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Corrole molecules deposited from aqueous solution on Au(111) arrange flat forming mesa-like clusters (islands), as evidenced by in situ scanning tunneling microscopy (STM). A morphology quantitative assessment of the entire image is given by STM data analysis, evaluating the islands’ fractal dimension as a whole. To this end, two methods are employed: the first exploits the power law that binds the perimeter and the area of all the islands; the second is simply a value of an appropriate average of the fractal dimensions of the islands. In fact the two methods return very close results.

Two-dimensional (2D) magnets such as chromium trihalides CrX

Two-dimensional (2D) magnets such as chromium trihalides CrX3 (X = I, Br, Cl) represent a frontier for spintronics applications and, in particular, CrCl3 has attracted research interest due its relative stability under ambient conditions without rapid degradation, as opposed to CrI3. Herein, mechanically exfoliated CrCl3 flakes are characterized at the atomic scale and the electronic structures of pristine, oxidized, and defective monolayer CrCl3 phases are investigated employing density functional theory (DFT) calculations, scanning tunneling spectroscopy (STS), core level X-ray photoemission spectroscopy (XPS), and valence band XPS and ultraviolet photoemission spectroscopy (UPS). As revealed by atomically resolved transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis, the CrCl3 flakes show spontaneous surface oxidation upon air exposure with an extrinsic long-range ordered oxidized O–CrCl3 structure and amorphous chromium oxide formation on the edges of the flakes. XPS proves that CrCl3 is thermally stable up to 200 °C having intrinsically Cl vacancy-defects whose concentration is tunable via thermal annealing up to 400 °C. DFT calculations, supported by experimental valence band analysis, indicate that pure monolayer (ML) CrCl3 is an insulator with a band gap of 2.6 eV, while the electronic structures of oxidized and Cl defective phases of ML CrCl3, extrinsically emerging in exfoliated CrCl3 flakes, show in-gap spin-polarized states and relevant modifications of the electronic band structures.

In this work we shed light on the early stage of the chemical vapor deposition of graphene on Ge(001) surfaces. By a combined use of m-Raman and x-ray photoelectron spectroscopies, and scanning tunneling microscopy and spectroscopy, we were able to individuate a carbon precursor phase to graphene nucleation which coexists with small graphene domains. This precursor phase is made of C aggregates with different size, shape and local ordering which are not fully sp(2) hybridized. In some atomic size regions these aggregates show a linear arrangement of atoms as well as the first signature of the hexagonal structure of graphene. The carbon precursor phase evolves in graphene domains through an ordering process, associated to a re-arrangement of the Ge surface morphology. This surface structuring represents the embryo stage of the hills-and-valleys faceting featured by the Ge(001) surface for longer deposition times, when the graphene domains coalesce to form a single layer graphene film. (C) 2018 Elsevier Ltd. All rights reserved.

We systematically investigate the chemical vapor deposition growth of graphene on Ge(110) as a function of the deposition temperature close to the Ge melting point. By merging spectroscopic and morphological information, we find that the quality of graphene films depends critically on the growth temperature improving significantly by increasing this temperature in the 910–930 °C range. We correlate the abrupt improvement of the graphene quality to the formation of a quasi-liquid Ge surface occurring in the same temperature range, which determines increased atom diffusivity and sublimation rate. Being observed for diverse Ge orientations, this process is of general relevance for graphene synthesis on Ge.

By tuning the growth parameters, we show that it is possible to drive the CVD synthesis of graphene on Ge(110) towards the formation of either ultrathin armchair nanoribbons or of continuous graphene films. The ribbons are aligned along specific high-symmetry directions of the Ge(110) surface and have a width of ~5 nm. Moreover, by merging spectroscopic and morphological information, we find that the quality of graphene films depends critically on the growth temperature improving significantly in a narrow range close to the Ge melting point. The abruptness of the temperature behavior observed indicates that achieving high-quality graphene is intimately connected to the quasi-liquid Ge layer formed close to 930 °C on the substrate. Being observed for diverse Ge orientations, this process, known as incomplete melting, is shown to be of general relevance for graphene synthesis on Ge, and explains why similar growth conditions present in literature lead to graphene of very diverse quality on these substrates.

By combining scanning probe microscopy with Raman and x-ray photoelectron spectroscopies, we investigate the evolution of CVD-grown graphene/Ge(001) as a function of the deposition temperature in close proximity to the Ge melting point, highlighting an abrupt change of the graphene's quality, morphology, electronic properties and growth mode at 930 degrees. We attribute this discontinuity to the incomplete surface melting of the Ge substrate and show how incomplete melting explains a variety of diverse and long-debated peculiar features of the graphene/Ge(001), including the characteristic nanostructuring of the Ge substrate induced by graphene overgrowth. We find that the quasi-liquid Ge layer formed close to 930 degrees is fundamental to obtain high-quality graphene, while a temperature decrease of 10 degrees already results in a wrinkled and defective graphene film., in press

Using high-resolution scanning tunneling microscopy, we investigate the periodicity of mixed arrays of single and triple steps and the atomic structure of triple steps on three vicinal Si(111) samples with off-angles 1.5 ∘ ≤ θ ≤ 9.45 ∘ towards the [ 1 ¯ 1 ¯ 2 ] direction. The comparison between the (556) and (557) triple-step structure demonstrates that only the number of 7x7 terraces is affected by miscut. At variance with the singular Si(111) case, Ge epitaxy is strongly correlated to step morphology, resulting, at the critical coverage and small misorientation, in the nucleation of holed nanoislands from step-edge protrusions. During step-flow growth, stress-driven bunching of atomic steps (ripples) is observed on the (557) surface, indicating that this mechanism of stress relief of Si(001) vicinal surfaces works also on Si(111) surfaces.

International audience; In Accumulated Low Schottky Barrier metal oxide semiconductor field effect transistors (MOSFET) on SOl structures, very thin silicide layers are used for ohmic contacts. Silicide contacts form due to metallurgical reaction of metal with semiconductor. In order to get a broad vision of the most interesting metal/silicide solution several material stacks were evaluated including platinum and iridium. In this work cross-sectional transmission electron microscopy was used to study the process of silicide formation in metal/Si and metal/SiGe/Si structures. Novel structure architectures have been developed. They are mainly based on the use of a very thin film SOl substrate with typical active silicon layer thicknesses ranging between 2 and 20 nm for 10-40 nm gate length MOSFETs. In Accumulation LowSchottky Barrier -SOI MOSFET structures very thin silicides are used for ohmic contacts. Silicide contacts form due to metallurgical reaction of metal with semiconductor.

An extended formation of faceted pit-like defects on Ge(001) and Ge(111) wafers was obtained by thermal cycles to T> 750 {\deg}C. This temperature range is relevant in many surface-preparation recipes of the Ge surface. The density of the defects depends on the temperature reached, the number of annealing cycles performed and correlates to the surface-energy stability of the specific crystal orientation. We propose that the pits were formed by preferential desorption from the strained regions around dislocation pile-ups. Indeed, the morphology of the pits was the same as that observed for preferential chemical etching of dislocations while the spatial distribution of the pits was clearly non-Poissonian in line with mutual interactions between the core dislocations., Comment: European Union (EU), Horizon 2020, Far-Infrared Lasers Assembled using Silicon Heterostructures,FLASH,Grant number: 766719

Corrole derivatives have been recently employed in many applications at the solid-liquid interface. Therefore, the structural arrangement of the molecular layers in direct contact with the liquid is of fundamental interest. We investigated in solution the deposition of molecular layers of the previously prepared water-soluble phosphorus complex of a 2-sulfonato-10-(4-sulfonatophenyl)-5,15-dimesitylcorrole [see synthesis in our previous paper, M. Naitana et al., Chem. Eur. J. 2017, 23, 905-916]. The layer formation of P corroles onto the Au(111) surface was monitored by STM in situ, that is, with the substrate immersed in the solution. Marked differences in the morphology between the organic layer formed on the substrate and that deposited after solvent evaporation (drop casting) are reported. In particular, the coating of gold was more effective and stable in the presence of liquid. Preservation of functionality of the corrole molecules after adsorption was verified. This result validates the relevance of corrole layers at the solid-liquid interface to exploit the peculiar properties of these molecules in real-world applications.

We present a joint experimental and theoretical study of the electronic properties of the rebonded-step reconstructed Ge/Si(1 0 5) surface which is the main strained face found on Ge/Si(0 0 1) quantum dots and is considered a prototypical model system for surface strain relaxation in heteroepitaxial growth. Using a vicinal surface as a model system for obtaining a stable single-domain film structure with large terraces and rebonded-step surface termination, we realized an extended and ordered Ge/Si planar hetero-junction suitable for direct study with angle-resolved photoemission spectroscopy. At the coverage of four Ge monolayers photoemission spectroscopy reveals the presence of 2D surface and film bands displaying energy-momentum dispersion compatible with the 5 × 4 periodicity of the system. The good agreement between experiment and first-principles electronic structure calculations confirms the validity of the rebonded-step structural model. The direct observation of surface features within 1 eV below the valence band maximum corroborates previously reported analysis of the electronic and optical behavior of the Ge/Si hetero-interface.

Graphene, the wonder material of the 21st century, has not yet achieved the expected outcomes in terms of applications in nanoelectronics. This is not surprising, as large-scale graphene growth is still mostly limited to CVD on metallic foils, followed by graphene transfer to the semiconductor substrate required for electronic devices, which is cumbersome and difficult to automatize. Moreover, graphene is gapless, and this is still seriously limiting its applications. This book is an attempt to dispel this pessimistic outlook, summarizing the latest achievements in the direct growth of graphene on semiconductors.SiC is the ideal semiconductor for graphene growth, which is typically achieved by thermal graphitization. Through high-temperature annealing in a controlled environment, it is possible to decompose the topmost SiC layers, obtaining quasi-ideal graphene by Si sublimation. Graphene on SiC with record electronic mobilities has been demonstrated, opening the way for applications in nanoelectronics, by exploiting selective growth on patterned structures and gap opening by quantum confinement. The book opens with a chapter on the significance and challenges of graphene growth on semiconductors, by Mishra et al., drawing a picture of the perspectives of this technology.The three following chapters, by Aristov et al., Gupta et al., and Tomellini et al., respectively, are dedicated to an up-to-date analysis of the synthesis of graphene on SiC in ultrahigh vacuum. The fifth chapter, by Forti, Starke, and Coletti, is a review of the effect of atomic intercalation at the SiC–graphene interface, with an in-depth discussion of the doping effects and of the electronic properties of lateral superlattices. The sixth chapter, written by the de Heer and Berger group, reporting graphene growth on SiC by sublimation, summarizes the whole history of graphene growth on SiC by confined controlled sublimation, up to the latest developments in the growth of templated graphene nanostructures. We hope that this book can be of inspiration to the many scientists striving to improve the growth of graphene on semiconductors and to the young researchers from industry and academia approaching this fascinating world. The developments sketched here show a promising outlook for the future, with many exciting outcomes on the horizon, from the artificial opening of a gap to the creation of 2D field-effect transistors with nanodimensions.

One of the problems that graphene is facing in electronic applications is its quality, which is still far from the level required to obtain an industrial scale production of reliable nanoscale devices, and it is ultimately related to the growth method. Understanding the kinetics of the graphene growth is an outstanding problem in physics, whose solution is the key to achieve full control on the graphene properties . This chapter deals with the microscopic phenomena occurring during epitaxial graphene growth on SiC by high temperature annealing. We discuss recent experimental and theoretical findings on the Si diffusion in the SiC matrix and on the kinetics of graphene growth as a function of temperature and of time. The theoretical framework developed in this chapter will help to understand the physical basis of the graphene formation, which is essential for a perfect control of the graphene quality, helping to define the optimal conditions for the growth of a continuous monolayer or bilayer graphene on SiC.

The synthesis, spectroscopic, and optical properties of the water-soluble phosphorus complex of a 2-sulfonato-10-(4-sulfonatophenyl)-5,15-dimesitylcorrole have been investigated. The compound was prepared by adopting a novel strategy for the corrole sulfonation, leading to the regioselective isomer in an almost quantitative yield. The phosphorus coordination has a key role in determining the corrole substitution pattern, limiting the formation of poly-substituted species, which affected the reaction of the corrole free base. The resulting complex shows excellent optical properties in terms of emission quantum yield, also in polar protic solvents, including water. 31P NMR spectroscopy in CD3OD indicates that the P sulfonate complex has been isolated in a hexacoordinated geometry with two different ligands (L1=-OH, L2=-OCH3), and it is prone to axial ligand exchange with methanol, with no evidence of intermediate pentacoordinated species. The morphological characterization of thin layers of the P corrole deposited onto an Au(111) surface showed that the addition of an intermediate layer of reduced graphene oxide allows for a better control of corrole aggregation, inducing also transformation of the Au(111) reconstructed surface. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

We have applied reflectance anisotropy spectroscopy (RAS) to investigate the rebonded-step (RS) reconstructed strained Ge/Si(105) surface. RAS spectra display a marked peak at 2.1 eV that is completely cancelled after exposure to about 1200 L of molecular oxygen. Ab initio calculations of the RAS signal explain the experimental spectra in terms of optical transitions between filled bulk-like states and empty surface bands. The early stages of exposure of the clean surface to molecular oxygen have been monitored by RAS and scanning tunneling microscopy (STM), correlating the evolution of the optical anisotropy to the bonding configuration of the adsorbed gas. Oxygen atoms are proposed to first adsorb onto the arms and later on the head dimers of the “horseshoe” motifs that comprise the RS reconstruction, thus gradually destroying the local order.

International audience; We fabricated flat, two-dimensional germanium sheets showing a honeycomb lattice that matches that of germanene by depositing submonolayers of Ge on graphite at room temperature and subsequent annealing to 350 degrees C. Scanning tunneling microscopy shows that the germanene islands have a small buckling with no atomic reconstruction and does not give any hints for alloy formation and hybridization with the substrate. Our density functional theory calculations of the structural properties agree well with our experimental findings and indicate that the germanene sheet interacts only weakly with the substrate underneath. Our band structure calculations confirm that the Dirac cone of free-standing germanene is preserved for layers supported on graphite. The germanene islands show a small but characteristic charge transfer with the graphite substrate which is predicted by our ab initio simulations in excellent agreement with scanning tunneling spectroscopy measurements.

© 2015 Elsevier Ltd. All rights reserved. We followed by X-ray Photoelectron Spectroscopy (XPS) the time evolution of graphene layers obtained by annealing 3C SiC(111)/Si(111) crystals at different temperatures. The intensity of the carbon signal provides a quantification of the graphene thickness as a function of the annealing time, which follows a power law with exponent 0.5. We show that a kinetic model, based on a bottom-up growth mechanism, provides a full explanation to the evolution of the graphene thickness as a function of time, allowing to calculate the effective activation energy of the process and the energy barriers, in excellent agreement with previous theoretical results. Our study provides a complete and exhaustive picture of Si diffusion into the SiC matrix, establishing the conditions for a perfect control of the graphene growth by Si sublimation.

A few layers of functionalized graphene (FLG) have been obtained by the oxidative unzipping reaction of single-walled carbon nanotubes. A detailed Scanning Tunneling Microscopy and Transmission Electron Microscopy study shows that several different morphologies are observed, depending on the substrate upon which they are deposited, thus providing useful hints for a real world application of these carbon nanostructures. In addition, a combined Scanning Tunneling Spectroscopy investigation has shown that the electronic properties of these FLG are affected by their functionalization degree, opening interesting perspectives for their use in sensor and biosensor devices. © Taylor & Francis Group, LLC.

Spatial organization of Ge islands, grown by physical vapor deposition, on prepatterned Si(001) substrates has been investigated. The substrates were patterned prior to Ge deposition by nanoindentation. Characterization of Ge dots is performed by atomic force microscopy and scanning electron microscopy. The nanoindents act as trapping sites, allowing ripening of Ge islands at those locations during subsequent deposition and diffusion of Ge on the surface. The results show that island ordering is intrinsically linked to the nucleation and growth at indented sites and it strongly depends on pattern parameters. © 2011 Elsevier B.V.

Controlled synthesis of carbon nanotubes (CNTs) is highly desirable for nanoelectronic applications. To date, metallic catalyst particles have been deemed unavoidable for the nucleation and growth of any kind of CNTs. Ordered arrays of nanotubes have been obtained by controlled deposition of the metallic catalyst particles. However, the presence of metal species mixed with the CNTs represents a shortcoming for most electronic applications, as metal particles are incompatible with silicon semiconductor technology. In the present paper we report on a metal-catalyst-free synthesis of CNTs, obtained through Ge nanoparticles on a Si(001) surface patterned by nanoindentation. By using acetylene as the carbon feed gas in a low-pressure Chemical Vapor Deposition (CVD) system, multi-walled carbon nanotubes (MWNT) have been observed to arise from the smallest Ge islands. The CNTs and the Ge three-dimensional structures have been analysed by SEM, EDX and AFM in order to assess their elemental features and properties. EDX and SEM results allow confirmation of the absence of any metallic contamination on the surface, indicating that the origin of the CNT growth is due to the Ge nanocrystals.

The photocurrent generation of nanometric Ge droplets has been investigated by using electrochemical measurements. Dots have been grown by annealing Ge layers of different nominal thicknesses (ranging from 0.5 to 5 nm) deposited on clean SiO2 surface at room temperature. The photocurrent signals for the largest dots show features, which can be ascribed to the Ge nanocrystals direct electronic transitions. Only in the case of 0.5 nm Ge film a broad and intense feature at 2.4 eV has been observed while the peaks at higher energy result to be dramatically reduced. Since this last sample is characterized by (5±1) nm nanodots size (the smallest among the measured samples) the appearance of this broad band in the photocurrent active spectrum can be ascribed to quantum confinement effect.

The aim of this work is to understand the surface interactions of Reduced Graphene Oxide (RGO) with a water soluble corrole using graphene as a versatile substrate for sensor devices. Scanning Tunneling Microscopy (STM) and UV-Vis Spectroscopy are employed for understanding the morphology and microstructure of the deposited corrole molecules on RGO at atomic level. Other surface characterization technique like X-Ray Photoelectron Spectroscopy (XPS) is also used for better understanding of the chemical distribution, the molecular environment and the hybridization of the corrole molecules on RGO.

Starting with the basic definition, a short description of a few relevant physical quantities playing a role in the growth process of heteroepitaxial strained systems, is provided. As such, the paper is not meant to be a comprehensive survey but to present a connection between the Stranski-Krastanov mechanism of nanostructure formation and the basic principles of nucleation and growth. The elastic field is described in the context of continuum elasticity theory, using either analytical models or numerical simulations. The results are compared with selected experimental results obtained on GeSi nanostructures. In particular, by tuning the value of quantities such as vicinality, substrate orientation and symmetry of the diffusion field, we elucidate how anisotropic elastic interactions determine shape, size, lateral distribution and composition of quantum dots.

Here, we present a reliable process to deposit transparent conductive films on silicon oxide, quartz, and sapphire using a solid carbon source. This layer consists of partially ordered graphene flakes with a lateral dimension of about 5 nm. The process does not require any catalytic metal and exploits a high current arc evaporation (Φ-HCA) to homogeneously deposit a layer of carbon on heated substrates. A gas atmosphere consisting of Argon or Argon/Hydrogen blend acting as a buffer influences the morphology of the growing film. scanning tunneling microscopy, transmission electron microscopy, and Raman spectra were used for a thorough characterization of the samples in order to optimize the growth parameters. The best carbon layers have a surface resistance of 5.7 × 103 Ω◻ whereas the optical transparency of the coatings is 88% with an excellent homogeneity over areas of several cm2. Such results are compatible with most semiconductor fabrication processes and make this method very promising for various industrial applications.

We first investigate the spontaneous formation of nanometric and highly dense (∼3×10 12 cm −2 ) Ge droplets on SiO 2 /Si(0 0 1) by scanning tunnelling microscopy and spectroscopy. Ge dots are grown using a two-step process: first, Ge deposition on the clean SiO 2 surface at room temperature (RT) and second, thermal annealing at 500 °C. Ge dots appear free of germanium oxides. Then we show the ordering of Ge nanocrystals (NCs) on SiO 2 /Si(0 0 1) substrates patterned by focused ion beam (FIB). Lateral ordering of the ultra-dense Ge nanodots was achieved by the combination of the following technological steps: (a) use of a FIB to create ordered two-dimensional (2D) arrays of regular holes on a field oxide on the silicon substrate, (b) chemical cleaning and restoring of the Si surface in the holes, (c) further oxidation to transfer the pattern from the field oxide to the silicon substrate, (d) removal of the field oxide and thermal re-oxidation of the sample in order to create a tunnelling oxide of homogeneous thickness on the patterned silicon surface and (e) self-assembly of the 2D arrays of Ge dots on the patterned tunnelling oxide. We show that Ge NCs are ordered in the FIB holes whatever is their dimension/density.

During the past few decades, the field of nanoscience and nanotechnology has undergone a revolution that parallels the extraordinary advances in surface science instruments and techniques. The nano-era is posited as having begun in the early 1980s with the invention of scanning probe microscopy which allowed one to monitor, measure, and manipulate matter at the nanoscale level. Dramatic new insights have come from the application of this and other new experimental tools. The ability to precisely control atoms and build molecules at extremely small length scales is leading to unprecedented breakthroughs in electronics [1, 2], photonics [3, 4], medicine [5], and energy production [6]. In particular, the formation of periodically ordered structures offers the possibility of direct fabrication of semiconductor quantum nanostructures in which a narrow gap material is embedded into a matrix of a wide-gap material providing a confined potential for carriers. Periodic structures of such inclusions create a superlattice comprising quantum wells, quantum wires, and quantum dots (QDs). QDs, the ultimate limit of low-dimensional structures, have become a fascinating subject both for the basic research and for device application. The most powerful and common method to obtain high-quality QDs consists in exploiting the Stranski–Krastanov (SK) growth mode during strained heteroepitaxial growth, in which QDs spontaneously form on top of a thin wetting layer (WL). A prototype system for studying the fascinating and complex phenomena related to the strain-driven heteroepitaxy and for investigating the properties of QDs’ spontaneous formation is Ge/Si. As a model system, Ge on vicinal Si(001) makes it possible to investigate strain relaxation, growth instabilities, and three-dimensional (3D) island formation and self-organization. Moreover, by changing the substrate miscut, it is possible to tune both the energetic and the kinetic factors governing the growth of single nanostructures [7]. There is a huge literature on the SK growth of Ge on Si surfaces and many excellent monographs and review papers surveying the different aspects of the subject have been written [7–11]. Most of them are aimed at researchers with some

Nanostructured substrates are an interesting path towards the production of quantum dots devoted to microelectronic applications. In this work we report results on the effects of different nanopatterning methods to obtain lateral ordering of Ge islands grown on Si. By using Scanning Tunneling Microscopy we have studied in real-time the wetting layer growth and islands formation on nanopatterned Si substrates at 500 °C. We compare results obtained on Si substrates nanopatterned by using two different techniques: STM lithography and natural patterning induced by surface instabilities such as step bunching. Different issues on both cases have been addressed: substrate preparation, Ge dots placement and growth mode. We have observed that, on Si(001), the Ge islands nucleate near the holes and on Si(111) step bunching can guide the growth of aligned rows of islands.

The first stages of acetylene reaction with the Si(1 1 1)7 × 7 reconstructed surface kept at 600 °C are studied by recording scanning tunneling microscopy (STM) images during substrate exposure at a C2H2 pressure of 2 × 10−4 Pa (2 × 10−2 mbar). We observed the progressive substitution of the 7 × 7 reconstruction with a carbon induced Si(1 1 1)√3×√3R30° reconstruction characterized by an atomic distance of 0.75 ± 0.02 nm, very close to that of the silicon 7 × 7 adatoms. This means that a carbon enrichment of the silicon outermost layers occurs giving rise to the formation of a Si–C phase different from the √3×√3R30° reconstruction typical of Si terminated hexagonal SiC(0 0 0 1) surface with an atomic distance of 0.53 nm. To explain STM images, we propose a reconstruction model which involves carbon atoms in T4 and/or S5 sites, as occurring for B doped Si(1 1 1) surface. Step edges and areas around the silicon surface defects are the first regions involved in the reaction process, which spreads from the upper part of the step edges throughout the terraces. Step edges therefore, progressively flakes and this mechanism leads, for the highest exposures, to the formation of large inlets which makes completely irregular the straight edge typical of the Si(1 1 1)7 × 7 terraces. These observations indicate that there occurs an atomic diffusion like that driving the meandering effect. Finally, the formation of a few crystallites is shown also at the lowest acetylene exposures. This is the first STM experiment showing the possibility to have carbon incorporation in a Si(1 1 1) matrix for higher amounts than expected, at least up to 1/6 of silicon atomic layer.

The growth mode of sapphyrin deposited on a gold substrate by the Langmuir-Blodgett technique has been studied by scanning tunneling microscopy. The results suggest that the efficiency of the LB deposition is low during the first dippings and it increases after the completion of the first monolayer. The tilt angle formed by the molecules with the substrate has been evaluated as a function of coverage. Scanning tunneling spectroscopy characterization suggests an electronic interaction with the substrate which is important for potential applications.

Quartz crystal microbalances (QMB) have been coated by thin films of different metal complexes of protoporphyrin IX dimethyl ester (M-PPIX), deposited by electropolymerization technique. The structure of these films has been characterized by scanning tunnelling microscopy (STM). The sensory behaviour of the obtained QMB have been studied in the presence of four volatile organic compounds (VOC).

We compare, by high-resolution electron-energy-loss spectroscopy (HREELS), the electronic structure of the GaAs(110)1x1 surface and that of the GaAs(001)2x4 As-rich surface in the energy-loss region 0.5-5 eV. The HREEL spectra are interpreted in terms of realistic calculations. The spectral features above the gap are assigned to electronic transitions involving surface and/or bulk states. Losses at energies within the gap are associated to defect states at the surface. [S0163-1829(98)51236-2].

We have followed by scanning tunneling microscopy (STM) the growth of thin Ge films obtained by reactive deposition epitaxy on Si(111) substrates kept at 500°C. For a Ge coverage less than 0.45 ML, STM images show large 7×7 flat areas without any protrusion. For increasing coverage, flat, triangular 5×5 islands start nucleating while the Si substrate retains the 7×7 reconstruction. The islands' evolution, up to the completion of the wetting layer, is described in the framework of a statistical model of growth. At 3 ML, the composition and ordering of the wetting layer are investigated by Current Imaging Tunneling Spectroscopy (CITS) measurements, revealing small differences in the atomic corrugations. The analysis of topographic and current images supports an elemental composition for the topmost layer. At coverages larger than 3 ML, thick Ge islands nucleate according to the Stranski–Krastanov mechanism of growth. We analyze the evolution of the lattice strain up to 15 ML coverage. A clear expansion of the lattice parameter as a function of coverage is found both on the islands' top and on the wetting layer.

We show that SiGe islands are transformed into nanoholes and rings solely by annealing treatments and without Si capping. Rings are produced by a rapid flash heating at temperatures higher than the melting point of Ge, whereas nanoholes are produced by several minutes of annealing. The rings are markedly rich in Si with respect to the pristine islands, suggesting that the evolution path from islands to rings is driven by the selective dissolution of Ge occurring at high temperatures. © 2013 Elsevier B.V. All rights reserved.

Common features of Ge growth on vicinal Si(001) and Si(111) surfaces are discussed. We show that surface vicinality has a twofold effect on three-dimensional islanding in this system. As long as the atomic structure of the singular surface is preserved, epitaxial islands undergo a morphological change which is dictated by the misorientation from the singular surface. When also the surface reconstruction is so affected by miscut that surface and interfacial energies are drastically modified, the islanding pathway diverges from that occurring on flat surfaces. © 2013 Elsevier B.V.

Educazione, innovazione, conoscenza, creatività, ricerca scientifica e didattica. Ecco alcuni dei pilastri culturali che sostengono il progetto degli Stage a Tor Vergata, destinato a studentesse e studenti del IV e V anno della scuola secondaria di secondo grado. Trenta studenti, meritevoli ma soprattutto motivati, vengono inseriti per cinque giorni e in due distinte fasi formative, in tre gruppi di ricerca, del Dipartimento di Fisica dell'Università di Roma Tor Vergata, attivi in settori d'avanguardia della scienza dei materiali e dei materiali innovativi per l'astrofisica sperimentale. Per cinque giorni "vivono" nei laboratori di ricerca, esplorano e apprendono le più recenti novità e tecnologie nella ricerca di materiali innovativi per lo sviluppo dell'ICT (Information and Communication Technology), della conversione fotovoltaica e dell'astrofisica dello spazio. Lavorano in piccoli gruppi, guidati da docenti universitari, identificano gli obiettivi a cui giungere, si distribuiscono incarichi e responsabilità, si confrontano, organizzano, gestiscono e presentano le fasi della ricerca tenendo in considerazione la teoria di riferimento.

Ge/Si alloys were prepared in UHV by solid phase epitaxy on Si(111) substrates. The alloy formation, as a function of the evaporation rate and the Ge layer thickness has been followed in situ by RHEED and scanning tunneling microscopy. The 5 × 5 surface reconstruction appeared after annealing at 450°C Ge layers (up to 10 A thick), obtained from a low rate Knudsen cell evaporator. In this case a nearly flat and uniform layer of reconstructed alloy was observed. When using an e-gun high rate evaporator we needed to anneal the Ge layer up to 780°C to obtain a 5 × 5 reconstruction. The grown layer was not flat, with many steps and Ge clusters; at high coverages (10 A and more) large Ge islands appeared. Moreover, we then succeeded in visualizing at atomic resolution the top of some of these Ge islands which displayed a 2 × 1 reconstruction, probably induced from the high compressive strain due to the lattice mismatch with the substrate. We suggest that this unusual behavior could be connected to the high evaporation rate, which helped the direct formation of Ge microcrystals on the Si substrate during the deposition process.

X-ray photoemission electron microscopy (XPEEM) is used to investigate the chemical composition of Ge/Si individual islands obtained by depositing Ge on Si(111) substrates in the temperature range 460–560 °C. We are able to correlate specific island shapes with a definite chemical contrast in XPEEM images, at each given temperature. In particular, strained triangular islands exhibit a Si surface content of 5%–20%, whereas it grows up to 30%–40% for “atoll-like” structures. The island’s stage of evolution is shown to be correlated with its surface composition. Finally, by plotting intensity contour maps, we find that island centers are rich in Si.

The growth mode of metal phthalocyanines (MPc, MNi, Cu) on clean Cu(001) and Si(001) (i.e. bonding and adsorption geometry) and their electronic structure are studied by a combination of spectroscopic techniques: x-ray photoemission, x-ray absorption at Metal L 2,3 edges and scanning tunnelling microscopy.

By using step-bunched Si(111) surfaces as templates, we demonstrate the self-assembly of an ordered distribution of Ge islands without lithographic patterning. Initially, islands nucleate and evolve at step edges, up to complete ripening, forming long ribbons. Subsequently, island nucleation takes place at the center of flat terraces. Ge islands appear to be regularly spaced in scanning tunneling microscope images. The exploitation of this effect provides a possible route to grow ordered arrays of semiconducting nanostructures.

By exploiting the misfit strain of Ge on Si epitaxy, we examine the significant changes induced by surface stress in the polar structural phase diagram of Si(001) surfaces. Under compressive strain, the atomic and mesoscale structures of the vicinal Si(001) surfaces are converted into a new singular (105) face which does not exist on the strain-free equilibrium shape of Si and Ge. The observed structural modifications of substrates have far-reaching implications for the Stranski-Krastanov evolutionary path of three-dimensional islanding. © 2012 American Physical Society.

The strain-induced self-assembly of suitable semiconductor pairs is an attractive natural route to nanofabrication. To bring to fruition their full potential for actual applications, individual nanostructures need to be combined into ordered patterns in which the location of each single unit is coupled with others and the surrounding environment. Within the Ge/Si model system, we analyze a number of examples of bottom-up strategies in which the shape, positioning, and actual growth mode of epitaxial nanostructures are tailored by manipulating the intrinsic physical processes of heteroepitaxy. The possibility of controlling elastic interactions and, hence, the configuration of self-assembled quantum dots by modulating surface orientation with the miscut angle is discussed. We focus on the use of atomic steps and step bunching as natural templates for nanodot clustering. Then, we consider several different patterning techniques which allow to harness the natural self-organization dynamics of the system, such as: scanning tunneling nanolithography, focused ion beam and nanoindentation patterning. By analyzing the evolution of the dot assembly by scanning probe microscopy, we follow the pathway which leads to lateral ordering, discussing the thermodynamic and kinetic effects involved in selective nucleation on patterned substrates.

Silicon surfaces with different reconstruction, Si(111)-7 × 7 and Si(001)-2 × 1, are exposed to a molecular beam of copper phthalocyanine. On Si(111) the adsorbate-substrate interaction is strong, as suggested by a partial reduction of copper shown in the XPS spectra and by the evidence provided by STM of a chemical reaction involving some of the Si adatoms. As a consequence, the molecules are not imaged at atomic scale by STM. At variance with this behaviour, on the single-domain Si(001)-2 × 1 face, the adsorbed molecules are clearly imaged by STM, suggesting an adsorption state more weakly bonded. This is the first observation of Cu phthalocyanine molecules imaged on a silicon surface, and it further illustrates the potential of STM for surface chemistry.

A morphological model of the Volmer-Weber type is developed for the reactive interface formed between Fe and a ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ single-crystal surface which takes into account microscopic aspects of the growth such as clustering, metal oxidation via the superconductor substrate, and diffusion through the cluster of elemental species released in the metal-surface redox reaction. The experimental findings of a local chemical analysis by core emission spectroscopy and an atomic-scale structural characterization by scanning tunneling microscopy are in good quantitative agreement with the proposed model indicating that the basic microscopic assumptions are correct.

Semiconductor epitaxial nanostructures have been recently proposed as the key building blocks of many innovative applications in materials science and technology. To bring their tremendous potential to fruition, a fine control of nanostructure size and placement is necessary. We present a detailed investigation of the self-ordering process in the prototype case of Ge/Si heteroepitaxy. Starting from a bottom-up strategy (step-bunching instabilities), our analysis moves to lithographic techniques (scanning tunneling lithography, nanomechanical stamping, focused ion beam patterning) with the aim of developing a hybrid approach in which the exogenous intervention is specifically designed to suit and harness the natural self-organization dynamics of the system. Copyright © 2011 American Scientific Publishers All rights reserved.

We present a novel approach to engineer the growth of strained epitaxial films based on tailoring the elastic-interaction potential between nanostructures with substrate vicinality. By modeling the island-island interaction energy surface within continuum elasticity theory, we find that its fourfold symmetry is broken at high miscuts, producing directions of reduced elastic-interaction energy. As a consequence, it is possible to direct the Ge island growth on highly misoriented Si(001) substrates towards desired pathways. © 2011 American Physical Society.

The pair interaction between Ge islands on vicinal Si(001) substrates is investigated by scanning tunneling microscopy measurements as a function of the miscut angle. By the analysis of the nearest-neighbor island distributions, we assess the dependence of the local strain field on the substrate misorientation. We support our results by modeling elastic relaxation for different shapes and arrangements of islands with finite element calculations. © 2010 The American Physical Society.