X-ray radiation is widely used in medical and industrial applications. The basic design of the x-ray tube has not changed significantly in the last century. In this paper, we demonstrate that medical diagnostic x-ray radiation can be generated using a carbon nanotube (CNT) based field-emission cathode. The device can readily produce both continuous and pulsed x-ray with a programmable waveform and repetition rate. A total emission current of 28 mA was obtained from a 0.2 cm 2 area CNT cathode. The x-ray intensity is sufficient to image human extremity at 14 kVp and 180 mAs. Pulsed x-ray with a repetition rate greater than 100 kHz was readily achieved by programming the gate voltage. The CNT-based cold-cathode x-ray technology can potentially lead to portable and miniature x-ray sources for industrial and medical applications.

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We report a field emission x-ray source that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal-oxide-semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis with a simplified experimental setup.

Ultra-high temperature ceramics (UHTCs) are generally referred to the carbides, nitrides, and borides of the transition metals, with the Group IVB compounds (Zr & Hf) and TaC as the main focus. The UHTCs are endowed with ultra-high melting points, excellent mechanical properties, and ablation resistance at elevated temperatures. These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles, particularly nozzles, leading edges, and engine components, etc. In addition to bulk UHTCs, UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics. Recently, highentropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials. This review presents the state of the art of processing approaches, microstructure design and properties of UHTCs from bulk materials to composites and coatings, as well as the future directions.

Uniform carbon nanotube films (see Figure) can be readily formed by electrophoretic deposition, as is presented in this communication. By varying deposition current and time, films with thicknesses in the range between several tens of nanometers and a few micrometers can be fabricated. The macroscopic nanotube films also show excellent electron field emission characteristics.

We report a dynamic radiography system with a carbon nanotube based field-emission microfocus x-ray source. The system can readily generate x-ray radiation with continuous variation of temporal resolution as short as nanoseconds. Its potential applications for dynamic x-ray imaging are demonstrated. The performance characteristics of this compact and versatile system are promising for noninvasive imaging in biomedical research and industrial inspection.

Fabrication of SOFC cathodes by infiltration of La0.8Sr0.2Co0.2Fe0.8O3-δ (LSCF) into porous scaffolds that were 50-wt% composites of La0.8Sr0.2FeO3-δ (LSF) and YSZ were investigated for purposes of reducing the number of infiltration steps required to make conductive electrodes. XRD patterns of porous, LSF-YSZ composites prepared by tape casting and calcined to 1723 K showed only fluorite and perovskite phases and were sufficiently conductive that 30-μm thick films attached to YSZ electrolytes did not substantially contribute to the ohmic resistance in symmetric cells or SOFC. Non-ohmic losses at 973 K were reduced from 1.4 Ωcm2 to 0.16 Ωcm2 by two infiltration cycles of LSCF.

Composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La 0.8 Sr 0.2 FeO 3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO 2 , La 2 O 3 , Fe 2 O 3 , or La 2 O 3 -Fe 2 O 3 codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe 2 O 3 and 523 K for ZrO 2 and La 2 O 3 were determined to be 0.024 nm ZrO 2 /cycle, 0.019 nm La 2 O 3 /cycle, and 0.018 nm Fe 2 O 3 /cycle. For ZrO 2 and Fe 2 O 3 , impedance spectra on symmetric cells at 873 K indicated that polarization resistances increased with coverage in a manner suggesting simple blocking of O 2 adsorption sites. With La 2 O 3 , the polarization resistance decreased with small numbers of ALD cycles before again increasing at higher coverages. When La 2 O 3 and Fe 2 O 3 were co-deposited, the polarization resistances remained low at high film coverages, implying that O 2 adsorption sites were formed on the co-deposited films. The implications of these results for future SOFC electrode development are discussed. Atomic Layer Deposition (ALD) is attracting an increasing level of attention as a method for modifying SOFC electrodes because the surface composition can be modified with unparalleled precision. 1-11Uniform, atomic-scale films are formed in ALD by repeated cycles in which the surface is first allowed to react with an organometallic precursor, followed by a subsequent oxidation step. Since the reaction of the precursor with the surface is performed under conditions which limit the extent of reaction to one monolayer at most, the thickness of the final oxide film can be precisely controlled by the number of cycles.In the case of SOFC cathodes, ALD has been used to improve both electrode stability and decrease impedance.1-4 For example, Gong et al. reported that degradation rates for cathodes based on La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) decreased significantly after depositing a 5-nm ZrO 2 film.3,4 While they reported a slight increase in the initial electrode impedance, the performance of the ALD-modified electrode surpassed that of the unmodified electrode after less than 100 h and exhibited a much lower impedance after 900 h of operation at 1073 K. In another example of cathodes modified by ZrO 2 ALD films, the initial impedance of composite cathodes of Sr-doped LaMnO 3 (LSM) and yttria-stabilized zirconia (YSZ) actually decreased following deposition of films as thick as 60 nm. 6 This latter study is particularly revealing because it had been previously reported that infiltration of CoO x nanoparticles could be used to decrease cathode polarization.13 Choi et al. suggested that addition of CoO x by ALD differs from infiltration because infiltration produces inhomogeneous layers that affect surface area and because the infiltration process may induce changes in the cathode morphology. 6 In principle, ALD allows catalytic materials to ...