23 research outputs found
Characterization of collective ground states in single-layer NbSe2
Layered transition metal dichalcogenides (TMDs) are ideal systems for
exploring the effects of dimensionality on correlated electronic phases such as
charge density wave (CDW) order and superconductivity. In bulk NbSe2 a CDW sets
in at TCDW = 33 K and superconductivity sets in at Tc = 7.2 K. Below Tc these
electronic states coexist but their microscopic formation mechanisms remain
controversial. Here we present an electronic characterization study of a single
2D layer of NbSe2 by means of low temperature scanning tunneling
microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy
(ARPES), and electrical transport measurements. We demonstrate that 3x3 CDW
order in NbSe2 remains intact in 2D. Superconductivity also still remains in
the 2D limit, but its onset temperature is depressed to 1.9 K. Our STS
measurements at 5 K reveal a CDW gap of {\Delta} = 4 meV at the Fermi energy,
which is accessible via STS due to the removal of bands crossing the Fermi
level for a single layer. Our observations are consistent with the simplified
(compared to bulk) electronic structure of single-layer NbSe2, thus providing
new insight into CDW formation and superconductivity in this model
strongly-correlated system.Comment: Nature Physics (2015), DOI:10.1038/nphys352
KINETIC-ANALYSIS OF C49-TISI2 AND C54-TISI2 FORMATION AT RAPID THERMAL ANNEALING RATES
We have used in situ resistance versus temperature measurements to demonstrate that a 60 nm titanium thin film on polycrystalline silicon heated at rates up to 3000-degrees-C/min always forms high-resistivity base-centered orthorhombic C49-TiSi2 before the low-resistivity face-centered orthorhombic C54-TiSi2 Phase. Kinetic analysis of the shift in transformation temperatures with heating rate indicates that the activation energies for the formation of C49-TiSi2 and C54-TiSi2 are 2.1 +/- 0.2 and 3.8 +/- 0.5 eV, respectively, when formed du ring the same annealing cycle. The higher activation energy of formation of C54-TiSi2 as compared to C49-TiSi2 suggests that under very high heating rates and annealing temperatures, the formation of C49-TiSi2 before C54-TiSi2 might be completely or partially bypassed
In situ monitoring of thin film reactions during rapid thermal annealing: Nickel silicide formation
P
Growth mechanism of epitaxial YSZ on Si by Pulsed Laser Deposition
The epitaxial growth of yttria-stabilized zirconia (YSZ) on silicon with native oxide was investigated in order to gain more insight in the growth mechanism. Specifically, attention was paid to the possibilities to control the chemical interactions between YSZ, silicon and oxygen during initial growth. The sources of oxygen during growth proved to play an important role in the growth process, as shown by individual manipulation of all sources present during Pulsed Laser Deposition. Partial oxidation of the YSZ plasma and sufficient delivery of oxygen to the growing film were necessary to prevent silicide formation and obtain optimal YSZ crystalline qualities. In these conditions, thickness increase of the silicon native oxide before growth just started to occur, while a much faster regrowth of silicon oxide at the YSZ-Si interface occurred during growth. Control of all these contributions to the growth process is necessary to obtain reproducible growth of high quality YSZ