Dissertations / Theses on the topic 'Physisorbed'
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Griffiths, Paul Thomas. "Photodissociation of physisorbed molecules." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267768.
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Palmer, R. E. "Inelastic electron scattering by physisorbed molecules." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383837.
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Papadantonakis, Kimberly Marshall Okumura Mitchio Lewis Nathan Saul. "Exploration of physisorbed monolayers for molecular-scale surface patterning /." Diss., Pasadena, Calif. : California Institute of Technology, 2009. http://resolver.caltech.edu/CaltechETD:etd-07222008-144633.
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Srepusharawoot, Pornjuk. "Computational Studies of Hydrogen Storage Materials : Physisorbed and Chemisorbed Systems." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132875.
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This thesis deals with first-principles calculations based on density functional theory to investigate hydrogen storage related properties in various high-surface area materials and the ground state crystal structures in alkaline earth dicarbide systems. High-surface area materials have been shown to be very promising for hydrogen storage applications owing to them containing numerous hydrogen adsorption sites and good kinetics for adsorption/desorption. However, one disadvantage of these materials is their very weak interaction with adsorbed hydrogen molecules. Hence, for any feasible applications, the hydrogen interaction energy of these materials must be enhanced. In metal organic frameworks, approaches for improving the hydrogen interaction energy are opening the metal oxide cluster and decorating hydrogen attracting metals, e.g. Li, at the adsorption sites of the host. In covalent organic framework-1, the effects of the H2-H2 interaction are also found to play a significant role for enhancing the hydrogen adsorption energy. Moreover, ab initio molecular dynamics simulations reveal that hydrogen molecules can be trapped in the host material due to the blockage from adjacent adsorbed hydrogen molecules. In light metal hydride systems, hydrogen ions play two different roles, namely they can behave as "promoter" and "inhibitor" of Li diffusion in lithium imide and lithium amide, respectively. By studying thermodynamics of Li+ and proton diffusions in the mixture between lithium amide and lithium hydride, it was found that Li+ and proton diffusions inside lithium amide are more favorable than those between lithium amide and lithium hydride. Finally, our results show that the ground state configuration of BeC2 and MgC2 consists of five-membered carbon rings connected through a carbon atom forming an infinitely repeated chain surrounded by Be/Mg ions, whereas the stable crystal structure of the CaC2, SrC2 and BaC2 is the chain type structure, commonly found in the alkaline earth dicarbide systems.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 712
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Guest, Richard James. "Spectroscopic studies of the structure and dynamics of physisorbed oxygen." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307039.
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Kagan, Mark R. "Raman spectroscopy of organic molecules physisorbed onto graphitic carbon surfaces /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487935958848054.
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Gameson, I. "An X-ray study of gases on solids." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233976.
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The work described in this thesis is concerned with the study of ph-ysisorbed phases by x-ray diffraction using a conventional sealed x-ray tube source. Diffraction data has been collected for a number of adsorption systems using graphite, a montmorillonite clay (Gel White) and zeolite rho as the substrate. It is well known that phases of unique two-dimensional character can be formed on the surface of graphite, and the structure of adsorbed benzene and hexaflurobenzene on graphite have been studied in this thesis. Contrary to current theoretical predictions the >/7x T/7R19" commensurate structure of submonolayer benzene has been confirmed. Submonolayer hexaflurobenzene appears to form a striped domain structure based upon the commensurate x3 lattice in which the molecules are incommensurate with the surface. ' In contrast to the homogeneous surface of graphite, the surface of a clay is microporous and heterogenous, and this gives rise to broad diffraction lines from an adsorbed phase. Despite this, the surface area of Gel White has been deduced from the evolution of the diffraction pattern of a krypton adlayer as a function of krypton loading. The formation of bulk krypton is readily identified and the small size of the three-dimensional crystallites suggests that they are formed within the micropores of the clay. The structure of adlayers of krypton and xenon within the interlayer spacing of Al-pillared Gel White has been studied in order to determine the mean inter-pillar separation. At all the coverages studied, xenon forms a close packed single layer structure whilst krypton appears to form a more complex bilayer phase. A tentative suggestion as to the mean pillar separation from this work is 30X. The adsorption site of krypton, xenon and CH3CI within zeolite rho has been determined using the method of x-ray Rietveld whole profile refinement. The principal site of adsorbed krypton and xenon is at the centre of the octagonal prism. The chlorine atom of CH3CI sits in the centre of the face of the octagonal prism and the methyl group is slightly displaced from the centre of the prism. 37-5354 Hydrodynamics of liquid encapsulation czochralski crystal growth Hicks, T.W. Bristol Ph.D. 1989 Dig. Certain aspects of crystal growth from a melt are investigated. We begin by describing the methods of producing single crystals. Particular emphasis is placed on the need for a better understanding of the hydrodynamics of the encapsulant region of the Liquid Encapsulation Czochralski (LEG) technique. We also introduce the basic physical processes which govern crystal growth. In Chapter 2 we develop a mathematical model of the encapsulant region of the LEC crystal growth system. The equations and boundary conditions that govern the encapsulant flow are formed using a vorticity-stream-function approach, after which the problem is recast in a dimensionless form. In Chapter 3 the equations of motion are represented in a finite difference form and a numerical method for solving the time-marching problem presented by the parabolic equations is developed. The elliptic stream-function equation is solved at each time level using the successive over-relaxation technique. Solutions of the model equations for the growth of GaAs crystals through B3O3 encapsulant are presented in Chapter 4. In all cases considered the flow field tends towards a steady state. For shallow encapsulants, the heat transfer in the encapsulant is conduction dominated, but for deeper encapsulants, advective heat transfer can be significant. In the last chapter we investigate the effect of Soret diffusion on the morphological stability of a freezing interface using linear stability theory. A Soret flux directed towards the interface has a destabilising effect. Over-stable modes of instability exist for very low crystal growth rates, but we are unable to find conditions under which the overstable mode is the most unstable.
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Phillips, Tamsin Katie. "The influence of the carbonyl group in physisorbed monolayers on graphite." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609212.
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Conner, Marilyn W. "Theory of solid physisorbed films within the Potts lattice gas model /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487266691096888.
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Stocker, Matthias [Verfasser]. "Investigations of the role of physisorbed hydrogen in STM experiments / Matthias Stocker." Ulm : Universität Ulm. Fakultät für Naturwissenschaften, 2015. http://d-nb.info/108056294X/34.
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Figueroa, Jhon J. "Immobilization and Characterization of Physisorbed Antibody Films Using Pneumatic Spray as Deposition Technique." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4889.
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The immobilization of antibodies on silica surfaces has been a wide and common practice via cross-linking with the formation of covalent bonds between surface and antibody. The formation of antibody thin films on solid surfaces using pneumatic spray (PS) as the deposition technique and the analysis of the surface morphology of these films were investigated during this study. The pneumatic spray method was compared with the covalent bonding method Avidin-Biotin Bridge (ABB). The intensities and capture efficiency tests showed similar results for both techniques with a lower signal-to-noise ratio (SNR) for the PS deposited films. Specificity tests suggested that the bio-sensitivity of the antibody films that were pneumatically sprayed maintained their capture abilities after the immobilization process. Analysis obtained from the attenuated total reflectance Fourier transform infrared ATR-FTIR support these results indicating that the antibodies retained their native structure and chemical stability thorough the induced physisorption process. The pneumatic spray films also preserve mechanical stability by adhering to the surface after the rinsing procedures.
Capture efficiency was tested for both immobilization techniques, the results of which were similar. The pneumatic spray technique was also tested using a diverse range of deposition times. It was shown that a 2 minute deposition time was sufficient to produce a film with similar capture efficiency to the avidin-biotin bridge technique. The surface density obtained for the 2 minute deposition was 9.05 ng/mm2, which is higher than the range of 2.2 to 4.74 ng/mm2 reported for the avidin-biotin bridge technique[1-3]. The contact angle measurements for the pneumatic spray films showed a higher hydrophobicity compared with the avidin-biotin bridge films. This is due to the higher surface roughness obtained for the avidin-biotin bridge films, a higher surface density for the PS and the random orientation of the antibodies in the pneumatic spray films. A study of shelf life showed that the pneumatic spray technique produces stable films that can be used for as long 100 days (study performed only up to 100 days) with similar capture efficiency to those prepared in the same day.
To further understand the improvement in capture efficiency of the pneumatic spray films, the surface morphology was investigated to determine its influence in the cell adhesion process. The surface was characterized by several different techniques: ellipsometry to determine the thickness of the films, atomic force microscopy (AFM) to calculate the surface roughness, optical microscopy to identify particle formation during antibody immobilization process, fluorescent microscopy and sandwich fluorescent immunoassay to observe the immobilization patterns of antibodies and antigens on the surface, contact angle measurements to analyze the wettability of the antibody films and X-ray photoelectron spectroscopy (XPS) to confirm the presence of antibody on both deposition methods and to propose a growth model for the pneumatic spray deposition technique.
A possible explanation for the similar results of capture efficiency for both techniques can be attributed to three main factors. First, the antibodies retained their native structure thorough the induced physisorption process allowing then to capture antigen normally. Second, the lack of orientation of the antibodies in the pneumatic films was compensated by high surface density thereby offering more binding sites to capture antigens. Third, hydrophobic surfaces are favorable to cell adhesion, therefore the high hydrophobicity of the pneumatic spray films increases the capture efficiency. It is important to mention that the time that it takes to produce the immunoassay surfaces was reduced dramatically from more than twenty four hours for the avidin-biotin bridge films to only a few minutes for the pneumatic spray films. In addition, pneumatic spray films significantly reduce the amount of materials and chemicals used in the deposition process. These factors make the pneumatic spray technique an excellent technique for the immobilization of antibodies on glass slides for commercial bio-sensor devices.
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Block, Stephan [Verfasser]. "On surface forces and morphology of linear polyelectrolytes physisorbed onto oppositely charged surfaces / Stephan Block." Greifswald : Universitätsbibliothek Greifswald, 2011. http://d-nb.info/1010396889/34.
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Morton, Robert Simon. "The formation of positronium and its application to the study of two-dimensional physisorbed films." Thesis, Royal Holloway, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314166.
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Kossler, Sarah [Verfasser], Peter A. [Akademischer Betreuer] Feulner, Wilfried [Akademischer Betreuer] Wurth, and Katharina [Akademischer Betreuer] Krischer. "Electronic properties of physisorbed helium / Sarah Kossler. Gutachter: Wilfried Wurth ; Katharina Krischer. Betreuer: Peter A. Feulner." München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/1019588926/34.
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Burns, Teresa Ellen. "Asymmetric Adsorbate and Substrate Interactions in Physisorbed Systems: N2 on Graphite and Dipolar Molecules on Ionic Substrates." DigitalCommons@USU, 1994. https://digitalcommons.usu.edu/etd/2090.
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Asymmetries in physisorbed systems give rise to interesting phases and phase transitions in two-dimensional (2D) monolayer and multilayer systems. The effects of asymmetric adsorbate and substrate interactions in monolayers of dipolar molecules on ionic substrates and N2 on graphite are studied.
In the case of dipolar molecules on ionic substrates, 2D dielectric phase transitions using a modified Blume-Emery-Griffiths (BEG) model are determined theoretically. A dipole adsorbed vertically above a metal ion lattice site, and pointing up (down), is assigned a spin s=+1 (s=-1). An empty lattice site is assigned a spin S=0. Analytic solutions for both ferroelectrically and antiferroelectrically ordered systems are found. The model is applied to CO adsorbed on MgO and NaCl, and preliminary results for the phase diagram of CH3F on NaCl, are presented.
Multilayer phase transitions for N2 on graphite are studied experimentally using synchrotron x-ray diffraction. The system is measured to undergo layering transitions, where the number of layers increases as the temperature of the system increases. A new multilayer phase diagram based on our results and the combined results published by other researchers is presented. The effects of capillary condensation on this multilayer system are quantified, and it is determined that its primary effect is to broaden the discrete layering transitions. The results for both studies are put into context with other adsorption systems with asymmetric interactions.
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McGinty, Kathryn Mary. "Surface Modification of Poly(vinyl chloride) by Physisorbed Free Radical Initiation for Reduced Plasticizer Migration and Antimicrobial Properties." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1226615844.
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Moine, Mohamed Moustapha. "Fonctionnalisation de surface d'une tôle de cuivre par greffage d'acides alkylphosphoniques auto-assemblés en vue d'améliorer ses propriétés en emboutissage." Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2075.
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Le procédé de mise en forme des tôles métalliques, généralement oxydées, par emboutissage est en pleine évolutionpour répondre à de nouveaux besoins : intervalles de tolérances dimensionnelles de plus en plus étroits, productionen grande série à faible coût, apparition de nouvelles nuances de matériaux, souci écologique. La réussite d’une telleopération est prédominée par le contrôle du frottement au niveau du contact entre tôle à former et outil enmouvement relatif. Pour ce faire, nous proposons dans cette thèse de fonctionnaliser la surface de la tôle en ygreffant des molécules organiques auto-assemblées, par simple immersion dans une solution contenant les moléculesréactives. Le couple métal/molécule retenu pour cette étude est un substrat massif de cuivre pur avec des moléculesd’acides alkylphosphoniques (CnH2n+1PO(OH)2) dans le but d’établir une corrélation entre les propriétésphysicochimiques des films ainsi formés et leur comportement tribologique. La réponse en frottement a été étudiéepar deux moyens de simulation expérimentale des conditions de contact (tribomètres bille/plan et étirage-plan). Nousavons considéré l’influence des trois facteurs de préparation de substrat suivant μ la nature de surface juste avant safonctionnalisation (présence d’une couche d’oxyde ou d’hydroxyde), le nettoyage de surface aux ultrasons après safonctionnalisation (élimination des espèces physisorbées) et la longueur de chaîne alkyle de la moléculeorganophosphonique (n=4, 12 et 16). Bien que la formulation de cette fonctionnalisation soit simple (élaborée àpartir d’une seule molécule), les techniques d’investigation de surface (PM-IRRAS, XPS, électrochimie, MEB,…)montrent que les films auto-assemblés sont constitués d’une bicouche de bonne qualité de greffage et de propriétésanticorrosion. Cette bicouche est composée d’une première monocouche de molécules chimisorbées à la surface (ouSAM) sur laquelle est déposée une deuxième couche d’amas physisorbés. D’autre part, notre étude a montréégalement que les amas physisorbés ont un rôle primordial dans le comportement tribologique du film auto-assemblé(abaissement et stabilité du coefficient de frottement et prévention contre le grippage)Sheet metal forming processes are quickly evolving to meet new requirements of deep drawing such as: continuousminimization of dimensional tolerances intervals, cost efficiency at mass production, appearance of new materialstypes, environmental concern. The success of such operation is predominated by controlling friction at the contactbetween the metal sheet and forming tool in relative motion. In the present work, we propose to functionalize themetal sheet surface using grafting of self-assembled organic molecules by simple immersion in a solution containingthe reactive molecules. Consequently, thin film of alkylphosphonic acid (CnH2n+1PO(OH)2) was grafted on copperoxide substrate in order to establish a correlation between the physicochemical properties of the films andtribological behavior. Frictional response was studied by two experimental means of contact conditions (stripdrawing testing and ball-on-plane tribometer). The influence of three factors for the preparation of substrate wasconsidered. Firstly, the nature of its surface just before functionalization including the presence of an oxide orhydroxide layer was studied. Then, the ultrasonic surface cleaning after functionalization (removal physisorbedspecies) and finally, the alkyl chain length of the organophosphonic molecule (n = 4, 12 and 16). Although theformation of this functionalization is simple (made from a single molecule), the surface investigation techniques(PM- IRRAS , XPS, electrochemistry , SEM, .., etc.) show that self-assembled films consist of a bilayer with a goodgrafting quality and anticorrosion properties. The bilayer is composed of a first monolayer of molecules chemisorbedon the surface (or SAM) on which a second layer of physisorbed species is deposited. Furthermore, this study alsoshowed that the physisorbed species have a key role in the tribological behavior of self-assembled film (lower andstable friction coefficient and high resistance to galling)
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Razafitianamaharavo, Angelina. "Étude structurale du film de cyclohexane physisorbé sur graphite : Étude thermodynamique et structurale du film mixte (krypton-cyclohexane) physisorbe sur graphite." Nancy 1, 1989. http://www.theses.fr/1989NAN10080.
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La caractérisation structurale du cyclohexane adsorbe sur graphite a été effectuée entre 77**(O)K et 260**(O)K par diffraction de neutrons et de rayons X. Elle a permis de proposer un diagramme de phases 2D rendant compte de trois structures solides qui sont par ordre de densité croissante, commensurable, hexagonale incommensurable et rectangulaire centrée
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Cafe, Peter F. "Towards reliable contacts of molecular electronic devices to gold electrodes." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3870.
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SYNOPSIS OF THIS THESIS The aim of this thesis is to more fully understand and explain the binding mechanism of organic molecules to the Au(111) surface and to explore the conduction of such molecules. It consists of five discreet chapters connected to each other by the central theme of “The Single Molecule Device: Conductance and Binding”. There is a deliberate concentration on azine linkers, in particular those with a 1,10-phenanthroline-type bidentate configuration at each end. This linker unit is called a “molecular alligator clip” and is investigated as an alternative to the thiol linker unit more commonly used. Chapter 1 places the work in the broad context of Molecular Electronics and establishes the need for this research. In Chapter 2 the multiple break-junction technique (using a Scanning Tunnelling Microscope or similar device) was used to investigate the conductance of various molecules with azine linkers. A major finding of those experiments is that solvent interactions are a key factor in the conductance signal of particular molecules. Some solvents interfere with the molecule’s interaction with and attachment to the gold electrodes. One indicator of the degree of this interference is the extent of the enhancement or otherwise of the gold quantized conduction peak at 1.0 G0. Below 1.0 G0 a broad range for which the molecule enhances conduction indicates that solvent interactions contribute to a variety of structures which could bridge the electrodes, each with their own specific conductance value. The use of histograms with a Log10 scale for conductance proved useful for observing broad range features. vi Another factor which affects the conductance signal is the geometric alignment of the molecule (or the molecule-solvent structure) to the gold electrode, and the molecular alignment is explored in Chapters 3 for 1,10-phenanthroline (PHEN) and Chapter 4 for thiols. In Chapter 3 STM images, electrochemistry, and Density Functional Theory (DFT) are used to determine 1,10-phenanthroline (PHEN) structures on the Au(111) surface. It is established that PHEN binds in two modes, a physisorbed state and a chemisorbed state. The chemisorbed state is more stable and involves the extraction of gold from the bulk to form adatom-PHEN entities which are highly mobile on the gold surface. Surface pitting is viewed as evidential of the formation of the adatom-molecule entities. DFT calculations in this chapter were performed by Ante Bilic and Jeffery Reimers. The conclusions to Chapter 3 implicate the adatom as a binding mode of thiols to gold and this is explored in Chapter 4 by a timely review of nascent research in the field. The adatom motif is identified as the major binding structure for thiol terminated molecules to gold, using the explanation of surface pitting in Chapter 3 as major evidence and substantiated by emergent literature, both experimental and theoretical. Furthermore, the effect of this binding mode on conductance is explored and structures relevant to the break-junction experiment of Chapter 2 are identified and their conductance values compared. Finally, as a result of researching extensive reports of molecular conductance values, and having attempted the same, a simple method for predicting the conductance of single molecules is presented based upon the tunneling conductance formula.
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Cafe, Peter F. "Towards reliable contacts of molecular electronic devices to gold electrodes." University of Sydney, 2008. http://hdl.handle.net/2123/3870.
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PhDSYNOPSIS OF THIS THESIS The aim of this thesis is to more fully understand and explain the binding mechanism of organic molecules to the Au(111) surface and to explore the conduction of such molecules. It consists of five discreet chapters connected to each other by the central theme of “The Single Molecule Device: Conductance and Binding”. There is a deliberate concentration on azine linkers, in particular those with a 1,10-phenanthroline-type bidentate configuration at each end. This linker unit is called a “molecular alligator clip” and is investigated as an alternative to the thiol linker unit more commonly used. Chapter 1 places the work in the broad context of Molecular Electronics and establishes the need for this research. In Chapter 2 the multiple break-junction technique (using a Scanning Tunnelling Microscope or similar device) was used to investigate the conductance of various molecules with azine linkers. A major finding of those experiments is that solvent interactions are a key factor in the conductance signal of particular molecules. Some solvents interfere with the molecule’s interaction with and attachment to the gold electrodes. One indicator of the degree of this interference is the extent of the enhancement or otherwise of the gold quantized conduction peak at 1.0 G0. Below 1.0 G0 a broad range for which the molecule enhances conduction indicates that solvent interactions contribute to a variety of structures which could bridge the electrodes, each with their own specific conductance value. The use of histograms with a Log10 scale for conductance proved useful for observing broad range features. vi Another factor which affects the conductance signal is the geometric alignment of the molecule (or the molecule-solvent structure) to the gold electrode, and the molecular alignment is explored in Chapters 3 for 1,10-phenanthroline (PHEN) and Chapter 4 for thiols. In Chapter 3 STM images, electrochemistry, and Density Functional Theory (DFT) are used to determine 1,10-phenanthroline (PHEN) structures on the Au(111) surface. It is established that PHEN binds in two modes, a physisorbed state and a chemisorbed state. The chemisorbed state is more stable and involves the extraction of gold from the bulk to form adatom-PHEN entities which are highly mobile on the gold surface. Surface pitting is viewed as evidential of the formation of the adatom-molecule entities. DFT calculations in this chapter were performed by Ante Bilic and Jeffery Reimers. The conclusions to Chapter 3 implicate the adatom as a binding mode of thiols to gold and this is explored in Chapter 4 by a timely review of nascent research in the field. The adatom motif is identified as the major binding structure for thiol terminated molecules to gold, using the explanation of surface pitting in Chapter 3 as major evidence and substantiated by emergent literature, both experimental and theoretical. Furthermore, the effect of this binding mode on conductance is explored and structures relevant to the break-junction experiment of Chapter 2 are identified and their conductance values compared. Finally, as a result of researching extensive reports of molecular conductance values, and having attempted the same, a simple method for predicting the conductance of single molecules is presented based upon the tunneling conductance formula.
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VENKATAPEN, VERONIQUE. "Simulation de melanges de gaz rares physisorbes sur graphite en monocouche." Paris 7, 1992. http://www.theses.fr/1992PA077205.
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Dans la premiere partie, on expose la methode que nous utilisons pour simuler numeriquement les monocouches de melanges de gaz rares non quantiques physisorbes sur graphite. Pour un melange ar-xe de concentration determinee, on degage l'influence des configurations, qui est suffisamment faible pour se restreindre a l'une d'entre elles seulement. Dans la deuxieme partie, on etudie la variation du parametre du reseau moyen de melanges ar-xe, kr-xe; on met en evidence un gonflement de la monocouche (par rapport a une interpolation lineaire) et l'on determine l'influence de differents parametres sur ce gonflement. L'etude des distances interatomiques montre une nette separation des paires de petits atomes. Enfin on compare les resultats numeriques avec les concentrations experimentales aux transitions commensurable-incommensurable. Dans la troisieme partie, on etudie le cas plus particulier des melanges dilues comme limite du cas general. La confrontation des resultats de simulation avec ceux de modeles tres simples permet de cerner leurs limitations. On elabore et on resout un modele analytique qui rend mieux compte des resultats principaux du calcul de simulation
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Makoudi, Younes. "Etudes par microscopie STM de molécules organiques physisorbées sur semi-conducteurs." Phd thesis, Université de Franche-Comté, 2009. http://tel.archives-ouvertes.fr/tel-00463079.
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L'élaboration d'auto-assemblages constitués par des molécules conjuguées, sur des surfaces semi-conductrices et stables à température ambiante, est l'un des défis majeurs qui doit être résolu pour permettre l'avènement de l'électronique moléculaire. Au cours de ma thèse, j'ai développé de nouveaux concepts permettant d'aboutir à ce type d'assemblage en évitant une trop forte interaction molécule/silicium. Pour cela, j'ai adopté trois stratégies distinctes en fonction de la dimensionnalité des édifices supramoléculaires recherchés : 1) minimiser l'interaction molécule/silicium en utilisant une surface de silicium très dopée en atomes de bore, 2) utiliser l'effet « template » d'une reconstruction 1D semi-métallique de l'interface SmSi pour créer et auto-aligner des molécules, 3) et protéger le squelette conjugué des molécules organiques et guider un assemblage bidimensionnel en utilisant des molécules zwitterioniques. Les images STM à très haute résolution sous ultravide et à température ambiante ont été obtenues. Tous les résultats expérimentaux sont confortés par des calculs de type « théorie de la fonctionnelle densité ».
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Makoudi, Younes. "Etude par microscope STM de molécules organiques physisorbées sur semi-conducteurs." Besançon, 2009. http://www.theses.fr/2009BESA2020.
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L'élaboration d'auto-assemblages constitués par des molécules conjuguées, sur des surfaces semi-conductrices et stables à température ambiante, est l'un des défis majeurs qui doit être résolu pour permettre l'avènement de l'électronique moléculaire. Au cours de ma thèse, j'ai développé de nouveaux concepts permettant d'aboutir à ce type d'assemblage en évitant une trop forte interaction molécule/silicium. Pour cela, j'ai adopté trois stratégies distinctes en fonction de la dimensionnalité des édifices moléculaires recherchés: 1) minimiser l'interaction molécule/silicium en utilisant une surface de silicium très dopée en atomes de bore, 2) utiliser l'effet « template » d'une reconstruction 1 D semi-métallique de l'interface SmSi pour créer et auto-aligner des molécules, 3) et protéger le squelette conjugué des molécules organiques et guider un assemblage bidimensionnel en utilisant des molécules zwitterioniques. Les images STM à très haute résolution sous ultra-vide et à température ambiante ont été obtenues. Tous les résultats expérimentaux sont confortés par des calculs de type « Théorie de la Fonctionnelle Densité »My project dealt with achievement and study of isolated molecules on boron silicon surface (OD system), molecular self-alignment on samarium/silicon interface (1D system) and 2 dimensionnel molecular self-assembly on Si(111)-7x7 and Si(111)-B surfaces (2D system). In order to circumvent the problem of traditional silicon surface reactivity with TT-conjugated molecules, we use the Si(111 )-B surface. This surface has the unique particularity to exhibit depopulated dangling bonds due to the presence 01 boron atoms under the top silicon layer. Consequently, TT-conjugated organic molecules can interact weakly with the pz depopulated dangling orbitals of the surface. To achieve self-alignment of organic molecules, we used an innovative concept based on the template effect of the pre-structured semi- conductive SmSi(111) interface. This substrate was selected because Sm deposition in the submonolayer range leads to a 8x2- reconstruction, which is a well-defined one-dimensional semi-metallic structure. Adsorption of aromatic molecules [1,4- di-(9- ethynyltriptycenyl)-benzene] on SmSi(111)-8x2leads to a good self-alignment of molecules along the [1-10] direction and the molecules are parallel to the atomic rows of the 1 D SmSi(111)- 8x2 structure. To create 2 dimensionnel molecular self-assemblies on silicon surface at room temperature,we proposed two new strategies: The first uses the zwitterionic molecules [4-methoXy-4'-(3-sulfonatopropyl)- stilbazolium ] and Si(111)- 7x7 surface. The second technique is based on the choice of the molecule/substrate system. We chose SiB surface in order to reduce molecules/substrate interaction and a highly polar molecule (4-aminobenzonitrile) to promote molecule/molecule interactions
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Bah, Abdellah. "Étude de films de chlorométhane et de trichlorométhane physisorbes sur les plans de base du graphite." Nancy 1, 1994. http://www.theses.fr/1994NAN10017.
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La caractérisation thermodynamique du film de chlorométhane (ch#3cl) adsorbé sur graphite, effectuée par volumétrie d'adsorption entre 129,7 et 181,4 k, a confirmé le diagramme de phases propose après une étude structurale, et l'a complété par la détermination de la température critique de condensation de la première couche (173,6 k) et par la mise en évidence de l'apparition d'une seconde couche adsorbée à partir de 161,5 k. L'étude thermodynamique du trichlorométhane (chcl#3) adsorbé sur graphite a été effectuée par volumétrie d'adsorption entre 206,9 et 227,7 k. Les isothermes présentent deux marches. La température critique de condensation de la première couche est 216 k. Le trace de la seconde marche fait apparaitre des problèmes de germination, mis en évidence par la cinétique d'adsorption et une hystérèse importante. Il semble que la formation d'une bicouche, particulièrement stable, implique une restructuration de la première couche. La cinétique d'adsorption redevient habituelle et l'hystérèse disparait après la fusion de la bicouche à 224,8 k. L'étude par diffraction de RX du même film adsorbé permet d'observer une perte d'ordre dans la première couche à 162 k. Le profil des spectres traduirait la formation d'un mélange microscopique de deux structures, l'une hexagonale et l'autre carrée. La phase hexagonale serait la plus stable et les séquences de la phase carrée seraient des fautes d'empilement
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ARANDA, PABLO. "Etude de la fusion bidimensionnelle par diffraction de rayons x : application a la monocouche de tetrachloromethane physisorbe sur graphite." Paris 6, 1994. http://www.theses.fr/1994PA066302.
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Cette these est consacree a l'etude de la fusion du tetrachloromethane physisorbe sur graphite et en particulier a la nature de l'ordre translationnel dans le solide et dans le liquide. A cette fin, nous utilisons l'information provenant de deux pics ou anneaux de diffraction, methode peu employee jusqu'a ce jour en physisorption a l'inverse des etudes 3d. Le premier chapitre du memoire est consacre a la description de la technique experimentale. Il presente en detail les divers elements constitutifs du dispositif experimental, en particulier la chaine d'acquisition depuis le detecteur, qui offre la possibilite d'observer simultanement deux pics de diffraction, jusqu'a la carte d'acquisition. La deuxieme partie presente un rappel des aspects theoriques de la fusion bidimensionnelle dans le cadre du modele kosterlitz-thouless-halperin-nelson-young: ce modele decrit la fusion comme une transition de separation des paires de defauts qui est precedee dans le solide par une renormalisation des constantes elastiques. La troisieme partie traite du pseudo-ordre translationnel qui existe dans ces systemes bidimensionnels et de ses consequences sur les profils de raies de diffraction. Nous y exposons le cas des profils de raies de poudres de cristaux de taille finie. La difficulte a determiner la nature de l'ordre a partir du profil d'un seul pic est soulignee et nous proposons une demarche qui verifie une relation simple entre les largeurs des pics (10) et (11) a travers le parametre de controle associe eta. Enfin dans la quatrieme partie, nous presentons nos resultats sur l'etude de la fusion de ccl#4 adsorbe sur graphite. Apres avoir rappele les resultats obtenus precedemment sur la molecule de ccl#4, nous decrivons le protocole experimental. Suit une presentation des spectres de diffraction obtenus puis une analyse qualitative de ces resultats. Nous etudions ensuite la largeur des pics: on calcule eta a partir de ces largeurs et on verifie dans le solide avant la fusion, la loi simple: eta(11)=3eta(10). L'etude de l'intensite permet de verifier pour le pic (10) les predictions theoriques aussi bien pour le solide que pour le liquide jusqu'a des longueurs de coherence de 3 nm
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Dubois, Mathieu. "Simulations de microscopie à effet tunnel : application à la surface (100) du silicium et aux molécules physisorbées." Lille 1, 2004. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2004/50376-2004-159.pdf.
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Ce travail se situe dans le cadre général des nanotechnologies. Après avoir présenté les enjeux et les challenges dans ce nouveau domaine, nous présentons le microscope à effet tunnel (STM) et nous montrons les possibilités offertes par cet outil pour les nanotechnologies. Largement utilisé pour l'étude des surfaces ainsi que pour celle de l'adsorption de molécules organiques, les résultats expérimentaux ne sont pas toujours suffisants pour comprendre parfaitement les phénomènes mis en jeu. Cette thèse propose donc une modélisation du courant tunnel permettant ainsi la simulation d'images et de courbes de spectroscopie obtenues en STM. Le courant est obtenu dans un formalisme de diffusion utilisant les fonctions de Green. L'ensemble des calculs des structures électroniques est effectué dans le cadre de l'approximation des liaisons fortes. Les perturbations électroniques à l'intérieur de la molécule. (interactions électron-électron) seront décrites à l'aide d'une théorie dérivée de la théorie orthodoxeDans un premier temps, ce modèle sera mis en application à l'étude des différentes reconstructions de la surface (100) du silicium. Les résultats théoriques reproduisent relativement bien les données expérimentales obtenues à 5\,K et permettent de comprendre la dépendance en tensions des images et de conclure que la surface est toujours semi-conductrice à basse température. Ces résultats mettent également en avant l'importance des interactions pointe-surface. Dans un deuxième temps, le modèle est utilisé pour étudier une classe de molécules, les thiénylènevinylènes, physisorbées sur la surface (100) du silicium. Nous proposons alors l'origine suivante pour la contribution principale au courant tunnel: cette contribution ne proviendrait pas de la mise en résonance de l'état HOMO de la molécule avec le niveau de Fermi de la pointe mais plutôt de l'abaissement, par la présence de la molécule, de la barrière tunnel entre la pointe et la surface, faisant ainsi ressortir, là où elle repose, les caractéristiques du silicium
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Hamdi, Alaoui Moulay Ahmed. "Étude thermodynamique et structurale des phases bidimensionnelles à plus d'un constituant physisorbées sur graphite : cas du film mixte krypton-méthane." Nancy 1, 1994. http://www.theses.fr/1994NAN10045.
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La caractérisation thermodynamique de notre système krypton-méthane sur graphite exfolie a été effectuée par volumétrie d'adsorption entre 72 et 86 k. Cette étude nous a permis de mettre en évidence les phénomènes d'entrainement et de déplacement qui s'effectuent selon une transformation du second ordre. D'autre part, une comparaison de nos résultats expérimentaux avec les prévisions théoriques établies dans le cadre du modèle champ-moyen a montré un bon accord entre les deux. De plus, elle nous a permis de confirmer le caractère quasi-idéal de la solution bidimensionnelle observé expérimentalement. L'étude structurale du même système a été effectuée par diffraction de neutrons. Elle nous a permis de mettre en évidence l'existence d'une limite de solubilité du krypton dans la couche mixte et qui varie en fonction de la température. Enfin, l'étude de la fusion de deux compositions du film mixte nous a permis de confirmer l'existence de la solution bidimensionnelle, ce qui rejoint les conclusions des études théoriques et thermodynamiques
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Abdelmoula, Mustapha. "Etude thermodynamique et structurale du film pur de tétrachlorure de carbone et des films mixtes (krypton-tétrachlorure de carbone) et (méthane-tétrachlorure de carbone) physisorbés sur graphite." Nancy 1, 1991. http://docnum.univ-lorraine.fr/public/SCD_T_1991_0022_ABDELMOULA.pdf.
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La caractérisation thermodynamique et structurale du film tétrachlorure de carbone sur les plans de base du graphite a été mesurée par volumétrie d'adsorption entre 205 et 260 kelvins et par diffraction de rayons x entre 45 et 240 kelvins. Elle a permis de proposer un diagramme de phases avec apparition de la deuxième couche adsorbée à 217 kelvins et fusion continue du film en première couche. Les températures critiques de condensation des première et deuxième couches sont respectivement 233 et 239 kelvins. L'étude thermodynamique et structurale (par diffraction de rayons x et diffraction de neutrons) des couches mixtes krypton-tétrachlorure de carbone et méthane-tétrachlorure de carbone met en évidence le déplacement partiel du film pré-déposé par l'adsorbat le moins condensable. La miscibilité du tétrachlorure de carbone avec le krypton ou le méthane dans la couche adsorbée est très faible sinon inexistante.
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Angerand, François. "Étude thermodynamique et structurale des changements de phase bidimensionnels dans des films de molécules physisorbées sur le graphite : Rôle de l'ordre orientationnel dans les phénomènes de mouillage et de transition rugueuse." Nancy 1, 1987. http://www.theses.fr/1987NAN10268.
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Ser, Frédéric. "Etude thermodynamique et structurale des changements de phase bidimensionnels dans des films de chlorure d'hydrogène et de quelques autres physisorbés sur la face de base du graphite : application au mouillage et à la transition rugueuse /." Saclay : Commissariat à l'énergie atomique, 1991. http://catalogue.bnf.fr/ark:/12148/cb35415552s.
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Ser, Frédéric. "Etude thermodynamique et structurale des changements de phase bidimensionnels dans des films de chlorure d'hydrogene et de quelques autres molecules physisorbees sur la face de base du graphite. Application au mouillage et a la transition rugueuse." Paris 11, 1990. http://www.theses.fr/1990PA112301.
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Notre these est consacree a l'etude des changements de phase bidimensionnels dans des films de molecules physisorbes sur la face de base du graphite et a l'application de ces phenomenes aux problemes du mouillage et de la transition rugueuse. Nous avons utilise deux techniques experimentales: volumetrie d'adsorption et diffraction neutronique. D'isothermes d'adsorption multicouche du xenon, nous deduisons qu'au-dessus de 100 k le xenon cristallin mouille parfaitement le graphite. Nos isothermes d'adsorption multicouche de c#2h#4 et c#2h#6 sur le graphite suggerent, en desaccord avec les resultats recents d'autres laboratoires, que la temperature critique de formation de couche varierait peu avec le nombre de couches jusqu'a la 4eme. La partie principale de notre these est consacree au film de chlorure d'hydrogene adsorbe sur le graphite. Des isothermes d'adsorption multicouche, nous deduisons que le cristal plastique de hcl mouille parfaitement le substrat. Le plus souvent, une telle conclusion implique une structure de la 1ere couche proche de celle de la face la plus dense du cristal d'adsorbat 3d. Pourtant, pour le chlorure d'hydrogene, l'etude structurale et thermodynamique suggere un ordre orientationnel des molecules different de celui existant en 3d. Une restructuration de la monocouche est donc necessaire lors de la condensation de la 2eme couche. Cette hypothese est fortement etayee par l'observation tout a fait originale d'un hysterese associee a la formation de la 2eme couche, suggerant l'existence d'une barriere a la nucleation de la bicouche a partir de la monocouche. De nos isothermes, nous deduisons que la temperature de transition rugueuse de la face (111) du cristal plastique de hcl est de 142 k
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Stocker, Pierre. "Ordre et désordre de couches minces: A/ préfusion de surface de films minces de méthane physisorbés sur graphite, étudiée par diffusion de neutrons: B / épitaxie de disiliciure de fer er de cobalt Si(111) : étudiée par diffusion de rayons X." Aix-Marseille 2, 1993. http://www.theses.fr/1993AIX22056.
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Le travail de these rapporte dans ce memoire s'articule autour du theme central de l'ordre et du desordre de surface et de couches minces, vu a travers des etudes structurales et dynamiques. Le premier axe de recherche est celui de la prefusion de surface. En realisant une experience de diffusion quasi elastique de neutrons sur des films de methane adsorbe sur des feuillets orientes de graphite, nous avons mis en evidence une anisotropie de la mobilite translationnelle suivant les directions parallele et perpendiculaire a la surface. Cette anisotropie est maximale vers 3 k au-dessous du point de fusion, et se reduit lorsque la couche prefondue s'epaissit au voisinage de la temperature de fusion tridimensionnelle. Le deuxieme axe de recherche repose sur l'etude par diffusion de rayons x de l'epitaxie de disiliciures de fer et de cobalt deposes sur silicium (111). Dans une premiere partie, nous nous sommes interesses a la caracterisation topologique comparative de couches minces de disiliciure -fesi#2 preparees par deux methodes differentes rde (reactive deposition epitaxy) et spe (solid phase epitaxy). Dans une deuxieme partie, des etudes structurales (diffraction) ont permis l'identification des couches deposees, ainsi que leur relation d'orientation epitaxiale avec le substrat. Pour des couches plus minces d'environ 40 a obtenues par epitaxie de jets moleculaires a 550c, la conjonction d'une analyse par diffraction rheed et par diffraction de rayons x en incidence rasante a permis de mettre en evidence l'existence d'une phase -fesi#2 normalement stable a haute temperature (>940c)
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Urban, Nathan Mark. "Thermodynamics and structure of fluids physisorbed on nanotubes." 2006. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-1354/index.html.
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Papadantonakis, Kimberly Marshall. "Exploration of Physisorbed Monolayers for Molecular-Scale Surface Patterning." Thesis, 2009. https://thesis.library.caltech.edu/2966/4/Chapter_4_Towards_Surface_Patterning_Using_Physisorbed_Monolayers_as_Masks.pdf.
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Many simple organic molecules, such as straight-chain alkanes and simple aromatics, spontaneously assemble into highly ordered monolayers at solid–liquid interfaces. These monolayers are composed of molecules that lie flat at the interface without forming chemical bonds to the surface of the solid. These monolayer structures are highly ordered and produce patterns with features on the scale of just a single nanometer in length. The exploitation of this physisorption phenomenon may provide a promising route toward an inexpensive nanometer-scale surface patterning technique. However, two fundamental challenges must be overcome before physisorbed monolayers can be useful in surface-patterning applications: (1) absence of control over the particular pattern formed by the molecules; and (2) pattern impermanence.
This document opens with an introductory chapter that contains background on physisorbed monolayers and a brief description of scanning tunneling microscopy, the experimental technique which is commonly used to study monolayers. The second and third chapters present details on the results of experiments with a monolayer templating technique. This templating technique involves replacement of the molecules comprising a monolayer of either normal alkanes or symmetrical thioethers by symmetrical ethers. The ethers are forced to conform to the structure of the existing template monolayer, which differs from the structure of an ether monolayer formed in the absence of the template. The monolayer templating technique offers researchers a limited method for exercising control over the surface patterns formed by particular molecules.
The challenge of pattern impermanence is addressed in the fourth chapter of this document. The molecules comprising physisorbed monolayers are free to exchange with molecules in the solution contacting the surface, thus the orientation of the monolayer structure within a particular surface region can change with time. A technique analogous to traditional lithographic methods that may allow physisorbed monolayers to be used for permanent surface patterning is described. The technique would employ physisorbed monolayers as surface masks while other molecular species chemically bond to regions of the surface left uncovered by the masking monolayer. Descriptions of the progress made toward the development of the patterning technique, and of the substantial challenges encountered during efforts to develop such a patterning method close the chapter.
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Miller, Brendan Paul. "Diffusion of physisorbed layers and their connection to MEMS effectiveness." 2009. http://www.lib.ncsu.edu/theses/available/etd-07212009-145828/unrestricted/etd.pdf.
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Boutchko, Rostyslav Dmytrovych. "Coupled dynamics of inert of intert gases physisorbed on crystal surfaces." 2001. http://www.library.wisc.edu/databases/connect/dissertations.html.
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Siegel, Amanda P. "Regulating Lipid Organization and Investigating Membrane Protein Properties in Physisorbed Polymer-tethered Membranes." 2012. http://hdl.handle.net/1805/2890.
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Indiana University-Purdue University Indianapolis (IUPUI)Cell membranes have remarkable properties both at the microscopic level and the molecular level. The current research describes the use of physisorbed polymer-grafted lipids in model membranes to investigate some of these properties on both of these length scales. On the microscopic scale, plasma membranes can be thought of as heterogenous thin films. Cell membranes adhered to elastic substrates are capable of sensing substrate/film mismatches and modulating their membrane stiffness to more closely match the substrate. Membrane/substrate mismatch can be modeled by constructing lipopolymer-enriched lipid monolayers with different bending stiffnesses and physisorbing them to rigid substrates which causes buckling. This report describes the use of atomic force microscopy and epimicroscopy to characterize these buckled structures and to illustrate the use of the buckled structures as diffusion barriers in lipid bilayers. In addition, a series of monolayers with varying bending stiffnesses and thicknesses are constructed on rigid substrates to analyze changes in buckling patterns and relate the experimental results to thin film buckling theory. On the molecular scale, plasma membranes can also be thought of as heterogeneous mixtures of lipids where the specific lipid environment is a crucial factor affecting membrane protein function. Unfortunately, heterogeneities involving cholesterol, labeled lipid rafts, are small and transient in live cells. To address this difficulty, the present work describes a model platform based on polymer-supported lipid bilayers containing stable raft-mimicking domains into which transmembrane proteins are incorporated (αvβ3, and α5β1integrins). This flexible platform enables the use of confocal fluorescence fluctuation spectroscopy to quantitatively probe the effect of cholesterol concentrations and the binding of native ligands (vitronectin and fibronectin for αvβ3, and α5β1) on protein oligomerization state and on domain-specific protein sequestration. In particular, the report shows significant ligand-induced integrin sequestration with a low level of dimerization. Cholesterol concentration increases rate of dimerization, but only moderately. Ligand addition does not affect rate of dimerization in either system. The combined results strongly suggest that ligands induce changes to integrin conformation and/or dynamics without inducing changes in integrin oligomerization state, and in fact these ligand-induce conformational changes impact protein-lipid interactions.
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Patil, Kalyan G. "Understanding Structure And Growth Of Physisorbed Films : A Combined Atomic Force Microscopy And Modeling Study." Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/2402.
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Surface modification has wide ranging implications in lubrication, microelectromechanical systems (MEMS), colloidal systems and biological membranes. Surface modification plays an important role in stabilizing gold nanoparticles, which have applications in targeted drug delivery and catalysis. A variety of surface modification techniques are used for controlling corrosion and wettability, as well as used extensively to understand the nature of interactions between surfaces. This thesis is mainly focused on understanding the kinetics, film growth and surface modification by long chain molecules physisorbed on a surface.
The time evolution of film growth and domain formation of octadecylamine on a mica surface is studied using ex-situ AFM and reflectance FTIR. A novel technique of interface creation is developed to measure the height of the adsorbed film. The results show three distinct regions of film growth mechanism. Region I, corresponds to thin film and the interface height is in the monolayer regime. The transient regime
(II) consists of a sharp increase in the film thickness, from 1.5 nm to 25 nm within a time span of 180 s. In the final stage of film growth the film thickness is invariant with time, during which domain coarsening is observed. Domain evolution reveals a non-monotonic variation in the domain size as a function of adsorption time. A three stage mechanism is proposed to explain the domain evolution on the surface.
In order to explain the observed film thickness variation, we have developed and tested various models to explain the thin to thick film transition observed in the AFM experiments. A model based on adsorption kinetics is solved to obtain the evolution of the adsorbed film. The model with a two-step adsorption isotherm quantitatively captures the thin to thick film transition observed in the AFM experiments. The statistical thermodynamics of adsorption of long chain molecules on a surface has been studied using a lattice model. The molecules are characterized by backbone chain, either lying parallel or perpendicular to the surface. A square lattice with nearest neighbour interactions and a mean field approximation are used to generate the adsorption isotherms for different molecules as a function of chain length. The molecules change their orientation from a surface parallel to an upright configuration with an increase in chemical potential. A similar transition (with time) in the molecular orientation has been observed in the AFM experiments. The transition between these two orientations is accompanied by an entropy maximum
The last part of the thesis is concerned with carbon-carbon interactions. More specifically, we are interested in the interactions between graphite surfaces and their modification in the presence of a lubricant or base oil. Diamond like carbon (DLC) AFM tips and highly oriented pyrolitic graphite (HOPG) have been used for this study. Experiments were carried out by treating HOPG graphite in hexadecane oil at different temperatures. It is observed that pull-off forces on bare graphite are smaller when compared to the treated surface. The magnitude of the pull-off forces increases with the temperature of the hexadecane oil bath. Presence of charged patches responsible for the higher adhesion have been confirmed using surface potential microscopy. Results also confirm the presence of a thin liquid-like hexadecane film at room temperature.
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Yeh, Chia-Wen, and 葉珈妏. "Application of Anion-Physisorbed Multi-walled Carbon Nanotubes on Photoelectrode for Dye-sensitized Solar Cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/35980155034475900674.
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碩士國立臺灣大學
高分子科學與工程學研究所
100
In this thesis, multi-walled carbon nanotubes(MWCNTs) physisorbing anionic and nonionic dispersing agent for surface modification were dispersed in TiO2 thin film utilizing as a photoelectrode for dye-sensitized solar cells (DSSCs). Anionic dispersing agents such as sodium dodecylbenzenesulfonate(SDBS) and poly (sodium4-styrenesulfonate) (NaPSS) with molecular weight of 9350, 20800 and 70000 were used to disperse MWCNTs. We also chose amphiphilic triblocks of PEG-PPG-PEG as nonionic surface modifying agents, such as P123、F68、and F108. The procedure for surface treatment MWCNTs is as following. Surface modifying agents and MWCNTs were dispersed and adsorbed in water by sonication. After fully adsorption, the solution was filtrated to remove the extra dispersing agents. After drying, the surface-modified MWCNTs were obtained. From the results of UV-vis spectroscopy, zeta potential and dynamic light scattering measurements, anionic surface modifying agents have better dispersing power than nonionic surface modifying agents because anionic agents have benzene ring to physisorb onto CNTs via π-π stacking. Furthermore, the electrostatic repulsion from the SO3- groups leads to the charge stabilization of MWCNTs compared to the nonionic agents. Then we dispersed anion-physisorbed MWCNTs onto the TiO2 system. From the XRD results, we found that TiO2 can crystallize into more anatase structures in the presence of MWCNTs. The resulting materials also had higher light transmittance. For the performance of DSSCs with MWCNT-TiO2 photoelectrode, the addition of 0.03wt% CNT to the TiO2 film could enhance the Jsc of DSSC from 18.65mA/cm2 to 19.26 mA/cm2. And the increase of Jsc resulted in higher power conversion efficiency and better charge collection efficiency because of good conductivity of MWCNTs, more anatase TiO2 crystal structures and higher light transmittance of the MWCNT-TiO2 films. The best Jsc and power conversion efficiency of 20.68mA/cm2 and 8.42% were achieved with MWCNT(70000) dispersing in TiO2. In addition, in order to enhance the light harvesting efficiency, the larger size of TiO2 scattering layer was deposited on the outer layer of MWCNT-TiO2 thin films. After addition of the scattering layer, the Jsc and power conversion efficiency were both increased to 21.44mA/cm2 and 8.84%.
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Chang, Yu-Hsun, and 張育勳. "The investigation on the dispersion of ionic liquids-physisorbed MWCNT and the applications of MWCNT/epoxy nanocomposites." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/10559186537794114300.
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博士國立臺灣大學
高分子科學與工程學研究所
102
The aim of this thesis was to discuss the dispersion of multi-walled carbon nanotube (MWCNT) modified by physical adsorption with ionic liquids. We investigated the cation-πinteraction between MWCNT and cation structure of ionic liquid. Pristine MWCNT and modified MWCNT would be incorporated individually into diglycidyl ether of bispheol-A (DGEBA) resin to fabricate epoxy/MWCNT suspension. We studied the processing and rheological behavior of epoxy/MWCNT suspensions, then the suspension was cured to form thin films or bulk nanocomposite. We also studied the electrical properties of nanocomposite films and the shear strength of bulk composite with the controlled applied normal stress. The thesis divided into four parts. In the first part, we synthesized three types of ionic liquids, 1-(2-acryloyloxy-ethyl)-3-methyl benzoimidazol-1-ium iodide (AMBImI), 10-Methyl-acridinium iodide(MAcI) and 1,3-dimethyl-3H-benzotriazolium iodide(DMBTAzI), to physisorb onto MWCNT and obtained MWCNT-AMBImI, MWCNT-MAcI and MWCNT-DMBTAzI. We also used pre-ionized compounds physisorbed onto MWCNT to compare with ionic liquid-physisorbed MWCNT. Then, we investigated the effect of physisorption by cation-π interaction. We observed the excess adsorption with ionic liquid by thermo gravimetric analysis (TGA), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Ionic liquid-physisorbed MWCNT also showed well dispersion in organic solvent and nanocomposite observed by TEM. Consequently, the glass transition temperature of nanocomposites contained modified MWCNT was enhanced to 129℃ due to the well interaction between MWCNT and epoxy resin. In the second part, we investigated the rheological behavior of epoxy/MWCNT suspension. MWCNT concentration effect on rheology was investigated in order to understand the processing and rheological properties of MWCNT composites. It was well known that storage modulus G’ and loss modulus G” of rheology were related to the degree of phase shift, δ, such that δ = tan-1(G” / G’). As the phase shift was higher than 45 degree, the G” was higher than G’ belonged to fluid behavior. On the contrary, as the phase shift was lower than 45 degree, it belonged to solid-like behavior. The suspension containing modified MWCNT gelled earlier than that containing pristine MWCNT because modified MWCNT had better dispersion to form network structure. We observed the plateau in storage modulus at lower angular frequency. The viscosity increased as the content of MWCNT was increased. We estimated volume fraction of particle domain aggregated by MWCNT through Thomas-modified Einstein viscosity equation and utilized small angle x-ray spectrum (SAXS) to measure the change of aggregated network structure. Besides, we also investigated rheological behavior of the epoxy/MWCNT suspension at various temperatures. At certain content of MWCNT, the suspensions showed more solid-like behavior as the temperature was increased. Increasing temperature facilitated the gelation of the suspension. The volume fraction of particle domain aggregated by MWCNT was changed by temperature effect. In the third part, we investigated electrical properties of epoxy/MWCNT nanocomposite for modified MWCNT. We observed AC volume conductivity displayed a plateau at low frequency region until the critical frequency (ωc) for the nanocomposite containing 0.4 wt% pristine MWCNT. Above critical frequency (ωc), AC volume conductivity also was increased with frequency. ωc shifted to higher frequency with the increasing of MWCNT contents. We utilized universal dynamic response (UDR) to fit AC volume conductivity of nanocomposite and got s value was about 0.7-1. The value also shifted to higher frequency due to nanocomposites containing well dispersion modified MWCNT. By incorporation of 2 wt% pristine MWCNT, the volume conductivity of nanocomposite enhanced from 10-11(S/cm) of insulator to 1.25×10-5(S/cm). Moreover, the highest volume conductivity was improved to 4.56×10-5(S/cm) as the nanocomposite containing 2 wt% MWCNT-MAcI or MWCNT-DMBTAzI. DC volume conductivity also obeyed percolation theory σDC＝σ0 (p-pc)t. For modified MWCNT, it showed higher index of t and σ0 constant, and pc was below 0.3 wt%. The lowest pc of modified MWCNT was 0.18wt%. In the last part of thesis, we measured the shear strength of bulk nanocomposite with controlled applied normal stress. The shear strength of cured DGEBA epoxy resin was 83.5 MPa. The shear strength of nanocomposite with 1 wt% MWCNT-MAcI or MWCNT-DMBTAzI was improved to 98.69MPa and 95.49MPa due to the excellently mechanical properties of MWCNT. In surface morphology, cross section of shear fracture of DGEBA epoxy resin dramatically changed from vein-like structure to rough chip-like structure as the inclined angle and compressive area was increased. With the incorporation of modified MWCNT-MAcI or MWCNT-DMBTAzI, the morphology of fracture clearly showed more branches in vein-like structure because of the improvement of MWCNT dispersion. As the inclined angle was increased to 60°, we could observe the fracture of nanocomposite containing modified MWCNT was damaged obviously due to the better dispersion. Finally, cation-π interaction between ionic liquid and MWCNT was investigated that could improve the dispersion of MWCNT. It was not necessary to modify MWCNT through many complex processes. The nanocomposites we prepared also had excellent properties and had graet potential for application in the future.
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Sallabi, Abdulwahab K. "Computer simulations of the structure, stability and phase transitions of diatomic molecules physisorbed on ionic surfaces : the CO/MgO(001), N2/MgO(001) and N2/NaCl(001) systems." Thesis, 2002. http://spectrum.library.concordia.ca/1715/1/NQ68200.pdf.
Full textAbstract:
Metropolis Monte Carlo simulations, using semiempirical potentials, are performed to study the structures, stability, and phase transitions of layers of CO and N 2 molecules physisorbed on the MgO(100) surface as well as a monolayer of N 2 physisorbed on NaCl(001) surface. In agreement with experiments [35-37], our simulations show that the c (4 x 2) structure of CO on the MgO(001) surface is the most stable structure below 41 K. The unit cell contains three CO molecules; two bridging molecules tilted in opposite directions by the same polar angle of 31 ̕with respect to the surface normal and a third molecule perpendicular to the surface. At 41 K the c (4 x 2) phase undergoes a transition into a less dense disordered phase accompanied by the desorption of some molecules. The density of this disordered phase is the same as for the p (3 x 2) phase. A model to compare the stability of the c (4 x 2) and the p (3 x 2) phases is constructed and suggests that at sufficiently high pressures and temperatures the p (3 x 2) phase is more stable than the c (4 x 2) phase as found by Panella et al . [35]. We propose that a sequence of transitions to a set of (n x 2) structure with ever decreasing density is possible under suitable conditions of temperature and pressure. This sequence of transitions is an example of the devil's staircase phenomenon as has been suggested by LEED experiments. Nitrogen molecules adsorbed on MgO(001) were studied and were also found to form a sequence of structures. A ([Special characters omitted.] ) R 33.7 ̕structure is found to form the most stable phase at low temperatures (below 20 K). This structure undergoes a phase transition into a less dense phase at 20 K and in all likelihood evolves into the less dense ([Special characters omitted.] ) R 36.9 ̕structure. The ([Special characters omitted.] )R36.9 ̕structure is stable up to 25 K. These results are in agreement with HAS results. This system might also prove to be an example of the devil's staircase phenomena. A monolayer of nitrogen molecules adsorbed on an NaCl(001) surface are used to test the validity of the theory of critical phenomena and its applicability to molecular systems. The simulations predict that this system undergoes a continuous order-disorder transition near 25 K with a logarithmically divergent heat capacity. The values of the critical exponents for the order parameter and susceptibility are calculated and found to deviate significantly from the Ising values but still satisfy Rushbrooke's scaling law. This behaviour is typical of the universality class containing the XY model with cubic anisotropy where the critical exponents are functions of the anisotropy and are thus "nonuniversal"