Dual resonance mechanisms facilitating enhanced optical transmission in coaxial waveguide arrays

We experimentally and computationally demonstrate high transmission through arrays of coaxial apertures with different geometries and arrangements in silver films. By studying both periodic and random arrangements of apertures, we were able to isolate transmission enhancement phenomena owing to surface plasmon effects from those owing to the excitation of cylindrical surface plasmons within the apertures themselves.This work was partially supported by the Office of Naval Research. The support of the Australian Research Council through its Centers of Excellence, Federation Fellow, and Discovery Programs is acknowledged

Field effect studies on rubrene and impurities of rubrene

Rubrene single crystals have been grown by a vapor-phase process. Two additional compounds that contaminate rubrene have been identified and their structures determined. Single crystals of rubrene show excellent crystallinity and very small rocking curve width. Field effect transistors based on pure rubrene single crystals with colloidal graphite electrodes and Parylene as a dielectric demonstrate a maximal mobility of 13 cm(2)/Vs with strong anisotropy. The mobility increases very slightly with cooling, but decreases significantly at low temperatures

Dielectric properties of amorphous phase-change materials

The dielectric function of several amorphous phase-change materials has been determined by employing a combination of impedance spectroscopy (9 kHz–3 GHz) and optical spectroscopy from the far- (20cm−1, 0.6 THz) to the near- (12000cm−1, 360 THz) infrared, i.e., from the DC limit to the first interband transition. While phase-change materials undergo a change from covalent bonding to resonant bonding on crystallization, the amorphous and crystalline phases of ordinary chalcogenide semiconductors are both governed by virtually the same covalent bonds. Here, we study the dielectric properties of amorphous phase-change materials on the pseudobinary line between GeTe and Sb2Te3. These data provide important insights into the charge transport and the nature of bonding in amorphous phase-change materials. No frequency dependence of permittivity and conductivity is discernible in the impedance spectroscopy measurements. Consequently, there are no dielectric relaxations. The frequency-independent conductivity is in line with charge transport via extended states. The static dielectric constant significantly exceeds the optical dielectric constant. This observation is corroborated by transmittance measurements in the far infrared, which show optical phonons. From the intensity of these phonon modes, a large Born effective charge is derived. Nevertheless, it is known that crystalline phase-change materials such as GeTe possess even significantly larger Born effective charges. Crystallization is hence accompanied by a huge increase in the Born effective charge, which reveals a significant change of bonding upon crystallization. In addition, a clear stoichiometry trend in the static dielectric constant along the pseudobinary line between GeTe and Sb2Te3 has been identified

Modernist landscapes of Ankara

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Following the collapse of the Ottoman Empire, Mustafa Kemal and the Kemalist revolutionaries believed that the new Turkey should be a ‘modern’ democracy and also a ‘green’ country in line with positivist science and modernist culture. In this context, the landscapes of Republican Ankara would become an experimental field for this Turkish nation-building and modernization. This article traces the development of modernist landscape ideology during the early Republican Era in Turkey and its translation by planner and architect Hermann Jansen into detailed design ideas for Ankara. It illustrates the interaction between Jansen’s cutting-edge social and landscape architectural ideas and the Anatolian landscapes after the First World War. Finally, it more widely defends the value of the fantasized and partly realized modernist landscapes of Ankara as part of the urban collective memory in Turkey and the modernist cultural heritage

Dielectric properties of amorphous phase-change materials

The dielectric function of several amorphous phase-change materials has been determined by employing a combination of impedance spectroscopy (9 kHz–3 GHz) and optical spectroscopy from the far- (20cm−1, 0.6 THz) to the near- (12000cm−1, 360 THz) infrared, i.e., from the DC limit to the first interband transition. While phase-change materials undergo a change from covalent bonding to resonant bonding on crystallization, the amorphous and crystalline phases of ordinary chalcogenide semiconductors are both governed by virtually the same covalent bonds. Here, we study the dielectric properties of amorphous phase-change materials on the pseudobinary line between GeTe and Sb2Te3. These data provide important insights into the charge transport and the nature of bonding in amorphous phase-change materials. No frequency dependence of permittivity and conductivity is discernible in the impedance spectroscopy measurements. Consequently, there are no dielectric relaxations. The frequency-independent conductivity is in line with charge transport via extended states. The static dielectric constant significantly exceeds the optical dielectric constant. This observation is corroborated by transmittance measurements in the far infrared, which show optical phonons. From the intensity of these phonon modes, a large Born effective charge is derived. Nevertheless, it is known that crystalline phase-change materials such as GeTe possess even significantly larger Born effective charges. Crystallization is hence accompanied by a huge increase in the Born effective charge, which reveals a significant change of bonding upon crystallization. In addition, a clear stoichiometry trend in the static dielectric constant along the pseudobinary line between GeTe and Sb2Te3 has been identified