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  • 1.
    Alvi, Naveed ul Hassan
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    ul Hasan, Kamran
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    The effect of the post-growth annealin g on the color rendering properties of n-Zn Onanorods /p-GaN light emitting diodes2011In: Lighting Research and Technology, ISSN 1477-1535, E-ISSN 1477-0938, Vol. 43, no 3, p. 331-336Article in journal (Refereed)
    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.

  • 2.
    Israr, Muhammad Qadir
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    ul Hasan, Kamran
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sadaf, Jamil Rana
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Engquist, Isak
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Danielsson, B.
    Pure and Applied Biochemistry, Lund University, Box 124, SE-221 00 Lund, Sweden.
    Structural characterization and biocompatible applications of graphene nanosheets for miniaturization of potentiometric cholesterol biosensor2011In: Journal of Biosensors & Bioelectronics, ISSN 2155-6210, Vol. 2, no 3Article in journal (Refereed)
    Abstract [en]

    The potentiometric cholesterol biosensor based on graphene nanosheets has been successfully miniaturized. Cholesterol oxidase (ChOx) has been immobilized onto graphene nanosheets exfoliated on copper wire through the process of physical adsorption,. The presented potentiometric biosensor renders effective selectivity and sensitivity (~82 mV/decade) for the detection of cholesterol biomolecules in 1 × 10−6 M to 1 × 10−3 M logarithmic range and quick output response within ~ 4 sec. The stability and reusability of the biosensor has also been investigated for the above mentioned range of cholesterol concentrations. The enzyme activity measurements on graphene nanosheets are studied using UV-Visible and FTIR spectrophotometers. Additionally, the functioning of the presented biosensor is studied for a range of temperatures (15-70 °C) and pH values (4-9).

  • 3.
    Sultana, Kishwar
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    ul Hasan, Kamran
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Alvi, N, H.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Klason, P.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    A comparative study of the electrodeposition and the aqueous chemical growth techniques for the utilization of ZnO nanorods on p-GaN for white light emitting diodes2011In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 49, no 1, p. 32-42Article in journal (Refereed)
    Abstract [en]

    Vertically well aligned zinc oxide nanorods (ZnO NRs) were grown on p-GaN by electrodeposition (ED) and aqueous chemical growth (ACG) techniques and the structures were employed to fabricate white light emitting diodes (LEDs). Room temperature current voltage (IV), photoluminescence (PL), and electroluminescence (EL) measurements were performed to investigate and compare both LEDs. In general, the IV characteristics and the PL spectra of both LEDs were rather similar. Nevertheless, the EL of the ED samples showed an extra emission peak shoulder at 730 nm. Moreover, at the same injection current, the EL spectrum of the ED light emitting diode showed a small UV shift of 12 nm and its white peak was found to be broader when compared to the ACG grown LED. The broadening of the EL spectrum of the LED grown by ED is due to the introduction of more radiative deep level defects. The presented LEDs have shown excellent color rendering indexes reaching a value as high as 95. These results indicate that the ZnO nanorods grown by both techniques possess very interesting electrical and optical properties but the ED is found to be faster and more suitable for the fabrication of white LEDs.

  • 4.
    ul Hasan, Kamran
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Graphene and ZnO Nanostructures for Nano- Optoelectronic & Biosensing Applications2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There has been a remarkable excitement in graphene research since the famous discovery in 2004 by isolating a monolayer with the help of scotch tape. Graphene, merely a single layer of carbon atoms, is progressively making inroads into a wide range of applications, from ballistic electronics to biosensors to flexible/transparent displays. Graphene is a matchless material that is strong, light, transparent, and an excellent conductor of heat and electricity. On the other hand, zinc oxide (ZnO) is a wide band semiconductor that demonstrates excellent electrical, optical, catalytic and sensing properties and has numerous applications in various fields. ZnO is a natural n-type semiconductor due to the presence of intrinsic defects such as Zn interstitials and O vacancies that also contribute strongly to optical emissions in the visible region.

    The amalgamation of the exceptional properties of graphene with good semiconducting properties of ZnO can pave the way towards the realization of future devices (LED, biosensors, photovoltaics etc.).

    In this thesis, graphene nanosheets and zinc oxide (ZnO) nanostructures have beensuccessfully synthesized by using chemical vapor deposition (CVD), vapor liquidsolid (VLS) or wet chemistry routines. These nanostructures were used to fabricatenano and optoelectronic devices, including field effect transistors (FETs), lightemitting diodes (LEDs), UV detectors and biosensors. Both nanomaterial’s propertiesand performances of the devices have been characterized and reported.

    List of papers
    1. Polycation stabilization of graphene suspensions
    Open this publication in new window or tab >>Polycation stabilization of graphene suspensions
    2011 (English)In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, no 493Article in journal (Refereed) Published
    Abstract [en]

    Graphene is a leading contender for the next-generation electronic devices. We report a method to produce graphene membranes in the solution phase using polymeric imidazolium salts as a transferring medium. Graphene membranes were reduced from graphene oxides by hydrazine in the presence of the polyelectrolyte which is found to be a stable and homogeneous dispersion for the resulting graphene in the aqueous solution. A simple device with gold contacts on both sides was fabricated in order to observe the electronic properties.

    Place, publisher, year, edition, pages
    SpringerOpen, 2011
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-72038 (URN)10.1186/1556-276X-6-493 (DOI)000296254800001 ()
    Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08Bibliographically approved
    2. Controlled Growth of ZnO Nanowires on Graphene surface
    Open this publication in new window or tab >>Controlled Growth of ZnO Nanowires on Graphene surface
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Graphene, a perfect two-dimensional (2D) and completely p-conjugated honeycomb network of carbon, can potentially be a platform to serve as a substrate for growth of semiconductor nanostructures. High quality graphene films are prepared by sublimation on semiinsulating SiC grown by high temperature chemical vapor deposition (HTCVD) and on SiO2 by wet chemistry routine. Selective growth of ZnO nanowires (NWs) is performed on the graphene surface by the hydrothermal method. Mechanical stability of the graphene-ZnO heterojunction is tested by a utilizing a very simple technique. 1D ZnO NWs exhibit strong binding with 2D graphene surface and the NWs grown on graphene are of high crystal quality. This result can be very important for realizing the ultimate goal of 3D assembly at the nanoscale. The electrical contact between graphene and ZnO was analyzed by current vs. voltage (I-V) characteristics. The graphene-ZnO junction behaved as a typical metal-semiconductor ohmic contact lacking a contact barrier. These combined graphene-ZnO 3D heterojunction can pave the way for the next-generation of nano and optoelectronic devices.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-78675 (URN)
    Available from: 2012-06-18 Created: 2012-06-18 Last updated: 2014-01-15Bibliographically approved
    3. Recent progress on growth and device development of ZnO and CuO nanostructures and graphene nanosheets
    Open this publication in new window or tab >>Recent progress on growth and device development of ZnO and CuO nanostructures and graphene nanosheets
    Show others...
    2012 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 6, p. 2337-2350Article in journal (Refereed) Published
    Abstract [en]

    Recent progress on the growth of zinc oxide (ZnO), copper oxide (CuO) and graphene nanosheets is presented and discussed. We here restrict the discussion to the hydrothermal low temperature growth regime. In view of this the most critical and important parameters for obtaining nanostructures with desired morphology are discussed and presented. Among all parameters, the temperature and the pH during growth were chosen due to their strong role in affecting the produced nanostructures. The application of this method to non-conventional substrates e. g. paper, is demonstrated. Different devices are fabricated using the grown material and their performance is discussed.

    Place, publisher, year, edition, pages
    Royal Society of Chemistry, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-75118 (URN)10.1039/c1jm15152e (DOI)000299178500001 ()
    Available from: 2012-02-21 Created: 2012-02-17 Last updated: 2017-12-07
    4. Structural characterization and biocompatible applications of graphene nanosheets for miniaturization of potentiometric cholesterol biosensor
    Open this publication in new window or tab >>Structural characterization and biocompatible applications of graphene nanosheets for miniaturization of potentiometric cholesterol biosensor
    Show others...
    2011 (English)In: Journal of Biosensors & Bioelectronics, ISSN 2155-6210, Vol. 2, no 3Article in journal (Refereed) Published
    Abstract [en]

    The potentiometric cholesterol biosensor based on graphene nanosheets has been successfully miniaturized. Cholesterol oxidase (ChOx) has been immobilized onto graphene nanosheets exfoliated on copper wire through the process of physical adsorption,. The presented potentiometric biosensor renders effective selectivity and sensitivity (~82 mV/decade) for the detection of cholesterol biomolecules in 1 × 10−6 M to 1 × 10−3 M logarithmic range and quick output response within ~ 4 sec. The stability and reusability of the biosensor has also been investigated for the above mentioned range of cholesterol concentrations. The enzyme activity measurements on graphene nanosheets are studied using UV-Visible and FTIR spectrophotometers. Additionally, the functioning of the presented biosensor is studied for a range of temperatures (15-70 °C) and pH values (4-9).

    Keywords
    Graphene nanosheets; Cholesterol; Potentiometric; Biosensor
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-71322 (URN)10.4172/2155-6210.1000109 (DOI)
    Note

    On the day of the defence day the status of this arcile was "Manuscript".

    Available from: 2011-10-11 Created: 2011-10-11 Last updated: 2014-11-24Bibliographically approved
    5. Needle-Type Glucose Sensor Based on Functionalized Graphene
    Open this publication in new window or tab >>Needle-Type Glucose Sensor Based on Functionalized Graphene
    2012 (English)In: Journal of Biosensors and Bioelectronics, ISSN 2155-6210, Vol. 3, no 1Article in journal (Refereed) Published
    Abstract [en]

    We demonstrate a novel, highly efficient glucose sensor based on functionalized graphene. Glucose oxidase (GOD) immobilization has been apprehendedbythe direct interaction between carboxyl acid groups of the reduced graphene oxide (RGO) and amines of GOD together with the electrostatic interactions existing between the positively charged polymeric ionic liquid (PIL) and GOD. This combined system can provide a favorable microenvironment for the GOD to retain its good bioactivity. The enzyme-coated graphene biosensor exhibited glucose-dependent electrochemical measurements against an Ag/AgCl reference electrode. The resulting sensor show broad range detection, up to 100 mM glucose concentration, with a sensitivity of 5.59 μA/ decade. It was found that glucose biosensor based on functionalized graphene can be seen as an effective candidate for the detection of sugar concentration in clinical diagnoses.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-78677 (URN)10.4172/2155-6210.1000114 (DOI)
    Available from: 2012-06-18 Created: 2012-06-18 Last updated: 2014-01-15Bibliographically approved
    6. Graphene-based Biosensor for Intracellular Glucose Measurements
    Open this publication in new window or tab >>Graphene-based Biosensor for Intracellular Glucose Measurements
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, we report a novel graphene-based glucose micro sensor for measuring intracellular glucose. A borosilicate glass capillary (0.7 um diameter) is coated first with a graphene ink and then with a graphene-enzyme conjugate. The functional groups, presumably on the edge plane of graphene, assist binding with the free amine terminals of the glucose oxidase enzyme to result in a better immobilization. The as-prepared graphene biosensor exhibits a glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference is linear over the concentration range of interest (10–1000μM). The measured glucose concentration in human adipocytes by using our graphene based sensor is consistent with reported values of glucose concentration. This device demonstrates a simple technique to measure intracellular glucose concentration.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-78679 (URN)
    Available from: 2012-06-18 Created: 2012-06-18 Last updated: 2014-01-15Bibliographically approved
    7. Single nanowire-based UV photodetectors for fast switching
    Open this publication in new window or tab >>Single nanowire-based UV photodetectors for fast switching
    Show others...
    2011 (English)In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, no 348Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    Springer Science Business Media, 2011
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-69918 (URN)10.1186/1556-276X-6-348 (DOI)000292290700003 ()
    Available from: 2011-08-09 Created: 2011-08-08 Last updated: 2017-12-08
    8. Screen printed ZnO UV photoconductive sensor on pencil drawn circuitry over paper
    Open this publication in new window or tab >>Screen printed ZnO UV photoconductive sensor on pencil drawn circuitry over paper
    2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 21, p. 211104-Article in journal (Refereed) Published
    Abstract [en]

    Many applications require a low-cost and large-scale mode of flexible electronics with reasonably high photoresponse that can be detected without high precision measurement systems. We demonstrate a very easy to fabricate ZnO UV sensor, made on common pencil drawn circuit over a paper. ZnO nanocrystals were extracted in a high throughput via a simple and green route. This sensor is well capable of detecting UV light and demonstrates features comparable to those of made with complex and expensive techniques.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-78686 (URN)10.1063/1.4720179 (DOI)000304489900004 ()
    Available from: 2012-06-18 Created: 2012-06-18 Last updated: 2017-12-07Bibliographically approved
    9. Electro-optical and Cathodoluminescence properties of low temperature grown ZnO nanorods/p-GaN white light emitting diodes
    Open this publication in new window or tab >>Electro-optical and Cathodoluminescence properties of low temperature grown ZnO nanorods/p-GaN white light emitting diodes
    Show others...
    2010 (English)In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, ISSN 1862-6300, Vol. 207, no 1, p. 67-72Article in journal (Refereed) Published
    Abstract [en]

    Vertically aligned ZnO nanorods (NRs) with a diameter in the range of 160-200 nm were grown on p-GaN/sapphire substrates by aqueous chemical growth technique and white light emitting I diodes (LEDs) are fabricated. The properties of this LED were investigated by parameter analyzer, cathodoluminescence (CL), electroluminescence (EL), and photoluminescence (PL). The I-V characteristics of the fabricated ZnO/GaN heterojunction revealed rectifying behavior and the LED emits visible EL when bias is applied. From the CL it was confirmed that both the ZnO NRs and the p-GaN are contributing to the observed peaks. The observed EL measurements showed two emission hands centered at 450 nm and a second broad deep level defect related emission centered at 630 nm and extending from 500 rim and up to over 700 rim. Moreover, the room temperature PL spectrum of the ZnO NRs/p-GaN reveals an extra peak at the green color wavelength centered at 550 nm. Comparison of the PL, CL, and EL data suggest that the blue and near red emissions in the EL spectra are originating from Mg acceptor levels in the p-GaN and from the deep levels defects present in the ZnO NRs, respectively. The mixture of high and low energy colors, i.e., blue, green, and red, has led to the white observed luminescence.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54058 (URN)10.1002/pssa.200925393 (DOI)000274280900010 ()
    Available from: 2010-02-22 Created: 2010-02-22 Last updated: 2014-01-15
  • 5.
    ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Asif, Muhammad H.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sandberg, Mats O.
    Acreo AB, Norrköping, Sweden.
    Nur, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Graphene-based Biosensor for Intracellular Glucose MeasurementsManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, we report a novel graphene-based glucose micro sensor for measuring intracellular glucose. A borosilicate glass capillary (0.7 um diameter) is coated first with a graphene ink and then with a graphene-enzyme conjugate. The functional groups, presumably on the edge plane of graphene, assist binding with the free amine terminals of the glucose oxidase enzyme to result in a better immobilization. The as-prepared graphene biosensor exhibits a glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference is linear over the concentration range of interest (10–1000μM). The measured glucose concentration in human adipocytes by using our graphene based sensor is consistent with reported values of glucose concentration. This device demonstrates a simple technique to measure intracellular glucose concentration.

  • 6.
    ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Asif, Muhammad H.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Needle-Type Glucose Sensor Based on Functionalized Graphene2012In: Journal of Biosensors and Bioelectronics, ISSN 2155-6210, Vol. 3, no 1Article in journal (Refereed)
    Abstract [en]

    We demonstrate a novel, highly efficient glucose sensor based on functionalized graphene. Glucose oxidase (GOD) immobilization has been apprehendedbythe direct interaction between carboxyl acid groups of the reduced graphene oxide (RGO) and amines of GOD together with the electrostatic interactions existing between the positively charged polymeric ionic liquid (PIL) and GOD. This combined system can provide a favorable microenvironment for the GOD to retain its good bioactivity. The enzyme-coated graphene biosensor exhibited glucose-dependent electrochemical measurements against an Ag/AgCl reference electrode. The resulting sensor show broad range detection, up to 100 mM glucose concentration, with a sensitivity of 5.59 μA/ decade. It was found that glucose biosensor based on functionalized graphene can be seen as an effective candidate for the detection of sugar concentration in clinical diagnoses.

  • 7.
    ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. CESAT, Islamabad, Pakistan.
    Asif, Muhammad
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. COMSATS Institute Informat Technology, Lahore, Pakistan.
    Umair Hassan, Muhammad
    COMSATS Institute Informat Technology, Lahore, Pakistan.
    Sandberg, Mats O.
    Acreo AB, Norrköping, Sweden.
    Nour, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    A Miniature Graphene-based Biosensor for Intracellular Glucose Measurements2015In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 174, p. 574-580Article in journal (Refereed)
    Abstract [en]

    We report on a small and simple graphene-based potentiometric sensor for the measurement of intracellular glucose concentration. A fine borosilicate glass capillary coated with graphene and subsequently immobilized with glucose oxidase (GOD) enzyme is inserted into the intracellular environment of a single human cell. The functional groups on the edge plane of graphene assist the attachment with the free amine terminals of GOD enzyme, resulting in a better immobilization. The sensor exhibits a glucose-dependent electrochemical potential against an Ag/AgCl reference microelectrode which is linear across the whole concentration range of interest (10 - 1000 mu M). Glucose concentration in human fat cell measured by our graphene-based sensor is in good agreement with nuclear magnetic resonance (NMR) spectroscopy.

  • 8.
    ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Magnusson, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Controlled Growth of ZnO Nanowires on Graphene surfaceManuscript (preprint) (Other academic)
    Abstract [en]

    Graphene, a perfect two-dimensional (2D) and completely p-conjugated honeycomb network of carbon, can potentially be a platform to serve as a substrate for growth of semiconductor nanostructures. High quality graphene films are prepared by sublimation on semiinsulating SiC grown by high temperature chemical vapor deposition (HTCVD) and on SiO2 by wet chemistry routine. Selective growth of ZnO nanowires (NWs) is performed on the graphene surface by the hydrothermal method. Mechanical stability of the graphene-ZnO heterojunction is tested by a utilizing a very simple technique. 1D ZnO NWs exhibit strong binding with 2D graphene surface and the NWs grown on graphene are of high crystal quality. This result can be very important for realizing the ultimate goal of 3D assembly at the nanoscale. The electrical contact between graphene and ZnO was analyzed by current vs. voltage (I-V) characteristics. The graphene-ZnO junction behaved as a typical metal-semiconductor ohmic contact lacking a contact barrier. These combined graphene-ZnO 3D heterojunction can pave the way for the next-generation of nano and optoelectronic devices.

  • 9.
    ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Screen printed ZnO UV photoconductive sensor on pencil drawn circuitry over paper2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 21, p. 211104-Article in journal (Refereed)
    Abstract [en]

    Many applications require a low-cost and large-scale mode of flexible electronics with reasonably high photoresponse that can be detected without high precision measurement systems. We demonstrate a very easy to fabricate ZnO UV sensor, made on common pencil drawn circuit over a paper. ZnO nanocrystals were extracted in a high throughput via a simple and green route. This sensor is well capable of detecting UV light and demonstrates features comparable to those of made with complex and expensive techniques.

  • 10.
    Ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sandberg, Mats O
    Acreo AB.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Polycation stabilization of graphene suspensions2011In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, no 493Article in journal (Refereed)
    Abstract [en]

    Graphene is a leading contender for the next-generation electronic devices. We report a method to produce graphene membranes in the solution phase using polymeric imidazolium salts as a transferring medium. Graphene membranes were reduced from graphene oxides by hydrazine in the presence of the polyelectrolyte which is found to be a stable and homogeneous dispersion for the resulting graphene in the aqueous solution. A simple device with gold contacts on both sides was fabricated in order to observe the electronic properties.

  • 11.
    Ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. Centres of Excellence in Science & Applied Technologies (CESAT), Islamabad, Pakistan.
    Sandberg, Mats O.
    Acreo AB, Norrköping, Sweden.
    Nur, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    ZnO/Polyfluorene Hybrid LED on an Efficient Hole-Transport Layer of Graphene Oxide and Transparent Graphene Electrode2014In: Advanced Optical Materials, ISSN 2195-1071, Vol. 2, no 4, p. 326-330Article in journal (Refereed)
    Abstract [en]

    A novel Inorganic/organic hybrid light emitting diodes (LEDs) have been fabricated using reduced graphene oxide (rGO) films as a transparent conductive electrode and graphene oxide (GO) as a hole transporting layer (HTL). ZnO nanowires (NWs) are obtained by low temperature solution-based procedure. The whole device is fabricated through simple approach of spin coating and screen printing. The results indicate that graphene can be a simple solution processable substitute for PEDOT: PSS as the effective hole transport (electron blocking) layer and the ITO as a transparent conductive electrode in optoelectronic devices.

  • 12.
    Ul Hasan, Kamran
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ul Hassan Alvi, Naveed
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Single nanowire-based UV photodetectors for fast switching2011In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, no 348Article in journal (Refereed)
    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.

  • 13.
    Ul Hassan Alvi, Naveed
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ul Hasan, Kamran
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes2011In: NANOSCALE RESEARCH LETTERS, ISSN 1931-7573, Vol. 6, no 1, p. 130-Article in journal (Refereed)
    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.

  • 14.
    Umair Hassan, Muhammad
    et al.
    COMSATS Institute Informat Technology, Pakistan; University of Cambridge, England.
    Liu, Yee-Chen
    University of Cambridge, England.
    Butt, Haider
    University of Birmingham, England.
    Hasan, Kamran
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Chang, Jui-Fen
    National Central University, Taiwan.
    Abigael Olawoyin, Ayooye
    COMSATS Institute Informat Technology, Pakistan.
    Henry Friend, Richard
    COMSATS Institute Informat Technology, Pakistan.
    Low Thresholds for a Nonconventional Polymer Blend-Amplified Spontaneous Emission and Lasing in F8(1-x):SYx System2016In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 54, no 1, p. 15-21Article in journal (Refereed)
    Abstract [en]

    A mixture of two polymer materials, poly (9,9-dioctylfluorene) (F8), and one of the poly(para-phenylenevinylene) derivatives, superyellow (SY) have been used to make F8(1-x):SYx polymer blend system. Under a 3-5 ns pulsed-laser excitation, this system showed excellent optical properties with low threshold values of approximate to 14 mJ/cm(2) and approximate to 8 mJ/cm(2) for amplified spontaneous emission and optically pumped lasing, respectively. The proposed system was also electroluminescent and an interesting candidate for future research on polymer injection lasers. (C) 2015 Wiley Periodicals, Inc.

  • 15.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Ul Hasan, Kamran
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zainelabdin, Ahmed
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Zaman, Saima
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Amin, Gul
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Recent progress on growth and device development of ZnO and CuO nanostructures and graphene nanosheets2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 6, p. 2337-2350Article in journal (Refereed)
    Abstract [en]

    Recent progress on the growth of zinc oxide (ZnO), copper oxide (CuO) and graphene nanosheets is presented and discussed. We here restrict the discussion to the hydrothermal low temperature growth regime. In view of this the most critical and important parameters for obtaining nanostructures with desired morphology are discussed and presented. Among all parameters, the temperature and the pH during growth were chosen due to their strong role in affecting the produced nanostructures. The application of this method to non-conventional substrates e. g. paper, is demonstrated. Different devices are fabricated using the grown material and their performance is discussed.

1 - 15 of 15
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