[en] We report on the chemical vapor deposition synthesis of MoO₂ nanoplatelets by sublimation of MoO₃ and its reduction in a hydrogen atmosphere at 750 °C. When grown on Si/SiO₂ substrates, the platelets primarily assume a rhomboidal shape and have thicknesses ranging from several to tens of nm. The morphology of MoO₂ crystals was found to depend on the chemical nature of substrates. MoO₂ platelets on Si/SiO₂ were characterized by a number of microscopic and spectroscopic techniques, and the electrical measurements revealed the metallic nature of their conductivity averaging at 2400 ± 1000 S cm⁻¹. Raman spectroscopy of MoO₂ platelets on graphene indicates their strong hole injection property. Small thickness, planar morphology, high chemical stability and metallic conductivity of ultrathin MoO₂ platelets make them potentially interesting for integration different other two-dimensional materials in a variety of electronic structures and devices. (paper)

[en] One of the exceptional features of the van der Waals (vdW) ferroelectrics is the existence of stable polarization at a level of atomically thin monolayers. This ability to withstand a detrimental effect of the depolarization fields gives rise to complex domain configurations characterized, among others, by the presence of layered "antipolar" head-to-head (H-H) or tail-to-tail (T-T) dipole arrangements. In this study, tomographic piezoresponse force microscopy (TPFM) is employed to study the 3D polarization arrangement in vdW ferroelectric α-In${}_2$Se${}_3$. Sequential removal of thin layers from the polar surface using the PFM tip reveals a complex 3D profile of the domain walls in the α-In${}_2$Se${}_3$ crystals. Antiparallel domain layers stacked along the polar direction are also observed by PFM imaging of the non-polar surfaces showing that H-H and T-T domain boundaries are commonly present in α-In${}_2$Se${}_3$. Application of TPFM to the electrically written domains allows evaluation of their geometrical lateral-to-vertical size aspect ratio, which shows a strong prevalence for the sidewise expansion in comparison to the forward growth. Local I-V measurements reveal a strong polarization direction dependence of conductivity due to the modulation of the energy barrier height as corroborated by theoretical modeling. (© 2024 The Author(s). Advanced Functional Materials published by Wiley‐VCH GmbH)

[en] The band structure of the quasi-one-dimensional transition metal trichalcogenide ZrS₃(001) was investigated using nanospot angle resolved photoemission spectroscopy (nanoARPES) and shown to have many similarities with the band structure of TiS₃(001). We find that ZrS₃, like TiS₃, is strongly n-type with the top of the valence band ∼1.9 eV below the Fermi level, at the center of the surface Brillouin zone. The nanoARPES spectra indicate that the top of the valence band of the ZrS₃(001) is located at $\stackrel{¯<!--\; ??\; -->}{\mathrm{\Gamma <!--\; ??\; -->}}$. The band structure of both TiS₃ and ZrS₃ exhibit strong in-plane anisotropy, which results in a larger hole effective mass along the quasi-one-dimensional chains than perpendicular to them. (letter)

[en] Arrays of nearly identical graphene devices on Si/SiO₂ exhibit a substantial device-to-device variation, even in case of a high-quality chemical vapor deposition (CVD) or mechanically exfoliated graphene. We propose that such device-to-device variation could provide a platform for highly selective multisensor electronic olfactory systems. We fabricated a multielectrode array of CVD graphene devices on a Si/SiO₂ substrate and demonstrated that the diversity of these devices is sufficient to reliably discriminate different short-chain alcohols: methanol, ethanol, and isopropanol. The diversity of graphene devices on Si/SiO₂ could possibly be used to construct similar multisensor systems trained to recognize other analytes as well

[en] Phase relations in the ternary system Ce-Pd-Si have been established for the isothermal section at 800 deg. C based on X-ray powder diffraction and EMPA techniques on about 130 alloys, which were prepared by arc-melting under argon or powder reaction sintering. Eighteen ternary compounds have been observed to participate in the phase equilibria at 800 deg. C. Atom order was determined by direct methods from X-ray single-crystal counter data for the crystal structures of τ₈-Ce₃Pd₄Si₄ (U₃Ni₄Si₄-type, Immm; a=0.41618(1), b=0.42640(1), c=2.45744(7) nm), τ₁₆-Ce₂Pd₁₄Si (own structure type, P4/nmm; a=0.88832(2), c=0.69600(2) nm) and also for τ₁₈-CePd_1-xSi_x (x=0.07; FeB-type, Pnma; a=0.74422(5), b=0.45548(3), c=0.58569(4) nm). Rietveld refinements established the atom arrangement in the structures of τ₅-Ce₃PdSi₃ (Ba₃Al₂Ge₂-type, Immm; a=0.41207(1), b=0.43026(1), c=1.84069(4) nm) and τ₁₃-Ce_3-xPd_20+xSi₆ (0≤x≤1, Co₂₀Al₃B₆-type, Fm3-barm; a=1.21527(2) nm). The ternary compound Ce₂Pd₃Si₃ (structure-type Ce₂Rh_1.35Ge_4.65, Pmmn; a=0.42040(1), b=0.42247(1), c=1.72444(3) nm) was detected as a high-temperature compound, however, does not participate in the equilibria at 800 deg. C. Phase equilibria in Ce-Pd-Si are characterized by the absence of cerium solubility in palladium silicides. Mutual solubility among cerium silicides and cerium-palladium compounds are significant whereby random substitution of the almost equally sized atom species palladium and silicon is reflected in extended homogeneous regions at constant Ce-content such as for τ₂-Ce(Pd_xSi_1-x)₂ (AlB₂-derivative type), τ₆-Ce(Pd_xSi_1-x)₂ (ThSi₂-type) and τ₇-CePd_2-xSi_2+x. The crystal structures of compounds τ₄-Ce_∼8Pd_∼46Si_∼46, τ₁₂-Ce_∼29Pd_∼49Si_∼22, τ₁₅-Ce_∼22Pd_∼67Si_∼11, τ₁₇-Ce_∼5Pd_∼77Si_∼18 and τ₁₈-CePd_1-xSi_x (x∼0.1) are still unknown. - Abstract: Phase relations in the ternary system Ce-Pd-Si have been established for the isothermal section at 800 deg. C based on X-ray powder diffraction, metallography, SEM and EMPA techniques on about 130 alloys. 18 ternary compounds were observed. Display Omitted

[en] Phase relations have been established in the ternary system Ce-Rh-Si for the isothermal section at 800 deg. C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 deg. C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ₇-Ce₃RhSi₃, (Ba₃Al₂Ge₂-type), τ₈-Ce₂Rh_3-xSi_3+x (Ce₂Rh_1.35Ge_4.65-type), τ₁₀-Ce₃Rh_4-xSi_4+x (U₃Ni₄Si₄-type), τ₁₁-CeRh₆Si₄ (LiCo₆P₄-type), τ₁₃-Ce₆Rh₃₀Si_19.3 (U₆Co₃₀Si₁₉-type), τ₁₈-Ce₄Rh₄Si₃ (Sm₄Pd₄Si₃-type), τ₂₁-CeRh₂Si (CeIr₂Si-type), τ₂₂-Ce₂Rh_3+xSi_1-x (Y₂Rh₃Ge-type) and τ₂₄-Ce₈(Rh_1-xSi_x)₂₄Si (Ce₈Pd₂₄Sb-type). For τ₂₅-Ce₄(Rh_1-xSi_x)₁₂Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ₃-CeRhSi₂ (CeNiSi₂-type) and τ₆-Ce₂Rh₃Si₅ (U₂Co₃Si₅-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ₄-Ce₂₂Rh₂₂Si₅₆, τ₅-Ce₂₀Rh₂₇Si₅₃ and τ₂₃-Ce_33.3Rh_58.2-55.2Si_8.5-11.5 are unknown. High temperature compounds with compositions Ce₁₀Rh₅₁Si₃₃ (U₁₀Co₅₁Si₃₃-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 deg. C. - Graphical abstract: Phase relations in the ternary system Ce-Rh-Si have been established for the isothermal section at 800 deg. C based on X-ray powder and single-crystal diffraction, metallography, SEM and EMPA techniques on about 80 alloys. 25 ternary compounds were observed.

[en] Optical characterization of anisotropic multicomponent nanostructures is generally not a trivial task, since the relation between a material's structural properties and its permittivity tensor is nonlinear. In this regard, an array of slanted cobalt nanopillars that are conformally coated with few-layer graphene is a particularly challenging object for optical characterization, as it has a complex anisotropic geometry and comprises several materials with different topologies and filling fractions. Normally, a detailed characterization of such complex nanostructures would require a combination of several microscopic and spectroscopic techniques. In this letter, we demonstrate that the important structural parameters of these graphene-coated sculptured thin films can be determined using a fast and simple generalized spectroscopic ellipsometry test combined with an anisotropic Bruggeman effective medium approximation. The graphene coverage as well as structural parameters of nanostructured thin films agree excellently with electron microscopy and Raman spectroscopy observations. The demonstrated optical approach may also be applied to the characterization of other nanostructured materials