540 Chemie und zugeordnete Wissenschaften
Refine
Document Type
- Article (4)
Language
- English (4)
Has Fulltext
- yes (4)
Is part of the Bibliography
- no (4)
Keywords
- CVD (1)
- FEBID (1)
- chemical vapor deposition (1)
- electrical transport characteristics (1)
- gold (1)
- manganese (1)
- metal carbonyl (1)
- nanoparticle (1)
- patterning (1)
- radiation-induced nanostructures (1)
Institute
- Physik (4)
- Biochemie und Chemie (2)
In the search for novel organic charge transfer salts with variable degrees of charge transfer we have studied the effects of two modifications of the recently synthesized donor–acceptor system [tetramethoxypyrene (TMP)]–[tetracyanoquinodimethane (TCNQ)]. One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of the TMP–F4TCNQ complex and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules stacked alternately (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP–TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our band structure calculations confirm the one-dimensional behavior of TMP–F4TCNQ with pronounced dispersion only along the stacking axis. Infrared measurements illustrating the C[triple bond, length as m-dash]N vibration frequency shift in F4TCNQ suggest however no improvement in the degree of charge transfer in TMP–F4TCNQ with respect to TMP–TCNQ. In both complexes about 0.1e is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on the designed TMP–TCNQ and TMP–F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP–TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer.
Vanadium and Manganese Carbonyls as Precursors in Electron-Induced and Thermal Deposition Processes
(2022)
The material composition and electrical properties of nanostructures obtained from focused electron beam-induced deposition (FEBID) using manganese and vanadium carbonyl precursors have been investigated. The composition of the FEBID deposits has been compared with thin films derived by the thermal decomposition of the same precursors in chemical vapor deposition (CVD). FEBID of V(CO)6 gives access to a material with a V/C ratio of 0.63–0.86, while in CVD a lower carbon content with V/C ratios of 1.1–1.3 is obtained. Microstructural characterization reveals for V-based materials derived from both deposition techniques crystallites of a cubic phase that can be associated with VC1−xOx. In addition, the electrical transport measurements of direct-write VC1−xOx show moderate resistivity values of 0.8–1.2 × 103 µΩ·cm, a negligible influence of contact resistances and signatures of a granular metal in the temperature-dependent conductivity. Mn-based deposits obtained from Mn2(CO)10 contain ~40 at% Mn for FEBID and a slightly higher metal percentage for CVD. Exclusively insulating material has been observed in FEBID deposits as deduced from electrical conductivity measurements. In addition, strong tendencies for postgrowth oxidation have to be considered.
In this paper we present first-order reversal curve (FORC) diagrams of ensembles of three-dimensional Co3Fe nanostructures as 2 × 2 arrays of nano-cubes and nano-trees. The structures are fabricated and investigated by an advanced platform of focused electron beam induced deposition combined with high-resolution detection of magnetic stray fields using a home-built micro-Hall magnetometer based on an AlGaAs/GaAs heterostructure. The experimental FORC diagrams are compared to macrospin simulations for both geometries at different angles of the externally applied magnetic field. The measured FORC diagrams are in good agreement with the simulated ones and reflect non-uniform magnetization reversal dominated by multi-vortex states within, and strong magnetic coupling between, the building blocks of our nanostructures. Thus, a FORC analysis of small arrays of 3D magnetic nanostructures provides more detailed insights into the mechanisms of magnetization reversal beyond standard major hysteresis loop measurements.
Directed deposition of silicon nanowires using neopentasilane as precursor and gold as catalyst
(2012)
In this work the applicability of neopentasilane (Si(SiH3)4) as a precursor for the formation of silicon nanowires by using gold nanoparticles as a catalyst has been explored. The growth proceeds via the formation of liquid gold/silicon alloy droplets, which excrete the silicon nanowires upon continued decomposition of the precursor. This mechanism determines the diameter of the Si nanowires. Different sources for the gold nanoparticles have been tested: the spontaneous dewetting of gold films, thermally annealed gold films, deposition of preformed gold nanoparticles, and the use of “liquid bright gold”, a material historically used for the gilding of porcelain and glass. The latter does not only form gold nanoparticles when deposited as a thin film and thermally annealed, but can also be patterned by using UV irradiation, providing access to laterally structured layers of silicon nanowires.