Shantanu Mishra's research while affiliated with Empa - Swiss Federal Laboratories for Materials Science and Technology and other places

Publications (40)

Article
Graphene Nanoribbons This work studies the growth, characterization, and device integration of 5‐armchair graphene nanoribbons (GNRs). 5‐AGNRs are synthesized under ultrahigh vacuum conditions from Br‐ and I‐substituted precursors. In article number 2202301, Gabriela Borin Barin, Pascal Ruffieux, and co‐workers show that I‐substituted precursors an...
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Stacking two-dimensional layered materials such as graphene and transitional metal dichalcogenides with nonzero interlayer twist angles has recently become attractive because of the emergence of novel physical properties. Stacking of one-dimensional nanomaterials offers the lateral stacking offset as an additional parameter for modulating the resul...
Article
The electronic, optical, and magnetic properties of graphene nanoribbons (GNRs) can be engineered by controlling their edge structure and width with atomic precision through bottom‐up fabrication based on molecular precursors. This approach offers a unique platform for all‐carbon electronic devices but requires careful optimization of the growth co...
Preprint
The electronic, optical and magnetic properties of graphene nanoribbons (GNRs) can be engineered by controlling their edge structure and width with atomic precision through bottom-up fabrication based on molecular precursors. This approach offers a unique platform for all-carbon electronic devices but requires careful optimization of the growth con...
Article
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The production of enantiopure materials and molecules is of uttermost relevance in research and industry in numerous contexts, ranging from non-linear optics to asymmetric synthesis. In the context of the latter, we have investigated dehalogenation, which is an essential reaction step for a broad class of chemical reactions. Specifically, dehalogen...
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Fractionalization is a phenomenon in which strong interactions in a quantum system drive the emergence of excitations with quantum numbers that are absent in the building blocks. Outstanding examples are excitations with charge e/3 in the fractional quantum Hall effect1,2, solitons in one-dimensional conducting polymers3,4 and Majorana states in to...
Article
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Nanographenes with zigzag edges are predicted to manifest non-trivial π-magnetism resulting from the interplay of concurrent electronic effects, such as hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenu...
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Beginning with the early work of Clar et al. in 1955, zethrenes and their laterally-extended homologues, super-zethrenes, have been intensively studied in the solution phase, and are widely investigated as optical and charge transport materials. Super-zethrenes are also considered to exhibit an open-shell ground state. Zethrenes may thus serve as m...
Preprint
Full-text available
Fractionalization is a phenomenon in which strong interactions in a quantum system drive the emergence of excitations with quantum numbers that are absent in the building blocks. Outstanding examples are excitations with charge e/3 in the fractional quantum Hall effect, solitons in one-dimensional conducting polymers and Majorana states in topologi...
Article
Triangulene and its π-extended homologues constitute non-Kekulé polyradical frameworks with high-spin ground states, and are anticipated to be key components of organic spintronic devices. We report a combined in-solution and on-surface synthesis of the hitherto largest triangulene homologue, [7]triangulene (C78H24), consisting of twenty-eight benz...
Article
Nanographenes (NGs) have gained increasing attention due to their immense potential as tailor-made organic materials for nanoelectronics and spintronics. They exhibit a rich spectrum of physicochemical properties that can be tuned by controlling the size, the edge structure or by introducing structural defects in the honeycomb lattice. Here, we rep...
Article
Zethrenes are model diradicaloids with potential applications in spintronics and optoelectronics. Despite a rich chemistry in solution, on-surface synthesis of zethrenes has never been demonstrated. We report the on-surface synthesis of super-heptazethrene on Au(111). Scanning tunneling spectroscopy investigations reveal that super-heptazethrene ex...
Article
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The on‐surface synthesis of covalently bonded triangulene dimers with or without a 1,4‐phenylene spacer was achieved on Au(111). Scanning tunneling spectroscopy measurements revealed collective magnetism in the dimers in the form of singlet–triplet spin excitations, demonstrating efficient and tunable intertriangulene magnetic coupling. Abstract T...
Article
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Triangular zigzag nanographenes, such as triangulene and its π‐extended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for high‐spin networks with long‐range magnetic order—of immense fundamental and technological relevance. As a first step toward these lines, we pre...
Article
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Cumulene compounds are notoriously difficult to prepare and study due to dramatically increasing reactivity with increasing number of consecutive double bonds. In this respect, the emerging field of on‐surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well‐controlled ultrahigh vacuum...
Article
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Superficial interactions : On‐surface investigations of tribenzoazulene molecules functionalized with two dibromomethylene groups at the pentagon and heptagon ends reveal, after sequential annealing steps, the unambiguous formation of polymers linked by cumulene‐like bonds via selective C−C coupling induced by the sequential activation of the precu...
Preprint
Full-text available
Nanographenes with zigzag edges are predicted to manifest non-trivial pi-magnetism resulting from the interplay of hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues toward organic spintronics. The mag...
Preprint
Triangular zigzag nanographenes, such as triangulene and its pi-extended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for high-spin networks with long-range magnetic order - of immense fundamental and technological relevance. As a first step toward these lines, we...
Article
The on-surface reactions of 10-bromo-10'-(2,6-dimethylphenyl)-9,9'-bianthracene on Au(111) have been investigated by scanning tunneling microscopy and spectroscopy, complemented by theoretical calculations. The reactions afford synthesis of two open-shell nanographenes (1a and 1b) exhibiting different scenarios of all-carbon magnetism. 1a, an all-b...
Article
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The chemical versatility of carbon imparts manifold properties to organic compounds, where magnetism remains one of the most desirable but elusive1. Polycyclic aromatic hydrocarbons, also referred to as nanographenes, show a critical dependence of electronic structure on the topologies of the edges and the π-electron network, which makes them model...
Article
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An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Polycyclic hydrocarbons have received great attention due to their potential role in organic electronics and, for open-shell systems with unpaired electron densities, in spintronics and da-ta storage. However, the intrinsic instability of polyradical hydrocarbons severely limits de-tailed investigations of their electronic structure. Here, we repor...
Article
Polycyclic hydrocarbons have received great attention due to their potential role in organic electronics and, for open-shell systems with unpaired electron densities, in spintronics and da-ta storage. However, the intrinsic instability of polyradical hydrocarbons severely limits de-tailed investigations of their electronic structure. Here, we repor...
Article
Non-benzenoid carbocyclic rings are postulated to serve as important structural elements toward tuning the chemical and electronic properties of extended polycyclic aromatic hydrocarbons (PAHs, or namely nanographenes), necessitating a rational and atomically-precise synthetic approach toward their fabrication. Here, using a combined bottom-up in-s...
Article
The electronic and magnetic properties of nanographenes strongly depend on their size, shape and topology. While many nanographenes present a closed-shell electronic structure, certain molecular topologies may lead to an open-shell structure. Triangular-shaped nanographenes with zigzag edges, which exist as neutral radicals, are of considerable int...
Article
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Acenes are an important class of polycyclic aromatic hydrocarbons which have recently gained exceptional attention due to their potential as functional organic semiconductors. Fundamentally, they are important systems to study the convergence of physico-chemical properties of all-carbon sp²-frameworks in the one-dimensional limit; and by virtue of...
Article
Polycyclic aromatic hydrocarbons exhibit a rich spectrum of physico-chemical properties depending on the size, and more critically, on the edge and bond topologies. Among them, open-shell systems – molecules hosting unpaired electron densities – represent an important class of materials for organic electronic, spintronic and optoelectronic devices,...
Article
Full-text available
Curved π-conjugated polycyclic aromatic hydrocarbons, buckybowls, constitute an important class of materials with wide applications in materials science. Heteroatom doping of buckybowls is a viable route to tune their intrinsic physicochemical properties. However, synthesis of heteroatom-doped buckybowls is a challenging task. We report on a combin...
Article
We report the on-surface formation of Au-directed heptacene organometallic complexes on a Au(111) template in an ultrahigh vacuum environment. Successive thermal annealing steps investigated by means of scanning tunneling microscopy, non-contact atomic force microscopy, temperature-programmed desorption and density functional theory reveal the form...

Citations

... There is a now a growing interest in the exploitation of quantum behaviour of this class of systems [15,16]. Surface-spin artificial arrays can display exotic quantum magnetism phenomena, including spin fractionalization in S = 1 Haldane chains [17], resonant valence bond states in spin plaquetes [18] and quantum criticality [19] that are known to host entangled states. However, experimental protocols that unambiguously determine the presence of entanglement in these systems are missing. ...
... 20 More importantly, enantioselective adsorption and elimination reaction towards prochiral molecules has been achieved on the (111) surface due to the different surface termination and the surface chirality originating from the second outmost surface layers. [21][22] With these experimental facts in mind, it is interesting to ask the question of whether the bulk crystal chirality initiates the enantioselective reactions. ...
... Their magnetic configurations including the spin quantum number S and magnetic exchange interactions can be precisely predicted by simple approximations, and are highly tunable through variations in molecular size, shape and edge structure. [6][7][8][9][10][11][12][13][14][15][16] Benzenoid polycyclic hydrocarbons (BPHs), also known as polycyclic π-conjugated hydrocarbons or nanographenes, are fragments of graphene with the carbons at the edge passivated by mono-hydrogens. Each carbon atom in BPHs hosts one conjugated π electron, which may contribute to the magnetic properties. ...
... Solely recent experiments employing on-surface synthesis in ultra-high vacuum conditions has shown effective for obtaining such pristine open-shell molecules 13-16 . Further characterization, by means of scanning tunneling microscopy (STM), has also probed the existence of local moments by measuring Kondo peaks [17][18][19] or inelastic steps [20][21][22] . To this day, this is a well-established technology, so there is a whole plethora of platforms with localized electrons and πmagnetism 23,24 . ...
... In standard conditions, open-shell molecules are very reactive and therefore not suitable for manipulation. However, thanks to the advances in on-surface chemical synthesis [12][13][14] , it has been possible to go around this problem, so that the controlled fabrication of triangulenes of various sizes [15][16][17][18] , as well as triangulene dimers 19 , chains 20 , rings 20,21 and * These authors contributed equally † On permanent leave from Departamento de Física Aplicada, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain ‡ joaquin.fernandez-rossier@inl.int other structures 22 , has been recently demonstrated. On the other hand, the on-surface synthesis of large-area carbon-based crystals has also been established [23][24][25] . ...
... By contrast, the curved segment is formed by the fluorene units presenting the same orientation of carbon atoms at the apexes in pentagonal rings (see inset image in Fig. 3d). It is worth mentioning that the methylene groups (-CH 2 ) located at the apex of pentagonal ring of polyfluorene still keep intact after the thermal treatment, which can be evidenced from the sharp kinks (highlighted by yellow dotted circles) in BR-STM image (as shown in Fig. 3d) [14,35,36]. ...
... However, the lack of macroscopic materials having graphyne structures as their basic units makes bottom-up approaches the most feasible strategy for graphyne synthesis in the near future. In fact, the development and improvement of surface-assisted chemical routes in the past decade allowed the scientific community to create several nanocarbon forms [33,[37][38][39][40][41][42]. These methods are based on tools such as the strategic choices of molecular precursors and specific substrates, as well as temperature conditions. ...
... Alternatively, C(sp)-containing skeletons have been successfully embedded in the sp 2 -hybridized GNRs and GNR-like nanostructures for better electronic tailoring, such as ethynylene-bridged [148][149][150][151] , diacetylene-bridged [152,153] , and cumulenebridged [154,155] polymers. Besides, 1D cumulene-linked polymers with the involvement of 5-and 7membered rings (based on a tribenzoazulene building block) [156] was also achieved. Notably, Écija and co-workers explored the topological order involved in such π-conjugated polymers [157] as shown in Figure 8. 1D C(sp)-bridged acene-containing polymers were synthesized on Au(111) using the same strategy (Figure 8a), which was based on precursors with various acene units (including anthracene, pentacene, and bisanthene). ...
... To identify the intermediates and unravel growth mechanisms as well as formation kinetics of 5-AGNRs, we carried out TP-XPS measurements, i.e., repeatedly recorded XPS spectra of the relevant core level signals during the annealing of the sample from -50 to 450 ˚C (heating rate of 0.2 °C·s −1 ) ( Figure 2). This investigation tracks on-surface reactions and unambiguously identifies the sequence of relevant reaction steps 24,[26][27][28][29][30][31] . The molecu-lar precursors were deposited onto a cold substrate (below -120 °C) to prevent their deiodination 32 . ...
... 6 For example, previous scanning tunneling microscopy and break junction experiments focused on allorganic radicals 7 display Kondo temperatures (T K ) ranging from a few 8 K up to tens 9−11 of K. Studies on other charge transport phenomena such as magnetoresistance 12,13 and magnetic-field induced variation of inelastic electron tunneling spectroscopy (IETS) have also been reported. 14,15 Using IETS, spin−spin interactions in all organic diradicals have been studied, demonstrating interesting properties such as large exchange couplings 16,17 or ground-state inversion by electrostatic gating. 18 Here, we report on measurements of all-organic mono-and diradical molecules in a mechanically controlled break junction (MCBJ). ...