Unravelling the growth mechanism of the coprecipitation of iron oxide nanoparticles

Applications involving iron oxide nanoparticles (IONPs) and nanomaterials in general, are expected to provide solutions to many problems in the fields of healthcare, energy and environment. Magnetic nanoparticles (such as IONPs) have been in the exploratory stage for cancer diagnostic (e.g.in the form of magnetic resonance imaging contrast agents) for more than three decades and treatment (e.g.via hypothermia) in the recent decade. However, success stories are rare, partly due to the limited performance of commercially available nanoparticles, related to the particle quality attributes such as size and shape, polydispersity, crystallinity and surface chemistry. Although today’s literature provides many reports on the synthesis of highly complex nanoparticles with superior properties respect the currently approved products, there seems to be a gap to the application of these materials to fully exploit their enhanced capabilities. This is due, at least partly, to obstacles such as low yield and, most importantly, the robustness and reproducibility of the synthesis method. Hence, detailed studies on nanoparticle formation mechanisms are essential to guarantee that successful syntheses are not a “one-off” but can be performed and reproduced at various research institutions at small to large scales. This work presents such a detailed study, unravelling the growth mechanism of the co-precipitation of IONPs in solution with the aid of synchrotron X-Ray diffraction.

>Read more on the Elettra website

Image: TEM images of the nanoparticles formed after 30 s, 1, 2, 3, 4, 5, 7 and 10 min of reaction.

Surface instability and chemical reactivity of ZrSiS and ZrSiSe nodal-line semimetals

Among topological semimetals, in nodal-line semimetals (NLSM) conduction and valence bands cross each other. In particular, in NLSM, topological constraints protect band crossings and, moreover, band touching forms nodal lines or rings. Recently, topological nodal lines have been observed in bulk ZrSiX compounds (X = S, Se, Te). In ZrSiX, a tetragonal structure is formed by the stacking of X-ZrSi-Zr-X slabs covalently bonded between each other, whose strength decreases by replacing S with Se or Te ions. This class of materials exhibits large and non-saturating magnetoresistance and ultrahigh mobility of charge carriers.
The control over surface phenomena, including oxidation, degradation, and surface reconstruction is a crucial step in order to evaluate the feasibility of the exploitation in technology of ZrSiX.
By means of X-ray photoelectron spectroscopy (XPS) carried out at the APE-HE beamline, high-resolution electron energy loss (HREELS) and density functional theory, an international team of researchers from Italy, China, Russia, Taiwan, and USA (coordinated by University of L’Aquila) has studied the evolution of ZrSiS and ZrSiSe surfaces in oxygen and ambient atmosphere.
The chemical activity of ZrSiX compounds is mainly determined by the interactions of Si layer with ZrX sublayer. Any adsorption provides distortion of the Si layer (flat in bulk). In the case of ZrSiS, the ZrS sublayer is almost the same as in bulk and therefore adsorption is unfavorable because it provides distortions of Si layer. In the case of ZrSiSe, the ZrSe sublayer is already strongly distorted (structure different from bulk), and, therefore, further distortion of Si layer by adsorption is favorable (see figure).

>Read more on the Elettra website

Image: Atomic structure of different steps of the process of the oxidation of ZrSiSe from (a-d) Zr-sites and (e-h) Si-sites. Red, light blue, black and yellow balls represent O, Zr, Se, and Si atoms, respectively. On panels (a) and (e) physical adsorption of single oxygen molecule is depicted. Panels (b) and (f) represent the situation of uniform coverage of the surfaces by molecular oxygen. In panels (c) and (g), decomposition of single oxygen molecule on the surfaces is represented. Panels (d) and (h) show total oxidation of the surfaces.

In-gap states and band-like transport in memristive devices

The creation of point defects in matter can profoundly affect the physical and chemical properties of materials. If appropriately controlled, these modifications can be exploited in applications promising advanced and novel functionalities. Redox-based memristive devices – one of the most attractive emerging memory technologies – provide one of the most striking examples for the potential exploitation of defects. Applying an external electric field to an initially insulating oxide layer is known to induce a non-volatile, voltage-history dependent switching between a low resistance state and a high resistance state, also named memristive device. This switching occurs through the creation and annihilation of the so-called conductive filaments, which are generated at the nanoscale by assembly of donor-type point defects such as oxygen vacancies.
To date, the exact relationship between concentration and nanoscale distribution of defects within the filament on the one hand and the electronic transport properties of the devices on the other hand is still elusive. Due to limitations in sensitivity or spatial resolution of most characterization methods, the electronic structure of conductive filaments has not yet been characterized in detail. However, this knowledge is crucially needed as input for the development of electronic transport models with high predictive power.

>Read more on the Elettra website

Image: (a) Ti3+ map based on the Ti 3p3/2 spectrum. (b) Ti 2p 3/2 spectra for the filament and the surrounding. (c) Spatial map of the in-gap state distribution. (d) Valence band spectrum extracted from the filament at a photon energy of 463.3 eV with a fit of the valence band maximum and the in-gap states (red lines). (e) Band diagram of the device calculated based on the position of the in-gap states. The blue line shows the conduction band and the dashed green lines shows position of the defect states obtained by PEEM in respect to the conduction band 

2 for the price of 1: how double ionization becomes an efficient process

Double ionization is a unique mechanism where two electrons are simultaneously emitted from an atom or molecule. Typically, it’s a very weak process occurring only a few percent of the time compared to single ionization where only one electron is emitted. This is due to double ionization requiring the correlated action of two electrons hit by an energetic photon or particle. However, in a recent experiment, is has been shown that double ionization doesn’t necessarily need to be a minor effect and can even be the primary ionization mechanism.
The enhancement is likely due to double ionization proceeding through a new type of energy transfer process termed double intermolecular Coulombic decay, or dICD, for short. To experimentally observe this mechanism, dimers consisting of two alkali metal atoms were attached to the surface of helium nanodroplets. The dICD process, schematically shown in Fig. 1, occurs through an electronically excited helium atom (red), produced by synchrotron radiation, interacting with the neighboring alkali dimer (blue and white) resulting in energy transfer and double ionization. To distinguish dICD from other processes, the kinetic energies of the emitted electrons were measured in coincidence with their alkali ion counterparts.

>Read more on the Elettra website

Image: schematic view of double Intermolecular Coulombic decay (dICd).

Magnetic patterning by electron beam assisted carbon lithography

The exploitation of the unique physical properties of thin films and heterostructures are opening intriguing opportunities for magnetic storage technology. These artificial materials will in fact enable novel architectures for a multitude of magnetic devices and sensors, promoting a significant improvement in storage density, functionality and efficiency. Their usage will also contribute to diminish the consumption of materials that are rare and difficult to extract, being often detrimental to the environment. With these objectives in mind, researchers are now looking with great attention at the combination of thin ferromagnetic layers with 2-dimensional crystals like graphene and transition metal dichalcogenides. Due to their layered structure, these systems exhibit very favorable magnetic properties, which can be tuned through thickness and interfacial interactions. For instance, graphene-cobalt stacks display an enhanced perpendicular magnetic anisotropy, a feature that is especially important for non-volatile memories.
The fabrication of layered materials, however, is still a very challenging process. Not only it requires atomic precision in the deposition of the various layers but also the ability to create nano or microstructures of arbitrary shape. Conventional lithography in conjunction with chemical etching permits nowadays to sculpture the matter with great accuracy, at lateral resolution close to the nanometer. Yet, this approach poses an important limitation, that is, the material can only be shaped by erosion. The ability to vary the chemical composition, by adding atoms for example, is instead very desirable for many applications. To date, this can be done by stimulating the fragmentation of suitable carrier molecules using photons or electrons. So far, various methods based on focused beam induced processing methods have been devised, which can be readily employed to deposit carbonaceous layers and metallic nanostructures. These methods, however, cannot be applied when ultra-clean, ultra-high vacuum (UHV) conditions are needed, as happens for the case of semiconductor industry.

>Read more on the Elettra website

Figure 1.  (left) Scheme of the protocol for printing chemo-magnetic patterns in ultrathin Co on Re(0001). (a) The film is exposed to CO at room temperature. The irradiation with a focused electron beam (yellow) stimulates the dissociation of the molecule, which results in the accumulation of atomic carbon on the surface. (b) Subsequently, the sample is annealed above 170 °C to desorb molecularly adsorbed CO from the non-irradiated surface regions. (c) LEEM image of an e-beam irradiated disk. Disk diameter: 1 μm; Co thickness: 4 atomic layers; irradiation energy: 50 eV; CO dose: 9.75 L; (d) Intensity profile across the orange line in the LEEM image in (c) and fit using a step function convoluted with a Gaussian of full width at half-maximum of 30 nm. The dashed blue lines indicate the 15–85% distance between minimum and maximum intensity. (e) XMCD-PEEM image of the same region at the Co L3 edge. (f) Intensity profiles across the blue and orange dashed lines in the XMCD-PEEM image in (e). The magnetic stripes indicate out-of-plane magnetic anisotropy. The stripe period is 120 nm. Adapted with permission from [1].
Copyright (2018) American Chemical Society.

Doped epitaxial graphene close to the Lifshitz transition

Graphene, an spbonded sheet of carbon atoms, is still attracting lots of interest almost 15 years after its discovery. Angle-resolved photoemission spectroscopy (ARPES) is a uniquely powerful method to study the electronic structure of graphene and it has been used extensively to study the coupling of electrons to lattice vibrations (phonons) in doped graphene. This electron-phonon coupling (EPC) manifests as a so-called “kink” feature in the electronic band structure probed by ARPES. What is much less explored is the effect of EPC on the phonon structure. A very accurate probe of the phonons in graphene is Raman spectroscopy.
M.G. Hell and colleagues from Germany, Italy, Indonesia, and Japan combined ARPES (carried out at the BaDelPhbeamline – see Figure 1) with low energy electron diffraction (LEED) and Raman spectroscopy (carried out at the University of Cologne in Germany) in a clever way to fully understand the coupled electron-phonon system in alkali metal doped graphene. LEED revealed ordered (1×1), (2×2), and (sqrt3xsqrt3)R30°adsorbate patterns with increasing alkali metal deposition. The ARPES analysis yielded not only the carrier concentration but also the EPC coupling constant. Ultra-High Vacuum (UHV) Raman spectra carried out using identically prepared samples with the very same carrier concentrations provided the EPC induced changes in the phonon frequencies.

>Read more on the Elettra Sincrotrone Trieste website

Image:  Top: ARPES spectra along the Γ-K-M high symmetry direction of the hexagonal Brillouin zone for Cs doped graphene/Ir(111) with increasing Cs deposition. The Dirac energy ED and the observed LEED reconstruction are also indicated. Bottom: Corresponding Fermi surfaces at the indicated charge carrier concentration. 

Ferroelectric control of the spin texture in GeTe

Spin-orbit coupling effects in materials with broken inversion symmetry are responsible for peculiar spin textures, giving rise to intriguing phenomena such as intrinsic spin Hall effect. Among these materials, ferroelectrics allow for non-volatile control of the spin degree of freedom through the electrical inversion of the spin texture, based on their reversible spontaneous polarization. Finding suitable ferroelectric semiconductors would be a fundamental achievement towards the implementation of novel electronic and spintronic devices combining memory and computing functionalities.
Germanium Telluride emerges as promising candidate, since theoretically proposed as the father compound of the new class of ferroelectric Rashba semiconductors. Its ferroelectricity provides a non-volatile state variable able to generate and drive a giant bulk Rashbatype spin splitting of the electronic bands. Its semiconductivity and silicon-compatibility allows for the realization of spin-based non-volatile transistors.
A European team of both experimentalists and theoreticians from Italy (Politecnico di Milano, IFN-CNR, CNR-SPIN, CNR-IOM) and Germany (Paul-Drude-Institut für Festkörperelektronik, Universität Würzburg) has demonstrated the ferroelectric control of the Rashba spin texture in GeTe probed by spin and angular resolved photoemission spectroscopy at the Advanced Photoelectric Effect experiments (APE) beamline and supported by NFFA.

>Read more on the Elettra Sincrotrone Trieste website

Image: (a, a’) PFM ferroelectric hysteresis loops and the pristine polarization states for the as-prepared Te- and Ge-terminated GeTe(111) surfaces, respectively. (b, b’) DFT calculations of the k-resolved spin polarization along two high symmetry crystallographic directions. The main bulk Rashba bands are marked as B1 and B2. The black dashed line indicates the wave vector k of SARPES measurements. (c, c’) Spin-polarized currents and spin asymmetries (Px) versus binding energy at the wave vector k. The peaks correspond to the intersection of the Rashba bands B1 and B2 with the vertical dashed line at k. (d, d’) Constant energy maps for the Te- and Ge-terminated surfaces. Blue and red arrows indicate the sense of circulation of spins, opposite for the two opposite ferroelectric polarizations.

Research on ancient teeth reveals complexity of human evolution

Fossil records enable a detailed reconstruction of our planet’s history and of the evolution of our species. In particular, teeth are a sort of biological archive that record in their structures (enamel, dentine and pulp chamber) the different phases of the human evolution. An international team of researchers led by Clément Zanolli from the Université Toulouse III Paul Sabatier (France) has characterized human dental remains from Fontana Ranuccio (Latium) and Visogliano (Friuli-Venezia Giulia), Italy through a comparative high-resolution endostructural analysis based on microfocus X-ray microtomography (mCT) scanning and detailed morphological analyses. We examined the shape and arrangement of tooth tissues (see Fig. 1) and compared them with teeth of other human species (see Fig. 2).

With an age of around 450,000 years before present, the analysed dental remains from the sites of Fontana Ranuccio, located 50 km south-east of Rome, and Visogliano, located 18 km north-west of Trieste, are part of a very short list of fossil human remains from Middle Pleistocene Europe and are among the oldest human remains on the Italian Peninsula.
From the data obtained through X-ray μ-CT measurements performed at the TomoLab station of Elettra and at the Multidisciplinary Laboratory of the ‘Abdus Salam’ International Centre for Theoretical Physics in Trieste (Italy), we found that the teeth of both sites share similarities with Neanderthals but they are distinct from modern humans. This study adds to an emerging picture of complex human evolution in Middle Pleistocene Eurasia.  The investigated fossil teeth show that Neanderthal dental features had evolved by around 450,000 years ago.

>Read more on the Elettra Sincrotrone Trieste website

Image: Volume rendering of the Fontana Ranuccio (FR1R and FR2) and Visogliano (Vis. 1-Vis. 6) tooth specimens. The enamel is represented in blue while the dentine in yellow. All specimens were imaged by X-ray μCT at the Tomolab station of Elettra and at the Multidisciplinary Laboratory of the ICTP.     
Credit:  doi: 10.1371/journal.pone.0189773

A shape-induced orientation phase within 3D nanocrystal solids

Designing nanocrystal (NC) materials aims at obtaining superlattices that mimic the atomic structure of crystalline solids. In such atomic systems, spatially anisotropic orbitals determine the crystalline lattice type. Similarly, in NC systems the building block anisotropy defines the order of the final solid: here, the NC shape governs the final superlattice structure. Yet, in contrast to atomic systems, NC shape-anisotropy induces not only positional, but also orientational order, ranging from full rotational disorder to a stable, fixed alignment of all NCs. This orientational relation is of special interest, as it determines to what extent atomically coherent connections between NCs are possible, thereby enabling complete wave function delocalization within the NC solid.
In addition to predicting the final NC orientation and position structure, the realization of NC materials demands a controllable fabrication process such that the designed order can be produced. Generally, such highly ordered NC superstructures are achieved through solvent evaporation induced self‐assembly on hard substrates. For applications where the 2D nature of this substrates process is limiting, nonsolvent into solvent diffusion, a technique commonly used to grow single crystals of dissolved molecules, is an attractive option. However, the precise influence of self-assembly parameters on the final superlattice outcome remains unknown. In this work, the researchers posed two closely related questions regarding the design of novel free-standing NC materials: (i) how can the NC self-assembly process be controlled to yield highly ordered free-standing supercrystals and (ii) what is the detailed positional and orientational order within the NC solid? A multidisciplinary team of collaborators, including the Austrian Small Angle X-ray Scattering (SAXS) beamline at Elettra, approached this challenge by a combined experimental and computational strategy.

>Read more on the Elettra Sincrotrone Trieste website

Image: Self‐assembly of 3D colloidal supercrystals built from faceted 20 nm Bi nanocrystals is studied by mens of in-situ synchrotron X‐ray scattering, combined with Monte Carlo simulations. 

Ultralow-fluence for phase-change process

Ultrafast active materials with tunable properties are currently investigated for producing successful memory and data-processing devices. Among others, Phase-Change Materials (PCMs) are eligible for this purpose. They can reversibly switch between a high-conductive crystalline state (SET) and a low-conductive amorphous state (RESET), defining a binary code. The transformation is triggered by an electrical or optical pulse of different intensity and time duration. 3D Ge-Sb-Te based alloys, of different stoichiometry, are already employed in DVDs or Blu-Ray Disks, but they are expected to function also in non-volatile memories and RAM. The challenge is to demonstrate that the scalability to 2D, 1D up to 0D of the GST alloys improves the phase-change process in terms of lower power threshold and faster switching time. Nowadays, GST thin films and nanoparticles have been synthetized and have beenshown to function with competitive results.
A team of researchers from the University of Trieste and the MagneDyn beamline at Fermi demonstrated the optical switch from crystalline to amorphous state of Ge2Sb2Te5nanoparticles (GST NPs) with size <10 nm, produced via magnetron sputtering by collaborators from the University of Groeningen. Details were reported in the journal Nanoscale.
This work aims at showing the very low power limit of an optical pulse needed to amorphize crystalline Ge2Sb2Te5 nanoparticles. Particles of 7.8 nm and 10.4 nm diameter size were deposited on Mica and capped with ~200nm of PMMA. Researchers made use of a table-top Ti:Sapphire regenerative amplified system-available at the IDontKerr (IDK) laboratory (MagneDyn beamline support laboratory) to produce pump laser pulses at 400 nm, of ~100 fs and with a repetition rate from 1kHz to single shot.

>Read more on the Elettra Sincrotrone Trieste website

Image (extract): Trasmission Electron Microscopy image of the nanoparticles sample. Ultafast single-shot optical process with fs-pulse at 400 nm. Microscope images of amorphized and amorphized/ablated areas obtained on the nanoparticles sample. Comparison of amorphization threshold fluences between thin films and nanoparticles cases.
Please see here the entire image.

Pressure tuning of light-induced superconductivity in K3C60

Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological application is hindered by their low operating temperature, which in the best case can reach -70 degrees Celsius. Researchers of the group of Prof. A. Cavalleri at the Max Planck Institute of the Structure and Dynamics of Matter (MPSD) in Hamburg have routinely used intense laser pulses to stimulate different classes of superconducting materials. Under specific conditions, they have detected evidences of superconductivity at unprecedented high temperatures, although this state persisted very shortly, just for a small fraction of a second.
An important example is that of K3C60, an organic molecular solidformed by weakly-interacting C60 “buckyball” molecules (60 carbon atoms bond in the shape of a football),which is superconducting at equilibrium below a critical temperature of -250 degrees Celsius. In 2016, Mitrano and coworkers at the MPSD discovered that tailored laserpulses, tuned to induce vibrations of the C60 molecules,can induce a short-lived, highly conducting state with properties identical to those of a superconductor, up to a temperature of at least -170 degrees Celsius, far higher than the equilibrium critical temperature (Mitrano et al., Nature, 530, 461–464 (2016)).

In their most recent investigation, A. Cantaluppi, M. Buzzi and colleagues at MPSD in Hamburg went a decisive step further by monitoring the evolution of the light-induced state in K3C60 once external pressure was applied by a diamond anvil cell (Figure 1). At equilibrium, when pressure is applied, the C60 molecules in the potassium-doped fulleride are held closer to each other. This weakens the equilibrium superconducting state and significantly reduces the critical temperature. The steady state optical response of K3C60 at different pressures and temperatures was determined via Fourier-transform infrared spectroscopy, by exploiting the high brightness of the synchrotron radiation available at the infrared beamline SISSI at Elettra.

>Read more on the Elettra website

Image:   Light-induced superconductivity in K3C60 was investigated at high pressure in a Diamond Anvil Cell.
Credit:
Jörg Harms / MPSD

An electrifying view on catalysis

The future of chemistry is ‘electrifying’: With increasing availability of cheap electrical energy from renewables, it will soon become possible to drive many chemical processes by electrical power. In this way, chemical products and fuels can be produced via sustainable routes, replacing current processes which are based on fossil fuels.

In most cases, such electrically driven reactions make use of so-called electrocatalysts, complex materials which are assembled from a large number of chemical componentAs. The electrocatalyst plays an essential role: It helps to run the chemical reaction while keeping the loss of energy minimal, thereby saving as much renewable energy as possible. In most cases, electrocatalysts are developed empirically and the chemical reactions at their interfaces are poorly understood. A better understanding of these processes is essential, however, for fast development of new electrocatalysts and for a directed improvement of their lifetime, one of the most important factors that currently limit their applicability.

>Read more on the Elettra website

Figure:  Introducing well-defined model electrocatalysts into the field of electrochemistry.

Megachirella -the mother of all lizards

A new international research rewrites the history of reptiles starting from a fossil found in the Dolomites.

The origin of lizards and snakes should be pushed back by about 75 million years, as documented by a small reptile, Megachirella wachtleri, found almost 20 years ago in the Dolomites and rediscovered today thanks to cutting-edge techniques in the field of 3D analysis and the reconstruction of evolutionary relationships. Evidence to this effect has been provided by an international paleontological research with the participation of the MUSE Science Museum of Trento, in collaboration with the “Abdus Salam” International Centre of Theoretical Physics of Trieste, the Enrico Fermi Centre of Rome and Elettra Sincrotrone Trieste. The results have been published in the prestigious science journal Nature, which has also dedicated its cover image to research.

The international team has identified Megachirella wachtleri – a small reptile which lived approximately 240 million years ago in what are today the Dolomites – the most ancient lizard in the world thereby providing key insight into the evolution of modern lizards and snakes.
The data – obtained by 3D X-ray imaging techniques and the analysis of DNA sequences – suggest that the origin of “squamates”, i.e. the group comprising lizards and snakes,is older than previously thought and that it can be dated to approximately 250 million years ago, before the most extensive mass extinction in history.

>Read more on the Elettra Sincrotrone Trieste website
>Watch here a video about the scientific discovery

Image: Megachirellawandering amidst the lush vegetation that approximately 240 million years ago surrounded the dolomitic beaches.
Credit: Davide Bonadonna

 

Tailoring the surface chemical reactivity of transition‐metal dichalcogenide PtTe2 crystals

Recently, the PtX2 (X=S, Se, Te) class of transition-metal dichalcogenides has emerged as one of the most promising among layered materials “beyond graphene” for the presence of high room-temperature electron mobility and, moreover, bulk type-II Dirac fermions, arising from a tilted Dirac cone.
Information on the ambient stability of PtTe2 is a crucial step in order to evaluate the feasibility of its exploitation in technology. Moreover, the possibility to tune surface chemical reactivity by appropriate surface modification is an essential step for its employment for diverse applications, especially in catalysis.
By means of experiments with several surface-science spectroscopies and density functional theory, an international team of researchers from Italy, Republic of Korea, and Taiwan (coordinated by Graphene Labs of Istituto Italiano di Tecnologia) has investigated the reactivity of the PtTe2 surface toward most common ambient gases (oxygen and water), under the framework of the European Graphene Flagship-Core1 project.
To assess the surface chemical reactivity of PtTe2, X-ray photoelectron spectroscopy (XPS) carried out at the APE-HE beamline has been combined with high-resolution electron energy loss (HREELS) experiments and with density functional theory.
From the analysis of Te 3d core-level spectra in XPS and from the featureless vibrational spectrum in HREELS, it has been demonstrated that as-cleaved defect-free PtTe2 surface is inert toward most common ambient gases (oxygen and water).
In the evaluation of the ambient stability of PtTe2, the possible influence of Te vacancies on surface chemical reactivity deserves particular attention. As a matter of fact, Te vacancies may appear on non-stoichiometric samples during the growth process. To check the influence of Te vacancies on ambient stability of PtTe2, Te vacancies have been intentionally introduced in stoichiometric PtTe2 samples by Ar-ion sputtering. After exposing to O2 the PtTe2 surface defected by ion sputtering, with a Pt:Te ratio of 39:61, spectral features related to Te(IV) species appear, arising from the formation of Te=O bonds in a tellurium-oxide phase. The Te(IV) components are the most intense lines in the Te 3d XPS spectra for the case of air-exposed defected samples (see Figure 1). Concerning reactivity to water, it adsorbs molecularly even at room temperature on defected PtTe2. These findings also imply that the presence of Te vacancies is able to jeopardize the ambient stability of uncapped PtTe2-based devices, with a subsequent necessity to reduce the amount of Te vacancies for a successful technological exploitation of PtTe2.

>Read more on the Elettra website

Figure: XPS spectra of Te-3d core levels acquired for: defected PtTe2 (green curve), the same surface exposed to 106 L of O2 (black curve) and air-exposed defected PtTe2 (yellow curve). The photon energy is 745 eV. 

LEAPS and FELs of Europe meetings at Elettra

On March 12-13 Elettra-Sincrotrone Trieste hosted the 2nd meeting of General Assembly (GA) of the League of European Accelerator-based Photon Sources (LEAPS), a strategic consortium that includes 16 Synchrotron Radiation and Free Electron Laser (FEL) user facilities in Europe based in 10 different European countries .
This followed the LEAPS Launch Event in Brussels on November 13, 2017. The main topics of the GA meeting were the LEAPS Governance Structure and the LEAPS Strategy Paper to be forwarded to the EU Commission during the Bulgarian Presidency Conference on Research Infrastructures in Sofia, 22-23 March.

>Read more on the Elettra and FERMI website

Image: LEAPS General Assembly and Coordination Board group picture.
Credit: Fotorolli

Functionalized graphdiyne nanowires

… on-surface synthesis and assessment of band structure, flexibility, and information storage potential

With their extraordinary mechanical and electronic properties carbon-based nanomaterials are central in 21st century research and carry high hopes for future nanotechnology applications. Established sp2-hybridized scaffolds include carbon nanotubes (CNTs), graphene sheets, and graphene nanoribbons. Recently, the interest in carbon allotropes incorporating both sp2and sp-hybridized atoms rose tremendously, especially for the most popular member, the so-called graphdiyne. According to theory, the related nanomaterials possess characteristics desirable for applications such as molecular electronics, energy storage, gas filtering and light harvesting. However, achieving the targeted materials with high quality remained challenging until now.
Here, we employed covalent on-surface synthesis on well-defined metal substrates under ultra-high vacuum (UHV) conditions to the homocoupling reaction of terminal alkyne compounds and fabricated the first functionalized graphdiyne (f-GDY) nanowires. Combining the substrate templating of the Ag(455) vicinal surface with specifically designed CN-functionalized precursors we achieved the controlled polymerization to atom-precise strands with their length reaching 40 nm. The left panel of Figure 1a depicts a scanning tunneling microscopy (STM) image of an area of the silver surface featuring two step edges where an example of such a f-GDY wire is lying at the lower side of the right step edge. The right panel displays a molecular model of the situation highlighting the structure of the nanowire adsorbed in the lower terrace (darker blue) consisting of covalently coupled monomers (red outline) with the CN moieties pointing towards the atoms of the upper terrace (brighter blue).

>Read more on the Elettra Sincrotrone website

Figure: (extract)  Synthesis and characterization of functionalized graphdiyne nanowires. a) STM topograph of a f-GDY polymer covering the left step edge. b) ARPES data: Before annealing a non-dispersing feature originates from the HOMO of the monomer. After annealing a dispersing features (blue) can be identified. c) Schematic representation of the deduced intrinsic band structure of the f-GDY nanowires. d) STM topograph of a strongly bent nanowire. e) Information storage thru conformational cis-trans switching of benzonitrile units. Full image here.