首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
郭元恒  贾存利 《物理学报》1988,37(7):1103-1109
长期暴露于大气的多晶镍样品,经700℃2小时真空退火及常温和500℃暴露氧20—60L后,发现其表面将产生两种电子诱导脱附(ESD)氧正离子。所对应的电子能量阈值分别为29eV和23eV。我们认为,两种氧正离子的产生机制为俄歇诱导脱附。29eV阈能者对应于镍表面化学吸附氧的2s能级电子向真空中电离;而23eV阈能者则对应于表面层中未与镍化合的自由氧的2s电子向体内费密能级跃迁。 关键词:  相似文献   

2.
Absolute cross sections for electron impact ionization and dissociation of OH+ and OD+ leading to the formation of the OH2+, O+, O2+, O3+ and D+ ions have been measured by applying the animated electron-ion beam method in the energy range from the respective reaction thresholds up to 2.5 keV. The maximum of the single ionization cross section is found to be (0.95? ± ?0.02) × 10?19 cm2 at 155 eV. The maximum total cross sections for O+ and D+ fragments production are observed to be (15.7? ± ?0.2) × 10?17 cm2 at 95 eV and (10.8? ± ?0.5) × 10?17 cm2 at 95 eV, respectively. The cross sections for O2+ and O3+ are much smaller, (5.37? ± ?0.04) × 10-18 cm2 at 135 eV and (7.95? ± ? 0.23) × 10-20 cm2 at 315 eV, respectively. The collected data are analyzed in details in order to determine separately the contributions of dissociative excitation and of dissociative ionization to the O+ and D+ fragments production.  相似文献   

3.
The photoabsorption, photoionization and fragmentation of O2 have been studied using electron impact coincidence methods to obtain branching ratios and dipole oscillator strengths (cross-sections). The photoabsorption measurements cover the energy range 5–300 eV while the formation of electronic states of O2+ (photoelectron spectroscopy) and the resulting ionic fragmentation (photoionization mass spectrometry) are both measured from close to threshold up to photon energies of 75 eV. The binding energy spectra of O2 show peaks at 33, 47 and 57 eV in addition to those reported elsewhere in the literature. These peaks are assigned to multiple final ion states arising from photoionization of the inner valence orbitals. Structure in the O2+ electronic state partial oscillator strength curves is in good agreement with recent theoretical work which predicts the existence of several shape resonances. A quantitative picture of the dipole-induced breakdown of O2 is obtained for the energy range 12–75 eV. The photoionization efficiency is found to be constant above 20 eV.  相似文献   

4.
《Solid State Ionics》1987,22(4):305-312
The relative attenuation of compressional sound waves of frequencies 10–60 MHz in mixed alkali (Na/K) mixed phase (β″/β)-aluminas is reported for temperatures 80–550 K. The internal friction peaks shift to higher frequencies at higher temperatures and are attributed to Na+ interactions in Naβ″/β alumina and Na+ and K+ in NaK β″/β alumina. The broad attenuation peaks occuring at low temperatures (< 300 K) and at higher temperatures (> 400 K) suggest multi-relaxation processes giving a distribution of activation energies. The estimated average activation energy for Na+ diffusion in Naβ″/βAl2 O3 at low temperatures and high temperatures is 0.183 eV and 0.387 eV respectively. In the NaK β″/βAl2o3 samples, the Na + values were 0.239 eV and 0.386 eV, respectively. The estimated average activation energies for K+ diffusion at low and high temperatures in the Kβ″/β-alumina samples were 0.269 eV and 0.371 eV and for K+ in the NaK β″/β samples, 0252 eV and 0.339 eV, respectively. The low temperature attenuation peaks were interpreted in terms of ionic interaction in the bulk and the high temperature peaks were related to interactions in the grain boundaries. The measured activation energies confirmed these interpretations. A reversal of the temperature appearance of the Na+ and K+ high temperature peaks in the NaKβ″/βAl2 O3 is explained by the disorder at the grain boundaries.  相似文献   

5.
Electron energy loss spectra (ELS) have been obtained from polycrystalline Cr and Cr2O3 before and after surface reduction by 2 keV Ar+ bombardment. The primary electron energy used in the ELS measurements was systematically varied from 100 to 1150 eV in order to distinguish surface versus bulk loss processes. Two predominant loss features in the ELS spectra obtained from Cr metal at 9.0 and 23.0 eV are assigned to the surface and bulk plasmon excitations, respectively, and a number of other features arising from single electron transitions from both the bulk and surface Cr 3d bands to higher-lying states in the conduction band are also present. The ELS spectra obtained from Cr2O3 exhibit features that originate from both interband transitions and charge-transfer transitions between the Cr and O ions as well as the bulk plasmon at 24.4 eV. The ELS feature at 4.0 eV arises from a charge-transfer transition between the oxygen and chromium ions in the two surface layers beneath the chemisorbed oxygen layer, and the ELS feature at 9.8 eV arises from a similar transition involving the chemisorbed oxygen atoms. The intensity of the ELS peak at 9.8 eV decreases after Ar+ sputtering due to the removal of chemisorbed oxygen atoms. Sputtering also increases the number of Cr2+ states on the surface, which in turn increases the intensity of the 4.0 eV feature. Furthermore, the ELS spectra obtained from the sputtered Cr2O3 surface exhibit features characteristic of both Cr0 and Cr2O3, indicating that Ar+ sputtering reduces Cr2O3. The fact that neither the surface- nor the bulk-plasmon features of Cr0 can be observed in the ELS spectra obtained from sputtered Cr2O3 while the loss features due to Cr0 interband transitions are clearly present indicates that Cr0 atoms form small clusters lacking a bulk metallic nature during Ar+ bombardment of Cr2O3.  相似文献   

6.
Studies have been made of the emission spectrum of MgO crystals induced by X-irradiation at 90 K. Two bands (half-widths ~0.8 eV) were observed to peak at 4.95 and 3.2 eV, respectively, in high purity crystals. Doping with 100 ppm or greater of Fe, Co, Cr, Cu, Mn, and Ni suppressed the luminescence, though in the MgO:Ni crystal the 2.3 eV Ni2+ band due to the 1T2g3A2g transition was observed. In deuterium-doped crystals the ratio of the intensity of 3.2–4.95 eV emission was found to be 1.2 as compared to 8 for the undoped crystals. Prior exposure of the pure crystals to ionizing radiation enhances the 4.95 eV band by a factor of three while not affecting the 3.2 eV band. This enhancement of intensity decays in several stages upon standing at room temperature in a way that reflects the thermal stability of the various components of the composite V-band absorption. These facts together with the observation that the 210 K thermoluminescence peak is composed entirely of 4.95 eV emission indicate that this luminescence band is associated with the recombination of an electron with a hole located in a V-type center, i.e. O?□ + e → (O2?□)1 → O2?□ + 4.95 eV, where the square indicates that the perturbing positive ion vacancy is adjacent to the oxugen ion which has captured the hole. In MgO:Li+, which exhibits no V-type centers upon irradiation, the 4.95 eV band was absent and a 2.9 eV emission which may be associated with recombination at the [Li]0 center was observe.  相似文献   

7.
We have studied the electron-induced desorption (EID) of O+ ions from oxygen-covered polycrystalline W, Mo and Cr surfaces. As the incident electron energy is increased, desorption begins at about 25 eV, and increases dramatically at the binding energy major low-lying substrate core levels. In the range of electron energy studied, below about 200 eV, there are also other variations in ion yield not associated with known core levels. The peak ion kinetic energy is 7.8, 5.3 and 3.4 eV for W, Mo and Cr respectively, and is independent of incident electron energy. These measurements imply that the desorption is initiated by a core level ionization event, although the subsequent electronic transitions leading to desorption apparently differ from those occurring on metallic oxide surfaces.  相似文献   

8.
虞心南  张青哲  谢侃  齐上雪  康瑾  林彰达 《物理学报》1983,32(10):1333-1338
本文用UPS,XPS研究了贮氢材料MlNi5(Ml=La,Ce,Pr,Nd)的CO,O2和H2O的中毒,在UPS谱中,我们观察到在EF以下峰α(0.3eV)和峰b(1.2eV)强度随中毒气体暴露量增加有显著变化,并向低动能端位移,逐渐形成肩峰,与此同时,峰c(6eV)和峰d(9.5eV)的强度随暴露量增加而增加,并有能量位移,配合XPS分析,分别确定相应的化学态。氧中毒后的MlNi5,经300℃加氢还原,从UPS谱可以看到峰α,b强度增加;H2O和CO中毒后,在超高真空条件下,分别经300℃加热处理,和Ar+剥离方法,均获得类似的效果,XPS分析进一步证实了这些结果。实验给出了贮氢材料MlNi5中过渡金属镍的d电子与气体自由分子轨道间电荷转移的信息,为在实际应用中认识此类贮氢合金的表面催化中毒和再生提供了依据。 关键词:  相似文献   

9.
The broad energy distributions of the condensing particles typically encountered in ion assisted vapor deposition techniques are often a drawback when attempting to understand the effect of the energetic bombardment on the film properties. In the current study, a monoenergetic Al+ beam generated by a filtered cathodic arc discharge is employed for the deposition of alumina (Al2O3) films at well defined Al+ ion energies between 4 eV and 200 eV at a substrate temperature of 720 °C. Structural analysis shows that Al+ energies of 40 eV or larger favor the formation of the thermodynamically stable α‐Al2O3 phase at the expense of other metastable Al2O3 polymorphs. The well defined ion energies are used as input for Monte‐Carlo based simulations of the ion–surface interactions. The results of these simulations reveal that the increase of the Al+ ion energy leads to an increase in the fraction of ions subplanted into the growing film. These findings underline the previously not considered role of subsurface processes on the phase formation of ionized physical vapor deposited Al2O3 films. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
Polyimide (PMDA-ODA) surface was irradiated by low energy reactive atomic beam with energy 160-180 eV to enhance the adhesion with metal Cu film. O2+ and N2+ ions were irradiated at the fluence from 5 × 1015 to 1 × 1018 cm−2. Wetting angle 78° of distilled deionized (DI) water for bare PI was greatly reduced down to 2-4° after critical ion flounce, and the surface energy was increased from 37 to 81.2 erg/cm. From the analysis of O 1s core-level XPS spectra, such improvement seemed to result from the increment of hydrophilic carbonyl oxygen content on modified PI surface. To see more carefully correlation of the peel strength with interfacial reaction between Cu and PI, flexible copper clad laminate with Cu (9 μm)/Cu (200 nm) on modified PI substrate (25 μm) was fabricated by successive sputtering and electroplating. Firstly, peel strength was measured by using t-test and it was largely increased from 0.2 to 0.5 kgf/cm for Ar+ only irradiated PI to 0.72-0.8 kgf/cm for O2+ or N2O+ irradiated PI. Chemical reaction at the interface was reasoned by analyzing C 1s, O 1s, N 1s, and Cu 2p core-level X-ray photoelectron spectroscopy over the as-cleaved Cu-side and PI side surface through depth profiling. From the C 1s spectra of cleaved Cu-side, by the electron transfer from Cu to carbonyl oxygen, carbonyl carbon atom became less positive and as a result shifted to lower binding energy not reaching the binding energy of C2 and C3. The binding energy shift of the peak C4 as small as 1.7 eV indicates that carbonyl oxygen atoms were not completely broken. From the analysis of the O 1s spectra, it was found that new peak at 530.5 eV (O3) was occurred and the increased area of the peak O3 was almost the same with reduced area of the peak carbonyl oxygen peak O1. Since there was no change in the relative intensity of ether oxygen (O2) to carbonyl oxygen (O1), and thus O3 was believed to result from Cu oxide formation via a local bonding of Cu with carbonyl oxygen atoms. Moreover, from X-ray induced Auger emission spectra Cu LMM which was very sensitive to chemical bonding, Cu oxide or CuOC complex formation instead of CuNO complex was clearly identified by the observation of the peak at 570 eV at higher 2 eV than that of metal Cu. In conclusion, when Cu atoms were sputtered on modified PI by low energy ion beam irradiation, it can be suggested that two Cu atoms locally reacted with carbonyl oxygen in PMDA units and formed Cu+OC complex linkage without being broken from carbon atoms and thus the chemically bound Cu was in the form of Cu2O.  相似文献   

11.
This paper reports on a study of electron-stimulated desorption (ESD) of O+ and Li+ ions from titanium dioxide as a function of the preheating temperature T and of the concentration of lithium adsorbed at 300 K, which was carried out with a static magnetic mass spectrometer combined with a retarding-field energy analyzer. For T>1500 K, the TiO2 surface undergoes irreversible rearrangement. At temperatures from 300 to 900 K and at lithium coverages Θ<1, the ESD cross sections of the O+ and Li+ ions vary in a reversible manner with temperature, while for lithium coverages Θ>1, the changes in the Li+ and O+ ESD cross sections become irreversible. For θ<1, the appearance threshold of the Li+ and O+ ions is 25 eV, whereas for θ>1, the ESD threshold of Li+ ions shifts to 37 eV.  相似文献   

12.
《Surface science》1986,172(1):90-120
Using a K+ ion beam and a K neutral beam at normal incidence on a W(110) surface, we have measured the angle and energy distributions of scattered K+ ions at different azimuthal angles. The primary energy is in the range 12–100 eV. The measured distributions show a complex peak structure. The peaks can be assigned to different scattering mechanisms, giving rise to various rainbow phenomena.  相似文献   

13.
Electron stimulated desorption of CO from the (111) face of a Nb single crystal produced both CO+ and O+ ions after adsorption at 150°K on a clean surface. When the surface was heated to above 250 °K only O+ ions were observed, and this current disappeared as the temperature was increased to 700 °K. Readsorption (at 150 °K) was inhibited following the 700 °K heating. These data indicate the formation on heating of a tightly bound surface phase with very low ionic desorption cross section. Threshold energies for CO+ and O+ ion production were 10.0 ± 0.5 eV and 19.0 ± 0.5 eV, respectively. The cross section for electron stimulated depopulation of the O+ producing phase was (4 ± 1) × 10?18 cm2 for 100 eV electrons.  相似文献   

14.
通过X射线光电子能谱和低能电子衍射实验研究了10~180 eV的Ar+、 He+、S+离子轰击n-InP(100)表面, 发现S+离子轰击可以产生In-S组分,减轻离子轰击对表面的物理损伤.对于Ar+离子轰击后的表面,经过S+离子处理和加热过程以后,表面损伤得到了修复,最终得到了2×2的InP表面,进一步验证了S+离子对InP表面的修复作用.  相似文献   

15.
We have studied the surface chemistry of the nickel-oxygen system using both temperature changes and ion bombardment as techniques for elucidating the surface structure. The spectra of metallic Ni, NiO and Ni2O3 were characterized from samples prepared directly in the spectrometer. The Ni2O3 species could be distinguished from an authentic Ni(OH)2 sample from both the X-ray photoelectron lines and the Auger transitions. The oxides of NiO and Ni2O3 could be prepared by bombardment with low energy (400eV) O2+ ions as well as by exposure of Ni to oxygen at reduced pressure (~ 100 torr). The Ni2O3 was found to be present on most nickel-oxygen surfaces except those prepared by exposing Ni to air for many hours at high temperature (> 600°C), indicating that the stability of Ni2O3 decreased as the temperature increased. Exposure of both NiO and Ni2O3 to 400 eV Ar+ ion bombardment caused reduction to metallic Ni. This observation has also been noted for several other oxides and a prediction of whether or not reduction should be observed is presented by examining the free energy of formation of the molecule.  相似文献   

16.
《Surface science》1986,177(3):577-592
Low-energy (<1 keV) N2+ and N+ ion scattering from the Cu(001) surface was directly observed by using a two-dimensional detection system. The two-dimensional pattern of the scattered ions changed when the primary ion energy was increased from 200 to 600 eV. The scattering peak shifted toward the [110] azimuth, to which the incident plane was not parallel, above 600 eV. The difference of ion-survival probabilities between N2+ and N+ was discussed from the full width at half maximum of the angular distribution of scattered ions.  相似文献   

17.
From photoemission and electron-energy-loss data the following picture of KMnO4, with MnVII (with a formal charge state Mn7+ (3d 0)) tetrahedrally surrounded by four O2–-ions, is deduced: strong covalent bonding between MnVII and O2– leads to a considerable occupation of the Mn-3 d shell. The ground state of the (MnO4)–1 molecule is an orbital and spin singlet as seen by the absence of any multiplet splitting in the Mn core levels. The valence band shows a four peak structure extending form 4 eV to 8 eV below the Fermi energy. The first peak at 4.2 eV has mainly O-2p character. The remaining peaks are of strongly mixed Mn-3d/O-2p character due to the covalent bonding. This mixing decreases with increasing binding energy. The electron energy loss data show a variety of structures between 2 eV and 10 eV independent of the primary electron energy which defines them as dipole allowed charge-transfer transitions. An additional excitation at 1.8 eV decreases quickly in intensity with increasing electron energy which classifies it as a dipole or spin forbidden transition in the compound. This energy is close to the value of 1.6 eV reported for the activation energy observed in electrical transport data. The results are compared to quantum chemical molecular orbital calculations of the (MnO4)–1 molecule.Physics Department, Allahabad University Allahabad 211002, India  相似文献   

18.
The theory presented explains quantitatively the experimentally observed increase in film density of a vapor-deposited CeO2 film when bombarded during growth with low-energy O 2 + ions. The density enhancement is expressed in terms of the yields for recoil implantation of surface atoms, ion incorporation and sputtering, which have been determined by employing a three-dimensional Monte Carlo cascade calculation. Ion-to-vapor flux ratios between 0 and 1.4 and O+ ion energies between 25 and 600 eV have been examined. The density shows an almost linear increase with the ratio of ion-to-vapor fluxes. An optimum O+ ion energy for densification is found at about 200 eV which is in agreement with experiment.  相似文献   

19.
The embedded-cluster numerical variational method has been developed to calculate the electronic structure of perfect MgO, F and F+-centers in MgO. The energy band, bulk density of states has been calculated by cluster Mg14O13, Mg14O12F+ and Mg14O12F. The calculated absorption energy for F+ and F centers is in good agreement with experimental data. In our calculated defect energy levels, that the first excited state of F+-center is at CB-3.46 eV, indicates the necessity of a large photoelectron yielding energy. We also calculate the radius of color center electron, and plot the map of charge-density distribution of valence electrons in which the structure of the color center is shown directly. Received 22 May 1998  相似文献   

20.
The electron energy loss spectra (EELS) of a pure metallic lanthanum surface and variations in these spectra at the initial stages of surface oxidation were studied. The measurements were performed at primary-electron beam energies E p from 200 to 1000 eV. A very pronounced peak at a loss energy of about 7.5 eV arises due to transitions from the La4d electronic states of the valence band into the empty La4f electronic states of the conduction band at 5.0–5.5 eV above the Fermi level. Marked changes are observed in the EELS during the oxidation of lanthanum: the peak at an energy of 7.5 eV disappears, and the peak at 13.5 eV corresponding to bulk collective energy loss in lanthanum oxide becomes more pronounced. The results obtained are discussed in terms of the electronic structure of lanthanum and lanthanum oxide.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号