Abstract:The RCA-cleaned 6H-SiC surface has a 1 nm native oxide layer, which was directly observed by high-resolution transmission electron microscopy and confirmed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The surface band bending caused by the native oxide layer was studied by synchrotron radiation photoelectron spectroscopy. The binding energy of Si 2p core level for the Ni/oxygen-free SiC interface showed almost zero shift (<0.07 eV). However, it red-shifted about 0.34 eV for the… Show more
“…The presence of a native SiO 2 layer and its influence on the ALD growth of the Al 2 O 3 and ZrO 2 films was evaluated experimentally through X-ray photoelectron spectroscopy (XPS) and also through numerical simulations (Supplementary Figure S4 and Figure S5). Although reported in the literature, 34 XPS analysis shows no indication of a native layer on the surface of the 4H-SiC. In addition, no mixing between the substrate with the ALD films is observed.…”
Chemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar 1 dielectric crystals (e.g. SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy (SEIRA). We report on the behaviour of SPhP resonances of SiC nanopillars following the incorporation of sub-and nanometric coatings of Al 2 O 3 and ZrO 2 obtained by atomic layer deposition. Concurrent anomalous red and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al 2 O 3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic (LO) phonon of Al 2 O 3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al 2 O 3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al 2 O 3 permittivity. Deposition of ZrO 2 , whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm-1 for films up to ≈ 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO 2 permittivity and provide evidence for a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, predicted shifts for thicker layers may thus provide a tool for real-time monitoring of ultrathin film growth.
“…The presence of a native SiO 2 layer and its influence on the ALD growth of the Al 2 O 3 and ZrO 2 films was evaluated experimentally through X-ray photoelectron spectroscopy (XPS) and also through numerical simulations (Supplementary Figure S4 and Figure S5). Although reported in the literature, 34 XPS analysis shows no indication of a native layer on the surface of the 4H-SiC. In addition, no mixing between the substrate with the ALD films is observed.…”
Chemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar 1 dielectric crystals (e.g. SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy (SEIRA). We report on the behaviour of SPhP resonances of SiC nanopillars following the incorporation of sub-and nanometric coatings of Al 2 O 3 and ZrO 2 obtained by atomic layer deposition. Concurrent anomalous red and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al 2 O 3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic (LO) phonon of Al 2 O 3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al 2 O 3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al 2 O 3 permittivity. Deposition of ZrO 2 , whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm-1 for films up to ≈ 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO 2 permittivity and provide evidence for a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, predicted shifts for thicker layers may thus provide a tool for real-time monitoring of ultrathin film growth.
“…Indeed, it is known that optical and electronic properties of molybdenum disulphide gradually deviate from the bulk response when the thickness of the material is reduced below 4–6 van der Waals layers 34 , 35 . Furthermore, the effects of a possible thin (~1 nm) native oxide layer 36 on the surface of silicon carbide may contribute to the deviation of experimental and theoretical data at low thickness of MoS 2 crystal. Fig.…”
Improvements in device density in photonic circuits can only be achieved with interconnects exploiting highly confined states of light. Recently this has brought interest to highly confined plasmon and phonon polaritons. While plasmonic structures have been extensively studied, the ultimate limits of phonon polariton squeezing, in particular enabling the confinement (the ratio between the excitation and polariton wavelengths) exceeding 102, is yet to be explored. Here, exploiting unique structure of 2D materials, we report for the first time that atomically thin van der Waals dielectrics (e.g., transition-metal dichalcogenides) on silicon carbide substrate demonstrate experimentally record-breaking propagating phonon polaritons confinement resulting in 190-times squeezed surface waves. The strongly dispersive confinement can be potentially tuned to greater than 103 near the phonon resonance of the substrate, and it scales with number of van der Waals layers. We argue that our findings are a substantial step towards infrared ultra-compact phonon polaritonic circuits and resonators, and would stimulate further investigations on nanophotonics in non-plasmonic atomically thin interface platforms.
The unique thermo-electro-mechanical properties of polycrystalline silicon carbide (poly-SiC) make it a desirable candidate for structural and electronic materials for operation in extreme environments. Necessitated by the need to understand how processing additives influence poly-SiC structure and electrical properties, the distribution of lattice defects and impurities across a specimen of hot-pressed 6H poly-SiC processed with p-type additives was visualized with high spatial resolution using a conductive atomic force microscopy approach in which a contact forming a nano-Schottky interface is scanned across the sample. The results reveal very intricate structures within poly-SiC, with each grain having a complex core-rim structure. This complexity results from the influence the additives have on the evolution of the microstructure during processing. It was found that the highest conductivities localized at rims as well as at the interface between the rim and the core. The conductivity of the cores is less than the conductivity of the rims due to a lower concentration of dopant. Analysis of the observed conductivities and current-voltage curves is presented in the context of nano-Schottky contact regimes where the conventional understanding of charge transport to diode operation is no longer valid.
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