Jun Li

1T-TiSe2 hosts a 3D charge-density-wave (CDW) state that also features exciton condensation. We find that photoexcitation suppresses the 3D CDW while creating a 2D CDW, a process controlled by the excitonic correlations in the system.

We report the formation of one- and two-dimensional metal-organic coordination structures from para-hexaphenyl-dicarbonitrile (NC-Ph₆-CN) molecules and Cu atoms on graphene epitaxially grown on Ir(111). By varying the stoichiometry between the NC-Ph₆-CN molecules and Cu atoms, the dimensionality of the metal-organic coordination structures could be tuned: for a 3:2 ratio, a two-dimensional hexagonal porous network based on three-fold Cu-coordination was observed, while for a 1:1 ratio, one-dimensional chains based on two-fold Cu-coordination were formed. The formation of metal-ligand bonds was supported by imaging the individual Cu atoms within the metal-organic coordination structures with scanning tunneling microscopy. Scanning tunneling spectroscopy measurements demonstrated that the electronic properties of NC-Ph₆-CN molecules and Cu atoms were different between the two-dimensional porous network and the one-dimensional molecular chains.

A comparative study on the self‐assembly of sexiphenyl‐dicarbonitrile on highly oriented pyrolytic graphite and single‐layer graphene on Cu(111) is presented. Despite an overall low molecule–substrate interaction, the close‐packed structures exhibit a peculiar shift repeating every four to five molecules. This shift has hitherto not been reported for similar systems and is hence a unique feature induced by the graphitic substrates.

We report on the observation of photoluminescence (PL) with a narrow 18 meV peak width from molecular beam epitaxy grown on graphene/Ir(1 1 1). This observation is explained in terms of a weak graphene-MoS ₂ interaction that prevents PL quenching expected for a metallic substrate. The weak interaction of MoS ₂ with the graphene is highlighted by angle-resolved photoemission spectroscopy and temperature dependent Raman spectroscopy. These methods reveal that there is no hybridization between electronic states of graphene and MoS ₂ as well as a different thermal expansion of both materials. Molecular beam epitaxy grown MoS ₂ on graphene is therefore an important platform for optoelectronics which allows for large area growth with controlled properties.

The self-assembly of 1,3,5-benzenetribenzoic acid (BTB) molecules on Both Cu(111) and epitaxial graphene grown on Cu(111 ) were studied by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) under ultrahigh vacuum conditions. On Cu(111) the BTB molecules were found to mainly arrange in close-packed structures through H-bonding between the (partially) deprotonated carboxylic acid groups. In addition, porous structures formed by intact BTB molecules - and also based on H-bonding - were observed. On graphene grown on Cu(111) the BTB molecules mainly form porous structures accompanied by small patches of disordered close-packed structures. Upon annealing, BTB adsorbed on Cu(111) is fully deprotonated and arranges in the close-packed structure while in contrast on graphene/Cu(111) the porous network is exclusively formed. This shows that the molecular self-assembly behavior is highly dependent on the first substrate layer: one graphene layer is sufficient to considerably alter the interplay of molecule substrate and intermolecular interactions in favor of the latter interactions.

Summary form only given. Due to significant application in medical treatment, magnetic record and cryogenic magneto-refrigeration, a great amount of researches on ferromagnetic nanoparticles were executed [1]. With decrease of the scale of ferromagnetic material, the magnetic order and magnetization gradually decrease and such decrease is attributed to the increasing surface disorder or surface spin canting. However, for the anti-ferromagnetic nanoparticles, their magnetization will increase when compared with its corresponding bulk material because its large surface will induce more un-compensated spins to increase the magnetization of the nanoparticles. For example, when the size of anti-ferromagnetic CoRh ₂ O ₄ decreases to 16nm, the increased surface spins induced the increased magnetization [2]. For exploiting more anti-ferromagnetic nanoparticles with high magnetization, the Gd-based anti-ferromagnetic GdH ₂ nanoparticles were prepared by arc-discharge technique. The GdH ₂ nanoparticles show irregularly polygonal shape and have size distribution of 30-80nm with the average particle size of 50nm. In further, the GdH ₂ nanoparticle has no core-shell structure and can be stably exist in the atmosphere (Figure1). At 5K, the GdH ₂ nanoparticles show magnetization of 109 emu/g under applied field of 50 kOe . With the high magnetization and low anisotropy constant, the GdH ₂ nanoparticles show large cryogenic entropy change (-ΔSM). The -ΔSM slowly increases with decreasing temperature from 80K to 30 K, and then rapidly increases from 30K to 5K. At 5K, the value of -ΔSM shows largest value of 12 .3J/( kg K) under the change of 50 kOe field (Figure 2). The large entropy change is attributed to large amount of un-compensated spins on the surface and weak anisotropy of the GdH ₂ nanoparticles.