Mechanically robust 39 GHz cut-off frequency graphene field effect transistors on flexible substrates.

Graphene has been regarded as a promising candidate channel material for flexible devices operating at radio-frequency (RF). In this work we fabricated and fully characterized double bottom-gate graphene field effect transistors on flexible polymer substrates for high frequency applications. We report a record high as-measured current gain cut-off frequency (ft) of 39 GHz. The corresponding maximum oscillation frequency (fmax) is 13.5 GHz. These state of the art high frequency performances are stable against bending, with a typical variation of around 10%, for a bending radius of up to 12 mm. To demonstrate the reliability of our devices, we performed a fatigue stress test for RF-GFETs which were dynamically bend tested 1000 times at 1 Hz. The devices are mechanically robust, and performances are stable with typical variations of 15%. Finally we investigate thermal dissipation, which is a critical parameter for flexible electronics. We show that at the optimum polarization the normalized power dissipated by the GFETs is about 0.35 mW µm(-2) and that the substrate temperature is around 200 degree centigrade. At a higher power, irreversible degradations of the performances are observed. Our study on state of the art flexible GFETs demonstrates mechanical robustness and stability upon heating, two important elements to assess the potential of GFETs for flexible electronics.

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems.

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Code interoperability and standard data formats in quantum chemistry and quantum dynamics: The Q5/D5Cost data model.

Code interoperability and the search for domain-specific standard data formats represent critical issues in many areas of computational science. The advent of novel computing infrastructures such as computational grids and clouds make these issues even more urgent. The design and implementation of a common data format for quantum chemistry (QC) and quantum dynamics (QD) computer programs is discussed with reference to the research performed in the course of two Collaboration in Science and Technology Actions. The specific data models adopted, Q5Cost and D5Cost, are shown to work for a number of interoperating codes, regardless of the type and amount of information (small or large datasets) to be exchanged. The codes are either interfaced directly, or transfer data by means of wrappers; both types of data exchange are supported by the Q5/D5Cost library. Further, the exchange of data between QC and QD codes is addressed. As a proof of concept, the H + H2 reaction is discussed. The proposed scheme is shown to provide an excellent basis for cooperative code development, even across domain boundaries. Moreover, the scheme presented is found to be useful also as a production tool in the grid distributed computing environment.

Ultrafast graphene oxide humidity sensors.

Sensors allow an electronic device to become a gateway between the digital and physical worlds, and sensor materials with unprecedented performance can create new applications and new avenues for user interaction. Graphene oxide can be exploited in humidity and temperature sensors with a number of convenient features such as flexibility, transparency and suitability for large-scale manufacturing. Here we show that the two-dimensional nature of graphene oxide and its superpermeability to water combine to enable humidity sensors with unprecedented response speed (∼30 ms response and recovery times). This opens the door to various applications, such as touchless user interfaces, which we demonstrate with a 'whistling' recognition analysis.

Huge (but finite) time scales in slow relaxations: beyond simple aging.

Experiments performed in the last years demonstrated slow relaxations and aging in the conductance of a large variety of materials. Here, we present experimental and theoretical results for conductance relaxation and aging for the case-study example of porous silicon. The relaxations are experimentally observed even at room temperature over time scales of hours, and when a strong electric field is applied for a time tw, the ensuing relaxation depends on tw. We derive a theoretical curve and show that all experimental data collapse onto it with a single time scale as a fitting parameter. This time scale is found to be of the order of thousands of seconds at room temperature. The generic theory suggested is not fine-tuned to porous silicon, and thus we believe the results should be universal, and the presented method should be applicable for many other systems manifesting memory and other glassy effects.

Structural features analysis and nonlinearity of end-cap-substituted polyacetylenes.

As part of a systematic study of the impact of donor-acceptor substitution on the structure and properties of pi-conjugated compounds, we present a theoretical investigation of the all-trans polyacetylene backbone, end-capped with moieties of different donor or acceptor natures and different strengths, focusing on the effects induced by these substituents on bond lengths and shape of the conjugated chain. Optimized geometries for polyacetylene containing 15 and 20 double bonds have been computed by means of density functional theory with the Coulomb-attenuating B3LYP (CAM-B3LYP) functional. We show that the simultaneous presence of two substituents has a cooperative effect on the lengths of single and double bonds. We also show that, depending on the substitution pattern, distortion toward bow- or S-shaped structures occurs. Two new geometric parameters are defined in order to evaluate the mode and intensity of this distortion. Cubic Bezier curves have been used as simple geometric models for the chain bending behavior.

A systematic analysis of the structure and (hyper)polarizability of donor-acceptor substituted polyacetylenes using a Coulomb-attenuating density functional.

In this paper we perform a systematic investigation on all-trans polyacetylene chains of different lengths, end-capped with moieties of different donor or acceptor natures and different strengths, to infer useful structure/property relationship rules and behavioral patterns. The values for bond length alternation (BLA), longitudinal polarizability, and first and second hyperpolarizabilities have been computed with the Coulomb-attenuating density function (CAM-B3LYP), using response theory. A comparison of the relative effect that each end-capping combination contributes to BLA, linear, and nonlinear optical coefficients has been performed. This results in useful insights and general rules to ad hoc tailoring the molecular response for a specific characteristic.

Experimental observation of glassy dynamics driven by gas adsorption on porous silicon.

We report on electrical resistance measurements of mesoporous silicon samples at room temperature, in the presence of various dosages of ammonia, showing very slow non-exponential responses of the system to any variation of ammonia pressure. Resistance always relaxes according to a stretched exponential law, independently of the sign of the variation. Moreover, the system remembers its own history, and memory effects can be accounted for in a very simple way in the framework of the same relaxation law. A possible extrinsic scenario based on rearrangement of trapped charges is proposed and discussed. These findings suggest that mesoporous silicon in the presence of polar molecules may be regarded as a suitable system for the study of glassy dynamics by means of electrical measurements at RT.

Advanced nanotechnological approaches for designing protein-based "lab-on-chips" sensors on porous silicon wafer.

In this article, we will review the more recent patented approaches related to the design and development of micro- and nano-patterns of biomolecules on solid substrates for the realization of innovative biochips, including inkjet and spotting technology, and Scanning Probe Methods In addition, we will report on some important patents based on the use of porous materials as substrates, exploiting the large specific surface for the design of highly sensitive biodevices. The main advantages and drawbacks related to each technological approach to the biochips fabrication will be pointed out, and future perspectives in the field will be discussed.

The Effect of the Basis-Set Superposition Error on the Calculation of Dispersion Interactions: A Test Study on the Neon Dimer.

The dispersion interactions of the Ne2 dimer were studied using both the long-range perturbative and supramolecular approaches: for the long-range approach, full CI or string-truncated CI methods were used, while for the supramolecular treatments, the energy curves were computed by using configuration interaction with single and double excitation (CISD), coupled cluster with single and double excitation, and coupled-cluster with single and double (and perturbative) triple excitations. From the interatomic potential-energy curves obtained by the supramolecular approach, the C6 and C8 dispersion coefficients were computed via an interpolation scheme, and they were compared with the corresponding values obtained within the long-range perturbative treatment. We found that the lack of size consistency of the CISD approach makes this method completely useless to compute dispersion coefficients even when the effect of the basis-set superposition error on the dimer curves is considered. The largest full-CI space we were able to use contains more than 1 billion symmetry-adapted Slater determinants, and it is, to our knowledge, the largest calculation of second-order properties ever done at the full-CI level so far. Finally, a new data format and libraries (Q5Cost) have been used in order to interface different codes used in the present study.

Writing 3D protein nanopatterns onto a silicon nanosponge.

A three-dimensional protein nanopatterning method has been developed, based on local activation of porous silicon by electron beam. Proteins specifically bind to irradiated regions, and the depth of biomolecule nanopatterns can be controlled by varying the electron energy. This unique feature permits exploitation of the huge surface area of the sponge-like material, thus allowing concentration of a large amount of proteins on nanosized patterns. Moreover, the grafted biomolecules retain their full functionality, and the feasibility of a glucose sensor has been demonstrated.

A combined freeze-and-cut strategy for the description of large molecular systems using a localized orbitals approach.

A technique to reduce the computational effort in calculating ab initio energies using a localized orbitals approach is presented. By exploiting freeze strategy at the self-consistent field (SCF) level and a cut of the unneeded atomic orbitals, it is possible to perform a localized complete active space (CAS-SCF) calculation on a reduced system. This will open the possibility to perform ab initio treatments on very large molecular systems, provided that the chemically important phenomena happen in a localized zone of the molecule. Two test cases are discussed, to illustrate the performance of the method: the cis-trans interconversion curves for the (7Z)-13 ammoniotridec-7-enoate, which demonstrates the ability of the method to reproduce the interactions between charged groups; and the cisoid-transoid energy barrier for the aldehydic group in the C13 polyenal molecule.

Ab initio n-electron valence state perturbation theory study of the adiabatic transitions in carbonyl molecules: formaldehyde, acetaldehyde, and acetone.

The application of the recently developed second-order n-electron valence state perturbation theory (NEVPT2) to small carbonyl molecules (formaldehyde, acetaldehyde, and acetone) is presented. The adiabatic transition energies are computed for the singlet and triplet n-->pi(*), pi-->pi(*), and sigma-->pi(*) states performing a full geometry optimization of the relevant states at the single state CASSCF level and taking into account the zero point energy correction in the harmonic approximation. The agreement with the known experimental values and with previously published high level calculations confirms that NEVPT2 is an efficient tool to be used for the interpretation of molecular electronic spectra. Moreover, different insight into the nature of the excited states has been obtained. Some of the transitions presented here have never been theoretically computed previously [(3)(pi-->pi(*)) and (3)(sigma-->pi(*)) adiabatic transitions in acetaldehyde and acetone] or have been studied only using moderate level (single reference based) ab initio methods (all adiabatic transitions in acetaldehyde). In the present work a consistent disagreement between NEVPT2 and experiment has been found for the (3)(pi-->pi(*)) adiabatic transition in all molecules: this result is attributed to the low intensity of the transition to the first vibrational levels of the excited state. The n-->pi(*) singlet and triplet vertical transition energies are also reported for all the molecules.

A quasidegenerate formulation of the second order n-electron valence state perturbation theory approach.

The n-electron valence state perturbation theory (NEVPT) is reformulated in a quasidegenerate (QD) approach. The new theory allows the treatment of cases where the proximity of the energies causes artifacts in the zero order description. Problems of quasidegeneration are relevant in the dynamics involving regions at avoided crossings (or conical intersections) and in spectroscopy where the energies and oscillator strengths can be strongly influenced by the mixing of states of different nature. Two test cases are analyzed concerning (a) the ionic-neutral avoided crossing in LiF and (b) the valence/Rydberg mixing in the excited states of ethene. The QD-NEVPT2 is shown to be a useful tool for such systems.