On-Surface Synthesis of Variable Bandgap Nanoporous Graphene

<p>Tuning the bandgap of nanoporous graphene is desirable for applications such as the charge transport layer in organic-hybrid devices. The holy grail in the field is the ability to synthesize 2D nanoporous graphene with variable pore sizes, and hence tuneable band gaps. Herein, we demonstrate the on-surface synthesis of nanoporous graphene with variable bandgaps. Two types of nanoporous graphene were synthesized via hierarchical C-C coupling, and verified by low-temperature scanning tunneling microscopy and non-contact atomic force microscopy with CO-terminated tip. Nanoporous graphene-1 is non-planar, and nanoporous graphene-2 is a single-atom thick planar sheet. Scanning tunneling spectroscopy measurements reveal that nanoporous graphene-2 has a bandgap of 3.8 eV, while nanoporous graphene-1 has a larger bandgap of 5.0 eV. Corroborated by first-principles calculations, we propose that the large bandgap opening is governed by the confinement of π-electrons induced by pore generation or the non-planar structure, and can be explained by Clar sextet theory. Our finding shows that by introducing nanopores, semimetallic graphene is converted into semiconducting nanoporous graphene-2 or insulating wide-bandgap nanoporous graphene-1. </p><br>

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Orientation Ordering and Chiral Superstructures in Fullerene Monolayer on Cd (0001)

Nanomaterials ◽

10.3390/nano10071305 ◽

2020 ◽

Vol 10 (7) ◽

pp. 1305

Author(s):

Yuzhi Shang ◽

Zilong Wang ◽

Daxiao Yang ◽

Yaru Wang ◽

Chaoke Ma ◽

...

Keyword(s):

Thin Films ◽

Charge Transfer ◽

Scanning Tunneling Spectroscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Orientational Disorder ◽

Temperature Scanning ◽

Orientation Ordering ◽

The Individual ◽

Misorientation Angles

The structure of C60 thin films grown on Cd (0001) surface has been investigated from submonolayer to second monolayer regimes with a low-temperature scanning tunneling microscopy (STM). There are different C60 domains with various misorientation angles relative to the lattice directions of Cd (0001). In the (2√3 × 2√3) R30° domain, orientational disorder of the individual C60 molecules with either pentagon, hexagon, or 6:6 bond facing up has been observed. However, orientation ordering appeared in the R26° domain such that all the C60 molecules adopt the same orientation with the 6:6 bond facing up. In particular, complex chiral motifs composed of seven C60 molecules with clockwise or anticlockwise handedness have been observed in the R4° and R8° domains, respectively. Scanning tunneling spectroscopy (STS) measurements reveal a reduced HOMO–LOMO gap of 2.1 eV for the C60 molecules adsorbed on Cd (0001) due to the substrate screening and charge transfer from Cd to C60 molecules.

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Molecular-Scale Structure of Pentacene Interfaces with Si (111)

MRS Proceedings ◽

10.1557/proc-0965-s12-24 ◽

2006 ◽

Vol 965 ◽

Author(s):

Soonjoo Seo ◽

Paul G. Evans

Keyword(s):

Scanning Tunneling Spectroscopy ◽

Structural Defects ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Semiconductor Thin Films ◽

Disordered Layer ◽

Temperature Scanning ◽

Molecular Layers ◽

Preparation Techniques ◽

Imaging Conditions

ABSTRACTThe morphology and crystal structure of the first few molecular layers of organic semiconductor thin films at organic-inorganic interfaces are important from both electronic and structural perspectives. The first upright layer of pentacene on Si (111) forms on top of a disordered layer of strongly bonded pentacene molecules in a structure similar to the pentacene monolayers formed on insulators. We describe a high-resolution structural study of this crystalline phase of pentacene using low-temperature scanning tunneling microscopy (STM). The arrangement of molecules in these layers observed with STM agrees the results of with structural studies using scattering techniques. The imaging conditions and sample preparation techniques necessary to achieve molecular resolution can be adapted to subsequent STM and scanning tunneling spectroscopy experiments probing individual structural defects including vacancies, dislocations and grain boundaries within and between islands.

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Structure-resistive property relationships in thin ferroelectric BaTiO$$_{3}$$ films

Scientific Reports ◽

10.1038/s41598-020-72738-5 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

N. V. Andreeva ◽

A. Petraru ◽

O. Yu. Vilkov ◽

A. E. Petukhov

Keyword(s):

Scanning Tunneling Microscopy ◽

Point Defects ◽

Ferroelectric Properties ◽

Piezoresponse Force Microscopy ◽

Scanning Tunneling Spectroscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Ferroelectric Films ◽

Force Microscopy ◽

Atomic Force

Abstract A combined study of local structural, electric and ferroelectric properties of SrTiO$$_{3}$$ 3 /La$$_{0.7}$$ 0.7 Sr$$_{0.3}$$ 0.3 MnO$$_{3}$$ 3 /BaTiO$$_{3}$$ 3 heterostructures was performed by Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy in the temperature range 30–295 K. The direct correlation of film structure (epitaxial, nanocrystalline or polycrystalline) with local electric and ferroelectric properties was observed. For polycrystalline ferroelectric films the predominant polarization state is defined by the peculiarity of screening the built-in field by positively charged point defects. Based on Scanning Tunneling Spectroscopy results, it was found that a sequent voltage application provokes the modification of local resistive properties related to the redistribution of point defects in thin ferroelectric films. A qualitative analysis of acquired Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy images together with Scanning Tunneling Spectroscopy measurements enabled us to conclude that in the presence of structural defects the competing processes of electron injection, trap filling and the drift of positively charged point defects drives the change of resistive properties of thin films under applied electric field. In this paper, we propose a new approach based on Scanning Tunneling Microscopy/Spectroscopy under ultrahigh vacuum conditions to clarify the influence of point defects on local resistive properties of nanometer-thick ferroelectric films.

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IN-SITU HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY STUDIES OF TWO-DIMENSIONAL ISLAND-DECAY KINETICS ON ATOMICALLY SMOOTH TiN(001)

Surface Review and Letters ◽

10.1142/s0218625x00000816 ◽

2000 ◽

Vol 07 (05n06) ◽

pp. 589-593 ◽

Cited By ~ 22

Author(s):

S. KODAMBAKA ◽

V. PETROVA ◽

A. VAILIONIS ◽

P. DESJARDINS ◽

D. G. CAHILL ◽

...

Keyword(s):

High Temperature ◽

Scanning Tunneling Microscopy ◽

Ostwald Ripening ◽

Single Atom ◽

Scanning Tunneling ◽

Two Dimensional ◽

Decay Kinetics ◽

Tunneling Microscopy ◽

Temperature Scanning

In-situ high-temperature scanning tunneling microscopy was used to follow the coarsening (Ostwald ripening) and decay kinetics of single and multiple two-dimensional TiN islands on atomically flat TiN (001) terraces and in single-atom deep vacancy pits at temperatures of 750–950°C. The rate-limiting mechanism for island decay was found to be surface diffusion rather than adatom attachment/detachment at island edges. We have modeled island-decay kinetics based upon the Gibbs–Thomson and steady state diffusion equations to obtain a step-edge energy per unit length of 0.23±0.05 eV/Å and an activation energy for adatom formation and diffusion of 3.4±0.3 eV.

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Influence of the adsorption geometry of PTCDA on Ag(111) on the tip–molecule forces in non-contact atomic force microscopy

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.5.9 ◽

2014 ◽

Vol 5 ◽

pp. 98-104 ◽

Cited By ~ 1

Author(s):

Gernot Langewisch ◽

Jens Falter ◽

André Schirmeisen ◽

Harald Fuchs

Keyword(s):

Force Spectroscopy ◽

Scanning Tunneling Spectroscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Atomic Force ◽

Organic Adsorbates ◽

Adsorption Geometry ◽

Spectroscopy Studies ◽

Tetracarboxylic Dianhydride

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) adsorbed on a metal surface is a prototypical organic–anorganic interface. In the past, scanning tunneling microscopy and scanning tunneling spectroscopy studies of PTCDA adsorbed on Ag(111) have revealed differences in the electronic structure of the molecules depending on their adsorption geometry. In the work presented here, high-resolution 3D force spectroscopy measurements at cryogenic temperatures were performed on a surface area that contained a complete PTCDA unit cell with the two possible geometries. At small tip-molecule separations, deviations in the tip-sample forces were found between the two molecule orientations. These deviations can be explained by a different electron density in both cases. This result demonstrates the capability of 3D force spectroscopy to detect even small effects in the electronic properties of organic adsorbates.

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Defect-Induced π-Magnetism into Non-Benzenoid Nanographenes

Nanomaterials ◽

10.3390/nano12020224 ◽

2022 ◽

Vol 12 (2) ◽

pp. 224

Author(s):

Kalyan Biswas ◽

Lin Yang ◽

Ji Ma ◽

Ana Sánchez-Grande ◽

Qifan Chen ◽

...

Keyword(s):

Theoretical Calculations ◽

Open Shell ◽

Scanning Tunneling Spectroscopy ◽

Membered Ring ◽

Structural Defects ◽

Scanning Tunneling ◽

Honeycomb Lattice ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Atomic Force

The synthesis of nanographenes (NGs) with open-shell ground states have recently attained increasing attention in view of their interesting physicochemical properties and great prospects in manifold applications as suitable materials within the rising field of carbon-based magnetism. A potential route to induce magnetism in NGs is the introduction of structural defects, for instance non-benzenoid rings, in their honeycomb lattice. Here, we report the on-surface synthesis of three open-shell non-benzenoid NGs (A1, A2 and A3) on the Au(111) surface. A1 and A2 contain two five- and one seven-membered rings within their benzenoid backbone, while A3 incorporates one five-membered ring. Their structures and electronic properties have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy complemented with theoretical calculations. Our results provide access to open-shell NGs with a combination of non-benzenoid topologies previously precluded by conventional synthetic procedures.

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Construction Of UHV-REM-PEEM for Surface Studies

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180501 ◽

1990 ◽

Vol 48 (1) ◽

pp. 350-351

Author(s):

Y. Kondo ◽

K. Yagi ◽

K. Kobayashi ◽

H. Kobayashi ◽

Y. Yanaka

Keyword(s):

Electron Microscopy ◽

Electronic Structure ◽

High Vacuum ◽

Scanning Tunneling Spectroscopy ◽

Ultra High Vacuum ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Surface Electronic Structure ◽

Electron Microscopes

Recent development of ultra-high vacuum electron microscopy (UHV-EM) is very rapid. This is due to the fact that it can be applied to variety of surface science fields.There are various types of surface imaging in UHV condition; low energy electron microscopy (LEEM) [1], transmission (TEM) and reflection electron microscopy (REM) [2] using conventional transmission electron microscopes (CTEM) (including scanning TEM and REM)), scanning electron microscopy, photoemission electron microscopy (PEEM) [3] and scanning tunneling microscopy (STM including related techniques such as scanning tunneling spectroscopy (STS), atom force microscopy and magnetic force microscopy)[4]. These methods can be classified roughly into two; in one group image contrast is mainly determined by surface atomic structure and in the other it is determined by surface electronic structure. Information obtained by two groups of surface microscopy is complementary with each other. A combination of the two methods may give images of surface crystallography and surface electronic structure. STM-STS[4] and LEEM-PEEM [3] so far developed are typical examples.In the present work a combination of REM(TEM) and PEEM (Fig. 1) was planned with use of a UHV CTEM. Several new designs were made for the new microscope.

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