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In-situ ion irradiation and transmission electron microscopy has been used to examine the effects of the He appm to DPA ratio, temperature and dose on the damage structure of tungsten (W). Irradiations were performed with 15 or 60 keV He+ ions, achieving He-appm/displacements per atom (DPA) ratios of ∼40,000 and ∼2000, respectively, at temperatures between 500 and 1000°C to a dose of ∼3 DPA. A high number of small dislocation loops with sizes around 5–20 nm and a He bubble lattice were observed for both He-appm/DPA ratios at 500°C with a bubble size ∼1.5 nm. Using the g.b=0 criterion the loops were characterised as b = ±1/2<111> type. At 750°C bubbles do not form an ordered array and are larger in size compared to the irradiations at 500°C, with a diameter of ∼3 nm. Fewer dislocation loops were observed at this temperature and were also characterised to be b = ±1/2<111> type. At 1000°C, no dislocation loops were observed and bubbles grew as a function of fluence attributed to vacancy mobility being higher and vacancy clusters becoming mobile.
We discuss two themes from Chandra cluster observations. First, we describe the interaction of buoyant, radio emitting plasma bubbles with the hot intracluster gas. Second we summarize the Chandra observations of “cold” fronts (sharp discontinuities in gas density and temperature) separating cool, denser gas clouds from the hotter intracluster medium.
To review our experience of cochlear implant failure and subsequent revision surgery, and to illustrate the experience we have gained by presenting a series of lessons learned.
A combined retrospective and prospective study of revision surgery in a UK regional cochlear implant centre.
Of the 746 cochlear implantations undertaken, 33 (4.7 per cent of adults and 4.1 per cent of children) had a registered failure requiring re-implantation. The mean time to device failure was 60 months in adults and 35 months in children. Causes of cochlear implant failure were medical (n = 11), electrode displacement (n = 2), ‘hard device failure’ (n = 15) and ‘soft device failure’ (n = 5). Chronic suppurative otitis media and post-auricular mastoid abscess were the commonest causes of medical failure. There was one case of electrode array displacement as a direct result of skin flap revision surgery. In 80 per cent of cases, audiological performances were stable or improved following re-implantation.
As the number of cochlear implants increase and patients outlive the lifespan of their devices, we will face a growing number of revision procedures. Audiologists and otologists should be competent in diagnosing and managing device failure and medical complications requiring cochlear re-implantation.
Adaptation, speciation and extinction
A. Donnelly, Trinity College Dublin, Ireland,
A. Caffarra, Istituto Agrario San Michele all'Adige, Italy,
E. Diskin, Trinity College Dublin, Ireland,
C. T. Kelleher, National Botanic Gardens, Glasnevin, Dublin, Ireland,
A. Pletsers, Trinity College Dublin, Ireland,
H. Proctor, Trinity College Dublin, Ireland,
R. Stirnemann, Trinity College Dublin, Ireland,
M. B. Jones, Trinity College Dublin, Ireland,
J. O'Halloran, University College Cork, Ireland,
B. F. O'Neill, Trinity College Dublin, Ireland,
J. Peñuelas, Campus Universitat Autònoma de Barcelona, Spain,
T. Sparks, Technische Universität München, Germany and Institute of Zoology, Poznań University of Life Sciences, University of Cambridge, UK
The impact of climate change, in particular increasing spring temperatures, on life-cycle events of plants and animals has gained scientific attention in recent years. Leafing of trees, appearance and abundance of insects, and migration of birds, across a range of species and countries, have been cited as phenotrends that are advancing in response to warmer spring temperatures. The ability of organisms to acclimate to variations in environmental conditions is known as phenotypic plasticity. Plasticity allows organisms to time developmental stages to coincide with optimum availability of environmental resources. There may, however, come a time when the limit of this plasticity is reached and the species needs to adapt genetically to survive. Here we discuss evidence of the impact of climate warming on plant, insect and bird phenology through examination of: (1) phenotypic plasticity in (a) bud burst in trees, (b) appearance of insects and (c) migration of birds; and (2) genetic adaptation in (a) gene expression during bud burst in trees, (b) the timing of occurrence of phenological events in insects and (c) arrival and breeding times of migratory birds. Finally, we summarise the potential consequences of future climatic changes for plant, insect and bird phenology.
The recent resurgence of interest in phenology (the timing of recurring life-cycle events in plants and animals) has stemmed from research on the impact of climate change, in particular, global warming.
Nanoindentation was used to assess the mechanical properties of lamellar and interlamellar tissue in dehydrated rabbit cancellous bone. The effects of surface roughness and maximum nanoindentation load on the measured mechanical properties were examined in two samples of differing surface roughness using maximum loads ranging from 250-3000 μN. As the ratio of indentation depth to surface roughness decreased below approximately 3:1, the variability in material properties increased substantially. At low loads, the indentation modulus of the lamellar bone was approximately 20% greater than that of the interlamellar bone, while at high loads the measured properties of both layers converged to an intermediate value. Relatively shallow indentations made on smooth surfaces revealed significant differences in the properties of lamellar and interlamellar bone that are consistent with microstructural observations of lamellar bone as more mineralized than interlamellar bone.
We report electron microscopy studies of nanoparticles ( 500 ≤ n ≤ 104, where n is the number of atoms in a given cluster) that are sputtered from the surface by high-energy ion impacts. Measurements of the sizes of these clusters yielded an inverse power-law distribution with an exponent of –2 that is independent of irradiating ion species and total sputtering yield. This inverse-square dependence indicates that these nanoclusters are produced when shock waves, generated by sub-surface displacement cascades, impact and ablate the surface. Such nanoparticles consist of simple fragments of the original surface, i.e., ones that have not undergone any large thermal excursion. As discussed below, this “ion ablation” technique should therefore be useful for synthesizing nanoparticles of a wide variety of alloy compositions and phases.
Fetal sensitivity to radiation-induced health effects is related to gestational age, and it is highly dependent on fetal dose. Typical fetal doses from diagnostic radiology are usually below any level of concern. Although rare, significant fetal radiation doses can result from interventional medical exposures (fluoroscopically guided techniques), radiation therapy, or radiological or nuclear incidents, including terrorism. The potential health effects from these large radiation doses (possibly large enough to result in acute radiation syndrome in the expectant mother) include growth retardation, malformations, impaired brain function, and neoplasia. If exposure occurs during blastogenesis (and the embryo survives), there is a low risk for congenital abnormalities. (In all stages of gestation, radiation-induced noncancer health effects have not been reported for fetal doses below about 0.05 Gy [5 rad].) The additional risk for childhood cancer from prenatal radiation exposure is about 12% per Gy (0.12%/rad) above the background incidence.
(Disaster Med Public Health Preparedness. 2011;5:62-68)
Recent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10-3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.
Hard carbon films have been deposited onto room-temperature silicon substrates in a de plasma of methane and hydrogen. The substrates are placed on the cathode. A stainless mesh is held at the same potential as the cathode and is set above the substrates. Although the deposited films are amorphous and contain 24.4 atomic percent hydrogen, they have the following diamondlike properties: hardness is almost equivalent to that of natural diamond; electrical resistivity is on the order of 1013Ωcm; chemical inertness is excellent to acids; thermal diffusivity is 5.2 cm2 /sec. However, the films have a large compressive stress of 1.3×1010 dyn/cm2.
Annealed films exhibit dehydrogenation, graphitization, an increase in chemical reactivity, volume expansion and stress relaxation above 400°C. The activation energy for the transformation from the diamondlikephase to the graphitic phase is 18 kcal/mole.
The dependence of the thermal diffusivity and hydrogen content on both the CH4/H2 gas mix ratio and the total pressure have been measured for the films deposited in a dc plasma without the mesh.
Electrically conducting palladium features have been produced by laser and ion beam irradiation of thin palladium acetate films. The photothermal reaction induced by scanned continuous wave Ar+ laser irradiation leads to metal lines that may exhibit periodic structure. This results from repeated propagation of “explosive” reaction fronts generated by coupling of the heat from the absorbed laser radiation with the heat of the decomposition reaction of the film. In contrast, 2 MeV He+ ion irradiation produces smooth metallic-looking features that contain up to 20% of the original carbon and 5% of the original oxygen content of the film. Films irradiated with 2 MeV Ne+ ions contain slightly lower amounts of carbon and oxygen residues, but fully exposed thick films (0.90 μm) appear black rather than metallic silver. In addition to having significantly higher purity, the laser-written features have lower resistivities than the ion beam-irradiated features. Infrared spectroscopy of the ion beam-irradiated films as a function of dose indicates a progressive loss in intensity of the characteristics acetate (COO-) vibrations. This occurs at doses lower than those associated with major C and O loss from the films. Partially ion-exposed films continue to decompose to metallic-looking material over a period of weeks after irradiation. Metallic palladium particles apparently catalyze this process.
This study describes the application of a dc-plasma to stimulate growth of InP in a MOCVD system using In(C2 H5)3 and PH3. Precracking of PH3 enables a substantial reduction of the growth temperature to well below 500 K. In addition, at temperatures where InP is commonly deposited (∼870 K) a significant lowering of the V/III input ratio is possible. The fact that InP is relatively insensitive to low energy ion bombardement permits deposition in a canal ray configuration.
The deep ultraviolet (250 nm) photopatterning of spin-on films of polymeric Au mercaptide results in formation of adherent Au patterns. Fxcimer laser projection patterning and standard contact printing techniques give excellent pattern resolution on the micron scale. Laser direct write produces lines at very fast writing speeds. Exposed areas are less soluble than unexposed areas, i.e. the film behaves as a negative photoresist. Bakeout of developed patterns at 250°C yields good purity Au micropatterns up to 500 Å thick. Mechanistic information about pattern formation is gained from uv-visible, infrared, and mass spectrometric monitoring of the photolysis process, and from Auger analysis of films. Adherent patterns are apparently formed by photochemical cleavage of Au-S bonds followed by evaporation of a small amount of free mercaptide. The loss of ligand in the exposed areas renders them less soluble than unexposed film. Thermal decomposition of both photolyzed and unphotolyzed films has the same result of volatilizing all film material except Au.
The general utility and selectivity of photochemical dry etching processes which require direct participation of photogenerated carriers is largely determined by the electronic properties of the semiconductor. The laser which is used to produce the carriers responsible for etching can also provide in situ measurement of some of the important electronic properties which influence the etching process.
Fine conducting features have been produced on Si and SiO2 substrates by irradiation of spin-on palladium acetate, [Pd(O2CCH3)2]3 films with a submicron focused ion beam. The exposures were made with a 20 keV Ga+, focused to a 0.2 micrometer spot. Electrical conductivity measuremnents were made on the resultant features as a function of ion dose for linewidths of one and ten micrometers. The sheet conductivity in the two cases was comparable and increased dramatically in the dose range between 2×1014 and 5×1014 ions/cm2. The conductivity of the exposed lines was further increased after heating in a hydrogen atmosphere. Measurements of carbon and oxygen content indicate that even at the highest ion doses a significant amount of organic material remains. Results are compared to those for 2 MeV He+ and Ne+ broad beam exposures. Potential applications are also discussed.
Very rapid room-temperature photochemical etching of n-type GaAs was achieved in aqueous hydrofluoric acid in conjunction with ultraviolet laser illumination. The etch rates of ˜500 μm/min represent an order of magnitude increase in etch rates over previously reported results for solutions that contained no hydrofluoric acid. Furthermore, incorporation of nitric acid into the hydrofluoric acid solution resulted in smooth etched surfaces thus allowing deep, waveguiding etching. This rapid process was used to etch deep, large-area structures in GaAs samples.
Chlorine-enhanced GaAs maskless etching using a novel focused-ion-beametching (FIBE) system has been examined for establishing high-rate and smooth FIBE. The system is composed of an air-locked ultrahigh-vacuum chamber, a 30 KeV Ga+ FIB column and two kinds of chlorine-irradiation nozzles. A fine nozzle enabled us to irradiate a high-density Cl2 flux on a desired, small area of the sample while retaining a sufficiently low surrounding-gas pressure for stable Ga+ FIB emission. Highly chemically-enhanced sputtering yields (up to 50 GaAs molecules per incident ion) were obtained. At the maximum yield, line-scanned deep-groove (6.5 um) etching with a smooth surface, capable of fabricating a laser-cavity optical mirror, was demonstrated. The chemical-enhancement effect showed high FIB-scanning-time dependence. This effect was also observed by irradiating with a plasma-dissociated Cl radicals using a novel radical beam gun. An analytical model, based on the Ga+-ion bombardment on the chlorine-adsorbed substrate surface, suggested that the maximum chemical enhancement is obtained when the Ga+-FIB scanning time is adjusted to the chlorine-coverage time, given by the Cl2-molecule or Cl-radical flux density.
We investigate the nature of the electronic transitions which lead to the desorption of ions from adsorbate-covered metal and semiconductor surfaces. F+ desorption from F/Si occurs via a Knotek-Feibelman mechanism, while H+ desorption from H/Si and O+ from CO/metals involve multi-electron transitions. The desorption of CO+ from CO/metals and NO+ from NO/Si apparently occurs via a simple Menzel-Gomer-Redhead mechanism.
AℓN deposited by D.C. triode sputtering and spin-on, phosphorus-doped glass (PSG) layers on GaAs and InP were investigated as encapsulants. These films have similar expansion coefficients to both GaAs and InP, minimizing the amount of strain induced in the near-surface region of the underlying wafer. We have quantified this effect by direct measurements of the stress in the films and by using secondary ion mass spectrometry profiling to measure the redistribution of Cr and Fe in encapsulated GaAs and InP respectively during high temperature processing. The dopant redistribution is considerably less for the AℓN and PSG films compared to the more conventional SiO2 and Si3N4 layers. The interaction of the films with the substrate at elevated temperatures is minimal as determined by Auger profiling and the electrical properties of the surface after removal of the encapsulants. The composition of the films remains essentially constant after annealing, as measured by Rutherford backscattering, and the thickness uniformity over large wafer diameters (2″) can be excellent with close control of the deposition parameters. The activation characteristics of low dose, Si-implanted layers in GaAs using either PSG or AℓN are comparable to those obtained using capless annealing or SiO2 or Si3N4 encapsulation.
Synthesis of diamond thin-films has been tried by an ArF excimer laser-induced chemical vapor deposition (LCVD) technique, using acetylene diluted with hydrogen as a source gas and a silicon wafer as a substrate. In these experiments, irradiation geometry, substrate temperature and laser power density were varied. Upon irradiation by a focused laser beam, deposition of diamond on substrates heated above 400°Cwas observed, and was confirmed by reflection electron diffraction (RED) photographs. Homogeneity of the diamond films was improved by irradiation parallel to the substrate. These facts suggest that the formation of diamond proceeds through multiple photon decomposition of the reactant gas, and that electronic excitation of gas phase rather than that of substrate or adsorbate layer is essential to form diamond.