Electrochemical Formation of Germanene: pH 4.5

Germanene is a single layer allotrope of Ge, with a honeycomb structure similar to graphene. This report concerns the electrochemical formation of germanene in a pH 4.5 solution. The studies were performed using in situ Electrochemical Scanning Tunneling Microscopy (EC-STM), voltammetry, coulometry, surface X-ray diffraction (SXRD) and Raman spectroscopy to study germanene electrodeposition on Au(111) terraces. The deposition of Ge is kinetically slow and stops after 2–3 monolayers. EC-STM revealed a honeycomb (HC) structure with a rhombic unit cell, 0.44 ± 0.02 nm on a side, very close to that predicted for germanene in the literature. Ideally the HC structure is a continuous sheet, with six Ge atoms around each hole. However, only small domains, surrounded by defects, of this structure were observed in this study. The small coherence length and multiple rotations domains made direct observation with surface X-ray diffraction difficult. Raman spectroscopy was used to investigate the multi-layer Ge deposits. A peak near 290 cm^(−1), predicted to correspond to germanene, was observed on one particular area of the sample, while the rest resembled amorphous germanium. Electrochemical studies of germanene showed limited stability when exposed to oxygen

A scanning probe investigation of the role of surface motifs in the behavior of p-WSe_2 photocathodes

The spatial variation in the photoelectrochemical performance for the reduction of an aqueous one-electron redox couple, Ru(NH_3)_6^(3+/2+), and for the evolution of H_2(g) from 0.5 M H_2SO_4(aq) at the surface of bare or Pt-decorated p-type WSe_2 photocathodes has been investigated in situ using scanning photocurrent microscopy (SPCM). The measurements revealed significant differences in the charge-collection performance (quantified by the values of external quantum yields, Φ_(ext)) on various macroscopic terraces. Local spectral response measurements indicated a variation in the local electronic structure among the terraces, which was consistent with a non-uniform spatial distribution of sub-band-gap states within the crystals. The photoconversion efficiencies of Pt-decorated p-WSe_2 photocathodes were greater for the evolution of H_2(g) from 0.5 M H_2SO_4 than for the reduction of Ru(NH_3)_6^(3+/2+), and terraces that exhibited relatively low values of Φ_(ext) for the reduction of Ru(NH_3)_6^(3+/2+) could in some cases yield values of Φ_(ext) for the evolution of H_2(g) comparable to the values of Φ_(ext) yielded by the highest-performing terraces. Although the spatial resolution of the techniques used in this work frequently did not result in observation of the effect of edge sites on photocurrent efficiency, some edge effects were observed in the measurements; however the observed edge effects differed among edges, and did not appear to determine the performance of the electrodes

Operando Synthesis of Macroporous Molybdenum Diselenide Films for Electrocatalysis of the Hydrogen-Evolution Reaction

The catalytically inactive components of a film have been converted, through an operando method of synthesis, to produce a catalyst for the reaction that the film is catalyzing. Specifically, thin films of molybdenum diselenide have been synthesized using a two-step wet-chemical method, in which excess sodium selenide was first added to a solution of ammonium heptamolydbate in aqueous sulfuric acid, resulting in the spontaneous formation of a black precipitate that contained molybdenum triselenide (MoSe_3), molybdenum trioxide (MoO_3), and elemental selenium. After purification and after the film had been drop cast onto a glassy carbon electrode, a reductive potential was applied to the precipitate-coated electrode. Hydrogen evolution occurred within the range of potentials applied to the electrode, but during the initial voltammetric cycle, an overpotential of ~400 mV was required to drive the hydrogen-evolution reaction at a benchmark current density of −10 mA cm^(–2). The overpotential required to evolve hydrogen at the benchmark rate progressively decreased with subsequent voltammetry cycles, until a steady state was reached at which only ~250 mV of overpotential was required to pass −10 mA cm^(–2) of current density. During the electrocatalysis, the catalytically inactive components in the as-prepared film were (reductively) converted to MoSe_2 through an operando method of synthesis of the hydrogen-evolution catalyst. The initial film prepared from the precipitate was smooth, but the converted film was completely covered with pores ~200 nm in diameter. The porous MoSe_2 film was stable while being assessed by cyclic voltammetry for 48 h, and the overpotential required to sustain 10 mA cm^(–2) of hydrogen evolution increased by <50 mV over this period of operation

Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein

Marine mussels secret protein-based adhesives, which enable them to anchor to various surfaces in a saline, intertidal zone. Mussel foot proteins (Mfps) contain a large abundance of a unique, catecholic amino acid, Dopa, in their protein sequences. Catechol offers robust and durable adhe-sion to various substrate surfaces and contributes to the curing of the adhesive plaques. In this article, we review the unique features and the key functionalities of Mfps, catechol chemistry, and strategies for preparing catechol-functionalized poly- mers. Specifically, we reviewed recent findings on the contributions of various features of Mfps on interfacial binding, which include coacervate formation, surface drying properties, control of the oxidation state of catechol, among other features. We also summarized recent developments in designing advanced biomimetic materials including coacervate-forming adhesives, mechanically improved nano- and micro-composite adhesive hydrogels, as well as smart and self-healing materials. Finally, we review the applications of catechol-functionalized materials for the use as biomedical adhesives, therapeutic applications, and antifouling coatings

ELECTROSTATIC MODEL CALCULATIONS FOR THE LATTICE ENERGY OF NaClO3NaClO_{3}

$^{1}$ G. J. Lewis, Ph.D. thesis, King's College, London, England, 1974. This work was supported by the National Science Foundation. Present address of G. J. Lewis: Department of Physics, King's College, London, England.""Author Institution: Department of Chemistry, University of HawaiiThe theoretical lattice energy of $NaClO_{3}$, calculated using the electrostatic model, will be reported. This will also be compared with the experimental value as determined from heats of hydration measurements. The electrostatic model is a extension of the original Born-Mayer rigid-ion model which takes into account only the Coulombic, repulsive and London terms. The electrostatic model considers the interactions between all possible combinations of charges, permanent-point multipoles and static-induced multipoles. The present calculations have been done to test the input data utilised, such as charge distribution and whole-ion polarizability, which are available from the literature. The ultimate aim is to use the electrostatic model for frequency prediction and calculations of frequency shift as a function of pressure for the IR spectra of NaClO$_{3}$ which have already been studied extensively in these laboratories. Present studies arc based on electrostatic model calculations previously carried out by $Lewis^{1}$ on $N_{3}^{-}$

THE INFRARED OPTICAL PROPERTIES OF LiF AS A FUNCTION OF TEMPERATURE AND PRESSURE

This work was supported by the National Science Foundation. Present address of G. J. Lewis: Department of Physics, King's College, London, England. Present address of A. Kachare: Department of Physics, University of Southern California, Los Angeles, California.""Author Institution: Department of Chemistry, University of HawaiiReliable infrared reflectance data of LiF have been obtained at various temperatures and processed by an Improved Kramers-Kronig dispersion analysis technique. A careful analysis of the imaginary dielectric index ($\epsilon$) spectra has provided important insights into the question of electrical and mechanical anharmonicity in the lattice modes of LiF. To further investigate this problem, work has been done on the IR transmission spectra of LiF thin films at high pressures. The optical indices as a function of pressure have been obtained through a Kramers-Kronig transmission dispersion analysis of the transmission values. Results will be presented and evaluated in terms of various models of anharmonicity. The proper methodology to obtain reliable high pressure IR transmission data of LiF thin films will also be outlined