Ion-beam crystallography of clean and sulfur covered Ni(110)

Medium energy ion scattering has been used to determine the atomic structure of a Ni(110) surface covered with 0.5 monolayer of sulfur. After having confirmed that the sulfur atom resides in a fourfold-coordinated hollow site, it was found that its distance above the plane of the first Ni layer is 0.87 ± 0.03 Å. We measured a 6 ± 3% outward relaxation effect for the sulfur covered Ni(110) surface layer and an inward relaxation of 4 ± 1% when this surface is clean.     

ToF atom-probe fim investigation of surface segregation in dilute alloys

A time-of-flight atom-probe field ion microscope was successfully employed for the first time to investigate surface segregation in dilute alloys. We were able to achieve a single atomic layer resolution and obtained the absolute concentrations of alloy species of each surface layer. Cr atoms are found to segregate to the surface of Stainless Steel 410 whereas no segregation of the minority species was found for Pt-8% W and Pt-5% Ru. The first layer concentration of Cr in the {110} plane of Stainless Steel 410 at 500°C was found to be 38.5 ± 12.5% and 63.4 ± 10.2% respectively for samples with near surface layers Cr average concentration of 6.3 ± 2.1% and 11.9 ± 2.5%. The heat of segregation of Cr to the {110} plane of Stainless 410 was found to be 3.43 and 3.92 kcal/mole respectively from the two sets of data. The data also gives the difference in surface tensions between iron and chromium at this plane to be 269 and 282 erg/cm² respectively. Segregation studies on the {012} plane as well as on a grain boundary of Stainless Steel 410 were also done. In some cases, though the first surface layer is enriched with Cr in Stainless Steel 410, the near surface layers show a depletion of Cr. In Pt-8% W and Pt-5% Ru, our concentration depth profiles with a single atomic layer resolution show no segregation or depletion of the minority species either for the top layers or for the near surface layers.     

Edge atom depression on stepped Cu(410)

The position of the edge atoms of a stepped Cu(410) surface has been measured by Ion Scattering Spectroscopy using 21 keV H⁺. The edge atoms are depressed 5.0±1.5% of the copper lattice spacing, corresponding to 0.18±0.05 Å.     

Estimation of daytime radiative and soil heat fluxes at Trombay, Bombay (19.1° N, 72.8° E) using routine weather data

Summary This note presents estimates of hourly averages of insolation, net radiation and soil heat flux during daytime from solar-elevation angle and routine weather data on cloud cover and screen level air temperature using a formulation procedure generally adopted in surface layer parametrisation schemes. The estimation procedure employs commonly used forms of empirical relationships and the estimates are compared with the concurrent field observations at Trombay site in Bombay (19.1° N, 72.8° E) India. Wherever possible site-specific empirical coefficients are derived. Using the observed insolation, the net radiation and soil heat flux are respectively estimated within ±18% and ±14% of their observed values. Estimated insolation was found to be within ±37% of the observed values and, when used to derive the fluxes, the uncertainty increases to ±25% and ±27%, respectively.     

Development of an online X-ray fluorescence analysis system for heavy metals measurement in cement raw meal

ABSTRACT

Particulate matters, gaseous chemicals, and heavy metals emitted from industrial processes into the environment could be directly transmitted to humans through air inhalation. In order to accurately estimate health risk and control the source of pollution caused by cement raw meal, an online X-ray fluorescence analyzer system, consisting of an X-ray fluorescence analyzer with data acquisition software and a laser rangefinder, was developed to carry out the measurement of heavy metals in cement raw meal. The X-ray fluorescence analyzer was mounted on a sled, which can effectively smooth the surface of cement raw meal and reduce the impact of surface roughness during online measurement. The laser rangefinder was mounted over the sled for measuring the distance between cement raw meal sample and the analyzer. Several heavy metals and other elements in cement raw meal were online measured by the X-ray fluorescence analyzer directly above a conveyor belt. The limits of detection for Pb, Cr, Fe, Ti, Ca, and S by the analyzer were 47 ± 1, 33 ± 1, 37 ± 1, 44 ± 1, 246 ± 4, and 118 ± 1 mg kg^?1, respectively. The relative standard deviation (RSD) for the elements mentioned was less than 10.7%. By comparison with the results by inductively coupled plasma mass spectrometry (ICP-MS) and CHNS/O elemental analyzer, relative deviation (D) of the online X-ray fluorescence analyzer was less than 7.4% for Fe, Ti, Ca, and S, between 1.71% and 12.10% for Pb and Cr.     

The geometrical and vibrational properties of the Rh(111) surface

Low-energy electron diffraction (LEED) data have been used to characterize the clean Rh(111) surface. The surface geometry, the degree of surface relaxation, and the Debye temperature have been determined. In the Debye temperature measurement, specular LEED beam intensities were monitored as a function of temperature over a range of electron energies from approximately 30 to 1000 eV. It was found that the bulk Debye temperature is 380 ± 23 K, and the normal component of the Debye temperature at the lowest electron energy used is 197 ± 12 K. The Rh(111) surface relaxation has been determined both by a convolution-transform analysis and by dynamical calculations. Within experimental error, neither expansion nor contraction of the topmost layer has been detected. The results of the convolution-transform analysis of specular beams at two angles of incidence and of a nonspecular beam at normal incidence suggest an expansion of the topmost layer of 3 ± 5% of the bulk layer spacing. In agreement with this, comparisons between the results of the dynamical calculation and experimental data for five nonspecular beams at normal incidence suggest that the surface layer relaxes by 0 ± 5%. In addition, the dynamical calculations indicate that the topmost layer maintains an fcc structure.     

The structure of the c(2 × 2) oxygen overlayer on the unreconstructed (110) surface of iridium

An Ir(110)-c(2 × 2)O structure has been prepared by adsorbing a half-monolayer of oxygen at room temperature on an unreconstructed (1 × 1)Ir surface stabilized by a quarter-monolayer of randomly adsorbed oxygen. Results of the low energy electron diffraction structural analysis indicate that the ordered oxygen atoms are residing on the short-bridged sites on the (110) surface. The Ir-O interlayer spacing is 1.37 ± 0.05 Å, and the bond length is 1.93 ± 0.07 Å. The topmost substrate interlayer spacing is found to be 1.33 ± 0.07 Å rather than 1.26 ± 0.07 Å which is the topmost interlayer spacing of the unreconstructed (1× 1)Ir surface.     

Atomic structure of Fe {111}

A clean Fe {111} surface was prepared and studied with LEED (low-energy electron diffraction) and AES (Auger electron spectroscopy). A LEED intensity analysis was carried out with a new computational scheme (THIN) specially designed for short interlayer spacings. The results are, for the fust interlayer spacing, d₁₂ = 0.70 ± 0.03 Å and for the inner potential V₀ = 11.1 ± 1.1 eV, the confidence intervals referring to 95% confidence level. Thus, the Fe {111} surface is contracted 15.4% with respect to the bulk (0.827 Å).     

Thermal accommodation coefficients by high speed vibration of solid samples: VI. O2 and N2 on As(111) and Sb(111) single crystal surfaces

Translational γ_t and rotational γ_r energy accommodation coefficients are measured using a high speed vibrational method described earlier. For N₂ on cleaved As(111) single crystal surfaces γ_t = 0.34 ± 0.03, γ_r = 0.03 ± 0.03; on cleaved Sb(111) single crystal surfaces γ_t = 0.49 ± 0.02, γ_r = 0.06 ± 0.04. For O₂ on As(111) γ_t = 0.39 ± 0.02, γ_r = 0.02 ± 0.02; on Sb(111) γ_t = 0.56 ± 0.05, γ_r = 0.07 ± 0.06. (Uncertainties are statistical estimates of precision. In addition, it is possible that the results are systematically low by up to 10%.) Comparison with N₂ and O₂ accommodation coefficients measured by the same method on other metal substrates suggests that the antimony surface is covered by chemisorbed oxygen but that the arsenic surface is somewhat cleaner. The results are consistent with oxidation of these semimetals occurring by way of physisorbed gas precursor states.     

Multilayer relaxation of the Mg(0001) surface

We have Investigated the interplanar relaxation of the clean (0001)-(1 × 1) surface of magnesium at 100 K using a dynamical LEED I-V analysis. In contrast to almost all other metal surfaces, an expansion has been observed for the first interlayer spacing of this clean surface. Using an extended database, the results indicate that the first three interlayer spacings are relaxed from the bulk value by Δd₁₂ = +1.9 ± 0.3%, Δd₂₃ = +0.8 ± 0.4%, and Δd₃₄ = −0.4 ± 0.5%. A comparison of this observed multi relaxation with experimental and theoretical results for similar free-electron closepacked metal surfaces, e.g. Al(111), suggests that a surface expansion is a normal property of high electron density simple metals.     

On the contraction of the W(001)-(1 × 1) surface using LEED intensity analysis

Three recent independent attempts at deducing the W(001)-(1 × 1) surface structure by LEED beam intensity analysis have yielded contractions of the topmost layer spacing of 6 ± 6%, 11 ± 2%, 4.4 ± 3% normal to the surface plane. We investigate possible reasons for the discrepancies by comparing published experimental and theoretical profiles of these workers as well as our own. Our main conclusions are that the direct comparison of experimental data of different investigators shows deviations which are comparable to the changes in the calculated profiles for various surface contractions. Also the deviations between calculated intensity profiles using different (but still realistic) assumed scatteting potentials are comparable to the changes in the calculated profiles for various surface contractions. The main uncertainty in the scattering potential is the choice between the Slater free electron exchange-correlation term (coefficient α = 1) or the Kohn-Sham version ($\text{α =}\text{2}\text{3}$) or a value in between. For tungsten the corrections due to relativistic atomic scattering must also be considered. These uncertainties in the calculated and experimental profiles lead to the conclusion that the surface layer contraction of W(001)-(1 × 1) is not known at the present time. To assess the potential of LEED in deducing surface structures of this type further comprehensive analyses are required where the uncertainties in the theoretical scattering potential are also examined.     

Diffusion von Protonen (Tritonen) in Eiskristallen

The diffusion coefficient of tritons in ice crystals has been measured at different temperatures between 0°C and ?35°C. The applied method excludes any surface diffusion. The absolute value of the diffusion coefficient at ?7°C was determined as 2·10^?11 cm²/sec (±10%) and the activation energy as 13,5 kcal/mole (±8%). The activation energy of proton (triton)-diffusion is therefore consistent with the activation energy found for the dielectric and mechanical relaxation of protons in ice. The importance of this consistency relative to the diffusion mechanism is discussed.     

Radiation damage in single-crystal ice studied by 100 keV proton channeling

A detailed study has been undertaken of the Ni{100} (2 × 2)C structure formed by cracking ethylene on a clean Ni{100} surface. The LEED pattern shows characteristic missing spots which can be attributed to the presence of glide lines and indicate a space group symmetry of p4g. We show that this can be readily interpreted in terms of a distortion of the top nickel layer both parallel and perpendicular to the surface, which accompanies the carbon adsorption. Detailed comparisons of LEED intensity data with dynamical calculations indicate that the top layer nickel atoms are displaced 0.35 ± 0.05 Å parallel to the surface, 0.20 ± 0.05 Å outwards from the surface, and that the carbon atoms are in 4-fold hollows (now distorted) at a spacing of 0.1 ± 0.1 Å from the surface. These conclusions lead to a nickel-carbon nearest neighbour spacing of 1.803 ± 0.015 Å.     

An in vitro thermal analysis during different light-activated hydrogen peroxide bleaching

This study measured the critical temperature reaching time and also the variation of temperature in the surface of the cervical region and within the pulp chamber of human teeth submitted to dental bleaching using 35% hydrogen peroxide gel activated by three different light sources. The samples were randomly divided into 3 groups (n = 15), according to the catalyst light source: Halogen Light (HL), High Intensity Diode Laser (DL), and Light Emmited Diode (LED). The results of temperature variation were submitted to the analysis of variance and Tukey test with p < 0.05. The temperature increase (mean value and standard deviation) inside the pulp chamber for the HL group was 6.8 ± 2.8°C; for the DL group was 15.3 ± 8.8°C; and for the LED group was 1.9 ± 1.0°C for. The temperature variation (mean value and standard deviation) on the tooth surface, for the group irradiated with HL was 9.1 ± 2.2°C; for the group irradiated with DL were 25.7 ± 18.9°C; and for the group irradiated with LED were 2.6 ± 1.4°C. The mean temperature increase values were significantly higher for the group irradiated with DL when compared with groups irradiated with HL and LED (p < 0.05). When applying the inferior limits of the interval of confidence of 95%, an application time of 38.7 s was found for HL group, and 4.4 s for DL group. The LED group did not achieve the critical temperatures for pulp or the periodontal, even when irradiated for 360 s. The HL and DL light sources may be used for dental bleaching for a short period of time. The LED source did not heat the target tissues significantly within the parameters used in this study.     

The effect of power bleaching actived by several light sources on enamel microhardness

The purpose of this study was to evaluate the influence of different light sources for in-office bleaching on surface microhardness of human enamel. One hundred and five blocks of third molars were distributed among seven groups. The facial enamel surface of each block was polished and baseline Knoop microhardness of enamel was assessed with a load of 25 g for 5 s. Subsequently, the enamel was treated with 35% hydrogen peroxide bleaching agent and photo-activated with halogen light (group A) during 38 s, LED (group B) during 360 s, and high intensity diode laser (group C) during 4 s. The groups D (38 s), E (360 s), and F (4 s) were treated with the bleaching agent without photo-activated. The control (group G) was only kept in saliva without any treatment. Microhardness was reassessed after 1 day of the bleaching treatment, and after 7 and 21 days storage in artificial saliva. The mean percentage and standard deviation of microhardness in Knoop Hardness Number were: A 97.8 ± 13.1 KHN; B 95.5 ± 12.7 KHN; C 84.2 ± 13.6 KHN; D 128.6 ± 20.5 KHN; E 133.9 ± 14.2 KHN; F 123.9 ± 14.2 KHN; G 129.8 ± 18.8 KHN. Statistical analysis (p < 0.05; Tukey test) showed that microhardness percentage values were significantly lower in the groups irradiated with light when compared with the non-irradiated groups. Furthermore, the non-irradiated groups showed that saliva was able to enhance the microhardness during the measurement times. The enamel microhardness was decreased when light sources were used during the bleaching process and the artificial saliva was able to increase microhardness when no light was used.     

SrTiO3基片的晶体质量及表面粗糙结构的X射线研究

用X射线双晶衍射摇摆曲线以及双晶X射线形貌对两个SrTiO₃基片的单晶质量进行了对比研究，并用X射线掠入射镜面反射及漫散射研究了它们的表面粗糙结构．结果表明，两个SrTiO₃基片中都存在镶嵌缺陷，其中一个样品的晶体质量相对较高．两个样品的表面粗糙结构相差很大，包括均方根粗糙度σ和横向相关长度ξ．σ分别为（0.5±0.1）和（1.3±0.1）nm，ξ分别为（1200±200）和（300±20）nm．样品的表面粗糙将增加Ｘ射线的漫散射强度而降低镜面反射的强度．晶体质 关键词：     

Intense mass-separated beams of halogens and beta-delayed neutron emission from heavy bromine isotopes

Improved production yields of short-lived halogens were obtained from a ThO₂ target, irradiated with 600 MeV protons, in combination with a negative surface ionization source. Mass-separated samples were studied by decay spectroscopy. Production yields of radioactive isotopes of chlorine, bromine, iodine and astatine are presented. Half-lives and relative neutron emission probabilities were measured for the heavy bromine isotopes^89?92Br. Normalizing to earlier publishedP _n values for⁸⁹Br, the results are:⁸⁹Br (4.30±0.14s,P _n =13.6±0.8%),⁹⁰Br (1.92±0.06s,P _n =24.8±1.5%),⁹¹Br (0.53 ±0.03 s,P _n =30.1 ±2.1%), and⁹²Br (0.31 ±0.02 s,P _n =34.6±2.5%). Energy spectra ofβ-delayed neutrons were measured.     

High temperature coadsorption study of zirconium and oxygen on the W(100) crystal face

The coadsorption of zirconium and oxygen on W(100) has been studied by Auger electron spectroscopy, low energy electron diffraction, mass spectroscopy, ion sputtering, and work function measurement techniques. Adsorption of zirconium onto W(100) followed by heating in an oxygen partial pressure produces rapid diffusion of a ZrO complex into the bulk and the formation of a tungsten oxide layer. Heating in vacuum causes desorption of the tungsten oxide and segregation of the ZrO complex to the surface. The activation energy for the ZrO bulk-to-surface diffusion is 30 ± 2 kcal/mole. Upon heating in vacuum at 2000 K the composite surface exhibits predominantly a (1 × 1) LEED structure with a room temperature field emission retarding potential work function of 2.67 ± 0.05 eV. The Richardson work function for this unusually thermally stable surface is 2.56 ± 0.05 eV with a pre-exponential of 6 ± 2. The effects of carbon and nitrogen contamination on this low work function ZrOW composite surface are discussed and a structural model for the surface is presented.     

Effect of temperature on surface composition of Cu-Sn and Ag-Sn alloys; an ESCA study

Cu-Sn and Ag-Sn alloys containing 5% Sn were studied by ESCA. The heats of surface segregation of Sn obtained from equilibrium measurements of the surface composition as a function of temperature were found to be 12.0 ± 1.0 and 3.5 ± 1.0 kcal/mol for Cu-Sn and Ag-Sn alloys, respectively. These results are compared with the predictions of existing theories. Possible reasons for the difference between the experimental result and theoretical prediction are also discussed.     

Atomic structure of the scandium (0001) surface

The atomic structure of the scandium (0001) surface has been determined through a lowenergy-electron-diffraction analysis. Intensity profiles calculated on the basis of different structural models corresponding to different terminations of the bulk structure were compared to the experimental data. The comparison showed that the surface of scandium terminated in hep stacking and that the outermost layer spacing is 2.59 ± 0.02 Å corresponding to a ～2% contraction with respect to the bulk spacing (2.64 Å).