Studying physical properties of nanoscale materials has gained a significant attention owing to their applications in the fields such as electronics, medicine, pharmaceutical industry, and materials science. However, owing to size constraints, number of techniques that measures physical properties of materials at nanoscale with a high accuracy and sensitivity is limited. In this context, development of atomic force microscopy (AFM) based techniques to measure physical properties of nanomaterials has led to significant advancements across the disciplines including chemistry, engineering, biology, material science and physics. AFM has recently been utilized in the quantification of physical-chemical properties such as electrical, mechanical, magnetic, electrochemical, binding interaction and morphology, which are enormously important in establishing structure-property relationship. The overarching objective of the investigations discussed here is to gain quantitative insights into the factors that control electrical and mechanical properties of nano-dimensional organic materials and thereby, potentially, establishing reliable structure-property relationships particularly for organic molecular solids which has not been explored enough. Such understanding is important in developing novel materials with controllable properties for molecular level device fabrication, material science applications and pharmaceutical materials with desirable mechanical stability. First, we have studied electrical properties of novel silver based organic complex in which, the directionality of coordination bonding in the context of crystal engineering has been used to achieve materials with structurally and electrically favorable arrangement of molecules for an enhanced electrical conductivity. This system have exhibited an exceptionally high conductivity compared to other silver based organic complexes available in literature. Further, an enhancement in conductivity was also observed herein, upon photodimerization and the development of such materials are important in nanoelecrtonics. Next, mechanical properties of a wide variety of nanocrystals is discussed here. In particular, an inverse correlation between the Young’s modulus and atomic/molecular polarizability has been demonstrated for members of a series of macro- and nano-dimensional organic cocrystals composed of either resorcinol (res) or 4,6-di-X-res (X = Cl, Br, I) (as the template) and trans-1,2-bis(4-pyridyl)ethylene (4,4’-bpe) where cocrystals with highly-polarizable atoms result in softer solids. Moreover, similar correlation has been observed with a series of salicylic acid based cocrystals wherein, the cocrystal former was systematically modified. In order to understand the effect of preparation method towards the mechanical properties of nanocrystalline materials, herein we have studied mechanical properties of single component and two component nanocrystals. Similar mechanical properties have been observed with crystals despite their preparation methods. Furthermore, size dependent mechanical properties of active pharmaceutical ingredient, aspirin, has also been studied here. According to results reduction in size (from millimetre to nanometer) results in crystals that are approximately four fold softer. Overall, work discussed here highlights the versatility of AFM as a reliable technique in the electrical, mechanical, and dimensional characterization of nanoscale materials with a high precision and thereby, gaining further understanding on factors that controls these processes at nanoscale.

The adsorbed layer morphology of a series of surfactants under different conditions has been examined primarily using atomic force microscopy (AFM). The morphologies of single and double chained quaternary ammonium surfactants adsorbed to mica have been characterised using AFM at concentrations below the cmc. Mixing these different types of surfactants systematically allowed a detailed examination of the change in adsorbed film curvature from the least curved bilayers through to most curved globules. From this study a novel mesh structure was discovered at curvatures intermediate to bilayers and rods. A mesh was again observed in studies examining the morphology change of adsorbed nonionic surfactant films on silica with variation in temperature. Other surfactant mixtures were also examined including grafting non-adsorbing nonionic surfactants and diblock copolymers into quaternary ammonium surfactant films of different morphologies.

To investigate the ultimate resolution in ion beam lithography (IBL) the resist material poly(methyl methacrylate) PMMA has been modified by single ion impacts. The latent damage tracks have been etched prior to imaging and characterisation. The interest in IBL comes from a unique advantage over more traditional electron beam or optical lithography. An ion with energy of the order of 1 MeV per nucleon evenly deposits its energy over a long range in a straight latent damage path. This gives IBL the ability to create high aspect ratio structures with a resolution in the order of 10 nm. Precise ion counting into a spin coated PMMA film on top of an active substrate enabled control over the exact fluence delivered to the PMMA from homogenously irradiated areas down to separated single ion tracks. Using the homogenous areas it was possible to macroscopically measure the sensitivity of the PMMA as a function of the developing parameters. Separated single ion tracks wer e created in the PMMA using 8 MeV F, 71 MeV Cu and 88 MeV I ions. These ion tracks were etched to create voids in the PMMA film. For characterisation the tracks were imaged primarily with atomic force microscopy (AFM) and also with scanning electron microscopy (SEM). The series of studies presented here show that the sensitivity of the resist-developer combination can be tailored to allow the etching of specific single ion tracks. With the ability to etch only the damage track, and not the bulk material, one may experimentally characterise the damage track of any chosen ion. This offers the scientific community a useful tool in the study and fabrication of etched ion tracks. Finally work has been conducted to allow the precise locating of an ion beam using a nanoscale mask and piezoelectrically driven scanning stage. This method of beam locating has been trailed in conjunction with single ion detection in an effort to test the practical limits of ion beam lithography in the single ion realm.

Methods based on the atomic force microscope (AFM) were implemented or developed to measure and map at the nanoscale the mechanical properties of polymer surfaces and of nanomaterials: force spectroscopy, force modulation, phase detection in intermittent-contact mode. Especially, a technique, referred as resonant contact-AFM, was developed. It is based on the electrostatic excitation of the cantilever vibration and on the measurement of its resonance frequency when the tip contacts the probed sample. A theoretical model was developed to determine the tip-sample contact stiffness from the measurement of the frequency shift. These methods were used to study several questions raised in the fields of polymer surfaces and interfaces and of nanomaterials. Surfaces of toughened polypropylene (PP) with ethylene-propylene copolymer (EP) were studied by force spectroscopy and force modulation microscopy (FMM) to characterise the effect of the blending and the moulding processes and the PP/EP viscosity ratio on the surface distribution of the EP rubber nodules. The contribution of the EP rubber to paint adhesion was also demonstrated. Surfaces of atactic polypropylene photo-grafted with acrylic acid monomers were analysed by intermittent-contact AFM (IC-AFM) with phase detection. The combination of these methods with other analytical techniques allowed characterising the chemical composition of the heterogeneous surface morphology obtained after photo-grafting. The tensile elastic modulus of polymer nanotubes and metallic nanowires was measured with force spectroscopy and resonant contact-AFM. These measurements confirmed the ability of resonant contact-AFM to quantitatively measure the mechanical properties of nanomaterials. Moreover, they showed that the measured modulus increased when the nanowires or nanotubes diameter decreases. This behaviour was explained by taking into account the effect of the surface deformation that added a surface stiffness proportional to the surface tension, or surface stress, of the material. Resonant contact-AFM was also used to characterise the variation of the mechanical properties at the interfaces in polymer blends. It was demonstrated that this technique allows the determination of the interfacial width in incompatible polymer blends. It also allowed characterising the mechanical property gradient that can appear in reactive polymer blends.

Metrological data from sample surfaces can be obtained by using a variety of profilometry methods. Atomic Force Microscopy (AFM), which relies on contact inter-atomic forces to extract topographical images of a sample, is one such method that can be used on a wide range of surface types, with possible nanometer range resolution. However, AFM images are commonly distorted by convolution, which reduces metrological accuracy. This type of distortion is more significant when the sample surface contains high aspect ratio features such as lines, steps or sharp edges - structures commonly found in semiconductor devices and applications. Aiming at mitigating these distortions and recovering metrology soundness, we introduce a novel image deconvolution scheme based on the principle of stereo imaging. Multiple images of a sample, taken at different angles, allow for separation of convolution artifacts from true topographic data. As a result, perfect sample reconstruction and probe shape estimation can be achieved in certain cases. Additionally, shadow zones, which are areas of the sample that cannot be probed by the AFM, are greatly reduced. Most importantly, this technique does not require a priori probe characterization. It also reduces the need for slender or sharper probes, which, on one hand, induce less convolution distortion but, on the other hand, are more prone to wear and damage, thus decreasing overall system reliability. / Singapore-MIT Alliance (SMA)

The goal of this project was to develop techniques and instrumentation to measure the elastic properties of the lens and lens capsule in situ and their changes with age using Atomic Force Microscopy (AFM). The studies include the construction, characterization, and calibration of laboratory-based Atomic Force Microscope (AFM) to measure mechanical properties of ophthalmic tissues. Atomic Force Microscopy is a nanoscale imaging technique that has been applied to mechanical property measurement through nanoindentation. Young's modulus of elasticity is determined by monitoring the cantilever deflections when it contacts the sample. The studies also include the development of tissue preparation techniques to enable measurement of the lens elasticity using AFM. This study found that lens capsule elasticity decreases with age, outer lens cortex elasticity remains constant with age, and the inner lens cortex is stiffer than the outer lens cortex. The effect of the changing biometry and mechanical properties with age was investigated by developing a mathematical model of accommodation. These changes will be the limiting factor to accommodative amplitude. Changes in lens capsule mechanical properties will affect the maximal accommodative amplitude in older eyes.

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. 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, namelyE/σyratio and strain hardening exponent orexperimental parameterhe/hmaxratio, and the contact friction. Anempirical model has been proposed to relate the contact area ofindentation to theE/σyratio and thehe/hmaxratio 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. 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. 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. Keywords: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.

The fabrication characteristic of etching and deposition of focused ion beam (FIB) on the submicron structure of silica and quartz glass was investigated. FIB has several advantages such as high sensitivity, high material removal rate, and direct fabrication in some selected areas without the use of etching mask, etc. In this study, silicon and quartz glass materials etched by FIB were used for fast fabrication of 3-D submicron structures to investigate the differences between the samples before and after fabrication. The expansion effect of silicon with sputtered platinum on surface is compared with Pyrex glass with sputtered chromium on surface. The result shows the side wall of structure in the center wouldn¡¦t be vertical after etching and trimming on the quartz glass and the silicon substrate. Trenches with different depth and width on the surface of silicon were etched by FIB and measured by Atomic Force Microscope. Lines with different interval were deposited by FIB on the surface of quartz glass and were measured by Atomic Force Microscope.

Several nanomaterials systems, both inorganic and organic in nature, have been extensively investigated by a number of characterization techniques including atomic force microscopy (AFM), electron microscopy, Fourier transform infrared spectroscopy (FTIR), and energy dispersive x-ray spectroscopy (EDX). The first system consists of boron nitride nanotubes (BNNTs) synthesized via two different methods. The first method, silica-assisted catalytic chemical vapour deposition (SA-CVD), produced boron nitride nanotubes with different morphologies depending on the synthesis temperature. The second method, growth vapour trapping chemical vapour deposition (GVT-CVD), produced multiwall boron nitride nanotubes (MWBNNTs). The bending modulus of individual MWBNNTs was determined using an AFM three-point bending technique, and was found to be diameter-dependent due to the presence of shear effects. The second type of nanomaterial investigated is the biomineralized calcareous shell of the serpulid Hydroides dianthus. This material was found to be an inorganic-organic composite material composed of two different morphologies of CaCO3, collagen, and carboxylated and sulphated polysaccharides. The organic components were demonstrated to mediate the mineralization of CaCO3 in vitro. The final system studied is the proteinaceous cement of the barnacle Amphibalanus amphitrite. The secondary structure of the protein components was investigated via FTIR, revealing the presence of β-sheet conformation, and nanoscale rod-shaped structures within the cement were identified as β-sheet containing amyloid fibrils via chemical staining. These rod-shaped structures exhibited a stiffer nature compared with other structures in the adhesive, as measured by AFM nanoindentation.

Background and aims: It is known that smooth muscle possesses substantial mechanical plasticity in that it is able to adapt to large changes in length without compromising its ability to generate force. It is believed that structural malleability of the contractile apparatus underlies this plasticity. There is strong evidence suggesting that myosin thick filaments of the muscle are relatively labile and their length in vivo is determined by the equilibrium between monomeric and filamentous myosin. The equilibrium in turn is governed by the state of phosphorylation of the 20-kD regulatory myosin light chain (MLC20, or RLC). It is known that phosphorylation of the myosin light chain favors formation of the filaments; it is not known how the light chain phosphorylation affects the lability of the filaments. The major aim of this thesis was to measure the mechanical integrity of the filaments formed from purified myosin molecules from bovine airway smooth muscle, and to determine whether the integrity was influenced by phosphorylation of the myosin light chain. Methods: Myosin was purified from bovine trachealis to form filaments, in ATP containing zero-calcium solution during a slow dialysis that gradually reduced the ionic strength. Sufficient myosin light chain kinase and phosphatase, as well as calmodulin, were retained after the myosin purification and this enabled phosphorylation of RLC within 20-40 s after addition of calcium to the filament suspension. The phosphorylated and non-phosphorylated filaments were then partially disassembled by ultrasonification. The extent of filament disintegration was visualized and quantified by atomic force microscopy. Results: RLC phosphorylation reduced the diameter of the filaments and rendered the filaments more resistant to ultrasonic agitation. Electron microscopy revealed a similar reduction in filament diameter in intact smooth muscle when the cells were activated. Conclusion: Our results suggest that RLC phosphorylation is a key regulatory step in modifying the structural properties of myosin filaments in smooth muscle, where formation and dissolution of the filaments are required in the cells’ adaptation to different cell length.