| 1. |
- Aristov, Victor Yu., et al.
(författare)
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Graphene Synthesis on Cubic SiC/Si Wafers. Perspectives for Mass Production of Graphene-Based Electronic Devices
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:3, s. 992-995
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Tidskriftsartikel (refereegranskat)abstract
- The outstanding properties of graphene, a single graphite layer, render it a top candidate for substituting silicon in future electronic devices, The so far exploited synthesis approaches, however, require conditions typically achieved in specialized laboratories and result in graphene sheets whose electronic properties are often altered by interactions with substrate materials. The development of graphene-based technologies requires an economical fabrication method compatible with mass production. Here we demonstrate for the fist Lime the feasibility of graphene synthesis on commercially available cubic SiC/Si substrates of >300 mm in diameter, which result in graphene flakes electronically decoupled from the substrate. After optimization of the preparation procedure, the proposed synthesis method can represent a further big step toward graphene-based electronic technologies.
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| 2. |
- Krasnikov, Sergey A., et al.
(författare)
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Formation of extended covalently bonded Ni porphyrin networks on the Au(111) surface
- 2011
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 4:4, s. 376-384
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Tidskriftsartikel (refereegranskat)abstract
- The growth and ordering of {5,10,15,20-tetrakis(4-bromophenyl)porphyrinato}nickel(II) (NiTBrPP) molecules on the Au(111) surface have been investigated using scanning tunnelling microscopy, X-ray absorption, core-level photoemission, and microbeam low-energy electron diffraction. When deposited onto the substrate at room temperature, the NiTBrPP forms a well-ordered close-packed molecular layer in which the molecules have a flat orientation with the porphyrin macrocycle plane lying parallel to the substrate. Annealing of the NiTBrPP layer on the Au(111) surface at 525 K leads to dissociation of bromine from the porphyrin followed by the formation of covalent bonds between the phenyl substituents of the porphyrin. This results in the formation of continuous covalently bonded porphyrin networks, which are stable up to 800 K and can be recovered after exposure to ambient conditions. By controlling the experimental conditions, a robust, extended porphyrin network can be prepared on the Au(111) surface that has many potential applications such as protective coatings, in sensing or as a host structure for molecules and clusters.
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| 3. |
- Ng, May Ling, et al.
(författare)
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Effect of substrate nanopatterning on the growth and structure of pentacene films
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:11, s. 115449-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of modulating the structure of thin pentacene (C22H14) films by a nanopatterned inert substrate, known as hexagonal boron nitride nanomesh, is reported. Films of different thickness are grown and characterized by x-ray absorption, core-level photoemission, low-energy electron microscopy, microbeam low-energy electron diffraction, and scanning tunneling microscopy. Initially the pentacene molecules adsorb with the molecular plane lying flat on the substrate but they tend to flip up with increasing coverage, forming well-ordered monolayer-thick islands of upright molecules with low nucleation density. The herringbone packing of the upright molecules is observed with scanning tunneling microscopy. The electronic structure of the adsorbed molecules is very similar to that of the gas-phase pentacene, implying weak interaction with the substrate and between the molecules. The periodic corrugation of the substrate surface causes the monolayer of upright pentacene molecules to form two different coincidence superstructures. The lattice parameters of the pentacene unit cell for each of these two substrate-induced domains are determined from the microdiffraction patterns. Both domains can occur in several equivalent configurations, thus resulting in a number of twins with a typical size of a few micrometers. The first monolayer grows in a layer-by-layer mode until it is completed while the second monolayer forms diffusion-limited fractal islands. Upon annealing, the pentacene films are thermally stable up to approximately 80 degrees C and thereafter the onset of desorption is observed.
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| 4. |
- Vinogradov, Nikolay, et al.
(författare)
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Formation and Structure of Graphene Waves on Fe(110)
- 2012
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 109:2
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Tidskriftsartikel (refereegranskat)abstract
- A very rich Fe-C phase diagram makes the formation of graphene on iron surfaces a challenging task. Here we demonstrate that the growth of graphene on epitaxial iron films can be realized by chemical vapor deposition at relatively low temperatures, and that the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a novel periodically corrugated pattern on Fe(110). Using low-energy electron microscopy and scanning tunneling microscopy, we show that it is modulated in one dimension forming long waves with a period of similar to 4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The observed topography of the graphene/Fe superstructure is well reproduced by density functional theory calculations, and found to result from a unique combination of the lattice mismatch and strong interfacial interaction, as probed by core-level photoemission and x-ray absorption spectroscopy.
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| 5. |
- Vinogradov, Nikolay, et al.
(författare)
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Hole doping of graphene supported on Ir(111) by AlBr3
- 2013
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Ingår i: Applied Physics Letters. - : American Chemical Society (ACS). - 0003-6951 .- 1077-3118. ; 102:6, s. 061601-
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter we report an easy and tenable way to tune the type of charge carriers in graphene, using a buried layer of AlBr3 and its derivatives on the graphene/Ir(111) interface. Upon the deposition of AlBr3 on graphene/Ir(111) and subsequent temperature-assisted intercalation of graphene/Ir(111) with atomic Br and AlBr3, pronounced hole doping of graphene is observed. The evolution of the graphene/Br-AlBr3/Ir(111) system at different stages of intercalation has been investigated by means of microbeam low-energy electron microscopy/electron diffraction, core-level photoelectron spectroscopy and angle-resolved photoelectron spectroscopy.
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| 6. |
- Vinogradov, Nikolay, et al.
(författare)
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One-Dimensional Corrugation of the h-BN Monolayer on Fe(110)
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:3, s. 1775-1781
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new nanopatterned structure represented by a single atomic layer of hexagonal boron nitride (h-BN) forming long periodic waves on the Fe(110) surface. The growth process and the structure of this system are characterized by X-ray absorption (XAS), core-level photo-emission spectroscopy (CL PES), low-energy electron microscopy (LEEM), microbeam low-energy electron diffraction (mu LEED), and scanning tunneling microscopy (STM). The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of A. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [(1) over bar 11] or [1 (1) over bar1] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110), with approximately equal area of the boron nitride domains of each orientation.
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| 7. |
- Ahmad, Y., et al.
(författare)
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NMR and NEXAFS Study of Various Graphite Fluorides
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:26, s. 13564-13572
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Tidskriftsartikel (refereegranskat)abstract
- Graphite fluorides with different structural types (CyF)(n) (y = 2.5, 2, and 1) and room temperature graphite fluorides were studied by solid state,NMR and NEXAFS. Data extracted from those two techniques are complementary, providing information about the C-F bonding and the hybridization character of the carbon atom valence states. The comparison of data obtained by different methods such as NMR, Raman, and X-ray absorption leads to similar conclusions regarding the chemical bonding in fluorographites. Several major configurations of fluorinated graphites are discussed, that is, planar sheets with mainly sp(2) hybridization in room temperature graphite fluorides and corrugated sheets with sp(3) hybridization in covalent high temperature graphite fluoride. Different references such as highly oriented pyrolytic graphite (HOPG), graphitized carbon nanodiscs (graph-CNDs) and nanodiamonds (NDs) have also been investigated for comparison.
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| 8. |
- Aristov, V. Yu., et al.
(författare)
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Electronic properties of potassium-doped FePc
- 2010
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Ingår i: Organic Electronics. - : Elsevier BV. - 1566-1199. ; 11:8, s. 1461-1468
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of electronic structure of the organic semiconductor iron-phthalocyanine with potassium doping has been studied by means of photoemission spectroscopy, near-edge X-ray absorption fine structure and density functional theory (DFT) calculations. The DFT study and detailed analysis of the core-level spectra permit us to suggest possible lattice sites for the potassium ions. The data disclosed filling of the lowest unoccupied molecular orbital upon doping and associated changes of the core level absorption spectra. None of the films prepared in our studies showed a finite electronic density of states at the Fermi level. (C) 2010 Elsevier B.V. All rights reserved.
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| 9. |
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| 10. |
- Doyle, Catherine M., et al.
(författare)
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Ni-Cu ion exchange observed for Ni(II)-porphyrins on Cu(111)
- 2014
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 50:26, s. 3447-3449
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Tidskriftsartikel (refereegranskat)abstract
- A Ni-Cu ion exchange has been observed for (5,15-dibromo-10,20-diphenylporphyrinato)nickel(II) (NiDBrDPP) and (5,10,15,20-tetrakis-(4-bromophenyl) porphyrinato)nickel(II) (NiTBrPP) on Cu(111). The ion exchange proceeds at a faster rate for the NiDBrDPP/Cu(111) system compared to NiTBrPP/Cu(111). This is explained in terms of the macrocycle-substrate distance and the distortions
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| 11. |
- Haberer, D., et al.
(författare)
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Anisotropic Eliashberg function and electron-phonon coupling in doped graphene
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 88:8
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate, with high-resolution angle-resolved photoemission spectroscopy, the spectral function of potassium-doped quasi-free-standing graphene on Au. Angle-dependent x-ray photoemission and density functional theory calculations demonstrate that potassium intercalates into the graphene/Au interface, leading to an upshift of the K-derived electronic band above the Fermi level. This empty band is what makes this system perfectly suited to disentangle the contributions to electron-phonon coupling coming from the pi band and K-derived bands. From a self-energy analysis we find an anisotropic electron-phonon coupling strength lambda of 0.1 (0.2) for the K Gamma (K M) high-symmetry directions in momentum space, respectively. Interestingly, the high-energy part of the Eliashberg function which relates to graphene's optical phonons is equal in both directions but only in K M does an additional low-energy part appear.
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| 12. |
- Kummer, Kurt, et al.
(författare)
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Electronic Structure of Genomic DNA: A Photoemission and X-ray Absorption Study.
- 2010
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 114:29, s. 9645-9652
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of genomic DNA has been comprehensively characterized by synchrotron-based X-ray absorption and X-ray photoelectron spectroscopy. Both unoccupied and occupied states close to the Fermi level have been unveiled and attributed to particular sites within the DNA structure. A semiconductor-like electronic structure with a band gap of approximately 2.6 eV has been found at which the pi and pi* orbitals of the nucleobase stack make major contributions to the highest occupied and lowest unoccupied molecular orbitals, respectively, in agreement with previous theoretical predictions.
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| 13. |
- Lisa Pinardi, Anna, et al.
(författare)
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Tailored Formation of N-Doped Nanoarchitectures by Diffusion-Controlled on-Surface (Cyclo)-Dehydrogenation of Heteroaromatics
- 2013
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 7:4, s. 3676-3684
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Tidskriftsartikel (refereegranskat)abstract
- Surface-assisted cyclodehydrogenation and dehydrogenative polymerization of polycyclic (hetero)aromatic hydrocarbons (PAH) are among the most important strategies for bottom-up assembly of new nanostructures from their molecular building blocks. Although diverse compounds have been formed in recent years using this methodology, a limited knowledge on the molecular machinery operating at the nanoscale has prevented a rational control of the reaction outcome. We show that the strength of the PAH-substrate interaction rules the competitive reaction pathways (cyclodehydrogenation versus dehydrogenative polymerization). By controlling the diffusion of N-heteroaromatic precursors, the on-surface dehydrogenation can lead to monomolecular triazafullerenes and diazahexabenzocoronenes (N-doped nanographene), to N-doped oligomeric or polymeric networks, or to carbonaceous monolayers. Governing the on-surface dehydrogenation process is a step forward toward the tailored fabrication of molecular 2D nanoarchitectures distinct from graphene and exhibiting new properties of fundamental and technological interest.
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| 14. |
- Lubben, Olaf, et al.
(författare)
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Self-assembly of Fe nanocluster arrays on templated surfaces
- 2012
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 111:7
-
Tidskriftsartikel (refereegranskat)abstract
- The growth of Fe nanoclusters on the Ge(001) and MoO2/Mo(110) surfaces has been studied using low-temperature scanning tunneling microscopy (STM) and X-ray magnetic circular dichroism (XMCD). STM results indicate that at low coverage Fe atoms self-assemble on both surfaces into well-separated nanoclusters, which nucleate at equivalent surface sites. Their size, shape, and the observed spatial separation are dictated by the substrate and depend on preparation conditions. Annealing the Fe nanoclusters on Ge(001) at 420 K leads to the formation of linear nanocluster arrays, which follow the Ge dimer rows of the substrate, due to cluster mobility at such temperature. In turn, linear Fe nanocluster arrays are formed on the MoO2/Mo(110) surface at room temperature at a surface coverage greater than 0.5 monolayer. This is due to the more pronounced row pattern of the MoO2/Mo(110) surface compared to Ge(001). These nanocluster arrays follow the direction of the oxide rows of the strained MoO2/Mo(110) surface. The Fe nanoclusters formed on both surfaces show a superparamagnetic behavior as measured by XMCD. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676207]
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| 15. |
- Luebben, Olaf, et al.
(författare)
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Fe Nanoclusters on the Ge(001) Surface Studied by Scanning Tunneling Microscopy, Density Functional Theory Calculations and X-Ray Magnetic Circular Dichroism
- 2011
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 4:10, s. 971-978
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Tidskriftsartikel (refereegranskat)abstract
- The growth of Fe nanoclusters on the Ge(001) surface has been studied using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM results indicate that Fe nucleates on the Ge(001) surface, forming well-ordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge(001) surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism.
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| 16. |
- Murphy, Barry E., et al.
(författare)
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Homolytic Cleavage of Molecular Oxygen by Manganese Porphyrins Supported on Ag(111)
- 2014
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 8:5, s. 5190-5198
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen binding and cleavage are important for both molecular recognition and catalysis. Mn-based porphyrins in particular are used as catalysts for the epoxidation of alkenes, and in this study the homolytic cleavage of O-2 by a surface-supported monolayer of Mn porphyrins on Ag(111) is demonstrated by scanning tunneling microscopy, X-ray absorption, and X-ray photoemission. As deposited, {5,10,15,20-tetraphenylporphyrinato}Mn(III)CI(MnCITPP) adopts a saddle conformation with the average plane of its macrocyde parallel to the substrate and the axial CI ligand pointing upward, away from the substrate. The adsorption of MnCITPP on Ag(111) Is accompanied by a reduction of the Mn oxidation state from Mn(III) to Mn(II) due to charge transfer between the substrate and the molecule. Annealing the Mn(II)CITPP monolayer up to 510 K causes the chlorine ligands to desorb from the porphyrins while leaving the monolayer intact. The Mn(II)TPP is stabilized by the surface acting as an axial ligand for the metal center. Exposure of the Mn(11)TPP/Ag(111) system to molecular oxygen results in the dissociation of O-2 and forms pairs of Mn(111)OTPP molecules on the surface. Annealing at 445 K reduces the Mn(111)OTPP complex back to Mn(II)TPP/Ag(111). The activation energies for Cl and 0 removal were found to be 0.35 +/- 0.02 eV and 0.26 +/- 0.03 eV, respectively.
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| 17. |
- Ng, May Ling, 1975-
(författare)
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Characterization and Functionalization of 2D Overlayers Adsorbed on Transition Metals
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two-dimensional layered materials, namely monolayer hexagonal boron nitride and graphene were grown by CVD on various transition metals. The physical and chemical properties of these systems were characterized systematically using synchrotron-based spectroscopic techniques, scanning tunneling microscopy and low energy electron diffraction. It is learned that the overlayer–substrate interaction is caused by the overlayer π–substrate d band hybridization. The physical properties of these overlayers depend on the strength of interaction and the degree of lattice matching at the interface. The strength of interaction between the boron nitride and graphene overlayers and the transition metal substrates is increasing from Pt(111)–Ir(111)–Rh(111)–Ru(0001). For overlayers adsorbed on Rh and Ru, the interplay between these two parameters can result in corrugation of the overlayer, i.e. a surface with bonding and non-bonding areas. The amplitude of corrugation is increasing with the strength of interfacial interaction. The corrugated BN overlayer (BN nanomesh) was used as a template for the growth of two-dimensional and highly dispersive Au nanoparticles. In addition, the inert BN nanomesh was used as a substrate for the deposition of pentacene molecules that conform to the corrugated surface while preserving the herringbone crystal structure. The coadsorption of oxygen and Co clusters on the nanomesh was investigated. Oxygen was utilized to lower the Co surface energy, i.e. to prevent Co agglomeration. It is observed that the smaller Co clusters intercalate through the BN overlayer upon soft annealing. Beside the surface structure, the substrate induced surface reactivity of the MG overlayer was employed to promote the hydrogenation of graphene on Pt, Ir and Ni. The graphene layer adsorbed on Pt and Ir shows higher H uptake than MG/Ni. Furthermore the uptake increases with the size of the bonded graphene. The small H uptake for MG/Ni was attributed to the electron localization in the C-Ni bonds.
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| 18. |
- Ng, May Ling, et al.
(författare)
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Controlling Hydrogenation of Graphene on Transition Metals
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:43, s. 18559-18565
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Tidskriftsartikel (refereegranskat)abstract
- A monatomic layer of graphite (MG or graphene) adsorbed on the (111) faces of transition metals Pt, Ir, and Ni, has been employed for controlling the atomic hydrogen adsorption site selectivity and the amount of hydrogen adsorbed upon saturation. The variations in the graphene-metal chemical bonding caused by hydrogenation and the values of saturated hydrogen coverage have been studied by X-ray photoemission and X-ray absorption spectroscopy. The hydrogenation of the graphene/metal systems has also been compared to the hydrogen adsorption on highly oriented pyrolytic graphite under the same experimental conditions. It has been found that graphene adsorption on the transition metal substrates can drastically enhance the hydrogen uptake values. The highest values have been observed for MG/Ir(111), less for MG/Pt(111), even less for MG/Ni and the least for the adsorption on bulk graphite. The high level of H coverage on MG/Ir and MG/Pt has been assigned to the preferential H adsorption on the more bonding patches (pores) of the MG/metal coincidence lattice. This adsorption creates unpaired electrons which contribute to a strengthening of the graphene-metal bonds. In this way, the densest possible graphane-like patches can be formed on MG/Pt and MG/Ir. On the MG/Ni interface the formation of graphane is obstructed by the strong interfacial bonding.
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| 19. |
- Rusz, Jan, et al.
(författare)
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Dynamical effects in x-ray absorption spectra of graphene and monolayered h-BN on Ni(111)
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:7, s. 073402-
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Tidskriftsartikel (refereegranskat)abstract
- We present first-principles calculations of x-ray absorption spectra of graphene and hexagonal BN monolayer on the Ni(111) substrate. Including dynamical core-hole screening effects according to the theory of Mahan-Nozieres-de Dominics (MND) results in an overall good agreement with previously published experimental data and our new observations. This approach provides a unified first-principles description of the electronic structure and core excitations in the sp(2)-bonded materials on metal surfaces and a better insight into the dynamics of screening effects. We demonstrate in particular that the observed spectral features of graphene and hexagonal BN can be well reproduced with the MND theory, and that they are determined by a delicate balance between initial and final-state effects.
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| 20. |
- Schulte, Karina, et al.
(författare)
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Bandgap formation in graphene on Ir(111) through oxidation
- 2013
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Ingår i: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 267, s. 74-76
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Tidskriftsartikel (refereegranskat)abstract
- A graphene monolayer on single crystal Ir(111) has been studied using angle-resolved photoemission spectroscopy (ARPES) before and after exposure to atomic oxygen. With increasing oxygen coverage the Dirac cone, centered on the K-point of the Brillouin zone, broadens and finally transforms to a parabolic rather than linear feature, introducing a pronounced energy bandgap at the Fermi level. The opening of a bandgap of at least 0.35 eV was observed at the oxygen exposure close to the saturation coverage. (C) 2012 Elsevier B. V. All rights reserved.
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| 21. |
- Simonov, K. A., et al.
(författare)
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Controllable oxidation of h-BN monolayer on Ir(111) studied by core-level spectroscopies
- 2012
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 606:3-4, s. 564-570
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Tidskriftsartikel (refereegranskat)abstract
- The effect of atomic oxygen adsorption on the structure and electronic properties of monolayer hexagonal boron nitride (h-BN) grown on Ir(111) has been studied using near edge X-ray absorption fine structure spectroscopy (NEXAFS), photoelectron spectroscopy (PES), and low-energy electron diffraction (LEED). It has been shown that the oxidation of the h-BN monolayer occurs through a gradual substitution of N by O in the h-BN lattice. This process leads to the formation of defect sites corresponding to three different types of the B atom environment (BN3-xOx with x=1,2,3). The oxidation of the h-BN monolayer is very different from the case of graphene on Ir(111), where adsorption of atomic oxygen results mainly in the formation of epoxy groups [J. Phys. Chem. C. 115, 9568 (2011)]. A post-annealing of the h-BN monolayer after oxygen exposure results in further destruction of the B N bonds and formation of a B2O3-like structure. (C) 2011 Elsevier B.V. All rights reserved.
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| 22. |
- Simonov, K. A., et al.
(författare)
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Features of metal atom 2p excitations and electronic structure of 3d-metal phthalocyanines studied by X-ray absorption and resonant photoemission
- 2013
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Ingår i: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 267, s. 132-135
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Tidskriftsartikel (refereegranskat)abstract
- The metal atom 2p core excitations in 3d-metal phthalocyanines (MPc's, M = Ni, Co, Fe) have been studied via a combination of near edge X-ray absorption fine structure (NEXAFS) and resonant photoemission (ResPE) spectroscopy. On the basis of comparison of the corresponding spectra of NiPc, CoPc and FePc it has been shown that the presence of a partly filled molecular orbital (MO) dramatically affects the formation and decay processes of the M 2p core excitation in CoPc and, to a greater extend, in FePc due to the significant 3d-3d exchange interaction. It has been found that the low-lying unoccupied electronic states of NiPc, CoPc and FePc are strongly localized within the MN4 quasi-molecule and have nearly pure 3d character. Moreover, mainly 3d metallic character of the high-lying occupied MOs of NiPc, CoPc and FePc has been proved. (C) 2012 Elsevier B. V. All rights reserved.
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| 23. |
- Simonov, Konstantin, 1988-, et al.
(författare)
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Effect of Substrate Chemistry on the Bottom-Up Fabrication of Graphene Nanoribbons : Combined Core-Level Spectroscopy and STM Study
- 2014
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:23, s. 12532-12540
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Tidskriftsartikel (refereegranskat)abstract
- Atomically precise graphene nanoribbons (GNRs) can be fabricated via thermally induced polymerization of halogen containing molecular precursors on metal surfaces. In this paper the effect of substrate reactivity on the growth and structure of armchair GNRs (AGNRs) grown on inert Au(111) and active Cu(111) surfaces has been systematically studied by a combination of core-level X-ray spectroscopies and scanning tunneling microscopy. It is demonstrated that the activation threshold for the dehalogenation process decreases with increasing catalytic activity of the substrate. At room temperature the 10,10'-dibromo-9,9'-bianthracene (DBBA) precursor molecules on Au(111) remain intact, while on Cu(111) a complete surface-assisted dehalogenation takes place. Dehalogenation of precursor molecules on Au(111) only starts at around 80 degrees C and completes at 200 degrees C, leading to the formation of linear polymer chains. On Cu(111) tilted polymer chains appear readily at room temperature or slightly elevated temperatures. Annealing of the DBBA/Cu(111) above 100 degrees C leads to intramolecular cyclodehydrogenation and formation of flat AGNRs at 200 degrees C, while on the Au(111) surface the formation of GNRs takes place only at around 400 degrees C. In STM, nanoribbons have significantly reduced apparent height on Cu(111) as compared to Au(111), 70 +/- 11 pm versus 172 +/- 14 pm, independently of the bias voltage. Moreover, an alignment of GNRs along low-index crystallographic directions of the substrate is evident for Cu(111), while on Au(111) it is more random. Elevating the Cu(111) substrate temperature above 400 degrees C results in a dehydrogenation and subsequent decomposition of GNRs; at 750 degrees C the dehydrogenated carbon species self-organize in graphene islands. In general, our data provide evidence for a significant influence of substrate reactivity on the growth dynamics of GNRs.
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| 24. |
- Syres, Karen L., et al.
(författare)
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Adsorbate-Induced Modification of Surface Electronic Structure: Pyrocatechol Adsorption on the Anatase TiO2 (101) and Rutile TiO2 (110) Surfaces
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:44, s. 23515-23525
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the adsorption of pyrocatechol on anatase TiO2 (101) and rutile TiO2 (110) single crystals. Photoemission results suggest the pyrocatechol molecule adsorbs on both surfaces predominantly in a bidentate geometry. Using the searchlight effect, the carbon K-edge NEXAFS spectra recorded for pyrocatechol on anatase TiO2 (101) and rutile TiO2 (110) show the phenyl rings in the pyrocatechol molecule to be oriented at 27 +/- 6 degrees and 2.3 +/- 8 degrees, respectively, from the surface normal. Experimental data and computational models of the pyrocatechol-anatase TiO2 interface indicate the appearance of new occupied and unoccupied states on adsorption due to hybridization between the electronic states of the pyrocatechol molecule and the surface. The atomic character of the new orbitals created facilitates direct photoinjection from pyrocatechol into anatase TiO2 and induces a strong final state effect in the carbon K-edge NEXAFS spectrum.
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| 25. |
- Syres, K. L., et al.
(författare)
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Pyrocatechol as a surface capping molecule on raffle TiO2 (110)
- 2012
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 606:3-4, s. 273-277
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Tidskriftsartikel (refereegranskat)abstract
- A 'cap and dip' method of adsorbing ruthenium di-2,2'-bipyridy1-4,4'-dicarboxylic acid diisocyanate (N3 dye) on a rutile TiO2 (110) surface was investigated using pyrocatechol as a capping molecule. This method involves cleaning the rutile surface in ultra-high vacuum (UHV), depositing pyrocatechol onto the surface to 'cap' the adsorption sites, removing from vacuum, 'dipping' in an N3 dye solution and returning to vacuum. Photoemission measurements following the return of the crystal to vacuum suggest that the pyrocatechol keeps the surface free from contamination on exposure to atmosphere. Photoemission spectra also indicate that the pyrocatechol capping molecules are replaced by the N3 dye in solution and that the N3 dye is adsorbed intact on the nitile TiO2 (110) surface. This technique may allow other large molecules, which are thermally unstable to evaporation in UHV, to be easily deposited onto TiO2 surfaces. (C) 2011 Elsevier B.V. All rights reserved.
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