A study of N doping using N2O and NO sources on ZnO, which may prove important for the N doping of oxide materials, was performed by investigating the doping processes of N atoms by each source together with the various properties for the grown N doped ZnO films. N2O was employed as the radio-frequency (rf) plasma source to produce radical N2* species that could effectively incorporate N atoms above 1020 cm−3 into ZnO, which was similar to N doping using N2 as the source. In contrast, it was found that the ZnO films doped with a N concentration above 1020 cm−3 were easily obtained using a gas flow of NO. The N concentration could be controlled systematically by the simultaneous gas flow of NO and O2 sources. The basis of N doping using a NO source could be related to the free radical characteristic of NO molecular. This idea was proposed from the results that the N concentrations doped to ZnO using a gas flow of N2O and N2, which have the characteristics of neutral and nonreactive molecules in air, were in the ranges from 1018 to 1019 cm−3. Further, our investigations clarified that the structural, optical, and electrical properties for the N doped ZnO films were not quite dependent on the N2, N2O and NO sources used as N dopants. This work proposes that NO is a promising source as a N dopant that can be employed without using a rf plasma source in the application of physical vapor deposition techniques that are indispensable for producing radical N2* species through a rf plasma source to achieve the efficient incorporation of N atoms when N2 and N2O sources are used as N dopants.
Plasmon resonances on 2D nanosquare arrays and their temperature‐dependent modulations are demonstrated using the insulator‐to‐metal transition (IMT) of VO2. A comparison between observed experimental trends and electromagnetic simulations reveals that the plasmon coupling is effective in the periodic 2D alignment of metallic VO2 nanosquares and results in a collective plasmon excitation. This plasmon excitation affects the optical responses of VO2 nanosquares in the mid‐infrared (IR) range through reduction of plasmon damping in relation to the specific band structure of VO2. This preliminary understanding is important for the elucidation of temperature‐dependent plasmon resonances. The IMT of VO2 produces temperature‐dependent plasmon resonances with respect to spectral features. The electrodynamic simulations reveal that these phenomena are based on plasmon coupling in the nanosquare array when each nanosquare acts as a single metallic domain. The hysteretic plasmon resonances are derived from resonant coupling between metallic VO2 nanosquares via the IMT nature of VO2, which results in temperature‐dependent changes in collective plasmon excitations in the nanosquare array.
ZnO layers doped simultaneously with Ga and N (codoping), and magnetic elements (V, Co) were characterized by Raman scattering to study their structural stability. Five impurity modes were observed in range 200-900 cm −1 in the doped samples, and showed characteristic variation with the doping level. It is shown that these modes can be used as a good measure of lattice defects induced by doping. The Raman spectra showed that the magnetic elements were incorporated up to 5 mol% without serious deterioration in crystallinity.
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