/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.

http://repository.ust.hk/ir/bitstream/1783.1-77094/1/acs.chemrev.5b00462_withlink.pdf

Recent Advances in Electrocatalysts for Oxygen Reduction Reaction

Atomic layer deposition(ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions,reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.

Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process

Surface science studies of model fuel cell electrocatalysts

Real surface area measurements in electrochemistry

Electrochemical atomic layer epitaxy (ECALE)

Nanoprobes for MRI and optical imaging are demonstrated. Gd@C-dots possess strong fluorescence and can effectively enhance signals on T1 -weighted MR images. The nanoprobes have low toxicity, and, despite a relatively large size, can be efficiently excreted by renal clearance from the host after systemic injection.

/pdf/gd-encapsulated-carbonaceous-dots-with-efficient-renal-16efo4l6zh.pdf

Gd-encapsulated carbonaceous dots with efficient renal clearance for magnetic resonance imaging.

Mise en evidence de la formation de couches ordonnees d'adsorption lors de l'immersion d'une surface de Pt(111) dans des solutions ioniques aqueuses de KCN, KSCN, K 2 S, KBr, KI et d'hydroquinonesulfonate de K. Resultats d'etudes par diffraction d'electrons lents et par spectrometrie Auger

Ordered ionic layers formed on platinum(111) from aqueous solutions

Thin films of CdTe, CdSe, and CdS have been electrodeposited by electrochemical atomic layer epitaxy (ECALE), using an automated electrochemical deposition system. Previous reports of an automated system for forming ECALE deposits involved use of a small thin layer flow cell, which revealed several drawbacks. Conversion of the thin layer cell to a thick layer design resulted in greatly improved deposit quality and reproducibility. Deposits were analyzed using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and grazing incident X‐ray diffraction (XRD). The results were consistent with a layer by layer growth mode and the principles of atomic layer epitaxy. CdTe films were grown using up to 1000 ECALE cycles, and were stoichiometric through 500. The 1000 cycle films were a few percent rich in Te, under the conditions used. CdSe and CdS films formed also contained some excess chalcogenide, probably the result of less then ideal deposition parameters. Increasing amounts of particulates and surface roughening were observed for the 500 and 1000 cycle CdTe and CdSe films, relative to the 200 cycle deposits normally formed. This roughening may result from the excess chalcogenide. XRD of the films indicated cubic crystal structures with preferred (111) orientations for all three compounds.

Formation of Thin Films of CdTe, CdSe, and CdS by Electrochemical Atomic Layer Epitaxy

In this paper the method of electrochemical atomic layer epitaxy (ECALE) is described. It involves the alternated electrochemical deposition of atomic layers of elements to form compound semiconductors. It is being investigated as a method for forming epitaxial thin films. Presently, it appears that the method is applicable to a wide range of compound semiconductors composed of a metal and one of the following main group elements: S, Se, Te, As, Sb, or Br. Initial studies have involved CdTe deposition. Factors controlling deposit structure and composition are discussed here. Preliminary results which show that ordered electrodeposits of CdTe can be formed by the ECALE method are also presented. Results reported here were obtained with both a polycrystalline Au thin-layer electrochemical cell and a single-crystal Au electrode with faces oriented to the (111), (110), and (100) planes. The single-crystal electrode was contained in a UHV surface analysis instrument with an integral electrochemical cell. Deposits were examined without their exposure to air using LEED and Auger electron spectroscopy. Coverages were determined using coulometry in the thin-layer electrochemical cell.

John L. Stickney

Papers

Electrochemical atomic layer epitaxy (ECALE)

Gd-encapsulated carbonaceous dots with efficient renal clearance for magnetic resonance imaging.

Ordered ionic layers formed on platinum(111) from aqueous solutions

Formation of Thin Films of CdTe, CdSe, and CdS by Electrochemical Atomic Layer Epitaxy

Conditions for the Deposition of CdTe by Electrochemical Atomic Layer Epitaxy