Pei-Cheng Hsu

Electrochemistry: building on bubbles in metal electrodeposition.

In the electrodeposition of metals, a widely used industrial technique, bubbles of gas generated near the cathode can adversely affect the quality of the metal coating. Here we use phase-contrast radiology with synchrotron radiation to witness directly and in real time the accumulation of zinc on hydrogen bubbles. This process explains the origin of the bubble-shaped defects that are common in electrodeposited coatings.

Hydrogen Bubbles and the Growth Morphology of Ramified Zinc by Electrodeposition

Real-time X-ray microscopy was used to study the influence of hydrogen-bubble formation on the morphology of ramified zinc electrodeposit. The experimental results show that when intense hydrogen bubbling occurs at high potential, the morphology of the ramified zinc deposit changes from dense-branching to fern-shaped dendrite. The fern-shaped dendrite results in part from the constricted growth due to hydrogen bubbles but also from the highly concentrated electric field. The fern-shaped dendrite morphology was observed during the early stages of electroplating for both the potentiostatic and galvanostatic modes; however, the deposit plated in the galvanostatic mode densified via lateral growth during the later plating stages. This indicates that potentiostatic plating for which the hydrogen-bubble formation steadily occurs throughout the electrodeposition process is better than galvanostatic plating for fabricating fern-shaped deposits, which are ideal electrodes for Zn-air batteries due to the relatively large specific area

Properties and microstructure of nickel electrodeposited from a sulfamate bath containing ammonium ions

A 70 μm thick Ni layer was electrodeposited from a sulfamate bath containing various amounts of ammonium ions onto a copper plate. The detailed microstructure of the Ni deposits was characterized using a plane-view and cross-sectional transmission electron microscopy (TEM). The textures of the Ni deposits were also determined using conventional X-ray diffraction. Experimental results indicated that ammonium ions suppressed the lateral growth of Ni deposits and favoured out growth, thus leading to the growth of [1 1 0] and [3 1 0] oriented deposits. A structural refinement effect was observed after ammonium ions were added to the sulfamate bath. Ammonium ions also increased the internal stress and hardness of the deposits. A general Hall–Petch relationship was observed for the dependence of deposit hardness on the average grain size of the Ni deposits. The adsorption of atomic hydrogen and the polar NH3 molecule explains the effect of ammonium ions on the electrocrystallization of Ni.

Dynamical growth behavior of copper clusters during electrodeposition

Ultrahigh resolution full-field transmission x-ray microscopy enabled us to observe detailed phenomena during the potentiostatic copper electrodeposition on polycrystalline gold. We detected two coexisting cluster populations with different sizes. Their growth behaviors are different, with a shape transitions only occurring for large clusters. These differences influence the micromorphology and general properties of the overlayer.

Photosynthesis and structure of electroless Ni–P films by synchrotron x-ray irradiation

The authors describe an electroless deposition method for thin films, based on the irradiation by an x-ray beam emitted by a synchrotron source. Specifically, Ni–P films were deposited at room temperature. This synthesis is a unique combination of photochemical and electrochemical processes. The influence of the pH value on the formation and structural properties of the films was examined by various characterization tools including scanning electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Real time monitoring of the deposition process by coherent x-ray microscopy reveals that the formation of hydrogen bubbles leads to a self-catalysis effect without a preexisting catalyst. The mechanisms underlying the deposition process are discussed in details.

Real-time observation of Zn electro-deposition with high-resolution microradiology

We used phase contrast radiography to study the electro-deposition of Zn in real time and with high lateral resolution. Using unmonochromatic synchrotron X-rays and an optics-less imaging setup, we were able to obtain real-time radiographs of the electro-deposition in situ with gm resolution. A detailed analysis of the microstructure evolution relates the different growth parameters - such as the electric current density, the voltage bias, the pH value and the ion concentration - to very different growth morphology, ranging from film, porous, whisker and dendrite deposition. This link is both global and local. Local variations of the metal ion concentration in the electrolyte were also successfully imaged and the density profile is used to compare with the standard theory to explain the phenomenon of metal ion depletion near the electrode. The potential application of this technique to study growth with micropatterned electrodes and pulsed electric current is evaluated

Real-time microradiology of disintegration of iron ore sinteres

Abstract We first present real-time microradiology of disintegration of self-fluxing iron ore sinters in low temperature reduction using highly collimated synchrotron source. The experiments were performed on the 5C1 beamline at PLS (Pohang Light Source, Pohang, Korea), operating at 2.5 GeV. We used unmonochromatized (“white”) light with no optical elements except beryllium windows. The images of the crack superimpose, on the two-dimensional projection of a three-dimensional phenomenon, suggest that cracks are always initiated from pores in the sinters and propagate along neighboring pores. Interestingly, cracking occurs mostly on macropores (>800 μm), preferentially initiated from stress concentrated sites on pore surfaces. This dynamic study of the disintegration of sinters clearly shows that the crack initiation temperature is as low as 450 °C.

Edge-enhanced radiology with broadband synchrotron X-rays

Broadband synchrotron X-rays with limited coherence can be used for high resolution phase contrast radiology. Our experimental results confirm the prediction that the extreme spatial coherence of third-generation synchrotron sources although helpful but not strictly necessary for refraction-based or diffraction-based edge enhancement. Source with rather limited lateral coherence can produce Fresnel diffraction fringes. The direct observation of the same fringes using broadband synchrotron lights demonstrates that high time coherence is also not required. Broadband light produces a high photon flux and high average photon energy, that was exploited for real-time radiology (5 ms frame) studies with high lateral resolution (1 mum) and excellent contrast, without using a sophisticated detecting system. These results enhance the potential impact of phase contrast on medical X-ray applications, materials science and other domains

X‐ray‐induced Cu deposition and patterning on insulators at room temperature

X-ray irradiation is shown to trigger the deposition of Cu from solution, at room temperature, on a wide variety of insulating substrates: glass, passivated Si, TiN/Ti/SiO2/Si and photoresists like PMMA and SU-8. The process is suitable for patterning and the products can be used as seeds for electroplating of thicker overlayers.