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IR spectroscopy in the range 12–230 μm with the SPace IR telescope for Cosmology and Astrophysics (SPICA) will reveal the physical processes governing the formation and evolution of galaxies and black holes through cosmic time, bridging the gap between the James Webb Space Telescope and the upcoming Extremely Large Telescopes at shorter wavelengths and the Atacama Large Millimeter Array at longer wavelengths. The SPICA, with its 2.5-m telescope actively cooled to below 8 K, will obtain the first spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples. Densities, temperatures, radiation fields, and gas-phase metallicities will be measured in dust-obscured galaxies and active galactic nuclei, sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. Active galactic nuclei and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. The SPICA’s large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of z ~ 6.
Recent archaeological investigations at Pueblo Bonito in Chaco Canyon reveal that residents constructed a large diversion channel during the eleventh century A.D. as dramatic growth resulted in the expansion of the building onto the main valley floor. Sediments in the diversion channel reflect repeated episodes of flooding, rather than slow moving water typically found in irrigation canals, and archaeobotanical data indicate deposition during late summer or early fall. Although an agricultural function is possible, the channel may have been built primarily to divert floodwaters away from Pueblo Bonito while providing a nearby water source for construction and domestic use. The diversion channel was destroyed by the entrenchment of the “Bonito paleo-channel” in the late A.D. 1000s, and then buried by a combination of cultural debris and valley flooding. Although the canyon stream system changed throughout the occupation of Pueblo Bonito, there is no evidence that the formation of a deep natural channel in the floodplain had any negative effect on the growth of the great house
Observations in the 1 µm to 1 cm wavelength band give important information on the physical processes occurring in and immediately around active galactic nuclei. Concentrating on recent results on ionic, atomic, and molecular emission lines, we discuss as examples the first ISO results on the nature of ultra-luminous infrared galaxies, and near-infrared and millimeter measurements of the central 100 parsecs of the Seyfert 2 galaxy NGC 1068.
We discuss 2.5–45 µm spectra of the Circinus galaxy and of Cen A, obtained with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory. The large number of detected ionic fine structure lines, observable also in visually obscured sources, provides strong constraints on the shape of the ionizing spectrum, which is found to exhibit a UV bump peaking at ~ 70 eV in the case of Circinus. Pure rotational emission of molecular hydrogen, directly probing warm molecular gas, can for the first time be detected in external galaxies.
Various AGNs, starburst galaxies, and ultraluminous infrared galaxies (ULIRGs) are observed as part of the ISO-SWS central program of mid-infrared spectroscopy on bright galactic nuclei. Prototypical template sources are scanned over the full spectral range of SWS (2.5–45µm) in order to get a complete census of spectral features in this wavelength domain. As an example we present the spectrum of the Seyfert 2 galaxy Circinus. The application of results from this survey to the study of the nature and evolution of other galaxies can be demonstrated by an analysis of the ultraluminous infrared galaxy Arp 220.
Recent X-ray emission events in the Galactic center would be expected to generate an X-ray reflection response within the surrounding clouds of the central molecular zone, in the Galactic disk and even, if powerful enough, in clouds outside our Galaxy. We review here the current constraints on Sgr A*'s past activity obtained through this method, with particular emphasis on the strong evidence that has been gathered for multiple X-ray flashes during the past few hundred years.
The Herschel Key Project SHINING performs a study of the ISM in star forming and active
infrared bright galaxies (starbursts, AGN, (U)LIRGs, interacting and low metallicity
galaxies) at local and intermediate redshifts. Here we present some surprising and
promising first results from parts of this programme, including spatially resolved PDR
diagnostics, line deficit diagnostics, and large scale molecular outflows traced by the OH
The Herschel Dwarf Galaxy Survey investigates the interplay of star formation activity and the the metal-poor gas and dust of local universe dwarf galaxies using FIR and submillimetre imaging spectroscopic and photometric observations in the 50 to 550 μm window of the Herschel Space Observatory. The dust spectral-energy distributions are well constrained with the new Herschel and MIR Spitzer data. A submillimetre excess is often found in low metallicity galaxies, which, if tracing very cold dust, would highlight large dust masses not easily reconciled in some cases, given the low metallicities and expected gas-to-dust mass ratios. The galaxies are also mapped in the FIR fine-structure lines (63 and 145 μm OI, 158 μm CII, 122 and 205 μm NII, 88 μm OIII) probing the low density ionised gas, the HII regions and photodissociation regions. While still early in the mission we can already see, along with earlier studies, that line ratios in the metal-poor ISM differ remarkably from those in the metal-rich starburst environments. In dwarf galaxies, L[CII]/L(CO) (≥104) is at least an order of magnitude greater than in the most metal-rich starburst galaxies. The 88 μm [OIII] line usually dominates the FIR line emission over galaxy-wide scales, not the 158 μm [CII] line which is the dominant FIR cooling line in metal-rich galaxies. All of the FIR lines together can contribute 1% to 2% of the LTIR. The Herschel Dwarf Galaxy survey will provide statistical information on the nature of the dust and gas in low metallicity galaxies and place constraints on chemical evolution models of galaxies.
The objectives of this study were to determine the incidence density and the occurrence of horizontal spread of highly resistant gram-negative rods (HR-GNRs) in Dutch hospitals. The factors that influence these outcome measures were also investigated.
All patients with HR-GNRs, as determined by sample testing, who were hospitalized in 1 of 18 hospitals during a 6-month period (April through October 2007) were included in this study. For all available isolates, the species was identified, susceptibility was determined (including the presence of extended-spectrum β-lactamases [ESBLs]), and molecular typing was performed. On the basis of a combination of species identification, molecular typing, and epidemiological data, the occurrence of nosocomial transmission was determined.
The mean incidence density of patients with HR-GNRs was 55 per 100,000 patient-days (cumulative incidence, 39 per 10,000 patients admitted). A facility being a university hospital was a statistically significant (P = .03) independent determinant of a higher incidence of patients with HR-GNRs. The majority of HR-GNR isolates were ESBL producers. The adjusted transmission index—the ratio between secondary and primary cases—in the participating hospitals ranged from 0.0 to 0.2. The overall adjusted transmission index of HR-GNRs was 0.07. No determinants for a higher transmission index were identified.
The nosocomial transmission rate of HR-GNRs was relatively low in all hospitals where well-established transmission-based precautions were used. The incidence density of patients with HR-GNRs was higher in university hospitals, probably due to the patient population and the complexity of the care provided.
Experiments were conducted with SiGe film islands on a layer of borophosphorosilicate glass (BPSG). Initially the SiGe is under compression. Upon annealing, the glass flows and the SiGe islands relax by both inplane expansion and wrinkling. This paper provides a two-dimensional (2D) model for inplane expansion. The results from the model are compared with the experiments with small SiGe islands. The effect of winkling, which is ignored in the present model, is discussed qualitatively.
Substitutional carbon is known to locally reduce silicon self-interstitial concentrations and act as a barrier to self-interstitial migration through the carbon rich regions. A silicon spacer between two carbon rich SiGe layers is fabricated in this work to examine self-interstitial generation in a region that is isolated from self-interstitial formation at the surface or in the silicon bulk. Boron marker layers above, below and in between two SiGeC layers are used to monitor the self-interstitial concentration between the substitutional carbon. No evidence of self- interstitial depletion in the silicon spacer is observed, despite annealing in conditions believed sufficient to allow the self-interstitials to reach and react with surrounding substitutional carbon. Simulations of the self-interstitial and carbon indicate that the silicon self interstitial concentration in the spacer layer can be sustained in part due to a silicon self-interstitial recycling process through a reverse “kick-out” reaction.
Hf and Zr incorporation from thermally annealed high-κ gate dielectric thin films (4-5 nm) candidates HfSixOy and ZrSixOy into Si are presented. The dielectric films were subjected either to rapid thermal annealing (RTA) or standard furnace annealing in an N2 atmosphere. After annealing, the films were removed by chemical etching prior to depth profiling using both time of flight secondary ion mass spectroscopy (ToF-SIMS), and Heavy Ion Rutherford Backscattering Spectrometry (HI-RBS) combined with UV-ozone oxidation/etching cycles. As-deposited and annealed films were studied using monochromatic X-ray Photoelectron Spectroscopy (XPS), and high resolution TEM. A Zr incorporation depth after annealing of up to 20 nm into the Si substrate was observed. Depth profiling shows that, although most of the remnant Zr after annealing/etching is located at or near the surface of the Si substrate, incorporation into the substrate is also present. No significant Hf diffusion into Si was observed for either RTP or furnace-annealed films
An advanced FSG film of k=3.4 was developed, which exhibited excellent resistance for moisture absorption. Physical and chemical properties of this advanced FSG film were compared by typical FSG films deposited in both high density plasma (HDP) and PE-CVD reactors, for the same k value.
The advanced FSG film appears to be superior to the HDP-FSG film by a wide margin in the following tests. The moisture absorption rate by TDS (after 4 days of air exposure) is about 5 times lower, the hardness was 1.8 times more, and the hygroscopicity (after 1 hr. boiling) was 2.6 times lower.
We conclude that these differences are mainly due to the unique film structure of the advanced FSG film.
Polycrystalline diamond films previously grown on silicon were polished to an RMS roughness of 15 nm and bonded to the silicon in a dedicated ultrahigh vacuum bonding chamber. Successful bonding under a uniaxial mechanical stress of 32 MPa was observed at temperatures as low as 950°C. Scanning acoustic microscopy indicated complete bonding at fusion temperatures above 1150°C. Cross-sectional transmission electron microscopy later revealed a 30 nm thick intermediate amorphous layer consisting of silicon, carbon and oxygen.
There is a growing interest in the application of large area electronics on curved surfaces. One approach towards realizing this goal is to fabricate circuits on planar substrates of thin plastic or metal foil, which are subsequently deformed into arbitrary shapes. The problem that we consider here is the deformation of substrates into a spherical shape, where the strain is determined by geometry and cannot be reduced by simply using a thinner substrate. The goal is to achieve permanent, plastic deformation in the substrates, without exceeding fracture or buckling limits in the device materials.
Our experiments consist of the planar fabrication of amorphous silicon device structures onto stainless steel or Kapton® polyimide substrates, followed by permanent deformation into a spherical shape. We will present empirical experiments showing the dependence of the results on the island/line size of the device materials and the deformation temperature. We have successfully deformed Kapton® polyimide substrates with 100 [.proportional]m wide amorphous silicon islands into a one steradian spherical cap, which subtends 66 degrees, without degradation of the silicon. This work demonstrates the feasibility of building semiconductor devices on plastically deformed substrates despite a 5% average biaxial strain in the substrate after deformation.
To predict the optical power that could be harvested from light emission that is waveguided in the substrate of organic light emitting devices (OLEDs), a quantitative quantum mechanical model of the light emitted into the waveguided modes has been developed. The model was used to compute the exact distribution of energy in external, substrate and ITO/organic modes as a function of the distance of the emission zone from the cathode. The results are compared to the classical ray optics model and to experiments in two-layer OLED devices. Classical ray optics is found to substantially over-predict the light in waveguided modes.
We have explored the possibility of fabricating a metal base transistor in the Si/CoSi2 material system. Utilizing recent advances in the growth of thin, pinhole free, CoSi2 layers on Si(111) we have measured the transistor characteristics of a Si/CoSi2/Si structure. The observed low common emitter current gain is attributed to an absence of current carrying states in the CoSi2 transistor base.
As-deposited polycrystalline silicon and argon ion laser recrystallized silicon thin film transistors (TFT's) have been fabricated on Corning Code 1729 glass substrates. This novel aluminosilicate glass has an expansion coefficient matched to that of silicon and a chemical durability comparable to that of fused silica. N-channel enhancement mode transistors were made using conventional IC device fabrication procedures (including thermal oxidation to form the gate insulator) modified to have a maximum processing temperature of 800 C. The- polycrystalline silicon TFT's exhibit leakage currents of less than 2x10-11 A/ μm; of channel width and good stability and reproducibility. Transistors made in the recrystallized silicon show field effect electron mobilities as high as 270 cm2/V s, approximately 15 times the mobility of comparable devices made in as-deposited polycrystalline silicon. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do the comparable polycrystalline silicon devices. Major advantages of this TFT technology include the use of a novel, potentially low cost glass substrate and the simultaneous processing of both polycrystalline and recrystallized silicon devices on the same substrate material. This approach represents a new avenue for the incorporation of active devices into a variety of applications including integrated active matrix displays.
Recrystallization of silicon-on-insulator (SOI) films using a line-source electron beam is described. This unique heat source can continuously emit several kilowatts of - 5 keV electrons into a beam 150 mm in length and - 2.5 mm in width, an exposure area which allows processing of 100 mm substrates in a single pass. An attractive aspect of this beam is the ability to control the beam profile, which in turn allows one to influence the thermal gradients present during recrystallization. Using a tightly focussed beam to recrystallize the SOI layer results in a film whose physical properties are generally attributed to films grown with a high thermal gradient at the solidifying liquid-solid interface (highly branched subboundaries with a maximum spacing of - 20 microns and several degrees of angular mismatch.) By reducing the gradient at the growth interface it is possible to achieve unbranched sub-boundaries with over 70 micron spacing and less than 0.5 degrees of out-of-plane tilt misalignment.