556 research outputs found
Impedance-matched High-overtone Bulk Acoustic Resonator
A high-overtone bulk acoustic resonator (HBAR), in which a piezoelectric
transducer is set on an acoustic cavity, has been attracting attention in both
fundamental research and RF applications due to its scalability, high
frequency, and high quality factor. The acoustic impedance matching in HBARs is
crucial for efficient acoustic power transfer from the piezoelectric transducer
to the cavity. However, impedance mismatch remains in most HBARs due to the
metal layer insertion between the piezoelectric layer and cavity substrate. In
this study, we fabricated a nearly impedance-matched high-quality HBAR using an
epitaxial AlN piezoelectric layer directly grown on a conductive SiC cavity
substrate with no metal layer insertion. The small impedance mismatch was
verified from the variation in the free spectral range (FSR), which is
comparable to the best value in previously reported HBARs. The experimentally
obtained FSR spectra was greatly reproduced by using the Mason model. Broadband
phonon cavity modes up to the K-band (26.5 GHz) were achieved by reducing the
thickness of the AlN layer from 800 to 200 nm. The high figure of merit of
at 10 GHz was also
obtained. Our nearly impedance-matched high-quality HBAR will enable the
development of RF applications, such as low-phase noise oscillators and
acoustic filters, as well as research on high-frequency acoustic systems
hybridized with electric, optical, and magnetic systems
残留性有機フッ素化合物の環境動態メカニズム解明
取得学位:博士(工学),学位授与番号:博甲第829号,学位授与年月日:平成18年3月22日,学位授与年:200
Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films
Epitaxially strained SrRuO3 films have been a model system for understanding
the magnetic anisotropy in metallic oxides. In this paper, we investigate the
anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties
using high-quality epitaxially strained (compressive and tensile) SrRuO3 films
grown by machine-learning-assisted molecular beam epitaxy. The element-specific
magnetic properties and the hybridization between the Ru 4d and O 2p orbitals
were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption
spectroscopy and X-ray magnetic circular dichroism measurements. The
magnetization curves for the Ru 4d and O 2p magnetic moments are identical,
irrespective of the strain type, indicating the strong magnetic coupling
between the Ru and O ions. The electronic structure and the orbital magnetic
moment relative to the spin magnetic moment are isotropic despite the
perpendicular and in-plane magnetic anisotropy in the compressive-strained and
tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a
negligibly small contribution to the magnetic anisotropy. This result
contradicts Bruno model, where magnetic anisotropy arises from the difference
in the orbital magnetic moment between the perpendicular and in-plane
directions. Contributions of strain-induced electric quadrupole moments to the
magnetic anisotropy are discussed, too
Magnetic anisotropy driven by ligand in 4d transition metal oxide SrRuO3
The origin of magnetic anisotropy in magnetic compounds is a longstanding
issue in solid state physics and nonmagnetic ligand ions are considered to
contribute little to magnetic anisotropy. Here, we introduce the concept of
ligand driven magnetic anisotropy in a complex transition-metal oxide. We
conducted X ray absorption and X ray magnetic circular dichroism spectroscopies
at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic
variation of the sample thickness in the range below 10 nm allowed us to
control the localization of Ru 4d t2g states, which affects the magnetic
coupling between the Ru and O ions. We found that the orbital magnetization of
the ligand induced via hybridization with the Ru 4d orbital determines the
magnetic anisotropy in SrRuO3
Evaluation of perfluoroalkyl substances in field-cultivated vegetables
Abstract(#br)Perfluoroalkyl substances (PFASs) were investigated in three types of vegetables (fruit, leafy, and root vegetables) that were cultivated and harvested from 2014 to 2017. The cultivated soil was mainly affected by perfluoroalkyl carboxylic acid (PFCAs; 91.8% detection rate) rather than perfluoroalkyl sulfonic acids (PFSAs; 8.2%). The cultivated soil (i.e., a volcanic cohesive soil) had a high total organic carbon (TOC = 3.4%) and therefore showed strong adsorption of long-chain PFASs. Short-chain PFCAs (i.e., under C9) were mainly detected in vegetables; specifically, PFBA showed high concentration in tomato shoots. Principal component analysis (PCA) plots clearly showed that PFASs in vegetables were different from those of cultivated soil, air, and rainwater. Interestingly, the whole potato (i.e., including peel) was in the same group as soil, indicating that the whole potato can easily be affected by the cultivated soil. Energy Dispersive X-ray Spectrometry-Scanning Electron Microscope (EDS-SEM) results showed that presence of unremovable micron-sized cultivated soil particles on the potato surface. Comparing the regional differences between the cultivated area of Tsukuba city (East Japan) and Osaka city (West Japan), PFASs patterns were similar in cucumber but differed in green perilla and potato
- …