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Assessment of a nanoparticle bridge platform for molecular electronics measurements
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.ORCID-id: 0000-0002-8360-1877
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.ORCID-id: 0000-0002-5496-9664
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2010 (Engelska)Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, nr 43, s. 435204-Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
2010. Vol. 21, nr 43, s. 435204-
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:uu:diva-132279DOI: 10.1088/0957-4484/21/43/435204ISI: 000282511100005OAI: oai:DiVA.org:uu-132279DiVA, id: diva2:357383
Projekt
KoF U3MECTillgänglig från: 2010-10-18 Skapad: 2010-10-18 Senast uppdaterad: 2019-04-24Bibliografiskt granskad
Ingår i avhandling
1. Building Systems for Electronic Probing of Single Low Dimensional Nano-objects: Application to Molecular Electronics and Defect Induced Graphene
Öppna denna publikation i ny flik eller fönster >>Building Systems for Electronic Probing of Single Low Dimensional Nano-objects: Application to Molecular Electronics and Defect Induced Graphene
2011 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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. 

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2011. s. 109
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 877
Nyckelord
Graphene, defect induced graphene, molecular electronics, nanoelectrodes, nanoparticles, conductivity, junction, nanomaterial, focused ion beam, surface functionalization, electrical characterization
Nationell ämneskategori
Nanoteknik Teknik och teknologier
Forskningsämne
Teknisk fysik med inriktning mot materialanalys
Identifikatorer
urn:nbn:se:uu:diva-160630 (URN)978-91-554-8212-1 (ISBN)
Disputation
2011-12-12, Häggsalen, Ångströmlab, Lägerhyddsvägen 1, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2011-11-21 Skapad: 2011-10-27 Senast uppdaterad: 2011-11-23Bibliografiskt granskad
2. Theoretical studies of a nanoparticle bridge platform for molecular electronics measurements
Öppna denna publikation i ny flik eller fönster >>Theoretical studies of a nanoparticle bridge platform for molecular electronics measurements
2011 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The main focus of this thesis is the theoretical investigations of a nanogap platform used for molecular electronics measurements under ambient conditions. The nanogap is about 20 nm wide, while the molecules investigated here (octanethiol(OT) and octanedithiol(ODT)) are about 1-1.5 nm long making it impossible to bridge the gap with one molecule. Two different approaches are investigated. In the first approach the electrodes of the nanogap are coated with a layer of OT molecules, and large gold nanoparticles (diameter of about 30 nm) are trapped in the gap creating two molecular junctions with assemblies of molecules. In the second approach the electrodes are kept clean, but instead the gold nanoparticles are coated with doubly functionalized molecules (ODT) and trapped in the gap. Here the nanoparticles are limited in size to about 5 nm, hence it is necessary to consider nanoparticle-molecule chains or small networks to bridge the gap. The first principles modeling of the structure of the metal-molecule junctions combined with elastic and inelastic transport properties is performed using the density functional theory (DFT) combined with the non-equilibrium Green’s functions (DFT-NEGF) method.

In the first approach with the coated electrodes and the large nanoparticles, simulations show that structural irregularities at the electrode interface can lead to a significant variation of the conductance through the molecular film. Due to the size of the nanoparticles, the shape and orientation of the facets will have great influence on how many molecules are connected, affecting the measured resistance of the device.

With the second approach utilizing the functionalized nanoparticles, more stable junctions are obtained since the nanogap is bridged by molecular junctions chemisorbed in both ends. To make chemical bonds to both sides of the junctions, the outer functional group needs to be protected before the trapping of nanoparticles in the gap. Deprotected nanoparticles agglomerate and cannot be trapped. We have inves- tigated the most probable configurations of the molecules in these junctions. During deprotection of the functional group in the gap, a conduction increase have been observed. We have found that the removal of the protection group is not responsible for the increased conduction. Instead, since the deprotected molecule is shorter and the nanoparticles are mobile during deprotection, a reorganization of the nanopar- ticles in the gap occurs. This reorganization leads to decreasing of the tunneling length for the electrons, hence increasing the conduction.

We also demonstrate, that we can obtain the inelastic electron tunneling spectroscopy (IETS) signature of an octanedithiol molecule in this platform. This is done on the network of chemisorbed ODT junctions, where we are able to relate the low-bias Au-S and C-S stretch modes of the molecule to observed peaks in IETS. From this we estimate that the main contribution in the signal comes from chains containing 5, 6 and 7 molecular junctions. To identify the peaks, we have calculated the theoretical spectra for one molecule, from which we are able to extract the important vibrational modes, and their couplings to the electrons. This we then use in a model, including the Coulomb blockade observed in the nanoparticles, to fit the theoretical spectra to the measured one. 

Ort, förlag, år, upplaga, sidor
Uppsala: Department of Physics and Astronomy, 2011. s. 31
Nationell ämneskategori
Den kondenserade materiens fysik Nanoteknik
Forskningsämne
Fysik med inriktning mot atom- molekyl- och kondenserande materiens fysik
Identifikatorer
urn:nbn:se:uu:diva-162061 (URN)
Presentation
2011-11-24, Oseenska rummet, Lägerhyddsvägen 1, Uppsala, 10:59 (Engelska)
Opponent
Handledare
Tillgänglig från: 2011-11-23 Skapad: 2011-11-23 Senast uppdaterad: 2011-11-24Bibliografiskt granskad
3. Computational Studies of Electron Transport in Nanoscale Devices
Öppna denna publikation i ny flik eller fönster >>Computational Studies of Electron Transport in Nanoscale Devices
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In this thesis, a combination of density functional theory (DFT) based calculations and nonequilibrium Green’s functions are employed to investigate electron transport in molecular switches, molecular cords and nanoscale devices.

  Molecular electronic devices have been proposed as an approach to complement today’s silicon based electronic devices. However, engineering of such miniature devices and design of functional molecular components still present significant challenges.

  First, the way to connect a molecule to conductive electrodes has to be controlled. We study, in a nanoelectrode-nanoparticle platform, how structural changes affect the measured conductance and how current fluctuations due to these structural changes can be decreased. We find that, for reproducible measurements, it is important to have the molecules chemically bonded to the surfaces of adjacent nanoparticles. Furthermore, we show by a combination of DFT and theoretical modeling that we can identify signals from single-molecules in inelastic electron spectroscopy measurements on these devices.

  Second, active elements based on molecules, some examples being switches, rectifiers or memory devices, have to be designed. We study molecular conductance switches that can be operated by light and/or temperature. By tuning the substituents on the molecules, we can optimize the shift of the most conducting molecular orbital and increase the effective coupling between the molecule and the electrodes when going from the OFF to the ON-state of the switches, giving high switching ratio (up to three orders of magnitude). We also study so called mechanoswitches that are activated by a mechanical force elongating the molecules, which means that these switches could operate as sensors.

  Furthermore, we have studied two different classes of compounds that may function either as rigid molecular spacers with a well-defined conductance or as molecular cords. In both cases, we find that it is of great importance to match the conjugation of the anchoring groups with the molecular backbone for high conductance.

  The last part of the thesis is devoted to another interesting semiconductor material, diamond. We have accurately calculated the band structure and effective masses for this material. Furthermore, these results have been used to calculate the Hall coefficient, the resistivity and the Seebeck coefficient.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2013. s. i-x, 89
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1090
Nyckelord
Density functional theory, Molecular electronics, Organosilicon chemistry, Diamond, Molecular switches, Nanoelectrode bridge platform, Molecular cords
Nationell ämneskategori
Den kondenserade materiens fysik Fysikalisk kemi
Forskningsämne
Fysik med inriktning mot atom- molekyl- och kondenserande materiens fysik
Identifikatorer
urn:nbn:se:uu:diva-209261 (URN)978-91-554-8781-2 (ISBN)
Disputation
2013-11-29, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2013-11-08 Skapad: 2013-10-16 Senast uppdaterad: 2014-01-23

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Jafri, S. Hassan M.Blom, TobiasLeifer, KlausStrömme, MariaLöfås, HenrikGrigoriev, AntonAhuja, RajeevWelch, Ken

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