We have demonstrated resistance switching using polycrystalline HfO2 film with a Cu top electrode for nonvolatile memory applications and revealed the Cu diffusion into the HfO2 layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO2/Pt structure by performing a current–voltage measurement. The current step from a high-resistive state to a low-resistive state was of the order of 103–104 Ω, which provided a sufficient on/off ratio for use as a switching device. The filament formation process was investigated by employing hard x-ray photoelectron spectroscopy under bias operation. The application of a bias to the structure reduced the Cu2O state at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2, providing evidence of Cu2O reduction and Cu diffusion into the HfO2 layer. These results also provide evidence that the resistance switching of the Cu/HfO2/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.

Laser interference patterning (LIP) and the hereby induced microstructure modifications have been investigated in gold/yttria-stabilized zirconia nanocomposite films. Transmission electron microscopy was used to study the influence of the laser treatment on the structure and microstructure of the samples. The impact of LIP on the friction coefficient has been evidenced. The initial microstructure consisted of gold nanograins homogeneously distributed in the yttria-stabilized zirconia matrix. A noticeable growth and coalescence of gold nanograins occurred near the surface in specific regions. Simultaneously, a foamy morphology, mostly consisting of gold crystals, was formed at the surface and is responsible for a drastic diminution of the friction coefficient after patterning. Furthermore, the influence of the film topography on the friction behavior is analyzed using Abbott–Firestone curves. In contrast to thermal annealing, the laser treatment proposed here is a fast procedure to partially relocate gold at the film surface and provide a local solid lubrication.

In situ transmission electron microscopy (TEM) was carried out to investigate the dynamics of resistance switching in a solid electrolyte, Cu-Ge-S. By applying voltage to Pt-Ir/Cu-Ge-S/Pt-Ir, where Pt-Ir constituted the electrodes, a deposit containing conductive filaments composed mainly of Cu was formed around the cathode. As voltage continued to be applied, the deposit grew and finally narrow conductive filaments made contact with the anode. This corresponded to resistance switching from high- to low-resistance states (HRS and LRS). By alternating the voltage, the deposit contracted toward the cathode and detached from the anode. The resistance immediately changed from LRS to HRS. By applying voltage, the deposit containing Cu-based filaments grew and shrank, and resistance switching occurred at the electrolyte-anode interface. This conductive filament-formation model, which was recently reported, was experimentally confirmed with TEM through dynamic observations of the deposit-containing filaments.

A common fingerprint of the electrically active point defects in semiconductors is the transition among their localized defect states upon excitation, which may result in characteristic absorption- or photoluminescence spectrum. Identification of such point defects by means of density functional theory (DFT) calculations with traditional (semi) local functionals suffers from two problems: the “band gap error” and the many-body nature of the electron-hole interaction of the excited state. We show that non local hybrid density functionals may effectively mimic the quasiparticle correction of the band edges and the defect levels within the band gap in group-IV semiconductors, thus they can effectively heal the “band gap error.” The electron-hole interaction can be calculated by time-dependent DFT (TD-DFT) method. Here, we apply TD-DFT on three topical examples: nitrogen-vacancy defect in diamond, silicon-vacancy and divacancy defects in silicon carbide that are candidates in effective development of solid-state quantum bits.

This article reports on microstructure and dielectric properties of Ba0.5Sr0.5Ti1−3y/2WyO3 ceramics. Dielectric peaks of the Ba0.5Sr0.5Ti1−3y/2WyO3 ceramics were markedly suppressed, broadened, and shifted to low temperature with increasing content of W. The limit of W incorporating into the barium strontium titanate (BST) lattice was y = 0.02. Two second phases (BaWO4 and Ba2Ti5O12) were formed above the solid solution limit of W in BST. The doping mechanism represents a new approach to develop microwave tunable materials. Dielectric properties of the Ba0.5Sr0.5Ti1−3y/2WyO3 ceramics could be optimized by the content of W. The sample with y = 0.05 had ε′ of 431, quality factor of 365 (at 2.111 GHz), and tunability of 11.5%, which makes a potential candidate for tunable microwave device applications in the wireless communication.

The (1−x)MgO–xLiF ceramics (x = 0.02–0.08) were successfully sintered when the ceramics were sintered at 950 °C for 4 h in covered crucible. From the crystal structure analysis, it was found that a small amount of Li+ cation occupied Mg2+ site in MgO ceramic; the formation of oxygen vacancy induced by Li substitution for Mg was suggested by the evaluation of the bulk conductivity and the calculation of density of state (DOS) for the (Mg13O43)−60 and (Mg11Li2O42)−58 cluster models. As for the microwave dielectric properties of the (1−x)MgO–xLiF ceramics, the dielectric constant εr and the temperature coefficient of resonant frequency values of the ceramic were independent of the lithium fluoride (LiF) content, and these values were approximately 9.5 and −62 ppm/°C. On the other hand, the quality factor values strongly depended on the LiF content. As a result, the highest value of 282,230 GHz was obtained at x = 0.04. From these results, it is determined that the LiF addition is effective in reducing the sintering temperature of MgO without any detrimental effect on the microwave dielectric properties of MgO ceramics.

The dielectric properties and tunability with external magnetic and electric fields for LuFe2-xMnxO4 (0 ≤ x ≤ 1) are systematically studied. It was found that the dielectric loss, the ferrimagnetic Curie temperature, and the conductivity reduce with increasing Mn doping. One of the most important results is that the room temperature dielectric tunability with low magnetic and electric fields can be achieved in these samples. The analysis demonstrates that the electron transfer between Fe2+ and Fe3+ is efficiently suppressed with Mn doping and thus results in the decreases of the leaky conductivity and the dielectric loss. Furthermore, from the studies on the combination of impedance and modulus complex planes for the samples with different electrodes, the tunability is found to be more closely related to the extrinsic effect than the intrinsic bulk effect.

NiMn2−xMgxO4 (0 ≤ x ≤ 0.4) ceramics have been studied by powder x-ray diffraction (XRD), infrared (IR) spectroscopy, and thermogravimetric analysis. NiMn2−xMgxO4 ceramics are all single-phase with spinel structure. XRD and IR spectroscopy results indicate that Mg2+ ions occupy A- and B-site of spinel lattice, which inhibits the formation of cation vacancies. Moreover, Mg2+ substitution enhances the tolerance of the oxidation in air. As a result, Mg substitution leads to a significant increase in ρ25, temperature coefficient of resistivity B25/85, and activation energy, which improves the aging property of NiMn2−xMgxO4 negative temperature coefficient thermistors.

A clickable surface was prepared using nanoporous SBA-15 support. Methylimidazolium, an ionic liquid, was immobilized on this surface through the click reaction. Detailed characterization using nitrogen adsorption, elemental analysis, x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis showed that the ionic system was fixed inside the channels and the ordered porous structure remained stationary. Influence of this material on photoluminescence emission of 5-amino-4-hydroxy-7-sulfonaphthalene-2-sulfonate anion (H-acid) in aqueous solutions was evaluated. This click reaction product can be used effectively for H-acid removal from wastewater.

Yttria-stabilized zirconia (YSZ)/Al2O3 multilayers deposited on Pt foil were studied by differential scanning calorimetry. Observed thermal effects were interpreted using additional evidence from x-ray diffraction and transmission electron microscopy. The crystallization temperature of YSZ increases from 344 to 404 °C as the layer thickness decreases from 15 to 4 nm. The enthalpy of crystallization becomes more exothermic with decreasing thickness, and it was measured to be −26 kJ/mol YSZ for 4-nm-thick layers and −12 kJ/mol for 15-nm-thick layers. The latter value is consistent with the reported crystallization enthalpy for YSZ powder of the same composition prepared by precipitation from aqueous solution. The more exothermic crystallization enthalpies for thinner films are indicative of a decrease in their degree of crystallinity. The 2–6-nm-thick Al2O3 layers remain amorphous when heated to 1000 °C. The described methodology enables thermal analysis of oxide thin films using commercial instruments.

Transmission electron microscopy (polycrystalline electron diffraction, nanoelectron diffraction, and energy dispersive x-ray spectroscopy) was used to determine the dispersion of crystal phase and Nb dopants in mixed-phase (anatase and rutile) Ti1−xNbyO2 thin films prepared by reactive sputtering. When co-sputtering mixed-phase TiO2 with a dopant, it is unclear how the crystal phases are distributed within thin film structures, what the dominant interfaces are, and how the dopant is distributed within the crystal phases. In the Ti1−xNbyO2 films, anatase and rutile grains were found to be homogeneously dispersed indicating that anatase/rutile interfaces are the dominant interfaces. Anatase/rutile interfaces are a critical feature of mixed-phase materials which impart high reactivity to the composite. Nb homogeneously dispersed at low concentrations, but at high concentrations, Nb segregated in the rutile phase. There is an apparent threshold beyond which Nb segregates according to its higher solubility in rutile due to a better lattice fit.

The standing porous nanoplate-built ZnO hollow microspheres with micro/nanostructure are fabricated based on a modified hydrothermal strategy, using citrate as structural director, and subsequent annealing treatment. The hollow spheres are composed of the vertically standing and cross-linked single crystalline porous nanoplates with the exposed surface of nonpolar (100) planes. Experiments have revealed the structural evolution: the formation of amorphous spheres in the initial reaction stage, followed by surface crystallization and nanoplate outward growth accompanied by inward dissolution of the amorphous spheres. Citrate in the precursor solution plays a dominant role in the formation of such porous ZnO hollow spheres. A model is presented, based on citrate-induced amorphous sphere formation and kinetically controlled dissolution and crystal growth. The model describes the formation of the hollow spheres, thermodynamically and kinetically.

The long afterglow phosphor, CaWO4: Eu3+, is synthesized and the intensity and duration of its afterglow can be enhanced by the Ti4+ and Mg2+ incorporation. The x-ray diffraction patterns depict pure tetragonal CaWO4 of all samples. The emission spectra show the Eu3+ emission and the charge transfer (CT) emission of WO42−. The intensity of CT increases with the Mg2+ incorporation. The excitation spectra monitoring 616 nm exhibit the strongest CT band with Ti4+ incorporation. These results indicate that Mg2+ enhances the efficiency of CT emission of WO42− while the Ti4+ enhances the energy transfer rate from CT to Eu3+. Since the thermoluminescence (TL) curves do not imply a new trap, the enhancement of the afterglow results from the coreinforcement of CT efficiency and energy transfer rate.

Dispersions of reduced tungsten oxide and tungsten bronze nanoparticles are known to show a remarkable absorption of near-infrared (NIR) light applicable to solar control filters for automotive and architectural windows. Origin of the NIR absorption has been investigated by analyzing dielectric constants of CsxWO3 (x = 0.15, 0.25, and 0.33) and WO2.72, and using Mie scattering theory. The optical analysis and Mie scattering theory analysis indicate that a localized surface plasmon resonance and polarons of localized electrons contribute alongside to the observed NIR absorption at different wavelengths.

Chemical wet etching on c-plane sapphire wafers by three etching solutions (H3PO4, H2SO4, and H3PO4/H2SO4 mixing solution) was studied. Among these etching agents, the mixing H3PO4/H2SO4 solution has the fastest etching rate (1.5 μm/min). Interestingly, we found that H2SO4 does not etch the c-plane sapphire wafer in thickness; instead, a facet pyramidal pattern is formed on the c-plane sapphire wafer. GaN light-emitting diode (LED) epitaxial structure was grown on the sapphire wafer with the pyramidal pattern and the standard flat sapphire wafer. X-ray diffraction and photoluminescence measurement show that the pyramidal pattern on the sapphire wafer improved crystalline quality but augmented the compressive stress level in the GaN LED epilayer. The horizontal LED chips fabricated on the pyramidal-patterned sapphire wafer have a larger light output than the horizontal LED chips fabricated on the standard flat sapphire wafer by 20%.