A new approach is proposed to analyze Bremsstrahlung X-rays that are emitted from laser-produced plasmas (LPP) and are measured by a stack type spectrometer. This new method is based on a spectral tomographic reconstruction concept with the variational principle for optimization, without referring to the electron energy distribution of a plasma. This approach is applied to the analysis of some experimental data obtained at a few major laser facilities to demonstrate the applicability of the method. Slope temperatures of X-rays from LPP are determined with a two-temperature model, showing different spectral characteristics of X-rays depending on laser properties used in the experiments.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

The organic thin-film transistors (OTFTs) incorporating pentacene/SU-8 interface were fabricated and characterized. SU-8, a reliable epoxy-based photoresist, is tested as a potential highly-stable polymeric gate dielectric for OTFTs. The fabricated devices showed promising electrical performance with on-off ratio up to 107 and field-effect mobility up to 0.56 cm2/V s. Several device characteristics are further analyzed. There existed a leakage current path due to the uncontrolled pentacene coverage and we revealed that precise alignment of the evaporation mask of pentacene is critical for eliminating this problem. Pentacene grain formation largely depended on the growth condition on the SU-8 surface and small-grain films offered outstanding performance possibly owing to enhanced inter-domain connections. Natural degradation of the OTFTs is also discussed in terms of environmental stability and the pentacene/SU-8 transistor operated with noticeable air stability under ambient conditions.

Organic metal-semiconductor field-effect transistors (OMESFETs) were fabricated with a polycrystalline organic semiconductor (pentacene) and characterized in order to systematically analyze their operation mechanism. Impedance measurements confirmed full depletion of the thick pentacene film (1 μm) due to the low doping concentration of unintentional doping (typically less than 1014 cm−3). The necessity of developing a specific device model for OMESFET is emphasized as the classical (inorganic) MESFET theory based on the depletion modulation is not applicable to a fully-depleted organic semiconductor. By means of joint electrical measurements and numerical simulation, it is pointed out that the gate voltage controls the bulk distribution of injected carriers, so that the competition between the gate and drain currents is critical for determining the operation mode. Finally, the geometrical effect is investigated with comparing a number of transistors with various channel widths and lengths.

We report soft X-ray spectra (4–18 nm) produced by the interaction of 25–100-fs laser pulses at an intensity of up to 7 × 1016 W/cm2 with a cryogenically cooled Ar gas jet. New spectral lines from Ar8+, Ar9+, and Ar10+ charge states appeared with decreasing preexpansion gas temperature. A nonlinear increase of X-ray line emission from Ar7+, Ar8+, and Ar9+ was observed with cooling, which saturated below a certain temperature. The drastic change in the spectrum is attributed to efficient collisional heating and collisional ionization of growing, small- to medium-sized (102–103 atoms) Ar clusters from the cooled jet. When the laser pulse was extended from 25 to 100 fs we observed considerably stronger emission on lines from high charge states, such as Ar8+, Ar9+, and Ar10+, which suggests that the resonance absorption condition could be reached for the 100-fs pulse.

The long-term dissolution behavior of spent PWR fuel in synthetic granitic groundwater has been investigated since June of 1998 in order to identify the release mechanism of spent fuel in contact with domestic Ca-bentonite, which was compacted as a density of 1.4g/cm3. Several spent fuel specimens were cut to around 3-mm thick, and these specimens were then loaded into each leaching cell. Every half year, one specimen was collected and the bentonite block was sliced into several pieces. The element distribution on the specimen surface was measured by EPMA and an optical microscope, and the gamma activities in the sliced bentonite pieces were measured. All the leachates were sampled and then the gamma and gross alpha activities were measured. By the results, coming from leaching up to about 1.5 years, the fraction of radiocesium released through the compacted bentonite layer from the spent fuel is approximately a hundredth lower than that without the bentonite layer. By the depth profile of the gamma activity on the bentonite, the activity gradually decreased in accordance with more distance from the specimen and the fractional release rates of cesium were nearly the same. On the other hand, the EPMA results indicate that more time and more information is required in order to identify the surface alteration of spent fuel by leaching. This experiment will therefore be continued at least into the year 2006.

We demonstrated that the quality of siloxane spin-on glass (SOG) films, widely used as interlevel planarization dielectrics, is improved significantly by curing in argon plasma. The wet etch rate of SOG film decreases with increasing plasma treatment temperature or treatment time, and is much lower than that cured in a furnace. Long-time plasma treatment reduces the density of silanols (Si-OH) and methyl (−CH3) group, which act as adsorption sites of water. The results were compared with those obtained from the N2O (or H2 ) plasma treated SOG films. The modification of the SOG film by Ar plasma is related to the radiation damage and the reconstruction of the atomic structure during the plasma exposure. The role of metastable Ar (Ar*) appears to be very important to improve the SOG film; SOG film is more relaxed by the energy released from the conversion of Ar* to Ar.

Internal cavities often develop during the deformation of superplastic alloys. Experiments were conducted to determine whether a nondestructive photoacoustic method may be used to detect the presence of internal cavities in two different commercial Al-based alloys. An analytical procedure was developed to provide quantitative information on the volume fraction of cavitation. The results confirm that the photoacoustic signal can be used to detect the presence of cavities, and it is demonstrated that the quantitative measurements derived from the photoacoustic data are consistent with observations obtained by sectioning and standard metallographic techniques.

Diamond is suitable for use as an ionizing particle detector for high rate, high radiation, and/or chemically harsh environments. A sampling calorimeter, a detector measuring the total energy of an incident particle, consisting of 20 alternating layers of diamond and tungsten has been constructed and tested. The diamond for the detector layers was grown by chemical vapor deposition with an averaged thickness of 500 μm. The active area of each layer was 3×3 cm2 with ohmic contacts on opposite faces forming a metal-insulator-metal structure. The calorimeter was tested with electrons of energies up to 5.0 GeV. The response of the diamond/tungsten calorimeter was found to be linear as a function of incident energy. A direct comparison of diamond/tungsten and silicon/tungsten calorimeters was made.

We have investigated the annealing effects of ultraviolet (UV) irradiation on the characteristics of hydrogenated amorphous silicon (a-Si:H) thin films and hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT's) using XeCl excimer laser. The pulse duration of laser was 30nsec/shot and its intensity was varied from 10mJ/cm2 to 80 mJ/cm2 . By irradiating the excimer laser on the a-Si:H TFT's degraded by the electrical stress and/or the visible light illumination, the characteristics of TFT's, such as the on- current, threshold voltage, field-effect mobility and subthreshold sharpness, have been effectively restored to those of virgin sample, while the leakage current changed little. It should be noted that the a-Si:H channel layer was not crystallized by varying the laser intensity.

A prevalence study was carried out on a 100-bed Veterans Administration nursing home care unit to determine the extent of colonization with gentamicin-resistant gram-negative bacilli (GRGNB). Hand cultures of 12 employees and 17 environmental cultures were negative. Twenty-six of 86 (30%) patients were colonized with 49 GRGNB. Sixteen patients (19%) had urinary colonization. Multivariate analysis revealed significant associations between rectal or perineal colonization (P<0.01), and the presence of a urinary device (82% condom catheters) (P<0.05), with urinary colonization. The most common isolates were Providencia stuartii (20), Escherichia coli (nine) and Klebsiella pneumoniae (nine). Twenty-six of 49 isolates carried plasmids. Restriction endonuclease digestion of plasmid DNA was performed for 21. Cross-colonization, as defined by the presence of the identical species with the identical restriction endonuclease digestion profile of purified plasmid DNA found in different patients, was observed for eight of 21 (38%) strains. All were geographically clustered. No strains could transfer gentamicin-resistance by conjugation and only two plasmids could transform our E coli recipient to gentamicin resistance. One E coli plasmid was identical to two Citrobacter freundii plasmids and a P stuartii plasmid isolated from three different patients. This 105 kb plasmid is conjugative and encodes resistance to ampicillin, carbenicillin, tetracycline, and sulfonamides. Thus, 57% of strains were cross-colonizing or contained identical R-plasmids. Southern hybridization using a 1 kb TEM-1 gene probe demonstrated sequences homologous to this probe in five of five nursing home plasmids examined. These data demonstrate the utility of plasmid analysis in epidemiologic typing of multiple species of Enterobacteriaceae, and suggest wide dissemination of R-plasmids bearing the TEM-1β-lactamase gene among gram-negative bacilli colonizing patients residing in our nursing home.

Techniques have been developed at NCSU for fabricating cross-sectional transmission electron microscopy (XTEM) foils from monocrystalline beta silicon carbide thin films grown by chemical vapor deposition. The results of the TEM observations are utilized to discern the efficacy of the various processing parameters in terms of film quality and defect structure as well as oxidation, ion implantation and annealing procedures.