Solid State Phenomena Vols. 124-126

Abstract: Monosized silica microspheres (100−500 nm) were prepared by a sol-gel process by using tetraethyl orthosilicate precursor. A well-dispersed suspension was obtained by adjusting suspension to be weakly basic for a better yield of electrophoretic self-assembly (EPSA). A perfect EPSA behavior of silica microspheres into the layered pattern with the FCC structure was created. EPSA technique has been demonstrated as a simple and effective route to make numerous templates, which are associated with 3-D structures of silica microspheres in asymmetric geometries, for design of photonic crystals.

Abstract: Simple process for the fabrication of Co/TiO2/Pt resistive random access memory, called ReRAM, has been developed by selective deposition of Co on micro-contact printed (μ-CP) self assembled monolayers (SAMs) patterns. Atomic Layer Deposition (ALD) was used to deposit TiO2 thin films, showing its ability of precise control over the thickness of TiO2, which is crucial to obtain proper resistive switching properties of TiO2 ReRAM. The fabrication process for Co/TiO2/Pt ReRAM involves the ALD of TiO2 on sputter-deposited Pt bottom electrode, followed by μ-CP with SAMs and then selective deposition of Co. This results in the Co/TiO2/Pt structure ReRAM. For comparison, Pt/TiO2/Pt ReRAM was produced and revealing the similar switching characteristics as that of Co/TiO2/Pt, thus indicating the feasibility of Co replacement with Pt top electrode. The ratios between the high-resistance state (Off state) and the low-resistance state (On state) were larger than 102. Consequently, the selective deposition of Co with μ-CP, newly developed in this study, can simplify the process and thus implemented into the fabrication of ReRAM.

Abstract: In this study, we measured work functions on various materials (i.e., metals and semiconductors) using Kelvin probe force spectroscopic method. Since the Kelvin probe force microscopic (KPFM) method allow to determine the work function difference between the metallic tip and unknown work function samples, it is very important that work function of the tip is accurately defined. Therefore, all the conductive tips were calibrated with a freshly cleavaged highly oriented pyrolytic graphite (HOPG). Work function measurements on various materials are conducted by using these calibrated tips. The values of work functions of metal films (i.e., Au and Pt) obtained in this method were found to correspond to the values reported in the literature, but those for semiconductor materials (i.e., n-, p-type Si and ITO films) show some deviations from their work functions which would be found in the literature. Surface electronic band bending and geometry of the tip could affect the differences in work functions measured by KPFM technique.

Abstract: The effects of paraffin addition on the optical properties and crystallinity of selfassembled SiO2 photonic crystal (PC) were examined using a silica nanopowder. The silica nanopowder was fabricated using the well-known Stöber process. During the evaporation process for self-assembly of PC, the nanopowder content was 0.05 or 0.2 wt%, the paraffin addition was fixed to 0.001 wt%, the process temperature was 80oC and the heat-treatment temperature after evaporation was 900oC. The addition of paraffin reduced the defects in the PC layer, thereby resulting in good crystallinity and transmittance. Our results suggested that paraffin can enhance the bonding force between silica nanopowders.

Abstract: Ion beam bombardment of proton, He+, Ar+, Xe+ ions were made on single crystal substrate by cyclotron. The GaN epi-layer material was grown by MOCVD on ion beam bombarded substrate. After deposition of GaN epi-layer heat treatment was made in flow of N2. The RMS roughness of the substrate was increased by ion bombardment. The GaN crystal quality for substrates of ion bombardment was better than that for bare substrates. Raman spectrum analysis indicated the induced stress in the GaN epi-layer during the heat treatment. The electrical property of GaN was improved after heat treatment. It is estimated that ion bombardment of proton with current of 1μA is the optimum condition in our experimental condition.

Abstract: In present paper, various industrial applications of the sol-gel technology will be briefly introduced. In particular, the current development status and technological issues of sol gel derived functional nanoparticles in electronic and industrial materials will be reviewed. Productions and surface modifications of nanoparticles by sol-gel processing, their incorporations into nanocomposites and final applications are described.

Abstract: As an alternative to a solid-state electrolyte for proton exchange membrane fuel cells (PEMFCs), ordered mesoporous membranes (OMMs) were prepared using a sol-gel technique, followed by a deep-UV irradiation. Structure and impedance spectroscopy analyses revealed that the porous architecture and proton conductivity of OMMs were influenced by the nature of the substrates. Compared with hydrophilic substrate, hydrophobic substrate was beneficial to an accessible porous architecture in the interface layer and an increase of proton conductivity of the whole membrane. The proton conductivity of the OMMs was up to 10-3 S cm-1.

Abstract: Solid-state potentiometric thin film hydrogen gas sensors were successfully fabricated using a sol-gel-derived high proton-conducting P2O5-SiO2 glass films. Manganese oxide thin film coated on an indium tin oxide (ITO)-coated glass substrate was used for reference electrode. The sensor exhibited high speed responsibility within 10 s and 120 s at 30 oC and -30oC, respectively, for 1 vol.% hydrogen gas. A linear relationship between the electromotive force (EMF) and the logarithmic hydrogen concentration of 0.1~1 vol.% was obtained in the temperature ranging from -30 to 30 oC. The sensing mechanism was also discussed to improve the sensitivity and sensing speed against low H2 concentration at low temperatures.

Abstract: This work reports the effect of doping aluminium in the Li[Li(1/3-x/3)Crx-0.05M0.05Mn(2/3- 2x/3)]O2 (x= 0.2; M= Al), layered cathode material. The cathode material was prepared by citric acid assisted sol-gel process. The sample is characterized by TG/DTA, XRD and FESEM measurements. The Al- doped cathode has delivered an initial discharge capacity of 250 mAh/g with a current density of 0.12 mA/cm2.

Abstract: Zn-Al layered double hydroxide (LDH) thin films intercalated with various organic anions were prepared by immersion of sol-gel derived amorphous Al2O3-ZnO thin films in hot water containing organic salts like sodium dodecyl sulfate (SDS), sodium p-toluenesulfonate, and benzenecarboxylates. In all the systems, extended interlayer spacing of the Zn-Al LDH was observed after immersion in distilled water with the organic salts in comparison to the LDH with carbonate anions, indicating that we have succeeded in direct formation of Zn-Al LDH films with various organic anions on the substrates. It is suggested that divalent anions such as terephthalate ion have higher selectivity than monovalent anions.