Line of sight techniques: Providing an inventory of all species arriving at and departing from a surface

Abstract

Articles you may be interested inElectron induced dissociation of trimethyl (methylcyclopentadienyl) platinum (IV): Total cross section as a function of incident electron energy Adsorption and reaction of methanol on clean and oxygen modified rhodium/vanadium surface alloys Line of sight ͑LOS͒ techniques comprise those methods in which species emanating from a surface ͑atoms, molecules, and radicals͒ undergo just a single pass through the ionization volume of a mass spectrometer before being pumped. This is achieved by enclosing the mass spectrometer within a cryoshield fitted with appropriate apertures, such that line of sight is established only between a patch on the sample surface ͑Ϸ7 mm diameter͒ and the ionization volume. All LOS techniques are free from extraneous signals and have approximately equal detection probabilities for all species. Line of sight temperature programmed desorption, sticking probability ͑LOSSP͒, and product desorption ͑LOSPD͒ provide powerful and reliable ways of studying all aspects of surface kinetics, by allowing an inventory of all species arriving at and departing from a surface, for any combination of partial pressures, surface temperature, surface composition, and surface structure. Here we illustrate LOSSP and LOSPD using the reactions of 1-bromo-2-chloroethane, BrCH 2 CH 2 Cl,͑BCE͒ and iodotrifluoromethane, CF 3 I, on Cu͑111͒. For BCE we show that there is a 1:1 correspondence of product ethene to reactant BCE during dissociative adsorption at TϾ253 K, and that the dissociative adsorption is nonactivated with a transition state 11Ϯ2.5 kJ mol Ϫ1 below zero ͑0ϭmolecule at infinity͒. For CF 3 I dissociative adsorption occurs at room temperature with a sticking probability of 0.96Ϯ0.02 to produce CF 2 • which can either desorb as gaseous CF 2 • radicals ͑observed͒ or undergo a coupling reaction and then desorb as gaseous C 2 F 4 ͑also observed͒. No other gas phase products were observed.

Controllable deformation of silicon nanowires with strain up to 24%

“…Additionally, the small diameter of the nanowires could possibly allow for dislocations to be "annealed" out of a structure by diffusing to the perimeter. 21 Unlike these studies, 21,22 since our deformation only occurred within the PMMA layer while the uncovered region remained unaffected, it was impossible to perform an in situ HRTEM on the strained region to atomistically quantify the deformation as either elastic or plastic. However, to SEM resolution each pillar appeared to undergo a macroscopically elastic deformation, returning to its original position after being freed from the PMMA even after several tens of bending and unbending cycles.…”

“…Furthermore, these values fall within the range of reported values for strain in silicon nanowires under fracture-free polymerization incited deformation. 21,22 Possible mechanisms that could allow such extreme behavior have been studied previously [14][15][16] and rely on the relatively small volumes of nanowires resulting in the fabrication of statistically "defectfree" structures that lack sites for fracture nucleation. Additionally, the small diameter of the nanowires could possibly allow for dislocations to be "annealed" out of a structure by diffusing to the perimeter.…”

“…[14][15][16][17][18][19] Specifically silicon nanowires can demonstrate yeild strength as well as total strain much greater than bulk silicon. 20,21 In two notable studies 21,22 grown silicon nanowires were shown to have an elongation ratio of 125% and a maximum strain of 21.5% without failure. Furthermore previous efforts have utilized the length contraction of polymerization to apply significant forces to induce elongation, buckling, and bending of silicon nanowires and carbon nanotubes.…”

“…Furthermore previous efforts have utilized the length contraction of polymerization to apply significant forces to induce elongation, buckling, and bending of silicon nanowires and carbon nanotubes. [21][22][23] However, common limitations shared by these approaches are the use of grown nanowires or nanotubes resulting in stochastically distributed structures 21,23 as well as the permanence of the deformed position achieved by the nanowire or nanotube.…”

A solution processable fluorene-benzothiadiazole small molecule for n-type organic field-effect transistors

“…1 In addition, n-type semiconductors based on perylene diimide or naphthalene diimide frameworks have been studied with OFETs comprised of evaporated films having high electron mobilities and ambient stability. [2][3][4][5] In this current work we report the n-type organic semiconductor properties of ͓2-͕͑7-͑9,9-di-n-propyl-9H-fluoren-2-yl͖benzo͓c͔͓1,2,5͔thiadiazol-4-yl͒methylene͔malononitrile ͑K12͒, Fig. 1͑a͒.…”