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Lighting and Sensing Applications of Nanostructured ZnO, CuO and Their Composites
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology. (Physical Electronics and Nanotechnology)
2012 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

Low dimensional nanostructures of zinc oxide (ZnO), cupric oxide (CuO), and their composite nanostructures possess remarkable physical and chemical properties. Fundamental understanding and manipulation of these unique properties are crucial for all potential applications. Integration of nanostructured ZnO and CuO and their hybrid composites may play a significant role in the existing technology while paving the way for new exciting areas. Solution based low temperature synthesis of ZnO and CuO nanostructures have attracted extensive research efforts during the last decade. These efforts resulted in a plenteous number of nanostructures ranging from quantum dots into very complex three dimensional nanomaterials. Among the various low temperature synthesis methods the hydrothermal technique became one of the most popular approaches. The use of hydrothermal approach enabled the synthesis of diversity of nanomaterials on conventional and nonconventional substrates such as metals, glass, plastic and paper etc.

The primary objectives of this thesis are to study and understand the characteristics of nanostructured ZnO, CuO, and their hybrid composites synthesized at low temperature. Likewise, the hybrid composites were successfully utilized to fabricate light emitting diodes and sensors. This thesis is organized into three major parts. In the beginning the synthesis and characterization of nanostructured ZnO, CuO, and their composite nanostructures are elaborated. Efforts have been made to understand the selective assembly of hierarchical CuO nanostructures on ZnO nanorods and to correlate it to the observed unique properties of the CuO/ZnO composite nanostructures. In the second part of the thesis fabrication, characterization, and device application of ZnO/p-polymer hybrid light emitting diode (HyLEDs) on flexible substrates are presented. In particular single and blended p-type light emissive polymers were controllably developed for potential greener and cheaper white light emitters. It was found that the HyLEDs exhibited rectifying diode characteristics together with white light emission covering the entire visible range. In the third part, pH and relative humidity sensing applications of CuO nanoflowers, and CuO/ZnO nanocorals, respectively, are described. A pH sensor based on CuO nanoflowers demonstrated good sensitivity and reproducibility over a wide range of pH. By taking the advantages of the selective growth of CuO nanostructures on ZnO nanorods and their naturally formed p-n heterojunction the realization of high sensitivity humidity sensor was achieved. The humidity sensor fabricated from the CuO/ZnO nanocorals displayed the highest sensitivity factor reported so far for its constituent materials; along with reasonably fast dynamic responses. A brief outlook into future challenges and opportunities are also presented in the last part of the thesis. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 79 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1484
Keyword [en]
ZnO, CuO, Nanostructures, Composites, ZnO/polymer LEDs, humidity sensor, p-n heterojunction
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-85111ISBN: 978-91-7519-755-5 (print)OAI: oai:DiVA.org:liu-85111DiVA: diva2:564811
Public defence
2012-12-06, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:00 (English)
Opponent
Supervisors
Projects
Nanophotonics
Available from: 2012-11-27 Created: 2012-11-05 Last updated: 2017-02-23Bibliographically approved
List of papers
1. Deposition of Well-Aligned ZnO Nanorods at 50 degrees C on Metal, Semiconducting Polymer, and Copper Oxides Substrates and Their Structural and Optical Properties
Open this publication in new window or tab >>Deposition of Well-Aligned ZnO Nanorods at 50 degrees C on Metal, Semiconducting Polymer, and Copper Oxides Substrates and Their Structural and Optical Properties
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2010 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 7, 3250-3256 p.Article in journal (Refereed) Published
Abstract [en]

A two-step chemical bath deposition was utilized to synthesize ZnO nanorod arrays (ZNRAs) on metals, poly(3,4-ethylenedioxythiophene)/poly(strenesulfonate) (PEDOT/PSS) coated flexible plastic foils, and copper oxides coated glass substrates. The whole synthesis procedure was carried out at a low temperature of 50 degrees C, without any other substrate treatments. The low growth temperature showed improved influence on both the ZNRAs structural and optical properties. Scanning electron microscopy (SEM) images revealed well-aligned ZNRAs with large aspect ratios, and X-ray diffraction (X RI)) analysis indicated that single crystalline ZNRAs were achieved with high c-axial orientation tendency. Room temperature photoluminescence (PL) measurements demonstrated excellent optical properties of the as-grown ZNRAs with very low defect concentration contrary to what was believed to be achieved when lowering the growth temperature. The impact of the low deposition temperature on the ZNRAs structure is discussed in connection to the thermodynamics constraints, while the temperature effect on the defects formation and density in the as-deposited ZNRAs is elaborated and compared with recent theoretical calculations that appeared in the literature.

Place, publisher, year, edition, pages
The American Chemical Society, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58270 (URN)10.1021/cg100390x (DOI)000279422700059 ()
Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2017-12-12
2. CuO/ZnO Nanocorals synthesis via hydrothermal technique: growth mechanism and their application as Humidity Sensor
Open this publication in new window or tab >>CuO/ZnO Nanocorals synthesis via hydrothermal technique: growth mechanism and their application as Humidity Sensor
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2012 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 23, 11583-11590 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate hydrothermal synthesis of coral-like CuO nanostructures by selective growth on ZnO nanorods (NR) at low temperatures. During the hydrothermal processing the resultant hydroxylated and eroded surface of ZnO NR becomes favorable for the CuO nanostructures growth via oriented attachments. Heterojunction p-n diodes fabricated from the CuO/ZnO nanocorals (NC) reveal stable and high rectification diode properties with a turn-on voltage ~1.52 V and negligible reverse current. The humidity sensing characteristics of the CuO/ZnO NC diodes exhibit a remarkable linear (in a semilogarithmic scale) decrease in the DC resistance by more than three orders when the relative humidity is changed from 30 – 90 %. The NC humidity sensor is also found to reveal the highest sensitivity factor ~6045 among available data for the constituent material’s and a response and recovery time of 6 s and 7 s, respectively.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2012
Keyword
Zinc oxide nanorods, copper oxide nanostructures, nanocorals, relative humidity, sensitivity factor
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-76676 (URN)10.1039/c2jm16597j (DOI)000304351400026 ()
Note
funding agencies|Swedish government||Available from: 2012-04-16 Created: 2012-04-16 Last updated: 2017-12-07Bibliographically approved
3. Optical and current transport properties of CuO/ZnO nanocoral p-n heterostructure hydrothermally synthesized at low temperature
Open this publication in new window or tab >>Optical and current transport properties of CuO/ZnO nanocoral p-n heterostructure hydrothermally synthesized at low temperature
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2012 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 108, no 4, 921-928 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate the synthesis and investigate the electrical and optical characteristics of nanocorals (NCs) composed of CuO/ZnO grown at low temperature through the hydrothermal approach. High-density CuO nanostructures (NSs) were selectively grown on ZnO nanorods (NRs). The synthesized NCs were used to fabricate p-n heterojunctions that were investigated by the current density-voltage (J-V) and the capacitance-voltage (C-V) techniques. It was found that the NC heterojunctions exhibit a well-defined diode behavior with a threshold voltage of about 1.52 V and relatively high rectification factor of similar to 760. The detailed forward J-V characteristics revealed that the current transport is controlled by an ohmic behavior for V andlt;= 0.15 V, whereas at moderate voltages 1.46 andlt;= V andlt; 1.5 the current follows a J alpha exp(beta V) relationship. At higher voltages (andgt;= 1.5 V) the current follows the relation J alpha V-2, indicating that the space-charge-limited current mechanism is the dominant current transport. The C-V measurement indicated that the NC diode has an abrupt junction. The grown CuO/ZnO NCs exhibited a broad light absorption range that is covering the UV and the entire visible parts of the spectrum.

Place, publisher, year, edition, pages
Springer Verlag (Germany), 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-81220 (URN)10.1007/s00339-012-6995-2 (DOI)000307332800022 ()
Available from: 2012-09-10 Created: 2012-09-10 Last updated: 2017-12-07
4. Effect of the polymer emission on the electroluminescence characteristics of n-ZnO nanorods/p-polymer hybrid light emitting diode
Open this publication in new window or tab >>Effect of the polymer emission on the electroluminescence characteristics of n-ZnO nanorods/p-polymer hybrid light emitting diode
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2011 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 104, no 4, 1203-1209 p.Article in journal (Refereed) Published
Abstract [en]

Hybrid light emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods and polymers (single and blended) were fabricated and characterized. The ZnO nanorods were grown by the chemical bath deposition method at 50A degrees C. Three different LEDs, with blue emitting, orange-red emitting or their blended polymer together with ZnO nanorods, were fabricated and studied. The current-voltage characteristics show good diode behavior with an ideality factor in the range of 2.1 to 2.27 for all three devices. The electroluminescence spectrum (EL) of the blended device has an emission range from 450 nm to 750 nm, due to the intermixing of the blue emission generated by poly(9,9-dioctylfluorene) denoted as PFO with orange-red emission produced by poly(2-methoxy-5(20-ethyl-hexyloxy)-1,4-phenylenevinylene) 1,4-phenylenevinylene) symbolized as MEH PPV combined with the deep-band emission (DBE) of the ZnO nanorods, i.e. it covers the whole visible region and is manifested as white light. The CIE color coordinates showed bluish, orange-red and white emission from the PFO, MEH PPV and blended LEDs with ZnO nanorods, respectively. These results indicate that the choice of the polymer with proper concentration is critical to the emitted color in ZnO nanorods/p-organic polymer LEDs and careful design should be considered to obtain intrinsic white light sources.

Place, publisher, year, edition, pages
Springer Verlag (Germany), 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-70328 (URN)10.1007/s00339-011-6411-3 (DOI)000293972100029 ()
Available from: 2011-09-02 Created: 2011-09-02 Last updated: 2017-12-08
5. Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes
Open this publication in new window or tab >>Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 6, 064324- p.Article in journal (Refereed) Published
Abstract [en]

The effects of the polymer concentration on the performance of hybrid light emitting diodes (LEDs) based on zinc oxide nanorods (ZnO NRs) and poly(9,9-dioctylfluorene) (PFO) was investigated. Various characterization techniques were applied to study the performance of the PFO/ZnO NR hybrid LEDs fabricated with various PFO concentrations. The fabricated hybrid LEDs demonstrated stable rectifying diode behavior, and it was observed that the turn-on voltage of the LEDs is concentration dependent. The measured room temperature electroluminescence (EL) showed that the PFO concentration plays a critical role in the emission spectra of the hybrid LEDs. At lower PFO concentrations of 2-6 mg/ml, the EL spectra are dominated by blue emission. However, by increasing the concentration to more than 8 mg/ml, the blue emission was completely suppressed while the green emission was dominant. This EL behavior was explained by a double trap system of excitons that were trapped in the β-phase and/or in the fluorenone defects in the PFO side. The effects of current injection on the hybrid LEDs and on the EL emission were also investigated. Under a high injection current, a new blue peak was observed in the EL spectrum, which was correlated to the creation of a new chemical species on the PFO chain. The green emission peak was also enhanced with increasing injection current because of the fluorenone defects. These results indicate that the emission spectra of the hybrid LEDs can be tuned by using different polymer concentrations and by varying the current injected into the device.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
Keyword
Hybrid light emitting diodes, ZnO nanorods, PFO, electroluminescence
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-81426 (URN)10.1063/1.4754542 (DOI)000309423200142 ()
Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2017-12-07Bibliographically approved
6. CuO nanoflowers as an electrochemical pH sensor and the effect of pH on the growth
Open this publication in new window or tab >>CuO nanoflowers as an electrochemical pH sensor and the effect of pH on the growth
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2011 (English)In: JOURNAL OF ELECTROANALYTICAL CHEMISTRY, ISSN 1572-6657, Vol. 662, no 2, 421-425 p.Article in journal (Refereed) Published
Abstract [en]

Well-crystallized flower-shaped cupric oxide (CuO) nanostructures composed of thin leaves have been synthesized by simple low-temperature chemical bath method and used to fabricate pH sensor. We examined the effect of the pH on the growth of the CuO nanostructures, by changing the pH of the precursor solutions different morphologies of the CuO nanostructures were obtained. CuO nanoflowers have recently become important as a material that provides an effective surface for electrochemical activities with enhanced sensing characteristics. The proposed sensor exhibited a linear electrochemical response within a wide pH range of (2-11). The experimental results (time response, electrochemical activity, reproducibility, absorption spectra, and XRD) indicate that the CuO nanoflowers can be used in pH sensor applications with enhanced properties.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
CuO nanoflower; Morphological effect; Electrochemical; pH sensor; Repeatability
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73334 (URN)10.1016/j.jelechem.2011.09.015 (DOI)000297881200020 ()
Available from: 2012-01-03 Created: 2012-01-02 Last updated: 2014-01-15
7. Synthesis and Characterization of CuO/ZnO Composite Nanostructures: Precursor’s Effects, and their Optical Properties
Open this publication in new window or tab >>Synthesis and Characterization of CuO/ZnO Composite Nanostructures: Precursor’s Effects, and their Optical Properties
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2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

A two steps hydrothermal method was developed to synthesize CuO/ZnO composite nanostructures (NSs) on glass substrate. The CuO NSs were selectively assembled on the lateral surface of ZnO nanorods (NRs) upon short growth duration. While the CuO NSs were entirely covered the surface of ZnO NRs at extended growth durations. The growth kinetics of CuO NSs is strongly dependent on the nature and the pH value of the precursor solution. When a single precursor solution of copper nitrate was applied in the synthesis process, a coral-like CuO/ZnO NSs were obtained. However, by adding a pH controlling agent to the precursor solution significant increase in the size of the grown CuO NSs was observed. The results revealed that the grown CuO NSs were robustly adhered to ZnO NRs, however, no explicit epitaxial relationship was found. The ZnO NRs band to band and defects emissions ratio was decreased compared to that of pure ZnO NRs, suggesting that oxygen vacancies are the probable growth sites of CuO NSs. The CuO/ZnO composite NSs exhibited a broad light absorption covering the whole visible range compared to the constituent materials. The low growth temperatures along with the optical properties of CuO/ZnO suggest these composite NSs may carry great potentials in light harvesting, sensing and emitting applications.

Keyword
Hydrothermal, ZnO nanorods, CuO nanostructures, deep level defects, composite
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-81428 (URN)
Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2014-01-15Bibliographically approved

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Elsharif Zainelabdin, Ahmed ELtahir

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