| 1. |
- Bordag, Michael, et al.
(författare)
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Shear stress measurements on InAs nanowires by AFM manipulation
- 2007
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Ingår i: Small. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 3:8, s. 1398-1401
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Tidskriftsartikel (refereegranskat)abstract
- On an upward curve? The curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximum static friction force, and hence the shear stress, between the nanowire and the surface. Here, InAs nanowires are bent in a controlled manner using the tip of an atomic force microscope (see image). The shear stress can be obtained from a simple analysis according to the standard theory of elasticity.
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| 2. |
- Chen, Jianing, et al.
(författare)
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Probing Strain in Bent Semiconductor Nanowires with Raman Spectroscopy.
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:4, s. 1280-1286
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Tidskriftsartikel (refereegranskat)abstract
- We present a noninvasive optical method to determine the local strain in individual semiconductor nanowires. InP nanowires were intentionally bent with an atomic force microscope and variations in the optical phonon frequency along the wires were mapped using Raman spectroscopy. Sections of the nanowires with a high curvature showed significantly broadened phonon lines. These observations together with deformation potential theory show that compressive and tensile strain inside the nanowires is the physical origin of the observed phonon energy variations.
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| 3. |
- Conache, Gabriela, et al.
(författare)
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AFM-based manipulation of InAs nanowires
- 2008
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Ingår i: Proceedings of the IVC-17 (17th International Vacuum Congress) [also] ICSS-13 (13th International Conference on Surface Science) [also] ICN+T-2007 (International Conference on Nanoscience and Technology). - Bristol : Institute of Physics (IOP). ; 100, s. 052051-052051
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Konferensbidrag (refereegranskat)abstract
- A controlled method of manipulation of nanowires was found using the tip of an Atomic Force Microscope (AFM). Manipulation is done in the ‘Retrace Lift’ mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. Using this method, we have studied InAs nanowires on different substrates. We have also investigated interactions between wires and with gold features patterned onto the substrates.
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| 4. |
- Conache, Gabriela, et al.
(författare)
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Bias-controlled friction of InAs nanowires on a silicon nitride layer studied by atomic force microscopy
- 2010
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Ingår i: Physical Review B Condensed Matter. - College Park, Md. : American Physical Society. - 0163-1829 .- 1095-3795. ; 82:3
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Tidskriftsartikel (refereegranskat)abstract
- By studying how nanowires lying on a surface bend when pushed by an atomic force microscopy tip we are able to measure the friction between them and the substrate. Here, we show how the friction between InAs nanowires and an insulating silicon nitride layer varies when a dc voltage is applied to the tip during manipulation. The bias charges the capacitor formed by the wire and the grounded silicon back contact. Electrostatic forces increase the contact pressure and allow us to tune the friction between the wire and the silicon nitride surface. Using nanowires of about 40-70 nm diameter and a few microns in length we have applied biases in the range +12 to -12 V. A monotonic increase of the sliding friction with voltage was observed. This increase in friction with the normal force implies that the mesoscopic nanowire-surface system behaves like a macroscopic contact, despite the nanometer size of the contact in the direction of motion. The demonstrated bias-controlled friction has potential applications in MEMS/NEMS devices.
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| 5. |
- Conache, Gabriela, et al.
(författare)
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Comparative friction measurements of InAs nanowires on three substrates
- 2010
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Ingår i: Journal of Applied Physics. - College Park, MD : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 108:9
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated friction between InAs nanowires and three different substrates: SiO2, fluorosilanized SiO2, and Si3N4. The nanowires were pushed laterally with the tip of an atomic force microscope and the friction force per unit length for both static and sliding friction was deduced from the equilibrium shape of the bent wires. On all three substrates, thick wires showed a difference between sliding and static friction of up to three orders of magnitude. Furthermore, all substrates display a transition to stick-slip motion for nanowires with a diameter of less than about 40 nm. Hydrophobic and hydrophilic substrates display similar friction behavior suggesting that a condensed water layer does not strongly influence our results. The patterns and trends in the friction data are similar for all three substrates, which indicates that they are more fundamental in character and not specific to a single substrate. ©2010 American Institute of Physics.
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| 6. |
- Conache, Gabriela, et al.
(författare)
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Friction measurements of InAs nanowires on Silicon nitride by AFM manipulation
- 2009
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Ingår i: Small. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 5:2, s. 203-207
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Tidskriftsartikel (refereegranskat)abstract
- A study was conducted to perform friction measurements of InAs nanowires (NW) on silicon nitride (Si 3N 4) through atomic force microscopy (AFM) manipulation. The investigations revealed the friction force per unit length for sliding and static friction over a range of nanowire diameters. It was found that there is a significant difference between the coefficients of the two sliding modes for large wires. It was also found that the difference between the two sliding modes disappears at smaller diameters and the sliding friction becomes equal with the static friction. The AFM investigations were performed on a Nanoscope IIIa Dimension 3100, using rectangular cantilevers, with a nominal spring constant of 30 N m -1. The nanowires were manipulated, using the 'Retrace Lift' mode of the AFM controller. The friction force per unit length was gathered from the local curvature of the NWs, using standard elasticity theory.
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| 7. |
- Conache, Gabriela, 1977-, et al.
(författare)
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Nanowire friction with an applied bias
- 2009
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Konferensbidrag (refereegranskat)abstract
- Recently, we have shown how the friction acting on nanowires pushed across a surface by an AFM tip can be determined by measuring the radius of curvature of the bent wire aŸer manipulation. This technique allows us to study the friction properties of an extended mesoscale contact. Our main focus has been to determine whether such contacts behave like macroscopic objects, in which dišerences between the 'true' and 'apparent' contact areas play a key role and friction varies linearly with the applied normal force, or whether they are more like atomic-scale point contacts, wheremore fundamental processes dominate and friction oŸen is independent of the normal force. In this work we show how the friction between InAs nanowires and an insulating silicon nitride layer on a conductive silicon substrate varies when a DC voltage is applied to the AFM tip during manipulation. e tip charges the capacitor formed by the wire and the grounded silicon back contact, giving rise to attractive Coulomb forces and thus increasing the contact pressure between the wire and the silicon nitride. In this way we can vary the normal force on the sliding surfaces using a single wire, with a constant structure and contact geometry. Using nanowires of about 40-50 nm diameter and a few microns in length we have applied tip voltages in the range +12 to -12 V. Simplemodeling indicates that these voltages su›ce to give similar levels of band-lling and depletion to when the same wires are used in working wrap-gate or back-gate devices. A monotonic increase of the sliding friction with the voltage applied on the tip was observed. is implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite the nanometer size of the contact in the direction of motion.
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| 8. |
- Gray, Struan, 1965-, et al.
(författare)
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Digital Forensic Atomic Force Microscopy of Semiconductor Memory Arrays
- 2019
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Ingår i: Advances in Digital Forensics XV. - Cham : Springer. - 9783030287528 - 9783030287511 ; , s. 219-237
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Konferensbidrag (refereegranskat)abstract
- Atomic force microscopy is an analytical technique that provides very high spatial resolution with independent measurements of surface topography and electrical properties. This chapter assesses the potential for atomic force microscopy to read data stored as local charges in the cells of memory chips, with an emphasis on simple sample preparation (“delidding”) and imaging of the topsides of chip structures, thereby avoiding complex and destructive techniques such as backside etching and polishing. Atomic force microscopy measurements of a vintage EPROM chip demonstrate that imaging is possible even when sample cleanliness, stability and topographical roughness are decidedly sub-optimal. As feature sizes slip below the resolution limits of optical microscopy, atomic force microscopy offers a promising route for functional characterization of semiconductor memory structures in RAM chips, microprocessors and cryptographic hardware. © IFIP International Federation for Information Processing 2019. Published by Springer Nature Switzerland AG 2019
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| 9. |
- Gurnett, M, et al.
(författare)
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Core-level spectroscopy study of the Li/Si(111)-3 x 1, Na/Si(111)-3 x 1, and K/Si(111)-3 x 1 surfaces
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 71:19
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Tidskriftsartikel (refereegranskat)abstract
- In this article we report Si 2p core-level spectroscopy results from the alkali (Li, Na, and K) induced Si(111)-3 x 1 reconstructions. The experimental results are compared to the theoretical honeycomb-chain channel (HCC) model for,the 3 x 1 reconstruction using density functional theory (DFT) to calculate core-level shifts using both initial and final-state calculation schemes. Si 2p core-level spectra for the Li, Na, and K reconstructions showed two surface related components lying on either side of the main bulk Si 2P(3/2) peak. An additional higher binding energy component was found for K. All core-level spectra showed strong similarities leading to the conclusion that the surfaces do indeed share a common structure. With increasing alkali metal size, the lower binding energy component was found to shift away from the main bulk peak. Our theoretical calculations also show a similar trend. It is concluded that the lower binding energy surface component originates from the alkali atom bonded Si atoms. The origin of the higher binding energy component was determined based on trends in the peak height and final-state DFT calculations. It was found that this component derives from several atoms in the first and second layers. Calculations which include final-state effects were found to be in good agreement with the experimentally determined surface core-level shifts.
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| 10. |
- Jaworowski, AJ, et al.
(författare)
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Mn-induced NO dissociation on Pd(100)
- 2002
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Ingår i: Surface Science. - 0039-6028. ; 501:1-2, s. 83-92
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Tidskriftsartikel (refereegranskat)abstract
- The changes in the NO adsorption properties of Pd(1 0 0) due to the addition of Mn have been investigated using high resolution core level photoelectron spectroscopy. The Pd(1 0 0) surface was modified by forming a c(2 x 2)-PdMn surface alloy at two different Mn coverages, giving surfaces partly and fully alloyed, respectively, as shown by scanning tunneling microscopy. NO adsorption on the alloy films was found to destroy the c(2 x 2) structure. Dissociation of the NO molecules upon heating is observed, in stark contrast to NO on the clean Pd(1 0 0) surface from which all the molecules desorb intact upon heating. The dissociation process on the c(2 x 2)-PdMn-(1 x 1)-Pd mixed surface is completed at a significantly higher temperature than for the homogeneous c(2 x 2) surface. It is suggested that Mn atoms give rise to NO dissociation at lower temperatures. whereas Pd atoms situated at c(2 x 2)-(1 x 1) boundaries are responsible for the NO decomposition at higher temperatures.
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| 11. |
- Jemander, Thorbjörn, 1970-
(författare)
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STM studies of overlayers on semiconductor or insulator surfaces
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Scanning tunneling microscopy (STM) operated in ultra-high vacuum (UHV) has been used to study overlayers on semiconductor or insulator surfaces. The overlayers have been deposited by magnetron sputtering, thermal evaporation or by gas exposure, and the investigated material systems include Mo on MgO, Ni on SiC, Sn on Si(lll), C on Si(lO0) and O on Si(lll). Besides STM, the surfaces have been characterized by using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), reflection high energy electron diffraction RHEED) and atomic force microscopy ( AFM).Thin Mo films were grown on MgO(00l) substrates by ultra-high vacuum DC magnetron sputter deposition. The generated surfaces were characterized with LEED, RHEED and STM and it was found that oxygen is present on the surfaces during the initial stages of growth. Oxygen-derived reconstructions of T e Mo(lO0) surfaces are found for film thicknesses below 50 nm and it is shown that the oxygen originates from the MgO substrates.Ni has been deposited on 6H-SiC(0001) substrates kept at 600° and subsequently annealed to 800, 900 and 1000°C. Characteristic islands are formed by the annealing. Most islands feature extremely sharp edges and exceptionally flat tops containing a peculiar "stitched" pattern on top. The islands formed at 1000°c were rv300 nm in diameter and rv30 nm high and separated rv5μm from each other. AES revealed that the islands contain Ni and C and that the C is graphitically bound, as opposed to in the substrate where it is carbidically bound. From comparison with literature, it is concluded that these islands are containing, or are made up from, a graphite intercalation compound (GIC) with the Ni as the intercalant.The ( )3 x v'3)-Sn/Si(lll) surface has been studied with STM and AES, and it is found that it contains 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 ( )3 x }3) adatom neighbours. Close to some defect configurations, a very local (3 x 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 configurations.Submonolayers of C and Si have been deposited on a Si(lO0) surface and ubsequently annealed to form the Si(100)-c(4x4) reconstruction. AES, LEED and STM investigations reveal that a sufficient amount of C to get a full coverage of the c( 4 x 4) reconstruction is equivalent to 0.07 ML. A deposition of 0.035 ML C produces a coverage of only 19%, indicating that there is not a complete separation of the C between the c(4x4) and 2xl reconstructed areas. We conclude that the c( 4x4) reconstruction is strain induced, and that a combination of the mixed ad-dimer and buckled ad-dimer models accurately explains the observed features.Initial oxidation stages of the Si(lll)-(7x7) surface have been studied and the first observation of metastable oxygen in STM has been made. Comparison between bias-dependent STM images and previous photoemission studies indicates that the metastable oxygen appears (as a protrusion) only in STM images with tip biases larger than 2.1 V.A software package called ProbeMaster for SPM image acquisition and processing is presented. The features include a plugin system for specialized SPM image processing, file format translations, tip movement, microscope drivers and general extensions.Included in the thesis, there is also a discussion of a model for the STM tip etching process. The possibility that the time evolution of the etching current can be basis for estimating the sharpness of tips is considered. The speed of the etching process and the timing needed to resolve tip-sized features are some of the issues that are discussed.
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| 12. |
- Lundgren, Edvin, et al.
(författare)
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The intermetallic oxidation of Pd(100)
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- We have studied the Pd(100)-(√5×√5)-O structure formed by adsorption of 0.8 ML of oxygen by Scanning Tunneling Microscopy (STM), High Resolution Core Level Spectroscopy (HRCLS) and Density Functional Theory (DFT). We show that a recent tensor Low Energy Electron Diffraction (LEED) analysis of the Pd(100)-(√5×√5)-O structure is incompatible with our results from this structure. A new model that is consistent with our results is suggested. We also demonstrate the existence of dislocations observed by STM in the Pd(100)-(√5×√5)-O structure and explain their geometrical arrangement
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| 13. |
- Pettersson, Håkan, et al.
(författare)
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Friction measurements on InAs NWs by AFM manipulation
- 2008
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Konferensbidrag (refereegranskat)abstract
- We discuss a new approach to measure the friction force between elastically deformed nanowires and a surface. The wires are bent, using an AFM, into an equilibrium shape determined by elastic restoring forces within the wire and friction between the wire and the surface. From measurements of the radius of curvature of the bent wires, elasticity theory allows the friction force per unit length to be calculated. We have studied friction properties of InAs nanowires deposited on SiO2, silanized SiO2 and Si3N4 substrates. The wires were typically from 0.5 to a few microns long, with diameters varying between 20 and 80 nm. Manipulation is done in a `Retrace Lift' mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. We will report on interesting static- and sliding friction experiments with nanowires on the different substrates, including how the friction force per unit length varies with the diameter of the wires.
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| 14. |
- Pettersson, Håkan, 1962-, et al.
(författare)
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Nanowire friction with an applied bias
- 2010
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Ingår i: Bulletin of the American Physical Society. - : American Physical Society.
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Konferensbidrag (refereegranskat)abstract
- Recently, we have shown how the friction experienced by nanowires pushed by an AFM tip can be determined by measuring their radius of curvature after manipulation [1]. It is of fundamental interest to know whether the wires behave like macroscopic objects, or if they are more like true atomic-scale point contacts where friction becomes independent of the applied normal force. Here we study how the friction between InAs nanowires and a SiN layer on conductive silicon varies when a DC voltage is applied. The tip charges the capacitor formed by the wire and the silicon back contact, causing attractive Coulomb forces and so increasing the contact pressure. A monotonic increase of the sliding friction with voltage was observed. This implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite being only nanometers in size in the direction of motion.
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| 15. |
- Sawcer, Stephen, et al.
(författare)
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Genetic risk and a primary role for cell-mediated immune mechanisms in multiple sclerosis
- 2011
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 476:7359, s. 214-219
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Tidskriftsartikel (refereegranskat)abstract
- Multiple sclerosis is a common disease of the central nervous system in which the interplay between inflammatory and neurodegenerative processes typically results in intermittent neurological disturbance followed by progressive accumulation of disability. Epidemiological studies have shown that genetic factors are primarily responsible for the substantially increased frequency of the disease seen in the relatives of affected individuals, and systematic attempts to identify linkage in multiplex families have confirmed that variation within the major histocompatibility complex (MHC) exerts the greatest individual effect on risk. Modestly powered genome-wide association studies (GWAS) have enabled more than 20 additional risk loci to be identified and have shown that multiple variants exerting modest individual effects have a key role in disease susceptibility. Most of the genetic architecture underlying susceptibility to the disease remains to be defined and is anticipated to require the analysis of sample sizes that are beyond the numbers currently available to individual research groups. In a collaborative GWAS involving 9,772 cases of European descent collected by 23 research groups working in 15 different countries, we have replicated almost all of the previously suggested associations and identified at least a further 29 novel susceptibility loci. Within the MHC we have refined the identity of the HLA-DRB1 risk alleles and confirmed that variation in the HLA-A gene underlies the independent protective effect attributable to the class I region. Immunologically relevant genes are significantly overrepresented among those mapping close to the identified loci and particularly implicate T-helper-cell differentiation in the pathogenesis of multiple sclerosis.
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| 16. |
- Schnadt, Joachim, et al.
(författare)
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Structural study of adsorption of isonicotinic acid and related molecules on rutile TiO2(110) I: XAS and STM
- 2003
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Ingår i: Surface Science. - 0039-6028. ; 540:1, s. 39-54
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) have been used to study the absorption of monolayers of the pyridinecarboxylic acid monomers (isonicotinic acid, nicotinic acid, and picolinic acid) and benzoic acid on a rutile TiO2(1 1 0) surface. We find that the pyridine and phenyl rings are oriented with their planes largely perpendicular to the surface. The azimuthal orientations are strongly influenced by adsorbate-adsorbate interactions, which in each case leads to at least two different molecular species. In order to reach this conclusion a detailed strategy has been developed for the interpretation of angle-dependent XAS data, which does not rely on any curve fitting procedures. (C) 2003 Elsevier B.V. All rights reserved.
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| 17. |
- Todorova, M, et al.
(författare)
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The Pd(100)-(root 5 x root 5)R27 degrees-O surface oxide revisited
- 2003
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Ingår i: Surface Science. - 0039-6028. ; 541:1-3, s. 101-112
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Tidskriftsartikel (refereegranskat)abstract
- Combining high-resolution core-level spectroscopy, scanning tunneling microscopy and density-functional theory calculations we reanalyze the Pd(100)-(root5 x root5)R27degrees-O surface oxide phase. We find that the prevalent structural model, a rumpled PdO(001) film suggested by previous low energy electron diffraction (LEED) work [Surf. Sci. 494 (2001) L799], is incompatible with all three employed methods. Instead, we suggest the two-dimensional film to consist of a strained PdO(101) layer on top of Pd(100). LEED intensity calculations show that this model is compatible with the experimental data of Saidy et al. (C) 2003 Elsevier B.V. All rights reserved.
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