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ACS Omega ; 6(6): 4440-4447, 2021 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-33644556


We study the structural, electronic, and magnetic properties of the antiferromagnetic-layered oxyarsenide (LaO)MnAs system from the first-principle calculation. The increasing Hubbard energy (U) in the Mn 3d orbital induces the increasing local-symmetry distortions (LSDs) in MnAs4 and OLa4 tetrahedra. The LSD in MnAs4 tetrahedra is possibly promoted by the second-order Jahn-Teller effect in the Mn 3d orbital. Furthermore, the increasing U also escalates the bandgap (E g) and the magnetic moment of Mn (µMn). The value of U = 1 eV is the most appropriate by considering the structural properties. This value leads to E g and µMn of 0.834 eV and 4.31 µB, respectively. The calculated µMn is lower than the theoretical value for the high-spin state of Mn 3d (5 µB) due to the hybridization between Mn 3d and As 4p states. However, d xy states are localized and show the weakest hybridization with valence As 4p states. The Mott-insulating behavior in the system is characterized by the E g transition between the valence and conduction d zx /d zy states. This work shows new physical insights for advanced functional device applications, such as spintronics.

Phys Chem Chem Phys ; 22(28): 16431, 2020 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-32639488


Correction for 'The effect of crystallinity on the surface modification and optical properties of ZnO thin films' by Muhammad Abiyyu Kenichi Purbayanto et al., Phys. Chem. Chem. Phys., 2020, 22, 2010-2018, DOI: 10.1039/C9CP05464B.

Phys Chem Chem Phys ; 22(4): 2010-2018, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31903459


We have studied the effects of crystallinity on the emergence of porous morphology and strong green emission in ZnO thin films after H2 annealing treatment. The unique multiple-stacked porous structure is observed after performing H2 annealing treatment on the film with low crystallinity. However, the annealed high-crystallinity film exhibits surface morphology with a shallow porous structure, as revealed by SEM images. To study the effects of these unique porous structures on the optical properties, photoluminescence (PL) spectroscopy, Raman spectroscopy, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS) are conducted. The multiple-stacked porous structure produces strong green emission as compared to the shallow porous structure centered at 2.5 eV, as detected by PL. Here, the green emission originates from the electronic transition related to the oxygen vacancy (VO). XPS spectra show that the high density of VO located on the multiple-stacked porous surface is much higher as compared to that for the shallow porous structure due to a high surface-to-volume ratio. The results show that the multiple-stacked porous structure has the potential to enhance the functionality of ZnO for applications in light-emitting.

Inorg Chem ; 57(16): 10214-10223, 2018 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-30088921


We study the new details of electronic and thermoelectric properties of polycrystalline layered oxychalcogenide systems of (BiO)Cu Ch ( Ch = Se, Te) prepared by using a solid-state reaction. The systems were characterized by using photoemission (PE) spectroscopy and four-probe temperature-dependent electrical resistivity ρ( T). PE spectra are explained by calculating the electronic properties using the generalized-gradient approximation method. PE spectra and ρ( T) show that (BiO)CuSe system is a semiconductor, while (BiO)CuTe system exhibits the metallic behavior that induces the high thermoelectric performance. The calculation of electronic properties of (BiO)Cu Ch ( Ch = S, Se, Te) confirms that the metallic behavior of (BiO)CuTe system is mainly induced by Te 5p states at Fermi energy level, while the indirect bandgaps of 0.68 and 0.40 eV are obtained for (BiO)CuS and (BiO)CuSe systems, respectively. It is also shown that the local symmetry distortion at Cu site strongly stimulates Cu 3d-t2g to be partially hybridized with Ch p orbitals. This study presents the essential properties of the inorganic systems for novel functional device applications.

Sci Rep ; 6: 33409, 2016 09 12.
Artigo em Inglês | MEDLINE | ID: mdl-27615374


Spin transistors have attracted tremendous interest as new functional devices. However, few studies have investigated enhancements of the ON/OFF current ratio as a function of the electron spin behavior. Here, we found a significantly high spin-dependent current ratio-more than 10(2) at 1.5 V-when changing the relative direction of the magnetizations between FePt nanodots (NDs) and the CoPtCr-coated atomic force microscope (AFM) probe at room temperature. This means that ON and OFF states were achieved by switching the magnetization of the FePt NDs, which can be regarded as spin-diodes. The FePt magnetic NDs were fabricated by exposing a bi-layer metal stack to a remote H2 plasma (H2-RP) on ~1.7 nm SiO2/Si(100) substrates. The ultrathin bi-layers with a uniform surface coverage are changed drastically to NDs with an areal density as high as ~5 × 10(11) cm(-2). The FePt NDs exhibit a large perpendicular anisotropy with an out-of-plane coercivity of ~4.8 kOe, reflecting the magneto-crystalline anisotropy of (001) oriented L10 phase FePt. We also designed and fabricated double-stacked FePt-NDs with low and high coercivities sandwiched between an ultra-thin Si-oxide interlayer, and confirmed a high ON/OFF current ratio when switching the relative magnetization directions of the low and high coercivity FePt NDs.

Nano Lett ; 15(12): 8331-5, 2015 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-26569579


Searching for new plasmonic building blocks which offer tunability and design flexibility beyond noble metals is crucial for advancing the field of plasmonics. Herein, we report that solution-synthesized hexagonal Bi2Te3 nanoplates, in the absence of grating configurations, can exhibit multiple plasmon modes covering the entire visible range, as observed by transmission electron microscopy (TEM)-based electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopy. Moreover, different plasmon modes are observed in the center and edge of the single Bi2Te3 nanoplate and a breathing mode is discovered for the first time in a non-noble metal. Theoretical calculations show that the plasmons observed in the visible range are mainly due to strong spin-orbit coupling induced metallic surface states of Bi2Te3. The versatility of shape- and size-engineered Bi2Te3 nanocrystals suggests exciting possibilities in plasmonics-enabled technology.