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The adsorbed state of ethylene on clean Pd(110) and Pd(110)(1 × 2)-Cs surfaces at 90 K and its thermal decomposition have been studied by the use of high-resolution electron energy loss spectroscopy (EELS), low-energy electron diffraction (LEED), and thermal desorption spectroscopy (TDS). It is shown that ethylene on the Pd(110)(1 × 2)-Cs surface is more weakly bonded to the surface as compared with ethylene on the clean Pd(110) surface and that the dehydrogenation and CC bond scission processes are promoted by the pre-adsorbed Cs atoms.

The adsorption and thermal evolution of acetylene and ethylene on Pd(110) have been studied using high-resolution electron energy loss Spectroscopy, multiplexed thermal desorption spectroscopy and low-energy electron diffraction. For a small exposure at 90 K, acetylene is chemisorbed molecularly in a single state, and is located in the μ 2 -site with its CC bond axis inclined to the surface plane; one of the CH groups is hydrogen-bonded to the surface. For a large exposure, acetylene is adsorbed in several states. Ethylene is π-bonded to the Pd(110) surface at 90 K. The dehydrogenation processes of acetylene and ethylene on Pd(110) by the heat treatment are discussed.

The adsorbed states of K atoms on the Si(100)(2 × 1) surface and the interactions of the K-covered surface with several gases, i.e. H, O2, CO and HCOOH, have been studied mainly by the use of high-resolution electron energy loss spectroscopy (EELS) and thermal desorption spectroscopy (TDS). Experimental evidence is given for the existence of two chemisorbed states of K atoms on the Si(100)(2 × 1) surface. Two adsorbed states of O atoms were found on the Si(100)(2 × 1)-K surface. HCOO adspecies of an ioniccharacter exist on the Si(100)(2 × 1)-K surface.

Electron energy-loss spectra have been measured on Ni(100) surfaces, clean and following oxygen and carbon monoxide adsorption, at primary energies of 40–300 eV. The observed peaks at 9.1, 14 and 19 eV in the clean-surface spectrum are ascribed to the bulk plasmon of the 4 s electrons, the surface plasmon, and the bulk plasmon of the coupled 3 d + 4 s electron, respectively, and the weak but sharp peak at 33 eV is tentatively attributed to the localized many-body effect in the final state. Assignments of the loss structures on the gas-covered surfaces have been attempted.

The adsorbed states of hydrogen on Pd(1 1 0) surfaces at 100–300 K have been studied using high-resolution electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED). The observed losses are at 96, 118 and ∼ 165 meV for the (2 × 1)-H surface; 96 and ∼ 125 (shoulder) meV for the (1 × 2)-H surface formed at 100 K; ∼ 90 and 118 meV for the streaky (1 × 2)-H surface formed at 300 K. Tentative assignments of the losses are made. The adsorbed states of hydrogen are discussed correlating the EELS-LEED results with the thermal desorption and molecular beam diffraction studies which have previously been reported.

Chemisorption of methanol on the Si(111)(7×7) surface has been studied at ∼ 300 K using high-resolution electron energy loss spectroscopy. Methanol reacts with the Si(111) surface to form the stable surface species SiOCH3 and SiH. The methoxy species (CH3O) is bonded to the Si surface with a covalent bond formed between its oxygen end and the dangling bond of the Si(111) surface atom. A structural model for methanol chemisorbed on the Si(111) is proposed.

High-resolution vibrational electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED) have been used to study the interactions of hydrogen with the Ni(110) surface in the temperature range from 100 to 300 K. H2 is adsorbed dissociatively on the Ni(110) surface. At 100 K, the (2 × 1)-H and (1 × 2)-H structures are formed; the streaky (1 × 2)-H structure is formed by heating the H-covered surface to above ~ 220 K or by the exposure of the Ni(110) surface to H2 at 300 K. For the (2 × 1)-H surface which is characterized by the vibrational losses at 79 and 130 meV, H atoms are adsorbed in the low-symmetry short-bridge sites of the bulk-like Ni(110) surface. Adsorbed sites of H atoms for the low-coverage phases (found by molecular beam diffraction and video-LEED) are similar to those for the (2 × 1)-H structure. For the (1 × 2)-H surface with losses at 76, 117 and 150 meV, H atoms are considered to be adsorbed in the low-symmetry short-bridge sites and high-symmetry short-bridge sites of the second layer Ni atoms. The streaky (1 × 2)-H surface with losses at ~ 80, 117 and 140 meV consists of the undistorted and distorted patches whose local structures are similar to those of the (2 × 1)-H and (1 × 2)-H surfaces, respectively. The (2 × 1) → (1 × 2) phase transition is considered to be the first-order transition.

High-resolution electron energy loss spectra of hydrogen-covered Ni(110) surfaces both at 100 and 300 K are presented. The adsorbed sites of hydrogen atoms are discussed.

High-resolution vibrational electron energy loss spectroscopy has been used to study the adsorbed state of NO on the Si(100)(2×1) surface. At 300 K, NO is adsorbed dissociatively on the Si(100) surface in the disordered structure, and the Si 3 N and SiOSi species are formed. By heating at 1200–1300 K, the O adatoms are removed from the surface and the silicon nitride is formed; the (2×1) structure is recovered, which is interpreted to indicate that the nitride is formed mainly in the subsurface region.

The interactions of a Pd(110) surface with (N2+N) have been studied by means of high-resolution vibrational electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). At 300 K, double- and triple-bonded N2 admolecules and N adatoms (located most probably in the long-bridge, short-bridge and on-top sites of the unreconstructed Pd(110) surface) are formed; some N atoms penetrate into the “bulk”. The double- and triple-bonded N2 admolecules are identified by the N-N stretching energies of 199 and 265 meV, respectively; the N adatoms in the long-bridge, short-bridge and on-top sites are identified by the Pd-N stretching energies of 55, 90 and ∼130 meV, respectively. By heating at ∼500 K, the triple-bonded N2 and most of the double-bonded N2 admolecules are desorbed. The Pd clean surface is recovered by heating at ∼900 K. The (2×3)-N structure is formed by a large (N2+N) exposure followed by heating at ∼500–800 K or by a large N2 exposure at ∼700 K. It is proposed that N atoms located in the long-bridge sites of the “distorted” Pd(110) surface form the (2×3)-N structure. Molecular nitrogen is not adsorbed on the (2×3)-N surface at 300 K.

Adsorbed states of hydrogen on the Ni(110) surface have been studied using high-resolution vibrational electron energy loss spectroscopy and low-energy electron diffraction. Structural models for the (2 × 1)−H, (1 × 2)−H and streaky (1 × 2)−H surfaces are discussed.

Electron energy-loss spectra of clean NiO (100), CoO (100), and MnO surfaces have been obtained using primary electrons of 100-900, 30-800, and 300-700 eV, respectively. The observed electronic transitions are interpreted on the basis of the primary electron energy dependence and comparison with optical data. The peaks below approximately 10 eV are due to the O2-2p to M2+3d and 4s(M=Ni, Co, and Mn) transitions. It is shown that the onset of the interband transitions is caused by the 2p to 3d charge-transfer excitons. The peaks between 10 and 50 eV are attributed to the one-electron excitations of O2-2p to M2+4p and M2+3d to 4p, and to the single- and multiple-bulk plasmon excitations associated with O2-2p, M2+3d, and coupled 2p and 3d electrons. The 3p-core excitation spectra are observed beyond 50-60 eV.

The adsorbed states of H 2 S on the Si(1 1 1)(7 x 7) surface have been studied using high-resolution electron energy loss spectroscopy. At 300 K, H 2 S is partially dissociated, and the SiH and SiSH species are formed. The SH species are adsorbed in a bent configuration. Results of heating experiments are presented, and the formation of SiSSi species is discussed.

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the band structure of the c(2×2) and (3×1) oxygen overlayers on Fe(110). The symmetries of the O-2p-derived states at the center of the surface Brillouin zone ( Γ ) were identified using polarized light. At Γ the p x p y - and p z -derived levels are at about 5.5 and 7.0 eV below the Fermi level, respectively, for both ordered overlayers. The p-states of the c(2×2)-O structure show very little dispersion (⪅0.1 eV) with k  . On the other hand, the c(3×1)-O overlayer exhibits considerable dispersion of ∼1.6 eV. The essential features of the measured dispersion are reproduced well by the dispersion predicted in a qualitative way for an isolated c(3×1) oxygen monolayer.

High-resolution electron energy-loss spectroscopy and monochromatic low-energy electron diffraction have been applied to the study of the Si(111)(7 × 7) surface and the thermally-quenched Si(111) (1 × 1) surface. For the (1 × 1) surface, the inelastic continuum, observed for the (7 × 7) surface, due to the Drude absorption of electrons in the dangling-bond surface states is not existent, which indicates that the surface-state band associated with the dangling-bonds of the (1 × 1) surface is insulating. The observed electronic transitions indicate that the (7 × 7) and (1 × 1) surfaces have similar local band geometries and that they differ only in long-range order. The (1 × 1) surface is considered to have a disordered structure. The defect model is favored for the (7 × 7) structure.

High-resolution vibrational electron energy-loss spectra of CO on an Ni(110) surface were studied at 300 K with the in-situ combination of LEED, Auger electron spectroscopy and work-function change measurement. The observed peaks are at 436 cm−1, 1855 cm−1 (shifting to 1944 cm−1 with increasing coverage) and at 1960 cm−1 (shifting to 2016 cm−1 with increasing coverage). The experimental results indicate that CO is adsorbed non-dissociatively at all coverages. Three adsorbed states of CO have been found. At fractional CO coverages less than θ ~ 0.9 where the disordered adsorbed structure dominates, CO is adsorbed in two inequivalent sites (short- and long-bridge sites) at random with its axis oriented perpendicular to the surface. At high coverages (θ > 0.9) where the (2 × 1) structure develops, our results indicate that the adsorbed CO molecules may occupy the distorted long-bridge sites forming zig-zag chains which lie essentially in the troughs of the (110) surface.

Chemisorption of ammonia on the Si(111)(7×7) surface has been studied by means of high resolution electron energy loss spectroscopy (EELS). Ammonia is decomposed on the Si(111)(7×7) surface at 300 K to form stable surface species SiNH2 and SiH. It is proposed that the amino species (NH2) is bonded to the Si(111) surface with a covalent bond formed between its nitrogen atom and the dangling bond of the Si(111) surface atom. Changes in the adsorbed state of ammonia by heat treatment are discussed.

The initial stages of the interaction of oxygen with an Fe(110) surface have been studied at 300 K by electron energy-loss spectroscopy with in-situ combined low energy electron diffraction, Auger electron spectroscopy and work-function change measurement. From all the results, four different stages of the oxygen interaction are distinguished: (I) a first dissociative chemisorption up to 3 L, characterized by the c(2×2)-O structure, (II) a second dissociative chemisorption between 3 and 7 L, characterized by the c(3×1)-O structure, (III) incorporation of O adatoms into the selvage between 7 and 30 L, and (IV) oxidation above 30 L leading to the formation of FeO(111), characterized by the diffuse hexagonal diffraction pattern. The sticking probability was found to be initially near unity and fall off rapidly to a minimum value of ≈0.05 at ≈1 L. Particular emphasis was placed upon the investigation of the change in surface electronic properties from those characteristic of them metal to those of the oxide. In stage (I) an energy-loss peak, being attributed to the transition from the 2p orbital of the chemisorbed oxygen, was observed at 6.0 eV, while in stage (II) two additional peaks of the same origin appeared at 7.5 and 9.3 eV due to the formation of the O 2p band. The energy-loss spectrum in the oxide phase was characterized by the peaks at 4.8 and 7.5 eV due to the O2− 2p → Fe2+3d charge-transfer transitions and by a peak at 2.4 eV due to the ligand-field d → d transitions of an Fe2+ ion in FeO. It is shown that the Fe 3dyz,zx and 4sp electrons play a major role in the chemisorption bond (O adatoms located in the long-bridge site), and that for the incorporation process the Fe 3dy2 electrons are also involved in bonding by the symmetry breaking. The change in the Fe 3p-excitation spectrum during oxidation was also investigated. The differences between the experimental results on Fe(100) and (110) surfaces are summarized.

Electron energy-loss spectra of CO-adsorbed Ni(100) surfaces have been observed with concomitant measurements of LEED, AES, work function change, and electron impact desorption. Five CO-induced loss peaks are observed for the first time. The loss peaks at 5.8 and 8.6 eV are ascribed to the charge-transfer transitions ( Ni d π → CO 2 π ∗ and Ni d σ → CO 2 π ∗ , respectively), and the weak peaks at 11.8, 12.6 and 16.0 eV to the intra-molecular transitions ( 5σ → 2π ∗ , 1π → 2π ∗ and 4σ → 2π ∗ , respectively). The COCO adsorbate interaction is shown to shift the loss energy of the 12.6 eV peak. The adsorbed state of CO consistent with the results of LEED, AES, work-function change and electron impact desorption is discussed.

The clean and hydrogen-covered Cr(110) surfaces have been investigated at 300 K by electron energy-loss spectroscopy (ELS) and secondary-electron emission spectroscopy (SES) (primary energy: Ep = 60−300 eV) with the in-situ combined supplementary techniques. The clean surface SES spectrum has peaks at 7.3, 9.2, 11.4, 13.2, 15.2, 17.6 and 20.6 eV above the Fermi level, which are thought to correspond to maxima in the unoccupied density of states. Only the 11.4 and 15.2 eV peak intensities are strongly reduced by irreversibe hydrogen adsorption. The clean surface ELS spectrum is characterized by peaks at 2, 3.5, 5.5, ∼ 10, 23, 35, 42, 48 and 55 eV. The ELS spectrum is interpreted by comparison with the optical data, the band calculation and the SES results. The 2 and 3.5 eV loss peaks are attributed to the interband transitions between d bands, and the 5.5 and ∼: 10 eV peaks to those associated with sp-like bands. By hydrogen adsorption, the damping and blurring of only the 5.5 and ∼: 10 eV peaks were observed, and a hydrogen-induced peak was found at ∼: 16 eV. These results are considered to indicate that the CrH bonding occurs mainly via sp bands; the role of d bands, however, cannot be neglected. Hydrogen-exposure dependence of the ELS spectrum is found to be practically independent of primary energy, in contrast to the Ni(100)H2 system, indicating that hydrogen is rapidly penetrated into the Cr selvedge lattice.

The excitation angle (β) and emission angle (θ) dependences of the Ni M2,3VV (61 eV) and Ni L3VV (850 eV) Auger emissions from clean polycrystalline Ni surfaces, and the S L2, 3 M2, 3M2, 3 (150 eV) Auger emission from S-adsorbed poly-Ni surfaces have been investigated. In the case of Ni (61 eV) and S Auger emissions, the β-dependence shows the 1 cos β distribution, while a significant deviation from 1 cos β is observed for Ni (850 eV) Auger emission. The cosθ distribution and the intermediate between isotropic and cosθ distributions are observed for Ni (61 eV), and for Ni (850 eV) and S Auger emissions, respectively. Those results have been found to be in fairly good agreement with the calculations based on the simple continuum model without consideration of the diffraction effect and the inherent anisotropic emission.

The discrete variational (DV) Xα cluster model is used to study the chemisorptions on (001) surfaces of bcc V, Cr and Fe. The adatom induced levels and the electronic charge densities are calculated and compared with experimental data such as UPS and LEED analysis. The oxygen induced levels and the change in valence-state density explain well the UPS spectra of oxygen on Fe surface. The results suggest that the four-fold hollow site of (001) surface is more stable than the on-top site for oxygen chemisorption, and that the first layer distance of the surface is expanded by chemisorption, consistent with the experiment.

The initial stages of the interaction of oxygen with a Cr(110) surface have been investigated at 300 K by LEED, AES, electron energy loss spectroscopy (ELS), secondary electron emission spectroscopy (SES) and work-function change measurement (Δφ). In the exposure region up to 2 L, the clean-surface ELS peaks due to interband transition weakened and then disappeared, while the ∼5.8 and 10 eV loss peaks attributed to the O 2p → Cr 3d transitions appeared, accompanied with a work-function increase ( Δφ = +0.19 eV at2L). In the region 2–6 L the work function decreased to below the original clean-surface value ( Δφ min = −0.24 eV at6L), and five additional ELS peaks were observed at ∼2, 4, 11, 20 and 32 eV: the 2 and 4 eV peaks are ascribed to the ligand-field d → d transitions of a Cr 3+ ion, the 11 eV peak to the O 2p → Cr 4s transition, the 20 eV peak to the Cr 3d → 4p transition of a Cr 3+ ion and the 32 eV peak probably to the Cr 3d → 4f transition. A new SES peak at 6.1 eV, being attributed to the final state for t he 11 eV ELS peak, was observed at above 3 L and identified as due to the unfilled Cr 4s state caused by charge transfer from Cr to oxygen sites in this region. In the region 6–15 L the work function increased again ( Δφ max = +0.32 eV at15 L), the 33 and 46 eV Auger peaks due to respectively the M 2,3 (Cr)L 2,3 (O)L 2,3 (O) cross transition and the M 2,3 VV transition of the oxide appeared and the 26 eV ELS peak due to the O 2s → Cr 4s transition was also observed. Above 10 L, the ELS spectra were found to be practically the same as that of Cr 2 O 3 . Finally, above 15 L, the work function decreased slowly ( Δφ = +0.13 eV at40L). From these results, the oxygen interaction with a Cr(110) surface can be classified into four different stages: (1) dissociative chemisorption stage up to 2 L, (2) incorporation of O adatoms into the Cr selvedge between 2–6 L, (3) rapid oxidation between 6–15 L leading to the formation of thin Cr 2 O 3 film, and (4) slow thickening of Cr 2 O 3 above 15 L. The change in the Cr 3p excitation spectrum during oxidation was also investigated. The oxide growth can be interpreted on the basis of a modified coupled current approach of low-temperature oxidation of metals.

The combined techniques in situ of Auger electron spectroscopy, electron energy loss spectroscopy, electron impact desorption, and work-function change measurement have been applied to the study of the adsorption of HCl and HBr on thermally cleaned Si(111) surfaces. Major results are summarized as follows: (1) HCl shows a fast adsorption to the saturation coverage of θs ⋍ 0.3 (estimated using the continuum approximation) by the exposure of about 1 L at room temperature. (2) The average sticking probabilities for HCl and HBr are ∼0.7. (3) Two adsorbed states of HCl or HBr at room temperature are discriminated. For HCl, the first state is characterized by the emission of ∼1.2 eV ions and the electronic transition at 8.4 eV, which is subsequently converted to the second state characterized by the emission of ∼3.2 eV ions and the electronic transitions at 7.0 and 8.4 eV. Heating the sample at ∼800 K causes the desorption of hydrogen and the appearance of the Cl-related peaks at 6.0, 7.0, and 9.0 eV in the loss spectra. For HBr, the first and the second states are characterizied by the emission of ∼1.2 and ∼3.2 eV ions, respectively. The electronic transition is observed at 7.8 eV in both states. (4) It is proposed that HCl and HBr are adsorbed as molecules initially, which are subsequently dissociated into atoms spontaneously at room temperature.

The interactions of nitrogen with an Ni(110) surface at both 90 and 300 K have been investigated by means of high-resolution vibrational electron energy loss spectroscopy (EELS). Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). N 2 molecules are chemisorbed nondissociatively at 90 K, and are desorbed at ~170 K. N 2 molecules are not adsorbed on Ni(110) at 300 K, however, as the Ni(110) surface is exposed to a mixture of N 2 molecules and N atoms at 300 K, N 2 admolecules (double- and triple-bonded N 2 ) are formed in addition to N adatoms (which are located, most probably, in the long-bridge, short-bridge and on-top sites, and also in the “subsurface” and “bulk”). It is suggested that N 2 admolecules are formed in the “active sites” on the Ni(110) surface which is distorted by the adsorption of N atoms. Thermal treatment of the (N 2 + N)-exposed Ni(110) surface is discussed. The N 2 admolecules ormed by the (N 2 + N) exposure are desorbed at ~400–450 K. The (2 × 3)-N structure is formed by heating at ~650–780 K. The Ni(110)-(N 2 + N) interaction is compared with the Pd(110)-(N 2 + N) interaction.

A number of adsorbed structures produced by chemisorption of SiH4, PH3 and HCl on Ni(100) surfaces have been investigated by LEED and angle-resolved Auger electron spectroscopy (ARAES). The room-temperature adsorption of SiH4 and PH3 produces the disordered structures, from which the Si(92 eV) and P (120 eV) Auger emissions respectively show a cos theta profile. The Si, P and Cl (180 eV) Auger emissions from the c(2*2)-Si, (2 square root 2* square root 2)R45 degrees -Si, ( square root 5* square root 5)R26.6 degrees -P, c(2*2)-HCl and c(2*2)-Cl structures show the anisotropic angular features as in the case of the c(2*2)-S and -Se on Ni(100) surfaces.

The chemisorbed state of nitrogen on a Cr(110) surface at 300 K has been investigated by means of electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and work function change measurement (Δφ). The dissociative state is suggested by our observations that the EELS spectrum and the N(KLL) Auger line shape of the Cr(110) surface after N 2 adsorption at 300 K are practically the same as those of the nitride-covered surface formed by NH 3 exposure at 800 K. From the Auger uptake curve, the initial sticking probability and the saturation coverage at 500 L N 2 are estimated respectively to be 0.09 and 0.36. Both the Auger uptake and the work function decrease (saturation value: -0.27 eV) show an abrupt change at about 10 L. The clean-surface EELS peaks due to the interband transitions in the low energy range of 2–20 eV have merely decreased and the high-energy side tailing of the loss peaks at 5.0 and 9.0 eV is observed after N 2 adsorption. Although the nitrogen-induced EELS peaks are not distinctly resolved in the low-energy range at less than 30 eV, the shift of the loss peak at 41.5 eV due to the Cr 3p core-level excitation is clearly observed at about 10 L in accordance with the AES and Δφ results. The above results strongly indicate the onset of transformation of the chemisorbed phase to the surface nitride phase on Cr(110) surface at about 10 L N 2 exposure even at 300 K.

High-resolution vibrational electron energy-loss spectroscopy has been used to study the reactions of N atoms with the Si(111)(7 × 7) surface. For the Si(111) surface reacted with N atoms at 300 K, nearly planar Si3N species which exhibit losses at ≈ 50 and 102 meV are formed. By heating the N-covered surface at 1240 K, the (8 × 8)-N structure which is characterized by the losses at 60, 91 and 141 meV is formed. By heating at 1350 K, the quadruplet structure which exhibits losses at ≈ 60 and 120 meV is formed. Assignments of these losses are made, and structures of the (8 × 8)-N and quadruplet surfaces are discussed. The Si nitride layer formed by nitridation of the (8 × 8)-N monolayer is also studied, and the local structure is found to be similar to that of the quadruplet surface.

Observations of CO adsorption on {100} nickel made previously by Park and Farnsworth have been repeated with a combined LEED and mass spectrometer (MS) system. The results confirm the previous observations and are in disagreement with those of Lichtman, Kirst, and McQuistan. Possible causes of the discrepancy are indicated. CO adsorption on the surface subsequent to prolonged heat treatment was greatly reduced due to diffusion of contamination from the bulk. No desorption of O2 or O was observed even when a CO-covered surface was exposed to O2 and heated subsequently, but only large desorptions of CO2 and CO with a c2 × 2-O structure remaining on the surface. Also, heating a surface, which had been exposed to O2 only, produced desorption of CO but no trace of O2 or O was found.

Results were obtained with combined LEED and Mass Spectrometer equipments. On first admission of N2O to the outgassed system in the pressure range 2 to 5 × 10−8 Torr, nitrogen was formed by decomposition but no oxygen was observed. In addition to some dissociation of N2O on (100) Ni, some adsorption of N2O occurred in a lattice structure similar to that of the nickel substrate. Subsequent heating at 200–300°C caused weak desorptions of CO and N2O, the oxygen being removed as CO. The adsorbed N2O was easily replaced by CO at room temperature. The work function of the clean surface was increased 0.1 eV by exposure to N2O, probably due to adsorbed oxygen as a decomposition product of N2O as well as adsorbed N2O. On first admission of NO, substitutional desorption of CO from tube components occurred and the resulting CO adsorbed on the crystal surface was later substitutionally desorbed by NO. NO was strongly adsorbed on the crystal surface primarily in an amorphous form but with some lattice structure similar to that of the nickel substrate. The adsorbed NO was removed as CO and N2 by heating. NO was strongly adsorbed on both clean and slightly contaminated surfaces. There was no evidence of a surface reaction between adsorbed NO and oxygen atoms to form NO2. Adsorption of NO caused a maximum decrease in work function of 0.38 eV. Admission of CO2 to the system caused no substitutional desorption of CO. Adsorbed CO2 molecules were dissociated on the clean crystal surface at room temperature to form adsorbed CO and O when the exposure reached a rather critical value of about 10−6 Torr-min, as indicated by both sharp decreases in LEED intensity and increases in work function. Heating the crystal at 200 to 300°C caused desorption of both CO and CO2. A slightly contaminated surface, produced by heating the crystal at 850°C for a few hours, was very inactive for CO2 adsorption or dissociation.

The electron energy loss spectra have been measured of oxygen-adsorbed Si (111) surfaces at the primary energies of 10–200 eV. The observed peaks are at the loss energies of 2.9, 3.6, 4.8, 5.7, 6.9, 8.2, 9.6, 12.0, and 13.0 eV. All the peaks are attributed to the one-electronic transitions related to the adsorbed oxygen, except for the 9.6 eV peak which could possibly be due to the relaxed surface plasmon excitation. It is shown that the “splitting” of surface plasmon reported by Ibach and Rowe does not exist.

The Ni-M2,3 VV Auger electron angular distributions have been measured from oxygen-adsorbed Ni (100) surfaces and from cleaved NiO (100) clean surfaces. Significant variations in the angular profiles have been observedin the second reaction stage of initial oxidation process. Present results support the island growth model of NiO layers. It is also shown that the new information on the ratio of domain area of NiO to that of c (2 × 2)-O on Ni (100) surface can be obtained by angle-resolved AES method.

Electron energy-loss spectroscopy of ∼ 200 eV electrons has been applied to the study of the electronic states of clean NiO (100) surfaces. Initial attempt has been made on the identification of observed peaks, and they are attributed to the one-electronic transitions (O 2- 2 p → Ni 2+ 3 d , 4 s and 4 p ; Ni 2+ 3 d → 4 p , 3 p → 3 d and 4 s ), and the collective excitations (bulk plasmons of O 2- 2 p , Ni 2+ 3 d electrons, and coupled 2 p and 3 d electrons).

Electron energy-loss spectra of clean and hydrogen-covered Cr(110) surfaces have been investigated in the spectral range of 0–80 eV for primary energies of 60–500 eV. The observed peaks for the clean surface are at the loss energies of 2, 3.5, 5.5, 9.6, 23, 35, 42, 48 and 55 eV. The 3 p -excitation spectra for high primary energies (> 250 eV) are in good agreement with the corresponding optical spectrum. The edge at & 42 eV observed for low primary energies is tentatively attributed to the onset of the transition from the 3 p subshell to the local 4 s -band in the vicinity of the core hole. A characteristic energy-loss at ≈ 15.5 eV is observed after hydrogen adsorption. The 3 p -spectrum is not influenced by hydrogen adsorption, indicating that the excitation is of a localized character.

Electron energy loss spectra of a Pd(110) clean surface have been measured at primary energies of 40–100 eV. The observed peaks are at the loss energies of ∼ 3, 4.3, 7.5, 11.5, 16, 21.3, 26.5 and 33.8 eV. The 7.5, 26.5, and 33.8 eV peaks are attributed mainly to the bulk plasmon excitations associated with 5 s electrons, coupled 5 s and a limited number of 4 d electrons, and total (4 d +5 s ) electrons, respectively. The rest of the peaks are ascribed mainly to one-electron excitations.

In addition to our previous results [Phys. Rev. B 38, 1131 (1988)], we report further photoemission evidence for the bulk magnetic phase transition in Cr. An emission from the ${\ensuremath{\Sigma}}_{4}$ and ${\ensuremath{\Sigma}}_{1}$ bands unique to the paramagnetic phase disappears at above the N\'eel temperature.

High-resolution vibrational electron energy loss spectroscopy, low-energy electron diffraction and Auger electron spectroscopy are used to study the reactions of NO with the Si(ll1) (7 x7) surface. At 300 K, NO is adsorbed dissociatively on the (7 X 7) surface in the disordered structure. The N and 0 atoms are chemisorbed in the on-top sites forming the Si-N and Si-0 single bonds which are characterized by the vibrational losses at 118-125 and loo-105 meV, respectively. The maximum fractional coverages of N and 0 atoms are both 6’ - 0.5. By heating the NO-saturated surface at 1150-1300 K, the adsorbed oxygen is removed from the surface and the N-covered surface is reconstructed to form the “(8 X 8)“-N structure which is characterized by the losses at 91 and 120 meV. This structure is proposed to arise from the overlayer in which each N atom is bonded to three Si atoms with the sp3-like bonds forming a hexagonal lattice with unit mesh vectors of S/11 times those of the unreconstructed Si(ll1) surface. As this surface is further heated at 1300-1350 K, the “quadruplet” structure which is characterized by the losses at 61 and 120 meV is formed. It is proposed that this structure has planar geometry with each N atom bonded to three Si atoms forming the sp2-like bonds. The Si-N bond length is estimated to be - 1.7 A. The local structure of the quadruplet surface is very similar to that of the bulk silicon nitride (Si,N,).

The electronic state of oxygen adsorbed on a Ni(110) surface at 300 K has been studied by angle-resolved photoemission spectroscopy using polarized synchrotron radiation. For the low-coverage (3×1)-O and subsequent (2×1)-O adsorbed structures, a dispersion of the O 2p-derived levels is observed, indicative of adsorbate band formation with a two-dimensional Bloch character. The energy bands of the O 2p and Ni 3d valence levels for NiO(100) formed on Ni(110) are also mapped out. The experimental results for the (3×1)-O and (2×1)-O are compared with the dispersion predicted for isolated oxygen monolayers in the respective configurations from a tight-binding model.

The interactions of H, O2, NO and H2O with the Si(111)(7×7) surface have been studied using high-resolution vibrational electron energy loss spectroscopy with in-situ combined supplementary techniques (low-energy electron diffraction and Auger electron spectroscopy). Adsorbed states and adsorbed structures of these gases on the Si(111) surface at 300 K are examined. Results of temperature-dependent measurements are presented, and surface reaction mechanisms and surface species produced by the thermal treatment are discussed.

The adsorption and decomposition of acetylene on Si(100) and vicinal Si(100)9° have been studied using high resolution electron energy loss spectroscopy and low-energy electron diffraction. Acetylene is predominantly chemisorbed molecularly in the temperature range between 80 and ~ 300 K; a small amount of acetylene is partially dissociated. The molecularly-chemisorbed acetylene is rehybridized, and has the hybridization state near sp3. It is proposed that molecular acetylene is di-σ bonded to adjacent Si atoms of a dimer on Si(100).The thermal decomposition of chemisorbed acetylene, and the (inactive) role played by steps are discussed.