Image of the Month

Sequence (A−D) of STM images (100 nm × 100 nm) showing dynamic behavior of a decanethiolate SAM on the Au(111) at room temperature (293 K). The surface exhibits three ordered phases (β, δ, and χ*) and one disordered phase (ε). The solid line marks a domain boundary between the ordered β phase and the disordered ε phase, while the dashed line marks a χ*−ε domain boundary. The sample bias is 1.2 V and the tunnel current is 190 pA. The time lapse between consecutive images is 420 s. (E, F) Line profiles taken across the β and δ phases, respectively. The stripe widths are (E) 3.3 nm and (F) 2.2 nm.

Credits: Kai Sotthewes,†,§ Hairong Wu,†,‡,§ Avijit Kumar,† G. Julius Vancso,‡ Peter M. Schön,‡
and Harold J. W. Zandvliet*,†Physics of Interfaces and Nanomaterials and ‡Materials Science and Technology of Polymers, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands

Microscope: UHV 3000

Control System: SPM 1000

Stability verification of RHK PanScan Freedom showing no influence of environmental or cryostat noise on the In doped Bi₂Se₃ atomic structure at 18 K (collected during the AVS 61st Exhibition)

Performance verification of RHK PanScan Freedom showing exceptional performance, at the AVS 2014 Exhibition, on the Si(111) 7×7 atomic structure at 18 K

RHK is proud to highlight the outstanding performance of our PanScan Freedom at the AVS 61st International Symposium & Exhibition 2014.

The extreme stability of this microscope is demonstrated in the Baltimore Convention Center exhibition hall using an Indium doped Bismuth Selinide sample, showing both a high-level of isolation from the vibration of the Closed-Cycle Cryostat as well as the environment of the hall, yielding excellent performance with the noise level below 1 pm. 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.

Professor Miquel Salmeron said, “I was really impressed by your PanScan Freedom working so smoothly in the noisy environment of the AVS exhibit! The stability was superb and I loved immensely the closed circuit of He gas. This is so cool and so great at a time when getting liquid He is not an easy thing (not to speak of the cost). I wish I had money right now to buy one!”

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

Credits: Dr. Byoung Choi, RHK Technology

Microscope: RHK PanScan Freedom

Control System: RHK R9-STM and PMC100

Stability verification of RHK PanScan Freedom showing no influence of cryostat operation on the Si(111) 7×7 atomic structure

Drift verification of RHK PanScan Freedom showing X,Y drift as low as 0.2Å/hour on the Si(111) 7×7 atomic structure at 18 K

RHK is proud to highlight the very low drift Si(111) 7×7 image acquired on our PanScan Freedom connected to a running Closed-Cycle Helium Cryostat.

The extreme stability of this microscope is demonstrated using a Si(111) 7×7 sample, showing both a high-level of isolation from the vibration of the Closed-Cycle Cryostat with the cryostat turned off in the lower half of the image and excellent drift performance as low as 0.2Å/hour.  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 Freedom enables every researcher to run their SPM at cryogenic temperatures, endlessly, without the trouble and expense of liquid helium.

Credits: Dr. Byoung Choi, RHK Technology

Microscope: RHK PanScan Freedom

Control System: RHK R9-STM and PMC100

Atomically resolved STM images from the Pd (110)-Ic(2×2) phase together with atomic structure models. Atomic distances are 5.5 Å in (−110) and 4.8 Å in (−111). The long red arrow points along (−110).

STM image of mixed the c(2×2) and q-hex phases.

Reference: J. Chem. Phys. 137, 204703 (2012); doi: 10.1063/1.4768165

Credits: Mats Göthelid, Michael Tymczenko, Winnie Chow, Sareh Ahmadi, Shun Yu, Benjamin Bruhn, Dunja Stoltz, Henrik von Schenck, Jonas Weissenrieder, and Chenghua Sun. – Materialfysik, ICT Electrum 229, Kungliga Tekniska Högskolan (KTH) and Australia Institute for Bioengineering and Nanotechnology, The University of Queensland

Microscope: RHK VT UHV STM/AFM Model UHV3500

Control System: RHK Technology SPM1000

Abstract: We use photoelectron spectroscopy, low energy electron diffraction, scanning tunneling microscopy, and density functional theory to investigate coverage dependent iodine structures on Pd(110). At 0.5 ML (monolayer), a c(2 × 2) structure is formed with iodine occupying the four-fold hollow site. At increasing coverage, the iodine layer compresses into a quasi-hexagonal structure at 2/3 ML, with iodine occupying both hollow and long bridge positions. There is a substantial difference in electronic structure between these two iodine sites, with a higher electron density on the bridge bonded iodine. In addition, numerous positively charged iodine near vacancies are found along the domain walls. These different electronic structures will have an impact on the chemical properties of these iodine atoms within the layer.

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)

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.

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.

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.

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

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 Goler^a,b, Camilla Coletti^a,c, Vincenzo Piazza^a, Pasqualantonio Pingue^b, Francesco Colangelo^b, Vittorio Pellegrini^b, Konstantin V. Emtsev^c, Stiven Forti^c, Ulrich Starke^c, Fabio Beltram^a,b, Stefan Heun^b
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.

Figure 1. (b) dI/dV measured at an applied load of 72 nN on fluorinated graphene and pristine graphene. A band gap of 2.9 eV was measured after fluorination.
Figure 2. 500 × 500 nm² images of (a) topography and (b) friction measured on the fluorinated graphene using contact mode AFM (applied load = 71 nN). (c) Plot of friction force versus applied load measured on pristine and on fluorinated graphene.

Credits:
Sangku Kwon,^†,⊥ Jae-Hyeon Ko,^‡,⊥ Ki-Joon Jeon,^§ Yong-Hyun Kim,^*,‡,∥ and Jeong Young Park^{*,†,∥
†}Graduate School of EEWS (WCU), KAIST, Daejeon 305-701, Republic of Korea
^‡Graduate School of Nanoscience and Technology (WCU), KAIST, Daejeon 305-701, Korea §School of Electrical Engineering, University of Ulsan, Ulsan 680-749, Republic of Korea
^∥KAIST Institute for the NanoCentury, KAIST, Daejeon 305-701, Republic of Korea

Microscope:
RHK Technology UHV 7500

Control System:
RHK Technology SPM 1000 Control System

Reference:
Nano Lett. 2012, 12, 6043−6048

Abstract:
Atomically thin graphene is an ideal model system for studying nanoscale friction due to its intrinsic two-dimensional (2D) anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nanomechanical devices. Here, we report unexpectedly enhanced nanoscale friction on chemically modified graphene and a relevant theoretical analysis associated with flexural phonons. Ultrahigh vacuum friction force microscopy measurements show that nanoscale friction on the graphene surface increases by a factor of 6 after fluorination of the surface, while the adhesion force is slightly reduced. Density functional theory calculations show that the out-of-plane bending stiffness of graphene increases up to 4-fold after fluorination. Thus, the less compliant F-graphene exhibits more friction. This indicates that the mechanics of tip-to- graphene nanoscale friction would be characteristically different from that of conventional solid-on-solid contact and would be dominated by the out-of-plane bending stiffness of the chemically modified graphene. We propose that damping via flexural phonons could be a main source for frictional energy dissipation in 2D systems such as graphene.

STM images of the Cu(100) surface with TPA and NaCl, after annealing to 160 °C. (a) Part of a large island made up of the Na−TPA α phase. (b) Molecular and atomic resolution of the island in (a). (c) Zoom in of (b), with a schematic representation of the orientation of the Na−TPA α phase on the copper surface.

Credits:
Daniel Skomski,^† Sabine Abb,^†,^‡ and Steven L. Tait*,^†
†Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
^‡University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany

Microscope:
RHK Technology AFM/STM UHV 7500

Control System:
RHK Technology SPM 1000 Control System

Reference:
J. Am. Chem. Soc. 2012, 134, 14165−14171

Abstract:
Ionic bonding in supramolecular surface networks is a promising strategy to self-assemble nanostructures from organic building blocks with atomic precision. However, sufficient thermal stability of such systems has not been achieved at metal surfaces, likely due to partial screening of the ionic interactions. We demonstrate excellent stability of a self-assembled ionic network on a metal surface at elevated temperatures. The structure is characterized directly by atomic resolution scanning tunneling microscopy (STM) experiments conducted at 165 °C showing intact domains. This robust nanometer-scale structure is achieved by the on-surface reaction of a simple and inexpensive compound, sodium chloride, with a model system for carboxylate interactions, terephthalic acid (TPA). Rather than distinct layers of TPA and NaCl, angle resolved X-ray photoelectron spectroscopy experiments indicate a replacement reaction on the Cu(100) surface to form Na−carboxylate ionic bonds. Chemical shifts in core level electron states confirm a direct interaction and a +1 charge state of the Na. High-temperature STM imaging shows virtually no fluctuation of Na−TPA island boundaries, revealing a level of thermal stability that has not been previously achieved in noncovalent organic-based nanostructures at surfaces. Comparable strength of intermolecular ionic bonds and intramolecular covalent bonds has been achieved in this surface system. The formation of these highly ordered structures and their excellent thermal stability is dependent on the interplay of adsorbate−substrate and ionic interactions and opens new possibilities for ionic self-assemblies at surfaces with specific chemical function. Robust ionic surface structures have potential uses in technologies requiring high thermal stability and precise ordering through self-assembly.