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  • 1.
    Alvi, Naveed ul Hassan
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Luminescence Properties of ZnO Nanostructures and Their Implementation as White Light Emitting Diodes (LEDs)2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, luminescence properties of ZnO nanostructures (nanorods, nanotubes, nanowalls and nanoflowers) are investigated by different approaches for possible future application of these nanostructures as white light emitting diodes. ZnO nanostructures were grown by different growth techniques on different p-type substrates. Still it is a challenge for the researchers to produce a stable and reproducible high quality p-type ZnO and this seriously hinders the progress of ZnO homojunction LEDs. Therefore the excellent properties of ZnO can be utilized by constructing heterojunction with other p-type materials.

    The first part of the thesis includes paper I-IV. In this part, the luminescence properties of ZnO nanorods grown on different p-type substrates (GaN, 4H-SiC) and different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) grown on the same substrate were investigated. The effect of the post-growth annealing of ZnO nanorods and nanotubes on the deep level emissions and color rendering properties were also investigated.

    In paper I, ZnO nanorods were grown on p-type GaN and 4H-SiC substrates by low temperature aqueous chemical growth (ACG) method. The luminescence properties of the fabricated LEDs were investigated at room temperature by electroluminescence (EL) and photoluminescence (PL) measurements and consistency was found between both the measurements. The LEDs showed very bright emission that was a combination of three emission peaks in the violet-blue, green and orange-red regions in the visible spectrum.

    In paper II, different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) were grown on p-GaN and the luminescence properties of these nanostructures based LEDs were comparatively investigated by EL and PL measurements. The nanowalls structures were found to be emitting the highest emission in the visible region, while the nanorods have the highest emissions in the UV region due to its good crystal quality. It was also estimated that the ZnO nanowalls structures have strong white light with the highest color rendering index (CRI) of 95 with correlated color temperature (CCT) of 6518 K.

    In paper III, we have investigated the origin of the red emissions in ZnO by using post-growth annealing. The ZnO nanotubes were achieved on p-GaN and then annealed in different ambients (argon, air, oxygen and nitrogen) at 600 oC for 30 min. By comparative investigations of EL spectra of the LEDs it was found that more than one deep level defects are involved in the red emission from ZnO nanotubes/p-GaN LEDs. It was concluded that the red emission in ZnO can be attributed to oxygen interstitials (Oi) and oxygen vacancies (Vo) in the range of 620 nm (1.99 eV) to 690 nm (1.79 eV) and 690 nm (1.79 eV) to 750 nm (1.65 eV), respectively.

    In paper IV, we have investigated the effect of post-growth annealing on the color rendering properties of ZnO nanorods based LEDs. ZnO nanorods were grown on p-GaN by using ACG method. The as grown nanorods were annealed in nitrogen, oxygen, argon, and air ambients at 600 oC for 30 min. The color rendering indices (CRIs) and correlated color temperatures (CCTs) were estimated from the spectra emitted by the LEDs. It was found that the annealing ambients especially air, oxygen, and nitrogen were found to be very effective. The LEDs based on nanorods annealed in nitrogen ambient, have excellent color rendering properties with CRIs and CCTs of 97 and 2363 K in the forward bias and 98 and 3157 K in the reverse bias.

    In the 2nd part of the thesis, the junction temperature of n-ZnO nanorods based LEDs at the built-in potential was modeled and experiments were performed to validate the model. The LEDs were fabricated by ZnO nanorods grown on different p-type substrates (4H-SiC, GaN, and Si) by the ACG method. The model and experimental values of the temperature coefficient of the forward voltage near the built-in potential (~Vo) were compared. It was found that the series resistance has the main contribution in the junction temperature of the fabricated devices.

    In the 3rd part of the thesis, the influence of helium (He+) ion irradiation bombardment on luminescence properties of ZnO nanorods based LEDs were investigated. ZnO nanorods were grown by the vapor-liquid-solid (VLS) growth method. The fabricated LEDs were irradiated by using 2 MeV He+ ions with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. It was observed that the He+ ions irradiation affects the near band edge emissions as well as the deep level emissions in ZnO. A blue shift about 0.0347 eV and 0.082 eV was observed in the PL spectra in the near band emission and green emission, respectively. EL measurements also showed a blue shift of 0.125 eV in the broad green emission after irradiation. He+ ion irradiation affects the color rendering properties and decreases the color rendering indices from 92 to 89.

    Delarbeid
    1. Fabrication and characterization of high-brightness light emitting diodes based on n-ZnO nanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN
    Åpne denne publikasjonen i ny fane eller vindu >>Fabrication and characterization of high-brightness light emitting diodes based on n-ZnO nanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN
    Vise andre…
    2010 (engelsk)Inngår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 25, nr 6, s. 065004-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Light emitting diodes (LEDs) based on n-ZnO nanorods (NRs)/p-4H-SiC and n-ZnO (NRs)/p-GaN were fabricated and characterized. For the two LEDs the ZnO NRs were grown using a low temperature (andlt;100 degrees C) aqueous chemical growth (ACG) technique. Both LEDs showed very bright nearly white light electroluminescence (EL) emission. The observed luminescence was a result of the combination of three emission lines composed of violet-blue, green and orange-red peaks observed from the two LEDs. Room temperature photoluminescence (PL) was also measured and consistency with EL was observed. It was found that the green and violet-blue peaks are red-shifted while the orange peak is blue-shifted in the EL measurement. It was also found that due to the effect of the GaN substrate the violet-blue peak in the EL measurement is more red-shifted in n-ZnO (NRs)/p-GaN LEDs as compared to n-ZnO (NRs)/p-4H-SiC LEDs.

    sted, utgiver, år, opplag, sider
    Iop Publishing Ltd, 2010
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-57158 (URN)10.1088/0268-1242/25/6/065004 (DOI)000277982700005 ()
    Tilgjengelig fra: 2010-06-11 Laget: 2010-06-11 Sist oppdatert: 2017-12-12bibliografisk kontrollert
    2. Fabrication and comparative optical characterization of n-ZnO nanostructures (nanowalls, nanorods, nanoflowers and nanotubes)/p-GaN white-light-emitting diodes
    Åpne denne publikasjonen i ny fane eller vindu >>Fabrication and comparative optical characterization of n-ZnO nanostructures (nanowalls, nanorods, nanoflowers and nanotubes)/p-GaN white-light-emitting diodes
    Vise andre…
    2011 (engelsk)Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 64, nr 8, s. 697-700Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    White light-emitting diodes (LED) based on ZnO (nanowalls, nanorods, nanoflowers and nanotubes)/p-GaN were fabricated and their electrical, optical and electro-optical characteristics were comparatively characterized. All the LED showed rectifying behavior. The nanowalls and nanorods structures have the highest photoluminescence emission intensity in the visible and UV (at 3.29 eV) regions, respectively. The nanowalls have the highest color rendering index, with a value of 95, and the highest electroluminescence intensity with peaks approximately centered at 420, 450 nm and broad peak covering the visible region.

    sted, utgiver, år, opplag, sider
    Elsevier Science B.V., Amsterdam., 2011
    Emneord
    Zinc oxide, Nanostructure, Aqueous chemical growth, Optical properties, Heterojunctions
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-66849 (URN)10.1016/j.scriptamat.2010.11.046 (DOI)000287908300002 ()
    Tilgjengelig fra: 2011-03-22 Laget: 2011-03-21 Sist oppdatert: 2017-12-11bibliografisk kontrollert
    3. The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes
    Åpne denne publikasjonen i ny fane eller vindu >>The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes
    2011 (engelsk)Inngår i: NANOSCALE RESEARCH LETTERS, ISSN 1931-7573, Vol. 6, nr 1, s. 130-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this article, the electroluminescence (EL) spectra of zinc oxide (ZnO) nanotubes/p-GaN light emitting diodes (LEDs) annealed in different ambients (argon, air, oxygen, and nitrogen) have been investigated. The ZnO nanotubes by aqueous chemical growth (ACG) technique on p-GaN substrates were obtained. The as-grown ZnO nanotubes were annealed in different ambients at 600 degrees C for 30 min. The EL investigations showed that air, oxygen, and nitrogen annealing ambients have strongly affected the deep level emission bands in ZnO. It was concluded from the EL investigation that more than one deep level defect is involved in the red emission appearing between 620 and 750 nm and that the red emission in ZnO can be attributed to oxygen interstitials (O-i) appearing in the range from 620 nm (1.99 eV) to 690 nm (1.79 eV), and to oxygen vacancies (V-o) appearing in the range from 690 nm (1.79 eV) to 750 nm (1.65 eV). The annealing ambients, especially the nitrogen ambient, were also found to greatly influence the color-rendering properties and increase the CRI of the as - grown LEDs from 87 to 96.

    sted, utgiver, år, opplag, sider
    Springer Science Business Media, 2011
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-68784 (URN)10.1186/1556-276X-6-130 (DOI)000290525700045 ()
    Merknad
    The original publication is available at www.springerlink.com: Naveed Ul Hassan Alvi, Kamran Ul Hasan, Omer Nur and Magnus Willander, The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes, 2011, NANOSCALE RESEARCH LETTERS, (6), 1, 130. http://dx.doi.org/10.1186/1556-276X-6-130 Licensee: Springer Science Business Media http://www.springerlink.com/ Tilgjengelig fra: 2011-06-08 Laget: 2011-06-07 Sist oppdatert: 2014-01-15
    4. The effect of the post-growth annealin g on the color rendering properties of n-Zn Onanorods /p-GaN light emitting diodes
    Åpne denne publikasjonen i ny fane eller vindu >>The effect of the post-growth annealin g on the color rendering properties of n-Zn Onanorods /p-GaN light emitting diodes
    2011 (engelsk)Inngår i: Lighting Research and Technology, ISSN 1477-1535, E-ISSN 1477-0938, Vol. 43, nr 3, s. 331-336Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The effect of post-growth annealing on the colour properties of the light emitted by n-ZnO nanorods/p-GaN white LEDs has been investigated. The as-grown ZnO nanorods were annealed in nitrogen, oxygen, argon and air atmospheres at 6008C for 30 minutes. The colour rendering indices and correlated colour temperatures were calculated from the spectra emitted by the LEDs. It was observed that the ambient atmosphere used for annealing is very effective for altering the colour properties of the fabricated LEDs. The LEDs annealed in nitrogen have excellent colour rendering properties with a colour rendering index and a correlated colour temperature of 97 and 2363 K, respectively, in the forward bias and 98 and 3157K in the reverse bias.

    sted, utgiver, år, opplag, sider
    Sage, 2011
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-69152 (URN)10.1177/1477153511398025 (DOI)000294134400008 ()
    Tilgjengelig fra: 2011-06-17 Laget: 2011-06-17 Sist oppdatert: 2017-12-11bibliografisk kontrollert
    5. Junction temperature in n-ZnO nanorods/(p-4H-SiC, p-GaN, and p-Si) heterojunction light emitting diodes
    Åpne denne publikasjonen i ny fane eller vindu >>Junction temperature in n-ZnO nanorods/(p-4H-SiC, p-GaN, and p-Si) heterojunction light emitting diodes
    Vise andre…
    2010 (engelsk)Inngår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 54, nr 5, s. 536-540Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The junction temperature of n-ZnO nanorods/(p-4H-SiC, p-GaN, and p-Si) heterojunction light emitting diodes (LEDs) at built-in potential was modeled and experiments were performed at various temperatures (15-65 degrees C) to validate the model. As the LEDs operate near the built-in potential thats why it is interesting to investigate the temperature coefficient of forward voltage near the built-in potential (similar to V-o). The model and experimental values of the temperature coefficient of forward voltage near the built-in potential (similar to V-o) were compared. We measured the experimental temperature coefficient of the series resistance. By including the temperature coefficient of the series resistance in the model, the theoretical and experimental values become very close to each other. It was found that the series resistance has the main contribution in the junction temperature of our devices. We also measured the junction temperature above the built-in potential and found that the model deviates at higher forward voltage. From this observation we concluded that the model is applicable for low power devices, operated near the built-in potential.

    sted, utgiver, år, opplag, sider
    Elsevier Science B.V., Amsterdam., 2010
    Emneord
    Junction temperature, ZnO nanorods, Heterojunction LEDs
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-55507 (URN)10.1016/j.sse.2010.01.020 (DOI)000276754100008 ()
    Tilgjengelig fra: 2010-04-30 Laget: 2010-04-30 Sist oppdatert: 2017-12-12bibliografisk kontrollert
    6. Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light emitting diodes
    Åpne denne publikasjonen i ny fane eller vindu >>Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light emitting diodes
    2011 (engelsk)Inngår i: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, nr 628Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Light emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid (VLS) catalytic growth method were irradiated with 2 MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. Scanning electron microscopy (SEM) images showed that the morphology of the irradiated samples is not changed. The as-grown and He+ irradiated LEDs showed rectifying behaviour with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 eV and 0.082 eV in the near band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centred at 398 nm was nearly disappeared after irradiations. The color rendering properties shows a small decrease in the color rendering indices of 3% after 2 MeV He+ ions irradiation.

    sted, utgiver, år, opplag, sider
    SpringerOpen, 2011
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-69154 (URN)10.1186/1556-276X-6-628 (DOI)000300300100001 ()
    Tilgjengelig fra: 2011-06-17 Laget: 2011-06-17 Sist oppdatert: 2017-12-11bibliografisk kontrollert
  • 2.
    Alvi, Naveed ul Hassan
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Hussain, S.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light emitting diodes2011Inngår i: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, nr 628Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Light emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid (VLS) catalytic growth method were irradiated with 2 MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. Scanning electron microscopy (SEM) images showed that the morphology of the irradiated samples is not changed. The as-grown and He+ irradiated LEDs showed rectifying behaviour with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 eV and 0.082 eV in the near band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centred at 398 nm was nearly disappeared after irradiations. The color rendering properties shows a small decrease in the color rendering indices of 3% after 2 MeV He+ ions irradiation.

  • 3.
    Alvi, Naveed ul Hassan
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Mohammad, Riaz
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Tzamalis, Georgios
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Fabrication and characterization of high-brightness light emitting diodes based on n-ZnO nanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN2010Inngår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 25, nr 6, s. 065004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Light emitting diodes (LEDs) based on n-ZnO nanorods (NRs)/p-4H-SiC and n-ZnO (NRs)/p-GaN were fabricated and characterized. For the two LEDs the ZnO NRs were grown using a low temperature (andlt;100 degrees C) aqueous chemical growth (ACG) technique. Both LEDs showed very bright nearly white light electroluminescence (EL) emission. The observed luminescence was a result of the combination of three emission lines composed of violet-blue, green and orange-red peaks observed from the two LEDs. Room temperature photoluminescence (PL) was also measured and consistency with EL was observed. It was found that the green and violet-blue peaks are red-shifted while the orange peak is blue-shifted in the EL measurement. It was also found that due to the effect of the GaN substrate the violet-blue peak in the EL measurement is more red-shifted in n-ZnO (NRs)/p-GaN LEDs as compared to n-ZnO (NRs)/p-4H-SiC LEDs.

  • 4.
    Alvi, Naveed ul Hassan
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    ul Hasan, Kamran
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    The effect of the post-growth annealin g on the color rendering properties of n-Zn Onanorods /p-GaN light emitting diodes2011Inngår i: Lighting Research and Technology, ISSN 1477-1535, E-ISSN 1477-0938, Vol. 43, nr 3, s. 331-336Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of post-growth annealing on the colour properties of the light emitted by n-ZnO nanorods/p-GaN white LEDs has been investigated. The as-grown ZnO nanorods were annealed in nitrogen, oxygen, argon and air atmospheres at 6008C for 30 minutes. The colour rendering indices and correlated colour temperatures were calculated from the spectra emitted by the LEDs. It was observed that the ambient atmosphere used for annealing is very effective for altering the colour properties of the fabricated LEDs. The LEDs annealed in nitrogen have excellent colour rendering properties with a colour rendering index and a correlated colour temperature of 97 and 2363 K, respectively, in the forward bias and 98 and 3157K in the reverse bias.

  • 5.
    Fulati, Alimujiang
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Usman Ali, Syed M.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Asif, Muhammad H.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan. Pakistan.
    Hassan Alvi, Naveed Ul
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Brännmark, Cecilia
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Strålfors, Peter
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Börjesson, Sara I.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Danielsson, Bengt
    Lund University, Sweden.
    An intracellular glucose biosensor based on nanoflake ZnO2010Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 150, nr 2, s. 673-680Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    In this study, an improved potentiometric intracellular glucose biosensor was fabricated with immobilization of glucose oxidase on a ZnO nanoporous material. The ZnO nanoporous material with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose sensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a linear glucosedependent electrochemical response over a wide range of glucose concentration (500 nM-10 mM). The measurements of intracellular glucose concentrations with our biosensor were consistent with the values of intracellular glucose concentrations reported in the literature. The sensor also demonstrated its capability by detecting an increase in the intracellular glucose concentration induced by insulin. We found that the ZnO nanoporous material provides sensitivity as high as 1.8 times higher than that obtained using ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the excellent performance of the developed nanosensor in sensitivity, stability, selectivity, reproducibility and anti-interference was achieved. All these advantageous features of this intracellular glucose biosensor based on functionalised ZnO nanoporous material compared to ZnO nanorods demonstrate a promising way of enhancing glucose biosensor performance to measure reliable intracellular glucose concentrations within single living cells.

  • 6.
    Muniza Faraz, Sadia
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Alvi, Naveed ul Hassan
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Henry, Arne
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Wahab, Qama ul
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Post fabrication annealing effects on electrical and optical characteristics of n-ZnO nanorods/p-Si heterojunction diodesManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Annealing effects on optical and electrical properties of n-ZnO/p-Si heterojunction diodes are studied. ZnO nanorods are grown on p-Si substrate by aquous chemical growth technique. As grown samples were annealed at 400 and 600 oC in air, oxygen and nitrogen ambient. Structural, optical and electrical characteristics are studied by Scanning Electron Microscopy (SEM), Photoluminescence (PL), Current–Voltage (I-V) and Capacitance-Voltage (CV) measurements. Well aligned hexagonal–shaped vertical nanorods are revealed in SEM. PL spectra indicated higher ultraviolet to visible emission ratio with a strong peak ofnear band edge emission (NBE) and weak broad deep-level emissions (DLE). For device fabrication Al/Pt non-alloyed ohmic contacts have been evaporated. I-V characteristics indicate that annealing in air and oxygen resulted in better rectifying behavior as well as decrease in reverse leakage current. An improvement in PL intensity has been shown by the samples annealed at 400 oC.

  • 7.
    Rahman, M. M.
    et al.
    Gothenburg University, Gothenburg, Sweden.
    Klason, P.
    Gothenburg University, Gothenburg, Sweden.
    Naveed, H.A.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Fabrication and characterization of white light emitting diode based on ZnO nanorods on p-Si2008Inngår i: 8th IEEE Conference on Nanotechnology, 2008. NANO '08., Piscataway, NJ, USA: IEEE , 2008, s. 51-54Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recently zinc oxide (ZnO) has drawn attention as it exhibits promising properties for making optoelectronic devices, biosensors. In this paper we will present our recent results from research work on the fabrication of light emitting diodes (LEDs) based on n-ZnO nanorods grown on p-Si by a low temperature chemical approach. The ideality factor of the p- Si/n-ZnO junctions was found to be 5.47+0.67. The high value is probably due to the presence of surface state. Structural, electrical and optical characterization from different processed LEDs will be presented and analyzed.          

  • 8.
    Riaz, M
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Fulati, Alimujiang
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Amin, Gul
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Alvi, N H
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Buckling and elastic stability of vertical ZnO nanotubes and nanorods2009Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 3, s. 034309-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Buckling and elastic stability study of vertical well aligned ZnO nanorods grown on Si substrate and ZnO nanotubes etched from the same nanorods was done quantitatively by nanoindentation technique. The critical load, modulus of elasticity, and flexibility of the ZnO nanorods and nanotubes were observed and we compared these properties for the two nanostructures. It was observed that critical load of nanorods (2890 mu N) was approximately five times larger than the critical load of the nanotubes (687 mu N). It was also observed that ZnO nanotubes were approximately five times more flexible (0.32 nm/mu N) than the nanorods (0.064 nm/mu N). We also calculated the buckling energies of the ZnO nanotubes and nanorods from the force displacement curves. The ratio of the buckling energies was also close to unity due to the increase/decrease of five times for one parameter (critical load) and increase/decrease of five times for the other parameter (displacement) of the two samples. We calculated critical load, critical stress, strain, and Young modulus of elasticity of single ZnO nanorod and nanotube. The high flexibility of the nanotubes and high elasticity of the ZnO nanorods can be used to enhance the efficiency of piezoelectric nanodevices. We used the Euler buckling model and shell cylindrical model for the analysis of the mechanical properties of ZnO nanotubes and nanorods.

  • 9.
    Ul Hasan, Kamran
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Ul Hassan Alvi, Naveed
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Single nanowire-based UV photodetectors for fast switching2011Inngår i: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, nr 348Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Relatively long (30 mu m) high quality ZnO nanowires (NWs) were grown by the vapor-liquid-solid (VLS) technique. Schottky diodes of single NW were fabricated by putting single ZnO NW across Au and Pt electrodes. A device with ohmic contacts at both the sides was also fabricated for comparison. The current-voltage (I-V) measurements for the Schottky diode show clear rectifying behavior and no reverse breakdown was seen down to -5 V. High current was observed in the forward bias and the device was found to be stable up to 12 V applied bias. The Schottky barrier device shows more sensitivity, lower dark current, and much faster switching under pulsed UV illumination. Desorption and re-adsorption of much smaller number of oxygen ions at the Schottky junction effectively alters the barrier height resulting in a faster response even for very long NWs. The NW was treated with oxygen plasma to improve the switching. The photodetector shows high stability, reversibility, and sensitivity to UV light. The results imply that single ZnO NW Schottky diode is a promising candidate for fabricating UV photodetectors.

  • 10.
    Ul Hassan Alvi, Naveed
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Riaz, Muhammad
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Tzamalis, G
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Junction temperature in n-ZnO nanorods/(p-4H-SiC, p-GaN, and p-Si) heterojunction light emitting diodes2010Inngår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 54, nr 5, s. 536-540Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The junction temperature of n-ZnO nanorods/(p-4H-SiC, p-GaN, and p-Si) heterojunction light emitting diodes (LEDs) at built-in potential was modeled and experiments were performed at various temperatures (15-65 degrees C) to validate the model. As the LEDs operate near the built-in potential thats why it is interesting to investigate the temperature coefficient of forward voltage near the built-in potential (similar to V-o). The model and experimental values of the temperature coefficient of forward voltage near the built-in potential (similar to V-o) were compared. We measured the experimental temperature coefficient of the series resistance. By including the temperature coefficient of the series resistance in the model, the theoretical and experimental values become very close to each other. It was found that the series resistance has the main contribution in the junction temperature of our devices. We also measured the junction temperature above the built-in potential and found that the model deviates at higher forward voltage. From this observation we concluded that the model is applicable for low power devices, operated near the built-in potential.

  • 11.
    Ul Hassan Alvi, Naveed
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Ul Hasan, Kamran
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes2011Inngår i: NANOSCALE RESEARCH LETTERS, ISSN 1931-7573, Vol. 6, nr 1, s. 130-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, the electroluminescence (EL) spectra of zinc oxide (ZnO) nanotubes/p-GaN light emitting diodes (LEDs) annealed in different ambients (argon, air, oxygen, and nitrogen) have been investigated. The ZnO nanotubes by aqueous chemical growth (ACG) technique on p-GaN substrates were obtained. The as-grown ZnO nanotubes were annealed in different ambients at 600 degrees C for 30 min. The EL investigations showed that air, oxygen, and nitrogen annealing ambients have strongly affected the deep level emission bands in ZnO. It was concluded from the EL investigation that more than one deep level defect is involved in the red emission appearing between 620 and 750 nm and that the red emission in ZnO can be attributed to oxygen interstitials (O-i) appearing in the range from 620 nm (1.99 eV) to 690 nm (1.79 eV), and to oxygen vacancies (V-o) appearing in the range from 690 nm (1.79 eV) to 750 nm (1.65 eV). The annealing ambients, especially the nitrogen ambient, were also found to greatly influence the color-rendering properties and increase the CRI of the as - grown LEDs from 87 to 96.

  • 12.
    Ul Hassan Alvi, Naveed
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    ul Hassan, Wasied
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Farooq, B
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Influence of different growth environments on the luminescence properties of ZnO nanorods grown by the vapor-liquid-solid (VLS) method2013Inngår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 106, s. 158-163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ZnO nanorods (NRs) are grown in different atmospheres (argon, air, oxygen and nitrogen) by using the vapor-liquid-solid (VLS) method. The influence of different growth atmospheres on the luminescence properties has been investigated by using the photoluminescence (PL), cathodoluminescence (CL) and electroluminescence (EL) spectra measurements at room temperature. The PL spectra investigations reveal that the air, the oxygen and the nitrogen growth atmospheres have strongly affected the oxygen interstitial (O-i) and oxygen vacancy (V-o) related deep level emission (DLE) bands in ZnO and this fact is also found consistent with the cathodoluminescence (CL) and electroluminescence (EL) spectra investigations. The color rendering investigations reveal that the growth atmospheres have also influenced the color quality of the emitted light. These results indicate that the defects related emissions from the band gap of ZnO NRs can be tuned by using different growth atmospheres. These results can be useful for the development of white light emitting diodes (WLEDs).

  • 13.
    Ul Hassan Alvi, Naveed
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Usman Ali, Syed
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Hussain, S
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Fabrication and comparative optical characterization of n-ZnO nanostructures (nanowalls, nanorods, nanoflowers and nanotubes)/p-GaN white-light-emitting diodes2011Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 64, nr 8, s. 697-700Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    White light-emitting diodes (LED) based on ZnO (nanowalls, nanorods, nanoflowers and nanotubes)/p-GaN were fabricated and their electrical, optical and electro-optical characteristics were comparatively characterized. All the LED showed rectifying behavior. The nanowalls and nanorods structures have the highest photoluminescence emission intensity in the visible and UV (at 3.29 eV) regions, respectively. The nanowalls have the highest color rendering index, with a value of 95, and the highest electroluminescence intensity with peaks approximately centered at 420, 450 nm and broad peak covering the visible region.

  • 14.
    Ul Hassan Alvi, Naveed
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    The effect of the post-growth annealing on the electroluminescence properties of n-ZnO nanorods/p-GaN light emitting diodes2010Inngår i: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 47, nr 6, s. 754-761Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we investigated the effect of post-growth annealing treatment on the electroluminescence (EL) of n-ZnO nanorods/p-GaN light emitting diodes. The ZnO nanorods were grown by the low temperature (less than100 degrees C) aqueous chemical growth (ACC) technique. The as-grown ZnO nanorods were annealed in nitrogen, oxygen, argon, and air ambients at 600 degrees C for 30 min. The electroluminescence (EL) measurements showed that the deep level defects related emissions in ZnO were greatly affected by the annealing of the n-ZnO nanorods in different ambients. By comparing the EL spectra of ZnO nanorods annealed in different ambients it was found that nitrogen annealing ambient is very effective in shifting the emission peak from the green region to the red region. It was also concluded that the red emission in ZnO was attributed to oxygen vacancies WO. The effect of the annealing ambient and the temperature dependence electroluminescence were discussed with relation to the intrinsic and extrinsic defects.

  • 15.
    Usman Ali, Syed
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Ul Hassan Alvi, Naveed
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Hussain Ibupoto, Zafar
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Danielsson, Bengt
    Acromed Invest AB.
    Selective potentiometric determination of uric acid with uricase immobilized on ZnO nanowires2011Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 152, nr 2, s. 241-247Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, a potentiometric uric acid biosensor was fabricated by immobilization of uricase onto zinc oxide (ZnO) nanowires. Zinc oxide nanowires with 80-150 nm in diameter and 900 nm to 1.5 mu m in lengths were grown on the surface of a gold coated flexible plastic substrate. Uricase was electrostatically immobilized on the surface of well aligned ZnO nanowires resulting in a sensitive, selective, stable and reproducible uric acid biosensor. The potentiometric response of the ZnO sensor vs Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (1-650 mu M) suitable for human blood serum. By applying a Nafion (R) membrane on the sensor the linear range could be extended to 1-1000 mu M at the expense of an increased response time from 6.25 s to less than 9 s. On the other hand the membrane increased the sensor durability considerably. The sensor response was unaffected by normal concentrations of common interferents such as ascorbic acid, glucose, and urea.

  • 16.
    Willander, Magnus
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Zaman, Siama
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Zainelabdin, Ahmed
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Amin, Gul
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Jamil Rana, Sadaf
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Israr Qadir, Muhammad
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Bano, Nargis
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Hussain, I
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Alvi, Naveed ul Hassan
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Intrinsic White Light Emission from Zinc Oxide Nanorods Heterojunctions on Large Area Substrates2011Inngår i: Proceedings of SPIE Volume 7940 / [ed] Ferechteh Hosseini Teherani, David C. Look, David J. Rogers, Bellingham, Washington, USA: SPIE - International Society for Optical Engineering, 2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Zinc oxide (ZnO) and especially in the nanostructure form is currently being intensively investigated world wide for the possibility of developing different new photonic devices. We will here present our recent findings on the controlled low temperature chemical growth of ZnO nanorods (NRs) on different large area substrates. Many different heterojunctions of ZnO NRs and p-substrates including those of crystalline e. g. p-GaN, p-SiC or amorphous nature e. g. p-polymer coated plastic and p-polymer coated paper will be shown. Moreover, the effect of the p-electrode of these heterojunctions on tuning the emitted wavelength and changing the light quality will be discussed. An example using ZnO NR/p-GaN will be shown and the electrical and electro-optical characteristics will be analyzed. For these heterojunctions the effect of post growth annealing and its effect on the electroluminescence (EL) spectrum will be shown. Finally, intrinsic white light emitting diodes based on ZnO NRs on foldable and disposable amorphous substrates (plastic and paper) will also be presented.

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