Monolayers of amphiphilic molecules at interface provide a unique system for understanding the thermodynamic and rheological properties of quasi two-dimensional systems. They are also an excellent model accessible for studying cell membranes. The feature of longrange organization of molecular tilt azimuth in monolayers at the air/water interface is one of the most interesting findings over the past two decades, which leads to the formation rich and defined textures. By observing the changes in these textures, the transitions between tilted monolayer phases can be detected. We study the boojum and stripe textures formed in the liquid-condensed phase of pentadecanoic acid (PDA) monolayers at the air/water interface and find that they can be preserved after being transferred to glass substrates at low dipping speeds at a temperature lower than the room temperature. Frictional force microscopy confirms the long-range tilt order in the transferred boojums and stripes of PDA, implying the interaction of the PDA molecules with the glass surface does not change the tilt order. Polymerized stripe textures of pentacosadiynoic acid (PCA) monolayers can also be transferred onto solid substrates. Atomic force microscopy shows that the PCA stripe textures represent the regular variations of molecular packing densities in PCA monolayers. Furthermore, we find that the molecular orientation and packing density changes in monolayers can induce the local order of nematic liquid crystals. Due to the longrange orientation correlation of nematic liquid crystals, the boojum and stripe textures in monolayers can be observed by an optical microscope after liquid crystal optical amplification.

No description available.

At the molecular level the entropic “hydrophobic effect” is responsible for high interfacial energies between hydrophobic solids and aqueous liquids, the low solubility of apolar solutes in aqueous solvents, and self-assembly in biological processes, such as vesicle formation and protein folding. Although it is known that a strong attraction between apolar molecules exists at the molecular level, it is not clear how this force scales up to objects with dimensions in the range 100 nm–1 m. This work sets out to measure the forces between particles with a radius of about 10 µm. Because we can only measure the total force, which includes the van der Waals force and the electrostatic forces, it is important to isolate the effect of “hydrophobicity”. We do this by measuring for systems where the particles are very hydrophobic (water contact angle, θ ~110°) and the van der Waals and electrostatic forces are very small. Under these conditions we find that the total force is very small: it is similar to the van der Waals force at separations exceeding 5 nm. Many early works on the hydrophobic force reported surface force at over 100 nm of separation. However, many of these strong, long-ranged attractive forces are likely caused by submicron interfacial bubbles, known as nanobubbles. Nanobubbles were imaged with an atomic force microscope to better understand their stability and dependence on solution properties, such as initial concentration of dissolved gas and changes in gas concentration. We found that nanobubbles still formed in degassed solutions and that lowering the dissolved gas concentration did not reduce the bubble size, implying that nanobubbles do not form from dissolved gas in the liquid phase or do not contain gas and are instead water vapor. Furthermore, addition of an oxygen scavenger agent, sodium sulfite, to a liquid phase that had been pressured with oxygen did not reduce bubble size which could be evidence that nanobubbles are impermeable to gas diffusion across the gas liquid interface, do not form from the dissolved gas in the surrounding liquid, or do not contain gas and are instead water vapor. / Ph. D.

Scanning probe microscopy was employed to characterize the piezotronic effect in both longitudinal and transverse force sensing modes in CdSe, and GaN nanowires, respectively. Both experimental results show exponential response of their conductivity change to applied forces. Theoretical models are also presented to explain this mechanism and quantify the relationship, where strain induced piezoelectric polarization changes the metal-semiconductor Schottky barrier height. An in-situ method based on SPM is developed to characterize the triboelectric process, including tribo-charge intensity, multi-cycle friction effect, as well as its surface diffusion. Beyond that, effect of external electric field was investigated as an approach to manipulate the polarization and intensity. Finally, a concept of self-powered motion sensing technology is developed and demonstrated experimentally with nanometer resolution, long working distance as well as high robustness. It provides a promising solution for application areas that need ultra-low power consumption devices.

No description available.

This dissertation presents research on scanning probe microscopy and spectroscopy of graphene and carbon nanotubes. In total three experiments will be discussed. The first experiment uses a scanning tunneling microscope (STM) to study the topographic and spectroscopic properties of graphene on hexagonal boron nitride (hBN). Graphene was first isolated and identified on SiO₂ substrates, which was later found to be the source of graphene quality degradation, e.g. large surface roughness, increased resistivity and random doping etc. Researchers have been trying to replace SiO₂ with other materials and hBN is by far the most successful one. Our STM study shows an order of magnitude reduction in surface roughness and electrostatic potential variation compared with graphene on SiO₂.The second experiment shows a novel quantum interference effect of electron waves in graphene, loosely referred to as "Friedel oscillations." These arise when incident electron waves interfere with waves scattered from defects in the sample. This interference pattern shows up as a spatial variation in the local density of states, which can be probed by the STM. We measured such Friedel oscillations in graphene near step edges of hBN. Due to its peculiar band structure, the oscillations in graphene have a faster decay rate and their wavelength is an order of magnitude longer than similar oscillations previously observed on noble metal surfaces. By measuring the dependence of the Friedel oscillations on electron energy, we map out the band structure of graphene. The last experiment studies a different system: carbon nanotube quantum dots. By combining scanning probe microscopy and transport measurements, we obtain spatial information about quantum dots formed in a carbon nanotube field effect transistor. We also demonstrate the ability to tune the coupling strength between two quantum dots in series.

No description available.

The highly specific recognition processes between biomolecules mediate various crucial biological processes. Uncovering the molecular basis of these interactions is of great fundamental and applied importance. This research work focuses on understanding the interactions of several biomolecular recognition systems and processes that can provide fundamental information to aid in the rational design of sensing and molecular recognition tools. Initially, a reliable and versatile platform was developed to investigate biomolecular interactions at a molecular level. This involved several techniques, including biomolecule functionalization to enable attachment to self-assembled monolayers as well as atomic force microscopy (AFM) based force spectroscopy to uncover the binding or rupture forces between the receptor and ligand pairs. It was shown that this platform allowed determination of molecular binding between single molecules with a high specificity. The platform was further adapted to a general sensing formulation utilizing a group of flexible and adaptive nucleic acid recognition elements (RNA and DNA aptamers) to detect specific target proteins. Investigation of interactions at the molecular level allowed characterization of the dynamics, specificity and the conformational properties of these functional nucleic acids in a manner inaccessible via traditional interaction studies. These interactions were then adapted to aptamer-based detecting methods that at the ensemble or bulk scale, specifically taking advantage of mechanisms uncovered in the biophysical study of this system. A quartz crystal microbalance (QCM) was used to detect protein targets at the bulk level and the affinities and binding kinetics of these systems were analyzed. Along with AFM-based force spectroscopy, ensemble-averaging properties and molecular properties of these interactions could be correlated to contribute to bridging the gap across length scales. Finally, more broadly applicable sensing platform was developed to take advantage of the unique properties of aptamers. DNA was employed both as a carrier and as a molecular recognition agent. DNA was used as a template for nanoconstruction and fabricating unique shapes that could enhance the aptamer-based molecular recognition strategies. With aptamers tagged to distinct nanoconstructed DNA, a novel shape-based detecting method was enabled at the molecular level. The results demonstrated that this is a flexible strategy, which can be further developed as ultrasensitive single molecule sensing strategy in complex environments.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Submitted by Evandro Martin Lanzoni (evandrolanzoni@yahoo.com.br) on 2018-05-28T18:03:48Z No. of bitstreams: 1 dissertação mestrado evandro lanzoni_versão final.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-05-28T19:02:57Z (GMT) No. of bitstreams: 1 lanzoni_em_me_bauru.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) / Made available in DSpace on 2018-05-28T19:02:57Z (GMT). No. of bitstreams: 1 lanzoni_em_me_bauru.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) Previous issue date: 2018-03-29 / As técnicas de microscopia de sonda Kelvin (KPFM) e de microscopia de força eletrostática (EFM) são amplamente utilizadas para analisar a distribuição do potencial de superfície, porém com pouca aplicação em nanoestruturas semicondutoras auto-organizadas embutidas em um substrato. Neste trabalho, investigamos diretamente o acúmulo de carga dentro de estruturas mesoscópicas de GaAs (MGS) [1]. As estruturas são fabricadas através do crescimento sobreposto de um modelo de nano orifícios usando epitaxia de feixe molecular. Para tal, uma combinação de desoxidação assistida por Ga e ataque químico por gotículas localizadas foram utilizadas para criar orifícios iniciais com uma profundidade de ca. 10 a 15nm, que são posteriormente cobertos com 15nm de barreira AlxGax-1As e GaAs com 1nm, 2nm, 5nm, 10nm de espessura. Microscopia de força atômica e microscopia eletrônica de transmissão mostraram que a forma do orifício é preservada durante o crescimento de AlGaAs. Em seguida, esses orifícios são preenchidos com GaAs formando uma estrutura alongada sobre o buraco [1]. Investigamos o potencial de superfície local e a distribuição das cargas nestas estruturas com a técnica KPFM de passagem única. Portanto, uma voltagem AC de 5 V é aplicada a uma ponta metalizada e varremos a amostra no modo de contato intermitente. Observamos uma clara diferença de potencial na região central da estrutura, onde esperamos o furo preenchido. Então, um estudo sistemático com a técnica de KPFM mostrou a influência no acúmulo de carga quando a espessura de GaAs é alterada, bem como, quando modificamos a concentração de Al na barreira de AlGaAs. O cálculo simulando um poço de potencial com barreiras semi-finitas e finitas mostrou que não ocorre acúmulo de carga quando a espessura do GaAs é menor que 1,5 nm, corroborando com nossos resultados. Simulações do diagrama de banda e da densidade de elétron da estrutura permitem atribuir o acumulo de carga observado, aos diferentes níveis de energia da estrutura mesoscópica de GaAs em comparação com as camadas de GaAs circundantes. / Kelvin probe force microscopy and electric force microscopy techniques are widely used to analyze the distribution of the surface potential with little application to self-assembled semiconductor nanostructures embedded into a substrate. In this work, we directly investigate the charge accumulation inside mesoscopic GaAs structures [1]. The structures are fabricated by overgrowth of a nanohole template using molecular beam epitaxy. Therefore, a combination of Ga assisted deoxidation and local droplet etching is used to create initial holes with a depth of ca. 10 to 15nm, which are covered subsequently with 15nm of AlxGax-1As barrier and GaAs caps with 1nm, 2nm, 5nm, 10nm thicknesses. Atomic force microscopy and transmission electron microscopy results showed that the hole shape is preserved during the AlGaAs overgrowth. Then filled with GaAs forming an elongated mount over the hole [1]. We investigate the local potential and the charge distribution in these structures with a single pass Kelvin probe force microscopy technique. Therefore, an AC voltage of 5 V is applied to a metalized tip and scanned in tapping mode over the sample. We observed a clear potential difference in Kelvin probe force microscopy measurements in the middle of the structure, where we expect a filled hole. We systematically study by Kelvin probe force microscopy the influence on the charge accumulation when the GaAs thickness is changed, as well as the Al concentration in the AlGaAs barrier. Calculation of the particle in the box for semi-finite and finite barriers were done and show that no charge accumulation is observed for GaAs thickness lower than 1.5nm in the semi-finite barrier, corroborating with our results. Simulations of band gap and electron wavefunction of the structure allow us to ascribe the charge accumulation observed, to the different confinement of carriers inside of the unstrained mesoscopic GaAs structure compared to the surrounding GaAs layers.