Supramolecular nesting of cyclic polymers

Advances in template-directed synthesis make it possible to create artificial molecules with protein-like dimensions, directly from simple components. These synthetic macromolecules have a proclivity for self-organization that is reminiscent of biopolymers. Here, we report the synthesis of monodisperse cyclic porphyrin polymers, with diameters of up to 21 nm (750 C–C bonds). The ratio of the intrinsic viscosities for cyclic and linear topologies is 0.72, indicating that these polymers behave as almost ideal flexible chains in solution. When deposited on ​gold surfaces, the cyclic polymers display a new mode of two-dimensional supramolecular organization, combining encapsulation and nesting; one nanoring adopts a near-circular conformation, thus allowing a second nanoring to be captured within its perimeter, in a tightly folded conformation. Scanning tunnelling microscopy reveals that nesting occurs in combination with stacking when nanorings are deposited under vacuum, whereas when they are deposited directly from solution under ambient conditions there is stacking or nesting, but not a combination of both

Evidence confirms an anthropic origin of Amazonian Dark Earths.

Arising from: Silva et al. Nature Communications https://doi.org/10.1038/s41467-020-20184-2 (2021

Plasma enhanced atomic layer deposited MoOx emitters for silicon heterojunction solar cells

A method for the deposition of molybdenum oxide MoOx with high growth rates at temperatures below 200 C based on plasma enhanced atomic layer deposition is presented. The stoichiometry of the overstoichiometric MoOx films can be adjusted by the plasma parameters. First results of these layers acting as hole selective contacts in silicon heterojunction solar cells are presented and discusse

Showcases of industrial symbiosis related to anaerobic digestion at the project UBIS

Industrial symbioses are intended to minimize greenhouse gas emissions, conserve resources and avoid waste through closed material cycles. The waste and residual materials of one actor become the resource of the other. The better use of raw materials can lead to cost and competitive advantages for the involved partners. The UBIS project investigates the realization of such industrial symbioses. Two showcases from the project region with focus on anaerobic digestion illustrate the effectiveness of industrial symbioses

Integrated low-temperature process for the fabrication of amorphous Si nanoparticles embedded in Al2O3 for non-volatile memory application (Phys. Status Solidi A 9∕2016)

Among electronic devices, flash memory is one of the most aggressively scaled technologies, already approaching minimum limits of miniaturization. The nano-floating-gate memory (NFGM), which is based on semiconductor or metal nanoparticles embedded in a dielectric matrix, is regarded as one promising route for future nonvolatile memory applications. In their article on pp. 2446–2451, Ilse et al. present a new fabrication process for multilayers of silicon nanoparticles (Si–NPs) embedded in amorphous Al2O3, combining a nonthermal low-pressure inductively coupled plasma process (LPICP) for Si–NPs and thermalatomic layer deposition (ALD) of Al2O3. This low-temperature process provides some advantages compared to common fabrication techniques of Si–NPs in Al2O3, which mostly include annealing steps with temperatures up to 1150 °C to enable Si–NP formation. At temperatures above 800 °C, the number of the typical fixed oxide charges in amorphous Al2O3 vanishes due to crystallization processes. The influence of the fixed oxide charges in Al2O3 on the programming process and retention is investigated and discussed as possibility to enhance long-term storage of information

Loess accumulation in the Tian Shan piedmont: Implications for palaeoenvironmental change in arid Central Asia

Whilst correlations have been made between the loess of Europe and China, deposits in Central Asia have remained largely overlooked by scientific investigation. The nature of the relationship between loess accumulation and palaeoclimate at the core of the Eurasian loess belt is particularly poorly understood. Here we reconstruct palaeoenvironmental change in Central Asia over the last 40 ky based on data from the Remizovka loess profile, in the northern foothills of the Tian Shan in southern Kazakhstan. Our interpretations are based on synthesis of chronostratigraphic, colour and magnetic susceptibility data, supported by chronostratigraphies from two additional sites nearby, Maibulak and Valikhanova. All three sites record substantially increased loess accumulation during late MIS 3 into the global last glacial maximum (gLGM). At Remizovka, increased loess flux occurred in two pulses at c. 38-25 ka and 22-18 ka, with the intervening period involving incipient pedogenesis. At Maibulak, two loess pulses at c. 40-30 ka and c. 28-22 ka are separated by a weakly developed paleosol which may date to the same time as pedogenesis at Remizovka. There is additional possible periglacial influence at Maibulak from c. 40–33.5 ka. At Valikhanova, there is some age overlap between paleosol and loess samples, but overall loess accumulation appears to have increased at c. 42-35 ka, c. 30 ka and the gLGM, with pedogenesis occurring >40 ka and c. 32 ka. At all three sites, Holocene loess accumulation is minimal; this period is characterised by pedogenesis. The chronostratigraphic variability between our sites highlights a need to interrogate climate-driven models for loess formation in piedmont environments. We interpret our data in the context of regional palaeoenvironmental archives to indicate that loess accumulation increased coeval with MIS 3 glacial advance in the Tian Shan, which was facilitated by northward expansion of the Asian monsoon and associated increase in precipitation. We hypothesise that increased ice volume impeded teleconnections with the temperate zone westerlies to the north; these were compressed against the piedmont resulting in increased wind strength and facilitating increased loess flux. Peak loess accumulation during the gLGM occurred under colder, drier climatic conditions, with reduced but sustained glacial ice volume and persistent influence of the westerlies in the arid Central Asian piedmont loess belt. In the absence of more widespread, reliably dated palaeoenvironmental records from the region, our data become of critical importance for understanding past environmental conditions in Central Asia, relative to elsewhere in Eurasia and globally

Passivation of different black silicon surfaces by ALD deposited Al 2O3

Optical properties of black silicon (b-Si) can be tailored to minimize reflection losses to less than 0.6 % between 300-1000 nm and to improve the absorption at the silicon band-edge by light-trapping. Recently, metal assisted wet-chemically etched (MACE) b-Si was exploited to fabricate high efficiency (18.2 %) solar cells with surface passivation by thermal SiO2 and recombination velocities (SRV) of 100 cm/s [1]. We compare surface passivation performance of ALD-Al2O3 on different dry and wet etched nanostructures. SRVs 8 cm/s on bifacially black 1 cm p-type Si FZ wafers were measured. This technological advance will enable higher efficiencies for various PV-cell concepts

Thermodynamics of a nanowire solar cell: Towards the ultimate limit

A lossless solar cell operating at the Shockley-Queisser (S-Q) limit generates an open-circuit voltage (VOC) equal to the radiative limit. At VOC, the highly directional beam of photons from the sun is absorbed and subsequently externally re-emitted into a 4p solid angle, providing a large photon entropy loss. Moreover, due to many total internal reflections and low internal radiative efficiency, a lot of light is lost in nonradiative recombination events. In our research, we perform a nanophotonic optimization of a semiconductor nanowire geometry with a top microlens in order to decrease the photon entropy loss and to increase the photon escape probability for the nanowire, therefore increasing the output voltage. The optimization leads us to a maximum VOC of 1178 mV which is 141 mV higher than the radiative limit and 172 mV lower than the ultimate limit. The photon entropy loss is also studied fundamentally from the thermodynamics point of view to better understand where the entropy is generated during the absorption-emission processes