Electrochemical Estimations of the Gold Nanoparticle Size Effect on Cysteine-Gold Oxidation,

Gold nanoparticles are interesting for nanobiomedical applications, such as for drug delivery and as diagnostic imaging contrast agents. However, their stability and reactivity in-vivo are influenced by their surface properties and size. Here, we investigate the electrochemical oxidation of differently sized citrate-coated gold nanoparticles in the presence and absence of L-cysteine, a thiol-containing amino acid with high binding affinity to gold. We found that smaller sized (5, 10 nm) gold nanoparticles were significantly more susceptible to electrochemical L-cysteine interactions and/or L-cysteine-facilitated gold oxidation than larger (20, 50 nm) sized gold nanoparticles, both for the same mass and nominal surface area, under the conditions investigated (pH 7.4, room temperature, stagnant solutions, and scan rates of 0.5 to 450 mV s−1). The electrochemical measurements of drop-casted gold nanoparticle suspensions on paraffin-impregnated graphite electrodes were susceptible to the quality of the electrode. Increased cycling resulted in irreversible oxidation and detachment/oxidation of gold into solution. Our results suggest that L-cysteine-gold interactions are stronger for smaller nanoparticles

Surprisingly Simple Mechanical Behavior of a Complex Embryonic Tissue

Background: Previous studies suggest that mechanical feedback could coordinate morphogenetic events in embryos. Furthermore, embryonic tissues have complex structure and composition and undergo large deformations during morphogenesis. Hence we expect highly non-linear and loading-rate dependent tissue mechanical properties in embryos. Methodology/Principal Findings: We used micro-aspiration to test whether a simple linear viscoelastic model was sufficient to describe the mechanical behavior of gastrula stage Xenopus laevis embryonic tissue in vivo. We tested whether these embryonic tissues change their mechanical properties in response to mechanical stimuli but found no evidence of changes in the viscoelastic properties of the tissue in response to stress or stress application rate. We used this model to test hypotheses about the pattern of force generation during electrically induced tissue contractions. The dependence of contractions on suction pressure was most consistent with apical tension, and was inconsistent with isotropic contraction. Finally, stiffer clutches generated stronger contractions, suggesting that force generation and stiffness may be coupled in the embryo. Conclusions/Significance: The mechanical behavior of a complex, active embryonic tissue can be surprisingly well described by a simple linear viscoelastic model with power law creep compliance, even at high deformations. We found no evidence of mechanical feedback in this system. Together these results show that very simple mechanical models can be useful in describing embryo mechanics. © 2010 von Dassow et al

Polymorphism and magnetic properties of Li2MSiO4 (M 5 Fe, Mn) cathode materials

Transition metal-based lithium orthosilicates (Li2MSiO4,M=Fe, Ni, Co, Mn) are gaining a wide interest as cathode materials for lithium-ion batteries. These materials present a very complex polymorphism that could affect their physical properties. In this work, we synthesized the Li2FeSiO4 and Li2MnSiO4 compounds by a sol-gel method at different temperatures. The samples were investigated by XRPD, TEM, 7Li MAS NMR, and magnetization measurements, in order to characterize the relationships between crystal structure and magnetic properties. High-quality 7Li MAS NMR spectra were used to determine the silicate structure, which can otherwise be hard to study due to possible mixtures of different polymorphs. The magnetization study revealed that the Neel temperature does not depend on the polymorph structure for both iron and manganese lithium orthosilicates

A theoretical approach to evaluate the rate capability of Li-ion battery cathode materials

Charge-discharge rate capability is one of the most important properties of cathode materials for lithium batteries, in particular when envisaging high power density applications such as automotive applications. Efforts to modify rate have been carried out by carbon coating and decreasing particle size in order to modify electronic and ionic conductivity. However, this approach cannot justify all experimental data reported in the literature. Here, we investigated the rate capability of cathode materials by considering their density of states (DOS) calculated by several density functional theory (DFT) methods, in both the lithiated and the delithiated case. We suggested that these structures could be interpreted as n- or p-type semiconductors, depending on the DOS configuration. On this basis, if the lithiated structure acted as an n-type and the delithiated one as a p-type semiconductor, the resulting cathode will only be capable of achieving a "low rate". If the opposite situation happened, the cathode would sustain high current rates. Li2FeSiO 4, LiFePO4, LiFeBO3 and LiFeSO4F were found to belong to the former class, whereas LiCoO2, LiFeO 2 and LiMn2O4 were assigned to the latter one. On the basis of the proposed model, we suggested some general strategies related to the synthetic approach to improve cathode rate capability

An ab initio investigation of Li2M0.5N0.5SiO4 (M, N = Mn, Fe, Co Ni) as Li-ion battery cathode materials

Li2MSiO4 (M = Fe, Mn, etc.) are promising cathode materials for Li-ion batteries. One appealing strategy for improving their cathode properties is to develop mixed transition metal compounds. Density Functional Theory calculations were performed to evaluate the structural, magnetic and electrochemical properties of Li2M0.5N0.5SiO4 compounds. Our theoretical study allows us to individuate the most promising candidates for practical applications in lithium batteries

Controlling Uniformity of RRAM Characteristics via the Forming Process

The proposed constant voltage forming (CVF) is shown to increase the resistances of the low resistance and high resistance states while reducing their variability. By forcing the forming in all devices to occur at the same predefined voltage,the CVF method eliminates a major cause of the device-to-device variation associated with the randomness of the forming voltage values. Moreover,both experiments and simulations show that CVF at lower voltages suppresses the parasitic overshoot current,resulting in a more controlled and smaller filament cross-section and lower operation currents

Controlling uniformity of RRAM characteristics through the forming process

The proposed constant voltage forming (CVF) is shown to increase the resistances of the low resistance and high resistance states while reducing their variability. By forcing the forming in all devices to occur at the same predefined voltage, the CVF method eliminates a major cause of the device-to-device variation associated with the randomness of the forming voltage values. Moreover, both experiments and simulations show that CVF at lower voltages suppresses the parasitic overshoot current, resulting in a more controlled and smaller filament cross-section and lower operation currents. © 2012 IEEE

Low Power RRAM with Improved HRS/LRS Uniformity through Efficient Filament Control Using CVS Forming

Resistance change memory (RRAM) based on transition metal oxides (TMO), whose operation is based on the change in resistivity of a conductive filament in the oxide material, has attracted a lot of attention in recent years due to its promise of high density, speed, and retention. However, achieving a low power operation and high device-to-device uniformity of the cell resistance states are the major challenges for practical applications of the RRAM technology. While some progress has been made on the understanding of the switching mechanism of TMO memory devices [1], lack of precise control over the filament formation, perceived to be a random process, which inturn introduces randomness into the switching characteristics ofthis class of devices, complicates further progress. This studydemonstrates a forming methodology, which addresses the abovediscussed issues by performing a forming operation under theconstant voltage stress (CVS) condition at lower voltages ratherthan by the conventionally used fast voltage ramp method. Thisapproach is shown to lower the reset current, increase resistivityof the low and high resistive states (LRS, HRS) and improvedevice to device uniformity in the HfO2-based RRAM devices