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Fabrication, functionalization and electrical conductance modulation of nanoparticle based molecular electronic Nano-devices
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Electron Microscopy and Nanoengineering)ORCID iD: 0000-0001-8978-0477
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the years many techniques have been proposed for the purpose of the formation of electrically conducting metal-molecule-metal junctions. One such technique utilizes gold-nanoparticles (AuNPs) that could assist in contacting small molecules between large gaps. The Ideal device structure then comprises of one nanoparticle and two molecules that are aligned as electrode1-molecule-AuNP-molecule-electrode2.

In present work these AuNP-molecule hybrids were fabricated inside sub 20 nm sized nanogaps between nanoelectrodes. The nanogaps were fabricated by milling of thin gold wires using focused ion beam. The tuning of the ion dosage resulted in the tuning of the gap size and the smallest nanogap of 2.3 nm was achieved.

The nano molecular electronic device (nanoMoED) platform comprised of the AuNPs that were assembled inside the nanogaps via dielectrophoresis. Two types of the AuNPs were used that were different from each other due to their functionalization chemistry. The low bias resistance 'RLB' of the nanoMoED platform was (i) reduced as compared to the nanogaps (ii) remained stable in toluene and air, and (iii) was reduced when exposed to the electron beam.

The nanoMoED platform was functionalized with various molecules using the molecular place exchange method. The successful functionalization resulted in the reduction of the 'RLB'. The smallest value of the 'RLBof the nanoMoED devices was achieved when the inserted molecule was not only highly conducting but also its length was same as the initial spacing between the AuNPs.

The nitrogen dioxide (NO2) molecules reduced the 'RLBof the nanoMoED devices that were made with 4,4'-biphenyl dithiol. The theoretical simulations showed that this reduction was due to the induced states at Fermi energy of the junction. The nanoMoED devices made with 1,8-octanedithiol showed conductance switching between two levels because of different geometries of the Au-S contact. This switching vanished when these devices were exposed to NO2 and a strong enhancement of signal to noise ratio was observed.

On the basis of these results this thesis suggests possible routes for the fabrication of highly conducting nanoMoED devices as well as elucidates the possibility of using the nanoMoED devices for gas sensing applications.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 98
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1667
Keywords [en]
Molecular electronics, gas sensor, hybrid materials, place exchange, random telegraph signal
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-347161ISBN: 978-91-513-0327-7 (print)OAI: oai:DiVA.org:uu-347161DiVA, id: diva2:1197122
Public defence
2018-05-30, Häggsalen, Ångström Laboratory, Regementsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2018-05-09 Created: 2018-04-12 Last updated: 2018-10-08
List of papers
1. Fabrication of reproducible sub-5 nm nanogaps by a focused ion beam and observation of Fowler-Nordheim tunneling
Open this publication in new window or tab >>Fabrication of reproducible sub-5 nm nanogaps by a focused ion beam and observation of Fowler-Nordheim tunneling
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 10, article id 103108Article in journal (Refereed) Published
Abstract [en]

Creating a stable high resistance sub-5 nm nanogap in between conductive electrodes is one of the major challenges in the device fabrication of nano-objects. Gap-sizes of 20 nm and above can be fabricated reproducibly by the precise focusing of the ion beam and careful milling of the metallic lines. Here, by tuning ion dosages starting from 4.6 x 10(10) ions/cm and above, reproducible nanogaps with sub-5 nm sizes are milled with focused ion beam. The resistance as a function of gap dimension shows an exponential behavior, and Fowler-Nordheim tunneling effect was observed in nanoelectrodes with sub-5 nm nanogaps. The application of Simmon's model to the milled nanogaps and the electrical analysis indicates that the minimum nanogap size approaches to 2.3 nm.

National Category
Physical Sciences Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-264851 (URN)10.1063/1.4930821 (DOI)000361640200043 ()
Available from: 2015-10-19 Created: 2015-10-19 Last updated: 2019-04-24Bibliographically approved
2. Designing sterically demanding thiolate coated AuNPs for electrical characterization of BPDT in a NP-molecule-nanoelectrode platform
Open this publication in new window or tab >>Designing sterically demanding thiolate coated AuNPs for electrical characterization of BPDT in a NP-molecule-nanoelectrode platform
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2017 (English)In: MOLECULAR SYSTEMS DESIGN & ENGINEERING, ISSN 2058-9689, Vol. 2, no 2, p. 133-139Article in journal (Refereed) Published
Abstract [en]

Molecular electronics with single or few molecules requires a stable metal-molecule nanojunction platform. Herein, we report the design and synthesis of gold nanoparticles coated with sterically demanding thiol ligands that are essential to fabricate a versatile and stable nanoelectrode-molecule-nanoparticle platform suitable for electrical characterization of small organic molecules. By combining.-tetraphenylmethane ether functionalized alkyl thioacetate and alkyl thiols, we prepared highly stable gold nanoparticles in a one-phase reaction providing simple and efficient purification. This robust preparation gives highly pure nanoparticles in very high yields (up to 90%) with long-time shelf stability. The synthesis in this work has superior reproducibility compared to previous synthesis processes that are currently being used for such molecular electronics platforms. Electron microscopy confirms the formation of uniform and small nanoparticles in the range of 5 to 7 nm. These nanoparticles with different ligand surface coverages were placed in a 20 nm nanoelectrode setup using dielectrophoretic forces. This setup was utilized to characterize the conductivity of the molecular wire 4,4'-biphenyldithiol introduced via ligand placeexchange under ambient conditions.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-323512 (URN)10.1039/c6me00095a (DOI)000400987200003 ()
Available from: 2017-06-14 Created: 2017-06-14 Last updated: 2018-04-12Bibliographically approved
3. Investigation of the factors that affect the fabrication of highly conducting NP-molecule junctions inside sub 20 nm molecular electronic devices.
Open this publication in new window or tab >>Investigation of the factors that affect the fabrication of highly conducting NP-molecule junctions inside sub 20 nm molecular electronic devices.
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(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348337 (URN)
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2019-04-24
4. Sub 20 nm metal-conjugated molecule junctions acting as a nitrogen dioxide sensor
Open this publication in new window or tab >>Sub 20 nm metal-conjugated molecule junctions acting as a nitrogen dioxide sensor
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(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348341 (URN)
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-12
5. Change of random telegraph conductance signal in different gas atmospheres in a nano molecular electronic device
Open this publication in new window or tab >>Change of random telegraph conductance signal in different gas atmospheres in a nano molecular electronic device
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(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348338 (URN)
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-12

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Wani, Ishtiaq Hassan

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