Showing papers on "Chemical binding published in 1990"
TL;DR: In this article, the control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified, and the chemical bond structures for native oxide films grown in air and in ultrapure water are also discussed.
Abstract: The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n +‐Si in ultrapure water saturates at 10 A. The native oxide growth on n‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure waterdrops and chemical binding energy. These chemical bond structures for native oxide filmsgrown in air and in ultrapure water are also discussed.
803 citations
TL;DR: A mathematical model for the exchange of neutral organic chemicals at fish gills was formulated based on limitations imposed by flows of water and blood to the gills, diffusion barriers defined by gill morphology, and chemical binding relationships.
122 citations
Abstract: The following properties have been measured for mercury clusters: (1) ionisation potentials of Hgn by electron-impact ionisation, (2) dissociation energies of Hg+n, and (3) mass spectra for negatively charged mercury cluster ions (n 3). Cohesive energies for neutral and ionised Hg clusters have been calculated from the data. The transitions in chemical binding are discussed. For small clusters Hgn is van der Waals bound (n⩽ 13), the binding changes to covalent for 30 ⩽n⩽ 70, and then to metallic (n 100). A sudden transition from covalent to metallic bonding is observed. It is discussed whether this can be considered as being analogous to a Mott transition for a finite system. The experimentally observed transitions in chemical bonding are much more pronounced than those calculated in a tight-binding calculation. This points to strong correlation effects in Hg clusters.
90 citations
TL;DR: In this article, the initial stages of oxide formation were studied in situ by AES and X-ray photoelectron spectroscopy (XPS) at low oxygen pressures, while the in-depth composition of the generated oxide layer was obtained by sputter depth profiling.
76 citations
TL;DR: New metabolic and environmental transformations were identified: the production of 3-MPA as a metabolite of methionine and the transformation of mercaptopyruvate to mercaptoethanol and Mercaptoacetate.
Abstract: Sulfur-containing amino acids were examined as precursors for thiols in anoxic coastal sediments. Substrates (10 to 100 μM) were anaerobically incubated with sediment slurries; thiols were assayed as isoindole derivatives by high-performance liquid chromatography; and microbial transformations of thiols, in contrast to their chemical binding by sediment particles, were identified by inhibition with a mixture of chloramphenicol and tetracycline. Methionine and homocysteine were transformed to methanethiol and 3-mercaptopropionate (3-MPA); methionine stimulated mainly methanethiol production, whereas homocysteine generated more 3-MPA than methanethiol. 2-Keto-4-methiolbutyrate yielded results similar to those with methionine, indicating that demethiolation yields methanethiol at the keto-acid level. Glutathione gave rise to cysteine, which was further transformed to 3-mercaptopyruvate and thence to mercaptoacetate and mercaptoethanol. Mercaptoethanol was oxidized to mercaptoacetate, which was biologically consumed. In conclusion, sulfurcontaining amino acids contribute to the range of thiols that occur in anoxic coastal sediments. New metabolic and environmental transformations were identified: the production of 3-MPA as a metabolite of methionine and the transformation of mercaptopyruvate to mercaptoethanol and mercaptoacetate.
62 citations
Patent•
05 Jun 1990
TL;DR: In this article, a method for separating cells and microorganisms from aqueous suspensions and also to the determination of an analyte in a sample suspected of containing the analyte is described.
Abstract: A method is disclosed for separating a substance from a liquid medium. The method comprises combining the liquid medium containing the substance with magnetic particles under conditions for non-specific chemical binding of the magnetic particles. Thereafter, the medium is subjected to a magnetic field gradient to separate the particles from the medium. The preferred non-specific binding is achieved as the result of charge interactions between the particles usually by means of a polyionic reagent. The method of the invention has particular application to the separation of cells and microorganisms from aqueous suspensions and also to the determination of an analyte in a sample suspected of containing the analyte. The analyte is a member of a specific binding pair (sbp). The sample is combined in an assay medium with magnetic particles and a sbp member complementary to the analyte. Magnetic or non-magnetic particles capable of specific binding to the analyte or its complementary sbp member must be included in the assay medium. The combination is made under conditions for non-specifically aggregating the magnetic particles or coaggregating the magnetic and non-magnetic particles when non-magnetic particles are present. The assay medium is subjected to a magnetic field gradient to separate the aggregated particles from the medium. Then, the medium or the particles are examined for the presence or amount of the analyte or an sbp member, the binding of which is affected by the presence of the analyte.
58 citations
TL;DR: In this paper, single crystals of SnS 2 were successfully grown using the chemical vapor transport technique at lower temperature than that ever reported, and the reverse temperature gradient was another characteristic feature in this method.
28 citations
TL;DR: Results suggest that selective TU incorporation in pigmented melanomas and other melanin-producing systems is due to the covalent binding to dopaquinone, produced by tyrosinase catalyzed oxidation of tyrosine.
19 citations
TL;DR: In this article, the authors measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies using crossed beams of metastable rare gas atoms Rg*(ms3P2,3P0) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s2S1/2) and found that the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depthsD* e [meV]
Abstract: Using crossed beams of metastable rare gas atoms Rg*(ms3P2,3P0) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s2S1/2), we have measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies. For Rg*(3P2)+Na(3s), the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depthsD* e [meV] decreasing slowly from Rg=Ne to Xe as follows: 676(18); 602(23); 565(26); 555(30). For Rg*(3P0)+Na(3s), the spectra vary strongly with the rare gas, indicating a change in the character of the interaction from van der Waals type attraction (Ne) to chemical binding for Kr and Xe with well depthsD* e [meV] of: 51(19); 107(25); 432(30); 530(50). These findings are explained through model calculations of the respective potential curves, in which the exchange and the spin orbit interaction in the excited rare gas and the molecular interaction between the two valences-electrons in terms of suitably chosen singlet and triplet potentials are taken into account. These calculations also explain qualitatively the experimental finding that the ratiosq2/q0 of the ionization cross sections for Rg*(3P2)+Na and Rg*(3P0)+Na vary strongly with the rare gas from Ne to Xe as follows: 15.8(3.2); 2.6(4); 1.4(2); 1.6(4).
14 citations
TL;DR: In this paper, the effect of boron content on film properties was investigated and the results showed that more than 13 mol'% B2O3 fraction resulted in degradation of chemical durability.
Abstract: ZrBxOy films for optical durable coating application were deposited by reactive dc magnetron sputtering of Zr–B alloy target on soda‐lime‐silica glass substrate without intentional heating. Effect of boron content on film properties was investigated. The refractive index of the film was decreased from 2.1 to 1.69 corresponding to the increase of B2O3 content from 0 to 64 mol %. The films containing more than 13 mol % B2O3 fraction were amorphous and showed remarkably improved mechanical durability compared with ZrO2 film. More than 51 mol % B2O3 content resulted in degrading of chemical durability. Measurement of mechanical properties was carried out together with characterization on crystalline structure and chemical binding state.
9 citations
01 Jan 1990
TL;DR: The question of biomethylation within the chemical cycle of organolead species in the environment is still controversial as discussed by the authors, however, it has been shown that it is possible to identify the species of the organoleads in the wild.
Abstract: Ecological pathways, bioavailability, and the toxicity of a metal are strongly influenced by its chemical binding forms which determine the hydrophilic or lipophilic properties of the compounds. Consequently, metal speciation is indispensable for risk assessment of hazardous and potentially toxic substances. Organolead compounds enter the biosphere mainly due to their worldwide use as antiknock additives in gasoline. Tetraethyl- and tetramethyllead are emitted into the atmosphere during industrial production and handling as well as from car exhausts together with their decomposition products (triand dialkyllead species). Environmental degradation takes place, e.g., by photolytic breakdown, reaction with ozone or OH-radicals, and by biodealkylation. The question of biomethylation within the chemical cycle of organolead species in the environment is still controversial.
TL;DR: In this article, the effect of chemical binding on resonance broadening was investigated for a harmonic crystal model to examine the chemical binding effect for resonant scattering, and it was shown that at high temperatures or high resonance energies, scattering can be treated using ideal gas with the same effective temperature as for absorption accounting for chemical binding effects.
Patent•
16 Aug 1990
TL;DR: A method and test kit to perform a simple detection assay for D-dimer, a fibrin breakdown product, which utilizes purified Fragment E of human Fibrinogen attached to a solid phase for direct chemical binding of D-Dimer from a biological sample is described in this paper.
Abstract: A method and test kit to perform a simple detection assay for D-dimer, a fibrin breakdown product, which utilizes purified Fragment E of human fibrinogen attached to a solid phase for direct chemical binding of D-dimer from a biological sample. This direct binding method to assay for D-dimer of the present invention can be performed in a number of ways. In one embodiment of the invention, Fragment E is conjugated to latex carrier particles and an agglutination assay performed.
TL;DR: In this paper, the magnetic properties, the microstructures and the chemical binding state of carbon atoms of Fe-polyethylene films prepared by co-evaporating Fe and polyethylene were investigated.
Abstract: The magnetic properties, the microstructures and the chemical binding state of carbon atoms of Fe-polyethylene films prepared by co-evaporating Fe and polyethylene were investigated. Magnetic property measurements revealed that the dependence of the saturation magnetization of Fe-polyethylene films on the carbon content was different from that of sputtered Fe–C films, and that Fe-polyethylene films with the carbon content of 11–13 at.% exhibited good soft magnetic properties. The magnetic properties of the Fe-polyethylene film with the carbon content of 11 at.% were as follows; Ms=1390 emu/cm3, Hc=2 Oe, µ=2000 (at 1 MHz), µ=900 (at 10 MHz). The temperature dependence of Ms and Hc indicated that the crystallization temperature was about 240–260°C. The results of XPS showed that most carbon atoms in the Fe-polyethylene films chemically combined with Fe atoms.
01 Jan 1990
TL;DR: In this article, the authors describe the surface behavior of the clean surface with no foreign species adsorbed or reacted and show that the surface can provide or accept single electrons in a level of energy suitable for covalent bonding.
Abstract: We are very fortunate in recent years that excellent theoretical models and excellent experimental techniques have been developed that permit a reasonable description of the solid surface with no foreign species adsorbed or reacted. Although from most practical points of view the more interesting system is that with foreign species present, a knowledge of the behavior of the clean surface is necessary as a starting point in understanding surface phenomena and as background to discuss the bonding of the foreign species. From the chemical point of view (of surface reactivity) one is interested in the available “intrinsic” surface orbitals present on the clean surface. We want to know their chemical binding characteristics, whether they can provide or accept single electrons in a level of energy suitable for covalent bonding, or whether they can provide or accept electron pairs in levels of energy suitable for acid/base bonding. We want to know the directional characteristics of such bonding orbitals. From the physical point of view (the electronic properties of the solid), the energy of the orbitals (surface state energy) and whether they donate or accept electrons is of first importance. But it is also important to know what surface states will result when these energy levels are altered by reconstruction or by foreign species adsorbing and interacting with the surface sites.
01 Jan 1990
TL;DR: In this article, the authors measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies using crossed beams of metastable rare gas atoms Rg*(ms 3P2, 3P0) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s 2S1/2).
Abstract: Using crossed beams of metastable rare gas atoms Rg*(ms 3P2, 3P0) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s 2S1/2), we have measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies. For Rg*(3P2)+Na(3s), the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depths De* [meV] decreasing slowly from Rg=Ne to Xe as follows: 676(18); 602(23); 565(26); 555(30). For Rg*(3P0)+Na(3s), the spectra vary strongly with the rare gas, indicating a change in the character of the interaction from van der Waals type attraction (Ne) to chemical binding for Kr and Xe with well depths De* [meV] of: 51(I9); 107(25); 432(30); 530(50). These findings are explained through model calculations of the respective potential curves, in which the exchange and the spin orbit interaction in the excited rare gas and the molecular interaction between the two valence s-electrons in terms of suitably chosen singlet and triplet potentials are taken into account. These calculations also explain qualitatively the experimental finding that the ratios q2/q0 of the ionization cross sections for Rg*(3P2)+Na and Rg*(3P0)+Na vary strongly with the rare gas from Ne to Xe as follows: 15.8(3.2); 2.6(4); 1.4(2); 1.6(4).
TL;DR: In this paper, the authors investigated the dependence of silylation on the exposure dose and the presilylation baking temperature by using Rutherford backscattering spectrometry and found that the higher dose UV-irradiation results the thicker silylated layer in the dyed resist.
Abstract: Silylation and dry development are the key processes of DESIRE, one of the surface imaging techniques in submicron lithography. The present work was carried out to achieve the improvement of develoment rate and anisotropic resist profile, and to characterize the silylated and dry developed resist. The dependence of silylation on the exposure dose and the presilylation baking temperature was investigated by using Rutherford backscattering spectrometry. The higher dose UV-irradiation results the thicker silylated layer in the dyed resist. The dry development of photoresisl patterns was processed newly by using the plasma of O2/He RIE plasma. It is particularly emphasized to obtain to optimize the RIE process, so that some improvements, i.e., vertical resist profiles with the high anisotropy, good selectivity, and the development rate of 0.4 µm/min were achieved. X-ray photoelectron spectroscopic study indicated that Si in the silylated and dry developed resist was present with the chemical binding states of SiO2 on surface, and SiO. SiC and very small amount of SiO2 in near-Surface region (at about 5 nm depth).