86 research outputs found
Surface symmetry-breaking and strain effects on orbital occupancy in transition metal perovskite epitaxial films
The electron occupancy of 3d-orbitals determines the properties of transition metal oxides. This can be achieved, for example, through thin-film heterostructure engineering of ABO(3) oxides, enabling emerging properties at interfaces. Interestingly, epitaxial strain may break the degeneracy of 3d-e(g) and t(2g) orbitals, thus favoring a particular orbital filling with consequences for functional properties. Here we disclose the effects of symmetry breaking at free surfaces of ABO(3) perovskite epitaxial films and show that it can be combined with substrate-induced epitaxial strain to tailor at will the electron occupancy of in-plane and out-of-plane surface electronic orbitals. We use X-ray linear dichroism to monitor the relative contributions of surface, strain and atomic terminations to the occupancy of 3z(2)-r(2) and x(2)-y(2) orbitals in La(2/3)Sr(1/3)MnO(3) films. These findings open the possibility of an active tuning of surface electronic and magnetic properties as well as chemical properties (catalytic reactivity, wettability and so on)
Symmetry of the Fermi surface and evolution of the electronic structure across the paramagnetic-helimagnetic transition in MnSi/Si(111)
MnSi has been extensively studied for five decades, nonetheless detailed
information on the Fermi surface (FS) symmetry is still lacking. This missed
information prevented from a comprehensive understanding the nature of the
magnetic interaction in this material. Here, by performing angle-resolved
photoemission spectroscopy on high-quality MnSi films epitaxially grown on
Si(111), we unveil the FS symmetry and the evolution of the electronic
structure across the paramagnetic-helimagnetic transition at T 40 K,
along with the appearance of sharp quasiparticle emission below T. The
shape of the resulting FS is found to fulfill robust nesting effects. These
effects can be at the origin of strong magnetic fluctuations not accounted for
by state-of-art quasiparticle self-consistent GW approximation. From this
perspective, the unforeseen quasiparticle damping detected in the paramagnetic
phase and relaxing only below T, along with the persistence of the d-bands
splitting well above T, at odds with a simple Stoner model for itinerant
magnetism, open the search for exotic magnetic interactions favored by FS
nesting and affecting the quasiparticles lifetime
Ultrafast carrier phonon dynamics in NaOH-reacted graphite oxide film
NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in
graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast
carrier dynamics of the sample were studied by time-resolved transient
differential reflection (\DeltaR/R). The data show two exponential relaxation
processes. The slow relaxation process (\sim2ps) is ascribed to low energy
acoustic phonon mediated scattering. The electron-phonon coupling and
first-principles calculation results demonstrate that - OH and -ONa groups in
the sample are strongly coupled. Thus, we attribute the fast relaxation process
(\sim0.17ps) to the coupling of hydroxyl and -ONa groups in the sample
Effect of the crystallographic c-axis orientation on the tribological properties of the few-layer PtSe2
Two-dimensional (2D) transition metal dichalcogenides are potential
candidates for ultrathin solid-state lubricants in low-dimensional systems
owing to their flatness, high in-plane mechanical strength, and low shear
interlayer strength. Yet, the effects of surface topography and surface
chemistry on the tribological properties of 2D layers are still unclear. In
this work, we performed a comparative investigation of nanoscale tribological
properties of ultra-thin highly-ordered PtSe2 layers deposited on the sapphire
substrates with the in-plane and out-of-plane crystallographic orientation of
the PtSe2 c-axis flakes, and epitaxial PtSe2 layers. PtSe2 c-axis orientation
was found to has an impact on the nanotribological, morphological and
electrical properties of PtSe2, in particular the change in the alignment of
the PtSe2 flakes from vertical (VA) to horizontal (HA) led to the lowering of
the coefficient of friction from 0.21 to 0.16. This observation was accompanied
by an increase in the root-mean-square surface roughness from 1.0 to 1.7 nm for
the HA and VA films, respectively. The epitaxial films showed lower friction
caused by lowering adhesion when compared to other investigated films, whereas
the friction coefficient was similar to films with HA flakes. The observed
trends in nanoscale friction is attributed to a different distribution of PtSe2
structure
UHV Deposition and Characterization of a Mononuclear Iron(III) \u3b2-diketonate Complex on Au(111)
The adsorption of the sterically hindered \u3b2-diketonate complex Fe(dpm)3, where Hdpm = dipivaloylmethane, on Au(111) was investigated by ultraviolet photoelectron spectroscopy (UPS) and scanning tunnelling microscopy (STM). The high volatility of the molecule limited the growth of the film to a few monolayers. While UPS evidenced the presence of the \u3b2-diketonate ligands on the surface, the integrity of the molecule on the surface could not be assessed. The low temperature STM images were more informative and at submonolayer coverage they showed the presence of regular domains characterized by a flat morphology and height of 480.3 nm. Along with these domains, tetra-lobed features adsorbed on the kinks of the herringbone were also observed. DFT-simulated images of the pristine molecule and its possible decomposition products allowed to assess the partial fragmentation of Fe(dpm)3 upon adsorption on the Au(111) surface. Structural features with intact molecules were only observed for the saturation coverage. An ex situ prepared thick film of the complex was also investigated by X-ray magnetic circular dichroism (XMCD) and features typical of high-spin iron(III) in octahedral environment were observed
A ferromagnetic Eu–Pt surface compound grown below hexagonal boron nitride
One of the fundamental applications for monolayer-thick 2D materials is their use as protective layers of metal surfaces and in situ intercalated reactive materials in ambient conditions. Here we investigate the structural, electronic, and magnetic properties, as well as the chemical stability in air of a very reactive metal, Europium, after intercalation between a hexagonal boron nitride (hBN) layer and a Pt substrate. We demonstrate that Eu intercalation leads to a hBN-covered ferromagnetic EuPt2 surface alloy with divalent Eu2+ atoms at the interface. We expose the system to ambient conditions and find a partial conservation of the di-valent signal and hence the Eu–Pt interface. The use of a curved Pt substrate allows us to explore the changes in the Eu valence state and the ambient pressure protection at different substrate planes. The interfacial EuPt2 surface alloy formation remains the same, but the resistance of the protecting hBN layer to ambient conditions is reduced, likely due to a rougher surface and a more discontinuous hBN coating
Chemical and physical analysis of phaco handpiece tip surfaces before and after cataract\ua0surgery
PURPOSE: To evaluate the surface chemical composition and roughness of different phaco tips before and after their use during cataract surgery.
SETTING:
Eye Clinic, University of Trieste, Trieste, Italy.
DESIGN:
Experimental study.
METHODS:
Of the 66 tips studied, 33 (15 new, 15 after single use, and 3 after multiple uses) were studied with X-ray photoemission spectroscopy and 33 (15 new, 15 after single use, and 3 after multiple uses) were examined using scanning electron microscopy with energy dispersive X-ray spectroscopy analysis and contact profilometry. All analyses were performed on the far end of the tip.
RESULTS:
Used phaco tips showed signs of wear at the end of the tip, with the deposition of debris. The cutting edge appeared to be rounded and irregular. After surgery, an increase in the surface roughness was detected. The chemical analyses showed modification of the superficial alloy composition and the biological origin of some debris deposited after surgery. The deterioration and wear observed were more remarkable after multiple surgical procedures.
CONCLUSIONS:
Used phaco tips showed relevant signs of deterioration and deposition of biological material, mostly involving the cutting edge. Reusable tips might release remnants of previous procedures. The adoption of single-use disposable phaco tips seems to be highly advisable
A ferromagnetic Eu-Pt surface compound grown below hexagonal boron nitride
One of the fundamental applications for monolayer-thick 2D materials is their use as protective layers of metal surfaces and in situ intercalated reactive materials in ambient conditions. Here we investigate the structural, electronic, and magnetic properties, as well as the chemical stability in air of a very reactive metal, Europium, after intercalation between a hexagonal boron nitride (hBN) layer and a Pt substrate. We demonstrate that Eu intercalation leads to a hBN-covered ferromagnetic EuPt2 surface alloy with divalent Eu2+ atoms at the interface. We expose the system to ambient conditions and find a partial conservation of the di-valent signal and hence the Eu-Pt interface. The use of a curved Pt substrate allows us to explore the changes in the Eu valence state and the ambient pressure protection at different substrate planes. The interfacial EuPt2 surface alloy formation remains the same, but the resistance of the protecting hBN layer to ambient conditions is reduced, likely due to a rougher surface and a more discontinuous hBN coating
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