Reverse electrochemical etching method for fabricating ultra-sharp platinum/iridium tips for combined scanning tunneling microscope/ atomic force microscope based on a quartz tuning fork

International audienceSharp Pt/Ir tips have been reproducibly etched by an electrochemical process using an inverse geometry of an electrochemical cell and a dedicated electronic device which allows us to control the applied voltages waveform and the intensity of the etching current. Conductive tips with a radius smaller than 10 nm were routinely produced as shown by field emission measurements through FowlereNordheim plots. These etched tips were then fixed on a quartz tuning fork force sensor working in a qPlus configuration to check their performances for both scanning tunneling microscopy (STM) and atomic force microscopy (AFM) imaging. Their sharpness and conductivity are evidenced by the resolution achieved in STM and AFM images obtained of epitaxial graphene on 6H-SiC(0001) surface. The structure of an epitaxial graphene layer thermally grown on the 6H-SiC(0001) (6R3x6R3)R30° reconstructed surface, was successfully imaged at room temperature with STM, dynamic STM and by frequency modulated AFM

Prognostic significance of anti-p53 and anti-KRas circulating antibodies in esophageal cancer patients treated with chemoradiotherapy

<p>Abstract</p> <p>Background</p> <p>P53 mutations are an adverse prognostic factor in esophageal cancer. P53 and KRas mutations are involved in chemo-radioresistance. Circulating anti-p53 or anti-KRas antibodies are associated with gene mutations. We studied whether anti-p53 or anti-KRas auto-antibodies were prognostic factors for response to chemoradiotherapy (CRT) or survival in esophageal carcinoma.</p> <p>Methods</p> <p>Serum p53 and KRas antibodies (abs) were measured using an ELISA method in 97 consecutive patients treated at Saint Louis University Hospital between 1999 and 2002 with CRT for esophageal carcinoma (squamous cell carcinoma (SCCE) 57 patients, adenocarcinoma (ACE) 27 patients). Patient and tumor characteristics, response to treatment and the follow-up status of 84 patients were retrospectively collected. The association between antibodies and patient characteristics was studied. Univariate and multivariate survival analyses were conducted.</p> <p>Results</p> <p>Twenty-four patients (28%) had anti-p53 abs. Abs were found predominantly in SCCE (p = 0.003). Anti-p53 abs were associated with a shorter overall survival in the univariate analysis (HR 1.8 [1.03-2.9], p = 0.04). In the multivariate analysis, independent prognostic factors for overall and progression-free survival were an objective response to CRT, the CRT strategy (alone or combined with surgery [preoperative]) and anti-p53 abs. None of the long-term survivors had p53 abs. KRas abs were found in 19 patients (23%, no difference according to the histological type). There was no significant association between anti-KRas abs and survival neither in the univariate nor in the multivariate analysis. Neither anti-p53 nor anti-KRas abs were associated with response to CRT.</p> <p>Conclusions</p> <p>Anti-p53 abs are an independent prognostic factor for esophageal cancer patients treated with CRT. Individualized therapeutic approaches should be evaluated in this population.</p

A second planet transiting LTT 1445A and a determination of the masses of both worlds

K.H. acknowledges support from STFC grant ST/R000824/1.LTT 1445 is a hierarchical triple M-dwarf star system located at a distance of 6.86 pc. The primary star LTT 1445A (0.257 M⊙) is known to host the transiting planet LTT 1445Ab with an orbital period of 5.36 days, making it the second-closest known transiting exoplanet system, and the closest one for which the host is an M dwarf. Using Transiting Exoplanet Survey Satellite data, we present the discovery of a second planet in the LTT 1445 system, with an orbital period of 3.12 days. We combine radial-velocity measurements obtained from the five spectrographs, Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, High Accuracy Radial Velocity Planet Searcher, High-Resolution Echelle Spectrometer, MAROON-X, and Planet Finder Spectrograph to establish that the new world also orbits LTT 1445A. We determine the mass and radius of LTT 1445Ab to be 2.87 ± 0.25 M⊕ and 1.304-0.060+0.067 R⊕, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of 1.54-0.19+0.20 M⊕ and a minimum radius of 1.15 R⊕, but we cannot determine the radius directly as the signal-to-noise ratio of our light curve permits both grazing and nongrazing configurations. Using MEarth photometry and ground-based spectroscopy, we establish that star C (0.161 M⊙) is likely the source of the 1.4 day rotation period, and star B (0.215 M⊙) has a likely rotation period of 6.7 days. We estimate a probable rotation period of 85 days for LTT 1445A. Thus, this triple M-dwarf system appears to be in a special evolutionary stage where the most massive M dwarf has spun down, the intermediate mass M dwarf is in the process of spinning down, while the least massive stellar component has not yet begun to spin down.Publisher PDFPeer reviewe

Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H–SiC(0001) surface during scanning tunneling and atomic force microscopy studies

International audienceTip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H–SiC(0001) surface during scanning tunneling and atomic force microscopy studies Abstract The structural and mechanical properties of an epitaxial graphene (EG) monolayer thermally grown on top of a 6H–SiC(0001) surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM). Experimental STM, dynamic STM and AFM images of EG on 6H–SiC(0001) show a lattice with a 1.9 nm period corresponding to the (6 × 6) quasi-cell of the SiC surface. The corrugation amplitude of this (6 × 6) quasi-cell, measured from AFM topographies, increases with the setpoint value of the frequency shift Δf (15–20 Hz, repulsive interaction). Excitation variations map obtained simultaneously with the AFM topography shows that larger dissipation values are measured in between the topographical bumps of the (6 × 6) quasi-cell. These results demonstrate that the AFM tip deforms the graphene monolayer. During recording in dynamic STM mode, a frequency shift (Δf) map is obtained in which Δf values range from 41 to 47 Hz (repulsive interaction). As a result, we deduced that the STM tip, also, provokes local mechanical distortions of the graphene monolayer. The origin of these tip-induced distortions is discussed in terms of electronic and mechanical properties of EG on 6H–SiC(0001)

Processing and analysis of X-ray photoelectron diffraction data using IGOR Pro

International audienceA software package is presented for nearly real-time display of diffractograms during X-ray photoelectron diffraction (XPD) data acquisition and for processing and analysis after an experiment. During the experiment, the package is able to automatically read X-ray photoelectron spectroscopy (XPS) data, perform initial data processing and project intensity values as XPD diffractograms. Four display modes are supported. After the experiment, the package is able to open, process and analyze XPD patterns. The processing functions include rotation, cropping, creating a full 2π pattern using symmetry operations, smoothing and converting a pattern to an image suitable for publication. The analysis functions include displaying polar angles, azimuthal angles, intensity, the core level spectrum at a selected angular data point, and azimuthal and radial profiles. The package also integrates fitting functions for core level spectra. The package is developed using the IGOR Pro scripting language. A graphical user interface has been developed to allow all the operations just by mouse clicking. The package is designed to interface directly with an XPD system at the Saclay center of the French Atomic Energy and Alternative Energies Authority, but the algorithms are generally applicable and can be readily adapted to other XPD systems

Understanding the STM images of epitaxial graphene on a reconstructed 6H-SiC(0001) surface: the role of tip-induced mechanical distortion of graphene

International audienceEpitaxial graphene (EG) grown on an annealed 6H-SiC(0001) surface has been studied under ultra-high vacuum (UHV) conditions by using a combined dynamic-scanning tunneling microscope/frequency modulation-atomic force microscope (dynamic-STM/FM-AFM) platform based on a qPlus probe. STM and AFM images independently recorded present the same hexagonal lattice of bumps with a 1.9 nm lattice period, which agrees with density functional theory (DFT) calculations and experimental results previously reported, attributed to the (6 x 6) quasi-cell associated with the 6H-SiC(0001) (6$\sqrt 3$x6$\sqrt 3$) R30 reconstruction. However, topographic bumps in AFM images and maxima in the simultaneously recorded mean-tunneling-current map do not overlap but appear to be spaced typically by about 1 nm along the [11] direction of the (6 x 6) quasi-cell. A similar shift is observed between the position of maxima in dynamic-STM images and those in the simultaneously recorded frequency shift map. The origin of these shifts is discussed in terms of electronic coupling variations between the local density of states (LDOS) of EG and the LDOS of the buffer layer amplified by mechanical distortions of EG induced by the STM or AFM tip. Therefore, a constant current STM image of EG on a reconstructed 6H-SiC(0001) surface does not reproduce its real topography but corresponds to the measured LDOS modulations, which depend on the variable tip-induced graphene distortion within the (6 x 6) quasi-cell

Tuning the properties of molecular organic layers at the micron-scale using low-energy electrons.

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Low-energy electron control over physical and chemical properties of organic aromatic thin layers at the micrometre scale

The collimated monochromatic low-energy (≤ 50 eV) electron beam delivered by a low energy electron microscope (LEEM) was used to locally modify organic molecular thin films at the micrometre-scale. Self-Assembled Monolayers (SAMs) of p-terphenylthiol (TPT) anchored on gold substrates were used as model organic layers. The local work function (WF) was observed to decrease as a consequence of electron irradiation and to be tuneable using the irradiation energy and/or the dose as control parameters. The chemical origin of the observed WF changes could be discussed in the light of available vibrational analyses of irradiated TPT SAMs performed using High-Resolution Electron Energy Loss Spectroscopy (HREELS) and by comparing the effective cross sections estimated for WF modulation and for chemical modifications, respectively. The hydrogen content of the organic thin film was shown to be the determining parameter, rather than the degree of aromaticity of the hydrogenated carbon centres. Finally, the imprinted modifications were observed to have a moderate stability after air exposure by combining Photoemission Electron Microscopy (PEEM) and HREELS

Crystallization-Induced Dynamic Resolution of Fox Chiral Auxiliary and Application to the Diastereoselective Electrophilic Fluorination of Amide Enolates

A highly efficient crystallization-induced dynamic resolution (CIDR) of <i>trans</i>-<b>Fox</b> (fluorinated oxazolidine) chiral auxiliary is reported. This chiral auxiliary was used for highly diastereoselective (>98% <i>de</i>) electrophilic fluorination of amide enolates. After removal of the chiral auxiliary, highly valuable enantiopure α-fluorocarboxylic acids and β-fluoroalcohols are obtained

Evidence of Ba-rich surface segregation in Ba 1-x Sr x TiO 3 and Ba-rich surfactant in SrTiO 3 / Ba 1-x Sr x TiO 3 stacks grown by combinatorial pulsed laser deposition

The interface of a La 0.7 Sr 0.3 MnO 3 /SrTiO 3 bilayer was modulated by introducing 3 unit cells of Ba 1-x Sr x TiO 3 using Combinatorial Pulsed Laser Deposition. A wide range of chemical compositions was studied within the same sample, with BSTx stoichiometry variable from 0.5 to 1 along Y-axis, while the SrTiO3 overlayer thickness was modified along the X direction [Fig. 1(a)]. We performed high-resolution, laboratory-based angle-resolved XPS studies of the BSTx film surface providing information on the thickness and composition of the surface and sub-surface layers. Based on the attenuation of the La 3d corelevel photoemission signal from the La 0.7 Sr 0.3 MnO 3 bottom layer, the BST layer is 1.2 nm thick. XPS Ba 3d 5/2 core-level spectra were acquired at positions corresponding to different nominal Ba/Sr stoichiometry. In all measurements, the Ba 3d 5/2 core-level spectra can be represented by two main components, i.e. one component at higher binding energy (BE = 780.54 eV) corresponding to surface contribution and the other one at lower binding energy (BE = 778.92 eV) corresponding to sub-surface contribution (Figs. 2 and 3). Going from normal to 60° emission angle and using a 3-unit cell thick film model, the surface to sub-surface intensity ratio clearly evolves providing evidence of a Ba-rich surfactant. The surfactant effect is more significant for lower nominal Ba stoichiometry