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Oxygen on Cu(100) — A case of an adsorbate induced reconstruction
A213 T. HASHIZUME,
I. K A M I Y A
and T. SAKURAI
The Institute for Solid State Physics, The Unioersi(~' of Tokyo, Roppongi, Minato-Ku, Tokyo 106, Japan Received 12 August 1988; accepted for publication 3 November 1988 The atom-probe field ion microscope was employed to study oxygen adsorption and oxidation on surfaces of two grades of copper: low-grade tough-pitch copper (99.9%) and high purity copper (99.999%). The source of the oxygen is the C u : O inclusions which were present in the low-grade tough-pitch copper. The 99.9% grade copper was annealed in ultra-high vacuum (UHV). During heating the C u 2 0 inclusions dissolve and the oxygen content of the matrix increases. Surface enrichment of oxygen and oxide formation on the surface were found depending on the annealing conditions. N o indication of oxidation and oxygen enrichment was found in the high purity copper (99.999%) under the same U H V conditions.
Surface Science 213 (1989) 103-136 North-llolland, A m s t e r d a m OXYGEN
ON
INDUCED M. WUTTIG,
Cu(100)
103
- A CASE
OF
AN ADSORBATE
RECONSTRUCTION R. FRANCHY
and
H. IBACH
Institut je~tr Grenzfl?ichenforschung und Vakuumphysik, Kernfor.whungsanlage Jilhch, Postfach 1913. 5170 Jiilich. Fed Rep. of Germany Received 8 September 1988; accepted for publication 9 November 1988
We show that at and above room temperature only a single long range ordered superstructure exists on Cu(100). This is the (v/2 ×2,,/2)R45 ° structure, which corresl:x~nds to a saturation coverage of 0o = 0.48+0.05. A well-ordered c(2X2) superstructure is not observed in the investigated range of adsorption temperatures (T,,,j~= 300-600 K). Above a critical oxygen coverage 0c = 0.34+0.02 long range order starts to develop. The disordered adsorption region below 0~ = 0.34 is characterized by two different adsorption sites. One of these sites already is saturated at relatively low coverages (0 o = 0.15). This site appears to corresponds to a local reconstruction with the neighbouring atoms of the adsorbate atom engaging in an intralayer contraction. Diffraction studies show a first order phase transition at ~ from the disordered phase to a phase with long range order. The long range ordered domains are larger than the coherence length of the EELS diffraction experiment already slightly above 0~. For the "'perfect'" (¢'2 × 2!/'2 )R45 ° structure only a single fourfold coordinated adsorption site is occupied. The large number of total symmetric vibrations as well as the observed LEED pattern show that the substrate surface is reconstructed. An assignment of the observed vibrations allows us to determine the reconstruction pattern which is characterized by a local symmetry reduction. This lowering of symmetry might be the driving force of the reconstruction pointing towards a Peierls instability or a cooperative Jahn-Teller effect.
I. K A M I Y A
and T. SAKURAI
The Institute for Solid State Physics, The Unioersi(~' of Tokyo, Roppongi, Minato-Ku, Tokyo 106, Japan Received 12 August 1988; accepted for publication 3 November 1988 The atom-probe field ion microscope was employed to study oxygen adsorption and oxidation on surfaces of two grades of copper: low-grade tough-pitch copper (99.9%) and high purity copper (99.999%). The source of the oxygen is the C u : O inclusions which were present in the low-grade tough-pitch copper. The 99.9% grade copper was annealed in ultra-high vacuum (UHV). During heating the C u 2 0 inclusions dissolve and the oxygen content of the matrix increases. Surface enrichment of oxygen and oxide formation on the surface were found depending on the annealing conditions. N o indication of oxidation and oxygen enrichment was found in the high purity copper (99.999%) under the same U H V conditions.
Surface Science 213 (1989) 103-136 North-llolland, A m s t e r d a m OXYGEN
ON
INDUCED M. WUTTIG,
Cu(100)
103
- A CASE
OF
AN ADSORBATE
RECONSTRUCTION R. FRANCHY
and
H. IBACH
Institut je~tr Grenzfl?ichenforschung und Vakuumphysik, Kernfor.whungsanlage Jilhch, Postfach 1913. 5170 Jiilich. Fed Rep. of Germany Received 8 September 1988; accepted for publication 9 November 1988
We show that at and above room temperature only a single long range ordered superstructure exists on Cu(100). This is the (v/2 ×2,,/2)R45 ° structure, which corresl:x~nds to a saturation coverage of 0o = 0.48+0.05. A well-ordered c(2X2) superstructure is not observed in the investigated range of adsorption temperatures (T,,,j~= 300-600 K). Above a critical oxygen coverage 0c = 0.34+0.02 long range order starts to develop. The disordered adsorption region below 0~ = 0.34 is characterized by two different adsorption sites. One of these sites already is saturated at relatively low coverages (0 o = 0.15). This site appears to corresponds to a local reconstruction with the neighbouring atoms of the adsorbate atom engaging in an intralayer contraction. Diffraction studies show a first order phase transition at ~ from the disordered phase to a phase with long range order. The long range ordered domains are larger than the coherence length of the EELS diffraction experiment already slightly above 0~. For the "'perfect'" (¢'2 × 2!/'2 )R45 ° structure only a single fourfold coordinated adsorption site is occupied. The large number of total symmetric vibrations as well as the observed LEED pattern show that the substrate surface is reconstructed. An assignment of the observed vibrations allows us to determine the reconstruction pattern which is characterized by a local symmetry reduction. This lowering of symmetry might be the driving force of the reconstruction pointing towards a Peierls instability or a cooperative Jahn-Teller effect.