[en] Silicene, a monolayer of silicon atoms arranged in a honeycomb lattice, is excellently compatible with the materials used in today’s semiconductor manufacturing. In this paper, silicene-terminated CaSi₂ is cleaved inside a transmission electron microscope using an in situ manipulator. HRTEM studies on a standard lift-out lamella performed from several crystallographic orientations confirm the cell parameters of a = 3.7 Å and c = 30.60 Å, and allow to determine its exact orientation in the SEM/FIB system. A FIB procedure with corrected tilting and rotating angles has been developed to ensure that the tensile force applied by the manipulator is perpendicular to the (0 0 1) plane, and that the [1 0 0] pole axis could be used for HRTEM imaging. A sharp and flat cleavage interface with a length of more than 1 μm was observed in one in situ experiment. HRTEM images from multiple regions confirm that the flat cleavage follows the (0 0 3) plane of the CaSi₂ crystal. The current in situ study demonstrates that a surface sheet with silicene-like atomic arrangement can be mechanically exfoliated from silicide compounds. (paper)

[en] In this work, we show the doping of graphene most likely from heteroatoms induced by the substrate using Raman spectra, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy and ab initio molecular dynamics (MD) simulations. The doping of graphene on a highly boron-doped silicon substrate was achieved by an annealing at 400 K for about 3 h in an oven with air flow. With the same annealing, only the Raman features similar to that from the pristine graphene were observed in the freestanding graphene and the graphene on a typical Si/SiO₂ wafer. Ab initio MD simulations were performed for defected graphene on boron-doped silicon substrate at several temperatures. All vacancy sites in the graphene are occupied either with B atoms or Si atoms resulting in the mixed boron–silicon doping of the graphene. The MD simulations validated the experimetal finding of graphene doped behavior observed by Raman spectrum. The electronic structure analysis indicated the p-type nature of doped graphene. The observed doping by the possible incorporation of heteroatoms into the graphene, simply only using 400 K annealing the boron-doped Si substrate, could provide a new approach to synthesize doped graphene in a more economic way. (paper)

[en] The paper is devoted to the study of microstructural and magnetic properties of the Fe-based amorphous ribbons after interference pulsed laser heating. The ternary amorphous alloy FeSiB, as well as the multi-component alloys FeCuSiB and FeCuNbSiB, was subjected to laser pulses to induce crystallization in many microislands simultaneously. Structure and properties changes occurred in laser-heated dots. Detailed TEM analysis from a single dot shows the presence of FeSi(α) nanocrystals in the amorphous matrix. The FeSiB alloy is characterized after conventional crystallization by a dendritic structure; however, the alloys with copper as well copper and niobium additions are characterized by the formation of equiaxed crystals in the amorphous matrix. Amorphous alloys before and after the laser heating are soft magnetic; however, conventional crystallization leads to a deterioration of the soft magnetic properties of the material.

[en] A trace (0.2 wt.%) addition of Ge significantly increased both the strength and elongation of Al–3.5Cu–0.4 Mg alloy. An aged Al–3.5Cu–0.4 Mg–0.2Ge (wt.%) alloy revealed good tensile properties after being exposed at 150 °C. Transmission electron microscopy observations showed that these properties are closely correlated to the high-density microstructure of nanoscale precipitates and the good coarsening resistance of those precipitates; Ge stimulated the formation of nanoscale precipitates and suppressed the formation of S′ precipitates in aged Al–3.5Cu–0.4 Mg–0.2Ge (wt.%) alloy.

[en] An in situ transmission-electron-microscopy methodology is developed to observe time-dependent dielectric breakdown (TDDB) in an advanced Cu/ultra-low-k interconnect stack. A test structure, namely a “tip-to-tip” structure, was designed to localize the TDDB degradation in small dielectrics regions. A constant voltage is applied at 25 °C to the “tip-to-tip” structure, while structural changes are observed at nanoscale. Cu nanoparticle formation, agglomeration, and migration processes are observed after dielectric breakdown. The Cu nanoparticles are positively charged, since they move in opposite direction to the electron flow. Measurements of ionic current, using the Triangular-Voltage-Stress method, suggest that Cu migration is not possible before dielectric breakdown, unless the Cu/ultra-low-k interconnect stacks are heated to 200 °C and above

[en] Highlights: • 3D graphite foam is fabricated from commercial graphite foil upon a rapid expansion process. • The Ir nanoparticles are well grown on the 3D graphite, where Ir content is as low as 5.91 wt%. • The Ir/GF exhibits excellent activities with overpotentials of ~7 mV for the HER and ~290 mV for the OER at 10 mA/cm² in acidic solution. • An acidic electrolyser using the Ir/GF steadily delivered a current density of 10 mA/cm² at an extremely low cell voltage of ~1.55 V. The proton-exchange-membrane (PEM) water-splitting electrolyser is a highly appealing technology for economical hydrogen production. Unfortunately, only Iridium (Ir)-based electrocatalysts show efficient and stable activity towards oxygen evolution reaction (OER) in acidic medium, which seriously hampers the large-scale utilization of PEM water splitting electrolyser as a result of high cost and scarcity of the Ir. Here, we report synthesis of Ir nanoparticles on 3D graphite foam (Ir/GF) upon a heat treatment of Ir³⁺/polyaniline complex that were beforehand prepared on the GF. Benefiting from low content of Ir (5.91 wt%) and excellent resistance of 3D graphite foam against oxidative corrosion, the resultant Ir/GF functionalizes as a novel bifunctional electrocatalyst for overall water splitting in a 0.5 M H₂SO₄ solution. Noticeably, the HER and OER overpotentials of the Ir/GF at 10 mA/cm² are only ~ 7 mV and ~ 290 mV, respectively, which are much lower than those of commercial Pt/C and Ir/C catalysts as well as reported Pt or Ir-based electrocatalysts. Significantly, an acidic water-splitting electrolyser with a current density of 10 mA/cm² is steadily driven by the Ir/GF at a cell voltage of only ~ 1.55 V, which is substantially lower than 1.65 V for commercial Pt/C and Ir/C couple.

[en] Raman mapping is performed to study the lateral damage in supported monolayer graphene carved by 30 keV focused Ga"+ beams. The evolution of the lateral damage is tracked based on the profiles of the intensity ratio between the D (1341 cm"−"1) and G (1582 cm"−"1) peaks (I_D/I_G) of the Raman spectra. The I_D/I_G profile clearly reveals the transition from stage 2 disorder into stage 1 disorder in graphene along the direction away from the carved area. The critical lateral damage distance spans from <1 μm up to more than 30 μm in the experiment, depending on the parameters used for carving the graphene. The wide damage in the lateral direction is attributed to the deleterious tail of unfocused ions in the ion beam probe. The study raises the attention on potential sample damage during direct patterning of graphene nanostructures using the focused ion beam technique. Minimizing the total carving time is recommended to mitigate the lateral damage

[en] Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin-film through solvothermal method and on-solid-surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin-film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to $\approx <!--\; ???\; -->$ 1.5 $\mathrm{\mu <!--\; ??\; -->}$m), the reported thin-film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two-dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF-PP or 2D BECOF-PN) by employing a surfactant-monolayer-assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF-PP is featured as free-standing thin film with large single-crystalline domains up to $\approx <!--\; ???\; -->$ 60 $\mathrm{\mu <!--\; ??\; -->}$m${}^2$ and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF-PP film on silicon nanowire-based field-effect transistor is demonstrated as a bio-inspired system to mimic neuronal synapses, displaying a learning-erasing-forgetting memory process. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)