Design,fabrication and characterization of a Schottky diode on an AlGaAs/GaAs HEMT structure for on-chip RF power detection

A Schottky diode was designed and fabricated on an n-AlGaAs/GaAs high electron mobility transistor (HEMT) structure for RF power detection. The processing steps used in the fabrication were the conventional steps used in standard GaAs processing. Current–voltage measurements showed that the devices had rectifying properties with a barrier height of 0.5289–0.5468 eV. The fabricated Schottky diodes detected RF signals well and their cut-off frequencies up to 20 GHz were estimated in direct injection experiments. To achieve a high cut-off frequency, a smaller Schottky contact area is required. The feasibility of direct integration with the planar dipole antenna via a coplanar waveguide transmission line without insertion of matching circuits was discussed. A higher cut-off frequency can also be achieved by reducing the length of the coplanar waveguide transmission line. These preliminary results represent a breakthrough as regards direct on-chip integration technology, towards the realization of a ubiquitous network society.     

Asymmetric top rotors in electric fields. II. Influence of internal torsions in molecular beam deflection experiments

We report on electric deflection experiments of aminobenzonitrile and (dimethylamino)benzonitrile molecules. They are used as prototypes to study the influence of the asymmetry and rotation-vibration couplings in deflection experiments. Experimental deflection profiles are compared to results of ab initio calculations in the frame of the rigid rotor Stark effect and of the statistical linear response. The change in symmetry and the introduction of methyl groups lead to a transition from the rigid rotor response to the linear response. From the experimental results, a total dipole of mu = 6.2 +/- 0.6 D has been deduced for the m-(dimethylamino)benzonitrile molecule (MDMABN).     

Radioactivity distribution of thorium in sediment core of the Sabah-Sarawak coast

Thorium activity concentrations were measured in seven marine sediment cores taken from Sabah-Sarawak coast on 2004 by using a gravity box corer. Collected sediments were generally homogenous mud which contained much more mixture of silt and clay compared to sand and relatively low content of organic carbon (i.e. less than 5% at all sampling stations). The results found that activity concentrations of ²³⁰Th, ²³²Th and ratios of ²³⁰Th/²³²Th were ranged from 6.5–20.4 Bq/kg dry wt., 6.8–27.8 Bq/kg dry wt. and 0.69–0.92, respectively. It seem that, ²³²Th activity concentrations are slightly higher than ²³⁰Th at all sampling stations and both radionuclides were generally high at Sabah compared to Sarawak coastal waters. ²³⁰Th activity concentrations in sediment core appear to be correlated with the activity concentrations of ²³²Th at some sampling station. These indicating both radionuclides were supplied from the same of environment and source origin of detrital from terrestrial and shallower water. The low ²³⁰Th/²³²Th activity ratio which is less than unity suggesting that ²³²Th was actively and rapidly regenerated compared to ²³⁰Th from ²³⁴U. It also can be attributed to less efficiently scavenge of ²³⁰Th onto particles prior deposited at the marine sediment bed.     

Non-enzymatic hydrogen peroxide sensor using an electrode modified with iron pentacyanonitrosylferrate nanoparticles

An electrochemical sensor was developed for determination of hydrogen peroxide (HP) based on a carbon ceramic electrode modified with iron pentacyanonitrosylferrate (FePCNF). The surface of an iron-doped CCE was derivatized in a solution of PCNF by cycling the electrode potential between ?0.2 and +1.3 V for about 60 times. The morphology and the composition of the resulting electrode were characterized by scanning electron microscopy and Fourier transform infrared techniques. The electrode displayed excellent response to the electro-oxidation of HP which is linearly related to its concentration in the range from 0.5 μM to 1300 μM. The detection limit is 0.4 μM, and the sensitivity is 849 A M ^?1?cm ^?2. The modified electrode was used to determination of HP in hair coloring creams as real samples.     

Solid State Deoximation with Clay SupportedAmmonium Chlorochromate: Regenerationof Carbonyl Compounds Using Microwavesin a Solventless System

Summary.  Ammonium chlorochromate adsorbed on montmorillonite K-10 rapidly regenerates carbonyl compounds from their corresponding oximes under microwave irradiation and solvent-free conditions. Received October 11, 1999. Accepted (revised) November 15, 1999     

Film thickness effects on calibrations of a narrowband thermochromic liquid crystal

Thermochromic liquid crystals (TLCs) have been widely employed by researchers in heat transfer and fluid flow communities as a reliable and non-intrusive temperature measurement tool due to their unique optical properties such as birefringence, optical activity, circular dichroism and selective reflection of colours in the visible spectrum as function of temperature. The use of narrowband TLCs are attractive for temperature and heat transfer measurements due to their higher precision in temperature measurements and due to the fact that narrowband TLCs are less affected by variations in illumination-viewing angles and illumination disturbances. Narrowband TLCs have been used with full intensity-matching methods to provide robust image processing for measurements of thermal parameters in transient heat transfer tests. Calibration of narrowband TLCs is necessary in order to obtain the intensity-temperature relationship of the TLCs. Film thickness is one of the factors which affects calibrations of TLCs. In this research, film thicknesses of 10, 20, 30, 40 and 50 μm were investigated on green intensity-based calibrations of R35C1W TLC during heating and cooling. Results showed an increase in magnitude of peak green intensity with increasing film thickness, with a percentage increase of nearly 18% when film thickness increased from 10 to 50 μm. Results also showed an inconsistent shift in temperature at which peak green intensity occurs, with a maximum shift of 0.40 °C, suggesting that film thickness effects may be insignificant for narrowband TLCs compared with wideband TLCs. A theoretical method for estimating the volume of TLC coating required to achieve a desired film thickness has also been described in this paper, based on the surface area and dry solids content of the TLC. The method is easily implemented and applicable for sprayable TLC coatings.     

Carboxylations of alkali metal phenoxides with carbon dioxide

The reaction mechanism of the Kolbe-Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali metal phenoxide-CO2 complex is not an intermediate that can be easily transformed into a carboxylic acid, such as salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO2 takes place even at room temperature, and is competitive with the formation of the CO2 complex. The resulting complex decomposes thermally (above ca. 100 degrees C) to phenoxide, which then undergoes further competitive reactions. Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the mechanism via a CO2 complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new carbonate-like structure for the CO2 complex.     

Titrimetric determination of microgram amounts of thallium(I) by thiocyanate amplification after precipitation as thallium hexathiocyanatochromate(III)

Summary Thallium (5–200g) is precipitated as Tl₃Cr(SCN)₆. The precipitate is collected, then treated with 10% sodium carbonate solution, and the thiocyanate dissolved is oxidized to sulphate by iodine at pH 8.2. After acidification, the excess of iodine is extracted into chloroform, and the iodide in the aqueous solution is determined by the Leipert amplification procedure. The method provides 76 iodine atoms for each original thallium(I) ion. Copper(II), mercury(II), bismuth, lead and silver interfere seriously, the first three causing negative errors and the other two positive errors.

---

Maanalytische Bestimmung von Mikrogrammengen Thallium(I) durch Vervielfachung mit Thiocyanat nach Fällung als Thalliumhexathiocyanatochromat(III)

Zusammenfassung Thallium (5–200g) wird als Tl₃Cr(SCN)₆ gefällt. Der gesammelte Niederschlag wird mit 10% iger Sodalösung behandelt und das gelöste Thiocyanat mit Jod bei pH 8,2 zu Sulfat oxydiert. Nach Ansäuern wird der Jodüberschuß mit Chloroform extrahiert und das Jodid in der wäßrigen Lösung nach Leipert titriert. Dabei entsprechen 76 Jodatome einem ursprünglichen Thallium(I)ion. Cu(II), Hg(II), Bi, Pb und Ag stören stark und verursachen negative bzw. im Falle Pb und Ag positive Fehler.