Atomic force microscopy (AFM) is an important technology that allows researchers to probe local surface properties at nanometer length scales. In addition to surface topography, the AFM can probe many types of tip-surface interactions (including adhesion and friction) to gain a better understanding of the chemical properties of surfaces. This thesis contains two experiments which utilize AFM to in addition to several other techniques to study (1) Self Assembled Monolayer (SAM) formation and corrosion and (2) intermolecular and surface/molecular effects on gramicidin film formation and molecular orientation. In the first experiment, N-octadecyltrichlorosilane (OTS) molecules were self-assembled onto silicon samples. We observed that OTS required a very short time (about 15 seconds) to complete the formation of the monolayer on surface. However, this SAM film was highly susceptible to corrosion by the strong oxidant (KMnO4), resulting in a chemical change to the film from hydrophobic functional groups (CH3) to hydrophilic functional groups (OH). In subsequent experiments, we observed that if the SAMs were formed using longer exposure times (about 24 hours), they were highly resistant to corrosion. Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) also showed that the 24 hour growth SAM films were densely packed. These results indicate that SAM films based on organosilane molecules can protect the surface from corrosion, and further that more densely packed SAMs exhibit better anti-corrosion performance than less dense films. In the second experiment, the antibacterial peptide Gramicidin was used to study how intermolecular and surface energy properties can influence the aggregation and film formation of molecules on several surfaces. Gramicidin has a unique physical and chemical structure with hydrophobic side chain and hydrophilic ends. Here, we have used three different substrates (Silicon, Mica, and Graphite) to study intermolecular interactions, aggregation, and orientation of Gramicidin peptide. Langmuir-Blodgett methods were also used to study aggregation and molecular orientation at the solid-liquid interface.

Self assembled monolayer films (SAMs) deposited on silicon surfaces have gained considerable interest due to their ability to modify surface properties for advanced applications in sensors, MEMS, and NEMS devices. These molecular films are typically deposited on silicon surfaces from solution using a variety of solvents, which can influence the molecular packing and quality of the films. To better understand these effects, we have performed a systematic solvent effect study of the growth of n-Octadecyltrichlorosilane (OTS) on silicon substrates using chloroform, dichloromethane, toluene, benzene and hexadecane. The films were characterized using contact angle measurements, Fourier Transform Infrared Spectroscopy (FTIR), and Atomic Force Microscopy (AFM) to evaluate the SAM growth rate and film quality. Lateral Force Microscopy (LFM) and transmission FTIR were used to characterize the molecular packing. Finally, we used AFM to make adhesion measurements on the films and correlated these results with friction data. These techniques provide a means to characterize the local nanoscale packing of the films. The Hertzian contact model was used to model and describe the adhesion and friction result. Our results show that using hexadecane as the solvent produced OTS films with the highest density molecular packing. By comparing to Langmuir-Blodgett SAM film deposition methods, we show that it is the intermolecular interaction between the solvent molecules and OTS that determines this density. Thus, the structure and chemical properties of the solvent molecule strongly influences the molecular packing, quality, and performance of the SAM film.

<p>In the past two decades depth-sensing indentation has becomea widely used technique to measure the mechanical properties ofmaterials. This technique is particularly suitable for thecharacterisation of materials at sub-micro or nano scale thoughthere is a tendency to extend its application to the micro ormacro scale. The load-penetration depth curve of depth-sensingindentation is a characteristic of a material and can be usedfor analysing various mechanical properties in addition tohardness. This thesis deals with the mechanicalcharacterisation of bulk materials, thin films and coatings,gradient materials, and composites using depth-sensingindentation. Finite element method has been resorted to as atool to understand the indentation behaviour of materials.</p><p>The piling-up or sinking-in behaviour of materials plays animportant role in the accurate determination of materialsproperties using depth-sensing indentation. Finite elementsimulations show that the piling-up or sinking-in behaviour isdetermined by the material parameters, namely<i>E/σ</i><i>y</i>ratio and strain hardening exponent orexperimental parameter<i>h</i><i>e</i><i>/h</i><i>max</i>ratio, and the contact friction. Anempirical model has been proposed to relate the contact area ofindentation to the<i>E/σ</i><i>y</i>ratio and the<i>h</i><i>e</i><i>/h</i><i>max</i>ratio and used to predict thepiling-up orsinking-in of materials. The existence of friction is found toenhance the sinking-in tendency of materials. A generalrelationship between the hardness and the indentationrepresentative stress valid for both soft and hard materialshas been obtained. A possible method to estimate the plasticproperties of bulk materials has been suggested.</p><p>Measuring the coating-only properties requires theindentation to be done within a critical penetration depthbeyond which substrate effect comes in. The ratio of thecritical penetration depth to the coating thickness determinedby nanoindentation is independent of coating thickness andabout 0.2 for gold / nickel, 0.4 for aluminium / BK7 glass, and0.2 for diamond-like-carbon / M2 steel and alumina / nickel.Finite element simulations show that this ratio is dependent onthe combination of the coating and the substrate and moresensitive to differences in the elastic properties than in theplastic properties of the coating/substrate system. Thedeformation behaviour of coatings, such as, piling-up of thesoft coatings and cracking of the hard coatings, has also beeninvestigated using atomic force microscope.</p><p>The constraint factors, 2.24 for WC phase and 2.7 for WC-Cocemented carbides, are determined through nanoindentation andfinite element simulations. A modified hardness model of WC-Cocemented carbides has been proposed, which gives a betterestimation than the Lee and Gurland hardness model. Finiteelement method has also been used to investigate theindentation behaviour of WC-Co gradient coatings.</p><p><b>Keywords:</b>depth-sensing indentation, nanoindentation,finite element method, atomic force microscope, mechanicalproperties, hardness, deformation, dislocations, cracks,piling-up, sinking-in, indentation size effect, thin coatings,composite, gradient materials, WC-Co, diamond-like-carbon,alumina, gold, aluminium, nickel, BK7 glass, M2 steel.</p>

Many proteins are known to actively interact with biological, as well as inorganic and synthetic surfaces that are widely used in nano- and bio-technology as biosensing platforms and in tissue engineering. Amyloid fibrils are insoluble protein aggregates in beta-sheet conformation that are implicated in at least 20 diseases for which no cure is currently available. The molecular mechanism of fibril formation, as well as the mechanism of fibril clusters interacting with lipid membrane surfaces is currently unknown. The lipid membrane surface has a complex biochemical composition and is also electrostatically non-homogeneous. Currently, the experimental data available for amyloid fibril formation both on lipid and artificial surfaces is limited. The goal of our study is to investigate how the physical properties of the surfaces affect binding of amyloid peptides and affect the fibril formation. We seek to elucidate the effect of electrostatic interactions of amyloid peptides with surfaces using Atomic Force Microscopy (AFM) and Kelvin probe force microscopy (KPFM). We show using KPFM that electrostatic domains readily form within biological systems such as lung surfactant and lipid monolayers. We compared three different implementations of KPFM to demonstrate that frequency modulated (FM-) KPFM provides significant advantages over other modes. We also present a study of Amyloid beta (1-42) fibril formation on model surfaces, which are uniformly charged or possess periodicity of charges and hydrophobic functionality based on thiol self-assembly. Effect of membrane composition, surface charge, and presence of steroids will be discussed.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 135-138).

Thesis (Ph. D.)--University of Chicago, Department of Physics, December 2003. / CD-ROM includes PDF files of figures 2.1-4.7. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 95-103).

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Aniosotropy; scanning instruments; scanning; surface metrology; surface; fractal. Includes bibliographical references (p. 52).

This dissertation will demonstrate the synergy of nanoscopic materials and surface metrology methods by the fabrication and implementation of CNT atomic force microscopy (AFM) tips, CNT scanning tunneling microscopy (STM) tips, Pt spike AFM tips, and Pt spike near-field scanning optical microscopy (NSOM) tips for the methods of critical dimension metrology, STM, AFM phase imaging, scanning surface potential AFM (SSPM), NSOM, and three-dimensional AFM. Chapter 1 provides a general overview of the information that will be discussed in this dissertation. Chapter 2 describes two methods for the simultaneous fabrication of carbon nanotube atomic force microscopy and scanning tunneling microscopy probes. The fabrication of these high resolution probes, as well as their imaging characteristics, is described in detail. Resolution standards were used to characterize their behavior and resolution limits. In Chapter 3, the effect of high aspect ratio probe length on AFM phase imaging is studied by fabricating highly controllable Pt spike AFM tips. By monitoring phase shifts on homogenous surfaces as a function of Pt spike length, it is shown that attractive forces at the tip are significantly reduced when high aspect ratio structures are added to conventional AFM probes. In Chapter 4, the effect of probe geometry on scanning surface potential microscopy (SSPM) is described. By studying the effect of scan height in SSPM, it was found that large surface area probe geometries, such as conventional Pt coated AFM tips, have lower surface potential resolution because of contributions from the sides of the tip as well as the cantilever. Spatial resolution standards were probed to evaluate the effect of probe geometry on SSPM sensitivity and resolution. Chapter 5 describes the fabrication of specialized probes for three-dimensional atomic force microscopy, scanning near-field optical microscopy, and scanning electrochemical -- atomic force microscopy (SECM-AFM). Using techniques described in Chapters 2-4, high aspect ratio structures were added to conventional probes used in 3D AFM, NSOM and SECM-AFM to solve limitations inherent to current probe designs for each method. Preliminary data indicates that each probe will have a significant beneficial effect on the resolution limit of its technique.

No description available.