Structural and Electrical Characterization of Organic Monolayers by Atomic Force Microscopy and Through the Nano-fabrication of a Coplanar Electrode-dielectric Platform PDF Download
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Author: Florent Martin
Publisher:
ISBN:
Category :
Languages : en
Pages : 268
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Correlating structural and electrical properties of organic thin films is a key requirement to understand charge transport in these materials. The electrical conductivity of organic films should be strongly dependent on how the molecules arrange to form films and crystals. Here we report on the structural and electrical characterization of organic monolayers by Atomic Force Microscopy and through the nano-fabrication of a coplanar electrode-dielectric platform. Organic monolayers were prepared using the solution-based Langmuir-Blodgett technique and transferred to a variety of substrates. Atomic Force Microscopy (AFM) was used to analyze the morphology and the microstructure of ultra-thin films at high resolution while electron diffraction measurements were instrumental in determining the lattice and orientation of crystalline domains within monolayers. A novel Conducting probe AFM method based on the presence of an insulating oxide layer between an organic film and a conductive silicon substrate made it possible to probe the in-plane electrical conductivity in the film. With this technique, we were able to investigate the correlation between conduction properties of oligothiophene monolayers and structural factors such as their molecular order and their lattice orientation. In order to make electrical contacts with monolayer films and study them in a Field Effect Transistor (FET) configuration, we developed coplanar electrode-dielectric substrates with roughness and surface topography in the sub-nanometer range. We present the first results on the electrical characterization of monolayers with this device which demonstrate that the coplanar geometry leads to a contact resistance by orders of magnitude lower than that found in conventional 20nm thick electrodes.
Author: Florent Martin
Publisher:
ISBN:
Category :
Languages : en
Pages : 268
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Book Description
Correlating structural and electrical properties of organic thin films is a key requirement to understand charge transport in these materials. The electrical conductivity of organic films should be strongly dependent on how the molecules arrange to form films and crystals. Here we report on the structural and electrical characterization of organic monolayers by Atomic Force Microscopy and through the nano-fabrication of a coplanar electrode-dielectric platform. Organic monolayers were prepared using the solution-based Langmuir-Blodgett technique and transferred to a variety of substrates. Atomic Force Microscopy (AFM) was used to analyze the morphology and the microstructure of ultra-thin films at high resolution while electron diffraction measurements were instrumental in determining the lattice and orientation of crystalline domains within monolayers. A novel Conducting probe AFM method based on the presence of an insulating oxide layer between an organic film and a conductive silicon substrate made it possible to probe the in-plane electrical conductivity in the film. With this technique, we were able to investigate the correlation between conduction properties of oligothiophene monolayers and structural factors such as their molecular order and their lattice orientation. In order to make electrical contacts with monolayer films and study them in a Field Effect Transistor (FET) configuration, we developed coplanar electrode-dielectric substrates with roughness and surface topography in the sub-nanometer range. We present the first results on the electrical characterization of monolayers with this device which demonstrate that the coplanar geometry leads to a contact resistance by orders of magnitude lower than that found in conventional 20nm thick electrodes.
Author: Jayne C. Garno
Publisher:
ISBN:
Category :
Languages : en
Pages : 398
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Author: Naining Yin
Publisher:
ISBN: 9781303792823
Category :
Languages : en
Pages :
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This thesis research focus has two parts. First, production and characterization of hierarchical micro/nanostructures of self-assembled monolayers and Langmuir-Blodgett film utilizing atomic force microscopy (AFM) was investigated. Second, application of these micro/nanostructures in cellular signaling study and organic conductive thin film was demonstrated. Three milestones have been achieved: 1) High-resolution atomic force microscopy (AFM) and AFM-based nanografting were utilized to characterize Dinitrophenyl (DNP) terminated self-assembled monolayers (SAMs) at the nanometer scale. DNP SAMs were prepared in dimethylformamide (DMF), dicholoromethane (DCM), 5% DMF in sec-butanol, 5% DCM in sec-butanol and 5% DMF in ethanol solvents to elucidate the effect of solvents on DNP SAMs packing and local structures. Individual DNP domain was visualized. Quantification analysis of height, molecular packing, domain size and distribution were performed at the nanometer scale. We found that height and packing of DNP SAMs were greatly affected by solvents. Diverse DNP SAMs local structures such as domain height, shape and separation from different solvents were illustrated. Understanding DNP SAM structure shall offer valuable structural insight for developing more effective antigen-antibody binding and regulating further cellular signaling event. 2) Oligothiophene thin films have been considered as a promising material for molecular electronics due to their desirable electronic properties and high structural stability under ambient conditions. To ensure performance in devices, the functional structures such as individual ordered domains, must be stable under practical operational conditions or environments including exposure to various media. This thesis investigates the structure of oligothiophene Langmuir-Blodgett (LB) films upon exposure to liquid media such as water, ethanol (EtOH), and mixed tetrahydrofuran (THF)/EtOH solutions. The LB films form islands ranging from 500 nm up to 1 ℗æm consisting of densely packed oligothiophene molecules. These islands are surrounded by bare substrate and loosely packed adsorbates. In-situ and time-dependent AFM images were acquired to reveal the structural evolution, from which degradation pathways and kinetics are extracted. Degradation of these LB films initiates and propagates from intra-island defect sites, such as cracks and pin holds, whereas the edges of islands remain intact on the surface. The observations appear to be in contrast to the known degradation mechanism among self-assembled monolayers, such as alkanethiols on gold, which initiates and progresses at domain boundaries. Rationale for the observed degradation processes will also be discussed. 3) Nanografting non-conductive organic molecules OEG onto D5TBA LB film on hydrophilic modified Au was successfully demonstrated for the first time. Height of D5TBA LB film on Au is around 2.5 nm, which is consistent with height of D5TBA on mica/Si. Friction of D5TBA island is lower than the substrate. Lateral conductivity of D5TBA LB film on hydrophilic Au was observed and consistent with the one on Si wafer. Geometry and line density of OEG nanostructures can be engineered by changing nanografting parameters, which could be as a promising platform for regulating lateral charge transport of D5TBA.
Author: Carla Ann Alves
Publisher:
ISBN:
Category :
Languages : en
Pages : 364
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Author: Vijay Jain
Publisher:
ISBN:
Category :
Languages : en
Pages : 124
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Author: Florent Martin
Publisher:
ISBN:
Category :
Languages : en
Pages : 98
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Author: Song Xu (Ph.D.)
Publisher:
ISBN:
Category : Thin films
Languages : en
Pages : 220
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Author: Richard Timothy Popoff
Publisher:
ISBN:
Category : Microelectronics
Languages : en
Pages : 0
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Metal/semiconductor (MS) junctions are fundamental in classical microelectronic devices. With device fabrication size approaching atomic scales, electronic performance will become unpredictable as a result of quantum effects becoming relevant in charge transport. The objective of this thesis is to investigate the potential application of thin organic films to modify MS junctions and to modulate their electrical properties. Knowing how the electronic parameters in a device change over time is necessary for commercial viability. I therefore studied the long-term structural and electronic stability of metal-monolayer-silicon junctions, with respect to silicon oxide formation (monitored by x-ray photoelectron spectroscopy (XPS)). Simple straight-chain n-alkyl (CH3-(CH2)11-Si[equivalence]) and phenyl-terminated (C6H5-(CH2)3-Si[equivalence]) monolayers were compared. Both samples had a significant change in surface, optical and electronic properties upon oxide formation. Although phenyl-terminated samples oxidized quicker than n-alkyl ones, their electrical properties were more similar to its original measurement before oxidation. There is a wide variety of deposition techniques available for placing metal contacts onto organically modified semiconductors, which are complex and costly. The investigation on monolayers that could withstand simple and inexpensive physical vapour deposition provides an alternative, molecular approach to overcome this technical challenge I discovered that phenyl-terminated monolayers have a significantly greater density than n-alkyl monolayers, based on XPS. This correlated with reducing metal penetration into the monolayer and improvements in electronic properties preservation of the molecular junctions, as observed with ballistic electron emission spectroscopy. In fact, molecular dipole moment (perpendicular vector to the surface) can also alter the charge transport in an MS junction. I have prepared a diverse series of monolayers on silicon (n-alkyl, thioether, phenyl and ether) and discovered a linear relationship between dipole moment, and both the barrier height and ideality factor. The calculated dipole moment has been normalized to account for the monolayer density on silicon which greatly improved the aforementioned linear correlation. A simple mathematical model to predict experimental current versus voltage behavior was then proposed. It was determined that relatively negative dipole moment (parallel to the direction of R-S[equivalence]) affect the charge transport pathways to a greater extent than neutral ones.
Author: Siddhartha Bhowmik
Publisher:
ISBN:
Category : Nanostructured materials
Languages : en
Pages : 496
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Periodic metal and metal-dielectric composite nanostructures have been of interest from the field of plasmonics and metamaterial fabrication. In order to exploit the behavior of these unique materials in the visible region of the optical spectrum, these structures need to be significantly shorter than the wavelength of response, and hence fabrication of these have posed unique challenges. One of the key fabrication aspects is the metal thin film deposition. This study has looked at key parameters in PVD which influence the grain structure and morphology, in one of the metals of interest, Ag, and further examined how these factors influence formation of these periodic nanostructures. Our findings indicate small grain sizes formed with high source-to-substrate spacing are optimal conditions for forming nanostructures with different geometries with size less than 100nm. Additionally our studies also indicate these conditions provide films with least agglomeration and a smooth texture which could have significant impact on their optical behavior. The study also looked at formation of nanostructures through different processes - (i) additive process via lift-off and electron beam lithography (EBL) and (ii) subtractive processes of ion beam milling, and reactive ion etch (RIE). This included examining three metals of interest in plasmonics- Ag, Au and Al. Our findings indicate that the optimized process is dependent on the metal systems and liftoff with EBL remains the most flexible option. RIE may be suitable for Al based systems where we form a volatile species during etch while it may not be as successful for Au and Ag. For isolated nanostructures as discussed in this paper, ion beam etch is highly dependent on grain sizes and may have some fundamental limitations in isolating structures. The structural and morphological characterization of nanostructures has also been of importance and has been carried out as part of this work with SEM, AFM, EDS, and TEM studies. The impact and application of these structures could be greatly enhanced by their formation in a flexible polymer membrane and this was also demonstrated as part of this thesis. Finally, we also present some optical data of these nanostructures where we see a difference in extinction coefficient of these structures based on both geometry and metal choice.
Author: Ripon Dey
Publisher:
ISBN:
Category : Lithography, Electron beam
Languages : en
Pages : 170
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This thesis is focused on nanofabrication and its application in atomic force microscopy (AFM). The contribution of this thesis is thus the development, investigation and characterization of novel nanofabrication technique (Part I); and application of nanofabrication in manufacturing the high aspect ratio AFM tips (Part II). In the first part of the thesis, firstly, unlike optical and mechanical lithography such as nanoimprint lithography, the throughput of EBL is very low, which demands for highly sensitive resists. We studied the dependency of e-beam exposure properties on molecular weight of the negative EBL resist polystyrene, and very high sensitivity of 1 [mu]C/cm2 was obtained for 900 kg/mol when exposed with electron beam of 2 keV. We also demonstrated that the exposure property of high PDI (polydispersity index) polystyrene resembles that of a monodisperse (PDI 1.06) polystyrene with similar number averaged molecular weight ("Mn" )́−, which indicates that it is ("Mn" )− rather than ("Mw" )− (weight averaged molecular weight) that dominates the exposure properties of polystyrene resist. Secondly, lift-off using negative resist is very challenging because the resist profile is typically positively tapered due to electron forward scattering, and upon exposure negative resist is cross-linked and thus insoluble in solvents. Here we demonstrated that low energy exposure could circumvent both issues simultaneously, and we achieved liftoff of Cr with polystyrene resist using a solvent xylene. Lastly, since low energy electrons are mostly stopped inside the resist layer, radiation damage to the sub-layer is greatly reduced. Thirdly, an electron beam resist is usually coated by conventional coating methods such as spin-coating, but this cannot be reliably applied on irregular surfaces. We here reported a monolayer resist can be grafted on nonflat surface. As a proof of concept of patterning on irregular surfaces, we chose PMMA mono-layer "brush" and grafted it on irregular surfaces by thermal treatment which accelerates a chemical reaction between PMMA molecules and hydroxyl group on substrate. We achieved nanofabrication of 30 nm resolution on an AFM cantilever. Fourthly, due to the lack of feedback, conventional electron beam lithography (EBL) is a “blind” open-loop process where the exposed pattern is examined only after ex-situ resist development, which is too late for any improvement. We reported that self-developing resist nitrocellulose, for which pattern shows up right after exposure without ex-situ development, can be used as in-situ feedback on the e-beam distortion and enlargement. Once the beam was optimized using nitrocellulose resist, under the same optimal beam condition, we exposed in the common resist PMMA. We achieved ~80 nm resolution across the entire large writing field of 1 mm2, as compared to 210 nm without the beam optimization process. We also reported that self-developing resist can provide in-situ feedback for writing field alignment accuracy, which in turn can be used to optimize the alignment. In the second part of the thesis, we demonstrated the batch fabrication of high aspect ratio (HAR) AFM tips. In order to obtain high quality and faithful images in AFM, very high aspect ratio tips are required in order to reach to the bottom of narrow and deep trenches/holes. But these HAR tips are extremely difficult to make and consequently very expensive. Currently all the commercially available HAR AFM tips are fabricated in a slow, costly (~5-20 that of regular AFM tips) and serial manner (one by one). We here developed a method to batch fabricate HAR AFM tips by forming a hard metal etching mask just on the apex of the pyramid tip followed by silicon dry etching to achieve the HAR pillar right below the metal island mask. Since it is a batch and lithography-free process, it has much higher throughput and much lower manufacturing cost per tip. This technique was first successfully applied on large-area pyramid arrays and then transferred to the commercial regular AFM tips, and has demonstrated the uniformity, reproducibility and yield of those HAR tips. The tip apex diameter and tip pillar height are controllable by tuning metal thickness and silicon dry etching time respectively. Finally, we demonstrated that the HAR tips fabricated using our technique gave a better imaging quality than the commercial regular tips.
