Ramanathan Srinivasan

Detection of nonlinearities in electrochemical impedance spectra by Kramers–Kronig Transforms

Nonlinear electrochemical impedance spectra (EIS) of electrochemical reactions with adsorbed intermediates were generated by numerical simulations and the conditions under which direct integration of Kramers–Kronig Transforms (KKT) flag the violations of linearity criterion were investigated. In addition, the spectra were validated using measurement model analysis and linear KKT method. A reaction with an adsorbed intermediate species, an electrochemical–chemical reaction with two adsorbed intermediate species and a third reaction with two adsorbed intermediate species and exhibiting negative resistance were chosen as candidate mechanisms. Large amplitude perturbations were used and the governing equations were solved without linearization. The results show that when the relationship between the logarithm of the faradaic current and dc potential is nonlinear, all the three methods are sensitive and successfully flag the nonlinear effect in the spectra. On the other hand, if the logarithm of the faradaic current is linearly related to the dc potential, the nonlinear effects are not identified by the direct integration of KKT. However, even in these cases, measurement model analysis and linear KKT validation method are sensitive to the violation of linearity criterion.

Kinetics of anodic dissolution of Zr in acidic fluoride media

The kinetics of anodic dissolution of Zr in hydrofluoric acid (HF) was investigated using potentiodynamic polarization experiments. At lower potentials, an active region with a rapid increase in current with the potential was observed and at higher potentials, a large passivation current plateau was observed. The current decreased only slightly with potential in the passive region. Scanning electron micrographs confirmed that the passivation is incomplete in the region where current exhibits a plateau and x-ray photoelectron spectroscopic analysis showed that oxides and oxyfluorides are present on the surface. A four-step mechanism with two adsorbed intermediate species was evaluated and the model captures the essential characteristics of the polarization plots. The results suggest that HF2−

Numerical investigations of solution resistance effects on nonlinear electrochemical impedance spectra

{HF}_2^{-}

Analysis of Copper Dissolution in Glutamic Acid and Hydrogen Peroxide Using EIS

species participates in the chemical dissolution step and actual HF participates in the electrochemical dissolution step.

Microwave heating characteristics of graphite based powder mixtures

The dissolution of niobium electrode in anodic regime in hydrofluoric acid was studied using electrochemical techniques. In the active region, complex plane plots of the impedance spectra exhibited mainly two capacitive loops. In the passive region, the spectra exhibited a mid-frequency pseudo-inductive loop and a low-frequency negative resistance. X-ray photoelectron spectroscopic analysis showed that the surface contains Nb2+ and Nb5+. The impedance data were analysed using equivalent circuit with Maxwell elements as well as mechanistic modelling. A four-step mechanism with a chemical and electrochemical dissolution step is proposed to explain the results. The results show that Nb with an oxidation state of 2 is likely to be an intermediates species. The simulations predict that at low over potentials, the surface is covered mainly with bare metal, whereas at high over potentials, the surface is entirely covered by passivating Nb5+ film.

Shallow Trench Isolation Chemical Mechanical Planarization: A Review

The effect of solution resistance on the nonlinear electrochemical impedance spectra under quasi-potentiostatic conditions was investigated by numerical simulations. An electron transfer reaction, a reaction with an adsorbed intermediate and a reaction exhibiting negative resistance were chosen as the candidates and large amplitude perturbations were employed. The potential across the interface drifts initially and stabilizes after a certain time, which depends on the solution resistance and the kinetic parameter values. The fraction of the applied potential drop occurring across the metal–solution interface depends on the frequency and the amplitude of the perturbation as well as the value of solution resistance. This in turn leads to the possibility that, for a given conditions, a part of the spectrum may be acquired in the linear regime while the remaining part may be acquired in the nonlinear regime. The sensitivity of the Kramers Kronig transform (KKT) to identify these cases is evaluated. The results show that although the spectra are distorted by poorly conducting solution, the sensitivity of KKT to identify the nonlinear effects is not enhanced by the introduction of significant solution resistance.

Electrochemical characterization of copper chemical mechanical polishing in l-glutamic acid–hydrogen peroxide-based slurries

AbstractCrosslinked polymers are three-dimensional network structures formed by interactions that range from weak physical associations to strong covalent bonding. The inherent complexity in their structures results in rich and diverse rheological response at large deformations. In the present work, we investigate two crosslinked materials based on poly(vinyl alcohol) (PVA) using large amplitude oscillatory shear (LAOS). Physically crosslinked PVA-borax exhibited Giesekus-like linear response, and a gradual intra-cycle strain stiffening and shear thinning at large strains. These signatures are attributed to temporary junction points and stretching of chains between crosslinks in the system. In contrast, chemically crosslinked PVA-hyaluronic acid (PVA-HA) gels exhibited a weak frequency dependence of linear moduli and intra-cycle strain stiffening and shear thickening at large strains. PVA-HA contains permanent crosslinks that move apart, along with stretching of crosslinked and uncrosslinked chains, and these features are responsible for such LAOS signatures. Based on these insights, we propose modifications to existing models and obtain quantitative description of LAOS response of both PVA-borax and PVA-HA crosslinked systems. Graphical AbstractLAOS behaviour of PVA based crosslinked systems.

Multi-Sine EIS- Drift, Non Linearity and Solution Resistance Effects

Copper chemical mechanical polishing (CMP) is a key step in microelectronic interconnect fabrication [1]. Slurries containing glycine and hydrogen peroxide have been widely studied as suitable candidates for Cu CMP[2,3]. Glycine based slurries show drastic changes in removal rate with changes in hydrogen peroxide concentration. Slurries based on glutamic acid (Glu) as complexing agent present a more robust removal rate trend. The dissolution of copper in solutions containing Glu and hydrogen peroxide is analyzed using EIS.