Zugl.: Berlin, Techn. Univ., Diss.

Bachelor-Arbeit Univ. St. Gallen, 2006.

Memory structure, memory assessment, Grober-Buschke paradigm, Alzheimer disease, and vascular dementia were discussed in the first part of the present thesis. Present study aims to examine the relationship between white matter changes, hippocampal atrophy and the performance in Enhanced Cued Recall test in nondemented geriatric population (n = 104). Partial neparametric correlations were used while controlling for age and Fazekas score. Medium correlations were found between left/right hippocampal volumes and free and total recall. No correlations were found between Fazekas score and ECR scores while controlling for age and left and right hippocampal volumes. Keywords: hippocampal atrophy, white matter changes, cued recall, ECR

Simultaneous measurement of electrical contact resistance (ECR) and coefficient of friction (COF) at the sliding interface is essential to assess the performance of selected material contact pairs for the transfer of current from stationary member to moving member (or vice-versa). Low and stable values of ECR and COF are desirable during the intended operating life of the contact members. These parameters may change with respect to time as a consequence of change in the surface properties of contact members due to their relative movement. Hence experimental investigations have been conducted to study the variation of ECR and COF while different riders sliding on copper and brass flat samples in different environments. As a part of the experimental investigation, a reciprocating sliding setup is designed and developed to study the variation of ECR and COF in terms of normal force, sliding speed, current and environment. The details of the experimental setup are described along with its construction and operation. The sample preparation, instrumentation, data acquisition and presentation are explained in detail. The variations of ECR and COF at different normal forces, currents and sliding speeds by moving OFHC copper, brass, silver, Ag10Cu and Ag20Cu riders on OFHC copper and brass flat samples in vacuum, argon, nitrogen and air are studied in detail. Studies are also conducted to evaluate the performance of metallic contacts under lubricated condition using general purpose lubricating oils of different viscosity. Metallic contacts show a decrease in ECR with increase in normal force at all sliding speeds in all media. Sliding metallic contacts show a significant decrease in both ECR and COF during the initial sliding cycles at constant normal force in all media. Surface roughness of flat sample is found to have a significant effect on both ECR and COF in all media. Wear of rider is found to be significant as compared to wear of flat samples. Metallic contacts show an inverse relationship between ECR and COF in all media under mild wear regime (0.2< COF≤ 0.4). ECR and COF of sliding metallic contacts are independent of current (≤ 4A) in mild wear regime in all media. Reasonably low values of ECR and COF are observed for prolonged duration with lubricants having low viscosity. The presence of wear fragments at the sliding zone is found to have significant effect on both ECR and COF in all media. Low values of ECR are observed while copper rider sliding on brass sample as compared to silver rider under same operating conditions. Significant amount of metal transfer is observed with silver based riders sliding on copper and brass flat samples in different media. The present investigations are useful in understanding the contact behaviour of copper and brass flat samples for similar and dissimilar riders sliding on them in various environments.

The aim of thesis The Importance of Category Management for Sale is to analyze the appropriateness and effectiveness of rules and process of Category management, described in the specialized literature, in practice, on the example of two stores. Using the gaining knowledge, in conclusion there will be given adequate recommendations how to increase the efficiency of cooperation between Nestlé Czech Republic sro and retailers on traditional market.

McMaster University DOCTOR OF PHILOSOPHY (2017) Hamilton, Ontario (Engineering Physics) TITLE: Luminescent Silicon Carbonitride Thin Films Grown using ECR PECVD: Fabrication and Characterization AUTHOR: Zahra Khatami , M.A.Sc. (Shahid Behehsti University) SUPERVISOR: Professor Peter Mascher NUMBER OF PAGES: xx, 268 / Silicon, the cornerstone semiconductor of microelectronics, has seen growing interest as a low-cost material in photonics. Nanoscience has employed various strategies to overcome its fundamentally inefficient visible light emission such as developing new silicon-based nanostructures and materials. Each of the proposed materials has its own advantages and disadvantages in attempting to reach commercialization. Silicon carbonitride (SiCxNy) is a less-studied and multi-functional material with tunable optical features. Despite reports on promising mechanical properties of SiCxNy thin films, they have not yet been well explored optically. This thesis presents the first in-depth analysis of the luminescent properties of SiCxNy thin films at a broad range of compositions and temperatures. To better understand this ternary structure, the reported data of the two fairly well studied binary structures was used as a reference. Therefore, three classes of silicon-based materials were produced and explored; SiCxNy, SiNx, and SiCx. Samples were fabricated using one of the common methods in the semiconductor industry; electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR PECVD). A multitude of characterization techniques were utilized including; optical methods (ultraviolet-visible spectroscopy (UVVIS), variable angle spectroscopic ellipsometry (VASE), photoluminescence (PL)) and structural techniques (elastic recoil detection (ERD), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM)). In view of the exploring of emission properties of SiCxNy materials, our approach was towards the enhancement of the visible emission by adjusting the film composition and subsequent thermal treatment. First, a systematic study of the influence of carbon on the optical, compositional, and structural properties of SiCxNy was carried out. This investigation was followed by an exploration of influence of growth conditions on the visible emission and its connection with the other film properties including hydrogen concentration, microstructure, and composition. In addition, hydrogen diffusion was explored and associated with two featured annealing temperatures. The key element of this thesis is the comprehensive report on the interdependency of the visible light emission and all optical, structural, and compositional features of SiCxNy structures. Unlocking the potential of this ternary and less studied material can appeal to the silicon photonics community to implement it in anti-reflection, solar cell, and sensing applications, and in particular as a substitution of SiNx used in existing microelectronic devices. / Thesis / Doctor of Philosophy (PhD)

Niobium thin films are expected to be free of solid inclusions commonly seen in solid niobium. For particle accelerators, niobium thin film has the potential to replace the solid niobium in the making of the accelerating structures. In order to understand and improve the superconducting performance of niobium thin films at cryogenic temperature, an energetic vacuum deposition system has been developed to study deposition energy effects on the properties of niobium thin films on various substrates. The system directly uses microwave power to create a pure niobium plasma, which can be used to extract niobium ion flux with controllable kinetic energy for direct deposition. The ultra high vacuum avoids the gaseous inclusions in thin films. A retarding field energy analyzer is developed and used to measure the kinetic energy of niobium at the substrate location. A systematic process for thin film characterization is developed and used to analyze the niobium thin films made by this energetic condensation. The properties of niobium thin films at several deposition energies are obtained, and the results show that there exists a preferred deposition energy around 115eV. / Ph. D.

Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. From those bridges 24% are considered structurally deficient or functionally obsolete based on the latest, December 2010, statistic from the Federal Highway Administration (FHWA). Mainly, this is due to chloride attack present in deicing salts which causes the reinforcing steel to corrode. Different solutions have been developed and used in practice to delay and prevent corrosion initiation. The purpose of this research is to investigate the influence of corrosion on the failure mechanism that occurred on an Interstate 81 bridge deck. After 17 years in service, a 3ft x3ft closure pour section punched through. It was part of the left wheel path of the south bound right lane of the bridge deck. The bridge deck was replaced in 1992 as part of a bridge rehabilitation project, epoxy coated reinforcement were used as the reinforcing steel. Four slabs from the bridge deck, containing the closure, were removed and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, three lab cast slabs were fabricated as part of the assessment program. Corrosion evaluation and concrete shrinkage characterization were conducted in this research. The corrosion evaluation study included visual observation, clear concrete cover depth, concrete resistivity using single point resistivity, half-cell potential, and linear polarization using the 3LP device. Shrinkage characteristics were conducted on the lab cast slabs only, which consisted of monitoring shrinkage behavior of the specimens for 180 days and comparison of the data with five different shrinkage models. Based on the research results, guidance for assessment of other bridge decks with similar conditions will be constructed to avoid similar types of failures in the future. / Master of Science

This study is an evaluation of epoxy coated reinforcing steel (ECR) and its ability to effectively provide corrosion protection in reinforced concrete highway bridge decks. An analysis was conducted on 10 bridge decks built in the state of Virginia between the years 1981 and 1995. A total of 141 cores containing either ECR or bare steel were evaluated. A chloride solution was applied to the surface on a weekly cycle (for a total duration of 3.06 years) and a nondestructive electrochemical testing was performed on each core on a monthly cycle. Cores were also inspected for surface cracks, the thermal properties of the epoxy coating, and the concrete conditions at bar depth. The concrete was tested for saturation percentages, diffusion coefficients, and chloride contents, while the epoxy was tested for its glass transition temperature, moisture content, and amount of surface cracking. The results indicate that the best predictor for estimating the times to corrosion initiation and cracking is the amount of chlorides present in the concrete encasing the ECR. The presence of chloride ions will have a determining effect on corrosion regardless of the epoxy coating condition. As a result, it is likely that ECR is not the solution to corrosion prevention and it is recommended that closer attention be given to improving concrete conditions that reduce the diffusion of chloride ions. The conclusion that ECR is an unreliable corrosion prevention method is in agreement with the results of previous studies. / Master of Science

Recent developments in the field of nano-structured materials for technological as well as scientific prospective are quite interesting. In this context carbon plays a dominant role. Few examples such as carbon nanotubes (CNTs), fullerene, nanostructured diamond, as well as, amorphous carbon film, particularly, diamond-like carbon (DLC) coating are the areas of today’s research. This thesis deals with ECR plasma deposition of carbon in two different forms, i.e., Diamond-like carbon (DLC) and carbon nanotubes (CNTs) In the case of DLC coatings the chemical vapor deposition (CVD) and sputtering CVD configuration has been used. The carbon nanotubes have been grown using CVD configuration. DLC films were deposited by ECR-rf CVD mode, as well as, ECR sputtering mode. In case of CVD films, about 0 — 100 Watts rf bias was employed in steps of 20 Watts, corresponding to effective negative self bias voltage of 15 — 440 V. CH4 and C2H2 have been used as source gas for CVD films. Microwave power was optimized at 300 Watts. In case of sputtering, a cylindrical graphite target (diameter 9 cm and length 6 cm) kept at the exit of the Ar plasma was biased with -200 V. Films were deposited on floating substrate (temperature ~100 oC). Films were deposited on Si, quartz, and steel substrates and characterized by FT-IR, Raman, UV-Visible, Photoluminescence spectroscopy (PL), spectroscopic ellipsometry. Nanoindentation was used to evaluate the film’s elastic property. Pin-on-disk measurement was used to study the tribological property of the films. Electrical properties of the films deposited on Si [p-(100), 10 Ω cm] were studied using picoammeter / source measuring instrument by two probe method. FT-IR analysis showed sp3C-H absorption peak at 2930 cm-1 for the CVD films, while sputtered films did not show any C-H absorption. Raman spectroscopy was used to evaluate bonding aspects as well as hydrogen content of the films. Comparison of sp3C : sp2C among the films was done based on I(D) / I(G) of the Raman peaks, while hydrogen content was estimated based on background slope of the Raman spectra. It was observed that increase in rf bias induces more sp2C while hydrogen content decreases. An optimum substrate bias of 40 Watts was predicted from the Raman spectra. For sputtered films Raman spectra indicated the formation of nanocrystal diamond in a-C matrix. UV-Visible-NIR optical transmission spectroscopy was used to determine the band gap (Tauc), E0, of the films. It showed that increase in rf bias increases the absorption coefficient α. The films deposited from CH4 with a substrate bias of 0 and 20 Watts (i.e., high hydrogen content in the film) followed (hνα)1/2 = const. (hν –E0), while other films hνα = const. (hν –E0) ( h is Plank constant ν is frequency of light). E0 varied from 1.1 — 2.5 eV. It was assumed that for π--π* transition follows root relation while π--σ * transition follows linear relation. Spectroscopic ellipsometry was used to determine optical constants, film thickness, and interface thickness. Deposition rate found out to be ~100 nm / mints for C2H2, ~10 nm / mints for CH4, and ~2.5 nm /mints for sputtered films. Formation of interface layer of thickness about 5 —30 nm due to high energy ion bombardment takes place for the films deposited at 40 Watts rf bias or higher. Band gap and related phenomena was revisited from the data that was obtained from this instrument which reasonably matches with the earlier results. PL experiments were carried out at room temperature using lamp excitation source as well as laser excitation source (457.9 nm wavelength). In case of lamp excitation source any wavelength from 200 —900 nm region can be selected. PL spectra showed that there are two sources of PL signal, one from nanocrystal diamond and other from sp2C phase. To obtain PL signal from diamond UV excitation wavelength was required. This diamond phase is highly efficient emitter as compared to sp2C phase. Based on the closeness of diamond’s optical centre labeling of the peaks was done. For CVD films N3 ( 457 nm), H4 (495 nm), H3 (520 nm), [N-V]0 (~590 nm) optical centers of diamond was observed. For sputtered films [N-V]0 (2.08 eV), H3 (2.38 eV), H4 (2.50 eV), N3 (2.81eV), N3 (2.96 eV), 3.3 eV ( undocumented peak), 5RL ( 4.14 eV) optical centers of diamond as well as band-edge emission (5.01 eV ) was observed. Nanoindentation technique was used to estimate the elastic property and related phenomena of the films. It shows that the films are having hardness of 5—17 GPa and reduced modulus of 20 —120 GPa depending on the deposition parameters. All the films show highly elastic response at lower load, i.e., at low indentation depth where elastic recovery is 85—95 %. At higher load substrate effect comes into the picture. Further morphology in and around the region was evaluated using scanning probe microscopy (SPM). It was shown that substrate effect comes into picture that is based on film’s thickness as well as its elastic property. Films were further characterized by pin-on-disk experiments. C2H2 based films were used because of high deposition rate. Since 40 Watts, 60 Watts, and 100 Watts films adhere well with steel only on these films tribological test was possible. A hardened bearing-steel was used as substrate and a 2 mm diameter cylindrical pin made of tool steel was use as pin. Studies were carried out with three different loads of 20, 40, and 60 N. Friction coefficient varied from 0.02 — 0.04 and wear rate was found to be 10-6 — 10-9 mm3 / N m. A sputtered film of 0.1 μ m on the top of the CVD film, in many respects, enhances the tribological properties. It was shown that certain amount of wear is required for low friction of DLC. Electrical characterization of the films deposited from CH4 showed that they are highly insulating with resistivity of 1013 —1011 Ω-cm, and current conduction mechanism has been found to be predominantly space charge limited conduction (SCLC). Similar to the observations of Tauc’s relation, the film deposited with 0 and 20 Watts bias behave differently and followed the relation , where as, all other films exhibited the relation ( α, n are constants). It signifies that for 0 and 20 Watts rf biased films traps are uniformly distributed across the band gap while for others it decreases from the conduction band. For 0 and 20 Watts rf biased films no Ohmic current was observed at a detection level of 10-11 A. 40 Watts and higher rf biased films showed that three distinct regions in the I-V curves; initially Ohmic region, next to it SPLC region, and finally breakdown region. Increase in rf bias causes increase in Ohmic current. Film deposited from C2H2 showed diode-like behavior with higher conduction current limited by resistive control, and the resistivity of the films was ~ 109 — 105 Ω-cm. Difference in resistivity between the films deposited from CH4 and C2H2 was explained by considering the impurities in the source gas resulting in nitrogen doping concentration. Increase in Ohmic current for the CH4 films was explained by assuming the widening of the σ--σ * gap. Similar diode-like behavior was observed with the sputtered film. The last part of the work deals with the growth mechanism of aligned CNTs and their field emission (FE) properties. Nanotubes were grown at 700 0C on Ni coated (thickness 40 nm, 70 nm, and 150 nm) Si substrate using a mixture of CH4 and H2 gas. Microwave power of 500 Watts was optimized for nanotube growth. Nickel nanoparticle formation mechanism from a continuous Ni film was explained by considering the stress that is generated due to the difference in thermal expansion coefficients of Si and Ni at 700 oC. Though the thicker film such as 150 nm does not form nanoparticle due to stress, hydrogen induced fragmentation of the film due the brittleness of the film even causes formation of finer nanoparticles. A substrate bias in the range 0— 250 V was used to align the nanotubes. Perfectly aligned CNTs were obtained at -250 V substrate bias. The density of the tubes varied from 108 —109 / cm2 while its length was 0.5 — 2 μ m. Due to hydrogen induced fragmentation of the films, 150 nm Ni thick film showed smallest diameter 2 — 5 nm CNTs. 40 nm films showed nanotube diameter of 10 — 30 nm and 150 — 300 nm while 70 nm showed 10 — 30 nm diameter nanotubes. Diameter of the nanotubes was estimated using transmission electron microscopy (TEM). Field emission analysis of these CNTs was done using Fowler-Nordheim (F-N) plot and the investigation revealed that the field emission properties strongly depend on density and aspect ratios. The non-linearity in the F-N plot or current saturation phenomena was explained in terms of change in work function due to heating effect during FE which was pronounced in case of longer nanotube. Suitable efficient cold-cathode emitters for a particular usage (assuming that the variables are applied field and emission current) could be designed from the obtained results. An ammonia gas sensor using thick nonaligned CNTs was realized. For this purpose a thick film of CNTs (~ 0.5 μm) was deposited. This sensor can detect 100 ppm level of ammonia. About 1.5 — 4.5 % change of resistance depending on ammonia concentration (100 —1000 ppm) was observed.