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Kelvin probe force microscopy images show that the surface potential of graphite changes with time as the contamination covers its surface. Using mass spectrometry we identify the molecular mass of the contaminants to be compatible with that of tetracene, a polycyclic aromatic hydrocarbon (PAH), and its isomers. A combination of desorption and Kelvin probe force microscopy experiments plus theoretical calculations confirms that these molecules are the main contaminant for graphitic surfaces in air ambient conditions. Interestingly, when the sample temperature is increased above ∼50 °C the molecules are desorbed and the surface potential becomes fairly homogeneous, suggesting that graphitic surfaces should be almost atomically clean above this temperature. PAHs are potent atmospheric pollutants, potentially carcinogenic, that consist of fused aromatic rings. Incomplete combustion of organic materials can increase the concentration of PAHs in the atmosphere, which in urban regions is enough to totally cover the surface of graphite in a time period that varies from minutes to a few hours. One of the consequences of the adsorption of molecules on graphene is the doping of its surface and the variation of the charge neutrality point originated by the charge transfer between graphene and the contamination layer.

The present study is aimed at elucidating the factors governing the organization on surfaces of some aromatic alcohol molecules. The ability to self-assemble on an Au (111) surface monolayer structures of three different polyalcohols with trigonal symmetry, 1,3,5-trihydroxybenzene (THB), 1,3,5-tris(4-hydroxyphenyl)benzene (THPB), and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), has been evaluated. The characterization has been performed in situ by means of ultrahigh vacuum scanning tunneling microscopy (STM), and the obtained networks have been rationalized by density functional theory (DFT) calculations. One single phase consisting of trimers has been identified for each of the trialcohols studied, whereas for HHTP two additional phases have been characterized. The use of HHTP molecules has shown more versatility in the interaction modes of the hydroxyl groups, leading to larger structural variety on Au (111).

Carbon and silicon pentagonal low-dimensional structures attract a great interest as they may lead to new exotic phenomena such as topologically protected phases or increased spin–orbit effects. However, no pure pentagonal phase has yet been realized for any of them. Here we unveil through extensive density functional theory calculations and scanning tunnelling microscope simulations, confronted to key experimental facts, the hidden pentagonal nature of single- and double-strand chiral Si nano-ribbons perfectly aligned on Ag(110) surfaces whose structure has remained elusive for over a decade. Our study reveals an unprecedented one-dimensional Si atomic arrangement solely comprising almost perfect alternating pentagons residing in the missing row troughs of the reconstructed surface. We additionally characterize the precursor structure of the nano-ribbons, which consists of a Si cluster (nano-dot) occupying a silver di-vacancy in a quasi-hexagonal configuration. The system thus materializes a paradigmatic shift from a silicene-like packing to a pentagonal one., The atomic structure of Si nanoribbons on metallic surfaces has been disputed for years and yet remained elusive. Here, the authors unveil the nature of aligned Si nanoribbons on Ag(110), shifting the focus from a hexagonal silicene-like arrangement to a 1D phase solely comprising Si pentagons.

We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) on the clean and on the oxygen pre-covered Cu(100) surface [referred to as (√2 × 2√2)R45° – 2O/Cu(100)] by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Our results confirm the (4√2 × 5√2)R45° superstructure of PTCDA/Cu(100) reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100). Quite differently, after preadsorption of oxygen and formation of the (√2 × 2√2)R45° – 2O/Cu(100) superstructure on Cu(100), PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

The reaction between 1,3,5-tris(4-hydroxyphenyl)benzene and benzene-1,3,5-tricarbonyl trichloride leads to polyester condensation and formation of a novel COF on an Au(111) surface. The characterization performed in situ by means of variable temperature STM and XPS reveals the formation of an array of hexagonal cavities with ca. 2 nm size.

We have investigated the geometry and electronic structure of two different types of self-aligned silicon nanoribbons (SiNRs), forming either isolated SiNRs or a self-assembled 5 × 2/5 × 4 grating on an Ag(110) substrate, by scanning tunnelling microscopy and high resolution x-ray photoelectron spectroscopy. At room temperature we further adsorb on these SiNRs either atomic or molecular hydrogen. The hydrogen absorption process and hydrogenation mechanism are similar for isolated or 5 × 2/5 × 4 ordered SiNRs and are not site selective; the main difference arises from the fact that the isolated SiNRs are more easily attacked and destroyed faster. In fact, atomic hydrogen strongly interacts with any Si atoms, modifying their structural and electronic properties, while molecular hydrogen has first to dissociate. Hydrogen finally etches the Si nanoribbons and their complete removal from the Ag(110) surface could eventually be expected.