Monolayer and bilayer graphene on Ru(0001): layer-specific and moiré-site-dependent phonon excitations. - In: The journal of physical chemistry letters, ISSN 1948-7185, Bd. 12 (2021), 29, S. 6889-6894
Graphene phonons are excited by the local injection of electrons and holes from the tip of a scanning tunneling microscope. Despite the strong graphene-Ru(0001) hybridization, monolayer graphene unexpectedly exhibits pronounced phonon signatures in inelastic electron tunneling spectroscopy. Spatially resolved spectroscopy reveals that the strength of the phonon signal depends on the site of the moiré lattice with a substantial red-shift of phonon energies compared to those of free graphene. Bilayer graphene gives rise to more pronounced spectral signatures of vibrational quanta with energies nearly matching the free graphene phonon energies. Spectroscopy data of bilayer graphene indicate moreover the presence of a Dirac cone plasmon excitation.
https://doi.org/10.1021/acs.jpclett.1c01802
Determination of piezo-resistive coefficient π44 in p-type silicon by comparing simulation and measurement of pressure sensors. - In: AIP Advances, ISSN 2158-3226, Bd. 11 (2021), 8, 085005, insges. 6 S.
https://doi.org/10.1063/5.0060034
Bismuth nanoparticles confined in carbonaceous nanospheres as anodes for high-performance potassium-ion batteries. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 13 (2021), 27, S. 31766-31774
Bismuth (Bi) has been considered as a promising alloying-type anode for potassium-ion batteries (PIBs), owing to its high theoretical capacity and suitable working voltage plateaus. However, Bi suffers from dramatic volume fluctuation and significant pulverization during the discharge/charge processes, resulting in fast capacity decay. Herein, we synthesize Bi nanoparticles confined in carbonaceous nanospheres (denoted as BiC) for PIBs by first utilizing BiOCl nanoflakes as a hard template and a Bi precursor. The construction of the loose structure buffers the mechanical stresses resulting from the volume expansion of Bi during the alloying reaction and avoids the fracture of the electrode structure, thus improving the cycling performance. Moreover, the carbonaceous layers increase the electronic conductivity and disperse the Bi nanoparticles, enhancing the charge transportation and ionic diffusion, which further promotes the rate capability of Bi@C. It exhibits a superior capacity (389 mAh g^-1 at 100 mA g^-1 after 100 cycles), excellent cycling stability (206 mAh g^-1 at 500 mA g^-1 over 1000 cycles), and an improved rate capability (182 mAh g^-1 at 2.0 A g^-1). This work provides a new structuring strategy in alloying materials for boosting reversible and stable potassium-ion storage.
https://doi.org/10.1021/acsami.1c09286
Band bending at heterovalent interfaces: hard X-ray photoelectron spectroscopy of GaP/Si(0 0 1) heterostructures. - In: Applied surface science, Bd. 565 (2021), 150514
https://doi.org/10.1016/j.apsusc.2021.150514
Atomic surface control of Ge(100) in MOCVD reactors coated with (Ga)As residuals. - In: Applied surface science, Bd. 565 (2021), 150513
Heteroepitaxy of planar, low-defect III-V semiconductor layers on Ge(100) requires a single-domain substrate surface, where dimer rows are aligned in parallel on atomically well-ordered terraces, which are separated by steps of even numbered atomic height. The presence of Ga and As in the sample ambience crucially impacts the preparation of such Ge(100) surfaces. Ga and As are commonly omnipresent, when applying metalorganic chemical vapor deposition (MOCVD), either directly supplied by precursors, in the form of MOCVD reactor residuals, or both. We study the impact of the growth conditions on the Ge(100) surface formation in situ, in dependence on the reactor pre-conditioning, the type of As supply, and/or temperature, utilizing surface-sensitive reflection anisotropy spectroscopy. We benchmark the in situ spectra to in system X-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. We find that interaction of tertiarybutylarsine (TBAs) with a coating of the inner MOCVD reactor walls by GaAs residuals favors desorption of As from reactor parts resulting in As-dimers on the Ge(100) surface, which are rotated by 90˚ compared to preparation routes employing TBAs in Ga-free ambience. The optical in situ control enables precise adjustment and switching between distinct Ge(100) surface reconstructions for subsequent III-V heteroepitaxy.
https://doi.org/10.1016/j.apsusc.2021.150513
Electric-field control of a single-atom polar bond. - In: Physical review letters, ISSN 1079-7114, Bd. 126 (2021), 21, 216801, insges. 6 S.
We expose the polar covalent bond between a single Au atom terminating the apex of an atomic force microscope tip and a C atom of graphene on SiC(0001) to an external electric field. For one field orientation, the Au-C bond is strong enough to sustain the mechanical load of partially detached graphene, while for the opposite orientation, the bond breaks easily. Calculations based on density-functional theory and nonequilibrium Green's function methods support the experimental observations by unveiling bond forces that reflect the polar character of the bond. Field-induced charge transfer between the atomic orbitals modifies the polarity of the different electronegative reaction partners and the Au-C bond strength.
https://doi.org/10.1103/PhysRevLett.126.216801
Electrical conductivity adjustment for interface capacitive-like storage in sodium-ion battery. - In: Advanced functional materials, ISSN 1616-3028, Bd. 31 (2021), 24, 2101081, insges. 11 S.
Sodium-ion battery (SIB) is significant for grid-scale energy storage. However, a large radius of Na ions raises the difficulties of ion intercalation, hindering the electrochemical performance during fast charge/discharge. Conventional strategies to promote rate performance focus on the optimization of ion diffusion. Improving interface capacitive-like storage by tuning the electrical conductivity of electrodes is also expected to combine the features of the high energy density of batteries and the high power density of capacitors. Inspired by this concept, an oxide-metal sandwich 3D-ordered macroporous architecture (3DOM) stands out as a superior anode candidate for high-rate SIBs. Taking Ni-TiO2 sandwich 3DOM as a proof-of-concept, anatase TiO2 delivers a reversible capacity of 233.3 mAh g^-1 in half-cells and 210.1 mAh g^-1 in full-cells after 100 cycles at 50 mA g^-1. At the high charge/discharge rate of 5000 mA g^-1, 104.4 mAh g^-1 in half-cells and 68 mAh g^-1 in full-cells can also be obtained with satisfying stability. In-depth analysis of electrochemical kinetics evidence that the dominated interface capacitive-like storage enables ultrafast uptaking and releasing of Na-ions. This understanding between electrical conductivity and rate performance of SIBs is expected to guild future design to realize effective energy storage.
https://doi.org/10.1002/adfm.202101081
Molecular dynamics and proton hyperpolarization via synthetic and crude oil porphyrin complexes in solid and solution states. - In: Langmuir, ISSN 1520-5827, Bd. 37 (2021), 22, S. 6783-6791
The use of vanadyl porphyrins either in synthetic compounds or naturally occurring in asphaltenes is investigated as a source of proton hyperpolarization via dynamic nuclear polarization (DNP) in nuclear magnetic resonance (NMR) experiments. The features of dynamics and location of the vanadyl VO2+ complex in aggregates within the oil asphaltene molecules are studied by means of DNP, electron paramagnetic resonance (EPR), and NMR field cycling relaxometry. Both the solid effect and Overhauser DNP were observed for the asphaltene solution in benzene, as well as in the solution and solid states for synthetic compounds. By comparison with a solution of synthetic vanadyl porphyrins, it is shown that vanadyl porphyrins in asphaltene aggregates are localized outside of the interface of the asphaltene aggregates and more exposed to the maltene molecules than free carbon-centered radicals associated with the core of asphaltene molecules. The perceptible contribution of scalar interaction is observed in solutions for both synthetic and asphaltene vanadyl porphyrins.
https://doi.org/10.1021/acs.langmuir.1c00882
Tunning of templated CuWO4 nanorods arrays thickness to improve photoanode water splitting. - In: Molecules, ISSN 1420-3049, Bd. 26 (2021), 10, 2900, insges. 14 S.
Im Titel ist "4" tiefgestellt
The fabrication of the photoanode of the n-type CuWO4 nanorod arrays was successfully carried out through electrochemical deposition using anodic aluminum oxide (AAO) control templates and for the first time produced distinct gaps between the nanorod arrays. The effectiveness and efficiency of the resulting deposition was shown by the performance of the photoelectrochemical (PEC) procedure with a current density of 1.02 mA cm^-2 with irradiation using standard AM 1.5G solar simulator and electron changed radiation of 0.72% with a bias potential of 0.71 V (vs. Ag/AgCl). The gap between each nanorod indicated an optimization of the electrolyte penetration on the interface, which resulted in the expansion of the current density as much as 0.5 × 1024 cm^-3 with a flat band potential of 0.14 V vs. Ag/AgCl and also a peak quantum efficiency of wavelength 410 nm. Thus, also indicating the gaps between the nanorod arrays is a promising structure to optimize the performance of the PEC water splitting procedure as a sustainable energy source.
https://doi.org/10.3390/molecules26102900
High-performance quasi-solid-state Na-air battery via gel cathode by confining moisture. - In: Advanced functional materials, ISSN 1616-3028, Bd. 31 (2021), 22, 2011151, insges. 9 S.
https://doi.org/10.1002/adfm.202011151