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Building Systems for Electronic Probing of Single Low Dimensional Nano-objects: Application to Molecular Electronics and Defect Induced Graphene
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Electron Microscopy and Nanoenginnering)
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 [en]
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: urn:nbn:se:uu:diva-160630ISBN: 978-91-554-8212-1 (print)OAI: oai:DiVA.org:uu-160630DiVA: diva2:452087
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
List of papers
1. Conductivity engineering of graphene by defect formation
Open this publication in new window or tab >>Conductivity engineering of graphene by defect formation
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2010 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 4, 045404- p.Article in journal (Refereed) Published
Abstract [en]

Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behaviour around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices.

Place, publisher, year, edition, pages
IOP Publishing, 2010
National Category
Nano Technology Electrical Engineering, Electronic Engineering, Information Engineering Materials Engineering
Research subject
Chemistry with specialization in Organic Chemistry; Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-112356 (URN)10.1088/0022-3727/43/4/045404 (DOI)000273551300016 ()
Available from: 2010-01-13 Created: 2010-01-13 Last updated: 2017-12-12Bibliographically approved
2. An In-Situ Prepared Nano-Manipulator Tip for Electrical Characterization of Free Standing Graphene Like Sheets Inside a Focused Ion Beam/Scanning Electron Microscope
Open this publication in new window or tab >>An In-Situ Prepared Nano-Manipulator Tip for Electrical Characterization of Free Standing Graphene Like Sheets Inside a Focused Ion Beam/Scanning Electron Microscope
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2011 (English)In: Journal of Nanoelectronics and Optoelectronics, ISSN 1555-130X, E-ISSN 1555-1318, Vol. 6, no 2, 162-168 p.Article in journal (Refereed) Published
Abstract [en]

Although contacting and moving atoms has been demonstrated using probe techniques, for many nano-objects, a fast and reproducible nano-probe technique is needed to acquire a large number of electrical measurements on nano-objects that are often similar but not the identical. Nano-manipulators have become a common tool in many scanning electron microscopes (SEM) and focussed ion beam devices (FIB). They can be rapidly and reproducibly moved from one nano-object to another. In this work we present a procedure to obtain reproducible electrical measurements of nano- to micron-sized objects by using a sharp, tungsten tip with well defined surface properties. The tip is a part of a manipulator and is sharpened in-situ by using the gallium ion beam inside a focused ion beam/scanning electron microscope (FIB/SEM). The contact resistance between a Au surface and the tip is 70 kΩ before the sharpening procedure and 10 Ω after sharpening. The leakage current of the total set-up of 10pA makes it possible to measure currents through a variety of nano-objects. This measurement technique is applied to measure the resistance of as grown, water treated and two HCl treated carbon nanosheets (CNS). These CNS vary in size and morphology. Using this nano-contacting set-up, we could obtain measurements of more than 400 different CNS. The obtained histograms allow us to observe a clear decrease of the resistance between original and 3 hour acid treated CNSs. We observe that longer periods of exposure of the CNS to the HCl do not further modify the resistance.

Place, publisher, year, edition, pages
American Scientific, 2011
Keyword
Focused ion beam, FIB, electrical characterization, Nano-sized object
National Category
Nano Technology Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Analysis; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-122954 (URN)10.1166/jno.2011.1154 (DOI)000296210100013 ()
Available from: 2010-04-21 Created: 2010-04-21 Last updated: 2017-12-12Bibliographically approved
3. In-situ electrical characterization during defect insertion in exfoliated graphene sheets with a focused gallium ion beam at room and cryogenic temperatures
Open this publication in new window or tab >>In-situ electrical characterization during defect insertion in exfoliated graphene sheets with a focused gallium ion beam at room and cryogenic temperatures
(English)Manuscript (preprint) (Other academic)
Keyword
Focused Ion beam, Graphene, defects, conductivity, cryogenic temperatures
National Category
Nano Technology Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Analysis
Identifiers
urn:nbn:se:uu:diva-160615 (URN)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2011-11-23
4. Fabrication and characterization of high resistance sub-5 nm gaps made by electrodeposition of gold in 30 nm gaps cut by using a focused gallium ion beam
Open this publication in new window or tab >>Fabrication and characterization of high resistance sub-5 nm gaps made by electrodeposition of gold in 30 nm gaps cut by using a focused gallium ion beam
(English)Manuscript (preprint) (Other academic)
Keyword
Electrodeposition, gold nanogap, focused ion beam
National Category
Nano Technology
Research subject
Engineering Science with specialization in Materials Analysis
Identifiers
urn:nbn:se:uu:diva-160620 (URN)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2012-12-07
5. Large Variations in Shelf-life of Gold Nanoelectrode Gaps and Molecular Electronic Devices Stored in Air, Water and Organic Solvents
Open this publication in new window or tab >>Large Variations in Shelf-life of Gold Nanoelectrode Gaps and Molecular Electronic Devices Stored in Air, Water and Organic Solvents
(English)Manuscript (preprint) (Other academic)
Keyword
Nanoelectronics, molecular electronics, shelf-life, storage conditions
National Category
Nano Technology Materials Chemistry
Research subject
Engineering Science with specialization in Materials Analysis; Chemistry with specialization in Bioorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-160621 (URN)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2011-11-23
6. Assessment of a nanoparticle bridge platform for molecular electronics measurements
Open this publication in new window or tab >>Assessment of a nanoparticle bridge platform for molecular electronics measurements
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2010 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, no 43, 435204- p.Article in journal (Refereed) Published
Abstract [en]

A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal–molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the IV curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132279 (URN)10.1088/0957-4484/21/43/435204 (DOI)000282511100005 ()
Projects
KoF U3MEC
Available from: 2010-10-18 Created: 2010-10-18 Last updated: 2017-12-12Bibliographically approved
7. Low-temperature synthesis of photoconducting CdTe nanotetrapods
Open this publication in new window or tab >>Low-temperature synthesis of photoconducting CdTe nanotetrapods
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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.

National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113700 (URN)10.1039/b916208a (DOI)000273961900028 ()
Available from: 2010-02-03 Created: 2010-02-03 Last updated: 2017-12-12Bibliographically approved
8. Control of junction resistances in molecular electronic devices fabricated by FIB
Open this publication in new window or tab >>Control of junction resistances in molecular electronic devices fabricated by FIB
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2011 (English)In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 88, no 8, 2629-2631 p.Article in journal (Refereed) Published
Abstract [en]

A major hurdle to realize molecular electronic devices (MEDs) is to make reliable electrical contacts to a single or a few molecules. Our nano-contact platform with a gap size of less than 25 nm with resistances above 1000 TΩ was built using combined techniques of photolithography, electron beam lithography and focused ion beam milling. In this study, we have used gold nanoparticles (AuNPs) to bridge the nanoelectrode gaps by dielectrophoretic trapping and thus obtain electrical contacts. The electrodes and/or the nanoparticles were functionalised with 1–2 nm long alkane-thiol molecules so that the electronic structure of these molecules determines the properties of the electrical junction. Molecules were introduced both by functionalising the nanogap and the nanoparticles and the results of both functionalisation protocols are compared. Here, we show the nanogap–nanoparticle bridge set-up containing metal–molecule junctions that can be used as a base for the development of molecular electronics containing only a few molecules under ambient conditions. Current–voltage (IV) characterization of alkanethiol/gold junction showed non-linear response where mean geometric resistance of four different junctions could be tuned from 20 GΩ to 20 TΩ. The results from the measurements on 1-alkanethiol in such devices is a first step to demonstrate that this platform has the potential to obtain stable electronic devices having relatively small numbers of molecules with reliable metal molecule junction by combing top-down and bottom-up approaches.

Keyword
Nanoelectrodes, Nanogap-nanoparticle bridge set-up, Molecular electronics, Metal-moleculejunctions, 1-alkanethiol, Electrical characterizatio
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-138234 (URN)10.1016/j.mee.2010.11.040 (DOI)000293663400250 ()
Available from: 2010-12-16 Created: 2010-12-16 Last updated: 2017-12-11Bibliographically approved
9. Formation and NMR Spectroscopy of ω-Thiol Protected α,ω-Alkanedithiol Coated Gold Nanoparticles and Their Usage in Molecular Charge Transport Junctions
Open this publication in new window or tab >>Formation and NMR Spectroscopy of ω-Thiol Protected α,ω-Alkanedithiol Coated Gold Nanoparticles and Their Usage in Molecular Charge Transport Junctions
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2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 14, 9057-9067 p.Article in journal (Refereed) Published
Abstract [en]

Gold nanoparticles (AuNPs) coated with stabilizing molecular monolayers are utilized in areas ranging from life sciences to nanoelectronics. Here we present a novel and facile one-pot single phase procedure for the preparation of stable AuNPs with good dispersity, which are coated with α,ω-alkanedithiols whose outer ω-thiol is protected by a triphenylmethyl group. Using dielectrophoresis we were able to trap these AuNPs, coated with ω-thiol protecting groups, in a 20 nm gold electrode nanogap. The ω-thiol group was then deprotected under acidic conditions in situ once the AuNPs were correctly positioned in the device. The subsequent deprotection resulted in an increase of conductance by three orders of magnitude, indicating that the isolated dithiol coated AuNPs were fused into a covalently bonded network with AuNP-molecule-AuNP as well as electrode-molecule-AuNP linkages. Furthermore, complete characterization of the AuNP surface-bonded alkanedithiols was achieved using a series of one- and two-dimensional NMR spectroscopy techniques. Our spectra of the molecule-coated AuNPs show well resolved signals, only slightly broader than for free molecules in solution, in contrast to many earlier reported NMR spectral data of molecules attached to AuNPs. Complementary diffusion NMR spectroscopic experiments were performed to prove that the observed alkanedithiols are definitely surface bonded species and do not exist in free and unattached form.

Keyword
Chemistry, Materials Science
National Category
Chemical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-154968 (URN)10.1021/la2019007 (DOI)000292617800056 ()
Projects
KoF U3MEC
Funder
Swedish Research Council
Available from: 2011-06-14 Created: 2011-06-14 Last updated: 2017-12-11Bibliographically approved
10. Realization of highly reproducible molecular junctions in a nanoparticle-alkanedithiol-nanoelectrode bridge platform
Open this publication in new window or tab >>Realization of highly reproducible molecular junctions in a nanoparticle-alkanedithiol-nanoelectrode bridge platform
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(English)Manuscript (preprint) (Other academic)
Keyword
Molecular electronic devices, electrical characterization, alkanedithiols, chemisorbed molecular junctions, nanoparticle-nanoelectrode
National Category
Nano Technology Other Electrical Engineering, Electronic Engineering, Information Engineering Atom and Molecular Physics and Optics
Research subject
Engineering Science with specialization in Materials Analysis; Physics and Astronomy specializing in Theoretical Physics
Identifiers
urn:nbn:se:uu:diva-160622 (URN)
Projects
KoF U3MEC
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2013-11-08
11. Vibrational signatures in inelastic tunneling spectroscopy from short molecule-nanoparticle chains trapped in versatile nanoelectrodes
Open this publication in new window or tab >>Vibrational signatures in inelastic tunneling spectroscopy from short molecule-nanoparticle chains trapped in versatile nanoelectrodes
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(English)Manuscript (preprint) (Other academic)
Keyword
Molecular vibrations, Inelastic electron tunneling spectroscopy, nanoparticle-nanoelectrode bridge platform, octandithiol
National Category
Nano Technology Other Electrical Engineering, Electronic Engineering, Information Engineering Atom and Molecular Physics and Optics
Research subject
Engineering Science with specialization in Materials Analysis; Physics and Astronomy specializing in Theoretical Physics
Identifiers
urn:nbn:se:uu:diva-160626 (URN)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2012-04-01

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