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Fabrication and Photoelectrochemical Applications of II-VI Semiconductor Nanomaterials
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work we investigated fabrication of semiconductor nanomaterials and evaluated their potential for photo-chemical and photovoltaic applications. We investigated different II-VI semiconductor nanomaterial systems; (i) ZnO oriented nanowire arrays non-epitaxially grown from a substrate; and (ii) colloidal CdE (E=Te,Se,S) quantum structures synthesized by solution-based thermal decomposition of organo-metallic precursors.

We have studied the synthesis of vertically aligned ZnO nanowire arrays (NWA), by a wet chemical process on various substrates. We have extended this method wherein nanofibers of poly-L-lactide act as a substrate for the radially oriented growth of ZnO nanowires. By combining the large surface area and the flexibility of the PLLA-ZnO hierarchical nanostructure we have shown the proof-of-principle demonstration of a ‘continuous-flow’ water treatment system to decompose known organic pollutants in water, as well as render common waterborne bacteria non-viable.

We have studied synthesis of colloidal quantum dots (QD), and show size, morphology and composition tailored nanocrystals for CdE (E=S, Se, Te) compositions. We have studied the influence of crystal growth habits of the nanocrtsyals on the final morphology. Furthermore we have synthesized core-shell, CdSe-CdS QDs with spherical and tetrahedral morphologies by varying the reaction conditions. We show that these core-shell quantum dots show quasi-type II characteristics, and demonstrate with I-V measurements, the spatial localization of the charge carriers in these hetero-nanocrystals. For this purpose, we developed hybrid materials consisting of the core-shell quantum dots with electron acceptors (ZnO nanowires) and hole acceptors (polymeric P3HT nanofibers).

In addition we have also compared the synthesis reaction when carried out with conventional heating and microwave-mediated heating. We find that the reaction is enhanced, and the yield is qualitatively better when using microwave induced heating.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , viii, 55 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:09
Keyword [en]
ZnO, nanowire arrays, photocatalysis, CdTe, CdSe, CdS, nanotetrapods, nanotetrahedrons, photoconduction, nano-gap electrodes, Type-II QDs, P3HT nanofibers, microwave synthesis.
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-95410ISBN: 978-91-7501-382-4 (print)OAI: oai:DiVA.org:kth-95410DiVA: diva2:528172
Public defence
2012-05-31, Sal/Hall C2, KTH-ICT Electrum, Isafjordsgatan-22, Kista, 10:00 (English)
Opponent
Supervisors
Note
QC 20120525Available from: 2012-05-25 Created: 2012-05-24 Last updated: 2012-05-25Bibliographically approved
List of papers
1. Zinc oxide nanowires in chemical bath on seeded substrates: Role of hexamine
Open this publication in new window or tab >>Zinc oxide nanowires in chemical bath on seeded substrates: Role of hexamine
2006 (English)In: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 39, no 1, 49-56 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:kth:diva-13234 (URN)10.1007/s10971-006-6969-y (DOI)000239432100006 ()
Note
QC20100614Available from: 2010-06-07 Created: 2010-06-07 Last updated: 2017-12-12Bibliographically approved
2. Radially Oriented ZnO Nanowires on Flexible Poly-L-Lactide Nanofibers for Continuous-Flow Photocatalytic Water Purification
Open this publication in new window or tab >>Radially Oriented ZnO Nanowires on Flexible Poly-L-Lactide Nanofibers for Continuous-Flow Photocatalytic Water Purification
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2010 (English)In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 93, no 11, 3740-3744 p.Article in journal (Refereed) Published
Abstract [en]

Several oxide ceramics, notably ZnO and TiO2 are known to catalyze decomposition of organic molecules in water under ultraviolet (UV) irradiation. Here we describe fabrication of highly flexible ZnO-based hierarchical nanostructure obtained by growing radially oriented ZnO nanowires on poly-L-lactide nanofibers. Utilizing the flexibility and high surface area of polymeric nanofibers as novel substrate for growth of the photochemically active ZnO nanowires we show a proof-of-principle demonstration of a continuous flow water treatment setup. We have monitored photocatalytic decomposition of known organic pollutants, such as methylene blue, monocrotophos, and diphenylamine under illumination with UV light using this highly flexible hierarchical nanostructure.

Keyword
ZINC-OXIDE, NANOROD ARRAYS, DEGRADATION, SUSPENSIONS, TIO2, PHOTODEGRADATION, LIGHT
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27677 (URN)10.1111/j.1551-2916.2010.03986.x (DOI)000283987400042 ()2-s2.0-78549235835 (Scopus ID)
Conference
34th International Conference and Exposition on Advanced Ceramics and Composites Daytona Beach, FL, JAN 26, 2010
Note
34th International Conference and Exposition on Advanced Ceramics and Composites Daytona Beach, FL, JAN 26, 2010 QC 20101223Available from: 2010-12-23 Created: 2010-12-20 Last updated: 2017-12-11Bibliographically approved
3. Low-temperature synthesis of photoconducting CdTe nanotetrapods
Open this publication in new window or tab >>Low-temperature synthesis of photoconducting CdTe nanotetrapods
Show others...
2010 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 20, no 6, 1208-1214 p.Article in journal (Refereed) Published
Keyword
SHAPE-CONTROLLED SYNTHESIS, CDSE NANOCRYSTALS, SOLAR-CELLS, NANORODS, GROWTH, TETRAPODS, NANOPARTICLES, MONODISPERSE, COMPOSITES, EVOLUTION
National Category
Physical Chemistry Materials Engineering
Identifiers
urn:nbn:se:kth:diva-13235 (URN)10.1039/b916208a (DOI)000273961900028 ()2-s2.0-77949558021 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, UAW2004.0224
Note
QC 20110121Available from: 2010-06-07 Created: 2010-06-07 Last updated: 2017-12-12Bibliographically approved
4. Microwave mediated synthesis of semiconductor quantum dots
Open this publication in new window or tab >>Microwave mediated synthesis of semiconductor quantum dots
Show others...
2012 (English)In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, 1551-1556 p.Article in journal (Refereed) Published
Abstract [en]

Colloidal quantum dots (QD) have tuneable optoelectronic properties and can be easily handled by simple solution processing techniques, making them very attractive for a wide range of applications. Over the past decade synthesis of morphology controlled high quality (crystalline, monodisperse) colloidal QDs by thermal decomposition of organometallic precursors has matured and is well studied. Recently, synthesis of colloidal QDs by microwave irradiation as heating source is being studied due to the inherently different mechanisms of heat transfer, when compared to solvent convection based heating. Under microwave irradiation, polar precursor molecules directly absorb the microwave energy and heat up more efficiently. Here we report synthesis of colloidal II-VI semiconductor QDs (CdS, CdSe, CdTe) by microwave irradiation and compare it with conventional synthesis based on convection heating. Our findings show that QD synthesis by microwave heating is more efficient and the chalcogenide precursor strongly absorbs the microwave radiation shortening the reaction time and giving a high reaction yield.

Keyword
CdSe, Microwave, Quantum dots, Reaction rate
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-95406 (URN)10.1002/pssc.201100545 (DOI)000306479300007 ()2-s2.0-84864000771 (Scopus ID)
Conference
16th International Semiconducting and Insulating Materials Conference (SIMC-XVI) Location: Royal Inst Technol (KTH), Stockholm, Sweden Date: JUN 19-23, 2011
Note
QC 20120810Available from: 2012-05-24 Created: 2012-05-24 Last updated: 2017-12-07Bibliographically approved
5. Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots
Open this publication in new window or tab >>Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots
Show others...
2011 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 22, no 42, 425202- p.Article in journal (Refereed) Published
Abstract [en]

Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.

National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-95416 (URN)10.1088/0957-4484/22/42/425202 (DOI)000295467800003 ()2-s2.0-80053281966 (Scopus ID)
Note
QC 20120524Available from: 2012-05-24 Created: 2012-05-24 Last updated: 2017-12-07Bibliographically approved
6. Size-tuneable synthesis of photoconducting poly-(3-hexylthiophene) nanofibres and nanocomposites
Open this publication in new window or tab >>Size-tuneable synthesis of photoconducting poly-(3-hexylthiophene) nanofibres and nanocomposites
Show others...
2012 (English)In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, 1546-1550 p.Article in journal (Refereed) Published
Abstract [en]

Poly-(3-hexylthiophene) (P3HT) has been applied in many fields such as organic solar cells, printed electronic circuits, due to superior semiconducting properties compared to other semiconducting polymers. The presence of p-p interaction causes regio-regular P3HT to form ordered lamellar stacks during crystallisation. Here we report a simple room temperature, solution based method to synthesise P3HT nanofibres with controllable sizes. Our method is based on differing solubility of P3HT in various solvents. In a mixed solvent environment, we could control the precipitation of P3HT to obtain nanofibres with various diameters by varying the ratios of the solvents. We found that the lengths of the nanofibres could be controlled with concentration of the solution. Other methods to obtain nanofibres of P3HT invariably involves heating and controlled cooling which makes reproducibility and morphology control difficult. Furthermore, we synthesised a nanocomposite consisting of P3HT nanofibres and quasi-type-II quantum dots and evaluated the photoelectric properties of the nanofibres as well as the nanocomposites using interdigitated gold microelectrodes.

Keyword
P3HT, nanofibres, quantum dots, nanocomposites
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-95407 (URN)10.1002/pssc.201100540 (DOI)000306479300006 ()2-s2.0-84863997565 (Scopus ID)
Conference
16th International Semiconducting and Insulating Materials Conference (SIMC-XVI) Location: Royal Inst Technol (KTH), Stockholm, Sweden Date: JUN 19-23, 2011
Note

QC 20121221

Available from: 2012-05-24 Created: 2012-05-24 Last updated: 2017-12-07Bibliographically approved

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