Impact of MoS2 layer transfer on electrostatics of MoS2/SiO2 interface.

Using internal photoemission of electrons from few-monolayer thin MoS2 films into SiO2 we found that the MoS2 layer transfer processing perturbs electroneutrality of the interface, leading to an increase of the electron barrier height by ≈0.5-1 eV as compared to the case of the same films synthesized directly on SiO2. This effect is associated with the formation of an interface dipole, tentatively ascribed to interaction of H2O molecules with the SiO2 surface resulting in the incorporation of silanol (SiOH) groups. This violation of the interface electroneutrality may account for additional electron scattering in ultrathin transferred films and threshold voltage instabilities. Post-transfer annealing in H2S is shown to reduce the transfer-induced interface degradation.

A systematic study of various 2D materials in the light of defect formation and oxidation.

The thermodynamic aspects of various 2D materials are explored using Density Functional Theory (DFT). Various metal chalcogenides (MX2, M = metal, chalcogen X = S, Se, Te) are investigated with respect to their interaction and stability under different ambient conditions met in the integration process of a transistor device. Their interaction with high-κ dielectrics is also addressed, in order to assess their possible integration in Complementary Metal Oxide Semiconductor (CMOS) field effect transistors. 2D materials show promise for high performance nanoelectronic devices, but the presence of defects (vacancies, grain boundaries,…) can significantly impact their electronic properties. To assess the impact of defects, their enthalpies of formation and their signature levels in the density of states have been studied. We find, consistently with literature reports, that chalcogen vacancies are the most likely source of defects. It is shown that while pristine 2D materials are in general stable whenever set in contact with different ambient atmospheres, the presence of defective sites affects the electronic properties of the 2D materials to varying degrees. We observe that all the 2D materials studied in the present work show strong reactivity towards radical oxygen plasma treatments while reactivity towards other common gas phase chemical such as O2 and H2O and groups present at the high-κ surface varies significantly between species. While energy band-gaps, effective masses and contact resistivities are key criteria in selection of 2D materials for scaled CMOS and tunneling based devices, the phase and ambient stabilities might also play a very important role in the development of reliable nanoelectronic applications.

Structural characterization of SnS crystals formed by chemical vapour deposition.

The crystal and defect structure of SnS crystals grown using chemical vapour deposition for application in electronic devices are investigated. The structural analysis shows the presence of two distinct crystal morphologies, that is thin flakes with lateral sizes up to 50 µm and nanometer scale thickness, and much thicker but smaller crystallites. Both show similar Raman response associated with SnS. The structural analysis with transmission electron microscopy shows that the flakes are single crystals of α-SnS with [010] normal to the substrate. Parallel with the surface of the flakes, lamellae with varying thickness of a new SnS phase are observed. High-resolution transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), first-principles simulations (DFT) and nanobeam diffraction (NBD) techniques are employed to characterise this phase in detail. DFT results suggest that the phase is a strain stabilised ß' one grown epitaxially on the α-SnS crystals. TEM analysis shows that the crystallites are also α-SnS with generally the [010] direction orthogonal to the substrate. Contrary to the flakes the crystallites consist of two to four grains which are tilted up to 15° relative to the substrate. The various grain boundary structures and twin relations are discussed. Under high-dose electron irradiation, the SnS structure is reduced and ß-Sn formed. It is shown that this damage only occurs for SnS in direct contact with SiO2 .

Intrinsic point defects in buckled and puckered arsenene: a first-principles study.

Using first-principles calculations, we study the structural, energetic, and electronic properties of various point defects in arsenene. Stone-Wales defects are found to be thermodynamically favorable and are predicted to be stable at room temperature. Defects are found to significantly influence the electronic properties in buckled phase. In particular, single vacancies generate gap states whereas strain induced states close to the valence and conduction band edges are observed for Stone-Wales and di-vacancy defects. The computed band structures of di-vacancy defects in puckered phase are less disturbed compared to the corresponding band structures in the buckled one. The influence of a hydrogen-rich atmosphere on the electronic properties of defective arsenene is also investigated. Hydrogen termination of mono/di-vacancies is an exothermic process which removes all defect induced gap states.

The lead acceptor in p-type natural 2H-polytype MoS2 crystals evidenced by electron paramagnetic resonance.

A low-temperature (T = 1.5-8 K) electron paramagnetic resonance study of p-type 2H-polytype natural MoS2 crystals reveals a previously unreported anisotropic signal of corresponding defect density (spin S = ½) ~5 × 1014 cm-3. For the applied magnetic field B//c-axis, the response is comprised of a single central asymmetric Zeeman peak at zero-crossing g = 2.102(1), amid a symmetrically positioned hyperfine doublet of splitting 6.6(2) G. Field angular observations reveal a two-branch g pattern, indicative of a defect of lower than axial symmetry, likely orthorhombic (C 2v). Based on the signal specifics, it is ascribed to a system of decoupled Pb impurities substituting for Mo, the defect operating as an acceptor, with estimated thermal activation energy >10 meV. Supporting theoretical anticipation, the results pinpoint the conduct of the Pb impurity in layered MoS2.

[Predictors of prolonged ICU stay following elective adult cardiac surgery: Monocentric retrospective study on 5 and half years]. / Facteurs prédictifs de long séjour en réanimation après chirurgie cardiaque programmée de l'adulte : étude rétrospective monocentrique sur 5 ans et demi.

AIM: The aim of our study was to identify predictors for prolonged ICU stay following elective adult cardiac surgery under cardiopulmonary bypass. PATIENTS AND METHODS: A retrospective study was conducted during 5 years and a half period. Were included, patients age≥18 years old, underwent elective cardiac surgery under cardiopulmonary bypass. Patients who died within 48hours of surgery were excluded. Prolonged ICU stay was defined as stay in the ICU for 48hours or more. RESULTS: During the review period, 610 patients were included. One hundred and sixty-four patients have required a prolonged ICU stay (26.9 %). In multivariate analysis, 5 predictors were identified: ejection fraction<30 % (OR 19.991, IC 95 % [1.382-289.1], P=0.028], pulmonary hypertension (OR 2.293, IC 95 % [1.058-4.973], P=0.036), prolonged ventilation (≥12hours) (OR 4.026, IC 95 % [2.407-6.733], P<0.001). Number of blood units transfused (OR 1.568, IC 95 % [1.073-2.291], and postoperative acute renal failure (OR 2.620, IC 95 % [1.026-6.690], P=0.044]. Prolonged ICU stay is significantly associated with prolonged hospital stay (17 days vs 13 days ; P<0.001) and higher in hospital mortality (22 % vs. 3 %, P<0.001). CONCLUSION: The identification of these patients at risk of prolonged ICU stay is crucial. It will aid to plan prophylactic measures to optimize their support.

Impact of point defects on the electronic and transport properties of silicene nanoribbons.

We study the impact of various point defects on the structural, electronic and ballistic transport properties of armchair silicene nanoribbons, using the density functional theory and the non equilibrium Green's function method. The effect of a Stone-Wales defect, an interior/edge vacancy and an edge dangling bond is examined. Our results show that structural imperfections can alter the electronic structure (energy band structure and density of states) of the nanoribbons and can either increase or decrease the ballistic current. The dependence of the transport properties on the position of the defects (sublattice A or B) and on their distance from the contact is also investigated.

Silicene: a review of recent experimental and theoretical investigations.

Silicene is the silicon counterpart of graphene, i.e. it consists in a single layer of Si atoms with a hexagonal arrangement. We present a review of recent theoretical and experimental works on this novel two dimensional material. We discuss first the structural, electronic and vibrational properties of free-standing silicene, as predicted from first-principles calculations. We next review theoretical studies on the interaction of silicene with different substrates. The growth and experimental characterization of silicene on Ag(1 1 1) is next discussed, providing insights into the different phases or atomic arrangements of silicene observed on this metallic surface, as well as on its electronic structure. Recent experimental findings about the likely formation of hexagonal Si nanosheets on MoS2 are also highlighted.

An electric field tunable energy band gap at silicene/(0001) ZnS interfaces.

The interaction of silicene, the silicon counterpart of graphene, with (0001) ZnS surfaces is investigated theoretically, using first-principles simulations. The charge transfer occurring at the silicene/(0001) ZnS interface leads to the opening of an indirect energy band gap of about 0.7 eV in silicene. Remarkably, the nature (indirect or direct) and magnitude of the energy band gap of silicene can be controlled by an external electric field: the energy gap is predicted to become direct for electric fields larger than about 0.5 V Å(-1), and the direct energy gap decreases approximately linearly with the applied electric field. The predicted electric field tunable energy band gap of the silicene/(0001) ZnS interface is very promising for its potential use in nanoelectronic devices.

[Results of coronary artery bypass grafting with left ventricular dysfunction (comparison of off-pump versus on-pump)]. / Résultats du pontage coronaire en cas de dysfonction ventriculaire gauche (comparaison du cœur battant et de la CEC).

BACKGROUND: The aim of this study was to compare the results of myocardial revascularisation with or without cardiopulmonary bypass in patients with impaired left ventricular function. PATIENTS AND METHODS: Five hundred and sixteen consecutive patients who underwent coronary artery bypass grafting from January 2000 through December 2007 were analyzed retrospectively. One hundred and eight cases had a left ventricular EF (ejection fraction) of 45% or less. Of these patients, 78 underwent conventional coronary artery bypass (CCABG) and 30 underwent off-pump procedure (OCABG). The CCABG group received 300IU/kg of heparin while the OCABG received 100IU/kg. The off-pump coronary surgery was carried out using a tissue stabilizer Octopus II. Different pre-, per- and postoperative variables were evaluated among both groups. Statistical analysis was performed by SPSS 11.5. The variables were compared between these two groups using univariate analysis (Chi(2) test, Fisher's test exact) for qualitative variable and (Student's t test, Mann-Whitney's test) for quantitative variable. RESULTS: Patients profiles and risk factors were similar among both groups except for age (CCABG: 57.8±9.2 year vs OCABG: 52±9.9 year; P=0.004) and left ventricular EF (CCABG: 37.4±6.3% vs OCABG: 34±7.8%; P=0.02). The number of grafts performed per patient was significantly more among patients who underwent extracorporeal circulation (CCABG: 2.53±0.7 graft/patient vs OCABG: 1.77±0.8 graft/patient; P<0.0001). The hospital mortality was more among CCABG group 9% vs 3.3% in OCABG but the difference was not significant (P=0.3). However, the operative time and the operative room stay were long in CCABG (252±61min vs 175±38min; P<0.0001 - 389±70min vs 298±54min; P<0.0001). The ventilation time was also long in CCABG (32.3±67hour vs 10.4±5.9hour; P=0.15). There was more postoperative myocardial infarction in CCABG (P=0.008), but the EF increased and was better in CCABG. CONCLUSION: Off-pump coronary artery bypass surgery provides satisfactory operative results for most patients with reduced left ventricular function. Prospective and randomly study will be necessary before concluding.

[Antifibrinolytic agents and repeat open-heart surgery: a comparison of tranexamic acid and low dose aprotinin]. / Antifibrinolytiques et réinterventions chirurgicales à coeur ouvert: comparaison de l'acide tranexamique aux faibles doses d'aprotinine.

PURPOSE: This retrospective study has for objective to compare the effect of tranexamic acid with low-dose of aprotinin therapy on blood loss in reoperative cardiac surgery. METHODS: Ninety-one adult patients underwent repeated open-heart surgery. Two groups of patients were collected. The aprotinin group AP (N=60) has received an intravenous full low dose of 500000 UIK of aprotinin. The tranexamic group TA (N=31) has received 30 mg/kg of tranexamic acid. Criteria for assessment included: cumulative blood loss at 4 hours and 20 hours after operation, need for transfusion and parameters of coagulation (platelet, fibrinogen count). RESULTS: Demographics characteristics and echocardiographic data were similar between the tow groups. Postoperative blood loss at 4th hour and at 20th hour were reduced in tranexamic group compared with aprotinin group (P=0,009, P=0,001). The transfusion requirement was frequent in the AP group 39% vs 19.4% in TA group. The TA group received fewer total unit of red blood (0.38 unit RBC/patient vs 1.06 in AP group) [RBC=red blood cells]. There was no statistically significant difference in platelet and fibrinogen profiles. CONCLUSION: This study concludes that tranexamic acid and low dose aprotinin effectively reduces postoperative bleeding in repeat open-heart surgery. However, the marked difference in superiority between these tow drug therapies needs the randomized and controlled study.

[Upper digestive bleedings after cardiac surgery]. / Hémorragies digestives hautes après chirurgie cardiaque.

INTRODUCTION: Upper gastrointestinal haemorrhage (UGH) following cardiac surgery is infrequent with high mortality. The aim of this study is to compare the frequency and outcome of UGH in patients who had undergone open heart surgery at our institution. PATIENTS AND METHODS: From January 1994 to December 2005, 1278 cardiac operations were performed. A systematic prophylaxis antiacid was used by antagonists of histaminic receptor (anti-H2, ranitidine 150 mg/12 h) in all patients. The diagnosis was based on clinical symptoms (haematemesis and/or melaena) in the postoperative period and confirmed by fibroscopy. We conducted a retrospective study of these patients. RESULTS: Only 8 of the 1278 (0,6%) cardiac operations were complicated by UGH. Demographic data were reported in Table 1. The mean interval between surgery and UGH was 10+/-3,7 days (range 5,15 days). Gastro-duodenal ulcer was the most common cause of UGH in 5 patients (62%), ulcero-hemorrhagic eosophagitis was developed in one patient (12,5%), candidosic eosophagitis in one and multiple gastric ulcer in one patient (12,5%). Medical treatment was applied in 6 patients (72%) with successful result. Surgical intervention was necessary in 2 patients (25%). 2 patients had repeat gastrointestinal bleeding. One patient was died; he was recorded as having severe sepsis and multiple organ failure in addition to UGH. CONCLUSION: UGH in patients undergoing heart operation is rare but associated with poor prognosis despite antiacid prophylaxis. These complications occurred in patients who had in postoperative bad hemodynamic conditions.

[Tranexamic acid versus aprotinin for the prevention of bleeding during mitral valve surgery ]. / Prévention du saignement dans la chirurgie de la valve mitrale: comparaison de l'acide tranexamique aux faibles doses d'aprotinine.

PURPOSE: This retrospective stady has for objective to compare the effect of Tranexamic Acid (TA) to the low dose of aprotinin (AP) in primary mitral valve surgery in terms of blood loss and transfusion requirements. METHODS: Are included in the study operated patients of a valvulopathy mitral isolated. Two groups of 50 patients are collected. The tranexamic acid group has received 30 mg kg-1 the acid tranexamic and the aprotinin group has received a low regimen as 500,000 UIK of aprotinin. Blood loss by the chest drains are assessed to different times during first 24 hours post cardiopulmonary bypass. In the same way, we have measured the platelet and fibrinogen count. Blood products were administered according to a classic protocol. RESULTS: The two groups are comparable clinic and echocardiographic parameters what authorizes us an appariement acceptable. Various cardiopulmonary bypass times are almost similar. We noticed a tendency to excessive blood loss processed by low regimen aprotinin and a significant rate difference of platelet and the fibrinogen level. But no complication has been recorded in the two groups. CONCLUSIONS: This study demonstrates relatively different effect of the two fibrinolytics inhibitors in primary mitral valve surgery. As for the superiority of one of the two produces, it needs a confirmation by a randomised and controlled clinical trial.

[Arterial manifestations of Behcet's disease. A report of five operated cases]. / Manifestations artérielles de la maladie de Behçet. A propos de 5 cas opérés.

Vascular involvement in Behcet's disease is common, especially in deep vein thrombosis. Aneurysmal or occlusive arterial disease is, however, rare. The authors report five cases of vascular Behcet's disease reviewed over a period of 4 years (1996-1999). All these patients were men and the mean age was 38 years. The arterial disease was the presenting symptom of Behcet's disease in 3 cases. The other patients had been followed up for Behcet's disease for 4 years. The average time of onset of arterial disease was 7.2 years with respect to the presenting symptom, the range being 2 to 20 years. In all, seven arteries were involved, two patients having two arterial sites at the same time. The femoral artery was involved in 3 cases. The iliac artery was involved twice. One patient had a coronary thrombosis and the last case was of a pseudoaneurysm of the infra-renal abdominal aorta which ruptured into the retroperitoneal space. Six lesions were aneurysmal. All patients underwent surgery. The histological analysis of the resected lesions showed non-specific panvasculitis. The postoperative period was marked by short and medium term complications: four prosthetic thromboses and two anastomotic pseudo-aneurysms which required several surgical procedures and which led to two deaths. These results and a review of the literature underline the need to search for Behcet's disease in all cases of aneurysmal or occlusive arterial disease in young patients, especially those born in the Mediterranean regions. Surgical treatment should not be delayed. In these inflammatory conditions with pronounced perivascular involvement, the surgery is difficult and postoperative complications are common, especially anastomotic disunion. Medical treatment has no surgical implication, but does not prevent progression of the disease.

[Renal hydatid cyst. Apropos of 22 cases]. / Le kyste hydatique rénal. A propos de 22 cas.

Renal hydatid cyst ranks third among all visceral localisations. It is most often latent due to the deep situation of the kidney. The authors report their experience with 22 cases of hydatid disease of the kidney, and place special emphasis on wedge resection of the cyst which is a simple and effective operation.