Adsorption of glycine on a NiAl(1 1 0) alloy surface

The adsorption and desorption of glycine (NH₂CH₂COOH), vacuum deposited on a NiAl(1 1 0) surface, were investigated by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED), temperature-programmed desorption, work function (Δφ) measurements, and ultraviolet photoelectron spectroscopy (UPS). At 120 K, glycine adsorbs molecularly forming mono- and multilayers predominantly in the zwitterionic state, as evidenced by the UPS results. In contrast, the adsorption at room temperature (310 K) is mainly dissociative in the early stages of exposure, while molecular adsorption occurs only near saturation coverage. There is evidence that this molecularly adsorbed species is in the anionic form (NH₂CH₂COO⁻). Analysis of AES data reveals that upon adsorption glycine attacks the aluminium sites on the surface. On heating part of the monolayer adsorbed at 120 K is converted to the anionic form and at higher temperatures dissociates further before desorption. The temperature-induced dissociation of glycine (<400 K) leads to a series of similar reaction products irrespective of the initial adsorption step at 120 K or at 310 K, leaving finally oxygen, carbon and nitrogen at the surface. AES and LEED measurements indicate that oxygen interacts strongly with the Al component of the surface forming an “oxide”-like Al-O layer.     

Room-temperature-adsorption behavior of acetic anhydride on a TiO2(1 1 0) surface

We have studied the adsorption structure of acetic anhydride on a TiO₂(1 1 0) surface using XPS (X-ray photoelectron spectroscopy), LEED (low energy electron diffraction) and HREELS (high resolution electron energy loss spectroscopy) to determine the origins of the unique adsorption properties of carboxylic acids on a TiO₂(1 1 0) surface. The C 1s XPS data indicated that the saturation carbon amount of adsorbed acetic anhydride was 12 ± 3% larger than that of the adsorbed acetic acid. LEED showed p(2 × 1) weak spots for the acetic anhydride adsorbed surface. The HREELS spectra revealed the dissociative adsorption of acetic anhydride. Based on these findings, we concluded that the neutralization of the bridging oxygen atoms associated with the dissociative adsorption is necessary for the stable adsorption of carboxylates on the 5-fold Ti sites.     

Electron spectroscopy of the interface carbon layer formation on the cleavage surfaces of the layered semiconductor In4Se3 crystals

The results of the quantitative X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) of the interface carbon layer formation on the cleavage surfaces of the layered semiconductor In₄Se₃ crystals are presented. The carbon coating formation occurs as the result of interaction of the air and residual gases atmosphere in ultra high vacuum (UHV) Auger spectrometer chamber with atomic clean interlayer cleavage surfaces of the crystals. The kinetics and peculiarities of interfacial carbon layer formation on the cleavage surfaces of the crystals, elemental and phase composition of the interface have been studied by quantitative XPS, AES and mass-spectroscopy.     

Cs adsorption on a polar NbC(111) surface: photoemission and auger electron spectroscopy studies

The Cs adsorption process on a NbC(111) surface has been studied with core-level photoemission spectroscopy (PES) and Auger electron spectroscopy (AES). Coverage-dependent Cs 4d core-level PES shows that the polarization-depolarization transition of the Cs overlayer occurs in the coverage region of 0.5 ≤ θ ≤ 0.8 ML where the work function shows a minimum value. The charge transfer in the initial stage of adsorption is investigated using valence-related AES, and it is found that the transfer of the Cs 6s charge to the substrate occurs in the polarized phase.     

Interactions of water vapor with polycrystalline uranium surfaces - The low temperature regime

The initial interaction of water vapor with polycrystalline uranium surfaces at low temperatures (LT, 200 K), was studied by combined measurements utilizing Direct Recoil Spectrometry (DRS), Auger electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). Three stages of water dissociation and adsorption can be observed: Stage (1) 0-0.6 oxygen monolayer coverage: full (H₂O → O + 2H) dissociation is dominant, coexisting with partial dissociation (H₂O → OH + H). In contrast to room temperature, where the adsorption is of a Langmuir type, in the present low temperature case it is a precursor-state type - the oxygen accumulation is linear, indicating that a constant fraction of the water molecules impinging on the surface diffuses to a dissociation and adsorption site. Only minor oxidation of the uranium occurs. Stage (2) 0.6-full oxygen coverage: only partial dissociation occurs. Still only minor oxidation of uranium takes place. Stage (3) buildup of a second hydroxyl layer, concurrent with slow continuous oxidation of uranium. Subsequent heating of the sample after the described exposure was accompanied by additional continuous oxidation. Above ∼230 K, the main process seems to be OH decomposition and desorption. A comparison is made to the dissociation and adsorption processes at room temperature.     

Effects of potassium on the reaction pathways of CH2 fragment over Mo2C/Mo(1 0 0)

The adsorption and surface reactions of CH₂I₂ on the K-dosed Mo₂C/Mo(1 0 0) have been studied by high resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. Potassium is an effective promoter for the rupture of C-I bond in the adsorbed CH₂I₂. A partial dissociation of this compound occurred even at 100 K and was completed at 190 K at monolayer K coverage. The dissociation was further promoted by the illumination of coadsorbed layer at 100 K. As revealed by HREELS and XPS measurements the primary products of the dissociation are CH₂ and I. Methylene was converted to π-bonded ethylene characterized by T_p = 160 K, and di-σ-ethylene with T_p = 350 K. Other products of the surface reaction are hydrogen and methane. The coupling reaction of CH₂ species was clearly facilitated by potassium. The effect of potassium was explained by the extended electron donation to adsorbed alkyl iodide in one hand, and by the direct interaction between potassium and I on the other hand.     

Oxidation of GaN{0001}-11 surfaces at room temperature

The interaction of unexcited oxygen molecules with clean GaN{0001}-11 surfaces was investigated using X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). Clean surfaces were prepared by a HF dip followed either by desorption of Ga films deposited at room temperature or by nitrogen-ion bombardment and annealing. During exposures in the range from 0.3 up to 10¹⁵ L-O₂ any excitations of the oxygen were avoided. Oxygen coverages determined from the XPS and the AES data differ by a factor of two. The larger XPS-derived coverages are considered to be more reliable since the AES signals decayed during data recording. The oxygen uptake takes place in two consecutive stages. The first one is identified as dissociative chemisorption and the second one is tentatively attributed to field-assisted diffusion by the Mott-Cabrera mechanism. The dissociative chemisorption is characterized by an initial sticking coefficient of and a saturation coverage of monolayers that is reached after exposures of 10³ L-O₂. The second mechanism sets in at exposures to 10⁸ L-O₂ but reaches no saturation even with the largest doses applied. Received 4 September 1998 and Received in final form 6 November 1998     

Growth and vibrational properties of MnOx thin films on Rh(111)

The growth, structures, and vibrational properties of ultrathin manganese oxide films on Rh(111) had been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), low energy ion scattering spectroscopy (LEIS) and Auger electron spectroscopy (AES). MnO_x grew in a layer-by-layer fashion on the Rh(111) surface. HREELS phonon features and XPS binding energies showed that an OMnO like tri-layer formed initially. Which was stable on the Rh(111) surface with MnO_x coverage less than one monolayer. At above one monolayer, Mn₃O₄ was preferred as indicated from a four-phonon feature peaked at 13.3, 39, 68 and 83 meV in HREELS. Higher temperature oxidation and annealing were found to improve the long-range order of the MnO_x films.     

Ru(0001)表面上O-Ru伸缩振动的覆盖度依赖特性

在Ru(0001)表面上,通过氧气以及二氧化氮气体的分解吸附,制备了具有不同氧覆盖度的氧覆盖层.高分辨电子能量损失谱的测量表明,O-Ru伸缩振动具有强烈的覆盖度依赖特性,其振动能量从低覆盖度时(θ_O→0.0)的54meV变化到高覆盖度时(θ_O=1.0)的81meV. 关键词：     

Quantitative examination of electron beam induced carbon deposition at a polycrystalline tungsten surface,studied by Auger electron spectroscopy

Electron beam induced carbon deposition on a polycrystalline tungsten ribbon has been examined by Auger electron spectroscopy, (AES). Deposition occurs from carbon monoxide, through dissociation of weakly held α-CO, and also from carbon dioxide and methane. In each case the saturation coverage is 3.0–3.3 × 10¹⁵ atoms cm^?2, approaching the monolayer of the basal plane of graphite. The Auger line shape indicates that the deposited layer is graphitic in nature and incorporation of carbon into the graphite layer is suggested to be rate determining.     

Molecular binding states on clean and oxidized surfaces: SiO(g) + W(clean) and SiO(g) + W(oxidized)

The interactions between a molecular beam of SiO(g) and a clean and an oxidized tungsten surface were examined in the surface temperature range 600 to 1700 K by mass spectrometrically determined sticking probabilities, by flash desorption mass spectrometry (FDMS) and by Auger electron spectroscopy (AES). The sticking probability, S, of SiO has been determined as a function of coverage and of surface temperature for the clean and the oxidized tungsten surface. Over the temperature range studied and at zero coverage S = 1.0 and 0.88 for the clean and oxidized tungsten surfaces respectively. The results are consistent with both FDMS and AES. For coverage up to one monolayer there is one major adsorption state of SiO on the clean tungsten surface. FDMS shows that T_m = constant (T_m is the surface temperature at which the desorption rate is maximum) and that desorption from this state is described by a simple first order desorption process with activation energy, E_d = 85.3 kcal mole^?1 and pre-exponential factor, ν = 2.1 × 10¹⁴ sec^?1. AES shows that the 92 eV peak characteristic of silicon dominates. In contrast on the oxidized tungsten surface, T_m shifts to higher temperatures with increasing coverage. The data indicate a first order desorption process with a coverage dependent activation energy. At low coverage (θ ? 0.14) there is an adsorption state with E_d = 120 kcal mole^?1 and ν = 7.6 × 10¹⁹, while at θ = 1.0, E_d = 141 kcal mole^?1. This variation is interpreted as due to complex formation on the surface. AES shows that on oxidized tungsten, in contrast to clean tungsten, the dominant peaks occur at 64 and 78 eV, and these peaks are characteristic of higher oxidation states of silicon. Thus, it is concluded that SiO exists in different binding states on clean and oxidized tungsten surfaces.     

Bromine adsorption on Cu(111)

The dissociative chemisorption of molecular bromine on Cu(111) at 300 K has been studied using ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and work function change measurements. A (√3 × √3)R30° structure is formed initially at a bromine coverage of 0.33 ML. This then converts to a (9√3 × 9√3)R30° compression structure with a coverage of 0.41 ML. The coincidence distance of the compression structure is determined entirely by the van der Waals diameter of adsorbed bromine. The applicability of using the van der Waals diameters of the three halogens, Cl, Br and I, to predict the saturation compression structures on Cu(111), is discussed.     

Adsorption and co-adsorption of CH<Subscript>3</Subscript> and H on flat and defective nickel (111) surfaces

We use a periodic density functional theory (DFT) code to study the adsorption of CH₃ and H, as well as their co-adsorption on a Ni(111) surface with and without Ni ad-atom, at a surface coverage of 0.25 monolayer (ML). We systematically investigate the site preference for CH₃ and H. Then we combine CH₃ and H in many co-adsorbed configurations on both surfaces. Methyl and hydrogen adsorption on a flat Ni(111) surface favours the hollow site over the top site. The presence of a Ni ad-atom stabilizes the adsorption of CH₃ better than a flat surface, while hydrogen is more stable on a flat Ni(111) surface. When H and CH₃ are co-adsorbed at nearest Ni neighbours on the (111) surface, their interaction is always repulsive. However, the dissociative adsorption of CH₄ is stabilised when the fragments are infinitely separated. For the co-adsorbed fragments CH₃ and H, in the presence of an ad-atom, the repulsive interaction is lowered, so that the dissociative form of CH₄ is locally stable.     

Reaction intermediates of methanol synthesis and the water–gas-shift reaction on the ZnO(0001) surface

The polar Zn-ZnO(0001) surface is involved in the catalysis of methanol synthesis and the water–gas-shift reaction. We use density functional theory calculations to explore the favorable binding geometries and energies of adsorption of several molecular species relevant to these reactions, namely carbon monoxide (CO), carbon dioxide (CO₂), water (H₂O) and methanol (CH₃OH). We also consider several proposed reaction intermediates, including hydroxymethyl (CH₂OH), methoxyl (CH₃), formaldehyde (CH₂O), methyl (CH₃), methylene (CH₂), formic acid (HCOOH), formate (HCOO), formyl (HCO), hydroxyl (OH), oxygen (O) and hydrogen (H). For each, we identify the preferred binding geometry at a coverage of 1/4 monolayers (ML), and report calculated vibrational frequencies that could aid in the identification of these species in experiment. We further explore the effects on the binding energy when the adsorbate coverage is lowered to 1/9 and 1/16 ML.     

SiC外延层表面化学态的研究

用高分辨X射线光电子能谱仪(XPS)和傅里叶变换红外(FTIR)光谱仪研究了SiC外延层表面的组分结构. XPS宽扫描谱,红外掠反射吸收谱及红外镜面反射谱的解析结果说明SiC外延层表面是由Si—O—Si和Si—CH₂—Si聚合体构成的非晶SiC_xO_y:H. SiC外延层表面的化学态结构为Si(CH₂)₄,SiO(CH₂)₃,SiO₂(CH₃)₂,SiO₃(CH₃),Si—Si,游离H₂O,缔合OH,Si—OH,O和O₂. 根据化学态结构和元素电负性确定了化学态的各原子芯电子束缚能顺序,并与XPS窄扫描谱拟合结果相对比,建立了化学态与其束缚能的对应关系,进而用Si(CH₂)₄的实际C 1s束缚能值进行校正,确定了各化学态的束缚能. 结果发现,除了SiC_xO_y(x=1,2,3,4,x+y=4)的Si 2p束缚能彼此不同外,其C 1s和O 1s彼此也不相同,其中SiO₂(CH₃)₂和SiO₃(CH₃)的C 1s束缚能与CH_m和C—O中C 1s的相近,对此从化学态结构,元素电负性和邻位效应进行了解释. 关键词： SiC 化学态 XPS FTIR     

X-ray photoelectron spectroscopy study of the chemisorption of water on uranium and thorium and oxygen on uranium

The initial stages of water and oxygen adsorption on clean uranium and thorium and oxygen adsorption on uranium has been studied by X-ray photoelectron spectroscopy. These measurements are made in the vicinity of 120 K; in some cases the effect of temperature was followed up to 500 K. Three oxygen (1s) photoelectron peaks are observed for water adsorbed on uranium and thorium. All three peaks have binding energies different from the adsorption of oxygen. The uranium and thorium ($\text{4}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$) lines also have different binding energies for water adsorption than for oxygen adsorption. Oxygen and an OH complex combine with uranium and thorium in a complex way, precluding the initial formation of simple oxides and confirming the importance of OH in the interaction of water with uranium and thorium.     

Adsorption of H2O on Al(111)

The adsorption of H₂O on Al(111) has been studied by ESDIAD (electron stimulated desorption ion angular distributions), LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and thermal desorption in the temperature range 80–700 K. At 80 K, H₂O is adsorbed predominantly in molecular form, and the ESDIAD patterns indicate that bonding occurs through the O atom, with the molecular axis tilted away from the surface normal. Some of the H₂O adsorbed at 80 K on clean Al(111) can be desorbed in molecular form, but a considerable fraction dissociates upon heating into OH_ads and hydrogen, which leaves the surface as H₂. Following adsorption of H₂O onto oxygen-precovered Al(111), additional OH_ads is formed upon heating (perhaps via a hydrogen abstraction reaction), and H₂ desorbs at temperatures considerably higher than that seen for H₂O on clean Al(111). The general behavior of H₂O adsorption on clean and oxygen-precovered Al(111) (θ_O ? monolayer) is rather similar at low temperature, but much higher reactivity for dissociative adsorption of H₂O to form OH _adsis noted on the oxygen-dosed surface around room temperature.     

Adsorption of silane and methylsilane on gold surfaces

The adsorption of silane and methylsilane on the (1 1 0) and polycrystalline surfaces of gold is examined using vibrational electron energy loss spectroscopy (VEELS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and X-ray photoelectron spectroscopy (XPS). Adsorption of silane onto the Au(1 1 0) surface at low temperatures is dissociative and yields an SiH₂ and possibly also SiH₃ surface species. Further dissociation occurs at room temperature to yield adsorbed SiH, which is tilted on the surface, with complete dissociation to Si occurring by 110 °C. The similarity in the UP spectra for silane adsorbed on the polycrystalline sample suggests that the same surface species are present over that temperature range. Above 200 °C, spectral changes suggest rearrangement of the Si atoms, which, by 350 °C, have diffused into the bulk. Adsorption of methylsilane onto the (1 1 0) surface at low temperatures initially produces adsorbed CH₃SiH or CH₃SiH₂, with undissociated methylsilane physisorbing at higher exposures. By room temperature, desorption and decomposition leaves (or direct adsorption yields) only adsorbed CH₃Si. After further heating, the hydrogen-carbon bonds of the CH₃ group break to leave an adsorbed SiC species. On the polycrystalline surface, methylsilane adsorption is the same at low temperatures as on (1 1 0). In contrast to the latter, though, the UP spectra indicate that direct exposures at room temperature yield adsorbed Si or SiC initially, with CH₃Si again adsorbing at higher exposures. Upon further heating to 330 °C, little if any methyl-groups remain on the surface and the Si has started to diffuse into the bulk.     

The adsorption of acetylene on W(100) at room temperature: An electron spectroscopic study

The adsorption of acetylene on W(100) at room temperature has been studied by AES, ELS, thermal desorption, mass spectrometry, work function and LEED in one vacuum chamber. AES line profile analysis shows that there are at least two adsorption processes occurring at room temperature. Further, it is possible to explain all the AES results by assuming non-sequential adsorption into just two states, denoted by α and β. This picture was substantiated and embellished by comparison with other standard surface techniques. The α-state comprises either a C₂H₂ unit with an activation energy for desorption of $\text{2.3}\text{eV}\text{molecule}\text{(53}\text{kcal mole}{}^{\mathrm{?1}}\text{)}$ or CH units bounded through the carbon of the β-state. Saturation coverage for the α-state is 3 × 10¹⁴ molecules cm^?2. The β-state is dissociative at low acetylene exposures and comparison between a carbon covered surface and the β-state suggest the latter to be dissociative up to saturation. There also appears to be ca. 10¹⁴ hydrogen atoms cm^?2 on W(100) on room temperature acetylene saturation, the carbon content of the β-state being 9 × 10¹⁴ atoms cm^?2. The residual C?C bond from the molecule in the β-state remains unknown. No sign of ordering in the adsorbed species was detected, save the possibility of (1 × 1) in the β-state. Acetylene adsorption at 580 K showed hydrogen from the β-state to block acetylene adsorption by 15% at saturation. A two-site adsorption model for the β-state is proposed to explain the results. The α-state is bonded through the carbon of the β-state and it is speculated that the former adsorbs onto “β” domains where there is a critical minimum size for the latter.     

Fuchs-Kliewer phonon spectrum of Co3O4(110) single crystal surfaces by high resolution electron energy loss spectroscopy

The Fuchs-Kliewer phonon spectrum of single crystal Co₃O₄(110) has been analyzed by high resolution electron energy loss spectroscopy (HREELS) and the four fundamental phonon losses have been identified at 26.8, 47.5, 71.1 and 84.7 meV (216, 383, 573 and 683 cm⁻¹). This is the first HREELS study reported for an intrinsic spinel single-crystal surface with primary focus on the Fuchs-Kliewer phonon structure. The Co₃O₄ crystal is first characterized by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED), which establish the composition, cleanliness, and order of the (110) surface. Electron scattering is then used to obtain a series of well-resolved Fuchs-Kliewer phonon spectra over 2.25-14.25 eV incident electron energy range. The variation in phonon intensity with primary beam energy is shown to agree with that predicted by dielectric theory.