Abstract: Photoluminescence (PL), ultraviolet-visible (UV-VIS) absorption spectroscopy and spectroscopic ellipsometry (SE) are combining to study the optical transitions and electronic structures of Cu doped ZnO films with Cu concentration of 0, 2 and 8 at. %. By increasing Cu concentration, PL spectra show the enhancement of optical transition through the significantly increase of the green emission. Correspondingly, the in-plane UV visible absorption spectra show the redshift of first interband transition as the evidence of ZnO film become less insulating. More interestingly, extracted optical properties such as n and k clearly shows the mid-gap optical states, interband transitions and excitons. The excitonic peak decrease by increasing Cu concentration accompanied by a new broad structure assigned as a mid-gap state located under the conduction band area. Excitonic states are screened as decreasing its intensities by increasing Cu doping. Our results are beneficial to define interband transition and explain the mid-gap state in the oxide based semiconductor.
Abstract: Erbium doped zinc borotellurite glasses were prepared by using melt-quenching method. The structural properties of the glass samples were determined by using x-ray diffraction (XRD) method and was confirmed its amorphous nature. The density and molar volume is shown to be increased with increasing content of erbium. The refractive index is found to be increased with increasing content of erbium.
Abstract: Mg0.8Zn0.2TiO3 powder was synthesized by dissolved method and calcined at 550 °C for 4 hours. The powder exhibited single phase of Mg0.8Zn0.2TiO3 and nano size particle. Sintered pellet samples were prepared by compacting calcined powder which contains 4wt% B2O3 (MZTA), 4wt% Bi2O3 (MZTB) as liquid additive and non-additive sample (MZTC). Phase identification and its percentage were analyzed based on XRD pattern using Rietveld method. The result shows major phase Mg0.8Zn0.2TiO3 ranging from 72.83% for MZTA, 77.9% for MZTB and 82.61% for MZTC. Furthermore, minor phases were identified as Mg2TiO4 and other trace compound Mg3TiO2(BO3)2 for boron additive. Sintered pellet densities were determined by Archimedes method indicate that Bi2O3 additive has the most effective for densification. Microstructure characterization using SEM show that MZTB possesses the largest grain size ≈3.4µm followed by MZTA 2.3µm and MZTC 1.78µm. Dielectrics characterizations within frequency 1 Hz – 32 MHz exhibited space charge polarization characteristic for frequency <1 kHz, however for frequency >1 kHz showed frequency independence of dipolar polarizations and low dielectric loss having εr~17.
Abstract: In this research, the physical and electrical properties of 0.8K0.5Na0.5NbO3-0.2Ba0.5Ca0.5Zr0.5Ti0.5O3 (0.8KNN-0.2BCZT) were characterized. Lead-free material, 0.8KNN-0.2BCZT with and without alkaline excess was synthesized via solid state reaction method. KNN and BCZT were calcined at 700°C and 1200°C for 2 hours respectively and mixed by planetary milling. The mixed powder was recalcined at 1250°C for an hour then sintered at 1150°C, 1200°C and 1250°C for 2 and 4 hours. XRD analysis of 0.8KNN-0.2BCZT for excessive (8% Na, 2% K) sample sintered at 1150°C for 4 hours has single phase showing ABO3 structure (A=K, Na, Ba, Ca and B=Ti, Zr, Nb) and multi phases for the other ones. The microstructure analysis (SEM) showed cubic-like grain shape in which excessive sample possessed greater average grain size than other. Dielectric properties and Curie temperature of single phase sample in this research were higher than those of pure KNN. The conductivity analysis reveals two regimes. The first regime (<300°C) showed no significant role of BCZT in KNN and the second one (>300°C) showed that BCZT increased conductivity of KNN and factor dissipation as well.
Abstract: Synthesis of Zn doped Barium M-Hexaferrite (BaFe12-xZnxO19) has been performed by co-precipitation method. The purified iron sand from Tulungagung is used as a precursor of Fe3O4. Synthesis of Zn doped Barium M-Hexaferrite (BaFe12-xZnxO19) with variations of x = 0.3, 0.5, and 0.7 wt % has been calcined at temperatures of 1000°C for 5 hours. Ion Zn2+ (with 0 ≤ x ≤ 0.7 wt %) does not change the crystal structure of Barium M-Hexaferrite (BaM), but give a slight displacement of the peak position of the diffraction pattern. SEM figures showed that Zn doped Barium M-Hexaferrite (BaFe12-xZnxO19) have a hexagonal structure, similar to BaM structure. Doping of Zn has changed the magnetic properties of Barium M-Hexaferrit (BaM), from hard magnetic become soft magnetic. Barium M-Hexaferrit (BaM) has a value of Coercivity Field (Hc) and Remanence Magnetization (Mr) is 0.03734 T and 8.334 emu/g. At variation x = 0.3, the Remanence Magnetization (Mr) reaches the highest value. At this point, a value of Coercivity Field (Hc) and Remanence Magnetization (Mr) is 0.0506 T and 14.782 emu/gram respectively.
Abstract: The dream to have multifunctional materials has triggered an intense study of multiferroicity, i.e. of materials in which magnetic and electric polarizations are simultaneously present and strongly coupled. Here we study TbMnO3, a perovskite manganite exhibiting multiferroicity. It has an incommensurate antiferromagnetic ordering transition at 41 K and a transition into a multiferroic spin spiral state at 26 K. In this study, Raman spectroscopy has been used to elucidate the nature of the excitations related to phase transitions. We show that the optical phonons in TbMnO3 resemble the phonon characteristics typical for perovskite manganites, corresponding to MnO6 octahedral vibrations. The appearance of a new low energy modes at 32 cm-1, 40 cm-1, and 63 cm-1 observed below 41 K signifies the antiferromagentic ordering in TbMnO3. The 32 cm- 1 and 63 cm-1 are interpreted as spin ordering activated phonon while the 40 cm-1 is interpreted as spin ordering induced splitting of Tb quasi doublet cystal field level.
Abstract: A spark plasma sintering technique was used to consolidate NdFeB compacts at four different temperatures as 750°C, 850°C, 950°C and 1030°C. The surface of specimens was polished to remove the carbon paper on the surface of NdFeB compacts by using SiC paper for up to #1500 in grit. The polished NdFeB compacts were then magnetized by using impulse magnetizer K-series. In this study, the effects of temperature on the structure and magnetic properties of NdFeB magnet were studied. The results show that depending on the fabrication temperature, the X-ray diffraction patterns of NdFeB compacts are distinct. This suggests that the structure of NdFeB compacts is changed with increase in fabrication temperature. Meanwhile, the remanance Br and energy product BH(max) of NdFeB magnets tend to decrease as fabrication temperature increase.
Abstract: Microring resonators (MRRs) is a compact and multi-functioned device which is mainly characterized by free spectral range (FSR) and quality factor (Q-factor). In this paper, the influence of glucose concentration to the resonant wavelength shift of MRRs is presented. The calculation was carried out using semi-numerical method for different values of FSR and Q-factor. The parameters used in the calculation including incident wavelength, ring radii of circular waveguide, gap sizes between circular and straight waveguides, the dimension of both waveguides, and refractive index of polymer, SiO2 and glucoce solution. The results show that glucose affects the resonant wavelength shift for each values of FSR and Q-factor. The increase of the glucose concentration causes the increase of the resonant wavelength shift, therefore this polymer-based MRR’s can be used for glucose sensing application.
Abstract: The verification of calculation results of the isotropic and anisotropic-isotropic mass models in Al/SiO2/Si MOS capacitor against the experimental data is presented, using electron transversal velocity as a fitting parameter. In the accumulation condition, the comparison yields the electron velocity of 2.8 x 106 m/s for both isotropic and isotropic-anisotropic mass models. The tunneling current values for both models are slighly different with experimental data. In the inversion condition, the values of electron velocity for isotropic and isotropic-anisotropic model are 1.55 x 106 m/s and 1 x 105 m/s, respectively. The calculation results of isotropic-anisotropic mass model appear to be closer to the experimental data compared to those of isotropic mass model, due to the effect of electron effective mass.