Method for measuring chemical diffusion coefficients in solids

Experiments were performed with temperature programmed desorption of hydrogen and deuterium adsorbates on small platinum spheres. Beyond the expected desorption peak of these adsorbates at around 300 K sample temperature an additional desorption peak at higher temperatures was observed. This additional peak is explained by the diffusion of hydrogen or deuterium atoms from the inside of the spheres to their surfaces with final desorption from these surfaces. The visibility of this second high temperature desorption peak is supported by a small diameter of the platinum spheres. Platinum spheres with diameters around 64 μm were used. The sample temperature at which the second peak was observed depends on the parameters: diameter of the platinum spheres, heating rate of the sample and chemical diffusion coefficient of hydrogen or deuterium in platinum. A theory, which assumes that the chemical diffusion coefficient can be described with an Arrhenius ansatz, was developed to simulate the occurrence of the second peak. The combination of these kinds of experiments with the theory gives a method to measure chemical diffusion coefficients. This method can be called temperature programmed diffusion. At 510 K sample temperature the diffusion coefficient 1.61×10⁻¹² m²/s of hydrogen in platinum and the diffusion coefficient 1.40×10⁻¹² m²/s of deuterium in platinum was measured.     

Polarisation resistance of the O2, Au/O2− and H2-H2O, Au/O2− electrode systems

Gold electrodes with known contact geometries were studied using impedance spectroscopy. From these data it was possible to determine the specific polarisation conductivity per unit length of three-phase boundary (TPB). The values were found to be (3÷22)×10⁻⁴ S·cm⁻¹ dependent on the electrode history in pure oxygen at 977 °C and 2×10⁻⁶ S·cm⁻¹ at 977 °C in “pure” hydrogen (P_O2=10⁻²⁰ atm at 1001 °C). The results are compared with previous data obtained for platinum electrodes.     

Electron stimulated desorption of H3O from 316L stainless steel

Surface ions generated by electron stimulated desorption from mass spectrometer ion source grids are frequently observed, but often misidentified. For example, in the case of mass 19, the source is often assumed to be surface fluorine, but since the metal oxide on grid surfaces has been shown to form water and hydroxides, a more compelling case can be made for the formation of hydronium. Further, fluorine is strongly electronegative, so it is rarely generated as a positive ion. A commonly used metal for ion source grids is 316L stainless steel. Thermal vacuum processing by bakeout or radiation heating from the filament typically alters the surface composition to predominantly Cr₂O₃. X-ray photoelectron spectral shoulders on the O 1s and Cr 2p_3/2 peaks can be attributed to adsorbed water and hydroxides, the intensity of which can be substantially increased by hydrogen dosing. On the other hand, the sub-peak intensities are substantially reduced by heating and/or by electron bombardment. Electron bombardment diode measurements show an initial work function increase corresponding to predominant hydrogen desorption (H₂) and a subsequent work function decrease corresponding to predominant oxygen desorption (CO). The fraction of hydroxide concentration on the surface was determined from X-ray photoelectron spectroscopy and from the deconvolution of temperature desorption spectra. Electron stimulated desorption yields from the surface show unambiguous H₃O⁺ peaks that can be significantly increased by hydrogen dosing. Time of flight secondary ion mass spectrometry sputter yields show small signals of H₃O⁺, as well as its constituents (H⁺, O⁺ and OH⁺) and a small amount of fluorine as F⁻, but no F⁺ or F⁺ complexes (HF⁺, etc.). An electron stimulated desorption cross-section of σ⁺ ∼ 1.4 × 10⁻²⁰ cm² was determined for H₃O⁺ from 316L stainless steel for hydrogen residing in surface chromium hydroxide.     

Progress in pion-decay channelling: Refractory bcc metals at high and low temperatures

By means of π⁺/μ⁺ channelling, positive pions (π⁺) implanted intoTa, Mo, andW are investigated up to high temperatures. A striking observation is that the channelling effect disappears in a rather narrow temperature interval centred at 0.26 (Ta) to 0.51 (W) of the melting temperature. From studies of π⁺ trapping by oxygen atoms inTa estimates for the low-temperature π⁺ diffusivity inTa [D _π(23K)=1.4·10^−10±0.3 m²s⁻¹,D _π(47K)=5.7·10^−10±0.3 m²s⁻¹] as well as for the binding enthalpy of π⁺ to 0 atoms (H _B=7·10⁻² eV) have been obtained. The diffusion data are in reasonable agreement with the theory of phonon-assisted tunnelling.     

Polarisation conductivity of the O2,Pt/Zr(Y)O2 and H2-H2O, Pt/Zr(Y)O2 electrodes

Pt electrodes with defined contact geometries were studied by using impedance spectroscopy. The specific polarisation conductivity per unit length of the three-phase boundary was determined. It is found to be 1 × 10⁻⁴ S·cm⁻¹ at 977 °C in an atmosphere of “pure” hydrogen with an oxygen partial pressure of 10⁻²⁰ atm at 1000 °C. Investigations carried out in an atmosphere of pure oxygen revealed a pronounced dependence of the polarisation conductivity on the electrode history. The polarisation conductivity was found to be in a range of 2 × 10⁻⁴ to 6.5 × 10⁻⁴ S·cm⁻¹ at a temperature of 977 °C. It was possible to estimate the area of the electrolyte surface which takes part in the electrode reaction. The real exchange current density was determined.     

Electron-stimulated desorption of negative O? ions from the oxidized O/Ru surface

This paper reports on a study of the electron-stimulated desorption of negative oxygen ions from the O/Ru surface, which represents an additional factor responsible for the destruction of the protective oxide layer of the mirrors used in ultraviolet lithography. The cross section of degradation of the O/Ru layer due to the electron-stimulated desorption of the O⁺ and O⁻ ions and the O atoms has been found to be 1.6 × 10⁻¹⁹ cm². A comparison of the dependences of the electron-stimulated desorption yield of O⁺ and O⁻ ions on the incident electron energy E with the ionization cross section of the adsorbate core level σ _O2s (E) has revealed that the ionization of the O 2s level is the main channel of the electron-stimulated desorption of O⁻ ions.     

Preliminary results on the operation of a 2270 kg cryogenic gravitational-wave antenna with a resonant capacitive transducer and a d.c. SQUID amplifier

Summary In November 1985 the gravitational-wave antenna of the Rome group, installed at CERN, has started operating. It consists of a 5056 aluminium cilinder 3 m long, 2270 kg heavy, cooled at 4.2 K. The antenna vibrations are detected by means of a resonant capacitive transducer that together with the bar makes a two-coupled-oscillator system. The low-noise amplification is obtained with a d.c. SQUID amplifier. The frequencies of the two resonant modes are:v _-=907.116 Hz andv ₊=923.083 Hz, with merit factorsQ ₋=3.2·10⁶ andQ ₊=5.6·10⁶. The sensitivity to short gravitational bursts, expressed in terms of effective noise temperature, is 18 mK. This corresponds to a change in the metric tensor whose Fourier transform isH=1.1·10⁻²¹ Hz⁻¹. For monochromatic waves the antenna is sensitive (SNR=1) toh∼2·10⁻²⁵ in a band width of about 1/3 Hz, with a three months integration time.

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Riassunto Nel novembre 1985 è stata messa in funzione l'antenna gravitazionale del gruppo di Roma, installata al CERN. Questa consiste di un cilindro d'alluminio 5056 lungo 3 m e pesante 2270 kg, raffeeddato a 4.2 K. Le vibrazioni dell'antenna vengono rivelate mediante un transduttore capacitivo risonante, che assieme alla sbarra forma un sistema di due oscillatori accoppiati. L'amplificazione a basso rumore è ottenuta con un amplificatore a d.c.-SQUID. Le frequenze dei due modi risonanti sono:v _-=907.116 Hz ev ₊=923.083 Hz, con fattori di meritoQ ₋=3.2·10⁶ eQ ₊ =5.6·10⁶. La sensibilità per brevi fiotti di onde gravitazionali, espressa in termini di temperatura efficace di numore, è 18 mK. Questa corrisponde a una variazione di tensore metrico con trasformata di Fourier:H=1.1·10⁻²¹ Hz. Per le onde monocromatiche l'antenna è sensibile (SNR=1) ah∼2·10⁻²⁵ in una banda di circa 1/3 Hz, con tempo d'integrazione di tre mesi.

     

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Thermal expansion of thin C60 films

The thermal expansion coefficient a and structure of C₆₀ films with thickness t∼3–10 nm were investigated in the temperature interval from room to liquid-nitrogen temperature by electron-optical methods. The thermal expansion coefficient was determined from the temperature shift of the diffraction maxima in the electron diffraction patterns. The objects of investigation were epitaxial C₆₀ films condensed in vacuum on a (100) NaCl cleavage surface and oriented in the (111) plane. A surface-induced size effect in the thermal expansion coefficient was observed. It was established that as t decreases α _f increases and is described well by the relation α _f=17·10⁻⁶ K⁻¹+8.3·10⁻⁵ nm K⁻¹ t ⁻¹. This relation was used to estimate the linear expansion coefficient α _s of the C₆₀ surface in the (111) plane as α _s=60·10⁻⁶K⁻¹, which is several times larger than the bulk value. The experimental results agree satisfactorily with the theoretical calculations of the mean-square displacements of molecules located in a region near the surface. Zh. éksp. Teor. Fiz. 114, 1868–1875 (November 1998)     

Reactions and anion desorption induced by low-energy electron exposure of condensed acetonitrile

Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are employed to investigate mechanisms responsible for the formation of C₂H₆ in electron irradiated multilayer films of acetonitrile (CH₃CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H⁻, CH₂ ⁻, CH₃ ⁻ and CN⁻. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C₂H₆ (i.e., at mass 30 amu). It is proposed that C₂H₆ is formed by the reactions of CH₃ radicals generated following DEA to CH₃CN which also yields CN⁻. Between 2 and 5 eV, a second resonant feature is seen in the C₂H₆ signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH₂ ⁻ ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH₃ ⁻ and CN is hindered by adjacent molecules.     

The adsorption of hydrogen and the reaction of hydrogen with oxygen on Pt (100)

The adsorption of hydrogen on Pt (100) was investigated by utilizing LEED, Auger electron spectroscopy and flash desorption mass spectrometry. No new LEED structures were found during the adsorption of hydrogen. One desorption peak was detected by flash desorption with a desorption maximum at 160 °C. Quantitative evaluation of the flash desorption spectra yields a saturation coverage of 4.6 × 10¹⁴ atoms/cm² at room temperature with an initial sticking probability of 0.17. Second order desorption kinetics was observed and a desorption energy of 15–16 kcal/mole has been deduced. The shapes of the flash desorption spectra are discussed in terms of lateral interactions in the adsorbate and of the existence of two substates at the surface. The reaction between hydrogen and oxygen on Pt (100) has been investigated by monitoring the reaction product H₂O in a mass spectrometer. The temperature dependence of the reaction proved to be complex and different reaction mechanisms might be dominant at different temperatures. Oxygen excess in the gas phase inhibits the reaction by blocking reactive surface sites. At least two adsorption states of H₂O have to be considered on Pt (100). Desorption from the prevailing low energy state occurs below room temperature. Flash desorption spectra of strongly bound H₂O coadsorbed with hydrogen and oxygen have been obtained with desorption maxima at 190 °C and 340 °C.     

Modification of nanostructured states in ion-implanted platinum

The formation of nanostructures in subsurface volumes of Pt as a result of the implantation of Ar⁺ ions (E = 30 keV, F = 10¹⁶−10¹⁸ cm⁻²) was studied by the method of field ion microscopy. This phenomenon was observed at distances not less than 60 nm from the irradiated surface of the metal (at F = 10¹⁸ cm⁻²). It was established that the optimum regime for obtaining nanocrystalline structures in subsurface volumes of ion-implanted platinum is irradiation to F = 10¹⁷ cm⁻² (E = 30 keV, j = 200 μA cm⁻²). In such a regime, the formation of nanoblock structures is observed at distances not less than 20 nm from the irradiated surface, rather than the formation of vacancy pores.     

Photoionization spectra of silver atoms adsorbed on the surface of a ZnS single crystal

We have used photostimulated flash luminescence to study deep electronic states arising when silver ions Ag⁺ are deposited under high vacuum onto the surface of a ZnS single crystal, followed by creation of the conditions for neutralization of the silver ions. The flux density of the silver ion beam was 10⁷ cm⁻²·sec⁻¹. We have observed the appearance of two types of deep electronic states with photoionization energies 1.60 eV and 1.80 eV, arising after depositing the silver ions onto the surface of the ZnS single crystal. We have hypothesized that there may be two different preferred sites for adsorption of silver atoms on the zinc sulfide surface. The corresponding photoionization spectra of the adsorbed silver atoms have maxima at 775 nm and 690 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 335–338, May–June, 2006.     

Hydrogen implantation in Ni(111) — A study of H2 desorption dynamics from the bulk

Hydrogen implanted in Ni(111) has been investigated by the use of temperature programmed desorption (TPD) as a function of implantation energy (0.08–5.0 keV) and dose (0−2.6 × 10¹⁷ H⁺₂cm⁻²). The amount of hydrogen implanted was calibrated by comparison to the amount chemisorbed on the surface since separation of the desorption features for the two types of hydrogen was possible. It is shown that trap formation plays an important role in the observed behavior of the implanted hydrogen desorption features for implantation energies above 1.0 keV. The desorption of implanted hydrogen is found to be strongly forward-peaked along the crystal surface normal. Since the surface was saturated with hydrogen when the implanted hydrogen was released, this effect is explained by recombination of an implanted and a chemisorbed hydrogen atom. Here, a translationally excited H₂ molecule desorbing from the surface is produced by a hydrogen atom originating from an elevated potential region inside the solid.     

Binding of Quercetin to Lysozyme as Probed by Spectroscopic Analysis and Molecular Simulation

The binding of quercetin to lysozyme (LYSO) in aqueous solution was investigated by fluorescence spectroscopy, UV-vis absorption spectroscopy and molecular simulation at pH 7.4. The fluorescence quenching of LYSO by addition of quercetin is due to static quenching, the binding constants, K _a , were 3.63 × 10⁴, 3.31 × 10⁴ and 2.85 × 10⁴ L·mol⁻¹ at 288, 298 and 308 K, respectively. The thermodynamic parameters, enthalpy change, ∆H, and entropy change, ∆S, were noted to be −7.56 kJ·mol⁻¹ and 61.07 J·mol⁻¹·K⁻¹. The results indicated that hydrophobic interaction may play a major role in the binding process. The distance r between the donor (LYSO) and acceptor (quercetin) was determined as 3.34 nm by the fluorescence resonance energy transfer. The synchronous fluorescence spectroscopy showed the polarity around the tryptophan residues increased and the hydrophobicity decreased. Furthermore, the study of molecular simulation indicated that quercetin could bind to the active site (a pocket made up of 24 amino-acid residues) of LYSO mainly via hydrophobic interactions and that there were hydrogen interactions between the residues (Gln 57, Ile 98) of LYSO and quercetin. The accessible surface area (ASA) calculation verified the important roles of tryptophan (Trp) residues during the binding process.     

Surface-functionalization of spherical silver nanoparticles with macrocyclic polyammonium cations and their potential for sensing phosphates

The synthesis of aqueous dispersion of spherical, underivatized silver nanoparticles (Ag-NPs) stabilized by macrocyclic polyammonium chlorides (MCPAC), [28]ane-(NH₂ ⁺)₆O₂·6Cl⁻ (28-MCPAC) and [32]ane-(NH₂ ⁺)₈·8Cl⁻ (32-MCPAC), which are evidently anion receptors, is reported. As-synthesized Ag-NPs are characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The 28/32-MCPAC-stabilized Ag-NPs show the surface plasmon band around 400 nm. The TEM-images show that the particles are spherical and well-dispersed. By tuning the 28/32-MCPAC:Ag-OAc (silver acetate) ratio, nanoparticles with different core diameters ranging from 13 to 8 nm for 28-MCPAC and from 10 to 6 nm for 32-MCPAC can be obtained. The advantage of using MCPAC as stabilizers is that they make the particles functionalized for sensing anions. Thus, the potential of the as-synthesized Ag-NPs for sensing phosphates: H₂PO₄ ⁻ (monobasic phosphate, MBP), HPO₄ ²⁻ (dibasic phosphate, DBP) and PO₄ ³⁻ (tribasic phosphate, TBP) is investigated spectroscopically. Interaction of phosphate ions with macrocyclic polyammonium cations makes the Ag-NPs bare, leading agglomeration. The phosphate-assisted agglomeration of 32-MCPAC-Ag-NPs follow the order TBP > DBP ≫ MBP. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Elektronenverluste in einem abklingenden Wasserstoffplasma

The time dependence of the electron density in the afterglow period of an electrodeless discharge in hydrogen was measured by means of 4- and 8-mm microwave interferometry. An exponential decay was observed in the late afterglow permitting the evaluation of a time constant in the density range from 10¹²–10¹⁰ electrons per cm³. The decay time of the plasma was influenced by the discharge conditions. Electron losses could be explained by ambipolar diffusion and attachment to impurities. Two diffusion coefficients were found correlated to the discharge duration. The mobility value H₀=10.1±1.0 cm²/V · sec calculated from the diffusion coefficient found for short discharge pulses agrees with Saporoschenkos mobility value μ₀=10.2 cm²/V · sec for the H ₃ ⁺ -ion. A second mobility value μ₀=14.8±1.2cm²/V · sec found for longer discharge pulses might refer to the H⁺-ion.     

New Fluorescent Antitumour Cisplatin Analogue Complexes. Study of the Characteristics of their Binding to DNA by Flow Injection Analysis

The flow injection technique is applied to study the binding to DNA of new platinum complexes—E₁: ethylenediaminechlorocholylglycinateplatinum(II): [PtCl(CG)(en)], C₅₄H₉₂O₁₂Pt and E₂: ethylenediaminebischolylglycinateplatinum(II): [Pt(CG)₂(en)], C₂₈H₅₀ClN₃O₆Pt—derived from cisplatin in which the exchangeable ligands were replaced by bile acids, such that these anticancer drugs have less toxicity and less resistance is developed towards them. Both compounds are fluorescent and their fluorescence is enhanced when they form adducts with DNA, a property that is extremely useful for monitoring the cytotoxic activity and their mechanisms of action. The binding parameters to DNA of E₁ [apparent intrinsic binding constant K_E1: (11.2 ± 0.4) × 10³ M⁻¹ and maximum number of binding sites per nucleotide, n _E1: 0.121 ± 2 × 10⁻³) and E₂ (K_E2: 9.2 ± 0.7) × 10³ M⁻¹ and n _E2 0.098 ± 2 × 10⁻³] were determined following the Scatchard method and the type of binding was studied experimentally through the modifications introduced by each of the compounds into the ethidium bromide–DNA bond.     

Chemisorption of H2 on W(100): Absolute sticking probability,coverage, and electron stimulated desorption

Measurements of both the absolute sticking probability near normal incidence and the coverage of H₂ adsorbed on W(100) at ~ 300K have been made using a precision gas dosing system; a known fraction of the molecules entering the vacuum chamber struck the sample crystal before reaching a mass spectrometer detector. The initial sticking probability S₀ for H₂/W(100) is 0.51 ± 0.03; the hydrogen coverage extrapolated to S = 0 is 2.0 × 10¹⁵ atoms cm^?2. The initial sticking probability S₀ for D₂/W(100) is 0.57 ± 0.03; the isotope effect for sticking probability is smaller than previously reported. Electron stimulated desorption (ESD) studies reveal that the low coverage β₂ hydrogen state on W(100) yields H⁺ ions upon bombardment by 100 eV electrons; the ion desorption cross section is ~ 1.8 × 10^?23 cm². The H⁺ ion cross section at saturation hydrogen coverage when the β₁ state is fully populated is ? 10^?25 cm². An isotope effect in electron stimulated desorption of H⁺ and D⁺ has been found. The H⁺ ion yield is ? 100 × greater than the D⁺ ion yield, in agreement with theory.     

Ion transport in proton conducting solid polymer electrolytes

In this communication the ion transport properties of polyvinyl alcohol complexed with orthophosphoric acid (H₃PO₄) have been investigated. The proton conduction is confirmed by hydrogen gas evolved at the cathode of the coulometer and the transference number of H⁺ ion has been determined. The transient ionic current (TIC) technique has been used to detect the mobile ionic species and their mobilities are evaluated. The ionic mobility was found to be of the order of 10⁻⁴ cm².V⁻¹.s⁻¹ for H⁺ ions. It is observed that the bulk electrical conductivity increases with the temperature following the Arrhenius type behaviour. Variation of charge carrier concentration with the molar ratio of H₃PO₄ in the sample reveals that the carrier concentration is largely affected by the amount of dopant in the complexes.