- Email: [email protected]
LEED investigations on the interaction of Pd and Ni with different Si(111) surfaces
A367 Received 16 February 1984; accepted for publication 3 May 1984 The adsorption of methyl iodide on uranium and on uranium dioxide has been studied at 25°C. Surfaces of the substrates were characterized before and after adsorption by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The XPS binding energy results indicate that CH31 adsorption on uranium yields a carbide-type carbon, UC, and uranium iodide, UI 3. On uranium dioxide the carbon electron binding energy measurements are consistent with the formation of a hydrocarbon, -CH3-type moiety. The interpretation of XPS and AES spectral features for CH31 adsorption on uranium suggest that a complex dissociative adsorption reaction takes place. Adsorption of CH31 on UO 2 occurs via a dissociative process. Saturation coverage occurs on uranium at approximately two langmuir (1 L =10 -6 Torr s) exposure whereas saturation coverage on uranium dioxide is found at about five langmuir.
Surface Science 145 (1984) 87 100 North-Holland, Amsterdam LEED
INVESTIGATIONS
87 ON THE
DIFFERENT
S i ( l 11) S U R F A C E S
J.G. CLABES
*
INTERACTION
OF Pd AND Ni WITH
lnstitut fur Festk~rperphysik, Universit~t Hannover, D- 3000 Hannover, Fed. Rep. of German)' Received 28 February 1984; accepted for publication 17 May 1984 The structural properties of Pd and N i on cleaved Si(ll 1)-2 x 1 and - 7 × 7 surfaces have been studies under ultrahigh vacuum conditions by LEED to evaluate the microstructure in the early stages of silicide-silicon interface formation, in contrast to the indifferent behavior of Ni, the reaction of Pd reveals strong evidence for the dependence of the nucleation and growth of epitaxial Pd2Si on the initial surface reconstruction. A 5 x 1 superstructure emerges on the 2 x 1 surface after deposition of submonolayer Pd at room temperature, suggesting a rather well ordered lateral arrangement of Pd 2Si(1000)-I × 1 nuclei, whereas epitaxial Pd2Si on 7 × 7 is only established at much higher coverage (0 >/3). An unexpected ~ × ~/3 reconstruction is formed after annealing at 200 o C for 0 ~< 3 monolayers of Ni, independent of the initial reconstruction and well below the formation temperature of epitaxial NiSi 2. The coverage dependence of the 7r3 structure implies the presence of an unknown epitaxial film. This finding represents the first evidence of a well defined intermediate state of reaction between unreacted Ni and NiSi 2, which has not been anticipated from other UHV experiments. The qualitative difference in the interaction of Pd and Ni with the Si lattice is demonstrated further by the reappearance of the 7 × 7 reconstruction even after several monolayers of Ni, which has not been achieved with Pd under any process condition, and the pronounced faceting of stepped surfaces under Pd.
Surface Science 145 (1984) 87 100 North-Holland, Amsterdam LEED
INVESTIGATIONS
87 ON THE
DIFFERENT
S i ( l 11) S U R F A C E S
J.G. CLABES
*
INTERACTION
OF Pd AND Ni WITH
lnstitut fur Festk~rperphysik, Universit~t Hannover, D- 3000 Hannover, Fed. Rep. of German)' Received 28 February 1984; accepted for publication 17 May 1984 The structural properties of Pd and N i on cleaved Si(ll 1)-2 x 1 and - 7 × 7 surfaces have been studies under ultrahigh vacuum conditions by LEED to evaluate the microstructure in the early stages of silicide-silicon interface formation, in contrast to the indifferent behavior of Ni, the reaction of Pd reveals strong evidence for the dependence of the nucleation and growth of epitaxial Pd2Si on the initial surface reconstruction. A 5 x 1 superstructure emerges on the 2 x 1 surface after deposition of submonolayer Pd at room temperature, suggesting a rather well ordered lateral arrangement of Pd 2Si(1000)-I × 1 nuclei, whereas epitaxial Pd2Si on 7 × 7 is only established at much higher coverage (0 >/3). An unexpected ~ × ~/3 reconstruction is formed after annealing at 200 o C for 0 ~< 3 monolayers of Ni, independent of the initial reconstruction and well below the formation temperature of epitaxial NiSi 2. The coverage dependence of the 7r3 structure implies the presence of an unknown epitaxial film. This finding represents the first evidence of a well defined intermediate state of reaction between unreacted Ni and NiSi 2, which has not been anticipated from other UHV experiments. The qualitative difference in the interaction of Pd and Ni with the Si lattice is demonstrated further by the reappearance of the 7 × 7 reconstruction even after several monolayers of Ni, which has not been achieved with Pd under any process condition, and the pronounced faceting of stepped surfaces under Pd.