Table of contents

Open-circuit measurements and magic-angle spinning (MAS) NMR spectroscopy were used to study Li coordination in partly reduced spinels prepared by hydrothermal reaction. The reduced spinels show four different Li sites. Signals at −0.2 and 0.3 ppm correspond to Li in 16d and 8a positions. The signal at 0.9 ppm corresponds to a tetrahedrally coordinated Li and represents the primary site for the inserted lithium. The signal at −0.7 ppm appears simultaneously with a decrease of the population of Li in 8a position and indicates a local phase transition connected with ordering of Li into 16c positions. © 2004 The Electrochemical Society. All rights reserved.

Short-range ordering in was investigated with NMR and first principles structure computations. NMR indicates that the tendency for to replace in the layers decreases with decreasing nickel content. Li in the Ni/Mn layers preferentially occupies sites near and avoids the ions, leading to nonrandom configurations. Calculations indicate that the ground state of contains zigzag rows of and ions. Although a disordering temperature of approximately 1000 K is calculated, ordered fragments persist above the phase transition and these materials contain significant short-range order, even when quenched from high temperature. © 2004 The Electrochemical Society. All rights reserved.

Ta-doped and nanocomposite thin films were successfully synthesized by co-sputtering. The Ta-doped films formed a solid solution that induced structural changes from rutile to anatase phases. In the nanocomposite films, Au particles with a diameter of about 15 nm were homogeneously distributed in the matrix. The anodic photocurrents of the Ta-doped electrodes and nanocomposite electrodes were observed not only in the UV but also in the visible light range. The photoresponse in visible light between Ta-doped and nanocomposite are due to bandgap reduction and photoexcitation of electrons from the interface states. © 2004 The Electrochemical Society. All rights reserved.

Substituted cobalt oxides, and , have been synthesized using solid-state technique and their performance in a 2032-type lithium rechargeable coin cell is reported. The synthesized powders were structurally analyzed using X-ray diffraction (XRD) and the surface morphology evaluated with scanning electron microscopy. XRD patterns indicate that single-phase materials were formed involving Al-doped Electrochemical studies were carried out in the voltage range 3.5-4.5 V (vs. Li metal) using 1 M in ethylene carbonate/dimethyl carbonate as electrolyte. The doping involving 5% Mg resulted in a charge/discharge capacity of ∼160 mAh/g at C/5 rate and remained stable even after 50 cycles. To the best of our knowledge, this is the first time that such high stable capacities have been obtained involving doped when cycled up to 4.5 V. © 2004 The Electrochemical Society. All rights reserved.

A type of rocking chair Li-ion battery was reported using composite films with and without lithiation as anode and cathode materials, respectively. The discharge capacity can reach 22 μAh/μm cm² with low capacity fading up to 100 cycles at a current of 10 μA/cm². An all-solid-state lithium battery of exhibited a typical reversible capacity of 42-72 μAh/μm cm² and the reduction of capacity is about 1.1% every cycle. These results suggest that a composite thin-film electrode is a promising cathode material for all-solid-state thin-film rechargeable lithium batteries. © 2004 The Electrochemical Society. All rights reserved.

Colloidal cadmium sulfide containing cadmium selenide films were prepared by electrochemical codeposition to explore possibilities of obtaining enhanced photoresponsivenesss and increased resistance toward electrochemical corrosion. Inclusion of colloidal particles was inferred on the basis of current-voltage and photoaction spectral studies. Tafel plots were constructed for examination of corrosion behavior of the electrodeposits. The results show that colloidal cadmium sulfide inclusion improves photoactivity and electrochemical corrosion of the electrodeposited cadmium selenide in a significant measure. © 2004 The Electrochemical Society. All rights reserved.

The electrochemical reaction of with lithium occurs via a multistep process that leads to the formation of metallic copper, and as shown by electrochemical and X-ray diffraction measurements. The structural similarity between these three phases facilitates this topotactic "displacement" reaction that is almost fully reversible on oxidation, re-forming crystalline and expulsing Li. The system shows high reversibility during the first cycle, with an irreversibility of only 17%, good cyclability, and a reversible volumetric capacity of 2500 mAh/cm³. These properties suggest it could be an interesting anode material for lithium batteries. © 2004 The Electrochemical Society. All rights reserved.

Lithium nickel oxide, a potential candidate for cathode material for lithium-ion batteries, showed a distinct deterioration after storage in air for a time. The origin of this deterioration was explored by investigating surface structure, surface species, and ionic oxidation state of fresh and stored materials. Rietveld analysis of X-ray diffraction patterns showed not only the formation of on the surface, but also a weakening of ordered layered structure for the stored materials. X-ray photoelectron spectroscopy revealed that transforms to and active oxygen species exist on the surface of stored materials. Temperature programmed desorption-mass spectroscopy measurements gave evidence that active oxygen species occur on the surface of after storage. A surface reaction mechanism based on the transformation of and the evolution of active oxygen species is proposed. © 2004 The Electrochemical Society. All rights reserved.

Liquid electrolytes typically used in commercial lithium-ion batteries are comprised of lithium hexafluorophosphate in carbonate solvents. This electrolyte undergoes thermal decomposition at moderately elevated temperatures (80–100°C), encountered in the normal operation of these rechargeable power sources, to quantitatively generate highly toxic alkylfluorophosphates. The decomposition occurs via an autocatalytic mechanism initiated by trace impurities of water or alcohol. The thermal decomposition is inhibited in the presence of lithium metal oxides frequently used as the cathode of lithium-ion batteries or Lewis basic additives. © 2004 The Electrochemical Society. All rights reserved.

Four different single chamber fuel cell designs were compared using propane-air gas mixtures. Gas flow around the electrodes has a significant influence on the open-circuit voltage and the power density of the cell. The strong influence of flow geometry is likely due to its effect on gas composition, particularly on the oxygen chemical potential at the two electrodes as a result of gas mixing. The chamber design which exposes the cathode first to the inlet gas yielded the best performance at lower flow rates, while the open tube design with the electrodes equally exposed to the inlet gas worked best at higher flow rates. © 2004 The Electrochemical Society. All rights reserved.

In ethylene carbonate- and propylene carbonate-based electrolytes, ethylene and propylene gas evolution have been monitored by on line mass spectrometry. The gases evolve on graphite but not on the lithium storage alloy. The results point to a difference in the electrolyte decomposition mechanism and thus in the solid electrolyte interphase (SEI) formation mechanism. This is discussed in view of solvent co-intercalation reactions, which only arise when graphite anodes are used. The ultimate conclusion is that, due to the different side reactions occurring on graphite and lithium storage alloys, the SEI compositions and the requirements on the SEI performance are different. © 2004 The Electrochemical Society. All rights reserved.

Addition of silver hexafluorophosphate to propylene carbonate (PC)-based electrolyte may suppress the cointercalation and decomposition of PC in mesocarbon microbeads (MCMB). During the first charge/discharge cycle, silver ions are reduced at a potential (2.15 V vs. higher than that of the PC cointercalation potential (0.75 V vs. to form a protective film on the MCMB surface, thereby obstructing PC cointercalation. Results show an increasing trend for both reversible capacity and cycle life performance with increasing A satisfactory reversible capacity may be obtained when the silver addition is greater than 5 wt %. © 2004 The Electrochemical Society. All rights reserved.

The degradation study of the membrane electrode assembly (MEA) for proton exchange membrane fuel cells (PEMFCs) under low humidity conditions was conducted. The MEA degradation was observed during low humidity open-circuit voltage tests. To investigate the degradation mechanism, we conducted electron spin resonance studies of the degenerated MEA, and confirmed the formation of radicals in the catalyst layers. The MEA degradation mechanism that includes the radical formation reaction was verified. © 2004 The Electrochemical Society. All rights reserved.

Experimental results indicated that transition metal borides and electrodes can deliver exceptionally high discharge capacity of over 3100 and 1600 mAh/g, respectively, corresponding to an 11 and 6 electron oxidation reaction, although their parent elements V, Ti, and boron, are almost completely electrochemically inert. The reasons for the observed extraordinary capacities of diborides are probably due to the electrochemical activation of boron, which alleviates the passivation of the transition metal by clamping the electrode potential to a less positive range of potential. © 2004 The Electrochemical Society. All rights reserved.

Structural change of with two different crystallographic structures of and was studied during Li extraction. Ex situ X-ray diffraction and transmission electron microscopy studies on partially delithiated revealed that structure lost its characteristic diagonal glide symmetry, suggesting a structural transition arising from the possible migration of cations during oxidation from to For the ordering of cations was destroyed by random migration of cations during Li extraction, resulting in the formation of intermediate phase with the structure. The phase transitions were reversible, meaning that migration of cations is highly reversible during lithiation/delithiation. © 2004 The Electrochemical Society. All rights reserved.

The cathodic protection property of coatings under UV illumination suffers from certain disadvantages, which prevents its use for wider applications. being an n-type semiconductor is also expected to behave like under illumination. Based on this expectation, the photoelectrochemical properties of pure coatings on indium-tin oxide glass substrates using synthesized by two different wet-chemical processes were studied. prepared by Pechini process behaved favorably for cathodic protection applications. © 2004 The Electrochemical Society. All rights reserved.

The self-ordering behavior of porous anodic alumina induced by the burning phenomenon on the specimen where extremely high and local current concentrations occurred was studied. The domains of highly self-ordered cell arrangement were found at the locally thickened film formed by burning. At the center of the burnt area, the regularity of cell arrangement was higher and the barrier layer thickness as well as the cell size was remarkably lower. These results clearly suggest that the condition inducing film growth under high current density, i.e., high electric field is the key factor determining the self-ordering. © 2004 The Electrochemical Society. All rights reserved.

Lanthanum-containing oxide films are emerging candidates for gate-oxide films, due to expected high dielectric constants as well as promising crystal and electronic band structure. We have used tris(bistrimethylsilylamido)-lanthanum to achieve atomic layer deposition of on a (100) Si wafer. Crystalline and electrical properties of the resulting films have been characterized. Dielectric constant values in the range of 20-23, and a dielectric breakdown field of about 4.2 MV/cm were observed. The electrical properties of our structures remain consistent even after prolonged ambient exposure. © 2004 The Electrochemical Society. All rights reserved.

We report a study of influence of charging and discharging in Si nanocrystals (nc-Si), which are embedded throughout the gate oxide in metal-oxide-semiconductor (MOS) structures, on the current-voltage and capacitance-voltage characteristics of the MOS structures. Very large current and capacitance are observed for the as-fabricated structures. However, charge trapping in the nanocrystals can reduce both the current and the capacitance dramatically. The trapped charges can also tunnel out from the nc-Si, leading to the recovery of both the current and the capacitance. The current reduction is attributed to the breaking of the nc-Si tunneling paths due to charge trapping in the nc-Si, while capacitance reduction is explained by an equivalent circuit in terms of the change of the nc-Si capacitance as a result of the charge trapping. © 2004 The Electrochemical Society. All rights reserved.

A superior oxide/nitride/oxide (ONO) gate stack was demonstrated. High density plasma chemical vapor deposition was used to deposit the silicon nitride layer instead of the conventional low-pressure chemical vapor deposition for silicon/oxide/nitride/oxide/silicon technology. The densified nitride layer was performed by high-temperature dry oxidation to form a thermally grown blocking oxide layer on the silicon nitride rather than a deposited oxide layer. The ONO gate stack shows large memory window, high breakdown voltage, and reliable endurance characteristics, which is a potential candidate for future nonvolatile memory technology. © 2004 The Electrochemical Society. All rights reserved.

Understanding the pH and down pressure effects is critical in elucidating the chemical and mechanical mechanisms in chemical mechanical polishing (CMP). This paper describes the variation in polishing rate by nonagglomerated silicon dioxide particles. The repulsive interaction force, solubility of amorphous silica, and total contact area at the pad-particles-wafer interface are important factors in determining polishing performance. In situ friction force measurements are used to detect the variation of interfacial contact during polishing. Surface finishes and interaction force of silica/silica were investigated using atomic force microscopy. © 2004 The Electrochemical Society. All rights reserved.

Thin films of oriented, polycrystalline p-type were deposited on n-type indium-tin oxide (ITO)-coated glass substrates by pulsed laser deposition at 400°C to form transparent wide bandgap heterojunctions. The characteristics of Au, Ni, or Pt contacts subsequently deposited on these heterojunction layers were examined. In each case, rectifying behavior of the p-n junction was obtained. The junctions display a negative temperature coefficient for reverse breakdown voltage. This approach looks promising as a means of realizing low-cost-substrate transparent electronics. © 2004 The Electrochemical Society. All rights reserved.

High-performance polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with oxide/nitride/oxynitride (ONO) multilayer gate dielectrics were fabricated. The low-temperature (≦300°C) ONO multilayer dielectric uses three stacked layers: the bottom layer is a very thin -plasma oxynitride deposited by plasma-enhanced chemical vapor deposition (PECVD), the middle layer is PECVD and the top layer is tetraethoxysilane (TEOS) oxide. The ONO gate dielectric on poly-Si films shows a very high breakdown field of 9.4 MV/cm, a longer time-dependent dielectric breakdown lifetime and a lower charge trapping rate than single-layer PECVD TEOS oxide or nitride. The fabricated poly-Si TFTs with ONO gate dielectric exhibited excellent transfer characteristics, high field-effect mobility of 213 cm²/V s, and an ON/OFF current ratio of over © 2004 The Electrochemical Society. All rights reserved.

Noble metal impregnation has resulted in the inclusion of metal nanostructures within the SBA-15 mesoporous silica hexagonal pores (from nanoclusters to nanowires). A bright-field transmission electron microscopy three-dimensional reconstruction is proposed to analyze the localization of nanostructures within the pores of mesoporous nanotemplates. The method allows corroboration whether the nanostructures are synthesized inside the pores or they are synthesized alternatively on the nanotemplate aggregates exterior surface. © 2004 The Electrochemical Society. All rights reserved.

Peculiar photoluminescence (PL) emission properties of ZnO films on Si buffered with and were found. The ZnO films deposited on substrate show two double peaks in the room-temperature PL spectra, one double (374 and 394 nm) in the ultraviolet region and the other double (495 and 605 nm) located in the visible region. If the ZnO film was grown on a very strong UV along with invisible deep-level emission was detected because the can effectively reduce the defect formation of oxygen vacancies and Zn interstitials compared to ZnO on and Si. © 2004 The Electrochemical Society. All rights reserved.

Photostimulated red long-lasting phosphorescence in was observed and investigated by fluorescence, phosphorescence, and thermoluminescence spectra. The present sample emits intense red long-lasting phosphorescence after irradiation by 254 nm UV light. The red long-lasting phosphorescence appears once again after further excitation by 365 nm UV light when the sample is kept in the dark for 24 h, and the 254 nm UV light-induced long-lasting phosphorescence cannot be detected. A mechanism responsible for the photostimulated long-lasting phosphorescence is proposed. © 2004 The Electrochemical Society. All rights reserved.