Contains reports on one research project.Joint Services Electronics Program (Contract DAAB07-74-C-0630

Cardillo, Mark J.

Ching, Clifton S. Y.

Look, Yum H.

DSpace@MIT

III. PHYSICAL ELECTRONICS AND SURFACE PHYSICSAcademic and Research StaffProf. Robert E. StickneyDr. Mark J. CardilloGraduate StudentsClifton S. Y. ChingA. INTERACTION OF GASES WITH SOLIDS JSEPJoint Services Electronics Program (Contract DAAB07-74-C-0630)Mark J. Cardillo, Clifton S. Y. Ching, Yum H. LookWithin the last six months we have nearly completed a mass spectrometric studyof the transport of tungsten that is due to chemical reactions with CO 2 and D20 at hightemperatures and low pressures. We have covered a pressure range of 10-5-10 - 3 Torrfor each gas and surface temperatures from 1400'K to 3200 K. We have measured theprobability of reaction and the rate of formation and evaporation of a variety of volatiletungsten oxide species. Typical reduced data are presented in Figs. III-1 and 11-2.We have compared these results with a quasi-equilibrium model of gas-surfacereactions formulated by Batty and Stickney. 1We are now working on refinements to the quasi-equilibrium model and on the2.experimental techniques in order to test quantitatively the idea of equilibrium, inparticular, we are incorporating a double ionizer into our detection system. As canbe observed from the form of the tungsten curves in Figs. III-1 and III-2, a substantialamount of fragmentation occurs during the ionization process used to detect the prod-ucts. This is unavoidable at the electron. energies that are necessary to obtain reason-able signals and get good estimates of the ionization probabilities, and it is the causeof considerable uncertainty in general for reaction rates and thermochemical tables of2high-temperature species. By introducing a double ionization technique, we can avoidthe problems associated with fragmentation and obtain a meaningful quantitative com-parison between the quasi-equilibrium model and experiment.We are also developing an analogous analytical scheme to evaluate the effect ofthe competitive formation of neutral species in the theory of the production of negativeions at surfaces.On another apparatus in which we incorporate mass spectrometry, Auger electronspectroscopy, and nozzle molecular beams to study gas-surface reactions we arelooking at the reaction of a variable energy oxygen molecular beam with a Si (111) crys-tal. We have constructed a rotatable stage to support a new Extranuclear LaboratoriesELFS high-resolution quadrupole and we are completing the measurement of velocity JSEPPR No. 116(III. PHYSICAL ELECTRONICS AND SURFACE PHYSICS)JSEPU)L_z 10LiJZZz0Li10-JLicr10-90W+ WOa W0 3oW 2063 4 5104 /TOK165I10U)w-7U) 10zwI-zz0wS-5JJwM1696 7 iIO3 3Fig. III-1.Relative flux signals of reaction productsdesorbing from a tungsten ribbon sub-jected to a molecular beam of D 2 0.Effective pressure of the beam on theribbon, 1. 9 X 10 Torr. Humps in theW and WO curves give clear indicationof dissociative ionization occurring inthe mass spectrometer ionizer.Fig. III-2.Relative flux signals of reaction prod-ucts desorbing from a tungsten ribbonsubjected to a CO 2 flux with an effective-3pressure of I. 6 X 10 Torr.distributions of mixed beams of He and 02. We are using He to obtain collisionalacceleration of the 02 to high velocities by extracting the center line of high-pressurefree jet expansions. This will provide 02 incident energies over a range of .01-2 eV.We are looking at the effect of this variation in kinetic energy, the target surfacestructure, and surface temperature on the reaction probabilities of 02 with Si and Ge.At the higher crystal temperatures employed and low steady-state oxygen coverages(less than 1 monolayer), we can monitor the reaction probability by measuring the rateof formation of the volatile monoxide.References1. J. C. Batty and R. E. Stickney, J. Chem. Phys. 51, 4485 (1969).2. C. K. Crawford, Proceedings of Electron Beam Symposium, Boston, Mass., March1963, J. R. Morley (Ed.).PR No. 1160W+ WOo WO2A W0 35 610 /T-KJSEPI I I

Physical Electronics and Surface Physics

http://dspace.mit.edu/bitstream/handle/1721.1/56545/RLE_PR_116_III.pdf?sequence=1

Physical Electronics and Surface Physics

Abstract

Similar works

Full text

Available Versions

DSpace@MIT