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Microwave mediated synthesis of semiconductor quantum dots
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.ORCID iD: 0000-0002-1002-6699
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.ORCID iD: 0000-0001-5678-5298
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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.

Place, publisher, year, edition, pages
2012. Vol. 9, no 7, 1551-1556 p.
Keyword [en]
CdSe, Microwave, Quantum dots, Reaction rate
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-95406DOI: 10.1002/pssc.201100545ISI: 000306479300007Scopus ID: 2-s2.0-84864000771OAI: oai:DiVA.org:kth-95406DiVA: diva2:528150
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
In thesis
1. Fabrication and Photoelectrochemical Applications of II-VI Semiconductor Nanomaterials
Open this publication in new window or tab >>Fabrication and Photoelectrochemical Applications of II-VI Semiconductor Nanomaterials
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
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:nbn:se:kth:diva-95410 (URN)978-91-7501-382-4 (ISBN)
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
2. Green Chemical Synthesis of II-VI Semiconductor Quantum Dots
Open this publication in new window or tab >>Green Chemical Synthesis of II-VI Semiconductor Quantum Dots
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanotechnology is the science and technology of manipulating materials at atomic and molecular scale with properties different from bulk. Semiconductor QDs are important class of nanomaterials with unique physical and chemical properties owing to the quantum confinement effect. Size dependent optical properties make research on semiconductor QDs more attractive in the field of nanotechnology. Semiconductor QDs are usually composed of combination of elements from groups II–VI, III–V, or IV–VI of the periodic table. Group II-VI semiconductor QDs (ZnS, ZnSe, ZnO, CdSe, CdS) are most extensively studied systems, having bandgap which can be engineered through the variation of the material composition and size. Most common QDs are made of CdE (E=S, Se, Te) which are toxic. Recent environmental regulations restrict the use of toxic metals and therefore QDs containing nontoxic metals such as Zn are of great importance.

The chemical synthesis of QDs involves different methods. Usually high temperature thermal decomposition of organometallic compounds in high boiling point organic solvents is used which needs long reaction time and involves complex synthesis procedures. New simpler and efficient synthetic routes with alternative solvents are required. Recently the synthesis of non-toxic QDs using green chemical routes is a promising approach receiving increasing attention.

The aim of this Thesis is to develop novel routes for synthesis of semiconductor QDs employing green nanomaterial synthesis techniques. Therefore, in this work, we developed different green chemical routes mainly for the synthesis Zn-based QDs. Low temperature synthesis routes were developed for the synthesis of ZnS and ZnO QDs. Microwave irradiation was also used as efficient heating source which creates numerous nucleation sites in the solution, leading to the formation of homogeneous nanoparticles with small size and narrow size distribution. Different polar solvents with high MW absorption were used for synthesis of ZnS QDs. We also introduced ionic liquids as solvents in the synthesis of ZnS QDs using microwave heating. ILs are excellent reaction media for absorbing microwaves and are recognized as ‘green’ alternative to volatile and toxic organic solvents.

For ZnS systems, the QDs produced by different methods were less than 5 nm in size as characterized by high-resolution transmission electron microscopy (HR-TEM). Selected area electron diffraction (SAED) patterns revealed that ZnS QDs synthesized by low temperature synthesis technique using conventional heating are of cubic crystalline phase while the QDs synthesized by using MW heating are of wurtzite phase. The optical properties were investigated by UV-Vis absorption spectrum and show a blue shift in absorption as compared to bulk due to quantum confinement effect. The photoluminescence (PL) spectra of ZnS QDs show different defect states related emission peaks and depend on different synthesis methods, high bandedge related emission is observed for ZnS QDs synthesized by using ionic liquids. ZnO QDs synthesized by low temperature route were found to be less than 4 nm in size and also show a blue shift in their absorption. The PL spectrum show bandedge related emission which is blue shifted compared with bulk with no emission originating from surface defect levels. The results show that QDs are of high crystalline quality with narrow size distribution. A comparative study of using conventional and MW heating in the synthesis of CdSe QDs was performed. The reactions involving microwave heating showed enhanced rates and higher yields.

The developed methods involve all principles for green nanomaterials synthesis i.e. design of safer nanomaterials, reduced environmental impact, waste reduction, process safety, materials and energy efficiency.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vii, 39 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:20
Keyword
Semiconductor, Quantum Dots, Microwave, Ionic Liquids, Green Chemical Syntheis, Quantum Confinement, Optical Properties
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-104980 (URN)978-91-7501-550-7 (ISBN)
Public defence
2012-11-29, Sal C-1 Electrum, KTH-ICT, Isafjordsgatan 26, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20121115

Available from: 2012-11-15 Created: 2012-11-14 Last updated: 2012-11-15Bibliographically approved

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Afrasiabi, RoodabehToprak, Muhammet S.

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