Design and Simulation of a Miniature Cylindrical Mirror Auger Electron Energy Analyzer with Secondary Electron Noise Suppression

In the nanoscale metrology industry, there is a need for low-cost instruments, which have the ability to probe the structrure and elemental composition of thin films. This dissertation, describes the research performed to design and simulate a miniature Cylindrical Mirror Analyzer, (CMA), and Auger Electron Spectrometer, (AES). The CMA includes an integrated coaxial thermionic electron source. Electron optics simulations were performed using the Finite Element Method, (FEM), software COMSOL. To address the large Secondary Electron, (SE), noise, inherent in AES spectra, this research also included experiments to create structures in materials, which were intended to suppress SE backgound noise in the CMA. Laser Beam Machining, (LBM), of copper substrates was used to create copper pillars with very high surface areas, which were designed to supress SE’s. The LBM was performed with a Lumera SUPER RAPID‐HE model Neodymium Vanadate laser. The laser has a peak output power of 30 megawatts, has a 5x lens and a spot size of 16 μm. The laser wavelength is in the infrared at 1064 nm, a pulse width of 15 picoseconds, and pulse repetition rate up to 100 kHz. The spectrometer used in this research is intended for use when performing chemical analysis of the surface of bulk materials and thin films. It is applicable for metrology of thin films, as low as 0.4 nm in thickness, without the need to perform destructive sample thinning, which is required in Scanning Tranmission Electron Microscopy, (STEM). The spectrometer design is based on the well known and widely used coaxial cylinder capacitor design known as the Cylindrical Mirror Analyzer, (CMA). The coaxial tube arrangement of the CMA allows for placing an electron source,which is mounted in the center of the inner cylinder of the spectrometer. Simulation of the electron source with an Einzel Lens was also performed. In addtion, experiments with thin film coatings and Laser Beam Machining to supress Secondary Electron emission noise within the Auger electron spectrum were completed. Design geometry for the miniature CMA were modeled using Computer Aided Design, (CAD). Fixed Boundary Conditions, (BC), were applied and the geometry was then meshed for FEM. The electrostatic potential was then solved using the Poisson equation at each point. Having found the solution to the electrostatic potentials, electron flight simulations were performed and compared with the analytical solution. From several commercially available FEM modeling packages, COMSOL Multiphysics was chosen as the research platform for modeling of the spectrometer design. The CMA in this design was reduced in size by a factor of 4 to 5. This enabled mounting the CMA on a 2 ¾ in flange compared to the commercial PHI model 660 CMA which mounts onto a 10 in flange. Results from the Scanning Electron Microscopy measurements of the Secondary Electron emission characteristics of the LBM electron suppressor will also be presented

Time-Gating of Pulsed Eddy Current Signals for Defect Characterization and Discrimination in Aircraft Lap-Joints

Pulsed eddy current (PEC) nondestructive testing differs from conventional eddy current techniques in that the probe coil is excited by a pulse, rather than continuous excitation at a single frequency. Reviews of early work on pulsed eddy currents are given by Waidelich1 and by Renkin.2 Pulsed excitation causes the propagation of a highly attenuated traveling wave, which is governed by the diffusion equation.3 The diffusive propagation of the eddy current pulse results in spatial broadening and a delay, or travel time, proportional to the square of the distance traveled. It was realized in early work on pulsed eddy current systems that this time dependence offered certain advantages over conventional eddy currents.4 In the current study we demonstrate the ability of a prototype pulsed eddy current instrument, described elsewhere,5,6 to take advantage of this time dependence to discriminate flaws from such interfering signals as probe liftoff, air gaps, and fasteners

Quantitative Assessment of Corrosion in Aircraft Structures Using Scanning Pulsed Eddy Current

Eddy current nondestructive testing techniques are used extensively in industry for detection of hidden cracks and corrosion in multi-layer conductive structures such as those found in aircraft. Most conventional eddy current techniques employ a probe coil excited with a continuous sine wave. The changes in the probe’s impedance are detected (usually with an electronic bridge circuit) and displayed in real time on an impedance plane CRT display. Interpretation of the impedance-plane trajectories that result from scanning the probe over a defect is difficult; it involves a considerable amount of operator skill and knowledge and the equipment is sometimes difficult to set up and operate. We have developed an eddy current inspection system using the pulsed eddy current technique, which greatly reduces the possibility of operator errors and subjectivity in the quantitative interpretation of test results

Skin microbiome prior to development of atopic dermatitis:early colonization with commensal staphylococci at 2 months is associated with a lower risk of atopic dermatitis at 1 year

Background: Disease flares of established atopic dermatitis (AD) are generally associated with a low-diversity skin microbiota and Staphylococcus aureus dominance. The temporal transition of the skin microbiome between early infancy and the dysbiosis of established AD is unknown. Methods: We randomly selected 50 children from the Cork Babies After SCOPE: Evaluating the Longitudinal Impact Using Neurological and Nutritional Endpoints (BASELINE) longitudinal birth cohort for microbiome sampling at 3 points in the first 6 months of life at 4 skin sites relevant to AD: the antecubital and popliteal fossae, nasal tip, and cheek. We identified 10 infants with AD and compared them with 10 randomly selected control infants with no AD. We performed bacterial 16S ribosomal RNA sequencing and analysis directly from clinical samples. Results: Bacterial community structures and diversity shifted over time, suggesting that age strongly affects the skin microbiome in infants. Unlike established AD, these patients with infantile AD did not have noticeably dysbiotic communities before or with disease and were not colonized by S aureus. In comparing patients and control subjects, infants who had affected skin at month 12 had statistically significant differences in bacterial communities on the antecubital fossa at month 2 compared with infants who were unaffected at month 12. In particular, commensal staphylococci were significantly less abundant in infants affected at month 12, suggesting that this genus might protect against the later development of AD. Conclusions: This study suggests that 12-month-old infants with AD were not colonized with S aureus before having AD. Additional studies are needed to confirm whether colonization with commensal staphylococci modulates skin immunity and attenuates development of AD

Design and Simulation of a Miniature Cylindrical Mirror Auger Electron Energy Analyzer with Secondary Electron Noise Suppression

In the nanoscale metrology industry, there is a need for low-cost instruments, which have the ability to probe the structrure and elemental composition of thin films. This dissertation, describes the research performed to design and simulate a miniature Cylindrical Mirror Analyzer, (CMA), and Auger Electron Spectrometer, (AES). The CMA includes an integrated coaxial thermionic electron source. Electron optics simulations were performed using the Finite Element Method, (FEM), software COMSOL. To address the large Secondary Electron, (SE), noise, inherent in AES spectra, this research also included experiments to create structures in materials, which were intended to suppress SE backgound noise in the CMA. Laser Beam Machining, (LBM), of copper substrates was used to create copper pillars with very high surface areas, which were designed to supress SE’s. The LBM was performed with a Lumera SUPER RAPID‐HE model Neodymium Vanadate laser. The laser has a peak output power of 30 megawatts, has a 5x lens and a spot size of 16 μm. The laser wavelength is in the infrared at 1064 nm, a pulse width of 15 picoseconds, and pulse repetition rate up to 100 kHz. The spectrometer used in this research is intended for use when performing chemical analysis of the surface of bulk materials and thin films. It is applicable for metrology of thin films, as low as 0.4 nm in thickness, without the need to perform destructive sample thinning, which is required in Scanning Tranmission Electron Microscopy, (STEM). The spectrometer design is based on the well known and widely used coaxial cylinder capacitor design known as the Cylindrical Mirror Analyzer, (CMA). The coaxial tube arrangement of the CMA allows for placing an electron source,which is mounted in the center of the inner cylinder of the spectrometer. Simulation of the electron source with an Einzel Lens was also performed. In addtion, experiments with thin film coatings and Laser Beam Machining to supress Secondary Electron emission noise within the Auger electron spectrum were completed. Design geometry for the miniature CMA were modeled using Computer Aided Design, (CAD). Fixed Boundary Conditions, (BC), were applied and the geometry was then meshed for FEM. The electrostatic potential was then solved using the Poisson equation at each point. Having found the solution to the electrostatic potentials, electron flight simulations were performed and compared with the analytical solution. From several commercially available FEM modeling packages, COMSOL Multiphysics was chosen as the research platform for modeling of the spectrometer design. The CMA in this design was reduced in size by a factor of 4 to 5. This enabled mounting the CMA on a 2 ¾ in flange compared to the commercial PHI model 660 CMA which mounts onto a 10 in flange. Results from the Scanning Electron Microscopy measurements of the Secondary Electron emission characteristics of the LBM electron suppressor will also be presented

Synthesis of Nanoscale Structures in Single Crystal Silicon Carbide by Electron Beam Lithography

Nanostructures were formed on diced specimens of several silicon carbide polytypes and silicon using electron beam lithography. A general introduction to nanostructure synthesis and electron beam lithography,are presented. A scanning electron microscope was retrofitted with a commercially available electron beam lithography package and an electrostatic beam blanker to permit nanoscale lithography to be performed. A process was first developed and optimized on silicon substrates to expose, poly-methyl-methacrylate (PMMA) resist with an electron beam to make nanoscale nickel masks for reactive ion etching. The masks consist of an array of nickel dots that range in size from 20 to 100 nm in diameter. Several nanoscale structures were then fabricated in silicon carbide using electron beam lithography. The structures produced are characterized by field emission Scanning Electron Microscopy

Project Calcium

Fouling problems in utility boilers have been classified into two principal types: high-temperature and low-temperature fouling. A multiclient-sponsored program was initiated at the Energy and Environmental Research Center (EERC) to better understand the causes of low-temperature fouling when burning high-calcium western US coals. The goals of Project Calcium were to define the low-temperature deposition problem, identify the calcium-based components that are responsible for the formation of the deposits, develop ways to predict their formation, and identify possible methods to mitigate the formation of these deposits. To achieve the goals of Project Calcium, detailed sampling of utility boilers and laboratory-scale studies coupled with state-of-the-art methods to determine the inorganic components in coals and coal ash-derived materials were conducted. Boiler Sampling was also performed. The work involved sampling coal, entrained ash, deposits and slags from five full-scale utility boilers combined with detailed advanced characterization of the materials. The results of this work aided in identifying the key phenomena to focus the laboratory studies and in model verification. Field testing was conducted at three utilities

Task 6.5 -- Gas separation and hot-gas cleanup. Semi-annual report, January 1--June 30, 1995

The objective of this task is to develop and test superior gas separation membranes. Several methods will be tested to prepare new membrane materials, including physical vapor deposition via electron beam evaporation. Other ceramic filter materials used in hot-gas particulate filters will be obtained from selected suppliers for use as substrates to develop a thin-film membrane selective to hydrogen permeation. This thin-film membrane will be modified via an EERC proprietary process. The base filter materials will already have been characterized for hydrothermal and chemical stability and pore size. The selectivity of these membrane materials for separating undesired gases will be determined. Selectivity will be measured by mixing bottled gases in a manifold, feeding the gases to the membrane, and sampling the inlet, permeate, and raffinate streams for gas composition and volumetric flow rate. Specific questions to be answered include the following: What are the effects of ceramic membrane properties (i.e., surface area, pore size, and coating thickness) on permeability and selectivity of the desired gases? What are the effects of operating conditions (i.e., temperature, pressure, and flow rate) on permeability and selectivity