Collective electronic states such as the charge density wave (CDW) order and superconductivity (SC) respond sensitively to external perturbations. Such sensitivity is dramatically enhanced in two dimensions (2D), where 2D materials hosting such electronic states are largely exposed to the environment. In this regard, the ineludible presence of supporting substrates triggers various proximity effects on 2D materials that may ultimately compromise the stability and properties of the electronic ground state. In this work, we investigate the impact of proximity effects on the CDW and superconducting states in single-layer (SL) NbSe 2 on four substrates of diverse nature, namely, bilayer graphene (BLG), SL-boron nitride (h-BN), Au(111), and bulk WSe 2 . By combining low-temperature (340 mK) scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy, we compare the electronic structure of this prototypical 2D superconductor on each substrate. We find that, even when the electronic band structure of SL-NbSe 2 remains largely unaffected by the substrate except when placed on Au(111), where a charge transfer occurs, both the CDW and SC show disparate behaviors. On the insulating h-BN/Ir(111) substrate and the metallic BLG/SiC(0001) substrate, both the 3 × 3 CDW and superconducting phases persist in SL-NbSe 2 with very similar properties, which reveals the negligible impact of graphene on these electronic phases. In contrast, these collective electronic phases are severely weakened and even absent on the bulk insulating WSe 2 substrate and the metallic single-crystal Au(111) substrate. Our results provide valuable insights into the fragile stability of such electronic ground states in 2D materials.

C60 molecules adsorbed on graphene/Ru(0001) substrate were investigated by scanning tunneling microscopy (STM) at 5 K. On high quality substrates, C60 molecules adopt a commensurate growth mode, leading to formation of a supramolecular structure with perfect periodicity and few defects. On under-annealed substrates with imperfections and domains, the molecules form the same closely packed hexagonal structures in spite of underlying corrugations, disorders or steps, indicating a weak molecule-substrate interaction—a conclusion that is also supported by DFT calculations. This system may be beneficial to the fabrication of carbon based devices and of other types of organic functional overlayers.

In certain unconventional superconductors with sizable electronic correlations, the availability of closely competing pairing channels leads to characteristic soft collective fluctuations of the order parameters, which leave fingerprints in many observables and allow the phase competition to be scrutinized. Superconducting layered materials, where electron–electron interactions are enhanced with decreasing thickness, are promising candidates to display these correlation effects. In this work, the existence of a soft collective mode in single‐layer NbSe2, observed as a characteristic resonance excitation in high‐resolution tunneling spectra is reported. This resonance is observed along with higher harmonics, its frequency Ω/2Δ is anticorrelated with the local superconducting gap Δ, and its amplitude gradually vanishes by increasing the temperature and upon applying a magnetic field up to the critical values (TC and HC2), which sets an unambiguous link to the superconducting state. Aided by a microscopic model that captures the main experimental observations, this resonance is interpreted as a collective Leggett mode that represents the fluctuation toward a proximate f‐wave triplet state, due to subleading attraction in the triplet channel. These findings demonstrate the fundamental role of correlations in superconducting 2D transition metal dichalcogenides, opening a path toward unconventional superconductivity in simple, scalable, and transferable 2D superconductors.

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Room‐temperature phosphorescence (RTP) emitters with ultralong lifetimes are emerging as attractive targets because of their potential applications in bioimaging, security, and other areas. But their development is limited by ambiguous mechanisms and poor understanding of the correlation of the molecular structure and RTP properties. Herein, different substituents on the 9,9‐dimethylxanthene core (XCO) result in compounds with RTP lifetimes ranging from 52 to 601 ms, which are tunable by intermolecular interactions and molecular configurations. XCO‐PiCl shows the most persistent RTP because of its reduced steric bulk and multiple sites of the 1‐chloro‐2‐methylpropan‐2‐yl (PiCl) moiety for forming intermolecular interactions in the aggregated state. The substituent effects reported provide an efficient molecular design of organic RTP materials and establishes relationships among molecular structures, intermolecular interactions, and RTP properties.

A deep grasp of the properties of the interface between organic molecules and hexagonal boron nitride (h-BN) is essential for the full implementation of these two building blocks in the next generation of electronic devices. Here, using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), we report on the geometric and electronic features of C60 evaporated on a single layer of h-BN grown on a Rh(110) surface under ultra-high vacuum. Two different molecular assemblies of C60 on the h-BN/Rh(110) surface were observed. The first STM study at room temperature (RT) and at low temperatures (40 K) looked at the molecular orientation of C60 on a two-dimensional layered material. Intramolecular-resolution images demonstrate the existence of a phase transition of C60 over the h-BN/Rh(110) surface similar to that found on bulk solid C60. At RT molecules exhibit random orientations, while at 40 K such rotational disorder vanishes and they adopt a common orientation over the h-BN/Rh(110) surface. The decrease in thermal energy allows recognition between C60 molecules, and they become equally oriented in the configuration at which the van der Waals intermolecular interactions are optimized. Bias-dependent submolecular features obtained by means of high-resolution STM images are interpreted as the highest occupied and lowest unoccupied molecular orbitals. STS data showed that fullerenes are electronically decoupled from the substrate, with a negligible charge transfer effect if any. Finally, the very early stages of multilayer growth were also investigated.

partially driven to complement and fulfill the absence of electronic band gap in graphene, [5] as this property is technologically relevant in some applications. In this sense, the synthesis of a large number of 2D materials from group IV and V elements like silicene, [6,7] germanene, [8,9] or antimonene [10,11] has been reported in the literature. In particular, metallic substrates have been commonly adopted as the growing support for these novel materials, providing a platform to explore their properties. However, several issues have recently been raised by different authors regarding the successful synthesis of pure layers of these bidimensional materials, especially when they are grown on metal substrates. [12][13][14][15][16][17][18][19] Therefore, further research is necessary to throw light on this present controversy.Among this vast portfolio of 2D materials, antimonene has received a strong amount of interest due to its attractive properties. It has been theoretically predicted to feature a tunable semiconducting band gap, [20,21] a relatively high carrier mobility [22] or quantum spin Hall effect. [23] Experimentally, different methods have been employed to synthesize antimonene. From top-down approaches, few-layer antimonene crystals can be obtained through liquid-phase [24] or mechanical [25] exfoliation. In the latter, thickness down to monolayer can be isolated. [25] Bottomup synthesis also constitutes a versatile method. In particular, the growth of antimonene sheets have been reported by depositing Sb on metal chalcogenides, [26,27] semiconductors, [28] and metal [10,11] substrates. Nevertheless, other studies on the growth and adsorption of Sb on metallic substrates suggest a different nature of Sb atoms. According to these studies, on gold, copper, and silver single-crystal, the experimental results are best explained as a substitutional surface alloy presenting a stacking fault with respect to the underlying metal support. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Such substitutional adsorption of Sb was also theoretically found to be the most energetically favored for Sb compared to on surface sites. [37,[44][45][46] In this article, the growth of Sb on single-crystal Pt(111) has systematically been investigated via a combination of scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) techniques under ultra-high vacuum (UHV) conditions. Pt(111) has been chosen as the substrate since it differs from the coinage metals (Cu, Ag and Au) that have been used in mainly all the studies performed until now. Therefore, understanding the behavior of Understanding the growth behavior of group-V elements on metal surfaces provides valuable information that can shed light on the feasibility of tailoring atomically thin monoelemental 2D polymorphs composed of pnictogens on these metallic substrates. Here, by combining scanning tunneling microscopy (STM), low energy electron diffraction and Auger electron spectroscopy measurements...

The structural and electronic properties of chloro‐aluminum phthalocyanine (ClAlPc) molecules on insulating hexagonal boron nitride (h‐BN) monolayers (MLs) grown on Pt(111) surfaces are studied via scanning tunneling microscopy and spectroscopy (STM/STS) along with low energy electron diffraction in ultra‐high vacuum conditions. As a reference, the structural properties of the h‐BN/Pt(111) surface are studied, where various moiré patterns associated to different orientations of the h‐BN lattice with respect to the Pt(111) surface below are characterized, for the first time, at the atomic scale. Room temperature deposition of ClAlPc molecules on h‐BN/Pt(111) gives rise to the formation of mainly bilayer molecular structures, where the ClAlPc molecules adopt an alternating Cl‐up and Cl‐down stacking configuration. Upon annealing, bilayer molecular structures become islands comprising only a single layer of molecules adsorbed in a Cl‐up configuration. In the ML regime, the possible influence of the moiré pattern superstructure and the h‐BN lattice on the molecular ordering is also studied. Finally, the electronic properties of ClAlPc on h‐BN/Pt(111) are investigated through high‐resolution STM imaging of the frontier molecular orbitals and differential conductance plots. The results point toward a weak molecule–substrate interaction.