blue by Mn3O4, NiMn2O4 and alloys of Ni-manganates thin films

This work highlights the sensitivity properties of thin films based on nickel manganese oxides (NiMnO) which were grown by the spray pyrolysis technique on glass substrates at T = 350 °C. First, the films were characterized by XRD and Raman spectroscopy in order to identify their phases and microstructures. Results of these measurements prove that at a percentage of nickel element Ni/Mn equal to 33%, Mn3O4 thin film was changed to the pure nickel manganese ternary oxide NiMn2O4. Both UV–Vis–NIR spectrophotometry measurements and the room temperature photoluminescence (PL) spectra of NiMnO thin films confirm the dependence of the optical band gap (Eg) with Ni content. Second, NiMnO thin films exhibit a promising photocatalytic activity for the degradation of methylene blue (MB) dye. The DC conductivity based ethanol sensing measurements showed that the pure NiMn2O4 and Mn3O4 thin film have ready clear sensing response toward ethanol vapor. Finally, these materials may be of interest for other gas and organic pollutants.

Bipolar Resistive Switching in Epitaxial Mn3O4 Thin Films on Nb-Doped SrTiO3 Substrates**Supported by the National Basic Research Program of China under Grant Nos 2011CB921904 and 2012CB927402, the National Natural Science Foundation of China under Grant Nos 11074142 and 11021464, the Key Project of the Ministry of Education of China under Grant No 309003.

Spinel (001)-orientated Mn3O4 thin films on Nb-doped SrTiO3 (001) substrates are fabricated via the pulsed laser deposition method. X-ray diffraction and high-resolution transmission electron microscopy indicate that the as-prepared epitaxial film is well crystallized. In the film plane the orientation relationship between the film and the substrate is [100]Mn3O4‖[110] Nb-doped SrTiO3. After an electroforming process, the film shows bipolar nonvolatile resistance switching behavior. The positive voltage bias drives the sample into a low resistance state, while the negative voltage switches it back to a high resistance state. The switching polarity is different from the previous studies. The complex impedance measurement suggests that the resistance switching behavior is of filament type. Due to the performance reproducibility and state stability, Mn3O4 might be a promising candidate for the resistive random access memory devices.

Persistence of the orthorhombic phase in YMnO3 hexagonal thin films

ABSTRACTYMnO3 thin films were prepared based on a chemical solution deposition route. Their structure was studied as a function of the annealing temperature using X-ray diffraction, Raman spectroscopy, and electron backscatter diffraction. For annealing temperatures above 850°C the films, though crystallizing predominantly in a P63cm hexagonal structure, exhibit a thin Pnma orthorhombic phase close to the film-substrate interface. It is shown that the residual orthorhombic structure is associated with a substrate induced strain state, characterized by an expansion in the in-plane a direction, and a compression in the out of plain c direction.

Spray deposited Hausmannite Mn3O4 thin films using aqueous/organic solvent mixture for supercapacitor applications

Manganese oxide (Mn3O4) is considered one of the most promising materials for high-performance supercapacitors due to its extraordinary theoretical specific capacitance, low-cost, environmental benignity and natural abundance. Mn3O4 thin films have been deposited by spray pyrolysis using aqueous/organic solvent mixture. These films were characterized for structural, morphological, optical and electrical measurements. The electrochemical performance of the supercapacitor was studied by using cyclic voltammetry curves recorded at different scan rates. The porous Mn3O4 thin film electrode exhibits significantly improved supercapacitive performance in 1M Na2SO4 electrolyte with highest specific capacitance of 394Fg−1 at scan rate of 10mVs−1 for film deposited at 350°C. The specific energy and specific power are found to be 8.27Whkg−1 and 850Wkg−1, respectively, at a current density of 1Ag−1. The specific capacitance of the Mn3O4 electrode maintains 93.01% of its initial value after 1000 cycles, at a current density of 1Ag−1 showing a good cycling stability.

Influence of electrode mass-loading on the properties of spray deposited Mn3O4 thin films for electrochemical supercapacitors

Mn3O4 thin film electrodes with various mass-loadings are deposited by spray pyrolysis using aqueous/organic solvent mixture. The influence of mass-loading on the electrochemical properties of Mn3O4 thin film electrodes is studied. The results showed that, the as-prepared Mn3O4 exhibited ideal capacitive behavior in a voltage window of −0.2 to 0.4V. With increasing of Mn3O4 mass-loading from 0.47mgcm−2 to 0.64mgcm−2, the specific capacitance calculated from the cyclic voltammetry curves at 5mVs−1 increased from 520 to 597F·g−1. The specific energy and specific power are found to be 3735Whkg−1 and 12.45Wkg−1 respectively at a current density of 4.0A·g−1 for film having 0.64mgcm−2 mass-loading. Ragone plots indicated that the Mn3O4 electrode with 0.64mgcm−2 mass-loading possessed good power-energy density characteristics. The electrochemical performances of 0.64mgcm−2 mass-loading Mn3O4 thin film electrode suggest suitability of this material as a potential electrode material for supercapacitors.

Evolution and sign control of square-wave-like anisotropic magneto-resistance in spatially confined La0.3Pr0.4Ca0.3MnO3/LaAlO3(001) manganite thin films

We investigated magneto-transport properties of a compressively strained spatially confined La0.3Pr0.4Ca0.3MnO3 (LPCMO) thin film micro-bridge deposited on LaAlO3. Angular dependence of the magneto-resistance R(θ) of this bridge, where θ is the angle between the magnetic field and the current directions in the film plane, exhibits sharp positive and negative percolation jumps near TMIT. The sign and the magnitude of these jumps can be tuned using the magnetic field. Such behavior has not been observed in LPCMO micro-bridges subjected to tensile strain, indicating a correlation between the type of the lattice strain, the distribution of electronic domains, and the anisotropic magneto-resistance in spatially confined manganite systems.

Improved electrical and magnetic transport properties of La0.8Ba0.2MnO3 thin films by oxygen annealing

Improved electrical and magnetic transport properties of La0.8Ba0.2MnO3 thin films by oxygen annealing

Carrier tuning the metal-insulator transition of epitaxial La0.67Sr0.33MnO3 thin film on Nb doped SrTiO3 substrate

La0.67Sr0.33MnO3 (LSMO) thin films were deposited on (001)SrTiO3(STO) and n-type doped Nb:SrTiO3(NSTO) single crystal substrates respectively. The metal to insulator transition temperature(TMI) of LSMO film on NSTO is lower than that on STO, and the TMI of LSMO can be tuned by changing the applied current in the LSMO/NSTO p-n junction. Such behaviors were considered to be related to the carrier concentration redistribution in LSMO film caused by the change of depletion layer thickness in p-n junction which depends greatly on the applied electric field. The phenomenon could be used to configure artificial devices and exploring the underlying physics.

Transport dynamics analysis in ferromagnetic heterojunction using Raman spectroscopy and magnetic force microscopy

The ZnO/La0.7Sr0.3MnO3 thin film was epitaxially fabricated on LaAlO3 (100) by pulse laser deposition. The Raman scattering on the single layer LaSrMnO and junction ZnO/La0.7Sr0.3MnO3 was investigated in a giant softening by 490cm−1 John-Teller, 620 and 703cm−1 optical phonon modes. The Raman spectra LaSrMnO and ZnO/La0.7Sr0.3MnO3 were observed with distinct features, i.e., the thickness was in dependent of frequency and intensity. The dynamics results showed that the spin–orbital coupling was caused by anomalies tilt of MnO6 octahedron. The LSMO/ZnO junction exhibited excellent junction positive magneto-resistance behavior in the temperature range of 77–300K. The kinetic energy gain was achieved by orbital competition, strong crystal field and charge order of energy band splitting. The transport orbits were in the environment of the ferromagnetic-orbital ordering. The structures of barriers could be adjusted by junction interface and domain boundary condition in terms of the presence of spin–orbital fluctuating.

Promotion Effect of Electrodeposition Parameters on the Performances of MnO2 Thin Films Used As Photoelectrocatalysts for Water Oxidation

The development of alternative energy sources, especially green energy sources for traditional fossile fuels is a major challenge that humankind is currently facing. The conversion of solar energy into chemical fuels is a promising method. Inspired by photosynthesis taking place in the green plants, artificial photosynthesis was proposed. The targeted reaction is as follows: 2 H2O (l) → 2 H2 (g) + O2 (g) Theoretically, the half redox equation related to water oxidation, also called oxygen evolution reaction (OER), which is a key step for water splitting, needs a high potential bias, as a consequence of the very slow kinetics of this reaction. This latter could be improved by employing a catalyst in order to make it energetically less expensive. Catalysts based on metal oxides have shown bright prospects for this application [1]. As a consequence of the determination of the fine structure of photosystem II in charge of this redox process in plants, it was revealed that the oxygen evolving complex (OEC) was a Mn4CaO5 entity resembling strongly the one that can be found in manganese oxides. These latter attracted consequently a considerable attention of scientists over the last years as possible OER photoelectrocatalysts. After comparison with traditional catalysts based on precious metals, manganese oxides, and mainly MnO2, have the advantages of being abundant on Earth, and therefore inexpensive, and also environmentally friendly. In particular, many investigations reported in literature showed in a rather convincing manner that MnO2 is a promising candidate as OER photoelectrocatalysis. In a work published in 2011, T. F. Jaramillo et al. showed that birnessite-type MnO2 could be a good solar water splitting catalyst [2], whereas S.S. Stahl et al. found that the OER activity of manganese oxides depends on their crystalline structure [3]. D.G. Nocera and co-workers investigated the nucleation and growth mechanism of MnOx thin films electrodeposited in potentiostatic conditions using a potential value selected inside a narrow potential range [4]. Few studies were thus focused on large variations of the potential used during the electrodeposition of MnO2thin films in potentiostatic conditions, and on the corresponding performances of these films towards photoelectrocatalysis of water oxidation. In this work, manganese dioxide (MnO2) thin films with different morphologies were prepared by one-step potentiostatic deposition using an aqueous electrolyte containing MnSO4 and NaClO4 in a traditional three-electrode cell. Fluorine doped tin oxide (FTO) substrates were used as working electrodes, and a platinum grid and a K2SO4 saturated Hg/Hg2SO4 electrode (SSE) were used as counter- and reference electrodes, respectively. The same setup was used during the OER tests except that a 0.1 M KOH Hg/HgO reference electrode (MOE) and a 0.1 M NaOH electrolyte were used instead of SSE and NaClO4respectively. Our results show that the value of the electrodeposition potential has a strong influence on the morphology and crystallinity of resulting MnO2 thin films, as evidenced by SEM-FEG and XRD characterisations. The birnessite type crystalline structure was obtained only for films electrodeposited at potential values close to the peak potential related to MnO2 electrodeposition, whereas MnO2thin layers electrodeposited at potential values situated far beyond this peak potential value and before the foot of the anodic wall related to water oxidation were found to be amorphous, which clearly promoted their activity towards OER, by comparison with those of the birnessite variety. In the course of our investigations, chronoamperometry experiments were carried out for all the samples. They allowed us to find out that the stability of the electrocatalytic behaviour, as well as the adherence on the underlying substrate, were both better for amorphous films. Electrochemical impedance spectroscopy (EIS) experiments were also carried out to develop a better understanding of their electrochemical properties in the course of water oxidation experiments. Moreover, their semi-conductor behaviour was evidenced using water oxidation experiments in the presence of a solar simulator, and deeply investigated with the help of Incident Photon to electron Conversion Efficiency (IPCE), UV-visible spectrophotometry and Current Sensing Atomic Force Microscopy (CS-AFM).

Effect of Annealing Temperature on The physical Properties of Mn3O4 Thin Film Prepared by Chemical Bath Deposition

Effect of Annealing Temperature on The physical Properties of Mn3O4 Thin Film Prepared by Chemical Bath Deposition

Large room-temperature magnetoresistance in epitaxial La0.7Ca0.25Sr0.05MnO3 thin films prepared by sol–gel method

Epitaxial La0.7Ca0.25Sr0.05MnO3 (LCSMO) thin films were successfully prepared on LaAlO3 (LAO) substrates by ordinary aqueous sol–gel method. X-ray diffraction result shows that the films have perfect crystalline orientation. The HRTEM results confirm that the films have epitaxial structure and the interface is very sharp and no misfit dislocations. The selected area electron diffraction patterns and fast Fourier transformation patterns mean that there exist three domains in the thin film. The single-particle spin-flip excitations are dominant for the metallic ferromagnets in low-temperature range. In paramagnetic range, the temperature dependence of resistivity can be well analyzed using a small polaron theory. The magnetoresistance value for the films reaches maximum about 65 % with 7 T magnetic field at 285 K which is promising for highly demanding applications. The conventional sol–gel method produces the lanthanum manganese oxide thin films with excellent epitaxial structure and large magnetoresistance at room temperature which can be used for either fundamental studies or real applications. The conventional sol–gel method produces the lanthanum manganese oxide thin films with excellent epitaxial structure and giant magnetoresistance at room temperature which can be used for either fundamental studies or real applications.

Electrical transport and magnetic properties of epitaxial [formula omitted] thin films on (001)-oriented LaAlO3 substrate

Nd0.7Sr0.3MnO3 thin films were deposited using RF-magnetron sputtering on (001) oriented LaAlO3 substrate by varying thickness in the range of 12–200nm. X-ray diffraction patterns of both air annealed and oxygen annealed films show epitaxial growth along (00l) orientation with decrease in lattice strain with increase in film thickness. Raman spectra show the presence of strong peaks corresponding to rotational and stretching modes of MnO6 octahedra and their intensity is found to decrease with increase in film thickness. Both air and oxygen annealed films except for 12nm thickness exhibit ferromagnetic transition with a maximum TC of 200K. The magnetic anisotropic constant was estimated from the analysis of M–H curve and its value is found to decrease with increase in film thickness. Metal-insulator transitions have been observed in all films including the 12nm thick film. The electrical resistivity data in the metallic region, i.e. close to TMI, were analysed by considering electron–magnon scattering mechanism and in the low temperature region far below TMI; the analysis was carried out by considering the combination of electron–electron scattering and charge localisation effect. The resistivity data in the insulating region (T>TMI) were analysed by considering Mott-variable range hopping model.