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Image of the Month
Posted Date: January 1, 2016
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Non-contact AFM images showing metal-organic coordination chains of platinum(II)dipyridinyl-tetrazine on the reconstructed Au(100) surface.  The model in the lower right panel is based on the molecular resolution image shown in the lower left.

Credits:
Daniel Skomski, Christopher D. Tempas, Kevin A. Smith, and Steven L. Tait*
Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States

Microscope:
RHK Technology AFM/STM UHV 7500

Control System:
RHK Technology SPM 1000 Control System

Reference:
D. Skomski, C. D. Tempas, K. A. Smith, and S. L. Tait

“Redox-Active On-Surface Assembly of Metal-Organic Chains with Single-Site Pt(II),”
Journal of the American Chemical Society136, 9862-9865 (2014).
DOI: 10.1021/ja504850f

Abstract:
The formation and stabilization of well-defined transition-metal single sites at surfaces may open new routes to achieve higher selectivity in heterogeneous catalysts. Organic ligand coordination to produce a well-defined oxidation state in weakly reducing metal sites at surfaces, desirable for selective catalysis, has not been achieved. Here, we address this using metallic platinum interacting with a dipyridyl tetrazine ligand on a single crystal gold surface. X-ray photoelectron spectroscopy measurements demonstrate the metal−ligand redox activity and are paired with molecular-resolution scanning probe microscopy to elucidate the structure of the metal−organic network. Comparison to the redox-inactive diphenyl tetrazine ligand as a control experiment illustrates that the redox activity and molecular-level ordering at the surface rely on two key elements of the metal complexes: (i) bidentate binding sites providing a suitable square-planar coordination geometry when paired around each Pt, and (ii) redox-active functional groups to enable charge transfer to a well-defined Pt(II) oxidation state. Ligand-mediated control over the oxidation state and structure of single-site metal centers that are in contact with a metal surface may enable advances in higher selectivity for next generation heterogeneous catalysts.

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Image of the Month
Posted Date: December 1, 2015
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Figure 1: Clean H terminated Si 100 surface 100nm*100nm
Scanning parameters:
Sample bias: -3V;   Current:-0.45nA;  Scanning angle:45 deg; Integral gain: 200 m/As; Pixel: 1024*1024; Scanning speed: 476 nm/s

Preparing atomically clean samples are a primary requirement for developing patterned dopant devices based on hydrogen resist lithography.  The samples from this study are used to develop moderately low temperature silicon overgrowth to ensure epitaxial Si on Si growth.  The overall process involves, hydrogen lithography, phosphine dosing and subsequent dopant activation, and then silicon overgrowth to encapsulate the patterned devices.  Quality Si epitaxial overgrowth is essential to good local electronic properties for the encased atomic-scale phosphor-based donor devices.  The silicon (100) samples ( 4 mm x 10 mm ) were first chemically cleaned using  an RCA Piranha recipe and HF dipped to passivate the surface. The samples were then load locked into a UHV system for thermal processing. Thermal processing includes a couple of 1200 °C flashes (maintaining low -10 Torr pressure all the time) and a 1050 °C anneal for a few hours. The samples were then hydrogen terminated in situ with an atomic hydrogen source and moved to the Pan Scan STM chamber for RT imaging using the recent new design RHK all metal tip holder.  W polycrystalline tips were used.

Credits:
Images and data graciously provided by Richard Silver, NIST.

Microscope:
RHK PanScan Microscope

Control System:
RHK Technology Control System

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Panscan Freedom SPM,  VT Beetle
Events
Event Date: December 1, 2015

Dec. 1-3
2015 MRS Fall Meeting Exhibit, Boston, MA

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Panscan Freedom SPM,  VT Beetle
Events
Event Date: September 17, 2015

Sept. 17-21
NC-AFM 2015, Cassis, France

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