Tesi sul tema "Computer controlled scanning electron microscopy"

For years crystalline silica has been recognized as an occupational hazard of the dusty trades with exposures resulting in silicosis. As recently as 1997, IARC categorized the respirable portion of crystalline silica as a Grade 1 human carcinogen indicating that silica may be implicated in the development of lung cancer. Evidence in the literature indicates that silica may be not only an occupational hazard, but an environmental hazard as well, with patients with no known exposure showing measurable quantities of silica within cancerous tissue samples. This study aims to establish a methodology using computer-controlled scanning electron microscopy to examine silica content in lung cancer tissue. Furthermore, demonstrating that silica is not evenly distributed within the tissue will establish the need to use automated full scanning techniques, such as CCSEM, in order to guarantee that the analysis is not subject to random sampling error or researcher driven error, which may be rendering the traditional random sampling of zones for analysis under-representative of silica concentration in the tissue.

We present the development of a novel, UHV-compatible device fabrication strategy for the realisation of nano- and atomic-scale devices in silicon by harnessing the atomic-resolution capability of a scanning tunnelling microscope (STM). We develop etched registration markers in the silicon substrate in combination with a custom-designed STM/ molecular beam epitaxy system (MBE) to solve one of the key problems in STM device fabrication ??? connecting devices, fabricated in UHV, to the outside world. Using hydrogen-based STM lithography in combination with phosphine, as a dopant source, and silicon MBE, we then go on to fabricate several planar Si:P devices on one chip, including control devices that demonstrate the efficiency of each stage of the fabrication process. We demonstrate that we can perform four terminal magnetoconductance measurements at cryogenic temperatures after ex-situ alignment of metal contacts to the buried device. Using this process, we demonstrate the lateral confinement of P dopants in a delta-doped plane to a line of width 90nm; and observe the cross-over from 2D to 1D magnetotransport. These measurements enable us to extract the wire width which is in excellent agreement with STM images of the patterned wire. We then create STM-patterned Si:P wires with widths from 90nm to 8nm that show ohmic conduction and low resistivities of 1 to 20 micro Ohm-cm respectively ??? some of the highest conductivity wires reported in silicon. We study the dominant scattering mechanisms in the wires and find that temperature-dependent magnetoconductance can be described by a combination of both 1D weak localisation and 1D electron-electron interaction theories with a potential crossover to strong localisation at lower temperatures. We present results from STM-patterned tunnel junctions with gap sizes of 50nm and 17nm exhibiting clean, non-linear characteristics. We also present preliminary conductance results from a 70nm long and 90nm wide dot between source-drain leads which show evidence of Coulomb blockade behaviour. The thesis demonstrates the viability of using STM lithography to make devices in silicon down to atomic-scale dimensions. In particular, we show the enormous potential of this technology to directly correlate images of the doped regions with ex-situ electrical device characteristics.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 91-92).
Scanning electron micrographs at high magnification (100,000x and up) are distorted by motion of the sample during image acquisition, a phenomenon called drift. We propose a method for correcting drift distortion in images obtained on scanning electron and other scanned-beam microscopes by registering a series of images to create a drift-free composite. We develop a drift-distortion model for linear drift and use it as a basis for an affine correction between images in the sequence. The performance of our correction method is evaluated with simulated datasets and real datasets taken on both scanning electron and scanning helium-ion microscopes; we compare performance against translation only correction. In simulation, we exhibit a 12.5 dB improvement in SNR of our drift-corrected composite compared to a non-aligned composite, and a 3 dB improvement over translation correction. A more modest 0.4 dB improvement is measured on the real image sets compared to translation correction alone.
by Michael T. Snella.
M.Eng.

The sizes, shapes, volumes and compositions of nanoparticles are very important parameters determining many of their properties. Efforts to measure these parameters for individual nanoparticles and to obtain reliable statistics for a large number of nanoparticles require a fast and reliable method for 3-D characterization. In this dissertation, a direct measurement method for thicknesses, volumes or compositions of nanomaterials by quantitative atomic number contrast in High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM) is presented. A HAADF detector collects electrons scattered incoherently to high angles. The HAADF signal intensity is in first-order approximation proportional to the sample thickness and increases with atomic number. However, for larger sample thicknesses this approach fails. A simple description for the thickness dependence of the HAADF-STEM contrast has been developed in this dissertation. A new method for the calibration of the sensitivity of the HAADF detector for a FEI F30 transmission electron microscope (TEM) is developed in this dissertation. A nearly linear relationship of the HAADF signal with the electron current is confirmed. Cross sections of multilayered samples provided by TriQuint Semiconductors in Apopka, FL, for contrast calibration were obtained by focused ion-beam (FIB) preparation yielding data on the interaction cross section per atom. To obtain an absolute intensity calibration of the HAADF-STEM intensity, Convergent Beam Electron Diffraction (CBED) was performed on Si single crystals. However, for samples prepared by the focused ion beam technique, CBED often significantly underestimates the sample thickness. Multislice simulations from Dr. Kirkland's C codes are used for comparison with experimental results. TEM offers high lateral resolution, but contains little or no information on the thickness of samples. Thickness maps in energy-filtered TEM (EFTEM), CBED and tilt series are so far the only methods to determine thicknesses of particles in TEM. In this work I have introduced the use of wedge-shaped multilayer samples prepared by FIB for the calibration of HAADF-STEM contrasts. This method yields quantitative contrast data as a function of sample thickness. A database with several pure elements and compounds has been compiled, containing experimental data on the fraction of electrons scattered onto the HAADF detector for each nanometer of sample thickness. The use of thick samples reveals an increased signal at the interfaces of high- and low-density materials. This effect can be explained by the transfer of scattered electrons from the high density material across the interface into the less-absorbing low-density material. The calibrations were used to determine concentration gradients in nanoscale Fe-Pt multilayers as well as thicknesses and volumes of individual Au-Fe, Pt, and Ag nanoparticles. Volumes of nanoparticles with known composition can be determined with accuracy better than 15%. Porosity determination of materials becomes available with this method as shown in an example of porous Silicon.?
ID: 031001418; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Helge H. Heinrich.; Co-adviser: Yongho Sohn.; Title from PDF title page (viewed June 17, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 116-130).
Ph.D.
Doctorate
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

There has been an urge for increasing the efficiency in advanced gas turbine engines. To fulfill these needs the inlet gas temperatures should be increased in the gas turbine engines, thermal barrier coatings (TBCs) have gained significant applications in increasing the gas inlet temperatures. Insulating characteristics of ceramic TBCs allow the operation at up to 150~250 °C higher gas temperatures. Because of the severe turbine engine operating conditions that include high temperature, steep temperature gradient, thermal cycling, oxidation and hot-corrosion, TBCs can fail by spallation at the interface between the metal and ceramic. The lack of understanding in failure mechanisms and their prediction warrant a development of non-destructive evaluation technique that can monitor the quality and degradation of TBCs. In addition, the development of NDE technique must be based on a robust correlation to the characteristics of TBC failure. The objective of this study is to develop electrochemical impedance spectroscopy (EIS) as a Non-destructive evaluation (NDE) technology for application to TBCs. To have a better understanding of the multilayer TBCs using EIS they were divided into individual layers and EIS were performed on them. The individual layers included polycrystalline ZrO2-7~8 wt.%Y?O? (YSZ) (topcoat) of two different densities were subjected to sintering by varying the sintering temperature and holding time for three different thickness and hot extruded NiAl alloy buttons which were subjected to isothermal oxidation with varying temperature and time. NiAl is as similar to the available commercial bondcoats used in TBCs. Then degradation monitoring with electrolyte penetration was carried out on electron beam physical vapor deposited (EB-PVD) TBCs as a function of isothermal exposure. Quality control for air plasma sprayed TBCs were carried out as a function of density, thickness and microstructure. Dense vertically cracked TBCs were tested as a function of vertical crack density and thickness. Electrochemical impedance response was acquired from all specimens at room temperature and analyzed with an AC equivalent circuit based on the impedance response as well as multi-layered structure and micro-constituents of specimens. Physical and microstructural features of these specimens were also examined by optical and electron microscopy. The EIS measurement was carried out in a three-electrode system using a standard Flat Cell (K0235) from Princeton Applied Research and IM6e BAS ZAHNER TM frequency response analyzer. The electrolyte employed in this investigation was 0.01M (molar) potassium Ferri/Ferro Cyanide [(K?Fe(CN)?/K?Fe(CN)?x3H?O)]. The thickness and density were directly related to the resistance and capacitance of the polycrystalline YSZ with varying thickness and open pores. As the effective thickness of the YSZ increased with sintering time and temperature, the resistance of the YSZ (R[subscript YSZ]) increased proportionally. The variation in capacitance of YSZ (C[subscript YSZ]) with respect to the change in porosity/density and thickness was clearly detected by EIS. The samples with high porosity (less dense) exhibited large capacitance, C[subscript YSZ]), compared to those with less porosity (high density), given similar thickness. Cracking in the YSZ monoliths resulted in decrease of resistance and increase in capacitance and this was related to the electrolyte penetration. Growth and spallation of TGO scale on NiAl alloys during isothermal oxidation at various temperatures and holding time was also correlated with resistance and capacitance of the TGO scale. With an increase in the TGO thickness, the resistance of the TGO (R[subscript TGO]) increased and capacitance of the TGO (C[subscriptTGO]) decreased. This trend in the resistance and capacitance of the TGO changed after prolonged heat treatment. This is because of the spallation of the TGO scale from the metal surface. The parabolic growth of TGO during high temperature oxidation was inversely proportional to the capacitance of TGO, excluding the abrupt changes associated with the failure. As a function of isothermal exposure for EB -PVD TBCs, initial increase in the resistance of YSZ with thermal exposure was observed perhaps due to the high temperature sintering of YSZ. The parabolic growth of TGO during high temperature oxidation was inversely proportional to the capacitance of TGO. An explanation based on electrolyte penetration into sub-critical damage is proposed for the gradual decrease in the resistances of YSZ and TGO with prolonged thermal exposure. Observation of exposed metallic bond coat surface on the fracture surface, which readily provides conduction, was related to the abrupt and large increase in the capacitance of YSZ and TGO. A direct relation between the resistance of the YSZ (R[subscript YSZ]) and density of the YSZ was observed for APS TBCs with varying topcoat density. APS TBCs with varying topcoat chemistry and thickness were tested and directly related to resistance of topcoat. With the increase in the topcoat thickness, the capacitance decreased and the resistance increased. The higher values of C[subscript CAT] and R[subscript CAT] compared to that of CYSZ and RYSZ were related to the higher dielectric constant and resistivity of CaTiO?. Dense vertically cracked TBCs were tested with varying crack density were tested and the variation in the resistance was related indirectly to the cracks and directly to the difference in the thickness of the topcoat. EB-PVD TBCs with varying density (dense and columnar) were tested and the variation in resistance was attributed to the dense structure and columnar structure of the topcoat with columnar structure having lower resistance because of more electrolyte penetration through the columnar structure. From this study, EIS showed a potential as a NDE technique for quality assurance and lifetime remain assessment of TBCs. Future work should continue on developing a mathematical model to study the impedance curves and come up with a model for individual layers of TBC and then sum them up to get the multilayered TBC response. The flexible instrument probe of EIS needs to be designed and tested for field evaluation of TBCs.
M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering

This thesis describes the development and use of a computer-automated microscopy routine for characterization of respirable dust particles from coal mines. Respirable dust in underground coal mining environments has long been known to pose an occupational health hazard for miners. Typically following years of exposure, coal workers' pneumoconiosis (CWP) and silicosis are the most common disease diagnoses. Although dramatic reductions in CWP and silicosis cases were achieved across the US between about 1970-1999 through a combination of regulatory dust exposure limits, improved ventilation and dust abatement practices, a resurgence in disease incidence has been noted more recently – particularly in parts of Appalachia. To shed light on this alarming trend and allow for better understanding of the role of respirable dust in development of disease, more must be learned about the specific characteristics of dust particles and occupational exposures. This work first sought to develop an automated routine for the characterization of respirable dust using scanning electron microscopy with energy dispersive x-ray (SEM-EDX). SEM-EDX is a powerful tool that allows determination of the size, shape, and chemistry of individual particles, but manual operation of the instrument is very time consuming and has the potential to introduce user bias. The automated method developed here provides for much more efficient analysis – with a data capture rate that is typically 25 times faster than that of the manual method on which it was based – and also eliminates bias between users. Moreover, due to its efficiency and broader coverage of a dust sample, it allows for characterization of a larger and more representative number of particles per sample. The routine was verified using respirable dust samples generated from known materials commonly observed in underground coal mines in the central Appalachian region, as well as field samples collected in this region. This effort demonstrated that particles between about 1-9μm were accurately classified with respect to defined chemical categories, and suggested that analysis of 500 particles across a large area of a sample filter generally provides representative results. The automated SEM-EDX routine was then used to characterize a total of 210 respirable dust samples collected in eight Appalachian coal mines. The mines were located in three distinct regions (i.e., northern, mid-central and south-central Appalachia), which differed in terms of primary mining method, coal seam thickness and mining height, and coal and/or rock mineralogy. Results were analyzed to determine whether number distributions of particle size, aspect ratio, and chemistry classification vary between and within distinct mine regions, and by general sampling location categories (i.e., intake, feeder, production, return). Key findings include: 1) Northern Appalachian mines have relatively higher fractions of coal, carbonate, and heavy mineral particles than the two central Appalachian regions, whereas central Appalachian mines have higher fractions of quartz and alumino-silicate particles. 2) Central Appalachian mines tended to have more mine-to-mine variations in size, shape, and chemistry distributions than northern Appalachian mines. 3) With respect to particle size, samples collected in locations in the production and return categories have the highest percentages of very small particles (i.e., 0.94-2.0μm), followed by the feeder and then the intake locations. 4) With respect to particle shape, samples collected in locations in the production and return categories have higher fractions of particles with moderate (i.e., length is 1.5 to 3x width) to relatively high aspect ratios (i.e., length is greater than 3x width) compared to feeder and intake samples. 5) Samples with relatively high fractions of alumino-silicates have higher fractions of particles with moderate aspect ratios than samples with low alumino-silicate fractions. 6) Samples with relatively high fractions of quartz particles have higher fractions of particles with moderate aspect ratios and higher percentages of very small particles than samples with no identified quartz particles. 7) Samples with high fractions of carbonates have higher percentages of particles with relatively low aspect ratios (i.e., length and width are similar) than samples with no identified carbonate particles.
Master of Science

Dans ce travail, il est question d'étudier la faisabilité d'une valorisation en techniques routières de granulats de Mâchefers d'Incinération des Dèchets Non Dangereux (MIDND). Cette étude se base en premier lieu sur une analyse expérimentale ayant permis d'obtenir leurs propriétés élastiques. Ces propriétés servent de données d'entrée à une modélisation multi-échelle hiérarchique développée pour étudier le comportement mécanique de graves base de MIDND traitées aux liants (ciment et bitume). La campagne expérimentale originale sur des particules de mâchefers a permis de les cartographier au Microscope Electronique à Balayage (MEB Pour ces particules, des modules d'élasticité moyens réduits variant de 15 à 68 GPa ont été trouvés par le biais de tests d'indentation en appliquant méthode de «Olivier and Pharr ». Les analyses chimiques ponctuelles qualitatives (EDS) effectuées ont permis d'obtenir la composition chimique des granulats de mâchefers. Partant d'une granulométrie de particules de MIDND 0/25 qui a fait l'objet d'une étude expérimentale [BEC 07], nous avons mis en place des modèles numériques 3D de grave routière traitée aux liants dans des Volumes Elémentaires Représentatifs (VER). Ces modèles sont basés sur une stratégie de modélisation dite « multi-échelles » hiérarchique. Deux types de liant sont étudiés : le ciment CEM 1 42,5 R et le bitume de [NGU 08). Pour les deux types de liant, les agrégats traités ont été décomposés en deux VER : sub-mesoscopique (0/6) et mesoscopique (6/25). Une application à valorisation des MIDND en techniques routières est faite dans les deux cas. Avec un traitement à 3% de ciment, une campagne de simulations numériques "Laboratoire virtuel" a été menée. A l'échelle sub-mesoscopique, des simulations multiaxiales menées sur le VER, ont conduit à l'obtention des paramètres permettant d'alimenter un modèle d'endommagement plastique utilisé à l'échelle mesoscopique pour différents degrés d'hydratation. A l'échelle mesoscopique, les caractéristiques mécaniques de la grave routière traitée au ciment, habituellement déterminées par le biais d'expérimentations, ont été retrouvées. La modélisation développée a ensuite été validée e comparant nos résultats numériques et quelques résultats expérimentaux de [BEC 07]. Avec un traitement à 5% de bitume, des tests de relaxation de contraintes ont été effectués aux deux échelles ct ont permis d'obtenir les propriétés thermo-rhéologiques de la grave de mâchefers traités au bitume : les modules de relaxation sont exprimés sous la forme de séries de Prony à une température de référence de 0 °C ; par ailleurs, les constantes de la loi Williams-Landel-Ferry (WLF) pour décrire le comportement thermo- rhéologiquement simple sont identifiées. Les séries de Prony sont obtenues par l'intermédiaire des modules élastiques normalisés. Les constantes de 1 WLF obtenues sont C 1 = 20 °C-1 ct C2 = 130 °C. La validation des paramètres identifiés a été faite en comparant les réponses du matériau hétérogène de grave-bitume et celles d'un matériau homogène à qui nous avons donné les propriétés identifiées tirées du matériau hétérogène
In this work, the feasibility of a valorisation in road engineering of non-hazardous waste incineration bottom ash aggregates (NHWI) is investigated. This study is first based on an experimental determination of the elastic properties of the bottom ash particles. These properties serve as input data for hierarchical multi-scale modelling developed to study the mechanical behaviour of aggregates treated with binders (cement and bitumen). The original experimental campaign on the bottom ash particles allowed them to be mapped to the Scanning Electron Microscope (SEM). For the particles, a mean reduced modulus of elasticity in between 15 and 68 GPa was found by means of indentation tests and applying the "Olivier and Phan method. The chemical analysis of the aggregates was obtained using qualitative point chemical analyzes (OHS). Based on a 0/25 particle size distribution of NHWI, which was the subject of an experimental study [BEC 07] , we have implemented two 30 models < road materials treated with binders in Representative Elementary Volumes (REV). These models are based on a hierarchical multi-scale modelling strategy. Two types of binder are studied: cement CEM I 42.5 R and bitumen of [NGU 08]. For both types of binder, the treated aggregates we divided into two REV, at respectively the sub-mesoscale (0/6 mm) and the mesoscale (6/25 mm). An application to the valorisation of NHWI bottom ashes in road engineering is studied in both cases. With a 3% cement treatment, a numerical simulation campaign "Virtual Laboratory" was conducted. At the sub-mesoscale, the input parameters for the Concrete Damaged Plasticity Model used at the mesoscale are determined. At the mesoscale, the mechanical characteristics of the road materials usually determined through experiments have been found. The developed simulation strategy has been validated by comparing our numerical results and son experimental results of [BEC 07]. With a 5% bitumen treatment, stress relaxation tests carried out at the two scales enable one to obtain the thermo-rheological properties of the Bitumen Bound Gravel. These properties are the Prony series at a reference temperature of 0°C and the Williams-Landei- Ferry (WLF) law constants. Prony series are obtained by means of standardized elastic moduli. The obtained WLF law constants are Cl = 20 °C-1 and C2 = 130 °C. The numeric simulations have been validated by comparing the responses of heterogeneous and corresponding homogeneous materials

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

A major difficulty in the fabrication of nanostructure based electronics is the lack of effective processes capable of precisely arranging nanostructures into predefined positions. Top-down approaches introduce increased complexity and a high cost for practical industrial use, while bottom-up approaches are probabilistic in nature and do not provide precise control of nanostructure properties (i.e., number, diameter), which influence device performance. Alternatively, nanomanipulation promises specificity, precision and programmed motion and its automation may facilitate the large-scale fabrication of nanostructure based devices. This study focuses on the development of an automated contact detection algorithm which positions an end-effector in contact with a target surface without the need for additional equipment, devices or sensors. We demonstrate this algorithm as an enabling feature for automated nano-FET biosensor construction with precise control over nanowire parameters thereby reducing device-to-device variability and also potentially allowing us to optimize individual device performance.

Indiana University-Purdue University Indianapolis (IUPUI)
The objective of this study was to evaluate the in vivo performance of the novel press-fit dental implant fabricated via electron beam melting (EBM, Southern Methodist Univ.) and compare it to a commercially-available porous-coated press-fit dental implant (Endopore, Innova Corp.). Twelve cylindrical shaped implants 3 mm in diameter x 5 mm long were made by EBM (Southern Methodist Univ.) using Ti6Al4V ELI alloy. Twelve commercial implants (Endopore, Innova Corp.) of the same geometry were used as controls. Samples were implanted in rabbit tibia and retrieved six weeks postoperatively. Six specimens from each implant type were embedded undecalcified, sectioned, and stained with toluidine blue (Sigma) for histomorphometry analysis. Bone-to-implant contact (BIC) was measured. On the six remaining samples from each implant type, the mechanical properties were evaluated by pushout test on a material testing machine. The samples were loaded at a loading rate of 1 mm/min. The pushout strength was measured and the apparent shear stiffness was calculated. The results were analyzed with a paired-t test. The histology shows osteointegration of surrounding bone with both implant types. Bone was found to grow into the porous space between the beads. Both the Endopore (Innova Corp.) and the EBM (Southern Methodist Univ.) showed similar BIC. The mean BIC for the Endopore (Innova Corp.) and EBM (Southern Methodist Univ.) implant were 35 ± 6% and 32 ± 9%, respectively. It failed to reach statistical significance (p > 0.05). The peak pushout force for Endopore (Innova Corp.) and EBM (Southern Methodist Univ.) implants were 198.80 ± 61.29 N and 243.21 ± 69.75 N, respectively. The apparent shear stiffness between bone and implant for the Endopore (Innova Corp.) and EBM (Southern Methodist Univ.) implants were 577.36 ± 129.99 N/mm; and 584.48 ± 146.63 N/mm, respectively. Neither the peak pushout force nor the apparent shear stiffness of the implants was statistically different between the two groups (p > 0.05). The results suggest that the implants manufactured by EBM (Southern Methodist Univ.) perform equally well as the commercial implant Endopore (Innova Corp.) in this current animal model.