Periodic Pulse Technique Research Articles

Preparation of GaAs Films by Periodic Pulse Technique

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Electrochemical preparation of bioactive calcium phosphate coatings on porous substrates by the periodic pulse technique

The authors used periodic pulses of potential to obtain uniformly deposited bioactive calcium phosphate coatings on porous titanium substrates. Titanium wire (99.9% purity, O.25 mm in diameter) was used to form porous substrates having an average pore diameter of approximately 300 μm.

Thin film deposition and characterization of CuInSe 2

Thin film CuInSe 2 was successfully electrodeposited from an aqueous solution containing CuSO 4, In 2(SO 4) 3 and SeO 2 onto titanium and graphite substrates by the potentiostatic and periodic pulse technique. The deposited material was characterized by X-ray photoelectron spectroscopy and voltammetry. A theoretical model was developed to construct the linear sweep voltammograms. This model, which is based on Butler-Volmer kinetics, was successfully employed to construct the voltammograms for various values of activity and rate constants of the species and pH and temperature of the electrolyte. The results obtained are discussed.

Radiation Effects on GaAs Charge Coupled Devices with High Resistivity Gate Structures

The results of a study on the effects of 1 MeV electrons and 1 MeV neutrons on the operation of high speed GaAs Charge Coupled Devices (CCDs) are presented. Radiation-induced trapping levels are characterized using a linear array CCD structure and the periodic pulse technique. 1 MeV electron irradiation introduced traps at 0.1 eV and 0.39 eV with bulk trap introduction rates of 1 cm-1 and 0.33 cm-1, respectively. The devices were irradiated to a maximum fluence of 9×1014 electrons/cm2. 1 MeV neutron irradiation introduced an electron trap level at 0.64 eV with a bulk trap introduction rate of 0.5 cm-1. Catastrophic device failure occurred at neutron fluences of 6×1013 neutrons/cm2. Device charge transfer efficiency was characterized pre- and post-irradiation over the temperature range of 80°K to 300°K.

A novel scheme to measure the interface trap density near band edges using CCD's

A new CCD-based technique to measure the interface trap density is proposed in this paper and the measured values agree with those obtained from the periodic pulse technique. The proposed technique has an operational advantage of measuring the interface state density near the band edge while operating the CCD at any convenient low frequency.

Production of concentrated hydrogen from dilute, lean reducing gas by use of the steam-oxide process (Part 1). Behavior of iron oxide medium in the reduction-oxidation cycles.

Concentrated hydrogen was produced from dilute hydrogen gas by use of the periodic pulse technique coupled with the use of iron oxide medium. The amount of concentrated H2 thus produced was almost proportional to the width of the dilute H2 pulse and to the concentration of H2 in the pulse, but it was independent of the width of the H2O pulse. The yield of concentrated H2 from dilute H2 gas was as high as 50-60% at 700°C. However, the yield decreased markedly with decreasing reaction temperature, and concentrated H2 was scarcely produced at 400°C. Detailed kinetics of the reaction of dilute H2 with the preoxidized iron oxide medium and the reaction of H2O with the prereduced medium were investigated by use of high speed gaschromatograph. It was shown that the reaction of dilute H2 with the preoxidized medium proceed edreadily at 700°C and the conversion of H2 in this process was close to the equilibrium conversion. At lower temperatures such as 300 and 500°C, the reaction of the medium with dilute H2 was decreased by decreased equilibrium conversion and by decreased rate of the surface reaction and/or diffusion of the oxygen or iron ion in the bulk of the medium. The oxidation of the prereduced medium with H2O proceeded rapidly at 700°C, and the conversion of H2O was close to equilibrium conversion. At lower temperatures, the rate of oxidation of the medium with H2O was decreased significantly by decreased rate of surface reaction and/or by the migration of the oxygen or iron ion in the bulk of the medium. From these results and discussion, the characteristics of the iron oxide medium were clarified, and the necessity for developing new kinds of media was emphasized.

Performance of periodic pulse technique. 3. Oxidative dehydrogenation of isobutyraldehyde.

The oxidative dehydrogenation of isobutyraldehyde to methacroleine was investigated by the periodic pulse technique in which isobutyraldehyde and oxygen were fed alternately. Among the catalysts selected by the single pulse technique, Sb2O3•V2O5 and Sb2O3•MoO3 catalysts gave good yields of methacroleine in the periodic pulse techique. The catalysts containing arsenic oxide that gave good results in the single pulse technique, however, did not appear to be good catalysts for the periodic pulse technique because of the sublimation of the arsenic oxide. These results suggest that mild oxidation and oxidative dehydrogenation of labile compounds can be done by the periodic pulse technique.

Performance of periodic pulse technique. 2. Dehydrogenation of ethylbenzene on various catalysts.

The dehydrogenation of ethylbenzene on five catalysts was carried out with the periodic pulse technique and the flow technique. Roughly speaking, the activity and the selectivity in the periodic pulse technique were close to those in the flow technique. However, on less active catalysts, the conversion in the pulse technique was lower than that in the flow technique. While on more active catalysts the conversion in the pulse technique, sometimes, was higher than that in the flow technique; and, in a few cases, even higher than the equilibrium conversion. The conversion and the selectivity depended on such operating parameters as the carrier gas, the pressure of pulse, the pulse width, and the period of the periodic pulse technique.

A New Technique for Hardening CCD Imagers by Suppression of Interface State Generation

A new technique has recently been developed to suppress dark current generation by interface states in buried channel CCD imagers by a change in the operating biases of the CCD during the integration cycle. In this work, this technique is successfully applied to suppressing interface state generated dark current in two irradiated CCDs. A dark current of only 1.3 nA/cm2 at 1 Mrad dose has been obtained on a CCD fabricated with radiation hardened oxides using this technique, compared to 360 nA/cm2 in the normal mode of operation. Experimental data on the irradiated CCDs show an excellent correlation between dark current generated by interface states in the normal mode of operation and the density of interface states measured using the periodic pulse technique.

Performance of periodic pulse technique. 1. Dehydrogenation of cyclohexane on a platinum-alumina catalyst.

Performance of periodic pulse technique. 1. Dehydrogenation of cyclohexane on a platinum-alumina catalyst.

Performance of periodic pulse technique. 4. Periodic pulse reaction kinetics of oxidative dehydrogenation of isobutyraldehyde.

Performance of periodic pulse technique. 4. Periodic pulse reaction kinetics of oxidative dehydrogenation of isobutyraldehyde.

Study on olefin oxidation by periodic-pulse technique: II. Oxidative dehydrogenation of 1-butene using various oxide catalysts

The oxidative dehydrogenation of 1-butene proceeds with a higher selectivity than does the oxidation of propylene. Butadiene and 2-butenes are shown to be produced by the reactions between gaseous 1-butene and surface oxygen. Carbon oxides are formed between the adsorbed residue and oxygen from the gas phase in the BiMo oxide catalyst. Some of the active sites over the BiMo and BiW oxide catalysts seem to be inhibited by the poisoning of the adsorbed residue at a higher partial pressure of 1-butene. The rate of isomerization in the continuous-flow technique is smaller or greater than that in the periodic-pulse technique for reducible catalysts like SnP and BiW oxides, or for oxidizable ones like SnSb and SbMo oxides, respectively. An intermediate trend is notable in BiMo oxide and MoO 3. It follows that the catalysts used in this experiment can be placed in this order with regard to the reducibilities of the catalyst; BiW SnP MoO 3 BiMo SnSb SbMo where the more to the left the catalyst lies, the more easily it can be reduced. This is supported by the partial pressure dependence in the periodic-pulse technique and by the variation in the rate of isomerization with the pulse number in the one-shot pulse technique. The results in the oxidative dehydrogenation of 1-butene were similar to those in the oxidation of propylene reported previously. It seems that isomerization takes place via the allyl intermediate.

Study on olefin oxidation by periodic-pulse technique: I. Propylene oxidation into acrolein using various oxide catalysts

By the periodic-pulse technique, distinguished from the conventional continuous-flow reaction by the alternate feeding of oxygen and hydrocarbon, the oxidation of propylene was investigated over various oxide catalysts. It is shown that the reaction takes place according to the same mechanism, i.e., the reoxidation-reduction mechanism, irrespective of the reaction technique. We attempted to characterize various oxide catalysts by the periodic-pulse technique and by electrical-conductivity measurements. The speculations regarding surface oxidation states on the basis of a separative analysis of the combustion reaction and the electrical conductivity during the reaction are consistent. Combustion is found to take place at the oxygen-regeneration pulse (O-pulse) over the Sn-P, Bi-W, and Bi-Mo oxide catalysts, which are severely reduced, while at the propylene-reaction pulse (R-pulse) over the Sn-Sb and Sb-Mo oxide catalysts, the catalysts maintain higher oxidation states. The catalysts can also be classified into three groups on the basis of the period dependence; (a) Bi-Mo, B-iW (b) Sn-Sb, Sb-Mo (c) MoO 3, Sn-P The catalysts are divided into Group (b) and Groups (a) and (c) on the basis of the results of the combustion reaction; these results are correlated with the characterization of the separative analysis and electrical-conductivity measurements. On the basis of these findings, some discussions are made of the catalyst properties controlling their surface oxidation states. Furthermore, the roles of bismuth and antimony are speculated on.