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It has been recognized that a connection may exist between defects of oxide coating and its corrosion protection. Such a link has not been substantiated. We prepare two coatings of anodized aluminum oxide (AAO) and plasma electrolytic oxidation (PEO), and analyze them with Mott-Schottky plots and potentiodynamic polarization scans. The as-grown and annealed AAO coatings exhibit both p-type and n-type semiconductor behaviors. Polarization resistance of the AAO coating increases from (1.8 &plusmn, 1.7) &times, 108 to (4.3 &plusmn, 0.5) &times, 108 &Omega, &middot, cm2, while corrosion current decreases from (6.1 &plusmn, 3.6) &times, 10&minus, 7 to (2.3 &plusmn, 0.9) &times, 7 A&middot, cm&minus, 2, as annealing temperature increases from room temperature to 400 &deg, C. The parameter analysis on AAO indicates a positive correlation between corrosion current and donor density, a negative correlation between polarization resistance and donor density. The attempt on correlating corrosion potential gives rise to considerable deviation from a linear fit. The results suggest protection of AAO hinges on its donor density, not acceptor. On the PEO coatings, only the n-type behavior is observed. Intriguingly, the donor density of PEO coating is influenced by the annealing temperature of its pre-anodized layer. The most resistant PEO coating, with pre-anodized and 400 &deg, C annealed AAO, exhibits polarization resistance (2.1 &plusmn, 0.4) &times, 109 &Omega, cm2 and corrosion current (1.7 &plusmn, 8 A&middot, 2.

Given that the amphoteric Li3V2(PO4)3 (LVP) crystal exhibits different capacities in the high and low potential regions, we study its asymmetric capacitor and the mass balancing. Both the positive and the negative electrodes are prepared with 50 wt.% LVP balanced by activated carbon which provide battery and double-layer storage mechanisms; respectively. To retain the capacitor power feature with a sizable capacity, a proper internal hybridization is required to keep the battery mechanism functioning at high-rate cycling. The involvement of battery storage is assured if a high-voltage bulge is observed on the galvanostatic discharge curve. To preserve such a feature, the capacitor analysis indicates three factors are vital. A voltage window is wide enough, 4.0 V, such that the plateau of LVP around 3.6 V (vs. Li/Li+) may operate in discharging the positive electrode. The negative electrode is prelithiated to pin down the negative potential and allow the cell to utilize the permissible potential window. A proper mass ratio 2(+):1(−) provides sufficient but not too much battery storage in the positive electrode. Among the five mass ratios being studied, the 2(+):1(−) capacitor shows a respectable combination of specific energy 43 W h kg−1 and power 520 W kg−1 at 0.2 A g−1, with over 80 % capacity retention in 200 cycles.

Incorporated as the negative electrode, the LiSn2(PO4)3 (LSP) crystals requires a prelithiation step to decompose LSP partially and yield tin metal for a relatively steadied capacity in cycling the hybrid capacitor of LiPF6 electrolyte. The charge transfer reactions of lithium alloying tin at low potentials offer a substantial amount of electrical capacity. Hence, several capacitors of LSP negative and activated carbon (AC) positive are prepared to understand the effects of prelithiation and LSP:AC mass ratio on how to exploit this electrochemical capacity. Among two prelithiation levels and three mass ratios, the combination of LSP-I (10% tin) and 1:1 (LSP:AC) mass ratio stands out as the best choice over a wide range of specific current. On the other hand, the selection of a specific current low enough to match the charge-transfer reaction kinetics enables the LSP electrode of high prelithiation level, LSP-II (45% tin), to utilize its battery-like capacity thoroughly. The maximum energy of hybrid capacitor LSP-II/AC is measured 28.7 W h kg−1 at a minimum specific current 0.03 A g−1.

The electrode of sol–gel derived Li3VO4 (LVO), which exhibits a capacity of 2 mol lithium between 0.01 and 2.0 V (vs. Li/Li+), is studied as an anode of the capacitor in conjunction with a cathode of activated carbon (AC). Before assembling the hybrid capacitor of AC/LVO, Li3VO4 has been prelithiated. The end potential of prelithiation affects the lithium loading and the resultant cell capacity. The cell, with LVO prelithiation ending at 0.5 V (vs. Li/Li+), displays 34% more capacity than the other with LVO ending at 2.0 V (vs. Li/Li+). The higher capacity is caused by reducing the electrode potential of the hybrid capacitor at 0% state-of-charge, which also depends on the AC : LVO mass ratio and the specific current. We develop a scheme to estimate the optimal mass ratio for the capacitor. The optimal ratio is verified later by galvanostatic charge–discharge experiments, involving four capacitors with AC : LVO mass ratios of 0.5 : 1, 1 : 1, 2 : 1, 3 : 1. The optimal 2 : 1 cell demonstrates a capacity of specific energy 49.1 W h kg−1 at 0.05 A g−1 and 3.5 V, and 81% retention in the voltage hold test persisting for 100 h.

Large surface area nanostructural IrOx films were deposited on stainless steel substrates by reactive radio frequency magnetron sputtering using Ir metal target. The structural and spectroscopic properties of the nanostructural IrOx were characterized. The micrographs of field emission scanning electron microscopy showed the formation of folded leaves with chiffon-like structure for the as-deposited samples. X-ray photoelectron spectroscopy analysis provided the information of the oxidation states and the stoichiometry of IrOxNL. Raman spectra revealed the amorphous-like phase of the as-deposited nanostructural IrOx. The chiffon-like structure provides ultra-high surface area for electrical charge storage which makes the IrOxNL as an attractive candidate for the supercapacitor application.

Ultracapacitors of asymmetric configuration have been prepared with activated carbon (AC) and undoped or Mo-doped manganese oxide (MnO 2 ) in 1.0 M Na 2 SO 4 electrolyte. Phase analysis shows the AC powder, 1–15 μm in size, contains both disordered and graphitic structures, and the undoped and Mo-doped oxide powder, 0.05–0.20 μm in particle size, mainly involves amorphous MnO 2 and MoO 2 . CV results indicate the single electrode of AC plus 10 wt% Mo-doped MnO 2 (A9O M 1) is superior to the electrode with undoped MnO 2 or high content of doped MnO 2 , exhibiting features of double layer capacitance at high scan rate and pseudocapacitance characteristics at low scan rate. When assembled with a negative electrode of AC, the capacitor of positive A9O M 1 electrode demonstrates the least power loss among three asymmetric capacitors. This asymmetric capacitor also shows a higher capacitance than the symmetric AC capacitor when the current density is less than 8.0 A g −1 in 1.8 V potential window. But a higher electrode resistance of A9O M 1, in contrast with AC, compromises its capacitance plus. When the energy density of A9O M 1 asymmetric capacitor is compared with that of symmetric AC capacitor at the same power level, the capacitance benefit on energy density is restricted to current density ≤ 3.0 A g −1 .

Large surface area IrO x nanofoils (IrO x NF) were deposited on multi-wall carbon nanotube (MWCNT) templates, forming IrO x /MWCNT nanocomposites, by reactive radio frequency magnetron sputtering using Ir metal target. The structural and spectroscopic properties of IrO x NF were characterized. The micrographs of field emission scanning electron microscopy showed the formation of foil-like structure for the as-deposited samples. Transmission electron microscopy analysis revealed the contiguous presence of glassy iridium oxide, iridium metal, and iridium dioxide nanocrystals in the foil. X-ray photoelectron spectroscopy analysis provided the information of the oxidation states and the stoichiometry of IrO x NF. Raman spectra revealed the amorphous-like phase of the as-deposited IrO x NF. The nanofoil structure provided ultra-high surface area for electrical charge storage which made the IrO x /MWCNT nanocomposites as an attractive candidate for the supercapacitor applications.

a b s t r a c t The crystal structure and proton conductivity of cerium pyrophosphate are investigated to explore its potential electrolyte applications for intermediate temperature fuel cell. Among the CeP2O7 thin plates, which are sintered at 300-900 ◦ C, the 450 ◦ C CeP2O7 sample exhibits superior proton conduc- tivity under humidified conditions. Its conductivity, measured with impedance spectroscopy, is higher than 10 −2 S cm −1 in the intermediate temperature range, with a maximum value 3.0 × 10 −2 S cm −1 at 180 ◦C. When 10 mol% Mg is doped on the Ce site of CeP2O7, the maximum conductivity is raised to 4.0 × 10 −2 S cm −1 at 200 ◦ C. The Mg doping not only raises the conductivity, but also shifts and widens its temperature window for electrolyte applications. Ce0.9Mg0.1P2O7 is considered a more appropriate composition, with conductivity >10 −2 S cm −1 between 160 and 280 ◦ C. Accordingly, a hydrogen-air cell is built with the Ce0.9Mg0.1P2O7 electrolyte and its performance is measured. The fuel cell generates electricity up to 122 mA cm−2 at 0.33 V using 50% H2 at 240 ◦C.

Well-aligned densely-packed rutile phase TiO 2 nanocrystals (NCs) have been grown on sapphire (100) and (012) substrates by reactive magnetron sputtering using Ti metal target. The surface morphology, structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. FESEM micrographs reveal the growth of vertically aligned NCs on sapphire (100), whereas the NCs on sapphire (012) were grown with a tilt angle of ∼ 33° from the normal to substrate. The XRD results reveal TiO 2 NCs with either (002) orientation on sapphire (100) substrate or (101) orientation on sapphire (012) substrate. A strong substrate effect on the alignment of the TiO 2 NCs growth has been demonstrated and the probable mechanism for the formation of these NCs has been discussed. XPS analyses show the oxygen vs. titanium ratio of 2.0 ± 0.1 for the as-grown TiO 2 NCs. Raman spectra of NCs exhibit a slight redshift in the peak position and a small broadening in linewidth with respect to that of the bulk counterpart. The results indicate the formation of good quality of nanocrystalline rutile phase TiO 2 .

Deoxygenation of the IrO 2 (1 1 0) surface is investigated at 403–493 K, using the core-level spectroscopy and density functional theory (DFT) calculation. The Ir-4f 7/2 signals of 1f-cus-Ir with and without on-top oxygen (O top ) emerge as surface features of the baked-out surface, whose positive and negative shifts in binding energy are in line with the DFT computation results. Progressively increasing the reduction temperature, the 1f-cus-Ir feature quickly disappears and the signal of 2f-cus-Ir emerges at 403 K. Meanwhile the feature of 1f-cus-Ir + O top diminishes but persists when the Ir metal signal is evident. The intriguing coexistence of 1f-cus-Ir + O top and Ir metal at 433–443 K is elucidated in the theoretical pathway study. DFT calculation reveals that O 2 desorption via pairing two neighboring O top atoms is the rate-determining step of surface deoxygenation. Under the UHV conditions, O top is replenished via migration of the surface oxygen species, including the threefold coordinated oxygen (O 3f ) of a reduced surface. Hence the O top atom is an active and long-lived surface species, which does not vanish until O 3f is consumed and surface Ir begins to cluster. Under the realistic pressure conditions, O top can also be refreshed via the dissociative adsorption of gas-phase oxygen. In either pathway, O top is a critical intermediary of IrO 2 (1 1 0) oxidation catalysis.

Nanostructural (3 0 1) and (1 0 1) twins of RuO2 were grown on top of rutile phase TiO2 nanorods (NRs) sitting on LiNbO3(1 0 0) substrate. The surface morphology, structural and spectroscopic properties of the as-deposited nanocrystals (NCs) were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and selected-area electron diffractometry (SAED). The FESEM images and XRD patterns indicated growth of V-shaped RuO2 (3 0 1) and (1 0 1) twins with angles of 51° and 110° between two arms, respectively. The Raman spectrum showed the nanosize induced redshift and peak broadening of the RuO2 and rutile phase of TiO2 signatures with respect to that of the bulk counterparts. XPS spectra indicated the existence of higher oxidation states of ruthenium in RuO2 NCs. TEM and SAED characterizations of the V-shaped RuO2 NCs showed that the nanorods were crystalline RuO2 with twin planes of (3 0 1)/(1 0 1) and twin directions of [ 1 ¯ 0 3 ] / [ 1 ¯ 0 1 ] at the V-junction. The probable formation mechanisms of the twins are discussed.

The RuO 2 nanorods array is grown selectively on the SiO 2 -patterned sapphire (SA) wafers using reactive sputtering. The area-selectivity is attributed to an early nucleation of RuO 2 and its fast surface coverage on SA (1 0 0) and (0 1 2), in contrast to the sluggish nucleation on glassy SiO 2 in the initial sputtering period. The growth domain is explored by investigating the temperature windows at sputtering power 40, 50, and 60 W. The low-temperature bound is limited by the mobility of precursors on SiO 2 surface, which enables the precursors to depart before aggregating into a large size to smear the non-growth region. The high-temperature bound is set by the horizontal growth which enlarges the rod width and deteriorates its one-dimensional feature. The temperature window shrinks with increasing sputtering power. The X-ray photoelectron spectra indicate the as-sputtered rod surface is ruthenium rich. The X-ray diffraction analysis shows that RuO 2 growth on SA (1 0 0) and (0 1 2) follows the epitaxial relations between RuO 2 and SA crystals.

The electrochemical performance and structural features of (La1−yCay)(CoxFe1−x)O3 cathode prepared via a citrate acid gel route are studied when it is interfaced with the (La1.8Dy0.2)(Mo2−zWz)O9 electrolyte. The resistance and chemical capacitance of a low-frequency arc are extracted from the impedance results to evaluate its catalytic activity in oxygen reduction reaction (ORR). (La0.75Ca0.25)(Co0.8Fe0.2)O3 cathode exhibits the minimum area-specific resistance of 0.9 Ω cm2 and maximum capacitance of 5.7 mF/cm2 at 800°C among the compositions of x=0.1–0.9 and y=0.25. As the Co content increases, the decrease in resistance outweighs the increase in capacitance so that the product of resistance and capacitance (RC time constant) decreases. In contrast, when varying the Ca content of the A-site, the changes in resistance and the capacitance compensate each other; hence the RC time constant is virtually unchanged with respect to the calcium content. Thus, Co is a more influential element than Ca on the ORR catalytic activity. The pore structure study reveals a small amount of Mo diffuses from the electrolyte into the cathode, and its quantity is reduced when interfaced to an electrolyte of high W content.

We report a detailed study of thermal-induced phase transformation in TiO 2 nanocrystals (NCs) via X-ray diffraction (XRD) and Raman scattering (RS) spectroscopy. Vertically aligned anatase TiO 2 (1 1 0) NCs were grown on the sapphire (SA)(1 0 0) substrate at 550 °C by metal organic chemical vapor deposition, using titanium-tetraisopropoxide (TTIP, Ti[OCH(CH 3 ) 2 ] 4 ), as the source reagent. The effects of thermal annealing of TiO 2 NCs in oxygen atmosphere between 600 and 1000 °C were investigated. XRD and RS spectra showed the onset of the phase transformation process from the as-grown anatase TiO 2 (1 1 0) NCs into rutile TiO 2 (0 0 1) at the annealing temperature of 800 °C. At annealing temperature higher than 900 °C, pure rutile phase of TiO 2 (0 0 1) NCs were formed and the crystalline quality of TiO 2 NCs could be further improved upon higher annealing temperature.

RuO2 single crystal is thermally reduced to generate a surface of coexisting Ru and RuO2 (Ru/RuO2) on its (110) facet, which is investigated using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The reduced RuO2 (110) facet exhibits longitudinal fissures parallel to stripes of Ru nuclei in the c -axis of the rutile structure, suggesting that the anisotropic lattice degradation commences at the weak links between the infinite chains of RuO6 octahedrons. Raman spectra of Ru/RuO2 surfaces reveal an additional feature at ∼190 cm−1 of the Ru phase among the RuO2 modes. The red-shifts and the asymmetric line width broadening of E g mode of RuO2 features are analyzed by a spatial correlation model. The fitted correlation length estimates the size of RuO2 grains which remained on the partially decomposed surface. The XPS O 1s line of the Ru/RuO2 surface provides a sensitive indication of crystal decomposition, especially at high take-off angles.

Lanthanum calcium cobalt ferrite (LCCF), a potential cathode composition for the LAMOX electrolyte, is studied on its electrocatalytic performance in oxygen reduction reaction (ORR) using impedance spectroscopy. Nyquist plots of LCCF impedance at 600–800 °C display two arcs, in which the low-frequency arc is constantly larger than the high-frequency arc. When interfaced to the electrolyte containing 20 mol% tungsten, the ORR polarization resistance of LCCF exhibits a strong temperature dependency whose activation energy increases with increasing Co content, 190 (10 mol%)–220 (90 mol%) kJ mol− 1. Among the cathode compositions, LCCF82 (80 mol% Co) exhibits the best catalytic performance. Its zero-bias ORR resistance is 242.4 at 600 °C, 0.845 Ω cm2 at 800 °C, along with the capacitance 7.79 (600 °C), 14.93 mF cm− 2 (800 °C). The ORR resistance of LCCF82 decreases with increasing dc bias at 600 and 700 °C, hardly changes at 800 °C. The electrocatalytic activity of LCCF82 is also influenced by the tungsten content of its interfacing electrolyte. The exchange current density of LCCF82 correlates positively with the electrolyte ion conductivity which increases with decreasing tungsten content.

Raman spectroscopy (RS) was used to study the phase transformations of nanocrytalline TiO2 thin films. The films were grown by a vertical-flow cold-wall metal organic chemical vapour deposition system, using Ti(C10H14O5) as the source reagent, at different substrate temperatures. The results indicate that the anatase phase is present at around 550 °C and the rutile phase starts to form at 620 °C. The anatase phase completely transforms into the rutile phase at 680 °C. We have demonstrated that RS can be used as a powerful nondestructive technique for a quick and efficient determination of the phase of TiO2 thin films.

Structures and properties of PtRu electrocatalyts, derived from the aligned RuO2 nanorods (RuO2NR), are investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry toward COads and methanol oxidation. The catalytic activity of methanol oxidation and the CO tolerance are promoted significantly by reducing RuO2 into Ru metal before decorating with Pt. Reduction of RuO2NR was carried out by either thermal decomposition at 650 degrees C in vacuum or H2-reduction at 130 degrees C in low-pressure hydrogen. Reduction assisted by hydrogen allows infiltrating decomposition at low temperature and produces an array of nanorods with rugged walls featuring small Ru nuclei and larger surface area. Pt-RuNR, whose surface Pt:Ru ratio=0.58:0.42 was prepared by decorating with 0.1 mg cm(-2) Pt on the H2-reduced array containing 0.39 mg cm(-2) Ru, demonstrates a favorable combination of CO tolerance and high methanol oxidation activity superior to other RuO2NR-derived catalysts. When compared with a commercial electrocatalyst of PtRu (1:1) alloy (4 nm), the activity of Pt-RuNR in methanol oxidation is shown to be somewhat lower at potential0.48 V and higher at potentialor=0.48 V.

Structural electrodes of anhydrous RuO2 vertical nanorods encased in hydrous RuO2 have been prepared via chemical vapor deposition (CVD) followed by electrochemical deposition. The composite structures are studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The capacitive properties are measured using cyclic voltammetry and impedance spectroscopy. In a miniaturized configuration, the CVD grown structure provides a connecting backbone of electron paths and open channels for ion migration to facilitate the charge delivery or acceptance from the electrodeposited hydrous RuO2 of high pseudocapacitance. The sample of thermally reduced nanorods encased in RuO2·0.46H2O (RuRuO2VR-H2) exhibits a total capacitance of ∼520 F g-1 (870 mF cm-2) at 5 mV s-1, superior to that of the RuO2·0.46H2O coated as-grown nanorods (RuO2VR-H) ∼260 F g-1 (300 mF cm-2). Despite having twice the charge storage capability, RuRuO2VR-H2 demonstrates a capa...

The structural stability and ion conductivity of (La 1.8 Dy 0.2 )(Mo 2− x W x )O 9 are studied using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy. The structural stabilization effect of W is demonstrated by comparing the microstructures and the oxidation states of ions of as-sintered and H 2 -reduced samples. Without tungsten, the H 2 -reduced surface of (La 1.8 Dy 0.2 )Mo 2 O 9 is engraved with deep notches at grain boundaries and shallow cuts in the grain interior. At a sufficient W level, the H 2 -reduced surface is similar to the surface without H 2 reduction. The XPS analysis concludes that 20% Mo on the (La 1.8 Dy 0.2 )Mo 2 O 9 surface is reduced to Mo 4+ and Mo 0 , whilst all Mo is detected at the oxidation state of + 6 in (La 1.8 Dy 0.2 )(Mo 1 W 1 )O 9 after 600 °C 3%H 2 reduction. No α–β phase transformation is experienced in any specimens of (La 1.8 Dy 0.2 )(Mo 2− x W x )O 9 , when heated from 300 to 800 °C. The room-temperature lattice parameter of β-phase increases with increasing W content, reaches a maximum at x = 1.0, then decreases. Considering the W structural stabilization effect, its unfavorable influence on conductivity is tolerable because the sample of (La 1.8 Dy 0.2 )(Mo 1 W 1 )O 9 exhibits a conductivity of 0.18 S cm − 1 at 800 °C, still higher than 0.08 S cm − 1 of La 2 Mo 2 O 9 . The temperature dependence of ion conductivity in this doubly substituted LAMOX is correlated to the Arrhenius form from 350 to 450 °C and the Vogel–Tamman–Fulcher form from 450 to 800 °C, and discussed.

Mixed ionic and electronic conductors of La 1− x Ca x FeO 3− δ (LCF, x =0.0–0.5) have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometry, and four-probe electrical conductivity measurements. Ca substitution on La site reduces the LaFeO 3 sinterability and the cell volume of this orthorhombic crystal. Dense samples for property studies can be sintered at 1320 °C. Nevertheless, the sintering temperature is near the decomposition temperature of LCF for those solid solutions of x ≥ 0.3. The LCF decomposition is evident when a La-poor secondary phase, not detected in XRD, was revealed in SEM micrographs of 1270 °C thermally etched samples of x ≥ 0.3. Dilatometric studies demonstrate linear increments in thermal expansion with increasing temperature in samples of x ≤ 0.2, while show strange bendings in thermal expansion curves of x = 0.4 and 0.5. The bending in thermal expansion indicates influences of the secondary phase. The TEC value of compositions of x ≤ 0.2 is between 10.8 and 11.7 × 10 −6 °C −1 . The LCF electrical conductivity increases with the Ca content and its temperature dependence can be described by the small polaron hopping mechanism. The composition around x = 0.15 promises to be a superior cathode for SOFC since it thermally matches with 8 mol% YSZ and 10 mol% Dy, Er substituted LAMOX electrolytes and possesses electrical conductivity near 90 S cm −1 at 800 °C.

The structural features and catalytic activities of PtIr electrocatalysts derived from vertical IrO2 nanotubes (IrO2NT) of 1100 nm in height and 80−100 nm in diameter have been studied using scanni...

Raman spectroscopy (RS) has been used as a technique for the characterization of well-aligned IrO2 and RuO2 nanocrystals (NCs) grown on a number of different oriented substrates under various conditions. The IrO2 and RuO2 NCs were grown via metalorganic chemical vapor deposition and reactive magnetron sputtering. The relative intensity of the three strongest Raman-active modes, namely, the A1g, B2g and Eg modes, depends on the orientation of NCs and has been used to determine the preferred growth direction of the NCs. The redshifts and asymmetric linewidth broadening of the Raman features of IrO2 and RuO2 NCs with respect to that of their bulk counterparts were analyzed by a modified spatial correlation (MSC) model, which includes a factor of stress-induced shift. The MSC model showed that the effects of stress and nanometric size could be separated in analyzing the observed Raman features. The usefulness of experimental RS together with the MSC model analysis as a structural and residual stress characterization technique for NCs has been demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.

SiH 4 and GeH 4 dissociative adsorptions on a buckled SiGe(1 0 0)-2 × 1 surface have been analyzed using density functional theory (DFT) at the B3LYP level. The Ge alloying in the Si(1 0 0)-2 × 1 surface affects the dimer buckling and its surface reactivity. Systematic Ge influences on the reaction energetics are found in SiH 4 and GeH 4 reactions with four dimers of Si ∗ –Si, Ge ∗ –Si, Ge ∗ –Ge, and Si ∗ –Ge (∗ denotes the protruded atom). On a half H-covered surface, the energy barriers for silane and germane adsorption are higher than those on the pristine surface. The energy barrier for silane adsorption is higher than the corresponding barrier for germane adsorption. Rate constants are also calculated using the transition-state theory. We conclude that the SiGe surface reactivity in adsorption reaction depends on the Ge presence in dimer form. If the surface Ge is present in form of Ge ∗ –Ge, the surface reactivity decreases as the Ge ∗ –Ge content increases. If the surface Ge prefers to be in form of Ge ∗ –Si at low Ge contents, the surface reactivity increases first, then decreases at high Ge surface contents when Ge ∗ –Ge prevails. The calculated rate constant ratio of GeH 4 adsorption on Si ∗ –Si over Ge ∗ –Ge at 650 °C is 2.1, which agrees with the experimental ratio of GeH 4 adsorption probability on Si(1 0 0) over Si(1 0 0) covered by one monolayer Ge. The experimental ratio is 1.7 measured through supersonic molecular beam techniques. This consistency between calculation and experimental results supports that one monolayer of Ge on Si(1 0 0) exists in form of Ge ∗ –Ge dimer.

We report the preparation of vertically aligned one dimensional (1D) IrO2 nanocrystals (NCs) on LiNbO3 (100) by reactive magnetron sputtering using Ir metal target. The effects of sputtering conditions such as distance between gun and substrate, pressure, power of radio frequency generator and substrate temperature have been presented and discussed. The surface morphology, structural and spectroscopic properties of the as-grown NCs were characterized in detail using field emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and micro-Raman scattering. FESEM micrographs reveal that vertically aligned NCs were grown on LiNbO3 (100) substrates. The XRD results indicate that the IrO2 NCs are (002) oriented on LiNbO3 (100). The probable mechanism for the formation of the vertically aligned 1D NCs has been discussed. The XPS examination shows the existence of extra features at higher-binding-energy sites of Ir 4f and O 1s which is a common property for IrO2 1D NCs. The red shift and asymmetric broadening of Raman lineshape have been analyzed and attributed to both the size effect and residual stress.

We review the results of the synthesis of IrO2 nanocrystals (NCs) on different substrates via metal-organic chemical vapour deposition (MOCVD) using (MeCp)(COD)Ir as the source reagent. The surface morphology, structural and spectroscopic properties of the as-deposited NCs were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAD), x-ray diffractometry (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The roles of different substrates for the formation of various textures of nanocrystalline IrO2 are studied. Several one-dimensional (1D) nanostructures have evolved by decreasing the degree of interface instability. The morphological evolution occurs from triangular/wedged nanorods via incomplete/scrolled nanotubes to square nanotubes and square nanorods (NRs), with increasing morphological stability. The results show that the three-dimensional (3D) grains composing traditional film belong to the most stable form as compared to all the 1D NCs, and the sequential shape evolution has been found to be highly correlated to a morphological phase diagram based on the growth kinetics. In addition, area selective growth of IrO2 NRs has been demonstrated on sapphire(012) and sapphire(100) substrates which consist of patterned SiO2 as the nongrowth surface. The initial growth of IrO2 nuclei is studied. Selectivity, rod orientation, and other morphological features of the nanorod forest can find their origins in the nucleation behaviour during initial growth. XPS analyses show the coexistence of higher oxidation states of iridium in the as-grown IrO2 NCs. The usefulness of the experimental Raman scattering together with the modified spatial correlation (MSC) model analysis as a residual stress and structural characterization technique for 1D IrO2 NCs has been demonstrated. The field emission properties of the vertically aligned IrO2 NRs are studied and demonstrated as a high-performance and robust field emitter material owing to its low work function, low resistivity and excellent stability against oxygen.

Raman scattering (RS) has been used as a technique for characterization of IrO 2 one dimensional (1D) nanocrystals (NCs) deposited on sapphire(100) and LiNbO 3 (100) substrates under various conditions. The IrO 2 NCs were grown via metalorganic chemical vapor deposition method using (MeCp)(COD)Ir as the precursor and reactive magnetron sputtering using Ir metal target. The red-shifts and asymmetric broadening of the Raman lineshape for the NCs were analyzed by a modified spatial correlation (MSC) model, which includes the factor of stress induced shift. The proposed MSC model showed that the effects of stress and nanometric size can be separated in analyzing the observed Raman features. The usefulness of the experimental RS together with the MSC model analysis as a residual stress and structural characterization technique for 1D NCs has been demonstrated.

Well aligned densely packed IrO2 nanocrystals (NCs) have been grown on sapphire (SA) substrates with different orientations by reactive magnetron sputtering using an Ir metal target. The surface morphology, structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. FESEM micrographs reveal that NCs with parallel in-plane alignment were gown on SA(001), vertically aligned NCs were grown on SA(100), while the NCs on SA(012) and SA(110) contained, respectively, single- and double-aligned directions with a tilt angle of ~35° from the normal to the substrates. The XRD results indicate that the NCs are (100), (001), and (101) oriented on SA(001), SA(001), and SA(012)/SA(110) substrates, respectively. A strong substrate effect on the alignment of the IrO2 NCs growth has been demonstrated and the probable mechanism for the formation of these NCs has been discussed. XPS analyses show the coexistence of higher oxidation states of iridium in the as-grown IrO2 NCs. The Raman spectra show the red-shift and asymmetric peak broadening with a low frequency tail of the IrO2 signatures with respect to that of the bulk counterpart, which are attributed to both the size and residual stress effects.

Raman spectroscopy (RS) was used for the characterization of well-aligned IrO2 nanocrystals (NCs) grown on sapphire substrates with different orientations via reactive magnetron sputtering. Three Raman-active modes, Eg, B2g and A1g, were observed in the range 500–800 cm−1. The intensity of certain modes depended on the orientation of NCs and followed the selection rules reasonably well. The result indicates the possibility of determining the preferred growth direction of NCs using RS. Raman spectra show red shifts and peak broadening of the IrO2 signatures with respect to those of the bulk counterpart. The red shifts and asymmetric broadening of the Raman line shapes of the NCs were analyzed by a modified spatial correlation (MSC) model, which included a factor of stress-induced shift. The MSC model showed that the effects of stress and nanometric size could be separated by analyzing the observed Raman features. The usefulness of experimental RS together with the MSC model analysis as a structural and residual stress characterization technique for NCs is demonstrated. Copyright © 2006 John Wiley & Sons, Ltd.

The effects of post-thermal treatment and rod diameter on the field emission (FE) properties of RuO2 nanorod films are reported. The FE properties of RuO2 nanorods with pyramidal tips have been studied on samples of two average rod diameters, 48 and 35 nm. Both of them exhibit a transient behaviour in emission current under a fixed electric field. Thermal annealing at 400 and 500 °C generally improves the FE characteristics in lowering the emission barriers of nanorods, as manifested by a decrease in the turn-on field, the threshold field, the slope of the Fowler–Nordheim plot, and the time-span of the transient period. Reduction in emission barrier appears to be particularly evident for the 35 nm nanorods. Yet 500 °C annealing also degrades the emission current stability of 35 nm nanorods. The standard deviation of emission current density of 35 nm nanorods after 500 °C annealing is around 44%. On the other hand, both specimens after 400 °C annealing display a much more stable emission current density, whose fluctuations are 26% of their average values. The transient period is regarded as a consequence of gas molecules being desorbed from the RuO2 tips during emission, resulting in a reduction of the emission barrier. Thermal annealing weakens the bonding between the adsorbed gas and the tip surface, and facilitates the gas desorption and electron tunnelling processes.

The ion conductivities and phase transitions of lanthanum molybdate (La2Mo2O9) substituted with lanthanide rare-earths are investigated using impedance spectroscopy, dilatometry, and X-ray powder diffraction. Among the substituted La2Mo2O9 of 10 mol% Ce, Nd, Sm, Gd, Dy, Er, Yb, the specimens containing Er, and Dy exhibit depressed α–β phase transformation and high conductivities. Their 700 °C conductivities are approximately five to seven times that of La2Mo2O9, around 0.26 S cm−1, comparable with those of (LaSr)(GaMg)O3 and Gd-substituted CeO2. Among the three compositions of 10 mol% Gd, Dy, Er showing depressed phase transition, Er- and Dy-substituted La2Mo2O9 possess relatively low thermal expansion coefficient 11×10−6 K−1, compared with that of the Gd-substituted La2Mo2O9, 18×10−6 K−1, which is near that of La2Mo2O9. Hence, Dy and Er are valuable dopants in improving the La2Mo2O9 properties. Across the lanthanide series, 10 mol%-substituted La2Mo2O9 demonstrates systematic variations in the conductivity–temperature relation. Hysteresis phenomena in both of conductivity and thermal expansion are also observed in those compositions which display phase transition.

Complex Pb(Zn 1/3 Nb 2/3 )O 3 (PZN)-based ceramics have been prepared by three different columbite methods: conventional columbite (CC), B-site precursor columbite (BSPC) and A-site sequential mixing columbite (ASMC) method. The pyrochlore was not removed completely by IC and BSPC process for PZN-rich compositions. The transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) observation of the BSPC samples show that the BaO was segregated at triple junctions, implying that stabilization of the perovskite structure of the specimens was not completely achieved due to element segregation. On the other hand, full perovskite phase could be obtained by ASMC method for all compositions. Although the pyrochlore phase could mostly be removed by all three processes for specimens with PZN contents less than 50%, the dielectric behavior of PZN-based ceramics was markedly affected by the processing procedures.

Self-assembled and well aligned RuO2 nanorods (NRs) have been grown on sapphire (SA) substrates via metal–organic chemical vapour deposition (MOCVD), using bis(ethylcyclopentadienyl)ruthenium as the source reagent. The surface morphology, structural, and spectroscopic properties of the as-deposited NRs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAD), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned nanorods (NRs) were grown on SA(100), while the NRs on the SA(012) were grown with a tilt angle of from the normal to the substrates. TEM and SAD measurements showed that the RuO2 NRs with square cross-section have the long axis directed along the [001] direction. The XRD results indicate that the RuO2 NRs are (002) oriented on SA(100) and (101) oriented on SA(012) substrates. A strong substrate effect on the alignment of the RuO2 NRs growth has been demonstrated and the probable mechanism for the formation of these NRs has been discussed. XP spectra show the coexistence of higher oxidation state of ruthenium in the as-grown RuO2 NRs. Micro-Raman spectra show the red-shift and peak broadening of the RuO2 signatures with respect to that of the bulk counterpart which may be indicative of a phonon confinement effect for these NRs.

Conductive iridium dioxide (IrO 2 ) nanorods have been successfully grown on the Si(1 0 0) substrates via metalorganic chemical vapor deposition (MOCVD). A wedge-shaped morphology and naturally formed sharp tips are observed for IrO 2 nanorods using field-emission scanning electron microscopy (FESEM). High-resolution transmission electron microscopy (TEM) image and electron diffraction pattern show the growth of IrO 2 nanorods preferentially along c -axis. Structure and composition of IrO 2 nanorods have also been characterized using the techniques of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. It is noted that the IrO 2 nanorods are self-mediated instead of the conventional vapor–liquid–solid (VLS) approach or catalyst-mediated method.

Raman scattering (RS) and field emission scanning electron microscopy (FESEM) have been used to extract microstructural information of RuO 2 nanorods (NRs) and a two-phase system comprising NRs embedded in polycrystalline matrix deposited on different substrates by the metal-organic chemical vapor deposition method. The red shifts and asymmetric broadening of the Raman line shape for the NRs are analyzed by the spatial correlation model. The deduced spatial correlation length l is found to be much smaller than that of the average size L 0 estimated from the FESEM images. The Raman features for the two-phase system can be resolved into two parts: a Lorentzian line shape feature corresponding to the polycrystallite at higher frequency side and an asymmetrically broadened NRs' signature located at lower frequency end. The volume fraction of NRs in the two-phase system can be determined from the analysis. These results demonstrate the significance of RS as a structural characterization method when used in conjunction with FESEM.

PZT thin films have been prepared via metalorganic CVD (MOCVD) on four substrates of conducting oxides of ruthenates, SrRuO 3 /Pt/Ti/SiO 2 /Si(1 0 0), SrRuO 3 /SiO 2 /Si(1 0 0), CaRuO 3 /Pt/Ti/SiO 2 /Si(1 0 0), CaRuO 3 /SiO 2 /Si(1 0 0). The conducting ruthenate layers were also grown using MOCVD. Ferroelectric properties of polarization fatigue and leakage current density are measured. The internal strain of PZT thin crystal which is mainly constrained by the bottom electrode seems to be the decisive factor in ferroelectric properties. The internal strain of PZT is represented by its tetragonality ratio. The PZT thin film in the capacitor Au/PZT/SrRuO 3 /Pt/Ti/SiO 2 /Si, with the largest tetragonality ratio 1.026, exhibits an optimum combination of large polarization, less fatigue, and low leakage current density. Both SrRuO 3 and CaRuO 3 are good diffusion barriers to prevent interdiffusion of cations between the ferroelectric and the electrode. The slightly higher intermixing at the CaRuO 3 -to-Pt/Ti interface is owing to the high annealing temperature needed in CaRuO 3 synthesis.

Synthesis of conducting oxide strontium ruthenate is carried out in a hot-wall tubular reactor, using Sr(C11H19O2)2/Ru(C5H5)2/O2 reaction system. Owing to a large difference in depositing efficiency between strontium and ruthenium precursors, the stoichiometric ratio of thin film is controlled in one cycle of two consecutive depositions at different temperatures. Thin films of SrRuO3 single phase are synthesized in the subsequent 700°C annealing. Thin films of SrRuO3 with extra ruthenium oxide can also be prepared by adjusting the molar ratio of RuO2 and SrO layers. The deposition sequence of ruthenium oxide first, strontium oxide later is preferred. If the deposition sequence is reverse, the thin film is plagued with unreacted oxides even when the annealing temperature is raised to 800°C. The relative ease of preparing SrRuO3 thin films, when RuO2 is under SrO, is attributed to evaporation of ruthenium oxide in O2 and diffusion in its open columnar microstructure. The sheet resistivity of thin film decreases with the ruthenium content. The room temperature resistivity of SrRuO3 film of Ru/(Sr + Ru) = 0.5 is around 910 μohm-cm. The room-temperature resistivity of Ru/(Ru + Sr) = 0.53 decreases to 470 μohm-cm. The root mean square surface roughness of 700°C synthesized SrRuO3 thin film is 22 nm, in a 2 × 2 μm2 area of film thickness 280 nm.

Ferroelectric PZT thin films were deposited on Pt and SrRuO3 substrates in a cold-wall reactor, using the Pb(C2H5)4/Zr(OBu)4/Ti(OPri)4/O2 reaction system. In comparison with Pt substrate, the growth rate of lead zirconate titanate (PZT) thin film was higher on SrRuO3. Lead content of the thin film deposited on either substrate at low temperatures (723–863 K) was much more temperature dependent than the other two metal contents. The strong temperature dependence originated from the high activation energy in the initial decomposition of Pb(C2H5)4 vapor, which was 54 kcal/mol. The surface reaction constant of lead precursor had much lower temperature dependence. The activation energy of surface reaction for PbO, estimated from deposition in a mini-chamber, was 6 kcal/mol on Pt and 9 kcal/mol on the SrRuO3 substrate. Therefore, the incorporation path of component oxide PbO, whose apparent activation energy was 31 kcal/mol on Pt and 29 kcal/mol on SrRuO3, essentially involved considerable gas-phase reaction. The PZT (50/50) thin film on SrRuO3 bottom electrode possessed a lower coercive field and a smaller remnant polarization than that on Pt. The PZT capacitor on SrRuO3 was also less vulnerable to polarization fatigue.

Reactive sticking coefficients (RSC) of silicon hydride radicals are evaluated, between 853 and 903 K, from simulating the film thickness contours of trenches deposited in a SiH4/Ar reaction system. The RSC values of SiH4, Si2H6 and Si3H8, calculated from the hydrogen desorption kinetics and the surface hydrogenation kinetics at each trench location, are used to estimate their contributions in film growth. The radical RSC values and concentration are the fitting parameters in the trench simulation, in which the sum of SiH4, Si2H6 and Si3H8 contributions is referred to a film-forming species of low sticking coefficient, and the radicals as the other species of high sticking coefficient. The correlated RSC value of the radicals, generally less than 1, is higher than that of silane by approximately five orders of magnitude. The radical RSC linearly increases with the surface fraction of dangling bonds θ. The extrapolated RSC value at θ=1 is unity, which suggests that a radical has probability of reaction with dangling bonds of unity. The deviation from this idealized value is due to a large percentage of the growing surface being hydrogen-passivated. The probability of the reaction of a radical with the hydrogen-terminated surface, which is extrapolated at θ=0, has an activation energy of 4.6 kcal/mol.

Capacity degradation and ion insertion of a miniaturized electrochemical capacitor are studied using ionic liquid [EMI] [TFSI] as the electrolyte. This capacitor is featured with two comb-like electrodes of vertical carbon nanotubes, ∼70 μm in height and 20 μm in interelectrode gap. We quantify the levels of ion insertion damage with Raman spectroscopy after the electrode experiences 120 consecutive voltammetric cycles to various potential limits. Distinct structural damage emerges due to [EMI] when the negative potential reaches -1.7 V, and those due to [TFSI] arise when the positive potential reaches 1.7 V vs. RHE. Judging from the peak broadenings, [EMI] is more detrimental than [TFSI]. When the voltage window ΔU is set as less than or equal to 2.8 V, both electrode potentials are within the two intercalation limits, little or no decay is observed in 10(4) charge/discharge cycles. When ΔU is 3.4 V, the positive potential exceeds the upper limit, but the negative potential stays within the lower limit, the cell capacitance decreases moderately. When ΔU increases to 3.8 V, both electrodes suffer from damages because of exceeding the intercalation limits. And the cell capacitance decreases substantially, even leading to a premature failure.

Formation of ordered structure in flux-grown Ba(Mg1/3Ta2/3)O3(BMT) single crystals was studied using x-ray diffraction, electron diffraction, and high-resolution electron microscopy. The low-temperature-grown crystals exhibited no sign of B-site ordering. Annealing at 1500 °C induced the 1:2 ordered phase, and its content increased with the annealing time. The superlattice diffraction peaks were broad initially; they sharpened rapidly with the annealing time. Diffuse superlattice reflections were found in electron diffraction patterns of 1500 °C annealed BMT; they turned into sharp reflections under long annealing time or higher temperature, 1600 °C. The intensity of diffuse reflections was sparsely distributed, but the maximum intensity location was determined in the digitized recording of image plate. The maximum intensity sites of two diffuse reflections in the 〈111〉 direction deviated from the presumed 1/3 and 2/3 positions and shifted towards the center. The diffuse reflection and the deviation from regular positions were interpreted as the composition modulation during B-site cation diffusion.

The deposition of silicon carbide thin film on Si (1 0 0) wafer, using low pressure CVD of SiH2Cl2/C2H2/H2 reaction system, is investigated. The SiC film deposited at 1023 K is amorphous, 1073 K is microcrystalline, and 1173 K is (1 1 0) preferentially oriented. The deposition rate increases significantly with temperature. Deposition kinetics of surface and gas-phase paths is separated by varying the volume/surface ratio of deposition environment. The activation energy for gas-phase reaction path is estimated to be 76 kcal/mol, and that for surface reaction path is 71 kcal/mol. The experimental barrier for gas-phase reaction path is close to the values by ab initio calculation (Su and Schlegel), which range from 73 to 76 kcal/mol for the step of H2 elimination from SiH2Cl2.

Ceramics of Ba(Mg 1/3 Ta 2/3 )O 3 -BaSnO 3 (BSMT) are synthesized by a two-stage calcination method. Microstructures are analyzed, using X-ray diffractometry, transmission electron microscopy, Raman spectroscopy, and scanning electron microscopy. The addition of BaSnO 3 reduces the cation ordering of Ba(Mg 1/3 Ta 2/3 )O 3 and its sinterability. Variations in ordered structure with BaSnO 3 content are revealed by the reduction in intensity of the superlattice reflections, the domain size, the c/a ratio, and the shifting and broadening in Raman lines. The relations between microstructure and quality factors of BSMT are discussed. ©

Well-aligned 1D RuO2 nanocrystals (NCs) have been grown on sapphire (SA)(1 0 0), SA(0 0 1) and LiNbO3 (LNO)(1 0 0) substrates via reactive magnetron sputtering using a Ru metal target. The surface morphology, structural and spectroscopic properties of the as-deposited NCs are characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and micro-Raman spectroscopy (RS). FESEM micrographs show that NCs grown on SA(1 0 0)/LNO(1 0 0) are vertically aligned, while NCs grown on SA(0 0 1) show in-plane alignment with mosaic structure. The XRD results indicate that the NCs are (0 0 1) and (1 0 0) oriented on SA(1 0 0)/LNO(1 0 0) and SA(0 0 1) substrates, respectively. A strong substrate effect on the alignment of the RuO2 NCs deposition has been observed and the probable mechanism for the formation of these NCs has been discussed. The usefulness of the Raman spectroscopy as a structural characterization technique of NCs has been demonstrated.

We report in detail the synthesis and characterization of V-shaped IrO(2) nanowedges (NWs) with an angle of 110° between the two arms. The NWs were grown on top of rutile (R) phase TiO(2) nanorods (NRs) sitting on a sapphire (SA)(100) substrate via metal-organic chemical vapor deposition (MOCVD) by using (C(6)H(7))(C(8)H(12))Ir and titanium-tetraisopropoxide (TTIP, Ti[OCH(CH(3))(2)](4)) as the source reagents. The surface morphology, structural, and spectroscopic properties of the as-deposited nanocrystals (NCs) were characterized by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), micro-Raman spectroscopy, transmission electron microscopy (TEM), and selected-area electron diffractometry (SAED). The FESEM images and XRD patterns indicated growth of V-shaped IrO(2)(101) NWs on top of R-TiO(2) NRs. The Raman spectrum showed the nanosize induced redshift and peak broadening of the IrO(2) and rutile phase of TiO(2) signatures with respect to that of the bulk counterparts. TEM and SAED characterizations of IrO(2) NCs showed that the nanowedges were crystalline IrO(2) with a twin plane of (101) and twin direction of [Formula: see text] at the V-junction. The probable mechanisms for the formation of well-aligned IrO(2) NWs are discussed.

Well-aligned anatase (A)–TiO2nanocrystals (NCs) were grown by cold-wall metalorganic chemical vapor deposition (MOCVD) on fused silica using titanium-tetraisopropoxide (Ti(OC3H7)4) as the source reagent. Field emission scanning electron microscopy (FESEM) micrographs showed the growth of vertically aligned NCs. X-ray diffractometry (XRD) pattern revealed the aligned A–TiO2 with a preferential orientation of (220). Raman spectrum confirmed the deposition of pure anatase phase TiO2 on fused silica. Luminescence of self-trapped excitons and oxygen vacancies were observed in anatase NCs. The indirect band gap of A–TiO2 was determined to be 3.14 ± 0.01 eV by analyzing the surface photovoltage spectrum. Energy-dispersive X-ray spectroscopy (EDS) and X ray photoelectron spectroscopy (XPS) analyses showed oxygenvs.titanium ratio of 2.0 ± 0.1 for the as-deposited TiO2 NCs. Further structural characterization of the well-aligned A–TiO2 NCs was studied using transmission electron microscopy (TEM) technique. The formation of building units bonded along {112} facets with preferred (220) orientation of the well-aligned A–TiO2 NCs on fused silica were presented and the probable growth mechanisms were discussed.

Ab initio calculations have been carried out to investigate the pathways of H-atom migration and H2 desorption on a mixed SiGe(100)-2×1 surface using the cluster model. The H2 recombinative desorption is the rate-determining step in hydrogen migration and desorption on SiGe(100) surfaces, since the energy barrier to H-atom migration is generally lower than that of H2 desorption. The energy barriers for H2 desorption from the interdimer, the Si–Ge pair, (52.8 kcal/mol), and the Ge–Ge pair, (45.1 kcal/mol), are lower than that for the Si–Si pair by 7.5 and 15.2 kcal/mol, respectively. Thus, the SiGe(100)-2×1 surface in chemical vapor deposition provides more dangling bonds than the Si(100)-2×1 surface because of Ge inclusion. In contrast, the chemisorbed H tends to stay on the Si-site, since the barrier for H-migration from the Ge-site to the Si-site is lower that in the opposite direction by 5.6 kcal/mol. Hence, a considerably higher percentage of Ge sites are dangling bonds, compared with Si sites on the SiGe(100) surface. Related transition state structures in the migration and desorption steps are also discussed.

The electrochemical properties of RuO2/LNO and RuO2/SA electrodes made of RuO2 rods and plates of nanometre size on LiNbO3(100) and sapphire(0001) substrates are investigated. Both rods and plates are grown vertically using chemical vapor deposition. The RuO2/LNO electrode has a higher electrolyte/solid surface area compared with the RuO2/SA electrode. When immersed in H2SO4 acid, voltammograms of both electrodes exhibit chemisorption and pseudocapacitive characteristics of the RuO2 single crystal. The chemisorption features decrease after repeated cyclic voltammetry (CV) sweeps, and the voltammograms become more mirror-like. The specific capacitance of the RuO2/LNO electrode measured in CV is 569 F g−1, that of RuO2/SA 357 F g−1. These values are reconfirmed in charging–discharging measurements. The measured capacitance decreases with the sweep rate, and the decreasing trend of RuO2/LNO is higher than that of RuO2/SA. Reduction of accessible charge at high sweep rates results from higher internal resistance of the RuO2/LNO electrode which is distributed because of its porous nature. The impedance spectrum of the RuO2/LNO electrode confirms its higher internal resistance. It also indicates the electrode is a nearly ideal capacitor below a knee frequency 200 Hz. Since the knee frequency is less than 1 Hz for most electrochemical capacitors, both RuO2/LNO and RuO2/SA are electrodes for fast charging–discharging applications.

Iridium dioxide (IrO2) nanorods with pointed tips have been grown on Si(100) and transition-metal-coated-Si(100) substrates, via metal–organic chemical vapor deposition (MOCVD), using (MeCp)Ir(COD) as the source reagent. The as-deposited nanorods were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FESEM micrographs revealed that the majority of the nanorods are a wedge shape in cross section and converge at top; occasionally several of them pack into a column of a spiral tip. The vertical alignment and packing density are significantly improved by prior deposition of a thin layer of Ti on Si. TEM and XRD results indicate that the sputtered Ti thin layer erects the nanorods in the c-axis direction. XPS spectra show that iridium in IrO2 nanorods also exist in a higher oxidation state.