Image of the Month

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Image of the Month
Posted Date: April 1, 2015
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3C-AFM current maps of Array 1 at various applied magnetic fields between ±434 Oe. Insets show position on a resistance versus field hysteresis loop measured for one particle. Saturated antiparallel (low current) and parallel (high current) states are marked with antiparallel or parallel arrows.

Arrays of nanoscale magnetic tunnel junctions (MTJs) are being pursued for bit patterned media (BPM) and magnetoresistive random access memory (MRAM). Device performance depends on coercive field and critical bias switching distributions. Many well-established techniques allow for the characterization of ensemble average behavior, but conventional device-by-device characterization requires cumbersome processing steps. In addition to costly and complicated fabrication steps, the devices are often obscured for imaging.

Credits: Stephan K. Piotrowski, Samuel D. Oberdick, and Sara A. Majetich
Physics Department, Carnegie Mellon University

Microscope: RHK Technology AFM/STM UHV 350

Control System: RHK Technology R9 Control System

Abstract:
Arrays of nanoscale magnetic tunnel junctions (MTJs) are being pursued for bit patterned media (BPM) and magnetoresistive random access memory (MRAM). Device performance depends on coercive field and critical bias switching distributions. Many well-established techniques allow for the characterization of ensemble average behavior, but conventional device-by-device characterization requires cumbersome processing steps. In addition to costly and complicated fabrication steps, the devices are often obscured for imaging.

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Image of the Month
Posted Date: March 1, 2015
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This image, recorded with molecular resolution at 150 °C, provides direct evidence for the stability of the metal-organic chains at high temperature on the Au(100) surface. Elevated-temperature STM image collected with the sample held at 425 K showing platinum(II) dipyridyltetrazine 1D chains on the reconstructed Au(100) surface.

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.

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

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Image of the Month
Posted Date: February 1, 2015
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Mid infrared plasmon mode observed in doped semiconductor SrTiO3 fabricated by Argon ion etching. Color represents near field optical signal, which is overlaid on top of the topography profile in a 24µm square area.

The image is obtained by a RHK broadband variable temperature scanning near field optical microscope.

Credits: Professor Cheng Cen, Department of Physics and Astronomy, West Virgina University, Morgantown, WV

Microscope: RHK broadband variable temperature scanning near field optical microscope.

Control System: RHK R9-STM and PMC100

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Image of the Month
Posted Date: January 1, 2015
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These figures show the arrangement of 5 and 6-membered rings of D2O on the Pt(111) surface, imaged at 80 K.

Credits: Daniel Killelea, Rachael Farber and Jon Derouin at Loyola University,Chicago and Ludo Juurlink at Leiden University, The Netherlands

Microscope: RHK PanScan Flow-LT STM

Control System: RHK R9-STM and PMC100

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