Chemical inhomogeneity of SiOx dissociation by catalytic Au at a relatively low temperature

Sporadic catalytic decomposition because of the presence of Au grains is a significant issue to be clarified in electronic devices. Here, we report the inhomogeneous dissociation of native silicon oxide depending on the electronic structure of Au grains using scanning photoelectron microscopy. Upon annealing, the oxygen atoms dissociated from native SiO_x layer out‐diffuses in non‐uniform manner, resulting in oxidize the Au layer. Valence band spectra showed that the spit‐orbit splitting, directly related to the coordination number, differs from site to site. Scanning photoelectron microscopy images show that dissociated SiO_x coincides with the regions where low‐coordinated Au resides. These results imply that Au with low coordination number activated the dissociation of SiO_x and open new pathway to remove undesirable oxide layer at relatively low temperature. Copyright © 2016 John Wiley & Sons, Ltd.     

Two-photon absorption in the collisionless gas phase: lifetimes of new vibrational levels in benzene

Two-photon photoselection has been demonstrated for a molecule in the low pressure gas phase. The excitation has been used to populate new vibrational levels in benzene under isolated molecule conditions down to 0.1 torr. The new states display unusual behaviour as compared to the lifetimes of one-photon excited states. Most unexpectedly the lifetimes of the strongest two-photon inducing mode ν₁₄ is longer than all other lifetimes, including that of the vibrationless ¹B_2u origin. Some theoretical explanations are offered.     

Effect of cation absorption on ionization/dissociation of cycloketone molecules in a femtosecond laser field

The mass spectra of a series of cycloketone molecules, cyclopentanone (CPO), cyclohexanone (CHO), cycloheptanone (CHPO), and cyclooctanone (COO) are measured in a 788 or 394 nm laser field with 90 fs pulse duration and the intensity ranging from 5 x 10(13) W/cm(2) to 2 x 10(14) W/cm(2). At 788 nm, a dominated parent ion peak and some weak peaks from the fragment ions C(n)H(m)+ are observed for CPO and CHO (a ratio P(+)/T(+), the parent ion yield to the total ion yield, is 81.6% and 52.6%, respectively). But the extensive fragment ion peaks are observed with the greatly reduced parent ion peak for CHPO (P(+)/T(+) = 5.5%) and that are even hard to be identified for COO. These observations are interpreted explicitly in the frame of the significant resonant effect of their cation photoabsorption on ionization and dissociation of these molecules. The present work also suggests that a nonadiabatic ionization occurs with a nuclear rearrangement due to the H movement in these molecules during the ionization in an intense femtosecond laser field.     

The absorption spectrum and dissociation constants of 4-hydroxybenzthiazole

The absorption spectra of 4-hydroxybenzthiazole and the parent compound, benzthiazole, have been determined in acidic, basic and neutral solutions, and compared with the corresponding absorption spectra of 8-hydroxyquinoline and quinoline. The dissociation constants of 4-hydroxybenzthiazole obtained by a spectrophotometric method as well as a potentiometric method, show that it is a stronger acid and a weaker base than 8-hydroxyquinoline.     

Effect of charge inhomogeneity and mobility on colloid aggregation

The aggregation of inhomogeneously charged colloids with the same average charge is analyzed using Monte Carlo simulations. We find aggregation of colloids for sizes in the range 10-200 nm, which is similar to the range in which aggregation is observed in several experiments. The attraction arises from the strongly correlated electrostatic interactions associated with the increase in the counterion density in the region between the particles; this effect is enhanced by the discreteness and mobility of the surface charges. Larger colloids attract more strongly when their surface charges are discrete. We study the aggregation as functions of the surface charge density, counterion valence, and volume fraction.     

Studies on the absorption spectra of aqueous l-tyrosine and its dissociation equilibria

The UV absorption spectra of aqueous tyrosine at various total ionic strengths were measured at known pH values at 298.2+/-0.2 K. The standard third dissociation constant of tyrosine was determined from the spectra by linear extrapolation and polynomial approximation. The results obtained from both methods are in good agreement within experimental error.     

UV absorption study of the dissociation of SO2 and SO in shock waves

The thermal decomposition of SO₂ and of the primary dissociation product SO have been studied in shock waves by the uv absorption technique. The controversy about SO₂ dissociation data from uv absorption signals was resolved and attributed to the extensive overlap of SO₂ and SO uv absorption spectra. The derived rate coefficients are k₁/[Ar] = 10^15.6 exp(-420 kJmol^?1/RT) cm³mol^?1 s^?1 (temperature range 3000–5000 K) for SO₂ dissociation, and k₃/[Ar] = 10^14.6 exp(-448 kJmol^?1/RT) cm³ mol^?1 s^?1 (temperature range 4000–6000 K) for SO dissociation. Anomalously high values of the apparent collision efficiencies β_c in SO₂ dissociation are attributed to marked contributions from excited electronic states.     

IR multiphoton absorption and isotopically selective dissociation of CHCIF2 in a herriott multipass cell

The small absorption is a major problem in isotopically selective IR multiphoton dissociation. Usually the radiation diverges before it is fully absorbed. To solve this problem, we have demonstrated the application of a refocusing (Herriott) multipass cell. It can generally help in laser isotope separation to use the photons more efficiently. Employing such a cell and a Q-switched CO₂ laser at high repetition rate, the dissociation yield of CHCIF₂ was 23 times higher than in a single pass. The number of passes used (up to 60) was more than is conventionally possible in such small cells. The increased number was permitted by making use of spherical aberration. With 18 passes, we also measured the multiphoton absorption for various wavelengths and pressures, in part separately for¹²CHCIF₂ and¹³CHCIF₂, and also for two-wavelength irradiation. Appropriate change of pressure or wavelength increased the absorption. But the corresponding increase of the dissociation was larger in every case. To explain this and other observations, we invoke the molecular distribution over the energy levels.     

Effect of induced and biographical inhomogeneity of the surface on multicenter adsorption equilibrium

We have studied the effect of inhomogeneity of the adsorbing surface on multicenter adsorption equilibrium. We have shown that in certain cases, the dependences obtained in the experiment can be equally well approximated by equations obtained on the basis of the concepts of one-center and multicenter adsorption. In the considered cases, multicenter adsorption equilibrium on an inhomogeneous surface is described by a logarithmic isotherm.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 746–749, November–December, 1989.     

Effect of rotational relaxation on isotopic selectivity of IR multiphoton dissociation

It is shown in experiments on CF₃Br that rotational relaxation may either increase or decrease the value of multiphoton dissociation selectivity. The mechanism of the influence of rotational relaxation on selective dissociation is analyzed.     

Emergence of charge-transfer-to-solvent band in the absorption spectra of hydrogen halides on ice nanoparticles: spectroscopic evidence for acidic dissociation

Extensive ab initio calculations complemented by a photodissociation experiment at 193 nm elucidate the nature of hydrogen halide molecules bound on free ice nanoparticles. Electronic absorption spectra of small water clusters (up to 5 water molecules) and water clusters doped with hydrogen fluoride, hydrogen chloride and hydrogen bromide were calculated. The spectra were modeled at the time-dependent density functional (TDDFT) level of theory with the BHandHLYP functional using the reflection principle. We observe the emergence of a charge-transfer-to-solvent (CTTS) band in the absorption spectra upon the acidic dissociation of the hydrogen halides. The CTTS band provides a spectroscopically observable feature for the acidic dissociation. The calculated spectra were compared with our new experimental photodissociation data for larger water clusters doped with HCl and HBr. We conclude that HCl and HBr dissociate to a large extent on the surface of ice nanoparticles at temperatures near 120 K and photoactive products are formed. The acidic dissociation of HX leads to an enhancement by about 4 orders of magnitude of the HCl photolysis rate in the 200-300 nm region, which is potentially relevant for the halogen budget in the atmosphere.     

Effect of different target gases on low-energy collision-activated dissociation of peptides

Experimental variables affecting the daughter-ion spectra of a series of protonated peptides [MH]+, produced by fast-atom bombardment ionization, using a low energy (0-450 eV) quadrupole collision cell are investigated. The parameters studied include target gas pressure, collision energy, cross-sectional area and acidity of the target gas. The results show that low-mass immonium ions are preferentially formed both at high collision energies (greater than 200 eV) and at target gas pressures greater than 10(-6) mBar (where multiple collisions occur in the gas cell). Positive fragment ion abundance is maximized when acidic gases are used as the target gases, and this is rationalized on the basis of a proton-transfer reaction from the target gas to the amide nitrogen of the peptide bond promoting fragmentation.     

Study of spatial inhomogeneity in inverted all‐polymer solar cells: Effect of solvent and annealing

The efficiency optimization of bulk heterojunction solar cells requires the control of the local active materials arrangement in order to obtain the best compromise between efficient charge generation and charge collection. Here, we investigate the large scale (10–100 μm) inhomogeneity of the photoluminescence (PL) and the external quantum efficiency (EQE) in inverted all‐polymer solar cells (APSC) with regioregular poly(3‐hexylthiophene) (P3HT):poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) active blends. The morphology and the local active polymer mixing are changed by depositing the active layer from four different solvents and by thermal annealing. The simultaneous PL and EQE mapping allowed us to inspect the effects of local irregularities of active layer thickness, polymer mixing, polymer aggregation on the charge generation and collection efficiencies. In particular, we show that the increase of the solvent boiling point affects the EQE non‐uniformity due to thickness fluctuations, the density non‐uniformity of rrP3HT aggregate phase, and the blend components clustering. The thermal annealing leads to a general improvement of EQE and to an F8BT clustering in all the samples with locally decrease of the EQE. We estimate that the film uniformity optimization can lead to a total EQE improvement between 2.7 and 6.3 times. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 804–813     

Quantitative characteristics of structure inhomogeneity of water

Inhomogeneity of the local surroundings of molecules was studied for water models obtained by the molecular dynamic method. For all 3456 molecules in an independent unit cell, the volume of the Voronoi polyhedron (VVP) constructed around the oxygen atom, the tetrahedricity index (T), and the potential energy of the molecule (E _pot) were calculated. Based on the values of these parameters, the molecules were grouped into two classes. The first class included molecules for which this parameter was smaller than a certain critical value; the second included molecules for which the parameter exceeded the critical value. The critical value was chosen (for each configuration) such that each class contained exactly 50% of all molecules. Then it was investigated how many molecules belonged to each of these classes among the four nearest neighbors of the given sort. Deviation from the value obtained for random distribution of molecules of two sorts can serve as a measure of structure inhomogeneity, which shows itself as the tendency of a molecule to be surrounded by alike molecules. Since approximately half of all molecules are donors (and acceptors) for two hydrogen bonds at room temperature (a ₂ d ₂ type of coordination), a similar procedure is applicable to types of coordination of molecules. Molecules with a ₂ d ₂ coordination can be assigned to one class, while all other molecules can be considered as belonging to the other. Inhomogeneity of structure is most conspicuous for distribution of molecules with low and high values of the VVP (this is especially true of the surroundings of molecules with small values of VVP). The environment of molecules with high values of E _pot and of molecules with surroundings other than a ₂ d ₂ is nearly random.     

Effect of broadband amplified spontaneous emission on absorption measurements in phase-shift off-axis cavity enhanced absorption spectroscopy

Phase-shift cavity enhanced absorption spectroscopy has been described for the case of an off-axis alignment of an optical cavity formed by high reflectivity mirrors. The effect of laser broadband amplified spontaneous emission (ASE) from a DFB diode laser (1605 nm) has been analysed for absorption measurements extracted from the phase-shift of the intensity modulated beam. A simple model has been proposed for extraction of actual absorption spectra and linestrengths from the phase and amplitude measurements. It has been shown that omitting the ASE contribution to the cavity output light intensity may lead to an overestimation of absorption linestrength.     

Effect of rapidly depressurizing and rising temperature on methane hydrate dissociation

Two methods, rapidly depressurizing to 0.1 MPa at a constant temperature and rising temperature under equilibrium P, T conditions, were used to study the dissociation of pure CH4 hydrate formed below the ice point. At a constant temperature with rapidly depressurizing to 0.1 MPa, CH4 hydrate dissociated rapidly at initial dissociation and then the dissociation rate gradually decreased. However, the dissociation of CH4 hydrate at temperatures of 261 to 266 K was much faster than that at temperatures of 269 to 272 K, indicating its anomalous preservation. Under an equilibrium P, T conditions, rising temperature had extensively controlling impact on dissociation of CH4 hydrate at equilibrium pressures of 2.31, 2.16 and 1.96 MPa. In this study, we report the effect of pressure on CH4 hydrate dissociation, especially the effect of equilibrium pressure on dissociation at various melting temperatures. And we find that the ice particles size of CH4 hydrate formed may dominant the CH4 hydrate dissociation. Dissociation of CH4 hydrate formed from ice particles of smaller than 250 μm may not have an anomalous preservation below the ice point, while particles larger than 250 μm may have more extensive anomalous preservation.     

Effect of pressure on dissociation of poly(methacrylic acid) in aqueous solution

The effect of pressure (up to 6300 atm) on the electrical conductivity of poly(methacrylic acid) (PMA) in aqueous solution was investigated in the concentration range 0.001M to 0.1M (in equivalents of carboxyl groups) at 30°C. The degree of ionization α calculated from the conductivity data increased linearly with pressure. From dilatometric measurements of volume changes when PMA was partially neutralized with NaOH, a conformational transition was confirmed to take place above α = 0.12, and the volume change accompanying the dissociation of the side chain groups (carboxyl groups) was found to be ? 12.5 ml/H⁺. It may be inferred from the values of α at each polymer concentration and from the dilatometric data that there is no conformational transition from a compact structure to the coiled form below at least 6,000 atm in the absence of Na⁺ counterions.