Impact Ionization Conditions Research Articles

Contact chemoreceptive mate recognition in Cerambyx welensii Küster (Coleoptera: Cerambycidae)

Abstract Cerambyx welensii Küster (Coleoptera: Cerambycidae) is a wood‐borer responsible for the decline of Mediterranean oaks in open woodlands. To establish that contact pheromones are involved in mate recognition of C. welensii, we extracted the cuticular hydrocarbons by solid phase microextraction at pre‐reproductive, beginning and ending of the reproductive period, and by solvent extraction of prothorax and elytra. The extracts were analysed by GC–MS under electron impact and chemical ionization conditions. Cuticular hydrocarbon profiles varied according to the reproductive period, although differences between sexes were not significant. Two compounds, 11/13‐methylheptacosane and 11‐methylnonacosane were more abundant in females at the beginning and ending of the reproductive periods. Compound 11/13‐methylheptacosane was also more representative in female prothorax than in males, and 2‐methyloctacosane was richer in male elytra than in females. We also studied the role of cuticular hydrocarbons in mate recognition in arena bioassays. Treatment of solvent‐washed dead females and glass dummies with one female equivalent (FE) of cuticular extract elicited mating responses in males, especially at the beginning of the reproductive period, with copulation attempts reaching 61.9% on solvent‐washed dead females and 23.8% on dummies. The successive treatment with synthetic compounds approaching a male cuticular profile inhibited male response. Our results confirm that contact pheromones mediate mate recognition in C. welensii. Knowledge of the precise role played by the major compounds 11/13‐methylheptacosane and 11‐methylnonacosane and other minor compounds representative in female prothorax may contribute to the development of novel management strategies against C. welensii.

Polarization anisotropy of electroluminescence in indium antimonide

Mid-infrared electroluminescence spectra under impact ionization conditions in strong electric fields are studied experimentally in monocrystalline n-InSb. The emission band observed in electroluminescence spectra is associated with a radiative recombination of electrons and holes between the conduction and valence bands. Spectral measurements of the electroluminescence intensity for different light polarizations relative to the direction of the applied electric field reveal the polarization anisotropy of the electroluminescence intensity in InSb, which is caused by the anisotropy of the distribution function of nonequilibrium electrons as well as by the anisotropy of the angular dependence of the interband optical matrix element in momentum space.

N-Aryl-7-hydroxy-5-oxo-2,3-dihydro-1H,5H-pyrido-[3,2,1-ij]quinoline-6-carboxamides. The Synthesis and Effects on Urinary Output.

Continuing a targeted search for new leading structures with diuretic action among tricyclic derivatives of hydroxyquinolines, which are of interest as potential inhibitors of aldosterone synthase, the synthesis of a series of the corresponding pyrido[3,2,1-ij]quinoline-6-carboxanilides was carried out by amidation of ethyl-7-hydroxy-5-oxo-2,3-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-6-carboxylate with aniline, aminophenols and O-alkylsubstituted analogs with high yields and purity. The optimal conditions of this reaction are proposed; they make it possible to prevent partial destruction of the original heterocyclic ester and thereby avoid formation of specific impurities of 7-hydroxy-2,3-dihydro-1H,5H-pyrido[3,2,1-ij]quinolin-5-one. To confirm the structure of all substances obtained, elemental analysis, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry were used. Moreover, the peculiarities of their 1H and 13C-NMR spectra, as well as their mass spectrometric behavior under conditions of electron impact ionization, were discussed. The effect of pyrido[3,2,1-ij]quinoline-6-carboxanilides on the urinary function of the kidneys was studied in white rats of both genders by the standard method of oral administration at a dose of 10 mg/kg. Testing was conducted in comparison with hydrochlorothiazide, as well as with structurally close pyrrolo[3,2,1-ij] quinoline-5-carboxanilides studied earlier with the same substituents in the anilide fragments. It was found that addition of one methylene unit to the heterocycle partially hydrogenated and annelated with the quinolone core has a positive impact on biological properties—most of the substances studied exhibit a statistically significant diuretic effect exceeding the activity of not only hydrochlorothiazide, in some cases, but also the action of the structural analogs. The important structural and biological regularities, which are common with pyrroloquinolines and introduced by a chemical modification, were revealed. The importance of the presence in the structure of terminal amide fragments of tricyclic quinoline-3-carboxamides of a 4-methoxy-substituted aromatic ring was particularly marked. The expediency of further study of pyridoquinolines as promising diuretic agents has been shown.

Impact ionization of excitons in Ge/Si structures with Ge quantum dots grown on the oxidized Si(100) surfaces

Photoconductivity (PC) of Si/Ge structures with Ge quantum dots (QDs) grown on the Si(100) surfaces covered with the ultrathin, about 0.3–0.5 nm thick, SiO2 films is studied as a function of the interband light intensity under various lateral voltages. The structures exhibit PC with steps and a step with a peak at the step edge for low- and high-temperature grown structures, respectively. These PC features are associated with the impact ionization of QD-related excitons. The PC at step edges increases by several orders of magnitude for a certain value which is governed by the balance between rates of photo-generation, recombination, and impact ionization of excitons. The electron localization deeper in Si from the Ge QD layer in conjunction with a narrow binding-energy distribution of excitons is suggested to be the main reason that provides the sharpness of PC steps. The PC appears to be very sensitive to the impact ionization and QD preparation conditions. This allows revealing the specific characteristics of QD structures, related to their electronic and structural properties.

Monte Carlo simulation of THz frequency Gunn effect in GaAs MOSFET with excess of electrons in channel at impact ionization conditions

The results of Monte Carlo simulation of GaAs MOSFETs under impact ionization conditions in the conduction channel are presented. The main attention is paid to the transistor operation at a positive gate bias when the electron concentration in the channel under the gate considerably exceeds the channel doping level. The stationary characteristics including current voltage relation and velocity, energy and field profiles in the channel are calculated. Also, the drain current noise spectra at various drain biases are presented. The Gunn-effect dynamics in excess of electrons in the channel is investigated. The optimization of transistor geometrical, doping, and biasing parameters for high frequency generation is performed. It is shown that GaAs MOSFET can generate at 325 GHz frequency.

Monte Carlo simulation of THz frequency Gunn effect in GaAs MOSFET with excess of electrons in channel at impact ionization conditions

The results of Monte Carlo simulation of GaAs MOSFETs under impact ionization conditions in the conduction channel are presented. The main attention is paid to the transistor operation at a positive gate bias when the electron concentration in the channel under the gate considerably exceeds the channel doping level. The stationary characteristics including current voltage relation and velocity, energy and field profiles in the channel are calculated. Also, the drain current noise spectra at various drain biases are presented. The Gunn-effect dynamics in excess of electrons in the channel is investigated. The optimization of transistor geometrical, doping, and biasing parameters for high frequency generation is performed. It is shown that GaAs MOSFET can generate at 325 GHz frequency.

Cyclic Acyloxonium Ions as Diagnostic Aids in the Characterization of Chloropropanol Esters under Electron Impact (EI), Electrospray Ionization (ESI), and Atmospheric Pressure Chemical Ionization (APCI) Conditions

During mass spectrometric analysis of various lipids and lipid derivatives such as the chlorinated counterparts of triacylglycerols, the detailed structure of the characteristic and common ions formed under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions by the loss of a single fatty acid remains ambiguous. These ions are designated in the literature as "diacylglyceride ions" and are frequently depicted with a molecular formula without showing any structural features and sometimes represented as cyclic acyloxonium ions. Characterization of these ions is of considerable importance due to their utility in structural identification of lipid derivatives. This study provides complementary evidence on the cyclic nature of "diacylglyceride ions" through the use of the simplest 3-monochloropropanediol diester as a model and the use of isotope labeling technique. Tandem MS/MS studies have indicated that the ion at m/z 135.6 generated from 1,2-bis(acetoyl)-3-chloropropane through the loss of an acetyl group was identical to the ion at m/z 135.6 generated from 4-chloromethyl-2,2-dimethyl-1,3-dioxolane, the latter being generated from a cyclic precursor through the loss of a methyl radical, keeping the dioxolane ring structure intact, thus confirming the cyclic nature of these ions. The corresponding cyclic oxonium ions generated from longer chain chloropropanol diesters, such as the ion at m/z 331.2 originating from 3-monochloropropanediol (3-MCPD) diesters containing palmitic acid(s), could serve as chemical markers for the presence chloropropanol esters.

Single-transistor latch-up and large-signal reliability in SOI CMOS RF power transistors

RF power transistors are typically operated at extreme drain voltage and current peaks, which cause severe impact ionization conditions at the channel pinch-off region. On a SOI CMOS technology platform, the resulting large body currents may eventually lead to single transistor latch-up, unless the length of the gate/body finger is properly chosen. In this work, the effect of single-transistor latch-up on the large-signal performance of SOI CMOS RF power transistors is investigated for the first time. Extensive multi-harmonic load–pull measurements have been performed to characterize the resulting current runaway phenomenon and its detrimental effect on the device efficiency. Useful guidelines have been derived to avoid such limitations and a prototype power transistor has been designed accordingly. Thanks to the proposed design criteria, the device achieves latch-up-free operation at the nominal 2-V supply voltage, while exhibiting an excellent 72% power-added efficiency at a 19.5-dBm output power level under 1.9-GHz continuous-wave excitation. Moreover, an experimental study on the gate oxide degradation kinetics under RF stress has been carried out to characterize the long-term device reliability of the adopted SOI CMOS process.

Performance stability of AlGaN/GaN HFET: effect of plasma processing

AbstractEffect of fluoride‐based plasma treatment on performance stability of AlGaN/GaN HFET was systematically investigated. The plasma‐based processes can introduce different type of damage that can be permanent or temporary, depending on electrical field in the device, plasma density, and energy of radicals and total process thermal budget. In order to understand more clearly the mechanism of fluorine based plasma treatment on device performance, we compare the effects of Ar, O2 and CF4 based plasma treatments applied before gate definition. Ar plasma was chosen for comparison with CF4 because of high ionization rate of Ar and chemically neutral behavior of Ar ions. Under the same medium range of 40 V DC bias in RIE system for these two gases, the shift of drain current and threshold voltage was similar that indicate the common mechanism of plasma damage. We supposed that the major effect for this phenomenon is a negative electron charge inserted in semiconductor during plasma treatment, because at the same accelerated field the penetration depth for electrons is higher than the penetration depth for fluoride ions. Devices stressed under impact ionization conditions show an improvement of breakdown voltage (for O2 plasma treatment) and some recovery of threshold voltage similar to “walkout effect”. This performance non‐stability raise the serious concern about application of fluorine based technology for power applications, where large voltage/current swing may push device to the impact ionization region. The experimental results show that the implementation of fluoride based plasma treatment for power device manufacturing can affect the performance stability of AlGaN/GaN power HFET. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mass Spectral Fragmentation of ( S, S)- N, N′-Bis [1-(hydroxymethyl) alkyl] anthracene/Naphthalene-1, 8-dicarboxamides under Electron Impact Ionization Conditions

The mass spectrometric fragmentation of ( S, S)- N, N′-bis[1-(hydroxymethyl) alkyl] anthracene/naphthalene-1, 8-dicarboxamides was investigated with the aid of mass-analyzed ion kinetic energy spectrometry and the elemental compositions of important fragment ions were determined by accurate mass measurement under electron impact ionization conditions. All the compounds could eliminate formaldehyde. The [M-CH 2O] ions could also eliminate imine, aziridine, aziridinone, 2-amonoalkan-1-ol, water, and other fragments. Several cyclizations were observed under electron impact ionization.

Mass Spectrometric Fragmentation of 2a,4-Disubstituted 2,2a,3,4-Tetrahydro-2-phenyl-1H-azeto[2,1-d]- [1,5]benzothiazepin-1-ones Under Electron Impact Ionization Conditions and Comparison with their 2-Heteroatom Substituted Analogues

The mass spectrometric behavior of seven 2a,4-disubstituted 2,2a,3,4-tetrahydro-2-phenyl-1H-azeto[2,1-d][1,5]benzothiazepin-1-ones has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a phenylketene molecule, an ethyl or benzyl radical, or a phenylketene molecule plus an SH radical. The mass spectrometric behavior of the title compounds was compared to those of 2-heteroatom-substituted analogues.

Interpretation of alkyl diselenide and selenosulfenate mass spectra

The mass spectral fragmentation of aliphatic diselenides and selenosulfenates is analyzed to gain a better understanding of the behavior of these species. The main fragmentation pathways of these species include the fragmentation along the SeC bond, fragmentation along the SeSe or SeS bonds and intra-molecular rearrangements. In general, negative ionization favors the fragmentation along the SeSe or SeS bonds while positive ionization leads to stable molecular ions. Density functional theory calculations of bond dissociation energies and molecular orbital analysis was undertaken to explain the observed trends in molecular fragmentation. Besides the analysis of molecular fragmentation, a phenomenon of molecular association in negative electron impact and positive chemical ionization conditions was observed and investigated using a high resolution time-of-flight mass spectrometer. Molecular association that occurs during the ionization of species includes the formation of symmetrical diselenides from asymmetrical selenosulfenates and formation of alkylseleno adducts from the corresponding diselenides. For species which is hard to resolve by mass analysis, such as isobars of CHSe, CH2Se, and CH3Se, the isotope pattern superimposition procedure was applied to define the overlapping clusters.

Intermolecular Phenolic Hydroxy Methylation Occurring between Chiral N,N′‐Bis(2‐hydroxyphenyl)‐2,2‐dimethyl‐1,3‐dioxolane‐4,5‐dicarbamide and Co‐crystallized Methanol under Electron Impact Ionization Conditions

AbstractAn intermolecular phenolic hydroxy methylation occurring between chiral N,N′‐bis(2‐hydroxyphenyl)‐2,2‐dimethyl‐1,3‐dioxolane‐4,5dicarbamide and co‐crystallized methanol under electron impact ionization conditions was observed. The result was confirmed by X‐ray diffraction structural analysis of a co‐crystalline of (R,R)‐enantiomer and methanol.

Laboratory simulations of the transformation of peas as a result of heating: the change of the molecular composition by DTMS

Peas ( Pisum sativum L.) consist mainly of cotyledons and their bulk material is starch and proteins. Their structure is rather confined. Peas were heated at temperatures ranging from 130 to 700 °C under anoxic conditions for maximum 2 h. For each temperature a separate experiment was carried out in a pre-heated oven. Direct temperature-resolved mass spectrometry (DTMS) under electron impact (EI) and chemical ionization (CI, NH 3) conditions measured the molecular composition of each solid residue. Fourier-transform infrared (FTIR) spectroscopy was carried out on residues heated at higher temperatures. The resulting solid products of the heating process still show the original markers for polysaccharides and proteins up to 270 °C. Concurrently three phases can be considered, each characterized by its own products. The first phase, from 270 up to 310 °C, shows monosaccharides, protein fragments and aromatic compounds. The second phase, from 310 °C up to a transitional stage from 400 to 440 °C, releases various aromatic and heterocyclic compounds. The third phase at higher temperatures shows a highly C-enriched product that releases CO, CO 2, HCN, SO and SO 2. The EI and CI experiments fail to discriminate between the pyrolysis products of polysaccharides and proteins between 250 and 400 °C. FTIR shows in this temperature range the development of an aromatic network. An earlier classification based on the changes of the physical and bulk chemical properties as a function of the temperature corresponds well with the classification based on the molecular changes. Residues of heated peas, usually called carbonized peas, are found in the archaeological record. Our study suggests that peas should have been heated up to least 310 °C before their residues survive natural degradation processes.

Mass spectral fragmentation of (S,S)-2-substituted 4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes: ring contraction of pyrrolidine and 1,3-oxazolidine in mass spectrometry.

The mass spectral behaviour of (S,S)-2-substituted 4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under fast atom bombardment (FAB) and electron impact (EI) ionization conditions. Under FAB ionization, all compounds show a tendency to form protonated aldehyde or benzophenone ions and to form protonated 1-azabicyclo[3.1.0]hexane ions, which can further lose an ethylene or cyclopropane from the pyrrolidine ring to produce protonated 1-azabicyclo[1.1.0]butane ions and 3H-azirine ions, respectively. Under EI ionization, a similar fragmentation to that under FAB ionization was observed. The title compounds also show a tendency to yield oxirane ions and oxirenium ions by loss of pyrrolidine and pyrrolidine plus H. Ring contractions of 1,3-oxazolidine by loss of an aldehyde or ketone and of pyrrolidine by loss of an ethylene or cyclopropane were observed under both FAB and EI ionization conditions.

Mass Spectrometry Study of Acylthioureas and Acylthiocarbamates

A variety of acylthiocarbamates and acylthioureas have been investigated under electron impact ionization (EI), chemical ionization (CI) and electrospray ionization (ESI) conditions. Sequential product-ion fragmentation (MSn) was performed to elucidate the degradation pathways for these compounds. Comparisons are made between positive and negative even-electron ions from ESI and CI and the odd-electron ions obtained under EI conditions. The data collected in this paper provide information on the strong differences found in the fragmentation process of these compounds.

Electron impact mass spectral fragmentation of chiral bisbenzoxazole, bisbenzothiazole and biscarbamide derivatives of 2,2-dimethyl-1,3-dioxolane.

The mass spectrometric fragmentation behaviour of five pairs of (R,R)- and (S,S)-4,5-bis(benzoxazol-2-yl)-2,2-dimethyl-1,3-dioxolane derivatives, one pair of (R,R)- and (S,S)-4,5-bis(benzothiazol-2-yl)-2,2-dimethyl-1,3-dioxolanes, and three pairs of (R,R)- and (S,S)-N,N'-bis(2-hydroxyaryl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamides, all important compounds for asymmetric catalysis (P. Jiao et al., Tetrahedron Asymmetry 2001; 12: 3081), has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization conditions. The spectral observations have been rationalized in terms of fragment ion structures and fragmentation mechanisms that will provide an aid to spectral interpretation for new compounds of this type.

Emergence of a multidomain regime and spatiotemporal chaos in Gunn diodes under impact ionization conditions

Nonlinear spatiotemporal dynamics of carrier densities in Gunn diodes under impact ionization conditions is numerically investigated using a set of model partial differential equations. Numerical results show that a multidomain regime emerges as a result of the decrease in domain size caused by impact ionization, and that the spatiotemporal evolution of the domains becomes chaotic in the presence of strong impact ionization.

Far infrared stimulated and spontaneous radiation in uniaxially deformed zero-gap Hg1−x CdxTe

Stimulated radiation in the range of 80–100 µm was observed in uniaxially stressed zero-gap Hg1−xCdxTe (x=0.10–0.14) under conditions of impact ionization by an electric field. The abrupt increase in emission occurs under the threshold values of elastic strain and electric-field strength and is followed by an abrupt increase in the current in the sample. The field and deformation dependences of spontaneous radiation are also determined. The mechanism of the effect observed is suggested taking into account the transformation of energy bands and impurity acceptor levels by the uniaxial elastic stress.

Autosolitons in an electron-hole plasma/excitons system in silicon at 4.2K

Results are presented of the experimental discovery and study of auto-oscillations in an electron-hole plasma/excitons system in silicon under conditions of impact ionization of the excitons in a constant electric field. It is shown that the current auto-oscillations are due to disruption of the uniform density distribution of the electron-hole plasma and its stratification, where the latter is caused by the formation of strongly nonequilibrium structures, namely, autosolitons. The microplasma breakdown of the reverse-biased Schottky barrier is the cause of the spontaneous excitation of autosolitons.