Surface nano-patterning through styrene adsorption on Si(100)

We present an ab initio study of the structural and electronic properties of styrene molecules adsorbed on the dimerized Si(100) surface at different coverages, ranging from the single-molecule to the full monolayer. The adsorption mechanism primarily involves the vinyl group via a [2+2] cycloaddition process that leads to the formation of covalent Si-C bonds and a local surface derelaxation, while it leaves the phenyl group almost unperturbed. The investigation of the functionalized surface as a function of the coverage (e.g. 0.5 -- 1 ML) and of the substrate reconstruction reveals two major effects. The first results from Si dimer-vinyl interaction and concerns the controlled variation of the energy bandgap of the interface. The second is associated to phenyl-phenyl interactions, which gives rise to a regular pattern of electronic wires at surface, stemming from the pi-pi coupling. These findings suggest a rationale for tailoring the surface nano-patterning of the surface, in a controlled way.Comment: 19 pages (preprint), 4 figures, supplementary materia

Exciton binding energies in carbon nanotubes from two-photon photoluminescence

One- and two-photon luminescence excitation spectroscopy showed a series of distinct excitonic states in single-walled carbon nanotubes. The energy splitting between one- and two-photon-active exciton states of different wavefunction symmetry is the fingerprint of excitonic interactions in carbon nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are supported by ab-initio calculations of the linear and non-linear optical spectra, prove that the elementary optical excitations of carbon nanotubes are strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole pairs, stable even at room temperature. This alters our microscopic understanding of both the electronic structure and the Coulomb interactions in carbon nanotubes, and has direct impact on the optical and transport properties of novel nanotube devices.Comment: 5 pages, 4 figure

The effects of interface morphology on Schottky barrier heights: a case study on Al/GaAs(001)

The problem of Fermi-level pinning at semiconductor-metal contacts is readdressed starting from first-principles calculations for Al/GaAs. We give quantitative evidence that the Schottky barrier height is very little affected by any structural distortions on the metal side---including elongations of the metal-semiconductor bond (i.e. interface strain)---whereas it strongly depends on the interface structure on the semiconductor side. A rationale for these findings is given in terms of the interface dipole generated by the ionic effective charges.Comment: 5 pages, latex file, 2 postscript figures automatically include

Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions

We investigate the optical properties of edge-functionalized graphene nanosystems, focusing on the formation of junctions and charge transfer excitons. We consider a class of graphene structures which combine the main electronic features of graphene with the wide tunability of large polycyclic aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we show that, upon convenient choice of functional groups, low energy excitations with remarkable charge transfer character and large oscillator strength are obtained. These properties can be further modulated through an appropriate width variation, thus spanning a wide range in the low-energy region of the UV-Vis spectra. Our results are relevant in view of designing all-graphene optoelectronic nanodevices, which take advantage of the versatility of molecular functionalization, together with the stability and the electronic properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres

Writing Technique Across Psychotherapies—From Traditional Expressive Writing to New Positive Psychology Interventions: A Narrative Review

Writing Therapy (WT) is defined as a process of investigation about personal thoughts and feelings using the act of writing as an instrument, with the aim of promoting self-healing and personal growth. WT has been integrated in specific psychotherapies with the aim of treating specific mental disorders (PTSD, depression, etc.). More recently, WT has been included in several Positive Interventions (PI) as a useful tool to promote psychological well-being. This narrative review was conducted by searching on scientific databases and analyzing essential studies, academic books and journal articles where writing therapy was applied. The aim of this review is to describe and summarize the use of WT across various psychotherapies, from the traditional applications as expressive writing, or guided autobiography, to the phenomenological-existential approach (Logotherapy) and, more recently, to the use of WT within Acceptance and Commitment Therapy (ACT). Finally, the novel applications of writing techniques from a positive psychology perspective will be analyzed. Accordingly, the applications of WT for promoting forgiveness, gratitude, wisdom and other positive dimensions will be illustrated. The results of this review show that WT yield therapeutic effects on symptoms and distress, but it also promotes psychological well-being. The use of writing can be a standalone treatment or it can be easily integrated as supplement in other therapeutic approaches. This review might help clinician and counsellors to apply the simple instrument of writing to promote insight, healing and well-being in clients, according to their specific clinical needs and therapeutic goals

Designing all-graphene nanojunctions by covalent functionalization

We investigated theoretically the effect of covalent edge functionalization, with organic functional groups, on the electronic properties of graphene nanostructures and nano-junctions. Our analysis shows that functionalization can be designed to tune electron affinities and ionization potentials of graphene flakes, and to control the energy alignment of frontier orbitals in nanometer-wide graphene junctions. The stability of the proposed mechanism is discussed with respect to the functional groups, their number as well as the width of graphene nanostructures. The results of our work indicate that different level alignments can be obtained and engineered in order to realize stable all-graphene nanodevices

Raman Fingerprints of Atomically Precise Graphene Nanoribbons.

Bottom-up approaches allow the production of ultranarrow and atomically precise graphene nanoribbons (GNRs) with electronic and optical properties controlled by the specific atomic structure. Combining Raman spectroscopy and ab initio simulations, we show that GNR width, edge geometry, and functional groups all influence their Raman spectra. The low-energy spectral region below 1000 cm(-1) is particularly sensitive to edge morphology and functionalization, while the D peak dispersion can be used to uniquely fingerprint the presence of GNRs and differentiates them from other sp(2) carbon nanostructures.We acknowledge funding from: the Alexander von Humboldt Foundation in the framework of the Sofja Kovalevskaja Award, endowed by the Federal Ministry for Education and Research of Germany; the ESF project GOSPEL (Ref. No. 09-EuroGRAPHENE-FP-001); the European Research Council (grant NOC-2D, NANOGRAPH, and Hetero2D); the Italian Ministry of Research through the national projects PRIN-GRAF (Grant No. 20105ZZTSE) and FIRB-FLASHit (Grant No. RBFR12SWOJ); the DFG Priority Program SPP 1459; the Graphene Flagship (Ref. No. CNECT-ICT-604391); the EU project MoQuaS; EPSRC Grants (EP/K01711X/1, EP/K017144/1); the EU grant GENIUS; a Royal Society Wolfson Research Merit Award. Computer time was granted by PRACE at the CINECA Supercomputing Center (Grant No. PRA06 1348), and by the Center for Functional Nanomaterials at Brookhaven National Laboratory, supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract number DE-SC0012704.This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/acs.nanolett.5b0418

Optical Excitations and Field Enhancement in Short Graphene Nanoribbons

The optical excitations of elongated graphene nanoflakes of finite length are investigated theoretically through quantum chemistry semi-empirical approaches. The spectra and the resulting dipole fields are analyzed, accounting in full atomistic details for quantum confinement effects, which are crucial in the nanoscale regime. We find that the optical spectra of these nanostructures are dominated at low energy by excitations with strong intensity, comprised of characteristic coherent combinations of a few single-particle transitions with comparable weight. They give rise to stationary collective oscillations of the photoexcited carrier density extending throughout the flake, and to a strong dipole and field enhancement. This behavior is robust with respect to width and length variations, thus ensuring tunability in a large frequency range. The implications for nanoantennas and other nanoplasmonic applications are discussed for realistic geometries

Schottky barrier heights at polar metal/semiconductor interfaces

Using a first-principle pseudopotential approach, we have investigated the Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100) junctions, and their dependence on the semiconductor chemical composition and surface termination. A model based on linear-response theory is developed, which provides a simple, yet accurate description of the barrier-height variations with the chemical composition of the semiconductor. The larger barrier values found for the anion- than for the cation-terminated surfaces are explained in terms of the screened charge of the polar semiconductor surface and its image charge at the metal surface. Atomic scale computations show how the classical image charge concept, valid for charges placed at large distances from the metal, extends to distances shorter than the decay length of the metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure

Effectiveness of Home_Positivity: A VR Program for Promoting Positive Mental Health. A Pilot Feasibility Study

Virtual reality (VR) has been recently used for the treatment of mental health conditions. While research shows symptom reduction, further investigation is required to ascertain the impact of VR on well-being indicators. This pilot study aims to assess the effectiveness of a new VR software, H.O.M.E (How to Observe and Modify Emotion)_Positivity, in promoting positive mental health, which implies addressing both psychological distress and well-being. A sample of 16 healthy college students participated in a six-session intervention involving individual interviews and VR experiences using H.O.M.E delivered at the university of Bologna. They were assessed before and after intervention and at 3-month follow-up with indicators of negative symptoms (i.e., Depression Anxiety Stress Scales (DASS) and the Negative affect scale of (PANAS) and of well-being (i.e., Mental Health Continuum (MHC) and the Positive Affect (PA) subscale of the PANAS. Moreover, they were asked to report their satisfaction and comments on the experience of the VR software. Following the intervention, participants reported significantly lower scores at DASS and higher scores at MHC and PA. In contrast, NA subscale score did not change significantly after the intervention or at three months follow-up. The results provide support to the use of H.O.M.E_Positivity for the promotion of positive mental health. Participants reported a reduction of psychological distress and improvement in well-being, and they were all highly satisfied and engaged while using the VR software. These findings indicate the potential value of this intervention, particularly in an increasingly digital society