Reliability and degradation behaviors of semi-insulating Fe-dopedInP buried heterostructure lasers fabricated by RIE and MOVPE

We clarified the degradation behaviors of semi-insulating buried heterostructure lasers in which mesa structures were fabricated by reactive ion etching (RIE) and then buried in semi-insulating Fe-doped InP grown by metal organic vapor phase epitaxy (MOVPE). The degradation rate and mode correlated with the quality of the buried heterostructure (BH) interface. Based on the correlation, a condition for highly stable semi-insulating Fe-doped InP buried heterostructure (SIBH) lasers was demonstrated and confirmed experimentally and statistically     

Regiocontrolled Syntheses of 3- or 5-Fluorinated Pyrazoles from 2,2-Difluorovinyl Ketones(1)

2,2-Difluorovinyl ketones 1 react with monosubstituted hydrazines to afford 5-fluoropyrazoles in a regioselective manner via replacement of the fluorine by the substituted nitrogen of the hydrazines and dehydration between the carbonyl group of 1 and the NH(2) end. The reactions are successfully effected for both aliphatic and aromatic hydrazines in aqueous ethanol under neutral conditions and in THF under basic conditions with butyllithium, respectively. A similar ring-forming reaction of 1 with hydrazine monohydrate is induced by the addition of trifluoroacetic acid to give N-unsubstituted 3-fluoropyrazoles, which in turn react with alkyl and aryl halides in the presence of sodium hydride, leading to a regiocontrolled synthesis of 3-fluoropyrazoles.     

Mechanisms and kinetics of noncatalytic ether reaction in supercritical water. 1. Proton-transferred fragmentation of diethyl ether to acetaldehyde in competition with hydrolysis

Noncatalytic reaction pathways and rates of diethyl ether in supercritical water are determined in a quartz capillary by observing the liquid- and gas-phase 1H and 13C NMR spectra. The reaction is investigated at two concentrations (0.1 and 0.5 M) in supercritical water at 400 degrees C and over a water-density range of 0.2-0.6 g/cm3, and in subcritical water at 300 and 350 degrees C. The neat reaction (in the absence of solvent) is also studied for comparison at 0.1 M and 400 degrees C. The ether is found to decompose through (i) the proton-transferred fragmentation to ethane and acetaldehyde and (ii) the hydrolysis to ethanol. Acetaldehyde from reaction (i) is consecutively subjected to the unimolecular and bimolecular redox reactions: (iii) the unimolecular proton-transferred decarbonylation forming methane and carbon monoxide, (iv) the bimolecular self-disproportionation producing ethanol and acetic acid, and (v) the bimolecular cross-disproportionation yielding ethanol and carbonic acid. Reactions (ii), (iv), and (v) proceed only in the presence of hot water. Ethanol is produced through the two types of disproportionations and the hydrolysis. The proton-transferred fragmentation is the characteristic reaction at high temperatures and is much more important than the hydrolysis at densities below 0.5 g/cm3. The proton-transferred fragmentation of ether and the decarbonylation of aldehyde are slightly suppressed by the presence of water. The hydrolysis is markedly accelerated by increasing the water density: the rate constant at 400 degrees C is 2.5 x 10(-7) s(-1) at 0.2 g/cm3 and 1.7 x 10(-5) s(-1) at 0.6 g/cm3. The hydrolysis becomes more important in the ether reaction than the proton-transferred fragmentation at 0.6 g/cm3. In subcritical water, the hydrolysis path is dominant at 300 degrees C (0.71 g/cm3), whereas it becomes less important at 350 degrees C (0.57 g/cm3). Acetic acid generated by the self-disproportionation autocatalyzes the hydrolysis at a higher concentration. Thus, the pathway preference can be controlled by the water density, reaction temperature, and initial concentration of diethyl ether.     

Immobilized aminoacylase on porous glass beads

Aminoacylase was immobilized on porous glass by two different coupling methods. One aminoacylase preparation was covalently bound to an alkylaminosilane derivative of porous glass with glutaraldehyde [alkylamino-porous glass-CVB-aminoacylase]; the other aminoacylase derivative was prepared by covalently binding the enzyme to arylaminosilane glass by diazotization [arylamino-porous glass-CVB-aminoacylase]. The enzyme activities of the immobilized aminoacylases were 3.2-13.0 U/ml glass for the former and 1.9-6.8 U/ml glass for the latter. The alkylamino-porous glass-CVB-aminoacylase showed excellent stability at pH 6-9 and at temperatures below 50°C. The derivative could be stored for more than 6 mo without appreciable loss of the activity. Continuous hydrolysis using the alkylamino-porous glass-CVB-aminoacylase packed in column was carried out for 54 days at 37°C, with a calculated half-life of 78 days. It was determined that alkylamino-porous glass-CVB-aminoacylase would be applicable in an industrial preparation of various l-amino acids from their dl forms.     

Laser-Induced formation of transient polyelectrolyte in solution

Ionic photodissociation of N-ethylcarbazole and poly(N-vinylcarbazole) quenched with dimethylterephthalate was investigated by nanosecond laser photolysis. In the case of the polymer system about a tenth of the carhazole chromophores is ionized by intense laser excitation, which indicates photo-induced formation of a transient polyelectrolyte.     

In-situ scanning tunneling microscopy of carbon monoxide adsorbed on Au(111) electrode

In-situ scanning tunneling microscopy (STM) coupled with cyclic voltammetry was used to examine the adsorption of carbon monoxide (CO) molecules on an ordered Au(111) electrode in 0.1 M HClO4. Molecular resolution STM revealed the formation of several commensurate CO adlattices, but the (9 x radical 3) structure eventually prevailed with time. The CO adlayer was completely electrooxidized to CO2 at 0.9 V versus RHE in CO-free 0.1 M HClO(4), as indicated by a broad and irreversible anodic peak which appeared at this potential in a positive potential sweep from 0.05 to 1.6 V. A maximal coverage of 0.3 was estimated for CO admolecules from the amount of charge involved in this feature. Real-time in-situ STM imaging allowed direct visualization of the adsorption process of CO on Au(111) at 0.1 V, showing the lifting of (radical 3 x 22) reconstruction of Au(111) and the formation of ordered CO adlattices. The (9 x radical 3) structure observed in CO-saturated perchloric acid has a coverage of 0.28, which is approximately equal to that determined from coulometry. Switching the potential from 0.1 to -0.1 V restored the reconstructed Au(111) with no change in the (9 x radical 3)-CO adlattice. However, the reconstructed Au(111) featured a pairwise corrugation pattern with two nearest pairs separated by 74 +/- 1 A, corresponding to a 14% increase from the ideal value of 65.6 A known for the ( radical 3 x 22) reconstruction. Molecular resolution STM further revealed that protrusions resulting from CO admolecules in the (9 x radical 3) structure exhibited distinctly different corrugation heights, suggesting that the CO molecules resided at different sites on Au(111). This ordered structure predominated in the potential range between 0.1 and 0.7 V; however, it was converted into new structures of (7 x radical 7) and ( radical 43 x 2 radical 13) on the unreconstructed Au(111) when the potential was held at 0.8 V for ca. 60 min. The coverage of CO adlayer decreased accordingly from 0.28 to 0.13 before it was completely removed from the Au(111) surface at more positive potentials.     

Electrochemical redox control of ferrocene using a supramolecular assembly of ferrocene-linked C(60) derivative and metallooctaethylporphyrin array on a Au(111) electrode

Supramolecular assembled layers of ferrocene-linked C(60) derivative (C(60)Fc) and various metal ions coordinated to octaethylporphyrin (MOEP) were formed on the surface of a Au(111) single-crystal electrode by immersing the Au substrate successively into a benzene solution containing MOEP and one containing C(60)Fc molecules. The MOEPs used were zinc(II) (ZnOEP), cobalt(II) (CoOEP), copper(II) (CuOEP), and iron(III) chloride (FeClOEP) of OEP (2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine). The molecules of C(60)Fc directly attached to the Au(111) electrode showed poorly defined electrochemical redox response, whereas a clear electrochemical redox reaction of the ferrocene group in the C(60)Fc molecule was observed at 0.78 V versus reversible hydrogen electrode on ZnOEP, CoOEP, and CuOEP adlayers, but not on the FeClOEP adlayer. Adlattices of the underlying layer and the top layer of C(60)Fc were determined by in situ scanning tunneling microscopy. Adlayer structures of MOEP were independent of the central metal ion; that is, MOEP molecules were arranged hexagonally with two different orientations. Highly ordered C(60)Fc arrays were formed with 1:1 composition on the ZnOEP-, CoOEP-, and CuOEP-modified Au(111) surface, whereas a disordered structure of C(60)Fc was found on the FeClOEP-modified Au(111) surface. The presence of Cl ligand was found to prevent the formation of supramolecularly assembled layers with C(60)Fc molecules, resulting in an ill-defined unclear electrochemical response of the Fc group. The well-defined electrochemical response of the Fc group in C(60)Fc was clearly due to the control of orientation of C(60)Fc molecules.     

Role of the anion in the underpotential deposition of cadmium on a Rh(111) electrode: probed by voltammetry and in situ scanning tunneling microscopy

In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were employed to examine the underpotential deposition (UPD) of cadmium on a rhodium(111) electrode in sulfuric and hydrochloric acids. The (bi)sulfate and chloride anions in the electrolytes played a main role in controlling the number and arrangement of Cd adatoms. Deposition of Cd along with hydrogen adsorption occurred near 0.1 V (vs reversible hydrogen electrode) in either 0.05 M H2SO4 or 0.1 M HCl containing 1 mM Cd(ClO4)2. These coupled processes resulted in an erroneous coverage of Cd adatoms. The process of Cd deposition shifted positively to 0.3 V and thus separated from that of hydrogen in 0.05 M H2SO4 containing 0.5 M Cd2+. The amount of charge (80 microC/cm2) for Cd deposition in 0.5 M Cd2+ implied a coverage of 0.17 for the Cd adatoms, which agreed with in situ STM results. Regardless of [Cd2+], in situ STM imaging revealed a highly ordered Rh(111)-(6 x 6)-6Cd + HSO4- or SO42- structure in sulfuric acid,. In hydrochloric acid, in situ STM discerned a (2 x 2)-Cd + Cl structure at potentials where Cd deposition commenced. STM atomic resolution showed roughly one-quarter of a monolayer of Cd adatoms were deposited, ca. 50% more than in sulfuric acid. Dynamic in situ STM imaging showed potential dependent, reversible transformations between the (6 x 6) Cd adlattices and (square root 3 x square root 7)-(bi)sulfate structure, and between (2 x 2) and (square root 7 x square root 7)R19.1 degrees -Cl structures. The fact that different Cd structures observed in H2SO4 and HCl entailed the involvement of anions in Cd deposition, i.e. (bi)sulfate and chloride anions were codeposited with Cd adatoms on Rh(111).