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Adam, R. E., Alnoor, H., Pozina, G., Liu, X., Willander, M. & Nur, O. (2020). Synthesis of Mg-doped ZnO NPs via a chemical low-temperature method and investigation of the efficient photocatalytic activity for the degradation of dyes under solar light. Solid State Sciences, 99, Article ID 106053.
Open this publication in new window or tab >>Synthesis of Mg-doped ZnO NPs via a chemical low-temperature method and investigation of the efficient photocatalytic activity for the degradation of dyes under solar light
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2020 (English)In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 99, article id 106053Article in journal (Refereed) Published
Abstract [en]

Doped semiconductors nanostructures (NSs) have shown great interest as a potential for green and efficient photocatalysis activities. Magnesium (Mg)-doped zinc oxide (ZnO) nanoparticles (NPs) has been synthesized by a one-step chemical low temperature (60 °C) co-precipitation method without further calcination and their photocatalytic performance for photodegradation of Methylene blue (MB) dye under the illumination of solar light is investigated. The crystal structure of the synthesized NPs is examined by X-ray diffraction (XRD). XRD data indicates a slight shift towards higher 2θ angle in Mg-doped samples as compared to the pure ZnO NPs which suggest the incorporation of Mg2+ into ZnO crystal lattice. X-ray photoelectron spectroscopy (XPS), UV–Vis spectrophotometer and cathodoluminescence (CL) spectroscopy, were used to study electronics, and optical properties, respectively. The XPS analysis confirms the substitution of the Zn2+ by the Mg2+ into the ZnO crystal lattice in agreement with the XRD data. The photocatalytic activities showed a significant enhancement of the Mg-doped ZnO NPs in comparison with pure ZnO NPs. Hole/radical scavengers were used to reveal the mechanism of the photodegradation. It was found that the addition of the Mg to the ZnO lattices increases the absorption of the hydroxyl ions at the surface of the NPs and hence acts as a trap site leading to decrease the electron-hole pair and consequently enhancing the photodegradation.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
ZnO nanoparticles, Mg-doped ZnO NPs, Photocatalytic, Photodegradation, Methylene blue, Congo red
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-164333 (URN)10.1016/j.solidstatesciences.2019.106053 (DOI)000516720100024 ()2-s2.0-85074706430 (Scopus ID)
Available from: 2020-03-18 Created: 2020-03-18 Last updated: 2020-03-24Bibliographically approved
Adam, R. E., Chalangar, E., Pirhashemi, M., Pozina, G., Liu, X., Palisaitis, J., . . . Nur, O. (2019). Graphene-based plasmonic nanocomposites for highly enhanced solar-driven photocatalytic activities. RSC Advances, 9(52), 30585-30598
Open this publication in new window or tab >>Graphene-based plasmonic nanocomposites for highly enhanced solar-driven photocatalytic activities
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2019 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 52, p. 30585-30598Article in journal (Refereed) Published
Abstract [en]

High-efficiency photocatalysts are crucial for the removal of organic pollutants and environmental sustainability. In the present work, we report on a new low-temperature hydrothermal chemical method, assisted by ultrasonication, to synthesize disruptive plasmonic ZnO/graphene/Ag/AgI nanocomposites for solar-driven photocatalysis. The plasmonic nanocomposites were investigated by a wide range of characterization techniques, confirming successful formation of photocatalysts with excellent degradation efficiency. Using Congo red as a model dye molecule, our experimental results demonstrated a photocatalytic reactivity exceeding 90% efficiency after one hour simulated solar irradiation. The significantly enhanced degradation efficiency is attributed to improved electronic properties of the nanocomposites by hybridization of the graphene and to the addition of Ag/AgI which generates a strong surface plasmon resonance effect in the metallic silver further improving the photocatalytic activity and stability under solar irradiation. Scavenger experiments suggest that superoxide and hydroxyl radicals are responsible for the photodegradation of Congo red. Our findings are important for the fundamental understanding of the photocatalytic mechanism of ZnO/graphene/Ag/AgI nanocomposites and can lead to further development of novel efficient photocatalyst materials.

Place, publisher, year, edition, pages
Royal Meteorological Society, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160568 (URN)10.1039/C9RA06273D (DOI)000487989300064 ()
Note

Funding agencies: Department of Science and Technology (ITN) at Campus Norrkoping, Linkoping University, Sweden; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation

Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2020-03-18Bibliographically approved
Duc Tran, T., Pozina, G., Amano, H., Monemar, B., Janzén, E. & Hemmingsson, C. (2016). Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy. Physical Review B, 94(4), Article ID 045206.
Open this publication in new window or tab >>Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy
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2016 (English)In: Physical Review B, ISSN 2469-9950, Vol. 94, no 4, article id 045206Article in journal (Refereed) Published
Abstract [en]

Deep levels in Mg doped GaN have been studied using deep level transient spectroscopyand minority charge carrier transient spectroscopy. Two traps are revealed in the investigatedtemperature range. In the substrate, one electron trap labelled ET1 (EC – 0.158 eV) is observedand in the Mg-doped layer, one hole trap labelled HT1 has been revealed. By varying theelectric field, it is found that the hole trap HT1 exhibits an electric field enhanced hole emissionrate. Using four theoretical models based on 3-dimensional Coulombic Poole-Frenkel effect, 3-dimensional square well Poole-Frenkel effect, phonon assisted tunneling, and 1-dimensionalCoulombic Poole-Frenkel effect including phonon assisted tunneling, the experimental data arefitted in order to justify the field enhanced emission process. It is found that the 1-dimensionalCoulombic Poole-Frenkel model including phonon assisted tunneling is consistent with theexperimental data. Since the trap exhibits Poole-Frenkel effect, we suggest it is acceptor like.From the theoretical model, the zero field activation energy of HT1 and an estimate of the holecapture cross section have been determined as Ev+0.57 eV and 1.9x10-15 cm2, respectively.Since the level is only observed in Mg-doped material, it is suggested that the trap can beassociated with a Mg related defect.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121705 (URN)10.1103/PhysRevB.94.045206 (DOI)000381484500007 ()
Note

Funding agenices: Swedish Research Council [621-2010-3850]; Swedish Energy Agency [38338-1]

Vid tiden för disputation förelåg publikationen endast som manuskript

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2016-09-26Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Kordina, O., Janzén, E., Ohshima, T. & Hemmingsson, C. (2016). Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy. Journal of Applied Physics, 119(9)
Open this publication in new window or tab >>Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 9Article in journal (Refereed) Published
Abstract [en]

By minority carrier transient spectroscopy on as-grown n-type bulk GaN produced by halide vapor phase epitaxy (HVPE) one hole trap labelled H1 (EV + 0.34 eV) has been detected. After 2 MeV-energy electron irradiation, the concentration of H1 increases and at fluences higher than 5×1014 cm-2, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (EC - 0.12 eV) and T2 (EC - 0.23 eV) increases. By studying the increase of the concentration versus electron irradiation fluences, the introduction rate of T1 and T2 using 2 MeV-energy electrons was determined to 7X10-3 cm-1 and 0.9 cm-1, respectively. Due to the low introduction rate of T1 and the low threading dislocation density in the HVPE bulk GaN material, it is suggested that the defect is associated with a primary defect decorating extended structural defects. The high introduction rate of the trap H1 suggests that the H1 defect is associated with a primary intrinsic defect or a complex.

Keywords
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121709 (URN)10.1063/1.4943029 (DOI)000372351900075 ()
Note

Funding agencies:  Swedish Research Council (VR); Swedish Energy Agency

Vid tiden för disputation förelåg publikationen som manuskript

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-12-01Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Ohshima, T., Janzén, E. & Hemmingsson, C. (2016). Electronic properties of defects in high-fluence electron irradiated bulk GaN. Physica status solidi. B, Basic research, 253(3), 521-526
Open this publication in new window or tab >>Electronic properties of defects in high-fluence electron irradiated bulk GaN
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2016 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 3, p. 521-526Article in journal (Refereed) Published
Abstract [en]

Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121707 (URN)10.1002/pssb.201552521 (DOI)000371634800018 ()
Note

Funding agencies: Swedish Research Council (VR); Swedish Energy Agency

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-12-01Bibliographically approved
Shubina, T. V., Jmerik, V. N., Davydov, V. Y., Kazanov, D. R., Smirnov, A. N., Nechaev, D. V., . . . Ivanov, S. V. (2016). III-nitride microcrystal cavities with quasi whispering gallery modes grown by molecular beam epitaxy. Physica status solidi. B, Basic research, 253(5), 845-852
Open this publication in new window or tab >>III-nitride microcrystal cavities with quasi whispering gallery modes grown by molecular beam epitaxy
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2016 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 5, p. 845-852Article in journal (Refereed) Published
Abstract [en]

This paper analyzes current trends in fabrication of III-nitride microresonators exploiting whispering gallery modes. Novel cup-cavities are proposed and their fabrication from GaN and InN by molecular beam epitaxy on patterned substrates is described. These cup-cavities can concentrate the mode energy in a subwavelength volume. Their mode energies are stable up to room temperature, being identical in large microcrystals. In these cavities, mode switching can be realized by means of refractive index variation. Cup-cavity modes, being inferior to plasmonic resonances in the respect of integral emission enhancement, have advantages for spectrally selective amplification of quantum transitions in site-controlled nano-emitters. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2016
Keywords
III-nitride semiconductors; microresonators; molecular beam epitaxy; whispering gallery modes
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-129499 (URN)10.1002/pssb.201552657 (DOI)000376593800009 ()
Note

Funding Agencies|Russian Science Foundation [14-22-00107]

Available from: 2016-06-20 Created: 2016-06-20 Last updated: 2017-11-28
Alnoor, H., Pozina, G., Khranovskyy, V., Liu, X., Iandolo, D., Willander, M. & Nur, O. (2016). Influence of ZnO seed layer precursor molar ratio on the density of interface defects in low temperature aqueous chemically synthesized ZnO nanorods/GaN light-emitting diodes. Journal of Applied Physics, 119(16), 165702
Open this publication in new window or tab >>Influence of ZnO seed layer precursor molar ratio on the density of interface defects in low temperature aqueous chemically synthesized ZnO nanorods/GaN light-emitting diodes
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 16, p. 165702-Article in journal (Refereed) Published
Abstract [en]

Low temperature aqueous chemical synthesis (LT-ACS) of zinc oxide (ZnO) nanorods (NRs) has been attracting considerable research interest due to its great potential in the development of light-emitting diodes (LEDs). The influence of the molar ratio of the zinc acetate (ZnAc): KOH as a ZnO seed layer precursor on the density of interface defects and hence the presence of non-radiative recombination centers in LT-ACS of ZnO NRs/GaN LEDs has been systematically investigated. The material quality of the as-prepared seed layer as quantitatively deduced by the X-ray photoelectron spectroscopy is found to be influenced by the molar ratio. It is revealed by spatially resolved cathodoluminescence that the seed layer molar ratio plays a significant role in the formation and the density of defects at the n-ZnO NRs/p-GaN heterostructure interface. Consequently, LED devices processed using ZnO NRs synthesized with molar ratio of 1:5M exhibit stronger yellow emission (similar to 575 nm) compared to those based on 1:1 and 1:3M ratios as measured by the electroluminescence. Furthermore, seed layer molar ratio shows a quantitative dependence of the non-radiative defect densities as deduced from light-output current characteristics analysis. These results have implications on the development of high-efficiency ZnO-based LEDs and may also be helpful in understanding the effects of the ZnO seed layer on defect-related non-radiative recombination. Published by AIP Publishing.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-129174 (URN)10.1063/1.4947593 (DOI)000375929900043 ()
Note

Funding Agencies|Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2017-11-28
Pozina, G., Ciechonski, R., Bi, Z., Samuelson, L. & Monemar, B. (2015). Dislocation related droop in InGaN/GaN light emitting diodes investigated via cathodoluminescence. Applied Physics Letters, 107(25), 251106
Open this publication in new window or tab >>Dislocation related droop in InGaN/GaN light emitting diodes investigated via cathodoluminescence
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 25, p. 251106-Article in journal (Refereed) Published
Abstract [en]

Todays energy saving solutions for general illumination rely on efficient white light emitting diodes (LEDs). However, the output efficiency droop experienced in InGaN based LEDs with increasing current injection is a serious limitation factor for future development of bright white LEDs. We show using cathodoluminescence (CL) spatial mapping at different electron beam currents that threading dislocations are active as nonradiative recombination centers only at high injection conditions. At low current, the dislocations are inactive in carrier recombination due to local potentials, but these potentials are screened by carriers at higher injection levels. In CL images, this corresponds to the increase of the dark contrast around dislocations with the injection (excitation) density and can be linked with droop related to the threading dislocations. Our data indicate that reduction of droop in the future efficient white LED can be achieved via a drastic reduction of the dislocation density by using, for example, bulk native substrates. (C) 2015 AIP Publishing LLC.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2015
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-125162 (URN)10.1063/1.4938208 (DOI)000368442100006 ()
Note

Funding Agencies|Swedish Research Council (VR); Swedish Energy Agency

Available from: 2016-02-15 Created: 2016-02-15 Last updated: 2017-11-30
Forsberg, M., Hemmingsson, C., Amano, H. & Pozina, G. (2015). Dynamic properties of excitons in ZnO/AlGaN/GaN hybrid nanostructures. Scientific Reports, 5(7889), 1-5
Open this publication in new window or tab >>Dynamic properties of excitons in ZnO/AlGaN/GaN hybrid nanostructures
2015 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, no 7889, p. 1-5Article in journal (Refereed) Published
Abstract [en]

Hybrid samples based on ZnO colloidal nanocrystals (NCs) deposited on AlGaN/GaN quantum well (QW) structures with different top barrier thickness d = 3, 6 and 9 nm are studied by time-resolved photoluminescence. Thermal behavior of the QW exciton lifetime in the hybrids and in the bare QW structures has been compared and it has been found that the QW exciton recombination rate increases in the hybrid having d = 3 nm and decreases in the hybrid with d = 6 nm, while no change has been observed for the structure with d = 9 nm. It is suggested that non-radiative resonance energy transfer from the QW excitons to the ZnO NCs and a variation of the surface potential can both influence the QW exciton lifetime in the hybrids.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
Keywords
Ultrafast photonics; Two-dimensional materials
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113739 (URN)10.1038/srep07889 (DOI)000348028300008 ()25601650 (PubMedID)
Note

Article

Available from: 2015-01-29 Created: 2015-01-29 Last updated: 2017-12-05Bibliographically approved
Alnoor, H., Chey, C. O., Pozina, G., Liu, X., Khranovskyy, V., Willander, M. & Nour, O. (2015). Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods. AIP Advances, 5(8), Article ID 087180.
Open this publication in new window or tab >>Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
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2015 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 5, no 8, article id 087180Article in journal (Refereed) Published
Abstract [en]

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 degrees C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (mu-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-122070 (URN)10.1063/1.4929981 (DOI)000360655900089 ()
Note

Funding Agencies|Avdanced Functional Materials (AFM) SFO project at Linkoping Univeristy, Sweden

Available from: 2015-12-18 Created: 2015-10-19 Last updated: 2017-12-01
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ORCID iD: ORCID iD iconorcid.org/0000-0002-9840-7364

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