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Publications (10 of 101) Show all publications
Fang, M., Liu, F., Li, T., Zhang, W., Xia, H., Rao, K. ,. & Belova, L. (2019). Inkjet printing Ag-TiO2 thin films with suppressed photoluminescence. Semiconductor Science and Technology, 34(10), Article ID 105027.
Open this publication in new window or tab >>Inkjet printing Ag-TiO2 thin films with suppressed photoluminescence
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2019 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 34, no 10, article id 105027Article in journal (Refereed) Published
Abstract [en]

With ultraviolet sensitive photochemistry and photoelectric properties, TiO2 is attractive for applications like photocatalysis, photovoltaic devices, and sunscreen products, among others. By coating Ag on TiO2 surface, the sensitivity can be extended to visible light, endowing enhanced properties with potential new applications. In this work we inkjet print Ag-TiO2 films from particle suspensions, and investigate the structure, morphology, Ag distribution and the photoluminescence of the films It is found that Ag nanoparticles form bridges among TiO2 particles during the post-annealing. These metallic bridges can transport the excited electrons and suppress the recombination of electrons and holes with the photoluminescence of the film reduced by more than half. The work provides an industrial applicable, low-cost, environment friendly route of preparing Ag-TiO2 films for attractive photochemistry and photoelectric device applications.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
Ag-TiO2, inkjet printing, photoluminescence, annealing
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-262779 (URN)10.1088/1361-6641/ab3d77 (DOI)000488008800006 ()2-s2.0-85073218570 (Scopus ID)
Note

QC 20191022

Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-10-22Bibliographically approved
Fang, M., Li, H., Riazanova, A., Rao, K. V. & Belova, L. (2019). Tuning room temperature ferromagnetism of 'in-situ' inkjet printed Fe-doped ZnO films. Semiconductor Science and Technology, 34(5), Article ID 055006.
Open this publication in new window or tab >>Tuning room temperature ferromagnetism of 'in-situ' inkjet printed Fe-doped ZnO films
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2019 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 34, no 5, article id 055006Article in journal (Refereed) Published
Abstract [en]

ZnO is a wide-band gap semiconductor widely used in optical and electric devices, associating with ferromagnetism at low dimension endowing its possibility for functional applications with magneto-optical and magneto-electric properties. We prepared ZnO and Fe-doped ZnO thin films 'in-situ' on substrate by inkjet printing, and tuned the room temperature ferromagnetism (RTFM) of the film by Fe-doping concentration, film thickness and post annealing temperature. It was found that by Fe doping the saturation magnetization (M-s) of the film can be enhanced by more than 4 folds comparing with the un-doped film, i.e. from 0.9 emu g(-1) for the ZnO film to 3.8 emu g(-1) for the Fe-doped ZnO film with comparable thickness. The enhancement was attributed to the introduction of un-paired 3d electrons which formed long range ferromagnetic ordering, as well as the consequent structure changes with smaller grains which increased the interface induced magnetism. By changing the annealing temperature and the film thickness, the defect-induced ferromagnetism was investigated. The RTFM shows thickness dependence with peak saturation magnetization value of 4.44 emu g(-1) for the 45 nm thick film. The work provides an effective way of tuning magnetism in ZnO based films for functional device applications.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
ferromagnetism, ZnO thin films, Fe-doping, inkjet printing
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-251198 (URN)10.1088/1361-6641/ab0aa2 (DOI)000464182200004 ()2-s2.0-85067593204 (Scopus ID)
Note

QC 20190724

Available from: 2019-07-24 Created: 2019-07-24 Last updated: 2019-07-24Bibliographically approved
Ali, A., Raza, R., Khalil, R. M., Ahmad, M. A., Rafique, A., Ullah, M. K., . . . Belova, L. (2018). A potential electrolyte (Ce1-x CaxO2-delta) for fuel cells:Theoretical andexperimental study. Ceramics International, 44(11), 12676-12683
Open this publication in new window or tab >>A potential electrolyte (Ce1-x CaxO2-delta) for fuel cells:Theoretical andexperimental study
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2018 (English)In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 11, p. 12676-12683Article in journal (Refereed) Published
Abstract [en]

First-principles calculations are performed using density function theory to explore the effects of dopant Ca in ceria (Ce1-x CaxO2-delta). The impact of oxygen vacancy on band gap and density of states is examined in doped ceria using generalized gradient approximations. Vacancy association and vacancy formation energies of the doped ceria are calculated to reveal the effect of dopant on ion conduction. The experimental study of the sample Ce0.875Ca0.125O2-delta) was performed to compare with the theoretical results. The obtained results from theoretical calculation and experimental techniques show that oxygen vacancy increases the volume, lattice constant (5.47315 angstrom) but decrease the band gap (1.72 eV) and bulk modulus. The dopant radius (1.173 angstrom) and lattice constant (5.4718 angstrom) are also calculated by equations which is close to the DFT lattice parameter. The result shows that oxygen vacancy shifts the density of states to lower energy region. Band gap is decreased due to shifting of valence states to conduction band. Vacancy formation shows a significance increase in density of states near the Fermi level. Density of states at Fermi level is proportional to the conductivity, so an increase in density of states near the Fermi level increases the conductivity. The experimental measured ionic conductivity is found to 0.095 S cm(-1) at 600 degrees C. The microstructural studies is also reported in this work.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Fermi level, Band gap, Vacancy formation energy, Density of states, Association energy
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-232384 (URN)10.1016/j.ceramint.2018.04.068 (DOI)000436351700098 ()2-s2.0-85047612214 (Scopus ID)
Note

QC 20180727

Available from: 2018-07-27 Created: 2018-07-27 Last updated: 2018-07-27Bibliographically approved
Singh, V., Belova, L., Singh, B. & Sharma, Y. C. (2018). Biodiesel production using a novel heterogeneous catalyst, magnesium zirconate (Mg2Zr5O12): Process optimization through response surface methodology (RSM). Energy Conversion and Management, 174, 198-207
Open this publication in new window or tab >>Biodiesel production using a novel heterogeneous catalyst, magnesium zirconate (Mg2Zr5O12): Process optimization through response surface methodology (RSM)
2018 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 174, p. 198-207Article in journal (Refereed) Published
Abstract [en]

A heterogeneous catalyst, magnesium zirconate (Mg2Zr5O12) was synthesized by co-precipitation and was used for biodiesel production via transesterification. Kusum oil was used as a feedstock. Catalyst characterization was accomplished by TGA, XRD, ATR FTIR, SEM, and EDX. The parameters viz. particle size, zeta potential, BET surface area and basicity of the catalyst were also determined. Characterization of catalyst supports the formation of single phase Mg2Zr5O12 and the catalyst was able to catalyse the transesterification reaction for economically viable biodiesel production. Various reaction parameters such as molar ratio (methanol: oil), catalyst concentration and reaction time were optimized in presence of Mg2Zr5O12 by using Response Surface Methodology (RSM) based on Box-Behnken design. The catalyst was reusable up to seven runs with ∼75% conversion in the seventh run. Maximum conversion of 97.98% FAME was obtained at 18:1 M ratio (methanol: oil), 2.5 wt% of catalyst at 65 °C temperature for 150 min. Physicochemical properties of FAME were also studied as per ASTM standard method. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Heterogeneous catalyst, Kusum oil, Magnesium zirconate, Response surface methodology, Transesterification, ASTM standards, Biodiesel, Magnesium, Magnesium compounds, Methanol, Optimization, Particle size, Surface properties, Synthetic fuels, Zirconium compounds, Catalyst characterization, Characterization of catalysts, Physicochemical property, Transesterification reaction, Zirconates, Catalysts
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-236629 (URN)10.1016/j.enconman.2018.08.029 (DOI)000447102100017 ()2-s2.0-85051465124 (Scopus ID)
Note

Export Date: 22 October 2018; Article; CODEN: ECMAD; Correspondence Address: Sharma, Y.C.; Renewable Energy and Biofuels Research Laboratory, Department of Chemistry, Indian Institute of Technology (BHU)India; email: ysharma.apc@itbhu.ac.in; Funding details: BHU, Banaras Hindu University; Funding details: IITB, Indian Institute of Technology Bombay; Funding text: The authors are thankful to Department of Science & Technology , Govt. of India, New Delhi for funding the IBSA project and gratefully acknowledge Indian Institute of Technology (BHU) for providing TA ship to Ms Veena Singh. QC 20181114

Available from: 2018-11-14 Created: 2018-11-14 Last updated: 2018-11-14Bibliographically approved
Davydova, A., Tselikov, G., Dilone, D., Rao, K. V., Kabashin, A. V. & Belova, L. (2018). Fabrication of thin ZnO films with wide-range tuned optical properties by reactive magnetron sputtering. Semiconductor Science and Technology, 33(2), Article ID 025004.
Open this publication in new window or tab >>Fabrication of thin ZnO films with wide-range tuned optical properties by reactive magnetron sputtering
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2018 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 33, no 2, article id 025004Article in journal (Refereed) Published
Abstract [en]

We report the manufacturing of thin zinc oxide films by reactive magnetron sputtering at room temperature, and examine their structural and optical properties. We show that the partial oxygen pressure in DC mode can have dramatic effect on absorption and refractive index (RI) of the films in a broad spectral range. In particular, the change of the oxygen pressure from 7% to 5% can lead to either conventional crystalline ZnO films having low absorption and characteristic descending dependence of RI from 2.4-2.7 RIU in the visible to 1.8-2 RIU in the near-infrared (1600 nm) range, or to untypical films, composed of ZnO nano-crystals embedded into amorphous matrix, exhibiting unexpectedly high absorption in the visible-infrared region and ascending dependence of RI with values varying from 1.5 RIU in the visible to 4 RIU in the IR (1600 nm), respectively. Untypical optical characteristics in the second case are explained by defects in ZnO structure arising due to under-oxidation of ZnO crystals. We also show that the observed defect-related film structure remains stable even after annealing of films under relatively high temperatures (30 min under 450 degrees C). We assume that both types of films can be of importance for photovoltaic (as contact or active layers, respectively), as well as for chemical or biological sensing, optoelectronics etc.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
reactive magnetron sputtering, thin films, optical properties, zinc oxide
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-221921 (URN)10.1088/1361-6641/aaa050 (DOI)000419805700003 ()2-s2.0-85040975282 (Scopus ID)
Note

QC 20180131

Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2018-02-05Bibliographically approved
Shen, Z., Grüner, D., Eriksson, M., Belova, L., Nan, C.-W. -. & Yan, H. (2017). Ordered coalescence of nano-crystals in alkaline niobate ceramics with high remanent polarization. Journal of Materiomics, 3(4), 267-272
Open this publication in new window or tab >>Ordered coalescence of nano-crystals in alkaline niobate ceramics with high remanent polarization
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2017 (English)In: Journal of Materiomics, ISSN 2352-8478, Vol. 3, no 4, p. 267-272Article in journal (Refereed) Published
Abstract [en]

Lead-free alkali niobates Na0.5K0.5NbO3 (NKN) ceramics, with significantly enhanced ferroelectric remanent polarization (Pr), were prepared using Spark Plasma Sintering (SPS). Three types of boundaries were observed in the ceramics, being grain boundaries between faceted grains, domain boundaries that separate ferroelectric domains inside individual grains, and nanoscale sub-grain boundaries that reveal the nano-scale mosaicity of individual grains. Part of the sub-grain boundaries were from initial powder particles. The other sub-grain boundaries were built by ordered coalescence of nano-crystals during rapid SPS process. It was worthwhile to emphasize that the ordered coalescence of nano-crystals in bulk ceramics during sintering takes place and completes within minutes. These sub-grain features would disappear at higher temperature by long time sintering. Rapid Spark Plasma Sintering allowed us to capture this transient microstructure. The significantly enhanced ferroelectric Pr of NKN was attributed to nanoscale sub-boundaries, which stimulated the dynamics of ferroelectric domain formation and switching.

Place, publisher, year, edition, pages
Chinese Ceramic Society, 2017
Keywords
Lead-free, NKN, Ordered coalescence, Remanent polarization, SPS
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-218116 (URN)10.1016/j.jmat.2017.08.004 (DOI)000423882800004 ()2-s2.0-85033501079 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Research Council
Note

QC 20171124

Available from: 2017-11-24 Created: 2017-11-24 Last updated: 2018-02-16Bibliographically approved
Riazanova, A. V., Costanzi, B. N., Aristov, A. I., Rikers, Y. G., Mulders, J. J., Kabashin, A. V., . . . Belova, L. M. (2016). Gas-assisted electron-beam-induced nanopatterning of high-quality titanium oxide. Nanotechnology, 27(11), Article ID 115304.
Open this publication in new window or tab >>Gas-assisted electron-beam-induced nanopatterning of high-quality titanium oxide
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2016 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 27, no 11, article id 115304Article in journal (Refereed) Published
Abstract [en]

Electron-beam-induced deposition of titanium oxide nanopatterns is described. The precursor is titanium tetra-isopropoxide, delivered to the deposition point through a needle and mixed with oxygen at the same point via a flow through a separate needle. The depositions are free of residual carbon and have an EDX determined stoichiometry of TiO2.2. High resolution transmission electron microscopy and Raman spectroscopy studies reveal an amorphous structure of the fabricated titanium oxide. Ellipsometric characterization of the deposited material reveals a refractive index of 2.2-2.4 RIU in the spectral range of 500-1700 nm and a very low extinction coefficient (lower than 10(-6) in the range of 400-1700 nm), which is consistent with high quality titanium oxide. The electrical resistivity of the titanium oxide patterned with this new process is in the range of 10-40 G Omega cm and the measured breakdown field is in the range of 10-70 V mu m(-1). The fabricated nanopatterns are important for a variety of applications, including field-effect transistors, memory devices, MEMS, waveguide structures, bio-and chemical sensors.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
gas-assisted EBID, 3D nanopatterning, high-purity insulator, titanium tetra-isopropoxide (TTIP), purification
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-183607 (URN)10.1088/0957-4484/27/11/115304 (DOI)000370259800016 ()26878568 (PubMedID)2-s2.0-84959010416 (Scopus ID)
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20160319

Available from: 2016-03-19 Created: 2016-03-18 Last updated: 2017-11-30Bibliographically approved
Guo, F., Belova, L. M. & McMichael, R. D. (2015). Nonlinear ferromagnetic resonance shift in submicron Permalloy ellipses. Physical Review B. Condensed Matter and Materials Physics, 91(6), Article ID 064426.
Open this publication in new window or tab >>Nonlinear ferromagnetic resonance shift in submicron Permalloy ellipses
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 6, article id 064426Article in journal (Refereed) Published
Abstract [en]

We report a systematic study of nonlinearity in the ferromagnetic resonance of a series of submicron Permalloy ellipses with varying aspect ratios. At high excitation powers, the resonances are found to shift to higher or lower applied field. We focus here on the sign of the shift and its dependence on the applied field and shape-induced anisotropy of the ellipses. Using ferromagnetic resonance force microscopy, we find that the measured nonlinear coefficient changes sign as a function of anisotropy field and applied field in qualitative agreement with a macrospin analysis. This macrospin analysis also points to origins of the nonlinearity in a combination of hard-axis in-plane anisotropy and precession ellipticity. In comparison of the macrospin predictions with both experimental and micromagnetic modeling results, we measure/model values of the nonlinear coefficient that are more positive than predicted by the macrospin model. The results are useful in understanding nonlinear physics in nanomagnets and applications of spin-torque oscillators.

Keywords
Oscillator, Modes
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-163468 (URN)10.1103/PhysRevB.91.064426 (DOI)000350317300016 ()2-s2.0-84924036582 (Scopus ID)
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20150408

Available from: 2015-04-08 Created: 2015-04-07 Last updated: 2017-12-04Bibliographically approved
Araujo, C. M., Nagar, S., Ramzan, M., Shukla, R., Jayakumar, O. D., Tyagi, A. K., . . . Rao, K. V. (2014). Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites. Scientific Reports, 4, 4686
Open this publication in new window or tab >>Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites
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2014 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4686-Article in journal (Refereed) Published
Abstract [en]

We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-145262 (URN)10.1038/srep04686 (DOI)000334286200001 ()2-s2.0-84926453514 (Scopus ID)
Funder
VinnovaSwedish Research CouncilCarl Tryggers foundation Knut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20140516

Available from: 2014-05-16 Created: 2014-05-15 Last updated: 2017-12-05Bibliographically approved
Riazanova, A. V., Aristov, A., Rikers, Y. G. M., Ström, V., Mulders, J. J. L., Kabashin, A. V. & Belova, L. M. (2014). Gas-assisted electron-beam-induced nanopatterning of high-quality Si-based insulator. Nanotechnology, 25(15), 155301
Open this publication in new window or tab >>Gas-assisted electron-beam-induced nanopatterning of high-quality Si-based insulator
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2014 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, no 15, p. 155301-Article in journal (Refereed) Published
Abstract [en]

An oxygen-assisted electron-beam-induced deposition (EBID) process, in which an oxygen flow and the vapor phase of the precursor, tetraethyl orthosilicate (TEOS), are both mixed and delivered through a single needle, is described. The optical properties of the SiO(2+delta) (-0.04 <= delta <= +0.28) are comparable to fused silica. The electrical resistivity of both single-needle and double-needle SiO(2+delta) are comparable (greater than 7 G Omega cm) and a measured breakdown field is greater than 400 V mu m(-1). Compared to the double-needle process the advantage of the single-needle technique is the ease of alignment and the proximity to the deposition location, which facilitates fabrication of complex 3D structures for nanophotonics, photovoltaics, micro- and nano-electronics applications.

Keywords
gas-assisted EBID, 3D nanopatterning, high-purity insulator, tetraethyl orthosilicate (TEOS), purification
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-132364 (URN)10.1088/0957-4484/25/15/155301 (DOI)000333394100005 ()2-s2.0-84897861464 (Scopus ID)
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20140508. Updated from submitted to published.

Available from: 2013-10-25 Created: 2013-10-25 Last updated: 2017-12-06Bibliographically approved
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