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As part of a multi-epoch and multi-wavelength study of the physics of core dominated radio sources we have investigated the occurrence of apparent superluminal motion and other indications for bulk relativistic motion (b.r.m) in a statistically complete, flux density limited (S5GHz ≥ 1Jy) sample of 13 objects with flat radio spectra These sources come from the S5-survey (Kühr et al., 1981) and are optically identified as 7 quasars and 6 BL-Lac objects. They have been observed over a wide range of frequencies, from radio through X-rays (s. Eckart et al., 1986 and references therein). Radiomaps have been obtained at frequencies from 327 MHz to 22.2 GHz with resolutions from arcseconds to 0.2 mas, using the VLA, MERLIN and telescopes of the US- and European-VLBI networks. A recent status report on the VLBI-observations is given by Witzel (1987). In this paper we summarize the results on the direct evidence for b.r.m. in this sample as derived from repeated VLBI-observations at 5 GHz, as well as supporting evidence from SSC-calculations and flux density variability of the 5GHz VLBI core components (Table 1).
We present phase resolved spectra of the Be binary ϕ Per. It is shown that orbital phase variations of the He I line profiles are due to a sector emission region in the circumprimary disk facing the secondary. The increasing asymmetry of Fe II emission lines indicates a density inhomogeneity in the circumprimary disk that developed after 1996.
In the wake of the recent terrorist attacks, such as the 2008 Mumbai hotel explosion or the December 25th 2009 “underwear bomber”, our group has developed a technique (US patent #7368292) to apply differential reflective spectroscopy to the problem of detecting explosives in order to detect terrorist threats. Briefly, light (200-500 nm) is shone on a surface such as a piece of luggage at an airport or a parcel at a courier distribution center. Upon reflection, the light is collected with a spectrometer combined with a camera. A computer processes the data and produces in turn a differential reflection spectrum taken between two adjacent areas of the surface. This differential technique is highly sensitive and provides spectroscopic data of explosives. As an example, 2,4,6, trinitrotoluene (TNT) displays strong and distinct features in differential reflectograms near 420 nm. Similar, but distinctly different features are observed for other explosives such as RDX, PETN or ANFO. Our detection system uses a two dimension detector (CCD camera) which provide spatial and spectroscopic information in each of the two dimensions. By scanning (involving fixed optical equipment and scanning moving bags or parcels on a conveyor belt), the surface to be surveyed the system provide the spatial location of the potential threat. We present in this paper how our detector works and how it is applied to the problem of explosive screening for explosives at airports and mail sorting centers. Additionally, we will present the effect of the explosives morphology on the detection response. In particular we will evaluate the implication on the limit of detection of the instrument as well as discuss the sample morphology with respect to a realistic threat scenario.
Possible mechanisms which may explain the strong blue/violet (410 nm) photoluminescence (PL) in spark-processed Si (sp-Si) are critically reviewed and discussed. They include involvement of silicon-oxides, silicon-hydrides, silanol groups, siloxene, and silicon carbide. It is concluded from the experimental evidence that none of the above mechanisms can satisfactorily explain the major contribution(s) to PL in sp-Si.
Porous silicon which has been prepared by a “dry” technique, that is, by spark erosion, yields similar photoluminescence spectra as anodically etched porous silicon which has been prepared in aqueous solutions. Fourier transform infrared spectra reveal that the dominant features in spark eroded silicon are the Si-O-Si stretching mode and the Si-O-Si bending mode. No infrared vibrational modes characteristic for siloxene have been found in spark eroded Si. Results from X-ray and electron diffraction studies suggest that spark eroded Si involves minute polycrystalline silicon particles which are imbedded in an amorphous matrix.
The effects of energetic Ar cluster ion impacts on Si(111) surfaces have been studied for cluster energies up to l5keV. The mean cluster size was about 1000 atoms, and the smaller sizes could be systematically excluded. Si samples irradiated at different cluster ion energies were analyzed by RBS, ellipsometry, and differential reflectometry. Implantation of Ar in samples irradiated with cluster ions was found by RBS to be detectable, but very small in comparison with samples irradiated with monomer ions of the same energy. The thickness of the damage layer as measured by both ellipsometry and differential reflectometry was also much smaller in the cluster ion irradiated samples.
Transparent, nanophase-separated, inorganic-organic hybrid polymers with dielectric constants below 3.0 have been prepared from reactively functionalized poly(amic ester) derivatives and substituted, oligomeric silsesquioxanes. These hybrid materials are stable to 400 °C and above and form tough, crack-free films. Induced cracking and crack propagation studies performed with the application of external stress suggest a maximum critical film thickness of at least 2.0 μm under severe stress conditions. These hybrid materials appear to be significantly toughened by the chemical incorporation of the polyimides relative to organically modified silicates and spin-on-glasses without significantly effecting other important polymer properties of the silicates.
Electrical resistance data were gathered from AI(Cu) VLSI metallization test structures during pulsed DC current stressing (15 mA peak) at elevated temperature (200 °C). Duty cycles of 50%, 67%, and 80% were applied at a frequency (repetition rate) of 133 MHz. Also, a duty cycle of 50% was applied at frequencies of 100 KHz, I MHz, and 133 MHz. The resistance-to-starting resistance ratio, R/Ro, was logged over time, and the data were used to extract the median time dependence of the resistance change. This, in effect, reveals the dependence of the median “failure” time on the R/Ro (or ΔR/Ro) criterion. An “enhancement factor” was defined as the ratio of the median “failure” time from a given pulsed test to that from a DC test with the same peak current. A weak dependence of this enhancement factor on R/Ro was found in the range examined. The degree of enhancement corresponds more closely to the average current density prediction than to the on-time prediction, although there is some small variation according to duty cycle and frequency.
The electromigration resistance, the sub-micron contact area filling capability, the crystal structure, the preferred orientation, and the CMOS device characteristics of self-ion-enhanced physical vapor deposited aluminum metallizations have been studied. It has been found that optimal conditions can be achieved by increasing the deposition rate and by applying some ionization and acceleration of the aluminum particles.
A study of temperature-induced crystallinity changes in fluorinated and nonfluorinated parylene thin films using differential scanning calorimetry, thermal stress and wide angle x-ray diffraction measurements is presented. The nonfluorinated parylene (ppx-N) is shown to undergo two phase transitions between 200°C and 300°C. Both transitions show at least some degree of reversibility. The high temperature (β1 -β2) transition is accompanied by a sudden shift in stress, which is attributed to a contraction of the polymers chains. A single, reversible phase transition, occurring between 360°C and 400°C, is observed for fluorinated parylene (ppx-F). This transition is likewise marked by a significant shift in stress, and is apparently due to a similar chain contraction.
The fluorinated low-k dielectrics SiO:F and Teflon AF were investigated for process integration with aluminum and copper interconnects. To minimize fluorine diffusion, several potential barrier materials were deposited onto the fluorinated dielectrics and characterized after heat treatment at temperatures up to 450°C. The barrier layers studied include conventional materials such as Ta, TaN, and TiN, in addition to several novel materials. Barrier layer materials were deposited using evaporation, and sputtering. The materials were characterized using nuclear reaction analysis (NRA) to determine the fluorine concentration profile. A reaction zone was noted at the dielectric-barrier interface on several samples, corresponding to the formation of a fluoride complex. In some instances, this fluoride layer was self-limiting and prevented further fluorine diffusion through the remainder of the barrier layer.
The industry is strongly interested in integrating low-κ dielectrics with Damascene copper. Otherwise, with conventional materials, interconnects cannot continue to scale without limiting circuit performance. Integration of copper wiring with silicon dioxide (oxide) requires barrier encapsulation since copper drifts readily in oxide. An important aspect of integrating copper wiring with low-κ dielectrics is the drift behavior of copper ions in these dielectrics, which will directly impact the barrier requirements and hence integration complexity.
This work evaluates and compares the copper drift properties in six low-κ organic polymer dielectrics: parylene-F; benzocyclobutene; fluorinated polyimide; an aromatic hydrocarbon; and two varieties of poly(arylene ether). Copper/oxide/polymer/oxide/silicon capacitors are subjected to bias-temperature stress to accelerate penetration of copper from the gate electrode into the polymer. The oxide-sandwiched dielectric stack is used to overcome interface instabilities occurring when a low-κ dielectric is in direct contact with either the gate metal or silicon substrate. The copper drift rates in the various polymers are estimated by electrical techniques, including capacitance-voltage, current-voltage, and current-time measurements. Results correlate well with timeto-breakdown obtained by stressing the capacitor dielectrics. Our study shows that copper ions drift readily into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene. A qualitative comparison of the chemical structures of the polymers suggests that copper drift in these polymers may possibly be retarded by increased crosslinking and enhanced by polarity in the polymer.
This paper reports degradation characteristics of low-k dielectric (FOX) in multi-level metal structures (comb-type capacitors) submitted to moisture stress. A large increase of leakage current (>105) and capacitance (up to ×3) is observed after moisture stress when only FOX is used as lateral dielectric, while moderate degradation takes place when an oxide liner is placed between FOX and metal lines. Enhanced moisture induced degradation is found on previously probed dices with respect to virgin devices. Systematic electrical measurements, combined with SEM analysis, are performed to find out the moisture diffusion path. When contact pads are damaged by previous probing (owing to the mechanical weakness of FOX in the pad stack), they provide a direct entry path for enhanced humidity intake. Humidity is also shown to enter through wafer border. Using a SiO2 liner combined with FOX improves considerably the resistance to moisture degradation.
We have succeeded to prepare high resistivity and rather low dielectric constant amorphous carbon nitride films a-CNx (0.52<x<0.86) by the reactive radio frequency magnetron sputtering of a graphite target using nitrogen molecules as a sputter gas.
The resistivity of a-CNx are 5×1016 to 1017 Ω-cm and be estimated to 1020 Ω-cm, when the ratio of the carbon and nitrogen becomes chemically stoichiometry 3 to 4, i.e. C3N4. The resistivity of a-CNx films prepared by a layer-by-layer method, LL-a-CNx, is 1018 Ω -cm for x=0.6. The layer-by-layer method is a cyclic process of a deposition by the sputtering and an etching by atomic hydrogen. The sample LL-a-CNx made by a layer-by-layer method are compared with that of usual method a-CNx. The dielectric constant of a-CNx films calculated from the refractive index n are 3.6 to 2.8 corresponds to nitrogen contents, 0.52<x<0.86. The dielectric constants ε of a-CNx films decrease with the content of nitrogen x. At an ultimate component of a-CNx, at x=4/3, the dielectric constant is estimated to 1.8.
Parylene-N films vapor deposited near liquid nitrogen temperature (77 K) undergo a unique ‘wave’ polymerization process in which a rapidly moving reaction front is apparent as the film changes from translucent to optically opaque. This moving reaction front produces a highly porous polymer film. The porosity of these films is approximately 80%. By capturing the wave process on video we have quantified the moving ‘wave’ velocity, which averages 11 cm/s. Timeaveraged deposition rates of the resulting opaque, porous films are more than 8 μm/min. This rate is more than two orders of magnitude greater than the measured deposition rates of nonporous films that are deposited at higher temperatures, at otherwise fixed conditions of monomer delivery rate and deposition chamber pressure.