Large-Area Epitaxial Mott Insulating 1T-TaSe2 Monolayer on GaP(111)B

Two-dimensional Mott materials have recently been reported in the dichalcogenide family with high potential for Mottronic applications. Nevertheless, their widespread use as a single or few layers is hampered by their limited device integration resulting from their growth on graphene, a metallic substrate. Here, we report on the fabrication of 1T-TaSe2 monolayers grown by molecular beam epitaxy on semiconducting gallium phosphide substrates. At the nanoscale, the charge density wave reconstruction and a moiré pattern resulting from the monolayer interaction with the substrate are observed by scanning tunneling microscopy. The fully open gap unveiled by tunneling spectroscopy, which can be further manipulated by the proximity of a metal tip, is confirmed by transport measurements from micrometric to millimetric scales, demonstrating a robust Mott insulating phase at up to 400 K.

Improving the intrinsic conductance of selective area grown in-plane InAs nanowires with a GaSb shell

The nanoscale intrinsic electrical properties of in-plane InAs nanowires grown by selective area epitaxy are investigated using a process-free method involving a multi-probe scanning tunneling microscope. The resistance of oxide-free InAs nanowires grown on an InP(111)_Bsubstrate and the resistance of InAs/GaSb core-shell nanowires grown on an InP(001) substrate are measured using a collinear four-point probe arrangement in ultrahigh vacuum. They are compared with the resistance of two-dimensional electron gas reference samples measured using the same method and with the Van der Pauw geometry for validation. A significant improvement of the conductance is achieved when the InAs nanowires are fully embedded in GaSb, exhibiting an intrinsic sheet conductance close to the one of the quantum well counterpart.

Assessing the insulating properties of an ultrathin SrTiO3shell grown around GaAs nanowires with molecular beam epitaxy

We have studied electronic transport in undoped GaAs/SrTiO₃core-shell nanowires standing on their Si substrate with two-tip scanning tunneling microscopy in ultrahigh vacuum. The resistance profile along the nanowires is proportional to the tip separation with resistances per unit length of a few GΩ/μm. Examination of the different transport pathways parallel to the nanowire growth axis reveals that the measured resistance is consistent with a conduction along the interfacial states at the GaAs{110} sidewalls, the 2 nm thick SrTiO₃shell being as much as resistive, despite oxygen deficient growth conditions. The origin of the shell resistivity is discussed in light of the nanowire analysis with transmission electron microscopy and Raman spectroscopy, providing good grounds for the use of SrTiO₃shells as gate insulators.

Iuliacumite: A Novel Chemical Short-Range Order in a Two-Dimensional Wurtzite Single Monolayer InAs1-xSbx Shell on InAs Nanowires

A chemical short-range order is found in single monolayer InAs_1-xSb_x shells, which inherit a wurtzite structure from the underlying InAs nanowire, instead of crystallizing in the energetically preferred zincblende structure. The chemical order is characterized by an anticorrelation ordering vector in the ⟨112̅0⟩ direction and arises from strong Sb-Sb repulsive interactions along the atomic chains in the ⟨112̅0⟩ direction.

Composition modulation by twinning in InAsSb nanowires

We observe a composition modulated axial heterostructure in zincblende (ZB) InAs_0.90Sb_0.10 nanowires initiated by pseudo-periodic twin boundaries using scanning tunneling microscopy. The twin boundaries exhibit four planes with reduced Sb concentration due to a lower Sb incorporation during lateral overgrowth of a 4H wurtzite as compared to a ZB stacking sequence. We anticipate that this leads to compositional band offsets in addition to known structural band offsets present between 4H and ZB polytypes, changing the band alignment from type II to type I.

Correction: Transport mechanisms in a puckered graphene-on-lattice

Correction for 'Transport mechanisms in a puckered graphene-on-lattice' by T. Xu et al., Nanoscale, 2018, 10, 7519-7525.

Transport mechanisms in a puckered graphene-on-lattice

Understanding the fundamental properties of graphene when its topography is patterned by the use of a compliant substrate is essential to improve the performances of graphene sensors. Here we suspend a graphene monolayer on SiO2 nanopillar arrays to form a puckered graphene-on-lattice and investigate the strain and electrical transport at the nanoscale. Despite a nonuniform strain in the graphene-on-lattice, the resistivity is governed by thermally activated transport and not the strain. We show that the high thermal activation energy results from a low charge carrier density and a periodic change of the chemical potential induced by the interaction of the graphene monolayer with the nanopillars, making the use of graphene-on-lattice attractive to further increase the electrical response of graphene sensors.

Coulomb energy determination of a single Si dangling bond

Determination of the Coulomb energy of single point defects is essential because changing their charge state critically affects the properties of materials. Based on a novel approach that allows us to simultaneously identify a point defect and to monitor the occupation probability of its electronic state, we unambiguously measure the charging energy of a single Si dangling bond with tunneling spectroscopy. Comparing the experimental result with tight-binding calculations highlights the importance of the particular surrounding of the localized state on the effective charging energy.

[Epidemiologic aspects of pulmonary tuberculosis with positive bacilloscopy in the decade of 1995-2004]

The purpose of this study is to make an epidemiological description of pulmonary tuberculosis with sputum smear positive in Mali. This is a retrospective study conducted from January 1st, 1995 to December 31st, 2004 by the National Program for fighting against tuberculosis (located at the National Department of health), and where data were centralized. From this ten years period, 33,000 cases of tuberculosis (all forms of TB) have been notified in Mali, which represented an annual rate of 2750. Of those, 22,275 cases (67.5%) were sputum smear positive (with Ziehl Nielsen), this represented 1856 as annual rate. The prevalence of pulmonary TB with sputum smear positive is 185/100,000. During the study period a total of 13,638 (61.22%) cases of 22,275 cases of pulmonary TB with sputum smear positive have been given ant tuberculosis drugs; From these patients under therapy 2371 cases (17.38% ) disappear before the end of treatment.; 5851 cases (42.90%) have been considered as cured; 161 (1.18%) cases of treatment failure and 523 (3.93%) cases of death. The sex-ratio was 3.57 with young adults representing the majority of cases. Pulmonary TB with sputum smear positive treatment remains a challenge for National Programs for fighting against TB as well as its prevention.

Electron transport via local polarons at interface atoms

Electronic transport is profoundly modified in the presence of strong electron-vibration coupling. We show that in certain situations, the electron flow takes place only when vibrations are excited. By controlling the segregation of boron in semiconducting Si(111)-square root 3 x square root 3 R 30 degrees surfaces, we create a type of adatom with a dangling-bond state that is electronically decoupled from any other electronic state. However, probing this state with scanning tunnelling microscopy at 5 K yields high currents. These findings are rationalized by ab-initio calculations that show the formation of a local polaron in the transport process.