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The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the interaction physics is explored numerically. Diffraction and speckle patterns are measured in the specularly reflected light in the cases of targets with regular groove and needle-like structures, respectively, highlighting the potential to use this as a diagnostic of the evolving plasma surface. It is shown, via ray-tracing and numerical modelling, that for a laser focal spot diameter smaller than the periodicity of the target structure, the reflected light patterns can potentially be used to diagnose the degree of plasma expansion, and by extension the local plasma temperature, at the focus of the intense laser light. The reflected patterns could also be used to diagnose the size of the laser focal spot during a high-intensity interaction when using a regular structure with known spacing.
Two single-nucleotide polymorphisms (SNPs) (rs4281084 and rs12155594) within the neuregulin-1 (NRG1) gene have been associated with psychosis transition. However, the neurobiological changes associated with these SNPs remain unclear. We aimed to determine what relationship these two SNPs have on lateral ventricular volume and white matter integrity, as abnormalities in these brain structures are some of the most consistent in schizophrenia.
Structural (n = 370) and diffusion (n = 465) magnetic resonance imaging data were obtained from affected and unaffected individuals predominantly of European descent. The SNPs rs4281084, rs12155594, and their combined allelic load were examined for their effects on lateral ventricular volume, fractional anisotropy (FA) as well as axial (AD) and radial (RD) diffusivity. Additional exploratory analyses assessed NRG1 effects on gray matter volume, cortical thickness, and surface area throughout the brain.
Individuals with a schizophrenia age of onset ⩽25 and a combined allelic load ⩾3 NRG1 risk alleles had significantly larger right (up to 50%, padj = 0.01) and left (up to 45%, padj = 0.05) lateral ventricle volumes compared with those with allelic loads of less than three. Furthermore, carriers of three or more risk alleles, regardless of age of onset and case status, had significantly reduced FA and elevated RD but stable AD in the frontal cortex compared with those carrying fewer than three risk alleles.
Our findings build on a growing body of research supporting the functional importance of genetic variation within the NRG1 gene and complement previous findings implicating the rs4281084 and rs12155594 SNPs as markers for psychosis transition.
Among dialysis facilities participating in a bloodstream infection (BSI) prevention collaborative, access-related BSI incidence rate improvements observed immediately following implementation of a bundle of BSI prevention interventions were sustained for up to 4 years. Overall, BSI incidence remained unchanged from baseline in the current analysis.
With a population of 34 million and an extremely high reliance on charcoal, Tanzania is a classic example of the social and environmental risks faced by many developing countries. About 85% of the total urban population uses charcoal for household cooking and energy provision for small and medium enterprises (Sawe 2004). In 1992 the total amount of charcoal consumed nationwide was estimated to be about 1.2 million tons (Sawe 2004). In 2002, the charcoal business generated revenues of more than 200 billion TShs (US$ 200 million), with more than 70 000 people from rural and urban areas employed in the industry (TaTEDO 2002b). Dar es Salaam, Tanzania’s largest city, accounts for more than 50% of all charcoal consumed in the country.
The charcoal sector is far from sustainable. The forest resources that the industry is relying on are disappearing rapidly and the productivity of the sector has not seen any improvement either. The charcoal sector in Tanzania is operating economically, socially and environmentally in a suboptimal manner. However, solutions that safeguard the charcoal sector’s future are not straightforward.
The maskless ion implantation with the focused ion beam as a new method for ion beam synthesis of cobalt sulicide wires is presented. In order to perform the implantation a special achromatic mass separator was implemented into the ion column, liquid alloy ion sources for cobalt ions were developed and a substrate heating was built. Ion implantation was performed with 30 keV Co+ and 60 keV Co++ ions. The dose dependence for room temperature implantation and the influence of the substrate temperature were investigated.
We performed a series of dissolution experiments with well-characterized pyrochlore ceramics with the formula A2Ti2O7, where A = Y3+, Gd3+, or Lu3+ in H2O- and D2Obased solutions [pH(D) = 2] at 90°C. Normalized log10 dissolution rates (g·m−2·d−1) in H2O-based solutions increase from Lu2Ti2O7 (−3.2 to –3.3) to Gd2Ti2O7 (−2.6 to –2.9), to Y2Ti2O7 (−1.9 to –2.0). Rates in D20-based solutions are indistinguishable from rates in H2O, indicating that release of elements is probably not diffusion controlled. A recent dissolution model, based on ligand-exchange reactions, suggests that the rate of reaction should increase in inverse order of the cation field strength: Lu < Y < Gd (where the cation denotes the appropriate pyrochlore composition), which is not observed. Evaluation of the thermodynamic stability of the three solids was performed using a linear free-energy model and reported free energies of formation. The calculations indicate that reactivity should follow in the progression Lu < Gd < Y, as observed in the dissolution experiments. Our data indicates, therefore, that dissolution models based on ligand-exchange reactions may not be strictly applicable to simple pyrochlore minerals.
A process for reactive ion etching of 1μm and sub-micron WSi0.6 gates for GaAs MESFET integrated circuits has been developed.Using a CF4/O2 plasma, a 200am film of WSi0.6 could be etched in ≃ 5 minutes.This is sufficiently long for accurate process monitoring.A vertical edge profile has been obtained which is desirable for a self-aligned MESFET process.To achieve the vertical edge, careful control of the degree of over etch was necessary.This was accomplished by monitoring the intensity profile of a laser beam reflected from the wafer being etched.The widths of lines etched in WSi0.6 closely matched those of the resist pattern.Both 1μm and sub-micron FET's were fabricated.with excellent linewidth control and electrical characteristics
Experimental measurements and theoretical modeling of methane deposition plasmas have made it possible to determine the most likely homogeneous and heterogeneous chemical reaction paths leading to deposition of hydrogenated carbon from the fragments of electron dissociated methane.The methane plasma was modeled as a plug-flow reactor.Gas phase reactions, diffusive transport, variable surface reflection coefficients, and surface chemical reactions are included in the model which follows a “plug” of gas as it flows through the reactor.Boltzmann equation and Monte Carlo calculations were used to determine the electron energy distribution and the resulting dissociation and ionization rate coefficients averaged over space and time.Experimental measurements of the time dependent electrical properties of the plasma are used as input to the model.Deposition rates, deposition uniformity, downstream mass spectroscopy, and the dependences of these quantities on power and mass flow rates are compared to the model to arrive at a consistent representation of the deposition chemistry.
The maskless ion implantation with the focused ion beam as a new method for ion beam synthesis of cobalt suicide wires is presented. In order to perform the implantation a special achromatic mass separator was implemented into the ion column, liquid alloy ion sources for cobalt ions were developed and a substrate heating was built. Ion implantation was performed with 30 keV Co+ and 60 keV Co++ ions. The dose dependence for room temperature implantation and the influence of the substrate temperature were investigated.
We have begun a detailed study of the physical properties of Si3 N4 films deposited at low temperatures using a PECVD process based on dilution of reactive gases with inert carrier gas  in order to investigate their feasibility for use as post-implant encapsulants and/or device passivation layers for GaAs. The films and substrates are analyzed by ion channeling, ellipsometry, IR spectrometry, ESR, RBS, and SEM to evaluate implantationinduced substrate and interface damage as well as the films’ optical properties, surface morphology, stoichiometry, uniformity, stress, and electrical trapping characteristics. Following furnace or RTA annealing they are recharacterized, adding SIMS to evaluate As diffusion into the films. Both Schottky and ohmic contacts are then formed and used to measure Hall mobility, trap density and 1/f noise. Preliminary results of these studies are presented and compared with those obtained using other techniques such as wafer-to-wafer As entrapment, arsine overpressure, or conventional CVD.
We have characterized the step coverage and film quality of (tetraethoxysilane) TEOS-based silicon oxides which are directionally deposited on horizontal surfaces of trench features under oxygen-lean conditions in a high frequency (14 MHz) discharge. The film thickness on the sidewalls depends most strongly on the O2 :TEOS feed ratio. Water uptake after ambient exposure was used as a measure of film quality and the amount of water absorbed in the film correlated well with changes in the refractive index and stress. Oxide quality on horizontal surfaces could be improved by decreasing the TEOS feed or increasing the discharge power, but the sidewall oxide quality could not be improved by these methods. Small NF3 additions to the discharge markedly improved sidewall quality, altered the angle between the sidewall and the bottom of trench features from 90° to ˜115° (tapered profile) and increased the deposition rate, while preserving the directionality of deposition.
Ion-beam-induced amorphization in single crystal α-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar+ ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe+ irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation.
Silicon layers evaporated on crystalline Si have been crystallized by Q-switched Nd:YAG laser irradiation. A strong correlation was observed between the density of a-Si films and the quality of the epitaxial regrowth from the liquid phase. Dense films crystallized epitaxially in a wide range of laser energy densities. Layers with 20% lower density, as determined by spectroscopic ellipsometry, had higher crystallization thresholds and suffered from severe pitting of the surface. Coalescence of the excess void volume into microbubbles, stabilized by gaseous contaminants, is responsible for the surface degradation.
In polycrystalline films on amorphous insulating substrates laser melting changes the grain distribution. Rapid melting and solidification of small diameter spots creates concentric rings of large crystallites. This characteristic pattern is explained by a simple model, based on the kinetics of crystallization.
Two techniques have been used to measure the velocity of the amorphous-crystalline boundary during scanned laser crystallization of amorphous Ge films on fused-silica substrates. Values in the vicinity of 200 cm sec-1 have been measured by both methods. The results obtained by the first technique, an optical transmission method, confirm our theoretical model for the periodic motion of the boundary. The measurements made by the second technique, which is based on an examination of the structural features obtained at laser scanning rates up to about 600 cm sec-1 , show the boundary velocity to be rather insensitive to film thickness and background temperature. Controlled crystallization is expected to require stability of the laser beam power.
The growth of high quality amorphous hydrogenated semiconductor films was explored with different in situ spectroscopic methods. Nucleation of ArF laser-induced CVD of a-Ge:H on different substrates was investigated by real time ellipsometry, whereas the F2 laser (157nm) deposition of a-Si:H was monitored by FTIR transmission spectroscopy. The ellipsometric studies reveal a significant influence of the substrate surface on the nucleation stage, which in fact determines the electronic and mechanical properties of the bulk material. Coalescence of initial clusters occurs at a thickness of 16 Å for atomically smooth hydrogen-terminated c-Si substrates, whereas on native oxide covered c-Si substrates the bulk volume void fractions are not reached until 35 Å film thickness. For the first time we present a series of IR transmission spectra with monolayer resolution of the initial growth of a-Si:H. Hereby the film thickness was measured simultaneously using a quartz crystal microbalance with corresponding sensitivity. The results give evidence for cluster formation with a coalescence radius of about 20 Å. Difference spectra calculated for layers at different depths with definite thickness reveal that the hydrogen-rich interface layer stays at the substrate surface and does not move with the surface of the growing film. The decrease of the Urbach energy switching from native oxide to H-terminated substrates suggests a strong influence of the interface morphology on the bulk material quality.
The use of an antireflection oxide film applicable to laser annealing process has been investigated. The optical properties of the antireflection oxide film are changed by ion implantation although the antireflection characteristics are similar to calculations based on nominal optical constants. Implantation annealing can be achieved at powers lower than predicted by calculations. Using the antireflection(AR) technique, n+-p junction diodes were fabricated. Reverse bias junction leakage is around 10-9 A/cm2 , comparable to those annealed thermally. Short channel MOS devices were also fabricated and indicated much better resistance to the short channel effect than those thermally annealed.
Laser processing of amorphous thin films of amorphous Ge often results in an explosive or self-sustaining crystallization reaction. The reaction is sustained by the heat liberated during crystallization. In a theoretical analysis of the process that was presented at this symposium last year, Gilmer and Leamy postulated the existence of a thin layer of liquid at the propagating interface. The liquid layer forms at temperatures above Ta, the melting point of amorphous Ge, and is predicted to be ~ 0.02 – 0.1 of the film thickness in width. We have obtained experimental confirmation of the presence of this liquid layer.
The low energy electron diffraction (LEED) patterns obtained from clean (111) oriented Si, Ge and GaAs single crystals subsequent to their irradiation with the output of a pulsed ruby laser in an ultra-high vacuum (UHV) environment suggest that metastable (1×1) surface structures are produced in the regrowth process. Conventional LEED analyses of the Si and Ge surfaces suggest that they terminate in registry with the bulk but that the two outermost interlayer spacings differ from those of the bulk. For the case of Si these changes are a contraction of 25.5 ± 2.5% and an expansion of 3.2 ± 1.5% between the first and second and second and third layers respectively.
A scanned cw Nd: YAG laser was used to anneal ion-implanted GaAs and InP wafers. Measurements show that electrical activation is greater for p-type than for n-type dopants in GaAs, while in InP, the opposite is observed. A simple Fermi-level pinning model is presented to explain not only the electrical properties we have measured, but also those observed by other workers. We have fabricated GaAs and InP solar cells with junctions formed by ion implantation followed by laser annealing. The GaAs cells have much better conversion efficiencies than the InP cells, and this difference can be explained in terms of the model.
Single crystals of
with 1% Nd substituted for La, were irradiated with 0.8 MeV Ne+
and 1.5 MeV Kr+ ions over the temperature range from 15 K to 773
K. The irradiations were carried out using the HVEM-Tandem Facility at
Argonne National Laboratory. The structural changes and the ion fluence for
complete amorphization were determined by in situ
transmission electron Microscopy. The ion fluence for complete amorphization
increased with temperature in two stages associated with defect annealing
processes. The critical temperature for amorphization increased from -360 K
for 0.8 MeV Ne+ to -710 K for 1.5 MeV Kr+. During
in situ annealing studies, irradiation-enhanced
recrystallization was observed at 923 K. Spatially-resolved fluorescence
spectra of the Nd ion excited with 488.0 nm laser excitation showed marked
line-broadening toward the center of the amorphous regions. Initial
Measurements indicate the subtle shifts of the 9I9/2
groundstate energy levels can be measured by pumping directly into the
excited state 4F3/2 Manifold suggesting that the line
broadening observed originates from a distribution of geometrically
distorted Nd sites.