Self-assembled indium linear chains on the Si(111) surface are found to exhibit instability of the metallic phase and 1D charge density wave (CDW). The room-temperature metallic phase of these chains undergoes a temperature-induced, reversible transition into a semiconducting phase. The 1D CDW along the chains is observed directly in real space by scanning tunneling microscopy at low temperature. The Fermi contours of the metallic phase measured by angle-resolved photoemission exhibit a perfect nesting predicting precisely the CDW periodicity. [S0031-9007(99)09330-8]

Our scanning tunneling microscopy and electron diffraction experiments revealed that a new twodimensional allotrope of Bi forms on the Si111-7 7 surface. This pseudocubic f012g-oriented allotrope is stable up to four atomic layers at room temperature. Above this critical thickness, the entire volume of the film starts to transform into a bulk single-crystal (001) When the size and shape of the materials are downsized to a nanometer scale, they often reveal anomalous atomic structures as well as exotic functional properties that do not exist in bulk. A variety of novel structures discovered in nanoparticles and nanowires have been attracting broad interest [1][2][3][4]. Group V elements are known to show rich allotropic transformation because their semimetallic bonding character can be easily shifted to either the metallic or covalent side, for example, by changing the applied pressure [5][6][7][8]. In this context, a question arises whether a new allotrope can be realized by tuning the dimensionality or size, such as thickness of the film, instead of tuning the pressure or temperature.In this Letter, we report on our finding that ultrathin film of Bi really shows such an allotropic transformation as a function of thickness on the scale of several atomic layers. Our electron diffraction and scanning tunneling microscopy (STM) experiments revealed that, over the wetting layer formed initially on the Si111-7 7 surface, Bi grows with a new f012g-oriented phase whose structure is significantly different from bulk Bi and that it transforms into the bulk-like single-crystal Bi(001) phase above the critical thickness which increases with the substrate temperature. Our ab initio theory revealed that the f012g phase with even-number layers is stabilized by forming a puckered-layer structure. The resulting film is very flat, compared to the growth of any known metal films, reflecting the inherent two-dimensional (2D) structure of this f012g phase. To the best of our knowledge, puckered-layer structure was never observed before except for the case of black phosphorus, which is a famous teratoid phase in group V elements.Bismuth ultrathin films were grown in ultrahigh vacuum (UHV) and characterized in situ using STM and reflection high-energy electron diffraction (RHEED). The spot-profile-analyzing low-energy electron diffraction (SPA-LEED) was performed with momentum reso-

A bulk material comprising stacked nanosheets of nickel bis(dithiolene) complexes is investigated. The average oxidation number is -3/4 for each complex unit in the as-prepared sample; oxidation or reduction respectively can change this to 0 or -1. Refined electrical conductivity measurement, involving a single microflake sample being subjected to the van der Pauw method under scanning electron microscopy control, reveals a conductivity of 1.6 × 10(2) S cm(-1), which is remarkably high for a coordination polymeric material. Conductivity is also noted to modulate with the change of oxidation state. Theoretical calculation and photoelectron emission spectroscopy reveal the stacked nanosheets to have a metallic nature. This work provides a foothold for the development of the first organic-based two-dimensional topological insulator, which will require the precise control of the oxidation state in the single-layer nickel bisdithiolene complex nanosheet (cf. Liu, F. et al. Nano Lett. 2013, 13, 2842).

The electronic structure of Bi(001) ultrathin films (thickness > or =7 bilayers) on Si(111)-7x7 was studied by angle-resolved photoemission spectroscopy and first-principles calculations. In contrast with the semimetallic nature of bulk Bi, both the experiment and theory demonstrate the metallic character of the films with the Fermi surface formed by spin-orbit-split surface states (SSs) showing little thickness dependence. Below the Fermi level, we clearly detected quantum well states (QWSs) at the M point, which were surprisingly found to be non-spin-orbit split; the films are "electronically symmetric" despite the obvious structural nonequivalence of the top and bottom interfaces. We found that the SSs hybridize with the QWSs near M and lose their spin-orbit-split character.