Nanosystems Initiative Munich

About: Nanosystems Initiative Munich is a facility organization based out in Munich, Germany. It is known for research contribution in the topics: Quantum dot & Perovskite (structure). The organization has 323 authors who have published 549 publications receiving 24316 citations.

Monitoring the morphological evolution in mixed-dimensional lead bromide perovskite films with lamellar-stacked perovskite nanoplatelets

Abstract: Mixed-dimensional lead bromide perovskite films combine the properties of both three-dimensional (3D) and two-dimensional (2D) perovskite crystals, and due to their good humidity tolerance, they emerge as promising candidates for long-term stable optoelectronic applications. In order to further tailor the film morphology aiming for a better device performance, it is important to unravel the structural formation mechanism in these perovskite thin films. In the present study, the formation of 3D lead bromide perovskite crystals and the self-assembly of lamellar-stacked 2D perovskite nanoplatelets are comprehensively studied. Samples are prepared through a two-step vapor assisted route with different vapor exposure times in order to monitor the detailed morphology at the specific reaction stage. With grazing incidence X-ray scattering techniques, the preferential orientation of the 3D crystals is found to decrease upon increasing the reaction time. Also, it is evidenced that well-ordered in-plane lamellar-stacked 2D nanoplatelets form aggregates in the bulk structure only. The obtained hierarchical morphology shows excellent structural stability in a humid atmosphere even at a relative humidity level of 80%. Our findings statistically offer a morphological understanding, which is important for the optimization of the sample preparation route and thus the resulting performance of moisture-tolerant perovskite based optoelectronic devices.

Transferable Organic Semiconductor Nanosheets for Application in Electronic Devices.

Abstract: A method has been developed to stabilize and transfer nanofilms of functional organic semiconductors. The method is based on crosslinking of their topmost layers by low energy electron irradiation. The films can then be detached from their original substrates and subsequently deposited onto new solid or holey substrates retaining their structural integrity. Grazing incidence X-ray diffraction, X-ray specular reflectivity, and UV-Vis spectroscopy measurements reveal that the electron irradiation of similar or equal to 50 nm thick pentacene films results in crosslinking of their only topmost similar or equal to 5 nm (3-4 monolayers), whereas the deeper pentacene layers preserve their pristine crystallinity. The electronic performance of the transferred pentacene nanosheets in bottom contact field-effect devices is studied and it is found that they are fully functional and demonstrate superior charge injection properties in comparison to the pentacene films directly grown on the contact structures by vapor deposition. The new approach paves the way to integration of the organic semiconductor nanofilms on substrates unfavorable for their direct growth as well as to their implementation in hybrid devices with unusual geometries, e.g., in devices incorporating free-standing sheets.

New Light on an Old Story: The Crystal Structure of Boron Tetrathiophosphate Revisited

Abstract: The crystal structure of boron tetrathiophosphate BPS4 was reinvestigated using single-crystal X-ray diffraction. The structure shows unidimensional chains similar to SiS2 as structural motifs. BPS4 crystallizes in the orthorhombic space group Ibam (no. 72), with a = 5.6173(3), b = 8.9929(4), c = 5.2433(3) angstrom and V = 264.87(2) angstrom(3) and is closely related to the orthorhombic high-temperature modification of AlPS4 (ht-AlPS4). The SiS2-like chains are all oriented parallel to the c axis, which explains the needle-like morphology and that the crystals easily cleave to thinner needles under mechanical stress. While ht-AlPS4 shows an ordered Al-P sublattice, the B-P sublattice in BPS4 is substantially disordered. The thermal properties of BPS4 were investigated by DTA measurements and a detailed analysis of the Raman spectrum assisted by quantum mechanical calculations is presented. The crystallographic disorder in BPS4 is the result of inter-chain disorder, whereas local intra-chain ordering of B and P can be concluded from Raman spectroscopy.

Postsynthetische Entkopplung oberflächensynthetisierter kovalenter Nanostrukturen von Ag(111)

Abstract: Die Oberflachensynthese von organischen Nanoschichten mithilfe reaktiver Metalloberflachen fuhrt zu stark adsorbierten organischen Nanostrukturen, deren intrinsische Eigenschaften jedoch durch die starke Bindung zur Oberflache verdeckt werden. Daher ist die Reduzierung der elektronischen Kopplung zwischen den organischen Netzwerken und den ublicherweise verwendeten Metalloberflachen ein erster wichtiger Schritt zur Charakterisierung der wahren Eigenschaften. Wir zeigen, dass postsynthetische Iodexposition zur Interkalation einer Iodmonolage zwischen kovalenten Polyphenylen-Netzwerken und Ag(111)-Oberflachen fuhrt. Die experimentell beobachteten Veranderungen zwischen oberflachengebundenen und abgelosten Nanolagen werden anhand von DFT-Simulationen nachvollzogen. Die erzielten Erkenntnisse zeigen, dass Iodinterkalation zu einem Material fuhrt, dessen geometrische und elektronische Eigenschaften denen freistehender Netzwerke sehr ahnlich sind.