Heterostructures for High Performance Devices

Contains an introduction, reports on thirteen research projects and a list of publications.Charles S. Draper Laboratory Contract DL-H-418483DARPA/NCIPT Subcontract 542383Joint Services Electronics Program Contract DAAL03-89-C-0001IBM Corporation FellowshipNational Science Foundation FellowshipVitesse SemiconductorAT&T Bell LaboratoriesHertz Foundation FellowshipNational Science FoundationTRWBelgian American Education Foundation (BAEF) FellowshipNational Science Foundation Grant ECS 90-08485Harvard University. Division of Applied PhysicsAT&T Bell Laboratories FellowshipNational Science Foundation Grant ECS 90-0774

Heterostructures for High Performance Devices

Contains table of contents for Part I, table of contents for Section 1, an introduction, reports on eighteen research projects and a list of publications.Charles S. Draper Laboratories Contract DL-H-418483DARPA/NCIPTJoint Services Electronics Program Contract DAAL03-89-C-0001Joint Services Electronics Program Contract DAAL03-92-C-0001IBM Corporation FellowshipNational Science Foundation FellowshipVitesse SemiconductorGTE LaboratoriesCharles S. Draper LaboratoriesElectronics and Telecommunications Research Institute (ETRI) FellowshipNational Science Foundation/Northeastern UniversityTRW SystemsU.S. Army Research OfficeNational Science FoundationAT&T Bell Laboratories FellowshipNational Science Foundation Grant ECS 90-0774

Design of a Molecular Beam Surface Scattering Apparatus for Velocity and Angular Distribution Measurements

A molecular beam surface scattering apparatus designed for the study of corrosion and catalyticsurfacereactions is described. The apparatus incorporates two molecular or atomic beams aimed at a surface characterized by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES), a rotatable, differentially pumped quadrupole mass spectrometer, and a versatile manipulator. Angular distributions and energy distributions as a funcion of angle and independent of the surface residence time can be measured. Typical data for the oxidation of deuterium to D{sub 2}O on a Pt(lll) crystal surface are presented

Distinctive reactivities of surface-bound H and bulk H for the catalytic hydrogenation of acetylene

We report that both surface-bound H atoms and bulk H atoms, upon moving out from the bulk of a Ni single crystal to its surface of a (111) orientation, are reactive with adsorbed C2H2, but the two kinds of H atoms have unique product distributions. Both bulk H and surface-bound H react with C2H2 to produce adsorbed ethylidyne, CCH3, while only bulk H hydrogenates C2H2 to gas-phase ethylene and ethane, the products of interest in acetylene hydrogenation catalysis for the purification of ethylene streams. Their distinct reactivities arise from both their different directions of approach to the Π orbitals of the unsaturated hydrocarbon and their substantially different energetics. These observations demonstrate that H embedded in the metal catalyst is a reactant in alkyne hydrogenation and is not solely a source of surface-bound H which then reacts with acetylene, as proposed from correlations between the hydrogenation activity of Raney Ni and Pd catalysts and the amount of H absorbed in these catalysts. The reactivities of these two kinds of H atoms are clearly distinguished in this experiment because of the capability to synthesize either bulk H or surface-bound H cleanly in an ultrahigh vacuum environment

Catalytic hydrogenation of acetylene on Ni(111) by surface-bound H and bulk H

The reactions of hydrogen atoms adsorbed on a Ni(111) surface (surface-bound H) and hydrogen atoms just below the surface (bulk H) with coadsorbed acetylene are probed under ultrahigh vacuum conditions. Bulk H is observed to react with acetylene upon emerging onto the surface at 180 K. Gas-phase hydrogenation products, ethylene and ethane, are produced as well as an adsorbed species, ethylidyne. Ethylidyne is identified by high-resolution electron energy loss spectroscopy. Surface-bound H reacts with adsorbed acetylene above 250 K to produce a single product, adsorbed ethylidyne. No gas-phase hydrogenation products, such as ethylene or ethane, are observed. The reaction of surface-bound H is extremely slow, with a rate constant determined from measurements of the initial reaction rate to be in the range of 10-5−10-3 (ML s)-1 for a temperature range of 250−280 K. The activation energy for the rate-determining step, which is shown to be the addition of the first surface-bound H to acetylene to form an adsorbed vinyl species, increases from 9 to 17 kcal/mol as the total coverage decreases from 0.92 to 0.74 ML. The reaction rate cannot be described by a simple first-order dependence on the coverage of either reactant, indicating the presence of strong interactions between reactants. Measurements of the equilibrium constant reveal strong interactions between the reactant surface H and the product ethylidyne, possibly resulting in island formation. Mechanisms for the formation of ethylidyne by the reactions of both surface-bound and bulk H are proposed, as well as mechanisms for the formation of ethylene and ethane by bulk H. The different product distributions resulting from the reaction of acetylene with the two forms of hydrogen are discussed in terms of the large energy difference between bulk and surface-bound H