Image of the Month

Image of the Month
Posted Date: July 1, 2013
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12nm x 12nm STM and IETS maps simultaneously acquired on the surface of the 9 ML Pb island at a 1 nA tunneling current.The STM image (a) was obtained at a tunnel bias of 750 mV. The IETS image (b) was acquired at a tunnel bias of 9 mV.(c) Cross section of the IETS image in (b)

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The inelastic electron tunneling spectrum measured on top of the 9 ML Pb island. Resonant phonon emission peaks develop at a 9 mV tunnel bias. Inset: tunnel I-V curve for the same island measured in a broader bias range.Steps on this curve are due to QW resonances from transverse electron interference. The decrease of the barrier height at large bias was compensated by a slow increase of a tunneling gap, at a rate of 0.4 Å per |V|.

Reference:
PhysRevLett.109.166402 DOI 10.1103/Physlet.109.166402

Credits:
Igor Altfeder, K. A. Matveev, A. A. Voevodin

Microscope:
RHK Technology VT UHV STM Model UHV300

Control System:
RHK Technology SPM 1000

Abstract:
Thin Pb films epitaxially grown on 7 7 reconstructed Si(111) represent an ideal model system for studying the electron-phonon interaction at the metal-insulator interface. For this system, using a combination of scanning tunneling microscopy and inelastic electron tunneling spectroscopy, we performed direct real-space imaging of the electron-phonon coupling parameter. We found that ! increases when the electron scattering at the Pb=Sið111Þ interface is diffuse and decreases when the electron scattering is specular. We show that the effect is driven by transverse redistribution of the electron density inside a quantum well.

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Image of the Month
Posted Date: June 1, 2013
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STM image (0.7 V/2 pA) showing two CoPc islands with kinks in different directions of the CoPc lattice. (b) Possible model to explain the kinks, where the shifted row jumps to the neighboring equivalent site. Image acquired at 50K.

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150 × 150 nm2 STM image (100 pA/0.16 V) of graphene on the Ir(111) surface before CoPc deposition. (inset) Atomically resolved STM image of the moiré (1 nA/0.1 V). The hexagonal pattern is the moiré caused by the lattice mismatch between graphene and Ir.

Reference:

The Journal of Physical Chemistry C – dx.doi.org/10.1021/jp306439h | J. Phys. Chem. C 2012, 116, 20433−20437

Credits:

Sampsa K. Hamalaïnen, Mariia Stepanova, Robert Drost, Peter Liljeroth, Jouko Lahtinen, and Jani Sainio – Department of Applied Physics, Aalto University School of Science in Otakaari, Finland.

Microscope:

RHK Technology VT UHV 7500 Scanning Tunneling Microscope (STM)

Control System:

RHK Technology SPM 1000 Control System

Abstract:

We have studied the adsorption and self assembly of cobalt phthalocyanine (CoPc) on epitaxial graphene grown on iridium (111) by scanning tunneling microscopy (STM), Auger electron spectroscopy, and low energy electron diffraction (LEED). CoPc deposited on graphene/Ir(111) at room-temperature self-assembles into large, well-ordered domains with a nearly square unit cell. On the basis of the observed LEED pattern and STM images, a detailed structure for the overlayer is proposed. Despite the corrugation of the moiré pattern of graphene on Ir(111), its hexagonal symmetry is not translated to the CoPc layer. This is in contrast to systems with stronger graphene−metal interaction that makes graphene on Ir(111) a convenient, clean, and well defined model system for studying molecular doping of graphene.

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Image of the Month
Posted Date: May 1, 2013
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Initial test of Nazin Group RHK PanScan-STM with Closed Cycle Cryostat provides atomic resolution with HOPG at 14 K.

RHK is proud to highlight the first atomic resolution image acquired on our PanScan SPM connected to a running Closed-Cycle Helium Cryostat.  This unique STM was developed in collaboration with Dr. George Nazin in the Chemistry Department at the University of Oregon, whose group acquired this image.

In addition to being an extremely stable SPM, this microscope includes an integrated parabolic mirror with three-axis manipulator to allow highly efficient light collection from the tunnel junction.   This first atomically resolved image acquired at 14K demonstrates a high-level of isolation from the vibration of the Closed-Cycle Cryostat.  The goal of a helium-free STM has been an elusive dream for the many researchers unable to secure a steady supply of affordable liquid helium.

RHK’s new helium-free PanScan STM enables every researcher to run their SPM at cryogenic temperatures endlessly without the trouble and expense of liquid helium.

Credits:

Dr. George Nazin, Assistant Professor, Physical Chemistry, University of Oregon

Microscope:

RHK LT PanScan-STM customized for light collection

Control System:

RHK R9-STM and PMC100

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Image of the Month
Posted Date: April 1, 2013
institution

Left Image – STM images of (a, b) the buffer layer and (d) QFMLG. Panel (a) shows the long-range periodicity imposed on the buffer layer by the substrate. The solid and dashed diamond designates the (6 x 6). Images in panel (a) were taken with a sample bias of +1.7 V. Under optimal tunneling conditions (main image in panel a) as opposed to earlier stages (inset in (a)) the atomic lattice superimposed on the (6 · 6) periodicity is revealed. Panels (b, d) are zoomed-in images of the buffer layer and QFMLG imaged with a sample bias of -0.223 V and +0.103 V, respectively. The upper insets in (b, d) present the structural models of the buffer layer and QFMLG, respectively. The lower insets in panels (b) and (d) are zoomed in 2D Fast Fourier Transforms (2DFFT) of one of the (1 · 1) spots of the graphene lattice with the quasi-(6 · 6) satellite spots visible only on the buffer layer. Scale bar 0.58 nm-1. Panel (c) shows atomically resolved STM images taken on the buffer layer and QFMLG and the corresponding line profiles along the graphene periodicity. The STM images in panel (c) have been filtered to remove noise. All measurements were taken in constant-current mode with the current set to 0.3 nA.

Right Image– (a) Current vs. voltage (I–V) curves and (b) differential conductance spectra acquired on the buffer layer (red line) and on QFMLG (blue line). The I–V curves in (a) are an average of multiple curves. The spectrum of the buffer layer reveals a low density of states ranging from around -0.5 V to +0.5 V, whereas hydrogen intercalation restores the semimetallic behavior of QFMLG expected for pristine graphene. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Credits:
Sarah Golera,b, Camilla Colettia,c, Vincenzo Piazzaa, Pasqualantonio Pingueb, Francesco Colangelob, Vittorio Pellegrinib, Konstantin V. Emtsevc, Stiven Fortic, Ulrich Starkec, Fabio Beltrama,b, Stefan Heunb
aCenter for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
bNEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
cMax-Planck-Institut fuer Festkoerperforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany

Microscope:
RHK Technology UHV 7000

Control System:
RHK Technology SPM 1000 Control System

Reference :
CARBON 51 (2013) 249–254

Abstract:
On the SiC(0001) surface (the silicon face of SiC), epitaxial graphene is obtained by subli- mation of Si from the substrate. The graphene film is separated from the bulk by a car- bon-rich interface layer (hereafter called the buffer layer) which in part covalently binds to the substrate. Its structural and electronic properties are currently under debate. In the present work we report scanning tunneling microscopy (STM) studies of the buffer layer and of quasi-free-standing monolayer graphene (QFMLG) that is obtained by decou- pling the buffer layer from the SiC(0001) substrate by means of hydrogen intercalation. Atomic resolution STM images of the buffer layer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no detectable defect sites.

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