Exploiting optical near fields for phase change memories

We apply a recently developed technique based on optical near fields to achieve reversible phase switching in Ge2 Sb2 Te 5 films. By placing dielectric microspheres at the film surface and exposing them to pulsed laser light, a complex intensity distribution due to the optical near field can be created at the film surface. We demonstrate writing and erasing operations of patterns through phase switching. Spheres can be removed after an operation by optical near fields without ablation. Data erasure is achieved with and without near fields. The erasure method used can be determined from the result and erased information can be retrieved although being inverted. Three distinct material states are identified within patterns, showing clear contrast and sharp borders between them, thus opening the possibility of three-level data storage. Our results suggest that optical near fields are a promising candidate for developing strategies in data storage, encryption, and multiplexing. © 2011 American Institute of Physics.Peer Reviewe

Exploiting optical near fields for phase change memories

We apply a recently developed technique based on optical near fields to achieve reversible phase switching in Ge2 Sb2 Te 5 films. By placing dielectric microspheres at the film surface and exposing them to pulsed laser light, a complex intensity distribution due to the optical near field can be created at the film surface. We demonstrate writing and erasing operations of patterns through phase switching. Spheres can be removed after an operation by optical near fields without ablation. Data erasure is achieved with and without near fields. The erasure method used can be determined from the result and erased information can be retrieved although being inverted. Three distinct material states are identified within patterns, showing clear contrast and sharp borders between them, thus opening the possibility of three-level data storage. Our results suggest that optical near fields are a promising candidate for developing strategies in data storage, encryption, and multiplexing. © 2011 American Institute of Physics.Peer Reviewe

Quantitative imaging of the optical near field

When exposing small particles on a substrate to a light plane wave, the scattered optical near field is spatially modulated and highly complex. We show, for the particular case of dielectric microspheres, that it is possible to image these optical near-field distributions in a quantitative way. By placing a single microsphere on a thin film of the photosensitive phase change material Ge2Sb5Te5 and exposing it to a single short laser pulse, the spatial intensity modulation of the near field is imprinted into the film as a pattern of different material phases. The resulting patterns are investigated by using optical as well as high-resolution scanning electron microscopy. Quantitative information on the local optical near field at each location is obtained by calibrating the material response to pulsed laser irradiation. We discuss the influence of polarization and angle of incidence of the laser beam as well as particle size on the field distribution. The experimental results are in good quantitative agreement with a model based on a rigorous solution of Maxwell's equations. Our results have potential application to near-field optical lithography and experimental determination of near fields in complex nanostructures. © 2012 Optical Society of America.We also acknowledge partial funding from Spanish National Research Projects (Grants No. TEC2011-22422 and TEC2008-01183, MAT2010-14885, and Consolider NanoLight.es) and by Deutsche Forschungsgemeinschaft (SFB 767 and SPP1327).Peer Reviewe

Dichotome Differenzen und antirassistische Praxis

Die Autoren untersuchen Konzept und Methoden der US-amerikanischen Antirassismus-Trainerin Jane Elliott. Dabei hinterfragen sie, ob die zuvor genannte Einschätzung der Trainerin zu antirassistischen Lernzielen zu teilen ist und ob die vorgeschlagenen Mittel geeignet sind, diese zu erreichen. „Zuvor geht es um einen wichtigen Unterschied interkultureller und antirassistischer Konzepte: Beide beanspruchen, geeignete Mittel gegen rassistische Diskriminierung bereitzustellen, allerdings haben sie einen unterschiedlichen Differenz-Begriff, was Konsequenzen für die jeweilige Praxis hat. Gleichzeitig – so wird deutlich – scheinen einige antirassistische Konzepte eine dichotome Differenzstruktur zu konstruieren, die ebenfalls problematisch ist. Zum Schluss fragen (… die Autoren), wie geeignete antirassistische Konzepte im Bereich pädagogischer Arbeitsfelder aussehen könnten.“ (DIPF/ ssch

Weight-bearing MRI with a knee flexion angle of 20°: a study on additional MRI investigation modalities to support a more accurate understanding of patellofemoral instability

Background!#!Diagnosing patellofemoral instability disorders correctly, weight-bearing MRI (WB-MRI) has become an option. Aiming for a best possible accuracy in displaying potentially underlying causes, the named MRI modalities were sporadically even investigated in different knee flexion angles. However, despite confirmed MRI-outcome-differences between WB-MRI and non-WB-MRI, none of the described MRI modalities have so far established themselves. Mainly this is due to an unfeasibility in daily clinical routine in regard to time and economic aspects. Thus, we intended to evaluate an additional but reduced patellofemoral MR-imaging solely in a relevant 20° of knee flexion under WB- and non-WB-MRI conditions.!##!Methods!#!Seventy-three subjects with and without patellofemoral instability were investigated under supine as well as under WB-MRI conditions in a 20° of knee flexion angle. Patellofemoral risk indices in the sagittal plane (Insall-Salvati-Index, Caton-Deschamps-Index, Patellotrochlear Index) and the axial plane (Patella tilt of Fulkerson and Sasaki) were detected and compared between the different MRI conditions. Significance, reliability and Cohen's effect size was calculated.!##!Results!#!Nearly all assessed indices showed significant differences between patients and controls in the different MRI positions. Comparing pairwise, all measured indices failed to show significant differences between the two MRI positions. However, patella tilt angles of the patient group showed an elevation from supine to WB-MRI (14.00 ± 7.54° to 15.97 ± 9.10° and 16.34 ± 7.84° to 18.54 ± 9.43°). Here, Cohen's d showed small to medium effects between supine and WB-MRI.!##!Conclusion!#!In comparison to standard MRI in supine position, axial risk indices seem to be accentuated under WB-MRI and a knee flexion angle of 20°. In particular, symptomatic cases with inconspicuous conventional MRI imaging, additional MRI imaging only in the axial plane in a 20° of knee flexion could be beneficious and useful in clinical daily routine

Exploiting optical near-fields for phase switching and nanopatterning

European Symposium on Phase Change and Ovonic Science, Politecnico di Milano, Milan, Italy, September 6-7, 2010We report a novel technique for exploiting optical near-fields of dielectric micro- and nanospheres upon illumination with short laser pulses for phase switching in Ge2Sb2Te5 films. The complex intensity distribution of the optical nearfield at the crystalline film surface is imprinted and leaves behind a characteristic amorphous fingerprint, which can be read out with optical microscopy, AFM and field emission SEM. We achieve full control over the resulting patterns by playing with the illumination conditions (laser wavelength, angle of incidence, polarization) and the size and arrangement of the particles. The experimental results are well described by a model based on Mie scattering theory solving Maxwell’s equations. We demonstrate that a written pattern can be erased also by near-fields and that erased patterns can be recovered by adjusting the light intensity. The influence of pulse duration and light wavelength on the minimum recordable features size and surface roughness of the pattern is explored. Minimum features with sizes well below 200 nm can be written, which are down scaleable by reducing pulse duration and wavelength.This project was performed within a Bilateral Agreement (2008IT0072) between CSIC (Spain) and CNR (Italy), as well as within a Joint Project between CSIC and Konstanz University, funded by the Spanish Government and DAAD. We also acknowledge partial funding from EU-FP6 Project NMP4-SL-2008-213669 “ENSEMBLE,” Spanish national research projects (TEC2008-01183, TEC2008-03379-E, MAT2007-66050, and Consolider NanoLight.es), and by Deutsche Forschungsgemeinschaft (Grant No. Le 315/24)N