| 1. |
- Göthelid, M., et al.
(författare)
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Adatom and rest-atom contributions in Ge(111)c(2×8) and Ge(111)-Sn(7×7) core-level spectra
- 1993
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Ingår i: Physical Review B. - 0163-1829. ; 48:3, s. 2012-2015
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Tidskriftsartikel (refereegranskat)abstract
- We have identified the adatom contribution in the Ge 3d core-level spectra from the clean Ge(111)c(2×8) surface, shifted 0.17 eV to higher binding energy compared to the bulk. This adatom component vanishes in the Ge(111)-Sn(7×7) surface core-level spectra where Sn occupies the adatom site. Moreover we report the observation of an earlier proposed difference between the rest atoms in the c(2×8) structure, and also a shift to lower binding energy for the rest atoms in both structures studied. © 1993 The American Physical Society.
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| 2. |
- Törnevik, C., et al.
(författare)
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Adsorption of Sn onSi(111)7 × 7 : reconstructions in the monolayer regime
- 1994
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Ingår i: Surface Science. - 0039-6028. ; 314:2, s. 179-187
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Tidskriftsartikel (refereegranskat)abstract
- Different monolayer phases of Sn on Si(111)7 × 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 3 × 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 3 ×3 phase is formed for temperatures between 500 and 800°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°C a second 3×3 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 3 × 2 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. © 1994.
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| 3. |
- Vaitkus, J., et al.
(författare)
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Scanning tunneling microscopy of CdSe single crystal cleaved and "real" surface
- 1994
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 138:1-4, s. 545-549
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Tidskriftsartikel (refereegranskat)abstract
- Ultrahigh vacuum-cleaved and as-grown surfaces of CdSe single crystals were investigated by scanning tunneling microscopy. The single crystals were grown by Reynolds-Green method. Striations and terrace-step structure have been found. The surface atomic geometry was found and investigated. The (1120) face geometry (structure formed by elementary cell of 0.75 × 0.7 nm2) as well as other type structures (e.g., 2.1 × 0.75 nm2 elementary cell) have been determined. The variations of the band gap at the surface have been found. The band values in the range 2.0-2.6 eV on a cleaved surface and 1.1-2.0 eV on an as-grown surface were measured and explained as being the influence of surface relaxation and gas adsorption. © 1994.
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| 4. |
- Castleton, C. W. M., et al.
(författare)
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Hydrogen on III-V (110) surfaces : Charge accumulation and STM signatures
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:4, s. 045319-
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of hydrogen on the 110 surfaces of III-V semiconductors is examined using ab initio density functional theory. It is confirmed that adsorbed hydrogen should lead to a charge accumulation layer in the case of InAs, but shown here that it should not do so for other related III-V semiconductors. It is shown that the hydrogen levels due to surface adsorbed hydrogen behave in a material dependent manner related to the ionicity of the material, and hence do not line up in the universal manner reported by others for hydrogen in the bulk of semiconductors and insulators. This fact, combined with the unusually deep Gamma point conduction band well of InAs, accounts for the occurrence of an accumulation layer on InAs(110) but not elsewhere. Furthermore, it is shown that adsorbed hydrogen should be extremely hard to distinguish from native defects (particularly vacancies) using scanning tunneling and atomic force microscopy, on both InAs(110) and other III-V (110) surfaces.
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| 5. |
- Chen, W., et al.
(författare)
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Electronic and geometric structure of clean Pt3Ti(111)
- 1994
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Ingår i: Physical Review B. - 0163-1829 .- 1095-3795. ; 50:8, s. 5620-5627
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission spectra and scanning tunneling microscopy (STM) images of the clean Pt3Ti(111) surface are presented. Grazing-emission core-level spectra show that the topmost layer is pure platinum, modified compared with the Pt(111) surface. The Pt 4f levels at the surface are shifted 0.4 eV toward the Fermi level relative to bulk Pt3Ti while the Pt 4f and Ti 2p levels in the bulk are shifted 0.4 and 1.3 eV to higher binding energy relative to pure bulk platinum and titanium, respectively, Tunneling measurements show a surface with only metallic atoms and a small p(2×2) buckling. Our observations of molecularly adsorbed CO are not compatible with metallic titanium atoms at the surface and the STM data thus indirectly confirm that only platinum atoms are present in the topmost layer. Linear muffin-tin-orbital calculations of the bulk band structure and valence-band photoemission spectra reveal highly hybridized electron states between the Pt d and Ti d levels. The calculations give a minor charge transfer from Ti to Pt, 0.37 electrons per Ti atom, but the large core-level shifts reflect the stability of the alloy and the response to the excitation rather than the amount of charge transfer. The observed segregation of platinum to the surface and the altered electronic structure of the topmost layer, due to interaction with the underlying alloy, are in full agreement with earlier conclusions based on low-energy electron-diffraction measurements and on the chemical properties of the surface. © 1994 The American Physical Society.
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| 6. |
- Chen, W., et al.
(författare)
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Redox properties of titanium oxides on Pt3Ti
- 1995
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 99:34, s. 12892-12895
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and electronic structure of surface-segregated titanium oxides on Pt3Ti(111) are presented. Core level photoemission spectra at grazing emission reveal two states of oxidation: a dominant and reducible four-valent oxide together with a small amount of a three-valent oxide is produced by oxidation in 0 2 at and below 400°C; an irreducible three-valent oxide by oxidation in 02 at and above 450 °C. The ratio between the active four-valent and the inactive three-valent oxides decreases with increasing oxidation temperature. The probability for reduction by CO is almost unity for the Ti 4+ oxide, and the conclusion must be that the four-valent oxide plays an active role for catalytic reactions. Scanning tunneling measurements relate these observations to changes in the dispersion and nucleation of the oxide overlayer. The four-valent oxide grows as islands with remaining areas open for CO adsorption while the three-valent oxide spreads on and blocks the crystal surface. Photoemission spectra relate these dispersion effects to an electronic interaction between the Ti 3+ oxide and adjacent Pt atoms. The above observations are in accordance with the common picture of dispersion effects in titania-supported SMSI catalysts and prove that interfacial energies play a crucial role whether the dominant phase is metallic or an oxide.
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| 7. |
- Davila, M. E., et al.
(författare)
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Surface phase transitions at metal-semiconductor interfaces : a revisit is needed
- 2004
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 234:04-jan, s. 274-285
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we review some of the most recent progress and understanding in the low temperature surface phase transitions at prototypical metal-semiconductor interfaces. We essentially focus on quantitative surface structural information obtained by using a significant variety of specialised techniques for the individual phases of a model system, namely, tin on Ge(1 1 1) substrates. The strengths and limitations of the structural results obtained by using scanning tunnelling microscopy, photoelectron diffraction and surface X-ray diffraction are discussed in relation to their support with respect to possible mechanisms recently invoked in the literature as being at the origin of the phase transition. These investigations show that a large progress has been made in this field, taking into account the very valuable experimental and theoretical contributions provided by different groups. There remain, however, essential unresolved problems, which will be analysed in the light of the limitations of these structural methods and the difficulty presented by the complex adsorbate systems studied.
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| 8. |
- Gauthier, Y., et al.
(författare)
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Reconstruction of the Pt50Ni50(100) surface : a LEED and STM study
- 1995
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Ingår i: Surface Science. - 0039-6028. ; 327:1-2, s. 100-120
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the Pt50Ni50(100) surface was investigated by low energy electron diffraction (LEED) and scanning tunnelling spectroscopy (STM). Superstructures corresponding to 12 × 1 and 19 × 1 reconstructions were observed in the LEED pattern, and these reconstructions were identified with atomic resolution by STM. The reconstructed surface layer has a quasi-hexagonal atomic mesh with almost (111) atomic density and is divided into terraces and domains the size of which can be more than a thousand ångströms. The domains are corrugated with protrusions made up by 5 × 1 subunits of the quasi-hexagonal mesh and with valleys containing depressed atoms or 2 × 1 subunits. The 12 × 1 and 19 × 1 periodicities are determined by the sequence of valleys; depending on the thermal treatment, one or the other dominates but both generally coexist on the terrace. Owing to the complexity of the structure, LEED calculations were performed for a simplified model with surface atoms situated in a planar net and uniform quasi-hexagonal meshes. We find that in both reconstructions the two surface layers are significantly enriched with platinum. The top layer enrichment is consistent with previous Auger measurements. © 1995.
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| 9. |
- Ghadami Yazdi, M., et al.
(författare)
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Naphthalene on Ni(111) : Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:40, s. 22199-22207
-
Tidskriftsartikel (refereegranskat)abstract
- An attractive solution to mitigate tars and also to decompose lighter hydrocarbons in biomass gasification is secondary catalytic reforming, converting hydrocarbons to useful permanent gases. Albeit that it has been in use for a long time in fossil feedstock catalytic steam reforming, understanding of the catalytic processes is still limited. Naphthalene is typically present in the biomass gasification gas and to further understand the elementary steps of naphthalene transformation, we investigated the temperature dependent naphthalene adsorption, dehydrogenation and passivation on Ni(111). TPD (temperature-programmed desorption) and STM (scanning tunneling microscopy) in ultrahigh vacuum environment from 110 K up to 780 K, combined with DFT (density functional theory) were used in the study. Room temperature adsorption results in a flat naphthalene monolayer. DFT favors the dibridge[7] geometry but the potential energy surface is rather smooth and other adsorption geometries may coexist. DFT also reveals a pronounced dearomatization and charge transfer from the adsorbed molecule into the nickel surface. Dehydrogenation occurs in two steps, with two desorption peaks at approximately 450 and 600 K. The first step is due to partial dehydrogenation generating active hydrocarbon species that at higher temperatures migrates over the surface forming graphene. The graphene formation is accompanied by desorption of hydrogen in the high temperature TPD peak. The formation of graphene effectively passivates the surface both for hydrogen adsorption and naphthalene dissociation. In conclusion, the obtained results on the model naphthalene and Ni(111) system, provides insight into elementary steps of naphthalene adsorption, dehydrogenation, and carbon passivation, which may serve as a good starting point for rational design, development and optimization of the Ni catalyst surface, as well as process conditions, for the aromatic hydrocarbon reforming process.
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| 10. |
- Giovanelli, L., et al.
(författare)
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Electronic structure of self-assembled organic/inorganic semiconductor interfaces : lead phthalocyanine on InSb and InAs(100)-4X2/c(8 X2)
- 2001
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 114, s. 375-381
-
Tidskriftsartikel (refereegranskat)abstract
- The interfacial properties of ultra thin films of lead-phthalocyanine deposited in situ onto InSb and InAs(100)-4X2/c(8X2) clean surfaces have been studied by synchrotron radiation core level and valence band photoelectron spectroscopy. The interaction between the overlayers and the substrates was determined upon analyzing the changes in the photoemission spectra between room and higher annealing temperatures, leading to ordered monolayer films. While weaker than on other substrates, a reactivity is nevertheless present: the organic macrocycle preserves its integrity up to 320 degreesC but the Pb central atom first leaves the molecules most probably to be incorporated in the substrate surface, before being desorbed at higher temperatures.
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| 11. |
- Grehk, T. M., et al.
(författare)
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Li-induced phase transition from the Ge(111)3X1 : Li surface reconstruction to the Ge(111)root 3X root 3 : Li lithium germanide
- 2000
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:7, s. 4963-4967
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the Li-induced phase transition from the Ge(111)3X1:Li to the Ge(111)root 3X root 3:Li reconstruction with photoemission. The Ge(111)3X1:Li reconstruction can be described as parallel rows of Ge atoms separated by single rows of Li atoms. The Ge(111)root 3X root 3:Li reconstruction, on the other hands, has to be described in terms of a Li-germanide phase extending over at least two atomic layers.
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| 12. |
- Göthelid, M., et al.
(författare)
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Sn-induced surface reconstructions on the Ge(111) surface studied with scanning tunneling microscopy
- 1992
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Ingår i: Surface Science. - 0039-6028. ; 271:3, s. L357-L361
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) has been used to study different Sn induced reconstructions on the Ge(111) surface; namely the (7 × 7), (5 × 5) and ( 3 × 3) R30° structures. The first two have been confirmed to be of the dimer adatom stacking faults (DAS) type with adatoms mainly being Sn. The ( 3 × 3)R30° superstructure was found at different Sn depositions. At 0.4 monolayer (ML) Sn coverage a homogeneous Sn adatom layer is adsorbed on the(1 × 1) surface in threefold sites directly over second-layer atoms (T4), while at low coverage, 0.1 ML, the top layer is a mixture of Sn and Ge atoms. We also propose the chemical identities of the different atoms seen in the STM images as related to their apparent height. © 1992.
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| 13. |
- Hammar, M., et al.
(författare)
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Initial growth of silver on Ge(111) studied by scanning tunneling microscopy
- 1993
-
Ingår i: Physical Review B. - 0163-1829. ; 47:23, s. 15669-15674
-
Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) has been used to study the Ge(111) surface after submonolayer depositions of Ag. At the lowest coverages a (4×4) reconstruction, with small insets of a (3×1) edge structure, is observed. Based on the STM images we propose a mixed Ag and Ge adatom structure for the (4×4) reconstruction, in which the adatoms have local (1×1) and (2×2) arrangements corresponding to a Ag coverage of 6/16 monolayers. The (3×1) structure appears to have a configuration similar to the Si(111)/Ag-(3×1) reconstruction, although in this case it has a much more limited extension, restricted to a few unit cells in the near vicinity of step edges and phase boundaries. At higher coverages, after the completion of a full (4×4)/(3×1) surface, a (3 × 3) R30°structure appears showing STM images similar to those previously published for the Si(111)/Ag system. © 1993 The American Physical Society.
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| 14. |
- Hammar, M., et al.
(författare)
-
Morphology and atomic structure of the sputtered and annealed Mo3Si and Cr3Si (110) surfaces
- 1994
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Ingår i: Physical Review B. - 0163-1829. ; 50:23, s. 17639-17642
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy was used to study the sputtered and annealed (110) surfaces of Mo3Si and Cr3Si. Both surfaces show extended and atomically flat terraces, but in the case of Mo3Si there is also a uniform distribution of Mo crystallites. This difference in morphology is discussed in terms of different preferential sputtering effects. In both cases, measured step heights show that the ideally bulk-truncated surfaces are either purely Si or metal terminated. Atomically resolved images suggest that the Mo3Si surface is Si terminated, but although no atomic resolution could be obtained for the Cr3Si surface, there are indications that this surface is instead metal terminated. © 1994 The American Physical Society.
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| 15. |
- Håkansson, K. L., et al.
(författare)
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High-resolution core-level studies of VC0.80 surfaces
- 1993
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Ingår i: Physical Review B. - 0163-1829. ; 47:16, s. 10769-10774
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution core-level-photoemission investigations of the (100), (111)-1×1, and (111)-8×1 surfaces of VC0.80 using synchrotron radiation are reported. Surface-shifted C 1s levels were observed on all three surfaces while surface-shifted V 2p levels could not be identified on any of the surfaces. The surface core-level shifts were extracted using a curve-fitting procedure. For the major surface-shifted component which was identified on all three surfaces, a shift of -0.33(±0.02) eV was determined. For the (111)-8×1 surface a second shifted component having a shift of +0.44(±0.02) eV was identified. © 1993 The American Physical Society.
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| 16. |
- Kanerva, M., et al.
(författare)
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Automatization and stress analysis data of CoCr laser weld fatigue tests
- 2019
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Ingår i: Data in Brief. - : Elsevier. - 2352-3409. ; 26
-
Tidskriftsartikel (refereegranskat)abstract
- This work includes raw and analyzed test data when using a recently developed fatigue test method for miniature laser welds in cobalt-chromium (CoCr) alloy joints [1]: 10.1016/j.jmbbm.2019.07.004. The automization of fatigue tests is crucial for saving costs and personnel resources and that is the reason why the atomization threshold and the resulting spectrum data related to CoCr welds are provided here. The finite element method based stress computation output is provided related to shearing-mode tests to support the dataset as a whole. In addition, the compositional data of the parent material and the laser weld are given.
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| 17. |
- Kanerva, M., et al.
(författare)
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Miniature CoCr laser welds under cyclic shear : Fatigue evolution and crack growth
- 2019
-
Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : ELSEVIER. - 1751-6161 .- 1878-0180. ; 99, s. 93-103
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Tidskriftsartikel (refereegranskat)abstract
- Miniature laser welds with the root depth in the range of 50-300 pm represent air-tight joints between the components in medical devices, such as those in implants, growth rods, stents and various prostheses. The current work focuses on the development of a fatigue test specimen and procedure to determine fatigue lives of shear-loaded laser welds. A cobalt-chromium (CoCr) alloy is used as a benchmark case. S-N graphs, damage process, and fracture surfaces are studied by applying x-ray analysis, atomic force microscopy, and scanning electron microscopy both before and after the crack onset. A non-linear material model is fitted for the CoCr alloy to run finite element simulations of the damage and deformation. As a result, two tensile-loaded specimen designs are established and the performance is compared to that of a traditional torque-loaded specimen. The new generation specimens show less variation in the determined fatigue lives due to well-defined crack onset point and, therefore, precise weld seam load during the experiments. The fatigue damage concentrates to the welded material and the entire weld experiences fatigue prior to the final, fracture-governed failure phase. For the studied weld seams of hardened CoCr, a regression fatigue limit of 10.8-11.8 MPa, where the stress refers to the arithmetic average shear stress computed along the region dominated by shear loading, is determined.
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| 18. |
- Landälv, Ludvig, 1982-, et al.
(författare)
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Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings
- 2019
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 688
-
Tidskriftsartikel (refereegranskat)abstract
- Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.
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| 19. |
- Le Lay, G., et al.
(författare)
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Nature of the root 3 alpha to 3 x 3 reversible phase transition at low temperature in Sn/Ge (111)
- 2001
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 175, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- Metal-induced superstructures on semiconductors at sub-monolayer coverages have been mostly studied at, or above, room temperature. Yet, recently, several reversible phase transitions, like, e.g. the root3 x root3 alpha to 3 x 3 transition in the Pb, Sn/Ge (111) prototypical systems, have been discovered below RT. The origin of these new reconstructions is very intriguing and is a matter of strong debate. Some groups privilege electronic instabilities leading to charge ordered states at low temperature (LT), while other favor dynamical effects and the formation a kind of bond density waves (BDW's) at LT. Besides these intrinsic behaviors, the role played by inevitable defects has also been emphasized by several authors. Focussing especially on the Sn/Ge (111) system, we present a detailed analysis of the spectroscopic signatures of each phase in photoemission measurements. We show that static models are impossible to reconcile with these measurements.
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| 20. |
- Papageorgiou, N., et al.
(författare)
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High resolution synchrotron radiation PES study of PbPc deposited on Pt(111)
- 2000
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 162, s. 178-183
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Tidskriftsartikel (refereegranskat)abstract
- We studied lead phthalocyanine (PbPc) films sublimated under UHV conditions on a clean Pt(111) substrate. We report results from high resolution photoelectron spectra of the Pb 5d, Ph 4f, C 1s, N 1s and Pt 4f core level using synchrotron radiation. Comparison between ultra thin films and thicker films shows that the first molecular adlayer interacts strongly with the substrate and we report evidence of Pb-Pt alloy formation on the surface. For the thick films, the C Is and N Is core level spectra show usual characteristics, however in the case of ultra thin films, we note important differences with respect to some previous results.
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| 21. |
- Rad, M. G., et al.
(författare)
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Influence of charged impurities on the surface phases of Sn/Ge(111)
- 2001
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 477:03-feb, s. 227-234
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Tidskriftsartikel (refereegranskat)abstract
- The root3 alpha and 3 x 3 reconstructions on the Ge(111)-Sn surface have been perturbed by small amounts of iodine and potassium to test the spectral response in the course of a synchrotron radiation photoemission study. We demonstrate the inadequacy of the static model of the root3 alpha phase at room temperature and of the surface charge density wave model of the 3 x 3 phase at low temperature. Instead, the influence of the charged impurities is consistently explained when considering that dynamical fluctuations in the tin adatom positions are frozen in upon passing the phase transition temperature.
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| 22. |
- Stoltz, D., et al.
(författare)
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Atomic origin of the scanning tunneling microscopy images of charge-density-waves on 1T-TaSe2
- 2008
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 403
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Tidskriftsartikel (refereegranskat)abstract
- We show atomically resolved scanning tunneling microscopy (STM) images of charge density waves (CDWs) at room temperature together with angle-resolved photoelectron band-mapping of 1T-TaSe2. By comparing the results of these two techniques, we demonstrate the atomic structure of the CDW-features observed by the STM and atomic origin of the reconstructed band-structure in this material.
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| 23. |
- Wigren, C., et al.
(författare)
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Sm- and Yb-induced reconstructions of the Si(111) surface
- 1993
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Ingår i: Physical Review B. - 0163-1829. ; 48:15, s. 11014-11019
-
Tidskriftsartikel (refereegranskat)abstract
- Low-energy electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy results from the submonolayer Sm- and Yb-induced surface structures are presented. Several similar metal-induced surface reconstructions are found to exist for Yb and Sm on Si(111) for low submonolayer coverages: 3×2, 5×1, and 7×1. At higher submonolayer coverage, Yb induces a 2×1 reconstruction while Sm induces a (3 × 3) R30°-like reconstruction. Yb is found to be divalent in all structures, whereas the Sm valence increases with increasing coverage. In the 3×2 structure only divalent Sm is present, in the 5×1 and 7×1 structures a small amount of trivalent Sm appears, and, finally, in the (3 × 3) R30°structure approximately half of the Sm atoms are trivalent. The surface Fermi-level position in the band gap for the different Sm and Yb reconstructions has been measured. The difference in valence stability between Sm and Yb is suggested to be the cause of the difference in the high-coverage structures found and the differences in pinning level for the two elements observed for the 5×1 and 7×1 structures. © 1993 The American Physical Society.
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| 24. |
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| 25. |
- Ahmadi, Sareh, et al.
(författare)
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Molecular layers of ZnPc and FePc on Au(111) surface : Charge transfer and chemical interaction
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:8, s. 084705-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the pi-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; pi-system and the central atom.
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| 26. |
- Ahmadi, Sareh, et al.
(författare)
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Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:17, s. 174702-
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and scanning tunneling microscopy. Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and an inhomogeneous charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I(root 3x root 3) or Pt(111)-I(root 7x root 7), and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.
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| 27. |
- Ghadami Yazdi, Milad, et al.
(författare)
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Structure dependent effect of silicon on the oxidation of Al(111) and Al(100)
- 2019
-
Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 684, s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of sub-monolayer silicon on the oxidation of Al(111) and Al(100) surfaces was investigated using X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. On both surfaces the adatom site is preferred over substituting Si into the Al-lattice; on Al(100) the four fold hollow site is vastly favored whereas on Al(111) bridge and hollow sites are almost equal in energy. Upon O 2 exposure, Si is not oxidized but buried at the metal/oxide interface under the growing aluminum oxide. On Al(111), Si has a catalytic effect on both the initial oxidation by aiding in creating a higher local oxygen coverage in the early stages of oxidation and, in particular, at higher oxide coverages by facilitating lifting Al from the metal into the oxide. The final oxide, as measured from the Al2p intensity, is 25–30% thicker with Si than without. This observation is valid for both 0.1 monolayer (ML) and 0.3 ML Si coverage. On Al(100), on the other hand, at 0.16 ML Si coverage, the initial oxidation is faster than for the bare surface due to Si island edges being active in the oxide growth. At 0.5 ML Si coverage the oxidation is slower, as the islands coalesce and he amount of edges reduces. Upon oxide formation the effect of Si vanishes as it is overgrown by Al 2 O 3 , and the oxide thickness is only 6% higher than on bare Al(100), for both Si coverages studied. Our findings indicate that, in addition to a vanishing oxygen adsorption energy and Mott potential, a detailed picture of atom exchange and transport at the metal/oxide interface has to be taken into account to explain the limiting oxide thickness.
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| 28. |
- Giovanelli, L., et al.
(författare)
-
Synchrotron radiation photoelectron spectroscopy study of Pb-Pc thin films on InSb(100)-(4x2)/c(8x2)
- 2001
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 486:02-jan, s. 55-64
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Tidskriftsartikel (refereegranskat)abstract
- The electronic properties and the thermal stability of a thin film of lead-phthalocyanine deposited on the InSb(100)-(4 x 2)/c(8 x 2) surface were studied by synchrotron radiation core level and valence band photoelectron spectroscopy. The interaction between the overlayer and the substrate was determined by analyzing the photoemission spectra of a thin film and of a single monolayer of adsorbed molecules. Subsequently the monolayer was annealed at increasing temperatures, leading first to a gradual change of the oxidation state of the central lead atom, then to a fragmentation of the macrocycle itself.
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| 29. |
- Göthelid, Mats, et al.
(författare)
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Adsorption site, core level shifts and charge transfer on the Pd(111)-I(root 3 x root 3) surface
- 2006
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 600:15, s. 3093-3098
-
Tidskriftsartikel (refereegranskat)abstract
- We use core level photoelectron spectroscopy and density functional theory (DFT) to investigate the iodine-induced Pd(1 1 1)-I(root 3 x root 3) structure formed at 1/3 NIL coverage. From the calculations we find that iodine adsorbs preferentially in the fcc hollow site. The calculated equilibrium distance is 2.06 angstrom and the adsorption energy is 68 kcal/mol, compared to 2.45 angstrom and 54 kcal/mol in the atop position. The adsorption energy difference between fcc and hcp hollows is 1.7 kcal/mol. Calculated Pd 3d surface core level shift on clean Pd(1 1 1) is 0.30 eV to lower binding energy, in excellent agreement with our experimental findings (0.28-0.29 eV). On the Pd(1 1 1)-I(root 3 x root 3) we find no Pd 3d surface core level shift, neither experimentally nor, theoretically. Calculated charge transfer for the fcc site, determined from the Hirshfeld partitioning method, suggests that the iodine atom remains almost neutral upon adsorption.
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| 30. |
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| 31. |
- Hirschauer, B., et al.
(författare)
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Oxidation of Ce on Si(111) studied by high-resolution photoelectron spectroscopy
- 2000
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 464:03-feb, s. 117-122
-
Tidskriftsartikel (refereegranskat)abstract
- The Si(lll)-Ce (2x2) surface was studied by photoelectron spectroscopy during oxidation and annealing. Detailed analysis of the Si 2p core-level spectra and the Ce valence band levels shows that Ce is first oxidised and then promotes oxidation of Si at room temperature by improving the oxygen uptake of the surface. Initially, no oxidation of Si can be recorded, but at exposures of 3 L O-2 or more, SiOx and higher silicon oxides are formed. After annealing to 750 degreesC, a temperature that is generally used to oxidise Si, almost all O leaves the surface. At 1045 degreesC, the Si 2p and the Ce valence band spectra of the sample show almost the same shape as for the original Si(lll)-Ce 2x2 surface. This means that oxidation/reduction of the Si(lll)-Ce 2x2 surface is reversible.
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| 32. |
- Hoglund, A., et al.
(författare)
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Breakdown of cation vacancies into anion vacancy-antisite complexes on III-V semiconductor surfaces
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:15
-
Tidskriftsartikel (refereegranskat)abstract
- An asymmetric defect complex originating from the cation vacancy on (110) III-V semiconductor surfaces which has significantly lower formation energy than the ideal cation vacancy is presented. The complex is formed by an anion from the top layer moving into the vacancy, leaving an anion antisite-anion vacancy defect complex. By calculating the migration barrier, it is found that any ideal cation vacancies will spontaneously transform to this defect complex at room temperature. For stoichiometric semiconductors the defect formation energy of the complex is close to that of the often-observed anion vacancy, giving thermodynamic equilibrium defect concentrations on the same order. The calculated scanning tunneling microscopy (STM) plot of the defect complex is also shown to be asymmetric in the [1(1)over bar0] direction, in contrast to the symmetric one of the anion vacancy. This might therefore explain the two distinct asymmetric and symmetric vacancy structures observed experimentally by STM.
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| 33. |
- Janin, E., et al.
(författare)
-
Bridge-bonded atomic oxygen on Pt(110)
- 2000
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 61:19, s. 13144-13149
-
Tidskriftsartikel (refereegranskat)abstract
- We use hybrid density-functional theory (DFT) and scanning tunneling microscopy (STM) to study oxygen adsorption on the Pt(110) surface. In the STM images oxygen appear as bright protrusions on the ridges of the missing row reconstructed surface. DFT calculations of binding energies for atomic oxygen on a bridge site shows a clear preference over hollow sites.
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| 34. |
- Johansson, Malin B., 1972-, et al.
(författare)
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Highly crystalline MAPbI3 perovskite grain formation by irreversible poor-solvent diffusion aggregation, for efficient solar cell fabrication
- 2020
-
Ingår i: Nano Energy. - : Elsevier Ltd. - 2211-2855 .- 2211-3282. ; 78
-
Tidskriftsartikel (refereegranskat)abstract
- Energy efficient synthesis providing high quality crystalline thin films are highly desired in many applications. Here we devise a non-toxic solvent approach for production of highly crystalline MAPbI3 perovskite by exploiting diffusion aggregation processes. Isopropanol solution based methylammonium lead triiodide (MAPbI3) is used in this context, where the crystal growth initiation starts in an unstable suspension far from equilibrium and the subsequent crystallization is driven by the solubility parameters. The crystal formation is monitored by scanning transmission electron microscope (STEM), observing small crystallization centers growing as time evolves to large grains with high crystal purity. Energy dispersive X-ray spectroscopy (EDS) in STEM mode revealed a Pb rich core-shell structure in newly formed grains. Nano-beam Electron Diffraction (NBED) scan defined PbI2 crystallites in the Pb rich shell with a single crystal MAPbI3 core in newly formed grains. After a week stirring, the same aggregated suspension exhibited grains with only single crystal MAPbI3 structure. The NBED analysis shows a kinetically slow transition from a core shell structure to a single crystal grain. This research presents an impactful insight on the factors that may cause sub-stoichiometric grain boundary effects which can influence the solar cell performance. In addition, the structure, morphology and optical properties of the perovskite grains have been presented. A powder of highly crystalline particles was subsequently prepared by evaporation of the solvent in a low-vacuum oven. Thin film MAPbI3 solar cells were fabricated by dissolving the powder and applying it in a classical fabrication route. The MAPbI3 solar cells gave a champion efficiency of 20% (19.9%) and an average efficiency at approximately 17% with low hysteresis effects. Here a strategy to manufacture the material structure without toxic solvents is highlighted. The single-crystal growth devised here opens both for shelf storage of materials as well as a more flexible manufacturing of devices. The process can likely be extended to other fields, where the intermediate porous framework and large surface area would be beneficial for battery or super capacitor materials.
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| 35. |
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| 36. |
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| 37. |
- Palmgren, Pål, et al.
(författare)
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Ordered phthalocyanine superstructures on Ag(110)
- 2008
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:6, s. 064702-
-
Tidskriftsartikel (refereegranskat)abstract
- Organic-metal interfaces, in particular, self-assembling systems, are interesting in the field of molecular electronics. In this study, we have investigated the formation of the Ag(110)-iron phthalocyanine (FePc) interface in a coverage range of less than 1 and up to 2 ML using synchrotron based photoelectron spectroscopy and low energy electron diffraction. As-deposited FePc forms a densely packed first layer exhibiting a 3x2/c(6x2) symmetry. Upon thermal treatment the order at the interface is modified depending on the initial FePc coverage, resulting in less densely packed but still ordered superstructures. The first monolayer is relatively strongly bound to the substrate, leading to the formation of an interface state just below the Fermi level. The highest occupied molecular orbital of FePc in the second layer is found at 1 eV higher binding energy compared to the interface state.
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| 38. |
- Papageorgiou, N., et al.
(författare)
-
Lead phthalocyanine thin films on InAs(100)-(4 x 2)/c(8 x 2) studied by synchrotron radiation photoelectron spectroscopy
- 2001
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 482, s. 1199-1204
-
Tidskriftsartikel (refereegranskat)abstract
- We used synchrotron radiation photoelectron spectroscopy to study the interface between a thin film and an ordered single monolayer of lead phthalocyanine (PbPc) deposited on the clean InAs(1 0 0)-(4 x 2)/c(8 x 2) reconstructed surface. Analysis of the core level and valence band spectra gave information about the electronic properties of the interface, the interaction between the molecule and the substrate and the valence band offset of the heterojunction.
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| 39. |
- Qian, M. C., et al.
(författare)
-
Atomic and electronic properties of anion vacancies on the (110) surfaces of InP, InAs, and InSb
- 2002
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:15
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and the electronic structure of the anion vacancy on the (110) surfaces of InP, InAs, and InSb. An inward relaxation of the three neighboring In atoms next to the anion vacancy is obtained, but the stable atomic structure depends critically on the vacancy charge state. The +1 charged vacancy exhibits a nonsymmetric configuration with one rebonded dimer, while both 0 and -1 charged vacancies show a symmetric configuration with loosely rebonded and rebonded trimer, respectively. For InP and InAs, the charge-transfer levels epsilon(+1/0) and epsilon(0/-1) are located around the center of the band gap; whereas for InSb, the -1 charge state is stable in the whole band gap. In contrast to bulk, the surface vacancy is a positive-U center. The band structures and the density of states have been calculated. Three vacancy states, one deep in the valence band and two around the band gap, are identified. Our results show that the character of the vacancy states is mainly dependent on the atomic configuration.
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| 40. |
- Qian, M. C., et al.
(författare)
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Structure of the P vacancy on the InP(110) surface from first principles
- 2003
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:3
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed density functional theory (DFT) calculations to study the geometric structure of the phosphorus vacancy on the InP(110) surface. The stable structure of the P vacancy depends critically on its charge state. For a (+1) charged P vacancy, the nonsymmetric configuration with one rebonded dimer is favored, while the symmetric configuration shows a saddle point behavior. For a (-1) charged P vacancy, both the symmetric and nonsymmetric configurations are local minima, where the symmetric configuration has the lowest energy. Using the nudged elastic band method, we have determined the reaction path and energy barrier between two configurations for both (+1) and (-1) charged vacancies. The simulated scanning tunneling microscopy (STM) images of the P vacancy on p-type and n-type InP(110) surfaces are calculated and compared with the available experimental results. We support the point of view that the observed STM image of the P vacancy is an average result of thermal flipping between two possible configurations.
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| 41. |
- Rad, M. G., et al.
(författare)
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Surface structure and local bonding on the Si(111)-Ce surface
- 2000
-
Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 166:04-jan, s. 209-213
-
Tidskriftsartikel (refereegranskat)abstract
- We used scanning tunnelling microscopy (STM) and photoelectron spectroscopy (PES) to study the cerium-induced (3 x 2) surface reconstruction of cerium (Ce) on Sn(111). Comparison with similar rare-earth-metal-induced low-coverage reconstructions on the Sn(111) surface reveals a similar nature of the chemical bond independent of the valence of the rare earth metal.
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| 42. |
- Salomon, E., et al.
(författare)
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Etching of silicon nanowires on Ag(110) by atomic hydrogen
- 2009
-
Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 603:23, s. 3350-3354
-
Tidskriftsartikel (refereegranskat)abstract
- Scanning Tunnelling Microscopy, High Resolution Electron Energy Loss Spectroscopy and High Resolution X-Ray Photoelectron Spectroscopy have been used to study the adsorption of atomic hydrogen onto Si nanowires grown on Ag(1 1 0). We demonstrate that the hydrogen strongly interacts with the Si nanowires modifying their structural and electronic properties. Hydrogen atoms etch the Si nanowires and eventually lead to their complete removal from the Ag(1 1 0) surface.
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| 43. |
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| 44. |
- Sinner-Hettenbach, M., et al.
(författare)
-
Electronic structure of SnO2(110)-4 x 1 and sputtered SnO2(110) revealed by resonant photoemission
- 2002
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 499:1, s. 85-93
-
Tidskriftsartikel (refereegranskat)abstract
- The surface properties of SnO2(1 1 0)-4 x 1 and sputtered SnO2(1 1 0) were studied comparatively by resonant photoemission of the valence band states in a photon energy range of 60-130 eV. Resonating energetic levels could be observed on the 4 x I reconstructed surface and the resonance behavior could be switched off by sputter treatment. Additionally, the Sn 4d core-levels were recorded at two photon energies in order to allow a statement about the surface's stoichiometry. A tentative explanation of the observed resonance and of the discrepancy between ordered and sputtered surface is given with regard to recent STM results on similar prepared surfaces.
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| 45. |
- Sinner-Hettenbach, M., et al.
(författare)
-
High resolution photoemission study on SnO2 gas sensors
- 2001
-
Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 391:2, s. 192-197
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Tidskriftsartikel (refereegranskat)abstract
- Pd-, Pt-doped and undoped SnO2 gas sensors were studied by synchrotron radiation photoelectron spectroscopy (SRPES) and laboratory source UPS (ultraviolet photoelectron spectroscopy). Valence band spectra were recorded for photon energies of 60-120 eV (SRPES) and for 40.81 eV (UPS). The spectra were analyzed by factor analysis and generation of difference spectra. A comparison of the samples shows that the doping material of these sensors is not introducing additional states to the surface electronic structure within the limit of detection. This leads to the conclusion that the surfaces of the grains are not enriched with the metal additives.
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| 46. |
- Sinner-Hettenbach, M., et al.
(författare)
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Oxygen-deficient SnO2(110) : a STM, LEED and XPS study
- 2001
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 477:1, s. 50-58
-
Tidskriftsartikel (refereegranskat)abstract
- The reconstruction process of SnO2(110) was investigated by scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The high-temperature 1 x 1 reconstruction could be identified as an intermediate face, transferable either to the 1 x 2 surface by annealing to higher temperature or back to the 4 x 1 reconstruction by annealing again at lower temperature. In this way, a new method to prepare well-ordered 4 x 1 terminated surfaces is introduced and the O/Sn ratio as well as the core-level positions of Sn 3d and O 1s were traced by XPS over a temperature range of 700-1200 K on freshly sputtered and on low-temperature long-time annealed SnO2(110). STM images of the 1 x 1 surface show a new structure of in-plane oxygen, ordered locally in zigzag rows that contribute to the LEED pattern as a very diffuse 2 x 1 intensity.
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| 47. |
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| 48. |
- von Schenck, H., et al.
(författare)
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CO bonding on tin modified Pt(110)-(1 x 2)
- 2003
-
Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 526:02-jan, s. 184-192
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of tin on the bonding of CO to Pt(l 10) has been studied using high-resolution electron energy loss spectroscopy, density functional theory and photoelectron spectroscopy. CO binds on-top to platinum at all investigated tin and CO coverages. Bonding of CO in Sn-Pt alloy rows is weakened compared to clean Pt(l 10). However, several different adsorption sites in Pt-only rows, inequivalent with regard to their coordination environment, show very similar characteristics with respect to CO adsorption.
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| 49. |
- Wang, Qin, et al.
(författare)
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Surface states characterization and simulation of type-II In(Ga)Sb quantum dot structures for processing optimization of LWIR detectors
- 2013
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819494955
-
Konferensbidrag (refereegranskat)abstract
- Quantum structures base on type-II In(Ga)Sb quantum dots (QDs) embedded in an InAs matrix were used as active material for achieving long-wavelength infrared (LWIR) photodetectors in this work. Both InAs and In(Ga)Sb are narrow band semiconductor materials and known to possess a large number of surface states, which apparently play significant impact for the detector's electrical and optical performance. These surface states are caused not only by material or device processing induced defects but also by surface dangling bonds, oxides, roughness and contaminants. To experimentally analyze the surface states of the QD structures treated by different device fabrication steps, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) measurements were performed. The results were used to optimize the fabrication process of the LWIR photodetectors in our ongoing project. The dark current and its temperature dependence of the fabricated IR photodetectors were characterized in temperature range 10 K to 300 K, and the experiment results were analyzed by a theoretic modeling obtained using simulation tool MEDICI.
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