Long-range magnetic order in a purely organic 2D layer adsorbed on epitaxial graphene

Garnica, Manuela; Stradi, Daniele; Barja, Sara; Calleja, F.; Dı́az, Cristina; Alcamı́, Manuel; Martı́n, Nazario; Parga, Amadeo L. Vázquez de; Martı́n, Fernando; Miranda, Rodolfo

doi:10.1038/nphys2610

Cited by 171 publications

(238 citation statements)

References 33 publications

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“…Studies of TCNQ based salts on Au(111) surface have shown supermolecular states along the 1D TCNQ chains dependent on the geometry of neighboring molecules and hybridization with the underlying metal substrate [8]. Most recently weak charge-transfer induced magnetism was reported for TCNQ adsorbed on graphene [9].…”

Section: Introductionmentioning

confidence: 99%

Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces

et al. 2014

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The energy scale of interactions that control molecular adsorption and assembly on surfaces can vary by several orders of magnitude, yet the importance of each contributing interaction is not apparent a-priori.Tetracyanoquinodimethane (TCNQ) is an archetypal electron acceptor molecule and it is a key component of organic metals. On metal surfaces, this molecule also acts as an electron acceptor, producing negatively charged adsorbates. It is therefore rather intriguing to observe attractive molecular interactions in this system that was reported previously for copper and silver surfaces. Our experiments compared TCNQ adsorption on noble metal surfaces of Ag(100) and Ag(111). In both cases we found net attractive interactions down to the lowest coverage. However, the morphology of the assemblies was strikingly different, with 2D islands on Ag(100) and 1D chains on Ag(111) surfaces. This observation suggests that the registry effect governed by the molecular interaction with the underlying lattice potential is critical in determining the dimensionality of the molecular assembly. Using first-principles 2 density functional calculations with van der Waals correction scheme, we revealed that the strengths of major interactions (i.e., lattice potential corrugation, intermolecular attraction, and charge transferinduced repulsion) are all similar in energy. Van der Waals interactions, in particular, almost double the strength of attractive interactions, making the intermolecular potential comparable in strength to the diffusion potential and promoting self-assembly. However, it is the anisotropy of local intermolecular interactions that is primarily responsible for the difference in the topology of the molecular islands on Ag(100) and Ag(111) surfaces. We anticipate that the intermolecular potential will become more attractive and dominant over the diffusion potential with increasing molecular size, providing new design strategies for the structure and charge-transfer within molecular layers.

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Section: Introductionmentioning

confidence: 99%

Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces

et al. 2014

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“…Our work focuses on utilizing the molecule TCNQ (7,7,8,8-tetracyanoquinodimethane) that is a symmetric, planar molecule capable of forming a radical anion [7,8] and has a long history of being used to synthesize novel materials [9][10][11]. The radical electron density is delocalized across the * adam.berlie@stfc.ac.uk † Present address: Cardiff School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, United Kingdom.…”

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Tuneability and criticality in a three-dimensional stacked molecular system

et al. 2016

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“…An appealing approach is to grow ultra thin layers of insulators (like NaCl, KCl, etc) on singlecrystal metal surfaces. By just varying the thickness of the ultra thin layer, which is a standard procedure in surface physics, one would like to exert some control on the metal response, similar to that required to gradually modify the catalytic activity of metallic species [51][52][53][54][55][56] , to decouple molecules and self-assembled molecular networks from the metal substrate that holds them [57][58][59][60], and, what is more important in the context of the present work, to gradually modify the response of metal surface electrons [61][62][63][64][65][66][67]. Inspired by the latter works, we propose a similar strategy to tune the harmonic cut-off.…”

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Tuning high-harmonic generation by controlled deposition of ultrathin ionic layers on metal surfaces

Aguirre

Martín

2016

Phys. Rev. B

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High harmonic generation (HHG) from semiconductors and insulators has become a very active area of research due to its great potential for developing compact HHG devices. Here we show that by growing monolayers (ML) of insulators on single-crystal metal surfaces, one can tune the harmonic spectrum by just varying the thickness of the ultrathin layer, not the laser properties. This is shown from numerical solutions of the time-dependent Schrödinger equation for nML NaCl/Cu(111) systems (n = 1 − 50) based on realistic potentials available in the literature. Remarkably, the harmonic cutoff increases linearly with n and as much as an order of magnitude when going from n = 1 to 30, while keeping the laser intensity low and the wavelength in the near-infrared range. Furthermore, the degree of control that can be achieved in this way is much higher than by varying the laser intensity. The origin of this behavior is the reduction of electronic "friction" when moving from the essentially discrete energy spectrum associated with a few-ML system to the continuous energy spectrum (bands) inherent to an extended periodic system. PACS numbers: 42.65. Ky,78.66.Nk, Discovered in the 1980's [1-3], high harmonic generation (HHG) has become the fundamental tool of modern attoscience [4][5][6]. In HHG from atomic or molecular gases, a strong laser field ionizes an electron, which then gains energy from the field and returns to the parent ion, where it finally recombines converting the gained energy into high-frequency radiation [7][8][9][10]. The process repeats every half-cycle of the ionizing field, thus leading to a sequence of attosecond light bursts that contain multiples of the fundamental laser frequency, ω 0 . Since electronic motion in atomic and molecular systems occurs in the attosecond time scale, light pulses arising from HHG are currently used to probe electron dynamics in those systems [11][12][13][14][15][16][17][18]. Furthermore the HHG process itself contains the signature of the parent-ion dynamics occurring during the round trip of the traveling electron. Thus the analysis of the HHG spectral features can also reveal important aspects of such dynamics [19][20][21][22][23][24][25].HHG from condensed matter systems was first observed in the mid 90s [26,27]. In these early experiments, bulk metals and dielectrics irradiated with very intense near-infrared laser fields (of the order of 10 18 W/cm 2 ) were shown to emit harmonic radiation as a result of plasma oscillations induced in the system (see also [28]) Due to the high intensity of the field, HHG was always accompanied by sample damage. More recent experiments have made use of nano tips and nano spheres [29][30][31][32][33], from which HHG has been produced by using relatively moderate fields (of the order of 10 12 W/cm 2 ). HHG has also been observed in bulk semiconductors and insulators [34][35][36][37][38][39][40] by using similar low intensities (even lower than those usually needed to generate high harmonics in the gas phase) and longer wavelengths, down ...

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Long-range magnetic order in a purely organic 2D layer adsorbed on epitaxial graphene

Cited by 171 publications

References 33 publications

Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces

Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces

Tuneability and criticality in a three-dimensional stacked molecular system

Tuning high-harmonic generation by controlled deposition of ultrathin ionic layers on metal surfaces

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