Many deductions made about STM images are based upon the model of Tersoff and Hamann, in which images are given in principal by a combination of surface atomic positions and local charge density. There is a now a need for a fuller understanding of this technique in order to explain experimental evidence which indicates that the tip and sample can interact strongly during normal imaging. In order to investigate the fundamental STM imaging process, a method for deducing the tunnel barrier height has been developed which is based on corrugation height measurements of constant current topographs. From experiments on clean Cu(100), values of the tunnel barrier height have been shown to be somewhat below the workfunction (~ 1-2.5eV) but are in good agreement with other reports of atomically resolved barrier height data. At large values of the tunnel conductance (~ 1μS), a fall-off (based upon extrapolation of large separation data) in the corrugation heights is observed with increasing conductance. This effect is quantitatively explained using a Molecular Dynamics simulation of the tip approaching the sample. The simulation gives a good estimate of both the absolute tip-sample separation and site-dependent tip-surface forces. Distributions of corrugation heights indicate that variations in both tip geometry and chemistry are likely to occur in practice and strongly influence the phenomena described above. Similarly, it is found that increased local tunnel barrier heights are measured when the Cu(100) surface is modified with small numbers of single halogen atoms. This data has been used to estimate the contributions to the increase in local barrier height of both adsorbate induced dipoles and geometric topography. Values for the charge transfer between the surface and adsorbate have been established. The process of tip-induced adsorbate manipulation has also been demonstrated at room temperature.

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.

Mammalian cells require a continuous and sufficient supply of oxygen to carry out their functions. The oxygen pathway has an overall direction taking O2 from the air to the mitochondria, which is a result of the mitochondrial O2 consumption (VO2) NO various effects on the mitochondria: at low concentrations for short periods NO specifically and irreversibly inhibits cytochrome c and reversibly inhibits cytochrome c oxidase, to decrease VO2. Thus, NO can modulate VO2 of skeletal muscle. The purpose of the present study was to measure VO2 of the rat spinotrapezius muscle under conditions of altered NO. The methods used provide a direct way to measure PO2 in the interstitium (PISFO2) and use it as indicator of local metabolic changes. Intravital microscopy and phosphorescence quenching were used to record PISFO2 in resting muscle for 120 s before, 60 s during, and 420 s after a period of tissue compression that abruptly halted perfusion. Control VO2 measurements were made, followed by those in which the spinotrapezius muscle had been treated by topical application of agents known to alter NO levels (L-NAME, C-PTIO, Sperm/NO). The compression was achieved by rapid inflation of a Saran film air bag, attached to a X20 objective lens, which pressed the muscle against the animal platform. The rapid pressure onset (0-120 mmHg in ISFO2, which started immediately after the airbag inflation, was used to calculate VO2 and was based on the assumption that the amount of blood in the tissue after compression was small. Control VO2 was 5.91 ± 0.2 ml O2 · kg-1 · min-1. Since the presence of RBCs sequestered in capillaries cannot be ruled out during compression, this value can be considered a lower limit for VO2 by resting muscle. Comparison of baseline and treatment measurements of VO2 showed no significant differences between them. This was unexpected based on in vitro studies and may reflect an impaired ability of the agents used to alter NO at the mitochondrial level.

Charles University in Prague, Faculty of Pharmacy in Hradec Králové Department of Pharmacognosy Candidate: Lenka Applová Consultant: doc. Dr. Jiřina Spilková, CSc. Microscopy of Sambuci fructus from cultivars of Sambucus nigra Sambucus nigra L. is the important plant of the traditional folk medicine, its knowledge is accepted in the pharmaceutical and food industry. The elderberry fruits are used as diaphoretic, diuretic, during the migraine and neurological difficulties. On the grounds of the rising demand the collection of the wild-growing berries do not suffice and that is the reason for growing the elderberry and its cultivated varieties in plantations. The cultivated varieties of elderberry, which are grown for the use of the fruits in the food industry, could be exactly provided the quality drug for pharmaceutical use. The thesis is focused on the research of the microscopic characteristics of the elderberries fruits wild-growing elderberry and its cultivated varieties Allesö, Bohatka, Haschberg, Mamut, Sambo, Sambu, Samdal, Sampo, Samyl and Weihenstephan, which originated from the Research and Breeding Institute of Pomology Holovousy Ltd. The berries of the wild- growing elderberry were obtained in the Botanical Garden of Medicinal Herbs of Faculty of Pharmacy in Hradec Králové. The...

Charles University in Prague Faculty of Pharmacy in Hradec Králové Department of Pharmaceutical Technology Student: Veronika Ščuryová Supervisor: doc. RNDr. Pavel Doležal, CSc. Title of thesis: AFM in Pharmaceutical Technology 3 The theoretical part deals first with the construction of AFM microscope, the principle of the method, determining the surface topography and regimes which can be used. Described therein are distinct advantages over previous traditional methods but also its pitfalls. Next, I compare the results of measurements using AFM and declared size and devote also determine the shape of the particles. Experimental part is focused first on the detailed description of sample preparation for AFM measurement of nanoparticles. This procedure was followed by practical use to characterize the magnitude of the four types of commercially available nanoparticles Chromeonov (Sigma-Aldrich) using atomic force microscopy. The laboratory prepared Ag- nanoparticles could not be evaluated due to of technical and methodological reasons. The magnitude of the measured results nanoparticles were processed in histograms, which provide a description of the distribution of the measured values of the nanoparticle size. I found that compared to the size of the nanoparticles declared by the manufacturer are...

The theoretical part deals with topics related to the formation of nanofibers and nanomembranes by different ways of electrospinning. The literary search focused on "medicated nanofibrous membrane" gives recent information on nanomembranes containing drugs and also shows the perspective of the use of nanofibers in this area. The experimental part deals with AFM parameters needed for characterisation of the samples of six selected polymer nanomembranes with the content of naproxen, folic acid and diosmin. The appearance and thickness of the nanofibers was examined. The set up parameters of the AFM measurements allowed to observe the distribution of the drug in non- crystalline state within the nanofibers, regular fibrous shapes of crystal-like nanofibers as well as distinguished nanoingots of the polymers. The captured scans are stored and available for further analysis. Keywords: electrospinning, nanomembrane, naproxen, AFM, drug-loaded nanofibers

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Doctor of Philosophy / Department of Chemical Engineering / Peter H. Pfromm / Characterization of the interactions of hydrogen with catalytic metal surfaces and the mass transfer processes involved in heterogeneous catalysis are important for catalyst development. Although a range of technologies for studying catalytic surfaces exists, much of it relies on high-vacuum conditions that preclude in-situ research. In contrast, atomic force microscopy (AFM) provides an opportunity for direct observation of surfaces under or near actual reaction conditions. Tapping-mode AFM was explored here because it expands AFM beyond the usual topographic information toward speciation and other more subtle surface information. This work describes using phase-angle data from tapping-mode AFM to follow the interactions of hydrogen with palladium. Both gas-solid and liquid-solid interfaces were studied. Real-time AFM phase-angle data allowed for the observation of multiphase mass transfer to and from the surface of palladium at atmospheric pressure and room temperature without the need for complex sample preparation. The AFM observations were quantitatively benchmarked against and confirm mass transfer predictions based on bulk hydrogen diffusion estimates. Additionally, they support recent studies that demonstrate the existence of multiple hydrogen states during interactions with palladium surfaces.

Quantum dots (QDs), especially colloidal semiconductor QDs, possess properties including high quantum yields, narrow fluorescence spectra, broad absorption and excellent photostability, making them extremely powerful in bioimaging. In this thesis, we studied the fluorescence properties of QDs and attempted multiple ways to boost applications of QDs in bioimaging field. By time-correlated single photon counting (TCSPC) measurement, we quantitatively interpreted the fluorescence mechanism of colloidal semiconductor QDs. To enhance QD fluorescence, we used a porous alumina membrane as a photonic crystal structure to modulate QD fluorescence. We studied the acid dissociation of 3-mercaptopropionic acid (MPA) coated QDs mainly through electrophoretic mobility of 3-MPA coated CdSe QDs and successfully demonstrated the impact of pH change and Ca2+ ions. Blinking phenomena of both CdSe-CdS/ZnS core-shell QDs and 3C-SiC nanocrystals (NCs) were studied. A general model on blinking characteristics relates the on-state distribution to CdSe QD surface conditions. The energy relaxation pathway of fluorescence of 3C-SiC NCs was found independent of surface states. To examine QD effect on ciliated cells, we conducted a 70-day long experiment on the bioelectric and morphological response of human airway epithelial Calu-3 cells with periodic deposition of 3-MPA coated QDs and found the cytotoxicity of QDs was found very low. In a brief summary, our study of QD could benefit in bioimaging and biosensing. Especially, super-resolution fluorescent bioimaging, such as, stochastic optical reconstruction microscopy (STORM) and photo-activated localization microscopy (PALM), may benefit from the modulation of the QD blinking in this study. And fluorescence lifetime imaging (FLIM) microscopy could take advantage of lifetime modulation based on our QD lifetime study. / <p>QC 20160905</p>

Thesis advisor: Vidya Madhavan / Spin-orbit coupling (SOC) is the interaction of an electron's intrinsic angular momentum (spin) with its orbital momentum. The strength of this interaction is proportional to Z<super>4</super> where Z is the atomic number, so generally it is stronger in atoms with higher atomic number, such as bismuth (Z=83) and iridium (Z=77). In materials composed of such heavy elements, the prominent SOC can be sufficient to modify the band structure of the system and lead to distinct phase of matter. In recent years, SOC has been demonstrated to play a critical role in determining the unusual properties of a variety of compounds. SOC associated materials with exotic electronic states have also provided a fertile platform for studying emergent phenomena as well as new physics. As a consequence, the research on these interesting materials with any insight into understanding the microscopic origin of their unique properties and complex phases is of great importance. In this context, we implement scanning tunneling microscopy (STM) and spectroscopy (STS) to explore the surface states (SS) of the two major categories of SOC involved materials, Bi-based topological insulators (TI) and Ir-based transition metal oxides (TMO). As a powerful tool in surface science which has achieved great success in wide variety of material fields, STM/STS is ideal to study the local density of states of the subject material with nanometer length scales and is able to offer detailed information about the surface electronic structure. In the first part of this thesis, we report on the electronic band structures of three-dimensional TIs Bi₂Te₃ and Bi₂Se₃. Topological insulators are distinct quantum states of matter that have been intensely studied nowadays. Although they behave like ordinary insulators in showing fully gapped bulk bands, they host a topologically protected surface state consisting of two-dimensional massless Dirac fermions which exhibits metallic behavior. Indeed, this unique gapless surface state is a manifestation of the non-trivial topology of the bulk bands, which is recognized to own its existence to the strong SOC. In chapter 3, we utilize quasiparticle interference (QPI) approach to track the Dirac surface states on Bi₂Te₃ up to ~800 meV above the Dirac point. We discover a novel interference pattern at high energies, which probably originates from the impurity-induced spin-orbit scattering in this system that has not been experimentally detected to date. In chapter 4, we discuss the topological SS evolution in (Bi_1-xIn_x)₂Se₃ series, by applying Landau quantization approach to extract the band dispersions on the surface for samples with different indium content. We propose that a topological phase transition may occur in this system when x reaches around 5%, with the experimental signature indicating a possible formation of gapped Dirac cone for the surface state at this doping. In the second part of this thesis, we focus on investigating the electronic structure of the bilayer strontium iridate Sr₃Ir₂O₇. The correlated iridate compounds belong to another domain of SOC materials, where the electronic interaction is involved as well. Specifically, the unexpected Mott insulating state in 5<italic>d</italic>-TMO Sr₂IrO₄ and Sr₃Ir₂O₇ has been suggested originate from the cooperative interplay between the electronic correlations with the comparable SOC, and the latter is even considered as the driving force for the extraordinary ground state in these materials. In chapter 6, we carried out a comprehensive examination of the electronic phase transition from insulating to metallic in Sr₃Ir₂O₇ induced by chemical doping. We observe the subatomic feature close to the insulator-to-metal transition in response with doping different carriers, and provide detailed studies about the local effect of dopants at particular sites on the electronic properties of the system. Additionally, the basic experimental techniques are briefly described in chapter 1, and some background information of the subject materials are reviewed in chapter 2 and chapter 5, respectively. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.