CW operation of DFB-BH GaInAsP/InP lasers in 1.5 ?m wavelength region

Distributed-feedback buried heterostructure (DFB-BH) GaInAsP/InP lasers in the 1.5 ?m wavelength region have been operated continuously at heat-sink temperatures as high as 310 K. A threshold current of 55 mA at 300 K and single longitudinal mode operation have been obtained.     

Chiral Iodotriptycenes: Synthesis and Catalytic Applications

New iodotriptycenes, including some chiral derivatives, have been synthesised, and their catalytic potential towards oxidative transformations has been investigated. The enantioselectivities observed in the products using chiral iodotriptycene catalysts are low, probably owing to the large distances between the coordinating groups and the iodine moieties in these compounds.     

In situ scanning tunneling microscopy imaging of mercury film electrodeposited on Ir(1 1 1)

In situ scanning tunneling microscopy (STM) was used to examine multilayer Hg film electrodeposited on a well-ordered Ir(1 1 1) single crystal electrode in 0.1 M HClO₄ + 1 mM Hg(ClO₄)₂. Topography STM scans showed that the Ir(1 1 1) – supported Hg film electrode contained well-defined terraces separated by monatomic steps (Δz = 2.3 Å). The STM’s tip could be used to induce local dissolution of the Hg deposit under proper operating conditions and the depth of the etched pit informed directly the thickness of Hg deposit. Although in situ STM imaging with a tungsten tip could not result in atomic structure of bare Hg film in 0.1 M HClO₄, it discerned highly ordered iodine adlayers, represented by a (2 × 8√3)rect – I structure, on the Hg film in solution containing potassium iodide. These STM results suggested that the Hg substrate could have an ordered atomic structure.     

Electrochemical control of the structure of two-dimensional supramolecular organization consisting of phthalocyanine and porphyrin on a gold single-crystal surface

Two-component adlayers consisting of cobalt(II) phthalocyanine (CoPc) and a metalloporphyrin such as 5,10,15,20-tetraphenyl-21H,23H-porphine copper(II) (CuTPP), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine copper(II) (CuOEP), or 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (CoTPP) were prepared by immersing either an Au(111) or Au(100) substrate in a benzene solution containing those molecules. The mixed adlayers thus prepared were investigated in 0.1 M HClO4 by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM). The composition of the mixed adlayer consisting of CoPc and CuTPP molecules was found to vary with immersion time. CoPc molecules displaced CuTPP molecules during the modification process with increasing immersion time, and the CuTPP molecules were completely displaced by CoPc molecules in the mixed solution after a prolonged modification time, during which the underlying Au(100) substrate underwent phase transition from the reconstructed (hex) lattice to the unreconstructed (1 x 1) lattice. The two-component adlayer of CoPc and CuTPP was found to form a supramolecular adlayer with the constituent molecules arranged alternately on Au(100)-(hex). The striped structure was stable on Au(100)-(hex) at or near the open circuit potential (OCP), whereas the mixed adlayer was disordered on Au(100)-(1 x 1) at potentials more positive than OCP, where the phase transition of the arrangement of underlying Au atoms (i.e., the lifting of reconstruction) was induced electrochemically. A similar two-component supramolecular adlayer consisting of CoPc and CuTPP was formed on Au(111). A highly ordered, compositionally disordered adlayer of CoTPP and CuTPP was formed on Au(100)-(hex), suggesting that the adlayer structure is independent of the coordinated central metal ion for the formation of supramolecular nanostructures composed of those molecules. A supramolecular organization of CoPc and CuOEP was also found on Au(111). The surface mobility and the molecular reorganization of CoPc and CuOEP on Au(111) were tuned by modulation of the electrode potential. It is concluded that molecular assemblies of the two-component structure consisting of phthalocyanine and porphyrin were controlled not only by the crystallographic orientation of Au but also by the modulation of electrochemical potential.     

Ordered molecular assemblies of substituted bis(phthalocyaninato) rare earth complexes on Au(111): in situ scanning tunneling microscopy and electrochemical studies

Substituted bis(phthalocyaninato) rare earth complexes ML2 (M = Y and Ce; L = [Pc(OC8H17)8]2, where Pc = phthalocyaninato) were adsorbed onto single crystalline Au(111) electrodes from benzene saturated with either YL2 or CeL2 complex at room temperature. In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to examine the structures and the redox reactions of these admolecules on Au(111) electrodes in 0.1 mol dm(-3) HClO4. The CVs obtained with YL2- and CeL2-coated Au(111) electrodes respectively contained two and three pairs of redox peaks between 0 and 1.0 V (versus reversible hydrogen electrode). STM molecular resolution revealed that YL2 and CeL2 admolecules were imaged as spherical protrusions separated by 2.3 nm, which suggests that they were oriented with their molecular planes parallel to the unreconstructed Au(111)-(1 x 1). Both molecules when adsorbing from approximately micromolar benzene dosing solutions produced mainly ordered arrays characterized as (8 x 5 radical3)rect (theta = 0.0125). The redox reactions occurring between 0.2 and 1.0 V caused no change in the adlayer, but they were desorbed or oxidized at the negative and positive potential limits. The processes of adsorption and desorption at the negative potentials were reversible to the modulation of potential. Electrochemical impedance spectroscopy (EIS) and CV measurements showed that YL2 and CeL2 adlayers could block the adsorption of perchlorate anions and mediating electron transfer at the Au(111) electrode, leading to the enhancement of charge transfer for the ferro/ferricyanide redox couple.     

Formation of highly ordered porphyrin adlayers induced by electrochemical potential modulation

Molecular self-assembly of porphyrin derivatives formed with intermolecular hydrogen bonding on the surface of Au(111) electrode in acidic solution can be controlled by varying the number of peripheral carboxy groups and the applied electrochemical potential.     

Scanning tunneling microscopy of sulfur and benzenethiol chemisorbed on Ru(0001) in 0.1 M HClO4

In situ scanning tunneling microscopy (STM) combined with linear sweep voltammetry was used to examine spatial structures of sulfur adatoms (SA) and benzenethiol (BT) molecules adsorbed on an ordered Ru(0001) electrode in 0.1 M HClO4. The Ru(0001) surface, prepared by mechanical polishing and electrochemical reduction at -1.5 V (vs RHE) in 0.1 M HClO4, contained atomically flat terraces with an average width of 20 nm. Cyclic voltammograms obtained with an as-prepared Ru(0001) electrode in 0.1 M HClO4 showed characteristics nearly identical to those of Ru(0001) treated in high vacuum. High-quality STM images were obtained for SA and BT to determine their spatial structures as a function of potential. The structure of the SA adlayer changed from (2 x mean square root of 3)rect to domain walls to (mean square root of 7 x mean square root of 7)R19.1 degrees and then to disordered as the potential was scanned from 0.3 to 0.6 V. In contrast, molecules of BT were arranged in (2 x mean square root of 3)rect between 0.1 and 0.4 V, while they were disordered at all other potentials. Adsorption of BT molecules was predominantly through the sulfur headgroup. Sulfur adatoms and adsorbed BT molecules were stable against anodic polarization up to 1.0 V (vs RHE). These two species were adsorbed so strongly that their desorption did not occur even at the onset potential for the reduction of water in 0.1 M KOH.     

Syntheses and absolute configurations of the cytokinins 1′-methylzeatin and its 9-riboside

On the basis of the chiral syntheses of (1′R)-I and (1′S)-I and of their 9-ribosides (1″R)-III and (1″S)-III from D- and L-alanines, the structures of the cytokinins 1′-methylzeatin and its 9-riboside have been established to be (1′R)-I and (1″R)-III.     

Counterion binding to poly(allylammonium) cation

Chloride ion activity coefficients in aqueous solutions of poly(allylamine) hydrochloride (PAA · HCl) have been determined both in the absence and the presence of simple salts. Without added salt, the activity coefficient depends on the polymer concentration. With added salt, the binding of added counterions by PAAH⁺ is evaluated from the release of chloride ion. The extent of interaction between counterions and PAAH⁺ at a given polymer concentration decreases in the order SO ? ClO > NO > Cl^? > Br^? > I^?. This order of counterion selectivity agrees with the previous estimation of potentiometric titrations. The result shows that the hydration of the counterion, as well as its charge, plays an important part in counterion binding to the polyion.