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Developing smart, environmentally friendly, and effective antibacterial surfaces is fundamental to contrast the diffusion of human infections and diseases for applications in the biomedical and food packaging sectors. To this purpose, here we combine aluminum-doped zinc oxide (AZO) and Ag to grow nanostructured composite coatings on bioplastic polylactide (PLA) substrates. The AZO layers are grown by RF magnetron sputtering, and then functionalized with Ag in atomic form by RF magnetron sputtering and in form of nanoparticles by supersonic cluster beam deposition. We compare the morphology, wettability, and antimicrobial performance of the nanostructured coatings obtained by the two methods. The different growth modes in the two techniques used for Ag functionalization are found to produce some differences in the surface morphology, which, however, do not induce significant differences in the wettability and antimicrobial response of the coatings. The antibacterial activity is investigated against Escherichia coli and Staphylococcus aureus as representatives of Gram-negative and Gram-positive bacteria, respectively. A preferential antimicrobial action of Ag on the first species and of AZO on the second one is evidenced. Through their combination, we obtain a hybrid composite coating taking advantage of the synergistic dual action of the two materials deposited, with a total bacterial suppression within few minutes for the first species and few hours for the second one, thus representing a valuable solution as a wide-spectrum bactericidal device.

Antimicrobial coatings are a promising strategy to counteract the spreading of multidrug resistant pathogens through cross-contamination of surfaces. Coatings with nanostructured characteristics can exploit the different antimicrobial mechanisms of nanomaterials if the synthesis methods are able to tune the composition, morphology, and mechanical properties of the film. This chapter addresses the synthesis of antibacterial nanostructured coatings with a focus on physical synthesis methods. After a short description of the bacteria-NP interaction mechanism leading to killing of the cells, few examples of coatings obtained by magnetron sputtering and supersonic cluster beam deposition are discussed, with an emphasis on the possibility of combining different elements into the coating to widen the bactericidal spectrum.

Nanocomposite systems and nanoparticle (NP) films are crucial for many applications and research fields. The structure-properties correlation raises complex questions due to the collective structure of these systems, often granular and porous, a crucial factor impacting their effectiveness and performance. In this framework, we investigate the optical and morphological properties of Ag nanoparticles (NPs) films and of Ag NPs/TiO2porous matrix films, one-step grown by supersonic cluster beam deposition. Morphology and structure of the Ag NPs film and of the Ag/TiO2(Ag/Ti 50-50) nanocomposite are related to the optical properties of the film employing spectroscopic ellipsometry (SE). We employ a simple Bruggeman effective medium approximation model, corrected by finite size effects of the nano-objects in the film structure to gather information on the structure and morphology of the nanocomposites, in particular porosity and average NPs size for the Ag/TiO2NP film. Our results suggest that SE is a simple, quick and effective method to measure porosity of nanoscale films and systems, where standard methods for measuring pore sizes might not be applicable.

Ultrathin metal nanoparticles coatings, synthesized by gas-phase deposition, are emerging as go-to materials in a variety of fields ranging from pathogens control and sensing to energy storage. Predicting their morphology and mechanical properties beyond a trial-and-error approach is a crucial issue limiting their exploitation in real-life applications. The morphology and mechanical properties of Ag nanoparticle ultrathin films, synthesized by supersonic cluster beam deposition, are here assessed adopting a bottom-up, multitechnique approach. A virtual film model is proposed merging high resolution scanning transmission electron microscopy, supersonic cluster beam dynamics, and molecular dynamics simulations. The model is validated against mechanical nanometrology measurements and is readily extendable to metals other than Ag. The virtual film is shown to be a flexible and reliable predictive tool to access morphology-dependent properties such as mesoscale gas-dynamics and elasticity of ultrathin films synthesized by gas-phase deposition.

In the synthesis of nanostructures by pulsed laser deposition (PLD), a crucial role is played by the environmental deposition pressure and the substrate temperature. Due to the high temperature of nanoparticles (NPs) at landing, other factors may determine the structure of the resulting aggregates. Here, Au and TiO2nanostructures are obtained by non-thermal fs-PLD in ambient conditions. On Si(100), only TiO2 NPs form fractals with areas up to ~ 1 x10^6 nm^2, while on quartz Au NPs also form fractals with areas up to ~ 5 x10^3 nm^2, a much smaller size with respect to the TiO2 case. The aggregation is described by a simple diffusive model, taking into account isotropic diffusion of the NPs, allowing quantitative simulations of the NPs and fractal area. The results highlight the key role of substrate thermal conductivity in determining the formation of fractals. [Figure not available: see fulltext.].

Ultrathin coatings based on bi-elemental nanoparticles (NPs) are very promising to limit the surface-related spread of bacterial pathogens, particularly in nosocomial environments. However, tailoring the synthesis, composition, adhesion to substrate, and antimicrobial spectrum of the coating is an open challenge. Herein, we report on a radically new nanostructured coating, obtained by a one-step gas-phase deposition technique, and composed of bi-elemental Janus type Ag/Ti NPs. The NPs are characterized by a cluster-in-cluster mixing phase with metallic Ag nano-crystals embedded in amorphous TiO2 and present a promising antimicrobial activity including also multidrug resistant strains. We demonstrate the flexibility of the method to tune the embedded Ag nano-crystals dimension, the total relative composition of the coating, and the substrate type, opening the possibility of tailoring the dimension, composition, antimicrobial spectrum, and other physical/chemical properties of such multi-elemental systems. This work is expected to significantly spread the range of applications of NPs coatings, not only as an effective tool in the prevention of healthcare-associated infections but also in other technologically relevant fields like sensors or nano-/micro joining.

The specific mechanisms which lead tothe formation of fractal nanostructuresbypulsed laser deposition remain elusive despite intense research efforts, motivated mainly by the technological interest in obtaining tailored nanostructures with simple and scalable production methods. Here we focus on fractal nanostructures of titanium dioxide, TiO2, a strategic material for many applications, obtainedby femtosecond laser ablation atambient conditions.We compare a theoretical model of fractal formation with experimental data. The comparison of theory and experiment confirms that fractal aggregates are formed after landing of the ablated material on the substrate surface by a simple diffusive mechanism. Wemodel the fractal formation through extensive Monte Carlo simulations based ona set of minimal assumptions: TiO2 nanoparticles arrive already formed onthe substrate, then they diffuseinasize/mass independent way and stick irreversibly upon touching, thus forming fractal clusters. Despite its simplicity, our model explains the main features of the fractal structures arising from the complex interaction of large TiO2 nanoparticles with different substrates. Indeed our model is able to reproduce both the fractal dimensions and the area distributions of the nanostructures for different densities of the ablated material. Finally we discuss the role of the thermal conductivity of the substrate and the laser fluence on the properties of the fractal nanostructures. Our results represent an advancement towards controlling the production of fractal nanostructures by pulsed laser deposition.

The synthesis of hybrid metallic-dielectric substrates as reliable SERS platforms relies on core-shell nanoparticles, obtained by wet chemistry, with an outer dielectric shell composed of SiO2 or TiO2. Apart from the shell composition, the nanoparticle density and aggregation type strongly affect the surface-enhanced SERS. Going beyond a single layer by building random aggregates of hybrid NPs would result in a step forward in the production of reliable hybrid SERS platforms. Here we achieve the fabrication of a 3D nanogranular film of Ag metallic cores not fully enclosed in a TiO2 capping layer, defined as a Ag@TiO2 quasi-shell-isolated Raman substrate (Ag@TiO2 QuaSIRS) by an environmentally friendly gas phase synthesis technique (SCBD). The Ag core drives the electromagnetic enhancement with plasmonic hotspots while the TiO2 shell passivates it and leads to different possible surface functionalization. The SERS capabilities of the Ag@TiO2 QuaSIRS peak at a film thickness of 60 nm providing a detection limit of 10-9 M concentration for Methylene Blue at 632.81 nm. The importance of the nanogranular 3D morphology is evidenced by the very good detection of analytes dispersed in aqueous solutions, since the liquid can penetrate the pores hence exploiting most of the plasmonic hotspots present in the film. The versatility of SCBD to deposit such reliable hybrid SERS platforms by a single step at room temperature over different substrates provides an opportunity to design a new generation of hybrid SERS-active substrates based on hybrid nanoparticles.

Environment friendly, thin and flexible devices require the synthesis of Indium-free new transparent conducting materials (TCM) with improved structural, thermal, electrical and optical properties. To overcome the critical issues raised by thinning the TCM, we propose a multilayer structure in which nanogranular Ag film obtained by supersonic cluster beam deposition is sandwiched in between Alluminum doped Zinc Oxide (AZO) thin layers. The introduction of the nanogranular Ag film, when compared to the standard sputtered one, yields higher optical transmittance in the technologically relevant VIS-NIR region and superior mechanical reliability while preserving low electrical resistance. The present results open new perspectives to exploit the nanogranular nature of conductive films, synthesized via Supersonic Cluster Beam Deposition, to engineer transparent conducting materials.

The morphological and mechanical properties of nanoparticles-based ultrathin Ag films, synthesized by supersonic cluster beam deposition over a sapphire substrate, are unveiled exploiting ultrafast optoacoustic, atomic force microscopy, X-ray photoelectron spectroscopies, and X-ray diffraction techniques. The films, with thicknesses in the 10–50 nm range, have a porous structure composed of metallic Ag nanoparticles with a crystalline structure and average diameter of 6 nm. The films acoustic modes are in the hypersonic frequency range, the thinner films frequencies exceeding 100 GHz. The acoustic spectra are well accounted for modeling the nanoparticles film as an effective continuous medium. The modes quality factors show the existence of acoustically quasi-dark and bright states. The film effective density and effective elastic stiffness constants are respectively 0.8 and 0.5 that of bulk Ag. The present results are relevant in view of applications for optoacoustic transducers in the hypersonic frequency range, for optical coatings technology and for the production of mechanically stable bactericidal coatings.

The structure and thermal evolution of Fe nanoparticles deposited on a wetting TiOx ultrathin film epitaxially grown on Pt(111) has been characterized by various surface science techniques. Combining the results obtained it is shown that, at room temperature, metallic Fe nucleates randomly and oxidizes at the interface. A thermal treatment causes Fe migration through the TiOx layer, forming a mixed oxide and a new hexagonal ultrathin film phase. Finally, the pristine TiOx phase motif is restored, due to the complete diffusion of Fe into the Pt substrate.

Polyvinyl alcohol (PVA) electrospun nanofibers containing Ag nanoparticles (NPs) have been deposited on glass substrates. The aim of the work was to test the feasibility of this approach for the detection of biogenic amines by using either the Ag localized surface plasmon resonance quenching caused by the adsorption of amines on Ag NPs or by detecting the amines by surface enhanced Raman spectroscopy (SERS) after adsorption, from the gas phase, on the metal NPs. Two different approaches have been adopted. In the first one an ethanol/water solution containing AgNO3 was used directly in the electrospinning apparatus. In this way, a simple heat treatment of the nanofibers mat was sufficient to obtain the formation of Ag NPs inside the nanofibers and a partial cross-link of PVA. In the second procedure, the Ag NPs were deposited on PVA nanofibers by using the supersonic cluster beam deposition method, so that a beam of pure Ag NPs of controlled size was obtained. Exposure of the PVA mat to the beam produced a uniform distribution of the NPs on the nanofibers surface. Ethylendiamine vapors and volatile amines released from fresh shrimp meat were chemisorbed on the nanofibers mats. A SERS spectrum characterized by a diagnostic Ag–N stretching vibration at 230 cm−1 was obtained. The results allow to compare the two different approaches in the detection of ammines.

Scanning tunneling microscopy and X-ray spectroscopy measurements are combined to first-principles simulations to investigate the formation of graphene nanoribbons (GNRs) on Au(110), as based on the surface-mediated reaction of 10,10′-dibromo-9,9′-bianthracene (DBBA) molecules. At variance with Au(111), two different pathways are identified for the GNR self-assembly on Au(110), as controlled by both the adsorption temperature and the surface coverage of the DBBA molecular precursors. Room-temperature DBBA deposition on Au(110) leads to the same reaction steps obtained on Au(111), even though with lower activation temperatures. For DBBA deposition at 470 K, the cyclodehydrogenation of the precursors preceds their polymerization, and the GNR formation is fostered by increasing the surface coverage. While the initial stages of the reaction are found to crucially determine the final configuration and orientation of the GNRs, the molecular diffusion is found to limit in both cases the formation of high-density long-range ordered GNRs. Overall, the direct comparison between the Au(110) and Au(111) surfaces unveils the delicate interplay among the different factors driving the growth of GNRs. © 2014 American Chemical Society.

In this paper we compare by temperature programmed desorption the intercalation rate of Fe nanoparticles supported on pure and nitrogen doped graphene grown on Pt (111). Carbon monoxide desorption from Fe sites is used to probe the overall quantity of Fe present onto the graphene surface. We do not observe any appreciable difference of CO desorption temperature induced by N functionalities of graphene; however we notice a faster intercalation for Fe nanoparticles deposited on N-doped graphene with respect the those supported on pure graphene. We relate this phenomenon to nanoholes created by pyridinic and pyrrolic functionalities and/or to the lower bond enthalpy of CN with respect to CC bonds. Scanning tunneling microscopy and X-ray photoelectron spectroscopy are used as complementary techniques to identify the N functionalities and to characterize the morphological defectivity of the graphene films. © 2014 Elsevier B.V. All rights reserved.

We present a detailed experimental and theoretical investigation of the ultrathin titania z'-TiOx/Pt(111) phase and Au nanoparticles assembled on it. Scanning tunneling spectroscopy (STS) at two different tip stabilization biases (TSB) is measured at three different locations on the bare titania phase and on top of the Au nanoparticles (NPs). STS data are compared with the results of first-principles calculations based on a Tersoff-Hamann approach for simulating tunneling currents. We obtain a coherent framework in which STS features can be used as fingerprints with atomistic resolution of the local density of states. On the bare titania, Shockley states coming from the 0 atoms dominate the occupied DOS, while resonant states coming from the Ti atoms dominate the DOS above the Fermi level. The ultrathin film is partially metallized, with DOS empty channels at the hole sites, hence lying in an intermediate state between a semiconducting oxide and a conductor. Finally, STS data on top of Au nanoparticles provide information on the coordination environment of the Au atom in direct contact with the titania phase, discriminating between the Au metallic or nonmetallic regime.

In this paper we report on the photocatalytic behavior in gas phase propane oxidation of well-defined TiO2 nanoparticle (NP) coatings prepared via Supersonic Cluster Beam Deposition (SCBD) on Si-wafers and quartz substrates. The temperature dependent crystal phase of the coatings was analyzed by Raman spectroscopy, and the morphology by High Resolution-Scanning Electron Microscopy. SCBD deposition in the presence of oxygen enables the in situ synthesis of TiO2 layers of amorphous NP at room temperature. Adapting the deposition temperature to 500 degrees C or 650 degrees C leads to Anatase crystals of variable size ranges, and layers showing significant porosity. At 800 degrees C mainly Rutile is formed. Post annealing by wafer heating of the amorphous NP prepared at room temperature results in comparable temperature dependent phases and morphologies. Photocatalytic activity in propane oxidation was dependent on the morphology of the samples: the activity decreases as a function of increasing particle size. The presence of water vapor in the propane feed generally increased the activity of the wafer-heated samples, suggesting OH groups are not profoundly present on SCBD synthesized layers. In addition, a remarkable effect of the substrate (Si or Quartz) was observed: strong interaction between Si and TiO2 is largely detrimental for photocatalytic activity. The consequences of these findings for the application of SCBD to synthesize samples for fundamental (spectroscopic) study of photocatalysis are discussed. (C) 2013 Elsevier B.V. All rights reserved.

Recent studies indicated that noncompensated cation-anion codoping of wide-band-gap oxide semiconductors such as anatase TiO2 significantly reduces the optical band gap and thus strongly enhances the absorption of visible light [W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)]. We used soft x-ray spectroscopy to fully determine the location and nature of the impurity levels responsible for the extraordinarily large (similar to 1 eV) band gap reduction of noncompensated codoped rutile TiO2. It is shown that Cr/N codoping strongly enhances the substitutional N content, compared to single element doping. The band gap reduction is due to the formation of Cr 3d(3) levels in the lower half of the gap while the conduction band minimum is comprised of localized Cr 3d and delocalized N 2p states. Band gap reduction and carrier delocalization are critical elements for efficient light-to-current conversion in oxide semiconductors. These findings thus raise the prospect of using codoped oxide semiconductors with specifically engineered electronic properties in a variety of photovoltaic and photocatalytic applications.

Fractal TiO2 nanostructures in crystalline form are obtained at ambient pressure and temperature by pulsed laser deposition with femtosecond pulses. The synthesized structures have been studied by scanning electron microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. We show that the dendritic aggregations deposited on silicon wafers at room temperature are fractals. They are composed by nanoparticles with an average diameter in a range below 20 nm, with the presence of larger nanoparticles with a diameter above 50 nm. We demonstrate that the fractal dimension and area can be tuned by varying laser fluence and sample/target distance. X-ray photoemission spectroscopy shows that the as-deposited nanostructures are TiO2 while Raman spectroscopy reveals that the crystalline structure of fractals and nanoparticles are composed either by rutile or anatase phase, with a dominant relative concentration of anatase. We discuss possible mechanism of fractals and nanoparticles formation in comparison with the literature results.

The competition between rectangular and hexagonal phases in TiOx ultrathin (monolayer) films grown on a Pt(111) surface is discussed and rationalized on the basis of general building principles for these pseudoepitaxial oxide phases on a (111) metal substrate. A novel hexagonal reduced phase is also presented for the first time, obtained by thermal treatment at high temperature (similar to 1000 K), and its atomistic structure is unveiled through a combination of STM experiments and theoretical simulations. A consistent picture is obtained for a class of structural families for ultrathin oxide phases on close-packed single-crystal metal surfaces.

By using reactive Ti evaporation, we have grown on Pt(111) stoichiometric TiO2 ultrathin (UT) films of increasing thickness, presenting different polymorphic structures and surface terminations, that is, the thickness-limited lepidocrocite-like nanosheet, TiO2(B) (001) and rutile-TiO2, (100), respectively. This allowed us to study comparatively for the first time the reactivity toward water of different polymorph surfaces in the form of ultrathin films by adopting several in situ surface science tools. There is no evidence for water interaction with lepidocrocite-TiO2 nanosheets, in agreement with theoretical predictions found in the literature. For the first time evidence for some water dissociation on TiO2(B) surfaces is reported. A higher water interaction is observed on the high coverage films, and the observed behavior is in line with the previous literature data obtained on the rutile (100) bulk surface: our data confirm the common interpretation that rutile-TiO2 (100) surface termination is highly reactive toward water dissociation. In this paper we demonstrate that this ability is maintained also in the case of UT films.

A major obstacle toward employing TiO2 as an efficient photoactive material is related to its large optical band gap, strongly limiting visible light absorption. Substitutional doping with both donors and acceptors (codoping) potentially leads to a significant band gap reduction, but the effectiveness of the codoping approach remains limited by the low solubility of dopants inside TiO2. Here we show that nanostructured Cr and Ncodoped TiO2 thin films can be obtained by supersonic cluster beam deposition (SCBD) with a high concentration of dopants and a strongly reduced band gap. Complementary spectroscopic investigations show that doping effectively occurs in substitutional lattice sites, inducing dopant levels in the gap that are remarkably delocalized. The high surface-to-volume ratio, typical of SCBD nanostructured films, likely facilitates the dopant incorporation. The present results indicate that SCBD films are highly promising photoactive nanophase materials.

In this work we present some significant paradigmatic examples of directed self assembling of transition metals deposited on ultrathin oxide layers grown on single crystal metal surfaces. Two major driving factors are considered in the description of the self assembling process on these systems, giving rise to ordered arrays of metal nanoparticles (NPs): the presence of defects in the oxide layer and the metal/oxide interaction. We first summarize the structure of different oxide layers, and we discuss the role of geometric and electronic factors in the formation of ordered Au and Fe NP arrays on the selected systems. The discussion suggests that the defective oxide template can drive the self organization of NPs, if the defects are accessible through the diffusion of metal adatoms on the surface, which in turn, is determined by the metal/oxide interaction.

Studies of the healing of artificial defects in the surface of highly oriented pyrolitic graphite (HOPG) by chemical vapor deposition (CVD) of acetylene show that only single-layer depth defects could be healed completely during the CVD treatment. A promising method is introduced for defect control in surfaces of graphite, graphene, and graphene-based materials, with important implications for their application.

In this work we analyse three paradigmatic examples of directed self-assembling and self-organisation of transition metal nanoparticles (NPs) on oxide ultrathin layers grown on single crystal metal surfaces. The major driving forces considered in the description of the NPs assembling process on these nanotemplate systems are the presence in the oxide layer of trapping centres in the form of defects and the metal/oxide interaction. We first summarise the structure of the different oxide nanotemplates, and then we discuss the role of geometric and electronic factors in the formation of ordered NP arrays on the selected systems. It turns out that a defective nanostructured oxide template can drive the organisation of the NPs if the metal NPs are efficiently trapped by the defects and these are accessible via the diffusion of metal adatoms on the surface, which is in turn strongly dependent on the metal/oxide interaction. (C) 2011 Elsevier Ltd. All rights reserved.

We present experimental and theoretical evidence of sequential redox processes and structural transformations occurring by increasing temperature in a metal/oxide/metal system obtained via deposition of Fe atoms onto a z'-TiO(1.25)/Pt(111) ultrathin film in UHV. The initial reduction of the z'-TiO(x) phase by Fe at room temperature is followed by Fe diffusion and partial penetration into the substrate at intermediate temperatures. This triggers the formation of a bi-component material in which mixed FeO/TiO(2) nanoislands coexist on a h-TiO(1.14) ultrathin film, notably restructured (from rectangular to hexagonal) and reduced (from Ti : O = 1 : 1.25 to 1 : 1.14) with respect to the original TiO(1.25) phase. Further heating recovers the pristine z'-TiO(x) phase while Fe completely dissolves into the substrate.

This work presents a complete surface science investigation of a model system obtained depositing different amounts of Fe on the z'-TiOx/Pt(111) ultrathin (UT) film, whose structure is known in great detail. The system has been investigated both at room temperature (RT) and after thermal treatments in an ultrahigh vacuum at temperatures in the room temperature to 900 K range. In contrast with standard thermodynamic predictions, we show that Fe nanoparticles (NPs) strongly compete with Ti to bind oxygen, i.e, a redox reaction where Fe oxidizes and Ti is further reduced to an extent proportional to the amount of deposited Fe is observed. The z'-TiOx UT film is first destabilized by the presence of Fe, but as soon as the temperature is raised, so activating an interdiffusion of Fe into the Pt substrate, a rather ordered UT TiOx film is formed again. However, a new hexagonal h-TiOx phase replaces the z'-TiOx one in the room temperature to 800 K range, which progressively transforms into the most stable z'-TiOx form at the highest temperature (900 K). At the intermediate temperatures, the system is present in the form of FeOx/TiOx mixed oxide NPs. This is a paradigmatic example where the nanoscale effects produce unexpected transformations different from those observed in the bulk.

We present a morphologic and spectroscopic study of cluster-assembled TiO (x) films deposited by supersonic cluster beam source on clean silicon substrates. Data show the formation of nanometer-thick and uniform titanium silicides film at room temperature (RT). Formation of such thick TiSi (x) film goes beyond the classical interfacial limit set by the Ti/Si diffusion barrier. The enhancement of Si diffusion through the TiO (x) film is explained as a direct consequence of the porous film structure. Upon ultra high vacuum annealing beyond 600 A degrees C, TiSi2 is formed and the oxygen present in the film is completely desorbed. The morphology of the nanostructured silicides is very stable for thermal treatments in the RT-1000 A degrees C range, with a slight cluster size increase, resulting in a film roughness an order of magnitude smaller than other TiO (x) /Si and Ti/Si films in the same temperature range. The present results might have a broad impact in the development of new and simple TiSi synthesis methods that favour their integration into nanodevices.

Graphene structures, obtained by catalytic chemical vapor deposition of methane on highly oriented pyrolitic graphite (HOPG), were examined using scanning tunneling microscopy Depending on the Fe catalyst coverage and localization on the substrate steps and terraces, different graphene structures were obtained. curved graphene sheets at the edges of topmost stacked graphene bilayers, laterally grown terraces at the edges of individual graphene layers parallel to the HOPG basal plane and planar graphene islands on the terraces A growth mechanism is proposed that takes into account the specific features of the spatial distribution of Fe catalytic nanoparticles on the substrate surface, driven by metal film-substrate interaction The present synthesis approach is promising for the controlled growth and modification of graphene layers, as well as for engineering the edge characteristics of graphene systems at the atomic scales (C) 2010 Elsevier Ltd All rights reserved

The stability of three ultrathin TiOx/Pt(111) films with different stoichiometry and defectivity and the corresponding Au/TiOx/Pt(111) model catalysts in CO or a CO-O-2 (1 : 1) gas mixture up to a pressure of 100 mbar has been investigated. According to previous studies, the ultrathin films proved to be effective substrates to deposit in UHV Au nanoparticles with specific morphologies and lateral sizes ranging between 1 and 6 nm. The films have been characterized before and after the exposure using X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). Additional in situ measurements of the CO chemisorption behavior were performed using polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS). A fully oxidized film is stable in CO and CO-O-2 (1 : 1) ambient, while the reduced films undergo an oxidative dewetting process at RT in the latter atmosphere. This process ultimately produces a nano-composite surface, where very tiny (from 0.5 to 3 nm lateral sizes) titania nanograins are mixed with open, uncovered areas of the Pt substrate. IRAS measurements on the corresponding Au/TiOx/Pt(111) model catalysts demonstrated that the CO chemisorption strongly depends on the Au nanoparticle size and morphology, while the actual Ti oxidation state of the oxide support does not seem to play a significant role.

The evolution of a Fe/z'-TiOx/Pt(111) model catalyst in ultrahigh vacuum, studied by advanced surface science tools, reveals various phenomena occurring in different temperature ranges. In the room temperature (RT) < T < 460 K range, the deposited Fe atoms assemble as heterogeneous Fe and FeOx nanoparticles (NPs), templated by the ordered array of defects (troughs and picoholes) of the oxide film. At 460 < T < 810 K, FeOx NPs become predominant, and a metastable FeOx/TiOx mixed oxide is formed, assisted by the interdiffusion of Fe through the oxide into the Pt substrate, which triggers the z'-TiOx structure transformation into a different TiOx phase with a hexagonal pattern. At 810 < T < 1000 K, a Fe-mediated extraction of Pt produces Pt(111) islands, surrounded and partly encapsulated by the same z'-TiOx phase, demonstrating the intrinsic high stability of the ultrathin oxide film. This represents one of the first examples of a phase transformation in a ultrathin oxide layer induced by an external metal deposit.

We report a synthesis route of a carbon-based structure, curved graphene sheet (CGS). The CGS grows by catalytic chemical vapor deposition autoselectively at the stacked bilayer edges of graphite support, providing an atomically smooth connection of the edges. We propose a growth mechanism based on Fe nanoparticle diffusion along the step edges, acting as a nanozipper. The work addresses with a simple experimental method, the edge engineering in graphene bilayer systems. The results may have a significant impact on the fabrication of new carbon nanostructures and their integration into nanoelectronics.

We present an in-depth investigation of Au nanoparticles self-assembled on a zigzag-like TiOx/Pt(111) ultrathin polar film, whose structure is known in great detail. The peculiar pattern of defects (picoholes) templates a linear array of size-selected (ca. 1 nm) Au nanoparticles without disruption of the titania layer, as observed by scanning tunneling microscopy. Their structure and electronic properties have been investigated by several large-area spectroscopic tools, i.e. high-resolution core and valence level photoemission and angle-scanned and energy-scanned photoelectron diffraction. The comparison between experimental data and density functional theoretical calculations indicates that the Au atoms landing on the oxide film are rather mobile, and that the picoholes can act as effective trapping and nucleation centers for the growth of the Au nanoparticles. All the experimental results are in concord in indicating that the Au NPs are flat islands with a maximum thickness of 2-3 layers exposing the (111) surface.

The essential role of O affinity in the directed assembly of size-selected Au and Fe nanoparticles (NPs) on a TiOx/Pt(111) ultrathin oxide phase, an effective template for size selected metal NP growth, is revealed through scanning tunneling microscopy and density-functional calculations. A weakly interacting element (Au) diffuses rapidly and gets trapped in the vacancy defects (picoholes) located inside parallel rows (troughs, spaced 1.44 nm apart) peculiar to the film structure, producing size-selected NPs arranged in regular linear arrays aligned along the troughs. In contrast, an element with greater O affinity (Fe) experiences higher diffusion barriers, and the growth is dominated by kinetic effects, with a less effective preferential nucleation and the appearance of irregular NP morphologies.