Phonon plasmon interaction in ternary group-III-nitrides

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 101, 041909 (2012) and may be found at https://doi.org/10.1063/1.4739415.Phonon-plasmon-coupling in the ternary group-III-nitrides InGaN and AlGaN is investigated experimentally and theoretically. Based on the observation of broadening and shifting of the A1(LO) mode in AlGaN upon Si-doping, a lineshape analysis was performed to determine the carrier concentration. The results obtained by this method are in excellent agreement to those from Hall measurements, confirming the validity of the employed model. Finally, neglecting phonon and plasmon damping, the Raman shift of the A1(LO) mode in dependence of the carrier concentration for AlGaN and InGaN is calculated. This enables a fast and contactless determination of carrier concentrations in the future.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Signature of the two-dimensional phonon dispersion in graphene probed by double-resonant Raman scattering

The contributions of the two-dimensional phonon dispersion to the double-resonant Raman scattering process in graphene is determined from the line shape of the two-phonon combination mode around 2450 cm(-1). This mode is usually referred to as G* or D + D ''. By combining Raman experiments with excitation energies up to 2.8 eV and a full two-dimensional calculation of the double-resonant Raman process based on fourth-order perturbation, we can describe in detail the composition of this two-phonon mode and explain the asymmetry on the high-frequency side. The asymmetry directly reflects phonon contributions with wave vectors away from the high-symmetry lines in the Brillouin zone. The main peak of this mode originates from the K Gamma high-symmetry line highlighting and supporting two important findings: first, the existence of so-called inner processes and, second, the dominant contribution along the high-symmetry line. DOI: 10.1103/PhysRevB.87.07540

Nanoarchitecture Effects on Persistent Room Temperature Photoconductivity and Thermal Conductivity in Ceramic Semiconductors: Mesoporous, Yolk–Shell, and Hollow ZnO Spheres

A gas-phase approach is applied to synthesize a set of spherical particles with mesoporous, yolk−shell, or hollow character. A special arrangement of the ZnO lattice results in a polar character of the particle shell, and this facilitates effective separation of electrons and holes on different sides of the interface

Optical and mechanical properties of nanofibrillated cellulose: toward a robust platform for next-generation green technologies

Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in Nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applicationsComment: in press in Carbohydrate Polymers (2015

Nanoarchitecture Effects on Persistent Room Temperature Photoconductivity and Thermal Conductivity in Ceramic Semiconductors: Mesoporous, Yolk–Shell, and Hollow ZnO Spheres

Whereas size effects have been investigated extensively and are largely understood, it is significantly more challenging to elucidate how functional properties of semiconductors can be altered and ultimately be improved by a hierarchical nanoarchitecture. For semiconductor applications, such as in photovoltaics or photocatalysis, it is of great importance to learn how to avoid the recombination of photogenerated charge carriers and how to enhance their lifetime. A gas-phase synthesis method is explored, which enables the generation of spherical zinc oxide nanostructures with compact, mesoporous, a special type of core−shell, so-called yolk−shell, or hollow character. The particles with hollow character exhibit an extraordinarily long persistence of photogenerated charge carriers. It is demonstrated that the presence of the ZnO shell and its special orientation with respect to the polar character of the wurtzite lattice represent deciding factors. After photoexcitation, electrons and holes migrate to opposite sides of the interfaces, where they are stabilized. Moreover, photoluminescence thermometry was used to determine the thermal conductivity of the samples, which is lowered by a factor of ∼100 compared with bulk ZnO. The thermal conductivity of this type of nanostructure is found to be only 10 times larger than that of air, and this points toward potential applications as thermoelectrics

Optical and mechanical properties of nanofibrillated cellulose: Toward a robust platform for next-generation green technologies

Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in Nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applicationsComment: in press in Carbohydrate Polymers (2015

8th International Conference on Spectroscopic Ellipsometry: Conference Program & Abstracts

Programa y libro de abstracts de las ponencias del ICSE 8, 8th International Conference on Spectroscopic Ellipsometry (Barcelona World Trade Center, 26-31 de mayo de 2019) https://congresses.icmab.es/icse8/N