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The research provides facts about the surface plastic deformation (SPD) effect on the coatings surface parameters formed by electro-spark alloying (ESA). The complex for nonabrasive ultrasonic finishing (NUF) was used as the installation for SPD. It was found out that when processing bronze by NUF several passes of indenter were needed to provide substantial decrease of the surface roughness parameters. The NUF effect on roughness parameters of intermetallic coatings on steel 20X13 was studied. NUF proved to be perspective when it is necessary to reduce the number of transverse cracks in the coatings formed by ESD method. In order to assess the efficiency of coating surface treatment by NUF method the use of additional parameters Rk, Rpk, Rvk alongside with Ra are recommended as they allow assessing the resulting surface as triple. It is found out that the number of passes during the processing of intermetallic coatings should not exceed 6. For achieving maximum processing efficiency it is necessary to take into consideration the initial roughness value.

The regularities of changes in the composition and properties (micro- and nanohardness, HB hardness) of the structural components - α-solid solution and eutectic components of the AK7ch alloy (AL9) depending on the value of the addition of Al-Y-Ce-La master alloy are established. With an increase in the addition of Al-Y-Ce-La master alloy a sharp change is observed in the composition and properties of the structural components of the AK7ch alloy - α-solid solution Si in aluminum and eutectic α + Si, as well as complex-doped aluminides from Si, Fe and rear earth metals (REM). The structural components of the AK7ch alloy are identified with the addition of an increasing amount of Al-Y-Ce-La master alloy (α-solid solution of Si in aluminum, eutectic α+Si, complex-doped aluminides of rare-earth metals of variable composition AlxSiyREMz and AlxSiyFezREMν). A correlation between the solubility of silicon in α-solid solution and its microhardness is found. To increase microhardness of the eutectic and hardness of the AK7ch alloy, it is necessary to add the synthesized ligature in the amount of 0.1 wt.%.

The technology of producing ligatures containing rear earth metals (REM) for modification of silumins has been developed. The optimum content ratio of yttrium, cerium and lanthanum 2: 1: 0.5 (15-20 wt.% Y, 7-10 wt.% Ce, 3.5-5.0 wt.% La) for the synthesis of REM aluminides has been established. The peculiarities of the REM aluminides synthesis is studied using the methods of optical and electron microscopy and X-ray microanalysis, followed by the identification of the structural components of the Al-REM alloy. The microstructure of the master alloy is proved to consists of: REM aluminides (yttrium-containing and cerium-containing), metal base (Al), Al eutectic + REM aluminide and α + Si.

Helicenes represent an important class of chiral organic material with promising optoelectronic properties. Hence, functionalization of surfaces with helicenes is a key step towards new organic material devices. This review presents different aspects of adsorption and modification of metal surfaces with different helicene species. Topics addressed are chiral crystallization, that is, 2D conglomerate versus racemate crystallization, breaking of mirror-symmetry in racemates, chirality-induced spin selectivity, and stereoselective on-surface chemistry., (© 2024 The Author(s). Chirality published by Wiley Periodicals LLC.)

On-surface synthesis has become a prominent method for growing low-dimensional carbon-based nanomaterials on metal surfaces. However, the necessity of decoupling organic nanostructures from metal substrates to exploit their properties requires either transfer methods or new strategies to perform reactions directly on inert surfaces. The use of on-surface light-induced reactions directly on semiconductor/insulating surfaces represents an alternative approach to address these challenges. Here, exploring the photochemical activity of different organic molecules on a SnSe semiconductor surface under ultra-high vacuum, we present a novel on-surface light-induced reaction. The selective photodissociation of the anhydride group is observed, releasing CO and CO 2 . Moreover, we rationalize the relationship between the photochemical activity and the π-conjugation of the molecular core. The different experimental behaviour of two model anhydrides was elucidated by theoretical calculations, showing how the molecular structure influences the distribution of the excited states. Our findings open new pathways for on-surface synthesis directly on technologically relevant substrates., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

We report on-surface synthesis of heterochiral 1D heptahelicene oligomers after deposition of a racemic heptahelicene monomer on an Au(111) surface followed by Ullmann coupling under ultrahigh vacuum conditions. Structure, chirality and mode of adsorption of the resulting dimers to octamers are inferred from the scanning probe microscopy and theoretical calculations., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The interplay between chirality and magnetism is a source of fascination among scientists for over a century. In recent years, chirality-induced spin selectivity (CISS) has attracted renewed interest. It is observed that electron transport through layers of homochiral molecules leads to a significant spin polarization of several tens of percent. Despite the abundant experimental evidence gathered through mesoscopic transport measurements, the exact mechanism behind CISS remains elusive. This study reports spin-selective electron transport through single helical aromatic hydrocarbons that are sublimed in vacuo onto ferromagnetic cobalt surfaces and examined with spin-polarized scanning tunneling microscopy (SP-STM) at a temperature of 5 K. Direct comparison of two enantiomers under otherwise identical conditions revealed magnetochiral conductance asymmetries of up to 50% when either the molecular handedness is exchanged or the magnetization direction of the STM tip or Co substrate is reversed. Importantly, the results rule out electron-phonon coupling and ensemble effects as primary mechanisms responsible for CISS., (© 2023 The Authors. Small published by Wiley‐VCH GmbH.)

From the beginning of molecular theory, the interplay of chirality and magnetism has intrigued scientists. There is still the question if enantiospecific adsorption of chiral molecules occurs on magnetic surfaces. Enantiomer discrimination was conjectured to arise from chirality-induced spin separation within the molecules and exchange interaction with the substrate's magnetization. Here, it is shown that single helical aromatic hydrocarbons undergo enantioselective adsorption on ferromagnetic cobalt surfaces. Spin and chirality sensitive scanning tunneling microscopy reveals that molecules of opposite handedness prefer adsorption onto cobalt islands with opposite out-of-plane magnetization. As mobility ceases in the final chemisorbed state, it is concluded that enantioselection must occur in a physisorbed transient precursor state. State-of-the-art spin-resolved ab initio simulations support this scenario by refuting enantio-dependent chemisorption energies. These findings demonstrate that van der Waals interaction should also include spin-fluctuations which are crucial for molecular magnetochiral processes., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Helicenes represent an important class of chiral organic material with promising optoelectronic properties. Hence, functionalization of surfaces with helicenes is a key step toward new organic materials devices. The deposition of a heterohelicene containing two furano groups and two hydroxyl groups onto copper(111) surface in ultrahigh vacuum leads to different adsorbate modifications. At low coverage and low temperature, the molecules tend to lie on the surface in order to maximize van der Waals contact with the substrate. Thermal treatment leads to deprotonation of the hydroxyl groups and in part into a reorientation from lying into a standing adsorbate mode., (© 2024 The Authors. Chirality published by Wiley Periodicals LLC.)

It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

Two-dimensional (2D) layered group IV-VI semiconductors attract great interest due to their potential applications in nanoelectronics. Depending on the dimensionality, different phases of the same material can present completely different electronic and optical properties, expanding its applications. Here, we present a combined experimental and theoretical study of the atomic structure and electronic properties of epitaxial SnSe structures grown on a metallic Au(111) substrate, forming almost defect-free 2D layers. We describe a coverage-dependent transition from a metallic β -SnSe to a semiconducting α -SnSe phase. The combination of scanning tunneling microscopy/spectroscopy, non-contact atomic force microscopy, x-ray photoelectron spectroscopy/diffraction and angle-resolved photoemission spectroscopy, complemented by density functional theory, provides a comprehensive study of the geometric and electronic structure of both phases. Our work demonstrates the possibility to grow two distinct SnSe phases on Au(111) with high quality and on a large scale. The strong interaction with the substrate allows the stabilization of the previously experimentally unreported β -SnSe, while the ultra-thin films of orthorhombic α -SnSe are structurally and electronically equivalent to bulk SnSe., (Creative Commons Attribution license.)

The on-surface dimerization into bis(hexahelicene) on a gold(111) surface has been studied by means of scanning tunneling microscopy and time-of-flight secondary mass spectrometry. C-C Ullmann coupling of (rac)-2-bromo-hexahelicene leads to formation of the (M,M)- and (P,P)-diastereomers of 2,2'-bis(hexahelicene), whilst formation of the (M,P)-diastereomer is not observed. Upon cooling, the bis(hexahelicene) aggregates into an ordered two-dimensional lattice with partly randomly distributed enantiomers. The highly specific diastereomeric coupling is explained by the surface alignment of educt in combination with the strong steric overcrowding in a possible surface-confined (M,P)-product., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Excitation of single molecules with electrons tunneling between a sharp metallic tip of a scanning tunneling microscope and a metal surface is one way to study and control dynamics of molecules on surfaces. Electron tunneling induced dynamics may lead to hopping, rotation, molecular switching, or chemical reactions. Molecular motors that convert rotation of subgroups into lateral movement on a surface can in principle also be driven by tunneling electrons. For such surface-bound motor molecules the efficiency of motor action with respect to electron dose is still not known. Here, the response of a molecular motor containing two rotor units in the form of overcrowded alkene groups to inelastic electron tunneling has been examined on a Cu(111) surface in ultrahigh vacuum at 5 K. Upon vibrational excitation, switching between different molecular conformations is observed, including conversion of enantiomeric states of chiral conformations. Tunneling at energies in the range of electronic excitations causes activation of motor action and movement across the surface. The expected unidirectional rotation of the two rotor units causes forward movements but with a low degree of translational directionality.

The discovery of chirality-induced spin selectivity (CISS), resulting from an interaction between the electron spin and handedness of chiral molecules, has sparked interest in surface-adsorbed chiral molecules due to potential applications in spintronics, enantioseparation, and enantioselective chemical or biological processes. We study the deposition of chiral heptahelicene by sublimation under ultra-high vacuum onto bare Cu(111), Co bilayer nanoislands on Cu(111), and Fe bilayers on W(110) by low-temperature spin-polarized scanning tunneling microscopy/spectroscopy (STM/STS). In all cases, the molecules remain intact and adsorb with the proximal phenanthrene group aligned parallel to the surface. Three degenerate in-plane orientations on Cu(111) and Co(111), reflecting substrate symmetry, and only two on Fe(110), i.e., fewer than symmetry permits, indicate a specific adsorption site for each substrate. Heptahelicene physisorbs on Cu(111) but chemisorbs on Co(111) and Fe(110) bilayers, which nevertheless remain for the sub-monolayer coverage ferromagnetic and magnetized out-of-plane. We are able to determine the handedness of individual molecules chemisorbed on Fe(110) and Co(111), as previously reported for less reactive Cu(111). The demonstrated deposition control and STM/STS imaging capabilities for heptahelicene on Co/Cu(111) and Fe/W(110) substrate systems lay the foundation for studying CISS in ultra-high vacuum and on the microscopic level of single molecules in controlled atomic configurations., Competing Interests: The authors declare no conflict of interest.

Flattening helices while keeping the handedness: On-surface cyclodehydrogenation of bishelicene enantiomers leads stereospecifically to (M,M) and (P,P) chiral planar polyaromatic hydrocarbons. This is followed by their homochiral aggregation into a 2D conglomerate. Thermally induced cyclodehydrogenation proceeds stereospecifically to chiral, planar coronocoronene. Such a reaction is a special example of topochemistry in which enantiospecific conversion is supported by the alignment of the reactant by the surface., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The chiral self-assembly of trispentahelicene propellers on a gold surface has been investigated in ultrahigh vacuum by means of scanning tunneling microscopy and time-of-flight secondary ion mass spectrometry. The trispentahelicene propellers aggregate into mirror domains with an enantiomeric ratio of 2 : 1. Thermally induced cyclodehydrogenation leads to planarization into nanographenes, which self-assemble into closed-packed layers with two different azimuths. Further treatment induces in part dimerization and trimerization by intermolecular cyclodehydrogenation., (© 2021 The Authors. Published by Wiley-VCH GmbH.)

African swine fever (ASF), classical swine fever (CSF) and foot-and-mouth disease (FMD) are considered to be three of the most detrimental animal diseases and are currently foreign to the U.S. Emerging and re-emerging pathogens can have tremendous impacts in terms of livestock morbidity and mortality events, production losses, forced trade restrictions, and costs associated with treatment and control. The United States is the world's top producer of beef for domestic and export use and the world's third-largest producer and consumer of pork and pork products; it has also recently been either the world's largest or second largest exporter of pork and pork products. Understanding the routes of introduction into the United States and the potential economic impact of each pathogen are crucial to (a) allocate resources to prevent routes of introduction that are believed to be more probable, (b) evaluate cost and efficacy of control methods and (c) ensure that protections are enacted to minimize impact to the most vulnerable industries. With two scoping literature reviews, pulled from global data, this study assesses the risk posed by each disease in the event of a viral introduction into the United States and illustrates what is known about the economic costs and losses associated with an outbreak., (© 2020 Wiley-VCH GmbH.)

The front cover artwork is provided by Prof. Ernst from Empa. The image shows determination of the sense of helicity of trioxa[11]helicene enantiomers with an atomic force microscope, which allows discrimination between homo- and heterochiral 2D self-assembly. Read the full text of the Article at 10.1002/cphc.202000853., (© 2021 Wiley-VCH GmbH.)

Functionalization of surfaces with derivatives of Buckminsterfullerene fragment molecules seems to be a promising approach toward bottom-up fabrication of carbon nanotube modified electrode surfaces. The modification of a Cu(100) surface with molecules of the buckybowl pentaindenocorannulene has been studied by means of scanning tunneling microscopy, carbon monoxide-modified noncontact atomic force microscopy, time-of-flight secondary mass spectrometry, and quantum chemical calculations. Two different adsorbate modes are identified, in which the majority is oriented such that the bowl cavity points away from the surface and the convex side is partially immersed into a four-atom vacancy in the Cu(100) surface. A minority is oriented such that the convex side points away from the surface with the five benzo tabs oriented basically parallel to the surface. Thermal annealing leads to hydrogenation and planarization of the molecules in two steps under specific C-C bond cleavage. The benzo tabs of the convex side up species serve as a hydrogen source. The final product has an open-shell electron structure that is quenched on the surface.

The thermally induced cyclodehydrofluorization of iron tetrakis(pentafluorophenyl)porphyrin proceeded highly stereoselectively to give a prochiral product on a gold surface in an ultrahigh vacuum, whereas dehydrocyclization of the respective iron tetrakisphenylporphyrin did not show such selectivity. Stereoselectivity was predominantly observed for closely packed layers, which is an indication of intermolecular cooperativity and steric constraints induced by adjacent species. Density functional theory identified intermolecular packing constraints as the origin of such selectivity during the reaction. Scanning tunneling microscopy revealed the formation of an enantiomerically pure two-dimensional self-assembly as a conglomerate of mirror domains. On-surface two-dimensional topochemistry, as reported herein, may open new routes for stereoselective synthesis., (© 2020 Wiley-VCH GmbH.)

Resolution of enantiomers of chiral compounds via crystallization is the dominant method in chemical industry, but chiral recognition at the molecular level during this process is still poorly understood. Using single metal surfaces in ultrahigh vacuum as model system, the enantio-related transition from the monolayer structure into a double layer of the racemic mixture of heptahelicene has been studied with scanning tunneling microscopy. Submolecular resolution reveals enantiopure second layers on Ag(111) and almost enantiopure second layers on Au(111). In analogy to previous results on Cu(111), it is concluded that transition from the 2D first layer racemate into a layered racemate occurs., (© 2020 Wiley Periodicals LLC.)

From Sunday February 2 nd , 2020 until the following Friday, 75 scientists from all over the world gathered in Hotel Laudinella in St. Moritz to discuss their latest findings about surface, cluster and gas phase physics and chemistry. A program consisting of 25 invited speakers, 16 hot topic oral contributions and 27 poster presentations has been put together by the organizers from Empa.

From October 13 to 17, 2019, nearly 90 scientists from all over the world gathered on the Monte Verità congress site of the ETH Zurich to discuss their latest findings about chirality in different fields of physical sciences. A program consisting of 20 invited speakers, 18 hot topic oral contributions and 27 poster presentations have been put together by the organizers.

The growth of carbon layers, defective graphene, and graphene by deposition of polycyclic aromatic hydrocarbons (PAHs) on Cu(111) is studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Two different PAHs are used as starting materials: the buckybowl pentaindenocorannulene (PIC) which contains pentagonal rings and planar coronene (CR). For both precursors, with increasing sample temperature during deposition, porous carbon aggregates (350 °C), dense carbon layers (400-450 °C), disordered defective graphene (500 °C-550 °C), and extended graphene (≥600 °C) are obtained. No significant differences for defective graphene grown from PIC and CR are observed. C 1s X-ray photoelectron spectra of PIC and CR derived samples grown at 350-550 °C exhibit a characteristic C-Cu low binding energy component. Preparation at ≥600 °C eliminates this C-Cu species and only C-C bonded carbon remains., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion-enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two-dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C-H⋅⋅⋅π bonding., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Chiral recognition among three differently functionalized heptahelicene derivatives on Ag(111) and Au(111) surfaces has been studied with scanning tunnelling microscopy. All three species were found to self-assemble into racemic zigzag structures, with alternation of (M)- and (P)-enantiomers.

Wild pigs (Sus scrofa) are a non-native invasive species in the United States that cause significant economic loss, transmit disease, and inflict damage upon natural resources, agriculture, livestock, and property. Geographic distribution of wild pigs in the United States has nearly tripled since 1982, with anthropogenic influences playing a significant role in the expansion. In this regard, there is speculation that a driver of the expansion may be human-mediated movement of wild pigs to new areas for the purpose of sport hunting. In response, states have implemented a variety of wild pig control policies, including legal restrictions on their transport. The success of such policies depends, in part, on their level of public support, which in turn may be influenced by individuals' attitudes concerning wild pigs, their interest in maintaining wild pig populations (e.g., for sport hunting), and their knowledge and awareness of the threats wild pigs pose. Multiple regression was used to analyze data collected from a nationwide survey concerning attitudes toward wild pigs and policies that restrict their transport. Results indicate that a majority of individuals in the United States have negative attitudes toward wild pigs and support policies that restrict their transport and penalize transgressors. Consistent with other invasive species research, findings suggest that as knowledge and awareness of wild pigs increase, so too does support for policies restricting and penalizing transport of wild pigs. Contrary to previous studies, this research also finds that hunters are more likely to support restrictions on wild pig transport than are non-hunters. Overall, these findings suggest that legal restrictions on the transport of wild pigs, even in states with large hunter populations, enjoy broad public support and may help to curb the expansion of wild pig populations., (Published by Elsevier Ltd.)

The on-surface synthesis of bisheptahelicene by Ullmann coupling of 9-bromoheptahelicene on Au(111) and its temperature-induced dehydrogenation is studied using temperature-programmed reaction spectroscopy and time-of-flight secondary ion mass spectrometry. Specific dehydrogenation products of bisheptahelicene after loss of 6, 8 and 10 hydrogen atoms are identified, corresponding to molecules having undergone Diels-Alder transformations and intramolecular C-C coupling reactions. By combining with atomic hydrogen produced by dehydrogenation, the Ullmann coupling side-product bromine desorbs as HBr. H 2 desorption emerges only after all Br has desorbed. Such characteristic behavior is explained by a kinetic model which explicitly considers the coverage of transient atomic H on the surface. Heating experiments performed with saturated layers of different Br-containing molecules reveal that the onset of HBr desorption depends strictly on the dehydrogenation step and therefore on the structure of the molecules.

The comparison of the self-assembly 9,9'-bisheptahelicene on the Au(111) surface, studied with scanning tunneling microscopy, with the self-assembly of the same species obtained by on-surface synthesis via Ullmann coupling from 9-bromoheptahelicene reveals a diastereomeric excess for the ( M, P)- meso-form of 50%. The stereoselectivity is explained by a topochemical effect, in which the surface-alignment of the starting material and the organometallic intermediate sterically favor the ( M, P)-transition state over the homochiral transition states.

Stereochemical effects during two-dimensional crystallization of bisheptahelicene diastereomers on a Cu(111) surface have been studied with scanning tunnelling microscopy. The (M,M)- and (P,P)-enantiomers crystallize into a monolayer racemate lattice, whereas the (M,P)-diastereomers aggregate into their own monolayer phase.

Molecular rotors on solid surfaces are fundamental components of molecular machines. No matter whether the rotation is activated by heat, electric field or light, it is determined by the intrinsic rotational potential landscape. Therefore, tuning the potential landscape is of great importance for future applications of controlled molecular rotors. Here, using scanning tunneling microscopy (STM), we demonstrate that both tip-molecule distance and sample bias can modify the rotational potential of molecular rotors. We achieve the potential energy difference variations of ∼0.3 meV/pm and ∼18 meV/V between two configurations of a molecular rotor, a tetra- tert-butyl nickel phthalocyanine molecule on Au(111) substrate. Further analysis indicates that the mechanism of modifying the rotational potential is a combination of the van der Waals interaction and the interaction between the molecular dipole and an electric field. This work provides insight into the methods used to modify the effective rotational potential energy of molecular rotors.

Rabies is an economically important zoonosis. This paper describes the extent of the economic impacts of the disease and some of the types of economic analyses used to understand those impacts, as well as the trade-offs between efforts to manage rabies and efforts to eliminate it. In many cases, the elimination of rabies proves more cost-effective over time than the continual administration of postexposure prophylaxis, animal testing and animal vaccination. Economic analyses are used to inform and drive policy decisions and focus political will, placing economics at the heart of rabies control.

The on-surface Ullmann coupling of 2,3-dibromo[4]helicene molecules is studied on Au(111) and Cu(111) surfaces. Bis-helicene and tris-helicene are identified with scanning tunnelling microscopy and X-ray photoelectron spectroscopy as reaction products. The produced star-shaped tris-helicenes self-assemble on Au(111) spontaneously into large homochiral domains.

The first comparison of heterochiral crystals with their homochiral counterparts was given by Otto Wallach in an account on carvone bromide crystals in 1895 in Liebigs Annalen der Chemie. Although the well-known mineralogist Theodor Liebisch, professor in Göttingen from 1887 to 1908, performed the analyses and wrote the last four pages of that Annalen paper, his colleague from chemistry, Wallach served as sole author. We discuss whether Wallach or Liebisch had the idea of a comparative study of crystal densities of racemates and their homochiral analogues and who of the two should be credited.

Autocatalytic processes are important in many fields of science, including surface chemistry. A better understanding of its mechanisms may improve the current knowledge on heterogeneous catalysis. The thermally induced decomposition of eight different polycyclic aromatic hydrocarbons (PAHs) on a saturated monolayer of atomic oxygen on a Cu(100) surface is studied using temperature-programmed reaction spectroscopy (TPRS), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). 9-Bromo-heptahelicene decomposes autocatalytically in a narrow temperature range into CO 2 and H 2 O, while non-halogenated heptahelicene decomposes into the same products but does not show autocatalytic behavior. Fixation of the hydrocarbon to the surface via the organometallic bond after elimination of the bromine is identified as a prerequisite for the autocatalytic reaction mechanism. Of all the hydrocarbons studied, only those being sterically overcrowded decompose autocatalytically. Such an observation can be explained by facile dehydrogenation of the overcrowded PAHs. The reaction of such hydrogen with oxygen creates vacancies in the oxygen layer which act as active sites and catalyze further decomposition.

The interaction of low-energy photoelectrons with well-ordered monolayers of enantiopure helical heptahelicene molecules adsorbed on metal surfaces leads to a preferential transmission of one longitudinally polarized spin component, which is strongly coupled to the helical sense of the molecules. Heptahelicene, composed of only carbon and hydrogen atoms, exhibits only a single helical turn but shows excess in longitudinal spin polarization of about P Z = 6 to 8% after transmission of initially balanced left- and right-handed spin polarized electrons. Insight into the electronic structure, that is, the projected density of states, and the spin-dependent electron scattering in the helicene molecule is gained by using spin-resolved density functional theory calculations and a model Hamiltonian approach, respectively. Our results support the semiclassical picture of electronic transport along a helical pathway under the influence of spin-orbit coupling induced by the electrostatic molecular potential.

In a recent letter on the "Optical activity from racemates", discussed at the 16th International Conference on Chiroptical Spectroscopy in Rennes (June 2017), scientists claimed to have measured the circular dichroism of colored, racemic crystals of two transition metal complexes, observations that "serve to correct a clear deficit in our understanding of the optical properties of racemates." In fact, there is no deficit in our understanding of the optical properties of racemates. Moreover, the measurements presented are unconvincing as evidence of circular dichroism measured in anisotropic crystals and therefore do not inform our understanding of the specific crystals investigated, or racemates generally speaking., (© 2018 Wiley Periodicals, Inc.)

The adsorption of diastereoisomers of tartaric acid, namely, meso (R,S)-tartaric acid, (R,R)-tartaric acid, and the racemic mixture of (R,R) and (S,S) tartaric acid on the (111) surface of a copper single crystal has been studied by means of reflection-absorption IR Spectroscopy, X-ray photoelectron spectroscopy, low-energy electron diffraction, and thermal desorption spectroscopy. Two distinct adsorption modes are identified for all three adsorbate systems. All molecules undergo an identical thermally induced autocatalytic decomposition reaction above 510 K. The pure enantiomers show 2D chiral long-range ordered structures of opposite handedness., (© 2018 Wiley Periodicals, Inc.)

Modification of metal electrode surfaces with functional organic molecules is an important step toward organic electronics. The interaction of the buckybowl indenocorannulene with a Cu(111) surface and the two-dimensional self-assembly on the same surface was studied by means of scanning tunneling microscopy and dispersion-enabled density functional theory. Based on the conjecture of maximizing van der Waals interaction with the surface one would expect the indeno group to be aligned parallel to the surface. Theoretical investigations predict a nonparallel arrangement with the benzo ring of the indeno group located higher above the surface than the bowl rim connected to the indeno group. This adsorbate geometry is due to strong electronic interaction between molecule and surface, including substantial Pauli repulsion. The long-range ordered monolayer shows differences for two molecules of the unit cell in scanning tunneling microscopy contrast, suggesting either different polar alignments, and therefore a different tilt of the indeno group, or occupation of different adsorption sites.

Surface-adsorbed macrocycles exhibit a number of interesting physical and chemical properties; many of them are determined by their transition-metal centers. The hierarchical exchange of the central metal atom in such surface-adsorbed complexes is demonstrated, specifically in the porphyrin-like macrocycle pyrphyrin adsorbed on Cu(111). Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, we show that Cu as central metal atom is easily exchanged with Ni or Fe atoms supplied in trace amounts to the surface. Atom exchange of Ni centers with Fe atoms also occurs, with moderate yield. These results allow ranking the stability of the surface-adsorbed Cu, Ni, and Fe complexes. The fact that the atom exchange occurs at 423 K shows that surface-adsorbed macrocycles can be surprisingly easily transformed.

A 2D self-assembly of a C 32 H 12 buckybowl on the Cu(111) surface has been studied by means of scanning tunnelling microscopy. Additional aromatic rings at the rim of the corannulene core cause the bowl-shaped molecule to stand on its edge. This adsorption mode allows distinct π-π and C-Hπ interactions between the convex bowl surfaces as well as between the hydrogen-terminated rim and the convex bowl faces.