Low-energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy measurements have been performed on GaAs samples cleaved in ultra-high vacuum and subject to in situ isochronous anneals up to 850 degrees C. The properties of the cleaved (110) surface remain unchanged up to about 350 degrees C. Around this temperature, a dissociation occurs inducing a local reconstruction of the surface; at the same time, new states appear which may be attributed to Ga vacancies. Then, around 580 degrees C, the well known dissociation of GaAs sets in with formation of As2, and the Ga-Ga bonds which then form, determine the electronic properties of the sample. Evaporation of arsenic would become dominant around 650 degrees C. Beyond about 780 degrees C, the excess Ga coalesces into Ga-metal droplets and the GaAs substrate undergoes faceting.
artificial monolayers each year, and a multitude of techniques like, e.g., molecular beam epitaxy, chemical deposition on surfaces, synthesis in wet environment and many others. Initially mainly studied for their fundamentally new and exotic properties, 2D materials have now attracted widespread interest due to their high potential for novel nanotechnological applications. [3][4][5][6][7][8][9] In this context, 2D materials composed of metal atoms and organic linkers have emerged as promising candidates to combine the advantages of both realms, also called 2D metal-organic frameworks (MOFs). For potential applications, we may cite, for example, their abilities in molecular recognition and functionalities for heterogeneous asymmetric catalysis, while their peculiar topological properties are interesting for new spintronic devices. [10][11][12][13][14][15][16][17][18] Most of the 2D metalorganic frameworks (MOFs) synthesized so far are almost perfect insulators but there is a major exception, namely the subclass of conductive MOFs or c-MOFs which are either metallic or at least semiconducting. The development of these c-MOFs is an important challenge for future decades due to their novel electronic, optical, mechanical, and catalytic properties. [19][20][21][22][23] Graphene is of fundamental interest since its linearly dispersing highly mobile electrons may be viewed as a 2D versionThe on-surface synthesis of metal-organic covalent coordination networks with a dense Kagomé lattice of metallic centers is reported. Tetrahydroxyquinone and metal atoms (M = Cu or Mn) are codeposited on Ag( 111) substrate to build well-ordered 2D lattices M 3 C 6 O 6 . The surface is studied by scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) reveals a Cu + charge state and no local magnetic moments for the Cu-organic network. For the Mn-organic network, the charge state Mn 2+ and a local spin S = 5/2 are found. Charge transfer stabilizes the Cu + and Mn 2+ charge states. DFT calculations show a Dirac point, i.e., a band crossing with linear electron dispersion at the K-point g g a b (2 / 3) +(1/3) of the Brillouin zone. This Dirac point is at the Fermi level without charge transfer but drops by 100 meV if electron doping of Cu 3 C 6 O 6 on Ag(111) surface is acknowledged. The magnetic couplings of an isolated Mn 3 C 6 O 6 monolayer to be short range and antiferromagnetic leading to high frustration at the Kagomé lattice and a tendency toward a spin-liquid ground state are predicted. In the case of hole transfer from the substrate, ferromagnetic ordering is introduced, making Mn 3 C 6 O 6 an interesting candidate for the quantum anomalous Hall effect.
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