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Ab inition CI investigation of the interaction of a hydrogen atom with clusters which model the (100) and (110) surfaces of bcc Li-lattice
A330 Surface Science 120 (1982) 103-126 North-Holland Publishing Company INTERACTION
O F K , N a , L i A N D TI W I T H
A N D (100) S U R F A C E S ; OF DESORPTION E.F. GREENE,
103
SURFACE
J.T. K E E L E Y
SILICON
IONIZATION
(111)
AND KINETICS
and M.A. PICKERING
Metcalf Chemical Laboratories, Brown University, Providence, Rhode Island 02912, USA Received 18 February 1982 Atomic beams of K, Na, Li and T1 are used to determine the work function and desorption energies for Si(11 I) and (100) surfaces. The (I 11) surface appears to go through a surface transition at ca. 1100 K. Below 1000 K, the (111) surface appears stable with a surface ionization work function ~+ =4.80±0.05 eV. The desorption of K and Na from this surface has both a first- and second-order component with activation energies for desorption of Eal = 3.15 ± 0.15 eV, E,a = 2.53 ---+0.10 eV for K, and Eal =3.47-4-0.15 eV, Ea: =2.39±0.13 eV for Na. The second-order part of the desorption is probably due to interactions or collisions of the atoms as they move along the surface. Above 1100 K the work function decreases by 0.03±0.01 eV and the desorption of K and Na from this surface is predominantly first order with Eal =2.35±0.07 eV for K and Eal =2.45± 0.12 eV for Na. The (100) surface in the temperature range of 800 to 1550 K has ~+ =4.67-+-0.08 eV and a first order desorption energy Eal -----2.54±0.14 eV for K. The work functions from the thermionic emission of electrons are ~e- = 4.55 ± 0.1 and '/'e- = 4.53 ± 0.1 eV for the (111) and (100) surfaces, respectively, for T ~ 1000 K.
Surface Science 120 (1982) 127-149 North-Holland Publishing Company AB INITIO CI INVESTIGATION OF THE INTERACTION HYDROGEN ATOM WITH CLUSTERS WHICH MODEL A N D (110) S U R F A C E S H.-O. BECKMANN
127 OF A T H E (100)
OF bee Li-LA'ITICE
a n d J. K O U T E C K ~ r
lnstitut fi~r Physikalische Chemic, Freie Universiti~t Berlin, D-IO00 Berlin 33, Fed. Rep. of Germany Received 21 January 1982 Correlation effects are important for the proper description of the electronic structure of the clusters which can serve as models for the interaction between an H atom and the (I00) and/or (110) bee Li surfaces. A majority of the clusters investigated exhibits lowest singlet and lowest triplet states with almost degenerate energies. The models used to describe the interaction of hydrogen with lithium surface show that a dissolution of hydrogen atoms inside the Li lattice in interstationary positions is very probable when the less "compact" (100) bcc surface is exposed to hydrogen. The more "compact" (110) surface should also allow the entry of a H atom inside the Li lattice although under energetically less favorable conditions. These consequences of the study with rigid Li-cluster models would certainly be even more pronounced if the relaxation effects were taken into account. It is generally observed that a smaller number of nearest neighbors in the plane perpendicular to the line of approach of the H atom favors stronger bonds to the hydrogen atom. This fact can cause higher surface activity if irregularities in the form of "peaks", "ridges" or "hills" are present in the surface. The higher surface activity is indicated by an increase in the H concentration inside the region of the irregularities. This effect is enhanced when the surface irregularities have a high degree of biradicaloid character.
O F K , N a , L i A N D TI W I T H
A N D (100) S U R F A C E S ; OF DESORPTION E.F. GREENE,
103
SURFACE
J.T. K E E L E Y
SILICON
IONIZATION
(111)
AND KINETICS
and M.A. PICKERING
Metcalf Chemical Laboratories, Brown University, Providence, Rhode Island 02912, USA Received 18 February 1982 Atomic beams of K, Na, Li and T1 are used to determine the work function and desorption energies for Si(11 I) and (100) surfaces. The (I 11) surface appears to go through a surface transition at ca. 1100 K. Below 1000 K, the (111) surface appears stable with a surface ionization work function ~+ =4.80±0.05 eV. The desorption of K and Na from this surface has both a first- and second-order component with activation energies for desorption of Eal = 3.15 ± 0.15 eV, E,a = 2.53 ---+0.10 eV for K, and Eal =3.47-4-0.15 eV, Ea: =2.39±0.13 eV for Na. The second-order part of the desorption is probably due to interactions or collisions of the atoms as they move along the surface. Above 1100 K the work function decreases by 0.03±0.01 eV and the desorption of K and Na from this surface is predominantly first order with Eal =2.35±0.07 eV for K and Eal =2.45± 0.12 eV for Na. The (100) surface in the temperature range of 800 to 1550 K has ~+ =4.67-+-0.08 eV and a first order desorption energy Eal -----2.54±0.14 eV for K. The work functions from the thermionic emission of electrons are ~e- = 4.55 ± 0.1 and '/'e- = 4.53 ± 0.1 eV for the (111) and (100) surfaces, respectively, for T ~ 1000 K.
Surface Science 120 (1982) 127-149 North-Holland Publishing Company AB INITIO CI INVESTIGATION OF THE INTERACTION HYDROGEN ATOM WITH CLUSTERS WHICH MODEL A N D (110) S U R F A C E S H.-O. BECKMANN
127 OF A T H E (100)
OF bee Li-LA'ITICE
a n d J. K O U T E C K ~ r
lnstitut fi~r Physikalische Chemic, Freie Universiti~t Berlin, D-IO00 Berlin 33, Fed. Rep. of Germany Received 21 January 1982 Correlation effects are important for the proper description of the electronic structure of the clusters which can serve as models for the interaction between an H atom and the (I00) and/or (110) bee Li surfaces. A majority of the clusters investigated exhibits lowest singlet and lowest triplet states with almost degenerate energies. The models used to describe the interaction of hydrogen with lithium surface show that a dissolution of hydrogen atoms inside the Li lattice in interstationary positions is very probable when the less "compact" (100) bcc surface is exposed to hydrogen. The more "compact" (110) surface should also allow the entry of a H atom inside the Li lattice although under energetically less favorable conditions. These consequences of the study with rigid Li-cluster models would certainly be even more pronounced if the relaxation effects were taken into account. It is generally observed that a smaller number of nearest neighbors in the plane perpendicular to the line of approach of the H atom favors stronger bonds to the hydrogen atom. This fact can cause higher surface activity if irregularities in the form of "peaks", "ridges" or "hills" are present in the surface. The higher surface activity is indicated by an increase in the H concentration inside the region of the irregularities. This effect is enhanced when the surface irregularities have a high degree of biradicaloid character.