Ordering a rhenium catalyst on Ag(001) through molecule-surface step interaction

AbstractAtomic scale studies of the anchoring of catalytically active complexes to surfaces may provide valuable insights for the design of new catalytically active hybrid systems. In this work, the self-assembly of 1D, 2D and 3D structures of the complex fac-Re(bpy)(CO)3Cl (bpy = 2,2′-bipyridine), a CO2 reduction catalyst, on the Ag(001) surface are studied by a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. Infrared and sum frequency generation spectroscopy confirm that the complex remains chemically intact under sublimation. Deposition of the complexes onto the silver surface at 300 K leads to strong local variations in the resulting surface coverage on the nanometer scale, indicating that in the initial phase of deposition a large fraction of the molecules is desorbing from the surface. Low coverage regions show a decoration of step edges aligned along the crystal’s symmetry axes <110>. These crystallographic directions are found to be of major importance to the binding of the complexes to the surface. Moreover, the interaction between the molecules and the substrate promotes the restructuring of surface steps along these directions. Well-aligned and decorated steps are found to act as nucleation point for monolayer growth (2D) before 3D growth starts.

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Subsurface cation vacancy stabilization of the magnetite (001) surface

Science ◽

10.1126/science.1260556 ◽

2014 ◽

Vol 346 (6214) ◽

pp. 1215-1218 ◽

Cited By ~ 133

Author(s):

R. Bliem ◽

E. McDermott ◽

P. Ferstl ◽

M. Setvin ◽

O. Gamba ◽

...

Keyword(s):

Iron Oxides ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Atomic Scale ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Material Interface ◽

Functional Theory ◽

Ordered Array ◽

Low Energy Electron

Iron oxides play an increasingly prominent role in heterogeneous catalysis, hydrogen production, spintronics, and drug delivery. The surface or material interface can be performance-limiting in these applications, so it is vital to determine accurate atomic-scale structures for iron oxides and understand why they form. Using a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory calculations, we show that an ordered array of subsurface iron vacancies and interstitials underlies the well-known (2×2)R45° reconstruction of Fe3O4(001). This hitherto unobserved stabilization mechanism occurs because the iron oxides prefer to redistribute cations in the lattice in response to oxidizing or reducing environments. Many other metal oxides also achieve stoichiometry variation in this way, so such surface structures are likely commonplace.

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Template-controlled on-surface synthesis of a lanthanide supernaphthalocyanine and its open-chain polycyanine counterpart

Nature Communications ◽

10.1038/s41467-019-13030-7 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 2

Author(s):

Qitang Fan ◽

Jan-Niclas Luy ◽

Martin Liebold ◽

Katharina Greulich ◽

Malte Zugermeier ◽

...

Keyword(s):

Electronic Properties ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Scanning Tunneling ◽

Electron Systems ◽

Silver Surface ◽

Tunneling Microscopy ◽

Open Chain ◽

Chemical Structures ◽

Optical And Electronic Properties

Abstract Phthalocyanines possess unique optical and electronic properties and thus are widely used in (opto)electronic devices, coatings, photodynamic therapy, etc. Extension of their π-electron systems could produce molecular materials with red-shifted absorption for a broader range of applications. However, access to expanded phthalocyanine analogues with more than four isoindoline units is challenging due to the limited synthetic possibilities. Here, we report the controlled on-surface synthesis of a gadolinium-supernaphthalocyanine macrocycle and its open-chain counterpart poly(benzodiiminoisoindoline) on a silver surface from a naphthalene dicarbonitrile precursor. Their formation is controlled by the on-surface high-dilution principle and steered by different metal templates, i.e., gadolinium atoms and the bare silver surface, which also act as oligomerization catalysts. By using scanning tunneling microscopy, photoemission spectroscopy, and density functional theory calculations, the chemical structures along with the mechanical and electronic properties of these phthalocyanine analogues with extended π-conjugation are investigated in detail.

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Imaging and identification of point defects in PtTe2

npj 2D Materials and Applications ◽

10.1038/s41699-020-00196-8 ◽

2021 ◽

Vol 5 (1) ◽

Author(s):

Kuanysh Zhussupbekov ◽

Lida Ansari ◽

John B. McManus ◽

Ainur Zhussupbekova ◽

Igor V. Shvets ◽

...

Keyword(s):

Point Defects ◽

Density Functional ◽

Transition Metal Dichalcogenides ◽

Density Functional Theory Calculations ◽

Charge Carrier Mobility ◽

Scanning Tunneling Spectroscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Recombination Rates ◽

And Performance

AbstractThe properties and performance of two-dimensional (2D) materials can be greatly affected by point defects. PtTe2, a 2D material that belongs to the group 10 transition metal dichalcogenides, is a type-II Dirac semimetal, which has gained a lot of attention recently due to its potential for applications in catalysis, photonics, and spintronics. Here, we provide an experimental and theoretical investigation of point defects on and near the surface of PtTe2. Using scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements, in combination with first-principle calculations, we identify and characterize five common surface and subsurface point defects. The influence of these defects on the electronic structure of PtTe2 is explored in detail through grid STS measurements and complementary density functional theory calculations. We believe these findings will be of significance to future efforts to engineer point defects in PtTe2, which is an interesting and enticing approach to tune the charge-carrier mobility and electron–hole recombination rates, as well as the site reactivity for catalysis.

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Dual role of CO in the stability of subnano Pt clusters at the Fe3O4(001) surface

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1605649113 ◽

2016 ◽

Vol 113 (32) ◽

pp. 8921-8926 ◽

Cited By ~ 64

Author(s):

Roland Bliem ◽

Jessi E. S. van der Hoeven ◽

Jan Hulva ◽

Jiri Pavelec ◽

Oscar Gamba ◽

...

Keyword(s):

Density Functional ◽

Elevated Temperatures ◽

Time Lapse ◽

Dual Role ◽

Oxidation Catalyst ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Active Metal ◽

Catalytically Active ◽

The Stability

Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1–CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase.

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Self-assembly of N-heterocyclic carbenes on Au(111)

Nature Communications ◽

10.1038/s41467-021-23940-0 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Alex Inayeh ◽

Ryan R. K. Groome ◽

Ishwar Singh ◽

Alex J. Veinot ◽

Felipe Crasto de Lima ◽

...

Keyword(s):

Self Assembly ◽

Density Functional ◽

Surface Coverage ◽

High Mobility ◽

Heterocyclic Carbenes ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Surface Geometry ◽

Functional Theory ◽

Interesting Alternative

AbstractAlthough the self-assembly of organic ligands on gold has been dominated by sulfur-based ligands for decades, a new ligand class, N-heterocyclic carbenes (NHCs), has appeared as an interesting alternative. However, fundamental questions surrounding self-assembly of this new ligand remain unanswered. Herein, we describe the effect of NHC structure, surface coverage, and substrate temperature on mobility, thermal stability, NHC surface geometry, and self-assembly. Analysis of NHC adsorption and self-assembly by scanning tunneling microscopy and density functional theory have revealed the importance of NHC-surface interactions and attractive NHC-NHC interactions on NHC monolayer structures. A remarkable way these interactions manifest is the need for a threshold NHC surface coverage to produce upright, adatom-mediated adsorption motifs with low surface diffusion. NHC wingtip structure is also critical, with primary substituents leading to the formation of flat-lying NHC2Au complexes, which have high mobility when isolated, but self-assemble into stable ordered lattices at higher surface concentrations. These and other studies of NHC surface chemistry will be crucial for the success of these next-generation monolayers.

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Unlocking surface octahedral tilt in two-dimensional Ruddlesden-Popper perovskites

Nature Communications ◽

10.1038/s41467-021-27747-x ◽

2022 ◽

Vol 13 (1) ◽

Author(s):

Yan Shao ◽

Wei Gao ◽

Hejin Yan ◽

Runlai Li ◽

Ibrahim Abdelwahab ◽

...

Keyword(s):

Density Functional ◽

Carrier Transport ◽

Plane Surface ◽

Structural Phase ◽

Density Functional Theory Calculations ◽

Spin Splitting ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Out Of Plane ◽

Inversion Asymmetry

AbstractMolecularly soft organic-inorganic hybrid perovskites are susceptible to dynamic instabilities of the lattice called octahedral tilt, which directly impacts their carrier transport and exciton-phonon coupling. Although the structural phase transitions associated with octahedral tilt has been extensively studied in 3D hybrid halide perovskites, its impact in hybrid 2D perovskites is not well understood. Here, we used scanning tunneling microscopy (STM) to directly visualize surface octahedral tilt in freshly exfoliated 2D Ruddlesden-Popper perovskites (RPPs) across the homologous series, whereby the steric hindrance imposed by long organic cations is unlocked by exfoliation. The experimentally determined octahedral tilts from n = 1 to n = 4 RPPs from STM images are found to agree very well with out-of-plane surface octahedral tilts predicted by density functional theory calculations. The surface-enhanced octahedral tilt is correlated to excitonic redshift observed in photoluminescence (PL), and it enhances inversion asymmetry normal to the direction of quantum well and promotes Rashba spin splitting for n > 1.

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Atomistic investigation of surface characteristics and electronic features at high-purity FeSi(110) presenting interfacial metallicity

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2021203118 ◽

2021 ◽

Vol 118 (17) ◽

pp. e2021203118

Author(s):

Biao Yang ◽

Martin Uphoff ◽

Yi-Qi Zhang ◽

Joachim Reichert ◽

Ari Paavo Seitsonen ◽

...

Keyword(s):

Low Temperature ◽

Density Of States ◽

Density Functional ◽

Iron Silicide ◽

Density Functional Theory Calculations ◽

Surface Characteristics ◽

Scanning Tunneling ◽

Magnetic Characteristics ◽

Tunneling Microscopy ◽

Single Crystal Surfaces

Iron silicide (FeSi) is a fascinating material that has attracted extensive research efforts for decades, notably revealing unusual temperature-dependent electronic and magnetic characteristics, as well as a close resemblance to the Kondo insulators whereby a coherent picture of intrinsic properties and underlying physics remains to be fully developed. For a better understanding of this narrow-gap semiconductor, we prepared and examined FeSi(110) single-crystal surfaces of high quality. Combined insights from low-temperature scanning tunneling microscopy and density functional theory calculations (DFT) indicate an unreconstructed surface termination presenting rows of Fe–Si pairs. Using high-resolution tunneling spectroscopy (STS), we identify a distinct asymmetric electronic gap in the sub-10 K regime on defect-free terraces. Moreover, the STS data reveal a residual density of states in the gap regime whereby two in-gap states are recognized. The principal origin of these features is rationalized with the help of the DFT-calculated band structure. The computational modeling of a (110)-oriented slab notably evidences the existence of interfacial intragap bands accounting for a markedly increased density of states around the Fermi level. These findings support and provide further insight into the emergence of surface metallicity in the low-temperature regime.

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Understanding molecular self-assembly of a diol compound by considering competitive interactions

Physical Chemistry Chemical Physics ◽

10.1039/c6cp05818c ◽

2016 ◽

Vol 18 (39) ◽

pp. 27390-27395 ◽

Cited By ~ 4

Author(s):

Oscar Díaz Arado ◽

Maike Luft ◽

Harry Mönig ◽

Philipp Alexander Held ◽

Armido Studer ◽

...

Keyword(s):

Density Functional Theory ◽

Scanning Tunneling Microscopy ◽

Self Assembly ◽

Density Functional ◽

Competitive Interactions ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Functional Theory ◽

Chemical Groups

With a combination of scanning tunneling microscopy and density functional theory, effects on molecular self-assembly involving two distinct chemical groups were investigated.

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