2D Mater. 4, 025030 (2017)
We report on a scanning confocal Raman spectroscopy study investigating the strain-uniformity and the overall strain and doping of high-quality chemical vapour deposited (CVD) graphenebased heterostuctures on a large number of different substrate materials, including hexagonal boron nitride (hBN), transition metal dichalcogenides, silicon, different oxides and nitrides, as well as polymers. By applying a hBN-assisted, contamination free, dry transfer process for CVD graphene, high-quality heterostructures with low doping densities and low strain variations are assembled. The Raman spectra of these pristine heterostructures are sensitive to substrate-induced doping and strain variations and are thus used to probe the suitability of the substrate material for potential highquality graphene devices. We find that the flatness of the substrate material is a key figure for gaining, or preserving high-quality graphene.

The Graphene Flagship’s new Spotlight series aims to promote the contributions of the younger members of the Graphene Flagship. First up: Luca Banszerus discusses his excellent work in developing a reliable transfer process for high-quality CVD graphene (more).

J. Phys.: Condens. Matter 28, 495501 (2016)
Ternary (Bi_1−xSb_x)₂Te₃ films with an Sb content between 0 and 100% were deposited on a Si(1 1 1) substrate by means of molecular beam epitaxy. X-ray diffraction measurements confirm single crystal growth in all cases. The Sb content is determined by x-ray photoelectron spectroscopy. Consistent values of the Sb content are obtained from Raman spectroscopy. Scanning Raman spectroscopy reveals that the (Bi_1−xSb_x)₂Te₃ layers with an intermediate Sb content show spatial composition inhomogeneities. The observed spectra broadening in angular-resolved photoemission spectroscopy (ARPES) is also attributed to this phenomena. Upon increasing the Sb content from x = 0 to 1 the ARPES measurements show a shift of the Fermi level from the conduction band to the valence band. This shift is also confirmed by corresponding magnetotransport measurements where the conductance changes from n- to p-type. In this transition region, an increase of the resistivity is found, indicating a location of the Fermi level within the band gap region. More detailed measurements in the transition region reveals that the transport takes place in two independent channels. By means of a gate electrode the transport can be changed from n- to p-type, thus allowing a tuning of the Fermi level within the topologically protected surface states.

Appl. Phys. Lett. 109, 143507 (2016)
We present a microelectromechanical system, in which a silicon beam is attached to a comb-drive actuator, which is used to tune the tension in the silicon beam and thus its resonance frequency. By measuring the resonance frequencies of the system, we show that the comb-drive actuator and the silicon beam behave as two strongly coupled resonators. Interestingly, the effective coupling rate (∼1.5 MHz) is tunable with the comb-drive actuator (+10%) as well as with a side-gate (−10%) placed close to the silicon beam. In contrast, the effective spring constant of the system is insensitive to either of them and changes only by ±0.5%. Finally, we show that the comb-drive actuator can be used to switch between different coupling rates with a frequency of at least 10 kHz.

The 2nd Institute of physics successfully took part in the "ATG Herbstlauf 2016" with 5 runners. In the 10.6 km run with more than 320 participants through the hilly city forrest Michael Schmitz, Alexander Epping, Nils Freitag, Guido Geulen and Margarete Betger managed to achieve a very good 7th place in the team rating with a best 23th place for Michael in the mens overall rating.