Mn-doped SnO2 Research Articles

An insight into the origin of room-temperature ferromagnetism in SnO2 and Mn-doped SnO2 quantum dots: an experimental and DFT approach.

SnO2 and Mn-doped SnO2 single-phase tetragonal crystal structure quantum dots (QDs) of uniform size with control over dopant composition and microstructure were synthesized using the high pressure microwave synthesis technique. On a broader vision, we systematically investigated the influence of dilute Mn ions in SnO2 under the strong quantum confinement regime through various experimental techniques and density functional theoretical (DFT) calculations to disclose the physical mechanism governing the observed ferromagnetism. DFT calculations revealed that the formation of the stable (001) surface was much more energetically favorable than that of the (100) surface, and the formation energy of the oxygen vacancies in the stable (001) surface was comparatively higher in the undoped SnO2 QDs. X-ray photoelectron spectroscopy (XPS) and first-principles modeling of doped QDs revealed that the lower doping concentration of Mn favored the formation of MnO-like (Mn2+) structures in defect-rich areas and the higher doping concentration of Mn led to the formation of multiple configurations of Mn (Mn2+ and Mn3+) in the stable surfaces of SnO2 QDs. Electronic absorption spectra indicated the characteristic spin allowed ligand field transitions of Mn2+ and Mn3+ and the red shift in the band gap. DFT calculations clearly indicated that only the substitutional dopant antiferromagnetic configurations were more energetically favorable. The gradual increase of magnetization at a low level of Mn-doping could be explained by the prevalence of antiferromagnetic manganese-vacancy pairs. Higher concentrations of Mn led to the appearance of ferromagnetic interactions between manganese and oxygen vacancies. The increase in the concentration of metallic dopants caused not just an increase in the total magnetic moment of the system but also changed the magnetic interactions between the magnetic moments on the metal ions and oxygen. The present study provides new insight into the fundamental understanding of the origin of ferromagnetism in transition metal-doped QDs.

Enhancement of visible-light-driven photoresponse of Mn-doped SnO2 quantum dots obtained by rapid and energy efficient synthesis

Mn-doped SnO2 quantum dots (QDs) with different Mn concentrations were prepared by solution combustion synthesis. The crystallite size was under 5nm was confirmed from XRD and HR-TEM. A considerable decrease in band gap energy was observed with the increase in Mn content. The PL spectra show orange emission at about 590nm due to the ultra-small crystallite size and crystal defects of SnO2 QDs. The photocatalytic degradation of MO dye was measured under visible light irradiation using the Mn-doped SnO2 QDs as catalysts. 3mol% Mn-doped SnO2 QDs showed the 17 times higher photocatalytic performance than SnO2 QDs within 240min.

Effect of (Mn-Co) co-doping on the structural, morphological, optical, photoluminescence and electrical properties of SnO2

Mn and Mn-Co doped SnO2 have been successfully synthesized using co-precipitation technique. The structural properties and surface morphology were studied using x-ray diffractometer (XRD) and scanning electron microscopy (SEM) respectively. Composition analysis of the samples has been carried out from EDX data. Optical properties were studied using reflectance spectroscopy in the wavelength range 200 nm-800 nm and IR absorption spectroscopy in the wave number range 400 cm−1–4000 cm−1. Reflectance spectra revealed that the band gap of prepared samples changes with doping concentration and found to be in the range 3.91 eV–3.95 eV. Infrared (IR) absorption spectra describe the different mode of band related to a functional group present in the materials. Mn and Mn-Co doped SnO2 exhibit very strong emission near the wavelength 413 nm and 434 nm. DC resistivity measurement shows that the activation energy increases with increasing concentration of dopant.

Development of a selective hydrogen leak sensor based on chemically doped SnO2 for automotive applications

The development of a selective hydrogen leak conductometric sensor for automotive applications based on transition metal ion (Mn, Co) doped SnO2 nanoparticles is presented. Co and Mn-SnO2 nanoparticles were synthesized by microwave irradiation method. XRD, Raman, XPS and TEM studies confirmed that the dopants enter into the tetragonal rutile-type structure of SnO2. As a result, the average crystallite sizes of the doped samples decrease with the increase in dopant concentrations. Sensors performances have been assessed by studying the signal response to hydrogen (H2) at different temperatures and concentrations. The selectivity of the fabricated sensors against the potential interfering gas carbon monoxide (CO) was also investigated. Results demonstrate that Co is more effective in enhancing the sensing performance of SnO2 NPs when compared to pristine and Mn-doped SnO2, allowing the fabrication of a hydrogen leak sensor with excellent response, good selectivity and reproducibility at the operating temperature of 250 °C.

Effect of Mn-substituted SnO2 particle toward photocatalytic degradation of methylene blue dye

SnO2 and Mn-doped SnO2 were successfully prepared by wet chemical synthetic route. The understanding of substituted Mn into SnO2 leads to transfer the energy band gap by small amount of metal dopant. Fourier transform infrared and X-ray diffraction were used to determine chemical bonding and crystal structure, respectively. It showed that small amount of Mn can be completely substituted into SnO2 lattice. 40%wt of Mn was completely substituted. EDX was used to confirm the existence of Mn-doped SnO2. Scanning electron microscope revealed that their particles exhibits blocky particle with irregular sharp. The efficiency of SnO2 and Mn-doped SnO2 was investigated on the photocatalytic activity on methylene blue degradation for 4h. The photocatalytic activity of SnO2 and Mn-doped SnO2 exhibited the excellent performance in wastewater treatment in textile industry.

Manipulating resistive states in oxide based resistive memories through defective layers design

In this work, multilevel switching was achieved by a strategically designed alternative multi-layer structure with pure and Mn-doped SnO2.

Magnetic properties of microwave-synthesized Mn-doped SnO2 nanoparticles

Semiconductor nanostructures with dilute magnetic property are of great importance for different applications. However, this property depends on several factors including the synthesis route. In this work, manganese (Mn)-doped tin dioxide (SnO2) nanoparticles (NPs) at different concentrations were synthesized by the microwave-assisted synthesis method and evaluated for their magnetic properties. The X-ray diffraction analyses revealed a single-phase rutile-type tetragonal structure, while SEM and TEM images showed fine NPs with average sizes around 10 nm. A considerable increase in value of the energy band gap by around 0.18 eV as a result of Mn doping was observed. This dopant has also increased the lattice d-spacing value, but slightly decreased the lattice constant c. The magnetic measurement result showed that all the microwave-synthesized Mn-doped SnO2 NPs including the pure one have distinctly wide hysteresis loops, indicating that samples have room temperature ferromagnetism (RTFM). RTFM was further enhanced by Mn doping reaching maximum at a concentration of 0.3 mol%. This magnetism could be attributed to the presence of defects at the grain boundaries within the NPs, interfacing sites between the NPs, oxygen or tin vacancies and an optimum level of Mn dopant. The observed wide hysteresis loops in these samples might be due to the use of a surfactant at high concentration that could provide highly compact/tight NPs. These results might be useful for producing nanoscale magnets and magnetic memory devices.

Formation of Mn-Doped SnO2 Nanoparticles Via the Microwave Technique: Structural, Optical and Electrical Properties

Ultrafine pure and Mn-doped SnO2 nanoparticles (NPs) were synthesized via the microwave technique. They were produced using tin chloride and hexamethylenetetramine at the molar ratio of 1:20. The c...

Energetics of Oriented Attachment of Mn-Doped SnO2 Nanoparticles

Growth of nanoparticles by oriented attachment (OA) can occur in electrolyte solutions, in vacuum, or even in air. The energy change in this event is determined by the difference between the excess interface energies of the free nanoparticles and the arrangement with attached grains. Therefore, low energy boundaries (highly coherent) are more likely to attach, and after attachment, atomic rearrangement will allow crystals to effectively grow by coalescing two or more grains. However, if the energy of the boundary formed by attachment is low but the activation energy for coalescence is high, it is possible for the system to enter a metastable state that disables nanocrystals’ growth (enabling design of growth resistant nanocrystals). In this work, we test this hypothesis in manganese-doped SnO2 nanoparticles in the absence of organic agents. We observe that manganese dramatically lowers the energies of (noncoherent) grain boundaries of SnO2, which enhances nanostability and slows grain growth due to the in...

Influence of dopant concentrations (Mn = 1, 2 and 3 mol%) on the structural, magnetic and optical properties and photocatalytic activities of SnO2 nanoparticles synthesized via the simple precipitation process

We have successfully synthesized pure and Mn (1–3mol%)-doped SnO2 nanoparticles via the facile precipitation method. The influence of Mn concentrations on SnO2 nanoparticles properties were systematically investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, vibrating sample magnetometer (VSM), ultraviolet visible (UV–Vis) spectroscopy and photoluminescence (PL) spectroscopy. On the other hand, the photocatalytic degradation of the Methyl orange dye was comparatively investigated, by using pure and 1–3% concentration of Mn-doped SnO2 samples and the mechanism has been discussed. All the results demonstrate that doping levels have strong influences on the structural, magnetic, and optical properties and photocatalytic activity performances.

Doped SnO₂ transparent conductive multilayer thin films explored by continuous composition spread.

Mn-doped SnO₂ thin films were fabricated by a continuous composition spread (CCS) method on a glass substrate at room temperature to find optimized compositions. The fabricated materials were found to have a lower resistivity than pure SnO₂ thin films because of oxygen vacancies generated by Mn doping. As Mn content was increased, resistivity was found to decrease for limited doping concentrations. The minimum thin film resistivity was 0.29 Ω-cm for a composition of 2.59 wt % Mn-doped SnO₂. The Sn-O vibrational stretching frequency in FT-IR showed a blue shift, consistent with oxygen deficiency. Mn-doped SnO₂/Ag/Mn-doped SnO₂ multilayer structures were fabricated using this optimized composition deposited by an on-axis radio frequency (RF) sputter. The multilayer transparent conducting oxide film had a resistivity of 7.35 × 10⁻⁵ Ω-cm and an average transmittance above 86% in the 550 nm wavelength region.

Effects of metal doping on photoinduced hydrophilicity of SnO2 thin films

The influence of metal dopants (Mn2+, Al3+ and Cu2+) on the wetting properties of SnO2 thin films deposited by thermal evaporation is reported. The undoped and doped SnO2 films crystallize into the orthorhombic structure upon annealing at 200°C for 110 h. It is shown that wettability behaviour, before and after ultraviolet (UV) irradiation, is dependent on the ionic radius of the dopant. The contact angle of un-irradiated samples increases with increase in ionic radius of the dopant and also in comparison with the undoped sample. It is 54° for pure SnO2 and increases to 77.5°, 92.3° and 95.9° for the Al3+,Mn2+ and Cu2+ doped samples, respectively. After UV irradiation, the value is 5.4° for the undoped sample. This increases to 21.2° for Al doping reaching a minimum of 6.4° for the Mn-doped sample increasing thereafter to 63.3° for the Cu-doped sample. It is observed that pre-irradiation contact angle behaviour can be correlated with the change in roughness of the films with increasing ionic radius. In contrast, photoinduced hydrophilicity of the films correlates with their optical bandgap. The contact angle is lowest for the lowest bandgap material, i.e., Mn-doped SnO2, with a bandgap of 2.48 eV. Thus, the band structure of SnO2 that can be controlled by dopant ionic radius can in turn be employed to manipulate the wettability of these surfaces.

Formation of orthorhombic SnO2 originated from lattice distortion by Mn-doped tetragonal SnO2

In this article, orthorhombic phase SnO2 from Mn-doped tetragonal phase SnO2 has been successfully prepared by a chemical co-precipitation method.

Influence of Mn doping on structural, optical and acetone gas sensing properties of SnO2 nanoparticles by a novel microwave technique

In the present work we have successfully synthesized pristine and manganese (Mn) doped SnO2 nanoparticles by using simple microwave irradiation technique for the first time. Powder X-ray diffraction results confirms that both the pure and doped SnO2 in tetragonal rutile type structure. Transmission electron microscopy studies illustrate that both the undoped and Mn doped SnO2 crystallites form in spherical shapes with an average diameter of 35–19 nm, which is in good agreement with the average crystallite sizes calculated by Scherrer’s formula. A considerable red shift in the absorbing band edge was observed with increasing of Mn content (0–10 wt%) by using UV–Vis diffuse reflectance spectroscopy . Oxygen-vacancies, tin interstitial and structural defects were analyzed using photoluminescence spectroscopy. The functional groups were analyzed by using Fourier transform infrared spectra. Acetone gas sensing measurement of pure and Mn-doped (10 wt%) SnO2 nanoparticles were experimented at ambient temperature using optical fiber based on clad modified method. By modifying the clad exposure to acetone vapor, the sensitivities were estimated to be 53 and 78 counts/100 ppm for undoped and Mn-doped SnO2 nanoparticles, respectively. These results show that the Mn doping into SnO2 enhances acetone gas sensing properties.

Experimental and Theoretical Investigation of Ferromagnetism in Mn-Doped SnO

In this paper, Mn doped SnO nanomaterial is studied both experimentally and theoretically. Hexagonal-shaped Mn-doped SnO nanostructures are successfully synthesized by the simple template-free hydrothermal method. All theoretical results are calculated using ADF-BAND 2012.01. The experimental and the theoretical results prove the ferromagnetism of Mn doped SnO. The morphology, crystalline phase, particle sizes and atomic weight percentage of atoms are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS), respectively. FESEM results show that the sheets-like SnO structure are in the range of 10 mu m and the average size of nano-hexagonal plates is about 100 nm. The average crystalline size of the tetragonal phase SnO particles is calculated to be about 25 nm from XRD results. Two Raman active modes A(1g) = 205 cm(-1) and B-1g = 106 cm(-1) and about 7 cm(-1) redshift are observed by the Raman spectroscopy. The experimental results are consistent with theoretical results.

Optical and magnetic properties of Sn1−xMnxO2 dilute magnetic semiconductor nanoparticles

Sn1−xMnxO2 (x=0.05, 0.10 and 0.15) nanoparticles with tetragonal structure have been successfully synthesized by solvothermal method using oxalate precursor route. The oxalate precursors and its corresponding oxides were characterized by powder X-ray diffraction (PXRD), thermogravimetric (TG), fourier transform infrared (FTIR) and transmission electron microscopic (TEM) studies. PXRD studies showed the highly crystalline and monophasic nature of the solid solutions. The shifting of X-ray reflections towards higher angle is attributed to the incorporation of Mn2+ ions in SnO2 host lattice. The average particle size was found to be in the range of 5–11nm. Reflectance measurements showed blue shift in energy band gap which increases with increasing Mn2+ concentration. Surface area of these nanoparticles (59–388m2/g) was found to be high which increases with increasing the dopant ion concentration. Mn-doped SnO2 showed distinct magnetic behaviour with different manganese concentration. Sn1−xMnxO2 (x=0.05 and 0.10) revealed the parasitic ferromagnetism, however on increasing x=0.15, sample showed paramagnetic behaviour.

Fabrication, characterization and magnetic properties of Mn-doped SnO nanostructures via hydrothermal method

In the present study we report synthesis of Mn-doped SnO nano sheets and nano cubes via facile hydrothermal technique with controlled morphology. X-ray diffraction, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy and alternating gradient magnetometer techniques were used to investigate the physiochemical characterizations. Field-emission scanning electron microscopy results exhibited the rectangular shape of the sheets with diagonal length of 1–2µm which were found in the form of bundles, the average size of nano-hexagonal plate and the average size of the quadrilateral face of three dimensional nano-cube were about 100nm. Experimental results confirmed that the different chemical bases exhibit a strong influence on morphology of the resulting product and doping concentration had effect on the size of nano-cubes. Furthermore, room temperature ferromagnetism increases monotonically for Mn doping and reaches maximum saturation magnetization emu/g for 3% Mn-doped SnO.

Magnetic and electronic properties of Cr- and Mn-doped SnO2: ab initio calculations

The ab initio calculations, based on the Korringa–Kohn–Rostoker (KKR) approximation method combined with the coherent potential approximation (CPA), indicated as KKR–CPA, have been used to study the stability of ferromagnetic and ferrimagnetic states, for systems that are SnO2 doped and co-doped with two transition metals, that is, chromium and manganese. Our results indicate that the ferromagnetic state is more stable than the spin-glass state for the (Sn1−xCrxO2; x = 0.07, 0.09, 0.12 and 0.15)-doped system, while the spin-glass state is more stable than the ferromagnetic state for the (Sn1−xMnxO2; x = 0.02 and 0.05)-doped system. However, the ferromagnetic and/or the ferrimagnetic states are stable for the (Sn0.98−xMn0.02CrxO2; x = 0.05, 0.09 and 0.13)-doped system depending on the Cr concentration. Moreover, we estimated the Curie temperature (Tc) for the Cr-doped tin dioxide (SnO2), and we explained the origin of magnetic behaviour through the total density of states for different doped and co-doped SnO2 systems.

Electronic structures and ferromagnetism of SnO2 (rutile) doped with double-impurities: First-principles calculations

The electronic and magnetic properties of double-impurities-doped SnO2 (rutile) are explored using first-principles calculations within the generalized gradient approximation to examine their potential use as spintronic system. Calculations are performed for double impurities (M1 and M2) from M1 = Cr, and M2 = Mn, and Re. The origins of ferromagnetism are shown to be different in the two cases. For Sn1-2xCrxMnxO2, the hybridization between Cr-3d and O-2p results in Cr becoming ferromagnetic with a magnetic moment of about 5.0 μB per supercell. The Cr-and Mn-doped SnO2 system exhibits half-metallic ferromagnetism. The strong ferromagnetic couplings between local magnetic moments can be attributed to p-d hybridization. In contrast, in (Cr, Re) codoped TiO2, the local magnetic moments of the impurities and their oxidation states agree with the charge transfer between Cr and Re, which would lead to the ferromagnetic through the double-exchange mechanism in transition metal oxides. Since there are two possible couplings between the impurities, we studied both configurations (ferromagnetic and antiferromagnetic (AF)) for double-impurities-doped SnO2. Our calculations show that a ferromagnetic alignment of the spins is energetically always more stable than simple AF arrangements, which makes these materials possible candidates for spin injection in spintronic devices.

Structural and optical properties of undoped and Mn-doped SnO<SUB align="right">2 nanoparticles by hydrothermal method

Structural and optical properties of undoped and Mn-doped SnO<SUB align="right">2 nanoparticles by hydrothermal method