Ambient pressure dried TEOS-based silica aerogels: good absorbents of organic liquids

The experimental work has been carried out to study the absorption–desorption properties of the hydrophobic silica aerogel for the application of oil spill cleanup. Aerogels were synthesized by sol–gel route prior to ambient pressure drying, by keeping TEOS:MeOH:Acidic H₂O:NH₄F:NH₄OH:HMDZ molar ratio constant at 1:16.5:0.81:0.62:0.63:0.41, respectively. The absorption of organic liquids by as-prepared aerogels has been carried out by adding the aerogel samples in organic liquid, viz. three alkanes: hexane, heptane, octane; the aromatic compounds: benzene, toluene, xylene; the alcohols: methanol, ethanol, propanol, and the three oils: petrol, diesel, and kerosene until it is totally wetted. It was observed that surface-modified TEOS-based aerogel absorbed the organic liquids and oils by nearly 12 times its own mass. After absorption, desorption time of liquids from the aerogel at various temperatures, i.e., at 30, 60, 80, and 100 °C was measured. The 50% volume shrinkage of the aerogel in case of oils and 20% in case of organic liquid was observed, after total desorption of liquids. No significant change in hydrophobicity of the aerogel was observed and it can be reused two times.     

Effect of Composition on Thermoelectric Properties in PbTe-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Composites

The solidification of alloys in the Bi₂Te₃-PbTe pseudobinary system at off- and near-eutectic compositions was investigated for their microstructure and thermoelectric properties. Dendritic and lamellar structures were clearly observed due to the phase separation and the existence of a metastable ternary phase. In this system, three phases with different compositions were observed: binary Bi₂Te₃, PbTe, and metastable PbBi₂Te₄. The Seebeck coefficient, electrical resistivity, and thermal conductivity of ternary alloys as well as binary compounds were measured. The phonon thermal conductivities of Pb-Bi-Te alloys were lower than those in binary PbTe and Bi₂Te₃, which could have resulted from the increased interfacial area between phases due to the existence of the metastable ternary phase and the resultant phase separation.     

Thermal-stress stability of yttrium oxide as a buffer layer of metal-ferroelectric-insulator-semiconductor field effect transistor

The effect of thermal stress on the electrical properties of ferroelectric/semiconductor structure was investigated when introducing Y₂O₃ film as a barrier layer in the structure. Two different thermal stress states could be obtained by fast (400 °C/min) or slow (30 °C/min) cooling of sputter-deposited Y₂O₃ films on silicon wafer from 800 °C. The formation of interfacial layer containing Y-Si-O and SiO₂ layers while annealing could be characterized by using a spectroscopic ellipsometry. The introduction of strain-induced defects from thermal stress of the fast cooled sample showed a soft breakdown at low applying voltage. In the capacitance-voltage relation, a flat band voltage shift, hysteresis, and stretch-out phenomena were also observed. Nd₂Ti₂O₇ was spin deposited using sol-gel procedure on the Y₂O₃/Si to form a metal-ferroelectric-insulator field effect transistor structured sample. These Nd₂Ti₂O₇/Y₂O₃/Si samples were also furnace-annealed at 800 °C and cooled down to room temperature fast or slowly. One order lower value of leakage current, 1E−8 A/cm² was observed with these samples when comparing with the Y₂O₃/Si samples. A soft breakdown of the fast cooled sample seemed to have the same origin as the fast cooled Y₂O₃/Si sample, i.e., the strain-induced defects in the interfacial layer containing Y-Si-O and SiO₂ phases. Hysteretic gaps of the Nd₂Ti₂O₇/Y₂O₃/Si samples showed a possibility to be used as a memory window for ferroelectric gate.     

A Study on Modified Silicon Surface after CHF3/C2F6 Reactive Ion Etching

The effects of reactive ion etching (RIE) of SiO₂ layer in CHF₃ / C₂F₆ on the underlying Si surface have been studied by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometer, Rutherford backscattering spectroscopy, and high resolution transmission electron microscopy. We found that two distinguishable modified layers are formed by RIE : (i) a uniform residue surface layer of 4 nm thickness composed entirely of carbon, fluorine, oxygen, and hydrogen with 9 different kinds of chemical bonds and (ii) a contaminated silicon layer of about 50 nm thickness with carbon and fluorine atoms without any observable crystalline defects. To search the removal condition of the silicon surface residue, we monitored the changes of surface compositions for the etched silicon after various post treatments as rapid thermal anneal, O₂, NF₃, SF₆, and Cl₂ plasma treatments. XPS analysis revealed that NF₃ treatment is most effective. With 10 seconds exposure to NF₃ plasma, the fluorocarbon residue film decomposes. The remained fluorine completely disappears after the following wet cleaning.     

Incorporation of carbon nanotube into direct-patternable ZnO thin film formed by photochemical solution deposition

Direct-patterning of ZnO hybrid films containing MWNT was realized without using photoresist and dry etching. Photosensitive 2-nitrobenzaldehyde was introduced into the solution precursors as a stabilizer and contributed to form a cross-linked network structure during photochemical reaction. According to the incorporation of multi-walled nanotube (MWNT) into ZnO films, the transmittance of ZnO hybrid film containing MWNT did not change but the sheet resistance was improved due to the enhancement of charge mobility due to π-bonding nature of MWNT. These results suggested a possibility that a micro-patterned system can be fabricated relatively easily and without high-cost processes, for example, by conventional etching procedure.     

Microwave dielectric properties of barium substituted screen printed CaBi2Nb2O9 ceramic thick films

In the present study, Aurivillius-structured Ba²⁺ substituted CaBi₂Nb₂O₉ (CBNO) ceramic powder was synthesized by co-precipitation method. The CBNO thick films were delineated by screen printing method on alumina substrates using co-precipitated ceramic powder. The overlay method was adopted to measure the microwave dielectric properties of prepared thick films. Single phase layered perovskite structure of the prepared thick films was confirmed by X-ray Diffraction. The effects of Ba²⁺ substitution on the surface morphology, bonding, and microwave dielectric properties of thick films were systematically presented. The maximum value of microwave dielectric constant for the CBNO thick films at 11.8 GHz is 15.6 for Ba²⁺=0.8 substitution. The shift in the stretching vibration modes of the Nb-O bond of NbO₆ octahedron in the Raman spectra with a substitution of Ba²⁺ in CBNO was observed. The substitution of Ba²⁺ on A-site of CBNO improves the microwave dielectric properties of prepared thick films. This work may provide a new approach to enhance the microwave dielectric performance of Aurivillius-structured ceramic thick films.     

New Insight into Microstructure Engineering of Ni-Rich Layered Oxide Cathode for High Performance Lithium Ion Batteries

Ni-rich layered LiNi_xCo_yMn_1−x−yO₂ (LNCM) with Ni content over >90% is considered as a promising lithium ion battery (LIB) cathode, attributed by its low cost and high practical capacity. However, Ni-rich LNCM inevitably suffers rapid capacity fading at a high state of charge due to the mechanochemical breakdown; in particular, the microcrack formation has been regarded as one of the main culprits for Ni-rich layered cathode failure. To address these issues, Ni-rich layered cathodes with a textured microstructure are developed by phosphorous and boron doping. Attributed by the textured morphology, both phosphorous- and boron-doped cathodes suppress microcrack formation and show enhanced cycle stability compared to the undoped cathode. However, there exists a meaningful capacity retention difference between the doped cathodes. By adapting the various analysis techniques, it is shown that the boron-doped Ni-rich layered cathode displays better cycle stability not only by its ability to suppress microcracks during cycling but also by its primary particle morphology that is reluctant to oxygen evolution. The present work reveals that not only restraint of particle cracks but also suppression of oxygen release by developing the oxygen stable facets is important for further improvements in state-of-the-art Li ion battery Ni-rich layered cathode materials.     

Optical and electrical properties of ZnO thin film containing nano-sized Ag particles

Low-temperature crystallized ZnO thin film was achieved by sol–gel process using zinc acetate dihydrate and 2-methoxyethanol as starting precursor and solvent, respectively. Ag nanoparticles were prepared with uniform size at 4.4 nm by spontaneous reduction method of Ag 2-ethylhexanoate in dimethyl sulfoxide (DMSO). The optical and electrical properties of ZnO thin films containing various contents of Ag-nanoparticles were monitored. Light scattering and charge emission and scattering behaviors of Ag nanoparticles in ZnO film were found. The incorporation of Ag nanoparticles into Al-doped ZnO film was also investigated. The optical transmittance was not degraded but the increase of electrical sheet resistance was found. The effect of Al-dopant on the transmittance and electrical sheet resistance of ZnO film was found too great to distinguish the positive effect of the incorporation of Ag nanoparticles into Al-doped ZnO thin films.     

Piezoelectric properties of highly densified 0.01Pb (Mg1/2W1/2)O3–0.41Pb (Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3+0.1 wt% Y2O3+1.5 wt% ZnO thick films on alumina substrate

This paper reports on the formation of highly densified piezoelectric thick films of 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃+0.1 wt% Y₂O₃+1.5 wt% ZnO (PMW–PNN–PT–PZ+YZ) on alumina substrate by the screen-printing method. To increase the packing density of powder in screen-printing paste, attrition milled nano-scale powder was mixed with ball milled micro-scale powder, while the particle size distribution was properly controlled. Furthermore, the cold isostatic pressing process was used to improve the green density of the piezoelectric thick films. As a result of these processes, the PMW–PNN–PT–PZ+YZ thick film, sintered at 890 °C for 2 h, showed enhanced piezoelectric properties such as P_r=42 μC/cm², E_c=25 kV/cm, and d₃₃=100 pC/N, in comparison with other reports. Such prominent piezoelectric properties of PMW–PNN–PT–PZ+YZ thick films using bi-modal particle distribution and the CIP process can be applied to functional thick films in MEMS applications such as micro actuators and sensors.