Scanning Probe Studies of Thin Films

The first part of this thesis deals with the phenomenon of thermoelectricity. It involves the improvement of the thermoelectric properties of silicon using innovative nanostructures. My contribution was to help fabricate these thermoelectric devices, and is the focus of this part of the thesis. The second part and primary focus of this thesis is the analysis of thin films using scanning probe techniques. These surface techniques include atomic force microscopy, electric force microscopy, Kelvin probe force microscopy, and scanning tunneling microscopy. The thin films studied are graphene and molybdenum disulfide, two remarkable materials that display unique two-dimensional qualities. These materials are shown to be useful in studying the properties of adsorbates trapped between them and the substrate on which they rest. Moreover, these adsorbed species are seen to affect the structural and electronic properties of the thin films themselves. Scanning probe analyses are particularly useful in elucidating the properties of these materials, as surface effects play a significant role in determining their characteristics. The final part of this thesis is concerned with the study of Akt in live cells using protein capture agents previously developed by my colleagues. The activation and degradation of Akt is investigated using various biological assays, including Western blots, in vitro kinase assays, and cell viability assays. Finally, the usefulness of synthetic capture agents in perturbing protein pathways and as delivery agents is assessed and analyzed.</p

The Microscopic Structure of Adsorbed Water on Hydrophobic Surfaces under Ambient Conditions

The interaction of water vapor with hydrophobic surfaces is poorly understood. We utilize graphene templating to preserve and visualize the microscopic structures of adsorbed water on hydrophobic surfaces. Three well-defined surfaces [H–Si(111), graphite, and functionalized mica] were investigated, and water was found to adsorb as nanodroplets (~10–100 nm in size) on all three surfaces under ambient conditions. The adsorbed nanodroplets were closely associated with atomic-scale surface defects and step-edges and wetted all the hydrophobic substrates with contact angles < ~10°, resulting in total water adsorption that was similar to what is found for hydrophilic surfaces. These results point to the significant differences between surface processes at the atomic/nanometer scales and in the macroscopic world

Characterization of forest fire frequency using fire scar mapping of temporal satellite data for forest fire management

One of the most complex problems facing in tropical forests, particularly in deciduous forests, is the recurrent incidence of fire. It is well known that fire caused extensive damage in the forest ecosystem by quantitatively and qualitatively. To reduce occurrences of forest fire, proper management of fire is highly important which entails mapping of forest fire frequency and identification of suitable area for watchtowers. In the present study, fire frequency analysis of Melghat Tiger Reserve, Maharashtra was done for the last seven years (2014-2020) based on the fire scar on the temporal Landsat data during fire season (January-June). Fire frequency analysis shows that an area of 1053.64 ha (0.52%) of the reserve was burned all seven years followed by 3050.53 ha (1.49%) for six times, 3849.52 ha (1.88%) for five times, 5520.04 ha (2.70%) for four times, 11845.63 ha (5.80%) for three times, 36863.52 ha (18.03%) for two times, 70126.33 ha (34.31%) for once and 72093.02 ha (35.27%) remains unburned all these seven years. The fire frequency map generated was used as an input for prioritizing the locations of watch towers as well as prioritizing grazing closure areas and fires lines. Identification of suitable sites for locating new watchtowers has been done by integrating and modeling of forest fire frequency map, existing watchtowers and viewshed analysis in GIS. Based on these results only thirteen watchtowers were categorized under retainable among the existing watchtowers and 27 new watchtowers are proposed to cover the entire area

Visualizing Local Doping Effects of Individual Water Clusters on Gold(111)-Supported Graphene

The local charge carrier density of graphene can exhibit significant and highly localized variations that arise from the interaction between graphene and the local environment, such as adsorbed water, or a supporting substrate. However, it has been difficult to correlate such spatial variations with individual impurity sites. By trapping (under graphene) nanometer-sized water clusters on the atomically well-defined Au(111) substrate, we utilize scanning tunneling microscopy and spectroscopy to characterize the local doping influence of individual water clusters on graphene. We find that water clusters, predominantly nucleated at the atomic steps of Au(111), induce strong and highly localized electron doping in graphene. A positive correlation is observed between the water cluster size and the local doping level, in support of the recently proposed electrostatic-field-mediated doping mechanism. Our findings quantitatively demonstrate the importance of substrate-adsorbed water on the electronic properties of graphene

Prelaunch optical characterization of the Laser Geodynamic Satellite (LAGEOS 2)

The optical range correction (the distance between the apparent retroreflective skin of the satellite and the center of mass) of the LAGEOS 2 was determined using computer analysis of theoretical and experimentally measured far field diffraction patterns, and with short pulse lasers using both streak camera-based range receivers and more conventional PMT-based range receivers. The three measurement techniques yielded range correction values from 248 to 253 millimeters dependent on laser wavelength, pulsewidth, and polarization, location of the receiver in the far field diffraction pattern and detection technique (peak, half maximum, centroid, or constant fraction). The Lidar cross section of LAGEOS 2 was measured at 4 to 10 million square meters, comparable to the LAGEOS 1

Capillary Filling of Anodized Alumina Nanopore Arrays

The filling behavior of a room temperature solvent, perfluoromethylcyclohexane, in approximately 20 nm nanoporous alumina membranes was investigated in situ with small angle x-ray scattering. Adsorption in the pores was controlled reversibly by varying the chemical potential between the sample and a liquid reservoir via a thermal offset, $\Delta$T. The system exhibited a pronounced hysteretic capillary filling transition as liquid was condensed into the nanopores. These results are compared with Kelvin-Cohan theory, with a modified Derjaguin approximation, as well as with predictions by Cole and Saam.Comment: 4 pages, 3 figures, pre-proof

The Fourth Element: Characteristics, Modelling, and Electromagnetic Theory of the Memristor

In 2008, researchers at HP Labs published a paper in {\it Nature} reporting the realisation of a new basic circuit element that completes the missing link between charge and flux-linkage, which was postulated by Leon Chua in 1971. The HP memristor is based on a nanometer scale TiO$_2$ thin-film, containing a doped region and an undoped region. Further to proposed applications of memristors in artificial biological systems and nonvolatile RAM (NVRAM), they also enable reconfigurable nanoelectronics. Moreover, memristors provide new paradigms in application specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs). A significant reduction in area with an unprecedented memory capacity and device density are the potential advantages of memristors for Integrated Circuits (ICs). This work reviews the memristor and provides mathematical and SPICE models for memristors. Insight into the memristor device is given via recalling the quasi-static expansion of Maxwell's equations. We also review Chua's arguments based on electromagnetic theory.Comment: 28 pages, 14 figures, Accepted as a regular paper - the Proceedings of Royal Society

The anaerobic bacteriology of intrapulmonary infections in Kuwait

Objective: The primary objective of this study was to ascertain the association of anaerobic bacteria in intrapulmonary infections and their susceptibility pattern to commonly prescribed antibiotics. Methods: One hundred clinical samples (85 broncho-alveolar lavage and 15 lung abscess aspirates) from suspected intrapulmonary infection cases were investigated in order to determine the role of anaerobic bacteria in these infections. The anaerobic bacterial isolates were identified by using the Vitek Anaerobic Card System and conventional methods. Susceptibility of these isolates was determined by Etest method against eight commonly prescribed antibiotics. Results: A total of 42 anaerobes were isolated, of which Prevotella spp. were the commonest isolates, made up of 42.9% (18/42), followed by Peptostreptococcus spp. 33.3% (14/42). Only two Bacteroides fragilis strains were isolated. All the isolates were sensitive to metronidazole, clindamycin, imipenem and meropenem; however, one Prevotella was resistant to piperacillin-tazobactam. The two B. fragilis isolates were susceptible to metronidazole, imipenem, meropenem and piperacillin-tazobactam, and one was found to be resistant to clindamycin. Conclusion: Overall, Prevotella spp. were found to be the predominant anaerobic bacteria associated with intrapulmonary infections in Kuwait. All the commonly prescribed antibiotics had excellent in vitro activities against nearly all the isolates