197 research outputs found
Reagan’s innovation dividend? Technological impacts of the 1980s US defense build-up
No full textUS government spending since World War II has been characterized by large
investments in defense related goods, services and R&D. In turn, this means that the
Department of Defense (DoD) has had a large role in funding corporate innovation in the
US. This paper looks at the impact of military procurement spending on corporate
innovation among publicly traded firms for the period 1966-2003. The study utilizes a
major database of detailed, historical procurement contracts for all Department of
Defense (DoD) prime contracts since 1966. Product-level spending shifts – chiefly
centered around the Reagan defense build-up of the 1980s – are used as a source of
exogenous variation in firm-level procurement receipts. Estimates indicate that defense
procurement has a positive absolute impact on patenting and R&D investment, with an
elasticity of approximately 0.07 across both measures of innovation. In terms of
magnitudes, the contribution of defense procurement to innovation peaked during the
early Reagan build-up, accounting for 11.4% of the total change in patenting intensity
and 6.5% for R&D. This compares to a defense sector share in output of around 4%. The
later defense cutbacks under Bush Senior and Clinton then curbed the growth in
technological intensity by around 2%
Methanol adsorption on Si(111)-(7x7), investigated by core-line photoemission and mass spectrometry of photodesorbed ions
No full textDeuterated methanol adsorption on Si(111)-(7 x 7) has been studied by C Is and O Is core-line synchrotron radiation photoemission and mass spectrometry of photodesorbed ions. Experiments were performed as a function of coverage and temperature. Two different C Is photoemission peaks hint at two different adsorbed species, the first one related to the methoxy fragment produced after dissociative adsorption, the second one is attributed to a CD, species. Both peaks disappear after heating at 350 degrees C, though the methoxy species is more reactive, and a third peak appears. The nature of the species producing the third peak was deduced by means of the mass spectra after heating the sample at 400 degrees C and attributed to C dispersed on the silicon surface
Initial stage of NO adsorption on Si(100)-(2 x 1) studied by synchrotron radiation photoemission and photodesorption
No full textThe NO adsorption on the Si(100)-(2 x 1) surface was investigated by synchrotron radiation photoemission and photodesorption in the energy ranges including the valence band and the Si 2p, N 1s and O 1s core levels. The study was performed both ass function of NO exposure and as a function of temperature in the range 20-300 K. The photoemission experiments show clear evidence of a dissociative adsorption process both at room temperature as well as at temperatures as low as 20 K. Furthermore, the silicon surface states are involved in the adsorption process. The core level spectroscopy shows a complex adsorption pattern of the atomic species, which might involve a sub-surface migration of nitrogen atoms. The photodesorption yields only O+ in the Si 2p and O Is energy ranges. No nitrogen ion desorption is detected. In the Si 2p energy range the O+ photodesorption pattern follows the enhanced secondary electron yield when crossing the ionization threshold. In the O Is energy range the O+ photodesorption pattern is interpreted in terms of a partial sub-surface migration of oxygen atoms. (C) 2000 Elsevier Science B.V. All rights reserved
Different role of filled and empty surface states in a polyfunctional molecule adsorption: Geranyl acetone on Si(111)7x7
No full textNew perspectives in molecular electronics are opening up through controlled surface molecular synthesis. The first step of such a synthesis implies the adsorption of a polyfunctional molecule, which might use one functional group for the surface adsorption, and the other one(s) for further reactions. Here we present an adsorption study of Si(111)7x7 of geranyl-acetone (C13H22O, E-5,9 undecadien-one) characterized by a ketone and two unconjugated double bonds. The study has been performed by temperature and coverage dependent valence band photoemission and room temperature scanning tunneling microscopy. The use of these combined techniques allows us to infer that the interaction between the geranyl acetone and the silicon surface occurs selectively through the rest atom and the carbonyl group, most likely through the oxygen atom. The geranyl acetone does not undergo any fragmentation upon adsorption Si(111)7x7, as has been observed for smaller molecules on the same surface {acetaldehyde [Y. Bu, J. Breslin, M. C. Lin, J. Phys. Chem. B 101, 1872 (1997)] for instance}. The interaction of the chain with the surface is weak and is characterized in the STM images as a darkening of one adatom in positive bias, around the reacted rest atom. (C) 2002 American Institute of Physics
Études régionales : Mégare. G. Despinis, Μεγαρικά (= Megarika) Nills Hellner, Η «κρήνη του Θεαγένους» στα Μέγαρα. Ιστορία και αρχιτεκτονική ενός μνημείου του 5ου αι. π. Χ. (= La «fontaine de Théagène» à Mégara. Histoire et architecture d’un monument du 5e s. av. J.-C.)
No full textDoukellis Panagiotis N. Études régionales : Mégare. G. Despinis, Μεγαρικά (= Megarika) Nills Hellner, Η «κρήνη του Θεαγένους» στα Μέγαρα. Ιστορία και αρχιτεκτονική ενός μνημείου του 5ου αι. π. Χ. (= La «fontaine de Théagène» à Mégara. Histoire et architecture d’un monument du 5e s. av. J.-C.). In: Dialogues d'histoire ancienne, vol. 37, n°2, 2011. p. 250
Photon-stimulated desorption of methanol on Si(111)7 x 7 and Si(100)2 x 1 at the C 1s and O 1s thresholds
No full textSynchrotron radiation photoemission and photostimulated desorption of deuterated methanol on Si(111)7 × 7 and Si(100)2 × 1
No full textDeuterated methanol adsorption on Si(111)7 × 7 and Si(100)2 × 1 surfaces has been investigated, at room temperature, by synchrotron radiation photoemission and photostimulated desorption. Photoemission experiments as a function of methanol coverage show that deuterated methanol adsorption is dissociative on both surfaces and occurs via σO-D bond breakage and σSi-O bond formation. Site selectivity is displayed by the methoxy species on Si(111)7 × 7 surface, since the S2 surface state related to the rest atoms is quickly quenched upon low coverage adsorption. The S1 surface state is quenched only subsequently at much higher coverages. The photostimulated desorption pattern is similar for the two surfaces and strongly depends on the investigated energy range. D+ is always the most abundant ion produced, but higher mass fragments are present too in the energy range including the C Is threshold, where multiple desorption processes are possibly taking place
Études régionales : Mégare. G. Despinis, Μεγαρικά (= Megarika) Nills Hellner, Η «κρήνη του Θεαγένους» στα Μέγαρα. Ιστορία και αρχιτεκτονική ενός μνημείου του 5ου αι. π. Χ. (= La «fontaine de Théagène» à Mégara. Histoire et architecture d’un monument du 5e s. av. J.-C.)
No full textDoukellis Panagiotis N. Études régionales : Mégare. G. Despinis, Μεγαρικά (= Megarika) Nills Hellner, Η «κρήνη του Θεαγένους» στα Μέγαρα. Ιστορία και αρχιτεκτονική ενός μνημείου του 5ου αι. π. Χ. (= La «fontaine de Théagène» à Mégara. Histoire et architecture d’un monument du 5e s. av. J.-C.). In: Dialogues d'histoire ancienne, vol. 37, n°2, 2011. p. 250
Toluene adsorption on Si(111)7 x 7 studied by synchrotron-radiation photoemission
No full textThe toluene adsorption oil Si(1 1 1)7 x 7 was studied by valence band synchrotron-radiation photoemission at roorn temperature as a function of exposure and time. We found that the adsorption process occurs preferentially on rest atoms and that toluene adsorption is time dependent, since the adsorption features disappear and the rest atoms related feature re-appears as a function of time. The features time evolution is quadratic, hinting at a thermal desorption process. The high desorption rate allows us to rule out a dissociative adsorption involving the methyl group, Our conclusion is that toluene is molecularly pi-bonded through the aromatic electrons on silicon rest atoms. (C) 2001 Published by Elsevier Science B.V
Photon-stimulated desorption and fragmentation processes: formic acid on Si(111)7x7
No full textA photon-stimulated desorption (PSD) process consists of the production of ions and neutrals upon irradiation with light of proper wavelength. Here, we present a short review on the PSD mechanisms and the parameters influencing it, such as the adsorbate-substrate coupling, the light polarization, the surface orientation, the temperature, the mass of the leaving fragments as well as the co-adsorption effects. Furthermore, as an example, we will present a PSD investigation of formic acid on Si(111)7 x 7 in the energy ranges including the C 1s and the O 1s thresholds. D+, C+, CD+, O+', CO+, DCO+ ions are produced in both energy ranges. The excitation in the C 1s energy range offers a less efficient substrate-mediated quenching with respect to the excitation in the 0 Is one, with a consequent more structured photoexcitation spectrum. In the energy range including the O 1s the transitions to pi*((C=O)) and sigma*((C-D)) levels produce selectively either D+ or CDO+. O+ is produced both by a transition to a pi*((C=O)) level on through a shake-off process, and the remaining fragments are generally produced through secondary electrons. (C) 2002 Elsevier Science B.V. All rights reserved
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