Cross-calibration of a combined electrostatic and time-of-flight analyzer for energy- and charge-state-resolved spectrometry of tin laser-produced plasma.

We present the results of the calibration of a channeltron-based electrostatic analyzer operating in time-of-flight mode (ESA-ToF) using tin ions resulting from laser-produced plasma, over a wide range of charge states and energies. Specifically, the channeltron electron multiplier detection efficiency and the spectrometer resolution are calibrated, and count rate effects are characterized. With the obtained overall response function, the ESA-ToF is shown to accurately reproduce charge-integrated measurements separately and simultaneously obtained from a Faraday cup (FC), up to a constant factor the finding of which enables absolute cross-calibration of the ESA-ToF using the FC as an absolute benchmark. Absolute charge-state-resolved ion energy distributions are obtained from ns-pulse Nd:YAG-laser-produced microdroplet tin plasmas in a setting relevant for state-of-the-art extreme ultraviolet nanolithography.

Extreme ultraviolet light from a tin plasma driven by a 2-µm-wavelength laser.

An experimental study of laser-produced plasmas is performed by irradiating a planar tin target by laser pulses, of 4.8 ns duration, produced from a KTP-based 2-µm-wavelength master oscillator power amplifier. Comparative spectroscopic investigations are performed for plasmas driven by 1-µm- and 2-µm-wavelength pulsed lasers, over a wide range of laser intensities spanning 0.5 - 5 × 1011 W/cm 2. Similar extreme ultraviolet (EUV) spectra in the 5.5-25.5 nm wavelength range and underlying plasma ionicities are obtained when the intensity ratio is kept fixed at I1µm/I2µm = 2.4(7). Crucially, the conversion efficiency (CE) of 2-µm-laser energy into radiation within a 2% bandwidth centered at 13.5 nm relevant for industrial applications is found to be a factor of two larger, at a 60 degree observation angle, than in the case of the denser 1-µm-laser-driven plasma. Our findings regarding the scaling of the optimum laser intensity for efficient EUV generation and CE with drive laser wavelength are extended to other laser wavelengths using available literature data.

Time- and space-resolved optical Stark spectroscopy in the afterglow of laser-produced tin-droplet plasma.

The afterglow emission from Nd:YAG-laser-produced microdroplet-tin plasma is investigated, with a focus on analyzing Stark effect phenomena and the dynamical evolution of the plasma. Time- and space-resolved optical imaging spectroscopy is performed on 11 lines from Sn i-iv ions, in the 315-425-nm wavelength range. Stark shift-to-width ratios serve as the basis for unambiguous experimental tests of atomic physics theory predictions. Experiment and theory, where available, are found to be in poor agreement, and are in disagreement regarding the sign of the ratio in several cases. Spectroscopic measurements of the Stark widths in tandem with Saha-Boltzmann fits to Sn i and Sn ii lines, establish the evolution of the local temperature and density of the plasma afterglow, 20-40 ns after the end of the 15-ns-long temporally box-shaped laser pulse. A clear cool-down from ∼2 to 1 eV is observed of the plasma in this time window, having started at ∼30 eV when emitting extreme-ultraviolet (EUV) light. An exponential reduction of the density of the plasma from ∼10^{18}-10^{17}e^{-} cm^{-3} is observed in this same time window. Our work is relevant for understanding the dynamics of the decaying, expanding plasma in state-of-the-art EUV nanolithography machines.

Prominent radiative contributions from multiply-excited states in laser-produced tin plasma for nanolithography.

Extreme ultraviolet (EUV) lithography is currently entering high-volume manufacturing to enable the continued miniaturization of semiconductor devices. The required EUV light, at 13.5 nm wavelength, is produced in a hot and dense laser-driven tin plasma. The atomic origins of this light are demonstrably poorly understood. Here we calculate detailed tin opacity spectra using the Los Alamos atomic physics suite ATOMIC and validate these calculations with experimental comparisons. Our key finding is that EUV light largely originates from transitions between multiply-excited states, and not from the singly-excited states decaying to the ground state as is the current paradigm. Moreover, we find that transitions between these multiply-excited states also contribute in the same narrow window around 13.5 nm as those originating from singly-excited states, and this striking property holds over a wide range of charge states. We thus reveal the doubly magic behavior of tin and the origins of the EUV light.

Selection of CD34+ cells from cryopreserved PBPC can be significantly improved by the addition of recombinant human DNase (Pulmozyme).

BACKGROUND: It has been reported previously that PBPC can be recovered from cryopreservation and can be efficiently CD34-selected, to provide a product of high purity (> 80% CD34) with good yield (> 50% recovery). METHODS: In this study, we have investigated the effects of thawing and CD34-selecting cryopreserved PBPC in the presence of recombinant human deoxyribonuclease (rhDNase; Pulmozyme) and magnesium chloride (MgCl2 injection). RESULTS: The addition of Pulmozyme and MgCl2 significantly improves the yield of CD34+ cells, compared with the standard procedure (65.2% and 39.7%, respectively). Following CD34 selection, significantly greater recovery of CFC in the selected fraction can be obtained from Pulmozyme-treated cells, compared with standard cells. The use of recombinant human Pulmozyme and i.v. grade MgCl2 should facilitate the application of this procedure to the clinical setting. CD34+ cells selected from cryopreserved PBPC, can in turn be cryopreserved for a second time. When thawed, these cells still retained good viability (> 80%). DISCUSSION: Cells originally processed in the presence of Pulmozyme gave significantly superior yields of CD34+ cells and CFC compared with standard cells. The functional ability of these CD34+ cells was demonstrated further in an ex vivo expansion culture system with extensive proliferation of cells and CFC. In addition, the presence of significant numbers of primitive hemopoietic cells could be readily demonstrated in a cobblestone-area forming assay.

Xylem sap composition of beech (Fagus sylvatica L.) trees: seasonal changes in the axial distribution of sulfur compounds.

During different phases of the annual growth cycle, xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by the water displacement technique. Irrespective of the height of the trunk, both sulfate and reduced sulfur compounds were detected in the xylem sap throughout the year. Sulfate was the predominant sulfur compound in all samples analyzed. Its concentration in the xylem sap varied between 10 and 350 micro mol l(-1), with highest concentrations in April, shortly before bud break. In contrast to other tree species, cysteine and not glutathione was the predominant thiol transported in the xylem sap of beech trees. The cysteine concentration ranged between 0.1 and 1 micro mol l(-1). As observed for sulfate, maximum cysteine concentrations were found in April. Apparently, both sulfate and cysteine transport contribute to the sulfur supply of the developing leaves. Seasonal changes in the axial distribution of cysteine and sulfate differed, indicating differences in the source-sink relations of these sulfur compounds. High, but uniform, xylem sap sulfate concentrations in April may originate from balanced sulfate uptake by the roots, whereas high cysteine concentrations in April, increasing with increasing height of the trunk, may originate in part from protein breakdown in the trunk. Reversal of the axial distribution of xylem sap cysteine in late summer-early fall to higher concentrations in the lower part of the trunk than in the upper part of the trunk suggests that the upper part of the trunk becomes a sink for cysteine as a result of the synthesis of storage proteins at this time of the year.

Cysteine, gamma-Glutamylcysteine, and Glutathione Levels in Maize Seedlings : Distribution and Translocation in Normal and Cadmium-Exposed Plants.

The levels of cysteine (Cys), gamma-glutamylcysteine (gammaEC), and glutathione (GSH) were measured in the endosperms, scutella, roots, and shoots of maize (Zea mays L.) seedlings. GSH was the major thiol in roots, shoots, and scutella, Cys predominated in endosperms. The endosperm, scutellum, and functional phloem translocation were required for maintenance of GSH pools in roots and shoots of 6-day-old seedlings. Exposure of roots to 3 micromolar Cd, besides causing a decline in GSH, caused an accumulation of gammaEC, as if the activity of GSH synthetase was reduced in vivo. [(35)S]Cys injected into endosperms of seedlings was partly metabolized to [(35)S]sulfate. The scutella absorbed both [(35)S]sulfate and [(35)S]Cys and transformed 68 to 87% of the radioactivity into [(35)S]GSH. [(35)S]GSH was translocated to roots and shoots in proportion to the tissue fresh weight. Taken together, the data supported the hypothesis that Cys from the endosperm is absorbed by the scutellum and used to synthesize GSH for transfer through the phloem to the root and shoot. The estimated flux of GSH to the roots was 35 to 60 nanomoles per gram per hour, which totally accounted for the small gain in GSH in roots between days 6 and 7. For Cd-treated roots the GSH influx was similar, yet the GSH pool did not recover to control levels within 24 hours. The estimated flux of GSH to the entire shoot was like that to the roots; however, it was low (11-13 nanomoles per gram per hour) to the first leaf and high (76-135 nanomoles per gram per hour) to the second and younger leaves.

Reductive drug metabolism in isolated perfused rat liver under restricted oxygen supply.

1. Hepatic azo and nitro reductase activities were studied in the perfused rat liver under normal and restricted oxygen supply. 2. Formation of sulphanilamide or p-aminobenzoic acid from neoprontosil or p-nitrobenzoic acid under aerobic conditions of liver perfusion was negligible, even at a reduced oxygen saturation of a pO2 of 300 mm Hg in the haemoglobinfree perfusion system. At a pO2 of 200 mm Hg reductase activities were almost maximal. 3. Conjugation of sulphanilamide (0-08 mM) was similar under aerobic and anaerobic conditions. Hepatic elimination of p-aminobenzoic acid (0-08 mM) showed an oxygen-dependent increase for 15 min after addition of substrate. 4. p-Nitroanisole demethylation was inhibited 80% under hypoxic perfusion at 200 mm Hg pO2 and was completely inhibited after gassing with anoxic mixtures. 5. Restitution of aerobic conditions after 30 min anaerobic perfusion restored hepatic respiration, lactate pyruvate ratio, and pH value to levels found under aerobic conditions, but bile flow remained 50% reduced.