| 1. |
- Janin, E, et al.
(author)
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Hydrogen adsorption on the Pt(111)(root 3x root 5)R30 degrees-Sn surface alloy studied by high resolution core level photoelectron spectroscopy
- 1996
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 99:4, s. 371-378
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Journal article (peer-reviewed)abstract
- Investigation of the clean and atomic hydrogen covered Pt(111)(root 3 x root 3)R30 degrees-Sn surface alloy has been carried out using high resolution core level photoelectron spectroscopy, The Pt 4(7/2) spectrum recorded from the clean surface alloy shows a single surface peak shifted - 0.25 eV relative to the bulk. Its interpretation by means of a thermodynamical model using Born-Haber cycles confirms the surface alloy model. Adsorption of H does not change the line shape of the Sn 4d core level while a new surface component shifted by 0.59 eV compared to the bulk peak appears in the Pt 4(7/2) spectrum. These results are discussed in the light of the thermodynamical calculations, H atoms are believed to bind only to Pt atoms, and their adsorption site seems to be influenced by the tin present in the surface layer.
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| 2. |
- Bjorkqvist, M, et al.
(author)
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NH3 on Si(111)7x7 : Dissociation and surface reactions
- 1998
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:4, s. 2327-2333
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Journal article (peer-reviewed)abstract
- Core-level and valence-band photoelectron spectroscopy on the dissociative adsorption of ammonia on Si(111) 7 X 7 is presented. Adsorption at room temperature produces three nitrogen 1s components, of which two are assigned to NH2 and one to NH, with an initial tendency for double dissociation. These doubly dissociated species can be connected to the development of silicon atoms coordinated with two nitrogen atoms, necessitating silicon-silicon bonds to be broken. The dominating picture evolving is thus adatoms saturated by NH2 with a NH group inserted into one backbond, and hydrogen preferentially capping restatoms. The dissociation proces is hence much more complex than generally proposed before. This is further accentuated by the fact that not all adatoms appear reacted. When annealed above 600 K the dissociation process progresses and atomic nitrogen appears at 700 K, to be the only remaining specie at 850 K. At 1200 K, further changes in the N 1s core level indicates true silicon nitride formation.
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| 3. |
- Gothelid, M, et al.
(author)
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Etching and a disordered overlayer on the Ge(100)-S surface
- 1997
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 115:1, s. 87-95
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Journal article (peer-reviewed)abstract
- High resolution core level photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) have been used to study the adsorption and desorption of S on and off the Ge(100) surface. The previously proposed bridge adsorption site of S is consistent with our results at low coverage. At saturation the substrate contains several GeSx species, with x = 0.5 to 4. Both photoemission and STM reveals a non-ideal surface, with a saturation coverage above one monolayer. Furthermore, S is found to etch the substrate. The reaction products forms a disordered overlayer on top of the interface. This overlayer is transparent in the filled state STM images.
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| 4. |
- Gothelid, M, et al.
(author)
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Ge/(111)3x1:K/Sn; On the influence of tin substitution in a metal induced 3x1 reconstruction
- 1996
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In: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 104, s. 113-117
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Journal article (peer-reviewed)abstract
- Go-adsorption of tin and potassium is found to induce a 3x1 reconstruction on the Ge(lll) surface. A very small amount of tin influences the Ge 3d core level spectra substantially compared to the Ge(111)3x1:K reconstruction. This is interpreted as resulting from a relaxation of the strain in the rows Ge atoms running along the surface, as proposed for this structure.
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| 5. |
- GOTHELID, M, et al.
(author)
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GEOMETRY OF THE GE(111)-AU(ROOT-3X-ROOT-3)R 30-DEGREES RECONSTRUCTION
- 1994
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 50:7, s. 4470-4475
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Journal article (peer-reviewed)abstract
- A structure model for the Ge(111)-Au(root 3X root 3)R30 degrees surface reconstruction is proposed based on scanning tunneling microscopy (STM) and photoelectron spectroscopy on the Ge 3d and Au 4f core lines. The basic unit is a Au3Ge molecule binding in one-third of the T-1 substrate sites with a gold trimer pointing out of the surface. This leaves two-thirds of a monolayer of unoccupied T-1 sites which make up a hexagonal honeycomb pattern. Two types of STM images have been obtained which are explained within this model, where either the trimers or the substrate Ge atoms are probed depending on the specific tip conditions in combination with the sample bias voltage. Furthermore, small insets of a metallic (1X1) structure are found at low gold coverage together with a distorted (2X2) surface structure.
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| 6. |
- Le Lay, G., et al.
(author)
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STM and synchrotron radiation studies of "prototypical" metal{plus 45 degree rule}semiconductor systems
- 1994
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In: Surface Science. - 0039-6028. ; 307-309:PART A, s. 280-294
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Journal article (peer-reviewed)abstract
- Since the origin of surface science noble metal{plus 45 degree rule}elemental semiconductor couples have been considered as "prototypical" systems. After three decades of research their structural and electronic properties remain an intriguing maze despite recent advances made, especially thanks to the development of the near-field microscopies and the extensive use of synchrotron radiation in surface crystallography and in high-resolution photoelectron spectroscopy. In the last few years, lead, as a replacement inert metal, has nearly gained the pole position in the display of exotic behaviour. This paper gives a flavour of this mystery story and highlights some puzzling questions. © 1994.
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| 7. |
- LELAY, G, et al.
(author)
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STM AND SYNCHROTRON-RADIATION STUDIES OF PROTOTYPICAL METAL-SEMICONDUCTOR SYSTEMS
- 1994
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 307, s. 280-294
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Journal article (peer-reviewed)abstract
- Since the origin of surface science noble metal/elemental semiconductor couples have been considered as ''prototypical'' systems. After three decades of research their structural and electronic properties remain an intriguing maze despite recent advances made, especially thanks to the development of the near-field microscopies and the ''tensive use of synchrotron radiation in surface crystallography and in high-resolution photoelectron spectroscopy. In the last few years, lead, as a replacement inert metal, has nearly gained the pole position in the display of exotic behaviour. This paper gives a flavour of this mystery story and highlights some puzzling questions.
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| 8. |
- TORNEVIK, C, et al.
(author)
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ADSORPTION OF SN ON SI(111)7X7 - RECONSTRUCTIONS IN THE MONOLAYER REGIME
- 1994
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 314:2, s. 179-187
-
Journal article (peer-reviewed)abstract
- Different monolayer phases of Sn on Si(111)7 x 7 have been studied by means of scanning tunneling microscopy (STM), core-level photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS). The STM results show that square-root 3 x square-root 3 reconstructions are obtained for room-temperature deposition of 1/3 ML of Sn followed by sample annealing in a broad temperature range. A T4 Sn adatom square-root 3 x square-root 3 phase is formed for temperatures between 500 and 800-degrees-C, with a concentration of defects that is strongly dependent on the temperature and which is as high as 25% for the lowest temperatures. Above 825-degrees-C a second square-root 3 x square-root 3 adatom reconstruction is formed, a mosaic-like phase with a 1: 1 mixture of Si and Sn atoms in T4 positions. The results from investigations of the higher coverage 2 square-root 3 x 2 square-root 3 reconstruction by XPS and RBS support the theory that this phase is a two-layer epitaxial Sn structure with all Si(111) dangling bonds saturated. The Sn coverage for this phase was determined to be between 1 and 1.2 ML.
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| 9. |
- Varekamp, P R, et al.
(author)
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Reaction of I-2 with the (001) surfaces of GaAs, InAs, and InSb .1. Chemical interaction with the substrate
- 1996
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:3, s. 2101-2113
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Journal article (peer-reviewed)abstract
- InAs(001)-c(8x2), InSb(001)-c(8x2), and several reconstructions of GaAs(001) are exposed at room temperature to iodine molecules (I-2). Low-energy electron diffraction (LEED) and synchrotron soft x-ray photoelectron spectroscopy (SXPS) are employed to study the surfaces as a function of I-2 dose and sample anneal. In the exposure range studied, GaAs and InAs become saturated with I-2, resulting in removal of the clean surface reconstruction and the formation of a very strong 1x1 LEED pattern. Iodine bonds primarily to the dominant elemental species present on the clean surface, whether it is a group-III or -V element. The InSb(001)-c(8x2) reconstruction is also removed by I-2 adsorption, and a strong 1x1 LEED pattern is formed. SXPS data, in conjunction with scanning tunneling microscopy images, however, reveal that InSb(001)-c(8x2) does not saturate at room temperature, but is instead etched with a preferential loss of In. Heating the iodine-covered group-III-rich InAs(001)-c(8x2) and InSb(001)-c(8x2) surfaces causes removal of the iodine overlayer and transformation to a group-V-rich reconstruction. When the iodine-covered As-rich GaAs(001)-c(2x8) surface is heated to remove iodine, however, the c(2x8) reconstruction is simply regenerated.
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| 10. |
- Varekamp, P R, et al.
(author)
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Reaction of I-2 with the (001) surfaces of GaAs, InAs, and InSb .2. Ordering of the iodine overlayer
- 1996
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:3, s. 2114-2120
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Journal article (peer-reviewed)abstract
- The overlayer formed by the reaction of molecular iodine (I-2) with GaAs(001), InAs(001), and InSb(001) is investigated with synchrotron soft x-ray photoelectron spectroscopy (SXPS) and scanning tunneling microscopy (STM). Two components, separated by about 0.5 eV, are present in all of the I 4d SXPS spectra. At very low iodine coverages, the high binding energy (BE) component dominates. When the iodine coverage saturates, however, the two components have equal intensities. In contrast to GaAs and InAs, exposure of InSb(001)-c(8x2) to additional I-2 results in a further increase of the relative intensity of the low-BE component. STM images of I-2 covered InSb(001)-c(8x2) directly reveal the ordering in the overlayer. Islands are visible for submonolayer coverages, suggesting that adsorption occurs via a mobile precursor state. STM images feature occupies a 1x1 unit cell with the same spacing as bulk-terminated InSb(001). The other feature has a coverage of similar to 1/3 ML and is arranged in pairs oriented along the [110] azimuth.
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