Thesis (Ph. D.)--Brigham Young University. Dept. of Physics and Astronomy, 2004. / Includes bibliographical references (p. 71-75).

Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010. / Committee Chair: Lawrence A. Bottomley; Committee Member: Aldo A. Ferri; Committee Member: Andrew Lyon; Committee Member: Jean-Luc Bredas; Committee Member: Robert L. Whetten. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 113-116). Also available in electronic version.

Proefschrift Rijksuniversiteit Groningen. / Datum laatste controle: 22-12-1997. Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

Atomic Force Microscopy (AFM) is a powerful technique that has evolved from being a purely imaging tool to a one capable of providing multifunctional information, offering exciting new possibilities for nano-biotechnology. The project focuses on the use of the AFM in order to morphologically and mechanically characterise cells and biomaterials demonstrating how versatile this instrument can be. The project is divided in the following parts:Part 1: establishment of AFM protocols for the nano-scale morphological and mechanical characterisation of soft and hard macroscopic substrates and of objects such as adsorbed nanoparticles. In particular, these techniques were tested on:Hyaluronic acid (HA)/poly(ethylene glycol) (PEG)-based hydrogels, which provide an artificial model for the mechanical behaviour of some biological tissues and organs. The elastic modulus, measured via AFM nanoindentation, of these hydrogels increased by decreasing the concentration and the molecular weight (MW) of HA in the hydrogels. We have then verified a clear relation between the mechanical properties of the hydrogels and the proliferation of cells cultured on them. Chitosan nanoparticle (popular carriers for the delivery of negatively charged macromolecular payloads, e.g. nucleic acids) cross-linked with triphosphate (TPP) and then coated with HA. We focussed on the influence of chitosan molecular weight (Mw) on nanoparticle properties. HA was able to penetrate into the more porous nanoparticles (high MW chitosan), whereas it formed a corona around the more cross-linked ones (low MW chitosan). AFM imaging was used to highlight the presence of this corona and also to estimate its apparent thickness to about 20-30 nm (in dry state).Silicone substrates modified with amphiphilic triblock copolymer (Sil-GMMA) layers. Extensive AFM (imaging and nanoindentation) provided evidence that silicone substrates are prevalently coated with Sil-GMMA thin layers that exhibit negligible hydrophobic recovery during drying and change the surface from more to less cell-adhesive. Part 2: AFM mechanical characterisation of fibroblast-to-myofibroblast differentiation process. Fibroblasts were stimulated to differentiate into myofibroblasts by Transforming Grow Factor β1 (TGFβ1) on hard substrate. AFM force maps performed both on fibroblasts (untreated cells) and myofibroblasts (TGFβ1-treated cells) revealed a significant increase in the elastic modulus in treated cells. Part 3: preparation and AFM characterisation of poly(ethylene glycol) diacrylate/acrylate (PEGDA/A) hydrogels. Since the mechanical properties of the substrate plays a pivotal role in fibroblast-to-myofibroblast differentiation process, hydrogels were prepared and characterised at the macro/nanoscale with AFM indentation, providing us with cell-adhesive substrates that cover a wide range of elastic modulus. These substrates are optimal candidates for future investigations to better understand and possibly control the differentiation process.

The conventional atomic force microscope (AFM) is equipped with a single optical detection system. Probe-sample separation is determined in an independent deflection with respect to AFM z-translation experiment. This method of determining probe-surface separation is relative, susceptible to drift and does not provide real time separation information. The evanescent wave atomic force microscope (EW-AFM) utilizes a second, independent detection system to determine absolute probe-surface separation in real time. The EW-AFM can simultaneously acquire real-time force and probe-sample separation information using the optical lever and evanescent scattering detection systems, respectively. The EW-AFM may be configured with feedback on the optical-lever system for constant force applications or with feedback on evanescent wave scattering intensity for constant height applications. Scattering of the evanescent wave exponential decay profile is used to determine probe-surface separation. Sub-micron sized dielectric and metallic probes show exponential scattering profiles, micron sized polystyrene and borosilicate microspheres show non-exponential profiles when they are affixed beneath the cantilever tip. By affixing the microspheres to the end of the AFM cantilever exponential and non-exponential profiles were observed. The EW-AFM can be used to conduct force-distance and imaging experiments. The EW-AFM was used to measure the thickness of surfactant bilayers formed at the silica-solution interface using silicon nitride AFM tips. The presence of a refractive index difference between the surfactant bilayer and the solution does not influence the accuracy of the surfactant bilayer thickness measurement. The EW-AFM was used to scan a 2 x 2 micron area in constant height mode. The probe was brought to within 6 nanometers of a planar dielectric surface using the evanescent wave intensity as a height reference with accuracy of ± 1 nm. This capability may be utilized to observe charge heterogeneity at the solid-liquid interface with nanometer lateral resolution or to map chemical functional group heterogeneity based on perturbations to the electrical double layer. The EW-AFM evanescent scattering system has an absolute separation resolution of 0.3 nm compared to 1.0 nm relative separation resolution for the optical lever system. In constant scattering (constant height) mode the real time separation precision is about 2 nm. / Ph. D.

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Graphene, an atomically-thin layer of hexagonally bonded carbon atoms, is the strongest material ever tested. The unusual electrical and mechanical properties of graphene are particularly useful for next-generation transparent touch screens, flexible electronic displays, and photovoltaics. As such applications arise, it is critically important to characterize the resistance of this material under impact and deformation by nanoscale contact. The objective of this thesis is to study the physics of deformation in graphene sheets on a flat substrate under nanoindentation, as a function of number of graphene layers and applied force. In this work, the nanoindentation behavior of single and few layer graphene sheets was investigated by using atomic force microscopy (AFM). Graphene was created by mechanical exfoliation and deposited on a flat SiO2 substrate. The system of graphene on SiO2 simulates many of graphene’s applications, but its characterization by nanoindentation is not fully understood. Here, it was found that the deformation of the atomically-thin film remains purely elastic during nanoindentation, while the amorphous substrate deforms plastically. Also, both modulus of elasticity and contact stiffness were found to increase by 18% when few layer graphene sheets were added to a SiO2 substrate. However, no pronounced change in nanohardness was observed in the substrate with and without the addition of graphene. Furthermore, three modes of deformation were observed including purely elastic deformation, plastic deformation and an abnormal force-depth step mechanism. Each of these mechanisms was analyzed in detail using force-displacement curves and AFM images, and a deformation mechanism map, as a function of number of graphene layers and contact force, was developed. In addition to nanomechanical experiments, computer simulations by finite element analysis (FEA) were conducted in order to better understand the nanonindentation process and underlying deformation mechanisms in this system.