Carlos H. Castano

Nitrogen incorporated ultrananocrystalline diamond based field emitter array for a flat-panel x-ray source

A field emission based flat-panel transmission x-ray source is being developed as an alternative for medical and industrial imaging. A field emitter array (FEA) prototype based on nitrogen incorporated ultrananocrystalline diamond film has been fabricated to be used as the electron source of this flat panel x-ray source. The FEA prototype was developed using conventional microfabrication techniques. The field emission characteristics of the FEA prototype were evaluated. Results indicated that emission current densities of the order of 6 mA/cm2 could be obtained at electric fields as low as 10 V/μm to 20 V/μm. During the prototype microfabrication process, issues such as delamination of the extraction gate and poor etching of the SiO2 insulating layer located between the emitters and the extraction layer were encountered. Consequently, alternative FEA designs were investigated. Experimental and simulation data from the first FEA prototype were compared and the results were used to evaluate the performance ...

Electron field emission Particle-In-Cell (PIC) coupled with MCNPX simulation of a CNT-based flat-panel x-ray source

A novel x-ray source based on carbon nanotubes (CNTs) field emitters is being developed as an alternative for medical imaging diagnostic technologies. The design is based on an array of millions of micro sized x-ray sources similar to the way pixels are arranged in flat panel displays. The trajectory and focusing characteristics of the field emitted electrons, as well as the x-ray generation characteristics of each one of the proposed micro-sized x-ray tubes are simulated. The electron field emission is simulated using the OOPIC PRO particle-in-cell code. The x-ray generation is analyzed with the MCNPX Monte Carlo code. MCNPX is used to optimize both the bremsstrahlung radiation energy spectra and to verify the angular distribution for 0.25-12 μm thick molybdenum, rhodium and tungsten targets. Also, different extracting, accelerating and focusing voltages, as well as different focusing structures and geometries of the micro cells are simulated using the OOPIC Pro particle-in-cell code. The electron trajectories, beam spot sizes, I-V curves, bremsstrahlung radiation energy spectra, and angular distribution are all analyzed for a given cell. The simulation results show that micro x-ray cells can be used to generate suitable electron currents using CNT field emitters and strike a thin tungsten target to produce an adequate bremsstrahlung spectrum. The shape and trajectory of the electron beam was modified using focusing structures in the microcell. Further modifications to the electron beam are possible and can help design a better x-ray transmission source.

Simulation of the electron field emission characteristics of a flat panel x-ray source

A distributed flat panel x ray source is designed as an alternative for medical and industrial imaging fields. The distributed x ray source corresponds to a two dimensional array of micro (93 μm) x ray cells similar in format to a field emission display. In this paper the field electron emission characteristics of a single micro x ray cell are presented. The field electron emission from a carbon-nanotube- (CNT-) based cold cathode is simulated using the particle-in-cell code oopic pro. The electron source is simulated as a triode structure, composed of an emitting cathode, extracting grid and anode. The possibility of using focusing lenses to control the trajectory of emitted electrons is also evaluated. The layer of CNT emitters is modeled as Fowler–Nordheim emitters. The field emission characteristics were analyzed for extracting voltages between 20 and 70 V and accelerating voltages between 30 and 120 kV. Under these conditions, JFN-V curves, energy, and electron distributions at the anode surface were...

A Monte Carlo simulation study of a flat-panel X-ray source

A novel flat-panel transmission X-ray source based on nitrogen-incorporated ultra-nano-crystalline diamond (N-UNCD) field emitters is being developed for medical and industrial X-ray imaging. X-ray generation characteristics of the X-ray tubes were simulated with the MCNPX 2.6.0 Monte Carlo code. The simulation results showed that 0.25-12 μm thick tungsten targets could generate an adequate intensity of Bremsstrahlung X-rays. Generated X-ray output intensities of 1.48×10(12)MeV/mA-s of 100 kVp electrons hitting the target were found before collimation.

Construction of a ultrananocrystalline diamond-based cold cathode arrays for a flat-panel x-ray source

A novel cold cathode field emission array (FEA) X-ray source based on ultra-nanocrystalline diamond (UNCD) field emitters is being constructed as an alternative for detection of obscured objects and material. Depending on the geometry of the given situation the flat-panel X-ray source could be used in tomography, radiography, or tomosynthesis. Furthermore, the unit could be used as a portable X-ray scanner or an integral part of an existing detection system. UNCD field emitters show great field emission output and can be deposited over large areas as the case with carbon nanotube “forest” (CNT) cathodes. Furthermore, UNCDs have better mechanical and thermal properties as compared to CNT tips which further extend the lifetime of UNCD based FEA. This work includes the first generation of the UNCD based FEA prototype which is being manufactured at the Center for Nanoscale Materials within Argonne National Laboratory with standard microfabrication techniques. The prototype is a 3x3 pixel FEA, with a pixel pitch of 500 μm, where each pixel is individually controllable.

Ionic debris measurement of three extreme ultraviolet sources

Generation of debris in extreme ultraviolet (EUV) light sources is an inherent and real threat to the lifetime of collection optics. Debris measurement of these sources is useful to enable source suppliers to estimate collector lifetime. At the Center for Plasma Material Interactions (CPMI) at the University of Illinois, an Illinois calibrated spherical sector electrostatic energy analyzer (ICE) was built to measure the ion debris flux in absolute units. In addition to ion flux, the detector is also capable of identifying different ion species present in the plasma utilizing energy-to-charge ratio discrimination. The lifetime of the collector optics is calculated using the measured ion flux. In the current investigation we compare the measurement of ion debris production in three different EUV sources: the Energetiq EQ-10M, the AIXUV-100, and the XTREME XTS 13-35. In the EQ-10M source, three angular measurements are coupled with three variations in operating pressure to measure consequent effects on debri...

Magnetic characterization of a hydrogen phase trapped inside deep dislocation cores in a hydrogen-cycled PdHx (x≈4.5 × 10 -4) single crystal

The magnetic characterization of Pd single crystals deformed by cycling in a hydrogen atmosphere has been performed. Based on evidence obtained from thermal desorption analysis, it is shown that the condensed hydrogen phase formed inside deep dislocation cores in PdHx (x = H/Pd ≈ 4.5 × 10−4) is tightly bound with a Pd matrix. The activation energy of hydrogen desorption from these cores was found to be as high as e = 1.6eV/H-atom, suggesting the occurrence of a strong band overlapping between Pd and H atoms. SQUID measurements carried out in a weak magnetic field (H < 5.0 Oe) showed an anomalous diamagnetic contribution to the DC and AC magnetic susceptibilities of the PdHx sample at T < 30 K resulting in the presence of the hydrogen phase. It is suggested that the anomalous diamagnetic response in PdHx is caused by the presence of a hydrogen dominant phase, tightly bound with a Pd matrix inside the dislocation cores (nanotubes).

Characterization a Bending Fatigue Mini‐Specimen Technique (Krause Type) of Nuclear Materials

A bending fatigue mini-specimen (Krouse type) was used to study the fatigue properties of nuclear materials for (SS304L, HT9). The objective of this paper study fatigue for HT9 ferritic-martensitic steel and SS304L using a mini-specimen (Krouse type) suitable for reactor irradiation studies. These mini-specimens are similar in design (but smaller) to that described in the ASTM B593 standard. A bending fatigue machine was modified to test the mini-specimen. This study was conducted to evaluate the high cycle bending fatigue behavior of HT9 and SS304 and compare its bending properties with simulations conducted with the Abaqus FEA code. Other properties including tensile strength and hardness were also measured. The S-N fatigue results were affected by polishing of surface and bending fatigue reported values for HT9 were lower than the typical S-N curve for SS304L.

Investigation of Coating and Corrosion Mitigation Strategies in Magnesium/Mixed Metal Assemblies

The US Automotive Materials Partnership through the Magnesium-Intensive Front End Development Project (MFERD) is currently investigating a number of joining, coating and corrosion mitigation strategies to incorporate magnesium components into the automotive body-in-white with the ultimate goal of decreasing vehicle curb weight, thus improving fuel economy. Because Mg is anodic to all other structural metals, this is a key hurdle to Mg component implementation in vehicles. This paper will discuss the results of a study to examine the effectiveness of different corrosion mitigation strategies in joined plate assemblies and provide some insight into the systems challenges of incorporation of Mg parts into a vehicle. Details of a statistically-designed experiment developed to explore the interaction of several materials of construction (magnesium, steel and aluminum), pretreatment and topcoatings, joining methods and standardized test protocols including SAE J-2334 and ASTM B-117 are discussed. A number of avenues have emerged from this study as potential strategies for corrosion mitigation.

Visual and Electrical Evidence Supporting a Two-Plasma Mechanism of Vacuum Breakdown Initiation

The energy available during vacuum breakdown between copper electrodes at high vacuum was limited using resistors in series with the vacuum gap and arresting diodes. Surviving features observed with SEM in postmortem samples were tentatively correlated with electrical signals captured during breakdown using a Rogowski coil and a high-voltage probe. The visual and electrical evidence is consistent with the qualitative model of vacuum breakdown by unipolar arc formation by Schwirzke [1, 2]. The evidence paints a picture of two plasmas of different composition and scale being created during vacuum breakdown: an initial plasma made of degassed material from the metal surface, ignites a plasma made up of the electrode material.