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1.
Photostimulated ion desorption at the 4a 1 ← N 1s resonant transition of condensed NH 3 was studied using electron emission spectroscopy and Auger-electron photoion coincidence (AEPICO) spectroscopy. The total ion yield divided by the Auger-electron yield exhibited a threshold peak at hν = 399 eV which is ascribed to the resonant transition from the N 1s to the N---H antibonding 4a 1 orbital. The electron emission spectrum at the 4a 1 ← N 1s resonance is decomposed into three components: a valence photoelectron emission spectrum, and normal- and resonant-Auger-electron emission spectra. We ascribe the resonant-Auger-electron emission spectrum mainly to spectator-Auger transitions on the basis of the peak assignment. A series of AEPICO spectra at the 4a 1 ← N 1s resonance was also measured as a function of the Auger-electron kinetic energy. The electron kinetic energy dependence of the H + AEPICO yield displays a shape approximately similar to that of the mixed spectrum of normal- and spectator-Auger-electron emission spectra. Based on this result the H + desorption at the 4a 1 ← N 1s resonance is concluded to originate from the spectator-Auger transitions and from the normal-Auger transitions following the delocalization of the excited electron. 相似文献
2.
Auger-electron-photoion coincidence (AEPICO) studies of photon-stimulated ion desorption (PSID) for condensed acetonitrile induced by carbon core excitation have been performed to elucidate the desorption mechanism related to the Auger process. We have detected only the H + ion in AEPICO spectra. The total ion yield spectrum divided by the total electron yield shows that the desorption efficiency is largely increased at the resonant excitation to C---H*. We have also measured the Auger electron spectrum and the AEPICO yield spectrum at the C---H* excitation. The AEPICO yield spectrum shows enhancement at 245–250 eV electron energy. This seems to be related to the spectator resonant Auger stimulated ion desorption. That is, H + desorption is enhanced due to a two-hole-one-electron state at which the electron is in an anti-bonding C---H* orbital and the two holes can be in a 1π bonding orbital localized on the ---CH 3 group. We have also measured similar spectra for other resonant excitation (π* CN, σ* CC, σ* CN). The results are discussed in connection with the bonding/anti-bonding character and localized character of the excited state. 相似文献
3.
Auger electron-photoion coincidence (AEPICO) spectroscopy, which has been recently developed and proved to be a very powerful technique for investigating the dynamics of desorption induced by the core-level excitation, is applied to the investigation of Auger-stimulated ion desorption from the chemisorbed-water-Si(100) surface induced by O 1s excitation. It is shown that the fast relaxation of the excited state with a core hole and an excited electron takes place before the core hole decay, and that the desorption yield is enhanced by the shake-up (and/or shake-off) excitation. The relative cross-section for Auger-stimulated ion desorption is estimated, and is shown to increase as holes are created at deeper levels of the valence bands as the final state of the Auger decay. A comparison is also made with condensed H 2O. 相似文献
4.
The electron-stimulated desorption (ESD) of D − and H − ions from condensed D 2O and H 2O films is investigated. Three low-energy peaks are observed in the ESD anion yield, which are identified as arising from excitation of 2B 1, 2A 1 and 2B 2 dissociative electron attachment (DEA) resonances. Additional structure is observed between 18 and 32 eV, which may be due to ion pair formation or to DEA resonances involving the 2a 1 orbital. The ion yield resulting from excitation of the 2B 1 resonance increases as the film is heated. We attribute the increase in the ion yield to thermally induced hydrogen bond breaking near the surface, which enhances the lifetimes of the excited states that lead to desorption. 相似文献
5.
The adsorption of D 2O on Zr(0001) at 80 K and its subsequent reactions at higher temperatures have been studied by thermal desorption spectroscopy (TDS), work-function measurements (Δф), nuclear reaction analysis (NRA), LEED, infrared reflection spectroscopy (FTIR-RAS), Auger electron spectroscopy (AES), and static secondary ion mass spectroscopy (SSIMS). D 2O adsorption on Zr(0001) at 80 K is accompanied by a Δф of −1.33 eV. The adsorbed D 2O can be characterized into three layers by TDS: a chemisorbed layer (up to 0.23 ML), a second adsorbed layer, and an ice layer. The chemisorbed D 2O dissociates into OD ad and D ad at 80 K (possibly also into O ad) and no desorption products could be detected, implying that the reaction products dissolved into the zirconium at temperatures appropriate for each component. The ice layer and most of the second adsorbed layer desorb as molecular water during heating. The water adsorbed at 80 K did not form any long-range ordered structure, but a (2 × 2) LEED pattern that was formed by heating the sample to temperatures above 430 K is believed due to be an ordered oxygen superstructure. 相似文献
6.
The reactions of Si(100) and Si(111) surfaces at 700 °C (973 K) with ethylene (C 2H 4) at a pressure of 1.3×10 −4 Pa for various periods of time were studied by using Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS). For a C 2H 4 exposure level, the amount of C on the (111) surface was larger than that on the (100) surface. The formation of β-SiC grain was deduced by comparing the C KLL spectra from the sample subjected to various C 2H 4 exposure levels, and from β-SiC crystal. 相似文献
7.
Photon-stimulated ion desorption from deuterated formic acid chemisorbed on Si(100) has been studied using pulsed synchrotron radiation in the energy region of the oxygen 1s electron excitation. The O 1s electrons of hydroxyl oxygen and carbonyl oxygen could be selectively excited in the O K-edge region because the chemical environments are different. It is found that the CDO + yield is enhanced at the O 1s(C---O)→σ*(C---O) resonance and the CD + yield at the O 1s(C=O)→σ*(C---O) resonance. The results indicate that ion desorption is related both to the antibonding character of excited molecular orbitals and the local character of core hole orbitals. 相似文献
8.
The oxidation of CoGa(1 0 0) at 700 K was studied by means of high resolution electron energy loss spectroscopy (EELS), scanning tunneling microscopy, low energy electron diffraction and Auger electron spectroscopy (AES). At 700 K, thin well-ordered β-Ga 2O 3 films grow on CoGa(1 0 0). The EEL spectrum of the Ga-oxide films exhibit Fuchs–Kliewer phonons at 305, 455, 645, and 785 cm −1. For low oxygen exposure (<0.2 L), the growth of oxide-islands starts at step edges and on defects. The oxide films have the shape of long, rectangular islands and are oriented in the [1 0 0] and [0 1 0] directions of the substrate. For higher oxygen exposure, islands of β-Ga 2O 3 are found also on the terraces. After an exposure of 200 L O 2 at 700 K, the CoGa(1 0 0) surface is homogeneously covered with a thin film of β-Ga 2O 3. 相似文献
9.
The room temperature adsorption of N 2O on the clean Si(001)2 × 1 surface was used as a model system in an Auger electron spectroscopy (AES) study presented in this paper. Earlier experimental and recent theoretical work have provided evidence that this reaction evolves in discernible stages each exhibiting different adsorption geometries for the oxygen atom. In this AES study the intensity ratio of the KL 1L 1 and KL 2,3L 2,3 O Auger transitions, , was measured as a function of the fractional oxygen coverage, θ, and compared with our calculated intensity ratios and binding energy measurements of the O 1s photoelectron from literature. As a result we have found, for the first time, that (θ) can be related to a specific adsorption geometry in the submonolayer range. Moreover, we have found experimental evidence for an intermediate stable O adsorption state on the dimer at low coverage (θ 0.2 monolayer), as proposed earlier from theoretical studies. 相似文献
10.
We have studied the interaction of low-energy (5–50 eV) electrons with nanoscale (10 ML) ice films by probing the yields and quantum-state distributions of the neutral dissociation products using laser resonance-enhanced multiphoton ionization spectroscopy. In particular, we have observed the electron-stimulated desorption (ESD) of D ( 2S), O ( 3P 2) and O ( 1D 2) from amorphous D 2O films. These products are observed at threshold energies (relative to the vacuum level) between 6.5–7 eV and desorb with low kinetic energies (60–85 meV) which are independent of the incident electron energy. We associate the ESD of atomic fragments from ice with dissociation of Frenkel-type excitons of 4a 1 character which are near the bottom of the ice conduction band. These excitons are created either directly or via electron-ion recombination. Changing the surface temperature from 88 to 145 K results in an increase in the thermal component of the time-of-flight (kinetic energy) distributions and an overall increase in the neutral fragment yield. We suggest that the change in neutral yield with substrate temperature results from a combination of: (1) increased electron-ion recombination; (2) exciton transport to the near-surface region; and (3) dissociation followed by inelastic scattering and desorption. 相似文献
11.
Atomic oxygen coverages of up to 1.2 ML may be cleanly adsorbed on the Au(111) surface by exposure to O 3 at 300 K. We have studied the adsorbed oxygen layer by AES, XPS, HREELS, LEED, work function measurements and TPD. A plot of the O(519 eV)/Au(239 eV) AES ratio versus coverage is nearly linear, but a small change in slope occurs at ΘO=0.9 ML. LEED observations show no ordered superlattice for the oxygen overlayer for any coverage studied. One-dimensional ordering of the adlayer occurs at low coverages, and disordering of the substrate occurs at higher coverages. Adsorption of 1.0 ML of oxygen on Au(111) increases the work function by +0.80 eV, indicating electron transfer from the Au substrate into an oxygen adlayer. The O(1s) peak in XPS has a binding energy of 530.1 eV, showing only a small (0.3 eV) shift to a higher binding energy with increasing oxygen coverage. No shift was detected for the Au 4f 7/2 peak due to adsorption. All oxygen is removed by thermal desorption of O 2 to leave a clean Au(111) surface after heating to 600 K. TPD spectra initially show an O 2 desorption peak at 520 K at low ΘO, and the peak shifts to higher temperatures for increasing oxygen coverages up to ΘO=0.22 ML. Above this coverage, the peak shifts very slightly to higher temperatures, resulting in a peak at 550 K at ΘO=1.2 ML. Analysis of the TPD data indicates that the desorption of O 2 from Au(111) can be described by first-order kinetics with an activation energy for O 2 desorption of 30 kcal mol −1 near saturation coverage. We estimate a value for the Au–O bond dissociation energy D(Au–O) to be 56 kcal mol −1. 相似文献
12.
The effect of adsorbate coverage, adsorption sequence and temperature on the structure, composition and reactivity of coadsorbed layers, produced by dissociative adsorption of O 2 and H 2 at 200 K on a Rh(100) surface, has been studied by combined TPD, XPS and LEED measurements. The emphasis is on the impact of the structure and composition of the mixed O + H layers on the synthesis of hydroxyl and water as a result of the O + H surface reaction. The difference in the O 1s binding energies of adsorbed O (529.9 eV) and OH species (530.8 eV) was used as a fingerprint to monitor the formation of the OH species. The H 2O TPD spectra show substantial variations of the desorption temperature range and the amount of water evolved with coadsorbate coverage and structure: from 270 to 350 K and from 0 to 0.08 ML, respectively. It has been found that dense O + H adlayers, where the O coverage is in the range 0.25-0.4 ML, favor the formation of stable OH species. The maximum amount of stable hydroxyl OH species ( 0.16 ML) can be produced by heating of these dense adlayers to 260 K. This results in reordering of the adspecies to form a new O + OH − (2 × 6) structure, where hydroxyls react readily to evolve 0.08 ML of water in a sharp desorption peak at 280 K. The effect of the adlayer density and restructuring on the production of OH and H 2O is discussed. 相似文献
13.
The surface chemistry of indium tin oxide (ITO) has been investigated with Auger electron spectroscopy (AES) and high resolution electron energy loss spectroscopy (HREELS). A vibrating Kelvin probe (KP) with a graphite reference was used to monitor the absolute work function ( Φ) of ITO as a function of chemical modification. The ITO was exposed in situ to molecular hydrogen (H 2), hot-filament-activated oxygen (O 2*), and hot-filament-activated deuterium (D 2*). The initial Φ of ITO was determined to be 5.2 eV, and surface chemical changes had strong effects on this value, as seen by KP. Exposure of clean ITO to O 2* increased Φ to 5.6 eV, but the increase was short-lived. The changes in Φ over time were correlated with the uptake of carbon impurities in ultra high vacuum (UHV), as monitored by AES. The HREELS of ITO revealed significant hydrocarbon impurities. Chemical reduction of ITO produced a metallic surface and dehydrogenated the adsorbed hydrocarbons. Both re-oxidation of metallic ITO and oxidation of clean ITO temporarily removed adventitious carbon from the surface, but oxidized ITO adsorbed an even larger quantity of carbon over time. 相似文献
14.
This paper extends a previous study (Pehrsson and Mercer, submitted to Surf. Sci.) on unheated, hydrogenated, natural diamond (100) surfaces oxidized with thermally activated oxygen (O *2). In this paper, the oxidation is performed at substrate temperatures from Tsub=24 to 670°C. The diamond surface composition and structure were then investigated with high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and low energy electron diffraction (LEED). The oxygen coverage (θ) increased in two stages, as it did during oxidation at T<80°C. However, there are fundamental differences between the oxidation of nominally unheated and heated diamond surfaces. This difference is attributed to simultaneous adsorption and rapid desorption of oxygen species at higher temperatures; the desorption step is much slower without heating. The initial oxidation rates were similar regardless of the substrate temperatures, but the peak coverage (θ) was lower at higher temperatures. For example, θ plateaued at 0.4±0.1 ML at 600°C. The lower saturation coverage is again attributed to oxygen desorption during oxidation. Consistent results were obtained on fully oxidized surfaces, which when heated in vacuum to Tsub=600°C, lost 60% of their adsorbed oxygen. ELS revealed few C=C dimers on the oxidized surfaces, and more graphitization than on unheated surfaces. Oxidation at elevated temperatures also increased the carbonyl to ether ratio, reflecting etching-induced changes in the types of surface sites. The carbonyl and C–H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. The oxygen types did not interconvert when the oxidized surfaces were heated in vacuum. Oxygen desorption generated a much more reactive surface than heating-induced dehydrogenation of the smooth, hydrogenated surface. 相似文献
16.
In order to study the effect of chromium ion implantation on the aqueous corrosion behavior of zirconium, specimens were implanted by chromium ions with a dose range from 1×10 16 to 1×10 17 ions/cm 2, using MEVVA source at an extracted voltage of 40 kV. The valence and elements penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the micro-morphology and microstructure of chromium-implanted samples. The potentiodynamic polarization measurement was employed to value the aqueous corrosion resistance of zirconium in a 1N H 2SO 4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium compared with that of as-received zirconium. The mechanism of the corrosion resistance improvement of chromium-implanted zirconium is probably due to the addition of the chromium oxide dispersoid into the zirconium matrix. 相似文献
17.
The chemistry of methyl species resulting from the decomposition of dimethylmercury (DMM) and dimethylzinc (DMZ) on Pt(111) in the range 300–400 K has been investigated by temperature prograrnmed desorption (TPD) and Auger electron spectroscopy (AES). In each case at 300 K, dissociative adsorption of the precursor results in the formation of an adlayer of methylmetal (CH 3M) moieties. These species are thermally stable to around 350 K before decomposing to yield mainly gaseous products, methane and hydrogen, and surface bound metal atoms. For DMM, subsequent heating to 400 K or direct dissociative adsorption at 400 K results in the formation of ethylidyne species. Ethylidyne formation is not observed in the thermal chemistry of DMZ at temperatures below 400 K and only transiently in the chemistry at 400 K. Complementary TPD and AES data indicate that, for DMM, desorption of the mercury atoms produced by CH 3Hg decomposition is the limiting factor in allowing the prevailing C 1 species to couple to form ethylidyne. In contrast, AES evidence indicates that zinc atoms remain on the surface to temperatures in excess of 750 K and hence prevent C---C coupling by blocking surface sites. 相似文献
18.
The effects of potassium on the adsorption and dissociation of CH 3Cl on a Pd(100) surface has been investigated by ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy (AES), electron energy loss spectroscopy (in the electronic range EELS), temperature-programmed desorption (TPD) and work function change. In contrast to the clean surface, the adsorption of CH 3Cl caused a significant work function increase, 0.9-1.4 eV, of potassium-dosed Pd. Preadsorbed K enhanced the binding energy of CH 3C1 to the surface and induced the dissociation of adsorbed molecules. The extent of the dissociation increased almost linearly with the potassium content. The appearance of a new emission in the UPS spectrum at 9.2 eV, attributed to adsorbed CH 3 species, and the low-temperature formation of ethane suggest that a fraction of adsorbed CH 3Cl dissociates even at 115–125 K on potassium-dosed Pd(100). At the same time, a significant part of adsorbed CH 3 radical is stabilized, the reaction of which occurs only at 250–300 K. By means of TPD measurements, H 2, CH 4, C 2H 6, C 2H 4, KCl and K were detected in the desorbing gases. The results are interpreted by assuming a through-metal electronic interaction at low potassium coverage and by a direct interaction of the Cl in the adsorbed CH 3Cl with potassium at high potassium coverage. The latter proposal is supported by the electron excited Auger fine structure of the Cl signal and by the formation of KCl in the desorbing gases. 相似文献
19.
The relative spectral intensity of the band-like two M 4,5-hole state to the atomic-like localized one is much suppressed in the coincidence M 3–M 4,5M 4,5 super Coster–Kronig (sCK) electron spectrum of Cu metal compared to the one in the coincidence L 3–M 4,5M 4,5 Auger electron spectroscopy (AES) spectrum. The M 3-hole lifetime width of Cu metal is calculated by an ab initio atomic many-body theory (the extended relaxed core random phase approximation with exchange). The calculated M 3-hole lifetime width of Cu metal agrees well with the experimental one. The M 3–M 4,5M 4,5 sCK decay width of Cu metal decreases much with delocalization of the two M 4,5 holes in the sCK final state, whereas the Auger decay width is fairly independent of localization and delocalization of the two M 4,5 holes in the Auger final state. Thus, the relative spectral intensity of the band-like state is much suppressed in the coincidence M 3–M 4,5M 4,5 sCK-electron spectrum of Cu metal compared to the one in the coincidence L 3–M 4,5M 4,5 AES spectrum. 相似文献
20.
Adsorption and decomposition of triethylindium (TEI: (C 2H 5) 3In) on a GaP(0 0 1)-(2×1) surface have been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). It is found from the TPD result that ethyl radical and ethylene are evolved at about 300–400 and 450–550 K, respectively, as decomposition products of TEI on the surface. This result is quite different from that on the GaP(0 0 1)-(2×4) surface. The activation energy of desorption of ethyl radical is estimated to be about 93 kJ/mol. It is suggested that TEI is adsorbed molecularly on the surface at 100 K and that some of TEI molecules are dissociated into C 2H 5 to form P–C 2H 5 bonds at 300 K. The vibration modes related to ethyl group are decreased in intensity at about 300–400 and 450–550 K, which is consistent with the TPD result. The TEI molecules (including mono- and di-ethylindium) are not evolved from the surface. Based on the TPD and HREELS results, the decomposition mechanism of TEI on the GaP(0 0 1)-(2×1) surface is discussed and compared with that on the (2×4) surface. 相似文献
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