The Focused Ion Beam (FIB) instrument has been utilized for site-specific specimen preparation for a wide range of analytical techniques due to its ability to achieve high spatial resolution imaging, milling, and deposition [1,2]. The understanding of FIB damage is important to ensure that the region being analyzed is indeed representative of the material, and is not due to a specimen preparation artifact. The interaction between the incident ions (e.g., Ga + ) and the target material during FIB operation (e.g., imaging or milling mode) may lead to surface damage and consequently limit the ability to achieve high quality high-resolution TEM images. Amorphization of a FIB milled crystalline surface may occur due to sufficient atom displacement within the collision cascade resulting in the loss of long-range order when the density of point defects reaches a critical value [3]. Redeposition of sputtered atoms has also been reported as a result of FIB milling [4]. The propensity for redeposition increases when FIB milling is performed in a confined and/or a high aspect ratio trench, or when FIB conditions are used that contribute to factors that increase the sputtering rate (e.g., using a higher beam current) [5]. Observations have shown that FIB milling with Ga at an energy of 30 keV will produce amorphization damage along a Si side-wall that is ~ 28 nm thick and up to 20 wt% Ga may be present within the damage region [6]. Previous work in our lab has shown that the side-wall damage thickness in Si varies with beam current [7]. In addition, while significant amounts of Ga were observed in the side-wall damage [8], Ga was not detectable in side-wall damage when Si was FIB milled using gas assisted etching (GAE) [9]. The following study was performed in an attempt to better understand FIB damage. In this study, three square trenches (2x2 µm 2 , 4x4 µm 2 , and 6x6 µm 2 ) were FIB milled to 1 µm in depth in a (100) Si wafer using an FEI 200TEM FIB workstation equipped with a Ga liquid metal ion source and an Omniprobe in-situ W probe. An accelerating voltage of 30 keV and a beam current of 1000 pA was used to mill the trenches. The specimen was removed from the FIB and sputter-coated with Cr to preserve the FIB milled damage layers. The specimen was put back into the FIB and the trenches were filled with CVD Pt deposition using a beam current of 100 pA. A cross-section TEM specimen was prepared across the trenches using the in-situ FIB lift-out method [10]. The specimen was observed using a Philips EM430 operating at 300 keV. A bright field (BF) TEM image of the trenches is shown as FIG. 1 (a). A BF image from the top of the wafer is shown in FIG. 1(b). A BF image from the side-wall of the middle trench is shown in FIG. 1(c). Note that the side-wall damage clearly consists of two regions with different contrast. This layer clearly indicates that the side-wall damage consists of two regions: (i) an amorphization layer and (ii) a redeposition layer. X-ray energy dispersive spectrometry (XEDS) results showed that significa...

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This study developed a device to solve welding problems that occur in the manufacturing of a pressure vessel for cryogenic applications under the ASME Section VIII Division 1. The cylindrical body of the vessel was assembled with short pre-fabricated cylinders and caps using submerged arc welding. The rotatable grounding electrode was mounted to the top half of the spherical cap. However, the relatively long distance between the welding and the electrode grounding locations, especially in longer vessels, restricts the flow and the distribution of the electrical current. Radiographic testing identified lack of fusion as the major reason for the restricted flow of the electrical current. This also caused additional work on welding repair. To address this issue that compromised both top-outer and bottom-inner vertical positions for circumference welding, a new grounding device was developed to reduce the flow distance. The electrical conductivity was also improved through a series of welding tests. The investigation showed that a greater average welding current increased arc stability. Radiographic testing confirmed that the vessels were welded completely suggesting the grounding device utility for increasing welding joint soundness of the circumference weldment.

A processing approach using a copper backing-wheel device was developed to aid the fabrication process of industrial cryogenic storage tanks manufactured under the ASME Section VIII Division 1. This research focused on the welding processes related to the cylindrical-body assembly. Two processing steps involving the root-run formation and the replacement with a sound outer-circumference joint were studied. Initially, tank fabrication is achieved through the application of both flux-cored arc welding and submerged arc welding. A new processing approach was proposed with the modified method in cross-section preparation, and a low-cost reusable copper backing-wheel device was developed to facilitate the root-run formation using only submerged arc welding. Temperature gradient through the device components along the heat-conduction path was monitored to assure the conductivity of the backing device. The results suggest that the proposed approach reduced manufacturing time by removing the initial flux-cored arc welding process used in the conventional welding method. As an effect, the new approach show promise reduces the overall manufacturing cost of tank fabrication. Based on radiographic testing of tanks fabricated using the new approach found that circumference joints required little or no welding repair suggesting higher joint quality.

This study explored the possibility of recycling pre-fabricated carbon to use as filler in conjunction with talc to produce glass-fiber reinforced unsaturated polyester composites. Specimens with six different resin compositions were prepared using hand lay-up technique. The structure and property relationship was characterized through tensile test and microstructure analysis. Mechanical properties incorporated with the failure analysis suggest that the recycling of carbon is feasible. The application of the recycled carbon showed the improvement on the less variation on the mechanical properties. The percent elongation at break tended to reduce, and traded-off with the deterioration on tensile strength at break and elastic modulus. Mixing with 10-15 wt% recycled carbon and 5-10 wt% talc powder was suggested to yield the optimal tensile properties. Moreover, the recycled carbon previously coated with unsaturated polyester guides the uniform distribution when required to process with a high-polarity material by reducing the polarity effect.