Image of the Month

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Image of the Month
Posted Date: November 1, 2017

Reference:
Physical Chemistry Chemical Physics 19.30 (2017): 20281-20289

Fig. 4 Overview of the supramolecular phases and the derived structural models for 2HTPTBP on Cu(111) at different coverages (a–c: relatively low coverage; d–f: medium coverage; g–i: monolayer coverage; all the STM images were measured at RT). The red and yellow ovals indicate the individual molecules with different orientations. The intermolecular T-type-like interactions and p–p stacking interactions in the structural models are highlighted by green lines and black parallel lines, respectively. The van der Waals interactions between the phenyl groups of two neighbouring molecules are marked by green dashed lines. Tunnelling parameters: (a) U = 1.0 V, I = 30 pA; (b) U = 1.6 V, I = 30 pA; (d, e, g and h) U = 1.1 V, I = 30 pA.

Fig. 4 Overview of the supramolecular phases and the derived structural models for 2HTPTBP on Cu(111) at different coverages (a–c: relatively low coverage; d–f: medium coverage; g–i: monolayer coverage; all the STM images were measured at RT). The red and yellow ovals indicate the individual molecules with different orientations. The intermolecular T-type-like interactions and p–p stacking interactions in the structural models are highlighted by green lines and black parallel lines, respectively. The van der Waals interactions between the phenyl groups of two neighbouring molecules are marked by green dashed lines. Tunnelling parameters: (a) U = 1.0 V, I = 30 pA; (b) U = 1.6 V, I = 30 pA; (d, e, g and h) U = 1.1 V, I = 30 pA.

Abstract
The adsorption behaviour of 2H-5,10,15,20-tetraphenyltetrabenzoporphyrin (2HTPTBP) on different metal surfaces, i.e., Ag(111), Cu(111), Cu(110), and Cu(110)–(2 􏰀 1)O was investigated by scanning tunnelling microscopy at room temperature. The adsorption of 2HTPTBP on Ag(111) leads to the formation of a well- ordered two-dimensional (2D) island structure due to the mutual stabilization through the intermolecular p–p stacking and T-type-like interactions of phenyl and benzene substituents of neighboring molecules. For 2HTPTBP on Cu(111), the formed 2D supramolecular structures exhibit a coverage-dependent behaviour, which can be understood from the interplay of molecule–substrate and molecule–molecule interactions. In contrast, on Cu(110) the 2HTPTBP molecules form dispersed one-dimensional (1D) molecular chains along the [11%0] direction of the substrate due to relatively strong attractive molecule– substrate interactions. Furthermore, we demonstrate that the reconstruction of the Cu(110) surface by oxygen atoms yields a change in dimensionality of the resulting nanostructures from 1D on Cu(110) to 2D on (2 􏰀 1) oxygen-reconstructed Cu(110), induced by a decreased molecule–substrate interaction combined with attractive molecule–molecule interactions. This comprehensive study on these prototypical systems enables us to deepen the understanding of the particular role of the substrate concerning the adsorption behavior of organic molecules on metal surfaces and thus to tweak the ordering in functional molecular architectures.

Reference:
Physical Chemistry Chemical Physics 19.30 (2017): 20281-20289

Credits:
Liang Zhang, ab Michael Lepper, ab Michael Stark,ab Teresa Menzel,ab
Dominik Lungerich,bc Norbert Jux,bc Wolfgang Hieringer,bd Hans-Peter Steinru ̈ckab and Hubertus Marbach*ab

a Lehrstuhl fu ̈r Physikalische Chemie II, Universita ̈t Erlangen-Nu ̈rnberg, Egerlandstr. 3, 91058 Erlangen, Germany. E-mail: [email protected]

b Interdisciplinary Center for Molecular Materials (ICMM), Universita ̈t Erlangen-Nu ̈rnberg, Germany

c Lehrstuhl fu ̈r Organische Chemie II, Universita ̈t Erlangen-Nu ̈rnberg, Henkestr. 42, 91054 Erlangen, Germany

d Lehrstuhl fu ̈r Theoretische Chemie, Universita ̈t Erlangen-Nu ̈rnberg, Egerlandstr. 3, 91058 Erlangen, Germany

† Electronic supplementary information (ESI) available: The structure models of 2HTPTBP on Cu(111), the STM images of 2HTPTBP on Cu(110) after annealing and the atomic Cartesian coordinates for the calculated gas phase model. See DOI: 10.1039/c7cp03731g

Microscope:
UHV VT Beetle 300

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Image of the Month
Posted Date: October 18, 2017

Reference:
The Journal of Physical Chemistry C 121.19 (2017): 10470-10475

Figure 3. STM images after exposing Rh(111) to AO: (A) θO,total = 6.4 ML at Tdep = 700 K; (B) θO,total = 2.9 ML at Tdep = 350 K followed by 600 s anneal at 700 K; (C) θO,total = 0.9 ML at Tdep = 350 K followed by 600 s anneal at 700 K. Insets are LEED patterns (62 eV) taken after deposition. STM images were obtained at 30 K and conditions were (L to R) (A) 100 mV, 137 pA; 181 mV, 170 pA; 140 mV, 153 pA; (B) 50 mV, 400 pA; 70 mV, 410 pA; 50 mV, 400 pA; (C) 20 mV, 200 pA; 20 mV, 150 pA; 20 mV, 150 pA.

Figure 3. STM images after exposing Rh(111) to AO: (A) θO,total = 6.4 ML at Tdep = 700 K; (B) θO,total = 2.9 ML at Tdep = 350 K followed by 600 s anneal at 700 K; (C) θO,total = 0.9 ML at Tdep = 350 K followed by 600 s anneal at 700 K. Insets are LEED patterns (62 eV) taken after deposition. STM images were obtained at 30 K and conditions were (L to R) (A) 100 mV, 137 pA; 181 mV, 170 pA; 140 mV, 153 pA; (B) 50 mV, 400 pA; 70 mV, 410 pA; 50 mV, 400 pA; (C) 20 mV, 200 pA; 20 mV, 150 pA; 20 mV, 150 pA.

Abstract
Recent studies have shown the importance of oxide surfaces in heterogeneously catalyzed reactions. Because of the difficulties in reproducibly preparing oxidized metal surfaces, it is often unclear what species are thermodynamically stable and what factors effect the oxide formation process. In this work, we show that the thermodynamically stable phases on Rh(111) after exposure to atomic oxygen are the (2×1)- O adlayer and the trilayer surface oxide, RhO2. Formation of RhO2 was facilitated by surface defects and elevated concentrations of dissolved O atoms in the subsurface region. As the concentration of subsurface O atoms decreased, the coverage of RhO2 decreased so that only the (2×1)- O adlayer was present on the surface. The importance of subsurface oxygen species in RhO2 formation and stability indicates a complex relationship between surface structure and subsurface oxygen concentration.

Reference:
The Journal of Physical Chemistry C 121.19 (2017): 10470-10475

Credits:
Rachael G. Farber,† Marie E. Turano,† Eleanor C. N. Oskorep,† Noelle T. Wands,† Erin V. Iski,‡ and Daniel R. Killelea*,†

†Department of Chemistry & Biochemistry, Loyola University Chicago, 1068 West Sheridan Road, Chicago, Illinois 60660, United States

‡Department of Chemistry and Biochemistry, The University of Tulsa, 800 South Tucker Drive, Tulsa, Oklahoma 74104, United States

Microscope:
Closed Cycle Pan Freedom System

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Image of the Month
Posted Date: September 4, 2017

Reference:
Scientific Reports 7 (2017): 43214

Figure 3. STM images of quasi-freestanding WSe2 islands. (a) STM image of 90 × 75 Å2 area of elevated
1 ML island obtained at 2 V sample bias. (b) Image of the same area at 3 V bias. (c) Cross-section of type-B (multi-ring) pattern from (a). (d) Cross-section of type-A (single-ring) pattern from (a). The STM cross- sections are oriented perpendicular to atomic rows, and the horizontal axes are normalized to a0. The central minima in (c,d) have slightly different shapes due to different contributions of cosine modes (see Discussion part and Supplementary Note 2). (e) The larger scale, 260 × 260 Å2, STM image of phonon interference patterns on elevated 1 ML island. The image uses gradient contrast. One of type-B and one of type-A patterns are schematically surrounded by dotted lines. For gradient contrast, the missing half-rings are less visible. Bright- contrast features originate from residual contaminating particles. (Left inset) The left inset shows different absorption sites for defects, H-site vs. TM-site, that may also cause type-A vs. type-B standing wave patterns. (Right inset) STM image in the right inset clarifies the horizontal axis units in (c,d) and the orientation of crystal axes in (a,b,e). The pattern on this STM image (surrounded by dotted line type-C pattern) only contains a broad central minimum.

Figure 3. STM images of quasi-freestanding WSe2 islands. (a) STM image of 90 × 75 Å2 area of elevated
1 ML island obtained at 2 V sample bias. (b) Image of the same area at 3 V bias. (c) Cross-section of type-B (multi-ring) pattern from (a). (d) Cross-section of type-A (single-ring) pattern from (a). The STM cross- sections are oriented perpendicular to atomic rows, and the horizontal axes are normalized to a0. The central minima in (c,d) have slightly different shapes due to different contributions of cosine modes (see Discussion part and Supplementary Note 2). (e) The larger scale, 260 × 260 Å2, STM image of phonon interference patterns on elevated 1 ML island. The image uses gradient contrast. One of type-B and one of type-A patterns are schematically surrounded by dotted lines. For gradient contrast, the missing half-rings are less visible. Bright- contrast features originate from residual contaminating particles. (Left inset) The left inset shows different absorption sites for defects, H-site vs. TM-site, that may also cause type-A vs. type-B standing wave patterns. (Right inset) STM image in the right inset clarifies the horizontal axis units in (c,d) and the orientation of crystal axes in (a,b,e). The pattern on this STM image (surrounded by dotted line type-C pattern) only contains a broad central minimum.

Abstract
Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase- and frequency-synchronized dynamics of
all phonon modes, and indicates the formation of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature.

Reference:
Scientific Reports 7 (2017): 43214

Credits:
Igor Altfeder1, Andrey A. Voevodin1,2, Michael H. Check1, Sarah M. Eichfeld3, Joshua A. Robinson3 & Alexander V. Balatsky4,5

1Nanoelectronic Materials Branch, Air Force Research Laboratory, Wright Patterson AFB, OH 45433, USA.
2Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, USA.
3Department of Materials Science and Engineering and The Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA.
4Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
5Nordita, Center for Quantum Materials, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden. Correspondence and requests for materials should be addressed to I.A. (email: [email protected])

Microscope:
UHV Beetle 300 STM

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PRIcon
Image of the Month
Posted Date: August 1, 2017

Reference:
Scientific reports 7 (2017): 43451.

Figure 2. Scanning tunneling microscopy of the Graphene-Ice-Mica interface. (a) UHV STM topography (190 × 190 nm2) of a few layers graphene deposited on mica recorded at 0.2 V and 100 pA. Ice crystals (darker regions) are observed intercalated between graphene and mica surrounded by two water layers (brighter region). (b) A high resolution image (17 × 17 nm2) at the edges between an ice crystal and two water layers. A ripple-like structure is observed. (c) An atomic resolution image (6 × 6 nm2) clearly showing the ripple-like structure of graphene. (d) FFT of the hills (red circle in panel (c)) and valleys (green circle in panel (c)) of the rippled graphene surface and the higher edges of the fractal (blue circle in panel (b)).

Figure 2. Scanning tunneling microscopy of the Graphene-Ice-Mica interface. (a) UHV STM topography (190 × 190 nm2) of a few layers graphene deposited on mica recorded at 0.2 V and 100 pA. Ice crystals (darker regions) are observed intercalated between graphene and mica surrounded by two water layers (brighter region). (b) A high resolution image (17 × 17 nm2) at the edges between an ice crystal and two water layers. A ripple-like structure is observed. (c) An atomic resolution image (6 × 6 nm2) clearly showing the ripple-like structure of graphene. (d) FFT of the hills (red circle in panel (c)) and valleys (green circle in panel (c)) of the rippled graphene surface and the higher edges of the fractal (blue circle in panel (b)).

Abstract
The distribution of potassium (K+) ions on air-cleaved mica is important in many interfacial phenomena such as crystal growth, self-assembly and charge transfer on mica. However, due to experimental limitations to nondestructively probe single ions and ionic domains, their exact lateral organization
is yet unknown. We show, by the use of graphene as an ultra-thin protective coating and scanning probe microscopies, that single potassium ions form ordered structures that are covered by an ice layer. The K+ ions prefer to minimize the number of nearest neighbour K+ ions by forming row-like structures as well as small domains. This trend is a result of repulsive ionic forces between adjacent ions, weakened due to screening by the surrounding water molecules. Using high resolution conductive atomic force microscopy maps, the local conductance of the graphene is measured, revealing a direct correlation between the K+ distribution and the structure of the ice layer. Our results shed light on the local distribution of ions on the air-cleaved mica, solving a long-standing enigma. They also provide a detailed understanding of charge transfer from the ionic domains towards graphene.

Reference:
Scientific reports 7 (2017): 43451.

Credits:
Pantelis Bampoulis1,2,*, Kai Sotthewes1,*, Martin H. Siekman1, Harold J. W. Zandvliet1 & Bene Poelsema1

1Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.
2Physics of Fluids and J.M. Burgers Centre for Fluid Mechanics, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.
*These authors contributed equally to this work. Correspondence and requests for materials should be addressed to P.B. (email: [email protected])

Microscope:
UHV Beetle 3000 STM

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