Recent highlights


Overview of the transformation of spongin scaffolds to a carbonized 3D structure at 1200°C

Overview of the transformation of spongin scaffolds to a carbonized 3D structure at 1200°C. (A) Typical cellular and hierarchical morphology of Hippospongia communis demosponge organic skeleton after purification remains unchanged during the process of carbonization in spite of a decrease in volume by up to 70%. (B) Carbonized 3D scaffold can be sawn into 2-mm-thick slices (C). Stereomicroscopy (D and E) images of carbonized spongin network confirm its structural integrity, typical for sponge-like constructs.(F) NEXAFS C1s K-edge spectra of native and carbonized spongin heated at different temperatures, HOPG, and nanocomposite MWCNT/Cr2O3.

Extreme biomimetics: Preservation of molecular detail in centimeter-scale samples of biological meshes laid down by sponges

 Ia. Petrenko, A.P. Summers, P. Simon, S. Żółtowska-Aksamitowska, M. Motylenko, C. Schimpf, D. Rafaja, F. Roth, K. Kummer, E. Brendler, O.S. Pokrovsky, R. Galli, M. Wysokowski, H. Meissner, E. Niederschlag, Y. Joseph, S. Molodtsov, A. Ereskovsky, V. Sivkov, S. Nekipelov, O. Petrova, O. Volkova, M. Bertau, M. Kraft, A. Rogalev, M. Kopani, T. Jesioniowski, and H. Ehrlich

A chemical procedure for modification of double-walled carbon nanotubes (DWCNTs) to enhance their response to humidity was developed. The DWCNTs walls were etched by hot concentrated sulfuric acid, after what the edge carbon sites were saturated by chlorine via reaction with CCl4 vapor. This treatment increases the dispersibility of DWCNTs in solvents, removes oxygen groups, and produces chlorine-decorated holes in the outer walls. Networks of chlorinated holey DWCNTs showed a high repeatable response to humid environment and a good reversible behavior after the sensor purging by dry air. The density functional theory calculations predict enhanced polarization of the DWCNTs when they contain chlorine-decorated holes in the outer walls and physisorption of H2O molecules near chlorine atoms. These two effects are the cause of an intense low-noise signal to gaseous H2O and easy sensor recovery.

Science Advances 5 (2019) eaax2805.


Chlorinated holey double-walled carbon nanotubes for relative humidity sensors

L.G. Bulusheva, V.I. Sysoev, E.V. Lobiak, Yu.V. Fedoseeva, A.A. Makarova, M. Dubois, E. Flahaut, and A.V. Okotrub

A chemical procedure for modification of double-walled carbon nanotubes (DWCNTs) to enhance their response to humidity was developed. The DWCNTs walls were etched by hot concentrated sulfuric acid, after what the edge carbon sites were saturated by chlorine via reaction with CCl4 vapor. This treatment increases the dispersibility of DWCNTs in solvents, removes oxygen groups, and produces chlorine-decorated holes in the outer walls. Networks of chlorinated holey DWCNTs showed a high repeatable response to humid environment and a good reversible behavior after the sensor purging by dry air. The density functional theory calculations predict enhanced polarization of the DWCNTs when they contain chlorine-decorated holes in the outer walls and physisorption of H2O molecules near chlorine atoms. These two effects are the cause of an intense low-noise signal to gaseous H2O and easy sensor recovery.

Carbon 148 (2019) 413.


Milling-induced chemical decomposition of the surface of EuBaCo2O5.5 powders studied by means of soft X-ray absorption spectroscopy

V.R. Galakhov, M.S. Udintseva, V.V. Mesilov, B.A. Gizhevskii, S.V. Naumov, S.V. Telegin, and D.A. Smirnov

We present results of soft X-ray absorption spectroscopy studies of EuBaCo2O5.5 powders subjected to mechanical impact (milling in a ball mill). We show that in the near-surface region (5-10 nm) of particles of the powder, EuBaCo2O5.5 decomposes into Co3O4, BaCO3, and EuCoO3. A knowledge of the low-spin state of Co3+ ions in EuCoO3 and Co3O4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo2O5.5 sample subjected to mechanical impact near its surface, which is inaccessible to standard X-ray phase analysis.

Applied Surface Science 493 (2019) 1048.


SEM micrographs of: (a) SiNW-15 nanostructured silicon surface using 15 s silver deposition in the first MAWCE etching step; (b) SiNW-45 nanostructured silicon surface using 45 s silver deposition in the first MAWCE etching step; (c) typical cross sectional view for MAWCE SiNWs array; (d) in-situ mechanically modified nanostructured silicon surface. (e) XANES Si L2,3 spectra for the references (from down to top) crystalline silicon c-Si, amorphous silicon a-Si, silicon suboxides SiO1.3 and SiO1.7, thermally grown 40 nm film of silicon dioxide SiO2; (f) XANES Si L2,3 registered from the initial arrays obtained under different etching time (15 and 45 sec) and their in-situ mechanically modified surface parts. Arrows indicate the presence of differently pronounced dip.

Surface deep profile synchrotron studies of mechanically modified top-down silicon nanowires array using ultrasoft X-ray absorption near edge structure spectroscopy

S. Yu. Turishchev, E. V. Parinova, A. K. Pisliaruk, D. A. Koyuda, D. Yermukhamed, T. Ming, R. Ovsyannikov, D. Smirnov, A. Makarova, and V. Sivakov

Atomic, electronic structure and composition of top-down metal-assisted wet-chemically etched silicon nanowires were studied by synchrotron radiation based X-ray absorption near edge structure technique. Local surrounding of the silicon and oxygen atoms in silicon nanowires array was studied on as-prepared nanostructured surfaces (atop part of nanowires) and their bulk part after, first time applied, in-situ mechanical removal atop part of the formed silicon nanowires. Silicon suboxides together with disturbed silicon dioxide were found in the composition of the formed arrays that affects the electronic structure of silicon nanowires. The results obtained by us convincingly testify to the homogeneity of the phase composition of the side walls of silicon nanowires and the electronic structure in the entire length of the nanowire. The controlled formation of the silicon nanowires array may lead to smart engineering of its atomic and electronic structure that infuences the exploiting strategy of metal-assisted wet-chemically etched silicon nanowires as universal matrices for different applications.

Scientific Reports 9 (2019) 8066.


Morphological and structural characterization of the 1% LSO sample. a) TEM image of 1% LSO. b) HRTEM image of 1% LSO, from the inset rectangle in (a). c,d) The SAED pattern and identities of the different diffraction rings, corresponding to the layered, spinel, and Li2SnO3 structures, respectively. e-i) STEM image and EDS maps of O, Mn, Ni, and Sn.
XAS Spectra of the four samples in TEY Mode. k) Ni L2,3 edge. l) Mn L2,3 edge. m) O K edge.

Tuning Anionic Redox Activity and Reversibility for a High-Capacity Li-Rich Mn-Based Oxide Cathode via an Integrated Strategy

Q. Li, D. Zhou, L. Zhang, D. Ning; Z. Chen, Z. Xu, R. Gao, X. Liu, D. Xie, G. Shcumacher, and X. Liu

When fabricating Li-rich layered oxide cathode materials, anionic redox chemistry plays a critical role in achieving a large specific capacity. Unfortunately, the release of lattice oxygen at the surface impedes the reversibility of the anionic redox reaction, which induces a large irreversible capacity loss, inferior thermal stability, and voltage decay. Therefore, methods for improving the anionic redox constitute a major challenge for the application of high-energy-density Li-rich Mn-based cathode materials. Herein, to enhance the oxygen redox activity and reversibility in Co-free Li-rich Mn-based Li1.2Mn0.6Ni0.2O2 cathode materials by using an integrated strategy of Li2SnO3 coating-induced Sn doping and spinel phase formation during synchronous lithiation is proposed. As an Li+ conductor, a Li2SnO3 nanocoating layer protects the lattice oxygen from exposure at the surface, thereby avoiding irreversible oxidation. The synergy of the formed spinel phase and Sn dopant not only improves the anionic redox activity, reversibility, and Li+ migration rate but also decreases Li/Ni mixing. The 1% Li2SnO3-coated Li1.2Mn0.6Ni0.2O2 delivers a capacity of more than 300 mAh g-1 with 92% Coulombic efficiency. Moreover, improved thermal stability and voltage retention are also observed. This synergic strategy may provide insights for understanding and designing new high-performance materials with enhanced reversible anionic redox and stabilized surface lattice oxygen.

Advanced Functional Materials (2019) 1806706.


hBN monolayer on curved Ni(1 1 1). Top, STM and, bottom, LEED for a monolayer of hBN homogeneously covering the curved Ni crystal sketched in the center. The STM images have been taken at the positions roughly indicated over the sample. LEED patterns correspond to the center ((1 1 1) plane), midway (vicinal angle α = ±7°), and densely stepped edges (α = ±15°) of the sample and have been acquired using 63 eV electron impinging parallel to the [1 1 1] direction in all cases. Insets in STM images belong to the indicated line profiles, which prove the presence of hBN-covered microfacets.

Boron nitride monolayer growth on vicinal Ni(111) surfaces systematically studied with a curved crystal

L. Fernandez, A. Makarova, C. Laubschat, D. V. Vyalikh, D. Yu. Usachov, J.E. Ortega, and F. Schiller

The structural and electronic properties of hexagonal boron nitride (hBN) grown on stepped Ni surfaces are systematically investigated using a cylindrical Ni crystal as a tunable substrate. Our experiments reveal homogeneous hBN monolayer coating of the entire Ni curved surface, which in turn undergoes an overall faceting. The faceted system is defined by step-free hBN/Ni(1 1 1) terraces alternating with strongly tilted hBN/Ni(1 1 5) or hBN/Ni(1 1 0) nanostripes, depending on whether we have A-type or B-type vicinal surfaces, respectively. Such deep substrate self-organization is explained by both the rigidity of the hBN lattice and the lack of registry with Ni crystal planes in the vicinity of the (1 1 1) surface. The analysis of the electronic properties by photoemission and absorption spectroscopies reveal a weaker hBN/Ni interaction in (1 1 0)- and (1 1 5)-oriented facets, as well as an upward shift of the valence band with respect to the band position at the hBN/Ni(1 1 1) terrace.

2D Matter (2019).


(a) Large scale STM topograph of MoS2 islands on fully covered Gr/Ir(1 1 1) grown in two successive growth cycles and subsequently imaged in situ. The inset shows a zoomed in part of the image marked with a blue box. The arrows in the inset mark different features of the topograph. Green: monolayer MoS2 island, black: bilayer MoS2 island, white: mirror twin boundary, blue: metallic edge state. Image information: tunneling voltage -1.5 V, tunneling current 20 pA, image size 250 × 250 nm2. (b) Corresponding LEED pattern at 86 eV. (c) XPS spectra of the Mo 3d peak. The doublet peak is split into Mo 3d5/2 and Mo 3d3/2 components. The red color traces show the peak for elemental Mo, green color for MoS2 which is shifted by 0.95 eV to a higher binding energy. The additional peak in the green spectrum around 226.5 eV binding energy is due to the S 2s core level. The spectra were recorded using an excitation energy of 370 eV. (d) S 2p doublet.

Narrow photoluminescence and Raman peaks of epitaxial MoS2 on graphene/Ir(1 1 1)

N. Ehlen, J. Hall, B.V. Senkovskiy, M. Hell, J. Li, A. Herman, D. Smirnov, A. Fedorov, V.Yu. Voroshnin, G. Di Santo, L. Petaccia, T. Michely, and A. Grüneis

We report on the observation of photoluminescence (PL) with a narrow 18 meV peak width from molecular beam epitaxy grown MoS2 on graphene/Ir(1 1 1). This observation is explained in terms of a weak graphene-MoS2 interaction that prevents PL quenching expected for a metallic substrate. The weak interaction of MoS2 with the graphene is highlighted by angle-resolved photoemission spectroscopy and temperature dependent Raman spectroscopy. These methods reveal that there is no hybridization between electronic states of graphene and MoS2 as well as a different thermal expansion of both materials. Molecular beam epitaxy grown MoS2 on graphene is therefore an important platform for optoelectronics which allows for large area growth with controlled properties.

2D Mater. 6 (2019) 011006.


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