[en] An N-glycosylase activity that released cis-[³H]-5,6-dihydroxy-5,6-dihydrothymine (thymine glycol, TG) from chemically oxidized poly(dA-[³H]dT) was unambiguously characterized both in extracts of HeLa cells and in purified Escherichia coli endonuclease III. This was accomplished by use of a microderivatization procedure that quantitatively converted cis-TG to 5-hydroxy-5-methylhydantoin (HMH). The reaction products were analyzed by high-pressure liquid chromatography before and after derivation by using cis-[¹⁴C]TG and [¹⁴C]HMH, which had been independently synthesized, as reference compounds. This technique facilitated construction of a v/[E]/sub t/ plot for the enzyme activity in HeLa cells, permitting estimation of its specific activity. The results obtained prove the existence of both human and bacterial N-glycosylase activities that effect removal of TG from DNA

[en] The photoabsorption spectra of La V, La VI and La VII have been recorded in the 85-96 eV region using the dual laser plasma technique. 4d → 5p transitions from their ground configurations were observed and identified with the aid of Hartree-Fock with configuration interaction calculations. The excited states were found to decay by autoionization involving 5s or 5p electrons and rates for the different processes and resulting linewidths were calculated and compared with experiment

[en] The photoabsorption spectrum of Xe-like La³⁺ and I-like La⁴⁺ has been obtained in the extreme ultraviolet (euv) spectral region with the dual laser produced plasma technique. Photoexcitation from the 4d subshell is the dominant process in the 80-150 eV energy range. Strong discrete structure, corresponding to 4d→np, mf (n>6, m>4) transitions in La³⁺ was observed at lower laser power densities, but with increasing laser flux the discrete features were suppressed and replaced by broad features in the 4d→5p and 4d→4f regions. This behavior can be attributed to the presence of absorption from excited states containing open 5p and 4f subshells in La³⁺ and the onset of similar absorption in La⁴⁺

[en] Full text: The wavelength of choice for the next extreme UV lithography (EUVL) step, 13.5 nm, is based on the availability of MoSi multilayer mirrors with excellent reflectivity (Approx. 72%) at this wavelength with a reflectance bandwidth of approximately 0.5 nm. A wide variety of pulsed discharge sources using xenon or xenon/helium mixtures are being actively investigated and developed by a number of companies and laboratories. However all of the conversion efficiencies reported to date for these devices are close to 0.5%. Considerable work has also been expended on exploring the feasibility of using laser produced plasmas of xenon clusters produced by supersonic jets or gas puffs from nozzles or solid xenon targets. The highest conversion efficiencies (1.2% into 2% bandwidth) have been achieved using solid xenon. In xenon, the transitions responsible are 4d - 5p in Xe XI. Since this is an open shell species, plasma modeling puts the maximum population attainable at 45%. The required conversion efficiency figure has now been revised upwards to better than 3% conversion into a 2% bandwidth. We have proposed that tin should be potentially the brightest emitter at this wavelength. The transitions responsible in tin arise from n=4-n=4 lines from stages VIII through XIII that merge to form an unresolved transition array (UTA). If the tin concentration is reduced to 10%, the peak brightness increases due to enhanced radiation transport at lower density. Furthermore, if the remaining 90% of the constituents are low Z materials the radiation emitted is concentrated in a band 1-2-nm wide centred near 13.5 nm. The extreme brightness of these features is a direct result of the transfer of oscillator strength from the continuum 4d- ef resonance known to dominate the EUV absorption of the neutral and low ion stages to discrete 4d-4f transitions

[en] The photoabsorption spectra of Ba IV-Ba VI have been recorded using the dual laser plasma technique. Discrete structure due to 4d → 5p transitions has been observed in the 75-85 eV region and identified using Hartree-Fock with configuration interaction calculations. The excited states decay by autoionization involving ejection of 5s or 5p electrons and rates for the different processes and resulting linewidths were also calculated. From these calculations, synthetic spectra were produced and show excellent agreement with the experimental data

[en] Extreme ultraviolet lithography schemes for the semiconductor industry are currently based on coupling radiation from a plasma source into a 2% bandwidth at 13.5 nm (91.8 eV). In this paper, we consider the case for a laser-produced plasma (LPP) and address the calculation of ionic level populations in the 4p⁶4d^N, 4p⁶4d^N-14f¹, 4p⁵4d^N+1, and 4p⁶4d^N-15p¹ configurations in a range of tin ions (Sn⁶⁺ to Sn¹³⁺) producing radiation in this bandwidth. The LPP is modeled using a one-dimensional hydrodynamics code, which uses a hydrogenic, average atom model, where the level populations are treated as l degenerate. Hartree-Fock calculations are used to remove the l degeneracy and an energy functional method to calculate the nl level populations involved in n=4-4 transitions as a function of distance from the target surface and time. Detailed data are presented for the tin ions that contribute to in-band emission

[en] This paper reviews the current practice in the published sources for the production of rare earths, describing the mineralogy and beneficiation techniques employed at these plants and the underlying chemistry. GBM have reviewed and summarised over a dozen published processes from SEDAR(1) and other sources. This paper assumes the reader is familiar with common techniques in comminution and beneficiation and focusses on aspects that are unique to rare earth projects. Since the reports used are preliminary in nature, the processes detailed within are subject to change as more advanced test work is carried out. Despite this, the reports do show that the processes have the ability to economically extract rare earths from their minerals. Of the thirteen projects reviewed, the most common processing methods are: Physical beneficiation by flotation (used in eight projects); Acid or alkali cracking of the concentrate at elevated temperatures prior to leaching (used in eight projects); Leaching to separate the rare earths from their host mineral. All thirteen projects use leaching. Seven projects use a water leach following an acid or alkali crack, with the remainder using an acid or alkali leach; Precipitation from solution. The rare earth elements are then most commonly precipitated from solution as carbonates, via addition of sodium carbonate (used in seven of the thirteen projects). Despite these common unit operations, no two flowsheets are identical, highlighting the variations required to accommodate site specific mineralogy.

[en] Efficiency optimization of a stable and debris free plasma source at 13.5 nm, is at the forefront of current extreme ultraviolet lithographic (EUVL) research efforts. To date, 1-2.5% soft x-ray conversion efficiencies (CEs) within a 2% bandwidth (BW) around 13.5 nm and into 2π steradians have been attained experimentally for laser-produced plasmas containing Sn at power densities of 0.5-5 x 10¹¹ W cm^-2. In order to complement these experimental endeavours, we have undertaken to study the CE, for the given wavelength regime, in the optically thick limit. We have achieved this by coupling time-dependent and steady-state collisional-radiative (CR) equations to the output of the one-dimensional hydrodynamic code MED103 (MEDUSA), where a solid sphere of radius 50 μm was uniformly irradiated by a high intensity laser pulse with a Gaussian temporal profile. The ion populations obtained from these CR results were then used in an integrated spatio-temporal figure of merit (FOM) together with in-band weighted dipole oscillator strengths and transition energies. The maximum FOM, when divided by the laser energy, was found to occur in the range of peak power densities of 2-3 x 10¹¹ W cm^-2 for the steady-state and time-dependent models, respectively. The hydrodynamic variables of these peak power densities were then used in a radiative transfer calculation in which the many-celled spherical plasma was treated as a multi-component blackbody. It is found that CEs of 3.5-6% within the 2% BW per 2π steradians may be achieved. These results are of particular relevance to EUVL technologies where a minimum CE of 3% is required by industry

[en] One key aspect in the drive to optimize the radiative output of a laser-produced plasma for extreme ultraviolet lithography is the radiation transport through the plasma. In tin-based plasmas, the radiation in the 2% bandwidth at 13.5 nm is predominantly due to 4d-4f and 4p-4d transitions from a range of tin ions (Sn⁷⁺ to Sn¹²⁺). The complexity of the configurations involved in these transitions is such that a line-by-line analysis is, computationally, extremely intensive. This work seeks to model the emission profiles of each ion by treating the transition arrays statistically, thus greatly simplifying radiation transport modeling. The results of the model are compared with experimental spectra from tin-based laser-produced plasmas

[en] We use numerical simulations to investigate the spin Hall effect in quantum wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We find that the intrinsic spin Hall effect is highly anisotropic with respect to the orientation of the wire, and that the nature of this anisotropy depends strongly on the electron density and the relative strengths of the Rashba and Dresselhaus spin-orbit couplings. In particular, at low densities, when only one subband of the quantum wire is occupied, the spin Hall effect is strongest for electron momentum along the [1-bar 10] axis, which is the opposite of what is expected for the purely 2D case. In addition, when more than one subband is occupied, the strength and anisotropy of the spin Hall effect can vary greatly over relatively small changes in electron density, which makes it difficult to predict which wire orientation will maximize the strength of the spin Hall effect. These results help to illuminate the role of quantum confinement in spin-orbit-coupled systems, and can serve as a guide for future experimental work on the use of quantum wires for spin-Hall-based spintronic applications. (paper)