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This paper reports the pressureless sintering behavior and the activation energy of the powdered MAX phases Ti3SiC2 and Ti2AlC. A non-isothermal technique was used to determine the sintering kinetic parameter. The Ti3SiC2 and Ti2AlC MAX phases showed the maximum sintering rate at 1723 K, 0.14 and 0.10 µm/s, respectively. The sintering rate of the sample at different temperatures followed a cubic equation which was determined. The sintering activation energy (Ea) for the Ti3SiC2 and Ti2AlC samples was 362.1 kJ/mol and 640.3 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

The synthesis of lanthanide‐based organometallic sandwich compounds is very appealing regarding their potential for single‐molecule magnetism. Here, it is exploited by on‐surface synthesis to design unprecedented lanthanide‐directed organometallic sandwich complexes on Au(111). The reported compounds consist of Dy or Er atoms sandwiched between partially deprotonated hexahydroxybenzene molecules, thus introducing a distinct family of homoleptic organometallic sandwiches based on six‐membered ring ligands. Their structural, electronic, and magnetic properties are investigated by scanning tunneling microscopy and spectroscopy, X‐ray absorption spectroscopy, X‐ray linear and circular magnetic dichroism, and X‐ray photoelectron spectroscopy, complemented by density functional theory‐based calculations. Both lanthanide complexes self‐assemble in close‐packed islands featuring a hexagonal lattice. It is unveiled that, despite exhibiting analogous self‐assembly, the erbium‐based species is magnetically isotropic, whereas the dysprosium‐based compound features an in‐plane magnetization. [ABSTRACT FROM AUTHOR]

The incorporation of non‐benzenoid motifs in graphene nanostructures significantly impacts their properties, making them attractive for applications in carbon‐based electronics. However, understanding how specific non‐benzenoid structures influence their properties remains limited, and further investigations are needed to fully comprehend their implications. Here, we report an on‐surface synthetic strategy toward fabricating non‐benzenoid nanographenes containing different combinations of pentagonal and heptagonal rings. Their structure and electronic properties were investigated via scanning tunneling microscopy and spectroscopy, complemented by computational investigations. After thermal activation of the precursor P on the Au(111) surface, we detected two major nanographene products. Nanographene Aa−a embeds two azulene units formed through oxidative ring‐closure of methyl substituents, while Aa−s contains one azulene unit and one Stone‐Wales defect, formed by the combination of oxidative ring‐closure and skeletal ring‐rearrangement reactions. Aa−a exhibits an antiferromagnetic ground state with the highest magnetic exchange coupling reported up to date for a non‐benzenoid containing nanographene, coexisting with side‐products with closed shell configurations resulted from the combination of ring‐closure and ring‐rearragement reactions (Ba−a, Ba−s, Bs‐a and Bs−s). Our results provide insights into the single gold atom assisted synthesis of novel NGs containing non‐benzenoid motifs and their tailored electronic/magnetic properties. [ABSTRACT FROM AUTHOR]

The synthesis of two-dimensional metal–organic networks (2D-MOCNs) on solid substrates is a rapidly growing field of research due to their potential applications in gas sensing, catalysis, energy storage, spintronics, and quantum information. In addition, the possibility of using lanthanides as coordination nodes makes them a very straightforward alternative to create an ordered array of magnetic atoms on a surface, thus paving the way for their use in information storage at the single-atom level. This feature article reviews the strategies to design two-dimensional periodic nanoarchitectures comprising lanthanide atoms in ultra-high vacuum (UHV) environment, focusing on lanthanide-directed 2D-MOCNs on metal surfaces and decoupling substrates. The characterization of their structure, electronic, and magnetic properties is also discussed, including the use of state-of-the-art scanning probe microscopies and photoelectron spectroscopies, complemented by density functional theory calculations and multiplet simulations. [ABSTRACT FROM AUTHOR]

The design of a well‐ordered arrangement of atoms on a solid surface has long been sought due to the envisioned applications in many different fields. On‐surface synthesis of metal‐organic networks is one of the most promising fabrication techniques. Hierarchical growth, which involves coordinative schemes with weaker interactions, favours the formation of extended areas with the desired complex structure. However, the control of such hierarchical growth is in its infancy, particularly for lanthanide‐based architectures. Here the hierarchical growth of a Dy‐based supramolecular nanoarchitecture on Au(111) is described. Such an assembly is based on a first hierarchical level of metallo‐supramolecular motifs, which in a second level of hierarchy self‐assemble through directional hydrogen bonds, giving rise to a periodic two‐dimensional supramolecular porous network. Notably, the size of the metal‐organic based tecton of the first level of hierarchy can be tailored by modifying the metal‐ligand stoichiometric ratio. [ABSTRACT FROM AUTHOR]

On‐surface synthesis has recently emerged as a powerful strategy to design conjugated polymers previously precluded in conventional solution chemistry. Here, an N‐containing pentacene‐based precursor (tetraazapentacene) is ex‐professo synthesized endowed with terminal dibromomethylene (:CBr2) groups to steer homocoupling via dehalogenation on metallic supports. Combined scanning probe microscopy investigations complemented by theoretical calculations reveal how the substrate selection drives different reaction mechanisms. On Ag(111) the dissociation of bromine atoms at room temperature triggers the homocoupling of tetraazapentacene units together with the binding of silver adatoms to the nitrogen atoms of the monomers giving rise to a N‐containing conjugated coordination polymer (P1). Subsequently, P1 undergoes ladderization at 200 °C, affording a pyrrolopyrrole‐bridged conjugated polymer (P2). On Au(111) the formation of the intermediate polymer P1 is not observed and, instead, after annealing at 100 °C, the conjugated ladder polymer P2 is obtained, revealing the crucial role of metal adatoms on Ag(111) as compared to Au(111). Finally, on Ag(100) the loss of :CBr2 groups affords the formation of tetraazapentacene monomers, which coexist with polymer P1. Our results contribute to introduce protocols for the synthesis of N‐containing conjugated polymers, illustrating the selective role of the metallic support in the underlying reaction mechanisms. [ABSTRACT FROM AUTHOR]

The synthesis of long n‐peri‐acenes (n‐PAs) is challenging as a result of their inherent open‐shell radical character, which arises from the presence of parallel zigzag edges beyond a certain n value. They are considered as π‐electron model systems to study magnetism in graphene nanostructures; being potential candidates in the fabrication of optoelectronic and spintronic devices. Here, we report the on‐surface formation of the largest pristine member of the n‐PA family, i.e. peri‐heptacene (n=7, 7‐PA), obtained on an Au(111) substrate under ultra‐high vacuum conditions. Our high‐resolution scanning tunneling microscopy investigations, complemented by theoretical simulations, provide insight into the chemical structure of this previously elusive compound. In addition, scanning tunneling spectroscopy reveals the antiferromagnetic open‐shell singlet ground state of 7‐PA, exhibiting singlet–triplet spin‐flip inelastic excitations with an effective exchange coupling (Jeff) of 49 meV. [ABSTRACT FROM AUTHOR]

We have measured STM movies to study the diffusion of individual vacancies in a self-assembled layer of a tetrathiafulvalene derivative (exTTF) on Au(111) at room temperature. The diffusion is anisotropic, being faster along the compact direction of the molecular lattice. A detailed analysis of the anisotropic displacement distribution of the single vacancies shows that the relative abundance of double jumps (that is, the collective motion of molecular dimers) with respect to single jumps is rather large, the number of double jumps being more than 20% of the diffusion events. We conjecture that the relative abundances of long jumps might be related to the strength of the intermolecular bonding and the misfit of the molecular overlayer with the substrate lattice. [ABSTRACT FROM AUTHOR]

Among the plethora of polycyclic structures that have emerged in recent years, indenofluorenes comprise a unique class of compounds due to their potential in organic electronic systems such as OLEDs, OFETs, and OPVCs. However, the synthesis of fully conjugated indenofluorenes without bulky groups on the apical carbons under standard chemistry conditions is not easily accessible. In this regard, on-surface synthesis has appeared as a newly developing field of research, which exploits the use of well-defined solid surfaces as confinement templates to initiate and develop chemical reactions. Here, we demonstrate the successful fabrication of indeno[1,2-b]fluorene π-conjugated polymers linked via cumulene-like connections on well-defined metallic surfaces under ultra-high vacuum conditions. The structure and electronic properties of the formed polymers have been precisely characterized by scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy, complemented by computational investigations. [ABSTRACT FROM AUTHOR]

The interest in exploiting the unique properties of lanthanides has led to the recent design of two-dimensional coordination networks incorporating f-block elements on metallic surfaces. In order to take this field to the next step of progression, it is necessary to electronically decouple these two-dimensional architectures from the metallic surface underneath. As a first step in this direction, we report the formation of dysprosium-directed metal–organic networks employing three-fold ligands as molecular linkers equipped with terminal carbonitrile functional groups on weakly interacting substrates such as Au(111) and graphene/Ir(111). We observe on both substrates identical quasi-hexagonal Dy–carbonitrile coordination networks based on majority five-fold nodes. Our findings provide perspectives for the formation of lanthanide coordination networks on graphene and related sp2 materials grown on metals. [ABSTRACT FROM AUTHOR]

The growth of a fullerene derivative (PCBM) on top of a layer of a tetrathiafulvalene (TTF) derivative previously deposited on Au(111) has been studied by scanning tunneling microscopy (STM). The results show that the preferential interaction with the gold substrate induces the exchange of PCBM molecules with the exTTF monolayer, expelling exTTF molecules to the outer surface. This exchange process is forbidden when the thickness of the exTTF layer increases above the monolayer, and the larger surface energy of PCBM leads to the growth of 3D islands. [ABSTRACT FROM AUTHOR]

Keywords: Carbon Magnetism; Open-Shell Character; Periacenes; Scanning Tunneling Microscopy; Surface Chemistry EN Carbon Magnetism Open-Shell Character Periacenes Scanning Tunneling Microscopy Surface Chemistry 1 1 1 06/01/22 20220607 NES 220607 B Die Vorstufe b 4,5,9,10-Tetrakis(3-methylnaphthalen-2-yl)pyren wurde in Lösung synthetisiert, unter Ultrahochvakuumbedingungen auf einem Au(111)-Substrat sublimiert und durch thermische Aktivierung mittels oberflächenunterstützter oxidativer Ringschluss- und Cyclodehydrierungsreaktionen in das Periheptacen-Molekül umgewandelt. Carbon Magnetism, Open-Shell Character, Periacenes, Scanning Tunneling Microscopy, Surface Chemistry Einzelheiten zu dieser Forschung finden sich in der Zuschrift von José I. Urgel, Pavel Jelínek, Xinliang Feng, David Écija et al. (e202114983). [Extracted from the article]

Details of this research can be found in the Communication by José I. Urgel, Pavel Jelínek, Xinliang Feng, David Écija, and co-workers (e202114983). Keywords: Carbon Magnetism; Open-Shell Character; Periacenes; Scanning Tunneling Microscopy; Surface Chemistry EN Carbon Magnetism Open-Shell Character Periacenes Scanning Tunneling Microscopy Surface Chemistry 1 1 1 06/01/22 20220607 NES 220607 B The precursor b 4,5,9,10-tetrakis(3-methylnaphthalen-2-yl)pyrene is synthesized in solution, sublimed on an Au(111) substrate under ultrahigh vacuum conditions, and converted into the I peri i -heptacene molecule by thermal activation via surface-assisted oxidative ring-closure and cyclodehydrogenation reactions. Carbon Magnetism, Open-Shell Character, Periacenes, Scanning Tunneling Microscopy, Surface Chemistry. [Extracted from the article]

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. [ABSTRACT FROM AUTHOR]

π‐Electron magnetic compounds on surfaces have emerged as a powerful platform to interrogate spin interactions at the atomic scale, with great potential in spintronics and quantum technologies. A key challenge is organizing these compounds over large length scales, while elucidating their resulting magnetic properties. Herein, we offer a relevant contribution toward this objective, which consists of using on‐surface synthesis coupled with coordination chemistry to promote the self‐assembly of π‐electron magnetic porphyrin species. A porphyrin precursor equipped with carbonitrile moieties in a trans arrangement was prepared by solution synthesis and deposited on Au(111)/mica. Depending on the specific growth protocol, surface‐promoted reactions led to the transformation of the precursor into non‐magnetic Au‐CN coordinated porphyrin monomers, covalent porphyrin dimers, and one‐dimensional porphyrin polymers (based on porphyrin monomers or covalent porphyrin dimers), as revealed by scanning probe microscopy studies combined with theoretical calculations. Interestingly, the scanning tunneling microscopy tip could convert such closed‐shell porphyrin units into open‐shell species by the removal of some peripheral hydrogen atoms. The magnetic features (i.e., singlet or triplet ground state) of the porphyrin units comprising the polymers were investigated for polymers of different lengths. No magnetic exchange coupling between adjacent units was observed, suggesting protection of the magnetic entities. [ABSTRACT FROM AUTHOR]

Kagome lattices have attracted much attention due the very interesting properties they can exhibit, both from the electronic and the magnetic points of view, although much of the experimental studies have been reported on 3D metals or 2D nanosheets. In the past few years, on‐surface synthesis has allowed the fabrication of strictly monolayer 2D metal‐organic networks, many of them containing transition metals. In this paper we report the fabrication and the study of the electronic and magnetic properties of a monolayer 2D metal‐organic network where the nodes are lanthanide atoms forming a kagome lattice. [ABSTRACT FROM AUTHOR]

TCNQ derivatives adsorbed on a metal surface undergo a selflimited decyanation reaction that only affects two out of the four cyano groups in the molecule. Combined Scanning Tunneling Microscopy/X-ray Photoelectron Spectroscopy experiments and Density Functional Theory calculations relate the self-limiting behavior to the transfer of electrons from the metal to the molecule. [ABSTRACT FROM AUTHOR]

Ultra high vacuum scanning tunnelling microscopy revealed chlorosubphthalocyanine to self-organize into discrete well-defined bilayer and trilayer triangular nanocrystallites when evaporated onto a Cu(111) surface. [ABSTRACT FROM AUTHOR]