| 1. |
- Jemander, S.T., et al.
(författare)
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STM study of the C-induced Si(100)-c(4×4) reconstruction
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Sociaty. - 1098-0121 .- 1550-235X. ; 65:11, s. 115321-
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Tidskriftsartikel (refereegranskat)abstract
- We report a direct and reliable way to produce the Si(100)-c(4×4) reconstruction by submonolayer deposition from a SiC source and subsequent annealing. Auger electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) investigations reveal that a C amount equivalent to 0.07 monolayers (ML’s) is sufficient to obtain full coverage of the c(4×4) reconstruction. A deposition of 0.035 ML’s C produces a c(4×4) coverage of only 19%, indicating that C is not only present in the c(4×4) areas, but also in the 2×1 areas. There is not enough C to make it a regular part of the c(4×4) reconstruction and we therefore conclude that the c(4×4) reconstruction is strain induced. We find that a combination of the mixed ad-dimer and buckled ad-dimer models explains all main features observed in the STM images. Images of freshly prepared c(4×4) surfaces exhibit a decoration of approximately 50% of the unit cells, which is attributed to perpendicular ad-dimers. Long exposures (>20 h) to the UHV background gas quench these features and the c(4×4) reconstruction appears as if more homogeneous.
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| 2. |
- Jemander, S.T., et al.
(författare)
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STM study of the surface defects of the (v3×v3)-Sn/Si(1 1 1) surface
- 2001
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Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 475:1-3, s. 181-193
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Tidskriftsartikel (refereegranskat)abstract
- The (v3×v3)-Sn/Si(1 1 1) surface has been studied with scanning tunneling microscopy (STM) and Auger electron spectroscopy, and it is found that it contains basically five different types of defects originating from substitutional atoms and vacancies. The influence the defects have on their immediate neighbourhood is investigated and found to extend to the third nearest (v3×v3) adatom neighbour. Close to some defect constellations, a very local (3×3) periodicity in the apparent height in the STM images is found. This periodicity is shown to be a linear superposition of the perturbations generated by the individual defects in the constellations. The superposition of the height modulation is accurate and linear for a wide range of tip biases, as for combinations of different types of defects. Its linearity is explained in terms of small perturbations in the surface electronic structure. We also provide an explanation why the linearity breaks down when large perturbations are probed with small tip biases.
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| 3. |
- Jemander, S.T., et al.
(författare)
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Surface structure of Si(100) with submonolayer coverages of C
- 2002
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Elsevier. - 1073-5615 .- 1543-1916. ; 89:1-3, s. 415-419
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Konferensbidrag (refereegranskat)abstract
- We report a combined STM, LEED and AES study of Si(100) surfaces prepared by coevaporation from two MBE-sources with Si and SiC, respectively. The flux from the SiC source contains 10% C, enabling studies of deposited layers with C-concentrations in the range 0-10%. After room temperature deposition, the structures have been annealed at 600 °C to generate a c(4 × 4) reconstruction. This has previously been reported to contain from 0.0 to 0.5 monolayers (ML) of C. Annealing at 800 °C irreversibly transforms the c(4 × 4) surface to a 2 × 1-reconstructed surface that contains precipitates of SiC. Since only 0.07 ML of C is needed to have 98% of the surface covered with the c(4 × 4) reconstruction, we conclude that the c(4 × 4) reconstruction is impurity-induced rather than having C-atoms in well defined positions within each unit cell. The c(4 × 4) reconstruction is attributed to a basic structure containing buckled parallel ad-dimers, which in approximately 50% of the reconstructed unit cells is decorated with perpendicular dimers. © 2002 Elsevier Science B.V. All rights reserved.
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| 4. |
- Priebe, Gisela, et al.
(författare)
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Sexual abuse and associations with psychosocial aspects of health : A population-based study with Swedish adolescents
- 2010
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Ingår i: Nordic Journal of Psychiatry. - : Taylor & Francis. - 0803-9488 .- 1502-4725. ; 64:1, s. 40-48
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Tidskriftsartikel (refereegranskat)abstract
- Background: Few population-based Nordic studies with adolescents investigate the associations between sexual abuse (SA) and psychosocial health. Aim: Associations between adolescents' self-reported experiences of SA different severity and aspects of psychosocial health such as emotional and behavioral problems, sense of coherence and self-esteem were investigated. Methods: A school-based study with 1107 Swedish high school seniors was conducted. The students completed the Strengths and Difficulties Questionnaire (SDQ), the Sense of Coherence Scale (SOC), I think I am and a self-report survey that included questions about SA, socio-demographic variables and family variables. Results: SA was related to more emotional and behavioral problems, weaker SOC and lower self- esteem when compared with non-abuse. There was also a dose-response effect insofar as more severe abuse was related to poorer psychosocial health. When adjusted for socio-demographic and family-related variables, the associations between penetrating SA and most of the health variables weakened or disappeared. SOC was associated with penetrating SA even after adjustment. Conclusions: This population-based study suggests that SA should not be regarded as an isolated factor in relation to psychosocial health as the associations at a group level may be smaller than expected. Among a number of covariates, family variables such as parental bonding showed to be especially important. Sense of Coherence may be of special interest in further research and clinical treatment.
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| 5. |
- Razado-Colambo, Ivy, et al.
(författare)
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Hydrogen-induced metallization on Ge(1 1 1) c(2 × 8)
- 2006
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 252:15, s. 5300-5303
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Tidskriftsartikel (refereegranskat)abstract
- We have studied hydrogen adsorption on the Ge(1 1 1) c(2 × 8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2 × 8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states.
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| 6. |
- Razado-Colambo, Ivy, 1977-, et al.
(författare)
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STM study of site selective hydrogen adsorption on Si(111) 7×7
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 71:23, s. 235411-
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of atomic hydrogen has been studied by scanning tunneling microscopy (STM) and photoelectron spectroscopy with a focus on the different adsorption sites provided by the Si(111) 7×7 surface. At low temperature, the hydrogen atoms adsorb preferentially on adatoms while at elevated temperatures the rest atoms are the first to become hydrogen terminated. The hydrogen-terminated rest atoms are no longer visible in the STM images and the surrounding adatoms appear brighter compared to the clean 7×7 surface. This indicates that there is a local charge transfer back to the adatoms from the rest atoms. Three kinds of modified triangular subunit cells of the 7×7 reconstruction have been identified corresponding to one, two, and three hydrogen-terminated rest atoms, respectively. A detailed study of the apparent height using STM line profiles through the adatom and rest atom positions on the surface is presented. These line profiles show a characteristic and reproducible variation of the apparent heights of the adatoms for the different kinds of triangular subunit cells and the changes are interpreted in terms of charge transfer. The very local nature of the charge transfer is concluded from the fact that only the hydrogen termination of neighboring rest atoms is significantly affecting the apparent height of an adatom.
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| 7. |
- Razado, Ivy, et al.
(författare)
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Electronic structure of Ge(111)c(2x8) : STM, angle-resolved photoemission, and theory
- 2009
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 79
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Tidskriftsartikel (refereegranskat)abstract
- The surface electronic structure of Ge(111)c(2x8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (A(T),A(R)) and rest atoms (R-T,R-R) confirming the presence of asymmetries within the c(2x8) cell. The ARPES study resulted in a more detailed picture of the surface electronic structure of the Ge(111)c(2x8) surface compared to earlier studies. The energy dispersion curves showed the presence of seven surface bands labeled A1, A2, A2(), A3, A4, A4(), and A5. The experimental surface bands were compared to the calculated band structure of the full c(2x8) unit cell. The most important results are (i) we have identified a split surface-state band in the photoemission data that matches a split between R-T and R-R derived rest atom bands in the calculated surface band structure. This allows us to identify the upper A2 band with the R-R and the lower A2() band with the R-T rest atoms. (ii) The uppermost highly dispersive band (A1) originates from states below the adatom and rest atom layers and should not be confused with rest atom bands A2 and A2(). (iii) The bias-dependent changes in the adatom/rest atom contrast in the experimental STM images were closely reproduced by simulated STM images generated from the calculated electronic structure. (iv) A split was observed in the back-bond derived surface band at higher emission angles (A4 and A4()).
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| 8. |
- Uhrberg, Roger, et al.
(författare)
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Electronic structure of Sn/Si(111) √3×√3 : Indications of a low-temperature phase
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 62:12, s. 8082-8086
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Tidskriftsartikel (refereegranskat)abstract
- The Sn/Si(111) √3×√3 surface has been studied by photoelectron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy. Unlike Sn/Ge(111), the Sn/Si(111) surface shows a √3×√3 LEED pattern at low temperature also (70 K). The electronic structure, however, is inconsistent with a pure √3×√3 phase. Sn 4d spectra exhibit two major components and the valence band shows two surface bands. These features have been associated with the low-temperature 3×3 phase in the case of Sn/Ge(111). The similarity in the electronic structure points to stabilization of a low-temperature phase for Sn/Si(111) also, but at a significantly lower temperature (<70 K).
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| 9. |
- Zhang, Hanmin, et al.
(författare)
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High-temperature annealing and surface photovoltage shifts on Si(111)7×7
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:3, s. 035318-
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Tidskriftsartikel (refereegranskat)abstract
- The relation between annealing temperature and surface photovoltage (SPV) shifts on the Si(111)7×7 surface of lightly n-doped substrates has been studied by core-level and valence-band photoelectron spectroscopies at 100 K. The SPV shift was found to depend strongly on the annealing temperature and the photon flux. Between 900 and 1150 °C the magnitude of the SPV shift shows a general decrease with annealing temperature. After a narrow plateau, the SPV shift becomes positive for annealings at 1250 and 1270 °C. As a consequence, the adatom surface state of the 7×7 surface appears above the Fermi level. The unexpected SPV shift can be explained by the formation of a p-type layer during high-temperature annealing of the Si sample. The role of boron and carbon contaminations has been discussed in this context in the literature. By correlating the SPV shifts with the C 1s and B 1s core-level signals, we conclude that carbon, but not boron, is involved in the formation of the p-type layer. Further, our results show that the annealing temperature plays a crucial role when binding energies are determined from photoemission spectra at low temperature. The effect is of particular importance in the study of surface band-gap openings related to phase transitions at low temperature.
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