arXiv subjects

Yuri Hasegawa

Publications and source records attributed to Yuri Hasegawa.

4 recordsLinked to original sources

arXiv2023

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 EuPt$_2$ surface alloy with divalent Eu$^{2+}$ 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 EuPt$_2$ 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.

cond-mat.mtrl-sci↗

arXiv2023

Proving weak electronic interaction between molecules and substrate: a study of pentacene monolayer on graphite

The impact of van der Waals interaction on the electronic structure between a pentacene monolayer and a graphite surface was investigated. Upon cooling the monolayer, newly formed dispersive bands, showing the constant final state nature overlapping with the non-dispersive, discrete molecular orbital state, is observed by low-energy angle-resolved photoelectron spectroscopy. The dispersive band consists of positive and negative intensities depending on the final state energy, indicating Fano resonance involving a discrete molecular state that couples a continuum state upon photoionization. A wave-function overlap is demonstrated according to their larger spread in unoccupied states even at the weakly bounded interface by Fano spectral analysis.

cond-mat.mes-hall↗

arXiv2021

Silabenzene Incorporated Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a promising material for various applications such as gas storage/separation, catalysis, and energy storage, besides offering a confined space for chemical reaction. The introduction of unconventional elements into their frame structures and expanding their structural scope remains a major challenge in COF chemistry. Here, we present syntheses of two-dimensional and liner COFs substructures linked with 1,4-disilabenzene (C4Si2) by co-depositing silicon atoms and bromo-substituted poly aromatic hydrocarbons on Au(111). A combination of high-resolution scanning tunneling microscopy, photoelectron spectroscopy and density functional theory calculations reveal the detailed structures of the Si-incorporated COF, as well as its chemical properties. We find that each Si in a hexagonal C4Si2 ring is terminated by one Br atom. Furthermore, the C4Si2 ring can be transformed to the C4Si pentagonal ring by annealing. Silabenzene incorporated COFs may open up new possibilities in organosilicon chemistry and a wide range of practical applications.

cond-mat.mtrl-sci↗

arXiv2021

Temperature-dependent electronic ground state charge transfer in van der Waals heterostructures

Electronic charge rearrangement between components of a heterostructure is the fundamental principle to reach the electronic ground state. It is acknowledged that the density of states distribution of the components governs the amount of charge transfer, but a notable dependence on temperature has not yet been considered, particularly for weakly interacting systems. Here, we experimentally observe that the amount of ground state charge transfer in a van der Waals heterostructure formed by monolayer MoS2 sandwiched between graphite and a molecular electron acceptor layer increases by a factor of three when going from 7 K to room temperature. State-of-the-art electronic structure calculations of the full heterostructure that account for nuclear thermal fluctuations reveal intra-component electron-phonon coupling and inter-component electronic coupling as the key factors determining the amount of charge transfer. This conclusion is rationalized by a model applicable to multi-component van der Waals heterostructures.

cond-mat.mtrl-sci↗