Ferroelastic Twin Angles at the Surface of CaTiO_{3} Quantified by Photoemission Electron Microscopy

We use photoemission electron microscopy to measure the ferroelastic twin wall angles at the surface of CaTiO_{3} (001) and deduce the strain ordering. We analyze the angular dependence of the photoelectron emission from different domain surfaces, each with its own characteristic tilt angle in the factory rooflike topography. By considering the surface topography as a field perturbation, the offset in the photoemission threshold can be directly related to the tilt angles. With knowledge of the symmetry allowed twin walls we quantify the twin angles between 179.1° to 180.8°.

Surface Proximity Effect, Imprint Memory of Ferroelectric Twins, and Tweed in the Paraelectric Phase of BaTiO3

We have used energy-filtered photoemission electron microscopy (PEEM) at the photoemission threshold to carry out a microscopic scale characterization of the surface charge and domain structure of the (001) surface in BaTiO₃. Signatures of ferroelectric and ferroelastic domains, and tweed, dominate the surface structure of BaTiO₃ at room temperature. The surface ferroic signatures are maintained on heating to temperature (~550 K), well above the transition temperature (393 K). This surface proximity effect provides the mechanism for memory of the bulk ferroelectric domain arrangement up to 150 K above T_C and thus can be considered as a robust fingerprint of the ferroelectric state near the surface. Self-reversal of polarization is observed for the tweed below T_C and for the surface domains above T_C. Annealing at higher temperature triggers the dynamic tweed which in turn allows a full reorganization of the ferroic domain configuration.

Operando x-ray photoelectron emission microscopy for studying forward and reverse biased silicon p-n junctions

Significant progress in the understanding of surfaces and interfaces of materials for new technologies requires operando studies, i.e., measurement of chemical, electronic, and magnetic properties under external stimulus (such as mechanical strain, optical illumination, or electric fields) applied in situ in order to approach real operating conditions. Electron microscopy attracts much interest, thanks to its ability to determine semiconductor doping at various scales in devices. Spectroscopic photoelectron emission microscopy (PEEM) is particularly powerful since it combines high spatial and energy resolution, allowing a comprehensive analysis of local work function, chemistry, and electronic structure using secondary, core level, and valence band electrons, respectively. Here we present the first operando spectroscopic PEEM study of a planar Si p-n junction under forward and reverse bias. The method can be used to characterize a vast range of materials at near device scales such as resistive oxides, conducting bridge memories and domain wall arrays in ferroelectrics photovoltaic devices.

Atomic force microscopy imaging using a tip-on-chip: opening the door to integrated near field nanotools

We describe in detail how atomic force microscopy (AFM) images can be routinely achieved with macroscopic silicon-based chips integrating mesoscopic tips, paving the way for the development of new near field devices combining AFM imaging with any kind of functionality integrated on a chip. The chips have been glued at the end of the free prong of 100 kHz quartz tuning forks mounted in Qplus configuration. Numerical simulations by modal analysis have been carried out to clarify the nature of the vibration modes observed in the experimental spectra. It is shown that two low frequency modes can be used to drive the system and scan the surface with a great stability in amplitude modulation as well as in frequency modulation AFM under ultrahigh vacuum. The AFM capabilities are demonstrated through a series of examples including phase and dissipation contrast imaging, force spectroscopy measurements, and investigations of soft samples in weak interaction with the substrate. The lateral resolution with the tips grown by focused ion beam deposition already matches the one achieved in standard amplitude modulation mode AFM experiments.

[Bronchiolitis viruses]

In Normandy (France), human respiratory syncytial virus (hRSV) was detected in 64.1% of acute bronchiolitis in hospitalized children, rhinovirus in 26.8%, human metapneumovirus (hMPV) in 7.6%, and parainfluenza virus (PIV) in 3.4%. The viruses causing acute bronchiolitis in the community were hRSV (42%), rhinovirus (19.5%), coronavirus (8%), PIV (3.5%), and hMPV (2.5%). In 53.7% of the cases, hRSV infected infants (86.9%), 53.7% being less than 6 months of age. Of the hRSV cases, 48.2% were detected in November and December and 44.5% in January and February. The hRSV epidemic started the 1st or 2nd week of October but it varied from one year to another and from one region to another. hRSV acute bronchiolitis increased from 261 cases in epidemics from 1999-2003 to 341 cases from 2004-2009. Rhinoviruses gave acute bronchiolitis in 38.4% of cases. A rate of 54.6% of viruses was detected in September and October and 38.5% in March and April. A total of 34.2% of infected infants were under 6 months of age, 37.8% between 6 months and 2 years, and 19.5% were between 2 and 5 years old. hMPV epidemics coincided with hRSV epidemics, but they accounted for one-sixth the number of cases. HMPV infected infants (74%) who were older than those infected with hRSV, and the diagnosis was bronchiolitis (59%) and pneumonia (17%). PIV infections (about 100 cases per year) included PIV3 (62.7%), PIV1 (25.3%), and PIV2 (7.3%). PIV1 infections occurred every 2 years in the fall. PIV3 infections were observed every year during the fall and winter, with peaks of infections in the spring in the years without PIV1. There were acute cases of bronchiolitis in 29.8% of PIV3 infections and 18.3% in PIV1 infections.

Experimental three-dimensional description of the liquid hexadecane/graphite interface

By using an atomic force microscope based on a quartz tuning fork sensor, a 3-dimensional description of the interface between liquid hexadecane and a highly oriented pyrolytic graphite surface can be achieved at room temperature. The C16H34 monolayer in contact with the substrate surface exhibits a lamellar structure whereas no observation at the liquid/graphite interface by scanning tunnelling microscopy was reported for this alkane. The second layer shows very weak corrugations corresponding to lamella boundaries. Force/distance curves show at least four oscillations separated by 0.4 nm except for the first period with a 0.38 nm distance that corresponds to the layer closer the substrate. Such a description agrees well with molecular dynamics results obtained on alkane/solid interfaces.