Graphene samples can have a very high carrier mobility if influences from the substrate and the environment are minimized. Embedding a graphene sheet into a heterostructure with hexagonal boron nitride (hBN) on both sides was shown to be a particularly efficient way of achieving a high bulk mobility [1]. Nanopatterning graphene can add extra damage and drastically reduce sample mobility by edge disorder [2][3][4]. Preparing etched graphene nanostructures on top of an hBN substrate instead of SiO2 is no remedy, as transport characteristics are still dominated by edge roughness [5]. Here we show that etching fully encapsulated graphene on the nanoscale is more gentle and the high mobility can be preserved. To this end, we prepared graphene antidot lattices [6] where we observe magnetotransport features stemming from ballistic transport. Due to the short lattice period in our samples we can also explore the boundary between the classical and the quantum transport regime.In single layer graphene the charge carriers are completely exposed to the environment, which limits their mobility. Placing graphene on hexagonal boron nitride (hBN) was shown to improve the carrier mobility [7], allowing the observation of ballistic transport or the fractional quantum Hall effect in bulk graphene [8]. Recently, a dry stacking technique was introduced, which allows complete encapsulation of graphene into layers of hBN and excludes any contamination from process chemicals such as electron beam resist [1]. To obtain graphene nanodevices, chemically prepared graphene nanostructures [9-11] are a potential route for certain applications, however, the high flexibility of a top down patterning approach is extremely desirable. Graphene antidot lattices can help circumventing the problem of the missing band gap in transistor applications [12], and were even predicted to serve as the technological basis for spin qubits [13]. Clearly, for advanced graphene nanodevices, not only the bulk mobility has to be improved, but the nanopatterning has to be optimised.Here we present experiments on graphene antidot lattices [6,14,15] etched into hBN/graphene/hBN heterostructures with lattice periods going down to a = 50 nm. Magnetotransport on those samples shows commensurability features stemming from ballistic orbits around one or several antidots. This allows us to prove that the high carrier mobility is preserved in the nanopatterning step even though the zero field resistance is dominated by scattering on the artificial nanopattern, giving an apparent reduction of the mobility. The small feature size of our samples also allows us to approach the region where the classical picture of cyclotron orbits no longer applies. This classical to quantum crossover is governed by the ratio between the Fermi wavelength λ F of the carriers and the dimensions of the nanopattern.To obtain embedded graphene samples, hBN/graphene/hBN stacks were prepared using the dry stacking technique, patterned into Hall bar shape, and contacted using Cr/Au [1]. In hBN/graphene/h...

The delivery of therapeutic drugs to a specific cellular site is a challenge in the treatment of different diseases. Liposomes have been widely studied as vehicles for drug delivery, and recent research begins to show the potential of the light-controlled opening of liposomes. Liposomes with photoactive molecules can release their cargo upon light irradiation for localized drug release. Light as an external trigger can be controlled temporally and spatially with high precision. In this study, we investigate the potential of light-sensitive liposomes with four photosensitizers and two lipid formulations for light-induced release. To investigate the permeabilization of the liposomes, calcein was encapsulated in high concentration inside the liposomes so that the calcein fluorescence is quenched. If calcein is released from the liposome, quenching is avoided, and the fluorescence increases. We demonstrated that liposomes with the sensitizers benzoporphyrine derivative monoacid (BPD), chlorine e6 (Ce6), Al­(III) phthalocyanine chloride disulfonic acid (AlPcS2), and 5,10-di-(4-hydroxyphenyl)-15,20-diphenyl-21,23H-porphyrin (5,10-DiOH) release cargo effectively after irradiation. Liposomes with 5,10-DiOH showed a quicker release compared to the other sensitizers upon irradiation at 420 nm. Further, we observed through fractionated irradiation, that most of the release took place during light application, while the permeability of the liposome decreased shortly after light exposure. This effect was stronger with liposomes containing less cholesterol.

A general and very efficient synthesis of new carbohydrate-substituted porphyrins is described. Reaction of porphyrin 6 with different glycosyl imidates 7 a ± g leads to the formation of carbohydrate-substituted porphyrins 9 a ± g in good yield. Subsequent demetallation and removal of the carbohydrate protection groups leads to the metal-free compounds 11 a ± g. In aqueous solution, compounds 11 a ± g tend to form defined water-soluble aggregates in a self-assembling process. In methanol/water mixtures the aggregation process depends upon the configuration of the anomeric carbon in the carbohydrate moiety. The porphyrinic aggregates are characterized by strong exciton splitting in the Soret absorption spectrum and a red shift for all absorption bands. Interaction of the porphyrinic aggregates with phosphatidylethanolamine and DMPC liposomes leads to very efficient incorporation of mainly monomeric porphyrins 11 a ± g into the liposomes, as was indicated by very large binding constants. At low liposome concentrations noncovalent porphyrin dimers were detected.

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Bio-based carbon 3Synthetic ester, Figure 1 [5] 4,5Natural ester The mineral oil-based transformer oil 1 is a mixture of paraffinic and aromatic hydrocarbons (C 15 -C 50 ). The more biodegradable mixture 2 based on hydrocarbons from renewable sources contains almost no aromatics (see Section 2.1). The synthetic ester oil 3 is a tetraester based on pentaerythritol with linear and branched fatty acids (C 5 -C 10 ) as shown in Figure 1.In liquid-filled transformers, the oil fulfils two important functions in that it provides electrical insulation and removes the heat generated by Joule losses mainly from the windings. The dielectric properties, such as permittivity, dissipation factor, and field strength of the electrical breakdown are important parameters when selecting oil for use in HV power transformers. As an important criterion for the insulation quality, breakdown voltage (BDV) and the partial discharge behavior (PD) of the oils are evaluated and compared in this work. The breakdown field strength, which is difficult to calculate for arbitrary geometries, is usually estimated by measuring the breakdown voltage using standardized test procedures. [3] Some insulation quality tests are required after the transformers have been manufactured, but also during their operating time. In most cases, insulation faults are associated with partial discharges.The heat transfer in transformer oils depends on the thermal conductivity and convection. We determined the viscosity and specific heat capacity that have the greatest impact on heat transfer.This work examines the aging mechanisms of the oil and the solid material used to insulate the windings, which also play an important role in the selection of a suitable insulating fluid. Traces of water in the oil have a significant influence on the long-term stability of Kraft paper. [9] A good indicator of the age of the oil is its acidity, as free carboxylic acids are released through hydrolytic cleavage and oxidation. We therefore examined the water content, the acid number and the peroxide number before and after the high-voltage tests. Results Chemical Composition of Transformer OilsIn order to reveal chemical and structural changes in the molecules as a result of repeated exposure to high voltage, the oil samples were carefully analyzed before and after the long-term Against the background of environmental compatibility and unrestricted technical usability, synthetic, and natural transformer oils are critically compared in long-term tests under high voltage using electrical and instrumental analytical methods. Synthetic alkyl esters of pentaerythrol appear to be sustainable and sometimes superior substitutes for mineral oils in terms of chemical stability, viscosity, permittivity, and heat transport. Natural esters of unsaturated fatty acids are found to be unsuitable for equipment exposed to moist air. Adsorbed water appears to be a general problem in transformer oils. The aging mechanisms and molecular changes during long-term operation include radical reactions, and th...

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