Direct observation of a gate tunable band-gap in electrical transport in ABC-trilayer graphene

Few layer graphene systems such as Bernal stacked bilayer and rhombohedral (ABC-) stacked trilayer offer the unique possibility to open an electric field tunable energy gap. To date, this energy gap has been experimentally confirmed in optical spectroscopy. Here we report the first direct observation of the electric field tunable energy gap in electronic transport experiments on doubly gated suspended ABC-trilayer graphene. From a systematic study of the non-linearities in current \textit{versus} voltage characteristics and the temperature dependence of the conductivity we demonstrate that thermally activated transport over the energy-gap dominates the electrical response of these transistors. The estimated values for energy gap from the temperature dependence and from the current voltage characteristics follow the theoretically expected electric field dependence with critical exponent $3/2$. These experiments indicate that high quality few-layer graphene are suitable candidates for exploring novel tunable THz light sources and detectors.Comment: Nano Letters, 2015 just accepted, DOI: 10.1021/acs.nanolett.5b0077

Phase transitions and phase diagram of the ferroelectric perovskite NBT-BT by anelastic and dielectric measurements

The complex elastic compliance and dielectric susceptibility of (Na_{0.5}Bi_{0.5})_{1-x}Ba_{x}TiO_{3} (NBT-BT) have been measured in the composition range between pure NBT and the morphotropic phase boundary included, 0 <= x <= 0.08. The compliance of NBT presents sharp peaks at the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the tetragonal region of the phase diagram, up to now impossible due to the strong lattice disorder and small distortions and polarizations involved. In spite of ample evidence of disorder and structural heterogeneity, the R-T transition remains sharp up to x = 0.06, whereas the T-C transition merges into the diffuse and relaxor-like transition associated with broad maxima of the dielectric and elastic susceptibilities. An attempt is made at relating the different features in the anelastic and dielectric curves to different modes of octahedral rotations and polar cation shifts. The possibility is also considered that the cation displacements locally have monoclinic symmetry, as for PZT near the morphotropic phase boundary.Comment: 11 pages, 9 figures, submitted to Phys. Rev.

Magneto-transport through graphene nano-ribbons

We investigate magneto-transport through graphene nano-ribbons as a function of gate and bias voltage, and temperature. We find that a magnetic field systematically leads to an increase of the conductance on a scale of a few tesla. This phenomenon is accompanied by a decrease in the energy scales associated to charging effects, and to hopping processes probed by temperature-dependent measurements. All the observations can be interpreted consistently in terms of strong-localization effects caused by the large disorder present, and exclude that the insulating state observed in nano-ribbons can be explained solely in terms of a true gap between valence and conduction band.Comment: 4 pages, 5 figure

Functionalised hexagonal-domain graphene for position-sensitive photodetectors

LetterThis is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.Graphene's unique photoresponse has been largely used in a multitude of optoelectronics applications ranging from broadband photodetectors to wave-guide modulators. In this work we extend the range of applications to position-sensitive photodetectors (PSDs) using FeCl3-intercalated hexagonal domains of graphene grown by atmospheric pressure chemical vapour deposition (APCVD). The FeCl3-based chemical functionalisation of APCVD graphene crystals is affected by the presence of wrinkles and results in a non-uniform doping of the graphene layers. This doping profile creates multiple p–p+ photoactive junctions which show a linear and bipolar photoresponse with respect to the position of a focused light spot, which is ideal for the realization of a PSD. Our study paves the way towards the fabrication of flexible and transparent PSDs that could be embedded in smart textile and wearable electronics.S Russo and M F Craciun acknowledge financial support from EPSRC (Grant no. EP/J000396/1, EP/K017160/1, EP/K010050/1, EPG036101/1, EP/M001024/1, EPM002438/1), from Royal Society international Exchanges Scheme 2016/R1, from European Commission (FP7-ICT-2013-613024-GRASP) and from the Leverhulme Trust (grant title 'Quantum Drums' and 'Room temperature quantum electronics'). I Amit received funding from the People Programme (Marie Curie Actions) of the European Union's Eighth Framework Programme Horizon 2020 under REA grant agreement number 701704

Acute mesenterial ischemia: optimal diagnosis and treatment modality

Al XI-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” din Republica Moldova și cea de-a XXXIII-a Reuniune a Chirurgilor din Moldova „Iacomi-Răzeșu” 27-30 septembrie 2011Introducere: La momentul actual nu există criterii şi principii desăvârşite pentru diagnosticarea şi tratamentul ischemiei mezenteriale acute bazate pe probe controlate ştiințific, iar rezultatele tratamentului acestor pacienți este nesatisfăcător. Rata mortalității la acest grup de pacienți variază de la 70-90%. Scopul: aprecierea rezultatelor inițiale de diagnostic şi tratament al ischemiei mezenteriale acute. Material şi Metodă: În perioada ianuarie 2009 mai 2011 au fost 29 cazuri consecutive de ischemie mezenterială acută. Vârsta medie a fost 70.3±2.4(35-95) ani, pacienții fiind internați la 37.1±8.1 (1-168) ore de la debutul bolii, scorul APACHE fiind de 24.79±1.9, scorul ASA - 3.32±0.1, scorul POSSUM - 37.45±1.9. Diagnoza a fost stabilit prin aprecierea: leucocitelor, lactatului seric, procalcitoninei, 3D-CT-angiogrfie si laparoscopie. Pacienții au fost tratați conform principiului ”second look” (n=21), anastomozei primare (n=2), laparatomii exploratorii (n=6). Ischemie mezenterială venoasă 5 cazuri și aretrială 24 cazuri Rezultate: Media leucocitelor la internare a fost de 17.88±1.7x109/L, media nesegmentatelor-29.0±4.2%, media lactatului seric 2.56±0.5mmol/L, la 8 pacienți testul PCT-Q a fost ≥10ng/ml, media glucozei sangvine la internare 11.3±1.2 mmol/L, la 21 de pacienți ea fiind mai mare de 6 mmol/L. Mortalitatea postoperatorie a fost 68.9% (n=20). Concluzie: Experiența inițială demonstrează că principiile anastomozei amânate, anastomozei primare pot fi considerate ca opțiuni chirurgicale pentru tratamentul pacienților cu ischemie mezenterială acută. Însă concluziile definitive privind momentul aplicării lor, vor fi formulate după analiza unui lot mai mare de pacienti.Introduction: Up to date there are no widely accepted evidence based principles for the diagnosis and treatment of acute mesenterial ischemia and the treatment outcomes are poor. The death rate in this group of patients varies between 70 and 90 %. Aim: to appreciate the initial diagnostic and treatment results of acute mesenterial ischemia. Material and methods: During January 2009 – May 2011 29 consecutive patients with mesenterial ischemia. The mean age was 70.3±2.4 (35-95) years, the mean time from onset to hospitalization was 37.1±8.1 (1-168) hours, the mean APACHE score was 24.79±1.9, ASA score – 3.32±0.1, POSSUM score was – 37.45±1.9. The diagnosis was established upon WBC, blood lactate level, procalcitonine, 3D-CT angiography and laparoscopy. The patients were treated using the “second look” principle (n=21), resection and primary anastomosis (n=2), diagnostic laparotomy (n=6). Venous and arterial mesenterial ischemia was diagnosed in 5 and 24 patients respectively. Results: The mean WBC upon admittance was 17.88±1.7x109/L, mean nonsegmented WBC was 29.0±4.2%, mean value of blood lactate level was 2.56±0.5mmol/L. In 8 patients the PCT-Q test was ≥10ng/ml, mean glucose level was 11.3±1.2 mmol/L and in 6 patients it was over 6 mmol/L. The postoperative death rate was 68.9% (n=20). Conclusions: The initial experience favors the “second look” principle and resection with primary anastomosis for the treatment of acute mesentery ischemia. Larger patients’ series are necessary in order to drag definitive conclusions regarding the optimal time for anastomosis

Surgical treatment of acute mesenteric ischemia

Introduction: Acute mesenteric ischemia (AMI) is an abdominal catastrophe. Advanced age and diagnosis delay are associated with increased morbidity and mortality rates. The optimal surgical strategy for AMI is under evaluation. Aim: To evaluate the early results of different treatment strategies for AMI. Material and methods: During last three years a total of 35 consecutive pts with AMI were admitted to our unit. The mean (±SD) time interval between AMI symptoms onset and admission was 34.7±2.1 h. Physiological parameters (mean±SD) of pts were: ASA score - 3.3±0.1, APACHE score - 25.2±1.6 and POSSUM - 36.9±1.8. In most cases AMI was induced by superior mesenteric artery (SMA) embolism (54.3%, n = 19) followed by SMA thrombosis (25.7%, n= 9) and venous thrombosis (VT) (20%, n=7). Results: The affected bowel segments were: small intestine (n=16), small intestine + colon (n=13) and total ischemia (n=6). Surgical procedures were as follows: small intestine resection (n=14) with SMA embolectomy (n=2), small intestine + right colon (n=12) and small intestine + subtotal colectomy (n=l). In two cases of VT affected intestinal segments were not resected, instead anticoagulation treatment was initiated and the intestinal viability was confirmed by second-look laparotomy. Explorative laparotomy was used only in advanced intestinal gangrene (n=6). Twenty five pts with massive injury were scheduled for staged damage control approach (immediate resection of the involved bowel without gastrointestinal continuity reconstruction, patients’ resuscitation in ICU) combined with Negative Pressure Wound Therapy (V.A.C., KCI or homemade) and later on definitive reconstructive procedure (delayed anastomosis). Primary anastomoses were performed only in 2 pts with short segmental intestinal infarction. The overall 30-days mortality rate was 24/35, 68.5% (in non-total AMI - 18/29, 62%, in VT zero). Conclusions: Early diagnosis and prompt surgery improves the AMI outcome. Colon involved in AMI is a poor prognosis sign. Damage control approach improves the AMI patients’ survival

Large scale flood risk mapping in data scarce environments: An application for Romania

Large-scale flood risk assessment is essential in supporting national and global policies, emergency operations and land-use management. The present study proposes a cost-efficient method for the large-scale mapping of direct economic flood damage in data-scarce environments. The proposed framework consists of three main stages: (i) deriving a water depth map through a geomorphic method based on a supervised linear binary classification; (ii) generating an exposure land-use map developed from multi-spectral Landsat 8 satellite images using a machine-learning classification algorithm; and (iii) performing a flood damage assessment using a GIS tool, based on the vulnerability (depth-damage) curves method. The proposed integrated method was applied over the entire country of Romania (including minor order basins) for a 100-year return time at 30-m resolution. The results showed how the description of flood risk may especially benefit from the ability of the proposed cost-efficient model to carry out large-scale analyses in data-scarce environments. This approach may help in performing and updating risk assessments and management, taking into account the temporal and spatial changes in hazard, exposure, and vulnerability

Role of charge traps in the performance of atomically-thin transistors

Transient currents in atomically thin MoTe2 field-effect transistors (FETs) are measured during cycles of pulses through the gate electrode. The curves of the transient currents are analyzed in light of a newly proposed model for charge-trapping dynamics that renders a time-dependent change in the threshold voltage as the dominant effect on the channel hysteretic behavior over emission currents from the charge traps. The proposed model is expected to be instrumental in understanding the fundamental physics that governs the performance of atomically thin FETs and is applicable to the entire class of atomically thin-based devices. Hence, the model is vital to the intelligent design of fast and highly efficient optoelectronic devices