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Low-temperature synthesis of photoconducting CdTe nanotetrapods
Royal Institue of Technology (KTH). (Division of Functional Materials)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics. (Division of Electron Microscopy and Nanoengineering)
Royal Institue of Technology (KTH). (Division of Functional Materials)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics. (Division of Electron Microscopy and Nanoengineering)
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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
Abstract [en]

We show that CdTe nanotetrapods are formed by two distinct growth regimes depending on the reaction temperature. At a low temperature (180 C) the combination of slow reaction kinetics and Ostwald ripening results in a novel pathway for the formation of a tetrapodal morphology. We also report, to the best of our knowledge, the first direct evaluation of the photoconductivity of CdTe nanotetrapods by employing gold ‘nanogap’ electrodes that were fabricated in-house. Our preliminary findings include I–V responses showing current enhancement, due to illumination, of up to 100 times.

Place, publisher, year, edition, pages
2010. Vol. 20, no 6, 1208-1214 p.
National Category
Chemical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-113700DOI: 10.1039/b916208aISI: 000273961900028OAI: oai:DiVA.org:uu-113700DiVA: diva2:291704
Available from: 2010-02-03 Created: 2010-02-03 Last updated: 2016-04-18Bibliographically approved
In thesis
1. Fabrication and Applications of a Focused Ion Beam Based Nanocontact Platform for Electrical Characterization of Molecules and Particles
Open this publication in new window or tab >>Fabrication and Applications of a Focused Ion Beam Based Nanocontact Platform for Electrical Characterization of Molecules and Particles
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The development of new materials with novel properties plays an important role in improving our lives and welfare. Research in Nanotechnology can provide e.g. cheaper and smarter materials in applications such as energy storage and sensors. In order for this development to proceed, we need to be able to characterize the material properties at the nano-, and even the atomic scale. The ultimate goal is to be able to tailor them according to our needs.

One of the great challenges concerning the characterization of nano-sized objects is how to achieve the physical contact to them. This thesis is focused on the contacting of nanoobjects with the aim of electrically characterizing them and subsequently understanding their electrical properties. The analyzed nanoobjects are carbon nanosheets, nanotetrapods, nanoparticles and molecular systems.

Two contacting strategies were employed in this thesis. The first strategy involved the development of a focused ion beam (FIB) based nanocontact platform. The platform consists of gold nanoelectrodes, having nanogaps of 10-30 nm, on top of an insulating substrate. Gold nanoparticles, double-stranded DNA and cadmium telluride nanotetrapods have been trapped in the gaps by using dielectrophoresis. In certain studies, the gold electrodes have also been coated with conducting or non-conducting molecules, prior to the trapping of gold nanoparticles, in order to form molecular junctions. These junctions were subsequently electrically characterized to evaluate the conduction properties of these molecular systems. For the purpose of better controlling the attachment of molecules to the nanoelectrodes, a novel route to synthesize alkanedithiol coated gold nanoparticles was developed. The second contacting strategy was based on the versatility of the FIB instrument as a platform for in-situ manipulation and electrical characterization of non-functionalized and functionalized carbon nanosheets, where it was found that the functionalized samples had an increased conductivity by more than one order of magnitude.

Both contacting strategies proved to be valuable for building knowledge around contacting and electrical characterization of nanoobjects

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 88 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 745
Keyword
Focused Ion Beam, FIB, Scanning Electron Microscopy, SEM, Nanogap electrodes, Nanostructuring, Nanofabrication, Electron Beam Lithography, Electrical characterization, Dielectrophoresis
Identifiers
urn:nbn:se:uu:diva-122940 (URN)978-91-554-7809-4 (ISBN)
Public defence
2010-06-07, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, 75121, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-05-17 Created: 2010-04-21 Last updated: 2010-05-18Bibliographically approved
2. Building Systems for Electronic Probing of Single Low Dimensional Nano-objects: Application to Molecular Electronics and Defect Induced Graphene
Open this publication in new window or tab >>Building Systems for Electronic Probing of Single Low Dimensional Nano-objects: Application to Molecular Electronics and Defect Induced Graphene
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nano-objects have unique properties due to their sizes, shapes and structure. When electronic properties of such nano-objects are used to build devices, the control of interfaces at atomic level is required.

In this thesis, systems were built that can not only electrically characterize nano-objects, but also allow to analyze a large number of individual nano-objects statistically at the example of graphene and nanoparticle-molecule-nanoelectrode junctions.

An in-situ electrical characterization system was developed for the analysis of free standing graphene sheets containing defects created by an acid treatment. The electrical characterization of several hundred sheets revealed that the resistance in acid treated graphene sheets decreased by 50 times as compared to pristine graphene and is explained by the presence of di-vacancy defects. However, the mechanism of defect insertion into graphene is different when graphene is bombarded with a focused ion beam and in this case, the resistance of graphene increases upon defect insertion. The defect insertion becomes even stronger at liquid N2 temperature.

A molecular electronics platform with excellent junction properties was fabricated where nanoparticle-molecule chains bridge 15-30nm nanoelectrodes. This approach enabled a systematic evaluation of junctions that were assembled by functionalizing electrode surfaces with alkanethiols and biphenyldithiol. The variations in the molecular device resistance were several orders of magnitude and explained by variations in attachment geometries of molecules. 

The spread of resistance values of different devices was drastically reduced by using a new functionalization technique that relies on coating of gold nanoparticles with trityl protected alkanedithiols, where the trityl group was removed after trapping of nanoparticles in the electrode gap. This establishment of a reproducible molecular electronics platform enabled the observation of vibrations of a few molecules by inelastic tunneling spectroscopy. Thus this system can be used extensively to characterize molecules as well as build devices based on molecules and nanoparticles. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 109 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 877
Keyword
Graphene, defect induced graphene, molecular electronics, nanoelectrodes, nanoparticles, conductivity, junction, nanomaterial, focused ion beam, surface functionalization, electrical characterization
National Category
Nano Technology Engineering and Technology
Research subject
Engineering Science with specialization in Materials Analysis
Identifiers
urn:nbn:se:uu:diva-160630 (URN)978-91-554-8212-1 (ISBN)
Public defence
2011-12-12, Häggsalen, Ångströmlab, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-11-21 Created: 2011-10-27 Last updated: 2011-11-23Bibliographically approved

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