SHINERS Study of Chloride Order-Disorder Phase Transition and Solvation of Cu(100).

Shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) are used to probe Cl adsorption and the order-disorder phase transition associated with the c(2 × 2) Cl adlayer on Cu(100) in acid media. A two-component ν(Cu-Cl) vibrational band centered near 260 ± 1 cm is used to track the potential dependence of Cl adsorption. The potential dependence of the dominant 260 cm component tracks the coverage of the fluctional c(2 × 2) Cl phase on terraces in good agreement with the normalized intensity of the c(2 × 2) superstructure rods in prior surface X-ray diffraction (SXRD) studies.

Superconformal Film Growth: From Smoothing Surfaces to Interconnect Technology.

ConspectusElectronics manufacturing involves Cu electrodeposition to form 3D circuitry of arbitrary complexity. This ranges from nanometer-wide interconnects between individual transistors to increasingly large multilevel intermediate and global scale on-chip wiring. At larger scale, similar technology is used to form micrometer-sized high aspect ratio through-silicon vias (TSV) that facilitate chip stacking and multilevel printed circuit board (PCB) metallization.

Filament Growth and Related Instabilities during Adsorbate Suppressed Electrodeposition.

Anisotropic growth of a single filament on a microelectrode is demonstrated by galvanostatic electrodeposition in a bistable passive-active critical system. Specifically, a Cu filament is formed by disruption of a passivating polyether-halide bilayer triggered by metal deposition with positive feedback guiding highly localized deposition. For macroscale electrodes, complex passive-active Turing patterns develop, while for micrometer-sized electrodes, bifurcation is frustrated and a single active zone develops, which is reinforced by hemispherical transport.

Extreme Bottom-up Gold Filling of High Aspect Ratio Features.

ConspectusWhere copper interconnects fabricated using superconformal electrodeposition processes have enabled dramatic advances in microelectronics over the past quarter century, gold filled gratings fabricated using superconformal Bi-mediated bottom-up filling electrodeposition processes promise to enable a new generation of X-ray imaging and microsystem technologies. Indeed, bottom-up Au-filled gratings have demonstrated excellent performance in X-ray phase contrast imaging of biological soft tissue and other low Z element samples even as studies using gratings with inferior Au fill have captured the potential for broader biomedical application. Four years ago, the Bi-stimulated bottom-up Au electrodeposition process was a scientific novelty where gold deposition was localized entirely on the bottoms of metallized trenches 3-μm-deep and 2-μm-wide, an aspect ratio of only 1.

Fabrication of a fractal pattern device for focus characterizations of X-ray imaging systems by Si deep reactive ion etching and bottom-up Au electroplating.

Precisely aligned optical components are crucial prerequisites for X-ray tomography at high resolution. We propose a device with a fractal pattern for precise automatic focusing. The device is etched in a Si substrate by deep reactive ion etching and then filled by a self-terminating bottom-up Au electroplating process.

Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry.

Electrochemical mass spectrometry (EC-MS) is combined with chronoamperometry to quantify H coverage associated with the surface hydride phase on Cu(111) in 0.1 mol/L HSO. A two-step potential pulse program is used to examine anion desorption and hydride formation, and the inverse, by tracking the 2 atomic mass unit (amu) signal for H production in comparison to the charge passed.

Surface Hydride Formation on Cu(111) and Its Decomposition to Form H in Acid Electrolytes.

Mass spectrometry and Raman vibrational spectroscopy were used to follow competitive dynamics between adsorption and desorption of H and anions during potential cycling of three low-index Cu surfaces in acid electrolytes. Unique to Cu(111) is a redox wave for surface hydride formation coincident with anion desorption, while the reverse reaction of hydride decomposition with anion adsorption yields H by recombination rather than oxidation to HO. Charge imbalance between the reactions accounts for the asymmetric voltammetry in SO, ClO, PO, and Cl electrolytes with pH 0.

Resolving the Geometry/Charge Puzzle of the c(2 × 2)-Cl Cu(100) Electrode.

Potential-induced changes in charge and surface structure are significant drivers of the reactivity of electrochemical interfaces but are frequently difficult to decouple from the effects of surface solvation. Here, we consider the Cu(100) surface with a c(2 × 2)-Cl adlayer, a model surface with multiple geometry measurements under both ultrahigh vacuum and electrochemical conditions. Under aqueous electrochemical conditions, the measured Cu-Cl interplanar separation () increases by at least 0.

Self-terminating electrodeposition of Pt on WC electrocatalysts.

Self-terminated electrochemical deposition is used to grow Pt nanoparticles on tungsten monocarbide (WC) from a pH 4 electrolyte of 3 mmol/L KPtCl-0.5 mol/L NaCl. An unconventional potentiodynamic deposition program is used where nucleation is promoted at large overpotentials followed by growth termination at still larger overpotentials to yield a high coverage of Pt nanoparticles.

Bottom-up Cu filling of annular through silicon vias: Microstructure and texture.

Microstructural and morphological evolution during bottom-up Cu filling of annular through silicon vias (TSV) in a CuSO-HSO-Cl-poloxamine electrolyte is examined. Deposition proceeds in two distinct stages beginning with a passive-to-active state transition on the via sidewalls whose depth and ultimate thickness depends on the polymer flux. Growth is conformal or tapered with columnar grains whose width and texture differ between the outer and inner sidewalls of the annulus due to area reduction and expansion respectively.

Halide-induced Step Faceting and Dissolution Energetics from Atomistic Machine Learned Potentials on Cu(100).

Adsorbates impact the surface stability and reactivity of metallic electrodes, affecting the corrosion, dissolution, and deposition behavior. Here, we use density functional theory (DFT) and DFT-based Behler-Parrinello neural networks (BPNN) to investigate the geometries, surface formation energies, and atom removal energies of stepped and kinked surfaces vicinal to Cu(100) with a c(2×2) Cl adlayer. DFT calculations indicate that the stable structures for the adsorbate-free vicinal surfaces favor steps with <110> orientation, while the addition of the c(2×2) Cl adlayer leads to <100> step facets, in agreement with scanning tunneling microscopy (STM) observations.

Mapping Electron Transfer at MoS Using Scanning Electrochemical Microscopy.

Understanding the role of macroscopic and atomic defects in the interfacial electron transfer properties of layered transition metal dichalcogenides is important in optimizing their performance in energy conversion and electronic devices. Means of determining the heterogeneous electron transfer rate constant, k, have relied on the deliberate exposure of specific electrode regions or additional surface characterization to correlate proposed active sites to voltammetric features. Few studies have investigated the electrochemical activity of surface features of layered dichalcogenides under the same experimental conditions.

SEIRAS Study of Chloride-Mediated Polyether Adsorption on Cu.

Surface-enhanced infrared absorption spectroscopy is used to examine the co-adsorption of a selection of polyethers with Cl under conditions relevant to superconformal Cu electrodeposition in CuSO-HSO electrolytes. In 0.1 mol/L HSO, a potential-dependent mixed SO -HO/HO layer forms on weakly textured (111) Cu thin-film surfaces.

Ultramicroelectrode Studies of Self-Terminated Nickel Electrodeposition and Nickel Hydroxide Formation upon Water Reduction.

The interaction between electrodeposition of Ni and electrolyte breakdown, namely the hydrogen evolution reaction (HER) HO and HO reduction, was investigated under well-defined mass transport conditions using ultramicroelectrodes (UME's) coupled with optical imaging, generation/collection scanning electrochemical microscopy (G/C-SECM), and preliminary microscale pH measurements. For 5 mmol/L NiCl + 0.1 mol/L NaCl, pH 3.

Deconvoluting the Influences of 3D Structure on the Performance of Photoelectrodes for Solar-Driven Water Splitting.

Three-dimensionally (3D) structured photoelectrodes offer a number of potential benefits for solar fuels production compared to conventional planar photoelectrodes, including decreased optical losses, higher surface area for catalysis, easier removal of product species, and enhanced carrier collection efficiency. However, 3D structures can also present challenges, such as lower photovoltage and larger surface recombination. Quantifying and understanding the advantages and disadvantages of 3D structuring can maximize benefits, but this goal is not trivial because the factors that affect photoelectrode performance are intertwined.

Enhanced Performance of Si MIS Photocathodes Containing Oxide-Coated Nanoparticle Electrocatalysts.

Electrodepositing low loadings of metallic nanoparticle catalysts onto the surface of semiconducting photoelectrodes is a highly attractive approach for decreasing catalyst costs and minimizing optical losses. However, securely anchoring nanoparticles to the photoelectrode surface can be challenging-especially if the surface is covered by a thin insulating overlayer. Herein, we report on Si-based photocathodes for the hydrogen evolution reaction that overcome this problem through the use of a 2-10 nm thick layer of silicon oxide (SiO) that is deposited on top of Pt nanoparticle catalysts that were first electrodeposited on a 1.

Formic acid oxidation on platinum: a simple mechanistic study.

The oxidation of small organic acids on noble metal surfaces under electrocatalytic conditions is important for the operation of fuel cells and is of scientific interest, but the basic reaction mechanisms continue to be a matter of debate. Formic acid oxidation on platinum is one of the simplest of these reactions, yet even this model system remains poorly understood. Historically, proposed mechanisms for the oxidation of formic acid involve the acid molecule as a reactant, but recent studies suggest that the formate anion is the reactant.

H2 evolution at Si-based metal-insulator-semiconductor photoelectrodes enhanced by inversion channel charge collection and H spillover.

Photoelectrochemical (PEC) water splitting represents a promising route for renewable production of hydrogen, but trade-offs between photoelectrode stability and efficiency have greatly limited the performance of PEC devices. In this work, we employ a metal-insulator-semiconductor (MIS) photoelectrode architecture that allows for stable and efficient water splitting using narrow bandgap semiconductors. Substantial improvement in the performance of Si-based MIS photocathodes is demonstrated through a combination of a high-quality thermal SiO2 layer and the use of bilayer metal catalysts.

Self-terminating growth of platinum films by electrochemical deposition.

A self-terminating rapid electrodeposition process for controlled growth of platinum (Pt) monolayer films from a K(2)PtCl(4)-NaCl electrolyte has been developed that is tantamount to wet atomic layer deposition. Despite the deposition overpotential being in excess of 1 volt, Pt deposition was quenched at potentials just negative of proton reduction by an alteration of the double-layer structure induced by a saturated surface coverage of underpotential deposited H (H(upd)). The surface was reactivated for further Pt deposition by stepping the potential to more positive values, where H(upd) is oxidized and fresh sites for the adsorption of PtCl(4)(2-) become available.