Black phosphorus (BP) has attracted significant interest as a monolayer or few-layer material with extraordinary electrical and optoelectronic properties. However, degradation in air and other environments is an unresolved issue that may limit future applications. In particular the role of different ambient species has remained controversial. Here, we report systematic experiments combined with ab-initio calculations that address the effects of oxygen and water in the degradation of BP. Our results show that BP rapidly degrades whenever oxygen is present, but is unaffected by deaerated (i.e., O 2 depleted) water. This behavior is rationalized by oxidation involving a facile dissociative chemisorption of O 2 , whereas H 2 O molecules are weakly physisorbed and do not dissociate on the BP surface. Oxidation (by O 2 ) turns the hydrophobic pristine BP surface progressively hydrophilic. Our results have implications on the development of encapsulation strategies for BP, and open new avenues for exploration of phenomena in aqueous solutions including solution-gating, electrochemistry, and solutionphase approaches for exfoliation, dispersion, and delivery of BP.

Using in situ liquid cell electron microscopy we investigate Pd growth in dilute aqueous Pd salt solutions containing Au nanoparticle seeds. Au-Pd core-shell nanostructures are formed via deposition of Pd(0), generated by the reduction of chloropalladate complexes by radicals, such as hydrated electrons (eaq(-)) induced by the electron beam in the solution. The size and shape of the Au seeds determine the morphology of the Pd shells, via preferential Pd incorporation in low-coordination sites and avoidance of extended facets. Analysis of the Pd incorporation on Au particles at different distances from a focused electron beam provides a quantitative picture of the growth process and shows that the growth is limited by the diffusion of eaq(-) in the solution.

Galvanic replacement reactions provide an elegant way of transforming solid nanoparticles into complex hollow morphologies. Conventionally, galvanic replacement is studied by stopping the reaction at different stages and characterizing the products ex situ. In situ observations by liquid-cell electron microscopy can provide insight into mechanisms, rates and possible modifications of galvanic replacement reactions in the native solution environment. Here we use liquid-cell electron microscopy to investigate galvanic replacement reactions between silver nanoparticle templates and aqueous palladium salt solutions. Our in situ observations follow the transformation of the silver nanoparticles into hollow silverpalladium nanostructures. While the silver-palladium nanocages have morphologies similar to those obtained in ex situ control experiments the reaction rates are much higher, indicating that the electron beam strongly affects the galvanic-type process in the liquid-cell. By using scavengers added to the aqueous solution we identify the role of radicals generated via radiolysis by high-energy electrons in modifying galvanic reactions.

The die is cast: The electrocatalytic performance of Pt and Pt‐Cu nanocubes with different compositions was investigated. Pt80Cu20 nanocubes were found to have high electrocatalytic activity and remarkable long‐term stability for formic acid oxidation.

An inexpensive, fast, selective, and sensitive technique for surface area measurement of metallic nanoporous materials (MNPM) is developed, systematically tested, and validated. The approach employed is based on underpotential deposition (UPD) of metals on foreign substrates. In this work, Pb UPD on Au is chosen to illustrate the applicability of and reveal the advantages and limitations of the proposed method. Experiments are designed for surface area measurement of nanoporous gold (NPG) electrodes with pore sizes in the range of 5−15 nm, prepared by electrochemical dealloying of single phase AupAg1−p (atomic fraction p = 0.1, 0.2, and 0.3). Dealloying is performed galvanostatically at a current density of 1 mA cm−2 in a AgClO4 solution, acidified to pH 1. The experimental results suggest a linearly increasing charge in the Pb UPD layer with NPG thickness. This finding hints at (i) uniformity of the NPG structure and (ii) the general ability of this method to work for analysis of bulk materials. The proposed approach is tested by studying the dependence of the NPG surface area upon the original alloy composition and correlating the results with the NPG structure and morphology imaged by high-resolution scanning electron microscopy. An anomalously high surface area is registered in dealloyed Au0.1Ag0.9 samples and is attributed to the lack of a pre-existing percolation backbone. Unlike the instantaneous Pb UPD process on a flat metal surface, the slow and thickness-dependent kinetics of Pb layer formation on NPG is associated with hindered mass transport through pores. Further validation of the Pb UPD method is made by experimental monitoring of heat treatment-enforced coarsening and the basic modeling of the correlation between surface area and ligament size in NPG. Finally, a critical comparison with Brunauer−Emmett−Teller (BET) analysis reveals important advantages of the developed method for surface area measurement in MNPM specimens.

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Die Würfel sind gefallen: Die elektrokatalytische Aktivität von Pt‐ und PtCu‐Nanowürfeln unterschiedlicher Zusammensetzung wurde untersucht. Vor allem die Pt80Cu20‐Nanowürfel zeichneten sich durch eine hohe Aktivität und bemerkenswerte Langzeitstabilität in der Ameisensäureoxidation aus.

The sporadic voiding phenomenon in Cu 3 Sn intermetallic compound (IMC) formed during thermal aging, sometimes referred to as "Kirkendall voiding", has been found to lead to degradation of solder joint reliability in board level shock testing. It was suggested that the voiding phenomenon resulted from the incorporation of specific impurities in the copper during electroplating. In this study, Cu samples were electroplated from a generic suppressor-brightener additive system using a rotation disk electrode (RDE) apparatus. Overpotential during plating, surface morphology and the propensity for voiding of plated samples were investigated. Galvanostatic (constant current density) plating was conducted at 10 mA/cm 2 sequentially up to 18 hours. The solution exhibited dependences of overpoential and voiding propensity on bath aging, due to the breakdown of the organic additives. Cu samples were also plated in the current density range of 0.8-40 mA/cm 2 . In the 10-20 mA/cm 2 , current density range, a fine-grain, smooth, deposit surface was observed, accompanied by an especially low voiding level of samples plated in that range.