Gyana Pattanaik

Influence of Chloride Anions on the Mechanism of Copper Electrodeposition from Acidic Sulfate Electrolytes

We investigate the influence of chloride Cl - ions in a broad range of chloride concentrations on the kinetics and mechanism of copper electrodeposition from sulfate-based acidic electrolytes. Chloride ions influence copper deposition through two competitive effects: at low Cl - concentration (few mM), chloride ions depolarize the Cu reduction process, while higher Cl - concentrations induce complexation of copper species and cause a cathodic polarization of the deposition process. Cu reduction proceeds through two parallel mechanisms, a direct two-step reduction and a chloride-mediated route, whose relative importance depends on the amount of chloride present. A transition between these two mechanisms can be identified both by steady-state and impedance methods; however, the chloride concentration at which it occurs depends on the time scale probed by the two techniques. Impedance measurements further demonstrate that the presence of chlorides changes the double-layer structure.

Morphology and Magnetic Properties of Co-rich Co-Pt Thin Films Electrodeposited on Cr Seed Layers

Co-Pt (Pt ∼ 20 atom %) alloy films were electrochemically grown at constant current density on Cr seed layers in order to study the influence of the Cr surface on their morphology and magnetic properties. The Cr seed layer favors the growth of a hexagonal close-packed phase, as revealed by X-ray diffraction. Morphological investigation using a scanning electron microscope revealed the electrocrystallization of Co-Pt on Cr to be proceeding through the nucleation and growth of three-dimensional (3D) clusters with columns growing outward in all directions from isolated nucleation centers. The 3D growth is likely due to the presence of a thin oxide layer on the Cr seed. At lower current density, individual micrometer-sized clusters were formed with distinct hexagonally shaped faces. Increasing current density results in a finer grain microstructure. At early stages of growth and low current density, the clusters exhibit a faceted morphology similar to that of the substrate. Samples prepared at higher current density or with larger thickness show larger coercivities, reaching values as high as 3490 Oe (278 kA/m) and 2275 Oe (181 kA/m) in the perpendicular and parallel directions, respectively, for a 500-nm-thick film deposited at 50 mA/cm 2 .

Magnetization processes in hard Co-rich Co–Pt films with perpendicular anisotropy

We present a study of the magnetic properties and magnetization processes in hard Co-Pt (Pt∼20at.%) films. Co-rich Co-Pt films, with thickness t ranging from 5nm up to 2μm, were prepared by electrodeposition on (0001)-oriented Ru underlayers. All samples displayed strong perpendicular magnetic anisotropy and high coercivity. Virgin magnetic domain structures for varying thickness were investigated by magnetic force microscopy (MFM). The observed increase of domain width with film thickness is well understood by full two-dimensional micromagnetic computations with no adjustable parameters. The easy-axis magnetization process, as observed by measuring virgin curves by magnetometry and imaging the corresponding magnetization configurations by MFM in variable field, consists of two stages separated by a well-defined critical field, marking the onset of domain wall propagation. A thorough analysis of the out-of-plane angular dependence of the switching field points out that unpinning of domain walls is the dom...

Study of the room temperature molecular memory observed from a nanowell device

We tested the electrical characteristics of an oligo(phenylene ethynylene) (OPE) molecule with one nitro side group, an OPE with two nitro side groups, and an OPE with no nitro side groups in our nanowell device. The OPE molecule with nitro side group(s) showed switching behavior with memory as well as nonreversible negative differential resistance (NDR). Current-voltage (I‐V) characteristics showed a high conductivity state that switched to a low conductivity state upon the application of a threshold voltage. This low state held until the opposite threshold voltage was applied and the device switched back to the high conductivity state. The OPE with no nitro side groups did not show memory or NDR. In this work, we report the complete switching behavior observed including the device yield, average threshold voltage, and the average high to low current ratios.

Perpendicular anisotropy in electrodeposited, Co-rich Co–Pt films by use of Ru underlayers

Co-rich Co–Pt alloys were electrodeposited from an amino-citrate-based solution on a Si (011)∕Cu(111)∕Ru(0001) seed layer. Such a template provides an appropriate interface structure for the growth of a (0002)-oriented hexagonal phase, stabilized at larger thickness by the electrolyte chemistry, providing for a columnar structure with no detectable grain coarsening. This results in as-deposited Co–Pt films exhibiting perpendicular anisotropy (anisotropy constant up to 1.2MJ∕m3) and hard magnetic properties (coercivity up to 358.2kA∕m) in a wide thickness range, from 5to2000nm. Crystalline, magnetoelastic, and interface effects are discussed as possible origins of the observed perpendicular anisotropy.

Effects of Molecular Environments on the Electrical Switching with Memory of Nitro-Containing OPEs

An oligo(phenylene ethynylene) (OPE) molecule with a nitro side group has exhibited electrical switching with memory and thus has potential for use in molecular electronic devices. However, different research groups have reported different electrical behaviors for this molecule. In addition to variations among test structures, differences in local molecular environments could be partially responsible for the differences in the reported results. Thus, we tested four variations of a nitro-OPE/dodecanethiol monolayer in the same type of nanowell test device to study how the environment of the nitro-OPE affects the observed electrical behavior. We found that the density of the nitro-containing molecules in the device altered the observed electrical switching behavior. Further, we found a positive correlation between the disorder of the monolayer and the observed electrical switching behavior. This correlation is consistent with suggestions that nitro molecule switching may depend on a conformational change of the molecule, which may be possible only in a disordered monolayer.

Electrochemical Nucleation and Growth of Copper from Acidic Sulfate Electrolytes on n-Si ( 001 ) Effect of Chloride Ions

We present a study of the effect of chloride anion additions on the electrochemical nucleation and growth of copper on n-Si(100) from acidic sulfate solutions. Chloride additions in the millimolar range depolarize copper reduction, while additions in the 100 mM range and above have the opposite effect. Chlorides have no effect on the nucleation and growth mode. Deposition at constant potential in the presence of small amounts of chloride leads to an increased deposition overpotential, but contrary to the predictions of nucleation theory, this results in a lower density of nuclei with larger size. We hypothesize that adsorption of chlorides on the copper islands enhances surface diffusion processes which lead to island coarsening through Ostwald ripening. Morphological changes during deposition are possible at room temperature due to the high values of diffusivities at the electrolyte/ solid interface.

Magnetic properties of Co-rich Co–Pt thin films electrodeposited on a Ru underlayer

Co-rich Co–Pt films were grown by electrodeposition from an amino-citrate based electrolyte on Si(011)∕Cu(111)∕Ru(0001) templates. The Ru(0001) surface provides an interface which induces the growth of an oriented hexagonal phase, thereby yielding hard magnetic properties and perpendicular anisotropy in films as thin as 10nm. Increase in film thickness only marginally compromises the hard magnetic properties probably due to the limited coarsening of the microstructure, oriented columnar growth, and magnetic grain isolation. The deposition current density plays an important role in optimizing microstructure and hard magnetic properties. Perpendicular squareness close to 1 and coercivities as high as 4.5kOe were obtained in thin as-deposited Co–Pt films.

Electrodeposited CoNiP Films with Perpendicular Magnetic Anisotropy

CoNiP alloy films have been grown by electrodeposition from a chloride bath under galvanostatic control. Film growth, structure, composition, magnetic properties, and morphology have been found to depend significantly on deposition current density. Hard magnetic films were successfully grown at the current density of 7 mA/cm 2 with thickness up to 10 μm, at which a perpendicular coercivity of 188 kA/m was achieved. The magnetic hardness and perpendicular anisotropy of these films are the combined result of a microstructure composed of columnar grains and of a hexagonal phase oriented with the c axis perpendicular to the film plane. Preliminary investigations of magnetization reversal processes suggest the presence of pinning sites located probably at grain boundaries.

Electrolytic Gold Deposition on Dodecanethiol-Modified Gold Films

The electrochemical nucleation and growth of Au from a Au sulfite electrolyte onto dodecanethiol-modified Au surfaces is investigated by a combination of microscopy and chronoamperometry methods. The self-assembled dodecanethiol monolayers are continuous but exhibit defects in correspondence of the Au grain boundaries and on top of Au terraces. Nucleation of Au films occurs initially at these defect sites, but only a small fraction of these nuclei survive an initial competition process. The remaining nuclei expand through three-dimensional progressive nucleation followed by diffusion-limited growth. The resulting Au films exhibit microstructures which are widely different from those observed in the electrochemical growth of Au on Au and that depend on the applied potential: while at low overpotentials the film grows as an assembly of hemispherical clusters, at intermediate overvoltages the films are smooth and at high overvoltages become dendritic. Metal growth onto self-assembled monolayer-modified substrates can thus provide an alternative method for controlling film morphology for a wide range of applications.