and Applications of Fullerenes, Carbon Dots, Nanotubes, Graphene, Nanodiamonds, and Combined Superstructures Vasilios Georgakilas,† Jason A. Perman,‡ Jiri Tucek,‡ and Radek Zboril*,‡ †Material Science Department, University of Patras, 26504 Rio Patras, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University in Olomouc, 17 listopadu 1192/12, 771 46 Olomouc, Czech Republic

Broad family of carbon nanoallotropes: classification, chemistry, and applications of fullerenes, carbon dots, nanotubes, graphene, nanodiamonds, and combined superstructures.

A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnO and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. The versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.

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Penta-graphene: A new carbon allotrope

Photoelectron spectroscopy revealed that a 20-atom gold cluster has an extremely large energy gap, which is even greater than that of C60, and an electron affinity comparable with that of C60. This observation suggests that the Au20 cluster should be highly stable and chemically inert. Using relativistic density functional calculations, we found that Au20 possesses a tetrahedral structure, which is a fragment of the face-centered cubic lattice of bulk gold with a small structural relaxation. Au20 is thus a unique molecule with atomic packing similar to that of bulk gold but with very different properties.

http://cluster.physik.uni-freiburg.de/lehre/SS11/ueb11/Li2003b.pdf

Au20: A Tetrahedral Cluster

An architectural rationale and an experimental program aimed at the development of molecular electronics switching devices for memory and computing applications are discussed. Two-terminal molecular switch tunnel junctions are identified as the critical device components of molecular electronics-based circuitry. They can be tiled in two dimensions and are tolerant of manufacturing defects. Singly and multiply configurable solid-state switching devices that are based upon electrochemically switchable molecular and supramolecular systems are discussed in terms of both the synthesis of the molecular components and the fabrication and performance of the devices.

Switching devices based on interlocked molecules.

Metal−molecule−metal junctions were fabricated by contacting Au-supported alkyl or benzyl thiol self-assembled monolayers (SAMs) with an Au-coated atomic force microscope (AFM) tip. The tip−SAM microcontact is approximately 15 nm2, meaning the junction contains ∼75 molecules. Current−voltage (I−V) characteristics of these junctions were probed as a function of SAM thickness and load applied to the microcontact. The measurements showed:  (1) the I−V traces were linear over ±0.3 V, (2) the junction resistance increased exponentially with alkyl chain length, (3) the junction resistance decreased with increasing load and showed two distinct power law scaling regimes, (4) resistances were a factor of 10 lower for junctions based on benzyl thiol SAMs compared to hexyl thiol SAMs having the same thickness, and (5) the junctions sustained fields up to 2 × 107 V/cm before breakdown. I−V characteristics determined for bilayer junctions involving alkane thiol-coated tips in contact with alkane thiol SAMs on Au also ...

Fabrication and Characterization of Metal−Molecule−Metal Junctions by Conducting Probe Atomic Force Microscopy

Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

Electron-impact ionization in a time-of-flight mass spectrometer of C20H0–3Br14–12 probes—secured from C20H20 dodecahedrane by a “brute-force” bromination protocol—provided bromine-free C20H0–2(3) anions in amounts that allowed the clean mass-separation of the hydrogen-free C20− ions and the photoelectron (PE) spectroscopic characterization as C20 fullerene (electron affinity (EA)=2.25±0.03 eV, vibrational progressions of 730±70). The extremely strained C20 fullerene ions surfaced as kinetically rather stable entities (lifetime of at least the total flight time of 0.4 ms); they only very sluggishly expel a C2 unit. The HOMO and LUMO are suggested to be almost degenerate (ΔE=0.27 eV). The assignment as a fullerene was corroborated by the PE characterization of the C20 bowl (EA=2.17±0.03 eV, vibrational progression of 2060±50 cm−1) analogously generated from C20H10 corannulene (C20H1–3Br9–8 samples) and comparably stable. Highly resolved low-temperature PE spectra of the known C20 ring (EA=2.49±0.03 eV, vibrational progressions 2022±45 and 455±30 cm−1), obtained from graphite, display an admixture of, most probably, a bicyclic isomer (EA=3.40±0.03 eV, vibrational progression 455±30 cm−1). The C20+(−) and C20H2+(−) cluster ions generated from polybrominated perylene (C20H0–2Br12–10) have (most probably) retained the planar perylene-type skeleton (sheet, EA=2.47±0.03 eV, vibrational progressions of 2089±30 and 492±30 cm−1 and EA=2.18±0.03 eV, vibrational progressions of 2105±30 and 468±30 cm−1).

Daniela Olevano

Papers

Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

C20 Carbon Clusters: Fullerene–Boat–Sheet Generation, Mass Selection, Photoelectron Characterization

C20 Carbon Clusters: Fullerene—Boat—Sheet Generation, Mass Selection Photoelectron Characterization.